JP2006209098A - Optical element and manufacturing method thereof - Google Patents

Abstract

Provided is an optical element capable of improving adhesion between an orientation-imparting layer for imparting orientation to a refractive-index anisotropic layer and a refractive-index anisotropic layer and improving the durability of each layer. To do.
An optical element 10 includes an orientation imparting layer 12 laminated on a transparent substrate 11, and a refractive index anisotropic layer 13 laminated on the orientation imparting layer 12. The refractive index anisotropic layer 13 is a liquid crystal layer formed by curing (polymerizing) a liquid crystalline composition containing a polymerizable liquid crystal material. The refractive index anisotropic layer 13 is a portion of the refractive index anisotropic layer 13 that is located on the side closer to the orientation imparting layer 12, and the degree of cure of the portion located on the side far from the orientation imparting layer 12 is cured. The degree of cure of the refractive index anisotropic layer 13 changes monotonously with a predetermined gradient in the thickness direction so as to be larger than the degree. The average degree of curing of the refractive index anisotropic layer 13 is preferably 90% or more.
[Selection] Figure 1

Description

  The present invention relates to an optical element such as a retardation plate, a polarizing plate, and a color filter for display, and in particular, an optical device including a liquid crystal layer made of a liquid crystalline composition containing a polymerizable liquid crystal material as a refractive index anisotropic layer. The present invention relates to an element and a manufacturing method thereof. In this specification, the term “liquid crystal layer” is used to mean an optically liquid crystal layer, and the state of the layer is a solid state that is solidified while maintaining the molecular arrangement of the liquid crystal phase. It also includes what is taken.

  In general, the liquid crystal is used as a display medium such as a display element represented by a TN (twisted nematic) type or STN (super twisted nematic) type by utilizing the reversible mobility of the molecular arrangement. Utilizing refractive index anisotropy, it is also used as an optical element such as a phase difference plate, a polarizing plate, and a display color filter.

  Here, regarding the latter application, in recent years, many optical elements including a liquid crystal layer made of a polymerizable liquid crystal material as a refractive index anisotropic layer have been proposed. Specifically, for example, Patent Document 1 describes an optical element having functions of wavelength selective reflectivity and polarization selective reflectivity, which is produced using a special polymerizable liquid crystal compound. Patent Document 2 describes a birefringent plate manufactured using a polymerizable liquid crystal compound having a rod-like structure. Further, Patent Documents 3 and 4 describe an optical compensation sheet produced using a polymerizable liquid crystal compound having a disc-like structure.

  By the way, as such an optical element, a plastic film or the like is used as a support, and a liquid crystal layer (refractive index anisotropic layer) made of a polymerizable liquid crystal material is laminated on the support through an alignment film. Commonly used.

  Here, the alignment film provided between the support and the refractive index anisotropic layer has an alignment regulating force that regulates the alignment direction of the liquid crystal molecules in the refractive index anisotropic layer. Such an alignment film is formed by, for example, forming an oriented polymer layer such as polyimide, polyvinyl alcohol, or gelatin on a support and then subjecting the polymer layer to an orientation treatment such as a rubbing treatment. Can be formed. In the case where the rubbing process is performed as the alignment process, static electricity and dust are generated on the surface of the alignment film. Therefore, a technique for expressing the alignment regulating force in the alignment film without performing the rubbing process has been studied. One of them is a photo-alignment method that generates an alignment regulating force (anisotropy) on the surface of the alignment film by irradiating light having an arbitrary polarization state (polarized light). Such photo-alignment methods include “photoisomerization” that reversibly changes the alignment state by changing only the shape of the molecule, and “photoreaction type” that changes the molecule itself. The latter “photoreactive type” is further divided into dimerization, decomposition type, bond type, decomposition-bond type, and the like.

  In the optical element composed of the support, the alignment film and the refractive index anisotropic layer as described above, it is of course important that the optical characteristics of each layer of the optical element are good. It is also important that each layer has good durability. Regarding the latter problem, for example, when the adhesion between the alignment film constituting the optical element and the refractive index anisotropic layer is poor, there is a problem that the refractive index anisotropic layer is easily peeled off from the alignment film. Further, when the optical element is used or stored under high temperature and high humidity, there is also a problem that a net-like wrinkle is generated in the refractive index anisotropic layer.

  In order to solve such problems, conventionally, the following methods have been proposed.

  That is, in Patent Document 4, a modified polyvinyl alcohol is used as a material for the alignment film, and a chemical bond at the interface between the alignment film and the refractive index anisotropic layer improves the adhesion between the layers. Has been proposed. Patent Document 5 proposes a technique for improving the adhesion between layers by inserting an anchor coat layer between layers with low adhesion. Furthermore, Patent Document 6 proposes a technique for improving the durability of the refractive index anisotropic layer by adding a monomer to the material of the refractive index anisotropic layer. Specifically, as a material of the refractive index anisotropic layer, by containing a non-mesogenic compound having two or three or more polymerizable functional groups with respect to the reactive mesogenic compound in an amount of 20% or less, Methods for changing the glass transition temperature, thermal stability and mechanical stability have been proposed.

JP 2002-533742 A Japanese Patent Application Laid-Open No. 5-215921 JP-A-8-338913 JP 9-152509 A Japanese Patent Laid-Open No. 10-10320 Special Table 2000-514202

  However, among the above-described conventional methods, the method described in Patent Document 4 has a high boiling point of the solvent used for the modification reaction of polyvinyl alcohol, and is used as a coating liquid while containing such a solvent. Therefore, the process of reprecipitation and purification of polyvinyl alcohol becomes indispensable, and there is a problem that the manufacturing cost increases. In addition, the technique described in Patent Document 5 has a problem that liquid crystal molecules are not well aligned on the anchor coat layer when a liquid crystal compound is used as the material of the refractive index anisotropic layer. Furthermore, in the method described in Patent Document 6, when the alignment state of the liquid crystal molecules is fixed after the alignment treatment to form a refractive index anisotropic layer, the additive becomes an impurity when the liquid crystal molecules are aligned. Since the alignment of the liquid crystal molecules is hindered, there is a problem that the optical characteristics deteriorate (for example, display unevenness occurs).

  The present invention has been made in consideration of such points, and is an optical element using a liquid crystal layer made of a liquid crystal composition containing a polymerizable liquid crystal material as a refractive index anisotropic layer, and having a refractive index different from that of the refractive index anisotropic layer. To provide an optical element capable of enhancing adhesion between an orientation-imparting layer that imparts orientation to an anisotropic layer and a refractive index anisotropic layer and improving the durability of each layer, and a method for producing the same. With the goal.

  As the first solution, the present invention provides a transparent base material, an orientation imparting layer laminated on the transparent base material, and an orientation regulation of the orientation imparting layer laminated on the orientation imparting layer. An alignment layer formed from a composition for alignment film capable of expressing the alignment regulating force by a photo-alignment method. The refractive index anisotropic layer comprises a liquid crystal layer formed by curing a liquid crystalline composition containing a polymerizable liquid crystal material, and the orientation-imparting is provided among the refractive index anisotropic layers. The degree of cure of the refractive index anisotropic layer with respect to the thickness direction is such that the degree of cure of the part located on the side closer to the layer is larger than the degree of cure of the part located on the side far from the orientation imparting layer. An optical element characterized by monotonously changing with a predetermined gradient To provide.

  In the first solving means described above, the average degree of curing of the refractive index anisotropic layer is preferably 90% or more.

  In the first solving means described above, the liquid crystalline composition for forming the refractive index anisotropic layer preferably contains a nematic liquid crystal compound as the polymerizable liquid crystal material.

  Furthermore, in the first solving means described above, the alignment film composition for forming the orientation imparting layer preferably contains a polymer having a cinnamoyl group. Here, the alignment film composition preferably includes a monomer or oligomer having one or more functional groups in addition to the polymer. The monomer or oligomer is preferably a polymerizable liquid crystal material. Furthermore, it is preferable that the polymerizable liquid crystal material in the orientation imparting layer and the polymerizable liquid crystal material in the refractive index anisotropic layer are the same type of material.

  As a second solution, the present invention provides a transparent substrate in which an alignment film formed from an alignment film composition capable of expressing an alignment regulating force by a photo-alignment method is laminated as an alignment layer. A step of preparing, a step of applying a liquid crystalline composition containing a polymerizable liquid crystal material on the alignment layer of the transparent substrate, and the liquid crystal composition not adjacent to the alignment layer. The orientation of the transparent substrate is cured by curing the liquid crystalline composition while retarding the curing rate near the surface on the side, compared with the curing rate near the surface on the side adjacent to the orientation-imparting layer. Forming a refractive index anisotropic layer comprising a liquid crystal layer whose degree of cure monotonously changes with a predetermined gradient with respect to the thickness direction on the application layer. A manufacturing method is provided.

  In the second solving means described above, in the step of forming the refractive index anisotropic layer, only the side of the liquid crystalline composition not adjacent to the orientation providing layer is exposed to an air atmosphere. It is preferable to irradiate the liquid crystalline composition with radiation. Here, the radiation is ultraviolet light, and the liquid crystalline composition preferably contains a polymerization initiator together with the polymerizable liquid crystal material.

  According to the first solving means of the present invention, the orientation-imparting layer that imparts orientation to the refractive index anisotropic layer is formed from an alignment film composition capable of expressing an orientation regulating force by a photo-alignment method. The refractive index anisotropic layer is formed of a liquid crystal layer formed by curing a liquid crystalline composition containing a polymerizable liquid crystal material. The degree of cure of the refractive index anisotropic layer is such that the degree of cure of the portion located on the side closer to the orientation imparting layer is larger than the degree of cure of the portion located on the side far from the orientation imparted layer. Since it changes monotonously with a predetermined gradient with respect to the direction, the adhesion between the orientation imparting layer and the refractive index anisotropic layer is excellent, and the durability of each layer is excellent. For this reason, the problem that a refractive index anisotropic layer peels can be eliminated effectively. Further, if the average degree of curing of the refractive index anisotropic layer is 90% or more, the adhesion between the orientation imparting layer is further improved, and even when the optical element is rolled, There is no blocking problem caused by the refractive index anisotropic layer sticking to the back surface of the transparent substrate. For this reason, the problem that a refractive index anisotropic layer peels off, or a haze raise, the expression of nonuniformity, etc. resulting from an orientation defect can be solved more effectively.

  According to the second solving means of the present invention, the orientation-imparting layer of the liquid crystalline composition is formed on the orientation-imparting layer of the transparent substrate and the orientation-given liquid crystalline composition. By irradiating the liquid crystalline composition with only the side not adjacent to the air atmosphere, the curing rate near the surface of the liquid crystalline composition on the side not adjacent to the orientation-imparting layer is adjusted. The liquid crystalline composition is cured while being delayed as compared with the curing rate in the vicinity of the surface adjacent to the application layer. As a result, in the liquid crystalline composition, it gradually cures gradually from the portion on the orientation imparting layer side toward the portion on the air interface side, and uncured as it approaches the portion on the air interface side from the portion on the orientation imparting layer side. A curing gradient with more components occurs. For this reason, the polymerizable liquid crystal material in the liquid crystalline composition is cured in a process in which the refractive index anisotropic layer is formed while curing shrinkage is suppressed as much as possible, and is applied to the orientation imparting layer of the liquid crystalline composition. Adhesion is maintained, and internal stress generated in the liquid crystalline composition is relieved. Thereby, the optical element finally manufactured is excellent in the adhesion between the orientation imparting layer and the refractive index anisotropic layer, and the durability of each layer is excellent. For this reason, it is possible to effectively solve the problem that the refractive index anisotropic layer is peeled off or haze is increased or unevenness is caused due to poor alignment.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the configuration of an optical element according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the optical element 10 according to the present embodiment is laminated on a transparent base material 11, an orientation imparting layer 12 laminated on the transparent base material 11, and an orientation imparting layer 12. And a refractive index anisotropic layer 13.

Among these, the transparent base material 11 is a support body which supports the orientation provision layer 12 and the refractive index anisotropic layer 13, and is formed from glass or a transparent resin film. Here, transparent resin films include cellulose resins such as triacetate cellulose (TAC), diacetyl cellulose, and acetate butyrate cellulose, polyester resins such as polyethylene terephthalate (PET) and polyester, olefin resins such as polyethylene, and polyacrylic. A film made of a resin such as a resin, polyurethane resin, polyethersulfone, polycarbonate, polysulfone, polyether, polymethylpentene, polyetherketone, or (meth) acrylonitrile can be used. In addition, as such a transparent resin film, the film which consists of a triacetate cellulose (TAC) without birefringence is used suitably.

  In addition, it is preferable that the transparent base material 11 is about 25 micrometers-1000 micrometers in thickness. Further, the transparent base material 11 may be a continuous long film having a certain length, and more specifically, a continuous film that is generally used industrially and supplied in a rolled form. It may be a film. Although the length of such a long film can be taken arbitrarily, if it is the form wound by roll, it can also be set as long, for example about 10000 m.

  The orientation imparting layer 12 is an orientation film having an orientation regulating force that imparts orientation to the refractive index anisotropic layer 13, and from an alignment film composition capable of expressing the orientation regulating force by a photo-alignment method. Is formed. The orientation imparting layer 12 preferably has a thickness of about 0.01 μm to 0.5 μm. Here, the photo-alignment method is a method in which alignment regulating force (anisotropy) is expressed on the surface of the alignment film by irradiating the alignment film with light having an arbitrary polarization state (polarized light).

  Here, as the alignment film composition for forming the orientation imparting layer 12, a polymer, a coupling agent, or the like can be used. Specifically, examples of the polymer include polymethyl methacrylate, acrylic acid-methacrylic acid copolymer, styrene-maleimide polymer, polyvinyl alcohol, modified polyvinyl alcohol, gelatin, styrene-vinyl toluene copolymer, chlorosulfone. And polymers such as chlorinated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene, and polycarbonate. Moreover, a silane coupling agent etc. are mentioned as an example of a coupling agent.

  In addition, as described above, in the photo-alignment method in which the orientation-imparting layer 12 formed from such an alignment film composition exhibits an alignment regulating force, the alignment state is reversibly changed only by changing the molecular shape. There are “photoisomerization” that changes the molecule and “photoreaction type” that changes the molecule itself. The latter “photoreactive type” is further divided into dimerization, decomposition type, bond type, decomposition-bond type, and the like. Of these, the “dimerization” method generally used as the photo-alignment method is taken as an example. In this method, the surface of the alignment film is irradiated with light having an arbitrary polarization state (polarized light). Thus, a chemical reaction such as a dimerization reaction is caused in the polarization direction, and the alignment regulating force is expressed. In addition, polyvinyl cinnamate (PVCi) is mentioned as a typical example of a polymer that exhibits an orientation regulating force by such “dimerization”. In such polyvinyl cinnamate (PVCi), a double bond portion of two side chains parallel to the polarized light is opened by dimerization reaction, for example, by irradiation with polarized ultraviolet rays, and recombined with each other. In addition, polymers having a cinnamoyl group, a coumarin group, or a chalcone group are preferably used as such a polymer that exhibits orientation regulating power by “dimerization” (for example, Japanese Patent Application Laid-Open No. 7-138380 or a special technique). (See Kaihei 10-324690).

  In addition to the polymer as described above, a monomer or oligomer having one or more functional groups may be added to the alignment film composition as described above. As such a monomer or oligomer, a monofunctional monomer having a functional group such as acrylate or cinnamoyl (for example, reactive ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, N-vinylpyrrolidone) And polyfunctional monomers (for example, polymethylolpropane tri (meth) acrylate, hexanediol (meth) acrylate, triethylene (polypropylene) glycol diacrylate, tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol Tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (me ) Acrylate, and isocyanuric acid EO-modified diacrylate), bisphenol fluorene derivatives (e.g., bisphenoxyethanolfluorene acrylate, can be used as a bisphenol fluorene epoxy acrylate), etc. were alone or mixed. When such a monomer or oligomer is added to the alignment film composition, the structure of the orientation imparting layer 12 formed from the alignment film composition becomes a strong network structure. improves. Further, in the vicinity of the interface between the orientation imparting layer 12 and the refractive index anisotropic layer 13, the monomer or oligomer in the orientation imparting layer 12 is in the refractive index anisotropic layer 13 adjacent to the orientation imparting layer 12. Since it crosslinks with the molecule, the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is also improved.

  Here, the addition amount of the monomer or oligomer described above is within a range in which the optical properties of the optical element 10 are not impaired if the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is sufficiently improved. It can be adjusted arbitrarily. However, in general, it is preferably 0.01% by weight or more and 3% by weight or less based on the weight of the solid content (polymer). This is because at 0.01% by weight or less, the effect of improving the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is not sufficiently exhibited. On the other hand, if it is 3% by weight or more, the effect of improving the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is sufficient, but sufficient orientation for the refractive index anisotropic layer 13 is achieved. It may not be possible to confer sex. That is, as will be described later, the refractive index anisotropic layer 13 is obtained through a process of aligning liquid crystal molecules and fixing the alignment state. However, the monomer or oligomer as described above inhibits alignment during alignment of liquid crystal molecules. This is because it becomes a substance, which may cause an increase in haze or unevenness due to poor alignment and may impair the optical function.

  The monomer or oligomer described above is preferably a polymerizable liquid crystal material. In particular, the monomer or oligomer made of such a polymerizable liquid crystal material is preferably the same type of material as the polymerizable liquid crystal material in the refractive index anisotropic layer 13. Thereby, the monomer or oligomer in the orientation imparting layer 12 is more easily cross-linked with the molecules in the refractive index anisotropic layer 13 adjacent to the orientation imparting layer 12, and the orientation imparting layer 12 is anisotropic with the refractive index. The adhesiveness with the adhesive layer 13 can be further improved.

  Furthermore, when the transparent substrate 11 is a long film and the roll is rolled when the orientation imparting layer 12 is laminated on the transparent substrate 11, the monomer or oligomer described above is the type and It is preferable to adjust the addition amount as appropriate so that the orientation imparting layer 12 is close to solid at room temperature. In this case, it is preferable to use a high molecular weight monomer or oligomer. Thereby, even when it rolls at the time of the orientation provision layer 12 being laminated | stacked on the transparent base material 11, the problem of the blocking which arises when the orientation provision layer 12 sticks to the back surface of the transparent base material 11 does not arise. .

The refractive index anisotropic layer 13 is an optical functional layer that realizes functions as a retardation plate, a polarizing plate, a display color filter, and the like, and cures (polymerizes) a liquid crystalline composition containing a polymerizable liquid crystal material. It consists of a liquid crystal layer formed. As shown in FIG. 2, the refractive index anisotropic layer 13 has a degree of cure of a portion located on the side closer to the orientation imparting layer 12 in the refractive index anisotropic layer 13 so that the orientation imparting layer 12 The degree of cure of the refractive index anisotropic layer 13 changes monotonously with a predetermined gradient with respect to the thickness direction so that the degree of cure of the portion located on the far side from the distance increases. Here, the “front surface” in FIG. 2 means the interface between the refractive index anisotropic layer 13 and air, and the “back surface” in FIG. 2 indicates the relationship between the refractive index anisotropic layer 13 and the orientation imparting layer 12. Means an interface.
The average degree of curing of the refractive index anisotropic layer 13 is preferably 90% or more. Here, “monotonic change” means that the degree of cure increases or decreases with a certain tendency in the thickness direction, and is not limited to a linear change, Including any change such as exponential change. Moreover, it is not limited to a monotonous change (monotonic increase or monotonic decrease) in a strict sense, but also includes a step-like increase or decrease. In addition, the “average degree of cure” is the average value of the degree of cure in the entire thickness direction of the refractive index anisotropic layer 13.

  The thickness of the refractive index anisotropic layer 13 is determined by desired optical characteristics.

  Here, the liquid crystalline composition for forming the refractive index anisotropic layer 13 is not limited to the polymerizable liquid crystal material as described below, but can be optionally added within a range that does not affect the alignment and optical characteristics of the liquid crystal material. It is preferable that an agent (for example, a polymerization initiator, a plasticizer, a surfactant, a silane coupling agent) is included. The amount of such an additive is appropriately adjusted according to the liquid crystal material in the liquid crystal composition, but is generally based on the weight of the solid content (polymerizable liquid crystal material). It is preferably 0.001% by weight or more and 10% by weight or less. Further, such a liquid crystalline composition can be applied as it is on the orientation imparting layer 12, but an appropriate solvent such as an organic solvent is used for the purpose of adjusting the viscosity to a coating apparatus or obtaining a good orientation state. It may be dissolved in a solvent.

  On the other hand, a nematic liquid crystal compound having nematic regularity is preferably used as the polymerizable liquid crystal material contained in such a liquid crystal composition. Specifically, for example, compounds described in JP-A-7-258638, JP-T-10-508882, JP-A-2003-287623 can be used as appropriate, and more specifically, It is preferable to use compounds represented by the following chemical formulas (1) to (10).

  However, as the nematic liquid crystal compound used in this embodiment, any liquid crystal compound having nematic liquid crystal properties and having one or more functional groups (for example, an ultraviolet curable polymerization group) at the terminal may be used. It is not limited to such a type, and any type can be used as appropriate. In addition, among the types of nematic liquid crystal compounds described above, several types of materials can be appropriately mixed and used.

  Here, the liquid crystalline composition containing such a nematic liquid crystal compound is applied on the orientation imparting layer 12 by a method as described later and cured (polymerized) by irradiation with ultraviolet rays or the like. The refractive index anisotropic layer 13 finally formed in this way is composed of a liquid crystal layer fixed with nematic liquid crystal molecules aligned parallel to the transparent substrate 11 as shown in FIG. In addition, like the refractive index anisotropic layer 13A shown in FIG. 3, it may consist of a liquid crystal layer fixed in a state in which nematic liquid crystal molecules are aligned vertically with respect to the transparent substrate 11. The liquid crystal structure of the refractive index anisotropic layer 13 shown in FIG. 1 is a homogeneous structure (parallel alignment structure), and an optical functional layer called an A plate is obtained by this structure. On the other hand, the liquid crystal structure of the refractive index anisotropic layer 13A shown in FIG. 3 has a homeotropic structure (vertical alignment structure), and an optical functional layer called a positive (+) C plate is obtained by this structure.

  On the other hand, as the polymerizable liquid crystal material contained in the liquid crystal composition, a mixture of the polymerizable nematic liquid crystal compound as described above and a chiral agent may be used (see JP-A-2003-287623). ). The chiral agent is used for the purpose of inducing a helical structure in the nematic regularity expressed by the nematic liquid crystal compound. As long as this purpose is achieved, the chiral agent is in a solution state or a molten state with the nematic liquid crystal compound. Any type can be used as long as it is compatible and can induce a desired helical structure without impairing the liquid crystal properties of the nematic liquid crystal compound. Specifically, for example, it is preferable to use a low molecular compound having axial asymmetry in the molecule as represented by the following general formula (11), (12) or (13).

  In the general formula (11) or (12), R4 represents hydrogen or a methyl group. Y is any one of formulas (i) to (xxiv) shown above, and among them, any one of formulas (i), (ii), (iii), (v), and (vii) Preferably there is. Moreover, although c and d which show the chain length of an alkylene group can each take arbitrary integers in the range of 2-12, it is preferable that it is the range of 4-10, and is the range of 6-9. Is more preferable. The compound of the above general formula (11) or (12) in which the value of c or d is 0 or 1 lacks stability, is susceptible to hydrolysis, and has high crystallinity. On the other hand, a compound having a value of c or d of 13 or more has a low melting point (Tm). In these compounds, compatibility with a polymerizable liquid crystal material exhibiting nematic regularity is lowered, and phase separation or the like may occur depending on the concentration. In addition, such a chiral agent does not need to have polymerizability in particular. However, when the chiral agent has polymerizability, it is polymerized with a polymerizable liquid crystal material exhibiting nematic regularity, and the cholesteric regularity is stably fixed, so in terms of thermal stability, etc. Highly preferred. In particular, it is preferable to have a polymerizable functional group at both ends of the molecule in order to obtain the refractive index anisotropic layer 13 having good heat resistance.

  In this case, the refractive index anisotropic layer finally formed on the orientation imparting layer 12 is a nematic liquid crystal with respect to the transparent substrate 11 like the refractive index anisotropic layer 13B shown in FIG. It is composed of a liquid crystal layer in which molecules are fixed in a planar structure (state having cholesteric regularity) in a planar orientation. In this case, the liquid crystal structure of the refractive index anisotropic layer 13B is a cholesteric structure, and an optical functional layer called a negative (−) C plate is obtained by this structure.

  The refractive index anisotropic layer finally formed on the orientation imparting layer 12 is the same as the refractive index anisotropic layer 13 shown in FIG. 1 like the refractive index anisotropic layer 13C shown in FIG. The refractive index anisotropic layer 13B shown in FIG. 4 may be laminated on each other. In addition, two or more of the same or different types of liquid crystal layers 13, 13A, and 13B shown in FIGS. 1, 3, and 4 may be stacked on each other.

  Further, as shown in FIG. 6, a barrier layer (intermediate layer) 14 that blocks elution of a plasticizer and the like contained in the transparent substrate 11 is provided between the transparent substrate 11 and the orientation imparting layer 12. It may be. Examples of the material of the barrier layer 14 include an ultraviolet curable acrylic urethane resin, an ultraviolet curable polyester acrylate resin, an ultraviolet curable epoxy acrylate resin, an ultraviolet curable polyol acrylate resin, and an ultraviolet curable epoxy resin. Can be mentioned. In general, UV-curable acrylic urethane resins include 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate (hereinafter referred to as acrylates) in addition to products obtained by reacting polyester polyols with isocyanate monomers and prepolymers. It can be easily obtained by reacting an acrylate monomer having a hydroxyl group such as 2-hydroxypropyl acrylate. In general, the ultraviolet curable polyester acrylate resin can be easily obtained by reacting polyester polyol with 2-hydroxyethyl acrylate or 2-hydroxy acrylate monomer. Specific examples of the ultraviolet curable epoxy acrylate resin include those obtained by reacting epoxy acrylate with an oligomer, a reactive diluent and a photoreaction initiator added thereto. As the photoreaction initiator, one or more kinds selected from benzoin derivatives, oxime ketone derivatives, benzophenone derivatives, thioxanthone derivatives and the like can be selected and used. Specific examples of ultraviolet curable polyol acrylate resins include trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, alkyl-modified dipentaerythritol pentaacrylate. Etc. These resins are usually used together with known photosensitizers.

  Here, if it considers improving the adhesiveness between the barrier layer 14 and the orientation provision layer 12, as mentioned above, in the composition for alignment films for forming the orientation provision layer 12 While adding the monomer or oligomer which has one or more functional groups, it is preferable to add the same kind of monomer or oligomer as the material of the barrier layer 14 as the monomer or oligomer added to the alignment film composition. Thereby, the monomer or oligomer in the barrier layer 14 is adjacent to the barrier layer 14 as in the case described above (in the case where the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is improved). The adhesion between the barrier layer 14 and the orientation imparting layer 12 can be improved by crosslinking with the molecules in the orientation imparting layer 12 to be performed.

Instead of the barrier layer 14, an intermediate layer such as an adhesive layer that improves the adhesion between the transparent substrate 11 and the orientation imparting layer 12 may be provided.

  Next, a manufacturing method of the optical element 10 having such a configuration will be described with reference to FIG.

  First, for example, a transparent resin film is prepared as the transparent substrate 11 (FIG. 7A), and then a barrier layer 14 is formed on one surface of the transparent substrate 11 (FIG. 7B).

  If, for example, an ultraviolet curable resin is used as the material of the barrier layer 14 formed on the transparent substrate 11, it is cured (polymerized) by irradiation with ultraviolet rays or the like after the barrier layer composition is applied. Is done.

Next, an alignment film composition containing a polymer and a coupling agent is applied on the barrier layer 14 formed on the transparent substrate 11 to form a coating film 12 'of the alignment film composition (FIG. 7). (C)).
At this time, the composition for alignment films is applied in the form of a composition solution for alignment films obtained by dissolving in an organic solvent. As a coating method, for example, spin coating, bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, or the like can be used, but is not limited thereto.

  After that, heat H is applied to the coating film 12 'of the composition for alignment film formed on the barrier layer 14 in this way to perform heat drying treatment, and then the ultraviolet ray L1 having an arbitrary polarization state is irradiated. To do. Thereby, the orientation regulating force is expressed on the surface of the coating film 12 'of the composition for alignment film, and the orientation imparting layer 12 as the alignment film is formed (FIG. 7 (d)).

  Next, a liquid crystalline composition containing a polymerizable liquid crystal material is applied on the orientation imparting layer 12 thus formed on the barrier layer 14 to form a coating film 13 ′ of the liquid crystalline composition. (FIG. 7 (e)). At this time, the liquid crystalline composition is applied in the form of a liquid crystalline composition solution obtained by dissolving in an organic solvent. As a coating method, for example, spin coating, bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, or the like can be used, but is not limited thereto.

  Thereafter, the coating film 13 ′ of the liquid crystal composition thus formed on the orientation imparting layer 12 is subjected to a heat drying treatment, and the orientation regulating force expressed on the surface of the orientation imparting layer 12, By regulating the orientation direction of the liquid crystal molecules in the coating film 13 'of the liquid crystalline composition, a coating film 13 ″ of the liquid crystalline composition to which the orientation is imparted is formed (FIG. 7 (f)).

  Then, the coating film 13 ″ of the liquid crystalline composition thus imparted with orientation is irradiated with ultraviolet rays (radiation) L2 as energy rays to cure the coating film 13 ″ of the liquid crystalline composition ( Polymerization) to fix the alignment state of the liquid crystal molecules. At this time, the coating film 13 ″ of the liquid crystalline composition was irradiated with ultraviolet light L2 in a state where only the side not adjacent to the orientation providing layer 12 of the coating film 13 ″ of the liquid crystalline composition was exposed to the air atmosphere, and the liquid crystal While delaying the curing rate in the vicinity of the surface on the side not adjacent to the orientation imparting layer 12 in the coating film 13 ″ of the property composition as compared with the curing rate in the vicinity of the surface on the side adjacent to the orientation imparting layer 12, The coating film 13 ″ of the liquid crystal composition is cured. That is, when the surface of the coating film 13 ″ of the liquid crystalline composition is exposed to the air atmosphere and cured by irradiating the ultraviolet ray L2, the surface on the air interface side of the coating film 13 ″ of the liquid crystalline composition is oxygenated. The radical polymerizable compound containing a (meth) acryloyl group is inhibited from curing, and the vicinity of the air interface side surface of the coating film 13 ″ of the liquid crystalline composition is hard to be cured. In the coating film 13 ″, the coating gradually cures gradually from the portion on the orientation imparting layer 12 side toward the portion on the air interface side, and the uncured component as it approaches the portion on the air interface side from the portion on the orientation imparting layer 12 side. A curing gradient is generated such that the amount of As a result, the refractive index anisotropic layer 13 made of a liquid crystal layer whose degree of cure monotonously changes with a predetermined gradient in the thickness direction is formed on the orientation imparting layer 12 (FIG. 7 ( g)). The degree of cure of the refractive index anisotropic layer 13 formed in this manner is preferably about 99% in the vicinity of the orientation imparting layer 12 side and about 85% in the vicinity of the air interface side. Note that the average degree of curing of the refractive index anisotropic layer 13 finally formed is preferably 90% or more, and the refractive index anisotropic layer 13 is formed by a process in which a curing gradient is generated as described above. After forming, it may be sufficiently cured by irradiating with ultraviolet rays again.

  Such a cured state of the refractive index anisotropic layer 13 can be obtained by observing the remaining amount of reactive groups. In order to observe the distribution of the degree of cure of the refractive index anisotropic layer 13, it is necessary to prepare a cross section of the layer. For this reason, in a specific measuring method, first, the refractive index anisotropic layer 13 is cut by an oblique cutting method. If the refractive index anisotropic layer 13 is cut obliquely in this way, the resulting cross section is different from a normal cross section, and the apparent thickness increases, so that the remaining amount of reactive groups is observed thereafter. In doing so, the spatial resolution can be increased. Next, after the cross section of the refractive index anisotropic layer 13 is obtained in this way, the remaining amount of reactive groups is observed. In addition, as a typical method for observing the remaining amount of the reactive group, there are a method of observing molecular vibration derived from the reactive group by infrared absorption and a method of measuring the mass attributed to the structure of the reactive group. is there. More specifically, (1) a method of measuring the strength distribution of stretching vibration of a carbon double bond (C = C) belonging to a reactive group using a reflection measurement method of a micro-infrared spectrophotometer, (2) A method of performing mapping at a mass number caused by a reactive group using a time-of-flight secondary ion mass spectrometer (TOF-SIMS), and (3) using a X-ray photoelectron spectrometer in total carbon. Examples thereof include a method for measuring the signal intensity due to the reactive group. Not only the measurement method using such a structural analysis technique but also a method of measuring the surface hardness of the cross section of the refractive index anisotropic layer 13 using a micro hardness meter or a nanoindenter, the refractive index difference is different. The cured state of the isotropic layer 13 can be determined.

  In the present invention, the degree of cure is expressed as%. The relationship between the measured value (signal intensity) and the degree of cure in the methods (1), (2) and (3) is based on the following criteria. Suppose you want. That is, the refractive index anisotropic layer is formed by coating a liquid crystalline composition containing a polymerizable liquid crystal material as described above to form a coating film of the liquid crystalline composition and irradiating it with ultraviolet rays. Although each of the measured values (signal intensity) when the above measurements (1), (2), and (3) were measured on the coating film before the ultraviolet irradiation was performed, the degree of cure was 0%. The signal intensity 0 in the above (1), (2) and (3) was set to 100% curing.

  Further, the atmosphere in which the side of the coating film 13 ″ of the liquid crystalline composition that is not adjacent to the orientation providing layer 12 is exposed is not limited to the air atmosphere, but depends on the type of polymerizable liquid crystal compound contained in the liquid crystalline composition. May be exposed to an atmosphere containing water, that is, a cationically polymerizable compound containing an epoxy group causes curing inhibition by water, so that the above-described air can be used for a liquid crystalline composition containing such a liquid crystal compound. As in the case of the atmosphere, a curing gradient is generated such that the uncured component increases as the orientation-imparting layer 12 side approaches the atmosphere interface side portion.

  Furthermore, it is preferable to irradiate ultraviolet-ray L2 irradiated to coating-film 13 '' of a liquid crystalline composition only for a short time with high illuminance, for example, it is preferable to irradiate with illuminance of 100 mW only for 2 seconds. L2 is preferably light including a wavelength in the range of 100 nm to 450 nm, and more preferably light including a wavelength in the range of 250 to 400 nm. This is because a chemical reaction such as UV curing can be obtained more easily and efficiently by using a commercially available polymerization initiator.

  In addition, although ultraviolet-ray L2 is used as a radiation irradiated to the coating film 13 '' of a liquid crystalline composition in order to form the refractive index anisotropic layer 13, such a radiation includes the above-described polymerizable liquid crystal. Any material can be used as long as the material can be cured, and in addition to ultraviolet rays, electron beams, visible rays, infrared rays (heat rays), and the like can be appropriately used depending on conditions. From the viewpoint of process easiness and the like, ultraviolet rays are preferable.

  As described above, according to the present embodiment, the orientation-imparting layer 11 that imparts orientation to the refractive index anisotropic layer 13 can exhibit an alignment regulating force by the photo-alignment method. The refractive index anisotropic layer 13 is made of a liquid crystal layer formed by curing a liquid crystalline composition containing a polymerizable liquid crystal material, and has a refractive index anisotropic layer. 13 of the refractive index anisotropic layer 13 so that the degree of cure of the portion located on the side closer to the orientation imparting layer 12 is larger than the degree of cure of the portion located on the side farther from the orientation imparted layer 12. Since the degree of cure is monotonously changing with a predetermined gradient in the thickness direction, the adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13 is excellent, and the durability of each layer is It will be excellent. For this reason, the problem that the refractive index anisotropic layer 13 peels can be effectively eliminated.

  In particular, according to the present embodiment, the liquid crystal composition is applied to the coating film 13 ″ of the liquid crystal composition with the orientation provided on the orientation provision layer 12 of the transparent substrate 11. The coating film 13 ″ of the liquid crystalline composition is irradiated with ultraviolet light L2 in a state where only the side not adjacent to the orientation imparting layer 12 of the coating film 13 ″ is exposed to the air atmosphere, and the coating film 13 ″ of the liquid crystalline composition is irradiated with ultraviolet rays L2. The coating film 13 of the liquid crystalline composition is delayed while the curing rate in the vicinity of the surface not adjacent to the orientation imparting layer 12 is delayed as compared with the curing rate in the vicinity of the surface adjacent to the orientation imparting layer 12. As a result, the coating film 13 of the liquid crystal composition is gradually and slowly cured from the portion on the orientation imparting layer 12 side toward the portion on the air interface side. Uncured as it approaches the part on the air interface side from the part Min cure gradient as increases occur. For this reason, the polymerizable liquid crystal material in the coating film 13 ″ of the liquid crystal composition is cured in a process in which the refractive index anisotropic layer 13 is formed, with curing shrinkage suppressed as much as possible. Thus, the adhesion of the coating film 13 ″ to the orientation imparting layer 12 is maintained, and the internal stress generated in the coating film 13 ″ of the liquid crystalline composition is alleviated. The optical element 10 has excellent adhesion between the orientation imparting layer 12 and the refractive index anisotropic layer 13, and the durability of each layer is excellent. The problem of peeling 13 can be effectively solved.

  In addition, according to the present embodiment, if the average degree of curing of the refractive index anisotropic layer 13 of the optical element 10 to be finally manufactured is 90% or more, it is between the orientation imparting layer 12 and the optical element 10. Even when the optical element 10 is rolled, the problem of blocking caused by the refractive index anisotropic layer 13 sticking to the back surface of the transparent substrate 11 does not occur. For this reason, the problem that the refractive index anisotropic layer 13 is peeled off or the haze is increased or unevenness occurs due to poor alignment can be more effectively solved.

  Next, specific examples of the above-described embodiment will be described.

Example 1
First, cyclohexanone (98 parts by weight) was added to and dissolved in an alignment film composition (2.0 parts by weight) containing a polymer having a cinnamoyl group to obtain an alignment film composition solution. Then, this solution was coated on a triacetyl cellulose (TAC) film (thickness 80 μm) as a transparent substrate by a wire bar coater, and then dried with warm air at 80 ° C. for 2 minutes, and the thickness was 0.1 μm. Coating film was obtained. This coating film was irradiated with polarized ultraviolet rays at 10 mJ / cm ² to form an alignment film in which an alignment regulating force was expressed on the surface.

  Next, a liquid crystalline composition containing the polymerizable nematic liquid crystal compound represented by the above chemical formula (1) is dissolved in a toluene solution at a ratio of 20% by mass, and further a polymerization initiator (Irgacure 907 (trade name), Ciba Specialty). Chemicals) was added to obtain a liquid crystal composition solution. Then, this solution was applied onto the alignment film prepared in the above step by a wire bar coater and dried to obtain a coating film having a thickness of 1 μm. Subsequently, this coating film was heated at 85 ° C. for 2 minutes, and the liquid crystal molecules in the coating film were aligned by the alignment regulating force expressed on the surface of the alignment film. Then, 300 mJ ultraviolet rays were irradiated in an air atmosphere using a high-pressure mercury lamp, the coating film was cured, and the alignment state of the liquid crystal molecules was fixed. As a result, a nematic liquid crystal layer was formed on the alignment film, and finally the optical element according to Example 1 was manufactured.

(Example 2)
First, an alignment film was formed on a triacetyl cellulose (TAC) film as a transparent substrate by the same method as in Example 1.

  Next, a liquid crystalline composition containing the polymerizable nematic liquid crystal compound represented by the above chemical formula (1) is dissolved in a toluene solution at a ratio of 20% by mass, and further a polymerization initiator (Irgacure 907 (trade name), Ciba Specialty). Chemicals) was added to obtain a liquid crystal composition solution. Then, this solution was applied onto the alignment film prepared in the above step by a wire bar coater and dried to obtain a coating film having a thickness of 1 μm. Subsequently, this coating film was heated at 85 ° C. for 2 minutes, and the liquid crystal molecules in the coating film were aligned by the alignment regulating force expressed on the surface of the alignment film. Thereafter, 100 mJ ultraviolet rays were irradiated in an air atmosphere using a high-pressure mercury lamp, the coating film was cured, and the alignment state of the liquid crystal molecules was fixed. As a result, a nematic liquid crystal layer was formed on the alignment film, and an optical element according to Example 2 was finally manufactured.

(Comparative example)
First, an alignment film was formed on a triacetyl cellulose (TAC) film as a transparent substrate by the same method as in Example 1.

  Next, a liquid crystalline composition containing the polymerizable nematic liquid crystal compound represented by the above chemical formula (1) is dissolved in a toluene solution at a ratio of 20% by mass, and further a polymerization initiator (Irgacure 907 (trade name), Ciba Specialty). Chemicals) was added to obtain a liquid crystal composition solution. Then, this solution was applied onto the alignment film prepared in the above step by a wire bar coater and dried to obtain a coating film having a thickness of 1 μm. Subsequently, this coating film was heated at 85 ° C. for 2 minutes, and the liquid crystal molecules in the coating film were aligned by the alignment regulating force expressed on the surface of the alignment film. Then, 100 mJ ultraviolet rays were irradiated in a nitrogen atmosphere using a high pressure mercury lamp, the coating film was cured, and the alignment state of the liquid crystal molecules was fixed. Thereby, a nematic liquid crystal layer was formed on the alignment film, and finally an optical element according to a comparative example was manufactured.

(Evaluation results)
Regarding each optical element according to Example 1, Example 2, and Comparative Example, the degree of cure of the nematic liquid crystal layer was measured. The degree of cure was obtained by cutting a nematic liquid crystal layer by an oblique cutting method, and using the reflection measurement method of a micro-infrared spectrophotometer to obtain a cross section of carbon double bonds (C = C) belonging to a reactive group. It was determined by measuring the strength distribution of the stretching vibration. The results are shown in Table 1 below.
As shown in Table 1 below, the optical element according to Example 1 had an average degree of cure of 98% and a gradient in the degree of cure. Further, the optical element according to Example 2 had a gradient in the degree of cure, but the average degree of cure was 85%, which was lower than that of Example 1.
On the other hand, in the optical element according to Comparative Example 1, the average degree of cure was 98%, but there was no gradient in the degree of cure.

  Table 1 below shows the results of visual evaluation of the orientation of the liquid crystal molecules with respect to the optical elements according to Example 1, Example 2, and Comparative Example. As is clear from Table 1 below, in the optical elements according to Example 1 and the comparative example, the alignment state of the liquid crystal molecules was uniform. Further, when the optical element according to the comparative example was left in a roll shape, the nematic liquid crystal layer was stuck to the back surface of the TAC film, blocking occurred, and the alignment state of the liquid crystal molecules was also disturbed.

  Furthermore, regarding each optical element according to Example 1, Example 2, and Comparative Example, a cross-cut tape peeling test was performed in accordance with JIS 5400 as a test for evaluating adhesion. Specifically, cellotape (registered trademark) (CT24, manufactured by Nichiban Co., Ltd.) was used, and the film was peeled after being adhered to the film with the belly of the finger. The determination was made based on the number of squares that were not peeled out of 100 squares. The case where the nematic liquid crystal layer did not peel at all was 100/100, and the case where the nematic liquid crystal layer completely peeled was 0/100. The results are shown in Table 1 below. As is clear from Table 1 below, the optical element according to the comparative example did not have good adhesion.

1 is a cross-sectional view showing an outline of an optical element according to an embodiment of the present invention. Schematic which shows distribution in a layer of the curing degree in the refractive index anisotropic layer of the optical element shown in FIG. Sectional drawing which shows the outline of the modification of the optical element shown in FIG.1 and FIG.2. Sectional drawing which shows the outline of the other modification of the optical element shown in FIG.1 and FIG.2. Sectional drawing which shows the outline of the other modification of the optical element shown in FIG.1 and FIG.2. Sectional drawing which shows the outline of the other modification of the optical element shown in FIG.1 and FIG.2. Process drawing for demonstrating the manufacturing method of the optical element which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical element 11 Transparent base material 12 Orientation provision layer 12 'Coating film 13, 13A, 13B, 13C of composition for alignment films Refractive index anisotropic layer 13', 13 "Coating film 14 of liquid crystalline composition Barrier layer (Middle layer)
L1 UV light (polarized light for alignment film formation)
L2 UV (energy rays for curing the liquid crystal layer)
H fever

Claims (10)

A transparent substrate;
An orientation-imparting layer laminated on the transparent substrate;
A refractive index anisotropic layer laminated on the orientation imparting layer and imparted with orientation by the orientation regulating force of the orientation imparting layer;
The orientation-imparting layer is composed of an orientation film formed from a composition for an orientation film capable of expressing the orientation regulating force by a photo-alignment method,
The refractive index anisotropic layer is composed of a liquid crystal layer formed by curing a liquid crystalline composition containing a polymerizable liquid crystal material, and is close to the orientation providing layer in the refractive index anisotropic layer. The degree of cure of the refractive-index anisotropic layer has a predetermined gradient with respect to the thickness direction so that the degree of cure of the part located in the region is larger than the degree of cure of the part located far from the orientation-imparting layer. An optical element characterized by having a monotonous change.   The optical element according to claim 1, wherein the refractive index anisotropic layer has an average degree of curing of 90% or more.   The optical element according to claim 1, wherein the liquid crystal composition for forming the refractive index anisotropic layer contains a nematic liquid crystal compound as the polymerizable liquid crystal material.   The optical element according to claim 1, wherein the alignment film composition for forming the orientation imparting layer contains a polymer having a cinnamoyl group.   The optical element according to claim 4, wherein the alignment film composition includes a monomer or oligomer having one or more functional groups in addition to the polymer.   The optical element according to claim 5, wherein the monomer or oligomer is a polymerizable liquid crystal material.   The polymerizable liquid crystal material in the orientation imparting layer and the polymerizable liquid crystal material in the refractive index anisotropic layer are the same type of material. Optical elements. A step of preparing a transparent substrate in which an alignment film formed from a composition for alignment film capable of expressing an alignment regulating force by a photo-alignment method is laminated as an alignment layer;
Applying a liquid crystalline composition containing a polymerizable liquid crystal material on the orientation-imparting layer of the transparent substrate;
While delaying the curing rate in the vicinity of the surface on the side not adjacent to the orientation imparting layer in the liquid crystalline composition as compared with the curing rate in the vicinity of the surface on the side adjacent to the orientation imparting layer, the liquid crystalline composition A refractive index anisotropic layer comprising a liquid crystal layer whose degree of cure monotonously changes with a predetermined gradient with respect to the thickness direction on the orientation imparting layer of the transparent substrate by curing the product And a step of forming the optical element.   In the step of forming the refractive index anisotropic layer, the liquid crystalline composition is irradiated with radiation in a state where only the side of the liquid crystalline composition not adjacent to the orientation providing layer is exposed to an air atmosphere. 9. A method according to claim 8, characterized in that   The method according to claim 9, wherein the radiation is ultraviolet light, and the liquid crystalline composition includes a polymerization initiator together with the polymerizable liquid crystal material.

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