Liquid crystal display apparatus, a liquid crystal projector using same, and a method of manufacturing the liquid crystal display apparatus

A liquid crystal display apparatus comprises a first polymer-containing liquid crystal area forming a first area including a display area, and a second polymer-containing liquid crystal area including a second area other than the first area, and is characterized in that polymer of the first polymer-containing liquid crystal area and polymer of the second polymer-containing liquid crystal area respectively have network structures different from each other.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a liquid crystal display apparatus in
 which high polymer is mixed in liquid crystal, a liquid crystal projector
 using the liquid crystal apparatus, and a method of manufacturing the
 liquid crystal display apparatus.
 2. Related Background Art
 In recent years, liquid crystal display apparatuses have been widely used
 in various devices because of their advantages of thin sizes, low voltage
 driving ability, and saved power consumption, and the like, as is
 representatively known from a display of a direct view type having a
 diagonal size exceeding 10 inches. Also, liquid crystal projectors which
 realize display on a larger screen by providing a liquid crystal display
 panel together with an optical system have come to be introduced as
 practically useful commercial products having high resolution and
 brightness, as computers have spread popularly.
 Liquid crystal used in those liquid crystal panels is generally TN (Twisted
 Nematic) liquid crystal which achieves higher response speed and contrast
 in comparison with STN (Super Twisted Nematic) liquid crystal used mainly
 in conventional panels, so that images of higher quality can be displayed.
 However, in a display apparatus using TN liquid crystal, loss of light is
 largely due to a polarizing plate and the brightness is therefore limited.
 Particularly, the drawback of the TN liquid crystal display apparatus is
 remarkable in case of a projection type liquid crystal display apparatus
 which requires high brightness.
 As countermeasures against the drawback, proposals have been made as to
 liquid crystal display apparatuses using various liquid crystal, such as
 "PNLC (Polymer Network Liquid Crystal)" in which TN liquid crystal is
 dispersed in a liquid crystal continuous phase or a sponge-like polymer
 network, a "high-polymer/liquid crystal composite film" capable of forming
 a display of a large screen by using an electro-optic effect accompanying
 light diffusion without using a polarizing plate, or "polymer dispersed
 liquid crystal" having a structure in which spherical liquid crystal
 grains are dispersed in a high-polymer matrix between transparent
 electrode and liquid crystal molecules are oriented along a wall surface
 of the high-polymer matrix within the grains in the following manner.
 Specifically, incident light is diffused when a difference exists between
 the average refractive index of the liquid crystal grains and the
 refractive index of the high-polymer matrix. As the refractive indexes is
 increased when a voltage is applied to the high-polymer dispersed cell,
 liquid crystal is released from restrictions from the wall surface of the
 high-polymer matrix, to be oriented to be vertical to the surfaces of the
 transparent electrodes. When the refractive index of the high-polymer
 matrix is close to the refractive index of the liquid crystal molecules in
 the short-axis direction of the molecules, incident light is transmitted
 without being dispersed.
 The PNLC is provided as a type of liquid crystal in which light is
 transmitted at a high transmit rate by making the refractive index of TN
 liquid crystal be substantially equal to the refractive index of the
 polymer network when a voltage is applied, while incident light is
 diffused to produce black by a difference between the refractive index of
 the TN liquid crystal oriented randomly and the refractive index of the
 polymer network when no voltage is applied. A display apparatus using the
 PNLC does not use a polarizing plate, and therefore essentially realizes
 display with a higher light use efficiency, i.e., brighter display than a
 TN liquid crystal display apparatus. These phenomena and applications are
 common to the "high-polymer/liquid crystal composite film" and the
 "polymer dispersed liquid crystal".
 In order to more advantageously use the high light use efficiency of the
 "polymer network liquid crystal" and the like, it is effective that the
 active matrix substrate is of a reflective type. Since a reflective type
 substrate can be embedded below a reflective electrode to shield light,
 the aperture can be increased to be close to 100%, resulting in a
 potential that the light use efficiency is not decreased unlike a
 transparent type even when the pixel size is reduced.
 In case of manufacturing a liquid crystal display apparatus using
 "high-polymer/liquid crystal composite film", "polymer dispersed liquid
 crystal", or "polymer network liquid crystal" of a reflective type, an
 active element is embedded below a reflective electrode with respect to a
 reflective type substrate and high-polymer, and liquid crystal are
 injected and sealed between the substrate and a transparent electrode.
 Thereafter, ultraviolet light (UV) is irradiated thereon, and thus, a
 liquid crystal panel is prepared.
 In particular, a method of manufacturing the (polymer dispersed liquid
 crystal" is described in Japanese Patent Laid-open Application No.
 5-61016. According to this publication, an acrylate-based
 ultraviolet-polymerized composite material (using a light-polymerization
 starting agent of DAROQUA (phonetic translation) 1116 available from Merck
 & Co., Inc.) and a liquid crystal composite material (E8 available from
 BDH-SHA (phonetic translation)) are uniformly dissolved and injected into
 glass cell having an ITO electrode. Thereafter, ultraviolet light is
 irradiated thereon (at 1 mW for 500 seconds), thereby to prepare the
 polymer dispersed liquid crystal (PDLC) cell. The grain diameter of the
 liquid crystal composite material in the PDLC material is set to 0.1 to 10
 .mu.m which is adjusted by the content of the liquid crystal composite
 material. That is, a liquid crystal composite material of 65 to 75 weight
 % is used with respect to a total weight of the high-polymer matrix and
 the liquid crystal composite material, to mix samples having different
 grain diameters.
 However, in case of a conventional liquid crystal panel using ultra-violet
 irradiation, it has been found that uneven display occurs. Particularly,
 in case of irradiating ultra-violet light of parallel light onto the
 entire surface of liquid crystal area, there appears a phenomenon that the
 reflection light amount decreases concentrically from the center portion
 of the liquid crystal panel to the peripheral portion thereof, i.e., the
 transmittance rate decreases. In case of a color three-plate type,
 irregular color appears concentrically. These drawbacks are caused by
 unevenness of the polymerization condition or unevenness of liquid crystal
 grain diameters, and are estimated to be due to a stress during
 polymerization. Another factor is estimated to be that an influence from a
 seal differs in accordance with a distance from the seal during
 polymerization.
 In addition, it has been found that there is a problem concerning the
 stability of liquid crystal. That is, the liquid crystal phase lacks the
 stability because of an existence of a non-reactive liquid crystal phase
 exists during preparation using ultraviolet light.
 A liquid crystal display apparatus into which liquid crystal has been
 injected will be explained with reference to a cross-section shown in FIG.
 5. The applicant filed Japanese Patent Application No. 7-186473 concerning
 a method of manufacturing an active matrix substrate. The active matrix
 substrate is constructed as follows. A lower portion of liquid crystal 214
 is comprised of an n-type silicon semiconductor substrate 201 having an
 impurity density of 10.sup.15 cm.sup.-3 or less, LOCOS 202, a PWL 203 as a
 p-type impurity region having an impurity density of about 10.sup.16
 cm.sup.-3, an NLD 206 as an n-type impurity region having an impurity
 density of about 10.sup.16 cm.sup.-3, source and drain regions 207 and
 207' having an impurity density of about 10.sup.19 cm.sup.-3, an AI
 electrode 209, a PSG 211, an SiN 210, and a pixel electrode 213.
 Next, an upper portion of the liquid crystal 214 is comprised of a
 transparent substrate 220, a color filter 221, a black matrix 222, and a
 common electrode consisting of an ITO or the like. However, the color
 filter 221 which does not transmit ultra-violet light and the black matrix
 222 are not used to achieve the object of the present invention, and
 layers for these components are not required. This is because the active
 matrix substrate adopted in the present invention uses one sheet per color
 and the color filter of the present invention does not transmit
 ultra-violet light. Therefore, to achieve the object of the present
 invention, the upper portion of the liquid crystal 214 may have a
 structure comprised of a transparent substrate 220 made of glass or the
 like on which a transparent electrode is vapor-deposited on the side
 facing the liquid crystal 214 or a structure comprised of a common
 substrate 223 and a transparent substrate 220. Note that color filters and
 a black matrix must allow ultraviolet light to be transmitted to some
 extent, in case of adopting a liquid crystal display apparatus for a RGB
 matrix. In the active matrix substrate having a structure as described
 above, the surfaces of pixel electrodes 213 are flat and smooth, and
 insulating layers are embedded in clearances between adjacent pixel
 electrodes, resulting in an advantage in that the entire surface is not
 concave or convex but is flat and smooth.
 A plan view of the liquid crystal apparatus will be explained with
 reference to FIG. 6. This figure shows a relationship between a seal
 structure and a panel structure. References 51, 52, 53, and 54
 respectively denote a seal portion, an electrode pad, a clock buffer
 circuit, and an amplifier. The amplifier 54 is used as an output amplifier
 for an electric inspection of a panel. References 55, 56, and 57
 respectively denote an Ag paste portion for obtaining an electric
 potential of an opposite electrode, a display portion, and a peripheral
 circuit portion including, for example, vertical and horizontal shift
 registers (HST and VSR) and the like. As shown in FIG. 6, circuits are
 arranged to have a small total chip size both inside and outside the seal.
 Although leads from the pad are concentrated at one side of edges of the
 panel in this embodiment, leads can be extracted from both sides of longer
 edges of the panel or from sides of more edges thereof, resulting in an
 advantage when responding to a high-speed clock.
 SUMMARY OF THE INVENTION
 The present invention has been made as a result of making eager studies and
 experiments to solve the problem as described above, i.e., the problem
 concerning unevenness of display luminance and stability of liquid
 crystal.
 According to the present invention, there is provided a liquid crystal
 display apparatus comprising: a first polymer-containing liquid crystal
 area forming a first area including a display area; and a second
 polymer-containing liquid crystal area including a second area other than
 the first area, characterized in that polymer of the first
 polymer-containing liquid crystal area and polymer of the second
 polymer-containing liquid crystal area respectively have network
 structures different from each other.
 Further, according to the present invention, there is provided a method of
 manufacturing a liquid crystal display apparatus, comprising: a step of
 providing a liquid crystal material and a pre-polymer material between a
 pair of substrates at least one of which is transparent; and a step of
 irradiating the pre-polymer with light which causes the pre-polymer
 material to make a polymerization reaction, to polymerize the pre-polymer
 material, characterized in that first light irradiation is performed on a
 first area including a display area, and thereafter, second light
 irradiation is performed on the first area and a second area other than
 the first area.
 Furthermore, according to the present invention, there is provided a liquid
 crystal projector for irradiating the above liquid crystal display
 apparatus with light from a light source, and for projecting reflection
 light from the liquid crystal display apparatus onto a screen, to display
 an image.
 According to the liquid crystal display apparatus of the present invention,
 the second area serves as a stress absorbing area so that the polymer
 network in the first area including the display area is rendered uniform.
 As a result, display unevenness and luminance unevenness can be prevented.
 In addition, according to the present invention, the second area serves as
 an absorbing layer for absorbing a force from the seal portion, which
 restricts orientation of liquid crystal, so that influences from the seal
 portion of the display area are less effected. As a result, unevenness of
 display luminance and color is greatly improved.
 Further, according to the present invention, two-step light irradiation is
 carried out as first irradiation and second irradiation, so that all
 components mixed in liquid crystal are caused to make a reaction, thereby
 reducing instability of liquid crystal. As a result, reliability of the
 liquid crystal apparatus can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention has been made on the basis of knowledge that
 unevenness in display is reduced in a manner in which strong ultra-violet
 rays (which will be referred to only as ultra-violet rays or UV rays) are
 irradiated for a short time period onto a liquid crystal panel enclosing
 polymer and liquid crystal and provided with a seal frame including at
 least a display area and weak ultra-violet rays are thereafter irradiated
 onto the entire surface of the liquid crystal area.
 When irradiating UV rays, a stress caused due to a polymerization reaction
 during irradiation of UV rays is released to the outside of a UV ray
 irradiation area, by irradiating UV rays onto only a display area (or an
 area including a display area). Therefore, the polymerization reaction
 (for forming polymer or a network) is performed uniformly within the
 irradiation area and is not directly influenced from the surface of a seal
 agent, so that unevenness of display characteristics is improved. Also, it
 has been found that the hysteresis and response speed of the display area
 can be improved by performing irradiation in two steps.
 In addition, after irradiation of relatively strong UV rays in the first
 step which causes a polymerization reaction as described above,
 irradiation of relatively weak UV rays is performed in the second step so
 that a weak polymerization reaction is generated in areas onto which UV
 rays are not irradiated in the first step. Therefore, reliability is
 ensured, and the hysteresis and response speed of the display area are
 improved in comparison with a case of adopting no irradiation in the first
 step.
 Depending on irradiation of UV rays, a small polymer network structure is
 formed in a UV-ray-irradiated area in the first step, and a large polymer
 network structure is formed in an area other than the UV-ray-irradiated
 area.
 FIG. 8 shows a cross-section of a liquid crystal layer used in a liquid
 crystal display apparatus according to the present invention. In the
 figure, references A and B respectively denote a polymer material portion
 and a liquid crystal material portion. A pre-polymer material forms a
 mesh-like network structure shown in FIG. 8 through photopolymerization.
 The average hole diameter of a mesh formed by the polymer material is
 small in a UV-ray-irradiated area obtained by the first step, the average
 hole diameter of a mesh is relatively large in the other area than the
 UV-ray-irradiated area.
 The present invention includes an embodiment of performing UV-ray
 irradiation adopting different irradiation intensities in first and second
 steps, respectively. In this manner, network forming process and residual
 monomer removing process can be controlled independently when forming
 polymer network liquid crystal, and therefore, the characteristics of
 polymer network liquid crystal can be totally optimized.
 According to the present invention, it is possible to obtain liquid crystal
 characteristics of a high response speed and low hysteresis without
 deteriorating the contrast ratio. Therefore, total image quality can be
 improved for a display apparatus.
 [Embodiment 1]
 (1: Constitution of Liquid Crystal Display Apparatus)
 A liquid crystal panel according to a first embodiment of the present
 invention will be explained with reference to FIGS. 1A and 1B. In FIGS. 1A
 and 1B, reference 1 denotes an active matrix substrate having a reflective
 electrode on its surface, prepared by a semiconductor process. The
 reflective electrode of the active matrix substrate preferably has high
 flatness and a high reflectance with respect to visible light. For
 example, the present embodiment uses aluminum or aluminum containing a
 slight amount (about 0.5 to 3.0%) of another element (such as silicon,
 copper, titanium or the like), as an electrode material. Since the
 substrate surface in contact with a liquid crystal layer is almost
 perfectly flattened, unevenness in display characteristics caused by a
 variation of the thickness of liquid crystal layer and uneven injection of
 liquid crystal caused by a gap can be eliminated advantageously. A drain
 portion of a switching element is connected to each of pixel electrodes in
 active matrix substrate 1. As for switching elements, a MIM switch as a
 two-terminal device, a diode switch, a thin-film transistor of a
 three-terminal type, a mono-crystal silicon transistor using bulk silicon
 are preferred. As a thin-film transistor, an amorphous silicon transistor,
 a polysilicon transistor, and a SOI (Silicon On Insulator) mono-crystal
 transistor are known. The present embodiment can be realized with use of
 any of the switching elements described above. In the present embodiment,
 a mono-crystal silicon transistor using bulk silicon was adopted to
 constitute a switching element.
 In addition, a light shielding layer (made of, for example, titanium) for
 shielding an incident light is provided between the switching element and
 the reflective electrode, and prevents the element from causing an
 operating error.
 The active matrix substrate described above internally comprises on-chip
 drive circuits including horizontal and vertical shift registers and the
 like, and realizes high-speed signal processing which coops with many
 pixels and high precision, at low costs.
 Although the present embodiment adopts an active matrix substrate of a
 reflective type, the present invention is applicable to an active matrix
 substrate of a transmissible type with the same advantages as described
 above.
 Next, reference 2 denotes opposite glass. The glass preferably has a
 thickness of about 0.5 mm to 3.0 mm, high flatness, and a thermal
 expansion characteristic similar to that of the active matrix substrate.
 For example, the present embodiment used non-alkaline glass having a
 thickness of 1.0 mm (NH-35 available from NH TECHNO GLASS CORPORATION). In
 a reflection type liquid crystal panel, surface reflection from the
 opposite glass and interface reflection from an interface between liquid
 crystal and glass are factors which deteriorate contrast. As a
 countermeasure thereof, the present embodiment provides an anti-reflection
 coating on the surface and takes into consideration the film structure in
 the side of the interface to liquid crystal. Specifically, a transparent
 film (such as MgF.sub.2 :n=1.38) having a lower refractive index than ITO
 (Indium-Tin-Oxide) and glass is provided between the glass and an ITO
 transparent electrode having a contact with the liquid crystal surface,
 and the film thickness of the transparent film is selected such that
 minimum reflection is obtained with respect to the wavelength of incident
 light.
 The liquid crystal panel can be used as a component of a color display
 apparatus of a single plate type by providing an on-chip color filter on
 active matrix substrate 1. In case of using the liquid crystal panel for a
 projection type display of a three-plate type, anti-reflection should
 preferably be provided in compliance with wavelengths of colors of R, G,
 and B.
 Reference 3 denotes a main seal agent which maintains a distance in
 parallel between opposite glass 2 and active matrix substrate 1 and
 encloses liquid crystal. A thermosetting resin, a UV-curing resin, or a
 UV-curing/thermosetting resin and so forth can be used as a main seal
 agent 3. A spacer agent 4 for controlling the thickness of a polymer
 network liquid crystal layer is uniformly mixed in the main seal agent 3,
 and is uniformly applied with a pressure so that the display
 characteristics are uniform within the panel. A material of spacer 4 may
 be silica, a resin, or the like. The shape of spacer 4 may be circular or
 spherical and any of circular and spherical shapes can be used. In order
 to form a gap with high accuracy, a circular spacer made of silica was
 used with attention paid so as not to damage a backing layer. A seal area
 is formed with a proper space margin kept at the outer circumference of
 display area 5, so that a second area in which liquid crystal grains are
 large functions effectively.
 Reference 6 denotes an injection port for liquid crystal. The injection
 port is sealed by an end seal. The end seal may be, for example, an allyl
 resin, a denatured epoxy resin, an epoxy-acrylate resin, or the like.
 Reference 91 denotes liquid crystal in the second area. Reference 92
 denotes a boundary between the first and second area.
 In addition, reference 7 denotes a polymer network liquid crystal layer. A
 polymer material may be polyacrylate, polymethacrylate, or the like. As
 the liquid crystal material, nematic liquid crystal, cholesteric liquid
 crystal, or the like may be used, and it is possible to cite a liquid
 crystal composite material of being biphenyl-based, phenylbenzoate-based,
 or phenylcyclohexane-based. In addition, the structure control may be
 performed by photopolymerization using a pre-mixture of three components
 of liquid crystal, monomer, and oligomer. The liquid crystal, for example,
 may be "E-8" available from BDH Inc. and having large anisotropies in
 dielectric constant and refractive index, the monomer may be
 2-ethylhexylacrylate, and the oligomer may be urethaneacrylate oligomer.
 (2: Projection Type Liquid Crystal Display Apparatus and Evaluation
 Apparatus)
 Explanation will be conceptionally made of a system in case of evaluating a
 projector using a polymer network liquid crystal display apparatus as
 described above.
 Projection display with high luminance, high resolution, and high quality
 can be realized by constructing a projector with three of liquid crystal
 panels for R, G, and B provided in an optical system.
 In the present embodiment, a prepared liquid crystal panel was provided as
 a liquid crystal panel 78 in an optical system of a projection type liquid
 crystal display apparatus shown in FIG. 7, and the characteristics thereof
 were evaluated. In FIG. 7, the apparatus is comprised of a light source 71
 which emits parallel light from a metal halide lamp, a xenon lamp or the
 like, a converging lens 72 for converging the parallel light, a Fresnel
 lens 73 for transferring the converged light into parallel light, a
 reflection mirror 74 for reflecting parallel light from the Fresnel lens
 73, a Fresnel lens 75 for converging reflection light from the reflection
 mirror 74, a reflection mirror 76 for reflecting the converged light
 toward the liquid crystal panel, a view lens 77 for converting the
 reflection light from the reflection mirror 76 into parallel light, a
 liquid crystal panel 78 as a target of evaluation, and an optical system,
 and a screen 81 on which an image driven by the liquid crystal panel 78 is
 projected. The optical system comprises a projection lens for passing
 reflection light of liquid crystal panel 78 through a diaphragm 79 via the
 view lens 77 to converge and enlarge the reflection light, and a color
 separation mirror.
 The parallel light projection optical system of the liquid crystal panel
 has a F-value of 8.0. Light emitted from light source 71 is modulated and
 reflected by liquid crystal panel 78 and is magnified by projection lens
 80, to be projected onto screen 81. Although evaluation was carried out
 with use of a metal halide lamp of 250 (W) as light source 71, a
 projection type display apparatus is naturally capable of using a
 high-pressure mercury lamp or a xenon lamp. In addition, the output power
 is not limited to the above value. The evaluation was carried out with of
 a G-channel and the center wavelength thereof is 550(nm), as long as
 special notes are added.
 In case of constructing a projection type display apparatus using three
 plates of R, G and B, light from the light source is subjected to color
 separation by a dichroic mirror, and liquid crystal panels corresponding
 to the colors may be arranged spatially such that the colors are layered
 on screen 81. In this case, even if three liquid crystal panels for R, G
 and B are used, the light source system including the light source, the
 converging lenses and the like, the optical system including projection
 lenses and the like and the screen are used in common so that a liquid
 crystal display apparatus of full-surface projection type can be formed
 with a small size, or a liquid crystal display apparatus of a back-surface
 projection type can be formed as a thin type even including a large size
 reflection mirror to the screen.
 (3: Method of Manufacturing Liquid Crystal Panel)
 In the following, a method of manufacturing a liquid crystal panel will be
 explained.
 An active matrix substrate 1 cut out for every panel and an opposite glass
 member 2 corresponding to the substrate were prepared, and both were
 washed in a clean environment so that foreign materials might not be mixed
 therein. Ultrapure water applied with a surfactant and subjected to
 CO.sub.2 bubbling, or ultrapure water with an ultrasonic wave applied was
 effective for washing. Since the surface of a reflection electrode is
 easily affected by chemical solutions, a very thin protect film may
 previously be formed on the surface in several cases. In case of aluminum,
 it is effective to previously form a natural oxide film on the surface by
 any method.
 After rinsing sufficiently with ultrapure water, sufficient drying was
 carried out after paper drying of IPA.
 Next, a main seal agent mixed with a spacer agent was coated in a desired
 shape on active matrix substrate 1. The main seal agent used was Worldlock
 706 available from KYORITSU-KAGAKU-SANGYO Inc. which is of a
 UV-curing/thermosetting type applicable to both UV-curing and thermal
 hardening. Although a possible thickness of a liquid crystal layer is 5
 .mu.m to 20 .mu.m, the present embodiment adopts a thickness of 13 .mu.m.
 Therefore, a spacer agent for 13 .mu.m was used.
 A silver paste was coated on a predetermined position in order to attain a
 conductivity between active matrix substrate 1 and the ITO transparent
 electrode on the surface of opposite glass member 2.
 Next, active matrix substrate 1 and opposite glass member 2 were adhered on
 each other by an adhering device. When adhering both together, a pressure
 was applied in a substantially parallel direction with respect to the
 substrate, and the substrate and the member are uniformly pressed so that
 the diameter of the spacer agent is substantially equal to the thickness
 of liquid crystal in the front surface side of the panel.
 In case of the main seal agent used in the present embodiment, an
 irradiation with UV rays are carried out in this stage, and further, a
 heat treatment at 120.degree. C. is carried out as a after-cure for 60
 minutes, to finish the hardening of the main seal agent. In case of a
 UV-hardening type, UV rays are irradiated in this stage, to harden the
 main seal agent. Particularly, in case of thermosetting type, the
 thickness of a gap is easily changed due to shrinkage and expansion during
 the thermosetting. As a countermeasure thereof, it is effective to perform
 a heat treatment while appropriately pressing the panel. In addition, in
 order to effectively remove gasses and volatile components contained in
 the main seal agent, it is advantageous to carry out evacuation for
 degassing after the hardening.
 (4: Liquid Crystal Injection Step)
 Liquid crystal injection is carried out for the cell already subjected to
 adhering as described above. Liquid crystal injection is carried out as
 follows. A cell and a syringe containing and a
 liquid-crystal/prepolymer-mixture composite material are set in a liquid
 crystal injection device, and the liquid crystal/prepolymer-mixture
 composite material is dipped through an injection port for injecting the
 material, which is provided in the cell. The
 liquid-crystal/prepolymer-mixture composite material means a solution in
 which liquid crystal material components and prepolymer components are
 mixed. The solution should preferably be uniform.
 In the following, the liquid crystal injection step will be explained in
 details. The liquid crystal injection device is comprised of a degassing
 chamber for performing degassing with respect to the
 liquid-crystal/prepolymer-mixture composite material, and a cell chamber
 for performing high-vacuum exhaustion of the inside of the cell and liquid
 crystal injection. At first, the liquid-crystal/prepolymer-mixture
 composite material is heated for 30 minutes in an oven previously heated
 to about 50.degree. C. and is then stirred for one minute, to make a
 uniform phase. Thereafter, the liquid-crystal/prepolymer-mixture composite
 material is filled in the syringe for injecting the
 liquid-crystal/prepolymer-mixture composite material. The syringe filled
 with the liquid-crystal/prepolymer-mixture composite material is set in
 the degassing chamber, and subsequently, the cell is mounted on a cell
 holding cassette, which is set at a predetermined position in the cell
 chamber. The liquid crystal injection device is arranged so as to perform
 degassing of the liquid-crystal/prepolymer-mixture composite material,
 high-vacuum exhaustion inside the cell, heating of the cell, pressure
 control of the inside of the cell chamber and the degassing chamber,
 opening/closing of valves, injection of the
 liquid-crystal/prepolymer-mixture composite material from the syringe to
 the cell, and release of the cell to air after injection, as an automatic
 sequence.
 In the liquid crystal injection step, the vacuum degree of the degassing
 chamber should preferably be 0.01 Torr to 10 Torr, in order that the
 composition of the liquid-crystal/prepolymer-mixture composite material is
 prevented from being changed due to differences in vaporization amounts
 between those components having different vaporization pressures among
 components of the liquid-crystal/prepolymer-mixture composite material.
 The present embodiment adopts 0.5 Torr. The degassing period is preferably
 1 to 100 minutes, and the present embodiment adopts 10 minutes. In
 addition, it is effective to heat the cell in order to remove impurities
 in the cell and slight components generated from during vacuum exhaustion
 in the cell chamber. Effective heating is within a range from a room
 temperature to a decomposition temperature of the main seal agent, and the
 present embodiment adopts heating at 100.degree. C. The vacuum degree is
 10 Torr or less, and a higher effect can be obtained as the vacuum degree
 and the heating period increase. The present embodiment adopts 0.001 Torr
 and one hour. After completion of vacuum exhaustion of the cell, the
 pressure inside the cell chamber is decreased by introducing a slight
 amount of nitrogen, so that changes of the composition of the
 liquid-crystal/prepolymer-mixture composite material can be reduced as
 much as possible. In the present embodiment, the vacuum degree when
 injecting liquid crystal is 0.5 Torr. Further, dummy dispensing is always
 carried out before dripping the liquid-crystal/prepolymer-mixture
 composite material from the syringe into the injection port provided in
 the cell, so that a portion of liquid-crystal/prepolymer-mixture composite
 material sticking to the top end of the syringe, whose composition has
 changed, might not be introduced into the cell.
 Injection of the liquid-crystal/prepolymer-mixture composite material was
 completed by 15 minutes after dripping of the
 liquid-crystal/prepolymer-mixture composite material into the injection
 port of the cell.
 The present embodiment shows an example of a method of dripping
 liquid-crystal/prepolymer-mixture composite material into an injection
 port of the cell, as a method of liquid crystal injection. However, the
 other methods were attempted, by a method in which a container containing
 the liquid-crystal/prepolymer-mixture composite material was brought into
 contact with the injection port of the cell in the cell chamber, a method
 in which the liquid-crystal/prepolymer-mixture composite material was
 dripped into the injection port under a normal pressure, and a method in
 which a container containing the liquid-crystal/prepolymer-mixture
 composite material was brought into contact with the injection port of the
 cell under a normal pressure. In any of these methods, injection was
 confirmed to be completed properly.
 During the liquid crystal injection step and until UV-ray irradiation is
 carried out in a UV-ray irradiation step as a post step, attention should
 be paid so that the temperature of the liquid-crystal/prepolymer-mixture
 composite material and the cell might not decrease to the phase separation
 temperature of the liquid-crystal/prepolymer-mixture composite material.
 If the temperature of the material and the cell decreases to be the phase
 separation temperature or lower, a polymer network structure to be formed
 later cannot be constructed properly, resulting in a factor which
 deteriorates display characteristics.
 Further, until UV-irradiation onto the cell surface is performed as
 described later after injection of the liquid crystal, it is necessary to
 remove factors, as much as possible, which promotes a polymerization
 reaction with respect to the liquid-crystal/prepolymer-mixture composite
 material, e.g., irradiation of UV rays, an increase of temperature, and
 elapse of time.
 After completion of cleaning of foreign materials and portions of the
 liquid-crystal/prepolymer-mixture composite material sticking to the cell
 surface, UV-irradiation is carried out onto the cell surface. The
 UV-irradiation onto the cell surface is carried out to polymerize
 prepolymer components and simultaneously promote phase separation between
 the liquid crystal components and the prepolymer components, by
 irradiating the liquid-crystal/prepolymer-mixture composite material
 injected in the cell with UV rays within a sensitive wavelength range to
 form a polymer network made of a UV-hardening resin inside the cell.
 (5: Light Irradiation Step)
 The UV-irradiation onto the liquid crystal panel as described above will be
 explained below with reference to FIG. 2. In FIG. 2, UV rays are emitted
 from a light emission tube 11 and a parabolic mirror 12 is provided behind
 the tube 11 so that parallel light is emitted. The liquid crystal panel is
 irradiated with the light through a short-wave cut filter 13. Reference 1
 denotes an active matrix substrate. Reference 15 denotes a temperature
 adjust stage.
 In first irradiation, a light shielding member 20 is provided on glass
 member 2, and a light shielding frame thereof is set so as to be hindered
 inside a seal material 3. The first irradiation is carried out with a
 strong light intensity for a short time period. Next, in second
 irradiation, shielding member 20 is removed, and irradiation is carried
 out with a weak light intensity for a long time. The strong and weak light
 intensities can be obtained by adjusting the height of the power source
 voltage, or by providing a light reducing filter between the light
 emission tube 11 and the liquid crystal panel.
 The UV-irradiation device used in the present embodiment adopts an
 ultra-high-voltage mercury lamp of 4 kW as a light source. The
 UV-irradiation device comprises an optical filter for cutting UV rays
 having a short wavelength of 350 nm or less, in order to prevent
 decomposition of the liquid-crystal/prepolymer-mixture composite material
 14 and components of a polymer network structure to be formed after the
 UV-irradiation.
 The cell temperature during the UV-irradiation was set to 19.0 .degree. C.
 The temperature of the cell was controlled by providing a thermal chuck
 (TC2800 available from TRIO-TECH), and the cell temperature was monitored
 by causing a thermocouple to have a direct contact on the thermal chuck.
 The temperature of the thermal chuck achieved a time-based stability of
 .+-.0.2.degree. C.
 In order to selectively irradiate UV rays at a desired position on the cell
 surface, a light shielding frame for UV rays was prepared. A steel plate
 having a thickness of 0.3 mm and a surface galvanized with black zinc was
 used as a material of the light shielding frame, and an opening portion
 was formed at the UV-irradiation area. After the light shielding frame was
 fitted and fixed to the cell surface, the cell was set on the thermal
 chuck in the UV-irradiation device, and then, UV-irradiation was carried
 out.
 Once the cell surface was subjected to UV-irradiation, liquid crystal
 material caused phase separation and polymerization in a few seconds, and
 the color of the inside of the cell which was transparent before the
 UV-irradiation turned into milk-white due to a polymer network structure
 formed by the UV-irradiation. Subsequently, the light shielding frame was
 taken off from the cell surface, and continuously, UV-irradiation of in
 the second step was carried out with the irradiation time period changed.
 In UV-irradiation onto the cell surface, prepolymer components are
 polymerized by irradiating UV rays of a sensitive wavelength range onto
 the liquid-crystal/prepolymer-mixture composite material injected in the
 cell. At the same time, phase separation between the liquid crystal
 components and the prepolymer components, thereby to form a polymer
 network structure made of a UV-hardening resin in the cell.
 Parameters relating to the UV-irradiation are a UV-irradiation method (such
 as single step irradiation or two-step irradiation), a wavelength of UV
 rays, UV-irradiation, a UV-irradiation period, a UV-irradiation cell
 temperature, and a shelf period and a shelf environment between the
 irradiation of the first step and that of the second step in case of
 two-step irradiation.
 In the present embodiment, the UV-irradiation method, UV-irradiation
 intensity, and the UV-irradiation period were discussed as parameters for
 UV-irradiation.
 Specifically, liquid crystal panels were manufactured on the following
 conditions. For making comparison, two kinds of panels were manufactured,
 one kind using only one step described above and the other kind using two
 steps according to the present embodiment.
 (i) Irradiation in one step:
 Irradiation intensity: 20 to 150 mW/cm.sup.2
 Irradiation period: 0.5 to 120 seconds
 (ii) Irradiation in two steps of first and second:
 First step
 Irradiation intensity: 20 to 150 mW/cm.sup.2
 Irradiation period: 0.5 to 120 seconds
 Second step
 Irradiation intensity: 1 to 20 mW/cm.sup.2
 Irradiation period: 50 to 3000 seconds
 The irradiation periods and the stage temperature were investigated within
 a range from the phase separation temperature (15 to 18.degree. C.) to
 30.degree. C.
 A range of 50 to 3000 .mu.m was considered for the width of the
 transmissible area of the shielding member 20 as a second liquid crystal
 area and the seal frame. The present embodiment due to the processing
 accuracy of the light shielding member 20 and stray light during
 irradiation, the boundary portion had irregularity of about 100 .mu.m. On
 these conditions, improvements of color unevenness can be efficiently
 achieved if the second liquid crystal area is 200 .mu.m or more.
 The liquid crystal panel thus obtained was remarkably improved in in-plane
 dispersion and color unevenness was reduced to an extent at which no
 problems are caused in practical use. In addition, the cross-section of
 the polymer network was observed by a scanning electron microscope, to
 find out the network structure schematically shown in FIG. 8 (in which
 references A and B respectively denote polymer and liquid crystal
 portions). In the first area including the display area subjected to the
 two-step irradiation in both the first and second steps, the average
 diameter of holes of a mesh of the polymer was 0.5 to 5 .mu.m. On the
 other side, in the second area subjected to only the weak irradiation in
 the second step, the average diameter was 5 to 100 .mu.m.
 For example, when the irradiation in the first step was performed at 40
 mW/cm.sup.2 for 6 seconds and the irradiation in the second step was
 performed at 5 mW/cm.sup.2 for 430 seconds, the unevenness of luminance
 was reduced to .+-.5% or less. As for improvements of dispersion, similar
 effects ware found in the case of performing the irradiation in the first
 step at 40 mW/cm.sup.2 for 60 seconds without performing irradiation in
 the second step. In addition, the hysteresis, response speed, and contrast
 were more excellent than in a conventional method.
 Liquid crystal panels according to the present embodiment were optimized
 for R, G, and B, respectively, and were set in a projector of a
 three-plate type. Then, the in-plane distribution of color unevenness was
 improved so that the image quality was greatly improved.
 (6: End Sealing of Liquid Crystal Injection Port)
 End sealing was carried out for a cell subjected to UV-irradiation. An end
 seal agent used was an epoxy-acrylate resin of a UV-hardening type
 (30Y-195B available from THREE BOND Inc.). The liquid crystal injection
 port of the cell was coated with an end seal agent and light shielding of
 the liquid crystal display portion of the cell was carried out.
 Thereafter, the end seal agent was subjected to UV-hardening by
 UV-irradiation, thus completing the end sealing. Other end seal agents
 which could be used were a UV-hardening type aryl resin A704 available
 from SEKISUI FINE CHEMICAL Inc., and an agent available from
 KYORITSU-KAGAKU-SANGYO Inc. Next, foreign materials sticking to the cell
 surface were removed, and thereafter, the cell was adhered to a holder for
 assembly into an optical system. Further, a flexible print board was
 connected to the holder, and the electrode pad of the active matrix
 substrate was connected to the flexible print board by means of wire
 bonding. Thus, a liquid crystal panel was prepared.
 The contrast ratio of the liquid crystal panel thus prepared will be
 explained below. As for the two-step irradiation, it has been found that
 the UV-irradiation in the first step requires a UV-irradiation intensity
 of at least 20 mW/cm.sup.2 or more. When the irradiation intensity in the
 first step was set to 50 mW/cm.sup.2 or more, deterioration of the
 contrast ratio was not found within a range up to 120 mW/cm.sup.2. It is
 considered that this phenomenon appeared because the diffusion
 characteristic with respect to light of R having the longest wavelength
 began falling as the size of the formed polymer network became small due
 to an increase of the irradiation intensity in the first step.
 Therefore, the upper limit of the irradiation intensity in the first step
 is defined by the deterioration of the diffusion characteristic caused by
 a decrease in size of the polymer network, and it is desirable that the
 irradiation intensity in the first step is substantially 150 mW/cm.sup.2
 or less.
 (Embodiment 2)
 FIG. 3 shows a schematic structure of a light irradiation device according
 to a second embodiment 2 of the present invention. In FIG. 3, reference 11
 denotes a light source as a light emission tube such as a metal halide
 lamp, a halogen lamp, a xenon lamp, or the like. Reference 16 denotes a
 light shielding mask, and reference 20 denotes a liquid crystal panel
 including a glass member 2 opposed to an active matrix substrate 1.
 Reference 17 denotes a band-pass filter which transmits light within a
 wavelength range of UV rays. Reference 18 denotes a converging lens for
 converging light into a direction toward the liquid crystal panel 20.
 Reference 19 denotes a converging lens for outputting parallel light to
 the liquid crystal panel 4. Reference 15 denotes a X-Y stage with a
 temperature adjust function.
 In the present invention, like in Embodiment 1, a cell is prepared by
 adhering the reflective active matrix substrate 1 and glass substrate 2 on
 each other with a seal agent and a spacer agent inserted between the two
 substrates, and a liquid-crystal/prepolymer-mixture material obtained by
 mixing nematic liquid crystal into polyacrylate polymer at a ratio of 4:1
 is injected under a normal pressure.
 In the present invention, the structure adopted in the UV-irradiation is
 arranged as shown in FIG. 3. Specifically, light from the light source 11
 having a peak at a wavelength range of 350 to 400 nm is shaped by a light
 shielding mask, and only components of 350 to 400 nm is transmitted by the
 optical (or band-pass) filter 17. Those components of light are converged
 to a desired size by the converging lenses 18 and 19, and are irradiated
 onto the liquid crystal panel 20 set on the X-Y stage 15 with a
 temperature adjust function.
 In this system, fine adjustment of the irradiation position can be achieved
 by the X-Y stage, so that the second liquid crystal can be controlled
 accurately.
 In addition, the irradiation period and the light shielding area can be
 changed by moving light shielding mask 16, so that irradiation in both of
 the two steps can be performed by one apparatus, contributing to
 improvements of productivity.
 Conditions of UV-irradiation were set in the same range as in Embodiment 1.
 50 to 5000 .mu.m was chosen as the width of the second liquid crystal
 area.
 In the present embodiment, improvements of unevenness were found with
 respect to the width of 100 .mu.m to 3000 .mu.m, because light entered
 vertically into the panel and the positional accuracy of the irradiation
 area was .+-.1 .mu.m.
 The reflection ratio versus voltage characteristic of liquid crystal panel
 20 thus obtained was improved in comparison with a conventional method and
 display unevenness was eliminated.
 Also, characteristics such as the contrast, hysteresis, and response speed
 were more excellent than a conventional method.