KR20170095181A - Polyvinyl alcohol film - Google Patents

Abstract

The present invention is characterized in that when the refractive indexes A and B on the respective surfaces of the PVA film are measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film surface A is from 1.524 to 1.530; And a film forming apparatus comprising a drying roll and a heat treatment roll whose rotation axes are parallel to each other are used. The film forming stock solution containing PVA is discharged onto the first drying roll in a film form, partially dried, The PVA film is manufactured by further drying and then heat treated with a plurality of heat treatment rolls to produce a PVA film. The heat treatment roll _X is placed on the most downstream side with respect to the peripheral velocity S _X of the heat treatment roll X located on the most upstream side of the heat treatment roll, And the ratio (S _Y / S _X ) of the peripheral velocity (S _Y ) of the roll (Y) is set to 0.993 or more and 0.997 or less.

Description

[0001] POLYVINYL ALCOHOL FILM [0002]

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

The polyvinyl alcohol film (hereinafter, sometimes abbreviated as " PVA ") is excellent in mechanical properties, transparency, oxygen barrier property, oil resistance and the like, Heat-insulating films, films for growing vegetables, etc.), gas barrier materials, filters, and fabric films for producing polarizing films.

There has been known a method in which the refractive index in each of both the center and the thickness direction of the PVA film is specified for the purpose of in-plane uniformity of the polarizing film (see Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2006-219638 Japanese Patent Application Laid-Open No. 2006-305923

However, since the polarizing film is generally produced by highly stretching the PVA film, it is a problem to solve the cutting trouble when stretching the PVA film. However, according to the method described in Patent Document 1 or 2, improvement in stretchability was not sufficient. Therefore, it is an object of the present invention to provide a PVA film excellent in stretchability and an optical film such as a polarizing film using the PVA film.

The inventors of the present invention have found that the refractive index in a specific direction on the surface of the PVA film and the stretching property of the PVA film are closely related to each other in order to achieve the above object. Further, it has been found that the PVA film in which the refractive index is specified can be smoothly and continuously produced by specifying the peripheral speed of the heat treatment roll at the time of film formation (film formation). Based on these findings, the present inventors have repeatedly studied to complete the present invention.

That is,

[1] The refractive index of each face of the PVA film is measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film face of the PVA film, and the refractive index on one face is taken as A And B is the refractive index on the other surface (where A > = B), A is 1.524 or more and 1.530 or less,

[2] The PVA film of the above-mentioned [1], wherein the A is 1.526 or more and 1.530 or less,

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

[4] A film-forming apparatus having a drying roll and a heat-treating roll whose rotation axes are parallel to each other is used, and a film-forming stock solution containing PVA is discharged onto a first drying roll located at the most upstream side among the drying rolls, And then further dried with a drying roll after the second drying roll followed by heat treatment with a plurality of heat treatment rolls to produce a PVA film, wherein the peripheral speed of the heat treatment roll X located on the most upstream side of the heat treatment roll peripheral speed of the heat treatment roll (Y) which is located at the most downstream side with respect to the (S _{X) (Y} S) ratio _(Y S / _X S) of 0.993 or more, 0.997 or less for a method of producing a PVA film,

[5] The method according to [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,

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

[7] An optical film produced from the PVA film of any one of [1] to [3]

[8] The optical film of [7], which is a polarizing film,

[9] A process for producing an optical film, comprising a step of uniaxially stretching using the PVA film of any one of [1] to [3]

[10] The production method of the above [9], which is a production method of a polarizing film,

.

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

Hereinafter, the present invention will be described in detail.

[PVA film]

In the PVA film of the present invention, the refractive index on each surface of the PVA film is measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film surface, and the refractive index on one surface is A And B is the refractive index on the other surface (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 easily occur in the PVA film. If A exceeds 1.530, there is a problem that the stretchability is lowered. The present invention is not limited at all, but the following can be considered as the reason why A affects the stretchability. That is, the stretching property of the PVA film is more related to the refractive index of the surface than the refractive index of the center portion of the PVA film in the thickness direction, and is more preferably in a direction inclined from the direction perpendicular to the film surface of the PVA film to the film flow direction MD The refractive index measured by the incident light in a direction inclined from the direction perpendicular to the film surface to the film surface in the width direction TD is more relevant than the refractive index measured by the incident light so that the breakage of the PVA film can be prevented , And this influence can be considered to be due to the fact that the higher refractive index side is larger.

In view of the above, A is preferably more than 1.524, more preferably 1.526 or more, more preferably more than 1.526, even more preferably 1.527 or more, most preferably more than 1.527, It is preferably less than 1.530, more preferably 1.529 or less.

Further, A and B can be obtained as measurement values based on laser light having a wavelength of 532 nm using a prism coupler apparatus. Here, the incident light in the direction inclined in the width direction of the film from the direction perpendicular to the film surface of the PVA film means that when the incident light is projected in the direction perpendicular to the film surface, (Perpendicular to the longitudinal direction MD of the PVA film), and can be obtained by a prism in the prism coupler device. Specifically, A and B can be measured by the method described later in Examples.

In the PVA film of the present invention, A + B is preferably 3.050 or more, more preferably 3.055 or more, further preferably 3.057 or more, further preferably 3.060 or less, more preferably 3.059 or less, and further preferably 3.058 or less. When A + B is equal to or more than the lower limit, generation of wrinkles of the PVA film can be suppressed more effectively. On the other hand, when A + B is less than or equal to the upper limit, the stretchability is further improved.

Examples of the PVA for forming the PVA film of the present invention include PVA obtained by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester, modified PVA obtained by graft copolymerizing a comonomer with a main chain of the PVA, a vinyl ester and a comonomer Modified polyvinyl acetal produced by saponifying a modified polyvinyl ester copolymerized with an aldehyde such as formaldehyde, benzaldehyde or the like, and a polyvinyl acetal obtained by crosslinking a part of the hydroxyl groups of the unmodified PVA or modified PVA with formaldehyde, benzaldehyde or the like.

When the PVA forming the PVA film of the present invention is a modified PVA, the amount of modification in the 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, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate and vinyl benzoate have. These vinyl esters can be used singly or in combination of two or more kinds. Of these vinyl esters, vinyl acetate is preferable from the viewpoint of productivity.

Examples of the comonomer include olefins having 2 to 30 carbon atoms (e.g.,? -Olefins, etc.) such as ethylene, propylene, 1-butene and isobutene; Acrylic acid or a salt thereof; Acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and octadecyl acrylate For example, alkyl esters of 1 to 18 carbon atoms in acrylic acid); Methacrylic acid or a salt thereof; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2- Methacrylic acid esters such as ethylhexyl, octadecyl methacrylate and the like (for example, alkyl esters having 1 to 18 carbon atoms in methacrylic acid); Acrylamide; N, N-dimethylacrylamide, diacetone acrylamide, acrylamidepropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, N-methylolacrylamide or An acrylamide derivative such as a derivative; Methacrylamide; Methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide propanesulfonic acid or salts thereof, methacrylamidopropyldimethylamine or salts thereof, N-methylolmethacrylamide or derivatives thereof; N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide and N-vinyl pyrrolidone; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether Ethers; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Unsaturated dicarboxylic acids such as maleic acid and itaconic acid, and salts and esters thereof; Vinylsilyl compounds such as vinyltrimethoxysilane; Isopropenyl acetate; Unsaturated sulfonic acid or a derivative thereof. Of these,? -Olefins are preferable, and ethylene is particularly preferable.

The average degree of polymerization of the PVA for forming the PVA film of the present invention is preferably 1,500 or more, more preferably 1,700 or more, and still more preferably 2,000 or more, from the viewpoint of the polarizing performance and durability of the resulting polarizing film. On the other hand, the upper limit of the average degree of polymerization of PVA is preferably 8,000 or less, more preferably 6,000 or less, from the viewpoints of ease of production and stretchability of the homogeneous PVA film.

Here, the "average degree of polymerization" of PVA in the present specification means the average degree of polymerization measured in accordance with JIS K6726-1994. The degree of polymerization is determined from the intrinsic viscosity measured in water at 30 ° C after saponification and purification of PVA.

The degree of saponification of the PVA is preferably 98.0 mol% or more, more preferably 98.5 mol% or more, and further preferably 99.0 mol% or more from the viewpoint of the water resistance of the polarizing film produced using the obtained PVA film. When the saponification degree is less than 98.0 mol%, the water resistance of the resultant polarizing film tends to deteriorate. The saponification degree of PVA in the present specification means the degree of saponification of the PVA with respect to the total mole number of a structural unit (typically a vinyl ester unit) of PVA that can be converted into a vinyl alcohol unit by saponification and a vinyl alcohol unit, (Mole%) occupied by the number of moles. The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The PVA film of the present invention preferably contains a plasticizer. The plasticity is further improved by containing the plasticizer. The plasticizer may be added at the time of preparation of the film forming solution for forming the PVA film. In this case, dissolution or melting of the PVA into the liquid medium is promoted, and the process passability at the time of film production is improved.

As the plasticizer, a polyhydric alcohol is preferably used. Examples of the polyhydric alcohol include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. The plasticizer may be used alone or in combination of two or more. Of these, glycerin is preferable because it is excellent in the effect of improving the stretchability.

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, and particularly preferably 5 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of PVA. When the content of the plasticizer is less than or equal to the upper limit, handling properties of the obtained PVA film are improved.

The PVA film of the present invention preferably contains a surfactant. The handling property of the PVA film is improved by containing the surfactant. The surfactant may be added at the time of preparation of the film forming stock solution for forming the PVA film. In this case, the releasability from the drying roll at the time of producing the PVA film is 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 carboxylic acid type such as potassium laurate, sulfuric acid ester type such as octylsulfate, and sulfonic acid type such as dodecylbenzenesulfonate.

Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether and the like, alkylphenyl ether types such as polyoxyethylene octylphenyl ether and the like, alkyl ester types such as polyoxyethylene laurate, poly Alkylamines such as oxyethylene lauryl amino ether, alkyl amides such as polyoxyethylene lauric acid amide, polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether, lauric acid diethanolamide, oleic acid diethanolamide , And allylphenyl ether types such as polyoxyalkylene allylphenyl ether. One type of surfactant may be used alone, or two or more types may be used in combination.

The content of the surfactant is preferably 0.01 parts by mass or more and 1 part by mass or less, 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, based on 100 parts by mass of PVA. When the content of the surfactant is lower than the lower limit described above, film formability and peelability are improved. On the other hand, when the content of the surfactant is lower than or equal to the upper limit, the handling property of the obtained PVA film is improved.

The PVA film of the present invention may further contain components other than the PVA, the plasticizer and the surfactant such as a stabilizer (an antioxidant, an ultraviolet absorber, a heat stabilizer, etc.), a compatibilizer, an antiblocking agent, a flame retardant, an antistatic agent, , Dispersing agents, fluidizing agents, antibacterial agents, and the like. These other components may be used singly or in combination of two or more.

The thickness of the PVA film is not particularly limited and may be, for example, 100 占 퐉 or less, and further, 80 占 퐉 or less. The thickness may be 10 占 퐉 or more, more preferably 20 占 퐉 or more, or more than 50 占 퐉.

Although the width of the PVA film is not particularly limited, since the liquid crystal television or monitor has been enlarged in recent years, the width of the PVA film is preferably 2 m or more, more preferably 3 m or more And more preferably 4 m or more. Further, in the case of industrially producing a polarizing film, if the width of the film is excessively wide, uniform uniaxial stretching may become difficult. Therefore, the width of the PVA film is preferably 8 m or less.

Although the shape of the PVA film is not particularly limited, it is preferable that the PVA film is a long film because it is possible to continuously produce a more uniform PVA film and to continuously use it even in the case of producing a polarizing film by using it . The length (length in the flow direction) of the elongate film is not particularly limited and may be suitably set according to the use, for example, within a 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, still more preferably 170% or more and 230% or less. The degree of mass swelling is higher than the lower limit described above, whereby the stretchability is further improved. On the other hand, when the mass swelling degree is not more than the upper limit, the processability at the time of stretching is improved and the durability of the resulting polarizing film is improved.

The mass swelling degree in this specification means the percentage of the value obtained by dividing the mass when the PVA film is immersed in distilled water at 30 DEG C for 30 minutes and the mass after drying the PVA film after immersion for 16 hours at 105 DEG C do. The degree of swelling of the PVA film can be lowered by strengthening the conditions of the heat treatment.

[Production method of PVA film]

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

That is, the method of the present invention for producing a PVA film is characterized in that a film forming apparatus including a drying roll (whose downstream side is sequentially referred to as a first drying roll, a second drying roll ...) and a heat- The apparatus is used and a film forming stock solution containing PVA is discharged onto the first drying roll located on the most upstream side of the drying rolls in a film form and partially dried and then further dried by a drying roll after the second drying roll, Thereafter, a heat treatment roll (Y) positioned at the most downstream side with respect to the peripheral speed (S _X ) of the heat treatment roll (X) positioned at the most upstream side among the heat treatment rolls is manufactured, (S _Y / S _X ) of the circumferential speed (S _Y ) of the nonwoven fabric (A) to the peripheral speed (S _Y ) of the nonwoven fabric 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 comprising a drying roll and a heat treatment roll whose rotation axes are parallel to each other is used, and a PVA-containing film is formed on a first drying roll, After the film-forming raw solution is discharged in a film form and partially dried, the film is further dried with a drying roll after the second drying roll followed by heat treatment with a plurality of heat-treating rolls to prepare a PVA film. In this film-forming apparatus, the number of the drying rolls is preferably 4 or more, more preferably 5 or more, and further preferably 6 to 30.

The drying roll and / or the heat treatment roll are preferably formed from a metal such as, for example, nickel, chromium, copper, iron or stainless steel, and in particular, the surface of the roll is not corroded well, More preferably, it is formed of a metal material. In order to increase the durability of the drying roll and / or the heat treatment roll, it is preferable to use a single layer or a combination of two or more layers of a nickel layer, a chromium layer, and a nickel / chromium alloy layer or the like as a drying roll and / or a heat treatment roll desirable.

In addition to the drying roll and the heat treatment roll, the film forming apparatus may further include a hot air drying apparatus, a hot air drying type heat treatment apparatus, a humidity adjusting apparatus, and the like, if necessary.

The film can be dried more uniformly with respect to the heating direction at the time of drying the film in the process from the first drying roll to the final drying roll. Therefore, in any portion of the film, (Hereinafter sometimes referred to as a " first dry roll contact surface ") and a film surface not contacting the first dry roll (hereinafter, referred to as a " first dry roll non- It is preferable that the drying rolls are alternately opposed to the respective drying rolls from the roll to the final drying roll.

When the film-forming stock solution containing PVA is discharged onto the first drying roll of the film-forming apparatus in the form of a film, a known film-like discharging device such as a T-shaped slit die, a hopper plate, an I- (Flexible apparatus), the film forming stock solution containing PVA may be discharged (softened) on the first drying roll in a film form.

The film forming stock solution containing PVA can be prepared by mixing PVA with a liquid medium to prepare a solution, or by melting a PVA pellet containing a liquid medium or the like to prepare a melt. The melting of the PVA in the liquid medium or the melting of the PVA pellet including the liquid medium can be carried out using a stirring mixer, a melt extruder or the like. Examples of the liquid medium to be used at this time include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine and diethylenetriamine, , One kind may be used alone, or two or more kinds may be used in combination. Of these, water, dimethylsulfoxide, or a mixture of both is preferably used, and water is more preferably used.

It is preferable that one or more kinds of plasticizers, surfactants, other components, etc., as described above in the description of the PVA film, are mixed in the above amounts in the film-forming solution.

The volatilization ratio of the film forming stock solution used in the production of the PVA film is preferably 50 mass% or more and 90 mass% or less, more preferably 60 mass% or more and 75 mass% or less. By setting the volatile fraction of the undiluted solution to be equal to or more than the lower limit described above, the viscosity of the undiluted solution can be kept low to facilitate filtration and defoaming, and the film formation itself becomes easy. On the other hand, when the volatile fraction of the film-forming raw liquid is equal to or less than the upper limit, the viscosity of the undiluted film-forming liquid can be prevented from becoming too low, and the uniformity of thickness of the obtained PVA film can be improved.

The surface temperature of the first drying roll is not particularly limited, but is preferably 80 deg. C or more and 99 deg. C or less, more preferably 85 deg. C or more and 99 deg. C or less, more preferably 90 deg. C or more and 98 deg. Deg.] C or lower. Since the surface temperature of the first drying roll is 99 DEG C or lower, foaming of the film forming stock solution on the first drying roll can be prevented more effectively. On the other hand, when the surface temperature of the first drying roll is 80 DEG C or higher, the peeling from the first drying roll is improved.

The film-forming raw material solution discharged on the film may be dried only on the first drying roll by heating from the first drying roll. At the same time as heating with the first drying roll, hot air is sprayed onto the first drying roll non- From the viewpoints of drying uniformity, drying speed, and the like.

In the case of spraying hot air onto the non-contact surface of the first dry roll of the film on the first dry roll, the extensibility of the obtained PVA film is further improved. m / second is preferably sprayed. It is more preferable to spray hot air at an air speed of 2 to 8 m / sec., more preferably to spray hot air at an air speed of 3 to 8 m / sec. If the air velocity of the hot air blown onto the non-contact surface of the first dry roll is excessively small, condensation such as water vapor occurs during drying on the first drying roll, and drops of water are dropped on the film to cause defects in the finally obtained PVA film There is a concern. On the other hand, if the air velocity of the hot air blown onto the non-contact surface of the first dry roll is excessively large, the PVA film finally obtained will have thickness irregularities, thereby causing troubles such as uneven dyeing.

From the viewpoints of drying efficiency and uniformity of drying, the temperature of the hot air jetted onto the non-contact surface of the first dry roll of the film is preferably 50 ° C or more and 99 ° C or less, more preferably 70 ° C or more and 98 ° C or less, Lt; 0 > C to 95 < 0 > C. It is also preferable that the dew point temperature of the hot air jetted onto the non-contact surface of the first dry roll of the film is 10 ° C or more and 15 ° C or less.

The method for spraying the hot air onto the non-contact surface of the first dry roll of the film is not particularly limited, and a hot air having uniform air velocity and temperature can be uniformly sprayed onto the first dry roll non-contact surface of the film, A nozzle system, a rectifying plate system, a combination system thereof, and the like are preferably employed. The direction of the hot air blowing to the non-contact surface of the first dry roll of the film may be the direction opposite to the direction of the non-contact surface of the first dry roll, The direction substantially along the circumference of the roll surface), or in other directions.

In drying the film on the first drying roll, it is preferable to discharge the volatile matter generated from the film by drying and the hot air after spraying. The exhausting method is not particularly limited, but it is preferable to adopt an exhausting method in which the wind speed deviation and the temperature deviation of the hot air blown onto the non-contact surface of the first dry roll of the film do not occur.

The peripheral velocity S ₁ of the first drying roll is preferably 5 m / min or more and 50 m / min or less, more preferably 10 m / min or more and 45 m / min or more, from the viewpoints of uniformity of drying, Min or less, more preferably 15 m / min or more and 40 m / min or less. If the peripheral velocity S ₁ of the first drying roll is equal to or more than the lower limit, the value of the refractive index can be lowered. On the other hand, a peripheral speed of the first drying roll (S ₁₎ this is the upper limit or less, the uniformity of a PVA film thickness obtained is improved.

The film forming stock solution discharged onto the first drying roll on the first drying roll is dried on the first drying roll and the volatile fraction of the film (the volatile fraction of the film upon peeling from the first drying roll) is preferably at least 17 mass% 30 mass% or less, more preferably 17 mass% or more and 29 mass% or less, further preferably 18 mass% or more and 28 mass% or less.

The film dried on the first drying roll, preferably to a volatile content of not less than 17 mass% and not more than 30 mass%, is peeled from the first drying roll, and then the first drying roll non-contact surface of the film is opposed to the second drying roll , It is preferable to dry the film with a 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. When the ratio (S ₂ / S ₁ ) is within the above range, the PVA film of the present invention can be produced more smoothly. On the other hand, if the ratio (S ₂ / S ₁ ) is too low, the peeling position of the film from the first drying roll becomes uneven and the deviation of the birefringence ratio in the width direction tends to increase. From the above viewpoints, the ratio (S _Y / S _X ) is preferably 1.020 or more, more preferably 1.030 or more, and more preferably 1.038 or less.

The PVA film dried with the second drying roll is peeled off from the second drying roll, and the third drying roll, the fourth drying roll, the fifth drying roll, Or the like, by a plurality of drying rolls.

The surface temperature of each drying roll from the second drying roll to the final drying roll is preferably 40 占 폚 or higher, more preferably 45 占 폚 or higher, still more preferably 50 占 폚 or higher, and lower than 100 占 폚, More preferably 98 占 폚 or lower, further preferably 96 占 폚 or lower, and lower than 90 占 폚.

In addition, since the PVA film of the present invention can be produced more smoothly and the generation of wrinkles can be prevented more effectively, the surface temperature of the final drying roll (drying roll immediately before the heat treatment roll) More preferably less than 57 캜.

The film that has been dried by the drying rolls as described above is subjected to heat treatment by a plurality of heat treatment rolls. Here, in the method of the present invention for producing the PVA film, the peripheral velocity of the heat treatment roll Y positioned at the most downstream side with respect to the peripheral velocity S _X of the heat treatment roll X positioned at the most upstream side among the plurality of heat treatment rolls (S _Y / S _X ) of the ratio (S _Y ) is made not less than 0.993 and not more than 0.997. If the ratio (S _Y / S _X ) deviates from the above range, it becomes difficult to obtain the PVA film of the present invention. From the above viewpoints, the ratio (S _Y / S _X ) is preferably 0.994 or more, more preferably 0.995 or more, and more preferably 0.996 or less.

The surface temperature of the heat treatment roll is preferably 100 占 폚 or higher, more preferably 140 占 폚 or lower, more preferably 130 占 폚 or lower, and even more preferably 120 占 폚 or lower. 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 lower than 100 ° C may be regarded as a dry roll.

In the method of the present invention for producing a PVA film, only two of the heat treatment rolls X and the heat treatment rolls Y may be present, and other heat treatment rolls may be additionally provided between these heat treatment rolls .

There is no particular limitation on the heat treatment time when the heat treatment is performed by the heat treatment roll. However, since the PVA film of the present invention can be produced more efficiently, it is preferably 3 seconds or more, more preferably 4 seconds or more, More preferably 120 seconds or less, more preferably 90 seconds or less, and even more preferably 60 seconds or less.

The film subjected to the heat treatment as described above may further be subjected to a humidity treatment, a cut at both ends of the film (ear portion), and finally, a roll of the film may be wound in a roll to form a PVA film of the present invention .

The volatile fraction of the PVA film finally obtained by the series of treatments is preferably in the range of 1% by mass to 5% by mass, more preferably in the range of 2% by mass to 4% by mass.

[Use of PVA film]

The use of the PVA film of the present invention is not particularly limited, but it is preferable that the PVA film of the present invention is used as a raw material film for producing an optical film such as a polarizing film and a retardation film because of its high tensile elongation and excellent stretchability. Such an optical film can be produced, for example, by performing a treatment such as uniaxial stretching using the PVA film of the present invention.

The method for producing a polarizing film using the PVA film of the present invention as a raw film is not particularly limited and any conventionally employed method may be employed. Such a method includes, for example, dyeing and uniaxial stretching on a PVA film, or uniaxial stretching on a PVA film containing a dye. As a more specific method for producing the polarizing film, a method of swelling, dyeing, uniaxial stretching, and further fixing treatment and drying, if necessary, may be applied to the PVA film of the present invention. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments may be simultaneously carried out. For example, dyeing may be performed before uniaxial stretching Or may be dyed at the same time as uniaxial stretching or may be stained after uniaxial stretching. In addition, one or two or more of the 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 when immersed in water is preferably in the range of 20 ° C to 40 ° C, more preferably in the range of 22 ° C to 38 ° C, and more preferably in the range of 25 ° C to 35 ° C . The time for immersing in water is preferably within a range of, for example, 0.1 minutes to 5 minutes, more preferably 0.5 minutes to 3 minutes. In addition, 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.

Examples of dyes used for dyeing include iodine dyes or dyed organic dyes (for example, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, Direct Color 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270, DirectViolet 9, 12, 51, 98, Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87, Direct Color 26, 39, 106, 107, etc.). These dyes may be used singly or in combination of two or more. The dyeing can be carried out usually by immersing the PVA film in a solution (dyeing bath) containing the dye. The treatment conditions and the treatment method are not particularly limited.

When an iodine dye is used as the 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 the range of 0.01 mass% or more and 0.5 mass% or less, and the concentration of potassium iodide is preferably in the range of 0.01 mass% or more and 10 mass% or less. 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 or more and 5% by mass or less. The temperature of the dyeing bath is preferably 20 占 폚 to 50 占 폚, particularly preferably 25 占 폚 to 40 占 폚.

The uniaxial stretching may be performed by either a wet stretching method or a 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 fixed bath of the dyeing bath or in a fixing treatment bath described later. In the case of the dry heat stretching method, the PVA film after the absorption can be used in air. Among them, the wet drawing method is preferable, and the uniaxial drawing is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the aqueous solution of boric acid is preferably in the range of 0.5% by mass to 6.0% by mass, more preferably in the range of 1.0% by mass to 5.0% by mass, and more preferably in the range of 1.5% It is more preferable that it is inner. The boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably within a range of 0.01 mass% or more and 10 mass% or less. The uniaxial stretching is preferably carried out in the flow direction of the PVA film.

The stretching temperature in the uniaxial stretching is not particularly limited, but in the case of the wet stretching method, it is preferably within the range of 30 占 폚 to 90 占 폚, more preferably within the range of 40 占 폚 to 70 占 폚, Or more and 65 ° C or less, and in the case of the dry heat stretching method, it is preferably within a range of 50 ° C or more and 180 ° C or less.

From the viewpoint of the polarization performance, it is preferable that the stretching magnification of uniaxial stretching (in the case of uniaxial stretching in multiple stages, the total stretching ratio) is preferably stretched as far as possible just before the film is cut, More preferably 5 times or more, and still more preferably 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but is preferably 8.0 times or less in order to perform uniform drawing.

The thickness of the film (polarizing film) after stretching is preferably 5 mu m or more and 35 mu m or less, particularly preferably 20 mu m or more and 30 mu m or less.

In the production of the polarizing film, in order to strengthen the adsorption of the dye to the uniaxially stretched film, fixing treatment is often performed. As a fixing treatment, a method in which a film is immersed in a fixed treatment bath to which boric acid and / or a boron compound is added is generally widely used. At this time, if necessary, an iodine compound may be added to the fixed treatment bath.

It is preferable that the film subjected to uniaxial stretching or uniaxial stretching and fixing treatment is subsequently dried. The drying temperature is preferably 30 ° C or more and 150 ° C or less, particularly preferably 50 ° C or more and 140 ° C or less. If the drying temperature is too low, the dimensional stability of the resulting polarizing film tends to deteriorate. On the other hand, if the temperature is too high, the polarization performance accompanying decoloration of the dye tends to decrease.

A polarizing plate can be obtained by bonding a protective film having optically transparent and mechanical strength to both sides or one side of the polarizing film obtained as described above. Examples of the protective film in this case include a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, an acetic acid-butyric acid cellulose (CAB) film, an acrylic film, a polyester film, a polypropylene film, a norbornene resin Film or the like is used. As the adhesive for bonding the protective film, a PVA adhesive, an acrylate adhesive, a urethane adhesive or the like is generally used, and among them, a PVA adhesive is preferably used.

The polarizing plate obtained as described above can be used as a component of a liquid crystal display device after being coated with a pressure-sensitive adhesive such as acrylic or the like and then adhered to a glass substrate. A retardation film, a viewing angle improving film, a luminance improving film, and the like may be further added when the polarizing plate is bonded to the glass substrate.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples at all. A method of measuring the refractive index in the flow direction on the surface of the PVA film and a method of measuring the tensile elongation of the PVA film employed in the following Examples and Comparative Examples are shown below.

[Refractive index of PVA film]

The PVA film obtained in the following Examples or Comparative Examples was subjected to humidity control for 7 days under an environment of 23 占 폚 and 50% RH. Thereafter, using a prism coupler apparatus (Model 2010 / M) manufactured by Metricon under the same environment, A laser beam having a wavelength of 532 nm is made into a light in a direction inclined in the width direction of the film from a direction perpendicular to the film surface of the PVA film by the prism of the prism coupler apparatus and is incident on one surface of the PVA film And the refractive index (the refractive index based on the surface concerned) on the surface was obtained from the reflected light. The refractive index was similarly obtained on the other surface of the PVA film. The values of the two obtained refractive indexes were A and B so as to satisfy the relation of A ≥ B.

[Tensile elongation of PVA film]

The PVA film obtained in the following examples or comparative examples was stored under the environment of 20 ° C and 65% RH for 24 hours and subjected to a humidity treatment. Thereafter, under the same environment, a tensile test was carried out using an autograph manufactured by Shimadzu Corporation Respectively. The width of the PVA film sample was 15 mm, the distance between the grippers was 30 mm, the tensile speed was 500 mm / min, and the tensile direction was the flow direction of the PVA film. In the tensile test, the distance between grippers when the PVA film was broken was divided by the original gripper distance (30 mm), and the tensile elongation (%) was evaluated by the average value measured ten times.

[Example 1]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2,400) obtained by saponification of a homopolymer of vinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and 66% by mass of volatile matter- The film was discharged in the form of a film on a first drying roll (surface temperature: 90 캜, peripheral speed (S ₁ ) 13.5 m / min) from the die. On the first drying roll, hot air of 90 캜 was supplied to the entire first drying roll non- m / sec. < / RTI > Then peeled off from the first drying roll, and further dried so that the first drying roll non-contact surface was opposed to the second drying roll. 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. Subsequently, the film was further dried with a drying roll after the third drying roll so that the front surface and back surface of the film alternately opposed to the respective drying rolls. The surface temperature of the drying roll from the second drying roll to the drying roll just before the final drying roll was about 85 ° C and the surface temperature of the final drying roll was 55 ° C.

Thereafter, heat treatment was performed with a heat treatment roll (X) having a surface temperature of 104 占 폚 and a heat treatment roll (Y) having a surface temperature of 109 占 폚 succeeding the heat treatment roll (X) and then taken up to obtain a long PVA film (thickness 60 占 퐉 and width 3m). The ratio (S _Y / S _X ) of the peripheral speed (S _Y ) of the heat treatment roll Y to the peripheral speed (S _X ) of the heat treatment roll ( _X ) was 0.995.

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

[Example 2]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2,400) obtained by saponification of a homopolymer of vinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and 66% by mass of volatile matter- The film was discharged in the form of a film on a first drying roll (surface temperature: 90 캜, peripheral speed (S ₁ ) 13.5 m / min) from the die. On the first drying roll, hot air of 90 캜 was supplied to the entire first drying roll non- m / sec. < / RTI >

Then peeled off from the first drying roll, and further dried so that the first drying roll non-contact surface was opposed to the second drying roll. 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. Subsequently, the film was further dried with a drying roll after the third drying roll so that the front surface and back surface of the film alternately opposed to the respective drying rolls. The surface temperature of the drying roll from the second drying roll to the drying roll immediately before the final drying roll was about 85 ° C and the surface temperature of the final drying roll was 50 ° C.

Thereafter, the film was heat-treated with a heat treatment roll (X) having a surface temperature of 101 ° C and a heat treatment roll (Y) having a surface temperature of 107 ° C succeeding the heat treatment roll (X) and then taken up to obtain a long PVA film (thickness 60 m and width 3 m). The ratio (S _Y / S _X ) of the peripheral speed (S _Y ) of the heat treatment roll Y to the peripheral speed (S _X ) of the heat treatment roll ( _X ) was 0.995.

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

[Example 3]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2,400) obtained by saponification of a homopolymer of vinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and 66% by mass of volatile matter- The film was discharged in the form of a film on a first drying roll (surface temperature: 90 캜, peripheral speed (S ₁ ) 13.5 m / min) from the die. On the first drying roll, hot air of 90 캜 was supplied to the entire first drying roll non- m / sec. < / RTI >

Then peeled off from the first drying roll, and further dried so that the first drying roll non-contact surface was opposed to the second drying roll. 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. Subsequently, the film was further dried with a drying roll after the third drying roll so that the front surface and back surface of the film alternately opposed to the respective drying rolls. The surface temperature of the drying roll from the second drying roll to the drying roll immediately before the final drying roll was about 85 ° C and the surface temperature of the final drying roll was 50 ° C.

Thereafter, heat treatment was performed with a heat treatment roll (X) having a surface temperature of 104 占 폚 and a heat treatment roll (Y) having a surface temperature of 109 占 폚 succeeding the heat treatment roll (X) and then taken up to obtain a long PVA film (thickness 60 占 퐉 and width 3m). The ratio (S _Y / S _X ) of the peripheral speed (S _Y ) of the heat treatment roll Y to the peripheral speed (S _X ) of the heat treatment roll ( _X ) was 0.997.

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

[Comparative Example 1]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2,400) obtained by saponification of a homopolymer of vinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and 66% by mass of volatile matter- The film was discharged in the form of a film on a first drying roll (surface temperature: 90 캜, peripheral speed (S ₁ ) 13 m / min) from the die. On the first drying roll, hot air of 90 캜 was supplied to the entire non- m / sec. < / RTI >

Then peeled off from the first drying roll, and further dried so that the first drying roll non-contact surface was opposed to the second drying roll. 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. Subsequently, the film was further dried with a drying roll after the third drying roll so that the front surface and back surface of the film alternately opposed to the respective drying rolls. The surface temperature of the drying roll from the second drying roll to the drying roll immediately before the final drying roll was about 85 ° C and the surface temperature of the final drying roll was 60 ° C.

Thereafter, heat treatment was performed with a heat treatment roll (X) having a surface temperature of 102 占 폚 and a heat treatment roll (Y) having a surface temperature of 107 占 폚 succeeding the heat treatment roll (X) and then taken up to obtain a long PVA film (thickness 60 占 퐉 and width 3m). The ratio (S _Y / S _X ) of the peripheral speed (S _Y ) of the heat treatment roll Y to the peripheral speed (S _X ) of the heat treatment roll ( _X ) was 1.000.

The refractive index of the obtained PVA film measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film surface was 1.531 on one surface and 1.530 on the other surface (A = 1.531, B = 1.530, A + B = 3.061). The tensile elongation of the obtained PVA film was measured and found to be 415%.

[Comparative Example 2]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2,400) obtained by saponification of a homopolymer of vinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and 66% by mass of volatile matter- The film was discharged in the form of a film on a first drying roll (surface temperature: 90 DEG C, peripheral speed (S ₁ ) 15.5 m / min) from the die. On the first drying roll, hot air of 90 DEG C m / sec. < / RTI >

Then peeled off from the first drying roll, and further dried so that the first drying roll non-contact surface was opposed to the second drying roll. 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. Subsequently, the film was further dried with a drying roll after the third drying roll so that the front surface and back surface of the film alternately opposed to the respective drying rolls. The surface temperature of the drying roll from the second drying roll to the drying roll immediately before the final drying roll was about 85 캜 and the surface temperature of the final drying roll was 72 캜.

Thereafter, heat treatment was performed with a heat treatment roll (X) having a surface temperature of 108 占 폚 and a heat treatment roll (Y) having a surface temperature of 114 占 폚 succeeding the heat treatment roll (X) and then taken up to obtain a long PVA film (thickness 60 占 퐉 and width 3m). The ratio (S _Y / S _X ) of the peripheral speed (S _Y ) of the heat treatment roll Y to the peripheral speed S _X of the heat treatment roll _X was 0.998.

The refractive index of the obtained PVA film measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film surface 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 measured and found to be 431%.

Claims (10)

The refractive index on each surface of the polyvinyl alcohol film was measured by incident light in a direction inclined in the width direction of the film from the direction perpendicular to the film surface of the polyvinyl alcohol film, And B is the refractive index on the other side (where A? B), A is 1.524 or more and 1.530 or less. The method according to claim 1,
A is from 1.526 to 1.530. 3. The method according to claim 1 or 2,
A + B is 3.050 or more and 3.060 or less. A film forming apparatus comprising a drying roll and a heat treatment roll in which the rotating shafts are parallel to each other is used and the film forming stock solution containing polyvinyl alcohol is discharged onto the first drying roll located at the most upstream side among the drying rolls to be partially dried The polyvinyl alcohol film is further subjected to a heat treatment with a plurality of heat treatment rolls to produce a polyvinyl alcohol film, wherein the heat treatment rolls X of the heat treatment rolls located on the most upstream side of the heat treatment rolls peripheral speed of the heat treatment roll (Y) a peripheral speed (S _Y) ratio _(Y S / _X S) the method of producing a polyvinyl alcohol film in a range of 0.997 0.993 of which is located at the most downstream side with respect to the (S _X). 5. The method of 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. The method according to claim 4 or 5,
And the surface temperature of the final drying roll is lower than 60 占 폚. An optical film produced from the polyvinyl alcohol film according to any one of claims 1 to 3. 8. The method of claim 7,
Polarizing film. A process for producing an optical film, which comprises a step of uniaxially stretching using the polyvinyl alcohol film according to any one of claims 1 to 3. 10. The method of claim 9,
A method for producing an optical film, which is a method for producing a polarizing film.