JP2009051992A - Liquid crystal composition, optical element, and liquid crystal display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal composition, which can form a phase difference layer never yellowed even if the phase difference layer surface is irradiated with ultraviolet ray in ultraviolet cleaning during a manufacturing process, or never yellowed even if the surface is exposed to sunlight for a long time, an optical element having a phase difference layer formed using the liquid crystal composition, and a liquid crystal display device provided with the optical element. <P>SOLUTION: The liquid crystal composition is produced so as to contain at least a polymerizable liquid crystal compound for constituting the phase difference layer and a yellowing preventing agent for preventing yellowing of the phase difference layer even if exposed to ultraviolet ray or sunlight. The optical element is produced so as to be provided with a phase difference layer formed by applying the liquid crystal composition to a substrate surface. The liquid crystal display device is produced by using the optical element as a display-side substrate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal composition, an optical element including a retardation layer formed using the liquid crystal composition, and a liquid crystal display device including the optical element as a display-side substrate.

  In recent years, liquid crystal display devices have a great advantage of being thin and light and have low power consumption, and thus are actively used in display devices such as personal computers, mobile phones, and electronic notebooks. These liquid crystal display devices perform light switching by utilizing the birefringence of the driving liquid crystal material. Therefore, the liquid crystal display device has a viewing angle dependency derived from the birefringence of the driving liquid crystal, and various retardation layer forming films have been developed to solve this problem. This retardation layer forming film is usually produced by stretching a film of polyacrylate, polycarbonate, triacetyl cellulose or the like, and placed outside the liquid crystal cell.

However, the retardation layer forming film is usually used by being attached to a substrate using an adhesive, and the refractive index of the adhesive applied to the substrate is different from that of the retardation film, so that the display display surface There was a problem of causing irregular reflection. In particular, when the retardation film is attached to the outside of the substrate, there is a problem that the exposed film absorbs moisture and expands. Furthermore, the retardation film cannot be patterned in accordance with the pixel size of the display, and further has low heat resistance, so there are problems such as changes in optical characteristics due to shrinkage over time.

In contrast, recently, a method of forming a retardation layer inside a liquid crystal cell using a liquid crystal material such as a polymerizable liquid crystal or a polymer liquid crystal has been proposed. When a retardation layer is formed inside the liquid crystal cell, a method of forming a retardation layer by applying a liquid crystal material to the surface of the substrate on which the retardation layer is formed is employed. It is possible to easily control the alignment of the liquid crystal material applied to the substrate surface in a desired direction by forming an alignment film on the surface of the substrate in advance by a method such as rubbing, photo-alignment or ion beam. There is (for example, Patent Document 1). In particular, in a retardation layer formed by aligning a polymerizable liquid crystal compound vertically (homeotropic alignment) with respect to the substrate surface, various methods can be used to stabilize the vertical alignment of the polymerizable liquid crystal compound. It has been studied (for example, Patent Document 2). In addition, for the purpose of reducing the thickness of the display device and reducing the number of manufacturing steps, a polymerizable liquid crystal composition capable of obtaining homeotropic alignment without using an alignment film has been studied (for example, Patent Document 3).

Japanese Patent Laid-Open No. 10-319408 JP-A-11-240890 Special table 2004-524385 gazette

  The retardation layer composed of the polymerizable liquid crystal compound has various advantages as described above. However, the retardation layer is yellowed during the handling process of the optical element including the retardation layer or in use over time after commercialization. It was a problem.

As a result of examining the problem of the retardation layer in detail, the inventor has prepared a retardation layer prepared by curing a polymerizable liquid crystal compound in a deep ultraviolet cleaning step for cleaning the surface of the retardation layer. It is easy to be colored, and after the retardation layer is formed, it may be yellowed by a baking process performed as a manufacturing process of other components to be formed, and by being exposed to sunlight for a long time. It was also found that the retardation layer may turn yellow.

  The retardation layer is a layer for adjusting the phase of transmitted light transmitted through the optical element and performing optical compensation. However, as a result of yellowing of the layer, chromaticity as designed is not obtained, and as a result In a display device including the optical element, the color gamut of color display may be narrowed or high quality display may not be provided.

The present invention has been made in view of the above-mentioned problems, and does not turn yellow even when the surface of the retardation layer is irradiated with ultraviolet rays in ultraviolet cleaning during the manufacturing process, and is exposed to sunlight for a long period of time. However, it is an object of the present invention to provide a liquid crystal composition capable of forming a retardation layer that does not yellow. Still another object of the present invention is to provide an optical element including a retardation layer formed using the liquid crystal composition of the present invention, and a liquid crystal display device including the optical element. .

The present invention relates to a liquid crystal composition for forming a retardation layer, a polymerizable liquid crystal compound for constituting the retardation layer, and prevention of yellowing of the retardation layer even when exposed to ultraviolet rays or sunlight. It is characterized by containing at least a yellowing preventive agent.

That is, the present invention
A liquid crystal composition comprising a polymerizable liquid crystal compound and a yellowing inhibitor;
In the yellowing inhibitor, for example, an ultraviolet absorber and / or an antioxidant can be used, and in addition, the liquid crystal composition has other photopolymerization initiators and the like. A compound can be blended.

Still further the present invention provides:
A retardation layer is formed directly or indirectly on a light-transmitting substrate, and the retardation layer is formed by applying and curing the liquid crystal composition of the present invention on a substrate surface. An optical element,
Is a summary.

In addition, some terms used in this specification are defined as follows.
"Liquid crystal composition" is a composition that includes at least a polymerizable liquid crystal compound and a yellowing inhibitor, and is a mixture in which other substances used for forming a retardation layer are blended as necessary. And a composition in a solution state prepared by dissolving or suspending the above mixture in a solvent. Here, as the yellowing prevention agent, an ultraviolet absorber or an antioxidant may be used, or a mixture of an ultraviolet absorber and an antioxidant may be used. In the present specification, the liquid crystal composition of the present invention which is the above-described “composition in a solution state” is also referred to as a “liquid crystal composition solution” for convenience.

The “(meth) acryloyl group” is used as a general term for two functional groups, “acryloyl group” and “methacryloyl group”. Examples of acryloyl groups include acrylate groups (acryloyloxy groups), and methacryloyl groups include methacrylate groups.

“Comparison value of compound” means that when the liquid crystal composition of the present invention is the above mixture, each compound when the total weight of each compound formulated as a substance constituting the mixture is 100 In the case where the liquid crystal composition of the present invention is a solution obtained by dissolving or mixing the above-mentioned composition with a solvent, the weight obtained by subtracting the weight of the solvent from the weight of the solution (that is, dissolved or suspended in the solvent). It means the weight ratio of each compound when the total weight of each compound before turbidity is taken as 100.

The “retardation layer” means a layer having a retardation control function that can optically compensate for a change in retardation of light.

“Homeotropic alignment” refers to an alignment state in which the optical axes of liquid crystal molecules constituting the retardation layer rise perpendicularly or substantially perpendicularly to the substrate surface. Further, “the retardation layer is homeotropically aligned” means that liquid crystal molecules constituting the retardation layer are homeotropically aligned. In the present invention, the ideal homeotropic alignment of the liquid crystal molecules means that the xyz orthogonal coordinate is assumed in the x-axis direction when the xyz orthogonal coordinate is assumed with the thickness direction of the retardation layer as the z-axis. The refractive index ny is substantially the same value, and the phase difference value when the measurement angle is 0 ° is 4 nm or less, preferably 3.5 nm or less, more preferably 3 nm or less. .

  Since the liquid crystal composition of the present invention contains an anti-yellowing agent, the retardation layer formed using the liquid crystal composition of the present invention may be yellowed by irradiation with ultraviolet rays or sunlight. Absent. Therefore, for example, in the process of manufacturing an optical element having a retardation layer, the retardation layer does not turn yellow even when an ultraviolet cleaning process is performed.

If it is an optical element provided with the phase difference layer formed with the liquid-crystal composition of the said invention, there is no worry of yellowing, it exhibits the outstanding phase difference function and contributes greatly to the viewing angle improvement effect.

Particularly, in the optical element of the present invention, when the yellowness YI ₀ of the retardation layer is 1 or less and the yellowing degree before and after the ultraviolet treatment is measured according to JIS K 7373, it is 1.5 or less. If so, a very good display can be provided.

When the optical element of the present invention having the retardation layer is used as a display-side substrate of a liquid crystal display device, it provides a stable and excellent viewing angle improvement effect and provides a high-quality image display with a wide color gamut. be able to.

  Hereinafter, the best mode of a liquid crystal composition of the present invention, an optical element including a retardation layer formed using the liquid crystal composition, and a liquid crystal display device including the optical element will be described in order.

(About liquid crystal composition)
As described above, the liquid crystal composition of the present invention contains at least a polymerizable liquid crystal compound and a yellowing inhibitor. More specifically, the yellowing inhibitor includes an ultraviolet absorber or an antioxidant described later.
In addition, although the mechanism in which the phase difference layer comprised with a polymeric liquid crystal compound yellows is not clear, this inventor estimates as follows.
As a first mechanism, it is presumed that organic matter is oxidized due to generation of active oxygen (free radical). That is, it is known that oxygen molecules absorb deep ultraviolet rays (deep UV) of 182 nm to become ozone, and further this ozone absorbs deep ultraviolet rays (deep UV) of 254 nm to generate active oxygen. Even during the manufacturing process of the optical element, the above reaction occurs due to the ultraviolet rays used in the ultraviolet cleaning step of the surface of the retardation layer, and the resulting active oxygen is oxidized to the inside of the retardation layer to cause the retardation layer to yellow. Inferred to change.
As a second mechanism, when a liquid crystal compound having an aromatic ring in the molecule is used among the polymerizable liquid crystal compounds, the molecular structure is mutated after the aromatic ring absorbs far ultraviolet rays and is excited. As a result, it is assumed that the absorption wavelength of the liquid crystal molecules is shifted and yellowing occurs in the retardation layer.

Polymerizable liquid crystal compound:
As the polymerizable liquid crystal compound used in the liquid crystal composition of the present invention, a crosslinkable nematic liquid crystal can be used. As the crosslinkable nematic liquid crystal, for example, a (meth) acryloyl group, an epoxy group, an oktacene group, Monomers, oligomers, polymers and the like having at least one polymerizable group such as an isocyanate group can be mentioned. As such a polymerizable liquid crystal compound, one or more of a compound represented by the general formula (1) shown in the following chemical formula 1 and a compound represented by the general formula (2) shown in the following chemical formula 2 are used. A mixture of these compounds, one or a mixture of two or more of the compounds shown in Chemical Formula 3 and Chemical Formula 4, or a mixture of these may be used. In particular, it is preferable that at least one of the crosslinkable nematic liquid crystal molecules constituting the polymerizable liquid crystal compound in the present invention has one or more (meth) acryloyl groups in one molecule.

In the general formula (1) shown in Chemical Formula 1, R ¹ and R ² each represent hydrogen or a methyl group, but R ¹ or R ² is preferably hydrogen in order to broaden the temperature range showing the liquid crystal phase. R ¹ and R ² are more preferably hydrogen. X in the general formula (1) and Y in the general formula (2) may be any of hydrogen, chlorine, bromine, iodine, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a cyano group, or a nitro group. Is preferably a chlorine or methyl group. Moreover, a and b which show the chain length of the alkylene group between the (meth) acryloyloxy group and aromatic ring of the both ends of the molecular chain of General formula (1), and d and e in General formula (2) are respectively 2 Although an arbitrary integer can be taken in the range of -12, it is preferable that it is the range of 4-10, and it is further more preferable that it is the range of 6-9. General formula (1) in which a = b = 0 or general formula (2) in which d = e = 0 is poor in stability, is susceptible to hydrolysis, and has high crystallinity. Further, the general formula (1) or the general formula (2) in which a and b or d and e are each 13 or more has a low isotropic phase transition temperature (TI). For this reason, both of these compounds have a narrow temperature range (temperature range in which the liquid crystal phase is maintained) that stably exhibits liquid crystallinity, and are not preferable for use in the birefringence functional layer composition liquid.
Although the monomer of the polymerizable liquid crystal compound is exemplified in the above-described chemical formula 1 to chemical formula 4, an oligomer of the polymerizable liquid crystal compound, a polymer of the polymerizable liquid crystal compound, and the like can be appropriately selected from conventionally known ones. In general, the retardation amount and orientation characteristics of the retardation layer are determined by the birefringence Δn of the polymerizable liquid crystal compound and the thickness of the retardation layer. For example, when forming a retardation layer formed by homeotropic alignment of a polymerizable liquid crystal monomer, that is, a so-called positive C plate, Δn of the polymerizable liquid crystal monomer is preferably about 0.03 to 0.20, 0.05 to 0 About 15 is more preferable.

In the liquid crystal composition of the present invention, the polymerizable liquid crystal compound is preferably contained so as to be 70% by weight (compared to the compound equivalent) or more preferably 75% by weight (compared to the compound equivalent). By making the addition amount 70% by weight (vs. compound equivalent) or more, the liquid crystallinity is improved, and the occurrence of poor alignment of the polymerizable liquid crystal compound in the retardation layer can be reduced to a negligible level. When the addition of the polymerizable liquid crystal compound is 70% by weight or more (as a value in terms of the compound), there is no particular problem from the viewpoint of the orientation of the liquid crystal molecules, so the amount of the other additive in the liquid crystal composition The addition amount can be determined as appropriate based on the balance.

Yellowing prevention agent:
The liquid crystal composition of the present invention contains a yellowing inhibitor, and examples of the yellowing inhibitor include an ultraviolet absorber and an antioxidant. By adding a yellowing inhibitor to the liquid crystal composition containing the polymerizable liquid crystal compound, the retardation layer formed using the liquid crystal composition is irradiated with ultraviolet rays or exposed to sunlight for a long time. Even if it is done, it does not turn yellow. Although the mechanism for preventing yellowing is not clear, it is considered that the yellowing inhibitor effectively blocks the absorption and oxidation reaction of ultraviolet rays in the mechanism of yellowing estimated above.

Examples of the ultraviolet absorber include 2-hydroxy-octyloxybenzophenone (Sumisorb 130 manufactured by Sumitomo Chemical Co., Ltd.), 2,4-dihydroxybenzophenone (SEESORB100 manufactured by Cypro Kasei Co., Ltd.), and 2-hydroxy-4-methoxybenzophenone (manufactured by Cypro Kasei Co. SEESORB101), 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid trihydrate (SEESORB101S manufactured by Cypro Kasei), 4-dodecyloxy-2-hydroxybenzophenone (SEESORB103 manufactured by Cypro Kasei), 2, 2'4 4′-tetrahydroxybenzophenone (SEESORB106 manufactured by Cypro Kasei Co., Ltd.), 2,2′-dihydroxy-4,4′-dimethoxybenzophenone (SEESORB107 manufactured by Cypro Kasei Co., Ltd.), 1,4-bis (4- Benzophenone ultraviolet absorbers such as Nzoyl-3-hydroxyphenoxy) -butane (SEESORB151 manufactured by Cypro Kasei Co., Ltd.), 2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole (SEESORB 701 manufactured by Cypro Kasei Co., Ltd.), 2 -(3-tert-butyl-2-hydroxy-5-methylphenyl) -5-chloro-2H-benzotriazole (SEESORB703 manufactured by Cypro Kasei Co., Ltd.), 2- (3,5-di-tert-pentyl-2-hydroxy Phenyl) -2H-benzotriazole (SEESORB 704 manufactured by Cypro Kasei Co., Ltd.), 2- (2H-benzotriazol-2-yl) -4-methyl-6- (3,4,5,6-tetrahydrophthalimidyl) methylphenol (SEPRORB 706 manufactured by Sipro Kasei Co., Ltd.), 2- (2 Benzo such as hydroxy-4-octyloxyphenyl) -2H-benzotriazole (SEESORB 707 manufactured by Cypro Kasei), 2- (2-hydroxy-5-tert-octylphenyl) -2H-benzotriazole (SEESORB 709 manufactured by Cypro Kasei) Triazole-based ultraviolet absorbers, phenyl salicylate (SEPRORB201 manufactured by Sipro Kasei), 4-tert-butylphenyl salicate (SEESORB 202 manufactured by Sipro Kasei), ethyl 2-cyano-3,3-diphenyl acrylate (Cipro Kasei) SEESORB 501), 2′-ethylhexyl 2-cyano-3,3-diphenyl acrylate (SEESORB 502 manufactured by Cypro Kasei Co., Ltd.), 2 ′, 4′-di-tert-butylphenyl 3,5-di-tert-butyl-4 − An ultraviolet absorber such as hydroxybenzoate (SEESORB712 manufactured by Sipro Kasei Co., Ltd.) can be used.

  In particular, the ultraviolet absorber preferably has a maximum absorption wavelength of around 254 nm. By incorporating an ultraviolet absorber in the retardation layer at the maximum absorption wavelength of about 254 nm, when the retardation layer is irradiated with ultraviolet rays, the absorption of far ultraviolet rays into the retardation layer can be reduced, and the absorption of far ultraviolet rays This is because the yellowing of the retardation layer due to the variation in the molecular structure due to can be prevented well.

Examples of the antioxidant include 2,6-di-tert-butyl-p-cresol (Yosinox BHT manufactured by API Corporation), 4,4′-butylidenebis- (6-tert-butyl-3-methylphenol) ( Yoshinox BB manufactured by API Corporation), 2,2'-methylenebis- (4-methyl-6-tert-butylphenol) (Yoshinox 2246G manufactured by API Corporation), 2,2'-methylenebis- (4-ethyl-6) -Tert-butylphenol (Yoshinox 425 manufactured by API Corporation), 2,6-di-tert-butyl-4-ethylphenol (250 manufactured by API Corporation), 1,1,3-tris (2-methyl-4 Hydroxy-5-butylphenyl) bu (Yoshinox 930 manufactured by API Corporation), n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Tominox SS manufactured by API Corporation), tetrakis [methylene-3 -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane (Tominox TT manufactured by API Corporation), triethylene glycol bis [3- (3-tert-butyl-4-hydroxy-5 -Methylphenyl) propionate] (Tominox 917 manufactured by API Corporation), tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Yosinox 314 manufactured by API Corporation), and the like. Nol antioxidant, dilauryl thiodipropionate (DLTP manufactured by API Corporation), distearyl thiodipropionate (DSTP manufactured by API Corporation), dimyristyl thiodipropionate (DMTP manufactured by API Corporation) , Sulfur-based antioxidants such as ditridecylthiodipropionate (DTTP manufactured by API Corporation), N-isopropyl-N′-phenyl-p-phenylenediamine (Antage 3C manufactured by Kawaguchi Chemical Co., Ltd.), N- (1 , 3-Dimethylbutyl) -N′-phenyl-p-phenylenediamine (Antage 6C manufactured by Kawaguchi Chemical Industry Co., Ltd.), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (manufactured by Kawaguchi Chemical Industrial Co., Ltd.) Amines such as (Antage AW) Antioxidants can be used. In the present invention, two or more different anti-yellowing agents can be used in combination.

In the above yellowing inhibitor, the content of the liquid crystal composition of the present invention is 0.1 to 10% by weight (compared to a compounded value), preferably 0.5 to 3% by weight (compared to a compounded value). Add as follows. In addition, in the following description of this specification, when it describes as "weight%" without a notice, it shall mean the conversion value with respect to a compound in the composition of this invention. By adding 0.1% by weight or more of the yellowing inhibitor, it is possible to impart sufficient yellowing resistance to the retardation layer, and by adding 10% by weight or less, yellowing can be achieved. By adding the inhibitor, it is possible to suppress an alignment failure of liquid crystal molecules in the retardation layer or a decrease in electrical reliability of the retardation layer to a negligible level.
The compounding ratio of the polymerizable liquid crystal compound used in the liquid crystal composition of the present invention and the yellowing inhibitor is preferably 100: 5 to 100: 3. As the yellowing inhibitor, either an ultraviolet absorber or an antioxidant, or a mixture of an ultraviolet absorber and an antioxidant can be used. When the ultraviolet absorber and the antioxidant are mixed and used, the total amount of these may be within a preferable range of the blending ratio of the yellowing inhibitor described above.

Photopolymerization initiator:
When the polymerizable liquid crystal compound used in the present invention is photopolymerizable, a photopolymerization initiator can be further added to the liquid crystal composition of the present invention.
When the liquid crystal composition of the present invention is applied onto a substrate to form a retardation layer, the photopolymerization initiator irradiates the applied liquid crystal composition with ultraviolet rays or the like, and is contained in the composition. It acts as an initiator for polymerizing the liquid crystalline compound. As the photopolymerization initiator, a radical polymerizable initiator can be used. Radical polymerizable initiators are compounds that generate free radicals by the energy of ultraviolet rays, for example, benzophenone derivatives such as benzoin and benzophenone or derivatives thereof; xanthone and thioxanthone derivatives; chlorosulfonyl, chloromethyl polynuclear aromatic compounds Halogen-containing compounds such as chloromethyl heterocyclic compounds and chloromethylbenzophenones; triazines; fluorenones; haloalkanes; redox couples of a photoreductive dye and a reducing agent; organic sulfur compounds; It is done. More specific examples of the photopolymerization initiator include Irgacure 184, Irgacure 369, Irgacure 651, Irgacure 907 (all manufactured by Ciba Specialty Chemicals), Darocur (Merck), Adeka 1717. (Asahi Denka Kogyo Co., Ltd.), 2,2′-bis (o-chlorophenyl) -4,5,4′-tetraphenyl-1,2′-biimidazole (Kurokin Kasei Co., Ltd.) and other ketones Biimidazole compounds and the like are preferably used. These photopolymerization initiators can be used alone or in combination of two or more. When using 2 or more types together, it is preferable to combine initiators having different absorption wavelengths so as not to inhibit the absorption spectral characteristics.
The liquid crystal composition of the present invention containing the photopolymerization initiator is applied onto a substrate to form a coating film, and after aligning the polymerizable liquid crystal compound present in the coating film, the photopolymerization is started. By irradiating the coating film with light having a photosensitive wavelength of the agent, the aligned polymerizable liquid crystal compounds can be favorably crosslinked and polymerized.

It is necessary to add the photopolymerization initiator within a range that does not significantly impair the alignment of the liquid crystal. It is added so that it may become 5 to 8 weight% (vs. compound conversion value), more preferably 1 to 5 wt% (vs. compound conversion value). When using 2 or more types of photopolymerization agents together, it adjusts so that the weight ratio of the total amount of the photopolymerization agents used may be in the said numerical range.

In the liquid crystal composition of the present invention composed of a polymerizable liquid crystal compound, a yellowing inhibitor, and a photopolymerization initiator, the blending ratio of these three blends is adjusted as appropriate within the preferred range described above. In addition, as the yellowing prevention agent, either the ultraviolet absorber or the antioxidant, or a mixture of the ultraviolet absorber and the antioxidant can be used. In particular, it is desirable that the polymerizable liquid crystal compound is adjusted to 92% by weight, the ultraviolet absorber is 3%, and the photopolymerization initiator is 5%.

solvent:
The liquid crystal composition of the present invention can be used for forming a retardation layer by directly applying, aligning and curing on a substrate. In such a case, in order to improve applicability, among the liquid crystal compositions of the present invention, in particular, a liquid crystal composition solution in which a compound such as a polymerizable liquid crystal compound or a yellowing inhibitor is dissolved in a solvent is used. Is preferred.

The solvent is not particularly limited as long as it can dissolve solid components such as the above-described polymerizable liquid crystal compound and yellowing inhibitor, and does not impair the performance of the counterpart material to be applied. Specifically, hydrocarbons such as benzene, toluene, xylene, n-butylbenzene, diethylbenzene and tetralin, ethers such as methoxybenzene, 1,2-dimethoxybenzene and diethylene glycol dimethyl ether, acetone, methyl ethyl ketone, methyl isobutyl ketone, Ketones such as cyclohexanone and 2,4-pentanedione, ethyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone, 2-pyrrolidone, N-methyl Amide solvents such as 2-pyrrolidone, dimethylformamide, dimethylacetamide, chloroform, dichloromethane, carbon tetrachloride, dichloroethane Halogen solvents such as tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene, t-butyl alcohol, diacetone alcohol, glycerin, monoacetin, ethylene glycol, triethylene glycol, hexylene glycol, ethylene glycol monomethyl ether, ethyl cellosolve, Alcohols such as butyl cellosolve, phenols such as phenol and parachlorophenol, and the like can be used alone or in admixture of two or more. In cases where the use of a single solvent is insufficient in the solubility of the solids such as the polymerizable liquid crystal compound, or the material on the other side (ie, the colored layer surface) to be applied may be affected. These disadvantages can be avoided by using a mixture of two or more solvents. Among the above-mentioned solvents, hydrocarbon solvents, glycol monoether acetate solvents and the like are particularly preferable as the solvent used alone. Similarly, a particularly preferable solvent used by mixing two or more kinds includes a mixed system of ethers or ketones and glycols. The concentration of the liquid crystal composition solution of the present invention varies depending on the solubility of the solid content contained in the composition and the desired thickness of the retardation layer formed using the composition, but is usually 1 to 60% by weight. It is preferable to prepare at a concentration, particularly 3 to 40% by weight. The concentration can be obtained by multiplying the weight obtained by subtracting the weight of the solvent from the weight of the liquid crystal composition solution by the total weight of the liquid crystal composition solution and multiplying by 100.

Other additives:
In addition to the photopolymerization initiator, the liquid crystal composition of the present invention may contain a polymerization inhibitor that can control the polymerization rate in a range that does not impair the purpose, and absorbs electromagnetic waves such as ultraviolet rays. It is also possible to add a sensitizer for assisting. Examples of polymerization inhibitors include p-benzoquinone, hydroquinone, pt-butylcatechol, di-t-butyl paracresol, 2,4,6-tri-tert-butylphenol, hydroquinone monomethyl ether, α-naphthol or Acetanidin acetate or the like can be used. Further, a surfactant or a vertical alignment aid can be added as appropriate.

Vertical alignment aid:
The addition of the vertical alignment aid is effective particularly when forming a retardation layer homeotropically aligned directly or indirectly on the upper surface of the substrate using the liquid crystal composition of the present invention. That is, due to the presence of the vertical alignment aid, the liquid crystal composition is directly applied to the upper surface of the substrate without the presence of an alignment film, and the polymerizable liquid crystal compound contained in the liquid crystal composition is vertically aligned (homeotropic alignment). It is possible to make it. Thus, by cross-linking and fixing the vertically aligned liquid crystal compound, the optical axis of the liquid crystal molecules is oriented in the normal direction of the retardation layer, and an extraordinary ray refractive index greater than the ordinary ray refractive index is provided in the retardation layer. A so-called positive C plate having the normal direction can be formed.

  Examples of vertical alignment aids include surface coupling agents having vertically aligned alkyl or fluorocarbon chains such as lecithin and quaternary ammonium surfactants, HTAB (hexadecyl-trimethylammonium bromide), DMOAP (N, (N-dimethyl-N-octadecyl-3-aminopropyltrimethoxysilyl chloride), N-perfluorooctylsulfonyl-3-aminopropyltrimethylammonium iodide, long-chain alkyl alcohol or silane polymer.

(About optical elements)
The liquid crystal composition of the present invention can form a retardation layer that is irradiated with ultraviolet rays as described above, subjected to a baking process, or does not turn yellow even when exposed to sunlight for a long time. Therefore, the optical element of the present invention having the retardation layer can obtain excellent chromaticity as designed, can provide a high-quality image, and the quality is maintained. And a liquid crystal display provided with the optical element of this invention exhibits the outstanding viewing angle improvement effect. Hereinafter, an optical element provided with a retardation layer will be exemplarily described based on the drawings.

FIG. 1 shows an optical element 1 according to an embodiment of the present invention. In order to form the optical element 1, first, the colored layer 3 is provided on the light-transmitting substrate 2, and then the liquid crystal composition solution of the present invention is applied onto the colored layer 3 and contained in the liquid crystal composition solution. The polymerizable liquid crystal compound is aligned in a desired direction, then cross-linked and fixed to form the retardation layer 4. Further, the optical element 1 of the present invention is formed by arranging a plurality of spacers 9 made of a cured product of the ionizing radiation curable resin composition on the upper surface of the retardation layer 4 at an arbitrary interval.
In addition, although the protective layer is not formed in the optical element 1 shown in FIG. 1, it protects in arbitrary positions, such as between the colored layer 3 and the phase difference layer 4, or the upper surface of the phase difference layer 4 in this invention. A layer may be formed. In consideration of the type of driving liquid crystal material used in the liquid crystal display device, a functional layer used for a display-side substrate of a generally known liquid crystal display device may be appropriately formed in the optical element of the present invention. . Below, the structure and formation method of each layer are demonstrated using the optical element 1 of this invention shown in FIG.

Substrate having optical transparency:
The substrate 2 used in the present invention preferably has optical transparency and is optically isotropic. However, if necessary, a region having optical anisotropy or light shielding properties can be locally provided. The light transmittance can be appropriately selected according to the use of the optical element. Specifically, a plate, a sheet, or a film formed of an inorganic material or an organic material can be used. Examples of the inorganic material include glass, silicon, and quartz. In particular, when the optical element of the present invention is used for a liquid crystal display, it is preferable to use an alkali-free glass containing no alkali component in the glass as the substrate. Quartz is preferred from the viewpoint of low thermal expansion and good dimensional stability and excellent workability in high-temperature heat treatment. On the other hand, as the organic substrate, acrylic such as polymethyl methacrylate, polyamide, polyacetal, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, triacetyl cellulose, or syndiotactic polystyrene, polyphenylene sulfide, polyether ketone, Polyetheretherketone, fluororesin, polyethernitrile, etc., polycarbonate, modified polyphenylene ether, polycyclohexene, polynorbornene resin, etc., or polysulfone, polyethersulfone, polypropylene, polyarylate, polyamideimide, polyetherimide , Polyetherketone, or thermoplastic polyimide. It can be used those composed of specific plastics. Regarding the thickness of the light-transmitting substrate 2, for example, a thickness of about 5 μm to 3 mm is used depending on the application.

Colored layer:
The colored layer 3 is a red (R) sub-pixel which is a colored pixel that forms a black matrix 5 that blocks visible light in a predetermined wavelength region on a light-transmitting substrate 2 and then transmits visible light in a predetermined wavelength region. 6, green (G) sub-pixel 7 and blue (B) sub-pixel 8 are sequentially provided.
The black matrix 5 is also referred to as red (R) sub-pixel 6, green (G) sub-pixel 7, and blue (B) sub-pixel 8 (hereinafter simply referred to as “colored pixels 6, 7, 8”) that are colored pixels. ) Prevents overlapping of each other and fills the gaps between the colored pixels to suppress leakage of light from adjacent colored pixels (leakage light). Accordingly, the black matrix 5 is formed on the light-transmitting substrate 2 so as to partition the area corresponding to the position where the colored pixels 6, 7, and 8 are planned to be arranged in a plan view for each colored pixel. The The colored pixels 6, 7, and 8 are each arranged so as to cover the area partitioned by the black matrix 5 in plan view.
The black matrix 5 can be formed by patterning a light-shielding or light-absorbing metal thin film such as a metal chromium thin film or a tungsten thin film on the surface of the light-transmitting substrate 2 in a predetermined shape. The black matrix 5 can also be formed by printing an organic material such as a black resin in a predetermined shape by an inkjet method or the like.

The colored pixels 6, 7, and 8 formed after the black matrix 5 are formed by arranging colored pixels that transmit light of each color wavelength band in a predetermined pattern for each of red, green, and blue. The arrangement form of the red (R) sub-pixel 6, the green (G) sub-pixel 7, and the blue (B) sub-pixel 8 constituting the coloring pixel is various arrangement patterns such as a stripe type, a mosaic type, and a triangle type. Can be selected. More specifically, each colored pixel 6, 7, 8 is formed by patterning a coating film of a coloring material dispersion liquid in which a coloring material is dispersed in a solvent into a predetermined shape by, for example, a photolithography method. be able to. As another method, it can be formed by applying a coloring material dispersion liquid in a predetermined shape for each of the colored pixels 6, 7, and 8 by an ink jet method or the like. In addition, instead of the red (R) sub-pixel 6, the green (G) sub-pixel 7, and the blue (B) sub-pixel 8, a colored pixel that transmits light in the wavelength band of the complementary color of each color is used. Is also possible.
The colored layer 3 in the present invention is not limited to the case where the three-color sub-pixels exemplified above are provided. For example, it may be composed of four or more colored pixels, or may be composed of a single color or two colors. In accordance with this, the black matrix 5 can be omitted.

In general, the surface of the colored layer 3 is subjected to a surface modification treatment such as a deep ultraviolet cleaning treatment or a corona treatment before the retardation layer 4 is formed after the colored layer 3 is formed. By performing such a treatment, the wettability with respect to the liquid crystal composition applied to the surface of the colored layer, particularly the polymerizable liquid crystal compound contained therein, can be improved.

When performing the deep-UV cleaning process, the amount of UV irradiation ^{500mJ / cm 2 ~3000mJ / cm 2} , more preferably at a range of ^{900mJ / cm 2 ~3000mJ / cm 2} . The 500 mJ / cm ² or less of the dose, it is impossible to impart sufficient wettability to the substrate surface, in 3000 mJ / cm ² or more dose, there is a problem such optical element is discolored.

Retardation layer:
Next, the retardation layer 4 will be described. The retardation layer 4 in the optical element 1 of the present invention is polymerized by coating the liquid crystal composition of the present invention on the upper surface of the colored layer 3, homeotropic alignment of the polymerizable liquid crystal compound in the liquid crystal composition, and crosslinking polymerization. It can be formed by fixing the liquid crystalline compound in a homeotropically aligned state. At this time, it is desirable to use a liquid crystal composition in a solution state, that is, a liquid crystal composition solution so that the liquid crystal composition can be easily applied to the surface of the colored layer 3.

Examples of methods for applying the liquid crystal composition solution onto the colored layer 3 include various printing methods such as gravure printing, offset printing, relief printing, screen printing, transfer printing, electrostatic printing, and plateless printing. Coating method such as gravure coating method, roll coating method, knife coating method, air knife coating method, bar coating method, dip coating method, kiss coating method, spray coating method, die coating method, comma coating method, ink jet method, etc. Combination methods can be used as appropriate.
Then, a coated substrate coated with the liquid crystal composition solution (hereinafter, also simply referred to as “coated substrate”, and a layer formed on the surface of the coated substrate is also referred to as “coated film”) is dried. The drying may be naturally dried under atmospheric pressure, but the solvent in the liquid crystal composition solution is vaporized by reducing the pressure to about 1.5 × 10 ⁻¹ Torr or less in a sealed container and performing a drying under reduced pressure. Is desirable.

In the drying under reduced pressure, simultaneously with drying, the polymerizable liquid crystal compound contained in the liquid crystal composition can be aligned in the direction perpendicular to the substrate surface, that is, homeotropically aligned. In such a method, the coating film can be brought into a supercooled state by bringing the coating substrate into a reduced pressure state, and the polymerizable liquid crystal compound contained in the coating film is homeotropically aligned, and then this coating is maintained while maintaining this state. Bring the substrate to room temperature. Thereby, the polymerizable liquid crystal compound can be efficiently maintained in a homeotropic alignment state until a crosslinking reaction is performed in the subsequent steps. Furthermore, in order to remove the remaining solvent and to ensure the orientation of the polymerizable liquid crystal compound contained in the coating film, the coated substrate may be baked. The firing method is not particularly limited, but for example, a coated substrate can be placed on a hot plate and fired at a temperature range of 70 ° C. to 120 ° C. for about 2 minutes to 30 minutes.
The above description does not limit the alignment treatment for homeotropic alignment of the polymerizable liquid crystal compound contained in the liquid crystal composition of the present invention. A method generally known as an alignment treatment for homeotropic alignment of a polymerizable liquid crystal compound, for example, a method of applying an electric field or a magnetic field from a predetermined direction to the coating film can be appropriately selected and used.

Next, the polymerizable liquid crystal compound that is homeotropically aligned in the coating film is cross-linked to fix the alignment. This cross-linking reaction proceeds by irradiating the coating film surface with light. At this time, the wavelength of light applied to the coating film is appropriately selected according to the absorption wavelength of the liquid crystal composition constituting the coating film. More specifically, it is appropriately selected according to the absorption wavelength of the photopolymerization initiator contained in the liquid crystal composition. The light applied to the coating film is not limited to monochromatic light but may be light having a certain wavelength range including the photosensitive wavelength of the polymerizable liquid crystal compound. Specifically, it is common to irradiate active radiation such as ultraviolet rays. For example, when the polymerizable liquid crystal compound is cross-linked and cured by irradiating with ultraviolet rays, the ultraviolet rays having a wavelength of about 200 to 500 nm are generally irradiated. As the ultraviolet light source, a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, or the like is used. The amount of irradiation light varies depending on the type and composition of the polymerizable liquid crystal compound and the type and amount of the photopolymerization initiator, but is usually about 10 to 3000 mJ / cm ² .

  The crosslinking reaction of the polymerizable liquid crystal compound is preferably performed while heating the coated substrate to a temperature 1 to 10 ° C. lower than the temperature at which the liquid crystal phase transitions from the liquid crystal phase to the isotropic phase. By doing so, disorder of homeotropic alignment of the liquid crystal can be reduced during the crosslinking reaction. From this viewpoint, the temperature at which the crosslinking reaction is carried out is more preferably 3 to 6 ° C. lower than the temperature at which the liquid crystal transitions from the liquid crystal phase to the isotropic phase.

  As another method of crosslinking reaction of the polymerizable liquid crystal compound, the coating film may be irradiated with light having a photosensitive wavelength of the polymerizable liquid crystal compound while heating the coated substrate to the liquid crystal phase temperature in an inert gas atmosphere. it can. In this method, the liquid crystal molecules are cross-linked under an inert atmosphere, and compared with the case where the liquid crystal molecules are cross-linked under an air atmosphere, the liquid crystal molecules located at a position away from the substrate (that is, the liquid crystal molecules close to the coating film surface) ) Is preferable in that disorder of homeotropic alignment can be suppressed.

As another method for the crosslinking reaction of the polymerizable liquid crystal compound, the coating film is irradiated with light having a photosensitive wavelength of the polymerizable liquid crystal compound while heating the coated substrate to the liquid crystal phase temperature in an inert gas atmosphere or an air atmosphere. Then, the crosslinking reaction is partially advanced (referred to as a partial crosslinking step), and after the partial crosslinking step, the coated substrate is cooled to a temperature (Tc) at which the liquid crystal becomes a crystalline phase. It can also be completed by irradiating light on the coating film of the coated substrate to advance the crosslinking reaction. The temperature Tc described above is a temperature at which the liquid crystal molecules become a crystal phase on the coated substrate before the crosslinking reaction proceeds.

  In the partial crosslinking step, the crosslinking reaction proceeds to such an extent that the homeotropic orientation of the polymerizable liquid crystal compound contained in the coating film is maintained even when the coated substrate is cooled to the temperature Tc. Accordingly, the degree of progress of the crosslinking reaction in the partial crosslinking step is appropriately selected according to the type of the polymerizable liquid crystal compound 5 contained in the coating film, the film thickness of the coating film, and the like. The crosslinking reaction is preferably allowed to proceed until the degree of crosslinking of the compound is 5-50.

Thus, a base material having the colored layer 3 and the retardation layer 4 in which the polymerizable liquid crystal compound is homeotropically aligned and cross-linked and the alignment is fixed is formed on the light-transmitting substrate 2. In the above description, the optical element 1 in which the light transmissive substrate 2, the colored layer 3, and the retardation layer 4 are sequentially formed has been described as one embodiment of the present invention. However, the configuration of the present invention is not limited to this, For example, an optical element in which a transparent substrate, a retardation layer, and a colored layer are sequentially formed is not excluded, and an optical element that includes the substrate 2 and the retardation layer 4 without the colored layer 3 may be used. In addition, although there is no restriction | limiting in particular in the thickness of the phase difference layer 4, About 0.5-10 micrometers is preferable normally considering productivity etc.

  In the above description, the example in which the retardation layer 4 is formed by homeotropic alignment of the polymerizable liquid crystal compound is shown. However, the retardation layer in the optical element of the present invention is not limited to a so-called positive C plate. Absent. For example, by using the liquid crystal composition of the present invention, the optical axis of liquid crystal molecules is parallel to the retardation layer and has an extraordinary ray refractive index larger than the ordinary ray refractive index in the in-plane direction of the retardation layer. A retardation layer can be formed as the A plate. In such a case, the polymerizable liquid crystal compound is loaded with the alignment regulating force by the horizontal alignment film subjected to rubbing treatment or the like, or a leveling agent for suppressing the surface free energy of the liquid crystal molecules with respect to the air interface is added to the liquid crystal composition. Thus, the liquid crystal molecules can be horizontally aligned.

  Furthermore, using the liquid crystal composition of the present invention, the optical axis of the liquid crystal molecules is parallel to the retardation layer and has an extraordinary ray refractive index smaller than the ordinary ray refractive index in the normal direction of the retardation layer. C plates can be made. The negative C plate means a retardation layer in which a chiral nematic liquid crystal structure is realized by imparting cholesteric regularity to the polymerizable liquid crystal compound contained in the liquid crystal composition. Specifically, a known chiral agent may be added after the polymerizable liquid crystal compound is horizontally aligned in the same manner as the positive A plate. The chiral agent used in the present invention is not particularly required to have crosslinkability, but in consideration of the thermal stability of the obtained retardation layer, the polymerizable liquid crystal compound contained in the liquid crystal composition and It is preferable to use a chiral agent having a crosslinking performance that can be polymerized and fix a state in which the polymerizable liquid crystal compound is imparted with cholesteric regularity. As such a chiral agent, those having a crosslinkable functional group at both ends of the molecular structure are more preferable for improving the heat resistance of the retardation layer.

Deep UV cleaning treatment of the surface of the retardation layer:
In general, after forming the retardation layer 4 as described above, the surface of the retardation layer 4 is subjected to a deep ultraviolet cleaning treatment. By the ultraviolet cleaning treatment, the surface of the retardation layer 4 can be cleaned, and the wettability of the spacer 9 forming composition applied to the surface of the retardation layer 4 in a later step can be improved.

The deep ultraviolet cleaning process is performed as follows.
When performing the deep-UV cleaning process, the amount of UV irradiation ^{500mJ / cm 2 ~3000mJ / cm 2} , more preferably at a range of ^{900mJ / cm 2 ~3000mJ / cm 2} . The 500 mJ / cm ² or less of the dose, it is impossible to impart sufficient wettability to the substrate surface, in 3000 mJ / cm ² or more dose, the surface roughness is deteriorated, it may cause problems in flatness is there.
Conventionally, there has been a case where yellowing of the retardation layer is caused by performing the above ultraviolet treatment, but the present invention forms the retardation layer with the liquid crystal composition containing the yellowing prevention agent. The yellowing of the retardation layer is prevented by the action of the yellowing inhibitor.

The optical element 1 of the present invention is completed by further forming a spacer 9 on the retardation layer 4 in the base material.

spacer:
The spacer 9 is formed by applying a photocurable photosensitive paint made of a material such as an acrylic, amide or ester polymer containing a polyfunctional acrylate onto the retardation layer 4 and drying it. After the paint is cured by exposure through a mask pattern corresponding to the planned formation position 9, the uncured portion is removed by etching, and the whole is baked.

When a protective layer is provided in the optical element of the present invention, the protective layer is a transparent resin material made of a material such as an acrylic, amide or ester polymer containing a polyfunctional acrylate, or a polyfunctional epoxy. It can be formed by applying, drying, and curing a transparent resin coating made of a material such as an acrylic, amide, or ester-based polymer.

The optical element of the present invention obtained as described above has very little yellowing and exhibits a stable and excellent viewing angle improvement effect when the substrate is used in a liquid crystal display device.
In addition, although the optical element 1 which is one Embodiment of this invention was demonstrated above, the optical element of this invention does not necessarily need to provide a colored layer and a spacer. Moreover, it does not deny that the optical element of this invention is equipped with the member required when using as a display side board | substrate in a liquid crystal display device, for example, a transparent conductive film. The optical element of the present invention needs to have at least a transparent substrate and a retardation layer. In particular, the retardation layer contains a yellowing inhibitor, and as a result, the retardation layer is yellowed. It is important that this is prevented.

(About evaluation of liquid crystal composition and retardation layer)
It is important that the retardation layer formed by the liquid crystal composition of the present invention does not turn yellow due to the influence of ultraviolet rays or sunlight, and good alignment is realized because the retardation layer functions sufficiently. It is important that Therefore, the retardation layer formed using the liquid crystal composition of the present invention is comprehensively evaluated by evaluation of orientation, measurement of chromaticity, and evaluation of yellowing.

In the liquid crystal composition of the present invention, a retardation layer is formed on a glass substrate using the liquid crystal composition, and this is used as a sample to measure chromaticity and evaluate yellowing in the same manner as the retardation layer. Thus, it is evaluated that the liquid crystal composition can form a retardation layer without a yellowing problem.
In the present invention, when a yellowing evaluation test of a liquid crystal composition is performed, the liquid crystal composition to be subjected to the test is directly applied on a glass substrate and oriented in a desired direction, and then ultraviolet rays are applied at 20 mW / cm. ² for 10 seconds to cross-link the polymerizable liquid crystal compound contained in the liquid crystal composition solution, and then baked in an oven at 230 ° C. for 30 minutes to have a retardation layer having a thickness of 1.0 μm. Can be evaluated by calculating the yellowness YI ₀ and the yellowing degree ΔYI in the same manner as described later, using as a sample of the optical element and the glass substrate as a reference.

Orientation evaluation:
Whether or not the retardation layer in the optical element 1 of the present invention is well oriented can be evaluated by the presence or absence of light leakage of the optical element. Specifically, it can be evaluated by conducting the following light transmission test and observing the presence or absence of the transmitted light with the naked eye.

That is, the optical element 1 is installed between two polarizing plates installed in a crossed Nicol state in a polarizing microscope. By transmitting light in that state and observing with a polarizing microscope in a so-called black display state, the presence or absence of light leakage can be confirmed. An optical element that does not leak light shows that the retardation layer in the optical element is well homeotropically aligned, and when the optical element is used for a display-side substrate of a liquid crystal display device, the optical element has excellent contrast. This can contribute to the provision of high quality display. On the other hand, an optical element that leaks light indicates that the orientation of the retardation layer in the optical element is disordered. When the optical element is used for a display-side substrate of a liquid crystal display device, the contrast is poor and sufficient. May not be able to provide a good display quality.

In the above light transmission test, the state that there is no light leakage or the light leakage is negligible is as shown in FIG. 2 as a reference. Say something. In FIG. 2, a red colored pixel monochromatic colored layer is formed on a transparent substrate, and after the surface of the colored layer is washed with ultraviolet rays, a retardation layer is formed on the surface using the liquid crystal composition of the present invention. It is the photograph at the time of using for the said optical transmission test the optical element of this invention formed. On the other hand, the state of light leakage in the light transmission test is as shown as a symmetrical example in FIG. 3. The entire optical element is thin and bright even in the above-described black display environment, and light transmission is possible even with the naked eye. The state to be confirmed.

Measurement of yellowness of retardation layer and evaluation of yellowing degree:
The phase difference layer formed using the liquid crystal composition of the present invention and the yellowness of the phase difference layer in the optical element of the present invention can be measured using a constituent layer other than the phase difference layer in the optical element as a reference. More specifically, in an optical element composed of a glass substrate and a retardation layer, the glass substrate is used as a reference, and in an optical element composed of a glass substrate, a colored layer, and a retardation layer, the glass substrate and the colored layer are used. The yellowness of the retardation layer can be obtained using the laminate as a reference.

Further, the yellowing degree ΔYI of the retardation layer can be evaluated by a change in yellowness before and after the ultraviolet treatment described later. Specifically, it can be determined by evaluating the yellowing degree of the retardation layer before and after the ultraviolet treatment according to JIS K 7373.

The measurement of the yellowness and yellowing degree of the retardation layer will be specifically described below.
First, an optical element having at least a retardation layer on a glass substrate is used as a sample, and the chromaticity of the retardation layer is used as a reference except for the retardation layer in the optical element, and D65 is used as a light source. (Measured by Olympus Optical Co., Ltd., trade name “OSP-SP200”). The yellowness (YI ₀ ) is calculated from the tristimulus values X, Y, and Z values obtained by the above measurement using the following formula (Formula 1).
YI ₀ = 100 (1.2985X-1.1335Z) / Y (Formula 1)
Next, after irradiating far-ultraviolet rays to the retardation layer at 1000 mJ / cm ² , a colorimeter (manufactured by Olympus Optical Co., Ltd., trade name “OSP-SP200”) was used with D65 as the chromaticity of the retardation layer. ) To measure. The yellowness (YI) is calculated from the obtained X, Y and Z values using the following formula (formula 2), and the yellowing degree (ΔYI) is further calculated by the following formula (3).
YI = 100 (1.2985X-1.1335Z) / Y (Formula 2)
ΔYI = YI−YI ₀ (Formula 3)

Here, YI represents the yellowness of the retardation layer after the ultraviolet treatment, and YI ₀ represents the yellowness of the retardation layer before the ultraviolet treatment. The retardation layer in the present invention has a yellowness YI ₀ before ultraviolet treatment of 1 or less, and is not yellowed by ultraviolet treatment. In the retardation layer, a desirable yellowness is always maintained. Therefore, when an optical element including the retardation layer is used for a display-side substrate of a liquid crystal display device, an excellent high-quality display with a wide color gamut is achieved. Since it contributes to provision, it is preferable. On the other hand, when a retardation layer having yellowing is used for a display-side substrate of a liquid crystal display device, the color gamut of the liquid crystal display device may be narrowed and sufficient display quality may not be provided.
In the evaluation of the yellowing degree of the retardation layer, there is no yellowing or a state where yellowing is negligible. The yellowing degree is 1.5 or less in the yellowing degree evaluation method of JIS K 7373. It means being in a certain state.

(Liquid crystal display device of the present invention)
The optical element 1 of the present invention can be used as a display side substrate of a liquid crystal display device. The liquid crystal display device 12 shown in FIG. 4 uses the optical element 1 of the present invention for the display side substrate 13 installed on the viewer side (corresponding to the upper side in the figure), and the display side substrate 13 and the liquid crystal drive side substrate 14 The liquid crystal layer 16 for drive is comprised by enclosing the liquid crystal material 15 for drive between both the board | substrates via the spacer 9, and enclosing between both board | substrates. Here, the retardation layer 4 is disposed so as to be sandwiched between the light-transmitting substrate 2 of the optical element 1 and the transparent substrate 31 constituting the liquid crystal driving side substrate 14, and forms a so-called in-cell type. A functional layer 20 in which a transparent conductive film 21 and a positive A plate 22 are sequentially laminated is formed on the side surface of the light transmissive substrate 2 opposite to the colored layer 3. A linear polarizing plate 23 is laminated on the outer surface of the display side substrate 13, and a linear polarizing plate 32 is laminated on the outer surface of the liquid crystal driving side substrate 14.

  When the liquid crystal display device 12 is in the IPS mode, the linear polarizing plate 23 on the display side substrate 13 and the linear polarizing plate 32 on the liquid crystal driving side substrate 14 are arranged so that their transmission axes are orthogonal to each other. Is done.

  The liquid crystal driving side substrate 14 is provided with a driving circuit 33 on the in-cell side of the transparent substrate 31 (side where the driving liquid crystal material 15 is sealed), and a driving electrode 34 by which the voltage load is controlled. ing.

The liquid crystal display device 12 described above is only one embodiment of the present invention, and the liquid crystal display device of the present invention is not limited to this configuration. The liquid crystal display device of the present invention has at least the optical element of the present invention as a display side substrate, the display side substrate and the liquid crystal drive side substrate face each other with a spacer interposed therebetween, and a driving liquid crystal between them. It is important that the material is encapsulated. This configuration is advantageous because the retardation layer formed using the liquid crystal composition of the present invention is implemented as a so-called in-cell type that exists between the substrates.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
Using the compounds (a) to (d) shown in the chemical formula 4, a composition A having the following composition was prepared. Composition A was prepared by mixing the materials listed below according to the description in JP-T-2004-524385. In addition, the weight ratio of each substance in the composition A shown below is the weight ratio of each substance to the total weight of the composition A.

Liquid crystal composition A
Compound (a) 32.67% by weight
Compound (b) 18.67% by weight
Compound (c) 21.00% by weight
Compound (d) 21.00% by weight
Dodecanol 1.02% by weight
BHT 0.04% by weight
Irgacure 907 5.60% by weight

Next, 3% by weight (as a compound equivalent value) of an ultraviolet absorber 2,4-dihydroxybenzophenone (SEESORB201 manufactured by Sipro Kasei Co., Ltd.) is added as an anti-yellowing agent to the composition A, and the liquid crystal of the present invention. A composition was obtained. The maximum absorption wavelength of the ultraviolet absorber 2,4-dihydroxybenzophenone (SEESORB201, manufactured by Sipro Kasei Co., Ltd.) is slightly below 250 nm, and corresponds to around 254 nm, which is preferable as the maximum absorption wavelength of the ultraviolet absorber in the present invention. It can absorb UV light of 254 nm satisfactorily.
Next, the liquid crystal composition was dissolved in propylene glycol monomethyl ether acetate (PGMEA) to obtain a liquid crystal composition solution having a concentration of 20%.
Next, an appropriate cleaning process was performed to prepare a glass plate (Corning 1737 glass) having a size of 100 × 100 mm and a thickness of 0.7 mm as a cleaned transparent substrate. Next, the liquid crystal composition solution was spin-coated on a transparent substrate using a spin coater (trade name 1H-360S, manufactured by Mikasa), and then dried under reduced pressure. Subsequently, ultraviolet rays were irradiated at 20 mW / cm ² for 10 seconds with an ultraviolet irradiation device having an ultra-high pressure mercury lamp (“trade name TOSCURE 751” manufactured by Harrison Toshiba Lighting Co., Ltd.) in an air atmosphere and contained in the liquid crystal composition solution. The polymerizable liquid crystal compound was crosslinked. Finally, the substrate having been subjected to the crosslinking treatment was placed in an oven at 230 ° C., and baked for 30 minutes to form the optical element of the present invention having a retardation layer having a thickness of 1.0 μm. The orientation state of the obtained retardation layer was confirmed by crossed Nicols observation with a polarizing microscope, and confirmed to be oriented without any problem.

(Evaluation 1)
Measurement of Yellowness YI ₀ and Evaluation of Yellowing Degree Yellowness YI ₀ and yellowing degree ΔYI of the optical element obtained in Example 1 are the same as the above-mentioned “Measurement of Yellowness of Yellowing Retardation Layer and Evaluation of Yellowing” It measured based on the method of description. When measuring the yellowness YI ₀ , the glass plate (Corning 1737 glass) used in Example 1 was used as a reference.

The yellowness YI ₀ of the retardation layer in Example 1 is 0.5 and the yellowing degree is 0.8, and the retardation layer in the optical element of Example 1 has its transparency before the ultraviolet treatment. It was confirmed that the material was not yellowed even after the ultraviolet treatment.

Example 2
The same as in Example 1 except that the ultraviolet absorber to be added was changed to 2 ′, 4′-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzoate (SEESORB 712 manufactured by Cypro Kasei Co., Ltd.). An optical element was prepared. The orientation state of the obtained retardation layer was confirmed by crossed Nicols observation with a polarizing microscope, and confirmed to be oriented without any problem. Incidentally, the maximum absorption wavelength of 2 ′, 4′-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzoate (SEESORB 712 manufactured by Cypro Kasei Co., Ltd.) is about 270 nm, and UV absorption in the present invention It corresponds to around 254 nm, which is preferable as the maximum absorption wavelength of the agent, and can absorb UV light of 254 nm well.

Regarding Example 2, the evaluation was performed according to Evaluation 1 described above. As a result, the yellowness YI ₀ is 0.6, the yellowing degree is 0.8, the transparency of the retardation layer in the optical element of Example 2 is ensured before the ultraviolet treatment, and the ultraviolet treatment It was confirmed that there was no yellowing later.

Example 3
Example, except that the yellowing inhibitor to be added was changed from an ultraviolet absorber to an antioxidant 4,4′-butylidenebis- (6-tert-butyl-3-methylphenol) (Yosinox BB manufactured by API Corporation). An optical element was prepared in the same manner as in 1. The orientation state of the obtained retardation layer was confirmed by crossed Nicols observation with a polarizing microscope, and confirmed to be oriented without any problem.

Regarding Example 3, the evaluation was performed according to Evaluation 1 described above. As a result, the yellowness YI ₀ is 0.6, the yellowing degree is 1.1, the transparency of the retardation layer in the optical element of Example 3 is ensured before the ultraviolet treatment, and the ultraviolet treatment. It was confirmed that there was no yellowing later.

Example 4
An optical element was produced in the same manner as in Example 1 except that the antioxidant to be added was changed to 2,6-di-tert-butyl-4-ethylphenol (250 manufactured by API Corporation). The orientation state of the obtained retardation layer was confirmed by crossed Nicols observation with a polarizing microscope, and confirmed to be oriented without any problem.

Regarding Example 4, the evaluation was performed according to the above evaluation 1. As a result, the yellowness YI ₀ is 0.6, the yellowing degree is 1.2, the transparency of the retardation layer in the optical element of Example 4 is ensured before the ultraviolet treatment, and the ultraviolet treatment. It was confirmed that there was no yellowing later.

Comparative Example 1
An optical element was produced in the same manner as in Example 1 except that no yellowing inhibitor was used, and used as Comparative Example 1. The orientation state of the obtained retardation layer was confirmed by crossed Nicols observation with a polarizing microscope, and confirmed to be oriented without any problem.

The comparative example 1 was evaluated according to the above evaluation 1. As a result, the yellow degree YI ₀ was 0.7 and the yellowing degree was 2.1, and it was confirmed that the optical element of Comparative Example 1 was yellowed.

The ultraviolet ray treatment corresponds to the deep ultraviolet ray washing treatment performed as the retardation layer washing treatment in the optical element manufacturing process. In each of Examples 1 to 4, the yellowness YI ₀ before the ultraviolet ray treatment is 1 or less. In addition, it was shown that yellowing does not occur even by the ultraviolet treatment. On the other hand, in Comparative Example 1 including a retardation layer made of a liquid crystal composition not containing a yellowing inhibitor, yellowing of the retardation layer was confirmed by the ultraviolet treatment. This indicates that yellowing of the retardation layer is prevented by the presence of the antioxidant in the liquid crystal composition.

(Table 1)

1 is a schematic longitudinal sectional view showing an embodiment of the optical element of the present invention. It is a surface photograph figure of an optical element without light leakage when observing light leakage of an optical element in a crossed Nicol state. It is a surface photograph figure of the optical element with a light leak when observing the light leak of an optical element in a crossed Nicol state. 1 is a schematic longitudinal sectional view showing one embodiment of a liquid crystal display device using the optical element of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2 Transparent substrate 3 Colored layer 4 Phase difference layer 5 Black matrix 6 Red sub pixel 7 Green sub pixel 8 Blue sub pixel 9 Spacer

Claims (10)

A liquid crystal composition comprising a polymerizable liquid crystal compound and a yellowing inhibitor. The liquid crystal composition according to claim 1, wherein the yellowing inhibitor contains an ultraviolet absorber and / or an antioxidant. 3. The liquid crystal composition according to claim 2, wherein the ultraviolet absorber has a maximum absorption wavelength in the vicinity of 254 nm. 4. The liquid crystal composition according to claim 1, further comprising a photopolymerization initiator. 99.8 to 80% by weight (based on solids) of (meth) acryloyl group-containing polymerizable liquid crystal compound, 0.1 to 10% by weight (based on solids) of yellowing inhibitor and 0.1 The liquid crystal composition according to claim 4, comprising 10 to 10% by weight (based on solid matter) of a photopolymerization initiator. 6. The liquid crystal according to claim 1, wherein in the yellowing evaluation test shown below, the yellowness YI ₀ is 1 or less and the yellowing degree ΔYI is 1.5 or less according to the evaluation standard of JIS K 7373. Composition.
Yellowing evaluation test: A liquid crystal composition is applied directly on a glass substrate, aligned in a desired direction, and then irradiated with ultraviolet rays at 20 mW / cm ² for 10 seconds to be contained in the liquid crystal composition solution. A liquid crystal compound is crosslinked and polymerized, and then baked in an oven at 230 ° C. for 30 minutes to form a sample having a retardation layer having a thickness of 1.0 μm. The glass substrate is used as a reference, and D65 is used as a light source. The tristimulus value XYZ value is measured, the yellowness (YI ₀ ) is calculated from the obtained value using the following formula (formula 1), and then far ultraviolet rays are applied to the surface of the retardation layer in the sample at 1000 mJ / Cm ^{2 is} irradiated, and then the tristimulus value XYZ value of the sample is measured using D65 as a light source in the same manner as described above, and the yellowness (YI) is calculated from the obtained value using the following formula (Formula 2). Calculate Following equation using the YI ₀ and the YI by (Equation 3) determining the yellowing factor △ YI before and after the ultraviolet irradiation treatment.
YI ₀ = 100 (1.2985X-1.1335Z) / Y (Formula 1)
YI = 100 (1.2985X-1.1335Z) / Y (Formula 2)
ΔYI = YI−YI ₀ (Formula 3) A retardation layer is formed directly or indirectly on a light-transmitting substrate, and the retardation layer is formed by applying and curing the liquid crystal composition according to claim 1 on a substrate surface. An optical element characterized by the above. The retardation layer measured by using D65 as a light source has a yellowing degree YI ₀ of 1 or less as a light source using a substrate composed of the constituent layers excluding the retardation layer in the optical element as a reference, and the retardation layer After irradiating the surface with far-ultraviolet rays of 1000 mJ / cm ^2, the yellowing degree ΔYI obtained from the measured yellowness YI and the above YI ₀ is 1.5 or less based on the evaluation standard of JIS K 7373 The optical element according to claim 7. The optical element according to claim 7 or 8, wherein the polymerizable liquid crystal compound contained in the retardation layer is homeotropically aligned. A liquid crystal display device comprising a display side substrate, a driving liquid crystal side substrate opposite to the display side substrate, and a driving liquid crystal layer formed by enclosing a driving liquid crystal material between the substrates, wherein the display side substrate is claimed. Item 10. A liquid crystal display device using the optical element according to any one of Items 7 to 9.

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