JP4892688B2 - Protective film for polarizing plate lamination and protective film laminated polarizing plate - Google Patents

Description

  The present invention relates to a protective film for polarizing plate lamination laminated on a polarizing plate used in a liquid crystal display device, and a protective film laminated polarizing plate obtained by laminating the protective film.

  In general, a polarizing plate used in a liquid crystal display device is formed by laminating a polarizer protective film 2 on both sides of a polarizer 1 as shown in FIG. Then, a pressure-sensitive adhesive layer 4 for bonding is provided on one side of the polarizing plate 3, and the other side of the polarizing plate 3 protects the polarizing plate surface having poor scratch resistance, and the manufacturing process of the liquid layer display device A surface protective film 5 for preventing wrinkles in handling and adhesion of dust is laminated. Further, a release protective film 6 is laminated on the surface of the pressure-sensitive adhesive layer 4 in order to prevent wrinkling during handling and adhesion of dust. The polarizing plate 3 is shipped in the form of a protective film laminated polarizing plate 7 in which protective films are laminated on the front and back in this way.

  In recent years, liquid crystal display devices have a larger screen and higher brightness, and very small foreign objects and wrinkles present in the liquid crystal display device become bright spot defects. There are cases where these bright spot defects are caused by very small foreign matter or wrinkles mixed in the polarizer and polarizer protective film that make up the polarizing plate. Need to be removed. The defect inspection of the polarizing plate is generally performed by visual inspection using a crossed Nicols method. That is, when two polarizing plates are overlapped with each other so that their orientation axes are perpendicular to each other and darkened, and a backlight is applied, foreign matter, wrinkles, etc. will be visually recognized as bright spot defects. The part can be detected.

  In the defect inspection of this polarizing plate, the surface protective film and the release protective film laminated on both sides of the polarizing plate are originally unnecessary, and these films may be removed and inspected. Since it is inevitable that the polarizing plate surface becomes wrinkled in handling, the defect inspection is performed in a state where the surface protective film or the release protective film is laminated.

  Conventionally, biaxially stretched polyester films with excellent transparency have often been used as surface protective films and release protective films. However, in biaxially stretched polyester films, the orientation is constant by bowing when oriented. In contrast, if the crossed Nicols method is used in an orthogonal manner, the darkening contrast will not be constant and the interference color due to the phase difference of the film will appear. There was a drawback that it was difficult to see.

  In order to eliminate the disadvantages when using such an oriented film, Patent Document 1 discloses a three-layer unstretched, non-oriented film in which a polyester film is laminated on both sides of a polycarbonate film having optical isotropy. Proposed to use as a protective film, and to compose a release protective film by applying a release agent on one side of the same film, and to laminate these surface protective film and release protective film on a polarizing plate Yes. However, in the inspection using the crossed Nicols method, the non-oriented polyester film is soft on the surface of the release protective film that is the inside of the two polarizing plates, and therefore is easily scratched during handling. As a result of the stress generated in the very small part of the surface, the phase difference locally increases and becomes visible as a bright spot in the inspection using the crossed Nicols method. It has the disadvantage of disappearing.

Prior art documents relating to the present invention include the following.
JP 2004-077783 A

  The present invention makes it easy to detect a bright spot defect caused by a polarizing plate when a defect is inspected using the crossed Nicols method in a state where a protective film is laminated on the polarizing plate. It aims at providing the protective film for polarizing plate lamination which does not become a defect, and the protective film laminated polarizing plate formed by laminating the protective film.

(1) The protective film for laminating a polarizing plate of the present invention is
A protective film for laminating a polarizing plate comprising a low photoelastic resin having a phase difference of 20 nm or less and an absolute value of a photoelastic coefficient of 50 × 10 ⁻¹² m ² / N or less,
The low photoelastic resin is an acrylic resin;
A homopolymer consisting of polymethyl methacrylate (PMMA) or a copolymer thereof, alone or blended,
Or
A homopolymer consisting of polyethyl methacrylate (PEMA) or a copolymer thereof, alone or blended,
A film formed by extrusion ,
The film contains 0.05 to 3% by weight of a lubricant having a particle size of 0.1 to 3.0 μm,
A release agent is coated on the surface .
(2) The protective film of the present invention is characterized in that, in (1), the absolute value of the photoelastic coefficient of the low photoelastic resin is 10 × 10 ⁻¹² m ² / N or less.
(3) The protective film of the present invention is characterized in that, in the above (1) or (2), the protective film is a non-oriented film.
(4) The protective film laminated polarizing plate of this invention is characterized by laminating | stacking the protective film in any one of said (1)-(3) on a polarizing plate.

The protective film for laminating a polarizing plate of the present invention comprises a low photoelastic resin having an absolute value of photoelastic coefficient of 50 × 10 ⁻¹² m ² / N or less, more preferably 10 × 10 ⁻¹² m ² / N or less, It is comprised with the resin film whose phase difference is 20 nm or less. This protective film is laminated on one side of the polarizing plate so as to be in contact with the pressure-sensitive adhesive layer of the polarizing plate, and this protective film is laminated on the other side of the polarizing plate. Are inspected using the crossed Nicols method so that the orientation axes of the polarizing plates are orthogonal to each other. At this time, since the protective film of the present invention is non-oriented and has a low retardation, a dark visual field is obtained, and the contrast with the bright spot defect of the polarizing plate is high, so that the bright spot defect is easily detected.
Even if the surface of the protective film is wrinkled due to handling, etc., the low photoelastic resin is used so that it does not appear as a bright spot. improves.

  Embodiments of the present invention will be described below. When the protective film of the present invention is used as the release protective film 6, as shown in FIG. 2, a resin film 8 made of a low photoelastic resin as a base material is produced as an unstretched, non-oriented film using an extrusion method. After the film is formed, the release agent 9 is applied to one surface thereof using an application means such as a roll coating method and dried and solidified.

  The mold release protective film 6 shown in FIG. 2 is non-stretched and non-oriented in order to obtain a uniform dark visual field on the entire surface during defect inspection of the polarizing plate 3 by the crossed Nicols method, and has a phase difference of 20 nm or less. There is a need.

Further, the surface of the release protection film 6 is likely to be wrinkled by rubbing on the surface by handling or the like. In the case of a large wrinkle that can be recognized with the naked eye, this flaw due to abrasion is detected as a defect by itself, but even if a small wrinkle that cannot be recognized with the naked eye is attached, Stress is applied and the phase difference is locally increased to be detected as a bright spot. Therefore, as the resin film 8 serving as a base material, a film made of a low photoelastic resin that hardly increases the phase difference even when stress is applied to the resin is used. Examples of the low photoelastic resin film 8 include a film made of a resin having a low photoelastic coefficient having an absolute value of 50 × 10 ⁻¹² m ² / N or less, more preferably 10 × 10 ⁻¹² m ² / N or less. it can.
When a film made of a resin having an absolute value of the photoelastic coefficient exceeding 50 × 10 ⁻¹² m ² / N is used, if the resin surface is wrinkled, stress is applied to the resin at the wrinkled portion and the phase difference is high. It is not preferable because it is detected as a bright spot in the defect inspection using the Nari Cross Nicol method.

Examples of these resins having a low photoelastic coefficient include acrylic resins, cyclic olefin resins, and copolymerized polycarbonate resins, but the low photoelastic resins that can be used in the protective film of the present invention are not limited thereto. Any resin having a low photoelastic coefficient within the above range can be used.
Moreover, it is also possible to blend and use two or more types of low photoelastic resins as long as they are compatible and do not become cloudy by blending. It is also possible to use a laminate of two or more films made of different low photoelastic resins.

  As an acrylic resin, the homopolymer which consists of methacrylic acid ester, such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, and the copolymer of these methacrylic acid ester and the monomer which has a copolymerizability are mentioned. Examples of the copolymerizable monomer include methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, and methacrylic acid. Methacrylates such as benzyl, glycidyl methacrylate, 2-hydroxydiethyl methacrylate, 2-hydroxypropyl methacrylate, and methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, Such as 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, glycidyl acrylate, 2-hydroxydiethyl acrylate, 2-hydroxypropyl acrylate, etc. Acrylic acid esters, and acrylic acid, and unsaturated acids such as methacrylic acid. Further, these homopolymers and copolymer polymers can be blended at an arbitrary ratio and used. Furthermore, these homopolymers and copolymers alone or blends are blended with acrylic rubber such as polyalkyl acrylate ester-styrene copolymer or modified acrylic elastomer for the purpose of improving impact resistance. It is also possible.

  The cyclic olefin resin has an alicyclic structure in the main chain or side chain. Examples of the cyclic olefin resin include norbornene resins, cyclic conjugated diene resins, and hydrogenated products thereof, and norbornene resins and hydrogenated products thereof are particularly preferable. Examples of norbornene resins include 5-methoxycarbonylbicyclo [2,2,1] hept-2-ene, 5-methyl-5-methoxycarbonylbicyclo [2,2,1] hept-2-ene, and 5-cyano. Addition polymers of norbornene monomers such as bicyclo [2,2,1] hept-2-ene, copolymers of these norbornene monomers and olefin monomers such as ethylene and propylene, cyclobutene, cyclopentene, cyclohexene After modifying a ring-opening polymer of norbornene-based monomers such as putene, cyclooctene, bicyclo [2,2,1] hept-2-ene, 5-ethylidene-2-norbornene, cyclopentadiene with maleic acid or cyclopentadiene A hydrogenated resin or the like can be used.

  The thickness of the low photoelastic resin film 8 serving as a substrate is preferably 10 to 200 μm. When the thickness is less than 10 μm, the effect of protecting the surface of the polarizing plate 3 is not sufficient, and when it exceeds 200 μm, the effect of protecting the polarizing plate 3 is saturated and is not economical. Moreover, it is preferable that a phase difference is 20 nm or less. If the phase difference exceeds 20 nm, a dark visual field cannot be obtained due to the influence of the phase difference of the film in the defect inspection using the crossed Nicols method, and it becomes difficult to visually recognize the bright spot defect caused by the polarizing plate.

The resin film 8 made of the above low photoelastic resin can be manufactured using a known film manufacturing method such as an extrusion method. Further, the low photoelastic resin film 8 is manufactured in the shape of a long band, and the release agent 9 is applied while being wound around the coiler or unwound from the coiler. When a lubricant such as 0.0 μm silica powder is contained in an amount of 0.05 to 3% by weight, the winding operation and the rewinding operation can be performed smoothly.
If it does not contain a lubricant, it is particularly difficult to wind it around a coiler. If the particle size and content of the lubricant are within the above ranges, the detection of optical defects of the polarizing plate 3 will not be adversely affected.

  As the release agent 9 to be applied to the surface of the low photoelastic resin film 8, a silicon release agent, a higher fatty acid, a higher fatty acid amide, a higher fatty acid ester, a metal soap, a fluorocarbon, and the like can be used. A solution or emulsion diluted by dissolving or dispersing any of these is applied using a coating method such as a roll coating method, and then dried and solidified. When the release protective film 6 having the release agent 9 is adhesively laminated on the polarizing plate 3 through the adhesive layer 4 as described above, it can be easily peeled off after being subjected to defect inspection when attached to the liquid crystal display device. .

  Further, a surface protective film 5 is laminated on the side of the polarizing plate 3 opposite to the side on which the release protective film 6 is laminated. As the surface protective film 5, a release agent 9 is added to the low photoelastic resin film 8. The protective film of this embodiment can be used as a surface protective film by applying a pressure-sensitive adhesive instead of applying the adhesive.

Hereinafter, the present invention will be described in detail with reference to examples.
(Creation of low photoelastic resin film)
Using an extrusion method, long strip-shaped unstretched and non-oriented resin films (sample numbers 1 to 4) composed of an acrylic resin, a cyclic olefin resin and a copolymer polycarbonate resin shown in Table 1 were prepared. For comparison, a non-oriented film of polycarbonate (sample number 5) shown in Table 1 and a non-oriented film (sample number 6) consisting of three resin layers obtained by laminating the polyester layer shown in Table 1 on the front and back of the polycarbonate layer. )created.

(Measurement of phase difference)
A release agent was applied to the resin films of sample numbers 1 to 6 and dried to prepare a release protective film. After this release protection film was cut out to a size of 40 mm × 40 mm, the phase difference was measured using KOBRA-WPR manufactured by Oji Scientific Instruments (measured at a wavelength of 590 nm).

(Verification of visibility of bright spot defects caused by polarizing plate)
A release agent was applied to the resin films of sample numbers 1 to 6 and dried to prepare a release protective film. This release protective film was affixed to a polarizing plate containing a foreign substance that causes bright spot defects, and two test pieces having a size of 100 mm × 100 mm were cut out. The two specimens were overlapped so that the orientations of the polarizing plates were perpendicular to each other, in a crossed Nicol state, a backlight was applied from below, and the specimens were visually observed from above. The visibility of the bright spot defect at this time was evaluated according to the following criteria.
○: A dark visual field is obtained, the contrast with the bright spot defect is high, and the visibility of the bright spot defect is good.
X: A dark visual field cannot be obtained, the contrast with a bright spot defect is low, and the visibility of the bright spot defect is poor.
These evaluation results are shown in Table 2. As shown in Table 2, when the mold release protective film of the present invention is used, a dark visual field is obtained, so that the visibility of the bright spot defect caused by the polarizing plate is excellent and the inspection becomes easy.

(Confirmation of occurrence of bright spots due to surface defects on the release protection film)
A release agent was applied to the resin films of Sample Nos. 1 to 6 and dried, and then affixed to a polarizing plate and two test pieces having a size of 100 mm × 100 mm were cut out. Among these, a copper plate whose surface was roughened by etching was placed on the surface of the mold release protective film of one of the specimens to form scratches on the tensile surface. Next, the specimens on which the scratches were formed and the other specimens on which the scratches were not formed were overlapped so that the orientations of the polarizing plates were perpendicular to each other, put into a crossed Nicol state, applied with a backlight from below, and from above The specimen was observed. The generation state of the bright spot at this time was visually observed and evaluated.
These evaluation results are shown in Table 2. As shown in Table 2, the release protective film of the present invention is not visually recognized as a bright spot even if the surface is wrinkled, and does not become an obstacle when the polarizing plate 3 is inspected for defects.

The protective film 6 of the present invention has a low photoelasticity having a phase difference of 20 nm or less and an absolute value of a photoelastic coefficient of 50 × 10 ⁻¹² m ² / N or less, more preferably 10 × 10 ⁻¹² m ² / N or less. Because it is made of resin, it is easy to see the bright spot defects caused by the polarizing plate, and even if the surface of the protective film is wrinkled due to handling etc., it does not appear as a bright spot because it uses a low photoelastic resin. It is possible to greatly improve the inspection accuracy because only the defects are visible as bright spots.
Industrial applicability is extremely high.

It is a schematic sectional drawing which shows an example of a structure of a polarizing plate. It is a schematic sectional drawing which shows one Embodiment of the protective film of this invention.

Explanation of symbols

1: Polarizer 2: Polarizer protective film 3: Polarizing plate 4: Adhesive layer 5: Surface protective film 6: Release protective film 7: Protective film laminated polarizing plate 8: Low photoelastic resin film 9: Release agent

Claims (4)

A protective film for laminating a polarizing plate comprising a low photoelastic resin having a phase difference of 20 nm or less and an absolute value of a photoelastic coefficient of 50 × 10 ⁻¹² m ² / N or less,
The low photoelastic resin is an acrylic resin;
A homopolymer consisting of polymethyl methacrylate (PMMA) or a copolymer thereof, alone or blended,
Or
A homopolymer consisting of polyethyl methacrylate (PEMA) or a copolymer thereof, alone or blended,
A film formed by extrusion ,
The film contains 0.05 to 3% by weight of a lubricant having a particle size of 0.1 to 3.0 μm,
A protective film for laminating a polarizing plate , wherein a release agent is applied to the surface . The protective film according to claim 1, wherein an absolute value of a photoelastic coefficient of the low photoelastic resin is 10 × 10 ⁻¹² m ² / N or less. The protective film according to claim 1, wherein the protective film is a non-oriented film. The protective film laminated polarizing plate formed by laminating | stacking the protective film in any one of Claims 1-3 on a polarizing plate.

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