TW201420313A - Polyvinyl alcohol-based polymer film and manufacturing process therefor - Google Patents

Abstract

To provide a polyvinyl alcohol (PVA) film capable of yielding an optical film such as a polarizing film which exhibits little color irregularity even in a case wherein the light transmittance of the film is high or in a case wherein a backlight having a higher intensity is used. A PVA film in which when the in-plane orientation axes of the film are measured at 20-mm pitches in the widthwise direction of the film, all the angles (within a range of 0 to 90 ) between orientation axes which are observed at each pair of adjacent measuring positions are 2.3 or less. In the PVA film, it is preferable that the average of the angles between orientation axes which are observed at each pair of adjacent measuring positions is 0.6 or less.

Description

Polyvinyl alcohol polymer film and method of producing the same

The present invention relates to a polyvinyl alcohol polymer film (hereinafter, "polyvinyl alcohol polymer" is abbreviated as "PVA"), a method for producing the same, an optical film such as a polarizing film produced from the PVA film, and the like. A method of manufacturing a film.

A polarizing plate having a light penetrating and shielding function is an important component of a liquid crystal display device (LCD) similarly to a liquid crystal having a light switching function. The field of application of this liquid crystal display device has also expanded from small devices such as computers and watches at the beginning of development to notebook computers, liquid crystal displays, liquid crystal color projectors, LCD TVs, in-vehicle navigation systems, mobile phones, indoors and outdoors. A wide range of measuring machines and the like are used, and in particular, liquid crystal displays and liquid crystal televisions are moving toward large screens.

The polarizing plate is usually obtained by winding a long PVA film rolled into a roll shape, uniaxially stretching, and then dyeing with an iodine or a dichroic dye, dyeing the rolled PVA film and uniaxially. After the stretching, the method of fixing with a boron compound, the method of performing dyeing in any of the above methods, and the simultaneous fixing treatment, etc., are used to produce a polarizing film, and the one or both sides of the polarizing film obtained thereby are used. Cellulose triacetate film or acetic acid. A protective film such as a cellulose butyrate film is industrially produced.

Heretofore, various techniques have been known for improving the optical performance of a polarizing film, obtaining a wide polarizing film, and improving the productivity of a polarizing film. For example, in the case of a polarizing film which can produce a disorder with less optical axis, it is known that the maximum value of the absolute value of the inclination angle and the local variation of the inclination angle with respect to the longitudinal direction of the film of the major axis of the birefringence ellipsoid are known. The PVA film having a specific ratio is specified (see Patent Document 1). Further, in order to prevent the color unevenness of the polarizing film or the occurrence of wrinkles during stretching of the PVA film, it is known that a PVA film having a hysteresis difference between two points in the width direction of the film at a distance of 1 cm is in a specific range ( Refer to Patent Document 2). In addition, a polarizing film having a uniform optical performance even in a large area can be produced, and a specific PVA film having a thickness variation of 1 mm in the film width direction within a specific range is known (see Patent Document 3).

In addition, it is known that the occurrence of wrinkles in the swelling of the PVA film or the streaky stain spots existing in the longitudinal direction of the polarizing film is known to be the inclination of the optical axis across the entire film width direction of the film. A specific PVA film having a long side direction of 45 to 135° with respect to the film (refer to Patent Document 4); for a polarizing film having high polarization performance, it is known that an angle formed by a flow direction and an optical axis is a specific PVA film having a hysteresis of 15 to 90 nm in the thickness direction of the central portion in the width direction of the range of 70 to 110° (see Patent Document 5); and, in the uniaxial stretching step, the shrinkage can be reduced to produce more. In the case of a polarizing film having a wide polarizing film and a polarizing film exhibiting high polarizing performance, it is known that the direction in which the uniaxial stretching should be performed when the polarizing film is formed and the optical axis are in the range of 0 to 20°. A specific PVA film having a hysteresis in the range of 50 to 150 nm (see Patent Document 6).

Further, a PVA film containing a specific surface layer/core layer/surface layer is known as a stretched film which can be uniformly stretched and which can suppress the occurrence of fine cracks or voids during stretching (refer to Patent Document 7). Patent Document 7 discloses that a film forming stock solution containing a PVA having a volatility of 50 to 90% by mass is heated by a first drying roll, and hot air is blown to a PVA film surface which is not in contact with the first drying roll under a predetermined condition, and When the volatile matter ratio is 15 to 30% by mass, the PVA film is peeled off from the first drying roll and brought into contact with the second drying roll to be dried. At this time, the peripheral speed (S ₁ ) of the first drying roll and the first drying roll are used. 2 The ratio of the peripheral speed (S ₂ ) of the drying rolls (S ₂ /S ₁ ) is set to a method for producing a PVA film of 1.000 to 1.100.

Prior technical literature Patent literature

Patent Document 1 Japanese Patent Laid-Open No. Hei 6-138320

Patent Document 2 Japanese Patent Laid-Open Publication No. 2002-28938

Patent Document 3 Japanese Patent Laid-Open Publication No. 2002-31720

Patent Document 4 International Publication No. 2009/028141

Patent Document 5 Japanese Patent Laid-Open Publication No. 2010-191293

Patent Document 6 Japanese Patent Laid-Open Publication No. 2011-252937

Patent Document 7 Japanese Patent Laid-Open Publication No. 2005-324355

In the past, in order to improve the brightness of the screen of the LCD, the intensity of the backlight has been mainly improved. Therefore, it is important for the polarizing plate or the polarizing film to have less color spots even under strong light. However, in recent years, the reduction in power consumption is more strongly demanded, and in LCDs, the point at which high picture brightness can be maintained even in the case where the backlight intensity is low becomes more important. In order to achieve the above, it is considered that the thickness of the polarizing film is made thinner, or the degree of dyeing is weakened, and the light transmittance of the polarizing film or even the polarizing plate is improved. However, if a conventional PVA film is used to produce a polarizing plate having an improved light transmittance, it is known that a polarizing plate having a low light transmittance will have a color spot type which is different from the conventional one and which is attempted to be improved. The stain becomes noticeable and becomes a problem. It is also known that even a polarizing plate having a light transmittance of a conventional level is similarly noticeable in the case of using a backlight having a higher intensity.

Therefore, an object of the present invention is to provide a PVA film which can produce an optical film such as a polarizing film having a reduced color spot even in the case where the light transmittance is high or a case where a backlight having a higher intensity is used, and a good productivity is obtained. A method for producing a PVA film of such a PVA film is continuously and smoothly produced. Another object of the present invention is to provide an optical film such as a polarizing film produced by using the PVA film described above, and a method for producing the optical film.

In order to achieve the above-mentioned object, the inventors of the present invention have repeatedly conducted intensive studies and found that when the alignment axis in the plane of the PVA film is measured at a pitch of 20 mm in the width direction of the film, the two adjacent measurement positions are When the angle formed by the alignment axes is equal to or lower than the specific value of all the two adjacent measurement positions, the PVA film which is not used before is used as the material, even in the case where the light transmittance is high or the backlight having a higher intensity is used, A polarizing film with reduced color spots can still be obtained. Also found that In the case of using a PVA film having a small average value of the angles at all two adjacent measurement positions, the above-mentioned color spots are further reduced.

Further, the inventors of the present invention found that the film forming raw liquid containing PVA is discharged onto the first drying roll of the film forming apparatus having three or more drying rolls, and then dried by the three or more drying rolls to form a film. In this case, the volatility of the PVA film at the time of peeling from the first drying roll is 20 to 40% by mass, and the ratio of the peripheral speed of the second drying roll to the peripheral speed of the first drying roll is set to a specific value. In the range, the volatile matter of the drying roller (xth drying roller) to the PVA film when the volatility of the PVA film from the second drying roller or the downstream drying roller is 20% by mass is 10% by mass. The peripheral speed ratio between the two drying rolls adjacent to each other between the drying rolls (the y-th drying rolls) is set to a specific numerical range, whereby the polarizing film having reduced color spots can be provided, and productivity and smoothness can be obtained. The polarizing film of the above PVA film was continuously produced.

The inventors of the present invention have completed the present invention by further repeating the research based on the above findings. That is, the present invention relates to: [1] A PVA film which is adjacent to all two adjacent measurement positions when the alignment axis is measured at a pitch of 20 mm in the width direction of the film in the plane of the film. The angle formed by the alignment axes of the two measurement positions (but in the range of 0 to 90°) is 2.3° or less; [2] The PVA film of the above [1], wherein all of the adjacent two measurement positions are [3] The PVA film of the above [1] or [2], wherein the measurement position of the alignment axis has a hysteresis value of 5 to 100 nm in all the measurement positions; The PVA film according to any one of the above [1], wherein an alignment axis of at least one of the measurement positions of the alignment axes forms an angle with a longitudinal direction of the PVA film (but in the range of 0 to 90). [5] The PVA film according to any one of the above [1] to [4], wherein the width is 2 m or more; [6] a manufacturing method, which is a PVA film. The method includes the steps of: (a) using a film forming apparatus having three or more drying rolls having mutually parallel rotating axes, and placing the drying rolls on the first drying roll on the most upstream side, After the film forming raw material having PVA is discharged into a film form and partially dried, it is further dried by a subsequent drying roll to form a film; in this case, (b) the volatile matter of the PVA film when peeled off from the first drying roll. The ratio 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 set to 1.015 to 1.050. (d) In the second drying roll or the drying roll on the downstream side, the volatilization rate of the drying roll (xth drying roll) to the PVA film when the volatilization ratio of the PVA film is 20% by mass becomes 10 mass. drying roller peripheral speed of the downstream side of the roll between adjacent drying (first drying rollers y) of the drying rollers 2% of the time (S _{n + 1)} drying roller circumferential speed of the upstream side (S _n) of The ratio (S _n+1 /S _n ) is set to 0.992 to 0.999; [7] The manufacturing method of the above [6], wherein the surface of all the drying rolls existing between the xth drying roll and the yth drying roll is present [8] The manufacturing method of the above [6] or [7], wherein the first drying roll has a peripheral speed (S ₁ ) of 8 to 25 m/min; [9] as described above [6] The manufacturing method according to any one of [8], wherein a peripheral speed (S _y ) of the y-th dry roll is applied to a peripheral speed of the x-th dry roll (S _x) ratio (S _y / S _x) is set to 0.940 to 0.990; [10] An optical film, which is based [5] PVA film manufactured from any one of the above [1] to; [11] The optical film according to the above [10], which is a polarizing film; [12] a method for producing an optical film, which comprises uniaxial stretching using the PVA film according to any one of [1] to [5] above; step.

By using the PVA film of the present invention as a raw material, an optical film such as a polarizing film having reduced color spots can be produced even in the case where the light transmittance is high or when a backlight having a higher intensity is used. Further, according to the method for producing a PVA film of the present invention, the PVA film of the present invention having the above-described excellent characteristics can be continuously produced with good productivity and smoothly. Further, the optical film of the present invention can also reduce the color unevenness of the type of the stain which is different from the conventional problem.

The invention is described in detail below.

In the PVA film of the present invention, when the alignment axis is measured at a pitch of 20 mm in the width direction of the film in the plane of the film, the alignment axes of the adjacent two measurement positions are in the two adjacent measurement positions. The angle formed (but in the range of 0 to 90°) is 2.3 or less. That is, if the angle to be measured two adjacent positions of all of the maximum value of △ Z _max, the △ Z _max PVA film of the present invention was 2.3 ° or less. The conventional PVA film has a high ΔZ _max , and a polarizing film manufactured using the same or a polarizing plate is used, especially in the case of a high light transmittance or a use of a higher intensity backlight, which is different from the prior art. The stain of the type of stain that is tried to improve the problem has become a problem. On the other hand, the PVA film of the present invention has a ΔZ _max of 2.3 or less, which is different from the conventional PVA film. When such a PVA film of the present invention is used as a raw material, an optical film such as a polarizing film having reduced color spots can be produced even in the case where the light transmittance is high or when a backlight having a higher intensity is used. Further, in Patent Document 1, it is described that the maximum value of the absolute value of the inclination angle in the longitudinal direction of the film with respect to the long axis of the birefringent ellipsoid is 5 degrees or less, and the local rate of change of the inclination angle (at any 5 cm) In the case of the PVA film having a tilt angle of the optical axis in the wide range of 1 degree or less, the local change rate of the tilt angle is 1 degree or less as in Patent Document 1, and Patent Document 1 cannot be obtained in the film. When the alignment axis is measured at a pitch of 20 mm in the width direction of the film in the plane, the PVA film having the maximum value (ΔZ _max ) of the angle formed between the alignment axes of all the two adjacent measurement positions is in the above range, and at least In this regard, the PVA film of the present invention is different from the PVA film described in Patent Document 1.

If ΔZ _max exceeds 2.3°, there is a problem of color spots in the obtained optical film. From the viewpoint of color spots in the optical film, ΔZ _max is preferably 2.2 or less, more preferably 2.0 or less, further preferably 1.9 or less, and particularly preferably 1.8 or less. Further, since △ Z _max is too small there will be situations in which the PVA film produced with reduced manufacturing, △ Z _max or more, for example 0.3 °.

The in-plane alignment axis of the film means the retardation axis in the plane of the film, which is determined by the alignment state of the PVA molecules in the measurement position of the alignment axis. The alignment axis can be measured by light (for example, light having a wavelength of 590 nm) traveling in a direction perpendicular to the film surface (thickness of the film) using a birefringence measuring device, a cell gap measuring device, or the like, specifically, The measurement can be carried out by a method described later in the examples.

In the present invention, a plurality of positions determined so as to have a pitch of 20 mm in the width direction of the film are used as measurement positions of the alignment axes. Here, the width direction of the film is the in-plane direction (TD) of the film perpendicular to the longitudinal direction of the film. When an optical film such as a polarizing film is produced using a long PVA film as a raw material, it is usually uniaxially stretched in the longitudinal direction (mechanical flow direction; MD) of the elongated PVA film. Therefore, in general, when an optical film such as a polarizing film is produced, the longitudinal direction of the film is aligned with the direction in which the polarizing film PVA film is uniaxially stretched, and the in-plane direction of the film perpendicular to the longitudinal direction is the width direction. Further, in the case of a non-stripe PVA film, the direction in which the uniaxial stretching is performed is the longitudinal direction of the film when the optical film such as a polarizing film is produced, and the in-plane direction of the film perpendicular thereto is set to The width direction can be.

In the present invention, it is important that the measurement pitch of the alignment axis is a pitch of 20 mm in the width direction of the film. If the increase is larger than the measurement pitch, even if the maximum value of the angle formed by the alignment axes of the two adjacent measurement positions is reduced, the color spot of the type which is a problem in the present invention is not reduced. Conversely, even if the reduction is smaller than the measurement pitch, the maximum value of the angle formed by the alignment axes of the two adjacent measurement positions is reduced, which is not only the ΔZ when the measurement pitch is set to a pitch of 20 mm. _max in the range corresponding to the case of the present invention is predetermined, in the case of the measurement pitch is set to △ Z _max at 20mm pitch outside a predetermined range corresponding to the present invention, also still can not reduce the above-mentioned stain .

The method of determining the measurement position of the alignment axis is not particularly limited. For example, one measurement position can be determined in the center portion in the width direction of the film, and the measurement position can be sequentially determined from the measurement position toward the both end portions in the width direction at a pitch of 20 mm. Further, the measurement position can exclude a region which is smaller than 20 mm from the both end portions in the width direction toward the center portion in the width direction. For example, when the PVA film having a width of 2020 mm is used to determine the measurement position in accordance with the above-described determination method, first, one measurement position is determined in the center portion in the width direction. Then, from the measurement position, the measurement position is sequentially determined at a pitch of 20 mm from one end portion in the width direction, and the distance from the end portion of the 50th point to the width direction is 10 mm, which is located at the width from the above. In the field in which both end portions in the direction are smaller than 20 mm in the center portion in the width direction, the ends are excluded from the measurement position, and finally the measurement position at 49 points is determined. Similarly, the measurement position at 49 points is determined from the measurement position at the center portion in the width direction toward the other end portion in the width direction. In this way, the determined total of 99 points (1 point + 49 points + 49 points) can be used as the measurement position of the alignment axis.

Then, in order to obtain ΔZ _max , the angles formed by the alignment axes of the adjacent two measurement positions are obtained for all the adjacent two measurement positions from the measured alignment axes at the respective measurement positions, and The maximum value is set to Δ Z _max . For example, in the above example in which the measurement position of 99 points is determined, an angle formed by 98 alignment axes at two adjacent measurement positions can be obtained, and the maximum value among the 98 is ΔZ _max . Further, in the present specification, the angle formed by the alignment axes of the two adjacent measurement positions is in the range of 0 to 90°. That is, in the case where the directions of the two alignment axes are parallel, the angle is 0°, and in the case of vertical, the angle is 90°. In other cases, the angle on the acute angle side is the angle formed by the alignment axes. .

In the PVA film of the present invention, the angle formed by the alignment axes of the adjacent two measurement positions obtained as described above is the average value (ΔZ _ave ) of the angles at all of the two adjacent measurement positions. It is preferably 0.6 or less, preferably 0.58 or less, and further preferably 0.56 or less. On the other hand, the lower limit of _{ΔZ ave} is not particularly limited, and from the case where the PVA film which is too small in ΔZ _{ave has} a decrease in productivity in production, ΔZ _ave is preferably 0.01 or more, and 0.05 or more is Preferably, 0.1 or more is further preferred.

In the PVA film of the present invention, the hysteresis value at the measurement position of the alignment axis is preferably in the range of 5 to 100 nm at all measurement positions. A PVA film satisfying such conditions has improved stretchability and an improved polarizing property when a polarizing film is manufactured. From the viewpoint of the stretchability of the PVA film and the polarizing performance of the polarizing film, the hysteresis value of the measurement position of the alignment axis is preferably 10 nm or more, and more preferably 15 nm or more, in all the measurement positions. More than 20nm is especially good. In addition, from the viewpoint of the stretchability of the PVA film, the hysteresis value of the measurement position of the alignment axis is preferably 70 nm or less at all measurement positions, and more preferably 50 nm or less.

In the PVA film of the present invention, it is preferred that the alignment axis of at least one of the measurement positions of the alignment axis and the longitudinal direction of the PVA film (but in the range of 0 to 90°) is preferably 45 to 90°. A PVA film satisfying such conditions has improved stretchability and an improved polarizing property when a polarizing film is manufactured. From the viewpoint of the stretchability of the PVA film and the polarizing performance of the polarizing film, it is preferable that an angle between at least one of the measurement axes of the alignment axes and the longitudinal direction of the PVA film is 70 to 90°. 80 to 90° is further preferred.

In the PVA film of the present invention, the ΔZ _max , the ΔZ _ave , the hysteresis value, and the angle formed by the alignment axis and the longitudinal direction of the PVA film can be described as long as they conform to the arbitrarily set film width direction. However, it is preferable that the physical properties in the longitudinal direction of the film are not deviated from the viewpoint of continuously and smoothly producing a uniform optical film. Therefore, it is preferable that the above description conforms to 50% or more in the longitudinal direction of the film. More than 80% is preferred, and more than 95% is further preferred. Further, in the case of continuously producing a long PVA film, the physical properties in the longitudinal direction generally do not change much. Therefore, if the above descriptions are consistent on the straight line in the width direction of the arbitrarily set film, it is usually The above description of the width direction of the film will also be met.

The thickness of the PVA film of the present invention is not particularly limited. When it is too thick, drying when an optical film such as a polarizing film is produced is not easily performed rapidly. On the other hand, when it is too thin, it is uniaxially pulled during the production of the optical film. In the case where the film is easily broken, it is preferably in the range of 5 to 150 μm, more preferably in the range of 20 to 120 μm, and further preferably in the range of 50 to 80 μm.

The width of the PVA film of the present invention is not particularly limited, and in recent years, the liquid crystal television or the screen is large in size, and in order to be able to use them effectively, it is preferably 2 m or more, more preferably 4 m or more. Further, in the case of producing an optical film such as a polarizing film by a real production machine, since the uniform uniaxial stretching becomes difficult when the width of the film is too wide, the width of the PVA film is preferably 8 m or less.

The length of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be continuously and smoothly produced, and even when it is used to manufacture an optical film, it can be continuously used, in the range of 5 to 50,000 m. The inside is better, and the range of 100 to 20,000 m is better.

The PVA which forms the PVA film of the present invention can be produced by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester. Examples of the vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, trimethyl vinyl acetate, and neodymium. Acid vinyl ester and the like. Among the above vinyl esters, vinyl acetate is preferred from the viewpoints of ease of handling, cost, ease of PVA production, and the like.

The above-mentioned polyvinyl ester-based polymer is preferably one or two or more kinds of vinyl esters as a monomer, and it is more preferable to use only one type of vinyl ester as a monomer, but it may be one type. Or a copolymer of two or more vinyl esters and other monomers copolymerizable therewith.

Examples of the other monomer copolymerizable with such a vinyl ester include ethylene; olefins having an alkyl group of 3 to 30 such as propylene, 1-butene or isobutylene (such as α-olefin); acrylic acid or a salt thereof; and acrylic acid. Methyl ester, acrylic acid Ethyl ester, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. Acrylate; methacrylic acid or a salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, Methacrylates such as tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methyl propylene oxime An amine, N-ethyl acrylamide, N,N-dimethyl decylamine, diacetone acrylamide, acrylamidamine sulfonic acid or a salt thereof, acrylamide dimethylamine or a salt thereof, A acrylamide derivative such as N-methylol acrylamide or a derivative thereof; methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacryl oxime Aminopropane sulfonic acid or a salt thereof, methacrylamide propyl dimethylamine or a salt thereof, N-methylol methacrylamide or a methacrylamide derivative such as a derivative; N-vinylamine such as N-vinylformamide, N-vinylacetamide or N-vinylpyrrolidone; methyl vinyl ether; Ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, Vinyl ether such as stearyl allyl vinyl ether; vinyl cyanide such as acrylonitrile or methacrylonitrile; halogenated ethylene such as vinyl chloride, vinylidene chloride, vinyl fluoride or vinylidene fluoride Allyl compound of allyl acetate, allyl chloride, etc.; maleic acid or its salt, ester or anhydride; itaconic acid or its salt, ester or anhydride; ethylene such as vinyl trimethoxy decane Alkranyl compound; isopropenyl acetate and the like. The above polyvinyl ester-based polymer may have one or two or more kinds of structural units derived from such other monomers.

The ratio of the structural unit derived from the other monomer to the above-mentioned polyvinyl ester-based polymer is preferably 15 mol% or less, based on the number of moles of the entire structural unit constituting the polyvinyl ester polymer, and 5 mol%. The following is better.

The above PVA may be modified by one or two or more kinds of graft copolymerizable monomers. Examples of the graft copolymerizable monomer include an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, and an α-olefin having 2 to 30 carbon atoms. The proportion of the structural unit derived from the graft-copolymerizable monomer in the PVA is preferably 5 mol% or less based on the number of moles of the entire structural unit constituting the PVA.

The above-mentioned PVA is a part of the hydroxyl group which may be crosslinked or may not be crosslinked. Further, a part of the PVA-based hydroxy group may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with these compounds without forming an acetal structure.

The degree of polymerization of the PVA is not particularly limited, and is preferably 500 or more, more preferably 1,000 or more, more preferably 1,500 or more, and more preferably 2,000 or more from the viewpoint of film strength or durability of the obtained optical film. . On the other hand, if the degree of polymerization is too high, the production cost may increase or the passability may be poor at the time of film formation. The polymerization degree of PVA is preferably 10,000 or less, more preferably 9,000 or less, and 8,000 or less is further. Preferably, 7,000 or less is particularly preferred. In addition, the degree of polymerization of PVA in this specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of PVA is not particularly limited, and the optical properties or durability of the optical film produced from the obtained PVA film are not particularly limited. In view of the above, the degree of saponification of PVA is preferably 95 mol% or more, 98 mol% or more is preferable, 99 mol% or more is further more preferable, and 99.2 mol% or more is particularly preferable. Further, the degree of saponification of PVA in the present specification means a total number of moles of a structural unit (typically a vinyl ester unit) and a vinyl alcohol unit which can be converted into a vinyl alcohol unit by saponification with respect to PVA, the ethylene The ratio of the number of moles occupied by the alcohol unit (% by mole). The degree of saponification of PVA can be measured in accordance with the description of JIS K6726-1994.

In the PVA system in which the PVA film of the present invention is formed, one type of PVA may be used alone, or two or more types of PVA which are different from each other, such as a modified type, a modification ratio, a polymerization degree, and a degree of saponification, may be used. However, in the case where the PVA film of the present invention is required to have excellent secondary workability as in the case of producing an optical film, the PVA film contains an acidic functional group having a carboxyl group, a sulfonic acid group or the like. PVA; PVA having an acid anhydride group; PVA having a basic functional group such as an amine group; and PVA having such a neutralizing substance and the like having a functional group capable of promoting a crosslinking reaction, sometimes due to cross-linking between PVA molecules The secondary processability of the PVA film is lowered by the reaction. Therefore, in the case as described above, the PVA film is preferably one which does not contain PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group, and any such neutralizing agent, PVA Preferably, the method comprises: PVA produced by saponifying a polyvinyl ester polymer obtained by using only a vinyl ester in a monomer, and/or using only vinyl ester and ethylene and/or carbon number in the monomer. PVA produced by saponification of a polyvinyl ester-based polymer obtained from an olefin of 30, PVA further preferably comprises only PVA produced by saponifying a polyvinyl ester-based polymer obtained by using only a vinyl ester in a monomer, and/or A PVA produced by saponifying a polyvinyl ester polymer obtained by using only a vinyl ester and ethylene in a monomer.

The preparation method of the PVA film of the present invention is not particularly limited, and the PVA film of the present invention can be continuously produced more smoothly by the production method of the present invention including the following steps: (a) using a rotating shaft parallel to each other The film forming apparatus of three or more drying rolls is formed on the first drying roll on the most upstream side of the drying roll, and the film forming raw liquid containing PVA is discharged into a film form and partially dried, and then it is succeeded. The drying roll is further dried to form a film. In this case, (b) the volatilization ratio of the PVA film when peeling from the first drying roll is 20 to 40% by mass; (c) the peripheral speed of the second drying roll (S ₂ ) The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₁ ) of the first drying roll is set to 1.015 to 1.050; (d) the second drying roll or the drying roll on the downstream side thereof is When the volatility of the PVA film is 20% by mass, the drying roller (the x-th drying roller) to the PVA film has a volatility of 10% by mass, and the drying roller (the y-drying roller) is adjacent to the two drying rollers. than the peripheral speed of the downstream side of the drying roll (S _{n + 1)} circumferential speed of the upstream side of the drying roll (S _n) in _{(S n + 1 / S n} ) are set to 0.992 to 0.999.

The present invention is not limited at all, but it is considered that, in the method for producing a PVA film according to the present invention, the adjacent two drying rolls are collectively provided in a state in which the volatilization ratio of the PVA film is 20% by mass to 10% by mass. Since the peripheral speed ratio is set to a specific range of less than 1.000, the uniformity in the width direction of the obtained PVA film is improved, and the PVA film of the present invention can be produced with good productivity and smoothly and continuously.

The method for producing the PVA film of the present invention described above will be more specifically described below.

The film forming stock solution containing PVA can be prepared by mixing PVA with a liquid medium to form a solution, or by melting a PVA chip containing a liquid medium or the like to form a molten liquid. The dissolution of the PVA in a liquid medium or the melting of PVA chips containing a liquid medium or the like can be carried out using a stirring type mixing device, a melt extruder or the like. The liquid medium to be used at this time may, for example, be water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine or diethylene. These liquid mediums may be used alone or in combination of two or more. Among these, it is preferred to use water, dimethyl hydrazine, or a mixture of the two, especially water.

The film forming stock solution preferably contains a plasticizer from the viewpoint of promoting the dissolution or melting of the PVA in the liquid medium, improving the passageability in the production of the film, and improving the stretchability of the obtained PVA film. A PVA film containing a plasticizer can be obtained by using a film forming stock solution containing a plasticizer. The plasticizer is preferably a polyhydric alcohol, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. . The plasticizer may be used alone or in combination of two or more. Among these, one or two or more kinds of glycerin, diglycerin, and ethylene glycol are preferably used from the viewpoint of the improvement of the stretchability.

The content of the plasticizer is preferably from 0 to 30 parts by mass, more preferably from 3 to 25 parts by mass, particularly preferably from 5 to 20 parts by mass, per 100 parts by mass of the PVA. When the content of the plasticizer is 30 parts by mass or less based on 100 parts by mass of the PVA, the handleability of the obtained PVA film is improved.

From the viewpoint of the improvement of the peeling property of the drying roller and the workability of the obtained PVA film at the time of producing the PVA film, it is preferred that the film forming stock solution contains a surfactant. A PVA film containing a surfactant can be obtained by using a film forming stock solution containing a surfactant. The kind of the surfactant is not particularly limited, and an anionic surfactant or a nonionic surfactant is preferably used.

The anionic surfactant is, for example, a carboxylic acid type such as potassium laurate or a sulfonic acid type anionic surfactant such as a sulfate type such as octyl sulfate or a dodecylbenzenesulfonate.

Further, the nonionic surfactant is, for example, an alkyl ether type such as polyoxyethylene oleyl ether or an alkylphenyl ether type such as polyoxyethylene octylphenyl ether or polyoxyethylene laurate. Alkylamine type such as alkyl ester type or polyoxyethylene lauryl amine ether, alkyl guanamine type such as polyoxyethylene laurate decylamine, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, and oil An allyl phenyl ether type nonionic surfactant such as an alkanoguanamine type such as an acid diethanolamine or a polyoxyalkylene allylic phenyl ether is suitable.

These surfactants may be used alone or in combination of two or more.

The content of the surfactant is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, more preferably 0.05 to 0.3 part by mass, per 100 parts by mass of the PVA. When the content of the surfactant is 0.01 parts by mass or more based on 100 parts by mass of the PVA, the stretchability or the dyeability is improved. In addition, when the content of the surfactant is 1 part by mass or less based on 100 parts by mass of the PVA, the workability of the PVA film is improved.

The film forming solution may contain a stabilizer (antioxidant, ultraviolet absorber, heat stabilizer, etc.), a phase solvent, an anti-caking agent, a flame retardant, an antistatic agent, a slip agent, a dispersant, a fluidizer, an antibacterial agent. Various additives such as. These additives may be used alone or in combination of two or more.

The volatilization ratio of the film forming stock solution used in the production of the PVA film is preferably in the range of 50 to 90% by mass, more preferably in the range of 55 to 80% by mass. When the volatile content is 50% by mass or more, the viscosity is excessively increased and the film formability is improved. On the other hand, by setting the volatile content to 90% by mass or less, the thickness uniformity of the obtained PVA film is improved. In addition, the volatilization rate of the film-forming stock solution in this specification is a volatile fraction obtained by the following formula [i].

A={(Wa-Wb)/Wa}×100 [i]

[In the formula, A represents the volatilization ratio (% by mass) of the film forming solution, Wa represents the mass (g) of the film forming solution, and Wb represents the film forming solution of Wa (g) in an electric dryer at 105 ° C for 16 hours. Mass after drying (g). ]

For the production of a PVA film, a film forming apparatus having three or more drying rolls in which the rotating shafts are parallel to each other is preferably four or more, and more preferably 5 to 30. In addition, the first drying roller is referred to as the first drying roller, and the remaining drying roller is sequentially referred to as the second drying roller, the third drying roller, and the first drying roller from the first drying roller. 4 drying rolls, . . . The drying roll is preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel or the like, and is preferably formed of a metal material having a specular gloss which is not easily corroded by the surface of the roll. Moreover, in order to improve the durability of the drying roll, a nickel layer, a chromium layer, and a nickel layer are used. A single layer of a chrome alloy layer or a combination of two or more layers of a drying roll is preferred.

The film forming apparatus used in the present invention may contain a hot air oven type hot air drying device, a heat treatment device, a humidity control device, and the like after the drying roller as needed.

When the film forming raw material is discharged into a film form on the first drying roll of the film forming apparatus, a known film such as a T-slot die, a hopper plate, an I-die, or a lip coater can be used. The film discharge device (membrane casting device) discharges (casts) the film forming solution onto the first drying roll into a film shape.

The PVA-containing liquid which is discharged onto the first drying roll is dried on the first drying roll to remove a part of the volatile component (partially dried), and the volatilization rate in the PVA film is up to When it is 20 to 40% by mass, it is peeled off from the first drying roll.

When the volatility of the PVA film is less than 20% by mass when peeled off from the first drying roll, the ΔZ _{max of} the obtained PVA film tends to deviate from the range corresponding to the specification of the present invention. The PVA film preferably has a volatility of 21% by mass or more when it is peeled off from the first drying roll, and is preferably 22% by mass or more, more preferably 23% by mass or more. On the other hand, when the volatility of the PVA film is more than 40% by mass when peeled off from the first drying roll, the peeling property from the first drying roll is deteriorated, and the uniformity in the width direction of the film is lowered, and the obtained PVA is obtained. The ΔZ _{max of the} film is liable to deviate from the range corresponding to the specification of the present invention. The PVA film has a volatile content of 30% by mass or less, preferably 28% by mass or less, and more preferably 27% by mass or less, more preferably from the first drying roll.

Here, the volatility of the PVA film or the PVA film in the present specification means a volatility ratio obtained by the following formula [ii].

B={(Wc-Wd)/Wc}×100 [ii]

Wherein B represents the volatility (% by mass) of the PVA film or the PVA film, Wc represents the mass (g) of the PVA film or the sample taken from the PVA film, and Wd represents the temperature of the sample Wc (g) placed therein. Mass (g) when dried in a vacuum dryer at 50 ° C and a pressure of 0.1 kPa or less for 4 hours. ]

The PVA film or the PVA film formed by using a film-forming stock solution prepared by using a polyol (plasticizer) such as PVA or glycerin, a surfactant, and water is the above-mentioned "at a temperature of 50 ° C and a pressure of 0.1 kPa or less. When drying under the condition of 4 hours, only water volatilizes, and other components other than water remain in the PVA film or PVA film, so the volatilization rate of the PVA film or the PVA film can be determined by measuring the PVA film or the PVA film. The amount of water (water content) contained in the product is obtained.

When drying on the first drying roll, the surface temperature of the first drying roll is preferably from 80 to 120 ° C, preferably from 85 to 105 ° C, from 93 to 99, from the viewpoints of drying uniformity, drying speed, and the like. °C is further preferred. By setting the surface temperature of the first drying roll to 120 ° C or lower, the foaming of the film can be more effectively suppressed. On the other hand, by setting it to 80 ° C or higher, the drying efficiency on the first drying roll is improved.

The peripheral speed (S ₁ ) of the first drying roll is preferably from 8 to 25 m/min, preferably from 10 to 23 m/min, from the viewpoints of drying uniformity, drying speed, and productivity of the PVA film. ~22 m / min is further preferred.

The film forming stock solution containing PVA which is formed into a film form is partially dried on the first drying roll, and can be carried out only by heat from the first drying roll, but is heated by the first drying roll. (1) The film surface which the drying roller contacts (it is called "the 1st drying roller non-contact surface", and the film surface of the 1st drying roller contact side is called "1st drying roller contact surface". Drying is performed by applying heat to both surfaces of the PVA film, and it is preferable from the viewpoints of drying uniformity, drying speed, and the like.

When the hot air is blown to the non-contact surface of the first drying roll of the PVA film on the first drying roll, the hot air having a blowing speed of 1 to 10 m/sec in the entire area of the non-contact surface of the first drying roll is preferable, and the blowing speed is high. The hot air of 2 to 8 m/sec is preferred, and the hot air with a wind speed of 3 to 8 m/sec is further preferred.

When the wind speed of the hot air blown to the non-contact surface of the first drying roll is too small, dew condensation of water vapor or the like occurs when drying on the first drying roll, and the water drop drops to the PVA film, and defects are likely to occur in the finally obtained PVA film. On the other hand, when the wind speed of the hot air blown to the non-contact surface of the first drying roll is too large, a thickness spot is formed in the finally obtained PVA film, and damage such as stains is likely to occur.

The temperature of the hot air blown to the non-contact surface of the first drying roll of the PVA is preferably 50 to 150 ° C, preferably 70 to 120 ° C, and 80 to 95 ° C from the viewpoints of drying efficiency and uniformity of drying. It is further preferred. It is preferable that the hot air has a dew point of 10 to 15 ° C which is blown to the non-contact surface of the first drying roll of the PVA film. When the temperature of the hot air blown to the non-contact surface of the first drying roll of the PVA film is too low, drying efficiency, uniformity of drying, and the like are likely to be lowered, and when it is too high, foaming is likely to occur.

The method for blowing the hot air to the non-contact surface of the first drying roll of the PVA film is not particularly limited, and a non-contact surface of the first drying roll that faces the PVA film with a uniform wind speed and a uniform temperature can be used. Any one of the methods of uniformly blowing all of them is preferably a nozzle method, a rectifying plate method, or a combination thereof. The direction in which the hot air is blown toward the non-contact surface of the first drying roll of the PVA film may be a direction facing the non-contact surface of the first drying roll, or may be a circumference substantially along the non-contact surface of the first drying roll of the PVA film. The direction of the shape (substantially along the direction of the circumference of the roll surface of the first drying roll) may be other directions.

Further, when the PVA film is dried on the first drying roll, the volatile matter generated from the PVA film by drying and the hot air after blowing are preferably exhausted. The method of the exhaust gas is not particularly limited, but an exhaust method in which wind speed unevenness and temperature unevenness of the hot air which is blown to the non-contact surface of the first drying roll of the PVA film are not generated is preferable.

The PVA film dried on the first drying roll to a volatile matter ratio of 20 to 40% by mass was peeled off from the first drying roll, and further dried by the drying roll after the second drying roll. When the PVA film is dried on the second drying roll, it is preferred that the first drying roll of the PVA film is non-contacted and dried toward the second drying roll.

In the range of 1.015 ~ 1.050, the second drying roll peripheral speed (S ₂₎ than the first drying roller circumferential speed (S ₁₎ of (S ₂ / S ₁₎ is preferably the range of 1.020 ~ 1.048, the It is preferably in the range of 1.023 to 1.046, and further preferably in the range of 1.025 to 1.045. When the ratio (S ₂ /S ₁ ) is less than 1.020, the peeling property of the PVA film from the first drying roll is deteriorated and the uniformity in the width direction of the film is deteriorated, and the ΔZ _{max of the} obtained PVA film is liable to deviate from the specification of the present invention. The corresponding range. Further, when the ratio (S ₂ /S ₁ ) exceeds 1.050, the spot of the tension applied to the PVA film between the first drying roll and the second drying roll is enlarged, and the ΔZ _{max of the} obtained PVA film is easily deviated. A range corresponding to the provisions of the present invention.

In the case where the second drying roller is further located on the upstream side than the x-th drying roller described later, all of the drying roller (the (x-1) drying roller) from the second drying roller to the x-th drying roller exists. The surface temperature of the drying roll (including the second drying roll and the (x-1)th drying roll) is preferably 80 ° C or higher, preferably 83 ° C or higher, and more preferably 85 ° C or higher. Further, the surface temperature of the drying rolls is preferably 95 ° C or lower, preferably 92 ° C or lower, and more preferably 90 ° C or lower. By the surface temperature of the drying rolls being in the above range, a moderate drying speed can be maintained and the uniformity of drying can be improved.

The drying roller when the volatility of the second drying roller or the PVA film in the drying roller on the downstream side is 20% by mass is referred to as an x-th drying roller, and when the volatility of the PVA film is 10% by mass. When the drying roller is referred to as a y- _th drying roller, between the xth drying roller and the y- _th drying roller, the peripheral speed (S _n+1 ) of the downstream drying roller is on the upstream side of the adjacent two drying rollers. The ratio of the peripheral speed (S _n ) of the drying rolls (S _n+1 /S _n ) must be in the range of 0.992 to 0.999. That is, for example, x-drying roll 5 for the first drying roller and the first roller for the first y sulfate drying roller 8 in case of the first drying roller circumferential speed 6 (S ₆₎ to the first drying roller circumferential speed of 5 (S ₅ Ratio (S ₆ /S ₅ ), the ratio of the peripheral speed of the seventh drying roll (S ₇ ) to the peripheral speed (S ₆ ) of the sixth drying roll (S ₇ /S ₆ ), and the circumference of the eighth drying roll The ratio (S ₈ /S ₇ ) of the speed (S ₈ ) to the peripheral speed (S ₇ ) of the seventh drying roll must all be in the range of 0.992 to 0.999. When some or all of the ratio (S _n+1 /S _n ) deviates from the above-described specification of the present invention, the uniformity in the width direction is lost and it is difficult to obtain the intended PVA film. From the viewpoint of uniformity in the width direction, the ratio (S _n+1 /S _n ) is preferably 0.993 or more, more preferably 0.994 or more, and further preferably 0.995 or more. Similarly, from the viewpoint of uniformity in the width direction, the ratio (S _n+1 /S _n ) is preferably 0.998 or less. Further, in general, the volatility of the PVA film on the drying roll is lowered, and in the case where the volatility between the adjacent two drying rolls becomes 20% by mass or 10% by mass, the drying rolls on the downstream side thereof are respectively It is called the xth drying roll or the yth drying roll. Moreover, when the PVA film has a volatile content of 20% by mass when peeled off from the first drying roll, the second drying roll is referred to as an xth drying roll.

The first drying roller circumferential speed of y _(y S) ratio of the first drying roller circumferential speed x (S _x) of (S _y / S _x), from a further improved uniformity in the width direction of view can, 0.940 ~ It is preferably in the range of 0.990, preferably in the range of 0.955 to 0.985, and further preferably in the range of 0.960 to 0.980.

The number of the drying rolls existing between the xth drying roll and the yth drying roll is preferably from the xth drying roll and the yth drying roll in order to further improve the uniformity in the width direction. More than 6 are preferred, 8 or more are further preferred, and 20 or less are preferred.

The surface temperature of all the drying rolls (including the xth drying roll and the yth drying roll) existing between the xth drying roll and the yth drying roll is preferably 60° C. or higher, preferably 62° C. or higher, and further 65° C. or higher. Preferably. Moreover, the surface temperature of these drying rolls is preferably 85 ° C or less, and 82 ° C is The lower is preferred, and the temperature below 80 ° C is further preferred. By setting the surface temperature of these drying rolls to the above range, the uniformity in the width direction can be further improved.

If the PVA film dried on the y-th drying roll is further dried by a subsequent drying roll, a PVA film having a lower volatile content can be obtained. The surface temperature of the drying roller on the downstream side from the y-th drying roll is preferably in the range of 60 to 85 ° C, preferably in the range of 62 to 82 ° C, and further preferably in the range of 65 to 80 ° C, and finally dried. The roll, or near the final drying roll and the final drying roll, can increase the surface temperature thereof as a heat treatment roll. In the case where a drying roll is used as the heat treatment roll, the surface temperature is preferably in the range of 90 to 140 ° C, and more preferably in the range of 95 to 130 ° C.

In the process from the first drying roll to the final drying roll, the direction of the PVA film for each drying roll is not particularly limited, and from the viewpoint of further drying the PVA film, the surface and the inside of any part of the PVA film are made It is preferred that the drying rolls from the first drying roll to the final drying roll are dried in such a manner as to alternately face each other.

The final drying roller circumferential speed (S _L) is not particularly limited than the first drying roller the peripheral speed (S ₁₎ of the (S _L / S _1), preferably in the range of 0.900 to 1.100, 0.950 to 1.050 The range is preferably in the range of 0.980 to 1.020, and further preferably in the range of 0.990 to 1.010. Further, among the peripheral speed ratios between the two adjacent drying rolls, the ratio of the peripheral speed of the downstream drying roll to the peripheral speed of the upstream drying roll may be, for example, 0.980 to 1.020. Within the range, and further in the range of 0.990 to 1.010.

The PVA film obtained by the above-described drying treatment can be subjected to a humidity control treatment or the like as needed, and the PVA film of the present invention can be obtained by winding into a roll shape with a predetermined length. Moreover, both ends (ears) in the width direction of the PVA film can be cut and removed before the winding into a roll shape, at the stage of the roll shape, and at any one or a plurality of stages after the roll is rolled out.

After the above-described series of treatments, the volatile content of the finally obtained PVA film is preferably in the range of 1 to 5% by mass, more preferably in the range of 2 to 4% by mass.

The use of the PVA film of the present invention is not particularly limited, but it can be produced from an optical film such as a polarizing film having a reduced color spot, even in the case where the light transmittance is high or when a backlight having a higher intensity is used. It is preferably used as a raw material for the production of optical films. The optical film may be a retardation film or the like in addition to the polarizing film. These optical films can be produced by a production method having a step of uniaxially stretching using the PVA film of the present invention.

More specifically, when a polarizing film is produced using the PVA film of the present invention as a raw material, for example, dyeing, uniaxial stretching, fixing treatment, and drying treatment may be carried out using the PVA film of the present invention, and further, heat treatment may be performed as needed. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, dyeing may be performed while uniaxial stretching, or may be performed after uniaxial stretching. Further, the steps of uniaxial stretching, dyeing, and the like may be repeated plural times.

For dyes for PVA film dyeing, iodine or dichroic organic dyes can be used (for example, Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28 , 31, 37, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, etc. dichroic dyes). These dyes may be used alone or in combination of two or more. Although the dyeing is usually carried out by immersing the PVA film in a solution containing the above dye, the treatment conditions or treatment methods are not particularly limited.

The uniaxial stretching of the PVA film can be carried out by any of a wet stretching method or a dry heat stretching method. When uniaxially stretching by a wet stretching method, uniaxial stretching can be carried out in warm water containing boric acid, and uniaxial stretching can be carried out in a solution containing the aforementioned dye or in a post-fixing treatment bath, and can be used. The water-absorbed PVA film is uniaxially stretched in air, and may be uniaxially stretched by other methods. The stretching temperature at the time of the uniaxial stretching treatment is not particularly limited, and in the case where the PVA film is stretched (wet stretching) in warm water, it is preferably 30 to 90 ° C, more preferably 40 to 70 ° C. Further preferably, the temperature is 45 to 65 ° C, and the dry heat drawing is preferably carried out at a temperature of 50 to 180 ° C. Further, the stretching ratio of uniaxial stretching (in the case of uniaxial stretching in a multistage manner is a total stretching ratio), and it is preferable to stretch as much as possible from the viewpoint of polarizing performance before the film is cut. Specifically, it is preferably 4 times or more, more preferably 5 times or more, and further preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, and is preferably 8.0 times or less for uniform stretching. Further, the stretching ratio in the present specification is based on the length of the film before stretching, and the state in which the film is not stretched corresponds to a stretching ratio of 1 time.

The thickness of the stretched film (polarizing film) is preferably 5 to 35 μm , particularly preferably 20 to 30 μm .

The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching or transverse uniaxial stretching in the longitudinal direction can be employed, which is superior in terms of obtaining polarizing performance. In the case of the polarizing film, uniaxial stretching in the longitudinal direction is preferred. The uniaxial stretching in the longitudinal direction is carried out by using a stretching device having a plurality of rolls parallel to each other, and changing the peripheral speed between the rolls. On the other hand, the transverse uniaxial stretching can be carried out using a tenter type stretching machine.

When the polarizing film is produced, in order to firmly adsorb the dye to the uniaxially stretched film, it is preferred to carry out the fixing treatment. The fixing treatment may be a method of immersing the film in a fixed treatment bath in which a boron compound such as boric acid or borax is added. At this time, an iodine compound may be added to the fixed treatment bath as needed.

It is preferred to carry out uniaxial stretching, or uniaxial stretching and fixing treatment, followed by drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150 ° C, particularly 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 lowered. On the other hand, when the temperature is too high, the polarization performance is likely to be deteriorated due to decomposition of the dye or the like.

A polarizing plate can be formed by laminating a protective film which is optically transparent and has mechanical strength on both surfaces or one surface of the polarizing film obtained above. The protective film in this case can use cellulose triacetate (TAC) film, acetic acid. A cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like. Further, examples of the adhesive for bonding the protective film include a PVA-based adhesive. Or a urethane-based adhesive or the like, and among these, a PVA-based adhesive is particularly preferable.

The polarizing plate obtained above is coated with an adhesive such as acrylic or the like, and then bonded to a glass substrate to be used as a component of a liquid crystal display device. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle enhancement film, a brightness enhancement film, or the like can be bonded.

[Examples]

The present invention will be more specifically described below by the examples, but the present invention is not limited by the following examples.

In the following examples and comparative examples, the ΔZ _max , Δ Z _ave , hysteresis value of the PVA film, the angle formed by the alignment axis and the longitudinal direction of the PVA film, and the measurement of the color unevenness and the polarizing performance of the polarizing film were evaluated. It is obtained by the following method.

(1) ΔZ _max , Δ Z _ave , hysteresis value of the PVA film and the angle formed by the alignment axis and the longitudinal direction of the PVA film

From the arbitrary position in the longitudinal direction (MD) of the long PVA film obtained in each of the following Examples or Comparative Examples, the length direction (MD) of the PVA film has a full length (3 m) band shape of 40 mm length. Sample. In the strip-shaped sample, one measurement position was determined in the center portion in the width direction of the film, and the measurement positions (74 points, respectively) were sequentially determined from the measurement positions at both ends in the width direction at a pitch of 20 mm. Further, each of the 75th points in the field of less than 20 mm from the both end portions in the width direction of the film toward the central portion in the width direction is excluded from the measurement position. Further, each measurement position is determined at a central portion (a position of 20 mm from both end portions in the mechanical flow direction) in the mechanical flow direction of the strip sample.

In addition, "KOBRA-WFD" manufactured by Oji Scientific Instruments Co., Ltd. was used at each measurement position (total 149 points), and the in-plane alignment axis of the film was measured based on light having a wavelength of 590 nm traveling in a direction perpendicular to the film surface. And the hysteresis value, the ΔZ _max and ΔZ _ave are obtained from the data of the alignment axes of the respective measurement positions, and the minimum value and the maximum value are obtained from the data of the hysteresis values at the respective measurement positions. Moreover, the angle formed by the alignment axis and the longitudinal direction (MD) of the PVA film was determined at the measurement position of the center portion in the width direction of the film.

(2) The color spot of the polarizing film

In a dark room, a polarizing plate (using a polarizing film having a transmittance of about 43%) was placed on a surface light source (backlight), and a polarizing plate for the observation was placed thereon to form a crossed Nicols. The polarizing film produced. Then, the polarizing film was irradiated with light (15,000 cd) from the backlight through the observation polarizing plate, and the polarizing film was visually observed from a position immediately above the polarizing film by a distance of 1 m, and the polarizing film was evaluated by functional evaluation based on the following criteria. Evaluation of the stains.

○: No stain was observed, or even if it was observed, there was no practical problem.

×: A color spot that is considered to be a problem in practical use.

In addition, according to the manufacturing conditions of "(2) Production of polarizing film (i)" which will be described later, a polarizing film having a high transmittance of 44% or more is easily obtained by using such a polarizing film having high transmittance. According to the above method, the presence or absence of the problematic stain in the present invention can be clearly evaluated.

(3) Polarization performance of polarizing film (a) Determination of penetration rate (Y)

From the central portion in the width direction of the polarizing film obtained in each of the following examples or comparative examples, two square samples having a length of 4 cm and a width of 4 cm were taken. For the sample of one piece, the light transmittance of the case where the longitudinal direction is inclined by 45° to the measuring device and the light transmittance of the case of the inclination of −45° are measured, and the average value (Y ₁ ) (%) of these is obtained. . Further, for each of the samples, the light transmittance of the case where the inclination was 45° and the light transmittance of the case of the inclination of -45° were measured in the same manner, and the average value (Y ₂ ) (%) of these was obtained. Further, the above-mentioned transmittance was measured by using a spectrophotometer "U-4100" manufactured by Hitachi, Ltd. (attached to the integrating sphere). Further, the measurement of the transmittance was carried out in accordance with the method of JIS Z8722 (Method for Measuring Object Color), and the C-light source was used to correct the visibility in the visible light region of the 2° field of view.

Y ₁ and Y ₂ obtained by the above method were averaged by the following formula [iii] as the transmittance (Y) (%) of the polarizing film.

Transmission rate (Y) = (Y ₁ + Y ₂ ) / 2 [iii]

(b) Determination of the degree of polarization (V)

Measurement of two pieces of the sample of the polarizing film taken in the above-mentioned "(a) Measurement of transmittance (Y)": light transmittance (Y∥) (%) in the case where the longitudinal directions are parallel And the light transmittance (Y⊥) (%) in the case where the lengthwise directions are orthogonal. In addition, Y∥ and Y⊥ are obtained by the same method as the above-mentioned "(a) measurement of transmittance (Y)". Thus, Y ∥ and Y ⊥, the degree of polarization (V) (%) was obtained by the following formula [iv].

Polarization degree (V)={(Y∥-Y⊥)/(Y∥+Y⊥)} ^1/2 ×100 [iv]

"Embodiment 1" (1) Manufacture of PVA film

(i) 100 parts by mass of PVA (saponified product of homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.9 mol%), 12 parts by mass of glycerin, 0.1 part by mass of lauric acid diethanolamine and The membrane-forming stock solution having a water content of 66% by mass was formed by a film forming apparatus having 20 drying rolls having parallel axes of rotation, and a film thickness of 75 μm, a width of 3 m, a length of 10,000 m, and a volatile matter ratio of 3 mass% were continuously formed. Strip PVA film.

Specifically, the film forming stock solution described above is discharged from a T-sew die to a first drying roll (surface temperature: 93° C., peripheral speed (S ₁ ): 13.6 m/min), and is formed into a film on the first drying roll. While the hot air (temperature: 90° C., dew point temperature: 10° C.) was uniformly blown to the entire non-contact surface of the first drying roll at a wind speed of 5 m/sec, the volatility of the PVA film was dried to 25% by mass, and then, When peeling off from the first drying roll (the volatility when peeling off from the first drying roll is 25% by mass), the first drying roll contact surface of the PVA film and the first drying roll non-contact surface are alternately opposed to each drying roll. The drying method was carried out by using a drying roll after the second drying roll, and the both ends (ears) in the width direction were cut and removed, and then wound into a roll to obtain the PVA film described above.

Further, in the above film formation, the xth drying roll is the fifth drying roll, and the yth drying roll is the 13th drying roll. Further, the ratio (S ₂ /S ₁ ) was 1.040, and the ratio (S _n+1 /S _n ) of the peripheral speed between the two drying rolls adjacent between the xth drying roll and the yth drying roll was 0.995 ( The minimum value is ~0.998 (maximum value), the ratio (S _y /S _x ) is 0.973, and the ratio (S _L /S ₁ ) is 1.007. Further, the surface temperature of all the drying rolls existing between the second drying roll to the (x-1)th drying roll is 85 ° C (minimum value) to 90 ° C (maximum value), and the xth drying roll to the yth drying roll The surface temperature of all the drying rolls present between them is 67 ° C (minimum value) ~ 75 ° C (maximum value).

With respect to the obtained PVA film, ΔZ _max , Δ Z _ave , hysteresis value, and an angle formed by the alignment axis and the longitudinal direction of the PVA film were obtained by the above method. The results are shown in Table 1.

(2) Manufacture of polarizing film

(i) From the center portion in the width direction (TD) of the PVA film obtained in the above (1), a rectangular test piece having a length of 12 cm × a width of 20 cm was taken, and both ends of the test piece in the longitudinal direction were fixed to the stretch. In the jig, the size of the stretched portion was 10 cm in the longitudinal direction × 20 cm in the width direction, and immersed in water at a temperature of 30 ° C for 38 seconds, and uniaxially stretched in the longitudinal direction at a tensile speed of 24 cm/min (1st) After being stretched to 2.2 times the original length, it was immersed in an iodine/potassium iodide aqueous solution containing a concentration of 0.03 mass% of iodine and 3% by mass of potassium iodide at a temperature of 30 ° C for 60 seconds, and was pulled at 24 cm/min. The stretching speed was uniaxially stretched in the longitudinal direction (second stretching) to 3.3 times the length, and then impregnated in a boric acid/potassium iodide aqueous solution containing a concentration of 3 mass% of boric acid and 3 mass% of potassium iodide at a temperature of 30 °C. While immersing for about 20 seconds, uniaxially stretching (third-stage stretching) in the longitudinal direction at a stretching speed of 24 cm/min to 3.6 times the original length, followed by immersion in boric acid having a concentration of 4% by mass and About 5 mass% of potassium iodide at a temperature of 60 ° C boric acid / Potassium aqueous solution, while a tensile speed of 24cm / min in the longitudinal direction of the uniaxially stretched (stretch mesh segment 4) prior to ultimate tensile ratio of The draw ratio (the draw ratio at the time of film breakage obtained by the same operation in advance is regarded as the limit draw ratio, and the draw ratio is 0.2 times lower than that), and the potassium iodide having a concentration of 3 mass% is contained. The potassium iodide aqueous solution was immersed for 10 seconds, fixed, and then dried in a dryer at 60 ° C for 4 minutes to prepare a polarizing film (thickness: 28 μm).

The coloring film was evaluated by the above method for the polarizing film. The results are shown in Table 1.

(ii) In addition to the above-mentioned (i), the immersion time in the "iodine/potassium iodide aqueous solution at a temperature of 30 ° C" in the second stage stretching is changed from 60 seconds to 75 seconds, 90 seconds, and 105 seconds. The same operation as in the above (i) was carried out for a clock or 120 seconds to produce four polarizing films (thickness: 28 μm) having different transmittances.

(iii) for the five polarizing films having different transmittances (Y) obtained in the above (i) and (ii), the transmittance (Y) and the degree of polarization (V) are obtained by the above method. The five points are plotted on the graph where the horizontal axis is the transmittance (Y) and the vertical axis is the degree of polarization (V). Further, the approximate curve of the five points is plotted on the graph, and the value of the degree of polarization (V) when the transmittance (Y) is 44.25% is obtained from the approximate curve. The results are shown in Table 1.

<<Example 2 and Comparative Examples 1 to 5>>

A PVA film was formed in the same manner as in Example 1 except that the production conditions of the PVA film were as shown in Table 1, and a polarizing film was produced in the same manner as in Example 1. The results are shown in Table 1.

Claims (12)

A polyvinyl alcohol polymer film obtained by measuring two axes at a distance of 20 mm in the width direction of the film in the plane of the film, and two adjacent measurement positions among two adjacent measurement positions The angle at which the alignment axes form each other (but in the range of 0 to 90°) is 2.3 or less. The polyvinyl alcohol-based polymer film of claim 1, wherein an average value of the aforementioned angles of all two adjacent measurement positions is 0.6 or less. The polyvinyl alcohol-based polymer film according to claim 1 or 2, wherein the hysteresis value of the measurement position of the alignment axis is 5 to 100 nm at all measurement positions. The polyvinyl alcohol-based polymer film according to any one of claims 1 to 3, wherein an angle of formation of at least one of the alignment axes of the measurement axes of the alignment axes and the longitudinal direction of the polyvinyl alcohol-based polymer film ( However, it is 45 to 90° in the range of 0 to 90°. The polyvinyl alcohol-based polymer film according to any one of claims 1 to 4, which has a width of 2 m or more. A method for producing a polyvinyl alcohol-based polymer film, comprising: (a) using a film forming apparatus having three or more drying rolls having mutually parallel rotating axes, wherein the drying roll is located at the most upstream On the first drying roll on the side, the film forming stock solution containing the polyvinyl alcohol polymer is discharged into a film form and partially dried, and then dried by a subsequent drying roll to form a film; at this time, (b) The volatilization ratio of the polyvinyl alcohol-based polymer film when peeling from the first drying roll is 20 to 40% by mass; (c) The peripheral speed (S ₂ ) of the second drying roll is applied to the first drying roll The ratio of the peripheral speed (S ₁ ) (S ₂ /S ₁ ) is set to 1.015 to 1.050; (d) the volatile matter of the polyvinyl alcohol-based polymer film in the second drying roll or the drying roll on the downstream side thereof Two drying rolls adjacent to each other between the drying roll (y-th drying roll) when the volatilization rate of the polyvinyl alcohol-based polymer film is 10% by mass at a rate of 20% by mass than the peripheral speed of the downstream side of the drying roll (S _{n + 1)} circumferential speed of the upstream side of the drying roll (S _n) in _{(S n + 1 / S n} ) are set to 0.992 to 0.999. The manufacturing method of claim 6, wherein the surface temperature of all the drying rolls existing between the xth drying roll and the yth drying roll is set to 60 to 85 °C. The manufacturing method of claim 6 or 7, wherein the first drying roll has a peripheral speed (S ₁ ) of 8 to 25 m/min. Method according to any one of items 6 to 8, such as a request, wherein the first drying roller circumferential speed of y _(y S) ratio of the first drying roller circumferential speed x (S _x) of (S _y / S _x) to 0.940~0.990. An optical film produced by the polyvinyl alcohol-based polymer film according to any one of claims 1 to 5. An optical film according to claim 10, which is a polarizing film. A method for producing an optical film, comprising the step of uniaxially stretching using a polyvinyl alcohol-based polymer film according to any one of claims 1 to 5.