WO2011138887A1 - Optical film, method for producing optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

Disclosed is an optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a proportion by mass of 95:5 - 30:70. The acrylic resin (A) is represented by general formula (1) and has a weight average molecular weight Mw of 80,000 - 1,000,000. The optical film is characterized by containing 1 - 30% of the total mass of the optical film by mass of an additive agent (C) obtained by polymerization of a vinyl monomer having amide bonds, or copolymerization of a vinyl monomer having amide bonds and a random vinyl monomer and by this additive agent having a weight average molecular weight Mw of 1000 - 55,000. General formula (1): -(MMA)p-(X)q-(Y)r-

Description

Optical film, method for producing optical film, polarizing plate, and liquid crystal display device

The present invention relates to an optical film, an optical film manufacturing method, a polarizing plate, and a liquid crystal display device.

Demand for liquid crystal display devices is expanding for applications such as liquid crystal televisions and personal computer liquid crystal displays. In general, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a transparent electrode, a liquid crystal layer, a color filter and the like are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. Is configured by sandwiching a polarizer (also referred to as a polarizing film or a polarizing film) between two optical films (polarizing plate protective film).

As the polarizing plate protective film, a cellulose ester film is usually used. Cellulose ester film is excellent in optical isotropy and excellent in polarizer obtained by dyeing polyvinyl alcohol resin film generally used as polarizer with iodine or dichroic dye. By using a roll-to-roll, the cellulose ester film can be bonded with water glue without using a pressure-sensitive adhesive at the time of bonding to the polarizer. It is widely adopted because it can be bonded. Further, in recent years, a technique for providing a function as an optical film such as an optical compensation film as well as a polarizing plate protective film by giving the cellulose ester film specific optical characteristics by stretching treatment or the like has also been adopted. ing.

On the other hand, due to recent technological advances, the enlargement of liquid crystal display devices has accelerated, and the applications of liquid crystal display devices have diversified. For example, it can be used as a large display installed on a street or in a store, or used as an advertising display in a public place using a display device called digital signage. Thus, as the use of liquid crystal display devices expands to outdoor use, stability against severe environmental fluctuations is strongly demanded for polarizing plates used there. However, when placed in such a very severe environment, there may be a problem that the optical performance of the cellulose ester film varies. Cellulose ester film has a relatively small photoelastic coefficient compared to polycarbonate and other resins used as a general retardation film, but it is a compound produced by compressive stress and tensile stress generated when exposed to severe environmental fluctuations. This is thought to be because the change in optical characteristics due to refraction cannot be sufficiently suppressed.

It is possible to use acrylic resin such as polymethylmethacrylate as a resin suitable for optical film because it shows excellent transparency, high dimensional stability, and low hygroscopicity. When it is employed as a film, heat resistance and hard and brittle properties are problematic. Moreover, since the adhesiveness to a polarizer is low, it was necessary to adhere | attach using an adhesive, and there existed a subject in practical use.

For such problems, both cellulose ester resin films and acrylic resin films can be obtained by using an optical film obtained by forming an acrylic resin having a specific molecular weight and a specific cellulose ester resin into a compatible state. It has been proposed that the above-mentioned problem be solved (see, for example, Patent Document 1). According to the technique of Patent Document 1, an acrylic resin and a cellulose ester resin, which were conventionally difficult to mix, could be made into a highly transparent film without causing haze, but the temperature change from high heat to low heat over a long period of time. It has been found that when exposed to a more severe environment that is repeated many times, haze that was not initially seen may occur and transparency may be reduced.

Therefore, as a result of further studies by the present inventors, it has been found that such problems can be reduced by mixing a cellulose ester resin with a specific acrylic resin having a methyl methacrylate monomer and an amide bond. Such an acrylic resin has been known to be able to be used as a plasticizer highly compatible with a cellulose ester resin, but it has not been known that the above-mentioned effects can be obtained (for example, see Patent Document 2). .)

It is thought that by using a film in which such an acrylic resin and a cellulose ester resin are mixed, an optical film for a polarizing plate protective film having excellent adhesion to a polarizer and small changes in optical properties due to environmental fluctuations can be obtained. It is done. However, new problems have arisen with the recent increase in the speed of polarizing plate production and the diversification of optical performance required for optical films. As described above, in the production of a polarizing plate, the optical film is subjected to a saponification treatment with an alkaline solution to enhance the adhesion to the polarizer, and then the adhesion to the polarizer is performed. For saponification treatment in order to reduce the processing time in saponification treatment and to suppress the elution of additives added to the optical film due to diversification of optical films in order to cope with higher speed of polarizing plate production When the polarizing plate is dried at a low temperature in order to reduce the concentration of the alkaline solution of the saponification treatment and further to suppress the deterioration of the polarizer, It has been found that sufficient adhesion may not be obtained, and problems such as film peeling from the polarizer of the optical film and film floating may occur.

International Publication No. 2009/047924 Pamphlet Japanese Patent No. 4138984

Accordingly, the object of the present invention is excellent in environmental resistance, high transparency over a long period of time, and when used as a protective film for a polarizing plate, it has excellent adhesion to a polarizer and weak saponification conditions. However, it is to provide an optical film in which film peeling or film floating from the polarizer does not occur and a method for producing the same, and to provide a polarizing plate and a liquid crystal display device using such an optical film.

In view of the present situation, the present inventors have made further studies, and as a result, an optical film obtained by mixing a cellulose ester resin with a specific acrylic resin having a methyl methacrylate monomer and an amide bond, and further a vinyl having an amide bond. By adding an additive having a relatively low molecular weight obtained by polymerization of a monomer or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer, while maintaining the original functions such as environmental resistance and transparency, The present inventors have found that the adhesiveness with a polarizer can be improved and have reached the present invention.

That is, the present invention has the following forms.

1. An optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70,
The acrylic resin (A) is represented by the following general formula (1), and the weight average molecular weight Mw is 80000 to 1000000,
In the optical film, an additive (C) obtained by polymerization of a vinyl monomer having an amide bond or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer is added in an amount of 1 to 30 with respect to the total mass of the optical film. An optical film comprising: mass%, wherein the additive has a weight average molecular weight Mw of 1,000 to 55,000.

General formula (1)
-(MMA) p- (X) q- (Y) r-
(However, MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having an amide bond, Y represents a monomer unit copolymerizable with either MMA or X, and p, q, and r are mol%. And 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100.)
2. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.0 or more and 3.0 or less, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 or more and 3.0. 2. The optical film as described in 1 above, wherein the cellulose ester resin (B) has a weight average molecular weight Mw of from 75,000 to 300,000.

3. 3. The optical film as described in 1 or 2 above, wherein the monomer unit X copolymerizable with the MMA having the amide bond constituting the acrylic resin (A) is N-vinylpyrrolidone or acryloylmorpholine.

4. 4. The optical film as described in any one of 1 to 3 above, wherein the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 90:10 to 40:60.

5. 5. The optical film as described in 4 above, which contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 80:20 to 50:50.

6. 6. Polarized light obtained by bonding the optical film according to any one of 1 to 5 above to at least one surface of a polarizer obtained by dyeing a polyvinyl alcohol resin film with iodine or a dichroic dye. Board.

7. 7. The polarizing plate according to 6, wherein the optical film is bonded to one surface of the polarizer, and a cellulose ester film having a thickness of 20 μm to 75 μm is bonded to the other surface.

8. 8. A liquid crystal display device, wherein the polarizing plate described in 6 or 7 is provided on at least one surface of a liquid crystal cell.

9. Optical film containing acrylic resin (A) and cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and containing additive (C) in an amount of 1 to 30% by mass relative to the total mass of the optical film A manufacturing method of
Heating and melting the resin composition containing the acrylic resin (A), the cellulose ester resin (B) and the additive (C), and casting the film to produce an optical film,
The acrylic resin (A) is represented by the following general formula (1), and the weight average molecular weight Mw is 80000 to 1000000,
The additive (C) is an additive obtained by polymerization of a vinyl monomer having an amide bond or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer, and the weight average of the additive (C) A method for producing an optical film, wherein the molecular weight Mw is 1000 to 55000.

General formula (1)
-(MMA) p- (X) q- (Y) r-
(However, MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having an amide bond, Y represents a monomer unit copolymerizable with either MMA or X, and p, q, and r are mol%. And 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100.)

According to the above aspect of the present invention, it has excellent environmental resistance, high transparency over a long period of time, and when used as a protective film for a polarizing plate, it has excellent adhesion to a polarizer and weak saponification conditions. Even in this case, an optical film in which film peeling or film floating from the polarizer does not occur can be obtained. In addition, cellulose ester resins may be mixed with impurities having a desired degree of substitution or low molecular weight polymers as impurities during the synthesis process, and when such impurities are mixed with acrylic resins, they precipitate as foreign matters. However, it may be a problem that the transparency is impaired, but it has been found that the occurrence of such foreign matters can be suppressed according to the configuration of the present invention. Although the mechanism by which such an effect is obtained is not clear, it is presumed that the low molecular weight polymer added as an additive prevents such impurities from growing as foreign matter.

It is the figure which showed typically the process of the melt casting film forming method preferable for this invention.

Hereinafter, modes for carrying out the present invention will be described in detail, but the present invention is not limited to these.

<Optical film of the present invention>
The optical film of the present invention is an optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70,
The acrylic resin (A) is represented by the following general formula (1), and the weight average molecular weight Mw is 80000 to 1000000,
In the optical film, an additive (C) obtained by polymerization of a vinyl monomer having an amide bond or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer is added in an amount of 1 to 30 with respect to the total mass of the optical film. The additive is characterized in that the additive has a weight average molecular weight Mw of 1000 to 55000.

General formula (1)
-(MMA) p- (X) q- (Y) r-
(However, MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having an amide bond, Y represents a monomer unit copolymerizable with either MMA or X, and p, q, and r are mol%. And 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100.)
<Acrylic resin (A)>
The acrylic resin used in the present invention includes a methacrylic resin.

The acrylic resin (A) according to the present invention is represented by the following general formula (1), and has a weight average molecular weight Mw of 80000 to 1000000.

General formula (1)
-(MMA) p- (X) q- (Y) r-
MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having at least one amide group, and Y represents a monomer unit copolymerizable with MMA and X. p, q, and r are mol%, and are 50 <= p <= 99, 1 <= q <= 50, and p + q + r = 100.

X is a vinyl monomer having at least one amide group copolymerizable with MMA, and X may be one type or two or more types, and one monomer unit may have a plurality of functional groups.

Specific monomers for X include acrylamide, N-methylacrylamide, N-butylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, acryloylmorpholine, N-hydroxyethylacrylamide, acryloylpyrrolidine, acryloylpiperidine, Methacrylamide, N-methylmethacrylamide, N-butylmethacrylamide, N, N-dimethylmethacrylamide, N, N-diethylmethacrylamide, methacryloylmorpholine, N-hydroxyethylmethacrylamide, methacryloylpyrrolidine, methacryloylpiperidine, N-vinyl Examples include formamide, N-vinylacetamide, N-vinylpyrrolidone and the like.

Preferably, acryloylmorpholine and N-vinylpyrrolidone are used.

These monomers are commercially available.

Q is 1 ≦ q ≦ 50 and is appropriately selected depending on the properties of the monomer, but preferably 5 ≦ q ≦ 30. X may be a plurality of monomers.

The monomer X contributes to the improvement of heat resistance because the functional group contains oxygen atoms and nitrogen atoms in the structure and is polarized, which may increase the interaction and entanglement of the materials constituting the film. I guess it contributes.

Also, since the functional group is non-dissociable, it is considered that it is physically stable without acid generation due to decomposition over time.

Furthermore, since the weight average molecular weight is high, it is satisfactory for self-supporting properties as an optical film.

Y in the acrylic resin (A) according to the present invention represents a monomer unit copolymerizable with MMA and X.

Examples of Y include acrylic monomers other than MMA, methacrylic monomers, olefins, acrylonitrile, styrene, vinyl acetate, and the like, as described in International Publication No. 2009/047924, JP2009-1744, JP2009-179731, and the like. These monomers are mentioned. Y may be two or more.

Y can be used as needed and is most preferably not used.

The acrylic resin (A) according to the present invention has a weight average molecular weight (Mw) of 80000 or more from the viewpoint of improving transparency particularly when it is compatible with the cellulose ester resin (B).

The weight average molecular weight (Mw) of the acrylic resin (A) is more preferably in the range of 80,000 to 600,000, and most preferably in the range of 100,000 to 400,000.

The upper limit value of the weight average molecular weight (Mw) of the acrylic resin (A) is preferably 1000000 or less from the viewpoint of production.

The weight average molecular weight of the acrylic resin (A) according to the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

As the method for producing the acrylic resin (A) in the present invention, any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used.

The polymerization temperature may be 30 to 100 ° C. for suspension or emulsion polymerization, and 80 to 160 ° C. for bulk or solution polymerization. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

Commercially available acrylic resins can be used as the acrylic resin according to the present invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. . Two or more acrylic resins can be used in combination.

<Cellulose ester resin (B)>
The cellulose ester resin (B) according to the present invention has a total acyl group substitution degree (T) of 2.0 to 3 from the viewpoint of transparency particularly when it is improved in brittleness and is compatible with the acrylic resin (A). 0.0, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 2.0 to 3.0. preferable.

That is, the cellulose ester resin (B) according to the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used. Is preferably used.

When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups at the 2, 3, and 6 positions of the cellulose ester molecule is more than 1.0, the acrylic ester When the resin (A) is not sufficiently compatible with the resin (A) and used as an optical film, haze becomes a problem.

Even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility cannot be obtained.

For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased.

Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

The acyl substitution degree of the cellulose ester resin (B) according to the present invention is such that the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. If it is 3.0, there is no problem, but the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms, is preferably 1.3 or less. .

Further, the total substitution degree (T) of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

The cellulose ester resin (B) according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, Those having an acyl group having 3 or 4 carbon atoms as a substituent are preferred.

Among these, particularly preferable cellulose ester resins are cellulose acetate propionate and cellulose propionate.

The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

Incidentally, the substitution degree of the acetyl group and the substitution degree of other acyl groups were determined by the method prescribed in ASTM-D817-96.

The weight average molecular weight (Mw) of the cellulose ester resin (B) according to the present invention is 75,000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and is in the range of 75,000 to 300,000. Preferably, it is more preferably in the range of 100,000 to 240,000, particularly preferably 160000 to 240000.

When the weight average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the effect of improving heat resistance and brittleness decreases. Moreover, when it exceeds 300,000, a viscosity becomes high and film formation becomes difficult.

In the present invention, two or more kinds of cellulose ester resins can be mixed and used.

The weight average molecular weight of the cellulose ester resin (B) according to the present invention can be measured by the GPC.

<Acrylic resin (A) and cellulose ester resin (B)>
In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a compatible state at a mass ratio of 95: 5 to 30:70, more preferably 90:10 to 40: 60, particularly preferably a mass ratio of 80:20 to 50:50.

If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 30:70, the photoelastic coefficient is increased.

In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state can be determined by, for example, the glass transition temperature Tg.

For example, when the two resins have different glass transition temperatures, when the two resins are mixed, there are two or more glass transition temperatures for each resin because there is a glass transition temperature for each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which is the glass transition temperature of the compatible resin.

The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a heating rate of 20 ° C./min. The point glass transition temperature (Tmg).

In the optical film of the present invention, the weight average molecular weight (Mw) of the acrylic resin (A), the weight average molecular weight (Mw) of the cellulose ester resin (B), and the degree of substitution are different in solubility in the solvent of both resins. It is obtained by measuring each after use.

When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be.

The resin may be separated by combining two or more of these solvent combinations. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying.

These fractionated resins can be identified by general structural analysis of polymers. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), it can be separated by the same method.

If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin.

It is also possible to detect each of the compatible resins by measuring the molecular weight distribution of each of the resins separated in advance by the difference in solubility in a solvent by GPC.

The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the optical film of the present invention is preferably 55% by mass or more of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

<Additive (C)>
The optical film of the present invention was obtained by polymerizing a vinyl monomer having an amide bond with the acrylic resin (A) or cellulose ester resin (B) or copolymerizing a vinyl monomer having an amide bond and an arbitrary vinyl monomer. Additive (C) (hereinafter simply referred to as vinyl polymer (C) having an amide bond) is contained in an amount of 1 to 30% by mass based on the total mass of the optical film, and the additive has a weight average molecular weight Mw of 1000 to 55000. It is characterized by being.

The vinyl polymer (C) having an amide bond in the present invention is any polymer that can be copolymerized with a polymer of a vinyl monomer having an amide bond in a side chain (hereinafter also referred to as a polymer) or a vinyl monomer having an amide bond in a side chain. A copolymer with a vinyl monomer (hereinafter also referred to as a copolymer).

Examples of the vinyl monomer having an amide bond include N-vinylpyrrolidone, N-vinyl-2-methylpyrrolidone, acryloylmorpholine, acryloyl-2-methylmorpholine, and vinylacetamide. A mixture of two or more kinds of these vinyl monomers having an amide bond can also be used.

Examples of vinyl monomers that can be copolymerized with vinyl monomers having a functional group having an amide bond include, for example, ethylene, propylene, styrene, vinyl acetate, and vinyl alcohol. ), (Meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl Examples thereof include vinyl monomers having an arbitrary functional group such as (meth) acrylate and acrylonitrile.

These can be used as a mixture of two or more. Of these, vinyl acetate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and butyl acrylate are preferred. The copolymerization ratio of the vinyl monomer having an amide bond is preferably 20 to 100% of the total vinyl monomers constituting the polymer.

The production of a vinyl polymer having an amide bond in the side chain, or a vinyl copolymer, is made of azobisisobutyronitrile (AIBN) alone or together with other vinyl monomers capable of copolymerization having an amide bond. Using such a radical polymerization initiator, polymerization is carried out by a conventional method in the presence of a solvent if necessary.

The weight average molecular weight of the vinyl polymer having an amide bond in the side chain is 1000 to 55000, preferably 2000 to 10,000. If it is 1000 or less, a problem occurs in bleed-out, and if it exceeds 55000, transparency deteriorates.

The vinyl polymer (C) having an amide bond in the side chain according to the present invention is 1 to 30% by mass and preferably 1 to 10% by mass with respect to the total mass of the optical film.

<Other additive resins>
When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is used for the optical film of the present invention, it is preferable to adjust the addition amount within a range that does not impair the function of the optical film of the present invention.

A preferred resin is a low molecular acrylic resin obtained by polymerizing an ethylenically unsaturated monomer described in paragraphs (0072) to (0123) of JP 2010-32655 A (weight average molecular weight Mw is 500 or more and 30000 or less). Polymer).

Particularly preferably, Mw is 2000 to 30000. If it is 1000 or less, a problem occurs in bleed-out, and if it exceeds 30000, the transparency deteriorates.

Also, a vinyl polymer having an amide bond described in Japanese Patent No. 4138654 can be used.

The low molecular acrylic resin and the vinyl polymer having an amide bond are 0 to 15% by mass, preferably 0 to 10% by mass, based on the total mass of the optical film.

<Acrylic particles (D)>
The optical film of this invention may contain the acrylic particle (D) which is a multilayer structure acrylic type granular composite.

Examples of such a commercial product of a multilayer structure acrylic granular composite include, for example, “Metablene W-341” manufactured by Mitsubishi Rayon Co., “Kaneace” manufactured by Kaneka Chemical Co., Ltd., “Paraloid” manufactured by Kureha Chemical Co., Ltd. Examples include "Acryloid" manufactured by Rohm and Haas, "Staffroid" manufactured by Gantz Kasei Kogyo, Chemisnow MR-2G, MS-300X (manufactured by Soken Chemical Co., Ltd.), and "Parapet SA" manufactured by Kuraray. These can be used alone or in combination of two or more.

The optical film of the present invention preferably contains 0 to 30% by mass of acrylic particles (D) with respect to the total mass of the resin constituting the film, and is contained in the range of 1.0 to 15% by mass. More preferably.

<Other additives>
The optical film of the present invention includes a retardation control agent for controlling retardation, a plasticizer for imparting processability to the film, an antioxidant for preventing deterioration of the film, and an ultraviolet ray for imparting an ultraviolet absorbing function. It is preferable to contain additives such as fine particles (matting agent) that impart slipperiness to the absorbent and film.

<Polyester polyol of glycol and dibasic acid>
Examples of the polyester polyol that can be used in the present invention include a dehydration condensation reaction between a glycol having an average carbon number of 2 to 3.5 and a dibasic acid having an average carbon number of 4 to 5.5, or the glycol. It is preferably one produced by a conventional method by addition of a dibasic anhydride having an average carbon number of 4 to 5.5 and a dehydration condensation reaction.

<Polyester of aromatic dicarboxylic acid and alkylene glycol>
As the retardation control agent used in the present invention, an aromatic terminal polyester represented by the following general formula (I) can be used.

Formula (I) B- (GA) nGB
(Wherein B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (I), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of ordinary polyester.

Specific examples of the aromatic terminal polyester used in the present invention include paragraphs (0183) to (0186) of JP-A 2010-32655.

The content of the aromatic terminal polyester used in the present invention is preferably 0 to 20% by mass, more preferably 1 to 11% by mass in the optical film.

<Polyhydric ester compound>
The optical film of the present invention can contain a polyhydric alcohol ester compound.

Examples of the polyhydric alcohol ester compound include paragraphs (0218) to (0170) of JP-A 2010-32655.

<Sugar ester compound>
As the sugar ester compound used in the present invention, a sugar ester compound in which at least one pyranose structure or furanose structure is 1 to 12 and all or a part of the OH groups of the structure is esterified is used. It is preferable.

Examples of the sugar ester compound used in the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc. What has is preferable. An example is sucrose.

The sugar ester compound used in the present invention is one in which part or all of the hydroxyl groups of the sugar compound are esterified or a mixture thereof.

Specific examples of the sugar ester compound include paragraphs (0060) to (0070) of JP 2010-32655 A.

<Other additives>
In the optical film of the present invention, a plasticizer, a retardation control agent, an antioxidant, an ultraviolet absorber, matte particles, and the like can be used in combination.

Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

For phosphate plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate and the like can be used.

Of these, polyester-based and phthalate-based plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

In particular, when adipic acid, phthalic acid, or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

The ester plasticizer may be any of ester, oligoester and polyester types, and the molecular weight is preferably in the range of 100 to 10000, but preferably in the range of 600 to 3000, the plasticizing effect is large.

Also, the viscosity of the plasticizer has a correlation with the molecular structure and molecular weight, but in the case of an adipic acid plasticizer, the range of 200 to 5000 mPa · s (25 ° C.) is preferable because of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the composition containing an acrylic resin. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use. These plasticizers may be used alone or in combination of two or more.

<Other phase difference control agents>
Other than the above retardation control agent, those containing bisphenol A in the molecule are preferred. A compound in which ethylene oxide or propylene oxide is added to both ends of bisphenol A can be used.

For example, BP series such as New Paul BP-2P, BP-3P, BP-23P, BP-5P, BPE-20 (F), BPE-20NK, BPE-20T, BPE-40, BPE-60, BPE-100, There are BPE series (manufactured by Sanyo Chemical Co., Ltd.) such as BPE-180, and BPX series (manufactured by Adeka Co., Ltd.) such as Adeka Polyether BPX-11, BPX-33, BPX-55.

Diallyl bisphenol A, dimethallyl bisphenol A, tetrabromobisphenol A in which bisphenol A is substituted with bromine, oligomers and polymers obtained by polymerizing this, bisphenol A bis (diphenyl phosphate) substituted with diphenyl phosphate, etc. Can be used.

Polycarbonate obtained by polymerizing bisphenol A, polyarylate obtained by polymerizing bisphenol A with a dibasic acid such as terephthalic acid, and an epoxy oligomer or polymer polymerized with an epoxy-containing monomer can also be used.

Modiper CL130D or L440-G obtained by graft polymerization of bisphenol A and styrene or styrene acrylic can also be used.

Also preferred are those having a triazine structure. The compounds described in JP-A-2001-166144 can be used.

<Antioxidant>
In this invention, what is generally known can be used as an antioxidant. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used.

For example, those including those commercially available from BASF Japan under the trade names “IrgafosXP40” and “IrgafosXP60” are preferable.

The phenolic compound preferably has a 2,6-dialkylphenol structure. For example, BASF Japan Ltd., “Irganox 1076”, “Irganox 1010”, and ADEKA “ADEKA STAB AO-50” are trade names. What is marketed is preferable.

The above phosphorus compounds are, for example, from Sumitomo Chemical Co., Ltd., “Sumilizer GP”, ADEKA Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36” and “ADK STAB 3010”, “BASF Japan Co., Ltd.” IRGAFOS P-EPQ ", commercially available from Sakai Chemical Industry Co., Ltd. under the trade name" GSY-P101 "is preferred.

The hindered amine compound is preferably commercially available from BASF Japan KK under the trade names of “Tinuvin 144” and “Tinvin 770”, and from ADEKA Corporation as “ADK STAB LA-52”.

The above-mentioned sulfur compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names “Sumilizer TPL-R” and “Sumilizer TP-D”.

The above-mentioned double bond compound is preferably commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer GM” and “Sumilizer GS”.

Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

The amount of these antioxidants and the like to be added is appropriately determined in accordance with the process for recycling and use, but generally 0.05 to 20% by mass, preferably with respect to the resin as the main raw material of the film Is added in the range of 0.1 to 1% by mass.

These antioxidants can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Colorant>
In the present invention, it is preferable to use a colorant. The colorant means a dye or a pigment. In the present invention, the colorant refers to a colorant having an effect of making the color tone of a liquid crystal screen a blue tone, adjusting a yellow index, and reducing haze.

Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective.

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

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

The matting agent used in the present invention may be either an inorganic compound or an organic compound as long as it does not impair the transparency of the obtained film and has heat resistance during melting. These matting agents can be used alone or in combination of two or more.

High transparency and slipperiness can be achieved at the same time by using particles having different particle sizes and shapes (for example, needle shape and spherical shape).

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

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

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

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

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

<Viscosity reducing agent>
In the present invention, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity.

Hydrogen-bonding solvent refers to J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” that occurs between an electronegative atom and a covalently bonded hydrogen atom, that is, a bond having a large bonding moment and containing hydrogen, such as OH (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), FH (fluorine hydrogen bond), and an organic solvent that can arrange adjacent molecules.

These can reduce the viscosity by substituting a part of intermolecular hydrogen bonds of the cellulose ester resin with the above-mentioned solvent having hydrogen bonding properties.

The hydrogen bonding solvent used in the melt casting method performed in the present invention is desirably low in volatility or non-volatile when used as a melting step or film. In the melt casting method performed in the present invention, the melting temperature of the cellulose ester resin composition can be lowered by the addition of a hydrogen-bonding solvent or the same melting temperature than the glass transition temperature of the cellulose ester resin used alone. The melt viscosity of the cellulose ester resin composition containing a hydrogen bonding solvent can be lowered than that of the cellulose ester resin.

(Physical properties of optical film)
Hereinafter, the characteristics of the optical film according to the present invention will be described.

<transparency>
As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used.

In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

Further, the total light transmittance is preferably 90% or more, and more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%.

According to the optical film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property, By reducing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and acrylic particles (D), an increase in haze value can be prevented.

In addition, the optical film of the present invention preferably has a defect with a diameter of 5 μm or more in the film plane of 1 piece / 10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

Here, the diameter of the defect indicates the diameter when the defect is circular, and when it is not circular, the range of the defect is determined by observing with a microscope according to the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. If the defect is a change in surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

In addition, when observing with reflected light, if the size of the defect is not clear, aluminum or platinum is vapor-deposited on the surface for observation.

In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

When the number of defects is more than 1/10 cm square, for example, when a tension is applied to the film during processing in a later process, the film may be broken with the defect as a starting point and productivity may be reduced. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

<Retardation>
For the retardation, a 35 mm × 35 mm sample was cut from the produced optical film, conditioned for 2 hours at 25 ° C. and 55% RH, and measured from the vertical direction at 590 nm with an automatic birefringence meter (KOBRA WR, Oji Scientific Instruments). Ro and Rth at each wavelength were calculated from the measured values and the extrapolated values of the retardation values measured in the same manner while tilting the film surface.

The optical film of the present invention has an in-plane retardation value Ro (590) defined by the following formula (I) in the range of 0 to 100 nm, and a retardation in the thickness direction defined by the following formula (II). It is preferable to adjust so that the value Rth (590) is in the range of −100 to 100 nm.
Formula (I): Ro (590) = (nx−ny) × d (nm)
Formula (II): Rth (590) = {(nx + ny) / 2−nz} × d (nm)
[In the above formula, Ro (590) represents the in-plane retardation value in the film at a measurement wavelength of 590 nm, and Rth (590) represents the retardation value in the thickness direction in the film at 590 nm.

D represents the thickness (nm) of the optical film, nx represents the maximum refractive index in the plane of the film at 590 nm, and is also referred to as the refractive index in the slow axis direction. ny represents the refractive index in the direction perpendicular to the slow axis in the film plane at 590 nm, and nz represents the refractive index of the film in the thickness direction at 590 nm. ]
The in-plane retardation value Ro (590) is preferably in the range of 0 to 250 nm.

On the other hand, the retardation value Rth (590) in the thickness direction is preferably in the range of −50 to 50 nm.

For the desired retardation, the composition of the acrylic resin and the cellulose ester resin is adjusted within a mass ratio of 95: 5 to 30:70, and the ratio of each resin is adjusted. This is done by adjusting the amount to be added.

Furthermore, by adjusting and controlling the stretching temperature (combination of the temperatures of the respective sections), the magnification, the stretching speed, the stretching order, the residual solvent amount of the film when stretching, and the like according to the composition of the film. The retardation value can be set to a desired value.

By adjusting the retardation to such a range, the viewing angle of the liquid crystal display device using the optical film of the present invention can be widened, and the front contrast can be improved.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The viewing angle is an angle at which a certain level of contrast can be maintained when the viewing direction of the liquid crystal display device is tilted from the normal direction.

Uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the film width direction, more preferably in the range of −1 to + 1 °, particularly −0. A range of 5 to + 0.5 ° is preferable, and a range of −0.1 to + 0.1 ° is particularly preferable. These variations can be achieved by optimizing the stretching conditions.

In the optical film of the present invention, it is preferable that the height from the top of the adjacent mountain to the bottom of the valley is 300 nm or more, and there is no streak continuous in the longitudinal direction with an inclination of 300 nm / mm or more.

The shape of the streaks was measured using a surface roughness meter. Specifically, using a SV-3100S4 manufactured by Mitutoyo, a stylus (diamond needle) with a tip shape of 60 ° cone and a tip curvature radius of 2 μm was used. The film is scanned in the width direction of the film at a measurement speed of 1.0 mm / sec while applying a load of 0.75 mN, and a cross-sectional curve is measured with a Z-axis (thickness direction) resolution of 0.001 μm.

From this curve, the height of the streak reads the vertical distance (H) from the top of the mountain to the bottom of the valley. The slope of the streak is obtained by reading the horizontal distance (L) from the top of the mountain to the bottom of the valley and dividing the vertical distance (H) by the horizontal distance (L).

The thickness of the optical film of the present invention is preferably 20 μm or more and 150 μm or less. More preferably, it is 30 μm or more and 80 μm or less.

The optical film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

<Method for producing optical film>
The optical film of the present invention can be produced by a solution casting method or a melt casting method, but is preferably produced by a melt casting extrusion film forming method from the viewpoint of flatness and thinning.

The following optical film manufacturing method is an example, and the present invention is not limited to this.

<Method for producing optical film by melt casting extrusion film forming method>
In the method for producing an optical film of the present invention, at least an acrylic resin (A), a cellulose ester resin (B), and a vinyl polymer (C) having an amide bond are melted and coextruded from a die and cast onto a cooling roll. This is a method for producing an optical film.

FIG. 1 is a diagram schematically showing the steps of a melt casting film forming method preferable for the present invention.

In FIG. 1, the manufacturing method of the optical film by this invention is the 1st cooling from the casting die 4 using the extruder 1 after mixing film materials, such as an acrylic resin (A) and a cellulose-ester resin (B). It is melt extruded on the roll 5 and circumscribed to the first cooling roll 5, and is further circumscribed by a total of three cooling rolls, the second cooling roll 7 and the third cooling roll 8, in order to cool and solidify the film 10. To do. Next, after the film 10 peeled off by the peeling roll 9 is gripped at both ends of the film by the stretching device 12 and stretched in the width direction, it is wound up by the winding device 16. In addition, a touch roll 6 is provided that clamps the molten film on the surface of the first cooling roll 5 in order to correct the flatness. The touch roll 6 has an elastic surface and forms a nip with the first cooling roll 5.

Hereinafter, the whole manufacturing method will be described.

<Melted pellet manufacturing process>
A mixture of acrylic resin (A), cellulose ester (including cellulose ester resin (B)), vinyl polymer (C) having an amide bond, plasticizer and other additives used for melt extrusion is usually kneaded in advance. It is preferable to pelletize.

Pelletization may be performed by a known method. For example, dry acrylic resin (A), dry cellulose ester resin (B), vinyl polymer (C) having a dry amide bond, a plasticizer, and other additives are fed into an extruder. It can be supplied by kneading using a single-screw or twin-screw extruder, extruding into a strand from a die, water-cooling or air-cooling, and cutting.

It is important to dry the raw material before extruding to prevent the raw material from being decomposed. In particular, since cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer so that the moisture content is 200 ppm or less, and further 100 ppm or less.

Additives may be fed into the extruder and fed into the extruder, or may be fed through individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

Mixing of antioxidants may be performed by mixing solids or, if necessary, an antioxidant is dissolved in a solvent, and an acrylic resin (A), a cellulose ester resin (B), or a vinyl polymer having an amide bond. (C) may be impregnated and mixed, or may be mixed by spraying.

A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Further, if the contact with air, such as the exit from the feeder unit or die, it is preferable that the atmosphere such as dehumidified air and dehumidified N ₂ gas.

The extruder is preferably processed at as low a temperature as possible so as to be able to be pelletized so that the shear force is suppressed and the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

Film formation is performed using the pellets obtained as described above. It is also possible to feed the raw material powder directly to the extruder with a feeder and form a film as it is without pelletization.

<Process for extruding molten mixture from die to cooling roll>
A line for introducing the acrylic resin (A) from the molten mixture to the casting die and a line for introducing the cellulose tellur resin (B) from the molten mixture to the casting die are provided side by side. Laminated.

First, the pellets produced are extruded using a single-screw or twin-screw type extruder, the melting temperature Tm when being extruded is about 200 to 300 ° C., filtered through a leaf disk type filter or the like to remove foreign matters, and then the T-die The film is coextruded into a film, solidified on a cooling roll, and cast while pressing with an elastic touch roll.

When introducing into the extruder from the supply hopper, it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere. Tm is the temperature of the die exit portion of the extruder.

∙ If foreign matter such as scratches or plasticizer aggregates adheres to the die, streaky defects may occur. Such defects are also referred to as die lines, but in order to reduce surface defects such as die lines, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

The inner surface that comes into contact with the molten resin, such as an extruder or a die, is preferably subjected to surface treatment that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material with low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

Although there is no particular limitation on the cooling roll used in the present invention, it is a roll having a structure in which a heat medium or a refrigerant body whose temperature can be controlled is flowed with a highly rigid metal roll, and its size is not limited, The film may be of a size sufficient to cool the melt-extruded film, and the diameter of the cooling roll is usually about 100 mm to 1 m.

The surface material of the cooling roll includes carbon steel, stainless steel, aluminum, titanium and the like. Further, in order to increase the surface hardness or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

The surface roughness of the cooling roll surface is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable that the surface processed is further polished to have the above-described surface roughness.

Examples of the elastic touch roll used in the present invention include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97-028950, JP-A-11-235747, As described in JP-A-2002-36332, JP-A-2005-172940 and JP-A-2005-280217, a thin-film metal sleeve-covered silicon rubber roll can be used.

When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

<Extension process>
In the present invention, it is preferable that the film obtained as described above is further stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll. The sharpness of the streaks becomes gentle by stretching and can be highly corrected.

Preferably, the film is stretched 1.1 to 2.0 times in both the longitudinal (film transport direction) and lateral (width direction) directions.

As the stretching method, a known roll stretching machine or tenter can be preferably used. In particular, in the case where the optical film is a retardation film that also serves as a polarizing plate protective film, it is preferable to stack the polarizing film in a roll form by setting the stretching direction to the width direction.

The slow axis of the optical film becomes the width direction by stretching in the width direction.

Usually, the draw ratio is 1.1 to 3.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually Tg to Tg + 50 ° C. of the resin constituting the film, preferably Tg to Tg + 40 ° C. Performed in the temperature range.

The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

The film may be contracted in the longitudinal direction or the width direction for the purpose of reducing the retardation of the optical film produced by the above method and reducing the dimensional change rate.

In order to shrink in the longitudinal direction, for example, there is a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

Since the optical film of the present invention is produced by the melt casting coextrusion film forming method, the amount of the solvent contained is 0.01% by mass or less when wound up as a roll film. The amount of the solvent can be measured by the following method.

<Contained solvent amount>
Each sample was placed in a 20 ml sealed glass container, treated under the following headspace heating conditions, and then a calibration curve was prepared and measured for the solvent used in advance by the following gas chromatography. The amount of solvent contained was expressed in parts by mass relative to the total mass of the optical film.
Equipment: HP 5890SERIES II
Column: J-W DB-WAX (inner diameter 0.32 mm, length 30 m)
Detection: FID
GC temperature rising condition: held at 40 ° C. for 5 minutes, then heated to 80 ° C./min to 100 ° C. Headspace heating condition: 120 ° C. for 20 min
In the optical film of the present invention, the return material can be used in the production process. The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

The optical film of the present invention is preferably a long film. Specifically, the optical film has a thickness of about 100 m to 10000 m and is usually provided in a roll shape.

In addition, the width of the optical film is preferably 1.3 to 4 m, and more preferably 1.4 to 3 m.

The film thickness of the optical film of the present invention is not particularly limited, but when used for a polarizing plate protective film described later, it is preferably 20 to 200 μm, more preferably 25 to 100 μm, and 30 to 80 μm. It is particularly preferred.

<Functional layer>
The optical film of the present invention includes a hard coat layer, an antistatic layer, a back coat layer, a slippery layer, an adhesive layer, a barrier layer, an antiglare layer, an antireflection layer, an optical compensation layer and the like before or after stretching. A functional layer may be applied.

<Polarizing plate>
The optical film of the present invention can be used for a polarizing plate and a liquid crystal display device using the polarizing plate.

The polarizing plate is characterized in that it is a polarizing plate in which the optical film of the present invention is bonded to at least one surface of a polarizer. The liquid crystal display device of the present invention is characterized in that the polarizing plate according to the present invention is bonded to at least one liquid crystal cell surface via an adhesive layer.

The polarizing plate can be produced by a general method. The optical film of the present invention is preferably bonded to at least one surface of a polarizer prepared by subjecting the polarizer side of the optical film to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution.

On the other side, the optical film of the present invention may be used, or another polarizing plate protective film may be used. For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC4UA, KC6UA, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, C4, R4 -4, KC4HR-1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

A preferred embodiment of the present invention is a polarizing plate in which the optical film of the present invention is bonded to one surface of a polarizer and a cellulose ester film having a thickness of 20 μm to 75 μm is bonded to the other surface.

A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

The above-mentioned pressure-sensitive adhesive may be a one-component type or a type in which two or more components are mixed before use.

The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The concentration of the pressure-sensitive adhesive liquid may be appropriately determined depending on the film thickness after adhesion, the coating method, the coating conditions, and the like, and is usually 0.1 to 50% by mass.

<Liquid crystal display device>
By incorporating the polarizing plate bonded with the optical film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate of the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

The polarizing plate of the present invention includes various types such as a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), and an IPS type (including an FFS type). It is preferably used in a drive type LCD. In particular, in a large-screen display device with a VA screen of 30 or more, particularly 30 to 54, there is no white spot at the periphery of the screen and the effect is maintained for a long time.

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

Example 1
<Material synthesis>
(Acrylic resin (A))
Acrylic resins A1 to A29 in Table 1 were produced by a known method. In the table, ACMO is acryloylmorpholine, MACMO is methacryloylmorpholine, AAm is acrylamide, VP is N-vinylpyrrolidone, DMAAm is N, N-dimethylacrylamide, HEAAm is N-hydroxyethylacrylamide, and VFAAm is N-vinyl. Formamide and ACPIPE are acryloylpiperidine, HEMA is 2-hydroxyethyl methacrylate, and HPMA is 2-hydroxypropyl methacrylate.

(Cellulose ester resin (B))
Table 2 describes the details of the cellulose ester resins CE1 to CE30 used in the examples.

In the table, ac: acetyl group, pr: propionyl group, bt: butyryl group, pen: pentyl group, hep: heptyl group, bz: benzoyl group, oct: octyl group, ph: phenyl group.

(Vinyl polymer having amide bond (C))
Vinyl polymers C1 to C11 having an amide bond shown in Table 3 were prepared by a known method. In the table, VP is N-vinylpyrrolidone, VAc is vinyl acetate, MMA is methyl methacrylate, and HEMA is 2-hydroxyethyl methacrylate.

<Production of optical film>
(Preparation of optical film 1)
The following materials were further dried while being mixed at 80 ° C. and 1 Torr for 3 hours with a vacuum nauter mixer, and the resulting mixture was melt-mixed at 235 ° C. using a twin-screw extruder and pelletized.

Acrylic resin (A): A5 (dried at 90 ° C. for 3 hours and water content 1000 ppm) 65 parts by weight Cellulose ester resin (B): CE1 (cellulose acetate propionate: acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 200000, dried at 100 ° C. for 3 hours and water content 500 ppm) 35 parts by weight Vinyl polymer having amide bond (C): C3 3.5 parts by weight Tinuvin 928 (BASF Japan) 1.1 parts by mass GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.) 0.25 parts by mass Irganox 1010 (manufactured by BASF Japan Ltd.) 0.5 parts by mass Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0.24 parts by mass Aerosil NAX50 (Japan) 0.2 parts by weight Seahoster KEP-30 (manufactured by Nippon Shokubai Co., Ltd.) 0.02 parts by weight The obtained pellets were dried by circulating 70 ° C. dehumidified air for 5 hours or more. While maintaining the temperature of 100 ° C., it was introduced into a single-screw extruder in the next step. A small amount of the pellet was taken out and the water content was measured and found to be 120 ppm.

Film formation was performed with the manufacturing apparatus shown in FIG.

The above pellets were melt extruded from a T die onto a first cooling roll having a surface temperature of 90 ° C. at a melting temperature of 240 ° C. using a single screw extruder to obtain a 120 μm cast film. At this time, the film was pressed on the first cooling roll with an elastic touch roll having a 2 mm thick metal surface.

First, the obtained film was stretched 60% in the transport direction at 175 ° C. by a stretching machine using a difference in peripheral speed of the roll. Next, it is introduced into a tenter having a preheating zone, a stretching zone, a holding zone, and a cooling zone (there is also a neutral zone for ensuring thermal insulation between the zones), and is 70 ° C at 175 ° C in the width direction. The film was cooled to 30 ° C., then released from the clip, and the clip gripping part was cut off to obtain an optical film sample 1 having a film thickness of 40 μm and a film width of 2500 mm.

(Preparation of optical films 2 to 80)
As in the production of the optical film 1, the types and amounts of the acrylic resin (A), the cellulose ester resin (B), and the vinyl polymer (C) having an amide bond are changed as shown in Tables 4, 5, and 6. The optical film samples 2 to 80 were prepared by mixing. At this time, the melting temperature was set for each resin mixture as a temperature at which the melt viscosity became 1000 Pa · s.

(Preparation of optical films 81 to 83)
Cellulose derivative compositions 1 and 3 were prepared by the methods described in Examples 1 and 3 of Japanese Patent No. 4138984. Optical films 81 and 82 were produced from this resin composition in the same manner as described above.

Also, a film was produced according to the production method of the optical film 1 described in Example 1 of International Publication No. 2009/047924, and this was designated as film 83.

<< Evaluation of optical film >>
<Various measurement methods>
(Film endurance haze)
For each of the produced film samples, one film sample was conditioned for 24 hours in an atmosphere of 23 ° C. and 55% RH, and then the haze meter (NDH2000 type, Nippon Denshoku Industries Co., Ltd.) according to JIS K-7136. ).

Next, this film is placed in a thermostatic chamber, first treated in an environment of −35 ° C. for 30 minutes, and then immediately set in an environment of 95 ° C. From the time when the temperature in the thermostatic bath reaches 95 ° C. The treatment was performed for 30 minutes. After that, set the temperature to -35 ° C again and perform the treatment for 30 minutes when the same environment is reached. Thereafter, the treatment at -35 ° C and the treatment at 95 ° C are regarded as one cycle, and the durability is evaluated for a total of 100 cycles. Went.

Finally, the film sample was conditioned for 24 hours in an atmosphere of 23 ° C. and 55% RH, and then the haze was measured by the same method as described above, and the difference in haze between before and after endurance (Δ%) Was calculated.

(Polarizer adhesion)
A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 5 times in the transport direction at 50 ° C. to prepare a polarizer.

Next, the above-prepared optical film 1 applied with a polyvinyl alcohol-based adhesive on both sides of the polarizer and subjected to alkali saponification treatment with a 1.5N KOH solution at 40 ° C. for 60 seconds on one side of the polarizer, KC6UY (manufactured by Konica Minolta Opto Co., Ltd.) that had been subjected to the same saponification treatment was laminated on the other surface, bonded together with a roll machine, and then dried at 60 ° C. for 120 seconds to produce polarizing plate 1. Similarly, polarizing plates 2 to 83 were produced using optical films 2 to 83, respectively.

The produced polarizing plate is cut into a square of 5 cm × 5 cm, left in an atmosphere of 23 ° C. and 55% RH for 24 hours, and then peeled off from the corner at the interface between the polarizer and the film. Observed. This operation was performed with 10 polarizing plates for one type of sample, and the number of polarizing plates in which peeling was observed between the polarizer and the film was counted and evaluated as follows.

○: No peeling ○ △: 1 to 2 sheets peeled △: 3 to 4 sheets peeled △ ×: 5 to 6 sheets or more ×: 7 sheets or more Polarizer adhesion is practically at the level of ○ △ to ○ Preferably there is.

(Rth environmental fluctuation)
A sample of 35 mm × 35 mm was cut out from the produced optical film, conditioned at 23 ° C. and 80% RH for 24 hours, and measured with an automatic birefringence meter (KOBRA WR, Oji Scientific Co., Ltd.) from the vertical direction at 590 nm and film Rth was measured while tilting the surface.

Next, after the humidity was adjusted at 23 ° C. and 20% RH for 24 hours, the same measurement was performed, and the difference between Rth at 23 ° C. and 80% RH and Rth value at 23 ° C. and 20% RH was calculated.

(Contamination aptitude)
For each of the above prepared film samples, the number of foreign substances and granular materials of 30 to 100 μm existing on the film surface was counted in the reflection mode using a commercially available reflection type optical microscope in the range of 100 mm × 100 mm. The average value was converted into the number per 1 m ² and calculated.

Tables 4, 5, and 6 show the details of the optical film sample contents and the results of the above evaluation.

From the above table, it can be seen that the optical film of the present invention is excellent in film durability haze, polarizing plate adhesion, and Rth environmental fluctuation. Furthermore, it was found that the optical film of the present invention is also excellent in contamination suitability such as foreign matter.

Example 2
<Production of liquid crystal display device>
The polarizing plates on both sides of Hitachi LCD TV Woo32 H-90, which were previously bonded, were peeled off, and the above-prepared polarizing plates 1 to 83 were bonded to both sides of the glass surface of the liquid crystal cell.

At that time, the direction of bonding of the polarizing plate is such that the absorption axis of the polarizing plate previously bonded and the absorption axis of the prepared polarizing plates 1 to 83 are directed in the same direction, respectively. Liquid crystal display devices 1 to 83 were produced.

When the visibility of the produced liquid crystal display device was evaluated, the liquid crystal display device equipped with the polarizing plate bonded with the optical film of the present invention was clear and high in contrast, and had good visibility even after long-term use. Had.

DESCRIPTION OF SYMBOLS 1 Extruder 2 Filter 3 Static mixer 4 Casting die 5 Rotating support body (1st cooling roll)
6 Nipping pressure rotating body (touch roll)
7 Rotating support (second cooling roll)
8 Rotating support (3rd cooling roll)
9, 11, 13, 14, 15 Transport roll 10 Optical film 12 Stretching device 16 Winding device

Claims (9)

1. An optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70,
   The acrylic resin (A) is represented by the following general formula (1), and the weight average molecular weight Mw is 80000 to 1000000,
   In the optical film, an additive (C) obtained by polymerization of a vinyl monomer having an amide bond or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer is added in an amount of 1 to 30 with respect to the total mass of the optical film. An optical film comprising: mass%, wherein the additive has a weight average molecular weight Mw of 1,000 to 55,000.
   General formula (1)
   -(MMA) p- (X) q- (Y) r-
   (However, MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having an amide bond, Y represents a monomer unit copolymerizable with either MMA or X, and p, q, and r are mol%. And 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100.)
2. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.0 or more and 3.0 or less, and the substitution degree of the acyl group having 3 or more and 7 or less carbon atoms is 1.2 or more and 3.0. The optical film according to claim 1, wherein the cellulose ester resin (B) has a weight average molecular weight Mw of 75,000 or more and 300,000 or less.
3. 3. The optical film according to claim 1, wherein the monomer unit X copolymerizable with MMA having the amide bond constituting the acrylic resin (A) is N-vinylpyrrolidone or acryloylmorpholine.
4. 4. The optical film according to claim 1, wherein the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 90:10 to 40:60.
5. The optical film according to claim 4, wherein the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 80:20 to 50:50.
6. The optical film according to any one of claims 1 to 5 is bonded to at least one surface of a polarizer obtained by dyeing a polyvinyl alcohol resin film with iodine or a dichroic dye. Polarizer.
7. The polarizing plate according to claim 6, wherein the optical film is bonded to one surface of the polarizer, and a cellulose ester film having a thickness of 20 μm to 75 μm is bonded to the other surface.
8. A liquid crystal display device, wherein the polarizing plate according to claim 6 or 7 is provided on at least one surface of the liquid crystal cell.
9. Optical film containing acrylic resin (A) and cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and containing additive (C) in an amount of 1 to 30% by mass relative to the total mass of the optical film A manufacturing method of
   Heating and melting the resin composition containing the acrylic resin (A), the cellulose ester resin (B) and the additive (C), and casting the film to produce an optical film,
   The acrylic resin (A) is represented by the following general formula (1), and the weight average molecular weight Mw is from 80,000 to 1,000,000,
   The additive (C) is an additive obtained by polymerization of a vinyl monomer having an amide bond or copolymerization of a vinyl monomer having an amide bond and an arbitrary vinyl monomer, and the weight average of the additive (C) A method for producing an optical film, wherein the molecular weight Mw is 1000 to 55000.
   General formula (1)
   -(MMA) p- (X) q- (Y) r-
   (However, MMA represents methyl methacrylate, X represents a monomer unit copolymerizable with MMA having an amide bond, Y represents a monomer unit copolymerizable with either MMA or X, and p, q, and r are mol%. And 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100.)

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