JP6255300B2 - Method for producing polyvinyl alcohol resin - Google Patents

Description

  The present invention relates to a method for producing a polyvinyl alcohol resin capable of easily producing a polyvinyl alcohol resin with little coloration, a polyvinyl alcohol resin produced by the production method, and a polyvinyl alcohol produced using the polyvinyl alcohol resin. Related to film.

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 polyvinyl alcohol film (hereinafter referred to as “polyvinyl alcohol”). iodine based dye "and may be referred to as" PVA ") in a matrix formed by uniaxial stretching (I ₃ ^- and I ₅ ^-, etc.) or a dichroic dye such as dichroic organic dyes which are adsorbed It has become 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 measuring devices used indoors and outdoors. In recent years, durability in particular outdoors has been demanded. Accordingly, heat resistance is also required for the polarizing film, and specifically, a polarizing film that is difficult to be colored under a high temperature environment of 100 ° C. is expected on the assumption of use in a vehicle. .

  A dichroic organic dye is relatively often used for a polarizing film used in a car. However, the cause of the change over time in the degree of coloration in the polarizing film is due to fading due to deterioration of the dichroic organic dye, and PVA. It can be roughly divided into coloring due to film deterioration. Among these, as a method for reducing the deterioration of the PVA film related to the latter, it is effective to reduce the coloring of the PVA resin as a raw material of the PVA film. In other words, the fact that there is already a lot of coloring at the PVA resin stage means that the deterioration of the PVA resin has already progressed after undergoing the PVA resin manufacturing process in which mild temperature conditions generally below 100 ° C. are adopted. In the case where a PVA film and thus a polarizing film are produced using such a PVA resin, the degree of coloring tends to change over time in a high temperature environment of 100 ° C. In other words, the degree of coloring of the PVA resin is an index of the ease of coloring in a polarizing film under a high temperature environment of 100 ° C.

  So far, several methods for obtaining a PVA resin with little coloring are known. For example, when producing a modified PVA resin, the aldehyde concentration in the polymerization system after copolymerization is kept low, and the resulting modified PVA resin is dried at a low drying temperature or in an atmosphere with a low oxygen concentration. It is known that coloring of the modified PVA resin can be effectively suppressed by combining methods such as selecting the type of solvent to be used and selecting the type of catalyst used in the saponification reaction (see Patent Document 1). Moreover, since it will become easy to color a PVA chip | tip if it drys in presence of oxygen before manufacturing a PVA film using a PVA chip | tip, the method of drying in a nitrogen atmosphere or a vacuum or a pressure-reduced state is known (patent document). 2).

JP 2003-342322 A JP 2004-226707 A

  However, in recent years, the requirements for coloring of polarizing films have become more and more severe. From such a viewpoint, the conventionally known method is further advantageous in that a polarizing film that is difficult to be colored under a high temperature environment of 100 ° C. is obtained. There was room for improvement.

  Accordingly, the present invention provides a method for producing a PVA resin that can easily produce an optical film such as a polarizing film that is less colored and is less likely to be colored in a high-temperature environment at 100 ° C. An object of the present invention is to provide a low-colored PVA resin and a PVA film produced using the PVA resin.

  As a result of intensive studies by the present inventors to achieve the above object, the above problem is solved by setting the total amount of vinyl crotonate and crotonaldehyde to vinyl esters such as vinyl acetate used in a specific range. The present invention has been completed through further studies based on the findings.

That is, the present invention
[1] A step of subjecting a vinyl ester composition containing at least one selected from the group consisting of vinyl crotonate and crotonaldehyde and a vinyl ester (excluding vinyl crotonate) to a polymerization reaction, and an obtained polyvinyl ester The total content of vinyl crotonate and crotonaldehyde in the vinyl ester composition is 0 on a mass basis relative to the vinyl ester (excluding vinyl crotonate). 1-10 ppm production method;
[2] The production method of the above [1], wherein the vinyl ester is vinyl acetate;
[3] The production method of the above [1] or [2], wherein the vinyl ester composition contains vinyl crotonate;
[4] The content of vinyl crotonate in the vinyl ester composition is 7 ppm or less on a mass basis with respect to the vinyl ester (excluding vinyl crotonate), any one of the above [1] to [3] Production method;
[5] Production of any one of [1] to [4] above, wherein the content of crotonaldehyde in the vinyl ester composition is 10 ppm or less on a mass basis with respect to the vinyl ester (excluding vinyl crotonate). Method;
[6] The production method according to any one of the above [1] to [5], wherein the content of vinyl alcohol units in the PVA contained in the PVA resin exceeds 80 mol%;
[7] The production method according to any one of the above [1] to [6], wherein the PVA resin is in a chip form or a powder form;
[8] The production method of any one of the above [1] to [7], wherein the YI value of the PVA resin is 25 or less;
[9] PVA resin produced by the production method of any one of [1] to [8] above;
[10] A PVA film produced using the PVA resin of [9] above;
[11] The PVA film of the above [10], which is a film for producing an optical film;
About.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of PVA resin which can manufacture PVA resin with little coloring easily, PVA resin with little coloring manufactured by the said manufacturing method, and PVA manufactured using the said PVA resin A film is provided.

[Production method of PVA resin]
The production method of the present invention for producing a PVA resin is a polymerization reaction of a vinyl ester composition containing at least one selected from the group consisting of vinyl crotonate and crotonaldehyde, and a vinyl ester (excluding vinyl crotonate). And a step of saponifying the obtained polyvinyl ester.

  The vinyl ester is not particularly limited as long as it is a vinyl ester other than vinyl crotonate. For example, vinyl acetate, vinyl formate, vinyl propionate, vinyl pivalate, vinyl versatate, vinyl laurate, stearin And vinyl acid benzoate, vinyl benzoate, and isopropenyl acetate. These vinyl esters may be used alone or in combination of two or more. Among these vinyl esters, vinyl acetate is preferable from the viewpoint of ease of production, availability, and cost of PVA.

  The vinyl ester composition to be subjected to the polymerization reaction contains at least one selected from the group consisting of vinyl crotonate and crotonaldehyde, and a vinyl ester (excluding vinyl crotonate). That is, the vinyl ester composition may contain vinyl crotonate and other vinyl esters and does not contain crotonaldehyde, or may contain crotonaldehyde and vinyl esters and does not contain vinyl crotonate. Alternatively, it may contain vinyl crotonate, crotonaldehyde, and vinyl esters other than vinyl crotonate. Among these, the vinyl ester composition contains vinyl crotonate, that is, contains vinyl crotonate and other vinyl esters and does not contain crotonaldehyde because the effects of the present invention are more remarkably exhibited. Or it is preferable that it contains both vinyl crotonate, crotonaldehyde, and vinyl esters other than vinyl crotonate.

  The total content of vinyl crotonate and crotonaldehyde in the vinyl ester composition is 0.1 on a mass basis relative to the vinyl ester (excluding vinyl crotonate) from the viewpoint of the degree of coloring of the obtained PVA resin. -10 ppm, preferably 0.3 ppm or more, more preferably 0.5 ppm or more, further preferably 1 ppm or more, particularly preferably 2 ppm or more, 8 ppm or less, more preferably 6 ppm or less, and even more preferably 4 ppm or less.

  The content of vinyl crotonate in the vinyl ester composition is 7 ppm or less on a mass basis with respect to the vinyl ester contained therein (excluding vinyl crotonate) from the viewpoint of coloring degree of the obtained PVA resin. Is preferably 5 ppm or less, more preferably 3 ppm or less, and preferably 0.1 ppm or more, more preferably 0.2 ppm or more, and 0.4 ppm or more. More preferably.

  The content of crotonaldehyde in the vinyl ester composition is 10 ppm or less on a mass basis with respect to the vinyl ester contained therein (excluding vinyl crotonate) from the viewpoint of the degree of coloring of the obtained PVA resin. Preferably, it is 7 ppm or less, more preferably 5 ppm or less, more preferably 0.1 ppm or more, more preferably 0.2 ppm or more, and 0.4 ppm or more. Is more preferably 1 ppm or more, and most preferably 2 ppm or more.

  The vinyl ester composition may be subjected to a polymerization reaction as it is, or may be subjected to a polymerization reaction after being mixed with a solvent or other components. The purity of the vinyl ester (excluding vinyl crotonate) in the vinyl ester composition before mixing with a solvent or other components is preferably 80% by mass or more, more preferably 95% by mass or more. Preferably, it may be 97% by mass or more, 98% by mass or more, and further 99% by mass or more.

  The polymerization method for subjecting the vinyl ester composition to the polymerization reaction may be any of batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc., and polymerization methods include bulk polymerization, solution polymerization, suspension, and the like. Known methods such as a turbid 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 the case of obtaining a polyvinyl ester having a high degree of polymerization, an emulsion polymerization method is also preferable. 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 according to the degree of polymerization of the target PVA. For example, when the solvent is methanol, the solvent and all monomers contained in the polymerization system The mass ratio {= (solvent) / (total monomer)} is preferably within the range of 0.01 to 10, more preferably within the range of 0.05 to 3.

  The polymerization initiator used when subjecting the vinyl ester composition to the polymerization reaction is selected from known polymerization initiators such as azo initiators, peroxide initiators, and redox initiators depending on the polymerization method. That's fine. 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 relative to the vinyl ester (excluding vinyl crotonate) contained in the vinyl ester composition. 0.2 mol% is preferable, and 0.02 to 0.15 mol% is more preferable. 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 above polymerization reaction 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; phosphinic acid salts such as sodium phosphinate monohydrate and the like. 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 used and the degree of polymerization of the target PVA. Generally, the vinyl ester contained in the vinyl ester composition (however, crotonic acid is used). 0.1-10 mass parts is preferable with respect to 100 mass parts) except vinyl.

  In the manufacturing method of this invention, it has the process of saponifying the polyvinyl ester obtained as mentioned above. By saponifying the polyvinyl ester, the vinyl ester unit in the polyvinyl ester is converted into a vinyl alcohol unit.

  The saponification of the polyvinyl ester can be performed, for example, in a state where the polyvinyl ester is dissolved in an alcohol or a hydrous alcohol. As alcohol used for saponification, lower alcohols, such as methanol and ethanol, are mentioned, for example, Preferably it is 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 is precipitated as saponification proceeds, the product can be pulverized, washed and dried to obtain the target PVA resin. The saponification method is not limited to the method described above, and a known method can be applied.

  The PVA contained in the PVA resin may be composed only of vinyl alcohol units, but may further contain a structural unit derived from another monomer copolymerizable with the vinyl ester. Examples of the other monomer include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; methyl (meth) acrylate, (meth ) Ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, (Meth) acrylic acid esters such as (meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid dodecyl, (meth) acrylic acid octadecyl; (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl ( (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide Lopansulfonic acid or its salt, (meth) acrylamide propyldimethylamine or its salt, (meth) acrylamide derivatives such as N-methylol (meth) acrylamide or its derivatives; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc. N-vinyl amides; vinyl ethers such as 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, stearyl vinyl ether; (meth) acrylonitrile, etc. Of vinyl cyanide; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl such as allyl acetate and allyl chloride Compound; maleic acid or a salt thereof, ester or acid anhydride; itaconic acid or a salt thereof, ester or acid anhydride; vinylsilyl compound such as vinyltrimethoxysilane; unsaturated sulfonic acid and the like. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer. The other monomer is preliminarily present in the polymerization system when the vinyl ester composition is subjected to the polymerization reaction, or added to the system during the polymerization reaction, etc. Can be used.

  The PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA.

  In the PVA, a part of the hydroxyl groups may be cross-linked or may not be cross-linked. Moreover, said PVA may react with aldehyde compounds, such as acetaldehyde and a butyraldehyde, etc. to form an acetal structure, and the said PVA does not react with these compounds and does not form an acetal structure. May be.

  The content of the vinyl alcohol unit in the PVA contained in the PVA resin is preferably more than 80 mol% based on the number of moles of all structural units constituting the PVA since the effects of the present invention are more remarkably exhibited. More preferably, exceeding 85 mol%, more preferably exceeding 90 mol%, especially when water resistance is required, such as when the obtained PVA film is used as a raw film for optical film production, etc. In the above, the content is preferably 95 mol% or more, more preferably 97 mol% or more, further preferably 98 mol% or more, 99 mol% or more, 99.5 mol% or more. Furthermore, 99.8 mol% or more may be sufficient.

  The degree of polymerization of PVA is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and in the range of 2,000 to 4,000. More preferably it is. When the polymerization degree is 1,500 or more, the durability of the optical film can be further improved when the obtained PVA film is used as a raw film for producing an optical film. 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 PVA in this specification means the average degree of polymerization measured according to description of JIS K6726-1994.

  Although there is no restriction | limiting in particular in the shape of PVA resin, From a viewpoint, such as the ease of manufacture and handling, it is preferable that it is a chip form or a powder form. Although there is no restriction | limiting in particular in the content rate of PVA in PVA resin, For example, it is 80 mass% or more, 90 mass% or more, 93 mass% or more, 95 mass% or more, Furthermore, it can be 98 mass% or more. Examples of components other than PVA in the PVA resin include water.

  According to the production method of the present invention, a PVA resin with little coloring can be produced easily. The degree of coloring of the PVA resin is preferably 25 or less, more preferably 22 or less, further preferably 21 or less, and particularly preferably 18 or less, as the YI value. The lower limit of the YI value is not particularly limited, but the YI value is, for example, 5 or more. The YI value of the PVA resin can be measured by the method described later in Examples.

  There is no restriction | limiting in particular in the use of PVA resin manufactured by the manufacturing method of this invention, Although it can use preferably for a conventionally well-known use as a use of PVA resin, according to the manufacturing method of this invention, PVA with little coloring Since the resin can be easily produced, the PVA resin is preferably used as a raw material for producing a PVA film. In particular, a film for producing an optical film (raw material) for producing an optical film such as a polarizing film or a retardation film. It is preferably used as a raw material for the production of anti-film.

[PVA film]
The PVA film produced using the above PVA resin can contain a plasticizer in addition to 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 PVA film 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 PVA film is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 17 parts by mass with respect to 100 parts by mass of PVA contained therein. More preferably, it is in the range of ˜15 parts by mass. When the content is 1 part by mass or more, the stretchability of the PVA film is further improved. On the other hand, when the content is 20 parts by mass or less, it can be suppressed that the PVA film becomes too flexible and the handleability is lowered.

  The PVA film 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, a flame retardant, and other thermoplastic resins. Necessary additives such as lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, crosslinking agents, fungicides, preservatives, crystallization rate retarders, etc. It can mix | blend suitably according to it.

  The proportion of the total of PVA and plasticizer in the PVA film is preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass or more based on the mass of the PVA film. Is more preferable.

  The thickness of the PVA film is not particularly limited, but is generally 1 to 100 μm, more preferably 5 to 75 μm, and particularly preferably 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, there exists a tendency for a stretch spot to generate | occur | produce at the time of the uniaxial stretching process for manufacturing an optical film.

  The width | variety in particular of a PVA film is not restrict | limited, It can determine according to the use etc. of the polarizing film manufactured. In recent years, it is suitable for these uses when the width of the PVA film is set to 3 m or more in view of the trend toward larger screens of liquid crystal televisions and liquid crystal monitors. The width of the PVA film is preferably 4 m or more. On the other hand, if the width of the PVA film is too large, it is difficult to uniformly carry out uniaxial stretching itself when manufacturing a polarizing film with a device that has been put into practical use, so the width of the PVA film is 7 m or less. Is preferably 6 m or less, and particularly preferably 5 m or less.

  The shape of the PVA film is not particularly limited, but a more uniform PVA film can be produced continuously and smoothly, and can also be used continuously in the case of producing a polarizing film using it. A long film is preferred. The length of the long film (length in the length direction) is not particularly limited, and can be appropriately set according to the application, for example, within a range of 5 to 30,000 m.

  The degree of swelling of the PVA film is preferably in the range of 160 to 240%, more preferably in the range of 170 to 230%, and particularly preferably in the range of 180 to 220%. 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 PVA film is obtained by dividing the mass when the PVA film is immersed in distilled water at 30 ° C. for 30 minutes by the mass after drying at 105 ° C. for 16 hours. Means percentage of value.

  The manufacturing method at the time of manufacturing a PVA film using said PVA resin is not specifically limited, The manufacturing method from which the thickness and width | variety of the film after film forming become more uniform can be employ | adopted preferably, For example, a PVA film A film-forming stock solution in which one or two or more of the above-described PVA and the above-described plasticizer, additive, and surfactant described below are dissolved in a liquid medium, Manufacture using a film-forming stock solution containing PVA and, if necessary, one or more of a plasticizer, an additive, a surfactant, a liquid medium and the like, in which 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 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. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. 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 the production of an industrial PVA film becomes easy.

  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 PVA film is produced from a film-forming stock solution containing a surfactant, the PVA 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 PVA contained in the film-forming stock solution, and 0.02 More preferably, it is in the range of -0.3 parts by mass, and particularly preferably in the range of 0.05-0.1 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 PVA film to cause blocking and deterioration in handleability.

  Examples of the film forming method for forming a PVA film using the above-described film forming stock solution include a cast film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. 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 PVA film having a uniform thickness and width and good physical properties can be obtained. The formed PVA film can be dried or heat-treated as necessary.

  As an example of a specific method for producing a PVA film, for example, a T-type 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. The volatile component is uniformly discharged or cast on the peripheral surface of the first roll (or belt) and the volatile component is discharged from one surface of the film discharged or cast on the peripheral surface of the first roll (or belt). Evaporate to dry, then further dry on the circumference of one or more rotating heated rolls located downstream, or pass through a hot air dryer and further dry, 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.

[Polarized film]
The method in particular when manufacturing a polarizing film using said PVA film is not restrict | limited, You may employ | adopt any method employ | adopted conventionally. Examples of such a method include a method of dyeing and uniaxially stretching the above PVA film, or uniaxially stretching the above PVA film containing a dye. As a more specific method for producing a polarizing film, a method of subjecting the above PVA film to swelling, dyeing, uniaxial stretching, and, if necessary, crosslinking treatment, fixing treatment, drying, heat treatment, etc. Is mentioned. 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 PVA 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 PVA 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 the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath, and such a dyeing method is also preferably used in the present invention. . 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 PVA film to a crosslinking treatment, it is possible to more effectively prevent 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 PVA 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 a PVA 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.

  The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching or lateral uniaxial stretching in the long direction can be adopted, but a polarizing film having excellent polarization performance can be obtained. To uniaxial stretching in the longitudinal direction. 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.

The YI value of the PVA resin obtained in Examples or Comparative Examples below the YI value of the PVA resin was measured using “LabScan” XE manufactured by Hunter Lab. Specifically, about 20 g of PVA resin was put in a round cell, filled while tapping the side of the container, covered with a black cup, and then the YI value was measured.

The PVA film obtained in Examples or Comparative Examples below the YI value of the PVA film is overlapped to a thickness of about 600 μm, and the YI value (heated) is measured using a spectrophotometer “U-3000” manufactured by Hitachi, Ltd. Before) was measured. Moreover, after heating the PVA film obtained in the following Examples or Comparative Examples at 100 ° C. for 20 hours, the PVA film was stacked to a thickness of about 600 μm, and a spectrophotometer “U-3000” manufactured by Hitachi, Ltd. was used. The YI value (after heating) was measured.

[Example 1]
(1) A vinyl acetate composition containing each component in the amount shown in Table 1 in a reactor equipped with a stirrer, a reflux condenser, an argon inlet, and an initiator addition port (purity of vinyl acetate is 99% by mass or more) 700 parts by mass and 300 parts by mass of methanol were charged, and the system was purged with argon for 30 minutes while performing argon bubbling. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 parts by mass of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. After polymerization at 60 ° C. for 180 minutes, the polymerization was stopped by cooling. The polymerization rate when the polymerization was stopped was 40 mol%. Subsequently, unreacted monomers were removed while sometimes adding methanol at 30 ° C. under reduced pressure to obtain a methanol solution of polyvinyl acetate (PVAc) (concentration: 30% by mass).
Next, 497 parts by mass of a methanol solution of PVAc prepared by adding methanol thereto (the amount of PVAc in the solution is 100 parts by mass), 14.0 parts by mass of a sodium hydroxide methanol solution (concentration 10.0% by mass) And saponification reaction was carried out at 40 ° C. A gelled product was formed in about 1 minute after the addition of the sodium hydroxide methanol solution. This was pulverized with a pulverizer and allowed to stand at 40 ° C. for 59 minutes to proceed saponification, and then 500 parts by mass of methyl acetate was added. In addition, the remaining alkali was neutralized. After confirming that neutralization was completed using a phenolphthalein indicator, a white solid was obtained by filtration, and 2,000 parts by mass of methanol was added thereto, followed by heating under reflux for 1 hour. After repeating the above washing operation three times, the white solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain a polymerization degree of 2,400 and a vinyl alcohol unit content of 99. A chip-like PVA resin substantially composed of 9 mol% PVA (PVA purity of 98% by mass or more) was obtained. The YI value of the PVA resin was measured by the above method, and the results are shown in Table 1.

(2) 100 parts by mass of the above PVA resin, 10 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant are mixed with water, and the content of PVA is 10 masses. % Aqueous solution. Using this aqueous solution as a film-forming stock solution, this was dried on a metal roll at 80 ° C., and the resulting film was heat-treated at a predetermined temperature for 1 minute in a hot air dryer to adjust the degree of swelling to 200%. Thus, a PVA film having a thickness of 30 μm was produced. The YI value (before and after heating) of the PVA film was measured by the above method, and the results are shown in Table 1.

[Examples 2 and 3 and Comparative Examples 1 and 2]
From PVA having a polymerization degree of 2,400 and a vinyl alcohol unit content of 99.9 mol%, except that a vinyl acetate composition containing the respective components in the amounts shown in Table 1 was used. A substantially chip-like PVA resin (PVA purity of 98% by mass or more) was obtained. The YI value of the PVA resin was measured by the above method, and the results are shown in Table 1. A PVA film having a thickness of 30 μm was produced in the same manner as in Example 1 except that the obtained PVA resin was used. The YI value (before and after heating) of the PVA film was measured by the above method, and the results are shown in Table 1.

Claims (10)

A vinyl ester composition comprising at least one selected from the group consisting of vinyl crotonate and crotonaldehyde and a vinyl ester (excluding vinyl crotonate), wherein the vinyl ester composition containing vinyl crotonate is used for the polymerization reaction. And a step of saponifying the obtained polyvinyl ester, wherein the total content of vinyl crotonate and crotonaldehyde in the vinyl ester composition is vinyl ester (however, crotonic acid The production method is 0.1 to 10 ppm on a mass basis with respect to (excluding vinyl).   The production method according to claim 1, wherein the vinyl ester is vinyl acetate. The manufacturing method of Claim 1 or 2 whose content of vinyl crotonate in a vinyl ester composition is 7 ppm or less on a mass basis with respect to vinyl ester (however, except vinyl crotonate). The production method according to any one of claims 1 to 3 , wherein the content of crotonaldehyde in the vinyl ester composition is 10 ppm or less on a mass basis with respect to the vinyl ester (excluding vinyl crotonate). The manufacturing method of any one of Claims 1-4 in which the content rate of the vinyl alcohol unit in polyvinyl alcohol contained in polyvinyl alcohol resin exceeds 80 mol%. The manufacturing method of any one of Claims 1-5 whose polyvinyl alcohol resin is a chip form or a powder form. The manufacturing method of any one of Claims 1-6 whose YI value of a polyvinyl alcohol resin is 25 or less. Polyvinyl alcohol resins prepared by the process according to any one of claims 1-7. A polyvinyl alcohol film produced using the polyvinyl alcohol resin according to claim 8 . The polyvinyl alcohol film of Claim 9 which is a film for optical film manufacture.