JP2009276442A - Quarter wave plate, image display device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quarter wave plate capable of imparting the phase difference of 1/4 wavelength to light of wide-band wavelength, and suppressing the generation of variation of hue or reflection of light from an oblique direction due to variation of phase difference values and the like. <P>SOLUTION: The quarter wave plate is made by laminating at least a first optical anisotropic layer and a second optical anisotropic layer, wherein the first optical anisotropic layer is a cellulose ester film and has a retardation value Ro<SB>1</SB>in an in-plane direction at a wavelength λ satisfying λ/4<Ro<SB>1</SB><λ/2, the second optical anisotropic layer includes positive wavelength dispersion properties and a retardation value Ro<SB>2</SB>in an in-plane direction at the wavelength λ satisfying 0<Ro<SB>2</SB><λ/4, the difference Ro<SB>d</SB>between the Ro<SB>1</SB>and Ro<SB>2</SB>satisfies λ/4.5<Ro<SB>d</SB><λ/3.5, and a lagging axis of the first optical anisotropic layer and a lagging axis of the second optical anisotropic layer are orthogonal to each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a broadband quarter-wave plate used in an image display device such as a liquid crystal display device. More specifically, the present invention can suppress good external light reflection, reflection of light from an oblique direction, and change in color. The present invention relates to a possible quarter-wave plate and an image display device using the same.

  A quarter wave plate that can convert linearly polarized light into circularly or elliptically polarized light, or convert circularly polarized light or elliptically polarized light into linearly polarized light, is widely used in various optical applications such as image display devices and optical pickup devices. ing.

  When used in an optical device using a laser light source having a specific wavelength, such as an optical pickup device, it is only necessary to give a phase difference of ¼ wavelength to only the specific wavelength. However, when it is used for a color image display device or used as an antireflection film for visible light, it is required to give a phase difference of a quarter wavelength over the entire visible light.

  Therefore, a quarter-wave plate for a liquid crystal display device is required to be a film having a so-called negative wavelength dispersion that gives a larger phase difference to light having a longer wavelength than light having a shorter wavelength. However, there is no material exhibiting sufficient negative wavelength dispersion (also called reverse wavelength dispersion) while giving a phase difference of 1/4 wavelength, and it is difficult to obtain a broadband 1/4 wavelength plate with a single layer. It was.

  A technique of a quarter-wave plate is known by pasting together in a state where optical axes of a quarter-wave plate and a half-wave plate having different wavelength dispersion are crossed (see, for example, Patent Document 1).

  However, according to these methods, it is necessary to adjust the laminated films to ¼ wavelength and ½ wavelength, respectively, which is difficult to manufacture and the retardation value is limited. The range that can be adjusted is limited, and it has not been possible to obtain a retardation plate that exhibits a quarter wavelength in a sufficiently wide band.

  Moreover, in order to make each film express the phase difference of 1/4 wavelength and 1/2 wavelength, since it was necessary to increase the thickness of a film, there existed a problem which the thickness of an image display apparatus increased.

  When a material with a large retardation is used as a film material to suppress the thickness of the film, the thickness can be reduced, but in addition to the in-plane retardation, the thickness direction retardation value is slight. Because of the large variation due to the difference, the phase difference value is difficult to control, and the problem of uneven color and reduced contrast due to thickness variation has occurred.

  In patent document 2, the structure which provides a liquid-crystal layer on a film support body is proposed in the waveplate which laminates | stacks the phase difference layer which shows 1/4 wavelength and 1/2 wavelength.

  However, in this method as well, the retardation of each retardation layer is limited to ¼ wavelength and ½ wavelength as in the above-described technique, so that it is difficult to sufficiently control wavelength dispersion. .

  In Patent Documents 3 and 4, the fast axes or slow axes of the two retardation films are orthogonal to each other, and the difference between the retardation values in the plane is substantially ¼ wavelength. A technique for obtaining one quarter-wave plate has been proposed.

However, in this technique, in order to have a wavelength dispersion characteristic that shows a sufficient broadband property by the difference value of each retardation film, it is necessary to increase the retardation value of both retardation films. In the case of using a material that causes an increase in film thickness and is likely to exhibit a phase difference in order to reduce the film thickness, the phase difference value changes greatly due to slight film thickness variations, and light is reflected from an oblique direction. And changed the color.
JP-A-10-68816 Japanese Patent Laid-Open No. 2001-91741 JP 2004-145282 A JP 2008-70635 A

  Therefore, the object of the present invention can be manufactured by a simple method, can give a phase difference of ¼ wavelength to light with a wide wavelength, and can be viewed from an oblique direction due to variations in phase difference values. It is to provide a quarter-wave plate that can suppress the occurrence of light reflection and color change.

  In particular, a quarter-wave plate that can be used for an image display device such as a VA-type liquid crystal display device or an organic EL image display device, and can provide sufficient contrast even in a large-sized image display device or outdoor use, and the like An object of the present invention is to provide an image display device using the.

The above object of the present invention is to
1. A quarter-wave plate in which at least a first optical anisotropic layer and a second optical anisotropic layer are laminated, wherein the first optical anisotropic layer is a cellulose ester film; And the retardation value Ro ₁ in the in-plane direction at the wavelength λ satisfies λ / 4 <Ro ₁ <λ / 2,
The second optically anisotropic layer has positive wavelength dispersion, and an in-plane retardation value Ro _{2 at a} wavelength λ satisfies 0 <Ro ₂ <λ / 4,
The difference Ro _d between Ro ₁ and Ro ₂ satisfies λ / 4.5 <Ro _d <λ / 3.5,
A quarter-wave plate, wherein the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer are orthogonal to each other.

However, said Ro ₁ and Ro ₂ are respectively defined by the following formulas.

Ro _n = (nx−ny) × d
n represents 1 or 2, the refractive index in the slow axis direction in the plane of each optical anisotropic layer is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, and d is each Represents thickness (nm). λ is an arbitrary wavelength of 400 to 700 nm.
2. 2. The quarter-wave plate according to 1 above, wherein the retardation value Rt in the thickness direction at a wavelength λ is 100 nm or less.

  However, Rt is defined by the following equation.

Rt = ((nx + ny) / 2−nz) × d
The refractive index in the slow axis direction in the plane of the quarter-wave plate is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, the refractive index in the direction perpendicular to the film surface is nz, and d Represents the thickness of the quarter-wave plate.
3. 3. An image display device comprising: the quarter-wave plate according to 1 or 2; an image forming cell in which a plurality of self-luminous elements are arranged in a planar shape; and a reflector.
4). A first polarizing plate, a second polarizing plate, a vertical alignment type liquid crystal cell provided between the first polarizing plate and the second polarizing plate, and a back provided on the second polarizing plate side A liquid crystal display device having a light source, wherein the quarter wavelength plate described in 1 or 2 is provided between the vertical alignment type liquid crystal cell and the second polarizing plate. Display device.

  According to the present invention, it can be manufactured by a simple method, can impart a quarter-wave phase difference to light having a wide wavelength, and can reduce contrast and color due to variations in phase difference values. A quarter-wave plate in which the occurrence of unevenness is suppressed is obtained. Furthermore, a quarter-wave plate that can be used for an image display device such as a VA liquid crystal display device or an organic EL image display device to obtain sufficient contrast even in a large image display device or outdoor use, and the like An image display device using is obtained.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

Hereinafter, each element of the present invention will be described in detail.
<Measurement of retardation>
The in-plane direction and thickness direction retardation values Ro and Rt of the present invention can be measured at a predetermined wavelength in an environment of 23 ° C. and 55% RH using KOBRA 21ADH manufactured by Oji Scientific Instruments.

  The wavelength λ to be measured can be arbitrarily selected and is in the range of visible light of 400 to 700 nm.

When calculating retardation, the value which measured the refractive index of the applicable wavelength of each sample using Abbe's refractometer 1T (made by Atago Co., Ltd.) is used. In the case of a laminate, the average refractive index of each layer is used. For the film thickness d (nm), a commercially available micrometer is used to measure the thickness of the sample at several points, and an average value is used.
<Configuration of image display device>
The quarter wavelength plate of the present invention is a quarter wavelength plate in which at least a first optical anisotropic layer and a second optical anisotropic layer are laminated.

The first optically anisotropic layer is a cellulose ester film, and an in-plane retardation value Ro ₁ at a wavelength λ satisfies λ / 4 <Ro ₁ <λ / 2,
The second optically anisotropic layer has positive wavelength dispersion, and an in-plane retardation value Ro _{2 at a} wavelength λ satisfies 0 <Ro ₂ <λ / 4,
The difference Ro _d between Ro ₁ and Ro ₂ satisfies λ / 4.5 <Ro _d <λ / 3.5,
The slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer are perpendicular to each other.

Here, orthogonal, horizontal, vertical, and parallel in the present invention refer to a range of ± 10 ° with respect to a strict angle.
<First optically anisotropic layer>
The first optically anisotropic layer used in the quarter-wave plate of the present invention is a cellulose ester film, and the retardation value Ro ₁ in the in-plane direction at the wavelength λ is λ / 4 <Ro ₁ < λ / 2 is satisfied.

In the present invention, since the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer are orthogonal to each other, The in-plane retardation value is not limited to ¼ wavelength or ½ wavelength as in the past, and the difference from the second optically anisotropic layer is λ / 4.5 <Ro _d <λ / 3.5. Therefore, as long as the range satisfies λ / 4 <Ro ₁ <λ / 2, the design can be freely performed, and the phase difference value can be easily adjusted.

  In addition, in order to show a quarter wavelength in a wide band due to the difference between the first optical anisotropic layer and the second optical anisotropic layer, the difference in retardation value is changed from a short wavelength to a long wavelength. Therefore, it needs to be large.

  Therefore, the first optical anisotropic layer of the present invention is a cellulose ester film exhibiting negative wavelength dispersion.

  Usually, since a cellulose-ester film shows a negative wavelength dispersion characteristic, what is necessary is just to adjust addition amounts, such as an additive, to such an extent that the characteristic is not impaired.

(Cellulose ester film)
The cellulose ester used in the cellulose ester film which is the first optically anisotropic layer is an aliphatic carboxylic acid ester or aromatic carboxylic acid ester having about 2 to 22 carbon atoms, or an aliphatic carboxylic acid ester and an aromatic carboxylic acid ester. The mixed ester is preferably used, and is particularly preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. Specifically, as described in cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate phthalate, and the like, JP-A Nos. 10-45804, 8-231761, U.S. Pat. No. 2,190,052 and the like. These are mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate. Among the above description, the lower fatty acid ester of cellulose that is particularly preferably used for the third protective film is the following cellulose acetate propionate.

  The cellulose ester has an acyl group having 2 to 22 carbon atoms as a substituent, and when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group is Y, the cellulose that simultaneously satisfies the following formulas 1 and 2 Ester.

Formula 1 2.00 ≦ X + Y ≦ 2.95
Formula 2 0.10 ≦ Y ≦ 1.00
Among them, 2.30 ≦ X + Y ≦ 2.70 is preferable, and 2.40 ≦ X + Y ≦ 2.55 is more preferable. Further, 0.50 ≦ Y ≦ 0.90 is preferable, and 0.70 ≦ Y ≦ 0.90 is more preferable.

  The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods. Moreover, these acyl group substitution degrees can be measured according to the method prescribed | regulated to ASTM-D817-96.

  Moreover, the cellulose ester obtained from these can be mixed and used in arbitrary ratios, respectively. These cellulose esters are prepared by using an organic acid such as acetic acid or an organic solvent such as methylene chloride when sulfuric acid is used as the acylating agent (acetic anhydride, propionic anhydride, butyric anhydride). It can obtain by making it react by a conventional method using a protic catalyst like.

  The ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the cellulose ester used in the present invention is preferably 1.4 to 3.0. In the present invention, the cellulose ester film may contain, as a material, a cellulose ester having a Mw / Mn value of 1.4 to 3.0, but the cellulose ester contained in the film (preferably cellulose triacetate). Or the value of Mw / Mn of cellulose acetate propionate) is more preferably in the range of 1.4 to 3.0.

  In the process of synthesizing cellulose ester, it is difficult to make it less than 1.4, and cellulose ester having a uniform molecular weight can be obtained by fractionation by gel filtration or the like. However, this method is very expensive. Moreover, it is preferable that it is 3.0 or less because the flatness is easily maintained. In addition, More preferably, it is 1.7-2.2.

  The molecular weight of the cellulose ester used in the present invention is preferably a number average molecular weight (Mn) of 80,000 to 200,000. More preferred are 100,000 to 200,000, particularly preferably 150,000 to 200,000.

  The average molecular weight and molecular weight distribution of the cellulose ester can be measured by a known method using gel permeation chromatography (GPC). Using this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

The measurement conditions are as follows.
Solvent: Methylene chloride column: Shodex K806, K805, K803G (used by connecting 3 products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. It is preferable to obtain 13 samples at approximately equal intervals.

  The cellulose ester can be produced by a known method such as the method described in JP-A-10-45804.

  Moreover, it is preferable that a cellulose ester is 1 ppm or less about an iron (Fe) component.

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. About a magnesium (Mg) component, it is preferable that it is 0-70 ppm, and it is especially preferable that it is 0-20 ppm.

  Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After performing, it can obtain | require by performing an analysis using ICP-AES (inductively coupled plasma optical emission spectrometry).

  The cellulose ester film used in the present invention preferably has a refractive index of 1.45 to 1.60 at 550 nm. As a method for measuring the refractive index of the film, an Abbe refractometer is used, and measurement is performed based on Japanese Industrial Standard JIS K 7105.

(Additive)
The cellulose ester film can contain additives such as a plasticizer, an ultraviolet absorber, an antioxidant, and a matting agent.

  Examples of these additives include plasticizers, ultraviolet absorbers, and fine particles.

  The present invention preferably contains the following plasticizer. Examples of plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, glycolate plasticizers, citrate ester plasticizers, and polyesters. A plasticizer, a polyhydric alcohol ester plasticizer, and the like can be preferably used.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Further, all of the OH groups in the polyhydric alcohol may be esterified with carboxylic acid, or a part of the OH groups may be left as they are.

  The amount of these plasticizers used is preferably from 1 to 20% by mass, particularly preferably from 3 to 13% by mass, based on the cellulose ester, in terms of film performance, processability and the like.

  The ultraviolet absorber that can be used in the present invention aims to improve durability by absorbing ultraviolet rays of 400 nm or less, and preferably has a transmittance of 10% or less at a wavelength of 370 nm. More preferably, it is 5% or less, and further preferably 2% or less.

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body. It is good also as a polymer type ultraviolet absorber.

(Matting agent)
In the present invention, it is preferable to add a matting agent in order to impart film slipperiness.

  As the matting agent used in the present invention, any inorganic compound or organic compound may be used as long as it has heat resistance at the time of melting without impairing the transparency of the obtained film. For example, talc, mica, zeolite, diatomaceous earth, Calcined siliceous clay, kaolin, sericite, bentonite, smectite, clay, silica, quartz powder, glass beads, glass powder, glass flakes, milled fiber, wollastonite, boron nitride, boron carbide, titanium boride, magnesium carbonate, Heavy calcium carbonate, light calcium carbonate, calcium silicate, aluminum silicate, magnesium silicate, magnesium aluminosilicate, alumina, silica, zinc oxide, titanium dioxide, iron oxide, magnesium oxide, zirconium oxide, aluminum hydroxide, calcium hydroxide, water Magnesium oxide Beam, calcium sulfate, barium sulfate, silicon carbide, aluminum carbide, titanium carbide, aluminum nitride, silicon nitride, titanium nitride, and white carbon. These matting agents can be used alone or in combination of two or more.

  By using particles having different particle sizes and shapes (for example, acicular and spherical), both transparency and slipperiness can be made highly compatible.

  Among these, silicon dioxide is particularly preferably used since it has a refractive index close to that of cellulose ester and is excellent in transparency (haze).

  Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP- 30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), nip seal E220A (manufactured by Nippon Silica Kogyo Co., Ltd.), Admafine SO (manufactured by Admatechs), etc. Goods etc. can be preferably used.

  The shape of the particles can be used without particular limitation, such as indefinite shape, needle shape, flat shape, spherical shape, etc. However, the use of spherical particles is particularly preferable because the transparency of the resulting film can be improved.

  When the particle size is close to the wavelength of visible light, light is scattered and the transparency is deteriorated. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . If the size of the particles is too small, the slipperiness may not be improved, so the range of 80 nm to 180 nm is particularly preferable.

  The particle size means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

(Retardation increasing agent)
In order to adjust the retardation value of the cellulose ester film and to achieve retardation at a drawing ratio as low as possible, a retardation increasing agent may be added to the cellulose ester. The retardation increasing agent is preferably used in the range of 0.05 to 20 parts by mass, more preferably in the range of 0.1 to 10 parts by mass, with respect to 100 parts by mass of the polymer. It is more preferable to use in the range of 5 to 5 parts by mass, and most preferable to use in the range of 0.5 to 2 parts by mass. Two or more types of retardation increasing agents may be used in combination. The retardation increasing agent preferably has a maximum absorption in a wavelength region of 250 to 400 nm. It is preferable that the retardation increasing agent has substantially no absorption in the visible region.

Specific examples of the retardation increasing agent preferably having a molecular weight of the retardation increasing agent of 300 to 800 include compounds described in JP-A Nos. 2000-1111914 and 2000-275434.
<Method for producing cellulose ester film>
Next, the manufacturing method of the cellulose ester film used for this invention is demonstrated.

  The cellulose ester film used in the present invention is preferably a cellulose ester film produced by a solution casting method or melt casting. Hereinafter, the solution casting method will be described.

  The cellulose ester film used in the present invention was produced by dissolving a cellulose ester and an additive in a solvent to prepare a dope, casting a dope onto an endless metal support, and casting the dope. It is performed by a step of drying the dope as a web, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. The concentration of cellulose ester in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of cellulose ester is too high, the load during filtration increases and the filtration accuracy is poor. Become. The concentration for achieving both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by mass.

  The solvent used in the dope may be used alone or in combination of two or more, but it is preferable to use a mixture of a good solvent and a poor solvent of cellulose ester in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of the solubility of the cellulose ester.

  The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose ester to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent.

  Therefore, depending on the average acetylation degree (acetyl group substitution degree) of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  Although the good solvent used for this invention is not specifically limited, Organic halogen compounds, such as a methylene chloride, dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. are mentioned. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the poor solvent used for this invention is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope. Moreover, the solvent used for melt | dissolution of a cellulose ester collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again.

  A general method can be used as a dissolution method of the cellulose ester when preparing the dope described above. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos. A method in which a cellulose ester is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature with the addition of a solvent is preferably higher from the viewpoint of the solubility of the cellulose ester, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester can be dissolved in a solvent such as methyl acetate.

  Next, this cellulose ester solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester by filtration.

The bright spot foreign matter was placed in a crossed Nicols state with two polarizing plates, a rolled cellulose ester was placed between them, and light was applied from the side of one polarizing plate, and observed from the side of the other polarizing plate. It is a point (foreign matter) where light from the opposite side sometimes leaks, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (called differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and even more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

  Here, the dope casting will be described.

  The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate. A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable.

  Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

  The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

  In order for the cellulose ester film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Especially preferably, it is 20-30 mass% or 70-120 mass%.

  Further, in the drying step of the cellulose ester film, the web is peeled off from the metal support, and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, Especially preferably, it is 0-0.01 mass% or less.

  In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged on the upper and lower sides are alternately passed through and dried) or a tenter method is used while drying the web.

The film thickness of the cellulose ester film used in the present invention is preferably in the range of 20 to 200 μm, more preferably 20 to 100 μm, and even more preferably 20 to 80 μm.
<Ro value control by stretching>
The cellulose ester film of the present invention adjusts the refractive index (the refractive index nx in the in-plane slow axis direction, the refractive index ny in the direction perpendicular to the in-plane slow axis and the refractive index nz in the thickness direction) by stretching. It is preferable to do.

  Cellulose esters usually have a positive intrinsic birefringence. When the intrinsic birefringence is positive, the refractive index increases in the direction in which the polymer chains are oriented. When such a polymer having a positive intrinsic birefringence is stretched, the refractive index is usually nx> ny ≧ nz.

  This is because a polymer chain oriented in the in-plane direction has a larger x component and a smaller z component due to stretching. Thereby, the relationship of 1 ≦ (nx−nz) / (nx−ny) can be satisfied. Furthermore, in order to satisfy the relationship of (nx−nz) / (nx−ny) ≦ 2, the refractive index should be adjusted by controlling the stretching ratio of uniaxial stretching or by performing unbalanced biaxial stretching. That's fine.

  The stretching temperature is preferably at least 10 ° C. higher than the glass transition temperature of the cellulose ester, preferably at least 20 ° C. lower than the crystallization temperature, more preferably at least 10 ° C. higher than the glass transition temperature and at least 40 ° C. lower than the crystallization temperature. Here, the glass transition temperature and the crystallization temperature are values measured using a differential scanning calorimeter (DSC) at a heating rate of 10 ° C./min.

  The stretching speed is not particularly limited, but is preferably 1% / second to 40% / second. In the case of a stretching speed of 40% / second or more, uneven retardation tends to occur. The stretching process may be performed a plurality of times, and may be a simultaneous process or a sequential process.

  In the case of a film formed by a co-casting method, the residual solvent amount during stretching is preferably 0 to 5% by mass, and more preferably 0 to 2% by mass. In the case of a single layer casting method, it is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and most preferably 10 to 40% by mass.

  The stretched cellulose ester film may be heat-treated. The heat treatment is preferably performed at a temperature 20 ° C. to 10 ° C. higher than the glass transition temperature of the cellulose ester film. The heat treatment time is preferably 1 second to 3 minutes, more preferably 1 second to 2 minutes, and most preferably 1 second to 1 minute. The heating method may be zone heating or partial heating such as an infrared heater.

  In order to obliquely stretch the thermoplastic resin film in a direction substantially 45 ° with respect to the longitudinal direction, a known method can be used.

  The draw ratio is preferably 2 to 30 times, and more preferably 3 to 10 times. When stretching, assuming that the glass transition temperature of the thermoplastic resin film is Tg, the film is heated and stretched within the range of (Tg-30) to (Tg + 100) ° C, more preferably (Tg-20) to (Tg + 80) ° C. It is preferable. In particular, it is preferable that the film is stretched within a temperature range of (Tg-20) to (Tg + 20) ° C. and then heat-set. It is also preferable to perform relaxation treatment after the stretching step.

  Diagonal stretching may be carried out in several steps. In particular, in the case of high-magnification stretching, it is preferable to obtain a uniform stretching result by dividing the process into several steps.

  Further, for the purpose of preventing shrinkage in the width direction, a slight stretching process in the transverse direction or the longitudinal direction may be performed before the oblique stretching. Diagonal stretching can be carried out by performing tenter stretching, which is employed for normal film biaxial stretching, in steps different from each other as described above.

  Since the left and right layers are stretched at different speeds, the thickness of the film before stretching is adjusted to be different between the left and right sides. What is necessary is just to adjust so that the flow volume of a solution may differ in right and left, when casting and forming a polyvinyl alcohol solution into a film. The flow rate can be easily adjusted by a method that tapers the die.

  Furthermore, the oblique stretching apparatus described in FIGS. 2 to 7 of JP-A-2004-20827, FIGS. 1 to 4 of JP-A-2007-94007, or FIGS. 1 to 4 of JP-A-2007-203556 are also suitable. Can be used.

  Moreover, when manufacturing the retardation film of this invention, it is preferable to extend | stretch to the said diagonal direction before coating the vertical alignment liquid crystal layer mentioned later. At the time of stretching, in the sense of increasing the degree of freedom of control in the slow axis direction in the plane of the retardation film, the film is stretched in the longitudinal direction and then stretched obliquely with respect to the longitudinal direction, or It is preferable to stretch in the longitudinal direction after stretching in the oblique direction with respect to the longitudinal direction.

As an example of a specific apparatus for realizing this, it is also preferable to use a film expansion / contraction apparatus described in JP-A-2007-30466.
<Second optically anisotropic layer>
The second optically anisotropic layer of the present invention has positive wavelength dispersion, and the in-plane retardation value Ro _{2 at the} wavelength λ satisfies 0 <Ro ₂ <λ / 4.

  Examples of the optical film that can form an optically anisotropic layer satisfying the above conditions include polyester polymers (for example, polyethylene terephthalate, polybutylene terephthalate, etc.), polyarylene sulfide polymers (for example, polyphenylene sulfide), polycarbonate-based polymers. Polymers, polyarylate polymers, polyethersulfone polymers, polysulfone polymers, polyallyl sulfone polymers, polyvinyl chloride polymers, and the like are preferable, and polyester polymers, polyarylene sulfide polymers, and polyarylate polymers are particularly preferable. A polymer, a material having a large value of Re (450) / Re (550) described in JP-A No. 2004-145282, and the like are preferable.

  In particular, polystyrene polymers and polycarbonate polymers are preferred.

  For the second optically anisotropic layer of the present invention, a known material can be produced by a known method. Commercial products may also be used.

  In addition, an optically anisotropic layer containing liquid crystalline molecules is preferable, and a vertical alignment liquid crystal layer, a horizontal alignment liquid crystal layer, and a hybrid alignment layer are preferable, and a vertical alignment liquid crystal layer is particularly preferable.

<Vertical alignment liquid crystal layer>
The second optically anisotropic layer of the present invention has a vertically aligned liquid crystal layer (a layer in which liquid crystal molecules aligned in the thickness direction of the film are applied and fixed) on a base film. It is.

The base film of the present invention requires that Ro ₂ satisfies the scope of the present invention as a film after the liquid crystal layer is applied. In order to produce the base film, it was peeled off from the metal support. It is preferable to stretch in the width direction by a tenter method in which the web is stretched in the conveying direction (= long direction) where the residual solvent amount of the web is large, and the both ends of the web are gripped by clips or the like.

  Furthermore, in order to adjust the angle formed between the slow axis in the plane of the base film and the coating direction when forming a layer composed of liquid crystal molecules to 10 ° to 80 °, the aforementioned oblique stretching apparatus is used. It is preferable to stretch.

  In the vertical alignment liquid crystal layer of the present invention, a liquid crystal material or a liquid crystal solution is applied onto the substrate film of the present invention, dried and heat-treated (also referred to as an alignment treatment), and fixed in a liquid crystal alignment by ultraviolet curing or thermal polymerization. It is preferable to form a second optically anisotropic layer made of a rod-like liquid crystal aligned in the vertical direction.

  Here, the term “aligned in the vertical direction” means that the rod-like liquid crystal molecules are aligned in a range of 70 to 90 ° (the vertical direction is 90 °) with respect to the film surface. The rod-like liquid crystal may be oriented obliquely or the orientation angle may be gradually changed. Preferably it is the range of 80-90 degrees.

  The vertically aligned liquid crystal layer of the present invention has an optical anisotropy due to a vertically aligned rod-shaped liquid crystal having an in-plane retardation value Ro of 0 to 10 nm and a thickness retardation value Rt of -50 to -400 nm. A layer is preferred. Further, Ro is more preferably in the range of 0 to 5 nm.

  Here, Rt is defined by the following formula.

Rt = {(nx + ny) / 2−nz} × d
(Where nx is the refractive index in the slow axis direction in the plane of the second optical anisotropic layer (maximum refractive index in the plane), and ny is the slow phase in the plane of the second optical anisotropic layer. (The refractive index in the direction perpendicular to the axis, nz is the refractive index in the thickness direction of the film, and d is the thickness (nm) of the second optically anisotropic layer.)
As the substrate film, a cellulose ester film is preferable.

  The Rt of the vertical alignment liquid crystal layer is intended to improve the viewing angle characteristics of the circularly polarizing film by setting the Rt of the base film so as to cancel out. Therefore, the Rt of the vertical alignment liquid crystal layer depends on the Rt of the base film. It is important to appropriately select coating conditions (type of liquid crystal molecules, concentration of liquid crystal molecules in the coating liquid, film thickness after drying, etc.).

  For example, when the vertical alignment liquid crystal layer is formed under the same liquid crystal molecules and the same coating liquid conditions using materials having different Rt of the base film, in order to provide excellent viewing angle characteristics as a circularly polarizing film, The object can be achieved by changing the thickness of the vertically aligned liquid crystal layer according to the value of Rt of the material film.

  When a rod-like liquid crystal layer is formed by aligning rod-like liquid crystals, an alignment film coated with a vertical alignment agent that aligns so-called liquid crystal materials in the vertical direction is used, and the liquid crystal material is vertically oriented and then fixed. be able to.

  When the liquid crystal material itself is aligned in the vertical direction at the air interface, the alignment regulating force extends to the interface opposite to the air interface, and the alignment film is not particularly necessary, and this is also preferable from the viewpoint of simplifying the configuration. preferable.

  As a specific method for vertically aligning the liquid crystal material, an alignment film composed of a cross-linked product of a block polymer composition containing a (meth) acrylic block polymer described in JP-A-2005-148473 and the like is used. Known methods such as a method of using, a method of using a vertical alignment film described in JP 2005-265889 A, and a method of using an air interface vertical alignment agent can be used.

  In order to bring the rod-shaped liquid crystal layer into the above range, it is preferable to control the alignment of the rod-shaped liquid crystal layer, the film thickness control, the temperature during UV curing, the tilt angle control, and the pretilt angle at the support / air interface.

  The liquid crystal layer is formed by curing a liquid crystal material capable of forming a liquid crystal phase at a predetermined temperature with a predetermined liquid crystal regularity. The upper limit of the temperature showing the liquid crystal phase is not particularly limited as long as the cellulose ester film of the base film is not damaged.

  Specifically, a temperature of 120 ° C. or lower is preferable from the viewpoint of easy control of process temperature and maintenance of dimensional accuracy, and a liquid crystal material that becomes a liquid crystal phase at a temperature of 100 ° C. or lower is preferably used. On the other hand, the lower limit of the temperature showing the liquid crystal phase can be said to be a temperature at which the liquid crystal material can maintain the alignment state when used as a polarizing plate.

  As the liquid crystal material used for the rod-like liquid crystal layer of the present invention, a polymerizable liquid crystal material is preferably used. The polymerizable liquid crystal material can be used by being polymerized by irradiating with predetermined actinic radiation. In the polymerized state, the vertical alignment state is fixed.

  As the polymerizable liquid crystal material, any of a polymerizable liquid crystal monomer, a polymerizable liquid crystal oligomer, and a polymerizable liquid crystal polymer can be used, and they can also be mixed with each other.

  Of the above, a polymerizable liquid crystal monomer is preferably used as the polymerizable liquid crystal material because of its high sensitivity during alignment and easy vertical alignment.

  Specific examples of the polymerizable liquid crystal monomer include a rod-like liquid crystal compound (I) represented by the following general formula (MV1) and a rod-like liquid crystal compound (II) represented by the following general formula (MV2). be able to. As the compound (I), a mixture of two or more compounds included in the general formula (MV1) can be used. Similarly, the compound (II) is included in the general formula (MV2). Two or more kinds of compounds may be mixed and used. In addition, one or more compounds (I) and one or more compounds (II) may be mixed and used.

In the general formula (MV1) representing the compound (I), R ¹ and R ² each represent hydrogen or a methyl group, but R ¹ and R ² are both hydrogen due to the wide temperature range showing the liquid crystal phase. preferable. X may be hydrogen, chlorine, bromine, iodine, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a cyano group, or a nitro group, but is preferably chlorine or a methyl group.

  Moreover, a and b which show the chain length of the alkylene group which is a spacer with the (meth) acryloyloxy group of both ends of the molecular chain of a compound (I), and an aromatic ring are respectively arbitrary integers in the range of 2-12. Although it can take, it is preferable that it is the range of 4-10, and it is more preferable that it is the range of 6-9.

  Compound (I) can be synthesized by any method. For example, compound (I) wherein X is a methyl group can be obtained by an esterification reaction of 1 equivalent of methylhydroquinone and 2 equivalents of 4- (m- (meth) acryloyloxyalkoxy) benzoic acid. In the esterification reaction, the benzoic acid is usually activated with an acid chloride or a sulfonic anhydride, and this is reacted with methylhydroquinone.

  In addition, a carboxylic acid unit and methylhydroquinone can be reacted directly using a condensing agent such as DCC (dicyclohexylcarbodiimide).

  As other methods, esterification reaction of 1 equivalent of methylhydroquinone and 2 equivalents of 4- (m-benzyloxyalkoxy) benzoic acid is first performed, and then the resulting ester is debenzylated by hydrogenation reaction or the like. Then, compound (I) can also be synthesized by a method in which the molecular terminal is acryloylated.

  When performing esterification reaction of methylhydroquinone and 4- (m-benzyloxyalkoxy) benzoic acid, methylhydroquinone is introduced into diacetate and then reacted with the above benzoic acid in a molten state to obtain an ester directly. It is also possible.

  The compound (I) in which X in the general formula (MV1) is not a methyl group can also be obtained by performing the same reaction as above using a hydroquinone having a corresponding substituent instead of methylhydroquinone.

In the general formula (MV2) representing the compound (II), R ³ represents hydrogen or a methyl group, but R ³ is preferably hydrogen because of the wide temperature range showing the liquid crystal phase. As for c indicating the chain length of the alkylene group, the compound (II) having this value of 2 to 12 does not exhibit liquid crystallinity.

  However, considering the compatibility with the compound (I) having liquid crystallinity, c is preferably in the range of 4 to 10, and more preferably in the range of 6 to 9.

  Compound (II) can also be synthesized by any method. For example, compound (II) can be synthesized by esterification reaction of 1 equivalent of 4-cyanophenol and 1 equivalent of 4- (n- (meth) acryloyloxyalkoxy) benzoic acid. II) can be synthesized. In the esterification reaction, the benzoic acid is generally activated with an acid chloride or a sulfonic acid anhydride and reacted with 4-cyanophenol, as in the case of synthesizing the compound (I). Moreover, you may make the said benzoic acid and 4-cyanophenol react using condensing agents, such as DCC (dicyclohexyl carbodiimide).

  In addition to the above, in the present invention, a polymerizable liquid crystal oligomer, a polymerizable liquid crystal polymer, or the like can be used. As such a polymerizable liquid crystal oligomer and a polymerizable liquid crystal polymer, those conventionally proposed can be appropriately selected and used.

  The film thickness of the liquid crystal layer in the present invention is preferably in the range of 0.1 μm to 20 μm, and more preferably in the range of 0.2 to 10 μm.

  Although it is very difficult to directly verify the alignment level of the liquid crystal in the vertically aligned liquid crystal layer provided on the substrate film having the in-plane retardation value, as one guideline, the azobenzene liquid crystal is A sample prepared by mixing about 1% by mass to 2% by mass with respect to the sample and applying and immobilizing the sample is assumed to show the same orientation of liquid crystal molecules as that of the sample not containing an actual azobenzene liquid crystal. By measuring the absorbance in the vicinity of 550 nm to 650 nm with a total, it is possible to know the rough degree of orientation.

  That is, if the absorbance is a considerably low value, it can be determined that the liquid crystal molecules are almost completely aligned and fixed vertically. Conversely, when the absorbance is relatively high, it can be interpreted that the liquid crystal molecules that should be aligned vertically are not necessarily aligned vertically, and the light absorption area of the azobenzene-based liquid crystal filling the gap is widened.

<Method for producing liquid crystal layer>
A polymerizable liquid crystal material is prepared by using a composition for forming a liquid crystal layer by blending a photopolymerization initiator, a sensitizer, etc., if necessary, and coating on a substrate to form a liquid crystal layer forming layer. To do.

  In the present invention, a liquid crystal layer is formed by providing a photo-alignment layer, adding a solvent as a liquid crystal composition, applying the composition on a substrate using a coating composition in which other components are dissolved, and removing the solvent. It is preferable to form a layer having a fixed orientation. This is simple in terms of process as compared with other methods.

  The solvent is not particularly limited as long as it is a solvent capable of dissolving the above-described polymerizable liquid crystal material and the like and does not deteriorate the properties of the transparent resin film.

  If only a single type of solvent is used, the solubility of the polymerizable liquid crystal material or the like may be insufficient, or the substrate may be eroded as described above. However, this inconvenience can be avoided by using a mixture of two or more solvents.

  Of the above-mentioned solvents, preferred as a single solvent are a hydrocarbon solvent and a glycol monoether acetate solvent, and a preferred mixed solvent is a mixed system of ethers or ketones and glycols. It is.

  The concentration of the solution depends on the solubility of the polymerizable liquid crystal material and the like and the film thickness of the liquid crystal layer to be produced, but cannot be defined unconditionally, but is usually preferably 1% by mass to 60% by mass, more preferably 3%. It adjusts in the range of mass%-40 mass%.

  Compounds other than those described above can be added to the composition for forming a liquid crystal layer used in the present invention within a range not impairing the object of the present invention.

  Examples of compounds that can be added include polyester (meth) acrylate obtained by reacting (meth) acrylic acid with a polyester prepolymer obtained by condensing polyhydric alcohol and monobasic acid or polybasic acid; A polyurethane (meth) acrylate obtained by reacting a compound having two isocyanate groups with each other and then reacting the reaction product with (meth) acrylic acid; bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak Type epoxy resin, polycarboxylic acid polyglycidyl ester, polyol polyglycidyl ether, aliphatic or cycloaliphatic epoxy resin, amine epoxy resin, triphenolmethane type epoxy resin, dihydroxybenzene type epoxy resin and the like (meth) Ak Photopolymerizable compounds such as epoxy (meth) acrylate obtained by reacting le acid, or a photopolymerizable liquid crystal compound, and the like having an acrylic group or methacrylic group.

  The amount of these compounds added to the composition for forming a liquid crystal layer of the present invention is selected within a range that does not impair the purpose of the present invention, and is generally 40% by mass or less of the composition for forming a liquid crystal layer of the present invention. It is preferable that there is, more preferably 20% by mass or less.

  In the present invention, a photopolymerization initiator is used as required in addition to the polymerizable liquid crystal material. When polymerizing a polymerizable liquid crystal material by electron beam irradiation, a photopolymerization initiator may not be necessary. However, in the case of curing by, for example, ultraviolet (UV) irradiation, which is generally used, photopolymerization is usually performed. An initiator is used to promote polymerization.

  As photopolymerization initiators, benzyl (also called bibenzoyl), benzoin isobutyl ether, benzoin isopropyl ether, benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-benzoyl-4'-methyldiphenyl sulfide, benzylmethyl ketal, dimethylamino Methylbenzoate, 2-n-butoxyethyl-4-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 3,3′-dimethyl-4-methoxybenzophenone, methylobenzoylformate, 2-methyl-1- (4 -(Methylthio) phenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, 1- (4-dodecylphenyl) -2- Droxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2- Examples include methylpropan-1-one, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, or 1-chloro-4-propoxythioxanthone. it can.

  In general, the addition amount of the photopolymerization initiator is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and still more preferably 0.5% by mass to In the range of 5% by mass, it can be added to the polymerizable liquid crystal material of the present invention.

  Addition of these compounds improves the curability of the liquid crystal material in the present invention, increases the mechanical strength of the resulting liquid crystal layer, and improves its stability.

  In addition, a surfactant or the like can be added to the composition for forming a liquid crystal layer containing a solvent in order to facilitate coating.

  Examples of surfactants that can be added include cationic surfactants such as imidazoline, quaternary ammonium salts, alkylamine oxides and polyamine derivatives; polyoxyethylene-polyoxypropylene condensates, primary or secondary Alcohol ethoxylates, alkylphenol ethoxylates, polyethylene glycol and esters thereof, sodium lauryl sulfate, ammonium lauryl sulfate, lauryl sulfate amines, alkyl-substituted aromatic sulfonates, alkyl phosphates, aliphatic or aromatic sulfonic acid formalin condensates, etc. Anionic surfactants; amphoteric surfactants such as laurylamidopropylbetaine and laurylaminoacetic acid betaine; nonionics such as polyethylene glycol fatty acid esters and polyoxyethylene alkylamine Surfactant: Perfluoroalkyl sulfonate, perfluoroalkyl carboxylate, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl trimethyl ammonium salt, perfluoroalkyl group / hydrophilic group-containing oligomer, perfluoroalkyl / lipophilic group Fluorosurfactants such as containing oligomer perfluoroalkyl group-containing urethanes.

  The amount of surfactant added depends on the type of surfactant, the type of liquid crystal material, the type of solvent, and the type of alignment film on which the solution is applied. 10 ppm-10 mass% is preferable, More preferably, it is 100 ppm-5 mass%, More preferably, it is the range of 0.1-1 mass%.

  As a method for coating the composition for forming a liquid crystal layer, a spin coating method, a roll coating method, a printing method, a dip pulling method, a die coating method, a casting method, a bar coating method, a blade coating method, a spray coating method, a gravure coating method , Reverse coating method or extrusion coating method.

  The method for removing the solvent after coating the composition for forming a liquid crystal layer is performed, for example, by air drying, heat removal, or removal under reduced pressure, or a combination thereof. By removing the solvent, a layer in which the alignment of the liquid crystal is fixed is formed.

  In the step of curing the polymerizable liquid crystal material, energy for curing the polymerizable liquid crystal material is given, and thermal energy may be used, but it is usually performed by irradiation with ionizing radiation capable of causing polymerization.

  If necessary, a polymerization initiator may be contained in the polymerizable liquid crystal material. The ionizing radiation is not particularly limited as long as it is a radiation capable of polymerizing the polymerizable liquid crystal material, but usually ultraviolet light or visible light is used from the viewpoint of the ease of the apparatus, and the wavelength is The light of 150-500 nm is preferable, More preferably, it is 250-450 nm, More preferably, it is an ultraviolet-ray with a wavelength of 300-400 nm.

  In the present invention, a method of performing radical polymerization by irradiating ultraviolet rays (UV) as actinic radiation and generating radicals from the polymerization initiator with ultraviolet rays is preferable. Since the method using UV as the actinic radiation is an already established technique, it can be easily applied to the present invention including the polymerization initiator to be used.

  As a light source for irradiating ultraviolet rays, a low-pressure mercury lamp (sterilization lamp, fluorescent chemical lamp, black light), a high-pressure discharge lamp (high-pressure mercury lamp, metal halide lamp), or a short arc discharge lamp (ultra-high pressure mercury lamp, xenon) Lamp, mercury xenon lamp) and the like.

  In particular, the use of metal halide lamps, xenon lamps, high-pressure mercury lamps, etc. is recommended. The irradiation intensity may be appropriately adjusted depending on the composition of the polymerizable liquid crystal material used for forming the layer in which the alignment of the liquid crystal is fixed and the amount of the photopolymerization initiator.

  The alignment fixing step by irradiation with actinic radiation may be performed under the processing temperature in the above-described step of forming the liquid crystal layer forming layer, that is, the temperature condition in which the polymerizable liquid crystal material becomes a liquid crystal phase, and the temperature at which the liquid crystal phase becomes a liquid crystal phase. It may be performed at a lower temperature.

<Horizontal alignment liquid crystal layer>
Horizontally aligned liquid crystal layers described in JP-A Nos. 2001-91741 and 2004-191803 can be used. For example, the optically anisotropic layer B described in paragraph 0060 of JP-A-2001-91741 and the liquid crystal alignment layer described in paragraph 0105 of JP-A-2004-191803 can be used.

<Hybrid alignment layer>
For example, a liquid crystal layer described in paragraph 0127 of JP-A-06-347742 can be used.
<Image display device>
Examples of the image display device suitably used in the present invention include a VA liquid crystal display device and an organic EL image display device.

  The VA liquid crystal display device can be applied to a known one, and is provided between the first polarizing plate, the second polarizing plate, and the first polarizing plate and the second polarizing plate. A vertical alignment liquid crystal cell and a VA liquid crystal display device having a backlight light source provided on the second polarizing plate side, the vertical alignment liquid crystal cell, the first and second polarizing plates, In the meantime, by providing the quarter wavelength plate of the present invention, it is possible to improve the contrast while reducing the occurrence of color unevenness from the front and oblique directions.

  Further, as a viewing angle compensation film for expanding the viewing angle of the VA liquid crystal display device, when an optical film having a retardation in the thickness direction is provided between the liquid crystal cell and the polarizer, a quarter wavelength plate If the phase difference value in the thickness direction is unnecessary, this function may be impaired. Therefore, the quarter-wave plate of the present invention that can easily control the thickness direction retardation value is particularly useful.

  The organic EL image display device is not particularly limited, and in a conventionally known organic EL image display device, a plurality of self-luminous elements (organic EL elements) are arranged in a plane on the quarter wavelength plate of the present invention. What is necessary is just to provide in the visual recognition side of an image formation cell.

The present invention will be specifically described below with reference to examples.
Example 1
<Production of first optically anisotropic layer>
<Fine particle dispersion>
Fine particles 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle additive solution>
Cellulose ester A was added to a dissolution tank containing methylene chloride and heated to completely dissolve, and this was then added to Azumi filter paper No. 3 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244. The fine particle dispersion was slowly added thereto while sufficiently stirring the filtered cellulose ester solution.

  Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.

Methylene chloride 99 parts by weight Cellulose ester A (acetyl group substitution degree 1.6 propionyl group substitution degree 0.9 total substitution degree 2.7) 4 parts by weight Fine particle dispersion 11 parts by weight A main dope liquid having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose ester A was added to a pressurized dissolution tank containing a solvent while stirring. This was heated and stirred to completely dissolve, and a plasticizer and an ultraviolet absorber were further added and dissolved. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

  In addition to adding 100 parts by mass of the main dope solution and 2 parts by mass of the fine particle additive solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting apparatus to adjust the width. It was cast uniformly on a 2 m stainless steel band support. On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off.

Thereafter, using the apparatus shown in FIG. 1 of the present invention, the temperature is 170 ° C., the magnification is 2.0 times, the slow axis is inclined at 45 ° to the film width direction, and the first optical is dried. A 90 μm cellulose ester film 1 as an anisotropic layer 1 was obtained. Ro ₁ = 212 nm and Rt = 175 nm.

<Composition of main dope solution>
Methylene chloride 300 parts by mass Ethanol 57 parts by mass Cellulose ester A 100 parts by mass Plasticizer (A), (B), (C) Added at a mass ratio of 1: 1: 5.5 parts by mass Plasticizer (D) Trimethylol Propane tribenzoate 5.5 parts by weight UV absorber (A) Tinuvin 326 (manufactured by Ciba Japan) 0.4 parts by weight UV absorber (B) Tinuvin 109 (manufactured by Ciba Japan) 0.7 Part by mass UV absorber (C) Tinuvin 171 (manufactured by Ciba Japan) 0.6 parts by mass

<Preparation of second optically anisotropic layer>
(Polycarbonate film 1)
An unstretched polycarbonate film (Mitsubishi Gas Chemical Co., Ltd., film thickness 100 μm) is stretched 3.0 times, stretched at 140 ° C., and the slow axis forms −45 ° with the film width direction. In this manner, the film was stretched obliquely to obtain a film (second optically anisotropic layer 1) having a thickness of 35 μm. Ro ₂ = 75 nm and Rt = 33 nm.

(Polystyrene film 1)
An unstretched polystyrene film (film thickness: 100 μm) is stretched in an oblique direction so that the stretching ratio is 2.5 times, the stretching temperature is 105 ° C. and the slow axis is −45 ° with the film width direction, and the film 8 (second film thickness) is 40 μm. An optically anisotropic layer 2) was obtained. Ro ₂ = 75 nm and Rt = −37 nm.
<Preparation of 1/4 wavelength plate of the present invention>
Using an acrylic adhesive with a thickness of 10 μm so that the slow axes of the cellulose ester film 1 and the second optically anisotropic layers 1 and 2 as the first optically anisotropic layer are orthogonal to each other, It bonded together with the roll tool roll. The quarter-wave plates 1 and 2 after being bonded were Ro = 138 nm, Rt = 208 nm, Ro = 138 nm, and Rt = 138 nm, respectively.
<Lamination of second optically anisotropic layer and first optically anisotropic layer as liquid crystal layer>
The prepared long-sized cellulose ester film 1 was continuously applied to the saponified surface with an alignment film coating solution having the following composition using a # 14 wire bar. The alignment film was formed by drying with warm air of 60 ° C. for 60 seconds and further with warm air of 100 ° C. for 120 seconds. The alignment film was rubbed at an angle of −45 ° so as to be orthogonal to the slow axis of the cellulose ester film 1.
(Composition of alignment film coating solution)
The following modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde 0.5 parts by weight

  Next, the following coating liquid A is applied onto the alignment film with an extrusion coater, dried by applying hot air, and then irradiated with UV to cure the entire layer to provide a horizontal alignment liquid crystal layer. An optically anisotropic layer 3 was produced. The thickness of the horizontal alignment liquid crystal layer after curing was adjusted to 0.50 μm.

(Liquid crystal coating liquid A)
Horizontal alignment liquid crystal compound (Palicolor LC242 manufactured by BASF Corporation)
16 parts by mass Photoinitiator (Irgacure 907 manufactured by Ciba Japan Co., Ltd.) 0.6 parts by mass Methyl ethyl ketone 16.8 parts by mass Propylene glycol monomethyl ether 67.2 parts by mass As the quarter-wave plate 3, Ro = 138 nm, Rt = 236 nm.

(Liquid crystal coating liquid B)
A second optically anisotropic layer 4 was produced in the same manner as the application of the liquid crystal coating liquid A. The thickness of the vertically aligned liquid crystal layer after curing was adjusted to 0.65 μm.

Vertical alignment liquid crystal compound: UCL-018 (manufactured by Dainippon Ink & Chemicals, Inc.) 16 parts by mass Photoinitiator (Irgacure 907, manufactured by Ciba Japan) 0.6 parts by mass Methyl ethyl ketone 16.8 parts by mass Propylene glycol monomethyl ether 67.2 parts by mass The quarter-wave plate 4 was Ro = 138 nm and Rt = 0 nm.
<Comparison>
A laminate comprising a polycarbonate film and a polycycloolefin film described in Example 1 of JP-A-2004-145282 was prepared (Comparative 1).

Moreover, the wave plate A described in Example 1 of JP-A-2008-70635 was produced (Comparative 2).
Example 2
<Preparation of polarizing plate>
A long film of polyvinyl alcohol having a thickness of 120 μm was uniaxially stretched in the MD direction (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer film.

  Then, after saponifying the cellulose ester film side of the quarter wavelength plates 1 to 5 and Comparative Examples 1 and 2 described in Example 1 on one surface of the polarizer film according to the following steps 1 to 5, A 2% by weight polyvinyl alcohol adhesive was used for bonding.

On the other side of the polarizer film, Konica Minoltak KC8UE (manufactured by Konica Minolta Opto Co., Ltd.) was similarly saponified and then bonded together.
<Evaluation>
The quarter-wave plate was peeled off from the display panel mounted on the mobile phone W56T (manufactured by Toshiba Corporation), and the quarter-wave plate of the present invention was attached. About this display apparatus, the external light reflectance was measured by CM-2500d.

All of the present invention exhibited high external light antireflection performance.
Example 3
After coating the alignment film described in Example 1 on the cellulose ester film surface side of the prepared quarter-wave plates 1 to 3, the liquid crystal coating liquid B described in Example 1 is the same as in Example 1, respectively. 1/4 wavelength plates 6 to 8 and 9 to 11 were produced. In this case, the thickness of the liquid crystal layer was adjusted so that the quarter-wave plates 6 to 8 were Rt = 0 nm, and the quarter-wave plates 9 to 11 were 90 nm.

  With respect to this quarter-wave plate, the color change from the oblique direction of external light reflection was evaluated visually.

<Evaluation of color change angle dependence of external light reflection>
The above display device is stored in a room at 23 ° C. and 55% RH for 48 hours (state 1), is not applied with voltage and is not emitting light, is placed in an environment with an illuminance of about 100 lx, and is obliquely 45 degrees to the front. The blackness level of the reflected color was visually evaluated from the direction of, and the difference was compared. The results are shown in Table 2.

<Evaluation scale for color change angle dependency>
◎: No change in the color of external light reflection between the front and perspective. ○: A slight difference in the color of external light reflection is seen between the front and perspective. State where color difference of external light reflection is worrisome ×: State where color difference of external light reflection is very worrisome between front and perspective

  In any of the present inventions, reflection of light from the oblique direction and change in color did not occur.

It is a schematic plan view which shows an example of the manufacturing apparatus of the stretched film of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermoplastic resin film 2 Preheating zone 3 Heating extension zone 4 Cooling zone 5 Stretched film 6,7 Screw 61,71 Flight 8,81 Clip 9,91 Belt 101 Thermoplastic resin film 102 Tenter 103 Conveying direction 104L Left chuck position 104R Right Chuck position 105L Film left moving position 105R Film right moving position 106L Left moving speed 106R Right moving speed

Claims (4)

A quarter-wave plate in which at least a first optical anisotropic layer and a second optical anisotropic layer are laminated, wherein the first optical anisotropic layer is a cellulose ester film; And the retardation value Ro ₁ in the in-plane direction at the wavelength λ satisfies λ / 4 <Ro ₁ <λ / 2,
The second optically anisotropic layer has positive wavelength dispersion, and an in-plane retardation value Ro _{2 at a} wavelength λ satisfies 0 <Ro ₂ <λ / 4,
The difference Ro _d between Ro ₁ and Ro ₂ satisfies λ / 4.5 <Ro _d <λ / 3.5,
A quarter wavelength plate, wherein a slow axis of the first optically anisotropic layer and a slow axis of the second optically anisotropic layer are orthogonal to each other.
However, said Ro ₁ and Ro ₂ are respectively defined by the following formulas.
Ro _n = (nx−ny) × d
n represents 1 or 2, the refractive index in the slow axis direction in the plane of each optical anisotropic layer is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, and d is each Represents thickness (nm). λ is an arbitrary wavelength of 400 to 700 nm. 2. The quarter-wave plate according to claim 1, wherein a retardation value Rt in the thickness direction at a wavelength λ is 100 nm or less.
However, Rt is defined by the following equation.
Rt = ((nx + ny) / 2−nz) × d
The refractive index in the slow axis direction in the plane of the quarter-wave plate is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, the refractive index in the direction perpendicular to the film surface is nz, and d Represents the thickness of the quarter-wave plate.   3. An image display device comprising: the quarter wavelength plate according to claim 1; an image forming cell in which a plurality of self-luminous elements are arranged in a planar shape; and a reflector.   A first polarizing plate, a second polarizing plate, a vertical alignment type liquid crystal cell provided between the first polarizing plate and the second polarizing plate, and a back provided on the second polarizing plate side A liquid crystal display device having a light source, wherein the quarter-wave plate according to claim 1 or 2 is provided between the vertical alignment type liquid crystal cell and the second polarizing plate. Liquid crystal display device.

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