WO2020184587A1

WO2020184587A1 - Polyvinyl alcohol film, polarizing film, and polarizing plate

Info

Publication number: WO2020184587A1
Application number: PCT/JP2020/010392
Authority: WO
Inventors: 絵美川崎; 孝徳磯崎
Original assignee: 株式会社クラレ
Priority date: 2019-03-14
Filing date: 2020-03-10
Publication date: 2020-09-17
Also published as: JP7345541B2; CN113544555A; TW202045557A; JPWO2020184587A1; KR20210139234A

Abstract

Provided are: a polyvinyl alcohol film with which can produce a polarizing film that can sufficiently suppress reductions in light transmittance of a polarizing plate in high temperature durability tests; a polarizing film obtained by using such a polyvinyl alcohol film; and a polarizing plate obtained by using said polarizing film. The polyvinyl alcohol film contains polyvinyl alcohol, and has an absorbance A1 at a wavelength of 210 nm and an average thickness D1 (mm) that satisfy equation (1) below. The polarizing film is formed from the abovementioned polyvinyl alcohol film. The polarizing plate comprises the abovementioned polarizing film and a protective film containing a cellulose ester resin.　(1): A1/D1≥9

Description

Polyvinyl alcohol film, polarizing film, and polarizing plate

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

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a triacetyl cellulose (TAC) film is bonded to the surface of the polarizing film. The polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" and "PVA" and is sometimes abbreviated) uniaxially stretched iodine to stretched film was oriented dye (I ₃ ^- Ya I ₅ ^- etc.) And dichroic organic dyes that adsorb dichroic dyes are the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film containing a dichroic dye in advance, adsorbing a bicolor dye at the same time as uniaxially stretching the PVA film, or uniaxially stretching the PVA film and then dichroic. Manufactured by adsorbing dyes.

LCDs have come to be widely used in small devices such as calculators and wristwatches, notebook computers, LCD TVs, mobile phones, tablet terminals, and the like. In recent years, LCDs have also been used as in-vehicle image display devices such as car navigation devices and back monitors. Along with this, LCDs are required to have high durability in harsher environments than before.

An image display device configured by laminating a polarizing plate between an image display cell and a transparent plate such as a front plate or a touch panel via an adhesive layer is provided at a high temperature for a long time required for an in-vehicle display. It is known that the light transmittance of a polarizing plate decreases when it is subjected to a durability test. One of the causes is the polyene formation of PVA constituting the polarizing film, and the higher the temperature condition, the more remarkable the decrease in the light transmittance of the polarizing plate.

Regarding the problem of polyene formation of such a polarizing plate, Patent Document 1 describes that polyene formation can be suppressed by adopting a polarizing plate having a protective film having a high moisture permeability on the surface of the polarizing film. Patent Document 2 describes that polyene formation can be suppressed by adjusting the thickness of the pressure-sensitive adhesive used for bonding the polarizing plate to the image display cell or the transparent plate and the absorbance of the polarizing film.

Japanese Unexamined Patent Publication No. 2014-102353 JP-A-2018-25764

However, according to the studies by the inventors, although the methods described in Patent Documents 1 and 2 tend to suppress the decrease in the light transmittance of the polarizing plate, the temperature is 105 ° C. or higher, which has been required in recent years. In the durability test in a high temperature environment, a sufficient effect of suppressing polyene formation could not be confirmed.

The present invention has been made based on the above circumstances, and is a PVA film capable of producing a polarizing film capable of sufficiently suppressing a decrease in the light transmittance of a polarizing plate in a high temperature durability test, such a PVA. It is an object of the present invention to provide a polarizing film obtained by using a film and a polarizing plate obtained by using the polarizing film.

As a result of diligent studies to achieve the above object, the present inventors have found that the polyene formation of PVA in the polarizing film provided on the polarizing plate is promoted by the acid generated from the protective film, and that the polarizing film or the polarizing film is promoted. It was found that polyene formation was suppressed by imparting a function of capturing acid to the PVA film, which is the original film of the above, and further studies were carried out based on these findings to complete the present invention.

That is, the present invention
[1] A polyvinyl alcohol film containing polyvinyl alcohol and having an absorbance A1 at a wavelength of 210 nm and an average thickness D1 (mm) satisfying the following formula (1);
A1 / D1 ≧ 9 ・・・ (1)
[2] The polyvinyl alcohol film of [1], wherein the absorbance A1 and the average thickness D1 (mm) satisfy the following formula (2);
9 ≤ A1 / D1 ≤ 80 ... (2)
[3] The polyvinyl alcohol film of [1] or [2] containing an acid scavenger;
[4] A polyvinyl alcohol film containing polyvinyl alcohol and an acid scavenger, wherein the content of the acid scavenger with respect to 100 parts by mass of the polyvinyl alcohol is 0.1 part by mass or more.
[5] The polyvinyl alcohol film of [3] or [4], wherein the acid scavenger is an organic compound;
[6] The polyvinyl alcohol film of [5], wherein the acid scavenger is a carbodiimide compound having at least one carbodiimide group.
[7] The polyvinyl alcohol film according to any one of [3] to [6], wherein the acid scavenger is water-soluble;
[8] The polyvinyl alcohol film of [7], wherein the acid scavenger is a polymer;
[9] The polyvinyl alcohol film according to any one of [1] to [8], wherein the degree of saponification of the polyvinyl alcohol is 90 mol% or more;
[10] The polyvinyl alcohol film according to any one of [1] to [9] for producing a polarizing plate;
[11] A polarizing film formed from the polyvinyl alcohol film according to any one of [1] to [10];
[12] A polarizing film containing polyvinyl alcohol and having an absorbance A2 at a wavelength of 210 nm and an average thickness D2 (mm) satisfying the following formula (3) after being allowed to stand in a 90% RH atmosphere at 60 ° C. for 100 hours;
A2 / D2 ≧ 9 ・・・ (3)
[13] A polarizing plate having the polarizing film of [11] or [12] and a protective film containing a cellulose ester resin;
Regarding.

According to the present invention, a PVA film capable of producing a polarizing film capable of sufficiently suppressing a decrease in the light transmittance of a polarizing plate in a high temperature durability test, a polarizing film obtained by using such a PVA film, and a polarizing film thereof. A polarizing plate obtained by using a film can be provided.

FIG. 1 is an absorption spectrum of PVA films of Examples 1 to 3 and Comparative Example 1.

Hereinafter, embodiments of the present invention will be described in detail.
<PVA film>
The PVA film according to the embodiment of the present invention is a PVA film containing PVA and having an absorbance A1 at a wavelength of 210 nm and an average thickness D1 (mm) satisfying the following formula (1).
A1 / D1 ≧ 9 ・・・ (1)

Here, the average thickness D1 of the PVA film means an average value of values measured at arbitrary 10 points. Hereinafter, the same applies to the average thickness of the film. The unit of A1 / D1 is mm ^-1 .

Absorption at a wavelength of 210 nm is derived from a group capable of capturing an acid. As shown in Comparative Example 1 described later, even in a PVA film to which a component having a group capable of capturing an acid is not added, there is some absorption in the vicinity of a wavelength of 210 nm, and the value of A1 / D1 is 8 mm ^-1. (See Table 1 and Fig. 1). On the other hand, by adding a component having a group capable of capturing an acid, absorption near a wavelength of 210 nm is increased (see Examples 1 to 3 in FIG. 1). When there are many groups capable of capturing acid in the PVA film and the value of A1 / D1 is 9 mm ^-1 or more, that is, when the PVA film satisfies the above formula (1), the PVA film sufficiently captures the acid. can do. On the other hand, when a polarizing plate including a polarizing film which is a stretched PVA film and a protective film containing a cellulose ester is exposed to a high temperature for a long period of time, the cellulose ester constituting the protective film is hydrolyzed to generate acid. Generate. It is speculated that this acid catalyzes the dehydration reaction of PVA and PVA becomes polyene. On the other hand, in the polarizing plate provided with the polarizing film obtained by using the PVA film satisfying the formula (1), the acid generated from the protective film is captured by the group capable of capturing the acid existing in the polarizing film. It is possible to suppress polyene formation of PVA in the polarizing film in the polarizing plate. That is, according to the PVA film, it is possible to produce a polarizing film capable of sufficiently suppressing a decrease in the light transmittance of the polarizing plate in the high temperature durability test.

Examples of the group capable of capturing an acid and having absorption at a wavelength of 210 nm include a carbodiimide group (-N = C = N-). The PVA film according to one embodiment of the present invention may contain a compound having a carbodiimide group (acid scavenger), or PVA having a carbodiimide group may be used, but it may contain an acid scavenger. Is preferable. A compound having a carbodiimide group (acid scavenger) usually has a maximum absorption near a wavelength of 210 nm. The PVA film according to one embodiment of the present invention may exhibit absorption at a wavelength of 210 nm derived from an acid scavenger. The PVA film according to one embodiment of the present invention may have an acid scavenger having an absorption maximum in the vicinity of a wavelength of 210 nm. Further, the PVA film according to the embodiment of the present invention may be a substantially transparent film. The specific form of the acid scavenger will be described later. The substantially transparent film preferably has an absorbance of 0.2 or less, and more preferably 0.1 or less in the entire wavelength range of 360 nm to 780 nm.

In relation to the absorbance A1 and the average thickness D1, the lower limit of the A1 / D1 is preferably 10 mm ^-1, more preferably 12 mm ^-1, further preferably 14 mm ^-1, further preferably more that 20 mm ^-1, 25 mm ^-1 Is particularly preferable. By setting A1 / D1 to the above lower limit or higher, a polarizing film capable of further enhancing the acid trapping ability, exhibiting a sufficient polyene formation suppressing function in a high temperature durability test, and more sufficiently suppressing a decrease in the light transmittance of the polarizing plate can be obtained. Can be manufactured. On the other hand, the upper limit of A1 / D1 may be, for example, 100 mm ^-1 , but 80 mm ^-1 is preferable, and 50 mm ^-1 is more preferable. By setting A1 / D1 to the above upper limit or less, the film surface is improved and the polarization performance of the obtained polarizing film can be improved. In the PVA film according to the embodiment of the present invention, it is preferable that the absorbance A1 and the average thickness D1 (mm) satisfy the following formula (2).
9 ≤ A1 / D1 ≤ 80 ... (2)

The above A1 / D1 depends on the abundance of groups having absorption at a wavelength of 210 nm. For example, the value of A1 / D1 can be adjusted by the amount of the compound having a carbodiimide group, which is a group having absorption at a wavelength of 210 nm.

(PVA)
PVA is a polymer having a vinyl alcohol unit (-CH _2- CH (OH)-) as a main structural unit. The PVA may have a vinyl ester unit or another unit in addition to the vinyl alcohol unit.

As the PVA, one obtained by saponifying a polyvinyl ester obtained by polymerizing one or more kinds of vinyl esters can be used. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatic acid, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate and the like. Among vinyl esters, ease of manufacture, ease of availability, in terms of cost and the like, are preferable compounds having a vinyl oxycarbonyl group _{(H 2 C = CH-O} -CO-) in the molecule, vinyl acetate is more preferable.

The polyvinyl ester is preferably obtained by using only one kind or two or more kinds of vinyl esters as a monomer, and more preferably the polyvinyl ester obtained by using only one kind of vinyl ester as a monomer. A copolymer resin of one kind or two or more kinds of vinyl esters and another monomer copolymerizable therewith may be used as long as the effect of the present invention is not significantly impaired.

The upper limit of the proportion of structural units derived from other copolymerizable monomers is preferably 15 mol%, more preferably 10 mol%, based on the number of moles of all structural units constituting PVA. Is even more preferable, and 1 mol% is even more preferable.

Other monomers copolymerizable with vinyl ester include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth) acrylic acid or a salt thereof; (meth) acrylic. Methyl acid acid, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth) acrylic (Meta) acrylic acid esters such as t-butyl acid acid, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (meth) acrylamide , N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamidepropyldimethylamine or a salt thereof, N-methylol (Meta) acrylamide derivatives such as (meth) acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether , N-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; vinyl cyanide such as (meth) acryliconitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and the like. Vinyl halide; Acrylic compounds 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; Saturated sulfonic acid or a salt thereof and the like can be mentioned.

The polyvinyl ester can have a structural unit derived from one or more of the above-mentioned monomers.

As the PVA, one that has not been graft-copolymerized can be preferably used. However, PVA may be modified with one or more graft copolymerizable monomers. Graft copolymerization can be carried out on at least one of the polyvinyl ester and the PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

Part of the hydroxy group of PVA may or may not be crosslinked. In addition, a part of the hydroxy group of PVA may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure.

As the lower limit of the degree of polymerization of PVA, 1,000 is preferable, 1,500 is more preferable, and 1,700 is further preferable. When the degree of polymerization of PVA is at least the above lower limit, the flexibility of the PVA film can be improved. On the other hand, the upper limit of the degree of polymerization is preferably 10,000, more preferably 8,000, and even more preferably 5,000. When the degree of polymerization of PVA is not more than the above upper limit, it is possible to suppress an increase in the production cost of PVA and the occurrence of defects during film formation. The degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, and more preferably 99 mol% or more, because the obtained polarizing film has good moisture and heat resistance. It is more preferably 99.5 mol% or more, and particularly preferably 99.5 mol% or more. The upper limit of the saponification degree is not particularly limited, and may be 100 mol% or 99.99 mol%. The degree of saponification of PVA is the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification. Say. The degree of saponification can be measured according to the description of JIS K6726-1994.

The lower limit of the PVA content in the PVA film according to the embodiment of the present invention is preferably 50% by mass, more preferably 80% by mass, and even more preferably 85% by mass. By setting the PVA content to the above lower limit or higher, a good polarizing film can be obtained. On the other hand, the upper limit of the PVA content is preferably 99% by mass, more preferably 95% by mass.

(Acid scavenger)
The acid scavenger, which is a suitable component of the PVA film according to the embodiment of the present invention, is a compound that reacts with the acid to inactivate the acid. Examples of the acid trapping agent include compounds having a carbodiimide group, compounds having an epoxy group, compounds having an oxazoline group, alkyl phosphate metal salts, strongly basic amino compounds, terpene compounds, organic compounds such as oxazine compounds, and Examples thereof include inorganic compounds such as hydrotalcite stones. The organic compound means a compound containing carbon, and the inorganic compound means a compound other than the organic compound. The acid scavenger may be referred to as an acid scavenger, an acid scavenger, an acid catcher, etc., but in the present invention, it can be used without any difference depending on these names. The acid scavenger may be used alone or in combination of two or more.

The acid scavenger is preferably an organic compound. By using an organic compound as the acid scavenger, the acid scavenger is likely to be deformed together with PVA in the stretching direction when the PVA film is stretched in the polarizing film manufacturing process. Therefore, defects such as voids are less likely to occur in the obtained polarizing film, and the polarization performance of the obtained polarizing film is improved.

Among the acid scavengers, a carbodiimide compound having at least one carbodiimide group is more preferable. The carbodiimide compound has a large effect of suppressing polyene formation, and is also preferable from the viewpoint of handleability and safety.

The mass (molecular formula amount) per 1 mol of the group capable of capturing the acid in the acid scavenger is preferably, for example, 200 g / mol or more and 1,000 g / mol or less. When the acid scavenger is a carbodiimide compound, the mass (molecular formula amount) per 1 mol of the group capable of capturing the acid is also referred to as the carbodiimide group equivalent and is the mass per 1 mol of the carbodiimide group.

The acid scavenger is preferably water-soluble. By using a water-soluble acid trapping agent that is easily compatible with PVA, it is possible to obtain a PVA film having high light transmittance, low haze, and a good film surface, and a polarizing film having good polarization performance. In addition, "water-soluble" means that the solubility in water is 1 g / 100 g or more of water. Solubility in water refers to the limit amount (mass) of dissolution in 100 g of water at 20 ° C. As the lower limit of the solubility of the acid scavenger in water, 2 g / 100 g of water is preferable, and 3 g / 100 g of water is more preferable. By setting the solubility in water to the above lower limit or more, the acid trapping agent and PVA are more easily compatible with each other, the film surfaces of the obtained PVA film and polarizing film can be improved, and the polarizing performance of the polarizing film can be improved. .. On the other hand, the upper limit of the solubility may be, for example, 200 g / 100 g of water, but 100 g / 100 g of water is preferable, and 50 g / water 100 g, 20 g / water 100 g, and further 8 g / water 100 g may be more preferable. By setting the solubility in water to the above upper limit or less, it is possible to suppress elution of the acid scavenger when the PVA film is stretched in the treatment liquid to produce a polarizing film.

The molecular weight of the acid scavenger is not particularly limited, and for example, an acid scavenger having a molecular weight of 100 or more or 200 or more can be used, but the acid scavenger is preferably a polymer. When a polarizing film is produced by subjecting a PVA film to a swelling treatment, a dyeing treatment, a stretching treatment or the like in a treatment liquid, it is preferable that the acid scavenger in the PVA film is difficult to elute into the treatment liquid. When the acid scavenger is a polymer, the elution of the acid scavenger in the treatment liquid is suppressed due to the entanglement of the PVA molecular chain and the acid scavenger molecular chain, and the light transmission of the polarizing plate in the high temperature durability test. It is possible to obtain a polarizing film capable of more sufficiently suppressing a decrease in the rate. As described above, from the viewpoint of the polarization performance of the obtained polarizing film, it is preferable to use an acid scavenger having water solubility compatible with PVA. However, the water-soluble acid scavenger tends to elute into the treatment liquid which is an aqueous solution, especially when the molecular weight is low. Therefore, by using an acid scavenger that is water-soluble and is a polymer, a polarizing film that has good polarization performance and can more sufficiently suppress a decrease in the light transmittance of the polarizing plate in a high-temperature durability test can be obtained. Can be manufactured.

The "polymer" refers to a molecule having a weight average molecular weight of 300 or more, and the weight average molecular weight is preferably 1,000 or more, more preferably 3,000 or more. On the other hand, the upper limit of the weight average molecular weight of the high molecular weight acid scavenger may be, for example, 100,000 or 10,000. Examples of commercially available products of high molecular weight acid scavengers include the Epocross series manufactured by Nippon Shokubai Co., Ltd. and the carbodilite series manufactured by Nisshinbo Chemical Co., Ltd., which is a water-soluble polycarbodiimide resin.

The lower limit of the content of the acid scavenger in the PVA film is preferably 0.1 part by mass, more preferably 0.5 part by mass, further preferably 2 parts by mass, and more preferably 5 parts by mass with respect to 100 parts by mass of PVA. More preferred. By setting the content of the acid scavenger to the above lower limit or higher, the acid scavenging ability is enhanced, a sufficient polyene formation suppressing function is exhibited in a high temperature durability test, and a polarization capable of more sufficiently suppressing a decrease in the light transmittance of the polarizing plate. Films can be produced. On the other hand, the upper limit of this content is preferably 40 parts by mass, more preferably 20 parts by mass, and even more preferably 15 parts by mass. By setting the content of the acid scavenger to the above upper limit or less, the film surface is improved and the polarization performance of the obtained polarizing film can be improved.

(Plasticizer)
The PVA film may contain a plasticizer. When the PVA film contains a plasticizer, the handleability and stretchability of the PVA film can be improved. Polyhydric alcohol is preferably used as the plasticizer, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like, and PVA films. Can contain one or more of these plasticizers. Of these, glycerin is preferable because the stretchability of the PVA film becomes better.

The lower limit of the content of the plasticizer in the PVA film is preferably 2 parts by mass, more preferably 3 parts by mass, and even more preferably 4 parts by mass with respect to 100 parts by mass of PVA. On the other hand, the upper limit of this content is preferably 20 parts by mass, more preferably 17 parts by mass, and even more preferably 14 parts by mass with respect to 100 parts by mass of PVA. When the content of the plasticizer in the PVA film is 2 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, it is possible to prevent the plasticizer from bleeding out to the surface of the PVA film and deteriorating the handleability of the PVA film. be able to.

(Surfactant)
The PVA film may contain a surfactant. When a PVA film is produced using a film-forming stock solution as described later, by adding a surfactant to the film-forming stock solution, the film-forming property is improved and the occurrence of thickness unevenness of the film is suppressed. At the same time, when a metal roll or belt is used for film formation, the PVA film can be easily peeled off from the metal roll or belt. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film may contain the surfactant. The type of surfactant contained in the film-forming stock solution for producing PVA film, and thus the type of surfactant contained in PVA film, is not particularly limited, but from the viewpoint of peelability from metal rolls and belts, anions are used. Sexual surfactants and nonionic surfactants are preferable, and nonionic surfactants are particularly preferable. One type of surfactant may be used alone, or two or more types may be used in combination.

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

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene lauryl amino ether. Alkylamine type such as; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxyalkylene Examples thereof include allylphenyl ether type such as allylphenyl ether.

When a surfactant is mixed in the film-forming stock solution for producing a PVA film, the lower limit of the surfactant content in the film-forming stock solution, and by extension, the surfactant content in the PVA film is the film-forming stock solution or 0.01 parts by mass is preferable, and 0.02 parts by mass is more preferable with respect to 100 parts by mass of PVA contained in the PVA film. On the other hand, the upper limit of the content of the surfactant in the film-forming stock solution and the content of the surfactant in the PVA film is 0.5 parts by mass with respect to 100 parts by mass of PVA contained in the film-forming stock solution or the PVA film. Preferably, 0.1 part by mass is more preferable. When the content of the surfactant is 0.01 part by mass or more with respect to 100 parts by mass of PVA, the film-forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, the surfactant bleeds out on the surface of the PVA film, causing blocking and lowering the handleability. It can be suppressed.

(Other ingredients, etc.)
The PVA film contains other components other than the above-mentioned PVA, acid scavenger, plasticizer and surfactant, such as antioxidant, antifreeze agent, pH adjuster, concealing agent, anticoloring agent and oil agent, if necessary. May be contained. However, the content of components other than PVA, acid scavenger, plasticizer and surfactant in the PVA film may be preferably 1% by mass or less, and more preferably 0.1% by mass or less. Further, the content of the inorganic compound in the PVA film may be preferably 1% by mass or less, and more preferably 0.1% by mass or less. The other components and inorganic compounds may cause defects such as voids in the obtained polarizing film. Therefore, by reducing the content of the other components and inorganic compounds, the polarization performance of the obtained polarizing film tends to be improved.

Further, it is preferable that the PVA film does not substantially contain a component having a large absorption at a wavelength of 210 nm other than PVA and an acid scavenger. For these reasons, the content of components other than PVA, acid scavenger, plasticizer and surfactant in the PVA film may be preferably 1% by mass or less, more preferably 0.1% by mass or less. It may be preferable.

The upper limit of the average thickness D1 of the PVA film is not particularly limited, but is, for example, 100 μm, preferably 80 μm, more preferably 60 μm, and even more preferably 40 μm. On the other hand, the lower limit of the average thickness D1 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. When the average thickness of the PVA film is within the above range, handleability and the like can be improved.

The shape of the PVA film is not particularly limited, but a long film is preferable because the polarizing film can be continuously produced with good productivity. The length of the long film is not particularly limited, and can be appropriately set according to the intended use of the polarizing film to be manufactured, and can be, for example, in the range of 5 to 20,000 m. The width of the long film is not particularly limited and may be, for example, 50 cm or more. However, since a wide polarizing film has been demanded in recent years, it is preferably 1 m or more, and more preferably 2 m or more. It is preferably 4 m or more, and more preferably 4 m or more. There is no particular limitation on the upper limit of the width of the long film, but if the width is too wide, it tends to be difficult to uniformly stretch the polarizing film when manufacturing the polarizing film with a practical device. Therefore, the width of the PVA film is preferably 7 m or less.

The shape of the PVA film is not particularly limited and may be a single-layer film or a multilayer film (laminated body), but from the viewpoint of complexity and cost of laminating (coating, etc.) work, a single-layer film may be used. It is preferably a film. The PVA film may be a stretched film or a non-stretched film, but is preferably a non-stretched film. The non-stretched PVA film is suitably used as a raw film for a polarizing film described later.
Since the polarizing film obtained by using the PVA film can sufficiently suppress a decrease in the light transmittance of the polarizing plate in the high temperature durability test, it is used for manufacturing a polarizing plate, more specifically, for a polarizing film provided on the polarizing plate. It can be preferably used. The PVA film may be used as an optical film such as another retardation film, an agricultural film, a packaging film, or the like.

(Other embodiments)
The PVA film according to another embodiment of the present invention is a PVA film containing PVA and an acid scavenger, and the content of the acid scavenger with respect to 100 parts by mass of the PVA is 0.1 part by mass or more. The PVA film contains 0.1 part by mass or more of an acid scavenger with respect to 100 parts by mass of PVA, and the absorbance A1 and the average thickness D1 (mm) at a wavelength of 210 nm satisfy the above formula (1). Is the same as the PVA film according to the above-described embodiment, except that the above-mentioned is not essential. As the specific embodiment and the preferred embodiment of the PVA film according to the other embodiment, the description relating to the PVA film according to the above-described embodiment can be applied.

(Manufacturing method of PVA film)
The method for producing the PVA film of the present invention is not particularly limited, and a production method in which the thickness and width of the film after film formation become more uniform can be preferably adopted. For example, a film-forming stock solution in which one or more of the above-mentioned PVA, acid trapping agent, and, if necessary, a plasticizer, a surfactant, and other components constituting the PVA film are dissolved in a liquid medium. A film-forming stock solution containing PVA, an acid trapping agent, and, if necessary, one or more of a plasticizer, a surfactant, other components, and a liquid medium, in which PVA is melted. Can be manufactured. The method of adding the acid scavenger to the film-forming stock solution is not particularly limited, and the acid scavenger may be added after the acid scavenger is charged together with PVA, or the acid scavenger may be added after the PVA is dissolved or melted. Good. When the film-forming stock solution contains at least one of an acid scavenger, a plasticizer, a surfactant and other components, it is preferable that those components are uniformly mixed.

Examples of the liquid medium used for preparing the membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and the like. Examples include trimethylolpropane, ethylenediamine and diethylenetriamine. Of these, water is preferable because it has a small impact on the environment and is recoverable.

The volatile content of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc. 50% by mass is preferable, 55% by mass is more preferable, and 60% by mass is further preferable. On the other hand, as the upper limit, 95% by mass is preferable, 90% by mass is more preferable, and 85% by mass is further preferable. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, filtration and defoaming during preparation of the film-forming stock solution are smoothly performed, and PVA with few foreign substances and defects. Film production becomes easier. On the other hand, when the volatile content of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy.

Examples of the film-forming method for forming a PVA film using the above-mentioned film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. The method and the extrusion film forming method are preferable. Above all, the extrusion film forming method is more preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat treated as needed.

The heat treatment temperature is not particularly limited, and may be appropriately adjusted according to the degree of swelling of the PVA film in each range. The heat treatment temperature is preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably 150 ° C. or lower, because discoloration or deterioration of the PVA film is observed if the heat treatment temperature is too high. The lower limit of the heat treatment temperature can be, for example, 80 ° C.

The heat treatment time is not particularly limited and may be appropriately adjusted according to the degree of swelling of the PVA film, etc., but from the viewpoint of efficiently producing the PVA film of the present invention, 1 to 60 minutes is preferable, and 2 to 40 minutes is more preferable. It is preferable, and 3 to 30 minutes is more preferable.

<Polarizing film>
The polarizing film according to an embodiment of the present invention is a polarizing film formed from the above-mentioned PVA film of the present invention. In the polarizing film, a dichroic dye such as an iodine dye or a dichroic organic dye is usually adsorbed on a stretched film obtained by uniaxially stretching and orienting a non-stretched PVA film according to an embodiment of the present invention. It is a film that becomes.

The polarizing film according to another embodiment of the present invention contains PVA, and has the absorbance A2 and the average thickness D2 (mm) at a wavelength of 210 nm after being allowed to stand in a 90% RH atmosphere at 60 ° C. for 100 hours according to the following formula ( It is a polarizing film that satisfies 3). By allowing the film to stand in a 90% RH atmosphere at 60 ° C. for 100 hours, a dichroic dye such as an iodine-based dye is volatilized to form a substantially transparent film. Therefore, by measuring the absorbance after allowing to stand in a 90% RH atmosphere at 60 ° C. for 100 hours, it is necessary to confirm the existence of an acid-capturing group having absorption at a wavelength of 210 nm and the degree of its content. Can be done. The unit of A2 / D2 is mm ^-1 .
A2 / D2 ≧ 9 ・・・ (3)

In relation to the average thickness D2 and the absorbance A2, the lower limit of A2 / D2 is preferably 10 mm ^-1, more preferably 12 mm ^-1, further preferably 14 mm ^-1, still more preferably from 20 mm ^-1, is 25 mm ^-1 Especially preferable. By setting A2 / D2 to the above lower limit or more, the polarizing film can further enhance the acid trapping ability, sufficiently suppress polyene formation in the high temperature durability test, and more sufficiently suppress the decrease in the light transmittance of the polarizing plate. On the other hand, the upper limit of A2 / D2 may be, for example, 100 mm ^-1 , but 80 mm ^-1 is preferable, and 50 mm ^-1 is more preferable. By setting A2 / D2 to the above upper limit or less, the film surface becomes good and the polarization performance of the polarizing film can be improved.

The polarizing film of another embodiment of the present invention also has a dichroism such as an iodine dye or a dichroic organic dye on a stretched film obtained by uniaxially stretching and orienting a non-stretched PVA film according to an embodiment of the present invention. It may be a film formed by adsorbing a dye.

The upper limit of the average thickness D2 of the polarizing film of the present invention is, for example, 100 μm, preferably 50 μm, and more preferably 30 μm. On the other hand, the lower limit of this average thickness may be 1 μm, preferably 5 μm.

(Manufacturing method of polarizing film)
The method for producing the polarizing film of the present invention is not particularly limited, and any conventionally adopted method may be adopted. For example, a polarizing film can be produced by subjecting the PVA film of the present invention to a swelling treatment, a dyeing treatment, a uniaxial stretching treatment, and if necessary, a cross-linking treatment, a fixing treatment, a drying treatment, a heat treatment, and the like. .. In this case, the order of each treatment such as swelling treatment, dyeing treatment, uniaxial stretching, and fixing treatment is not particularly limited, and one or more treatments can be performed at the same time. It is also possible to perform one or more of each process twice or more.

The swelling treatment can be performed by immersing the PVA film in water. The lower limit of the temperature of water when immersed in water is preferably 20 ° C, more preferably 22 ° C, and even more preferably 25 ° C. On the other hand, the upper limit is preferably 40 ° C, more preferably 38 ° C, and even more preferably 35 ° C. The time for immersion in water is preferably 0.1 to 5 minutes, for example. The water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The dyeing treatment is performed using a dichroic dye such as an iodine dye or a dye, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is generally carried out by immersing the PVA film in a solution containing iodine-potassium iodide (particularly an aqueous solution) as a dyeing bath. The concentration of iodine in the dyeing bath is preferably 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 60 ° C.

The cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a cross-linking agent. When the cross-linking treatment is performed, cross-linking is introduced into the PVA film, and uniaxial stretching can be performed at a relatively high temperature. As the cross-linking agent used, one or more kinds of boron compounds such as borate such as boric acid and borax can be used. The concentration of the cross-linking agent in the aqueous solution containing the cross-linking agent is preferably 1 to 15% by mass, more preferably 2 to 7% by mass. The temperature of the aqueous solution containing the cross-linking agent is preferably 20 to 60 ° C.

Uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, in the above-mentioned dyeing bath or in the fixing treatment bath described later. Further, in the case of the dry stretching method, it can be carried out in air. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, still more preferably 1.5 to 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably 0.01 to 10% by mass.

In the wet stretching method, the stretching temperature in uniaxial stretching is preferably 30 to 90 ° C, more preferably 40 to 80 ° C, and even more preferably 50 to 70 ° C.

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

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. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by mass, particularly preferably about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C., particularly preferably 25 to 40 ° C.

The drying treatment is preferably performed at 30 to 150 ° C., and more preferably 50 to 130 ° C. By drying at a temperature within the above range, a polarizing film having excellent dimensional stability can be easily obtained.

<Polarizer>
The polarizing plate of the present invention has the polarizing film of the present invention and a protective film containing a cellulose ester resin. The polarizing plate according to the embodiment of the present invention has, for example, a protective film laminated on at least one surface of the polarizing film with an adhesive.

The protective film is usually a cellulose ester film containing a cellulose ester resin as a main component. The content of the cellulose ester resin in the protective film is preferably 70% by mass or more, more preferably 90% by mass or more. Examples of the cellulose ester resin include cellulose triacetate (triacetyl cellulose: TAC), cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, and cellulose buty. Rate, cellulose acetate biphenylate, cellulose acetate propionate biphenylate and the like can be mentioned, and among these, cellulose triacetate is preferable.

Normally, in a polarizing plate in which a protective film containing a cellulose ester resin is used, when exposed to a high temperature for a long period of time, an acid that promotes polyene formation of the polarizing film is generated by hydrolysis of the cellulose ester of the protective film. Generate. On the other hand, in the polarizing plate, since the polarizing film can capture the acid, polyene formation can be suppressed and a decrease in light transmittance can be suppressed.

Examples of the adhesive for adhering the polarizing film and the protective film include PVA-based adhesives and ultraviolet curable adhesives, but PVA-based adhesives are particularly preferable. An acid scavenger can also be contained in this PVA-based adhesive. As the PVA-based adhesive, an aqueous solution of PVA or the like can be used.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. The evaluation methods adopted in the following examples and comparative examples are shown below.

[Measurement of swelling degree of PVA film]
About 1.5 g of PVA film was collected and cut into about 2 mm × 10 cm. Then, the cut PVA film was wrapped in a mesh (“N-N0110S 115” manufactured by NBC Meshtec Inc.) and immersed in distilled water at 30 ° C. for 15 minutes. Subsequently, the PVA film wrapped in the mesh was subjected to centrifugal dehydration at 3,000 rpm for 5 minutes to remove the mesh, and then the mass (W1) of the PVA film was determined. Subsequently, the PVA film was dried in a dryer at 105 ° C. for 16 hours, and then the mass (W2) was determined. Then, the degree of swelling of the PVA film was calculated by the following formula.
Swelling degree (%) = {(W1) / (W2)} x 100

[Measurement of absorbance A1]
A PVA film was cut into 4 cm squares, and the absorbance in the wavelength range of 200 to 780 nm was measured using a spectrophotometer (“U-4100” manufactured by Hitachi High-Tech Science Co., Ltd.) to determine the absorbance A1 at a wavelength of 210 nm.

[Measurement of absorbance A2]
The polarizing film was cut into 4 cm squares, fixed to a metal frame, and then allowed to stand in a constant temperature and humidity chamber set at 60 ° C. and 90% RH for 100 hours to obtain a transparent film. Then, using a spectrophotometer (“U-4100” manufactured by Hitachi High-Tech Science Corporation), the absorbance of the transparent film in the wavelength range of 200 to 780 nm was measured, and the absorbance A2 at a wavelength of 210 nm was determined.

[Measurement of average thickness D1 and D2]
The average thickness D1 of the PVA film and the average thickness D2 of the polarizing film were measured using a contact type thickness gauge (linear gauge sensor "GS-3813" manufactured by Ono Sokki Co., Ltd.).

[Polarization performance]
(A) Measurement of light transmittance Ts Two square samples of 3 cm in the length direction and 2 cm in the width direction were collected from the polarizing film. In accordance with JIS Z8722: 2009 (measurement method of object color), a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation) was used, and one sample was tilted 45 ° with respect to the length direction. The light transmittance in the case and the light transmittance when tilted by −45 ° were measured, and the average value Ts1 (%) of them was obtained. The measurement was performed by correcting the luminosity factor in the visible light region of the C light source and the 2 ° visual field. In the same manner for the other sample, the light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. The average value of Ts1 and Ts2 was defined as the light transmittance Ts (%) of the polarizing film.
In the following measurement of the degree of polarization V, a sample was prepared so that the light transmittance Ts was 44.0% by adjusting the dyeing treatment conditions, and the degree of polarization was measured.

(B) Measurement of degree of polarization V Light when two samples collected in the above measurement of light transmittance Ts are stacked so that their length directions are parallel and tilted by 45 ° with respect to the length direction. The transmittance and the light transmittance when tilted by −45 ° were measured, and their average value T∥ (%) was obtained. Next, they are stacked so that the length directions are orthogonal to each other, and the light transmittance when tilted by 45 ° with respect to the length direction and the light transmittance when tilted by −45 ° are measured, and their average value T ⊥ (%) was calculated, and the degree of polarization V (%) was calculated by the following formula.
V = {(T∥-T⊥) / (T∥ + T⊥)} ^1/2 × 100
Based on the obtained degree of polarization V, the polarization performance was determined according to the following criteria. In addition, A, B, and C were judged to be good because they could be used without any problem in practical use, and D was judged to be defective.
A: Polarization degree V is 99.0% or more when the transmittance Ts44.0% B: Polarization degree V is 95.0% or more and less than 99.0% when the transmittance Ts44.0% C: Transmittance Ts44 When the degree of polarization V is 9.0% or more and less than 95.0% D: When the transmittance Ts44.0%, the degree of polarization V is less than 90.0%

[High temperature durability test]
(A) Sample preparation Using a polarizing plate cut into 4 cm squares, a 10 cm square glass plate (1 mm thick), and an adhesive sheet cut into 10 cm squares (“MCS70” manufactured by Mitate Imaging Co., Ltd .; thickness 25 μm). Then, the glass plate / adhesive sheet / polarizing plate / adhesive sheet / glass plate were laminated in this order and pressure-bonded using a laminator. At this time, the polarizing plate was laminated on the central portion of the glass plate. Then, using a vacuum laminator (“1522N” manufactured by Nisshinbo Mechatronics Co., Ltd.), a pressure of 10 kPa was applied at 50 ° C. for 5 minutes for further pressure bonding. The obtained sample for high temperature durability test had a light transmittance in the range of 35 to 40% measured by a method for measuring the light transmittance described later.

(B) High temperature durability test The prepared sample for high temperature durability test was put into a dryer at 105 ° C. for 250 hours. Then, the light transmittance of the sample was measured by the method described later. After that, the sample was put into a dryer at 115 ° C. for 70 hours. Then, the light transmittance of the taken-out sample was measured by the method described later.

(C) Measurement of light transmittance About the central part of the sample for high temperature durability test, 45 with respect to the absorption axis direction of the polarizing film using a spectrophotometer with an integrating sphere (“U4100” manufactured by Hitachi High-Tech Science Co., Ltd.). The light transmittance when tilted by ° and the light transmittance when tilted by −45 ° were measured, and their average value T (%) was obtained.
High temperature durability was judged according to the following criteria. In addition, A, B, and C were judged to be good because they could be used without any problem in practical use, and D was judged to be defective.
A: Light transmittance after high temperature durability test is 20% or more B: Light transmittance after high temperature durability test is 10% or more and less than 20% C: Light transmittance after high temperature durability test is 1% or more and less than 10% D: Light transmittance after high temperature durability test is less than 1%

The acid scavengers used in Examples and Comparative Examples are shown below.
Acid trapping agent A: "Carbodilite V-04" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 5 g / water 100 g, carbodiimide group equivalent 339 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.
Acid trapping agent B: "Carbodiimide V-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g / water 100 g, carbodiimide group equivalent 602 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.
Acid trapping agent C: "Carbodiimide SV-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g / water 100 g, carbodiimide group equivalent 429 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.
Acid scavenger D: N, N'-dicyclohexylcarbodiimide (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., solubility less than 1 g / 100 g of water)
Acid scavenger E: 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., solubility 10 g / water 100 g)

[Example 1]
(1) Production of PVA film PVA (a saponified product of a homopolymer of vinyl acetate, the degree of polymerization of PVA is 2,400, and the degree of saponification of PVA is 99.95 mol%) and glycerin (relative to 100 parts by mass of PVA). 10 parts by mass), a surfactant (0.03 parts by mass with respect to 100 parts by mass of PVA) and water were mixed and dissolved at 90 ° C. for 4 hours to obtain an aqueous PVA solution. Then, as an acid scavenger, 10 parts by mass of acid scavenger A was added to 100 parts by mass of PVA, and the mixture was stirred at 85 ° C. for 30 minutes. The amount of the acid scavenger added shown in Table 1 indicates the solid content (parts by mass) of the acid scavenger with respect to 100 parts by mass of PVA, and is equal to the content in the obtained PVA film. Then, the PVA aqueous solution was kept warm at 85 ° C. for 16 hours for defoaming of the PVA aqueous solution.

The obtained PVA aqueous solution was dried on a metal roll at 80 ° C., and the obtained film was heat-treated in a dryer at 110 ° C. for 10 minutes to obtain a PVA film (average thickness 30 μm) having a swelling degree of 200%.

For the obtained PVA film, the absorbance A1 and the average thickness D1 were measured based on the above method, and the ratio A1 / D1 of these was determined. The results are shown in Table 1. In addition, the absorption spectrum of the PVA film obtained in FIG. 1 in the wavelength range of 200 to 400 nm is shown.

(2) Production of Polarizing Film From the obtained PVA film, a test piece having a length direction of 9 cm and a width direction of 10 cm was collected. Both ends of the test piece in the length direction are fixed to a stretching jig so that the size of the stretched portion is 5 cm in the length direction × 10 cm in the width direction, and 24 cm while immersed in water at a temperature of 30 ° C. for 38 seconds. At a stretching rate of / min, uniaxial stretching (first step stretching) was performed in the length direction to 2.2 times the original length. Then, the test piece was immersed in an aqueous iodine / potassium iodide solution at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3% by mass of potassium iodide for 60 seconds at 24 cm / min. In the length direction, uniaxial stretching (second-stage stretching) was performed up to 3.3 times the original length at the stretching rate of. The test piece was then immersed in a boric acid / potassium iodide aqueous solution containing 3% by mass of boric acid and 3% by mass of potassium iodide at a temperature of 30 ° C. for about 20 seconds at 24 cm / min. In the length direction, uniaxial stretching (third step stretching) was performed up to 3.6 times the original length at the stretching rate of. Subsequently, the test piece was immersed in an aqueous solution of boric acid / potassium iodide at a temperature of 58 ° C. containing a concentration of 4% by mass of boric acid and about 5% by mass of potassium iodide at 24 cm / min. In the length direction, uniaxial stretching (fourth step stretching) was performed up to 5.5 times the original length at the stretching rate of. Then, the test piece is immersed in an aqueous potassium iodide solution containing 1.5% by mass of boric acid and 3% by mass of potassium iodide for 10 seconds for fixing treatment, and then dried at 60 ° C. It was dried in a machine for 4 minutes to obtain a polarizing film (average thickness 13 μm).

With respect to the obtained polarizing film, the absorbance A2 and the average thickness D2 were measured based on the above method, and the ratio A2 / D2 of these was determined. In addition, the polarization performance was evaluated by the above method. The results are shown in Table 1.

(3) Production of Polarizing Plate From the obtained polarizing film, test pieces having a length direction of 10 cm and a width direction of 5 cm were collected. A polarizing plate is manufactured by laminating a triacetyl cellulose film on both sides of this test piece (polarizing film) using a PVA-based adhesive (3.5% by mass aqueous solution of PVA) and drying at 60 ° C. for 10 minutes. did. The PVA in the PVA-based adhesive used was a saponification of a homopolymer of vinyl acetate, the degree of polymerization of PVA was 2,400, and the degree of saponification of PVA was 99.95 mol%.

Using a polarizing plate, a high temperature durability test was performed based on the above method to evaluate the light transmittance. The results are shown in Table 1.

[Example 2]
A PVA film, a polarizing film, and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger B was used as the acid scavenger. Each evaluation was performed for these in the same manner as in Example 1. The results are shown in Table 1. In addition, the absorption spectrum of the PVA film obtained in FIG. 1 in the wavelength range of 200 to 400 nm is shown.

[Example 3]
A PVA film, a polarizing film, and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger C was used as the acid scavenger. Each evaluation was performed for these in the same manner as in Example 1. The results are shown in Table 1. In addition, the absorption spectrum of the PVA film obtained in FIG. 1 in the wavelength range of 200 to 400 nm is shown.

[Example 4]
A PVA film, a polarizing film and a polarizing plate were produced in the same manner as in Example 1 except that the content (addition amount) of the acid scavenger A was 1 part by mass with respect to 100 parts by mass of PVA. Each evaluation was performed for these in the same manner as in Example 1. However, the high temperature durability test at 115 ° C. for 70 hours has not been performed. The results are shown in Table 1.

[Example 5]
A PVA film, a polarizing film and a polarizing plate were produced in the same manner as in Example 1 except that the content (addition amount) of the acid scavenger A was 30 parts by mass with respect to 100 parts by mass of PVA. Each evaluation was performed for these in the same manner as in Example 1. However, the high temperature durability test at 115 ° C. for 70 hours has not been performed. The results are shown in Table 1. Since the amount of the acid scavenger added was too large, the film surfaces of the obtained PVA film and polarizing film were poor.

[Example 6]
A PVA film, a polarizing film, and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger D was used as the acid scavenger. Each evaluation was performed for these in the same manner as in Example 1. However, the high temperature durability test at 115 ° C. for 70 hours has not been performed. The results are shown in Table 1. Since the acid scavenger D does not have water solubility and has poor compatibility with PVA, the film surfaces of the obtained PVA film and polarizing film are poor.

[Example 7]
A PVA film, a polarizing film, and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger E was used as the acid scavenger. Each evaluation was performed for these in the same manner as in Example 1. However, the high temperature durability test at 115 ° C. for 70 hours has not been performed. The results are shown in Table 1. Since the molecular weight of the acid scavenger E was small and it was easy to elute during the polarizing film manufacturing process, the amount of the carbodiimide compound remaining in the polarizing film was small, and the A2 / D2 value was small.

[Comparative Example 1]
A PVA film, a polarizing film and a polarizing plate were produced in the same manner as in Example 1 except that no acid scavenger was added. Each evaluation was performed for these in the same manner as in Example 1. The results are shown in Table 1. In addition, the absorption spectrum of the PVA film obtained in FIG. 1 in the wavelength range of 200 to 400 nm is shown.

[Comparative Example 2]
A PVA film, a polarizing film and a polarizing plate were produced in the same manner as in Example 1 except that the content (addition amount) of the acid scavenger A was 0.01 part by mass with respect to 100 parts by mass of PVA. Each evaluation was performed for these in the same manner as in Example 1. The results are shown in Table 1.

As shown in FIG. 1, in the PVA films of Examples 1 to 3 to which an acid scavenger having a carbodiimide group, which is a group capable of capturing an acid, was added, a large absorption appeared in the vicinity of a wavelength of 210 nm. Recognize. As shown in Table 1, the polarizing plate including the polarizing film obtained from the PVA films of Examples 1 to 7 having A1 / D1 of 9 mm ^-1 or more transmits light in a high temperature durability test (105 ° C., 250 h). The decrease in the rate is sufficiently suppressed. In Example 5 in which the amount of the acid scavenger added was large, and in Example 6 in which the water-insoluble acid scavenger was used, the polarization performance of the obtained polarizing film was slightly low due to the deterioration of the film surface. The result was. Further, in Example 4 in which the amount of the acid scavenger added is relatively small, and in Example 7 in which the low molecular weight acid scavenger is used, the residual amount of the acid scavenger in the obtained polarizing film is small, and the high temperature durability is achieved. The result was a little low sex. Comparing Examples 1 to 3 based on the results of the high temperature durability test (105 ° C., 250 ° C. + 115 ° C., 70 h), it can be seen that the higher the value of A2 / D2, the higher the high temperature durability.

The PVA film according to the present invention is suitably used as a raw film or the like of a polarizing film used for a polarizing plate.

Claims

A polyvinyl alcohol film containing polyvinyl alcohol and having an absorbance A1 at a wavelength of 210 nm and an average thickness D1 (mm) satisfying the following formula (1).
A1 / D1 ≧ 9 ・・・ (1)
The polyvinyl alcohol film according to claim 1, wherein the absorbance A1 and the average thickness D1 (mm) satisfy the following formula (2).
9 ≤ A1 / D1 ≤ 80 ... (2)
The polyvinyl alcohol film according to claim 1 or 2, which contains an acid scavenger.
A polyvinyl alcohol film containing polyvinyl alcohol and an acid scavenger, wherein the content of the acid scavenger with respect to 100 parts by mass of the polyvinyl alcohol is 0.1 part by mass or more.
The polyvinyl alcohol film according to claim 3 or 4, wherein the acid scavenger is an organic compound.
The polyvinyl alcohol film according to claim 5, wherein the acid scavenger is a carbodiimide compound having at least one carbodiimide group.
The polyvinyl alcohol film according to any one of claims 3 to 6, wherein the acid scavenger is water-soluble.
The polyvinyl alcohol film according to claim 7, wherein the acid scavenger is a polymer.
The polyvinyl alcohol film according to any one of claims 1 to 8, wherein the degree of saponification of the polyvinyl alcohol is 90 mol% or more.
The polyvinyl alcohol film according to any one of claims 1 to 9, which is used for manufacturing a polarizing plate.
A polarizing film formed from the polyvinyl alcohol film according to any one of claims 1 to 10.
A polarizing film containing polyvinyl alcohol and having an absorbance A2 at a wavelength of 210 nm and an average thickness D2 (mm) satisfying the following formula (3) after being allowed to stand in a 90% RH atmosphere at 60 ° C. for 100 hours.
A2 / D2 ≧ 9 ・・・ (3)
A polarizing plate having the polarizing film according to claim 11 or 12 and a protective film containing a cellulose ester resin.