TW201627381A - 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

Polyvinyl alcohol film

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

Polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is abbreviated as "PVA"), and it is excellent in mechanical properties, transparency, oxygen barrier property, oil resistance, etc., and is conventionally used for fiber packaging materials and agricultural films (vegetables). Uses such as a film for heat preservation and vegetable growth, a gas barrier material, a filter, and a raw material film for producing a polarizing film.

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

[Previous Technical Literature] [Patent Literature]

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

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

However, the polarizing film is generally used to make the PVA film highly Extending manufacturing, there is a problem to solve the problem of cracking when extending the PVA film. However, according to the method described in Patent Document 1 or 2, the elongation cannot be sufficiently improved. Therefore, an object of the present invention is to provide an optical film such as a PVA film excellent in stretchability and a polarizing film using the same.

The inventors of the present invention have repeatedly studied in order to achieve the above object, and found that the refractive index in a specific direction of the surface of the PVA film is closely related to the extensibility of the PVA film. Further, it has been found that the refractive index is a specific PVA film, and the peripheral speed of the heat-treating roll at the time of film formation is made specific, and it can be continuously and continuously manufactured. The inventors of the present invention have further studied the present invention based on the knowledge of the above.

That is, the invention is related to the following:

[1] A PVA film in which a refractive index of each side of the PVA film is measured by incident light in a direction oblique to a width direction of the film with respect to a film surface of the PVA film, and a refractive index of one side of the PVA film is measured When A is used as A and B is used as B (where A ≧ B), A is 1.524 or more and 1.530 or less.

[2] The PVA film according to [1] above, wherein A is from 1.526 to 1.530.

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

[4] A method for producing a PVA film, which comprises using a film forming apparatus including a drying roll and a heat-treating roll in which rotating axes are parallel to each other, and a first drying roll on the most upstream side of the drying roll, which contains PVA After the film forming raw material is discharged into a film form and partially dried, the film is further dried by a drying roll after the second drying roll, and then heat-treated by a plurality of heat-treating rolls to produce a PVA film. Here, the heat-treated roll is used. 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 production method according to the above [4], wherein the ratio (S ₂ /S ₁ ) of the circumferential speed (S2) of the second drying roll to the circumferential speed (S ₁ ) of the first drying roll is 1.000 or more. Below 1.040.

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

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

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

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

[10] The production method according to [9] above, which is a method for producing a polarizing film.

The PVA film of the present invention has high tensile elongation and excellent elongation. Therefore, when the PVA film of the present invention is used on a raw material film, an optical film such as a polarizing film excellent in optical performance can be produced with good productivity. Moreover, according to the method for producing a PVA film of the present invention, the PVA film can be continuously produced continuously.

[Formation of the Invention]

Hereinafter, the present invention will be specifically described.

[PVA film]

In the PVA film of the present invention, the refractive index of each surface of the PVA film is measured by incident light in a direction oblique to the width direction of the film with respect to the film surface, and the refractive index of one side is regarded 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 likely to occur in the PVA film. Moreover, when A exceeds 1.530, there is a problem that the elongation is lowered. The present invention is not particularly limited, but the reason why A affects the elongation is considered as follows. That is, the elongation of the PVA film is higher in the refractive index of the surface than in the central portion of the thickness direction of the PVA film, and is compared with the film surface relative to the PVA film by the vertical direction. The refractive index measured by incident light in a direction in which the direction of flow (MD) of the film is inclined, and the refractive index measured by incident light in a direction oblique to the width direction (TD) of the film with respect to the film surface Higher, the fracture of the PVA film is caused by breaking the starting point of the surface portion of the film, and then the effect is due to the larger surface having a higher refractive index.

From the viewpoint of the above, A is preferably more than 1.524, more preferably 1.526 or more, more preferably more than 1.526, further more preferably 1.527 or more, more preferably more than 1.527, and further preferably less than 1.530 and more preferably 1.529 or less.

Furthermore, A and B can be used with 稜鏡 coupling devices, based on waves. The laser light having a length of 532 nm was obtained as a measured value. Here, the incident light in the direction inclined from the vertical direction toward the width direction of the film is projected on the film surface of the PVA film so that the incident light is projected in the vertical direction with respect to the film surface, and the direction becomes PVA. The incident light in the direction in which the width direction (TD) of the film is parallel (perpendicular to the longitudinal direction (MD) of the PVA film) can be obtained by the above-described 稜鏡 coupling device. A and B, specifically, can be measured by the method described later in the examples.

In the PVA film of the present invention, A+B is preferably 3.050 or more, more preferably 3.055 or more, more preferably 3.057 or more, further preferably 3.075 or less, more preferably 3.059 or less, and most 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 elongation 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 a vinyl ester, and a modified PVA obtained by graft-copolymerizing a comonomer in a main chain of PVA. A modified PVA produced by saponifying a modified polyvinyl ester copolymerized with a vinyl ester and a comonomer, and a part of a hydroxyl group of the unmodified PVA or the modified PVA is treated with an aldehyde such as formaldehyde, butyraldehyde or benzaldehyde. Cross-linked so-called polyvinyl acetal.

When the PVA forming the PVA film of the present invention is a modified PVA, the amount of modification of PVA is preferably 15 mol% or less, 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. Vinyl acetate, vinyl stearate, vinyl benzoate, and the like. B of these The enoyl esters may be used singly or in combination of two or more. Among these vinyl esters, vinyl acetate is preferred from the viewpoint of productivity.

In addition, examples of the comonomer include olefins (α-olefins) having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; and methyl acrylate. Acrylic acid, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. An ester (for example, an alkyl ester having 1 to 18 carbon atoms of acrylic acid); methacrylic acid or a salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, Methacrylic acid such as n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Esters (for example, alkyl esters having 1 to 18 carbon atoms of methacrylic acid); acrylamide; N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl decylamine, Diacetone acrylamide, acrylamide sulfonic acid or its salt, acrylamidopropyl dimethylamine or its salt, N-hydroxyl a acrylamide derivative such as acrylamide or a derivative thereof; methacrylamide; N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide sulfonic acid a methacrylamide derivative thereof, or a salt thereof, methacrylamidamine dimethylamine or a salt thereof, N-methylol methacrylamide or a derivative thereof; N-vinylformamide, N - N-vinyl decylamine such as ethylene acetamide or N-vinyl pyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and different Vinyl ethers such as butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.; acrylonitrile, methacrylonitrile, etc. Nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated two of maleic acid and itaconic acid a derivative of a carboxylic acid, a salt thereof or an ester thereof; an ethylene mercapto compound such as ethylene trimethoxyoxane; an isopropenyl acetate; an unsaturated sulfonic acid or a derivative thereof. Among these, an α-olefin is preferable, and ethylene is particularly preferable.

From the viewpoint of the polarizing performance and durability of the obtained polarizing film, the PVA of the PVA film of the present invention has an average polymerization degree of preferably 1,500 or more, more preferably 1700 or more, and particularly preferably 2,000 or more. On the other hand, from the viewpoints of easiness of production and elongation of a homogeneous PVA film, the upper limit of the average degree of polymerization of PVA is preferably 8,000 or less, particularly preferably 6,000 or less.

Here, the "average degree of polymerization" of the PVA in the present specification means the average degree of polymerization measured in accordance with JIS K6726-1994, and can be obtained by re-saponifying PVA and purifying the ultimate viscosity measured in water at 30 ° C.

From the viewpoint of water resistance of the polarizing film produced by 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 be deteriorated. In addition, the degree of saponification of the PVA of the present specification means a total number of moles of a structural unit (typically a vinyl ester unit) and a vinyl alcohol unit which PVA has with respect to conversion to a vinyl alcohol unit by saponification, the ethylene The proportion of the molar number of the alcohol unit (% by mole). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The PVA film of the present invention preferably comprises a plasticizer. By package Contains a plasticizer to further enhance the extensibility. The plasticizer may be blended at the time of preparation of the film forming stock solution for forming the film PVA film, and as described above, the dissolution or melting of the PVA into the liquid medium may be promoted, and the step passability in film production may be improved.

As the plasticizer, a polyol is preferably used. Examples of the polyhydric alcohol include ethylene glycol, glycerin, diglycerin, 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 viewpoint that the effect of improving the elongation is good.

The content of the plasticizer is preferably 0 parts by mass or more and 30 parts by mass or less, more preferably 3 parts by mass or more and 25 parts by mass or less, more preferably 5 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the PVA. According to the content of the plasticizer 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 at the time of preparation of the film forming stock solution for film-forming PVA film, and as described above, the peeling property of the drying roll from the production of the PVA film can be improved.

The kind 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 dodecyl benzenesulfonate.

In addition, examples of the nonionic surfactant include alkyl ethers such as polyether oleyl ether and polyoxyethylene octyl phenyl ether. Type, alkoxylate type such as polyoxyethylene laurate, alkylamine type such as polyoxyethylene laurylamine ether, alkyl guanamine type such as polyoxyethylene laurate decylamine, polyoxyethylene polyoxypropylene ether, etc. Examples of the allyl phenyl ether type such as a polypropylene glycol ether type, a lauric acid diethanol amide, an oleic acid diethanol amide, or a polyoxyalkylene phenyl ether. The surfactant may be used singly or in combination of two or more.

The content of the surfactant is preferably 0.01 parts by mass or more and 1 part by mass or less based on 100 parts by mass of the 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 at least the above lower limit, film formability or peelability can be improved. On the other hand, if the content of the surfactant is less than or equal to the above upper limit, the rationality of the obtained PVA film can be improved.

The PVA film of the present invention may contain other components other than the above PVA, a plasticizer, and a surfactant, for example, a stabilizer (antioxidant, ultraviolet absorber, heat stabilizer, etc.), a compatibilizing agent, and an anti-caking agent. , 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, for example, 100 μm or less, or even 80 μm or less. Further, the thickness may be set to 10 μm or more, or even 20 μm or more, and may be a thickness exceeding 50 μm.

The width of the PVA film is not particularly limited. However, in recent years, liquid crystal televisions or monitors have been developed to have a large screen. Therefore, in order to be effective for use, the width is preferably 2 m or more, more preferably 3 m or more, and particularly preferably 4 m or more. Moreover, when manufacturing a polarizing film industrially, the width of the film becomes If it is wide, uniform uniaxial stretching becomes difficult, and therefore the width of the PVA film is preferably 8 m or less.

The shape of the PVA film is not particularly limited, but a long-length film is preferable from the viewpoint that a more uniform PVA film can be continuously produced and a polarizing film can be used in the case of using it. The length of the long film (the length in the flow direction) is not particularly limited, and may be appropriately set depending on the application, and the like, and may be, for example, in the range of 5 m or more and 20,000 m or less.

The PVA film of the present invention preferably has a mass swelling degree of 150% or more and 250% or less, more preferably 160% or more and 240% or less, and particularly preferably 170% or more and 230% or less. The elongation can be further improved by setting the mass swelling degree to be equal to or higher than the above lower limit. On the other hand, when the mass swelling degree is equal to or less than the above upper limit, the step passability at the time of stretching can be improved, and the durability of the obtained polarizing film can be improved.

In addition, the mass swell degree referred to in the present specification means a mass obtained by immersing a PVA film in distilled water at 30 ° C for 30 minutes, and dividing the mass of the immersed PVA film at 105 ° C for 16 hours. The percentage of the value. The degree of swelling of the PVA film can be lowered by enhancing the conditions of the heat treatment.

[Method of Manufacturing PVA Film]

The method for producing the PVA film of the present invention is not particularly limited, but the PVA film of the present invention described above can be smoothly and continuously produced according to the production method of the present invention described below.

That is, the method of the present invention for producing a PVA film is a manufacturing method using a drying roll having a rotating shaft parallel to each other (from the most upstream side toward the downstream side, sequentially referred to as a first drying roll, a second drying roll, etc. The film forming apparatus of the heat treatment roll is formed on the first drying roll located on the most upstream side of the drying roll, and the film forming raw material containing PVA is discharged into a film form and partially dried, and then, second. The drying roller after the drying roller is further dried, and then heat-treated with a plurality of heat-treating rollers to produce a PVA film, where the circumferential speed (S _Y ) of the heat-treating roller (Y) on the most downstream side of the heat-treating roller 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 having a drying roll and a heat-treating roll having mutually parallel rotating axes is used, and a first drying roll on the most upstream side of the drying roll is used, and PVA is contained. After the film forming raw material is discharged into a film form and partially dried, the film is further dried by a drying roll after the second drying roll, and then heat-treated by a plurality of heat treatment rolls to produce a PVA film. In the film forming apparatus, the number of drying rolls 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 are preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel or the like, in particular, the surface of the roll is preferably formed of a metal material which is not easily corroded and has a specular gloss. Further, in order to improve the durability of the drying roll and/or the heat-treating roll, a single layer or a roll of two or more nickel layers, a chromium layer, a nickel/chromium alloy layer or the like is used as a drying roll and/or a heat-treating roll. good.

In addition to the drying roll and the heat-treating roll, the above-mentioned film forming apparatus may further have a hot air oven type hot air drying device, Hot air furnace type heat treatment device, humidity control device, and the like.

Regarding the heating direction when the film is dried by the first drying roll to the final drying roll, the film surface in contact with the first drying roll is formed in any portion of the film from the viewpoint of more uniform drying of the film ( Hereinafter, it may be referred to as "the first drying roll contact surface"), and the film surface not in contact with the first drying roll (hereinafter referred to as "the first drying roll non-contact surface") and the first drying roll to the final. It is preferred that each of the drying rolls until the drying rolls are alternately dried.

When the film forming stock solution containing PVA is discharged into a film shape on the first drying roll of the film forming apparatus, for example, a known film shape such as a T-slot die, a hopper plate, an I-die, or a lip-mouth coating die is used. In the discharge device (membrane casting device), the film forming stock solution containing PVA may be discharged (cast) into a film shape on the first drying roll.

The film forming stock solution containing PVA can be prepared by mixing PVA with a liquid medium to form a solution, and melting a PVA pellet containing a liquid medium or the like to obtain a melt or the like. The dissolution of the PVA by the PVA or the melting of the PVA pellets including the liquid medium can be carried out using a stirring type mixing device, a melt extruder or the like. Examples of the liquid medium used at this time include water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, and diethylenetriamine. The liquid medium may be used singly or in combination of two or more. Among these, water, dimethyl hydrazine, or a mixture of the two is preferably used, and water is particularly suitable.

In the film forming solution, the plasticizer, surfactant, and other components are blended in the above amount as described above in the description of the PVA film. One type or two or more types are preferable.

The volatilization ratio of the film forming stock solution used for the production of the PVA film is preferably 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 75% by mass or less. Depending on the volatility of the film forming solution, the viscosity of the film forming solution can be kept low, and the filtration or defoaming can be easily performed, and the film itself can be easily formed. On the other hand, depending on the volatility of the film forming stock solution being equal to or lower than the above upper limit, the viscosity of the film forming stock 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 roll is not particularly limited. From the viewpoint of uniformity of drying of the film, productivity, and the like, it is preferably 80° C. or higher and 99° C. or lower, more preferably 85° C. or higher and 99° C. or lower, and 90° C. or higher and 98° C. or lower. Very good. According to the surface temperature of the first drying roll being 99 ° C or lower, it is possible to more effectively prevent the film forming stock solution from being foamed on the first drying roll. On the other hand, according to the surface temperature of the first drying roll being 80 ° C or more, the peeling property from the first drying roll can be improved.

The drying on the first drying roll which is formed into a film-form film forming solution can be performed only by heating from the first drying roll, but from the viewpoint of uniformity of drying, drying speed, etc., the first drying roll is also used. At the same time as heating, hot air is blown to the non-contact surface of the first drying roll, and heat is applied from both surfaces of the film to perform drying.

When hot air is blown on the non-contact surface of the first drying roll of the film on the first drying roll, the blowing speed is sprayed with respect to the entire area of the non-contact surface of the first drying roll from the viewpoint of further enhancing the elongation of the PVA film obtained. The hot air of 1~10m/sec is better, the hot air of 2~8m/sec is better, and the hot air of 3~8m/sec is excellent. Spray on the non-contact surface of the first drying roller When the wind speed of the hot air blows is too small, condensation of water vapor or the like occurs during drying on the first drying roll, and water droplets are dropped on the film, and the finally obtained PVA film may easily cause defects. On the other hand, when the wind speed of the hot air blown on the non-contact surface of the first drying roll is too large, the PVA film finally obtained has a thickness unevenness, and the problem of occurrence of uneven dyeing tends to occur as described above.

From the viewpoints of drying efficiency, uniformity of drying, and the like, the temperature of the hot air blown 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. Excellent below 95 °C. Further, it is preferable that the dew point of the hot air blown on the non-contact surface of the first drying roll of the film is 10 ° C or more and 15 ° C or less.

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

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

The circumferential speed (S ₁ ) of the first drying roll 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, from the viewpoints of uniformity of drying, drying speed, productivity of a PVA film, and the like. Good, 15m / min or more and 40m / min or less. When the peripheral speed (S ₁ ) of the first drying roll is at least the above lower limit, the value of the refractive index can be lowered. On the other hand, when the peripheral speed (S ₁ ) of the first drying roll is equal to or less than the above upper limit, the uniformity of the thickness of the obtained PVA film can be improved.

The film forming stock solution which is discharged into the film on the first drying roll is dried on the first drying roll, and the volatilization ratio of the film (volatility of the film at the time of peeling from the first drying roll) is preferably 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 is possible to peel off from the first drying roll.

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

The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is preferably 1.000 or more and 1.040 or less. According to the ratio (S ₂ /S ₁ ) within the above range, the PVA film of the present invention can be more smoothly produced. In addition, 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 be large. From the viewpoint of the above, the ratio (S _Y /S _X ) is preferably 1.020 or more, more preferably 1.030 or more, and further preferably 1.038 or less.

The PVA film dried by the second drying roll is peeled off from the second drying roll, and the number of drying rolls provided in the film forming apparatus is used, etc. The plurality of drying rolls of the third drying roll, the fourth drying roll, the fifth drying roll, and the like may be sequentially dried.

The surface temperature of each of the drying rolls from the second drying roll to the final drying roll is preferably 40° C. or more, more preferably 45° C. or more, more preferably 50° C. or more, further preferably less than 100° C., and more preferably 98° C. or less. It is particularly preferred at 96 ° C or less, and may be less than 90 ° C.

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

The heat treatment was performed using a plurality of heat treatment rolls with respect to the film dried by the drying roll 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) on the most downstream side among the plurality of heat treatment rolls is made relative to the heat treatment roll located on the most upstream side ( The ratio (S _Y /S X ) of the circumferential speed (S _X ) of _X ) is 0.993 or more and 0.997 or less. When the ratio (S _Y /S _X ) is outside the above range, it becomes difficult to obtain the PVA film of the present invention. From the viewpoint of the above, the ratio (S _Y /S _X ) is preferably 0.994 or more, more preferably 0.995 or more, and further preferably 0.996 or less.

The surface temperature of the heat treatment roll is preferably 100 ° C or more, more preferably 140 ° C or less, more preferably 130 ° C or less, and particularly preferably 120 ° C or less. Further, in the method of the present invention for producing a PVA film, a roll having a surface temperature of 100 ° C or higher is used as a heat treatment roll, and a roll having a surface temperature of less than 100 ° C is used as a drying roll.

In the method of the present invention for producing a PVA film, the heat treatment roll may have only two heat treatment rolls (X) and heat treatment rolls (Y). Further, there may be further heat treatment rolls other than the heat treatment rolls between the heat treatment rolls.

The heat treatment time when the heat treatment is performed by the heat treatment roll is not particularly limited, but from the viewpoint of more efficiently producing the PVA film of the present invention, it is preferably 3 seconds or more, more preferably 4 seconds or more, more preferably 5 seconds or more, and further 120 Preferably, the second or lower is better than 90 seconds, and the best is less than 60 seconds.

The film which is subjected to the heat treatment as described above may be further subjected to a humidity control treatment, a cut of both end portions (ears) of the film, and the like, and may be wound into a roll shape at a predetermined length to obtain the PVA of the present invention. film.

The volatile content of the PVA film finally obtained by the above-described series of processes is preferably in the range of 1% by mass or more and 5% by mass or less, and more preferably in the range of 2% by mass or more and 4% by mass or less.

[Use of PVA film]

The use of the PVA film of the present invention is not particularly limited. However, the PVA film of the present invention has a high tensile elongation and excellent elongation, and is used as a raw material film for producing an optical film such as a polarizing film or a retardation film. Use is better. The optical film as described above can be produced, for example, by performing a treatment such as uniaxial stretching using the PVA film of the present invention.

The method of producing the polarizing film by using the PVA film of the present invention as a raw material film is not particularly limited, and a method from any of the conventional methods may be employed. As the method as described above, for example, a method of performing dyeing and uniaxial stretching on a PVA film or uniaxial stretching on a dye-containing PVA film can be mentioned. More specific methods for producing a polarizing film include the implementation of the PVA film of the present invention. Swelling, dyeing, uniaxial stretching, and further methods such as fixing treatment, drying, and the like are performed as needed. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixation treatment is not particularly limited, and one or two or more treatments may be simultaneously performed. For example, dyeing may be performed before uniaxial stretching. Dyeing simultaneously with uniaxial stretching can also be done after uniaxial stretching. Further, one or two or more of the respective treatments may be performed twice or more.

The swelling can be carried out by immersing the PVA film in water. The temperature of the water immersed in water is preferably 20° C. or higher and 40° C. or lower, more preferably 22° C. or higher and 38° C. or lower, and particularly preferably 25° C. or higher and 35° C. or lower. In addition, the time of immersion in water is preferably in the range of 0.1 minute or more and 5 minutes or less, and more preferably 0.5 minute or more and 3 minutes or less. Further, the water immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

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

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

Uniaxial stretching can be carried out by any wet stretching method or dry heat stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution containing boric acid, or in a dye bath or in a fixed treatment bath to be described later. Further, in the case of the dry stretching method, the PVA film after water absorption can be used in the air. Among these, the wet stretching method is preferred, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of the boric acid in the boric acid aqueous solution is preferably in the range of 0.5% by mass or more and 6.0% by mass or less, and more preferably in the range of 1.0% by mass or more and 5.0% by mass or less, and more preferably in the range of 1.5% by mass or more and 4.0% by mass or less. good. Further, the aqueous boric acid solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01% by mass or more and 10% by mass or less. Uniaxial stretching is preferred in the flow direction of the PVA film.

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

The stretching ratio of the uniaxial stretching (the total stretching ratio when the uniaxial stretching is performed in multiple stages) is preferably extended as far as possible from the viewpoint of the polarizing performance until the film is about to be broken, specifically, more than 4 times, preferably 5 times. The above is better, 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film does not break, and is preferably 8 times or less in order to perform uniform stretching.

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

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

Next, it is preferred to dry the film which has been subjected to uniaxial stretching, or uniaxial stretching and fixing treatment. The drying temperature is preferably 30 ° C or more and 150 ° C or less, and particularly preferably 50 ° C or more and 140 ° C or less. When the drying temperature is too low, the dimensional stability of the obtained polarizing film is likely to be lowered. On the other hand, when it is too high, the polarizing performance due to decomposition of the dye or the like is likely to be lowered.

A protective film which is optically transparent and has mechanical strength can be bonded to the double-sided or single-sided surface of the polarizing film obtained as described above as a polarizing plate. As the protective film in this case, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, an acetic acid/cellulose butyrate (CAB) film, an acrylic film, a polyester film, and a polypropylene are used. Film, drop An olefin resin film or the like. Moreover, as an adhesive agent for bonding a protective film, a PVA-based adhesive, an acrylate-based adhesive, a urethane-based adhesive, etc. are generally used, and among them, a PVA-based adhesive is particularly preferably used.

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

[Examples]

Hereinafter, the present invention will be described in further detail by way of examples, but the invention is not limited to the examples. In the following, the method for measuring the refractive index in the flow direction of the surface of the PVA film used in the following examples and comparative examples and the method for measuring the tensile elongation of the PVA film are shown below.

[PVA film refractive index]

The PVA film obtained in the following examples or comparative examples was subjected to humidity conditioning for 7 days in an environment of 23 ° C and 50% RH, and then a 稜鏡 coupling device (Model 2010/M) manufactured by Metricon Co., Ltd. was used under the same environment. The laser light having a wavelength of 532 nm is used as the incident light by the light of the 稜鏡 coupling device as the film surface of the PVA film, which is inclined in the direction perpendicular to the width direction of the film, and is used as the incident light. On one side of the film, the refractive index of the face (based on the refractive index of the surface) is obtained from the reflected light. The other faces of the PVA film were also carried out in the same manner to obtain a refractive index. The values of the two obtained refractive indices are set to A and B, respectively, so as to satisfy the relationship of A ≧ B.

[Drawing elongation of PVA film]

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

[Example 1]

From the T-die, PVA (saponification degree: 99.9 mol%, degree of polymerization 2400) obtained by saponifying a separate polymer of polyvinyl acetate, 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamine 0.1 The film forming stock solution having a mass fraction and a water content of 66% by mass of water was discharged into a film shape on the first drying roll (surface temperature: 90° C., peripheral speed (S ₁ ): 13.5 m/min), and was applied to the first drying roll. In the upper part, the hot air of 90 ° C was blown at the wind speed of 5 m / sec on the entire non-contact surface of the first drying roll, and partial drying was performed.

Then, the first drying roll is peeled off, and the first drying roll non-contact surface is opposed to the second drying roll to be further dried. At this time, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll was 1.035. Next, the front and back surfaces of the film were alternately opposed to the respective drying rolls, and further dried by the drying rolls after the third drying rolls. Further, the surface temperature of the drying roller from the second drying roll to the drying roll directly in front of the final drying roll was about 85 ° C, and the surface temperature of the final drying roll was 55 ° C.

Thereafter, the heat treatment roll (X) having a surface temperature of 104 ° C and a heat treatment roll (Y) having a surface temperature of 109 ° C were heat-treated, and then wound 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.

With respect to the film surface of the obtained PVA film, the refractive index measured by incident light in a direction oblique to the width direction of the film in the vertical direction was 1.529 on one side and 1.529 on the other side (A = B = 1.529, A). +B=3.058). Further, when the tensile elongation of the obtained PVA film was measured, it was 438%.

[Embodiment 2]

From the T-die, PVA (saponification degree: 99.9 mol%, degree of polymerization 2400) obtained by saponifying a separate polymer of polyvinyl acetate, 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamine 0.1 The film forming stock solution having a mass fraction and a water content of 66% by mass of water was discharged into a film shape on the first drying roll (surface temperature: 90° C., peripheral speed (S ₁ ): 13.5 m/min), and was applied to the first drying roll. In the upper part, the hot air of 90 ° C was blown at the wind speed of 5 m / sec on the entire non-contact surface of the first drying roll, and partial drying was performed.

Then, the first drying roll is peeled off, and the first drying roll non-contact surface is opposed to the second drying roll to be further dried. At this time, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll was 1.035. Next, the front and back surfaces of the film were alternately opposed to the respective drying rolls, and further dried by the drying rolls after the third drying rolls. Further, the surface temperature of the drying roller from the second drying roller to the drying roller directly in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 50 °C.

Thereafter, the heat treatment roll (X) having a surface temperature of 101 ° C was heat-treated with a heat treatment roll (Y) having a surface temperature of 107 ° C, and then wound 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.

With respect to the film surface of the obtained PVA film, the refractive index measured by incident light in a direction oblique to the width direction of the film in the vertical direction was 1.530 on one side and 1.528 on the other side (A = 1.530, B = 1.528). , A+B=3.058). Further, when the tensile elongation of the obtained PVA film was measured, it was 437%.

[Example 3]

From the T-die, PVA (saponification degree: 99.9 mol%, degree of polymerization 2400) obtained by saponifying a separate polymer of polyvinyl acetate, 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamine 0.1 The film forming stock solution having a mass fraction and a water content of 66% by mass of water was discharged into a film shape on the first drying roll (surface temperature: 90° C., peripheral speed (S ₁ ): 13.5 m/min), and was applied to the first drying roll. In the upper part, the hot air of 90 ° C was blown at the wind speed of 5 m / sec on the entire non-contact surface of the first drying roll, and partial drying was performed.

Then, the first drying roll is peeled off, and the first drying roll non-contact surface is opposed to the second drying roll to be further dried. At this time, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll was 1.035. Next, the front and back surfaces of the film were alternately opposed to the respective drying rolls, and further dried by the drying rolls after the third drying rolls. Further, the surface temperature of the drying roller from the second drying roller to the drying roller directly in front of the final drying roller was about 85 ° C, and the surface temperature of the final drying roller was 50 °C.

Thereafter, the heat treatment roll (X) having a surface temperature of 104 ° C and a heat treatment roll (Y) having a surface temperature of 109 ° C were heat-treated, and then wound 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.

With respect to the film surface of the obtained PVA film, the refractive index measured by incident light in a direction oblique to the width direction of the film in the vertical direction was 1.530 on one side and 1.529 on the other side (A = 1.530, B = 1.529). , A+B=3.059). Further, when the tensile elongation of the obtained PVA film was measured, it was 435%.

[Comparative Example 1]

From the T-die, PVA (saponification degree: 99.9 mol%, degree of polymerization 2400) obtained by saponifying a separate polymer of polyvinyl acetate, 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamine 0.1 The film-forming stock solution having a mass fraction and a water content of 66% by mass of water was discharged into a film shape on the first drying roll (surface temperature: 90 ° C, peripheral speed (S ₁ ): 13 m/min), and was placed on the first drying roll. Partial drying was performed while blowing hot air of 90 ° C to the entire non-contact surface of the first drying roll at a wind speed of 5 m/sec.

Then, the first drying roll is peeled off, and the first drying roll non-contact surface is opposed to the second drying roll to be further dried. At this time, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll was 1.050. Next, the front and back surfaces of the film were alternately opposed to the respective drying rolls, and further dried by the drying rolls after the third drying rolls. Further, the surface temperature of the drying roller from the second drying roller to the drying roller directly 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) having a surface temperature of 102 ° C was heat-treated with a heat treatment roll (Y) having a surface temperature of 107 ° C, and then wound 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.

With respect to the film surface of the obtained PVA film, the refractive index measured by incident light in a direction oblique to the width direction of the film in the vertical direction was 1.531 on one side and 1.530 on the other side (A = 1.531, B = 1.530). , A+B=3.061). Further, when the tensile elongation of the obtained PVA film was measured, it was 415%.

[Comparative Example 2]

From the T-die, PVA (saponification degree: 99.9 mol%, degree of polymerization 2400) obtained by saponifying a separate polymer of polyvinyl acetate, 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamine 0.1 The film forming stock solution having a mass fraction and a water content of 66% by mass of water was discharged into a film shape on the first drying roll (surface temperature: 90° C., peripheral speed (S ₁ ): 15.5 m/min), and was applied to the first drying roll. In the upper part, the hot air of 90 ° C was blown at the wind speed of 5 m / sec on the entire non-contact surface of the first drying roll, and partial drying was performed.

Then, the first drying roll is peeled off, and the first drying roll non-contact surface is opposed to the second drying roll to be further dried. At this time, the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll was 1.050. Next, the front and back surfaces of the film were alternately opposed to the respective drying rolls, and further dried by the drying rolls after the third drying rolls. Further, the surface temperature of the drying roller from the second drying roller to the drying roller directly 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) having a surface temperature of 108 ° C was heat-treated with a heat treatment roll (Y) having a surface temperature of 114 ° C, and then wound 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 refractive index measured by incident light in a direction oblique to the width direction of the film in the vertical direction was 1.531 on one side and 1.529 on the other side (A = 1.531, B = 1.529). , A+B=3.060). Further, when the tensile elongation of the obtained PVA film was measured, it was 431%.

Claims (10)

A polyvinyl alcohol film for measuring the refractive index of each surface of the polyvinyl alcohol film by using incident light in a direction oblique to the width direction of the film with respect to the film surface of the polyvinyl alcohol film. When the refractive index is taken as A and the refractive index of the other side is taken as B (where A ≧ B), A is 1.524 or more and 1.530 or less. The polyvinyl alcohol film of claim 1, wherein A is from 1.526 to 1.530. The polyvinyl alcohol film according to claim 1 or 2, wherein A+B is from 3.050 to 3.060. A method for producing a polyvinyl alcohol film, which comprises using a drying roll having a rotating shaft parallel to each other and a heat-forming roll, and a first drying roll on the most upstream side of the drying roll, comprising polyvinyl alcohol After the film-forming raw material is discharged into a film form and partially dried, the film is further dried by a drying roll after the second drying roll, and then heat-treated by a plurality of heat-treating rolls 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. The method for producing a polyvinyl alcohol film according to claim 4, wherein the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is 1.000 or more and 1.040 or less. A method of producing a polyvinyl alcohol film according to claim 4 or 5, wherein the surface temperature of the final drying roll is less than 60 °C. An optical film which is obtained by the polyethylene according to any one of claims 1 to 3 Enol film production. The optical film of claim 7, which is a polarizing film. A method of producing an optical film, which comprises the step of uniaxially stretching using a polyvinyl alcohol film according to any one of claims 1 to 3. The manufacturing method of claim 9, which is a method of producing a polarizing film.