JP2019211799A - Manufacturing method of polarizing plate - Google Patents

Abstract

To provide a polarizing plate excellent in durability.SOLUTION: A manufacturing method of a polarizing plate of the present invention includes: preparing a polarization film laminate 10 having a polarizer 11 and protective films 21 and 22 arranged at least on one side of the polarizer 11; shrinking the polarization film laminate 10; and cutting the shrunk polarization film laminate.SELECTED DRAWING: Figure 1

Description

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

  Polarizers are used in image display devices (for example, liquid crystal display devices) such as mobile phones and notebook personal computers. In recent years, it has been desired to use a polarizing plate for a meter display unit of an automobile, a smart watch, and the like, and it is desired that the polarizing plate has a shape other than a rectangular shape and a through hole is formed in the polarizing plate. However, when such a form is adopted, a problem of durability is likely to occur. For the purpose of improving the durability, for example, a method has been proposed in which a polarizer is heat-treated at a temperature of 95 ° C. or higher and a protective film is laminated on the heat-treated polarizer to obtain a polarizing plate (see Patent Document 1). ), Further improvement in durability is demanded.

Japanese Patent Application Laid-Open No. 07-333425

  The present invention has been made to solve the above-mentioned problems, and a main object thereof is to provide a polarizing plate having excellent durability.

The method for producing a polarizing plate of the present invention comprises preparing a polarizing film laminate having a polarizer and a protective film disposed on at least one side of the polarizer , shrinking the polarizing film laminate , and Cutting the shrunk polarizing film laminate .
In one embodiment, the polarizing film laminate is contracted by 0.2% or more in the transmission axis direction of the polarizer.
In one embodiment, the cutting is performed through the through-hole, a portion having a substantially V shape whose outer edge is convex inward in the plane direction, a portion having an outer edge having a round shape that is convex inward in the plane direction, and a combination thereof. Forming one selected from the group consisting of:

  According to this invention, the polarizing plate excellent in durability can be obtained by shrink | contracting the polarizing film laminated body obtained by laminating | stacking a polarizer and a protective film.

It is sectional drawing of the polarizing film laminated body by one Embodiment of this invention. 1 is a plan view of a polarizing plate according to one embodiment of the present invention. (A) is a photograph showing the periphery of the through hole of the polarizing plate of Example 1 after the heat cycle test, (b) is a photograph showing the periphery of the through hole of the polarizing plate of Example 2 after the heat cycle test, (C) is a photograph showing the periphery of the through hole of the polarizing plate of Example 3 after the heat cycle test, and (d) is a photograph showing the periphery of the through hole of the polarizing plate of Comparative Example 1 after the heat cycle test. (A) shows the state around the polarizing plate edge side along the transmission axis direction of the test sample of Example 1 after the heat cycle test, and (b) shows the state around the polarizing plate edge side along the absorption axis direction. Indicates. (A) shows the state around the polarizing plate edge along the transmission axis direction of the test sample of Comparative Example 1 after the heat cycle test, and (b) shows the state around the polarizing plate edge along the absorption axis direction. Indicates.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

  The manufacturing method of the polarizing plate of this invention includes preparing the polarizing film laminated body which has a polarizer and the protective film arrange | positioned at least one side of this polarizer, and shrinking a polarizing film laminated body.

A. Polarizing Film Laminate FIG. 1 is a cross-sectional view of a polarizing film laminate according to one embodiment of the present invention. The polarizing film laminate 10 includes a polarizer 11, a first protective film 21 disposed on one side of the polarizer 11, and a second protective film 22 disposed on the other side of the polarizer 11. Although not shown, the protective films 21 and 22 are typically bonded to the surface of the polarizer 11 via an adhesive layer. In the illustrated example, the protective film is disposed on both sides of the polarizer, but the protective film may be disposed only on one side.

A-1. Polarizer The polarizer is typically composed of a resin film containing a dichroic substance. Examples of the dichroic substance include iodine and organic dyes. These may be used alone or in combination of two or more. Preferably, iodine is used.

  Arbitrary appropriate resin may be used as resin which forms the said resin film. Preferably, a hydrophilic resin (for example, polyvinyl alcohol (PVA) resin) is used. Examples of the PVA resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 to 100 mol%, preferably 95.0 mol% or more, more preferably 99.0 mol% or more, and particularly preferably 99.93 mol% or more. . The saponification degree can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizer having excellent durability can be obtained.

  The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. Average polymerization degree is 1000-10000 normally, Preferably it is 1200-6000, More preferably, it is 2000-5000. The average degree of polymerization can be determined according to JIS K 6726-1994.

  The polarizer preferably exhibits absorption dichroism in the wavelength range of 380 nm to 780 nm. The single transmittance (Ts) of the polarizer is preferably 40% or more, more preferably 41% or more, still more preferably 42% or more, and particularly preferably 43% or more. The theoretical upper limit of the single transmittance is 50%, and the practical upper limit is 46%. In addition, the single transmittance (Ts) is a Y value measured by a 2 degree visual field (C light source) of JIS Z8701 and corrected for visibility. For example, a spectrophotometer (manufactured by JASCO Corporation, V7100) is used. Can be measured. The polarization degree of the polarizer is preferably 99.8% or more, more preferably 99.9% or more, and further preferably 99.95% or more.

  The thickness of the polarizer can be set to any appropriate value. The thickness is typically 1 μm to 80 μm, preferably 3 μm to 40 μm.

  The polarizer can be typically obtained by subjecting the resin film to treatment such as swelling treatment, stretching treatment, dyeing treatment with the dichroic substance, crosslinking treatment, washing treatment, and drying treatment. The number, order, timing, and the like of each process can be set as appropriate. When performing each treatment, the resin film may be a resin layer formed on a substrate.

  The said crosslinking process is performed by making a boric acid solution (for example, boric acid aqueous solution) contact a resin film, for example. Moreover, when employ | adopting a wet extending | stretching system in an extending | stretching process, it is preferable to extend | stretch, making a boric acid solution contact a resin film. From the viewpoint of obtaining excellent polarization characteristics, the resin film is usually uniaxially stretched 3 to 7 times. The stretching direction in the stretching treatment can correspond to the absorption axis direction of the obtained polarizer. The transmission axis direction can be orthogonal to the absorption axis direction. In one embodiment, the long resin film is stretched in the transport direction (MD) while being transported in the longitudinal direction. In this case, the absorption axis direction of the obtained polarizer can be the longitudinal direction (MD), and the transmission axis direction can be the width direction (TD).

A-2. Protective film Examples of the material for forming the protective film include cellulose resins such as diacetyl cellulose and triacetyl cellulose (TAC), (meth) acrylic resins, cycloolefin resins, olefin resins such as polypropylene, and polyethylene terephthalate systems. Examples thereof include ester resins such as resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The “(meth) acrylic resin” refers to an acrylic resin and / or a methacrylic resin.

  The thickness of the protective film is preferably 10 μm to 200 μm. A surface treatment layer may be formed on one side of the protective film (side where the polarizer is not disposed). Specifically, a hard coat treatment, an antireflection treatment, or treatment for diffusion or antiglare may be performed. The protective film may function as a retardation film. In addition, when a protective film is arrange | positioned at both sides of a polarizer like the example of illustration, both structure (formation material, thickness, etc.) may be the same structure, and a different structure may be sufficient as them. .

A-3. Others Any appropriate adhesive can be adopted as the adhesive used for bonding the protective film. For example, a water-based adhesive, a solvent-based adhesive, an active energy ray curable adhesive, or the like is used. As the water-based adhesive, an adhesive containing a PVA-based resin is preferably used.

B. Shrinkage Shrink the polarizing film laminate. A polarizing plate excellent in durability can be obtained by shrinking the polarizing film laminate. Specifically, the contracted polarizing plate has a very small shape change due to a change in the external environment, and is adjacent to another member (for example, a glass substrate such as a liquid crystal cell) via an adhesive layer. The effect on the adhesive layer is very small. Therefore, the change in the shape of the pressure-sensitive adhesive layer due to a change in the external environment is suppressed, and the occurrence of stress between the members (for example, stress generated when the elastic modulus of the pressure-sensitive adhesive layer increases at a low temperature) can be prevented. As a result, the polarizing plate can have extremely excellent durability without causing cracks in the polarizing plate.

  A typical example of the shrinking method is a method of heating the polarizing film laminate. The heating temperature is, for example, 50 ° C to 120 ° C, preferably 70 ° C to 90 ° C. If it is such a range, it can be made to shrink | contract efficiently, ensuring the optical characteristic (for example, hue, transmittance | permeability, polarization degree) of a polarizing film laminated body. The heating time is, for example, 1 hour to 100 hours, preferably 2 hours or more, and more preferably 10 hours or more. Heating may be performed in one stage or in multiple stages. The heating temperature may be kept substantially constant, or may be changed continuously or stepwise.

  For example, the shrinkage rate is preferably 0.2% or more, and more preferably 0.3% or more in the transmission axis direction of the polarizer contained in the polarizing film laminate. On the other hand, the shrinkage rate in the transmission axis direction is, for example, 0.6% or less. With such a shrinkage rate, it can be determined that the polarizing film laminate was shrunk to a sufficient level. In addition, since the polarizing film laminate can contract more greatly in the absorption axis direction than in the transmission axis direction, in the initial stage of contraction, the dimension in the transmission axis direction of the polarizing film laminate may sometimes temporarily increase. In this case, as shrinkage progresses, the dimension in the transmission axis direction can also decrease from the dimension at the start of shrinkage (at the start of heating).

The shrinkage rate in the absorption axis direction of the polarizing film laminate is preferably 0.3% or more, more preferably 0.4% or more. On the other hand, the shrinkage rate in the absorption axis direction is, for example, 1.0% or less. In addition, a shrinkage rate can be calculated | required by a following formula.
Shrinkage rate (%) = {1- (dimension after heating / dimension before heating))} × 100

C. Cutting Since the polarizing plate of the present invention has excellent durability, it can be formed into a desired shape. A typical example of a method for forming into a desired shape is a method of cutting (punching) the polarizing film laminate. The cutting may be performed before shrinkage of the polarizing film laminate or after shrinkage. It should be noted that excellent durability can be obtained whether cutting is performed before shrinkage or after shrinkage. From the viewpoint of more precisely forming the desired shape, it is preferable to cut after shrinkage.

  Any appropriate method can be adopted as the cutting (punching) method. Examples thereof include a method of irradiating laser light and a method of using a cutting blade (punching die) such as a Thomson blade or a picnal blade. According to the laser beam irradiation, a smooth cut surface can be obtained, the generation of crack starting points (initial cracks) can be suppressed, and the durability can be further improved. Even when a cutting blade is used (even if an initial crack has occurred), excellent durability can be obtained by the above shrinkage.

Any appropriate laser can be adopted as the laser as long as the polarizing film laminate (polarizing plate) can be cut. Preferably, a laser that can emit light having a wavelength in the range of 150 nm to 11 μm is used. Specific examples include a gas laser such as a CO ₂ laser; a solid laser such as a YAG laser; and a semiconductor laser. Preferably, a CO ₂ laser is used.

The irradiation condition of the laser beam can be set to any appropriate condition depending on, for example, the laser to be used. The output conditions are preferably 10 W to 1000 W, more preferably 100 W to 400 W, when a CO ₂ laser is used.

D. Polarizing Plate FIG. 2 is a plan view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 is suitably used for an automobile meter panel. The polarizing plate 100 is configured by connecting a first display unit 50 and a second display unit 60, and through holes 51 and 61 for fixing various meter needles are provided near the center of each display unit. Each is formed. The diameter of the through hole is, for example, 0.5 mm to 100 mm. The outer edges of the display units 50 and 60 are formed in an arc shape along the rotation direction of the meter needle.

  When forming a through-hole like the example of illustration, the position of a through-hole can be suitably set according to the use of a polarizing plate, for example. The crack is likely to be generated starting from the periphery of the through hole, and the tendency of the crack becomes more prominent as the position of the through hole is away from the outer edge of the polarizing plate. As a result, as the position of the through hole is farther from the outer edge of the polarizing plate (for example, 15 mm or more from the outer edge of the polarizing plate), the effect of improving the durability due to the shrinkage can be obtained remarkably. In addition, the part where the outer edges such as the boundary parts 41 and 42 of each display part form a V-shape (including a round shape) that is convex inward in the surface direction is likely to be a starting point of a crack, similarly to the periphery of the through hole.

  The polarizing plate of the present invention is not limited to the configuration of the illustrated example, and can be changed as appropriate. For example, the shape of the polarizing plate, the presence / absence of the through hole, the shape and size of the through hole, the number of the through holes and the formation position can be appropriately changed.

  For example, the polarizing plate of the present invention is bonded to another member (for example, a glass substrate such as a liquid crystal cell) via an adhesive layer. The thickness of the pressure-sensitive adhesive layer is preferably 4 μm to 50 μm. An acrylic pressure-sensitive adhesive is preferably used as the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. The dimensional change rate is a value calculated by the following formula.
Dimensional change rate (%) = {(dimension after heating / dimension before heating)) − 1} × 100

[Example 1]
(Preparation of polarizing film laminate sheet)
As the polarizer, a film (thickness 28 μm) obtained by containing iodine in a long PVA-based resin film and uniaxially stretching in the longitudinal direction (MD) was used.
A PVA adhesive was applied to one side of the polarizer so that the thickness after drying was 100 nm, and a long TAC film having a thickness of 40 μm was bonded so that the longitudinal directions thereof were aligned.
Subsequently, a PVA adhesive was applied to the other side of the polarizer so that the thickness after drying was 100 nm, and a long acrylic film having a thickness of 30 μm was bonded so that the longitudinal directions thereof were aligned.
Thus, a polarizing film laminate sheet having a TAC film / polarizer / acrylic film structure was obtained.

The obtained polarizing film laminate sheet was cut using a CO ₂ laser (wavelength: 9.35 μm, output: 150 W), and a size of 112 mm × 112 mm in which a through hole having a diameter of 2 mm was formed at a site 55 mm from the outer edge A cut piece of was obtained.
The obtained cut piece was placed in an atmosphere at 85 ° C. for 50 hours to obtain a polarizing plate. The dimensional change rate in the absorption axis direction before and after heating is -0.74% (shrinkage rate is 0.74%), and the dimensional change rate in the transmission axis direction is -0.44% (shrinkage rate is 0.44%). Met. For the dimensional change rate before and after heating, separately prepare a cut piece cut into a size of 100 mm × 100 mm from the polarizing film laminate sheet (this cut piece is not formed with a through hole), and the corner of the cut piece It was determined by measuring the position. Here, the cut pieces were cut out such that one set of opposite sides corresponded to the transmission axis direction of the polarizer and another set of opposite sides corresponded to the absorption axis direction of the polarizer.

[Example 2]
A polarizing plate was obtained in the same manner as in Example 1 except that the obtained cut piece was placed in an atmosphere of 85 ° C. for 5 hours. The dimensional change rate in the absorption axis direction before and after heating measured by the same method as in Example 1 was −0.45% (shrinkage rate was 0.45%), and the dimensional change rate in the transmission axis direction was −0.37. % (Shrinkage rate was 0.37%).

[Example 3]
A polarizing plate was obtained in the same manner as in Example 1 except that the obtained cut piece was placed in an atmosphere of 85 ° C. for 2.5 hours. The dimensional change rate in the absorption axis direction before and after heating measured by the same method as in Example 1 is -0.34% (shrinkage rate is 0.34%), and the dimensional change rate in the transmission axis direction is -0.25. % (Shrinkage was 0.25%).

[Example 4]
A polarizing plate was obtained in the same manner as in Example 1 except that the size of the cut piece was 52 mm × 52 mm and the through hole was formed at a site 25 mm from the outer edge.

[Comparative Example 1]
A polarizing plate was obtained in the same manner as in Example 1 except that the cut piece was not heated.

[Comparative Example 2]
A polarizing plate was obtained in the same manner as in Example 4 except that the cut piece was not heated.

  The durability of the obtained polarizing plate was evaluated by a heat cycle (HS) test. Specifically, the obtained polarizing plate was bonded to a glass plate using an acrylic pressure-sensitive adhesive (thickness 20 μm) to obtain a test sample. This was left for 30 minutes in an atmosphere at −40 ° C. and then left for 30 minutes in an atmosphere at 85 ° C. After repeating this operation as 100 cycles for 100 cycles, it was confirmed whether or not cracks occurred in the polarizing plate.

FIG. 3 is an observation photograph by an optical microscope (manufactured by OLYMPUS, MX61, magnification: 5 times) around the through holes of the polarizing plates of Examples 1 to 3 and Comparative Example 1 after the HS test. In Comparative Example 1, cracks that can be clearly recognized visually are confirmed, whereas in Example 1, generation of cracks (including microcracks) is not recognized. In Examples 2 and 3, the occurrence of cracks is suppressed as compared with Comparative Example 1, although microcracks that cannot be clearly recognized visually are confirmed. In addition, the crack has generate | occur | produced along the extending direction.
In Example 4, as in Example 1, the occurrence of cracks (including microcracks) is not observed. In Comparative Example 1, the crack reaches the edge of the polarizing plate starting from the through hole, whereas in Comparative Example 2, the crack length is 12 mm.

  4 shows the state of the polarizing plate end portion of the test sample after the HS test of Example 1, and FIG. 5 shows the state of the polarizing plate end portion of the test sample before and after the HS test of Comparative Example 1. In the comparative example 1, the area | region where the adhesive layer used when bonding a polarizing plate on a glass plate was exposed was formed.

  The polarizing plate of the present invention can be suitably used for, for example, a rectangular image display device (liquid crystal display device, organic EL device), for example, an abnormal image display unit represented by a meter display unit of an automobile or a smart watch. obtain.

DESCRIPTION OF SYMBOLS 10 Polarizing film laminated body 11 Polarizer 21, 22 Protective film 100 Polarizing plate

Claims (3)

Preparing a polarizing film laminate having a polarizer and a protective film disposed on at least one side of the polarizer ,
Thereby contracting the pre Kihen light film laminate, and
The manufacturing method of a polarizing plate including cut | disconnecting the polarizing film laminated body after the said shrinkage | contraction .   The manufacturing method of Claim 1 which shrinks | contracts the said polarizing film laminated body 0.2% or more in the transmission-axis direction of the said polarizer. The cutting is selected from the group consisting of a through-hole, a portion having a substantially V shape whose outer edge is convex inward in the plane direction, a portion in which the outer edge is convex inward in the plane direction, and combinations thereof. The manufacturing method of Claim 1 or 2 including forming one.