JP2005128294A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in moisture resistance and heat resistance by improving the adhesiveness of an adhesive layer for adhering a polarizing film and a protective film.
An adhesive layer for bonding a polarizing film and a protective film contains a particulate material having a particle size of 0.1 to 1.0 μm, a water-soluble epoxy compound or glyoxal, and a polyvinyl alcohol-based adhesive. It is formed using an adhesive composition.
[Selection] Figure 1

Description

  The present invention relates to a polarizing plate. More specifically, the present invention relates to a polarizing plate excellent in adhesion between the polarizing film and the protective film, moisture resistance and heat resistance.

  The polarizing plate is an optical member having a function of transmitting only a light component that vibrates in a specific direction perpendicular to the traveling direction of light, and converts the light component that vibrates in other directions into polarized light by absorbing the light component. It is an indispensable component for a liquid crystal display (LCD), and is widely used for liquid crystal televisions, OA equipment, liquid crystal projectors and the like. In general, a polarizing plate in which a polarizing film and a protective film are laminated via an adhesive layer is widely used.

  Here, the polarizing film refers to a film having a function of converting transmitted light into polarized light. For example, a polyvinyl alcohol (hereinafter abbreviated as PVA) film is stretched while being heated, and iodine (I) or two A film with a polarizing function is used by bringing iodine molecules and dye molecules into alignment in the stretching direction by contacting with a chromatic dye solution.

  The protective film refers to a film that prevents the polarizing film from being deteriorated and holds the polarizing film to give a practical strength to the polarizing plate. Cellulose acetate such as a triacetyl cellulose (hereinafter abbreviated as TAC) film The film is widely used because it is excellent in optical transparency and non-orientation. The protective film is used by being laminated on one side or both sides of the polarizing film.

  Lamination of the polarizing film and the protective film is carried out through an adhesive layer. Since both the PVA film and the cellulose acetate film are hydrophilic, the adhesive constituting the adhesive layer is a hydrophilic adhesive, for example, A water-soluble PVA adhesive or the like is used. However, since the hydrophilic adhesive has a large water absorption rate, when the polarizing plate is kept under a high humidity condition for a long time, it gradually absorbs moisture and the adhesive force is lowered, and there is a problem that the end faces of the polarizing film and the protective film are easily peeled off.

  In order to solve this, a method of improving the moisture resistance and heat resistance by saponifying the cellulose acetate film surface of the protective film to strengthen the adhesive force is known (for example, see Patent Document 1). In addition, a method for improving the adhesive strength by once treating the surface of the polarizing film with an adhesive and then adhering a protective film again through the adhesive is known (for example, see Patent Document 2). In addition, a technique for improving adhesive strength and moisture resistance by using a resin solution containing an acetoacetyl group-containing PVA resin and a crosslinking agent as an adhesive has been proposed (see, for example, Patent Document 3). Furthermore, a technique for improving adhesive strength, moisture resistance, heat resistance, and the like by combining a PVA adhesive and a crosslinking agent is also disclosed (see, for example, Patent Document 4 and Patent Document 5). A technique for improving adhesiveness by adding particles to a PVA-based adhesive is also disclosed (see, for example, Patent Document 6).

  However, although the adhesiveness and moisture resistance are improved by these adhesives, it is not always sufficient, and a polarizing plate on which a protective film having further improved adhesion and wet heat resistance is laminated is desired.

JP-A-56-50301 JP 61-245107 A JP-A-7-198945 JP 7-134212 A Japanese Patent Laid-Open No. 9-258023 JP 2000-214323 A

  The objective of this invention is improving the adhesiveness of the contact bonding layer which adhere | attaches a polarizing film and a protective film, and is providing the polarizing plate excellent in moisture resistance and heat resistance.

  In the present invention, the polarizing film and the protective film are provided with an adhesive layer containing a particulate material having a particle size of 0.1 to 1.0 μm, a water-soluble epoxy compound or glyoxal, and a polyvinyl alcohol-based adhesive. A polarizing plate characterized by being laminated.

  According to the present invention, the polarizing film and the protective film are formed by forming the adhesive layer for adhering the polarizing film and the protective film by containing the particulate matter and the water-soluble epoxy resin or glyoxal in the adhesive composition. Thus, a polarizing plate having improved moisture resistance and heat resistance can be provided.

  In the present invention, the adhesive layer contains a particulate matter, a water-soluble epoxy compound, and a polyvinyl alcohol-based adhesive in a ratio of 0.2 to 45/5 to 50/100 in terms of solid content. It is formed from an adhesive composition.

  Further, the present invention is characterized in that the polyvinyl alcohol-based adhesive is a carboxyl group-modified polyvinyl alcohol and the water-soluble epoxy compound is a reaction product of polyamide and epichlorohydrin.

  According to the present invention, a particulate matter, a water-soluble epoxy compound, particularly an epoxy compound obtained by a reaction of polyamide and epichlorohydrin, and a polyvinyl alcohol adhesive, particularly a carboxyl group-modified polyvinyl alcohol, are contained in a specific ratio. By forming an adhesive layer using the adhesive composition, the epoxy compound functions as a crosslinking agent, so strong adhesion between the polarizing film and the protective film is obtained, and it is excellent in moisture resistance, heat resistance and durability A polarizing plate can be provided.

  Moreover, the present invention provides an adhesive composition in which the adhesive layer contains particulate matter, glyoxal, and polyvinyl alcohol-based adhesive in a ratio of 0.2 to 50/1 to 65/100 by weight. It is formed.

  According to the present invention, by forming an adhesive layer using an adhesive composition containing a specific amount of particulate matter, glyoxal, and polyvinyl alcohol-based adhesive, glyoxal is crosslinked like an epoxy compound. Since it acts as an agent, the adhesiveness between the polarizing film and the protective film is enhanced, and a polarizing plate excellent in moisture resistance, heat resistance and durability can be obtained.

  As described above, according to the present invention, by forming an adhesive layer that adheres the polarizing film and the protective film using the adhesive composition containing the particulate matter, the adhesive property is excellent and the durability is high. In addition, since the end surfaces of the polarizing film and the protective film do not peel even under a high temperature and high humidity condition for a long period of time, it is possible to provide a polarizing plate in which the polarization characteristics do not deteriorate.

  Hereinafter, the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view showing a layer structure of a polarizing plate 1 according to an embodiment of the present invention. In the polarizing plate 1, protective films 3 are laminated on both surfaces of the polarizing film 2 with an adhesive layer 4 interposed therebetween.

  As the polarizing film 2, a conventionally known PVA polarizing film can be used. For example, an iodine polarizing film obtained by adsorbing and orienting iodine on a PVA film, a dye polarizing film obtained by adsorbing and orienting a dichroic dye, and a polyene polarizing film obtained by partially dehydrating these films. it can. Examples of the PVA film include a PVA film, a polyvinyl butyral film, a polyvinyl acetal film, a polyvinyl formal film, and a poly (ethylene-vinyl acetate) copolymer saponified film. The thickness of the polarizing film 2 is about 10-50 micrometers.

  As the protective film 3, a protective film similar to that used for a normal polarizing plate can be used, but a cellulose acetate film excellent in optical transparency and mechanical strength is preferred. Examples of the cellulose acetate film include diacetyl cellulose (DAC) and triacetyl cellulose (TAC). The surface of these films can be saponified with alkali, corona discharge treatment, plasma treatment, glow Those subjected to discharge treatment, high frequency treatment, electron beam treatment, etc. are more effective. The thickness of the protective film 3 is about 10-200 micrometers.

  The adhesive layer 4 contains a particulate material 5, and is formed using an adhesive composition containing the particulate material 5, a cross-linking agent, and a PVA adhesive. In the case where a water-soluble epoxy compound is used as a crosslinking agent, for example, a PVA-based adhesive is dissolved in water, and the water-soluble epoxy compound is added to and dissolved in the obtained aqueous solution. Is added and dispersed. The ratio of the PVA adhesive and water is not particularly limited, but is about 1 to 10/100 by weight.

  Examples of the PVA adhesive include PVA modified with a carboxyl group, an acetoacetyl group, a methylol group, an amino group, and the like, and carboxyl group-modified PVA is particularly preferable. The molecular weight is preferably about 40,000 to 120,000.

  Examples of the water-soluble epoxy compound include a reaction product of polyamide and epichlorohydrin. Specifically, it is a product obtained by reacting epichlorohydrin with a polyamide obtained by reacting an alkylpolyamine compound such as diethylenetriamine or hexamethylenediamine with an alkyldicarboxylic acid such as adipic acid. Examples of commercially available products include polyamide epoxy additives (Sumitomo Chemical Co., Ltd., Sumires Resin 650, Sumires Resin 675) and polyamide epichlorohydrin (WS-525, manufactured by Japan PMC).

  As the particulate substance 5, a substance having a particle diameter of 0.1 to 1.0 μm, more preferably 0.2 to 0.5 μm is used. When the particulate matter 5 supplies the adhesive composition between the polarizing film 2 and the protective film 3 to form the adhesive layer 4 and pastes them together, the interval between the polarizing film 2 and the protective film 3 is increased. Serves as a spacer to keep a certain distance. That is, since the layer thickness of the adhesive layer 4 is determined based on the particulate material 5 having the maximum particle size contained in the adhesive composition, it is desirable that the particulate material 5 has a certain particle size distribution. . When the particle diameter of the particulate material 5 is less than 0.1 μm, the improvement in adhesive strength is insufficient. If the particle diameter exceeds 1.0 μm, the transmitted light tends to scatter due to the particles and the transmittance tends to decrease. Therefore, the particle diameter should be about the wavelength of visible light (0.5 μm) or less. Is preferred. The shape of the particles is not particularly limited and may be amorphous, but is preferably spherical.

  The material of the particulate substance 5 is not particularly limited, and may be an inorganic substance or an organic substance. Examples of the inorganic substance include silicon compounds such as silicon oxide, aluminum compounds such as aluminum oxide and aluminum hydroxide, and examples of the organic substance include resin latex such as acrylic resin.

  The blending ratio of the particulate material 5 constituting the adhesive composition, the water-soluble epoxy compound, and the PVA-based adhesive is 0.2 to 45/5 to 50/100 in terms of solid content, preferably 1-10 / 5-20 / 100. If the amount of the particulate matter 5 is less than this range, the adhesive layer 4 having a uniform thickness cannot be obtained, and if it exceeds this range, the light transmittance decreases. On the other hand, if the amount of the water-soluble epoxy compound is less than this range, the adhesive force is not sufficiently improved.

  In addition, zinc chloride, tin chloride, boro-fukka zinc, tertiary amine, quaternary ammonium salt, imidazole compound, and the like may be added to the adhesive composition containing a water-soluble epoxy compound in order to accelerate curing.

  When the adhesive layer 4 is formed using glyoxal as a crosslinking agent, examples of the PVA-based adhesive used include fully saponified PVA having a polymerization degree of 1500 to 3500, partially saponified PVA, polyvinyl butyral, partially acetalized PVA, Partially formalized PVA, poly (ethylene-vinyl acetate) copolymer saponified product and the like can be mentioned. These may contain other copolymer components and may have a functional group such as a carboxyl group or an ester thereof, an amino group, a silyl group, or a methylol group.

  The PVA-based adhesive is, for example, dissolved in water at the same ratio as in the case of the epoxy compound. Glyoxal is added to the obtained aqueous solution to dissolve, and the particulate matter 5 is further added and dispersed. A composition is prepared. The mixing ratio of the particulate matter 5, glyoxal, and the PVA adhesive is 0.2 to 50/5 to 50/100, preferably 1 to 10/10 to 50/100, by weight. If the amount of the particulate matter 5 is less than this range, the adhesive layer 4 having a uniform thickness cannot be obtained, and if it exceeds this range, the light transmittance decreases. On the other hand, if the amount of glyoxal is less than this range, the adhesive strength is not sufficiently improved, and if it exceeds this range, the adhesive layer becomes brittle.

  Zinc chloride, cobalt chloride, magnesium chloride, boron trifluoride-etherate, ammonium chloride, alkyl iodide, barium oxide, and the like may be added to the adhesive composition containing glioxal to accelerate curing .

  As a method of bonding the polarizing film 2 and the protective film 3, for example, the adhesive composition described above is applied to one surface of the polarizing film 2 or the protective film 3, and the protective film 3 or the polarizing film 2 is applied to the coated surface. The method of laminating, bonding with a roll, etc., and drying is mentioned. Examples of a method for uniformly applying the adhesive composition include a gravure coating method, a dip coating method, a spray coating method, and a casting method.

  In addition, when the protective film 3 is laminated on both surfaces of the polarizing film 2 as in the polarizing plate 1 according to the embodiment of the present invention, the protective film 3 is supplied to both surfaces of the polarizing film 2 using a pair of rolls. At the same time, the adhesive composition may be supplied between the supplied polarizing film 2 and the protective film 3. The adhesive composition is cast and applied between the polarizing film 2 and the protective film 3 by the pressure between the rolls.

  The bonding temperature is usually in the range of 15-30. The drying temperature is usually in the range of 30 to 85, preferably in the range of 40 to 80.

  In addition, in the polarizing plate by the other actual form of this invention, a protective film is laminated | stacked on the single side | surface of a polarizing film through an contact bonding layer.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
A 75 μm-thick PVA film (average polymerization degree 1700, saponification degree 99.9% or more) was uniaxially stretched at a draw ratio of 5 times, and an aqueous solution containing iodine and potassium iodide (iodine / iodine) while maintaining a tension state. Potassium chloride / water = 0.05 / 5/100 (weight ratio)) for 60 seconds. Subsequently, it was immersed in an aqueous solution of 65C containing potassium iodide and boric acid (potassium iodide / boric acid / water = 2.5 / 7.5 / 100 (weight ratio)) for 300 seconds. After washing with 25 C pure water for 20 seconds, it was dried at 50 C to obtain a PVA polarizing film.

  Polyamide epichlorohydrin (WS-525, manufactured by Japan PMC) as a water-soluble epoxy compound in a 5% by weight aqueous solution of a PVA adhesive (KL-318, saponification degree 87.8%, molecular weight 85000, manufactured by Kuraray Co., Ltd.) 25% by weight aqueous solution, and silicon oxide (spherical particles, particle diameter 0.2 μm) as a particulate material, and the particulate material / water-soluble epoxy compound / PVA adhesive = 1.7 / 10 / It added so that it might become a ratio of 100, and prepared the adhesive composition.

  The obtained adhesive composition was applied to one surface of a TAC film having a thickness of 50 μm (Fujitac SH-50, manufactured by Fuji Photo Film Co., Ltd.) under a 28C atmosphere by a casting method. Two TAC films were prepared, and the polarizing film obtained earlier was sandwiched between them and laminated to obtain a polarizing plate.

  When the peel strength between the polarizing film and the protective film of the obtained polarizing plate was measured according to JIS-C2107 (180 ′ peel strength), it was 1430 g / 25 mm width. The polarizing plate was allowed to stand for 240 hours under a wet heat of 60 ° C. and 90% RH, and then the end face was observed. As a result, no end face peeling between the TAC film and the polarizing film was observed.

[Example 2]
PVA (average polymerization degree: about 1700, saponification degree: 99.6% or more) is used as the PVA adhesive, and the component ratio of the adhesive composition is particulate matter / glyoxal / PVA adhesive = 1 by weight. It was carried out in the same manner as in Example 1 except that the ratio was 7/15/100.

  The peel strength of the obtained polarizing plate was 1310 g / 25 mm width. As a result of leaving it under wet heat, no peeling was observed on the end face.

[Comparative Example 1]
It carried out like Example 1 except not having used a water-soluble epoxy compound.

  The peel strength of the obtained polarizing plate was 1150 g / 25 mm width. As a result of leaving it under wet heat, some peeling was observed on the end face.

[Comparative Example 2]
The same procedure as in Example 1 was performed except that the particulate material and the water-soluble epoxy compound were not used.

  The peel strength of the obtained polarizing plate was 240 g / 25 mm width. As a result of leaving it under wet heat, peeling was observed on the end face.

It is the cross-sectional schematic diagram which showed the laminated constitution of the polarizing plate 1 by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Polarizing film 3 Protective film 4 Adhesive layer 5 Particulate matter

Claims (4)

  A polarizing film and a protective film are laminated via an adhesive layer containing a particulate material having a particle size of 0.1 to 1.0 μm, a water-soluble epoxy compound or glyoxal, and a polyvinyl alcohol-based adhesive. A polarizing plate characterized by having   From the adhesive composition in which the said adhesive layer contains a particulate matter, a water-soluble epoxy compound, and a polyvinyl alcohol-type adhesive agent in the ratio of 0.2-45 / 5-50 / 100 by solid content weight ratio. The polarizing plate according to claim 1, wherein the polarizing plate is formed.   The polarizing plate according to claim 2, wherein the polyvinyl alcohol-based adhesive is a carboxyl group-modified polyvinyl alcohol, and the water-soluble epoxy compound is a reaction product of polyamide and epichlorohydrin.   The adhesive layer is formed from an adhesive composition containing particulate matter, glyoxal, and polyvinyl alcohol-based adhesive in a weight ratio of 0.2 to 50/1 to 65/100. The polarizing plate according to claim 1.

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