WO2022145441A1

WO2022145441A1 - Polyvinyl alcohol film, polarizing film using same, and polarizing plate

Info

Publication number: WO2022145441A1
Application number: PCT/JP2021/048716
Authority: WO
Inventors: 洋平鷹取; 稔岡本; 修風藤
Original assignee: 株式会社クラレ
Priority date: 2020-12-28
Filing date: 2021-12-27
Publication date: 2022-07-07
Also published as: JPWO2022145441A1; KR20230121805A; CN116685628A; TW202233739A

Abstract

The purpose of the present invention is to provide: a PVA film that is less likely to be broken through stretching when stretched uniaxially during production of an optical film such as a polarizing film; a polarizing film using the PVA film; and a polarizing plate.　This polyvinyl alcohol film is a source material film which is for producing an optical film and in which the average value of the intensities of detection of positive silicon fragment ions as determined by positive ion analysis using time-of-flight secondary ion mass spectrometry, on at least one surface of the polyvinyl alcohol film is 0.001-0.01. [The average value of the intensities of detection of positive silicon fragment ions refers to the average value of the intensities of detection of positive silicon fragment ions as determined by positive ion analysis using time-of-flight secondary ion mass spectrometry at five points that are on an arbitrarily-defined straight line parallel to the TD direction of the polyvinyl alcohol film and that equally divide the polyvinyl alcohol film into six parts in the TD direction.]

Description

Polyvinyl alcohol film, polarizing film using it, and polarizing plate

The present invention relates to a polyvinyl alcohol film, a polarizing film using the same, and a polarizing plate.

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 having a light switching function. The fields of application of this LCD are also used from small devices such as calculators and wristwatches in the early stages of development to notebook computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones and indoors and outdoors in recent years. It is expanding to various fields such as measuring instruments.

The polarizing plate is manufactured by laminating a protective film such as a cellulose triacetate (TAC) film or a cellulose acetate / butyrate (CAB) film on the surface of a polarizing film. Then, the polarizing film is uniaxially stretched or dyed after dyeing a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA" and "polyvinyl alcohol film" may be referred to as "PVA film"). However, it is generally produced by uniaxially stretching or uniaxially stretching and then dyeing to produce a dyed uniaxially stretched film, and then immobilizing the uniaxially stretched film with a boron compound. In addition, uniaxial stretching is generally controlled by adjusting the rotation speed of a set of nip rolls with a drive function (material is NBR rubber). The immobilization treatment with this boron compound may be performed at the same time as the uniaxial stretching or dyeing treatment.

High-contrast and clear images are required for products with large LCDs such as LCD monitors and LCD TVs. Along with this, the polarizing film is also required to have higher performance, and specifically, it is required to increase the degree of polarization of the polarizing film. In order to increase the degree of polarization of the polarizing film, it is necessary to increase the draw ratio when the PVA film is uniaxially stretched. However, when the draw ratio is increased, the stretch breakage of the PVA film is likely to occur. As a result, the productivity and yield of the polarizing film are lowered, and the cost tends to be high.

As a method for reducing stretch breakage during uniaxial stretching of a PVA film, for example, in Patent Documents 1 and 2, a PVA layer is formed on a plastic film by a coating method, and the laminate is subjected to stretching treatment, dyeing treatment, or the like. Therefore, a method of processing the PVA layer into a polarizing film is known.

Japanese Unexamined Patent Publication No. 2012-133303 Japanese Unexamined Patent Publication No. 2012-073570

However, the method of using a laminate obtained by forming a PVA layer on a plastic film by a coating method has the following problems.
(I) The coating work and the subsequent drying work are complicated.
(Ii) Since the heat treatment for the insolubilization treatment of the PVA layer needs to be performed in the state of the laminated body, the plastic film used is limited to the one that can be stretched even after the heat treatment, resulting in high cost.
Therefore, there has been a demand for a PVA film that is less likely to cause stretch breakage in uniaxial stretching when manufacturing an optical film such as a polarizing film and can contribute to cost reduction of the optical film such as a polarizing film.

Therefore, an object of the present invention is to provide a PVA film in which stretch fracture is unlikely to occur in uniaxial stretching when manufacturing an optical film such as a polarizing film, a polarizing film using the same, and a polarizing plate.

As a result of diligent studies to achieve the above object, the present inventors have obtained the detection intensity of silicon fragment ions obtained by positive ion analysis by time-of-flight secondary ion mass spectrometry on at least one surface of the PVA film. It was found that the above problem can be solved by adjusting the average value of. Although the detailed reason is not clear, the moderate presence of silicon ions on the surface of the PVA film causes the friction between the PVA film and the nip roll to be moderate in uniaxial stretching when manufacturing an optical film such as a polarizing film. Therefore, it is presumed that the stretch breakage of the PVA film is suppressed. Based on these findings, the present inventors further studied and completed the present invention.

That is, the present invention
[1] On at least one surface of the polyvinyl alcohol film, the average value of the detection intensities of positive silicon fragment ions obtained by positive ion analysis by time-of-flight secondary ion mass spectrometry is 0.001 to 0.01. , Polyvinyl alcohol film, which is a raw film for manufacturing optical films.
[The average value of the detection intensity of positive silicon fragment ions is on an arbitrary straight line parallel to the TD direction of the polyvinyl alcohol film, and the flight time type secondary at 5 points that divide the polyvinyl alcohol film into 6 equal parts in the TD direction. It is the average value of the detection intensity of the positive silicon fragment ion obtained by the positive ion analysis by the ion mass analyzer. ];
[2] In the above [1], the difference between the maximum value and the minimum value of the detection intensity of positive silicon fragment ions at five points that divide the polyvinyl alcohol film into six equal parts in the TD direction is 0.0005 to 0.002. The polyvinyl alcohol film described. ;
[3] The polyvinyl alcohol film according to the above [1] or [2], wherein the average value of the coefficient of variation of the thickness of the polyvinyl alcohol film is 0.01 to 0.03.
[The average value of the coefficient of variation of the thickness passes through each of the five points that divide the polyvinyl alcohol film into six equal parts in the TD direction, and is a straight line having a length of 1.2 m parallel to the MD direction of the polyvinyl alcohol film. It is the average value of the coefficient of variation of the thickness. ];
[4] The polyvinyl alcohol film according to any one of [1] to [3] above, wherein the degree of swelling when immersed in water at 30 ° C. for 30 minutes is 180 to 240%;
[5] The polyvinyl alcohol film according to any one of [1] to [4], wherein the length in the TD direction is 1.5 m or more.
[6] The polyvinyl alcohol film according to any one of [1] to [5], wherein the length in the MD direction is 3,000 m or more.
[7] The polyvinyl alcohol film according to any one of the above [1] to [6], which has a thickness of 10 to 40 μm;
[8] A polarizing film produced from the polyvinyl alcohol film according to any one of [1] to [7] above;
[9] A polarizing plate having a protective film bonded to at least one surface of the polarizing film according to the above [8];
Regarding.

According to the present invention, there is provided a PVA film in which stretch breakage is unlikely to occur in uniaxial stretching when manufacturing an optical film such as a polarizing film, a polarizing film using the same, and a polarizing plate.

It is a figure which showed the measurement point at the time of obtaining the average value of the detection intensity of the positive silicon fragment ion of a PVA film by the positive ion analysis by the time-of-flight type secondary ion mass spectrometry. It is a figure which showed the measurement point at the time of obtaining the coefficient of variation of the thickness of a PVA film. In the Example or Comparative Example, it is a figure which showed the measurement point at the time of obtaining the average value of the detection intensity of the positive silicon fragment ion of a PVA film by the positive ion analysis by the time-of-flight type secondary ion mass spectrometry. It is a figure which showed the measurement point at the time of obtaining the coefficient of variation of the thickness of a PVA film in an Example or a comparative example.

Hereinafter, the present invention will be described in detail.

<Time-of-flight secondary ion mass spectrometry>
Time-of-flight secondary ion mass spectrometry (hereinafter, may be referred to as TOF-SIMS) is known as a method for analyzing components existing on the film surface and their distribution state. In this analysis method, by identifying fragment ions derived from various additives contained in the film, it is possible to understand how and to what extent the components such as various additives derived from those fragments are distributed on the film surface. It is possible to do.

For example, when PVA film is measured by TOF-SIMS, a wide variety of fragment ions are detected. Among these fragment ions, by analyzing the signals of the fragment ions derived from the plasticizer and the surfactant contained in the PVA film and comparing the signal intensities, the distribution state and the segregation state on the surface of these films can be determined. It is possible to know.

In the present invention, attention was paid to a silicon-derived positive fragment ion (hereinafter, may be referred to as a positive silicon fragment ion) detected by performing positive ion analysis by TOF-SIMS on a PVA film. As a result of diligent studies by the present inventors, one axis for manufacturing an optical film such as a polarizing film is set in a specific range by setting the average value of the detection intensities of positive silicon fragment ions on at least one surface of the PVA film as a specific range. It is possible to obtain a PVA film in which stretching breakage is unlikely to occur during stretching. Here, the detection intensity of positive silicon fragment ions is the count number of all fragment ions (T.c .: total count intensity) detected by the positive ion analysis by TOF-SIMS, which is the count number of positive silicon fragment ions. The divided value was used.

<PVA film>
In the PVA film of the present invention, the average value of the detection intensities of positive silicon fragment ions obtained by positive ion analysis by TOF-SIMS is 0.001 to 0.01 on at least one surface of the PVA film. FIG. 1 shows the measurement points for obtaining the average value of the detection intensities of positive silicon fragment ions. The average value of the detected intensities is on an arbitrary straight line A parallel to the TD direction of the PVA film, and the PVA film is divided into 6 equal parts in the TD direction at 5 points (points P ₁ , P ₂ , P ₃ , P ₄ and P). It is the average value of the detection intensity of the positive silicon fragment ion in ₅ ). In the present invention, the average value of the detection intensities of positive silicon fragment ions at the five measurement points is 0.001 to 0.01.

In the present invention, the average value of the detection intensities of silicon fragment ions on at least one surface of the PVA film may be 0.001 to 0.01, but the detection intensities of silicon fragment ions on both sides of the PVA film may be 0.001 to 0.01. The average value may be 0.001 to 0.01. If the average value of the detected intensities is less than 0.001, excessive tension may be applied to the PVA film in uniaxial stretching when manufacturing an optical film such as a polarizing film, and stretching fracture may occur. It is presumed that this is because if the amount of silicon fragment ions present on the surface of the PVA film is too small, the friction between the PVA film and the nip roll becomes strong. On the other hand, when the average value of the detected strength exceeds 0.01, the PVA film is not stretched in the uniaxial stretching when manufacturing an optical film such as a polarizing film, but is completely melted in the stretching treatment liquid and stretched and fractured. There is a risk. It is presumed that this is because if the amount of silicon fragment ions present on the surface of the PVA film is too large, slippage occurs between the nip roll and the film. The average value of the detected intensities is preferably 0.002 or more, more preferably 0.003 or more, and even more preferably 0.004 or more. The average value of the detected intensities is preferably 0.01 or less, more preferably 0.009 or less, further preferably 0.008 or less, and most preferably 0.007 or less.

The method for setting the average value of the detected intensities to 0.001 to 0.01 is not particularly limited, and examples thereof include a method in which a silicon-containing compound is contained in a PVA film. Among the silicon-containing compounds, a silicone-type surfactant is preferable. In this case, the content of the silicone-type surfactant, the volatile content of the PVA water-containing chip or the film-forming stock solution, the number of rotations of the screw of the extruder when melt-kneading the PVA, and the surface of the support for flowing the film-forming stock solution. By appropriately adjusting the temperature, the contact time between the PVA film and the support, the temperature of the hot air blown on the PVA film, the temperature of the drying roll or the drying furnace, etc., the average value of the detected intensity is 0.001 to 0.01. Can be.

In the present invention, the detection intensity of positive silicon fragment ions at _five points ( _points P1 to P5) that are on an arbitrary straight line A parallel to the TD direction of the PVA film and divide the PVA film into six equal parts in the TD direction. The difference between the maximum value and the minimum value of is preferably 0.0005 or more, more preferably 0.0007 or more, and further preferably 0.0008 or more. The difference between the maximum value and the minimum value of the detection intensity of the positive silicon fragment ion is preferably 0.002 or less, more preferably 0.0018 or less, and further preferably 0.0016 or less. Since the difference between the maximum value and the minimum value is 0.0005 to 0.002, in uniaxial stretching when manufacturing an optical film such as a polarizing film, stretching is uniformly performed in the plane of the PVA film, and stretching is performed. It is possible to suppress the occurrence of breakage.

The method for setting the difference between the maximum value and the minimum value of the detection intensity to 0.0005 to 0.002 is not particularly limited, but for example, a method of incorporating a silicon-containing compound such as a silicone-type surfactant into a PVA film is used. can give. In this case, the content of the silicone-type surfactant, the volatile content of the PVA water-containing chip or the film-forming stock solution, the number of rotations of the screw of the extruder when melt-kneading the PVA, and the surface of the support for flowing the film-forming stock solution. By appropriately adjusting the temperature, the contact time between the PVA film and the support, the temperature of the hot air blown on the PVA film, the temperature of the drying roll or the drying furnace, etc., the difference between the maximum value and the minimum value of the detected intensity is set to 0. It can be 0005 to 0.002.

In the present invention, the average value of the coefficient of variation of the thickness of the PVA film is preferably 0.01 to 0.03. FIG. 2 shows the measurement points when determining the coefficient of variation of the thickness of the PVA film. In the present invention, as shown in FIG. 2, a length of 1.2 m parallel to the MD direction of the PVA film passes through _each of the _five points (points P1 to P5) that divide the PVA film into six equal parts in the TD direction. The thickness of the PVA film is measured at points on the straight lines B ₁ to B ₅ , and the fluctuation coefficient of the thickness of the PVA film is calculated. Each of the 1.2 m long straight lines B ₁ to B ₅ may be, for example, a straight line such that the five points (P ₁ to P ₅ ) that divide the PVA film into six equal parts in the TD direction are at the center. can. When measuring the thickness of a plurality of points on the straight lines B ₁ to B ₅ , the measurement interval can be appropriately set, and for example, the measurement can be performed at intervals of 0.5 mm.

The average value of the coefficient of variation is preferably 0.01 or more, more preferably 0.011 or more, further preferably 0.012 or more, and most preferably 0.013 or more. The average value of the coefficient of variation is preferably 0.03 or less, more preferably 0.025 or less, further preferably 0.022 or less, and most preferably 0.018 or less. When the average value of the coefficient of variation is 0.01 to 0.03, in uniaxial stretching when manufacturing an optical film such as a polarizing film, stretching is uniformly performed in the plane of the PVA film, and stretching breakage occurs. Can be suppressed.

The method for setting the average value of the coefficient of variation to 0.01 to 0.03 is not particularly limited, but for example, the temperature of the hot air blown onto the PVA film, which increases the volatile content of the PVA water-containing chip or the film-forming stock solution, and , A method of lowering the temperature of the drying roll or the drying furnace. In this case, the content of the silicone-type surfactant, the volatile content of the PVA water-containing chip or the film-forming stock solution, the number of rotations of the screw of the extruder when melt-kneading the PVA, and the surface of the support for flowing the film-forming stock solution. By appropriately adjusting the temperature, the contact time between the PVA film and the support, the temperature of the hot air blown on the PVA film, the temperature of the drying roll or the drying furnace, etc., the difference between the maximum value and the minimum value of the detected intensity is set to 0. It can be 0005 to 0.002.

In the present invention, the degree of swelling when the PVA film is immersed in water at 30 ° C. for 30 minutes is preferably 180% or more, more preferably 190% or more, and further preferably 195% or more. preferable. The degree of swelling when the PVA film is immersed in water at 30 ° C. for 30 minutes is preferably 240% or less, more preferably 210% or less, still more preferably 205% or less. When the degree of swelling is 180 to 240%, the PVA film becomes moderately soft when immersed in water such as swelling treatment when manufacturing an optical film such as a polarizing film, and the tension becomes excessive when the PVA film is uniaxially stretched. As a result, it is possible to suppress the occurrence of stretch breakage.

In the present invention, the MD direction of the PVA film means the length direction of the PVA film, which coincides with the mechanical flow direction when the PVA film is manufactured. On the other hand, the TD direction of the PVA film means the width direction of the PVA film, and is a direction orthogonal to the machine flow direction when manufacturing the PVA film. In the PVA film of the present invention, whether one direction is the MD direction or the TD direction can be determined ex post facto even after the production of the PVA film by measuring the phase difference spots of the PVA film. That is, since it is usually difficult to make the thickness unevenness of the film completely uniform during the production of the PVA film, it can be determined that the direction in which the phase difference unevenness of the PVA film is large is the TD direction. On the other hand, it can be determined that the direction in which the phase difference unevenness of the PVA film is small is the MD direction.

(PVA)
In the PVA film of the present invention, as PVA, a polymer produced by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer can be used. Examples of the vinyl ester-based monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. Among these, vinyl acetate is preferable as the vinyl ester-based monomer.

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

Other monomers include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or a salt thereof; methylacrylic acid, ethylacrylic acid, n-propyl acrylate, i-acrylic acid. -Acrylic acid esters such as propyl, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or salts thereof; methacrylic acid. Methyl, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid Methacrylic acid esters such as octadecyl; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamide propanesulfonic acid or its salts, acrylamidepropyldimethylamine or its salts, N-methylolacrylamide. Or an acrylamide derivative such as a derivative thereof; methacrylicamide, N-methylmethacrylicamide, N-ethylmethacrylicamide, methacrylicamide propanesulfonic acid or a salt thereof, methacrylicamidepropyldimethylamine or a salt thereof, N-methylolmethacrylicamide or a derivative thereof, etc. Methacrylic acid derivative; N-vinylamide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether, n-butylvinyl ether, i-butylvinyl ether. Vinyl ethers such as t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylic nitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl acetate and allyl chloride. Allyl compounds such as; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. The vinyl ester-based polymer can have a structural unit derived from one or more of these other monomers.

The proportion of structural units derived from other monomers in the vinyl ester polymer is not necessarily limited as long as it does not interfere with the effects of the present invention, but is based on the number of moles of all structural units constituting the vinyl ester polymer. It is preferably mol% or less, more preferably 5 mol% or less, further preferably 1 mol% or less, and particularly preferably 0.1 mol% or less.

The degree of polymerization of PVA is not particularly limited. The degree of polymerization of PVA is preferably 1,000 or more, and preferably 8,000 or less. The lower limit of the degree of polymerization of PVA is more preferably 1,500 or more, and further preferably 2,000 or more, from the viewpoint of enhancing the optical performance and the heat resistance to moisture of the obtained optical film. On the other hand, the upper limit of the degree of polymerization of PVA is more preferably 5,000 or less, and further preferably 4,000 or less, from the viewpoint of increasing the productivity of PVA.

Here, the degree of polymerization means the average degree of polymerization measured according to the description of JIS K 6726-1994. That is, in the present invention, the degree of polymerization (Po) is determined by the following formula from the ultimate viscosity [η] (deciliter / g) measured in water at 30 ° C. after remineralizing and purifying the residual acetic acid group of PVA. Be done.

Degree of polymerization Po = ([η] × 10 ⁴ / 8.29) ^{(1 / 0.62)}

In the present invention, the lower limit of the saponification degree of PVA is 98.7 mol%, preferably 99.0 mol%, more preferably 99.5 mol%, further preferably 99.8 mol%, and 99.9 mol%. % Is particularly preferable. When the saponification degree is at least the above lower limit, an optical film having excellent optical performance and moisture heat resistance tends to be obtained. On the other hand, the upper limit of the saponification degree is not particularly limited, but is preferably 99.99 mol% or less from the viewpoint of PVA productivity.

Here, the degree of saponification of PVA is the number of moles of vinyl alcohol units with respect to the total number of moles of structural units (typically vinyl ester monomer units) that can be converted into vinyl alcohol units by saponification. It refers to the proportion (mol%). The degree of saponification of PVA can be measured according to the description of JIS K 6726-1994.

The PVA film of the present invention may contain one type of PVA alone, or may contain two or more types of PVA having different degrees of polymerization, saponification, modification, and the like.

The upper limit of the ratio of the PVA content in the PVA film is not particularly limited. On the other hand, the lower limit of the content ratio of PVA is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 85% by mass or more.

(Plasticizer)
The PVA film of the present invention preferably contains a plasticizer. Since the PVA film contains a plasticizer, the stretchability of the PVA film can be enhanced in the stretching step when producing the optical film. A polyhydric alcohol is preferable as the plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Among these, glycerin is preferable from the viewpoint of improving the stretchability. The plasticizer 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 3 parts by mass or more, and further preferably 5 parts by mass or more with respect to 100 parts by mass of PVA. preferable. On the other hand, the content of the plasticizer is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less with respect to 100 parts by mass of PVA. When the content of the plasticizer is within the above range, the PVA film becomes too flexible and the handleability is deteriorated, and it is possible to prevent the plasticizer from bleeding out to the surface of the PVA film.

(Silicone type surfactant)
The PVA film of the present invention preferably contains a silicon-containing compound. Among the silicon-containing compounds, it is more preferable to contain a silicone-type surfactant. By containing a silicone-type surfactant, it becomes easy to adjust the average value of the detection intensities of positive silicon fragment ions within the above range. Specific examples of the silicone-type surfactant include a silicone-type surfactant having a polyether structure at one end of the silicone (“SN Wet 125” and “SN Wet 126” manufactured by Sannopco), and both ends of the silicone are polyether. Silicone type surfactant with structure ("X-22-4952", "X-22-4272" and "X-22-6266" manufactured by Shin-Etsu Chemical Co., Ltd.), Silicone with a polyether structure on the side chain of silicone Type Surface Activator ("KF-351A", "KF-352A", "KF-353", "KF-354L", "KF-355A", "KF-615A", "KF-945" manufactured by Shin-Etsu Chemical Co., Ltd. , "KF-640", "KF-642", "KF-643", "KF-6020", "KS-604", "X-50-1039A", "X-50-1105G", "X" -22-6191 ”,“ X-22-4515 ”,“ KF-6011 ”,“ KF-6012 ”,“ KF-6015 ”and“ KF-6017 ”), and having a polyether structure at both ends of the silicone. Surface active agents ("KF-6004", "KF-889", "X-22-4471", "KF-1002", "X-22-4952", "X-22-4272" manufactured by Shin-Etsu Chemical Co., Ltd. And "X-22-6266") and the like.

In the PVA film of the present invention, the content of the silicone-type surfactant is preferably 0.02 part by mass or more, more preferably 0.04 part by mass or more, and 0.06 by mass with respect to 100 parts by mass of PVA. It is more preferably more than parts by mass. On the other hand, the content of the silicone-type surfactant is preferably 0.14 parts by mass or less, more preferably 0.12 parts by mass or less, and further preferably 0.10 parts by mass or less. .. When the content of the silicone-type surfactant is in the above range, it becomes easy to adjust the average value of the detection intensities of positive silicon fragment ions to the above range.

(Other surfactants)
The PVA film of the present invention preferably contains a surfactant other than the silicone-type surfactant. By including such a surfactant, it is possible to improve the handleability of the PVA film and the peelability of the PVA film from the film forming apparatus at the time of production. The surfactant other than the silicone-type surfactant is not particularly limited, and for example, an anionic surfactant and a nonionic surfactant are preferably used.

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

Examples of the nonionic surfactant include an alkyl ether type surfactant such as polyoxyethylene lauryl ether and polyoxyethylene oleyl ether; an alkylphenyl ether type surfactant such as polyoxyethylene octylphenyl ether; and polyoxyethylene lau. Alkyl ester-type surfactants such as rates; Alkylamine-type surfactants such as polyoxyethylene laurylamino ether; Alkylamide-type surfactants such as polyoxyethylene lauric acid amide; Polypropylene such as polyoxyethylene polyoxypropylene ethers Glycol ether type surfactants; alkanolamide type surfactants such as lauric acid diethanolamide and oleic acid diethanolamide; allylphenyl ether type surfactants such as polyoxyalkylene allylphenyl ether and the like can be mentioned.

As the surfactant other than the silicone type surfactant, one type may be used alone or two or more types may be used in combination. As the surfactant other than the silicone type surfactant, a nonionic surfactant is preferable, an alkanolamide type surfactant is more preferable, and a fat Dialkanolamides (eg, diethanolamides, etc.) of group carboxylic acids (eg, saturated or unsaturated aliphatic carboxylic acids having 8 to 30 carbon atoms) are more preferable.

The content of the surfactant other than the silicone-type surfactant in the PVA film of the present invention is preferably 0.01 part by mass or more, and preferably 0.02 part by mass or more with respect to 100 parts by mass of PVA. More preferably, it is more preferably 0.05 parts by mass or more. On the other hand, the content of the surfactant other than the silicone type surfactant is preferably 10 parts by mass or less, more preferably 1 part by mass or less, and 0.5 part by mass with respect to 100 parts by mass of PVA. It is more preferably 0 parts by mass or less, and particularly preferably 0.3 parts by mass or less. When the content of the surfactant other than the silicone-type surfactant is in the above range, the peelability of the PVA film from the film forming apparatus at the time of manufacturing is improved, and the PVA film is stuck between the PVA films (hereinafter referred to as "blocking"). It can be prevented from occurring. Further, it is possible to prevent a surfactant other than the silicone-type surfactant from bleeding out to the surface of the PVA film and to prevent the appearance of the PVA film from being deteriorated due to the aggregation of the surfactant.

(Other ingredients)
In addition to PVA, the PVA film of the present invention includes water-soluble polymers, moisture, antioxidants, ultraviolet absorbers, lubricants, cross-linking agents, colorants, fillers, preservatives, fungicides, other polymer compounds, etc. Ingredients may be contained within a range that does not interfere with the effects of the present invention. The ratio of the total mass of PVA, the surfactant, the plasticizer, and other components other than PVA to the total mass of the PVA film is preferably 60 to 100% by mass, preferably 80 to 100% by mass. Is more preferable, and 90 to 100% by mass is further preferable.

(Physical characteristics)
The PVA film of the present invention is water-insoluble. Since the PVA film is water-insoluble, when uniaxial stretching for producing an optical film such as a polarizing film is performed in an aqueous solution, the PVA film is broken during uniaxial stretching even if the maximum stretching speed is high. It can be stretched without causing it. Here, the term "water-insoluble" in the present invention means that the PVA film is not completely dissolved when the PVA film is immersed in water (deionized water) at 30 ° C. according to the following procedures <1> to <4>. It means that it remains undissolved even in the part.

<1> The PVA film is placed in a constant temperature and humidity chamber adjusted to 20 ° C.-65% RH for 16 hours or more to adjust the humidity.
<2> After cutting out a rectangular sample of 40 mm in length × 35 mm in width from the humidity-controlled PVA film, two 50 mm × 50 mm plastic plates having a rectangular window (hole) of 35 mm in length × 23 mm in width opened. The sample is sandwiched and fixed so that the length direction of the sample is parallel to the length direction of the window and the sample is located substantially in the center of the width direction of the window.
<3> Put 300 mL of deionized water in a 500 mL beaker, and adjust the water temperature to 30 ° C. while stirring with a magnetic stirrer equipped with a 3 cm long bar at a rotation speed of 280 rpm.
<4> The sample fixed to the plastic plate in <2> above is immersed in deionized water in a beaker for 1000 seconds, being careful not to contact the bar of the rotating magnetic stirrer.

(shape)
In the present invention, the thickness of the PVA film is preferably 10 μm or more, preferably 15 μm or more, more preferably 18 μm or more, still more preferably 20 μm or more. The thickness of the PVA film is preferably 40 μm or less, more preferably 38 μm or less, further preferably 36 μm or less, particularly preferably 34 μm or less, and even more preferably 32 μm or less. preferable. When the thickness is within the above range, it is possible to suppress the occurrence of stretch fracture in uniaxial stretching when manufacturing an optical film such as a polarizing film. The "thickness" means the average value of the thickness measured at any five points.

In the present invention, the length of the PVA film in the TD direction is preferably 1.5 m or more, and more preferably 3 m or more. In recent years, the screen size of liquid crystal televisions and liquid crystal monitors has been increasing, so if the length of the PVA film in the TD direction is set to 1.5 m or more, it is suitable for applications in which these are final products. On the other hand, the length of the PVA film in the TD direction is preferably 7 m or less, more preferably 6 m or less. By setting the length in the TD direction to 7 m or less, it is possible to efficiently perform the uniaxial stretching process when manufacturing an optical film with a practical device.

The shape of the PVA film of the present invention is not particularly limited, but it is long because it can continuously and smoothly produce a more uniform PVA film and it is continuously used when producing an optical film or the like. It is preferably a long film. The length of the long film (length in the flow direction) is not particularly limited and can be set as appropriate. The length of the film is preferably 3,000 m or more, and more preferably 5,000 m or more. On the other hand, the length of the film is preferably 30,000 m or less. It is preferable that a long film is wound around a core to form a film roll.

(Use)
The PVA film of the present invention is used as a raw film for producing an optical film. Examples of the optical film of the present invention include a polarizing film, a viewing angle improving film, a retardation film, and a brightness improving film, and they can be suitably used for a polarizing film.

<Manufacturing method of PVA film>
The method for producing the PVA film of the present invention is not particularly limited, and for example, any method as follows can be adopted. As such a method, a cast film forming method, a wet film forming method (a method of discharging into a poor solvent), a dry-wet film forming method, etc. A gel film-forming method (a method in which a film-forming stock solution is once cooled and gelled and then the solvent is extracted and removed), a method of forming a film by a combination of these methods, or a film-forming stock solution obtained by using an extruder or the like is used as T. Examples thereof include a melt extrusion film forming method and an inflation forming method in which a film is formed by extruding from a die or the like. Among these, as a method for producing a PVA film, a casting film forming method and a melt extrusion film forming method are preferable. By using these methods, a homogeneous PVA film can be obtained with high productivity. Hereinafter, a case where the PVA film is manufactured by the casting film forming method or the melt extrusion film forming method will be described.

When the PVA film of the present invention is produced by the casting film forming method or the melt extrusion film forming method, first, a film forming stock solution containing PVA, a solvent, and if necessary, an additive such as a plasticizer is prepared. prepare. Next, this film-forming stock solution is salivated (supplied) in the form of a film onto a rotating support such as a metal roll or a metal belt. As a result, a liquid film of the film-forming stock solution is formed on the support. The liquid film is solidified and formed into a film by being heated on the support to remove the solvent. Examples of the method of heating the liquid film include a method of heating the support itself to a high temperature with a heat medium and the like, and a method of blowing hot air on the opposite surface of the surface in contact with the support of the liquid film. The solidified long film (PVA film) is peeled off from the support, dried by a drying roll, a drying furnace or the like as necessary, further heat-treated as needed, and wound into a roll.

Normally, the drying of the PVA film proceeds by volatilizing the volatile matter from the released film surface that is not in contact with the support, the drying roll, or the like. Since the silicone-type surfactant moves to the surface together with the volatile water, the temperature and draw conditions at that time affect the detection intensity of positive silicon fragment ions in the process during drying. The detection intensity of this positive silicon fragment ion is the content of the silicone-type surfactant, the volatile content of the PVA water-containing chip or the film-forming stock solution, the number of rotations of the screw of the extruder when melt-kneading the PVA, and the film-forming stock solution. It can be adjusted by adjusting the surface temperature of the support that causes the PVA film to flow, the contact time between the PVA film and the support, the temperature of the hot air blown onto the PVA film, the temperature of the drying roll or the drying furnace, and the like.

The volatile fraction of the film-forming stock solution (concentration of volatile components such as a solvent removed by volatilization or evaporation during film-forming) is preferably in the range of 50 to 80% by mass. When the volatile fraction is in the above range, the viscosity of the film-forming stock solution can be adjusted to a suitable range, so that the film-forming property of the liquid film flowed on the support is improved and the film-forming property has a uniform thickness. It becomes easier to obtain a PVA film. The film-forming stock solution may contain a dichroic dye, if necessary. The volatile fraction of the film-forming stock solution is a value calculated by the following formula.

Volatile fraction of membrane-forming stock solution (mass%) = {(Wa-Wb) / Wa} x 100

In the above formula, Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) of the film-forming stock solution of Wa (g) after being dried in an electric heat dryer at 105 ° C. for 16 hours. ..

The method for preparing the undiluted film-forming solution is not particularly limited, and for example, a method of dissolving PVA and additives such as a plasticizer and a surfactant in a solvent in a dissolution tank or the like, a uniaxial extruder or a twin-screw extruder or a biaxial extrusion is performed. Examples thereof include a method of melt-kneading water-containing PVA together with additives such as a plasticizer and a surfactant using a machine.

The undiluted film-forming solution generally passes through the die lip of a die such as a T-die and is spilled into a film on a support such as a metal roll or a metal belt. On the support, the solvent volatilizes from the surface of the flowed film-like stock solution that is not in contact with the support (hereinafter, may be referred to as a free surface), while in contact with the support. Since it does not substantially volatilize from the existing surface (hereinafter, may be referred to as a touch surface), the distribution is such that the solvent concentration on the free surface side is low and the solvent concentration on the touch surface side is high with respect to the thickness direction of the film. Occurs. Therefore, the solidification of PVA also proceeds from the free side first.

PVA crystallization progresses in parallel with PVA solidification. Crystallization of PVA is difficult to proceed even if the solvent concentration is too high or too low, and although it depends on the primary structure of the PVA molecule, the volatile fraction of the flowed film-forming stock solution is in the range of 20 to 60% by mass. It is easy to progress at one time. Further, the rate of crystallization of PVA increases as the temperature increases, but the rate of volatilization of the solvent increases as the temperature increases.

<Manufacturing method of optical film>
The PVA film of the present invention can be used 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 of the present invention can be produced from the PVA film of the present invention. By using the PVA film of the present invention, stretch breakage is less likely to occur in uniaxial stretching when producing a polarizing film, and as a result, a polarizing film can be produced in high yield. 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. 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. Further, the temperature of the cleaning treatment liquid is preferably 40 ° 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, and preferably 40 ° C. or lower. 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 thereof 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, and potassium iodide / iodine (mass) is preferably in the range of 20 to 100. The temperature of the dyeing treatment liquid is preferably 20 ° C. or higher, and preferably 50 ° 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, it is preferable to carry out a cross-linking treatment 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 carry out sufficient stretching in the subsequent stretching treatment, and if it is too low, the effect of the cross-linking treatment tends to be difficult. Tends to decrease. 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 preferably 6% 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 reason is unknown, but the heat resistance of the obtained polarizing film tends to decrease. 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. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1% by mass or more, and preferably 6% by mass or less.

If the temperature of the cross-linking treatment liquid is too high, the dichroic dye elutes and the obtained polarizing film tends to have uneven dyeing, and if it is too low, the effect of the cross-linking treatment may be reduced. .. The temperature of the cross-linking treatment liquid is preferably 20 ° C. or higher, and preferably 45 ° C. or lower.

Apart from the stretching treatment described later, the PVA film may be stretched during or between the above-mentioned treatments. By performing 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-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 based on the original length of the PVA film. The draw ratio in the swelling treatment is preferably 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 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 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. The concentration of the boron-containing compound in the stretching treatment liquid is preferably 7% by mass or less because the stretchability of the PVA film can be improved.

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 the concentration of the iodine-containing compound in the stretching solution is too low. Although it 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. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 8% 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 it is too low, the stretchability tends to decrease. The temperature of the stretching treatment liquid is preferably 50 ° C. or higher, and preferably 67.5 ° 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 it is too high, stretch breakage is likely to occur, so it 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.

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, more preferably 300% / min or more, and 400% / min. More than min 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. Further, the stretching speed means an 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 the speed at which the PVA film is deformed from the length before stretching to twice the length in one 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. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 15% by mass or less. The temperature of the fixing treatment liquid is preferably 15 ° C. or higher. The temperature of the fixing treatment liquid is preferably 60 ° 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 in the range of 5 to 40 ° C. When the temperature 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 is 40 ° C. or lower, the optical characteristics of the obtained polarizing film are improved. The temperature of the cleaning treatment liquid is preferably 5 ° C. or higher. Further, the temperature of the cleaning treatment liquid is preferably 40 ° C. or lower.

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 of the present invention is manufactured by attaching a protective film to at least one side in order to supplement the mechanical strength. The polarizing film of the present invention is usually 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. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

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

<Positive ion analysis by TOF-SIMS>
The PVA film rolls obtained in the following Examples or Comparative Examples were fed out, and a PVA film having a thickness of 30 μm, a width (length in the TD direction) of 1.65 m, and a length (length in the MD direction) of 1 m was cut out. Positive ion analysis by TOF-SIMS was performed on five points on a straight line parallel to the width direction (TD direction) of the PVA film and dividing the PVA film into six equal parts in the TD direction. Specifically, as shown in FIG. 3, in a straight line passing through the center of the PVA film in the MD direction and parallel to the TD direction, 0.275 m, 0.55 m, 0.825 m, 1 from one end of the PVA film. The PVA film was cut into a size of 5 mm × 5 mm at positions of 1 m and 1.375 m (points P ₁ , P ₂ , P ₃ , P ₄ and P ₅ ), respectively, and used as a measurement sample. Each of these measurement samples was set on the pedestal of the TOF-SIMS measuring device via a conductive double-sided tape, and positive ion analysis by TOF-SIMS was performed under the following measurement conditions.

<Measurement conditions>
Measuring device: TOF-SIMS 5 (manufactured by ION-TOF)
Analysis software: Surface Lab 6 (manufactured by ION-TOF)
Primary ion source: Bi ₃ ⁺⁺
Measurement current: 0.2pA at 25keV (10kHz)
Measurement range: 200 μm x 200 μm
Number of measured pixels: 128Pix x 128Pix
Charge neutralization condition: Neutralization electron gun Not used Count count: Number of fragments captured by the detector (detector strength)

<Measurement method of detection intensity of positive silicon fragment ion>
Positive ion analysis by TOF-SIMS was performed on each of the above five measurement samples, and the positive silicon fragment ion count was divided by the total detected fragment ion count to obtain positive silicon fragment ion. The detection intensities were obtained, and the average value of these detection intensities was calculated. In addition, the difference between the maximum value and the minimum value of these detection intensities was calculated.

<Measurement of PVA film thickness>
The PVA film roll obtained in the following Example or Comparative Example was fed out, and a PVA film having a thickness of 30 μm, a width (length in the TD direction) of 1.65 m, and a length (length in the MD direction) of 1.5 m was cut out. .. The thickness of the PVA film is about a point on a straight line parallel to the width direction (TD direction) of the PVA film, passing through five points on the straight line parallel to the MD direction, passing through five points that divide the PVA film into six equal parts in the TD direction. The fluctuation coefficient of was calculated. Specifically, as shown in FIG. 4, in a straight line A passing through the center of the PVA film in the MD direction and parallel to the TD direction, 0.275 m, 0.55 m, 0.825 m from one end of the PVA film. A straight line B with a length of 1.2 m parallel to the MD direction (straight line B ₁ respectively) so as to pass through the positions of 1.1 m and 1.375 m (points P ₁ , P ₂ , P ₃ , P ₄ and P ₅ ). , B ₂ , B ₃ , B ₄ and B ₅ ) were provided, and the thickness of the PVA film was measured at a plurality of points on each straight line B. At this time, the thickness of the PVA film was measured at intervals of 0.5 mm, and a contact-type thickness meter "Continuous Thickness Measuring Instrument Film Tester S2246" (manufactured by Fujiwork Co., Ltd.) was used as the measuring device. Further, as shown in FIG. 4, a straight line having a length of 1.2 m parallel to the MD direction coincides with five points whose midpoints divide the PVA film into six equal parts in the width direction (TD direction). Provided. In this way, the thickness of the PVA film is measured in each of the straight lines having a length of 1.2 m parallel to the MD direction, and the fluctuation coefficient (standard deviation) of the PVA film thickness is obtained from the average value and standard deviation of the obtained PVA film thickness. / Average value) was calculated. Then, the coefficient of variation of the thickness of the PVA film was obtained for each of the straight lines having a length of 1.2 m parallel to the MD direction, and the average value of these coefficients of variation was calculated.

<Measurement of swelling degree of PVA film>
The PVA film rolls obtained in the following Examples or Comparative Examples were fed out, and a PVA film having a thickness of 30 μm, a width (length in the TD direction) of 1.65 m, and a length (length in the MD direction) of 1 m was cut out. About 1.5 g of a test piece was cut out from this PVA film and immersed in 1000 g of distilled water at 30 ° C. After soaking for 30 minutes, the test piece was taken out, the water on the surface was absorbed with a filter paper, and then the mass (We) was measured. Subsequently, the test piece was placed in a hot air dryer and dried at 105 ° C. for 16 hours, and then its mass (Wf) was measured. From the obtained masses We and Wf, the degree of swelling of the PVA film was determined by the following formula.
Swelling degree (%) = (We / Wf) × 100

<Evaluation of stretch fracture of PVA film>
A PVA film was unwound from the PVA film rolls obtained in the following Examples or Comparative Examples, and the stretch fracture property of the PVA film was evaluated in the following steps. First, the PVA film was uniaxially stretched in the length direction to 1.6 times the original length while immersing the PVA film in water (swelling treatment liquid) having a temperature of 30 ° C. for 1 minute. Next, while immersing the PVA film in an iodine / potassium iodide aqueous solution (dyeing solution) (iodine 0.053% by mass, potassium iodide 5.3% by mass) at a temperature of 30 ° C. for 1 minute, the PVA film was kept in its original length. It was uniaxially stretched (second step stretched) in the length direction up to 2.7 times the amount of potassium iodide. Next, while immersing the PVA film in a boric acid / potassium iodide aqueous solution (boric acid 3% by mass, potassium iodide 3% by mass) (crosslinking treatment solution) at a temperature of 30 ° C. for 2 minutes, the PVA film was brought to its original length. It was uniaxially stretched (third step stretched) in the length direction up to 3 times. Next, while immersing the PVA film in a boric acid / potassium iodide aqueous solution (crosslinking treatment liquid) (boric acid 4.5% by mass, potassium iodide 6% by mass) at a temperature of 62 ° C., the PVA film was brought to its original length. Uniaxial stretching (fourth step stretching) was performed in the length direction up to 6 times. Then, the PVA film is immersed in a boric acid / potassium iodide aqueous solution (washing solution) (boric acid 1.5% by mass, potassium iodide 3% by mass) at a temperature of 30 ° C. for 5 seconds, and then a dryer at 60 ° C. By drying for 240 seconds in, a polarizing film having a thickness of 13 μm was continuously produced. Here, the uniaxial stretching was controlled by adjusting the rotation speeds of a set of nip rolls with a drive function (material is NBR rubber). In this test, when the number of breaks of the PVA film was 0 times per 60 minutes, it was evaluated as A, when it was 1 time, it was evaluated as B, when it was 2 times, it was evaluated as C, and when it was 3 times or more, it was evaluated as D. ..

<Example 1>
<Manufacturing and evaluation of PVA film>
After immersing 100 parts by mass of PVA (polymerization degree 2400, saponification degree 99.9 mol%) in 2500 parts by mass of distilled water at 70 ° C. for 24 hours, centrifugal dehydration is performed, and PVA water content with a volatile content of 70% by mass is performed. I got a chip. It is a surfactant having a polyether structure at both ends of glycerin as a plasticizer and polydimethylsiloxane as a silicone-type surfactant with respect to 333 parts by mass of the PVA-containing chip (100 parts by mass of dried PVA). After mixing 0.08 parts by mass of "SN-wet126" (manufactured by Sannopco), the obtained mixture is heated and melted by a twin-screw extruder with a vent (maximum temperature 130 ° C., screw rotation speed of the extruder is 20 rpm). It was used as a film-forming stock solution. After cooling this film-forming stock solution to 100 ° C. with a heat exchanger, the film is extruded from a 180 cm wide coat hanger die onto a support having a surface temperature of 90 ° C., and the PVA film is further supported using a hot air drying device. Hot air at 114 ° C. was blown on the non-contact surface side with the body to dry it. The contact time between the PVA film and the support was 100 seconds, and the PVA film was peeled off from the support. Next, by cutting off both ends of the film thickened by the neck-in during film formation, a PVA film having a thickness of 30 μm, a width (length in the TD direction) of 1.65 m, and a swelling degree of 200% was continuously produced. Of the PVA film, 4000 m in length (length in the MD direction) was wound around a cylindrical core to form a PVA film roll. Using the obtained PVA film roll, the detection intensities of positive silicon fragment ions were obtained by the above method, and the average value and the difference between the maximum value and the minimum value of these detection intensities were calculated. Further, using the obtained PVA film roll, the average value of the coefficient of variation of the thickness of the PVA film was obtained by the above method, and the stretch breakability was further evaluated. The results are shown in Table 1.

<Examples 2 to 4, Comparative Examples 1 to 4>
The production and evaluation of the PVA film were carried out in the same manner as in Example 1 except that the production conditions of the PVA film were changed as shown in Table 1. The results are shown in Table 1.

As shown in Table 1, when the polarizing film was produced using the PVA films of Examples 1 to 4, the film was broken 0 to 2 times per 60 minutes. Therefore, it can be said that the PVA films of Examples 1 to 4 are suppressed from breaking during stretching (at the time of uniaxial stretching). On the other hand, when the polarizing film was produced using the PVA films of Comparative Examples 1 to 4, the film was broken three times or more per 60 minutes. Table 1 shows the evaluation results of the average value of the detection intensity of positive silicon fragment ions, the difference between the maximum value and the minimum value, and the average value of the coefficient of variation of the thickness on the contact surface side of the PVA film with the support. As described, the same evaluation result was obtained for the non-contact surface side of the PVA film with the support.

Claims

On at least one surface of the polyvinyl alcohol film, the average value of the detection intensities of positive silicon fragment ions obtained by positive ion analysis by time-of-flight secondary ion mass spectrometry is 0.001 to 0.01, and the optical film. Polyvinyl alcohol film, which is a raw fabric film for manufacturing.
[The average value of the detection intensity of positive silicon fragment ions is on an arbitrary straight line parallel to the TD direction of the polyvinyl alcohol film, and the flight time type secondary at 5 points that divide the polyvinyl alcohol film into 6 equal parts in the TD direction. It is the average value of the detection intensity of the positive silicon fragment ion obtained by the positive ion analysis by the ion mass analyzer. ]
The polyvinyl alcohol according to claim 1, wherein the difference between the maximum value and the minimum value of the detection intensity of positive silicon fragment ions at five points that divide the polyvinyl alcohol film into six equal parts in the TD direction is 0.0005 to 0.002. the film.
The polyvinyl alcohol film according to claim 1 or 2, wherein the average value of the coefficient of variation of the thickness of the polyvinyl alcohol film is 0.01 to 0.03.
[The average value of the coefficient of variation of the thickness passes through each of the five points that divide the polyvinyl alcohol film into six equal parts in the TD direction, and is a straight line having a length of 1.2 m parallel to the MD direction of the polyvinyl alcohol film. It is the average value of the coefficient of variation of the thickness. ]
The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the degree of swelling when immersed in water at 30 ° C. for 30 minutes is 180 to 240%.
The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the length in the TD direction is 1.5 m or more.
The polyvinyl alcohol film according to any one of claims 1 to 5, wherein the length in the MD direction is 3,000 m or more.
The polyvinyl alcohol film according to any one of claims 1 to 6, which has a thickness of 10 to 40 μm.
A polarizing film produced from the polyvinyl alcohol film according to any one of claims 1 to 7.
A polarizing plate in which a protective film is bonded to at least one surface of the polarizing film according to claim 8.