JP6656444B2 - Manufacturing method of polarizing plate - Google Patents

Description

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

  A liquid crystal display device, which is a typical image display device, has polarizing films disposed on both sides of a liquid crystal cell due to the image forming method. As a method for manufacturing a polarizing film, for example, a method has been proposed in which a laminate having a resin base material and a polyvinyl alcohol (PVA) -based resin layer is stretched and subjected to a dyeing treatment to obtain a polarizing film on the resin base material. (For example, Patent Document 1). According to such a method, a polarizing film having a small thickness can be obtained, and thus, it is noted that it can contribute to a reduction in thickness of an image display device in recent years.

  By the way, the polarizing film is usually used as a polarizing plate with a protective film attached thereto. When a protective film is bonded to the polarizing film (laminated body) formed on the resin substrate, there is a problem that the end portion is easily broken or wrinkled. Therefore, it has been proposed to remove the end of the laminate before attaching the protective film (Patent Document 2). However, according to such a method, there is a problem that the appearance of the obtained polarizing plate is inferior.

JP 2000-338329 A Patent No. 5124704

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

The method for producing a polarizing plate of the present invention includes a step of forming a long resin substrate and a polyvinyl alcohol-based resin layer on one side of the resin substrate to obtain a laminate, and a step of stretching the laminate in the air. A step of dyeing the polyvinyl alcohol-based resin layer, a step of stretching the laminate in water, and a step of slitting the width direction end of the laminate after the aerial stretching and before the underwater stretching; and And after the underwater stretching, laminating a long protective film to the polyvinyl alcohol-based resin layer, wherein the width of the laminate after the underwater stretching corresponds to the width of the laminate at the time of the lamination. .
In one embodiment, the method further includes a step of winding the laminate into a roll.

  According to the present invention, by slitting before stretching, it is possible to effectively prevent foreign substances from being mixed between the PVA-based resin layer and the protective film in the step of bonding to the protective film. Specifically, when slitting is performed in a state in which the orientation of the PVA-based resin layer is increased by stretching, creases are likely to be generated at the slit ends, and the creases may become foreign matters during bonding. Further, the PVA-based resin layer in a state of high orientation is easily torn, and slitting may be difficult. Therefore, by performing slitting before stretching, it is possible to effectively prevent foreign matter from being mixed and air bubbles caused by foreign matter from being mixed, while performing the slitting satisfactorily. As a result, a polarizing plate having excellent appearance can be obtained. Furthermore, the above-mentioned wrinkles, folds, irregularities such as tightness, and the like, when the knurling is formed in advance in the width direction end of the laminate, the knurling and the like can be removed before stretching, so that stable stretching can be performed. Can be.

1 is a partial cross-sectional view of a laminate according to one embodiment of the present invention. It is an external appearance perspective view showing an example of a slit process of the present invention.

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

  The method for producing a polarizing plate of the present invention includes a step of forming a long resin base material and a PVA-based resin layer on one side of the resin base material to obtain a laminate (lamination step), and a step of dyeing the PVA-based resin layer. (Staining step), stretching the laminate (stretching step), slitting the widthwise end of the laminate (slit step), and attaching a long protective film to the PVA-based resin layer. Combining step (laminating step). Hereinafter, each step will be described.

A. Lamination Step FIG. 1 is a partial sectional view of a laminate according to a preferred embodiment of the present invention. The laminate 10 has a resin substrate 11 and a polyvinyl alcohol-based resin layer 12. The laminate 10 is produced by forming a polyvinyl alcohol-based resin layer 12 on a long resin substrate 11. As a method for forming the polyvinyl alcohol-based resin layer 12, any appropriate method can be adopted. In one embodiment, a PVA-based resin layer 12 is formed by applying a coating solution containing a polyvinyl alcohol-based resin (hereinafter, referred to as “PVA-based resin”) on a resin base material 11 and drying the applied solution.

  Any appropriate material can be adopted as a material for forming the resin base material. Examples thereof include ester resins such as polyethylene terephthalate resins, olefin resins such as cycloolefin resins and polypropylene, (meth) acrylic resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Preferably, a polyethylene terephthalate resin is used. Among them, amorphous polyethylene terephthalate resin is preferably used. Specific examples of the amorphous polyethylene terephthalate-based resin include a copolymer further containing isophthalic acid as a dicarboxylic acid and a copolymer further containing cyclohexanedimethanol as a glycol.

  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 stretchability (particularly in underwater stretching) can be sufficiently ensured while suppressing the crystallization of the PVA-based resin layer. As a result, a polarizing film having excellent optical characteristics (for example, a degree of polarization) can be manufactured. On the other hand, the glass transition temperature of the resin substrate is preferably 60 ° C. or higher. The glass transition temperature (Tg) is a value determined according to JIS K7121.

  The water absorption of the resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. Such a resin substrate absorbs water, and the water acts as a plasticizer and can be plasticized. As a result, the stretching stress can be significantly reduced, and the stretchability can be 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 base material, it is possible to prevent problems such as dimensional stability of the resin base material being remarkably reduced at the time of production and deterioration in appearance of the obtained polarizing film. In addition, it is possible to prevent breakage during stretching in water and peeling of the PVA-based resin layer from the resin substrate. The water absorption is a value determined according to JIS K 7209.

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

  Any appropriate resin can be adopted as the PVA-based resin forming the PVA-based resin layer. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. . The saponification degree can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

  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, and more preferably from 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

  As the coating liquid, a solution obtained by dissolving the PVA-based resin in a solvent is typically used. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferable. 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 or the degree of saponification of the PVA-based resin. The PVA-based resin concentration of the solution is, for example, 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent.

  The coating liquid may contain an additive. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include a nonionic surfactant. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer. In addition, examples of the additive include an easily adhesive component. By using the easily adhesive component, the adhesiveness between the resin substrate and the PVA-based resin layer can be improved. As a result, for example, it is possible to suppress inconveniences such as peeling of the PVA-based resin layer from the resin base material, and to favorably perform dyeing and stretching in water described below. As the easily adhesive component, for example, a modified PVA such as an acetoacetyl-modified PVA is used.

  Any appropriate method can be adopted as a method of applying the coating liquid. For example, a roll 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 mentioned. The coating / drying temperature of the coating solution is, for example, 20 ° C. or higher, preferably 50 ° C. or higher.

  The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 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 (laminate) is stretched in advance. For example, the PVA-based resin layer (laminate) is stretched in the longitudinal direction (for example, by an air stretching method). The stretching ratio of the stretching is, for example, 1.5 times to 3.5 times, and preferably 2.0 times to 3.0 times. The stretching temperature is, for example, 95 ° C to 150 ° C.

B. Dyeing Step The above-described dyeing is typically performed by dyeing a PVA-based resin layer with a dichroic substance. Preferably, it is performed by adsorbing a dichroic substance on the PVA-based resin layer. As the adsorption method, for example, a method of immersing a PVA-based resin layer (laminate) in a staining solution containing a dichroic substance, a method of applying the staining solution to a PVA-based resin layer, and a method of applying the staining solution to a PVA-based resin layer A method of spraying the resin layer and the like can be mentioned. A preferred method is to immerse the PVA-based resin layer in a dyeing solution. This is because dichroic substances can be satisfactorily adsorbed.

  Examples of the dichroic substance include iodine and organic dyes. These can be used alone or in combination of two or more. The dichroic substance is preferably iodine. When iodine is used as the dichroic substance, the dyeing solution is preferably an aqueous iodine solution. The amount of iodine is preferably 0.1 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to an aqueous iodine solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. And the like. Among these, potassium iodide is preferable. The amount of iodide is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of water.

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

C. Stretching Step Any appropriate method can be adopted as a method for stretching the laminate. Specifically, fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, uniaxial stretching through a laminate between rolls having different peripheral speeds) may be used. Simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) or sequential biaxial stretching may be used. The stretching of the laminate may be performed in one stage or may be performed in multiple stages. In the case of performing in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is a product of the stretching ratios in each stage.

  Stretching may be an underwater stretching method in which the laminate is immersed in a stretching bath, or may be an air stretching method. Preferably, underwater stretching is performed at least once, and more preferably, air stretching and underwater stretching are combined. According to the in-water stretching, the resin substrate or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80 ° C.), and the PVA-based resin layer is formed while suppressing the crystallization thereof. And can be stretched at a high magnification. As a result, a polarizing film having excellent optical characteristics can be manufactured. When air stretching and underwater stretching are combined, it is preferable to perform underwater stretching after air stretching.

  Any appropriate direction can be selected as the stretching direction of the laminate. In one embodiment, the elongate laminate is stretched in the longitudinal direction. Specifically, the laminate is transported in the longitudinal direction, and is in the transport direction (MD). In another embodiment, the elongate laminate is stretched in the width direction. Specifically, it is a direction (TD) orthogonal to the transport direction (MD) of transporting the laminate in the longitudinal direction.

  The stretching temperature of the laminate can be set to any appropriate value according to the forming material of the resin substrate, the stretching method, and the like. When the aerial stretching method is employed, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate + 10 ° C., and particularly preferably Tg + 15 ° C. That is all. 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 the rapid progress of crystallization of the PVA-based resin, and to suppress problems caused by the crystallization (for example, hinder the orientation of the PVA-based resin layer by stretching). it can.

  When employing the underwater stretching method 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. At such a temperature, the film can be stretched at a high magnification while suppressing the 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 higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., there is a possibility that the stretching may not be performed well even in consideration of the plasticization of the resin substrate by water. On the other hand, the higher the temperature of the stretching bath is, the higher the solubility of the PVA-based resin layer is, and there is a possibility that excellent optical properties cannot be obtained.

  When the underwater stretching method is employed, the laminate is preferably immersed in a boric acid aqueous solution and stretched (boric acid in water stretching). By using a boric acid aqueous solution as the stretching bath, it is possible to provide the PVA-based resin layer with rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, stretching can be performed favorably, and a polarizing film having excellent optical characteristics can be manufactured.

  The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The concentration of boric acid is preferably 1 to 10 parts by weight based on 100 parts by weight of water. 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 manufactured. In addition to the boric acid or the borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent can also be used.

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

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

  The stretch ratio (maximum stretch ratio) of the laminate is preferably at least 5.0 times the original length of the laminate. Such a high stretching ratio can be achieved, for example, by employing an underwater stretching method (boric acid in water stretching). The draw ratio of the laminate by underwater stretching is preferably 2.0 times or more. In the present specification, the “maximum stretch ratio” refers to a stretch ratio immediately before the laminate is broken, and separately refers to a stretch ratio at which the laminate is broken, and refers to a value 0.2 lower than the value. .

  Preferably, the stretching in water is performed after the above-mentioned dyeing.

D. Slit Step FIG. 2 is an external perspective view showing an example of the slit step. As shown in FIG. 2, before the stretching, the width direction ends 10 a and 10 a of the laminate 10 are slit along the longitudinal direction 20 of the laminate 10. The slit slit piece 10a includes the resin base and the PVA-based resin layer. The slit width (the width of the slit piece) is typically 10 mm to 1000 mm. In one embodiment, the slit width is set such that the width of the laminate after stretching (the width of the laminate at the time of lamination described later) corresponds to the width of the protective film described later. By adjusting the widths of the two in this way, the wrinkles at the ends in the width direction can be eliminated, and the laminate and the protective film can be stably bonded. When the stretching is longitudinal stretching (MD stretching), the slit width can be set in consideration of the fact that the width of the laminate can be reduced by stretching. Specifically, the slit width can be set smaller than the slit width after stretching.

  By slitting before stretching, it is possible to effectively prevent foreign substances from being mixed between the PVA-based resin layer and the protective film in a bonding step with the protective film described below. Specifically, when slitting is performed in a state in which the orientation of the PVA-based resin layer is increased by stretching, creases are likely to be generated at the slit ends, and the creases may become foreign matters during bonding. Further, the PVA-based resin layer in a state of high orientation is easily torn, and slitting may be difficult. Therefore, by performing slitting before stretching, it is possible to effectively prevent foreign matter from being mixed and air bubbles caused by foreign matter from being mixed, while performing the slitting satisfactorily. As a result, a polarizing plate having excellent appearance can be obtained. Furthermore, the above-mentioned wrinkles, folds, irregularities such as tightness, and the like, when the knurling is formed in advance in the width direction end of the laminate, the knurling and the like can be removed before stretching, so that stable stretching can be performed. Can be.

  In addition to the above, by slitting before stretching, a polarizing film having extremely excellent optical properties can be obtained. Specifically, when stretching is performed by a peripheral speed difference between rolls (longitudinal uniaxial stretching), by slitting the widthwise end portion before stretching, the L / W is increased, and the orientation and optical properties of the obtained polarizing film are increased. Characteristics can be significantly improved. In addition, L indicates the distance between stretching (the distance to which tension is applied due to the difference in peripheral speed between rolls), and W indicates the width of the laminate.

  When the stretching of the laminate is performed in multiple stages, the laminate may be stretched before slitting as described above. Specifically, the slit may be formed at least before the final stretching. By performing slitting and stretching in a state where the orientation of the PVA-based resin layer has been increased by stretching in advance, the orientation and optical characteristics of the obtained polarizing film can be further improved. In this case, it is preferable to perform stretching before the slit to such an extent that the above-mentioned sacrificing does not occur at the time of the slit. Further, it is preferable to set the stretching ratio of the stretching after the slit to be higher. The stretching ratio of the stretching after the slit is, for example, 1.5 times or more, preferably 2.0 times or more. This is because the orientation and optical characteristics of the obtained polarizing film can be further improved by stretching the film in a state where the L / W is high.

  Preferably, the slit is performed before the dyeing. By slitting before dyeing, it is possible to more effectively prevent foreign substances from being mixed between the PVA-based resin layer and the protective film in a bonding step with the protective film described later. Specifically, the PVA-based resin layer may be cross-linked (eg, by iodine) to be brittle by dyeing. If slitting is performed in such a state, slit chips are likely to be generated, and the slit chips may become foreign matters during bonding. Therefore, by slitting before dyeing, it is possible to more effectively prevent foreign substances from being mixed and air bubbles due to the foreign substances from being mixed. As a result, a polarizing plate having excellent appearance can be obtained.

  Any appropriate method can be adopted as the method of slitting the laminate. For example, the long laminate may be slit while being wound in the longitudinal direction, or may be slit without being wound. As the slit (cutting) means, for example, a cutting blade such as a round blade or a dish blade, or a laser can be used. Preferably, the slit pieces are removed by winding or suction.

E. FIG. Others In addition to the above, a treatment for making the PVA-based resin layer a polarizing film may be appropriately performed on the laminate. Examples of the treatment for forming a polarizing film include an insolubilization treatment, a crosslinking treatment, a washing treatment, and a drying treatment. The number, timing, order, and the like of these processes are not particularly limited.

  The insolubilization treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably from 20C to 50C. Preferably, the insolubilization treatment is performed before the underwater stretching or the dyeing treatment.

  The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. When a crosslinking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further add an iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide is preferably 1 to 5 parts by weight based on 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably from 20C to 60C. Preferably, the crosslinking treatment is performed before the above-mentioned underwater stretching. In a preferred embodiment, the dyeing treatment, the crosslinking treatment, and the stretching in water are performed in this order.

  The above-described cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. The drying temperature in the above drying treatment is preferably 30C to 100C.

  In one embodiment, the laminate is wound into a roll to form a raw roll, and the slit is formed after winding. The winding tension is typically 300N to 600N. The winding may be performed so that the PVA-based resin layer is on the inner side (core side) or the PVA-based resin layer is on the outer side. When the laminate is taken up in the manufacturing process of the polarizing film, for example, if the laminate has partial film thickness unevenness, tight winding or wrinkling occurs. Such a problem is likely to occur at the end in the width direction. Therefore, stretching can be stably performed by performing the slit after winding. Further, since the slit is formed after the winding, the material roll having the same width can be used irrespective of the width of the protective film to be bonded, which can contribute to an improvement in productivity.

F. Laminating Step After the above-described dyeing and stretching, a protective film is laminated to the PVA-based resin layer (polarizing film) of the laminate. Specifically, a long protective film is attached to the PVA-based resin layer so that their longitudinal directions are aligned. In one embodiment, the width of the laminate after stretching corresponds to the width of the laminate at the time of lamination. Specifically, between the stretching step and the laminating step, substantially no new slit processing is performed on the laminate.

  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.

  Any appropriate resin film can be adopted as the protective film. Examples of the material for forming the protective film include a cellulose resin such as triacetyl cellulose (TAC), a cycloolefin resin such as a norbornene resin, an olefin resin such as polyethylene and polypropylene, a polyester resin, and a (meth) acrylic resin. Resins. The “(meth) acrylic resin” refers to an acrylic resin and / or a methacrylic resin.

  The thickness of the protective film is typically from 10 μm to 100 μm. The protective film may be subjected to various surface treatments. The protective film can function not only as a protective film for the polarizing film but also as a retardation film or the like.

  For bonding the protective film, any appropriate adhesive or pressure-sensitive adhesive is used. In one embodiment, an adhesive is applied to the surface of the polarizing film, and a protective film is attached. The adhesive may be a water-based adhesive or a solvent-based adhesive. Preferably, an aqueous adhesive is used.

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

  The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the adhesion between the PVA-based resin layer and the protective film is excellent, and the durability can be excellent. The acetoacetyl group-containing PVA-based resin is obtained, for example, by reacting the PVA-based resin with diketene by any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, more preferably 1 mol% to 20 mol. %, Particularly preferably 2 mol% to 7 mol%. The degree of acetoacetyl group modification is a value measured by NMR.

  The resin concentration of the aqueous 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 applying the adhesive can be set to any appropriate value. For example, it is set so that an adhesive layer having a desired thickness is obtained after heating (drying). The thickness of the adhesive layer is preferably 10 nm to 300 nm, more preferably 10 nm to 200 nm, and particularly preferably 20 nm to 150 nm.

  It is preferable to heat after attaching the protective film to the PVA-based resin layer. The heating temperature is preferably at least 50 ° C, more preferably at least 60 ° C, particularly preferably at least 80 ° C. In addition, the heating performed after bonding the protective film may also serve as the above-described drying treatment.

G. FIG. Peeling Step In one embodiment, the resin substrate is peeled from the PVA-based resin layer (polarizing film). Preferably, before peeling the resin base material, the width direction end of the polarizing film laminate in which the protective film is bonded to the laminate is slit. At the joining portion between the width direction end of the laminate and the protective film, poor joining (for example, wrinkles) is likely to occur, and by removing this portion with a slit, excellent peelability of the resin substrate is achieved. Can be. Specifically, it is possible to prevent the resin base material from being poorly peeled (for example, broken) from the bonding failure portion as a starting point, and to satisfactorily peel the resin base material. As a result, a polarizing plate with better appearance can be obtained.

H. Polarizing plate The polarizing plate of the present invention has the above-mentioned polarizing film and the above-mentioned protective film arranged on one side of this polarizing film. The polarizing film is substantially a PVA-based resin film on which a dichroic substance is adsorbed and oriented. 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, more preferably 1.0 μm or more. The polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single transmittance of the polarizing film is preferably at least 40.0%, more preferably at least 41.0%, further preferably at least 42.0%, particularly preferably at least 43.0%. The degree of polarization of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, and further preferably 99.95% or more.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. In addition, the measuring method of each characteristic is as follows.
1. The thickness was measured using a digital micrometer (manufactured by Anritsu Corporation, product name “KC-351C”).
2. Glass transition temperature (Tg)
It measured according to JISK7121.

[Example 1]
(Preparation of laminate)
As the resin substrate, a long, amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (width: 4000 mm, thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75 ° C. was used.
One surface of the resin substrate is subjected to corona treatment, and the corona-treated surface is provided with 90 parts by weight of polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (degree of polymerization: 1200, degree of acetoacetyl modification) An aqueous solution containing 10 parts by weight of 4.6%, a saponification degree of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd. and having a trade name of “Gosefimer Z200”) is applied at 60 ° C. and dried to obtain a 10 μm-thick film. A PVA-based resin layer was formed to produce a laminate.

The obtained laminate was uniaxially stretched 2.0 times in the longitudinal direction between rolls having different peripheral speeds in an oven at 115 ° C. (air stretching). Thereafter, the laminate was wound into a roll.
While unwinding the laminate from the laminate roll wound up in a roll shape, both ends in the width direction of the laminate were slit so that the width after slitting was 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 (insolubilizing treatment).
Next, it was immersed in a dyeing bath at a liquid temperature of 30 ° C. while adjusting the iodine concentration and the immersion time so that the obtained polarizing plate had a predetermined transmittance. In this example, 0.2 parts by weight of iodine was added to 100 parts by weight of water, and the resultant was immersed in an aqueous solution of iodine obtained by mixing 1.0 part by weight of potassium iodide for 60 seconds (dyeing treatment). .
Next, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 30 ° C. (a 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) (crosslinking treatment). ).
Thereafter, the laminate was immersed in a boric acid aqueous solution (aqueous solution obtained by blending 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 70 ° C. Uniaxial stretching was performed 2.7 times in the longitudinal direction between rolls having different speeds (underwater stretching).
Thereafter, the laminate is immersed in a washing bath at a liquid temperature of 30 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) for 10 seconds, and then immersed in hot air at 60 ° C. for 60 seconds. It was dried for 2 seconds (washing / drying step).
Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate.

  Subsequently, an aqueous solution of a PVA-based resin (trade name “Gosefimer (registered trademark) Z-200”, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., resin concentration: 3% by weight) was applied to the surface of the polarizing film of the laminated body. A triacetyl cellulose film (manufactured by Konica Minolta, trade name “KC4UY”, thickness: 40 μm) having a width corresponding to the width of the polarizing film is stuck together, and heated in an oven maintained at 60 ° C. for 5 minutes. I got

[Example 2]
A polarizing plate was produced in the same manner as in Example 1 except that the slit was slit so that the width after the slit was 2100 mm.

[Comparative Example 1]
A polarizing plate was produced in the same manner as in Example 1 except that the slit was performed after stretching in water.

(Evaluation)
The following evaluation was performed about the obtained polarizing plate. Table 1 summarizes the evaluation results.
1. Appearance The obtained polarizing plate was visually observed.
2. Polarization degree Using a UV-visible spectrophotometer (manufactured by JASCO Corporation, product name “V7100”), the single transmittance (Ts), parallel transmittance (Tp) and orthogonal transmittance (Tc) of the polarizing plate were measured. The degree of polarization (P) was determined by the following equation.
Degree of polarization (P) (%) = {(Tp−Tc) / (Tp + Tc)} ^1/2 × 100
The above Ts, Tp, and Tc are Y values measured with a two-degree visual field (C light source) according to JIS Z8701 and corrected for visibility.
3. Orientation (Evaluation method of orientation function of PVA)
The measuring device was a Fourier transform infrared spectrophotometer (FT-IR) (Perkin
Elmer, trade name: "SPECTRUM2000") was used. The surface of the PVA-based resin layer was evaluated by attenuated total reflection (ATR) measurement using polarized light as measurement light. The calculation of the orientation function was performed in the following procedure. The measurement was performed in a state where the measurement polarization was set to 0 ° and 90 ° with respect to the stretching direction. Using the intensity of 2941 cm ^-1 of the obtained spectrum, it was calculated according to (Equation 1) described below. The following intensity I as a reference peak to 3330cm ^-1, using the value of 2941cm ^-1 / 3330cm -1. When f = 1, the orientation is perfect, and when f = 0, the orientation is random. Further, the peak at 2941 cm ⁻¹ is said to be absorption due to vibration of the main chain (—CH ₂ —) of PVA.
(Equation 1) f = (3 <cos2θ> -1) / 2 = (1-D) / [c (2D + 1)]
However,
c = (3cos2β-1) / 2
β = 90deg⇒f = -2 × (1-D) / (2D + 1)
θ: molecular chain / stretching direction β: molecular chain / transition dipole moment D = (I⊥) / (I //), (the value of D increases as the PVA is oriented.)
I⊥: Intensity measured when polarized light is incident in the direction perpendicular to the stretching direction I //: Intensity measured when polarized light is incident in the direction parallel to the stretching direction

  The polarizing plate of the present invention can be used for a liquid crystal panel such as a liquid crystal television, a liquid crystal display, a mobile phone, a digital camera, a video camera, a portable game machine, a car navigation system, a copier, a printer, a facsimile, a clock, a microwave oven, and the like. It is suitably used as a protective film.

Reference Signs List 10 laminated body 11 resin base material 12 polyvinyl alcohol-based resin layer (polarizing film)

Claims (2)

Step of forming a polyvinyl alcohol-based resin layer on one side of the long resin substrate and the resin substrate to obtain a laminate,
A step of stretching the laminate in the air,
Dyeing the polyvinyl alcohol-based resin layer,
A step of stretching the laminate underwater,
After the air stretching, before the underwater stretching, slitting the width direction end of the laminate,
After the dyeing and stretching in water, a step of attaching a long protective film to the polyvinyl alcohol-based resin layer,
The width of the laminate after the underwater stretching corresponds to the width of the laminate at the time of the lamination,
A method for manufacturing a polarizing plate. The manufacturing method according to claim 1, further comprising winding the laminate into a roll.

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