TW201930441A - Polyvinyl alcohol film - Google Patents

Abstract

The present invention is: a PVA film such that when the refractive indices A and B are measured for each surface of the PVA film by means of incident light that is angled in the widthwise direction of the film relative to the direction perpendicular to the surface of the film, the refractive index A is 1.524-1.530, inclusive (with the caveat that A ≥ B); and a PVA film formation method for forming a PVA film using a film formation device comprising drying rolls and heat treatment rolls that have mutually parallel rotational axes by spraying and partially drying a film formation starting solution that includes PVA onto a first drying roll in the form of a film, then further drying by means of a second drying roll and subsequent drying rolls, and thereafter performing a heat treatment by means of a plurality of heat treatment rolls. Therein, the ratio (SY/SX) of the peripheral speed (SX) of the heat treatment roll (X) positioned the furthest towards the upstream side among the heat treatment rolls and the peripheral speed (SY) of the heat treatment roll (Y) positioned the furthest towards the downstream side is 0.993-0.997, inclusive.

Description

   Manufacturing method of polyvinyl alcohol film   

The present invention relates to a polyvinyl alcohol film having high tensile elongation and excellent extensibility.

Polyvinyl alcohol film (hereinafter sometimes referred to as "polyvinyl alcohol" is simply referred to as "PVA"). It has excellent mechanical properties, transparency, oxygen barrier properties, and oil resistance. It has been used in fiber packaging materials and agricultural films (vegetables) in the past. Films for thermal insulation, vegetable growth, etc.), gas barriers, filters, raw film for polarizing film manufacturing, etc.

For the purpose of in-plane uniformity of a polarizing film, a method has been known in which the refractive index of both the PVA film and the central portion in the thickness direction are individually specified (see Patent Documents 1 and 2).

    [Prior technical literature]         [Patent Literature]    

[Patent Document 1] Japanese Patent Laid-Open No. 2006-219638

[Patent Document 2] Japanese Patent Laid-Open No. 2006-305923

However, in order to manufacture a polarizing film in a highly stretched manner, a polarizing film generally has a problem of solving the problem of breakage when the PVA film is stretched. However, according to the method described in Patent Documents 1 or 2, the extensibility cannot be sufficiently improved. Therefore, an object of the present invention is to provide a PVA film having excellent stretchability, and an optical film using a polarizing film or the like.

In order to achieve the above-mentioned object, the inventors of the present invention repeatedly and carefully studied and found that the specific refractive index of the surface of the PVA film is closely related to the elongation of the PVA film. In addition, it was found that this PVA thin film having a specific refractive index can be smoothly and continuously produced by using the peripheral speed of the heat treatment roller during film formation as the specific one. Based on such knowledge, the inventor of the present case further repeated the discussion to complete the present invention.

That is, the present invention is related to the following:

[1] A PVA film, in which the refractive index of each side of the PVA film is measured using incident light in a direction inclined from the vertical direction toward the width direction of the film with respect to the film surface of the PVA film, When A is taken as the refractive index of the other surface as B (where A ≧ B), A is 1.524 or more and 1.530 or less.

[2] The PVA film according to the above [1], wherein A is 1.526 or more and 1.530 or less.

[3] The PVA film according to the above [1] or [2], wherein A + B is 3.050 or more and 3.060 or less.

[4] A method for manufacturing a PVA film, which uses a film forming apparatus having a drying roll and a heat treatment roll in which rotation axes are parallel to each other. A first drying roll on the most upstream side of the drying rolls will include a PVA-containing film. After the film-forming stock solution is discharged into a film shape and partially dried, it is further dried with a drying roller after the second drying roller, and then heat-treated with a plurality of heat-treatment rollers to produce a PVA film. heat treatment roll (Y) of the downstream side of the most peripheral speed (S _Y) with respect to the circumferential velocity (S _X) located in the heat treatment roll most upstream side of the (X) of the ratio (S _Y / S _X) becomes 0.993 or more 0.997 the following.

[5] The manufacturing method as described in [4] above, wherein 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 1.000. Above 1.040.

[6] The manufacturing method according to the above [4] or [5], wherein the surface temperature of the final drying roller is less than 60 ° C.

[7] An optical film manufactured from the PVA film according to any one of [1] to [3] above.

[8] The optical film according to the above [7], which is a polarizing film.

[9] A method for producing an optical film, which comprises the step of uniaxially stretching using the PVA film according to any one of the above [1] to [3].

[10] The manufacturing method as described in [9] above, which is a manufacturing method of a polarizing film.

The PVA film of the present invention has high stretch elongation and excellent extensibility. Therefore, as long as the PVA film of the present invention is used for a raw material film, an optical film such as a polarizing film having excellent optical properties can be manufactured with good productivity. Moreover, according to the manufacturing method of the PVA film of this invention, the said PVA film can be manufactured continuously smoothly.

    [Form of Implementing Invention]    

Hereinafter, the present invention will be specifically described.

〔PVA film〕

In the PVA film of the present invention, the refractive index of each side of the PVA film is measured using incident light in a direction inclined from the vertical direction to the width direction of the film with respect to the film surface, and the refractive index of one side is taken as A When the refractive index of the other surface is taken as B (where A ≧ B), A is 1.524 or more and 1.530 or less.

When A is less than 1.524, there is a problem that wrinkles are easily generated in the PVA film. In addition, when A exceeds 1.530, there is a problem that the extensibility decreases. The present invention is not particularly limited, but the reason why A affects extensibility is considered as follows. That is, the extensibility of the PVA film is higher than the refractive index of the central portion of the PVA film in the thickness direction, and the correlation of the refractive index of the surface is higher, and compared with the film surface of the PVA film, the vertical direction is used. Relativity of refractive index measured with incident light inclined in the direction of flow (MD) of the film with respect to the film surface using incident light inclined in the direction perpendicular to the film's width direction (TD) The higher the breakage of the PVA film is, the more the starting point of the surface portion of the film is destroyed. Then, the effect is caused by the larger refractive index surface.

From the viewpoints described above, A is preferably more than 1.524, more preferably 1.526 or more, particularly preferably more than 1.526, more preferably 1.527 or more, most preferably more than 1.527, and more preferably less than 1.530, and more preferably 1.529 or less.

In addition, A and B can be obtained as measured values based on a laser light having a wavelength of 532 nm using a europium coupling device. Here, with respect to the film surface of the PVA film, the incident light in a direction inclined from the vertical direction to the width direction of the film is used so that when the incident light is projected in a vertical direction with respect to the film surface, the direction is the same as that of the PVA. The incident light in a direction in which the width direction (TD) of the film is parallel (perpendicular to the length direction (MD) of the PVA film) can be obtained by using the above-mentioned 稜鏡 coupling device. A and B are specifically measured by the method mentioned later in an Example.

In the PVA film of the present invention, A + B is preferably 3.050 or more, more preferably 3.055 or more, particularly preferably 3.057 or more, and preferably 3.060 or less, more preferably 3.059 or less, and particularly preferably 3.058 or less. When A + B is at least the above lower limit, the occurrence of wrinkles in the PVA film can be more effectively suppressed. On the other hand, if A + B is equal to or less than the above upper limit, the extensibility can be further improved.

Examples of the PVA forming the PVA film of the present invention include PVA obtained by saponifying a polyvinyl ester obtained by polymerizing vinyl esters, modified PVA graft-copolymerized with a comonomer in the main chain of PVA, and Modified PVA manufactured by saponifying a modified polyvinyl ester copolymerized with a vinyl ester and a comonomer, and unmodified PVA or a part of the hydroxyl groups of the modified PVA are provided with aldehydes such as formaldehyde, butyraldehyde, benzaldehyde, and the like. Cross-linked so-called polyvinyl acetals and the like.

When the PVA forming the PVA film of the present invention is a modified PVA, the modified amount of PVA is preferably 15 mol% or less, and more preferably 5 mol% or less.

Examples of the vinyl ester used in the production of PVA include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl neodecanoate, and laurel. Acid vinyl ester, vinyl stearate, vinyl benzoate and the like. These vinyl esters can be used singly or in combination of two or more kinds. Among these vinyl esters, vinyl acetate is preferred from the viewpoint of productivity.

Examples of the comonomer include olefins (α-olefins, etc.) having 2 to 30 carbon atoms, such as ethylene, propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; methyl acrylate, Acrylic acid such as ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, third butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, stearyl acrylate, etc. Esters (for example, alkyl esters of 1 to 18 carbon atoms of acrylic acid); methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, Methacrylic acid such as n-butyl methacrylate, isobutyl methacrylate, third butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, stearyl methacrylate, etc. Esters (for example, alkyl esters of methacrylic acid having 1 to 18 carbons); acrylamide; N-methacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, Diacetone acrylamide, acrylamide propanesulfonic acid or its salt, acrylamide propyldimethylamine or its salt, N-hydroxymethyl Acrylamide derivatives of methacrylamide or derivatives thereof; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamine propanesulfonic acid Or a salt thereof, methacrylamide propyl dimethylamine or a salt thereof, a methacrylamide derivative such as N-methylolmethacrylamide or a derivative thereof; N-vinylmethaneamine, N -N-vinylamines such as ethylene acetamide, N-vinyl pyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isopropyl Vinyl ethers such as butyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile, methacrylonitrile; vinyl chloride, vinylidene chloride, fluorine Halogenated vinyls such as ethylene and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid and itaconic acid, their salts or derivatives thereof ; Ethylene silicon compounds such as ethylene trimethoxysilane; isopropenyl acetate; unsaturated sulfonic acid or derivatives thereof; Of these, α-olefins are particularly preferred, and ethylene is particularly preferred.

From the viewpoint of the polarization performance and durability of the obtained polarizing film, the average degree of polymerization of the PVA forming the PVA film of the present invention is preferably 1500 or more, more preferably 1700 or more, and particularly preferably 2000 or more. On the other hand, the upper limit of the average degree of polymerization of the PVA is preferably 8,000 or less, and particularly preferably 6000 or less, from the viewpoints of ease of production and extensibility of a homogeneous PVA film.

Here, the "average degree of polymerization" of PVA in the present specification refers to the average degree of polymerization measured in accordance with JIS K6726-1994, which can be determined from the limiting viscosity measured after re-saponification of PVA in 30 ° C water.

From the viewpoint of the water resistance of the polarizing film produced using the obtained PVA film, the saponification degree of the PVA is preferably 98.0 mol% or more, more preferably 98.5 mol% or more, and particularly preferably 99.0 mol% or more. When the degree of saponification is less than 98.0 mol%, the water resistance of the obtained polarizing film tends to deteriorate. In addition, the degree of saponification of PVA in this specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that PVA has relative to vinyl alcohol units obtained by saponification conversion. The proportion of moles of alcohol units (mole%). The degree of saponification can be measured in accordance with JIS K6726-1994.

The PVA film of the present invention preferably contains a plasticizer. By including a plasticizer, the extensibility can be further improved. The plasticizer may be blended during the preparation of the film forming stock solution used to form the PVA film. As described above, it can promote the dissolution or melting of PVA to the liquid medium, and improve the passability of the steps in film production.

As the plasticizer, a polyhydric alcohol is preferably used. Examples of the polyhydric alcohol include ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The plasticizer may be used alone or in combination of two or more. Among these, glycerin is preferred from the standpoint of good elongation improvement effect.

The content of the plasticizer is preferably 0 to 30 parts by mass relative to 100 parts by mass of PVA, more preferably 3 to 25 parts by mass, and even more preferably 5 to 20 parts by mass. When the content of the plasticizer is below the above upper limit, the rationality of the obtained PVA film can be improved.

The PVA film of the present invention preferably contains a surfactant. By including a surfactant, the rationality of the PVA film can be improved. The surfactant may be blended during the preparation of the film-forming dope used to form the PVA film. As described above, the peelability of the drying roller during the production of the PVA film can be improved.

The type of the surfactant is not particularly limited, and an anionic surfactant or a nonionic surfactant is preferably used.

Examples of the anionic surfactant include a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type such as dodecylbenzenesulfonate.

Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octyl phenyl ether, and alkane such as polyoxyethylene laurate. Ester type, alkylamine type such as polyoxyethylene lauryl ether, alkyl amine type such as polyoxyethylene laurate amine, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, diethanol laurate Alkylamine type such as amine, diethanolammonium oleate, etc., allylphenyl ether type such as polyoxyalkylallyl phenyl ether and the like. The surfactant may be used singly or in combination of two or more kinds.

The content of the surfactant is preferably 0.01 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of PVA, more preferably 0.02 parts by mass or more and 0.5 parts by mass or less, and particularly preferably 0.05 parts by mass or more and 0.3 parts by mass or less. When the content of the surfactant is greater than or equal to the above-mentioned lower limit, film-forming properties or peeling properties can be improved. On the other hand, according to the content of the surfactant being below the above upper limit, the rationality of the obtained PVA film can be improved.

The PVA film of the present invention may contain components other than the above-mentioned PVA, plasticizer, and surfactant, such as stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers, and anticaking agents. , Flame retardant, antistatic agent, slip agent, dispersant, fluidizer, antibacterial agent, etc. These other components may be used alone or in combination of two or more.

The thickness of the PVA film is not particularly limited, and may be set to 100 μm or less, or even 80 μm or less, for example. The thickness may be set to be 10 μm or more, or even 20 μm or more, and may be more than 50 μm.

The width of the PVA film is not particularly limited, but in recent years, as LCD televisions or monitors have developed large screens, in order to be effectively used in these, a width of 2 m or more is preferred, 3 m or more is preferred, and 4 m or more is particularly preferred. When industrially manufacturing a polarizing film, if the film width becomes too wide, uniform uniaxial stretching becomes difficult. Therefore, the width of the PVA film is preferably 8 m or less.

The shape of the PVA film is not particularly limited, but from the viewpoint that a more uniform PVA film can be continuously produced, and a polarizing film can also be continuously used, the long film is preferred. The length (length in the direction of flow) of the elongated film is not particularly limited and can be appropriately set depending on the application and the like. For example, it can be set to a range of 5 m to 20,000 m.

The PVA film of the present invention preferably has a mass swelling degree of 150% to 250%, more preferably 160% to 240%, and particularly preferably 170% to 230%. According to the mass swelling degree, the extensibility can be further improved by being above the lower limit. On the other hand, according to the mass swelling degree being equal to or lower than the above-mentioned upper limit, it is possible to improve the passability of the step at the time of stretching, and also to improve the durability of the obtained polarizing film.

The term “mass swelling degree” as used in this specification refers to the mass obtained by immersing a PVA film in distilled water at 30 ° C. for 30 minutes, divided by the mass obtained by drying the PVA film after the impregnation at 105 ° C. for 16 hours. The percentage of the value. The swelling degree of PVA film can be reduced by enhancing the conditions of heat treatment.

[Manufacturing method of PVA film]

The method for manufacturing the PVA film of the present invention is not particularly limited, but according to the following manufacturing method of the present invention, it is preferable that the PVA film of the present invention described above can be smoothly and continuously manufactured.

That is, the method of the present invention for manufacturing a PVA film is a manufacturing method using drying rollers having rotation axes parallel to each other (from the most upstream side to the downstream side, which are sequentially referred to as a first drying roller and a second drying roller. …) And a film-forming device with a heat treatment roller, on the first drying roller located on the most upstream side among the drying rollers, the film-forming dope containing PVA is discharged into a film shape and partially dried, and then the second The drying rollers subsequent to the drying roller are further dried, and thereafter, a plurality of heat treatment rollers are subjected to heat treatment to produce a PVA film. Here, the peripheral speed (S _Y ) of the heat treatment roller (Y) located on the most downstream side among the heat treatment rollers is made. The ratio (S _Y / S _X ) to the peripheral speed (S _X ) of the heat-treatment roll (X) located on the most upstream side is 0.993 or more and 0.997 or less.

In the method of the present invention for producing a PVA film, a film forming apparatus including a drying roll and a heat treatment roll having rotation axes parallel to each other is used. On the first drying roll on the most upstream side of the drying roll, a PVA-containing After the film-forming stock solution is discharged into a film shape and partially dried, it is further dried with a drying roller subsequent to the second drying roller, and then heat-treated with a plurality of heat-treatment rollers to produce a PVA film. In the film forming device, the number of the drying rollers is preferably 4 or more, more preferably 5 or more, and particularly preferably 6 to 30.

The drying roll and / or the heat-treating roll, for example, are preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel, etc. In particular, the surface of the roll is more preferably formed of a metal material that is not easily corroded and has a mirror gloss. In addition, in order to improve the durability of the drying roller and / or the heat-treating roller, a single-layer or a combination of two or more nickel, chromium, and nickel / chromium alloy layers are used as the drying roller and / or the heat-treating roller. good.

In addition to the drying roll and the heat treatment roll, the above-mentioned film forming apparatus may further include a hot-air stove type hot-air drying device, a hot-air stove-type heat treatment device, a humidity control device, and the like, as necessary.

Regarding the heating direction when the film is dried from the first drying roller to the final drying roller, from the viewpoint that the film can be dried more uniformly, the film surface in contact with the first drying roller in any part of the film ( Hereinafter, it is sometimes referred to as "the first drying roller contact surface"), and the film surface that is not in contact with the first drying roller (hereinafter sometimes referred to as the "first drying roller non-contact surface") and the first drying roller to the final It is preferable that the drying rollers up to the drying rollers alternately face each other and dry.

When the film-forming stock solution containing PVA is discharged into a film form on the first drying roll of a film forming apparatus, for example, a known film form such as a T-slot die, a hopper plate, an I-die, and a lip nozzle applicator is used. The discharge device (film-like casting device) may discharge (cast) the film-forming stock solution containing PVA into a film shape on a first drying roll.

The film-forming dope containing PVA can be prepared by mixing PVA with a liquid medium as a solution, and melting PVA pellets containing a liquid medium or the like into a molten liquid. The dissolution of PVA into a liquid medium or the melting of PVA pellets including a liquid medium can be performed using a stirring type mixing device, a melt extruder, or the like. Examples of the liquid medium used at this time include water, dimethylformamide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, and diethylenetriamine. These liquid media can be used alone or in combination of two or more. Among these, water, dimethylarsin, or a mixture of the two is preferably used, and water is particularly applicable.

In the film-forming dope, one or two or more plasticizers, surfactants, and other components are preferably blended in the above-mentioned amounts in the description of the PVA film as necessary.

The volatile content of the film-forming dope used in the production of a PVA film is preferably 50% by mass to 90% by mass, and more preferably 60% by mass to 75% by mass. According to the volatile content of the film-forming dope, the viscosity of the film-forming dope can be kept low, and filtration or defoaming becomes easier, and the film-making itself becomes easier. On the other hand, according to the volatile content of the film-forming solution, the viscosity of the film-forming solution can be prevented from becoming too low, and the thickness uniformity of the obtained PVA film can be improved.

The surface temperature of the first drying roller is not particularly limited, but from the viewpoint of uniformity and productivity of the drying of the film, 80 ° C to 99 ° C is preferred, 85 ° C to 99 ° C is more preferred, and 90 ° C to 98 ° C is preferred. Extraordinary. Since the surface temperature of the first drying roller is 99 ° C. or lower, it is possible to more effectively prevent the film-forming dope from foaming on the first drying roller. On the other hand, when the surface temperature of the first drying roll is 80 ° C. or higher, the peelability from the first drying roll can be improved.

The drying on the first drying roller that discharges the film-forming film-forming solution can be performed by heating only from the first drying roller. However, from the viewpoint of uniformity of drying and drying speed, it is also the same as using the first drying roller. While heating, it is preferable to blow hot air against the non-contact surface of the first drying roll together, and apply heat from both sides of the film to dry.

When the hot air is sprayed on the non-contact surface of the first drying roller of the film on the first drying roller, from the viewpoint of further improving the stretchability of the PVA film obtained, the blowing speed is relative to the entire area of the non-contact surface of the first drying roller. Hot air with a speed of 1 ~ 10m / s is better, hot air with a speed of 2 ~ 8m / s is better, and hot air with a speed of 3 ~ 8m / s is particularly good. When the wind speed of the hot air sprayed on the non-contact surface of the first drying roller is too small, condensation of water vapor or the like occurs during drying on the first drying roller, and water droplets drip on the film. The resulting PVA film is prone to defects. Possible. On the other hand, when the wind speed of the hot air sprayed from the non-contact surface of the first drying roll is too large, the thickness of the PVA film finally obtained is uneven, and the problems of uneven dyeing and the like are likely to occur with the foregoing.

From the viewpoints of drying efficiency and drying uniformity, the temperature of the hot air sprayed on the non-contact surface of the first drying roll of the film is preferably 50 ° C or higher and 99 ° C or lower, more preferably 70 ° C or higher and 98 ° C or lower, and 80 ° C or higher. Particularly preferred below 95 ° C. The dew point temperature of the hot air sprayed on the non-contact surface of the first drying roll of the film is preferably 10 ° C or higher and 15 ° C or lower.

The method for blowing hot air on the non-contact surface of the first drying roller of the film is not particularly limited, and any hot air with uniform wind speed or temperature can be sprayed on the non-contact surface of the first drying roller of the film, preferably on the non-contact surface of the first drying roller of the film. As a method of uniformly blowing the whole, a nozzle method, a rectifying plate method, or a combination of these methods is preferable. The blowing direction of the hot air on the non-contact surface of the first drying roller of the film may be a direction opposite to the non-contact surface of the first drying roller, or may be a circumferential shape almost along the non-contact surface of the first drying roller of the film. The direction (a direction almost along the circumference of the roll surface of the first drying roll) or a direction other than the above may be used.

When drying the film on the first drying roller, it is preferable to exhaust the volatiles generated from the film and the hot air after blowing according to the drying. The method of exhausting is not particularly limited, but it is preferable to adopt an exhaust method that does not cause uneven wind speed and uneven temperature of the hot air that is not blown on the non-contact surface of the first drying roll of the film.

From the viewpoints of uniformity of drying, drying speed, and productivity of the PVA film, the peripheral speed (S ₁ ) of the first drying roller is preferably 5 m / min or more and 50 m / min or less, and more preferably 10 m / min or more and 45 m / min or less. Good, 15m / min or more and 40m / min or less are particularly good. When the peripheral speed (S ₁ ) of the first drying roller is equal to or more than the above lower limit, the value of the refractive index can be reduced. On the other hand, when the peripheral speed (S ₁ ) of the first drying roller is equal to or lower than the above-mentioned upper limit, the thickness uniformity of the obtained PVA film can be improved.

The film-forming dope is discharged on the first drying roll, and dried on the first drying roll. The volatile content of the film (the volatile content of the film when peeled from the first drying roll) is preferably When it is 17% by mass or more and 30% by mass or less, more preferably 17% by mass or more and 29% by mass or less, and particularly preferably 18% by mass or more and 28% by mass or less, it can be peeled off from the first drying roll.

The film is dried on the first drying roller until the film having a volatile content of preferably 17% by mass or more and 30% by mass or less is peeled from the first drying roller, and then the non-contact surface of the first drying roller of the film is opposed to the second drying roller. It is preferred to dry the film with a second drying roller.

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 preferably 1.000 or more and 1.040 or less. When the ratio (S ₂ / S ₁ ) is within the above range, the PVA film of the present invention can be produced more smoothly. When the ratio (S ₂ / S ₁ ) is too low, the peeling position of the film from the first drying roll becomes uneven, and the birefringence unevenness in the width direction tends to become large. From the viewpoint described above, the ratio (S _Y / S _X ) is preferably 1.020 or more, more preferably 1.030 or more, and still more preferably 1.038 or less.

The PVA film dried by the second drying roller is peeled from the second drying roller, and the number of the drying rollers installed in the film forming apparatus is adjusted by the third drying roller, the fourth drying roller, the fifth drying roller, and the like. ． ． The multiple drying rollers can be sequentially dried.

The surface temperature of each drying roller from the second drying roller to the final drying roller is preferably 40 ° C or higher, more preferably 45 ° C or higher, particularly preferably 50 ° C or higher, and preferably less than 100 ° C, and more preferably 98 ° C or lower, It is particularly preferred below 96 ° C, and can also be lower than 90 ° C.

In addition, from the viewpoint that the PVA film of the present invention can be manufactured more smoothly and the occurrence of wrinkles is more effectively prevented, the surface temperature of the final drying roll (drying roll located directly in front of the heat treatment roll) is preferably less than 60 ° C, and less than 57 ° C is better.

The heat treatment is performed using a plurality of heat treatment rollers with respect to the film dried by the drying roller as described above. Here, in the method of the present invention for producing a PVA film, the peripheral speed (S _Y ) of the heat-treatment roll (Y) located on the most downstream side among the plurality of heat-treatment rolls described above is made relative to the heat-treatment roll (located on the most upstream side) ( X) The peripheral velocity (S _X ) ratio (S _Y / S _X ) is 0.993 or more and 0.997 or less. When the ratio (S _Y / S _X ) exceeds the above range, it becomes difficult to obtain the PVA film of the present invention. From the viewpoint described above, the ratio (S _Y / S _X ) is preferably 0.994 or more, more preferably 0.995 or more, and still more preferably 0.996 or less.

The surface temperature of the heat-treating roller is preferably 100 ° C or higher, more preferably 140 ° C or lower, more preferably 130 ° C or lower, and particularly preferably 120 ° C or lower. Furthermore, in the method of the present invention for producing a PVA film, a roll having a surface temperature of 100 ° C or higher may be regarded as a heat treatment roll, and a roll having a surface temperature of less than 100 ° C may be regarded as a drying roll.

In the method of the present invention for producing a PVA film, only two heat treatment rolls (X) and heat treatment rolls (Y) may be used as the heat treatment rolls, and there may be further heat treatment rolls other than the heat treatment rolls. No matter what.

The heat treatment time when heat treatment is performed by a heat treatment roller is not particularly limited, but from the viewpoint of more efficiently manufacturing the PVA film of the present invention, 3 seconds or more is preferable, 4 seconds or more is preferable, 5 seconds or more is particularly preferable, and 120 It is preferably less than 90 seconds, more preferably less than 90 seconds, and particularly preferably less than 60 seconds.

The film subjected to the heat treatment as described above may be further subjected to humidity control treatment, cutting at both ends (ear portions) of the film, etc., and wound into a roll shape with a final predetermined length to obtain the PVA of the present invention. film.

The PVA film finally obtained through the above-mentioned series of treatments preferably has a volatile content ranging from 1% by mass to 5% by mass, and more preferably from 2% by mass to 4% by mass.

〔Application of PVA film〕

The application of the PVA film of the present invention is not particularly limited, but from the viewpoint that the PVA film of the present invention has high tensile elongation and excellent extensibility, it is used as a raw material film for producing optical films such as polarizing films and retardation films. Use better. The optical film as described above can be produced, for example, by using the PVA film of the present invention and performing a treatment such as uniaxial stretching.

The method for producing a polarizing film by using the PVA film of the present invention as a raw material film is not particularly limited, and any method from the past may be used. Examples of the method described above include a method of dyeing and uniaxially stretching a PVA film, or a method of uniaxially stretching a PVA film containing a dye. As a more specific method for producing a polarizing film, the PVA film of the present invention may be subjected to swelling, dyeing, uniaxial stretching, and if necessary, further fixing treatment, drying, and the like. In this case, the order of the respective processes such as swelling, dyeing, uniaxial stretching, and fixed processing is not particularly limited, and one or two or more processes may be performed simultaneously. For example, dyeing may be performed before uniaxial stretching, or Dyeing is performed at the same time as uniaxial extension, or dyeing can be performed after uniaxial extension. Furthermore, one or two or more of the processes may be performed twice or more.

Swelling can be performed by immersing a PVA film in water. The temperature of water when immersed in water is preferably in a range of 20 ° C to 40 ° C, more preferably in a range of 22 ° C to 38 ° C, and particularly preferably in a range of 25 ° C to 35 ° C. The time for immersion in water is, for example, preferably within a range of 0.1 minutes to 5 minutes, and more preferably within a range of 0.5 minutes to 3 minutes. The water to be immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

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

When an iodine-based dye is used as a dye, a solution containing iodine and potassium iodide is generally used in a dyeing bath. In this case, the concentration of iodine in the dyeing bath is preferably in a range of 0.01% by mass to 0.5% by mass, and the concentration of potassium iodide is preferably in a range of 0.01% by mass to 10% by mass. When a dichroic organic dye is used as the dye, the concentration of the dichroic organic dye in the dyeing bath is preferably within a range of 0.1% by mass to 5% by mass. The temperature of the dyeing bath is preferably 20 ° C or higher and 50 ° C or lower, particularly preferably 25 ° C or higher and 40 ° C or lower.

Uniaxial stretching can be performed by any wet stretching method or dry heat stretching method. In the case of the wet elongation method, it may be performed in an aqueous solution containing boric acid, or it may be performed in the above-mentioned dyeing bath or a fixed treatment bath described later. In the case of the dry stretching method, it can be performed in the air using a water-absorbent PVA film. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the aqueous boric acid solution is preferably within a range of 0.5% by mass to 6.0% by mass, and more preferably within a range of 1.0% by mass to 5.0% by mass, and within a range of 1.5% by mass to 4.0% by mass. good. The boric acid aqueous solution may contain potassium iodide, and its concentration is preferably within a range of 0.01% by mass to 10% by mass. Uniaxial stretching is better in the flow direction of PVA film.

The stretching temperature for uniaxial stretching is not particularly limited, but in the case of the wet stretching method, it is preferably in the range of 30 ° C to 90 ° C, more preferably in the range of 40 ° C to 70 ° C, and in the range of 45 ° C to 65 ° C. The range is particularly preferable. In the case of the dry heat stretching method, a range of 50 ° C to 180 ° C is preferred.

For uniaxial stretching, the stretching ratio (total stretching ratio when uniaxial stretching is performed in multiple stages) is better from the viewpoint of polarizing performance until the film is about to break. Specifically, 4 times or more is better, 5 times is better. Above is better, 5.5 times is especially good. The upper limit of the stretching ratio is not particularly limited as long as the film does not break, and it is preferably 8 times or less for uniform stretching.

The thickness of the stretched film (polarizing film) is 5 μm or more and 35 μm or less, particularly preferably 20 μm or more and 30 μm or less.

In the manufacture of polarizing films, in order to strengthen the adsorption of dyes on films stretched uniaxially, most of them are fixed. The fixing treatment is generally a method in which a thin film is immersed in a fixing treatment bath in which boric acid and / or a boron compound is added. In this case, if necessary, an iodine compound may be added to the fixed treatment bath.

Next, it is preferable to dry the film that has been subjected to uniaxial stretching, or uniaxial stretching and fixing. The drying temperature is preferably from 30 ° C to 150 ° C, particularly preferably from 50 ° C to 140 ° C. When the drying temperature is too low, the dimensional stability of the obtained polarizing film tends to decrease. On the other hand, when the drying temperature is too high, it is easy to cause degradation in polarizing performance due to decomposition of the dye and the like.

A protective film that is optically transparent and has mechanical strength can be bonded on both sides or single sides of the polarizing film obtained as described above to serve as a polarizing plate. As the protective film in this case, cellulose triacetate (TAC) film, cyclic olefin polymer (COP) film, acetate / cellulose butyrate (CAB) film, acrylic film, polyester film, polypropylene are used. Thin film, drop Ethylene resin film and the like. Moreover, as an adhesive agent for bonding a protective film, a PVA-type adhesive agent, an acrylate-type adhesive agent, a urethane-type adhesive agent, etc. are used normally, Especially among these, a PVA-type adhesive agent is used suitably.

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

    [Example]    

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. In addition, the following shows the measuring method of the refractive index in the flow direction of the surface of the PVA film used in the following Examples and Comparative Examples, and the measuring method of the tensile elongation of the PVA film.

[Refractive index of PVA film]

The PVA films obtained in the following examples or comparative examples were humidity-conditioned for 7 days in an environment of 23 ° C and 50% RH, and thereafter, a tritium coupling device (Model 2010 / M) manufactured by Metricon was used in the same environment. The laser light with a wavelength of 532 nm is used by the 稜鏡 coupling device as the light for the film surface of the PVA film, which is inclined from the vertical direction to the width direction of the film, and is used as the incident light in the PVA film. The refractive index (based on the refractive index of the surface) of the surface of the thin film is obtained from the reflected light. The other surfaces of the PVA film were also processed in the same manner to obtain a refractive index. The two numerical values of the obtained refractive indices are set to A and B, respectively, so as to satisfy the relationship of A ≧ B.

[Stretch of PVA film]

The PVA films obtained in the following examples or comparative examples were stored in an environment of 20 ° C. and 65% RH for 24 hours and subjected to a humidity-conditioning treatment, and then stretched in the same environment using an automatic plotter manufactured by Shimadzu Corporation. test. Furthermore, the width of the PVA film sample is set to 15 mm, the distance between the clamps is set to 30 mm, the stretching speed is set to 500 mm / min, and the stretching direction is set to the flow direction of the PVA film. In this tensile test, the inter-clamp distance when the PVA film was broken was divided by the original inter-clamp distance (30 mm) as the tensile elongation (%), and the average value was measured 10 times and evaluated.

[Example 1]

100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained from a separate polymer of saponified polyvinyl acetate from a T-die, 12 parts by mass of glycerol, and diethanolamine laurate 0.1 The film-forming stock solution with a mass part and a volatile content of 66% by mass of water is discharged into a film form on a first drying roll (surface temperature of 90 ° C. and a peripheral speed (S ₁ ) of 13.5 m / min), and is discharged on the first drying roll. On the other hand, the entire non-contact surface of the first drying roll was partially dried while blowing hot air at 90 ° C at a wind speed of 5 m / sec.

Then, it peeled from the 1st drying roll, and made the non-contact surface of a 1st drying roll oppose a 2nd drying roll, and further dried. At this time, 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 was 1.035. Next, the front and back surfaces of the film are alternately opposed to each of the drying rollers, and further dried by the drying rollers subsequent to the third drying roller. The surface temperature of the drying roller from the second drying roller to the drying roller located immediately in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 55 ° C.

Then, the heat treatment roll (X) with a surface temperature of 104 ° C and the heat treatment roll (Y) connected to the surface temperature of 109 ° C were heat-treated, and then rolled up to obtain a long PVA film (thickness: 60 μm, width: 3 m). . Here, the heat treatment roll (Y) of the circumferential velocity (S _Y) with respect to the heat roll (X), the circumferential velocity (S _X) ratio (S _Y / S _X) is 0.995.

As for the film surface of the obtained PVA film, the above-mentioned refractive index measured by incident light from a direction inclined perpendicular to the film width direction was 1.529 on one side and 1.529 on the other side (A = B = 1.529, A + B = 3.058). The tensile elongation of the obtained PVA film was 438%.

[Example 2]

100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained from a separate polymer of saponified polyvinyl acetate from a T-die, 12 parts by mass of glycerol, and diethanolamine laurate 0.1 The film-forming stock solution with a mass part and a volatile content of 66% by mass of water is discharged into a film form on a first drying roll (surface temperature of 90 ° C. and a peripheral speed (S ₁ ) of 13.5 m / min), and is discharged on the first drying roll. On the other hand, the entire non-contact surface of the first drying roll was partially dried while blowing hot air at 90 ° C at a wind speed of 5 m / sec.

Then, it peeled from the 1st drying roll, and made the non-contact surface of a 1st drying roll oppose a 2nd drying roll, and further dried. At this time, 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 was 1.035. Next, the front and back surfaces of the film are alternately opposed to each of the drying rollers, and further dried by the drying rollers subsequent to the third drying roller. The surface temperature of the drying roller from the second drying roller to the drying roller located immediately in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 50 ° C.

Then, the heat treatment roll (X) with a surface temperature of 101 ° C. and the heat treatment roll (Y) connected to the surface temperature of 107 ° C. were heat-treated, and then rolled up to obtain a long PVA film (thickness: 60 μm, width: 3 m). . Here, the heat treatment roll (Y) of the circumferential velocity (S _Y) with respect to the heat roll (X), the circumferential velocity (S _X) ratio (S _Y / S _X) is 0.995.

For the film surface of the obtained PVA film, the above-mentioned refractive index measured by incident light from a direction inclined perpendicular to the width direction of the film was 1.530 on one side and 1.528 on the other side (A = 1.530, B = 1.528). , A + B = 3.058). The tensile elongation of the obtained PVA film was 437%.

[Example 3]

100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained from a separate polymer of saponified polyvinyl acetate from a T-die, 12 parts by mass of glycerol, and diethanolamine laurate 0.1 The film-forming stock solution with a mass part and a volatile content of 66% by mass of water is discharged into a film form on a first drying roll (surface temperature of 90 ° C. and a peripheral speed (S ₁ ) of 13.5 m / min), and is discharged on the first drying roll. On the other hand, the entire non-contact surface of the first drying roll was partially dried while blowing hot air at 90 ° C at a wind speed of 5 m / sec.

Then, it peeled from the 1st drying roll, and made the non-contact surface of a 1st drying roll oppose a 2nd drying roll, and further dried. At this time, 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 was 1.035. Next, the front and back surfaces of the film are alternately opposed to each of the drying rollers, and further dried by the drying rollers subsequent to the third drying roller. The surface temperature of the drying roller from the second drying roller to the drying roller located immediately in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 50 ° C.

Then, the heat treatment roll (X) with a surface temperature of 104 ° C and the heat treatment roll (Y) connected to the surface temperature of 109 ° C were heat-treated, and then rolled up to obtain a long PVA film (thickness: 60 μm, width: 3 m). . Here, the heat treatment roll (Y) of the circumferential velocity (S _Y) with respect to the heat roll (X), the circumferential velocity (S _X) ratio (S _Y / S _X) was 0.997.

As for the film surface of the obtained PVA film, the above-mentioned refractive index measured by incident light from a direction inclined perpendicular to the width direction of the film was 1.530 on one side and 1.529 on the other side (A = 1.530, B = 1.529). , A + B = 3.059). When the tensile elongation of the obtained PVA film was measured, it was 435%.

[Comparative Example 1]

100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained from a separate polymer of saponified polyvinyl acetate from a T-die, 12 parts by mass of glycerol, and diethanolamine laurate 0.1 The film-forming stock solution with a mass part and a volatile content of 66% by mass of water is discharged into a film form on a first drying roll (surface temperature of 90 ° C., peripheral speed (S ₁ ) 13 m / min), and is placed on the first drying roll. Partial drying was performed while blowing hot air at 90 ° C. at a wind speed of 5 m / sec on the entire non-contact surface of the first drying roll.

Then, it peeled from the 1st drying roll, and made the non-contact surface of a 1st drying roll oppose a 2nd drying roll, and further dried. At this time, 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 was 1.050. Next, the front and back surfaces of the film are alternately opposed to each of the drying rollers, and further dried by the drying rollers subsequent to the third drying roller. The surface temperature of the drying roller from the second drying roller to the drying roller located immediately in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 60 ° C.

Thereafter, the heat treatment roll (X) with a surface temperature of 102 ° C. and the heat treatment roll (Y) connected to the surface temperature of 107 ° C. were heat-treated, and then rolled up to obtain a long PVA film (thickness 60 μm, width 3 m). . Here, the heat treatment roll (Y) of the circumferential velocity (S _Y) with respect to the heat roll (X), the circumferential velocity (S _X) ratio (S _Y / S _X) is 1.000.

For the film surface of the obtained PVA film, the above-mentioned refractive index measured by incident light from a direction inclined perpendicular to the film width direction was 1.531 on one side and 1.530 on the other side (A = 1.531, B = 1.530 , A + B = 3.061). When the tensile elongation of the obtained PVA film was measured, it was 415%.

[Comparative Example 2]

100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained from a separate polymer of saponified polyvinyl acetate from a T-die, 12 parts by mass of glycerol, and diethanolamine laurate 0.1 The film-forming stock solution with a mass part and a volatile content of 66% by mass of water is discharged into a film form on a first drying roll (surface temperature 90 ° C., peripheral speed (S ₁ ) 15.5 m / min), and the first drying roll On the other hand, the entire non-contact surface of the first drying roll was partially dried while blowing hot air at 90 ° C at a wind speed of 5 m / sec.

Then, it peeled from the 1st drying roll, and made the non-contact surface of a 1st drying roll oppose a 2nd drying roll, and further dried. At this time, 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 was 1.050. Next, the front and back surfaces of the film are alternately opposed to each of the drying rollers, and further dried by the drying rollers subsequent to the third drying roller. The surface temperature of the drying roller from the second drying roller to the drying roller located immediately in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 72 ° C.

Thereafter, the heat treatment roll (X) with a surface temperature of 108 ° C. and the heat treatment roll (Y) connected to the surface temperature of 114 ° C. were heat-treated, and then rolled up to obtain a long PVA film (thickness 60 μm, width 3 m). . Here, the heat treatment roll (Y) of the circumferential velocity (S _Y) with respect to the heat roll (X), the circumferential velocity (S _X) ratio (S _Y / S _X) of 0.998.

With respect to the film surface of the obtained PVA film, the above-mentioned refractive index measured by incident light in a direction oblique to the width direction of the film was 1.531 on one side and 1.529 on the other side (A = 1.531, B = 1.529 , A + B = 3.060). The tensile elongation of the obtained PVA film was 431%.

Claims (3)

A method for producing a polyvinyl alcohol film, which uses a film forming apparatus having a drying roller and a heat treatment roller in which rotation axes are parallel to each other, and a first drying roller on the most upstream side of the drying rollers will contain polyvinyl alcohol After the film-forming dope was discharged into a film shape and partially dried, it was further dried with a drying roller after the second drying roller, and then heat-treated with a plurality of heat-treatment rollers to produce a polyvinyl alcohol film. heat roller is positioned downstream side of most of the heat treatment rollers (Y) of the circumferential velocity (S _Y) with respect to the circumferential velocity (S _X) located in the heat treatment roll most upstream side of the (X) of the ratio (S _Y / S _X) becomes 0.993 or more and 0.997 or less. For example, the method for producing a polyvinyl alcohol film according to claim ₁ , wherein 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 Above 1.000 and below 1.040.     If the method for manufacturing a polyvinyl alcohol film according to claim 1 or 2 is to make the surface temperature of the final drying roller less than 60 ° C.