JP6383664B2 - Raw film for optical film production - Google Patents

Description

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

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a 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 a polarizing film. As a polarizing film constituting the polarizing plate, a vinyl alcohol polymer film (hereinafter, referred to as a polarizing film). "vinyl alcohol polymer" and may be referred to as "PVA") was uniaxially stretched to become matrix iodine dye (I ₃ ^- and I ₅ ^-, etc.) or a dichroic dye such as dichroic organic dyes What is adsorbed is the mainstream.

  LCDs have come to be used in a wide range of small devices such as calculators and watches, mobile phones, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, and measurement devices used indoors and outdoors. In recent years, there has been a demand for higher display quality. Accordingly, there is a demand for higher grades for polarizing films. Specifically, there is a need for polarizing films that have high polarization and transparency, excellent optical properties, and excellent hue.

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

JP-A-8-201626 JP 2009-24076 A

  However, when a raw film for producing an optical film containing a conventionally known modified PVA is used, there is room for further improvement in that an optical film excellent in both optical properties and hue is obtained. In addition to this, when using an optical film production raw film containing a conventionally known modified PVA, troubles such as stretch breakage are still likely to occur particularly in the case of producing an optical film continuously, There was room for further improvement in the productivity of optical films.

  Therefore, the present invention is excellent in stretchability, can produce an optical film with good productivity, and can easily produce an optical film excellent in both optical properties and hue. It aims at providing the manufacturing method of a film and an optical film using the film.

  As a result of intensive studies by the present inventors to achieve the above-mentioned object, according to a film containing a hydroxymethyl group-containing PVA containing a specific structural unit having a 1,3-diol structure in the main chain, the above-mentioned problem is present. The present invention has been completed by finding that it can be solved and by further studying based on the findings.

That is, the present invention
[1] A raw film for producing an optical film comprising a vinyl alcohol unit and a hydroxymethyl group-containing PVA containing a structural unit represented by the following formula (1) , wherein the formula (1) The raw film for producing an optical film, wherein the content of the structural unit represented by

[ 2 ] The raw film for producing an optical film according to [1] , wherein the hydroxymethyl group-containing PVA further contains an ethylene unit;
[ 3 ] The raw film for producing an optical film according to [ 2 ], wherein the content of ethylene units in the hydroxymethyl group-containing PVA is 1 to 4 mol%;
[ 4 ] The raw film for producing an optical film according to any one of [1] to [ 3 ], wherein the saponification degree of the hydroxymethyl group-containing PVA is 95 mol% or more;
[ 5 ] The raw film for producing an optical film according to any one of [1] to [ 4 ], which is an original film for producing a polarizing film;
[ 6 ] A method for producing an optical film, comprising the step of uniaxially stretching using the raw film for producing an optical film according to any one of [1] to [ 5 ];
About.

  According to the present invention, an optical film can be produced with good stretchability, an optical film can be produced with good productivity, and an optical film excellent in both optical properties and hue can be easily produced. An anti-film and a method for producing an optical film using the same are provided.

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

  The raw film for producing an optical film of the present invention has improved stretchability when the hydroxymethyl group-containing PVA contained therein contains a structural unit having a 1,3-diol structure represented by the above formula (1). Yes. In addition to this, according to the raw film for producing an optical film of the present invention, an optical film excellent in both optical characteristics and hue can be easily produced. Although the present invention is not limited in any way, the reason why the above advantages can be obtained is that the crystallinity is lowered by the structural unit represented by the formula (1) and the 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 is 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 still more preferably in the range of 0.3 to 1.8 mol%. When the said content rate is 0.1 mol% or more, the drawability of a film improves more and the optical film which is excellent in a hue is obtained. On the other hand, when the content is 2 mol% or less, dissolution of the film during the production of the optical film can be more effectively prevented, and an optical film excellent in optical properties can be obtained. In the present specification, the structural unit refers to a repeating unit constituting a 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 2,000 to 4,000. More preferably, it is in the range. 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, poor process passability during film formation, and the like. In addition, the polymerization degree of the hydroxymethyl group-containing PVA in the present specification means an average polymerization degree 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. Preferably, it is 98 mol% or more. The saponification degree of the hydroxymethyl group-containing PVA in this specification is a structural unit (typical) that can be converted into a vinyl alcohol unit (—CH ₂ —CH (OH) —) by saponification, which the hydroxymethyl group-containing PVA has. Is 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 degree of saponification can be measured according to the description of JIS K6726-1994, taking into account the amount of the structural unit represented by formula (1) and its derivatives.

  The method for producing the hydroxymethyl group-containing PVA is not particularly limited. For example, a vinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and an unsaturated monomer copolymerizable therewith and convertible to the structural unit represented by the formula (1) Are converted to vinyl alcohol units, while structural units derived from unsaturated monomers that can be converted to structural units represented by formula (1) are converted to structural units represented by formula (1). A method is mentioned. A specific example of the unsaturated monomer that can be converted into the structural unit represented by the formula (1) is 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 partially have a branched or cyclic structure. Moreover, a part may be substituted with other functional groups. R is preferably an alkyl group having 1 to 5 carbon atoms. 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, Examples thereof include a linear or branched alkyl group such as a pentyl group. Examples of the substituent that R may have include an alkoxy group, a halogen atom, and a hydroxyl group. A plurality of R 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. -Methylenepropane and the like. Among 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 monomer compared with other allylic unsaturated monomers (for example, allyl glycidyl ether) generally used for modification of PVA. The copolymerization reaction proceeds easily. 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 degree of modification and a high degree of polymerization can be easily obtained. In addition, since the amount of the unreacted unsaturated monomer remaining at the end of the polymerization can be reduced, the hydroxymethyl group-containing PVA in the present invention is excellent in terms of environment and cost during industrial production. Yes.

  The vinyl ester monomer used for the production of the hydroxymethyl group-containing PVA is not particularly limited. For example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, capron Examples thereof include vinyl acidate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. From the economical viewpoint, vinyl acetate is preferred.

  The polymerization method for copolymerizing the unsaturated monomer represented by formula (2) and the vinyl ester monomer may be any method such as batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. As the polymerization method, known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method can be applied. A bulk polymerization method or a solution polymerization method in which polymerization is allowed to proceed in a solvent-free or solvent such as alcohol is usually employed. In order to obtain a vinyl ester copolymer having a high degree of polymerization, an emulsion polymerization method is also preferred. Although the solvent of the solution polymerization method is not particularly limited, for example, alcohol. The alcohol used as the solvent for the solution polymerization method is, for example, a lower alcohol such as methanol, ethanol, or propanol. The amount of solvent used in the polymerization system may be selected in consideration of the chain transfer of the solvent in accordance with the degree of polymerization of the target hydroxymethyl group-containing PVA. For example, when the solvent is methanol, it is included in the solvent and the polymerization system. The mass ratio with respect to all monomers {= (solvent) / (total monomers)} is preferably selected within the range of 0.01 to 10, more preferably within the range of 0.05 to 3.

  The polymerization initiator used for copolymerization of the unsaturated monomer represented by the formula (2) and the vinyl ester monomer is a known polymerization initiator such as an azo initiator or a peroxide initiator. The redox initiator may be selected according to the polymerization method. Examples of the azo initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethylvaleronitrile). Examples of the peroxide initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α- Perester compounds such as cumylperoxyneodecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like may be combined with the above initiator to form a polymerization initiator. The redox initiator is, for example, a polymerization initiator in which the peroxide initiator is combined with a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or longalite. The amount of the polymerization initiator used varies depending on the type of the polymerization initiator and cannot be determined unconditionally, but 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 monomer, and 0.02 to 0 More preferred is 15 mol%. The polymerization temperature is not particularly limited, but is suitably 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 monomer may be performed in the presence of a chain transfer agent. Examples of the chain transfer agent include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinic acid salts such as sodium phosphinate monohydrate. Of these, aldehydes and ketones are preferably used. The amount of chain transfer agent used can be determined according to the chain transfer coefficient of the chain transfer agent to be used and the degree of polymerization of the target hydroxymethyl group-containing PVA. The amount is preferably 0.1 to 10 parts by mass.

  The above hydroxymethyl group-containing PVA can be obtained by saponifying a vinyl ester copolymer obtained by copolymerization of an unsaturated monomer represented by formula (2) and a vinyl ester monomer. . By saponifying the vinyl ester copolymer, the vinyl ester unit in the vinyl ester copolymer is converted to 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 to 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 copolymer can be performed, for example, in a state where the vinyl ester copolymer is dissolved in alcohol or hydrous alcohol. Examples of the alcohol used for saponification include lower alcohols such as methanol and ethanol, preferably methanol. The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate, and benzene at a ratio of 40% by mass or less of the mass, for example. 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 performed is not limited, but is preferably in the range of 20 to 60 ° C. When a gel-like product precipitates as saponification proceeds, the product is 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 include other 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 monomer. Further, a structural unit derived from an unsaturated monomer that can be copolymerized with the above-described vinyl ester monomer and can be converted to a structural unit represented by the formula (1) (shown by the formula (1) by saponification). A structural unit that has not been converted to a structural unit).

  In the hydroxymethyl group-containing PVA, the proportion of the total of the structural unit represented by the formula (1), the vinyl alcohol unit and the vinyl ester unit is 100 mol% of the number of moles of all the structural units constituting the hydroxymethyl group-containing PVA. 80 mol% or more, preferably 90 mol% or more, more 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-butene, isobutylene and 1-hexene; acrylic acid and a salt thereof; an unsaturated monomer having an acrylate group. Body; methacrylic acid and salt thereof; unsaturated monomer having methacrylic acid ester group; acrylamide; N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and salt thereof Acrylamide derivatives such as acrylamidopropyldimethylamine and salts thereof (for example, quaternary salts); methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, methacrylamidepropyl Methacrylamide derivatives such as methylamine and its salts (for example, quaternary salts); methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether , Vinyl ethers such as stearyl vinyl ether and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene chloride and fluoride Vinylidene halides such as vinylidene; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, allyl chloride; maleic acid, itaconic acid, fumaric acid, etc. Unsaturated dicarboxylic acids and salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate. Among these, since the stretchability is improved and the film can be stretched at a higher temperature, the occurrence of troubles such as breakage of the stretch during the production of the optical film is reduced, and the productivity of the optical film is further improved. preferable. When the hydroxymethyl group-containing PVA contains an ethylene unit, the content of the ethylene unit is 100 in terms of the number of moles of all structural units constituting the hydroxymethyl group-containing PVA from the viewpoints of stretchability and stretchable temperature as described above. As mol%, 1-4 mol% is preferable and 2-3 mol% is especially preferable.

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

  The raw film for producing an optical film of the present invention can contain a plasticizer in addition to the 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 raw film for producing an optical film of the present invention can contain one or more of these plasticizers. Among these, glycerin is preferable in terms of the effect of improving stretchability.

  The content of the plasticizer in the raw film for producing an optical 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 3 to 17 parts by mass. More preferably, 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 handling properties from being lowered.

  The raw film for producing an optical film of the present invention further 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, Flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, cross-linking agents, fungicides, preservatives, crystallization rate retarders Additives such as can be blended as needed.

  The proportion of the total of the hydroxymethyl group-containing PVA and the plasticizer in the raw film for producing an optical film of the present invention is preferably 80% by mass or more based on the mass of the original film for producing an optical film, 90 More preferably, it is more than 95 mass%, and it is still more preferable that it is 95 mass% or more.

  The degree of swelling of the raw film for producing an optical film of the present invention is preferably in the range of 160 to 240%, more preferably in the range of 170 to 230%, and in the range of 180 to 220%. It is particularly preferred. When the degree of swelling is 160% or more, the crystallization can be prevented from proceeding extremely, and the film can be stably stretched to a higher magnification. On the other hand, when the degree of swelling is 240% or less, dissolution during stretching is suppressed, and stretching is possible even under higher temperature conditions. In this specification, the degree of swelling of the optical film-producing original film refers to the mass when the optical film-producing original film is immersed in distilled water at 30 ° C. for 30 minutes, and is dried at 105 ° C. for 16 hours after immersion. It means the percentage of the value obtained by dividing by the mass after the measurement, and can be specifically measured by the method described later in the examples.

  Although the thickness of the raw film for producing an optical film of the present invention is not particularly limited, it is generally 1 to 100 μm, more preferably 5 to 75 μm, and particularly preferably about 10 to 60 μm. When the thickness is too thin, there is a tendency that stretching breakage is likely to occur during uniaxial stretching treatment for producing an optical film such as a polarizing film. Moreover, when the said thickness is too thick, at the time of the uniaxial stretching process for manufacturing an optical film, it will become easy to generate | occur | produce a stretching spot.

  The width | variety in particular of the raw film for optical film manufacture of this invention is not restrict | limited, It can determine according to the use etc. of the optical film manufactured. In recent years, since the enlargement of screens of liquid crystal televisions and liquid crystal monitors has progressed, it is preferable for these applications to have a width of the original film for producing optical films of 3 m or more. On the other hand, if the width of the raw film for producing an optical film is too large, it is difficult to uniformly carry out uniaxial stretching itself when producing an optical film with an apparatus that has been put into practical use. The width of the anti-film is preferably 7 m or less.

  The production method of the raw film for producing an optical film of the present invention is not particularly limited, and a production method in which the thickness and width of the film after film formation are more uniform can be preferably employed. One or two or more of the above-described hydroxymethyl group-containing PVA constituting the anti-film and, if necessary, the above-described plasticizer, additive, and surfactant described later are dissolved in the liquid medium. The film-forming stock solution, hydroxymethyl group-containing PVA, and optionally further containing one or more of plasticizers, additives, surfactants, liquid media, etc., and hydroxymethyl group-containing PVA Can be produced using a film-forming stock solution in which is melted. When the film-forming stock solution contains at least one of a plasticizer, an additive, and a surfactant, it is preferable that these components are uniformly mixed.

  Examples of the liquid medium used for the preparation of 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 them can be used. Among these, water is preferable from the viewpoint of environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (content ratio in the film-forming stock solution of volatile components such as liquid media removed by volatilization or evaporation during film formation) varies depending on the film-forming method, film-forming conditions, etc. Specifically, it is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass, and still more preferably in the range of 60 to 85% by mass. The film-forming stock solution has a volatile content of 50% by mass or more, so that the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during the preparation of the film-forming stock solution, and there are 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 is facilitated.

  The film-forming stock solution preferably contains a surfactant. By including the surfactant, the film-forming property is improved and the occurrence of uneven thickness of the film is suppressed, and the film is easily peeled off from the metal roll or belt used for film formation. When a raw film for producing an optical film is produced from a film-forming stock solution containing a surfactant, the film may contain a surfactant. Although the kind of said surfactant is not specifically limited, From a viewpoint of the peelability from a metal roll or a belt, an anionic surfactant or a nonionic surfactant is preferable.

  Suitable examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzene sulfonate.

  Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; 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 allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.

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

  When the film-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of the hydroxymethyl group-containing PVA contained in the film-forming stock solution. , 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 said content is 0.01 mass part or more, film forming property and peelability improve more. 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 on the surface of the optical film-producing raw film and causing blocking to deteriorate handling properties. .

  Examples of the film forming method for forming an optical film manufacturing raw film using the above 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. Can be mentioned. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable because a raw film for producing an optical film having a uniform thickness and width and good physical properties can be obtained. The formed film can be dried or heat-treated as necessary.

  As a specific example of the method for producing the raw film for producing an optical film of the present invention, for example, using the T-type slit die, hopper plate, I-die, lip coater die, etc. The film discharged or cast uniformly on the peripheral surface of the rotating heated first roll (or belt) located on the upstream side and discharged or cast on the peripheral surface of the first roll (or belt) Volatile components are evaporated and dried from one side, and then further dried on the peripheral surface of one or more rotating heated rolls arranged downstream thereof, or in a hot air dryer After passing and further drying, the method of winding with a winding device can be preferably employed industrially. Drying with a heated roll and drying with a hot air dryer may be performed in an appropriate combination.

  The original film for producing an optical film of the present invention is used as an original film for producing an optical film. Examples of such an optical film include a polarizing film and a retardation film. Such an optical film can be produced, for example, by subjecting the raw film for producing an optical film of the present invention to a treatment such as uniaxial stretching.

  The method in particular when manufacturing a polarizing film using the raw film for optical film manufacture of this invention is not restrict | limited, You may employ | adopt any method employ | adopted conventionally. As such a method, for example, dyeing and uniaxial stretching are performed on the original film for manufacturing an optical film of the present invention, or uniaxial stretching is performed on an original film for manufacturing an optical film of the present invention containing a dye. The method of giving is mentioned. As a more specific method for producing a polarizing film, the raw film for producing an optical film of the present invention is swelled, dyed, uniaxially stretched, and if necessary, further crosslinked, fixed, dried. And a method of performing a heat treatment. In this case, the order of each treatment such as swelling, dyeing, crosslinking treatment, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments can be performed simultaneously. Also, one or more of each process can be performed twice or more.

  The swelling can be performed by immersing the raw film for producing an optical film in water. The temperature of the water when immersed in water is preferably within a range of 20 to 40 ° C, more preferably within a range of 22 to 38 ° C, and within a range of 25 to 35 ° C. Further preferred. Moreover, as time to immerse in water, it is preferable to exist in the range of 0.1 to 5 minutes, for example, and it is more preferable to be in the range of 0.5 to 3 minutes. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  Dyeing can be performed by bringing a dichroic dye into contact with the original film for producing an optical film. As the dichroic dye, an iodine dye is generally used. The dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally performed by immersing an original film for optical film production in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath. In the present invention, such a dyeing method is also used. Preferably employed. The iodine concentration in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the potassium iodide concentration is preferably in the range of 0.01 to 10% by mass. Moreover, it is preferable that the temperature of a dyeing bath shall be 20-50 degreeC, especially 25-40 degreeC.

  By subjecting the raw film for optical film production to a crosslinking treatment, it is possible to more effectively prevent the hydroxymethyl group-containing PVA from eluting into water when wet-stretching at a high temperature. From this viewpoint, the crosslinking treatment is preferably performed after the treatment for bringing the dichroic dye into contact and before the uniaxial stretching. The crosslinking treatment can be performed by immersing the raw film for producing an optical film in an aqueous solution containing a crosslinking agent. As the crosslinking agent, one or more of boron compounds such as boric acid and borate such as borax can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking 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. More preferably. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is in the range of 1 to 15% by mass. The aqueous solution containing a crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 50 ° C, particularly in the range of 25 to 40 ° C. It can bridge | crosslink efficiently by making the said temperature into the range of 20-50 degreeC.

Uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. In the case of the dry stretching method, the stretching may be performed at room temperature, may be performed while heating, or may be performed in the air using the raw film for producing an optical 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, It is especially preferable to be within the range of ˜4.0% by mass. Moreover, the boric acid aqueous solution may contain potassium iodide, and the concentration is preferably in the range of 0.01 to 10% by mass.
The stretching temperature in the 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 polarizing performance of the obtained polarizing film. Is particularly preferred. 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 in the case of uniaxially stretching a raw optical film for producing a long optical film, and uniaxial stretching or lateral uniaxial stretching in the long direction can be adopted, but polarization with excellent polarization performance. Uniaxial stretching in the longitudinal direction is preferred because a film is obtained. Uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

  In producing the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dichroic dye (iodine dye or the like) to the film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the fixing treatment bath is generally about 2 to 15% by mass, particularly about 3 to 10% by mass. By making the said density | concentration in the range of 2-15 mass%, adsorption | suction of a dichroic dye can be strengthened more. 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 the drying at a temperature within the range of 30 to 150 ° C, particularly within the range of 50 to 130 ° C. A polarizing film excellent in dimensional stability is easily obtained by drying at a temperature in the range of 30 to 150 ° C.

  The polarizing film obtained as described above is usually used as a polarizing plate by bonding a protective film having optical transparency and mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for bonding include PVA adhesives and urethane adhesives, among which PVA adhesives are suitable.

  The polarizing plate obtained as described above can be used as a component of an LCD after being coated with an acrylic adhesive or the like 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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In addition, each measurement or evaluation method employ | adopted in the following examples and comparative examples is shown below.

Primary structure of PVA The primary structure of PVA (hydroxymethyl group-containing PVA in Examples and various modified PVA in Comparative Examples) used in the following examples and comparative examples was analyzed using 270 MHz ¹ H-NMR. Deuterated DMSO was used as a solvent for ¹ H-NMR measurement.

The degree of swelling of the raw film for optical film production The raw film for optical film production obtained in the following examples or comparative examples was cut to 1.5 g and immersed in distilled water at 30 ° C. for 30 minutes. After immersion for 30 minutes, the film was taken out, the surface water was taken out with a filter paper, and the mass “N” was determined. Subsequently, the film was dried with 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 raw film for optical film production was calculated by the following formula (3).
Swelling degree (%) = 100 × N / M (3)

Stretchability of the optical film production raw film From the center in the width direction of the optical film production raw film obtained in the following examples or comparative examples, the width of the width 5 cm × length 5 cm is uniaxially stretched. A 5 cm × 8 cm long sample was cut. This sample was uniaxially stretched in the length direction by a factor of 1.5 while being immersed in pure water at 30 ° C. Subsequently, while being 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, the ratio is 1.6 times (2.4 in total). Uniaxially stretching in the length direction to adsorb iodine. Next, the length was 1.1 times (2.6 times in total) while being immersed in an aqueous solution (crosslinking bath) (temperature 30 ° C.) containing 3% by weight of boric acid and 3% by weight of potassium iodide. Uniaxially stretched in the direction. Further, while being immersed in an aqueous solution (stretching bath) containing 4% by mass of boric acid and 6% by mass of potassium iodide, the film is uniaxially stretched in the length direction until it is cut, and the raw film for producing an optical film before stretching. The ratio of the length at the time of cutting with respect to the length of the film was defined as the limit stretch ratio. However, the temperature of the stretching bath was changed by 1 ° C. from an appropriate temperature, the limiting stretching ratio was measured, and the temperature at which the limiting stretching ratio was the highest was selected.

Optical properties of polarizing film (dichroic ratio)
(1) Measurement of transmittance Ts From the central part of the polarizing film obtained in the following examples or comparative examples, two 2 cm samples were taken in the length direction of the polarizing film, and a spectrophotometer with an integrating sphere (Japan) Using “V7100” manufactured by Spectroscopic Co., Ltd., in accordance with JIS Z 8722 (measuring method of object color), the visibility of the visible light region of the C light source and 2 ° field of view is corrected. The light transmittance when tilted by + 45 ° with respect to the vertical direction and the light transmittance when tilted by −45 ° were measured, and an average value Ts1 (%) thereof was obtained. In the same manner for the other sample, the light transmittance when tilted by + 45 ° and the light transmittance when tilted by −45 ° were measured, and an average value Ts2 (%) thereof 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 by measurement of transmittance Ts are stacked so that their length directions are parallel to each other. Are measured in the same manner as in the case of “(1) Measurement of transmittance Ts”, and the degree of polarization V ( %).
V = {(T‖−T⊥) / (T‖ + T⊥)} ^1/2 × 100 (5)

(3) Calculation of dichroic ratio when transmittance is 44% In each of the following Examples and Comparative Examples, the iodine concentration in the dyeing bath is 0.02 to 0.04% by mass, and the potassium iodide concentration is 2. The same operation was carried out by changing 4 times within the range of 0 to 4.0% by mass (however, the iodine concentration: potassium iodide concentration = 1: 100), and each example or comparative example was produced. Four polarizing films having different dichroic dye adsorption amounts were produced. For each of these four polarizing films, the transmittance Ts (%) and the degree of polarization V (%) were determined by the method described above, and the transmittance Ts (%) was plotted on the horizontal axis and the degree of polarization for each example and comparative example. With V (%) as the vertical axis, a total of 5 points including one point based on the transmittance Ts (%) and the degree of polarization V (%) of the polarizing film obtained in each example or comparative example are plotted on a graph. Thus, an approximate curve was obtained, and from the approximate curve, the degree of polarization V ₄₄ (%) when the transmittance Ts (%) was 44% was obtained.
From the obtained degree of polarization V ₄₄ (%), a dichroic 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)

Color of polarizing film (parallel b value)
In the above “optical properties (dichroic ratio) of the polarizing film”, when obtaining the polarization degree V of four polarizing films having different amounts of adsorption of the dichroic dye, the transmittance T） (%) and the transmittance are obtained. Lab is measured at the time of measuring T⊥ (%), b value at the time of measuring transmittance T‖ (%) is a parallel b value, and b value at the time of measuring transmittance T 透過 (%) is an orthogonal b value. . For each example and comparative example, including the parallel b value as the horizontal axis and the orthogonal b value as the vertical axis, including one point based on the parallel b value and orthogonal b value of the polarizing film obtained in each example or comparative example A total of 5 points were plotted on a graph to obtain an approximate curve, and a parallel b value when the orthogonal b value was −4 was obtained from the approximate curve. Note that the closer the parallel b value is to 0, the better the hue of the polarizing film.

[Example 1]
(1) 100 parts by mass of a hydroxymethyl group-containing PVA shown in Table 1 obtained by saponifying a copolymer of vinyl acetate and 1,3-diacetoxy-2-methylenepropane as a modified PVA, and 10 parts by mass of glycerin as a plasticizer Part and an aqueous solution containing 0.1 part by weight of sodium polyoxyethylene lauryl ether sulfate as a surfactant and having a modified PVA content of 10% by weight as a film-forming stock solution. The film thus obtained was heat-treated at a predetermined temperature for 1 minute in a hot air dryer to adjust the degree of swelling to 200%, thereby producing an optical film-manufacturing raw film having a thickness of 30 μm.
The stretchability was evaluated by the above-described method using the obtained optical film for optical film production. The results are shown in Table 1.

(2) A sample having a width of 5 cm and a length of 8 cm was cut from the central portion in the width direction of the original film for producing an optical film obtained in (1) so that a range of width 5 cm × length 5 cm could be uniaxially stretched. . This sample was uniaxially stretched in the length direction by a factor of 1.5 while being immersed in pure water at 30 ° C. Subsequently, while being 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, the ratio is 1.6 times (2.4 in total). Uniaxially stretching in the length direction to adsorb iodine. Next, the length was 1.1 times (2.6 times in total) while being immersed in an aqueous solution (crosslinking bath) (temperature 30 ° C.) containing 3% by weight of boric acid and 3% by weight of potassium iodide. Uniaxially stretched in the direction. Further, an aqueous solution (stretching bath) containing 4% by mass of boric acid and 6% by mass of potassium iodide (a temperature at which the limit stretching ratio determined in the above “stretchability of the raw film for producing optical film” becomes the highest) ) Was uniaxially stretched in the length direction to a magnification 0.2 times lower than the limit draw ratio. Thereafter, it was immersed in an aqueous solution (cleaning bath) containing 3% by mass of potassium iodide (temperature 30 ° C.) for 5 seconds, and finally dried at 60 ° C. for 4 minutes to produce a polarizing film.
Using the obtained polarizing film, the optical properties (dichroic ratio) and hue (parallel b value) of the polarizing film were evaluated by the method described above. The results are shown in Table 1.

[Comparative Examples 1-3]
In Example 1, unmodified PVA shown in Table 1 obtained by saponifying a vinyl acetate homopolymer instead of modified PVA (Comparative Example 1); vinyl acetate and 3,4-diacetoxy-1 as modified PVA -Modified PVA obtained by saponifying a copolymer with butene (Comparative Example 2) shown in Table 1; or obtained by saponifying a copolymer of vinyl acetate and itaconic acid as modified PVA. Except that the modified PVA shown in Table 1 (Comparative Example 3) was used, a raw film for optical film production 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.

[Examples 2 to 4]
In Example 1, hydroxymethyl group-containing PVA shown in Table 1 obtained by saponifying a copolymer of vinyl acetate and 1,3-diacetoxy-2-methylenepropane as a modified PVA (Examples 2 and 3) Or a hydroxymethyl group-containing PVA shown in Table 1 obtained by saponifying a terpolymer of vinyl acetate, 1,3-diacetoxy-2-methylenepropane and ethylene as a modified PVA (Example 4) Except having used each, the raw film for optical film manufacture and the polarizing film were manufactured similarly to Example 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 the raw films for producing optical films of Examples 1 to 4 that satisfy the regulations of the present invention are excellent in stretchability and can be produced with high productivity. In addition, since the stretchability is high, the area of the obtained optical film can be widened, and more optical films can be obtained. Moreover, in addition to the above, it can be seen that according to the raw film for producing an optical film of Examples 1 to 4 satisfying the rules of the present invention, an optical film excellent in both optical properties and hue can be easily produced. Furthermore, in Example 4 using the hydroxymethyl group-containing PVA further containing an ethylene unit, the stretchability is further improved, the stretchable temperature is also increased, and it can be seen that the optical film can be produced with higher productivity.

Claims (6)

A raw film for producing an optical film comprising a vinyl alcohol unit and a hydroxymethyl group-containing vinyl alcohol polymer containing a structural unit represented by the following formula (1), the hydroxymethyl group-containing vinyl alcohol polymer: The raw film for optical film manufacture whose content rate of the structural unit shown by following formula (1) in is 0.1-2 mol%.


The raw film for producing an optical film according to claim 1 , wherein the hydroxymethyl group-containing vinyl alcohol polymer further comprises an ethylene unit. The raw film for optical film production according to claim 2 , wherein the content of ethylene units in the hydroxymethyl group-containing vinyl alcohol polymer is 1 to 4 mol%. The raw film for optical film production according to any one of claims 1 to 3 , wherein the hydroxymethyl group-containing vinyl alcohol polymer has a saponification degree of 95 mol% or more. The original film for optical film manufacture according to any one of claims 1 to 4 , which is an original film for manufacturing a polarizing film. The manufacturing method of an optical film which has the process of carrying out uniaxial stretching using the original film for optical film manufacture of any one of Claims 1-5 .