JP2003096207A - Transparent film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel transparent film of which the phase difference has little dependence on wavelength, the deviation in phase difference due to stress is small and the phase difference is imparted easily and also provide a phase difference film using the same. SOLUTION: This transparent film contains a cellulose derivative in which the hydroxy group of cellulose is substituted with an ether group and which has a degree of ether substitution of 0.1-0.3. An alkylether group or an aralkylether group is a desirable ether group.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has excellent optical characteristics,
The present invention relates to a novel optical film.

[0002]

2. Description of the Related Art In recent years, retardation films have been widely used in liquid crystal display devices, as is typically seen in reflective TFT liquid crystal display devices. A polycarbonate film is generally used as the retardation film.

The applications of retardation films are further expanding, and accordingly, more sophisticated functions are required. Particularly important among these requirements is that the wavelength dependency of the phase difference is small. The wavelength dependence of this phase difference is Re (441.6) / Re (514.
5), where Re (441.6) represents the retardation of the film measured with monochromatic light of wavelength 441.6 nm and Re (514.5) is monochromatic light of wavelength 514.5 nm. The retardation of the measured film is shown.

On the other hand, when used as a quarter-wave plate or a half-wave plate, the film has a phase difference corresponding to a quarter wavelength or a half wavelength for each wavelength of visible light. It is desirable to have. However, the polycarbonate retardation film has a large wavelength dependence, and the degree of retardation received by polarized lights having different wavelengths is different. Therefore, when displaying black in a reflective TFT liquid crystal display device using such a retardation film having a large wavelength dependence,
Since the light from the backlight cannot be completely blocked, the contrast and gradation display are deteriorated.

On the other hand, for example, Japanese Patent Application Laid-Open No. 5-271
No. 18, JP-A-5-27119, and JP-A-5-27119.
In Japanese Patent Laid-Open No. 100114 and Japanese Patent Application Laid-Open No. 10-68816, a polycarbonate film can be made into a retardation film having small wavelength dependence by laminating two retardation films at a predetermined angle.

[0006]

However, when the above-mentioned method is applied to a polycarbonate retardation film, there are the following problems. Since polycarbonate originally tends to cause retardation, variations in retardation are apt to occur due to slight fluctuations in tension in the stretching step in manufacturing a retardation film. Further, when laminating such a retardation film, not only the desired retardation is displaced due to the tension during laminating, but also the retardation is changed due to contraction of the polarizing plate after laminating.

Further, as described above, even if a plurality of retardation films are laminated at a predetermined angle to reduce the apparent wavelength dependence of polycarbonate, it is still impossible to sufficiently compensate, and it is desired. There is a problem that contrast cannot be obtained.

Therefore, Japanese Patent Laid-Open No. 2001-124925, Japanese Patent Laid-Open No. 2001-126311, and Japanese Patent Laid-Open No. 08-075.
By using a cyclic polyolefin-based polymer as disclosed in Japanese Patent Application Laid-Open No. 921, Japanese Patent Application Laid-Open No. 2-042441, Japanese Patent Application Laid-Open No. 4-245202, etc., the wavelength dependence of the retardation film can be reduced. Therefore, it is a preferable configuration. However, when laminating with a polarizing film or glass using an adhesive, the affinity with the adhesive is insufficient and peeling or microfoaming easily occurs under the long-term durability test. Is difficult to impart, and the required thickness of the retardation film becomes thicker.
It is difficult to obtain a special retardation film having a three-dimensional orientation as disclosed in Japanese Patent No. 11 publication. Further, since the retardation film needs to control the film thickness to a high degree, it is generally formed into a film by a solvent casting method, but the solvent which can be used for the olefin-based polymer is limited, and particularly toluene or When a solvent such as xylene is used, it has various problems different from polycarbonate, such as poor productivity due to high boiling point.

Therefore, the present invention provides a new transparent film having a small wavelength dependence of the retardation, a small displacement of the retardation due to the stress, and an easy provision of the retardation, and a retardation film using the transparent film. To aim.

[0010]

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have conducted diligent research, and as a result, found that a cellulose derivative having a specific structure can achieve the intended purpose, and arrived at the present invention. .

That is, the present invention is a film containing a cellulose derivative in which the hydroxyl groups of cellulose are substituted with ether groups, wherein the degree of ether substitution of the cellulose derivative is 0.1 to 3.0. And the transparent film.

According to yet another aspect of the invention, 550
Phase difference from 0 nm to 2000 nm for monochromatic light of nm
A transparent film is provided.

Furthermore, according to the present invention, there is provided an elliptical polarizing plate or a circular polarizing plate in which the transparent film of the present invention and a polarizing plate are laminated and integrated.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The transparent film of the present invention contains a cellulose derivative in which the hydroxyl group of cellulose is substituted with an ether group, and the degree of ether substitution of the cellulose derivative is
It is characterized by being 0.1 to 3.0.

The ether substituent of the cellulose derivative is-
It can be represented by OR. As a preferred example of the R group,
Substituted or unsubstituted alkyl group such as methyl group, ethyl group, propyl group, hydroxyethyl group, 2-hydroxypropyl group, cyanoethyl group or carboxymethyl group, substituted or unsubstituted aralkyl group such as benzyl group, substituted such as phenyl group Or an unsubstituted aryl group. More preferably, a substituted or unsubstituted alkyl group having no dissociative substituent such as a carboxyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, and further preferably a methyl group or ethyl. A substituted or unsubstituted alkyl group having 1 to 10 carbon atoms such as a group or a cyanoethyl group, or a substituted or unsubstituted benzyl group.
An alkyl group having 2 or more carbon atoms or a benzyl group is particularly preferable because it can form a transparent film having a low water content and is stable to the environment during use.

These ether substituents may have a single substituent, but may have a plurality of substituents.

Cellulose has three substitutable hydroxyl groups as repeating units, and the degree of ether substitution of the cellulose derivative in the present invention is 0.1 to 3. The degree of cellulose substitution can be measured by a known method such as hydrolyzing with dilute sulfuric acid and then quantifying liberated alcohol. The preferred degree of substitution is 2-3, and more preferably,
It is 2.3 to 2.9, and more preferably 2.4 to 2.8. If the degree of substitution is low, the solvent capable of dissolving the cellulose derivative will be low, and thermoforming will be difficult, and it will be difficult to form a film by the solvent casting method and impart retardation by stretching. Further, the water absorption of the obtained film is increased, which adversely affects the dimensional stability and the like. On the other hand, unnecessarily increasing the degree of substitution undesirably lowers the solubility in a solvent and makes the cellulose derivative expensive.

The cellulose derivative may have a substituent other than the ether group. Examples of such substituents are ester groups such as acetate, propionate and butyrate.

The number average molecular weight of the cellulose derivative is preferably 5,000 to 100,000, more preferably 10,000 to 7
10,000, more preferably 20,000 to 60,000. An unnecessarily high molecular weight lowers the solubility in a solvent, and the viscosity of the obtained solution is too large to be suitable for the solvent casting method,
It causes problems such as making thermoforming difficult. On the other hand, too low a molecular weight is not preferable because it lowers the mechanical strength of the obtained film. The heat resistance of the cellulose derivative film can be evaluated by the thermal softening temperature by thermomechanical analysis (TMA). Generally 90 ℃ or more 200
℃ or less, more preferably 110 ℃ or more 180
C. or lower, more preferably 120 to 160.degree.

The cellulose derivative constituting the transparent film of the present invention may be one kind, but if necessary, a plurality of kinds of the cellulose derivative may be used or a blend of two or more kinds with another polymer. It can be the body. As such another polymer, cellulose acetate, cellulose propionate, cellulose ester derivative such as cellulose butyrate, cellulose mixed ester derivative such as cellulose acetate propionate,
And the like can be preferably used. In particular, a blend of cellulose acetate having a specific degree of substitution and cellulose acetate propionate has a total light transmittance of 85.
%, Preferably 90% or more, and it is preferable because the wavelength dependence of the obtained retardation film can be continuously changed by the blending ratio. The preferred degree of substitution of the ester group is
2.0 or more and 3.0 or less, more preferably 2.5
It is at least 2.95, and more preferably at least 2.7 and at most 2.9. The preferable blend ratio is determined by the characteristics of the obtained film such as the required wavelength dependence, but generally, the cellulose derivative substituted with an ether group is 10% by weight or more and 90% by weight or less,
9 cellulose ester derivatives substituted with ester groups
It is 0% by weight to 10% by weight.

The cellulose derivative substituted with an ether group can be produced by a method known per se. For example, cellulose is treated with a strong caustic soda solution to give alkali cellulose, which is then etherified with an alkyl halide such as ethyl chloride. It can be manufactured by

The film according to the present invention can be obtained by a known film forming method such as a melt extrusion method, a melt molding method such as an inflation method, or a solution casting method.
The film forming method is not particularly limited. 2 as described above
In forming a film of a blend of two or more kinds, it may be possible to simply mix two or more kinds of resins to form a film, or both resins may be melt-kneaded in advance and formed into pellets and then formed into a film. . Pre-drying the resin or pellets to be used prior to forming a film is useful for preventing defects such as foaming of the film. Since the film of the present invention is characterized in that retardation due to molecular orientation during processing is less likely to occur, film formation by a melt molding method is also a preferable method. When a film is formed by a melt molding method, a known method such as a melt extrusion method such as a T-die method or an inflation method, a calender method, a heat press method, an injection molding method can be adopted, but a wide range having good thickness accuracy. The melt extrusion method using a T-die is preferable because it is easy to obtain the film. In addition, the solution casting method is a particularly preferable method in order to reduce the thickness variation in that a film having extremely uniform thickness accuracy can be obtained. By the solution casting method, it is possible to easily obtain an optically isotropic film having no defects such as die lines and having a small film thickness variation of 5% or less, preferably 1% or less and having a small retardation. it can.

The presence of water at the time of forming a film into the cellulose derivative unfavorably affects the strength of the obtained film. Therefore, it is particularly preferable to previously dry the resin, pellets, solvent and the like used for forming the film.

Solvents that can be used in the solution casting method are
It is selected from known solvents. A halogenated hydrocarbon solvent such as methylene chloride or trichloroethane is one of the suitable solvents because it easily dissolves the resin material and has a low boiling point. Further, a highly polar non-halogen solvent such as dimethylformamide or dimethylacetamide can also be used. In addition, aromatic compounds such as toluene, xylene and anisole, cyclic ether compounds such as dioxane, dioxolane, tetrahydrofuran and pyran, ketone compounds such as methyl ethyl ketone, ester compounds such as ethyl acetate and ethyl propionate, ethanol and ethyl cellosolve, etc. Alcohol-based solvents can also be used. Further, in order to obtain a film having excellent surface properties, it is also possible to control the evaporation rate of the solvent by using a good solvent for the cellulose derivative, or a combination of a non-solvent and / or a poor solvent and a good solvent and mixing them with each other. Is the preferred method. In particular, when a ketone-based or ester-based solvent is used in combination with an alcohol-based solvent, the cellulose derivative exhibits good solubility in a wide range. Since the selection of these solvents affects the mechanical properties of the obtained film such as tensile strength, it is necessary to determine the type of solvent and the mixing ratio while taking the mechanical properties of the obtained film into consideration. As particularly preferable solvents, halogen solvents such as methylene chloride, toluene, aromatic solvents such as xylene, aliphatic ester solvents such as ethyl acetate, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, or, It is a mixed solvent of these and an alcohol having 4 or more carbon atoms, such as butyl alcohol.

When a film is formed by a solution casting method, the cellulose derivative of the present invention is dissolved in the above solvent, then cast on a support and dried to form a film. The viscosity of the solution is preferably 10 poise or more and 50 poise or less, more preferably 15 poise or more and 30 poise or less. As a preferable support, a stainless steel endless belt, a film such as a polyimide film, a biaxially stretched polyethylene terephthalate film, or the like can be used.

The film of the present invention can be dried while being supported on a support, but if necessary, the pre-dried film can be peeled from the support and further dried. For the film drying, generally, a float method, a tenter or a roll conveying method can be used.
In the case of the float method, the film itself receives complicated stress,
Non-uniformity of optical characteristics is likely to occur. Also, in the case of the tenter method, it is necessary to balance the width shrinkage of the film due to solvent drying and the tension to support its own weight, depending on the distance between the pins or clips supporting both ends of the film. There is a need. On the other hand, in the case of the roll transportation method, the tension for stable film transportation is applied in the film flow direction (MD direction) in principle, so that it has a feature that the direction of stress is easily made constant. Therefore, it is most preferable to dry the film by the roll transportation method. Also, so that the film does not absorb moisture when drying the solvent,
Drying in an atmosphere where the humidity is kept low is an effective method for obtaining the film of the present invention having high mechanical strength and transparency.

The thickness of the film of the present invention is from 10 μm to 3
00 μm, preferably 20 to 200 μm,
More preferably, it is 30 μm to 100 μm. The surface roughness of the film represented by the surface roughness Ra is preferably 1
It is 00 nm or less, and more preferably 20 nm or less.

The light transmittance of the film is preferably 85% or more, more preferably 90% or more. The haze of the film is preferably 2% or less, more preferably 1% or less. The retardation of the film is 20 nm
The following is preferable, more preferably 10 nm or less, and further preferably 5 nm or less. It is important to control not only the in-plane retardation of the film but also the retardation in the thickness direction in order to reduce the viewing angle dependency of the film retardation. The retardation in the film thickness direction is expressed by the following formula (where nx is the maximum in-plane refractive index, ny is the refractive index in the direction orthogonal to nx, nz is the film thickness direction refractive index, and d is the film thickness). It is represented by I).

| (Nx + ny) / 2−nz) | × d (I) Since the film of the present invention is less likely to exhibit a retardation as compared with polycarbonate or the like, a film having a small retardation in the thickness direction can be obtained. The preferred thickness direction retardation is 2
00 nm or less, more preferably 100 nm or less,
More preferably 50 nm or less, particularly preferably 20 nm
It is the following. If necessary, by appropriately selecting the drying conditions, that is, by keeping the film on the support until the residual solvent amount of the film is 20% or less, preferably 10% or less and drying, the in-plane position of the film It is also possible to increase the phase difference in the thickness direction while keeping the phase difference small. By such a method, a film having a retardation in the thickness direction of 100 nm or more, preferably 200 nm or more can be obtained.

The film of the present invention, as it is or after various processing, is subjected to an optical isotropic film, a retardation film,
It can be suitably used as a polarization protection film for known optical applications such as around a liquid crystal display device. Further, it is also possible to apply a coating such as an antireflection layer or an antiglare hard coat on the film of the present invention.

In order to obtain a retardation film, the film obtained above can be at least uniaxially stretched by a known stretching method and subjected to orientation treatment to impart a uniform retardation. When the film is stretched to form a retardation film, it is possible to obtain a retardation film having a smaller wavelength dependence of retardation for measurement than a retardation film made of polycarbonate. As a stretching method, a uniaxial or biaxial thermal stretching method can be adopted. The optical film of the present invention is unlikely to exhibit a retardation during stretching and, unlike conventional polycarbonates, needs to have a large stretching ratio, so longitudinal uniaxial stretching is preferable. Further, when the optical uniaxiality of the obtained retardation film is important, free end longitudinal uniaxial stretching is a particularly preferable stretching method. In addition, JP-A-5-157
Special biaxial stretching as shown in Japanese Patent No. 911,
It is also possible to control the refractive index of the film in three dimensions. Even when the retardation is applied, the retardation due to the orientation hardly appears, so that a film having a small retardation variation in the film plane can be obtained.

The retardation of the retardation film is from 10 nm to 2000 nm and can be selected according to the purpose. The retardation can be set to a desired value by controlling the film thickness, the stretching temperature and the stretching ratio. Generally, the stretching ratio is 1.05 to 3 times, and the stretching temperature is (Tg-30) ° C with respect to the glass transition temperature Tg.
To (Tg + 30) ° C. A particularly preferred stretching temperature is from (Tg-20) ° C to (Tg + 2).
0) Range up to ° C. By setting this temperature range, it is possible to prevent whitening of the film at the time of stretching, and reduce the retardation variation of the obtained retardation film.

When the retardation film of the present invention is used for color compensation of an STN liquid crystal display device, the retardation is generally selected in the range of 300 nm to 2000 nm. When the retardation film of the present invention is used as a λ / 2 wavelength plate, the retardation is generally 20.
It is selected in the range of 0 nm to 400 nm. A more preferable retardation as a λ / 2 wave plate is from 230 nm to 30 nm.
It is selected from the range of 0 nm. When the retardation film of the present invention is used as a λ / 4 wavelength plate, its retardation is generally selected in the range of 90 nm to 200 nm. A more preferable phase difference as a λ / 4 wave plate is 1
It is selected from the range of 00 nm to 180 nm.

Such a retardation film according to the present invention makes it possible to obtain a retardation film having a smaller wavelength dependency of the retardation as compared with a known retardation film made of polycarbonate, and a reflective TFT liquid crystal display device. It can be preferably used for applications. In addition, since the phase difference is less likely to change due to stress, when used by being attached to a polarizing plate, the phase difference is less likely to change due to the deformation stress of the polarizing plate. Suitable for

The wavelength dependence of the phase difference is Re (441.
6) / Re (514.5), where Re
(441.6) represents the retardation of the film measured with monochromatic light having a wavelength of 441.6 nm, and Re (514.5) is
The phase difference of the film measured with monochromatic light having a wavelength of 514.5 nm is shown. In the case of polycarbonate retardation film,
Re (441.6) / Re (514.5) is 1.06, whereas the retardation film of the present invention generally depends on the type of ether substituent and the degree of substitution, but generally 1. 04
Or less, preferably 1.03 or less, more preferably 1.0
It is 2 or less. Although the lower limit of the wavelength dependence is not limited, it is generally 0.8 or more. By using the retardation film of the present invention, compared to a polycarbonate retardation film, particularly when used for reflection prevention of a reflection type TFT or STN liquid crystal display device, a touch panel, etc., a display showing little contrast and high contrast You can give a statue.

As the retardation film of the present invention, a plurality of retardation films are used together with the retardation film of the present invention or with another retardation film.
No. 18, JP-A-5-27119, and JP-A-5-27119.
As disclosed in Japanese Unexamined Patent Publication No. 100114 and Japanese Unexamined Patent Publication No. 10-68816, it is possible to further reduce the wavelength dependence of the retardation by laminating the retardation films at a predetermined angle.

The retardation film of the present invention can be laminated and adhered to a known iodine type or dye type polarizing plate via an adhesive. When laminating, it is necessary to laminate the polarizing axis of the polarizing plate and the slow axis of the retardation film at a specific angle depending on the application. The retardation film of the present invention can be used as a circularly polarizing plate by laminating and laminating it with a polarizing plate. In that case, in general,
The polarization axis of the polarizing plate and the slow axis of the retardation film are substantially 4
Laminated with a relative angle of 5 °. Also, the retardation film of the present invention may be used as a polarizer protective film constituting a polarizing plate and laminated. Furthermore, the retardation film of the present invention can be used as an elliptically polarizing plate by laminating and laminating it with a polarizing plate for a STN liquid crystal display device.

Further, when forming a film, a small amount of additives such as a plasticizer, a heat stabilizer and an ultraviolet stabilizer may be added, if necessary. Particularly when the obtained film is brittle, it is effective to add a plasticizer for the purpose of improving processing characteristics such as stretching.

Examples of preferable plasticizers include phthalic acid plasticizers such as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, and di-n-ethylhexyl phthalate. Diisooctyl phthalate, di-n-octyl phthalate, di-n phthalate
-Decyl, diisodecyl phthalate, di-n-dodecyl phthalate, diisotridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate, di-2-phthalate
Ethylhexyl, di-2-ethylhexyl isophthalate, trimellitic acid ester-based plasticizers, tri-2-ethylhexyl trimellitic acid, triisodecyl trimellitic acid, and aliphatic polybasic acid-based plasticizers, diisobutyl adipate, adipine Hexyl acid, di-n-decyl adipate, diisodecyl adipate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, methoxyethyl adipate, o- Tributyl acetyl citrate, triethyl o-acetyl citrate, and phosphate ester-based plasticizers include triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, diphenylethyl phosphate, tricresyl phosphate,
As the epoxy plasticizer, epoxidized soybean oil, epoxidized tall oil fatty acid-2-ethylhexyl, and as the fatty acid ester plasticizer, butyl stearate, butyl oleate, chlorinated paraffin, chlorinated fatty acid methyl, butyrate butyrate. Ethyl, methoxyethyl oleate, 2- (p-tert-butylphenoxyethyl) acetate, and polyhydric alcohol ester plasticizers include butylphthalyl butyl glycolate, glycerol tributyrate, triethylene glycol dipelargonate, alcohol. Examples of the plasticizer include 2- (p-tert-amylphenoxy) ethanol, 2- (p-tert-butylphenoxy) ethanol, diamylphenoxyethanol, cetyl alcohol, myristyl alcohol, stearyl alcohol, and fat. Acid-based plasticizers include oleic acid, ricinoleic acid, stearic acid, and amide-based plasticizers include adipic acid bisdibutylamide, lauric acid dibutylamide, diethyldiphenylurea, p-toluenesulfonamide, ethyl-p-toluenesulfone. Amide,
As the polymer plasticizer, polyethylene glycol dimethyl ether, polyethylene glycol benzoate, a polymer compound containing an ester group (adipic acid,
Dibasic acids such as sebacic acid and phthalic acid and polycondensates such as 1,2-propylene glycol and 1,3-propylene glycol). Further, mineral oil or vegetable oil can also be used. Among these plasticizers, plasticizers containing no aromatic group, such as di-n-decyl adipate, diisodecyl adipate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate, sebacic acid. Di-2-ethylhexyl, tributyl phosphate, tri-2-ethylhexyl phosphate, 2-ethylhexyl phosphate, tricresyl phosphate, epoxidized soybean oil, epoxidized tall oil fatty acid-2-ethylhexyl butyl stearate, oleic acid Butyl, chlorinated paraffin, chlorinated fatty acid methyl, polyethylene glycol dimethyl ether, or polymer compounds containing ester groups (dibasic acids such as adipic acid and sebacic acid and 1,2-propylene glycol, 1,3-propylene glycol, etc. Polycondensation product) Preferred.

These plasticizers are particularly preferable additives because they do not show absorption on the short wavelength side in the visible region and do not adversely affect the wavelength dependence of retardation. 2 to 20 parts by weight of these plasticizers are added to 100 parts by weight of the film of the present invention. If it exceeds 20 parts by weight, the stability of the retardation during continuous stretching of the roll film may be impaired, which is not preferable.

Further, a filler may be contained for the purpose of improving the slipperiness of the film. Inorganic or organic fine particles can be used as the filler. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, aluminum oxide, metal oxide fine particles such as zirconium oxide, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, silicate fine particles such as magnesium silicate,
Calcium carbonate, talc, clay, calcined kaolin, calcium phosphate and the like can be used. As the organic fine particles, resin fine particles such as silicon-based resin, fluorine-based resin, acrylic resin, and cross-linked styrene-based resin can be used.

By containing an ultraviolet absorber in the film of the present invention, the weather resistance of the film of the present invention can be improved, and the durability of the liquid crystal display device using the film of the present invention can be improved, which is preferable in practice. 2 as UV absorber
-(2H-benzotriazol-2-yl) -p-cresol, 2-benzotriazol-2-yl-4,6-
Benzotriazole-based UV absorbers such as di-t-butylphenol, 2- (4,6-diphenyl-1,3,5-
Triazin-2-yl) -5-[(hexyl) oxy]
-Triazine-based UV absorbers such as phenol, benzophenone-based UV absorbers such as octabenzone, and 2,4-di-t-butylphenyl-3,5-
Also used are benzoate-based light stabilizers such as di-t-butyl-4-hydroxybenzoate and hindered amine-based light stabilizers such as bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate. it can.

The film of the present invention usually has a surface energy of 50 dyne / cm or less. The surface energy of the film can be measured by a known method. The details are described in D. K. Owens, Journal
of Applied Polymer Science
ce, vol 13, p. 1741 (1969), etc.
Have been described. When another film or glass is bonded to such a surface showing low surface energy via an adhesive or a pressure-sensitive adhesive, sufficient adhesive strength or adhesive strength cannot be obtained, and peeling easily occurs. . Further, even if the initial strength is obtained, there is a problem that peeling easily occurs due to a decrease in adhesive strength or adhesive strength even if environmental conditions are slowed down due to long-term use. Electrical treatment such as corona discharge treatment or spark treatment for the above film, plasma treatment under low pressure or normal pressure, ultraviolet irradiation treatment in the presence or absence of ozone, acid treatment with chromic acid, flame treatment, silane series By performing a known surface activation treatment such as a primer treatment of titanium or titanium, etc.
The film of the present invention can stably exceed dyne / cm.

The degree of corona discharge treatment can be controlled by the discharge amount represented by the following formula (II).

H = P / (LS × M) (II) where H is the discharge amount, P is the high frequency power (W), LS is the film passing speed (m / min), and M is the discharge width (m). Is. The preferable condition of the corona discharge treatment is 10 to
It is 500 W · min / m ² . Considering productivity,
The more preferable upper limit of the discharge amount is 300 W · min / m ²
And more preferably 100 W · min / m ² . The preferable plasma treatment is atmospheric pressure plasma treatment in a single gas or a mixed gas of hydrogen, carbon dioxide, nitrogen, argon, helium, oxygen or the like as an atmosphere gas. Generally, as the atmosphere gas, one or more active gases such as oxygen, air, carbon dioxide, etc. are added to an inert gas such as nitrogen, helium, or argon in an amount of 1% by volume to.
It is preferable to use a mixture of 20% by volume. Further, the film according to the present invention has a feature that the surface energy can be increased by exposing the film to an acidic solution. Preferably, sulfuric acid or hydrochloric acid or the like is used as the acid component, water or alcohols such as methyl alcohol, ethyl alcohol or isopropyl alcohol is used as the solvent, and these are used as a single or mixed solution and added to the film surface as necessary. The surface energy of the film can be increased by performing the contact reaction at a temperature.

The film having a high surface energy obtained in this manner has a high affinity with a pressure-sensitive adhesive or an adhesive, and when laminated with another film or glass, has a large peeling strength and has high peeling strength under high temperature and high humidity. Also has a feature that the peel strength is high. The preferred surface energy value depends on the type of adhesive or pressure-sensitive adhesive used, but is generally 5
0 dyne / cm or more and 80 dyne / cm or less,
More preferably 55 dyne / cm or more and 70 dyne /
cm or less. The surface energy value can be adjusted by appropriately selecting the treatment method and the treatment conditions.

On the surface of the transparent film of the present invention, a coating layer such as an antireflection layer, an antiglare layer or a hard coat layer may be formed alone or in a laminated form, if necessary. The coating layer has a thickness of 0.1 μm to 1
The thickness is preferably 0 μm, more preferably 1 μm to 5 μm.

Examples of preferred coating layers include melamine resin-based, acrylic resin-based, urethane resin-based, alkyd resin-based, and fluorine-containing resin-based organic coating layers, and organic-silicone composite-based coating layers. Examples thereof include polyester polyol and etherified methylol melamine mixed with a partial hydrolyzate of alkyltrialkoxysilane and tetraalkoxysilane. Further, silicone-based materials such as a partial hydrolyzate of aminosilane or epoxysilane, a partial hydrolyzate of a silane coupling agent and an alkyltrialkoxysilane / tetraalkoxysilane, and a hydrolyzate of colloidal silica and an alkyltrialkoxysilane are also suitable. Can be used. Solvents for coating liquids that form these coating layers include ketones such as methyl ethyl ketone, alcohols such as methanol, cell solves such as ethyl cellosolve, aromatic hydrocarbons such as toluene, cyclic ethers such as dioxane, etc. Well-known solvents can be preferably used. In order to obtain good adhesion between the transparent film of the present invention and the coating layer, these solvents can be used alone or in combination. A suitable concentration of the coating liquid is 1% by weight to 10% by weight.

A coating film can be obtained by coating one or both surfaces of the transparent film of the present invention with these coating materials and then drying as it is. It is particularly preferable to obtain a film having a solvent resistant coating film by thermosetting. At this time, simultaneous use of a low temperature curing type catalyst is a preferable method for suppressing undesired thermal denaturation of the film. Further, a hardened layer obtained by adding a photosensitizer to a monomer or oligomer such as a polyfunctional acrylate and using ultraviolet rays or electron beams can also be suitably used. If necessary, various fillers can be added to the coating layer. By providing the coating layer to which the filler is added, it is possible to obtain a surface (anti-glare layer) that suppresses specular reflection of external light and has less glare.

Preferred fillers are organic fillers such as polymethacrylic acid ester-based, polyacrylic acid ester-based, polyolefin-based, polystyrene-based, divinylbenzene-based, benzoguanamine-based and organic silicone-based fillers, silica, alumina, titanium oxide and the like. Inorganic fillers can be used. On the other hand, when it is used in a display part such as a liquid crystal display device by adding a filler, the display image may give a glaring feeling. By optimizing the shape of the filler, the coating agent and the coating conditions, JIS K 7
It is desirable that the transmitted image image sharpness measured by the method described in 6.6 of 105 using an optical comb of 0.125 mm is 80% or more.

A preferred use of the transparent film of the present invention is an optical isotropic film, and another preferred use is a retardation film. In particular, since the retardation film comprising the transparent film of the present invention has a small wavelength dependence of the retardation, it can be suitably used for a reflection type liquid crystal display device or as a λ / 4 plate. The optical isotropic film is further applied to various uses. One of such preferable uses is an electrode substrate of a plastic liquid crystal display device or a resistive film type touch panel, and another preferable use is a polarizer protective film.
When the transparent film of the present invention is used as a polarizer protective film, it may be laminated with a suitable adhesive to a polarizer containing iodine or a dye in a stretched polyvinyl alcohol film to form a polarizing plate. I can. Depending on the type of adhesive, the film of the present invention that has been surface-treated,
The adhesive strength with polyvinyl alcohol is 5 × 10 ⁶ N /
It can be m ² or more, preferably 20 × 10 ⁶ N / m ² or more. In particular, since the film of the present invention has an appropriate water vapor transmission rate, a polyvinyl alcohol-based water-based adhesive can also be suitably used. Further, another preferred use is as a support film for a recording medium or a protective film for a recording layer. For details, see Nikkei Microdevices (published by Nikkei Inc.) July 17, 2000.
It is described on page 155 of the Japanese issue.

[0052]

[Examples] The methods for measuring the physical properties shown in Examples and Comparative Examples are shown below.

<Heat distortion temperature> Using TMA, width 5 mm,
A film with a length of 10 mm is loaded with a load of 5 g, and the relationship between the heating temperature and the deformation amount is obtained in the film tension mode.
The heat distortion temperature was determined according to the method for determining the softening temperature described in K7196-1991.

<Measurement of Re value> Using a microscopic polarization spectrophotometer (TFM-120AFT) manufactured by Oak Manufacturing Co., Ltd., 5
The Re value at a wavelength of 50 nm was measured by the rotation analyzer method.

<Measurement of wavelength dependence> Oak Manufacturing Co., Ltd.
Using a microscopic polarization spectrophotometer (TFM-120AFT), each Re value at a wavelength of 441.6 nm and 514.5 nm was measured by a rotation analyzer method, and the ratio of the respective values, Re (441.6) / Re (514.5) was calculated.

<Measurement Method of Light Transmittance> JIS K71
It was measured by the method described in 5.5 of 05-1981.

<Method of measuring haze> JIS K7105
It was measured by the method described in 6.4 of -1981.

<Photoelastic coefficient> The birefringence of the film is determined by a microscopic polarization spectrophotometer (TFM-120AFT manufactured by Oak Manufacturing Co., Ltd.).
-PC) using a measuring wavelength of 514.5 nm. One of the films cut into strips with a width of 1 cm in the optical axis direction was fixed, and weights of 50 g, 100 g, and 150 g were applied to the other, and the amount of change in birefringence due to unit stress was calculated.

The present invention will be described below with reference to examples.

Example 1 Ethyl cellulose having an ethoxy group substitution degree of 2.45 and a number average molecular weight of 30,000 was dissolved in toluene as a solvent to a solid content concentration of 15% by weight, and spread on a glass plate. It was cast on a biaxially stretched PET film and left at room temperature for 15 minutes. After that, after drying for 15 minutes at 70 ℃ with the glass plate,
Peel off the film, sandwich it with a four-piece fixing jig, and
Dry for 0 minutes and then at 120 ° C for 30 minutes to obtain a thickness of 4
A film of 3 μm was obtained. The phase difference of this film is 3n
m, the light transmittance was 92%, and the haze was 0.3%.
The heat distortion temperature of the film measured using TMA is 129.
It was ℃.

A sample film of 30 cm × 10 cm was cut out from this film, and a stretching test apparatus (X4HD-HT, manufactured by Toyo Seiki Seisaku-sho, Ltd.) was used to stretch at a speed of 10 cm /
Min., A draw ratio of 1.2 times, and a drawing temperature of 125 ° C., the sample film was stretched in the longitudinal direction with uniaxial free ends to obtain a retardation film having a thickness of 40 μm and a retardation of 142.8 nm. When Re (441.6) / Re (514.5) was calculated to evaluate the wavelength dependence of this retardation film, it was 1.013. The photoelastic coefficient of this retardation film is 11 × 10 ⁻¹³ cm ² / dyne.
Met.

Example 2 Using a film having a thickness of 40 μm obtained in the same manner as in Example 1, a sample film of 30 cm × 10 cm was cut out, and the stretching ratio was 1.4 with the same apparatus and stretching speed as in Example 1. Double stretching was performed in the longitudinal direction of the sample film in the longitudinal direction of the free end under conditions of a stretching temperature of 125 ° C. to obtain a retardation film having a thickness of 30 μm and a retardation of 260 nm. To evaluate the wavelength dependence of this retardation film, Re
The calculated value of (441.6) / Re (514.5) was 1.015.

Example 3 A film having a thickness of 30 μm was obtained in the same manner as in Example 1 except that ethyl cellulose having a substitution degree of ethoxy groups of 2.55 and a number average molecular weight of 80,000 was used. From the obtained film, 3
A 0 cm × 10 cm sample film is cut out, and the same apparatus and stretching speed as in Example 1 are used, and the stretching ratio is 1.15 times.
The sample film was stretched uniaxially in the longitudinal direction at the stretching temperature of 135 ° C. to obtain a retardation film having a thickness of 26 μm and a retardation of 114 nm. In order to evaluate the wavelength dependence of this retardation film, Re (441.
6) / Re (514.5) was calculated to be 1.02
It was 6.

Comparative Example 1 A polycarbonate containing bisphenol A as a bisphenol component (C-1400, Teijin Chemicals Ltd., glass transition temperature 149 ° C.) was added to a methylene chloride solution at a concentration of 15
Melt to be a weight%, cast on a glass plate, leave at room temperature for 60 minutes, peel off the film, sandwich it with a 4-piece fixing jig,
It was dried at 100 ° C. for 10 minutes and further at 120 ° C. for 10 minutes to obtain a film having a thickness of about 65 μm. The retardation of this film was 21 nm, the light transmittance was 90%, and the haze was 0.3%.

A sample film of 30 cm × 10 cm was cut out from this film, and a stretching test apparatus (X4HD-HT, Toyo Seiki Seisaku-sho, Ltd.) was used to stretch at a speed of 10 cm /
Min, a draw ratio of 1.1 times, and a drawing temperature of 150 ° C., to obtain a retardation film having a thickness of 61 μm and a retardation of 250 nm. In order to evaluate the wavelength dependence of this retardation film, Re (441.6) / Re (514.
When 5) was calculated, it was 1.064. The photoelastic coefficient of this film is 61 × 10 ^-13 cm ² / dyn.
It was e.

Example 4 When the retardation film obtained in Example 1 was subjected to corona treatment, the wettability of the corona-treated surface was 57 dyne / cm.
Met. Using an acrylic pressure-sensitive adhesive, the polarizing axis of the polarizing plate and the slow axis of the corona-treated retardation film were arranged at 45 °, and laminated and laminated to obtain a circularly polarizing plate. Set this circularly polarizing plate to a temperature of 40
No peeling was observed at the interface between the polarizing plate and the retardation film, even after being left for a long period of time in a humid heat environment of ℃ and 95% humidity.

[0067]

INDUSTRIAL APPLICABILITY As described above, the optical film of the present invention provides a retardation film having a small wavelength dependence of retardation and a small displacement of retardation due to tension. Furthermore, when the retardation film of the present invention is used as a constituent film of a reflective TFT liquid crystal display device, a display image with high contrast and color purity can be obtained.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C08L 1:26 C08L 1:26

Claims (6)

[Claims] 1. A film containing a cellulose derivative in which hydroxyl groups of cellulose are substituted with ether groups,
The degree of ether substitution of the cellulose derivative is 0.1 to 3.
A transparent film which is 0. 2. The transparent film according to claim 1, wherein the ether group is an alkyl ether group and / or an aralkyl ether group. 3. The transparent film according to claim 1, wherein the phase difference of the transparent film is 0 nm to 2000 nm for monochromatic light having a wavelength of 550 nm. 4. The transparent film according to claim 1, wherein the transparent film is stretched in at least a uniaxial direction. 5. A ratio of a phase difference (Re (441.6)) for 441.6 nm monochromatic light to a phase difference (Re (514.5)) for 514.5 nm monochromatic light, Re (44).
1.6) / Re (514.5) is 1.04 or less, The transparent film as described in any one of Claim 1 to 4 characterized by the above-mentioned. 6. A circular or elliptically polarizing plate comprising at least one transparent film according to claim 1 and a polarizing plate laminated and integrated.