TW201539068A - Method for manufacturing polyvinyl alcohol based polymer film - Google Patents

Abstract

The present invention provides a PVA based polymer film which can produce a polarizing film with little unevenness of the transmittance between a central portion and an end portion. The present invention provides a PVA based polymer film that satisfies the condition of 0.5 mm ≤ W0-W ≤ 5 mm when W (mm) is the amount of dimensional change of a central portion in water and W0 (mm) is the amount of dimensional change of the positions that are 0.3 m from the both ends in water (the average value) (the amount of dimensional change in water is the amount of elongation in the length direction of a portion in the direction of 250 mm length before immersion when the PVA based polymer film is immersed in pure water at 30 DEG C for 5 minutes) in the straight line of the width direction (the direction perpendicular to the length direction) of the PVA based polymer film.

Description

Method for producing polyvinyl alcohol polymer film

The present invention relates to a polyvinyl alcohol polymer film (hereinafter, "polyvinyl alcohol" is abbreviated as "PVA"), a method for producing the same, and a polarizing film produced from the PVA polymer film. More specifically, the present invention relates to a PVA-based polymer film which can produce a polarizing film having a small transmittance unevenness between a center portion and an end portion, a method for producing the same, and a center for manufacturing the PVA-based polymer film. A polarizing film having less uneven transmittance between the portion and the end portion.

A polarizing plate having light transmission and shielding functions and a liquid crystal having a switching function of light are essential components of a liquid crystal display (LCD). In the early days of development, such as computers and small devices such as watches, the application fields of LCDs in recent years have also been applied to laptop computers, word processors, liquid crystal projectors, car navigation systems, LCD TVs, personal phones, and indoor and outdoor offices. The measuring equipment used and the like exhibit a wide range of expansion. With the expansion of the application field of the LCD as described above, in order to make the polarizing performance higher than that of the conventional product and to improve the color display quality, a polarizing plate of a neutral gray color is required.

Polarizers, in general, are made by using PVA The polymer film is uniaxially stretched and dyed, or dyed and uniaxially stretched, and then fixed with a boron compound (in some cases, two or more operations of dyeing, stretching, and fixing may be simultaneously performed) On the obtained polarizing film, a protective film of a cellulose triacetate (TAC) film or a cellulose acetate butyrate (CAB) film was bonded.

In order to improve the hue of the polarizing film, the structure of the PVA polymer or the PVA polymer film which is a raw material for the production of the polarizing film, and the manufacturing conditions for producing the polarizing film are mainly discussed. For example, it is known to produce a denatured PVA polymer having a polymerization degree of 1,500 to 5,000, an ethylene unit content of 1 to 4 mol%, and a 1,2-diol bond amount of 1.4 mol% or less. A polarizing film having a b value of 3 or less produced by uniaxially stretching a PVA film having a YI value of 20 or less (see Patent Document 1)

Further, it is known that a PVA obtained by using a plurality of heat rolls used for producing a PVA-based polymer film by using a heat roller (drying roll) having a larger roll diameter than the center portion of the roll portion on the end side is used. In the case of a polymer film, a polarizing film having high transmittance, high polarizability, and excellent in-plane uniformity of polarizing performance can be obtained (see Patent Document 2).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-342322

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2012-42929

In recent years, with the increase in size or high contrast of LCDs, uneven transmittance (optical unevenness) between the central portion and the end portion of a polarizing film which is conventionally not problematic has become a problem. In general, when a polarizing film is produced by a uniaxial stretching method used as a method for producing a polarizing film, the width of the end portion in the width direction of the PVA-based polymer film shrinks more than the central portion. At the end, the PVA-iodine complex is well aligned to have higher optical performance than the central portion, and there is a problem that optical unevenness occurs between the central portion and the end portion. This tendency, in particular, the width of the PVA-based polymer film is more pronounced with respect to the distance between stretching. Therefore, as described in Patent Document 2, it is difficult to eliminate the optical properties of the polarizing film obtained by uniaxially stretching the PVA-based polymer film by using a drying roll having a larger roll diameter on the end side than the roll diameter at the center portion. Not uniform.

Therefore, an object of the present invention is to provide a PVA-based polymer film which can produce a polarizing film having a small transmittance unevenness between a central portion and an end portion, a method for producing the same, and a central portion manufactured from the PVA-based polymer film. A polarizing film having less uneven transmittance with the end portion.

In order to achieve the above object, the inventors of the present invention have repeatedly conducted intensive investigations and found that a film forming apparatus having a plurality of drying rolls having mutually parallel rotating shafts is provided on the first drying roll provided on the most upstream side of the film forming apparatus. The film forming stock solution containing the PVA-based polymer is discharged into a film form and dried, and continues on the flow side of the first drying roll, and is further dried by a drying roll after the second drying roll to produce a PVA-based polymer film. When a drying roller having a larger outer diameter than the outer diameter of the both end portions is used as the drying roller after the second drying roller, the length of the water on both sides in the width direction can be continuously and smoothly produced for the length. A specific amount of the PVA-based polymer film which is less than the amount of elongation in the central portion and which has not been conventionally used in the direction; and if the PVA-based polymer is used, the transmission between the center portion and the end portion can be easily produced. The polarizing film having a non-uniformity is less, and the present invention is further repeated based on the above knowledge.

That is, the present invention relates to the following:

[1] A PVA-based polymer film which has a dimensional change in water in the center portion as W (mm) and a distance from both ends in a line in the width direction of the PVA-based polymer film (in a direction perpendicular to the longitudinal direction) The amount of change in water size (average value) at a point of 0.3 m is taken as W ₀ (mm) (in this case, the dimensional change amount in water is before impregnation when the sample of the PVA-based polymer film is immersed in pure water at 30 ° C for 5 minutes) When the elongation in the longitudinal direction of the portion of the length of 250 mm in the longitudinal direction is satisfied, it satisfies 0.5 mm ≦ W _{0 -} W ≦ 5 mm.

[2] The PVA-based polymer film according to [1] above, wherein (W+W ₀ )/2 is 50 to 65 mm.

[3] The PVA-based polymer film according to [1] or [2] above, wherein W is 50 to 60 mm and W ₀ is 55 to 65 mm.

[4] The PVA-based polymer film according to any one of [1] to [3] wherein the volatile matter ratio is 1 to 5% by mass.

[5] The PVA-based polymer film according to any one of [1] to [4] above, wherein the width is from 2 to 7.5 m.

[6] The PVA-based polymer film according to any one of the above [1] to [5], which is an initial film for producing a polarizing film.

[7] A method for producing a PVA-based polymer film, which comprises using a film forming apparatus including a plurality of drying rolls having mutually parallel rotating axes, and comprising a PVA-based polymer on a first drying roll of the film forming apparatus. The membrane stock solution is discharged into a film form and dried, and then, when the PVA-based polymer film is formed by further drying with a drying roll after the second drying roll, the outer diameter of the center portion is larger than the outer diameter of both end portions by 0.5. The drying roller of ~3 mm is used as at least one of the drying rollers after the second drying roller.

[8] A polarizing film produced by the PVA-based polymer film of the above [6].

According to the present invention, it is possible to provide a PVA-based polymer film which can produce a polarizing film having a small transmittance unevenness between a central portion and an end portion, and a PVA-based polymer film which can smoothly and continuously manufacture the PVA-based polymer film. A manufacturing method; and a polarizing film having a small transmittance unevenness between a central portion and an end portion produced by the PVA-based polymer film.

[Formation of the Invention]

In the PVA-based polymer film of the present invention, in the line in the width direction (the direction perpendicular to the longitudinal direction), the amount of change in the size of the water in the center portion is W (mm), and the water is 0.3 m from both ends. When the dimensional change amount (average value) is W ₀ (mm), it satisfies 0.5 mm ≦ W _{0 -} W ≦ 5 mm. In the present invention, it is important to satisfy 0.5 mm ≦W _{0 -} W ≦ 5 mm, and the difference in the amount of dimensional change in water in the end portion and the central portion in the width direction as described above can be obtained as the present invention. A polarizing film having a small transmittance unevenness between the central portion and the end portion of the object. From the viewpoint of uneven transmittance of the polarizing film, W ₀ -W is preferably 1 mm or more, more preferably 1.5 mm or more, and particularly preferably 2 mm or more, and more preferably 4.5 mm or less, more preferably 4 mm or less, and particularly preferably 3.5 mm or less. .

In the present invention, the amount of dimensional change in water refers to the elongation in the longitudinal direction (unit: mm) of the portion in the longitudinal direction of 250 mm before the immersion of the sample of the PVA-based polymer film in pure water at 30 ° C for 5 minutes. And can be obtained by the following method. In other words, in the width direction of the PVA-based polymer film (the direction perpendicular to the longitudinal direction; hereinafter, abbreviated as TD), the center portion (one portion) and the portion from the both end portions are 0.3 m ( The total of the two places is three, and a rectangular sample of 27 cm in the width direction (TD) of 4 cm × length direction (hereinafter sometimes abbreviated as MD) is cut out. Here, the center of gravity of each sample is present at each position on the straight line. Then, the line was drawn with an oily mic pen (line thickness of 0.3 mm) on the inner side of each of the 27 cm long ends of each sample. The outer part of the reticle from both ends is clamped with a commercially available clip (4 cm in width, 7.8 g in mass (7.3 g in water)), and the clip on the other hand is a rod-like fixture such as an annealing line. fixed. After confirming that the distance between the lines is 250 mm, the sample stored in a cylindrical transparent water tank (measuring cylinder, etc.) is adjusted to a temperature of 30 ° C, and the sample with the clip is placed in the water as a whole. Side immersed vertically (vertically). Immediately after immersion, a rod-shaped tool is placed on the upper part of the water tank to make the long side of the sample vertical (vertical) and fixed. Thereafter, a metal ruler was immersed in water, and the distance between the lines was measured after immersion for 5 minutes. The measured value is read from the scale of 0.5 mm, and the distance between the original lines (250 mm) is pulled out to calculate the amount of elongation (the amount of change in the size of the water in the center: W (mm), and the position from the both ends 0.3 m) The amount of dimensional change in the water: W ₀ (mm)). Here, W ₀ (mm) is obtained by averaging two elongation amounts of a sample obtained from a position of 0.3 m from both end portions. Further, in the present invention, the reason why the amount of dimensional change in water is obtained at a position of 0.3 m from both end portions is not because the thickness of the portion smaller than 0.3 m from both end portions after processing into a polarizing film. Since the unevenness becomes large, etc., most of them are removed, and therefore it is not preferable as a measurement position.

In the present invention, it means that the water W and the size change amount of the average value W ₀ (W + W ₀₎ / 2 is preferably 50 ~ 65mm, 52 ~ 62mm more preferably, 55 ~ 60mm particularly preferred. According to the PVA-based polymer film as described above, a polarizing film having a high degree of polarization and an increase in absorbance in a long wavelength region can be easily obtained. Then, according to the polarizing film which enhances the absorbance in the long wavelength region, the red color as the LCD can be reduced. Further, in the present invention, the amount of change in the amount of water in the width direction of the PVA-based polymer film is inclined from the point of 0.3 m from both end portions toward the center portion and is reduced.

According to the polarizing film which can easily obtain the high degree of polarization and the absorbance in the long wavelength region, the specific value of the amount of change in the size of the water W is preferably in the range of 50 to 60 mm, and in the range of 55 to 59 mm. good. Further, according to the polarizing film which can easily obtain the high degree of polarization and the absorbance in the long wavelength region, the specific value of the water dimensional change amount W ₀ is preferably in the range of 55 to 65 mm, and is in the range of 60 to 63 mm. Better in the range.

The PVA-based polymer which forms the PVA-based polymer film is, for example, PVA (undenatured PVA) obtained by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester, and grafting a comonomer in a main chain of PVA. a copolymerized denatured PVA-based polymer, a denatured PVA-based polymer produced by saponifying a copolymerized vinyl ester and a conjugated polyvinyl ester of a comonomer, and a part of a hydroxyl group of an undenatured PVA or a denatured PVA-based polymer A so-called polyvinyl acetal resin in which an aldehyde such as formaldehyde, butyraldehyde or benzaldehyde is crosslinked.

When the PVA-based polymer forming the PVA-based polymer film is a denatured PVA-based polymer, the amount of denaturation of the PVA-based polymer is preferably 15 mol% or less, more preferably 5 mol% or less.

Examples of the vinyl ester used for the production of the PVA-based polymer include vinyl acetate, vinyl formate, vinyl laurate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, and new Vinyl phthalate, vinyl stearate, vinyl benzoate, and the like. These vinyl esters can be used singly or in combination. Among these vinyl esters, vinyl acetate is preferred from the viewpoint of productivity.

In addition, examples of the comonomer include olefins (α-olefins) having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; and methyl acrylate. Ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. Acrylates (for example, 1 to 18 alkyl esters of acrylic acid, etc.); methacrylic acid or a salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate , n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Acrylates (for example, 1 to 18 alkyl esters of methacrylic acid, etc.); acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl propylene oxime a acrylamide derivative such as an amine, diacetone acrylamide, acrylamidamine sulfonic acid or a salt thereof, acrylamide propyl dimethylamine or a salt thereof, N-methylol acrylamide or a derivative thereof; Methyl acrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide sulfonic acid or a salt thereof, methacrylamide propyl dimethylamine or a methacrylamide derivative such as a salt, N-methylol methacrylamide or a derivative thereof; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc. N-vinyl decylamine; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, Tributyl Vinyl ethers such as alkenyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, and difluoro a vinyl halide such as ethylene; an allyl compound such as allyl acetate or allylic chloride; a derivative of an unsaturated dicarboxylic acid such as maleic acid or itaconic acid, a salt thereof or an ester thereof; a vinyl decyl compound such as oxoxane; an isopropenyl acetate; an unsaturated sulfonic acid or a derivative thereof. Among these, an α-olefin is preferable, and ethylene is particularly preferable.

From the viewpoint of the polarizing performance and durability of the obtained polarizing film, the average polymerization degree of the PVA-based polymer forming the PVA-based polymer film is preferably 1,000 or more, more preferably 1,500 or more, and particularly preferably 2,000 or more. . On the other hand, the upper limit of the average degree of polymerization of the PVA-based polymer is preferably 8,000 or less from the viewpoint of easiness of production of a homogeneous PVA-based polymer film, stretchability, and the like, and is preferably 6,000 or less. good.

Here, the "average degree of polymerization" of the PVA-based polymer in the present specification means the average degree of polymerization measured according to JIS K6726-1994, and the saponification of the PVA-based polymer is carried out, and after purification, it is measured in water at 30 ° C. The ultimate viscosity is determined.

The degree of saponification of the PVA-based polymer forming the PVA-based polymer film is preferably 95.0 mol% or more, more preferably 98.0 mol% or more, and 99.0 mol%, from the viewpoints of the polarizing performance and durability of the obtained polarizing film. The above is especially good, 99.3% of the above is the best.

Here, the "saponification degree" of the PVA-based polymer of the present specification means the total number of moles of a structural unit (typically a vinyl ester unit) and a vinyl alcohol unit converted into a vinyl alcohol unit by saponification energy, the ethylene The proportion of the molar number of the alcohol unit (% by mole). The degree of saponification of the PVA-based polymer can be measured in accordance with the description of JIS K6726-1994.

In addition to the PVA-based polymer, the PVA-based polymer film may further contain, as described later, a plasticizer, a surfactant, and various additives other than the above, as described later.

The volatility (typically water content) of the PVA-based polymer film is preferably in the range of 1 to 5% by mass, and more preferably in the range of 2 to 4% by mass.

The thickness of the PVA-based polymer film is not particularly limited. However, it is preferably 5 to 80 μm when used as an initial use for producing a polarizing film. A more suitable thickness is 20 to 80 μm. When the thickness of the PVA-based polymer film is equal to or less than the above-described upper limit, the drying of the PVA-based polymer film can be performed more quickly, and the thickness of the PVA-based polymer film can be more effectively suppressed. Breakage of the film produced during uniaxial stretching to produce a polarizing film.

The width of the PVA-based polymer film is not particularly limited. However, in recent years, the liquid crystal television or the monitor has a large screen. Therefore, in order to be effectively used for such applications, the width is preferably 2 m or more, and more preferably 3 m or more. More than 4m is ideal. The wider the width of the PVA-based polymer film, the more remarkable the effect of the present invention is, and a large-area polarizing film can be obtained, which is preferable. On the other hand, when a polarizing plate is produced by a real production machine, if the width of the film is too wide, uniform uniaxial stretching is difficult. Therefore, the width of the PVA polymer film is preferably 7.5 m or less, and 7 m is preferable. The following is more desirable. The length of the PVA-based polymer film is not particularly limited, and may be, for example, 50 to 30000 m.

The retardation value of the PVA-based polymer film is not particularly limited, but the phase difference in the width direction of the polarizing film obtained as the retardation value is smaller tends to be improved, so that 40 nm or less is more preferable.

The method for producing the PVA-based polymer film of the present invention is not particularly limited, but the PVA-based polymer film of the present invention can be continuously and smoothly produced by the following production method of the present invention.

In other words, the production method of the present invention for producing a PVA-based polymer film uses a plurality of drying rolls having rotation axes parallel to each other (from the uppermost flow side toward the downstream side, which are sequentially referred to as a first drying roll, and second. dry In the film forming apparatus of the drying roll, the film forming stock solution containing the PVA-based polymer is discharged into a film form and dried on the first drying roll of the film forming apparatus, and then, after the second drying roll When the drying roll is further dried to form a PVA-based polymer film, a drying roll having an outer diameter of the center portion of 0.5 to 3 mm larger than the outer diameter of both end portions is used as at least one of the drying rolls after the second drying roll.

In the production method of the present invention, a film forming apparatus including a plurality of drying rolls having mutually parallel rotating axes is used, and a film forming raw material containing a PVA-based polymer is discharged into a film on the first drying roll of the film forming apparatus. The film was dried, and the flow was continued on the lower side of the first drying roll, and further dried by a drying roll after the second drying roll to form a PVA-based polymer film.

In the film forming apparatus, the number of drying rolls (the number of drying rolls including the first drying roll (casting roll)) is preferably from 9 to 30, more preferably from 12 to 26.

The plurality of drying rolls are preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel or the like, and in particular, the surface of the drying roll is preferably formed of a metal material which is not easily corroded and has a specular gloss. Moreover, in order to improve the durability of the drying roll, it is more preferable to use a plating roll or a combination of two or more nickel layers, a chromium layer, a nickel/chromium alloy layer, and the like.

The heating direction when the film is dried from the first drying roll to the last drying roll is not particularly limited, but the film may be further uniformly dried, in any part of the film, and the first The film surface that the drying roller contacts (hereinafter sometimes referred to as "the first drying roller" The contact surface") and the film surface not in contact with the first drying roll (hereinafter sometimes referred to as "first drying roll non-contact surface") are such that the drying rolls from the first drying roll to the last drying roll interact It is ideal to dry the ground in the opposite direction.

When the film forming stock solution containing the PVA-based polymer is discharged into a film form on the first drying roll (casting roll) of the film forming apparatus, for example, a T-slot die, a hopper plate, an I-die, and a lip-mouth coating are used. In a known film discharge device (film-like casting device) such as a mold, the film-forming raw material liquid containing the PVA-based polymer may be discharged (cast) into a film on the first drying roll.

The film forming stock solution containing the PVA polymer film can be prepared by mixing a PVA polymer with a liquid medium to form a solution, and melting a PVA polymer pellet containing a liquid medium or the like into a molten liquid or the like.

As the liquid medium to be used at this time, for example, water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine may be mentioned. The liquid medium may be used singly or in combination of two or more. Among these, it is preferred to use water, dimethyl hydrazine, or a mixture of the two, and it is more preferable to use water in particular.

Adding a plasticizer to the film forming solution from the viewpoint of promoting the dissolution or melting of the liquid medium of the PVA-based polymer, improving the processability of the PVA-based polymer film, and improving the stretchability of the PVA-based polymer film obtained. More ideal.

As the plasticizer, a polyhydric alcohol is preferably used, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. One type of these plasticizers may be used alone or two or more types may be used in combination. Among these, from lifting In view of the fact that the extensibility is excellent, one or two or more of glycerin, diglycerin, and ethylene glycol are preferable.

The amount of the plasticizer added is preferably from 0 to 30 parts by mass, more preferably from 3 to 25 parts by mass, particularly preferably from 5 to 20 parts by mass, per 100 parts by mass of the PVA-based polymer. When the amount of the plasticizer added is 30 parts by mass or less based on 100 parts by mass of the PVA-based polymer, the obtained PVA-based polymer film does not become too soft, and the deterioration of handleability can be suppressed.

It is preferable to add a surfactant to the film forming stock solution from the viewpoint of improving the peeling property of the drying roll from the production of the PVA-based polymer film, the handleability of the obtained PVA-based polymer film, and the like. The kind of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferably used.

As the anionic surfactant, for example, an anionic surfactant such as a carboxylic acid type such as potassium laurate or a sulfate type such as octyl sulfate or a sulfonic acid type such as dodecylbenzenesulfonate is suitable.

In addition, examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether, an alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, and an alkyl ester type such as polyoxyethylene laurate. An alkylamine type such as polyoxyethylene lauryl amine ether, a polydecylamine type such as polyoxyethylene laurate decylamine, a polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, or diethanolamine laurate. A nonionic surfactant such as an alkenyl oxime type such as oleic acid diethanolamine or an allyl phenyl ether type such as a polyoxyalkylallyl phenyl ether is suitable.

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

The amount of surfactant added, relative to the PVA polymer 100 parts by mass is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, and particularly preferably 0.05 to 0.3 part by mass. When the amount of the surfactant to be added is 0.01 parts by mass or more based on 100 parts by mass of the PVA-based polymer, the effect of improving the film forming property and the peeling property can be easily exhibited. On the other hand, the content can be suppressed by 1 part by mass or more. The active agent dissolves on the surface of the film to cause agglomeration, and the deterioration of handleability can be suppressed.

In the film forming stock solution, in addition to the above-mentioned components, various additives may be contained, for example, a stabilizer (antioxidant, ultraviolet absorber, heat stabilizer, etc.), a phase solvent, an anti-caking agent, a flame retardant, and an anti-blocking agent. Electrostatic agents, lubricants, dispersants, fluidizers, antibacterial agents, and the like. These additives may be used alone or in combination of two or more.

The film-forming stock solution used for the production of the PVA-based polymer film preferably has a volatility of 50 to 90% by mass, more preferably 55 to 80% by mass, more preferably 60 to 75% by mass, and most preferably 65 to 70% by mass. When the volatilization rate of the film-forming raw material solution is too low, the viscosity of the film-forming raw material solution becomes too high, and filtration or defoaming becomes difficult, and the film formation itself becomes difficult. On the other hand, if the volatilization rate of the film forming raw material is too high, the viscosity may become too low and the uniformity of the thickness of the PVA polymer film may be impaired.

Here, the "volatility of the film forming solution" referred to in the present specification means a volatile matter ratio obtained by the following formula (I). Volatile fraction (% by mass) of the film forming solution solution = {(Wa - Wb) / Wa} × 100 (I) (here, Wa represents the mass (g) of the film forming stock solution, and Wb represents the system of Wa (g). The mass (g) of the film stock solution after drying for 16 hours in an electric dryer at 105 ° C.)

When the first drying roller is dried, it is uniformly dried and dried. From the viewpoint of the drying speed and the like, the surface temperature of the roll of the first drying roll is preferably from 80 to 120 ° C, more preferably from 85 to 105 ° C.

The drying on the first drying roll which discharges the film forming film forming solution may be performed only by heating from the first drying roll, but the first drying roll is used from the viewpoints of uniform drying property, drying speed, and the like. At the same time as heating, hot air is sprayed on the non-contact surface of the first drying roll, and it is preferable to apply heat from both sides of the film to perform drying.

When hot air is sprayed on the non-contact surface of the first drying roll of the film on the first drying roll, it is preferable to spray hot air of 1 to 10 m/sec in the entire area of the non-contact surface of the first drying roll, and the spraying wind speed is 2 to 8 m. The hot air of /second is more ideal, and the hot air with a wind speed of 3~8m/sec is ideal. When the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too small, there is a condensation of water vapor or the like during drying on the first drying roll, and the PVA-based polymer film which is finally obtained by dripping the water droplets on the film is generated. The possibility of defects. On the other hand, when the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too large, there is a problem in that the PVA-based polymer film finally obtained is uneven in thickness, and the occurrence of dye spots is caused.

From the viewpoints of drying efficiency, uniformity of drying, etc., the temperature of hot air sprayed on the non-contact surface of the first drying roll of the film is preferably 50 to 150 ° C, more preferably 70 to 120 ° C, and particularly ideal at 80 to 95 ° C. . When the temperature of the hot air sprayed on the non-contact surface of the first drying roll of the film is too low, condensation of water vapor or the like may occur, and water droplets may fall on the film, and the PVA-based polymer film finally obtained may be defective. On the other hand, when the temperature is too high, dry spots are generated along the wind direction of the hot air, and the PVA-based polymer film finally obtained may have uneven thickness.

Further, the dew point temperature of the hot air sprayed on the non-contact surface of the first drying roll of the film is preferably 5 to 20 ° C, more preferably 10 to 15 ° C, and particularly preferably 11 to 13 ° C. When the dew point temperature of the hot air sprayed on the non-contact surface of the first drying roll of the film is too low, drying efficiency, uniform drying property, and the like are liable to lower. On the other hand, when the dew point temperature is too high, foaming is likely to occur.

The method for spraying hot air on the non-contact surface of the first drying roll of the film is not particularly limited, and any non-contact surface of the first drying roll which can spray the hot air having uniform wind speed and uniform temperature on the film can be used, preferably A method of uniformly spraying the whole, wherein a nozzle method, a rectifying plate method, or a combination thereof is preferably employed. The spraying direction of the hot air on the non-contact surface of the first drying roll of the film may be a direction facing the non-contact surface of the first drying roll, or may be a circumferential shape of the non-contact surface of the first drying roll of the film. The direction (almost the direction along the circumference of the roll surface of the first drying roll) may be a direction other than the above.

Further, when the film on the first drying roll is dried, it is preferable to evacuate the hot air sprayed from the volatile component generated by the film by drying. The method of exhausting is not particularly limited, but an exhaust method in which wind speed unevenness and temperature unevenness of hot air which does not spray on the non-contact surface of the first drying roll of the film are not preferable is preferable.

The peripheral speed (S ₁ ) of the first drying roll is preferably 5 to 30 m/min, more preferably 7 to 25 m/min, from the viewpoints of uniform drying property, drying speed, productivity of the PVA-based polymer film, and the like. When the peripheral speed (S ₁ ) of the first drying roll is less than 5 m/min, the productivity is lowered, and the stretchability of the obtained PVA-based polymer film tends to decrease. On the other hand, when the peripheral speed (S ₁ ) of the first drying roll exceeds 30 m/min, the peeling from the first drying roll tends to be uneven, and the disadvantage tends to occur.

The film-forming raw material liquid which was formed into a film on the first drying roll was dried on the first drying roll and peeled off from the first drying roll. When the volatility of the film at the time of peeling off from the first drying roll is too low, the productivity of the PVA-based polymer film tends to be lowered, and on the other hand, the volatilization of the film at the time of peeling from the first drying roll When the rate is too high, peeling from the first drying roll tends to be difficult, and it is easy to be broken and uneven due to the situation. From the viewpoint of the above, the volatility of the film at the time of peeling from the first drying roll is preferably 10% by mass or more, more preferably 15% by mass or more, particularly preferably 18% by mass or more, and more preferably 30% by mass or less. 29% by mass or less is more preferably 28% by mass or less, and particularly preferably 27% by mass or less.

Here, the "volatility of the film" in the present specification means the volatilization ratio obtained by the following formula (II). M (% by mass) = {(Wc - Wd) / Wc} × 100 (II) (here, M represents the volatilization ratio (% by mass) of the film, and Wc represents the mass (g) of the sample taken from the film, Wd The mass (g) when the sample Wc (g) was placed in a vacuum dryer having a temperature of 50 ° C and a pressure of 0.1 kPa or less and dried for 4 hours.

Further, in the film formed of a film-forming stock solution prepared using a polyol (plasticizer) such as a PVA-based polymer or glycerin, a surfactant, and water, the above-mentioned "at a temperature of 50 ° C and a pressure of 0.1" When drying under the conditions of kPa or lower for 4 hours, only water is mainly volatilized, and other components other than water remain in the film and remain in the film. Therefore, the volatile matter of the film can be measured by the moisture contained in the film. The amount (water content) is obtained.

The film dried on the first drying roll is peeled off from the first drying roll. This time, it is preferable that the first drying roll non-contact surface of the film faces the second drying roll, and the film is dried by the second drying roll.

The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is preferably 1.005 to 1.060, more preferably 1.010 to 1.050. When the ratio (S ₂ /S ₁ ) is too low, the peeling from the first drying roll tends to be uneven, and the disadvantage tends to occur. In addition, when the ratio (S ₂ /S ₁ ) is too high, when the obtained PVA-based polymer film is stretched and processed into a polarizing film, the absorbance in the long-wavelength region of the polarizing film tends to be low.

In the manufacturing method of the present invention, a drying roll having an outer diameter of the center portion which is larger than the outer diameter of both end portions by 0.5 to 3 mm is used as at least one of the drying rolls after the second drying roll. Generally, as the drying roller, a cylindrical drying roller (plate roller) having the same outer diameter and the outer diameter of both end portions is used. However, in the manufacturing method of the present invention, the central portion can be used. The above-described drying roll having a diameter larger than the outer diameter of both end portions is used to smoothly produce the PVA-based polymer film of the present invention. The present invention is not particularly limited. For this reason, it is considered that the difference in the tension in the longitudinal direction can be made into a specific range in the central portion and the end portion in the width direction of the film. The PVA-based polymer film of the present invention can be produced more smoothly, and the outer diameter of the central portion of the drying roller is preferably 0.7 mm or more larger than the outer diameter of both end portions, and is preferably 2.5 mm or less, and more preferably 2 mm or less. Good, big 1mm or less is especially good. Further, the outer diameter of each end portion may satisfy the above relationship with respect to the outer diameter of the central portion. The specific outer diameter of the central portion of the drying roller can be, for example, 300 to 800 mm (or even 350 to 700 mm).

The outer diameter of the drying roller is preferably inclined from the both end portions toward the center portion. Examples of the inclination include a straight slope, a curved slope, and a straight line and a curved blend. However, the center portion has a slight flat portion.

In the manufacturing method of the present invention, the specific drying roller is used as at least one of the drying rollers after the second drying roller, and only one of the second drying roller to the last drying roller may be the specific one. The drying roller, which may be two or more of the second drying roller to the last drying roller, may be the specific drying roller, or all of the second drying roller to the last drying roller may be the specific drying roller. Anyone can do the above. Further, the shape of the first drying roller is a general cylindrical shape, that is, the outer diameter of the central portion and the outer diameter of both end portions are preferably the same.

According to the PVA-based polymer film of the present invention, the surface temperature of the drying roller after the second drying roller is preferably 50 to 80 ° C, and further, 60 to 75 ° C in terms of production stability. ideal.

Only the last drying roll of the drying rolls after the second drying roll, or the last one or two or more drying rolls and the last drying roll may be used as a heat treatment roll by increasing the surface temperature thereof. That is, the drying roll of the above-described film forming apparatus means that the heat-treated roll is also included in the case of using a heat-treating roll. When the drying roll is used as a heat treatment roll, the surface temperature of the drying roll is preferably from 90 to 120 ° C, more preferably from 100 to 110 ° C. By performing the heat treatment at the temperature as described above, crystallization can be appropriately performed and the hot water resistance will be improved.

In order to produce the PVA-based polymer film of the present invention more smoothly, the ratio (S _T /S ₁ ) of the peripheral speed (S _T ) of the final drying roll to the peripheral speed (S ₁ ) of the first drying roll is 0.960~ 1.100 is preferred. When the ratio (S _T /S ₁ ) is too low, the film tends to collapse between the drying rolls, and when it is too high, the retardation value becomes large, and the phase difference in the width direction tends to become large. From the viewpoint of the above, the ratio (S _T /S ₁ ) is preferably 0.980 or more, and 0.985 or more is particularly preferable, and more preferably 1.050 or less, and particularly preferably 1.030 or less.

The above-mentioned film forming apparatus may have a hot air oven type hot air drying device, a heat treatment device, a humidity control device, and the like as needed, for example, after the drying by the drying roller (including heat treatment using a heat treatment roller) deal with. Further, both ends (ears) of the film can be cut as needed.

The volatility (typically water content) of the PVA-based polymer film finally obtained by the above-described series of processes is preferably in the range of 1 to 5% by mass, more preferably in the range of 2 to 4% by mass. When the volatile fraction is too high, the amount of dimensional change in water tends to become high. The obtained PVA-based polymer film is preferably wound into a roll shape with a predetermined length.

In order to produce a polarizing film from the PVA-based polymer film of the present invention, for example, a PVA-based polymer film may be dyed, uniaxially stretched, fixed, dried, and heat-treated as needed. The order of dyeing and uniaxial stretching is not particularly limited, and the dyeing treatment may be performed before the uniaxial stretching treatment, or the dyeing treatment may be performed simultaneously with the uniaxial stretching treatment, or the dyeing treatment may be performed after the uniaxial stretching treatment. . Further, the steps of uniaxial stretching, dyeing, and the like may be repeated a plurality of times. In particular, it is preferable to divide the uniaxial stretching into two or more stages and to easily perform uniform stretching.

As the dye used for dyeing the PVA-based polymer film, iodine or a dichroic organic dye can be used (for example, Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; DirectYellow 8, 12, 44, 86, 87; DirectOrange 26, 39, 106, 107 and other dichroic dyes). These dyes may be used alone or in combination of two or more. The dyeing can be usually carried out by immersing the PVA-based polymer film in a solution containing the aforementioned dye, but the treatment conditions or treatment methods are not particularly limited.

The uniaxial stretching of the PVA-based polymer film in the longitudinal direction (MD) or the like can be carried out by either a wet stretching method or a dry heat stretching method, but the properties of the obtained polarizing film and The wet stability method is ideal for the stability of quality. The wet stretching method is a method of stretching a PVA-based polymer film in an aqueous solution containing various components such as pure water, an additive, or an aqueous medium, or an aqueous dispersion in which various components are dispersed; Specific examples of the uniaxial stretching method by the stretching method include a method of uniaxial stretching in warm water containing boric acid, a method of uniaxial stretching in a solution containing the dye, or a fixed treatment bath to be described later. Further, the PVA-based polymer film after water absorption can be used for uniaxial stretching in air, and may be uniaxially stretched by other methods.

The stretching temperature at the time of uniaxial stretching is not particularly limited, but it is preferably 20 to 90 ° C, more preferably 25 to 70 ° C, and particularly preferably 30 to 65 ° C in wet stretching. Temperature, dry heat stretching is better Use a temperature in the range of 50 to 180 °C.

From the viewpoint of polarizing performance, the film is preferably stretched as much as possible immediately before the cutting, and the stretching ratio of the uniaxial stretching treatment (the total stretching ratio when uniaxially stretching in multiple stages), specifically 4 More than double, preferably more than 5 times, more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less for uniform stretching.

In the production of a polarizing film, in order to reinforce the adsorption of the dye to the uniaxially stretched film, a fixing treatment is often performed. In the fixing treatment, a method of immersing a film in a treatment bath in which boric acid and/or a boron compound is added is generally employed. At this time, an iodine compound may be added to the treatment bath as needed.

The film subjected to the uniaxial stretching treatment, the uniaxial stretching treatment, and the fixing treatment is preferably subjected to a drying treatment (heat treatment). The drying treatment (heat treatment) has a temperature of 30 to 150 ° C, particularly preferably 50 to 140 ° C. When the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film is likely to be lowered. On the other hand, when it is too high, the polarization performance is likely to be lowered due to decomposition of the dye or the like.

A polarizing plate can be bonded to both surfaces or one surface of the polarizing film obtained as described above by bonding a protective film which is optically transparent and has mechanical strength. As a protective film in this case, a cellulose triacetate (TAC) film, acetic acid is used. A cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like. Further, as the adhesive for bonding the protective film, a PVA-based adhesive or a urethane-based adhesive is generally used, and a PVA-based adhesive is preferably used.

The polarizing plate obtained as described above can be bonded to a glass substrate after being coated with an adhesive such as acrylic, and used as a component of a liquid crystal display device. When the polarizing plate is bonded to the glass substrate, a phase difference film, a viewing angle lifting film, a brightness enhancement film, or the like may be bonded at the same time.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples.

In the following examples and comparative examples, the volatility (water content) of the film forming solution, the volatility (water content) of the film, the surface temperature of the drying roll, the amount of change in the size of the water, and the optical properties of the polarizing film were utilized. The following methods were measured or evaluated.

(1) Volatile fraction of the film forming solution (water content)

A heat-resistant container made of a film-forming stock solution of about 10 g was placed in a heat-resistant container, and the heat-resistant container was sealed, and the mass Wa (g) of the film-forming stock solution from which the package was removed was measured up to four decimal places. Next, the film forming stock solution was placed in an electric heat dryer having a temperature of 105 ° C in each heat-resistant container, and dried for 16 hours in a state in which the lid of the heat-resistant container was opened, and then the mass Wb (g) of the film-forming stock solution from which the package was removed was measured until 4 digits below the decimal point. From the obtained masses Wa and Wb, the volatile matter ratio (% by mass) of the film forming stock solution was determined based on the above formula (I).

(2) Volatile fraction of film (water content)

About 5 g of the film sample cut from the center portion in the width direction (TD) of the film between the drying rolls between the adjacent drying rolls, or the center portion of the width direction (TD) of the obtained PVA film is cut. About 5g of the film sample is placed in a heat-resistant container made of glass and sealed. The mass of the packaged film Wc (g) was determined to be 4 points below the decimal point. Next, the film was placed in a vacuum dryer having a temperature of 50 ° C and a pressure of 0.1 kPa or less in each heat-resistant container, and dried in a state in which the lid of the heat-resistant container was opened for 4 hours, and then the quality of the film from which the package was removed was measured (W). Up to 4 digits below the decimal point. From the obtained masses Wc and Wd, the volatile matter ratio M (% by mass) of the film was determined from the above formula (II).

(3) Drying roll surface temperature

The surface temperature (°C) of the drying roller was measured with a non-contact surface thermometer to one position below the decimal point.

(4) Dimensional change in water

In the straight line in the width direction (TD) of the PVA film, the total width of the center portion (1 point) and the point (0.3 points) from the end portions of 0.3 m are cut out in the width direction (TD) 4 cm × A rectangular sample with a length of (MD) of 27 cm. Here, the center of gravity of each sample is present at each position on the straight line. Then, the line was drawn with an oily mic pen (line thickness of 0.3 mm) on the inner side of each of the 27 cm long ends of each sample. The outer part of the reticle from both ends is clamped with a commercially available clip (4 cm in width, 7.8 g in mass (7.3 g in water)), and the clip on the other hand is a rod-like fixture such as an annealing line. fixed. After confirming that the distance between the marking lines is 250 mm, the sample with the clip is placed in the water in a pure water adjusted to a temperature of 30 ° C in a cylindrical transparent water tank, and the long side of the sample is quickly vertical (vertically). Impregnation. Immediately after immersion, a rod-shaped tool is placed on the upper part of the water tank to make the long side of the sample vertical (vertical) and fixed. Thereafter, a metal ruler was immersed in water, and the distance between the lines was measured after immersion for 5 minutes. The measured value is read from the scale of 0.5 mm, and the distance between the original lines (250 mm) is pulled out to calculate the amount of elongation (the amount of change in the size of the water in the center: W (mm), and the position from the both ends 0.3 m) The amount of dimensional change in the water: W ₀ (mm)). Here, W ₀ (mm) is obtained by averaging two elongation amounts of a sample obtained from a position of 0.3 m from both end portions.

(5) Optical properties of polarizing film

(i) Translucency with a transmittance of 43.5%

As described in the following examples and comparative examples, in each of the examples and the comparative examples, the five kinds of polarizing films which were produced by changing the iodine concentration in the iodine/potassium iodide/boric acid aqueous solution at the time of stretching in the second stage were as follows. The method is to obtain the single transmittance (Y) and the degree of polarization (V). According to the respective examples or comparative examples, the single transmittance (Y) is taken as the horizontal axis and the polarization (V) is taken as the vertical axis, and 5 The dots are plotted to form an approximate curve, and the degree of polarization (V) when the single transmittance (Y) is 43.5% is obtained from the approximate curve, and this is referred to as "the degree of polarization of the transmittance of 43.5%".

Determination of the monomer transmittance (Y) of "1":

From the center portion in the width direction of the polarizing film, two square samples of 4 cm (stretching direction of uniaxial stretching) × 4 cm (direction perpendicular to the direction of stretching of the uniaxial stretching) were taken. For the samples, the transmittance of the light was measured using a spectrophotometer "V-7100" manufactured by JASCO Corporation. In addition, in the measurement, according to JIS Z 8722 (measurement method of object color), the C-light source is used to perform the visibility correction of the visible light region of the 2 degree field of view. For one sample, the light transmittance at a tilt angle of +45 degrees with respect to the uniaxial stretching direction and the light transmittance at a tilt angle of -45 degrees with respect to the uniaxial stretching direction were measured and determined. The average value of these (Y ₁ ) (%). In the other sample, the light transmittance at the time of +45 degree tilt and the light transmittance at the time of -45 degree tilt were measured in the same manner, and the average value (Y ₂ ) (%) of these was obtained. Then, the obtained Y ₁ and Y ₂ are averaged by the following formula (III) as the monomer transmittance (Y) (%) of the polarizing film.

Monomer transmittance (Y) (%) = (Y ₁ + Y ₂ ) / 2 (III)

Determination of the degree of polarization (V) of "2":

In the above-mentioned "1" method for measuring the transmittance (Y) of a single monomer, the light transmittance (Y∥) when the two samples taken are overlapped in parallel with the stretching direction of the uniaxial stretching is measured. (%) and light transmittance (Y⊥) (%) when they overlap with the stretching direction of the uniaxial stretching. The transmittance (Y∥) and (Y⊥) are the same as the above-mentioned "Measurement method of "1" single transmittance (Y)", and the tensile direction of the uniaxial stretching of the sample on the other hand is obtained. The average of the light transmittance at +45 degrees tilt and the light transmittance at -45 degrees tilt. The degree of polarization (V) (%) of the polarizing film was determined from the transmittance (Y∥) and (Y⊥) based on the following formula (IV).

Polarization (V) (%) = {(Y∥-Y⊥) / (Y∥ + Y⊥)} ^1/2 × 100 (IV)

(ii) Absorbance at a measurement wavelength of 700 nm at a transmittance of 43.5% (A)

First, as shown in the following examples and comparative examples, in each of the examples and the comparative examples, five kinds of polarizing films (for the iodine concentration in the iodine/potassium iodide/boric acid aqueous solution at the time of stretching in the second stage were changed ( The single transmittance (Y) was in the range of 42 to 44%, and the absorbance (A) at a measurement wavelength of 700 nm was determined as follows. In detail, Glan-Taylor稜鏡 is installed in a spectrophotometer "V-7100" manufactured by JASCO Corporation, and a sample of a polarizing film is placed at a position orthogonal to the optical axis (the above "(i) transmittance) 43.5% of the degree of polarization "1" measurement method of the monomer transmittance (Y)", for any one of the two samples taken for each polarizing film), the measurement is made to cause linear polarization by passing the light source through the crucible. The transmittance of light having a wavelength of 380 to 780 nm which penetrates the sample at a wavelength of 700 nm is measured. At this time, the sample is rotated in a plane orthogonal to the optical axis, the transmittance change is measured, and the maximum value T ₀ of the transmittance and the minimum value T _{90 of} the transmittance are obtained, and the sample is calculated according to the following formula (V). The polarized film was measured for the orthogonal transmittance Tc at a wavelength of 700 nm.

Tc=T ₀ ×T ₉₀ /100 (V)

Then, using the orthogonal transmittance Tc, the absorbance (A) of the polarizing film at a measurement wavelength of 700 nm was calculated from the following formula (VI).

A=2-logTc (VI)

Next, the monomer of the polarizing film is transmitted according to the above-mentioned "(i) the measurement method of the partial transmittance (Y) of the polarizing degree "1" of the transmittance of 43.5%" and the absorbance (A) of the measurement wavelength of 700 nm. The ratio (Y) is plotted on the horizontal axis, and the absorbance (A) at a measurement wavelength of 700 nm is plotted on the vertical axis, and five points corresponding to the five types of polarizing films are plotted to form an approximate straight line, and the approximate straight line is obtained. When the single transmittance (Y) of the polarizing film was 43.5%, the absorbance (A) at a measurement wavelength of 700 nm was used as "absorbance (A) at a measurement wavelength of 700 nm at a transmittance of 43.5%".

(iii) Optical unevenness

The polarizing film continuously produced in the following examples or comparative examples was placed in a completely crossed Nichol state on one polarizing plate (single transmittance: 43.5%, polarization degree: 99.9%). Using a backlight having a brightness of 15,000 candelas, the transmittance between the central portion and the end portion of the width direction (TD) of the polarizing film was observed to be uneven (optical unevenness), and the following The benchmark evaluation was optically uneven.

○··· The uniformity of the difference between light and dark due to the difference in transmittance is not seen in the center portion and the both end portions.

×··· The central part is bright or dark with respect to both ends, and there is a difference in shading.

"Embodiment 1"

(1) Manufacture of PVA-based polymer film

The T-die will contain 100 parts by mass of PVA (saponification degree: 99.9 mol%, average degree of polymerization 2400) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, and 0.1 part by mass of lauric acid diethanolamine. And a film forming stock solution having a water volatilization ratio of 66% by mass, and a first drying roll (a surface temperature of 90 ° C and a peripheral speed (S ₁ ) of 10.0 m/) in a film forming apparatus including a plurality of drying rolls having mutually parallel rotating axes. On the first drying roll, the hot air of 90° C. was sprayed on the first drying roll at a wind speed of 5 m/sec on the first drying roll, and dried to a volatile content of 18% by mass. Next, it peeled from the 1st drying roll, and the surface of the arbitrary part of the film and the back surface were mutually contact-contacted on the drying roll, and drying after the 2nd drying roll was performed. Here, as the drying roller after the second drying roller, 16 drying rolls (coronal rolls) having a diameter larger than the outer diameter of both end portions of the center portion and having a curved diameter from the center portion to the end portion are used. Further, the surface temperature of the drying rolls was changed to 75 ° C. However, the final two were made to have a surface temperature of 105 ° C as a heat treatment roll. Further, the peripheral speed (S ₁₇ ) of the last drying roll (17th drying roll (heat treatment roll)) was set to 9.8 m/min. After that, it was taken up in a roll shape to obtain a PVA film (thickness: 60 μm, width: 4 m, volatility (water content): 3% by mass, water content change (W) at the center portion, 58 mm, and 0.3 m from both ends). The amount of dimensional change in water (average value; W ₀ ) 61 mm).

In the first embodiment, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roller to the peripheral speed (S ₁ ) of the first drying roller is set to 1.025, and will be relative to The ratio (S ₁₇ /S ₁ ) of the peripheral speed (S ₁₇ ) of the last drying roll of the peripheral speed (S ₁ ) of the first drying roll was set to 0.980. The film formation conditions described above are shown in Table 1 below.

(2) Manufacture of polarizing film

(i) The test piece taken from the center of the width direction (TD) of the PVA film obtained in the above (1) is uniaxially stretched in the longitudinal direction (MD) while being immersed in water at a temperature of 30 ° C ( After the first stage stretching is 1.5 times the original length, it is immersed in an iodine/potassium iodide/boric acid aqueous solution containing a concentration of 0.028% by mass of iodine and 1% by mass of potassium iodide, and 1% by mass of boric acid at a temperature of 30 ° C. During the uniaxial stretching (length 2 stretching) in the longitudinal direction (MD) up to 2.25 times the original length, then boric acid at a temperature of 53 ° C containing a concentration of 4% by mass of boric acid and 4% by mass of potassium iodide / While immersing in the potassium iodide aqueous solution, the film was uniaxially stretched in the longitudinal direction (MD) (third-stage stretching) to 5.8 times the original length, and then dried in a dryer at 60° C. to produce a polarizing film.

(ii) In the above (i), except that the concentration of iodine in the iodine/potassium iodide/boric acid aqueous solution at a temperature of 30 ° C at the time of stretching in the second stage is changed from 0.028 mass% to 0.03 mass%, The same operation was carried out to produce a polarizing film.

(iii) In the above (ii), except that the concentration of iodine in the iodine/potassium iodide/boric acid aqueous solution at a temperature of 30 ° C at the time of stretching in the second stage is changed from 0.028 mass% to 0.032 mass%, The same operation was carried out to produce a polarizing film.

(iv) in the above (i), except that the temperature at the second stage is 30 ° C The polarizing film was produced in the same manner as in the above (i) except that the concentration of iodine in the iodine/potassium iodide/boric acid aqueous solution was changed from 0.028 mass% to 0.034 mass%.

(i) In the above (i), except that the concentration of iodine in the iodine/potassium iodide/boric acid aqueous solution at a temperature of 30 ° C at the time of stretching in the second stage is changed from 0.028 mass% to 0.036 mass%, The same operation was carried out to produce a polarizing film.

(vi) using the five types of polarizing films produced in the above (i) to (v), in the item "(5) Optical properties of polarizing film (i) Translucency of 43.5% transmittance", by the aforementioned method The degree of polarization was measured to be 99.9%. Further, in the item "(5) Optical property of polarizing film (ii) absorbance (A) at a measuring wavelength of 700 nm of a transmittance of 43.5%", the absorbance (A) was measured by the above method to be 2.9.

In addition, in order to evaluate the optical unevenness, the PVA film obtained above was used to continuously produce a polarizing film under the same conditions as the above (i), and "(5) optical properties of the polarizing film (iii) optical unevenness" In the item, the optical unevenness was evaluated by the above method to be ○.

The results of these are shown in Table 1 below.

<<Examples 2, 3, Comparative Examples 1 and 2>>

In the first embodiment, a PVA film and a polarizing film were produced in the same manner as in Example 1 except that the film forming conditions (including the film forming apparatus) of the PVA film were changed to those shown in Table 1 below.

Each of the PVA film and the polarizing film produced was subjected to measurement or evaluation in the same manner as in Example 1. The results are shown in Table 1.

[Industrial availability]

According to the PVA-based polymer film of the present invention, a polarizing film having a small transmittance unevenness between the central portion and the end portion can be produced. Therefore, the PVA-based polymer film is particularly used as an initial film for producing a large-area polarizing film. Useful.

Claims (7)

A method for producing a polyvinyl alcohol-based polymer film, which comprises using a film forming apparatus including a plurality of drying rolls having mutually parallel rotating axes, and comprising a polyvinyl alcohol-based polymer on a first drying roll of the film forming apparatus. The membrane-forming raw material is discharged into a film form and dried, and then, when the polyvinyl alcohol-based polymer film is formed by further drying with a drying roll after the second drying roll, the outer diameter of the center portion is used outside the both ends. A drying roll having a diameter of 0.5 to 3 mm is used as at least one of the drying rolls after the second drying roll. The manufacturing method of the first aspect of the invention, wherein the amount of change in the size of the water in the central portion is W (mm) on a straight line in the width direction (the direction perpendicular to the longitudinal direction) of the polyvinyl alcohol polymer film. The amount of change in water size (average value) at a position of 0.3 m from both end portions is taken as W ₀ (mm) (in this case, the amount of dimensional change in water is a sample in which a sample of a polyvinyl alcohol-based polymer film is immersed in pure water at 30 ° C 5 In the case of the elongation in the longitudinal direction of the portion having a length of 250 mm before the immersion at the time of the immersion, it is 0.5 mm ≦W _{0 -} W ≦ 5 mm. The manufacturing method of claim 2, wherein (W+W ₀ )/2 is 50 to 65 mm. For example, the manufacturing method of claim 2, wherein W is 50 to 60 mm, and W ₀ is 55 to 65 mm. The manufacturing method of the first aspect of the invention, wherein the polyvinyl alcohol-based polymer film has a volatile matter content of 1 to 5% by mass. The manufacturing method of claim 1, wherein the polyvinyl alcohol-based polymer film has a width of 2 to 7.5 m. The production method according to any one of claims 1 to 6, wherein the polyvinyl alcohol-based polymer film is a raw film for producing a polarizing film.