WO2012144016A1 - Optical film, polarizing plate and liquid crystal display device - Google Patents

Abstract

The purpose of the present invention is to provide an optical film which has improved heat resistance over time. This purpose has been achieved by an optical film, which contains an acrylic resin (A) and a cellulose ester resin (B) at a mass ratio from 95:5 to 51:49, and wherein the acrylic resin (A) has a weight average molecular weight (Mw) of 80,000 or more but 1,000,000 or less and is represented by general formula (1) and the cellulose ester resin (B) has a total degree (T) of substitution of acyl groups of 2.0 or more but 3.0 or less, a degree of substitution of acyl groups having 3-7 carbon atoms of less than 1.2 and a weight average molecular weight (Mw) of 75,000 or more but 300,000 or less. General formula (1): -(MMA)p-(X)q-(Y)r- (In the formula, MMA represents methyl methacrylate; X represents a monomer unit that has at least one kind of amide group and is copolymerizable with MMA; Y represents a monomer unit that is copolymerizable with MMA and X; and p, q and r represent molar percentages of respective constituent units and satisfy 55 ≤ p ≤ 99, 1 ≤ q ≤ 50, and p + q + r = 100.)

Description

Optical film, polarizing plate, and liquid crystal display device

The present invention relates to an optical film, a polarizing plate, and a liquid crystal display device, and more particularly to an optical film, a polarizing plate, and a liquid crystal display device that do not cause display unevenness.

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 liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. The optical element (polarizer or polarizing film) is sandwiched between two optical films (polarizing plate protective film).

As this polarizing plate protective film, a cellulose triacetate film is usually used.

However, recent TV screens have become larger and thinner, and LED backlights have been used as light sources. In conventional liquid crystal display devices using optical films, panels and diffusers have been designed due to display device design. Due to the deformation, the member comes into contact, and there is a problem that display unevenness (egg-like unevenness, hereinafter referred to as egg unevenness) occurs locally, and an improvement thereof has been demanded.

The mechanism of egg unevenness is not clearly understood yet, but egg-shaped unevenness may gradually occur under wet heat conditions, and it is thought that this is due to the contact between the panel and the diffusion plate accompanying the deformation of the member. It came.

On the other hand, a method of improving heat resistance by mixing a general-purpose acrylic resin and a cellulose resin and further improving the brittleness of the acrylic resin has been proposed (Patent Documents 1, 2, and 3). However, the above unevenness was not sufficiently effective.

In addition, an optical film in which cellulose ester resin is the main component and acrylic resin is mixed is also known, but it uses the properties of cellulose ester resin, and the acrylic resin has excellent transparency (low haze). (Patent Documents 4 and 5).

International Publication No. 2009/047924 JP 2009-1744 A JP 2009-179731 A International Publication No. 2009/130969 JP 2009-271510 A

In view of the above problems, an object of the present invention is to provide an optical film that improves heat resistance over time and has no display unevenness.

The above object of the present invention can be achieved by the following configuration.

1. The acrylic resin (A) and the cellulose ester resin (B) are contained at a mass ratio of 95: 5 to 51:49, the weight average molecular weight Mw of the acrylic resin (A) is 80000 to 1000000, and the following general formula ( Substitution of an acyl group represented by 1), wherein the cellulose ester resin (B) has a total acyl substitution degree (T) of 2.0 or more and 3.0 or less, and a carbon number of 3 or more and 7 or less. An optical film having a degree of less than 1.2 and a weight average molecular weight Mw of from 75,000 to 300,000.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, 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 55 <= p <= 99, 1 <= q <= 50, and p + q + r = 100. ]
2. 2. The optical film as described in 1 above, wherein X in the acrylic resin (A) is N-vinylpyrrolidone or acryloylmorpholine.

3. A polarizing plate using at least one film according to the above 1 or 2.

4. 3. A liquid crystal display device using at least one film according to 1 or 2 above.

In the present invention, an optical film that improves heat resistance over time can be provided, thereby providing a polarizing plate and a liquid crystal display device that do not have egg unevenness using the optical film.

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

Hereinafter, the best mode for carrying out the present invention will be described in detail.
<Optical film of the present invention>
The optical film of the present invention contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95: 5 to 51:49, and the weight average molecular weight Mw of the acrylic resin (A) is 80000 to 1000000. It is represented by the following general formula (1), and the cellulose ester resin (B) has a total substitution degree (T) of acyl groups of 2.0 or more and 3.0 or less, and has 3 or more carbon atoms, The substitution degree of the acyl group of 7 or less is less than 1.2, and the weight average molecular weight Mw is from 75,000 to 300,000.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, 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 55 <= 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) of 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-
[Wherein, 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 has an electron loan pair and coordinates the water molecule, thereby causing the retardation of the optical film generated over time. It is speculated that the crystal orientation of a certain resin may be suppressed.

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 large, the self-supporting property as an optical film is also satisfied.

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

Examples of Y include monomers described in Patent Documents 1, 2, and 3, such as acrylic monomers other than MMA, methacrylic monomers, olefins, acrylonitrile, styrene, and vinyl acetate. Y may be two or more. Y can be used as needed.

The weight average molecular weight (Mw) of the acrylic resin (A) of the present invention is 80,000 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 1,000,000, particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000. preferable.

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 of 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. Thirteen samples are 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.
<Cellulose ester resin (B)>
The cellulose ester resin (B) of the present invention has a total acyl group substitution degree (T) of 2.0 to 3.3 from the viewpoint of transparency particularly when it is improved in brittleness and is compatible with the acrylic resin (A). The degree of substitution of the acyl group having 0 and 3 to 7 carbon atoms is preferably less than 1.2, more preferably 1.0 or less, and the degree of substitution of the acetyl group is preferably 2.0 to 3.0.

The acyl group having 3 to 7 carbon atoms in the cellulose ester resin (B) of the present invention is preferably a propionyl group, a butyryl group or the like, and particularly preferably a propionyl group.

When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, haze becomes a problem when used as an optical film because it is not sufficiently compatible with the acrylic resin (A).

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 1.2 or more, compatibility is obtained, but the display device has When incorporated, the effect on display unevenness (egg unevenness) cannot be expected.

The weight average molecular weight (Mw) of the cellulose ester resin (B) of the present invention is 75,000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and is preferably in the range of 75,000 to 300,000. More preferably, it is within 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 (B) 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 resins can be mixed and used.

The weight average molecular weight of the cellulose ester resin (B) of 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 preferably contained in a mass ratio of 95: 5 to 51:49, preferably 80:20 to 60:40. is there.

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 51:49, the effects of the acrylic resin such as photoelastic coefficient and moisture resistance are impaired.

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.

It is preferable that the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other, and whether or not the acrylic resin (A) and the cellulose ester resin (B) are compatible can be determined, for example, based on 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.
<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 of the present invention 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 the present invention may contain acrylic particles (D) described in Patent Document 1.

Examples of commercial products of such a multilayer structure acrylic granular composite include, for example, “Metablene W-341” manufactured by Mitsubishi Rayon Co., Ltd., “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 Co., Ltd. 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 of 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 of the present invention include paragraphs (0183) to (0186) of JP-A 2010-32655.

The content of the aromatic terminal polyester of 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 of the present invention, it is possible to use a sugar ester compound having at least one pyranose structure or at least one furanose structure and esterifying all or part of the OH groups of the structure. 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 of the present invention include paragraphs (0060) to (0070) of JP-A 2010-32655.

<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 of the present invention, 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 Corporation) 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”, ADEKA Corporation “ADEKA STAB AO-50” are commercially available. What is done is preferable.

The above phosphorus compounds are, for example, from Sumitomo Chemical Co., Ltd., “Sumizer GP”, from ADEKA Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36” and “ADK STAB 3010”, from 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, for example, from BASF Japan Co., Ltd. under the trade names “Tinuvin 144” and “Tinvin 770” and from ADEKA Co., Ltd. under the name “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 have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin. In the melt casting method performed in the present invention, the glass transition temperature of the cellulose resin used alone is higher than that. The melting temperature of the cellulose resin composition can be lowered by the addition of a hydrogen bonding solvent, or the melt viscosity of the cellulose resin composition containing a hydrogen bonding solvent can be lowered at the same melting temperature as the cellulose 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. When the defect is a change in the 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 Co., Ltd.). Ro and Rt 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 retarder in the thickness direction defined by the following formula (II). It is preferable to adjust so that the foundation value Rt (590) is in the range of −100 to 100 nm.
Formula (I): Ro (590) = (nx−ny) × d (nm)
Formula (II): Rt (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 Rt (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 Rt (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 51:49, 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 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 streak was measured using a surface roughness meter. Specifically, using a Mitutoyo SV-3100S4, a stylus (diamond needle) having 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>
An example of a method for producing an optical film will be described, but the present invention is not limited to this.

As the method for forming the optical film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the standpoint of suppressing optical defects such as die lines and optical defects such as die lines, solution casting by casting is preferred.

(Organic solvent)
The organic solvent useful for forming the dope when the optical film of the present invention is produced by the solution casting method is one that simultaneously dissolves the acrylic resin (A), the cellulose ester resin (B), and other additives. It can be used without any limitation. For example, as a chlorinated organic solvent, methylene chloride, as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the ratio of alcohol in the dope increases, the web gels and peeling from the metal support becomes easy. When the ratio of alcohol is small, acrylic resin (A) and cellulose ester in non-chlorine organic solvent system. There is also a role of promoting dissolution of the resin (B).

In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, acrylic resin (A), cellulose ester resin (B), and acrylic fine particles (C) 3 A dope composition in which at least 15 to 45% by mass of the seed is dissolved is preferable.

Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

Hereinafter, a preferable method for forming the optical film of the present invention will be described.

1) Dissolution Step In an organic solvent mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B), the acrylic resin (A), the cellulose ester resin (B), and the acrylic resin (C) in a dissolution vessel. The step of dissolving the additive while stirring to form a dope, or the acrylic resin (C) solution and additive solution are mixed with the acrylic resin (A) and cellulose ester resin (B) solution to form a dope. It is a process.

For dissolving the acrylic resin (A) and the cellulose ester resin (B), a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544 Various dissolution methods such as a method of performing a cooling dissolution method as described in JP-A-9-95557 or JP-A-9-95538, a method of performing at a high pressure as described in JP-A-11-21379, and the like. Although it can be used, a method in which pressure is applied at a temperature higher than the boiling point of the main solvent is particularly preferable.

The total of three types of acrylic resin (A), cellulose ester resin (B), and acrylic fine particles (C) in the dope is preferably in the range of 15 to 45% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

For the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. In this method, the aggregate remaining when the fine particles are dispersed and the aggregate generated when the main dope is added are only aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can be removed. In the main dope, since the concentration of fine particles is sufficiently thinner than that of the additive solution, aggregates do not adhere to each other during filtration and the filtration pressure does not increase rapidly.

FIG. 1 is a diagram schematically showing a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention. Large agglomerates are removed from the acrylic fine particle charging vessel 41 by the filter 44 and fed to the stock vessel 42. Thereafter, the acrylic fine particle additive solution is added from the stock kettle 42 to the main dope dissolving kettle 1. Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

In many cases, the main dope may contain about 10 to 50% by weight of recycled material. Since the return material contains acrylic fine particles, it is preferable to control the addition amount of the acrylic fine particle addition liquid in accordance with the addition amount of the return material. The additive liquid containing acrylic fine particles preferably contains 0.5 to 10% by mass of acrylic fine particles, more preferably 1 to 10% by mass, and more preferably 1 to 5% by mass. Most preferably. The above range is preferred because the smaller the content of acrylic fine particles, the lower the viscosity and the easier the handling, and the higher the content of acrylic fine particles, the smaller the addition amount and the easier the addition to the main dope. 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. .

Also, those obtained by previously kneading and pelletizing acrylic resin and acrylic fine particles can be preferably used.

2) Casting process An endless metal belt 31, such as a stainless steel belt or a rotating metal drum, which feeds the dope through a liquid feed pump (for example, a pressurized metering gear pump) to the pressure die 30 and transfers it infinitely. This is a step of casting the dope from the pressure die slit to the casting position on the support.

¡Pressure dies that can adjust the slit shape of the die base and make the film thickness uniform are preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or heat by means such as infrared rays.

From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

The temperature at the peeling position on the metal support is preferably 10 to 40 ° C., more preferably 11 to 30 ° C.

The residual solvent amount at the time of peeling of the web on the metal support at the time of peeling is preferably peeled in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. When peeling off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be impaired, and slippage and vertical stripes are likely to occur due to peeling tension, so the balance between economic speed and quality The amount of residual solvent is determined.

The amount of residual solvent in the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the metal support from the film is usually 196 to 245 N / m. However, if wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension of ˜166.6 N / m, and then peel at a minimum tension of ˜137.2 N / m, and particularly preferable to peel at a minimum tension of ˜100 N / m.

In the present invention, the temperature at the peeling position on the metal support is preferably −50 to 40 ° C., more preferably 10 to 40 ° C., and most preferably 15 to 30 ° C.

5) Drying and stretching step After peeling, a drying device 35 that alternately conveys the web through a plurality of rolls arranged in the drying device and / or a tenter stretching device 34 that clips and conveys both ends of the web with a clip are used. And dry the web.

The drying means is generally to blow hot air on both sides of the web, but there is also a means to heat by applying microwaves instead of wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout, drying is generally performed at 40-250 ° C. In particular, drying at 40 to 160 ° C. is preferable.

When using a tenter stretching apparatus, it is preferable to use an apparatus capable of independently controlling the film gripping length (distance from the start of gripping to the end of gripping) by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

The stretching operation may be performed in multiple stages, and it is also preferable to perform biaxial stretching in the casting direction and the width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise. In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferred draw ratio for simultaneous biaxial stretching can be in the range of x1.01 to x1.5 in both the width direction and the longitudinal direction.

When the tenter is used, the amount of residual solvent in the web is preferably 20 to 100% by mass at the start of the tenter, and drying is preferably performed while the tenter is applied until the amount of residual solvent in the web is 10% by mass or less. More preferably, it is 5% by mass or less.

When performing the tenter, the drying temperature is preferably 30 to 150 ° C, more preferably 50 to 120 ° C, and most preferably 70 to 100 ° C.

In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.

6) Winding step This is a step of winding the optical film by the winder 37 after the residual solvent amount in the web is 2% by mass or less, and the dimensional stability is achieved by setting the residual solvent amount to 0.4% by mass or less. A film with good properties can be obtained.

As a winding method, a generally used one may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc., and these may be used properly.

The optical film of the present invention is preferably a long film. Specifically, the optical film shows a thickness of about 100 m to 5000 m, and is usually in the form of a roll. The film width is preferably 1.3 to 4 m, more preferably 1.4 to 2 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.
<Polarizing plate>
The polarizing plate used in the present invention can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

The film may be used on the other surface, 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, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KV8UY-HA, KV8UX-RHA, KV8UX-RHA Etc.) are preferably used.

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, various liquid crystal display devices with excellent visibility can be produced. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

The polarizing plate according to the present invention is a reflective type, transmissive type, transflective type LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type, etc. It is preferably used for a liquid crystal display device of an LED backlight.

Especially in the case of a large screen display device with a 30- to 54-inch screen, there is no egg unevenness at the periphery of the screen and the effect is maintained for a long time. In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

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

Acrylic resins A-1 to 83 in Tables 1 and 2 were prepared by a known method. The monomers used in Table 1 are as follows.
ACMO: acryloylmorpholine MACMO: methacryloylmorpholine VP: N-vinylpyrrolidone AAm: acrylamide DMAAm: N, N-dimethylacrylamide HEAAm: N-hydroxyethylacrylamide VFAAm: N-vinylformamide APIPED: N-acryloylpiperidine HEMA: 2-hydroxyethyl Methacrylate A-82 and 83 are PMMA homopolymers.

Abbreviations in Table 3 are as follows.
ac: acetyl group p: propionyl group b: butyryl group

<Production of optical film>
(Preparation of optical film F-3)
(Preparation of dope solution)
A-1 75 parts by mass B-1 25 parts by mass Methylene chloride 252 parts by mass Ethanol 48 parts by mass (Formation of optical film)
The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the amount of residual solvent reached 100%, and peeling was performed from the stainless steel band support with a peeling tension of 162 N / m.

The solvent was evaporated from the peeled web at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while being stretched 1.1 times in the width direction by a tenter.

At this time, the residual solvent amount when starting stretching with a tenter was 10%. After stretching with a tenter and relaxing at 130 ° C for 5 minutes, drying was completed while transporting the drying zone at 120 ° C and 130 ° C with a number of rolls, slitting to a width of 1.5 m, and 10 mm wide at both ends of the film. A 5 μm knurling process was performed, and the film was wound around a 6-inch inner diameter core with an initial tension of 220 N / m and a final tension of 110 N / m to obtain an optical film F-3.

The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.1 times. The residual solvent amount of the optical film F-3 shown in Table 3 was 0.1%, the film thickness was 40 μm, and the winding number was 4000 m.

Hereinafter, the optical films F-1 and F-4 and F-4 were the same as the optical film F-3 except that the acrylic resin (A), the cellulose ester resin (B), and the composition ratio were changed as shown in Table 3. -96 were produced.

"Evaluation methods"
The obtained optical films F-1 to F-96 were evaluated as follows.

(Haze)
For each of the produced film samples, one film sample was measured according to JIS K-6714 using a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.).

Thereafter, each optical film was exposed to an environment of 60 ° C. and 90% RH for 120 hours, and then the haze after durability was measured according to JIS K-6714 as described above.

Separately, a film exposed to an 80 ° C. and 5% RH environment for 120 hours was measured in the same manner. For each film, the difference between the initial value and the environmental test was calculated.

(Preparation of polarizing plate)
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 in the transport direction 5 times at 50 ° C. to produce a polarizer.

Next, the optical film F-1 produced in Example 1 was bonded to one side of the polarizer using an acrylic adhesive (thickness 20 μm). Further, KC4UY manufactured by Konica Minolta Opto Co., Ltd., which had been subjected to alkali saponification treatment, was bonded to the other surface of the polarizer and dried to prepare polarizing plate P-1. Similarly, polarizing plates P2 to 96 were produced.

(Characteristic evaluation as a liquid crystal display device)
The rear-side polarizing plate of 42-inch TV LED REGZA 42RE1 manufactured by Toshiba Corporation, which is an IPS-type liquid crystal display device, is peeled off, and F-1 to 96 of the present invention are used as the above-mentioned polarizing plates, respectively. The liquid crystal display devices were each fabricated by bonding so that the absorption axis was oriented in the same direction as the polarizing plate that had been bonded in advance so as to be the glass surface of the cell.

After that, the display device was exposed to an environment of 50 ° C. and 80% RH for 72 hours, and then left in an environment of 23 ° C. and 55% RH for 2 hours. Then, the power source (backlight) was turned on. Display unevenness (egg unevenness) after time was observed. The evaluation was performed according to the following criteria.
Image display is uniform: ◎
Image display is almost uniform: ○
There is a slight outline in the center and around: △
There is a clear outline in the center and the periphery: ×

As is clear from Tables 4 and 5, the liquid crystal display device using the optical film of the present invention can obtain a uniform image quality without egg unevenness.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Conduit 10 Ultraviolet absorber charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter

Claims (4)

The acrylic resin (A) and the cellulose ester resin (B) are contained at a mass ratio of 95: 5 to 51:49, the weight average molecular weight Mw of the acrylic resin (A) is 80000 to 1000000, and the following general formula ( Substitution of an acyl group represented by 1), wherein the cellulose ester resin (B) has a total acyl substitution degree (T) of 2.0 or more and 3.0 or less, and a carbon number of 3 or more and 7 or less. An optical film having a degree of less than 1.2 and a weight average molecular weight Mw of from 75,000 to 300,000.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, 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 55 <= p <= 99, 1 <= q <= 50, and p + q + r = 100. ] 2. The optical film according to claim 1, wherein X of the acrylic resin (A) is N-vinylpyrrolidone or acryloylmorpholine. A polarizing plate using at least one film according to claim 1 or 2. A liquid crystal display device using at least one film according to claim 1 or 2.

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