JP7042583B2 - Raw film for manufacturing optical film and method for manufacturing optical film using it - Google Patents

Description

The present invention relates to a raw film for producing an optical film containing polyvinyl alcohol having a narrow molecular weight distribution and a method for producing an optical film using the same.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film, and the polarizing film is a polyvinyl alcohol (hereinafter, may be abbreviated as PVA) film. The mainstream is a matrix in which a dichroic dye such as an iodine-based dye (I ^3- , I ^5- , etc.) or a dichroic organic dye is adsorbed on a matrix formed by uniaxially stretching the film.

LCDs are widely used in small devices such as calculators and wristwatches, smartphones, notebook computers, liquid crystal monitors, liquid crystal projectors, liquid crystal televisions, in-vehicle navigation systems, and measuring devices used indoors and outdoors. In recent years, these devices are required to improve display quality. Along with this, there is a demand for higher performance of the polarizing film, and specifically, there is a demand for a polarizing film having excellent optical performance such as degree of polarization and transmittance.

As a method for improving the optical performance of a polarizing film, a method using PVA having a high molecular weight is known (Patent Document 1). However, it has been difficult to industrially produce a film using PVA having a high molecular weight because the moldability decreases as the molecular weight increases.

Technological development aimed at enhancing the functionality of polarizing films is underway, and the following raw fabric films for manufacturing optical films have been reported. Patent Document 2 describes a PVA film for raw material of a polarizing film made of PVA containing 0.01 to 1 mol% of hydrophilic functional groups such as a carboxylic acid group and an ω-hydroxy-α-olefin group. There is. Patent Document 2 describes that the PVA film is excellent in stretching / orientation treatment property and adsorption treatment property of dichroic substances. Patent Document 3 describes an optical PVA film formed by forming a PVA resin, wherein the PVA resin is composed of a PVA resin (X) and a PVA resin (Y) containing a 1,2-diol bond in a side chain. An optical PVA film is described. Patent Document 3 describes that the PVA film is excellent in optical performance and stretchability. However, when the molecular weight of PVA used in the films described in Patent Documents 2 and 3 is increased in order to enhance the optical performance of the obtained polarizing film, the moldability may be insufficient.

By the way, in recent years, with the progress of so-called living radical polymerization technology, some methods for controlling the radical polymerization reaction of vinyl acetate have been proposed. For example, a method has been proposed in which a radical polymerization reaction of vinyl acetate is carried out in the presence of a radical polymerization initiator and a specific control agent to obtain polyvinyl acetate having a narrow molecular weight distribution and a high molecular weight. In such a polymerization reaction, the growth radical terminal of the molecular chain of polyvinyl acetate covalently bonds with a regulator to form a dormant species, and an equilibrium is formed between the dormant species and the radical species generated by dissociation thereof. Polymerization proceeds while forming. Such a polymerization reaction is called controlled radical polymerization.

Patent Document 4 describes that the number average molecular weight (Mn) is 92,000 and the molecular weight distribution (Mw / Mn) is obtained by carrying out a radical polymerization reaction of vinyl acetate in the presence of a radical polymerization initiator and a control agent composed of an iodine compound. ) Synthesized 1.57 polyvinyl acetate and saponified it to produce PVA. However, in the polymerization method using an iodine compound as a control agent, it is known that an aldehyde group is formed at the polymerization terminal of polyvinyl acetate (see, for example, Non-Patent Document 1). It is known that when polyvinyl acetate having such an aldehyde group at the end is saponified, a conjugated polyene structure in which a plurality of carbon-carbon double bonds are conjugated is formed, and PVA with remarkable coloring can be obtained. A film made of PVA colored in this way is not suitable as an optical film.

Recently, a method for synthesizing polyvinyl acetate by controlled radical polymerization using an organic cobalt complex as a control agent has been proposed. In this polymerization reaction, the growth radical terminal of the molecular chain of polyvinyl acetate is covalently bonded to the cobalt atom of the organic cobalt complex to form a dormant species, and the dormant species and the radical species generated by dissociation thereof are formed. Polymerization proceeds while forming an equilibrium. For example, in Non-Patent Document 2, vinyl acetate is polymerized in the presence of cobalt (II) acetylacetonate to have a number average molecular weight (Mn) of 99,000 and a molecular weight distribution (Mw / Mn) of 1.33. An example of synthesizing polyvinyl acetate has been reported.

Non-Patent Document 3 describes that a polyvinyl acetate chain obtained by polymerizing vinyl acetate in the presence of cobalt (II) acetylacetonate is treated with 1-propanethiol. The polyvinyl acetate chain forms a dormant species with a cobalt (III) complex bonded to the end, and the terminal radical formed by cleavage of the dormant species reacts with 1-propanethiol to form polyacetate. The cobalt complex can be separated from the vinyl chain. Although the polyvinyl acetate forming the Dormant species is green, it is described that the polyvinyl acetate with reduced coloring was obtained by precipitating the separated cobalt complex and then filtering it off with cerite. ing. Further, by using TEMPO (2,2,6,6-tetramethylpiperidine1-oxyl) which is a stable radical compound instead of 1-propanethiol, TEMPO is bound to the terminal radical to capture the radical. You can also. Also in this case, it is described that colorless polyvinyl acetate was obtained by filtering and removing the cobalt complex with acidic alumina.

As described above, according to the method described in Non-Patent Document 3, it is said that polyvinyl acetate with reduced coloring can be obtained. However, it is not described in Non-Patent Document 3 that the polyvinyl acetate thus obtained is saponified to obtain PVA. As a result of experiments by the present inventors, it was found that PVA obtained by saponifying the polyvinyl acetate obtained in Non-Patent Document 3 is colored.

Japanese Unexamined Patent Publication No. 1-105204 Japanese Unexamined Patent Publication No. 8-201626 Japanese Unexamined Patent Publication No. 2009-24076 Japanese Unexamined Patent Publication No. 11-147914

Controlled / Living Radical Polymerization of Vinyl Acetate by Degenerative Transfer with Alkyl Iodides, Macromolecules, 2003, vol.36, p9346-9354 Highly Efficient Cobalt-Mediated Radical Polymerization of Vinyl Acetate, Angewandte Chemie International Edition, 2005, vol.44, p1101-1104 Synthesis of End-Functional Poly (vinyl acetate) by Cobalt-Mediated Radical Polymerization, Macromolecules, 2005, vol.38, p5452-5458

The present invention has been made to solve the above problems, and an object of the present invention is to provide a raw film capable of obtaining an optical film having excellent moldability and excellent optical performance. Another object of the present invention is to provide a method for manufacturing an optical film using such a raw film.

The above-mentioned problems are that the weight average molecular weight (Mw) is 100,000 to 1,000,000, the molecular weight distribution (Mw / Mn) is 1.05 to 1.95, and the saponification degree is 80 to 99.99 mol%. It is solved by providing a raw film for manufacturing an optical film containing PVA.

The thickness of the raw film is preferably 1 to 75 μm. It is also preferable that the b value of the raw film is 0.35 or less.

It is preferable that the raw fabric film for manufacturing an optical film is a raw fabric film for manufacturing a polarizing film.

A method for producing an optical film, which comprises a step of uniaxially stretching the raw film for producing an optical film, is a preferred embodiment of the present invention. A more preferred embodiment of the present invention is a method for producing a polarizing film, which comprises a step of dyeing the raw film for producing a polarizing film with a dichroic dye and a step of uniaxially stretching.

According to the original film of the present invention, it is possible to improve the optical performance of the obtained optical film while suppressing the deterioration of moldability.

It is a figure which plotted the weight average molecular weight (Mw) on the horizontal axis, and the dichroism ratio on the vertical axis about the polarizing film of Examples 1 to 3 and Comparative Examples 1 to 3. It is a figure which plotted the shrinkage stress on the horizontal axis, and the dichroism ratio on the vertical axis about the polarizing film of Examples 1 to 3 and Comparative Examples 1 to 3.

The raw film for manufacturing an optical film of the present invention has a weight average molecular weight (Mw) of 100,000 to 1,000,000, a molecular weight distribution (Mw / Mn) of 1.05 to 1.95, and is saponified. It contains PVA having a degree of 80 to 99.99 mol%.

The weight average molecular weight (Mw) of the PVA is 100,000 to 1,000,000. When the weight average molecular weight (Mw) is 100,000 or more, an optical film having excellent optical performance can be obtained. The weight average molecular weight (Mw) is preferably 150,000 or more, more preferably 200,000 or more, further preferably 250,000 or more, and particularly preferably 300,000 or more. On the other hand, when the weight average molecular weight (Mw) is 1,000,000 or less, the formability of the raw film is improved. The weight average molecular weight (Mw) is preferably 800,000 or less, and more preferably 500,000 or less. The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) in the present invention are measured by a gel permeation chromatography (GPC) method. In this measurement, polymethylmethacrylate is used as a standard substance. Further, HFIP (hexafluoroisopropanol) is used as the mobile phase, and a column for HFIP is used as the column. Specifically, the measurement by the GPC method in the present invention is performed by the method described in the examples.

The molecular weight distribution (Mw / Mn) of PVA needs to be 1.05 to 1.95. As described above, by using PVA having a narrow molecular weight distribution (Mw / Mn), the optical performance of the optical film surprisingly obtained can be obtained by using PVA having the same weight average molecular weight (Mw). Significantly improved compared to optical film. Therefore, it is possible to improve the optical performance of the obtained optical film while suppressing the deterioration of moldability. The molecular weight distribution (Mw / Mn) is preferably 1.8 or less.

The degree of saponification of PVA is 80 to 99.99 mol%. When the saponification degree is 80 mol% or more, an optical film having excellent optical performance and durability can be obtained. The saponification degree is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and particularly preferably 99.2 mol% or more. On the other hand, if the degree of saponification exceeds 99.99 mol%, it may be difficult to produce PVA. The saponification degree is preferably 99.95 mol% or less. The degree of saponification of PVA in the present specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units possessed by PVA that can be converted into vinyl alcohol units by saponification. The ratio (mol%) of the number of moles of vinyl alcohol unit. The degree of saponification of PVA can be measured according to the description of JIS K6726-1994.

The total amount of the vinyl ester unit and the vinyl alcohol unit with respect to all the monomer units in the PVA is preferably 50 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and 95 mol% or more. Is particularly preferable, and may be 100 mol%.

The content of the 1,2-glycol bond in the PVA is preferably 0.7 to 1.5 mol%. When the content of the 1,2-glycol bond is 1.5 mol% or less, the optical performance of the obtained optical film is further improved. The content of the 1,2-glycol bond is more preferably 1.4 mol% or less. On the other hand, if the content of the 1,2-glycol bond is less than 0.7 mol%, the water solubility may decrease and it may become difficult to handle. The content of the 1,2-glycol bond is more preferably 1 mol% or more.

A suitable method for producing PVA is a polymerization step of polymerizing a vinyl ester monomer by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex; after the polymerization step, it is represented by the following formula (I). It has a termination step of terminating the polymerization to obtain a polyvinyl ester by adding a polymerization terminator or a proton donating polymerization terminator; and a saponification step of saponifying the polyvinyl ester obtained in the terminator step to obtain PVA. .. According to this method, PVA having a narrow molecular weight distribution, a high weight average molecular weight, and a good hue can be obtained. Hereinafter, the manufacturing method will be described in detail.

（式中、Ｒ^１は置換基を有してもよい炭素数６～２０の芳香族基を表し、Ｒ^２は水素原子、炭素数１～２０のアルキル基、または置換基を有してもよい炭素数６～２０の芳香族基を表す。）

(In the formula, R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent, and R ² may have a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a substituent. Represents a good aromatic group with 6 to 20 carbon atoms.)

First, the polymerization process will be described. In the polymerization step, the vinyl ester monomer is polymerized by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex. Controlled radical polymerization is a polymerization reaction in which the growth radical terminal (active species) is placed in an equilibrium state with a covalent bond species (dormant species) bonded to a control agent and the reaction proceeds. By performing controlled radical polymerization, side reactions are suppressed, so that a polyvinyl ester having a high weight average molecular weight (Mw) and a narrow molecular weight distribution (Mw / Mn) can be obtained. In the above-mentioned production method, an organic cobalt complex is used as a control agent.

Examples of the vinyl ester monomer used in the above-mentioned production method include vinyl formate, vinyl acetate, trifluorovinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl capricate, and laurin. Examples thereof include vinyl acetate, vinyl stearate, vinyl benzoate, vinyl versatic acid and the like, but vinyl acetate is preferably used from an economical point of view.

The produced polyvinyl ester may contain a monomer unit derived from an ethylenically unsaturated monomer copolymerizable with the vinyl ester monomer as long as the effect of the present invention is not impaired. Examples of the ethylenically unsaturated monomer include olefins such as ethylene, propylene, 1-butene and isobutene; acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid and the like. Unsaturated carboxylic acid, its salt, its mono or dialkyl ester or its anhydride; acrylamide, N-alkylacrylamide, N, N-dimethylacrylamide, 2-acrylamide propanesulfonic acid or its salt, acrylamidepropyldimethylamine or its acid Acrylic acid such as a salt or a quaternary salt thereof; methacrylicamide, N-alkylmethalkylamide, N, N-dimethylmethacrylicamide, 2-methacrylamide propanesulfonic acid or a salt thereof, methacrylicamidepropyldimethylamine or an ester thereof or 4 thereof. Methacrylates such as grade salts; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; Cyanide vinyls such as acrylonitrile and methacrylonitrile; Vinyl ether; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide; vinylsilane such as trimethoxyvinylsilane, allyl acetate, allyl chloride, allyl alcohol, dimethylallyl alcohol, trimethyl- (3-) Acrylamide-3-dimethylpropyl) -ammonhydride chloride, acrylamide-2-methylpropanesulfonic acid and the like can be mentioned. The carbon number of the ethylenically unsaturated monomer to be copolymerized is not particularly limited, but the carbon number is preferably 2 to 20.

Examples of the method for polymerizing the vinyl ester monomer include known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, a bulk polymerization method of polymerizing without a solvent or a solution polymerization method of polymerizing in various organic solvents is usually adopted. In order to obtain a polymer having a narrow molecular weight distribution, a massive polymerization method that does not use a solvent or dispersion medium that may cause side reactions such as chain transfer is preferable. On the other hand, solution polymerization may be preferable from the viewpoint of adjusting the viscosity of the reaction solution and controlling the polymerization rate. Examples of the organic solvent used as a solvent in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; and the like. Of these, esters and aromatic hydrocarbons are preferably used to prevent chain transfer. The amount of the solvent used may be determined in consideration of the viscosity of the reaction solution according to the weight average molecular weight of the target PVA. For example, the mass ratio (solvent / monomer) is selected from the range of 0.01 to 10. The mass ratio (solvent / monomer) is preferably 0.1 or more, and preferably 5 or less.

As the radical initiator used in the polymerization step, conventionally known azo-based initiators, peroxide-based initiators, redox-based initiators and the like are appropriately selected. Examples of the azo-based initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2,4-). Dimethylvaleronitrile) and the like, and examples of the peroxide-based initiator include percarbonate compounds such as diisopropylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethylperoxydicarbonate; t-butyl. Perester compounds such as peroxyneodecaneto, α-cumylperoxyneodecaneate, t-butylperoxyneodecanete; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2 -Peroxyphenoxyacetate and the like can be mentioned. Further, potassium persulfate, ammonium persulfate, hydrogen peroxide and the like can be combined with the above-mentioned initiator to prepare the initiator. Examples of the redox-based initiator include a combination of the above-mentioned peroxide and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and longalit. The amount of the initiator used differs depending on the polymerization catalyst and cannot be unconditionally determined, and is arbitrarily selected according to the polymerization rate.

The organic cobalt complex used as a control agent in the polymerization step may contain a divalent cobalt atom and an organic ligand. Suitable organic cobalt complexes include, for example, cobalt (II) acetylacetonate [Co (acac) ₂ ], cobalt (II) porphyrin complex and the like. Of these, cobalt (II) acetylacetonate is preferable from the viewpoint of manufacturing cost.

In the controlled radical polymerization, theoretically, one polyvinyl ester chain is generated from one molecule of the organic cobalt complex to be added. Therefore, the amount of the organic cobalt complex added to the reaction solution is determined in consideration of the target polymerization average molecular weight and the polymerization rate. Usually, it is preferable to use 0.001 to 1 mol of an organic cobalt complex with respect to 100 mol of the vinyl ester monomer.

The number of moles of the radical initiator used in the controlled radical polymerization is preferably 1 times or more, more preferably 1.5 times or more the number of moles of the organic cobalt complex. On the other hand, if the number of moles of the generated radicals is too large to be larger than the number of moles of the organic cobalt complex, the proportion of uncontrolled radical polymerization increases and the molecular weight distribution widens. The number of moles of the radical initiator used is preferably 10 times or less, more preferably 6 times or less, the number of moles of the organic cobalt complex.

The method for mixing the radical initiator, the organic cobalt complex and the vinyl ester monomer is not particularly limited as long as the dormant species can be produced and the high degree of polymerization of the polyvinyl ester can be controlled. For example, a method of mixing the obtained mixture and the vinyl ester monomer after mixing the radical initiator and the organic cobalt complex, a method of mixing the radical initiator, the organic cobalt complex and the vinyl ester monomer at once, an organic method. Examples thereof include a method of mixing the obtained mixture and the radical initiator after mixing the cobalt complex and the vinyl ester monomer. Further, the radical initiator, the organic cobalt complex and the vinyl ester monomer may be divided and mixed. For example, by mixing a radical initiator and an organic cobalt complex with a part of a vinyl ester monomer, after the organic cobalt (III) complex is covalently bonded to the short chain polyvinyl ester terminal, a dormant species is generated. Examples thereof include a method of mixing the dormant species and the remainder of the vinyl ester monomer to increase the degree of polymerization. The dormant species may be isolated as a macroinitiator and then mixed with the rest of the vinyl ester monomer to increase the degree of polymerization.

The polymerization temperature is preferably, for example, 0 ° C to 80 ° C. When the polymerization temperature is less than 0 ° C., the polymerization rate becomes insufficient and the productivity tends to decrease. From this point of view, the polymerization temperature is more preferably 10 ° C. or higher, further preferably 20 ° C. or higher. On the other hand, when the polymerization temperature exceeds 80 ° C., the molecular weight distribution of the obtained polyvinyl ester tends to be widened. From this point, the polymerization temperature is more preferably 65 ° C. or lower, and even more preferably 50 ° C. or lower. The time required for the polymerization step of the vinyl ester monomer is usually 3 to 50 hours.

When the desired polymerization rate is reached in the polymerization step, the polymerization reaction is stopped by adding a polymerization terminator represented by the above formula (I) or a proton donating polymerization terminator.

Examples of the polymerization inhibitor represented by the above formula (I) include 1,1-diphenylethylene, styrene, α-methylstyrene, 4-tert-butylstyrene and the like.

The proton donating polymerization inhibitor is a polymerization terminator capable of providing a proton radical to the radical at the end of the polyvinyl acetate chain, and preferably has a chain transfer constant of 0.1 or more with respect to vinyl acetate at 60 ° C. .. For example, sorbic acid and the like can be mentioned. Further, an organometallic compound having a metal-hydrogen bond or the like can also be used.

The number of moles of the polymerization inhibitor added is preferably 1 to 100 mol with respect to 1 mol of the added organic cobalt complex. If the number of moles of the polymerization inhibitor is too small, the radicals at the end of the polymer cannot be sufficiently captured, and the color tone of the obtained PVA may deteriorate. Therefore, the number of moles of the polymerization inhibitor is more preferably 3 mol or more with respect to 1 mol of the organic cobalt complex. On the other hand, if the number of moles of the polymerization inhibitor is too large, the production cost may increase. The number of moles of the polymerization inhibitor is more preferably 50 mol or less with respect to 1 mol of the organic cobalt complex.

The temperature of the reaction solution in the termination step is the temperature at which the polymerization inhibitor represented by the above formula (I) can react with the radical at the end of the polyvinyl acetate chain, or the proton-donating polymerization inhibitor is the radical at the end of the polyvinyl acetate chain. The temperature may be any temperature at which proton radicals can be provided, preferably 0 to 80 ° C. If the temperature of the reaction solution is less than 0 ° C., the stopping step takes too much time and the productivity is lowered. From this point of view, the temperature of the reaction solution in the stopping step is more preferably 10 ° C. or higher, further preferably 20 ° C. or higher. On the other hand, when the temperature of the reaction solution exceeds 80 ° C., unnecessary polymerization of vinyl acetate proceeds and the molecular weight distribution (Mw / Mn) tends to increase. From this point, the temperature is more preferably 70 ° C. or lower, further preferably 60 ° C. or lower. The time required for the stop process is usually 10 minutes to 5 hours.

After the stopping step, it is preferable to carry out an extraction step of contacting the obtained polyvinyl ester solution with an aqueous solution containing a water-soluble ligand to extract and remove the cobalt complex from the polyvinyl ester solution. As described above, by performing the saponification step after removing the cobalt complex contained in the polyvinyl ester solution in advance, PVA having a good hue and being hard to gel can be obtained. Specifically, the aqueous solution and the polyvinyl ester solution, which are insoluble in each other, are vigorously stirred so that the area of the interface between the two is large, and then allowed to stand, separated into an oil layer and an aqueous layer, and then the aqueous layer is formed. All you have to do is remove it. This operation may be repeated a plurality of times.

The water-soluble ligand used in the extraction step is preferably an acid having a pKa of 0 to 12 at 25 ° C. When a strong acid having a pKa of less than 0 is used, it is difficult to efficiently extract the cobalt complex, and the pKa is preferably 2 or more. Further, it is difficult to efficiently extract the cobalt complex even when a weak acid having a pKa of more than 12 is used, and the pKa is preferably 7 or less. When the acid is a polyvalent acid, the first dissociation constant (pKa1) needs to be in the above range. The acid having a pKa of 0 to 12 is preferably a carboxylic acid or a phosphoric acid (pKa1 is 2.1), and more preferably a carboxylic acid. Of these, acetic acid (pKa is 4.76) is particularly preferable.

The pH of the aqueous solution containing the water-soluble ligand is preferably 0 to 5. The pH is more preferably 1 or more, and even more preferably 1.5 or more. The pH is more preferably 4 or less, still more preferably 3 or less.

In the saponification step, the polyvinyl ester obtained in the stop step is saponified to obtain PVA. At this time, the extraction step may be performed after the stop step, and then the saponification step may be performed.

In the saponification step, the polyvinyl ester produced by the above method is saponified in a state of being dissolved in alcohol or a hydrous alcohol to obtain PVA. Examples of the alcohol used in the saponification reaction include lower alcohols such as methanol and ethanol, and methanol is particularly preferably used. The alcohol used in the saponification reaction may contain acetone, an ester such as methyl acetate or ethyl acetate, or a solvent such as toluene. Examples of the catalyst used for the saponification reaction include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkaline catalysts such as sodium methylate, and acid catalysts such as mineral acid. As for the temperature of the saponification reaction, for example, the range of 20 to 60 ° C. is appropriate. When a gel-like product precipitates as the saponification reaction progresses, PVA is obtained by pulverizing the product at that time, washing the product, and then drying the product.

The original film of the present invention is produced using the PVA thus obtained. The method for producing the raw film is not particularly limited, and a method for producing a film having a more uniform thickness and width after film formation can be preferably adopted. For example, the above-mentioned PVA and, if necessary, further. A film-forming stock solution in which one or more of the plasticizers, additives and surfactants described below are dissolved in a liquid medium, PVA and, if necessary, further plasticizers, additives and surfactants. And one or more of liquid media and the like, and can be produced using a film-forming stock solution in which PVA is melted. When the film-forming stock solution contains at least one of a plasticizer, an additive and a surfactant, it is preferable that the components are uniformly mixed.

Examples of the liquid medium used for preparing the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of these can be used. Of these, water is preferable from the viewpoint of environmental load and recoverability.

The volatile content of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is generally used. It is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass, and even more preferably in the range of 60 to 85% by mass. Since the volatile fraction of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, filtration and defoaming during preparation of the film-forming stock solution are smoothly performed, and a film with few foreign substances and defects is performed. Is easy to manufacture. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and industrial film production becomes easy.

The membrane-forming stock solution preferably contains a surfactant. By containing the surfactant, the film-forming property is improved, the occurrence of thickness unevenness of the film is suppressed, and the film can be easily peeled off from the metal roll or belt used for the film-forming. When a raw film is produced from a film-forming stock solution containing a surfactant, the film may contain a surfactant. The type of the above-mentioned surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of peelability from a metal roll or a belt.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino. Alkylamine type such as ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxy An allylphenyl ether type such as alkylene allylphenyl ether is suitable.

These surfactants can be used alone or in combination of two or more.

When the membrane-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of PVA contained in the membrane-forming stock solution, 0.02. It is more preferably in the range of about 0.3 parts by mass, and particularly preferably in the range of 0.05 to 0.1 parts by mass. When the content is 0.01 parts by mass or more, the film-forming property and the peelability are further improved. On the other hand, when the content is 0.5 parts by mass or less, it is possible to prevent the surfactant from bleeding out to the surface of the raw film to cause blocking and deterioration of handleability.

Examples of the film-forming method for forming the raw film using the above-mentioned undiluted film-forming solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. As these film forming methods, only one kind may be adopted or two or more kinds may be adopted in combination. Among these film-forming methods, the cast film-forming method and the extrusion film-forming method are preferable because a raw film having a uniform thickness and width and good physical characteristics can be obtained. The formed raw film can be dried or heat-treated as needed.

As an example of a specific method for producing the raw film of the present invention, for example, a T-shaped slit die, a hopper plate, an I-die, a lip coater die, or the like is used, and the above-mentioned film-forming stock solution is positioned on the most upstream side. Discharge or spread uniformly on the peripheral surface of the rotating heated first roll (or belt), and from one surface of the film discharged or spread on the peripheral surface of the first roll (or belt). The volatile components are evaporated and dried, followed by further drying on the perimeter of one or more rotating heated rolls placed downstream thereof, or by passing through a hot air drying device. After drying, a method of winding with a winding device can be industrially preferably adopted. Drying with a heated roll and drying with a hot air drying device may be carried out in an appropriate combination.

The raw film of the present invention may contain a plasticizer in addition to the above-mentioned PVA. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Further, one or more of these plasticizers can be contained. Among these, glycerin is preferable from the viewpoint of improving the stretchability.

The content of the plasticizer in the raw film of the present invention is preferably 1 to 20 parts by mass with respect to 100 parts by mass of PVA. When the content is 1 part by mass or more, the stretchability of the film is further improved. The content is more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the film from becoming too flexible and the handleability from being lowered. The content is more preferably 17 parts by mass or less, and further preferably 15 parts by mass or less.

The raw film of the present invention further includes a filler, a processing stabilizer such as a copper compound, a weathering stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and the like. Additives such as thermoplastic resins, lubricants, fragrances, defoamers, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, cross-linking agents, fungicides, preservatives, and crystallization rate retarders. Can be appropriately blended as needed.

The ratio of the total of PVA and the plasticizer in the raw film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass, based on the mass of the raw film. % Or more is more preferable.

The thickness of the original film of the present invention is not particularly limited, but is generally 1 to 75 μm, more preferably 5 to 60 μm, and particularly preferably 10 to 45 μm. If the thickness is too thin, stretch breakage tends to occur easily during the uniaxial stretching process for producing a polarizing film. Further, if the thickness is too thick, stretching spots are likely to occur during uniaxial stretching for producing a polarizing film. The thickness here means the thickness of the PVA layer in the case of a multilayer film.

The raw film may be a single-layer film or a multilayer film having a PVA layer and a base resin layer. In the case of a single-layer film, the thickness of the film is preferably 20 μm or more, more preferably 30 μm or more, in order to ensure handleability. On the other hand, in the case of a multilayer film, the thickness of the PVA layer can be 20 μm or less, or 15 μm or less. The thickness of the base resin layer in the multilayer film is usually 20 to 500 μm.

When a multilayer film having a PVA layer and a base resin layer is used as the raw film, the base resin must be uniaxially stretchable together with PVA. Polyester, polyolefin resin and the like can be used. Of these, an amorphous polyester resin is preferable, and polyethylene terephthalate and an amorphous polyester resin obtained by copolymerizing polyethylene terephthalate with a copolymerization component such as isophthalic acid or 1,4-cyclohexanedimethanol are preferably used. It is preferable to produce a multilayer film by applying a PVA solution to a base resin film. At this time, in order to improve the adhesiveness between the PVA layer and the base resin layer, the surface of the base resin film may be modified or an adhesive layer may be formed between both layers.

The b value of the original film of the present invention is preferably 0.35 or less. By using such an original film having a low b value, an optical film having excellent optical performance can be obtained. By producing the raw fabric film using the PVA obtained by the above-mentioned manufacturing method, it is possible to manufacture the raw fabric film having a narrow molecular weight distribution and a low b value. The b value of the raw film is more preferably 0.3 or less, and further preferably 0.2 or less. The b value of the raw film is measured by the method described in Examples.

The width of the original film of the present invention is not particularly limited and can be determined according to its use and the like. In recent years, since the screen size of liquid crystal televisions and liquid crystal monitors has been increasing, if the width of the raw film is set to 3 m or more, it is suitable for applications in which these are final products. On the other hand, if the width of the raw film is too large, there may be a problem that it tends to be difficult to perform uniaxial stretching itself uniformly when manufacturing an optical film with a practical device. The width of the raw film is preferably 7 m or less.

According to the original film of the present invention thus obtained, it is possible to improve the optical performance of the obtained optical film while suppressing the deterioration of moldability. Therefore, the raw film is suitably used for producing an optical film. Examples of such an optical film include a polarizing film and a retardation film, and a polarizing film is preferable.

A method for producing an optical film having a step of uniaxially stretching the raw film is a preferred embodiment of the present invention. A more preferred embodiment of the present invention is a method for producing a polarizing film, which comprises a step of dyeing the raw film with a dichroic dye (dyeing step) and a step of uniaxially stretching (stretching step).

As a more specific method for producing a polarizing film using the raw fabric film, a dyeing step of dyeing the raw fabric film, a stretching step of uniaxially stretching, and a swelling step of further swelling as necessary, Examples thereof include a method having a cross-linking step for cross-linking, a fixing treatment step for fixing treatment, a washing step for washing, a drying step for drying, a heat treatment step for heat treatment, and the like. In this case, the order of each step such as the swelling step, the dyeing step, the crosslinking step, the stretching step, and the fixing treatment step is not particularly limited, and one or two or more steps can be performed at the same time. It is also possible to perform one or more of each step twice or more.

The swelling step can be performed by immersing the PVA film (raw film) in water. The temperature of the water when immersed in water is preferably in the range of 20 to 50 ° C, more preferably in the range of 22 to 45 ° C, and preferably in the range of 25 to 43 ° C. More preferred. The time for soaking in water is preferably, for example, in the range of 0.1 to 5 minutes, and more preferably in the range of 0.5 to 3 minutes. The water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

The dyeing step can be performed by contacting the PVA film with a dichroic dye. Iodine-based dyes are generally used as the dichroic dyes. The dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide, which is a dyeing bath, and such a dyeing method is also preferably adopted in the present invention. To. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C. A suitable staining time is 0.2-5 minutes.

By performing the cross-linking step of cross-linking the PVA film, it is possible to more effectively prevent PVA from elution into water during wet stretching at a high temperature. From this viewpoint, it is preferable that the crosslinking step is performed after the dyeing step and before the stretching step. The cross-linking step can be performed by immersing the PVA film in an aqueous solution containing a cross-linking agent. As the cross-linking agent, one or more kinds of boron compounds such as borate such as boric acid and borax can be used. The concentration of the cross-linking agent in the aqueous solution containing the cross-linking agent is preferably in the range of 1 to 15% by mass, more preferably in the range of 1.5 to 7% by mass, and in the range of 2 to 6% by mass. Is more preferable. Sufficient stretchability can be maintained when the concentration of the cross-linking agent is in the range of 1 to 15% by mass. The aqueous solution containing a cross-linking agent may contain potassium iodide or the like. The temperature of the aqueous solution containing the cross-linking agent is preferably in the range of 20 to 60 ° C, particularly preferably in the range of 25 to 55 ° C. By setting the temperature within the range of 20 to 60 ° C., cross-linking can be performed efficiently.

The stretching step of uniaxially stretching the PVA film may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, in the above-mentioned dyeing bath or in the fixing treatment bath described later. Further, in the case of the dry stretching method, stretching may be carried out at room temperature, stretching may be carried out while heating, or may be carried out in the air using a PVA film after water absorption. Among these, the wet stretching method is preferable because it can be uniformly stretched in the width direction, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, and 1.5. It is particularly preferable that it is in the range of about 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The stretching temperature in uniaxial stretching is preferably in the range of 30 to 90 ° C, more preferably in the range of 40 to 80 ° C, and particularly preferably in the range of 50 to 70 ° C.

Further, the draw ratio in uniaxial stretching (total draw ratio from the original film) is preferably 5 times or more, and more preferably 5.5 times or more from the viewpoint of the polarization performance of the obtained polarizing film. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

When a long PVA film is uniaxially stretched, the direction of uniaxial stretching is not particularly limited, and uniaxial stretching or lateral uniaxial stretching in the long direction can be adopted, but a polarizing film having excellent polarizing performance can be obtained. Uniaxial stretching in the long direction is preferable. Uniaxial stretching in the long direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, the horizontal uniaxial stretching can be performed using a tenter type stretching machine.

In the production of the polarizing film, a fixing treatment step can be performed after the stretching step in order to strengthen the adsorption of the dichroic dye (iodine-based dye or the like) on the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by mass, particularly preferably about 3 to 10% by mass. By setting the concentration in the range of 2 to 15% by mass, the adsorption of the dichroic dye can be further strengthened. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

The cleaning step is generally performed by immersing the PVA film in distilled water, pure water, an aqueous solution or the like. At this time, from the viewpoint of improving the polarization performance, it is preferable to use an aqueous solution containing an iodide such as potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5 to 10% by mass. The temperature of the aqueous solution in the cleaning treatment is generally 5 to 50 ° C, preferably 10 to 45 ° C, and even more preferably 15 to 40 ° C. From an economical point of view, it is not preferable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the polarization performance may deteriorate.

The conditions of the drying step are not particularly limited, but it is preferable to dry the PVA film at a temperature in the range of 30 to 150 ° C., particularly in the range of 50 to 130 ° C. By drying at a temperature in the range of 30 to 150 ° C., a polarizing film having excellent dimensional stability can be easily obtained.

The dichroism ratio (R) of the polarizing film thus obtained is preferably 100 or more. By using the original film of the present invention, a polarizing film having such a high dichroism ratio (R) can be produced with high productivity. The dichroism ratio (R) is more preferably 150 or more, and even more preferably 190 or more. The method for calculating the dichroism ratio (R) of the polarizing film is as follows. First, the relationship between the transmittance (T') excluding surface reflection and the simple substance transmittance (T) is shown by the equation (1). At this time, the refractive index of PVA was 1.5, and the reflectance on the surface was 4%. The relationship between the transmittance (T'), the degree of polarization (V) and the dichroism ratio (R) is expressed by the equation (2). Therefore, after measuring the single transmittance (T) and the degree of polarization (V), the dichroism ratio (R) of the polarizing film is calculated by solving the equations (1) and (2) using these values. can do.
T'= T / (1-0.04) ² (1)
R = {-ln [T'(1-V)]} / {-ln [T'(1 + V)]} (2)

The polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate / butyrate cellulose (CAB) film, an acrylic film, a polyester film and the like are used. In addition, examples of the adhesive for bonding include a PVA-based adhesive, a urethane-based adhesive, and an acrylate-based ultraviolet curable adhesive.

The polarizing plate obtained as described above can be used as a component of an LCD by being coated with an adhesive such as acrylic and then bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The methods of each measurement and evaluation are as follows.

[Measurement of weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)]
The number average molecular weight (Mn) and the molecular weight distribution (Mw / Mn) were measured using a size exclusion high performance liquid chromatograph "HLC-8320GPC" manufactured by Tosoh Corporation. The measurement conditions are as follows.
Column: HFIP-based column "GMHR-H (S)" manufactured by Tosoh Corporation, connected in series Standard sample: Polymethylmethacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20 mM)
Flow rate: 0.2 mL / min
Temperature: 40 ° C
Sample solution concentration: 0.1 wt% (filtered with a 0.45 μm aperture filter)
Injection volume: 10 μL
Detector: RI

[Measurement of 1,2-glycol binding amount (mol%)]
PVA, which had been dried under reduced pressure at 90 ° C. for 2 days, was dissolved in DMSO _- d6, and a sample to which a few drops of trifluoroacetic acid was added was prepared and used for measurement. ¹ H-NMR measurement was performed at 80 ° C. using a nuclear magnetic resonance apparatus "LAMBDA 500" manufactured by JEOL Ltd. After confirming that the degree of saponification was 99.9 mol% or more from the amount of residual acetyl groups in polyvinyl alcohol, the amount of 1,2-glycol bound was measured. The peak derived from methine of vinyl alcohol unit is assigned to 3.2 to 4.0 ppm (integral value A), and the peak derived from one methine of 1,2-glycol bond is assigned to 3.25 ppm (integral value B). The 1,2-glycol bond content can be calculated with.
1,2-Glycol binding amount (mol%) = (B / A) × 100

[Softening point of PVA film]
The softening point of the PVA film to be measured was measured using an automatic softening point measuring device "EX-820" manufactured by Daiichi Rika Co., Ltd. Specifically, a square sample with a size of 3 cm square is cut out from the PVA film, and this sample is cut into a stainless plate with a thickness of 1 mm and a rectangular hole of 1 cm x 2 cm in the center with a circular hole with a diameter of 1 cm in the center. Place it on a pedestal with the stainless steel plate with a circular hole facing up, sandwiched between a stainless steel plate with a thickness of 1 mm and a 3 cm square, and place it on the film located in the center of the circular hole. A steel ball (nominal: 3/8 (diameter 9.525 mm), grade: G60, mass: 3.5 g ± 0.05 g) specified in 2009 was placed. Subsequently, 750 mL of distilled water at 25 ° C. was added, the temperature was raised at 5 ° C. per minute, and the temperature when the film dropped to a position of 25 mm from the gantry was defined as the softening point of the PVA film.

[Evaluation of hue of PVA film]
From the PVA films obtained in the following examples and comparative examples, a rectangular sample of 3 cm × 2.5 cm was taken, and a spectrophotometer with an integrating sphere (“U-4100” manufactured by Hitachi-Nippon Technologies) was used to JIS. The b value was measured after correcting the visual sensitivity of the visible light region of the C light source and the 2 ° field in accordance with Z 8722 (measurement method of object color).

[Optical characteristics of polarizing film]
From the central part of the width direction of the polarizing film obtained in the following examples and comparative examples, a rectangular sample of 4 cm in the length direction of the polarizing film was taken, and a spectrophotometer with an integrating sphere (manufactured by Nippon Spectral Co., Ltd. V7100 ”) is used to correct the visibility of the visible light region of the C light source and 2 ° field in accordance with JIS Z 8722 (measurement method of object color), and then the single transmittance (T) and the degree of polarization. (V) was measured.

The dichroism ratio (R) of the polarizing film was calculated by solving the following equations (1) and (2) from the values of T and V thus obtained. Here, the refractive index of PVA is 1.5, and the reflectance on the surface is 4%.
T'= T / (1-0.04) ² (1)
R = {-ln [T'(1-V)]} / {-ln [T'(1 + V)]} (2)

[Shrink stress of polarizing film]
The contraction stress is the autograph AG-X with a constant temperature bath manufactured by Shimadzu Corporation and the video type extensometer TR V.
It was measured using iewX120S. A polarizing film whose humidity was controlled at 20 ° C./20% RH for 18 hours was used for the measurement. After the constant temperature bath of Autograph AG-X was set to 20 ° C, a polarizing film (15 cm in the length direction, 1.5 cm in the width direction) was attached to the chuck (chuck interval 5 cm), and at the same time as the tension was started, the constant temperature bath was set to 80 ° C. The temperature rise was started. The polarizing film was pulled at a speed of 1 mm / min, the tension was stopped when the tension reached 2N, and the tension was measured up to 4 hours later in that state. At this time, since the distance between the chucks changes due to thermal expansion, a marked line sticker is attached to the chuck, and the distance between the chucks is corrected by the amount that the marked line sticker attached to the chuck using the video type extensometer TR ViewX120S moves. Measurements were made as possible. The value obtained by subtracting the initial tension 2N from the measured value of the tension after 4 hours was defined as the shrinkage force of the polarizing film, and the value obtained by dividing the value by the cross-sectional area of the sample was defined as the shrinkage stress (MPa).

Synthesis example 1
A reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port is charged with 100 parts by mass of vinyl acetate and 0.04 part by mass of cobalt (II) acetylacetonate as an organic cobalt complex for nitrogen bubbling. The inside of the reactor was replaced with an inert gas for 30 minutes. The temperature of the reactor was started by heating the water bath, and when the internal temperature reached 40 ° C., 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) was added as a radical initiator. After adding 13 parts by mass and stirring for 2 hours, the temperature was lowered and the internal temperature was maintained at 30 ° C. to initiate polymerization. Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion of vinyl acetate reached 20%, 0.13 part by mass of 1,1-diphenylethylene was added as a polymerization inhibitor, and the temperature was 30 ° C. Was stirred with. It took 3 hours from the start of polymerization to the target conversion rate. After the polymerization inhibitor was added, 92 parts by mass of an acetic acid aqueous solution having a concentration of 25% by mass was further added, and after stirring for 5 minutes, the mixture was allowed to stand for 30 minutes to separate into two layers, and the aqueous layer was removed. After repeating the above liquid separation operation a total of 3 times, the acetic acid aqueous solution was changed to deionized water and the same liquid separation operation was repeated a total of 3 times. After that, the reactor was connected to a vacuum line, and the remaining vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain a 20% by mass methanol solution of polyvinyl acetate. Next, 100 parts by mass of the obtained 20% by mass methanol solution of polyvinyl acetate and 20 parts by mass of methanol are added and dissolved in the same reactor as above, and then the water bath is heated to bring the internal temperature to 40 ° C. Was heated and stirred until. To this, 13.3 parts by mass (1.9 parts by mass as sodium hydroxide) of a methanol solution of sodium hydroxide (concentration 14% by mass) was added, and saponification was carried out at 40 ° C. The produced gelled product was pulverized with a pulverizer and left at 40 ° C. for 1 hour to proceed with saponification. To the obtained saponified product, 1.9 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was further added, and the saponification reaction was driven for another 1 hour under heating at 65 ° C. and reflux. Then, 30 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that the neutralization was completed using a phenolphthalein indicator, a solid was obtained by filtration, and 75 parts by mass of methanol was added thereto and the mixture was heated under reflux for 1 hour. Then, the solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain the desired PVA. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 2
Similar to Synthesis Example 1 except that cobalt (II) acetylacetonate was 0.02 parts by mass and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) was 0.07 parts by mass. Polymerization was carried out. When the conversion of vinyl acetate reached 20%, 0.07 parts by mass of 1,1-diphenylethylene was added as a polymerization inhibitor, and the mixture was stirred at 30 ° C. It took 3 hours from the start of polymerization to the target conversion rate. After that, the post-treatment and the saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain the desired PVA. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 3
Similar to Synthesis Example 1 except that cobalt (II) acetylacetonate was 0.02 parts by mass and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) was 0.07 parts by mass. Polymerization was carried out. When the conversion of vinyl acetate reached 36%, 0.07 parts by mass of 1,1-diphenylethylene was added as a polymerization inhibitor, and the mixture was stirred at 30 ° C. It took 5 hours from the start of polymerization to the target conversion rate. After that, the post-treatment and the saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain the desired PVA. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 4
A reactor equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and an initiator addition port was charged with 100 parts by mass of vinyl acetate and 39 parts by mass of methanol, and the inside of the reactor was replaced with an inert gas for 30 minutes while bubbling nitrogen. did. The temperature of the reactor was started by heating the water bath, and when the internal temperature reached 60 ° C., 0.02 part by mass of azobisisobutyronitrile was added as an initiator to start the polymerization. Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion of vinyl acetate reached 37%, 2.4 parts by mass of a hydroquinone methanol solution having a concentration of 1% by mass was added as a polymerization inhibitor, and 30 parts were added. The polymerization was stopped by cooling to ° C. It took 3 hours from the start of polymerization to the target conversion rate. It was connected to a vacuum line and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain a 20% by mass methanol solution of polyvinyl acetate. After that, the post-treatment and the saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain the desired PVA. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 5
Polymerization of vinyl acetate was carried out in the same manner as in Synthesis Example 1 except that the amount of methanol was 22 parts by mass and the amount of azobisisobutyronitrile was 0.01 part by mass. When the conversion of vinyl acetate reached 30%, 1.3 parts by mass of a 1% by mass hydroquinone methanol solution having a concentration of 1% by mass was added as a polymerization terminator, and the mixture was cooled to 30 ° C. to terminate the polymerization. It took 2.5 hours from the start of polymerization to the target conversion rate. After that, the desired PVA was obtained in the same manner as in Synthesis Example 4. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 6
Polymerization was carried out in the same manner as in Synthesis Example 1 except that methanol was used in an amount of 10 parts by mass and azobisisobutyronitrile was used in an amount of 0.005 part by mass. When the conversion of vinyl acetate reached 23%, 0.6 parts by mass of a 1% by mass hydroquinone methanol solution having a concentration of 1% by mass was added as a polymerization terminator, and the mixture was cooled to 30 ° C. to terminate the polymerization. It took 3 hours from the start of polymerization to the target conversion rate. After that, the desired PVA was obtained in the same manner as in Synthesis Example 4. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Synthesis example 7
Polymerization was carried out in the same manner as in Synthesis Example 1. When the conversion of vinyl acetate reached 20%, 0.11 part by mass of TEMPO (2,2,6,6-tetramethylpiperidine1-oxyl) was added as a polymerization inhibitor, and the mixture was stirred at 30 ° C. It took 3 hours from the start of polymerization to the target conversion rate. After that, the post-treatment and the saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain the desired PVA. Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), saponification degree, and 1,2-glycol binding amount of the obtained PVA.

Example 1
It contains 100 parts by mass of PVA obtained in Synthesis Example 1, 10 parts by mass of glycerin as a plasticizer, and 0.1 part by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and has a PVA content of 11.5% by mass. An aqueous solution is used as a film-forming stock solution, which is dried on a metal roll at 80 ° C., and the obtained film is heat-treated at a temperature of 90 ° C. for 10 minutes in a hot air dryer to reduce the softening point to 65.5 ° C. To prepare a PVA film having a thickness of 45 μm. The b value of the obtained PVA film was measured by the method described above. The results are shown in Table 1.

From the central portion of the PVA film thus obtained in the width direction, a sample having a width of 5 cm and a length of 9 cm was cut so that a range of 5 cm in width × 5 cm in length could be uniaxially stretched. This sample was uniaxially stretched 2.0 times in the length direction while being immersed in pure water at 40 ° C. for 60 seconds for swelling treatment. Then, while immersing in an aqueous solution (dyeing treatment bath) (temperature 32 ° C.) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide for 120 seconds, the concentration was increased 1.25 times (2.5 times in total). Iodine was adsorbed by uniaxial stretching in the length direction. Next, the boric acid was uniaxially stretched 1.44 times (3.6 times in total) while being immersed in an aqueous solution (boric acid cross-linking treatment bath) (temperature 50 ° C.) containing 2.6% by mass of boric acid for 120 seconds. did. Further, while immersing in a 57 ° C. aqueous solution (uniaxial stretching treatment bath) containing 2.8% by mass of boric acid and 5% by mass of potassium iodide, uniaxial stretching in the length direction up to 6.0 times as a whole. did. Then, the film was washed by immersing it in a potassium iodide aqueous solution (washing bath) having a temperature of 22 ° C. containing 1.5% by mass of boric acid and 5% by mass of potassium iodide for 5 seconds. Finally, it was dried at 80 ° C. for 4 minutes to produce a polarizing film.

Using the obtained polarizing film, the single transmittance (T) and the degree of polarization (V) were measured by the above method to determine the dichroism ratio (R). In addition, the shrinkage stress of the polarizing film was measured. The results are shown in Table 1.

Examples 2 and 3 and Comparative Examples 1 to 3
Using the PVA obtained in Synthesis Examples 2 to 6, Example 1 except that the PVA content of the film-forming stock solution and the heat treatment temperature were adjusted so that the thickness of the PVA film was 45 μm and the softening point was 65.5 ° C. The PVA film was prepared and evaluated in the same manner as above. Using the obtained PVA film, a polarizing film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

Reference example 1
Using the PVA obtained in Synthesis Example 7, the same as in Example 1 except that the PVA content of the film-forming stock solution and the heat treatment temperature were adjusted so that the thickness of the PVA film was 45 μm and the softening point was 65.5 ° C. The PVA film was prepared and evaluated. The results are shown in Table 1.

FIG. 1 is a diagram in which the weight average molecular weight (Mw) is plotted on the horizontal axis and the dichroism ratio is plotted on the vertical axis for the polarizing films of Examples 1 to 3 and Comparative Examples 1 to 3. FIG. It is the figure which plotted the shrinkage stress on the horizontal axis, and the dichroism ratio on the vertical axis about the polarizing film of. As shown in FIG. 1, when comparing the polarizing films obtained by using PVA having substantially the same weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn) of PVA is narrow (Examples 1 to 1 to Mn). 3) had a better dichroism ratio than those having a wide molecular weight distribution (Mw / Mn) of PVA (Comparative Examples 1 to 3). With respect to the shrinkage stress of the polarizing film, in general, the shrinkage stress tends to increase as the dichroism ratio increases. As shown in FIG. 2, such a tendency was also observed in the polarizing films of Examples 1 to 3 and Comparative Examples 1 to 3. At this time, no significant difference was observed due to the difference in the molecular weight distribution (Mw / Mn). As described above, it was confirmed that by narrowing the molecular weight distribution (Mw / Mn) of PVA, it is possible to improve the optical performance while suppressing the deterioration of moldability.

Claims (4)

Polyvinyl alcohol having a weight average molecular weight (Mw) of 100,000 to 1,000,000, a molecular weight distribution (Mw / Mn) of 1.05 to 1.95, and a degree of saponification of 80 to 99.99 mol%. The original film having a b value of 0.35 or less is obtained by performing a step of dyeing with a dichroic dye and a step of uniaxially stretching, and the dichroic ratio (R) is 100 or more. Polarizing film . The polarizing film according to claim 1, wherein the raw film has a thickness of 1 to 75 μm. The polarizing film according to claim 1 or 2, wherein the raw film further contains 1 to 20 parts by mass of a plasticizer with respect to 100 parts by mass of the polyvinyl alcohol. The method for producing a polarizing film according to any one of claims 1 to 3, further comprising a step of dyeing the raw film with a dichroic dye and a step of uniaxially stretching.

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