KR20180013908A - Polyvinyl alcohol polymer film and method for producing same - Google Patents

Abstract

The present invention relates to a PVA film having a thickness of 55 m or less, wherein a broken line stripe formed by arranging the concavities and convexities over 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.01 to 10 mm is 5 PVA film; And a thickness of 55 mu m or less, characterized in that a film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other is used, and a film forming stock solution containing PVA on a first drying roll of the film forming apparatus is formed into a film (S ₀ ) of the film forming liquid is set to 2.5 to 5.0 m / min when the PVA film is formed by discharging, drying, and further drying with a drying roll after the second drying roll succeeding thereto .

Description

FIELD OF THE INVENTION [0001] The present invention relates to a polyvinyl alcohol polymer film,

The present invention relates to a thin film of a polyvinyl alcohol polymer film (hereinafter sometimes referred to as " PVA ", sometimes abbreviated as " PVA ") capable of producing an optical film such as a polarizing film having few optical defects, A production method thereof, an optical film such as a polarizing film produced from the PVA film, and a process for producing the optical film.

A polarizing plate having light transmission and shielding functions is one of the important components of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The LCD is intended to be used in a wide range of small-sized devices such as an electronic desk calculator and a wrist watch, a notebook, a liquid crystal monitor, a liquid crystal color projector, a liquid crystal television, a vehicle navigation system, a mobile phone, a tablet terminal, have. Among the applications of these LCDs, liquid crystal televisions and liquid crystal monitors are becoming thinner in addition to being larger in size. In recent years, a thinner tablet terminal has also been made thinner. As a means for achieving thinning of the LCD, there is a method of thinning the glass used for the LCD. From the viewpoint of solving the problem of warping of the glass due to the shrinkage stress of the polarizing plate accompanied therewith, the polarizing plate is required to be thin .

The polarizing plate is generally produced by subjecting a PVA film to dyeing and uniaxial stretching to produce a polarizing film, and then adhering a protective film such as a cellulose triacetate (TAC) film to the surface of the polarizing film . Therefore, in order to attain thinning of the polarizing plate, it is required to produce a thin polarizing film by using a thinner PVA film, and it is required that the thickness of the PVA film is 55 탆 or less, more specifically 30 탆 or less have.

Various methods for producing PVA films have been known so far. For example, when the PVA-containing film forming raw material is discharged onto a rotating drum of a drum-shaped barrel or a running belt of a belt-type barrel and dried to produce a PVA film, the speed of the drum or belt, It is known that a PVA film having a uniform thickness and excellent smoothness can be produced even when the velocity ratio of the discharge speed of the film is set to 1 to 5 (see Patent Document 1). Specifically, Patent Document 1 discloses that a PVA film having a thickness of about 75 탆 and a thickness variation of about 1.6 to 3.0 탆 has been produced by the above method.

Japanese Patent Application Laid-Open No. 2002-79530

As described above, a thinner PVA film is required. However, when a thin PVA film is simply formed by the conventional film forming method, a stripe pattern on the broken line (a plurality of concavities and convexities on the nanometer order) Dashed lines) often occur. The inventors of the present invention have recognized that when using a conventional thin PVA film in which many such broken line stripes are present, a large number of optical defects occur in the resulting optical film.

Therefore, it is an object of the present invention to provide a thin PVA film capable of producing an optical film such as a polarizing film having less optical defects. Another object of the present invention is to provide an optical film produced from the PVA film and having a small amount of optical defects.

Means for Solving the Problems In order to achieve the above object, the present inventors have intensively studied and found that, when an optical film such as a polarizing film is produced using a thin PVA film, the number of broken- And an optical film having less optical defects can be easily obtained. In addition to this, a film-forming apparatus having a plurality of drying rolls 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 on the most upstream side of the film- And then further dried by a drying roll after the second drying roll to the downstream side of the first drying roll to make the discharge speed S ₀ of the stock film forming liquid in a specific range, It has been found that a conventional thin PVA film having a small number of stripes can be smoothly and continuously produced. Based on these findings, the present inventors have repeatedly studied to complete the present invention.

That is,

[1] A PVA film having a thickness of 55 탆 or less, wherein a dashed line stripe formed by arranging the concavities and convexities over 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.01 to 10 mm is 5 per 1 m in the width direction of the film Or less;

[2] The PVA film of the above [1], wherein the PVA film has a width of 2 m or more;

[3] A method for producing a PVA film having a thickness of 55 m or less, comprising the steps of: using a film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other; (S ₀ ) of the stock film-forming liquid is set to 2.5 to 5.0 m / min when the PVA film is formed by further drying by discharging it in the form of a film and further drying it with a drying roll after the second drying roll succeeding thereto.

[4] The method according to the above [3], wherein the ratio (S ₁ / S ₀ ) of the peripheral speed (S ₁ ) of the first drying roll to the discharge speed (S ₀ )

[5] The production method of the above [3] or [4], which is a production method of a PVA film having a width of 2 m or more;

[6] An optical film produced from the PVA film of the above [1] or [2];

[7] The optical film of [6] above, which is a polarizing film;

[8] A process for producing an optical film having a step of uniaxially stretching using the PVA film of the above [1] or [2];

[9] the production method of the above [8], which is a production method of a polarizing film;

.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a thin PVA film capable of producing an optical film such as a polarizing film having less optical defects and a method for producing the same, an optical film produced from the PVA film with less optical defects, / RTI >

Hereinafter, the present invention will be described in detail.

[PVA film]

The PVA film of the present invention has a thickness of 55 mu m or less and a broken line stripe formed by arranging the unevenness over 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.01 to 10 mm, m or less per m.

In the present invention, the broken line stripe defining the number is formed by arranging the irregularities over 10 cm or more in a substantially straight line in the flow direction of the film at a period of 0.01 to 10 mm. Typically, dashed lines occur along the flow direction of the film and the length of one dashed line pattern is well over 10 cm, but in this specification, to distinguish it from the drawbacks of less than 10 cm in length, For convenience, it is assumed to be treated as dashed stripes having a length of 10 cm or more (those in which the irregularities are arranged in a straight line over the length of 10 cm or more in the flow direction of the film in the above-mentioned period).

There is no particular limitation on the kind of the concavities and convexities, and for example, convex portions are formed by projecting convex portions projected from the film surface; The concave recesses are arranged from the film surface, thereby forming concave and convex portions; Convex portions protruding from the film surface and concave portions recessed from the film surface are alternately arranged, thereby forming irregularities as a result; And the like.

The broken line stripe is formed by arranging the irregularities over 10 cm or more in a substantially straight line in the flow direction of the film at a period of 0.01 to 10 mm. Here, this cycle means the length of the film in the flow direction with respect to one set of concavities and convexities (a set of adjacent concave portions and one convex portion), and in the above dashed line pattern, So that the period is within the range of 0.01 to 10 mm. The period may be, for example, in the range of 0.1 to 5 mm, and more preferably in the range of 0.2 to 1 mm.

In a set of unevenness constituting the broken line stripe, the height difference of the thickness at the point where the height is the highest and the point where the height is the lowest is within the range of 1 to 500 nm in most cases, For example, it may be in the range of 10 to 300 nm, further in the range of 20 to 100 nm, particularly in the range of 30 to 90 nm.

The number of the dashed line streaks is determined so that the number of the broken line streaks traversing the straight line passing through any one point in the flow direction of the PVA film in the width direction And then the number of the PVA films is divided by the width (unit: m) of the PVA film to obtain the number per 1 m width. Here, the dashed line pattern can be confirmed by, for example, a scanning white interference microscope or the like. Specifically, the number of broken line streaks can be obtained by the method described later in the embodiment.

In the PVA film of the present invention, it is necessary that the above-mentioned broken line stripe is 5 or less per 1 m in the width direction of the film, preferably 3 or less, more preferably 2 or less, 1.5 or less, Or less. When the number of the broken line streaks is within the above range, an optical film having less optical defects can be easily obtained. On the other hand, in the case of a thin PVA film having a thickness of 55 탆 or less, when the operating conditions are adjusted so that the number of dashed lines is less than 0.05 per 1 m in the width direction, optical defects on the stripe of the optical film are small, There is a tendency that the film tends to cause problems such as thickness unevenness. Therefore, the number of dashed lines is preferably 0.05 or more per 1 m in the width direction, more preferably 0.10 or more, more preferably 0.15 or more, and most preferably 0.20 or more.

Examples of the PVA forming the PVA film include PVA (unmodified 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, Modified PVA produced by saponification of a modified polyvinyl ester copolymerized with a monomer, so-called polyvinyl acetal resin obtained by crosslinking a part of the hydroxyl groups of unmodified PVA or modified PVA with aldehydes such as formalin, butylaldehyde, and benzaldehyde .

When the PVA forming the PVA film 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 acetate, vinyl formate, vinyl laurate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl stearate and vinyl benzoate . These vinyl esters can be used singly or in combination. Among 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, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and octadecyl acrylate For example, C1-18 alkyl esters of acrylic acid, etc.); 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 and the like); Acrylamide, N-methylacrylamide, N-ethyl acrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidepropanesulfonic acid or salts thereof, acrylamidopropyldimethylamine or salts thereof, An acrylamide derivative such as an amide or a derivative thereof; Methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid or a salt thereof, methacrylamide propyldimethylamine or a salt thereof, N-methylol methacrylamide or a derivative thereof Acrylamide derivatives; 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 PVA is preferably 1,000 or more, more preferably 1,500 or more, and still more preferably 2,000 or more, from the viewpoints of the polarizing performance and durability of the resulting polarizing film. On the other hand, with respect to the upper limit of the average degree of polymerization of PVA, the average degree of polymerization is preferably 8,000 or less, particularly preferably 6,000 or less, from the viewpoints of ease of production of a homogeneous PVA film,

Here, the "average degree of polymerization" of PVA in the present specification refers to the average degree of polymerization measured according to JIS K 6726-1994, and is determined from the intrinsic viscosity measured in water at 30 ° C after the PVA is saponified and purified .

The saponification degree of PVA is preferably 95.0 mol% or more, more preferably 98.0 mol% or more, and further preferably 99.0 mol% or more, from the viewpoints of the polarizing performance and durability of the resulting polarizing film.

Here, the "degree of saponification" of PVA in the present specification refers to the degree of saponification of PVA with respect to the total mole number of a structural unit (typically a vinyl ester unit) that can be converted into a vinyl alcohol unit by saponification and a vinyl alcohol unit (Mol%) of the number of moles. The saponification degree of PVA can be measured according to the description of JIS K 6726-1994.

The PVA constituting the PVA film may be one kind of PVA or two or more kinds of PVA in which one or more of the average polymerization degree, saponification degree, degree of modification and the like are different from each other. The content of PVA in the PVA film is preferably within a range of 50 to 100 mass%, more preferably within a range of 80 to 100 mass%, and still more preferably within a range of 85 to 100 mass%.

The PVA film preferably contains a plasticizer in terms of mechanical properties such as impact strength and the ability to improve processability and extensibility during secondary processing. Examples of suitable plasticizers include polyhydric alcohols. Specific examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane . The PVA film may contain one or two or more kinds of these plasticizers. Of these plasticizers, one or two or more of glycerin, diglycerin and ethylene glycol are preferably used, and glycerin is more preferably used from the viewpoint of improving the drawability of the PVA film when it is stretched.

The content of the plasticizer in the PVA film is preferably at least 1 part by mass, more preferably at least 3 parts by mass, further preferably at least 5 parts by mass, relative to 100 parts by mass of PVA contained in the PVA film, More preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. The content is 1 part by mass or more, whereby the stretchability of the PVA film can be further improved. On the other hand, when the content is 30 parts by mass or less, the PVA film becomes excessively flexible and the handling property can be prevented from being lowered.

The PVA film preferably contains a surfactant from the viewpoints of its handling property and the improvement of peelability from the film-forming apparatus when the PVA film is produced. The kind of the surfactant is not particularly limited, and examples thereof include anionic surfactants and nonionic surfactants.

As the anionic surfactant, for example, a 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 surfactants include alkyl ether types such as polyoxyethylene lauryl ether and polyoxyethylene oleyl ether; Alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as diethanolamide laurate, and diethanolamide oleic acid; And allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether.

The PVA film may contain one or more kinds of these surfactants. Of these surfactants, nonionic surfactants are preferable, alkanolamide surfactants are more preferable, and aliphatic carboxylic acids (for example, a carbon number (E.g., a saturated or unsaturated aliphatic carboxylic acid having 8 to 30 carbon atoms), and the like are more preferable (for example, diethanolamide and the like).

The content of the surfactant in the PVA film is preferably in the range of 1 to 20 parts by weight based on the total weight of the PVA film and the PVA film because the handling properties of the PVA film and the peeling property from the film forming apparatus at the time of producing the PVA film are further improved, More preferably 0.01 part by mass or more, more preferably 0.02 parts by mass or more, further preferably 0.05 part by mass or more, further preferably 1 part by mass or less, more preferably 0.5 part by mass or less , And further preferably 0.3 parts by mass or less.

The PVA film may further contain other components such as an antioxidant, an ultraviolet absorber, a lubricant, a colorant, an antiseptic, an antiseizing agent, a polymer compound other than the above-mentioned components, and water, if necessary. The PVA film may contain one or more of these other components.

In order to produce a thin optical film (polarizing film or the like), the thickness of the PVA film is required to be 55 占 퐉 or less, preferably 40 占 퐉 or less, 30 占 퐉 or less, further 20 占 퐉 or less . The broken line stripe is more likely to be a problem in a thinner PVA film, and the effect of the present invention is particularly remarkable in a PVA film having such a thickness. On the other hand, there is no particular limitation on the lower limit of the thickness of the PVA film. However, considering the handling properties of the PVA film, the processability in producing the optical film, and the optical performance (polarizing performance of the polarizing film) Is preferably at least 3 mu m, more preferably at least 5 mu m, and even more preferably at least 10 mu m. The thickness of the PVA film can be determined by measuring the thickness of any five points and calculating the average value thereof.

Although the shape of the PVA film is not particularly limited, it is possible to continuously and smoothly produce a more uniform PVA film, and also to use it continuously to produce an optical film such as a polarizing film, Of the film. The elongated film is preferably formed into a film roll by winding it on a cylindrical core. The length (the length in the flow direction) of the PVA film when the film is long is not particularly limited and may be suitably set according to the use. However, in the case of using the film in a continuous release from the film roll, The length is preferably not less than 500 m, more preferably not less than 1,000 m, further preferably not less than 5,000 m, and particularly preferably not less than 8,000 m in view of reducing the loss when the roll is switched. The upper limit of the length is not particularly limited, but the length may be 30,000 m or less, for example.

The shape of the PVA film is not particularly limited and may be a single layer form (single layer film), or a laminated body such as a PVA film formed on a thermoplastic resin film by a coating method or the like , The effect of the present invention is more conspicuous, the complexity of the lamination (coating and the like) work, the cost of the thermoplastic resin film, and the like are preferable.

The width of the PVA film is not particularly limited and may be suitably set according to the use of the optical film such as a PVA film or a polarizing film produced therefrom. In recent years, however, The width of the film is preferably at least 2 m, more preferably at least 3 m, further preferably at least 4 m, which is preferable for these applications. On the other hand, when the width of the PVA film is too large, it is difficult to uniformly conduct the uniaxial stretching in the case of producing an optical film with a device that is put into practical use. Therefore, the width of the PVA film is preferably 7 m or less.

[Production method of PVA film]

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

That is, the production method of the present invention for producing a PVA film having a thickness of 55 탆 or less is characterized in that a plurality of drying rolls whose rotation axes are parallel to each other (from the upstream side to the downstream side, sequentially from the first drying roll to the second drying roll, ), A film forming stock solution containing PVA is discharged onto the first drying roll of the film forming apparatus in the form of a film and dried, followed by further drying with a drying roll after the second drying roll (S ₀ ) of the stock film-forming liquid at a time of forming the PVA film is 2.5 to 5.0 m / min.

In the production method of the present invention, a film-forming apparatus having a plurality of drying rolls 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 of the film- The PVA film is further dried by a drying roll after the second drying roll which is continued to the downstream side of the first drying roll. In this film-forming apparatus, the number of the drying rolls is preferably 3 or more, more preferably 4 or more, and further preferably 5 to 30.

The plurality of drying rolls are preferably formed of a metal such as nickel, chrome, copper, iron, stainless steel, and the like. In particular, the surface of the drying roll is not corroded well, It is more preferable that it is formed. Further, in order to enhance the durability of the drying roll, it is more preferable to use a single layer or a combination of two or more layers of a dry roll plated with a nickel layer, a chromium layer, a nickel / chromium alloy layer or the like.

It is preferable that in any part of the film, the first drying roll and the second drying roll are provided in the same manner in that 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 (Hereinafter also referred to as " first dry roll contact surface ") and a film surface that does not contact the first dry roll (hereinafter, referred to as " It is preferable to dry each of the drying rolls from the first drying roll to the last drying roll so as to face alternately.

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 discharge speed (S ₀₎ is required to 2.5 ~ 5.0 m / min. In theory, on the other hand to reduce the film-forming stock solution discharge speed (S _0), even by a first ratio (S ₁ / S ₀₎ of the peripheral speed (S ₁₎ of the drying roll for the discharge speed (S ₀₎ of the film-forming stock solution significantly , or the contrary, to increase the discharge speed (S ₀₎ of the film-forming stock solution on the other hand, non-(S ₁ / S ₀ of a peripheral speed (S ₁₎ of the first drying roll to the extrusion rate (S ₀₎ of the film-forming stock solution The inventors of the present invention have found that when a thin PVA film having a thickness of 55 m or less is produced, the discharge speed (S ₀ ) of the stock solution for forming a film is made to be By setting the thickness within the above range, it has been found that a thin, non-conventional PVA film having a small number of broken line streaks, which is particularly problematic in a thin PVA film, can be smoothly and continuously produced. The discharge speed S ₀ of the film-forming raw material liquid is preferably 2.6 m / min or more, more preferably 2.7 m / min or more, and more preferably 2.8 m / min or less, for the reason that the number of broken- Or more. On the other hand, the discharge speed of such film-forming stock solution (S ₀₎ is too excessively high, in that it tends to be difficult to prepare a PVA film stably, the discharge speed of such film-forming stock solution (S ₀₎ is, 4.8 m / min or less More preferably 4.5 m / min or less, further preferably 4.2 m / min or less, particularly preferably 4.0 m / min or less. The discharge speed (S ₀ ) of the stock film-forming liquid means the linear velocity in the flow direction of the film-forming stock solution, and the volume per unit time of the film-forming stock solution discharged from the film- The product of the slit width of the discharge device and the average value of the slit opening degree).

The film forming stock solution containing the PVA film 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 form a melt.

Examples of the liquid medium to be used at this time include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, etc. These liquids One type of medium may be used alone, or two or more types 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 blended in the amounts described above, as desired, in the film-forming solution.

The volatile fraction of the film forming stock solution used in the production of the PVA film is preferably in the range of 50 to 90 mass%, more preferably in the range of 55 to 80 mass%, further preferably in the range of 60 to 75 mass% Do. If the volatile fraction of the stock solution is too low, the viscosity of the stock solution may become excessively high, which may make filtration and defoaming difficult or make the film itself difficult. On the other hand, if the volatile fraction of the stock solution is too high, the viscosity becomes too low and the uniformity of the thickness of the PVA film may be impaired.

Here, the "volatile matter content of the stock film-forming solution" in this specification means the volatile matter content determined by the following formula [I].

(% By mass) = {(Wa - Wb) / Wa} x 100 [I]

(G) represents the mass (g) of the stock solution for film formation, and Wb represents the mass (g) when the stock solution of Wa (g) is dried in a heat transfer dryer at 105 DEG C for 16 hours)

The surface temperature of the first drying roll is not particularly limited, but is preferably in the range of 70 to 120 ° C, more preferably in the range of 80 to 105 ° C, more preferably in the range of 85 to 85 ° C, from the viewpoints of uniformity of the film drying, To 95 < 0 > C.

The film-forming raw material solution discharged on the film may be dried on the first drying roll only by heating from the first drying roll, but hot air is sprayed onto the first drying roll non-contact surface while heating with the first drying roll, It is preferable that the drying is performed by providing heat from both sides of the film in view of uniform drying and drying speed.

When hot air is sprayed onto the non-contact surface of the first dry roll of the film on the first drying roll, it is preferable to spray hot air of 1 to 10 m / second in the wind speed over the entire area of the first dry roll non-contact surface, It is more preferable to spray hot air of 8 m / sec., More preferably, hot air of 3 to 8 m / sec of wind speed. 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 the water droplets 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, unevenness in thickness is finally generated in the finally obtained PVA film, and troubles such as occurrence of uneven dyeing are likely to occur.

The temperature of the hot air blown onto the non-contact surface of the first dry roll of the film is preferably 50 to 150 DEG C, more preferably 70 to 120 DEG C, and more preferably 80 to 95 DEG C, from the viewpoints of drying efficiency, Lt; 0 > C. Further, the dew point temperature of the hot air jetted onto the non-contact surface of the first dry roll of the film is preferably 5 to 20 캜, more preferably 10 to 15 캜.

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 hot air having uniform air velocity and uniform temperature is uniformly sprayed onto the first dry roll non- contact surface of the film, A nozzle system, a rectifying plate system, a combination of them, or the like is 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 hot air after spraying. The exhausting method is not particularly limited, but it is preferable to adopt an exhausting method in which the unevenness of the speed of the hot air blown onto the non-contact surface of the first dry roll of the film and the temperature unevenness do not occur.

The peripheral speed (S ₁ ) of the first drying roll is preferably within a range of 12 to 35 m / min, because the number of dashed stripe patterns can be further reduced and the stability during production is also excellent. More preferably, the peripheral velocity S ₁ of the roll is 15 m / min or more, more preferably 30 m / min or less, still more preferably 28 m / min or less, and particularly preferably 26 m / min or less .

The ratio (S ₁ / S ₀ ) of the peripheral speed (S ₁ ) of the first drying roll to the discharge speed (S ₀ ) of the raw film forming solution can further reduce the number of dashed line fringes, , More preferably not more than 6.8, even more preferably not more than 6.5, particularly preferably not more than 6.3, further preferably not less than 3, more preferably not less than 5, more preferably not more than 5 , More preferably more than 5.5, and most preferably more than 6. [0050]

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 (volatile fraction of the film at the time of peeling from the first drying roll) is preferably 5 to 30 mass %, More preferably from 7 to 20% by mass, and still more preferably from 8 to 15% by mass. Since the volatile fraction of the film at the time of peeling from the first drying roll is 5 mass% or more, the difference in drying speed between the first drying roll contact surface and the first drying roll non-contact surface becomes large, . In addition, since the volatile fraction of the film at the time of peeling from the first drying roll is 30 mass% or less, the thickness irregularity can be prevented from becoming large.

Here, the " volatile matter content of the film " in this specification means the volatile matter content determined by the following formula [II].

(% By mass) = {(Wc - Wd) / Wc} x 100 [II]

Wherein Wc represents the mass (g) of the sample taken from the film, and Wd represents the mass (Wc (g)) of the sample in a vacuum dryer at a temperature of 50 캜 and a pressure of 0.1 ㎪ or less after being dried for 4 hours g)

The film dried on the first drying roll, preferably to a volatile content of 5 to 30% by mass, is peeled from the first drying roll, and this time, the first drying roll non-contact surface of the film is opposed to the second drying roll, 2 It is preferable to dry the film with a dry roll.

The film dried by 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, And the like.

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, and even more preferably 50 占 폚 or higher, from the viewpoints of uniform drying and drying speed More preferably less than 100 ° C, more preferably less than 90 ° C, even more preferably less than 85 ° C, and particularly preferably less than 80 ° C.

As described above, it is preferable that the film subjected to drying in the final drying roll is subjected to heat treatment. The heat treatment can be carried out using a heat treatment roll or other known heat treatment apparatus. When the heat treatment is performed by the heat treatment roll, one heat treatment roll, a plurality of heat treatment rolls, or both may be used.

The surface temperature of the heat-treated roll is preferably 90 占 폚 or higher, more preferably 100 占 폚 or higher, and even more preferably 110 占 폚 or higher, in view of obtaining a PVA film with favorable crystallization and excellent thermal water resistance. From the viewpoint of improving the stretchability of the obtained PVA film, the surface temperature of the heat-treated roll is preferably 150 ° C or lower, more preferably 140 ° C or lower, and further preferably 130 ° C or lower.

Although the heat treatment time is not particularly limited, it is preferably in the range of 3 to 60 seconds, more preferably in the range of 5 to 30 seconds, in order to smoothly produce the desired PVA film.

The film-forming apparatus may have a hot-air drying device, a humidity control device, or the like, if necessary.

The film obtained as described above may be further subjected to a humidity treatment, a cut at both ends (ear portions) of the film, and the like. Finally, the PVA film of the present invention can be obtained by winding the film in a roll at a predetermined length.

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

[Use of PVA Film]

The use of the PVA film of the present invention is not particularly limited, but according to the PVA film of the present invention, it is possible to produce an optical film having few optical defects. Therefore, the PVA film of the present invention is excellent in optical properties such as polarizing film and retardation film It is preferably used as a raw film for producing a film. 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 of a PVA film or uniaxial stretching of a PVA film containing a dye. As a more specific method for producing the polarizing film, the PVA film of the present invention may be subjected to dyeing, uniaxial stretching, fixing treatment, drying treatment, and further heat treatment if necessary. The order of dyeing and uniaxial stretching is not particularly limited and may be dyed before uniaxial stretching, dyeing may be performed simultaneously with uniaxial stretching, or dyeing may be performed after uniaxial stretching. The uniaxial stretching, dyeing, and the like may be repeated a plurality of times. Particularly, it is preferable to divide the uniaxial stretching into two or more stages, since uniform stretching can be easily performed. In the case where the PVA film is in the form of a laminate formed on a thermoplastic resin film, the uniaxial stretching can be further reduced by performing uniaxial stretching while the thermoplastic resin film is laminated.

Dyes for use in dyeing PVA films include iodine or dichroic organic dyes (such as DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, Direct Blue 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). These dyes may be used singly or in combination of two or more. The dyeing can be usually carried out by immersing the PVA film in a solution containing the dye. The treatment conditions and the treatment method are not particularly limited.

The uniaxial stretching of the PVA film may be carried out by either a wet stretching method or a dry heat stretching method, and from the viewpoints of the stability of the obtained polarizing film and the quality thereof, the wet stretching method is preferable. Examples of the wet stretching method include a method of stretching a PVA film in an aqueous solution containing various components such as pure water, an additive and an aqueous medium, or an aqueous dispersion in which various components are dispersed, Specific examples of the method include a method of uniaxial stretching in hot water containing boric acid, a method of uniaxial stretching in a solution containing the above-mentioned dye or in a fixed treatment bath described later, and the like. In addition, the PVA film after absorption may be uniaxially stretched in the air, or may be uniaxially stretched by other methods. The uniaxial stretching is preferably carried out in the flow direction of the PVA film.

The stretching temperature at the time of uniaxial stretching is not particularly limited, but in the case of wet stretching, a temperature within a range of preferably 20 to 90 占 폚, more preferably 25 to 70 占 폚, and still more preferably 30 to 65 占 폚 is employed In the case of dry stretching, the temperature is preferably in the range of 50 to 180 ° C.

It is preferable that the stretching magnification (uniaxial stretching ratio in the case of uniaxial stretching in multiple stages) of the uniaxial stretching is as long as possible until the film is cut off from the viewpoint of the polarization performance, and more preferably four times or more 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 uniaxially stretched film (polarizing film) is preferably 1 to 30 μm, more preferably 3 to 25 μm. Further, the thickness can be obtained as an average value by measuring the thickness of any five points.

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 of immersing a film in a fixed treatment bath to which boric acid and / or a boron compound is added is generally widely used. At that time, if necessary, an iodine compound may be added to the treatment bath.

It is preferable that the film subjected to the uniaxial stretching treatment or the uniaxial stretching treatment and the fixing treatment is subsequently subjected to a drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably 30 to 150 ° C, particularly preferably 50 to 140 ° C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film tends to be deteriorated. On the other hand, if the temperature is too high, the polarization performance accompanying the decomposition 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. As the protective film in this case, a cellulose triacetate (TAC) film, an acetic acid-butyric acid cellulose (CAB) film, an acrylic film, a polyester film or the like is used. As the adhesive for bonding the protective film, a PVA 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. When the polarizing plate is adhered to the glass substrate, the retardation film, the viewing angle improving film, the brightness improving film and the like may be simultaneously bonded.

Example

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto at all. The measurement and evaluation methods employed in the following Examples, Comparative Examples and Reference Examples are shown below.

[Number of dashed lines]

A zone of 60 cm in the flow direction × the entire width direction was set at an arbitrary position of the PVA film to be measured, and the measurement was made by using a scanning white interference microscope ("New View" 7300, manufactured by ZYGO) A thickness profile in the vicinity of the stripe flaws in mind was measured and it was confirmed whether or not the flaws on the stripe were the broken line streaks defined in the present invention. In this manner, the number of dashed lines traversing a straight line in the width direction passing through any one point in the flow direction in the region section is measured over the entire width direction of the straight line, By dividing the width, the number of dashed lines per 1 m width was obtained.

[Optical defects of polarizing film]

After properly dividing the polarizing film in the width direction, the polarizing film was placed in an orthogonal direction between polarizing plates for observation (two polarized polarizers were overlapped with each other and the degree of polarization was 99.99% or more), and the degree of optical defects was visually observed. Respectively.

○: No or almost no optical defects are found

X: Optical defects can be easily detected

××: Optical defects can be detected very easily

[Example 1]

[Production of PVA film]

100 parts by mass of PVA (average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide laurate and 70% by mass of water with a volatile content of 70% A first drying roll (peripheral speed (S ₁ ) of 17 m / min) of a film forming apparatus having a plurality of drying rolls and a heat treatment roll whose rotation axes are parallel to each other at a discharge speed (S ₀ ) of 2.8 m / , And hot air of 90 DEG C was sprayed onto the entire first non-contact surface of the first dry roll on the first dry roll while being sprayed at an air velocity of 5 m / sec. Thereafter, the film was peeled off from the first dry roll, Was further dried between the second drying roll and the final drying roll immediately before the heat-treating roll so that the front surface and the back surface in the portion alternately opposed to the respective drying rolls, and then peeled off from the final drying roll. Subsequently, both ends (ear portions) were cut and wound around a cylindrical core, and finally, a thickness of 30.3 탆, a length of 2,000 m, a width of 2.6 m, a volatile content (moisture content) To prepare a 2% by mass long PVA film (single layer film).

With respect to the PVA film, the number of broken line streaks was measured by the above-mentioned method. As a result, the unevenness of 50 to 60 nm in height was spread over 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.3 to 0.7 mm It has been found that there are six arranged dashed lines (2.3 per 1 m in the width direction of the film). The above results are shown in Table 1.

[Production of polarizing film]

Each of the treatments was performed while releasing the obtained PVA film to continuously produce a polarizing film having a thickness of 12 占 퐉.

That is, after the PVA film was uniaxially stretched (first stage stretching) in the flow direction (MD) to 2.2 times the original length while immersing the PVA film in water at 30 占 폚, 0.03 mass% of iodine and 3 mass% of potassium iodide (Second stage stretching) in the flow direction (MD) up to 3.3 times the original length while immersing in an aqueous iodine / potassium iodide solution at 30 占 폚 containing a concentration of 3% by mass of boric acid and 3% by mass of potassium iodide (Third stage stretching) in the flow direction (MD) up to 3.6 times the original length while immersing in a boric acid / potassium iodide aqueous solution at 30 캜 in a concentration of 1% by mass and then 4% by mass of boric acid and iodine Uniaxial stretching (fourth-stage stretching) in the flow direction (MD) up to 6.7 times the original length while immersing in an aqueous solution of boric acid / potassium iodide at 63 DEG C containing potassium at a concentration of 5 mass% And further immersed in an aqueous solution of potassium iodide at 30 ° C containing potassium iodide in a concentration of 3% by mass, followed by drying in a drier at 60 ° C for 4 minutes to prepare a polarizing film.

For this polarizing film, optical defects were evaluated by the above-described method. The results are shown in Table 1.

[Example 2]

100 parts by mass of PVA (average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and water and a water content of 66% A first drying roll (peripheral speed (S ₁ ) of 17 m / min) of a film forming apparatus having a plurality of drying rolls and a heat treatment roll whose rotation axes are parallel to each other at a discharge speed (S ₀ ) of 2.8 m / , And hot air of 90 DEG C was sprayed onto the entire first non-contact surface of the first dry roll on the first dry roll while being sprayed at an air velocity of 5 m / sec. Thereafter, the film was peeled off from the first dry roll, Was further dried between the second drying roll and the final drying roll immediately before the heat-treating roll so that the front surface and the back surface in the portion alternately opposed to the respective drying rolls, and then peeled off from the final drying roll. Subsequently, both ends (ear portions) were cut and then wound around a cylindrical core. Finally, the thickness was 40.6 占 퐉, the length was 2,000 m, the width was 2.6 m, the volatile content (moisture content) To prepare a 2% by mass long PVA film (single layer film).

With respect to the PVA film, the number of dashed lines was measured by the above-described method. As a result, the unevenness of the height difference of 50 to 60 nm exceeded 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.3 to 0.7 mm It has been found that there are five arranged dashed lines (1.9 per 1 m in the width direction of the film). Using the obtained PVA film, a polarizing film having a thickness of 17 탆 was prepared in the same manner as in Example 1, and the optical defects were evaluated by the above-mentioned method. The above results are shown in Table 1.

[Comparative Example 1]

100 parts by mass of PVA (average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and water and a water content of 66% (S ₁ , 18 m / min) of a film-forming apparatus having a plurality of drying rolls and heat-treating rolls whose rotational axes are parallel to each other at a discharge speed (S ₀ ) of 2.4 m / , And hot air of 90 DEG C was sprayed onto the entire first non-contact surface of the first dry roll on the first dry roll while being sprayed at an air velocity of 5 m / sec. Thereafter, the film was peeled off from the first dry roll, Was further dried between the second drying roll and the final drying roll immediately before the heat-treating roll so that the front surface and the back surface in the portion alternately opposed to the respective drying rolls, and then peeled off from the final drying roll. Subsequently, both ends (ear portions) were cut and then wound around a cylindrical core. Finally, the thickness was 29.6 占 퐉, the length was 2,000 m, the width was 2.6 m, the volatile content (moisture content) To prepare a 2% by mass long PVA film (single layer film).

With respect to the PVA film, the number of dashed lines was measured by the above-described method. As a result, the unevenness of 60 to 70 nm in the height difference was found to be 10 cm or more in a straight line in the flow direction of the film in a period of 0.3 to 0.7 mm It has been found that there are 24 arranged dashed lines (9.2 per 1 m in the width direction of the film). Using the obtained PVA film, a polarizing film having a thickness of 12 占 퐉 was produced in the same manner as in Example 1, and the optical defects were evaluated by the above-mentioned method. The above results are shown in Table 1.

[Comparative Example 2]

100 parts by mass of PVA (average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and water and a water content of 66% (S ₁ ) 15 m / min) of a film-forming apparatus provided with a plurality of drying rolls and a heat treatment roll whose rotation axes are parallel to each other at a discharge speed (S ₀ ) of 2.0 m / , And hot air of 90 DEG C was sprayed onto the entire first non-contact surface of the first dry roll on the first dry roll while being sprayed at an air velocity of 5 m / sec. Thereafter, the film was peeled off from the first dry roll, Was further dried between the second drying roll and the final drying roll immediately before the heat-treating roll so that the front surface and the back surface in the portion alternately opposed to the respective drying rolls, and then peeled off from the final drying roll. Then, both ends (ear portions) were cut, and wound around a cylindrical core. Finally, the resultant was subjected to heat treatment at a surface temperature of 115 占 폚 and finally wound up with a thickness of 30.3 占 퐉, a length of 2,000 m, a width of 2.6 m, To prepare a 2% by mass long PVA film (single layer film).

With respect to the PVA film, the number of dashed lines was measured by the above-described method. As a result, the unevenness of 80 to 90 nm in height was spread over 10 cm or more in a substantially straight line in the flow direction of the film in a period of 0.3 to 0.7 mm It has been found that there are 37 arranged dashed lines (14.2 per 1 m in the width direction of the film). Using the obtained PVA film, a polarizing film having a thickness of 12 占 퐉 was produced in the same manner as in Example 1, and the optical defects were evaluated by the above-mentioned method. The above results are shown in Table 1.

[Reference Example]

100 parts by mass of PVA (average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide of lauric acid and water and a water content of 66% (At a peripheral speed (S ₁ ) of 11 m / min) of a film forming apparatus having a plurality of drying rolls and a heat treatment roll whose rotation axes are parallel to each other at a discharge speed (S ₀ ) of 2.4 m / , And hot air of 90 DEG C was sprayed onto the entire first non-contact surface of the first dry roll on the first dry roll while being sprayed at an air velocity of 5 m / sec. Thereafter, the film was peeled off from the first dry roll, Was further dried between the second drying roll and the final drying roll immediately before the heat-treating roll so that the front surface and the back surface in the portion alternately opposed to the respective drying rolls, and then peeled off from the final drying roll. Subsequently, both ends (ear portions) were cut and then wound around a cylindrical core. Finally, the thickness was 74.5 μm, the length was 2,000 m, the width was 2.6 m, the volatile content (moisture content) To prepare a 2% by mass long PVA film (single layer film).

With respect to the PVA film, the number of dashed lines was tried to be measured by the above method, but no dashed line was found. The above results are shown in Table 1.

Claims (9)

A polyvinyl alcohol polymer film having a thickness of 55 m or less,
Wherein the broken line stripe formed by arranging the unevenness over 10 cm or more in a substantially straight line in the film flow direction at a period of 0.01 to 10 mm is 5 or less per 1 m in the width direction of the film. The method according to claim 1,
A polyvinyl alcohol polymer film having a width of 2 m or more. A process for producing a polyvinyl alcohol polymer film having a thickness of 55 m or less,
A film forming apparatus comprising a plurality of drying rolls whose rotating shafts are parallel to each other is used, and a film forming stock solution containing a polyvinyl alcohol polymer is discharged onto a first drying roll of the film forming apparatus of the film forming apparatus and dried, (S ₀ ) of the stock film-forming liquid is set to 2.5 to 5.0 m / min when the polyvinyl alcohol-based polymer film is further dried by a drying roll after the drying roll. The method of claim 3,
The ratio (S ₁ / S ₀ ) of the peripheral velocity (S ₁ ) of the first drying roll to the discharge speed (S ₀ ) of the raw film forming solution is set to 7 or less. The method according to claim 3 or 4,
Wherein the polyvinyl alcohol polymer film has a width of at least 2 m. An optical film produced from the polyvinyl alcohol-based polymer film according to claim 1 or 2. The method according to claim 6,
Polarizing film. A process for producing an optical film, which comprises a step of uniaxially stretching using the polyvinyl alcohol polymer film according to any one of claims 1 to 3. 9. The method of claim 8,
A method for producing a polarizing film.