CN116547345A - Polyvinyl alcohol film, polarizing film and polarizing plate using same - Google Patents

Abstract

Provided are a PVA film which can suppress breakage during uniaxial stretching even when the maximum stretching speed is high in uniaxial stretching in the production of an optical film such as a polarizing film, and a polarizing film and a polarizing plate obtained using the PVA film. A polyvinyl alcohol film wherein the amount of bound amorphous component calculated from the relaxation curve obtained by pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 50 ℃ is set to (A2) _50℃ The bound amorphous component calculated from the relaxation curve obtained by pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 30℃was set as (A2) _30℃ Time, (A2) _50℃ Relative (A2) _30℃ Ratio ((A2) _50℃ /(A2) _30℃ ) 020 to 065.

Description

Polyvinyl alcohol film, polarizing film and polarizing plate using the same

Technical Field

The present invention relates to a polyvinyl alcohol film, and a polarizing film and a polarizing plate using the same.

Background Art

Polarizing plates that transmit and block light are the basic components of liquid crystal displays (LCDs) along with liquid crystals that change the polarization state of light. LCDs are used in a wide range of applications, including small devices such as calculators and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and indoor and outdoor measuring equipment.

Polarizing plates are generally manufactured by dyeing and uniaxially stretching a polyvinyl alcohol film (hereinafter sometimes referred to as "PVA"), and further performing a fixing treatment based on a boron compound or the like as needed to manufacture a polarizing film, and then attaching a protective film such as a triacetyl cellulose (TAC) film to the surface of the polarizing film. In recent years, the manufacturing process of these manufacturing processes has been accelerated with the main purpose of improving the manufacturing efficiency of optical films such as polarizing films. In conjunction with this, in the manufacturing process of optical films such as polarizing films, the PVA film is stretched at a higher speed than before.

On the other hand, Patent Document 1 describes that a polarizing film having excellent shrinkage force and hue is obtained by using a PVA film having a crystal structure determined by pulse NMR measurement within a specific range. In addition, Patent Document 2 describes that a polarizing film having excellent polarization performance and shrinkage force is obtained by using a PVA film having a crystal structure determined by pulse NMR measurement within a specific range.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 6408909

Patent Document 2: International Publication No. 2019/151206

Summary of the invention

Problems to be solved by the invention

As described above, in the manufacturing process of optical films such as polarizing films, the PVA film is stretched at a higher speed than before. Therefore, it is required that the PVA film can suppress the fracture during uniaxial stretching even when the maximum stretching speed of uniaxial stretching during the manufacture of optical films such as polarizing films is high. However, when the existing known PVA film is uniaxially stretched, if the maximum stretching speed is set to high speed, the PVA film cannot follow the deformation speed during stretching, and the stress during stretching increases and fracture occurs, which becomes a problem. In addition, in the prior art, the relationship between the fracture of such a PVA film during uniaxial stretching and the crystal structure of the PVA film has not been studied.

Therefore, an object of the present invention is to provide a PVA film capable of suppressing breakage during uniaxial stretching even at a high maximum stretching speed when manufacturing an optical film such as a polarizing film, and a polarizing film and a polarizing plate obtained using such a PVA film.

Means used to solve problems

As a result of intensive studies, the present inventors have found that the above-mentioned problems can be achieved by adjusting the ratio of the bound amorphous component of the PVA film to a specific range, and based on this finding, they have further conducted studies and completed the present invention.

That is, the present invention relates to:

[1] A PVA film, wherein, when the amount of bound amorphous components calculated based on a relaxation curve obtained by pulse NMR measurement in a 3 mass % boric acid deuterated water solution at 50°C is referred to as (A2) _50°C , and the amount of bound amorphous components calculated based on a relaxation curve obtained by pulse NMR measurement in a 3 mass % boric acid deuterated water solution at 30°C is referred to as (A2) _30°C , the ratio of (A2) ₅₀ °C to (A2) _30°C ((A2) _50°C /(A2) _30°C ) is 0.20 to 0.65;

[2] The PVA film according to [1], wherein (A2) _50°C is 15 or less, and when (A1) _50°C is the amount of crystalline component calculated from a relaxation curve obtained by pulse NMR measurement in a 3% by mass boric acid deuterated water solution at 50°C, the ratio of (A2) _50°C to (A1) _50°C ((A2) _50°C /(A1) _50°C ) is 0.60 to 1.6;

[3] The PVA film according to any one of [1] to [3] above, wherein the degree of swelling is 170 to 220%.

[4] The PVA film according to [1] or [2], wherein the degree of polymerization of PVA contained in the PVA film is 2,000 to 2,700;

[5] The PVA film according to any one of [1] to [4], which is a raw material film for producing an optical film;

[6] The PVA film according to [5] above, wherein the optical film is a polarizing film;

[7] A polarizing film produced using the PVA film described in [6] above;

[8] A polarizing plate obtained by attaching a protective film to at least one side of the polarizing film described in [7].

Effects of the Invention

According to the present invention, there can be provided a PVA film which can suppress breakage during uniaxial stretching even when the maximum stretching speed of uniaxial stretching is high when manufacturing an optical film such as a polarizing film, and a polarizing film and a polarizing plate manufactured using the PVA film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a crystal portion, a bound amorphous portion, and an amorphous portion of PVA in a PVA film.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in detail.

<PVA film>

(Pulsed NMR)

Regarding the PVA film of the present invention, when the amount of bound amorphous components calculated from a relaxation curve obtained by pulse NMR measurement in a 3 mass % boric acid deuterated water solution at 50°C is referred to as (A2) _50°C , and the amount of bound amorphous components calculated from a relaxation curve obtained by pulse NMR measurement in a 3 mass % boric acid deuterated water solution at 30°C is referred to as (A2) 30 _°C , the ratio of (A2) ₅₀ °C to (A2) _30°C ((A2) _50°C /(A2) _30°C ) is 0.20 to 0.65. (A2) _50°C /(A2) _30°C is preferably 0.20 or more. (A2) _50°C /(A2) _30°C is preferably 0.65 or less. If (A2) _50°C /(A2) _30°C is less than 0.20, the PVA film may be dissolved and broken in a stretching tank. On the other hand, if (A2) _50°C / (A2) _30°C is greater than 0.65, excessive tension may be applied to the PVA film, causing it to break. Methods for setting (A2) _50°C / (A2) _30°C to 0.20 to 0.65 include: a method for filtering the film-forming stock solution (e.g., the size of the mesh of the mesh filter); a method for appropriately adjusting the surface temperature of the support on which the film-forming stock solution is to be cast, the temperature of the hot air blown to the non-contact surface side of the film-forming stock solution cast on the support, the dew point of the hot air, the drying temperature, the heat treatment temperature, and the like.

The (A2) _50°C of the PVA film of the present invention is preferably 15 or less, more preferably 13 or less. If (A2) _50°C is greater than 15, there is a tendency that excessive tension is applied to the PVA film and it is easy to break. In addition, when the amount of crystalline component calculated from the relaxation curve obtained by pulse NMR measurement in a 3% by mass boric acid deuterated water solution at _50° C is set to (A1) _50°C , the ratio of (A2) _{50°C to (A1) 50 °C ((A2) 50°C} / (A1) _50°C ) is preferably 0.60 to 1.6. (A2) _50°C / (A1) _50°C is preferably 0.60 or more, more preferably 0.80 or more, and further preferably 1.0 or more. (A2) _50°C / (A1) _50°C is preferably 1.6 or less, more preferably 1.4 or less, and further preferably 1.3 or less. If (A2) _50°C / (A1) _50°C is less than 0.60, it tends to be difficult to exhibit sufficient optical properties. If (A2) _50° C / (A1) _50°C is greater than 1.6, excessive tension is sometimes applied to the PVA film, which may cause breakage. As a method for setting (A2) _50°C of the PVA film to 15 or less or a method for setting (A2) _50°C / (A1) _50°C to 0.60 to 1.6, there are: a method for filtering the film-forming stock solution (for example, the size of the mesh of the mesh filter); a method for appropriately adjusting the surface temperature of the support on which the film-forming stock solution is to be cast, the temperature of the hot air blown to the non-contact surface side of the film-forming stock solution cast on the support, the dew point of the hot air, the drying temperature, the heat treatment temperature, etc.

The (A1) _30°C of the PVA film of the present invention is preferably 20 or more, more preferably 25 or more. The (A1) _30°C is preferably 35 or less, more preferably 32 or less.

The (A2) _30°C of the PVA film of the present invention is preferably 15 or more, more preferably 20 or more. The (A2) _30°C is preferably 24 or less, more preferably 23 or less.

The (A3) _30°C of the PVA film of the present invention is preferably 40 or more, more preferably 42 or more. The (A3) _30°C is preferably 60 or less, more preferably 55 or less.

The (A1) _50°C of the PVA film of the present invention is preferably 3 or more, more preferably 5 or more. The (A1) _50°C is preferably 15 or less, more preferably 13 or less.

The (A2) _50°C of the PVA film of the present invention is preferably 5 or more, more preferably 7 or more. As described above, the (A2) _50°C is preferably 15 or less, more preferably 13 or less.

The (A3) _50°C of the PVA film of the present invention is preferably 70 or more, more preferably 73 or more. The (A3) _50°C is preferably 95 or less, more preferably 90 or less.

As methods for setting (A1) _30°C , (A2) _30°C , (A3) _30°C , (A1) _50°C , (A2) _50°C and (A3) _50°C of the PVA film of the present invention to the above ranges, there can be listed: a method for filtering the film-forming stock solution (for example, the mesh size of the screen filter); a method for appropriately adjusting the surface temperature of the support on which the film-forming stock solution is to be cast, the temperature of the hot air blown to the non-contact surface side of the film-forming stock solution cast on the support, the dew point of the hot air, the drying temperature, the heat treatment temperature, etc.

Here, pulsed NMR is different from general NMR used for determining the structure of organic compounds, and is an analytical method that can measure the relaxation time of ^1H nuclei related to the molecular mobility in a system. In addition, pulsed NMR can use its high quantitativeness to determine the abundance ratio of each motion component in a system.

In the pulsed NMR measuring device, there is a static magnetic field generated by the electromagnet in the device. In the static magnetic field, the direction of the nuclear spin of the hydrogen nucleus is oriented in the direction along the static magnetic field. If a pulsed magnetic field is applied in this state, the nuclear spin of the hydrogen nucleus presents a state (excited state) tilted 90° from the direction along the static magnetic field. Thereafter, the direction of the excited nuclear spin is macroscopically restored to the original direction along the static magnetic field. The process of restoring the direction of the nuclear spin from the excited state to the original state is called " _T2 relaxation", and the time required for this process is called relaxation time (tau). In the case of relaxation of a single component, the magnetization intensity (y) at time (t) uses the intensity (a), relaxation time (tau) and constant (y0, w) in the excited state, and is expressed by the following formula.

y＝y0+a×exp(-1/W×(t/tau) ^W )

It should be noted that W is called the Weibull coefficient. When W = 1, the formula is called the Exp type, and when W = 2, the formula becomes the Gauss type. In the case of general polymers, the range of 1≤W≤2 is adopted.

In the case of _T2 relaxation, hydrogen nuclei exchange energy with other hydrogen nuclei from an excited state while decaying to the original state. Therefore, when the molecular mobility of the sample is high, the interaction between protons close to each other is small, so it is not easy for the energy decay of the whole system to occur, and the relaxation time becomes longer. Along with this, when the molecular mobility of the sample is low, the relaxation time becomes shorter. Therefore, if it is a crystalline polymer, the relaxation time of the crystalline component becomes shorter and the relaxation time of the amorphous component becomes longer. Furthermore, the boundary between the crystalline component and the amorphous component, that is, the bound amorphous component (refer to Figure 1), presents a relaxation time between the two.

In conventional X-ray measurements, only the amount of crystalline components and the amount of amorphous components can be measured, but in pulsed NMR, on the basis of being able to measure the amount of crystalline components and the amount of amorphous components, the amount of bound amorphous components can also be measured. In particular, in pulsed NMR, the existence ratio of each motion component is determined based on the mobility of the crystalline polymer that cannot be obtained in X-ray measurements. The aforementioned existence ratio becomes a value that more accurately reflects the various properties sought for the PVA film. Therefore, by using pulsed NMR, the characteristics of the PVA film can be evaluated extremely appropriately.

It should be noted that in actual crystalline polymers, the above-mentioned crystalline components, bound amorphous components and amorphous components are mixed. Therefore, if a PVA film containing the above-mentioned crystalline polymer is measured by pulse NMR, the relaxation curve obtained is observed as the sum of the relaxation components derived from the crystalline component with a short relaxation time, the relaxation components derived from the amorphous component with a long relaxation time, and the relaxation components derived from the bound amorphous component with a relaxation time intermediate between the two.

In the present invention, the relaxation curve obtained by the linear least squares method is fitted in the following formula. When the relaxation time of the crystalline component is set to tau1, the relaxation time of the bound amorphous component is set to tau2, and the relaxation time of the amorphous component is set to tau3, the magnetization intensity (y) of the entire sample at time (t) is expressed by the following formula using the constant y0 and a1, a2, and a3 in the excited state.

y＝y0+a1×exp(-1/W1×(t/tau1) ^W1 )+a2×exp(-1/W2×(t/tau2) ^W2 )+a3×exp(-1/W3×(t/ tau3) ^W3 )

As a result of the in-depth verification this time, the following formula was used as a formula (fitting function) that can stably and reproducibly fit between films manufactured using various film-making conditions. The formula sets the crystalline component and the bound amorphous component to Gaussian relaxation (W1, W2=2), respectively, and fixes the amorphous component to Exp type relaxation (W3=1).

y＝y0+a1×exp(-0.5×(t/tau1) ² )+a2×exp(-0.5×(t/tau2) ² )+a3×exp(-t/tau3)

In the present invention, a1, a2, a3 and tau1, tau2, tau3, y0 derived from the above formula are obtained, and the ratio (%) of each component to the total of a1, a2 and a3 (a1+a2+a3) is defined as the crystalline component amount (A1), the bound amorphous component amount (A2), and the amorphous component amount (A3). For example, the value of the bound amorphous component amount (A2) is expressed by a2/(a1+a2+a3)×100.

(Swelling degree)

The swelling degree of the PVA film of the present invention is preferably 170% or more. The swelling degree of the PVA film is preferably 220% or less. If the swelling degree is less than 170%, there is a tendency for uneven swelling to occur, and uniform dyeing cannot be achieved during dyeing. If the swelling degree is greater than 220%, there is an undesirable tendency for wrinkles to occur during the process. As a method for adjusting the swelling degree of the PVA film to these ranges, for example, a method of appropriately adjusting the heat treatment temperature, the time of contact with the heat treatment roller, etc. can be cited.

The swelling degree is an index showing the water retention capacity of a PVA film when immersed in water, and can be obtained as a percentage by dividing the mass of the PVA film after immersion in water at 30°C for 30 minutes by the mass after drying at 105°C for 16 hours after immersion.

(PVA)

As the PVA contained in the PVA film of the present invention, there can be cited PVA obtained by saponifying polyvinyl esters obtained by polymerizing one or more of vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, etc. Among the above vinyl esters, vinyl acetate is preferred from the viewpoints of ease of manufacture, ease of acquisition, cost, etc. of PVA.

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

Examples of other monomers copolymerizable with the vinyl ester include α-olefins having 2 to 30 carbon atoms, such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salts; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamide propanesulfonic acid or its salts, (meth)acrylamide propanesulfonic acid or its salts, (meth)acrylamide derivatives such as (meth)acrylamide propyl dimethylamine or its salt, N-hydroxymethyl (meth)acrylamide or its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salt, ester, or anhydride; itaconic acid or its salt, ester, or anhydride; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acid, etc. The above-mentioned polyvinyl ester may have a structural unit derived from one or more of the above-mentioned other monomers.

The ratio of the structural units derived from other monomers in the polyvinyl ester is preferably 15 mol% or less, more preferably 10 mol% or less, and further preferably 5 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester.

As other monomers, ethylene is preferred. By copolymerizing ethylene, the polarization performance of the obtained polarizing film is sometimes improved. The content of ethylene units in PVA is preferably 0.5 mol% or more, more preferably 1 mol% or more, and further preferably 1.5 mol% or more. In addition, the content of ethylene units is preferably 8 mol% or less, and more preferably 5 mol% or less.

When other monomers such as (meth)acrylic acid, unsaturated sulfonic acid, etc. are monomers that may promote the water solubility of the obtained PVA, in order to prevent the dissolution of PVA when the obtained PVA film is used as a raw material film for manufacturing a polarizing film, the proportion of the structural units derived from these monomers in the polyvinyl ester is preferably 5 mol% or less, more preferably 3 mol% or less, based on the molar number of all structural units constituting the polyvinyl ester.

PVA can be modified with one or more graft copolymerizable monomers within the scope that does not impair the effects of the present invention. Examples of such graft copolymerizable monomers include unsaturated carboxylic acids or their derivatives; unsaturated sulfonic acids or their derivatives; α-olefins having 2 to 30 carbon atoms, etc. The proportion of structural units derived from graft copolymerizable monomers in PVA is preferably 5 mol% or less based on the molar number of all structural units constituting PVA.

A part of the hydroxyl groups in the PVA may be cross-linked or not cross-linked. In addition, a part of the hydroxyl groups in the PVA may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure or may not react with these compounds to form an acetal structure.

The degree of polymerization of PVA is preferably 2000 or more, preferably 2200 or more, and more preferably 2400 or more. When the degree of polymerization is less than 2000, the durability of the resulting polarizing film tends to decrease. The degree of polymerization of PVA is preferably 2700 or less, preferably 2650 or less, and more preferably 2600 or less. When the degree of polymerization exceeds 2700, the manufacturing cost tends to increase and the process qualification during film making tends to deteriorate. It should be noted that the degree of polymerization of PVA mentioned in this specification refers to the average degree of polymerization measured in accordance with the description of JIS K6726-1994.

From the viewpoint of water resistance of the polarizing film, the saponification degree of PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and further preferably 99 mol% or more. If the saponification degree is less than 98 mol%, the water resistance of the obtained polarizing film tends to deteriorate. It should be noted that 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 of PVA, and the proportion (mol%) of the mole number of the vinyl alcohol units. The saponification degree can be measured according to the description of JIS K6726-1994.

(Plasticizer)

The PVA film of the present invention preferably contains a plasticizer. As the plasticizer, polyols such as ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. can be listed, and the PVA film of the present invention can contain one or more of these plasticizers. Among these, glycerol is preferably used from the viewpoint of improving the effect of stretchability.

The content of the plasticizer in the PVA film of the present invention is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more relative to 100 parts by mass of PVA. By making the content of the plasticizer 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, the content of the plasticizer is preferably 20 parts by mass or less, more preferably 17 parts by mass or less, and further preferably 15 parts by mass or less relative to 100 parts by mass of PVA. By making the content of the plasticizer 20 parts by mass or less, it is possible to prevent the PVA film from being too soft and causing a decrease in handling properties.

(Surfactant)

The PVA film of the present invention preferably contains a surfactant. By using a film-forming stock solution containing a surfactant to manufacture the PVA film, the film-forming property of the PVA film is improved. As a result, the uneven thickness of the PVA film can be suppressed, and the PVA film can be easily peeled off from the metal roll or belt used for film-forming. In the case of manufacturing the PVA film from a film-forming stock solution containing a surfactant, the obtained PVA film contains a surfactant.

The type of surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferred from the viewpoint of peeling properties of the PVA film from a metal roll or a belt.

Preferred anionic surfactants include, for example, carboxylic acid-type surfactants such as potassium laurate; sulfate-ester-type surfactants such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid-type surfactants such as dodecylbenzenesulfonate.

As the nonionic surfactant, suitable ones include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkylamine types such as polyoxyethylene lauryl amino ether; alkyl amide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether, etc.

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 0.01 mass parts or more, more preferably 0.02 mass parts or more, and further preferably 0.05 mass parts or more relative to 100 mass parts of PVA. By setting the content of the surfactant to 0.01 mass parts or more, the film-forming property and peeling property of the PVA film are further improved. On the other hand, the content of the surfactant in the PVA film is preferably 0.5 mass parts or less, more preferably 0.3 mass parts or less, and further preferably 0.2 mass parts or less relative to 100 mass parts of PVA. By setting the content of the surfactant to 0.5 mass parts or less, it is easy to suppress the surfactant from oozing out to the surface of the PVA film and causing adhesion, and it is easy to suppress the reduction of the handleability.

(Other ingredients)

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

(Shape, etc.)

The shape of the PVA film of the present invention is not particularly limited, and is preferably a long film. Thus, a more uniform PVA film can be manufactured continuously and easily, and can be used continuously even when it is used to manufacture a polarizing film. The length (length in the longitudinal direction) of the long film is not particularly limited and can be appropriately set according to the purpose, etc., and can be set, for example, in 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 appropriately set according to the use of the PVA film and the polarizing film manufactured therefrom. From the perspective of the large screen of liquid crystal televisions and liquid crystal displays that are being developed in recent years, if the width of the PVA film is set to 3m or more, more preferably 4m or more, it can be suitably used for these purposes. On the other hand, if the width of the PVA film is too wide, when the polarizing film is manufactured using a practical device, the uniaxial stretching itself tends to become difficult to be uniformly performed, and therefore, the width of the PVA film is preferably 7m or less.

The thickness of the PVA film of the present invention is preferably 30 to 60 μm. If the thickness is less than 30 μm, the handling property during stretching is deteriorated, and if the thickness is 60 μm or more, it is not preferable as a polarizing plate for thin displays.

<Method for producing PVA film>

In the present invention, the method for manufacturing the PVA film is not particularly limited, and the following methods can be used: using a film-making stock solution obtained by adding a solvent, an additive, etc. to PVA and homogenizing it, a method of film-making by using a cast film method, a wet film method (spraying into a poor solvent), a dry-wet film method, a gel film method (a method of temporarily cooling and gelling the film-making stock solution, extracting and removing the solvent to obtain a PVA film), or a combination thereof; a melt extrusion film-making method in which the above-mentioned film-making stock solution is obtained by using an extruder, etc., and extruding it from a T-die, etc., to form a film; any method such as an inflation molding method. Among these, the cast film method and the melt extrusion film method can obtain a homogeneous film with good productivity, so they are preferred. Below, the cast film method or the melt extrusion film method of the PVA film is described.

When the PVA film is manufactured by the cast film method or the melt extrusion film method, the film-making stock solution is cast into a film on a support such as a metal roll or a metal belt, and the solvent is removed by heating, thereby solidifying to form a film. The solidified film is peeled off from the support, dried by a drying roll, a drying furnace, etc. as needed, and further heat-treated and wound up as needed, thereby obtaining a long PVA film in a roll.

The volatility (water content) of the film-making stock solution varies depending on the film-making method, film-making conditions, etc. If the volatility of the film-making stock solution is too low, there is a tendency that the viscosity of the film-making stock solution becomes too high, and it is difficult to filter and degas when preparing the film-making stock solution, and it is difficult to manufacture a PVA film with few impurities and defects. The volatility is preferably 50% by mass or more, more preferably 55% by mass or more, and further preferably 60% by mass or more. On the other hand, if the volatility of the film-making stock solution is too high, there is a tendency that the concentration of the film-making stock solution becomes too low, and it is difficult to industrially manufacture the PVA film. The volatility is preferably 95% by mass or less, preferably 90% by mass or less, and further preferably 85% by mass or less.

Here, the "volatile fraction of the membrane-forming stock solution" in the present invention means the volatile fraction determined by the following formula.

Volatile fraction of film-forming stock solution (mass %) = {(Wa-Wb)/Wa} × 100

(Wa represents the mass (g) of the film-forming stock solution; Wb represents the mass (g) of the film-forming stock solution when Wa (g) is dried in an electric drying machine at 105°C for 16 hours).

The method for adjusting the film-forming stock solution is not particularly limited, and examples thereof include: for example, a method in which PVA and additives such as plasticizers and surfactants are dissolved in a dissolving tank, etc.; a method in which the water-containing PVA is melt-kneaded together with plasticizers, surfactants, etc. using a single-screw extruder or a twin-screw extruder; etc.

Examples of the liquid medium for preparing the membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. One or more of these can be used. Among them, water is preferably used from the viewpoint of environmental burden and recyclability.

In the case of using a cast film method or a melt extrusion film method to manufacture a PVA film, when the film-making stock solution is cast into a film on a support such as a metal roller or a metal belt, it is preferred to filter the film-making stock solution in advance. As a filtering method for the film-making stock solution, filtration based on a mesh filter is preferred. The mesh size of the mesh filter used is preferably 180 mesh or more, more preferably 200 mesh or more. The mesh size of the mesh filter used is preferably 330 mesh or less, more preferably 320 mesh or less. If the mesh size is greater than 180 mesh, there is a tendency for the undissolved matter in the stock solution to remain in the film in the form of impurities. On the contrary, if the mesh size is less than 330 mesh, there is a tendency that the crystallization process of the PVA film is affected during drying, and the ratio of the bound amorphous component amount of the PVA film (A2) _50°C / (A2) _30°C does not satisfy the above range.

The surface temperature of the support on which the film-forming stock solution is to be cast is preferably 85° C. or higher, more preferably 88° C. or higher, and further preferably 90° C. or higher. The surface temperature of the support on which the film-forming stock solution is to be cast is preferably 100° C. or lower, more preferably 99° C. or lower, and further preferably 98° C. or lower. When the surface temperature of the support is not within the range of 85° C. to 100° C., the ratio of the bound amorphous component amount of the PVA film (A2) _{50° C.} /(A2) _{30° C.} tends to be difficult to satisfy the above range.

The drying speed can be adjusted by uniformly blowing hot air at a wind speed of 1 to 10 m/s to the entire area of the surface side of the PVA film that is not in contact with the support while heating the film-making stock solution (hereinafter sometimes abbreviated as PVA film) cast on the support. The temperature of the hot air blown to the non-contact surface side is preferably 80°C or more, more preferably 85°C or more, and further preferably 88°C or more. The temperature of the hot air blown to the non-contact surface side is preferably 110°C or less, more preferably 105°C or less, and further preferably 99°C or less. If the hot air temperature exceeds 110°C, there is a tendency that the PVA crystals in the PVA film grow excessively, and the ratio of the bound amorphous component amount of the PVA film (A2) _50°C /(A2) _30°C is difficult to satisfy the above range. On the other hand, if the hot air temperature is lower than 80°C, there is a tendency for the manufacturing process speed of the PVA film to decrease.

The dew point of the hot air blown to the non-contact surface side is also important from the viewpoint of controlling the crystallinity of the PVA film. The dew point of the hot air blown to the non-contact surface side is preferably above 10°C, more preferably above 14°C. The dew point of the hot air blown to the non-contact surface side is preferably below 20°C, preferably below 18°C. If the dew point is higher than 20°C, there is a tendency that the crystals of the PVA film grow excessively, and the ratio of the bound amorphous component of the PVA film (A2) _50°C /(A2) _30°C is difficult to satisfy the above range. If the dew point is lower than 10°C, the surface quality of the film may be damaged due to condensation in the cooling part around the manufacturing device.

The PVA film is preferably dried on the support until the volatile fraction is 5 to 50% by mass, then peeled off, and further dried as needed. The drying method is not particularly limited, and methods of contacting it with a drying furnace and a drying roller can be cited. In the case of using multiple drying rollers to dry it, it is preferred to make one side and the other side of the film contact the drying roller alternately so that both sides are uniform. The number of drying rollers is preferably 3 or more, more preferably 4 or more, and further preferably 5 or more. The number of drying rollers is preferably 30 or less. The temperature of the drying furnace or the average temperature of the drying roller (the average value of the surface temperature of the drying roller) is preferably 110°C or less, more preferably 100°C or less, more preferably 90°C or less, and further preferably 85°C or less. If the temperature of the drying furnace or the average temperature of the drying roller is too high, there is a tendency that the crystal growth of the PVA film is intensified, and the ratio of the bound amorphous component of the PVA film (A2) _50°C / (A2) _30°C is difficult to meet the above range. On the other hand, the temperature of the drying furnace or the average temperature of the drying roller is preferably 40°C or more, more preferably 45°C or more, and further preferably 50°C or more. If the temperature of the drying furnace or the average temperature of the drying roll is too low, the crystal growth of the PVA film becomes insufficient and the bound amorphous component ratio (A2) _{50° C.} /(A2) _{30° C.} of the PVA film tends to be difficult to satisfy the above range.

The dried PVA film can be further heat-treated as needed. By heat-treating, the strength, swelling degree, complex refractive index, etc. of the PVA film can be adjusted. The surface temperature of the heat treatment roller used for heat treatment is preferably above 60°C. The surface temperature of the heat treatment roller is preferably below 135°C, more preferably below 130°C. If the surface temperature of the heat treatment roller is too high, there is a tendency that too much heat is applied, the size of the lamellae in the PVA film becomes larger, and the ratio of the bound amorphous component of the PVA film (A2) _50°C / (A2) _30°C is difficult to meet the above range. The time that the PVA film is in contact with the heat treatment roller is preferably more than 1 second, more preferably more than 2 seconds. The time in contact with the heat treatment roller is preferably less than 60 seconds, more preferably less than 30 seconds.

The PVA film thus produced is further subjected to humidity conditioning treatment, cutting of both ends (edges) of the film, etc. as required, and is wound into a roll on a line of paper (line of paper) or a cylindrical core, and is moisture-proof packaged to form a product.

The volatility of the PVA film finally obtained by the above series of treatments is not necessarily limited. The volatility of the PVA film is preferably 1% by mass or more, more preferably 2% by mass or more. The volatility of the PVA film is preferably 5% by mass or less, more preferably 4% by mass or less.

<Method for producing optical film>

The PVA film of the present invention is used as a raw material film when manufacturing an optical film. As optical films, polarizing films, viewing angle improvement films, phase difference films, brightness enhancement films, etc. can be exemplified, and the PVA film of the present invention can be suitably used as a raw material film when manufacturing a polarizing film. Hereinafter, as an example of a method for manufacturing an optical film, a method for manufacturing a polarizing film is listed and described in detail.

The polarizing film can be generally manufactured by using a PVA film as a raw material film and undergoing treatment steps such as a swelling step, a dyeing step, a cross-linking step, a stretching step, and a fixing step. Specific examples of the treatment liquid used in each step include a swelling treatment liquid used in a swelling treatment, a dyeing treatment liquid (dyeing liquid) used in a dyeing treatment, a cross-linking treatment liquid used in a cross-linking treatment, a stretching treatment liquid used in a stretching treatment, a fixing treatment liquid used in a fixing treatment, and a cleaning treatment liquid (cleaning liquid) used in a cleaning treatment.

The following is a description of the various processing steps that can be used in the manufacturing method for manufacturing a polarizing film. It should be noted that in the manufacturing method of the polarizing film, one or more of the following processing steps can be omitted, the same processing step can be performed multiple times, and other processing steps can be performed simultaneously.

(Cleaning treatment before swelling treatment)

Before the PVA film is subjected to a swelling treatment, it is preferred to perform a cleaning treatment on the PVA film. By performing such a cleaning treatment before the swelling treatment, the anti-blocking agent attached to the PVA film can be removed, and the various treatment liquids in the manufacturing process of the polarizing film can be prevented from being contaminated by the anti-blocking agent. The cleaning treatment is preferably performed by immersing the PVA film in a cleaning treatment liquid, or by blowing the cleaning treatment liquid onto the PVA film. As a cleaning treatment liquid, water, for example, can be used. The temperature of the cleaning treatment liquid is preferably in the range of 20 to 40°C. By setting the temperature of the cleaning treatment liquid to above 20°C, it is easy to remove the anti-blocking agent attached to the PVA film. In addition, by setting the temperature of the cleaning treatment liquid to below 40°C, it is possible to prevent a portion of the surface of the PVA film from dissolving, the films from sticking to each other, and the handling properties from being reduced. The temperature of the cleaning treatment liquid is more preferably above 22°C, further preferably above 24°C, and particularly preferably above 26°C. In addition, the temperature of the cleaning treatment liquid is more preferably below 38°C, further preferably below 36°C, and particularly preferably below 34°C.

(Swelling treatment)

The swelling treatment can be carried out by immersing the PVA film in a swelling treatment solution such as water. The temperature of the swelling treatment solution is preferably above 20°C, more preferably above 22°C, and further preferably above 24°C. As the temperature of the swelling treatment solution, it is preferably below 40°C, more preferably below 38°C, and further preferably below 36°C. In addition, the time of immersion in the swelling treatment solution is, for example, preferably above 0.1 minutes, and more preferably above 0.5 minutes. The time of immersion in the swelling treatment solution is, for example, preferably below 5 minutes, and more preferably below 3 minutes. It should be noted that the water used as the swelling treatment solution is not limited to pure water, and can be an aqueous solution in which various components such as boron-containing compounds are dissolved, or a mixture of water and an aqueous medium. The type of boron-containing compound is not particularly limited, and from the viewpoint of handleability, boric acid or borax is preferred. When the swelling treatment solution contains a boron-containing compound, from the viewpoint of improving the stretchability of the PVA film, the concentration of the boron-containing compound is preferably below 6% by mass.

(Dyeing treatment)

The dyeing treatment can be carried out using an iodine-based dye as a dichroic dye, and the dyeing timing can be any stage before the stretching treatment, during the stretching treatment, or after the stretching treatment. The dyeing treatment is preferably carried out by using a solution containing iodine-potassium iodide (suitably an aqueous solution) as a dyeing treatment liquid, and immersing the PVA film in the dyeing treatment liquid. The concentration of iodine in the dyeing treatment liquid is preferably in the range of 0.005 to 0.2% by mass, and potassium iodide/iodine (mass) is preferably in the range of 20 to 100. The temperature of the dyeing treatment liquid is preferably above 20°C, more preferably above 25°C. The temperature of the dyeing treatment liquid is preferably below 50°C, more preferably below 40°C. Boric acid and other boron-containing compounds may be contained in the dyeing treatment liquid as a cross-linking agent. It should be noted that if the PVA film used as the original material film contains a dichroic dye in advance, the dyeing treatment can be omitted. In addition, the PVA film used as the original material film may also contain boric acid, borax and other boron-containing compounds in advance.

(Cross-linking treatment)

When manufacturing a polarizing film, for the purpose of making the dichroic dye firmly adsorbed on the PVA film, it is preferred to perform a cross-linking treatment after the dyeing treatment. The cross-linking treatment can be performed by using a solution containing a cross-linking agent (suitably an aqueous solution) as a cross-linking treatment liquid and immersing the PVA film in the cross-linking treatment liquid. As a cross-linking agent, one or more boron-containing compounds such as boric acid and borax can be used. If the concentration of the cross-linking agent in the cross-linking treatment liquid is too high, there is a tendency that the cross-linking reaction is excessively carried out, and it is difficult to fully stretch in the subsequent stretching treatment. In addition, if it is too little, there is a tendency that the effect of the cross-linking treatment is reduced. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and more preferably 2% by mass or more. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and more preferably 5% by mass or less.

In order to suppress the dissolution of dichroic dyes from the PVA film after dyeing, the cross-linking treatment liquid may contain iodine-containing compounds such as potassium iodide. If the concentration of the iodine-containing compound in the cross-linking treatment liquid is too high, although the reason is unclear, there is a tendency for the heat resistance of the resulting polarizing film to decrease. In addition, if it is too little, there is a tendency for the effect of suppressing the dissolution of dichroic dyes to decrease. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

If the temperature of the crosslinking treatment liquid is too high, the polarizing film obtained by eluting the dichroic dye tends to be easily unevenly dyed. In addition, if it is too low, the effect of the crosslinking treatment is sometimes reduced. The temperature of the crosslinking treatment liquid is preferably 20°C or more, more preferably 22°C or more, and further preferably 25°C or more. The temperature of the crosslinking treatment liquid is preferably 45°C or less, more preferably 40°C or less, and further preferably 35°C or less.

In each of the above-mentioned treatments and between the treatments, the PVA film can be stretched differently from the stretching treatment described later. By performing this stretching (pre-stretching), wrinkles can be prevented from forming on the surface of the PVA film. From the viewpoint of the polarization performance of the resulting polarizing film, the total stretching ratio of the pre-stretching (the ratio obtained by multiplying the stretching ratio in each treatment) is preferably 4 times or less, more preferably 3.5 times or less, based on the original length of the PVA film of the original material before stretching. From the viewpoint of the polarization performance of the resulting polarizing film, the total stretching ratio of the pre-stretching is preferably 1.5 times or more based on the original length of the PVA film of the original material before stretching. The stretching ratio in the swelling treatment is preferably 1.1 times or more, more preferably 1.2 times or more, and further preferably 1.4 times or more. The stretching ratio in the swelling treatment is preferably 3 times or less, more preferably 2.5 times or less, and further preferably 2.3 times or less. The stretching ratio in the dyeing treatment is preferably 2 times or less, more preferably 1.8 times or less, and further preferably 1.5 times or less. The stretching ratio in the dyeing treatment is preferably 1.1 times or more. The stretching ratio in the crosslinking treatment is preferably 2 times or less, more preferably 1.5 times or less, and further preferably 1.3 times or less. The stretching ratio in the crosslinking treatment is preferably 1.05 times or more.

(Stretching treatment)

The stretching process can be carried out by either a wet stretching method or a dry stretching method. In the case of a wet stretching method, a solution containing a boron-containing compound such as boric acid (suitable for an aqueous solution) can be used as a stretching treatment liquid, and it can be carried out in the stretching treatment liquid, or it can be carried out in a dyeing treatment liquid or a fixing treatment liquid described later. In addition, in the case of a dry stretching method, a PVA film after water absorption can be used and carried out in the air. Among these, a wet stretching method is preferred, and uniaxial stretching is more preferably carried out in an aqueous solution containing boric acid. In the case where the stretching treatment liquid contains a boron-containing compound, from the aspect of being able to improve the stretchability of the PVA film, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 1.5% by mass or more, more preferably 2.0% by mass or more, and further preferably 2.5% by mass or more. In the case where the stretching treatment liquid contains a boron-containing compound, from the aspect of being able to improve the stretchability of the PVA film, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 7% by mass or less, more preferably 6.5% by mass or less, and further preferably 6% by mass or less.

The stretching treatment liquid preferably contains an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching treatment liquid is too high, the hue of the resulting polarizing film tends to be obviously bluish. In addition, if it is too low, although the reason is unclear, there is a tendency for the heat resistance of the resulting polarizing film to decrease. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 2% by mass or more, more preferably 2.5% by mass or more, and further preferably 3% by mass or more. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 8% by mass or less, more preferably 7.5% by mass or less, and further preferably 7% by mass or less.

If the temperature of the stretching treatment liquid is too high, the PVA film tends to dissolve and become soft and easy to break. In addition, if it is too low, the stretchability tends to decrease. The temperature of the stretching treatment liquid is preferably 50°C or more, more preferably 52.5°C or more, and more preferably 55°C or more. The temperature of the stretching treatment liquid is preferably 70°C or less, more preferably 67.5°C or less, and more preferably 65°C or less. It should be noted that the preferred range of the stretching temperature when the stretching treatment is performed by the dry stretching method is also as described above.

Regarding the stretching ratio in the stretching treatment, it is preferably 1.2 times or more, more preferably 1.5 times or more, and further preferably 2 times or more, from the viewpoint of being able to obtain a polarizing film with better polarization performance when it is high. In addition, from the viewpoint of the polarization performance of the obtained polarizing film, the total stretching ratio (the ratio obtained by multiplying the stretching ratio in each step) including the stretching ratio of the above-mentioned pre-stretching is preferably 5.5 times or more, more preferably 5.7 times or more, and further preferably 5.9 times or more, from the viewpoint of the original length of the PVA film of the raw material before stretching. The upper limit of the stretching ratio is not particularly limited, but if it is too high, stretching fracture is likely to occur, and therefore, it is preferably 8 times or less.

The method of stretching by uniaxial stretching is not particularly limited, and uniaxial stretching in the length direction and transverse uniaxial stretching in the width direction can be used. In the case of manufacturing a polarizing film, uniaxial stretching in the length direction is preferred from the viewpoint of obtaining a polarizing film with excellent polarization performance. Uniaxial stretching in the length direction can be performed using a stretching device having a plurality of rollers parallel to each other, and by changing the circumferential speed between the rollers.

In the present invention, the maximum stretching speed (%/min) during the stretching treatment by uniaxial stretching is not particularly limited, and is preferably 200%/min or more, more preferably 300%/min or more, and further preferably 400%/min or more. Here, the maximum stretching speed means that when the PVA film is stretched in two or more stages using three or more rollers with different circumferential speeds, the stretching speed is the fastest in this stage. It should be noted that when the stretching treatment of the PVA film is carried out in one stage without being divided into two or more stages, the stretching speed in this stage becomes the maximum stretching speed. In addition, the stretching speed refers to the increase in the length of the PVA film increased by stretching relative to the length of the PVA film before stretching per unit time. For example, a stretching speed of 100%/min means: the speed at which the PVA film is deformed from the length before stretching to twice the length in 1 minute. The greater the maximum stretching speed, the faster the PVA film can be stretched (uniaxial stretching) at a high speed, and as a result, the productivity of the polarizing film is improved, so it is preferred. On the other hand, if the maximum stretching speed becomes too high, excessive tension may be applied to a part of the PVA film during the stretching process (uniaxial stretching) of the PVA film, and stretching breakage may occur easily. From this point of view, the maximum stretching speed is preferably not more than 900%/min.

(Fixed processing)

When manufacturing a polarizing film, in order to make the dichroic dye firmly adsorbed on the PVA film, it is preferably fixed. The fixing treatment can be carried out by using a solution containing one or more boron-containing compounds such as boric acid and borax (suitably an aqueous solution) as a fixing treatment liquid, and immersing the PVA film (suitably a PVA film after stretching treatment) in the fixing treatment liquid. In addition, as needed, the fixing treatment liquid may also contain iodine-containing compounds and metal compounds. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 2% by mass or more, more preferably 3% by mass or more. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 15% by mass or less, more preferably 10% by mass or less. The temperature of the fixing treatment liquid is preferably 15°C or more, more preferably 25°C or more. The temperature of the fixing treatment liquid is preferably 60°C or less, more preferably 40°C or less.

(Cleaning after dyeing)

After the dyeing treatment, the PVA film after the stretching treatment is preferably subjected to a cleaning treatment. The cleaning treatment is preferably carried out by immersing the PVA film in a cleaning treatment solution, or by blowing the cleaning treatment solution onto the PVA film. As the cleaning treatment solution, for example, water can be used. Water is not limited to pure water, and can contain iodine-containing compounds such as potassium iodide. It should be noted that the cleaning treatment solution can contain a boron-containing compound, in which case the concentration of the boron-containing compound is preferably 2.0 mass % or less.

The temperature of the cleaning treatment liquid is preferably in the range of 5 to 40°C. By setting the temperature to 5°C or higher, the breakage of the PVA film caused by freezing of water can be suppressed. In addition, by setting the temperature to 40°C or lower, the optical properties of the obtained polarizing film are improved. The temperature of the cleaning treatment liquid is more preferably 7°C or higher, and further preferably 10°C or higher. In addition, the temperature of the cleaning treatment liquid is more preferably 38°C or lower, and further preferably 35°C or lower.

As a specific method for manufacturing a polarizing film, a method of subjecting a PVA film to dyeing treatment, stretching treatment, crosslinking treatment and/or fixing treatment can be cited. As a preferred example, a method of subjecting a PVA film to swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment (especially uniaxial stretching treatment), and cleaning treatment can be cited. In addition, the stretching treatment can be performed in any treatment process before the above process, or it can be performed in multiple stages of two or more stages.

The polarizing film can be obtained by drying the PVA film after the above-mentioned treatments. The drying method is not particularly limited, and examples thereof include a contact method in which the film is brought into contact with a heating roller, a method in which the film is dried in a hot air dryer, and a floating method in which the film is dried by hot air while floating.

<Polarizing Film, Polarizing Plate>

The polarizing film of the present invention is applied to both sides or one side of the polarizing film with optically transparent and mechanically strong protective films to prepare a polarizing plate for suitable use. As the protective film, a triacetate cellulose (TAC) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, etc. can be used. In addition, as the adhesive for pasting, PVA-based adhesives, urethane-based adhesives, etc. can be listed, among which PVA-based adhesives are suitable.

The polarizing plate obtained as described above can be used as a component of LCD by applying an acrylic adhesive or the like and then laminating it to a glass substrate. A retardation film, a viewing angle improvement film, a brightness enhancement film, etc. may also be laminated at the same time.

Example

The present invention will be specifically described by the following examples, but the present invention is not limited to these examples at all. It should be noted that the measurement methods used in the following examples, comparative examples and reference examples are shown below.

<Quantification of Crystalline Component Amount (A1), Bound Amorphous Component Amount (A2), and Amorphous Component Amount (A3)>

The sample (100 mg) obtained from the PVA film obtained in the following examples or comparative examples was cut into a size of about 5 mm × 5 mm and placed in an NMR tube with an inner diameter of 10 mm. Next, a 3% by mass boric acid heavy aqueous solution was prepared as a measurement solvent, and 500 μL of the measurement solvent was supplied to the NMR tube containing the sample. After that, after being kept at 30°C or 50°C for 30 minutes, the pulse NMR measurement of the sample was performed under the following conditions to obtain a relaxation curve.

(Pulse NMR measurement conditions)

Measuring device: NMR Analyzer mq20 the mini spec

(Made by BRUKER)

Pulse series: Solid-Eco method

Pulse amplitude: 7.22μs

Pulse repetition time: 1s

Dummy Shoot: 0

Pulsed Atten: 0dB

Cumulative times: 300 times

Measuring temperature: 30℃ or 50℃

Gain: 70~110dB (adjusted according to the observation intensity of the sample)

The obtained relaxation curve was fitted using the above method to obtain the crystalline component (A1), bound amorphous component (A2) and amorphous component (A3) of the PVA film. At this time, after keeping it still at 30°C for 30 minutes, pulse NMR measurement was performed, and the crystalline component (A1), bound amorphous component (A2) and amorphous component (A3) obtained from the relaxation curve thus obtained were set to (A1) _30°C , (A2) _30°C and (A3) _30°C , respectively. In addition, after keeping it still at 50°C for 30 minutes, pulse NMR measurement was performed, and the crystalline component (A1), bound amorphous component (A2) and amorphous component (A3) obtained from the relaxation curve thus obtained were set to (A1) _50°C , (A2) _50°C and (A3) _50°C , respectively. Then, (A2) _50°C /(A2) _30°C and (A2) _50°C /(A1) _50°C were calculated based on the obtained values.

<Measurement of Swelling Degree of PVA Film>

A test piece of about 1.5 g is cut out from the PVA film obtained from the following examples or comparative examples. Next, the test piece is immersed in 1000 g of distilled water at 30°C. After immersion for 30 minutes, the test piece is taken out, and after absorbing the water on the surface with filter paper, its mass (We) is measured. Next, the test piece is placed in a hot air dryer, and after drying at 105°C for 16 hours, its mass (Wf) is measured. Based on the obtained masses We and Wf, the swelling degree of the PVA film is calculated using the following formula.

Swelling degree (%) = (We/Wf) × 100

<Evaluation of tensile fracture during high-speed tensile test>

The tensile fracture during high-speed stretching was evaluated based on the number of fractures of the PVA film during the manufacture of the polarizing film in the following examples or comparative examples. That is, the maximum stretching speed of the uniaxial stretching in the stretching process during the manufacture of the polarizing film was set to high speed (600%/min), and the number of fractures of the PVA film within 60 minutes was evaluated as "A" if it was 0 times, "B" if it was 1 time, "C" if it was 2 times, and "D" if it was 3 times or more.

[Example 1]

100 parts by mass of PVA (99.9 mol% saponification, 2400% polymerization), 10 parts by mass of glycerol as a plasticizer, 0.1 parts by mass of lauric acid diethanolamide as a surfactant, and 217.6 parts by mass of water were melt-mixed using a melt extruder to prepare a film-making stock solution (volatile fraction of 66% by mass). Next, the film-making stock solution was filtered with a 270-mesh mesh filter and then sprayed from a T-die head onto a support (surface temperature of 98°C) to form a film, thereby forming a PVA film on the support. On the support, hot air with a dew point of 14 degrees and a temperature of 98°C was blown onto the entire surface of the PVA film that was not in contact with the support at a speed of 5 m/s to dry it, thereby obtaining a PVA film (water content of 32% by mass). Next, the PVA film is peeled off from the support, and after further drying between the first drying roller and the final drying roller (the 19th drying roller) located directly in front of the heat treatment roller in a manner that one side and the other side of the PVA film alternately contact each drying roller, it is peeled off from the final drying roller. At this time, the surface temperature of each drying roller from the first drying roller to the final drying roller is set to 75°C. Furthermore, the PVA film is peeled off from the final drying roller, and heat-treated in a manner that one side and the other side of the PVA film alternately contact each heat treatment roller. At this time, the heat treatment is carried out using two heat treatment rollers, the surface temperatures of the heat treatment rollers are all set to 108°C, and the contact time between the PVA film and the heat treatment roller is set to 12 seconds. In this way, a PVA film with a thickness of 30μm (width of 1200mm) is obtained.

The obtained PVA film was cut into 650 mm width, and the film was subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, cleaning treatment, and drying treatment in sequence to continuously manufacture a polarizing film. The swelling treatment was performed by uniaxially stretching the film to 2.00 times in the length direction while immersing it in pure water (swelling treatment liquid) at 25°C. The dyeing treatment was performed by uniaxially stretching the film to 1.26 times in the length direction while immersing it in a potassium iodide/iodine water-soluble dyeing solution (dyeing treatment liquid) (potassium iodide/iodine (mass ratio) = 23, iodine concentration of 0.03-0.05 mass %) at a temperature of 32°C. In the dyeing treatment, the iodine concentration in the dyeing treatment liquid was adjusted in the range of 0.03-0.05 mass % so that the monomer transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment was in the range of 43.5%±0.2%. The cross-linking treatment is performed by uniaxially stretching to 1.19 times in the length direction while immersing in a 32°C boric acid aqueous solution (cross-linking treatment liquid) (boric acid concentration of 2.6 mass%). The stretching treatment is performed by uniaxially stretching to 2.00 times in the length direction while immersing in a 55°C boric acid/potassium iodide aqueous solution (stretching treatment liquid) (boric acid concentration of 2.8 mass%, potassium iodide concentration of 5 mass%). The maximum stretching speed of the uniaxial stretching in the stretching treatment is 600%/min. The cleaning treatment is performed by immersing in a 22°C potassium iodide/boric acid aqueous solution (cleaning treatment liquid) (potassium iodide concentration of 3-6 mass%, boric acid concentration of 1.5 mass%) for 12 seconds without stretching.

(Examples 2 to 4, Comparative Examples 1 and 2)

The PVA film was manufactured and evaluated in the same manner as in Example 1 except that the manufacturing conditions of the PVA film (the size of the mesh of the mesh filter, the surface temperature of the support, the hot air temperature on the surface not in contact with the support, the hot air dew point on the non-contact surface, the temperature of the heat treatment roller, the thickness of the film, etc.) were changed as shown in Table 1. The results are shown in Table 1.

The above results show that the PVA film of the present invention can suppress breakage during uniaxial stretching even when the maximum stretching speed is set to a high speed (600%/min) during uniaxial stretching when producing an optical film such as a polarizing film.

Claims (8)

1. A polyvinyl alcohol film wherein the amount of bound amorphous component calculated from the relaxation curve obtained by pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 50 ℃ is set to (A2) _50℃ ，

The bound amorphous component calculated from the relaxation curve obtained by pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 30℃was set as (A2) _30℃ In the time-course of which the first and second contact surfaces,

(A2) _50℃ relative (A2) _30℃ Ratio ((A2) _50℃ /(A2) _30℃ ) 0.20 to 0.65.

2. The polyvinyl alcohol film according to claim 1, wherein the (A2) _50℃ Is not more than 15 and is not more than,

the amount of the crystal component calculated from the relaxation curve obtained by pulse NMR measurement in a 3% by mass boric acid heavy aqueous solution at 50℃was set to A1 _50℃ In the time-course of which the first and second contact surfaces,

(A2) _50℃ relative (A1) _50℃ Ratio ((A2) _50℃ /(A1) _50℃ ) 0.60 to 1.6.

3. The polyvinyl alcohol film according to claim 1 or 2, having a swelling degree of 170 to 220%.

4. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the polyvinyl alcohol contained in the polyvinyl alcohol film has a polymerization degree of 2,000 to 2,700.

5. The polyvinyl alcohol film according to any one of claims 1 to 4, which is a raw film for producing an optical film.

6. The polyvinyl alcohol film according to claim 5, wherein the optical film is a polarizing film.

7. A polarizing film produced using the polyvinyl alcohol film according to claim 6.

8. A polarizing plate comprising a protective film attached to at least one side of the polarizing film according to claim 7.