JP6792456B2 - the film - Google Patents

Description

The present invention uses a specific film useful as a raw film for producing an optical film such as a polarizing film, which contains a hydroxymethyl group-containing vinyl alcohol-based polymer having a 1,3-diol structure, and a specific film using the same. The present invention relates to a method for producing an optical film.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of the polarizing film in order to prevent fading of the polarizing film or shrinkage of the polarizing film. As the polarizing film constituting the polarizing plate, an iodine-based dye (I ₃ ) is formed by uniaxially stretching a vinyl alcohol-based polymer film (hereinafter, "vinyl alcohol-based polymer" may be referred to as "PVA"). ^- and I ₅ ^-, etc.) or a dichroic dye such as dichroic organic dyes has become mainstream those adsorbed.

LCDs have come to be widely used in small devices such as calculators and wristwatches, mobile phones, notebook computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, and measuring devices used indoors and outdoors. In recent years, there has been a particular demand for thinness and weight reduction. Along with this, the thinning of each member of the LCD is progressing, and there is a concern that the function of preventing the shrinkage of the polarizing film is deteriorated as the protective film of the polarizing plate is thinned. Therefore, there is a demand for a polarizing film having high degree of polarization and transmittance, excellent optical characteristics, and reduced shrinkage.

By the way, some raw films for producing optical films containing modified PVA are known. For example, a polyvinyl alcohol film for raw material of a polarizing film made of a specific PVA containing 0.01 to 1 mol% of hydrophilic functional groups such as a carboxylic acid group and an ω-hydroxy-α-olefin group is stretched and oriented. It is known that it is excellent in processability and adsorption processability of dichroic substances and exhibits good optical performance (see Patent Document 1 and the like). Further, it is known that a specific optical PVA film containing a specific PVA containing a 1,2-glycol bond in the side chain is excellent in optical properties and stretchability (see Patent Document 2).

Japanese Unexamined Patent Publication No. 8-201626 JP-A-2009-24076

However, when a conventionally known raw film for producing an optical film containing modified PVA is used, there is room for improvement in obtaining an optical film having excellent optical characteristics and shrinkage reduction.

Therefore, an object of the present invention is to provide a film capable of easily producing an optical film having excellent optical characteristics and shrinkage reduction, and a method for producing an optical film using the film.

As a result of diligent studies to achieve the above object, the present inventors have included a hydroxymethyl group-containing PVA having a specific structural unit having a 1,3-diol structure in the main chain, and the softening point is within a specific range. It was found that the above-mentioned problems could be solved according to a certain film, and further studies were carried out based on the findings to complete the present invention.

That is, the present invention
[1] A film containing a vinyl alcohol unit and a hydroxymethyl group-containing PVA containing a structural unit represented by the following formula (1) and having a softening point of 63 ° C. or lower;

[2] The film according to [1], wherein the content of the structural unit represented by the formula (1) in the hydroxymethyl group-containing PVA is 0.1 to 2 mol%;
[3] The film according to [1] or [2], wherein the degree of saponification of the hydroxymethyl group-containing PVA is 95 mol% or more.
[4] The film according to any one of [1] to [3], which is a raw film for manufacturing an optical film;
[5] The film according to [4], wherein the optical film is a polarizing film;
[6] A method for producing an optical film, which comprises a step of uniaxially stretching using the film according to [4] or [5];
Regarding.

According to the present invention, there is provided a film capable of easily producing an optical film having excellent optical characteristics and shrinkage reduction, and a method for producing an optical film using the film.

The film of the present invention contains a vinyl alcohol unit and a hydroxymethyl group-containing PVA containing a structural unit represented by the following formula (1).

The film of the present invention has improved stretchability because the hydroxymethyl group-containing PVA contained therein contains a structural unit having a 1,3-diol structure represented by the above formula (1), and the film of the present invention has improved stretchability. According to the above, an optical film having excellent optical characteristics can be easily produced. Further, it has a feature that the shrinkage force of the optical film is reduced. Although not limiting the present invention, the reasons for obtaining the above-mentioned advantages are that the crystallinity is lowered by the structural unit represented by the formula (1) and that the crystallinity is high based on the 1,3-diol structure. The influence of hydrogen bonding force is considered.

The content of the structural unit represented by the formula (1) in the hydroxymethyl group-containing PVA is not particularly limited, but 0.1 to 2 when the number of moles of all the structural units constituting the hydroxymethyl group-containing PVA is 100 mol%. It is preferably in the range of mol%, more preferably in the range of 0.2 to 1.9 mol%, and even more preferably in the range of 0.3 to 1.8 mol%. When the content is 0.1 mol% or more, the stretchability of the film is further improved, and an excellent optical film can be obtained by reducing the shrinkage force. On the other hand, when the content is 2 mol% or less, it is possible to more effectively prevent the film from being melted during the production of the optical film, and an optical film having better optical characteristics can be obtained. In the present specification, the structural unit means a repeating unit constituting the polymer.

The degree of polymerization of the hydroxymethyl group-containing PVA is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and more preferably 2,000 to 4,000. It is more preferable that it is within the range of. When the degree of polymerization is 1,500 or more, the durability of an optical film such as a polarizing film obtained by uniaxially stretching the film can be further improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress an increase in manufacturing cost and a defect in process passability during film formation. The degree of polymerization of the hydroxymethyl group-containing PVA in the present specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of the hydroxymethyl group-containing PVA is preferably 95 mol% or more, more preferably 96 mol% or more, from the viewpoint of water resistance of an optical film such as a polarizing film obtained by uniaxially stretching the film. It is preferably 98 mol% or more, and more preferably 98 mol% or more. The degree of saponification of the hydroxymethyl group-containing PVA in the present specification is a structural unit (typically) possessed by the hydroxymethyl group-containing PVA that can be converted into a vinyl alcohol unit (-CH _2- CH (OH)-) by saponification. Refers to the ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the vinyl ester unit) and the vinyl alcohol unit. The saponification degree can be measured according to the description of JIS K6726-1994, taking into consideration the amount of the structural unit represented by the formula (1) and its derivative.

The method for producing the hydroxymethyl group-containing PVA is not particularly limited. For example, a vinyl ester-based monomer obtained by copolymerizing a vinyl ester-based monomer and an unsaturated monomer copolymerizable therewith and convertible into a structural unit represented by the formula (1). The vinyl ester unit of the above is converted into a vinyl alcohol unit, while the structural unit derived from the unsaturated monomer convertible to the structural unit represented by the formula (1) is converted into the structural unit represented by the formula (1). The method can be mentioned. Specific examples of unsaturated monomers that can be converted into structural units represented by the formula (1) are shown in the following formula (2).

In the formula (2), R represents an alkyl group having 1 to 10 carbon atoms. The structure of R is not particularly limited, and may have a partially branched or cyclic structure. Moreover, a part may be substituted with another functional group. R is preferably an alkyl group having 1 to 5 carbon atoms, and examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, and the like. Alkyl groups having a linear or branched such as a pentyl group can be mentioned. Examples of the substituent that R may have include an alkoxy group, a halogen atom, and a hydroxyl group. It should be noted that the plurality of Rs may be the same or different from each other.

Examples of the unsaturated monomer represented by the formula (2) include 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyryloxy-2. -Methylene propane and the like. Of these, 1,3-diacetoxy-2-methylenepropane is preferably used in terms of ease of production.

The unsaturated monomer represented by the formula (2) is a vinyl ester-based monomer as compared with other allyl-type unsaturated monomers generally used for modification of PVA (for example, allyl glycidyl ether and the like). The copolymerization reaction of the above is easy to proceed. Therefore, there are few restrictions on the amount of modification and the degree of polymerization during polymerization, and a hydroxymethyl group-containing PVA having a high amount of modification and degree of polymerization can be easily obtained. Further, since the amount of the unreacted unsaturated monomer remaining at the end of polymerization can be reduced, the hydroxymethyl group-containing PVA in the present invention is excellent in terms of environment and cost during industrial production. There is.

The vinyl ester-based monomer used for producing the hydroxymethyl group-containing PVA is not particularly limited, and for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatic acid, and capron. Examples thereof include vinyl acetate, vinyl caprylate, vinyl caproate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like. Vinyl acetate is preferable from an economic point of view.

The polymerization method for copolymerizing the unsaturated monomer represented by the formula (2) and the vinyl ester-based monomer may be any of batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization and the like. As the polymerization method, known methods such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method can be applied. A massive polymerization method or a solution polymerization method in which the polymerization proceeds in a solvent such as solvent-free or alcohol is usually adopted. When obtaining a vinyl ester-based copolymer having a high degree of polymerization, an emulsion polymerization method is also preferable. The solvent of the solution polymerization method is not particularly limited, but is, for example, alcohol. The alcohol used as the solvent in the solution polymerization method is a lower alcohol such as methanol, ethanol or propanol. The amount of the solvent used in the polymerization system may be selected in consideration of the chain transfer of the solvent according to the degree of polymerization of the target hydroxymethyl group-containing PVA. For example, when the solvent is methanol, it is contained in the solvent and the polymerization system. The mass ratio to all monomers {= (solvent) / (all monomers)} is preferably selected from the range of 0.01 to 10, and more preferably from the range of 0.05 to 3.

The polymerization initiator used for the copolymerization of the unsaturated monomer represented by the formula (2) and the vinyl ester-based monomer is a known polymerization initiator, for example, an azo-based initiator or a peroxide-based initiator. , The redox-based initiator may be selected according to the polymerization method. Examples of the azo-based initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2,4-). Dimethylvaleronitrile). Peroxide-based initiators are percarbonate-based compounds such as diisopropylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethylperoxydicarbonate; t-butylperoxyneodecanate, α-. Perester compounds such as cumyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide and the like may be combined with the above-mentioned initiator to obtain a polymerization initiator. The redox-based initiator is, for example, a polymerization initiator that is a combination of the above-mentioned peroxide-based initiator and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and longalit. The amount of the polymerization initiator used varies depending on the type of the polymerization initiator and cannot be unconditionally determined, but it may be selected according to the polymerization rate. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, 0.01 to 0.2 mol% is preferable with respect to the vinyl ester-based monomer, and 0.02 to 0 .15 mol% is more preferred. The polymerization temperature is not particularly limited, but is appropriately about room temperature to 150 ° C., preferably 40 ° C. or higher and lower than the boiling point of the solvent used.

The copolymerization of the unsaturated monomer represented by the formula (2) and the vinyl ester-based monomer may be carried out in the presence of a chain transfer agent. The chain transfer agent is, for example, aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphite monohydrate. Of these, aldehydes and ketones are preferably used. The amount of the chain transfer agent used can be determined according to the chain transfer coefficient of the chain transfer agent used and the degree of polymerization of the target hydroxymethyl group-containing PVA, but is generally 100 parts by mass of the vinyl ester-based monomer. On the other hand, 0.1 to 10 parts by mass is preferable.

The above-mentioned hydroxymethyl group-containing PVA can be obtained by saponifying the vinyl ester-based copolymer obtained by copolymerizing the unsaturated monomer represented by the formula (2) with the vinyl ester-based monomer. .. By saponifying the vinyl ester-based copolymer, the vinyl ester unit in the vinyl ester-based copolymer is converted into a vinyl alcohol unit. In addition, the ester bond of the structural unit derived from the unsaturated monomer represented by the formula (2) is also saponified and converted into a structural unit having a 1,3-diol structure represented by the formula (1). Therefore, the hydroxymethyl group-containing PVA can be produced without further reaction such as hydrolysis after saponification.

The saponification of the vinyl ester-based copolymer can be carried out, for example, in a state where the vinyl ester-based copolymer is dissolved in an alcohol or a hydrous alcohol. Examples of the alcohol used for saponification include lower alcohols such as methanol and ethanol, and methanol is preferable. The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate and benzene in a proportion of 40% by mass or less based on the mass thereof. The catalyst used for saponification is, for example, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as mineral acid. The temperature at which saponification is carried out is not limited, but is preferably in the range of 20 to 60 ° C. When a gel-like product is precipitated as the saponification progresses, the product can be pulverized, washed and dried to obtain a hydroxymethyl group-containing PVA. The saponification method is not limited to the method described above, and a known method can be applied.

The hydroxymethyl group-containing PVA can further contain structural units other than the structural unit represented by the formula (1), the vinyl alcohol unit and the vinyl ester unit. Examples of the other structural unit include a structural unit derived from an ethylenically unsaturated monomer copolymerizable with a vinyl ester-based monomer. Further, a structural unit derived from an unsaturated monomer that is copolymerizable with the vinyl ester-based monomer described above and can be converted into a structural unit represented by the formula (1) (represented by the formula (1) by saponification). It can also include structural units that have not been converted to structural units).

The ratio of the total of the structural unit, vinyl alcohol unit and vinyl ester unit represented by the formula (1) in the hydroxymethyl group-containing PVA is 100 mol% based on the number of moles of all the structural units constituting the hydroxymethyl group-containing PVA. , 80 mol% or more, more preferably 90 mol% or more, further preferably 95 mol% or more, and may be 99 mol% or more.

Examples of the ethylenically unsaturated monomer include α-olefins such as ethylene, propylene, n-butyl, isobutylene, and 1-hexene; allyl acid and a salt thereof; an unsaturated single amount having an allyl ester group. Body; methacrylic acid and its salt; unsaturated monomer having a methacrylic ester group; acrylamide; N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamide propanesulfonic acid and its salt , Acrylamide derivatives such as acrylamide propyl dimethylamine and salts thereof (eg, quaternary salts); methalkylamide; N-methylmethacrylate, N-ethylmethacrylate, methallylamide propanesulfonic acid and its salts, methacrylamide propyldimethylamine and its salts. Methacrylate derivatives such as salts (eg, quaternary salts); methylvinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, Vinyl ethers such as 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; halogens such as vinylidene chloride and vinylidene fluoride Vinylidene isomers; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid and salts or esters thereof; vinyltrimethoxysilane Vinyl silyl compounds such as isopropenyl acetate. Among these, ethylene is used because the stretchability is improved and the film can be stretched at a higher temperature, the occurrence of troubles such as stretch breakage is reduced during the production of the optical film, and the productivity of the optical film is further improved. preferable. When the hydroxymethyl group-containing PVA contains ethylene units, the content of the ethylene units is 100 moles of all structural units constituting the hydroxymethyl group-containing PVA from the viewpoint of stretchability and stretchable temperature as described above. As the mol%, 1 to 4 mol% is preferable, and 2 to 3 mol% is particularly preferable.

The sequence order of the structural unit represented by the formula (1), the vinyl alcohol unit, and any other structural unit in the hydroxymethyl group-containing PVA is not particularly limited, and may be random, block, alternate, or the like.

The film of the present invention may contain a plasticizer in addition to the above-mentioned hydroxymethyl group-containing PVA. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. The film of the present invention may contain one or more of these plasticizers. Among these, glycerin is preferable from the viewpoint of improving stretchability.

The content of the plasticizer in the film of the present invention is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the hydroxymethyl group-containing PVA contained therein, and is in the range of 3 to 17 parts by mass. It is more preferable, and it is further preferable that it is in the range of 5 to 15 parts by mass. When the content is 1 part by mass or more, the stretchability of the film is further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the film from becoming too flexible and the handleability from being lowered.

Further, the film of the present invention includes a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and other heat. Additives such as thermoplastic resins, lubricants, fragrances, defoamers, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, cross-linking agents, fungicides, preservatives, crystallization rate retarders, etc. It can be appropriately blended as needed.

The total proportion of the hydroxymethyl group-containing PVA and the plasticizer in the film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass, based on the mass of the film. It is more preferably% or more.

The film of the present invention has a softening point of 63 ° C. or lower. As a result, an excellent optical film can be obtained by reducing shrinkage. The softening point is preferably 60 ° C. or lower, more preferably 57 ° C. or lower, and even more preferably 55 ° C. or lower. The lower the softening point, the lower the shrinkage force of the obtained optical film. On the other hand, the lower limit of the industrial softening point is about 50 ° C. from the viewpoint of process passability during use such as when the film is uniaxially stretched.
The film having the softening point in the above range can be easily produced by appropriately adjusting the modification amount of the hydroxymethyl group-containing PVA, the saponification degree of the hydroxymethyl group-containing PVA, the heat treatment temperature for the film, and the like. A method of setting the temperature lower is convenient and preferable. As a specific heat treatment temperature, 150 ° C. or lower is preferable, 140 ° C. or lower is more preferable, 130 ° C. or lower is further preferable, 120 ° C. or lower is particularly preferable, and a temperature exceeding 90 ° C. is preferable. The softening point can be determined by a known measuring method, and specifically, it can be measured by the method described later in the examples.

The degree of swelling of the film of the present invention is preferably in the range of 190 to 500%, more preferably in the range of 200 to 400%, and even more preferably in the range of 230 to 350%. It is particularly preferably in the range of 270 to 320%. When the degree of swelling is 190% or more, it is possible to suppress the extremely progress of crystallization, and it is possible to stably stretch to a higher magnification. On the other hand, when the degree of swelling is 500% or less, dissolution during stretching is suppressed, and stretching can be performed even under higher temperature conditions. In the present specification, the degree of swelling of the film is a value obtained by dividing the mass when the film is immersed in distilled water at 30 ° C. for 30 minutes by the mass after drying at 105 ° C. for 16 hours after immersion. It means a percentage, and can be specifically measured by the method described later in the examples.

The thickness of the film of the present invention is not particularly limited, but is generally 1 to 100 μm, more preferably 5 to 75 μm, and particularly preferably about 10 to 60 μm. If the thickness is too thin, stretch breakage tends to occur easily during the uniaxial stretching process for producing an optical film such as a polarizing film. On the other hand, if the thickness is too thick, stretch spots are likely to occur during the uniaxial stretching treatment for producing an optical film.

The width of the film of the present invention is not particularly limited and can be determined according to the application of the manufactured optical film and the like. In recent years, since the screen size of liquid crystal televisions and liquid crystal monitors has been increasing, it is suitable for these applications if the width of the film is set to 3 m or more. On the other hand, if the width of the film is too large, it tends to be difficult to uniformly perform the uniaxial stretching itself when manufacturing an optical film with a practical device, so the width of the film is preferably 7 m or less. ..

The method for producing the film of the present invention is not particularly limited, and a method for producing a film having a more uniform thickness and width after film formation can be preferably adopted. For example, the above-mentioned hydroxymethyl group-containing PVA constituting the film can be preferably adopted. , And, if necessary, a film-forming stock solution in which one or more of the above-mentioned plasticizers, additives, and surfactants described later are dissolved in a liquid medium, and hydroxymethyl group-containing PVA. And, if necessary, produced using a film-forming stock solution containing one or more of plasticizers, additives, surfactants, liquid media, etc., and in which hydroxymethyl group-containing PVA is melted. can do. When the film-forming stock solution contains at least one of a plasticizer, an additive, and a surfactant, it is preferable that the components are uniformly mixed.

Examples of the liquid medium used for preparing the membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of these can be used. Of these, water is preferable from the viewpoint of environmental load and recoverability.

The volatile content of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is generally used. It is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass, and even more preferably in the range of 60 to 85% by mass. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, filtration and defoaming during preparation of the membrane-forming stock solution are smoothly performed, and a film with few foreign substances and defects. Is easy to manufacture. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and industrial film production becomes easy.

The film-forming stock solution preferably contains a surfactant. By containing the surfactant, the film-forming property is improved, the occurrence of thickness unevenness of the film is suppressed, and the film can be easily peeled off from the metal roll or belt used for the film-forming. When a film is produced from a film-forming stock solution containing a surfactant, the film may contain a surfactant. The type of the above-mentioned surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of peelability from a metal roll or a belt.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino. Alkylamine type such as ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxy An allylphenyl ether type such as alkylene allylphenyl ether is suitable.

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

When the membrane-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of the hydroxymethyl group-containing PVA contained in the membrane-forming stock solution. It is more preferably in the range of 0.02 to 0.3 parts by mass, and particularly preferably in the range of 0.05 to 0.1 parts by mass. When the content is 0.01 parts by mass or more, the film-forming property and the peelability are further improved. On the other hand, when the content is 0.5 parts by mass or less, it is possible to prevent the surfactant from bleeding out to the surface of the film, causing blocking and lowering the handleability.

Examples of the film-forming method for forming a film using the above-mentioned film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. These film forming methods may adopt only one kind or a combination of two or more kinds. Among these film-forming methods, the cast film-forming method and the extrusion film-forming method are preferable because a film having a uniform thickness and width and good physical properties can be obtained. The formed film can be dried or heat-treated as needed.

As an example of a specific method for producing the film of the present invention, for example, a T-shaped slit die, a hopper plate, an I-die, a lip coater die, or the like is used to rotate the above-mentioned film-forming stock solution on the most upstream side. It is uniformly discharged or cast on the peripheral surface of the heated first roll (or belt), and is volatile from one surface of the film discharged or cast on the peripheral surface of the first roll (or belt). The components were evaporated to dry and then further dried on the perimeter of one or more rotating heated rolls placed downstream thereof, or passed through a hot air dryer for further drying. After that, a method of winding with a winding device can be industrially preferably adopted. Drying with a heated roll and drying with a hot air drying device may be carried out in an appropriate combination.

The use of the film of the present invention is not particularly limited, and for example, a film for chemical packaging, a base film for hydraulic transfer, a base film for embroidery, a release film for artificial marble molding, a film for seed packaging, a film for a filth storage bag. Although it can be used for various water-soluble films such as, according to the film of the present invention, an optical film having excellent optical characteristics, durability performance and shrinkage reduction can be easily produced. Therefore, an optical film is produced. It is preferable to use it as a raw film (raw film for manufacturing an optical film). Examples of such an optical film include a polarizing film and a retardation film, and a polarizing film is preferable. Such an optical film can be produced, for example, by subjecting the film of the present invention to a treatment such as uniaxial stretching.

The method for producing a polarizing film using the film of the present invention is not particularly limited, and any conventionally adopted method may be adopted. Examples of such a method include a method of dyeing and uniaxially stretching the film of the present invention, and a method of uniaxially stretching the film of the present invention containing a dye. As a more specific method for producing a polarizing film, a method of swelling, dyeing, uniaxially stretching, and if necessary, further subjecting the film of the present invention to cross-linking treatment, fixing treatment, drying, heat treatment and the like. Can be mentioned. In this case, the order of each treatment such as swelling, staining, cross-linking treatment, uniaxial stretching, and fixing treatment is not particularly limited, and one or more treatments can be performed at the same time. It is also possible to perform one or more of each process twice or more.

The swelling can be performed by immersing the film in water. The temperature of the water when immersed in water is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and preferably in the range of 25 to 35 ° C. More preferred. The time for immersion in water is, for example, preferably in the range of 0.1 to 5 minutes, and more preferably in the range of 0.5 to 3 minutes. The water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

Dyeing can be performed by contacting the film with a dichroic dye. Iodine-based dyes are generally used as the dichroic dyes. The dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is generally carried out by immersing the film in a solution containing iodine-potassium iodide (particularly an aqueous solution) as a dyeing bath, and such a dyeing method is also preferably adopted in the present invention. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C.

By subjecting the film to a cross-linking treatment, it is possible to more effectively prevent the hydroxymethyl group-containing PVA from elution into water during wet stretching at a high temperature. From this point of view, the cross-linking treatment is preferably performed after the treatment of bringing the dichroic dye into contact and before the uniaxial stretching. The cross-linking treatment can be performed by immersing the film in an aqueous solution containing a cross-linking agent. As the cross-linking agent, one or more kinds of boron compounds such as borate such as boric acid and borax can be used. The concentration of the cross-linking agent in the aqueous solution containing the cross-linking agent is preferably in the range of 1 to 15% by mass, more preferably in the range of 2 to 7% by mass, and in the range of 3 to 6% by mass. Is even more preferable. Sufficient stretchability can be maintained when the concentration of the cross-linking agent is in the range of 1 to 15% by mass. The aqueous solution containing the cross-linking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the cross-linking agent is preferably in the range of 20 to 50 ° C., particularly preferably in the range of 25 to 40 ° C. By setting the temperature within the range of 20 to 50 ° C., cross-linking can be performed efficiently.

The uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, in the above-mentioned dyeing bath or in the fixing treatment bath described later. Further, in the case of the dry stretching method, stretching may be carried out at room temperature, stretching may be carried out while heating, or may be carried out in air using a film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, and 1.5. It is particularly preferably in the range of ~ 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10% by mass.
The stretching temperature in uniaxial stretching is preferably in the range of 30 to 90 ° C, more preferably in the range of 40 to 80 ° C, and particularly preferably in the range of 50 to 70 ° C.
Further, the draw ratio in uniaxial stretching is preferably 6.8 times or more, more preferably 6.9 times or more, and 7.0 times or more from the viewpoint of the polarization performance of the obtained polarizing film. Is particularly preferable. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

There is no particular limitation on the direction of uniaxial stretching when the long film is uniaxially stretched, and uniaxial stretching or lateral uniaxial stretching in the long direction can be adopted, but since a polarizing film having excellent polarization performance can be obtained. Uniaxial stretching in the long direction is preferable. Uniaxial stretching in the long direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, the horizontal uniaxial stretching can be performed by using a tenter type stretching machine.

In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dichroic dye (iodine-based dye, etc.) on the film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by mass, particularly preferably about 3 to 10% by mass. By setting the concentration within the range of 2 to 15% by mass, the adsorption of the dichroic dye can be further strengthened. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

The drying conditions are not particularly limited, but it is preferable to perform drying at a temperature within the range of 30 to 150 ° C., particularly within the range of 50 to 130 ° C. By drying at a temperature in the range of 30 to 150 ° C., a polarizing film having excellent dimensional stability can be easily obtained.

The polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, examples of the adhesive for bonding include PVA-based adhesives and urethane-based adhesives, and among them, PVA-based adhesives are preferable.

The polarizing plate obtained as described above can be used as a component of an LCD by being coated with an adhesive such as acrylic and then bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, each measurement or evaluation method adopted in the following Examples, Reference Examples and Comparative Examples is shown below.

Primary structure of PVA The primary structure of PVA (content rate and saponification degree of structural units of modified species) used in the following examples, reference examples and comparative examples was analyzed using 400 MHz ¹ H-NMR. ¹ Deuterated DMSO was used as the solvent for ¹ H-NMR measurement.

Film softening point The film was measured using an automatic softening point temperature measuring device manufactured by Elex Chemical. Specifically, the films obtained in the following Examples, Reference Examples or Comparative Examples are cut into 2.5 cm squares, fixed to a metal frame having a circular hole with a diameter of 1 cm, and the holes are formed. A ball with a diameter of 0.95 cm and a mass of 3.526 g is placed in the center of the film, and the temperature is measured by detecting the temperature when the ball drops 2.5 cm in the process of raising the temperature from 30 ° C to 5 ° C / min in pure water. did.

The film obtained in Examples, Reference Examples or Comparative Examples having a degree of swelling of the film or less was cut to 1.5 g and immersed in distilled water at 30 ° C. for 30 minutes. After soaking for 30 minutes, the film was taken out, water on the surface was removed with a filter paper, and the mass "N" was determined. Subsequently, the film was dried in a dryer at 105 ° C. for 16 hours, and then the mass "M" was determined. From the obtained masses "N" and "M", the degree of swelling of the film was calculated by the following formula (3).
Swelling degree (%) = 100 x N / M (3)

Optical characteristics of polarizing film (dichroism ratio)
(1) Measurement of Transmittance Ts Two 2 cm samples in the length direction of the polarizing film were taken from the central portion of the polarizing film obtained in the following Examples, Reference Examples or Comparative Examples, and the spectral luminosity with an integrating sphere was taken. Using a meter (“V7100” manufactured by Nippon Spectroscopy Co., Ltd.), the visibility of the visible light region of the C light source and 2 ° field is corrected in accordance with JIS Z 8722 (measurement method of object color), and one sample is used. The light transmittance when tilted by + 45 ° and the light transmittance when tilted by −45 ° with respect to the length direction were measured, and the average value Ts1 (%) of them was obtained. Similarly for the other sample, the light transmittance when tilted by + 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged by the following formula (4) to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2 (4)

(2) Measurement of polarization degree V Light transmittance T‖ (%) and length direction when two samples collected in the above-mentioned measurement of transmittance Ts are stacked so that their length directions are parallel to each other. The light transmittance T⊥ (%) when the lights are overlapped so as to be orthogonal to each other is measured in the same manner as in the case of “(1) Measurement of transmittance Ts” above, and the degree of polarization V (5) is calculated by the following equation (5). %) Was asked.
V = {(T‖-T⊥) / (T‖ + T⊥)} ^1/2 x 100 (5)

(3) Calculation of dichroic ratio when the transmittance is 44% In each of the following Examples, Reference Examples and Comparative Examples, the iodine concentration in the dyeing bath was 0.02 to 0.04% by mass and the potassium iodide concentration. Was changed four times within each range of 2.0 to 4.0% by mass (however, the concentration of iodine: the concentration of potassium iodide = 1: 100) and the same operation was performed. Four polarizing films having a different adsorption amount of the bicolor dye from the polarizing films produced in the example or the comparative example were produced. The transmittance Ts (%) and the degree of polarization V (%) were obtained for each of these four polarizing films by the above method, and the transmittance Ts (%) is set on the horizontal axis for each Example, Reference Example, and Comparative Example. , With the degree of polarization V (%) as the vertical axis, a total of 5 including one point based on the transmittance Ts (%) and the degree of polarization V (%) of the polarizing films obtained in each Example, Reference Example or Comparative Example. The points were plotted on a graph to obtain an approximate curve, and the degree of polarization V ₄₄ (%) when the transmittance Ts (%) was 44% was obtained from the approximate curve.
From the obtained degree of polarization V ₄₄ (%), the dichroism ratio at a transmittance of 44% was obtained by the following formula (6) and used as an index of polarization performance.
Dichroic ratio when the transmittance 44% = log (44 / 100-44 / 100 × V 44/100) / log (44/100 + 44/100 × V 44/100) (6)

Shrinkage force of polarizing film From the central part of the polarizing film obtained in the following Examples, Reference Examples or Comparative Examples, a rectangular sample of 12 cm in the length direction and 1.5 cm in the width direction of the polarizing film was collected, and the temperature was measured. The humidity was adjusted for 18 hours under the conditions of 20 ° C. and 20% relative humidity. Next, this sample was fixed to an autograph "AG-X" manufactured by Shimadzu Corporation so that the length direction was fixed at a distance of 5 cm between chucks, and 1 mm / min under the conditions of a temperature of 40 ° C. and a relative humidity of 5%. It stretches in the length direction at a speed, stops and holds the stretch when the tension reaches 2N, raises the temperature to 80 ° C. in that state, measures the tension after 4 hours, and shrinks the polarizing film. It was power.

[Example 1]
(1) The hydroxymethyl group-containing PVA100 shown in Table 1 obtained by saponifying a copolymer obtained by copolymerizing vinyl acetate and 1,3-diacetoxy-2-methylenepropane at a polymerization temperature of 40 ° C. A film-forming stock solution containing 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and a hydroxymethyl group-containing PVA content of 10% by mass. The film was dried on a metal roll at 80 ° C., and the obtained film was heat-treated at a predetermined temperature for 1 minute in a hot air dryer to adjust the softening point to 63 ° C. and have a thickness of 30 μm. Manufactured the film.

(2) A sample having a width of 5 cm and a length of 8 cm was cut from the central portion of the film obtained in (1) above in the width direction so that a range of 5 cm in width × 5 cm in length could be uniaxially stretched. This sample was uniaxially stretched 1.5 times in the length direction while being immersed in pure water at 30 ° C. Subsequently, it was immersed in an aqueous solution (dyeing bath) (temperature 30 ° C.) containing 0.03% by mass of iodine and 3.0% by mass of potassium iodide for 60 seconds while being immersed 1.6 times (2.4 in total). Iodine was adsorbed by uniaxially stretching in the length direction. Next, the length was increased 1.1 times (2.6 times as a whole) while being immersed in an aqueous solution (crosslinked bath) (temperature 30 ° C.) containing 3% by mass of boric acid and 3% by mass of potassium iodide. It was uniaxially stretched in the direction. Further, while immersing in an aqueous solution (stretching bath) (temperature 56 ° C.) containing 4% by mass of boric acid and 6% by mass of potassium iodide, uniaxial stretching was performed in the length direction to the stretching ratio immediately before breaking. Then, it was immersed in an aqueous solution (washing bath) (temperature 30 ° C.) containing potassium iodide in a proportion of 3% by mass for 5 seconds, and finally dried at 60 ° C. for 4 minutes to produce a polarizing film. A plurality of similar polarizing films were manufactured so that each measurement or evaluation could be performed. Using the obtained polarizing film, the optical characteristics (dichroism ratio) and shrinkage force of the polarizing film were measured or evaluated by the above-mentioned method. The results are shown in Table 1.

[Examples 2 and 3 and Reference Example 1]
Except that the temperature of the hot air dryer (heat treatment temperature) was adjusted to 60 ° C (Example 2); 55 ° C (Example 3); 64 ° C (Reference Example 1), respectively, as shown in Table 1. , A film and a polarizing film were produced in the same manner as in Example 1, and each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 1]
As the PVA, the unmodified PVA shown in Table 1 obtained by saponifying the polymer obtained by polymerizing vinyl acetate at a polymerization temperature of 60 ° C. is used, and the temperature (heat treatment temperature) of the hot air dryer is shown in Table 1. A film and a polarizing film were produced in the same manner as in Example 1 except that the softening point was adjusted to 63 ° C. as shown in FIG. 1, and each measurement or evaluation was performed. The results are shown in Table 1.

As is clear from the above results, it can be seen that according to the films of Examples 1 to 3 satisfying the provisions of the present invention, an optical film having excellent optical characteristics and shrinkage reduction can be easily produced.

Claims (6)

It contains a hydroxymethyl group-containing vinyl alcohol-based polymer having a vinyl alcohol unit and a structural unit represented by the following formula (1) having a content of 0.1 to 2 mol%, and has a softening point of 50 ° C. or higher and 63 ° C. or lower. A film, which is a raw film for producing a polarizing film.
The film according to claim 1, wherein the degree of saponification of the hydroxymethyl group-containing vinyl alcohol polymer is 95 mol% or more. The film according to claim 1 or 2, wherein the content of the structural unit represented by the formula (1) is 1 to 2 mol%. The film according to any one of claims 1 to 3, wherein the degree of swelling is 190 to 250%. The method for producing a film according to any one of claims 1 to 4.
A step of preparing a film-forming stock solution containing the hydroxymethyl group-containing vinyl alcohol-based polymer, and
The process of forming a film by forming a film-forming stock solution and
The step of drying the film and
A method for producing a film, which comprises a step of heat-treating the dried film at a temperature of 140 to 150 ° C. to obtain the film. A method for producing a polarizing film, which comprises a step of uniaxially stretching the film according to any one of claims 1 to 4.