JP6385106B2 - Method for producing polarizer and method for producing polarizing plate - Google Patents

Description

  The present invention relates to a method for producing a polarizer effective for producing a polarizing plate. More specifically, the present invention relates to a polarizer having excellent stability and excellent optical properties of a polyvinyl alcohol resin solution containing iodine. The present invention relates to a method that can be stably manufactured.

  Conventionally, a polyvinyl alcohol film is manufactured by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, forming a film by a solution casting method (casting method), and drying. The polyvinyl alcohol film thus obtained is used in many applications as a film having excellent transparency, and one of its useful applications is a polarizer. Such a polarizer is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to equipment that requires high quality and high reliability.

Polarizers are generally dyed with dichroic dyes and dyes such as iodine and then uniaxially stretched in the boron compound and before and after the process, so that the dichroic dye is oriented and polarizing performance. Is demonstrated. In general, iodine-based polarizers can obtain a high degree of polarization compared to dye-based polarizers, but have a problem of poor durability such as heat resistance.
Under such circumstances, there is a demand for improvement in durability such as heat resistance and heat-and-moisture resistance, as well as an increase in screen size, brightness, and definition of liquid crystal displays.

  In response to such demands, methods such as improving the polyvinyl alcohol resin, increasing the molecular weight of the polyvinyl alcohol resin, and improving the crystallinity of the stretched film by controlling the tacticity have been proposed. However, these methods have a problem that the film is difficult to be dyed when dyed with iodine, and uneven dyeing tends to occur.

  As a measure for improving these, a method is proposed in which iodine is pre-mixed in an aqueous solution containing a polyvinyl alcohol resin, and the film is formed using this aqueous solution, instead of dyeing iodine on the polyvinyl alcohol film. (For example, refer to Patent Documents 1 to 3.)

JP-A-8-190017 JP 2004-279651 A JP 2008-242308 A

  However, in the disclosure techniques of Patent Documents 1 to 3 described above, an ordinary polyvinyl alcohol resin is used to form a polyvinyl alcohol resin aqueous solution containing iodine and potassium iodide. Since the alcohol-based resin aqueous solution is easily gelled and has a problem in solution stability, it is necessary to maintain the solution at a high temperature, for example, 50 ° C. or higher, specifically, a high temperature of about 60 ° C.

  When the aqueous solution containing iodine is kept at a high temperature, the iodine contained in the corner will volatilize with time, and when a polarizer is continuously produced using such an aqueous solution, it is produced using an aqueous solution at the initial stage of compounding. There is a difference in transmittance between the polarizer and the polarizer manufactured using the aqueous solution at the later stage of blending, that is, a problem occurs in that the polarizer at the later stage of blending has higher transmittance than the polarizer at the early stage of blending. Therefore, there is a need for further improvement for producing a polarizer having stable optical characteristics even in continuous production.

  Therefore, in the present invention, under such a background, the polyvinyl alcohol resin solution containing iodine is excellent in stability, for example, it is not necessary to hold the resin solution at a high temperature exceeding 50 ° C., and 30 to 40 Provided is a method for producing a polarizer capable of stably producing a polarizer having stable optical properties such as gelation does not occur even in a temperature range of about 0 ° C., and further, optical properties do not deteriorate. It is for the purpose.

  However, as a result of intensive studies in view of such circumstances, the present inventors have made a side chain as a polyvinyl alcohol resin in producing a polarizer using a polyvinyl alcohol resin solution preliminarily containing iodine, particularly an aqueous solution. By using a polyvinyl alcohol resin having a 1,2-diol structure, the stability of the polyvinyl alcohol resin solution containing iodine is excellent. For example, it is necessary to hold the resin solution at a high temperature exceeding 50 ° C. It has been found that a polarizer having stable optical properties such as gelation does not occur even in a temperature range of about 30 to 40 ° C., and that optical properties do not deteriorate can be stably produced. The present invention has been completed.

That is, the gist of the present invention relates to a method for producing a polarizer which is uniaxially stretched after forming a solution containing a polyvinyl alcohol resin (A) having a 1,2-diol structure in the side chain and iodine.
Moreover, in this invention, the manufacturing method of the polarizer obtained by the said manufacturing method and also the polarizing plate which uses this polarizer are provided.

  According to the method for producing a polarizer of the present invention, since a polarizer is produced using a polyvinyl alcohol resin having a specific structure, the stability of the polyvinyl alcohol resin solution containing iodine is excellent, and the resin solution is high. Since there is no need to keep in the temperature range, there is an effect that a polarizer having stable optical characteristics such as no deterioration in optical characteristics can be stably produced even in continuous production of polarizers. The obtained polarizers are electronic desk calculators, electronic clocks, word processors, personal computers, liquid crystal televisions, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, eye protection glasses, stereoscopic glasses, display elements. It is effectively used for reflection reduction layers for (CRT, LCD, etc.), medical equipment, building materials, toys and the like.

The present invention is described in detail below.
The polyvinyl alcohol resin (A) used in the present invention is a polyvinyl alcohol resin having a 1,2-diol structure in the side chain, that is, usually a 1,2-diol structure represented by the general formula (1). Examples thereof include polyvinyl alcohol resins containing units.

（ここで、Ｒ¹、Ｒ²、Ｒ³はそれぞれ独立して水素又はアルキル基である。）

(Here, R ¹ , R ² and R ³ are each independently hydrogen or an alkyl group.)

  Such a polyvinyl alcohol resin (A) can be produced, for example, by saponifying a copolymer of (a) a vinyl ester monomer and 3,4-diacetoxy-1-butene.

  Such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, versatic. Although vinyl acid acid etc. are mentioned, Vinyl acetate is used preferably especially.

  Further, in the present invention, it is preferable to use the above-mentioned copolymer. However, in some cases, other monomers are added in a small amount, for example, 5 mol% or less, as long as the purpose of the present invention is not impaired other than the above-described copolymer components. For example, olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid. Unsaturated acids such as salts or mono- or dialkyl esters thereof, nitriles such as acrylonitrile and methacrylonitrile, amides such as diacetone acrylamide, acrylamide and methacrylamide, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, etc. Olefin sulfonic acid or its Glycerin monoallyl ether, alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, polyoxyalkylenes such as polyoxyethylene (meth) allyl ether, polyoxypropylene (meth) allyl ether (meta ) Polyoxyalkylene (meth) acrylates such as allyl ether, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, polyoxyalkylenes such as polyoxyethylene (meth) acrylamide, polyoxypropylene (meth) acrylamide ( (Meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene Vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, ethylene carbonate, allyl acetate, and the like.

  Furthermore, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidopropyltrimethylammonium chloride, 2-acryloxyethyltrimethylammonium chloride, 2-methacryloxyethyltrimethylammonium chloride, 2-hydroxy-3- Cationic group-containing monomers such as methacryloyloxypropyltrimethylammonium chloride, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, 3-butenetrimethylammonium chloride, dimethyldiallylammonium chloride, diethyldiallylammonium chloride, acetoacetyl group-containing monomers And so on.

In copolymerizing the above vinyl ester monomer and 3,4-diacetoxy-1-butene (and other monomers), the same polymerization conditions and polymerization methods as those of known vinyl ester monomers should be employed. Can do.
As a polymerization method, for example, a known method such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be employed, but solution polymerization is usually performed.

  In addition, the charging method of the monomer component at the time of copolymerization is not particularly limited, and any method such as batch charging, split charging, continuous charging, etc. is adopted, but 3,4-diacetoxy-1-butene is a polyvinyl ester polymer. Drop polymerization is preferred from the viewpoint of physical properties such as uniform distribution in the molecular chain and a decrease in the melting point of polyvinyl alcohol, and a polymerization method based on the HANNA method is particularly preferred.

  Examples of the solvent used in such copolymerization include usually lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone and methyl ethyl ketone, and industrially, methanol is preferably used.

  The amount of the solvent used may be appropriately selected in consideration of the chain transfer constant of the solvent in accordance with the degree of polymerization of the target copolymer. For example, when the solvent is methanol, S (solvent) / M ( Monomer) = 0.01 to 10 (weight ratio) is preferable, and particularly preferably selected from the range of 0.05 to 3 (weight ratio).

  In the copolymerization, a polymerization catalyst is used. Examples of the polymerization catalyst include an azo catalyst, a peroxide catalyst, and a redox catalyst. Specifically, azobisisobutyronitrile, acetyl peroxide, and the like can be given. And known radical polymerization catalysts such as benzoyl peroxide and lauryl peroxide, and low-temperature active radical polymerization catalysts such as azobisdimethylvaleronitrile and azobismethoxydimethylvaleronitrile.

The amount of the polymerization catalyst used varies depending on the type of catalyst and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate. For example, when azoisobutyronitrile or acetyl peroxide is used, 0.01 to 0.2 mol% is preferable with respect to the vinyl ester monomer, and 0.02 to 0.15 mol% is particularly preferable.
Moreover, it is preferable that the reaction temperature of a copolymerization reaction shall be about 40 degreeC-about a boiling point by the solvent and pressure to be used.

The obtained copolymer is then saponified, and this saponification reaction is basically the same as the saponification conditions of known polyvinyl alcohol resins. That is, usually, the copolymer obtained above is dissolved or dispersed in an alcohol or hydrous alcohol, and the saponification catalyst is used.
Examples of the alcohol include methanol, ethanol, propanol, tert-butanol and the like, and methanol is particularly preferably used. The concentration of the copolymer in the alcohol is appropriately selected depending on the viscosity of the system, but is usually selected from the range of 10 to 60% by weight. Examples of saponification catalysts include alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate and lithium methylate, sulfuric acid, hydrochloric acid, Examples include acid catalysts such as nitric acid, metasulfonic acid, zeolite, and cation exchange resin.

The amount of the saponification catalyst used is appropriately selected depending on the saponification method, the target degree of saponification, and the like. Usually, when an alkali catalyst is used, a vinyl ester monomer and 3,4-diacetoxy-1- A suitable amount is 0.1 to 30 mmol, preferably 2 to 17 mmol, based on 1 mol of butene.
Moreover, although the reaction temperature of saponification reaction is not specifically limited, 10-60 degreeC is preferable, More preferably, it is 20-50 degreeC.

  During the saponification, the ester portion of the vinyl ester monomer and the acetoxy portion of 3,4-diacetoxy-1-butene are simultaneously converted into hydroxyl groups, whereby the polyvinyl alcohol resin (A) can be produced.

  Thus, a polyvinyl alcohol resin (A) having a 1,2-diol structure in the side chain can be obtained. In the present invention, the average saponification degree of the polyvinyl alcohol resin (A) is relatively high. Preferably, it is preferably 90 mol% or more, particularly 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 99 mol% or more. If the average saponification degree is too small, the water resistance during the production of the polarizer is preferred. Tends to decrease.

  The average degree of saponification in the present invention is expressed as the rate of change (mol%) of the total amount of the ester portion of the vinyl ester monomer and the acetoxy portion of 3,4-diacetoxy-1-butene into hydroxyl groups (ken%). In the conversion reaction, the acetoxy part of 3,4-diacetoxy-1-butene is almost completely saponified).

  The viscosity of the polyvinyl alcohol-based resin (A) is usually 8 to 400 mPa · s, particularly 12 to 300 mPa · s, more preferably 16 to 270 mPa · s, as a 4 wt% aqueous solution viscosity at 20 ° C. If the viscosity of the 4% by weight aqueous solution is too small, the stretchability at the time of preparing the polarizer tends to decrease, and if too large, the flatness and transmittance of the film tend to decrease.

  Furthermore, the content of the 1,2-diol structure in the side chain of the polyvinyl alcohol resin (A) is preferably 0.01 to 20 mol%, particularly preferably 0.05 to 15 mol%, Preferably, it is 0.1 to 12 mol%, most preferably 0.1 to 6 mol%. If the content is too small, it is difficult to obtain the effect of the present invention. Not only does it tend to be difficult, but there is a tendency that the water resistance during the production of the polarizer decreases.

  In addition, as a manufacturing method of the polyvinyl alcohol-type resin (A) used by this invention, the method to saponify the copolymer of the said (a) vinyl ester-type monomer and 3, 4- diacetoxy-1-butene was explained in full detail. However, without being limited to such a method, for example, (i) a method of saponifying and decarboxylating a copolymer of a vinyl ester monomer and a vinyl ethylene carbonate represented by the general formula (2), (c) vinyl A method of saponifying and deketalizing a copolymer of an ester-based monomer and a 2,2-dialkyl-4-vinyl-1,3-dioxolane represented by the general formula (3), and (d) a vinyl ester-based monomer A method of saponifying a copolymer with glycerin monoallyl ether, and the like are also exemplified and are not particularly limited.

ここで、Ｒ¹、Ｒ²、Ｒ³はそれぞれ独立して水素又はアルキル基である。

Here, R ¹ , R ² and R ³ are each independently hydrogen or an alkyl group.

ここで、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４、Ｒ^５はそれぞれ独立して水素又はアルキル基である。

Here, R ¹ , R ² , R ³ , R ⁴ , and R ⁵ are each independently hydrogen or an alkyl group.

  In the present invention, as the polyvinyl alcohol resin (A), two or more kinds of polyvinyl alcohol resins having different side chain 1,2-diol structure contents, average saponification degree, viscosity and the like may be used in combination. Good.

  Furthermore, in this invention, from the point of the water resistance improvement effect at the time of polarizer preparation, as polyvinyl alcohol-type resin, polyvinyl alcohol-type resin other than the said polyvinyl alcohol-type resin (A) and the said polyvinyl alcohol-type resin (A) (B) may be used in combination.

  When the polyvinyl alcohol resin (A) and the polyvinyl alcohol resin (B) are used in combination, the average content of the side chain 1,2-diol structure calculated by the following formula is 0.1 to 20 mol%. A range is preferable.

Here, the average content (mol%) of the side chain 1,2-diol structure is calculated as follows.
That is, the content of the side chain 1,2-diol structure of the polyvinyl alcohol-based resin (A) is α mol%, and the polyvinyl alcohol-based content relative to the total amount of the polyvinyl alcohol-based resin (A) and the polyvinyl alcohol-based resin (B). It is calculated from the following formula when the content ratio of the resin (A) is X%.
Average content of side chain 1,2-diol structure (mol%) = (X / 100) × α

  In particular, from the viewpoint of the effect of improving stretchability, the polyvinyl alcohol resin (B) may be used in combination with the polyvinyl alcohol resin (A) as a main component. For example, the content ratio (A / B) (weight ratio) is Usually 95/5 to 50/50, preferably 90/10 to 55/45. From the viewpoint of the effect of improving water resistance, the polyvinyl alcohol resin (A) is used in combination with the polyvinyl alcohol resin (B) as a main component. For example, the content ratio (A / B) (weight ratio) is usually from 5/95 to 50/50, preferably from 10/90 to 45/55. Accordingly, the content ratio can be appropriately selected.

  As said polyvinyl alcohol-type resin (B), what is used for the polarizer use conventionally is sufficient, Usually, average saponification degree is 90 mol% or more, Preferably it is 95 mol% or more, Most preferably, it is 98. More than mol%, more preferably more than 99 mol%. If the average degree of saponification is too small, the water resistance during the production of the polarizer tends to decrease.

  Furthermore, the viscosity of the polyvinyl alcohol-based resin (B) is usually 8 to 500 mPa · s, particularly 20 to 400 mPa · s, more preferably 40 to 400 mPa · s, as a 4 wt% aqueous solution viscosity at 20 ° C. preferable. If the viscosity of the 4% by weight aqueous solution is too small, the stretchability at the time of preparing the polarizer tends to decrease, and if too large, the flatness and transparency of the film tend to decrease.

The polyvinyl alcohol resin (B) is not particularly limited as long as it is a polyvinyl alcohol resin other than the polyvinyl alcohol resin (A), but an unmodified polyvinyl alcohol resin is usually preferable. Also, small amounts of unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates For example, it may be a polyvinyl alcohol resin containing a component copolymerizable with vinyl acetate.
Moreover, you may use together 2 or more types of polyvinyl alcohol-type resin from which average saponification degree, 4 weight% aqueous solution viscosity, etc. differ as a polyvinyl alcohol-type resin (B).

  Moreover, in using together polyvinyl alcohol-type resin (A) and polyvinyl alcohol resin (B), the difference of the average saponification degree of polyvinyl alcohol-type resin (A) and polyvinyl alcohol-type resin (B) is 6 mol% or less. In view of compatibility, it is preferably 3 mol% or less, more preferably 2 mol% or less.

  In the present invention, the film is formed using the polyvinyl alcohol resin (A) and a solution containing iodine (hereinafter sometimes abbreviated as iodine-containing polyvinyl alcohol resin solution (a)). Such a resin solution (a) is, for example, (1) a method of blending iodine or an aqueous iodine solution into a solution (for example, an aqueous solution) of the polyvinyl alcohol resin (A), or (2) a polyvinyl alcohol resin and iodine. It is prepared by a method of blending in a solvent (for example, water, an organic solvent, a water-organic solvent mixture).

  The iodine content is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the polyvinyl alcohol-based resin (A). If the content of iodine is too small, the function as a polarizer tends not to be exhibited sufficiently. If the content is too large, it is difficult to suppress the formation of a complex, or the optical properties, water resistance, and heat resistance tend to be reduced. is there.

In the present invention, it is preferable from the viewpoint of workability to use iodine, for example, an iodide such as potassium iodide in addition to iodine.
Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, barrel iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Can be mentioned. Of these, potassium iodide is usually preferably used.

  The iodide content is generally 1 to 100 parts by weight, preferably 3 to 30 parts by weight, based on 1 part of iodine. If the iodide content is too small, iodine tends to be difficult to dissolve, and if it is too much, gelation tends to occur.

  In the present invention, in addition to the above iodine and iodide, inorganic salts such as lithium chloride, boron compounds such as boric acid and borax, plasticizers, surfactants and the like can be blended as necessary.

  Moreover, it is preferable that the polyvinyl alcohol-type resin density | concentration of an iodine containing polyvinyl alcohol-type resin solution (a) is 5 to 30 weight%, Furthermore, it is preferable that it is 8 to 20 weight%. If the concentration is too low, it tends to be difficult to form a coating film, and if it is too high, gelation of the solution tends to be difficult to control.

In this invention, it forms as follows using an iodine containing polyvinyl alcohol-type resin solution (a).
First, the iodine-containing polyvinyl alcohol resin solution (a) is applied on a resin film, a metal drum, or a metal belt by a cast casting method or a die casting method. After coating, drying and further heat treatment as necessary to form a film.

  The thickness of the film is usually 1 to 200 μm, preferably 2 to 100 μm, particularly preferably 3 to 80 μm, particularly preferably 4 to 60 μm. If the thickness is too thin, it tends to be too thin after stretching and the function as a polarizer is not sufficiently exhibited, and if it is too thick, the film thickness accuracy is lowered, and it tends to be difficult to dry and the production efficiency tends to be lowered.

  When cast on a metal drum or metal belt, (1) after film formation, the obtained film was peeled off from the metal drum or metal belt to obtain a single layer film, and then Uniaxial stretching is applied.

  In addition, when cast film is formed on a resin film, (2) after film formation, the obtained film is peeled from the resin film to obtain a single layer film, and then uniaxially stretched. There are a method and (3) a method of performing uniaxial stretching with a resin film without peeling off the obtained film from the resin film after film formation. Among these, (3) is often stretched at a high temperature, and in this case, the contained iodine may volatilize, so the methods (1) and (2) are preferred.

  In the present invention, when a single-layer film is obtained (the above-mentioned methods (1) and (2)), the thickness of the film is preferably 5 to 200 μm, particularly 10 to 100 μm, Is preferably 15 to 80 μm, more preferably 20 to 75 μm. If the thickness is too thin, it tends to be difficult to produce, and if it is too thick, the accuracy of the film thickness is lowered and drying is difficult to produce, resulting in a reduction in production efficiency.

  Moreover, when forming a film | membrane on a resin film without obtaining a single layer film (the method of said (3)), it is preferable that the thickness of the film | membrane is 1-50 micrometers, especially 2 It is preferably 40 μm, more preferably 3 to 30 μm. If the thickness is too thin, it tends to be too thin after stretching and does not sufficiently function as a polarizer, and if it is too thick, it tends to be floated or peeled off due to foaming or the like, resulting in poor appearance.

  As the resin film, for example, a film made of a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, stretchability, etc. is used, and an appropriate resin is selected according to their glass transition temperature or melting point. Used.

  Specific examples of the thermoplastic resin include, for example, polyolefin resins, polyester resins, cyclic polyolefin resins (norbornene resins), (meth) acrylic resins, cellulose ester resins, polycarbonate resins, and polyvinyl alcohol resins. Examples thereof include resins, vinyl acetate resins, polyarylate resins, polystyrene resins, polyether sulfone resins, polysulfone resins, polyamide resins, polyimide resins, and mixtures and copolymers thereof.

  The resin film may be a film made of only one kind of the above-mentioned thermoplastic resin, or may be a film made by blending two or more kinds of thermoplastic resins. The resin film may be a single layer film or a multilayer film.

  Arbitrary appropriate additives may be added to the resin film in addition to the above thermoplastic resin. Examples of such additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, and coloring agents.

  The thickness of the resin film can be determined as appropriate, but generally, from the viewpoint of workability such as strength and handleability, it is preferably 1 to 500 μm, more preferably 1 to 300 μm, still more preferably 5 to 200 μm, most preferably. Is 5 to 150 μm.

  In order to improve the adhesion with the iodine-containing polyvinyl alcohol resin solution (a), the resin film is subjected to corona treatment, plasma treatment, flame treatment, etc. on at least the surface on which the resin solution (a) is applied. You may go. Moreover, in order to improve adhesiveness, you may form thin layers, such as a primer layer and an adhesive bond layer, on the surface at the side by which the resin solution (a) of a resin film is coated.

In the present invention, a polarizer can be obtained by uniaxially stretching the film obtained above.
In addition, you may perform the dyeing | staining process further using an iodine solution in the front | former stage of uniaxial stretching, a back | latter stage, or during uniaxial stretching.

  Further, the boron compound treatment is preferably performed from the viewpoint of improving water resistance, and may be performed at any point such as before or after uniaxial stretching or during uniaxial stretching.

  In the present invention, stretching is desirably performed 3 to 10 times, preferably 3.5 to 7 times in a uniaxial direction. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The stretching temperature is preferably selected from 20 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

  As the boron compound used for the boron compound treatment, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.5 to 10% by weight, and the above-mentioned iodide (for example, the above-mentioned potassium iodide or the like) is contained in the solution at a concentration of 0.1. It is practically desirable to coexist about 10 to 10% by weight. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is preferably about 20 to 80 ° C., and the treatment time is preferably about 15 seconds to 20 minutes, and it is also preferable to perform a stretching operation during the treatment as necessary.

  Thus, a polarizer is obtained by the production method of the present invention, that is, by forming a film containing a polyvinyl alcohol resin (A) having a 1,2-diol structure in the side chain and iodine, and then uniaxially stretching. be able to.

The thickness of the obtained polarizer is usually 0.5 to 50 μm, particularly 1 to 45 μm, more preferably 3 to 40 μm. If the thickness is too thin, the optical durability performance as a polarizing plate tends to be low, and if it is too thick, the contraction force of the polarizing plate tends to increase.
Further, the single transmittance of such a polarizer is preferably 40% or more, particularly 41% or more, and more preferably 42% or more.
Further, the degree of polarization of the polarizer is preferably 95 to 100%, particularly 96 to 100%, and more preferably 97 to 100%.

In the present invention, an optically isotropic polymer film or sheet may be laminated and bonded as a protective film on one or both sides of a polarizer to be used as a polarizing plate.
As a protective film used for the polarizing plate of the present invention, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo type Or a film or sheet of norbornene-based polyolefin or the like can be mentioned.

  For the purpose of thinning the polarizer, instead of the protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied and laminated on one or both surfaces of the polarizer.

  A polarizer (including at least one surface laminated with a protective film or a curable resin) has a transparent pressure-sensitive adhesive layer formed on a surface of one of the surfaces as required by a generally known method. In some cases, it may be put to practical use. Examples of pressure-sensitive adhesive layers include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid. Since the main component is a copolymer with a monoolefin carboxylic acid (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene), the polarizing properties of the polarizing film are not impaired. Although it is particularly preferable, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

  Thus, according to the method for producing a polarizer of the present invention, it is not necessary to hold a resin solution at a high temperature, gelation does not occur even in a temperature range of about 30 to 40 ° C., and optical characteristics do not deteriorate. A polarizer having stable optical characteristics can be manufactured stably, and the obtained polarizer is an electronic desk calculator, electronic watch, word processor, personal computer, LCD TV, portable information terminal, automobile or machine. It is effectively used for liquid crystal display devices such as measuring instruments, sunglasses, eye protection glasses, stereoscopic glasses, a reflection reducing layer for display elements (CRT, LCD, etc.), medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis.

About each physical property, it carried out as follows.
(1) Content of side chain 1,2-diol structure (mol%)
It was calculated by measuring with ¹ H-NMR (internal standard substance: tetramethylsilane, solvent: d6-DMSO).
(2) Average saponification degree (mol%) of polyvinyl alcohol resin
The analysis was conducted with the alkali consumption required for hydrolysis of the residual vinyl acetate units.
(3) 4% aqueous solution viscosity of polyvinyl alcohol resin (mPa · s)
The water temperature was adjusted to 20 ° C. and measured with a Heppler viscometer.

Example 1
Polyvinyl alcohol (A) having a 1,2-diol structure in the side chain (content of side chain 1,2-diol structure: 1 mol%, average degree of saponification: 99.8 mol%, 4% aqueous solution viscosity (20 ° C): 85 mPa · s) to prepare a polyvinyl alcohol aqueous solution having a concentration of 13%. After heating this to 60 ° C., an iodine-kalim iodide aqueous solution at 25 ° C. was added and mixed to this, 8.7% polyvinyl alcohol (A), 0.11% iodine, and 0.79% potassium iodide. An aqueous solution (a) containing was obtained.
About the obtained iodine-containing polyvinyl alcohol aqueous solution (a), solution stability was evaluated as follows.

(Solution stability)
The obtained iodine-containing polyvinyl alcohol aqueous solution (a) was allowed to stand under the temperature conditions of (1) liquid temperature 40 ° C., (2) liquid temperature 60 ° C., (a) initial state, (b) solution state after 24 hours. Were visually observed and evaluated as follows.
<Presence of gel>
○ ・ ・ ・ No gel can be confirmed × ・ ・ ・ Gel can be confirmed

Next, using the iodine-containing polyvinyl alcohol aqueous solution (a) as shown in Table 2, polarizers were produced as follows.
That is, the iodine-containing polyvinyl alcohol aqueous solution (a) was cast on a glass plate at room temperature with an applicator, and then dried at room temperature for 48 hours to form a coating film. Then, it peeled from the glass plate and produced the unstretched polyvinyl alcohol film (thickness 70 micrometers).
Next, the unstretched film was uniaxially stretched 5 times in an aqueous solution (30 ° C.) of 4% boric acid and 3% potassium iodide. Subsequently, a polarizer (thickness: 35 μm) was obtained by drying at 60 ° C. for 2 minutes.
About the obtained polarizer, the optical characteristic was measured as follows.

(optical properties)
About the polarizer obtained above, the single-piece | unit transmittance | permeability (%) and the polarization degree (%) were measured using the spectrophotometer with an integrating sphere ("VAP7070" by JASCO Corporation). Furthermore, the rate of change between when the aqueous solution containing the iodine-containing polyvinyl alcohol aqueous solution (a) was allowed to stand for 24 hours and when the aqueous solution after being allowed to stand was used was also calculated. The calculation formula for the rate of change is as follows.
Rate of change (%) = (Transmittance of polarizer using aqueous solution after standing for 24 hours−Single transmittance of polarizer using aqueous solution before standing for 24 hours) × 100 / (24 hours Single transmittance of polarizer using aqueous solution before standing)

Example 2
In Example 1, as the polyvinyl alcohol (A) having a 1,2-diol structure in the side chain, the content of the side chain 1,2-diol structure: 0.3 mol%, the average saponification degree: 99.8 mol %, 4% aqueous solution viscosity (20 ° C.): An iodine-containing polyvinyl alcohol aqueous solution (a) was obtained in the same manner except that 62 mPa · s of polyvinyl alcohol was used.
The solution stability of the obtained iodine-containing polyvinyl alcohol aqueous solution (a) was evaluated in the same manner as in Example 1.

  Next, using this iodine-containing polyvinyl alcohol aqueous solution (a), a polarizer was produced in the same manner as in Example 1, and the optical properties of the obtained polarizer were measured.

Comparative Example 1
In Example 1, unmodified polyvinyl alcohol (average saponification degree: 99.7 mol%, 4% aqueous solution viscosity (20 ° C.): 63 mPa · s) was used in the same manner as polyvinyl alcohol. An aqueous alcohol solution was obtained, and the same procedure as in Example 1 was performed to obtain a polarizer.
Evaluation similar to Example 1 was performed about the solution stability of the obtained iodine containing polyvinyl alcohol aqueous solution, and the optical characteristic of a polarizer.
The evaluation results of Examples and Comparative Examples are shown in Tables 1 and 2.

From the above results, when the conventional polyvinyl alcohol as in Comparative Example 1 is used, when an aqueous polyvinyl alcohol solution containing iodine is prepared in advance, it is easy to gel and needs to be maintained at a high temperature such as 60 ° C. On the other hand, when the polyvinyl alcohol having the specific structure of Example 1 and Example 2 is used, the solution stability is good even at a temperature of about 40 ° C., and a good polarizer can be continuously produced. .
Further, in Comparative Example 1, since it is necessary to hold at a high temperature of 60 ° C., iodine volatilizes while holding the aqueous solution, and a polarizer is manufactured using the aqueous solution after long-term holding. In contrast, in Example 1 and Example 2, it is possible to stably produce a good polarizer that does not volatilize iodine and that does not deteriorate optical characteristics. It will be possible.

  In the method for producing a polarizer of the present invention, since a polarizer is produced using a polyvinyl alcohol resin having a specific structure, the polyvinyl alcohol resin solution containing iodine is excellent in stability, and the resin solution is in a high temperature range. Therefore, it is possible to stably produce a polarizer having stable optical properties such as no deterioration of optical properties even in continuous production of polarizers. Polarizers include electronic desk calculators, electronic clocks, word processors, personal computers, liquid crystal televisions, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, eye protection glasses, stereoscopic glasses, and display elements (CRT). , LCD, etc.), and is effectively used for medical devices, building materials, toys and the like.

Claims (6)

  A method for producing a polarizer, comprising forming a solution containing a polyvinyl alcohol-based resin (A) having a 1,2-diol structure in the side chain and iodine, and then uniaxially stretching.   The method for producing a polarizer according to claim 1, wherein the content of the 1,2-diol structure in the side chain of the polyvinyl alcohol-based resin (A) is 0.01 to 20 mol%.   The average saponification degree of a polyvinyl alcohol-type resin (A) is 90 mol% or more, The manufacturing method of the polarizer of Claim 1 or 2 characterized by the above-mentioned.   The method for producing a polarizer according to any one of claims 1 to 3, wherein the polyvinyl alcohol resin (A) has a viscosity of 8 to 400 mPa · s as a 4 wt% aqueous solution viscosity at 20 ° C.   The iodine content is 0.1 to 10% by weight based on the polyvinyl alcohol resin (A) having a 1,2-diol structure in the side chain. Manufacturing method of the polarizer. Method for producing a polarizing plate characterized by comprising using a polarizer obtained by the production method of claims 1-5 polarizer according to any one.