CN101778888B - Polyvinyl alcohol film - Google Patents

Abstract

A wide polyvinyl alcohol film which is effective in producing a high-performance polarizing film reduced in optical unevenness caused by dyeing unevenness or stretching unevenness. The polyvinyl alcohol film is one formed from a film-forming raw liquid containing a polyvinyl alcohol polymer and a plasticizer. In a TD area in the film, the maximum difference (Ry) between the plasticizer contents in the film and the average content is 2% or smaller. The film has a plasticizer-content trough/crest curve regarding TD content fluctuations which has an average distance (Sm) of 5 cm or longer.

Description

Polyvinyl alcohol film

Connected application

This application claims the priority of Japanese Patent Application No. 2007-213444 filed in Japan on August 20, 2007, the whole of which is referred to and incorporated as a part of this application.

technical field

The present invention relates to a polyvinyl alcohol-based film having uniform quality over a large area.

Background technique

A polarizing plate having a light-transmitting and shielding function is a basic constituent element of a liquid crystal having a light-converting function and a liquid crystal display (LCD).

The field of application of this LCD has expanded from small devices such as calculators and watches at the beginning of development to personal computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal TVs, car navigation systems, mobile phones, and indoor and outdoor devices in recent years. A wide range of measuring equipment, etc. In particular, in the fields of monitors, televisions, etc., the increase in screen size of liquid crystal displays is rapidly progressing, and polarizing plates excellent in uniformity of optical performance are required even in larger areas than conventional ones.

Polarizers are generally dyed with iodine or a dichroic dye after uniaxially stretching a polyvinyl alcohol-based film, or uniaxially stretched after dyeing to make a dyed uniaxially stretched film, which is then coated with a boron compound. The method of performing fixation treatment, or the method of performing fixation treatment with a boron compound at the same time as the above-mentioned uniaxial stretching and dyeing treatment, etc. to manufacture polarizing films, and by laminating triacetate cellulose (TAC) on the surface of the polarizing film Film, alicyclic polyolefin (COP) film and other protective films to manufacture polarizers. In order to obtain a polarizer with uniform polarizing performance, the thickness of the polyvinyl alcohol-based film used in its production is uniform, the polyvinyl alcohol-based film is uniformly dyed, and a protective film that does not cause spots is attached to the surface of the polarizing film, etc. is important, but more importantly, the polyvinyl alcohol-based film has uniform quality.

Contents of the invention

In order to cope with the increase in screen size of liquid crystal displays in the fields of monitors, televisions, etc., it is necessary to manufacture polarizing films using wide-width polyvinyl alcohol-based films. However, only making the polyvinyl alcohol-based film wide-width corresponds, compared with the case of using a narrow-width polyvinyl alcohol-based film, only the result of forming a noticeable optical spot on the obtained polarizing film is caused. Therefore, there is a problem that the area of the polarizing film that can be used is significantly reduced, and the yield as a polarizing film product is extremely reduced.

In addition, the optical spot referred to here is a general term for optically uneven spots that can be observed on a polarizing film, and in particular refers to a fine spot-like spot with a size of about 1 cm. Such optical spots are useful for monitoring The display quality of monitors and TVs may degrade. Most of them are caused by non-uniform dyeing and stretching of the polyvinyl alcohol-based film. That is, when a polyvinyl alcohol-based film is dyed with an iodine solution or a dichroic dye solution, dyeing unevenness occurs due to uneven dyeing, thereby causing the polarizing film to have uneven light transmittance and cannot be used for displays. In addition, when stretching a polyvinyl alcohol-based film, if there are parts with different thicknesses or elastic moduli in the TD direction of the film, it cannot be stretched uniformly, causing problems in the light transmittance and polarization of the polarizing film. fluctuations, and cause an extreme decrease in the yield of polarizing films usable for display applications.

In order to eliminate the disadvantages of polyvinyl alcohol-based films used to manufacture polarizing films, it is known that the thickness irregularity in the TD direction of the film is 12% or less (Patent Document 1), and the thickness variation in the TD direction of the film is 0.5 μm/mm or less ( Patent Document 2), the phase difference between two points at a distance of 1 cm in the TD direction of the film is 5 nm or less (Patent Document 3), the hot water cut-off temperature spot in the TD direction of the film is 1.5 °C or less (Patent Document 4), and in the film The ratio (S _M /S _T ) of the stretched length (S _M ) in the MD direction to the stretched length (S _T ) in the TD direction is 0.7 to 1.3 (Patent Document 5), etc., so that the structural irregularities of the polyvinyl alcohol-based film or Anisotropy reduction method.

However, even with these methods, there are still optical spots that cannot be eliminated in the polarizing film, and the present situation cannot fully satisfy the demand for providing a polarizing film that can correspond to a larger screen of a liquid crystal display.

Also, even when using an optical polyvinyl alcohol film (Patent Document 6), which is characterized in that the difference between the maximum value and the minimum value of the plasticizer concentration in the width direction of the film is 1% or less, although the variation of large spots can be suppressed, However, it was not possible to suppress the occurrence of the above-mentioned fine spot-like spots of about 1 cm.

The prior art document information related to the invention of this application is as follows.

Patent Document 1: Japanese Patent Laid-Open No. 2001-323077 (Claims)

Patent Document 2: Japanese Patent Laid-Open No. 2002-31720 (Claims)

Patent Document 3: Japanese Patent Laid-Open No. 2002-28938 (Claims)

Patent Document 4: Japanese Patent Laid-Open No. 2002-30163 (Claims)

Patent Document 5: Japanese Patent Laid-Open No. 2002-30164 (Claims)

Patent Document 6: Japanese Patent Laid-Open No. 2004-20630 (Claims)

An object of the present invention is to provide a polyvinyl alcohol-based film having a uniform quality with few fine optical spots in a large area.

As a result of intensive research by the present inventors to achieve the above object, it was found that a polyvinyl alcohol-based film formed from a film-forming stock solution containing a polyvinyl alcohol-based polymer and a plasticizer, and found that in the polyvinyl alcohol-based film In the TD direction (direction perpendicular to the film running direction (MD)), the maximum content difference (Ry) with respect to the average value of the plasticizer content contained in the film is 2% or less, and in the TD of the plasticizer content A polyvinyl alcohol-based film in which the average interval (Sm) of unevenness in the direction of variation is 5 cm or more, and finally completed the present invention.

The polyvinyl alcohol-based film of the present invention (hereinafter referred to simply as "PVA-based film") preferably has a ratio (Rye /Ryc) is not less than 0.8 and not more than 1.3.

In addition, in the PVA-based film of the present invention, it is preferable that the ratio (Sme/Smc) of the average interval (Sme) of the fluctuation amount unevenness in the film edge to the average interval (Smc) of the fluctuation amount unevenness in the film center is 0.7 or more. , Below 1.4.

In addition, here, the so-called film central portion refers to the range extending from 25% to the total of 50% from the center point of the total width of the TD direction of the film to the left and right, and the so-called film end portion refers to the range at the total width of the film. the rest of the range.

The PVA-based film of the present invention preferably has a width of 2 m or more.

Moreover, this invention also includes the manufacturing method of a polyvinyl-alcohol-type film. The above production method comprises: a stock solution preparation step of preparing a film-forming stock solution from a polyvinyl alcohol-based polymer, a plasticizer, and a solvent; mixing the film-forming stock solution using a mixing device to uniformly mix the polyvinyl alcohol-based polymer and the plasticizer a mixing step; a discharge step of discharging the homogeneously mixed film-forming stock solution from a die to a roll; a drying step of drying the discharged stock solution. In this production method, in the above-mentioned stock solution preparation step, a polyvinyl alcohol-based polymer, a plasticizer, and a solvent may be supplied to an extruder, and these may be kneaded to prepare a film-forming stock solution. In addition, the above-mentioned mixing device can also be selected from at least one of the group consisting of a mixer, a continuous vibrating mixer and a partial homogenizer.

The PVA-based film of the present invention has an excellent feature that the plasticizer is uniformly present in the TD direction. By using such a PVA-based film to produce a polarizing film, even a large area can obtain a polarizing film with less optical spots due to staining or stretching. High performance polarizing film.

The polarizing film obtained in this way exhibits the above-mentioned excellent characteristics, and can be effectively used in the manufacture of calculators, watches, personal computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, mobile phones, and computers for indoor and outdoor use. Polarizers are components of liquid crystal display devices that require high display quality, such as testing equipment.

Description of drawings

The present invention can be understood more clearly from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description only, and should not be used to limit the scope of the present invention.

FIG. 1 is a graph showing a variation curve of the plasticizer content in the TD direction of a PVA-based film. In addition, in this figure, each of Rp, Rv, Ry, and Smi is defined as follows. That is, Rp is the content corresponding to the difference between the average value of the plasticizer content and the peak line at which the plasticizer content is the maximum value in the variation curve, and Rv is the content corresponding to the plasticizer content in the variation curve. The content of the difference between the average value and the valley line where the content of plasticizer is the minimum value, Ry is the sum of Rp and Rv, and Smi is the peak portion exceeding the average value of plasticizer content and the peak portion adjacent to the peak and The interval in the TD direction occupied by the fluctuation amount concavo-convex shape consisting of one valley below the average value.

Detailed ways

Hereinafter, the present invention will be described in detail.

The film-forming stock solution used for film-forming the PVA-based film of the present invention contains a polyvinyl alcohol-based polymer and a plasticizer. Polyvinyl alcohol-based polymers (hereinafter, simply referred to as "PVA-based polymers") are produced, for example, by polymerizing vinyl esters and saponifying the obtained polyvinyl esters. Other PVA-based polymers include, for example, graft-copolymerized unsaturated carboxylic acids or their derivatives, unsaturated sulfonic acids or their derivatives, and α-olefins with 2 to 30 carbon atoms on the main chain of PVA. Modified PVA-based polymers, modified by copolymerizing vinyl esters with unsaturated carboxylic acids or their derivatives, unsaturated sulfonic acids or their derivatives, α-olefins with 2 to 30 carbon atoms, etc. Modified PVA-based polymers produced by saponification of polyvinyl esters, so-called polyvinyl alcohols in which part of the hydroxyl groups of unmodified or modified PVA-based polymers is cross-linked with aldehydes such as formalin, butyraldehyde, and benzaldehyde. Vinyl acetal resin, etc.

Examples of the vinyl esters used in the production of PVA-based polymers include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, and branched-chain alkane carboxylic acid (versatic acid) vinyl ester. , vinyl laurate, vinyl stearate, vinyl benzoate, etc., among them, vinyl acetate is preferable from the viewpoint of productivity.

The above-mentioned comonomers used for the production of the modified PVA-based polymer are mainly copolymerized for the purpose of modifying PVA, so they can be used within a range that does not impair the gist of the present invention. Examples of such comonomers include olefins such as ethylene, propylene, 1-butene, and isobutylene (for example, α-C _2-4 olefins); acrylic acid and its salts; methyl acrylate, ethyl acrylate, acrylic acid Acrylates such as n-propyl, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, octadecyl acrylate (e.g. , acrylate-C _1-6 alkyl ester); methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate Methacrylates such as isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, octadecyl methacrylate, etc. (e.g. , methacrylate-C _1-6 alkyl ester); acrylamide, N-methacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propane sulfonate Acrylamide derivatives such as acid and its salt, acrylamidopropyldimethylamine and its salt, N-methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N -Methyl methacrylamide, methacrylamide propane sulfonic acid and its salts, methacrylamidopropyl dimethylamine and its salts, N-methylol methacrylamide and its derivatives, etc. Acrylamide derivatives; N-vinyl amides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether, ethyl vinyl ether, n-propyl Vinyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Base ethers; nitriles such as acrylonitrile and methacrylonitrile; halogenated vinyls such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.; allyl acetate, allyl chloride, etc. Allyl compounds; derivatives of unsaturated carboxylic acids such as maleic acid and itaconic acid, and their salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate wait. Among them, α-olefins are preferred, and ethylene is particularly preferred. The modification amount of the modified PVA-based polymer is preferably less than 15 mol%, more preferably 5 mol% or less.

The degree of saponification of the PVA-based polymer is preferably 95 in terms of the polarizing performance and durability when the PVA-based film is uniaxially stretched to form a polarizing film, and the polarizing performance and durability of a polarizer made from the polarizing film. mol% or more, more preferably 98 mol% or more, more preferably 99 mol% or more, most preferably 99.3 mol% or more.

The so-called degree of saponification in this specification means the degree of saponification measured according to the method described in JIS K 6726, and among units converted into vinyl alcohol units by saponification, saponified units are actually represented among vinyl alcohol units proportion.

The degree of polymerization of the PVA-based polymer is preferably 1000 in terms of the polarizing performance and durability when the PVA-based film is uniaxially stretched to form a polarizing film, and the polarizing performance and durability of a polarizer produced from the polarizing film. or more, more preferably 1500 or more, particularly preferably 2000 or more. The degree of polymerization of the PVA-based polymer is preferably 8,000 or less, particularly preferably 6,000 or less, from the viewpoints of easiness of producing a homogeneous PVA-based film, elongation, and the like.

The degree of polymerization of the PVA-based polymer in this specification is the degree of polymerization measured in accordance with JIS K 6726, and is obtained from the intrinsic viscosity measured in water at 30°C after re-saponification and purification of the PVA-based polymer.

As a method of producing a PVA-based film using the above-mentioned PVA-based polymer, for example, a melt-extrusion film-forming method in which a PVA-based polymer in a water-containing state is melted and extruded, a PVA-based film obtained by dissolving a PVA-based polymer in a solvent, Polymer solution, casting film method, wet film method (discharging into a poor solvent), gel film method (after temporarily cooling and gelling the PVA-based polymer aqueous solution, extracting and removing the solvent to obtain a PVA-based film methods), and methods of combining them, etc. Among these, the cast film forming method and the melt extrusion film forming method are preferable from the viewpoint of obtaining a good polarizing film.

As a solvent for dissolving the PVA-based polymer used in the manufacture of the PVA-based film, for example, water, water-soluble organic solvents (for example, sulfoxides such as dimethyl sulfoxide; dimethylformamide, dimethylacetamide, etc. amide groups; ethers such as N-methylpyrrolidone; amines such as ethylenediamine and diethylenetriamine), etc., these solvents can be used alone or in combination of two or more. Among them, it is particularly preferable to use dimethyl sulfoxide, water, or a mixed solvent of dimethyl sulfoxide and water.

The concentration of the PVA-based polymer in the PVA-based polymer solution or the PVA-based polymer used in the PVA-based film can also vary according to the degree of polymerization of the PVA-based polymer, and is suitable for 20 to 70% by mass. 25-60 mass % is preferable, and 30-50 mass % is most preferable. When the concentration of the PVA-based polymer is higher than 70% by mass, the viscosity of the PVA-based polymer solution or the PVA-based polymer in a water-containing state becomes too high, and the filtration or defoaming performed during the production of the film-forming stock solution of the PVA-based film will be reduced. Obtaining is difficult, and it tends to be difficult to obtain a PVA-based film without foreign matter or defects. Also, when the concentration of the PVA-based polymer is lower than 20% by mass, the viscosity of the PVA-based polymer solution or the PVA-based polymer in a water-containing state becomes too low, and it may be difficult to manufacture a PVA-based film with the intended thickness. tendency.

A PVA-based polymer solution added with a plasticizer or a PVA-based polymer in a water-containing state can be used as a film-forming stock solution to manufacture the PVA-based film of the present invention. Polyols are preferably used as plasticizers which can be used for this purpose. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like, and these may be used alone or in combination of two or more. Among them, diglycerin, ethylene glycol, and glycerin are preferably used from the viewpoint of enhancing the extensibility effect, and glycerin is most preferably used.

The plasticizer is preferably used in an amount of 1 to 30 parts by mass, more preferably in an amount of 3 to 25 parts by mass, more preferably in an amount of 5 to 20 parts by mass, particularly preferably in an amount of 10 to 20 parts by mass, based on 100 parts by mass of the PVA-based polymer Serving amount. When the amount of the plasticizer is less than 1 part by mass, the dyeability or elongation of the PVA-based film may decrease, and when it is more than 30 parts by mass, the PVA-based film may become too soft and handleability may decrease.

In the film-forming stock solution used to manufacture PVA-based films, it is preferable to add a surfactant in advance. By adding the surfactant, the film-forming property can be improved and the occurrence of thickness spots of the PVA-based film can be suppressed. It is easy to peel off the PVA-based film with a roller or a conveyor belt. The type of surfactant is not particularly limited, but anionic or nonionic surfactants are preferred, and nonionic surfactants are particularly preferred from the viewpoint of releasability of metal rollers, conveyor belts, and the like. Examples of the anionic surfactant include carboxylic acid type such as potassium laurate, sulfate ester type such as octyl sulfate, and sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate. . Examples of nonionic surfactants include alkyl ether types such as polyethylene oxide oleyl ether, alkyl phenyl ether types such as polyethylene oxide octyl phenyl ether, polyethylene oxide surfactants, etc. Alkyl ester type such as alkane laurate, Alkylamine type such as polyethylene oxide lauryl amino ether, Alkylamide type such as polyethylene oxide lauric acid amide, Polyethylene oxide Non-ionic properties such as polypropylene glycol ether type such as polypropylene oxide ether, alkanolamide type such as oleic acid diethanolamide group, and allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether Surfactants are suitable. These surfactants can be used individually or in combination of 2 or more types.

When a surfactant is added to the film-forming stock solution, the amount added is 0.01 to 0.5 parts by mass, preferably 0.02 to 0.3 parts by mass, particularly preferably 0.05 to 0.1 parts by mass, based on 100 parts by mass of the PVA-based polymer. When the amount of the surfactant added is less than 0.01 parts by mass, it may be difficult to express the effect of improving the film-forming and peeling properties due to the addition of the surfactant. On the other hand, when it exceeds 0.5 parts by mass, there may be When the surfactant leaks from the surface of the PVA-based film to cause sticking and reduce handling.

The film-forming stock solution may also contain various additives, such as stabilizers (such as antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers, and antisticking agents, within the range that does not hinder the characteristics of the PVA-based film of the present invention. Bonding agent, flame retardant, antistatic agent, lubricant, dispersant, fluidizing agent, antibacterial agent, etc. These additives can be used individually or in combination of 2 or more types.

In the PVA-based film of the present invention, in the TD direction of the film, the percentage value of the maximum content difference (Ry) relative to the average value of the plasticizer content contained in the film is 2% or less, and in the TD direction of the film In the variation curve of the plasticizer content, the average interval (Sm) of the intervals (Smi) in the TD direction formed by one peak of the variation curve and one valley adjacent to the peak is 5 cm or more. The PVA-based film that satisfies this condition is very uniform in the TD direction due to the content of the plasticizer, and when such a PVA-based film is used to manufacture a polarizing film, it is possible to obtain optical spots caused by dyeing spots or stretch spots. High-performance polarizing film, especially can suppress the occurrence of fine spot-like spots of about 1 cm that cannot be suppressed in conventional large-area PVA films.

In the TD direction, when the maximum content difference (Ry) with respect to the average value of the plasticizer content is more than 2%, when the PVA-based film is swollen during the production of the polarizing film, due to the difference in the degree of swelling of the PVA-based film becomes larger, so staining or stretching spots are produced on the polarizing film. The maximum content difference (Ry) from the average plasticizer content is preferably 1.85% or less, more preferably 1.5% or less, and still more preferably 1% or less.

When the content of the plasticizer fluctuates in the TD direction and the average interval (Sm) of the concavo-convex shapes is less than 5 cm, the occurrence of optical speckles is remarkable because the sharp fluctuation of the stretched speckles occurs in the polarizing film. The average spacing (Sm) of the unevenness of the content of the plasticizer in the TD direction is preferably 6 cm or more, more preferably 7 cm or more, and still more preferably 9 cm or more.

Here, the maximum content difference (Ry) of the plasticizer content in the TD direction and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction can be obtained by the following method. That is, a rectangular (1 cm in the TD direction x 2 cm in the MD direction (lengthwise direction of the film)) sample was taken with an arbitrary width Lcm (20 cm or more) continuously from the end or center of the PVA-based film in the TD direction.

In addition, the values obtained at either the end portion or the central portion may be used as the representative values (Ry) and (Sm) of the film, but it is preferable to use the value obtained at the central portion as the representative value of the film. That is, in other words, the maximum content difference (Ry) of the plasticizer content in the TD direction and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction are sufficient at either the center or the end. It is only necessary to satisfy the value specified in the present invention, but it is particularly preferable that the central portion sufficiently satisfy the value specified in the present invention. In addition, the above-mentioned width L can be selected as desired according to the width of the PVA-based film, but it can be treated as a representative value of 1/10 of the film width.

Each sample obtained above was put into DMSO-d ₆ so that the concentration became about 5% by mass, and the temperature was raised to 90° C. or higher to dissolve in 2 hours. Using 500 MHz, ¹ H-NMR, PD (pulse delay time) 20 seconds , a measurement temperature of 30° C., and a cumulative number of 256 times, the measurement was performed, and the content of the plasticizer in each sample was determined from the obtained NMR spectrum. For example, when glycerin is used as a plasticizer, according to the NMR spectrum obtained by the above measurement, the peaks of the two hydrogen moieties of the methylene group of glycerin are around 3.3 ppm (integrated intensity of the peak is Sg), and that of PVA The peak of the two hydrogen moieties of the methylene group is detected near 1.5 ppm (integrated intensity of the peak is Sp), and the amount of glycerin R (mass %) in the PVA-based film can be calculated using the integrated intensity using the following formula (1) .

R＝(92/44)×(Sg/Sp)×100 (1)

Using the measured values obtained, a curve of variation of the plasticizer content per 1 cm in an arbitrary width (Lcm) in the TD direction is created (Fig. 1), and the plasticizer content is obtained from the following formula (2) The maximum content difference (Ry) in the TD direction.

Ry＝Rp+Rv (2)

In formula (2), Rp represents the content equivalent to the difference between the average value of the plasticizer content and the peak line where the plasticizer content is the maximum value, and Rv represents the difference between the average value of the plasticizer content and the plasticizer content. The content of is the content of the difference between the valley line of the minimum value.

The average interval (Sm) of the amount of variation in the plasticizer content in the TD direction can be determined from the peak above the average value of the plasticizer content in the variation curve (Figure 1) and the peak adjacent to the peak and below the average. The interval (Smi) occupied in the TD direction is obtained for the uneven shape of the amount of fluctuation constituted by one trough each, and is obtained by an arithmetic mean represented by the following formula (3). In addition, when the concave-convex shape is intermittent at both ends of the extraction portion, the intermittent concave-convex shape is not included in the interval (Smi).

$\mathrm{<span\; class="notranslate">\; SM</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; Smi</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the PVA-based film of the present invention, from the viewpoint of obtaining a polarizing film with few optical spots, it is preferable that the maximum content difference (Rye) of the plasticizer content in the end portion of the film is greater than the ratio of the plasticizer content in the central portion of the film. The ratio (Rye/Ryc) of the maximum content difference (Ryc) is 0.8 or more and 1.3 or less.

When the ratio of Rye to Ryc (Rye/Ryc) is less than 0.8 or exceeds 1.3, the uniformity of the plasticizer content at the end and center of the PVA-based film will be impaired, and optical spots may be observed when manufacturing polarizing films. tendency to become more prominent. The ratio of Rye to Ryc (Rye/Ryc) is preferably 0.9 to 1.2, more preferably 0.95 to 1.1.

In the PVA-based film of the present invention, from the viewpoint of obtaining a polarizing film with few optical spots, it is preferable that the average interval (Sme) of the unevenness of the fluctuation amount in the film end and the difference between the unevenness of the fluctuation amount in the central portion of the film The ratio (Sme/Smc) of the mean interval (Smc) is not less than 0.7 and not more than 1.4.

When the ratio of Sme to Smc (Sme/Smc) is less than 0.7 or more than 1.4, in the case of dyeing PVA-based films, the size difference between the ends and the center of the film with different dyeability becomes too extreme, so Optical spots tend to become conspicuous when producing a polarizing film. The ratio of Sme to Smc (Sme/Smc) is preferably not less than 0.85 and not more than 1.3, more preferably not less than 0.9 and not more than 1.2.

PVA can be obtained by extruding (casting) a film-forming stock solution containing a PVA-based polymer solution or a PVA-based polymer in a water-containing state from a T-shaped slit die onto a drum-shaped roller, and drying the formed PVA-based polymer film. Department of film. The material of the drum roller is not particularly limited, and stainless steel is generally suitable, and the surface of the roller is preferably coated with electroplated metal for scratch prevention. As the type of plating metal to be used, for example, chromium plating, nickel plating, zinc plating, etc. are suitable, and by using these, a single layer or two or more plating layers can be formed on the surface of the roll. From the viewpoint of smoothing the surface of the PVA-based film or obtaining a PVA-based film with excellent durability, the outermost surface of the drum roll is preferably chrome-plated. The surface of the drum-type roller is preferably able to maintain smoothness, and the surface roughness (the difference between the unevenness of the roller surface) is represented by the average interval S of the local peaks of the roughness curve of JIS B 0604, preferably 3S or less, more preferably 1.5S or less, particularly preferably 0.5S or less.

The surface temperature of the drum roll that discharges the PVA-based polymer solution or the PVA-based polymer in a water-containing state is preferably 50 to 120°C. The PVA-based polymer film formed on the drum roll is peeled off from the drum roll when its water content reaches 5 to 30% by mass, and then the surface and the back of the film are dried alternately, preferably using a multistage roll. The PVA-based polymer film subjected to drying treatment may be subjected to heat treatment, humidity-conditioning treatment, etc. as necessary, and finally the obtained PVA-based film is wound on a core tube to a predetermined length in a roll shape.

The PVA-based film is intended to prevent blocking, and an anti-blocking agent such as silicon oxide, titanium dioxide, clay, bentonite, stearic acid or its salt may be coated on the surface of the film.

As the die head used for the film production of PVA-based film, die heads such as the chocker bar method and the flexible lip method can be used. In particular, the integrally formed retention part is used as a non-flexible lip. In the case of a die head of the above method, it is preferable because a PVA-based film with a small local thickness variation in the TD direction can be obtained.

In order to adjust the PVA-based film to an appropriate state, it is preferable to attach a heat treatment device or a humidity control device, and a speed adjustment mechanism such as a motor or a speed changer for driving each roll.

In the drying process in the manufacturing step of PVA-based film, it is generally preferable to use a drying temperature of 50 to 50°C from the point of view that the extensibility and dyeability of the polarizing film are excellent, and the polarizing performance or durability of the polarizing film obtained is good. 150°C, especially at a temperature of 60°C to 120°C.

In the past, the characteristics of the plasticizer in the film-forming stock solution have not been paid attention to, and it is considered to be uniform with the PVA-based polymer in a series of processing steps. For this reason, in the past, PVA-based films were produced only by stirring when dissolving PVA-based polymers, or only by screw kneading when melt-extruding, and that the mixing of PVA and plasticizer was so-called sufficient. However, according to this new discovery, it is known that if the plasticizer is not uniformly mixed with the PVA-based polymer in a general processing step, concentration spots will occur. In addition, in a PVA-based film composed of a film-forming stock solution that causes irregularities in the concentration of the plasticizer, the distribution of the plasticizer content is not uniform in the TD direction of the film.

In order not to cause uneven concentration of the plasticizer in the film-forming stock solution, it is desirable to sufficiently knead the film-forming stock solution, and kneading may be performed using a mixer or a kneader, or the kneading time may be increased. Thereby, the variation in the TD direction of the content of the plasticizer contained in the PVA-based film can be adjusted.

In particular, in order to uniformly mix the PVA-based polymer and the plasticizer, a mixing device capable of mixing the plasticizer with the PVA-based polymer in a molten state is used in the flow path up to the discharge port of the die, such as In-line mixer represented by static mixer, or in-line continuous vibrating mixer represented by バイブロミキサ from Ryoka Kogyo Co., Ltd., or in-line partial homogenizer represented by instantaneous mixing device manufactured by Sakura Equipment Co., Ltd. Converter etc. These mixing devices may be used in addition to a general kneading step, and it is more preferable to use a combination of a plurality of mixing devices. From this point of view, it is preferable to use an in-line mixer and an in-line continuous vibrating mixer in combination, or to use an in-line mixer and an in-line partial homogenizer in combination.

The static mixer is preferably a spiral type from the viewpoint of handling the viscosity of the film-forming stock solution, and the number of components is preferably 12 or more, more preferably 24 or more. When the number of modules is less than 12, the mixing of PVA and the plasticizer in the film-forming stock solution may not be complete, and it is difficult to obtain the expected effect. Also, there is no upper limit to the number of modules, but it is preferably 48 or less, more preferably 42 or less, from the viewpoint of cost performance. Even if more than 48 modules are installed, it is difficult to obtain a better effect of improving the mixing properties of the membrane-forming stock solution. In addition, the number of modules referred to here is a number calculated by the number of modules per unit static mixer×the number of used units.

The present invention corresponds to the enlargement of the screen of liquid crystal displays, and it is important to obtain a PVA-based film having a width of 2 m or more and a large-area PVA-based film. Moreover, from the viewpoint of enlargement of the screen, the film width is preferably 2.3 m or more, more preferably 2.6 m or more.

On the other hand, when the width of the PVA-based film exceeds 6 m, it may be difficult to perform uniform uniaxial stretching when using a practical device to manufacture a polarizing film, so the width of the PVA-based film is preferably 6 m or less, more preferably 5 m or less.

In particular, when the width of the PVA-based film is narrow, the polarizing film produced using such a PVA-based film does not have a noticeable degree of optical spots originally caused by dyeing spots or stretch spots. However, when the width of the PVA-based film is more than 2 m, uniform extensibility cannot be ensured when manufacturing a polarizing film even if the conventionally implemented production method is adopted (the plasticization in the width direction of the PVA-based film, that is, in the TD direction). The concentration of the agent is presumed to be the cause), and in such a polarizing film, optical spots caused by dyeing spots or stretching spots appear very remarkably, and the light transmittance and polarization degree of the polarizing film fluctuate. Therefore, in order to suppress the occurrence of such plasticizer concentration irregularities, it is particularly important to adopt a production method that takes into account the uniformity of plasticizer distribution in the TD direction of the PVA-based film.

The average thickness of the PVA-based film is not particularly limited, but is generally 20 to 120 μm, preferably 40 to 120 μm, more preferably 50 to 100 μm. When the average thickness of the PVA-based film is less than 20 μm, there is a risk of stretch cracking at the time of uniaxial stretching for producing a polarizing film. Also, when the average thickness of the PVA-based film exceeds 120 μm, there is a possibility that stretching spots may occur during uniaxial stretching for producing a polarizing film.

The method for producing a polarizing film from a PVA-based film is not particularly limited, and any conventional method may be used when a PVA-based film is used as an unprocessed film to produce a polarizing film.

In order to produce a polarizing film from a PVA-based film, for example, moisture adjustment of the PVA-based film, dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment if necessary, the operation sequence of dyeing, uniaxial stretching, fixing treatment, etc. There are no particular restrictions. In addition, uniaxial stretching may be performed in multiple stages of two or more stages, and may be performed simultaneously with dyeing or fixing treatment.

Iodine can be used for staining, and the staining period can be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Usually, dyeing is performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide, but a dyeing method using an aqueous solution containing iodine and potassium iodide can also be suitably employed in the present invention. The concentration of iodine in the aqueous solution for dyeing is preferably 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. Moreover, the temperature of the dyeing bath is preferably 20 to 50°C, particularly preferably 25 to 40°C.

The uniaxial stretching can be carried out by either a wet stretching method performed in a solvent such as water or a dry heat stretching method performed in air. In the case of the wet stretching method, uniaxial stretching in water, uniaxial stretching in a dyeing solution not containing boric acid, uniaxial stretching in a dyeing solution containing boric acid, uniaxial stretching in a boric acid aqueous solution, transverse stretching, etc. Performed across multiple stretches of the steps above, etc.

The stretching temperature is not particularly limited, but is preferably 30 to 90°C for wet stretching of a PVA-based film, and preferably 50 to 180°C for dry heat stretching.

In addition, the stretching ratio of the uniaxial stretching (the total stretching ratio in the case of performing uniaxial stretching in multiple stages) is preferably 4 times or more, particularly preferably 5 times or more, in terms of the polarizing performance of the obtained polarizing film. The upper limit of the stretching ratio is not particularly limited, but it is preferably 8 times or less in terms of uniform stretching.

When manufacturing the polarizing film, in order to make the adsorption of iodine and the PVA film firm, the fixation treatment can be carried out multiple times, and the present invention is also preferably carried out when the polarizing film is produced. As a treatment bath in the fixation treatment, an aqueous solution to which one or more boron compounds such as boric acid and borax are added is generally used. In addition, an iodine compound or a metal compound may be added to the treatment bath for the fixation treatment as needed. The concentration of the boron compound in the treatment bath for fixation treatment is generally 2 to 15% by mass, particularly preferably about 3 to 10% by mass. The temperature of the treatment bath when performing the fixation treatment is preferably 15 to 60°C, particularly preferably 25 to 40°C.

The above-described uniaxial stretching, dyeing treatment, fixing treatment, and the like are performed, followed by drying the obtained polarizing film. The drying treatment of the obtained polarizing film is preferably performed at 30 to 150°C, particularly at 50 to 150°C. When the drying process is performed and the moisture content of the polarizing film is about 10% or less, when tension is applied to the polarizing film and heat treatment is performed at about 80 to 120°C for about 1 to 5 minutes, better dimensional stability, durability, etc. can be obtained. It is an excellent polarizing film.

The polarizing film obtained above is generally used as a polarizer by bonding an optically transparent and mechanically strong protective film to both surfaces or one surface thereof. As the protective film, triacetyl cellulose (TAC) film, cycloaliphatic polyolefin (COP) film, acrylic film, polyester film, etc. can be used. Moreover, as an adhesive agent for bonding, a PVA type adhesive agent, a urethane type adhesive agent, etc. are mentioned, for example, Among these, a PVA type adhesive agent is suitable especially.

The polarizing plate obtained as above is coated with an adhesive such as an acrylic system, and then bonded to a glass substrate to be used as a member of a liquid crystal display device. At the same time, it can also be laminated with retardation film, viewing angle improvement film, brightness improvement film, etc.

Example

Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited at all by these Examples. The scope of the invention is determined by the appended claims.

In addition, in the following examples and comparative examples, the measurement of the plasticizer content contained in the PVA-based film, the determination of the maximum content difference (Ry) and the average interval (Sm) of the unevenness of the fluctuation amount, and the optical properties of the polarizing film Measurement of performance and evaluation of optical spots were carried out in accordance with the methods shown below.

Content of plasticizer contained in PVA-based film:

From the TD direction of the PVA series film that embodiment or comparative example obtains to the central point of total width, get 1/10 of film total width to left and right (be 35cm in embodiment 1 and 2, in embodiment 3～5, Comparative Examples 1 and 2 are 30 cm), and the plasticizer content per 1 cm in the PVA-based film was measured according to the method described above.

The maximum content difference (Ry) and the average interval (Sm) of the concave-convex shape of the variation:

Based on the above-mentioned measured values, the variation curve of the plasticizer content in the TD direction of the PVA-based film was made, and the maximum content difference (Ry) and the average interval (Sm) of the variation unevenness were determined according to the method described above. In addition, Ry and Sm obtained here use Ryc and Smc which are the central part. In addition, regarding the MD direction of the film, the maximum content difference (Rye) and the average interval (Sme) of the uneven shape of the fluctuation amount at the end portion that exists at the same position as the above-mentioned central portion are determined by rolling the obtained PVA-based film below From the end on the left hand side, sample 1/10 of the total width of the film from the part inserted in the TD direction toward the center point of the 20 cm portion, measure the plasticizer content per 1 cm in the same way as the center, and make the variation curve to determine of.

Optical properties of polarizing film:

(i) light transmittance

From the central part of the width direction of the polarizing film obtained in the examples or comparative examples, take two 4 cm x 4 cm square samples parallel to the orientation direction of the polarizing film, and use a spectrophotometer manufactured by Hitachi High-Tech Co., Ltd. Meter U-4100 (with integrating sphere), according to JIS Z 8722 (determination method of object color), perform C light source, 2-degree visual field of visual sensitivity correction in the field of visible light, and measure the extension axis for one polarizing film sample Calculate the light transmittance when the direction is inclined at 45 degrees and the light transmittance when the direction is inclined at -45 degrees, and calculate their average value (Y1).

In the same manner as above for another polarizing film sample, measure the light transmittance of the case where the direction of the extension axis is inclined at 45 degrees and the light transmittance at the case of inclination -45 degrees to obtain their average value (Y2) .

Y1 and Y2 obtained above were averaged as the light transmittance (Y) (%) of the polarizing film.

(ii) Degree of polarization:

The two polarizing films taken in the above (i) are measured in the same way as the above-mentioned light transmittance measurement method, and the light transmittance (Y//) and the extending direction and The light transmittance (Y⊥) in the case of being vertically overlapped, and the degree of polarization is obtained from the following formula.

Degree of polarization (V/%)＝{(Y//-Y⊥)/(Y//+Y⊥)} ^1/2 ×100

Optical spot of polarizing film:

Between two polarizers in a parallel Nicol state (single light transmittance 42.3%, degree of polarization 99.99%), the polarizing film made is 90 degrees to the extension direction of the aforementioned two polarizers After insertion, use a light box with a brightness of 10,000 cd/ ^m2 in a dark room, and observe the optical spots (spot-like spots with a size of about 1 cm in the TD direction and about several cm to tens of cm in the MD direction) in the transmission mode. spot), and was evaluated according to the following criteria.

◯: No speckled optical spot was observed at all.

Δ: A speckled optical spot was slightly observed.

x: Speckle-like optical spots are clearly seen.

Example 1

100 parts by mass of a PVA-based polymer with a degree of saponification of 99.95 mol % and an average degree of polymerization of a viscosity of 2400, 12 parts by mass of glycerin, and 191 parts by mass of water were supplied to a single-screw extruder and melted as a film-forming stock solution [volatile fraction (moisture content Rate) 63% by mass]. In the piping of the film-making stock solution, three spiral static mixers (total number of components: 18) are arranged in series, and the film-making stock solution is discharged from the T-die to the drum roller (roller surface temperature 93° C.), the PVA film was peeled off when the moisture content of the PVA film was 24% by mass, and then dried on a metal roll to obtain a PVA-based film with a width of 3.5 m and a thickness of 75 μm.

The maximum content difference (Ry) of the obtained PVA film with respect to the average value of the plasticizer content in the TD direction was 1.8%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 6 cm. In addition, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 1.2, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 1.3.

Using this PVA-based film, pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment were sequentially performed in order to produce a polarizing film. That is, the PVA-based film was pre-swelled by immersing it in 30° C. water for 30 seconds, and immersed in a 35° C. aqueous solution having an iodine/potassium iodide concentration ratio of 1/100 for 3 minutes. Next, uniaxially stretched to 6 times in a 50°C aqueous solution with a boric acid concentration of 40g/liter, and then immersed in a 30°C aqueous solution with a potassium iodide concentration of 70g/liter and a boric acid concentration of 40g/liter for 5 minutes to perform a fixation treatment.

Then, the PVA-based film was taken out and dried with hot air at 40° C., and then heat-treated at 100° C. to obtain a polarizing film.

The light transmittance of the obtained polarizing film was 43.5%, and the degree of polarization was 99.92%. No dyeing unevenness was observed in this polarizing film, and when the degree of optical unevenness was evaluated, it was judged as good with ◯.

Example 2

In the same manner as in Example 1, except that two spiral-type static mixers with a number of modules of 6 (total number of modules: 12) were installed in the piping of the film-forming stock solution in Example 1, a width of 3.5 m and a thickness of 75 μm were obtained. PVA-based film.

The maximum content difference (Ry) of the obtained PVA-based film with respect to the average value of the plasticizer content in the TD direction was 2.0%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 5 cm. In addition, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 0.7, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 1.5.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.4%, and the degree of polarization was 99.91%. In this polarizing film, dyeing unevenness was not observed, and when the degree of optical unevenness was evaluated, it was judged as Δ, which was a level usable for a small liquid crystal display.

Example 3

In addition to using the static mixer in the stock solution piping of Example 2 (the total number of components is 12), an instant mixing device S-1 mixer (manufactured by Sakura Equipment Co., Ltd.) for further uniform mixing of the melted film-forming stock solution was used. ) except that in the same manner as in Example 1, a PVA-based film with a width of 3 m and a thickness of 75 μm was obtained.

The maximum content difference (Ry) of the obtained PVA-based film with respect to the average value of the plasticizer content in the TD direction was 1.7%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 7 cm. Also, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 0.9, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 1.3.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.5%, and the degree of polarization was 99.93%. No dyeing unevenness was observed in this polarizing film, and when the degree of optical unevenness was evaluated, it was judged as good with ◯.

Example 4

In the same manner as in Example 1, except that the static mixer in the stock solution piping in Example 1 was replaced with a continuous vibrating mixer Biblomikisa (manufactured by Ryoka Kogyo Co., Ltd.) for further uniform mixing of the melted film-forming stock solution , and a PVA-based film with a width of 3 m and a thickness of 75 μm was obtained.

The obtained PVA-based film had a maximum content difference (Ry) of 0.9% with respect to the average value of the plasticizer content in the TD direction, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 8 cm. Also, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 0.9, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 1.1.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.3%, and the degree of polarization was 99.96%. In this polarizing film, dyeing unevenness was not observed, and when the degree of optical unevenness was evaluated, it was judged as ◯ and good.

Example 5

In addition to using the static mixer in the stock solution piping of Example 1 (the total number of components is 18), and using a continuous vibrating mixer for further uniform mixing of the melted film-forming stock solution (manufactured by Ryoka Kogyo Co., Ltd.) , in the same manner as in Example 1, a PVA-based film with a width of 3 m and a thickness of 75 μm was obtained.

The maximum content difference (Ry) of the obtained PVA-based film with respect to the average value of the plasticizer content in the TD direction was 0.8%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 10 cm. Also, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 1.0, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 0.9.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.5%, and the degree of polarization was 99.93%. In this polarizing film, dyeing unevenness was not observed, and when the degree of optical unevenness was evaluated, it was judged as ◯ and good.

Comparative example 1

Except not having used the static mixer installed in piping in Example 1, it carried out similarly to Example 1, and obtained the PVA-type film of width 3m and thickness 75 micrometers.

The maximum content difference (Ry) of the obtained PVA-based film with respect to the average value of the plasticizer content in the TD direction was 3.0%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 2 cm. Also, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 1.8, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 1.6.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.5%, and the degree of polarization was 99.92%. When dyeing unevenness was observed in this polarizing film and the degree of optical unevenness was evaluated, it was judged that x was very bad, and it was at an insufficient level for liquid crystal displays such as television applications.

Comparative example 2

100 parts by mass of PVA with a degree of saponification of 99.95 mol % and a degree of polymerization of 2400, 10 parts by mass of glycerin, and 170 parts by mass of water were supplied to a single-screw extruder and melted to obtain a film-forming stock solution [volatility (moisture content) 60.7 mass % ]. Subsequently, film formation was carried out in the same manner as in Comparative Example 1, followed by a step of contacting with warm air at a temperature of 65°C and a humidity of 90%RH, followed by a step of contacting with warm air at a temperature of 50°C and a humidity of 45%RH, and a total of two steps The time required was 6 seconds to obtain a PVA-based film with a width of 3 m and a thickness of 40 μm.

The maximum content difference (Ry) of the obtained PVA-based film with respect to the average value of the plasticizer content in the TD direction was 2.4%, and the variation in the plasticizer content in the TD direction was 3.3 cm. . Also, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end of the PVA-based film to the maximum content difference (Ryc) at the center of the film is 1.1, and the variation at the end of the PVA-based film is uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the irregularities in the center of the film was 0.8.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The light transmittance of the obtained polarizing film was 43.9%, and the degree of polarization was 99.50%. Although dyeing unevenness was not seen in this polarizing film, when evaluating the degree of optical unevenness, x was judged to be very bad, and it was an insufficient level for liquid crystal displays, such as a television use.

Industrial Utilization Possibility

The PVA-based film of the present invention has the excellent feature that the plasticizer can be uniformly present in the TD direction, and by using such a PVA-based film to manufacture a polarizing film, it is possible to smoothly obtain optical properties caused by dyeing spots or stretch spots. Polarizing film with less speckle and high performance.

The polarizing film obtained in this way can be effectively used in the manufacture of a polarizing plate, which is a component of a liquid crystal display device requiring high display quality.

As described above, preferred embodiments were described with reference to the accompanying drawings, and those skilled in the art can easily conceive various changes and corrections within the scope of self-evidentness by referring to this specification. Therefore, such changes and corrections can also be construed as being within the scope of the invention defined by the claims.

Claims (6)

1. the manufacture method of a polyvinyl alcohol film, this polyvinyl alcohol film is the polyvinyl alcohol film that is formed by the made film of pleurodiaphragmatic in terspace liquid processed that contains vinol series polymer and softening agent, (a) in the TD of this film direction, the maximum level of the mean value of the plasticizer loading contained with respect to film poor (Ry) is below 2%, and (b) in the change curve of the plasticizer loading of the TD of this film direction, give average equispaced (Sm) at the shared interval of TD direction (Smi) for more than the 7cm by the peak portion of the mean value that surpasses plasticizer loading and in abutting connection with each 1 variation machicolated form that constitutes of paddy portion of this peak portion respectively, it is characterized in that this manufacture method comprises:

Modulated the stoste modulation step of pleurodiaphragmatic in terspace liquid processed by vinol series polymer, softening agent and solvent;

Use mixing device to mix above-mentioned pleurodiaphragmatic in terspace liquid processed, make the mixed uniformly mixing step of vinol series polymer and softening agent, this mixing device is the combination of tandem continuous shaking stirrer or static(al) mixing tank and tandem continuous shaking stirrer or the combination of static(al) mixing tank and the local homogenizer of tandem;

Will be through spue the step that spues to roller of mixed uniformly this pleurodiaphragmatic in terspace liquid processed from die head;

And make the drying step of the stoste drying that spues.

2. manufacture method as claimed in claim 1 is 0.8～1.3 in the maximum level of film end poor (Rye) with ratio (Rye/Ryc) in the maximum level of film central part poor (Ryc) wherein.

3. manufacture method as claimed in claim 1 is 0.7～1.4 in the cancavo-convex equispaced of the variation of film end (Sme) and the ratio (Sme/Smc) in the cancavo-convex equispaced of the variation of film central part (Smc) wherein.

4. manufacture method as claimed in claim 1, wherein with respect to vinol series polymer 100 mass parts, the ratio of softening agent is 1～30 mass parts.

5. manufacture method as claimed in claim 1, wherein the width of film is more than the 2m.

6. manufacture method as claimed in claim 1 wherein in above-mentioned stoste modulation step, is supplied to extrusion machine with vinol series polymer, softening agent and solvent, and they are mediated to modulate pleurodiaphragmatic in terspace liquid processed.

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