JP7345541B2 - Polyvinyl alcohol film, polarizing film, and polarizing plate - Google Patents

Description

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

A polarizing plate, which has the function of transmitting and blocking light, is a basic component of a liquid crystal display (LCD), along 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 a polarizing film. The polarizing film constituting the polarizing plate is a stretched film made by uniaxially stretching and orienting a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA"), and an iodine dye (I ₃ ^- or The mainstream is one in which dichroic dyes such as I ₅ ^- , etc.) and dichroic organic dyes are adsorbed. Such polarizing films can be produced by uniaxially stretching a PVA film pre-contained with a dichroic dye, by adsorbing a dichroic dye at the same time as the PVA film is uniaxially stretched, or by uniaxially stretching a PVA film and then adding dichroism to the film. It is manufactured by adsorbing pigments.

LCDs have come to be used in a wide range of applications, including small devices such as calculators and wristwatches, notebook computers, liquid crystal televisions, mobile phones, and tablet terminals. 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 higher durability under harsher environments than before.

An image display device constructed by laminating a polarizing plate between an image display cell and a transparent plate such as a front panel or touch panel through an adhesive layer can be used for long periods of time at high temperatures required for in-vehicle displays. It is known that the light transmittance of a polarizing plate decreases when subjected to a durability test. This is said to be one of the causes of polyenization of PVA constituting the polarizing film, and the lower the temperature is, the more remarkable the decrease in the light transmittance of the polarizing plate becomes.

Regarding such a problem of polyenization of a polarizing plate, Patent Document 1 describes that polyenization can be suppressed by employing a polarizing plate provided with a highly moisture permeable protective film on the surface of the polarizing film. Patent Document 2 describes that polyenization can be suppressed by adjusting the thickness of the adhesive used for bonding the polarizing plate and the image display cell or the transparent plate and the absorbance of the polarizing film.

Japanese Patent Application Publication No. 2014-102353 JP2018-25764A

However, according to the inventors' studies, the methods described in Patent Documents 1 and 2 tend to suppress the decrease in the light transmittance of the polarizing plate; In a durability test under a high-temperature environment, it was not possible to confirm a sufficient polyenization suppressing effect.

The present invention has been made based on the above-mentioned circumstances, and provides a PVA film that can produce a polarizing film that can sufficiently suppress a decrease in light transmittance of a polarizing plate in a high-temperature durability test, and a PVA film such as this. An object of the present invention is to provide a polarizing film obtained using the film and a polarizing plate obtained using the polarizing film.

As a result of intensive studies to achieve the above object, the present inventors found that the polyenization of PVA in the polarizing film included in the polarizing plate is promoted by the acid generated from the protective film, and that the polarizing film or the polarizing film It was discovered that polyenization can be suppressed by imparting an acid-trapping function to the PVA film, which is the original film of the invention, and based on these findings, further studies were conducted 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 is 0.1 parts by mass or more based on 100 parts by mass of the polyvinyl alcohol;
[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 of any one of [1] to [9], which is used for manufacturing a polarizing plate;
[11] A polarizing film formed from the polyvinyl alcohol film of any one of [1] to [10];
[12] A polarizing film containing polyvinyl alcohol, whose absorbance A2 at a wavelength of 210 nm and average thickness D2 (mm) satisfy the following formula (3) after being left to stand for 100 hours in an atmosphere of 60° C. and 90% RH;
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 that can sufficiently suppress a decrease in light transmittance of a polarizing plate in a high temperature durability test, a polarizing film obtained using such a PVA film, and a polarizing film obtained using this PVA film, A polarizing plate obtained using a film can be provided.

FIG. 1 shows the absorption spectra of the PVA films of Examples 1 to 3 and Comparative Example 1.

Embodiments of the present invention will be described in detail below.
<PVA film>
A PVA film according to an embodiment of the present invention is a PVA film that contains PVA and has an absorbance A1 at a wavelength of 210 nm and an average thickness D1 (mm) that satisfy the following formula (1).
A1/D1≧9...(1)

Here, the average thickness D1 of the PVA film refers to the average value of values measured at ten arbitrary points. The same applies to the average thickness of the film below. Further, the unit of A1/D1 is mm ⁻¹ .

Absorption at a wavelength of 210 nm is derived from a group capable of capturing acid. As shown in Comparative Example 1, which will be described later, even in a PVA film to which no component having a group capable of capturing acid is added, there is some absorption near the wavelength of 210 nm, and the value of A1/D1 is 8 mm ^-1. (See Table 1 and Figure 1). On the other hand, by adding a component having a group capable of capturing acid, the absorption near the wavelength of 210 nm increases (see Examples 1 to 3 in FIG. 1). If there are many acid-capturing groups in the PVA film and the value of A1/D1 is 9 mm ^-1 or more, that is, if the PVA film satisfies the above formula (1), the PVA film will sufficiently capture the acid. can do. On the other hand, when a polarizing plate comprising a polarizing film, which is a stretched PVA film, and a protective film containing cellulose ester is exposed to high temperatures for a long period of time, the cellulose ester that makes up the protective film is hydrolyzed, resulting in acid release. generate. It is presumed that this acid acts as a catalyst for the dehydration reaction of PVA and converts PVA into a polyene. On the other hand, in a polarizing plate equipped with a polarizing film obtained using a PVA film that satisfies formula (1), the acid generated from the protective film is captured by the acid-capturing group present in the polarizing film, Polyenization of PVA in a polarizing film in a polarizing plate can be suppressed. That is, according to the PVA film, it is possible to produce a polarizing film that can sufficiently suppress a decrease in the light transmittance of a polarizing plate in a high-temperature durability test.

A carbodiimide group (-N=C=N-) is an example of a group capable of capturing acid and having absorption at a wavelength of 210 nm. The PVA film according to one embodiment of the present invention may contain a compound having a carbodiimide group (acid scavenger), or may use PVA having a carbodiimide group, but may not contain an acid scavenger. is preferred. A compound having a carbodiimide group (acid scavenger) usually has 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 include an acid scavenger having an absorption maximum near a wavelength of 210 nm. Additionally, the PVA film according to one 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 over the entire wavelength range of 360 nm to 780 nm, more preferably 0.1 or less.

In the relationship between the absorbance A1 and the average thickness D1, the lower limit of A1/D1 is preferably 10 mm ^-1 , more preferably 12 mm ^-1 , even more preferably 14 mm ^-1 , even more preferably 20 mm ^-1 , and even more preferably 25 mm ^-1. is particularly preferred. By setting A1/D1 to the above lower limit or more, a polarizing film that can further enhance the acid scavenging ability, exhibit sufficient polyenization suppressing function in high temperature durability tests, and more fully suppress the decrease in light transmittance of the polarizing plate. can be manufactured. On the other hand, the upper limit of A1/D1 may be, for example, 100 mm ^-1 , but preferably 80 mm ^-1 and more preferably 50 mm ^-1 . By controlling A1/D1 to be less than or equal to the above upper limit, the film surface becomes good and the polarizing performance of the polarizing film obtained can be improved. In the PVA film according to one 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 amount of the group having absorption at a wavelength of 210 nm. For example, the value of A1/D1 can be adjusted by adjusting 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 vinyl alcohol units (-CH ₂ -CH(OH)-) as its main structural unit. PVA may have vinyl ester units and other units in addition to vinyl alcohol units.

As PVA, one obtained by saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters can be used. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, and the like. Among vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C=CH-O-CO-) in the molecule are preferred from the viewpoint of ease of production, availability, cost, etc., and vinyl acetate is more preferred. preferable.

The polyvinyl ester is preferably one obtained using only one type or two or more types of vinyl ester as a monomer, and more preferably a polyvinyl ester obtained using only one type of vinyl ester as a monomer. It may be a copolymer resin of one or more vinyl esters and other monomers copolymerizable with the vinyl esters, as long as the effects of the present invention are 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%, and 5 mol%, based on the number of moles of all structural units constituting PVA. is more preferable, and even more preferably 1 mol%.

Other monomers copolymerizable with vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salt; (meth)acrylic Methyl acid, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, (meth)acrylate (meth)acrylic acid esters such as t-butyl acid, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide; N-methyl (meth)acrylamide , N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamidopropanesulfonic acid or its salt, (meth)acrylamidopropyldimethylamine or its salt, N-methylol (Meth)acrylamide derivatives such as (meth)acrylamide or its derivatives; N-vinylamide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether , n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and other vinyl ethers; (meth)acrylonitrile and other vinyl cyanides; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc. Vinyl halides; allyl compounds such as allyl acetate and allyl chloride; maleic acid, or its salts, esters, or acid anhydrides; itaconic acid, or its salts, esters, or acid anhydrides; vinyl silyl compounds such as vinyltrimethoxysilane; Examples include saturated sulfonic acids or salts thereof.

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

As PVA, one that is not graft copolymerized can be preferably used. However, PVA may be modified with one or more graft copolymerizable monomers. Graft copolymerization can be performed on at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of monomers that can be graft copolymerized include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; and α-olefins having 2 to 30 carbon atoms. The proportion of structural units derived from graft copolymerizable monomers in 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.

PVA may have some of its hydroxy groups crosslinked or may not be crosslinked. Further, a part of the hydroxyl group of PVA may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure.

The lower limit of the degree of polymerization of PVA is preferably 1,000, more preferably 1,500, and even more preferably 1,700. 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 this 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 below the above upper limit, it is possible to suppress an increase in the manufacturing cost of PVA and the occurrence of defects during film formation. Note that the degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, and preferably 99 mol% or more, since the resulting polarizing film has good heat and humidity resistance. It is more preferable, and particularly preferably 99.5 mol% or more. The upper limit of this degree of saponification is not particularly limited, and may be 100 mol% or 99.99 mol%. The saponification degree 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) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. say. The degree of saponification can be measured according to the description in JIS K6726-1994.

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

(acid scavenger)
Acid scavengers, which are preferred components of the PVA film according to one embodiment of the present invention, are compounds that react with acids to inactivate them. Examples of acid scavengers include organic compounds such as compounds having a carbodiimide group, compounds having an epoxy group, compounds having an oxazoline group, alkyl phosphate metal salts, strong basic amino compounds, terpene compounds, and oxazine compounds; Examples include inorganic compounds such as hydrotalcite stones. An organic compound refers to a compound containing carbon, and an inorganic compound refers to a compound other than an organic compound. Note that the acid scavenger is sometimes referred to as an acid scavenger, an acid scavenger, an acid catcher, etc., but in the present invention, it can be used regardless of these names. One type of acid scavenger may be used alone, or two or more types may be used in combination.

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

Among the acid scavengers, carbodiimide compounds having at least one carbodiimide group are more preferred. Carbodiimide compounds have a large effect of suppressing polyenization, and are also preferable from the viewpoint of ease of handling and safety.

The mass (molecular formula weight) per mol of acid-capturing group 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 weight) per mol of acid-capturing group is also referred to as carbodiimide group equivalent, and is the mass per mol of carbodiimide group.

Preferably, the acid scavenger is water-soluble. By using a water-soluble acid scavenger that is easily compatible with PVA, it is possible to obtain a PVA film with high light transmittance, low haze, and a good film surface, and a polarizing film with good polarization performance. In addition, "water-soluble" means that the solubility in water is 1 g/100 g of water or more. Solubility in water refers to the limit amount (mass) that can be dissolved in 100 g of water at 20°C. The lower limit of the solubility of the acid scavenger in water is preferably 2 g/100 g of water, more preferably 3 g/100 g of water. By setting the solubility in water to the above lower limit or more, the acid scavenger and PVA become more compatible with each other, the film surface of the resulting 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 this solubility may be, for example, 200 g/100 g of water, preferably 100 g/100 g of water, more preferably 50 g/100 g of water, 20 g/100 g of water, and even more preferably 8 g/100 g of water. When the solubility in water is below the above upper limit, elution of the acid scavenger can be suppressed when a polarizing film is produced by stretching the PVA film in a treatment liquid.

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 producing a polarizing film by subjecting a PVA film to a swelling treatment, dyeing treatment, stretching treatment, etc. in a treatment liquid, it is preferable that the acid scavenger in the PVA film is difficult to dissolve into the treatment liquid. When the acid scavenger is a polymer, the elution of the acid scavenger in the processing liquid is suppressed due to entanglement between the molecular chains of PVA and the molecular chains of the acid scavenger, and the light transmission of the polarizing plate is reduced in the high temperature durability test. It is possible to obtain a polarizing film that can more fully suppress a decrease in polarization. As mentioned above, from the viewpoint of the polarizing performance of the resulting polarizing film, it is preferable to use an acid scavenger that has water solubility and is compatible with PVA. However, a water-soluble acid scavenger, especially if it has a low molecular weight, is likely to be eluted into the processing liquid, which is an aqueous solution. Therefore, by using an acid scavenger that is water-soluble and polymeric, we have created a polarizing film that has good polarizing performance and can more fully suppress the decrease in light transmittance of the polarizing plate in high-temperature durability tests. can be manufactured.

The term "polymer" refers to a molecule having a weight average molecular weight of 300 or more, preferably 1,000 or more, and more preferably 3,000 or more. On the other hand, the upper limit of the weight average molecular weight of the polymeric acid scavenger may be, for example, 100,000 or 10,000. Commercially available polymeric acid scavengers include, for example, 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 parts by mass, more preferably 0.5 parts by mass, even more preferably 2 parts by mass, and more preferably 5 parts by mass based on 100 parts by mass of PVA. More preferred. By setting the content of the acid scavenger to the above lower limit or more, the acid scavenging ability is increased, sufficient polyenization suppressing function is exhibited in the high temperature durability test, and the polarization can more fully suppress the decrease in 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 controlling the content of the acid scavenger to be less than or equal to the above upper limit, the film surface becomes good and the polarizing performance of the polarizing film obtained can be improved.

(Plasticizer)
The PVA film may contain a plasticizer. When the PVA film contains a plasticizer, it is possible to improve the handleability and stretchability of the PVA film. Polyhydric alcohols are preferably used as plasticizers, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. may contain one or more of these plasticizers. Among these, glycerin is preferred because it improves the stretchability of the PVA film.

The lower limit of the plasticizer content in the PVA film is preferably 2 parts by mass, more preferably 3 parts by mass, and even more preferably 4 parts by mass based on 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 based on 100 parts by mass of PVA. When the content of the plasticizer in the PVA film is 2 parts by mass or more based on 100 parts by mass of PVA, the stretchability of the PVA film is improved. On the other hand, by setting the content of plasticizer in the PVA film to 20 parts by mass or less per 100 parts by mass of PVA, it is possible to suppress the plasticizer from bleeding out onto the surface of the PVA film and reducing the handleability of the PVA film. be able to.

(surfactant)
The PVA film may contain a surfactant. When manufacturing a PVA film using a film-forming stock solution as described below, adding a surfactant to the film-forming stock solution improves film-forming properties and suppresses the occurrence of uneven film thickness. In addition, when metal rolls or belts are used for film formation, the PVA film can be easily peeled from these metal rolls or belts. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film may contain the surfactant. There are no particular limitations on the type of surfactant that is blended into the film-forming stock solution for producing the PVA film, and ultimately the type of surfactant that is contained in the PVA film. Preferred are surfactants and nonionic surfactants, with nonionic surfactants being particularly preferred. One kind of surfactant can be used alone or two or more kinds can be used in combination.

Examples of anionic surfactants include carboxylic acid types such as potassium laurate; sulfuric acid ester types such as octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene lauryl amino ether Alkylamine types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxyalkylene Examples include allyl phenyl ether types such as allyl phenyl ether.

When a surfactant is blended into a film-forming stock solution for producing a PVA film, the lower limit of the surfactant content in the film-forming stock solution and, ultimately, the lower limit of the surfactant content in the PVA film is determined by the film-forming stock solution or the lower limit of the surfactant content in the PVA film. It is preferably 0.01 parts by mass, more preferably 0.02 parts by mass, based on 100 parts by mass of PVA contained in the PVA film. On the other hand, the upper limit of the surfactant content in the film-forming stock solution and, ultimately, the surfactant content in the PVA film is 0.5 parts by mass per 100 parts by mass of PVA contained in the film-forming stock solution or PVA film. Preferably, 0.1 part by mass is more preferable. When the content of the surfactant is 0.01 parts by mass or more based on 100 parts by mass of PVA, film forming properties and peelability can be improved. On the other hand, by setting the surfactant content to 0.5 parts by mass or less per 100 parts by mass of PVA, the surfactant bleeds out on the surface of the PVA film, causing blocking and reducing the ease of handling. Can be suppressed.

(Other ingredients, etc.)
The PVA film may contain other components other than the above-mentioned PVA, acid scavenger, plasticizer, and surfactant, such as antioxidant, antifreeze agent, pH adjuster, masking agent, color inhibitor, and oil agent, as necessary. may contain. 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. Moreover, the content of the inorganic compound in the PVA film may also be preferably 1% by mass or less, and more preferably 0.1% by mass or less. The other components and inorganic compounds mentioned above may cause defects such as voids in the resulting polarizing film. Therefore, by reducing the content of the other components and inorganic compounds, the polarizing performance of the resulting polarizing film tends to improve.

Moreover, it is preferable that the PVA film does not substantially contain components having large absorption at a wavelength of 210 nm other than PVA and the acid scavenger. For this reason, the content of other components other than PVA, acid scavenger, plasticizer, and surfactant in the PVA film is preferably 1% by mass or less, and more preferably 0.1% by mass or less. There are some good things.

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 this 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, handling properties can be improved.

Although there is no particular restriction on the shape of the PVA film, a long film is preferred since polarizing films can be manufactured continuously with good productivity. The length of the long film is not particularly limited, and can be appropriately set depending on the use of the polarizing film to be produced, and can be, for example, within a range of 5 to 20,000 m. There is no particular restriction on the width of the long film, and it can be, for example, 50 cm or more, but since wide polarizing films have been in demand in recent years, it is preferably 1 m or more, and more preferably 2 m or more. Preferably, the length is more preferably 4 m or more. Although there is no particular restriction on the upper limit of the width of the long film, if the width is too wide, it tends to be difficult to stretch it uniformly when producing a polarizing film using a device that is in practical use. For this reason, the width of the PVA film is preferably 7 m or less.

There is no particular restriction on the shape of the PVA film, and it may be a single-layer film or a multi-layer film (laminate), but from the viewpoint of the complexity and cost of laminating (coating, etc.) work, single-layer film is preferred. Preferably, it is a film. The PVA film may be a stretched film or a non-stretched film, but is preferably a non-stretched film. A non-stretched PVA film is suitably used as a raw film for a polarizing film described below.
The polarizing film obtained using the PVA film can sufficiently suppress the decrease in light transmittance of the polarizing plate in a high temperature durability test, so it can be used for manufacturing polarizing plates, more specifically, for polarizing films included in polarizing plates. It can be suitably used. The PVA film may be used as other optical films such as retardation films, agricultural films, packaging films, and the like.

(Other embodiments)
A PVA film according to another embodiment of the present invention includes PVA and an acid scavenger, and the content of the acid scavenger is 0.1 parts by mass or more based on 100 parts by mass of the PVA. The PVA film contains 0.1 part by mass or more of an acid scavenger per 100 parts by mass of PVA, and the absorbance A1 at a wavelength of 210 nm and the average thickness D1 (mm) satisfy the above formula (1). It is the same as the PVA film according to the embodiment described above, except that it is not essential. The description regarding the PVA film according to one embodiment described above can be applied to specific aspects and preferred aspects of the PVA film according to other embodiments.

(PVA film manufacturing method)
The method for manufacturing the PVA film of the present invention is not particularly limited, and a manufacturing method that provides a more uniform thickness and width of the film after film formation can be preferably employed. For example, a film-forming stock solution in which one or more of the above-mentioned PVA, an acid scavenger, and, if necessary, a plasticizer, a surfactant, and other components constituting the PVA film are dissolved in a liquid medium. A membrane forming solution containing PVA, an acid scavenger, and, if necessary, one or more of a plasticizer, a surfactant, other components, and a liquid medium, and in which PVA is melted is used. It can be manufactured using The method of adding the acid scavenger to the membrane forming stock solution is not particularly limited, and the acid scavenger may be dissolved or melted after being charged with PVA, or the acid scavenger may be added after dissolving or melting PVA. 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 these 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, Examples include trimethylolpropane, ethylenediamine, and diethylenetriamine. Among these, water is preferable because it has a small impact on the environment and is easy to recover.

The volatile fraction of the film-forming stock solution (the content ratio in the film-forming stock solution of volatile components such as liquid media that are removed by volatilization or evaporation during film formation) varies depending on the film-forming method, film-forming conditions, etc., but its lower limit is The amount is preferably 50% by mass, more preferably 55% by mass, and even more preferably 60% by mass. On the other hand, this upper limit is preferably 95% by mass, more preferably 90% by mass, and even more preferably 85% by mass. By having a volatile fraction of the membrane-forming stock solution of 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, filtration and defoaming are performed smoothly during the preparation of the film-forming stock solution, and PVA is free from foreign substances and defects. Film manufacturing becomes easier. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and industrial production of a PVA film becomes easy.

Film forming methods for forming PVA films using the above film forming stock solution include, for example, cast film forming methods, extrusion film forming methods, wet film forming methods, gel film forming methods, etc. and extrusion film forming methods are preferred. Among these, the extrusion film forming method is more preferable because a PVA film with uniform thickness and width and good physical properties can be obtained. The PVA film can be subjected to drying or heat treatment if necessary.

There is no particular restriction on the heat treatment temperature, and it may be adjusted as appropriate depending on 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, and even more preferably 150°C or lower, since discoloration or deterioration of the PVA film may occur if the 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 adjusted appropriately depending on the degree of swelling of the PVA film, etc., but from the viewpoint of efficiently producing the PVA film of the present invention, the heat treatment time is preferably 1 to 60 minutes, more preferably 2 to 40 minutes. Preferably, 3 to 30 minutes is more preferable.

<Polarizing film>
A polarizing film according to one embodiment of the present invention is a polarizing film formed from the PVA film of the present invention described above. The polarizing film is usually made by adsorbing a dichroic dye such as an iodine dye or a dichroic organic dye to a stretched film that is an embodiment of the present invention, which is an unstretched PVA film that is uniaxially stretched and oriented. It's a film.

A polarizing film according to another embodiment of the present invention contains PVA, and has an absorbance A2 at a wavelength of 210 nm and an average thickness D2 (mm) of the following formula ( It is a polarizing film that satisfies 3). Note that by standing for 100 hours in an atmosphere of 60° C. and 90% RH, dichroic dyes such as iodine dyes are volatilized, resulting in a substantially transparent film. Therefore, by measuring the absorbance after standing in an atmosphere of 60°C and 90% RH for 100 hours, it is possible to confirm the presence and content of groups capable of capturing acids that have absorption at a wavelength of 210 nm. I can do it. Further, the unit of A2/D2 is mm ⁻¹ .
A2/D2≧9...(3)

In the relationship between the absorbance A2 and the average thickness D2, the lower limit of A2/D2 is preferably 10 mm ^-1 , more preferably 12 mm ^-1 , even more preferably 14 mm ^-1 , even more preferably 20 mm ^-1 , and even more preferably 25 mm ^-1 . Particularly preferred. By setting A2/D2 to the above-mentioned lower limit or more, a polarizing film that can further enhance acid scavenging ability, sufficiently suppress polyenization in a high-temperature durability test, and more fully suppress a decrease in light transmittance of a polarizing plate can be obtained. On the other hand, the upper limit of A2/D2 may be, for example, 100 mm ^-1 , but preferably 80 mm ^-1 and more preferably 50 mm ^-1 . By setting A2/D2 to the above upper limit or less, the film surface becomes good and the polarizing performance of the polarizing film can be improved.

Polarizing films according to other embodiments of the present invention also include dichroic dyes such as iodine dyes and dichroic organic dyes on stretched films that are oriented by uniaxially stretching the unstretched PVA film that is 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 employed method may be employed. For example, a polarizing film can be produced by subjecting the PVA film of the present invention to swelling treatment, dyeing treatment, uniaxial stretching, and, if necessary, further crosslinking treatment, fixing treatment, drying treatment, heat treatment, etc. . 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 simultaneously. Also, one or more of each process can be performed two or more times.

The swelling treatment can be performed by immersing the PVA film in water. The lower limit of the water temperature during immersion in water is preferably 20°C, more preferably 22°C, and even more preferably 25°C. On the other hand, this upper limit is preferably 40°C, more preferably 38°C, and even more preferably 35°C. Further, the time for immersion in water is preferably 0.1 to 5 minutes, for example. Note that the water used for immersion 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 may be performed at any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally carried out by immersing the PVA film in a solution (especially an aqueous solution) containing iodine and potassium iodide as a dye 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. Further, the temperature of the dyeing bath is preferably 20 to 60°C.

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

The 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, or it can be carried out in the above-mentioned dyeing bath or in the fixing bath described below. Moreover, in the case of a dry stretching method, it can be carried out in air. Among these, wet stretching is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. 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, and even more preferably 1.5 to 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and its concentration 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 stretching ratio in uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more from the viewpoint of polarizing performance of the polarizing film obtained. Although the upper limit of the stretching ratio is not particularly limited, it is preferable that the stretching ratio is 8 times or less.

When producing a polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dichroic dye onto the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more boron compounds such as boric acid and borax can be used. Further, an iodine compound or a metal compound may be added to the fixing treatment bath as necessary. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by weight, particularly about 3 to 10% by weight. The temperature of the fixing treatment bath is preferably 15 to 60°C, particularly 25 to 40°C.

The drying treatment is preferably carried out at a temperature of 30 to 150°C, particularly preferably 50 to 130°C. By drying at a temperature within the above range, a polarizing film with excellent dimensional stability can be easily obtained.

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

The protective film is usually a cellulose ester film containing cellulose ester resin as a main component. The content of cellulose ester resin in the protective film is preferably 70% by mass or more, more preferably 90% by mass or more. Examples of cellulose ester resins include cellulose triacetate (triacetylcellulose: TAC), cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, and cellulose butyrate. Among these, cellulose triacetate is preferred.

Normally, when a polarizing plate using a protective film containing cellulose ester resin is exposed to high temperatures for a long period of time, the acid that promotes polyenization of the polarizing film may cause hydrolysis of the cellulose ester in the protective film. generate. On the other hand, in the polarizing plate, since the polarizing film can capture acid, polyenization can be suppressed, and a decrease in light transmittance can be suppressed.

Examples of the adhesive for bonding the polarizing film and the protective film include PVA adhesives and ultraviolet curing adhesives, among which PVA adhesives are preferred. This PVA adhesive can also contain an acid scavenger. As the PVA adhesive, an aqueous solution of PVA or the like can be used.

The present invention will be specifically explained by the following examples, but the present invention is not limited to these examples in any way. In addition, each evaluation method adopted in the following examples and comparative examples is shown below.

[Measurement of swelling degree of PVA film]
Approximately 1.5 g of PVA film was collected and cut into approximately 2 mm x 10 cm. Thereafter, the cut PVA film was wrapped in a mesh ("N-N0110S 115" manufactured by NBC Meshtech Co., Ltd.) 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, and after removing the mesh, 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 its mass (W2) was determined. Then, the degree of swelling of the PVA film was calculated using the following formula.
Swelling degree (%) = {(W1)/(W2)}×100

[Measurement of absorbance A1]
The PVA film was cut into 4 cm square pieces, 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 the wavelength of 210 nm.

[Measurement of absorbance A2]
The polarizing film was cut into 4 cm square pieces, fixed to a metal frame, and left standing in a constant temperature and humidity machine set at 60° C. and 90% RH for 100 hours to obtain a transparent film. Thereafter, the absorbance of the transparent film in the wavelength range of 200 to 780 nm was measured using a spectrophotometer (“U-4100” manufactured by Hitachi High-Tech Science Co., Ltd.), and the absorbance A2 at the 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 thickness meter (linear gauge sensor "GS-3813" manufactured by Ono Sokki Co., Ltd.).

[Polarization performance]
(a) Measurement of light transmittance Ts Two square samples measuring 3 cm in the length direction x 2 cm in the width direction were taken from the polarizing film. In accordance with JIS Z8722:2009 (object color measurement method), one sample was tilted at 45° with respect to the length direction using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation). The light transmittance when tilted at -45° and the light transmittance when tilted at −45° were measured, and their average value Ts1 (%) was determined. Note that the measurements were performed using a C light source and with visibility correction in the visible light region with a 2° field of view. Similarly, for the other sample, the light transmittance when tilted at 45 degrees and the light transmittance when tilted at -45 degrees were measured, and their average value Ts2 (%) was determined. 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 polarization degree V The light obtained when the two samples collected in the measurement of the light transmittance Ts above are stacked so that their length directions are parallel and are tilted at 45 degrees with respect to the length direction. The transmittance and the light transmittance when tilted at −45° were measured, and their average value T∥(%) was determined. Next, stack them so that the length directions are perpendicular to each other, measure the light transmittance when tilted at 45 degrees with respect to the length direction, and the light transmittance when tilted at -45 degrees, and calculate the average value T. ⊥(%) was determined, and the degree of polarization V (%) was determined using the following formula.
V={(T∥−T⊥)/(T∥+T⊥)} ^1/2 ×100
Based on the obtained polarization degree V, the polarization performance was determined according to the following criteria. Note that A, B, and C were judged to be good because they could be used practically without any problem, and D was judged to be bad.
A: When transmittance Ts is 44.0%, polarization degree V is 99.0% or more. B: When transmittance Ts is 44.0%, polarization degree V is 95.0% or more and less than 99.0%. C: Transmittance Ts44 .0%, the degree of polarization V is 90.0% or more and less than 95.0% D: When the transmittance Ts is 44.0%, the degree of polarization V is less than 90.0%

[High temperature durability test]
(a) Sample preparation A polarizing plate was cut into 4 cm square pieces, and a 10 cm square glass plate (1 mm thickness) and an adhesive sheet (“MCS70” manufactured by Bidate Imaging Co., Ltd.; thickness 25 μm) cut into 10 cm square pieces were used. Then, the glass plate/adhesive sheet/polarizing plate/adhesive sheet/glass plate were laminated in this order and pressed together using a laminator. At this time, the polarizing plate was laminated at the center of the glass plate. Thereafter, using a vacuum laminator ("1522N" manufactured by Nisshinbo Mechatronics Co., Ltd.), a pressure of 10 kPa was applied at 50° C. for 5 minutes to further pressure bond. Note that the obtained sample for the high temperature durability test had a light transmittance within the range of 35 to 40% as measured by the method of measuring light transmittance described below.

(b) High-temperature durability test The prepared sample for high-temperature durability test was placed in a dryer at 105° C. for 250 hours. Thereafter, the light transmittance of the sample was measured by the method described below. Furthermore, after that, the sample was placed in a dryer at 115° C. for 70 hours. Thereafter, the light transmittance of the sample taken out was measured by the method described below.

(c) Measurement of light transmittance The central part of the sample for high temperature durability test was measured using a spectrophotometer with an integrating sphere (“U4100” manufactured by Hitachi High-Tech Science Co., Ltd.) at 45°C with respect to the absorption axis direction of the polarizing film. The light transmittance when tilted at an angle of -45° and the light transmittance when tilted at -45° were measured, and their average value T (%) was determined.
High temperature durability was determined based on the following criteria. Note that A, B, and C were judged to be good because they could be used practically without any problem, and D was judged to be bad.
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 scavenger A: "Carbodilite V-04" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 5 g/100 g water, carbodiimide group equivalent 339 g/mol), which is a high molecular weight (molecular weight approximately 1,000 to 5,000) carbodiimide compound.
Acid scavenger B: "Carbodilite V-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g/100 g water, carbodiimide group equivalent 602 g/mol), which is a high molecular weight (molecular weight approximately 1,000 to 5,000) carbodiimide compound.
Acid scavenger C: "Carbodilite SV-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g/100 g water, carbodiimide group equivalent 429 g/mol), which is a high molecular weight (molecular weight approximately 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 10g/water 100g)

[Example 1]
(1) Production of PVA film PVA (saponified vinyl acetate homopolymer, the degree of polymerization of PVA is 2,400, the degree of saponification of PVA is 99.95 mol%) and glycerin (per 100 parts by mass of PVA) (10 parts by mass), a surfactant (0.03 parts by mass based on 100 parts by mass of PVA), and water were mixed and dissolved at 90° C. for 4 hours to obtain a PVA aqueous solution. Thereafter, 10 parts by mass of acid scavenger A was added as an acid scavenger to 100 parts by mass of PVA, and the mixture was stirred at 85° C. for 30 minutes. Note that the amount of acid scavenger added in Table 1 refers to the solid content (parts by mass) of the acid scavenger relative to 100 parts by mass of PVA, and is equal to the content in the obtained PVA film. Thereafter, the PVA aqueous solution was kept at 85° C. for 16 hours to defoam 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) with a degree of swelling of 200%.

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

(2) Manufacture of polarizing film A test piece measuring 9 cm in the length direction x 10 cm in the width direction was taken from the obtained PVA film. Both ends of the test piece in the length direction were fixed to a stretching jig so that the size of the stretched portion was 5 cm in the length direction x 10 cm in the width direction, and while immersed in water at a temperature of 30 ° C. for 38 seconds, the length of the stretched portion was 24 cm. Uniaxial stretching (first stage stretching) was carried out in the longitudinal direction to 2.2 times the original length at a stretching speed of /min. Thereafter, the test piece was immersed for 60 seconds in an iodine/potassium iodide aqueous solution containing 0.03% by mass of iodine and 3% by mass of potassium iodide at a temperature of 30°C, at a rate of 24 cm/min. The film was uniaxially stretched in the length direction to 3.3 times the original length (second stage stretching) at a stretching speed of . Next, the test piece was immersed for about 20 seconds 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. The film was uniaxially stretched in the length direction to 3.6 times the original length (third stage stretching) at a stretching speed of . Subsequently, the test piece was immersed in a boric acid/potassium iodide aqueous solution containing 4% by mass of boric acid and about 5% by mass of potassium iodide at a temperature of 58°C at a rate of 24 cm/min. The film was uniaxially stretched in the length direction to 5.5 times the original length (fourth stage stretching) at a stretching speed of . Thereafter, the test piece was fixed by immersing it in a potassium iodide aqueous solution containing 1.5% by mass of boric acid and 3% by mass of potassium iodide, and then dried at 60°C. It was dried in a machine for 4 minutes to obtain a polarizing film (average thickness 13 μm).

About the obtained polarizing film, the absorbance A2 and the average thickness D2 were measured based on the method described above, and the ratio A2/D2 was determined. In addition, polarization performance was evaluated using the method described above. The results are shown in Table 1.

(3) Manufacture of polarizing plate A test piece measuring 10 cm in the length direction and 5 cm in the width direction was taken from the obtained polarizing film. Triacetylcellulose films are attached to both sides of this test piece (polarizing film) using a PVA adhesive (3.5% by mass aqueous solution of PVA), and a polarizing plate is manufactured by drying at 60°C for 10 minutes. did. The PVA in the PVA adhesive used was a saponified homopolymer of vinyl acetate, and 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 conducted to evaluate the light transmittance based on the method described above. 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 acid scavenger B was used as the acid scavenger. As in Example 1, each evaluation was performed on these. The results are shown in Table 1. Further, FIG. 1 shows the absorption spectrum of the obtained PVA film in the wavelength range of 200 to 400 nm.

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

[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 (added amount) of acid scavenger A was 1 part by mass per 100 parts by mass of PVA. As in Example 1, each evaluation was performed on these. However, a high temperature durability test at 115°C for 70 hours was not conducted. 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 (added amount) of acid scavenger A was 30 parts by mass based on 100 parts by mass of PVA. As in Example 1, each evaluation was performed on these. However, a high temperature durability test at 115°C for 70 hours was not conducted. The results are shown in Table 1. In addition, since the amount of 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 acid scavenger D was used as the acid scavenger. As in Example 1, each evaluation was performed on these. However, a high temperature durability test at 115°C for 70 hours was not conducted. The results are shown in Table 1. In addition, since acid scavenger D has no water solubility and poor compatibility with PVA, the film surfaces of the obtained PVA film and polarizing film were 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 acid scavenger E was used as the acid scavenger. As in Example 1, each evaluation was performed on these. However, a high temperature durability test at 115°C for 70 hours was not conducted. The results are shown in Table 1. In addition, since the molecular weight of acid scavenger E was small and it was easily eluted during the polarizing film manufacturing process, the amount of carbodiimide compound remaining in the polarizing film was small, and the value of A2/D2 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. As in Example 1, each evaluation was performed on these. The results are shown in Table 1. Further, FIG. 1 shows the absorption spectrum of the obtained PVA film in the wavelength range of 200 to 400 nm.

[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 (added amount) of acid scavenger A was 0.01 parts by mass based on 100 parts by mass of PVA. As in Example 1, each evaluation was performed on these. The results are shown in Table 1.

As shown in Figure 1, in the PVA films of Examples 1 to 3 to which acid scavengers having carbodiimide groups, which are groups capable of scavenging acids, were added, large absorption appeared at a wavelength of around 210 nm. Recognize. As shown in Table 1, polarizing plates equipped with polarizing films obtained from the PVA films of Examples 1 to 7 with A1/D1 of 9 mm ^-1 or more had light transmission in the high temperature durability test (105°C, 250 h). The decline in the rate has been sufficiently suppressed. In addition, in Example 5 where a large amount of acid scavenger was added and Example 6 where a water-insoluble acid scavenger was used, the polarizing performance of the obtained polarizing film was slightly low due to deterioration of the film surface. This was the result. In addition, in Example 4, in which the amount of acid scavenger added is relatively small, and in Example 7, in which low molecular weight acid scavenger was used, the remaining amount of acid scavenger in the resulting polarizing film was small, and the high temperature durability was The results showed that the quality was slightly lower. Comparing Examples 1 to 3 based on the results of the high temperature durability test (105°C, 250°C + 115°C, 70 hours), it can be seen that as the value of A2/D2 increases, the high temperature durability increases.

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

Claims (9)

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

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