JP4646356B2 - Production method of polyvinyl alcohol film - Google Patents

Description

【００４７】
上記の各実施例および比較例から明らかなように、第１ドラムの直径を２ｍより小さくすると、ＰＶＡフィルムの幅方向のレターデーションが不均一となる。このことから、幅方向全体にわたってレターデーションを均一化するためには、直径２ｍ以上の第１ドラムを用いる必要のあることが理解できる。
【００４８】
【発明の効果】
以上のように、本発明によれば、レターデーションが均一で偏光フィルム用に有用な広幅のＰＶＡフィルムを得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a wide polyvinyl alcohol film having excellent retardation uniformity useful as a material for producing a polarizing film.
[0002]
[Prior art]
A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. This LCD is also used in large screens, ranging from small devices such as calculators and watches in the early days to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal televisions in recent years. Therefore, there is a demand for a polarizing plate that is more uniform in polarization performance on a large screen than conventional products.
[0003]
The polarizing plate is generally a polyvinyl alcohol film (hereinafter abbreviated as “PVA film”, and the polyvinyl alcohol as a material thereof is referred to as a polyvinyl alcohol polymer, which may be abbreviated as “PVA”. ) Is uniaxially stretched and dyed, and a protective film such as a cellulose triacetate (TAC) film is bonded to both surfaces of a polarizing film.
[0004]
[Problems to be solved by the invention]
In order to make the polarizing performance of the polarizing film uniform, there are many precautions such as stretching the PVA film uniformly and laminating without unevenness. At this time, if the retardation of the PVA film is not uniform, uniform polarization performance cannot be obtained in a large area even if precision stretching is performed. Here, the retardation is represented by birefringence × film thickness of the PVA film. This birefringence is determined by the degree of molecular orientation of the PVA film. In order to make the retardation of the PVA film uniform, a belt is formed using a dilute PVA solution. According to this, a PVA film having a uniform retardation and a width of less than 2 m can be obtained. However, in the case of belt film formation, since a belt having a width of 2 m or more has a seam and this portion is transferred to the PVA film, industrially, a PVA film having a uniform retardation of 2 m or more in width is manufactured industrially. I can't. On the other hand, in drum film production, a seamless PVA film having a width of 2 m or more can be industrially produced, but the retardation in the width direction is not uniform in the conventional method.
[0005]
Then, the objective of this invention is providing the manufacturing method which can obtain a wide PVA film with uniform retardation.
[0006]
[Means for Solving the Problems]
  In order to achieve the above object, the method for producing a PVA film of the present invention uses one or more rotating drums, and PVA and the PVA100 are arranged on the peripheral surface of the first drum located on the most upstream side among these drums. When a film-forming raw material containing 0.01 to 1 part by weight of a surfactant with respect to parts by weight is supplied and dried to form a drum, the diameter as the first drum2.5While using a drum of m or more, wind is blown on the first drum to dry the PVA film to produce a PVA film having a width of 2 m or more. At the time of film formation, it is preferable to use a film-forming raw material having a volatile fraction of 50 to 90% by weight.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The drum film formation of the present invention uses one or more rotating, for example, metal drums, and contains a solution or PVA in a heated and melted state on the peripheral surface of the first drum located on the most upstream side among these drums. It means that a PVA film is produced by supplying a film-forming raw material and drying to form a PVA film, and sequentially drying the PVA film while passing through a peripheral surface of a downstream drum. For the drum film formation, a drying device, a humidity control device, a winding device, or the like is used. Moreover, a motor, a transmission, etc. are used for each drive, and speed adjustment is carried out. The drying temperature is generally 50 ° C to 150 ° C.
[0008]
The diameter of the first drum used in the present invention is important to be 2 m or more, preferably 2.4 m or more, more preferably 2.8 m or more, and further preferably 3 m or more. At this time, if the diameter of the first drum is smaller than 2 m, retardation in the width direction of the obtained PVA film becomes non-uniform. The drying method using each drum is not particularly limited as long as the drying is efficient and uniform drying in the width direction is obtained, but a method of heating each drum from the inside is generally used. Furthermore, a method of blowing warm air or hot air from the outside of each drum or heating with a heater is also useful, and it is more preferable to use a method of heating each drum from the inside and the outside. In particular, in order to dry the PVA film on the first drum, it is preferable to dry the first drum by blowing air (more preferably hot air or hot air). A uniform PVA film is obtained. Moreover, when heating a PVA film from the outside, it is preferable to use the hot air apparatus designed so that the water vapor | steam etc. which generate | occur | produce can be removed efficiently.
[0009]
At the time of drum formation of the PVA film, for example, a cast film formation method using a PVA solution in which PVA is dissolved in a solvent, or a melt extrusion film formation method using a PVA melt (which may contain an organic solvent). Etc. can be adopted. The volatile content of the film-forming raw material containing PVA used when producing this PVA film is preferably 50 to 90% by weight, particularly preferably 55 to 80% by weight. If the volatile content is less than 50% by weight, the viscosity becomes high and film formation may be difficult. When the volatile content is greater than 90% by weight, the viscosity tends to be too low, and the thickness uniformity of the PVA film tends to be impaired.
[0010]
As the polyvinyl alcohol polymer (PVA) constituting the PVA film of the present invention, a vinyl ester polymer obtained by polymerizing a vinyl ester monomer is saponified and the vinyl ester unit is used as a vinyl alcohol unit. Can be used. Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate and the like. Of these, vinyl acetate is preferably used.
[0011]
When copolymerizing the vinyl ester monomer, if necessary, the copolymerizable monomer is within the range not impairing the gist of the present invention (preferably 15 mol% or less, more preferably 5 mol% or less). Can also be copolymerized.
[0012]
Examples of the monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and salts thereof; methyl acrylate and acrylic acid. Acrylic acid such as ethyl, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, octadecyl acrylate Esters; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, methacrylic acid 2 -Ethylhexyl, dodecyl methacrylate, Methacrylic acid esters such as octadecyl tacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt, N Acrylamide derivatives such as methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts, N-methylolmethacrylamide and Methacrylamide derivatives such as derivatives thereof; N such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone Vinyl amides; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; acrylonitrile, methacrylonitrile, etc. Nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or its Esters; Vinylsilyl compounds such as vinyltrimethoxysilane; Isopropenyl acetate; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone and other N- Mention may be made of vinylamides.
[0013]
The average degree of polymerization of PVA constituting the PVA film is preferably 500 or more from the viewpoint of film strength, more preferably 1000 or more, further preferably 2000 or more, and particularly preferably 3500 or more from the viewpoint of polarization performance. On the other hand, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film formability.
[0014]
The degree of polymerization (P) of the PVA is measured according to JIS K 6726. That is, after re-saponifying and purifying PVA, it is obtained by the following equation from the intrinsic viscosity [η] (unit: dL / g, L is liter) measured in water at 30 ° C.
P = ([η] × 10^Three/8.29)^{(1 / 0.62)}
[0015]
The saponification degree of the PVA constituting the PVA film is preferably 90 mol% or more, more preferably 95 mol% or more, and further preferably 98 mol% or more from the viewpoint of the durability of the polarizing film. On the other hand, from the viewpoint of dyeability of the PVA film, it is preferably 99.99 mol% or less. The saponification degree of the PVA indicates a ratio of units that are actually saponified to vinyl alcohol units among units that can be converted into vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.
[0016]
In producing the PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like, and one or more of these can be used. Among these, ethylene glycol or glycerin is preferably used because of the effect of improving stretchability.
[0017]
As addition amount of a polyhydric alcohol, 1-30 weight part is preferable with respect to 100 weight part of PVA, 3-25 weight part is more preferable, and 5-20 weight part is especially preferable. If the amount is less than 1 part by weight, the dyeability and stretchability may be lowered. If the amount is more than 30 parts by weight, the film may be too soft and the handleability may be lowered.
[0018]
Moreover, when manufacturing the said PVA film, it is preferable to add surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate are suitable. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octylphenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.
[0019]
The addition amount of the surfactant is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, and particularly preferably 0.05 to 0.3 part by weight with respect to 100 parts by weight of PVA. . When the amount is less than 0.01 part by weight, the effect of improving stretchability and dyeability is hardly exhibited, and when the amount is more than 1 part by weight, it may elute on the film surface and cause blocking, and the handleability may be lowered.
[0020]
The thickness of the PVA film obtained as described above is preferably 20 to 150 μm, and more preferably 40 to 120 μm. Moreover, it is preferable that the width | variety of a PVA film shall be 2 m or more. This PVA film has a uniform retardation in the width direction and can cope with a large screen demanded in recent years. When the width of the PVA film is smaller than 2 m, it is difficult to cope with the enlargement of the screen.
[0021]
In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be dyed, uniaxially stretched, fixed, dried, and further heat treated as necessary. The order of each process is not particularly limited, and two processes such as dyeing and uniaxial stretching may be performed simultaneously. Each process may be repeated a plurality of times.
[0022]
Dyeing can be performed before uniaxial stretching, at the same time as uniaxial stretching, or after uniaxial stretching. However, PVA tends to increase the degree of crystallinity due to uniaxial stretching, and dyeability may be lowered. It is preferable to dye in the step or the uniaxial stretching step.
[0023]
As dyes used for dyeing, iodine-potassium iodide or 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; Direct blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct violet 9, 12, 51, 98; Direct green 1, 85; Direct Dichromatic dyes such as yellow 8, 12, 44, 86 and 87; Direct orange 26, 39, 106 and 107 can be used. Dyeing can usually be performed by immersing the PVA film in a solution containing the dye, but the treatment conditions and treatment method are not particularly limited.
[0024]
Uniaxial stretching performed in the length direction of the PVA film can use a wet stretching method or a dry heat stretching method. The PVA film can be used in warm water (in the solution containing the dye or in the fixing treatment bath described later) or after water absorption. May be used in air. The draw ratio is preferably 4 times or more, particularly preferably 5 times or more. If the draw ratio is less than 4, it is difficult to obtain practically sufficient polarization performance and durability performance. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched (wet stretching) in warm water, and 50 to 180 ° C. when it is dry heat stretched. 3-75 micrometers is preferable and, as for the thickness of the PVA film after extending | stretching, 10-50 micrometers is more preferable.
[0025]
For the purpose of strengthening the adsorption of the dye to the PVA film, a fixing treatment is performed. Boric acid and a boron compound are usually added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing bath as needed.
[0026]
The drying treatment (heat treatment) of the PVA film is preferably performed at 30 to 150 ° C, more preferably 50 to 150 ° C.
[0027]
The polarizing film obtained as described above is usually used as a polarizing plate by attaching a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.
[0028]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The PVA film in this example is formed using at least one drum. To obtain the intended PVA film, the first drum on the most upstream side to which the film forming raw material is directly supplied. Therefore, only the film forming conditions for the first drum are described in each example. Further, the evaluation and retardation of the dichroic ratio in Examples and Comparative Examples were measured by the following methods.
[0029]
Dichroic ratio:
The dichroic ratio was used as an index for evaluating the polarization performance of the obtained polarizing film. This dichroic ratio is a transmittance Ts obtained by measuring and calculating in a C light source and a 2 ° C. field of view using a spectrophotometer in accordance with the Japan Electronic Machinery Manufacturers Association (EIAJ) LD-201-1983. (%) And polarization degree P (%) were used to obtain the following formula.
Dichroic ratio = log (Ts / 100−Ts / 100 × P / 100) / log (Ts / 100 + Ts / 100 × P / 100)
[0030]
Retardation:
The retardation in the width direction was measured every 10 cm using an automatic birefringence meter KOBRA 21SDH manufactured by Oji Scientific Instruments.
[0031]
Example 1
A film-forming material having a saponification degree of 99.9 mol% and a polymerization degree of 4000 PVA of 100 parts by weight, glycerin 13 parts by weight, lauric acid diethanolamide 0.1 part by weight and water with a volatile fraction of 79% by weight is made of metal at 90 ° C. The first drum was discharged to form a film. The diameter of this drum is 3.4 m. Furthermore, the drum surface was dried with hot air at 90 ° C. to obtain a PVA film having an average thickness of 74 μm and a width of 2.0 m. This PVA film was uniform with a difference in retardation in the width direction (difference between the maximum value and the minimum value) of 41 nm. The retardation is shown in Table 1.
[0032]
This PVA film was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 3 minutes to be pre-swelled, and immersed in an aqueous solution at 40 ° C. having an iodine concentration of 0.4 g / L and a potassium iodide concentration of 40 g / L for 4 minutes. Subsequently, it was uniaxially stretched 5.5 times in an aqueous solution of boric acid 4% at 50 ° C. and immersed in a 30 ° C. aqueous solution of potassium iodide 40 g / L and boric acid 40 g / L for 5 minutes for fixing treatment. Went. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0033]
The thickness of the obtained polarizing film was 27 μm. The 10 cm square polarizing film had an average transmittance of 43.1%, an average degree of polarization of 99.8%, and an average dichroic ratio of 45.3. When the transmittance of a 10 cm square polarizing film was measured using a light source having a diameter of 100 μm at 1 cm intervals using Otsuka Electronics' RETS-2000, the difference between the maximum transmittance and the minimum transmittance was 0.7%. . When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, almost no optical unevenness was observed.
[0034]
Example 2
A film-forming material having a saponification degree of 99.9 mol% and a polymerization degree of 2400 PVA of 100 parts by weight, glycerin of 8 parts by weight, polyoxyethylene lauryl ether of 0.1 part by weight and water of 75% by weight of volatile fraction is 85 ° C in diameter. The film was discharged onto a 3.0 m first drum to form a film. Furthermore, the drum surface was dried with hot air at 85 ° C. to obtain a PVA film having an average thickness of 75 μm and a width of 2.6 m. This PVA film was homogeneous with a difference in retardation in the width direction (difference between the maximum value and the minimum value) of 31 nm. The retardation is shown in Table 1.
[0035]
This PVA film was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 3 minutes to be pre-swelled, and immersed in an aqueous solution at 40 ° C. having an iodine concentration of 0.4 g / L and a potassium iodide concentration of 40 g / L for 4 minutes. Subsequently, it is uniaxially stretched 5.0 times in an aqueous solution of boric acid 4% at 50 ° C., and immersed in a 30 ° C. aqueous solution of potassium iodide 40 g / L and boric acid 40 g / L for 5 minutes for fixing treatment. Went. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0036]
The thickness of the obtained polarizing film was 28 μm. The average transmittance of the 10 cm square polarizing film was 43.5%, the average degree of polarization was 99.7%, and the average dichroism ratio was 40.3. When the transmittance of a 10 cm square polarizing film was measured using a light source having a diameter of 100 μm at 1 cm intervals using RETS-2000 from Otsuka Electronics, the difference between the maximum transmittance and the minimum transmittance was 0.6%. . When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, almost no optical unevenness was observed.
[0037]
Example 3
A film-forming raw material having a saponification degree of 99.9 mol% and a polymerization degree of 1700 PVA of 100 parts by weight, glycerin of 10 parts by weight, polyoxyethylene lauryl ether sulfate of 0.1 part by weight and water of 63% by weight is obtained at 85 ° C. The film was discharged onto a first drum having a diameter of 2.5 m to form a film. Furthermore, the drum surface was dried with hot air at 85 ° C. to obtain a PVA film having an average thickness of 76 μm and a width of 2.2 m. This PVA film was homogeneous with a difference in retardation in the width direction (difference between the maximum value and the minimum value) of 31 nm. The retardation is shown in Table 1.
[0038]
This PVA film was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 3 minutes to be pre-swelled, and immersed in an aqueous solution at 40 ° C. having an iodine concentration of 0.4 g / L and a potassium iodide concentration of 40 g / L for 4 minutes. Subsequently, it is uniaxially stretched 4.5 times in an aqueous solution of boric acid 4% at 50 ° C., and immersed in a 30 ° C. aqueous solution of potassium iodide 40 g / L and boric acid 40 g / L for 5 minutes for fixing treatment. Went. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0039]
The thickness of the obtained polarizing film was 32 μm. The average transmittance of the 10 cm square polarizing film was 42.1%, the average degree of polarization was 99.6%, and the average dichroic ratio was 36.1. When the transmittance of a 10 cm square polarizing film was measured using a light source having a diameter of 100 μm at an interval of 1 cm using Otsuka Electronics' RETS-2000, the difference between the maximum transmittance and the minimum transmittance was 1.1%. . When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was observed visually, small optical unevenness was observed.
[0040]
Comparative Example 1
A film-forming material having a saponification degree of 99.9 mol% and a polymerization degree of 4000 PVA of 100 parts by weight, glycerin of 13 parts by weight, lauric acid diethanolamide of 0.1 part by weight and water of 82% by weight of volatile fraction was obtained at a temperature of 95 ° C. The film was discharged onto a first 8 m drum to form a film. Furthermore, the drum surface was dried with hot air at 100 ° C. to obtain a PVA film having an average thickness of 73 μm and a width of 2.0 m. This PVA film was heterogeneous with a difference in retardation in the width direction (difference between the maximum value and the minimum value) of 167 nm. The retardation is shown in Table 1.
[0041]
This PVA film was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 3 minutes to be pre-swelled, and immersed in an aqueous solution at 40 ° C. having an iodine concentration of 0.4 g / L and a potassium iodide concentration of 40 g / L for 4 minutes. Subsequently, it was uniaxially stretched 5.5 times in an aqueous solution of boric acid 4% at 50 ° C. and immersed in a 30 ° C. aqueous solution of potassium iodide 40 g / L and boric acid 40 g / L for 5 minutes for fixing treatment. Went. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0042]
The thickness of the obtained polarizing film was 28 μm. The average transmittance of the 10 cm square polarizing film was 43.0%, the average degree of polarization was 99.7%, and the average dichroic ratio was 44.8. When the transmittance of a 10 cm square polarizing film was measured using a light source having a diameter of 100 μm at 1 cm intervals using RETS-2000 from Otsuka Electronics, the difference between the maximum transmittance and the minimum transmittance was 6.0%. . When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, large optical unevenness was observed.
[0043]
Comparative Example 2
A film-forming material having a saponification degree of 99.9 mol% and a polymerization degree of 2400 PVA of 100 parts by weight, glycerin of 8 parts by weight, lauric acid diethanolamide of 0.1 part by weight and water and a volatile fraction of 74% by weight is obtained at a 95 ° C diameter 1 The film was discharged onto a first 8 m drum to form a film. Further, the surface of the metal drum was dried with hot air at 100 ° C. to obtain a PVA film having an average thickness of 74 μm and a width of 2.2 m. This PVA film was heterogeneous with a difference in retardation in the width direction (difference between the maximum value and the minimum value) of 84 nm. The retardation is shown in Table 1.
[0044]
This PVA film was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 3 minutes to be pre-swelled, and immersed in an aqueous solution at 40 ° C. having an iodine concentration of 0.4 g / L and a potassium iodide concentration of 40 g / L for 4 minutes. Subsequently, it was uniaxially stretched 5.5 times in an aqueous solution of boric acid 4% at 50 ° C. and immersed in a 30 ° C. aqueous solution of potassium iodide 40 g / L and boric acid 40 g / L for 5 minutes for fixing treatment. Went. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0045]
The thickness of the obtained polarizing film was 29 μm. The average transmittance of the 10 cm square polarizing film was 43.4%, the average degree of polarization was 99.7%, and the average dichroism ratio was 39.8. When the transmittance of a 10 cm square polarizing film was measured using a light source having a diameter of 100 μm at 1 cm intervals using RETS-2000 from Otsuka Electronics, the difference between the maximum transmittance and the minimum transmittance was 4.6%. . When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, large optical unevenness was observed.
[0046]
[Table 1]

[0047]
As is clear from the above examples and comparative examples, when the diameter of the first drum is smaller than 2 m, the retardation in the width direction of the PVA film becomes non-uniform. From this, it can be understood that in order to make the retardation uniform over the entire width direction, it is necessary to use a first drum having a diameter of 2 m or more.
[0048]
【The invention's effect】
As described above, according to the present invention, a wide PVA film having a uniform retardation and useful for a polarizing film can be obtained.

Claims (3)

One or more rotating drums are used, and 0.01 to 1 part by weight of a surfactant with respect to 100 parts by weight of polyvinyl alcohol and polyvinyl alcohol on the peripheral surface of the first drum located on the most upstream side among these drums When a film-forming raw material containing lye is supplied and dried to form a drum, a drum having a diameter of 2.5 m or more is used as the first drum, and air is blown onto the first drum to dry the polyvinyl alcohol film. And the manufacturing method of the polyvinyl alcohol film which manufactures the polyvinyl alcohol film whose width | variety is 2 m or more.   2. The method for producing a polyvinyl alcohol film according to claim 1, wherein the film-forming raw material containing polyvinyl alcohol has a volatile content of 50 to 90% by weight.   The method for producing a polyvinyl alcohol film according to claim 1 or 2, which is a method for producing a polyvinyl alcohol film for a polarizing film.