Optical sheet, light controlling member, surface light source device, image source unit, and display

To provide an optical sheet that makes it possible to efficiently control a light exiting angle as desired, an optical functional layer has a plurality of light transmissive portions extending in one direction, the light transmissive portions being arranged at intervals in a direction different from the one direction, and a light absorbing portion that is arranged between respective adjacent light transmissive portions, and the optical element layer extends so as to be offset from the one direction at an angle of 0° to 45° in a front view of the optical sheet, the optical element layer having a plurality of unit optical elements that are ridges aligned in a direction different from a direction in which the optical element layer extends.

TECHNICAL FIELD

The present invention relates to optical sheets to control an exiting direction of an incident light, and light controlling members, surface light source devices, image source units, and displays including the optical sheet.

BACKGROUND ART

Displays such as monitors for car navigation systems, televisions, and personal computers include an image source from which an image to be displayed exits, and an optical sheet for improving the quality of an image light to give the light on the watcher side.

Exiting directions of an image light are mostly the front, and offset up, down, left, and right from the front. This makes it possible to visually recognize an image shown on a screen from a desired position. Exiting directions of light are also limited as necessary, for example, for preventing peeks.

For example, Patent Literatures 1 to 3 disclose optical sheets to control light exiting angles.

CITED DOCUMENTS

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Diverse devices in recent years have required different or more precise control of an exiting direction of an image light than before. For example, car navigation systems do not always need a wide viewing angle because positions where people seat themselves are almost determined in an automobile, and thus car navigation systems have only to let images exit toward the positions where people are to exist, especially toward a driver. It is, therefore, easier for a driver to watch an image light exiting obliquely upwards than that exiting to the front. An image light exiting too upwards, however, leads to a problem of a reflection of the image in a windshield. Such a light exiting angle is different according to types of automobiles etc., which requires precise control thereof. For example, those patent literatures encompass the following problems:

For example, it is difficult to precisely control a viewing angle using an optical sheet as described in Patent Literature 1. Even if the viewing angle is controlled, the use efficiency of an image light lowers, which is problematic.

For example, an optical sheet as described in Patent Literature 2 gives high exiting performance of an image light in a desired direction, but limits the image light exiting in any other direction. This may lead to a relatively dark outer circumferential portion of a screen compared to its center although the center is bright especially when a display has a large screen. This tendency further notably manifests itself especially when the screen is viewed obliquely from the front.

For example, a technique as described in Patent Literature 3 requires that light transmissive portions and light absorbing portions on the center of the sheet are significantly different from those on the outer circumferential portion thereof in shape, and does not always make it possible to control light precisely. In this case, increased difficulty in production makes it also difficult to give an accurate shape.

An object of the present invention is to provide an optical sheet that makes it possible to efficiently control a light exiting angle as desired, and to provide a light controlling member, a surface light source device, an image source unit, and a display including this optical sheet.

Solution to Problem

Hereinafter the present invention will be described.

One aspect of the present invention is an optical sheet that is made of a plurality of laminated layers, the optical sheet comprising: an optical functional layer that is one of a plurality of the laminated layers; and an optical element layer that is another one of a plurality of the laminated layers, wherein the optical functional layer has a plurality of light transmissive portions extending in one direction, the light transmissive portions being arranged at intervals in a direction different from the one direction, and a light absorbing portion that is arranged between respective adjacent light transmissive portions, and the optical element layer extends so as to be offset from the one direction at an angle of 0° to 45° in a front view of the optical sheet, the optical element layer having a plurality of unit optical elements that are ridges aligned in a direction different from a direction in which the optical element layer extends.

Here, “a front view of the optical sheet” means a point of view when the optical sheet is viewed from a face of the sheet on the light exiting side. “At an angle of 0° to 45° in a front view of the optical sheet” means that the unit optical elements extend so as to be offset from the extending direction of the light transmissive portions (one direction) by 0° to 45° when the optical sheet is viewed in the front view of the optical sheet.

Each of the light transmissive portions may have a trapezoidal cross section, a longer lower base of the trapezoidal cross section facing the unit optical elements.

Each of the unit optical elements may have a main refracting face, a rise face, and a triangular cross section, and the main refracting face may be a face inclining in a direction of a normal line of a light exiting face of the optical functional layer at more than 45° and no more than 89°.

An angle formed by one of the main refracting faces of the unit optical elements and the normal line of the light exiting face of the optical functional layer may be different between a central area of the optical sheet and an outer circumferential area of the optical sheet. Here, the optical element layer may be made of a linear Fresnel lens.

Each of the unit optical elements may have a main refracting face, a rise face, and a triangular cross section, and the main refracting face may incline toward a face of the optical functional layer at more than 0° and less than 17°.

Each of the light transmissive portions may have a trapezoidal cross section, a shorter upper base of the trapezoidal cross section facing the unit optical elements.

A surface of each of the unit optical elements may be formed into a rough face.

Pmxmay be no more than 10000 (μm) where an aligning pitch of the light transmissive portions is Pa(μm), an aligning pitch of the unit optical elements is Po(μm), a and b are each integers of 1 to 10,
Pm=|(a·Pa·b·Po)/(a·Pa−b·Po)|, and
largest Pmobtained by all combinations of a and b for Paand Pois Pmx(μm).

A surface light source device comprising: a light source; and the optical sheet, which is arranged closer to a watcher than the light source is, may be provided.

A light controlling member, wherein the number of the optical sheets arranged is at least two, and an extending direction of the light transmissive portions of one of the optical sheets and that of the light transmissive portions of another one of the optical sheets cross each other in the front view of the optical sheets may be provided.

A surface light source device comprising: a light source; and the light controlling member, which is arranged closer to a watcher than the light source is, may be provided.

An image source unit comprising: the surface light source device; and a liquid crystal panel that is arranged on a light exiting side of the surface light source device may be provided.

In the image source unit, the light transmissive portions, the light absorbing portion, and the unit optical elements may extend in a horizontal direction, and may be aligned in a vertical direction.

A display comprising: a housing; and the image source unit, which is housed in the housing, may be provided.

Advantageous Effects of Invention

The present invention makes it possible to efficiently control a light exiting angle.

DESCRIPTION OF EMBODIMENTS

Hereinafter the present invention will be described based on the embodiments shown by the drawings. The present invention is not limited to these embodiments. In the drawings, the shapes may be enlarged, modified, and exaggerated for easy understanding, and the repeating symbols may be partially omitted.

FIG. 1, which is an explanatory view of the first embodiment, is an exploded perspective view of an image source unit10including an optical sheet30.FIG. 2partially shows an exploded cross-sectional view of the image source unit10taken along the line II-II (line in the vertical direction) inFIG. 1.FIG. 3partially shows an exploded cross-sectional view of the image source unit10taken along the line (line in the horizontal direction). The vertical and horizontal directions here indicate directions of the optical sheet30in a display when the display in which the optical sheet30is arranged is used.

Such an image source unit10is housed in a housing that is not shown, along with general devices necessary to operate as the image source unit10such as a power source to activate the image source unit10, and an electronic circuit to control the image source unit10, to constitute the display, detailed description of which is omitted. This embodiment will describe a liquid crystal image source unit as one aspect of the image source unit, and a liquid crystal display as one aspect of the display. Hereinafter the image source unit10will be described.

The image source unit10includes a liquid crystal panel15, a surface light source device20, and a functional film40. In this embodiment, the optical sheet30is included in the surface light source device20.FIGS. 1 to 3show the directions when the display is installed, together.

The liquid crystal panel15includes an upper polarizing plate13that is arranged on the watcher side, a lower polarizing plate14that is arranged on the surface light source device20side, and a liquid crystal layer12that is arranged between the upper polarizing plate13and the lower polarizing plate14. The upper polarizing plate13and the lower polarizing plate14have functions of: decomposing an incident light into two polarization components (P and S waves) that are orthogonal to each other; transmitting a polarization component in one direction (direction parallel to the transmission axis: for example, a P wave); and absorbing the polarization component in the other direction, which is orthogonal to the one direction (direction parallel to the absorption axis: for example, a S wave).

In the liquid crystal layer12, a plurality of pixels are two-dimensionally aligned vertically and horizontally along the layer face, which makes it possible to create an electric field for each region that forms one pixel. The orientation of a pixel where an electric field is created is changed. Thus, the polarization direction of the polarization component that is transmitted through the lower polarizing plate14arranged on the surface light source device20side (that is, the light entering side), and is parallel to the transmission axis (for example, a P wave) rotates by 90° C. when the polarization component passes through a pixel for which an electric field is created, whereas being maintained when the polarization component passes through a pixel for which an electric field is not created. As such, the polarization component transmitted through the lower polarizing plate14(for example, a P wave) may be controlled to be further transmitted through the upper polarizing plate13arranged on the light exiting side, or to be absorbed and blocked by the upper polarizing plate13according to the presence or absence of an electric field for a pixel.

As described above, the liquid crystal panel15has the structure to control transmission or block of light from the surface light source device20for each pixel, to display an image.

The type of the liquid crystal panel is not particularly limited in this embodiment, while there exit some types of liquid crystal panels. A liquid crystal panel of any known type may be used. Specific examples thereof include TN, STN, VA, MVA, IPS, and OCB.

The surface light source device20will be described.

The surface light source device20is arranged on the opposite side of the watcher side across the liquid crystal panel15, and is a lighting device to exit a planar light toward the liquid crystal panel15. As can be seen fromFIGS. 1 to 3, the surface light source device20in this embodiment is configured as an edge light type surface light source device, and includes a light guiding plate21, a light source25, a light diffusion plate26, a prism layer27, a reflection type polarizing plate28, the optical sheet30, and a reflection sheet39.

As can be seen fromFIGS. 1 to 3, the light guiding plate21includes a base portion22and back face optical elements23. The light guiding plate21is a member in the form of a plate as a whole, and is formed by a translucent material. In this embodiment, one plate face of the light guiding plate21which is on the watcher side forms a smooth face, and the opposite other plate face forms a back face. A plurality of the back face optical elements23are aligned over the back face.

Various materials may be used as the materials constituting the base portion22and the back face optical elements23as long as the materials are widely used as materials for an optical sheet to be incorporated into a display, have excellent mechanical characteristics, optical characteristics, stability, processability, etc., and are inexpensively available. Examples thereof include thermoplastic resins such as polymer resins having an alicyclic structure, methacrylate resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyether sulfone; and epoxy acrylate or urethane acrylate reactive resins (e.g. ionizing radiation curable resins).

The base portion22is a portion of the base of the back face optical elements23, the inside of which light is guided to, and is in the form of a plate having a suitable thickness.

Each of the back face optical elements23is a projecting element formed on the back face side of the base portion22, and is in the form of a triangular prism in this embodiment. The back face optical element23in this embodiment is in the form of a column, a ridge line of the projecting apex of which extends in the horizontal direction. A plurality of the back face optical elements23are aligned in the direction orthogonal to the extending direction of the ridge lines (vertical direction). The cross section of the back face optical element23in this embodiment is a triangle, but is not limited to this. The cross section thereof may be in any shape such as a polygonal shape, a hemispherical shape, a partial sphere, and a shape of a lens.

The aligning direction of a plurality of the back face optical elements23is preferably a light guiding direction. That is, the back face optical elements23are aligned in a separating direction from the light source25, and the ridge lines thereof extend in parallel to the aligning direction of the light source25, or the extending direction of the light source if one long light source is used.

In the present description, “triangular shape” encompasses not only an exact triangular shape, but also an approximate triangular shape due to limitations in a production technique, errors in molding, etc. Likewise, the meanings of the terms used in the present description to identify a shape and geometric conditions other than the above, for example, “parallel”, “orthogonal”, “oval”, and “circle”, are not limited to their strict meanings, but the terms shall be interpreted as encompassing some difference as long as similar optical functions may be expected.

The light guiding plate21having such a structure can be produced by extrusion molding or by forming the back face optical elements23over the base portion22. The base portion22and the back face optical elements23may be integrally shaped in the light guiding plate21produced by extrusion molding. When the light guiding plate21is produced by forming, the material of the back face optical elements23may be the resin material same as, or a different material from the base portion22.

Returning toFIGS. 1 and 3, the light source25will be described. The light source25is arranged on one of side faces (end faces) of the base portion22of the light guiding plate21which is along the aligning direction of the back face optical elements23. The type of the light source is not particularly limited, and the light source may be configured to have any aspect such as a fluorescent lamp like a linear cold cathode tube, a point-like LED (light emitting diode), and an incandescent light bulb. In this embodiment, the light source25is constituted of a plurality of LEDs, and is configured so that a controlling device not shown may separately and individually adjust the LEDs to turning on and off, and/or the brightness of a LED when the LED is turned on.

In this embodiment, the example of arranging the light source25on one side face (end face) is given. In another embodiment, however, a light source may be further arranged on the side face (end face) opposite to this face (end face), too. In this case, the shape of the back face optical elements is formed according to a known example so as to be suitable for the arrangement of the light sources.

The light diffusion plate26will be described. The light diffusion plate26is a layer arranged on the light exiting side of the light guiding plate21, and having a function of diffusing light entering the plate, to let the diffused light exit the plate. This improves uniformity of the light exiting the light guiding plate21further more, which makes it possible for scratches on the light guiding plate21to be less distinct.

An aspect of a known light diffusion plate may be used for a specific aspect of the light diffusion plate. Examples thereof include an embodiment of dispersing a light diffusing agent in a parent material.

The light diffusion plate26may be also used as a supporting plate of the prism layer27like this embodiment. When the light exiting face of the light guiding plate21is smooth, the light diffusion plate26may be laminated to, and united with the light guiding plate21.

The prism layer27is, as can be seen fromFIGS. 1 to 3, a layer that is provided closer to the liquid crystal panel15than the light diffusion plate26is provided, and includes unit prisms27aconvex toward the liquid crystal panel15. Each of the unit prisms27ain this embodiment has a triangular cross section, and extends in the direction orthogonal to the light guiding direction of the light guiding plate21(horizontal direction in this embodiment). A plurality of the unit prisms27aare aligned in the light guiding direction of the light guiding plate21(vertical direction in this embodiment). This makes it possible to collect light in a direction where light is controlled in an optical functional layer32(vertical direction in this embodiment), and to totally reflect light efficiently on the optical functional layer32, which makes it possible to improve the use efficiency of light.

A known shape (a triangle, a quadrangle, and other polygons) may be employed in a cross-sectional shape of each unit prism of such a prism layer depending on a necessary function. This shape makes it possible to collect light as described above on one hand, and to further diffuse light on the other hand.

The extending and aligning directions of the unit prisms are not limited to the above described embodiment. In another embodiment, for example, the unit prisms may extend in the light guiding direction of the light guiding plate, and a plurality of the unit prisms may be aligned in the direction orthogonal to the light guiding direction of the light guiding plate.

The reflection type polarizing plate28has functions of: decomposing an incident light into two polarization components (P and S waves) that are orthogonal to each other; transmitting a polarization component in one direction (direction parallel to the transmission axis: for example, a P wave); and reflecting the polarization component in the other direction, which is orthogonal to the one direction (direction parallel to the reflection axis: for example, a S wave). A known structure may be employed for the structure of such a reflection type polarizing plate.

The optical sheet30will be described.FIG. 4shows a partially enlarged optical sheet30from the point of view ofFIG. 2. As is seen fromFIGS. 1 to 4, the optical sheet30includes a base material layer31formed in a sheet shape, the optical functional layer32provided for one face of the base material layer31(face on the light guiding plate21side in this embodiment), and a light exiting side light controlling layer35arranged on the other face of the base material layer31(face on the liquid crystal panel15side in this embodiment).

The base material layer31is a plate-like sheet member supporting the optical functional layer32and the light exiting side light controlling layer35.

Various materials may be used as the materials constituting the base material layer31as long as the materials are widely used as materials for an optical sheet to be incorporated into a display, have excellent mechanical characteristics, optical characteristics, stability, processability, etc., and are inexpensively available. Examples thereof include polyethylene terephthalate resins (PET), triacetylcellulose resins (TAC), methacrylate resins, and polycarbonate resins. Among them, TAC, methacrylate resins, and polycarbonate resins which have low retardation are preferably used in view of the combination of the surface light source device20and the lower polarizing plate14. Further, for use where a high heat resisting property is required, such as on-vehicle use, polycarbonate resins having a high glass transition point is desirable. Specifically, the glass transition point of polycarbonate resins is 143° C., which is suitable for on-vehicle use where durability at 105° C. is generally required.

The optical functional layer32is a layer laminated on one face of the base material layer31(face on the light guiding plate21side in this embodiment), and is constituted of light transmissive portions33and light absorbing portions34. The optical functional layer32has a shape having the cross section shown inFIG. 4, and extending from the back to the front on the drawing sheet (horizontal direction when the image source unit10is viewed in the front view in this embodiment). The light transmissive portions33and the light absorbing portions34are alternately aligned along a face of the optical functional layer32in a direction different from the extending direction thereof (vertical direction in this embodiment).

Each of the light transmissive portions33is a portion whose main function is to transmit light. In this embodiment, the light transmissive portion33is an element having an approximately trapezoidal cross-sectional shape that has a longer lower base on the base material layer31side and a shorter upper base on the opposite side (light guiding plate21side) on the cross section shown inFIGS. 2 and 4.

A plurality of the light transmissive portions33extend in one direction (horizontal direction in this embodiment) along the layer face of the base material layer31as keeping the above described cross sections, and are aligned at intervals in a different direction from the extending direction (vertical direction in this embodiment). A gap (groove) having an approximately trapezoidal cross section is formed between respective adjacent light transmissive portions33. Therefore, each gap (groove) has a trapezoidal cross section having a longer lower base on the upper base side of the light transmissive portions33(light guiding plate21side), and a shorter upper base on the lower base side of the light transmissive portions33(base material layer31side). Necessary materials described later are filled in the gaps, to form the light absorbing portions34.

In this embodiment, a sheet-like sill portion32alinks a plurality of the light transmissive portions33at their lower base side (base material layer31side).

The refractive index of each of the light transmissive portions33is Nt. Such a light transmissive portion33may be formed by curing a light transmissive portion constituting composition. The value of the refractive index Ntis not particularly limited, and is preferably no less than 1.47 in view of reflecting (or totally reflecting) light suitably on interfaces with the light absorbing portions34which are oblique faces on the trapezoidal cross section as described later. The refractive index is preferably no more than 1.61 since a material having too high a refractive index tends to easily crack. The refractive index is more preferably 1.49 to 1.56, and further preferably 1.56.

Each of the light absorbing portion34functions as an in-between portion that is formed in the above described gap (groove) formed between respective adjacent light transmissive portions33, and has the same cross-sectional shape as that of the gap (groove). Therefore, the shorter upper base faces the liquid crystal panel15(base material layer31), and the longer lower base is on the opposite side thereof (light guiding plate21side in this embodiment). The refractive index of the light absorbing portion34is Nr. The light absorbing portion34is configured so as to be able to absorb light. Specifically, light absorbing particles are dispersed in a transparent resin whose refractive index is Nr. The refractive index Nris a lower index than the refractive index Ntof the light transmissive portion33. The refractive index of the light absorbing portion34is lower than that of the light transmissive portion33as described above, which makes it possible to totally reflect the light that satisfies conditions to enter the light transmissive portion33suitably on interfaces with the light absorbing portions34. Even if the conditions of total reflection are not satisfied, the light is partially reflected on the interfaces.

The value of the refractive index Nris not particularly limited, and is preferably no less than 1.47 assuming that the total reflection is suitably carried out. The refractive index is preferably no more than 1.61 since a material having too high a refractive index tends to easily crack. The refractive index is more preferably 1.49 to 1.56, and further preferably 1.49.

The difference between the refractive index Ntof the light transmissive portion33and the refractive index Nrof the light absorbing portion34is not particularly limited, and preferably more than 0 and no more than 0.14, and more preferably 0.05 to 0.14. A bigger difference in refractive index makes it possible to totally reflect more light.

The optical functional layer32is not specifically limited, and for example, may have the following shape.FIG. 5is a partially further enlarged view ofFIG. 4.

θ11shown inFIG. 5is an angle formed by an interface34a, and the normal line of the layer face of the optical functional layer32: the interface34ais one of each interface between the light transmissive portions33and the light absorbing portions34which is on the upper side of the light absorbing portion34when the optical sheet30is arranged in a state asFIG. 1. θ12is an angle formed by an interface34b, and the normal line of the layer face of the optical functional layer32: the interface34bis one of each interface between the light transmissive portions33and the light absorbing portions34which is on the lower side of the light absorbing portion34in the same state.

θ11is preferably 0° to 10°. θ11of more than 0° means downward inclination from the light guiding plate21side (light entering side) to the liquid crystal panel15side (light exiting side, base material layer31side).

θ12is preferably 0° to 10°. θ12of more than 0° means upward inclination from the light guiding plate21side (light entering side) to the liquid crystal panel15side (light exiting side, base material layer31side).

The relationship between the sizes of the angles θ11and θ12may be set as necessary.

The pitch of the light transmissive portion33and the light absorbing portion34, shown by PainFIG. 4, is preferably 20 μm to 100 μm, and more preferably 30 μm to 100 μm. The thickness of the light absorbing portion34shown by DainFIG. 4is preferably 50 μm to 150 μm, and more preferably 60 μm to 150 μm. The pitch and thickness within these ranges make it possible to give more suitably balanced transmission and absorption of light.

In this embodiment, the example where each interface between the light transmissive portions33and the light absorbing portions34is in the form of a straight line on the cross section is given. The interface may be in the form of a polygonal, a convex curved line, a concave curved line, etc. without limitation to the above. A plurality of the light transmissive portions33and the light absorbing portions34may have the same cross-sectional shape, or different cross-sectional shapes having regularity.

The example where the extending direction of the light transmissive portions33and the light absorbing portions34is horizontal is described above. This direction is preferably offset from the aligning direction of the pixels of the liquid crystal layer12in the front view of the image source unit (bias angle α1) in view of suppressing moire. This bias angle α1is not specifically restricted as long as moire is prevented, and is preferably 1° to 10°.

The light exiting side light controlling layer35will be described. The light exiting side light controlling layer35functions as a light controlling layer, to control the direction of light in combination with the optical functional layer32.

In this embodiment, the light exiting side light controlling layer35controls the direction of the light exiting the optical functional layer32, to let the light exit. That is, in this embodiment, the light exiting side light controlling layer35further controls the direction of the light which is controlled in the optical functional layer32, to make the angle where the light exits a desired angle.

The light exiting side light controlling layer35is therefore constituted of a supporting layer35aand an optical element layer35b.

The supporting layer35ais a transparent sheet-like member that functions as a supporting body of the optical element layer35b. The supporting layer35amay be made from materials same as those of the base material layer31and the light transmissive portions33.

The optical element layer35bis a layer to change the direction of the light exiting the optical functional layer32, and is formed of a plurality of unit optical elements35caligned over a face of the supporting layer35awhich is on the opposite side to the optical functional layer32.

The unit optical elements35cfurther control the direction of the light controlled in the optical functional layer32, so that, in this embodiment, the viewing angle is efficiently shifted upwards in the vertical direction in the state ofFIGS. 1 to 3.FIGS. 4 and 5show the cross-sectional shapes of the unit optical elements35c.

In this embodiment, the unit optical elements35cspecifically have the following structure:

Each of the unit optical elements35cis in the form of a triangular prism having a triangular cross section protruding opposite to the optical functional layer32, which is across the base material layer31, a ridge of which is constituted of a ridge line extending in the same direction as the extending direction of the light transmissive portions33and the light absorbing portions34(bias angle α2=0°), or extending as being offset in the front view of the optical sheet (bias angle α2≠0°, as having that cross section. A plurality of the unit optical elements35care aligned in a direction different from their extending direction.

When the ridge line of each of the unit optical elements35cextends as being offset from the extending direction of the light transmissive portions33and the light absorbing portions34in the front view of the optical sheet (bias angle α2≠0°, preferably, the extending direction of the light transmissive portions33of the optical functional layer32relatively inclines from the extending direction of the ridge lines of the unit optical elements35cby the bias angle α2of more than 0° and no more than 45° in the front view of the optical sheet30. This makes it possible to prevent moire due to the aligning structure of the light transmissive portions33and the light absorbing portions34, and the aligning structure of the unit optical elements35c. The angle α2of more than 45° leads to lowered efficiency of the control of the direction of light in the unit optical elements35c. The angle α2is more preferably 1° to 10°.

Each of the unit optical elements35cincludes a main refracting face35dand a rise face35eas seen fromFIG. 5. These main refracting face35dand rise face35eform two faces of a triangular prism, and the other one face is over the supporting layer35ato be fixed to the supporting layer35a.

In this embodiment, the main refracting face35dis a refracting face to change the direction of the light exiting the optical functional layer32so that the light is further directed upwards in the state ofFIGS. 1 to 5. This makes it possible to efficiently shift the range where light exits upwards in the vertical direction. In this case, the main refracting face35dinclines downwards as being close to the optical functional layer32(here, this direction is defined as a positive (+) direction). Thus, in one unit optical element35c, the main refracting face35dis the bottom and the rise face35eis the top. The inclination of the main refracting face35dforms an angle θ21shown inFIG. 5with the direction of the normal line of the optical functional layer32.

A specific angle of θ21is preferably more than 45° and less than 90° (the absolute value of the inclination angle of the main refracting face is more than 45° and less than 90°). This makes it possible to surely control light for improving brightness in a desired direction (control of a light exiting angle). θ21of no more than 45° makes it easy for total reflection to occur on the main refracting face35d, which may increase light that does not exit. θ21of no less than 90° makes it almost impossible for the main refracting face to function.

θ21is more preferably 80° to 89°. θ21of this range makes it possible to use a small rise face35e, to reduce a stray light due to the rise face35e.

The rise face35eis a face necessary for forming the main refracting face35d.

The rise face35epreferably forms the inclination angle, which is shown by θ22inFIG. 5, of 80° to 100° with the direction along the layer face of the optical functional layer32. θ22is more preferably 80° to 90° in view of production. θ22of less than 80°, and θ22of more than 100° may increase a stray light due to the rise face35e.

The vertex angle of the unit optical element35cis naturally determined by θ21and θ22, and is preferably no less than 45° and less than 90°.

The pitch of the unit optical element35cshown by PoinFIG. 4is preferably short from the viewpoint that moire of a short pitch makes it difficult for the moire to be seen even if the moire appears. Specifically, the pitch Pois preferably no more than 50 μm.

It is desirable that the pitch Poof the unit optical element35cbe shorter than the pitch Paof the light transmissive portion33of the optical functional layer32(seeFIG. 4) since the optical functional layer32is more difficult than the optical element layer35bin production. It is further desirable that Pobe no more than ½ of Pa. It is most desirable that an end part of the light transmissive portion33and an end part of the unit optical element35cbe not at the same location as long as possible when Pois regularly magnified like Pa/2, Pa/3, and Pa/4. In other words, it is desirable that the least common multiple of Poand Pabe a large number.

Pois preferably no less than 10 μm since a small unit optical element35clowers accuracy.

Pmx(μm) is more preferably no more than 10000 (μm) when the aligning pitch of the light transmissive portion33is Pa(μm) and the aligning pitch of the unit optical element35cis Po(μm). This makes it possible to more surely prevent moire. Here, Pmxcan be obtained as follows:

Pmxcan be obtained based on Pm, and Pmis represented by the following formula:
Pm=|(a·Pa·b·Po)/(a·Pa−b·Po)|

Here, Pa≥Po, and a and b are each integers of 1 to 10. All the combinations of Paand Po, which is a pitch from the same magnification (once) as, to ten times larger than Paare considered. This makes it possible to evaluate appearance of moire in a wide range of considering pitches at integral multiples.

The maximum Pmin Pmobtained from all the combinations of varied a and b in a certain combination of Paand Pois Pmx.

The protruding height of the unit optical element35cfrom the supporting layer35a, which is shown by DoinFIG. 4is preferably 1 μm to 10 μm. The height lower than this lower limit may lead to deteriorated accuracy of processing, which leads to defects such that stripe lines are visually recognized. The height higher than this upper limit makes it easy for moire to appear due to the light absorbing portions34and the unit optical elements35c.

In this embodiment, a plurality of the unit optical elements35care continuously arranged without any gaps, but not limited to this. In another aspect, a gap may be provided between adjacent unit optical elements35c, from which a face of the supporting layer35amay be partially exposed.

In this embodiment, the main refracting face35dof the unit optical element35cis linear on the cross section shown inFIGS. 4 and 5, but is not always limited to this. The main refracting face35dmay be in the form of a convex or concave curved line, or a polygonal line on its cross section.

The main refracting face35dand the rise face35emay be rough faces. This makes it possible to scatter light to suppress moire. A method for forming the main refracting face35dand the rise face35einto rough faces is not specifically limited. Examples thereof include direct blasting on the unit optical element, and blasting on a die for molding the unit optical element.

All of a plurality of the unit optical elements35care not always necessary to have the same shape, and may suitably have different shapes from each other.

In this embodiment, the supporting layer35ais provided for the light exiting side light controlling layer35. The supporting layer35ais not always necessary to be provided. For example, the optical element layer35bmay be directly formed over the base material layer31as shown by a light exiting side light controlling layer35′ inFIG. 6, which is a modification.

At this time, a face of the base material layer31which forms the interface with the optical element layer35bmay be formed into a rough face, and the base material layer31may be different from the optical element layer35bin refractive index. This makes it possible to scatter light on the rough face to suppress moire.

Such a supporting layer35aand an optical element layer35b(unit optical element35c) of the light exiting side light controlling layer35may be made from materials same as those of the base material layer31and the light transmissive portions33.

For example, the optical sheet30is made in the following manner:

First, the light transmissive portions33are formed on one face of the base material layer31: a base material sheet to become the base material layer31is inserted into a space between a die roll having on its surface a shape that enables the shapes of the light transmissive portions33to be transferred, and a nip roll arranged so as to be opposite to the die roll. At this time, a further space is provided between the die roll and the nip roll, to be the sill portion32a. The die roll and the nip roll are rotated while a composition to constitute the light transmissive portions is supplied to the space between the base material sheet and the die roll. This results in grooves filled with the composition to constitute the light transmissive portions, to allow the composition to be along the surface shape of the die roll: the grooves are formed over the surface of the die roll and correspond to the light transmissive portions (having a reversed shape of the light transmissive portions).

Here, examples of the composition to constitute the light transmissive portions include ionizing radiation-curable resins such as epoxy acrylate, urethane acrylate, polyether acrylate, polyester acrylate, and polythiol ionizing radiation-curable resins.

The composition between the die roll and the base material sheet to constitute the light transmissive portions with which the space between them is filled is irradiated with light for curing from a light irradiation device on the base material sheet side. This makes it possible to cure the composition, to fix its shape. The base material layer31and the molded light transmissive portions33are then released from the die roll by a release roll.

The light absorbing portions34will be formed. First, gaps (grooves) between the molded light transmissive portions33are filled with a composition to constitute the light absorbing portions. Thereafter, an excessive composition is scraped off by a doctor blade or the like. The remaining composition is then irradiated with an ultraviolet ray from the light transmissive portions33side, to cure the composition, which makes it possible to form the light absorbing portions34.

Materials used as the light absorbing portions are not particularly limited. Examples thereof include a composition formed of colored light absorbing particles dispersed in photocurable resins such as urethane(meth)acrylate, polyester(meth)acrylate, epoxy(meth)acrylate, and butadiene(meth)acrylate.

Instead of dispersion of light absorbing particles, the whole light absorbing portions may be colored by a pigment or dye.

When light absorbing particles are used, colored particles having a light absorbing property such as carbon black are preferably used. Light absorbing particles are however not limited to them, and colored particles which selectively absorb light of a certain wavelength may be employed in accordance with properties of an image light. Specific examples include: carbon black, graphite, metallic salts such as black iron oxide, and organic particulates or glass beads colored by a dye, a pigment, and the like. Especially, colored organic particulates are preferably used in view of costs, quality, availability, and the like. The mean particle diameter of the colored particles is preferably 1.0 μm to 20 μm, more preferably 1.0 μm to 10 μm, and further preferably 1.0 μm to 4.0 μm.

Here, “mean particle diameter” means a diameter calculated by: observing100light absorbing particles with an electron microscope to measure diameters thereof, and calculating the arithmetic mean of the measured diameters.

Other than the optical functional layer32, the light exiting side light controlling layer35formed of the optical element layer35blaminated onto one face of the supporting layer35ais prepared. This may be made in the same manner as the method of laminating the light transmissive portions33onto the base material layer31in the optical functional layer32. When the bias angle α2is not 0°, a groove to mold the unit optical elements35con a roll-mold to form the optical element layer35bis preferably formed spirally (like a thread groove) along the outer circumferential face of the roll-mold. This makes it possible to give a suitable bias angle α2in view of accuracy and efficiency.

The face of the base material layer31which is on the opposite side of the side where the optical functional layer32is arranged is adhered to the face of the supporting layer35aof the light exiting side light controlling layer35which is on the opposite side of the side where the optical element layer35bis arranged with an adhesive to be united, to obtain the optical sheet30.

Returning toFIGS. 1 to 3, the reflection sheet39of the surface light source device20will be described. The reflection sheet39is a member for reflecting the light exiting the back face of the light guiding plate21to let the light enter the light guiding plate21again. Any sheet that enables so-called specular reflection may be preferably employed as the reflection sheet39. Examples thereof include a sheet made of a material having a high reflectance such as metal, and a sheet including, as a surface layer, a thin film made of a material having a high reflectance (for example, thin metal film).

The functional film40is a layer that is arranged on the light exiting side of the liquid crystal panel15, and has functions of improving the quality of an image light, and protecting the image source unit10. Examples thereof include an anti-reflection film, an anti-glare film, a hard coating film, a color compensation film, and a light diffuser film. One or a plurality of them are used alone or in combination, to constitute the functional film40.

Operations of the image source unit10having the above described structure will be described as showing examples of an optical path. The examples of an optical path are for conceptualistic explanation, and do not strictly give degrees of reflection and refraction.

First, the light exiting the light source25enters the light guiding plate21from a light entering face that is a side face (end face) of the light guiding plate21as shown inFIG. 2.FIG. 2shows examples of the optical paths of lights L21and L22entering the light guiding plate21from the light source25as one example.

As shown inFIG. 2, the lights L21and L22entering the light guiding plate21repeat total reflection due to the difference in refractive index from the air, on a face of the light guiding plate21on the light exiting side, and the back face opposite to that face; and travel in the light guiding direction (downwards on the drawing sheet ofFIG. 2).

The back face optical elements23are arranged over the back face of the light guiding plate21. The traveling directions of the lights L21and L22travelling through the light guiding plate21are therefore changed by the back face optical elements23, and the lights L21and L22may enter the light exiting face and the back face at an incident angle narrower than the total reflection critical angle as shown inFIG. 2. In this case, the lights may exit the light exiting face of the light guiding plate21, and the back face that is opposite to the light exiting face.

The lights L21and L22exiting the light exiting face are directed toward the light diffusion plate26arranged on the light exiting side of the light guiding plate21. The light exiting the back face is reflected by the reflection sheet39arranged on the rear face of the light guiding plate21; and enters again the light guiding plate21to travel through the light guiding plate21.

The light travelling through the light guiding plate21and the light whose direction is changed on the back face optical elements23and which reaches the light exiting face at an incident angle narrower than the total reflection critical angle appear in each zone along the light guiding direction of the light guiding plate21. Therefore, the light travelling through the light guiding plate21exits the light exiting face little by little. This enables a light amount distribution of the light exiting the light exiting face of the light guiding plate21, along the light guiding direction, to be even.

The light exiting the light guiding plate21thereafter reaches the light diffusion plate26, which improves uniformity thereof. The light diffused or collected as necessary by the prism layer27to exit the prism layer27then reaches the reflection type polarizing plate28. Here, the light in a polarization direction along the transmission axis of the reflection type polarizing plate28is transmitted through the reflection type polarizing plate28, to be directed toward the optical sheet30.

The light in a polarization direction along the reflection axis of the reflection type polarizing plate28is reflected and returned to the light guiding plate21side as shown by the dotted arrows inFIG. 2. The returned light is reflected on the light guiding plate21, the back face optical elements23, or the reflection sheet39, to travel again toward the reflection type polarizing plate28. In this reflection, the polarization directions of some lights are changed, and these lights are partially transmitted through the reflection type polarizing plate28. The rest of the lights is returned again to the light guiding plate side. In this way, repeated reflection makes it possible for the light reflected on the reflection type polarizing plate28to be also transmitted through the reflection type polarizing plate28. This increases the use efficiency of the light from the light source25.

Here, the polarization direction of the light exiting the reflection type polarizing plate28is a direction along the transmission axis of the lower polarizing plate14, and this light is a light in a polarized state which allows the light to be transmitted through the lower polarizing plate14.

The light exiting the reflection type polarizing plate28reaches the optical sheet30. The light entering the optical sheet30travels as having an optical path as follows.FIG. 7shows examples of an optical path in the optical sheet30.

The light is directed toward the interface34aof interfaces between the light transmissive portions33and the light absorbing portions34, which is on the upper side of the light absorbing portion34in the direction where the light transmissive portions33and the light absorbing portions34are alternately aligned (vertical direction in this embodiment) as shown by the lights L21and L22inFIG. 2, and lights L71and L72inFIG. 7. Then the light is totally reflected on the interface34ato be an obliquely upward light directed toward the watcher side, to be controlled in a desired direction.

At this time, if the interface34bof interfaces of the light transmissive portions33and the light absorbing portions34, which is on the lower side of the light absorbing portion34, inclines obliquely upwards as being close to the watcher side, it becomes difficult for the light absorbing portions34to block light as the lights L21, L22, L71, and L72from travelling, which makes it possible to guide more light in a desired direction.

Since L73shown inFIG. 7travels obliquely upwards toward the watcher side at such an angle as to be transmitted through the interface34bbetween the light transmissive portion33and light absorbing portion34without total reflection on this interface, L73is transmitted through the interface34b, to be absorbed in the light absorbing portion34.

This makes it possible to efficiently absorb and block the light exiting at a viewing angle that is no less than a desired angle, and further to efficiently control the travelling direction of light.

This also makes it possible to absorb such light entering the liquid crystal panel to probably lead to defects such as deteriorated contrast and color inversion, and a low quality.

The direction of the light transmitted through the optical functional layer32is further changed in the optical element layer35b. Specifically, in this embodiment, the main refracting face35drefracts the lights L71and L72further upwards, to be exited as shown by the lights L71and L72inFIG. 7. This makes it possible to shift a light exiting range further upwards.

Therefore, the optical sheet30in this embodiment (B inFIG. 8) makes it possible to efficiently increase light exiting more upwards in the vertical direction than the case where no light exiting side light controlling layer35is included (A inFIG. 8) as shown inFIG. 8. InFIG. 8, the horizontal axis represents the light exiting angle with the normal line of the sheet face in the vertical direction; the positive indicates the upward and the negative indicates the downward. The vertical direction represents a relative brightness when a certain brightness is defined as 100%. It is difficult to adjust the light exiting angle as described above only by the optical functional layer. Even if do so, the adjustment can be accompanied with defects such as a lowered brightness. Against this, further including the optical element layer35blike the optical sheet30makes it possible to efficiently control the light exiting angle.

The optical element layer35bfor controlling light as described above has a simple structure as described above, and takes an effect with such an easy structure.

In this embodiment, θ11and θ12of the optical functional layer32(seeFIG. 5) of θ11<θ12makes it possible to control the viewing angle in a wider range.

The light exiting the optical sheet30enters the lower polarizing plate14of the liquid crystal panel15. The lower polarizing plate14transmits one polarization component in the incident light, and absorbs the other polarization component. The light transmitted through the lower polarizing plate14is selectively transmitted through the upper polarizing plate13in accordance with the state of creation of an electric field for each pixel. In this manner, the liquid crystal panel15selectively transmits the light from the surface light source device20for each pixel, which makes it possible for a watcher of the liquid crystal display to observe an image. At this time, an image light is given a watcher via the functional film40, to improve the quality of an image.

FIG. 9is an explanatory view of the second embodiment, and corresponds toFIG. 5. In this embodiment, a light exiting side light controlling layer135as a light controlling layer is employed instead of the light exiting side light controlling layer35. The other portions are the same as those of the image source unit10, and thus the structure and operations of the light exiting side light controlling layer135will be described here.

The light exiting side light controlling layer135controls the direction of the light exiting the optical functional layer32, to let the light exit. The light exiting side light controlling layer135is therefore constituted of the supporting layer35aand an optical element layer135b. The supporting layer35ais the same as the supporting layer35aof the light exiting side light controlling layer35.

The optical element layer135bis a layer to change the direction of the light exiting the optical functional layer32, and is formed of a plurality of unit optical elements135caligned over a face of the supporting layer35awhich is on the opposite side to the optical functional layer32.

In this embodiment, the unit optical elements135cspecifically have the following structure: each of the unit optical elements135cis in the form of a triangular prism having a triangular cross section protruding opposite to the optical functional layer32, a ridge of which is constituted of a ridge line extending in parallel to the extending direction of the light transmissive portions33and the light absorbing portions34(bias angle α2=0°), or extending as being offset by a bias angle (bias angle α2≠0°, as having that cross section. A plurality of the unit optical elements135care aligned in a direction different from their extending direction. The bias angle α2formed by the unit optical element135cand the light transmissive portions33is understood same as in the case of the unit optical element35c.

Each of the unit optical elements135cincludes a main refracting face135dand a rise face135eas seen fromFIG. 9. These main refracting face135dand rise face135eform two faces of a triangular prism, and the other one face is over the supporting layer35ato be fixed to the supporting layer35a.

In this embodiment, the main refracting face135dis a refracting face to change the angle of the light exiting upwards from the optical functional layer32so that the light is close to the front direction in a state asFIG. 1. This makes it possible to adjust the light exiting angle in the vertical direction to a desired direction. In this case, the main refracting face135dinclines downwards as being separate from the optical functional layer32(here, this direction is defined as a negative (−) direction). Thus, in one unit optical element135c, the main refracting face135dis the top and the rise face135eis the bottom.

The inclination of the main refracting face135dforms an angle θ31with the direction of the normal line of the light exiting face of the optical functional layer32as shown inFIG. 9.

A specific angle of θ31is preferably no less than −89° and less than −45° (the absolute value of the inclination angle is more than 45° and no more than 89°). This makes it possible to surely control light for improving brightness in a desired direction (control of the light exiting angle). θ31of no less than −45° may increase light totally reflected on the main refracting face135dnot to exit. θ31of less than −89° makes it almost impossible for the main refracting face to function.

θ31is more preferably −89° to −80° (the absolute value of the inclination angle is 80° to 89°). θ31of this range makes it possible to use a small rise face135e, to reduce a stray light due to the rise face135e.

The other preferred aspects of the unit optical elements135cin view of their shapes may be understood same as those in the unit optical elements35c.

Operations of an image source unit including the light exiting side light controlling layer135will be described.FIG. 10shows examples of an optical path. Optical paths in the other portions are the same as in the image source unit10, and thus description thereof will be omitted here.

The direction of the light transmitted through the optical functional layer32is further changed in the optical element layer135b. Specifically, in this embodiment, the main refracting face135drefracts lights L101and L102so that the lights L101and L102travels toward the front as close as possible, to be exited as shown by the lights L101and L102inFIG. 10. This leads to control of the light exiting angle in a desired direction.

Therefore, an optical sheet including the light exiting side light controlling layer135makes it possible to efficiently shift the viewing angle (C inFIG. 11) compared with the case where no light exiting side light controlling layer135is included (A inFIG. 11) as shown inFIG. 11. InFIG. 11, the horizontal axis represents a light exiting angle with the normal line of the sheet face in the vertical direction; the positive indicates the upward and the negative indicates the downward. The vertical direction represents a relative brightness when a certain brightness is defined as 100%. It is difficult to adjust the light exiting angle as described above only by the optical functional layer. Even if do so, the adjustment can be accompanied with defects such as a lowered brightness. Against this, further including the light exiting side light controlling layer135makes it possible to efficiently control the viewing angle.

The optical element layer135bfor controlling light as described above has a simple structure as described above, and takes an effect with such an easy structure.

FIG. 12is an explanatory view of the third embodiment, and is an exploded perspective view of an image source unit210including an optical sheet230. In this embodiment, the optical sheet30is arranged closer to the light entering side (light guiding plate21side) than the optical sheet230is, and these two optical sheets30and230constitute a light controlling member229. In this embodiment, the optical sheet30may be referred to as a first optical sheet30, and the optical sheet230may be referred to as a second optical sheet230for easy understanding.

FIG. 13is a partially exploded cross-sectional view of the image source unit210taken along the line XIII-XIII inFIG. 12(line along the vertical direction), andFIG. 14is an exploded cross-sectional view of the image source unit210taken along the line XIV-XIV inFIG. 12(line along the horizontal direction). The vertical and horizontal directions here indicate directions of the light controlling member229in a display when the display in which the light controlling member229is arranged is used.

Such an image source unit210is also housed in a housing that is not shown, along with general devices necessary to operate as the image source unit210such as a power source to activate the image source unit210, and an electronic circuit to control the image source unit, to constitute the display, detailed description of which is omitted. This embodiment will describe a liquid crystal image source unit as one aspect of the image source unit, and a liquid crystal display as one aspect of the display. Hereinafter the image source unit210will be described.

The image source unit210includes the liquid crystal panel15, a surface light source device220, and the functional film40. In this embodiment, the optical sheet230, and the light controlling member229including this sheet are included in the surface light source device220.FIGS. 12 to 14show the directions when the display is installed, together.

Here, the liquid crystal panel15and the functional film40may be understood same as in the image source unit10in the first embodiment, and thus the same reference signs are given them to omit description thereof.

The surface light source device220is arranged on a side opposite to the watcher side across the liquid crystal panel15, and is a lighting device to exit a planar light toward the liquid crystal panel15. As can be seen fromFIGS. 12 to 14, the surface light source device220in this embodiment is configured as an edge light type surface light source device, including the light guiding plate21, the light source25, the light diffusion plate26, the prism layer27, the reflection type polarizing plate28, the light controlling member229, and the reflection sheet39.

Here, the members other than the light controlling member229may be understood same as in the surface light source device20included in the image source unit10in the first embodiment, and thus the same reference signs are given them to omit description thereof.

In this embodiment, the light controlling member229is constituted of the first optical sheet30and the second optical sheet230. The first optical sheet30is arranged on the light guiding plate21side, and the second optical sheet230is arranged on the liquid crystal panel15side.

Here, the first optical sheet30may be understood same as the optical sheet30included in the surface light source device20, and thus the same reference sign is given it to omit description thereof.

FIG. 15partially shows an enlarged second optical sheet230from the point of view ofFIG. 14. As is seen fromFIGS. 12 to 15, the second optical sheet230includes a base material layer231formed in a sheet shape, an optical functional layer232provided for one face of the base material layer231(face on the first optical sheet30side in this embodiment), and a light exiting side light controlling layer235arranged on the other face of the base material layer231(face on the liquid crystal panel15side in this embodiment).

Here, the base material layer231may be understood same as the base material layer31in the optical sheet30.

The optical functional layer232is a layer laminated on one surface of the base material layer231(face on the first optical sheet30side in this embodiment), and is constituted of light transmissive portions233and light absorbing portions234. The optical functional layer232has a shape having the cross section shown inFIGS. 14 and 15, and extending from the back to the front on the drawing sheet (vertical direction when the image source unit210is viewed in the front view in this embodiment). The light transmissive portions233and the light absorbing portions234are alternately aligned along a face of the optical functional layer232in a direction different from the extending direction thereof (horizontal direction in this embodiment).

Each of the light transmissive portions233is a portion whose main function is to transmit light. In this embodiment, the light transmissive portion233is an element having an approximately trapezoidal cross-sectional shape that has a longer lower base on the base material layer231side and a shorter upper base on the opposite side (first optical sheet30side) on the cross section shown inFIGS. 14 and 15.

A plurality of the light transmissive portions233extend in one direction (vertical direction in this embodiment) along the layer face of the base material layer231as keeping the above described cross sections, and are aligned at intervals in a different direction from the extending direction (horizontal direction in this embodiment). A gap (groove) having an approximately trapezoidal cross section is formed between respective adjacent light transmissive portions233. Therefore, each gap (groove) has a trapezoidal cross section having a longer lower base on the upper base side of the light transmissive portions233(first optical sheet30side), and a shorter upper base on the lower base side of the light transmissive portions233(base material layer231side). Necessary materials described later are filled in the gaps, to form the light absorbing portions234.

In this embodiment, a sheet-like sill portion232alinks a plurality of the light transmissive portions233at their lower base side (base material layer231side).

Such a structure leads to such arrangement that the extending direction of the light transmissive portions33of the first optical sheet30and that of the light transmissive portions233of the second optical sheet230cross each other in the front view of the optical sheets.

The refractive indexes of the light transmissive portions233and the light absorbing portions234may be understood same as those of the light transmissive portions33and the light absorbing portions34of the optical sheet30.

The optical functional layer232is not specifically limited, and for example, may have the following shape.FIG. 16is a partially further enlarged view ofFIG. 15(top portion ofFIG. 15).

θ41shown inFIG. 16is an angle formed by an interface234a, and the normal line of the layer face of the optical functional layer232: the interface234ais left or right one of each interface between the light transmissive portions233and the light absorbing portions234in the horizontal direction when the second optical sheet230is arranged in a state asFIG. 12. θ42is an angle formed by an interface234b, and the normal line of the layer face of the optical functional layer232: the interface234bis the other left or right one of each interface between the light transmissive portions233and the light absorbing portions234in the horizontal direction when the second optical sheet230is arranged in a state asFIG. 12.

θ41and θ42are preferably 0° to 10° in this embodiment. The relationship between the sizes of the angles θ41and θ42may be set as necessary.

The pitch of the light transmissive portion233and the light absorbing portion234, shown by PbinFIG. 15, is preferably 20 μm to 100 μm, and more preferably 30 μm to 100 μm. The thickness of the light absorbing portion234shown by DbinFIG. 15is preferably 50 μm to 150 μm, and more preferably 60 μm to 150 μm. The pitch and thickness within these ranges make it possible to give suitably balanced transmission and absorption of light.

In this embodiment, the example where each interface between the light transmissive portions233and the light absorbing portions234is in the form of a straight line on the cross section is given. The interface may be in the form of a polygonal, a convex curved line, a concave curved line, etc. without limitation to the above. A plurality of the light transmissive portions233and the light absorbing portions234may have the same cross-sectional shape, or different cross-sectional shapes having regularity.

The example where the extending direction of the light transmissive portions233and the light absorbing portions234is vertical is described above. This direction is preferably offset from the aligning direction of the pixels of the liquid crystal layer12in the front view of the image source unit (bias angle α3) in view of suppressing moire. This bias angle α3is not specifically restricted as long as moire is prevented, and is preferably 1° to 10°.

The light exiting side light controlling layer235will be described. The light exiting side light controlling layer235controls the direction of light exiting the optical functional layer232, to let the light exit. In this embodiment, the light exiting side light controlling layer235controls the direction of the light which is controlled in the optical functional layer232, to make the angle where the light exits a desired angle. More specifically, the light exiting the outer circumference area of the sheet is controlled so as to travel as inclining to the center compared with the direction of the normal line of the sheet.

The light exiting side light controlling layer235is therefore constituted of a supporting layer235aand an optical element layer235b.

The supporting layer235ais a transparent sheet-like member that functions as a supporting body of the optical element layer235b, and may be understood same as the supporting layer35aof the optical sheet30.

The optical element layer235bis a layer to change the direction of the light exiting the optical functional layer232, and is formed of a plurality of unit optical elements235caligned over a face of the supporting layer235awhich is on the opposite side to the optical functional layer232.

In this embodiment, the optical element layer235bis arranged over the supporting layer235a. The optical element layer235bis not limited the above, and may be directly arranged over a face of the base material layer231which is opposite to the side where the optical functional layer232is arranged. In this case, the light exiting side light controlling layer does not have any supporting layer, and is constituted of the optical element layer235bonly.

In this embodiment, the optical element layer235bis a layer to change the direction of the light exiting toward the outer circumference of the sheet, which is controlled in the optical functional layer232, so that the light exits as inclining to the center compared with the direction of the normal line of the sheet in the aligning direction of a plurality of the unit optical elements235c(horizontal direction in this embodiment).

Each of the unit optical elements235cis in the form of a triangular prism having a triangular cross section protruding opposite to the optical functional layer232as shown inFIGS. 14 to 16, a ridge of which is constituted of a ridge line extending in the same direction as the extending direction of the light transmissive portions233and the light absorbing portions234(bias angle α4=0°), or extending as being offset in the front view of the optical sheet (bias angle α4≠0°) (extending in the vertical direction in this embodiment), as having that cross section. A plurality of the unit optical elements235care aligned in a direction different from their extending direction (horizontal direction in this embodiment).

When the ridge line of each of the unit optical elements235cextends as being offset from the extending direction of the light transmissive portions233and the light absorbing portions234in the front view of the optical sheet (bias angle α4≠0°), preferably, the extending direction of the light transmissive portions233of the optical functional layer232relatively inclines from the extending direction of the ridge lines of the unit optical elements235cby the bias angle α4of 0°<α4≤45° in the front view of the light controlling member229. This makes it possible to prevent moire due to the aligning structure of the light transmissive portions233and the light absorbing portions234, and the aligning structure of the unit optical elements235c. The angle α4of more than 45° leads to lowered efficiency of the control of the direction of light in the unit optical elements235c. The angle α4is more preferably 1°≤α4≤10°.

As seen fromFIG. 15, the cross-sectional shapes of the unit optical elements235care in symmetry on one and the other end sides of the optical element layer235bin this embodiment across the center of the sheet in the aligning direction of the unit optical elements235c, and a central area between the one and the other end sides does not include unit optical element235c(portion of W3inFIG. 15). That is, this portion is flat, and, in other words, is a portion where an angle formed by a main refracting face of the unit optical element and the normal line of the sheet face (θ51inFIG. 16) is 90°.

Such a portion where no unit optical element is included is not always necessary to be provided. The unit optical elements235cto be in symmetry may be adjacent to each other across the center of the sheet. The adjacent unit optical elements in symmetry across the center of the sheet as described above, however, cause a line along the boarder therebetween, which may be visually recognized. Thus, it is preferable that no unit optical element exist at least on the center of the sheet, and the center thereof be flat. For example, a surface of a die has only to be processed so that a cutting tool is over part of the surface which corresponds to the center of the sheet when the die for forming the optical element layer235is made by cutting, in order that no line appears on the center of the sheet as described above.

Such a plurality of the unit optical elements235cmay be aligned according to, for example, a linear Fresnel lens.

Each of the unit optical elements235cincludes a main refracting face235dand a rise face235eas seen fromFIG. 16. These main refracting face235dand rise face235eform two faces of a triangular prism, and the other one face is over the supporting layer235ato be fixed to the supporting layer235a.

In this embodiment, the main refracting face235dis a refracting face to change the direction of the light exiting the optical functional layer232in the horizontal direction so that the light travels as inclining toward the central side compared with the normal line of the sheet in the state ofFIGS. 12 to 16. This directs the light exiting an end part of a screen toward the central side in the aligning direction of the unit optical elements235c(horizontal direction in this embodiment), thus to direct the light from the end part of the screen toward a watcher who views the center of the screen in the front view, which makes it possible for the watcher to clearly watch the light exiting the end part of the screen. In this case, when one main refracting face235dis focused on, this main refracting face235dinclines in a separating direction (more protruding direction) from the optical functional layer232as being close to the central side of the sheet. Thus, when one unit optical element235cis focused on, the main refracting face235dis on the outer circumferential side of the sheet, and the rise face235eis on the central side of the sheet. The inclination of the main refracting face235dforms an angle θ51shown inFIG. 16with the direction of the normal line of the optical functional layer232.

A specific angle of θ51is preferably more than 45° and less than 90° (the absolute value of the inclination angle of the main refracting face is more than 45° and less than 90°). This makes it possible to surely control light for improving brightness in a desired direction (control of the light exiting angle). θ51of no more than 45° may increase light totally reflected on the main refracting face235dnot to exit. θ51of no less than 90° makes it almost impossible for the main refracting face to function. θ51is more preferably 80° to 89°. θ51of this range makes it possible to use a small rise face235e, to reduce a stray light due to the rise face235e.

θ51is preferably different between the unit optical elements235con the central side and those on the outer circumferential side in the aligning direction of the unit optical elements235c(horizontal direction in this embodiment). This makes it possible to further accurately control light. θ51is more preferably formed so as to be narrower from the unit optical element235con the central side to those on the outer circumferential side. This makes it possible to efficiently control the direction of light travelling to the center.

The rise face235eis a face necessary for forming the main refracting face235d.

The rise face235epreferably forms the inclination angle, which is shown as θ52inFIG. 16, of 80° to 100° with the direction along the light exiting face of the optical functional layer232. θ52is more preferably 80° to 90° in view of production. θ52of less than 80°, and θ52of more than 100° may increase a stray light due to the rise face235e.

The vertex angle of the unit optical element235cis naturally determined by θ51and θ52, and is preferably no less than 45° and less than 90°.

The pitch of the unit optical element235cshown by PpinFIG. 15is preferably short from the viewpoint that moire of a short pitch makes it difficult for the moire to be seen even if the moire appears. Specifically, the pitch Ppis preferably no more than 50 μm.

It is desirable that the pitch Ppof the unit optical element235cbe shorter than the pitch Pbof the light transmissive portion233of the optical functional layer232(seeFIG. 15) since the optical functional layer232is more difficult than the optical element layer235bin production. It is further desirable that Ppbe no more than ½ of Pb. It is most desirable that an end part of the light transmissive portion233and an end part of the unit optical element235cbe not at the same location as long as possible when Ppis regularly magnified like Pb/2, Pb/3, and Pb/4. In other words, it is desirable that the least common multiple of Ppand Pbbe a large number.

Ppis preferably no less than 10 μm since a small unit optical element235cleads to lowered accuracy.

Pmx(μm) is more preferably no more than 10000 (μm) when the aligning pitch of the light transmissive portions233is Pb(μm) and the aligning pitch of the unit optical elements235cis Pp(μm). Pmxmay be understood in the same way as described above.

The protruding height of the unit optical element235cfrom the supporting layer235a, which is shown by DpinFIG. 15is preferably 1 μm to 10 μm. The height lower than this lower limit may lead to deteriorated accuracy of processing, which leads to defects such that stripe lines are visually recognized. The height higher than this upper limit makes it easy for moire to appear due to the light absorbing portions234and the unit optical elements235c.

In this embodiment, a plurality of the unit optical elements235care continuously arranged without any gaps, but not limited to this. In another aspect, a gap may be provided between adjacent unit optical elements235c, from which a face of the supporting layer235amay be exposed.

In this embodiment, the main refracting face235dof the unit optical element235cis linear on the cross section shown inFIGS. 14 to 16, but is not always limited to this. The main refracting face235dmay be in the form of a convex or concave curved line, or a polygonal line on its cross section.

The main refracting face235dand the rise face235emay be rough faces. This makes it possible to scatter light to suppress moire. A method for forming the main refracting face235dand the rise face235einto rough faces is not specifically limited. Examples thereof include direct blasting on the unit optical element, and blasting on a die for molding the unit optical element.

All of a plurality of the unit optical elements235care not always necessary to have the same shape, and may suitably have different shapes from each other.

In this embodiment, the supporting layer235ais provided for the light exiting side light controlling layer235. The supporting layer235ais not always necessary to be provided as described above, and the optical element layer235bmay be directly formed over the base material layer231. At this time, a face of the base material layer231which forms the interface with the optical element layer235bmay be formed into a rough face, and the base material layer231may be different from the optical element layer235bin refractive index. This makes it possible to scatter light on the rough face to suppress moire.

The light exiting side light controlling layer is not always necessary to be united with the base material layer and the optical functional layer, and may be provided separately. Therefore, an air layer may be formed, or another functional layer may be arranged between the light exiting side light controlling layer, and the base material layer or the optical functional layer.

Such a supporting layer235aand optical element layer235b(unit optical element235c) of the light exiting side light controlling layer235may be made from materials same as those of the supporting layer35aand the optical element layer35bof the optical sheet30.

The second optical sheet230can be produced according to the optical sheet30as described above.

Operations of the image source unit210having the above described structure will be described as showing examples of an optical path. The examples of an optical path are for conceptualistic explanation, and do not strictly give degrees of reflection and refraction. The manner of exiting the light source25to reach the light controlling member229is the same as that in the examples of an optical path described concerning the image source unit10, and thus description thereof will be omitted (seeFIG. 2).

The light entering the light controlling member229enters the first optical sheet30first, and travels as having an optical path as follows.FIG. 17shows examples of an optical path in the first optical sheet30.

The entering light is directed toward the interface34aof interfaces between the light transmissive portions33and the light absorbing portions34, which is on the upper side of the light absorbing portion34in the direction where the light transmissive portions33and the light absorbing portions34are alternately aligned (vertical direction in this embodiment) as shown by lights L171and L172inFIG. 17. Then the light is totally reflected on the interface34ato be an obliquely upward light toward the watcher side, to be controlled in a desired direction.

At this time, if the interface34bof interfaces of the light transmissive portions33and the light absorbing portions34, which is on the lower side of the light absorbing portion34, inclines obliquely upwards toward the watcher, it becomes difficult for the light absorbing portions34to block light as the lights L171, and L172from travelling, which makes it possible to guide more light in a desired direction.

Since L173shown inFIG. 17travels obliquely upwards toward the watcher side at such an angle as to be transmitted through the interface34bbetween the light transmissive portion33and light absorbing portion34without total reflection on this interface, L173is transmitted through the interface34b, to be absorbed in the light absorbing portion34.

This makes it possible to efficiently absorb and block the light exiting at a light exiting angle that is no less than a desired angle, and further to efficiently control the travelling direction of light.

This also makes it possible to absorb such light entering the liquid crystal panel to probably lead to defects such as deteriorated contrast and color inversion, and the low quality of an image.

The direction of the light transmitted through the optical functional layer32is further changed in the optical element layer35b. Specifically, in this embodiment, the main refracting face35drefracts the lights L171and L172further upwards, to be exited as shown by the lights L171and L172inFIG. 17. This makes it possible to shift a light exiting range further upwards.

Therefore, the first optical sheet30in this embodiment (B inFIG. 8) also makes it possible to efficiently increase light exiting more upwards in the vertical direction than the case where no light exiting side light controlling layer35is included (A inFIG. 8) as shown inFIG. 8. It is difficult to adjust the light exiting angle as described above only by the optical functional layer32. Even if do so, the adjustment can be accompanied with defects such as a lowered brightness. Against this, further including the optical element layer35blike the first optical sheet30makes it possible to efficiently control the light exiting angle.

The optical element layer35bfor controlling light as described above has a simple structure as described above, and takes an effect with such an easy structure.

The light exiting the first optical sheet30reaches the second optical sheet230. The light entering the second optical sheet230travels as having an optical path as follows.FIG. 15shows examples of an optical path in the second optical sheet230.

Lights L151to L156inFIG. 15are totally reflected on interfaces between the light transmissive portions233and the light absorbing portions234in a direction where the light transmissive portions233and the light absorbing portions234are alternately aligned (horizontal direction in this embodiment), and are changed so as to direct toward the normal line of the sheet face. This makes it easy to control light in the optical element layer235bas desired.

Light L157is a light travelling almost in the front direction in the horizontal direction first of all, and is transmitted through the light transmissive portion233without reaching the light absorbing portion234.

Light L158shown inFIG. 15is a light travelling at a wide angle with the front in the horizontal direction. This light travels at such an angle as to be transmitted through an interface between the light transmissive portions233and the light absorbing portions234without total reflection on the interface, and thus is transmitted through the interface to be absorbed in the light absorbing portion234.

This makes it possible to efficiently absorb and block the light exiting at no less than a desired angle, and further to efficiently control the direction of travelling light. This also makes it possible to absorb such light entering the liquid crystal panel to probably lead to defects such as deteriorated contrast and color inversion.

The direction of the light transmitted through the optical functional layer232is further changed in the optical element layer235b. Specifically, in this embodiment, light may exit the main refracting face235dso as to travel as inclining toward the center compared with the normal line of the sheet face in the aligning direction of the unit optical elements235c(horizontal direction in this embodiment) as the lights L151, L152, L153, and L154shown inFIG. 15.

The lights L155, L156, and L157are transmitted through a portion where no unit optical element235cis included, which let light close to the front in the horizontal direction exit, to give the watcher side the light as it is.

FIGS. 18A and 18Bare explanatory graphs showing characteristics of the light exiting the sheet in the horizontal direction. InFIGS. 18A and 18B, the horizontal axis represents the light exiting angle with the direction of the normal line of the sheet face in the horizontal direction; the positive indicates the right and the negative indicates the left, to the front. The vertical direction represents a relative brightness when a certain brightness is defined as 100%

FIG. 18Ashows one example where the light exiting side light controlling layer235is not provided. In this case, light exits as its light exiting angle is kept regulated in the optical functional layer, which results in the light exiting only in a direction having a small inclination (only in a direction within a range of approximately −30° and +30° in the example ofFIG. 18A) from the normal line of the sheet face. Thus, a dark portion may be present especially at an outer circumferential end etc. of a screen when the screen is wide or when the screen is viewed a little obliquely.

FIG. 18Bshows, in contrast, an example where the light exiting side light controlling layer235is included as this embodiment. The unit optical elements235carranged on the outer circumferential ends of the light exiting side light controlling layer235make it possible to control the peaks of the exiting directions of the lights exiting the unit optical elements235con one side of the outer circumferential end of the sheet (C1) and that on the other side thereof (C2) respectively, so that the peaks shift to the direction of the normal line of the sheet face (direction at 0°) as shown by C1and C2inFIG. 18B. Light exits as it is in a close direction to the normal line of the sheet face as shown by D on the central area of the sheet which is formed between the unit optical elements235con both outer circumferential ends, and where no unit optical element235cis arranged. This makes it possible to prevent a dark portion from being present at an outer circumferential end etc. of a screen even when the screen is wide or when the screen is viewed a little obliquely since the light exiting the end part of the screen also inclines so as to direct to the direction where the watcher sees.

It is difficult to adjust the light exiting angle as described above only by the optical functional layer232. Even if do so, the adjustment can be accompanied with defects such as a lowered brightness, and necessity of a complex structure. Against this, including the optical element layer235blike the second optical sheet230makes it possible to efficiently control the light exiting angle.

The optical element layer235bfor controlling light as described above has a simple structure as described above, and takes an effect with such an easy structure.

Light is transmitted through such a light controlling member229, which makes it possible to let the light exit in a vertical direction as desired, and to control the light exiting the outer circumferential ends in the horizontal direction. Such control may be efficiently performed with a simple structure.

The light exiting the light controlling member229enters the lower polarizing plate14of the liquid crystal panel15. The lower polarizing plate14transmits one polarization component in the incident light, and absorbs the other polarization component. The light transmitted through the lower polarizing plate14is selectively transmitted through the upper polarizing plate13in accordance with the state of creation of an electric field for each pixel. In this manner, the liquid crystal panel15selectively transmits the light from the surface light source device220for each pixel, which makes it possible for a watcher of the liquid crystal display to observe an image. At this time, an image light is given a watcher via the functional film40, to improve the quality of an image.

This embodiment described the example where the first optical sheet30and the second optical sheet230are combined to be employed as the light controlling member229. Both are not always necessary to be combined, and the first optical sheet30and the second optical sheet230may be each independently employed. Each optical sheet may be separately used, or both may be combined according to an aspect of light control.

FIG. 19is an explanatory view of the forth embodiment, and is an exploded perspective view of an image source unit310including an optical sheet330.FIG. 20is a partially exploded cross-sectional view of the image source unit310taken along the line XX-XX inFIG. 19, andFIG. 21is a partially exploded cross-sectional view of the image source unit310taken along the line XXI-XXI.

Such an image source unit310is also housed in a housing that is not shown, along with general devices necessary to operate as the image source unit310such as a power source to activate the image source unit310, and an electronic circuit to control the image source unit, to constitute the display, detailed description of which is omitted. This embodiment will describe a liquid crystal image source unit as one aspect of the image source unit, and a liquid crystal display as one aspect of the display.

The image source unit310includes the liquid crystal panel15, a surface light source device320, and the functional film40. In this embodiment, the optical sheet330is included in the surface light source device320.FIGS. 19 to 21show the directions where the display is installed, together.

Here, the liquid crystal panel15and the functional film40are the same as those in the image source unit10, and thus the same reference signs are given them to omit description thereof.

The surface light source device320is arranged on a side opposite to the watcher side across the liquid crystal panel15, and is a lighting device to exit a planar light toward the liquid crystal panel15. As can be seen fromFIGS. 19 to 21, the surface light source device320in this embodiment is also configured as an edge light type surface light source device, including the light guiding plate21, the light source25, the light diffusion plate26, the prism layer27, the reflection type polarizing plate28, the optical sheet330, and the reflection sheet39.

Here, the members other than the optical sheet330are the same as those in the surface light source device20in the image source unit10, and thus the same reference signs are given them to omit description thereof. In this embodiment, however, the unit prisms27aof the prism layer27extend in a light guiding direction of the light guiding plate, and a plurality of the unit prisms27aare aligned in the direction orthogonal to the light guiding direction of the light guiding plate.

FIG. 22partially shows an enlarged optical sheet330in the point of view ofFIG. 20. As is seen fromFIGS. 19 to 22, the optical sheet330includes the base material layer31formed in a sheet shape, an optical functional layer332provided for one face of the base material layer31(face on the light guiding plate21side in this embodiment), and a light entering side light controlling layer335that functions as a light controlling layer.

Here, the base material layer31is the same as that included in the optical sheet30of the image source unit10, and thus the same reference signs are given it to omit description thereof.

The optical functional layer332is a layer laminated on one surface of the base material layer31(face on the light guiding plate21side in this embodiment), and light transmissive portions333and light absorbing portions334are alternately aligned along the layer face thereof.

The optical functional layer332has the cross section shown inFIG. 22, and has a shape extending from the back to the front on the drawing sheet (horizontal direction when the image source unit310is viewed in the front view). That is, the optical functional layer332includes the light transmissive portion333and the light absorbing portions334: each of the light transmissive portions333has an approximately trapezoidal shape, and each of the light absorbing portions334is formed between two adjacent light transmissive portions333and has an approximately trapezoidal cross section, on the cross section shown inFIG. 22.

Each of the light transmissive portions333is a portion whose main function is to transmit light. In this embodiment, the light transmissive portion333is an element having an approximately trapezoidal cross sectional shape that has a longer lower base on the base material layer31side and a shorter upper base on the opposite side (light guiding plate21side, light entering side light controlling layer335side) on the cross section shown inFIGS. 20 and 22. The light transmissive portions333extend in the above described direction (horizontal direction in this embodiment) along the layer face of the base material layer31as keeping the above described cross sections, and are aligned at intervals in a different direction from the extending direction (vertical direction in this embodiment). A gap (groove) having an approximately trapezoidal cross section is formed between respective adjacent light transmissive portions333. Therefore, each gap (groove) has a trapezoidal cross section having a longer lower base on the upper base side of the light transmissive portions333(light guiding plate21side, light entering side light controlling layer335side), and a shorter upper base on the lower base side of the light transmissive portions333(liquid crystal panel15side, base material layer31side). Necessary materials described later are filled in the gaps, to form the light absorbing portions334. In this embodiment, a sheet-like sill portion332alinks adjacent light transmissive portions333at their longer lower base side.

The materials forming the light transmissive portions333and the light absorbing portions334, and the refractive indexes thereof are understood same as those of the light transmissive portions33and the light absorbing portions34of the optical sheet30.

FIG. 23is an explanatory view of angles θ61and θ62formed by interfaces between the light transmissive portions333and the light absorbing portions334, and the normal line of the layer face of the optical functional layer332.FIG. 23is a partially further enlarged view ofFIG. 22.

θ61is an angle formed by an interface334a, and the normal line of the layer face of the optical functional layer332: the interface334ais one of each interface between the light transmissive portions333and the light absorbing portions334which is on the upper side of the light absorbing portion334when the optical sheet330is arranged in a state asFIG. 19. θ62is an angle formed by an interface334b, and the normal line of the layer face of the optical functional layer332: the interface334bis one of each interface between the light transmissive portions333and the light absorbing portions334which is on the lower side of the light absorbing portion334in the same state.

θ61is preferably 0° to 10° in this embodiment. θ61of more than 0° means downward inclination from the light guiding plate21side (light entering side, light entering side light controlling layer335) to the liquid crystal panel15side (light exiting side, base material layer31side). θ61is more preferably no more than 4.0°, further preferably no more than 1.0°, and especially preferably 0°.

θ61of less than 0° leads to difficulty in production. θ61of more than 10° leads to a lowered effect on control of the direction of light in the optical functional layer332in combination with the light entering side light controlling layer335. θ61of more than 10° also requires large light absorbing portions334in the aligning direction (widths of the light absorbing portions, size in the vertical direction on the drawing sheet ofFIG. 23), which tends to lead to defects such as a lowered transmittance ratio of light.

θ62is preferably 0° to 10°. θ62of more than 0° means upward inclination from the light guiding plate21side (light entering side, light entering side light controlling layer335) to the liquid crystal panel15side (light exiting side, base material layer31side). θ62is more preferably no more than 5.0°, and further preferably no more than 3.0°. This makes it possible to prevent a transmittance ratio of light from lowering, and to increase light directing upwards. θ62of more than 10° requires large light absorbing portions334in the aligning direction (widths of the light absorbing portions, size in the vertical direction on the drawing sheet ofFIG. 23), which tends to lead to defects such as a lowered transmittance ratio of light, and which may lead to reduced light directing upwards.

The relationship between θ61and θ62in size is preferably θ61<θ62. This makes it possible to widen the viewing angle of an image light given by the image source unit310on the upper side more than that on the lower side.

For example, the light transmissive portions333and the light absorbing portion334are formed as follows in the optical functional layer332without any specific restriction: that is, the pitch of the light transmissive portion333and the light absorbing portion334, shown by PcinFIG. 22is preferably 20 μm to 100 μm, and more preferably 30 μm to 100 μm. The thickness of the light absorbing portion334shown by DcinFIG. 22is preferably 50 μm to 150 μm, and more preferably 60 μm to 150 μm. The pitch and thickness within these ranges make it possible to give more suitably balanced transmission and absorption of light.

In this embodiment, the example where each interface between the light transmissive portions333and the light absorbing portions334is in the form of a straight line on the cross section is given. The interface may be in the form of a polygonal line, a convex curved line, a concave curved line, etc. without limitation to the above. A plurality of the light transmissive portions333and the light absorbing portions334may have the same cross-sectional shape, or different cross-sectional shapes having regularity.

The light entering side light controlling layer335will be described. The light entering side light controlling layer335functions as a light controlling layer, to change the direction of the light entering the optical functional layer332in advance. The light is controlled to exit in a desired direction in the light entering side light controlling layer335and the optical functional layer332.

In this embodiment, the light entering side light controlling layer335is formed so as to change the direction of the light travelling in the normal line direction of the optical sheet330to a desired direction. More specifically, in this embodiment, the light entering side light controlling layer335functions so that the direction of the light travelling in the normal line direction of the optical sheet330toward the watcher side is changed obliquely downwards on the watcher side in the state ofFIGS. 19 to 22. This makes it possible for light to be reflected on the upper interface334abetween the light transmissive portions333and light absorbing portions334, to be directed obliquely upwards as described later.

The light entering side light controlling layer335therefore is constituted of a supporting layer335aand an optical element layer335b.

The supporting layer335ais a transparent sheet-like member that functions as a supporting body of the optical element layer335b. The supporting layer335amay be made from materials same as those of the base material layer31and the light transmissive portions333.

The optical element layer335bis a layer to change the direction of the light entering the optical functional layer332, and is formed of a plurality of unit optical elements335caligned on a face of the supporting layer335awhich is on the opposite side to a face where the optical functional layer332is arranged. The unit optical elements335care formed so as to change the direction of the light travelling in the normal line direction of the optical sheet330to one direction as described above. In this embodiment, the unit optical elements335care formed so as to change the direction of the light travelling in the normal line direction of the optical sheet330obliquely downwards in the state ofFIGS. 19 to 22.

In this embodiment, the unit optical elements335cspecifically have the following structure:

Each of the unit optical elements335cis in the form of a triangular prism having a triangular cross section protruding opposite to the optical functional layer332, which is across the base material layer31, a ridge of which is constituted of a ridge line extending in the same direction as the extending direction of the light transmissive portions333and the light absorbing portions334(bias angle α5=0°) or extending as being offset in the front view of the optical sheet (bias angle α5≠0°, as having that cross section. A plurality of the unit optical elements335care aligned in a direction different from their extending direction.

When the ridge line of each of the unit optical elements335cextends as being offset from the extending direction of the light transmissive portions333and the light absorbing portions334in the front view of the optical sheet (bias angle α5≠0°), preferably, the extending direction of the light transmissive portions333of the optical functional layer332relatively inclines from the extending direction of the ridge lines of the unit optical elements335cby the bias angle α5of more than 0° and no more than 45° in the front view of the optical sheet330. This makes it possible to prevent moire due to the aligning structure of the light transmissive portions333and the light absorbing portions334, and the aligning structure of the unit optical elements335c. The angle α5of more than 45° leads to lowered efficiency of the control of the direction of light in the unit optical elements335c. The angle α5is more preferably 1° to 10°.

Each of the unit optical elements335cincludes a main refracting face335dand a rise face335eas seen fromFIG. 23. These main refracting face335dand rise face335eform two faces of a triangular prism, and the other one face is over the supporting layer335ato be fixed to the supporting layer335a.

The main refracting face335dis a refracting face that functions so that the direction of the light travelling in the normal line direction of the optical sheet330is directed obliquely downwards. Thus, the main refracting face335dinclines so as to be close to the supporting layer335a(optical functional layer332) on the upper side in the vertical direction, and separate from the supporting layer335a(optical functional layer332) on the lower side in the vertical direction. The inclination shown by θ71inFIG. 23has an angle with the direction along a light entering face332bof the optical functional layer332. A specific angle of θ71is preferably more than 0° and less than 17°. This makes it possible to surely control light for improving brightness in a desired direction.

The rise face335eis a face necessary for forming the main refracting face335d. The rise face335ealso has a function to more surely block light exiting in an undesirable direction since the light entering the rise face335eis refracted here, and travels through the optical functional layer332at such an angle that the light is easy to be absorbed in the light absorbing portion334as described later.

The inclination of the rise face335e, which is shown by θ72, is preferably no more than 90° with the direction along the light entering face332bof the optical functional layer332. This angle of no less than 90° leads to difficulty in production. θ72is preferably no less than 73°. This makes it possible to make the angle formed by the main refracting face335dand the rise face335e90° or approximately 90°, and for the light entering the main refracting face335din the normal line direction of the main refracting face335dto travel in a direction almost parallel to the rise face335e, which makes it possible to suppress the light from being reflected on the rise face335eto be a stray light.

The pitch of the unit optical element335cshown by PqinFIG. 22is preferably shorter than the pitch Pcof the light absorbing portion334, and further preferably not a pitch at an integral multiple of Pc, such as ⅔ and ⅖. This makes it possible to prevent moire due to the light absorbing portions334and the unit optical elements335c. Pqis more preferably no less than 3 μm as satisfying the above described conditions. Pqof less than this lower limit leads to a defect of a deteriorated accuracy of processing.

The protruding height of the unit optical element335cfrom the supporting layer335a, which is shown by DqinFIG. 22is preferably 1 μm to 15 μm. The height lower than this lower limit leads to a defect of a deteriorated accuracy of processing. The height higher than this upper limit makes it easy for moire to appear due to the light absorbing portions334and the unit optical elements335c.

In this embodiment, a plurality of the unit optical elements335care continuously arranged without any gaps, but not limited to this. In another aspect, a gap may be provided between adjacent unit optical elements335c, from which a face of the supporting layer335amay be partially exposed.

All of a plurality of the unit optical elements335care not always necessary to have the same shape, and may suitably have different shapes from each other.

Such a supporting layer335aand an optical element layer335b(unit optical element335c) of the light entering side light controlling layer335may be made from materials same as those of the base material layer31and the light transmissive portions33.

Operations of the image source unit310having the above described structure will be described as showing examples of an optical path. The examples of an optical path are for conceptualistic explanation, and do not strictly give degrees of reflection and refraction.

First, the light exiting the light source25enters the light guiding plate21from the light entering face that is a side face (end face) of the light guiding plate21as shown inFIG. 20.FIG. 20shows examples of the optical paths of lights L201and L202entering the light guiding plate21from the light source25as one example.

As shown inFIG. 20, the lights L201and L202entering the light guiding plate21repeat total reflection due to the difference in refractive index from the air, on the face of the light guiding plate21on the light exiting side, and the back face opposite to the face; and travel in the light guiding direction (downwards on the drawing sheet ofFIG. 20).

Here, the back face optical elements23are arranged over the back face of the light guiding plate21. The traveling directions of the lights L201and L202travelling through the light guiding plate21are therefore changed by the back face optical elements23, and the lights L201and L202may enter the light exiting face and the back face at an incident angle narrower than the total reflection critical angle as shown inFIG. 20. In this case, the lights may exit the light exiting face of the light guiding plate21, and the back face that is opposite to the light exiting face.

The lights L201and L202exiting the light exiting face are directed toward the light diffusion plate26arranged on the light exiting side of the light guiding plate21. The light exiting the back face is reflected by the reflection sheet39arranged on the rear face of the light guiding plate21; and enters again the light guiding plate21to travel through the light guiding plate21.

The light travelling through the light guiding plate21and the light whose direction is changed on the back face optical elements23and which reaches the light exiting face at an incident angle narrower than the total reflection critical angle appear in each zone along the light guiding direction of the light guiding plate21. Therefore, the light travelling through the light guiding plate21exits the light exiting face little by little. This enables a light amount distribution of the light exiting the light exiting face of the light guiding plate21, along the light guiding direction, to be even.

The light exiting the light guiding plate21thereafter reaches the light diffusion plate26, which improves uniformity thereof. The light diffused or collected as necessary by the prism layer27to exit the prism layer27then reaches the reflection type polarizing plate28. Here, the light in a polarization direction along the transmission axis of the reflection type polarizing plate28is transmitted through the reflection type polarizing plate28, to be directed toward the optical sheet330.

The light in a polarization direction along the reflection axis of the reflection type polarizing plate28is reflected and returned to the light guiding plate21side as shown by the dotted arrows inFIG. 20. The returned light is reflected on the light guiding plate21, the back face optical elements23, or the reflection sheet39, to travel again toward the reflection type polarizing plate28. In this reflection, the polarization directions of some lights are changed, and these lights are partially transmitted through the reflection type polarizing plate28. The rest of the lights is returned again to the light guiding plate side. In this way, repeated reflection makes it possible for the light reflected on the reflection type polarizing plate28to be also transmitted through the reflection type polarizing plate28. This increases the use efficiency of the light from the light source25.

Here, the polarization direction of the light exiting the reflection type polarizing plate28is a direction along the transmission axis of the lower polarizing plate14, and this light is a light in a polarized state which allows the light to be transmitted through the lower polarizing plate14.

The light exiting the reflection type polarizing plate28reaches the optical sheet330. The light entering the optical sheet330travels as having an optical path as follows.FIG. 24shows examples of an optical path in the optical sheet330.

At this time, if the interface334bof interfaces of the light transmissive portions333and the light absorbing portions334, which is on the lower side of the light absorbing portion334, inclines as being directed obliquely upwards on the watcher side, it becomes difficult for the light absorbing portions334to block light as the lights L201, L202, L241, and L242from travelling, which makes it possible to guide more light in a desired direction.

Therefore, in the optical sheet330, the combination of the inclination angle of the main refracting face335cshown by θ71inFIG. 23, and that of the interface334ashown by θ61inFIG. 23makes it easy to efficiently guide light in a desired direction. Either one of them limitedly guides directions of light, and combined effect of the combination makes it possible to easily control the travelling direction of light.

This makes it possible to efficiently absorb and block the light exiting at a viewing angle that is no less than a desired angle, and further to efficiently control the travelling direction of light.

This also makes it possible to absorb such light entering the liquid crystal panel to probably lead to defects such as deteriorated contrast and color inversion.

The light exiting the optical sheet330enters the lower polarizing plate14of the liquid crystal panel15. The lower polarizing plate14transmits one polarization component in the incident light, and absorbs the other polarization component. The light transmitted through the lower polarizing plate14is selectively transmitted through the upper polarizing plate13in accordance with the state of creation of an electric field for each pixel. In this manner, the liquid crystal panel15selectively transmits the light from the surface light source device320for each pixel, which makes it possible for a watcher of the liquid crystal display to observe an image. At this time, an image light is given a watcher via the functional film40, to improve the quality of an image.

As described above, the optical sheet330makes it easy for the light entering the optical sheet330to exit upwards, using refraction in the optical element layer335b, and total reflection on the interface334abetween the light transmissive portions333and the light absorbing portions334, and limits a downward exit. That is, for example, using the optical sheet330makes it possible for the incident light to efficiently exit upwards, that is, in a driver's point of view, and makes it possible to improve brightness of the light exiting upwards. Using the optical sheet330also makes it possible to prevent a reflection in a windshield since making it easy for the light exiting much upwards to be absorbed in the light absorbing portions.

Thus, using the optical sheet in this embodiment for a liquid display makes it possible to easily control light, to improve visibility in a driver's point of view, compared with the case of using a conventional optical sheet.

This can easily achieve light exiting characteristics as shown in, for example,FIG. 25.FIG. 25is a graph where the horizontal axis represents a viewing angle in the vertical direction, and the vertical axis represents a relative brightness. In the horizontal axis, the positive (+) indicates the upward in the vertical direction and the negative (−) indicates the downward in the vertical direction.

As seen fromFIG. 25, the peak of the relative brightness is approximately at +20° (20° upward in the vertical direction) as seen from the coordinates shown by D inFIG. 25when the viewing angle in the vertical direction is seen. That is, light is controlled so that the peak of the brightness is in a direction of a watcher's point of view, different from the front (0°). Further, as seen from the coordinates shown by E inFIG. 25, the relative brightness suddenly drops at approximately +50° (50° upward in the vertical direction). That is, such a light travelling much upwards which may be a cause of a reflection in a windshield in an automobile may be more surely blocked.

Optical sheets and image source units according to each of the above described embodiments were made, and the performance thereof was tested.

Test Example A

In Test Example A, a test was performed in view of control of the direction of exiting light in optical sheets according to the example of the image source unit10.

Structures of Optical Sheets in Test Example A

Test Example A1

In Test Example A1, optical sheets according to the example of the image source unit10including the light exiting side light controlling layer35, except that θ21shown inFIG. 5was changed were prepared. Specific shapes of the optical sheets other than θ21were as follows:

(Optical Functional Layer)pitch of a light transmissive portion and a light absorbing portion (PainFIG. 4): 39 μmwidth of an upper base of a light absorbing portion (WainFIG. 4): 4 μmwidth of a lower base of a light absorbing portion (WbinFIG. 4): 10 μmupper inclination angle of a light absorbing portion (θ11inFIG. 5): 3°lower inclination angle of a light absorbing portion (θ12inFIG. 5): 0°thickness of a light absorbing portion (DainFIG. 4): 102 μmthickness of the optical functional layer: 127 μmthickness of the sill portion: 25 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black—containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49inclination angle formed by the light transmissive portions and light absorbing portions, and the aligning direction of the pixels in the liquid crystal layer (bias angle α1): 5°

(Light Exiting Side Light Controlling Layer)angle of a rise face (θ22inFIG. 5): 90°pitch of a unit optical element (PoinFIG. 4): 18 μmmaterial of the unit optical elements: ultraviolet curable urethane acrylate resin having a refractive index of 1.50inclination angle with the bias angle α1(bias angle α2): 3°

Here, the bias angle α2was such an angle that the light exiting side light controlling layer rotated in the same direction as that where the bias angle α1was formed in the front view of the optical sheet (which is also applied to the following examples). Thus, in this example, the inclination angle formed by the extending direction of the unit optical elements, and the aligning direction of the pixels in the liquid crystal layer was: α1÷α2=8°.angle of a main refracting face (θ21inFIG. 5): 85° (Test Example A1-1), 80° (Test Example A1-2), 70° (Test Example A1-3), and 60° (Test Example A1-4)

Test Example A2

In Test Example A2, optical sheets according to the example of the image source unit including the light exiting side light controlling layer135shown inFIG. 9, except that θ31was changed were prepared. The structure other than the light exiting side light controlling layer135was the same as that in Test Example A1. The angle of a rise face was fixed, that is, 90°. The angle of a main refracting face (θ31inFIG. 9) was 85° (Test Example A2-1), 80° (Test Example A2-2), 70° (Test Example A2-3), and 60° (Test Example A2-4).

Test Example A3

In Test Example A3, the angle of a rise face (corresponding to θ22inFIG. 5) was changed to 80° (Test Example A3-1), and 100° (Test Example A3-2) from those of the optical sheets of Test Example A2-2. The other conditions were the same as those for Test Example A2-2.

Test Example A4

In Test Example A4, an optical sheet had a structure of excluding the light exiting side light controlling layer from the optical sheets of Test Example A1. The other portions were the same as in the optical sheets of Test Example A1.

[Evaluation Method for Test Example A]

Each of the above optical sheets was modeled, to obtain the relationship between a light exiting angle and brightness at each light exiting angle through simulation. Light Tools (Synopsys, Inc.) was used for simulation software. Characteristics of a light source are shown inFIG. 26. InFIG. 26, the horizontal axis represents a viewing angle in the vertical direction (the positive indicates the upward and the negative indicates the downward), and the vertical axis represents a relative brightness if a brightness when the viewing angle is 0° is defined as 100%.

Results of Test Example A

FIG. 27shows the results of Test Example A1,FIG. 28shows the results of Test Example A2, andFIG. 29shows the results of Test Example A3. InFIGS. 27 to 29, the graph showing Test Example A4is represented by A4.

InFIG. 27, Test Example A1-1 is represented by A1-1, Test Example A1-2 is represented by A1-2, Test Example A1-3 is represented by A1-3, and Test Example A1-4 is represented by A1-4.

Likewise, inFIG. 28, Test Example A2-1 is represented by A2-1, Test Example A2-2 is represented by A2-2, Test Example A2-3 is represented by A2-3, and Test Example A2-4 is represented by A2-4.

InFIG. 29, Test Example A3-1 is represented by A3-1, and Test Example A3-2 is represented by A3-2. InFIG. 29, A2-2 is also shown together.

In each graph, the horizontal axis represents a viewing angle in the vertical direction; the positive indicates the upward and the negative indicates the downward, and the vertical axis represents a relative brightness when characteristics of the light source shown inFIG. 26are 100%.

As is seen from these graphs, the optical sheets according to Test Examples A1, A2, and A3made it possible to more efficiently control the light exiting angle in a desired direction more precisely than the optical sheet according to Test Example A4.

When the light exiting angle is changed so as to largely shift as in Test Examples A1-3, A1-4, A2-3, and A2-4, and when the angle of a rise face is more than, or less than 90° as in Test Examples A3-1 and A3-2, a relative brightness at a light exiting angle within a range of 60° to 90° on the positive or negative side may increase. This is believed to be caused by a stray light on the rise face. Most of such a stray light may be absorbed in a polarizing plate. Thus, such a stray light is hard to result in defects.

Test Example B

In Test Example B, a test was performed in view of control of the direction of exiting light in optical sheets according to the example of the image source unit210.

Structures of Light Controlling Member in Test Example B1

In Test Example B1, a light controlling member was prepared according to the example of the light controlling member229. Specific aspect thereof was as follows:

(Optical Functional Layer)pitch of a light transmissive portion and a light absorbing portion (PainFIG. 4): 47 μmwidth of an upper base of a light absorbing portion (WainFIG. 4): 3 μmwidth of a lower base of a light absorbing portion (WbinFIG. 4): 22 μmupper inclination angle of a light absorbing portion (θ11inFIG. 5): 4.5°lower inclination angle of a light absorbing portion (θ12inFIG. 5): 4.5°thickness of a light absorbing portion (DainFIG. 4): 120 μmthickness of the optical functional layer: 145 μmthickness of the sill portion: 25 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black—containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49

(Light Exiting Side Light Controlling Layer)inclination angle of a main refracting face (θ21inFIG. 5): 70°inclination angle of a rise face (θ22inFIG. 5): 90°thickness of the supporting layer: 25 μmpitch of a unit optical element (PoinFIG. 4): 26 μmmaterial of the unit optical elements: ultraviolet curable urethane acrylate resin having a refractive index of 1.50bias angle α3formed by the extending direction of the light transmissive portions, and the extending direction of the unit optical elements: 5°

(Optical Functional Layer)pitch of a light transmissive portion and a light absorbing portion (PbinFIG. 15): 47 μmwidth of an upper base of a light absorbing portion (WcinFIG. 15): 3 μmwidth of a lower base of a light absorbing portion (WdinFIG. 15): 22 μminclination angle of a light absorbing portion on one side (θ41inFIG. 16): 4.5°inclination angle of a light absorbing portion on the other side (θ42inFIG. 16): 4.5°thickness of a light absorbing portion (DbinFIG. 15): 120 μmthickness of the optical functional layer: 145 μmthickness of the sill portion: 25 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black—containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49

(Light Exiting Side Light Controlling Layer)portion where no unit optical element was arranged: 5.0 mm across the center symmetrically in the aligning direction of unit optical elements (W3inFIGS. 14 and 15, by 2.5 mm on each of the left and right sides)inclination angle of a main refracting face (θ51inFIG. 16): continuously changing so as to be 90° on the central side of the sheet (portion where no unit optical element was provided substantially) and 68° at the most end portions thereof (size of the second optical sheet in the aligning direction of the unit optical elements (W4inFIG. 15) was 300 mm)inclination angle of a rise face (θ52FIG. 16): 90°thickness of the supporting layer: 25 μmpitch of a unit optical element (PpinFIG. 15): 26 μmmaterial of the unit optical elements: ultraviolet curable urethane acrylate resin having a refractive index of 1.50bias angle α4formed by the extending direction of the light transmissive portions, and the extending direction of the unit optical elements: 5°

The first optical sheet described above was arranged so that the extending direction of the light transmissive portions was in the horizontal direction, and the second optical sheet was laminated onto the first optical sheet to be arranged so as to be closer to the light exiting side than the first optical sheet was, to form the light controlling member. At this time, the extending direction of the light transmissive portions of the second optical sheet was in the vertical direction (seeFIG. 12).

Structure of Light Controlling Member of Test Example B2

In Test Example B2, a light controlling member of excluding the light exiting side light controlling layers of the first and second optical sheets from the light controlling member according to Test Example B1was used.

Evaluation Method for Test Example B

The light controlling members of Test Example B were modeled, to obtain the relationship between a light exiting angle and brightness in each of the vertical and horizontal directions through simulation.

Light Tools (Synopsys, Inc.) was used for simulation software. Characteristics of a light source are shown inFIG. 30. InFIG. 30, the horizontal axis represents a light exiting angle in the vertical and horizontal directions, and the vertical axis represents a relative brightness if a brightness when the light exiting angle is 0° is defined as 100%.

Results of Test Example B

FIGS. 31A and 31Bshow the evaluation results of the light controlling member of Test Example B1. InFIG. 31A, the horizontal axis represents a light exiting angle in the vertical direction, and the vertical axis represents a relative brightness to 100% inFIG. 30. InFIG. 31B, the horizontal axis represents a light exiting angle in the horizontal direction, and the vertical axis represents a relative brightness to 100% inFIG. 30.

FIGS. 32A and 32Bshow the evaluation results of the light controlling member of Test Example B2. InFIG. 32A, the horizontal axis represents a light exiting angle in the vertical direction, and the vertical axis represents a relative brightness to 100% inFIG. 30. InFIG. 32B, the horizontal axis represents a light exiting angle in the horizontal direction, and the vertical axis represents a relative brightness to 100% inFIG. 30.

As is seen from the comparison betweenFIGS. 31A and 32A, providing an optical element layer like the first optical sheet made it possible to control the light exiting angle so that the angle shifted.

As is seen from the comparison betweenFIGS. 31B and 32B, providing an optical element layer like the second optical sheet made it possible to control the light exiting angle in the horizontal direction as described inFIG. 18B.

Test Example C

In Test Example C, a test was performed in view of prevention of moire using a rough face in addition to control of the direction of exiting light according to the examples of the image source units10and210.

Structures of Optical Sheet in Test Example C

Test Example C1

In Test Example C1, optical sheets according to the example of the image source unit10including the light exiting side light controlling layer35, except that θ21shown inFIG. 5, and degrees of surface roughness of a refracting face and a rise face were changed, were prepared. Specific forms of the other portions were as follows:

(Optical functional layer)pitch of a light transmissive portion and a light absorbing portion (PainFIG. 4): 39 μmwidth of an upper base of a light absorbing portion (WainFIG. 4): 4 μmwidth of a lower base of a light absorbing portion (WbinFIG. 4): 10 μmupper inclination angle of a light absorbing portion (θ11inFIG. 5): 3°lower inclination angle of a light absorbing portion (θ12inFIG. 5): 0°thickness of a light absorbing portion (DainFIG. 4): 102 μmthickness of the optical functional layer: 127 μmthickness of the sill portion: 25 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black—containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49inclination angle formed by the light transmissive portions and the light absorbing portions, and the aligning direction of the pixels in the liquid crystal layer (bias angle α1): 0°

(Light Exiting Side Light Controlling Layer)angle of a rise face (θ22inFIG. 5): 90°pitch of a unit optical element (PoinFIG. 4): 18 μmmaterial of the unit optical elements: ultraviolet curable urethane acrylate resin having a refractive index of 1.50inclination angle with the bias angle α1(bias angle α2): 4°angle of a main refracting face (θ21inFIG. 5, four angles): 85°, 80°, 70°, and 60°formation of rough faces over a main refracting face and a rise face (two ways): formed by a molding die blasted with glass having a mean particle diameter of 10 μm; and formed by a molding die blasted with alumina having a mean particle diameter of 2 μm (seeFIG. 33)

Unit optical elements of “four angles of θ21×two types of rough faces=eight types in total” were molded using the blasted dies (seeFIG. 33). An optical sheet corresponding to each of them was prepared.

Test Example C2

In Test Example C2, image source units including optical sheets according to the example of the second optical sheet230instead of the optical sheet of Test Example C1were prepared. Specific forms thereof were as follows:

(Optical Functional Layer)pitch of a light transmissive portion and a light absorbing portion (PbinFIG. 15): 47 μmwidth of an upper base of a light absorbing portion (WcinFIG. 15): 3 μmwidth of a lower base of a light absorbing portion (WdinFIG. 15): 22 μminclination angle of a light absorbing portion on one side (θ41inFIG. 16): 4.5°inclination angle of a light absorbing portion on the other side (θ42inFIG. 16): 4.5°thickness of a light absorbing portion (DbinFIG. 15): 120 μmthickness of the optical functional layer: 145 μmthickness of the sill portion: 25 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49inclination angle formed by the light transmissive portions and the light absorbing portions, and the aligning direction of the pixels in the liquid crystal layer (bias angle α1): 0°

(Light Exiting Side Light Controlling Layer)portion where no unit optical element was arranged: 5.0 mm across the center symmetrically in the aligning direction of the unit optical elements (W3inFIGS. 14 and 15, by 2.5 mm on each of the left and right sides)inclination angle of a main refracting face (θ51inFIG. 16): continuously changing so as to be 90° on the central side of the sheet (portion where no unit optical element was provided substantially) and 68° on the most end portions (size of the second optical sheet in the aligning direction of the unit optical elements (W4inFIG. 15) was 300 mm)inclination angle of a rise face (θ52FIG. 16): 90°thickness of the supporting layer: 25 μmpitch of a unit optical element (PpinFIG. 15): 18 μmmaterial of the unit optical elements: ultraviolet curable urethane acrylate resin having a refractive index of 1.50bias angle α4formed by the extending direction of the light transmissive portions, and the extending direction of the unit optical elements: 4°formation of rough faces over a refracting face and a rise face (two ways): formed by a molding die blasted with glass having a mean particle diameter of 10 μm; and formed by a molding die blasted with alumina having a mean particle diameter of 2 μm (seeFIG. 33)

Unit optical elements having rough faces of two types were formed using the blasted dies. An optical sheet corresponding to each of them was prepared.

Test Example C3

In Test Example C3, an optical sheet according to the forms of the optical sheets of Test Example C1, except that no rough face was formed on a main refracting face or a rise face was prepared.

Test Example C4

In Test Example C4, an optical sheet according to the forms of the optical sheets of Test Example C2, except that no rough face was formed on a main refracting face or a rise face was prepared.

[Evaluation and Results of Test Example C]

Moire was observed for the image source units according to Test Example C by visual recognition. As a result, moire was slightly observed in Test Examples C3and C4where no rough face was formed. In contrast, no moire was observed in Test Examples C1and C2where rough faces were formed.

The direction of the exiting light was able to be suitably controlled in every Example.

Test Example D

In Test Example D, a test was performed according to the example of the image source unit10, except that the relationship between the aligning pitch of the light transmissive portions (light absorbing portions), and the aligning pitch of the unit optical elements was changed, in view of appearance of moire in addition to control of the direction of exiting light.

The pitch of a unit optical element (PoinFIG. 4) was changed from that in the forms of Test Example C1, to observe whether moire appeared by visual recognition. Table 1 shows the conditions and results. In Table 1, Pais the pitch of a light transmissive portion (light absorbing portion) (μm), and Pois a pitch of a unit optical element (μm).

The inventor focused on Pmxobtainable based on Pmas follows:

Here, Pa≥Po, and a and b are each integers of 1 to 10. The combinations of Paand Po, which is a pitch from the same magnification (once) as, to ten times larger than Paare considered. This makes it possible to evaluate appearance of moire in a wide range of considering pitches at integral multiples.

The maximum Pmin Pmobtained from all the combinations of varied a and b in a certain combination of Paand Pois Pmx. In this example, Pawas 39 μm, and Powas varied.

As for Pmx, the case where moire was observed as a result was expressed by “yes”, and the case where no moire was observed was expressed by “no”.

As is seen from Table 1, adjusting the pitches (Pa, Po) so that Pmxwas no more than 10000 (μm) made it possible to prevent appearance of moire.

Test Example E

In Test Example E, optical sheets according to the optical sheet330shown inFIGS. 19 to 23, and an optical sheet for comparison therewith were prepared, to perform a test.

Structures of Optical Sheets in Test Example E

Test Example E1

(Optical Functional Layer)pitch (PcinFIG. 22): 39 μmwidth of an upper base of a light absorbing portion (WainFIG. 22): 4 μmwidth of a lower base of a light absorbing portion (WbinFIG. 22): 10 μmupper inclination angle of a light absorbing portion (θ61inFIG. 23): 0°lower inclination angle of a light absorbing portion (θ62inFIG. 23): 3°thickness of a light absorbing portion (DcinFIG. 22): 102 μmthickness of the optical functional layer: 127 μmmaterial and refractive index of the light transmissive portions: ultraviolet curable urethane acrylate resin having a refractive index of 1.56material and refractive index of the light absorbing portions: 20 mass % of a carbon black—containing acrylic beads having a mean particle diameter of 4 μm was dispersed in an ultraviolet curable urethane acrylate resin having a refractive index of 1.49

(Light Entering Side Light Controlling Layer)thickness of the supporting layer (thickness of the supporting layer335ainFIG. 23): 130 μmpitch of a unit optical element (PqinFIG. 22): 30 μminclination angle of a main refracting face of a unit optical element (θ71inFIG. 23): 5°inclination angle of a rise face (θ72inFIG. 23): 90°material: ultraviolet curable urethane acrylate resin having a refractive index of 1.50

Test Example E2

The structure was the same as that in Test Example E1except that the inclination angle of a main refracting face of a unit optical element (θ71inFIG. 23) was 10°.

Test Example E3

The structure was the same as that in Test Example E1except that the inclination angle of a main refracting face of a unit optical element (θ71inFIG. 23) was 20°.

Test Example E4

As shown inFIG. 34, a main refracting face of a unit optical element inclined toward the light source side from the top to the bottom, and the angle of a main refracting face shown by θ81inFIG. 34was 5°. This state was defined as that the inclination angle of a main refracting face of a unit optical element is “−5°”. The other structure was the same as that in Test Example E1.

Test Example E5

The structure was the same as that in Test Example E1except that the inclination angle of a main refracting face of a unit optical element (θ71inFIG. 23) was 0°, that is, no optical element layer was formed.

Surface light source devices were formed by using the optical sheets according to Test Example E, and by arranging the other components according to the example shown inFIG. 19.

Brightness at the viewing angles of the following three types was measured for each Test Example, and was represented as a brightness ratio to a brightness of each type which was defined as 100% when a light source was lit as the optical sheet was excluded from the surface light source device, which is the example shown inFIG. 19.

(1) brightness ratio based on brightness from the center of a screen toward the direction of the normal line of the screen (front brightness)

(2) brightness ratio based on a brightness at a viewing angle of 40° in the horizontal direction and 20° upward in the vertical direction, with the center of the screen (so-called driver's point of view). A driver's point of view means a point of view when a display of a car navigation system etc. is seen from a driver's seat in a case where the display is arranged in the middle of the driver's seat and the passenger seat in an automobile.

(3) brightness ratio based on the total brightness at a viewing angle of 0° in the horizontal direction and 40° to 80° (by 5°) upward in the vertical direction with the center of the screen (light causing reflection).

Brightness of a transmitted light at each of the viewing angles (1) to (3) was measured using an automatic goniophotometer (GP-500 by MURAKAMI COLOR RESEARCH LABORATORY CO., Ltd.).

Table 2 shows the brightness ratio at each of the viewing angles.FIGS. 35A to 35Care graphs based on the results.FIG. 35Ashows the results of (1),FIG. 35Bshows the results of (2), andFIG. 35Cshows the results of (3). In each graph, the dotted line represents the standard of the brightness ratio when the inclination angle of a main refracting face (θ71inFIG. 23) is 0°.

At the viewing angle (1), the brightness ratio is preferably higher than that when the inclination angle of the main refracting face is 0° as shown by the straight arrow inFIG. 35A. A high ratio means that the front brightness is high.

At the viewing angle (2), the brightness ratio is preferably higher than that when the inclination angle of the main refracting face is 0° as shown by the straight arrow inFIG. 35B. A high ratio means that brightness at the driver's point of view is high.

At the viewing angle (3), the brightness ratio is preferably lower than that when the inclination angle of the main refracting face is 0° as shown by the straight arrow inFIG. 35C. A low ratio means that reflection in a windshield can be suppressed when a display of a car navigation system etc. is arranged in the middle of the driver's seat and the passenger seat in an automobile.

In view of the above, an inclination angle satisfying all the preferred results for (1) to (3) is between two dashed-and-dotted lines; specifically, such a form that the inclination angle of a main refracting face of a unit optical element included in the light entering side light controlling layer (θ71inFIG. 23) is more than 0° and less than 17° satisfies all the preferred results. This makes it possible to easily control light so as to satisfy a plurality of optical characteristics in a well-balanced manner.

REFERENCES SIGN LIST