JP5606704B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to, for example, a polarizing film that can be preferably used as a material for manufacturing a polarizing plate constituting a liquid crystal display device, and a method for manufacturing the polarizing film.

  In recent years, liquid crystal display devices (LCDs) have been used not only for small devices such as calculators and watches in the early days of development, but also for liquid crystal televisions, notebook computers, liquid crystal monitors, liquid crystal color projectors, in-vehicle navigation systems, mobile phones, indoors and outdoors. It is used in a wide range of applications, such as measuring instruments used in Japan. Especially in liquid crystal televisions and liquid crystal monitors, liquid crystal display devices and components constituting the liquid crystal display device are required to be further thinned as screens become larger and thinner, and usage environments and usage conditions diversify. Yes. In addition, with the expansion of usage of liquid crystal display devices and the increase in the amount of use, the cost reduction of each of the above members is required, and further cost reduction is required when manufacturing each of these members. Yes. In addition, when a large amount of liquid crystal display devices are discarded, there is a concern about an adverse effect on the environment, and therefore, there is a demand for a small influence on the environment at the time of disposal.

  A polarizing plate having a light transmission function and a light shielding function is an important member constituting a liquid crystal display device together with a liquid crystal having a light switching function. Under the circumstances as described above, the polarizing plate is required to have a wider area, a thinner thickness, and a lower cost in addition to excellent optical characteristics such as transmittance and polarization.

  In many cases, the polarizing plate has a configuration in which a protective film made of a cellulose triacetate (TAC) film or the like is bonded to a polarizing film produced by dyeing and uniaxially stretching a polyvinyl alcohol polymer film. And it becomes possible to satisfy the said request | requirement with respect to a polarizing plate by using the polyvinyl-alcohol-type polymer film which was excellent in the optical characteristic and was further achieved in the area expansion, thickness reduction, and cost reduction.

By the way, as a method for producing a polarizing film excellent in heat resistance, heat-and-moisture resistance, etc., a polyvinyl alcohol film on which a polarizing element (dichroic dye or the like) is adsorbed has a low concentration (less than 5% by weight; A method is known in which a uniaxial stretching is performed in a 3.0 wt% boric acid aqueous solution, which is then held in a high concentration boric acid aqueous solution, followed by heat treatment (see Patent Document 1).
In addition, as a method for producing a high contrast polarizing film, a polyvinyl alcohol resin film is uniaxially stretched using a dry heat roll, etc., and adsorbed and oriented with iodine or a dichroic dye, and then boric acid per 100 parts by weight of water. There is known a method of stretching 1.1 to 1.8 times while being immersed in a boric acid aqueous solution containing 2 to 18 parts by weight (7.5 parts by weight as a specific example) (see Patent Document 2).
Furthermore, as a method for producing a polarizer (polarizing film) having a high iodine content, a method using two iodine dyeing baths having different bath temperatures is known (see Patent Document 3). In Patent Document 3, a crosslinking process can be performed together with a stretching process, and a boric acid aqueous solution having a concentration of about 0.1 to 13% by weight (specifically, 3% by weight) is used in the crosslinking process. Is described.

  However, a polarizing film with a reduced content of boron atoms has not been known so far, and has a high transmittance and polarization degree and excellent optical characteristics, and further increases in area, thickness, and thickness. In order to obtain a polarizing film in which cost reduction has been achieved, further studies have been required.

Japanese Unexamined Patent Publication No. 06-337311 Japanese Patent Laid-Open No. 11-49878 JP 2009-9111 A

  The object of the present invention is a polarizing film that has a high transmittance and polarization degree and is excellent in optical properties, but has a low content of boron atoms and has a small impact on the environment at the time of disposal, and A method for producing a polarizing film that can efficiently produce the polarizing film, does not require a large amount of boric acid, and can produce a wide and thin polarizing film with a high draw ratio and a high yield, An object of the present invention is to provide a manufacturing method that can contribute to cost reduction.

  The present inventors have intensively studied to achieve the above object. As a result, when a polyvinyl alcohol polymer film is stretched at a high stretch ratio in a stretching tank having a specific boric acid concentration, the degree of neck-in phenomenon (a phenomenon in which the width direction is shortened) is reduced, and the chemical cost can be reduced. Thus, the present inventors have found that a polarizing film having a wide and thin thickness and a low boron atom content can be produced with a high yield and a low cost despite its excellent optical properties. In addition, the present inventors have also found that the polarizing film can reduce the influence on the environment at the time of disposal due to the low content of boron atoms. The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] A method for producing a polarizing film for dyeing and uniaxially stretching a polyvinyl alcohol polymer film, wherein the content of boron atoms in the polarizing film is 1.2-2. 0 is the mass%, the uniaxial stretching is carried out in an aqueous solution containing boric acid from 0.1 to 2.0 wt%, the stretching ratio is Ri 8x der than 7 times, the polyvinyl alcohol polymer film, A method for producing a polarizing film, characterized by not contacting with an aqueous solution containing boric acid at a concentration exceeding 2.0% by mass ,
[2] The method according to [1], wherein the polyvinyl alcohol-based polymer film contains 3 to 20 parts by mass of a plasticizer with respect to 100 parts by mass of the polyvinyl alcohol-based polymer .
[3 ] The method according to the above [1] or [2] , wherein the ratio of the thickness of the polarizing film to the thickness of the polyvinyl alcohol polymer film is 0.35 or less.
[ 4 ] The method according to any one of [1] to [ 3 ], wherein an effective area defined below of the polarizing film with respect to an area of the polyvinyl alcohol-based polymer film is 2.75 times or more,
Effective area: product of the shortest length of the TD (width direction) length of the polarizing film and the length of MD (stretch direction).
[ 5 ] The method according to any one of [1] to [ 4 ] above, wherein the polarizing film has a thickness of 10 to 40 μm.
About.

  Although the polarizing film of the present invention has high transmittance and polarization degree and excellent optical characteristics, the content of boron atoms is low and the influence on the environment is small when discarded. In addition, the production method of the present invention can produce the above polarizing film efficiently, does not require a large amount of boric acid, and can produce a wide and thin polarizing film with a high draw ratio and a high yield. , Can contribute to cost reduction.

The present invention is described in detail below.
The polarizing film of the present invention is obtained by dyeing and uniaxially stretching a polyvinyl alcohol polymer [hereinafter, the “polyvinyl alcohol polymer” may be abbreviated as “PVA”]. As the PVA constituting the PVA film, vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, etc. What can be obtained by saponifying the polyvinyl ester polymer obtained by superposing | polymerizing 1 type (s) or 2 or more types of ester can be used. Among the above vinyl esters, a compound having a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) in the molecule is preferable from the viewpoint of ease of production, availability, and cost of PVA. Vinyl is more preferred.

  The above-mentioned polyvinyl ester polymer is preferably obtained using only one or two or more kinds of vinyl esters as a monomer, and obtained using only one kind of vinyl ester as a monomer. Is more preferable, but may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith, as long as the effects of the present invention are not impaired. .

  Examples of other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide, N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amide, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamidepropyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogenated vinyl such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Allyl compounds such as allyl acid and allyl chloride; maleic acid or its salt, ester or acid anhydride; itaconic acid or its salt, ester or acid anhydride; vinylsilyl compound such as vinyltrimethoxysilane; unsaturated sulfonic acid be able to. Said polyvinyl ester-type polymer can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

The proportion of structural units derived from the other monomers in the polyvinyl ester polymer is 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester polymer. Preferably, it is 10 mol% or less, more preferably 5 mol% or less.
In particular, when the other monomer is a monomer that can be a monomer unit that promotes water solubility of the obtained PVA, such as (meth) acrylic acid or unsaturated sulfonic acid, The proportion of structural units derived from these monomers in the polyvinyl ester polymer in order to prevent the film from dissolving or fusing during processing in an aqueous solution, such as when producing a polarizing film from a film Is preferably 5 mol% or less, and more preferably 3 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester polymer.

  As the PVA constituting the PVA film used in the present invention, those not graft-copolymerized can be preferably used. However, within the range not impairing the effects of the present invention, one type of PVA or It may be modified with two or more types of graft copolymerizable monomers. The graft copolymerization can be performed on at least one of the polyvinyl ester polymer and the PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester polymer or PVA is 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester polymer or PVA. Preferably there is.

  In the PVA constituting the PVA film used in the present invention, a part of the hydroxyl groups may be crosslinked or may not be crosslinked. The PVA constituting the PVA film of the present invention may have a hydroxyl group partially reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or not reacted with these compounds. The structure may not be formed.

  The degree of polymerization of PVA constituting the PVA film used in the present invention is preferably 2000 or more from the viewpoint of the polarizing performance of the obtained polarizing film. When the degree of polymerization of PVA is 2000 or more, the polarizing performance of the polarizing film obtained from the PVA film can be improved and light leakage can be prevented from increasing, so that it is particularly suitable for liquid crystal display applications such as TV applications. This is preferable. Since the polarizing performance of the polarizing film obtained with a higher degree of polymerization of PVA becomes better, increasing the degree of polymerization has a certain effect on light leakage reduction. However, if the polymerization degree of PVA is too high, there is a tendency to lead to an increase in the production cost of PVA and poor processability during film formation, so the polymerization degree of PVA is in the range of 2000 to 10,000. More preferably, it is more preferably in the range of 2000 to 8000, and particularly preferably in the range of 2200 to 5000. In addition, the polymerization degree of PVA as used in this specification means the average polymerization degree measured according to description of JISK6726-1994.

Furthermore, the saponification degree of the PVA constituting the PVA film used in the present invention is preferably 99.0 mol% or more, more preferably 99.9 mol% or more, and 99.95 mol% or more. More preferably.
In this specification, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of PVA. The proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description of JIS K6726-1994.

  The PVA film used in the present invention may contain a plasticizer together with PVA. When a PVA film contains a plasticizer, the stretchability at the time of manufacturing a polarizing film from a PVA film can be improved. As the plasticizer, polyhydric alcohol is preferably used, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. The film can contain one or more of these plasticizers. Among these, glycerin is preferable because the stretchability of the PVA film becomes better.

  The content of the plasticizer in the PVA film is preferably 3 to 20 parts by mass, more preferably 4 to 18 parts by mass, and further preferably 5 to 15 parts by mass with respect to 100 parts by mass of PVA. preferable. When the content of the plasticizer is 3 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is improved, and the polarizing film can be easily collected in a large area. On the other hand, when the content of the plasticizer is 20 parts by mass or less with respect to 100 parts by mass of PVA, the plasticizer bleeds out on the surface of the PVA film, and the handleability of the PVA film is reduced or the stretchability is reduced. Can be suppressed.

  Moreover, when manufacturing using the stock solution for manufacturing the PVA film mentioned later, while forming property improves and generation | occurrence | production of the thickness variation of a film is suppressed, a metal roll or belt is used for film formation. When this is used, it is preferable to blend a surfactant in the stock solution because the PVA film can be easily peeled off from these metal rolls and belts. And when manufacturing a PVA film from the undiluted | mixed liquid with which surfactant was mix | blended, surfactant may contain in the said PVA film. There are no particular restrictions on the type of surfactant that is added to the stock solution for producing the PVA film, and thus the surfactant contained in the PVA film, but from the viewpoint of peelability from a metal roll or belt, an anionic interface is used. An activator or a nonionic surfactant is preferred, and a nonionic surfactant is more preferred.

  As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; a sulfonic acid type such as dodecylbenzene sulfonate and the like are suitable.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as oleic acid diethanolamide; polyoxyalkylene allyl phenyl ether The allyl phenyl ether type is preferred.
These surfactants can be used alone or in combination of two or more.

  When a surfactant is blended in a stock solution for producing a PVA film, the content of the surfactant in the stock solution, and thus the content of the surfactant in the PVA film, is 100 masses of PVA contained in the stock solution or the PVA film. Is preferably in the range of 0.01 to 0.5 parts by mass, more preferably in the range of 0.02 to 0.3 parts by mass, and 0.05 to 0.1 parts by mass with respect to parts. More preferably, it is within the range of parts. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, the film forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, the surfactant bleeds out on the surface of the PVA film, resulting in blocking, and handling properties are reduced. Can be suppressed.

The PVA film used in the present invention may be composed only of PVA or may be composed only of the PVA film and the above-described plasticizer and / or surfactant, but if necessary, an antioxidant, You may contain other components other than above-mentioned PVA, a plasticizer, and surfactant, such as an antifreezing agent, a pH adjuster, a masking agent, a coloring inhibitor, and an oil agent.
The proportion of the total of PVA, plasticizer and surfactant in the PVA film used in the present invention is preferably in the range of 50 to 100% by mass, and in the range of 80 to 100% by mass. It is more preferable that it is in the range of 95 to 100% by mass.

  The thickness of the PVA film used in the present invention is not particularly limited, but if it is too thin, there is a tendency that stretching breakage tends to occur during uniaxial stretching for producing a polarizing film, and if it is too thick, Since stretch spots tend to occur during uniaxial stretching for production, it is preferably in the range of 20 to 120 μm, more preferably in the range of 30 to 100 μm, and in the range of 40 to 80 μm. More preferably, it is within. In addition, the thickness of a PVA film can measure the thickness of arbitrary 5 places, and can obtain | require as those average values.

  The width | variety in particular of the PVA film used in this invention is not restrict | limited, It can determine according to the use etc. of the polarizing film manufactured from a PVA film. In recent years, the enlargement of screens of liquid crystal televisions and liquid crystal monitors has progressed. From this point of view, it is preferable that the width of the PVA film be 3 m or more. On the other hand, if the width of the PVA film is too wide, it is difficult to uniformly carry out uniaxial stretching itself when producing a polarizing film with a device that has been put to practical use. Therefore, the width of the PVA film should be 6 m or less. Is preferred.

  The method for producing the PVA film used in the present invention is not particularly limited, but the above-described PVA constituting the PVA film, and if necessary, a stock solution in which components such as a plasticizer and a surfactant are dissolved in a solvent. Can be used.

  Examples of the solvent used for preparing the stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylol. Propane, ethylenediamine, diethylenetriamine and the like can be mentioned, and one or more of these can be used. Among these, water is preferable from the viewpoint of environmental load and recoverability.

  The volatile content ratio of the stock solution used for film formation (the content ratio of volatile components such as a solvent removed by volatilization or evaporation during film formation in the stock solution) varies depending on the film forming method, film forming conditions, etc. It is preferably in the range of 95% by mass, more preferably in the range of 55-90% by mass, and still more preferably in the range of 60-85% by mass. When the volatile fraction of the stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming during the preparation of the stock solution are performed smoothly, and the production of PVA film with less foreign matter and defects is possible. It becomes easy. On the other hand, when the volatile fraction of the stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy.

  Examples of the film forming method for producing a PVA film using the above-described stock solution include a wet film forming method, a gel film forming method, a dry casting film forming method, and an extrusion film forming method. These film forming methods may be employed alone or in combination of two or more. Among these film forming methods, the extrusion film forming method is preferable because a PVA film having a uniform film thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as necessary.

As a specific method for forming a PVA film, for example, a T-type slit die, a hopper plate, an I-die, a lip coater die, or the like is used, or a cast film forming method is adopted. The undiluted solution is uniformly discharged or cast on the circumferential surface of the first heated roll (or belt) that is positioned on the most upstream side, and discharged or flowed on the circumferential surface of the first roll (or belt). Volatile components are evaporated from one side of the stretched film and dried, and then on the peripheral surface of the heated second roll (or drying roll) that rotates the other side of the discharged or cast film. Passing and drying, further drying on the peripheral surface of one or more rotating heated rolls arranged downstream thereof, or passing through a hot air drying device and further drying, and then winding Winding around the device The method can be industrially employed preferably. Drying with a heated roll and drying with a hot air dryer may be performed in an appropriate combination.
In order to adjust the PVA film to an appropriate state, it is desirable to provide a heat treatment device; a humidity control device; a motor for driving each roll; a speed adjustment mechanism such as a transmission.
The drying temperature in the drying process in the production process of the PVA film is such that a PVA film having excellent stretchability and dyeability when producing a polarizing film and excellent polarizing performance and durability of the obtained polarizing film is obtained. Therefore, it is preferably within the range of 50 to 150 ° C, and more preferably within the range of 60 to 140 ° C.

  The polarizing film of the present invention can be produced by dyeing and uniaxially stretching the above PVA film. In the production of the polarizing film, in addition to dyeing and uniaxial stretching, treatments such as moisture adjustment, washing, drying treatment, and heat treatment can be further performed as necessary.

  The staining can be performed using, for example, iodine. The dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing with iodine can be performed by immersing the PVA film in a solution (preferably an aqueous solution) containing iodine-potassium iodide. The concentration of iodine in the solution is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide in the solution is in the range of 0.01 to 10% by mass. It is preferable. Moreover, it is preferable that the temperature of the said solution exists in the range of 20-50 degreeC, and it is more preferable that it exists in the range of 25-40 degreeC.

  Uniaxial stretching can be performed in an aqueous solution containing 0.1 to 2.0% by mass of boric acid. When the content of boric acid in the aqueous solution is less than 0.1% by mass, the degree of polarization and durability of the obtained polarizing film tend to decrease. On the other hand, when the content exceeds 2.0% by mass, the amount of boric acid used increases and the production cost of the polarizing film increases, and the content of boron atoms in the resulting polarizing film tends to increase. . The content of boric acid in the aqueous solution is preferably in the range of 1.0 to 2.0% by mass, and more preferably in the range of 1.0 to 1.8% by mass.

  The temperature (stretching temperature) of the aqueous solution containing boric acid used in uniaxial stretching is preferably in the range of 30 to 90 ° C, more preferably in the range of 40 to 80 ° C, and 50 to 70. More preferably, it is within the range of ° C. Moreover, the said aqueous solution may contain potassium iodide, and it is preferable that the density | concentration exists in the range of 0.01-10 mass%.

  The stretch ratio at the time of uniaxial stretching is 5 times or more as the length of the obtained polarizing film with respect to the length of the PVA film before uniaxial stretching because excellent polarizing performance and a wide area polarizing film can be obtained. It is preferably 6 times or more, more preferably 6.5 times or more, and particularly preferably 7 times or more. On the other hand, the upper limit of the stretching ratio is not particularly limited, but the stretching ratio is preferably 10 times or less and more preferably 8 times or less because uniform stretching is possible.

  Regarding the thickness of the obtained polarizing film, the ratio of the thickness of the polarizing film to the thickness of the PVA film used is preferably 0.35 or less, more preferably 0.32 or less, and 0.315 or less. More preferably, it is particularly preferably 0.31 or less. The ratio can be controlled by adjusting the degree of the draw ratio. In addition, although the said ratio is so preferable that a thinner polarizing film is obtained as it is low, from the viewpoint of handleability, it is preferable that the said ratio is 0.1 or more.

  In addition, for the effective area of the obtained polarizing film, the effective area of the polarizing film with respect to the area of the PVA film used is preferably 2.75 times or more, more preferably 2.90 times or more, The ratio is more preferably 2.93 times or more, and particularly preferably 2.95 times or more. Here, the effective area is the shortest length (length of the narrowest portion) of the TD (width direction) length of the obtained polarizing film and the length of MD (stretching direction). Means product. The above-mentioned magnification can be controlled by adjusting the degree of the draw ratio. However, in the production method of the present invention, the degree of neck-in phenomenon can be reduced even when drawn at a higher magnification, so that it is wider. A polarizing film having an effective area can be obtained. In addition, as an upper limit of the said magnification, 4 times is mentioned, for example.

A polarizing film can be obtained by drying the uniaxially stretched PVA film. The temperature in the drying treatment is preferably in the range of 30 to 150 ° C, and more preferably in the range of 50 to 150 ° C.
Moreover, it is preferable to heat-process in the manufacture of a polarizing film. As a specific method of the heat treatment, for example, after the moisture content of the film is reduced to 10% by mass or less by the drying treatment, the film is tensioned and the heat treatment is performed at a temperature in the range of 80 to 120 ° C. The method of processing for 1 to 5 minutes is mentioned. According to this method, it is possible to obtain a polarizing film that is further excellent in dimensional stability, durability, and the like.

  When manufacturing a polarizing film using a PVA film, the PVA film before passing, during and after passing through each process is not brought into contact with an aqueous solution containing boric acid at a concentration exceeding 2.0 mass% throughout the manufacturing process. Preferably, the manufacturing cost of the polarizing film can be further reduced, and a polarizing film having a low boron atom content can be easily manufactured.

  The content of boron atoms in the polarizing film of the present invention is in the range of 0.1 to 2.0% by mass and in the range of 0.2 to 1.8% by mass based on the mass of the polarizing film. Is preferably within the range of 0.4 to 1.6% by mass. When the content of boron atoms in the polarizing film is in the above range, the influence on the environment can be reduced during disposal. When the content of boron atoms in the polarizing film is less than 0.1% by mass, the degree of polarization of the polarizing film is extremely deteriorated and the durability is also deteriorated. In addition, the content rate of the boron atom in a polarizing film can be measured using an ICP emission spectrometer.

  The thickness of the polarizing film of the present invention is preferably as thin as possible, but considering the handleability of the polarizing film, it is preferably in the range of 10 to 40 μm, more preferably in the range of 14 to 30 μm, More preferably, it is in the range of 18 to 24 μm. When the thickness of the polarizing film is within the above range, the polarizing film can contribute to further thinning of a member such as a liquid crystal display device. In addition, the thickness of a polarizing film can measure the thickness of arbitrary 5 places, and can obtain | require as those average values.

  The polarizing film of the present invention can be formed into a polarizing plate by attaching a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, for example, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. Examples of the adhesive for bonding include PVA adhesives and urethane adhesives. Among them, PVA adhesives are preferable.

  The polarizing plate obtained as described above can be preferably used as a member constituting a liquid crystal display device after being coated with an acrylic-based pressure-sensitive adhesive and then being bonded to a glass substrate. At this time, a retardation film, a viewing angle improving film, a brightness improving film, and the like may be further bonded.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.
In addition, the hot-water cutting temperature and swelling degree of a PVA film, the transmittance | permeability (T) of a polarizing film, a polarization degree (V), an effective area (S), and a polarizing film employ | adopted in the following manufacture examples, an Example, and a comparative example Each measuring method of the content rate of the boron atom in it is shown below.

Measurement of hot water cutting temperature of PVA film:
A weight was attached with a clip from the front end in the longitudinal direction of the PVA film cut to 5 mm (TD) × 30 mm (MD) to a portion 5 mm in the longitudinal direction from there. The weight of the weight, including the weight of the clip, was 0.05 g per 1 μm film thickness of the PVA film. Subsequently, up to 10 mm in the longitudinal direction from the end on the side where the clip of the PVA film was attached, including the part where the weight was attached with the clip, was immersed in distilled water at 40 ° C. Next, the temperature of distilled water was increased at a rate of temperature increase of 3 ° C./min, and the temperature at which the film was cut was defined as the hot water cutting temperature (° C.).

Measurement of swelling degree of PVA film:
The PVA film was cut to be 1.5 g or more and immersed in 1000 g of distilled water at 30 ° C. After dipping for 30 minutes, the PVA film was taken out, the surface water was blotted with a filter paper, and the mass “A” was measured. Subsequently, the PVA film was dried with a dryer at 105 ° C. for 16 hours, then the mass “B” was measured, and the degree of swelling was calculated by the following equation.
Swelling degree (% by mass) = A / B × 100

Measurement of transmittance (T) of polarizing film:
The transmittance (T) of the polarizing film was measured as follows using an ultraviolet-visible spectrophotometer “U-4100” (manufactured by Hitachi, Ltd.). In the measurement, an integral value (Y value) at 380 to 780 nm on which a wavelength-dependent weighting function based on the Japan Electronic Machine Industry standard was multiplied was measured.
The center part of the produced polarizing film was cut into a size of TD (width direction) × MD (stretching direction) = 4 cm × 8 cm, and the cut film was further cut into two at the center part of the MD, and two polarizing film samples (4 cm) × 4 cm) was obtained. Using one of these polarizing film samples, the transmittance when the MD (stretching direction) is set at an arbitrary angle with respect to the spectroscope, and this rotated by 90 ° on a plane perpendicular to the incident light The transmittance when measured was measured, and the average value thereof was defined as the transmittance (T) (unit:%) of the polarizing film.

Measurement of polarization degree (V) of polarizing film:
The transmittance (T _‖ ) (unit:%) when two polarizing film samples prepared in the measurement of the transmittance (T) of the polarizing film are stacked so that the MDs are parallel to each other is expressed as one polarized light. Similarly to the measurement of the transmittance (T) of the polarizing film using the film sample, the average value of the transmittance when set to an arbitrary angle and the transmittance when rotated by 90 ° was obtained. Moreover, permeability of the time of repeated polarizing film sample of two the so MD is perpendicular (T _⊥) (unit:%) and, in the same manner as described above, the permeability of the time set at any angle It calculated | required as an average value with the transmittance | permeability when it rotated 90 degrees. Using the obtained T _‖ and T _⊥ , the transmittance (V) (unit:%) of the polarizing film was calculated by the following formula.
V (%) = [( _T‖ − _T⊥ ) / ( _T‖ + _T⊥ )] ^1/2 × 100

Measurement of effective area (S) of polarizing film:
The effective area (S) of the polarizing film is expressed by the following formula, where “a” is the shortest length (length of the narrowest portion) of the TD length and “b” is the MD length: Calculated.
S = a × b

Measurement of boron atom content in polarizing film:
The measurement of the content of boron atoms in the polarizing film was performed using an ICP emission analyzer “IRIS AP” (manufactured by Thermo Fisher Scientific). The measurement sample was prepared by weighing 10 mg of the polarizing film, performing oxygen flask combustion using 20 mL of ion-exchanged water as an absorbing solution, and filtering with a 0.45 μm filter.

[Production Example 1]
Manufacture of PVA film samples:
An aqueous solution containing 100 parts by mass of polyvinyl alcohol having an average polymerization degree of 2400 and a saponification degree of 99.95 mol% and 12 parts by mass of glycerin as a plasticizer and having a polyvinyl alcohol concentration of 10% by mass is dried on a metal roll at 60 ° C. Thus, a PVA film having a thickness of 75 μm was obtained. The obtained PVA film was fixed to a frame and heat-treated at 140 ° C. for 3 minutes. The hot-water cutting temperature of the obtained heat-treated film was 68.2 ° C., and the degree of swelling was 200% by mass.
Moreover, the PVA film after the heat treatment was cut to obtain a sample. The size of the sample was 10 cm wide × 14 cm long in consideration of a portion 10 cm wide × 4 cm long corresponding to the uniaxially stretched portion and a fixed portion when uniaxially stretched. The width of the sample corresponds to TD (perpendicular to the longitudinal direction) at the time of manufacturing the PVA film, and the length corresponds to MD (longitudinal direction) at the time of manufacturing the PVA film.

[Example 1]
After two samples of the PVA film obtained in Production Example 1 were immersed in pure water at 30 ° C. for 1 minute, 0.05% by mass of iodine, 2.5% by mass of potassium iodide, and 1% by mass of boric acid Iodine was adsorbed by dipping in an aqueous solution (dye bath) at 30 ° C. contained in a proportion for 2.5 minutes. Next, in a 52.5 ° C. aqueous solution (stretching bath) containing 2% by mass of boric acid and 5% by mass of potassium iodide, the two samples were simultaneously uniaxially stretched in a parallel state. Since one sample broke when the draw ratio was 7.5, the drawing was stopped. Thereafter, the uniaxially stretched film that did not break was dried at 50 ° C. for 4 minutes to obtain a polarizing film.
The transmittance (T) of this polarizing film is 44.5%, the degree of polarization (V) is 99.4%, the shortest of the TDs is 4.1 cm, and the MD is 30.0 cm ( The effective area (S) was 123.0 cm ² ; 3.1 times the area of the uniaxially stretched portion of the sample used, and the thickness was 23 μm (0.31 times the thickness of the sample used). It was. Moreover, the content rate of the boron atom in a polarizing film was 1.2 mass%.

[Example 2]
After two samples of the PVA film obtained in Production Example 1 were immersed in pure water at 30 ° C. for 1 minute, 0.05% by mass of iodine, 2.5% by mass of potassium iodide, and 1% by mass of boric acid Iodine was adsorbed by immersing in an aqueous solution (dye bath) at 30 ° C. contained in a proportion for 3.5 minutes. Next, in a 52.5 ° C. aqueous solution (stretching bath) containing 1% by mass of boric acid and 5% by mass of potassium iodide, the two samples were simultaneously uniaxially stretched in a parallel state. Since one sample broke when the draw ratio was 7.5, the drawing was stopped. Thereafter, the uniaxially stretched film that did not break was dried at 50 ° C. for 4 minutes to obtain a polarizing film.
The transmittance (T) of this polarizing film is 44.4%, the degree of polarization (V) is 99.6%, the shortest of the TDs is 4.0 cm, and the MD is 30.0 cm ( The effective area (S) was 120.0 cm ² ; 3.0 times the area of the uniaxially stretched sample used) and the thickness was 22 μm (0.29 times the thickness of the used sample). It was. Moreover, the content rate of the boron atom in a polarizing film was 0.8 mass%.

[Comparative Example 1]
After two samples of the PVA film obtained in Production Example 1 were immersed in pure water at 30 ° C. for 1 minute, 0.05% by mass of iodine, 2.5% by mass of potassium iodide, and 1% by mass of boric acid Iodine was adsorbed by dipping in an aqueous solution (dye bath) at 30 ° C. contained in a proportion for 2.5 minutes. Next, in a 52.5 ° C. aqueous solution (stretching bath) containing 4% by mass of boric acid and 5% by mass of potassium iodide, when the two samples were simultaneously uniaxially stretched, Since one sample broke when the draw ratio was 6.0 times, the drawing was stopped. Thereafter, the uniaxially stretched film that did not break was dried at 50 ° C. for 4 minutes to obtain a polarizing film.
The transmittance (T) of this polarizing film is 44.5%, the degree of polarization (V) is 99.6%, the shortest of the TD lengths is 4.4 cm, and the MD length is 24.0 cm ( The effective area (S) was 105.6 cm ² ; 2.6 times the area of the uniaxially stretched sample used) and the thickness was 28 μm (0.37 times the thickness of the used sample). It was. Moreover, the content rate of the boron atom in a polarizing film was 3.2 mass%.

[Comparative Example 2]
After two samples of the PVA film obtained in Production Example 1 were immersed in pure water at 30 ° C. for 1 minute, 0.05% by mass of iodine, 2.5% by mass of potassium iodide, and 1% by mass of boric acid Iodine was adsorbed by dipping in an aqueous solution (dye bath) at 30 ° C. contained in a proportion for 2.5 minutes. Next, in a 52.5 ° C. aqueous solution (stretching bath) containing 3% by mass of boric acid and 5% by mass of potassium iodide, the two samples were simultaneously uniaxially stretched in a parallel state. Since one sample broke when the draw ratio was 6.6 times, the drawing was stopped. Thereafter, the uniaxially stretched film that did not break was dried at 50 ° C. for 4 minutes to obtain a polarizing film.
The transmittance (T) of this polarizing film is 44.8%, the degree of polarization (V) is 99.1%, the shortest length among the TD lengths is 4.3 cm, and the MD length is 26.4 cm ( The effective area (S) was 113.5 cm ² ; 2.8 times the area of the uniaxially stretched sample used) and the thickness was 25 μm (0.33 times the thickness of the used sample). It was. Moreover, the content rate of the boron atom in a polarizing film was 2.8 mass%.

  The above results are shown in Table 1 below.

  In Examples 1 and 2, it is possible to obtain a polarizing film that can be stretched at a high stretching ratio and has a wider effective area. Further, the obtained polarizing film is thin and has a low content of boron atoms. It was. On the other hand, in Comparative Examples 1 and 2, it was difficult to stretch at a high stretch ratio, a polarizing film having a narrow effective area was obtained, and the obtained polarizing film was thick and the boron atom content was high. .

  The polarizing film of the present invention produces a polarizing plate that is a member of a liquid crystal display device such as a liquid crystal television, a notebook computer, a liquid crystal monitor, a liquid crystal color projector, an in-vehicle navigation system, a mobile phone, and a measuring instrument used indoors and outdoors. It can preferably be used as a material for Above all, materials for manufacturing polarizing plates that make up liquid crystal display devices used in notebook PCs and mobile phones that are required to be thinner and lighter, and liquid crystal televisions and liquid crystal monitors that are required to have larger screens. Can be used particularly effectively.

Claims (5)

A method for producing a polarizing film for dyeing and uniaxially stretching a polyvinyl alcohol polymer film, wherein the content of boron atoms in the polarizing film is 1.2 to 2.0% by mass based on the mass of the polarizing film. , and the said uniaxial stretching is carried out in an aqueous solution containing boric acid from 0.1 to 2.0 wt%, the stretching ratio is Ri 8x der than 7 times, the polyvinyl alcohol polymer film, boric acid 2 A method for producing a polarizing film, wherein the polarizing film is not brought into contact with an aqueous solution containing a concentration exceeding 0.0 mass% . The manufacturing method of Claim 1 in which the said polyvinyl alcohol-type polymer film contains 3-20 mass parts of plasticizers with respect to 100 mass parts of polyvinyl alcohol-type polymers . The manufacturing method according to claim 1 or 2 , wherein the ratio of the thickness of the polarizing film to the thickness of the polyvinyl alcohol-based polymer film is 0.35 or less. The manufacturing method according to any one of claims 1 to 3 , wherein an effective area defined below of the polarizing film with respect to an area of the polyvinyl alcohol polymer film is 2.75 times or more.
Effective area: product of the shortest length of the TD (width direction) length of the polarizing film and the length of MD (stretch direction). The manufacturing method according to any one of claims 1 to 4 , wherein the polarizing film has a thickness of 10 to 40 µm.