WO2023182267A1

WO2023182267A1 - Poly(vinyl alcohol) film and production method therefor

Info

Publication number: WO2023182267A1
Application number: PCT/JP2023/010856
Authority: WO
Inventors: 真奈石原; 洋平鷹取; 慎二中井
Original assignee: 株式会社クラレ
Priority date: 2022-03-22
Filing date: 2023-03-20
Publication date: 2023-09-28
Also published as: TW202400695A

Abstract

A poly(vinyl alcohol) film having a degree of swelling (A) of 195-205 mass% and having a value of (B)/(A) of 1.27-1.40, where (B) is the degree of swelling of the film which has been stretched to 2.5 times in 30°C water under the conditions of a stretching rate of 240 %/min. When immersed in 30°C water for 30 seconds, the poly(vinyl alcohol) film has an average water absorption rate of 1.35 mass%/sec or greater. By using such poly(vinyl alcohol) film in polarizing-film production, polarizing films having excellent optical performance can be obtained while diminishing breakages even under high-speed stretching conditions.

Description

Polyvinyl alcohol film and its manufacturing method

The present invention relates to a polyvinyl alcohol film and a method for producing the same.

A polarizing plate, which has the function of transmitting and blocking light, is a basic component of a liquid crystal display (LCD), along with a liquid crystal that changes the polarization state of light. LCDs are now used in a wide range of applications, including small devices such as calculators and watches, notebook computers, LCD monitors, LCD color projectors, LCD televisions, in-vehicle navigation systems, mobile phones, and measuring instruments used indoors and outdoors. .

A polarizing plate is generally made by dyeing a polyvinyl alcohol film (hereinafter "polyvinyl alcohol" may be abbreviated as "PVA"), uniaxially stretching it, and if necessary further fixing it with a boron compound or the like. After manufacturing, a protective film such as triacetate cellulose (TAC) film is attached to the surface of the polarizing film. Since the optical performance such as the contrast ratio of an LCD greatly depends on the polarization performance such as the degree of polarization of a polarizing film, a PVA film having high stretchability has been proposed to improve the polarization performance.

For example, Patent Document 1 describes a PVA film that can reduce the occurrence of wrinkles during stretching, has low stretching stress, reduces breakage during stretching, and can produce a thin polarizing film with good yield. , a PVA film having a thickness of 40 μm or less and a swelling degree of 190 to 230%, and a PVA film having a swelling degree of 260% or more after being stretched at a stretching ratio of 3 times in water at 30° C. .

International Publication No. 2014/050697

In recent years, with the increase in demand for LCDs, there has been a demand for efficient production of polarizing film, which is one of the components. In order to increase the manufacturing efficiency of polarizing films, it is possible to manufacture polarizing films using wide PVA films, or to employ high-speed stretching conditions when manufacturing polarizing films. However, the former method requires a huge investment in equipment such as new construction or modification of manufacturing equipment for PVA films and polarizing films, which is not economically preferable. On the other hand, in the latter method, even if the stretching ratio is the same as in the conventional method, the PVA film frequently breaks during stretching, which tends to cause a problem of lowering the manufacturing efficiency of the polarizing film. This is presumed to be because the PVA film cannot follow the rapid increase in strain rate that accompanies the increase in the stretching conditions when producing a polarizing film. As a countermeasure, it is possible to reduce the breakage of the PVA film even under high-speed stretching conditions by lowering the softening point temperature of the PVA film or increasing the stretching temperature during the production of the polarizing film. However, these methods tend to cause abnormalities such as wrinkles during stretching of the PVA film and folding of the edges of the polarizing film, and also tend to cause the problem of deterioration of the optical performance of the manufactured polarizing film.

The present inventors investigated and found that even with the PVA film described in Patent Document 1, if high-speed stretching conditions are used during the production of a polarizing film, the breakage of the PVA film during stretching can be sufficiently reduced. There were times when it was difficult to do so. In addition, it has sometimes been difficult to sufficiently reduce wrinkles and folding of the edges during stretching of the PVA film and deterioration in the optical performance of the polarizing film.

The present invention was made to solve the above problems, and it is possible to obtain a polarizing film with excellent optical performance while reducing breakage even under high-speed stretching conditions during the production of the polarizing film. An object of the present invention is to provide a PVA film and a method for manufacturing the same.

As a result of extensive studies, the present inventors have found that the above problems can be solved by using a PVA film whose swelling ratio and average water absorption rate measured under predetermined conditions are within a specific range. Based on these findings, the present invention was completed after further studies.

That is, the present invention
[1] The degree of swelling (A) is 195 to 205% by mass, and the degree of swelling (B) after stretching 2.5 times in water at 30°C at a stretching rate of 240%/min is the degree of swelling ( A PVA film whose value divided by A) is 1.27 to 1.40, and whose average water absorption rate when immersed in water at 30°C for 30 seconds is 1.35% by mass/second or more. ;
[2] The PVA film according to [1], which has a dimensional change rate in the width direction of 14.6 to 16.2% when immersed in water at 30°C for 30 seconds;
[3] The PVA film according to [1] or [2], wherein the film has a thickness of 45 to 80 μm;
[4] The PVA film according to any one of [1] to [3], which is an optical film;
[5] A method for producing a PVA film in which a film-forming stock solution containing PVA is cast on a roll or belt heated to 50 to 99°C and dried, wherein the content of the plasticizing component is 20 to 99°C. The PVA film according to any one of [1] to [3], wherein the PVA film is dried to a concentration of 23% by mass, and then heat-treated on a roll or belt heated to 100 to 120°C. Production method;
[6] The method for producing a PVA film according to [5], wherein the heat treatment is performed on a roll heated to 100 to 120°C;
[7] The PVA film according to [5] or [6], wherein the plasticizing component consists of water and a plasticizer, and the plasticizer is at least one selected from the group consisting of glycerin, diglycerin, and propylene glycol. manufacturing method;
Regarding.

According to the present invention, there is provided a PVA film and a method for producing the same, which can reduce breakage even under high-speed stretching conditions during the production of a polarizing film and obtain a polarizing film with excellent optical performance.

<PVA film>
The PVA film of the present invention has a swelling degree (A) of 195 to 205% by mass, and a swelling degree (B) after stretching 2.5 times in water at 30°C at a stretching rate of 240%/min. The value divided by the swelling degree (A) (hereinafter sometimes abbreviated as swelling degree ratio (B/A)) is 1.27 to 1.40, and when immersed in water at 30 ° C. for 30 seconds The average water absorption rate is 1.35% by mass/second or more.

In the PVA film of the present invention, the degree of swelling (A) is 195 to 205% by mass. Swelling degree (A) is an index indicating the water retention capacity when a PVA film is immersed in water at 30°C, and is the mass after immersing the PVA film as it is (without stretching) in water at 30°C for 30 minutes. can be determined as a percentage by dividing by the mass after drying at 105° C. for 16 hours after immersion. Specifically, it can be measured by the method described in the Examples below.

If the degree of swelling (A) is less than 195% by mass, when the polarizing film is produced under high-speed stretching conditions, the stress applied to the PVA film during stretching becomes high, making it easy for the PVA film to break. On the other hand, if the degree of swelling (A) exceeds 205% by mass, wrinkles will occur in the PVA film during stretching when the polarizing film is manufactured under high-speed stretching conditions, resulting in a tendency for the optical performance of the resulting polarizing film to deteriorate. There is. The degree of swelling (A) is preferably 198% by mass or more, more preferably 199% by mass or more, and preferably 203% by mass or less, more preferably 201% by mass or less.

In the PVA film of the present invention, the value obtained by dividing the swelling degree (B) after stretching in water at 30 ° C. at a stretching rate of 2.5 times at a stretching rate of 240% / min by the swelling degree (A), That is, the swelling ratio (B/A) is 1.27 to 1.40. Here, the degree of swelling (B) is an index indicating the water retention capacity of the PVA film after stretching the PVA film in water at 30°C at a stretching ratio of 2.5 times, and It can be determined as a percentage by dividing the mass of the film after stretching at a stretching rate of /min to a stretching ratio of 2.5 times by the mass of the film after stretching and drying at 105° C. for 16 hours. Specifically, it can be measured by the method described in the Examples below. In addition, the stretching ratio (2.5 times) when measuring the degree of swelling (B) corresponds to the stretching ratio at the initial stage of stretching when producing a polarizing film. Therefore, if the swelling degree (B) measured under these conditions is relatively larger than the swelling degree (A), that is, the swelling degree ratio (B/A) is 1.27 to 1.40, the polarizing film It is thought that during the production of the PVA film, the PVA film easily absorbs water and stretches from the initial stage of stretching, and the breakage of the PVA film is reduced even under high-speed stretching conditions.

If the swelling ratio (B/A) is less than 1.27, the stress applied to the PVA film during stretching becomes high when the polarizing film is manufactured under high-speed stretching conditions, and the PVA film may break. It becomes easier. On the other hand, if the swelling ratio (B/A) exceeds 1.40, wrinkles will easily occur in the PVA film during stretching when the polarizing film is manufactured under high-speed stretching conditions. Optical performance tends to deteriorate. The swelling ratio (B/A) is preferably 1.29 or more, more preferably 1.30 or more, and preferably 1.35 or less, more preferably 1.33 or less.

In the PVA film of the present invention, the average water absorption rate when immersed in water at 30°C for 30 seconds is 1.35% by mass/second or more. The average water absorption rate is an index of the water absorption rate at the initial stage of immersion in water, and can be determined by subtracting the moisture content before immersion from the moisture content after immersing the PVA film in 30°C water for 30 seconds, and dividing by the immersion time. I can do it. Specifically, it can be measured by the method described in the Examples below.

Since the PVA film of the present invention has a sufficiently high average water absorption rate of 1.35% by mass/second or more, when it is stretched in various water baths in the manufacturing process of polarizing film, some of the lamellar crystals of PVA in the PVA film unravel. Easy to unravel and become amorphous. As a result, the degree of swelling of the PVA film increases more easily than before stretching, so it is thought that the breakage of the PVA film is reduced even under high-speed stretching conditions during the production of a polarizing film. Further, since the PVA film of the present invention has a sufficiently high average water absorption rate of 1.35% by mass/second or more, it easily absorbs boric acid contained in a stretching bath or the like in the manufacturing process of a polarizing film. As a result, a scaffold of an iodine complex exhibiting polarizing performance is likely to be formed, so it is thought that the optical performance of the resulting polarizing film is maintained. The average water absorption rate is preferably 1.36 mass%/second or more, more preferably 1.38 mass%/second or more, and preferably 1.44 mass%/second or less, and 1.42 mass%/second or less. More preferred. By having an average water absorption rate below the above upper limit, it is possible to further reduce wrinkles in the PVA film during stretching even under high-speed stretching conditions during the production of the polarizing film, and the optical properties of the polarizing film obtained can be further reduced. This makes it easier to prevent performance from deteriorating.

When the PVA film of the present invention is immersed in water at 30°C for 30 seconds, the dimensional change rate in the width direction (direction perpendicular to the machine flow direction; hereinafter sometimes abbreviated as TD) is 14.6 to 16.2. It is preferably within the range of %. This underwater dimensional change rate is calculated from the gauge line distance B in the width direction of the PVA film after immersing the PVA film in water at 30°C for 30 seconds to the gauge line distance A in the width direction of the film before dipping. It can be determined by calculating the ratio [100×(B−A)/A] of the value obtained by subtracting the distance A between the gauge lines in the width direction of the film. Specifically, it can be measured by the method described in the Examples below. From the viewpoint of process passability, the dimensional change rate in water is more preferably 14.8% or more, further preferably 15.0% or more, and more preferably 15.8% or less, even more preferably 15.6% or less. . Generally, when a PVA film is continuously formed, periodic or continuous unevenness in thickness or retardation occurs in the machine flow direction or width direction. By observing this unevenness, it is possible to determine the mechanical flow direction/width direction of the PVA film even if the film sample is not a long one.

The PVA film of the present invention has a stretching stress of 14.5 to 17.0 N/mm when it is uniaxially stretched in the length direction at a stretching speed of 480%/min after being immersed in pure water at 30°C for 8 seconds ^. It is preferable that it is within the range of . Specifically, the stretching stress can be measured by the method described in the Examples below. When the stretching stress is 14.5 N/mm ² or more, the optical performance of the polarizing film obtained can be improved. From such a viewpoint, the stretching stress is more preferably 14.7 N/mm ² or more, even more preferably 14.9 N/mm ² or more, and particularly preferably 15.1 N/mm ² or more. On the other hand, by setting the stretching stress to 17.0 N/mm ² or less, it is possible to reduce the occurrence of breakage of the PVA film during stretching when the polarizing film is manufactured under high-speed stretching conditions. From such a viewpoint, the stretching stress is more preferably 16.8 N/mm ² or less, even more preferably 16.7 N/mm ² or less, and particularly preferably 16.6 N/mm ² or less.

[PVA]
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 isoacetate. Examples include those obtained by saponifying polyvinyl esters obtained by polymerizing one or more vinyl esters such as propenyl. Among these vinyl esters, vinyl acetate is preferred from the viewpoint of ease of production, availability, cost, etc. of PVA.

The polyvinyl ester is preferably one obtained using only one type or two or more types of vinyl ester as a monomer, and more preferably one obtained using only one type of vinyl ester as a monomer, It may be a copolymer of one or more vinyl esters and another monomer copolymerizable with the vinyl ester, as long as it does not impair the effects of the present invention.

Other monomers copolymerizable with vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salt; (meth)acrylic acid or its salt; Methyl acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, (meth) (meth)acrylic acid esters such as t-butyl acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide, N-methyl (meth)acrylate Acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamidopropanesulfonic acid or its salt, (meth)acrylamidopropyldimethylamine or its salt, N- (Meth)acrylamide derivatives such as methylol (meth)acrylamide or its derivatives; N-vinylamide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl Vinyl ethers such as vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc. vinyl halides; 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; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated Examples include sulfonic acid. The above polyvinyl ester can have a structural unit derived from one or more of these other monomers.

The proportion of structural units derived from other monomers in the polyvinyl ester is preferably 15 mol% or less, and preferably 10 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester. is more preferable, and even more preferably 5 mol% or less. In particular, when the other monomers are monomers that may promote the water solubility of the resulting PVA, such as (meth)acrylic acid or unsaturated sulfonic acid, the resulting PVA film may be In order to prevent PVA from dissolving when used as a raw film for the production of polarizing films, the proportion of structural units derived from these monomers in polyvinyl ester is reduced to the total structural units constituting the polyvinyl ester. It is preferably 5 mol% or less, more preferably 3 mol% or less, based on the number of moles of.

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

PVA may or may not have some of its hydroxyl groups crosslinked. In addition, PVA may have some of its hydroxyl groups reacting with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or it may not react with these compounds and form an acetal structure. good.

The degree of polymerization of PVA is preferably within the range of 1,500 to 6,000, more preferably within the range of 1,800 to 5,000, and more preferably within the range of 2,000 to 4,000. It is even more preferable. If the degree of polymerization is less than 1,500, the durability of a polarizing film produced using the resulting PVA film tends to deteriorate. On the other hand, if the degree of polymerization exceeds 6,000, it tends to lead to increased manufacturing costs, poor passability during film formation, and increased shrinkage stress of the resulting polarizing film. Note that the degree of polymerization of PVA as used herein means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of PVA is preferably 98.0 mol% or more, more preferably 98.5 mol% or more, and 99. More preferably, it is .0 mol% or more. If the degree of saponification is less than 98.0 mol%, the polarizing film tends to have poor water resistance. In addition, the saponification degree of PVA in this specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification, which PVA has. It refers to the proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description in JIS K6726-1994.

[Surfactant]
The PVA film of the present invention preferably contains a surfactant. By containing a surfactant, the occurrence of thickness unevenness in the PVA film is suppressed, and the PVA film can be easily peeled off from a roll or belt during production. The type of surfactant is not particularly limited, but anionic surfactants or nonionic surfactants are preferred from the viewpoint of releasability from rolls, belts, etc. when producing PVA films.

Preferred examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; and polyoxyethylene lauryl amino. Alkyl amine type such as ether; Alkyl amide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanol amide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxy Allyl phenyl ether types such as alkylene allyl phenyl ether are preferred.

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

The content of the surfactant in the PVA film of the present invention is preferably within the range of 0.01 to 0.5 parts by mass, and preferably within the range of 0.02 to 0.3 parts by mass, based on 100 parts by mass of PVA. It is more preferable that the amount is within the range of 0.05 to 0.1 parts by mass. By keeping the content of the surfactant within the above range, while maintaining the film formability and peelability of the PVA film, the surfactant bleeds out onto the surface of the PVA film and blocks it, reducing the ease of handling. can be prevented.

[Plasticizer]
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, and trimethylolpropane. The plasticizer may contain at least one plasticizer. Among these, as described in the PVA film manufacturing method below, it is preferable that the plasticizer is at least one selected from the group consisting of glycerin, diglycerin, and propylene glycol, and that the plasticizer contains at least glycerin. is more preferable.

The content of the plasticizer in the PVA film of the present invention is preferably within the range of 1 to 20 parts by mass, more preferably within the range of 3 to 17 parts by mass, based on 100 parts by mass of PVA. It is more preferably within the range of 15 parts by mass. When the content of the plasticizer is within the above range, it is possible to further improve the stretchability of the PVA film while preventing the PVA film from becoming too flexible and having poor handling properties.

[Other additives]
The PVA film of the present invention may further contain components such as an antioxidant, an antifreeze agent, a pH adjuster, a masking agent, a coloring inhibitor, and an oil agent, if necessary.

[Shape, etc.]
Although the shape 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 also be used continuously when producing a polarizing film using it. It is preferable to use a long film because it allows for The length of the long film (length in the machine flow direction) is not particularly limited, and can be set as appropriate depending on the application, for example, within the range of 5 to 30,000 m.

The width of the PVA film of the present invention is not particularly limited, and can be set appropriately depending on the use of the PVA film and the polarizing film manufactured from it, but in recent years, the screens of LCD televisions and LCD monitors have become larger. Therefore, it is suitable for these uses if 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 will be difficult to uniformly uniaxially stretch it when manufacturing a polarizing film using a commercially available device, so the width of the PVA film should be 7 m or less. is preferred.

In the present invention, the thickness of the PVA film is preferably within the range of 45 to 80 μm, more preferably within the range of 45 to 60 μm. When the thickness of the PVA film is less than or equal to the above upper limit, drying when manufacturing a polarizing film is facilitated to be performed quickly. On the other hand, when the thickness of the PVA film is at least the above-mentioned lower limit, it is possible to more effectively suppress the occurrence of breakage of the PVA film during uniaxial stretching to produce a polarizing film.

The PVA film of the present invention is preferably an optical film. That is, the PVA film of the present invention is preferably used as a raw film used for manufacturing optical films such as polarizing films and retardation films. Among these, according to the PVA film of the present invention, it is possible to obtain a polarizing film with excellent optical performance while reducing breakage even under high-speed stretching conditions. It is preferable to use it as a film.

The production of the PVA film of the present invention is not particularly limited, and conventionally known methods such as wet film forming method, gel film forming method, casting film forming method, and extrusion film forming method can be adopted. By employing the manufacturing method described above, the PVA film of the present invention can be efficiently manufactured.

<PVA film manufacturing method>
The method for producing a PVA film of the present invention is a method for producing a PVA film in which a film-forming stock solution containing PVA is cast onto a roll or belt heated to 50 to 99°C and dried, and the method comprises plasticizing This is a method for producing a PVA film, in which the PVA film is dried until the content of the components is 20 to 23% by mass, and then the PVA film is heat-treated on a roll or belt heated to 100 to 120 ° C.

In the above method for producing a PVA film, the film-forming stock solution containing PVA (hereinafter sometimes abbreviated as film-forming stock solution) may be one in which PVA is dissolved in a liquid medium, or a PVA film containing PVA and a liquid medium. A molten one can be used. Specific aspects and preferred aspects of PVA contained in the film-forming stock solution are the same as those of PVA contained in the above-described PVA film.

Examples of the liquid medium contained in the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. , ethylenediamine, diethylenetriamine, etc., and one or more of these can be used. Among these, water is preferably used in view of its environmental impact and recoverability.

The volatile fraction of the film-forming stock solution (the content of volatile components such as liquid media removed by volatilization or evaporation during film-forming) varies depending on the film-forming method, film-forming conditions, etc., but is in the range of 50 to 95% by mass. It is preferably within the range of 55 to 90% by mass, more preferably within the range of 60 to 85% by mass. If the volatile fraction of the membrane-forming stock solution is too low, the viscosity of the membrane-forming stock solution becomes too high, making filtration and defoaming difficult when preparing the film-forming stock solution, making it difficult to produce PVA films with few foreign substances and defects. There is a tendency to On the other hand, if the volatile fraction of the film-forming stock solution is too high, the concentration of the film-forming stock solution becomes too low, which tends to make industrial production of PVA film difficult.

Here, the volatile fraction of the film-forming stock solution in this specification refers to a value determined by the following formula.
Volatile fraction (mass%) of film forming stock solution = {(Wa-Wb)/Wa}×100
In the above formula, Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) after drying the film-forming stock solution of Wa (g) for 16 hours in an electric dryer at 105°C. .

The membrane forming stock solution preferably contains a surfactant. Specific aspects and preferred aspects of the surfactant contained in the film-forming stock solution are the same as those of the surfactant contained in the PVA film described above.

It is preferable that the film forming stock solution contains a plasticizer. Specific aspects and preferred aspects of the plasticizer contained in the film-forming stock solution are the same as those of the plasticizer contained in the PVA film described above.

In the above method for producing a PVA film, a film-forming stock solution containing PVA is cast onto a roll or belt heated to 50 to 99°C and dried. From the viewpoint of PVA film production efficiency, the surface temperature of the heated roll or belt is more preferably within the range of 60 to 98°C, and even more preferably within the range of 70 to 97°C.

In the above method for producing a PVA film, the PVA film is dried until the amount of the plasticizing component becomes 20 to 23% by mass. By controlling the amount of the plasticizing component within the above range, the PVA film of the present invention can be efficiently produced. Here, the amount of plasticizing component refers to the amount of PVA film that is obtained by casting a film-forming stock solution containing PVA onto a roll or belt heated to 50 to 99°C and drying it. It is the mass fraction of the plasticizing component contained in the PVA film when it contacts the roll. This plasticizing component consists of a liquid medium and a plasticizer contained in the PVA film forming solution.

As mentioned above, the plasticizing component consists of a liquid medium and a plasticizer. The liquid medium is preferably water, and the plasticizer is preferably at least one selected from the group consisting of glycerin, diglycerin, and propylene glycol. That is, it is preferable that the plasticizing component consists of water and a plasticizer, and that the plasticizer is at least one selected from the group consisting of glycerin, diglycerin, and propylene glycol. By using a plasticizer with such a high plasticizing effect, the stretchability of the resulting PVA film can be easily improved. Further, among these plasticizers, glycerin has relatively low volatility and high plasticizing effect, so it is more preferable that the plasticizer contains at least glycerin.

In the above method for producing a PVA film, after drying the PVA film until the amount of plasticizing component becomes 20 to 23% by mass, the PVA film is heat-treated on a roll or belt heated to 100 to 120°C. do. By setting the heat treatment temperature within the above range, the degree of swelling (A), degree of swelling ratio (B/A), and average water absorption rate of the PVA film can be adjusted to desired ranges. Furthermore, properties such as mechanical strength of the PVA film can also be adjusted.

The heat treatment is preferably carried out on a roll heated to 100 to 120°C. Moreover, since the PVA film of the present invention can be manufactured more efficiently, the temperature of the heat treatment is preferably 102°C or higher, preferably 115°C or lower, and more preferably 108°C or lower. The heat treatment time is usually 10 to 30 seconds.

<Production method of polarizing film>
According to the PVA film of the present invention, it is possible to obtain a polarizing film with excellent optical performance while reducing breakage even under high-speed stretching conditions, and therefore it can be used as a raw film used in the production of polarizing films. is preferred. 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 methods include, for example, a method of dyeing and uniaxially stretching a PVA film. Specifically, the PVA film is subjected to swelling, dyeing, uniaxially stretching, and if necessary, further fixing treatment, Methods include drying, heat treatment, etc. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and one or more treatments can be performed simultaneously. Also, one or more of each process can be performed two or more times.

Swelling can be performed by immersing the PVA film in water. The temperature of the water during immersion is preferably within the range of 20 to 40°C, more preferably within the range of 22 to 38°C, and preferably within the range of 25 to 35°C. More preferred. Further, the time for immersion in water is preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.5 to 3 minutes. Note that the water used for immersion is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

Staining is preferably carried out using iodine, and the dyeing may be carried out at any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine and potassium iodide as a dye bath, and such a dyeing method is preferably adopted in the present invention. . The concentration of iodine in the dye bath is preferably within the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably within the range of 0.01 to 10% by mass. Further, the temperature of the dyeing bath is preferably within the range of 20 to 50°C, more preferably within the range of 25 to 40°C.

The uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or it can be carried out in the above-mentioned dyeing bath or in the fixing bath described below. Further, in the case of a dry stretching method, it can be carried out in air using a PVA film after water absorption. Among these, wet stretching is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. The concentration of boric acid in the boric acid aqueous solution is preferably within the range of 0.5 to 6.0% by mass, more preferably within the range of 1.0 to 5.0% by mass, and 1.5% 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 the concentration thereof is preferably within the range of 0.01 to 10% by mass. The stretching temperature in uniaxial stretching is preferably within the range of 30 to 90°C, more preferably within the range of 40 to 80°C, and particularly preferably within the range of 50 to 70°C. Further, the stretching 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 polarizing performance of the polarizing film obtained. Although the upper limit of the stretching ratio is not particularly limited, it is preferable that the stretching ratio is 8 times or less.

When manufacturing a polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of dyes (iodine, etc.) to the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more boron compounds such as boric acid and borax can be used. Further, an iodine compound or a metal compound may be added to the fixing treatment bath as necessary. The concentration of the boron compound in the fixing treatment bath is preferably within the range of 2 to 15% by mass, more preferably within the range of 3 to 10% by mass. The temperature of the fixing treatment bath is preferably within the range of 15 to 60°C, more preferably within the range of 25 to 40°C.

Drying is preferably carried out within the range of 30 to 150°C, more preferably within the range of 50 to 130°C. When the moisture content of the polarizing film decreases to 10% or less after drying, tension is applied to the polarizing film and heat treatment is performed at 80 to 120°C for 1 to 5 minutes, resulting in polarized light with even better dimensional stability and durability. You can get the film.

The polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film on both or one side thereof. 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 film, etc. Film etc. are used. Furthermore, examples of adhesives for bonding include PVA adhesives and urethane adhesives, among which PVA adhesives are preferred.

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

The thickness of the polarizing film is not particularly limited, and can be, for example, 30 μm or less, or even 25 μm or less. The thickness of the polarizing film is preferably 20 μm or less, and preferably 15 μm or less, from the viewpoint of reducing the shrinkage stress of the polarizing film and the polarizing plate using the polarizing film, and preventing the laminated thin glass from warping. It is more preferable that On the other hand, since a polarizing film that is too thin tends to be difficult to manufacture and handle, the thickness of the polarizing film is preferably 3 μm or more.

The present invention will be specifically explained below using examples, but the present invention is not limited to these examples in any way. The evaluation method was performed according to the method shown below.

[Swelling degree of PVA film (A)]
A rectangular sample of 100 mm in the width direction (TD) and 200 mm in the length direction (machine flow direction) was cut out from the PVA films obtained in the following Examples and Comparative Examples, and this sample was further cut into 2 to 3 mm width and length. It was cut into strips with a length of 200 mm. Thereafter, all of these strip-shaped samples were immersed as they were in 1000 g of pure water at 30°C. After 30 minutes of immersion, the strip sample was taken out, centrifuged for 5 minutes at 3000 rpm, and the mass Wa (g) (total of all strip samples) after dehydration was measured. Subsequently, after drying the strip-shaped sample for 16 hours in a dryer at 105 ° C., the mass Wb (g) (total of all strip-shaped samples) was measured, and the degree of swelling (A) was calculated using the following formula. . Note that similar measurements were performed three times and the average value was used.
Swelling degree (A) (%) = 100 x Wa/Wb

[Swelling degree of PVA film (B)]
A rectangular sample measuring 40 mm in the width direction (TD) and 110 mm in the length direction (machine flow direction) was cut out from the PVA films obtained in the following Examples and Comparative Examples. Two gauge lines (thickness: about 0.5 mm) were drawn in the width direction of the sample using a permanent marker so that the distance between the lines (between the centers in the thickness direction of the gauge lines) was 50 mm. This sample was set on a stretching jig so that each marked line was located at the end of the stretching jig (distance between chucks was 50 mm), and immersed in pure water at 30°C for 10 seconds, at a rate of 0.12 m/min. Uniaxial stretching was carried out at a stretching speed of 240%/min) so that the actual stretching ratio was 2.5 times. The actual stretching ratio here refers to the distance between the centers of the marked lines after stretching (the center in the thickness direction of the marked lines at the positions that equally divide the length of the marked lines) to the distance between the marked lines before stretching ( 50mm). After stretching, within 1 minute, wipe off moisture on the surface of the sample after stretching using filter paper, cut the film between the marked lines by cutting the sample along the marked line at the center part in the thickness direction of the marked line, The mass Wc (g) of the film between the marked lines was measured. Subsequently, the film was dried in a dryer at 105°C for 16 hours, the mass Wd (g) was measured, and the swelling degree (B ) was calculated. Note that similar measurements were performed five times, and the average value of the three measurements excluding the maximum and minimum values was adopted.
Swelling degree (B) (%) = 100 x Wc/Wd

[Dimensional change rate in the width direction of PVA film]
A rectangular sample measuring 40 mm in the length direction (machine flow direction) x 270 mm in the width direction (TD) was cut out from the center of the width direction of the PVA films obtained in the following Examples and Comparative Examples. Draw longitudinal markings 10mm inward from both ends of the 270mm length of this sample, and clip the parts outside from the markings at both ends (chuck width 40mm, mass 7.8g (weight in water 7.3g)) ), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the gauge lines was 250 mm, the entire sample was immediately immersed in pure water stored in a water tank and kept at a temperature of 30° C. so that the long side of the sample was vertical. At this time, immediately after immersion, a rod-shaped jig was hooked to the top of the water tank and fixed so that the long side of the sample was vertical (vertical), and the distance between the gauge lines W _TD of the sample was measured 30 seconds after immersion, and then the following The dimensional change rate was calculated using the formula.
Dimensional change rate (%) = 100 x {(W _TD -250)/250}

[Average water absorption rate of PVA film]
For the PVA films obtained in the following Examples and Comparative Examples, the moisture content M ₃₀ and M ₀ were determined by the methods (1) and (2) below, and the average water absorption rate (mass%/sec) of the PVA film was calculated using the following formula. ) was sought. In addition, when measuring a PVA film with a moisture content of less than 2.5% by mass or more than 4.0% by mass, adjust the moisture content M ₀ of the PVA film before water absorption to 2.5 to 4.0% by mass. After that, the average water absorption rate is determined by making the film absorb water using the method (1) below and measuring the moisture content _M30 after water absorption.
Average water absorption rate (mass%/sec) = {(M ₃₀ - M ₀ )/30}

(1) A rectangular sample measuring 50 mm in the width direction and 100 mm in the length direction was cut out from the PVA films obtained in the following Examples and Comparative Examples, and immersed in 1000 g of pure water at 30° C. for 30 seconds. The sample after immersion was taken out, and after absorbing the water on the surface with a filter paper, its mass We (g) was measured. Subsequently, the sample was dried in a dryer at 105° C. for 16 hours, and then its mass Wf (g) was measured. From the obtained masses We and Wf, the moisture content M ₃₀ (mass %) of the PVA film was calculated using the following formula. Similar measurements were performed three times, and the average value was used.
M ₃₀ (mass%) = {(We-Wf)/We}×100

(2) About 5 g of samples were cut out from the PVA films obtained in the following Examples and Comparative Examples. This sample was placed in a heat-resistant glass container and sealed, and the sample mass Wg (g) excluding the tare was measured to four decimal places. Next, this sample was placed in a vacuum dryer with the heat-resistant container at a temperature of 50°C and a pressure of 0.1 kPa or less, and dried for 4 hours with the lid of the heat-resistant container open. (g) was measured to four decimal places. From the obtained masses Wg and Wh, the moisture content M ₀ (mass %) of the PVA film was determined by the following formula.
M ₀ (mass%) = {(Wg-Wh)/Wg}×100

[Content of plasticizing component in PVA film before heat treatment]
In the following Examples and Comparative Examples, a sample of about 5 g was cut out from the center in the width direction of a PVA film dried on a heated metal drum (heated roll). For this sample, determine the moisture content M (mass%) and plasticizer content G (mass%) using methods (1) and (2) below, and calculate the total value of these as the content of plasticizing components in the PVA film before heat treatment. amount (mass%).

(1) The sample was placed in a heat-resistant glass container and sealed, and the mass Wi (g) of the sample excluding the tare was measured to four decimal places. Next, this sample was placed together with the heat-resistant container in a vacuum dryer at a temperature of 50°C and a pressure of 0.1 kPa or less, and dried for 4 hours with the lid of the heat-resistant container open, and then the weight of the sample after removing the tare Wj (g) was measured to four decimal places. From the obtained masses Wi and Wj, the moisture content M (mass %) of the PVA film was determined by the following formula.
M (mass%) = {(Wi-Wj)/Wi}×100

(2) 0.3 g of film was taken out from the sample and immersed in 9 g of pure water for 3 minutes at room temperature. After measuring the mass Wk (g) of the obtained extract, the separated liquid was collected by passing it through a solid phase extraction column, and the glycerin concentration CG (mass %) was measured using a refractometer (“ABBEMAT550” manufactured by Anton Paar). was measured. On the other hand, the immersed film from which the extract was removed was dried at 105° C. for 2 hours, and the mass Wl (g) of the dried film was measured. From the obtained masses Wk, Wl and concentration CG, the plasticizer ratio G (mass %) of the PVA film was determined by the following formula.
G (mass%) = CG x Wk/Wl

[Stretching stress of PVA film (480%/min)]
A sample of 30 mm in the width direction and 100 mm in the length direction is cut out from the center of the width direction of the PVA film obtained in the following Examples and Comparative Examples, and in order to uniaxially stretch it in the length direction, the sample is placed between chucks of 30 mm. The film was held in a stretching jig so that the shape of the film was maintained, and the film was immersed in pure water at 30°C for 8 seconds. Thereafter, while uniaxially stretching in the length direction at a stretching speed of 144 mm/min (480%/min), the stress with respect to the stretching ratio was continuously measured. At this time, the stress when the strain of the PVA film was 400% was defined as the stretching stress. Note that an autograph ("AG-I" manufactured by Shimadzu Corporation) was used to measure the stress, and the measured tension was divided by the cross-sectional area before stretching (sample thickness x sample width (30 mm)). The stress was determined by Similar measurements were performed three times, and the average value was taken as the stretching stress (480%/min) of the PVA film.

[Stretching stress of PVA film (240%/min)]
The stretching stress (240%/min) of the PVA film was determined in the same manner as "PVA film stretching stress (480%/min)" above except that the stretching speed was 72 mm/min (240%/min). Ta.

[Degree of polarization at 43.0% transmittance of polarizing film]
In each of the following Examples and Comparative Examples, the iodine concentration in the iodine/potassium iodide aqueous solution during the second-stage stretching when producing a polarizing film from a PVA film was changed to produce five types of polarizing films with different dyeing densities. was manufactured. For each of these five types of polarizing films, determine the single transmittance Y (%) and polarization degree V (%) using the methods (1) and (2) below, and plot the single transmittance Y on the horizontal axis and the polarization degree V on the vertical axis. An approximate curve was created by plotting the data of five types of polarizing films. From this approximate curve, the value of the degree of polarization V when the single transmittance Y was 43.0% was determined, and this was defined as the "degree of polarization (%) at a transmittance of 43.0%."

(1) Two square samples measuring 30 mm in the length direction x 30 mm in the width direction were taken from one of the five types of polarizing films. One of the samples was measured using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation) in accordance with JIS Z8722:2009 (method for measuring object color), using a C light source and a 2° field of view. Visibility correction in the visible light region is performed, and the light transmittance when tilted at 45 degrees and the light transmittance when tilted at -45 degrees with respect to the length direction are measured, and their average value TY1 (% ) was sought. Similarly, for the other sample, the light transmittance when tilted at 45 degrees and the light transmittance when tilted at -45 degrees were measured, and their average value TY2 (%) was determined. TY1 (%) and TY2 (%) were averaged using the following formula to determine the single transmittance Y (%) of the polarizing film. Such operations were performed for each of the five types of polarizing films.
Y (%) = (TY1+TY2)/2

(2) When the two polarizing film samples collected in the measurement of single transmittance Y in (1) above are stacked so that their length directions are parallel and tilted at 45 degrees with respect to the length direction. The light transmittance when tilted at -45° and the light transmittance when tilted at -45° were measured, and their average value T∥ (%) was determined. Next, stack them so that the length directions are perpendicular to each other, measure the light transmittance when tilted at 45 degrees with respect to the length direction, and the light transmittance when tilted at -45 degrees, and calculate the average of them. The value T⊥(%) was determined, and the degree of polarization V (%) was determined using the following formula. Such operations were performed for each of the five types of polarizing films.
V (%) = {(T∥−T⊥)/(T∥+T⊥)}1/2×100

[Example 1]
100 parts by mass of PVA (saponified homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.95 mol%), 13 parts by mass of glycerin as a plasticizer, 0.1 mass of lauric acid diethanolamide as a surfactant. A film-forming stock solution with a volatile content of 66% by mass was prepared. This film-forming stock solution was cast onto a metal drum with a surface temperature of 80°C, and dried until the content of plasticizing components was 20.1% by mass (moisture content: 7% by mass, plasticizer content: 13.1% by mass). After that, heat treatment was performed at 105° C. for 15 seconds to obtain a PVA film with a width of 65 cm and a thickness of 60 μm. Regarding the obtained PVA film, the degree of swelling (A), degree of swelling (B), average water absorption rate, underwater dimensional change rate in the width direction, stretching stress (240%/min) and stretching stress (480%/min) were determined by the method described above. minutes) was measured. Further, the degree of swelling (B) was divided by the degree of swelling (A) to obtain the degree of swelling ratio (B/A). These results are shown in Tables 1 and 2.

The above PVA film was uniaxially stretched in the length direction to twice its original length (first stage stretching) while immersed in water at a temperature of 30°C. While immersed in an iodine/potassium iodide aqueous solution containing 1.2% by mass of potassium iodide at 32°C, the film was uniaxially stretched (second stage stretching) to 2.5 times its original length. Next, while immersed in a 30°C aqueous boric acid solution containing 2.6% by mass of boric acid, it was uniaxially stretched in the length direction to three times the original length (third-stage stretching), and further stretched with boric acid. While immersed in a boric acid/potassium iodide aqueous solution at 55°C containing 2.8% by mass and 5% by mass of potassium iodide, it was uniaxially stretched ( 4th stage stretching). Subsequently, the film is washed by immersing it in a potassium iodide aqueous solution at 22°C containing 1.5% by mass of boric acid and 3.3% by mass of potassium iodide, and dried for 110 seconds in a dryer at 80°C. In this way, a polarizing film with a thickness of 24 μm was manufactured. Regarding the obtained polarizing film, the degree of polarization at a transmittance of 43.0% was measured by the method described above. The results are shown in Table 1.

[Examples 2 to 5, Comparative Examples 1 to 3]
The content of plasticizing components in the PVA film before heat treatment was changed as shown in Table 3 by adjusting the amount of glycerin added or the drying time of the PVA film, and the conditions of heat treatment temperature were changed as shown in Table 3. A PVA film and a polarizing film were obtained in the same manner as in Example 1 except for the above. Regarding the obtained PVA film, the degree of swelling (A), degree of swelling (B), average water absorption rate, underwater dimensional change rate in the width direction, stretching stress (240%/min) and stretching stress (480%/min) were determined by the method described above. minutes) was measured. Further, the degree of swelling (B) was divided by the degree of swelling (A) to obtain the degree of swelling ratio (B/A). Furthermore, the degree of polarization of the obtained polarizing film at a transmittance of 43.0% was measured by the method described above. These results are shown in Tables 1 and 2.

As shown in Table 1, the PVA films of Examples 1 to 5 had sufficiently low stretching stress under the stretching conditions of 480%/min, so even under high-speed stretching conditions during the production of polarizing films, the PVA films did not break. is reduced. Further, the polarizing films obtained from the PVA films of Examples 1 to 5 have a sufficiently high degree of polarization at a transmittance of 43.0%. That is, according to the PVA films of Examples 1 to 5, it is possible to produce a polarizing film with excellent optical performance while reducing breakage of the PVA film even under high-speed stretching conditions during production of the polarizing film. .

On the other hand, as shown in Table 1, although the PVA films of Comparative Examples 1 and 2 have excellent optical performance, the stretching stress under the stretching condition of 480%/min is large, so that during the production of the polarizing film, Under high-speed stretching conditions, the PVA film tends to break. In addition, since the PVA film of Comparative Example 3 has a sufficiently low stretching stress under the stretching condition of 480%/min, the breakage of the polarizing film is reduced even under high-speed stretching conditions during the production of the polarizing film. The polarizing film had an insufficient degree of polarization at a transmittance of 43.0%. Note that even in the PVA films of Comparative Examples 1 and 2, the stretching stress is sufficiently small under relatively low stretching conditions such as 240%/min. In other words, with the PVA films of Comparative Examples 1 and 2, polarizing films with excellent optical performance can be produced while reducing PVA film breakage under conventional relatively low-speed stretching conditions, but under high-speed stretching conditions such as 480%/min. Under the stretching conditions, the PVA film tends to break, and the manufacturing efficiency of the polarizing film decreases.

As shown in the above examples, according to the present invention, it is possible to produce a polarizing film with excellent optical performance while reducing breakage of the PVA film even under high-speed stretching conditions during production of the polarizing film. I can do it. Therefore, a polarizing film can be efficiently manufactured without impairing optical performance.

Claims

The degree of swelling (A) is 195 to 205% by mass, and the degree of swelling (B) after stretching 2.5 times in water at 30 ° C. at a stretching rate of 240%/min is the degree of swelling (A). A polyvinyl alcohol film having a divided value of 1.27 to 1.40, and having an average water absorption rate of 1.35% by mass/second or more when immersed in water at 30°C for 30 seconds.
The polyvinyl alcohol film according to claim 1, which has a dimensional change rate in the width direction of 14.6 to 16.2% when immersed in water at 30°C for 30 seconds.
The polyvinyl alcohol film according to claim 1 or 2, wherein the film has a thickness of 45 to 80 μm.
The polyvinyl alcohol film according to claim 1 or 2, which is an optical film.
A method for producing a polyvinyl alcohol film in which a film-forming stock solution containing polyvinyl alcohol is cast onto a roll or belt heated to 50 to 99°C and dried, the method comprising: a film forming solution containing polyvinyl alcohol having a plasticizing component content of 20 to 23 The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein after drying the polyvinyl alcohol film to a mass%, the polyvinyl alcohol film is heat-treated on a roll or belt heated to 100 to 120 ° C.
The method for producing a polyvinyl alcohol film according to claim 5, wherein the heat treatment is performed on a roll heated to 100 to 120°C.
The method for producing a polyvinyl alcohol film according to claim 5, wherein the plasticizing component consists of water and a plasticizer, and the plasticizer is at least one selected from the group consisting of glycerin, diglycerin, and propylene glycol.