TW201625998A - Method of manufacturing polarizer - Google Patents

Abstract

This invention provides a method of manufacturing polarizer with excellent appearance. The polarizer manufacturing method of this invention comprises: a step of obtaining a laminate of elongated resin substrate and polyvinyl alcohol-based resin layer formed on one side of the resin substrate; a step of dyeing the polyvinyl alcohol-based resin layer; a step of stretching the laminate; a step of cutting the edge from the terminal at width direction of the laminate prior to stretching; and, a step of adhering an elongated protective film on the polyvinyl alcohol-based resin layer after dyeing and stretching. After stretching, the width of the laminate and the width of the laminate during adhesion are corresponded to each other.

Description

Method for manufacturing polarizing plate

The present invention relates to a method of manufacturing a polarizing plate.

Background technique

In the liquid crystal display device which is a representative image display device, a polarizing film is disposed on both sides of the liquid crystal cell due to the image forming method. As a method of producing a polarizing film, for example, a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer is stretched, a dyeing treatment is performed, and a polarizing film is obtained on the resin substrate ( For example, Patent Document 1). According to this method, since a polarizing film having a small thickness can be obtained, it contributes to the reduction in thickness of the image display device in recent years, and thus has attracted attention.

The above polarizing film is usually used by bonding a protective film to a polarizing plate. When the protective film is bonded to the polarizing film (layered body) formed on the resin substrate, there is a problem that the end portion is likely to be bent or wrinkled. Therefore, a proposal has been made to remove the end portion of the laminated body before bonding the protective film (Patent Document 2). However, according to this method, there is a problem that the appearance of the obtained polarizing plate is poor.

Advanced technical literature Patent literature

Patent Document 1 Japanese Patent Laid-Open Publication No. 2000-338329

Patent Document 2 Japanese Patent No. 5124704

Summary of invention

The present invention has been made to solve the above problems, and an object of the invention is to provide a method for producing a polarizing plate having an excellent appearance.

The method for producing a polarizing plate of the present invention comprises the steps of: obtaining a laminate-shaped resin substrate and a laminate of a polyvinyl alcohol-based resin layer formed on one side of the resin substrate; and dyeing the polyvinyl alcohol-based resin layer a step of stretching the laminated body; a step of trimming the end portion in the width direction of the laminated body before the stretching; and, after the dyeing and stretching, on the polyvinyl alcohol-based resin layer In the step of bonding the long protective film, the width of the laminated body after the stretching corresponds to the width of the laminated body at the time of bonding.

In one embodiment, the trimming is performed in such a manner that the width of the stretched laminated body corresponds to the width of the protective film.

In one embodiment, the above trimming is performed prior to the dyeing described above.

In one embodiment, the method further includes the step of winding the laminated body into a roll shape, and performing the trimming after the winding.

In one embodiment, the stretching is longitudinal uniaxial stretching.

In one embodiment, the stretching is stretching in water.

In one embodiment, the stretching ratio of the above stretching is 2.0 times or more.

In one embodiment, the laminate is stretched in multiple stages.

In one embodiment, the laminated body is stretched in advance before the trimming.

According to other aspects of the invention, a polarizing plate is provided. This polarizing plate is obtained by the above manufacturing method.

According to the invention, it is possible to effectively prevent foreign matter from entering between the PVA-based resin layer and the protective film by performing the trimming before the stretching and the bonding step with the protective film. Specifically, when the trimming is performed in a state where the alignment property of the PVA-based resin layer is increased by stretching, burrs are likely to occur at the trimming end, and the burrs become foreign matter at the time of bonding. Further, the PVA-based resin layer having a high alignment property is likely to be cracked, and it may become difficult to cut the edge. Therefore, by trimming before stretching, the trimming can be performed satisfactorily, and the intrusion of foreign matter and the generation of bubbles accompanying foreign matter can be effectively prevented. As a result, a polarizing plate excellent in appearance can be obtained. In addition, when the embossing is formed in the end portion in the width direction of the laminated body, the pleats, the bends, and the rolls can be removed before the embossing or the like is stretched in advance. Since the unevenness is tight, the stretching can be performed stably.

10‧‧‧Layer

10a‧‧‧width end

11‧‧‧Resin substrate

12‧‧‧Polyvinyl alcohol resin layer (polarizing film)

20‧‧‧ Length direction

Fig. 1 is a partial cross-sectional view showing a laminated body according to an embodiment of the present invention.

Fig. 2 is an external perspective view showing an example of a trimming step of the present invention.

Way of implementing the invention

Hereinafter, one embodiment of the present invention will be described, but the present invention It is not limited to these embodiments.

The method for producing a polarizing plate of the present invention includes the steps of obtaining a laminate of a long resinous substrate and a PVA-based resin layer formed on one side of the resin substrate (layering step); and step of dyeing the PVA-based resin layer (dyeing step); a step of stretching the laminated body (stretching step); a step of trimming the end portion in the width direction of the laminated body (cutting step); and laminating the strip on the PVA-based resin layer The step of protecting the film (the bonding step). Hereinafter, each step will be described.

A. Lamination step

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial cross-sectional view showing a laminated body in accordance with a preferred embodiment of the present invention. The laminated body 10 has a resin base material 11 and a polyvinyl alcohol-based resin layer 12. The laminated body 10 is produced by laminating the polyvinyl alcohol-based resin layer 12 on the elongated resin substrate 11. As a method of forming the polyvinyl alcohol-based resin layer 12, any appropriate method can be employed. In one embodiment, a coating liquid containing a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") is applied onto the resin substrate 11 and dried to form a PVA-based resin layer 12.

Any suitable material can be used as the material for forming the resin substrate. For example, an ester resin such as a polyethylene terephthalate resin, a cycloolefin resin, an olefin resin such as polypropylene, a (meth)acrylic resin, a polyamine resin, or a polycarbonate system may be mentioned. A copolymer resin such as a resin or the like. A polyethylene terephthalate resin is preferably used. Among them, an amorphous polyethylene terephthalate resin is preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further comprising isophthalic acid as a dicarboxylic acid, and further comprising A copolymer containing cyclohexanedimethanol as a diol.

The glass transition temperature (Tg) of the resin substrate is preferably 120 ° C or lower, more preferably 100 ° C or lower. This is because when the laminate is stretched, the crystallization of the PVA-based resin layer can be suppressed, and the stretchability (especially in water) can be sufficiently ensured. As a result, a polarizing film having excellent optical characteristics (for example, a degree of polarization) can be produced. On the other hand, the glass transition temperature of the resin substrate is preferably 60 ° C or higher. In addition, the glass transition temperature (Tg) is a value calculated based on JIS K 7121.

The water absorption of the resin substrate is preferably 0.2% or more, more preferably 0.3% or more. This resin substrate absorbs water, and water acts as a plasticizer and can be plasticized. As a result, the tensile stress can be greatly reduced, and the stretchability is excellent. On the other hand, the water absorption of the resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a resin substrate, dimensional stability of the resin substrate is remarkably lowered at the time of production, and problems such as deterioration of the appearance of the obtained polarizing film can be prevented. Further, it is possible to prevent breakage during stretching in water or peeling of the PVA-based resin layer from the resin substrate. In addition, the water absorption rate is a value calculated based on JIS K 7209.

The thickness of the resin substrate is preferably from 20 μm to 300 μm, more preferably from 50 μm to 200 μm. For the surface of the resin substrate, a surface modification treatment (for example, corona treatment or the like) may be performed, or an easy adhesion layer may be formed. According to this treatment, a laminate having excellent adhesion between the resin substrate and the PVA-based resin layer can be obtained.

As the PVA-based resin forming the PVA-based resin layer, any appropriate resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. B The ene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually from 85 mol% to 100 mol%, preferably from 95.0 mol% to 99.95 mol%, more preferably from 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K 6726-1994. By using such a saponification degree PVA-based resin, a polarizing film excellent in durability can be obtained. When the degree of saponification is too high, there is a fear that gelation occurs.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually from 1,000 to 10,000, preferably from 1,200 to 4,500, more preferably from 1,500 to 4,300. In addition, the average degree of polymerization can be determined in accordance with JIS K 6726-1994.

The coating liquid is typically a solution obtained by dissolving the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and polyhydric alcohols such as trimethylolpropane. An amine such as ethylenediamine or diethylenetriamine. These may be used alone or in combination of two or more. Among these, water is preferred. The PVA-based resin concentration of the solution can be set to any appropriate value. For example, it is set according to the degree of polymerization of the PVA-based resin, the degree of saponification, and the like. The PVA-based resin concentration of the solution is, for example, 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent.

The coating liquid may contain an additive. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As a surfactant, a nonionic surfactant is mentioned, for example. These can be used to further improve the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer. In addition, As an additive, the easy-adhesion component is mentioned, for example. By using an easy-adhesive component, the adhesion between the resin substrate and the PVA-based resin layer can be improved. As a result, for example, it is possible to suppress problems such as peeling of the PVA-based resin layer from the resin substrate, and to perform dyeing and stretching in water as described below. As the easy-adhesive component, for example, a modified PVA such as an ethyl acetate-modified PVA can be used.

As a coating method of a coating liquid, any appropriate method can be employ|adopted. For example, a bar coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (such as a comma coating method), and the like can be given. The coating/drying temperature of the coating liquid is, for example, 20 ° C or higher, preferably 50 ° C or higher.

The thickness of the PVA-based resin layer is preferably from 3 μm to 40 μm, more preferably from 3 μm to 20 μm. The width of the laminate can be set to any appropriate value. Typically, it is 1500 mm or more, preferably 2000 mm to 5000 mm.

In one embodiment, the PVA-based resin layer (layered body) is stretched in advance. For example, the PVA-based resin layer (layered body) is stretched in the longitudinal direction (for example, by means of aerial stretching). The stretching ratio of the stretching is, for example, 1.5 to 3.5 times, preferably 2.0 to 3.0 times. The stretching temperature is, for example, 95 ° C to 150 ° C.

B. Dyeing step

The above dyeing is typically carried out by dyeing the PVA-based resin layer with a dichroic substance. It is preferable to carry out the adsorption of the dichroic substance to the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (layered body) in a dyeing liquid containing a dichroic substance, a method of applying the dyeing liquid on the PVA-based resin layer, and spraying the dyeing liquid. to A method of a PVA-based resin layer or the like. A method of immersing the PVA-based resin layer in the dyeing liquid is preferred. This is because the dichroic substance adsorbs well.

Examples of the dichroic substance include iodine and an organic dye. These may be used alone or in combination of two or more. The dichroic material is preferably iodine. When iodine is used as the dichroic substance, the dyeing liquid is preferably an aqueous iodine solution. The compounding amount of iodine is preferably 0.1 part by weight to 0.5 part by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferred to mix an iodide in an aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferred. The compounding amount of the iodide is preferably 0.02 part by weight to 20 parts by weight, more preferably 0.1 part by weight to 10 parts by weight per 100 parts by weight of the water.

In order to suppress the dissolution of the PVA-based resin, the liquid temperature at the time of dyeing the dyeing liquid is preferably from 20 ° C to 50 ° C. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably from 5 seconds to 5 minutes in order to secure the transmittance of the PVA-based resin layer. Further, the dyeing conditions (concentration, liquid temperature, immersion time) can be set such that the degree of polarization or the monomer transmittance of the finally obtained polarizing film is within a predetermined range. In one embodiment, the immersion time is set such that the degree of polarization of the obtained polarizing film is 99.98% or more. In another embodiment, the immersion time is set such that the obtained polarizing film has a monomer transmittance of 40% to 44%.

C. Stretching step

As the stretching method of the laminate, any appropriate method can be employed. Specifically, it can be stretched at a fixed end (for example, using a tenter stretching machine) The method may be a method of stretching at the free end (for example, a method of uniaxially stretching a laminate body between rolls having different circumferential speeds). In addition, it may be simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine), or may be a sequential biaxial stretching. The stretching of the laminate can be carried out in one stage or in multiple stages. When it progresses in multiple stages, the draw ratio (maximum draw ratio) of the laminated body mentioned later is the product of the draw ratio of each stage.

The stretching may be an underwater stretching method in which the layered body is immersed in a stretching bath, or may be an air stretching method. It is preferred to carry out at least one stretching in water, and it is more preferable to combine aerial stretching and water stretching. When it is stretched in water, it can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C) of the resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be prevented from crystallizing. Stretching at a high magnification. As a result, a polarizing film having excellent optical characteristics can be produced. It should be noted that, in combination with aerial stretching and underwater stretching, it is preferred to perform stretching in water after stretching in the air.

As the stretching direction of the laminated body, any appropriate direction can be selected. In one embodiment, the stretching is performed along the longitudinal direction of the elongated laminate. Specifically, the laminate is conveyed in the longitudinal direction in the direction of transport (MD). In other embodiments, the stretching is performed along the width direction of the elongated laminate. Specifically, the laminated body is conveyed in the longitudinal direction in a direction (TD) orthogonal to the transport direction (MD).

The stretching temperature of the laminate can be set to any appropriate value depending on the material to be formed of the resin substrate, the stretching method, and the like. When the air stretching method is used, the stretching temperature is preferably the glass transition temperature (Tg) of the resin substrate. More preferably, the glass transition temperature (Tg) of the resin substrate is +10 ° C or more, and particularly preferably Tg + 15 ° C or more. On the other hand, the stretching temperature of the laminate is preferably 170 ° C or lower. By stretching at such a temperature, it is possible to suppress rapid progress of crystallization of the PVA-based resin and to suppress defects caused by the crystallization (for example, to prevent alignment of the PVA-based resin layer due to stretching).

When the water stretching method is employed as the stretching method, the liquid temperature of the stretching bath is preferably from 40 ° C to 85 ° C, more preferably from 50 ° C to 85 ° C. When such a temperature is used, it is possible to perform stretching at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the resin substrate is preferably 60° C. or more from the relationship with the formation of the PVA-based resin layer. At this time, when the stretching temperature is lower than 40 ° C, there is a possibility that the resin base material is not easily stretched in consideration of plasticization of the resin base material by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the fact that excellent optical characteristics are not obtained.

When the water stretching method is employed, it is preferred to immerse the laminate in an aqueous boric acid solution and to perform stretching (boric acid in water). By using a boric acid aqueous solution as the stretching bath, it is possible to impart rigidity to the PVA-based resin layer that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid forms a tetrahydroborate anion in an aqueous solution, and can be crosslinked with a PVA-based resin by a hydrogen bond. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and stretching can be performed favorably, and a polarizing film having excellent optical characteristics can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water as a solvent. Boric acid concentration relative to 100 parts by weight of water It is preferably from 1 part by weight to 10 parts by weight. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent may be used.

Preferably, the iodide is compounded in the above stretching bath (aqueous boric acid solution). By mixing the iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of the iodide is preferably from 0.05 part by weight to 15 parts by weight, more preferably from 0.5 part by weight to 8 parts by weight, per 100 parts by weight of water.

The immersion time of the laminate to the stretching bath is preferably from 15 seconds to 5 minutes.

The draw ratio (maximum draw ratio) of the laminate is preferably 5.0 times or more with respect to the original length of the laminate. Such a high draw ratio can be achieved, for example, by a stretching method in water (stretching in boric acid water). The stretching ratio of the laminate based on stretching in water is preferably 2.0 times or more. In the present specification, the "maximum stretching ratio" means a stretching ratio until the laminate is about to be broken, and means a stretching ratio in which the laminated body is broken, and a value lower than 0.2 by the value. .

Preferably, the stretching in water is carried out after the above dyeing.

D. Trimming step

Fig. 2 is an external perspective view showing an example of a trimming step. As shown in Fig. 2, before the stretching, the widthwise end portions 10a and 10a of the laminated body 10 are trimmed along the longitudinal direction 20 of the laminated body 10. Trimmed piece 10a The resin substrate and the PVA-based resin layer are contained. The trim width (the width of the trimming sheet) is typically 10 mm to 1000 mm. In one embodiment, the trimming width is set so that the width of the laminated body after stretching (the width of the laminated body at the time of bonding described later) corresponds to the width of a protective film to be described later. By matching the widths of the two in this manner, the wrinkles at the ends in the width direction can be eliminated, and the laminated body and the protective film can be stably bonded together. When the above stretching is longitudinal stretching (MD stretching), it is conceivable to set the trimming width by reducing the width of the laminated body by stretching. Specifically, the trimming width can be set smaller than the trimming after stretching.

By performing trimming before stretching, it is possible to effectively prevent foreign matter from entering between the PVA-based resin layer and the protective film in the bonding step with the protective film described later. Specifically, when the trimming is performed in a state in which the alignment property of the PVA-based resin layer is increased by stretching, burrs are likely to occur at the trimming end, and the burrs become foreign matter when they are bonded. Further, the PVA-based resin layer in a state of high alignment property is likely to be cracked, and it may become difficult to cut the edge. Therefore, by trimming before stretching, the trimming can be performed satisfactorily, and the intrusion of foreign matter and the generation of bubbles accompanying foreign matter can be effectively prevented. As a result, a polarizing plate excellent in appearance can be obtained. Further, it is possible to remove irregularities such as wrinkles, bends, and curls, and to remove the wrinkles, bends, and crimps before the embossing or the like is stretched in the end portion of the laminate in the width direction. Since the irregularities are equal, the stretching can be performed stably.

In addition to the above, by performing trimming before stretching, a polarizing film having extremely excellent optical characteristics can be obtained. Specifically, when stretching is performed by the circumferential speed difference between the rolls (longitudinal uniaxial stretching), the width direction is before stretching. The end portion is trimmed so that the L/W is increased, and the alignment/optical characteristics of the obtained polarizing film are remarkably improved. In addition, L represents the inter-stretching distance (distance of the tension applied by the circumferential speed difference between rolls), and W shows the width of a laminated body.

When the laminate is stretched in multiple stages, the laminate may be stretched as described above before trimming. Specifically, the trimming may be performed at least before the final stage of stretching. By trimming and stretching in a state in which the orientation of the PVA-based resin layer is increased by stretching in advance, the alignment property and optical characteristics of the obtained polarizing film can be further improved. At this time, in the case of trimming, it is preferred to perform the stretching before the trimming to such an extent that the burr does not occur. Further, it is preferred to set the stretching ratio of the stretching after trimming to be high. The stretching ratio of the stretching after trimming is, for example, 1.5 times or more, preferably 2.0 times or more. This is because the alignment/optical characteristics of the obtained polarizing film can be further improved by stretching the L/W in a high state.

It is preferred to carry out the above-mentioned trimming before the above dyeing. By trimming before dyeing, it is possible to more effectively prevent foreign matter from entering between the PVA-based resin layer and the protective film in the bonding step with the protective film described later. Specifically, the PVA-based resin layer is crosslinked by dyeing (for example, due to iodine) to become brittle. When trimming is performed in this state, trimming chips are likely to be generated, and the trimming chips become foreign matter when they are bonded. Therefore, by trimming before dyeing, it is possible to more effectively prevent the intrusion of foreign matter and the generation of bubbles accompanying foreign matter. As a result, a polarizing plate excellent in appearance can be obtained.

As the trimming method of the laminated body, any appropriate method can be employed. For example, the long laminated body can be wound one side along its length The trimming may be performed while the trimming is performed without winding. Examples of the trimming (cutting) means include a cutting blade such as a circular blade or a disk blade, and a laser. It should be noted that the trimming sheet is preferably removed by winding or suction.

E. Other

In addition to the above, the above-mentioned laminated body can be suitably subjected to a treatment for forming a PVA-based resin layer into a polarizing film. Examples of the treatment for forming the polarizing film include insolubilization treatment, crosslinking treatment, washing treatment, and drying treatment. It should be noted that the number, timing, order, and the like of these processes are not particularly limited.

The insolubilization treatment is typically carried out by immersing a PVA-based resin layer in an aqueous boric acid solution. Water resistance can be imparted to the PVA-based resin layer by performing insolubilization treatment. The concentration of the aqueous boric acid solution is preferably from 1 part by weight to 4 parts by weight per 100 parts by weight of water. The liquid temperature of the insolubilizing bath (aqueous boric acid solution) is preferably from 20 ° C to 50 ° C. The preferred insolubilization treatment is carried out before the above-described stretching in water and the above dyeing treatment.

The crosslinking treatment is typically carried out by immersing a PVA-based resin layer in an aqueous boric acid solution. Water resistance can be imparted to the PVA-based resin layer by performing the crosslinking treatment. The concentration of the aqueous boric acid solution is preferably from 1 part by weight to 5 parts by weight per 100 parts by weight of water. Further, when the crosslinking treatment is carried out after the above dyeing treatment, it is preferred to further mix the iodide. By mixing the iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The compounding amount of the iodide is preferably from 1 part by weight to 5 parts by weight per 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably from 20 ° C to 60 ° C. Preferably, the crosslinking treatment is carried out before the stretching in the above water. Better In the embodiment, the dyeing treatment, the crosslinking treatment, and the stretching in water are sequentially performed.

The cleaning treatment is typically carried out by immersing a PVA-based resin layer in an aqueous solution of potassium iodide. The drying temperature of the above drying treatment is preferably from 30 ° C to 100 ° C.

In one embodiment, the laminated body is wound into a roll shape to form a primary roll, and the trimming is performed after winding. The take-up tension is typically from 300 N to 600 N. The winding may be performed such that the PVA-based resin layer is on the inner side (core material side), or the PVA-based resin layer may be formed on the outer side. When the laminated body is wound up in the manufacturing step of the polarizing film, for example, when there is a local film thickness unevenness in the laminated body, winding and wrinkles occur. This problem easily occurs at the ends in the width direction. Therefore, the stretching can be stably performed by performing the above-described trimming after the winding. Further, since the trimming is performed after the winding, regardless of the width of the bonded protective film, the original roll of the same width can be used, which contributes to an improvement in productivity.

F. Lamination step

After the dyeing and stretching, a protective film is bonded to the PVA-based resin layer (polarizing film) of the laminate. Specifically, the long protective film is bonded to the PVA-based resin layer so as to be aligned in the longitudinal direction of each other. In one embodiment, the width of the stretched laminated body corresponds to the width of the laminated body at the time of bonding. Specifically, between the stretching step and the bonding step, substantially no new trimming process is performed on the laminated body.

The width of the protective film can be set to any appropriate value. Typically, it is 500 mm or more and 3000 mm or less, preferably 1000 mm or more and 2500 mm or less.

As the protective film, any appropriate resin film can be used. Examples of the material for forming the protective film include a cellulose resin such as triacetin cellulose (TAC), a cycloolefin resin such as a norbornene resin, an olefin resin such as polyethylene or polypropylene, and a polyester resin. (Meth)acrylic resin or the like. In addition, “(meth)acrylic resin” means an acryl resin and/or a methacryl resin.

The thickness of the protective film is typically from 10 μm to 100 μm. It should be noted that various surface treatments can be applied to the protective film. The protective film functions not only as a protective film for a polarizing film but also as a retardation film.

The adhesive film is bonded using any suitable adhesive or adhesive. In one embodiment, an adhesive is applied to the surface of the polarizing film to adhere the protective film. The adhesive may be a water-based adhesive or a solvent-based adhesive. It is preferred to use a water-based adhesive.

Any suitable water-based adhesive can be used as the water-based adhesive. A water-based adhesive containing a PVA-based resin is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably from about 100 to 5,000, more preferably from 1,000 to 4,000, from the viewpoint of adhesion. The average degree of saponification is preferably from about 85 mol% to about 100 mol%, more preferably from 90 mol% to 100 mol%, from the viewpoint of adhesion.

The PVA-based resin contained in the water-based adhesive preferably contains an ethyl acetonitrile group. This is because the PVA-based resin layer is excellent in adhesion to the protective film and excellent in durability. The ethyl acetate-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by an arbitrary method. With B The degree of modification of the ethyl sulfonium group of the PVA-based resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, more preferably 1 mol% to 20 mol. Ear %, particularly preferably 2 mole % ~ 7 mole %. It should be noted that the degree of modification of the acetamidine group is a value measured by NMR.

The resin concentration of the water-based adhesive is preferably from 0.1% by weight to 15% by weight, more preferably from 0.5% by weight to 10% by weight.

The thickness at the time of application of the adhesive can be set to any appropriate value. For example, it is set in such a manner that an adhesive layer having a desired thickness can be obtained after heating (drying). The thickness of the adhesive layer is preferably from 10 nm to 300 nm, more preferably from 10 nm to 200 nm, and particularly preferably from 20 nm to 150 nm.

Preferably, the protective film is bonded to the PVA-based resin layer and then heated. The heating temperature is preferably 50 ° C or higher, more preferably 60 ° C or higher, and particularly preferably 80 ° C or higher. It should be noted that the heating performed after bonding the protective film may also serve as the above drying treatment.

G. Stripping step

In one embodiment, the resin substrate is peeled off from the PVA-based resin layer (polarizing film). Preferably, before the resin substrate is peeled off, the end portion in the width direction of the polarizing film laminate in which the protective film is bonded to the laminate is trimmed. In the joint portion between the end portion in the width direction of the laminate and the protective film, joint failure (for example, wrinkles) is likely to occur, and the portion is removed by trimming, whereby excellent peelability of the resin substrate can be achieved. Specifically, it is possible to prevent the bonding failure portion from becoming a starting point and causing peeling failure (for example, breakage) of the resin substrate, and it is possible to favorably peel the resin substrate. As a result, a polarizing plate having a more excellent appearance can be obtained.

H. Polarizer

The polarizing plate of the present invention has the above polarizing film and the protective film disposed on one side of the polarizing film. The polarizing film is a PVA-based resin film obtained by substantially adsorbing and aligning a dichroic substance. The thickness of the polarizing film is preferably 10 μm or less, more preferably 7 μm or less, and particularly preferably 5 μm or less. On the other hand, the thickness of the polarizing film is preferably 0.5 μm or more, and more preferably 1.0 μm or more. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The monomer transmittance of the polarizing film is preferably 40.0% or more, more preferably 41.0% or more, still more preferably 42.0% or more, and particularly preferably 43.0% or more. The degree of polarization of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, still more preferably 99.95% or more.

Example

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by the examples. In addition, the measuring method of each characteristic is as follows.

Thickness

It was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").

2. Glass transition temperature (Tg)

Measured in accordance with JIS K 7121.

[Example 1]

(production of laminates)

As a resin substrate, a long strip, water absorption ratio of 0.75%, Tg75 ° C amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerization) PET) film (width: 4000 mm, thickness: 100 μm).

One side of the resin substrate was subjected to corona treatment, and 90 parts by weight of polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and ethylene acetamyl group were coated on the corona-treated surface at 60 ° C. 10 parts by weight of an aqueous solution of PVA (having a degree of polymerization of 1200, a degree of modification of acetonitrile, 4.6%, a degree of saponification of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Co., Ltd., trade name "GOHSEFIMER Z200"), and drying. A PVA-based resin layer having a thickness of 10 μm was formed to prepare a laminate.

The obtained laminate was uniaxially stretched to 2.0 times (air stretch) in the longitudinal direction free end between rolls having different circumferential speeds in an oven at 115 °C. Then, the laminated body is taken up in a roll shape.

The laminated body is unwound and unwound from the roll of the laminated body, and the two end portions in the width direction of the laminated body are trimmed so that the width after the trimming is 2500 mm.

Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 30 ° C (a boric acid aqueous solution obtained by mixing 3 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).

Then, the immersion is performed while adjusting the iodine concentration and the immersion time so that the obtained polarizing plate has a predetermined transmittance in a dye bath having a liquid temperature of 30° C. In the present embodiment, the iodine aqueous solution obtained by mixing 0.2 part by weight of iodine with respect to 100 parts by weight of water and mixing 1.0 part by weight of potassium iodide was immersed for 60 seconds (dyeing treatment).

Next, the cross-linking bath having a liquid temperature of 30 ° C (the boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) is immersed in 30 Seconds (cross-linking processing).

Then, the laminate was immersed in a boric acid aqueous solution having a liquid temperature of 70 ° C (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) in the longitudinal direction between rolls having different circumferential speeds. Uniaxial stretching was carried out to 2.7 times (water stretching).

Then, the laminate was immersed in a cleaning bath at a liquid temperature of 30 ° C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) for 10 seconds, and then dried by hot air at 60 ° C for 60 seconds (washing/drying) step).

Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate.

Next, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight) was applied to the surface of the polarizing film of the laminate, and the strip was attached. A triacetyl cellulose film (manufactured by Konica Minolta Co., Ltd., trade name "KC4UY", thickness 40 μm) having a width corresponding to the width of the polarizing film was heated in an oven maintained at 60 ° C for 5 minutes to obtain Polarizer.

[Embodiment 2]

A polarizing plate was produced in the same manner as in Example 1 except that the trimming was performed so that the width after the trimming was 2,100 mm.

[Comparative Example 1]

A polarizing plate was produced in the same manner as in Example 1 except that the timing of trimming was performed after stretching in water.

(Evaluation)

The following evaluation was performed about the obtained polarizing plate. The evaluation results are summarized in Table 1.

Appearance

The obtained polarizing plate was visually observed.

2. Polarization

The transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) of the polarizing plate were measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), according to The degree of polarization (P) is obtained by the equation.

Polarization (P) (%) = {(Tp-Tc) / (Tp + Tc)} 1/2 × 100

In addition, the above Ts, Tp, and Tc are Y values measured by the 2 degree field of view (C light source) of JIS Z 8701 and the visibility correction.

3. Orientation (evaluation method of PVA alignment function)

The measurement apparatus used was a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer Co., Ltd., trade name: "SPECTRUM2000"). The polarized light was used as the measurement light, and the surface of the PVA-based resin layer was evaluated by measurement of total attenuated total reflection (ATR). The calculation of the alignment function is performed in the following steps. The measurement was carried out in a state where the measured polarized light was 0° and 90° with respect to the stretching direction. The intensity of 2941 cm-1 of the obtained spectrum was calculated based on (Formula 1) described below. Further, the following intensity I was 3330 cm-1 as a reference peak, and a value of 2941 cm to 1/3330 cm-1 was used. It should be noted that when f=1, it is a complete alignment, and when f=0, it is a random. Further, the peak of 2941 cm-1 can be said to be absorption caused by the vibration of the main chain (-CH2-) of PVA.

(Formula 1) f = (3 < cos2θ > -1) / 2 = (1 - D) / [c (2D + 1)] where c = (3cos2β-1)/2

θ: molecular chain ‧ stretching direction

:: molecular chain ‧ transition dipole moment

D=(I⊥)/(I//), (The more the PVA is aligned, the larger the value of D.)

I⊥: the intensity at which polarized light is incident in a direction perpendicular to the stretching direction and measured

I//: the intensity at which polarized light is incident in a direction parallel to the stretching direction and measured

Industrial availability

The polarizing plate of the present invention can be suitably used as a liquid crystal panel for a liquid crystal television, a liquid crystal display, a mobile phone, a digital camera, a video camera, a portable game machine, a vehicle navigation system, a photocopying machine, a printer, a facsimile machine, a clock, a microwave oven, or the like. An antireflection film of an organic EL device.

10‧‧‧Layer

10a‧‧‧width end

20‧‧‧ Length direction

Claims (10)

A method for producing a polarizing plate, comprising the steps of: obtaining a long resinous substrate and a laminate of a polyvinyl alcohol-based resin layer formed on one side of the resin substrate; and dyeing the polyvinyl alcohol-based resin layer Stretching the layered body; trimming the end portion in the width direction of the layered body before the stretching; and bonding the strip to the polyvinyl alcohol-based resin layer after the dyeing and stretching The protective film has a width corresponding to the width of the laminated body at the time of bonding. The manufacturing method of claim 1, wherein the trimming is performed in such a manner that the width of the stretched laminated body corresponds to the width of the protective film. The manufacturing method of claim 1, wherein the aforementioned trimming is performed before the dyeing. The manufacturing method of claim 1, further comprising the step of winding the laminated body into a roll shape, and performing the trimming after the winding. The manufacturing method of claim 1, wherein the stretching is longitudinal uniaxial stretching. The manufacturing method of claim 1, wherein the aforementioned stretching is stretching in water. The production method of claim 1, wherein the stretching ratio of the stretching is 2.0 times or more. The manufacturing method of claim 1, wherein the foregoing laminated body is multi-staged Line stretching. The manufacturing method of claim 1, wherein the laminated body is stretched in advance before the trimming. A polarizing plate obtained by the manufacturing method of claim 1.