WO2022145488A1

WO2022145488A1 - Polyvinyl alcohol film and polarizing film obtained therefrom

Info

Publication number: WO2022145488A1
Application number: PCT/JP2021/049004
Authority: WO
Inventors: 修風藤; 稔岡本
Original assignee: 株式会社クラレ
Priority date: 2020-12-28
Filing date: 2021-12-28
Publication date: 2022-07-07
Also published as: TW202231752A; JPWO2022145488A1

Abstract

The purpose of the present invention is to provide a PVA film that has a stable width even when produced at fast production line speeds, and that makes it possible to obtain a polarizing film having excellent polarization performance. The purpose of the present invention is also to provide a polarizing film using such a PVA film as the starting material.　Provided is a polyvinyl alcohol film that contains a polyvinyl alcohol having a degree of saponification of at least 98 mol%, the polyvinyl alcohol film containing a polyvinyl alcohol which satisfies formula (1) and formula (2) in the results of measuring the polyvinyl alcohol with a gel permeation chromatograph at a measurement temperature of 40°C and using hexafluoroisopropanol having 20 mM sodium trifluoroacetic acid added thereto as a mobile phase solvent.　Formula (1): Huv2/Hri2 ≤ 0.014; formula (2): 0.1 ≤ Hri2/Hri1 ≤ 0.2 (provided that: Huv2 is the detection strength at an absorption wavelength of 210 nm for a polymethyl methacrylate–based molecular weight in which the base 10 logarithm is 4.3, obtained using an ultraviolet/visible light detector (UV detector) of a gel permeation chromatograph; Hri2 is the detection strength for a polymethyl methacrylate–based molecular weight in which the base 10 logarithm is 4.3, obtained using a refractive index detector (RI detector) of a gel permeation chromatograph; and Hri1 is obtained using an RI detector and is the value at which the detection strength is the greatest.)

Description

Polyvinyl alcohol film and polarizing film using it

The present invention is a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA" and "polyvinyl alcohol film" may be abbreviated as "PVA film") preferably used for producing a polarizing film, and a method for producing the same. , And a polarizing film obtained by using the PVA film.

Liquid crystal displays (LCDs) are used in a wide range of fields such as small devices such as calculators and watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. Has been done. A polarizing film having a light transmitting and shielding function is a basic component of a liquid crystal display together with a liquid crystal having a light switching function.

As the polarizing film, a dichroic dye such as an iodine-based dye (I _3- ^, I _5- ^, etc.) is adsorbed on a matrix (stretched film oriented by uniaxial stretching) formed by uniaxially stretching a PVA film. Is the mainstream. In such a polarizing film, a PVA film containing a dichroic dye in advance is uniaxially stretched, a bicolor dye is adsorbed at the same time as the uniaxial stretching of the PVA film, or a dichroic after the PVA film is uniaxially stretched. Manufactured by adsorbing dyes.

In recent years, with the expansion of LCD applications, there is a demand for more efficient PVA film production. In order to efficiently manufacture PVA film, it is effective to increase the line speed of the production line, but if the line speed is too high, the film width of the PVA film will fluctuate and the edge of the film will be trimmed. It is necessary to widen the width of the film, which tends to cause problems such as a decrease in yield, a shortage of film width, and a variation in the thickness of the film edge, and there is a problem that the line speed cannot be increased as expected.

The present invention has been made to solve the above problems, and provides a PVA film capable of obtaining a polarizing film having a stable film width and excellent polarizing performance even when manufactured at a high line speed. The purpose is. Another object of the present invention is to provide a polarizing film made from such a PVA film as a raw material.

A gel permeation chromatograph (hereinafter, may be abbreviated as GPC) is known as a general-purpose analysis method as a method for grasping the molecular weight and the degree of polymerization of a resin, and generally, a standard having a known molecular weight. It is common to measure the relative molecular weight using a calibration line obtained from a substance.

The detector used is usually a differential refractive index detector (RI detector) that detects by the difference in refractive index between the mobile phase solvent and the sample, but in addition to this, an ultraviolet / visible absorption detector (UV detector). ), A light scattering detector (LS detector), and the like can be used in combination to evaluate the physical properties.

In recent years, a method for calculating the molecular weight and saponification degree of a polyvinyl alcohol-based material by using an RI detector and a UV detector in combination has been established (Reference Patent Document: JP-A-9-196905). According to this method, since the residual acetic acid group of polyvinyl alcohol has UV absorption, the phenomenon that the lower the amount of hydroxyl group (the degree of saponification) of PVA, the higher the UV detection intensity is utilized. On the other hand, since the RI detection intensity that depends on the concentration is almost independent of the degree of saponification, the degree of saponification at each molecular weight can be determined by obtaining the ratio of the peak heights of the molecular weight distribution curves obtained from each of the RI detector and the UV detector. It is possible to calculate.

As a result of diligent studies based on the knowledge of the degree of saponification distribution of various PVA films by GPC, the present inventors have conducted UV detection at a specific molecular weight when the film made of PVA is analyzed by GPC. It has been found that the above-mentioned problems can be solved if a PVA film satisfying a certain value in the ratio of the intensity to the RI detection intensity is obtained, and further studies are carried out based on the findings to complete the present invention.

That is, the present invention
[1] A polyvinyl alcohol film containing polyvinyl alcohol having a saponification degree of 98 mol% or more, and 20 mM Na trifluoroacetate is added as a mobile phase solvent to the polyvinyl alcohol on a gel permeation chromatograph at a measurement temperature of 40 ° C. A polyvinyl alcohol film containing polyvinyl alcohol, which satisfies the following formulas (1) and (2) in the results measured using the hexafluoroisopropanol.
Hub2 / Hri2 ≤ 0.014 (1)
0.1 ≤ Hri2 / Hri1 ≤ 0.2 (2)
(However, Hub2 has an absorption wavelength at a polymethylmethacrylate-converted molecular weight of 4.3 with a base number of 10 obtained by using an ultraviolet / visible absorbance detector (UV detector) of a gel permeation chromatograph. With a detection intensity of 210 nm, Hri2 is obtained using a differential refractive index detector (RI detector) of a gel permeation chromatograph and has a molecular weight converted to polymethyl methacrylate having a logarithmic value of 4.3. It is the detection intensity, and Hri1 is the maximum value of the detection intensity obtained by using the RI detector.);
[2] The polyvinyl alcohol film according to the above [1], which satisfies the following formula (3) in the result of measuring the polyvinyl alcohol by a gel permeation chromatograph.
0.001 ≦ Hub1 / Hri1-Huv2 / Hri2 ≦ 0.015 (3)
(However, Hub1 is obtained by using a UV detector and is the maximum value of the detection intensity at an absorption wavelength of 210 nm.);
[3] The polyvinyl alcohol has a degree of polymerization of 1500 or more and 3500 or less and a saponification degree of 98 mol% or more of polyvinyl alcohol (A), and a degree of polymerization of 50 or more and 800 or less and a saponification degree of 0 than that of polyvinyl alcohol (A). . The polyvinyl alcohol film according to the above [1] or [2], which contains a high polyvinyl alcohol (B) in the range of 1 mol% or more and 1.2 mol% or less;
[4] In the above [3], the blend ratio of the polyvinyl alcohol (A) and the polyvinyl alcohol (B) is in the range of polyvinyl alcohol (A): polyvinyl alcohol (B) = 80:20 to 97: 3. The polyvinyl alcohol film described;
[5] The polyvinyl alcohol film according to any one of the above [1] to [4], which is an optical film;
[6] The method for producing a polyvinyl alcohol film according to any one of the above [1] to [5], which comprises using polyvinyl alcohol satisfying the above formulas (1) and (2);
[7] A polarizing film made from the polyvinyl alcohol film according to the above [5];
Can be achieved by.

Since the PVA film of the present invention has a stable film width and little variation in the thickness of the end portion, the PVA film of the present invention can be used to efficiently produce a wide-width polarizing film having excellent polarization performance. Further, according to the production method of the present invention, the PVA film can be produced efficiently at high speed.

The polyvinyl alcohol film of the present invention was measured by a gel permeation chromatograph using hexafluoroisopropanol having a measurement temperature of 40 ° C. and 20 mM Na trifluoroacetate added as a mobile phase solvent. , The following equations (1) and (2) are satisfied.
Hub2 / Hri2 ≤ 0.014 (1)
0.1 ≤ Hri2 / Hri1 ≤ 0.2 (2)

However, Hub2 has an absorption wavelength of 210 nm at a polymethylmethacrylate-converted molecular weight having a logarithmic index of 4.3, which is obtained by using an ultraviolet / visible absorption detector (UV detector) of a gel permeation chromatograph. Hri2 is a detection in a polymethylmethacrylate-converted molecular weight having a logarithmic value of 4.3, which is obtained by using a differential refractive index detector (RI detector) of a gel permeation chromatograph. In terms of intensity, Hri1 is the maximum value of the detection intensity obtained by using the differential refractive index detector (RI detector) of the gel permeation chromatograph.

The PVA film of the present invention preferably satisfies the following formula (3) when the PVA contained in the film is analyzed by GPC.
0.001 ≦ Hub1 / Hri1-Huv2 / Hri2 ≦ 0.015 (3)

However, Hub1 is the maximum value of the detection intensity obtained by using the UV detector at the absorption wavelength of 210 nm.

As described above, the detection intensity by the GPC using the RI detector is almost independent of the degree of saponification of PVA, whereas the detection intensity at the absorption wavelength of 210 nm using the UV detector of the GPC becomes stronger as the degree of saponification becomes lower. .. Therefore, if the ratio of the detection intensity of the UV detector and the RI detector is obtained at each point of the molecular weight distribution curve and plotted against the molecular weight, the distribution curve of the degree of saponification with respect to the molecular weight of PVA can be obtained. .. It is presumed that the absorption at a wavelength of 210 nm is derived from the acetic acid group.
Hub1 / Hri1 of the first term on the left side in the formula (3) is the ratio of the detection intensity of the UV detector and the RI detector at the highest value of the molecular weight distribution curve, that is, the molecular weight at the peak top. On the other hand, Huv2 / Hri2 in the second term of the formula (3) has a molecular weight of 10 to the 4.3th power in terms of polymethyl methacrylate, that is, the detection intensity of the UV detector and the RI detector at a molecular weight of about 20,000. The ratio. A molecular weight of 20,000 corresponds to a degree of polymerization of about 450, where the molecular weight of the vinyl alcohol unit is 44.
Therefore, the formula (3) means that the saponification degree of the relatively low molecular weight PVA component having a molecular weight of about 20,000 is higher than that of the molecular weight PVA component at the peak top of the molecular weight distribution curve.

In the above, the "molecular weight converted to polymethyl methacrylate having a radix of 4.3 with a base of 10" used to define Hub2 and Hri2 does not necessarily completely match 10 to the 4.3th power. It does not refer to the molecular weight, but is a concept that includes the polymethylmethacrylate-converted molecular weight having a radix of 10 and having a logarithmic value of 4.25 to 4.35.

The reason why the film-forming property is good even when stretched at high speed when the degree of saponification of the low-molecular-weight component is high is not always clear, but in the film-forming of PVA film, the solvent evaporates from the film-forming stock solution containing PVA to form PVA. As crystal solidification progresses, PVA, which is a low molecular weight component and has a high degree of saponification, has a high crystallization rate, so it acts like a crystal nucleating agent and promotes the crystallization of PVA film, thereby forming a semi-solidified film. It is presumed to stabilize the morphology of the undiluted solution.

The value of Hub2 / Hri2 is 0.014 or less, preferably 0.012 or less, and more preferably 0.010 or less. When the value of Hub2 / Hri2 is less than 0.014, the stability of the film width during film formation tends to deteriorate.

The value of Hub1 / Hri1-Huv2 / Hri2 is preferably 0.015 or less, more preferably 0.01 or less, further preferably 0.005 or less, and more preferably 0.002 or less. Is particularly preferable. When the value of Hub1 / Hri1-Huv2 / Hri2 exceeds 0.015, the polarization performance of the obtained polarizing film tends to deteriorate. On the other hand, the value of Hub1 / Hri1-Huv2 / Hri2 is preferably 0.001 or more, more preferably 0.0012 or more, further preferably 0.0013 or more, and 0.0014 or more. It is particularly preferable to have. When the value of Hub1 / Hri1-Huv2 / Hri2 is less than 0.001, the stability of the film width during film formation tends to deteriorate.

Further, in the present invention, Hri2 / Hri1, which is the value obtained by dividing Hri2 by Hri1, is preferably 0.2 or less, and Hri2 / Hri1 is preferably 0.19 or less, more preferably 0.18 or less. preferable. When Hri2 / Hri1 exceeds 0.2, the polarization performance of the obtained polarizing film tends to deteriorate. On the other hand, Hri2 / Hri1 is 0.1 or more, preferably 0.12 or more, more preferably 0.13 or more, and even more preferably 0.14 or more. When Hri2 / Hri1 is less than 0.1, the film-forming property of the PVA film when stretched at high speed tends to deteriorate.

In the present invention, the method for obtaining a PVA film satisfying the formulas (1) and (2) and / or the formula (3) is not particularly limited, but for example, with PVA (A) having a high degree of polymerization and a low degree of saponification. A method of blending PVA (B) having a low degree of polymerization and a high degree of saponification can be mentioned (note that the degree of saponification of PVA (A) may be the same as the degree of saponification of PVA (B)). However, the PVA film of the present invention may satisfy the formulas (1) and (2) and / or the formula (3), and the PVA may contain only one type of PVA.

[GPC measurement]
In the present invention, Hub1, Hub2, Hri1 and Hri2 can be obtained by the following methods.
Generally, there are two types of molecular weights obtained from GPC measurement, relative molecular weight and absolute molecular weight. In the present invention, a differential refractive index detector (RI detector) and an ultraviolet / visible absorption detector (UV detector) are used. ) Was used for the relative molecular weight calculated by GPC measurement. In GPC measurement, it is necessary to completely dissolve the measurement sample in the solvent, and if a column suitable for each mobile phase solvent is used, it is possible to calculate the relative molecular weight in each solvent from the analysis software in the measuring device. .. In the present invention, a PVA film containing PVA can be analyzed under the following measurement conditions. Hexafluoroisopropanol (HFIP) is used as the mobile phase solvent so that the film can be completely dissolved.
The relative molecular weight distribution curve obtained from the RI detector and the UV detector is obtained by the analysis software attached to the analyzer using polymethyl methacrylate (PMMA) as a calibration curve standard. The maximum values of the detection intensities of the RI detector and the UV detector before conversion to the molecular weight distribution curve at the molecular weight (Mp) indicating the peak top of the molecular weight distribution curve are Hri1 and Hub1, respectively. Here, the detection intensity of the RI detector and the UV detector before conversion to the molecular weight distribution curve is the measurement intensity before the correction by the analysis software, and the measurement of the measurement data itself obtained from the RI detector and the UV detector. It is strength. Further, the detection intensities of the RI detector and the UV detector before the molecular weight distribution conversion at the molecular weight (Mp = 10 ^4.3 ) at the point where the logarithm with the relative molecular weight of 10 as the base number are Hri2 and Hub2, respectively. Is. The absorption wavelength used in the UV detector is 210 nm.

[Polyvinyl alcohol]
The PVA film in the present invention contains PVA. As the PVA, one produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer can be used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. Of these, vinyl acetate is preferable from the viewpoints of properties, cost, productivity of PVA, and the like.

The above vinyl ester polymer is preferably obtained by using only one kind or two or more kinds of vinyl ester monomers as a monomer, and is obtained by using only one kind of vinyl ester monomer as a monomer. It is more preferable, but it may be a copolymer of one kind or two or more kinds of vinyl ester monomers and another monomer copolymerizable therewith.

Other monomers copolymerizable with such vinyl ester monomers include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; methacrylic acid or salts thereof; methylacrylic acid, acrylic acid, etc. Acrylic such as ethyl, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. Acid ester; Methacrylic acid or a salt thereof; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2 methacrylic acid -Methacrylic acid esters such as ethylhexyl, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamide propanesulfonic acid or salts thereof, acrylamide. Acrylamide derivatives such as propyldimethylamine or a salt thereof, N-methylolacrylamide or a derivative thereof; methacrylicamide, N-methylmethacrylicamide, N-ethylmethacrylicamide, methacrylicamide propanesulfonic acid or a salt thereof, methacrylicamide propyldimethylamine or a derivative thereof. Methacrylic amide derivatives such as salts, N-methylol methacrylic amides or derivatives thereof; N-vinyl amides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ethers, ethylvinyl ethers, n-propylvinyl ethers, i-propyl Vinyl ethers such as vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylic nitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride Vinyl halides such as: Allyl halides such as allyl acetate and allyl chloride; Maleic acid or salts thereof, esters or acid anhydrides; Itaconic acid or salts thereof, esters or acid anhydrides; Vinylsilyl compounds such as vinyltrimethoxysilane; Acetic acid. Isopropenyl and the like can be mentioned. The vinyl ester polymer described above can have a structural unit derived from one or more of these other monomers.

The ratio of the structural units derived from the other monomers to the vinyl ester polymer is not particularly limited as long as the object of the present invention is not impaired, but the number of moles of all the structural units constituting the vinyl ester polymer is limited. Based on this, it is preferably 15 mol% or less, and more preferably 5 mol% or less.

In the present invention, the degree of polymerization of PVA is preferably 1200 or more, preferably 1500 or more, further preferably 2000 or more, and particularly preferably 2500 or more. The degree of polymerization of PVA is preferably 8000 or less, more preferably 6000 or less, further preferably 5000 or less, and particularly preferably 4000 or less. If the degree of polymerization of PVA is less than 1200, the polarization performance may be impaired. On the other hand, when the degree of polymerization of PVA exceeds 8000, the viscosity of the aqueous solution or the melted PVA becomes high, which may make film formation difficult. The degree of polymerization of PVA is preferably 6000 or less, more preferably 5000 or less, and particularly preferably 4000 or less. Here, the degree of polymerization means the average degree of polymerization measured according to the description of JIS K6726-1994, and the ultimate viscosity [η] measured in water at 30 ° C. after re-kenning PVA (A) and purifying it. ] (Unit: deciliter / g) can be calculated by the following equation.
Po = ([η] × 10 ³ / 8.29) ^{(1 / 0.62)}

In the present invention, the saponification degree of PVA is 98 mol% or more. If the saponification degree of PVA is less than 98 mol%, sufficient polarization performance may not be obtained. The degree of saponification of PVA is preferably 99 mol% or more, more preferably 99.5 mol% or more, and particularly preferably 99.9 mol% or more. Here, the degree of saponification of PVA is the vinyl relative to the total number of moles of the structural unit (typically a vinyl ester-based monomer unit) and the vinyl alcohol unit of PVA that can be converted into vinyl alcohol units by saponification. The ratio (mol%) of the number of moles of alcohol unit. The degree of saponification of PVA can be measured according to the description of JIS K6726-1994. When a plurality of PVAs having different saponification degrees are mixed, the saponification degree of the mixture of PVAs can be specified by obtaining a weighted average of the saponification degrees of these plurality of PVAs.

The PVA used for producing the PVA film of the present invention has a saponification degree of 98 mol% or more, a polymerization degree of 1200 or more and 8000 or less, and is not particularly limited as long as the formulas (1) and (2) are satisfied as a result of GPC analysis. do not have. For example, in the saponification of a vinyl ester polymer, the vinyl ester adjacent to the saponified vinyl ester unit is likely to be saponified preferentially (the saponification reaction proceeds in a chain reaction), so that a monomer other than the vinyl ester should be copolymerized. Taking advantage of the property that the degree of saponification is difficult to increase, the type of monomer other than vinyl ester, polymerization solvent, polymerization temperature, chain transfer agent, etc. are appropriately adjusted to determine the polymerization terminal and side chains that are easily cleaved during saponification. Examples include a method of reducing the degree of degeneration. Further, a method of blending PVA (A) having a high degree of polymerization and a low degree of saponification and PVA (B) having a low degree of polymerization and a high degree of saponification is also exemplified. Among these methods, from the viewpoint of cost and the degree of freedom of PVA obtained, a method of blending PVA (A) having a high degree of polymerization and a low degree of saponification and PVA (B) having a low degree of polymerization and a high degree of saponification is used. preferable.

In the method of blending PVA (A) having a high degree of polymerization and a low degree of saponification and PVA (B) having a low degree of polymerization and a high degree of saponification, the degree of polymerization of PVA (A) is preferably 1500 or more. It is more preferably 1800 or more, further preferably 2000 or more, and particularly preferably 2300 or more. The degree of polymerization of PVA (A) is preferably 3800 or less, more preferably 3300 or less, and even more preferably 3000 or less. If the degree of polymerization of PVA (A) is less than 1500, the polarization performance may be impaired. Further, when the degree of polymerization of PVA (A) exceeds 3500, the viscosity of the aqueous solution or the melted resin becomes high, which may make film formation difficult.

The degree of saponification of PVA (A) is preferably 97 mol% or more. When the saponification degree of PVA (A) is less than 97 mol%, it becomes difficult to increase the saponification degree of PVA after blending with PVA (B) to 98 mol% or more. The degree of saponification of PVA (A) is more preferably 98 mol% or more, further preferably 99 mol% or more, and particularly preferably 99.5 mol% or more.

On the other hand, the degree of polymerization of PVA (B) is preferably 50 or more, more preferably 100 or more, further preferably 200 or more, and particularly preferably 300 or more. The degree of polymerization of PVA (B) is preferably 800 or less, more preferably 700 or less, further preferably 600 or less, and particularly preferably 500 or less. When the degree of polymerization of PVA (B) is less than 50, the amount of PVA eluted in the treatment liquid in the polarizing element manufacturing process increases, and the aggregated PVA by boric acid cross-linking or the like adheres to the polarizing film and turns blue. It tends to be a brown foreign substance defect (hereinafter, may be abbreviated as blue stuff). Further, when the degree of polymerization of PVA (B) exceeds 800, the stability of the film width during high-speed film formation may be insufficient.

The degree of saponification of PVA (B) is preferably 0.1 mol% or more higher than PVA (A), more preferably 0.2 mol% or more, further preferably 0.3 mol% or more, and 0. It is particularly preferable that it is as high as 4 mol% or more. The saponification degree of PVA (B) is preferably lower than PVA (A) in the range not exceeding 1.2 mol%, more preferably lower in the range not exceeding 1 mol%, and exceeds 0.8 mol%. It is more preferable that it is as low as possible. If the degree of saponification of PVA (B) is lower than that of PVA (A) or higher than that of PVA (A), but the difference is less than 0.1 mol%, the stability of the film width during high-speed film formation is unsatisfactory. May be sufficient. Further, when the saponification degree of PVA (B) is higher than that of PVA (A) by more than 1.2 mol%, the polarization performance of the obtained polarizing film tends to be deteriorated.

As PVA (A) and PVA (B), one type of PVA may be used alone as long as the formulas (1) and (2) are satisfied, and the degree of polymerization, the degree of saponification, the degree of modification, etc. You may use a blend of two or more kinds of PVA which are different from each other.

The blend ratio of PVA (A) and PVA (B) in the present invention is not necessarily limited, but it is preferably in the range of PVA (A): PVA (B) = 80:20 to 97: 3 on a mass basis. When the ratio of PVA (A) is less than 80% by mass, the polarization performance of the obtained polarizing film tends to deteriorate. The ratio of PVA (A) is preferably 85% by mass or more, more preferably 88% by mass or more, and further preferably 90% by mass or more. On the other hand, the ratio of PVA (A) is preferably 97% by mass or less, more preferably 95% by mass or less, and further preferably 93% by mass or less. The ratio of PVA (A) is preferably 97% by mass or less, more preferably 95% by mass or less, and further preferably 93% by mass or less. If the ratio of PVA (A) exceeds 97% by mass, the stability of the film width during high-speed film formation may be insufficient.

The PVA content in the PVA film of the present invention is preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more, based on the total mass of the PVA film.

[Surfactant]
The PVA film of the present invention may contain a surfactant. By containing a surfactant, it prevents adhesion to metal supports such as drums in the film forming process, improves the slipperiness of PVA film, and suppresses the occurrence of wrinkles in long film rolls. Known effects such as can be obtained.

The content of the surfactant in the PVA film of the present invention is preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more, and 0.01 part by mass with respect to 100 parts by mass of PVA. It is more preferable to have more than one part. The content of the surfactant is preferably 1 part by mass or less, more preferably 0.8 part by mass or less, and further preferably 0.5 part by mass or less with respect to 100 parts by mass of PVA. .. If the content of the surfactant is less than 0.001 part by mass, the above effect may not be sufficiently obtained. Further, when the content of the surfactant exceeds 1 part by mass, coloring of the film and deterioration of transparency tend to occur easily. In addition, streaky defects may occur on the film surface.

The type of the surfactant is not particularly limited, and examples thereof include anionic surfactants and nonionic surfactants.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate;
Sulfate ester type such as octyl sulfate;
Examples thereof include sulfonic acid types such as dodecylbenzene sulfonate.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether;
Alkylphenyl ether type such as polyoxyethylene octylphenyl ether;
Alkyl ester type such as polyoxyethylene laurate;
Alkylamine type such as polyoxyethylene laurylamino ether;
Alkylamide type such as polyoxyethylene lauric acid amide;
Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether;
Alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide;
Examples thereof include allylphenyl ether types such as polyoxyalkylene allylphenyl ether.

Of these, nonionic surfactants are preferable, alkanolamide-type surfactants are more preferable, and saturated or unsaturated fats having 8 to 30 carbon atoms are preferable from the viewpoint of excellent effect of reducing membrane surface abnormalities during film formation. Dialkanolamides such as diethanolamides of aliphatic carboxylic acids such as group carboxylic acids are more preferred. In addition, one type of surfactant may be used alone, or two or more types may be used in combination.

[Plasticizer]
The PVA film of the present invention may contain a plasticizer. Since the PVA film is more rigid than other plastic films, it may not have sufficient impact strength, process passability during secondary processing, etc., but the PVA film contains the above-mentioned plasticizer. The inconvenience can be improved.

Examples of the plasticizer include polyhydric alcohols and the like. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Of these, ethylene glycol and glycerin are preferable from the viewpoint of improving the stretchability of the optical PVA film. In addition, these plasticizers may be used alone or in combination of two or more.

The content of the plasticizer in the PVA film of the present invention is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and 3 parts by mass or more with respect to 100 parts by mass of PVA. More preferred. The content of the plasticizer is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and further preferably 20 parts by mass or less with respect to 100 parts by mass of PVA. If the content of the plasticizer is less than 1 part by mass, the above effect may not be obtained, and if it exceeds 30 parts by mass, the PVA film may become too flexible and the handleability may be deteriorated.

[Other optional ingredients]
The PVA film of the present invention may further contain other optional components other than PVA, a surfactant and a plasticizer as long as the effects of the present invention are not impaired. Examples of such other optional components include water, antioxidants, ultraviolet absorbers, lubricants, colorants, preservatives, fungicides, and polymer compounds other than the above-mentioned components.

The content of the above-mentioned other optional components in the PVA film of the present invention is preferably 40% by mass or less, more preferably 20% by mass or less, and 10% by mass or less based on the total mass of the PVA film. It is more preferable, and it is particularly preferable that it is 5% by mass or less.

[Manufacturing method of PVA film]
The PVA film of the present invention can be produced by using a PVA satisfying the above formula (1) and adopting a conventionally known method. Examples of conventionally known methods include a casting film forming method, a wet film forming method, a dry wet film forming method, a gel film forming method, a melt extrusion film forming method, and a method combining these methods. Of these, the melt extrusion film forming method is preferable from the viewpoint of obtaining a PVA film having high transparency and less coloring.

The PVA film of the present invention can be produced, for example, as follows by the melt extrusion method. First, the PVA chips are immersed in distilled water at 10 ° C. to 50 ° C. for 10 hours to 48 hours and then subjected to centrifugal dehydration to obtain PVA water-containing chips having a volatile content concentration of 30% by mass to 90% by mass. An appropriate amount of a plasticizer such as glycerin, a surfactant, a solvent such as water, or the like is added to the PVA water-containing chip and mixed. This mixture is put into a twin-screw extruder, and melt extrusion film formation is continuously performed by a conventionally known method. Specifically, the above mixture is heated and melted by a twin-screw extruder having a maximum temperature of 100 ° C. to 200 ° C. and cooled to 80 ° C. to 120 ° C. by a heat exchanger to obtain a film-forming stock solution. This film-forming stock solution is discharged from a T-die at 80 ° C. to 120 ° C., cast on a metal drum at 75 ° C. to 115 ° C., and dried to obtain a water-containing film having a water content of 10% by mass to 40% by mass. After peeling this film from the metal drum, the film can be passed through a hot air drying furnace at 50 ° C to 100 ° C to produce the PVA film of the present invention.

The thickness of the PVA film of the present invention is not particularly limited, but when used as a raw material for a polarizing film, the average thickness is preferably in the range of 5 to 150 μm. The average thickness of the PVA film can be obtained as an average value by measuring the thickness of any 10 points (for example, any 10 points on a straight line drawn in the width direction of the PVA film). Further, the film width of the PVA film can be set to a size suitable for the intended use. The film width of the PVA film is usually preferably 0.1 m or more, preferably 0.5 m or more, and further preferably 1.0 m or more. The film width of the PVA film is usually preferably 7.5 m or less, more preferably 7.0 m or less, and even more preferably 6.5 m or less. The concentration of the volatile component of the PVA film of the present invention is preferably 0.5% by mass or more, and more preferably 1% by mass or more.

The film-formed PVA film can usually be wound into a roll around a cylindrical core using a conventionally known method to form a film roll. As a specific method for manufacturing the film roll, for example, both ends of the PVA film in the width direction are slit by 0.5 cm to 20 cm, and a conventionally known winder is used to make 1.0 Kgf / cm to 10 Kgf / cm. A PVA film roll can be manufactured by winding a film around a cylindrical core with the film tension of.

The outer diameter of the core (in the case of a square tube, the diameter of the circumscribed circle) is preferably 10 cm or more. If the outer diameter is less than 10 cm, the film roll may bend due to its own weight and wrinkle. The length of the core may be the same as the PVA film width or longer than the film width, but is preferably 10 cm or more longer than the film width. When the length of the core is shorter than the film width, breakage is likely to occur from the end portion in the film width direction during stretching, and uniform stretching may be difficult. Further, it is preferable that the core has a tubular shape whose outer surface is made of metal or plastic so as to prevent wrinkles during winding.

The length of the PVA film wound into a roll is preferably 1,300 m or more. If the length of the PVA film wound into a roll is less than 1,300 m, a loss due to film roll switching is large in the polarizing film manufacturing process or the like, which is not preferable. There is no particular limit to the upper limit of the length of the PVA film that is wound into a roll, but if it is too long, the weight of the film roll becomes too heavy and the handling becomes poor, or the film roll bends and wrinkles occur in the film. The length of the PVA film is preferably 20,000 m or less because it may cause problems such as facilitation.

It is preferable that the PVA film wound into a roll is moisture-proof packaged and stored and transported in a suspended state in which the weight is supported by the entire core of the film roll or both ends of the core. Preferred methods for storing and transporting the core in the suspended state include a method in which the core protruding from both end faces of the roll is placed on the support, a method in which the core protruding from both end faces of the roll is suspended by the support, and a part of the support is cored. There are a method of inserting into the core, a method of placing the rod-shaped jig inserted inside the core on the support, and a method of suspending the rod-shaped jig inserted inside the core by the support, and among these, the core protruding from both end faces of the roll. Is more preferred on the support. In addition, PVA has high hygroscopicity, and when stored and transported in an environment other than low humidity conditions, it easily absorbs moisture and swells, and there is a high possibility that the film will wrinkle. Sufficient moisture-proof packaging is required if transportation is expected.

The volatile fraction of the PVA film finally obtained by a series of treatments is not necessarily limited. The volatile fraction of the PVA film is preferably 1% by mass or more and 5% by mass or less.

[Manufacturing method of optical film]
The use of the PVA film of the present invention is not particularly limited, but it can be suitably used, for example, as a raw film for producing an optical film. Examples of the optical film include a polarizing film, a viewing angle improving film, a retardation film, and a brightness improving film, but a polarizing film is preferable. Hereinafter, as an example of the method for manufacturing an optical film, a method for manufacturing a polarizing film will be specifically described.

The polarizing film can usually be produced by using a PVA film as a raw film and undergoing treatment steps such as a swelling step, a dyeing step, a cross-linking step, a stretching step, and a fixing treatment step. Specific examples of the treatment liquid used in each step include a swelling treatment liquid used for swelling treatment, a dyeing treatment liquid (staining liquid) used for dyeing treatment, a cross-linking treatment liquid used for cross-linking treatment, and a stretching treatment liquid. Examples thereof include a stretching treatment liquid, a fixing treatment liquid used for the fixing treatment, and a cleaning treatment liquid (cleaning liquid) used for the cleaning treatment.

Each processing step that can be adopted in the manufacturing method for manufacturing the polarizing film will be described in detail below. In the method for producing a polarizing film, one or two or more of the following processes may be omitted, the same process may be performed a plurality of times, or another process may be performed at the same time.

(Washing treatment before swelling treatment)
It is preferable to perform a cleaning treatment on the PVA film before performing the swelling treatment on the PVA film. By such a cleaning treatment before the swelling treatment, the blocking inhibitor or the like adhering to the PVA film can be removed, and it is possible to prevent each treatment liquid in the polarizing film manufacturing process from being contaminated by the blocking inhibitor or the like. be able to. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but it can also be performed by spraying the cleaning treatment liquid on the PVA film. For example, water can be used as the cleaning treatment liquid. The temperature of the cleaning treatment liquid is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, further preferably 24 ° C. or higher, and particularly preferably 26 ° C. or higher. When the temperature of the cleaning treatment liquid is 20 ° C. or higher, it becomes easy to remove the blocking inhibitor and the like adhering to the PVA film. The temperature of the cleaning treatment liquid is preferably 40 ° C. or lower, more preferably 38 ° C. or lower, further preferably 36 ° C. or lower, and particularly preferably 34 ° C. or lower. When the temperature of the cleaning treatment liquid is 40 ° C. or lower, it is possible to prevent a part of the surface of the PVA film from melting and the films from sticking to each other to deteriorate the handleability.

(Swelling treatment)
The swelling treatment can be performed by immersing the PVA film in a swelling treatment liquid such as water. The temperature of the swelling treatment liquid is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, and even more preferably 24 ° C. or higher. The temperature of the swelling treatment liquid is preferably 40 ° C. or lower, more preferably 38 ° C. or lower, and even more preferably 36 ° C. or lower. The time for immersing in the swelling treatment liquid is, for example, preferably 0.1 minutes or longer, and more preferably 0.5 minutes or longer. Further, the time for immersing in the swelling treatment liquid is preferably, for example, 5 minutes or less, and more preferably 3 minutes or less. The water used as the swelling treatment liquid is not limited to pure water, and may be an aqueous solution in which various components such as a boron-containing compound are dissolved, or may be a mixture of water and an aqueous medium. The type of the boron-containing compound is not particularly limited, but boric acid or borax is preferable from the viewpoint of handleability. When the swelling treatment liquid contains a boron-containing compound, the concentration of the boron-containing compound in the swelling treatment liquid is preferably 6% by mass or less from the viewpoint of improving the stretchability of the PVA film.

(Dyeing process)
The dyeing treatment is preferably carried out using an iodine-based dye as the dichroic dye, and the dyeing time may be any stage before the stretching treatment, during the stretching treatment, or after the stretching treatment. The dyeing treatment is preferably carried out by using a solution containing iodine-potassium iodide (preferably an aqueous solution) as the dyeing treatment liquid and immersing the PVA film in the dyeing treatment liquid. The concentration of iodine in the dyeing solution is preferably in the range of 0.005 to 0.2% by mass. Potassium iodide / iodine (mass) is preferably in the range of 20-100. The temperature of the dyeing treatment liquid is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. The temperature of the dyeing treatment liquid is preferably 50 ° C. or lower, more preferably 40 ° C. or lower. The dyeing solution may contain a boron-containing compound such as boric acid as a cross-linking agent. If the PVA film used as the raw film contains a dichroic dye in advance, the dyeing process can be omitted. Further, it is also possible to preliminarily contain a boron-containing compound such as boric acid or borax in the PVA film used as the raw film.

(Crosslinking)
In the production of the polarizing film, a cross-linking treatment can be performed after the dyeing treatment for the purpose of strengthening the adsorption of the dichroic dye on the PVA film. The cross-linking treatment can be performed by using a solution containing a cross-linking agent (preferably an aqueous solution) as the cross-linking treatment liquid and immersing the PVA film in the cross-linking treatment liquid. As the cross-linking agent, one or more boron-containing compounds such as boric acid and borax can be used. If the concentration of the cross-linking agent in the cross-linking treatment liquid is too high, the cross-linking reaction tends to proceed too much and it tends to be difficult to perform sufficient stretching in the subsequent stretching treatment, and the concentration of the cross-linking agent in the cross-linking treatment liquid also tends to be difficult. If it is too small, the effect of the cross-linking treatment tends to be reduced. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

In order to suppress the elution of the dichroic dye from the PVA film after the dyeing treatment, the cross-linking treatment liquid may contain an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the cross-linking treatment liquid is too high, the heat resistance of the obtained polarizing film tends to decrease for unknown reasons. Further, if the concentration of the iodine-containing compound in the cross-linking treatment liquid is too low, the effect of suppressing the elution of the dichroic dye tends to be reduced. For the above reason, the concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

If the temperature of the cross-linking treatment liquid is too high, the polarizing film obtained by elution of the dichroic dye tends to have uneven dyeing, and if the temperature of the cross-linking treatment liquid is too low, the cross-linking treatment tends to occur. The effect may be reduced. The temperature of the cross-linking treatment liquid is preferably in the range of 20 ° C to 45 ° C. The temperature of the cross-linking treatment liquid is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, and even more preferably 25 ° C. or higher. The temperature of the cross-linking treatment liquid is preferably 45 ° C. or lower, more preferably 40 ° C. or lower, and even more preferably 35 ° C. or lower.

Apart from the stretching treatment described later, the PVA film may be stretched during or between the above-mentioned treatments. By such stretching (pre-stretching), it is possible to prevent wrinkles from being generated on the surface of the PVA film. The total stretching ratio of the pre-stretching (magnification obtained by multiplying the stretching ratio in each treatment) is 4 times or less based on the original length of the PVA film of the original fabric before stretching from the viewpoint of the polarization performance of the obtained polarizing film. Is preferable. The total draw ratio of the pre-stretch is more preferably 3.5 times or less. The total draw ratio of the pre-stretching is more preferably 1.5 times or more based on the original length of the PVA film of the original fabric before stretching from the viewpoint of the polarization performance of the obtained polarizing film. The draw ratio in the swelling treatment is preferably 1.1 times or more, more preferably 1.2 times or more, still more preferably 1.4 times or more, based on the original length of the PVA film. .. The draw ratio in the swelling treatment is preferably 3 times or less, more preferably 2.5 times or less, still more preferably 2.3 times or less, based on the original length of the PVA film. The draw ratio in the dyeing treatment is preferably 2 times or less, more preferably 1.8 times or less, still more preferably 1.5 times or less, based on the original length of the PVA film. The draw ratio in the dyeing treatment is more preferably 1.1 times or more based on the original length of the PVA film. The draw ratio in the crosslinking treatment is preferably 2 times or less, more preferably 1.5 times or less, still more preferably 1.3 times or less, based on the original length of the PVA film. The draw ratio in the crosslinking treatment is more preferably 1.05 times or more based on the original length of the PVA film.

(Stretching treatment)
The stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, a solution containing a boron-containing compound such as boric acid (preferably an aqueous solution) can be used as the stretching treatment liquid, and the stretching treatment liquid can be used. It can also be performed in the treatment liquid. Further, in the case of the dry stretching method, it can be carried out in the air using a PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. When the stretching treatment liquid contains a boron-containing compound, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 1.5% by mass or more because the stretchability of the PVA film can be improved. It is more preferably 0% by mass or more, and further preferably 2.5% by mass or more. The concentration of the boron-containing compound in the stretching treatment liquid is preferably 7% by mass or less, more preferably 6.5% by mass or less, and more preferably 6% by mass, because the stretchability of the PVA film can be improved. The following is more preferable.

It is preferable that the stretching treatment liquid contains an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching solution is too high, the hue of the obtained polarizing film tends to be bluish, and if the concentration of the iodine-containing compound is too low, the reason is unknown. The heat resistance of the obtained polarizing film tends to decrease. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 2% by mass or more, more preferably 2.5% by mass or more, and further preferably 3% by mass or more. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 8% by mass or less, more preferably 7.5% by mass or less, and further preferably 7% by mass or less.

If the temperature of the stretching treatment liquid is too high, the PVA film tends to melt and become soft and easily break, and if the temperature of the stretching treatment liquid is too low, the stretchability tends to decrease. The temperature of the stretching treatment liquid is preferably 50 ° C. or higher, more preferably 52.5 ° C. or higher, and even more preferably 55 ° C. or higher. The temperature of the stretching treatment liquid is preferably 70 ° C. or lower, more preferably 67.5 ° C. or lower, and even more preferably 65 ° C. or lower. The preferred range of the stretching temperature when the stretching treatment is performed by the dry stretching method is also as described above.

The stretching ratio in the stretching treatment is preferably 1.2 times or more, more preferably 1.5 times or more, and more preferably 1.5 times or more, because a polarizing film having better polarizing performance can be obtained when the stretching ratio is high. It is more preferable that the amount is double or more. Further, the total draw ratio (magnification multiplied by the draw ratio in each step) including the draw ratio of the pre-stretch described above is the polarization performance of the obtained polarizing film based on the original length of the raw material PVA film before stretch. From this point of view, it is preferably 5.5 times or more, more preferably 5.7 times or more, and further preferably 5.9 times or more. The upper limit of the draw ratio is not particularly limited, but if the draw ratio is too high, stretch breakage is likely to occur, so that the draw ratio is preferably 8 times or less.

There is no particular limitation on the method of performing the stretching process by uniaxial stretching, and uniaxial stretching in the long direction and lateral uniaxial stretching in the width direction can be adopted. In the case of producing a polarizing film, uniaxial stretching in the long direction is preferable from the viewpoint of obtaining an excellent polarizing film. 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.

In the present invention, the maximum stretching speed (% / min) when the stretching treatment is performed by uniaxial stretching is not particularly limited, but is preferably 200% / min or more, and more preferably 300% / min or more. , 400% / min or more is more preferable. Here, the maximum stretching speed is the fastest stretching speed among the three or more rolls having different peripheral speeds when the PVA film is stretched in two or more stages. Say that. When the stretching treatment of the PVA film is performed in one step without dividing into two or more steps, the stretching speed at that step becomes the maximum stretching rate. The stretching speed is the increase in the length of the PVA film increased by stretching with respect to the length of the PVA film before stretching per unit time. For example, the stretching speed of 100% / min is defined as. It refers to the speed at which the PVA film is deformed from the length before stretching to twice the length per minute. The higher the maximum stretching speed, the higher the stretching treatment (uniaxial stretching) of the PVA film can be performed, and as a result, the productivity of the polarizing film is improved, which is preferable. On the other hand, if the maximum stretching speed becomes too high, excessive tension may be locally applied to the PVA film in the stretching treatment (uniaxial stretching) of the PVA film, and stretching fracture is likely to occur. From this point of view, it is preferable that the maximum stretching speed does not exceed 900% / min.

(Fixed processing)
In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dichroic dye on the PVA film. For the fixing treatment, a solution containing one or more boron-containing compounds such as boric acid and borax (preferably an aqueous solution) is used as the fixing treatment liquid, and a PVA film (preferably after stretching treatment) is used as the fixing treatment liquid. This can be done by immersing the PVA film). Further, if necessary, the fixing treatment liquid may contain an iodine-containing compound or a metal compound. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 2% by mass or more, and more preferably 3% by mass or more. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 15% by mass or less, and more preferably 10% by mass or less. The temperature of the fixing treatment liquid is preferably 15 ° C. or higher, more preferably 25 ° C. or higher. The temperature of the fixing treatment liquid is preferably 60 ° C. or lower, more preferably 40 ° C. or lower.

(Washing treatment after dyeing treatment)
After the dyeing treatment, it is preferable to perform a washing treatment on the PVA film after the stretching treatment. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but it can also be performed by spraying the cleaning treatment liquid on the PVA film. For example, water can be used as the cleaning treatment liquid. The water is not limited to pure water, and may contain an iodine-containing compound such as potassium iodide. The cleaning treatment liquid may contain a boron-containing compound, but in that case, the concentration of the boron-containing compound is preferably 2.0% by mass or less.

The temperature of the cleaning treatment liquid is preferably 5 ° C. or higher, more preferably 7 ° C. or higher, and even more preferably 10 ° C. or higher. The temperature of the cleaning treatment liquid is preferably 40 ° C. or lower, more preferably 38 ° C. or lower, and even more preferably 35 ° C. or lower. When the temperature of the cleaning treatment liquid is 5 ° C. or higher, it is possible to suppress the breakage of the PVA film due to freezing of water. Further, when the temperature of the cleaning treatment liquid is 40 ° C. or lower, the optical characteristics of the obtained polarizing film are improved.

Specific methods for producing the polarizing film include a method of subjecting the PVA film to a dyeing treatment, a stretching treatment, a crosslinking treatment and / or a fixing treatment. As a preferable example, there is a method in which the PVA film is subjected to a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment (particularly a uniaxial stretching treatment), and a washing treatment in this order. Further, the stretching treatment may be performed in any of the treatment steps prior to the above, or may be performed in multiple stages of two or more stages.

A polarizing film can be obtained by subjecting the PVA film after each of the above treatments to a drying treatment. The drying treatment method is not particularly limited, and examples thereof include a contact type method in which the film is brought into contact with a heating roll, a method in which the film is dried in a hot air dryer, and a floating type method in which the film is dried by hot air while floating. ..

(Polarizer)
The polarizing film obtained as described above is preferably 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. Further, examples of the adhesive for bonding include PVA-based adhesives and urethane-based adhesives, but PVA-based adhesives are preferable.

The polarizing plate obtained as described above can be used as an LCD component by laminating an acrylic adhesive or the like and then bonding it to a glass substrate. The polarizing plate may be bonded to a retardation film, a viewing angle improving film, a luminance improving film, or the like at the same time.

The PVA film of the present invention can be used as an optical film, and specifically, can be suitably used as a raw material for an optical film such as a polarizing film having few optical defects, a retardation film, and a special light collecting film. It can also be used for other purposes such as packaging materials, water-soluble films for laundry bags, and release films for producing artificial marble and the like.

The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

(1) Relative molecular weight analysis by GPC measurement The method of analyzing the relative molecular weight by GPC analysis of PVA film is shown below.
<Sample adjustment>
In each of the following examples or comparative examples, a film sample of about 5 mg of PVA film was taken and weighed. Hexafluoroisopropanol (HFIP) containing 1 mL of 20 mM sodium trifluoroacetate was added to the collected sample and heated at 40 ° C. for 3 hours to dissolve it. Using this solution, GPC analysis was performed under the following conditions. The relative molecular weight distribution curve was calculated by converting the relative molecular weights obtained from the RI detector and the UV detector by the analysis software attached to the analyzer. The analysis was performed three times for the same sample, and the average value was used as the analysis result.
In the peak top molecular weight (Mp) of the obtained relative molecular weight distribution curve, the detection intensity of the RI detector and the detection intensity of the UV detector before conversion to the molecular weight distribution curve were set to Hri1 and Hub1, respectively. Further, the detection intensities of the RI detector and the detection intensities of the UV detector before the molecular weight distribution conversion at the molecular weight at the point where the logarithmic value of 10 in terms of relative molecular weight was a low number were set to Hri2 and Hub2, respectively. Using these values, the values of Hub2 / Hri2, the values of Hub1 / Hri1-Huv2 / Hri2, and the values of Hri2 / Hri1 were calculated.

<GPC analysis conditions>
Measuring device: HLC-8320GPC (manufactured by TOSOH, column length 15 cm, column diameter 4.6 mm)
Analysis software: Emporer (manufactured by Waters)
Sample concentration: 0.1 mg / mL
Mobile phase solvent: Hexafluoroisopropanol supplemented with 20 mM sodium trifluoroacetate Injection amount: 10 μL
Flow rate: 0.2 mL / min
Measurement temperature: 40 ° C
Sample dissolution conditions: 40 ° C x 3 hours Filter filtration: 0.45 μm PTFE filter column: GMMHR-H (S) (TOSOH) 2 detectors: RI detector and UV detector attached to the device (absorption wavelength 210 μm)
Equipment calibration standard: PMMA (4 ml tri-pack (90vils) Acrylic Visual (GPC / SEC Calibration Standards) manufactured by Agilent, Mp 2210000, 1020000, 538500, 265300, 146500, 72000, 2650 , 885,550 PMMA)

(2) Film-forming stability during film-forming In each of the following Examples or Comparative Examples, a film-forming stock solution containing PVA is placed on a support (rotation speed 15 m / min, surface temperature 85 ° C.) from a 1000 mm wide T-die. A liquid film was formed on the support by discharging the film into a film. On the support, hot air at 90 ° C. was blown on the entire non-contact surface of the liquid film with the support at a rate of 7.5 m / sec to dry the film, and a PVA film (moisture content: 25% by mass) was obtained. The difference between the maximum width and the minimum width of the film when this film formation was performed for 1 minute was measured and evaluated according to the following criteria.
A: The difference between the maximum width and the minimum width is less than 5 mm B: The difference between the maximum width and the minimum width is 5 mm or more and less than 10 mm C: The difference between the maximum width and the minimum width is 10 mm or more

(3) Blue lumps In the following Examples or Comparative Examples, when the polarizing film was continuously produced for 20 minutes, the blue lumps adhering to the surface of the polarizing film were visually observed and evaluated according to the following criteria.
A: No blue stuff was confirmed.
B: A few blue lumps were observed at a level where there was no problem in practical use.
C: Blue lumps were observed at a level that was practically problematic.

(4) Degree of polarization Two 1.5 cm × 1.5 cm square samples parallel to the orientation direction of the polarizing film were collected from the central portion in the width direction of the polarizing film obtained in the following Examples or Comparative Examples. For each, using a spectrophotometer V-7100 (attached to an integrating sphere) manufactured by Hitachi, Ltd., the visibility correction of the visible light region of the C light source and the 2 degree field of view is performed in accordance with JIS Z8722 (measurement method of object color). Then, for one polarizing film sample, the light transmittance when tilted by 45 degrees with respect to the stretching axis direction and the light transmittance when tilted by −45 degrees were measured, and their average values (Y1) were measured. ) Was asked. For the other polarizing film sample, the light transmittance when tilted by 45 degrees and the light transmittance when tilted by −45 degrees were measured in the same manner as described above, and their average values (Y2) were measured. Asked. The transmittances (Y) (%) of the polarizing film were obtained by averaging Y1 and Y2 obtained above.
Light transmittance (Y∥) when the two polarizing film samples collected above are stacked so that their orientation directions are parallel, and light transmittance when they are stacked so that their orientation directions are orthogonal to each other. (Y⊥) was measured by the same method as the above-mentioned transmittance measuring method, and the degree of polarization (V) (%) was obtained from the following formula.
Degree of polarization (V) (%) = {(Y∥－Y⊥) / (Y∥ + Y⊥)} ^1/2 × 100

[Example 1]
<Manufacturing of PVA film>
90 parts by mass of PVA having a degree of saponification of 99.3 mol% and a degree of polymerization of 2500 as PVA (A), 10 parts by mass of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 500 as PVA (B), plastic Using 12 parts by mass of glycerin as an agent, 0.2 parts by mass of laurate diethanolamide as a surfactant, and 217.6 parts by mass of water, melt-mix them with a melt extruder to make a film-forming stock solution (volatile content 66% by mass). ) Was prepared. Next, this film-forming stock solution was discharged from a 1000 mm wide T-die onto a support (rotation speed 15 m / min, surface temperature 85 ° C.) in the form of a film to form a liquid film on the support. On the support, hot air at 90 ° C. was blown on the entire non-contact surface of the liquid film with the support at a rate of 7.5 m / sec to dry the film, and a PVA film (moisture content: 25% by mass) was obtained. When the film formation was continued for 1 minute, the maximum value of the film width was 972 mm and the minimum value was 969 mm, and the difference was 3 mm. The PVA film is then stripped from the support and from the first drying roll to the final drying roll just before the heat treatment roll so that one side and the other side of the PVA film are in alternating contact with each drying roll. After further drying up to (19th drying roll), the film was peeled off from the final drying roll. At this time, the surface temperature of each dry roll from the first dry roll to the final dry roll was set to 70 ° C. Further, the PVA film was peeled off from the final dry roll, and heat treatment was performed so that one surface of the PVA film and the other surface were alternately in contact with each heat treatment roll. At this time, the heat treatment was performed using two heat treatment rolls, and the surface temperature of each of the heat treatment rolls was set to 100 ° C. Both ends of the obtained film were cut off so as to have a width of 900 m, and the film was wound into a roll on a cylindrical core.

<Manufacturing and evaluation of polarizing film>
The obtained PVA film was slit to a width of 650 mm, and the film was continuously subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, washing treatment, and drying treatment in this order to continuously produce a polarizing film. The swelling treatment was carried out by uniaxially stretching 2.00 times in the length direction while immersing in pure water (swelling treatment liquid) at 25 ° C. The dyeing treatment is performed by immersing in a potassium iodide / iodine staining solution (staining treatment solution) at a temperature of 32 ° C. (potassium iodide / iodine (mass ratio) is 23, iodine concentration is in the range of 0.03 to 0.05% by mass). While doing so, it was uniaxially stretched 1.26 times in the length direction. In this dyeing treatment, the iodine concentration in the dyeing treatment liquid is 0.03 to 0.05 so that the simple substance transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment is in the range of 43.5% ± 0.2%. Adjusted within the range of mass%. The cross-linking treatment was carried out by uniaxially stretching 1.19 times in the length direction while immersing in a boric acid aqueous solution (cross-linking treatment liquid) (boric acid concentration 2.6% by mass) at 32 ° C. The stretching treatment is performed 2.00 times in the length direction while being immersed in a 55 ° C. boric acid / potassium iodide aqueous solution (stretching treatment liquid) (boric acid concentration 2.8% by mass, potassium iodide concentration 5% by mass). It was uniaxially stretched. The maximum stretching speed of uniaxial stretching in this stretching treatment was 400% / min. The washing treatment is carried out by immersing in a potassium iodide / boric acid aqueous solution (washing liquid) (potassium iodide concentration 3 to 6% by mass, boric acid concentration 1.5% by mass) at 22 ° C. for 12 seconds without stretching. gone. The drying treatment was carried out by hot air drying at 80 ° C. for 1.5 minutes without stretching to obtain a polarizing film. When the production of the polarizing film was continued for 20 minutes, the number of stretch breaks during that period was 0, and no blue spots were observed on the surface of the polarizing film.
The obtained PVA film and polarizing film were evaluated by the above-mentioned method. The evaluation results are shown in Table 1.

[Comparative Example 1]
In Example 1, PVA is the same as in Example 1 except that the amount of PVA (A) is 100 parts by mass and the amount of PVA (B) is 0 parts by mass, that is, PVA is only PVA (A). Manufactured the film. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Example 2]
In Example 1, a PVA film was produced in the same manner as in Example 1 except that the PVA (A) was changed to one having a degree of polymerization of 3600 and a degree of saponification of 99.4 mol%. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 2]
In Example 1, a PVA film was produced in the same manner as in Example 1 except that the amount of PVA (A) was 60 parts by mass and the amount of PVA (B) was 40 parts by mass. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Example 3]
In Example 1, PVA (A) was changed to a saponification degree of 97.6 mol%, and PVA (A) was 80 parts by mass and PVA (B) was 20 parts by mass in the same manner as in Example 1. To produce a PVA film. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Example 4]
In Example 2, a PVA film was produced in the same manner as in Example 1 except that PVA (A) was 95 parts by mass and PVA (B) was 5 parts by mass. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Example 5]
In Example 1, a PVA film was produced in the same manner as in Example 1 except that PVA (A) was changed to one having a saponification degree of 99.9 mol%. Using the obtained PVA film, a polarizing film was produced in the same manner as in Example 1. The evaluation results are shown in Table 1.

Claims

A polyvinyl alcohol film containing polyvinyl alcohol having a saponification degree of 98 mol% or more, and the polyvinyl alcohol is added with 20 mM Na trifluoroacetate as a mobile phase solvent at a measurement temperature of 40 ° C. on a gel permeation chromatograph. A polyvinyl alcohol film containing polyvinyl alcohol, which satisfies the following formulas (1) and (2) in the results measured using isopropanol.
Hub2 / Hri2 ≤ 0.014 (1)
0.1 ≤ Hri2 / Hri1 ≤ 0.2 (2)
(However, Hub2 has an absorption wavelength at a polymethylmethacrylate-converted molecular weight of 4.3 with a base number of 10 obtained by using an ultraviolet / visible absorbance detector (UV detector) of a gel permeation chromatograph. With a detection intensity of 210 nm, Hri2 is obtained using a differential refractive index detector (RI detector) of a gel permeation chromatograph and has a molecular weight converted to polymethyl methacrylate having a logarithmic value of 4.3. It is the detection intensity, and Hri1 is the maximum value of the detection intensity obtained by using the RI detector.)
The polyvinyl alcohol film according to claim 1, which satisfies the following formula (3) in the result of measuring the polyvinyl alcohol by a gel permeation chromatograph.
0.001 ≦ Hub1 / Hri1-Huv2 / Hri2 ≦ 0.015 (3)
(However, Hub1 is obtained by using a UV detector and is the maximum value of the detection intensity at an absorption wavelength of 210 nm.)
The polyvinyl alcohol has a degree of polymerization of 1500 or more and 3800 or less and a saponification degree of 98 mol% or more of polyvinyl alcohol (A) and a degree of polymerization of 50 or more and 800 or less and a saponification degree of 0.1 mol from the polyvinyl alcohol (A). The polyvinyl alcohol film according to claim 1 or 2, which comprises a polyvinyl alcohol (B) having a high content in the range of% or more and 1.2 mol% or less.
The polyvinyl alcohol according to claim 3, wherein the blend ratio of the polyvinyl alcohol (A) and the polyvinyl alcohol (B) is in the range of polyvinyl alcohol (A): polyvinyl alcohol (B) = 80:20 to 97: 3. the film.
The polyvinyl alcohol film according to any one of claims 1 to 4, which is an optical film.
The method for producing a polyvinyl alcohol film according to any one of claims 1 to 5, wherein a polyvinyl alcohol satisfying the above formulas (1) and (2) is used.
A polarizing film made from the polyvinyl alcohol film according to claim 5.