WO2019054487A1

WO2019054487A1 - Polyvinyl alcohol film and method for manufacturing same

Info

Publication number: WO2019054487A1
Application number: PCT/JP2018/034204
Authority: WO
Inventors: 翔大朗森; 良治勝野; 太我油井; 修風藤
Original assignee: 株式会社クラレ
Priority date: 2017-09-15
Filing date: 2018-09-14
Publication date: 2019-03-21
Also published as: KR20200053523A; CN111405972B; TWI765093B; JPWO2019054487A1; JP7157751B2; CN111405972A; TW201920393A; KR102599701B1

Abstract

Provided is a polyvinyl alcohol film which has a width at least equal to 3 m, a length at least equal to 1,000 m and a thickness of 15 to 65 μm, wherein a retardation value measured using a length direction pitch of 15 m and a width direction pitch of 10 mm satisfies formulas (1) to (4). The film has excellent extensibility even when thin and wide, and also exhibits small fluctuation in width after extension. Employing this film therefore makes it possible for a thin, wide optical film or the like having an excellent optical performance to be manufactured with high productivity.

Description

Polyvinyl alcohol film and method for producing the same

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

A polarizing plate having a light transmission and shielding function is an important component of a liquid crystal display (LCD). Liquid crystal display devices are used in a wide range of fields such as notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, mobile phones, measuring instruments used indoors and outdoors.

The polarizing plate is usually produced by coloring a PVA film unwound from a roll and uniaxially stretching it, and then preparing a polarizing film by a fixation treatment with a boron compound, etc. It is manufactured industrially by bonding together protective films, such as a cellulose acetate film and a acetic acid * cellulose butyrate film.

In recent years, the increase in screen size of liquid crystal monitors and liquid crystal televisions, and the reduction in weight of notebook computers, mobile phones and the like have progressed. There is also a need to reduce the cost of the polarizing plate. From such a thing, a thin and wide polarizing film is calculated | required. Although a thin and wide PVA film is used as a raw fabric for manufacturing such a polarizing film, such a PVA film had a problem in that the stretchability was insufficient.

Patent Document 1 describes a method for producing a PVA film, which uses (a) a film forming apparatus provided with a plurality of drying rolls whose rotating shafts are parallel to each other, and uses PVA on the first drying roll of the film forming apparatus. The film-forming stock solution is discharged and partially dried, and then further dried with a subsequent drying roll to form a film; and in that case, (b) the circumferential speed of the final drying roll relative to the peripheral speed (S ₁ ) of the _first drying roll. Ratio (S _L / S ₁ ) of the speed (S _L ) to 0.955 to 0.980; (c) the width (H ₂₀ ) of the PVA film and the volatile content when the volatile content is 20% by mass Shrinkage rate [(1-H ₉ / H ₂₀ ) × 100] (%) calculated from the width (H ₉ ) of the PVA film when the percentage reaches 9% by mass is 1% or more; PVA film from the drying roll when the fraction reaches 20% by mass The surface temperature of each drying rolls to a dry roll when volatile content became 9 wt%, these average values above 85 ° C.; methods are described. However, the PVA film obtained by the method has insufficient stretchability.

Patent Document 2 describes a method for producing a PVA film, which uses (a) a film forming apparatus provided with three or more drying rolls whose rotation axes are parallel to each other, and which is positioned most upstream among the drying rolls. (1) After the film-forming stock solution containing PVA is discharged onto the drying roll and partially dried, it is further dried by the subsequent drying roll to form a film; in that case, (b) PVA when peeled off from the first drying roll The volatile fraction of the film is set to 20 to 40% by mass; (c) 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 (D) Of the second drying roll or the downstream drying roll, the drying roll (the xth drying roll) and the PVA film when the volatilization of the PVA film reaches 20% by mass. Volatile content of 10% by weight The ratio of dry roll between the (first y drying roll), the peripheral speed of the upstream of the drying roll of the adjacent two drying rolls (S _n) the peripheral speed of the downstream drying roll against (S n _{+ 1)} when the Both (S _{n + 1} / S _n ) are from 0.992 to 0.999; the preparation method is described. However, the method was not suitable for the production of thin PVA films.

WO 2016/084836 WO 2014/050696

The present invention has been made to solve the above problems, and provides a thin and wide PVA film having excellent stretchability and having a small variation in width after stretching, and a simple process for producing the same. With the goal.

The subject is a PVA film with a width of 3 m or more, a length of 1,000 m or more, and a thickness of 15 to 65 μm, and the retardation value measured with the pitch in the length direction of 15 m and the pitch in the width direction of 10 mm The problem is solved by providing a PVA film characterized by satisfying (1) to (4).

During the ceremony
Re _max (nm): maximum retardation Re _min (nm) at a position 10 mm from the edge: minimum retardation Re _ave (nm) at a position 10 mm from the edge: average retardation at a position 10 mm from the edge Value Re _i (nm): Retardation value Re _total (nm) of measurement point i (i = 1 to n, n is an integer) at a position of 10 mm from the end: Average value of retardation of all measurement points.

The said subject is a manufacturing method of the said PVA film, Comprising: The film forming apparatus provided with the several drying roll in which a rotating shaft is mutually parallel is used, The said several drying roll is the mth drying roll from the 1st drying roll ( m represents an integer of 3 or more, and after a film is prepared by discharging a film-forming stock solution containing PVA from the die onto the first drying roll and obtaining a film, the second to m-th drying rolls are used. Using the step of further drying the film, wherein the volatile fraction of the film when peeled from the first drying roll is 12 to 20%, and the second drying with respect to the peripheral speed (S ₁ ) of the first drying roll the ratio _(S 2 / _{S 1)} is 1.015 to 1.050 of the peripheral speed of the roll _{(S 2),} the peripheral speed of the second drying roll against _{(S 2),} the volatile fraction of the film is 11 mass At the beginning of becoming less than% Ratio (S _x / S ₂ ) of the peripheral speed (S _x ) of the drying roll (xth drying roll) in contact with each other is 0.970 to 0.995, and the roll from the second drying roll to the xth drying roll It is also solved by providing a method of making a PVA film, wherein the temperature average is 63-81 ° C.

At this time, it is preferable that the volatile fraction of the membrane-forming stock solution containing PVA is 60 to 75% by mass, and the peripheral speed (S ₁ ) of the first drying roll is 8 to 25 m / min.

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

It is the schematic diagram which showed the measurement point of the retardation in a PVA film.

The PVA film of the present invention has a width of 3 m or more, a length of 1,000 m or more, a thickness of 15 to 65 μm, and the retardation value measured with the pitch in the length direction of 15 m and the pitch in the width direction of 10 mm (1) to (4) are satisfied.

During the ceremony
Re _max (nm): maximum retardation Re _min (nm) at a position 10 mm from the edge: minimum retardation Re _ave (nm) at a position 10 mm from the edge: average retardation at a position 10 mm from the edge Value Re _i (nm): Retardation value Re _total (nm) of measurement point i (i = 1 to n, n is an integer) at a position of 10 mm from the end: average value of retardation of all measurement points,
It is.

In the PVA film of the present invention, the retardation value measured with the pitch in the length direction being 15 m and the pitch in the width direction being 10 mm, the above formulas (1) to (4) are satisfied. Here, the retardation Re (nm) of the film is represented by the following formula. Specifically, the retardation Re (nm) of the PVA film can be measured by the method described in the examples.
Re = d × Δn
[Wherein, d is the film thickness (nm) and Δn is the birefringence of the film. ]

Re _max, Re _min, Re _ave and Re _i in the formula (1) and (2) is determined by measuring the retardation value at 10mm position from the edge of the PVA film. FIG. 1 is a schematic view showing measurement points i (i = 1 to n, n is an integer) in the PVA film 1 at this time. The retardation is measured at 15 m pitch 5 in the lengthwise direction 4 of the PVA film 1 at positions of 10 mm from both ends 2 and 3 of the PVA film 1 respectively. At this time, the retardation value of each measurement point i (i = 1 to n, n is an integer) at a position of 10 mm from each of the ends 2 and 3 of the PVA film 1 is Re _i . The maximum value of retardation in all measurement points i at positions of 10 mm from both ends 2 and 3 of PVA film 1 is Re _max , the minimum value is Re _min , and the number average value is Re _ave . As described later, in the case of cutting both ends (ears) of the dried PVA film, the retardations at positions of 10 mm from both ends 2 and 3 of the PVA film 1 after cutting are measured, and Re _i , Find Re _max , Re _min and Re _ave .

As described later, the retardation of the entire PVA film 1 is measured in order to obtain Re _total in the formula (3). Usually, at this time, measurement is performed so that positions of 10 mm are included from both ends 2 and 3 of the PVA film 1 respectively. Re _i , Re _max , Re _min and Re _ave are also determined along with Re _total using the measurement value at this time.

Both A in the above-mentioned formula (1) and B in the above-mentioned formula (2) become an index of spots of retardation in the lengthwise direction of the PVA film of the present invention. The PVA film of the present invention which satisfies the above formulas (1) and (2) and has a small unevenness of retardation in the lengthwise direction is excellent in stretchability and also has a small fluctuation in width after stretching. An optical film produced by stretching the PVA film has excellent optical performance. When A in the above formula (1) exceeds 10 nm, the optical performance of the obtained optical film becomes insufficient. In addition, the stretchability and the uniformity of the film width after stretching are also reduced. As for A, 9.5 nm or less is preferable. When B in the above formula (2) exceeds 1.5 nm, the optical performance of the obtained optical film becomes insufficient. In addition, the stretchability and the uniformity of the film width after stretching are also reduced. B is preferably 1.2 nm or less. On the other hand, B is usually 0.1 nm or more.

The Re _total (nm) in the above equation (3) is the number of retardations at all measurement points when the retardation is measured for the entire PVA film with a pitch in the length direction of 15 m and a pitch in the width direction of 10 mm. It is an average value. The stretchability of the PVA film is improved by setting Re _{total in the range} represented by the above formula (3). Re _total is preferably 18 nm or less. As described above, in general, when measuring the retardation of the entire PVA film, the measurement is performed so that positions of 10 mm from each of the two ends 2 and 3 of the PVA film 1 are included. Re _i , Re _max , Re _min and Re _ave are also determined along with Re _total using the measured value at this time.

The formula (4) _is obtained by defining the ratio of A _{(A / Re total)} for _{Re total.} A is the difference between the maximum value Re _max and the minimum value Re _min of retardation at a position of 10 mm from the end of the PVA film, and the smaller the difference, the better the optical properties of the obtained optical film, which seems to be preferable Be However, the present inventors have conducted extensive studies to improve the optical performance of the optical film obtained with stretching of the PVA film, _{surprisingly,} the ratio of A to _{Re total} of _{(A / Re total)} By making it 0.3 or more, it has been found that the stretchability is significantly improved with almost no decrease in optical performance. The ratio (A / Re _total ) is more preferably 0.4 or more. On the other hand, the ratio (A / Re _total ) is preferably 2 or less, more preferably 1 or less.

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

From the viewpoint of further improving the stretchability of the PVA film, the thickness of the PVA film is preferably 20 μm or more. The width of the PVA film is preferably 3.5 m or more. On the other hand, when producing an optical film such as a polarizing film with a realistic production machine, the uniform uniaxial stretching may become difficult if the width of the film is too wide, so the width of the PVA film is 8 m or less Is preferred.

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

As PVA used for the film of this invention, what was manufactured by saponifying the polyvinyl ester obtained by polymerizing a vinyl ester can be used. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among the above-mentioned vinyl esters, vinyl acetate is preferable from the viewpoint of availability, cost, easiness of production of PVA, and the like.

The polyvinyl ester described above is preferably obtained using only one or two or more vinyl esters as a monomer, and more preferably obtained using only one vinyl ester as a monomer However, it may be a copolymer of one or more vinyl esters with other monomers copolymerizable therewith.

As other monomers copolymerizable with such vinyl esters, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, isobutene (α-olefin etc.), acrylic acid or a salt thereof Methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate Acrylic acid esters such as octadecyl acrylate; methacrylic acid or salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, methacrylic acid t-Butyl, 2-ethylhexyl methacrylate, methacrylic Methacrylic acid esters such as dodecyl and octadecyl methacrylate; acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamidopropane sulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof Acrylamide derivatives such as N-methylol acrylamide or derivatives thereof; methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropane sulfonic acid or salts thereof, methacrylamidopropyldimethylamine or salts thereof, N-methylol methacrylamide amide Or methacrylamide derivatives such as derivatives thereof; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolide N-vinyl amides 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, stearyl vinyl ether and the like; Vinyl cyanides such as ronitrile, vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt thereof, ester or acid anhydride; An acid or a salt thereof, an ester or an acid anhydride; a vinylsilyl compound such as vinyltrimethoxysilane; an isopropenyl acetate etc. can be mentioned. The above polyvinyl esters can have structural units derived from one or more of these other monomers.

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

The above PVA may be one modified by one or more graft copolymerizable monomers. Examples of the graft copolymerizable monomers include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; and α-olefins having 2 to 30 carbon atoms. The proportion of structural units derived from graft copolymerizable monomers in PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA.

In the above PVA, a part of the hydroxyl groups may or may not be crosslinked. In the above PVA, a part of the hydroxyl groups may be reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or not reacted with these compounds to form an acetal structure May be

The polymerization degree of PVA is not particularly limited, but is preferably 500 or more, more preferably 1,000 or more, and preferably 1,500 or more from the viewpoint of film strength and durability of the obtained optical film. Is more preferable, and 2,000 or more is particularly preferable. On the other hand, when the degree of polymerization is too high, the polymerization degree of PVA is preferably 10,000 or less, since it tends to lead to an increase in production cost and poor processability during film formation. Some are more preferable, 8,000 or less is more preferable, and 7,000 or less is particularly preferable. The degree of polymerization of PVA referred to in the present specification means an average degree of polymerization measured in accordance with the description of JIS K 6726-1994.

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

As a raw material of the PVA film of the present invention, one type of PVA may be used alone, or two or more types of PVA having different types of modification, modification rate, degree of polymerization, degree of saponification, etc. may be used in combination. However, when secondary processing is required for the PVA film of the present invention, such as when used as a raw fabric for producing an optical film, the PVA film has an acidic functional group such as a carboxyl group or a sulfonic acid group. Group-containing PVA; an acid anhydride group-containing PVA; a basic functional group-containing PVA such as an amino group; and a neutralized product of these, such as a PVA having a functional group that accelerates a crosslinking reaction The crosslinking reaction may reduce the secondary processability of the PVA film. Therefore, in the above case, it is preferable that the PVA film does not contain any of PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group and a neutralized product thereof. As PVA, PVA produced by saponifying polyvinyl ester obtained by using only vinyl ester as a monomer, and / or only vinyl ester and ethylene and / or only olefin having 3 to 30 carbon atoms It is more preferable to contain only PVA produced by saponifying polyvinyl ester obtained by using it for the body, and produced by saponifying polyvinyl ester obtained using only vinyl ester as a monomer as PVA. It is further preferable to contain only the PVA obtained by saponifying the obtained PVA and / or the polyvinyl ester obtained by using only the vinyl ester and ethylene as monomers.

The PVA film is produced using the PVA thus obtained. Although the manufacturing method of the PVA film of the present invention is not particularly limited, a film forming apparatus provided with a plurality of drying rolls whose rotation axes are parallel to each other is used, and the plurality of drying rolls are mth drying roll (m to m) Is an integer of 3 or more), and a film forming solution containing polyvinyl alcohol is discharged from the die onto the first drying roll and dried to obtain a film, and then the second to m-th drying rolls are produced. Using the step of further drying the film, wherein the volatile fraction of the film when peeled from the first drying roll is 12 to 20%, and the second drying with respect to the peripheral speed (S ₁ ) of the first drying roll the ratio _(S 2 / _{S 1)} is 1.015 to 1.050 of the peripheral speed of the roll _{(S 2),} the peripheral speed of the second drying roll against _{(S 2),} the volatile fraction of the film is 11 mass %less than The ratio (S _x / S ₂ ) of the peripheral speed (S _x ) of the drying roll (the x-th drying roll) which contacts for the first time is 0.970 to 0.995, and the second drying roll to the x-th drying roll It is preferred to produce by the process, the average of the roll temperature up to 63-81.degree.

As a film forming solution, a solution obtained by mixing PVA with a liquid medium or a melt obtained by melting a PVA chip containing a liquid medium or the like is used. These can be prepared using a stirring mixer, a melt extruder, and the like. Examples of the liquid medium used at that time include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine and the like. One of these liquid media may be used alone, or two or more thereof may be used in combination. Among these, water, dimethyl sulfoxide, or a mixture thereof is preferably used, and water is more preferably used.

The film-forming solution preferably contains a plasticizer, from the viewpoint of further improving the stretchability of the obtained PVA film. By using a film-forming solution containing a plasticizer, a PVA film containing a plasticizer is obtained. As the plasticizer, polyhydric alcohols are preferably used and, for example, ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like can be mentioned. The plasticizer may be used alone or in combination of two or more. Among them, one or more of glycerin, diglycerin and ethylene glycol are preferably used.

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

The film-forming solution preferably contains a surfactant from the viewpoint of improving the releasability from the drying roll when producing a PVA film, and the handleability of the obtained PVA film. A PVA film containing a surfactant can be obtained by using a film-forming solution containing a surfactant. The type of surfactant is not particularly limited, but anionic surfactants or nonionic surfactants are preferably used. These surfactants may be used alone or in combination of two or more.

As the anionic surfactant, for example, carboxylic acid type such as potassium laurate, sulfuric acid ester type such as octyl sulfate, and sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate are preferable.

Further, as the nonionic surfactant, for example, alkyl ether type such as polyoxyethylene oleyl ether, alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, alkyl ester type such as polyoxyethylene laurate, polyoxyethylene Alkyl amine type such as lauryl amino ether, alkyl amide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as lauric acid diethanolamide, oleic acid diethanolamide, Allylphenyl ether nonionic surfactants such as polyoxyalkylene allyl phenyl ether are preferred.

The content of the surfactant is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 parts by mass, and more preferably 0.05 to 0.3 based on 100 parts by mass of PVA. More preferably, it is part by weight. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability and the dyeability are further improved. Moreover, the handleability of a PVA film improves because content of surfactant is 1 mass part or less with respect to 100 mass parts of PVA.

The membrane forming solution is a stabilizer (antioxidant, ultraviolet absorber, heat stabilizer etc.), compatibilizer, antiblocking agent, flame retardant, antistatic agent, lubricant, dispersant, fluidizer, antibacterial agent, etc. And various additives may be included. These additives may be used alone or in combination of two or more.

It is preferable that the volatile fraction of the membrane-forming stock solution used for producing a PVA film is 60 to 75% by mass. The film-forming stock solution having a volatilization fraction of 60% by mass or more has an appropriate viscosity, so the film-forming property is improved. More preferably, the volatile fraction is 65% by mass or more. On the other hand, the uniformity of the thickness of the PVA film obtained improves because a volatile matter fraction is 75 mass% or less. In the present invention, the volatile fraction of the membrane-forming solution is determined by the following formula (i).

Volatile fraction (mass%) = {(Wa−Wb) / Wa} × 100 (i)
[Wherein, Wa represents the mass (g) of the membrane-forming solution, Wb represents the mass (g) of the component remaining after drying the membrane-forming solution of Wa (g) in the electrothermal dryer at 105 ° C. for 16 hours. ]

In the film forming apparatus used for producing the PVA film, the surface of the drying roll is resistant to corrosion and preferably has a mirror gloss. From such a viewpoint, the drying roll is preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel or the like. From the viewpoint of enhancing the durability of the drying roll, it is also preferable that a plated layer of nickel, chromium, nickel / chromium alloy or the like is formed in a single layer or a multilayer on the surface of the drying roll.

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

The number of drying rolls in the film forming apparatus is 3 or more, preferably 5 to 30. In the present invention, the first drying roll, the second drying roll, the third drying roll, the fourth drying roll,. The film forming apparatus has a known discharge device (casting device) such as a T-shaped slit die, a hopper plate, an I-die, and a lip coater die. The film forming solution is discharged (casted) into a film form from the die of the apparatus onto the first drying roll.

After a film is obtained by drying the film-forming stock solution discharged onto the first drying roll on the first drying roll, the film is peeled off from the first drying roll. Here, the volatile fraction of the film at the time of peeling from the first drying roll needs to be 12 to 20% by mass.

When the volatile fraction of the film when peeled off the first drying roll is less than 12% by mass, the stretchability is significantly reduced. On the other hand, when the volatilization fraction of the film at the time of peeling from the first drying roll exceeds 20% by mass, the peelability of the film from the first drying roll is deteriorated, and thickness unevenness in the flow direction becomes large. The volatile fraction is preferably 19% by mass or less, more preferably 18% by mass or less, and still more preferably 16% by mass or less. In the present invention, the volatile fraction of the film is determined by the following formula (ii) after collecting the film immediately after peeling from the first drying roll.

Volatile fraction (mass%) = {(Wc−Wd) / Wc} × 100 (ii)
[Wherein, Wc represents the mass (g) of the collected film, and Wd represents the mass (g) of the film after the film Wc (g) was dried in a dryer at a temperature of 105 ° C. for 16 hours. ]

When a PVA film obtained using a film-forming solution prepared using PVA, a polyhydric alcohol (plasticizer) such as glycerin, a surfactant and water is dried under the above conditions, the components other than water are substantially The volatile content of the film is substantially the same as the water content (water content) contained in the film because it remains in the film without volatilizing.

The surface temperature of the first drying roll is preferably 80 to 120 ° C. in terms of the uniformity of drying, the drying speed and the like. If the surface temperature is less than 80 ° C., drying on the first drying roll tends to be insufficient, which tends to cause peeling failure. The surface temperature is more preferably 85 ° C. or more. On the other hand, when the surface temperature exceeds 120 ° C., the film tends to foam easily. The surface temperature is more preferably 105 ° C. or less, and still more preferably 99 ° C. or less.

The circumferential speed (S ₁ ) of the first drying roll is preferably 8 to 25 m / min from the viewpoint of the uniformity of drying, the drying speed, the productivity, and the like. If the circumferential speed (S ₁ ) is less than 8 m / min, the productivity may be reduced. The circumferential speed (S ₁ ) is more preferably 10 m / min or more, further preferably 12 m / min or more. On the other hand, when the circumferential speed (S ₁ ) exceeds 25 m / min, the drying on the first drying roll tends to be insufficient. Moreover, it is more preferable that it is 23 m / min or less, and it is still more preferable that it is 22 m / min or less.

Although the film-forming stock solution discharged onto the first drying roll may be dried using only the first drying roll, by blowing hot air onto the film surface not in contact with the first drying roll. And heat may be applied from both sides of the film for drying. This further improves the uniformity of drying and the drying speed. The velocity of the hot air is preferably 1 to 10 m / sec, more preferably 2 to 8 m / sec, and still more preferably 3 to 8 m / sec.

If the wind speed is too low, dew condensation may occur on the first drying roll, and the water droplets may fall on the film to cause defects in the PVA film obtained. On the other hand, when the wind speed is too fast, thickness unevenness occurs in the obtained PVA film, which may cause troubles such as staining unevenness.

The temperature of the hot air is preferably 50 to 150 ° C., more preferably 70 to 120 ° C., and still more preferably 80 to 95 ° C. from the viewpoint of drying efficiency, uniformity of drying, and the like. Further, the dew point temperature of the hot air is preferably 10 to 15 ° C. When the temperature of the hot air is too low, the drying efficiency, the uniformity of drying, and the like are likely to be reduced. On the other hand, when the temperature of the hot air is too high, foaming tends to occur.

Although the system in particular at the time of blowing a hot air on a film on a 1st drying roll is not restrict | limited, A nozzle system, a baffle plate system, those combinations, etc. are employ | adopted preferably. Further, it is preferable to exhaust the volatile matter generated at the time of drying of the film on the first drying roll and the blown hot air.

The film dried to a volatile content of 12 to 20% by mass by the first drying roll is peeled off from the roll, and the film is further dried by the second drying roll. When drying the said film on a 2nd drying roll, it is preferable to make the surface on the opposite side to the side where the 1st drying roll of the said film was contacting contact a 2nd drying roll, and to make it dry.

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 1.015 to 1.050. If the ratio (S 2 _{/ S} ₁₎ is less than 1.015, the film from the first drying roll is difficult peeling, the uniformity of the width direction of the obtained PVA film may be lowered. On the other hand, when the ratio (S ₂ / S ₁ ) exceeds 1.050, tension unevenness applied to the film between the first drying roll and the second drying roll becomes large, and the uniformity of the obtained PVA film is increased. There is a risk of loss of

Ratio (S _x ) of the peripheral speed (S _x ) of the drying roll (Xth drying roll) to be contacted only after the volatile fraction of the film becomes 11% by mass or less with respect to the peripheral speed (S ₂ ) of the second drying roll It is preferable that _x ₂ / S ₂ ) be 0.970 to 0.995. Volatile fraction is measured immediately before the film contacts each drying roll. The dry roll with which the film comes into contact immediately after the volatile content rate first decreases to 11% by mass or less is the “dry roll (Xth dry roll) that contacts the film only after the volatile fraction of the film becomes 11% by mass or less). is there. When the ratio (S _x / S ₂ ) of the peripheral speed (S _x ) of the xth drying roll to the peripheral speed (S ₂ ) of the second drying roll is less than 0.970, A and B respectively have upper limits The optical performance of the resulting optical film may be insufficient. In addition, the stretchability of the PVA film and the uniformity of the film width after stretching may be reduced. On the other hand, when the ratio (S _x / S ₂ ) of the peripheral speed (S _x ) of the xth drying roll to the peripheral speed (S ₂ ) of the second drying roll exceeds 0.995, the obtained PVA film is obtained When Re _total exceeds 20 nm, stretchability may be reduced.

In the second to x-th drying rolls, the ratio (S _{a + 1} / S) of the peripheral speed (S _{a + 1} ) of the downstream drying roll to the peripheral speed (S _a ) of the upstream drying roll of the two adjacent drying rolls _a ) is preferably 0.975 to 1. In the second to x-th drying rolls, it is more preferable that the ratio (S _{a + 1} / S _a ) in all two adjacent drying rolls is 0.975 to 1.

It is preferable that the average of the roll temperature of the second drying roll to the xth drying roll is 63 to 81.degree. When the average of the roll temperature is less than 63 ° C. or more than 81 ° C., the optical performance of the obtained optical film may be insufficient when A and B exceed the upper limit. In addition, the stretchability of the PVA film and the uniformity of the film width after stretching may also be reduced.

It is preferable that all the roll temperatures of the second drying roll to the x-th drying roll be 50 to 95.degree. When the roll temperature is less than 50 ° C. or more than 95 ° C., the optical performance of the obtained optical film may be insufficient when A and B exceed the respective upper limits. In addition, the stretchability and the uniformity of the film width may be reduced.

When a further drying roll is disposed downstream of the x-th drying roll, downstream of the peripheral speed (S _b ) of the drying roll upstream of the two adjacent drying rolls in the x-th drying roll to the m-th drying roll The ratio (S _{b + 1} / S _b ) of the peripheral speed (S _{b + 1} ) of the drying roll is preferably 0.975 to 1. It is preferable that the roll temperatures of the (x + 1) th to the (m) th drying rolls are all 50 to 130 ° C.

If further drying rolls are arranged downstream of the x-th drying roll, the surface temperature of at least a part of the drying rolls may be increased. Thereby, drying and heat treatment of a PVA film can be performed simultaneously. The roll temperature at this time is preferably 90 to 140 ° C., and more preferably 95 to 130 ° C.

When bringing the respective drying rolls into contact with the film, it is preferable to alternately contact one side and the other side of the film with the respective drying rolls, from the viewpoint of being able to dry more uniformly.

The ratio (S _m / S ₁ ) of the peripheral speed (S _m ) of the mth drying roll to the peripheral speed (S ₁ ) of the first drying roll is not particularly limited, but is in the range of 0.900 to 1.100 Are more preferably in the range of 0.950 to 1.050, still more preferably in the range of 0.980 to 1.020, and in the range of 0.990 to 1.010. Is particularly preferred.

It is preferable to cut the width direction both ends (ears) of the dried PVA film. At this time, the ratio (W _T / W ₁ ) of the film width (W _T ) after both ends (ears) are cut to the film width (W ₁ ) when discharged from the die is 0.6 or more It is preferably present, and more preferably 0.7 or more. The edge part of the PVA film formed into a film by the conventional method had a high retardation value, and such a PVA film had inadequate ductility. Although the stretchability is improved by cutting the end of the PVA film wider, the width of the obtained PVA film is narrowed, and the cost is also increased due to an increase in the discarded portion, which causes a problem. It had become. On the other hand, according to the manufacturing method of the present invention, since the retardation value of the PVA film end after film formation can be reduced, there is no need to cut the end widely, and a wide PVA film excellent in stretchability Is obtained.

The dried PVA film may be subjected to a humidity control process, etc., as required, and may be wound into a roll. The volatile fraction of the PVA film finally obtained is preferably 1 to 5% by mass, and more preferably 2 to 4% by mass. Moreover, it is preferable that it is 50 mass% or more, and, as for content of PVA in the said PVA film, it is more preferable that it is 80 mass% or more.

The PVA film of the present invention has excellent stretchability even if it is thin and wide, and the variation in width after stretching is small. By using such a PVA film, a thin and wide optical film excellent in optical performance, particularly a polarizing film can be produced with high productivity. In recent years, the screen size of liquid crystal televisions and monitors has been increasing. In addition, weight reduction of notebook computers, mobile phones, etc. is also in progress. The PVA film of the present invention is suitably used as a raw material of an optical film used for these. The said optical film can be manufactured by the manufacturing method which has the process of uniaxially stretching using the PVA film of this invention.

Examples of a method of producing a polarizing film using the PVA film of the present invention as a raw fabric include a method of dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment if necessary, using the PVA film of the present invention. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, may be performed simultaneously with uniaxial stretching, or may be performed after uniaxial stretching. In addition, the steps such as uniaxial stretching and dyeing may be repeated multiple times.

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

The uniaxial stretching of the PVA film may be performed by either a wet stretching method or a dry heat stretching method. When uniaxially stretched by a wet stretching method, uniaxial stretching may be performed in warm water containing boric acid, uniaxial stretching may be performed in a solution containing the above-described dye or in a fixing treatment bath described later, or after water absorption The film may be uniaxially stretched in air using a PVA film of or any other method. The stretching temperature in uniaxial stretching is not particularly limited, but preferably 30 to 90 ° C., more preferably 40 to 70 ° C., still more preferably 45 to 65 ° C. when stretching a PVA film in warm water (wet stretching) In the case of dry heat drawing, a temperature of 50 to 180.degree. C. is preferably adopted. In addition, it is preferable to stretch as far as possible immediately before the film is cut from the viewpoint of polarization performance, specifically the stretching ratio of uniaxial stretching (total stretching magnification when performing uniaxial stretching in multiple stages) is specifically 4 times or more Is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film does not break, but in order to perform uniform drawing, it is preferably 8.0 times or less. In addition, the draw ratio in this specification is based on the length of the film before extending | stretching, and the state which is not extending | stretching is corresponded to draw ratio 1 time. The thickness of the film (polarizing film) after stretching is preferably 5 to 35 μm, particularly 20 to 30 μm.

There is no particular limitation on the direction of uniaxial stretching in the case of uniaxially stretching a long PVA film, and uniaxial stretching in the longitudinal direction or transverse uniaxial stretching can be adopted, but a polarizing film having excellent polarization performance can be obtained. Uniaxial stretching in the longitudinal direction is preferred. Uniaxial stretching in the longitudinal direction can be performed by changing the circumferential speed between the rolls using a stretching apparatus comprising a plurality of rolls parallel to one another. On the other hand, transverse uniaxial stretching can be performed using a tenter-type stretching machine.

In the production of a polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dye onto the uniaxially stretched film. As a fixing process, the method of immersing a film in the fixed process bath which added boron compounds, such as a boric acid and borax, is mentioned. At this time, if necessary, an iodine compound may be added to the fixing treatment bath.

It is preferable to dry-process (heat treatment) the film which performed uniaxial-stretching, or uniaxial-stretching and fixation processing next. The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150 ° C., particularly preferably in the range of 50 to 140 ° C. When the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film is likely to be reduced, while when it is too high, the polarization performance is apt to be degraded due to the decomposition of the dye.

A protective film having optical transparency and mechanical strength can be bonded to both surfaces or one surface of the polarizing film obtained as described above to make a polarizing plate. As a protective film in that case, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, etc. are used. Moreover, as an adhesive agent for bonding together a protective film, a PVA-type adhesive agent, a urethane type adhesive agent, etc. are mentioned, Among these, a PVA-type adhesive agent is preferable.

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

Hereinafter, the present invention will be specifically described by way of examples.

Measurement of Retardation Value The retardation value of the PVA film just before being taken up through the drying step was measured. The retardation value in the thickness direction of the film at 25 ° C. was measured based on the light having a wavelength of 590 nm using a plurality of retardation measurement devices arranged in the vertical direction with respect to the flow direction of the film. After measuring the retardation value of the whole film surface by setting the pitch in the length direction (flow direction) of the film to 15 m and the pitch in the width direction to 10 mm, the number average value Re _total of the retardation of all measurement points was determined. Furthermore, from the retardation (Re _i ) of the measurement point i (i = 1 to n, n is an integer) at a position of 10 mm from the end of the PVA film, its maximum value (Re _max ), minimum value (Re _min ), number After the average value (Re _ave ) was determined by the above method, A and B were calculated by introducing them into the above formulas (1) and (2).

Example 1
(1) Production of PVA film 100 parts by mass of PVA (saponified product of homopolymer of vinyl acetate, polymerization degree 2,400, degree of saponification 99.9 mol%), glycerin 12 parts by mass, lauric acid diethanolamide 0.1 mass A film-forming stock solution with a volatile fraction of 66% by mass, consisting of 1 part and water, was used. As a film forming apparatus, one provided with a T-shaped slit die (width 4.9 m) and 18 drying rolls whose rotation axes are parallel to each other was used. The casting dope first drying roll (surface temperature 93.5 ° C., a peripheral speed _(S 1) 14.5 m / min) from a T-slit die was discharged onto a film. At this time, hot air (temperature 90 ° C., dew point temperature 10 ° C.) was uniformly blown over the film on the first drying roll at a wind speed of 5 m / sec. Then, the film is peeled off from the first drying roll (the volatile fraction of the film immediately after peeling off from the first drying roll is 18.2% by mass), and the film surface not in contact with the first drying roll is the second drying roll It was dried by contacting with The film was dried by sequentially contacting the third drying roll to the eighteenth drying roll so that one side and the other side of the film alternately contact each drying roll. Then, after cutting both ends (ears) of the film, it was wound up in a roll to obtain a PVA film (thickness 60 μm, width 4 m, length 5,000 m, volatile fraction 3% by mass). After cutting both ends of the film, the retardation value of the PVA film was measured by the above method before winding. The volatile fraction of the film was determined as follows. Immediately after the film was peeled off from the first drying roll, a sample was taken from the center of the film. In addition, samples were collected from the center of the film immediately before contacting the second to eighteenth drying rolls. Each sample was dried in a dryer at 105 ° C. for 16 hours, and then the volatile fraction was determined from the mass of the film before and after drying. The surface temperature of each drying roll is shown in Table 2, and the peripheral speed ratio of adjacent drying rolls is shown in Table 3.

The volatile fraction of the film immediately before contacting the seventh drying roll was 10.8% by mass. That is, the drying roll contacted for the first time after the volatile content of the film became 11% by mass or less was the seventh drying roll (x = 7). The ratio (S ₇ / S ₂ ) of the peripheral speed (S ₇ ) of the seventh drying roll to the peripheral speed (S ₂ ) of the _second drying roll is 0.971, and the peripheral speed (S ₁ ) of the first drying roll The ratio (S ₂ / S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the above was 1.050. The average of the roll surface temperature of the second to x-th drying rolls was 80 ° C. The results are shown in Table 1. Also, calculated A, B, Re _total and A / Re _total using retardation values of the PVA film are shown in Table 1.

Evaluation of Stretchability As described below, a film roll of the obtained PVA film was continuously subjected to swelling treatment, dyeing, uniaxial stretching, and drying treatment in this order to produce a polarizing film. The PVA film was immersed in distilled water for 1 minute as swelling treatment. Subsequently, it was immersed in an aqueous solution containing an iodine dye (iodine concentration: 0.3% by mass, potassium iodide concentration: 2.1% by mass, temperature 30 ° C.) for 1 minute to contain the iodine dye. Subsequently, it was stretched 6.2 times in the flow direction in a boric acid aqueous solution (boric acid concentration: 4% by mass, potassium iodide concentration: 6% by mass, temperature: 60 ° C.). Then, it was made to dry at 60 degreeC for 1 minute, and the polarizing film was obtained. Evaluation of the stretchability is A when the number of breakage occurrence when stretching a 1,000 m PVA film roll is 0 under the above conditions is A, and the stretchability evaluation is B when it is 1 to 3 times, 4 or more times The evaluation of stretchability was C in the case of.

Evaluation of Width Variation The width of the obtained polarizing film was measured every 100 m, and the difference α (cm) between the maximum value and the minimum value was calculated. The percentage (100 × α / β) of the difference α (cm) to the PVA film width β (cm) of the raw fabric was calculated. When the percentage is less than 0.5%, the evaluation of the width fluctuation is A, and when the percentage is 0.5% or more and less than 1.0%, the evaluation of the width fluctuation is B, and the width is 1.0% or more Evaluation of fluctuation is C.

Examples 2, 3 Comparative Examples 1 to 4, Reference Examples 1 and 2
The production and evaluation of a PVA film were carried out in the same manner as in Example 1 except that the production conditions of the PVA film were as shown in Tables 1 to 3. The results are shown in Table 1.

The PVA film of the present invention satisfying the above formulas (1) to (4) is excellent in excellent stretchability, and the width at the time of stretching is also uniform. To the circumferential speed of the second drying roll _{(S 2),} the ratio of the peripheral speed of the x drying roll _{_{(S x) (S x /}} S 2) is less than 0.970, the x drying roll from the second drying roll When the average roll temperature exceeds 81 ° C. (Comparative Examples 1 and 2), A and B of the obtained PVA film exceed the upper limits defined by the above formulas (1) and (2), and the stretchability is And the uniformity of the width at the time of stretching decreased. Furthermore, A and B are indices of retardation spots in the lengthwise direction of the PVA film, and the PVA films of Comparative Examples 1 and 2 having large values of these are considered to have insufficient optical performance of the obtained optical film Be

Also when the average of the roll temperature from the second drying roll to the x-th drying roll is less than 63 ° C. (Comparative Example 3), A and B of the resulting PVA film are defined by the above formulas (1) and (2) When the content exceeds the upper limit, the stretchability and the width uniformity at the stretch decrease. The PVA film of Comparative Example 3 in which A and B are large is considered to be insufficient in the optical performance of the resulting optical film. The ratio (S _x ) of the peripheral speed (S _x ) of the xth drying roll to the peripheral speed (S ₂ ) of the second drying roll is lower than 63 ° C. on average of the roll temperature from the second drying roll to the xth drying roll _{If x} / _{S 2)} is more than 0.995 (Comparative example 4), _{Re total} of the obtained PVA film exceeds the upper limit defined by the formula (3), the uniformity of the width when stretchability and stretch Decreased.

Reference Example 1 is an example in which, when cutting both ends of a PVA film formed in the same manner as Comparative Example 3, the end portion is cut wider than in Comparative Example 3. Although the performance of the obtained PVA film was sufficient, since the width was narrow, there was a problem in practical use. Reference Example 2 is an example of a conventional thick (75 μm) PVA film.

1 PVA film 2, 3 end 4 length direction 5 pitch 6 width direction

Claims

A polyvinyl alcohol film with a width of 3 m or more, a length of 1,000 m or more, and a thickness of 15 to 65 μm,
A polyvinyl alcohol film characterized in that a retardation value measured by setting a pitch in the length direction to 15 m and a pitch in the width direction to 10 mm satisfies the following formulas (1) to (4).

During the ceremony
Re max (nm): maximum retardation Re min (nm) at a position 10 mm from the edge: minimum retardation Re ave (nm) at a position 10 mm from the edge: average retardation at a position 10 mm from the edge Value Re i (nm): Retardation value Re total (nm) of measurement point i (i = 1 to n, n is an integer) at a position of 10 mm from the end: Average value of retardation of all measurement points.
The method for producing a polyvinyl alcohol film according to claim 1,
Using a film forming apparatus comprising a plurality of drying rolls whose rotation axes are parallel to one another
The plurality of drying rolls consist of a first drying roll to an m-th drying roll (m represents an integer of 3 or more),
After a film is obtained by discharging a film-forming solution containing polyvinyl alcohol onto a first drying roll from a die and drying, a step of further drying the film using a second drying roll to a m-th drying roll is included. And
The volatile fraction of the film when peeled off from the first drying roll is 12 to 20%,
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 1.015 to 1.050,
Ratio (S x ) of the peripheral speed (S x ) of the drying roll (Xth drying roll) to be contacted only after the volatile fraction of the film becomes 11% by mass or less with respect to the peripheral speed (S 2 ) of the second drying roll x / S 2 ) is 0.970 to 0.995,
A method for producing a polyvinyl alcohol film, wherein the average roll temperature from the second drying roll to the x-th drying roll is 63 to 81 ° C.
The polyvinyl alcohol film according to claim 2, wherein the volatile content of the membrane-forming solution containing polyvinyl alcohol is 60 to 75% by mass, and the peripheral speed (S 1 ) of the first drying roll is 8 to 25 m / min. Production method.