WO2014050697A1

WO2014050697A1 - Polyvinyl alcohol film and polarizing film

Info

Publication number: WO2014050697A1
Application number: PCT/JP2013/075298
Authority: WO
Inventors: 康平下田; 磯▲ざき▼　孝徳
Original assignee: 株式会社クラレ
Priority date: 2012-09-26
Filing date: 2013-09-19
Publication date: 2014-04-03
Also published as: JP5587517B1; KR20140140129A; KR101571261B1; JP5563725B1; JPWO2014050697A1; JP2015057629A; KR20140139137A; CN104640912A; KR101624072B1; CN104640912B; TW201416218A; TWI611905B

Abstract

[Problem] To provide: a PVA film which can be inhibited from creasing when stretched and which is low in stretching stress and inhibited from breaking when stretched and from which a thin polarizing film can be efficiently produced; a process for producing the PVA film; and a polarizing film which is less apt to warp even when used for producing a thin polarizer and which has excellent polarizing performance. [Solution] A PVA film which has a degree of swelling (A) of 190-210% and a thickness of 40 µm or less and which, after having been stretched in 30ºC water in a stretch ratio of 3, has a degree of swelling (B) of 260% or more; a process for producing a PVA film that has a degree of swelling (A) of 190-210% and a thickness of 40 µm or less, the process comprising subjecting a PVA film having a degree of swelling (A) of 250% or more to a wet heat treatment for 200 seconds or longer at a temperature of 55-100ºC and a relative humidity of 80% RH or higher; and a polarizing film which has a dichroic ratio of 55 or more and which, after having been held for 1 hour at a temperature of 80ºC and a relative humidity of 5% in the state of having been fixed in the orientation direction, has an orientation-direction shrinkage stress of 73 N/mm² or less.

Description

Polyvinyl alcohol film and polarizing film

The present invention relates to a polyvinyl alcohol film suitable as a raw film for producing a polarizing film, a method for producing the same, and a method for producing a polarizing film using the same. The present invention also relates to a polarizing film excellent in polarizing performance useful for the production of a thin polarizing plate and a polarizing plate produced using the polarizing film.

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. LCDs are used in a wide range of devices such as small devices such as calculators and wrist watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. . Among these LCD application fields, liquid crystal televisions, liquid crystal monitors, and the like are becoming larger and thinner, and as the glass used is thinner, the polarizing plate is also required to be thinner from the viewpoint of shrinkage stress.

In general, a polarizing plate is obtained by dyeing, uniaxially stretching a polyvinyl alcohol film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”), and optionally further fixing with a boron compound or the like. After the production, it is produced by bonding a protective film such as a cellulose triacetate (TAC) film on the surface of the polarizing film. Therefore, in order to achieve thinning of the polarizing plate, it is required to produce a thin polarizing film using a thinner PVA film, and the specific thickness of the PVA film is 40 μm or less, and further 30 μm or less. It is requested to do.

By the way, a PVA film is usually produced by using a film-forming stock solution containing PVA, casting it on a support such as a metal roll and drying it, and further subjecting it to a heat treatment if necessary (for example, (See

Patent Documents

1 and 2, etc.). Patent Document 1 describes a method in which a PVA aqueous solution is cast on a drum-type roll, a PVA film is formed and dried, then heat treatment is performed, and humidity control is performed under specific conditions. Patent Document 2 describes a method in which a formed PVA film is cooled and heat-treated by a specific method. And in both

patent documents

1 and 2, manufacturing a polarizing film using the obtained PVA film is indicated.

JP 2004-160846 A JP 2006-188655 A

A PVA film used as a raw film for producing a polarizing film may need to have a degree of swelling of about 190 to 210% for reasons such as preventing wrinkles during stretching. However, when a thin PVA film having a thickness of about 40 μm or less is formed by a conventionally known method, it is easy to dry at the time of film formation as compared with the case where a PVA film having a conventional thickness is formed. Therefore, it becomes a PVA film having a high degree of swelling. In order to increase the crystallinity of such a PVA film and reduce the degree of swelling to about 190-210%, it is conceivable to perform heat treatment, but when the degree of swelling is reduced by a conventionally known heat treatment method, There was a problem that the film had a high stretching stress, and the film was easily broken in the uniaxial stretching process during the production of the polarizing film, leading to a decrease in the yield of the polarizing film.

Therefore, the present invention can reduce the generation of wrinkles at the time of stretching, and the PVA film capable of producing a thin polarizing film with high yield by reducing the stretching stress and reducing the breaking at the time of stretching. And it aims at providing the manufacturing method of a polarizing film using the same.

In addition, when a conventional polarizing film manufactured using a PVA film as a raw film is used for manufacturing a thin polarizing plate, the polarizing plate is likely to warp due to the thin glass used. . In particular, such a problem is likely to occur when the raw film is stretched at a higher stretch ratio in order to improve the polarization performance.

Accordingly, an object of the present invention is to provide a polarizing film excellent in polarization performance that hardly warps even when a thin polarizing plate is manufactured, and a polarizing plate manufactured using the polarizing film.

As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention have a swelling degree of 190 to 210% by subjecting a thin PVA film having a thickness of 40 μm or less to wet heat treatment under specific conditions. When a PVA film having a thickness of 40 μm or less is produced, an unprecedented PVA film having a swelling degree of 260% or more after being stretched in water can be efficiently obtained, and such a PVA film can be obtained at the time of stretching. It has been found that the generation of wrinkles is reduced, the stretching stress is low, and the breakage during stretching is reduced, so that a thin polarizing film can be produced with good yield. Moreover, according to the polarizing film excellent in the polarizing performance which has a contraction stress in a specific range, it discovered that the said objective concerning a polarizing film and a polarizing plate was achieved. The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] A PVA film having a degree of swelling (A) of 190 to 230% and a thickness of 40 μm or less, and having a degree of swelling (B) of 260% or more after being stretched at a stretch ratio of 3 in water at 30 ° C. A PVA film;
[2] The PVA film of the above [1], which is a raw film for producing a polarizing film;
[3] A method for producing a PVA film having a swelling degree (A) of 190 to 230% and a thickness of 40 μm or less, wherein a PVA film having a swelling degree (A) of 250% or more is treated at a temperature of 55 to 100 ° C. and a relative humidity A production method comprising a step of performing a wet heat treatment for 200 seconds or more under a condition of 80% RH or more;
[4] The production method of the above [3], further comprising a step of heat-treating at a temperature of 90 to 130 ° C. for 10 seconds or longer after the step of performing the wet heat treatment;
[5] A method for producing a polarizing film comprising the steps of dyeing and uniaxially stretching the PVA film of [2] above;
[6] A polarizing film having a dichroic ratio of 55 or more, and the shrinkage stress in the orientation direction is 73 N after 1 hour at a temperature of 80 ° C. and a relative humidity of 5% with the orientation direction fixed. / Mm ² or less polarizing film;
[7] The polarizing film of [6] above, having a thickness of 20 μm or less; and
[8] A polarizing plate produced using the polarizing film of [6] or [7] above;
About.

According to the present invention, it is possible to reduce the occurrence of wrinkles at the time of stretching, and the PVA film capable of producing a thin polarizing film with high yield by reducing the stretching stress and reducing the breaking at the time of stretching, and the production thereof. A method and a method for producing a polarizing film using the method are provided. Moreover, according to this invention, even when manufacturing a thin polarizing plate, the polarizing film excellent in the polarization performance which is hard to produce a curvature, and the polarizing plate manufactured using it are provided.

It is the schematic at the time of measuring the degree of swelling (B) after extending | stretching a PVA film in 30 degreeC water at the draw ratio of 3 times.

The present invention is described in detail below.
The PVA film of the present invention needs to have a swelling degree (A) of 190 to 230%, and the swelling degree (A) is preferably 195% or more, and preferably 210% or less. 205% or less is more preferable. If the degree of swelling (A) is less than 190%, the stretching stress increases, and breakage occurs frequently during stretching. On the other hand, when the degree of swelling (A) exceeds 230%, wrinkles are generated at the time of stretching, and the process passability decreases.

The degree of swelling (A) is an index showing the water retention ability when the PVA film is immersed in water, and the mass after immersion of the PVA film in water at 30 ° C. for 30 minutes as it is (without stretching) It can obtain | require as a percentage by dividing | segmenting by the mass after drying at 105 degreeC for 16 hours, and can measure specifically by the method mentioned later in an Example.

Further, the PVA film of the present invention needs to have a swelling degree (B) of 260% or more after being stretched at a stretching ratio of 3 in water at 30 ° C., preferably 265% or more, and 270%. More preferably. When the degree of swelling (B) is less than 260%, the stretching stress increases, and breakage tends to occur during stretching. If the degree of swelling (B) is too high, wrinkles are likely to occur during stretching and the process passability tends to decrease. Therefore, the degree of swelling (B) is preferably 320% or less, and 300% The following is more preferable.

The degree of swelling (B) is an index indicating the water retention capacity of the PVA film after stretching the PVA film in 30 ° C. water at a stretch ratio of 3 times, and stretching the PVA film in 30 ° C. water at 240% / min. It can be determined as a percentage by dividing the mass after stretching at a stretch ratio of 3 times by the mass after stretching and drying at 105 ° C. for 16 hours, specifically by the method described later in the examples. Can be measured. Although the present invention is not limited in any way, when the PVA film is stretched in water, the crystallites in the PVA film are dissolved at the initial stage of stretching to increase the degree of swelling. It is thought that the degree of swelling decreases due to crystallization. In the present invention, the PVA film is specified by specifying the degree of swelling (B) when stretched in water at a stretch ratio of 3 times.

Examples of the PVA constituting the PVA film of the present invention include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isolacetate. Examples thereof include those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters such as propenyl. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of ease of production of PVA, availability, cost, and the like.

The polyvinyl ester is preferably obtained using only one or two or more vinyl esters as monomers, and more preferably obtained using only one vinyl ester as a monomer. However, as long as it does not impair the effects of the present invention, it may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

Examples of the other monomer copolymerizable with the vinyl ester include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, (meth) acrylate n-propyl, (meth) acrylate i-propyl, (meth) acrylate n-butyl, (meth) acrylate i-butyl, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide, N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amides, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamide propyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; 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, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or acid anhydrides; itaconic acid or its salts, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids be able to. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

The proportion of structural units derived from the other monomers described above in the polyvinyl ester is preferably 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester, and is preferably 10 mol%. More preferably, it is more preferably 5 mol% or less.
In particular, when the other monomer described above is a monomer that may promote water solubility of the obtained PVA, such as (meth) acrylic acid or unsaturated sulfonic acid, the obtained PVA In order to prevent PVA from being dissolved when the film is used as a raw film for producing a polarizing film, the proportion of structural units derived from these monomers in the polyvinyl ester is the total amount of the polyvinyl ester. Based on the number of moles of the structural unit, it is preferably 5 mol% or less, and more preferably 3 mol% or less.

The above PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA.

The above PVA may have a part of its hydroxyl group cross-linked or not cross-linked. Moreover, said PVA may react with aldehyde compounds, such as acetaldehyde and a butyraldehyde, etc. to form an acetal structure, and the said PVA does not react with these compounds and does not form an acetal structure. May be.

The degree of polymerization of the PVA is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and in the range of 2,000 to 4,000. More preferably. When the degree of polymerization is less than 1,500, the durability of the polarizing film produced using the obtained PVA film tends to deteriorate. On the other hand, when the degree of polymerization exceeds 6,000, it tends to lead to an increase in production cost, poor process passability during film formation, and an increase in shrinkage stress of the resulting polarizing film. In addition, the polymerization degree of PVA as used in this specification means the average degree of polymerization measured according to description of JIS K6726-1994.

The saponification degree of the PVA is preferably 98.0 mol% or more, more preferably 98.5 mol% or more, and 99.0 mol% or more from the viewpoint of water resistance of the polarizing film. More preferably. When the degree of saponification is less than 98.0 mol%, the water resistance of the obtained polarizing film tends to deteriorate. In this specification, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of PVA. The proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description of JIS K6726-1994.

The PVA film of the present invention preferably contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the PVA film of the present invention One or more of these plasticizers can be included. Among these, glycerin is preferable in terms of the effect of improving stretchability.

The content of the plasticizer in the PVA film of the present invention is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 17 parts by mass with respect to 100 parts by mass of PVA contained therein. Preferably, it is in the range of 5 to 15 parts by mass. When the plasticizer is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the plasticizer is 20 parts by mass or less, it is possible to prevent the PVA film from becoming too flexible and handling properties from being lowered.

The PVA film of the present invention may further contain components such as an antioxidant, an antifreezing agent, a pH adjuster, a concealing agent, an anti-coloring agent, an oil agent, and a surfactant described later, if necessary.

The shape of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be produced continuously and smoothly, and it can also be used continuously in the case of producing a polarizing film using it. Therefore, it is preferable that the film is a long film. The length of the long film (length in the length direction) is not particularly limited, and can be set as appropriate according to the application, for example, within a range of 5 to 30,000 m.

The width of the PVA film of the present invention is not particularly limited, and can be appropriately set according to the use of the PVA film or the polarizing film produced therefrom, but in recent years, the screen size of liquid crystal televisions and liquid crystal monitors has increased. In view of this, it is suitable for these applications that the width of the PVA film is 3 m or more, more preferably 4 m or more. On the other hand, if the width of the PVA film is too large, it is difficult to uniformly perform uniaxial stretching itself when manufacturing a polarizing film with a device that has been put to practical use, and therefore the width of the PVA film should be 7 m or less. Is preferred.

The thickness of the PVA film of the present invention makes it possible to obtain a thin polarizing film, reduces the shrinkage stress of the polarizing film and further the polarizing plate using the polarizing film, and prevents the laminated thin glass from warping. In view of the above, it is necessary to be 40 μm or less, preferably 30 μm or less, more preferably 25 μm or less, further preferably 20 μm or less, and particularly preferably 15 μm or less. On the other hand, since a too thin PVA film tends to be difficult to manufacture and handle, the thickness is preferably 5 μm or more.

The present invention relates to a method for producing a PVA film having a degree of swelling (A) of 190 to 230% and a thickness of 40 μm or less, wherein the PVA film having a degree of swelling (A) of 250% or more is treated at a temperature of 55 to 100 ° C. The manufacturing method which has the process of carrying out the wet heat treatment for 200 second or more on the conditions of humidity 80% RH or more is included. According to the said manufacturing method, the above-mentioned PVA film of this invention which has swelling degree (B) in a specific range can be manufactured efficiently.

The degree of swelling (A) of the PVA film subjected to the wet heat treatment is 250% or more. By using a PVA film having such a degree of swelling (A), the effect of wet heat treatment is sufficiently exhibited. From the viewpoint of enhancing the effect of the wet heat treatment, the degree of swelling (A) of the PVA film subjected to the wet heat treatment is preferably 400 to 900%, and more preferably 450 to 800%.

The moisture content of the PVA film subjected to wet heat treatment (water content immediately before wet heat treatment) is not particularly limited, but is preferably 40% by mass or less from the viewpoint of increasing the efficiency of wet heat treatment, and 20% by mass. The content is more preferably 10% by mass or less, and more preferably 2% by mass or more.

There is no restriction | limiting in particular in the film-forming method of the PVA film provided to wet heat processing, By making a PVA film which has the desired thickness by a conventionally well-known method, the PVA film which has the above-mentioned swelling degree (A) is easy. Can get to. Specifically, for example, a film-forming stock solution in which PVA is dissolved in a liquid medium or a film-forming stock solution in which PVA and a liquid medium are included and PVA is melted can be used for film formation.

Examples of the liquid medium used for preparing the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Trimethylolpropane, ethylenediamine, diethylenetriamine and the like can be mentioned, and one or more of these can be used. Among them, water is preferably used from the viewpoint of environmental load and recoverability.

The volatile fraction of the raw film forming solution (content ratio of volatile components such as liquid medium removed by volatilization or evaporation during film formation) varies depending on the film forming method, film forming conditions, etc. It is preferably 95% by mass, more preferably 55 to 90% by mass, and particularly preferably 60 to 85% by mass. If the volatile fraction of the film-forming stock solution is too low, the viscosity of the film-forming stock solution becomes too high, making filtration and defoaming difficult when preparing the film-forming stock solution, making it difficult to produce a PVA film with few foreign matters and defects. Tend. On the other hand, when the volatile fraction of the film-forming stock solution is too high, the concentration of the film-forming stock solution becomes too low, and industrial PVA film tends to be difficult to form.

Further, it is preferable that the film forming stock solution contains a surfactant. By containing the surfactant, the occurrence of uneven thickness of the PVA film is suppressed, and the PVA film can be easily peeled from the roll or belt used for film formation. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film contains a surfactant. Although the kind of said surfactant is not specifically limited, Anionic surfactant or nonionic surfactant is preferable from a peelable viewpoint from a roll, a belt, etc.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfuric acid ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy An allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.

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

When the film-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of PVA, and 0.02 to 0.3 parts by mass Is more preferably in the range of 0.05 to 0.1 parts by mass. When the content of the surfactant is less than 0.01 parts by mass with respect to 100 parts by mass of PVA, the effect of improving the film forming property and the releasability due to the addition of the surfactant becomes difficult to appear, whereas on the other hand, 100 parts by mass of PVA On the other hand, when the amount exceeds 0.5 parts by mass, the surfactant may bleed out on the surface of the PVA film, causing blocking, and handling properties may be reduced.

Examples of the film forming method for forming a PVA film to be subjected to wet heat treatment using the above-described film forming stock solution include a wet film forming method, a gel film forming method, a casting film forming method, and an extrusion film forming method. Etc. can be adopted. A method based on a combination of these can also be employed. Among the above film forming methods, the casting film forming method or the extrusion film forming method is preferably employed because a PVA film having a uniform thickness and width and good physical properties can be obtained.

As a specific film forming method, a T-type slit die, hopper plate, I-die, lip coater die, etc. are used to uniformly discharge the film forming stock solution onto the peripheral surface of a heated roll (or belt) that rotates. Then, volatile components are evaporated from one surface of the film discharged onto the roll (or belt) and dried to form a PVA film, or one or more after being dried in this way And a method of forming a PVA film by further drying on the peripheral surface of a heated heated roll or by passing it through a hot air drying apparatus. The PVA film after film formation may be subjected to wet heat treatment to be described later by winding it as necessary after being wound up once by a winding device. However, the PVA film continuously formed as described above may be used. The film may be wound after the wet heat treatment described later is continuously applied.

The surface temperature of the roll used for film formation can be set to 50 to 100 ° C., for example. Further, the drying temperature when the film-forming stock solution is discharged onto the belt can be set to 50 to 100 ° C., for example.

The temperature in the wet heat treatment is in the range of 55 to 100 ° C. If the temperature of the wet heat treatment is less than 55 ° C., the effect of the wet heat treatment is not sufficiently exhibited, and it becomes difficult to obtain a PVA film having the degree of swelling (A) described above, or a heat treatment described later is further applied to the above. Even if the PVA film having the degree of swelling (A) is used, the degree of swelling (B) is less than 260%, the stretching stress is increased, and breakage is likely to occur during stretching. On the other hand, when the temperature of the wet heat treatment exceeds 100 ° C., the degree of swelling (B) of the obtained PVA film becomes less than 260%, the stretching stress increases, and breakage tends to occur during stretching. Since the PVA film of the present invention can be produced more efficiently, the wet heat treatment temperature is preferably in the range of 58 to 90 ° C, more preferably in the range of 60 to 80 ° C.

The relative humidity in the wet heat treatment is 80% RH or more. When the relative humidity of the wet heat treatment is less than 80% RH, it becomes difficult to obtain a PVA film having the degree of swelling (A) described above, or a PVA having the degree of swelling (A) described above after further heat treatment described below. Even if it is made into a film, the degree of swelling (B) becomes less than 260%, the stretching stress increases, and breakage tends to occur during stretching. The relative humidity of the wet heat treatment is preferably 85% RH or more from the viewpoint of enhancing the effect of the wet heat treatment.

The wet heat treatment time is 200 seconds or more. If the wet heat treatment time is less than 200 seconds, the effect of the wet heat treatment cannot be obtained sufficiently. From the viewpoint of enhancing the effect of the wet heat treatment, the wet heat treatment time is preferably 4 minutes or longer, and more preferably 5 minutes or longer. It should be noted that the wet heat treatment time is preferably 60 minutes or less because the effect reaches its peak even if the wet heat treatment is performed for an excessively long time, while the productivity tends to decrease.

In the method for producing a PVA film of the present invention, a PVA film having a swelling degree (A) of 190 to 230% by the wet heat treatment described above may be used, but the swelling degree (A) of the PVA film after the wet heat treatment is 230%. In the case of exceeding PVA, a PVA film having a degree of swelling (A) of 190 to 230% may be finally obtained by further heat treatment after the wet heat treatment. If such heat treatment is performed after the wet heat treatment, a PVA film having a swelling degree (B) in the above range can be produced in a shorter wet heat treatment time, which is preferable from the viewpoint of productivity.

From the viewpoint of enhancing the effect of the heat treatment, the heat treatment is preferably performed for 10 seconds or more under the condition of a temperature of 90 to 130 ° C. When the temperature of the heat treatment is 90 ° C. or higher, the degree of swelling (A) can be more efficiently made 190 to 230%. On the other hand, it can suppress that the swelling degree (B) of a PVA film falls because the temperature of heat processing is 130 degrees C or less. Since the PVA film of the present invention can be produced more efficiently, the temperature of the heat treatment is more preferably 100 to 125 ° C, and further preferably 110 to 120 ° C.

Also, the heat treatment effect can be enhanced by the heat treatment time being 10 seconds or longer. From the viewpoint of the effect of heat treatment, the heat treatment time is more preferably 30 seconds or more. On the other hand, regarding the upper limit of the heat treatment time, a time until the degree of swelling (A) of the PVA film becomes 190 to 230% can be adopted, but it is 15 minutes or less from the viewpoint of preventing the PVA film from yellowing. It is preferable.

The relative humidity in the heat treatment is not particularly limited, and any relative humidity can be adopted when the heat treatment is performed at a temperature exceeding 100 ° C., and the relative humidity is 80% RH when the heat treatment is performed at a temperature of 100 ° C. or less. Less than.

Although the present invention is not limited in any way, it is considered that the PVA film of the present invention is obtained by generating microcrystals in the PVA film by wet heat treatment in the method for producing the PVA film of the present invention. Even a PVA film in which such microcrystals are formed only by wet heat treatment, or a PVA film in which microcrystal nuclei are first formed by wet heat treatment and then microcrystals are formed by subsequent heat treatment. However, it is considered that the PVA film of the present invention which is not conventionally obtained can be efficiently obtained by the above-mentioned method because the microstructure is different from that of the PVA film crystallized without being subjected to the wet heat treatment.

Although there is no restriction | limiting in particular in the use of the PVA film of this invention, According to the PVA film of this invention, while being able to reduce the generation | occurrence | production of the wrinkle at the time of extending | stretching, it can reduce the fracture | rupture at the time of extending | stretching low. Since it can do, it is preferable to use as a raw film for polarizing film manufacture.

The method for producing a polarizing film using the PVA film of the present invention as a raw film is not particularly limited, and any conventionally employed method may be employed. Examples of such a method include a method of dyeing and uniaxially stretching the PVA film of the present invention, and specifically, swelling, dyeing, uniaxial stretching, and as required for the PVA film of the present invention. Furthermore, a method of performing fixing treatment, drying, heat treatment, etc. can be mentioned. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments can be performed simultaneously. Also, one or more of each process can be performed twice or more.

Swelling can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably in the range of 20 to 40 ° C., more preferably in the range of 22 to 38 ° C., and preferably in the range of 25 to 35 ° C. Further preferred. The time for immersion in water is preferably in the range of 0.1 to 5 minutes, for example, and more preferably in the range of 0.5 to 3 minutes. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

The dyeing is preferably performed using iodine, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally performed by immersing a PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath, and such a dyeing method is also preferably used in the present invention. . The iodine concentration in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the potassium iodide concentration is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C., particularly 25 to 40 ° C.

Uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet drawing method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. Moreover, in the case of the dry-type extending | stretching method, it can carry out in air using the PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, It is particularly preferably within the range of ˜4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass.
The stretching temperature in the uniaxial stretching is preferably in the range of 30 to 90 ° C, more preferably in the range of 40 to 80 ° C, and particularly preferably in the range of 50 to 70 ° C.
In addition, the draw ratio in uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more, and particularly preferably 6 times or more from the viewpoint of the polarizing performance of the polarizing film to be obtained. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

In the production of the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dye (iodine etc.) to the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the fixing treatment bath is generally about 2 to 15% by mass, particularly about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C., particularly 25 to 40 ° C.

Drying is preferably performed at 30 to 150 ° C, particularly 50 to 130 ° C. When the moisture content of the polarizing film becomes 10% or less due to drying, tension is applied to the polarizing film and heat treatment is performed at about 80 to 120 ° C. for about 1 to 5 minutes. A film can be obtained.

The polarizing film obtained as described above is usually used as a polarizing plate by attaching a protective film on both sides or one side. Examples of the protective film include those that are optically transparent and have mechanical strength. Specifically, for example, cellulose triacetate (TAC) film, cellulose acetate / butyrate (CAB) film, acrylic film, polyester-based film Film or the like is used. Examples of the adhesive for bonding include PVA adhesives and urethane adhesives, among which PVA adhesives are suitable.

The polarizing plate obtained as described above can be used as an LCD component after being coated with an acrylic adhesive or the like and bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

The polarizing film of the present invention has a dichroic ratio of 55 or more, and the orientation direction contracts after 1 hour at a temperature of 80 ° C. and a relative humidity of 5% with the orientation direction fixed. The stress is 73 N / mm ² or less. When the dichroic ratio is 55 or more, the polarizing film can be used for applications requiring high polarization performance. The dichroic ratio is preferably 60 or more. For example, the upper limit of the dichroic ratio is 80. The dichroic ratio is determined by using the single transmittance (Ts) (%) and the degree of polarization (P) (%) of the polarizing film, and the dichroic ratio = log (Ts / 100−Ts / 100 × P / 100) / Log (Ts / 100 + Ts / 100 × P / 100).

In addition, the polarizing film of the present invention has a shrinkage stress in the orientation direction when 1 hour has passed under conditions of a temperature of 80 ° C. and a relative humidity of 5% with the orientation direction (stretching direction at the time of producing the polarizing film) fixed. 73 N / mm ² or less. When the shrinkage stress is 73 N / mm ² or less, the polarizing film is less likely to warp. From warp aspect of the polarizing film, the shrinkage stress is preferably at 70N / mm ² or less, more preferably 68N / mm ² or less, and more preferably 67N / mm ² or less. Although there is no restriction | limiting in particular in the minimum of the said shrinkage stress, For example, the said shrinkage stress may be 20 N / mm < ² > or more, Furthermore, 50 N / mm < ² > or more.

As will be described later in the examples, the shrinkage stress was measured by taking a rectangular sample of 12 cm parallel to the alignment direction of the polarizing film and 1.5 cm in a direction orthogonal to the alignment direction, The autograph was fixed so that the orientation direction was fixed, and the shrinkage stress in the orientation direction was measured after 1 hour under the conditions of a temperature of 80 ° C. and a relative humidity of 5%, and this was measured as the cross-sectional area of the film (unit: mm ² ).

There is no restriction | limiting in particular in the thickness of the polarizing film of this invention, For example, although it can be set to 30 micrometers or less, Furthermore, it is 25 micrometers or less, The shrinkage stress of the polarizing film and the polarizing plate using the same is reduced, and it is thin laminated | stacked From the standpoint of preventing warping of the glass, the thickness is preferably 20 μm or less, and more preferably 15 μm or less. On the other hand, since a too thin polarizing film tends to be difficult to manufacture and handle, the thickness is preferably 3 μm or more.

The method for producing the polarizing film of the present invention is not particularly limited, and the polarizing film can be produced by dyeing and uniaxially stretching using a PVA film as a raw film, but the swelling degree (A) is 190 to 230%. A PVA film having a thickness of 40 μm or less and having a swelling degree (B) of 260% or more after being stretched at a stretching ratio of 3 times in water at 30 ° C. is used as the raw film. According to the manufacturing method of the polarizing film which has the process of dye | staining and uniaxially stretching a film, the polarizing film of this invention can be manufactured efficiently and it is preferable. As description regarding the polarizing film of this invention, since the above-mentioned content can be employ | adopted as it is, such as description in the case of manufacturing a polarizing film using the PVA film of this invention as an original fabric film, it overlaps here. Omitted.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. In addition, each measuring method employ | adopted in the following example, a comparative example, and a reference example is shown below.

Measurement of swelling degree (A) of PVA film A rectangular sample of 10 cm in the width direction and 20 cm in the length direction was cut out from the PVA film to be measured, and this sample was further striped with a width of 2 to 3 mm and a length of 20 cm. Cut into a shape. Thereafter, all these strip-like samples were immersed in 1,000 g of distilled water at 30 ° C. as they were. After stripping for 30 minutes, the strip-shaped sample is taken out and centrifuged using a centrifuge (KOKUSAN XEM-KL-5886) at 3,000 rpm for 5 minutes. ) Was measured. Subsequently, after drying the strip-shaped sample for 16 hours with a dryer at 105 ° C., the mass “M” (total of all the strip-shaped samples) is measured, and the swelling degree (A) is calculated by the following formula (i). Calculated. In addition, the same measurement was performed 3 times and the average value was employ | adopted.
Swelling degree (A) (%) = 100 × N / M (i)

Measurement of the degree of swelling (B) after stretching the PVA film in water at 30 ° C. at a stretch ratio of 3 times. A rectangular sample of 5 cm in the width direction and 15 cm in the length direction was cut out from the PVA film. 2 In the center of the length direction, use the oil-based pen to place a reference line (thickness of about 0.5 mm) in the width direction of the sample so that the distance between the reference lines (between the center of the reference line thickness direction) is 5 cm The book was drawn (see (a) of FIG. 1). This was set in a drawing jig so that each marked line was positioned at the end of the drawing jig (distance between chucks was 5 cm), and immediately immersed in distilled water at 30 ° C. to 0.12 m / min (240% / min) Uniaxially stretching so that the actual draw ratio is 3.0 times. The actual stretch ratio here is the distance between the center of the marked line after stretching (the center in the thickness direction of the marked line at the position where the length of the marked line is equally divided) (A in FIG. 1B). Is divided by the distance (5 cm) between the marked lines before stretching. After stretching, within 1 minute in an environment of temperature 20 ° C. and relative humidity 65% RH, wipe the moisture on the sample surface after stretching using filter paper, and follow the marked line at the center of the marked line in the thickness direction. The film between the marked lines was cut out by cutting the sample (see (c) of FIG. 1), and the mass “L” of the film between the marked lines was measured. Subsequently, the film was dried with a dryer at 105 ° C. for 16 hours, then the mass “K” was measured, and the degree of swelling (B) after stretching at a stretching ratio of 3 times in water at 30 ° C. according to the following formula (ii). ) Was calculated. In addition, the same measurement was performed 5 times and the average value was employ | adopted.
Swelling degree (B) (%) = 100 × L / K (ii)

Measurement of the stretching stress of the PVA film A sample of 3 cm in the width direction and 10 cm in the length direction is cut out from the PVA film to be measured and stretched so that the distance between the chucks is 1.5 cm in order to stretch uniaxially in the length direction. The sample was sandwiched between tools and immersed in distilled water at 30 ° C. for 60 seconds. Then, the stress with respect to the draw ratio was continuously measured while uniaxially stretching in the length direction at a stretching speed of 36 mm / min (240% / min). The stress when the draw ratio was 3.0 times was taken as the draw stress. The stress is measured by using an autograph (AG-I) manufactured by Shimadzu Corporation and dividing the measured force by the cross-sectional area before stretching (sample thickness × sample width (3 cm)). Stress was used. The same measurement was performed 5 times and the average value was adopted.

Measurement of Dichroic Ratio of Polarizing Film Two square samples of 4 cm × 4 cm were taken in parallel with the orientation direction of the polarizing film from the central part in the width direction of the polarizing film obtained in the following examples or comparative examples. .
The light transmittance of these samples was measured using a spectrophotometer “V-7100” manufactured by JASCO Corporation. At the time of measurement, in accordance with JIS Z 8722 (object color measurement method), the visibility correction of the visible light region of the 2-degree visual field was performed using a C light source. For one sample, the light transmittance when tilted by +45 degrees with respect to the orientation direction and the light transmittance when tilted by −45 degrees with respect to the orientation direction were measured, and an average value thereof ( Ts1) (%) was determined. Similarly, for the other sample, the light transmittance when tilted by +45 degrees and the light transmittance when tilted by −45 degrees are measured, and the average value (Ts2) (%) is calculated. Asked. And the calculated | required Ts1 and Ts2 were averaged, and it was set as the single-piece | unit transmittance | permeability (Ts) (%) of the polarizing film.
Next, the above two samples were stacked so that the light transmittance (T∥) (%) when the alignment directions were overlapped so that the alignment directions were parallel, and the alignment directions were orthogonal to each other. In this case, the light transmittance (T⊥) (%) was measured. The transmittances (T∥) and (T⊥) are the same as the measurement of the single transmittance (Ts) described above, the light transmittance when tilted +45 degrees with respect to the orientation direction of one sample, and −45. It was obtained as an average value with the light transmittance when tilted. From the transmittances (T∥) and (T⊥), the polarization degree (P) (%) of the polarizing film was determined based on the following formula (iii).
Polarization degree (P) (%) = {(T∥−T⊥) / (T∥ + T⊥)} ^1/2 × 100 (iii)
And from the obtained single transmittance (Ts) (%) and polarization degree (P) (%), the dichroic ratio of the polarizing film was calculated | required based on following formula (iv).
Dichroic ratio = log (Ts / 100−Ts / 100 × P / 100) / log (Ts / 100 + Ts / 100 × P / 100) (iv)

Measurement of Shrinkage Stress of Polarizing Film From the central part in the width direction of the polarizing film obtained in the following examples or comparative examples, a rectangle of 12 cm parallel to the orientation direction of the polarizing film and 1.5 cm in the direction perpendicular to the orientation direction Samples were taken. Next, this sample was fixed to an autograph “AG-X” manufactured by Shimadzu Corporation so that the orientation direction was fixed at a distance of 5 cm between chucks, and one hour had passed under conditions of a temperature of 80 ° C. and a relative humidity of 5%. The shrinkage stress in the orientation direction was measured, and this was divided by the cross-sectional area (unit: mm ² ) of the film to obtain the shrinkage stress of the polarizing film.

[Example 1]
100 parts by mass of PVA (saponified product of vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.95 mol%), 6 parts by mass of glycerin as a plasticizer, sodium polyoxyethylene lauryl ether sulfate as a surfactant 0 A PVA having a thickness of 30 μm is cast by casting a film-forming stock solution consisting of 1 part by mass and water and having a volatile content of 66% by mass onto a metal drum at 60 ° C. and drying until the volatile content (water content) becomes 5% by mass. A film (PVA film before treatment) was used. The degree of swelling (A) of this PVA film was 480%.

This PVA film was wet-heat treated for 50 minutes under the conditions of a temperature of 60 ° C. and a relative humidity of 90% RH. The obtained PVA film (treated PVA film) had a degree of swelling (A) of 200%, a thickness of 30 μm, a degree of swelling (B) of 272%, and a stretching stress of 6.8 MPa. In addition, generation | occurrence | production of wrinkles (generation | occurrence | production of the wrinkles at the time of extending | stretching) was not seen at the time of the measurement of extending | stretching stress.

While the above PVA film (processed PVA film) is immersed in water at a temperature of 30 ° C., it is stretched in the length direction (MD) to 1.1 times the original length at a stretching rate of 240% / min. After uniaxial stretching (first-stage stretching), while being immersed in an iodine / potassium iodide aqueous solution at a temperature of 30 ° C. containing 0.04% by mass of iodine and 4% by mass of potassium iodide, 240 The film is uniaxially stretched in the length direction (MD) up to 2.4 times the original length (stretching at the second stage) at a stretching speed of% / min, and then boric acid is 3% by mass and potassium iodide is 3% by mass. Uniaxial stretching in the length direction (MD) up to 2.7 times the original length at a stretching rate of 240% / min while immersed in an aqueous solution of boric acid / potassium iodide at a temperature of 30 ° C. (3rd stage stretching) and further boric acid 4 mass% and potassium iodide 6 mass% Uniaxial stretching in the length direction (MD) up to 6.4 times the original length at a stretching rate of 240% / min while immersed in an aqueous solution of boric acid / potassium iodide at a temperature of 56 ° C. Then, the film was washed by dipping for 5 seconds in an aqueous solution of potassium iodide containing 3% by weight of potassium iodide at a temperature of 30 ° C., followed by a dryer at 60 ° C. Was dried for 90 seconds to produce a polarizing film having a thickness of 12 μm.
When the dichroic ratio and shrinkage stress of the obtained polarizing film were measured by the method described above, the dichroic ratio was 63 and the shrinkage stress was 66.6 N / mm ² .

[Examples 2 to 5, Comparative Examples 1 to 4 and Reference Example 1]
Each PVA film (treated PVA film) was obtained in the same manner as in Example 1 except that the configuration of the PVA film before treatment, the wet heat treatment conditions and the heat treatment conditions were changed as shown in Table 1. In Example 3 where both wet heat treatment and heat treatment were performed, the heat treatment was performed after the wet heat treatment. In the heat treatment, conditions with a relative humidity of less than 30% RH were adopted.
Table 1 shows the degree of swelling (A), thickness, degree of swelling (B), stretching stress, and the presence or absence of wrinkles during stretching of each of the obtained PVA films.

Using the PVA film of Example 3 and Comparative Example 1 (PVA film after treatment), a polarizing film having a thickness of 12 μm was produced in the same manner as in Example 1. However, in order to optimize stretchability, the temperature of the boric acid / potassium iodide aqueous solution used in the fourth stage stretching was 57 ° C. in Example 3 and 58 ° C. in Comparative Example 1. In Comparative Example 1, the stretching speed during the fourth stage stretching was 120% / min in order to suppress breakage during stretching.
Table 1 shows the dichroic ratio and shrinkage stress of the obtained polarizing film.

[Comparative Example 5]
100 parts by mass of PVA (saponified product of vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.95 mol%), 6 parts by mass of glycerin as a plasticizer, sodium polyoxyethylene lauryl ether sulfate as a surfactant 0 A PVA having a thickness of 30 μm is cast by casting a film-forming stock solution consisting of 1 part by mass and water and having a volatile content of 66% by mass onto a metal drum at 60 ° C. and drying until the volatile content (water content) becomes 5% by mass. A film (PVA film before treatment) was used. The degree of swelling (A) of this PVA film was 480%.

The PVA film was heat-treated for 3 minutes under conditions of a temperature of 140 ° C. and a relative humidity of less than 30% RH. The swelling degree (A) of the obtained PVA film was 198%. Thereafter, the heat treatment was performed for 10 minutes under the conditions of a temperature of 60 ° C. and a relative humidity of 90% RH. The obtained PVA film (treated PVA film) had a degree of swelling (A) of 181% and a thickness of 30 μm.

1. Rectangular sample 2. 2. Mark in the width direction of the sample The center of the marked line after stretching (the center in the thickness direction of the marked line at the position where the length of the marked line is equally divided)
4). Film between marked lines

Claims

Polyvinyl alcohol film having a swelling degree (A) of 190 to 230% and a thickness of 40 μm or less, and having a swelling degree (B) of 260% or more after being stretched in water at 30 ° C. at a stretch ratio of 3 times Alcohol film.
The polyvinyl alcohol film according to claim 1, which is a raw film for producing a polarizing film.
A method for producing a polyvinyl alcohol film having a swelling degree (A) of 190 to 230% and a thickness of 40 μm or less, wherein a polyvinyl alcohol film having a swelling degree (A) of 250% or more is treated at a temperature of 55 to 100 ° C. and a relative humidity of 80 A manufacturing method comprising a step of performing a wet heat treatment for 200 seconds or more under a condition of% RH or more.
The production method according to claim 3, further comprising a step of heat-treating at a temperature of 90 to 130 ° C for 10 seconds or longer after the wet-heat treatment step.
A method for producing a polarizing film, comprising a step of dyeing and uniaxially stretching the polyvinyl alcohol film according to claim 2.
It is a polarizing film having a dichroic ratio of 55 or more, and the shrinkage stress in the orientation direction is 73 N / mm 2 when 1 hour has passed under conditions of a temperature of 80 ° C. and a relative humidity of 5% with the orientation direction fixed. The polarizing film which is the following.
The polarizing film according to claim 6, wherein the thickness is 20 μm or less.
A polarizing plate produced using the polarizing film according to claim 6 or 7.