JP2011081399A - Method for manufacturing polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin polarizing film with a small contraction stress using a means different from a conventional means. <P>SOLUTION: The method for manufacturing a polarizing plate 4 with a protective film has steps of: applying a polyvinyl alcohol resin to a base material resin film; uniaxially extending the obtained laminated film so that a thickness of the polyvinyl alcohol resin layer becomes 10 μm or below; staining the polyvinyl alcohol resin layer using a dichroism pigment; pasting the protective film 3 to a side of the polyvinyl alcohol resin layer 1 whose thickness becomes 10 μm or below and for which staining is performed through an adhesive; and peeling and removing the base material resin film 2 after the protective film 3 is pasted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

TECHNICAL FIELD OF THE INVENTION

  The present invention relates to a polarizing plate and a method for producing the same.

Conventional technology

  Flat display devices, particularly liquid crystal display devices, are used in various applications such as notebook personal computers and mobile phones. At present, a mobile information terminal such as a mobile phone is remarkably widespread, which is said to be an advanced information society. Along with this, multi-function and light weight thinning are rapidly progressing. Accordingly, there is an increasing demand for lighter and thinner optical functional films used in liquid crystal display devices. Of the optical functional films used in the liquid crystal display device, the thickest film is usually the polarizing plate. A general polarizing plate is a protective film on both sides of a polarizing film obtained by immersing a polyvinyl alcohol film subjected to uniaxial stretching and adsorption orientation of a dichroic substance in an aqueous solution containing boric acid, washing with water, and drying. It is made by pasting. The thickness of the polarizing film currently industrially produced is usually about 15 μm to 30 μm, and the thickness of the polarizing plate after the protective film is bonded is from 100 μm to 200 μm.

  Moreover, when the film thickness of a polarizing film is thick, there exists a problem also in the point of shrinkage stress besides light weight thinning. For example, if a polarizing plate with a protective film bonded to the current polarizing film is left under dry heat, the polarizing film in the polarizing plate will shrink, causing the polarizing plate to curl or significantly degrade the display quality of the display element. There is. Therefore, a polarizing plate having a small shrinkage stress is required.

  Therefore, the present inventors have made extensive research in order to reduce the thickness of the polarizing plate used as a component of the flat display device and reduce its shrinkage stress. By adopting a method different from the above, it was found that a thin polarizing film that could not be obtained by the conventional method could be produced, and that it was possible to reduce the shrinkage stress by using it, and the present invention was achieved. Accordingly, an object of the present invention is to provide a polarizing plate using a polarizing film that is thin and has a small shrinkage stress in response to a request for light weight and thinning, and to provide a method for manufacturing the polarizing plate by a method different from the conventional one. is there.

  That is, the present invention provides a polarizing plate in which a protective film is bonded to at least one surface of a polarizing film having a thickness of 10 μm or less mainly composed of a polyvinyl alcohol-based resin. The step of applying resin, the step of uniaxially stretching the resulting laminated film so that the thickness of the polyvinyl alcohol resin layer is 10 μm or less, and the adhesive on the side of the polyvinyl alcohol resin layer having a thickness of 10 μm or less The manufacturing method of the said polarizing plate including the process of bonding a protective film through, and the process of peeling and removing a base resin film after a protective film is bonded together is provided.

  Since the polarizing plate of the present invention is thin and has a small shrinkage stress, it contributes to the reduction in weight and thickness of flat display devices used in information portable terminals and the like. Further, according to the present invention, such a thin polarizing plate can be produced industrially advantageously.

BEST MODE FOR CARRYING OUT THE INVENTION

  In the polarizing plate of the present invention, a protective film is bonded to at least one surface of a polarizing film having a thickness of 10 μm or less mainly composed of a polyvinyl alcohol resin. Examples of the polyvinyl alcohol-based resin include those obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, vinyl ethers, and unsaturated sulfonic acids. The degree of saponification of the polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 to 100 mol%, and more preferably 99 mol% or more from the viewpoint of optical properties. The polyvinyl alcohol-based resin may be further modified, and examples of the modified polyvinyl alcohol-based resin include polyvinyl formal and polyvinyl acetal modified with aldehydes. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 10,000, and more preferably 2,000 to 10,000.

  In the present invention, in order to make such a polyvinyl alcohol-based resin and a thickness of less than 10 [mu] m, the polyvinyl alcohol-based resin is applied to the base resin film, a method of the laminated film uniaxially stretched obtained is employed. The base resin film used here is other than the polyvinyl alcohol resin, and specific examples thereof include a polyester resin film and a polyolefin resin film. As the polyester resin film, an amorphous polyethylene terephthalate film, the like, but also polyolefin resin film of polyethylene naphthalate film, polypropylene film, polyethylene film, ethylene - vinyl acetate copolymer film, ethylene - vinyl alcohol copolymer weight Examples of the combined film include, but are not limited to, of course. The base resin film is not particularly limited as long as it can be uniaxially stretched about 5 times in the subsequent step, but preferably has a glass transition temperature of 140 ° C. or lower. The thickness of the base resin film is preferably about 20 to 800 μm, more preferably about 100 to 400 μm.

  A polyvinyl alcohol-based resin is applied on such a base resin film. Here, a polyvinyl alcohol resin solution dissolved in an appropriate solvent is usually used, and after application, it is dried. Examples of the solvent for dissolving the polyvinyl alcohol-based resin include water, dimethyl sulfoxide, N-methylpyrrolidone, various glycols, and the like, and water is most preferable. When water is used, an organic solvent may be contained. The concentration of the polyvinyl alcohol resin in this solution is usually about 1 to 20% by weight, preferably about 2 to 10% by weight. In the polyvinyl alcohol resin solution, a plasticizer such as glycols, a leveling agent such as a surfactant, a dichroic dye, and the like may be blended.

  Application | coating of the polyvinyl alcohol-type resin solution to a base resin film can be performed by the method generally known. For example, there are a roll coating method, a gravure coating method, a spray coating method, a dipping method, etc. Of course, the method is not limited to these. Although drying is normally performed at 100 degrees C or less, if it is the temperature which a base resin film does not deform | transform, it will not specifically limit. The film thickness of the dried polyvinyl alcohol resin is about 2 to 50 μm, preferably about 3 to 20 μm. Moreover, you may surface-treat this base resin film prior to application | coating of the polyvinyl alcohol-type resin solution to a base resin film. Examples of the surface treatment method include corona treatment, flame treatment, plasma treatment, and primer treatment. For the primer treatment, a conventionally known primer resin such as polyurethane resin or polyester resin can be used. The surface treatment may be performed to such an extent that the base resin film and the polyvinyl alcohol-based resin layer do not peel off during a uniaxial stretching process or a dyeing process, which will be described later, and is not necessarily required until strong adhesion is obtained.

  Thus, the laminated film in which the polyvinyl alcohol-based resin is applied on the base resin film is uniaxially stretched. Uniaxial stretching may be performed by a method of stretching uniaxially between rolls having different peripheral speeds, or by a method of stretching uniaxially by a tenter method. Moreover, although it may extend | stretch uniaxially using a hot roll and you may roll using a hot roll, the tenter method is used optimally. The draw ratio is usually about 4 to 8 times. Before and after the stretching step, steps such as preheating, heat treatment and cooling may be appropriately provided. The stretching temperature varies depending on the properties of the selected base resin film. For example, when the base resin film is an amorphous polyester resin film, stretching is performed at a temperature of about 70 to 120 ° C., preferably about 85 to 110 ° C. It can be performed. In the case of uniaxial stretching, good stretching can be achieved by adjusting the water content of the polyvinyl alcohol-based resin on the base resin film to about 1 to 10% by weight, preferably about 2 to 8% by weight.

  A dichroic dye is adsorbed and oriented on a web in which a polyvinyl alcohol-based resin is applied to a base resin film, and is usually subjected to boric acid treatment. As the dichroic dye, iodine or a dichroic organic dye is used. The adsorption orientation of the dichroic dye is performed by uniaxial stretching of the web and dyeing using the dichroic dye. Dyeing may be performed before uniaxial stretching or may be performed after uniaxial stretching, but is performed in the order of application of polyvinyl alcohol resin to the base resin film, uniaxial stretching of the resulting web, and then dyeing. Is most preferred. For dyeing, for example, a method of immersing the web in an aqueous solution containing a dichroic dye can be employed.

  When the dichroic dye is iodine, an aqueous solution containing iodine and potassium iodide is used as the dyeing bath. The iodine content in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the potassium iodide content is usually about 0.5 to 10 parts by weight per 100 parts by weight of water. is there. The temperature of this aqueous solution is usually about 20 to 40 ° C., and the immersion time is usually about 30 to 300 seconds. In this operation, iodine is usually adsorbed only on the polyvinyl alcohol resin layer on the web.

  When a dichroic organic dye is used as the dichroic dye, the content of the dichroic organic dye in the dyeing bath is usually about 0.001 to 0.1 parts by weight per 100 parts by weight of water, and advantageously 0.01 parts by weight or less. This dyeing bath may contain a plurality of dichroic organic dyes or may contain an inorganic salt such as sodium sulfate. The dyeing temperature in the case of using the dichroic organic dye is appropriately selected within a temperature range in which the polyvinyl alcohol-based resin layer does not peel from the base resin film, and is, for example, about 20 to 80 ° C. The immersion time is usually about 30 to 300 seconds. Even in this operation, the dichroic organic dye is usually adsorbed only on the polyvinyl alcohol resin layer on the web.

  The boric acid treatment is performed by immersing a web having a uniaxially stretched polyvinyl alcohol-based resin layer dyed with a dichroic dye in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 0.5 to 15 parts by weight, preferably about 1 to 12 parts by weight per 100 parts by weight of water. The boric acid treatment may be performed at a temperature at which the polyvinyl alcohol-based resin layer does not peel from the base resin film. For example, it is appropriately selected from a temperature range of 30 ° C. or higher, preferably about 30 to 85 ° C. The boric acid treatment time is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. When the dichroic dye is iodine, the boric acid aqueous solution may contain potassium iodide. When it contains potassium iodide, its content is usually about 0.5 to 20 parts by weight, preferably 1 to 15 parts by weight per 100 parts by weight of water.

  The uniaxially stretched web after the boric acid treatment is usually washed with water. This water washing treatment is performed, for example, by immersing the uniaxially stretched web treated with boric acid in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. Next, a drying treatment is performed. This drying is usually performed at a temperature of 100 ° C. or lower, preferably 40 to 95 ° C. The drying time is usually about 120 to 600 seconds.

  The web thus obtained becomes a multilayer film in which a polarizing film is formed on a base resin film. For example, when a laminate film in which a 5 μm-thick polyvinyl alcohol-based resin is coated on a 250 μm-thick amorphous polyethylene terephthalate film is stretched 5 times as a starting film, the total thickness of the web with a polarizing film after the drying step is, for example, About 51 μm. The thickness of the polarizing film layer at this time is approximately 1 μm. In the polarizing plate of the present invention, the thickness of the polarizing film necessary for reducing the thickness and reducing the shrinkage stress is 10 μm or less, and preferably about 0.5 to 5 μm. As the film thickness increases, not only the purpose of reducing the weight and thickness cannot be achieved, but also the shrinkage stress increases and the resulting polarizing plate curls.

  When a transparent base material is used as the base resin film, the web with a polarizing film can be used as a polarizing plate as it is, but the base resin film may be damaged in the stretching process or the dyeing process. For reasons such as it is difficult to strengthen the adhesion between the base resin film and the polarizing film, or the crystallization of the base resin film proceeds in the stretching process, the transparency may decrease. It is generally difficult to use a resin film as a protective film as it is. Therefore, as a result of further studies, the present inventors have found that a polarizing plate without the above-mentioned problems can be produced by transferring the polarizing film to the protective film, instead of directly using the base resin film as a protective film. I found it.

  The transfer of the polarizing film to the protective film can be performed, for example, in the order shown in FIG. Drawing 1 is a mimetic diagram showing roughly the process after protection film pasting by the present invention. A coating apparatus 12 is used as an adhesive on the polyvinyl alcohol resin layer (polarizing film) 1 side of the laminated film in which the polyvinyl alcohol resin layer 1 is laminated on the base resin film 2 and uniaxially stretched and dyed. Is applied. On this adhesive layer, the protective film 3 delivered from the protective film supply means 13 is bonded by a bonding roll 14 and bonded through a drying furnace 15. What is important here is to make the peel strength between the polarizing film and the protective film after leaving the drying furnace 15 larger than the peel strength between the base resin film and the polarizing film. If the peel strength between the base resin film / polarizing film is larger than the peel strength between the polarizing film / protective film, not only a clean transfer but also a complete transfer may not be possible. After drying, the substrate resin film 2 is peeled off from the polarizing film 1 by being taken up by a take-up roll 16, and becomes a polarizing plate 4 in which the protective film 3 is bonded to one side of the polarizing film 1. Furthermore, a protective film can also be bonded to the other surface of the polarizing film.

  Examples of protective films include cyclic polyolefin resins such as cellulose acetate resin films such as triacetyl cellulose and diacetyl cellulose, acrylic resin films, polyester resin films, polyarylate resin films, polyethersulfone resin films, and polynorbornene films. Although a film etc. can be used, A triacetyl cellulose film and a cyclic polyolefin resin film are used preferably especially. The thickness of the protective film is usually about 30 to 200 μm. For the lamination, a transparent and optically isotropic adhesive is usually used, and examples of such an adhesive include a polyvinyl alcohol-based adhesive.

  When the polarizing film on the base resin film is transferred to another protective film and used, the film is charged when the base resin film is peeled and removed, and dust is attracted to induce defects in the subsequent process. Thus, the yield in the manufacturing process may be reduced. Therefore, it is preferable to subject the film to be used to antistatic treatment. The antistatic treatment is preferably applied to all of the base resin film, the primer layer of the base resin film, the polarizing film, the protective film, and the adhesive between the polarizing film and the protective film. Is also effective. In particular, it is effective to apply an antistatic treatment to the base resin film. Examples of methods for directly applying an antistatic treatment to the film include surfactants, cationic antistatic agents such as ammonium-based, organic antistatic agents such as anionic antistatic agents, tin oxide, indium oxide, and oxidation. There is a method in which an inorganic antistatic agent in which an inorganic compound having conductivity such as antimony is dispersed in a suitable binder such as pentaerythritol is applied to the surface of the base resin film. Further, the antistatic agent as described above may be mixed in the film or the adhesive from the beginning.

  The polarizing plate thus obtained may have a hard coat layer, an antireflection layer, an antiglare layer and the like on the surface. Usually, an adhesive is applied to at least one side of the polarizing plate.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these Examples.

Example 1
The surface of an amorphous polyethylene terephthalate sheet having a thickness of 250 μm subjected to antistatic treatment was subjected to corona treatment. On this corona-treated surface, a 5% by weight aqueous solution of a polyvinyl alcohol resin having a polymerization degree of 2400 and a saponification degree of 99.9% or more was coated with a bar coater, and then dried in a hot air drying oven at 50 ° C. for 5 minutes. A polyvinyl alcohol layer having a thickness of 5 μm was provided. This sheet was stretched 5 times on a horizontal axis at 100 ° C. using a tenter stretching machine to obtain a dyeing web. This dyeing web is immersed in pure water at 25 ° C. for 1 minute, and then immersed in an aqueous solution containing 0.25 parts by weight of iodine and 5 parts by weight of potassium iodide per 100 parts by weight of water at a temperature of 28 ° C. for 180 seconds. did. Subsequently, it was immersed in a boric acid aqueous solution containing 7.5 parts by weight of boric acid and 6 parts by weight of potassium iodide per 100 parts by weight of water at a temperature of 40 ° C. for 300 seconds. Thereafter, it was washed with pure water at 15 ° C. for 2 seconds. The film washed with water was dried at 50 ° C. for 300 seconds to obtain a polarizing film with a base resin film. At this time, the thickness of the polarizing film excluding the base resin film was 1 μm.

  A protective film having a thickness of 80 μm and made of triacetylcellulose and saponified on the surface is bonded to the polarizing film surface of the polarizing film with a base resin film through an adhesive made of a 5 wt% aqueous polyvinyl alcohol solution. And dried at 50 ° C. for 5 minutes. After drying, the base resin film was peeled off to obtain a polarizing plate with a triacetyl cellulose film. The thickness of this polarizing plate was 81 μm.

Comparative Example 1
A polyvinyl alcohol film having a thickness of 75 μm, a degree of polymerization of 2,400, and a degree of saponification of 99.9% or more was uniaxially stretched at a draw ratio of 5 times in a dry manner, and iodine was added to 100 parts by weight of water while maintaining a tension state. The film was immersed in an aqueous solution containing 05 parts by weight and 5 parts by weight of potassium iodide at a temperature of 28 ° C. for 60 seconds. Next, while maintaining the tension state, it was immersed in a boric acid aqueous solution containing 7.5 parts by weight of boric acid and 6 parts by weight of potassium iodide per 100 parts by weight of water at a temperature of 73 ° C. for 300 seconds. Then, it wash | cleaned for 10 second with 15 degreeC pure water. The film washed with water was dried at 70 ° C. for 300 seconds while keeping the tensioned state to obtain a polarizing film. The thickness of this polarizing film was 23 μm. In addition, the polarizing film marketed normally is such a film thickness. A polyvinyl alcohol-based adhesive was applied to both sides of the obtained polarizing film, and a protective film having a thickness of 80 μm and made of triacetylcellulose and subjected to saponification treatment on the surface was bonded to one side thereof at 50 ° C. It was dried for 5 minutes to obtain a polarizing plate. The thickness of this polarizing plate was 103 μm, which was thicker than the polarizing plate of Example 1.

  When the polarizing plate obtained in Example 1 and the polarizing plate obtained in Comparative Example 1 were each left in an oven at 80 ° C. for 2 hours, the polarizing plate obtained in Comparative Example 1 was compared with the polarizing plate obtained in Comparative Example 1. The obtained polarizing plate had a small curl.

It is a schematic diagram which shows roughly the process after bonding of a protective film at the time of manufacturing a polarizing plate by the method of this invention.

1 polyvinyl alcohol resin layer (polarizing film),
2 base resin film,
3 Protective film,
4 Polarizing plate with single-sided protective film,
12 Adhesive coating equipment,
13 Protective film supply means,
14 pasting rolls,
15 Drying furnace,
16 Winding device.

Claims (5)

Applying polyvinyl alcohol resin to the base resin film;
Stretching the resulting laminated film uniaxially by the tenter method so that the thickness of the polyvinyl alcohol-based resin layer is 10 μm or less,
Dyeing the polyvinyl alcohol-based resin layer using a dichroic dye,
A step of attaching a protective film via an adhesive to the side of the polyvinyl alcohol resin layer having a thickness of 10 μm or less, and the substrate resin film is peeled and removed after the protective film is attached; The manufacturing method of the polarizing plate characterized by including the process to do.   Furthermore, the boric acid treatment process of processing the laminated | multilayer film which has the polyvinyl alcohol-type resin layer dye | stained with the said dichroic dye with a boric acid aqueous solution before the process of bonding the said protective film is included. Manufacturing method.   The manufacturing method according to claim 1, wherein the protective film is a triacetyl cellulose film.   The manufacturing method according to claim 1, wherein the protective film is a cyclic polyolefin resin film.   The manufacturing method in any one of Claims 1-4 with which the antistatic process was performed to the base resin film.

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