Polarization conversion element and image projection device with the same, and method of manufacturing retardation element

Abstract

To provide a polarization conversion element that can be made thin and a retardation element used therefor.SOLUTION: A polarization conversion element comprises a polarization beam splitter consisting of a prism array and a retardation element laminated on the polarization beam splitter, wherein the retardation element comprises a film made of a liquid crystal material having a photosensitive group, and the film has an optical anisotropic region, imparting a phase difference to transmitted light, and an optical isotropic area arrayed alternately in stripes.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The present invention relates to a polarization conversion element that has a thin configuration and can adjust the vibration direction of polarized light to improve light utilization efficiency, an image projection device including such a polarization conversion element, and a method for manufacturing a phase difference element that constitutes the polarization conversion element. [Background technology]

[0002] Polarizing plates are used in image projectors and display devices with projection functions, such as head-up displays. However, when natural light is generally converted into polarized light, light other than that in one vibration direction is not used, which is disadvantageous in terms of light utilization efficiency. To solve this problem, a polarization conversion element has been proposed that separates P-polarized light and S-polarized light with a polarizing beam splitter and converts the vibration direction of one of the polarized lights with a phase difference element.

[0003] For example, Patent Document 1 describes a configuration in which a half-wave plate is provided on a polarizing beam splitter consisting of a prism array formed by stacking multiple pieces of glass and cutting them at a 45-degree angle, with an effective area that functions as a retardation plate and a passing area that allows light to pass as is arranged in a striped pattern, converting P-polarized light to S-polarized light in the effective area and allowing the S-polarized light to pass as is in the passing area, thereby utilizing all natural light as S-polarized light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2001-188123 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes how a 1 / 2 wavelength plate is formed by laminating multiple alignment films and liquid crystal layers on a transparent substrate placed on a polarizing beam splitter, and then the formed 1 / 2 wavelength plate is masked with a striped mask of a predetermined width in which passing sections and non-passing sections are repeated at regular intervals. Next, adhesive tape is attached to the non-passing sections and then peeled off, and the mask is peeled off, so that the 1 / 2 wavelength plate formed on the adhesive tape adheres to and is peeled off, thereby forming a rectangular 1 / 2 wavelength plate, i.e., a striped 1 / 2 wavelength plate.

[0006] However, in the invention of Patent Document 1, in addition to the fact that the manufacturing method of the 1 / 2 wavelength plate is complicated, there is a limit to reducing the stripe width and the thickness of the 1 / 2 wavelength plate due to the constraints of the multilayer structure and masking processing. On the other hand, in fields such as in-vehicle displays, there is a demand for thinning of the polarization conversion element due to the constraints of the installation space of the optical equipment. To achieve this, it is necessary to thin the polarizing beam splitter itself, but if the stripe width of the 1 / 2 wavelength plate cannot be reduced, the corresponding prism width cannot be reduced, and as a result, it is difficult to reduce the thickness of the prism array constituting the polarizing beam splitter.

[0007] The present invention aims to provide a polarization conversion element that uses a phase difference element that can be produced by a simple method and that makes it easy to reduce the arrangement distance between phase difference sections and non-phase difference sections, an image projection device that includes such a polarization conversion element, and a method for producing a phase difference element used therein. [Means for solving the problem]

[0008] The first configuration of the present invention is a polarizing beam splitter consisting of a prism array; a phase difference element laminated on the polarizing beam splitter, the retardation element includes a film made of a liquid crystalline material having a photosensitive group; In the film, optically anisotropic regions that impart a phase difference to transmitted light and optically isotropic regions are alternately arranged in a stripe pattern to form a polarization conversion element.

[0009] The above-mentioned polarization conversion element can be provided with a thin, narrow-pitch phase difference element in a simple manner, which also makes it possible to reduce the thickness of the corresponding polarization beam splitter, making it highly applicable to optical equipment in which the installation space for the polarization conversion element is limited.

[0010] The polarization conversion element may be a polarization conversion element in which the optically anisotropic regions and the optically isotropic regions of the phase difference element are alternately arranged at a pitch of 1 mm or less.

[0011] The phase difference element used in the above-mentioned polarization conversion element forms a striped optical pattern by adjusting the exposure method for the film, so that it is possible to accurately form a narrow-pitch pattern without the need to physically cut and paste the film or peel off parts of it.

[0012] The second aspect of the present invention is an image projection device including the polarization conversion element of the present invention. By using the element of the present invention as the polarization conversion element, it is possible to improve the light utilization efficiency even in an image projection device with a limited installation space.

[0013] A third aspect of the present invention is a method for producing a phase difference element used in the above polarization conversion element, comprising the steps of: forming a coating film made of a birefringence inducing material containing a photosensitive liquid crystal material on a substrate; a step of placing a mask having periodically arranged slits on the coating film and irradiating the coating film with polarized light through the mask; and heating the irradiated coating film and then slowly cooling it to induce birefringence in the area exposed through the slit. This is the method.

[0014] By using the above method, a retardation element to be used in a polarization conversion element can be produced in a simple manner. Effect of the Invention

[0015] According to the present invention, it is possible to provide a polarization conversion element that uses a phase difference element in which regions that impart phase difference are arranged in a stripe pattern at a narrow pitch, and that can be easily made thin, and an image projection device using the same. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view showing an example of a polarization conversion element according to a conventional technique. [Diagram 2] FIG. 1 is a diagram showing an example of an image projection device including a polarization conversion element. [Figure 3A] 1 is a schematic cross-sectional view showing a polarization conversion element according to one embodiment of the present invention. [Figure 3B] FIG. 11 is a schematic cross-sectional view showing a polarization conversion element according to another embodiment of the present invention. [Figure 4] 4A to 4C are diagrams for explaining a manufacturing direction of a phase difference element in one embodiment of the present invention. [Figure 5A] FIG. 2 is a schematic diagram showing a state in which a coating film in which side chains are randomly oriented is irradiated with linearly polarized light. [Figure 5B] FIG. 2 is a schematic diagram showing the state of a coating film in which side chains are oriented in a certain direction due to a photoreaction and rearrangement. [Figure 6] FIG. 2 is a partial enlarged view of a mask used in manufacturing a phase difference element. [Figure 7] FIG. 2 is a schematic diagram showing a phase difference element formed by the method of the present invention, observed with parallel Nicols. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the configuration of the present invention will be described with reference to the drawings. Note that the drawings are schematic diagrams for the purpose of explanation and do not reflect actual size ratios. FIG. 1 is a perspective view showing an example of a polarization conversion element according to the prior art. The polarizing beam splitter 10 is composed of a prism array in which a plurality of rod-shaped prisms 10a are arranged, and the interface 10b between the prisms 10a is inclined at a predetermined angle (e.g., 45 degrees) with respect to the surface 10c of the beam splitter 10. The prism array type polarizing beam splitter 10 can be produced, for example, by laminating a plurality of plates or sheets of glass, acrylic, etc., and cutting the laminate at an angle to cut out the plates. A polarization separation film 10d is provided at the interface 10b between adjacent prisms 10a, and non-polarized light (e.g., natural light) L is introduced into the polarizing beam splitter 10. N When the P wave L P Selectively transmits S waves L S The reflected S wave L S The reflected light is reflected again by the adjacent polarization separation film 10d and exits.

[0018] A phase difference plate (for example, a half-wave plate) 21 cut into a strip shape is attached onto the polarizing beam splitter 10. If the phase difference plate 21 is a half-wave plate, the P polarized light L P is given a phase difference of 180 degrees, and S-polarized L S Therefore, the unpolarized light L N All are S polarized L S It is emitted as

[0019] 2 is a schematic diagram showing an example of an image projection device 100 equipped with a polarization conversion element 1. This image projection device 100 converts light emitted from a light source 2 into polarized light and makes it incident on a transmissive liquid crystal display device 3. A first microlens array 4, a second microlens array 5, a polarization conversion element 1, and a lens 6 are arranged between the light source 2 and the transmissive liquid crystal display device 3, and non-polarized light emitted from the light source 2 is converted into S-waves by the polarization conversion element 1, so that the brightness of the projected image can be brighter than when a polarizing plate (not shown) is simply arranged between the light source 2 and the transmissive liquid crystal display device 3.

[0020] The image projection device 100, which projects an image from the liquid crystal display device 3, is also used for applications such as an in-vehicle head-up display (not shown), and in such cases, the size of the optical system is required to be reduced due to the constraints of the installation space. In the polarization conversion element 1 of FIG. 1, the polarization beam splitter 10 can be thinned by thinning the light-transmitting member constituting the prism 10a and reducing the width of the prism 10a, but in that case, the width and arrangement interval of the retardation plate 21 must also be reduced. However, in the conventional manufacturing method in which the cut-out retardation plate 21 is attached, it is difficult to reduce the width of the retardation plate 21 to a certain extent or more. Even if the method described in Patent Document 1 is used, it is difficult to make the stripe width very small due to the constraints of the manufacturing method in which the mask portion is peeled off with an adhesive tape. Therefore, in the past, it was difficult to suppress the thickness of the polarization beam splitter 10 due to the constraints on the retardation plate 21 side. In contrast, in the polarization conversion element 1 of the present invention, it is possible to reduce the width of the optically anisotropic region to 1 mm or less.

[0021] FIG. 3A is a schematic cross-sectional view for explaining the configuration of a polarization conversion element 1 according to one embodiment of the present invention. In the present invention, a retardation element 20 (also called a patterned retarder) including a retardation film 20a made of a liquid crystal material having a photosensitive group is disposed on an exit surface 10c of a polarizing beam splitter 10 made of a prism array. In the retardation film 20a, optically anisotropic regions 20b that impart a phase difference to incident light and optically isotropic regions 20c that transmit the incident light as it is are alternately formed in a stripe shape, and the width of each region corresponds to the width of the prism. For example, if the optically anisotropic region 20b is a half-wave plate that imparts a phase difference of 180° to incident light, the P-wave L-wave is generated in the optically anisotropic region 20b. P S wave L S , and the S wave is directly transmitted through the optically isotropic region 20b, so that the unpolarized L N S wave L S can be converted to

[0022] 3B is a schematic cross-sectional view showing a polarization conversion element 1 according to another embodiment of the present invention. In this example, the interface 10b of the prism 10a of the polarizing beam splitter 10 is alternately covered with a polarization separation film 10d and a reflection film 10e. The retardation element 20 is composed of a substrate film 20d made of an optically isotropic material and a retardation film 20a laminated on the substrate film 20d. The optically anisotropic region 20b is disposed on the prism 10a from which the S wave Ls is emitted, and the incident non-polarized light L N are all P waves L P is converted to

[0023] In the polarization conversion element of the present invention, the structure of the polarizing beam splitter 10 is not limited to that shown in the figure, and any known configuration can be adopted. For example, the polarization separation film 10d is not essential, and the interface between the prisms 10a may be configured to selectively transmit P waves and selectively reflect S waves due to the difference in reflectance between P waves and S waves. Also, two layers, the polarization separation film 10d and the reflection film 10e, may be laminated and provided on the interface of the prism 10a.

[0024] In the present invention, the retardation element 20 is formed in a film made of a liquid crystal material having a photosensitive group. Therefore, it is easy to prepare a thin-film retardation element 20, and the pitch (spacing) p of the optically anisotropic region 20b and the optically isotropic region 20c can be narrowed. The pitch p is not particularly limited, and may be, for example, 1 mm or less, 0.5 mm or less, or 0.3 mm or less. By narrowing the pitch p (FIG. 3A), it is possible to use a thin polarizing beam splitter 10 in which the width (width in the arrangement direction) w of the prism 10a is reduced. The thickness of the retardation film 20a constituting the retardation element 20 is determined by the wavelength used and the non-refractive property of the material, and may be, for example, 0.5 to 10 μm, or 2 to 5 μm.

[0025] [Method of manufacturing phase difference element] In the present invention, the retardation film 20a constituting the retardation element 20 can be produced by the following method using a liquid crystalline material having a photosensitive group. (Liquid crystal material having photosensitive groups)

[0026] In the above description, the liquid crystalline material having a photosensitive group is a material that includes a liquid crystalline polymer having a photosensitive group, and when formed into a film, can induce birefringence by a photoreaction and / or a heat treatment (hereinafter, sometimes referred to as a birefringence-inducing material). Preferably, the birefringence-inducing material may contain a liquid crystal polymer having a photosensitive group and a side chain structure capable of forming a liquid crystal structure, and may have a property in which molecular orientation is induced by the photoreaction of the photosensitive group in the side chain. In this case, the molecular orientation is preferably a photo-orientation caused by molecular motion due to, for example, light irradiation (preferably light irradiation and heating / cooling treatment). Examples of the photoreaction include a photodimerization reaction, a photoisomerization reaction, and a photo-fries rearrangement reaction.

[0027] When the side chain of a liquid crystalline polymer is capable of forming a liquid crystal structure, the side chain structure may have a mesogenic group, which is a rigid portion that exhibits liquid crystallinity, thereby exhibiting liquid crystallinity, or the side chain structure may have a structure that can form a dimer through hydrogen bonding with another polymer or another side chain of the same polymer, etc., and the liquid crystallinity may be exhibited by forming a mesogenic structure through dimerization.

[0028] A mesogenic group or mesogenic structure is composed of two or more aromatic or aliphatic rings and a linking group connecting them, and the linking group may be a covalent bond or a hydrogen bond. Examples of the aromatic ring include a benzene ring, a naphthalene ring, and a heterocycle (e.g., an oxygen-containing heterocycle such as a furan ring or a pyran ring; a nitrogen-containing heterocycle such as a pyrrole ring or an imidazole ring), and examples of the aliphatic ring include a cyclohexane ring. These aromatic rings or aliphatic rings may have a substituent, and the substituent may be an alkyl group (e.g., a C alkyl group, preferably a C 1-4 alkyl groups), alkyloxy groups (e.g., C 1-6 Alkyloxy groups, preferably C 1-4 Alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl groups, halogen atoms, and the like.

[0029] In the case of a covalent bond, examples of the linking group include a single bond, -O-, -COO-, -OCO-, -N=N-, -NO=N-, -C=C-, -C≡C-, -CO-C=C-, -CH=N-, an alkylene group, etc. In the case of a hydrogen bond, examples include a side chain structure having a carboxy group at the end, in which case a hydrogen bond is formed between the carboxy groups.

[0030] The photosensitive group is not particularly limited as long as it is a functional group capable of undergoing a photoreaction by light energy, and examples thereof include a chalcone group, a coumarin group, a cinnamoyl group, a cinnamic acid group, a cinnamylidene acetate group, a biphenylacryloyl group, a furyl acryloyl group, a naphthylacryloyl group, an azobenzene group, a benzylideneaniline group, or derivatives thereof, and preferably a cinnamoyl group.

[0031] A liquid crystalline polymer has at least a side chain structure in a repeating unit that has both a photosensitive group and a structure capable of forming a liquid crystal structure, and the photosensitive group may exist independently in the side chain structure from the mesogenic group or mesogenic structure, or may exist in a composite manner sharing a chemical structure.

[0032] Preferably, the birefringence inducing material may contain a liquid crystalline polymer having at least one structure selected from the group consisting of side chain structures represented by the following formulas (1) and (2).

[0033] [ka] (wherein t is an integer of 1 to 3, R1 is a hydrogen atom, an alkyl group (e.g., C 1-6 Alkyl groups, preferably C 1-4 alkyl groups), alkyloxy groups (e.g., C 1-6 Alkyloxy groups, preferably C1-4 Alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C 1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl groups), and halogen atoms.

[0034] [ka] (In the formula, k is 0 or 1, and when k is 0, l is 0, and when k is 1, l is an integer of 1 to 12; X is a single bond, a C1-3 alkylene group, -C=C-, -C≡C-, -O-, -N=N-, -COO-, or -OCO-; W is a coumarin group, a cinnamoyl group, a cinnamylidene acetic acid group, a biphenylacryloyl group, a furylacryloyl group, a naphthylacryloyl group, or a derivative group thereof; R2 and R3 are each the same or different and each represent a hydrogen atom, an alkyl group (e.g., a C1-6 alkyl group, preferably a C1-4 alkyl group), an alkyloxy group (e.g., a C 1-6 Alkyloxy groups, preferably C 1-4 Alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C 1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl group), a carboxy group, and a halogen atom.

[0035] The side chain structures represented by the above formulas (1) and (2) represent the chemical structures at the terminals of the side chains in the repeating units, and various chemical structures, such as a spacer (e.g., an (oxy)alkylene group having 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)) or an aromatic ring, may be included between these side chain structures and the main chain structure, as long as the effects of the present invention are not impaired.

[0036] The liquid crystal polymer may be a homopolymer consisting of the same repeating unit containing the above side chain structure, or a copolymer containing a repeating unit containing a different side chain structure in addition to the repeating unit containing the above side chain structure. Examples of the main chain structure include a structure formed by polymerization of hydrocarbon, acrylate, methacrylate, siloxane, maleimide, N-phenylmaleimide, etc.

[0037] When the liquid crystalline polymer is a copolymer, it may have a repeating unit that does not have a photosensitive group and / or a structure capable of forming a liquid crystal structure.

[0038] The liquid crystal material (birefringence-inducing material) of the present invention may contain a low molecular weight compound together with the liquid crystal polymer in order to promote the alignment of the side chains of the liquid crystal polymer. As the low molecular weight compound, a compound having a substituent such as biphenyl, terphenyl, phenylbenzoate, azobenzene, etc., which is known as a mesogenic component, and having liquid crystallinity in which such a substituent is bonded to a functional group such as allyl, acrylate, methacrylate, cinnamic acid group (or a derivative group thereof) via a spacer (for example, an (oxy)alkylene group having 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)) is preferably used. These low molecular weight compounds may be used alone or in combination of two or more kinds.

[0039] In the present invention, a coating solution in which the above liquid crystalline material is dissolved in a solvent is applied to a support to form a coating film (coating step), and then the solvent is removed with or without heating (drying step). The support may be an optically isotropic body such as a glass plate or a triacetyl cellulose film.

[0040] The solvent can be appropriately selected depending on the type of liquid crystal material, and examples thereof include dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol derivatives (e.g., ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, etc.), propylene glycol derivatives (e.g., propylene glycol monomethyl ether, propylene glycol 1-monomethyl ether 2-acetate, etc.), and the like. These solvents may be used alone or in combination of two or more kinds.

[0041] The solution can be applied by a general application method such as spin coating, roll coating, screen printing, knife coating, spray coating, etc. (application step). Next, when heating is performed for drying, it is preferable to perform the drying at a temperature of about 15 to 50°C (for example, room temperature of 20 to 30°C) at which the liquid crystalline polymer does not form microdomains (drying step).

[0042] There are various methods for producing a retardation element using the dried film, as described later. Below, the method used in the examples described later will be described.

[0043] FIG. 4 is a schematic diagram for explaining one embodiment of the method for producing a retardation element of the present invention. In this method, a light-shielding mask 23 with slits 23a is placed at a predetermined interval on a coating film 22 formed by coating and drying a liquid crystal material on a substrate 20d. Then, the coating film 22 in the portion corresponding to the slits is exposed by irradiating the mask with linearly polarized light. Next, the coating film 22 is heated and then slowly cooled, thereby inducing birefringence in the exposed portion, and an optically anisotropic region 20b (see FIG. 3A) can be formed. On the other hand, the portion masked by the light-shielding portion 23b does not undergo photoreaction, and becomes an optically isotropic region 20c (see FIG. 3A).

[0044] 5A and 5B are schematic diagrams for explaining the above process, in which the black spindle shapes (long ellipses) represent the side chains 22a of the liquid crystalline polymer that have a photosensitive group, and the white spindle shapes represent the side chains 22b that do not have a photosensitive group. In the coating film 22 in the state in which the liquid crystalline material has been applied and dried, the side chains 22a and 22b are randomly oriented. In contrast, when linearly polarized light L L When the coating film 22 is irradiated with light, the side chains 22a having photosensitive groups undergo a photoreaction, inducing orientation. At this time, due to the photoreaction and molecular motion within the coating film 22, the photoreacted side chains 22a are oriented in the direction of the irradiated light, or in approximately the same direction perpendicular to the direction of the irradiated light as shown in FIG. 5B, and the side chains 22b that have not undergone a photoreaction are also reoriented in the same direction as the photoreacted side chains due to molecular motion within the coating film 22. As a result, the side chains 22a, 22b are oriented in approximately the same inclination direction throughout the coating film 22, inducing birefringence and forming an optically anisotropic region 20b (see FIG. 3A). This reorientation is promoted by the heating step following the light irradiation step. On the other hand, when linearly polarized light L L In the areas where the exposure to the linearly polarized light L is blocked by the mask 23, no photoreaction occurs, and the random orientation shown in FIG. 5A is fixed by heating and gradual cooling, resulting in an optically isotropic region 20c (see FIG. 3A). L For the irradiation, linearly polarized ultraviolet light is preferably used. For example, an ultraviolet light irradiation device such as a high pressure mercury lamp may be used as a light source, and the light may be converted into linearly polarized light via a Glan-Taylor prism. Heating after exposure may be performed at a temperature of about 80 to 150°C, which is lower than the isotropic phase transition temperature of the liquid crystalline polymer, and preferably at about 100 to 140°C.

[0045] 6 is a partially enlarged view of a mask 23 used in the above-mentioned method. Mask 23 has light-shielding portions 23b and slits (light-transmitting portions) 23a with approximately the same widths W1 and W2 and spaced at equal intervals, and can be used for exposure of a line / space pattern.

[0046] 7 is a plan view showing a state where the retardation film 20a manufactured by the above method is observed in parallel Nicols. When observed in parallel Nicols, the optically isotropic region 20c is observed bright without quenching, while the optically anisotropic region 20b is observed dark due to quenching. In the polarization conversion element 1 of the present invention, the retardation film 20a formed by the above method can be peeled off from the substrate (support) 20d as necessary, or appropriately cut out while still on the substrate 20d, and used as the retardation element 20.

[0047] In the above method, the mask 23 may be a transparent film on which a light-shielding thin film such as a metal is printed, and the width of the slit 23a can be arbitrarily small. Therefore, the retardation element 20 of the present invention can have a very small pitch of the optically anisotropic regions 20b, for example, 1 mm or less. In addition, the film formed from the birefringence-inducing material has the advantage of being more heat-resistant than a commonly used half-wave plate.

[0048] If the above-mentioned liquid crystal material and mask 23 are used, a retardation element in which portions having different optical properties are arranged in a pattern can also be obtained by the following alternative method.

[0049] A method in which linearly polarized light is irradiated onto the entire surface of the coating film 22, and then linearly polarized light whose vibration direction is shifted by 90° is irradiated onto a portion of the surface. Method 2 A method in which the entire surface of the coating film 22 is irradiated with linearly polarized light, and then partially irradiated with unpolarized light. Method 3 A method in which the entire surface of the coating film 22 is irradiated with linearly polarized light, and then the coating film 22 is partially irradiated with unpolarized light and linearly polarized light. Method 4 A method of partially irradiating the coating film 22 with linearly polarized light.

[0050] By using the above-mentioned various methods, it is possible to provide a phase difference element 20 having fine patterns with different optical properties. The use of such a phase difference element 20 can accommodate thinning of the polarizing beam splitter, and contribute to size reduction of optical devices such as the polarization conversion element 1 and the image projection device 100 including the same. EXAMPLES

[0051] (Monomer 1) 4-(6-hydroxyhexyloxy)cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. This product was esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize monomer 1 shown in the following chemical formula 3.

[0052] [ka]

[0053] (Monomer 2) p-Hydroxybenzoic acid and 6-chloro-1-hexanol were heated under alkaline conditions to synthesize 4-(6-hydroxyhexyloxy)benzoic acid. This product was esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize monomer 2 shown in the following chemical formula 4.

[0054] [ka]

[0055] (Polymer 1) Monomer 1 and monomer 2 were dissolved in dioxane in a molar ratio of 3:7, and AIBN was added as a reaction initiator. The mixture was polymerized at 70°C for 24 hours to obtain photosensitive polymer 1. This polymer 1 exhibited liquid crystallinity.

[0056] [Example 1] A solution was prepared by dissolving the polymer 1 in tetrahydrofuran. A cover glass was used as the substrate (support) 20d, and the solution was applied to the substrate 20d with a spin coater to a thickness of 4.5 μm, followed by drying at room temperature (25° C.) to form a coating film 22 that was a precursor of the retardation film 20a.

[0057] A mask 23 with a line and slit width of 0.7 mm was placed on the coating film 22 formed on the substrate 20d, and light L, which was obtained by converting light from a high-pressure mercury lamp into linearly polarized light using a Glan-Taylor prism, was irradiated through the exposure mask 23 for 100 seconds. At this time, the polarization direction of the linearly polarized light was set to 45° with respect to the lines and slits of the exposure mask 23. Next, the film was oriented by heating to 130°C and then slowly cooled to induce birefringence. The retardation value of the portion of the coating film 22 corresponding to the slits 23a of the exposure mask 23 was 275 nm, and the fast axis of the retardation was 45° with respect to the lines and slits of the exposure mask 23. On the other hand, it was confirmed that the portion of the coating film 22 corresponding to the line portion (light-shielding portion) 23b of the exposure mask did not produce birefringence and maintained a transparent coating state, and that striped phase difference portions (optically anisotropic regions 20b) and isotropic portions (optically isotropic regions 20c) were formed alternately.

[0058] By the same method as above, it was possible to manufacture a pattern with a pitch of 0.25 mm. On the other hand, for comparison, when the material of Patent Document 1 was subjected to mask exposure, the light-shielded area did not become a transparent optical isotropic body, and it was confirmed that the method of the present invention cannot be used to manufacture a narrow-pitch phase difference element 20. [Explanation of symbols]

[0059] 1 Polarization conversion element 2 light source 3 Transmissive liquid crystal display device 4, 5 Microlens array 6 Lenses 10 Polarizing Beam Splitter 10a Prism 10b Prism interface 10c surface (output surface) 10d polarization separation film 10e reflective film 20 Phase difference element 20a Phase difference film 20b Optical anisotropy region 20c optically isotropic region 20d base material 21 Retardation plate 22 Paint film 22a Photosensitive side chain 22b Non-photosensitive side chain 23 Mask 23a Slit 23b Light shielding part

Claims

1. a polarizing beam splitter consisting of a prism array; a phase difference element laminated on the polarizing beam splitter, the retardation element includes a film made of a liquid crystalline material having a photosensitive group; A polarization conversion element, in which optically anisotropic regions that impart a phase difference to transmitted light and optically isotropic regions are arranged alternately in a striped pattern in the film.

2. 2. The polarization conversion element according to claim 1, wherein the optically anisotropic regions and the optically isotropic regions of the phase difference element are alternately arranged at a pitch of 1 mm or less.

3. 3. An image projection device comprising the polarization conversion element according to claim 1.

4. A method for producing a phase difference element used in the polarization conversion element according to claim 1 or 2, comprising the steps of: forming a coating film made of a birefringence inducing material containing a photosensitive liquid crystal material on a substrate; a step of placing a mask having periodically arranged slits on the coating film and irradiating the coating film with polarized light through the mask; and heating the irradiated coating film and then slowly cooling it to induce birefringence in the area exposed through the slit. method.

Images