TW202212433A - Polyvinyl alcohol film and method for manufacturing optical film in which same is used - Google Patents

Abstract

Provided are a PVA film with which it is possible to manufacture an optical film that has exceptional optical performance and low shrinkage stress at high temperature, and a method for manufacturing an optical film in which such a PVA film is used. In this polyvinyl alcohol film, the crystal long period Ds derived from small-angle X-ray scattering measurement performed in a water/methanol mixed solvent (volume ratio: 2/8) and the crystal long period Da derived from small-angle X-ray scattering measurement performed before immersion in the mixed solvent satisfy the expression 0.3 ≤ (Ds-Da)/Da < 0.5.

Description

Polyvinyl alcohol film and method for producing optical film using the same

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

The polarizer, which has the functions of penetrating and shielding light, is the basic component of a liquid crystal display (LCD) along with the liquid crystal that changes the polarization state of light. Polarizing plates are usually manufactured by applying a dyeing step, an extension step (uniaxial extension step) to a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA"), and further utilizing boron as needed After the polarizing film is produced in the fixing treatment step of the compound and the like, a protective film such as a triacetate cellulose (TAC) film is attached to the surface of the polarizing film.

LCDs are used in a wide range of small devices such as computers and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measuring instruments used indoors and outdoors. In response to the high performance of LCDs in recent years, high performance is also required for the polarizing plate, which is a component of the LCD. Specifically, a polarizing plate that has more excellent optical properties and is also excellent in dimensional stability at high temperature is required. Therefore, a polarizing film used for a polarizing plate is also required to have more excellent optical properties (polarizing properties) and a small shrinkage stress at high temperature.

However, in polarizing films, it is not easy to improve optical properties (polarization properties) on the one hand and reduce shrinkage stress at high temperature. This is because: Usually, the polarizing performance of polarizing film and shrinkage stress are in a trade-off relationship. That is, if the polarization performance of the polarizing film is to be improved, the shrinkage stress becomes large, and if the shrinkage stress is to be reduced, the polarization performance decreases.

Patent Document 1 describes that by using a PVA film containing PVA having an average degree of polymerization of 2,500 to 3,500 and using a predetermined crosslinking and stretching step, a polarizing film excellent in polarizing performance and small in shrinkage stress can be obtained. However, even if a polarizing film is produced by the method described in Patent Document 1, it is difficult to balance the polarization performance and shrinkage stress of the polarizing film obtained due to the film-forming conditions of the PVA film. room for improvement.

On the other hand, Patent Document 2 describes that by using a PVA film in which the long period determined by the small-angle X-ray scattering method and the thickness of the amorphous portion are within a specific range, polarization properties (degree of polarization, single It has excellent in-plane uniformity and corresponds to large-area and high-definition polarizing films. In addition, Patent Document 3 describes that by using a PVA film having a crystal long period in water within a specific range, a polarizing film having a high absorbance in a long wavelength region and a high degree of polarization can be produced. However, in Patent Documents 2 and 3, the shrinkage stress of the polarizing film is not considered, and it goes without saying that both the polarization performance and the shrinkage stress of the polarizing film are not considered. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2017-142347 [Patent Document 2] Japanese Patent Laid-Open No. 2006-188655 [Patent Document 3] WO2013/146147

[The problem to be solved by the invention]

Then, the objective of this invention is to provide the PVA film which can manufacture the optical film which is excellent in optical performance and the shrinkage stress at high temperature is small, and the manufacturing method of the optical film using such a PVA film. [means to solve the problem]

As a result of earnestly examining the crystal structure before and after the swelling of the PVA film, especially the change in the crystal long period, the inventors found that the amount of change in the crystal long period before and after the PVA film was immersed in a water/methanol mixed solvent was significantly different from that before the immersion. The ratio of the crystal long period to a specific range, and an optical film with excellent optical properties and low shrinkage stress at high temperature can be obtained. And based on this knowledge, the present invention was completed by further research.

That is, the present invention relates to the following [1] to [7]. [1] A PVA thin film obtained from the crystal long period Ds obtained by small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8), and a PVA film immersed in the mixed solvent The crystal long period Da obtained by the small-angle X-ray scattering measurement previously performed satisfies the following formula. 0.3≦(Ds-Da)/Da＜0.5 [2] The PVA thin film according to [1], wherein the crystal long period Da is 10.0 to 12.5 nm. [3] The PVA film according to [1] or [2], wherein the PVA contained in the PVA film contains ethylene units in an amount of 1 to 8 mol %. [4] The PVA film according to any one of [1] to [3], wherein the average thickness of the film is 15 to 60 μm. [5] The PVA film according to any one of [1] to [4], which is a blank film for optical film production. [6] A method for producing an optical film, wherein the PVA film according to any one of [1] to [5] is uniaxially stretched. [7] The method for producing an optical film according to [6], comprising a swelling step of swelling a PVA film. [Effect of invention]

According to the present invention, it is possible to provide a PVA film capable of producing an optical film having excellent optical properties and low shrinkage stress at high temperature, a method for producing an optical film using such a PVA film, and an optical film.

[Form for carrying out the invention]

The present invention will be specifically described below.

＜PVA film＞ (Small angle X-ray scattering measurement) The PVA film of the present invention is obtained from the crystal long-period Ds obtained by the small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8), and from the crystal long period Ds obtained before being immersed in the mixed solvent. The crystal long period Da obtained by the small-angle X-ray scattering measurement satisfies the formula of 0.3≦(Ds−Da)/Da<0.5.

In the small-angle X-ray scattering measurement, when a sample is irradiated with X-rays, X-rays are diffracted by X-ray scattering or interference by electrons around atoms. In particular, the structure of the sample to be measured can be evaluated by analyzing the diffraction occurring in the low-angle region of 2θ<10° or less, and it is generally considered that the structure with a size of several nanometers to several tens of nanometers can be evaluated. For example, the crystal long period (average value of the distance between crystals randomly existing in the polymer) of the sample to be measured can be evaluated.

Generally, when X-rays are incident on regularly arranged substances, the X-rays are scattered. Scattered X-rays interfere with each other and are constructive in specific directions. According to Bragg's law, when d is the distance between gratings, θ is the Bragg angle, and λ is the wavelength of X-rays, the scattering is observed only in the direction that satisfies the Bragg's law of 2d·sinθ=nλ Diffraction X-rays caused.

In the PVA film, there are crystalline parts (layered crystals) in which the molecular chains of PVA are folded, and amorphous parts in which the molecular chains of PVA are unfolded and released. Furthermore, in the present invention, the average value of the inter-crystal distances between crystal parts (layered crystals) is regarded as the crystal long period. The crystal long period can be determined from the diffraction peak of the scattering curve obtained by measuring the small-angle X-ray scattering of the PVA film. Furthermore, it is generally known that when the PVA film is a blank film for optical film production, the diffraction peak derived from the long period of the crystal appears in the vicinity of 0.5 nm ^-1 in the scattering spectrum q(nm ^-1 ).

(Calculation of crystal long period) In the present invention, a PVA film to be measured by small-angle X-ray scattering is prepared as follows, and used as a measurement sample. First, the PVA film to be measured is cut into several pieces with a size of 2 cm×1 cm without distinction between the width direction (TD direction) and the mechanical flow direction (MD direction). After the cut PVA film was stored for 24 hours under the conditions of a temperature of 20° C. and a humidity of 65%, 10 sheets were laminated in a measurement cell, and used as a measurement sample. Here, the crystal long period Da obtained from the scattering curve obtained when the measurement sample was subjected to small-angle X-ray scattering measurement in air (temperature 20°C, humidity 65%) was the crystal long period Da. Also, after immersing in a water/methanol mixed solvent (volume ratio: 2/8) for 24 hours, the PVA film cut into several pieces in the same manner was 2 cm×1 cm, and then 10 sheets were stacked in the measurement tank filled with the mixed solvent, as Assay samples. Here, the crystal long period obtained from the scattering curve obtained when the measurement sample is subjected to small-angle X-ray scattering measurement is the crystal long period Ds, which will be described later.

In the preparation of the measurement sample, a Kapton film with a thickness of 7.5 μm was used as the window material on the incident light side and the reflection light side in the measurement cell, and the interval between the window materials was set to about 1.5 mm. With such a structure, the measurement sample can be sealed in the measurement tank. Moreover, by using this measurement tank, the PVA thin film of a measurement object can be arrange|positioned in this mixed solvent by the arrangement|positioning of the normal measurement in the following measurement apparatus.

In the present invention, the small-angle X-ray scattering measurement is performed by a nanoscale X-ray structure evaluation apparatus "Nano Viewer" (manufactured by Rigaku Co., Ltd.). The measurement conditions are as follows.

Penetration assay X-ray: CuKα line Wavelength: 0.15418nm Output: 40kV-20mA The first slit: φ0.4mm The second slit: φ0.2mm The third slit: φ0.45mm Detector: Semiconductor 2-dimensional detector PILATUS-100K (measurement area = 33.5×83.8mm) Pixel size: 0.172mm corner Lens length: 1004.51mm Beam interceptor diameter: 4mm X-ray exposure time: 1 hour Measurement mode: normal measurement Ambient temperature: room temperature (20℃)

In the small-angle X-ray scattering measurement of the PVA film, since the scattering from devices such as slits, the air in the part where the X-ray passes, and the solvent inside the tank overlap with the scattering from the PVA film, it is necessary to use these scattering as the background for correction. . Therefore, the scattering intensity of the above-mentioned background calculated separately is subtracted from the scattering intensity obtained by measuring the measurement sample for correction. Furthermore, from the scattering intensity image of the small-angle X-ray scattering measured by the 2D detector, the scattering intensity relative to the scattering spectrum q(nm ^-1 ) is integrated in the azimuth direction, and the scattering spectrum q(nm ^-1 ) is derived. ) and the one-dimensional profile of the scattering intensity I(q) to obtain the scattering curve.

As described above, in the small-angle X-ray scattering measurement of the PVA thin film, diffraction peaks derived from the crystal long period of the PVA thin film appeared in the scattering curve, and the scattering spectrum q (nm ^-1 ) was around 0.5 nm ^-1 . In the present invention, the crystal long period Ds and the crystal long period Da are calculated from the value of the scattering spectrum q (nm ^-1 ) at the top of the diffraction peak. Here, the top of the peak is in the range of the scattering spectrum q(nm ^-1 ) being 0.2 or more and 1.0 or less, and the scattering curve becomes an upwardly convex inflection point (see FIG. 1 ).

The formula for obtaining the crystal long period Ds and the crystal long period Da from the value of the scattering spectrum q (nm ^-1 ) obtained above is as follows. Crystal long period (nm)=2π/q

In the present invention, the crystal long-period Ds obtained from the small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8) is different from the small crystal long period Ds obtained before immersion in the mixed solvent. It is important that the crystal long period Da obtained by the angle X-ray scattering measurement satisfies the formula of 0.3≦(Ds−Da)/Da<0.5.

Here, (Ds-Da)/Da means the increase rate of the crystallization long period before and after immersion in a water/methanol mixed solvent (volume ratio: 2/8). The crystal dissolution state at the initial stage of swelling when the PVA film is immersed in water can be evaluated by performing small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8). (Ds-Da)/Da (hereinafter sometimes referred to as "the increase rate of the crystal long period") is preferably less than 0.5, more preferably less than 0.4. The ratio of (Ds-Da)/Da is preferably 0.3 or more, more preferably 0.32 or more. When the increase rate of the crystal long period is too large, the distance between the layered crystals in the PVA film tends to widen because the PVA film is swelled by a solvent such as water in the swelling step in the production of the optical film. That is, it is considered that in the amorphous portion between the layered crystals existing in the PVA thin film, the interaction between the molecular chains of PVA tends to be small. As a result, the stretching stress applied to the PVA film cannot sufficiently contribute to the alignment of the molecular chains of PVA in the stretching step in the production of the optical film, and the optical properties of the obtained optical film may be lowered. On the other hand, when the increase rate of the crystal long period is too small, it is considered that the amorphous part in the PVA film is less likely to be swelled by a solvent such as water in the swelling step when producing an optical film. That is, in the stretching step in the production of the optical thin film, the layered crystals in the PVA thin film are difficult to dissolve and the stretching stress tends to concentrate on the crystal part. As a result, the molecular chains of PVA are not sufficiently aligned in the amorphous portion in the PVA film, and the optical properties and shrinkage stress of the obtained optical film may not be compatible.

In the present invention, the crystal long period Da of the PVA thin film obtained from the small-angle X-ray scattering measurement performed before immersion in a water/methanol mixed solvent (volume ratio: 2/8) is 10.0 nm or more. good. In addition, the crystal long period Da is preferably 12.5 nm or less. Here, the crystal long-period Da is obtained by performing small-angle X-ray scattering measurement in air (temperature 20°C, humidity 65%) before being immersed in a water/methanol mixed solvent (volume ratio: 2/8). The lower limit of the crystal long period Da is preferably 11.0 nm. The upper limit of the crystal long period Da is preferably 12.3 nm. When the crystal long period Da is less than 10.0 nm, it is estimated that the thickness of the layered crystal in the PVA thin film is a small crystal structure. When the thickness of the layered crystals is small, the microcrystals of the layered crystals in the PVA film are easily dissolved when the PVA film is immersed in a solvent such as water in the swelling step in the production of an optical film. As a result, the PVA film becomes soft, and there is a possibility that wrinkles are likely to be generated in the PVA film in the swelling step. On the other hand, when the crystal long period Da is larger than 12.5 nm, the thickness of the layered crystals in the PVA thin film is estimated to be large, or the distance between the layered crystals is long and the crystal structure has many amorphous parts. In the former case, the layered crystals in the PVA film are not sufficiently dissolved in the swelling step in the production of the optical film, and the stretching tension of the PVA film tends to be high in the stretching step in the production of the optical film. As a result, there exists a possibility that the shrinkage stress of the optical film obtained may become high. In the latter case, when the PVA film is immersed in a solvent such as water in the swelling step at the time of producing the optical film, the amorphous part in the PVA film tends to take in water. As a result, the PVA film becomes soft, the stretching tension of the PVA film becomes low in the stretching step at the time of producing the optical film, and the optical properties of the obtained optical film may become insufficient.

In the present invention, the crystal long period Ds obtained from the small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8) is preferably 12.0 nm or more. In addition, the crystal long period Ds is preferably 18.0 nm or less. The lower limit of the crystal long period Ds is preferably 13.0 nm. The upper limit of the crystal long period Ds is preferably 17.0 nm. If the crystal long period Ds is larger than 18.0 nm, when the PVA film is immersed in a solvent such as water in the swelling step during the production of an optical film, the molecular chain of PVA tends to widen, and the resulting optical film may have poor moisture and heat resistance. Danger. On the other hand, if the crystal long period Ds is less than 12.0 nm, the amorphous part in the PVA thin film may hardly take in water when the PVA thin film is immersed in a solvent such as water in the swelling step during optical thin film production. As a result, the stretching tension of the PVA film in the stretching step at the time of manufacturing the optical film may become high, and the shrinkage stress of the obtained optical film may become high.

In the present invention, the method of adjusting the crystal long period Ds and the crystal long period Da, and controlling the increase rate of the crystal long period to the above-mentioned range, include: (1) By changing the conditions of discharge, drying and heating during film formation The method of controlling and adjusting the crystalline state of PVA; (2) Adjusting the degree of interaction between the molecular chains of PVA and adjusting the amorphous part in the PVA film by the type of PVA (degree of saponification, quality of modification, etc.) (3) A method of adjusting the size of layered crystals by adding a plasticizer, etc.; (4) By adding a cross-linking agent, etc., adjusting the cross-linking structure between the molecular chains of PVA , and the method of adjusting the crystalline state of PVA or the expansion of the amorphous part; and the method of adjusting the combination of these.

When the increase rate of the crystal long period is controlled to the above range by the method of (1) above, the discharge conditions during thin film formation are, for example, such that the volatile matter rate of the film formation stock solution is 10% by mass or more, 40 mass % or less is preferable. In addition, the shear rate at the outlet of the film discharge device is preferably 75 s ^-1 or more and 1000 s ^-1 or less. In addition, the drying conditions at the time of film-forming are preferably 60°C or higher, and preferably 100°C or lower, for example, the surface temperature of the support of the dope-casting film-forming solution. The temperature of the hot air sprayed on the non-contact surface side of the PVA film on the support is preferably 50°C or higher, and preferably 150°C or lower. The temperature of the drying furnace or the average temperature of the drying roll (the average temperature of the surface of the drying roll) is preferably 40°C or higher, preferably 110°C or lower. The heating conditions at the time of forming the film into a film are preferably, for example, the surface temperature of the heat treatment roll being 135° C. or lower.

When the increase rate of the crystallization long period is controlled to the above range by the method of (2) above, the saponification degree of PVA is preferably 85 mol % or more and 95 mol % or less, for example. In addition, the modified mass of PVA (modified ratio of monomers other than polyvinyl alcohol units) is preferably, for example, 0.3 mol % or more and 8 mol % or less.

When the increase rate of the crystallization long period is controlled to the above range by the method of (3) above, the content of the plasticizer is preferably 2 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of PVA . Moreover, as a plasticizer, it is preferable to use ethylene glycol, glycerol, diethylene glycol, and diglycerol.

(PVA) As PVA contained in the PVA film of the present invention, a polymer produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer can be used. Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, and trimethylacetic acid. Vinyl Ester, Vinyl Visadic Acid, etc. Among the above, as the vinyl ester monomer, vinyl acetate is more preferable.

The vinyl ester polymer is not particularly limited, but a polymer obtained by using only one or two or more vinyl ester monomers as a monomer is preferable, and a polymer obtained by using only one vinyl ester monomer as a monomer Things are better. In addition, the vinyl ester polymer may be a copolymer of one or two or more vinyl ester monomers and other monomers that can be copolymerized with one or two or more vinyl ester monomers.

As for the other monomers, ethylene is preferred. That is, the PVA contained in the PVA film of the present invention preferably contains ethylene units. In addition, the content of the ethylene unit is based on the molar number of all the structural units constituting the vinyl ester polymer, and is preferably 1 mol % or more. In addition, the content of the ethylene unit is preferably 8 mol % or less, more preferably 5 mol % or less. The optical properties and shrinkage stress of the obtained optical film can be taken into consideration by the content of the ethylene unit being in the above range. The reason for this is not clear, but it is presumed that the dye in the dyeing step is easily adsorbed to the hydrophobic vinyl units in the PVA film in the dyeing step in the production of the optical film, and is adsorbed by the stretching stress applied to the PVA film. The orientation of the pigment is improved.

Examples of the other monomers include, in addition to ethylene, olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; methyl acrylate, ethyl acrylate, and n-propyl acrylate. , Acrylates such as isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or its salt; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tertiary butyl methacrylate, methyl methacrylate 2-ethylhexyl acrylate, dodecyl methacrylate, octadecyl methacrylate and other methacrylates; acrylamide, N-methacrylamide, N-ethylacrylamide, N,N - Dimethacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid or its salt, acrylamide propyl dimethylamine or its salt, N-methylol acrylamide or its derivatives, etc. Acrylamide derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid or its salt, methacrylamidopropyl methyl dimethylamine or its salts, N-methylol methacrylamide or its derivatives and other methacrylamido derivatives; N-vinylformamide, N-vinylacetamide, N- N-vinylamides such as vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl vinyl ethers such as vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride , vinylidene fluoride and other halogenated vinyl groups; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or anhydrides; Iconic acid or its salts, esters or anhydrides; vinyltrimethoxy Vinylsilyl compounds such as silanes; isopropenyl acetate, etc. In addition, the vinyl ester polymer may have a structural unit derived from one or two or more of the above-mentioned other monomers.

The ratio of the structural units derived from other monomers other than ethylene is not necessarily limited as long as the effect of the present invention is not hindered, but there are also 15 mol % based on the molar number of all the structural units constituting the vinyl ester polymer. The following is preferred, 5 mol % or less is more preferred, 1 mol % or less is further preferred, and 0.1 mol % or less is even more preferred.

The polymerization degree of PVA is not particularly limited, but is preferably 1,000 or more. In addition, the polymerization degree of PVA is preferably 8,000 or less. The degree of polymerization of PVA is more preferably 1,500 or more, and more preferably 2,000 or more, from the viewpoint of improving the optical properties and moisture-heat resistance of the optical film obtained. On the other hand, from the viewpoint of improving the productivity of PVA, the upper limit of the polymerization degree is more preferably 5,000 or less, and more preferably 4,000 or less.

Here, the degree of polymerization means the average degree of polymerization measured according to the description of JIS K 6726-1994. That is, in the present invention, the degree of polymerization (Po) is the limiting viscosity [η] (common/g) measured in water at 30° C. after re-saponifying and purifying the remaining acetic acid groups of PVA, by the following formula to find. Degree of polymerization Po=([η]×10 ⁴ /8.29) ^(1/0.62)

In the present invention, the lower limit of the saponification degree of PVA is preferably 98.7 mol %, more preferably 99.0 mol %, more preferably 99.5 mol %, particularly preferably 99.8 mol %, with 99.9 mol% is preferred. When the degree of saponification is at least the above lower limit, an optical film excellent in optical performance and heat and humidity resistance can be obtained. On the other hand, the upper limit of the saponification degree is not particularly limited, but is preferably 99.99 mol % or less from the viewpoint of the productivity of PVA.

Here, the degree of saponification of PVA refers to the total moles of vinyl alcohol units with respect to the structural units (typically vinyl ester monomer units) that can be converted into vinyl alcohol units by saponification, and the vinyl alcohol units are The proportion of moles (mol%). The degree of saponification of PVA can be measured according to the description of JIS K 6726-1994.

The PVA film of the present invention may contain one type of PVA alone, or may contain two or more types of PVA having different degrees of polymerization, degree of saponification, degree of modification, and the like.

The upper limit of the content ratio of PVA in the PVA film is not particularly limited. On the other hand, the lower limit of the ratio of the content of PVA is preferably 50 mass %, more preferably 80 mass %, and further preferably 85 mass %.

(Plasticizer) The PVA film of the present invention preferably contains a plasticizer. The stretchability of the PVA film can be improved during the stretching step in the production of the optical film by including a plasticizer in the PVA film. As the plasticizer, polyols are preferred. As a polyhydric alcohol, ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. are mentioned. Among these, glycerin is more preferable from the viewpoint of the effect of improving the extensibility. A plasticizer can be used individually by 1 type or in combination of 2 or more types.

The amount of layered crystals or the size of layered crystals can be adjusted by adjusting the content of the plasticizer in the PVA film. Although it also depends on the primary structure of the molecular chain of PVA, the PVA film containing a small amount of plasticizer is easier to crystallize due to heat treatment than the PVA film that does not usually contain a plasticizer. This is presumed to be because the PVA molecules in the PVA film become more mobile with a small amount of the plasticizer, and it becomes easier to adopt a more stable crystal structure in terms of energy. Furthermore, when the crystal growth of the PVA thin film proceeds, the size of the layered crystals in the PVA thin film increases, and the crystal long period Da tends to increase. On the other hand, when the PVA film contains an excessive amount of plasticizer, it becomes easy to inhibit crystal growth. It is presumed that this is because the amount of the plasticizer that interacts with the hydroxyl groups of the PVA molecules increases, and the interaction between the PVA molecules becomes weak. Moreover, when a PVA film contains a plasticizer, the amorphous part in a PVA film becomes easy to take in water, and there exists a tendency for the increase rate of a crystal long period to become large.

From the viewpoint of adjusting the size of the layered crystals in the PVA film to an appropriate range and adjusting the crystal long period Da and the increase rate of the crystal long period, the content of the plasticizer is based on 100 parts by mass of PVA, which is 2 mass parts or more is preferable. In addition, the content of the plasticizer is preferably 20 parts by mass or less with respect to 100 parts by mass of PVA. When the content of the plasticizer is less than 2 parts by mass and more than 20 parts by mass with respect to 100 parts by mass of PVA, the size of the layered crystals in the PVA film tends to be too small. As a result, the crystal long period Da becomes small, and the increase rate of the crystal long period of the PVA thin film may fall outside the predetermined range. The content of the plasticizer is more preferably 5 parts by mass or more, and more preferably 8 parts by mass or more, relative to 100 parts by mass of PVA. In addition, the content of the plasticizer is more preferably 17 parts by mass or less, and more preferably 15 parts by mass or less, with respect to 100 parts by mass of PVA.

(surfactant) The PVA film of the present invention preferably contains a surfactant. The film-forming property of the PVA film is improved by using the film-forming stock solution containing the surfactant to manufacture the PVA film. As a result, while suppressing the occurrence of thickness unevenness of the PVA film, peeling of the PVA film from the metal roll and belt used for film formation becomes easy. When a PVA film is produced from a film-forming stock solution containing a surfactant, the resulting PVA film contains the surfactant.

The type of the surfactant is not particularly limited, but from the viewpoint of the peelability of the PVA film from the metal roll and the belt, etc., an anionic surfactant and a nonionic surfactant are preferred.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecyl benzenesulfonate.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether; and alkyl groups such as polyoxyethylene laurate. Ester type; polyoxyethylene lauryl amino ether and other alkyl amine types; polyoxyethylene lauric acid amide and other alkyl amide types; polyoxyethylene polyoxypropylene ether and other polypropylene glycol ether types; lauric acid diethanolamide , oleic acid diethanolamide and other alkanolamide types; polyoxy allyl phenyl ether and other allyl phenyl ether types, etc.

Surfactant can be used individually by 1 type or in combination of 2 or more types.

When the PVA film contains a surfactant, the lower limit of the content of the surfactant in the PVA film is preferably 0.01 part by mass, more preferably 0.02 part by mass, and 0.05 part by mass relative to 100 parts by mass of PVA portion is further preferred. By making the content of the surfactant more than the above-mentioned lower limit, the film formability and peelability of the PVA film are further improved. On the other hand, the upper limit of the content of the surfactant in the PVA film is preferably 0.5 parts by mass, more preferably 0.3 parts by mass, and more preferably 0.2 parts by mass relative to 100 parts by mass of PVA good. By making content of a surfactant below the said upper limit, it can suppress that a surfactant oozes out to the surface of a PVA film, agglomeration occurs, and handleability falls.

(other additives, etc.) The PVA film of the present invention may further appropriately contain as required: fillers, processing stabilizers such as copper compounds, weathering stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants Agents, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, cross-linking agents, antifungal agents, preservatives, crystallization rate retarders, etc. additive.

The proportion of the total of PVA, plasticizer and surfactant in the PVA film of the present invention is also preferably 80% by mass or more, more preferably 90% by mass or more, and more preferably 95% by mass or more Preferably, 99% by mass or more is a more preferable case. The PVA film of the present invention can be substantially composed of PVA, a plasticizer and a surfactant, and a polarizing film with excellent polarizing performance can be obtained when the PVA film of the present invention is used to manufacture a polarizing film.

(shape, physical properties, etc.) The PVA film of the present invention is a so-called blank film for optical film production, which is used as a material of an optical film. However, the PVA film of the present invention is not limited to those formed in a roll shape.

The average thickness of the PVA film of the present invention is not particularly limited. The lower limit of the average thickness of the PVA film is preferably 1 μm, more preferably 5 μm, further preferably 10 μm, and particularly preferably 15 μm. The breakage of the PVA film can be suppressed in the stretching step at the time of producing the optical film by making the average thickness more than the above-mentioned lower limit. On the other hand, the upper limit of the average thickness is preferably 60 μm, more preferably 50 μm, more preferably 45 μm, and still more preferably 35 μm. The effect of this invention can fully be exhibited by an average thickness being below the said upper limit. In addition, "average thickness" means the average value of the thicknesses measured at arbitrary 5 points (it is the same about the average thickness below).

The PVA film of the present invention may be a single-layer film composed of one PVA layer, or may be a multi-layer film including one PVA layer. However, in the case of using the PVA film of the present invention as a blank film for the production of polarizing films, it is preferable to use a single-layer film. When the PVA film of the present invention is used as the PVA layer of the multilayer film, the lower limit of the average thickness of the PVA layer is preferably 1 μm, more preferably 5 μm, further preferably 10 μm, and particularly preferably 15 μm. The breakage of the PVA film can be suppressed in the stretching step at the time of producing the optical film by making the average thickness more than the above-mentioned lower limit. In addition, the upper limit of the average thickness of the PVA layer is preferably 60 μm, more preferably 50 μm, more preferably 45 μm, and still more preferably 35 μm. The effect of this invention can fully be exhibited by an average thickness being below the said upper limit.

The multilayer film refers to a film having two or more layers. The number of layers of the multilayer film may be 5 or less, or 3 or less. As a multilayer film, the laminated film which has a laminated structure of a base material resin layer and a PVA layer is mentioned. The average thickness of the base resin layer is preferably, for example, 20 μm or more. In addition, the average thickness of the base resin layer is preferably, for example, 500 μm or less. The base resin layer in the multilayer film is preferably one that can be uniaxially stretched together with the PVA layer. As the resin constituting the base resin layer, polyester, polyolefin, or the like can be used. Among them, amorphous polyester is preferable, and polyethylene terephthalate, and a copolymerization component such as isophthalic acid, 1,4-cyclohexanedimethanol, etc., and polyethylene terephthalate are preferably used. Amorphous polyester copolymerized with ethylene formate. An adhesive layer may also be provided between the base resin layer and the PVA layer.

The width of the PVA film of the present invention is not particularly limited, and can be determined according to its application and the like. For example, the lower limit of the width of the PVA film is preferably 3m. Since the lower limit of the width is 3m, it is suitable for the use of LCD TVs and LCD monitors, which have progressed in large screen in recent years. On the other hand, the upper limit of the width of the PVA film is preferably 7 m. By setting the upper limit of the width to 7 m, the stretching treatment (uniaxial stretching treatment) can be efficiently performed when producing optical films such as polarizing films with a practical apparatus.

The degree of swelling of the PVA film of the present invention is preferably 140% or more from the viewpoints of productivity and optical properties of the optical film obtained. In addition, the swelling degree of the PVA film of the present invention is preferably 400% or less. The lower limit of the degree of swelling is more preferably 170%, more preferably 180%, and particularly preferably 190%. In addition, the upper limit of the degree of swelling is more preferably 220%, and more preferably 210%. The swelling degree of the PVA film can be adjusted to a smaller value, for example, by increasing the temperature of the heat treatment of the PVA film.

Here, "swelling degree of PVA film" means the value calculated|required by the following formula. Swelling degree (%)=100×N/M In the formula, N represents the mass (g) of the sample taken from the PVA film after immersing the sample in distilled water at 30° C. for 30 minutes and removing the surface water. M represents the mass (g) of the sample after drying the sample in a dryer at 105°C for 16 hours.

The PVA film of the present invention is generally a substantially unstretched film (non-stretched film, unstretched film). In addition, the in-plane retardation of the PVA film is preferably 100 nm or less, and more preferably 50 nm or less. Usually, an optical film can be obtained by subjecting the PVA film of the present invention to a stretching treatment (uniaxial stretching treatment or biaxial stretching treatment).

According to the PVA film of the present invention, it is possible to manufacture an optical film which is excellent in optical properties and has a small shrinkage stress at high temperature. As an optical film which can be manufactured by the PVA film of this invention, a polarizing film, a retardation film, a viewing angle improvement film, a brightness improvement film etc. are mentioned, and a polarizing film is preferable.

<Manufacturing method of PVA film> In the present invention, the film-forming method of PVA film can be formed by the following method: using a film-forming stock solution obtained by adding solvents, additives, etc. to PVA and making it uniform, and by casting film-forming method, Wet film formation method (discharge into poor solvent), dry and wet film formation method, gel film formation method (the method of obtaining a PVA-based polymer film by extracting and removing the solvent after temporarily cooling and gelling the film formation stock solution) , or a combination of these to form a film; by using an extruder, etc. to obtain the above-mentioned film-making stock solution and extruding it from a T-die etc. to form a film, the melt extrusion film-making method and the blow molding method, etc. any method. Among them, the cast film forming method and the melt extrusion film forming method are preferable because they can obtain a homogeneous film with good productivity. The following will describe the casting method or the melt extrusion method of the PVA film.

When the PVA film is formed by the casting method or the melt extrusion method, the above-mentioned film forming solution is cast in a film form onto a support such as a metal roll and a metal belt, and is removed by heating Solvent, and curing and thin film. The cured film can be peeled off from the support, dried by drying rolls, drying ovens, etc. as needed, further heat-treated as needed, and rolled to obtain a roll-shaped long PVA film.

The crystallization of the film-forming stock solution (hereinafter, sometimes referred to as "PVA film") cast on the support is carried out on the support and during heating and drying in the subsequent drying step. In particular, when the membrane-forming stock solution is heated with a high volatile content (water content), the mobility of the molecular chains of PVA in the membrane-forming stock solution (PVA membrane) increases, and crystallization proceeds. As a result, the amount of layered crystals in the PVA thin film increases, and the crystal long period Da tends to decrease. Here, if the drying rate is too fast, the crystallization of the PVA thin film does not proceed sufficiently, the amount of layered crystals decreases, and the crystal long period Da tends to increase. On the other hand, if the drying rate is too slow, the crystal growth of the PVA film proceeds, the size of the layered crystal becomes larger, and the crystal long period Da tends to become larger. In addition, when the amount of heat applied is too large, the size of the layered crystals in the PVA thin film tends to increase, the crystal long period Da becomes too large, and the increase rate of the crystal long period tends to become too small.

The volatile matter ratio of the film-forming stock solution (the ratio of volatile components such as solvents removed by volatilization and evaporation during film-forming) is preferably 50% by mass or more, more preferably 55% by mass or more. Moreover, the volatile matter ratio of the membrane-forming stock solution is preferably 90 mass % or less, and more preferably 80 mass % or less. When the volatile content rate is less than 50 mass %, the viscosity of the film-forming stock solution may become high, and the film-forming of the PVA film may become difficult. On the other hand, when the volatile matter concentration exceeds 90 mass %, the viscosity becomes low and the uniformity of the thickness of the PVA film is easily impaired.

Here, "the volatile matter ratio of the membrane-forming stock solution" in the present invention means the volatile matter ratio obtained by the following formula. Volatile content of the film-forming solution (mass %)={(Wa-Wb)/Wa}×100 (In the formula, Wa represents the mass (g) of the film forming stock solution, and Wb represents the mass (g) when the film forming stock solution of Wa (g) is dried in an electric heating dryer at 105° C. for 16 hours).

The preparation method of the film-forming stock solution is not particularly limited, for example, a method of dissolving PVA and additives such as plasticizers and surfactants in a dissolving tank (tank) or the like; When melt-kneading PVA in a water-containing state, it is a method of melt-kneading together with a plasticizer, a surfactant, etc., etc.

In the case of film-forming a PVA film by a casting film-forming method or a melt-extrusion film-forming method, the above-mentioned film-forming stock solution is cast from a film-like discharge device to a support body such as a metal roll and a metal belt in a film-like form, and is carried out. By heating and removing the solvent, it is cured and formed into a thin film.

In the PVA film of the present invention, the increase rate of the long period of crystallization before and after immersion in a water/methanol mixed solvent (volume ratio: 2/8) is within a specific range. It is presumed that the increase rate is affected by the degree of entanglement of the molecular chains of PVA in the amorphous portion between the layered crystals in the PVA thin film. Therefore, the increase rate of the long period of crystallization of the PVA film can be controlled by adjusting the shear rate at the outlet of the film-like discharge device where the film-forming stock solution is subjected to strong shearing force. From such a viewpoint, the shear rate at the outlet of the film discharge device is preferably 75 s ^-1 or more, more preferably 100 s ^-1 or more, and even more preferably 125 s ^-1 or more. Moreover, the shear rate at the outlet of the film discharge device is preferably 1000 s ^-1 or less, more preferably 900 s ^-1 or less, and even more preferably 800 s ^-1 or less. When the shear rate is below the above-mentioned upper limit, the increase rate of the crystallization long period can be prevented from becoming too small. On the other hand, the increase rate of the crystal long period can be prevented from becoming too large by making the shear rate more than the above lower limit.

In the present invention, the shear rate at the outlet of the film-like discharge device, in the case of the usual T-die and I-die, refers to the shear rate of the wall surface of the film-forming stock solution flow path in the die lip, and can be calculated by the following formula . γ=6Q/Wh ² Here, γ means the shear rate at the wall surface (s ^-1 ), W means the width of the die lip (cm), h means the opening of the die lip (cm), and Q means The discharge speed of the film-forming stock solution from the die lip (cm ³ /s).

The surface temperature of the support body of the casting solution is preferably 50°C or higher. Moreover, it is preferable that the surface temperature of the support body of a casting film-forming stock solution is 110 degrees C or less. When the surface temperature is lower than 50° C., the time required for drying of the membrane-forming stock solution becomes longer, and the productivity tends to decrease. On the other hand, when the surface temperature is higher than 110° C., there is a tendency that an abnormality is likely to occur on the film surface of the PVA film due to foaming or the like. In addition, the crystallization of the PVA thin film does not proceed sufficiently due to the rapid drying of the film-forming stock solution, and the amount of layered crystals decreases, and the crystal long period Da tends to increase. The surface temperature of the support is preferably 60°C or higher, and more preferably 65°C or higher, from the viewpoint of easily adjusting the increase rate of the crystal long period of the PVA thin film. In addition, the surface temperature of the support is preferably 100°C or lower, more preferably 95°C or lower.

While heating the PVA film on the support, the drying rate may be adjusted by uniformly spraying hot air with a blow velocity of 1 to 10 m/sec over the entire area on the non-contact surface side of the PVA film. The temperature of the hot air blown to the non-contact surface side is preferably 50°C or higher, more preferably 70°C or higher, from the viewpoints of drying efficiency and drying uniformity. In addition, the temperature of the hot air blown to the non-contact surface side is preferably 150°C or lower, more preferably 120°C or lower, from the viewpoints of drying efficiency and drying uniformity.

The PVA film system is preferably dried to a volatile content rate of 5 to 50 mass % on a support, and then peeled off, and further dried as necessary. The drying method is not particularly limited, and examples thereof include a drying oven and a method of contacting a drying roll. When drying with a plurality of drying rolls, it is preferable that one side of the film is alternately contacted with the other side of the drying roll to uniformize both sides. The number of drying rolls is preferably 3 or more, more preferably 4 or more, and further preferably 5 or more. In addition, the number of drying rolls is more preferably 30 or less. The upper limit of 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, more preferably 100°C, more preferably 90°C, and further preferably 85°C. good. If the temperature of the drying furnace or the average temperature of the drying roll is too high, the crystal growth of the PVA film proceeds, and the size of the layered crystals in the PVA film tends to increase. As a result, there is a possibility that the crystal long period Da becomes large and the increase rate of the crystal long period becomes too small. On the other hand, the lower limit of the temperature of the drying furnace or the average temperature of the drying roll is preferably 40°C, more preferably 45°C, and further preferably 50°C. If the temperature of the drying furnace or the average temperature of the drying rolls is too low, the crystal growth of the PVA film tends to be insufficient, and the size of the layered crystals in the PVA film tends to decrease. As a result, the crystal long period Da may become too small, or the increase rate of the crystal long period may become too large.

The dried PVA film can be further heat-treated as needed. The strength, swelling degree, birefringence, etc. of the PVA film can be adjusted by heat treatment. The surface temperature of the heat treatment roll used for heat treatment is preferably 60°C or higher. In addition, the surface temperature of the heat treatment roll is preferably 135°C or lower, more preferably 130°C. If the surface temperature of the heat treatment roll is too high, too much heat is applied, the size of the layered crystals in the PVA film increases, the crystal long period Da becomes too large, or the increase rate of the crystal long period tends to become too small.

The PVA film produced in this way is further subjected to humidity control treatment, cutting of both ends (ears) of the film, etc., as required, and is wound into a roll shape on a cylindrical core, and is packaged in a moisture-proof form to become a product. .

The volatile matter rate of the PVA film finally obtained by the above-mentioned series of treatments is not necessarily limited, but the volatile matter rate of the PVA film is preferably 1 mass % or more, more preferably 2 mass % or more. In addition, the volatile matter ratio of the PVA film is preferably 5 mass % or less, and more preferably 4 mass % or less.

In addition, when the PVA film of the present invention is a multilayer film, the multilayer film can be produced, for example, by applying a film-forming stock solution on the base resin film (base resin layer). At this time, in order to improve the adhesiveness between the PVA layer and the base resin layer, the surface of the base resin film may also be modified, or an adhesive may be coated on the surface of the base resin film.

<Manufacturing method of optical film> The manufacturing method of the optical film of this invention is equipped with the process of uniaxially extending the above-mentioned PVA film. Hereinafter, as an example of the manufacturing method of an optical film, the manufacturing method of a polarizing film is mentioned, and it demonstrates concretely.

As far as the manufacturing method of the polarizing film is concerned, a method having the following steps can be exemplified: a dyeing step for dyeing the PVA film, a stretching step for performing uniaxial stretching, and a swelling step for further swelling the PVA film as required, so that the A crosslinking step for crosslinking, a fixation treatment step for fixing, a washing step for washing, a drying step for drying, a heat treatment step for performing heat treatment, and the like. At this time, the order of each step is not particularly limited, but may be performed in the order of, for example, a swelling step, a dyeing step, a crosslinking step, an extending step, and a fixing treatment step. In addition, one or two or more steps may be performed simultaneously, or each step may be performed twice or more. In particular, the PVA film of the present invention is useful as a film for use in a method for producing a polarizing film having a swelling step because the generation of swelling wrinkles in the swelling step can be suppressed.

The swelling step can be performed by immersing the PVA film in a swelling treatment bath containing water or the like. The temperature of the swelling treatment bath is preferably 20°C or higher, more preferably 22°C or higher, and further preferably 25°C or higher. In addition, the temperature of the swelling treatment bath is preferably 55°C or lower, more preferably 50°C or lower, and even more preferably 45°C or lower. In addition, the time of immersion in the swelling treatment bath is, for example, preferably 0.1 minutes or more, more preferably 0.5 minutes or more. The time of immersion in the swelling treatment bath is preferably, for example, 5 minutes or less, and more preferably 3 minutes or less. In addition, the water used for the swelling treatment bath 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.

The dyeing step can be carried out by contacting the PVA film with a solution (dyeing treatment bath) containing a dichroic dye. As a dichroic dye, an iodine-based dye is usually used. The timing of dyeing can be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. The dyeing treatment bath is preferably a solution containing iodine-potassium iodide, and the solution is preferably an aqueous solution. The concentration of iodine in the dyeing treatment bath is preferably 0.01% by mass or more. In addition, the concentration of iodine is preferably 0.5 mass % or less. The concentration of potassium iodide is preferably 0.01% by mass or more. Moreover, it is preferable that the density|concentration of potassium iodide is 10 mass % or less. In addition, the temperature of the dyeing treatment bath is preferably 20°C or higher, more preferably 25°C or higher. The temperature of the dyeing treatment bath is preferably 50°C or lower, more preferably 40°C or lower. The dyeing time is preferably 0.2 minutes or more. In addition, the dyeing time is preferably 5 minutes or less.

Elution of PVA to water during wet stretching at a high temperature can be effectively suppressed by performing a crosslinking step for crosslinking PVA in the PVA film. From this viewpoint, the crosslinking step is preferably performed after the dyeing step and before the extension step. The cross-linking step can be performed by dipping the PVA film in an aqueous solution (cross-linking treatment bath) containing a cross-linking agent. As a crosslinking agent, one type or two or more types of boron compounds, such as boric acid salts, such as boric acid and borax, can be used. The concentration of the crosslinking agent in the crosslinking treatment bath is preferably 1 mass % or more, more preferably 1.5 mass % or more, and even more preferably 2 mass % or more. Moreover, as for the density|concentration of a crosslinking agent, 15 mass % or less is preferable, 7 mass % or less is more preferable, and 6 mass % or less is further more preferable. The extensibility of the PVA film can be sufficiently maintained by the concentration of the cross-linking agent being within the above-mentioned range. The crosslinking treatment bath may contain potassium iodide or the like. The temperature of the crosslinking treatment bath is preferably 20°C or higher, more preferably 25°C or higher. In addition, the temperature of the crosslinking treatment bath is preferably 60°C or lower, more preferably 55°C or lower. The PVA film can be efficiently cross-linked by making the temperature within the above-mentioned range.

The stretching step of uniaxially stretching the PVA film can be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution (stretching treatment bath) containing boric acid, in the above-mentioned dyeing treatment bath, or in the fixing treatment bath described later. In addition, in the case of the dry stretching method, stretching may be performed at room temperature (25° C.), stretching may be performed while heating, or it may be performed in air using a PVA film after water absorption. Among these, from the viewpoint of being able to stretch with high uniformity in the width direction, the wet stretching method is more preferable, and the uniaxial stretching in the stretching treatment bath is more preferable. The concentration of boric acid in the stretching bath is preferably 0.5 mass % or more, more preferably 1.0 mass % or more, and even more preferably 1.5 mass % or more. Moreover, the boric acid concentration in the stretching bath is preferably 6.0 mass % or less, more preferably 5.0 mass % or less, and even more preferably 4.0 mass % or less. In addition, the stretching bath may contain potassium iodide, and the concentration of potassium iodide is preferably 0.01 mass % or more. Moreover, it is preferable that the density|concentration of potassium iodide is 10 mass % or less. The stretching temperature in uniaxial stretching is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher. In addition, the stretching temperature in uniaxial stretching is preferably 90°C or lower, more preferably 80°C or lower, and even more preferably 75°C or lower.

The stretching ratio in uniaxial stretching (the total stretching ratio calculated from the non-stretched PVA film) is preferably 5 times or more, and more preferably 5.5 times or more, from the viewpoint of the polarization performance of the obtained polarizing film. good. The upper limit of the stretching ratio is not particularly limited, but the stretching ratio is preferably 8 times or less.

The maximum elongation stress of the PVA film in uniaxial stretching is preferably below 50N/ ^mm2 , preferably below 25N/ ^mm2 , further preferably below 15N/ ^mm2 , and below 10N/ ^mm2 Excellent. Here, the maximum stretching stress is a value obtained by dividing the stretching tension of the PVA film applied between the adjacent rolls in the stretching treatment bath by the cross-sectional area of the PVA film. At this time, the stretching tension of the PVA film can be measured by the tension roll provided between the adjacent rolls in the stretching treatment bath, and when three or more rolls are used in the stretching treatment bath, the largest value among them is used, and the PVA The cross-sectional area of the film was obtained from the unstretched PVA film before the production of the polarizing film. By reducing the maximum elongation stress, a polarizing film with a small shrinkage stress can be obtained. In addition, the maximum elongation stress is usually 1 N/mm ² or more.

The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching in the longitudinal direction and lateral uniaxial stretching can be employed. From the viewpoint of obtaining a polarizing film with excellent polarization performance, it is preferable to extend uniaxially in the longitudinal direction. Uniaxial stretching in the longitudinal direction can be performed by using a stretching device including a plurality of rolls parallel to each other, and changing the peripheral speed between the rolls. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

When producing a polarizing film, in order to make the adsorption of a dichroic dye (iodine-based dye, etc.) to the PVA film firm, a fixing treatment step may be performed after the stretching step. As the fixation treatment bath used for fixation treatment, an aqueous solution containing one or two or more kinds of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound to a fixed process bath as needed. The concentration of the boron compound in the fixed treatment bath is preferably 2 mass % or more, more preferably 3 mass % or more. Moreover, it is preferable that the density|concentration of the boron compound in a stationary process bath is 15 mass % or less, and it is more preferable that it is 10 mass % or less. By making the concentration of the boron compound within the above range, the adsorption of the dichroic dye can be made stronger. The temperature of the fixed treatment bath is preferably 15°C or higher, more preferably 25°C or higher. In addition, the temperature of the fixing treatment bath is preferably 60°C or lower, more preferably 40°C or lower.

The washing step is usually performed by immersing the film in distilled water, pure water, aqueous solution, or the like. In this case, it is preferable to use an aqueous solution (washing treatment bath) containing an iodide such as potassium iodide as an auxiliary agent from the viewpoint of improving the polarization performance of the obtained polarizing film. The concentration of the iodide is preferably 0.5% by mass or more. Moreover, it is preferable that the density|concentration of iodide shall be 10 mass % or less. In addition, the temperature of the cleaning treatment bath is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. In addition, the temperature of the cleaning treatment bath is preferably 50°C or lower, more preferably 45°C or lower, and even more preferably 40°C. By making the temperature of the cleaning treatment bath into the above-mentioned range, the polarization performance of the obtained polarizing film can be further improved.

The conditions of the drying step are not particularly limited, but the drying temperature of the PVA film is preferably 30°C or higher, more preferably 50°C or higher. In addition, the drying temperature of the PVA film is preferably 150°C or lower, more preferably 130°C or lower. By drying at a temperature within the above range, a polarizing film excellent in dimensional stability at high temperature can be easily obtained.

In addition, optical films other than polarizing films such as retardation films can also be produced by a method including a step of uniaxially extending the PVA film of the present invention. For a specific production method, a conventionally well-known method can be adopted except that the PVA film of the present invention is used.

When the optical film of the present invention is a polarizing film, the dichroic ratio (R) of the polarizing film is preferably 100 or more. The dichroic ratio (R) is more preferably 150 or more, and more preferably 160 or more. The dichroic ratio (R) is, for example, preferably 350 or less, and more preferably 300 or less.

The calculation method of the dichroic ratio (R) of the polarizing film is as follows. First, the relationship between the transmittance (T') excluding surface reflection and the transmittance (T) of the monomer is represented by the following formula (a). At this time, the refractive index of the polarizing film was set to 1.5, and the reflectance on the surface was set to 4%. On the other hand, the relationship between the transmittance (T'), the degree of polarization (V) and the dichroic ratio (R) is represented by the following formula (b). Therefore, after measuring the single transmittance (T) and the degree of polarization (V), the dichroic ratio of the polarizing film can be calculated by solving the following formulas (a) and (b) by using these values (R). T'=T/(1-0.04) ²・・・(a) R={-ln[T'(1-V)]}/{-ln[T'(1+V)]}・・・( b)

The degree of polarization (V) at a predetermined single transmittance (T) can be calculated from the dichroic ratio (R) of the polarizing film. First, the transmittance (T') at a predetermined monomer transmittance (T) is obtained from the above formula (a). Then, by unraveling the transmittance (T') and the dichroic ratio (R) and substituting them into the following formula (c), which is a modification of the above formula (b), the predetermined monomer permeability can be obtained. Degree of polarization (V) at transmittance (T). In the present invention, by this method, the degree of polarization (V) when the transmittance (T) of the polarizing film alone is 44.0% is obtained. T'=[1-V] ^1/(R-1) /[1+V] ^R/(R-1)・・・(c)

The polarizing film obtained as described above is usually used as a polarizing plate by bonding an optically transparent and mechanically strong protective film on both sides or one side thereof. As the protective film, triacetate cellulose (TAC) film, cycloolefin polymer (COP) film, cellulose acetate-butyrate (CAB) film, acrylic film, polyester film, etc. can be used. Moreover, PVA-type adhesive agent, a urethane-type adhesive agent, an acrylate-type ultraviolet curable adhesive agent etc. are mentioned as an adhesive agent for bonding. That is, the polarizing plate has a polarizing film and a protective film laminated directly or via an adhesive layer on one side or both sides of the polarizing film.

For example, the polarizing plate can be used as a part of the LCD by being attached to a glass substrate after coating an adhesive such as acrylic. In addition, the polarizing plate can be further attached with retardation film, viewing angle enhancement film, brightness enhancement film, etc. [Example]

The present invention will be specifically described below with reference to Examples and the like, but the present invention is not limited by the following Examples. In addition, the evaluation items and methods used in the following Examples and Comparative Examples are as follows.

(1) Crystal long period Ds and Da of the PVA film For the PVA films obtained in the following examples and comparative examples, small-angle X-ray measurements were performed before and after immersion in a water/methanol mixed solvent (volume ratio: 2/8). . Specifically, first, the PVA film was cut into several pieces with a size of 2 cm×1 cm without distinction between the width direction (TD direction) and the mechanical flow direction (MD direction). After the cut PVA film was stored for 24 hours under the conditions of a temperature of 20° C. and a humidity of 65%, 10 sheets were laminated in the measurement tank, and used as measurement samples. Small-angle X-ray scattering measurement was performed on the measurement sample in air (temperature 20°C, humidity 65%) to obtain a scattering curve. From the value of the scattering spectrum q (nm ^-1 ) at the peak top of the scattering curve, the crystal long period Da was obtained as follows. Crystal long period Da(nm)=2π/q

In addition, the PVA films obtained in the following Examples and Comparative Examples were cut into several pieces with a size of 2 cm×1 cm without distinction between the width direction (TD direction) and the machine flow direction (MD direction). The cut PVA film was immersed in a water/methanol mixed solvent (volume ratio: 2/8) for 24 hours, and then 10 sheets were stacked in a measurement tank filled with the mixed solvent to obtain a measurement sample. Small-angle X-ray scattering measurement was performed on the measurement sample to obtain a scattering curve. From the value of the scattering spectrum q(nm ^-1 ) at the peak top of the scattering curve, the crystal long period Ds was determined as follows. Crystal long period Ds(nm)=2π/q

(2) Swelling degree of PVA film By the aforementioned method, the degree of swelling of the PVA films obtained in the following Examples and Comparative Examples was determined.

(3) Production of polarizing film Polarizing films were produced using the PVA films obtained in the following Examples and Comparative Examples. First, the PVA film was stretched 2.0 times in the MD direction in pure water at 25°C (swelling treatment bath), and then added to a 32°C aqueous solution (dyeing treatment bath) containing 0.03 mass % of iodine and 0.7 mass % of potassium iodide (dyeing treatment bath). It stretched so that the total stretching ratio became 2.4 times. Next, it was stretched in an aqueous solution (crosslinking treatment bath) at 32°C containing 2.6% by mass of boric acid so that the total stretching ratio was 3.0 times, and further at 58°C containing 2.8% by mass of boric acid and 5.0% by mass of potassium iodide. The stretching was performed in an aqueous solution (stretching treatment bath) until the total stretching ratio became 6.0 times. Next, it was immersed for 5 seconds in an aqueous solution (washing treatment bath) containing 1.5 mass % of boric acid and 2.5 mass % of potassium iodide at 22° C., and dried for 4 minutes in an 80° C. drying furnace.

(4) Maximum elongation stress of PVA film in the production of polarizing film In the production of the above polarizing film, the stretching tension of the PVA film applied between the adjacent rolls in the stretching treatment bath is measured with the tension roll set therebetween, and divided by the cross-sectional area of the PVA film to obtain the value. as the maximum extensional stress. At this time, the cross-sectional area of the PVA film was obtained from the unstretched PVA film before the production of the polarizing film.

(5) Optical properties of polarizing film From the center portion of the obtained polarizing film in the width direction (TD direction), a rectangular measurement sample of 4 cm in the mechanical flow direction (MD direction) of the polarizing film and 1.5 cm in the width direction (TD direction) was taken. For this measurement sample, using a spectrophotometer with integrating sphere (“V7100” manufactured by JASCO Corporation), according to JIS Z8722 (measurement method of object color), the luminous factor in the visible light region of C light source and 2° field of view is carried out After correction of the luminosity factor, the transmittance of the monomer and the degree of polarization were measured. By the above-mentioned method, the degree of polarization of the single transmittance of 44.0% was calculated.

(6) Shrinkage stress of polarizing film at high temperature The shrinkage stress was measured using Autograph AG-X with thermostatic bath by Shimadzu Corporation. In the measurement, a polarizing film (15 cm in the length direction, 1.5 cm in the width direction) that has been dehumidified at 20°C/20% RH for 18 hours is attached to a jig (the interval between the jigs is 5 cm), and the temperature of the thermostatic bath is started at the same time as the stretching is started. to 80°C. The polarizing film was stretched at a speed of 1 mm/min, the stretching was stopped when the tension reached 2 N, and the tension was measured until 4 hours later in this state. At this time, the distance between the clamps will change due to the thermal expansion of the shaft, so stick a marking sticker on the fixture, use the video extensometer TR ViewX120S, and use the marking sticker attached to the fixture to move how much you can correct it How much distance between fixtures is measured. In addition, the value obtained by subtracting the initial tension 2N from the measured value of the tension after 4 hours was set as the shrinkage force of the polarizing film, and the value divided by the cross-sectional area of the sample was defined as shrinkage stress (N/mm ² ).

<Example 1> A membrane-forming stock solution with a volatile content rate of 73% by mass was prepared, which contained 100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400) obtained by saponifying polyvinyl acetate as a plasticizer 14 parts by mass of glycerin, 0.1 part by mass of diethanolamide laurate as a surfactant, and water. The membrane-forming stock solution obtained by filtration was discharged from the T-die in the form of a film at a shear rate of 207 s ⁻¹ onto the support (surface temperature of 90° C.), and on the support, the entire non-contact surface with the support was Dry by blowing hot air at 85°C at a speed of 5m/sec. Next, it was peeled from the support, and the PVA film was further dried from the first drying roll to the final drying roll (19th drying roll) immediately before the heat treatment roll so that one side and the other side of the PVA film alternately contacted the drying rolls. , peeled off from the final drying roll. At this time, the average value of the surface temperature of each drying roll from the first drying roll to the final drying roll was 70°C. Finally, after heat-treating with the heat-processing roll of the surface temperature of 104 degreeC, it wound up in roll shape, and obtained the PVA film (thickness 45 micrometers, width 3.3m).

As a result of small-angle X-ray scattering measurement of the obtained PVA film, the crystal long period Da was 12.6 nm, the crystal long period Ds was 16.8 nm, and the increase rate of the crystal long period was 0.33. In addition, as a result of measuring the degree of swelling of the PVA film, it was 197%.

Furthermore, a polarizing film was produced using the obtained PVA film. At this time, the maximum elongation stress was 9.0 N/mm ² . As a result of measuring the optical properties of the obtained polarizing film, it was calculated that the monomer transmittance was 43.8%, the polarization degree was 99.935%, and the polarization degree when the monomer transmittance was 44.0% was 99.873%. In addition, as a result of measuring the shrinkage stress of the polarizing film, it was 43.7 N/mm ² .

<Example 2, Example 3, and Comparative Examples 1 to 4> A PVA film was obtained in the same manner as in Example 1, except that the type of PVA, the amount of plasticizer, and the production conditions were changed as shown in Table 1. In addition, in Table 1, the ethylene reformation in which the content of the ethylene unit is 3 mol% is abbreviated as "ΔEt3".

Table 1 shows the evaluation results of the obtained PVA film and polarizing film. Moreover, about the polarizing films obtained in Examples 1-3 and Comparative Examples 1-3, the graph which plotted the degree of polarization at the monomer transmittance of 44.0% versus shrinkage stress is shown in FIG. 2 . In addition, since the PVA film of Comparative Example 4 was dissolved in distilled water at 30°C, the degree of swelling could not be measured. Moreover, since the PVA film of the comparative example 4 melt|dissolved in the pure water (swelling process bath) of 25 degreeC, it was not able to manufacture a polarizing film.

[Table 1] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 PVA modification No modification No modification ΔEt3 No modification No modification ΔEt3 No modification degree of aggregation 2400 2400 2400 2400 2400 2400 1700 Saponification degree [mol%] 99.9 99.2 99.5 99.9 99.9 99.9 88 Plasticizer [mass%/PVA] 14 12 12 9 12 12 20 Manufacturing conditions Volatile rate [mass %] 73 66 66 73 66 66 64 Shear speed [s ^-1 ] 207 207 207 207 405 405 207 Support body temperature [℃] 90 85 85 90 85 85 80 Average temperature from the first drying roll to the final drying roll [°C] 70 61 61 55 61 61 75 Heat treatment roll temperature [℃] 104 110 105 110 110 109 75 Crystal long period Da[nm] 12.6 12.0 12.2 12.1 13.5 12.8 14.5 Ds[nm] 16.8 16.6 16.2 14.5 16.4 16.1 23.7 Increase rate (Ds-Da)/Da 0.33 0.38 0.33 0.20 0.21 0.26 0.63 Film physical property swelling degree [%] 197 205 202 195 202 197 Unable to measure Maximum extensional stress [N/mm ² ] 9.0 8.8 11.7 9.8 9.3 12.3 - Optical properties monomer transmittance [%] 43.8 44.2 44.1 44.1 43.9 43.8 - Degree of polarization [%] 99.935 99.751 99.889 99.831 99.899 99.957 - The degree of polarization [%] with a transmittance of 44.0% of the monomer 99.873 99.866 99.922 99.877 99.861 99.912 - Shrinkage stress [N/mm ² ] 43.7 40.9 48.4 50.2 46.0 60.4 -

It can be seen from Table 1 and FIG. 2 that the polarizing film produced from the PVA film of the present invention has excellent optical properties and small shrinkage stress at high temperature.

1: Peak of the scattering curve 2: Auxiliary line when setting the scattering spectrum q at the peak of the scattering curve 3: The scattering spectrum q at the peak of the scattering curve

[ Fig. 1 ] A reference diagram when the scattering spectrum q (nm ^-1 ) of the peak top is set in the scattering curve obtained by the small-angle X-ray scattering measurement. [ Fig. 2] Fig. 2 is a graph obtained by plotting the degree of polarization at a monomer transmittance of 44.0% versus shrinkage stress for the polarizing films obtained in Examples 1 to 3 and Comparative Examples 1 to 3. [Fig.

Claims (7)

A polyvinyl alcohol film obtained from the crystal long-period Ds obtained by small-angle X-ray scattering measurement in a water/methanol mixed solvent (volume ratio: 2/8), and obtained from before immersion in the mixed solvent The crystal long period Da obtained by the small-angle X-ray scattering measurement satisfies the following formula; 0.3≦(Ds-Da)/Da<0.5. The polyvinyl alcohol film according to claim 1, wherein the crystal long period Da is 10.0-12.5 nm. The polyvinyl alcohol film of claim 1 or 2, wherein the polyvinyl alcohol contained in the polyvinyl alcohol film contains ethylene units, and the content thereof is 1-8 mol %. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the average thickness of the film is 15-60 μm. The polyvinyl alcohol film according to any one of claims 1 to 4, which is a blank film for optical film production. A method for producing an optical film, wherein the polyvinyl alcohol film according to any one of claims 1 to 5 is uniaxially stretched. The method for producing an optical film according to claim 6, which comprises a swelling step of swelling the polyvinyl alcohol film.

Images