CN112334535B - Polyvinyl alcohol film, stretched film, and method for producing polyvinyl alcohol film - Google Patents

Abstract

Provided are a PVA film which can provide a stretched film having excellent stretch processability and excellent transparency and low retardation, a method for producing the PVA film, and a stretched film obtained from the PVA film. The polyvinyl alcohol film of the present invention comprises a polyvinyl alcohol (A) and polyisoprene rubber particles (B), wherein the average particle diameter of the polyisoprene rubber particles (B) is 85nm or more and 700nm or less, and the content of the polyisoprene rubber particles (B) is 3 parts by mass or more and 35 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A).

Description

Polyvinyl alcohol film, stretched film and method for producing polyvinyl alcohol film

technical field

The present invention relates to a polyvinyl alcohol film, a stretched film and a method for producing the polyvinyl alcohol film.

Background technique

Polyvinyl alcohol films (hereafter, "polyvinyl alcohol" may be abbreviated as "PVA") are used in a wide range of applications, including packaging films, water-soluble films, agricultural films, release films, and optical films.

As a PVA film, a film whose stretching processability has been improved by adding a plasticizer is generally used. However, such a PVA film has disadvantages in that the reduction of the plasticizer occurs over time and the stretching processability decreases. So far, as a method of imparting good drawing processability by adding a plasticizer, in the case of PVA fibers, a method of adding an emulsified dispersion of ethylene vinyl acetate copolymer to a spinning dope has been proposed (see Patent Document 1).

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Publication No. 47-42050.

Contents of the invention

The problem to be solved by the invention

Among the applications of PVA films, there are many applications requiring transparency such as optical applications and low retardation properties in the stretched film. However, use of a film-forming stock solution in which the emulsified dispersion liquid described in Patent Document 1 is used is not preferable because the obtained PVA film has low transparency after stretching or a large retardation.

In addition, regarding the stretching processability described above, it is important for a PVA film to have a low tensile stress value. That is, a PVA film showing low tensile stress is an index showing that it is a film excellent in stretching processability.

The present invention is based on the circumstances as above, and its object is to provide a PVA film capable of obtaining a stretched film having excellent stretch processability, transparency, and low phase difference. This PVA film is obtained as a stretch film.

method used to solve the problem

Inventions made to solve the above-mentioned problems are as follows.

[1] A polyvinyl alcohol film comprising polyvinyl alcohol (A) and polyisoprene rubber particles (B), the polyisoprene rubber particles (B) having an average particle diameter of not less than 85 nm and not more than 700 nm, Content of the said polyisoprene rubber particle (B) is 3 mass parts or more and 35 mass parts or less with respect to 100 mass parts of said polyvinyl alcohol (A).

[2] The polyvinyl alcohol film according to [1], wherein the degree of polymerization of the polyvinyl alcohol (A) is not less than 1,000 and not more than 10,000, and the degree of saponification is not less than 95 mol %.

[3] The polyvinyl alcohol film according to [1] or [2], which has a thickness of 1 μm or more and 60 μm or less.

[4] The polyvinyl alcohol film according to [1], [2] or [3], which is a raw material film for optical films.

[5] A stretched film obtained from the polyvinyl alcohol film according to any one of [1] to [4].

[6] The stretched film according to [5], which is an optical film.

[7] A method for producing a polyvinyl alcohol film, comprising a step of forming a film using a film-forming stock solution in which polyvinyl alcohol (A) and a dispersion containing polyisoprene rubber particles (B) are mixed. liquid, the average particle size of the above-mentioned polyisoprene rubber particles (B) in the above-mentioned dispersion liquid is not less than 70nm and not more than 500nm, and the content of the above-mentioned polyisoprene rubber particles (B) in the above-mentioned film-forming stock solution is relative to 100 mass parts of said polyvinyl alcohol (A) is 3 mass parts or more and 35 mass parts or less.

Invention effect

According to the present invention, there are provided a PVA film capable of obtaining a stretched film excellent in stretching processability and excellent in transparency and low phase difference, a method for producing such a PVA film, and a stretched film obtained from such a PVA film.

Detailed ways

Hereinafter, the PVA film of this invention, its manufacturing method, and embodiment of a stretched film are demonstrated in detail.

<PVA film>

The PVA film according to one embodiment of the present invention contains PVA (A) and polyisoprene rubber particles (B). This PVA film is usually a film that has not been stretched (unstretched film). As will be described in detail later, a stretched film can be obtained by stretching the PVA film.

(PVA)

PVA (polyvinyl alcohol) usually becomes the main component of this PVA film. PVA is a polymer having vinyl alcohol units (—CH ₂ —CH(OH)—) as main structural units. It should be noted that the main structural unit refers to the structural unit that occupies the largest proportion of all structural units, and the proportion of all structural units is preferably 50 mol% or more (the same applies to "main structural unit" below). In addition to vinyl alcohol units, PVA may have vinyl ester units and other units.

As PVA, the PVA obtained by saponifying the polyvinyl ester obtained by polymerizing 1 type or 2 or more types of vinyl esters can be used. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl tert-carbonate, vinyl laurate, vinyl stearate, and benzoic acid. Vinyl ester, isopropenyl acetate, etc. Among vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C=CH-O-CO-) in the molecule are preferable, and vinyl acetate is more preferable from the viewpoint of ease of manufacture, ease of acquisition, and cost. ester.

The polyvinyl ester is preferably obtained using only one type of vinyl ester or two or more types of vinyl esters as monomers, more preferably a polyvinyl ester obtained using only one type of vinyl ester as a monomer. As long as the effect of the present invention is not significantly impaired, it may be a copolymer resin formed of one or more vinyl esters and other monomers that can be copolymerized therewith.

The upper limit of the proportion of structural units derived from other monomers that can be copolymerized is preferably 15 mol %, more preferably 10 mol %, further preferably 5 mol %, and still more preferably 1, based on the number of moles of all structural units constituting the copolymerized resin. mole %. That is, the lower limit of the ratio of vinyl alcohol units to all structural units in PVA obtained by saponifying polyvinyl ester is preferably 85 mol%, more preferably 90 mol%, even more preferably 95 mol%, and still more preferably It is 99 mol%.

As other monomers that can be copolymerized with vinyl esters, for example, α-olefins with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salt; (meth)acrylic acid or its salt; ) methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, ( (meth)acrylates such as tert-butyl methacrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc.; ( 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)acrylamidopropyl dimethylamine or its salt, N-methylol (meth)acrylamide or its derivatives, etc. (meth)acrylic acid Amide derivatives; N-vinyl amides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, iso Propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; (methyl) Vinyl cyanide such as acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other halogenated vinyl compounds; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts and esters or acid anhydride; itaconic acid or its salt, ester or anhydride; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acid or its salt, etc.

A polyvinyl ester may have a structural unit derived from 1 type, or 2 or more types of monomers mentioned above.

As PVA, PVA that has not been graft-copolymerized can be preferably used. Among them, as long as the effect of the present invention is not significantly impaired, PVA may be modified with one or two or more graft-copolymerizable monomers. Graft copolymerization may be performed on at least one of polyvinyl ester and PVA obtained by saponification thereof. Examples of graft-copolymerizable monomers include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from 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 polyvinyl ester or PVA.

Some of the hydroxyl groups in PVA may be cross-linked or may not be cross-linked. In addition, some hydroxyl groups in PVA can react with aldehyde compounds such as acetaldehyde and 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 still more preferably 1,700. By making the polymerization degree of PVA more than the said minimum, toughness, etc. of a PVA film and the obtained stretched film can be improved. On the other hand, the upper limit of the degree of polymerization is preferably 10,000, more preferably 8,000, and still more preferably 5,000. By making the polymerization degree of PVA below the said upper limit, the increase of the manufacturing cost of PVA and the occurrence of a defect at the time of film formation can be suppressed. In addition, the degree of polymerization of PVA means the average degree of polymerization measured in accordance with the description of JISK6726-1994.

The lower limit of the degree of saponification of PVA is, for example, 80 mol % or 90 mol %, preferably 95 mol %, more preferably 98 mol %, and still more preferably 99 mol %. The effect of this invention can be exhibited more fully by making saponification degree more than the said minimum. In addition, in the case of the use of a water-soluble film, PVA with a low degree of saponification can be used. On the other hand, the upper limit of the degree of saponification may be 100 mol%. It should be noted that the degree of saponification of PVA refers to the number of moles of vinyl alcohol units relative to the total moles of structural units that can be converted into vinyl alcohol units through saponification (typically, vinyl ester units) and vinyl alcohol units. The ratio of the number (mol %). The degree of saponification can be measured in accordance with the description in JIS K6726-1994.

The lower limit of the PVA content in the PVA film is preferably 40% by mass, more preferably 60% by mass, still more preferably 65% by mass, still more preferably 70% by mass, still more preferably 75% by mass. By making content of PVA more than the said minimum, the characteristic of PVA can fully be exhibited, and transparency etc. of the obtained stretched film can be improved. On the other hand, the upper limit of the content is preferably 99% by mass, more preferably 98% by mass, and still more preferably 97% by mass. Drawing processability etc. can be improved by making content of PVA below the said upper limit.

(polyisoprene rubber particles)

The polyisoprene rubber particles are particles of polyisoprene rubber. The polyisoprene rubber particles may contain components other than polyisoprene rubber. Here, the lower limit of the polyisoprene rubber content in the polyisoprene rubber particles is, for example, 80% by mass, may be 90% by mass, may be 95% by mass. Examples of other components optionally contained in the polyisoprene rubber particles include emulsifiers adhering to the surface, other additives, and the like.

Polyisoprene rubber particles are usually uniformly dispersed in PVA as a base material. By containing polyisoprene rubber particles having a specific particle diameter and a specific amount, the PVA film can obtain a stretched film having excellent stretching processability and good transparency and low phase difference.

The polyisoprene rubber refers to a polymer having a structural unit derived from isoprene as a main structural unit, that is, rubber. The lower limit of the content ratio of the isoprene unit in all structural units constituting the polyisoprene rubber is, for example, 50 mol %, preferably 70 mol %, more preferably 90 mol %, still more preferably 95 mol % %. The polyisoprene rubber may be substantially a homopolymer of isoprene. It should be noted that polyisoprene has isomers, and polyisoprene rubber is generally cis-1,4 polyisoprene. When the polyisoprene rubber is a copolymer, examples of monomers other than isoprene include the above-mentioned monomers and other monomers as "other monomers that can be copolymerized with vinyl ester". Diene compounds such as diene, styrene, etc.

Polyisoprene rubber may be a modified body. For example, it may have a branched chain structure or Functional polyisoprene rubber.

The lower limit of the weight average molecular weight of the polyisoprene rubber is, for example, preferably 5,000, more preferably 10,000, further preferably 15,000, and still more preferably 20,000. On the other hand, the upper limit of the weight average molecular weight is preferably 80,000, more preferably 60,000, and still more preferably 40,000. By using the polyisoprene rubber whose weight average molecular weight is in the said range, stretch processability and each characteristic of the obtained stretched film can be improved further. The weight average molecular weight of polyisoprene rubber can be measured by the method described in the Example.

The upper limit of the average particle diameter of the polyisoprene rubber particles is 700 nm, preferably 600 nm, more preferably 500 nm, still more preferably 400 nm. When the average particle diameter of the polyisoprene rubber particles is not more than the upper limit, scattering of transmitted light can be suppressed, and the transparency of a stretched film obtained from the PVA film can be improved, thereby further enhancing the effects of the present invention. In addition, the lower limit of the average particle diameter is 85 nm, preferably 100 nm, more preferably 150 nm, and still more preferably 200 nm. By making the average particle diameter of the polyisoprene rubber particles not less than the above lower limit, the surface area of the particles can be reduced, and the retardation increase of the stretched film obtained from the PVA film can be suppressed, thereby further enhancing the effect of the present invention.

The average particle diameter of the polyisoprene rubber particles is a value obtained by measuring a dispersion liquid of polyisoprene rubber particles by a dynamic light scattering method. The specific measurement method is based on the method described in the Examples described later. Regarding the polyisoprene rubber particles in the PVA film, the PVA of the PVA film can be dissolved to take out the polyisoprene rubber particles, and a dispersion liquid is prepared, and the polyisoprene rubber particles in the dispersion liquid are measured. The average particle size.

The lower limit of the content of the polyisoprene rubber particles in the PVA film is 3 parts by mass relative to 100 parts by mass of PVA, preferably 5 parts by mass, more preferably 10 parts by mass, and still more preferably 15 parts by mass. By making content of a polyisoprene rubber particle more than the said minimum, the stretch processability etc. of this PVA film will improve. On the other hand, the upper limit of the content of the polyisoprene rubber particles is 35 parts by mass, preferably 30 parts by mass, more preferably 28 parts by mass, and still more preferably 25 parts by mass. When content of polyisoprene rubber particle is below the said upper limit, the transparency, low phase difference, etc. of the stretched film obtained from this PVA film can be made into a favorable state.

(Manufacturing method of polyisoprene rubber pellets)

The polyisoprene rubber particles can be prepared as a dispersion of polyisoprene rubber particles. The method for producing the dispersion of polyisoprene rubber particles is not particularly limited, and known methods such as anionic polymerization and post-emulsification can be used. Specifically, for example, polyisoprene rubber can be obtained by first synthesizing polyisoprene rubber, adding an emulsifier and water to the polyisoprene rubber, and stirring strongly with an emulsifier or the like. Dispersion of rubber particles. At this time, the average particle diameter of the polyisoprene rubber particles can be adjusted by adjusting the stirring intensity, stirring time, etc., selecting an emulsifier, and the like. In addition, a dispersion liquid of polyisoprene rubber particles can also be produced by a known emulsion polymerization method.

When the polyisoprene rubber is dispersed in water and used as an oil-in-water droplet type dispersion, it is preferable to prepare the dispersion in advance by a mechanical method or a chemical method, and use it at a specific concentration by dilution or the like. Examples of mechanical methods include homogenizers, homomixers, distribution mixers, colloid mills, inline mixers, high-pressure homogenizers, ultrasonic emulsifiers, and the like, and these may be used alone or in combination. As the chemical method, various methods such as inverse emulsification method, D-phase emulsification method, HLB temperature emulsification method, gel emulsification method, and liquid crystal emulsification method are listed. For inverse emulsification method. In addition, in order to obtain a dispersion with a fine particle size, it may be preferable to carry out the above operation while heating at an appropriate temperature (for example, 30 to 80° C.) for the purpose of reducing the viscosity of the polyisoprene rubber. When preparing the dispersion, from the viewpoint of improving the stability of the dispersion, it is preferably prepared at a solid content concentration of 20 to 80% by mass, more preferably 30 to 70% by mass.

As a catalyst for the polymerization of polyisoprene rubber, for example, tetrahalogenated titanium-trialkylaluminum series, diethylaluminum chloride-cobalt series, trialkylaluminum-boron trifluoride-nickel series, Ziegler catalysts such as diethylaluminum chloride-nickel series; lanthanide rare earth metal catalysts such as triethylaluminum-organic acid neodymium-Lewis acid series, or organic alkali metal compounds as in S-SBR.

The emulsifier used in the production of polyisoprene rubber particles is not particularly limited, and common emulsifiers such as anionic, nonionic, and nonionic-anionic emulsifiers are listed.

Specific examples of emulsifiers include, for example, sodium salts and potassium salts of aliphatic carboxylic acids such as laurate, myristate, palmitate, stearate, and alkenyl succinate as anionic emulsifiers. salt or ammonium salt; sodium, potassium or ammonium salt of disproportionated or hydrogenated natural rosin; sodium, potassium or ammonium salt of aliphatic sulfuric acid compounds such as lauryl sulfate, etc. In addition, examples of nonionic-anionic emulsifiers include sulfate ester soaps such as polyoxyethylene octylphenyl ether sulfonate, polyoxyethylene octylphenyl ether sulfate, and polyoxyethylene alkyl ether sulfate. , cetyl phosphate, polyoxyethylene lauryl ether phosphate, polyoxyethylene tridecyl ether phosphate, polyoxyethylene nonylphenyl phosphate and other anionic soaps such as phosphate soaps, etc. As a counter cation of these salts, sodium, potassium, or ammonium can be mentioned.

The usage-amount of an emulsifier is preferably 0.5-15 mass parts with respect to 100 mass parts of polyisoprene rubbers, More preferably, it is 1-10 mass parts. If the usage-amount of an emulsifier is below the said upper limit, it will not affect the stability of a polyisoprene rubber particle, and since excessive use of an emulsifier can be suppressed, it is economically advantageous. Moreover, when the usage-amount of an emulsifier is more than the said minimum, the particle diameter increase of polyisoprene rubber particle|grains can be suppressed, and the occurrence of creaming and separation phenomena can be suppressed. For the purpose of improving the stability of the polyisoprene rubber particles, alkaline substances such as sodium hydroxide, potassium hydroxide, and amines may be added as needed, and the pH may be adjusted before use.

In addition, the polyisoprene rubber or the dispersion liquid of polyisoprene rubber particle|grains can also use a commercial item.

(plasticizer)

The PVA film may further contain a plasticizer. By making this PVA film contain a plasticizer, stretch processability, handleability, roll quality, etc. can be improved. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylol propane etc. These plasticizers can be used 1 type or 2 or more types. Among these, glycerin is preferable from the viewpoint of the effect of improving drawing processability and roll quality.

The lower limit of the content of the plasticizer in the PVA film is preferably 1 part by mass, more preferably 5 parts by mass relative to 100 parts by mass of PVA. By making content of a plasticizer more than the said minimum, processing stretchability etc. will improve further. On the other hand, the upper limit of the content is preferably 20 parts by mass, more preferably 15 parts by mass. By making content of a plasticizer below the said upper limit, it can suppress that a PVA film becomes soft too much or the fall of handleability by a plasticizer bleeds out to the surface.

(other additives, etc.)

If necessary, fillers, processing stabilizers such as copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, etc. Thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, release agents, release agents, reinforcing agents, crosslinking agents, antifungal agents, preservatives, crystallization speed retarders, surfactants and other additives.

Among other additives, it is preferable to contain a surfactant from the viewpoint of film forming properties and the like. By containing the surfactant, the occurrence of uneven thickness of the PVA film is suppressed or the film is easily peeled from the metal roll or belt used for film formation. The type of the surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferred from the viewpoint of peelability from metal rolls and belts.

As anionic surfactants, for example, carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate are preferable.

As the nonionic surfactant, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; and alkyl ester types such as polyoxyethylene laurate are preferable. ; Alkyl amine type such as polyoxyethylene lauryl amino ether; Alkyl amide type such as polyoxyethylene lauramide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Lauric acid diethanolamide, oleic acid diethanolamide, etc. Alkanolamide type; allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether, etc.

These surfactants may be used alone or in combination of two or more.

When the PVA film contains a surfactant, the lower limit of the content is preferably 0.01 parts by mass, more preferably 0.03 parts by mass relative to 100 parts by mass of PVA. By making content of surfactant more than the said minimum, peelability, film forming property, etc. will improve further. On the other hand, the upper limit of the content is preferably 0.5 parts by mass, and more preferably 0.3 parts by mass. By making content of a surfactant below the said upper limit, it can suppress that a surfactant bleeds out to the surface of a PVA film, and the fall of handleability by adhesion|attachment of films can be suppressed.

The upper limit of the content of additives other than PVA, polyisoprene rubber particles, plasticizers, and surfactants in the PVA film is sometimes preferably 10% by mass, sometimes more preferably 5% by mass, and sometimes more It is preferably 1% by mass, and may be more preferably 0.2% by mass. When the content of other additives exceeds the above upper limit, the processing stretchability of the PVA film, the transparency of the obtained stretched film, and the like may be affected.

(shape)

The shape of the PVA film is not particularly limited, but it is preferably a long film because it can be continuously produced with good productivity. The length of the elongated PVA film is not particularly limited, and can be appropriately set according to applications and the like. For example, the length can be set within a range of not less than 5 m and not more than 20,000 m. The width of the PVA film is not particularly limited. For example, in the case of a water-soluble film, the lower limit can be set to 1 cm. Moreover, the lower limit is preferably 1 m, more preferably 2 m, and still more preferably 4 m from the viewpoint of seeking wide-width PVA films for various uses in recent years. The upper limit of the width of the PVA film is not particularly limited, and may be, for example, 7 m. When the width is too wide, it tends to be difficult to uniformly produce a PVA film with a practical apparatus.

The PVA film may be a single-layer film or a multilayer film (laminate).

The upper limit of the thickness (average thickness) of this PVA film is not specifically limited, For example, it is 100 micrometers, Preferably it is 60 micrometers, More preferably, it is 40 micrometers. On the other hand, the lower limit of the thickness is preferably 1 μm, more preferably 5 μm, and still more preferably 10 μm. By making the thickness of the PVA film into the above-mentioned range, handling properties, drawing processability, etc. can be improved. In addition, thickness (average thickness) was made into the average value of the value measured at arbitrary 5 places. Hereinafter, the same applies to the thickness (average thickness).

(use)

This PVA film can be used for various uses similar to conventional PVA films, such as a packaging film, a water-soluble film, an agricultural film, a release film, and an optical film. In addition, this PVA film is suitable as a raw material film of a stretched film. In particular, since the PVA film can obtain a stretched film excellent in stretching processability and excellent in transparency and low phase difference, it is suitable as a raw material film used as an optical film material. That is, an optical film can be obtained suitably by stretching this PVA film. In addition, a raw material film means the film used as a material, and is not limited to the film which showed roll shape.

The optical film refers to a light-transmitting film used in an optical device. As an optical device, display devices, such as a liquid crystal display device and an organic EL display, are mentioned as a representative example. Examples of the optical film include a polarizing film, a polarizing plate protective film, a color compensation film, a brightness enhancement film, a viewing angle expansion film, and a retardation film. Moreover, as another example of an optical film, this PVA film can be utilized also as a gas barrier film, such as an organic electroluminescent display, by utilizing the favorable transparency and gas barrier property. This PVA film is especially suitable as a raw material film of the polarizing film which requires high transparency, low retardation, etc. among optical films.

In addition, this PVA film can be suitably used as the raw material film of a stretched film as mentioned above, and can also be used for various uses without stretching.

<Manufacturing method of PVA film>

The manufacturing method of this PVA film is not specifically limited, The manufacturing method which makes the thickness and width|variety of the PVA film after film formation more uniform can be used preferably. For example, it can be obtained by forming a film using a film-forming stock solution obtained by dissolving PVA, polyisoprene rubber particles constituting the PVA film, and, if necessary, other components such as a plasticizer in a liquid medium. Moreover, it can also manufacture using the film-forming stock solution which melt|dissolved PVA as needed.

That is, the method for producing a PVA film according to one embodiment of the present invention includes a step of forming a film using a film-forming stock solution in which polyvinyl alcohol (A) and polyisoprene rubber particles ( B) a dispersion liquid, wherein the polyisoprene rubber particles (B) in the dispersion liquid have an average particle diameter of not less than 70 nm and not more than 500 nm, and the polyisoprene rubber particles (B) in the film-forming stock solution are The content of the polyvinyl alcohol is 3 parts by mass or more and 35 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A).

According to this production method, a PVA film capable of obtaining a stretched film excellent in stretching processability and excellent in transparency and low phase difference can be produced.

In the film-forming stock solution, the polyisoprene rubber particles are preferably uniformly mixed. It should be noted that by mixing the dispersion of polyisoprene rubber particles with a liquid medium, PVA and other additives, it is possible to efficiently obtain a film-forming stock solution in which polyisoprene rubber particles are uniformly mixed. In this case, the upper limit of the average particle diameter of the polyisoprene rubber particles in the dispersion liquid is 500 nm, preferably 450 nm, more preferably 400 nm, and still more preferably 350 nm. In addition, the lower limit of the average particle diameter is 70 nm, preferably 100 nm, more preferably 150 nm, and still more preferably 200 nm. By setting the average particle diameter of the polyisoprene rubber particles in the dispersion liquid within the above-mentioned range, the particle diameter of the polyisoprene rubber particles in the obtained PVA film can be adjusted to an appropriate size. In addition, this average particle diameter is the value measured by the dynamic light scattering method. In addition, when the film-forming stock solution contains a plasticizer, other additives, etc., it is preferable to mix these components uniformly.

Examples of the liquid medium include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and Diol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. These liquid media can be used 1 type or 2 or more types. Among these, water is preferable from the viewpoint of less burden on the environment and recyclability.

The volatile content of the film-forming stock solution (the proportion of volatile components in the film-forming stock solution such as the liquid medium that is removed due to volatilization and evaporation during film forming) also varies with the film-forming method and film-forming conditions. In other words, the lower limit is preferably 50% by mass, more preferably 55% by mass, and even more preferably 60% by mass. By making the volatile content of the film-forming stock solution more than the above-mentioned lower limit, the viscosity of the film-forming stock solution will not be too high, and the filtration and defoaming can be smoothly performed during the preparation of the film-forming stock solution, and it is easy to manufacture a PVA film free of foreign matter and defects. On the other hand, the upper limit of the volatile content is preferably 95% by mass, and more preferably 90% by mass. By making the volatile content of the film-forming stock solution below the above-mentioned upper limit, the concentration of the film-forming stock solution does not become too low, and it becomes easy to manufacture an industrial PVA film.

A conventionally known method can be used as a film-forming method in the case of producing a PVA film using a film-forming stock solution. The film forming method may be a method of producing a PVA film on the base material by applying a film forming stock solution on the base material, or may be a method of directly producing a single-layer PVA film. Examples of film forming methods include cast film forming, extrusion film forming, wet film forming, and gel film forming. These film forming methods may be used alone or in combination of two or more. . Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable from the viewpoint of obtaining a PVA film having uniform thickness and width and good physical properties.

The produced PVA film can be heat treated as needed. The heat treatment temperature is not particularly limited, and may be appropriately adjusted. If the heat treatment temperature is too high, discoloration and deterioration of the PVA film will be observed. Therefore, the upper limit of the heat treatment temperature is preferably 210°C, more preferably 180°C, and still more preferably 150°C. On the other hand, the lower limit of the heat treatment temperature is, for example, 60°C, preferably 90°C.

The heat treatment time is not particularly limited and may be appropriately adjusted, but the upper limit is preferably 30 minutes, more preferably 15 minutes, from the viewpoint of efficiently producing a PVA film. On the other hand, the lower limit thereof is, for example, preferably 10 seconds, more preferably 1 minute.

<Stretch film>

The stretched film according to one embodiment of the present invention is a stretched film obtained from the above-mentioned PVA film according to one embodiment of the present invention. In this stretched film, PVA is usually oriented in a specific direction (stretching direction). The stretched film had good transparency and low phase difference. The stretched film may be uniaxially stretched or biaxially stretched, preferably uniaxially stretched. This stretched film uniaxially stretched can be suitably used as optical films, such as a polarizing film. The stretched film may be a single-layer film or a multi-layer film, preferably a single-layer film.

The stretch film contains PVA (A) and polyisoprene rubber particles (B). The stretched film is obtained by stretching the above-mentioned PVA film. Therefore, the specific form and suitable form of each component of this stretched film may be the same as each component of this said PVA film. In addition, when the stretched film is a polarizing film, the stretched film usually has a dichroic dye adsorbed on the front and back sides. The dichroic dye is usually an iodine dye.

The upper limit of the thickness (average thickness) of the stretched film is, for example, 20 μm, preferably 16 μm. Sufficient thickness reduction can be achieved by making the thickness of this stretched film below the said upper limit. On the other hand, the lower limit of the thickness is preferably 5 μm, more preferably 8 μm. When the thickness of the stretched film is equal to or greater than the above-mentioned lower limit, it becomes difficult to crack, and handleability and the like can be improved.

The stretched film can be used as a packaging film, a water-soluble film, an agricultural film, a release film, an optical film, etc., preferably an optical film. When the stretched film is an optical film, the advantages of excellent transparency and low phase difference are fully exhibited.

As an optical film, a polarizing film, a polarizing plate protective film, a color compensation film, a brightness enhancement film etc. are mentioned, Among these, a polarizing film is preferable. When the stretched film is a polarizing film, the polarizing film is usually used as a polarizing plate by affixing an optically transparent and mechanically strong protective film to both surfaces or one surface thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. In addition, examples of the adhesive used for sticking include PVA-based adhesives, ultraviolet-curable adhesives, and the like, and PVA-based adhesives are preferable.

The polarizing plate obtained as described above may further have optical films such as retardation films, viewing angle improvement films, and brightness enhancement films attached thereto. In addition, the stretched film which concerns on one Embodiment of this invention can also be used as said viewing angle improvement film etc. The polarizing plate can be used as a member of a liquid crystal display device by applying an adhesive such as an acrylic type, and then affixing it to a glass substrate.

<Manufacturing method of stretched film>

The stretched film can be obtained by a production method including the step of stretching the above-mentioned PVA film. That is, this stretched film can be manufactured by the same method as conventional except using the said PVA film. That is, according to this production method, a stretched film having excellent transparency and low phase difference can be obtained relatively easily without going through a special process.

Hereinafter, the specific manufacturing method when this stretched film is a polarizing film is demonstrated. Specific methods for producing a polarizing film include performing swelling treatment, dyeing treatment, and uniaxial stretching treatment on the PVA film, and further performing crosslinking treatment, fixing treatment, washing treatment, drying treatment, and heat treatment as necessary. etc. method. At this time, the order of each treatment such as swelling treatment, dyeing treatment, crosslinking treatment, uniaxial stretching, and fixation treatment is not particularly limited, and two or more treatments may be performed simultaneously. In addition, one or two or more treatments may be performed two or more times. In addition, in the manufacturing process of all the stretched films including a polarizing film, it is optional except stretching process. For example, in the manufacturing process of the stretched film other than a polarizing film, dyeing process, fixing process, etc. may not be contained.

The swelling treatment can be performed by immersing the PVA film in water. The lower limit of the water temperature when immersed in water is preferably 20°C, more preferably 22°C, and still more preferably 25°C. On the other hand, the upper limit of the temperature is preferably 40°C, more preferably 38°C, and still more preferably 35°C. In addition, the lower limit of the immersion time in water is preferably 0.1 minutes, more preferably 0.5 minutes. On the other hand, the upper limit of the time is preferably 5 minutes, more preferably 3 minutes. In addition, the water at the time of immersion in water is not limited to pure water, It may be the aqueous solution which melt|dissolved various components, and may be the mixture of water and an aqueous medium.

The dyeing treatment can be performed by bringing a dichroic dye into contact with the PVA film. As a dichroic dye, an iodine-based dye is generally used. The timing of the dyeing treatment may be any of before the uniaxial stretching treatment, during the uniaxial stretching treatment, and after the uniaxial stretching treatment. The dyeing process is generally performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dyeing bath is preferably not less than 0.01% by mass and not more than 0.5% by mass, and the concentration of potassium iodide is preferably not less than 0.01% by mass and not more than 10% by mass. In addition, the lower limit of the temperature of the dyeing bath is preferably 20°C, more preferably 25°C. On the other hand, the upper limit of the temperature is preferably 50°C, more preferably 40°C.

By subjecting the PVA film to cross-linking treatment, it is possible to effectively prevent PVA from elution into water when wet stretching is performed at high temperature. From this viewpoint, the crosslinking treatment is preferably performed before the uniaxial stretching treatment. The crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. As the above-mentioned crosslinking agent, one or two or more kinds of boron inorganic compounds such as borates such as boric acid and borax can be used. The lower limit of the concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably 1% by mass, more preferably 2% by mass, and even more preferably 3% by mass. On the other hand, the upper limit of the concentration is preferably 15% by mass, more preferably 7% by mass, and still more preferably 6% by mass. Sufficient stretchability can be maintained by setting the concentration of the crosslinking agent within the above range. The aqueous solution containing a crosslinking agent may contain auxiliary agents such as potassium iodide. The lower limit of the temperature of the aqueous solution containing the crosslinking agent is preferably 20°C, more preferably 25°C. On the other hand, the upper limit of the temperature is preferably 50°C, more preferably 40°C. Crosslinking can be efficiently performed by making this temperature into the said range.

The uniaxial stretching treatment can be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be performed in a boric acid aqueous solution, or may be performed in the above-mentioned dyeing bath or a fixing treatment bath described later. In addition, in the case of the dry stretching method, the uniaxial stretching treatment can be performed directly at room temperature, or can be performed while heating, or can be uniaxially stretched in air using a PVA film after water absorption. Stretch treatment. Among these, a wet stretching method is preferable, and uniaxial stretching in a boric acid aqueous solution is more preferable. The lower limit of the boric acid concentration of the boric acid aqueous solution is preferably 0.5% by mass, more preferably 1.0% by mass, and even more preferably 1.5% by mass. On the other hand, the upper limit of the boric acid concentration is preferably 6% by mass, more preferably 5% by mass. In addition, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably 0.01% by mass or more and 10% by mass or less.

From the viewpoint of the polarization performance of the obtained polarizing film, the lower limit of the draw ratio in the uniaxial stretching treatment is preferably 4 times, more preferably 5 times. The upper limit of the draw ratio is not particularly limited, for example, it may be preferably 10 times, more preferably 8 times.

When producing a polarizing film, in order to firmly adsorb a dichroic dye (such as an iodine dye) to a PVA film, it is preferable to perform a fixation treatment after the uniaxial stretching treatment. As the fixing treatment bath used in the fixing treatment, an aqueous solution containing one or more boron inorganic compounds such as boric acid and borax can be used. In addition, iodine compounds and metal compounds may be added to the fixed treatment bath as needed. The lower limit of the concentration of the boron inorganic compound in the fixing treatment bath is preferably 0.5% by mass, more preferably 1% by mass. On the other hand, the upper limit of the concentration is preferably 15% by mass, more preferably 10% by mass. When the concentration is within the above range, the adsorption of the dichroic dye can be made stronger. The lower limit of the temperature of the fixed treatment bath is preferably 15°C. On the other hand, the upper limit of the temperature is preferably 60°C, more preferably 40°C.

The cleaning treatment is performed by immersing the PVA film in water or the like. At this time, from the viewpoint of improving the polarization performance, it is preferable that the water used for the cleaning treatment contains an auxiliary agent such as potassium iodide. At this time, the concentration of iodide such as potassium iodide is preferably 0.5% by mass or more and 10% by mass or less. In addition, the lower limit of the temperature of water etc. used for a washing process is 5 degreeC normally, Preferably it is 10 degreeC, More preferably, it is 15 degreeC. On the other hand, the upper limit of the temperature is usually 50°C, preferably 45°C, more preferably 40°C. From an economical point of view, it is not preferable that the temperature of water or the like is too low. On the other hand, when the temperature of water or the like is too high, the polarization performance may decrease.

The conditions of the drying treatment are not particularly limited, but the lower limit of the drying temperature is preferably 30°C, more preferably 50°C. On the other hand, the upper limit of the drying temperature is preferably 150°C, more preferably 130°C. By drying at the temperature within the above range, a polarizing film excellent in dimensional stability can be easily obtained.

By performing heat treatment after drying treatment, a polarizing film excellent in dimensional stability can be obtained. Here, the heat treatment refers to a treatment for improving the dimensional stability of the polarizing film by further heating the polarizing film having a moisture content of 5% or less after the drying treatment. The heat treatment conditions are not particularly limited, but the heat treatment is preferably performed within a range of 60°C to 150°C. If the heat treatment is performed at a temperature lower than 60° C., the dimensional stabilization effect by the heat treatment will be insufficient. On the other hand, when heat-processing at the temperature higher than 150 degreeC, yellowing may generate|occur|produce a polarizing film violently.

Example

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

[Measuring method of weight average molecular weight of liquid rubber (polyisoprene rubber)]

The weight-average molecular weights of the liquid rubbers 1 and 2 described later were determined by GPC (gel permeation chromatography) in terms of standard polystyrene-equivalent molecular weights.

In addition, the weight-average molecular weights of the rubber particles 6 and 11 described later are determined by GPC after drying the obtained aqueous dispersion and then calculating the molecular weight in terms of standard polystyrene.

The measurement apparatus and conditions of GPC are as follows.

Device: GPC device "GPC8020" manufactured by Tosoh Corporation

Separation column: "TSKgelG4000HXL" manufactured by Tosoh Corporation

Detector: "RI-8020" manufactured by Tosoh Corporation

Eluent: tetrahydrofuran

Eluent flow: 1.0ml/min

Sample concentration: 5mg/10ml

Column temperature: 40°C.

[Average particle size of rubber particles in the dispersion used for film formation]

The dispersion liquid of the rubber particles was kept warm at 25°C. The average particle diameter was determined by measuring the dynamic light scattering of the dispersion liquid using a zeta potential-particle diameter measurement system "ELS-Z2" of Otsuka Electronics Co., Ltd., and performing cumulant analysis. In addition, as the values for measuring the refractive index, viscosity, and relative permittivity of the solvent, 1.33 was used for the refractive index of water, 0.89 cP was used for the viscosity of water, and 78.3 was used for the relative permittivity of water. In addition, the noise cut level (noise cut level) was set to 0.3%, the number of accumulations was set to 70 times, and the pinhole was set to 50 μm.

[Average particle diameter of rubber particles in PVA film]

The PVA film was poured into hot water and stirred for 4 hours to dissolve the PVA. Thereafter, it was cooled to 25° C. to prepare a dispersion liquid of rubber particles. The average particle diameter was calculated|required by measuring the dynamic light scattering of this dispersion liquid using the zeta potential-particle diameter measuring system "ELS-Z2" of Otsuka Electronics Co., Ltd., and carrying out cumulative quantity analysis. In addition, as the values for measuring the refractive index, viscosity, and relative permittivity of the solvent, 1.33 was used for the refractive index of water, 0.89 cP was used for the viscosity of water, and 78.3 was used for the relative permittivity of water. In addition, the noise reduction level was set to 0.3%, the accumulation count was set to 70 times, and the pinhole was set to 50 μm.

[Stretch workability (tensile stress)]

The PVA film was conditioned at 23° C. and 50% RH for 24 hours, and a film piece of 30 mm in the longitudinal direction and 10 mm in the width direction was cut out from the PVA film. Thereafter, the PVA film was mounted on a tensile testing device ("single-column bench type testing machine: 5952") manufactured by Instron Corporation at a chuck interval of 10 mm, and pulled at a speed of 50 [mm/min]. Stretch test. The value obtained by dividing the test force [N] when the chuck distance reached 30 mm at this time by the cross-sectional area [mm ² ] of the raw material before stretching was taken as the tensile stress [N/mm ² ]. When the tensile stress is less than 70 N/mm ² , it is judged that stretching is easy and stretching workability is good.

[Transparency (380nm absorbance)]

The absorbance of the stretched film was measured using a spectrophotometer "V7100" of JASCO Corporation. Specifically, using the linearly polarized light source (Glan-Taylor prism) of the spectrophotometer, the stretched film was installed so that the polarization direction of the light source was oriented in a direction perpendicular to the stretching direction of the stretched film. The transmission spectrum at this time was measured. When the absorbance of light with a wavelength of 380 nm is less than 0.090, it is judged that the transparency is good.

[Low retardation (difference in absorbance)]

As the polarizer and the analyzer, a polarizer with a transmittance of 44 ± 0.1% and a degree of polarization of 99% or more was used, respectively, and the retardation of the stretched film was measured using a spectrophotometer "U4100" from Hitachi High Tech Systems Co., Ltd. Specifically, a polarizing plate was placed in front of a light source (non-polarized) of the spectrophotometer, and an analyzer was placed on the detector side so that its absorption axis was perpendicular to the absorption axis of the polarizing plate. The distance between the polarizing plate and the analyzer was 10 mm, and a stretched film was inserted in the middle so that the stretching direction of the stretched film faced the same direction as the absorption axis of the polarizing plate. The difference (A-B) between the absorbance (A) of light with a wavelength of 650 nm when the stretched film is not inserted and the absorbance (B) of light with a wavelength of 650 nm when the stretched film is inserted is used as an index of phase difference. When this value (A-B) is less than 0.5, it is determined that the phase difference is small.

[Synthesis Example 1] Synthesis of Rubber Particle 1

(1) Synthesis of liquid rubber 1

A fully dried 5 L autoclave was replaced with nitrogen, 1200 g of hexane and 26.2 g of n-butyllithium (a 17% by mass hexane solution) were charged, and the temperature was raised to 50°C. Thereafter, 1200 g of isoprene was gradually added under stirring conditions while controlling the polymerization temperature to reach 50° C., and the mixture was polymerized for 1 hour. Thereafter, methanol was added to stop the polymerization reaction to obtain a polymer solution. Water was added and stirred to the obtained polymer solution, and the polymer solution was washed with water. After the stirring was completed and the separation of the polymer solution phase and the water phase was confirmed, water was separated. The polymer solution after washing was vacuum-dried at 70° C. for 24 hours to obtain liquid polyisoprene (liquid rubber 1 ).

The weight average molecular weight of the obtained liquid rubber 1 (polyisoprene rubber) was 28,000.

(2) Preparation of the aqueous dispersion of rubber particles 1

15 g of an emulsifier (“Fosfanol RS-710” manufactured by Toho Chemical Industry Co., Ltd.) was added to 250 g of the above liquid rubber 1, followed by stirring for 20 minutes. Next, 177 g of water was added little by little while stirring. After adding a specific amount of water, the mixture was stirred for 20 minutes to obtain an aqueous dispersion of rubber particles 1 (polyisoprene rubber particles).

The average particle diameter of the rubber particles 1 in the obtained aqueous dispersion was 293 nm.

[Synthesis Example 2] Synthesis of rubber particles 2

(1) Synthesis of liquid rubber 2

500 g of the above-mentioned liquid rubber 1 was put into a 1 L autoclave replaced with nitrogen, and 25 g of maleic anhydride and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (large "ノクラック 6C" of Nei Shinshin Chemical Industry Co., Ltd.) 0.5 g. These were reacted at 170°C for 24 hours to obtain maleic anhydride-modified liquid polyisoprene (liquid rubber 2).

The weight average molecular weight of the obtained liquid rubber 2 (polyisoprene rubber) was 30,000.

(2) Preparation of aqueous dispersion of liquid rubber 2

Except using the liquid rubber 2 to replace the liquid rubber 1 of the above-mentioned synthesis example 1 (2), the same procedure as the preparation of the aqueous dispersion of the rubber particle 1 in the above-mentioned synthesis example 1 (2) was performed to obtain the rubber particle 2 (modified by maleic anhydride) aqueous dispersion of polyisoprene rubber particles).

The average particle diameter of the rubber particles 2 in the obtained aqueous dispersion was 460 nm.

[Synthesis Example 3] Synthesis of rubber particles 3

(Process 1)

Add 300 g of ion-exchanged water, 60.0 g of an emulsifier ("Latemur ASK" from Kao Corporation) and a water-soluble azo polymerization initiator ("VA-086" from Fuji Film Wako Pure Chemical Industries, Ltd.) to a dried 500 mL pressure-resistant polymerization tank. ”) after 1.0 g, was deoxidized by bubbling nitrogen gas for 30 minutes to obtain an aqueous solution. After raising the temperature of the aqueous solution to 60° C., 153.0 g of a deoxidized monomer mixture (isoprene:tert-dodecylmercaptan=100:3.0 (mass ratio)) was continuously added at a rate of 2 mL/min.

(Process 2)

When it was confirmed that the total monomer conversion rate exceeded 99% by mass, the temperature of the emulsion obtained in Step 1 was raised to 90° C. and stirred for 2 hours to decompose the residual polymerization initiator. The polymerization tank was cooled to 25° C. to obtain an aqueous dispersion of rubber particles 3 (polyisoprene rubber particles).

The average particle diameter of the rubber particles 3 in the obtained aqueous dispersion was 86 nm.

In addition, the total monomer conversion rate was calculated by the following method (the same applies hereinafter).

(total monomer conversion rate)

The particles were settled by dropping the emulsion (1 mL) sampled every 1 hour from the start of the polymerization into acetone (20 mL). The solid content obtained after removing the supernatant was vacuum-dried at 0.1 kPa and 60°C using a vacuum dryer (square vacuum constant temperature dryer "DP23" from Yamato Scientific Co., Ltd.) until the mass no longer changed. The monomer conversion rate (mass %) was calculated from the mass of the sampled emulsion, the monomer concentration at the start of the emulsion polymerization, and the mass of the dried solid content.

[Synthesis Example 4] Synthesis of rubber particles 4

(1) Synthesis of liquid rubber 3

Polystyrene was obtained by the same method as the synthesis of liquid rubber 1 in Synthesis Example 1 (1), except that 1,200 g of isoprene and 120 g of styrene were used instead of 1,200 g of isoprene in Synthesis Example 1 (1) above. Copolymerized liquid polyisoprene (Liquid Rubber 3).

(2) Preparation of aqueous dispersion of rubber particles 4

Except using the liquid rubber 3 instead of the liquid rubber 1 of the above-mentioned synthesis example 1 (2), the preparation of the aqueous dispersion of the rubber particle 1 in the above-mentioned synthesis example 1 (2) was performed in the same manner to obtain the rubber particle 4 (polyisoprene Aqueous dispersion of vinyl rubber particles).

The average particle diameter of the rubber particles 4 in the obtained aqueous dispersion was 819 nm.

[Synthesis Example 5] Synthesis of rubber particles 5

In Step 1 of Synthesis Example 3 above, the mass of the emulsifier was set at 60.0 g, and a monomer mixture (isoprene:tert-dodecylmercaptan=100:1.5 (mass ratio) was used as the monomer mixture ) was 152.3 g, and was synthesized by the same method as in Synthesis Example 3 to obtain an aqueous dispersion of rubber particles 5 (polyisoprene rubber particles).

The average particle diameter of the rubber particles 5 in the obtained aqueous dispersion was 63 nm.

[Synthesis Example 6] Synthesis of rubber particles 6

(Process 1)

After adding 300 g of ion-exchanged water, 10.6 g of emulsifier ("Eleminol JS-20" of Sanyo Chemical Industry Co., Ltd.) and 0.01 g of sodium peroxodisulfate to a dried 500 mL pressure-resistant polymerization tank, nitrogen gas was bubbled for 30 minutes. Deoxidation treatment was carried out to obtain an aqueous solution. After the above aqueous solution was heated to 70°C, the deoxidized monomer mixture (n-butyl acrylate: trimethylolpropane trimethacrylate: allyl methacrylate = 100: 1:1 (mass ratio)) 117g.

(Process 2)

When it was confirmed that the total monomer conversion rate exceeded 99% by mass, the temperature of the emulsion obtained in Step 1 was raised to 90° C. and stirred for 2 hours to decompose the residual polymerization initiator. The polymerization tank was cooled to 25° C. to obtain an aqueous dispersion of rubber particles 6 (polybutylacrylate (BA) rubber particles).

The average particle diameter of the rubber particles 6 in the obtained aqueous dispersion was 99 nm.

Moreover, the weight average molecular weight calculated|required by drying the obtained aqueous dispersion liquid was 87,200.

[Synthesis Example 7] Synthesis of rubber particles 7

(Process 1)

It synthesize|combined by the method similar to the process 1 of the synthesis example 6 except having made the mass of the monomer mixture into 87g in the process 1 of the said synthesis example 6.

(Process 2)

When it was confirmed that the total monomer conversion rate exceeded 99% by mass, 29 g of deoxygenated dicyclopentyl methacrylate (TCDMA) was continuously added to the emulsion obtained in the above step 1 at a rate of 1 mL/min.

(Process 3)

When it was confirmed that the total monomer conversion rate exceeded 99% by mass, the temperature of the emulsion obtained in the above-mentioned step 2 was raised to 90° C. and stirred for 2 hours to decompose the residual polymerization initiator. The polymerization tank was cooled to 25° C. to obtain an aqueous dispersion of TCDMA-coated rubber particles 7 (BA/TCDMA rubber particles).

The average particle diameter of the rubber particles 7 in the obtained aqueous dispersion was 96 nm.

[Synthesis Example 8] Synthesis of rubber particles 8

In step 1 of the above-mentioned synthesis example 7, the mass of the monomer mixture was set to 58.1 g, and in the step 2, the mass of dicyclopentyl methacrylate was set to 57.0 g. The method was used to synthesize, and the aqueous dispersion of rubber particles 8 (BA/TCDMA rubber particles) was obtained.

The average particle diameter of the rubber particles 8 in the obtained aqueous dispersion was 92 nm.

[Synthesis Example 9] Synthesis of rubber particles 9

In step 1 of the above-mentioned synthesis example 7, the mass of the monomer mixture is set to 27.9 g, and in the step 2, the mass of dicyclopentanyl methacrylate is set to 85.5 g. The method was used to synthesize, and the aqueous dispersion of rubber particles 9 (BA/TCDMA rubber particles) was obtained.

The average particle diameter of the rubber particles 9 in the obtained aqueous dispersion was 92 nm.

[Synthesis Example 10] Synthesis of Rubber Particles 10

(Process 1)

After adding 300 g of ion-exchanged water, 10.6 g of emulsifier ("Eleminol JS-20" of Sanyo Chemical Industry Co., Ltd.) and 0.01 g of sodium peroxodisulfate to a dried 500 mL pressure-resistant polymerization tank, nitrogen gas was bubbled for 30 minutes. Deoxidation treatment was carried out to obtain an aqueous solution. After raising the temperature of the aqueous solution to 70° C., 114 g of deoxygenated dicyclopentyl methacrylate was continuously added at a rate of 2 mL/min.

(Process 2)

When it was confirmed that the total monomer conversion rate exceeded 99% by mass, the temperature of the emulsion obtained in Step 1 was raised to 90° C. and stirred for 2 hours to decompose the residual polymerization initiator. The polymerization tank was cooled to 25° C. to obtain an aqueous dispersion of rubber particles 10 (TCDMA rubber particles).

The average particle diameter of the rubber particles 10 in the obtained aqueous dispersion was 106 nm.

[Synthesis Example 11] Synthesis of Rubber Particles 11

In Step 1 of Synthesis Example 10 above, 151 g of a monomer mixture (n-butyl acrylate:tert-dodecylmercaptan=100:0.8 (mass ratio)) was used instead of 114 g of dicyclopentanyl methacrylate, and Otherwise, synthesis was carried out in the same manner as in Synthesis Example 10 to obtain an aqueous dispersion of rubber particles 11 (BA rubber particles).

The average particle diameter of the rubber particles 11 in the obtained aqueous dispersion was 130 nm.

Moreover, the weight average molecular weight calculated|required by drying the obtained aqueous dispersion liquid was 77,200.

[Synthesis Example 12] Synthesis of Rubber Particles 12

(Process 1)

In step 1 of Synthesis Example 10 above, the mass of the emulsifier was set to 24.0 g, and a monomer mixture (n-butyl acrylate: trimethylolpropane trimethacrylate: allyl methacrylate=100: 1:1 (mass ratio)) 117 g instead of 114 g of dicyclopentanyl methacrylate, and it was the same as the process 1 of the synthesis example 10 except that.

(Process 2)

In the step 2 of the above-mentioned synthesis example 10, when the conversion rate of the total monomer was confirmed to exceed 99% by mass, the temperature of the emulsion obtained in the above-mentioned step 1 was raised to 90°C. 2. In the same manner, an aqueous dispersion of rubber particles 12 (BA rubber particles) was obtained.

The average particle diameter of the rubber particles 12 in the obtained aqueous dispersion was 47 nm.

[Synthesis Example 13] Synthesis of Rubber Particles 13

In step 1 of Synthesis Example 10 above, the mass of the emulsifier was set to 10.6 g, and a monomer mixture (n-butyl acrylate: trimethylolpropane trimethacrylate: allyl methacrylate=100: 1:1 (mass ratio)) 117 g instead of 114 g of dicyclopentyl methacrylate, and synthesized by the same method as in Synthesis Example 10, to obtain an aqueous dispersion of rubber particles 13 (BA rubber particles).

The average particle diameter of the rubber particles 13 in the obtained aqueous dispersion was 285 nm.

[Synthesis Example 14] Synthesis of Rubber Particles 15

(1) Synthesis of liquid rubber 4

Except for using 1200g of butadiene instead of 1200g of isoprene in Synthesis Example 1 (1), the same operation was performed as in Synthesis Example 1 (1) Liquid Rubber 1 to obtain liquid polybutadiene (Liquid Rubber 4 ).

(2) Preparation of aqueous dispersion of rubber particles 15

Except using the liquid rubber 4 instead of the liquid rubber 1 of the above-mentioned synthesis example 1 (2), the preparation of the aqueous dispersion of rubber particles 1 in the above-mentioned synthesis example 1 (2) was performed in the same manner to obtain rubber particles 15 (polybutadiene Aqueous dispersion of rubber particles).

The average particle diameter of the rubber particles 15 in the obtained aqueous dispersion was 463 nm.

(other used rubber particles)

As the rubber particles 14 , an aqueous dispersion of silicone rubber particles ("Seranet WSA-1070" manufactured by DIC Corporation) was prepared. The average particle diameter of the rubber particles 14 in this aqueous dispersion was 61 nm.

[Example 1]

(production of PVA film)

100 parts by mass of PVA (a saponified product of a homopolymer of vinyl acetate, a degree of polymerization of 2,400, and a degree of saponification of 99.5 mol%), 120 parts by mass of rubber particles as rubber particles, and 10 parts by mass of glycerin as a plasticizer 1. Mix 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant with water to prepare a film-forming stock solution with a volatile content of 85% by mass. It should be noted that the rubber particles 1 were mixed with other components in the state of the aqueous dispersion obtained in Synthesis Example 1 above. The above-mentioned film-making stock solution was cast on a metal drum at 80°C, and dried until the volatile matter (moisture content) reached 5% by mass to obtain a long PVA film with a thickness of 30 μm, a length of 1.5 m, and a width of 30 cm (PVA before heat treatment membrane). This PVA film was heat-treated at a temperature of 110° C. for 10 minutes to obtain the PVA film of Example 1.

(production of stretch film)

The PVA film was cut into a width of 100 mm x a length of 100 mm. Attach the PVA film to the stretching jig so that the distance between the chucks reaches 50mm, and immerse it in a 50°C, 4% by mass boric acid aqueous solution. The raw material is used as a reference at 0.12m/min, and the stretching ratio reaches 5.6 times. way to stretch. After the stretching was completed, the jig was pulled out from the boric acid aqueous solution, and the boric acid aqueous solution adhering to the surface and back of the film was removed with filter paper. Then, it was made to dry for 4 minutes with the dryer of 80 degreeC, and the stretched film of Example 1 was obtained.

[Examples 2~4, Comparative Examples 1~15]

The PVA films and stretched films of Examples 2 to 4 and Comparative Examples 1 to 15 were obtained in the same manner as in Example 1 except that the type and compounding amount of the rubber particles used were as shown in Table 1. In addition, in Comparative Example 1, no rubber particles were used.

[evaluate]

For each of the PVA films and stretched films obtained in Examples 1 to 4 and Comparative Examples 1 to 15, stretch processability, transparency, and low retardation properties were evaluated by the above-mentioned method. Table 1 shows the evaluation results. Moreover, the average particle diameter was measured by the said method about the rubber particle in each obtained PVA film. The measurement results are shown in Table 1. The average particle diameter of rubber particles such as polyisoprene rubber particles in the PVA film is slightly larger than the average particle diameter of the rubber particles in the film-forming stock solution used. It is presumed that this is because the result of measuring the average particle diameter of the rubber particles in the PVA film by dissolving and redispersing the PVA film is that the rubber particles at this time are in a state where PVA is attached to the surface of the rubber particles due to the protective colloid effect of PVA. Redispersion was carried out.

[Table 1]

As shown in Table 1, it can be seen that the stretching processability of the PVA films of Examples 1 to 4 was good, and the transparency and low phase difference of the obtained stretched film were good.

Industrial availability

The PVA film and stretched film of the present invention can be used for packaging films, water-soluble films, agricultural films, release films, optical films, and the like.

Claims (6)

1. A polyvinyl alcohol film comprising polyvinyl alcohol (A) and polyisoprene rubber particles (B),

the average particle diameter of the polyisoprene rubber particles (B) is more than 85nm and less than 700nm,

the content of the polyisoprene rubber particles (B) is 3 parts by mass or more and 35 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A), the degree of polymerization of the polyvinyl alcohol (A) is 1,000 or more and 10,000 or less, and the degree of saponification is 95 mol% or more.

2. The polyvinyl alcohol film according to claim 1, having a thickness of 1 μm or more and 60 μm or less.

3. The polyvinyl alcohol film according to claim 1 or 2, which is a raw material film for an optical film.

4. A stretched film obtained from the polyvinyl alcohol film according to any one of claims 1 to 3.

5. The stretched film according to claim 4, which is an optical film.

6. A method for producing a polyvinyl alcohol film, comprising a step of forming a film using a film-forming dope in which a polyvinyl alcohol (A) and a dispersion liquid containing polyisoprene rubber particles (B) are mixed,

the average particle diameter of the polyisoprene rubber particles (B) in the dispersion is 70nm to 500nm,

the content of the polyisoprene rubber particles (B) in the film-forming stock solution is 3 parts by mass or more and 35 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A), the degree of polymerization of the polyvinyl alcohol (A) is 1,000 or more and 10,000 or less, and the degree of saponification is 95 mol% or more.