JP7300378B2 - Polyvinyl alcohol film and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol film and a method for producing the same.

A polarizer, which has the function of transmitting and shielding 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 cellulose triacetate (TAC) film is attached to the surface of a polarizing film. As the polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") is uniaxially stretched and oriented, and an iodine-based dye (I ₃ ^- or I ₅ ^- , etc.) and dichroic organic dyes to which dichroic dyes are adsorbed are mainstream. Such a polarizing film can be produced by uniaxially stretching a PVA film containing a dichroic dye in advance, adsorbing a dichroic dye at the same time as the PVA film is uniaxially stretched, or dichroically stretching a PVA film after uniaxially stretching it. It is manufactured by, for example, adsorbing a dye.

LCDs have come to be used in a wide range of small devices such as calculators and wristwatches, notebook computers, liquid crystal televisions, mobile phones, and tablet terminals. With the recent improvement in performance of liquid crystal televisions, etc., polarizing films are required to have higher polarizing performance than ever before.

When a polarizing film is produced by adsorbing a dichroic dye while uniaxially stretching a PVA film, it is desirable to orient the PVA more in order to obtain a polarizing film with high polarizing performance. In order to obtain a highly oriented polarizing film by stretching, it is effective to use a PVA film having a large stretching stress in the stretching bath. In order to increase the stretching stress of the PVA film in the stretching bath and to further orient the PVA, it is effective to increase the hot water resistance of the PVA film, and it is known that heat treatment increases the hot water resistance of the PVA film. It is On the other hand, in the manufacturing process of the polarizing film, the PVA film is also required to have high water-swellability in order to allow the dichroic dye to be adsorbed into the swollen film. However, in the method of increasing the hot water resistance by heat treatment, the crystallinity of PVA tends to increase and the water swellability tends to decrease. On the other hand, Patent Document 1 describes adding specific cellulose nanofibers to a PVA film as a method for increasing the hot water resistance of a PVA film while maintaining water-swellability.

JP 2010-242063 A

According to the studies of the present inventors, the PVA film obtained by the method described in Patent Document 1 has improved hot water resistance while maintaining sufficient water swelling properties, and the stretching stress in the stretching bath is becomes a big one. However, it was confirmed that the PVA film obtained by the method described in Patent Document 1 has the disadvantage that the transparency is low and the polarizing performance of the polarizing film may be adversely affected (see Comparative Example 3). ).

The present invention has been made based on the circumstances as described above, and an object thereof is to provide a PVA film having a large drawing stress in a drawing bath and having high transparency, and a method for producing such a PVA film. to provide.

The present inventors have made intensive studies to achieve the above object, and found that by adding crystalline cellulose and a water-soluble cellulose derivative to the PVA film, the stretching in the polarizing film manufacturing process can be achieved while maintaining sufficient transparency. The inventors have found that the stretching stress increases under the conditions assumed to be in a bath.

That is, the present invention
[1] Contains PVA (A), crystalline cellulose (B) and water-soluble cellulose derivative (C), and the content of crystalline cellulose (B) is 0.1 parts by mass or more and 20 parts by mass based on 100 parts by mass of PVA (A) A PVA film having a content of 0.01 parts by mass or more of the water-soluble cellulose derivative (C) with respect to 100 parts by mass of the PVA (A);
[2] The PVA film of [1] above, which has a degree of swelling of 130% or more and 300% or less;
[3] The PVA film of [1] or [2] above, wherein the crystalline cellulose (B) has an average particle size of 1 μm or less;
[4] The PVA film of [1], [2] or [3] above, wherein the water-soluble cellulose derivative (C) is a salt of carboxymethylcellulose;
[5] A method for producing a PVA film comprising a step of forming a film using a film-forming stock solution, wherein the film-forming stock solution contains PVA (A), crystalline cellulose (B) and a water-soluble cellulose derivative (C), The content of crystalline cellulose (B) with respect to 100 parts by mass of PVA (A) in the membrane-forming solution is 0.1 parts by mass or more and 20 parts by mass or less, and the water solubility with respect to 100 parts by mass of PVA (A) in the membrane-forming solution A method for producing a PVA film, wherein the content of the cellulose derivative (C) is 0.01 parts by mass or more;
[6] The method for producing a PVA film according to [5] above, wherein the crystalline cellulose (B) has an average particle size of 1 μm or less;
Regarding.

According to the present invention, it is possible to provide a PVA film having a large stretching stress in a stretching bath and having high transparency, and a method for producing such a PVA film.

The present invention will be described in detail below.

<PVA film>
The PVA film of the present invention contains PVA (A), crystalline cellulose (B) and water-soluble cellulose derivative (C). The content of crystalline cellulose (B) relative to 100 parts by mass of PVA (A) in the PVA film of the present invention is 0.1 parts by mass or more and 20 parts by mass or less, and the water-soluble cellulose derivative (C ) is 0.01 parts by mass or more.

(PVA (A))
PVA (polyvinyl alcohol) (A) is usually the main component of the PVA film of the present invention. A main component means a component with the largest content on a mass basis. The content of PVA (A) in the PVA film of the present invention is, for example, preferably 50% by mass or more and 99% by mass, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. In some cases.

PVA (A) is a polymer having vinyl alcohol units ( _--CH.sub.2 --CH(OH)--) as main structural units. PVA (A) may have vinyl ester units and other units in addition to vinyl alcohol units.

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

The polyvinyl ester is preferably obtained by using only one or two or more vinyl esters as monomers, more preferably polyvinyl ester obtained by using only one vinyl ester as a monomer. Copolymer resins of one or more vinyl esters and other monomers copolymerizable therewith may be used as long as they do not significantly impair the effects of the present invention.

The upper limit of the ratio 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 the copolymer resin, and 5 mol % is more preferred, and 1 mol % is even more preferred.

Other monomers copolymerizable with vinyl esters include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth)acrylic acid or salts thereof; (meth)acrylic Methyl acid, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, (meth)acrylic (Meth)acrylic acid esters such as t-butyl 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)acrylamidopropanesulfonic acid or its salts, (meth)acrylamidopropyldimethylamine or its salts, N-methylol (Meth)acrylamide derivatives such as (meth)acrylamide or its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide and 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, vinyl ether such as stearyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; 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; Saturated sulfonic acid or its salt etc. can be mentioned.

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

As the PVA (A), one that has not undergone graft copolymerization can be preferably used. However, the PVA (A) may be modified with one or more graft-copolymerizable monomers as long as the effects of the present invention are not greatly impaired. Graft copolymerization can be performed on at least one of polyvinyl ester and PVA obtained by saponifying it. Graft-copolymerizable monomers include, for example, unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms. The proportion of structural units derived from graft-copolymerizable monomers 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 groups of PVA (A) may or may not be crosslinked. In addition, PVA (A) may form an acetal structure by reacting a part of its hydroxy groups with an aldehyde compound such as acetaldehyde or butyraldehyde.

The lower limit of the degree of polymerization of PVA (A) is preferably 1,000, more preferably 1,500, and even more preferably 1,700. When the degree of polymerization of PVA (A) 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, even more preferably 5,000. When the degree of polymerization of PVA (A) is equal to or less than the above upper limit, it is possible to suppress an increase in production cost of PVA (A) and 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 degree of saponification of PVA (A) is preferably 90 mol% or more, more preferably 95 mol% or more, since the PVA film and the obtained polarizing film have good moist heat resistance, and 99 mol. % or more, and particularly preferably 99.3 mol % or more. The upper limit of the degree of saponification of PVA (A) may be 100 mol%. The degree of saponification of PVA (A) is the ratio of the number of moles of vinyl alcohol units to the total number of moles of structural units that can be converted to vinyl alcohol units by saponification (typically vinyl ester units) and vinyl alcohol units. (mol %). The degree of saponification can be measured according to the description of JIS K6726-1994.

(Crystalline cellulose (B))
By containing the crystalline cellulose (B), the PVA film of the present invention can increase the stretching stress in the stretching bath. Moreover, by containing the water-soluble cellulose derivative (C) together with the crystalline cellulose (B), the dispersibility of the fine crystalline cellulose (B) is enhanced, and the transparency can be enhanced.

Crystalline cellulose (B) is usually a needle-like crystal. The crystalline cellulose (B) may be what is called cellulose nanocrystals or the like. The size of the crystalline cellulose (B) (the size of one needle crystal) is, for example, an average width of 1 nm or more and 50 nm or less and an average length of 100 nm or more and 1,000 nm or less. The crystalline cellulose (B) may have an average width of 10 nm or more and 50 nm or less, and an average length of 100 nm or more and 500 nm or less. The average width and average length of crystalline cellulose (B) are the average values of the measured values of arbitrary 10 crystalline cellulose (B) (needle crystals) observed with an electron microscope. Crystalline cellulose (B) can be obtained, for example, by pulverizing wood into nanofibrils and treating the nanofibrils with a strong acid to remove non-crystalline portions. In addition to crystalline cellulose, cellulose nanofibers are known as fine cellulose. Cellulose nanofibers are different from crystalline cellulose (B) in that they are usually fibrous substances having an average width of 4 nm or more and 100 nm or less and an average length of 5 μm or more. In addition, the crystalline cellulose (B) is substantially composed of only a crystalline portion, whereas the cellulose nanofibers are different in that they have a crystalline portion and an amorphous portion. For example, the crystalline portion in the crystalline cellulose (B) may be 99% by mass or more, and may be 100% by mass.

Crystalline cellulose (B) is not particularly limited, and various known ones can be appropriately selected and used. Moreover, a commercial item can be used for crystalline cellulose (B).

The content of crystalline cellulose (B) with respect to 100 parts by mass of PVA (A) in the PVA film of the present invention is 0.1 parts by mass or more and 20 parts by mass or less, preferably 0.3 parts by mass or more and 18 parts by mass or less, 0.5 to 16 parts by mass is more preferable, 1 to 14 parts by mass is more preferable, and 3 to 10 parts by mass is even more preferable. Furthermore, the content may be preferably 5 parts by mass or more or 10 parts by mass or more, and may be preferably 5 parts by mass or less. By setting the content of crystalline cellulose (B) to 0.1 parts by mass or more relative to 100 parts by mass of PVA (A), the stretching stress of the PVA film in the stretching bath can be increased. On the other hand, by setting the content of the crystalline cellulose (B) to 20 parts by mass or less, the PVA film has sufficient flexibility, and the handleability and the like are improved. By setting the content of crystalline cellulose (B) to 20 parts by mass or less, the transparency of the PVA film is also enhanced. The content of crystalline cellulose (B) is in the range of 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of PVA (A), considering the stretching stress, flexibility, transparency, etc. of the PVA film. It can be set as appropriate.

The average particle size of the crystalline cellulose (B) is preferably 1 μm or less, more preferably 900 nm or less, even more preferably 800 nm or less. When the average particle size of the crystalline cellulose (B) is 1 µm or less, the transparency of the PVA film can be enhanced. The lower limit of the average particle size of crystalline cellulose (B) may be, for example, 100 nm or 300 nm.

The average particle size of crystalline cellulose (B) can be measured by dissolving a PVA film containing crystalline cellulose (B) in water and dispersing crystalline cellulose (B) in water. This average particle size is measured by a dynamic light scattering method using a particle size distribution measuring instrument or the like, and is an average value of particle sizes obtained by cumulant analysis. Moreover, the average particle size of the crystalline cellulose (B) to be measured may be the average particle size of secondary particles formed by agglomeration of primary particles that are needle crystals.

(Water-soluble cellulose derivative (C))
Since the PVA film of the present invention contains the water-soluble cellulose derivative (C) together with the crystalline cellulose (B), the dispersibility of the fine crystalline cellulose (B) is enhanced and the transparency can be enhanced.

A water-soluble cellulose derivative (C) is a water-soluble polymer obtained by modifying cellulose. The water-soluble cellulose derivative (C) may be in the form of a salt, and is preferably in the form of a salt from the viewpoint of water solubility. In other words, the water-soluble cellulose derivative (C) is preferably ionic. Examples of the water-soluble cellulose derivative (C) include carboxymethylcellulose (CMC), CMC salts, hydroxyethylcellulose (HEC), hydroxypropylmethylcellulose (HPMC) and the like, with CMC salts being preferred. By using a CMC salt, the dispersibility of the crystalline cellulose (B) can be further enhanced, and the transparency of the PVA film can be further enhanced.

Salts of CMC include sodium salts (carboxymethylcellulose sodium), calcium salts (carboxymethylcellulose calcium), ammonium salts (carboxymethylcellulose ammonium) and the like, with sodium salts and calcium salts being preferred.

The content of the water-soluble cellulose derivative (C) with respect to 100 parts by mass of PVA (A) in the PVA film of the present invention is 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and 0.1 parts by mass or more. is more preferable, and 0.5 parts by mass or more is even more preferable. By setting the content of the water-soluble cellulose derivative (C) to 0.01 parts by mass or more relative to 100 parts by mass of the PVA (A), the dispersibility of the crystalline cellulose (B) is enhanced and the transparency of the PVA film is enhanced. The upper limit of the content of the water-soluble cellulose derivative (C) with respect to 100 parts by mass of PVA (A) is not particularly limited, but is preferably 20 parts by mass, more preferably 10 parts by mass, 5 parts by mass, 3 parts by mass, or 2 parts by mass. Part is more preferred in some cases. By setting the content of the water-soluble cellulose derivative (C) to 100 parts by mass of the PVA (A) to be equal to or less than the above upper limit, it is possible to suppress an excessive increase in the degree of swelling.

The lower limit of the content of the water-soluble cellulose derivative (C) relative to 100 parts by mass of crystalline cellulose (B) in the PVA film of the present invention is preferably 1 part by mass, more preferably 5 parts by mass, and even more preferably 10 parts by mass. By setting the content of the water-soluble cellulose derivative (C) to 100 parts by mass of the crystalline cellulose (B) at or above the above lower limit, the dispersibility of the crystalline cellulose (B) is further enhanced, and the transparency of the PVA film is further enhanced. On the other hand, the lower limit of the content of the water-soluble cellulose derivative (C) relative to 100 parts by mass of crystalline cellulose (B) may be, for example, 50 parts by mass, and may be 30 parts by mass or 20 parts by mass.

(other ingredients)
The PVA film of the present invention may contain a plasticizer. By including a plasticizer in the PVA film, it is possible to improve the handleability and stretchability of the PVA film. Polyhydric alcohols are preferred as plasticizers, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among these, glycerin is preferable because the stretchability of the PVA film is improved. One or more plasticizers can be used.

The content of the plasticizer in the PVA film of the present invention is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 3 parts by mass or more and 17 parts by mass or less, relative to 100 parts by mass of PVA (A), and 4 parts by mass or more. 14 parts by mass or less is more preferable. When the content of the plasticizer is 1 part by mass or more with respect to 100 parts by mass of PVA (A), the stretchability of the PVA film is improved. On the other hand, since the content of the plasticizer is 20 parts by mass or less with respect to 100 parts by mass of PVA (A), it is possible to prevent the plasticizer from bleeding out on the surface of the PVA film and reduce the handleability of the PVA film. can do.

In addition, when the PVA film of the present invention is produced using the film-forming stock solution described later, the film-forming property is improved and the occurrence of unevenness in the thickness of the film is suppressed, and a metal roll or belt is used for film formation. When this is done, the PVA film can be easily peeled off from these metal rolls and belts. 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 to be blended in the film-forming stock solution for producing the PVA film, and thus the type of surfactant contained in the PVA film, is not particularly limited. Surfactants and nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

Preferred examples of anionic surfactants include carboxylic acid type surfactants such as potassium laurate; sulfuric acid type surfactants such as octyl sulfate; and sulfonic acid type surfactants such as dodecylbenzenesulfonate.

Examples of nonionic surfactants include alkyl ether type such as polyoxyethylene oleyl ether; alkylphenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester type such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxyalkylene Allyl phenyl ether types such as allyl phenyl ether are preferred.

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

When a surfactant is blended in the membrane-forming stock solution for producing the PVA film of the present invention, the content of the surfactant in the membrane-forming stock solution, and thus the surfactant content in the PVA film, is determined by the film-forming stock solution. Or it is preferably 0.01 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of PVA (A) contained in the PVA film, and it is preferably 0.02 parts by mass or more and 0.3 parts by mass or less. more preferred. When the content of the surfactant is 0.01 parts by mass or more based on 100 parts by mass of PVA (A), it is possible to improve film formability and peelability. 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 (A), the surfactant bleeds out on the surface of the PVA film, causing blocking and poor handleability. It is possible to suppress the decrease.

The PVA film of the present invention may optionally contain antioxidants, antifreeze agents, pH adjusters, masking agents, anti-coloring agents, oil agents, etc., the above PVA (A), crystalline cellulose (B), and water-soluble cellulose. It may contain other components than the derivative (C), plasticizer and surfactant. However, the content of these other components may be preferably 10 parts by mass or less, or preferably 1 part by mass or less, or 0.1 part by mass or less based on 100 parts by mass of PVA (A).

(size, physical properties, application, etc.)
Although the upper limit of the average thickness of the PVA film of the present invention is not particularly limited, it 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 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, the handleability and the like can be improved.

Although the shape of the PVA film of the present invention is not particularly limited, it is preferably a long film because the polarizing film can be continuously produced with high productivity. The length of the long film is not particularly limited, and can be appropriately set according to the application of the polarizing film to be produced, and can be, for example, within the range of 5 m or more and 20,000 m or less. The width of the long film is not particularly limited, and can be, for example, 50 cm or more, but since wide polarizing films have been demanded in recent years, it is preferably 1 m or more, and more preferably 2 m or more. Preferably, it is more preferably 4 m or more. The upper limit of the width of the long film is not particularly limited, but if the width is too wide, it tends to be difficult to stretch uniformly when producing a polarizing film with a device that has been put into practical use. Therefore, the width of the PVA film is preferably 7 m or less.

The shape of the PVA film of the present invention is not particularly limited, and it may be a single layer film or a multilayer film (laminate). , preferably a single layer film.

The PVA film of the present invention is usually an unstretched film (unstretched film, unstretched film). Since the PVA film of the present invention is a non-stretched film, it can be suitably used as a raw film such as a polarizing film. It should be noted that stretched forms of PVA films are also within the scope of the present invention.

The degree of swelling of the PVA film of the present invention is preferably 130% or more and 300% or less, more preferably 150% or more and 280% or less, from the viewpoint of the productivity and polarizing performance of the polarizing film, and 170%. More preferably, it is at least 260%. In particular, when the degree of swelling is 130% or more, the film swells sufficiently in the drawing bath and the dichroic dye is easily adsorbed, so that a polarizing film having high polarizing performance can be produced. The degree of swelling of the PVA film can be adjusted by, for example, heat treatment conditions. Specifically, the degree of swelling can be adjusted to a small value by increasing the heat treatment conditions.

The degree of swelling of the PVA film can be determined as a percentage by dividing the mass after immersing the PVA film sample in distilled water at 30°C for 15 minutes by the mass after drying at 105°C for 16 hours after immersion. This swelling degree can be specifically measured by the method described later in Examples. In addition, as a sample of the PVA film, the central portion in the width direction of the PVA film may be taken as a representative position.

The softening point of the PVA film of the present invention is preferably 60° C. or higher and 80° C. or lower, more preferably 65° C. or higher and 75° C. or lower, from the viewpoint of the productivity of the polarizing film and the polarizing performance.

The softening point of the PVA film can be determined as the hot water deformation temperature when a PVA film sample is placed in distilled water at 25° C. and the temperature is raised at a rate of 5° C./min. This softening point can be specifically measured by the method described later in Examples. In addition, as a sample of the PVA film, the central portion in the width direction of the PVA film may be taken as a representative position.

The haze of the PVA film of the present invention is preferably 2.0% or less, more preferably 1.5% or less, from the viewpoint of optical properties and polarization performance of the obtained polarizing film. The lower limit of haze may be, for example, 0.1% or 0.3%. The haze can be obtained as a ratio (percentage) of the diffuse transmittance to the total light transmittance when the PVA film is irradiated with visible light. This haze can be specifically measured by the method described later in Examples. A sample of the PVA film for measuring the haze may be taken from the central portion in the width direction of the PVA film as a representative position.

The PVA film of the present invention has a large stretching stress in a stretching bath and high transparency. Moreover, the PVA film of the present invention has good water-swellability by adjusting the degree of swelling to a suitable range by heat treatment or the like. Therefore, a polarizing film having high polarizing performance can be produced from the PVA film, and it can be suitably used as a raw film for producing a polarizing film. The use of the PVA film of the present invention is not particularly limited, and it can also be used for raw films such as optical films and stretched films, agricultural films, packaging films, and the like.

<Method for producing PVA film>
The method for producing the PVA film of the present invention is not particularly limited, and a production method that makes the thickness and width of the film after film formation more uniform can be preferably employed. For example, the method for producing a PVA film of the present invention is a method for producing a PVA film comprising a step of forming a film using a film-forming stock solution, wherein the film-forming stock solution comprises PVA (A), crystalline cellulose (B) and water-soluble It contains a cellulose derivative (C), the content of crystalline cellulose (B) is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of PVA (A) in the membrane-forming solution, and the PVA ( A) The content of the water-soluble cellulose derivative (C) is 0.01 part by mass or more per 100 parts by mass. The film-forming stock solution usually contains a liquid medium, and if necessary, may further contain a plasticizer, a surfactant and other components. When preparing the membrane-forming undiluted solution, it is preferable that all the components contained are uniformly mixed.

Examples of the liquid medium used for preparing the membrane-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used. Among these, water is preferable from the point of view of less load on the environment and recoverability.

The specific form and preferred form of each component contained in the film-forming stock solution are the same as those contained in the PVA film of the present invention. Further, the specific content and preferable content of each component other than PVA (A) and the liquid medium contained in the film-forming solution relative to PVA (A) are the same as those of each component contained in the PVA film of the present invention.

The volatile content of the film-forming stock solution (the content of volatile components such as liquid media that are removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but is 50 mass. part or more and 95 mass % or less, more preferably 55 mass % or more and 90 mass % or less, and even more preferably 60 mass % or more and 85 mass % or less. 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 are performed smoothly during preparation of the membrane-forming stock solution, and the PVA has few foreign substances and defects. Film production is facilitated. On the other hand, when the volatile content of the membrane-forming stock solution is 95% by mass or less, the concentration of the membrane-forming stock solution does not become too low, thereby facilitating the industrial production of PVA films.

Examples of the film-forming method for forming a PVA film using the above-described film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, a gel film-forming method, and the like. methods and extrusion film-forming methods are preferred. These film forming methods may employ only one type, or may employ a combination of two or more types. Among these film-forming methods, the extrusion film-forming method is more preferable because a PVA film having uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as necessary.

The heat treatment temperature is not particularly limited, and may be appropriately adjusted according to the degree of swelling of the PVA film and the like. The heat treatment temperature is preferably 210° C. or lower, more preferably 200° C. or lower, and even more preferably 190° C. or lower, since discoloration or deterioration of the PVA film occurs if the temperature is too high. The lower limit of the heat treatment temperature is, for example, 100°C, and may be 120°C.

The heat treatment time is not particularly limited, and may be appropriately adjusted according to the degree of swelling of the PVA film. From the viewpoint of efficiently producing the PVA film of the present invention, the heat treatment time is preferably 1 second or more and 30 minutes or less, and 3 seconds or more and 15 minutes. The following are more preferable.

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

[Haze of PVA film]
A square sample of 5 cm in the width direction and 5 cm in the length direction is cut out from the central portion of the PVA film obtained in each of the following Examples or Comparative Examples in the width direction, and a haze meter "HZ-1" manufactured by Suga Test Instruments Co., Ltd. ” was used to measure the haze of the sample.

[Swelling degree of PVA film]
About 1.5 g of the PVA film obtained in each of the following Examples or Comparative Examples was sampled and cut to about 2 mm×10 cm. Wrap the cut PVA film in a mesh (100 mesh: NBC Meshtec Co., Ltd., N-N0110S 115), immerse in distilled water at 30 ° C. for 15 minutes, dehydrate by centrifugation at 3,000 rpm for 5 minutes, and remove the mesh. was removed and then the mass (W1) was obtained. Subsequently, the cut PVA film was dried in a drier 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.
Degree of swelling (%) = ((W1) / (W2)) x 100

[Softening point of PVA film]
A square sample of 3 cm in the width direction and 3 cm in the length direction was cut out from the central part of the PVA film obtained in each of the following examples or comparative examples in the width direction, and an automatic softening point measuring device manufactured by Daiichi Rika Co., Ltd. EX-820" was used to measure the softening point of the sample. Specifically, the sample was made of a stainless steel plate of 1 mm thickness and 3 cm square with a circular hole of 1 cm diameter in the center and a stainless steel plate of 1 mm thickness and 3 cm square with a rectangular hole of 1 cm × 2 cm in the center. It was sandwiched between them and placed on a frame with the stainless steel plate with a circular hole facing up. Then, a steel ball (nominal: 3/8 (diameter: 9.525 mm), grade: G60, mass: 3.5 g ± 0.05 g) specified in JIS B 1501: 2009 is placed on the film located in the center of the circular hole. I put it. Subsequently, 750 mL of distilled water at 25° C. was added, and the temperature was raised at 5° C. per minute.

[Average particle size of crystalline cellulose (B)]
An aqueous dispersion of crystalline cellulose (B) before being mixed with PVA (A) used in each of the following examples or comparative examples was diluted to a measurable concentration. For this diluted solution, dynamic light scattering was measured in an environment of 25 ° C. using a zeta potential / particle size measurement system "ELSZ" manufactured by Otsuka Electronics Co., Ltd., and dynamic light scattering was performed by performing cumulant analysis. The average particle size was obtained by a scattering method. As the values of the refractive index, viscosity, and dielectric constant of the measurement solvent, a refractive index of water of 1.33, a viscosity of water of 0.89 cP, and a dielectric constant of water of 78.3 were used. Also, the noise cut level was set to 0.3%, the number of accumulation times was set to 70, and the pinhole was set to 50 μm.
After dissolving the PVA film obtained in each of the following examples or comparative examples in water, the concentration was adjusted to a measurable level, and the average particle size was measured in the same manner as above, but the above aqueous dispersion was used. It was the same value as the average particle size measured by

[Stretching stress in boric acid aqueous solution (stretching bath)]
In order to evaluate the stress of the PVA film in the stretching bath in the manufacturing process of the polarizing film, the stretching stress of the PVA film was measured by the following tensile test in boric acid aqueous solution.
A sample of 3 cm in the width direction and 7 cm in the length direction was cut out from the center of the width direction of the PVA film obtained in each of the following examples or comparative examples, and a tensile tester "AUTOGRAPH AG-I" manufactured by Shimadzu Corporation was used. was used to measure the tensile stress of PVA films in aqueous boric acid solutions. Specifically, the above sample was placed in a tensile tester with a chuck interval of 3 cm, and a tensile test was performed in the longitudinal direction. The tensile test was performed in a 4% boric acid aqueous solution at 50°C at a tensile speed of 72mm/min. , and the stretching stress at a strain of 400% was determined.

[Example 1]
<Preparation of aqueous dispersion containing crystalline cellulose (B) and water-soluble cellulose derivative (C)>
A mixed powder of crystalline cellulose (B) and a water-soluble cellulose derivative (C), “Theorus RC-591” (crystalline cellulose: sodium carboxymethyl cellulose = 89:11 (mass ratio)) manufactured by Asahi Kasei Co., Ltd. was used. First, 1.5 parts by mass of CEOlus RC-591 is dispersed in water with respect to 100 parts by mass of water, and then stirred at 18,000 rpm for 20 minutes using a high-flex disperser Model: HG92 (manufactured by SMTE). to obtain an aqueous dispersion. Then, using a centrifuge, centrifugation was performed at 48,000 xg for 10 minutes, and the supernatant was collected. The average particle size of crystalline cellulose (B) measured using this supernatant was 796 nm. In addition, the solid content concentration of the supernatant was measured, and this supernatant was used to prepare the following membrane-forming stock solution.

<Preparation of membrane-forming stock solution (PVA aqueous solution)>
PVA (A) (saponified product of homopolymer of vinyl acetate, degree of polymerization: 2,400, degree of saponification: 99.95 mol%), crystalline cellulose (B) collected above and aqueous dispersion of sodium carboxymethylcellulose (C) The supernatant liquid (8 parts by mass of crystalline cellulose (B) and 1 part by mass of sodium carboxymethyl cellulose (C) with respect to 100 parts by mass of PVA), glycerin (10 parts by mass with respect to 100 parts by mass of PVA), and surfactant An agent (0.03 parts by mass with respect to 100 parts by mass of PVA) was mixed with water, and PVA (A) and the like were dissolved at 90°C over 4 hours to obtain a membrane-forming stock solution. Thereafter, the membrane-forming stock solution was kept at 85° C. for 16 hours for defoaming.

<Production of PVA film>
The film-forming stock solution obtained above was dried on a metal roll at 80° C. to obtain an untreated PVA film. After that, heat treatment was performed for 10 minutes in a drier at 148° C. to obtain a PVA film having a degree of swelling of 200% and an average thickness of 30 μm.
The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution by the methods described above. Table 1 shows the results.

[Example 2]
Example 1 except that the contents of the crystalline cellulose (B) and the water-soluble cellulose derivative (C) in the film-forming stock solution were set to 0.9 parts by mass and 0.1 parts by mass, respectively, with respect to 100 parts by mass of PVA. Similarly, a PVA film was produced. The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution. Table 1 shows the results.

[Example 3]
Example 1 except that the contents of the crystalline cellulose (B) and the water-soluble cellulose derivative (C) in the film-forming stock solution were set to 17.8 parts by mass and 2.2 parts by mass, respectively, with respect to 100 parts by mass of PVA. Similarly, a PVA film was produced. The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution. Table 1 shows the results.

[Comparative Example 1]
A PVA film was produced in the same manner as in Example 1, except that the crystalline cellulose (B) and the water-soluble cellulose derivative (C) were not included in the preparation of the film-forming stock solution. The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution. Table 1 shows the results.

[Comparative Example 2]
An aqueous dispersion containing crystalline cellulose (B) and a water-soluble cellulose derivative (C) is washed with water to remove the water-soluble cellulose derivative (C). A PVA film was produced in the same manner as in Example 1, except that 8 parts by mass of the water-soluble cellulose derivative (C) was not contained. The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution. Table 1 shows the results.

[Comparative Example 3]
In the preparation of the film-forming stock solution, instead of crystalline cellulose (B) and water-soluble cellulose derivative (C), 9 parts by mass of cellulose nanofiber (“nanoforest-S” manufactured by Chuetsu Pulp Industry Co., Ltd.) is contained with respect to 100 parts by mass of PVA. A PVA film was produced in the same manner as in Example 1, except that the The resulting PVA film was measured for haze, swelling degree, softening point, and stretching stress in an aqueous boric acid solution. Table 1 shows the results.

[Comparative Example 4]
Same as Example 1, except that the contents of crystalline cellulose (B) and water-soluble cellulose derivative (C) in the film-forming stock solution were set to 26.7 parts by mass and 3.3 parts by mass, respectively, with respect to 100 parts by mass of PVA. Similarly, a PVA film was produced. Since the PVA film obtained was hard and brittle, each measurement was stopped.

As shown in Table 1, the PVA films of Examples 1 to 3 had a large stretching stress in an aqueous boric acid solution (stretching bath), had a haze of less than 2.0%, and had high transparency. . These PVA films of Examples 1 to 3 were shown to be capable of producing polarizing films having high polarizing performance.

The PVA film of the present invention can be suitably used as a raw film (material film) or the like for producing a polarizing film.

Claims (6)

Polyvinyl alcohol (A), crystalline cellulose (B) and water-soluble cellulose derivative (C),
The content of crystalline cellulose (B) with respect to 100 parts by mass of polyvinyl alcohol (A) is 0.1 parts by mass or more and 20 parts by mass or less,
The content of the water-soluble cellulose derivative (C) with respect to 100 parts by mass of the polyvinyl alcohol (A) is 0.01 parts by mass or more and 10 parts by mass or less,
A polyvinyl alcohol film in which the content of the water-soluble cellulose derivative (C) is 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the crystalline cellulose (B). The polyvinyl alcohol film according to claim 1, having a swelling degree of 130% or more and 300% or less. 3. The polyvinyl alcohol film according to claim 1, wherein the crystalline cellulose (B) has an average particle size of 1 [mu]m or less. 4. The polyvinyl alcohol film according to claim 1, wherein the water-soluble cellulose derivative (C) is a salt of carboxymethylcellulose. A method for producing a polyvinyl alcohol film comprising a step of forming a film using a film-forming stock solution,
The film-forming stock solution contains polyvinyl alcohol (A), crystalline cellulose (B) and a water-soluble cellulose derivative (C),
The content of crystalline cellulose (B) with respect to 100 parts by mass of polyvinyl alcohol (A) in the film-forming stock solution is 0.1 parts by mass or more and 20 parts by mass or less,
The content of the water-soluble cellulose derivative (C) with respect to 100 parts by mass of the polyvinyl alcohol (A) in the film-forming stock solution is 0.01 parts by mass or more and 10 parts by mass or less,
A method for producing a polyvinyl alcohol film, wherein the content of the water-soluble cellulose derivative (C) is 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the crystalline cellulose (B). 6. The method for producing a polyvinyl alcohol film according to claim 5, wherein the crystalline cellulose (B) has an average particle size of 1 [mu]m or less.