JPWO2007018267A1 - Retardation film obtained from cellulose derivative - Google Patents

Abstract

A film produced by a cellulose derivative in which a hydroxyl group is substituted by an aliphatic acyl group (A) having 5 to 20 carbon atoms of the present invention, and the substitution degree of the hydroxyl group is 0.50 to 2.99 per cellulose monomer unit. When the refractive index in the slow axis direction in the plane is nx, the refractive index in the direction perpendicular to the slow axis direction in the film plane is ny, and the refractive index in the thickness direction is nz, nx> ny> nz. When an optically biaxial retardation film is used as a retardation film for VA mode compensation, the contrast is reduced in comparison with a conventional cellulose retardation film when displaying VA cell in a non-driven state. The light leakage during tilt observation, which is the cause of the above, can be largely suppressed over a wide range to maintain low luminance, and a wide viewing angle can be achieved.

Description

  The present invention is an optically biaxial retardation obtained by biaxial stretching of a C5-C20 aliphatic acyl-substituted cellulose derivative and having a refractive index in the film normal direction smaller than that in the fast axis direction. The present invention relates to a film, a polarizing plate using the film, and an image display device.

  Liquid crystal display devices are widely used in mobile applications such as mobile phones and PDAs (Personal Degital Assistance), car navigation monitors that require durability, and large-screen home televisions. In particular, twisted nematic (TFT-TN mode) liquid crystal display devices have been used for applications requiring high display quality such as high contrast and high viewing angle.

  However, the TFT-TN mode has a disadvantage that the viewing angle is poor in principle. Therefore, when observed from an oblique direction, it causes a decrease in contrast and inversion of gradation. Therefore, a new liquid crystal mode replacing the TFT-TN mode is required, and one of them is a vertical alignment nematic type (VA mode) liquid crystal display device. The VA mode is a display mode that can exhibit a wide viewing angle characteristic. For this reason, it has already been widely adopted in home televisions and recently used in small liquid crystal display devices such as mobile phones and digital camera monitors.

  Even in the VA mode, a retardation film can be used for viewing angle compensation as in other liquid crystal display systems, and has two elements to be compensated. The first is compensation for light leakage of a so-called polarizing plate caused by the fact that the absorption axes of the two polarizing plates are not apparently orthogonal when the liquid crystal display device is observed from an oblique direction. For this compensation, a retardation film called a positive A plate and a positive C plate is usually used.

  Secondly, when the VA cell is observed from an oblique direction, the birefringence of the liquid crystal molecules increases, and light leakage due to the cell occurs during black display, which is necessary compensation because a decrease in contrast is observed. In order to compensate the birefringence of the vertically aligned liquid crystal, a retardation film called a negative C plate is required. Negative C plates can be easily obtained by laminating retardation films. However, when many films and cells are bonded together using an adhesive or the like, interface reflection occurs due to the difference in refractive index, and the overall contrast decreases. Or interference unevenness occurs. Further, by using a plurality of retardation films, the increase in production cost becomes remarkable, and a large amount of investment is required for the retardation film that is only a part of the optical member. In addition, the yield is inevitably lowered as the number of bonding steps increases. Terms such as a positive A plate and a negative C plate are described in Patent Document 1 below.

  In Patent Document 1, a VA mode having high contrast, no interference unevenness, and good color reproducibility is realized by a compensation method in which a positive A plate and a negative C plate are laminated with a specific combination of wavelength dispersion. However, since it is used for a plurality of retardation films for compensation, it is not a fundamental solution to the problems caused by using the plurality of retardation films.

  Patent Document 2 proposes a method of compensating for the VA mode using a retardation film containing a discotic compound oriented in a special direction instead of a stretched birefringent film. In this method, since the alignment of the liquid crystal can be controlled in a complicated manner, precise cell compensation is possible. However, generally discotic compounds and processed products containing them are very expensive, and there remains a problem in terms of cost in the phase difference film market where both cost reduction and high performance are required.

  Patent Document 3 discloses a method of obtaining a viewing angle compensation retardation film that stretches a norbornene-based cyclic olefin polymer and satisfies the necessary optical characteristics with a single retardation film. However, in the current situation where thinning and weight reduction of liquid crystal display members are strongly desired, there are the following problems.

  A polarizing element combined with a retardation film is composed of a uniaxially stretched polyvinyl alcohol film containing a dichroic dye, so it is very brittle and has poor durability against temperature and moisture. Therefore, a protective film such as triacetyl cellulose is used on both sides. It is pinched. The polarizing element with the protective film is called a polarizing film. The retardation film of Patent Document 3 is bonded using a polarizing film and an adhesive. Here, for example, if the retardation film can be directly bonded to the polarizing element instead of the protective film, a retardation film-integrated polarizing film having a thickness reduced by one protective film can be obtained. However, norbornene-based and other cyclic olefin-based polymer films have poor adhesion to polarizing elements, and are not easily integrated while maintaining high durability.

As a retardation film material that can be integrated with a polarizing element, there is a cellulose polymer. It is known that triacetyl cellulose often used for a protective film can be bonded to a polarizing element using a polyvinyl alcohol-based adhesive after saponifying the film surface. Patent Document 4 discloses a method of compensating a VA cell by producing a retardation film integrated with a polarizing element using a single cellulose acylate film, particularly cellulose acetate or cellulose propionate. Patent Document 5 discloses a method of compensating for a VA cell with a single sheet, particularly using cellulose acetate propionate.
Patent Document 6 describes a retardation film obtained by uniaxially stretching a cellulose derivative in which a hydroxyl group is substituted by an aliphatic acyl group (A) having 5 to 20 carbon atoms. The effect is not sufficient for improving the viewing angle characteristics.
JP 2004-326089 A Japanese Patent No. 2866372 JP-A-11-95208 JP 2005-134863 A JP 2004-133171 A WO2005 / 022215

  However, the cellulose-based retardation films described in Patent Document 4 and Patent Document 5 are not yet satisfactory in view angle compensation effect according to the study by the present inventors, and further, the humidity changes near room temperature. In this case, the change in the retardation value (environment resistance) was large, and there was a problem in improving the viewing angle stably. Therefore, it is desired to develop a retardation film that can be easily integrated with a non-protected surface of the polarizing film, has an excellent viewing angle compensation effect, and has little change in retardation value due to environmental changes.

  As a result of intensive studies to solve the above-mentioned problems, the inventors have substituted hydroxyl groups with aliphatic acyl groups having 5 to 20 carbon atoms, and the substitution degree of the hydroxyl groups is 0.50 to 2 per cellulose monomer unit. The optically biaxial retardation film produced by biaxial stretching using a cellulose derivative of .99 has an excellent VA mode compensation effect, and further an additive for film production As a result, the inventors have found that a retardation film having excellent environmental resistance can be obtained.

That is, the present invention relates to (1) a cellulose derivative in which a hydroxyl group is substituted by an aliphatic acyl group (A) having 5 to 20 carbon atoms, and the substitution degree of the hydroxyl group is 0.50 to 2.99 per cellulose monomer unit. The film in-plane retardation value Re represented by the following formula (1) is 0 nm or more and 200 nm or less, and the retardation value in the film normal direction represented by the formula (2) Rth is 80 nm or more and 300 nm or less, and an optically biaxial retardation film in which nx>ny> nz, where each symbol represents the following meaning:
Re = (nx−ny) × d (1)
Rth = [(nx + ny) / 2−nz] × d (2)
nx: Refractive index in the slow axis direction in the film plane ny: Refractive index in the fast axis direction in the film plane nz: Refractive index in the film normal direction d: Film thickness (2) Substituent of the cellulose derivative (1) the aliphatic acyl group having 5 to 20 carbon atoms (A) alone, or (2) the aliphatic acyl group having 5 to 20 carbon atoms (A) and other substituents (B). An aliphatic acyl group, an aromatic acyl group, an alkylcarbamoyl group, an aromatic carbamoyl group, a tranalkyl group having a structure different from that of the aliphatic acyl group (A). The retardation film of (1), which is any of an acyl group having a skeleton, an acyl group having a biphenyl skeleton, or a polymerizable group,
(3) When the aliphatic acyl group (A) having 5 to 20 carbon atoms is a linear aliphatic acyl group having 5 to 7 carbon atoms and a linear aliphatic acyl group having 5 or 6 carbon atoms The degree of substitution is 2.0 to 2.8, and in the case of a C7 aliphatic acyl group, the degree of substitution is a cellulose derivative having a degree of substitution of 1.5 to 2.3. Retardation film,
(4) The film made of the cellulose derivative is produced from a resin composition containing the cellulose derivative and both a reactive monomer or a reactive monomer and a polymerization initiator. The retardation film according to any one of the above,
(5) The retardation film according to (4), wherein the reactive monomer is a thermosetting compound,
(6) The retardation film according to (5), wherein the thermosetting compound is a silane coupling agent,
(7) The position according to the above (1) to (6), wherein the aliphatic acyl group (A) is an n-hexanoyl group, and the degree of substitution of the hydroxyl group with the n-hexanoyl group is 1.80 to 2.90. Phase difference film,
(8) The retardation value Re in the film plane is 10 nm or more and 80 nm or less, the retardation value Rth in the film normal direction is 100 nm or more and 250 nm or less, and the thickness d of the film is 30 μm or more and 110 μm or less (1 ) To (7) The retardation film according to any one of
(9) When the phase difference value at a wavelength of 450 nm is Re450, the phase difference value at a wavelength of 550 nm is Re550, and the phase difference value at a wavelength of 750 nm is Re750, the relationship of the following formulas (3), (4), and (5) The retardation film according to any one of (1) to (7), characterized in that:
Re450 ≦ Re550 ≦ Re750 (3)
0.50 ≦ Re450 / Re550 <0.99 (4)
1.00 <Re750 / Re550 ≦ 1.50 (5)
(10) The retardation film according to any one of (1) to (9), wherein the film made of the cellulose derivative is a film produced by a solvent casting method.
(11) The retardation film according to any one of (1) to (10) above and a protective film protective surface or a polarizing element unprotected surface constituting the polarizing film are bonded using an adhesive or a pressure-sensitive adhesive. Combined functional polarizing film,
(12) An image display device comprising the retardation film according to any one of (1) to (10), the functional polarizing film according to (9),
(13) The image display device according to (12), wherein the image display device is a vertical alignment nematic (VA) liquid crystal display device,
About.

  The optically biaxial retardation film produced using the cellulose derivative used in the present invention (hereinafter also simply referred to as a cellulose derivative) is significantly more than the conventional retardation film for cellulose-based VA compensation. Excellent viewing angle compensation effect. Since it is a cellulose derivative, it can be in close contact with the polarizing element after the saponification treatment, and a retardation film integrated polarizing film can be produced. Further, the retardation film of the present invention comprising a film obtained by polymerizing or crosslinking (hereinafter also referred to simply as polymerization) a reactive monomer such as a cellulose derivative containing a silane coupling agent has durability and / or environmental resistance performance. And more preferable. Furthermore, since a single retardation film has a sufficient viewing angle compensation effect, it can contribute to thinning of the liquid crystal display device. In addition, although it is a cellulose derivative, it can be dissolved in a non-halogen solvent, and therefore has excellent processability and environmental resistance.

In each of the VA mode liquid crystal display devices using the polarizing film having the compensation function (the present invention Example 4 and Comparative Example 1) and the polarizing film having no compensation function (Comparative Example 2) each having the retardation film bonded thereto, From the black luminance measurement data in all directions, the cross section of the black luminance distribution in the film normal direction at 45 ° clockwise from the absorption axis of the polarizing plate is graphed. 6 is a graph showing changes in retardation value Re in a film plane in each environmental resistance test of the retardation film of Example 7 of the present invention and the retardation film made of cellulose acetate propionate of Comparative Example 1; It is the graph which showed the change of retardation value Rth of the film normal direction in each environmental resistance test of the retardation film of Example 7 of this invention and the retardation film which consists of a cellulose acetate propionate of the comparative example 1. .

Explanation of symbols

FIG.
□: Functional polarizing film of Example 4 (polarizing film obtained by laminating the retardation film of Example 3)
○: Polarizing film with a known retardation film bonded to Comparative Example 1 ×: Polarizing film without a compensation function of Comparative Example 2 FIGS. 2 and 3
◇: Retardation film of Example 7 ○: Retardation film A of Comparative Example 4: Vacuum drying conditions (10 mmHg, humidity 27%, temperature 30 ° C.)
The numerical value after A indicates the number of times.
B: High humidity conditions (normal pressure, humidity 80%, temperature 30 ° C)
The numerical value after B indicates the number of times.
init: indicates an initial value.

The present invention will be described in detail.
In the present invention, a hydroxyl group is substituted with an aliphatic acyl group (A) having 5 to 20 carbon atoms, which is used as a raw material for a retardation film, and the substitution degree of the hydroxyl group is 0.50 to 2.99 per one monomer unit of cellulose. In the case where the cellulose derivative is described in Patent Document 6 or is not described, it can be produced according to it.
The cellulose that can be used as a starting material for the cellulose derivative is as shown in the formula (6) regardless of the crystal form and the degree of polymerization.

Any structure in which D-glucopyranose is linked by β-1,4 bonds can be used. Specific examples include natural cellulose, powdered cellulose, crystalline cellulose, regenerated cellulose, cellulose hydrate, and rayon.

  The cellulose derivative used for producing the retardation film of the present invention is one in which the hydroxyl group of cellulose is substituted as shown in the formula (7).

In formula (7), R1, R2, and R3 are hydrogen atoms or substituents, and R1, R2, and R3 may be the same or different, but all of R1, R2, and R3 are hydrogen atoms. There is no such thing, and at least one is an aliphatic acyl group having 5 to 20 carbon atoms. In addition, these substituents may contain a substituent different from the aliphatic acyl group having 5 to 20 carbon atoms. When the different substituents are included, the abundance ratio of each substituent may be an arbitrary ratio. In the cellulose derivative having at least one kind of aliphatic acyl group having 5 to 20 carbon atoms, the sum of the number of substituents per unit of cellulose (degree of substitution) is 0.50 to 2.99, preferably It is 1.00-2.90. In some cases, the degree of substitution is preferably in the range of 1.5 to 2.95, more preferably 2.0 to 2.8. The substituent may be only the aliphatic acyl group or may contain other substituents. When other substituents are included, the aliphatic acyl group preferably occupies 40% or more, preferably 50% or more of the total substituents. Most preferred is a C5-C7 aliphatic acyl group alone.
N is preferably an integer of 10 or more, more preferably 50 or more, and still more preferably 100 or more. In some cases, 300 or more, 400 or more, and more preferably 500 or more are preferable. Although there is no upper limit, it is usually 10,000 or less, preferably 5000 or less, more preferably 2000 or less. Accordingly, 300 to 10000 is a preferable range of the degree of polymerization n, and more preferably 500 to 5000. In addition, n shows a weight average polymerization degree normally.
Preferred as the aliphatic acyl group having 5 to 20 carbon atoms is a C5 to C16 aliphatic acyl group, more preferably a C5 to C12 aliphatic acyl group, more preferably 5 to 7 carbon atoms. An aliphatic acyl group (preferably a linear aliphatic acyl group). In the case of a linear aliphatic acyl group having 5 or 6 carbon atoms, the degree of substitution is 2.0 to 2.8, preferably 2.0 to 2.6, and in the case of an aliphatic acyl group having 7 carbon atoms. The degree of substitution is 1.5 or more and less than 2.5, preferably 1.5 to 2.3. Specific examples of the aliphatic acyl group having 5 to 7 carbon atoms include an n-pentanoyl group, an n-hexanoyl group, and an n-heptanoyl group, and an n-hexanoyl group having 6 carbon atoms is most preferable. . The degree of substitution with an n-pentanoyl group or n-hexanoyl group may be in the above range, but is preferably about 1.8 to 2.9, more preferably about 2.0 to 2.8, More preferably, it is about 2.0 to 2.6. Further, the degree of substitution with an n-heptanoyl group is preferably about 1.5 to 2.5.

In the present invention, examples of the acyl group other than the aliphatic acyl group (A) having 5 to 20 carbon atoms include an acyl group having a structure different from that of the aliphatic acyl group (A) (for example, an aliphatic acyl group, an aromatic acyl group). , An acyl group having a tolan skeleton or an acyl group having a biphenyl skeleton), a carbamoyl group (for example, an aliphatic group having 1 to 10 carbon atoms or an aromatic carbamoyl group which may have a substituent such as a phenyl group or a halogen atom) Group), a polymerizable group, and the like. In addition, what is described as preferable in the next item described for the cellulose derivative of the formula (7) is more preferable.
In the formula (7), a substituent other than the aliphatic acyl group having 5 to 20 carbon atoms is preferably a carbamoyl group, an acyl group other than the aliphatic acyl group having 5 to 20 carbon atoms, or a polymerizable group. And more preferably an carbamoyl group or an acyl group other than an aliphatic acyl group having 5 to 20 carbon atoms.
As a preferable cellulose derivative, specifically, R1, R2, and R3 in the formula (7) are substituted under the condition that at least one is substituted with an aliphatic acyl group having 5 to 20 carbon atoms. Y-CO- group alone or a compound substituted with both Y-CO- group and Z-NH-CO- group, more preferably substituted only with a group contained in Y-CO- Is preferred. Y represents a substituted or unsubstituted hydrocarbon residue having 1 to 20 carbon atoms, for example, vinyl group, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group. Pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group, benzyl group, 1-naphthylmethyl group, trifluoromethyl group, aminomethyl group, 2-amino-ethyl group, 3-amino -N-propyl group or 4-amino-n-butyl group, or a substituent in which those amino groups are further converted to amide or urethane, a hydroxy-substituted (C1-C4) alkyl group, or a hydroxyl group thereof is further (C1 To C14) an acyl group or a group substituted with an (C1 to C14) alkyl group, or a (C1 to C3) alkyl group. Aliphatic groups having an unsaturated bond having 1 to 10 carbon atoms such as vinyl group, cyanobiphenyloxy (C3 to C10) alkyl group, acetylene group and cinnamoyl group, phenyl group, naphthyl group, anthracenyl group, fluorenyl group, biphenyl group Or an acyl group having an aromatic group such as a 4-trifluoromethylphenyl group, or as Z, an aliphatic group having 1 to 10 carbon atoms which may have a substituent (for example, a phenyl group, a halogen atom, etc.) For example, vinyl group, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group , Nonyl group, decyl group, benzyl group, 1-naphthylmethyl group, trifluoromethyl group, etc. . These substituents are appropriately selected according to the purpose in consideration of the birefringence, wavelength dispersion characteristics, viscosity, ease of orientation, processability, reactivity, etc. of the cellulose derivative used in the present invention, There may be one or more. The degree of substitution of cellulose hydroxyl groups with these substituents is also appropriately selected according to the purpose.

The cellulose derivatives used in the present invention are described in WO 2005/022215 and the like, and are all known or can be easily synthesized according to the method described in the publication. For example, first, cellulose as a starting material is dissolved in an organic solvent. As the organic solvent, any solvent other than alcohols may be used, but a halogen solvent such as chloroform or dichloromethane, or a polar solvent such as dimethylacetamide, dimethylformamide, acetone or cyclopentanone is preferable. . It is preferable that cellulose is impregnated with the organic solvent in advance before dissolution because the solubility of cellulose is improved. A cellulose solution of 2 to 20% by weight, preferably 5 to 10% by weight, is prepared using the organic solvent. A reagent for introducing a substituent is added to the cellulose solution, and the reaction is carried out while maintaining a constant temperature. Substituent introduction reagents are acylating agents such as carboxylic acid anhydrides and carboxylic acid chlorides, and carbamoylating agents such as isocyanates and di-n-butyltin dilaurate. The reaction temperature is appropriately set according to the reactivity of cellulose and the substituent introduction reagent. After the reaction, reprecipitation is performed by adding a reaction solution in water or methanol, and the precipitated solid content is dried, whereby the cellulose derivative used in the present invention can be obtained.
Adjustment of the degree of substitution of the cellulose derivative used in the present invention can be achieved by adjusting the amount of the substituent introduction reagent used during the synthesis of the cellulose derivative. The reagent for introducing a substituent can be used in the range of 0.5 to 100 equivalents relative to the amount of hydroxyl group of cellulose used as a reaction raw material, and a cellulose derivative with a higher degree of substitution can be obtained as more is used. Since the reactivity with the cellulose hydroxyl group varies depending on the type of the introduction reagent, the amount of the substituent introduction reagent necessary to achieve a certain degree of substitution varies. For example, when cellulose n-hexanate having a substitution degree of 2.14 is obtained, the reaction is performed for 4 hours or more using 1.05 equivalents of n-hexanoyl chloride with respect to the hydroxyl group of cellulose. On the other hand, when cellulose n-hexanate having a substitution degree of 2.74 is obtained, the reaction is carried out for 4 hours or more using 1.50 equivalents of n-hexanoyl chloride with respect to the hydroxyl group of cellulose.

  By introducing a polymerizable group into the cellulose derivative, the alignment state is fixed by irradiating with ultraviolet rays after the alignment treatment in the presence of a photopolymerization initiator, and the mechanical state, reliability, and solvent resistance are excellent. A retardation film can be obtained. Examples of the polymerizable group include those in which Y and Z are vinyl groups, that is, acryloyl groups and methacryloyl groups. As a photoinitiator, the compound used for normal ultraviolet curable resin can be used. Specific examples of the compound that can be used include 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1 (Irgacure 907 manufactured by Ciba Specialty Chemicals), 1-hydroxycyclohexyl phenyl ketone (Ciba Specialty). Irgacure 184 from Tea Chemicals), 4- (2-hydroxyethoxy) -phenyl (2-hydroxy-2-propyl) ketone (Irgacure 2959 from Ciba Specialty Chemicals), 1- (4-dodecylphenyl) -2- Hydroxy-2-methylpropan-1-one (Merck Darocur 953), 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one (Merck Darocur 1116), 2-hydroxy-2 -Methyl-1-phenylpropa -1-one (Irgacure 1173 manufactured by Ciba Specialty Chemicals) or acetophenone compounds such as diethoxyacetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, or 2,2-dimethoxy-2- Benzoin compounds such as phenylacetophenone (Irgacure 651 manufactured by Ciba Specialty Chemicals), benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyldiphenyl sulfide, or 3,3 ′ -Benzophenone compounds such as dimethyl-4-methoxybenzophenone (Nippon Kayaku MBP), thioxanthone, 2-chloro Oxanson (Nippon Kayaku Cayacure CTX), 2-methylthioxanthone, 2,4-dimethylthioxanthone (Kayacure RTX), isopropylthioxanthone, 2,4-dichlorothioxanthone (Nippon Kayaku Cayacure CTX) Thioxanthone compounds such as 2,4-diethylthioxanthone (Nippon Kayaku Kayacure DETX) or 2,4-diisopropylthioxanthone (Nippon Kayaku Kyakuure DITX). These photopolymerization initiators may be used alone or in combination at any ratio.

  When a benzophenone compound or a thioxanthone compound is used, an auxiliary agent can be used in combination in order to promote the photopolymerization reaction. Examples of such auxiliaries include triethanolamine, methyldiethanolamine, triisopropanolamine, n-butylamine, n-methyldiethanolamine, diethylaminoethyl methacrylate, Michler's ketone, 4,4′-diethylaminophenone, 4-dimethylaminobenzoic acid. Examples include amine compounds such as ethyl, ethyl 4-dimethylaminobenzoate (n-butoxy) or isoamyl 4-dimethylaminobenzoate. The content of the photopolymerization initiator is preferably 0.5 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of a (meth) acrylate compound (including an acryloyl group in the polymer). More preferably, it is about 2 to 8 parts by weight. The auxiliary agent is preferably about 0.5 to 2 times the amount of the photopolymerization initiator.

  Moreover, although the irradiation amount of an ultraviolet-ray changes with kinds of this liquid crystalline compounding composition, the kind and addition amount of a photoinitiator, and a film thickness, about 100-1000 mJ / cm <2> is good. In addition, the atmosphere during ultraviolet irradiation may be air or an inert gas such as nitrogen. However, when the film thickness is reduced, it does not cure sufficiently due to oxygen damage. In such a case, ultraviolet light is irradiated in an inert gas. It is preferable to cure.

  In addition to the photopolymerization initiator, a reactive monomer different from the cellulose derivative can be added to the cellulose derivative for producing the retardation film of the present invention. As the reactive monomer, a compound that can be photopolymerized by ultraviolet irradiation and a compound that can be polymerized by heat treatment are preferable in consideration of the treatment that can be practically performed on the production line. Examples of the photopolymerizable compound include (meth) acrylate compounds. When the retardation film of the present invention is produced from a cellulose derivative containing these, these additives are contained in place of the cellulose derivative solution when producing the retardation film of the present invention from the cellulose derivative described later. What is necessary is just to carry out similarly using this cellulose derivative solution.

  Examples of (meth) acrylate compounds include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol pentaacrylate, di Pentaerythritol hexaacrylate, reaction product of pentaerythritol tri (meth) acrylate and 1,6-hexamethylene diisocyanate, reaction product of pentaerythritol tri (meth) acrylate and isophorone diisocyanate, tris (acryloxyethyl) isocyanurate , Tris (methacryloxyethyl) isocyanurate, reaction product of glycerol triglycidyl ether and (meth) acrylic acid , Caprolactone-modified tris (acryloxyethyl) isocyanurate, reaction product of trimethylolpropane triglycidyl ether and (meth) acrylic acid, triglycerol di (meth) acrylate, propylene glycol diglycidyl ether and (meth) acrylic acid Reaction products of polypropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, pentaerythritol Di (meth) acrylate, reaction product of 1,6-hexanediol diglycidyl ether and (meth) acrylic acid, 1,6-hexanediol di (meth) acrylate , Glycerol di (meth) acrylate, reaction product of ethylene glycol diglycidyl ether and (meth) acrylic acid, reaction product of diethylene glycol diglycidyl ether and (meth) acrylic acid, bis (acryloxyethyl) hydroxyethyl isocyanate Nurate, bis (methacryloxyethyl) hydroxyethyl isocyanurate, reaction product of bisphenol A diglycidyl ether and (meth) acrylic acid, tetrahydrofurfuryl (meth) acrylate, caprolactone modified tetrahydrofurfuryl (meth) acrylate, 2 -Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, Enoxyhydroxypropyl (meth) acrylate, acryloylmorpholine, methoxypolyethylene glycol (meth) acrylate, methoxytetraethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, methoxyethyl ( (Meth) acrylate, glycidyl (meth) acrylate, glycerol (meth) acrylate, ethyl carbitol (meth) acrylate, 2-ethoxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, 2-cyanoethyl (meth) ) Acrylate, reaction product of butyl glycidyl ether and (meth) acrylic acid, butoxytriethylene glycol (meth) acrylate or butane All mono (meth) acrylate. These compounds may be used alone or in combination. By using such a reactive compound and polymerizing under appropriate conditions, a desired orientation state can be fixed.

  When the cellulose derivative solution is used as a composition containing a compound (also referred to as a thermally polymerizable compound) that can be polymerized (including cross-linked) by heat treatment or the like, the film is simultaneously formed with the heat treatment when the film is produced by a solvent casting method. It can be cured, can contribute to improving the durability of the film, and has an advantage that the process becomes simple. This method may be selected if it is more effective to perform thermosetting crosslinking treatment after film stretching.

Examples of the thermally polymerizable compound include isocyanate compounds. For example, as hexamethylene isocyanate polyisocyanate, Asahi Kasei Biuret type isocyanate 24A-100, 22A-75PX, 21S-75E, 18H-70B, isocyanurate type isocyanate TPA-100, THA-100, MFA-90X, TSA-100 , TSS-100, TSE-100, adduct type isocyanurate P-301-75E, E-402-90T, E-405-80T, bifunctional prepolymer type isocyanate D-101, D-201, block type isocyanate 17B- 60PX, TPA-B80X, MF-B60X, MF-K60X, E-402-B80T, water-dispersed isocyanate WB40-100 or monomer isocyanate 50M. Not limited to these, an epoxy compound or an aldehyde compound can be used as long as it exhibits thermal polymerization crosslinkability. These compounds may be used alone or in combination. By using such a reactive compound and polymerizing (crosslinking) under appropriate conditions such as heating, the orientation in the retardation film of the present invention can be fixed in a desired state, and the film is heated. It is possible to improve the durability and / or environmental resistance performance under the conditions of heat and humidity. The thermosetting temperature is usually in the range of 20 to 200 ° C, preferably 40 to 180 ° C, more preferably 60 to 160 ° C for the purpose of preventing thermal decomposition of the cellulose derivative. The thermosetting time is usually within 24 hours, preferably within 12 hours, and more preferably within 3 hours.
Note that the environmental resistance performance means that even when the retardation film is repeatedly exposed to a dry environment and a high humidity environment, the in-plane average retardation value Re and the retardation value Rth in the normal direction of the film are small. It is a performance indicating whether or not it can withstand in a state. When a retardation film is repeatedly exposed to a dry environment and a high humidity environment, its Re and Rth may vary greatly depending on the type of film, etc., and is constantly stable without being affected by environmental changes. In order to obtain compensation performance, it is desirable that the phase difference value change is small. The retardation film of the present invention to which a reactive polymer is added can improve the environmental resistance performance by this addition.
As the reactive polymer, any compound can be used as long as it is highly fat-compatible with the cellulose derivative of the present invention.
The above (meth) acrylate compounds, isocyanate compounds, silane coupling agents, and the like are preferable, and silane coupling agents are more preferable. These compounds have an effect of improving the environmental resistance performance of the retardation film of the present invention and suppressing a change in retardation value.

  Moreover, a silane coupling agent can be used as the thermally polymerizable compound other than the isocyanate type. As silane coupling agents, vinyltrichlorosilane, vinylmethoxysilane, vinyltriethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyl Methyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyl Trimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropi Methyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N- (vinylbenzyl) -2-aminoethyl-3-aminopropyltrimethoxy Silane hydrochloride, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, 3-isocyanate A monomer type silane coupling agent such as natepropyltriethoxysilane can be used. In addition to the monomer type, an alkoxy oligomer type can also be used, and examples thereof include X-41-1053 and X-41-1056 manufactured by Shin-Etsu Chemical Co., Ltd. More preferably, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, X -41-1053 and X-41-1056. The addition amount of the silane coupling agent is 0.1 to 50 parts by weight, more preferably 1 to 40 parts by weight, and even more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the cellulose derivative. The oligomer type is relatively mild in reactivity and requires a catalyst in order to sufficiently react with cellulose. Examples of the catalyst include organic metal-based, acid-based, and amine-based compounds. As the catalyst used in the present invention, an acid-based catalyst is preferable. Examples of the acid catalyst include X40-2309A (manufactured by Shin-Etsu Chemical Co., Ltd.). The amount to be added is about 0.1 to 50 parts by weight, preferably about 0.2 to 1 part by weight, based on 100 parts by weight of the silane coupling agent. The silane coupling agent may be added when the cellulose derivative is dissolved, or may be added to the cellulose derivative solution.

  The retardation film produced from the cellulose derivative of the present invention is optically biaxial. In general, an optically biaxial film means that the refractive index in the slow axis direction in the film plane is nx, the refractive index in the fast axis direction in the film plane is ny, and the refractive index in the film normal direction. It is a film in which nx, ny, and nz each have different values when nz is nz. Although the retardation film of the present invention also exhibits optical biaxiality, the refractive index in the film normal direction is the smallest and satisfies the relationship of nx> ny> nz.

The retardation value Re in the retardation film plane and the retardation value Rth in the normal direction are
Re = (nx−ny) × d
Rth = [(nx + ny) / 2−nz] × d
It is represented by Re and Rth of the biaxial retardation film can be calculated from measurement results using an automatic birefringence meter (for example, KOBRA-21ADH manufactured by Oji Scientific Instruments). In the retardation film of the present invention, Re is usually from 0 nm to 200 nm, preferably from 5 nm to 150 nm, and more preferably from 10 nm to 80 nm. Furthermore, depending on the case, 40-80 nm is preferable. Rth is usually 80 nm or more and 300 nm or less, preferably 90 nm or more and 275 nm or less, and more preferably 100 nm or more and 250 nm or less. Furthermore, depending on the case, 120-200 nm is preferable, More preferably, it is 135-200 nm. When Re and Rth have values in the above range, a retardation film showing an excellent viewing angle compensation effect is obtained.
Further, in the relationship between the Re value and the Rth value, it is preferable that the Rth value is larger than the Re value.
The thickness of the film is usually 20 to 200 μm, preferably 20 to 150 μm, and more preferably 30 to 110 μm. Depending on the case, about 30-100 micrometers is the most preferable.

  An ordinary material for producing a retardation film exhibits a so-called positive wavelength dispersion characteristic in which a large retardation value is exhibited with respect to a short wavelength component of incident light and a small retardation value is exhibited as the wavelength component becomes longer. . However, the retardation film of the present invention has a characteristic of having reverse wavelength dispersion, which shows a small retardation value with respect to a short wavelength component of incident light and a large retardation value as the wavelength component becomes longer. .

  The chromatic dispersion is determined by using, for example, an automatic birefringence meter (such as KOBRA-21ADH manufactured by Oji Scientific Instruments), a phase difference value Re450 for incident light having a wavelength of 450 nm, and a phase difference value Re550 for incident light having a wavelength of 550 nm. The phase difference value Re750 for light can be measured and evaluated using the values of the phase difference ratios Re450 / Re550 and Re750 / Re550. When Re450 / Re550 shows a value larger than 1, and Re750 / Re550 shows a value smaller than 1, it is positive wavelength dispersion. Further, when Re450 / Re550 is less than 1 and Re750 / Re550 shows a value greater than 1, it is reverse wavelength dispersion.

  The retardation film of the present invention always exhibits reverse wavelength dispersion. The preferred reverse wavelength dispersion is preferably 0.5 ≦ Re450 / Re550 <0.99 and 1.00 <Re750 / Re550 ≦ 1.50, more preferably 0.65 ≦ Re450. /Re550<0.99 and 1.0 <Re750 / Re550 ≦ 1.35, more preferably 0.8 ≦ Re450 / Re550 <0.99 and Re1.00 ≦ This is a case where 750 / Re550 <1.20.

  Production of the retardation film of the present invention using a cellulose derivative is performed by forming a cellulose derivative solution and performing an alignment treatment. As a specific method, first, a cellulose derivative is dissolved in an appropriate solvent to obtain a cellulose derivative solution. Solvents include acetates such as ethyl acetate, butyl acetate or methyl acetate, alcohols such as methanol, ethanol, propanol, isopropanol or benzyl alcohol, ketones such as 2-butanone, acetone, cyclopentanone or cyclohexanone. And basic solvents such as benzylamine, triethylamine or pyridine, nonpolar solvents such as cyclohexane, benzene, toluene, xylene, anisole, hexane or heptane. The weight concentration of the cellulose derivative is usually 1 to 99%, preferably 2.5 to 80%, more preferably 5 to 50%. More preferably, it is about 10% to 30%. Only one kind of these compounds may be blended, or a plurality of components may be blended. Further, if necessary, necessary additives such as the above reactive monomer, polymerization catalyst or plasticizer may be added. Plasticizers include phthalates such as dimethyl phthalate and diethyl phthalate, trimellitic esters such as tris (2-ethylhexyl) trimellitate, aliphatic dibasic esters such as dimethyl adipate and dibutyl adipate, tributyl phosphate and tributyl phosphate. Examples thereof include orthophosphate esters such as phenyl phosphate and acetate esters such as glyceryl triacetate and 2-ethylhexyl acetate. Only one kind of these compounds may be blended, or a plurality of components may be blended. The amount of the additive added as necessary is about 0 to 50 parts, preferably about 0 to 30 parts, per 100 parts (weight) of the cellulose derivative. Next, the cellulose derivative solution is applied onto a substrate having a flat surface and a release property, and then the solvent is removed by natural drying or heat drying to obtain a transparent cellulose derivative film. Since the retardation film in the present invention can achieve a sufficient compensation effect only with the cellulose derivative used in the present invention, an orientation compound other than the cellulose derivative or a retardation value increasing agent (retardation increasing agent) is added. do not have to. In addition, since the retardation film of the present invention has a degree of flexibility that is usually required, a plasticizer or the like does not usually have to be added. Therefore, as a preferable cellulose derivative film used for the preparation of the retardation film of the present invention, a cellulose derivative film composed of the above cellulose derivative that does not usually contain these and a reactive monomer (preferably a silane coupling agent) that does not include them. The cellulose derivative film containing is mentioned. However, these additions are not excluded.

  Next, the film is subjected to biaxial orientation treatment, preferably biaxial stretching, so that the relationship between the respective refractive indexes (three-dimensional refractive index) satisfies nx> ny> nz. The retardation film can be obtained. Examples of the biaxial orientation treatment in the present invention include biaxial stretching. The biaxial stretching in the present invention includes all cases where stress is applied in two directions, ie, a stretching direction and a direction orthogonal thereto, and the stretching is substantially performed in two directions. For example, in addition to simultaneous biaxial stretching or sequential biaxial stretching, for example, in order to suppress shrinkage in a direction perpendicular to the stretching direction, the film is stretched in one direction while fixing both ends of the film on the non-stretched side using a tenter or a chuck. A method is also included. In this method, by fixing both sides in the direction perpendicular to the stretching direction, the dimensional change due to shrinkage in the fixing direction (neck-in (shrinkage) that occurs during normal uniaxial stretching) is suppressed. Stretched to impart biaxiality to the film. Simultaneous biaxial stretching is a method in which stretching is performed simultaneously in directions perpendicular to each other in the film plane. Sequential biaxial stretching is a method in which a film first stretched in one direction is then stretched in a direction perpendicular to that direction. Each stretching process may be a multistage process. A preferred biaxial stretching is simultaneous biaxial stretching or sequential biaxial stretching.

  The stretching temperature can be arbitrarily selected as long as the cellulose derivative does not yellow due to thermal decomposition or seizure. Although the optimum stretching temperature varies depending on the substituent and substitution degree of the cellulose derivative, in the case of cellulose n-hexanate, it is usually 50 to 200 ° C, preferably 70 to 180 ° C, more preferably 90 to 160 ° C, and still more preferably 90 to 140. It is about ℃.

The optimum draw ratio varies depending on the substituent and degree of substitution of the cellulose derivative and cannot be generally specified, but is not particularly limited as long as the conditions of the present invention are satisfied. Usually, the film is stretched at a magnification of 1.05 to 5.0 times in one direction, and stretched at a magnification of 1.04 to 4.8 times in a direction orthogonal to this direction so that the stretching ratios in both directions are different. Is preferred. Preferably, the film is stretched at a magnification of 1.1 to 4.0 times in one direction, and stretched at a magnification of 1.08 to 3.8 times in a direction perpendicular to this direction. More preferably, the film is stretched in one direction at a magnification of 1.2 to 3.0 times, and stretched in a direction orthogonal to this direction at a magnification of 1.18 to 2.8 times. Furthermore, depending on the case, the stretching ratio in both directions is 1.4 times or more, more preferably 1.5 times or more, within 3 times, preferably within 2.5 times, and the stretching ratio on one side is the other stretching ratio. It is preferable to make it less. If the difference in the draw ratio in both directions is too large, the refractive index condition of the present invention may not be satisfied. Therefore, it is preferable that the difference in the draw ratio in both directions is within a range of 2 times, preferably 1. It is preferably within a range of not more than double, more preferably within 0.5 times, sometimes within 0.4 times or within 0.3 times, 0.01 times or more, preferably 0.05 times or more.
The above draw ratio means a value obtained by dividing the length after stretching by the length before stretching. When contraction occurs in a direction orthogonal to the stretching in one direction, the length after the contraction is divided by the length after the contraction.

  The three-dimensional refractive index, that is, the relationship between nx, ny and nz can be controlled by the draw ratio. Usually, the three-dimensional refractive index of a uniaxially stretched film is such that na> nb≈ where the refractive index in the maximum stretching direction is na, the refractive index in the direction perpendicular to the film plane is nb, and the refractive index in the thickness direction is nc. nc relationship is shown, but when producing a biaxial film, the stretching ratio in one direction (the refractive index in this direction is nα) is fixed, and the stretching ratio in the direction perpendicular to this (the refractive index in this direction is As nβ) becomes larger than 1.0 times, nα≈nβ> nγ (refractive index in the thickness direction) or nα> nβ> nγ, nβ> nα> nγ so as to exhibit optical biaxiality. Thus, when the draw ratio in the orthogonal direction exceeds a certain value, the properties of the uniaxially stretched film are again approached such that nβ> nα≈nγ. As an example, when producing a film showing optically strong biaxiality using cellulose n-hexanate, if the stretch ratio in one direction is 1.7, and the stretch ratio in the direction orthogonal thereto is 1.6, A retardation film having a relationship of nβ> nα> nγ is obtained. The direction showing the maximum value of the refractive index is the slow axis.

  The retardation film of the present invention can be used in an image display device depending on its optical characteristics. For example, the retardation film Re of the optically biaxial retardation film of the present invention has an in-plane retardation value Re at 550 nm of about 50 nm and a normal film direction retardation value Rth of about 170 nm. By laminating with roll-to-roll so that the relationship between the absorption axis of the liquid crystal and the slow axis of the retardation film is orthogonal, a functional polarizing film having a function of widening the viewing angle of a liquid crystal display device is obtained. Can do.

As the polarizing film, for example, a film in which both surfaces of the polarizing element are sandwiched by protective films such as a triacetyl cellulose film can be used, or only one surface can be protected.
In the case of a polarizing film that is protected on both sides, it is generally sufficient to use a pressure-sensitive adhesive to attach the retardation film on one of the protective films.
However, the retardation film of the present invention is bonded to a polarizing element by using, for example, a saponification treatment, using a polyvinyl alcohol-based adhesive or the like in the same manner as a triacetyl cellulose film generally used as a protective film. It has the feature that it can be. Therefore, it is possible to protect one side of the polarizing element with a saponified triacetyl cellulose film and the other side with the retardation film of the present invention without changing the current polarizing film manufacturing process. It is possible, and by doing so, the thickness of the functional polarizing film in which the retardation film of the present invention and the polarizing element are integrated can be reduced, which is more preferable. However, the adhesive is not limited to polyvinyl alcohol, and there is no particular limitation as long as it can adhere the polarizing element such as urethane or isocyanate based adhesive and the retardation film of the present invention. The film obtained by integrating the retardation film and the polarizing element of the present invention thus obtained is called a functional polarizing film, and can contribute to cost reduction and yield improvement by thinning the entire liquid crystal display device and reducing processing steps. .
In addition, it is possible to attach the non-protected surface of the single-side protected polarizing film with an adhesive or the like, but it is preferable to directly bond with an adhesive or the like in terms of durability. When directly adhering, the surface of the retardation film is preferably activated by saponification treatment, corona discharge treatment or plasma treatment, and then adhered using a polyvinyl alcohol-based adhesive. It is not necessary to limit the adhesive to polyvinyl alcohol, and any adhesive may be used as long as it can directly bond the non-protected surface of the polarizing film and the retardation film of the present invention. By directly bonding or bonding the retardation film of the present invention to an unprotected surface of a polarizing film, a functional polarizing film integrated with a retardation film can be obtained, which can contribute to thinning of the entire cell.

  The retardation film and functional polarizing film of the present invention can greatly contribute to widening the viewing angle of an image display device. For example, a transmissive liquid crystal display device has a structure in which a liquid crystal cell is sandwiched between two polarizing films, and in principle, light leaks greatly when tilted from the horizontal axis of 45 ° from the absorption axis of the polarizing film. . When the retardation film of the present invention is disposed between the polarizing films, or more preferably the functional polarizing film of the present invention is used instead of the polarizing film, light leakage can be greatly improved. A wide viewing angle of the liquid crystal display device can be achieved.

  In the functional polarizing film in which the retardation film of the present invention is integrated, the retardation film of the present invention acts as a protective film and retardation film for the polarizing film. Therefore, when the functional polarizing film is used, both sides are protected. Compared to the case of using a normal polarizing film and a retardation film each having a film, the liquid crystal display device can be thinned because it has the same function with a thin thickness. For example, for a liquid crystal display device using a VA cell, if the functional polarizing film using the retardation film of the present invention is used, the entire cell can be reduced in thickness, while the two compensations required for the VA cell can also be achieved. This film is particularly suitable because it can be achieved by the film and can achieve an effect of widening the viewing angle which is very excellent as compared with the conventional product.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1 Synthesis of cellulose n-hexanate (degree of substitution 2.30) and measurement of degree of substitution 126 g of lithium chloride was added to 1.5 l of N, N′-dimethylacetamide and stirred at 80 ° C. for 30 minutes for complete dissolution. Then, 30.0 g of N, N′-dimethylacetamide-impregnated cellulose (cellulose content: 56.4% by weight) was added. After stirring at 50 ° C. for 30 minutes, 47.6 g of n-hexanoyl chloride (relative to cellulose hydroxyl group) was added, and the mixture was again heated to 80 ° C. and stirred for 4 hours. Stirring was stopped and the reaction contents were poured into 2 liters of water to reprecipitate cellulose n-hexanate. After filtration, the solid content obtained by washing three times with 100 ml of water and twice with 50 ml of methanol was vacuum-dried for 6 hours to obtain 35.0 g of cellulose n-hexanate white powder.
The reaction solution was analyzed by gas chromatography immediately before reprecipitation, and the reaction rate was calculated from the decrease in n-hexanoyl chloride. The degree of substitution of cellulose n-hexanate (the number of substitutions by n-hexanate per monomer unit of cellulose) ) Was 2.30.

Example 2 Production of Cast Film Using Cellulose n-Hexanate Cellulose n-hexanate synthesized in Example 1 was dissolved in cyclopentanone to obtain a 25% by weight solution of polymer. A cellulose n-hexanate solution was cast on a release PET film with a dope thickness of 1.7 mm, and then dried at 110 ° C. for 40 minutes to prepare a transparent film of cellulose n-hexanate.

Example 3 Production of Optically Biaxial Retardation Film Using Cellulose n-Hexaneate The cast film obtained in Example 2 was stretched at 120 ° C. until a magnification of 1.7, then, The film was stretched in a direction orthogonal to the first stretching direction at 100 ° C. until a magnification of 1.6 was obtained to obtain a retardation film having optically biaxial properties. The obtained film was nx = 1.48500, ny = 1.488404, and nz = 1.48154. Next, when the retardation ratio of the retardation film was determined using an automatic birefringence meter (KOBRA-21ADH, manufactured by Oji Scientific), Re450 / Re550 was 0.97, and Re750 / Re550 was 1.03, which was reversed. It showed wavelength dispersion. Re showed 56 nm. Further, Rth calculated from the measurement result of the inclination phase difference value was 173 nm. The film thickness d was 58 μm.

Example 4 Production of Functional Polarizing Film The retardation film described in Example 3 was placed on a polarizing film UDN-10143P made by POLATECHNO, which was protected on one side only by triacetyl cellulose, through an adhesive layer, and the absorption axis and position of the polarizing film. The retardation film was laminated so that the slow axes were orthogonal to each other, and a functional polarizing film of the present invention using cellulose n-hexanate was produced.

Example 5 Compensation performance evaluation by measurement of viewing angle when VA cell is not driven using cellulose n-hexanate From the commercially available VA liquid crystal display device, the liquid crystal cell is left and all other retardation films and polarizing films are removed. Instead, the polarizing film (functional polarizing film) having the retardation film of the present invention on one surface produced in Example 4 on the observation surface was disposed so that the retardation film surface was on the cell side. Polatechno polarizing films (SKN18243T) were attached to the back surface so that the absorption axes of the polarizing films were orthogonal to each other. About the VA mode liquid crystal display device produced in this way, the black luminance distribution of all directions was measured using Ez-contrast160R by ELDIM. FIG. 1 shows a graph of the cross section of the black luminance distribution in the film normal direction, 45 ° clockwise from the absorption axis of the polarizing plate, from the omnidirectional black luminance measurement data.

Example 6 Production of cast film containing silane coupling agent (thermopolymerizable compound) using cellulose n-hexanate 25% by weight of cellulose n-hexanate synthesized in Example 1, 3-glycidoxypropyltriethoxysilane A compounded solution was prepared by dissolving in cyclopentanone such that (Shin-Etsu Chemical Silane Coupling Agent KBE-403) was 4 wt% and triphenyl phosphate was 2 wt%. A cellulose n-hexanate solution was cast on a release PET film with a dope thickness of 1.7 mm and dried at 110 ° C. for 40 minutes to prepare a transparent film of cellulose n-hexanate.

Example 7 Production of Optically Biaxial Retardation Film Using Cellulose n-Hexanate Film Thermally Polymerized by Adding Silane Coupling Agent The cast film obtained in Example 6 was magnified at 120 ° C. A retardation film having an optically biaxial property is obtained by stretching the film to 1.7 and then stretching the film in a direction orthogonal to the first stretching direction to a magnification of 1.6 at 100 ° C. Obtained. The obtained film was nx = 1.48500, ny = 1.44840, nz = 1.48331. Next, when the retardation ratio of the retardation film was determined using an automatic birefringence meter (KOBRA-21ADH, manufactured by Oji Scientific), Re450 / Re550 was 0.97, and Re750 / Re550 was 1.03, which was reversed. It showed wavelength dispersion. Re showed 61 nm. Moreover, Rth calculated from the measurement result of the inclination phase difference value was 140 nm. The thickness d of the film was 100 μm.

Example 8 Environmental Resistance Test of Retardation Film Consisting of Cellulose n-Hexaneate Thermally Polymerized with Silane Coupling Agent The retardation film produced in Example 7 was subjected to room temperature vacuum conditions and room temperature humidity of 60% or higher. The rate of change in the plane average retardation values Re and Rth was measured by repeatedly holding the conditions. The results are shown in FIG. 2 and FIG.

Comparative Example 1 Production of Retardation Film-Integrated Polarizing Film Using KC8UCR-3 KC8UCR-3 (80 μm thickness) manufactured by Konica Minolta Holdings, Inc., which is a cellulose-based retardation film (retardation film made of cellulose acetate propionate) Is laminated so that the absorption axis of the polarizing film and the slow axis of KC8UCR-3 are perpendicular to the non-protective surface of the polarizing film UDN-10143P made of Polatechno, which is protected with triacetylcellulose only on one side, A VA cell-compensating retardation film-integrated polarizing film using cellulose n-hexanate was produced. KC8UCR-3 had Re of 38 nm and Rth of 132 nm.

Comparative Example 2 Preparation of Comparative Polarizing Film A triacetyl cellulose film (thickness: 80 μm) is attached to a polarizing film UDN-10143P made by POLATECHNO, which is protected on one side only by triacetyl cellulose, through an adhesive layer, and the absorption axis of the polarizing film and triacetyl. Lamination was performed so that the MD directions of cellulose were parallel, and a comparative polarizing film was prepared.

Comparative Example 3 Viewing Angle Measurement of Polarizing Films Produced in Comparative Example 1 and Comparative Example 2 when VA Cell is Not Driven The polarizing film produced in Comparative Examples 1 and 2 is used instead of the polarizing film produced in Example 4 Except for the above, the black luminance distribution in all directions was measured in the same manner as in Example 4. The result is shown in FIG.

Comparative Example 4 Environmental Resistance Test of Retardation Film Made of Cellulose Acetate Propionate Similar to Example 8 except that instead of the retardation film produced in Example 7, a film produced from cellulose acetate propionate was used. An environmental resistance test was conducted. The results are shown in FIG. 2 and FIG.

Consideration of Test Results From FIG. 1, in the case of using the retardation film integrated polarizing film of the present invention and in the case of a polarizing film using a retardation film made of cellulose acetate propionate, Comparative Example 3 having no compensation effect Compared with the case where the polarizing film is used, it can be seen that the luminance increase around the circle in the figure at the time of tilting is small, the low luminance is maintained in a wide range, and the luminance expression is excellent. That is, light leakage during tilt observation, which is a cause of contrast reduction, is reduced, and a wide viewing angle is achieved. That is, the polarizing film of the present invention has the advantage that it can be directly bonded to the polarizing film, as well as the cellulose-based retardation film and triacetyl cellulose of Comparative Example 1, and the performance is greatly improved as a compensation film for VA. ing.
Also, from FIG. 2 and FIG. 3, the retardation film of the present invention of Example 7 polymerized (crosslinked) with a thermopolymerizable compound is more resistant to retardation film made of unpolymerized cellulose acetate propionate. It can be seen that the optical performance as a film can be stably exhibited with excellent environmental performance and little change in retardation value and Rth even in a high humidity environment. That is, according to the present invention, environmental conditions of vacuum drying conditions (10 mmHg, temperature 30 ° C., humidity 27%) for 20 hours and high humidity conditions (normal pressure, humidity 80%, temperature 30 ° C.) for 2 hours are repeated four times. The change rate of the in-plane average retardation value Re is within 10%, preferably within 8%, the change rate of the retardation value Rth in the normal direction of the film is within 4%, preferably within 3%, More preferably, a retardation film within 2% can be obtained.

Claims (13)

By biaxial stretching of a film comprising a cellulose derivative in which a hydroxyl group is substituted by an aliphatic acyl group (A) having 5 to 20 carbon atoms, and the substitution degree of the hydroxyl group is 0.50 to 2.99 per one monomer unit of cellulose. The retardation value Re in the film plane represented by the following formula (1) is 0 nm or more and 200 nm or less, and the retardation value Rth in the film normal direction represented by the following formula (2) is 80 nm or more and 300 nm or less. Yes, and optically biaxial retardation film satisfying nx>ny> nz, where each symbol has the following meaning.
Re = (nx−ny) × d (1)
Rth = [(nx + ny) / 2−nz] × d (2)
nx: refractive index in the slow axis direction in the film plane ny: refractive index in the fast axis direction in the film plane nz: refractive index in the film normal direction d: film thickness The substituent of the cellulose derivative is (1) an aliphatic acyl group having 5 to 20 carbon atoms (A) alone, or (2) an aliphatic acyl group having 5 to 20 carbon atoms (A) and the others An aliphatic acyl group, an aromatic acyl group, and an alkylcarbamoyl group, the latter substituent (B) having a structure different from that of the aliphatic acyl group (A). The retardation film according to claim 1, which is any one of: an aromatic carbamoyl group, an acyl group having a tolan skeleton, an acyl group having a biphenyl skeleton, or a polymerizable group. When the aliphatic acyl group (A) having 5 to 20 carbon atoms is a linear aliphatic acyl group having 5 to 7 carbon atoms and a linear aliphatic acyl group having 5 or 6 carbon atoms, substitution thereof The retardation film according to claim 2, wherein the retardation film is a cellulose derivative having a degree of substitution of 1.5 to 2.3 in the case of an aliphatic acyl group having a degree of 2.0 to 2.8 and a carbon number of 7. The phase difference film according to claim 1, wherein the film made of the cellulose derivative is prepared from a resin composition containing the cellulose derivative and both a reactive monomer or a reactive monomer and a polymerization initiator. The retardation film according to claim 4, wherein the reactive monomer is a thermosetting compound. The retardation film according to claim 5, wherein the thermosetting compound is a silane coupling agent. The retardation film according to claim 1, wherein the aliphatic acyl group (A) is an n-hexanoyl group, and the degree of substitution of the hydroxyl group by the n-hexanoyl group is 1.80 to 2.90. The retardation value Re in the film plane is 10 nm or more and 80 nm or less, the retardation value Rth in the film normal direction is 100 nm or more and 250 nm or less, and the thickness d of the film is 30 μm or more and 110 μm or less. Retardation film. When the phase difference value at a wavelength of 450 nm is Re450, the phase difference value at a wavelength of 550 nm is Re550, and the phase difference value at a wavelength of 750 nm is Re750, the following expressions (3), (4), and (5) are satisfied. The retardation film according to claim 1, wherein the retardation film is a feature.
Re450 ≦ Re550 ≦ Re750 (3)
0.50 ≦ Re450 / Re550 <0.99 (4)
1.00 <Re750 / Re550 ≦ 1.50 (5) The retardation film according to claim 1 or 4, wherein the film comprising the cellulose derivative is a film produced by a solvent casting method. The functional polarizing film which bonded together the retardation film and polarizing film as described in any one of Claims 1, 4, and 7. An image display device comprising the retardation film according to claim 1, or the functional polarizing film according to claim 11. The image display device according to claim 12, wherein the image display device is a vertical alignment nematic (VA) liquid crystal display device.

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