Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
  • B01D19/02—Foam dispersion or prevention
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
  • B29C39/003—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor characterised by the choice of material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
  • B29C39/02—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor for making articles of definite length, i.e. discrete articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C41/00—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor
  • B29C41/24—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor for making articles of indefinite length
  • B29C41/26—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor for making articles of indefinite length by depositing flowable material on a rotating drum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C41/00—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor
  • B29C41/34—Component parts, details or accessories; Auxiliary operations
  • B29C41/36—Feeding the material on to the mould, core or other substrate
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2029/00—Use of polyvinylalcohols, polyvinylethers, polyvinylaldehydes, polyvinylketones or polyvinylketals or derivatives thereof as moulding material
  • B29K2029/04—PVOH, i.e. polyvinyl alcohol
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2007/00—Flat articles, e.g. films or sheets
  • B29L2007/008—Wide strips, e.g. films, webs
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
  • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
  • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids

Definitions

• the present invention is an optical polyvinyl alcohol film, in particular, an optical polyvinyl alcohol film with few bubble defects and excellent transparency, and an optical for producing a high-quality polarizing film or polarizing plate without display defects.
• the present invention relates to a polyvinyl alcohol film for use, a production method thereof, and a polarizing film using the optical polyvinyl alcohol film.
• a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin and an additive such as a surfactant in water to prepare an aqueous solution (film forming stock solution), and then manufacturing the aqueous solution by a solution casting method (casting method). It is produced by filming and drying the resulting film.
• the polyvinyl alcohol film thus obtained is used in many applications as a film excellent in transparency and dyeability, and one of its useful applications is a polarizing film.
• a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to a device requiring high quality and high reliability.
• a polarizing film is made by swelling a polyvinyl alcohol film, which is an original fabric, with water (including warm water), dyeing with iodine, stretching for orienting iodine, and a boa for fixing the orientation state. It is manufactured through a process such as acid crosslinking. In order to produce a polarizing film having no display defects, it is necessary that the polyvinyl alcohol film as a raw material has no defects.
• the display defects of the polarizing film are Increasing and ultimately reducing the quality of the display.
• the bubbles in the polyvinyl alcohol film may cause color unevenness and film breakage during the production of the polarizing film.
• a method for producing a polyvinyl alcohol film in which a polyvinyl alcohol resin aqueous solution is defoamed with a multi-screw extruder see, for example, Patent Document 1
• a discharge temperature of the polyvinyl alcohol resin aqueous solution and a cast mold surface
• a method for producing a polyvinyl alcohol film having a temperature difference ⁇ T in a specific range for example, see Patent Document 2
• a method for replacing a filter used when filtering an aqueous solution of a polyvinyl alcohol resin for example, see Patent Document 3
• a method for producing a polarizing film using a polyvinyl alcohol-based film in which foreign matter having a size of 20 ⁇ m or more existing on the surface of the film is 10 or less per 1 m 2 see, for example, Patent Document 4
• a polyvinyl alcohol-based material having no undissolved material A method for producing a resin aqueous solution (for example,
• the resin temperature at the vent is set to 105 to 180 ° C.
• further improvement is desired for the production of a thin polyvinyl alcohol film having a thickness of 60 ⁇ m or less.
• the temperature difference ⁇ T between the discharge temperature of the polyvinyl alcohol resin aqueous solution and the surface of the cast mold is set to 5 to 10 ° C. (Example).
• further improvement is desired for the production of a thin polyvinyl alcohol film having a thickness of 60 ⁇ m or less.
• Patent Document 3 it is difficult to remove bubbles passing through the filter. Further, bubbles generated in the process after filtration cannot be avoided, and further improvement is required.
• Patent Document 4 a polyvinyl alcohol film in which foreign matter is reduced by filtration is used.
• Patent Document 5 can reduce undissolved material by pressure dissolution, it is difficult to remove fine bubbles unless appropriate defoaming is performed, and there is room for further improvement.
• Patent Document 6 relates to minute bubbles on the order of wavelengths and does not necessarily improve the bubble defects of polyvinyl alcohol films. Further, there is a problem that light scattering occurs due to minute bubbles and the haze of the film increases.
• an optical polyvinyl alcohol film having few bubble defects and excellent transparency, and it is possible to produce a high-quality polarizing film or polarizing plate with few display defects.
• An optical polyvinyl alcohol film, a method for producing the same, and a polarizing film using the optical polyvinyl alcohol film are provided.
• a bubble size which is a problem in the present invention, it includes not only those that can be visually confirmed, but also includes submicron-sized bubbles that cause light scattering.
• a spherical shape it includes an elliptical shape.
• All of the bubbles in the optical polyvinyl alcohol film for optical use are not necessarily the display defects of the polarizing film as they are, and for example, there are those that disappear in the swelling process and the subsequent polarizing film manufacturing process.
• the display defect of the polarizing film also increases. Therefore, it is necessary to reduce the number of bubbles per unit area in the optical polyvinyl alcohol film. .
• the present inventors have solved the above-mentioned problems by reducing the number of bubbles contained in the polyvinyl alcohol film for optics over a wide range up to a minute size. It was found that a high-quality polarizing film can be produced.
• the first gist of the present invention is a polyvinyl alcohol film having a width of 2 m or more and a length of 4 km or more, and an area surrounded by width A (m) ⁇ length B (km) (where A ⁇ 2 m). And B ⁇ 4 km), the number of bubbles having a diameter of 50 ⁇ m or more is 0.01 / m 2 or less.
• a second gist of the present invention is a method for producing an optical polyvinyl alcohol film according to the first gist, wherein a polyvinyl alcohol resin and a surfactant are dissolved in water to obtain a polyvinyl alcohol resin aqueous solution.
• An optical polyvinyl alcohol-based film manufacturing method comprising a film-forming step of casting and forming a film, and a drying step of drying the formed film.
• the 3rd summary of this invention is a polarizing film characterized by using the said polyvinyl alcohol film for optics.
• the number of bubbles having a diameter of 50 ⁇ m or more contained per unit area is 0.01 / m 2 or less, so that there are few bubble defects, low haze, and few display defects.
• a high-quality polarizing film can be obtained. Therefore, the polarizing film obtained using the above-mentioned optical polyvinyl alcohol film is excellent in polarizing performance.
• the haze of the optical polyvinyl alcohol film is 0.2% or less, it is possible to suppress a decrease in light transmittance of a polarizing film obtained using the film.
• the width is 4 m or more, it becomes possible to cope with an increase in the area of the polarizing film.
• a polyvinyl alcohol resin and a surfactant are dissolved in water to prepare a polyvinyl alcohol resin aqueous solution.
• a pretreatment is performed by filtration, and the pretreated polyvinyl alcohol resin aqueous solution is discharged and cast from a T-type slit die into a cast mold to form a film.
• the polyvinyl alcohol-type film for optics is manufactured by drying this formed film. For this reason, the said optical polyvinyl alcohol-type film with few bubble defects and low haze can be manufactured efficiently.
• the temperature difference ⁇ T (° C.) between the temperature T1 (° C.) of the polyvinyl alcohol resin aqueous solution discharged from the T-type slit die and the temperature T2 (° C.) of the cast mold surface is 4 in absolute value.
• the temperature is lower than or equal to ° C., a product having even fewer bubbles can be obtained.
• the thickness of the optical polyvinyl alcohol film is 45 ⁇ m or less, it is possible to cope with the thinning of the polarizing film obtained using the film.
• the optical polyvinyl alcohol-based film of the present invention has a width of 2 m or more and a length of 4 km or more, and is an area surrounded by width A (m) ⁇ length B (km) (A ⁇ 2 m and B ⁇ 4 km) ),
• the number of bubbles having a diameter of 50 ⁇ m or more is 0.01 / m 2 or less.
• the number of bubbles per 1 m 2 when inspecting (measuring) an area (A ⁇ 2 m and B ⁇ 4 km) surrounded by width A (m) ⁇ length B (km) in the polyvinyl alcohol film The number of bubbles having a diameter of 50 ⁇ m or more, preferably the number of bubbles having a diameter of 50 ⁇ m or more per 1 m 2 when measured over the entire length of the entire length of the polyvinyl alcohol film. For example, when inspecting a film of width 4 m ⁇ length 4 km (area 16,000 m 2 ), if 16 bubbles having a diameter of 50 ⁇ m or more are detected, the number of the bubbles is 0.001 / m 2 . Further, when the shape of the bubble was elliptical, (major axis + minor axis) / 2 was taken as the diameter.
• the number of bubbles having a diameter of 50 ⁇ m or more needs to be 0.01 / m 2 or less, preferably 0.001 / m 2 or less, particularly preferably 0.0001 / m 2 or less, more preferably 0.00001 pieces / m 2 or less.
• the number of bubbles exceeds 0.01 / m 2 , display defects of the polarizing film increase, and the object of the present invention cannot be achieved.
• the inspection (measurement) of the number of bubbles is performed as follows. First, a foreign matter (bright defect) having a diameter of 50 ⁇ m or more over a predetermined area is detected by an automatic foreign matter inspection apparatus while unwinding a polyvinyl alcohol film to be measured from a roll. Next, bubbles having a diameter of 50 ⁇ m or more are extracted from the enlarged photograph of the detected foreign matter, and the total number of bubbles is calculated. By dividing the total number by a predetermined area, the number of bubbles (number / m 2 ) is obtained. When the shape of the bubble is an ellipse, (major axis + minor axis) / 2 is the diameter.
• the “bright defect” is a defect that is detected as a bright luminescent spot with respect to the textured part (normal part of the film) when the defective part is detected by the automatic foreign matter inspection apparatus with the camera.
• the setting conditions of the automatic foreign matter inspection apparatus are as follows. Illumination: Transmission type, angle 90 ° (perpendicular to film), distance 300mm, light source halogen lamp 150W Detection: 20 CCD cameras, position 483 mm, 5000 pixels / unit, resolution 48 ⁇ m / pixel, 50 mm lens (F2.8)
• the long polyvinyl alcohol film for optics having a width of 2 m or more and a length of 4 km or more is swelled, dyed, boric acid crosslinked, stretched and washed while being conveyed in the length direction (flow direction: MD direction).
• the film is formed on the polarizing film through steps such as drying.
• the optical polyvinyl alcohol film is excellent in transparency and can produce a high-quality polarizing film or polarizing plate with few display defects.
• Methods for reducing the number of bubbles include the type and amount of surfactant added to the aqueous solution of the polyvinyl alcohol resin, the preparation method, the storage method of the polyvinyl alcohol resin aqueous solution, the defoaming conditions, the filtration conditions, and the film formation. And a method for optimizing the conditions. Among these, as will be described later, a method of optimizing the defoaming conditions for the aqueous solution and the film forming conditions for the film is particularly effective in the process for producing the optical polyvinyl alcohol film.
• the method for producing an optical polyvinyl alcohol film of the present invention comprises a step ( ⁇ ) of preparing a polyvinyl alcohol resin aqueous solution by dissolving a polyvinyl alcohol resin and an additive in water, and the polyvinyl alcohol resin aqueous solution.
• the said liquid preparation process ((alpha)) is demonstrated in detail.
• an unmodified polyvinyl alcohol resin that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used.
• a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can.
• components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like.
• the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.
• a polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be used as the polyvinyl alcohol resin.
• a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid.
• a method of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glyceryl monoallyl ether, or the like.
• the weight average molecular weight of the polyvinyl alcohol resin used in the present invention is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, the degree of polarization of the polarizing film tends to decrease, and if it is too large, stretching during the production of the polarizing film tends to be difficult.
• the weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by GPC-MALS method.
• the average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, and particularly preferably 99 mol%. .8 mol% or more. If the average degree of saponification is too small, the degree of polarization of the polarizing film tends to decrease.
• the average saponification degree in the present invention is measured according to JIS K 6726.
• polyvinyl alcohol resin used in the present invention two or more kinds having different modified species, modified amount, weight average molecular weight, average saponification degree, etc. may be used in combination.
• the aqueous solution used as the film-forming stock solution is prepared using the said polyvinyl alcohol-type resin. That is, the polyvinyl alcohol-based resin is preferably washed with water and dehydrated using a centrifugal separator or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. When the water content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.
• the obtained polyvinyl alcohol-based resin wet cake is charged into a dissolution tank together with additives such as water, glycerin and other plasticizers and surfactants, and heated and stirred to dissolve to obtain a polyvinyl alcohol-based resin aqueous solution.
• additives such as water, glycerin and other plasticizers and surfactants
• the aqueous polyvinyl alcohol resin solution in addition to the polyvinyl alcohol resin, commonly used plastics such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane are used. It is preferable from the viewpoint of the film forming property of the optical polyvinyl alcohol film to contain an agent and at least one surfactant of nonionic, anionic and cationic properties.
• the content of the plasticizer in the aqueous polyvinyl alcohol resin solution is preferably 1 to 20% by weight of the entire aqueous solution.
• the surfactant in order to reduce the bubbles of the optical polyvinyl alcohol film, for the surfactant to be blended in the liquid preparation step ( ⁇ ), (I) type of surfactant, (Ii) surfactant content, (Iii) Surfactant formulation procedure, (Iv) a method for dissolving the surfactant, (V) a method for storing an aqueous polyvinyl alcohol resin solution in which a surfactant is dissolved, It is useful to optimize these five. Among these optimizations related to surfactants, several proposals have been made regarding (i) types of surfactants, (ii) compounding amounts, and (iv) dissolution methods. There are currently no effective proposals regarding (iii) blending procedures and (v) storage methods for polyvinyl alcohol resin aqueous solutions, and in particular, (iii) blending procedures have been optimized. It was hard to say.
• surfactants are formulated to promote uniform dissolution of polyvinyl alcohol-based resins in water, but the present inventors have generated some of these surfactants by decomposition by heating. It was found that the bubbles of the film increase when the low-boiling organic decomposition product foamed. Moreover, even if it melt
• a nonionic surfactant and an anionic surfactant are used when preparing an aqueous polyvinyl alcohol resin solution.
• nonionic surfactant examples include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, and polyoxyethylene.
• Higher fatty acid alkanolamides such as propanolamide, butanolamide, caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, oleic acid amide and other higher fatty acid amides, hydroxyethyl laurylamine, Polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene Polyoxyethylene alkylamines such as oxyethylene decylamine,
• anionic surfactant examples include sulfate ester salt type, sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, Sodium octadecyl sulfate, sodium eicosyl sulfate, or alkyl sulfates such as potassium, calcium and ammonium salts thereof, sodium polyoxyethylene hexyl ether sulfate, sodium polyoxyethylene heptyl ether sulfate, sodium polyoxyethylene octyl ether sulfate, Sodium polyoxyethylene nonyl ether sulfate, sodium polyoxyethylene decyl ether sulfate, polyoxy
• fatty acid soaps N-acyl amino acids and salts thereof, polyoxyethylene alkyl ester carboxylates, carboxylate types such as acylated peptides, alkyl benzene sulfonates, alkyl naphthalene sulfonates , Naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin condensate, dialkyl sulfosuccinic acid ester salt, sulfosuccinic acid alkyl disalt, polyoxyethylene alkyl sulfosuccinic acid disalt, alkyl sulfoacetate, ⁇ -olefin sulfone Sulfonates such as acid salts, N-acylmethyl taurate salts, dimethyl-5-sulfoisophthalate sodium salts, polyoxyethylene alkyl ether phosphates, polyoxyethylene
• nonionic surfactant in the present invention, it is preferable to use a nonionic surfactant and an anionic surfactant in combination.
• the nonionic surfactant in both cases where the nonionic surfactant is used alone and when the anionic surfactant is used alone, it becomes difficult to dissolve the polyvinyl alcohol resin in water, and bubbles of the optical polyvinyl alcohol film are used. Tends to increase and haze tends to increase.
• the amount of the surfactant (ii) is preferably 0.15 parts by weight or less, particularly preferably 0.1 parts by weight or less, and still more preferably 0.005 parts by weight or less with respect to 100 parts by weight of the polyvinyl alcohol resin. 07 parts by weight or less. Moreover, a preferable minimum is 0.01 weight part. If the amount of such a surfactant is too large, the surfactant tends to be difficult to dissolve sufficiently in the dissolution process, and even if dissolved, it is likely to precipitate during film formation, so the bubbles in the polyvinyl alcohol film increase. And haze tends to increase.
• the blending order when using plural kinds of surfactants is blended in the dissolution tank in the order of anionic surfactant and nonionic surfactant.
• the nonionic surfactant is preferably compounded in the order of the nonionic surfactant, the anionic surfactant and the nonionic surfactant in two steps.
• the dissolution step is performed by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade in view of excellent solubility. Specifically, steam is blown into the dissolution tank, and stirring is started when the temperature in the tank reaches 40 to 80 ° C., and further, water vapor is blown and dissolution is performed at a temperature in the tank of 90 to 100 ° C. Is preferred.
• steam is further blown to pressurize the inside of the tank to 0.1 to 1 MPa and pressurize and dissolve at a temperature in the tank of 130 to 150 ° C. It is.
• Such pressure dissolution is preferably performed at 130 to 150 ° C. for 1 to 10 hours. If the pressure dissolution temperature is too low, sufficient dissolution of the polyvinyl alcohol resin and the surfactant cannot be obtained, and the haze of the optical polyvinyl alcohol film tends to increase. A decomposition product of a resin or a surfactant is generated, and bubbles of the optical polyvinyl alcohol film tend to increase.
• the pressure dissolution time is too short, sufficient dissolution of the polyvinyl alcohol resin or the surfactant cannot be obtained, and the haze of the optical polyvinyl alcohol film tends to increase. Decomposition products of alcohol-based resins and surfactants are generated, and bubbles in the optical polyvinyl alcohol-based film tend to increase.
• the concentration of the aqueous polyvinyl alcohol resin solution may be adjusted to obtain a desired concentration by exhausting steam or adding water.
• the resin concentration of the aqueous polyvinyl alcohol resin solution is preferably 15 to 60% by weight, particularly preferably 18 to 55% by weight, and further preferably 20 to 50% by weight. If the resin concentration is too low, the drying load of the film increases, and if it is too high, the viscosity tends to be too high and uniform dissolution tends to be difficult.
• the polyvinyl alcohol resin aqueous solution after the surfactant is dissolved is subjected to the film forming step ( ⁇ ). Before being stored, it is temporarily stored in a storage tank, but it is preferable to perform such storage in a heated state.
• the storage temperature is preferably 100 to 150 ° C., particularly preferably 110 to 145 ° C., and further preferably 120 to 140 ° C. If the storage temperature is too low, the polyvinyl alcohol resin or surfactant tends to precipitate and the haze of the optical polyvinyl alcohol film tends to increase. If it is too high, the polyvinyl alcohol resin or surfactant is decomposed. There is a tendency that bubbles are generated in the optical polyvinyl alcohol film.
• the storage time is preferably within 30 hours, particularly preferably within 25 hours, and more preferably from 1 to 20 hours.
• the pretreatment step ( ⁇ ) is a step of subjecting the obtained aqueous polyvinyl alcohol resin solution to defoaming treatment and filtration treatment.
• the greatest feature of the production method of the present invention lies in the pretreatment step ( ⁇ ). Specifically, it is characterized by two methods of (vi) defoaming method and (vii) filtration method of an aqueous polyvinyl alcohol resin solution. There is. In these circumstances, no effective proposal has been made, and it is difficult to say that (vi) the defoaming method has been optimized.
• defoaming is preferably performed using a twin screw extruder having a vent from the viewpoint of productivity, and particularly preferably 2 from the viewpoint of defoaming efficiency. This is carried out by a foaming process at 100 to 130 ° C. and a steam discharge process at 90 to 100 ° C. using a screw extruder.
• the vent for discharging bubbles is naturally provided during the steam discharging process.
• the temperature of the foaming step is preferably 100 to 130 ° C, particularly preferably 100 to 120 ° C, and more preferably 100 to 115 ° C. If the temperature of the foaming process is too low, gas discharge from the vent tends to be difficult, and conversely, if it is too high, bubbles in the optical polyvinyl alcohol film tend to increase.
• the temperature in the steam discharge process is preferably 90 to 100 ° C., particularly preferably 92 to 98 ° C. If the temperature of the discharge process is too low or too high, bubbles tend to increase.
• a normal disk filter can be used for filtration, but in the present invention, two or more stages of filtration are used by using a plurality of disk filters having different openings in terms of filtration efficiency. Processing is preferably performed. Particularly preferred is a three-stage filtration process of coarse / medium / finish using three types of disc filters having different openings in terms of further filtration efficiency.
• the coarse disk filter preferably has an opening of 10 to 100 ⁇ m
• the medium disk filter preferably has an opening of 1 to 50 ⁇ m
• the finished disk filter has an opening of 0. Those of 1 to 10 ⁇ m are preferable.
• the pretreated polyvinyl alcohol-based resin aqueous solution is promptly provided for film formation.
• the film forming step ( ⁇ ) is a step of forming a film by discharging and casting the pretreated aqueous solution into a cast mold. In order to reduce bubbles in the optical polyvinyl alcohol film, the film forming step is performed. In the step ( ⁇ ), (viii) it is useful to cast a polyvinyl alcohol resin aqueous solution into a cast mold under a specific temperature condition to form a film.
• the filtered polyvinyl alcohol-based resin aqueous solution is introduced into a T-shaped slit die by a certain amount, and cast types such as cast drums (drum-type rolls) and endless belts, preferably from the viewpoints of making wide, long, and thin. It is discharged onto the cast drum.
• cast types such as cast drums (drum-type rolls) and endless belts, preferably from the viewpoints of making wide, long, and thin. It is discharged onto the cast drum.
• cast drums drum-type rolls
• endless belts preferably from the viewpoints of making wide, long, and thin.
• the surface roughness Ra of the cast drum used in the present invention is preferably 5 to 20 nm, particularly preferably 6 to 17 nm, and further preferably 7 to 15 nm. If the surface roughness Ra is too small, the adhesion between the surface of the cast drum and the film tends to be reduced, and there is a tendency for the polyvinyl alcohol film to dent. If it is too large, the aqueous solution foams on the rough portion of the cast drum surface. This tends to increase the bubbles in the polyvinyl alcohol film.
• the surface roughness Ra of the cast drum is measured as follows.
• the diameter of the cast drum is preferably 2 to 5 m, particularly preferably 3 to 4 m. If the diameter of the cast drum is too small, the drying length is insufficient and the productivity tends to decrease, and if it is too large, the equipment load tends to increase.
• the width of the cast drum is preferably 2 to 7 m, particularly preferably 3 to 6 m. If the width of the cast drum is too narrow, the productivity tends to decrease, and if it exceeds 7 m, the equipment load tends to increase.
• the rotation speed of the cast drum is preferably 5 to 30 m / min, particularly preferably 6 to 20 m / min. If the rotational speed is too slow, the productivity tends to decrease, and if it is too fast, drying tends to be insufficient.
• the temperature T1 (° C.) of the aqueous polyvinyl alcohol resin solution discharged from the T-type slit die is preferably 70 to 100 ° C., particularly preferably 80 to 90 ° C. If the temperature is too low, there is a tendency to cause poor flow, and if it is too high, foaming tends to occur.
• the temperature T2 (° C.) of the cast drum surface is preferably 50 to 99 ° C., particularly preferably 60 to 98 ° C., and further preferably 70 to 97 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, the aqueous solution tends to foam and bubbles in the film tend to increase.
• the temperature difference ⁇ T (
• ) (° C.) between the temperature T1 (° C.) of the polyvinyl alcohol resin aqueous solution discharged from the T-type slit die and the temperature T2 (° C.) of the cast drum surface.
• the temperature difference ⁇ T (° C.) which is an absolute value, is too large, bubbles in the film tend to increase. Such bubbles are assumed to be generated not only from water vapor but also from dissolved gas in the aqueous solution.
• the dissolved gas in addition to oxygen and nitrogen, an organic gas which is a decomposition product of the surfactant is also included.
• the temperature unevenness on the cast drum surface is preferably 5 ° C. or less, particularly preferably 3 ° C. or less, and more preferably 2 ° C. or less from the viewpoint of film thickness accuracy.
• drying step ( ⁇ ) is a step in which the film formed is heated and dried.
• the drying method by heating is preferably performed by alternately bringing the front and back surfaces of the film formed into contact with a plurality of metal heating rolls (hereinafter referred to as “heat rolls”).
• the surface temperature of the hot roll is usually 40 to 150 ° C., preferably 50 to 140 ° C. If the surface temperature is too low, drying tends to be poor. If the surface temperature is too high, drying tends to be excessive, and appearance defects such as undulation tend to be caused.
• heat treatment process Furthermore, after the drying step ( ⁇ ) using the hot roll or the like, heat treatment may be performed as necessary.
• the heat treatment method include a method of blowing warm air on both surfaces of the film with a floating dryer (hereinafter sometimes referred to as “floating method”), a method of irradiating near infrared rays with an infrared lamp, and the like.
• the floating method is preferable because the dried state of both surfaces of the optical polyvinyl alcohol film can be made uniform.
• the gap between nips per 1 m of film width is preferable.
• a floating method with a tension of 1 to 10 N is particularly preferable.
• the heat treatment temperature is usually 70 to 150 ° C. If the heat treatment temperature is too low, the water resistance of the optical polyvinyl alcohol film tends to be insufficient, and if it is too high, the stretchability during the production of the polarizing film tends to decrease.
• Polyvinyl alcohol film for optics After the drying step ( ⁇ ), a long optical polyvinyl alcohol film of the present invention is obtained through a heat treatment step as necessary.
• This polyvinyl alcohol film for optics is produced into a film winding body by slitting both ends in the width direction of the film and winding the film around a core tube in a roll shape.
• optical polyvinyl alcohol film of the present invention is obtained.
• the thickness of the optical polyvinyl alcohol film of the present invention is preferably 60 ⁇ m or less, particularly preferably 15 to 45 ⁇ m from the viewpoint of avoiding breakage. If the thickness is too thick, it is difficult to reduce the thickness of the polarizing film.
• the optical polyvinyl alcohol-based film of the present invention needs to have a width of 2 m or more, preferably a width of 3 m or more, more preferably a width of 4 m or more, particularly preferably a width of 4 in terms of increasing the area of the polarizing film. ⁇ 7m.
• the optical polyvinyl alcohol-based film of the present invention is required to have a length of 4 km or more from the viewpoint of improving the productivity of the polarizing film, and preferably from the viewpoint of increasing the area of the polarizing film and thus the liquid crystal screen.
• the length is 5 km or more, and more preferably 5 to 30 km from the viewpoint of transportability.
• the optical polyvinyl alcohol film of the present invention preferably has a haze of 0.2% or less, particularly preferably 0.15% or less, and more preferably 0.1% or less. If the haze exceeds the upper limit, the light transmittance of the polarizing film tends to decrease.
• the optical polyvinyl alcohol film of the present invention has few defects and is preferably used as a raw film for a polarizing film.
• the polarizing film of the present invention is manufactured through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, drying, etc., by feeding the optical polyvinyl alcohol film from the film winding body and transferring it in the horizontal direction.
• the swelling process is performed before the dyeing process.
• water is usually used as the treatment liquid.
• the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, alcohol, and the like.
• the temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.
• the dyeing step is performed by bringing a liquid containing iodine or a dichroic dye into contact with the optical polyvinyl alcohol film.
• a liquid containing iodine or a dichroic dye into contact with the optical polyvinyl alcohol film.
• an iodine-potassium iodide aqueous solution is used.
• the iodine concentration is suitably 0.1-2 g / L
• the potassium iodide concentration is 1-100 g / L.
• the dyeing time is practically about 30 to 500 seconds.
• the temperature of the treatment bath is preferably 5 to 50 ° C.
• the aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent.
• the boric acid crosslinking step is performed using a boron compound such as boric acid or borax.
• the boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance.
• the temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.
• stretching in a uniaxial direction is preferably 3 to 10 times, preferably 3.5 to 6 times.
• a slight stretching may be performed in a direction perpendicular to the stretching direction.
• the temperature during stretching is preferably 30 to 170 ° C.
• the stretching ratio may be finally set within the above range, and the stretching operation may be performed not only once but plural times in the polarizing film manufacturing process.
• the washing step is performed, for example, by immersing the optical polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide, and removing precipitates generated on the surface of the optical polyvinyl alcohol film. it can.
• an aqueous potassium iodide solution such as water or potassium iodide
• the potassium iodide concentration is about 1 to 80 g / L.
• the temperature during the washing treatment is usually 5 to 50 ° C., preferably 10 to 45 ° C.
• the treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds.
• the optical polyvinyl alcohol film is dried in the air at 40 to 80 ° C. for 1 to 10 minutes.
• the polarization degree of the polarizing film of the present invention is preferably 99.8% or more, more preferably 99.9% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
• the single transmittance of the polarizing film of the present invention is preferably 42% or more, more preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
• the single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.
• the polarizing film of the present invention is suitable for producing a polarizing plate having no display defect.
• the manufacturing method of the polarizing plate of this invention is demonstrated.
• the polarizing plate is produced by bonding an optically isotropic resin film as a protective film to one or both sides of the polarizing film of the present invention via an adhesive.
• the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet.
• the bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded, and heated or activated. This is done by irradiating energy rays.
• a polarizing plate can be formed by applying a curable resin such as urethane resin, acrylic resin, urea resin or the like to one or both surfaces of the polarizing film and curing to form a cured layer.
• a curable resin such as urethane resin, acrylic resin, urea resin or the like
• the polarizing film or polarizing plate using the optical polyvinyl alcohol film of the present invention has no display defects or color unevenness, and is a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic watch, word processor, electronic Paper, game machine, video, camera, photo album, thermometer, audio, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable display, display elements (CRT, LCD, organic It is preferably used for antireflection layers for EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys and the like.
• ⁇ Evaluation method> Number of bubbles with a diameter of 50 ⁇ m or more (pieces / m 2 ) While the obtained polyvinyl alcohol film for optics was unwound from the film winding body, a foreign matter (bright defect) having a diameter of 50 ⁇ m or more over a width of 4 m ⁇ length of 4 km was detected by an automatic foreign matter inspection apparatus. Bubbles having a diameter of 50 ⁇ m or more were picked up from the enlarged photograph, and the total number of bubbles was calculated. The total number was divided by the area of 16,000 m 2 to obtain the number of bubbles (number / m 2 ).
• Example 1 Manufacture of optical polyvinyl alcohol film 1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, 0.2 kg of sodium dodecyl sulfate as an anionic surfactant (0.02 wt. %) was added to a pressure dissolution can and stirred at 90 ° C., then 0.2 kg of polyoxyethylene dodecyl ether (0.02 wt% based on the resin) as a nonionic surfactant and 100 kg of glycerin as a plasticizer The mixture was heated while being pressurized by blowing water vapor, and stirred at 140 ° C.
• the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 1.9 m / min) and cast from a T-type slit die discharge port onto a rotating cast drum to form a film.
• the film formed from the cast drum was peeled off, and after drying while alternately contacting the front and back surfaces of the film with a plurality of hot rolls, heat treatment was performed using a floating dryer, and the thickness was 45 ⁇ m.
• An optical polyvinyl alcohol film having a width of 5 m and a length of 5 km was obtained.
• the film winding body was obtained by slitting the film both ends of the obtained polyvinyl alcohol film for optics and winding it around the core tube in a roll shape.
• Table 3 shows the properties of the obtained optical polyvinyl alcohol film.
• the optical polyvinyl alcohol film thus obtained is unwound from the wound body and transported in the horizontal direction using a transport roll. First, it is immersed in a water bath at a water temperature of 25 ° C. and swollen in the flow direction (MD direction). The film was stretched 1.7 times. Next, it is stretched 1.6 times in the flow direction (MD direction) while being immersed in an aqueous solution at 28 ° C. composed of iodine 0.5 g / L and potassium iodide 30 g / L, and then boric acid 40 g / L.
• Examples 2 to 5 and Comparative Examples 1 to 4 An optical polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Tables 1 and 2 below. The properties of the obtained optical polyvinyl alcohol film and polarizing film are shown in Table 3 below.
• the number of bubbles is within the specific range of the present invention, so that the obtained polarizing film has few display defects, whereas the optical polyvinyl alcohol films of Comparative Examples 1 to 4 Since the number of bubbles is outside the specific range of the present invention, the polyvinyl alcohol film has many display defects of the obtained polarizing film.
• the polarizing film and polarizing plate obtained by using the optical polyvinyl alcohol film of the present invention have few display defects and excellent polarization performance
• portable information terminals personal computers, televisions, projectors, signage, electronic desk calculators , Electronic clock, word processor, electronic paper, game machine, video, camera, photo album, thermometer, audio, liquid crystal display devices such as automobiles and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable display, display It is preferably used for an antireflection layer for elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys and the like.
• elements CRT, LCD, organic EL, electronic paper, etc.

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