KR102163144B1 - Polyvinyl alcohol-based polymer film and manufacturing process therefor - Google Patents

Abstract

(assignment)
To provide a PVA film capable of producing an optical film such as a polarizing film with reduced color unevenness even when a high light transmittance or a backlight having a higher intensity is used.
(Solution)
When the orientation axis in the plane of the film is measured with a pitch of 20 mm in the width direction of the film, the angles formed by the orientation axes at two adjacent measurement positions (but within the range of 0 to 90°) are all PVA film of 2.3 degrees or less in two adjacent measurement positions. In the said PVA film, it is preferable that the average value of the said angle at all two adjacent measurement positions is 0.6 degrees or less.

Description

Polyvinyl alcohol-based polymer film and its manufacturing method TECHNICAL FIELD [POLYVINYL ALCOHOL-BASED POLYMER FILM AND MANUFACTURING PROCESS THEREFOR}

The present invention relates to a polyvinyl alcohol-based polymer film (hereinafter, "polyvinyl alcohol-based polymer" may be abbreviated as "PVA"), a manufacturing method thereof, an optical film such as a polarizing film manufactured from the PVA film, and the It relates to a method of manufacturing an optical film.

A polarizing plate having a function of transmitting and shielding light is an important component of a liquid crystal display device (LCD) together with a liquid crystal having a function of switching light. The application field of this liquid crystal display is also from small devices such as electronic calculators and wrist watches in the early stages of development, to notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, navigation systems for automobiles, mobile phones, and measuring equipment used indoors and outdoors. It is expanding to a wide range of, and in particular, a large screen is in progress in a liquid crystal monitor or a liquid crystal television.

Polarizing plate is usually a method of unwinding and uniaxially stretching a long PVA film wound in a roll shape, followed by dyeing using iodine or a dichroic dye, and dyeing the unwound PVA film and uniaxially stretching it, followed by fixing treatment with a boron compound. A polarizing film is produced by a method of performing a fixing treatment at the same time as dyeing in any of the above methods, and a protective film such as a cellulose triacetate film or a cellulose acetic acid-butyrate film is adhered to one or both sides of the polarizing film obtained thereby. It is manufactured industrially by doing (貼合).

So far, various techniques have been known for improving the optical performance of a polarizing film, acquiring a wide polarizing film, and improving productivity of a polarizing film. For example, as a polarizing film with less disturbance of the optical axis can be manufactured, the maximum value of the absolute value of the inclination angle with respect to the length direction of the film of the long axis of the birefringence ellipsoid and the local rate of change in the inclination angle are each within a specific range. A PVA film is known (refer to Patent Document 1). In addition, a PVA film in which the difference in retardation between two points separated by 1 cm in the width direction of the film is within a specific range is known as being capable of preventing the occurrence of uneven color of the polarizing film and the occurrence of wrinkles during stretching of the PVA film ( See Patent Document 2). Further, as a polarizing film having uniform optical performance even in a large area, a specific PVA film in which the thickness variation per 1 mm in the width direction of the film is within a specific range is known (refer to Patent Document 3).

In addition, it is possible to reduce the occurrence of wrinkles during swelling of the PVA film and non-uniformity in staining of stripes existing in the length direction of the polarizing film, and the inclination of the optical axis over the entire film width direction is in the length direction of the film. A specific PVA film of 45 to 135° (refer to Patent Document 4) and a polarizing film having high polarization performance can be produced, and the angle formed by the flow direction and the optical axis is in the range of 70 to 110°, and A specific PVA film (refer to Patent Document 5) having a retardation in the thickness direction in the center portion of 15 to 90 nm, and the neck-in in the uniaxial stretching step are reduced, while a wider polarizing film can be produced. A polarizing film exhibiting high polarization performance is obtained, and when producing a polarizing film, the angle formed by the direction to be uniaxially stretched and the optical axis is in the range of 0 to 20°, and the retardation is in the range of 50 to 150 nm. PVA films (refer to Patent Document 6) are known respectively.

Further, a PVA film comprising a specific skin layer/core layer/skin layer is known as providing a stretched film in which uniform stretching is possible and generation of fine cracks and voids when stretched is suppressed (see Patent Document 7). In Patent Document 7, a film-making stock solution containing PVA with a volatile fraction of 50 to 90% by mass was heated with a first drying roll, and hot air was sprayed on the PVA film surface not in contact with the first drying roll under predetermined conditions, When the volatile fraction becomes 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 dry. At that time, the circumferential speed (S ₁ ) of the first drying roll and the second drying roll are A method for producing a PVA film in which the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) is 1.000 to 1.100 is described.

Japanese Laid-Open Patent Publication No. Hei 6-138320 Japanese Unexamined Patent Publication No. 2002-28938 Japanese Unexamined Patent Publication No. 2002-31720 International Publication No. 2009/028141 Japanese Unexamined Patent Publication No. 2010-191293 Japanese Patent Application Publication No. 2011-252937 Japanese Patent Laid-Open Publication No. 2005-324355

However, in the past, mainly for the purpose of improving the screen luminance of the LCD, the intensity of the backlight has been improved. Therefore, it was important that the polarizing plate and the polarizing film have less color unevenness even under strong light. However, in recent years, since the reduction of power consumption is strongly demanded, it has become important for LCDs to be able to maintain high screen luminance even when the intensity of the backlight is low. As a means for achieving this, it is considered to improve the light transmittance in the polarizing film and furthermore the polarizing plate, such as making the thickness of the polarizing film thinner or reducing the degree of dyeing. However, when a polarizing plate with improved light transmittance is manufactured using a conventional PVA film, it becomes a problem in the conventional polarizing plate with a low light transmittance, and a different kind of color non-uniformity from the color non-uniformity that has been attempted to improve is noticeable. I knew it. It was also found that this color non-uniformity was similarly conspicuous even in the case of a polarizing plate having a conventional light transmittance or a backlight having a higher intensity.

Therefore, the present invention provides a PVA film capable of producing an optical film such as a polarizing film with reduced color unevenness even when a high light transmittance or a backlight having a higher intensity is used, and such a PVA film with good productivity. It aims at providing a manufacturing method of a PVA film which can be manufactured continuously. In addition, it is an object of the present invention to provide optical films such as polarizing films produced using the PVA film, and a method for producing the optical film.

In order to achieve the above object, the present inventors repeated intensive examinations. As a result, when the orientation axis in the plane of the PVA film was measured at a pitch of 20 mm in the width direction of the film, the orientation axes at two adjacent measurement positions were Polarizing film with reduced color non-uniformity even when a non-existent PVA film is used as a fabric with an angle made up of less than a certain value at two adjacent measurement positions, even when the light transmittance is high or a backlight with higher intensity is used. I found out that this was obtained. In addition, when a PVA film having a small average value of the angles at two adjacent measurement positions was used, it was found that the color unevenness is further reduced.

And the present inventors, after discharging the film-making stock solution containing PVA on the 1st drying roll of the film-making apparatus provided with 3 or more drying rolls, it dried it sequentially with the said 3 or more drying rolls to produce a film, at that time , The volatile fraction of the PVA film when peeled from the first drying roll is 20 to 40% by mass, the ratio of the circumferential speed of the second drying roll to the circumferential speed of the first drying roll is set to a specific numerical range, and the second drying roll Or a drying roll when the volatile content of the PVA film became 10% by mass from the drying roll when the volatile content of the PVA film became 20% by mass among the drying rolls on the downstream side (Yth drying roll) By setting each of the ratios of the circumferential speeds between two adjacent dry rolls to a specific numerical range, the PVA film capable of providing a polarizing film with reduced color unevenness can be produced continuously and smoothly with good productivity. Found out.

The inventors of the present invention have completed further studies based on the above findings. That is, the present invention,

[1] When the alignment axis in the plane of the film is measured at a pitch of 20 mm in the width direction of the film, the angle formed by the alignment axes at two adjacent measurement positions (but within the range of 0 to 90°) A, a PVA film of 2.3° or less in all adjacent two measurement positions,

[2] The PVA film of [1], wherein the average value of the angles at all two adjacent measurement positions is 0.6° or less,

[3] The PVA film of the above [1] or [2], wherein the retardation value at the measurement position of the orientation axis is 5 to 100 nm in all measurement positions,

[4] The above-mentioned [1] to [wherein the angle formed by the orientation axis in at least one of the measurement positions of the orientation axis and the longitudinal direction of the PVA film (but within the range of 0 to 90°) is 45 to 90°. 3] any one of the PVA film,

[5] The PVA film of any one of [1] to [4], having a width of 2 m or more,

[6] As a method for producing a PVA film,

(a) Using a film-making apparatus including three or more drying rolls with rotational axes parallel to each other, and discharging the film-making stock solution containing PVA on the first drying roll located on the uppermost side of the drying rolls in a film shape After performing partial drying, it is further dried with a subsequent drying roll to produce a film; Then,

(b) The volatile fraction of the PVA film when peeled from the first dry roll is set to 20 to 40 mass%;

(c) a first ratio (S ₂ / S ₁₎ of the peripheral speed (S ₂₎ of the second drying rolls to a peripheral speed (S ₁₎ of the drying roll with 1.015 ~ 1.050 and;

(d) When the volatile fraction of the PVA film became 10% by mass from the second drying roll or the drying roll when the volatile fraction of the PVA film became 20% by mass among the drying rolls on the downstream side thereof. The ratio of the peripheral speed (S _n+1 ) of the downstream drying roll to the peripheral speed (S _n ) of the drying roll on the upstream side among the two adjacent drying rolls ( All of S _n+1 /S _n ) to 0.992 to 0.999;

Manufacturing method,

[7] The production method of [6], wherein the surface temperature of all the dry rolls present between the x-th drying roll and the y-th drying roll is 60 to 85°C,

[8] The manufacturing method of the above [6] or [7], wherein the circumferential speed (S ₁ ) of the first dry roll is 8 to 25 m/min,

[9] Among [6] to [8], wherein the ratio (S _y /S _x ) of the peripheral speed (S _y ) of the _y- th drying roll to the peripheral speed (S _x ) of the _x- th drying roll is 0.940 to 0.990, Any one manufacturing method,

[10] An optical film produced from the PVA film in any one of [1] to [5],

[11] The optical film of [10], which is a polarizing film,

[12] A method for producing an optical film having a step of uniaxial stretching using the PVA film in any one of [1] to [5] above

It is about.

When the PVA film of the present invention is used as a raw material, even when a light transmittance is high or a backlight having a higher intensity is used, an optical film such as a polarizing film with reduced color unevenness can be produced. In addition, by the method for producing a PVA film of the present invention, the PVA film of the present invention having the above-described excellent properties can be produced smoothly and continuously with good productivity. In addition, the optical film of the present invention has reduced color unevenness of a kind different from that of a conventional problem.

Hereinafter, the present invention will be described in detail.

In the PVA film of the present invention, when the orientation axis in the plane of the film is measured at a pitch of 20 mm in the width direction of the film, the angle formed by the orientation axes at two adjacent measurement positions (only 0 to 90° Within the range) is 2.3° or less at all adjacent two measurement positions. That is, when the maximum value of the angle at all adjacent two measurement positions is ΔZ _max , the PVA film of the present invention has a ΔZ _max of 2.3° or less. Conventional PVA film has a high ΔZ _max , and in a polarizing film manufactured using it, or a polarizing plate, has been a problem in the prior art, especially when a light transmittance is high or when a backlight having a higher intensity is used, and the color unevenness that has been attempted to improve There was a problem that different kinds of color unevenness were noticeable. In contrast, the PVA film of the present invention has a ΔZ _max of 2.3° or less, and 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 with reduced color unevenness can be produced even when a light transmittance is high or a backlight having a higher intensity is used. In addition, in Patent Document 1, the maximum value of the absolute value of the inclination angle with respect to the longitudinal direction of the film of the long axis of the birefringence ellipsoid is 5 degrees or less, and the local rate of change of the inclination angle (in an arbitrary range of 5 cm width A PVA film having an inclination angle of the optical axis of) of 1 degree or less is described. For example, even if the local rate of change of the inclination angle is 1 degree or less as in Patent Document 1, according to Patent Document 1, in the plane of the film When the orientation axis is measured at a pitch of 20 mm in the width direction of the film, a PVA film in which the maximum value (ΔZ _max ) of the angle formed by the orientation axes at all adjacent two measurement positions is within the above range cannot be obtained. , At least in this respect, the PVA film of the present invention is different from the PVA film described in Patent Document 1.

When ΔZ _max exceeds 2.3°, color non-uniformity becomes a problem in the obtained optical film. From the viewpoint of color non-uniformity in the optical film, ΔZ _max is preferably 2.2° or less, more preferably 2.0° or less, still more preferably 1.9° or less, and particularly preferably 1.8° or less. Moreover, since the productivity of a PVA film with too small ΔZ _max may decrease in its production, ΔZ _max is, for example, 0.3° or more.

The orientation axis in the plane of the film means a slow axis in the plane of the film, and is determined according to the state of orientation of PVA molecules at the measurement position of the orientation axis. The orientation axis can be measured based on light (e.g., light having a wavelength of 590 nm) propagating in a direction perpendicular to the film surface (thickness direction of the film) using a birefringence measuring device or a cell gap measuring device, etc. Specifically, it can be measured by a method described later in Examples.

In the present invention, a plurality of positions determined to have a pitch of 20 mm in the width direction of the film are taken as the measurement positions of the orientation axis. Here, the width direction of the film is a direction (TD) in the plane of the film perpendicular to the longitudinal direction of the film. When manufacturing an optical film such as a polarizing film using a long PVA film as a raw material, it is usually uniaxially stretched in the longitudinal direction (machine flow direction; MD) of a long PVA film. Therefore, in general, the longitudinal direction of the film coincides with the direction in which the PVA film is to be uniaxially stretched when manufacturing an optical film such as a polarizing film, and the direction in the plane of the film perpendicular to this longitudinal direction is the width direction. do. In addition, in the case of a non-long PVA film, when manufacturing an optical film such as a polarizing film, the direction to be uniaxially stretched is the length direction of the film, and the direction in the plane of the film perpendicular to this is the width direction. do.

In the present invention, it is important that the measurement pitch of the orientation axis is a pitch of 20 mm in the width direction of the film. If the measurement pitch is larger than this, even if the maximum value of the angle formed by the orientation axes at two adjacent measurement positions is reduced, it will not lead to reduction of the color unevenness of the kind that is a problem in the present invention. Conversely, even if the measurement pitch was made smaller than this and the maximum value of the angle formed by the alignment axes at two adjacent measurement positions was reduced, ΔZ _max when the measurement pitch was a 20 mm pitch corresponds to the provisions of the present invention. It is not limited that it falls within the range, and when ΔZ _max when the measurement pitch is a 20 mm pitch deviates from the range corresponding to the regulation of the present invention, the color unevenness cannot be reduced again.

Although there is no particular limitation on the method of determining the measurement position of the orientation axis, for example, one measurement position is set at the center of the width direction of the film, and the measurement positions are sequentially determined at a pitch of 20 mm each toward both ends in the width direction from this measurement position. do. Further, regions less than 20 mm each from both ends in the width direction toward the center in the width direction can be excluded as a measurement position. For example, in the case of determining a measurement position according to the above-described determination method for a PVA film having a width of 2020 mm, first, one measurement position is determined in the central portion in the width direction. Next, from this measurement position, first, toward one end in the width direction, the measurement position is sequentially determined at a pitch of 20 mm. At the 50th point, the distance from one end in the width direction is 10 mm, and the width from both ends in the width direction is Since it is located in an area less than 20 mm toward the center of the direction, it is excluded from the measurement location, and the measurement location of 49 points is finally determined. Similarly, the measurement position of 49 points is determined from the measurement position of the central part in the width direction toward the other end of the width direction. The total 99 points (1 point + 49 points + 49 points) determined in this way can be used as the measurement position of the orientation axis.

And, in order to obtain ΔZ _max , the angle formed by the alignment axes at two adjacent measurement positions from the alignment axes measured at each measurement position is obtained for all adjacent two measurement positions, and The maximum value is set to ΔZ _max . For example, in the above example in which the measurement positions of 99 points are determined, 98 angles formed by the alignment axes at two adjacent measurement positions can be obtained, and the maximum value among these 98 is set to ΔZ _max . In addition, in this specification, the angle formed by the orientation axes in two adjacent measurement positions shall be in the range of 0 to 90°. In other words, when the directions of the two orientation axes are parallel, the angle is 0°, and when they are vertical, the angle is 90°, and in other cases, the angle on the acute angle is the angle formed by the orientation axes. .

In the PVA film of the present invention, the average value (ΔZ _ave ) of the angles at all adjacent two measurement positions with respect to the angle formed by the orientation axes at two adjacent measurement positions obtained as described above is 0.6 It is preferably less than or equal to °, more preferably less than or equal to 0.58 degrees, and still more preferably less than or equal to 0.56 degrees. On the other hand, the lower limit of ΔZ _ave is not particularly limited, ΔZ _ave is too little PVA film it is the case that the reduced productivity in a manufacturing, ΔZ _ave is more preferably not less than desirable, and 0.05 ° less than 0.01 °, and More preferably, it is 0.1° or more.

In the PVA film of the present invention, it is preferable that the retardation value at the measurement position of the orientation axis is in the range of 5 to 100 nm at all measurement positions. The PVA film which satisfies these conditions improves the stretchability and improves the polarization performance when producing a polarizing film. From the viewpoint of the stretchability of the PVA film and the polarization performance of the polarizing film, the retardation value at the measurement position of the orientation axis is more preferably 10 nm or more, further preferably 15 nm or more, in all measurement positions, It is particularly preferably 20 nm or more. In addition, from the viewpoint of the stretchability of the PVA film, the retardation value at the measurement position of the orientation axis is more preferably 70 nm or less, and still more preferably 50 nm or less at all measurement positions.

In the PVA film of the present invention, the angle formed by the orientation axis in at least one of the measurement positions of the orientation axis and the length direction of the PVA film (but within the range of 0 to 90°) is preferably 45 to 90°. . The PVA film which satisfies these conditions improves the stretchability and improves the polarization performance when producing a polarizing film. From the viewpoint of the stretchability of the PVA film and the polarization performance of the polarizing film, it is more preferable that the angle formed by the orientation axis in at least one of the measurement positions of the orientation axis and the length direction of the PVA film is 70 to 90°, It is more preferable that it is 80 to 90 degrees.

In the PVA film of the present invention, each description of the above-described ΔZ _max , ΔZ _ave , retardation value, and the angle formed by the orientation axis and the length direction of the PVA film corresponds to one straight line in the width direction of the film set arbitrarily. However, since it is possible to continuously and smoothly manufacture a uniform optical film, it is preferable that there is no variation in physical properties in the longitudinal direction of the film. Therefore, each of the above descriptions corresponds to 50% or more of the longitudinal direction of the film. It is preferable, it is more preferable to correspond in 80% or more, and it is still more preferable to correspond in 95% or more. In addition, in the case of continuously manufacturing a long PVA film, etc., since the physical properties in the longitudinal direction usually do not change very much, if each of the above descriptions correspond to one straight line in the width direction of the film set arbitrarily, usually , Each of the above descriptions corresponds to one straight line in any width direction of the film.

Although the thickness of the PVA film of the present invention is not particularly limited, if it is too thick, it becomes difficult to quickly dry when producing an optical film such as a polarizing film, while if it is too thin, 1 Since fracture of the film tends to occur during axial stretching, it is preferably in the range of 5 to 150 µm, more preferably in the range of 20 to 120 µm, and even more preferably in the range of 50 to 80 µm.

The width of the PVA film of the present invention is not particularly limited, but recently, since liquid crystal televisions and monitors have become large screens, in order to be able to use them effectively, it is preferably 2 m or more, and more preferably 4 m or more. . In addition, in the case of manufacturing an optical film such as a polarizing film with a realistic production machine, if the width of the film is too wide, uniform uniaxial stretching may become difficult, so the width of the PVA film is preferably 8 m or less.

Although the length of the PVA film of the present invention is not particularly limited, it is possible to continuously and smoothly produce a more uniform PVA film, and it can be used continuously even in the case of manufacturing an optical film using it, so 5 to 50,000 m It is preferably in the range of, and more preferably in the range of 100 to 20,000 m.

As the PVA for forming the PVA film of the present invention, one produced by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester can be used. Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among the vinyl esters, vinyl acetate is preferred from the viewpoints of availability, cost, and ease of production of PVA.

The polyvinyl ester polymer is preferably obtained using only one or two or more vinyl esters as a monomer, and more preferably one obtained using only one vinyl ester as a monomer, and one or two or more vinyl esters. And, it may be a copolymer of another monomer copolymerizable with this.

As another monomer copolymerizable with such a vinyl ester, For example, ethylene; Olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene (α-olefin, etc.); Acrylic acid or its salt; Acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; Methacrylic acid or a salt thereof; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-methacrylic acid Methacrylic acid esters such as ethylhexyl, dodecyl methacrylate, and octadecyl methacrylate; Acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamide propanesulfonic acid or its salt, acrylamide propyldimethylamine or its salt, N-methylolacryl Acrylamide derivatives such as amide or derivatives thereof; Methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propane sulfonic acid or a salt thereof, methacrylamide propyl dimethyl amine or a salt thereof, N-methylol methacrylamide or a derivative thereof, etc. Acrylamide derivatives; N-vinylamides, such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; Vinyls 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 Ether; Vinyl cyanide such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Maleic acid or its salt, ester, or acid anhydride; Itaconic acid or its salt, ester, or acid anhydride; Vinylsilyl compounds such as vinyl trimethoxysilane; Isopropenyl acetate, and the like. The polyvinyl ester polymer may have a structural unit derived from one or two or more of these other monomers.

The ratio of the structural units derived from the other monomers to the polyvinyl ester polymer 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 polymer. More preferable.

The PVA may be modified with one or two or more graft copolymerizable monomers. Examples of the graft copolymerizable monomer include unsaturated carboxylic acid or a derivative thereof; Unsaturated sulfonic acid or a derivative thereof; Α-olefins having 2 to 30 carbon atoms, and the like. It is preferable that the ratio of the structural unit derived from the monomer which can be grafted copolymerization in PVA is 5 mol% or less based on the number of moles of all structural units constituting PVA.

In the PVA, a part of the hydroxyl group may or may not be crosslinked. In addition, in the PVA, a part of the hydroxyl group may react with an aldehyde compound such as acetaldehyde and butylaldehyde to form an acetal structure, and it is not necessary to form an acetal structure without reacting with these compounds.

The degree of polymerization of PVA is not particularly limited, but from the viewpoints of film strength and durability of the resulting optical film, it is preferably 500 or more, more preferably 1,000 or more, still more preferably 1,500 or more, and particularly preferably 2,000 or more. On the other hand, if the degree of polymerization is too high, the degree of polymerization of PVA is preferably 10,000 or less, more preferably 9,000 or less, and even more preferably 8,000 or less, since it tends to lead to an increase in manufacturing cost or poor process passability during film production. And 7,000 or less is particularly preferred. In addition, the polymerization degree of PVA in this specification means the average degree of polymerization measured in accordance with the description of JIS K 6726-1994.

The saponification degree of PVA is not particularly limited, but from the viewpoint of optical performance and durability of the optical film produced from the obtained PVA film, the saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, It is more preferable that it is 99 mol% or more, and it is especially preferable that it is 99.2 mol% or more. In addition, the degree of saponification of PVA in this specification refers to the vinyl alcohol unit with respect to the total number of moles of the structural unit (typically a vinyl ester unit) and the vinyl alcohol unit that PVA has and can be converted into a vinyl alcohol unit by saponification. It refers to the ratio (mol%) occupied by the number of moles. The degree of saponification of PVA can be measured according to the description of JIS K 6726-1994.

As the PVA forming 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, polymerization degree, saponification degree, and the like may be used in combination. However, in a case where excellent secondary workability is required for the PVA film of the present invention, such as when used as a raw material for producing an optical film, the PVA film may include PVA having acidic functional groups such as carboxyl groups and sulfonic acid groups; PVA having an acid anhydride group; PVA having a basic functional group such as an amino group; When PVA having a functional group for accelerating a crosslinking reaction, such as a neutral product thereof, is included, the secondary workability of the PVA film may be deteriorated due to a crosslinking reaction between PVA molecules. Therefore, in the case as described above, the PVA film preferably does not contain any of PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group, and neutralized products thereof. As PVA, only vinyl ester PVA prepared by saponifying a polyvinyl ester polymer obtained by using as a monomer, and/or PVA prepared by saponifying a polyvinyl ester polymer obtained by using only vinyl ester and ethylene and/or an olefin having 3 to 30 carbon atoms as a monomer. It is more preferable to contain only, and as PVA, PVA prepared by saponifying a polyvinyl ester polymer obtained by using only vinyl ester as a monomer, and/or a polyvinyl ester polymer obtained by using only vinyl ester and ethylene as a monomer. It is more preferred to include only PVA prepared by saponification.

Although the manufacturing method of the PVA film of this invention is not specifically limited, The PVA film of this invention,

(a) Using a film-making apparatus including three or more drying rolls with rotational axes parallel to each other, and discharging the film-making stock solution containing PVA on the first drying roll located on the uppermost side of the drying rolls in a film shape After performing partial drying, it is further dried with a subsequent drying roll to produce a film; Then,

(b) The volatile fraction of the PVA film when peeling from the first dry roll is set to 20 to 40% by mass;

(c) a first ratio (S ₂ / S ₁₎ of the peripheral speed (S ₂₎ of the second drying rolls to a peripheral speed (S ₁₎ of the drying roll with 1.015 ~ 1.050 and;

(d) When the volatile fraction of the PVA film became 10% by mass from the second drying roll or the drying roll when the volatile fraction of the PVA film became 20% by mass among the drying rolls on the downstream side thereof. The ratio of the peripheral speed (S _n+1 ) of the downstream drying roll to the peripheral speed (S _n ) of the drying roll on the upstream side among the two adjacent drying rolls ( All of S _n+1 /S _n ) to 0.992 to 0.999;

By the production method of the present invention including a step, it can be produced continuously and smoothly with good productivity.

Although the present invention is not limited in any way, according to the method for producing a PVA film of the present invention, the ratio of the circumferential speed between two adjacent dry rolls is 1.000 over the entire state in which the volatile fraction of the PVA film is from 20% by mass to 10% by mass. Since it is set in a specific range that is less than that, the uniformity in the width direction in the resulting PVA film is improved, and it is considered that the PVA film of the present invention has been smoothly and continuously manufactured with good productivity.

The manufacturing method of the PVA film of the present invention described above will be described in more detail below.

The film-making 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 melt. Melting of PVA into a liquid medium or melting of PVA chips containing a liquid medium or the like can be performed using a stirring mixing device, a melt extruder, or the like. Examples of the liquid medium used at that time include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, and the like. These liquid media May be used singly or in combination of two or more. Among these, water, dimethyl sulfoxide, or a mixture of both is preferably used, and water is particularly preferably used.

From the viewpoints of promoting dissolution or melting of PVA into a liquid medium, improving process passability during film production, and improving stretchability of the resulting PVA film, the film-making stock solution preferably contains a plasticizer. A PVA film containing a plasticizer is obtained by using a film-making stock solution containing a plasticizer. Polyhydric alcohols are preferably used as the plasticizer, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Plasticizers may be used alone or in combination of two or more. Among these, one or two or more of glycerin, diglycerin and ethylene glycol are preferably used from the viewpoint of excellent effect of improving stretchability.

The content of the plasticizer is preferably 0 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass per 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.

It is preferable that the film-making stock solution contains a surfactant from the viewpoints of the improvement of the peelability from the dry roll when producing the PVA film and the handleability of the resulting PVA film. A PVA film containing a surfactant is obtained by using a film-making stock solution containing a surfactant. The type of surfactant is not particularly limited, but anionic surfactant or nonionic surfactant is preferably used.

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

In addition, examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octylphenyl ether, and alkyl ester types such as polyoxyethylene laurate, Alkylamine types such as polyoxyethylene laurylamino ether, alkylamide types such as polyoxyethylene lauric acid amide, polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether, and alkanolamides such as oleic acid diethanolamide Type, allylphenyl ether type nonionic surfactants such as polyoxyalkylene allylphenyl ether are preferable.

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

The content of the surfactant is preferably 0.01 to 1 parts by mass, more preferably 0.02 to 0.5 parts by mass, and still more preferably 0.05 to 0.3 parts by mass per 100 parts by mass of PVA. 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 dyeability are improved. Moreover, when the content of the surfactant is 1 part by mass or less with respect to 100 parts by mass of PVA, the handleability of the PVA film is improved.

The film-making stock solution may contain various additives such as stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers, anti-blocking agents, flame retardants, antistatic agents, lubricants, dispersants, fluidizing agents, and antibacterial agents. These additives may be used alone or in combination of two or more.

It is preferable that it is in the range of 50-90 mass %, and, as for the volatile content of the film production stock solution used for manufacture of a PVA film, it is more preferable that it is in a range of 55-80 mass %. When the volatile fraction is 50% by mass or more, excessive increase in viscosity can be suppressed, and film formability is improved. On the other hand, when the volatile fraction is 90 mass% or less, the thickness uniformity of the obtained PVA film is improved. In addition, the volatile fraction of the film-making stock solution referred to in the present specification refers to the volatile fraction obtained by the following formula [i].

A = {(Wa-Wb)/Wa} × 100 [i]

[In the formula, A is the volatile fraction (mass%) of the film-making stock solution, Wa is the mass (g) of the film-making stock solution, and Wb is the film-making stock solution of Wa (g) after drying for 16 hours in an electrothermal dryer at 105°C. It shows the mass (g).]

In a film manufacturing apparatus including three or more drying rolls in which rotational axes are parallel to each other, which is used in the production of a PVA film, the number of drying rolls is preferably 4 or more, and more preferably 5 to 30. In addition, the one positioned on the uppermost side of the drying rolls is referred to as a first drying roll, and for the remaining drying rolls, in order from the first drying roll toward the downstream side, the second drying roll, the third drying roll, and the fourth drying role, … It is called as. The drying roll is preferably made of a metal such as nickel, chromium, copper, iron, stainless steel, etc., and more preferably, the roll surface is made of a metal material that is hard to corrode and has a mirror gloss. Do. In addition, in order to increase the durability of the drying roll, it is more preferable to use a dry roll plated with a single layer or a combination of two or more layers of nickel, chromium, and nickel/chromium alloy layers.

The film production apparatus used in the present invention may have a hot air drying apparatus, a heat treatment apparatus, a humidity control apparatus, or the like following the drying roll as necessary.

In discharging the film-forming raw liquid onto the first drying roll of the film-making device in a film form, for example, a known film-shaped discharge device such as a T-type slit die, a hopper plate, an I-die, and a lip coater die. Using the (membrane casting apparatus), the film-forming stock solution is discharged (softened) onto the first drying roll in a film form.

By drying the liquid containing PVA discharged in the form of a film on the first drying roll on the first drying roll, some of the volatile components contained therein (partial drying) were removed, and the volatile fraction of the PVA film was 20 to 40% by mass. It peels off from the 1st dry roll when it became.

When the volatile fraction of the PVA film when peeled from the first dry roll is less than 20% by mass, ΔZ _max of the obtained PVA film is likely to deviate from the range corresponding to the provisions of the present invention. The volatile fraction of the PVA film when peeled from the first dry roll is preferably 21% by mass or more, more preferably 22% by mass or more, and still more preferably 23% by mass or more. On the other hand, when the volatile fraction of the PVA film when peeling from the first dry roll exceeds 40% by mass, the peelability from the first dry roll deteriorates, the uniformity in the width direction of the film is impaired, and the resulting PVA film ΔZ _max tends to deviate from the range corresponding to the provisions of the present invention. The volatile fraction of the PVA film when peeled from the first dry roll is preferably 30% by mass or less, more preferably 28% by mass or less, and still more preferably 27% by mass or less.

Here, the volatile fraction of the PVA film or the PVA film referred to in the present specification refers to the volatile fraction determined by the following formula [ii].

B = {(Wc-Wd)/Wc} × 100 [ii]

[In the formula, B is the volatile fraction (mass%) of the PVA film or PVA film, Wc is the mass (g) of the sample taken from the PVA film or PVA film, and Wd is the sample Wc (g) at a temperature of 50°C and pressure. The mass (g) when it was put in a 0.1 kPa or less vacuum dryer and dried for 4 hours is shown.]

In a PVA film or PVA film formed from a film-making stock solution prepared using a polyhydric alcohol (plasticizer) such as PVA and glycerin, a surfactant, and water, under the conditions of “4 hours at a temperature of 50° C. and a pressure of 0.1 kPa or less” When dried, only water is volatilized, and most of the components other than water do not volatilize and remain in the PVA film or PVA film, so the volatile fraction of the PVA film or PVA film is the amount of moisture contained in the PVA film or PVA film. It can be calculated|required by measuring (water content).

In drying on the first drying roll, from the viewpoints of uniformity of drying and drying speed, the surface temperature of the first drying roll is preferably 80 to 120°C, more preferably 85 to 105°C, and 93 It is more preferable that it is -99 degreeC. When the surface temperature of the first drying roll is 120°C or less, foaming of the film can be more effectively suppressed, while when it is 80°C or more, the drying efficiency on the first drying roll is improved.

The circumferential speed (S ₁ ) of the first drying roll is preferably 8 to 25 m/min, more preferably 10 to 23 m/min, from points such as uniformity of drying, drying speed, and productivity of the PVA film, It is more preferable that it is 12 to 22 m/min.

Partial drying of the film-making stock solution containing PVA discharged in the form of a film on the first drying roll may be carried out only by heat from the first drying roll, but it is heated with the first drying roll and is brought into contact with the first drying roll. Hot air is sprayed on the non-contacting surface (hereinafter referred to as the ``first dry roll non-contact surface'', and the opposite film surface on the side in contact with the first drying roll is sometimes referred to as the ``first dry roll contact surface'') , It is preferable to dry by applying heat from both sides of the PVA film from the viewpoint of uniformity of drying and drying speed.

In spraying hot air on the non-contact surface of the first drying roll of the PVA film on the first drying roll, it is preferable to spray hot air at a wind speed of 1 to 10 m/s to the entire area of the non-contacting surface of the first drying roll, It is more preferable to spray hot air with a wind speed of 2 to 8 m/sec, and even more preferably to spray hot air with a wind speed of 3 to 8 m/sec.

If the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too small, condensation such as water vapor occurs during drying on the first drying roll, and the water droplets drop on the PVA film to finally obtain a PVA film. It becomes easy to generate a defect. On the other hand, when the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too large, a thickness non-uniformity occurs in the finally obtained PVA film, and accordingly, troubles such as dyeing non-uniformity are liable to occur.

The temperature of the hot air sprayed on the non-contact surface of the first drying roll of PVA is preferably 50 to 150°C, more preferably 70 to 120°C, and more preferably 80 to 95 from the viewpoints of drying efficiency and drying uniformity. It is more preferable that it is °C. Further, the dew point temperature of the hot air sprayed on the non-contact surface of the first drying roll of the PVA film is preferably 10 to 15°C. When the temperature of the hot air sprayed on the non-contact surface of the first drying roll of the PVA film is too low, drying efficiency, drying uniformity, etc. are liable to deteriorate, while if it is too high, foaming is liable to occur.

The method for spraying hot air on the non-contact surface of the first drying roll of the PVA film is not particularly limited, and hot air having a uniform wind speed and a uniform temperature is uniformly sprayed on the non-contact surface of the first drying roll of the PVA film, preferably the whole. Any of the possible methods can be adopted, and among them, a nozzle method, a rectifying plate method, or a combination thereof are preferably adopted. Even if the spraying direction of the hot air to the non-contact surface of the first drying roll of the PVA film is a direction facing the non-contacting surface of the first drying roll, the direction substantially along the circumferential shape of the non-contacting surface of the first drying roll of the PVA film (roll of the first drying roll It may be a direction substantially along the circumference of the surface) or a direction other than that.

Further, at the time of drying the PVA film on the first drying roll, it is preferable to exhaust the volatile components generated from the PVA film by drying and the hot air after spraying. The evacuation method is not particularly limited, but it is preferable to employ an evacuation method in which non-uniformity in wind speed and temperature of the hot air sprayed onto the non-contact surface of the first drying roll of the PVA film do not occur.

The PVA film dried on the first drying roll to a volatile fraction of 20 to 40% by mass is peeled off from the first drying roll, and this time, it is further dried with a drying roll following the second drying roll. When drying the PVA film on the second drying roll, it is preferable to dry the first drying roll non-contact surface of the PVA film opposite to the second drying roll.

The ratio (S ₂ /S ₁ ) of the circumferential speed (S ₂ ) of the second drying roll to the circumferential speed (S ₁ ) of the first drying roll is in the range of 1.015 to 1.050, preferably in the range of 1.020 to 1.048, , It is more preferable to exist in the range of 1.023 to 1.046, and it is still more preferable to exist in the range of 1.025 to 1.045. When the ratio (S ₂ /S ₁ ) is less than 1.020, the ΔZ _max of the PVA film obtained is in accordance with the provisions of the present invention, such as deterioration of the peelability of the PVA film from the first dry roll and the uniformity in the width direction of the film. It is easy to deviate from the corresponding range. In addition, even when the ratio (S ₂ /S ₁ ) exceeds 1.050, the ΔZ _max of the obtained PVA film is seen, for example, the unevenness of the tension applied to the PVA film between the first dry roll and the second dry roll expands. It is easy to deviate from the range corresponding to the rules of the invention.

In the case where the second drying roll is positioned upstream from the x-th drying roll described later, it is present between the second drying roll and the drying roll immediately before the x-th drying roll (the (x-1) drying roll) The surface temperature of all the dry rolls (including the second dry roll and the (x-1) dry roll) is preferably 80°C or higher, more preferably 83°C or higher, and still more preferably 85°C or higher. Moreover, it is preferable that it is 95 degreeC or less, as for the surface temperature of these dry rolls, it is more preferable that it is 92 degreeC or less, and it is still more preferable that it is 90 degreeC or less. By setting the surface temperature of these drying rolls in the above range, drying uniformity can be improved while maintaining an appropriate drying rate.

The dry roll when the volatile content of the PVA film is 20 mass% among the second dry rolls or the dry rolls downstream thereof is referred to as the x dry roll, and a dry roll when the volatile content of the PVA film is 10 mass% is prepared. When referred to as a y dry roll, between the x- _th drying roll and the y- _th drying roll, the circumferential speed of the downstream drying roll with respect to the circumferential velocity (S _n ) of the upstream drying roll among two adjacent drying rolls ( ratio (S _{n + 1} / S _n of S _{n + 1)),} it is both necessary to the range of 0.992 ~ 0.999. That is, for example, when the x-th dry roll is the fifth dry roll and the y-th dry roll is the eighth dry roll, the circumferential speed (S ₆ ) of the sixth drying roll relative to the circumferential speed (S ₅ ) of the fifth drying roll Ratio of (S ₆ /S ₅ ), the ratio of the circumferential speed of the seventh drying roll (S ₇ ) to the circumferential speed of the sixth drying roll (S ₆ ) (S ₇ /S ₆ ), the circumferential speed of the seventh drying roll (S all of the _non-(8 S / S ₇₎ of the peripheral speed (S ₈₎ of the eighth drying roll to ₇₎ is required in a range of 0.992 ~ 0.999. If some or all of the ratio (S _n+1 /S _n ) deviates from the regulations of the present invention, uniformity in the width direction is lost, and it becomes difficult to obtain the target 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 even more preferably 0.995 or more. In addition, from the viewpoint of uniformity in the width direction, the ratio (S _n+1 /S _n ) is preferably 0.998 or less. In addition, the volatile fraction of the PVA film is usually lowered on the drying roll. However, when the volatile fraction becomes 20% by mass or 10% by mass between two adjacent drying rolls, the downstream drying rolls in the x-th It shall be referred to as dry roll or y-th dry roll. In addition, when the volatile fraction of a PVA film when peeling from a 1st dry roll is 20 mass %, it is assumed that a 2nd dry roll is referred to as an x-th dry roll.

The ratio (S _y /S _x ) of the peripheral speed (S _y ) of the y-th drying roll to the peripheral speed (S _x ) of the _x- th drying roll (S _y /S _x ) is 0.940 to in that the uniformity in the width direction can be further improved. It is preferably in the range of 0.990, more preferably in the range of 0.955 to 0.985, and even more preferably in the range of 0.960 to 0.980.

The number of drying rolls present between the x-th drying roll and the y-th drying roll is four or more, including the x-th drying roll and the y-th drying roll, in that uniformity in the width direction can be further improved. It is preferable, it is more preferable that it is 6 or more, it is still more preferable that it is 8 or more, and it is more preferable that it is 20 or less.

The surface temperature of all the dry rolls (including the x-th dry roll and the y-th dry roll) existing between the x-th dry roll and the y-th dry roll are preferably 60°C or higher, and more preferably 62°C or higher. And more preferably 65° C. or higher. Moreover, it is preferable that it is 85 degreeC or less, as for the surface temperature of these dry rolls, it is more preferable that it is 82 degreeC or less, and it is still more preferable that it is 80 degreeC or less. By making the surface temperature of these dry rolls into the said range, the uniformity in the width direction can be improved further.

When the PVA film dried with the y-th drying roll is further dried with a subsequent drying roll, a PVA film having a lower volatile content is obtained. The surface temperature of the drying roll downstream from the y-th dry roll is preferably in the range of 60 to 85°C, more preferably in the range of 62 to 82°C, and even more preferably in the range of 65 to 80°C. The dry roll or the dry roll close to the final and the final dry roll may be used as a heat treatment roll by raising the surface temperature thereof. When using a dry roll as a heat treatment roll, it is preferable that it exists in the range of 90-140 degreeC, and, as for the surface temperature, it is more preferable that it exists in the range of 95-130 degreeC.

In the process from the first drying roll to the final drying roll, the direction of the PVA film with respect to each drying roll is not particularly limited, but since the PVA film can be dried more uniformly, the surface and the back surface of any part of the PVA film It is preferable to dry so that it may alternately oppose each drying roll from this 1st drying roll to a final drying roll.

The ratio (S _L / S ₁ ) of the circumferential speed (S _L ) of the final dry roll to the circumferential speed (S ₁ ) of the _first drying roll is not particularly limited, but is preferably in the range of 0.900 to 1.100, and is preferably in the range of 0.950 to 1.050. It is more preferable to exist in the range, it is more preferable to exist in the range of 0.980 to 1.020, and it is especially preferable to exist in the range of 0.990 to 1.010. In addition, among the ratios of the circumferential speeds between two adjacent drying rolls, other than the above description, the ratio of the circumferential speed of the downstream drying roll to the circumferential speed of the upstream drying roll is, for example, 0.980 to 1.020. It can be set within the range, and further within the range of 0.990 to 1.010.

If necessary, the PVA film obtained by the drying treatment is subjected to a humidity control treatment or the like, and the PVA film of the present invention can be obtained by winding it up in a roll shape with a predetermined length. In addition, you may cut and remove both ends (ears) in the width direction of the said PVA film in any one or several steps before winding up in a roll shape, a step in a roll shape, and after unwinding from a roll.

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

Although there is no particular limitation on the use of the PVA film of the present invention, even when a light transmittance is high or a backlight having a higher intensity is used, an optical film such as a polarizing film with reduced color unevenness can be manufactured, so that an optical film can be manufactured. It is preferable to use it as a fabric for the time. As an optical film, in addition to a polarizing film, a retardation film etc. are mentioned. These optical films can be manufactured by the manufacturing method which has a process of uniaxially extending|stretching using the PVA film of this invention.

More specifically, in order to manufacture a polarizing film using the PVA film of the present invention as a raw material, for example, dyeing, uniaxial stretching, fixing treatment, drying treatment, additionally required using the PVA film of the present invention Accordingly, heat treatment may be performed. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, dyeing may be performed simultaneously with uniaxial stretching, or dyeing may be performed after uniaxial stretching. In addition, steps such as uniaxial stretching and dyeing may be repeated a plurality of times.

As a dye used for dyeing a PVA film, iodine or a dichroic organic dye (for example, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37 , 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; DirectYellow 8, 12, 44, 86, 87; Dichromatic dyes such as DirectOrange 26, 39, 106, 107) and the like can be used. These dyes may be used alone or in combination of two or more. Dyeing can usually be performed by immersing the PVA film in a solution containing the dye, but the treatment conditions and treatment methods 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. In the case of uniaxial stretching by a wet stretching method, uniaxial stretching may be performed in hot water containing boric acid, uniaxial stretching may be performed in a solution containing the above dye or in a post-fixing treatment bath, or PVA film after absorption It may be uniaxially stretched in air by using or may be uniaxially stretched by other methods. The stretching temperature in the uniaxial stretching treatment is not particularly limited, but when stretching the PVA film in warm water (wet stretching), preferably 30 to 90°C, more preferably 40 to 70°C, still more preferably 45 to A temperature of 65°C is employed, and in the case of dry heat stretching, a temperature of 50 to 180°C is preferably employed. In addition, the draw ratio of uniaxial stretching (in the case of performing uniaxial stretching in multiple stages, the total draw ratio) is preferably stretched as much as possible until immediately before the film is cut from the viewpoint of polarization performance, and specifically, it is 4 times or more. It is preferable, it is more preferable that it is 5 times or more, and it is still more preferable that it is 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less in order to perform uniform stretching. 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|stretched corresponds to the draw ratio 1 times.

It is preferable that the thickness of the film (polarizing film) after extending|stretching is 5 to 35 micrometers, and especially 20 to 30 micrometers.

In the case of uniaxial stretching of a long PVA film, there is no particular limitation on the direction of uniaxial stretching, and uniaxial stretching in the longitudinal direction or transverse uniaxial stretching may be adopted, but a polarizing film having better polarization performance is From the viewpoint of obtaining, uniaxial stretching in the longitudinal direction is preferable. Uniaxial stretching in the longitudinal direction can be performed by using a stretching device provided with a plurality of rolls parallel to each other and changing the circumferential speed between the rolls. On the other hand, transverse uniaxial stretching can be performed using a tenter type stretching machine.

In production of a polarizing film, in order to strengthen the adsorption of the dye to the uniaxially stretched film, it is preferable to perform a fixing treatment. Examples of the fixing treatment include a method of immersing a film in a fixing treatment bath to which a boron compound such as boric acid and borax was added. In that case, you may add an iodine compound to the fixed treatment bath as needed.

It is preferable to uniaxially stretch or dry (heat treatment) the film which performed the uniaxial stretch and fixed treatment subsequently. 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. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film is liable to decrease, while if it is too high, a decrease in polarization performance accompanying decomposition of the dye or the like is liable to occur.

A protective film that is optically transparent and has mechanical strength can be attached to both surfaces or one surface of the polarizing film obtained as described above to obtain a polarizing plate. As the protective film in that case, a cellulose triacetate (TAC) film, an acetic acid-butyrate cellulose (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive for bonding a protective film, a PVA-type adhesive, a urethane-type adhesive, etc. are mentioned, Among them, a PVA-type adhesive is preferable.

The polarizing plate obtained as described above can be bonded to a glass substrate and used as a component of a liquid crystal display device after coating an acrylic adhesive or the like. When bonding a polarizing plate to a glass substrate, you may bond a retardation film, a viewing angle improvement film, a brightness improvement film, etc.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited at all by the following examples.

In the following examples and comparative examples, each measurement or evaluation result of the ΔZ _max , ΔZ _ave , retardation value and orientation axis of the PVA film and the length direction of the PVA film, and the color non-uniformity and polarization performance of the polarizing film are It was calculated|required by the following method.

(1) ΔZ _max , ΔZ _ave of the PVA film , retardation value, and the angle formed by the orientation axis and the length direction of the PVA film

Tape of a total width length (3 m) having a length of 40 mm in the longitudinal direction (MD) of the PVA film from an arbitrary position in the longitudinal direction (MD) of the elongated PVA film obtained in each of the following Examples or Comparative Examples A sample of the phase was taken. With respect to this tape-shaped sample, one measurement position was set at the center portion in the width direction of the film, and measurement positions (74 points each) were sequentially determined from this measurement position toward both ends in the width direction at a pitch of 20 mm. In addition, each of the 75th points located in an area of less than 20 mm from both ends in the width direction toward the center in the width direction was excluded from the measurement position. In addition, each measurement position was set at the center part of the machine flow direction of the tape-shaped sample (positions 20 mm each from both ends in the machine flow direction).

And the orientation axis and retardation value in the plane of the film at each measurement position (total of 149 points), using ``KOBRA-WFD'' manufactured by Oji Measuring Equipment Co., Ltd., the wavelength 590 propagating in a direction perpendicular to the film plane It measured based on the light of nm, and obtained the ΔZ _max and ΔZ _ave from the data of the orientation axis at each measurement position, and the minimum and maximum values were obtained from the data of the retardation value at each measurement position. . In addition, the angle formed by the orientation axis in the measurement position of the center portion in the width direction of the film and the length direction (MD) of the PVA film was determined.

(2) Color unevenness of polarizing film

A polarizing film prepared so that a polarizing plate for observation (using a polarizing film having a transmittance of about 43%) is placed on a surface light source (backlight) in a dark room to become a cross Nicol with respect to the polarizing plate for observation. Was wit. Next, light is irradiated to the polarizing film from the backlight through the polarizing plate for observation (intensity of 15,000 cd), and the polarizing film is visually observed from a position of 1 m directly above the polarizing film, based on the following criteria. The color unevenness of the polarizing film was evaluated by sensory evaluation.

○: Color unevenness is not observed, or even if it is observed, it is a level with no problem in practical use.

X: Color non-uniformity at the level which becomes a problem in practical use was observed

In addition, according to the production conditions of "(2) Preparation of polarizing film (i)" described later, it is easy to obtain a polarizing film having a high transmittance of 44% or more, but the above method is employed using a polarizing film having such a high transmittance. By doing so, it is possible to clearly evaluate the presence or absence or degree of color unevenness as a problem in the present invention.

(3) Polarization performance of polarizing film

(a) Measurement of transmittance (Y)

From the widthwise central portion of the polarizing film obtained in each of the following Examples or Comparative Examples, two square samples having a length direction of 4 cm x a width direction of 4 cm were collected. For one sample, the transmittance of light in the case of a 45° inclination and the transmittance of light in the case of -45° inclination with respect to the measuring device in the longitudinal direction were measured, and their average value (Y ₁ ) (%) was calculated. Similarly for the other sample, the transmittance of light in the case of a 45° inclination and the transmittance of light in the case of a -45° inclination were measured, and their average value (Y ₂ ) (%) was obtained. In addition, for the measurement of the transmittance, a spectrophotometer "U-4100" (attached to the integrating sphere) manufactured by Hitachi Corporation was used. In addition, the measurement of the transmittance was carried out by a method conforming to JIS Z 8722 (measurement method of object color), and the luminous sensitivity of the visible light region at a 2° field of view was corrected using a C light source.

Y ₁ and Y ₂ calculated|required by the said method were averaged by the following formula [iii], and it was set as the transmittance|permeability (Y) (%) of a polarizing film.

Transmittance (Y) = (Y ₁ + Y ₂ )/2 [iii]

(b) Measurement of polarization degree (V)

) (％), 및 그들의 길이 방향이 직교하도록 겹친 경우의 광의 투과율 (Y⊥) (％) 을 측정하였다. 또

및 Y⊥ 는, 상기 「(a) 투과율 (Y) 의 측정」과 동일한 방법으로 구하였다. 이들의

및 Y⊥ 로부터, 이하의 식 [iv] 에 의해서 편광도 (V) (％) 를 구하였다. The transmittance of light when two samples of the polarizing film collected in the ``(a) measurement of transmittance (Y)'' are stacked so that their longitudinal directions are parallel to each other (

) (%), and the light transmittance (Y⊥) (%) in the case of overlapping so that their longitudinal directions are orthogonal were measured. In addition

And Y⊥ were obtained in the same manner as in the above "(a) measurement of transmittance (Y)". Of these

And from Y⊥, the polarization degree (V) (%) was calculated|required by the following formula [iv].

- Y⊥)/(

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

-Y⊥)/(

+ Y⊥)} ^1/2 × 100 [iv]

<< Example 1 >>

(1) Preparation of PVA film

(i) PVA (saponified product of vinyl acetate homopolymer, polymerization degree 2,400, saponification degree 99.9 mol%) 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamide 0.1 parts by mass, and water with a volatile fraction of 66 mass% Using a production stock solution, a long PVA film having a thickness of 75 µm, a width of 3 m, a length of 10,000 m, and a volatilization fraction of 3% by mass is continuously formed by a film production apparatus having 20 dry rolls with parallel rotation axes. Was prepared.

Specifically, the film-making stock solution is discharged in a film form from a T-type slit die onto a first drying roll (surface temperature 93° C., peripheral speed (S ₁ ) 13.6 m/min), and on the first drying roll, the first Hot air (temperature 90° C., dew point temperature 10° C.) is uniformly sprayed on the entire non-contact surface of the drying roll at a wind speed of 5 m/sec, drying until the volatile fraction of the PVA film becomes 25% by mass, and then from the first drying roll. After peeling (the volatile fraction at the time of peeling from the first dry roll is 25% by mass), the first dry roll contact surface and the first dry roll non-contact surface of the PVA film alternately oppose each dry roll. After drying with a drying roll, and cutting and removing both ends (ears) in the width direction further, it wound up in a roll shape, and the said PVA film was obtained.

Moreover, in the said film production, the x-th dry roll was a 5th dry roll, and the y-th dry roll was a 13th dry roll. In addition, the ratio (S ₂ /S ₁ ) is 1.040, and the ratio (S _n+1 /S _n ) of the peripheral velocity between two adjacent drying rolls between the _x-th drying roll and the y- _th drying roll is 0.995 It was (minimum value)-0.998 (maximum value), the ratio (S _y /S _x ) was 0.973, and the ratio (S _L /S ₁ ) was 1.007. In addition, the surface temperature of all the drying rolls existing between the second drying roll and the (x-1) drying roll is 85°C (minimum value) to 90°C (maximum value), and the y drying from the x drying roll The surface temperature of all the dry rolls present between the rolls was 67°C (minimum value) to 75°C (maximum value).

For the obtained PVA film, ΔZ _max , ΔZ _ave , retardation values, and angles formed by the orientation axis and the length direction of the PVA film were determined by the above-described method. Table 1 shows the results.

(2) Preparation of polarizing film

(i) From the central part of the width direction (TD) of the PVA film obtained in the above (1), a rectangular test piece of 12 cm in the length direction × 20 cm in the width direction is taken, and both ends of the test piece in the length direction are the size of the stretched portion. It is fixed to the stretching jig so that the length direction is 10 cm × 20 cm in the width direction, and while immersed in water at a temperature of 30° C. for 38 seconds, at a stretching speed of 24 cm/min, one axis in the length direction is 2.2 times the original length. After stretching (first-stage stretching), a stretching rate of 24 cm/min while immersed for 60 seconds in an iodine/potassium iodide aqueous solution at a temperature of 30° C. containing iodine at a concentration of 0.03 mass% and potassium iodide at a concentration of 3 mass% In a boric acid/potassium iodide aqueous solution at a temperature of 30° C. containing 3% by mass of boric acid and 3% by mass of potassium iodide in the longitudinal direction (2nd stage stretching) in the longitudinal direction to 3.3 times the original length of the furnace. While immersed for 20 seconds, uniaxially stretched (3rd-stage stretching) in the longitudinal direction at a stretching speed of 24 cm/min up to 3.6 times the original length, followed by 4% by mass of boric acid and about 5% by mass of potassium iodide. While immersed in an aqueous solution of boric acid/potassium iodide containing at a concentration of 60°C, the draw ratio just before the limit draw ratio at a draw rate of 24 cm/min (the draw ratio at the time of film breakage obtained by performing the same operation in advance is the limit draw ratio It was uniaxially stretched (4th-stage stretching) in the longitudinal direction up to (adopted a draw ratio 0.2 times lower than this), and then immersed in an aqueous potassium iodide solution containing 3% by mass of potassium iodide for 10 seconds to fix it. It carried out, and it dried for 4 minutes with a 60 degreeC dryer after that, and produced the polarizing film (28 micrometers in thickness).

About the said polarizing film, the evaluation of color nonuniformity was performed by the said method. Table 1 shows the results.

(ii) In the above (i), except that the immersion time in the ``30°C iodine/potassium iodide aqueous solution'' at the time of the second-stage stretching was changed from 60 seconds, 75 seconds, 90 seconds, 105 seconds, or 120 seconds. The same operation as in the above (i) was performed to prepare four polarizing films (28 μm in thickness) having different transmittances.

(iii) For each of the five polarizing films having different transmittances (Y) obtained in the above (i) and (ii), the transmittance (Y) and the polarization degree (V) were determined according to the method described above, and the horizontal axis is the transmittance. These five points were plotted on a graph using (Y) and the vertical axis as the degree of polarization (V). And the approximate curve of the said five points was drawn on a graph, and the value of the polarization degree (V) when transmittance (Y) was 44.25% was calculated|required from the said approximate curve. Table 1 shows the results.

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

A polarizing film was produced in the same manner as in Example 1 while producing a PVA film in the same manner as in Example 1, except that the production conditions of the PVA film were as shown in Table 1. Table 1 shows the results.

Claims (12)

When the orientation axis in the plane of the film is measured at a pitch of 20 mm in the width direction of the film, the angle α (but within the range of 0 to 90°) formed between the orientation axes at two adjacent measurement positions is all A polyvinyl alcohol-based polymer film that is 2.3° or less at two adjacent measurement positions, and an angle β formed by the orientation axis in at least one of the measurement positions of the alignment axis and the length direction of the polyvinyl alcohol-based polymer film (only 0 It is in the range of -90°) is a polyvinyl alcohol-based polymer film of 45 to 90°. The method of claim 1,
A polyvinyl alcohol-based polymer film in which the average value of the angle α at two adjacent measurement positions is 0.6° or less. The method of claim 1,
A polyvinyl alcohol-based polymer film in which a retardation value measured based on light having a wavelength of 590 nm at the measurement position of the orientation axis is 5 to 100 nm at all measurement positions. The method of claim 1,
Polyvinyl alcohol-based polymer film with a width of 2 m or more. As a method for producing the polyvinyl alcohol-based polymer film according to any one of claims 1 to 4,
(a) Using a film-making apparatus including three or more drying rolls with rotational axes parallel to each other, and a film-making stock solution containing a polyvinyl alcohol-based polymer on a first drying roll positioned on the uppermost side of the drying rolls After discharging in a film shape and partially drying, it is further dried with a drying roll following it to produce a film; Then,
(b) The volatile fraction of the polyvinyl alcohol-based polymer film at the time of peeling from the first dry roll is set to 20 to 40% by mass;
(c) a first ratio (S ₂ / S ₁₎ of the peripheral speed (S ₂₎ of the second drying rolls to a peripheral speed (S ₁₎ of the drying roll with 1.015 ~ 1.050 and;
(d) Volatilization fraction of the polyvinyl alcohol-based polymer film from the second drying roll or from the drying roll when the volatile content of the polyvinyl alcohol-based polymer film became 20% by mass in the drying roll on the downstream side thereof (No. x drying roll) The circumferential velocity of the downstream drying roll relative to the circumferential velocity (S _n ) of the upstream drying roll among the two adjacent drying rolls between the drying rolls when the amount is 10% by mass ( ratio (Preparation method all S _{n + 1} / S _n) to a 0.992 ~ 0.999 of S _{n + 1).} The method of claim 5,
A manufacturing method in which the surface temperature of all the dry rolls present between the x-th drying roll and the y-th drying roll is 60 to 85°C. The method of claim 5,
The manufacturing method in which the circumferential speed (S ₁ ) of the first dry roll is 8 to 25 m/min. The method of claim 5,
The manufacturing method for the non-y (S _y / S _x) of the peripheral speed (S _y) of the drying roll with 0.940 ~ 0.990 for the peripheral speed (S _x) of the x drying rolls. An optical film produced from the polyvinyl alcohol-based polymer film according to any one of claims 1 to 4. The method of claim 9,
Optical film which is a polarizing film. A method for producing an optical film having a step of uniaxial stretching using the polyvinyl alcohol-based polymer film according to any one of claims 1 to 4. delete