JP2019066533A - Raw material film for production of optical film and production method of optical film using the same - Google Patents

Abstract

To provide a raw material film from which an optical film excellent in moldability and having excellent optical performance can be obtained.SOLUTION: A raw material film for the production of an optical film is provided, which contains a 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 saponification degree of 80 to 99.99 mol%.SELECTED DRAWING: Figure 1

Description

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

A polarizing plate having a light transmitting and shielding function 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 attached to the surface of a polarizing film, and as the polarizing film, a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film Those in which a dichroic dye such as an iodine dye (I ^3- or I ^5- etc.) or a dichroic organic dye is adsorbed to a matrix formed by uniaxially stretching a film have become mainstream.

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

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

  Technology development aiming at high functionalization of a polarizing film is advanced, and the following raw films for optical film manufacture are reported. Patent Document 2 describes a PVA film for a raw film of a polarizing film made of PVA containing 0.01 to 1 mol% of a hydrophilic functional group such as a carboxylic acid group or an ω-hydroxy-α-olefin group. There is. Patent Document 2 describes that the PVA film is excellent in stretching and orientation processability and adsorption processability of a dichroic substance. Patent Document 3 shows an optical PVA film formed by forming a PVA resin, wherein the PVA resin is 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 for the film described in patent document 2 and 3 was raised in order to improve the optical performance of the polarizing film obtained, a moldability might become inadequate.

  By the way, in recent years, with the advancement of so-called living radical polymerization technology, several methods for controlling the radical polymerization reaction of vinyl acetate have been proposed. For example, there has been proposed a method of obtaining polyvinyl acetate having a narrow molecular weight distribution and a high molecular weight by conducting a radical polymerization reaction of vinyl acetate in the presence of a radical polymerization initiator and a specific controlling agent. In such a polymerization reaction, the growing radical end of the polyvinyl acetate molecular chain is covalently bonded to a control agent to form a dormant species, and an equilibrium is generated between the dormant species and the radical species generated by dissociation. Polymerization proceeds while forming. Such polymerization reactions are called controlled radical polymerization.

  Patent Document 4 discloses that the number average molecular weight (Mn) is 92,000 and the molecular weight distribution (Mw / Mn) is carried out by performing a radical polymerization reaction of vinyl acetate in the presence of a control agent comprising a radical polymerization initiator and an iodine compound. An example of synthesizing polyvinyl acetate of 1.57) and saponifying it to produce PVA has been reported. 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). When such polyvinyl acetate having an aldehyde group at the end is saponified, it is known that a conjugated polyene structure in which a plurality of carbon-carbon double bonds are conjugated is formed, and highly colored PVA can be obtained. A film made of such colored PVA is not suitable as an optical film.

  Also, recently, a method of synthesizing polyvinyl acetate by controlled radical polymerization using an organic cobalt complex as a control agent has been proposed. In this polymerization reaction, the growing radical end of the polyvinyl acetate molecular chain is covalently bonded to the cobalt atom of the organocobalt complex to form a dormant species, and the dormant species is dissociated to generate a radical species. Polymerization proceeds while forming an equilibrium. For example, Non-Patent Document 2 has a number average molecular weight (Mn) of 99,000 and a molecular weight distribution (Mw / Mn) of 1.33 by polymerizing vinyl acetate in the presence of cobalt (II) acetylacetonate. An example of the synthesis of 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 in which a cobalt (III) complex is bound to the end, and the dormant species is cleaved to react with a terminal radical formed to react with 1-propanethiol to form polyacetic acid. Cobalt complexes can be separated from vinyl chains. Although polyvinyl acetate forming dormant species is green, it was described that polyvinyl chloride with reduced color was obtained by precipitation after removal of separated cobalt complex and filtration through Celite. ing. Also, by using TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), which is a stable radical compound, instead of 1-propanethiol, to bind TEMPO 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 out the cobalt complex through acidic alumina.

  Thus, according to the method described in Non-Patent Document 3, it is believed that polyvinyl acetate with reduced color can be obtained. However, Non-Patent Document 3 does not describe 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 polyvinyl acetate obtained in Non-Patent Document 3 is colored.

Japanese Patent Application Laid-Open No. 1-105204 Japanese Patent Application Laid-Open No. 8-201626 JP, 2009-24076, A Japanese Patent Application Laid-Open 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, p 5452-5458

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a raw film which is excellent in moldability and can obtain an optical film having excellent optical performance. Moreover, it aims at providing the manufacturing method of the optical film using such a raw film.

  The said subject is a weight average molecular weight (Mw) 100,000-1,000,000, molecular weight distribution (Mw / Mn) is 1.05-1.95, and saponification degree is 80-99.99 mol% The present invention is solved by providing a raw film for producing an optical film, which comprises PVA.

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

  The raw film for producing an optical film is preferably a raw film for producing a polarizing film.

  The method for producing an optical film comprising the step of uniaxially stretching the raw film for producing an optical film is a preferred embodiment of the present invention. A method for producing a polarizing film comprising the steps of dyeing the raw film for producing polarizing film with a dichroic dye and uniaxially stretching is a more preferable embodiment of the present invention.

  According to the raw film of the present invention, it is possible to enhance the optical performance of the obtained optical film while suppressing the decrease in the formability.

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

  The raw film for producing an optical film of the present invention has a weight average molecular weight (Mw) of 100,000 to 1,000,000, and a molecular weight distribution (Mw / Mn) of 1.05 to 1.95, and is saponified. Containing 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. By the said weight average molecular weight (Mw) being 100,000 or more, the optical film which has the outstanding optical performance is obtained. The weight average molecular weight (Mw) is preferably 150,000 or more, more preferably 200,000 or more, still more preferably 250,000 or more, and particularly preferably 300,000 or more. On the other hand, when the said weight average molecular weight (Mw) is 1,000,000 or less, the moldability of an original fabric film becomes favorable. The weight average molecular weight (Mw) is preferably 800,000 or less, 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 gel permeation chromatography (GPC). In the measurement, polymethyl methacrylate is used as a standard substance. Also, HFIP (hexafluoroisopropanol) is used as the mobile phase, and a column for HFIP is used as the column. Specifically, 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 the PVA needs to be 1.05 to 1.95. Thus, 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 conventional PVA having the same weight average molecular weight (Mw). It significantly improves as compared to the optical film. Therefore, the optical performance of the obtained optical film can be improved, suppressing a fall of a moldability. The molecular weight distribution (Mw / Mn) is preferably 1.8 or less.

  The saponification degree of the PVA is 80 to 99.99 mol%. When the degree of saponification is 80 mol% or more, an optical film excellent in optical performance and durability can be obtained. The degree of saponification is preferably 95 mol% or more, more preferably 98 mol% or more, still more preferably 99 mol% or more, and particularly preferably 99.2 mol% or more. On the other hand, when the degree of saponification exceeds 99.99 mol%, production of PVA may be difficult. The degree of saponification 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) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units, which PVA has. It refers to the proportion (mol%) of the number of moles of vinyl alcohol units. The degree of saponification of PVA can be measured according to the description of JIS K6726-1994.

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

  It is preferable that content of the 1, 2- glycol coupling | bonding in said PVA is 0.7-1.5 mol%. When the content of 1,2-glycol bond is 1.5 mol% or less, the optical performance of the obtained optical film is further improved. The content of 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 be reduced to make it difficult to handle. The content of 1,2-glycol bond is more preferably 1 mol% or more.

  A preferred production method of the 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; represented by the following formula (I) after the polymerization step A termination step of terminating the polymerization to obtain a polyvinyl ester by adding a polymerization terminator or a proton donating terminator; and a saponification step of saponifying the polyvinyl ester obtained in the termination 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。）

(Wherein, R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent, and R ² has a hydrogen atom, an alkyl group having 1 to 20 carbons, or a substituent) Represents a good C 6-20 aromatic group.)

  First, the polymerization step 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 a reaction proceeds by being brought into equilibrium with a covalently bonded species (dormant species) in which a growing radical end (active species) is bound to a control agent. By performing controlled radical polymerization, side reactions are suppressed, and therefore, it is possible to obtain a polyvinyl ester having a high weight average molecular weight (Mw) and a narrow molecular weight distribution (Mw / Mn). In the above production method, an organic cobalt complex is used as a control agent.

  Examples of the vinyl ester monomer used in the above production method include vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, laurin Examples thereof include vinyl acid, vinyl stearate, vinyl benzoate and vinyl versatate, but vinyl acetate is preferably used from the economical viewpoint.

  The polyvinyl ester produced may contain monomer units derived from an ethylenically unsaturated monomer copolymerizable with a vinyl ester monomer, as long as the effects of the present invention are not impaired. Ethylenically unsaturated monomers such as olefins such as ethylene, propylene, 1-butene and isobutene; acrylic acid, methacrylic acid, crotonic acid, (anhydride) phthalic acid, (anhydride) maleic acid, (anhydride) itaconic acid and the like Unsaturated carboxylic acid, its salt, its mono- or dialkyl ester or its anhydride; acrylamide, N-alkyl acrylamide, N, N- dimethyl acrylamide, 2-acrylamidopropane sulfonic acid or its salt, acrylamido propyl dimethyl amine or its acid Acrylamide such as a salt or its quaternary salt; methacrylamide, N-alkyl methacrylamide, N, N-dimethyl methacrylamide, 2-methacrylamidopropane sulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or N-vinyl pyrrolidone such as N-vinyl pyrrolidone, N-vinyl formamide, N-vinyl acetamide and the like; N-vinyl amides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers and hydroxyalkyl vinyl ethers , Vinyl ethers such as alkoxyalkyl vinyl ethers; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide; vinyl silanes such as trimethoxyvinylsilane, allyl acetate, allyl chloride, allyl alcohol, dimethyl allyl alcohol And trimethyl- (3-acrylamido-3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid and the like. 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 polymerization method of the vinyl ester monomer include known methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Among them, a bulk polymerization method in which polymerization is performed without a solvent or a solution polymerization method in which polymerization is performed in various organic solvents is usually employed. In order to obtain a polymer having a narrow molecular weight distribution, a bulk polymerization method which does not use a solvent or a dispersion medium which may cause side reactions such as chain transfer is preferable. On the other hand, solution polymerization may be preferable in terms of adjusting the viscosity of the reaction solution, controlling the polymerization rate, and the like. Examples of the organic solvent used as a solvent in solution polymerization include esters of methyl acetate, ethyl acetate and the like; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; and the like. Among 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 in accordance with 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 initiators, peroxide initiators, redox initiators and the like are appropriately selected. As an azo initiator, 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,4-) Dimethyl valeronitrile) etc., and as peroxide based initiators, percarbonate compounds such as diisopropyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, diethoxyethyl peroxy dicarbonate etc .; t-butyl Perester compounds such as peroxy neodecanate, α-cumyl peroxy neodecanate, t-butyl peroxy neodecanate and the like; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2 -Peroxy phenoxy acetate etc. are mentioned. Furthermore, potassium persulfate, ammonium persulfate, hydrogen peroxide and the like can be combined with the above initiator to make an initiator. Moreover, as a redox system initiator, what combined said peroxide and reducing agents, such as sodium bisulfite, sodium hydrogencarbonate, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, Rongalite, etc. is mentioned. The amount of the initiator used differs depending on the polymerization catalyst and is not generally determined, and is arbitrarily selected according to the polymerization rate.

The organic cobalt complex used as a control agent in the polymerization step may be any one containing 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. Among them, cobalt (II) acetylacetonate is preferred from the viewpoint of production cost.

  In the above-mentioned controlled radical polymerization, theoretically, one polyvinyl ester chain is formed 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. In general, it is preferable to use 0.001 to 1 mol of organic cobalt complex per 100 mol of vinyl ester monomer.

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

  The method of mixing the radical initiator, the organic cobalt complex and the vinyl ester monomer is not particularly limited as long as the dormant species is generated and the degree of polymerization of the polyvinyl ester can be controlled. For example, after mixing a radical initiator and an organic cobalt complex, a method of mixing the obtained mixture and a vinyl ester monomer, a method of mixing a radical initiator, an organic cobalt complex and a vinyl ester monomer at one time, organic After mixing a cobalt complex and a vinyl ester monomer, the method of mixing the obtained mixture and a radical initiator etc. are mentioned. The radical initiator, the organic cobalt complex, and the vinyl ester monomer may be divided and mixed. For example, after mixing the radical initiator and the organic cobalt complex with a part of the vinyl ester monomer to form a dormant species in which the organic cobalt (III) complex is covalently bonded to the short-chain polyvinyl ester end, The method of mixing the remainder of the said dormant seed | species and a vinyl ester monomer, and making it highly polymerize etc. are mentioned. The dormant species may be isolated as a macroinitiator and then mixed with the remainder of the vinyl ester monomer to achieve a high 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 tends to be insufficient and the productivity is lowered. From this point, the polymerization temperature is more preferably 10 ° C. or more, and still more preferably 20 ° C. or more. On the other hand, when the polymerization temperature exceeds 80 ° C., the molecular weight distribution of the obtained polyvinyl ester tends to be broad. In this respect, the polymerization temperature is more preferably 65 ° C. or less, still more preferably 50 ° C. or less. The time required for the polymerization step of the vinyl ester monomer is usually 3 to 50 hours.

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

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

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

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

  The temperature of the reaction solution in the termination step is the temperature at which the polymerization terminator represented by the above formula (I) can react with the radical of the end of the polyvinyl acetate chain or the proton donating polymerization terminator is the radical of the end of the polyvinyl acetate chain. It should just be the temperature which can provide a proton radical with respect to these, and it is preferable that it is 0-80 degreeC. If the temperature of the reaction solution is less than 0 ° C., the stopping step takes too much time and productivity is reduced. As for the temperature of the reaction liquid in a stop process from this point, 10 degreeC or more is more preferable, and 20 degreeC or more is further more preferable. On the other hand, when the temperature of the reaction solution exceeds 80 ° C., polymerization of unnecessary vinyl acetate proceeds and the molecular weight distribution (Mw / Mn) tends to be large. As for the said temperature, 70 degrees C or less is more preferable from this point, and 60 degrees C or less is more preferable. The time required for the stopping step is usually 10 minutes to 5 hours.

  After the termination step, it is preferable to carry out an extraction step in which the obtained polyvinyl ester solution is brought into contact with an aqueous solution containing a water-soluble ligand to extract and remove the cobalt complex from the polyvinyl ester solution. Thus, by performing the saponification step after removing the cobalt complex contained in the polyvinyl ester solution in advance, it is possible to obtain PVA which has a good hue and is difficult to gelate. Specifically, the aqueous solution and the polyvinyl ester solution, which do not mutually dissolve, are vigorously stirred so as to increase the area of the interface between the two, and then allowed to stand to separate the oil layer and the water layer, and then the water layer is separated. Perform the operation excluding. This operation may be repeated multiple 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 extract the cobalt complex efficiently, and the pKa is preferably 2 or more. Further, even when a weak acid having a pKa of more than 12 is used, it is difficult to extract the cobalt complex efficiently, and the pKa is preferably 7 or less. When the acid is a polyvalent acid, it is necessary that the first dissociation constant (pKa1) is in the above range. It is preferable that the acid of pKa 0-12 is carboxylic acid or phosphoric acid (pKa1 is 2.1), and it is more preferable that it is carboxylic acid. Among them, acetic acid (pKa is 4.76) is particularly preferable.

  It is preferable that pH of the aqueous solution containing a water-soluble ligand is 0-5. The pH is more preferably 1 or more, and further preferably 1.5 or more. The pH is more preferably 4 or less, and even more preferably 3 or less.

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

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

  The raw 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 production method in which the thickness and width of the film after film formation can be made more uniform can be preferably adopted. For example, the above-mentioned PVA and, if necessary, A film-forming solution prepared by dissolving one or more of the plasticizer, additive, surfactant and the like described later in a liquid medium, PVA and, if necessary, further, a plasticizer, additive, surfactant And a liquid medium or the like, and can be manufactured using a film-forming solution in which PVA is melted. When the said film forming undiluted | stock solution contains at least 1 sort (s) of a plasticizer, an additive, and surfactant, it is preferable that those components are mixed uniformly.

  Examples of the liquid medium used for the preparation of the membrane-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol And trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of them can be used. Among them, water is preferable from the viewpoint of environmental load and recoverability.

  Although the volatilization fraction of the membrane-forming solution (the content ratio of volatile components such as liquid media to be removed by volatilization or evaporation during film-forming in the membrane-forming solution) varies depending on the film-forming method, film-forming conditions, etc In particular, it is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass, and still more preferably in the range of 60 to 85% by mass. When the volatilization fraction of the membrane forming solution is 50% by mass or more, the viscosity of the membrane forming solution does not become too high, and filtration and degassing are smoothly performed at the preparation of the membrane forming solution, and a film with few foreign matter and defects. Manufacture of On the other hand, when the volatilization fraction of the membrane-forming solution is 95% by mass or less, the concentration of the membrane-forming solution does not become too low, and industrial film production becomes easy.

  The membrane-forming solution preferably contains a surfactant. By including the surfactant, the film forming property is improved, generation of thickness unevenness of the film is suppressed, and peeling of the film from a metal roll or belt used for film formation becomes easy. When a raw film is produced from a film-forming stock solution containing a surfactant, the film may contain the surfactant. The type of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of releasability from a metal roll or a belt.

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

  Examples of nonionic surfactants include alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; alkyl ester type such as polyoxyethylene laurate; polyoxyethylene lauryl amino Alkyl amine type such as ether; alkyl amide 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; Allyl phenyl ether type such as alkylene allyl phenyl ether is preferable.

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

  When the membrane-forming solution contains a surfactant, the content 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 solution, 0.02 It is more preferable to be in the range of-0.3 parts by mass, and it is particularly preferable to be 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 releasability are further improved. On the other hand, when the said content is 0.5 mass part or less, surfactant can bleed out on the surface of a raw film, blocking can arise, and it can suppress that a handleability falls.

  As a film forming method at the time of forming an original film film using the above-mentioned film forming solution, for example, a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method and the like can be mentioned. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, a cast film forming method and an extrusion film forming method are preferable since uniform thickness and width can be obtained and a raw film having good physical properties can be obtained. Drying and heat treatment can be performed on the formed raw film as required.

  As an example of the specific manufacturing method of 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 to position the above film forming solution on the most upstream side The film is uniformly discharged or cast onto the circumferential surface of the rotating heated first roll (or belt), and from one surface of the film ejected or cast onto the circumferential surface of the first roll (or belt) The volatile components are evaporated to dryness and then further dried on the periphery of one or more rotating heated rolls located downstream thereof, or passed further through a hot air dryer. After drying, a method of winding with a winding device can be preferably adopted industrially. Drying with a heated roll and drying with a hot air drying apparatus may be carried out in combination as appropriate.

  The raw film of the present invention can 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. Furthermore, one or more of these plasticizers can be included. Among these, glycerin is preferable from the viewpoint of the effect of improving the stretchability.

  It is preferable that content of the plasticizer in the raw film of this invention is 1-20 mass parts with respect to 100 mass parts 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, further preferably 5 parts by mass or more. On the other hand, when the said content is 20 mass parts or less, it can suppress that a film becomes soft too much and a handleability falls. The content is more preferably 17 parts by mass or less, and still more preferably 15 parts by mass or less.

  The raw film of the present invention may further contain a filler, a processing stabilizer such as a copper compound, a weather resistant stabilizer, a colorant, an ultraviolet light absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and the like. Thermoplastic resins, lubricants, perfumes, antifoaming agents, deodorants, extenders, release agents, mold release agents, reinforcing agents, crosslinking agents, fungicides, preservatives, crystallization rate retarders, etc. Can be appropriately blended as needed.

  The proportion 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, based on the mass of the raw film. More preferably, it is at least%.

  The thickness of the raw film of the present invention is not particularly limited, but in general, it is preferably 1 to 75 μm, more preferably 5 to 60 μm, and particularly preferably 10 to 45 μm. When the said thickness is too thin, there exists a tendency for the stretch breakage | shortage to generate | occur | produce easily at the time of the uniaxial stretching process for manufacturing a polarizing film. Moreover, when the said thickness is too thick, it will become easy to generate | occur | produce an extending | stretching spot at the time of uniaxial stretching for manufacturing a polarizing film. The thickness referred to here refers to 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, and more preferably 30 μm or more, in order to ensure the handling property. 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 a raw film, the base resin must be capable of uniaxially stretching with PVA. Polyester, polyolefin resin, etc. can be used. Among them, amorphous polyester resin is preferable, and polyethylene terephthalate and amorphous polyester resin obtained by copolymerizing a copolymer component such as isophthalic acid and 1,4-cyclohexanedimethanol are preferably used. It is preferable to produce a multilayer film by applying a PVA solution to a substrate resin film. At this time, in order to improve the adhesion 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.

  It is preferable that b value of the raw film of this invention is 0.35 or less. By using such a raw film having a low b value, an optical film having excellent optical performance can be obtained. By producing a raw film using PVA obtained by the above-mentioned production method, a raw film having a narrow molecular weight distribution and a low b value can be produced. The b value of the raw film is more preferably 0.3 or less, still more preferably 0.2 or less. The b value of the raw film is measured by the method described in the examples.

  The width of the raw film of the present invention is not particularly limited, and can be determined depending on the application and the like. In recent years, from the viewpoint of increasing the screen size of liquid crystal televisions and liquid crystal monitors, if the width of the original film is 3 m or more, it is suitable for use as a final product. On the other hand, if the width of the raw film is too large, problems may arise in that it is likely to be difficult to perform uniaxial stretching itself uniformly when the optical film is manufactured using a commercially available apparatus. The width of the raw film is preferably 7 m or less.

  According to the raw film of the present invention obtained in this manner, the optical performance of the obtained optical film can be enhanced while suppressing the decrease in the formability. Therefore, the said raw film is used suitably for manufacture of an optical film. As such an optical film, a polarizing film, retardation film, etc. are mentioned, for example, It is preferable that it is a polarizing film.

  The manufacturing method of the optical film which has the process of uniaxially stretching the said raw film is a preferable embodiment of this invention. And the manufacturing method of the polarizing film which has the process (dye process) of dyeing | staining the said raw film with a dichroic dye (dye process), and the process of uniaxially stretching (stretching process) is a more preferable embodiment of this invention.

  As a more specific method for producing a polarizing film using the above-mentioned raw film, a dyeing step of dyeing the raw film, a stretching step of uniaxially stretching, and a swelling step of optionally further swelling, The method includes a crosslinking step for crosslinking, 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 the respective steps 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 more steps may be simultaneously performed. Also, one or more of each step can be performed twice or more.

  A swelling process can be performed by immersing a PVA film (raw film) in water. The temperature of 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 in the range of 25 to 43 ° C. More preferable. Moreover, as time to immerse in water, for example, it is preferable to be in the range of 0.1 to 5 minutes, and it is more preferable to be in the range of 0.5 to 3 minutes. In addition, the water at the time of immersing in water is not limited to a pure water, The aqueous solution which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  The dyeing step can be carried out by contacting the PVA film with a dichroic dye. It is common to use an iodine-based dye as the dichroic dye. As the time of dyeing, any stage before uniaxial stretching, at the time of uniaxial stretching, or after uniaxial stretching may be used. Dyeing is generally carried out by immersing the PVA film in a solution (in particular, an aqueous solution) containing iodine-potassium iodide which is a dyeing bath, and such a dyeing method is suitably employed in the present invention as well. Ru. 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. Further, the temperature of the dyeing bath is preferably 20 to 50 ° C, particularly 25 to 40 ° C. The preferred staining time is 0.2 to 5 minutes.

  By performing the crosslinking step of crosslinking the PVA film, elution of PVA into water can be more effectively prevented when wet stretching at high temperature. From this point of view, the crosslinking step is preferably performed after the dyeing step and before the drawing step. The crosslinking step can be carried out by immersing the PVA film in an aqueous solution containing a crosslinking agent. As the said crosslinking agent, 1 type (s) or 2 or more types of boron compounds, such as boric acid and boric acid salts, such as borax, can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking 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 It is further preferred that When the concentration of the crosslinking agent is in the range of 1 to 15% by mass, sufficient stretchability can be maintained. The aqueous solution containing the crosslinking agent may contain potassium iodide and the like. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 60 ° C., particularly in the range of 25 to 55 ° C. By setting the said temperature in the range of 20-60 degreeC, it can bridge | crosslink 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, or can be carried out in the above-mentioned dyeing bath or in a fixed treatment bath described later. In the case of the dry stretching method, stretching may be performed at room temperature, may be stretched while heating, or may be performed in air using a PVA film after water absorption. Among these, the wet stretching method is preferable because the film can be stretched uniformly in the width direction, and uniaxial stretching in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the aqueous boric acid 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 to be in the range of -4.0% by mass. 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.

  The stretching ratio in uniaxial stretching (total stretching ratio from the original film) is preferably 5 times or more, 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.

  There is no particular limitation on the direction of uniaxial stretching in the case of uniaxially stretching a long PVA film, and uniaxial stretching in the long direction or transverse uniaxial stretching can be adopted, but a polarizing film having excellent polarization performance can be obtained. Uniaxial stretching in the longitudinal direction is preferred. Uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the respective rolls using a stretching apparatus provided with a plurality of rolls parallel to one another. On the other hand, transverse 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) to the PVA film. As a fixing process bath used for a fixing process, the aqueous solution containing 1 type, or 2 or more types of boron compounds, such as boric acid and borax, can be used. In addition, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. In general, the concentration of the boron compound in the fixing treatment bath is preferably about 2 to 15% by mass, particularly 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 25 to 40 ° C.

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

  Although the conditions in particular of a drying process are not restrict | limited, It is preferable to dry a PVA film in the temperature within the range of 30-150 degreeC, especially 50-130 degreeC. By drying at a temperature in the range of 30 to 150 ° C., it is easy to obtain a polarizing film having excellent dimensional stability.

It is preferable that the dichroic ratio (R) of the polarizing film obtained in this way is 100 or more. By using the raw film of the present invention, a polarizing film having such a high dichroic ratio (R) can be produced with high productivity. The dichroism ratio (R) is more preferably 150 or more, and still more preferably 190 or more. The calculation method of the dichroic ratio (R) of a polarizing film is as follows. First, the relationship between the transmittance (T ′) excluding the surface reflection and the single transmittance (T) is represented by equation (1). At this time, the refractive index of PVA is 1.5, and the reflectance on the surface is 4%. The relationship between the transmittance (T '), the degree of polarization (V) and the dichroism ratio (R) is shown by 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 those 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 which is optically transparent and has mechanical strength on both sides or one side thereof. A cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate butyrate (CAB) film, an acrylic film, a polyester film, etc. are used as a protective film. Moreover, as an adhesive agent for bonding, a PVA-type adhesive agent, a urethane type adhesive agent, an acrylate type ultraviolet curing adhesive agent etc. can be mentioned.

  The polarizing plate obtained as described above can be used as an LCD component after being coated with an acrylic or other pressure-sensitive adhesive and then bonded to a glass substrate. At the same time, it may be laminated with a retardation film, a viewing angle improvement film, a brightness improvement film or the like.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited at all by these examples. The method of each measurement and evaluation is as follows.

[Measurement of weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)]
The number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) were measured using Tosoh Corp. size exclusion high performance liquid chromatography apparatus "HLC-8320 GPC". The measurement conditions are as follows.
Column: Toso Co., Ltd. HFIP column "GMHHR-H (S)" 2 series connection Standard sample: Polymethyl methacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20mM)
Flow rate: 0.2mL / min
Temperature: 40 ° C
Sample solution concentration: 0.1 wt% (filtration with a 0.45 μm opening filter)
Injection volume: 10 μL
Detector: RI

[Measurement of 1,2-glycol binding amount (mol%)]
The PVA to vacuum drying was carried out for 2 days at 90 ° C., and dissolved in DMSO-d _6, it was subjected to Samples were prepared measurement plus a few drops of trifluoroacetic acid. ¹ H-NMR measurement was performed at 80 ° C. using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by Nippon Denshi Co., Ltd. After confirming that the degree of saponification is 99.9 mol% or more from the amount of residual acetyl groups in polyvinyl alcohol, the amount of 1,2-glycol bonding was used for measurement. The methine-derived peak of vinyl alcohol unit is attributed to 3.2 to 4.0 ppm (integral value A), and the peak derived from one methine of 1,2-glycol bond is attributed to 3.25 ppm (integral value B). The 1,2-glycol bond content can be calculated by
1,2-glycol binding amount (mol%) = (B / A) x 100

[Softening point of PVA film]
The softening point of the PVA film to be measured was measured using an automatic softening point measuring apparatus "EX-820" manufactured by Daiichi Rika Co., Ltd. Specifically, a square sample of 3 cm square is cut out of a PVA film, and this sample is 1 cm in diameter with a 1 mm diameter circular hole at the center, a 3 cm square stainless plate with a thickness of 1 mm, and a 1 cm x 2 cm rectangular hole in the center Between the 1 mm thick and 3 cm square stainless steel plate, install it on a pedestal with the circular holed stainless steel plate facing up, and place on the film located at the center of the circular hole JIS B 1501: The steel ball (nominal number: 3/8 (diameter 9.525 mm), grade: G60, weight: 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./min, and the temperature when the film dropped to a position of 25 mm from the mount was taken as the softening point of the PVA film.

[Evaluation of hue of PVA film]
From a PVA film obtained in the following Examples and Comparative Examples, a rectangular sample of 3 cm × 2.5 cm is collected, and a JIS (Integrated Sphere) spectrophotometer (“U-4100” manufactured by Hitachi Sun Technologies, Ltd.) is used. The b value was measured after performing visual sensitivity correction of a C light source and a visible light region of a 2 ° visual field according to Z 8722 (a method of measuring an object color).

[Optical properties of polarizing film]
From the central part in the width direction of the polarizing film obtained in the following examples and comparative examples, a rectangular sample of 4 cm in the lengthwise direction of the polarizing film is collected, and a spectrophotometer equipped with an integrating sphere (manufactured by JASCO Corporation) After performing visual correction of the visible light region with a C light source and a 2 ° visual field according to JIS Z 8722 (a method of measuring an object color) using V7 100 ′ ′), single transmittance (T) and polarization degree (V) was measured.

The dichroism ratio (R) of the polarizing film was calculated by solving the following formulas (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)

[Shrinkage stress of polarizing film]
Shrinking stress is Shimadzu Autograph AG-X with thermostat and Video Extensometer TR V
It measured using iewX120S. For measurement, a polarizing film conditioned at 20 ° C./20% RH for 18 hours was used. After setting the thermostat bath of Autograph AG-X to 20 ° C, attach a polarizing film (15 cm in length direction and 1.5 cm in width direction) to the chuck (chuck spacing 5 cm), and simultaneously start pulling to 80 ° C. Heating started. The polarizing film was pulled at a speed of 1 mm / min, and when the tension reached 2 N, the pulling was stopped, and in this state, the tension was measured up to 4 hours later. At this time, since the distance between the chucks changes due to thermal expansion, a marked line seal is attached to the chuck, and the distance between the chucks is corrected by the movement of the marked line seal attached to the chuck using a video extensometer TR ViewX120S. The measurement was made as possible. In addition, the value which deducted initial tension 2N from the measured value of the tension after 4 hours was made into the contraction force of a polarizing film, and the value which remove | divided the value by the sample cross-sectional area was defined as contraction stress (MPa).

Synthesis example 1
100 parts by mass of vinyl acetate and 0.04 parts by mass of cobalt (II) acetylacetonate as an organic cobalt complex are charged into a reactor equipped with a stirrer, a reflux condenser, a nitrogen introducing pipe, and an initiator addition port, and nitrogen bubbling is performed. The interior of the reactor was purged with inert gas for 30 minutes. The water bath was heated to start raising the temperature of the reactor, and when the internal temperature reached 40 ° C., 0.2% of 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) was used as a radical initiator. 13 parts by mass was added and stirred for 2 hours, temperature was lowered, and the internal temperature was maintained at 30 ° C. to initiate polymerization. Conduct sampling appropriately to confirm the progress of polymerization from the solid content concentration, and when conversion of vinyl acetate reaches 20%, add 0.13 parts by mass of 1,1-diphenylethylene as a polymerization terminator, 30 ° C. Stir. It took 3 hours from the start of polymerization to reach the target conversion. After adding a polymerization terminator, 92 parts by mass of an aqueous solution of acetic acid having a concentration of 25% by mass was 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 three times, the same aqueous liquid separation operation was repeated a total of three times by changing the aqueous acetic acid solution to deionized water. Thereafter, the reactor was connected to a vacuum line, and the remaining vinyl acetate was distilled off at 30 ° C. under reduced pressure together with methanol. While the inside of the reactor was visually confirmed, evaporation was continued while appropriately adding methanol when the viscosity increased, to obtain a 20% by mass methanol solution of polyvinyl acetate. Next, 100 parts by mass of a 20% by mass methanol solution of polyvinyl acetate obtained and 20 parts by mass of methanol were added to the same reactor as above and dissolved, and then the water bath was heated to an internal temperature of 40 ° C. Heated and stirred until. To this was added 13.3 parts by mass (1.9 parts by mass as sodium hydroxide) of a methanol solution of sodium hydroxide (concentration 14% by mass) to perform saponification at 40 ° C. The gelled product was crushed by a grinder and allowed to stand at 40 ° C. to proceed saponification for 1 hour. Further, 1.9 parts by mass of a methanol solution (concentration 14% by mass) of sodium hydroxide was added to the obtained saponification product, and the saponification reaction was driven for an additional hour under heating at reflux of 65 ° C. Thereafter, 30 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirmation of completion of neutralization using a phenolphthalein indicator, the solid was separated by filtration to obtain a solid, to which 75 parts by mass of methanol was added, and the mixture was heated under reflux for 1 hour. Thereafter, the solid obtained by centrifugal dewatering was dried at 40 ° C. for 24 hours in a vacuum drier to obtain the target PVA. The weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), the degree of saponification, and the amount of 1,2-glycol bonding of the obtained PVA are shown in Table 1.

Synthesis example 2
In the same manner as in Synthesis Example 1 except that 0.02 parts by mass of cobalt (II) acetylacetonate and 0.07 parts by mass of 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) are used. The 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 terminator, and the mixture was stirred at 30 ° C. It took 3 hours from the start of polymerization to reach the target conversion. Thereafter, post-treatment and saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain a target PVA. The weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), the degree of saponification, and the amount of 1,2-glycol bonding of the obtained PVA are shown in Table 1.

Synthesis example 3
In the same manner as in Synthesis Example 1 except that 0.02 parts by mass of cobalt (II) acetylacetonate and 0.07 parts by mass of 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) are used. The 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 terminator, and the mixture was stirred at 30 ° C. It took 5 hours from the start of polymerization to reach the target conversion. Thereafter, post-treatment and saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain a target PVA. The weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), the degree of saponification, and the amount of 1,2-glycol bonding of the obtained PVA are shown in Table 1.

Synthesis example 4
100 parts by mass of vinyl acetate and 39 parts by mass of methanol are charged into a reactor equipped with a stirrer, a reflux condenser, a nitrogen introducing pipe, and an addition port for an initiator, and inert gas substitution is performed for 30 minutes while bubbling nitrogen did. The water bath was heated to start raising the temperature of the reactor, and when the internal temperature reached 60 ° C., 0.02 parts by mass of azobisisobutyronitrile as an initiator was added to initiate polymerization. Conduct sampling appropriately to confirm the progress of polymerization from the solid content concentration, and when the conversion of vinyl acetate reaches 37%, add 2.4 parts by mass of a 1% by mass hydroquinone methanol solution as a polymerization terminator, 30 The polymerization was stopped by cooling to ° C. It took 3 hours from the start of polymerization to reach the target conversion. It was connected to a vacuum line and residual vinyl acetate was distilled off at 30 ° C. under reduced pressure together with methanol. While the inside of the reactor was visually confirmed, evaporation was continued while appropriately adding methanol when the viscosity increased, to obtain a 20% by mass methanol solution of polyvinyl acetate. Thereafter, post-treatment and saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain a target PVA. The weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), the degree of saponification, and the amount of 1,2-glycol bonding of the obtained PVA are shown in Table 1.

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

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

Synthesis example 7
The polymerization was carried out in the same manner as in Synthesis Example 1. When the conversion of vinyl acetate reached 20%, 0.11 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) as a polymerization terminator was added, and the mixture was stirred at 30 ° C. It took 3 hours from the start of polymerization to reach the target conversion. Thereafter, post-treatment and saponification reaction were carried out in the same manner as in Synthesis Example 1 to obtain a target PVA. The weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), the degree of saponification, and the amount of 1,2-glycol bonding of the obtained PVA are shown in Table 1.

Example 1
100 parts by mass of PVA obtained in Synthesis Example 1, 10 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and the PVA content is 11.5% by mass The aqueous solution is used as a membrane forming solution, 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 have a softening point of 65.5 ° C. Were adjusted to make a 45 μm thick PVA film. The b value of the obtained PVA film was measured by the method described above. The results are shown in Table 1.

  From the center in the width direction of the PVA film thus obtained, a sample of width 5 cm × length 9 cm was cut so that a range of width 5 cm × length 5 cm can be uniaxially stretched. The sample was subjected to swelling treatment by uniaxial stretching in the lengthwise direction 2.0 times while immersed in pure water at 40 ° C. for 60 seconds. Subsequently, it is 1.25 times (2.5 times in total) while being immersed in an aqueous solution (dye treatment bath) (temperature 32 ° C.) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide for 120 seconds. The film was uniaxially stretched in the lengthwise direction to adsorb iodine. Then, while immersed in an aqueous solution (boric acid crosslinking treatment bath) (temperature 50 ° C.) containing 2.6% by mass of boric acid for 120 seconds, it is uniaxially stretched in the lengthwise direction by 1.44 times (3.6 times in total) did. Furthermore, while immersed 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, the film is uniaxially stretched in the longitudinal direction up to 6.0 times in total did. Thereafter, the film was washed by immersion for 5 seconds in an aqueous solution of potassium iodide (washing bath) at a temperature of 22 ° C. containing 1.5% by mass of boric acid and 5% by mass of potassium iodide. Finally, it was dried at 80 ° C. for 4 minutes to produce a polarizing film.

  The single transmittance (T) and the degree of polarization (V) were measured by the above-described method using the obtained polarizing film 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
Example 1 except that the PVA content of the membrane forming solution and the heat treatment temperature were adjusted so that the PVA film had a thickness of 45 μm and a softening point of 65.5 ° C. using the PVA obtained in Synthesis Examples 2 to 6 The preparation and evaluation of the PVA film were performed in the same manner as in the above. A polarizing film was produced and evaluated in the same manner as in Example 1 using the obtained PVA film. The results are shown in Table 1.

Reference Example 1
The PVA obtained in Synthesis Example 7 was used, and the PVA content and the heat treatment temperature of the membrane forming solution were adjusted so that the thickness of the PVA film was 45 μm and the softening point was 65.5 ° C. The preparation and evaluation of the PVA film were carried out. 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 dichroic ratio is plotted on the vertical axis for the polarizing films of Examples 1 to 3 and Comparative Examples 1 to 3, and FIG. The shrinkage stress is plotted on the horizontal axis and the dichroism ratio is plotted on the vertical axis for the polarizing film of As shown in FIG. 1, when the polarizing films obtained using PVA having substantially the same weight average molecular weight (Mw) are compared, those having a narrow molecular weight distribution (Mw / Mn) of PVA (Examples 1 to 4) 3) had a dichroic ratio which was superior to the one having a broad molecular weight distribution (Mw / Mn) of PVA (Comparative Examples 1 to 3). With regard to the shrinkage stress of polarizing films, generally, the higher the dichroism ratio, the higher the shrinkage stress. 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 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 decrease in the formability.

Claims (6)

  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% Raw film for optical film production including   The raw film film for optical film manufacture of Claim 1 whose thickness is 1-75 micrometers.   The raw film for optical film manufacture of Claim 1 or 2 whose b value is 0.35 or less.   The raw film for optical film manufacture in any one of Claims 1-3 which is a raw film for polarizing film manufacture.   The manufacturing method of the optical film which has the process of uniaxially stretching the raw film in any one of Claims 1-4.   The manufacturing method of the polarizing film which has the process of dyeing | staining the raw film film of Claim 4 with a dichroic dye, and the process of uniaxially stretching.

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