Polarization conversion element, image projection device provided with same, and method for manufacturing phase difference

Abstract

The invention provides a polarization conversion element, an image projection device provided with the polarization conversion element, and a manufacturing method of a phase difference element. The polarization conversion element capable of being thinned and the phase difference element used for the polarization conversion element are provided. This polarization conversion element is provided with a polarization beam splitter comprising a prism array and a phase difference element laminated on the polarization beam splitter, and is characterized in that the phase difference element is provided with a film comprising a liquid crystal material having a photosensitive group, the optically anisotropic regions and the optically isotropic regions, which impart a phase difference to transmitted light, are alternately arranged in a stripe shape.

Description

Technical Field

[0001] The present invention relates to a polarization conversion element capable of adjusting the vibration direction of polarized light with a thin structure to improve light utilization efficiency, an image projection device including the polarization conversion element, and a method for manufacturing a phase difference element constituting the polarization conversion element. Background Art

[0002] In display devices with projection functions such as image projection devices and head-up displays, polarizers are used for image display. However, when natural light is usually converted into polarized light, light other than one vibration direction is not used, which is disadvantageous in terms of light utilization efficiency. As a means to solve this problem, a polarization conversion element is proposed, in which P polarized light and S polarized light are separated by a polarization beam splitter, and the vibration direction of one polarized light is converted by a phase difference element.

[0003] For example, Patent Document 1 describes the following structure: on a polarization beam splitter composed of a prism array formed by laminating a plurality of glasses and cutting them at an inclination of 45 degrees, an effective area functioning as a phase difference plate and a half-wavelength plate arranged in stripes in a passing area through which light is directly passed are provided, P-polarized light is converted into S-polarized light in the effective area, and S-polarized light is directly passed in the passing area, thereby using all natural light as S-polarized light.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-188123 Summary of the invention

[0007] Problems to be solved by the invention

[0008] Patent document 1 describes the following: a 1 / 2 wavelength plate is formed by laminating a plurality of oriented films and a liquid crystal layer on a transparent substrate provided on a polarization beam splitter, the formed 1 / 2 wavelength plate is masked using a stripe-shaped mask having a specified width and having a pass portion and a non-pass portion repeated at a certain interval, then a tape with an adhesive material is adhered to the non-pass portion and then peeled off, the mask is peeled off, and the 1 / 2 wavelength plate thus formed is attached to the tape with the adhesive material and peeled off, thereby being able to form a long strip of 1 / 2 wavelength plate, i.e., a stripe-shaped 1 / 2 wavelength plate.

[0009] However, in the invention of Patent Document 1, in addition to the complicated method of manufacturing the 1 / 2 wavelength plate, there is a limit in reducing the stripe width and thickness of the 1 / 2 wavelength plate due to the limitations of the multilayer structure and masking processing. On the other hand, in the field of vehicle-mounted displays, due to the limitation of the installation space of optical equipment, the polarization conversion element is also required to be thinner. Therefore, it is necessary to make the polarization beam splitter itself thinner, but in the case where 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 suppress the thickness of the prism array constituting the polarization beam splitter.

[0010] The object of the present invention is to provide a polarization conversion element utilizing a phase difference element, an image projection device having such a polarization conversion element, and a method for manufacturing the phase difference element used therefor, wherein the phase difference element can be manufactured by a simple manufacturing method and the configuration interval between the phase difference portion and the non-phase difference portion can be easily reduced.

[0011] Means for solving problems

[0012] A first configuration of the present invention is a polarization conversion element, comprising:

[0013] a polarizing beam splitter formed by an array of prisms; and

[0014] The phase difference element stacked on the above polarization beam splitter,

[0015] The phase difference element comprises a film composed of a liquid crystal material having a photosensitive group.

[0016] In the above film, optically anisotropic regions and optically isotropic regions that impart a phase difference to transmitted light are alternately arranged in stripes.

[0017] The polarization conversion element described above can be used to easily set a thin and narrow-pitch phase difference element, thereby also achieving a thinner polarization beam splitter, and is highly applicable to optical devices where the installation space for the polarization conversion element is limited.

[0018] 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.

[0019] The phase difference element used in the polarization conversion element forms a stripe-shaped optical pattern by adjusting the exposure method of the film, so there is no need to physically cut and paste the film or peel off a part of the film, and a narrow pitch pattern can be accurately formed.

[0020] A second aspect of the present invention is an image projection device including the polarization conversion element of the present invention. By using the polarization conversion element of the present invention, it is possible to improve light utilization efficiency even in an image projection device with limited installation space.

[0021] A third aspect of the present invention is a method for manufacturing a phase difference element used in the polarization conversion element, wherein the method comprises the following steps:

[0022] forming a coating film composed of a birefringence inducing material including a photosensitivity liquid crystal material on a substrate;

[0023] placing a mask having periodically arranged slits on the coating film, and irradiating the coating film with polarized light through the mask; and

[0024] The irradiated coating film is heated and then slowly cooled, thereby inducing birefringence in the portion exposed through the slit.

[0025] By using the above method, a phase difference element used for a polarization conversion element can be produced by a simple method.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide a polarization conversion element that uses a phase difference element in which regions imparting a phase difference are arranged in a stripe shape at a narrow pitch and that can be easily reduced in thickness, and an image projection device using the polarization conversion element. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a perspective view showing an example of a conventional polarization conversion element.

[0029] Figure 2 This is a diagram showing an example of an image projection device including a polarization conversion element.

[0030] Figure 3A Schematic cross-sectional view showing a polarization conversion element according to one embodiment of the present invention.

[0031] Figure 3B is a schematic cross-sectional view showing a polarization conversion element according to another embodiment of the present invention.

[0032] Figure 4 It is a figure for demonstrating the manufacturing method of the phase difference element in one embodiment of this invention.

[0033] Figure 5A This is a schematic diagram showing a state in which a coating film having randomly oriented side chains is irradiated with linearly polarized light.

[0034] Figure 5BThis is a schematic diagram showing the state of a coating film in which side chains are oriented in a certain direction by photoreaction and rearrangement.

[0035] Figure 6 This is a partially enlarged view of a mask used in the manufacture of a phase difference element.

[0036] Figure 7 Schematic diagram showing a state where a phase difference element formed by the method of the present invention is observed using parallel Nicol. DETAILED DESCRIPTION

[0037] Hereinafter, the configuration of the present invention will be described with reference to the accompanying drawings. It should be noted that the accompanying drawings are schematic diagrams for explanation and do not reflect actual dimensional ratios.

[0038] Figure 1 1 is a stereoscopic diagram showing an example of a polarization conversion element of the prior art. The polarization beam splitter 10 is composed of a prism array formed by arranging a plurality of rod-shaped prisms 10a, and the interfaces 10b between the prisms 10a are inclined at a predetermined angle (for example, 45 degrees) relative to the surface 10c of the beam splitter 10. The prism array type polarization beam splitter 10 can be made, for example, by stacking a plurality of plates or sheets of glass, acrylic, etc., and cutting the stacked body at an angle to cut out the plates. A polarization separation film 10d is provided at the interface 10b of adjacent prisms 10a. When non-polarized light (for example, natural light) L N When incident on the polarization beam splitter 10, the P wave L is selectively transmitted P , reflected S wave L S The reflected S wave L S The light is reflected again by the adjacent polarization separation film 10d and emitted.

[0039] The phase difference plate (for example, a half-wave plate) 21 cut into a strip shape is attached to the polarization beam splitter 10. If the phase difference plate 21 is a half-wave plate, the P polarized light L emitted from the polarization beam splitter 10 P Give a 180-degree phase difference and convert it into S-polarized light L S Therefore, the non-polarized light L incident on the polarization conversion element N All as S polarized light L S Shoot out.

[0040] Figure 21 is a schematic structural diagram showing an example of an image projection device 100 having a polarization conversion element 1. The image projection device 100 converts light emitted from a light source 2 into polarized light and inputs the polarized light into 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. The polarization conversion element 1 converts the non-polarized light emitted from the light source 2 into an S wave, so that the brightness of the projected image can be brighter than when only a polarizing plate (not shown) is arranged between the light source 2 and the transmissive liquid crystal display device 3.

[0041] The image projection device 100 that projects the image of the liquid crystal display device 3 is also used for applications such as a head-up display (not shown) for vehicles. In this case, the size of the optical system is required to be reduced due to the limitation of the installation space. Figure 1 In the polarization conversion element 1, the thinning of the polarization beam splitter 10 can be achieved by thinning the translucent components constituting the prism 10a and reducing the width of the prism 10a, but in this case, it is necessary to also reduce the width and configuration interval of the phase difference plate 21. However, in the existing method of pasting the phase difference plate 21 after cutting, it is difficult to reduce the width of the phase difference plate 21 by more than a certain degree. In addition, even if the method described in patent document 1 is used, it is difficult to make the stripe width extremely small due to the limitation of the method of peeling off the mask part with tape. Therefore, in the past, the limitation on the side of the phase difference plate 21 became the reason, and it was difficult to suppress the thickness of the polarization beam splitter 10. In contrast, in the polarization conversion element 1 of the present invention, the width of the optical anisotropy region can be reduced to less than 1 mm.

[0042] Figure 3A It is a schematic cross-sectional view for illustrating the structure of a polarization conversion element 1 according to an embodiment of the present invention. In the present invention, a phase difference element 20 (also referred to as a patterned retarder) having a phase difference film 20a composed of a liquid crystal material having a photosensitive group is arranged on the output surface 10c of the polarization beam splitter 10 composed of a prism array. In the phase difference film 20a, an optical anisotropic region 20b that imparts a phase difference to incident light and an optically isotropic region 20c that allows incident light to pass directly are alternately formed in stripes, and the width of each region corresponds to the width of the prism. For example, if the optical anisotropic region 20b is a 1 / 2 wavelength plate that imparts a phase difference of 180° to incident light, then the P-wavelength L is shifted in the optical anisotropic region 20b. P Convert to S wave L S , the S wave is directly transmitted in the optically isotropic region 20b, thereby making it possible to convert the non-polarized light L incident on the prism 10a N Convert to S wave L S .

[0043] Figure 3B1 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 polarization beam splitter 10 is alternately covered with a polarization separation film 10d and a reflection film 10e. The phase difference element 20 includes a base film 20d composed of an optically isotropic body and a phase difference film 20a laminated on the base film 20d. The optical anisotropic region 20b is arranged on the prism 10a from which the S wave Ls is emitted, and the incident non-polarized light L N All are converted to P wave L P .

[0044] In the polarization conversion element of the present invention, the structure of the polarization beam splitter 10 is not limited to the structure shown in the drawings, and a known structure can be adopted. For example, the polarization separation film 10d is not necessary, and it can also be a structure that selectively allows P waves to pass and selectively reflects S waves at the interface between the prisms 10a according to the difference in reflectivity between the P waves and the S waves. In addition, the polarization separation film 10d and the reflection film 10e can be stacked and provided on the interface of the prism 10a.

[0045] In the present invention, the phase difference element 20 is formed in a film composed of a liquid crystal material having a photosensitive group. Therefore, the thin film phase difference element 20 is easy to make, and the spacing (interval) p between the optical anisotropic region 20b and the optical isotropic region 20c can be narrowed. The spacing p is not particularly limited, for example, it can be less than 1 mm, less than 0.5 mm, or less than 0.3 mm. By narrowing the spacing p ( Figure 3A ), a thin polarization beam splitter 10 with a reduced width (width in the arrangement direction) w of the prism 10a can be used. The thickness of the phase difference film 20a constituting the phase difference element 20 is determined by the wavelength used and the non-refractive property of the material, and can be, for example, 0.5 μm to 10 μm, or 2 μm to 5 μm.

[0046] [Method for manufacturing phase difference element]

[0047] In the present invention, the retardation film 20 a constituting the retardation element 20 can be produced by the following method using a liquid crystal material having a photosensitive group.

[0048] (Liquid crystal material having a photosensitive group)

[0049] In the above description, the liquid crystal material having a photosensitive group refers to a material that contains a liquid crystal polymer having a photosensitive group and can induce birefringence by photoreaction and / or heat treatment when formed into a film (hereinafter, sometimes referred to as a birefringence inducing material).

[0050] Preferably, the birefringence inducing material may include a liquid crystal polymer having a side chain structure, the side chain structure having a photosensitive group and being capable of forming a liquid crystal structure, and the birefringence inducing material may have the property of inducing molecular orientation by a photoreaction of the photosensitive group possessed by the side chain. In this case, the molecular orientation is preferably a photo-orientation brought about by molecular motion based on light irradiation (preferably light irradiation and heating and cooling treatment). The photoreaction may include photodimerization reaction, photoisomerization reaction, photo-Fries rearrangement reaction, and the like.

[0051] When the side chain of a liquid crystalline polymer is capable of forming a liquid crystal structure, the liquid crystal property may be exhibited by having a rigid portion, i.e., a mesogenic group, in the side chain structure that exerts liquid crystal property. Alternatively, the side chain structure may have a structure that can form a dimer through hydrogen bonds with other polymers or other side chains of the same polymer, and the mesogenic structure may be formed through dimerization, thereby exhibiting liquid crystal property.

[0052] The mesogenic group or mesogenic structure is composed of two or more aromatic rings or aliphatic rings and a linking group that connects them. The linking group may be a covalent bond or a hydrogen bond.

[0053] Examples of the aromatic ring include a benzene ring, a naphthalene ring, and a heterocyclic ring (e.g., an oxygen-containing heterocyclic ring such as a furan ring and a pyran ring; a nitrogen-containing heterocyclic ring such as a pyrrole ring and an imidazole ring); and examples of the aliphatic ring include a cyclohexane ring. It should be noted that these aromatic rings or aliphatic rings may also have a substituent, and examples of the substituent include an alkyl group (e.g., C 1-6 Alkyl, preferably C 1-4 alkyl), alkoxy (e.g., C 1-6 Alkoxy, preferably C 1-4 Alkoxy), alkenyl (e.g., C 1-6 Alkenyl, preferably C 1-4 alkenyl), alkynyl (e.g., C 1-6 Alkynyl, preferably C 1-4 alkynyl), halogen atom, etc.

[0054] As the linking group, when it is a covalent bond, there can be mentioned a single bond, -O-, -COO-, -OCO-, -N=N-, -NO=N-, -C=C-, -C≡C-, -CO-C=C-, -CH=N-, alkylene, etc. When it is a hydrogen bond, there can be mentioned a side chain structure having a carboxyl group at the end, in which case a hydrogen bond is formed between carboxyl groups.

[0055] The photosensitive group is not particularly limited as long as it is a functional group that can induce a photoreaction using light energy, and examples thereof include a chalcone group, a coumarin group, a cinnamoyl group, a cinnamic acid group, a cinnamylideneacetic acid group, a biphenyl acryloyl group, a furyl acryloyl group, a naphthyl acryloyl group, an azophenyl group, a benzylideneanilide group, or derivatives thereof, and a cinnamoyl group is also preferred.

[0056] The liquid crystal polymer has at least a side chain structure in the repeating unit, and the side chain structure has both a photosensitive group and a structure capable of forming a liquid crystal structure. The photosensitive group and the mesogenic group or the mesogenic structure may exist independently in the side chain structure, or may exist in combination by sharing a common chemical structure.

[0057] Preferably, the birefringence inducing material may include a liquid crystalline polymer having at least one structure selected from the group consisting of side chain structures represented by the following formulae (1) and (2).

[0058] [Chemistry 1]

[0059]

[0060] (wherein, t is an integer of 1 to 3, and R1 represents a group selected from a hydrogen atom, an alkyl group (e.g., C 1-6 Alkyl, preferably C 1-4 alkyl), alkoxy (e.g., C 1-6 Alkoxy, preferably C 1-4 Alkoxy), alkenyl (e.g., C 1-6 Alkenyl, preferably C 1-4 alkenyl), alkynyl (e.g., C 1-6 Alkynyl, preferably C 1-4 alkynyl) and halogen atoms.

[0061] [Chemistry 2]

[0062]

[0063] (wherein, k is 0 or 1, when k is 0, l is 0; when k is 1, l is an integer from 1 to 12; X is a single bond, C 1-3 alkylene, -C=C-, -C≡C-, -O-, -N=N-, -COO- or -OCO-; W is a coumarin group, a cinnamoyl group, a cinnamyl acetate group, a biphenyl acryloyl group, a furyl acryloyl group, a naphthyl acryloyl group, or a derivative thereof; R2 and R3 are the same or different and represent a group selected from a hydrogen atom, an alkyl group (e.g., C 1-6 Alkyl, preferably C 1-4 alkyl), alkoxy (e.g., C 1-6 Alkoxy, preferably C 1-4 Alkoxy), alkenyl (e.g., C1-6 Alkenyl, preferably C 1-4 alkenyl), alkynyl (e.g., C 1-6 Alkynyl, preferably C 1-4 alkynyl), carboxyl and halogen atoms.

[0064] It should be noted that the side chain structures represented by the above formulas (1) and (2) represent the chemical structures at the ends of the side chains in the repeating units, and various chemical structures such as spacers (for example, (oxy)alkylene groups having 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)) or aromatic rings may be included between these side chain structures and the main chain structure without impairing the effects of the present invention.

[0065] Liquid crystal polymer can also be a homopolymer consisting of the same repeating unit containing the above-mentioned side chain structure, or a copolymer containing repeating units containing side chain structures with different structures in addition to the repeating units containing the above-mentioned side chain structure. As the main chain structure, a structure formed by polymerization of hydrocarbons, acrylates, methacrylates, siloxanes, maleimides, N-phenylmaleimide, etc. can be cited.

[0066] When the liquid crystalline polymer is a copolymer, it may further have a repeating unit having no photosensitive group and / or a structure capable of forming a liquid crystal structure.

[0067] In addition, in order to promote the orientation of the side chain of the liquid crystal polymer, the liquid crystal material (birefringence inducing material) of the present invention can include liquid crystal polymer and low molecular weight compound at the same time. As low molecular weight compound, the following substances are preferably used: having substituents such as biphenyl, terphenyl, phenylbenzoate, azophenyl known as mesogen components and such substituents and functional groups such as allyl, acrylate, methacrylate, cinnamic acid (or its derivative) are combined via spacers (for example, (oxy) alkylene with 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)) and having liquid crystal properties. These low molecular weight compounds can be used alone or in combination of two or more.

[0068] In the present invention, a coating liquid prepared by dissolving the liquid crystal material in a solvent is applied to a support to form a coating film (coating step), and then the solvent is removed under heating or non-heating (drying step). Here, as the support, an optically isotropic body such as a glass plate or a triacetyl cellulose film can be used.

[0069] The solvent can be appropriately selected according to the type of liquid crystal material. 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.), etc. These solvents can be used alone or in combination of two or more.

[0070] The solution can be applied by a common coating method such as spin coating, roll coating, screen printing, blade coating, spray coating, etc. (coating step). Next, when heating is performed for drying, it is preferably performed at a temperature of 15°C to 50°C (e.g., room temperature of 20°C to 30°C) at which the liquid crystal polymer does not form microdomains (drying step).

[0071] As described later, various methods can be considered for producing a phase difference element using the dried film, and the method used in the examples described later will be described below.

[0072] Figure 4 Schematic diagram for explaining an embodiment of a method for manufacturing a phase difference element of the present invention. In this method, a light-shielding mask 23 having slits 23a at predetermined intervals is arranged on a coating 22 formed by coating a liquid crystal material on a substrate 20d and drying it. Next, by irradiating light converted into linearly polarized light from the mask, the portion of the coating 22 corresponding to the slit is exposed. Next, by heating the coating 22 and then slowly cooling it, birefringence is induced in the exposed portion, and an optical anisotropic region 20b can be formed (see Figure 3A On the other hand, the portion shielded by the light shielding portion 23b does not undergo photoreaction and becomes an optically isotropic region 20c (see Figure 3A ).

[0073] Figure 5A , 5B Schematic diagram for explaining the above process, black spindle (long ellipse) represents the side chain 22a of the liquid crystal polymer with a photosensitive group, and white spindle represents the side chain 22b without a photosensitive group. In the coating film 22 in the state of applying the liquid crystal material and drying, the side chains 22a and 22b are randomly oriented. In contrast, when the linear polarized light L is irradiated at a predetermined angle (e.g., 45°), the side chains 22a and 22b are randomly oriented. L When the side chain 22a having the photosensitive group undergoes a photoreaction, inducing orientation. At this time, due to the photoreaction and the molecular motion in the coating film 22, the side chain 22a that has undergone the photoreaction moves in the direction of the irradiated light, or Figure 5BAs shown in FIG. 2 , the side chains 22a and 22b are oriented in substantially the same direction perpendicular to the direction of travel of the irradiated light, and the side chains 22b that have not undergone photoreaction are also reoriented in the same direction as the side chains that have undergone photoreaction due to the molecular motion in the coating film 22. As a result, in the entire coating film 22, the side chains 22a and 22b are oriented in substantially the same tilted direction, inducing birefringence and forming an optically anisotropic region 20b (see FIG. 2 ). Figure 3A ). The reorientation is promoted by the heating step after the light irradiation step. L The portion of the exposed area shielded by the mask 23 does not undergo photoreaction, and by heating and slowly cooling, Figure 5A The random orientation shown is fixed to form an optically isotropic region 20c (see Figure 3A ). Linear polarized light L L The irradiation is preferably performed with linearly polarized ultraviolet light. For example, an ultraviolet irradiation device such as a high-pressure mercury lamp can be used as a light source, and the light is converted into linearly polarized light via a Glan-Taylor prism. The heating after exposure can be performed at a temperature of about 80°C to 150°C, preferably about 100°C to 140°C, which is lower than the isotropic phase transition temperature of the liquid crystal polymer.

[0074] Figure 6 2 is a partial enlarged view of the mask 23 used in the above method. The mask 23 has light shielding portions 23b and slits (light transmitting portions) 23a provided at equal intervals with substantially the same widths W1 and W2, and can be used for exposure of a line / space pattern.

[0075] Figure 7 1 is a top view schematically showing the state of the phase difference film 20a manufactured by the above method observed by parallel Nicol. When observed by parallel Nicol, the optically isotropic region 20c is not extinguished and is brightly observed, but the optically anisotropic region 20b is extinguished and becomes dark. In the polarization conversion element 1 of the present invention, the phase difference film 20a formed by the above method can be peeled off from the substrate (support) 20d as needed, or appropriately cut out in the state of being placed on the substrate 20d, and used as the phase difference element 20.

[0076] In the above method, the mask 23 can also be a mask formed by printing a light-shielding thin film such as metal on a transparent film, and the width of the slit 23a can be arbitrarily reduced. Therefore, the phase difference element 20 of the present invention can make the spacing of the optical anisotropic region 20b extremely small, for example, it can be less than 1mm. In addition, the film formed by the above-mentioned birefringence inducing material has the advantage of excellent heat resistance compared with the commonly used 1 / 2 wavelength plate.

[0077] It should be noted that, if the above-mentioned liquid crystal material and mask 23 are used, a phase difference element in which portions having different optical characteristics are arranged in a pattern can also be obtained by the following alternative method.

[0078] A method in which the entire surface of the coating film 22 is irradiated with linearly polarized light and then partially irradiated with linearly polarized light having a vibration direction different by 90°.

[0079] Method 2

[0080] A method in which the entire surface of the coating film 22 is irradiated with linearly polarized light and then partially irradiated with non-polarized light.

[0081] Method 3

[0082] A method in which the entire surface of the coating film 22 is irradiated with linearly polarized light and then partially irradiated with non-polarized light and linearly polarized light.

[0083] Method 4

[0084] A method of partially irradiating the coating film 22 with linearly polarized light.

[0085] The above-mentioned various methods can provide a phase difference element 20 formed with fine patterns having different optical characteristics. Using such a phase difference element 20 can support thinning of polarization beam splitters, and can contribute to size reduction of optical devices such as the polarization conversion element 1 and the image projection device 100 including the same.

[0086] Example

[0087] (Monomer 1)

[0088] 4-(6-hydroxyhexyloxy)cinnamic acid is synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. Methacrylic acid is added excessively to the product in the presence of p-toluenesulfonic acid to perform an esterification reaction, thereby synthesizing a monomer 1 represented by the following chemical formula 3.

[0089] [Chemistry 3]

[0090]

[0091] (Single 2)

[0092] 4-(6-hydroxyhexyloxy)benzoic acid is synthesized by heating p-hydroxybenzoic acid and 6-chloro-1-hexanol under alkaline conditions. In the presence of p-toluenesulfonic acid, methacrylic acid is added in excess to the product for esterification reaction to synthesize monomer 2 represented by the following chemical formula 4.

[0093] [Chemistry 4]

[0094]

[0095] (Polymer 1)

[0096] Monomer 1 and monomer 2 were dissolved in dioxane at a molar ratio of 3:7, and AIBN was added as a reaction initiator, and polymerization was carried out at 70° C. for 24 hours to obtain a photosensitive polymer 1. The polymer 1 exhibited liquid crystal properties.

[0097] [Example 1]

[0098] The polymer 1 was dissolved in tetrahydrofuran to prepare a solution. A cover glass was used as a substrate (support) 20d, and the solution was applied on the substrate 20d to a thickness of 4.5 μm using a spin coater and dried at room temperature (25° C.) to form a coating film 22 as a precursor of the phase difference film 20a.

[0099] A mask 23 with a line and slit width of 0.7 mm was arranged on the coating film 22 formed on the substrate 20d, and the light from the high pressure mercury lamp was converted into linearly polarized light L by a Glan-Taylor prism through the exposure mask 23 for 100 seconds. At this time, the polarization direction of the light converted into linear polarization was 45° relative to the line and slit of the exposure mask 23. Then, it was heated to 130°C and then slowly cooled to orient it and induce birefringence. The phase difference value of the portion of the coating film 22 corresponding to the slit 23a of the exposure mask 23 was 275nm, and the fast axis of the phase difference was 45° relative to the line and slit 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 it was confirmed that stripe-shaped phase difference portions (optically anisotropic regions 20b) and isotropic portions (optically isotropic regions 20c) were formed alternately.

[0100] On the other hand, for comparison, when the material of patent document 1 was exposed to a mask, it was confirmed that the light-shielded portion did not become a transparent optical isotropic body and could not be used for the manufacture of the narrow-pitch phase difference element 20 based on the method of the present invention.

[0101] Explanation of symbols

[0102] 1 Polarization conversion element

[0103] 2 Light Source

[0104] 3 Transmissive liquid crystal display device

[0105] 4.5 Microlens Array

[0106] 6 Lenses

[0107] 10 Polarization Beam Splitter

[0108] 10a Prism

[0109] 10b Prism interface

[0110] 10c surface (emission surface)

[0111] 10d polarization separation film

[0112] 10e Reflective film

[0113] 20 phase difference element

[0114] 20a Retardation Film

[0115] 20b Optically anisotropic region

[0116] 20c Optically isotropic region

[0117] 20d substrate

[0118] 21 phase difference plate

[0119] 22 coating

[0120] 22a Photosensitive group side chain

[0121] 22b Non-photosensitive side chain

[0122] 23 Mask

[0123] 23a Slit

[0124] 23b Light shielding part

Claims

1. A polarization conversion element, comprising: a polarizing beam splitter formed by an array of prisms; and a phase difference element stacked on the polarization beam splitter, in, The phase difference element comprises a film composed of a liquid crystal material having a photosensitive group. In the film, optically anisotropic regions and optically isotropic regions that impart a phase difference to transmitted light are alternately arranged in stripes.

2. The polarization conversion element according to claim 1, in, 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 . 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, in, The method comprises the following steps: forming a coating film composed of a birefringence inducing material including a photosensitivity liquid crystal material on a substrate; disposing a mask having periodically arranged slits on the coating film, and irradiating polarized light through the mask; and The irradiated coating film is heated and then slowly cooled, thereby inducing birefringence in the portion exposed through the slit.

Images