阅读说明：本技术 聚乙烯醇膜和其制造方法 (Polyvinyl alcohol film and method for producing same ) 是由 森翔大朗 胜野良治 油井太我 风藤修 于 2018-09-14 设计创作，主要内容包括：提供聚乙烯醇膜,其宽度3m以上、长度1,000m以上、厚度15~65μm,将长度方向的间距设为15m、宽度方向的间距设为10mm而测定得到的延迟值满足下述式(1)~(4)。该膜即使薄且宽度宽,也具有优异的拉伸性,而且拉伸后的宽度的变动小。因此,通过使用该膜,能够以高生产率制造光学性能优异的、薄且宽度宽的光学膜等。<Image he="131" wi="310" file="834255DEST_PATH_IMAGE002.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(Provided is a polyvinyl alcohol film having a width of 3m or more, a length of 1,000m or more, and a thickness of 15 to 65 [ mu ] m, wherein the retardation value measured with the pitch in the longitudinal direction set to 15m and the pitch in the width direction set to 10mm satisfies the following formulas (1) to (4). The film has excellent stretchability even when it is thin and wide, and has a small variation in width after stretching. Therefore, by using the film, it is possible toA thin and wide optical film or the like having excellent optical properties can be produced with high productivity.)

1. A polyvinyl alcohol film having a width of 3m or more, a length of 1,000m or more, and a thickness of 15 to 65 μm,

the retardation value measured with the pitch in the longitudinal direction of 15m and the pitch in the width direction of 10mm satisfies the following formulas (1) to (4),

in the formula (I), the compound is shown in the specification,

Re_max(nm): maximum value of delay at a position of 10mm from one end

Re_min(nm): minimum value of delay at position of 10mm from one end

Re_ave(nm): average value of delay at a position of 10mm from one end

Re_i(nm): a retardation value at a measurement point i (i =1 to n, n is an integer) at a position of 10mm from one end

Re_total(nm): average of the delays at all measurement points.

2. The method for producing a polyvinyl alcohol film according to claim 1,

using a film-forming apparatus having a plurality of drying rollers whose axes of rotation are parallel to each other,

the plurality of drying rollers comprise a 1 st drying roller to an m-th drying roller, wherein m represents an integer of more than 3;

the method comprises a step of spraying a film-forming stock solution containing polyvinyl alcohol from a die head onto a 1 st drying roller to dry the film to obtain a film, and then further drying the film by using a 2 nd to a m th drying rollers;

the volatile fraction of the film when peeled from the 1 st drying roller is 12 to 20%,

peripheral speed of No. 2 drying roll (S)₂) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)₂/S₁) 1.015 to 1.050 parts by weight,

the peripheral speed (S) of the drying roller (x-th drying roller) which starts to contact after the volatile component fraction of the film reaches 11 mass% or less_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) Is 0.970 to 0.995,

the average roller temperature from the 2 nd drying roller to the x th drying roller is 63-81 ℃.

3. The method for producing a polyvinyl alcohol film according to claim 2, wherein the volatile matter fraction of the film-forming raw solution containing polyvinyl alcohol is 60 to 75 mass%, and the peripheral speed (S) of the 1 st drying roller₁) 8 to 25 m/min.

Technical Field

The present invention relates to a polyvinyl alcohol film (hereinafter, the "polyvinyl alcohol" may be abbreviated as "PVA") and a method for producing the same.

Background

A polarizing plate having a light transmission and shielding function is an important component of a liquid crystal display device (L CD), and the liquid crystal display device is used in a wide range of fields such as a notebook computer, a liquid crystal monitor, a liquid crystal color projector, a liquid crystal television, a car navigation system, a mobile phone, and an indoor/outdoor measuring instrument.

Polarizing plates are generally manufactured industrially by dyeing a PVA film wound up from a roll, uniaxially stretching the film, fixing the film with a boron compound, and the like to produce a polarizing film, and then attaching a protective film such as cellulose triacetate film or cellulose acetate butyrate film to one surface or both surfaces of the obtained polarizing film.

In recent years, large screens of liquid crystal monitors, liquid crystal televisions, and the like, and light weights of notebook computers, mobile phones, and the like have been advanced. In addition, reduction in cost of the polarizing plate is also required. Accordingly, a thin and wide polarizing film is required. In the production of such a polarizing film, a thin and wide PVA film is used as a starting material, but such a PVA film has a problem of insufficient stretchability.

Patent document 1 describes a method for producing a PVA film, in which (a) the PVA films are arranged to be parallel to each other with a rotation axisA film forming apparatus including a plurality of drying rollers arranged in a line, wherein a film forming stock solution containing PVA is sprayed on a 1 st drying roller of the film forming apparatus to be partially dried, and then the film is further dried by the drying roller to form a film; at this time, (b) the peripheral speed (S) of the final drying roller_L) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)_L/S₁) Set to 0.955-0.980; (c) width (H) of PVA film from volatile fraction of 20 mass%₂₀) And the width (H) of the PVA film at a volatile fraction of 9 mass%₉) Calculated shrinkage [ (1-H)₉/H₂₀)×100](%) is set to be more than 1%; the average value of the surface temperatures of the drying rolls from the drying roll when the volatile fraction of the PVA film reaches 20 mass% to the drying roll when the volatile fraction of the PVA film reaches 9 mass% is 85 ℃ or higher. However, the PVA film obtained by this method is insufficient in stretchability.

Patent document 2 describes a method for producing a PVA film, wherein (a) a film is formed by using a film forming apparatus having 3 or more drying rollers whose rotation axes are parallel to each other, and spraying a film forming dope containing PVA on the 1 st drying roller located at the most upstream of the drying rollers to partially dry the film, and then further drying the film by using a drying roller; in this case, (b) the volatile fraction of the PVA film when peeled off from the 1 st drying roller is 20 to 40 mass%; (c) peripheral speed of No. 2 drying roll (S)₂) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)₂/S₁) Setting the value to be 1.015-1.050; (d) the peripheral speed (S) of the downstream drying roller among 2 drying rollers adjacent to each other between the drying roller (x-th drying roller) at which the evaporation fraction of the PVA film among the 2 nd drying roller or drying rollers further downstream therefrom reached 20 mass% and the drying roller (y-th drying roller) at which the evaporation fraction of the PVA film reached 10 mass% ("S")_n+1) Relative to the peripheral speed (S) of the upstream drying roller_n) Ratio of (S)_n+1/S_n) All set to be 0.992-0.999. However, this method is not suitable for manufacturing a thin PVA film.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a PVA film which has excellent stretchability, is small in width variation after stretching, is thin, and has a wide width, and a simple method for producing the same.

Means for solving the problems

The above problems are solved by providing a PVA film having a width of 3m or more, a length of 1,000m or more, and a thickness of 15 to 65 μm, wherein the retardation value measured with the pitch in the longitudinal direction of 15m and the pitch in the width direction of 10mm satisfies the following formulas (1) to (4),

in the formula (I), the compound is shown in the specification,

Re_max(nm): maximum value of delay at a position of 10mm from one end

Re_min(nm): minimum value of delay at position of 10mm from one end

Re_ave(nm): average value of delay at a position of 10mm from one end

Re_i(nm): a retardation value at a measurement point i (i =1 to n, n is an integer) at a position of 10mm from one end

Re_total(nm): average of the delays at all measurement points.

The above object is also achieved by providing a method for producing a PVA, in which a film forming apparatus having a plurality of drying rollers whose rotation axes are parallel to each other is used; the plurality of drying rollers include a 1 st drying roller to an m th drying roller (m represents an integer of 3 or more); a step of spraying a film-forming raw solution containing PVA from a die head onto a 1 st drying roller to dry the film to obtain a film, and then further drying the film by using a 2 nd drying roller to a m th drying roller; the volatile fraction of the film when peeled from the 1 st drying roller is 12-20%, and the peripheral speed (S) of the 2 nd drying roller₂) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)₂/S₁) 1.015 to 1.050, and a peripheral speed (S) of a drying roller (x-th drying roller) which comes into contact with the film after the volatilization fraction of the film reaches 11 mass% or less_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) 0.970 to 0.995, and the average roll temperature from the 2 nd drying roll to the x th drying roll is 63 to 81 ℃.

In this case, it is preferable that the evaporation fraction of the PVA-containing film-forming dope is 60 to 75 mass%, and the peripheral speed (S) of the No. 1 drying roller₁) 8 to 25 m/min.

ADVANTAGEOUS EFFECTS OF INVENTION

The PVA film of the present invention has excellent stretchability even when it is thin and wide, and has a small variation in width after stretching. According to the production method of the present invention, such a PVA film can be easily produced. By using such a PVA film, a thin and wide optical film or the like having excellent optical performance can be manufactured with high productivity.

Drawings

Fig. 1 is a schematic diagram showing measurement points of retardation in a PVA film.

Detailed Description

The PVA film of the invention has a width of more than 3m, a length of more than 1,000m and a thickness of 15-65 μm, and the retardation value measured by setting the distance in the length direction as 15m and the distance in the width direction as 10mm satisfies the following formulas (1) to (4),

in the formula (I), the compound is shown in the specification,

Re_max(nm): maximum value of delay at a position of 10mm from one end

Re_min(nm): minimum value of delay at position of 10mm from one end

Re_ave(nm): average value of delay at a position of 10mm from one end

Re_i(nm): a retardation value at a measurement point i (i =1 to n, n is an integer) at a position of 10mm from one end

Re_total(nm): all-purposeThe average value of the delays at the measurement points.

The retardation value of the PVA film of the present invention, which is measured with the pitch in the longitudinal direction of 15m and the pitch in the width direction of 10mm, satisfies the above-mentioned equations (1) to (4). The retardation Re (nm) of the film is represented by the following formula. Specifically, the retardation re (nm) of the PVA film can be measured by the method described in examples.

Re=d×Δn

[ in the formula, d is a film thickness (nm) and Δ n is a birefringence of the film ].

Re in the above formulae (1) and (2)_max、Re_min、Re_aveAnd Re_iThe retardation value was measured at a position 10mm from one end of the PVA film. Fig. 1 is a schematic diagram showing measurement points i (i =1 to n, n is an integer) in the PVA film 1 at this time. The retardation was measured at a distance 5 of 15m in the longitudinal direction 4 of the PVA film 1 at positions of 10mm each from both ends 2, 3 of the PVA film 1. In this case, the retardation value at each measurement point i (i =1 to n, n is an integer) at a position of 10mm from each of the ends 2 and 3 of the PVA film 1 is Re_i. The maximum value of retardation at all measurement points i at positions of 10mm from both ends 2, 3 of the PVA film 1 was Re_maxMinimum value of Re_minNumber average value of Re_ave. As will be described later, when both ends (ears) of the dried PVA film were cut, the retardation at the position of 10mm from each of both ends 2, 3 of the cut PVA film 1 was measured to determine Re_i、Re_max、Re_minAnd Re_ave。

As will be described later, to obtain Re in the above formula (3)_totalThe retardation of the entire PVA film 1 was measured. In general, the measurement is performed so as to include positions of 10mm from each of the two ends 2 and 3 of the PVA film 1. The measured value at this time was used together with Re_totalTogether determine Re_i、Re_max、Re_minAnd Re_ave。

A in the above formula (1) and B in the above formula (2) are both indicators of the nonuniformity of retardation in the longitudinal direction of the PVA film of the present invention. Satisfying the above equations (1) and (2), the PVA film of the present invention having little variation in retardation in the longitudinal direction is excellent in stretchability, and has little variation in width after stretching. An optical film produced by stretching the PVA film has excellent optical properties. When A in the above formula (1) is larger than 10nm, the optical properties of the obtained optical film become insufficient. Further, the stretchability and the uniformity of the film width after stretching are also reduced. A is preferably 9.5nm or less. In the case where B in the above formula (2) is larger than 1.5nm, the optical properties of the obtained optical film become insufficient. Further, the stretchability and the uniformity of the film width after stretching are also reduced. B is preferably 1.2nm or less. On the other hand, B is usually 0.1nm or more.

Re in the above formula (3)_total(nm) is a number average of retardations at all measurement points when the retardation is measured for the entire PVA film, with the pitch in the longitudinal direction set to 15m and the pitch in the width direction set to 10 mm. Re_totalThe stretching property of the PVA film is improved by the range represented by the above formula (3). Re_totalPreferably 18nm or less. As described above, in general, when the retardation is measured for the entire PVA film, the measurement is performed so as to include positions of 10mm from each of the both ends 2 and 3 of the PVA film 1. The measured value at this time was used together with Re_totalTogether determine Re_i、Re_max、Re_minAnd Re_ave。

The above formula (4) specifies A relative to Re_totalRatio (A/Re)_total). A is the maximum value Re of retardation at a position of 10mm from one end of the PVA film_maxWith a minimum value Re_minThe smaller the difference, the more improved the optical properties of the optical film obtained, and the more preferable the difference is. However, the present inventors have made intensive studies to improve the stretchability of a PVA film and the optical properties of the resulting optical film as much as possible, and have unexpectedly found that by comparing a with Re_totalRatio (A/Re)_total) When the amount is 0.3 or more, the optical performance is hardly deteriorated and the stretchability is improved to a large extent. The aforementioned ratio (A/Re)_total) More preferably 0.4 or more. On the other hand, the above ratio (A/Re)_total) Preferably 2 or less, more preferably 1 or less.

The PVA film of the present invention has a thickness of 15 to 65 μm and a width of 3m or more. The PVA film of the present invention satisfying the above formulae (1) to (4) has excellent stretchability even if it is thin and wide, and has a small variation in width after stretching. By using such a PVA film, a thin and wide optical film having excellent optical performance can be manufactured with high productivity.

From the viewpoint of further improving the stretchability of the PVA film, the thickness of the PVA film is preferably 20 μm or more. Further, the width of the PVA film is preferably 3.5m or more. On the other hand, in the case of manufacturing an optical film such as a polarizing film by a practical production machine, if the width of the film is too wide, uniform uniaxial stretching is difficult, and therefore the width of the PVA film is preferably 8m or less.

The PVA film of the present invention has a length of 1,000m or more. The PVA film of the present invention is excellent in stretchability. Therefore, by using the PVA film as a starting material of an optical film, the optical film can be stably manufactured for a long period of time. The length of the PVA film is preferably 50,000m or less, and more preferably 20,000m or less.

As the PVA used in the film of the present invention, a polyvinyl ester obtained by polymerizing a vinyl ester may be used, which is produced by saponification. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among the vinyl esters, vinyl acetate is preferable from the viewpoints of availability, cost, ease of production of PVA, and the like.

The polyvinyl ester is preferably obtained by using only 1 or 2 or more vinyl esters as a monomer, more preferably 1 vinyl ester as a monomer, and may be a copolymer of 1 or 2 or more vinyl esters and another monomer copolymerizable therewith.

Examples of such other monomers copolymerizable with vinyl esters include olefins having 3 to 30 carbon atoms (such as α -olefin) such as ethylene, propylene, 1-butene, isobutylene, acrylic acid or salts thereof, acrylic acid esters such as methyl acrylate, ethyl acrylate, N-propyl acrylate, isopropyl acrylate, N-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid or salts thereof, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, N-propyl methacrylate, isopropyl methacrylate, N-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylamide, N-methacrylamide, N-ethyl acrylamide, N-dimethyl acrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or salts thereof, acrylamidopropyl dimethylamine or salts thereof, N-methylolacrylamide or derivatives thereof, acrylamide derivatives such as methacrylamide, N-vinyl chloride, N-vinyl methyl acrylamide, N-butyl acrylamide, N-allyl methyl acrylamide, N-butyl acrylamide, N-allyl methyl acrylamide, vinyl methyl acrylamide, vinyl ethyl methyl acrylamide, vinyl ethyl vinyl methyl acrylamide, vinyl ethyl acrylamide, vinyl methyl acrylamide, vinyl ethyl vinyl methyl acrylamide, vinyl ethyl acrylamide, vinyl methyl acrylamide, vinyl ethyl acrylamide, vinyl methyl.

The proportion of the structural unit derived from the other monomer in the polyvinyl ester is preferably 15 mol% or less, more preferably 5 mol% or less, based on the number of moles of the total structural units constituting the polyvinyl ester.

The PVA can be modified with 1 or 2 or more kinds of graft-copolymerizable monomers, and examples of the graft-copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, and α -olefins having 2 to 30 carbon atoms, and the proportion of the structural unit derived from the graft-copolymerizable monomer in the PVA is preferably 5 mol% or less based on the number of moles of the total structural units constituting the PVA.

In the above PVA, a part of the hydroxyl groups may be crosslinked or uncrosslinked. In the above PVA, a part of the hydroxyl groups may react with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure, or may not react with such a compound to form an acetal structure.

The polymerization degree of PVA is not particularly limited, and is preferably 500 or more, more preferably 1,000 or more, further preferably 1,500 or more, and particularly preferably 2,000 or more, from the viewpoints of film strength, durability of the obtained optical film, and the like. On the other hand, if the polymerization degree is too high, there is a tendency that the production cost increases and the step-passing property in film formation is poor, and therefore, the polymerization degree of PVA is preferably 10,000 or less, more preferably 9,000 or less, further preferably 8,000 or less, and particularly preferably 7,000 or less. The polymerization degree of PVA referred to herein is an average polymerization degree measured according to JIS K6726-1994.

The saponification degree of the PVA is not particularly limited, and from the viewpoint of optical performance, durability, and the like of an optical film produced from the PVA film obtained, the saponification degree of the PVA is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and particularly preferably 99.2 mol% or more. The saponification degree of PVA in the present specification means a proportion (mol%) of the number of moles of a vinyl alcohol unit to the total number of moles of the structural unit (typically, a vinyl ester unit) that can be converted into the vinyl alcohol unit by saponification and the vinyl alcohol unit that the PVA has. The degree of saponification of PVA can be measured according to JIS K6726-1994.

As a raw material of the PVA film of the present invention, 1 kind of PVA may be used alone, or 2 or more kinds of PVA different from each other in the kind of modification, the modification rate, the degree of polymerization, the degree of saponification, and the like may be used in combination. However, in the case where the PVA film of the present invention is required to have excellent secondary processability, as in the case of being used as a starting material in the production of an optical film, if the PVA film contains a PVA having an acidic functional group such as a carboxyl group or a sulfonic acid group; PVA having an acid anhydride group; PVA having a basic functional group such as an amino group; PVA having a functional group that promotes a crosslinking reaction, such as a neutralized product thereof, may have a reduced secondary processability of the PVA film due to the crosslinking reaction between PVA molecules. Therefore, in the case as described above, the PVA film preferably does not contain any of PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group, and neutralized products thereof. More preferably: the PVA includes only PVA produced by saponifying a polyvinyl ester obtained by using only a vinyl ester as a monomer, and/or PVA produced by saponifying a polyvinyl ester obtained by using only a vinyl ester and ethylene and/or an olefin having 3 to 30 carbon atoms as a monomer, and more preferably: the PVA includes only PVA produced by saponifying a polyvinyl ester obtained by using a vinyl ester as a monomer, and/or PVA produced by saponifying a polyvinyl ester obtained by using a vinyl ester and ethylene as monomers.

The PVA obtained in this manner is used to produce the PVA film. The PVA film of the present invention can be produced by a method including, but not limited to, the following steps: a film forming apparatus using a plurality of drying rollers having rotation axes parallel to each other; the plurality of drying rollers include a 1 st drying roller to an m th drying roller (m represents an integer of 3 or more); the method comprises a step of spraying a film-forming stock solution containing polyvinyl alcohol from a die head onto a 1 st drying roller to dry the film to obtain a film, and then further drying the film by using a 2 nd to a m th drying rollers; the volatile fraction of the film when peeled from the 1 st drying roller is 12-20%, and the peripheral speed (S) of the 2 nd drying roller₂) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)₂/S₁) 1.015 to 1.050, and a peripheral speed (S) of a drying roller (x-th drying roller) which comes into contact with the film after the volatilization fraction of the film reaches 11 mass% or less_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) 0.970 to 0.995, and the average roll temperature from the 2 nd drying roll to the x th drying roll is 63 to 81 ℃.

As the film-forming stock solution, a solution obtained by mixing PVA with a liquid medium was used; a melt obtained by melting PVA pellets containing a liquid medium or the like. They can be prepared using a stirring type mixing device, a melt extruder, or the like. Examples of the liquid medium used in this case include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, and the like. These liquid media may be used alone in 1 kind, or may be used in combination in 2 or more kinds. Among these, water, dimethyl sulfoxide, or a mixture thereof is preferably used, and water is more preferably used.

From the viewpoint of further improving the stretchability of the PVA film obtained, the film-forming dope preferably contains a plasticizer. A PVA film containing a plasticizer is obtained by using a film-forming dope containing a plasticizer. The plasticizer is preferably a polyhydric alcohol, and examples thereof include ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The plasticizer may be used alone in 1 kind, or may be used in combination in 2 or more kinds. Among them, 1 or 2 or more of glycerin, dipropylene glycol and ethylene glycol are preferably used.

The content of the plasticizer is preferably 0.1 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass, based on 100 parts by mass of PVA. The content of the plasticizer is 30 parts by mass or less with respect to 100 parts by mass of PVA, whereby the handleability of the PVA film obtained is improved.

The film-forming stock solution preferably contains a surfactant from the viewpoints of improvement of releasability from a drying roll in the production of a PVA film, handleability of the resulting PVA film, and the like. A PVA film containing a surfactant is obtained by using a film-forming dope containing a surfactant. The type of the surfactant is not particularly limited, and an anionic surfactant or a nonionic surfactant is preferably used. These surfactants may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

Suitable anionic surfactants include carboxylic acid type anionic surfactants such as potassium laurate, sulfate type anionic surfactants such as octyl sulfate, and sulfonic acid type anionic surfactants such as dodecylbenzenesulfonate.

Further, examples of suitable nonionic surfactants include alkyl ether type surfactants such as polyoxyethylene oleyl ether, alkyl phenyl ether type surfactants such as polyoxyethylene octyl phenyl ether, alkyl ester type surfactants such as polyoxyethylene laurate, alkylamine type surfactants such as polyoxyethylene lauryl amino ether, alkylamide type surfactants such as polyoxyethylene lauramide, polypropylene glycol ether type surfactants such as polyoxyethylene polyoxypropylene ether, alkanolamide type surfactants such as lauric acid diethanolamide and oleic acid diethanolamide, and allylphenyl ether type surfactants such as polyoxyalkylene allylphenyl ether.

The content of the surfactant is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, and still more preferably 0.05 to 0.3 part by mass, based on 100 parts by mass of PVA. The surfactant content is 0.01 parts by mass or more per 100 parts by mass of PVA, whereby the stretchability and dyeability are further improved. Further, the content of the surfactant is 1 part by mass or less with respect to 100 parts by mass of the PVA, whereby the handleability of the PVA film is improved.

The film-forming stock solution may contain various additives such as a stabilizer (e.g., an antioxidant, an ultraviolet absorber, and a heat stabilizer), a compatibilizer, an antiblocking agent, a flame retardant, an antistatic agent, a lubricant, a dispersant, a fluidizing agent, and an antimicrobial agent. These additives may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The volatile fraction of the film-forming stock solution used for producing the PVA film is preferably 60 to 75 mass%. The film-forming stock solution having a volatile fraction of 60 mass% or more has an appropriate viscosity, and therefore the film-forming properties are improved. The volatile fraction is more preferably 65 mass% or more. On the other hand, the volatile fraction is 75 mass% or less, and the uniformity of the thickness of the PVA film obtained is improved. In the present invention, the volatile fraction of the film-forming dope is determined by the following formula (i).

Volatility fraction (% by mass) = { (Wa-Wb)/Wa } × 100 (i)

[ wherein Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) of the component remaining after drying the film-forming stock solution Wa (g) in an electrothermal dryer at 105 ℃ for 16 hours ]

The surface of the drying roller in the film forming apparatus used for producing the PVA film is preferably hard to corrode and has a mirror-like gloss. From such a viewpoint, the drying roller is preferably made of a metal such as nickel, chromium, copper, iron, and stainless steel. In addition, from the viewpoint of improving the durability of the drying roller, a plating layer of nickel, chromium, a nickel/chromium alloy, or the like may be formed in a single layer or in multiple layers on the surface of the drying roller.

The film forming apparatus used in the present invention may have a hot air drying apparatus of a hot air furnace type, a heat treatment apparatus, a humidity control apparatus, and the like, as necessary, following the drying roll.

The number of the drying rollers in the film forming apparatus is 3 or more, preferably 5 to 30. In the present invention, the drying rolls disposed upstream are referred to as a 1 st drying roll, a 2 nd drying roll, a 3 rd drying roll, a 4 th drying roll, and an · mth drying roll in this order. The film forming apparatus includes a known discharge apparatus (casting apparatus) such as a T-slot die, a hopper plate, an I-die, and a lip coater die. The film-forming dope was discharged (cast) from the die of the apparatus onto the 1 st drying roll in a film form.

The film-forming dope discharged onto the 1 st drying roll was dried on the 1 st drying roll to obtain a film, and then the film was peeled off from the 1 st drying roll. Here, the volatile fraction of the film when peeled from the 1 st drying roller needs to be 12 to 20 mass%.

In the case where the volatilization fraction of the film upon peeling from the 1 st drying roller is less than 12 mass%, the stretchability is significantly reduced. On the other hand, when the volatilization fraction of the film upon peeling from the 1 st drying roller is more than 20 mass%, the film peeling property from the 1 st drying roller is deteriorated, and the thickness unevenness in the flow direction becomes large. The volatile fraction is preferably 19% by mass or less, more preferably 18% by mass or less, and still more preferably 16% by mass or less. In the present invention, the volatile fraction of the film was determined by the following formula (ii) after collecting the film immediately after peeling from the 1 st drying roll.

Volatility fraction (% by mass) = { (Wc-Wd)/Wc } × 100 (ii)

[ wherein Wc represents the mass (g) of the collected film, and Wd represents the mass (g) of the film obtained by drying the film Wc (g) in a dryer at a temperature of 105 ℃ for 16 hours ]

When a PVA film obtained using a film-forming dope prepared using a polyol (plasticizer) such as PVA or glycerol, a surfactant, and water is dried under the aforementioned conditions, components other than water are substantially not volatilized and remain in the film, and therefore the volatilization fraction of the film is substantially the same as the amount of water (water fraction) contained in the film.

The surface temperature of the 1 st drying roller is preferably 80 to 120 ℃ from the viewpoints of uniformity of drying, drying speed, and the like. When the surface temperature is less than 80 ℃, the drying on the 1 st drying roller tends to be insufficient, and the peeling tends to be a cause of the peeling failure. The surface temperature is more preferably 85 ℃ or higher. On the other hand, if the surface temperature is higher than 120 ℃, the film tends to foam easily. The surface temperature is more preferably 105 ℃ or lower, and still more preferably 99 ℃ or lower.

From the viewpoint of uniformity of drying, drying speed and productivity, the peripheral speed (S) of the 1 st drying roller₁) Preferably 8 to 25 m/min. At the peripheral speed (S)₁) When the amount is less than 8 m/min, the productivity may be lowered. Peripheral speed (S)₁) More preferably 10 m/min or more, and still more preferably 12 m/min or more. On the other hand, at the peripheral speed (S)₁) If the amount is more than 25 m/min, the drying at the 1 st drying roller tends to be insufficient. Further, it is more preferably 23 m/min or less, and still more preferably 22 m/min or less.

The drying of the film-forming dope discharged in a film form onto the 1 st drying roller may be performed by using only the 1 st drying roller, but may be performed by blowing hot air to the film surface not in contact with the 1 st drying roller to apply heat from both sides of the film. This further improves the uniformity of drying and the drying speed. The wind speed of the hot wind is preferably 1 to 10 m/sec, more preferably 2 to 8 m/sec, and further preferably 3 to 8 m/sec.

If the air speed is too low, dew condensation occurs on the 1 st drying roller, and water drops thereof fall on the film, thereby possibly causing defects in the PVA film obtained. On the other hand, if the wind speed is too high, the thickness of the PVA film to be obtained may vary, and thus defects such as uneven dyeing may occur.

The temperature of the hot air is preferably 50 to 150 ℃, more preferably 70 to 120 ℃, and further preferably 80 to 95 ℃ from the viewpoints of drying efficiency, uniformity of drying, and the like. In addition, the dew point temperature of the hot air is preferably 10-15 ℃. If the temperature of the hot air is too low, the drying efficiency, drying uniformity, and the like are liable to be lowered. On the other hand, if the temperature of the hot air is too high, foaming tends to occur.

The method for blowing hot air to the film on the 1 st drying roll is not particularly limited, and a nozzle method, a rectifying plate method, a combination thereof, or the like is preferably used. In addition, it is preferable to discharge volatile components generated at the time of drying of the film on the 1 st drying roller and the blown hot air.

The film dried by the 1 st drying roller to a volatile fraction of 12 to 20 mass% is peeled off from the roller, and the film is further dried by the 2 nd drying roller. When the film is dried on the 2 nd drying roller, the surface of the film opposite to the surface in contact with the 1 st drying roller is preferably dried by being brought into contact with the 2 nd drying roller.

Peripheral speed of No. 2 drying roll (S)₂) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)₂/S₁) Preferably 1.015 to 1.050. At the ratio (S)₂/S₁) If the amount is less than 1.015, the film is less likely to peel off from the 1 st drying roller, and the uniformity of the PVA film obtained in the width direction may be lowered. On the other hand, in the above ratio (S)₂/S₁) If the amount is more than 1.050, the variation in tension applied to the film between the 1 st drying roller and the 2 nd drying roller becomes large, and the uniformity of the PVA film obtained may be impaired.

The peripheral speed (S) of the drying roller (x-th drying roller) which starts to contact after the volatile fraction of the film reaches 11 mass% or less_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) Preferably 0.970 to 0.995. The volatile fraction was measured immediately before the film was brought into contact with each drying roller. At the very beginning of the volatile fraction reaching 11The drying roller with which the film comes into contact after the mass% or less is a "drying roller (xth drying roller) with which contact is started after the volatile fraction of the film reaches 11 mass% or less". At the peripheral speed (S) of the x-th drying roller_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) When the amount is less than 0.970, a and B are each greater than the upper limit, and thus the optical performance of the resulting optical film may become insufficient. Further, the stretchability of the PVA film and the uniformity of the film width after stretching may be reduced. On the other hand, at the peripheral speed (S) of the x-th drying roller_x) Relative to the peripheral speed (S) of the 2 nd drying roller₂) Ratio of (S)_x/S₂) At more than 0.995, Re in the resulting PVA film_totalGreater than 20nm, whereby the stretchability may be reduced.

The peripheral speed (S) of the downstream drying roller among the 2 nd to x-th drying rollers adjacent to each other_a+1) Relative to the peripheral speed (S) of the upstream drying roller_a) Ratio of (S)_a+1/S_a) Preferably 0.975 to 1. The ratio (S) of all adjacent 2 drying rollers of the 2 nd to x th drying rollers_a+1/S_a) More preferably 0.975 to 1.

The average roll temperature of the 2 nd to the x th drying rolls is preferably 63 to 81 ℃. In the case where the average roll temperature is less than 63 ℃ or more than 81 ℃, a and B are each more than the upper limit, whereby the optical properties of the resulting optical film sometimes become insufficient. In addition, the stretchability of the PVA film and the uniformity of the film width after stretching may be reduced.

The roll temperatures of the 2 nd drying roll to the x th drying roll are all preferably 50 to 95 ℃. In the case where the roll temperature is less than 50 ℃ or more than 95 ℃, a and B are each more than the upper limit, whereby the optical properties of the resulting optical film sometimes become insufficient. In addition, the stretchability and the uniformity of the film width may be reduced.

In the case where the drying roller is further disposed downstream of the x-th drying roller, the peripheral speed (S) of the downstream drying roller among the adjacent 2 drying rollers among the x-th to m-th drying rollers_b+1) Relative to the peripheral speed (S) of the upstream drying roller_b) Ratio of (S)_b+1/S_b) Preferably 0.975 to 1. The roll temperatures of the x +1 th drying roll to the m-th drying roll are all preferably 50 to 130 ℃.

In the case where a drying roller is further disposed downstream of the x-th drying roller, the surface temperature of at least a part of them may be increased. Thus, the drying and the heat treatment of the PVA film can be performed simultaneously. The roller temperature at this time is preferably 90 to 140 ℃, more preferably 95 to 130 ℃.

When the drying rollers are brought into contact with the film, it is preferable to alternately bring one surface and the other surface of the film into contact with the drying rollers from the viewpoint of enabling more uniform drying.

Peripheral speed (S) of mth drying roll_m) Relative to the circumferential speed (S) of the 1 st drying roller₁) Ratio of (S)_m/S₁) The content is not particularly limited, but is preferably in the range of 0.900 to 1.100, more preferably in the range of 0.950 to 1.050, still more preferably in the range of 0.980 to 1.020, and particularly preferably in the range of 0.990 to 1.010.

It is preferable to cut both ends (ears) in the width direction of the dried PVA film. At this time, the film width (W) after cutting both end portions (ears)_T) Relative to the width (W) of the film when discharged from the die₁) Ratio of (W)_T/W₁) Preferably 0.6 or more, more preferably 0.7 or more. The PVA film obtained by the conventional method has a high retardation value at the end portion, and the stretchability of the PVA film is insufficient. The stretchability is improved by cutting the end portions of the PVA film wider, but the resulting PVA film has a narrower width and an increased amount of waste, which leads to a problem of increased cost. On the other hand, according to the production method of the present invention, since the retardation value of the end portion of the PVA film after film formation can be reduced, it is not necessary to widely cut the end portion, and a wide PVA film excellent in stretchability can be obtained.

The dried PVA film can be wound into a roll form by, for example, a humidity control treatment, if necessary. The volatile fraction of the finally obtained PVA film is preferably 1 to 5 mass%, more preferably 2 to 4 mass%. The content of PVA in the PVA film is preferably 50% by mass or more, and more preferably 80% by mass or more.

The PVA film of the present invention has excellent stretchability even when it is thin and wide, and has a small variation in width after stretching. By using such a PVA film, a thin and wide optical film, particularly a polarizing film, having excellent optical properties can be produced with high productivity. In recent years, liquid crystal televisions and monitors have been made larger in screen size. In addition, weight reduction of notebook computers, mobile phones, and the like is also promoted. The PVA film of the present invention is suitably used as a starting material for optical films used in these, and the like. The optical film can be produced by a production method having a step of uniaxially stretching the PVA film of the present invention.

The polarizing film is produced using the PVA film of the present invention as a starting material, and examples thereof include a method of dyeing, uniaxial stretching, fixing treatment, drying treatment, and, if necessary, heat treatment using the PVA film of the present invention. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, dyeing may be performed simultaneously with uniaxial stretching, or dyeing may be performed after uniaxial stretching. Further, the steps of uniaxial stretching, dyeing and the like may be repeated a plurality of times.

Examples of the dye used for dyeing the PVA film include iodine and dichroic organic dyes (e.g., 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 yellow 8, 12, 44, 86, 87; dichroic dyes such as direct orange 26, 39, 106, 107). These dyes may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The dyeing can be usually carried out by immersing the PVA film in a solution containing the above dye, and the treatment conditions and the treatment method are not particularly limited.

The uniaxial stretching of the PVA film may be performed by either a wet stretching method or a dry heat stretching method. In the case of uniaxial stretching by a wet stretching method, uniaxial stretching may be performed in warm water containing boric acid, uniaxial stretching may be performed in a solution containing the dye or in a fixation treatment bath, uniaxial stretching may be performed in air using a PVA film after water absorption, or uniaxial stretching may be performed by other methods. The stretching temperature in the uniaxial stretching treatment is not particularly limited, and when the PVA film is stretched in warm water (wet stretching), a temperature of preferably 30 to 90 ℃, more preferably 40 to 70 ℃, and still more preferably 45 to 65 ℃ is used, and when the PVA film is dry-heat stretched, a temperature of preferably 50 to 180 ℃ is used. The stretching ratio of the uniaxial stretching (total stretching ratio in the case of the uniaxial stretching in multiple stages) is preferably as high as possible just before the film is cut from the viewpoint of polarization performance, and specifically, is preferably 4 times or more, more preferably 5 times or more, and further preferably 5.5 times or more. The upper limit of the stretch ratio is not particularly limited as long as the film does not break, but is preferably 8.0 times or less for uniform stretching. The stretch ratio in the present specification is based on the length of the film before stretching, and the unstretched state corresponds to a stretch ratio of 1. The thickness of the stretched film (polarizing film) is preferably 5 to 35 μm, particularly 20 to 30 μm.

The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching in the longitudinal direction or transverse uniaxial stretching may be employed, and uniaxial stretching in the longitudinal direction is preferred from the viewpoint of obtaining a polarizing film having more excellent polarizing performance. The uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the rollers using a stretching apparatus having a plurality of rollers parallel to each other. On the other hand, the transverse uniaxial stretching may be performed using a tenter type stretching machine.

In the production of a polarizing film, it is preferable to perform a fixing treatment in order to secure the dye adsorption on the uniaxially stretched film. The fixing treatment may be a method of immersing the film in a fixing treatment bath to which a boron compound such as boric acid or borax is added. In this case, an iodine compound may be added to the fixing treatment bath as needed.

The film subjected to the uniaxial stretching, or uniaxial stretching and fixing treatment is preferably followed by a drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150 ℃, particularly 50 to 140 ℃. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film tends to be lowered, while if it is too high, the polarizing performance tends to be lowered due to decomposition of the dye.

An optically transparent protective film having mechanical strength can be laminated on both or one side of the polarizing film obtained as described above to produce a polarizing plate. As the protective film in this case, a cellulose Triacetate (TAC) film, a Cellulose Acetate Butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, as the adhesive for attaching the protective film, a PVA-based adhesive, a urethane-based adhesive, and the like can be given, and among them, a PVA-based adhesive is preferable.

The polarizing plate obtained in the above manner can be used as a member of a liquid crystal display device by covering it with an adhesive such as acrylic and then bonding it to a glass substrate. When the polarizing plate is bonded to a glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, and the like can be bonded.