JP2008242309A - Polarizing plate, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing plate, with which a triacetyl cellulose layer is efficiently and stably arranged on a surface of a film by applying a triacetyl cellulose solution onto the surface of the dyed and uniaxially stretched polyvinyl alcohol based resin film and drying the film, and to provide the polarizing plate obtained by the manufacturing method. <P>SOLUTION: The method for manufacturing the polarizing plate, having the triacetyl cellulose layers arranged on surfaces of both sides of the polyvinyl alcohol based resin film of which the surfaces of both sides are dyed with iodine or a dichroic dye, and which is uniaxially stretched, is characterized in that the triacetyl cellulose layers are formed by applying the triacetyl cellulose solution to the surfaces of both sides of the polyvinyl alcohol based resin film and drying the film and so on. The polarizing plate obtained by the manufacturing method is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention efficiently and stably applies a triacetyl cellulose layer on the surface of the film by applying and drying a triacetyl cellulose solution on the surface of the dyed and uniaxially stretched polyvinyl alcohol resin film. The present invention relates to a polarizing plate manufacturing method that can be provided, and a polarizing plate obtained by the manufacturing method.

  A polyvinyl alcohol resin film (hereinafter referred to as “PVA film”) whose surface is dyed with iodine or a dichroic dye is widely used as a polarizing element. However, when a PVA film coated with iodine is used as a polarizing element, the polarizing property is good, but the resistance to moisture and the resistance to heat are insufficient. For this reason, there has been a problem that the polarizing element deteriorates when used under relatively high humidity conditions or high temperature conditions, and sufficient performance cannot be obtained.

  A polarizing element in which a dichroic dye is applied to the surface of a PVA film is also widely used. However, when a PVA film coated with a dichroic dye is used as a polarizing element, a cationic group is introduced into the PVA film for the purpose of sufficiently adsorbing the dichroic dye to the PVA film. Alternatively, a copolymer of ethylene and polyvinyl alcohol is used as the base material of the polarizing element, but all of them have problems such as poor resistance to moisture.

  Therefore, a film of triacetyl cellulose is generally provided on the surface of the polarizing element for the purpose of protecting the polarizing element from moisture and heat. The triacetyl cellulose is excellent in transparency, has little influence on the performance of the polarizing element, and has excellent resistance to heat and water, and thus is widely used as a protective film for polarizing elements (for example, Patent Documents). 1 and 2).

  When a film of triacetyl cellulose is provided on the surface of a PVA film polarizing element dyed with iodine or the like, a method such as wet lamination such as adhesion with an adhesive or dry lamination such as melt adhesion by heating is employed. Has been.

JP 2006-137909 A JP 2006-178176 A

  However, the conventional method of providing a triacetylcellulose film on a polarizing element such as a PVA film has caused various disadvantages. That is, in the conventional method, it is necessary to separately manufacture a triacetylcellulose film, and it is necessary to manufacture under an environment in which precise thickness adjustment and dust do not adhere. However, when the triacetylcellulose film once produced is fed out again, the film may be subjected to uneven tension or static electricity may be generated. As a result, the thickness of the triacetyl cellulose film becomes non-uniform due to the tension, the film itself is distorted, dust adheres due to static electricity, and the like, which is a factor in reducing the production efficiency.

  In addition, in the wet lamination method in which the triacetyl cellulose film is attached through an adhesive layer obtained by drying and solidifying a polyvinyl alcohol solution, the adhesive is applied uniformly so as not to impair the performance of the polarizing element. This requires advanced technology, and the types of adhesives that can be used are considerably limited.

  Furthermore, after attaching the triacetyl cellulose film and the PVA film, it takes time until the adhesive dries, or the operation of cleaning the adhesive application device after the attaching operation of the triacetyl cellulose film is completed. The burden on the surface was large, and the production efficiency was not favorable.

  Also, equipment for applying and drying the adhesive is necessary, and maintenance of the equipment is added, which is also a problem from an economic aspect.

  Furthermore, in dry lamination such as melt adhesion by heating, the thickness may not be kept constant by the applied tension in the process even if the change in the laminating temperature is slight. Temperature control at the time of lamination of an acetylcellulose film is complicated, and further perfection has been desired.

Therefore, the present invention solves the above problems, and the invention according to claim 1 is a polyvinyl alcohol-based resin film in which both surfaces are dyed with iodine or a dichroic dye and are uniaxially stretched. A method for producing a polarizing plate in which a triacetyl cellulose layer is provided on both surfaces of a triacetyl cellulose by applying a triacetyl cellulose solution to the surfaces on both sides of the polyvinyl alcohol-based resin film and drying it. The present invention provides a polarizing plate manufacturing method characterized by forming a layer.

The invention according to claim 2 is characterized in that, in addition to the feature according to claim 1, the solvent of the triacetyl cellulose solution is composed of methylene chloride and methanol, the methylene chloride is 80 to 100% by weight, and the methanol is The present invention provides a method for producing a polarizing plate characterized by being 0 to 20% by weight.

Furthermore, the invention described in claim 3 provides a polarizing plate obtained by the manufacturing method described in claim 1 or 2.

  According to the production method of the present invention, since a triacetyl cellulose film is not used as a means for providing a triacetyl cellulose layer on the surface of a polarizing element that is a dyed and stretched PVA-based film, it is caused by static electricity generated from the film. There is no thickness variation or distortion caused by adhesion of dust or the tension applied when the film is fed.

  Also, according to the production method of the present invention, the protective layer is provided by applying and drying the triacetyl cellulose solution on the surface of the PVA film, so that it is much easier and quicker than the conventional production method. Thus, a triacetylcellulose layer can be formed, which can contribute to an improvement in production efficiency.

  Furthermore, according to the production method of the present invention, it can be carried out with simple equipment, and is inexpensive and easy to maintain as compared with equipment used for wet lamination in which a film is attached with a conventional adhesive.

  In addition, according to the production method of the present invention, temperature control is easy as compared with a conventional method using dry lamination such as melt adhesion by heating, and the formed triacetylcellulose layer has almost no tension in the process. Therefore, since the thickness is stable and distortion does not occur, a protective layer that is stable in terms of physical properties can be formed.

  Furthermore, the polarizing plate of the present invention has a stable triacetyl cellulose layer as a protective layer and is less susceptible to distortion in the process, so that both the functional and physical properties are compared with conventional polarizing plates. It is excellent.

Polyvinyl alcohol or a derivative thereof is used as a raw material for the PVA film applied to the production method of the present invention as long as the effects of the present invention are not impaired. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and alkyl esters thereof, acrylamide and the like. can give.

  The degree of polymerization of the polyvinyl alcohol resin is 1000 to 10000, preferably 1500 to 10000. The saponification degree is preferably 80 to 100 mol%.

  The PVA film may contain an additive such as a plasticizer. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the PVA film.

  Usually, a PVA film having a thickness of about 30 to 150 μm is used in an unstretched state.

  The PVA film is dyed with iodine or a dichroic dye. In the dyeing process, when dyed with iodine, an aqueous solution containing iodine ions such as an aqueous iodine solution or potassium iodide is used.

  As the aqueous iodine solution, one having an iodine concentration of 0.01 to 0.5% by weight can be used, and one having an iodine concentration of 0.2 to 0.4% by weight is preferably used.

  When an aqueous solution of iodide such as potassium iodide is used, one having an iodide concentration of 0.02 to 10% by weight is preferred, and one having an iodide concentration of 0.2 to 10% by weight is further added. preferable.

  As the dyeing treatment for the PVA film, the PVA film is applied to the iodine aqueous solution or the aqueous solution containing iodine ions (hereinafter referred to as “iodine aqueous solution”) uniformly. It is preferable to carry out the dyeing | staining process by being immersed in. Moreover, it is preferable to perform the time immersed in aqueous solutions, such as an iodine of a PVA-type film, for 10 second-300 seconds. After the immersion treatment of the aqueous solution such as iodine of the PVA-based film, a drying treatment by blowing air or the like is performed, and iodine is fixed to the surface of the PVA-based film.

 When the PVA film is dyed with a dichroic dye, Direct Black 17, 19, 154, Direct Brown 44, 106, 195, 210, 223, Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247, Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270, Direct Violet 9, 12, 51, 98, Dichroic dyes such as Direct Green 1, 85, Direct Yellow 8, 12, 44, 86, 87, Direct Orange 26, 39, 106, 107, etc. (Referred to as “dichroic dye aqueous solution”).

  In addition, as the dyeing treatment to the PVA film, the PVA film is changed to an aqueous dichroic dye solution from the viewpoint of uniformly applying the aqueous dichroic dye solution as in the case of dyeing with an aqueous solution such as iodine. It is preferable to perform a dyeing process by dipping. The time for immersing the PVA film in the aqueous dichroic dye solution is preferably 10 seconds to 300 seconds. As in the case of the aqueous solution of iodine or the like, after the immersion treatment of the dichroic dye aqueous solution of the PVA-based film, a drying process by blowing or the like is performed to fix the dichroic dye on the surface of the PVA-based film. It becomes.

  In the production method of the present invention, the PVA film needs to be oriented in the uniaxial direction by orienting the molecules constituting the PVA film from the viewpoint of ensuring polarization performance. The draw ratio of the PVA film in the drawing treatment is at least 4 times or more, preferably 5 to 8 times, from the viewpoint of imparting sufficient polarization performance. Moreover, the said extending | stretching process may be performed at the process before the dyeing | staining process by the said aqueous solutions, such as the said iodine, or dichroic dye aqueous solution, and may be performed at a subsequent process.

In the production method of the present invention, the triacetyl cellulose solution is applied to the surfaces on both sides of the uniaxially stretched polyvinyl alcohol resin film whose surfaces on both sides are dyed with iodine or a dichroic dye, and dried. An acetylcellulose layer is formed.

In the production method of the present invention, the applied triacetyl cellulose solution is obtained by dissolving triacetyl cellulose in an organic solvent. Various solvents can be used as the organic solvent, but methylene chloride is preferably used from the viewpoints of coating properties, rapid drying, and the like. Moreover, although a methylene chloride can also be used independently as a solvent of a triacetyl cellulose solution, it is preferable to use the mixed solution of a methylene chloride and methanol. When a mixed solution of methylene chloride and methanol is used as a solvent, the content of methylene chloride and methanol in the solvent is 80% by weight or more and less than 100% by weight of methylene chloride, and 0% by weight of methanol. It is preferably 20% by weight.

In the production method of the present invention, a triacetyl cellulose solution is applied to both surfaces of a PVA-based film dyed with iodine or a dichroic dye on both surfaces and uniaxially stretched by a coater. Examples of the coating apparatus include a knife coater, a gravure direct coater, a gravure reverse coater, a reverse roll coater, a gravure direct roll coater, a gravure reverse roll coater, and a roll coater.

After the triacetyl cellulose solution is applied to the surface of the PVA film by a coating apparatus, the triacetyl cellulose layer is formed by drying. As means for drying the triacetyl cellulose solution applied to the surface of the PVA film, known means such as warm air drying and vacuum drying can be employed. The coating thickness of the triacetyl cellulose solution is preferably adjusted so that the thickness of the triacetyl cellulose layer after drying is 3 to 100 μm.

  Since the production method of the present invention can easily and efficiently produce a polarizing plate, it can contribute to cost reduction and quality stabilization of the polarizing plate, and is very useful industrially.

Claims (3)

A method for producing a polarizing plate in which a triacetyl cellulose layer is provided on both surfaces of a polyvinyl alcohol-based resin film whose surfaces on both sides are dyed with iodine or a dichroic dye and uniaxially stretched. A method for producing a polarizing plate, comprising forming a triacetyl cellulose layer by applying a triacetyl cellulose solution on both surfaces of a resin film and drying the solution. 2. The production of a polarizing plate according to claim 1, wherein a solvent of the triacetylcellulose solution is composed of methylene chloride and methanol, wherein the methylene chloride is 80 to 100 wt% and methanol is 0 to 20 wt%. Method. A polarizing plate obtained by the production method according to claim 1.