JP5915291B2 - UV curable composition, adhesive and polarizing plate - Google Patents

Description

  The present invention relates to an ultraviolet curable composition that can be used in various applications including the production of polarizing plates for use in liquid crystal displays, for example.

  A polarizing plate used for a liquid crystal display or the like is generally formed by laminating a polarizer made of a polyvinyl alcohol (PVA) film impregnated with a dichroic material such as iodine and a transparent protective film via an adhesive. Are widely used.

  Conventionally, a triacetyl cellulose (TAC) film and a cycloolefin polymer (COP) film have been widely used as the transparent protective film. Along with this, many studies have been made on adhesives for the purpose of improving adhesion to the protective film (see, for example, Patent Document 1).

  On the other hand, in recent years, an inexpensive acrylic resin film has attracted attention as a protective film constituting a polarizing plate in place of a TAC film from the viewpoint of cost reduction or the like (see, for example, Patent Documents 2 to 4).

  Therefore, development of an adhesive having improved adhesiveness to the acrylic resin film has begun to be studied.

  Examples of the adhesive include a monofunctional monomer (A) containing an N-substituted amide monofunctional monomer (a) having a hydroxyl group and a branched polyester type having at least six (meth) acrylate groups. An adhesive for polarizing plates containing a polyfunctional monomer (b) is disclosed (for example, see Patent Document 5).

  However, even with the adhesive, the adhesiveness to the acrylic resin film has not yet reached a usable level.

JP 2010-32766 A JP 2008-134384 A JP 2008-134385 A JP 2010-209126 A JP 2010-78699 A

  The problem to be solved by the present invention is to provide an ultraviolet curable composition having excellent adhesive strength not only for various protective films, but particularly for acrylic resin films.

  The inventors of the present invention have made extensive studies on various (meth) acrylic monomers and combinations thereof while studying to solve the above problems. As a result, it has been found that the above problem can be solved by using a (meth) acrylamide compound having no hydroxyl group, a (meth) acrylic acid alkyl ester having a hydroxyl group, and boric acid, and the present invention has been completed.

  That is, this invention contains the (meth) acrylamide compound (A) which does not have a hydroxyl group, the (meth) acrylic-acid alkylester compound (B) which has a hydroxyl group, boric acid (C), and a photoinitiator (D). The present invention provides an ultraviolet curable composition, an adhesive obtained using the same, and a polarizing plate.

  The ultraviolet curable adhesive of the present invention has excellent adhesive strength not only for various protective films but also for acrylic resin films.

  Further, since the ultraviolet curable adhesive of the present invention has low viscosity and good curability, for example, even when the adhesive of the present invention is applied to a protective film or a polarizer, the adhesive is bonded. Unevenness does not occur in the agent layer, and the optical properties of the polarizing plate are not adversely affected.

  The (meth) acrylamide compound (A) has no hydroxyl group. For example, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, ( For example, (meth) acryloylmorpholine can be used. Among these, it is preferable to use at least one selected from the group consisting of N, N-dimethylacrylamide and N, N-diethylacrylamide from the viewpoint of improving the adhesive strength to the acrylic resin film. In addition, when the thing which has a hydroxyl group as said acrylamide compound (A) is used, desired adhesive strength to an acrylic resin film is not obtained.

  The (meth) acrylic acid alkyl ester compound (B) has a hydroxyl group, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, glycerin monoacrylate and the like can be used. Among these, it is preferable to use one or more selected from the group consisting of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate and glycerin monoacrylate from the viewpoint of easy availability of raw materials and adhesion to acrylic resin films. .

  The mass ratio [(A) / (B)] of the compound (A) and the compound (B) is in the range of 50/50 to 90/10, from the viewpoint of the adhesive strength to the acrylic resin film. To preferred.

  The boric acid (C) is indispensable particularly for imparting adhesive strength to an acrylic resin film. In addition, the boric acid (C) can give adhesion to the polarizer because pseudo-crosslinking occurs between the hydroxyl group in the polarizer described later and the compounds (A) and (B). It is guessed.

  The amount of the boric acid (C) used is in the range of 0.5 to 5 parts by mass with respect to 100 parts by mass in total of the compound (A) and the compound (B). In view of the above, the range of 1 to 5 parts by mass is more preferable.

  Examples of the photopolymerization initiator (D) include 4-phenoxydichloroacetophenone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and 1- (4-isopropylphenyl) -2- Hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 4- (2-hydroxyethoxy) -phenyl (2-hydroxy-2-propyl) ketone, 2-methyl- [4- (methylthio) phenyl An acetophenone compound such as 2-morpholino-1-propanone and 2,2-dimethoxy-2-phenylacetophenone; a benzoin compound such as benzoin, benzoin methyl ether, benzoin isoethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; Benzophenone compounds such as phenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyldiphenyl sulfide, 3,3′-dimethyl-4-methoxybenzophenone; thioxanthone, 2- Thioxanthone compounds such as chlorothioxanthone, 2,4-dichlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone; 4,4′-dimethylamino Thioxanthone (aka Minerals ketone), 4,4'-diethylaminobenzophenone, α-acyloxime ester, benzyl, methylbenzoylformate (“Bia Cure 55 "), anthraquinone compounds such as 2-ethylanthraquinone; 2,4,6-trimethylbenzoyldiphenylphosphine oxide (" Lucirin TPO "), bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide ( Acylphosphine oxide compounds such as “IRGACURE819”); 3,3 ′, 4,4′-tetra (tert-butylperoxycarbonyl) benzophenone [“BTTB” manufactured by NOF Corporation], acrylated benzophenone, etc. Can be used. These initiators may be used alone or in combination of two or more. Among these, 2-hydroxy-2-methyl-1-phenylpropan-1-one and 1-hydroxycyclohexyl phenyl ketone are preferable from the viewpoint of curability.

  The amount of the photopolymerization initiator (D) used is preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass in total of the compound (A) and the compound (B) from the viewpoint of curability and the like. A range of 0.5 to 5 parts by mass is more preferable.

  The ultraviolet curable composition of the present invention comprises the (meth) acrylamide compound (A), the (meth) acrylic acid alkyl ester compound (B), the boric acid (C), and the photopolymerization initiator (D). Although it contains, you may contain other additives as needed.

  Examples of the other additives include photosensitizers, photosensitizers, thixotropic agents, leveling agents, antioxidants, tackifiers, waxes, heat stabilizers, light stabilizers, and fluorescent brighteners. , Thermoplastic resins, thermosetting resins, organic solvents, conductivity-imparting agents, antistatic agents, hollow foams, antifoaming agents, antiblocking agents, hydrolysis inhibitors, and the like can be used.

  Moreover, the ultraviolet curable composition of this invention comprises low viscosity, and the viscosity in normal temperature is the range of 100 mPa * s or less. In addition, the viscosity of the said ultraviolet curable composition shows the value measured with the B-type viscosity meter at 25 degreeC.

  The ultraviolet curable composition of the present invention can be cured by irradiation with energy rays such as ultraviolet rays. In addition, the ultraviolet curable composition of this invention expresses adhesiveness only by irradiation of energy rays such as ultraviolet rays, and becomes an adhesive.

The irradiation of energy rays such as ultraviolet rays is preferably in the range of 0.02 to 2.5 J / cm ² , more preferably in the range of 0.03 to 1.5 J / cm ² .

  For example, a known lamp such as a xenon lamp, a xenon-mercury lamp, a metal halide lamp, a high-pressure mercury lamp, or a low-pressure mercury lamp can be used as the ultraviolet ray generation source. In addition, the ultraviolet irradiation amount is based on a value measured in a wavelength region of 320 to 390 nm using a UV checker; UV Power PucK (II) (manufactured by Electronic Instrumentation and Technology).

  By the above method, a cured product of the ultraviolet curable composition of the present invention is obtained. The glass transition temperature (Tg) of the cured product is 30 to 200 ° C. from the viewpoint of adhesion to an acrylic resin film. A range is preferable and the range of 35-130 degreeC is more preferable. In addition, Tg (degreeC) of the said hardened | cured material points out the value calculated from following General formula (1).

Tg (° C.) = 1 / Σ (mi / Tgi) -273 (1)
mi: Mass ratio of monomer i component Tgi; Glass transition temperature (K) of homopolymer of monomer i component

  Next, the polarizing plate of the present invention will be described.

  The polarizing plate of the present invention is obtained by adhering a polarizer and a protective film via an adhesive layer made of the ultraviolet curable composition.

  The polarizer is made of, for example, a plastic substrate made of a hydrophilic polymer such as polyvinyl alcohol, partially formalized polyvinyl alcohol, partially saponified ethylene / vinyl acetate copolymer, and two kinds of iodine and dichroic dyes. A film obtained by adsorbing a chromic material, uniaxially stretched, a film obtained by uniaxially stretching the plastic substrate, a film obtained by adsorbing the dichroic material, a polyvinyl alcohol dehydrated product or polyvinyl chloride A polyene-based oriented film such as a dehydrochlorinated product can be used. Among these, it is preferable to use a film in which a polyvinyl alcohol film and a dichroic substance such as iodine are adsorbed.

  Examples of the protective film include acrylic resin, silicon resin, epoxy resin, fluorine resin, polystyrene resin, polyester resin, polysulfone resin, polyarylate resin, polyvinyl chloride resin, polyvinylidene chloride, norbornene, and the like. Cycloolefin resin, amorphous polyolefin resin, polyimide resin, alicyclic polyimide resin, cellulose resin, PC (polycarbonate), PBT (polybutylene terephthalate), modified PPE (polyphenylene ether), PEN ( Polyethylene naphthalate), a film using PET (polyethylene terephthalate) or the like, or a biodegradable film such as a polylactic acid polymer can be used.

  As the acrylic resin, an acrylic resin or a thermoplastic acrylic resin having a glass transition temperature (Tg) of 100 ° C. or higher can be used, and elastic particles having a number average particle diameter of 2.0 μm or less are contained in the acrylic resin. It is good also as a protective film in which the elastic body particle is unevenly distributed in the thickness direction center part of the protective film.

  The thickness of the protective film used when producing the polarizing plate of the present invention varies depending on the application used, but is preferably in the range of about 20 μm to 100 μm. Moreover, it is preferable that the thickness of the polarizer is generally in the range of about 5 μm to 50 μm.

Moreover, as a manufacturing method of the polarizing plate of this invention, the said ultraviolet curable composition is apply | coated to the said protective film, for example, Then, a polarizer is mounted in this application | coating surface, Then, the said protective film side from the said side A method of manufacturing by irradiating with the amount of ultraviolet rays, or applying the ultraviolet curable composition on the polarizer, and then placing a protective film on the coated surface, and then, as described above from the protective film side. A method of manufacturing by irradiating an amount of ultraviolet rays can be used. When the polarizing plate of the present invention is produced, the thickness of the adhesive layer made of the ultraviolet curable composition is preferably as thin as possible for reasons such as impaired optical properties, and specifically 5 μm or less. Is preferred.
Moreover, the polarizing plate of the present invention is, for example, coated with the ultraviolet curable composition on one surface of two protective films, and placed on both surfaces of the polarizer on the coated surface, and then described above. It is also possible to produce a laminate by irradiating an amount of ultraviolet rays.

  As a method of applying the ultraviolet curable composition, for example, a slit coater method such as a curtain flow coater method or a die coater method, a knife coater method, a roll coater method, a gravure coater method, a method of applying by spraying or the like is used. Can do.

  The polarizing plate of the present invention obtained by the above method can be used as a member constituting a display such as a mobile communication terminal such as a mobile phone, a liquid crystal television, a personal computer, and a portable game machine.

  Hereinafter, the present invention will be described in detail with reference to examples.

[Example 1]
90 parts by mass of N, N-dimethylacrylamide, 10 parts by mass of 2-hydroxyethyl acrylate, 3 parts by mass of boric acid, and 1 part by mass of 2-hydroxy-2-methyl-1-phenylpropan-1-one An ultraviolet curable composition was obtained.

[Examples 2 to 4, Comparative Examples 1 to 4]
An ultraviolet curable composition was obtained in the same manner as in Example 1 except that the amounts of N, N-dimethylacrylamide, 2-hydroxyethyl acrylate and boric acid used were changed as shown in Tables 1-2.

[Comparative Example 5]
100 parts by mass of hydroxyethyl acrylamide and 1 part by mass of 2-hydroxy-2-methyl-1-phenylpropan-1-one as a photopolymerization initiator were mixed to obtain an ultraviolet curable composition.

[Production method of polarizer]
Kuraraypoval PVA-117H (polyvinyl alcohol manufactured by Kuraray Co., Ltd., degree of polymerization 1700, completely saponified product, powder) dissolved in water with a polyvinyl alcohol aqueous solution (non-volatile content 8% by mass), a bar coater The film was applied onto a release film and then dried for 5 minutes in an environment of 80 ° C., and then the release film was removed to prepare a polyvinyl alcohol film having a thickness of 75 μm.
Next, the obtained polyvinyl alcohol film was fixed to a stretching machine, and the film was stretched in hot water at 40 ° C. until it became three times larger in a uniaxial direction.
After removing water adhering to the surface of the stretched film obtained above, the stretched film was adjusted to 30 ° C. containing 0.02 parts by mass of iodine, 2 parts by mass of potassium iodide and 100 parts by mass of water. It was immersed in the aqueous solution.
Next, the stretched film was immersed in an aqueous solution adjusted to 56.5 ° C. containing 12 parts by mass of potassium iodide, 5 parts by mass of boric acid, and 100 parts by mass of water.
After the immersed stretched film is washed in pure water adjusted to 8 ° C. and dried in an environment of 65 ° C., a polarizer in which iodine is adsorbed and oriented on the surface of the stretched film made of polyvinyl alcohol (polarized light) Film).

[Preparation of polarizing plate]
Using an applicator on one surface of the corona-treated acrylic resin film, each of the ultraviolet curable compositions obtained in Examples and Comparative Examples was applied to a thickness of 2 μm, and then the polarizer was applied to the coating layer. And bonded to each other using a rubber roller. Then, using a conveyor type ultraviolet irradiation device (Fusion LH-6), ultraviolet light is irradiated from the acrylic resin film side so that ultraviolet light in a wavelength region of 320 to 390 nm has an integrated light amount of 0.8 J / cm ^2, and polarized. A plate was made.

[Evaluation method of curability]
Using the applicator on the polarizer, the UV curable compositions obtained in Examples and Comparative Examples were respectively applied so as to have a thickness of 2 μm, and then the release treatment surface of the release film of the transparent film Were bonded to the coated surface, and they were pressure-bonded using a rubber roller. Then, the above-mentioned amount of ultraviolet rays was irradiated from the side of the release-treated transparent film, and then the release-treated transparent film was peeled off, and the peeled surface was touched and judged as follows.
“○”: Completely cured “×”: Tackiness

[Evaluation method of adhesive strength]
The adhesive strength was evaluated by 90 degree peel strength.
Samples obtained by cutting the polarizing plates obtained in Examples and Comparative Examples into a width of 80 mm and a width of 25 mm were used as test pieces. The acrylic resin film side of the test piece is attached to an aluminum plate as an adherend, and adhesive No. Affixed with 5601 (manufactured by Nitto Denko Corporation), 90 degree peel strength was measured in accordance with JIS Z-0237 at a speed of 10 mm / min, an atmosphere of 23 ° C. and 50% RH.
In addition, it judged as follows with the value of 90 degree peel strength.
“◯”: 3.0 N / 25 mm or more “×”: less than 3.0 N / 25 mm

It turned out that Examples 1-4 which are the ultraviolet curable compositions of this invention are excellent in the adhesive strength and sclerosis | hardenability to an acrylic resin film.
On the other hand, although Comparative Examples 1-4 was an aspect which does not contain boric acid (C), it turned out that the adhesive strength to an acrylic resin film is inadequate.
Moreover, although the comparative example 5 is the aspect which used the hydroxyethyl acrylamide, it turned out that the adhesive strength to an acrylic resin film is inadequate.

Claims (5)

A polarizing plate in which a protective film and a polarizer are bonded via an adhesive, wherein the adhesive has a hydroxyl group-free (meth) acrylamide compound (A), a hydroxyl group-containing (meth) acrylic acid alkyl ester compound ( A polarizing plate obtained by using an ultraviolet curable composition containing B), boric acid (C) and a photopolymerization initiator (D). The polarizing plate according to claim 1, wherein a mass ratio [(A) / (B)] of the compound (A) and the compound (B) is in a range of 50/50 to 90/10. The polarizing plate according to claim 1 or 2, wherein the amount of the boric acid (C) used is in the range of 0.5 to 5 parts by mass with respect to 100 parts by mass in total of the compound (A) and the compound (B). . The polarizing plate according to claim 1, wherein the compound (A) is at least one selected from the group consisting of N, N-dimethylacrylamide and N, N-diethylacrylamide. The polarizing plate according to claim 1, wherein the compound (B) is at least one selected from the group consisting of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and glycerin monoacrylate.