Patent Description:
Conventionally, three-dimensional expression provided by the holographic technique is applied as forgery prevention means to improve security, such as a computer-generated hologram of which a light wave front is computed by a computing device, in particular.

A computer-generated hologram can be emboss-molded for duplication. Since development processing is not necessary in this case, the computer-generated hologram is a commercially excellent technique.

For example, Patent Literature <NUM> (Jpn. KOKAI Publication No. <CIT>) discloses a method of showing a phantom three-dimensional object as a solid body by using anisotropic scattering of light.

Further cited prior art documents are <CIT> showing a hologram recording medium, its manufacturing method and manufacturing apparatus, <CIT> showing a forgery prevention medium, <CIT> showing an optical element and <CIT> showing a pigment flake and image formation body using the same, and production method of the image formation body.

However, according to the method disclosed in the Patent Literature <NUM>, if light is incident on an inclined surface that is pseudo-stereoscopic, shading of light switches for each inclined surface although it lacks a stereoscopic effect.

If the apparent size of a light source of reference light irradiated on a hologram is large, a three-dimensional reproduced image is blurred.

In order to remedy these disadvantages, it is necessary to restrict observation conditions such as the size of the light source and the wavelength of the light source when observing a hologram. However, this imposes a strain on the observer.

Furthermore, in the computer hologram formed of a general kinoform, because of the thin groove-like diffraction grating structure on the surface, color shift is caused due to a viewing angle if the computer hologram is reproduced with a white light in which multiple wavelengths are mixed, and an iridescent diffraction light may be obtained by diffraction in an angle determined accordance with a wavelength. This is because if a white incident light is incident, the incident light is diffracted by the structure of the equal pitch of diffraction grating, and rays of the diffraction light with different wavelengths proceed in different directions.

Security labels for forming a hologram image, for example, is commercialized by using this rainbow color. For example, according to the conventional diffraction grating pattern, the color changes in an iridescent manner based on the positional relationship between an illumination, a display, and an observer.

However, holograms that appear rainbow color can be easily manufactured in recent years, and do not have a sufficient forgery prevention ability any more. Accordingly, needs for expressions in place of the rainbow color have become a market trend.

Thus, the computer hologram formed of a general kinoform cannot be applied for preventing forgery of, for example, securities such as gift vouchers, card media such as credit cards, passport and visa, etc., brand-name products, and equipment components.

Moreover, the hologram entails a characteristic blur. In recent years, there is a technique for eliminating a dynamic visual effect so as to reduce the blur; however, in this case, there is a problem of it lacking any difference from general printed materials since an image of an object does not change at all despite change in visual angle.

As described above, the computer hologram formed of a general kinoform cannot be applied for preventing forgery of, for example, securities such as gift vouchers, card media such as credit cards, passports and visas, etc., brand-name products, and equipment components; accordingly, an ink, in addition to a hologram, is generally used for authentication of these.

An ink of this type is required to have high durability so that the ink can be used without fading even over an extended period of time. Moreover, the ink preferably does not have a color-shift effect in a specific direction, so that its color tone does not change when seen from any direction.

Patent Literature <NUM> (<CIT>) is disclosed as a conventional technique related to durability improvement of an ink. Patent Literature <NUM> discloses a pigment of which color-shift effect is reduced by providing two reflection layers and using an interference color.

However, if a reflection layer is formed into a pigment and the pigment is used in printing, an inclination angle of the pigment is random upon printing, and its color tone in a specific direction is mixed depending on the direction in which the pigment is fixed. This makes it difficult to produce a color with high saturation.

There is a problem that if the orientation is controlled by a magnetic field and printing is performed, a color-shift effect is strongly expressed in a multi-layer film as a film before being formed into a pigment, and the color gradually varies in accordance with a radiation angle of the light; accordingly, there is a problem that it is difficult to determine which color is the true color. A similar problem occurs in a case of a structural color obtained by using a general quantization phase difference structure, since many of such colors have a strong color-shift effect.

To sum up, a hologram with diffraction grating has an advantage that an image with a high brightness can be obtained which leads to a high eye-catching effect, and a disadvantage that the color largely changes in accordance with an angle of the label and the color development is unstable.

Another known technique aims to realize a own color development by interference between the flat upper surface of a projecting portion and a flat surface other than the projecting portion, and to stabilize color development by scattering light at the projecting portion. The color development of interference between the flat upper surface of a projecting portion and a flat surface other than the projecting portion has an advantage that a color shift arising due to difference in viewpoint or location of light source is small, which provides a stable color development, and a disadvantage that stable color development necessarily involves wide diffusion, which reduces brightness. Reduction of the brightness may cause reduction of the eye-catching effect.

The embodiments of the present invention are contrived in light of such conditions, and can overcome the color instability and reduction of brightness as defects of a conventional technique such as diffraction and interference by application of the kinoform technique. One of the objectives thereof is to provide an optical structure and an authentication body that includes the optical structure, wherein the optical structure can enable three-dimensional expression regardless of a light source, improve the visual quality of the iridescent color, and obtain a sparkling and blinking appearance similar to jewels in accordance with a visual angle, when displaying graphic information such as a picture or character information as forgery prevention means to improve security of, for example, securities and card media, or passports and visas.

The other objective is to be applied to an ink preferably applied to printed materials such as securities and card media, or passports and visas, so that the ink has high durability, and to apply a kinoform which enables high brightness expression so as to provide an optical structure without a color-shift effect.

In order to achieve the above objectives, the embodiments of the present invention provide an optical structure and an authentication body according to the respective claims.

According to the present optical structure, it is possible to realize an optical structure and an authentication body that includes the optical structure, wherein the optical structure can enable three-dimensional expression regardless of a light source, improve the visual quality of the iridescent color that belong to the conventional hologram, and obtain a sparkling and blinking effect similar to jewels in accordance with a visual angle, which is different from the conventional hologram, when displaying graphic information such as a picture or character information as forgery prevention means to improve security of, for example, securities and card media, or passports and visas.

In particular, in this description, the design is made so that light spreads centering around the specular direction on the premise for computation that the light is incident from the direction opposite from the normal direction of the carrier by <NUM>°. Accordingly, even if the light is incident obliquely with respect to the normal direction of the carrier, the light is reflected in the direction approximately the same as a reflected direction of the light in a case where there is actually an inclined surface. Thus, the same shading of light as in a case where a phantom three-dimensional object actually exists there is observed, making it appear that a three-dimensional object exists there.

According to the present optical structure, the reflected direction of the light when the light is vertically incident on a flat surface can be specified by the quantization phase difference structure, and the light can be reflected in a plurality of directions by providing a plurality of spatial frequency components.

This effect realizes an effect equivalent to that when the light is reflected on an object, the regular reflection component is strongly reflected, and the more the angle is shifted from the specular direction, the less the reflected light intensity becomes. In addition, a bright spot of shading can be generated by making the spatial frequency components discrete, which generates a sparkling effect similar to jewels.

According to the present optical structure, it is also possible that a plurality of multiple-diffraction regions compose the quantization phase difference structure.

According to the present optical structure, it is also possible to determine the direction of the spatial frequency components in accordance with the direction toward which the inclined surface of spatial frequency multiplexing faces.

According to the present optical structure, it is also possible to obtain an effect that the light is reflected in the direction of a reproduction point without directly viewing the reproduction point by setting a diffraction region of the light that is diffracted from the multiple-diffraction region to a Fraunhofer region.

According to the present optical structure, it is also possible to substitute a reflected light effect of the light by pseudo computation of diffraction.

According to the present optical structure, it is also possible to realize an effect of light appearing to shine on a real surface by increasing the light intensity in the specular direction and reducing the intensity of light shifted from the regular reflection.

According to the present optical structure, it is also possible to reflect a reproduced image with a white color in a direction of dense reproduction points; on the other hand, in a part where the reproduction points are coarse, it is possible to reproduce an iridescent reproduced image such as a conventional hologram, and to control both of a white and iridescent colors.

According to the present optical structure, it is also possible to set the multiple-diffraction region to a cell type.

According to the present optical structure, it is also possible to control a reflection color of the light in accordance with the depth of the quantization phase difference structure when the light is reflected, which enables full-color expression of a three-dimensional image.

According to an optical structure including the present reflection layer, it is also possible to increase the reflectivity of the light.

According to the present authentication body, it is possible to create three-dimensional expression without depending on a light source, improve the visual quality of the rainbow color belonging to the conventional hologram, and realize a sparkling and blinking effect similar to jewels depending on a visual angle.

An embodiment of the present invention will be described in detail with reference to the drawings. The constituent elements exhibiting identical or similar functions will be referred to by the same reference symbols throughout all drawings, and overlapping explanations will be omitted.

<FIG> is a plan view showing an embodiment of a multiple diffraction region <NUM> in a quantization phase difference structure included in an optical structure <NUM> according to one embodiment of the present invention, and <FIG> is a graph showing an example of peak intensities of a spatial frequency components F1 to F5 at the five reproduction points in this multiple diffraction region <NUM>. The optical structure <NUM> has an embossed surface on one side or both sides of the embossed layer. The embossed surface has a multiple-diffraction region on a part or the entire surface thereof. A quantization phase difference structure is formed on the multiple-diffraction region.

As in <FIG>, in the quantization phase difference structure, a plurality of quantization projecting portions with a constant size and a plurality of quantization recessed portions with a constant size are aligned. In <FIG>, the light parts represent the quantization projecting portions, and the dark parts represent the quantization recessed portions. The quantization projecting portions and quantization recessed portions are arranged at a regular interval. A quantization recessed portion or a quantization projecting portion is arranged adjacently to a quantization projecting portion at a regular interval. A quantization projecting portion or a quantization recessed portion is arranged adjacently to a quantization recessed portion at a regular interval. For example, in the quantization phase difference structure, the quantization projecting portions and the quantization recessed portions are alternately arranged one by one, or for every set of multiple quantization projecting portions and quantization recessed portions.

In the quantization phase difference structure of the multiple diffraction region <NUM>, spatial frequency components with a coarse pitch and spatial frequency components with a fine pitch overlap with each other on an embossed surface in accordance with the arrangement of the quantization projecting portions and quantization recessed portions. The multiple diffraction region <NUM> may be a cell including the quantization phase difference structure. In the quantization phase difference structure of the multiple diffraction region <NUM>, the ribbed projecting portions where the quantization projecting portions are aligned are arranged adjacent to and alternately with the groove-like recessed portions having an element structure where the quantization recessed portions as recessed portions of a constant size are aligned in parallel with the ribbed projecting portions, and a size of the quantization projecting portion may be from a 20th to a half of a central wavelength of a visible wavelength. A size of the quantization recessed portion may be from a 20th to a half of the central wavelength of the visible wavelength. Specifically, a size of the quantization projecting portion may be from <NUM> to <NUM>. A size of the quantization recessed portion may be from <NUM> to <NUM>. The quantization projecting portion may take a square shape. The quantization recessed portion may take a square shape. A corner of the quantization projecting portion may be round. A corner of the quantization recessed portion may be round. The quantization projecting portions and the quantization recessed portions may be aligned on a imaginary grid. The height of the quantization projecting portion may be the same as or an integral multiple of the reference height. The depth of the quantization recessed portion may be the same as or an integral multiple of the reference depth. The reference height and the reference depth may be the same. The value of the integral multiple may be from <NUM> to <NUM>. It may also be from <NUM> to <NUM>. The reference height and the reference depth may be from <NUM> to <NUM>.

In the case where the reproduced image of a hologram reproduced by the multiple diffraction region <NUM> is a group of five reproduction points, if a spatial frequency component is computed along one predetermined direction D within the plane of the multiple diffraction region <NUM> as shown in <FIG>, there are five discrete peaks at the spatial frequency components F1 to F5 corresponding to the reproduction points as shown in <FIG>. The horizontal axis in <FIG> is a spatial frequency (<NUM>/mm), and the vertical axis is a strength of the spatial frequency component.

The reproduced image is in an iridescent color if the discrete spatial frequency components are coarse, and the reproduced image is in a white color if the discrete spatial frequency components are dense. It is possible to show a reproduced image in an iridescent color at a certain angle direction and in a white color at other angle directions by adjusting denseness and coarseness of the distribution of the spatial frequency components.

<FIG> is a plan view showing an example of an optical structure 10a provided with a plurality of multiple diffraction regions <NUM>.

In this manner, the number of the multiple diffraction region(s) <NUM> included in the optical structure <NUM> is not limited to one as in <FIG>, but may be plural as in <FIG>. The planar shape of each multiple diffraction region <NUM> shown in <FIG> and <FIG> is a rectangular shape, but shapes other than a rectangular shape may be used.

<FIG> is a cross-sectional view showing a quantization phase difference structure <NUM>.

A reflection layer (not shown) may be provided on the surface of the quantization phase difference structure <NUM> of which a cross-sectional view is shown in <FIG>. The reflection layer may be translucent or opacifying.

The reflection layer may be a reflection layer made of a metal material. The metal material may be Al, Ag, Sn, Cr, Ni, Cu, Au, or an alloy thereof, for example. A reflection layer made of metal may be an opacifying reflection layer. Alternatively, a reflection layer may be a dielectric layer of which a refractive index is different from a relief structure forming layer. Alternatively, a reflection layer may be a stacked body of dielectric layers in which adjacent layers have different refractive indices, namely, a dielectric multi-layer film. It is desirable that a dielectric layer, among the dielectric layers included in the dielectric multi-layer film, in contact with the relief structure forming layer has a different refractive index from the refractive index of the relief structure forming layer. The dielectric layer may be a metal compound or silicon oxide. The metal compound may be metal oxide, metal sulfide, or metal fluoride, for example. The dielectric layer may be made of TiO<NUM>, ZnO, Si<NUM>O<NUM>, SiO, Fe<NUM>O<NUM>, ZnS, CaF, or MgF. The reflection layer can be formed by a vapor-phase deposition method. A vacuum evaporation method and a sputtering method can be applied as the vapor-phase deposition method. The reflection layer of the dielectric layer may be translucent. The reflection layer may be from <NUM> to <NUM>.

The reflection layer can be formed by using an ink. This ink may be an offset ink, a letterpress ink, and a gravure ink in accordance with a printing method. A resin ink, an oil-base ink, and a water-base ink may be used in accordance with the composition difference. An oxidation polymerization ink, a penetration drying ink, an evaporation drying ink, and an ultraviolet curing ink can be used in accordance with differences among drying methods.

A reflection layer may be a functional ink in which color changes in accordance with the illumination angle or the observation angle. Such a functional ink may be an optical variable ink, a color-shifting ink, and a pearl ink.

In order to perform hologram computation for a pseudo polygon intended to be expressed by using a quantization phase difference structure <NUM>, an inclination angle of the polygon is determined, and the quantization phase difference structure <NUM> corresponding to an inclined surface <NUM> of the inclination angle (see <FIG> described later) is computed.

<FIG> is a front view showing a sphere <NUM> as an embodiment of a pseudo polygon that emerges because of the diffraction light of the quantization phase difference structure <NUM>. <FIG> is a plan view of an optical structure 10b where a plurality of multiple diffraction regions <NUM> having a plurality of spatial frequency components of different directions are arranged for expressing the sphere <NUM> as in <FIG> in a pseudo manner. <FIG> is a cross-sectional view showing a positional relationship between the optical structure <NUM> and the sphere <NUM>.

<FIG> is a cross-sectional view showing a part of a polygon in a pseudo 3D shape for a sphere <NUM>. It is formed of the inclined surface <NUM> having an inclination angle θ1 relative to the reference plane <NUM> of the multiple diffraction region <NUM>.

<FIG> also shows the positional relationship between the inclined surface <NUM> and the reproduction point <NUM>. As shown in <FIG>, the reproduction point <NUM> is arranged in the specular direction of the inclined surface <NUM> in the embodiment of the present invention, thereby providing a visual effect in which the phantom inclined surface <NUM> appears to exist when the light is incident.

In a case of computing the inclined surface <NUM> on which the light is vertically incident, the incident light vector perpendicular to the reference plane <NUM> is I =(<NUM>,<NUM>-<NUM>)·.

A normal vector relative to the inclined surface <NUM> of the polygon in a phantom 3D shape constructed on the reference plane <NUM> is n.

The angle between -<NUM> and the normal vector n is θ1, and the angle between the alignment direction a of plurality of reproduction points <NUM> (#<NUM>) to (#<NUM>) and a normal vector n is θ2. If θ1 = θ2 = θ, the plurality of reproduction points <NUM> (#<NUM>) to (#<NUM>) are distributed in accordance with the alignment direction a = I + 2cos(θ)·n·.

The shortest distance R from the reproduction points <NUM> (#<NUM>) to (#<NUM>) to the reference plane <NUM> satisfies the relationship as expressed R > D<NUM>/λ in which D is the length of the entire multiple diffraction region <NUM>, and λ is the wavelength of the light in the multiple diffraction region <NUM>.

The light intensity distribution of a plurality of reproduction points <NUM> (#<NUM>) to (#<NUM>) is determined in a manner that, among the reproduction points <NUM> (#<NUM>) to (#<NUM>), the reproduction point <NUM> (#<NUM>) existing in a direction in which the incident light is reflected on the inclined surface <NUM> of the polygon in a specular manner has the highest light intensity, and a reproduction point shifted further from the specular direction has a lower light intensity; in other words, the light intensity reduces in the order of the reproduction point <NUM> (#<NUM>), reproduction point <NUM> (#<NUM>), and reproduction point <NUM> (#<NUM>), and in the order of the reproduction point <NUM> (#<NUM>), reproduction point <NUM> (#<NUM>), and reproduction point <NUM> (#<NUM>).

This enables realization of the reflection intensity distribution of the inclined surface <NUM> by computation.

The above light intensity distribution and another light intensity distribution can be applied. <FIG> shows an embodiment in which the plurality of reproduction points <NUM> (#<NUM>) to (#<NUM>) are arranged at a regular interval in a space; however, the plurality of reproduction points <NUM> (#<NUM>) to (#<NUM>) may be arranged at an irregular interval. The above matters will be explained with reference to <FIG>. In <FIG>, the horizontal axis represents the aligned direction of the reproduction points <NUM>, and the vertical axis represents the intensity of the reproduction points <NUM>. a of the horizontal axis corresponds to the specular direction.

<FIG> shows an embodiment in which the reproduction points <NUM> with the same intensity are not arranged in the specular direction, but six reproduction points <NUM> are arranged at a regular interval with the specular direction at the center. <FIG> shows an embodiment in which <NUM> reproduction points <NUM> with the same intensity are arranged coarsely in the vicinity of the specular direction, and densely at a position away from the specular direction. <FIG> shows an embodiment in which the reproduction points <NUM> are not arranged in the specular direction, but reproduction points <NUM> are arranged at a regular interval in a manner that the intensity is high in the vicinity of the specular direction, and the intensity is lower in a position further away from the specular direction. <FIG> shows an embodiment in which the reproduction points <NUM> are not arranged in the vicinity of the specular direction, but reproduction points <NUM> are arranged at a regular interval in a manner that the intensity is higher in a position further away from the specular direction, and lower in a position closer to the specular direction. In the present embodiment, the intensity distribution of the reproduction points <NUM> can be set discretionarily.

As described above, in the embodiment of the present invention, the reproduction points <NUM> are arranged in a discrete manner with the specular direction at the center as shown in <FIG>, thereby providing a reproduced image with luster in which each polygon intricately changes in accordance with the viewpoint and the light source like jewels. The luster that intricately changes has a sparkling appearance.

<FIG> is a cross-sectional view showing an embodiment in which an optical structure 10c adheres to an adherend <NUM> so as to be applied to the authentication body.

To adhere to the adherend <NUM>, the optical structure 10c has the quantization phase difference structure <NUM> on a carrier <NUM>, a reflection layer <NUM> made of a metal thin film is formed on the surface of the quantization phase difference structure <NUM>, an adhesion layer <NUM> is provided on the surface of the reflection layer <NUM>, and the optical structure 10c adheres to the adherend <NUM> via the adhesion layer <NUM>.

The carrier <NUM> is transparent so as to reduce the loss of the reflected light. The carrier <NUM> can be made of a rigid body such as glass, or a film. The film may be a plastic film. The plastic film may be a PET (polyethylene terephthalate) film, PEN (polyethylene naphthalate) film, or a PP (polypropylene) film, for example. Depending on the use and purpose, a paper, a synthetic paper, a plastic multi-layer paper, a resin impregnated paper, etc. c be used as a carrier.

The material forming the quantization phase difference structure <NUM> can be thermoplastic resin such as urethane resin, polycarbonate resin, polystyrene resin, polyvinyl chloride resin, etc., thermoset resin such as unsaturated polyester resin, melamine resin, epoxy resin, urethane (meta-)acrylate, polyester (meta-)acrylate, epoxy (meta-)acrylate, polyol (meta-)acrylate, melamine (meta-)acrylate, triazine (meta-)acrylate, etc., a composite thereof, or a thermoformable material having a radical polymerizable unsaturated group, for example.

<FIG> is a cross-sectional view showing another embodiment in which an optical structure 10d adheres to an adherend <NUM> so as to be applied to the authentication body.

The optical structure 10d shown in <FIG> is different from the optical structure 10c shown in <FIG> in that a peeling layer <NUM> is provided between the carrier <NUM> and the quantization phase difference structure <NUM> for peeling off the carrier <NUM>.

After the optical structure 10d adheres to the adherend <NUM> via the adhesion layer <NUM>, the carrier <NUM> is peeled off by peeling of the peeling layer <NUM>; thus, the carrier <NUM> needs not be transparent.

The forming material of the peeling layer <NUM> may be resin. In addition, the peeling layer <NUM> may include a lubricant. The resin may include thermoplastic resin, thermoset resin, ultraviolet curable resin, and electron beam curable resin, for example. The resin may be acrylate resin, polyester resin, or polyamide resin.

The lubricant may be wax such as polyethylene powder, paraffin wax, silicone, and carnauba wax. These may be applied, as the peeling layer <NUM>, on the layer of the carrier <NUM>. Publicly known application methods may be applied to the application. The application may be a gravure coat, a micro gravure coat, a die coat, or a lip coat, for example. The thickness of the peeling layer <NUM> may be within the range from <NUM> to <NUM>.

In the optical structure <NUM> according to the above embodiments of the present invention, graphic information such as a picture or character information can be the rainbow-free colors, and the appearance can have luster like jewels depending on the viewpoint and the light source. This appearance is sparkling since blinking brightness is given by blinking in viewpoint and light source. This appearance can improve security of, for example, quantization phase difference structure securities and card media, or passports and visas.

In the embodiments of the present invention, as shown in <FIG>, a plurality of spatial frequency components are taken into consideration, and a plurality of reproduction points <NUM> are taken into consideration in accordance therewith. In the present comparative example, the number of reproduction points is set to N = <NUM> for comparison in computation of the hologram.

In the optical structure <NUM>, <NUM> by <NUM> multiple diffraction regions <NUM> constituted by quantization projecting portions and quantization recessed portions aligned on a grid of <NUM> × <NUM> are arranged. Each of a quantization projecting portion and a quantization recessed portion is a square having a side of <NUM>. This graphic resolution is the graphic resolution of drawing on a resist of an electron beam drawing device.

After drawing on a resist, Ni sputtering is performed, and a Ni plate is produced after Ni electrocasting. From this Ni plate, emboss molding is performed to a PET film by a UV curable resin. <NUM> of Al is evaporated on the surface of the structure after emboss molding.

As a result, a reproduced image which shines dimly in a rainbow color is reproduced. The reproduced image is reproduced in a rainbow color because the computation is performed using the number of reproduction points N = <NUM>, and there are few scattering components. Similarly, the reproduced image is dim because there are few scattering components and reflected light cannot be visually confirmed.

To be compared with the above comparative example, in the present example <NUM>, hologram computation is performed under the condition that the number of reproduction points is set to N = <NUM>, the light intensity of the reproduction points is set to cos (θ) ^ s, and s = <NUM>.

θ at this time is equal to the inclination angle of the inclined surface <NUM>. In <FIG>, the direction of a is θ = <NUM>. θ2 in <FIG> is set to <NUM> degrees.

In addition, the optical structure <NUM> is produced in the same manner as the comparative example. To sum up, <NUM> by <NUM> multiple diffraction regions <NUM> constituted by quantization projecting portions and s aligned on a grid of <NUM> × <NUM> are arranged; each of a quantization projecting portion and a quantization recessed portion is set to a square having a side of <NUM>; Ni sputtering is performed after drawing on a resist, a Ni plate is produced after Ni electrocasting; emboss molding is performed with this Ni plate to a PET film by UV curable resin; and <NUM> of Al is evaporated on the surface of the structure after emboss molding.

As a result, a reproduced image shining in an iridescent color is reproduced. Its brightness is greater than the comparative example. The reproduced image is reproduced in the iridescent color because the computation is performed using the number of reproduction points N = <NUM>, and the number of the reproduction points is not enough for reproduction in a white color although the reproduced image is reproduced more brightly than the comparative example since there are more reproduction points than the comparative example.

For comparison with the above comparative example and Example <NUM>, the computation of the phase is performed in the present Example <NUM>, while the number of reproduction points N is set to <NUM> and other conditions are not changed.

The optical structure <NUM> is produced similarly to the comparative example. To sum up, <NUM> by <NUM> multiple diffraction regions <NUM> constituted by quantization projecting portions and quantization recessed portions aligned on a grid of <NUM> × <NUM> are arranged, and each of a quantization projecting portion and a quantization recessed portion is set to a square having a side of <NUM>, Ni sputtering is performed after drawing on a resist and Ni plate is produced after Ni electrocasting, emboss molding is performed with this Ni plate to a PET film by UV curable resin, and <NUM> of Al is evaporated on the surface of the structure after emboss molding.

As a result, a reproduced image is reproduced in a white color. This is because the large number of the reproduction points, N = <NUM>, allows the iridescent color to mix sufficiently, which enables reproduction in a white color. Its brightness is greater than the comparative example and Example <NUM>. This is because the number of the reproduction points N has increased to increase scattering components.

In this manner, it is confirmed that the present optical structure can realize a brighter and whiter reproduced image by increasing the number of the reproduction points, as in the comparison between the comparative example and Examples <NUM> and <NUM>.

An optical structure according to an example useful for understanding the present invention will be described.

In the optical structure according to of the example useful for understanding the present invention, a peeling layer, an embossed layer, and a reflection layer are laminated on a film.

<FIG> are a cross-sectional view schematically showing a configuration of an optical structure according to an example useful for understanding the present invention.

As shown in <FIG>, an optical structure <NUM> is constituted by laminating a peeling layer <NUM>, an embossed layer <NUM>, and a reflection layer <NUM> on a film <NUM>.

As shown in <FIG>, further in the optical structure <NUM>, a protection layer <NUM> for protecting the reflection layer <NUM> may be layered on the non-embossed layer side of the reflection layer <NUM>.

The carrier <NUM> can be a rigid body such as glass, or a film. The film may be plastic. The plastic film may be a PET (polyethylene terephthalate) film, PEN (polyethylene naphthalate) film, or a PP (polypropylene) film, for example. Depending on the use and purpose, a paper, a synthetic paper, a plastic multi-layer paper, a resin impregnated paper, etc. may be used. The carrier may be a heat-resistant material. The heat-resistant material has small defomations and deteriorations due to heat and pressure, etc. applied when the embossed layer <NUM> is laminated.

The forming material of the peeling layer <NUM> can be resin. In addition, the peeling layer <NUM> may include a lubricant. The resin may be acrylate resin, polyester resin, or polyamide resin. The resin may be thermoplastic resin, thermoset resin, ultraviolet curable resin, and electron beam curable resin, for example. The lubricant may be wax such as polyethylene powder, paraffin wax, silicone, and carnauba wax. The peeling layer <NUM> may be formed by a publicly known application method. The peeling layer <NUM> may be formed on the carrier <NUM> by a gravure printing method or a micro gravure method, for example. The thickness of the peeling layer <NUM> may be within the range from <NUM> to <NUM>.

Next, the embossed layer <NUM> will be described.

<FIG> is a cross-sectional view schematically showing a structure of the embossed layer <NUM> of the optical structure <NUM>.

The embossed layer <NUM> is in an approximately flat shape, and has a quantization phase difference structure <NUM> on one side. A length L from the upper surface <NUM> of the quantization projecting portion of the quantization phase difference structure <NUM> to the lower surface <NUM> of the quantization recessed portion is constant regardless of a position on the surface of the embossed layer <NUM>. The upper surface <NUM> of the quantization projecting portion and the lower surface <NUM> of the quantization recessed portion can be approximately parallel to the carrier <NUM>. Such embossed layer <NUM> modifies a color of the reflected light based on the length L. The concavoconvex direction of the quantization phase difference structure <NUM> (namely, the vertical direction in <FIG>) is perpendicular to the extending direction of the ribbed recessed portion and the groove-like recessed portion formed by the top surface <NUM> of the quantization projecting portion and the bottom surface <NUM> of the quantization recessed portion. This structure enables broadening the emission distribution of light, and enables control without damaging the color tone of the light.

The embossed layer <NUM> has an embossed surface on one side or both sides. The embossed surface includes a phase angle recording region. A quantization phase difference structure is formed in the phase angle recording region. In a quantization phase difference structure, quantization projecting portions and quantization recessed portions are aligned. A quantization projecting portion and a quantization recessed portion has a horizontal width of the integral multiple of a unit length, and a vertical width of the integral multiple of a unit length. The unit length may be from a 20th to a half of the center wavelength of the visible wavelength. The unit length may be from <NUM> to <NUM>.

The quantization projecting portions are arranged at the portion where a phase angle to be recorded is equal to or more than <NUM> and less than π. If the height of the quantization projecting portions is constant, the phase angle equal to or more than <NUM> and less than π is quantized to π/<NUM>. The quantization projecting portions have a quantized height corresponding to π/<NUM>. If the quantization projecting portions have a plurality of heights, the heights are quantized at an interval of π/(<NUM>·n). The quantization projecting portions have respective quantized heights corresponding to respective phases. The quantization recessed portions are arranged at the portion where a phase angle to be recorded is equal to or more than π and less than 2π. If the depth of the quantization recessed portions is constant, the phase angle equal to or more than π and less than 2π is quantized to 3π/<NUM>. If there are a plurality of depths of the quantization recessed portions, the quantization is performed at an interval of π/(<NUM>·n). The quantization recessed portions have respective quantized heights corresponding to respective phases. A wavelength of the light, which is diffracted in a specific angle because of a mutual effect of the quantization projecting portions and the quantization phase difference structure where the quantization recessed portions are aligned, is determined in accordance the spatial frequency, the incident angle, and the diffraction angle determined in accordance with the arrangement of the quantization projecting portions and the quantization recessed portions. Accordingly, in the multiple diffraction region of the embossed surface, space frequencies of the quantization projecting portions and the quantization recessed portions are discrete; thus, only diffraction light corresponding to the spatial frequency is diffracted. Since the diffraction light is emitted with wavelengths at a certain interval, the observed diffraction light is in a mixed color of diffraction lights with a plurality of specific wavelengths.

If the quantization recessed portions have a constant depth and the quantization projecting portions have a constant height, the reflected light on the top surfaces of the quantization projecting portions interferes with the reflected light on the bottom surface of the quantization recessed portions due to the mutual effect with the quantization phase difference structure in which the quantization recessed portions are aligned. If the quantization recessed portions have a constant depth and the quantization projecting portions have a constant height, the depth and the height may be from <NUM> to <NUM>.

The interfering light becomes maximum when the phase difference between the reflected light of the top surface and the reflected light of the bottom surface with a uniform phase is <NUM> or an integral multiple of 2π, and the reflected light becomes <NUM> when the reflected light on the top surface and the reflected light on the bottom surface with opposite phases have the phase difference of an integer multiple of π and interfere with and annihilate each other. The reflected light seamlessly varies from the maximum to <NUM> between the phase difference when the phases are uniform and the phase difference when the phases are opposite. Since the phase difference is proportional to the wavelength of the reflected light, the intensity of the reflected light with each wavelength caused by the interference sequentially varies. Accordingly, the reflected light caused by the interference is in a specific band.

A quantization phase difference structure, in which the quantization recessed portions have a constant depth and the quantization projecting portions also have a constant height, emits reflected light by these interference and diffraction.

Accordingly, a quantization phase difference structure, in which the quantization recessed portions have a constant depth and the quantization projecting portions also have a constant height, selectively emits reflected light in a band of the interfering light among the diffraction light. With normal diffraction, diffraction light of a high level equal to or higher than a secondary level, which is normally determined as noise, is also emitted; thus, reflected light as designed cannot be obtained. However, since the interfering light among the diffraction light is selectively reflected in the quantization phase difference structure of the present invention, reflected light that does not include a high-level diffraction light can be obtained.

For modifying the band of interference by the quantization phase difference structure, the top surface of the quantization projecting portion or the bottom surface of the quantization recessed portion may be a rough surface. Thereby, a necessary band of interference by the quantization phase difference structure can be ensured.

The following operation is necessary for forming a quantization phase difference structure. First, as shown in <FIG>, the computing device computes a phase W (x, y) of the light from a reproduction point <NUM> (#a) with respect to quantization projecting portions and quantization recessed portions included in an overlapping region <NUM> (#<NUM>) where a computational element section <NUM> (#A) specified by one reproduction point <NUM> (#a) overlaps a phase angle recording region <NUM> (#a), and also in an overlapping region <NUM> (#<NUM>-<NUM>) where a computational element section <NUM> (#A) overlaps a part of a phase angle recording region <NUM> (#<NUM>).

There is one reproduction point <NUM>, or a plurality of reproduction points <NUM>. There is one computational element section <NUM> corresponding to one reproduction point <NUM>. If there are a plurality of reproduction points <NUM>, respective computational element sections <NUM> correspond to respective reproduction points <NUM> on a one-to-one basis, and there are the same number of computational element sections <NUM> as the number of the reproduction points <NUM>.

If there are a plurality of reproduction points <NUM>, the computing device further computes a phase W (x, y) of the light from a reproduction point <NUM> (#b) with respect to quantization projecting portions and quantization recessed portions included in an overlapping region <NUM> (#<NUM>) where a computational element section <NUM> (#B) determined another reproduction point <NUM> (#b) overlaps a phase angle recording region <NUM> (#<NUM>), as shown in <FIG>.

As shown in <FIG>, if two computational element sections <NUM> (#A) and <NUM> (#B) overlap each other, the sum of phases W (x, y) is computed.

The computing device further computes the phase angle ϕ (x, y) based on the computed phases W (x, y), and records information of numeral values of the computed phase angle ϕ (x, y) in the corresponding overlapping region <NUM> as retardation. A phase angle ϕ (x, y) is computed from the phase based on the formula φ(x,y) = arg(W(x,y)).

Herein, Wn (kx, ky) is a phase of a reproduction point n at the coordinates (kx, ky) in the computational element section <NUM> of the nth reproduction point, W (x, y) is a phase at the coordinates (x, y, <NUM>) to be recorded in the phase modulation structure, n is nth reproduction point (n = <NUM> to Nmax), ampn is the amplitude of the light of nth reproduction point, i is an imaginary number, λ is the wavelength of the light when reproducing a reproduced image to be reproduced with a group of reproduction points <NUM>, On (x) is a value of an x-coordinate of a reproduction point, On (y) is a value of an y-coordinate of a reproduction point, On (z) is a value of an z-coordinate of a reproduction point, (kx, Ky, <NUM>) are coordinates of a quantization projecting portion and a quantization recessed portion, and ϕn (kx, ky) is a phase angle of an nth reproduction point. Phase Wn (kx, ky) is obtained at all points in the computational element section <NUM>. Since a phase of a reproduction point n is the same at the points having the same distance from the reproduction point <NUM>, information of a computed phase can be copied for the phase of a reproduction point n. Furthermore, as will be described below, On (z) is a value of a z-coordinate of a reproduction point; in other words, since the phase Wn (kx, ky) of the reproduction points having the same distance from the recording surface has the same phase distribution, information of a computed phase can be copied for the phase Wn (kx, ky). Regarding the coordinates (kx, ky) in the computational element section <NUM>, if its central coordinate is set to (<NUM>, <NUM>), the x-coordinate of the corresponding reproduction point On is On (x) and the y-coordinate is On (y); thus, the coordinates (kx, ky) are related to the coordinates on the recording surface, (x, y), as follows: x = Kx + On(x), and y = Ky + On(y).

If the phase of the reproduction point <NUM> for recording the numeral value information in the quantization projecting portions and quantization recessed portions increases, the amount of information also increases along with the increase, and the computation time also increases. If the phase of the reproduction point <NUM> for recording is too large, it may decrease the contrast of the reproduced image reproduced at the reproduction point <NUM>. Thus, for example, as in the overlapping region <NUM> (#<NUM>-<NUM>), in order to obtain a clearer reproduced image for the part where the phase angle recording regions <NUM> of a plurality of reproduction points <NUM> (#a, #b) overlap with each other, it is preferable that overlapping of the computational element sections <NUM> is small, or in other words, the number of computational element sections existing in the phase angle recording regions <NUM> is small.

A phase angle recording region <NUM> may prevent overlapping of computational element sections <NUM>, or in other words, may have one computational element section <NUM>. Furthermore, if the phase angle recording region <NUM> has a plurality of computational element sections <NUM>, the number of the computational element sections <NUM> in the phase angle recording region <NUM> may be set to equal to or less than <NUM>. In this case, the computation is more efficiently performed. The number of the computational element sections <NUM> in the phase angle recording region <NUM> may be set to be equal to or less than <NUM>. In this case, it is easier to obtain a clear reproduced image.

Phase W (x, y) is computed with respect to the quantization projecting portions and quantization recessed portions in the overlapping region <NUM> where the computational element section <NUM> specified by the viewing angle θ overlaps the phase angle recording region <NUM>, and a phase angle ϕ (x, y) is computed based on the Phase W (x, y). As described above, the upper limit of the viewing angle θ is specified, and a region where the phase angle ϕ is computed is limited to the overlapping region <NUM>; thus, the computation time is shortened. The computed phase angle ϕ is recorded as retardation in a corresponding quantization projecting portion and a quantization recessed portion in the overlapping region <NUM>. <FIG> is an SEM image showing quantization projecting portions and quantization recessed portions in which phase angles ϕ are recorded. The quantization projecting portions and quantization recessed portions shown in <FIG> are squares of which side length is d, and are two-dimensionally arranged at an arrangement interval d in both the X direction and Y direction.

Other than the phase angle recording region <NUM>, a phase angle non-recording region <NUM> may be provided on the recording surface <NUM>. Even if the phase angle non-recording region <NUM> overlaps the computational element section <NUM>, the computing device does not perform computation, and the phase angle is not recorded in the phase angle non-recording region <NUM>. Instead, the phase angle non-recording region <NUM> may record information other than the phase angle, such as information related to scatter, reflection, and diffraction characteristics of the light. Alternatively, the phase angle non-recording region <NUM> may be translucent, and a printing may be carried out for the phase angle non-recording region <NUM>. This improves the designability of the phase modulation structure <NUM> having a recording surface.

For simplification, <FIG> shows the configuration where projections and recesses of the plurality of quantization phase difference structures <NUM> have the same pitch P; however, the configuration of the embossed layer <NUM> is not limited thereto. The embossed layer <NUM> may have different pitches P, different lengths L, different lengths T of the top surfaces <NUM> of the quantization projecting portions, and different lengths B of the bottom surfaces <NUM> of the quantization recessed portions. As will be described later, the embossed layer <NUM> has quantization phase difference structures <NUM> with locally different pitches P, lengths L, lengths T, and lengths B, so as to have a plurality of spatial frequency components in the quantization phase difference structures <NUM>. Since these quantization phase difference structures <NUM> are constituted by quantization projecting portions and quantization recessed portions of a constant size, a structure smaller than the size of the quantization projecting portions and quantization recessed portions is not formed. On the other hand, a structure of the integral multiple of a quantization projecting portion or a quantization recessed portion is formed in a region where quantization projecting portions are continuously arranged or a region where quantization recessed portions are continuously arranged.

<FIG> is a plan view showing a multiple diffraction region formed by an embossed layer <NUM> having a quantization phase difference structure <NUM>. <FIG> shows that a quantization phase difference structure <NUM> having many different pitches P is arranged over the entire surface of the embossed layer <NUM>, similarly to <FIG>. <FIG> is a plan view of five spatial frequency components f1 to f5 in the multiple diffraction region of <FIG>. <FIG> is a figure showing peak intensities of spatial frequency components f1 to f5 shown in <FIG>. In <FIG>, the horizontal axis represents a distance (pixels) on the plane, and the vertical axis represents gray values. In this manner, also in the optical structure <NUM>, multiple-diffraction regions, which respectively have specified spatial frequency components f1 to f5 respectively corresponding to respective reproduction points arranged in a discrete manner along one predetermined direction on a plane, are arranged in the quantization phase difference structure <NUM> on a plane, similarly to one embodiment of the present invention.

As shown in <FIG>, a plurality of spatial frequency components f1 to f5 are arranged separately in one direction. In <FIG>, five spatial frequency components f1 to f5 are shown as an example. However, in the example useful for understanding the present invention, the number of the spatial frequency components is from <NUM> to <NUM>.

<FIG>, and <FIG> are plan views showing spatial frequency components different from <FIG> for comparison.

Five spatial frequency components f1 to f5 shown in <FIG> to be compared are distributed separately in one direction, thereby restricting the range of color shift of the color of the reflected light. It is also possible to suppress decrease in brightness when viewed by eye or sensed with a measuring instrument, and suppress decrease in brightness of the reflected light, by changing the distance between adjacent spatial frequency components.

On the other hand, one spatial frequency component f6 shown in <FIG> is linear, thereby having a higher effect for suppressing color shift than <FIG>; this causes a decrease in brightness when viewed by eye or sensed with a measuring instrument, which leads to lower brightness than the case of <FIG>.

Since each of the three spatial frequency components f7 to f9 shown in <FIG> is a linear spatial frequency component, the light is diffused in multiple directions. Similarly to <FIG>, this improves the effect to suppressing color shift than <FIG>; this causes decrease in brightness when viewed through eyes or sensed with a measuring instrument, which leads to lower brightness than the case of <FIG>.

According to the only one dot-like spatial frequency component f10 shown in <FIG>, the light is diffused in a single direction, but the color shift cannot be restricted.

The embossed layer <NUM> may include a salt adsorbent. If the optical structure <NUM> includes the protection layer <NUM> as in <FIG>, at least one of the embossed layer <NUM> and the protection layer <NUM> includes a salt adsorbent.

<FIG> is a micrograph obtained by observing a part of the surface of the quantization phase difference structure <NUM> of the embossed layer <NUM> with a scanning electron microscope.

In the quantization phase difference structure <NUM>, ribbed projecting portions as one element structure, in which quantization projecting portions in a constant size are aligned in one direction, and groove-like recessed portions as the other element structure, in which quantization recessed portions in a constant size are aligned parallel to the ribbed projecting portions, are arranged adjacently and alternately. The depth from the top surface <NUM> of the quantization projecting portions of the ribbed projecting portions to the bottom surface <NUM> of the quantization recessed portions of the groove-like recessed portions is constant, and the structure is quantized into the element structures of the quantization projecting portion and the quantization recessed portion. The surface roughness of the bottom surface <NUM> of the quantization recessed portion of the quantization phase difference structure <NUM> is greater than the surface roughness of the top surface <NUM> of the quantization projecting portion, and the diffraction light of the quantization phase difference structure <NUM> reproduces a plurality of reproduction points discrete in one direction.

If the embossed layer <NUM> has many spatial frequency components, the surface of the quantization phase difference structure <NUM> of the embossed layer <NUM> has a structure that is regular to some extent but is complicated as shown in <FIG>. In the example useful for understanding the present invention shown in <FIG>, the bottom surface <NUM> of the quantization recessed portions of the quantization phase difference structure <NUM> have a constant depth, and the variation in the depth of the bottom surface <NUM> of the quantization recessed portions is equal to or less than a 10th of the length L. The surface of the bottom surface <NUM> of the quantization recessed portion may be rough.

The material of the embossed layer <NUM> can be thermoplastic resin such as urethane resin, polycarbonate resin, polystyrene resin, polyvinyl chloride resin, etc., thermoset resin such as unsaturated polyester resin, melamine resin, epoxy resin, urethane (meta-)acrylate, polyester (meta-)acrylate, epoxy (meta-)acrylate, polyol (meta-)acrylate, melamine (meta-)acrylate, triazine (meta-)acrylate, etc., a composite thereof, or a thermoformable material having a radical polymerizable unsaturated group, for example.

The reflection layer <NUM> may be formed by applying an ink. In accordance with the printing method, this ink may be an offset ink, a letterpress ink, a gravure ink, etc. In accordance with the difference of ink resolvent, this ink may be a solventless ink, an oil-based ink, or a water-based ink. In accordance with different drying methods, this ink may be an oxidation polymerization ink, a penetration drying ink, an evaporation drying ink, or an ultraviolet curing ink.

The reflection layer <NUM> may be a functional ink of which color shifts in accordance with the illumination angle or the observation angle. As such a functional ink, an optical variable ink, a color-shifting ink, and a pearl ink can be used.

The reflection layer <NUM> can be metal or a metal compound. The metal compound may be TiO<NUM>, Si<NUM>O<NUM>, SiO, Fe<NUM>O<NUM>, ZnS, etc. These metal compound has a high refractive index, and easily has high reflectivity. The metal may be Al, Ag, Sn, Cr, Ni, Cu, Au, etc. It is easy to increase the reflectivity of these metals.

Furthermore, the reflection layer <NUM> may have magnetism.

The protection layer <NUM> can be made of the same kind of material as the embossed layer <NUM>. The protection layer <NUM> may be made of the same material as the embossed layer <NUM>. If the protection layer <NUM> is made of the same material as the embossed layer <NUM>, the refractive index can be set to be the same as the embossed layer <NUM>, and thus the colors on the front and back sides of the optical structure <NUM> can be set to be the same.

An optical layer (not shown) that reflects the visible light and transmits infrared light may be further laminated on the optical structure <NUM>.

In the optical structure <NUM>, the structural colors of the embossed layer <NUM> and the reflection layer <NUM> preferably have a reflectance spectrum that has a peak at least in the wavelength region from <NUM> to <NUM>.

The optical structure according to the example useful for understanding the present invention is produced by peeling the embossed layer <NUM> and the reflection layer <NUM>, as materials for an optical structure, off of the carrier <NUM> of such optical structure <NUM> via the peeling layer <NUM>, and making these materials for an optical structure into fine powder. The optical structure produced in such a manner is dispersed in resin, and applied as a printable ink.

Next, the effect of such optical structure according to the example useful for understanding the present invention will be described.

In the optical structure according to the example useful for understanding the present invention, the length L from the top surface <NUM> of the quantization projecting portion of the quantization phase difference structure <NUM> to the bottom surface <NUM> of the quantization recessed portion is constant regardless of the position on the surface of the embossed layer <NUM>, and the light of a specific wavelength can be reflected more easily by adjusting the value of the length L.

Regarding the spatial frequency of the quantization phase difference structure <NUM>, the color shift can be reduced and the color variation along with change in the observation direction and the illumination direction can be reduced by separately arranging the peak intensities of a plurality of spatial frequency distribution f1 to f5 along one direction or a plurality of directions in a plane, as shown in <FIG>.

Meanwhile, as shown in <FIG>, the color-shift effect can be also reduced in the case of linearly and continuously arranging the peak intensity of the spatial frequency component f6. In this case, the brightness and saturation of the color is reduced.

If the peak intensities of the spatial frequency components f7 to f9 are set to a plurality of directions (not only one direction) in a plane as shown in <FIG>, there are too many reflected directions of the light, which leads to reduction in brightness.

If the peak intensity of the spatial frequency component f10 is arranged in a single direction (not a plurality of directions) as shown in <FIG>, when the light is incident, only the diffraction light is reflected only in a specific direction. In other words, in the case as shown in <FIG>, the embossed layer <NUM> has the simple diffraction grating of a single pitch P as shown in <FIG>; in this case, the number of reflected directions is too small, which leads to reduction of the entire brightness.

In the optical structure according to the example useful for understanding the present invention, as shown in <FIG>, the surface roughness of the bottom surface <NUM> of the quantization recessed portion is high, which is equal to or less than a 10th of the length L. Thus, the reflected directions of the light can be diffused without changing the color by setting the quantization phase difference structure <NUM> to an extent not dependent on the wavelength of light.

As described above, the light with a specific wavelength can be reflected by adjusting the length L from the top surface <NUM> of the quantization projecting portion to the bottom surface <NUM> of the quantization recessed portion; if neither the top surface <NUM> of the quantization projecting portion nor the bottom surface <NUM> of the quantization recessed portion has any surface roughness, the length L fluctuate in accordance with the tolerance relative to the designed value, thereby fluctuating the color sensitively.

However, in the optical structure according to the example useful for understanding the present invention, since the bottom surface <NUM> of the quantization recessed portion in the embossed layer <NUM> has surface roughness, the color changing degree with respect to the length L reduces, which leads to moderation of tolerances. Such an effect is not limited to the effect exhibited by the surface roughness of the bottom surface <NUM> of the quantization recessed portion, but is also exhibited by the surface roughness of the top surface <NUM> of the quantization projecting portion, similarly.

Therefore, it is only necessary that the average surface roughness of either one of the top surface <NUM> of the quantization projecting portion or the bottom surface <NUM> of the quantization recessed portion is equal to or less than a 10th of the reference length L. An arithmetic average roughness (Ra) can be applied to the surface roughness. In other words, the arithmetic average roughness (Ra) is equal to or less than <NUM>. The roughness may be equal to or more than a 100th of the length L. In other words, the arithmetic average roughness (Ra) is equal to or more than <NUM>.

The surface roughness of the top surface <NUM> of the quantization projecting portion may be smaller than the surface roughness of the bottom surface <NUM> of the quantization recessed portion. In this case, the tolerances of the structural color can be reduced, and reduction of saturation of the structural color is suppressed. In other words, both of stability and chromogenic of the structural color and can be achieved. The surface roughness of the bottom surface <NUM> of the quantization recessed portion may be smaller than the surface roughness of the top surface <NUM> of the quantization projecting portion. In other words, the surface roughness of the top surface <NUM> of the quantization projecting portion is different from the surface roughness of the bottom surface <NUM> of the quantization recessed portion.

In the optical structure according to the example useful for understanding the present invention, the concave-convex direction of the quantization phase difference structure <NUM> (namely, the vertical direction in <FIG>) is perpendicular to the extending direction of the ribbed recessed portion and the groove-like recessed portion formed by the top surface <NUM> of the quantization projecting portion and the bottom surface <NUM> of the quantization recessed portion, thereby scattering the light related to the structural color in the vertical direction in which the color tone of the light is not changed; accordingly, the optical structure according to the example useful for understanding the present invention can be realized even if there are manufacturing tolerances.

Moreover, if the optical structure according to the example useful for understanding the present invention is constituted by the optical structure <NUM> where the protection layer <NUM> is laminated as shown in <FIG>, the structural colors on the front and back sides of the optical structure may be set to the same by forming the protection layer <NUM> from a material having the same refractive index as the embossed layer <NUM>.

If the reflection layer <NUM> is magnetic, it enables manufacturing by a method of curing a resin after the optical structure is oriented in a magnetic field in a specific direction; thus, it is possible to control the direction of the optical structure and to provide an optical effect deriving therefrom.

If the reflection spectra of the structural colors of the embossed layer <NUM> and the reflection layer <NUM> have a peak at least in the wavelength region from <NUM> to <NUM>, it is possible to produce a printed material that looks black similarly to general printed materials printed in black under visible light but reacts to infrared light.

By using this characteristic, the optical structure according to the example useful for understanding the present invention can be applied to the degradation determination of a material such as concrete. If a material to be tested such as concrete includes the optical structure according to the example useful for understanding the present invention, the contrast between a cracked portion and an uncracked portion can be emphasized at the time of infrared light examination.

Deterioration of the reflection layer <NUM> due to salt in the air can be prevented by including a salt adsorbent in the embossed layer <NUM>, or in at least one of the embossed layer <NUM> or the protection layer <NUM> if the protection layer <NUM> is provided as shown in <FIG>.

As shown in <FIG> where explanations are added to <FIG>, projecting portions and recessed portions of constant length L are aligned in one direction, thereby providing interfering and diffraction function, setting the bottom surface <NUM> of the quantization recessed portions of the quantization phase difference structure <NUM> to be rough, and providing excessive scattering characteristics. Accordingly, stable highly-bright chromogenic can be realized by highly-bright color development of interference and diffraction and the scattering characteristics by the rough surface. Since the quantization phase difference structure <NUM> has a quantization structure based on the element structure, it is possible to eliminate extremely small structures and extremely large structures that are difficult to be formed.

An ink that does not fade even after time passes can be realized by applying flakes of the optical structure according to the example useful for understanding the present invention as pigments of the ink for a printed material required to have high durability. Since this ink can eliminate the color-shift effect in a specific direction, this ink can also realize a color tone that does not easily change as seen from any direction. Therefore, it is quite preferable for use as identification means for authentication for forgery of securities such as gift vouchers, credit cards, brand-name products, and equipment components.

If the optical structure according to the example useful for understanding the present invention is applied to an ink for infrared light, the ink is normally invisible to the human eye but can be detected by an infrared detector, etc. Based on this fact, the ink for infrared light can be utilized for detecting cracks of concrete with infrared light by including the ink in concrete.

Patent Literature <NUM> (<CIT>) discloses the technique of developing colors by interference between the top surface <NUM> of the quantization projecting portion and the bottom surface <NUM> of the quantization recessed portion similarly to the quantization phase difference structure <NUM> shown in <FIG> and <FIG>. However, the configuration disclosed in Patent Literature <NUM> has a constant relief height but has uneven widths. Thus, the configuration disclosed in Patent Literature <NUM> has a disadvantage that bad formation easily occurs in wide portions and narrow portions. However, in the quantization phase difference structure <NUM> shown in <FIG> and <FIG>, such bad formation does not occur since the relief width is constant.

According to such optical structure according to the example useful for understanding the present invention, the image is not in a rainbow color as in the conventional diffraction grating, as shown in <FIG>, and a brighter image than the image realized in the Patent Literature <NUM> can be obtained.

Next, an example in which the optical structure according to the example useful for understanding the present invention as described above is actually produced, its characteristics are checked, and it is applied to concrete deterioration detection, will be described below.

In order to produce the optical structure according to the example useful for understanding the present invention, first, the embossed layer <NUM> is designed. Specifically, <NUM> spatial frequency components are separately arranged on the quantization phase difference structure <NUM>, and the embossed layer <NUM> is designed so that adjacent rays of light are about <NUM> degrees apart and the light spreads in a direction of <NUM> degrees in a planar manner when the light is vertically incident.

Next, a positive resist having a film thickness of <NUM> is applied on a glass original plate, and the quantization phase difference structure <NUM> is drawn on the positive resist surface by using an electron beam drawing device. The dose amount of positive resist to be applied is determined by adjustment so that the length of the positive resist is around <NUM>.

After that, a conductive thin film of Ni is provided by a sputtering method on the glass original plate on the side where the quantization phase difference structure <NUM> is formed by image development. Then, the conductive thin film is plated with Ni, and the conductive thin film of Ni is peeled off the glass original plate to produce a duplicate plate, thereby obtaining an embossing plate.

Next, a peeling layer <NUM> is provided by applying Denka Poval (registered trademark) (polyvinyl alcohol) one surface of a polyester film (Toray industries, Inc. , product name: "Lumirror <NUM>"), which has a thickness of <NUM> and used as the carrier <NUM>, by the gravure coating method so that the film thickness of Denka Poval after drying is <NUM>.

Then, the embossed layer <NUM> is formed on the peeling layer <NUM> by applying UV-curable resin ("POLYSTER" produced by Washin Chemical Industry CO. ) to have a film thickness of <NUM> on the peeling layer <NUM>, pressing the above-described embossing plate on the application surface, and irradiating ultraviolet light of <NUM> mJ/cm<NUM> from a side of the surface of the polyester film as the carrier <NUM>, on which the peeling layer <NUM> is not applied, to cure the UV-curable resin. This embossing plate is peeled off, thereby forming the embossed layer <NUM> including the quantization phase difference structure <NUM> on the peeling layer <NUM>.

Furthermore, the reflection layer <NUM> covering the embossed layer <NUM> is formed by forming an Al deposited thin layer of a film thickness of <NUM> over the entire surface of the embossed layer <NUM>.

Moreover, the protection layer <NUM> is formed by applying UV-curable resin to have a film thickness of <NUM> again on the reflection layer <NUM> ("POLYSTER <NUM>" produced by Washin Chemical Industry CO. In this manner, the embossed layer <NUM> and the protection layer <NUM> are formed of the same material.

An optical structure formed in this manner is immersed in a liquid to dissolve the peeling layer <NUM>, thereby separating an optical structure material including the embossed layer <NUM>, the reflection layer <NUM>, and the protection layer <NUM> from the carrier <NUM>.

The optical structure material is then immersed in a MEK solvent and separated into pieces; after that, the optical structure material is pulverized with a planetary mill, thereby producing optical structures. The grain diameter of this optical structure is about ϕ20 µm as observed with a stereomicroscope.

The optical structures formed in the above manner are dispersed at <NUM> W% in the UV-curable resin, applied on PET with an applicator to have a dry film thickness of <NUM>, and cured by UV light, so that reflected light of which color is shifted to blue is visually confirmed.

In order to apply the optical structure as described above to concrete degradation detection, a concrete test body A of <NUM> cubic centimeters is produced by mixing cement, sand, gravel, and optical structure in the ratio of <NUM>:<NUM>:<NUM>:<NUM>, and adding an appropriate amount of water while stirring the mixture.

Next, a concrete test body B of <NUM> cubic centimeters is produced by mixing cement, sand, and gravel in the ratio of <NUM>:<NUM>:<NUM> without mixing the optical structure, and adding an appropriate amount of water while stirring the mixture.

A hole of ϕ30 mm and depth of <NUM> is formed on the back side of each of the concrete test bodies A and B, and an infrared photograph of each of the concrete test bodies A and B is taken by using the infrared thermograph TVS-<NUM> of Nippon Avionics Co.

As a result, a shape of the hole is not identified in a concrete test body B into which the optical structure is not mixed; however, a shape of the round hole is confirmed in a concrete test body A into which the optical structure is mixed. Deformation due to temperature differences is also confirmed.

In this manner, it is confirmed that the optical structure according to the example useful for understanding the present invention facilitates shape measurement of concrete, and can be applied to degradation determination.

Claim 1:
An optical structure (<NUM>, 10a, 10b, 10c, 10d) having a quantization phase difference structure (<NUM>) on one surface of a quantization phase difference structure layer, wherein
in the quantization phase difference structure, a plurality of quantization projecting portions are aligned in one direction in ribbed projecting portions, and a plurality of quantization recessed portions are aligned in groove-like recessed portions parallel to the ribbed projecting portions,
the ribbed projecting portions are arranged adjacent to and alternately with the groove-like recessed portions, and
in the quantization phase difference structure, plural spatial frequency components in accordance with an arrangement of the quantization projecting portions and the quantization recess portions overlap with each other;
the plural spatial frequencies are discrete in a predetermined direction and arranged regularly,
characterized in that
the plurality of quantization projecting portions has a constant size, and
the plurality of quantization recessed portions has a constant size.