JP7215160B2 - POLYVINYL ALCOHOL-BASED FILM FOR PRODUCING POLARIZING FILM, METHOD FOR MANUFACTURING THE SAME, AND POLARIZING FILM - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol film and a method for producing the same. More particularly, it relates to a polyvinyl alcohol-based film with few bubble defects and a method for producing the same.

BACKGROUND ART Conventionally, polyvinyl alcohol-based films have been used in many applications as films having excellent transparency and dyeability, and are used as optical polyvinyl alcohol-based films for polarizing films and the like. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has expanded to high-luminance, high-definition liquid crystal televisions. In addition to liquid crystal televisions, they are also widely used in smartphones, tablets, personal computers, projectors, and automotive panels. In such an optical polyvinyl alcohol film, a polarizing film with less display defects is required as the screens of liquid crystal televisions and the like become thinner and larger. In order to produce such a polarizing film, it is necessary to improve the original polyvinyl alcohol film.

In addition, the polyvinyl alcohol film is characterized by water solubility by adjusting the degree of saponification of the polyvinyl alcohol resin and introducing (denaturing) an anionic functional group into the polyvinyl alcohol molecular chain. It is also used as a water-soluble film. Specifically, packaging (unit packaging) for chemicals such as agricultural chemicals and detergents, (hydraulic) transfer film, sanitary products such as napkins and paper diapers, waste treatment products such as ostomy bags, medical supplies such as blood absorbing sheets, and seedling raising. It is used for temporary substrates such as sheets, seed tapes, and embroidery base fabrics. In particular, in unit packaging applications for chemicals such as agricultural chemicals and detergents, there is an advantage that the labor of measuring the amount of each chemical at the time of use can be saved and hands are not soiled. Such a polyvinyl alcohol-based water-soluble film is increasingly used for packaging liquid products such as liquid detergents, and from the viewpoint of preventing liquid leakage, there is a need for drug packages with few air bubbles. In order to manufacture such a drug package, it is necessary to improve the polyvinyl alcohol-based film that serves as the original fabric.

As a polyvinyl alcohol-based film used for such optical film applications, a polyvinyl alcohol-based film containing two or more surfactants in a polyvinyl alcohol-based resin (see, for example, Patent Documents 1 and 2) and the like are known. ing.

Further, as a polyvinyl alcohol film used for such a water-soluble film, for example, 5 to 30 parts by weight of a plasticizer, 1 to 10 parts by weight of starch and 0.01 to 2 parts by weight of a surfactant are added to 100 parts by weight of polyvinyl alcohol. A water-soluble film (see, for example, Patent Literature 3) is known in which a part is blended.

Japanese Patent Application Laid-Open No. 2005-206809 Japanese Patent Application Laid-Open No. 2005-206810 Japanese Patent Application Laid-Open No. 2001-329130

However, although the polyvinyl alcohol-based films disclosed in Patent Documents 1 and 2 have few optical streaks, optical spots and the like and are excellent in blocking properties, they are insufficient as countermeasures against air bubble defects generated in the film. However, there are concerns about quality problems such as the occurrence of display defects when used as a polarizing film, and further improvements have been desired.

Further, the polyvinyl alcohol-based film disclosed in Patent Document 3 is excellent in water solubility, blocking resistance, and impact bursting strength. There are concerns about quality issues such as liquid leakage when packaging liquid products using this method and storing them for a long period of time, and appearance defects due to ink splashing at air bubble defects when printed on packaging film, and further improvements are desired. It was something that could be done.

Under such circumstances, an object of the present invention is to provide a polyvinyl alcohol-based film with few bubble defects and a method for producing a polyvinyl alcohol-based film.

However, as a result of intensive research in view of such circumstances, the present inventors investigated in detail the relationship between the constituent components of the polyvinyl alcohol film and the blending method, and found that the polyvinyl alcohol resin contained a small amount of a lower monohydric alcohol component. The inventors have found that a polyvinyl alcohol-based film can achieve the above object, and completed the present invention.

That is, the gist of the present invention is a polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin (A) as a main component, containing 1-2000 ppm of a monohydric alcohol having 1 to 3 carbon atoms, and containing the polyvinyl alcohol-based resin ( A) Contains 1 to 35 parts by weight of a plasticizer per 100 parts by weight, the polyvinyl alcohol resin (A) has a weight average molecular weight of 100,000 to 300,000, and an average degree of saponification of 99.5 mol%. The present invention relates to a polyvinyl alcohol-based film for producing a polarizing film characterized by the above.
The present invention provides (I) a polyvinyl alcohol resin composition containing polyvinyl alcohol resin (A) as a main component and containing 1 to 35 parts by weight of a plasticizer with respect to 100 parts by weight of the polyvinyl alcohol resin (A). (II) a step of adding 0.001 to 3 % by weight of a monohydric alcohol having 1 to 3 carbon atoms to the polyvinyl alcohol resin aqueous solution; (III) a step of forming a film using the polyvinyl alcohol resin aqueous solution obtained in the step (II), in this order, the polyvinyl alcohol resin (A) having a weight average molecular weight of 100,000 to 300,000, The present invention also relates to a method for producing a polyvinyl alcohol film for producing a polarizing film, characterized by having an average degree of saponification of 99.5 mol % or more.
However, the polyvinyl alcohol film for producing a polarizing film of the present invention does not contain a dichroic dye.

Since the polyvinyl alcohol-based film of the present invention suppresses air bubble defects, it has few display defects when used as a polarizing film, and when used as a liquid product package, it has excellent liquid leakage resistance during long-term storage. Become.

The present invention will be specifically described below.
The polyvinyl alcohol-based film of the present invention must contain a polyvinyl alcohol-based resin as a main component and contain 1-2000 ppm of a monohydric alcohol having 1 to 3 carbon atoms.
Hereinafter, polyvinyl alcohol may be abbreviated as "PVA", and a film containing a polyvinyl alcohol-based resin as a main component may be abbreviated as "PVA-based film".

The content of monohydric alcohol having 1 to 3 carbon atoms is preferably 5 to 1000 ppm, particularly preferably 10 to 500 ppm. If the content of the monohydric alcohol having 1 to 3 carbon atoms is less than the lower limit, large bubbles are likely to be generated in the solution due to stirring during film production, and those that remain without disappearing until film formation form the film. It becomes a bubble defect. On the other hand, if the content exceeds the upper limit, a large amount of the lower alcohol component is vaporized when the film is dried at a high temperature after forming the film, resulting in the generation of fine air bubbles, resulting in air bubble defects in the film. I don't get it.
In addition, a monohydric alcohol having 4 or more carbon atoms is not preferable because the water solubility of the monohydric alcohol is low and the hydrophilicity is insufficient, so that the turbidity and viscosity stability of the aqueous PVA-based resin solution may decrease.

Such monohydric alcohols having 1 to 3 carbon atoms may contain an ether bond in their structure, and specific examples include methanol, ethanol, 1-propanol, 2-propanol, cyclopropanol, methoxymethanol, ethoxymethanol. , 2-methoxyethanol, and the like.

Among these, monohydric alcohols containing no ether bond in the structure are preferred from the viewpoint of safety, methanol and ethanol are particularly preferred from the viewpoint of hydrophilicity, and ethanol is more preferred from the viewpoint of environmental toxicity.

Moreover, these monohydric alcohols can be used alone, or two or more of them can be used in combination.

The content of monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film is quantitatively measured by gas chromatography/mass spectrometry (GC/MS) equipped with a dynamic headspace device.
Specifically, a film sample (approximately 5 mg) was volatilized at 120°C for 60 minutes in a dynamic headspace device to evaporate the monohydric alcohol component, and the gas components collected by the agglomeration device were transferred to the GC/MS device. identification and quantification. Identify the monohydric alcohol component from the MS spectrum of GC, determine the volatilization amount from the peak area of the abundance intensity obtained by GC based on the calibration curve of each alcohol component, and from the weight of the film sample subjected to measurement By conversion, the content of monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film can be obtained.
When two or more types of monohydric alcohols having 1 to 3 carbon atoms are contained together, the total value of the detected alcohol contents is calculated as the content of monohydric alcohols having 1 to 3 carbon atoms. be able to.

The PVA-based film of the present invention contains a PVA-based resin (A) as a main component.
First, the PVA-based resin (A) used in the present invention will be described.

As the PVA-based resin (A) used in the present invention, an unmodified PVA-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol % or less, preferably 5 mol % or less) of a component copolymerizable with vinyl acetate, or a saponified A resin obtained by chemically modifying the hydroxyl group later can also be used.

The weight average molecular weight of the PVA-based resin (A) is preferably 20,000 to 300,000, particularly preferably 50,000 to 280,000, further preferably 100,000 to 260,000. If the weight-average molecular weight is too small, the degree of polarization of the polarizing film tends to decrease, and if it is too large, stretching during the production of the polarizing film tends to be difficult. The weight average molecular weight of the PVA-based resin is the weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the PVA-based resin (A) used in the present invention is generally preferably 80 mol% or more, particularly preferably 90 mol% or more, still more preferably 99 mol% or more, particularly preferably 99.0 mol% or more. It is 5 mol % or more. If the average degree of saponification is too small, the degree of polarization of the polarizing film tends to decrease.
Here, the average degree of saponification in the present invention is measured according to JIS K6726.

As the PVA-based resin (A) used in the present invention, two or more resins having different weight average molecular weights, average saponification degrees, modified species, and modified amounts may be used in combination.

In the PVA-based film of the present invention, in addition to the PVA-based resin (A), additives such as a plasticizer (B) and A surfactant (C) is added.

The plasticizer (B) generally effectively contributes to stretchability when producing a polarizing film. Examples include alkylene glycols or polyalkylene glycols such as ethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and polypropylene glycol, and trimethylolpropane. These plasticizers (B) can be used alone or in combination of two or more. Particularly preferred among these are glycerin alone, a combination of glycerin and diglycerin, or a combination of glycerin and trimethylolpropane. When glycerin and diglycerin are used together, usually glycerin/diglycerin (weight ratio) = 20/80 to 80/20, when glycerin and trimethylolpropane are used together, usually glycerin/trimethylolpropane (weight ratio )=20/80 to 80/20.

The content of the plasticizer (B) is preferably 1 to 35 parts by weight, particularly 3 to 30 parts by weight, and further 5 to 25 parts by weight based on 100 parts by weight of the PVA resin (A). is preferably If the content of the plasticizer (B) is too small, the stretchability of the polarizing film will tend to deteriorate, and if it is too large, the resulting PVA-based film will tend to have reduced strength.

The surfactant (C) used in the present invention generally has the function of suppressing the smoothness of the film surface and adhesion between films when wound into a roll. , anionic surfactants and cationic surfactants can be used alone or in combination of two or more.

Examples of nonionic surfactants include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene Tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, coconut oil reduced alcohol ethylene oxide adduct, beef tallow reduced alcohol ethylene Polyoxyethylene alkyl ethers such as oxide adducts, caproic acid mono- or diethanolamide, caprylic acid mono- or diethanolamide, capric acid mono- or diethanolamide, lauric acid mono- or diethanolamide, palmitic acid mono- or diethanolamide, stearic acid mono- or Diethanolamide, oleic acid mono- or di-ethanolamide, coconut oil fatty acid mono- or di-ethanolamide, or higher fatty acid alkanolamide such as propanolamide, butanolamide, caproic acid amide, caprylic acid amide, capric acid amide instead of these ethanolamides , lauric acid amide, palmitic acid amide, stearic acid amide, higher fatty acid amide such as oleic acid amide, hydroxyethyllaurylamine, polyoxyethylenehexylamine, polyoxyethyleneheptylamine, polyoxyethyleneoctylamine, polyoxyethylenenonylamine , Polyoxyethylenedecylamine, Polyoxyethylenedodecylamine, Polyoxyethylenetetradecylamine, Polyoxyethylenehexadecylamine, Polyoxyethyleneoctadecylamine, Polyoxyethyleneoleylamine, Polyoxyethylenelaurylamine, Polyoxyethyleneeicosylamine polyoxyethylene alkylamine, polyoxyethylene caproamide, polyoxyethylene caprylic acid amide, polyoxyethylene capric acid amide, polyoxyethylene lauric acid amide, polyoxyethylene palmitic acid amide, polyoxyethylene stearic acid amide, etc. Polyoxyethylene higher fatty acid amide such as polyoxyethylene oleic acid amide, dimethyllaurylamine oxides, amine oxides such as dimethylstearyl oxide and dihydroxyethyllaurylamine oxide, and fluoroalkyl acids such as perfluorooctanoic acid.

Examples of the above anionic surfactants include, for example, sulfate salts of sodium hexylsulfate, sodium heptylsulfate, sodium octylsulfate, sodium nonylsulfate, sodium decylsulfate, sodium dodecylsulfate, sodium tetradecylsulfate, sodium hexadecylsulfate, octadecyl Sodium sulfate, sodium eicosyl sulfate, or alkyl sulfate ester salts such as potassium salts, calcium salts, and ammonium salts thereof, sodium polyoxyethylene hexyl ether sulfate, sodium polyoxyethylene heptyl ether sulfate, sodium polyoxyethylene octyl ether sulfate, poly Sodium oxyethylene nonyl ether sulfate, sodium polyoxyethylene decyl ether sulfate, sodium polyoxyethylene dodecyl ether sulfate, sodium polyoxyethylene tetradecyl ether sulfate, sodium polyoxyethylene hexadecyl ether sulfate, sodium polyoxyethylene octadecyl ether sulfate, poly Sodium oxyethylene eicosyl ether sulfate, or polyoxyethylene alkyl ether sulfates such as potassium salts and ammonium salts thereof, sodium polyoxyethylene hexylphenyl ether sulfate, sodium polyoxyethylene heptylphenyl ether sulfate, polyoxyethylene octylphenyl ether sodium sulfate, sodium polyoxyethylene nonylphenyl ether sulfate, sodium polyoxyethylene decylphenyl ether sulfate, sodium polyoxyethylene dodecylphenyl ether sulfate, sodium polyoxyethylene tetradecylphenyl ether sulfate, sodium polyoxyethylene hexadecylphenyl ether sulfate, Sodium polyoxyethylene octadecyl phenyl ether sulfate, sodium polyoxyethylene eicosyl phenyl ether sulfate, or polyoxyethylene alkyl phenyl ether sulfates such as potassium salts and ammonium salts thereof, sodium caproic acid ethanolamide sulfate, caprylic acid ethanolamide sulfate sodium, sodium capric ethanolamide sulfate, sodium lauric ethanolamide sulfate, sodium palmitic ethanolamide sulfate, sodium stearic ethanolamide sulfate, sodium oleic ethanolamide sulfate, or potassium Furthermore, in place of these ethanolamides, higher fatty acid alkanolamide sulfate ester salts such as propanolamide and butanolamide, sulfated oils, higher alcohol ethoxysulfate, monoglysulfate and the like can be used. In addition to the above sulfate ester salt type, fatty acid soap, N-acyl amino acid and its salt, polyoxyethylene alkyl ester carboxylate, carboxylate type such as acylated peptide, alkylbenzene sulfonate, alkylnaphthalene sulfonate , naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin condensate, dialkyl sulfosuccinic acid ester salt, alkyl sulfosuccinic acid di-salt, polyoxyethylene alkyl sulfosuccinic acid di-salt, alkyl sulfoacetate, α-olefin sulfone acid salts, N-acylmethyltaurate salts, sulfonate types such as dimethyl-5-sulfoisophthalate sodium salt, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, alkyl phosphates, etc. Phosphate ester salt type of is also included.

Examples of the cationic surfactant include laurylamine hydrochloride, lauryltrimethylammonium chloride, laurylpyridinium chloride and the like.

The surfactant (C) may be used alone, or two or more may be used in combination, and the combined use of an anionic surfactant and a nonionic surfactant improves the transparency of the film. is preferred.

Among these, nonionic surfactants are preferred, more preferably higher fatty acid alkanolamides, more preferably lauric acid mono- or diethanolamide, palmitic acid mono- or diethanolamide, stearic acid mono- or diethanolamide, oleic acid mono- or Diethanolamide, particularly preferably lauric acid mono- or diethanolamide, more preferably lauric acid diethanolamide.

The content of the surfactant (C) is preferably 0.01 to 1 part by weight, particularly preferably 0.02 to 0.5 part by weight, based on 100 parts by weight of the PVA resin (A). , more preferably 0.03 to 0.2 parts by weight. If the content of the surfactant (C) is too small, it tends to be difficult to obtain an anti-blocking effect, and if it is too large, the transparency of the film tends to decrease.

Further, when an anionic surfactant and a nonionic surfactant are used in combination, the anionic surfactant is 0.01 to 1 part by weight, particularly 0 part by weight, with respect to 100 parts by weight of the PVA resin (A). 0.02 to 0.2 parts by weight, preferably 0.03 to 0.1 parts by weight, and a nonionic surfactant of 0.01 to 1 part by weight, particularly 0.02 to 0.2 parts by weight parts, more preferably 0.03 to 0.1 parts by weight. If the amount of the anionic surfactant is too small, the dispersibility of the dye during the production of the polarizing film tends to decrease and staining spots tend to increase. If the amount of nonionic surfactant is too small, it will be difficult to obtain an anti-blocking effect.

In addition, as other additives, it is also useful to add an antioxidant to prevent yellowing of the film. Di-t-butyl-p-cresol, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol) and the like are preferred. . The antioxidant is preferably used in the range of about 2 to 100 ppm with respect to the PVA-based resin (A).

In the present invention, it is important that the PVA-based resin (A) is the main component of the PVA-based film from the viewpoint of film physical properties such as transparency, thickness accuracy, retardation uniformity, and dyeability. The content of the PVA-based resin (A) in the PVA-based film is preferably 35% by weight or more, particularly preferably 50% by weight or more, further preferably 80% by weight or more. If the content is too small, the strength of the PVA-based film tends to decrease. The upper limit of the content is usually not particularly limited, but from the viewpoint of stretchability when preparing a polarizing film, it is preferably 99% by weight or less, particularly preferably 97% by weight or less, and further preferably 95% by weight or less. be.

<Production of PVA-based film>
The PVA-based film of the present invention can be produced by the following method.
A PVA-based resin composition containing the PVA-based resin (A), preferably a plasticizer (B), a surfactant (C), etc. is obtained, and (I) the polyvinyl alcohol-based resin (A) is obtained. dissolution step of dissolving a polyvinyl alcohol resin composition as a main component to obtain an aqueous polyvinyl alcohol resin solution; A step of preparing a film-forming raw material containing 5% by weight, (III) a film-forming step of forming a film using the polyvinyl alcohol-based resin aqueous solution (film-forming raw material) obtained in the step (II), in this order. A PVA-based film is produced by a manufacturing method characterized by containing.

A lower alcohol may be used as a solvent in the polymerization process and the saponification process for the PVA-based resin, which is the raw material for the PVA-based film, and a small amount of alcohol-based solvent may remain in the produced PVA-based resin. There is However, in the dissolution process in film production, dissolution is generally performed for a long time at a temperature higher than the boiling point of the alcohol solvent, so the alcohol solvent remaining in the raw material volatilizes and is discharged outside the system. No alcohol-based solvent remains in the normally produced PVA-based film.
In the present invention, focusing on the effect of the solvent, the PVA-based aqueous solution after dissolution, in which the alcohol-based solvent usually disappears and does not remain, is dared to contain a monohydric alcohol to form a film, thereby forming air bubbles in the film. We have newly found that the generation can be controlled.
Each step will be specifically described below.

[[I] dissolving step]
In the dissolving step, the PVA-based resin composition is dissolved or dispersed in water to prepare a PVA-based resin aqueous solution or water dispersion.
In the present invention, the dissolving step refers to the step of dissolving or dispersing the PVA-based resin composition in water to obtain an aqueous solution or aqueous dispersion free of undissolved matter.
As the dissolution method for dissolving the PVA-based resin composition in water, normal temperature dissolution, high temperature dissolution, pressurized dissolution, etc. are usually adopted. Dissolution and pressurized dissolution are preferred.

The melting temperature is usually 80 to 100°C, preferably 90 to 100°C, in the case of high-temperature melting, and is usually 80 to 140°C, preferably 90 to 130°C, in the case of pressure melting. The dissolution time may be appropriately adjusted depending on the dissolution temperature and pressure during dissolution, and is usually 1 to 20 hours, preferably 2 to 15 hours, more preferably 3 to 10 hours. If the dissolution time is too short, undissolved matter tends to remain, and if it is too long, productivity tends to decrease.

In addition, in the dissolving step, examples of the stirring impeller include a paddle, full zone, Maxblend, twister, anchor, ribbon, propeller and the like.
Further, after dissolution, the obtained PVA-based resin aqueous solution is subjected to a defoaming treatment. be done. Among them, stationary defoaming and twin-screw extrusion defoaming are preferable. The temperature for stationary defoaming is usually 50 to 100° C., preferably 70 to 95° C., and the defoaming time is usually 2 to 30 hours, preferably 5 to 20 hours.

[[II] Monohydric alcohol compounding step having 1 to 3 carbon atoms]
The PVA-based film of the present invention is prepared by adding a monohydric alcohol having 1 to 3 carbon atoms to the aqueous PVA-based resin solution after the dissolution step, that is, after preparing the aqueous PVA-based resin solution in which the PVA-based resin composition is dissolved. It can be obtained by preparing a raw material for film formation with the content of 0.001 to 5% by weight, and then manufacturing in the order of film formation.

In the present invention, it is important to add a monohydric alcohol having 1 to 3 carbon atoms to the aqueous PVA-based resin solution after the dissolution step. When a monohydric alcohol having 1 to 3 carbon atoms is blended before the dissolving step, the alcoholic solvent volatilizes and is discharged outside the system during the dissolving step, so the desired PVA-based film cannot be obtained. do not have. In addition, since an explosion-proof reaction vessel is required to dissolve the PVA-based resin aqueous solution containing the alcohol-based solvent at a high temperature for a long time, it is not preferable in terms of equipment cost and safety.

Such monohydric alcohols having 1 to 3 carbon atoms may contain an ether bond in their structure, and specific examples include methanol, ethanol, methoxymethanol, 1-propanol, 2-propanol, 2-methoxyethanol, ethoxymethanol, cyclopropanol and the like. A monohydric alcohol having 4 or more carbon atoms is not preferable because the water solubility of the monohydric alcohol is low and the hydrophilicity is insufficient, which may reduce the turbidity and viscosity stability of the PVA-based aqueous solution.

Among these, monohydric alcohols containing no ether bond are preferred from the viewpoint of safety, methanol and ethanol having good hydrophilicity are preferred, and ethanol is particularly preferred from the viewpoint of environmental toxicity.

Moreover, these monohydric alcohols can be used alone, or two or more of them can be used in combination.

The content of monohydric alcohol having 1 to 3 carbon atoms in the aqueous PVA resin solution is preferably 0.001 to 5% by weight, particularly preferably 0.01 to 3% by weight, and more preferably 0.1%. ~2% by weight. If the concentration is too low, there is a tendency that the effect of suppressing the generation of air bubbles during solution preparation cannot be obtained, and if it is too high, fine air bubbles tend to be generated during film drying.

The solid content concentration of the film-forming raw material is preferably 5 to 50% by weight, particularly preferably 10 to 40% by weight. If the concentration is too low, the productivity of the film tends to decrease, and if it is too high, the viscosity becomes too high, and it takes time to degas the film-forming raw material, and there is a tendency for die lines to occur during film formation. There is

[[III] film forming process]
In the film-forming process, the film-forming raw material prepared in the dissolving process and the C1-3 monohydric alcohol compounding process is shaped into a film, and if necessary, dried to achieve a moisture content of 15% by weight. The following PVA-based film is prepared.
In forming the film, for example, a method such as a melt extrusion method or a casting method can be employed, and the casting method is preferable in terms of film thickness accuracy.
When performing the casting method, for example, (i) a method in which the film-forming raw material is passed through a gap using an applicator, bar coater, or the like, and cast onto a casting surface such as a metal surface; The PVA-based film of the present invention is produced by casting the film-forming raw material by a method of discharging it from a slit such as a slit die and casting it on a casting surface such as an endless belt or a metal surface of a drum roll, and then drying it. be able to.

A manufacturing method in which a film is formed by discharging and casting from a T-shaped slit die onto a casting mold such as a cast drum (drum-type roll) or an endless belt, followed by drying will be described below.

The temperature of the aqueous PVA-based resin solution at the exit of the T-shaped slit die is preferably 80 to 100°C, particularly preferably 85 to 98°C. If the resin temperature is too low, it tends to flow poorly, and if it is too high, it tends to foam.

The viscosity of the PVA-based resin aqueous solution is preferably 50 to 200 Pa·s, particularly preferably 70 to 150 Pa·s, when discharged. If the viscosity of such an aqueous solution is too low, it tends to flow poorly, and if it is too high, it tends to make drooling difficult.

When a cast drum is used as the casting mold in the present invention, the diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, further preferably 2.8 to 4 m.
If the diameter is too small, the dry length tends to be insufficient and the speed tends to be difficult to achieve.

The width of such a casting drum is preferably 4-7 m, particularly preferably 4.5-7 m, more preferably 5-7 m. If the width of the casting drum is too small, productivity tends to decrease, and if it is too large, transportability tends to decrease.

The surface temperature of the casting mold is preferably 40-99°C, particularly preferably 50-97°C. If the surface temperature is too low, there is a tendency for poor drying, and if it is too high, there is a tendency for foaming.

In the present invention, the water content of the film when it is peeled off from the casting mold is preferably 25% by weight or less, particularly preferably 10 to 20% by weight, from the viewpoint of transferability. If the moisture content is too high, the retardation of the PVA-based film tends to increase, and if it is too low, the PVA-based film tends to undulate.

In the present invention, the peel stress when peeling the film from the cast mold is preferably 0.1 to 100 mN/10 mm, particularly preferably 1 to 10 mN/10 mm. If the applied stress is too large, the film tends to break, and retardation unevenness of the PVA-based film tends to increase. Tend.

Thus, the film formation of the present invention is performed, and the obtained film is dried.
Drying of the film is accomplished by alternately contacting the front and back surfaces of the film with a plurality of drying rolls. Although the surface temperature of the drying roll is not particularly limited, it is usually 50 to 150°C, preferably 60 to 120°C. If the surface temperature is too low, the drying will be poor, and if the surface temperature is too high, the drying will be too dry, which tends to cause poor appearance such as waviness.

In the present invention, the film is preferably heat-treated after drying with hot rolls. The heat treatment temperature is preferably 60 to 150°C, particularly preferably 70 to 140°C. If the heat treatment temperature is too low, the water resistance of the PVA-based film tends to be insufficient, and if it is too high, stretchability during the production of the polarizing film tends to decrease. Such a heat treatment method includes, for example, a method using a floating dryer, a method in which the film is once cooled to room temperature after drying, and then brought into contact with a hot roll again, a method in which both surfaces of the film are irradiated with near infrared rays using an infrared lamp, and the like. Among them, the method using a floating dryer is preferable in that the heat treatment can be performed uniformly.

The original fabric of the PVA-based film thus obtained is slit at both ends in the width direction and wound up on a roll to form a product.

Thus, the PVA-based film of the present invention is produced.
The PVA-based film of the present invention preferably has a thickness of 100 μm or less, more preferably 5 to 30 μm from the viewpoint of avoiding breakage. If the thickness is too thick, it tends to be difficult to make the polarizing film thinner. Further, the PVA-based film of the present invention preferably has a width of 4 m or more from the viewpoint of productivity, and particularly preferably has a length of 4 km or more from the viewpoint of productivity.

The PVA-based film of the present invention preferably has a moisture content of 1 to 12% by weight, more preferably 2 to 8% by weight. If the moisture content of the film is too low, the swelling speed will decrease and wrinkles will tend to occur, and if it is too high, blocking will tend to occur.

The PVA-based film of the present invention preferably has a haze of 1% or less, particularly preferably 0.5% or less, and still more preferably 0.3% or less. If the haze is too high, the polarizing film tends to have minute unevenness in light transmittance.

The PVA-based film of the present invention preferably has a thickness variation coefficient of 1% or less, particularly preferably 0.9% or less, and still more preferably 0.8% or less. If the thickness variation coefficient is too large, the polarizing film tends to have fine color unevenness.

The PVA-based film of the present invention preferably has an in-plane retardation unevenness of 30 nm or less, particularly preferably 20 nm or less, further preferably 10 nm or less. If the in-plane retardation unevenness is too large, the polarizing film tends to have fine color unevenness.

Since the PVA-based film of the present invention thus obtained is characterized by having few bubble defects, it is used for polarizing film applications (liquid crystal televisions, smartphones, tablets, personal computers, projectors, vehicle-mounted panels, etc.) with strict requirements for display defects, Water-soluble film applications that require resistance to perforation by liquids (unit packaging applications for chemicals such as agricultural chemicals and detergents, (hydraulic) transfer films, sanitary products such as napkins and paper diapers, filth disposal products such as ostomy bags, blood-absorbing sheets and other medical supplies, seedling sheets, seed tapes, temporary substrates such as embroidery base fabrics, etc.).
Among them, the PVA-based film of the present invention is excellent in transparency, thickness accuracy, uniformity of retardation, and dyeability, and is preferably used as a raw material for a polarizing film.

The method for producing the polarizing film of the present invention will be described below.
The polarizing film of the present invention is produced by unwinding the PVA-based film from a roll, transporting it in the horizontal direction, and subjecting it to swelling, dyeing, cross-linking with boric acid, stretching, washing, drying, and the like.

The swelling step is performed before the dyeing step. By the swelling process, dirt on the surface of the PVA-based film can be cleaned, and the swelling of the PVA-based film also has the effect of preventing uneven dyeing. In the swelling step, water is usually used as the treatment liquid. As long as the main component of the treatment liquid is water, the treatment liquid may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, or the like. The temperature of the swelling bath is usually about 10 to 45° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing process is carried out by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used, and the concentration of iodine is usually 0.1 to 2 g/L, and the concentration of potassium iodide is usually 1 to 100 g/L. A practical dyeing time is usually about 30 to 500 seconds. The temperature of the treatment bath is preferably 5-50°C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the water solvent.

The boric acid cross-linking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture, usually at a concentration of about 10 to 100 g/L, and it is preferable to coexist with potassium iodide in the liquid from the viewpoint of stabilizing the polarization performance. . The treatment temperature is usually about 30 to 70° C., and the treatment time is preferably about 0.1 to 20 minutes.

The stretching step is preferably 3 to 10 times in the uniaxial direction, particularly preferably 3.5 to 6 times. At this time, the film may be slightly stretched in the direction perpendicular to the stretching direction (stretching to the extent that shrinkage in the width direction is prevented or more). The temperature during stretching is preferably 30 to 170°C. Furthermore, the final draw ratio may be set within the above range, and the drawing operation may be performed not only in one step but also in any range of steps in the manufacturing process.

The washing step is performed by, for example, immersing the PVA-based film in water or an aqueous solution of iodide such as potassium iodide to remove precipitates generated on the surface of the film. When an aqueous potassium iodide solution is used, the potassium iodide concentration may be about 1 to 80 g/L. The temperature during the washing treatment is usually 5 to 50°C, preferably 10 to 45°C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Note that washing with water and washing with an aqueous solution of potassium iodide may be appropriately combined.

The drying process may be carried out at 40 to 80° C. for 1 to 10 minutes in the normal atmosphere.

Also, the polarization degree of the polarizing film is preferably 99.8% or more, particularly preferably 99.9% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be ensured.
In addition, the degree of polarization is generally measured in a state where two polarizing films are superimposed so that their orientation directions are in the same direction, and the light transmittance (H ₁₁ ) measured at the wavelength λ, and the two polarized light It is calculated according to the following formula from the light transmittance (H ₁ ) measured at the wavelength λ in a state in which the films are superimposed so that the orientation directions are perpendicular to each other.
[(H ₁₁ −H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Furthermore, the single transmittance of the polarizing film of the present invention is preferably 42% or more, particularly preferably 43% or more. If the single transmittance is too low, there is a tendency that the liquid crystal display cannot achieve high brightness.
Single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Thus, the polarizing film of the present invention is obtained, and the polarizing film of the present invention is suitable for producing a polarizing plate with little unevenness in degree of polarization.

The obtained polarizing film can be used as a polarizing plate by laminating and adhering an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Protective films include, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, crosslinked methacrylate resin, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, Examples include films or sheets of polyphenylene oxide.
In addition, for the purpose of thinning the polarizing film, instead of the above protective film, a curable resin such as urethane resin, acrylic resin, or urea resin is applied to one side or both sides of the polarizing film, cured and laminated. can also

The polarizing film obtained from the PVA-based film of the present invention has no color unevenness and excellent in-plane uniformity of polarization performance, and is used in personal digital assistants, personal computers, televisions, projectors, signage, electronic desk calculators, and electronic clocks. , word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio equipment, liquid crystal display devices for automobiles and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT , LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, "parts" and "%" mean weight basis.

<Example 1>
100 parts of unmodified PVA resin having a weight average molecular weight of 142,000 and an average saponification degree of 99.8 mol% as PVA resin (A), 12 parts of glycerin as plasticizer (B), and laurin as surfactant (C) 0.05 part of acid diethanolamide and 1000 parts of water were mixed, heated to 130° C. in a pressure cooker, and dissolved under pressure for 60 minutes to obtain an aqueous PVA-based resin solution having a solid concentration of 10%. . After adjusting the temperature of the above PVA-based resin aqueous solution to 80 ° C., 3 parts of ethanol (0.3% by weight with respect to the PVA-based resin aqueous solution) is added to the above PVA-based resin aqueous solution, and a stirrer (AS ONE Stirring and mixing for 30 minutes was performed using MIX-ROTAR "MR-5" manufactured by the company. Next, the PVA-based resin aqueous solution mixed with ethanol was heated to 80° C. and left to stand for 30 minutes, after which the surface temperature was adjusted to 85° C. using an applicator with a gap of 560 μm. flowed upwards. After drying the cast PVA-based resin aqueous solution on a metal plate at a temperature of 85 ° C. for 5 minutes, the dry film was peeled off from the metal plate at a speed of 25 mm / sec. A 6.2% by weight PVA-based film was obtained. As a result of measuring the ethanol content of the obtained PVA-based film, it was 90 ppm.

<Example 2>
A PVA-based film was obtained in the same manner as in Example 1, except that the amount of ethanol added was changed to 25 parts (2.2% by weight with respect to the PVA-based resin aqueous solution). As a result of measuring the ethanol content of the obtained PVA-based film, it was 770 ppm.

<Comparative Example 1>
A PVA-based film was obtained in the same manner as in Example 1, except that ethanol was not added. As a result of measuring the ethanol content of the obtained PVA-based film, it was 0 ppm.

<Comparative Example 2>
A PVA-based film was obtained in the same manner as in Example 1, except that the amount of ethanol added was 70 parts (5.9% by weight with respect to the PVA-based resin aqueous solution). As a result of measuring the ethanol content of the obtained PVA-based film, it was 2200 ppm.

Using the PVA-based films obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the physical properties of the films were measured and evaluated according to the methods described below. The results are shown in Table 1 below.

[Moisture content of PVA-based film]
(Evaluation method)
A 5 cm×5 cm sample for moisture content measurement was cut out from the obtained PVA-based film at the central portion in the width direction. After weighing the film weight (W) of the cut film sample with an electronic balance, the film sample was immersed in 15 ml (S) of dehydrated methanol having a moisture content of 0.03% or less, and the inside of the film was allowed to stand at room temperature for 1 hour. of water was extracted. Using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Industry Co., Ltd., "MKA-610"), the water content of 10 ml of the extract (E) is measured by volumetric titration, and the film moisture content (% by weight) is calculated from the following formula. Calculated.

Ｆ： カールフィッシャー試薬の力価（ｍｇ／ｍｌ）
Ｖ： 抽出液１０ｍｌの滴定に用いたカールフィッシャー試薬量（ｍｌ）
Ｂ： 脱水メタノール１０ｍｌの滴定に用いたカールフィッシャー試薬量（ｍｌ）
Ｗ： ５ｃｍ×５ｃｍサイズにしたフィルム試料の重量（ｇ）
Ｅ： カールフィッシャー測定に使用した抽出液の量（ｍｌ）
Ｓ： フィルム試料の水分抽出に使用した脱水メタノールの量（ｍｌ）

F: Potency of Karl Fischer reagent (mg/ml)
V: Karl Fischer reagent amount (ml) used for titration of 10 ml of extract
B: Amount of Karl Fischer reagent used for titration of 10 ml of dehydrated methanol (ml)
W: Weight (g) of film sample with a size of 5 cm x 5 cm
E: Amount of extract used for Karl Fischer measurement (ml)
S: Amount (ml) of dehydrated methanol used to extract moisture from the film sample

[Content of monohydric alcohol having 1 to 3 carbon atoms in PVA-based film]
(Evaluation method)
The content of monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film was measured under the following conditions using GC/MS analysis equipped with a dynamic headspace device.
<Dynamic headspace conditions>
・ Thermal desorption device: TDS-3 (manufactured by Gestel)
・ Sample amount: about 5 mg
・ Heating conditions: 120 ° C., 60 minutes <GC / MS measurement conditions>
・ GC device: Agilent 7890GC (manufactured by Agilent Technologies)
・Column: DB-WAX (crosslinked PEG capillary column)
・Column temperature: 40°C x 5 minutes - 10°C/minute - 250°C x 10 minutes ・Inlet temperature: -150°C (collection) → 250°C
・Carrier gas: helium ・Column flow rate: 1.0 mL/min ・Split ratio: 1/30
・ MS unit device: Agilent 5977MSD (manufactured by Agilent Technologies)
・Mode: SCAN mode

[Bubble generation state after film drying]
(Evaluation method)
A sample having a size of 5 cm×5 cm was cut out from the obtained PVA-based film at the central portion in the width direction. Regarding the cut film sample, regarding the remaining state of bubbles generated during stirring (bubble diameter in the length direction or width direction is 250 μm or more) and small bubbles generated during drying (bubble diameter in the length direction or width direction is less than 250 μm) It was observed with a digital microscope and evaluated according to a five-grade evaluation standard.
(Evaluation criteria)
5: Good with no bubbles observed 4: Small bubbles with a bubble diameter of less than 250 μm are slightly present (1 or more and less than 3)
3: Small bubbles with a bubble diameter of less than 250 μm exist (3 or more and less than 10)
2: Only bubbles with a bubble diameter of 250 μm or more exist (one or more)
Alternatively, only small bubbles with a bubble diameter of less than 250 μm exist in large quantities (10 or more)
1: Bubbles with a bubble diameter of 250 μm or more exist (one or more),
In addition, small bubbles with a bubble diameter of less than 250 μm also exist (10 or more)

[Optical Defects of Polarizing Film]
The resulting PVA-based film was immersed in an aqueous solution containing 0.2 g/L iodine and 15 g/L potassium iodide at 30°C for 240 seconds. The film was immersed in an aqueous solution (55° C.) of and simultaneously uniaxially stretched 4 times and subjected to boric acid treatment for 5 minutes, followed by drying to obtain a polarizing film.
Optical linear defects on the surface of the obtained polarizing film were observed using a light box with a surface illumination of 14000 lux, and evaluated according to the following criteria.
(Evaluation criteria)
3: No linear defects observed 2: A small amount of linear defects observed 1: A large amount of linear defects observed

From the results in Table 1 above, the PVA-based films of Examples 1 and 2 satisfy the specific conditions for the content of the monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film. In addition, it can be seen that the generation of air bubbles during film drying is suppressed, and a PVA-based film with few air bubble defects can be obtained. Furthermore, it can be seen that the polarizing films produced using the PVA-based films of Examples 1 and 2 have few optical defects.

On the other hand, in Comparative Example 1, in which the content of the monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film is less than 1 ppm, air bubbles are easily generated after the solution is adjusted, and air bubbles generated during dissolution are also present in the film after drying. As a result, a bubble defect with a bubble diameter of 250 μm or more remained. In addition, in Comparative Example 2, in which the content of monohydric alcohol having 1 to 3 carbon atoms in the PVA-based film exceeds 2000 ppm, the generation of air bubbles during dissolution is suppressed, but small air bubbles with a diameter of less than 250 μm due to high-temperature drying during drying. was found to exist in large quantities. Further, linear optical defects were observed in the polarizing films produced using the PVA-based films of Comparative Examples 1 and 2. As described above, PVA-based films with bubble defects are concerned about display defects in polarizing film applications and liquid leakage when liquid products are packaged.

Since the PVA-based film of the present invention is characterized by having few air bubble defects, it can be used for polarizing films with strict requirements for display defects (liquid crystal televisions, smartphones, tablets, personal computers, projectors, vehicle-mounted panels, etc.) and liquid holes. Water-soluble film applications that require resistance to opening (unit packaging applications for chemicals such as agricultural chemicals and detergents, (hydraulic) transfer films, sanitary products such as napkins and disposable diapers, filth disposal products such as ostomy bags, medical care such as blood-absorbing sheets supplies, seedling sheets, seed tapes, temporary substrates for embroidery, etc.).
Among them, the PVA-based film of the present invention is excellent in transparency, thickness accuracy, uniformity of retardation, and dyeability, and is preferably used as a raw material for a polarizing film.

Claims (4)

A polyvinyl alcohol film containing a polyvinyl alcohol resin (A) as a main component, containing 1 to 2000 ppm of a monohydric alcohol having 1 to 3 carbon atoms, relative to 100 parts by weight of the polyvinyl alcohol resin (A) It contains 1 to 35 parts by weight of a plasticizer, and the polyvinyl alcohol resin (A) has a weight average molecular weight of 100,000 to 300,000 and an average degree of saponification of 99.5 mol% or more. Polyvinyl alcohol films for manufacturing polarizing films (excluding those containing dichroic dyes) . 2. The polyvinyl alcohol film for producing a polarizing film according to claim 1, wherein the monohydric alcohol having 1 to 3 carbon atoms is at least one selected from methanol and ethanol. A polarizing film comprising the polyvinyl alcohol-based film for manufacturing a polarizing film according to claim 1 or 2. (I) A polyvinyl alcohol-based resin composition containing polyvinyl alcohol-based resin (A) as a main component and containing 1 to 35 parts by weight of a plasticizer with respect to 100 parts by weight of the polyvinyl alcohol-based resin (A) is dissolved. a step of obtaining an alcohol-based resin aqueous solution;
(II) a step of adding 0.001 to 3 % by weight of a monohydric alcohol having 1 to 3 carbon atoms to the polyvinyl alcohol-based resin aqueous solution;
(III) a step of forming a film using the polyvinyl alcohol-based resin aqueous solution obtained in the step (II);
in this order, and the polyvinyl alcohol resin (A) has a weight average molecular weight of 100,000 to 300,000 and an average degree of saponification of 99.5 mol% or more. A method for producing a polyvinyl alcohol film (excluding those containing a dichroic dye) .