JP2011074308A - Transparent adhesive sheet and image display device including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent adhesive sheet that is prevented from causing display unevenness, bubbles, and peeling. <P>SOLUTION: The transparent adhesive sheet 3, 3' is used for sticking a surface protective layer 4 or a touch panel 7 in an image display device 30 to the display surface of an image display unit 1 or is used for sticking the surface protective layer 4 to the touch panel 7. The transparent adhesive sheet comprises a copolymer containing (A) an alkyl (meth)acrylate having a 4-18C alkyl group, (B) an amide group-containing monomer and (C) a (meth)acrylic ester having an ether group. Furthermore, the copolymer contains (D-1) an amino group-containing monomer (wherein, the amino group-containing monomer is copolymerizable with monomer components (A), (B) and (C), thus constructing a copolymer together with components (A), (B) and (C)) and (D-2) an amino group-containing alkoxysilane compound. The acid value of the copolymer is 5 mgKOH/g or lower. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transparent adhesive sheet and an image display device including the same.

  In recent years, the surface protective layer or the touch panel in the image display device or the gap between the touch panel and the display surface of the image display unit, or the gap between the surface protective layer and the touch panel has a refractive index compared with air. In addition, a method has been proposed in which the transparency is improved by replacing with a transparent material close to the display surface of the image display unit, and the decrease in luminance and contrast of the image display device is suppressed. Examples of the transparent substance include transparent polymer materials such as a transparent resin sheet, a pressure-sensitive adhesive (pressure-sensitive adhesive), and a curable adhesive (for example, silicone gel).

  In Patent Document 1, 51 to 100% by weight of (meth) acrylic acid alkylene oxide adduct, 0 to 49% by weight of other (meth) acrylic monomers, and 0 to 49% by weight of other polymerizable monomers are used as a single amount. A pressure-sensitive adhesive composition containing a (meth) acrylic (co) polymer as a body component and a crosslinking agent, and a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition are formed on a support film. The surface protection film is described.

  Patent Document 2 discloses that (meth) acrylic acid alkylene oxide adduct is 5 to 100% by weight, (meth) acrylic monomer having an alkyl group having 1 to 14 carbon atoms other than those described above, and other polymerizations. A pressure-sensitive adhesive composition comprising a (meth) acrylic polymer having 0 to 95% by weight of a monomer as a monomer component, and an alkali metal salt, wherein the acid value of the (meth) acrylic polymer is The pressure-sensitive adhesive composition is characterized in that the pressure-sensitive adhesive composition is 10 or less, and a pressure-sensitive adhesive sheet formed by forming a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition on one side or both sides of the support. is doing.

  Patent Document 3 is a pressure-sensitive adhesive composition for electronic display comprising a copolymer and / or a mixture of a (meth) acrylic acid alkyl ester monomer and a carboxyl group-containing monomer, and further a monomer having an alkyleneoxy group And a pressure-sensitive adhesive composition for an electronic display comprising a hydroxyl group-containing (meth) acrylic acid ester monomer, and a pressure-sensitive adhesive layer for an electronic display comprising the composition. .

  Patent Document 4 describes (meth) acrylic acid alkylene oxide adducts 0.01 to 50% by weight, (meth) acrylamide monomers 0.01 to 30% by weight, and (meth) acrylic acid esters other than those described above and other as required. An acrylic copolymer obtained by polymerizing 20 to 99.8% by weight of the polymerizable monomer, and at least 50% by weight of the (meth) acrylamide monomer is polymerized after at least 70% by weight of the total of other monomers is polymerized. The re-peelable pressure-sensitive adhesive composition added is described.

  Patent Document 5 comprises an acrylic polymer and an alkoxysilane compound having a hydrocarbon group and an alkoxy group as a functional group. The alkoxysilane compound is added in an amount of 0.01 to 4 with respect to 100 parts by weight of the acrylic polymer. It describes about the pressure sensitive adhesive composition for liquid crystal elements characterized by containing by the quantity of a weight part.

Japanese Patent Laid-Open No. 2005-200540 JP 2006-111446 A JP 2008-1739 A JP 05-9449 A JP 07-331204 A

  Compared with liquid curable adhesives, the manufacturing process is simple, and optical properties such as transparency and adhesive properties are superior compared to silicone gels. Has been. However, when a conventional acrylic pressure-sensitive adhesive sheet is applied to a small and thin image display device in recent years, a phenomenon in which a color is different, bright or dark in a part of the screen in the image display device, that is, display unevenness. Sometimes occurred. Particularly, when the surface protective layer in the image display device has an uneven shape, and an adhesive sheet is applied to the uneven surface, or an image display unit provided with a layer having an uneven shape (for example, a polarizing plate). When an adhesive sheet is applied to the display surface, it is desired to solve this display unevenness. Further, in addition to the occurrence of display unevenness, the surface protective layer in the image display device, the display surface of the image display unit, or the touch panel (hereinafter sometimes referred to as “adhered body”) even when placed in a high temperature and high humidity state. There is a need for a transparent adhesive sheet that does not cause bubbles or peeling at the interface with the.

  Furthermore, in recent years, in portable electronic devices, improvement in impact resistance has been demanded more than ever before. Therefore, a sheet including a polycarbonate layer may be used for the surface protective layer or the like in the image display device. Even when the sheet including the polycarbonate layer and the adhesive sheet are bonded (combined), the above-described display unevenness, air bubbles, There is an increasing demand for transparent adhesive sheets that do not peel off.

According to an aspect of the present invention, there is provided a transparent adhesive sheet for affixing a surface protective layer or a touch panel and a display surface of an image display unit in an image display device, or a surface protective layer and a touch panel.
The transparent adhesive sheet contains a copolymer of monomer components containing the following (A), (B) and (C),
(A) (meth) acrylic acid alkyl ester whose alkyl group has 4 to 18 carbon atoms;
(B) an amide group-containing monomer;
(C) (meth) acrylic acid ester represented by the following formula (1);
_{CH 2 = C (R) COO-} (AO) p- (BO) q-R '··· (1)
(Here, in formula (1),
A is at least one group selected from the group consisting of (CH ₂ ) rCO, CH ₂ CH ₂ , CH ₂ CH (CH ₃ ), CH ₂ CH ₂ CH ₂ CH ₂ ,
B is _{(CH 2) rCO, CO (} CH 2) r, CH 2 CH 2, CH 2 CH (CH 3), at least one group selected from the group consisting of _{CH 2 CH 2 CH 2 CH 2} ,
R is hydrogen or CH ₃ ;
R ′ is hydrogen, or an optionally substituted alkyl group or aryl group,
p, q and r are each an integer of 1 or more)
The copolymer is further
(D-1) 0.1 to 5 parts by mass of an amino group-containing monomer (wherein the amino group-containing monomer is a monomer component with respect to 100 parts by mass of the total amount of monomer components (A), (B) and (C)) (A), (B) and (C) can be copolymerized to form a copolymer with the monomer components (A), (B) and (C)), or (D-2) the monomer component Including 0.01 to 1 part by mass of an amino group-containing alkoxysilane compound with respect to 100 parts by mass of the total amount of (A), (B) and (C),
The said transparent adhesive sheet whose acid value of a copolymer is 5 mgKOH / g or less is provided.

  According to still another aspect of the present invention, an image display device including an image display unit, the transparent adhesive sheet, and a surface protective layer is provided.

  In addition, “(meth) acryl” used in the present specification means “acryl” or “methacryl”.

  The transparent pressure-sensitive adhesive sheet provided as one embodiment of the present invention displays a surface protective layer or touch panel in an image display device when attached to a display surface of an image display unit or a surface protective layer and a touch panel. Unevenness does not occur. In particular, when a transparent adhesive sheet is applied to the surface protective layer having an uneven shape, or the transparent adhesive sheet is applied to an image display unit display surface provided with a layer having an uneven shape (for example, a polarizing plate). Even in this case, display unevenness can be prevented.

  In addition, when the transparent adhesive sheet is attached to the surface protective layer in the image display device, the display surface of the image display unit or the touch panel, bubbles do not occur at the interface even in a high temperature and high humidity environment (no foaming occurs). ). Furthermore, it is possible to suppress peeling after the surface protective layer or the touch panel and the display surface of the image display unit in the image display device are attached and after the surface protective layer and the touch panel are attached.

  Furthermore, the transparent pressure-sensitive adhesive sheet is a polycarbonate layer for the surface protective layer or the like in the image display device (here, “polycarbonate” may be a polycarbonate homopolymer or copolymer, or other polymer. The above effect can be achieved even in the case of using a sheet containing a blend, which may be a blend. Here, when a sheet containing a polycarbonate layer is used as the surface protective layer, foaming is more likely to occur than in a sheet of an acrylic resin layer such as a glass plate or polymethylmethacrylate (PMMA), and peeling under high temperature and high humidity. It is difficult to achieve both prevention of display unevenness. Therefore, such a transparent adhesive sheet is particularly suitable for use in an image display device of a portable electronic device in which a sheet containing a polycarbonate layer is used.

Sectional drawing of 1 aspect of the image display apparatus containing the transparent adhesive sheet of this invention is shown. Sectional drawing of another aspect of the image display apparatus containing the transparent adhesive sheet of this invention is shown. Sectional drawing of another aspect of the image display apparatus containing the transparent adhesive sheet of this invention is shown. Sectional drawing of another aspect of the image display apparatus containing the transparent adhesive sheet of this invention is shown.

The transparent adhesive sheet provided as one embodiment of the present invention is used for attaching a surface protective layer or a touch panel in an image display device and a display surface of an image display unit, or attaching a surface protective layer and a touch panel. . Here, the transparent adhesive sheet is represented by (A) (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms, (B) an amide group-containing monomer, and (C) represented by the following formula (1). (meth) acrylic acid ester _{CH 2 = C (R) COO-} (AO) p- (BO) q-R '··· (1)
(Here, in formula (1),
A is at least one group selected from the group consisting of (CH ₂ ) rCO, CH ₂ CH ₂ , CH ₂ CH (CH ₃ ), CH ₂ CH ₂ CH ₂ CH ₂ ,
B is _{(CH 2) rCO, CO (} CH 2) r, CH 2 CH 2, CH 2 CH (CH 3), at least one group selected from the group consisting of _{CH 2 CH 2 CH 2 CH 2} ,
R is hydrogen or CH ₃ ;
R ′ is hydrogen, or an optionally substituted alkyl group or aryl group,
p, q and r are each an integer of 1 or more)
A copolymer of monomer components containing, the copolymer further comprising:
(D-1) Amino group-containing monomer (wherein the amino group-containing monomer is copolymerizable with the monomer components (A), (B) and (C), and the monomer components (A), (B) and ( C)) or (D-2) an amino group-containing alkoxysilane compound.

  Here, the (A) component (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group gives suitable tackiness to the obtained pressure-sensitive adhesive sheet and has good wettability to the adherend. can do.

  As (A) component alkyl group (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms, the component (A) alone provides sufficient tackiness (flexibility) to the resulting pressure-sensitive adhesive sheet. In view of the above, the glass transition temperature of the polymer composed of one or more monomers used as the component (A) is preferably 25 ° C. or lower. Specifically, monomers having a glass transition temperature of a homopolymer of 25 ° C. or lower, such as n-butyl acrylate, isobutyl acrylate, isoamyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) Acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, isomyristyl (meth) acrylate, isocetyl (meth) acrylate, 2-octyldecyl (meth) acrylate, Alkyl (meth) acrylates such as isostearyl (meth) acrylate, and mixtures thereof can be used.

  Here, the “glass transition temperature (Tg)” of a homopolymer is a glass state through a supercooled liquid when the heated and melted polymer is cooled under certain conditions. It means temperature. Specifically, in this specification, the glass transition temperature of a polymer composed of one or more monomers used as the component (A) is a value measured according to JIS K7121.

  Among these, the preferred component (A) is an alkyl acrylate from the viewpoint of excellent polymerizability in both thermal polymerization and photopolymerization methods, and specifically includes n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl. Examples include acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, isomyristyl acrylate, isocetyl acrylate, 2-octyl decyl acrylate, isostearyl acrylate, and the like. From the viewpoint of tackiness, 2-ethylhexyl acrylate, isooctyl acrylate, and 2-octyldecyl acrylate are particularly preferable.

  In addition to the above-described monomer, a (meth) acrylic acid alkyl ester monomer in which the homopolymer has a glass transition temperature of 25 ° C. or more and the alkyl group having 4 to 18 carbon atoms may be used in combination. Examples of the (meth) acrylic acid alkyl ester in which the homopolymer has a glass transition temperature of 25 ° C. or higher and the alkyl group having 4 to 18 carbon atoms include t-butyl (meth) acrylate, n-butyl methacrylate, isobutyl methacrylate and the like. And alicyclic alkyl (meth) acrylates such as linear or branched alkyl (meth) acrylate, cyclohexyl methacrylate, 4-t-butylcyclohexyl (meth) acrylate, and isobornyl (meth) acrylate. In addition, when using the (meth) acrylic-acid alkylester monomer whose carbon number of the alkyl group whose glass transition temperature of such a homopolymer is 25 degreeC or more is 4-18, multiple types used as (A) component It is preferable that the glass transition temperature of the polymer consisting of the monomer is 25 ° C. or lower.

  Next, the amide group-containing monomer as component (B) improves the cohesive strength of the resulting transparent pressure-sensitive adhesive sheet and imparts adhesiveness. Therefore, when the obtained transparent adhesive sheet is applied to an image display device, foaming and peeling particularly at high temperatures are prevented.

  Examples of amide group-containing monomers include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, Nt-butyl (meth) acrylamide, N, N-isopropyl (meth) acrylamide, and Nt-octyl. (Meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, substituted acrylamides such as diacetone acrylamide, vinyl monomers such as N-vinylpyrrolidone and N-vinylcaprolactam Can be mentioned. Among these, N, N-dimethylacrylamide, diacetone acrylamide and the like are particularly preferable.

  Subsequently, the component (C) will be described. (C) A component controls the moisture permeability of the transparent adhesive sheet obtained. That is, in addition to the above-described components (A) and (B), by using the component (C), the transparent adhesive sheet (copolymer) obtained has high flexibility and without impairing hydrophilicity. Adhesive strength can be obtained.

The (meth) acrylic acid ester that is the component (C) is represented by the following formula (1).
_{CH 2 = C (R) COO-} (AO) p- (BO) q-R '··· (1)
Here, A is at least one group selected from the group consisting of (CH ₂ ) rCO, CH ₂ CH ₂ , CH ₂ CH (CH ₃ ), and CH ₂ CH ₂ CH ₂ CH _2. From the viewpoint of moisture permeability control of the sheet and industrial availability, CH ₂ CH ₂ or CH ₂ CH (CH ₃ ) is preferable.
Further, B is _{(CH 2) rCO, CO (} CH 2) r, CH 2 CH 2, CH 2 CH (CH 3), at least one group selected from the group consisting of CH ₂ CH ₂ CH ₂ CH ₂ In the same manner as A, CH ₂ CH ₂ or CH ₂ CH (CH ₃ ) is preferable from the viewpoint of moisture permeability control of the resulting transparent pressure-sensitive adhesive sheet and industrial availability.
R is hydrogen or CH ₃ . In the case of copolymerization by photopolymerization, R is preferably H from the viewpoint of polymerizability.
R ′ is hydrogen or an optionally substituted alkyl group or aryl group, and the alkyl group or aryl group may be linear, branched or cyclic. In one embodiment, an alkyl group (specifically, a methyl group, an ethyl group, a butyl group, an octyl group) that is excellent in compatibility with the component (A) is used.
p, q, and r are each an integer of 1 or more. In addition, although there is no restriction | limiting in particular about an upper limit, Compatibility with (A) component can be improved by setting p as 10 or less, q as 10 or less, and r as 5 or less.

  From the viewpoint of foaming resistance at the time of wet heat of the transparent pressure-sensitive adhesive sheet to be obtained, the component (C) is the above formula (1), wherein R is hydrogen, R ′ is an alkyl group having 1 to 12 carbon atoms, and 2 A polyalkylene glycol alkyl ether acrylate satisfying ≦ p + q ≦ 10 is preferable.

  Specifically, polyethylene glycol acrylate (Blemmer AE series, manufactured by NOF Corporation), polyethylene glycol methacrylate (Blemmer PE series, manufactured by NOF Corporation), polyethylene glycol polypropylene glycol acrylate (Blemmer AEP series, manufactured by NOF Corporation), polypropylene glycol acrylate ( Polyalkylene glycol mono having a terminal hydroxyl group such as Blemmer AP series (manufactured by NOF), polypropylene glycol methacrylate (Blemmer PP series, manufactured by NOF), polypropylene glycol polytetramethylene glycol acrylate (Blemmer APT series, manufactured by NOF) (Meth) acrylate; methyl polyethylene glycol (meth) acrylate, methyldipropylene glycol Polyalkylene having an alkyl group at the terminal, such as coal (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, diethylene glycol 2-ethylhexyl ether (meth) acrylate, diethylene glycol decanol ether (meth) acrylate, diethylene glycol lauryl ether (meth) acrylate Glycol alkyl ether (meth) acrylate; Phenoxydiethylene glycol (meth) acrylate, Nonylphenoxypolyethylene glycol (meth) acrylate, etc. Polyalkylene glycol aryl ether (meth) acrylate having an aryl group at the terminal; β-carboxyethyl acrylate, ω-carboxy Polycaprolactone acrylate (M-5300, manufactured by Toagosei Co., Ltd.) caprolactone modification Tetrahydrofurfuryl acrylate (Kayarad TC110S, Nippon Kayaku), ethyl diethylene glycol oligoacrylate (Biscoat 190D, Osaka Organic Industries, CH2 = CHCOO- (CH2CH2O) 2-CH2CH3 and CH2 = CHCOO- (CH2CH2COO) n- (CH2CH2O) And polyester mono (meth) acrylates such as mixtures with 2-CH2CH3 (25:75 (weight ratio)), and modified products thereof, and these (meth) acrylic esters may be used in combination of two or more. Also good.

  As described above, the copolymer of the monomer components containing the components (A), (B) and (C) is further (D-1) an amino group-containing monomer or (D-2) an amino group-containing alkoxysilane. Contains compounds. The component (D-1) or (D-2) is used in combination with the components (A), (B), and (C) described above, and is attached when the obtained transparent adhesive sheet is attached to an adherend. The peeling of the transparent adhesive sheet with respect to a body can be prevented. In particular, even when the adherend is a sheet including a polycarbonate layer, the obtained transparent pressure-sensitive adhesive sheet can achieve good peeling prevention.

  First, the amino group-containing monomer which is the component (D-1) constitutes a copolymer together with the monomer components (A), (B) and (C). Such an amino group may be primary, secondary or tertiary, and in some embodiments, a tertiary amino group is preferably used. The amino group-containing monomer includes an amino group-containing monomer having a radical polymerizable group. Specifically, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) Examples include acrylamide, pentamethylpiperidyl (meth) acrylate, vinylimidazole, and vinylpyridine. In an embodiment, N, N-dimethylaminopropylmethacrylamide (manufactured by MRC Unitech Co., Ltd.) is preferably used. The amount of the component (D-1) is 0. 0 with respect to 100 parts by mass of the total amount of the monomer components (A), (B), and (C) from the viewpoint of preventing peeling of the adherend in the transparent adhesive sheet to be obtained. 1-5 parts by mass, preferably 0.3-3 parts by mass.

Next, the amino group-containing alkoxysilane compound as the component (D-2) does not react with the monomer components (A), (B), and (C) and is contained in the obtained copolymer. As the amino group-containing alkoxysilane compound, those represented by the following general formula (2) are preferable.
(R ¹ O) _n R ² _3-n Si—X—NR ³ R ⁴ (2)
Here, R ¹ represents an alkyl group, R ² represents hydrogen, an optionally substituted alkyl group or an aryl group, and R ³ and R ⁴ each independently represent hydrogen, an optionally substituted alkyl group. , An aralkyl group or an aryl group, or (R ⁵ O) _m R ⁶ _3-m Si—Y—, wherein R ³ and R ⁴ may form a ring. n is 2 or 3. X represents a divalent linking group. R ⁵ represents an alkyl group, and R ⁶ represents hydrogen, or an optionally substituted alkyl group or aryl group. m is 2 or 3, and Y represents a divalent linking group. Among these, R ¹ is preferably a methyl group or an ethyl group from the viewpoint of hydrolyzability and industrial availability, and R ² is preferably a methyl group. R ³ and R ⁴ are preferably hydrogen or an amino group-substituted alkyl group from the viewpoint of foam resistance. As the divalent linking group X, an alkylene group is preferably used.

  Specifically, N-2 (aminoethyl) -3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) -3-aminopropyltrimethoxysilane, N-2 (aminoethyl) -3-aminopropyltrimethoxysilane. Ethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-2 (benzylaminoethyl) -3- Examples include aminopropyltrimethoxysilane, N, N-bis (aminopropyltrimethoxysilane), and 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine. In an embodiment, N-2 (aminoethyl) -3-aminopropylmethyldimethoxysilane and N-2 (aminoethyl) -3-aminopropyltrimethoxysilane (both manufactured by Shin-Etsu Chemical Co., Ltd.) are preferably used. The amount of the component (D-2) is 100 parts by mass with respect to the total amount of the monomer components (A), (B), and (C) from the viewpoint of preventing peeling and outgassing of the adherend in the obtained transparent adhesive sheet. It is 0.01-1 mass part, and it is preferable that it is 0.05-0.5 mass part.

  The above copolymer has an acid value of 5 mgKOH / g or less. The acid value is an index of the content of an acidic component expressed by the amount (mg) of potassium hydroxide necessary to neutralize 1 g of a sample.

  When the acid value is larger than 5 mgKOH / g, it precipitates by forming a salt with the component (D-1) or (D-2) or accelerates the hydrolysis of the component (D-2). Therefore, the effect of the (D-1) or (D-2) component is inhibited. As a result, when the obtained transparent pressure-sensitive adhesive sheet is affixed to an adherend, peeling or foaming is likely to occur. In addition, even if the acid value of the copolymer is greater than 5, it does not affect the salt formation with the component (D-1) or (D-2) or the degree of hydrolysis in the component (D-2). In some cases. However, in this case as well, the effect of preventing peeling or foaming of the component (D-1) or (D-2) is inhibited.

  In general, when the acid value of the copolymer contained in the transparent adhesive sheet is high, when the transparent adhesive sheet is directly bonded to the surface of a transparent conductive film such as ITO of the touch panel, the ITO deteriorates and the resistance value is reduced. It is known to rise. Therefore, a protective film is generally provided on the surface of the transparent conductive film (ITO, etc.) of the touch panel in order to attach a transparent adhesive sheet, and the addition of such a protective layer causes an increase in the cost of the touch panel. It was. Furthermore, as described below, when the component (E) is added as a monomer component in the copolymer, whitening can be prevented when the obtained transparent adhesive sheet is used in an image display device. Therefore, the transparent conductive film (ITO etc.) of the touch panel in an image display apparatus is made by lowering the acid value in the copolymer contained in the transparent adhesive sheet obtained, and adding (E) component as a monomer component in a copolymer. ) It can be bonded directly to the surface.

  Therefore, in the present invention, a monomer containing an acid component such as acrylic acid cannot be used in such an amount that the acid value of the resulting copolymer is greater than 5. In addition, the acid value of the copolymer is preferably 2 mgKOH / g or less, more preferably 1 mgKOH / g or less, and 0 mgKOH / g (monomer component) from the viewpoint of foaming prevention properties of the transparent adhesive sheet to be obtained. It is particularly preferred that it is calculated from the charged amount of

  The acid value can be measured by an acid-base titration method using potassium hydroxide based on the method described in JIS K 2501. For example, a pH indicator is added to a solution containing a titration solvent capable of dissolving or swelling 1 g of the copolymer, and a diluted titration solvent of potassium hydroxide is added dropwise. When an indicator discoloration point or potentiometric titration apparatus is used, the end point is detected from the inflection point of the titration curve, and the acid value can be determined from the amount of the potassium hydroxide solution dropped. The acid value can also be calculated from the amount of monomer components charged during production. In either method, the acid value is almost the same.

  The copolymer may optionally contain (meth) acrylic acid hydroxyalkyl ester ((E) component) as a monomer component. Like the component (D-1), the component (E) can be copolymerized with the monomer components (A), (B), and (C), and can be copolymerized with the monomer components (A), (B), and (C). It constitutes a polymer. As described above, by including the component (E) in the copolymer, whitening under high temperature and high humidity in the image display device can be prevented.

  Here, the degree of whitening prevention (transparency) in the transparent adhesive sheet is affected by the combination of the materials to be bonded (substrate and transparent adhesive sheet). The ITO substrate is more likely to be whitened than the polarizing plate, and when the transparent adhesive sheet is directly bonded to the ITO substrate, the component (E) is preferably added for the purpose of suppressing whitening. The degree of whitening is determined by laminating a transparent adhesive sheet to a transparent adherend (for example, a surface protective layer of an image display device) to form a laminate, and the obtained laminate is at a temperature of 60 ° C. and a relative humidity (RH). It can be judged by visually observing the laminate after being left for 3 days in a 90% environment and left for 3 days.

  Examples of the component (E) include (meth) acrylic acid hydroxyalkyl esters having an alkyl group with 4 or less carbon atoms. Specifically, although not limited to the following, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2,3-dihydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4 -Hydroxybutyl methacrylate, 2,3-dihydroxypropyl methacrylate and the like.

The copolymer obtained from the monomer component described above has a tan δ at 140 ° C. and 1.0 Hz of 0.13 or more and a storage elastic modulus at 25 ° C. and 1.0 Hz of 8.9 × 10 ⁴ Pa or less. It is preferable. Such dynamic viscoelastic characteristics are important from the viewpoint of display unevenness (liquid crystal unevenness) and followability to uneven surfaces (step filling property) in the transparent adhesive sheet. Specifically, the occurrence of display unevenness in the transparent adhesive sheet is related to both the stress relaxation property and the initial residual stress of the copolymer.

  Here, “tan δ at 140 ° C. and 1.0 Hz” means the ratio of the storage elastic modulus G ′ (Pa) and the loss elastic modulus G ″ (Pa) at a temperature of 140 ° C. in a shear mode and a frequency of 1.0 Hz. This means the loss tangent represented by In addition, “storage elastic modulus at 25 ° C. and 1.0 Hz” means that viscoelasticity is measured in a temperature range of −60 ° C. to 200 ° C. at a rate of temperature increase of 5 ° C./min and a shear mode of 1.0 Hz. It means the storage elastic modulus at 25 ° C.

  Data of tan δ and storage elastic modulus (dynamic viscoelastic characteristics) can be measured using a viscoelasticity measuring device such as Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific. Since the dynamic viscoelasticity depends on the measurement temperature and the measurement frequency, as described above, the storage elastic modulus is the loss elastic modulus as the storage elastic modulus G ′ (Pa) at 25 ° C. in the shear mode and the frequency of 1.0 Hz. tan δ (G ″ / G ′) is an index based on values obtained from the storage elastic modulus G ′ (Pa) and loss elastic modulus G ″ (Pa) at 140 ° C. in a shear mode and a frequency of 1.0 Hz. .

  tan δ is an index of stress relaxation in the transparent adhesive sheet, and if the tan δ of the copolymer is 0.13 or more, the obtained transparent adhesive sheet is excellent in stress relaxation and does not cause display unevenness. . Preferred tan δ is 0.15 or more, more preferably 0.2 or more. On the other hand, the upper limit of tan δ is not particularly limited, but as the value of tan δ increases, the heat resistance (adhesiveness at high temperature) of the copolymer generally deteriorates and tends to foam easily when used as a transparent adhesive sheet. There is. Accordingly, the tan δ at 140 ° C. and 1.0 Hz of the copolymer can generally be 0.6 or less.

The storage elastic modulus is an index of the residual stress (initial residual stress) of the transparent adhesive sheet that is deformed at the time of lamination. If this value is 8.9 × 10 ⁴ Pa or less, display unevenness can be suppressed. For example, even when the transparent adhesive sheet is attached to an adherend having an uneven surface of about 10 μm, display unevenness can be suppressed. Furthermore, if the storage elastic modulus is 7.4 × 10 ⁴ Pa or less, display unevenness can be reduced even when a transparent adhesive sheet is bonded to an adherend having a large unevenness or a complicated uneven surface. It becomes.

  The tan δ and storage elastic modulus of the copolymer can be adjusted by appropriately changing the type, molecular weight, and composition of each monomer component. For example, when a large amount of the component (B) is used, the storage elastic modulus increases, and when the amount of the component (A) and the component (C) is increased, the storage elastic modulus can be decreased. Moreover, when the molecular weight in the copolymer of the monomer containing (A) component, (B) component, and (C) component is raised, there exists a tendency for a storage elastic modulus to become high. In addition, (C) component has a function which suppresses foaming of the transparent adhesive sheet obtained even when tan (delta) of a copolymer becomes high. Here, tan δ of the copolymer can be adjusted by the amount of the crosslinking agent described later. Specifically, when the amount of the crosslinking agent is increased, the value of tan δ is decreased, and when the amount of the crosslinking agent is decreased, the value of tan δ is increased.

  In general, in the above copolymer, the amount of the component (A), the component (B), and the component (C) is determined from the viewpoints of the adhesive strength of the obtained transparent pressure-sensitive adhesive sheet and the wettability to the adherend, respectively. Based on the total amount of monomers, it can be 50 to 94% by mass (in some embodiments 50 to 90% by mass), 1 to 10% by mass, and 5 to 40% by mass.

  When the component (E) is used as the monomer component, the amount of the component (E) is 5 to 20% by mass on the basis of the total amount of monomers. To preferred.

  When the copolymer of the monomer components has the above-mentioned preferable dynamic viscoelastic properties, the obtained transparent pressure-sensitive adhesive sheet (copolymer) can achieve sufficient flexibility and adhesion without impairing hydrophilicity. . By using such a transparent adhesive sheet having high flexibility, the surface of the image display unit provided with a surface protective layer having an uneven shape or a layer having an uneven shape (for example, a polarizing plate) is transparent. Even when the adhesive sheet is applied, irregularities can be absorbed, and as a result, display unevenness in the image display device can be prevented. Further, even when there is variation in the thickness of the sheet itself, it has high flexibility, so that it can be bonded to the surface of the adherend without any gap, and display unevenness in the image display device can be prevented.

  The obtained transparent adhesive sheet can have an adhesive strength of the transparent adhesive sheet to an adherend of 5 N / 25 mm or more (measured by a 90-degree peel test at a speed of 300 mm / min). In some embodiments, the adhesive strength of the transparent adhesive sheet to the adherend can be 10 N / 25 mm or more, or 15 N / 25 mm or more (measured by a 90-degree peel test at a speed of 300 mm / min). Adequate adhesion between the pressure-sensitive adhesive sheet and the adherend can be obtained. Therefore, even in a high-temperature and high-humidity environment, bubbles are not generated at the interface between the transparent pressure-sensitive adhesive sheet having such adhesive force and the adherend, and peeling after sticking can be suppressed. Such a transparent pressure-sensitive adhesive sheet can achieve sufficient adhesion even when applied to a surface protective layer made of a polymer sheet such as polymethyl methacrylate (PMMA) or polycarbonate.

  Furthermore, the transparent adhesive sheet has excellent transparency. That is, when the laminate is laminated on a transparent adherend (for example, the surface protective layer of the image display device), the total light transmittance (JIS K 7361) in the visible light wavelength region of the obtained laminate is 90%. That's it.

  The above copolymer of monomers can be crosslinked with a crosslinking agent in order to ensure cohesion. When the copolymer contains a cross-linking agent, the amount is 2 masses per 100 mass parts of the total mass of the component (A), the component (B), and the component (C) in terms of stress relaxation and foaming. Generally, it is less than or equal to parts. In a certain aspect, it is good also as 1 mass part or less. The lower limit of the amount of the crosslinking agent is not limited, but in general, when about 0.01 part by mass is added to 100 parts by mass of the total mass of the component (A), the component (B), and the component (C), The handling property of the copolymer is improved.

  In addition, the copolymer may contain a group capable of forming a crosslinked structure in the copolymer (a group capable of forming a crosslink) in order to form a crosslink. As the group capable of forming a crosslink, any functional group having reactivity with a crosslinker such as a polyfunctional isocyanate, epoxy, or aziridine compound may be used, and examples thereof include a hydroxyl group. Specifically, when a hydroxyl group is present in the copolymer, it reacts with a polyfunctional isocyanate to form a crosslink by a urethane bond. In order to include such a crosslinkable group in the copolymer, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate may be used as the monomer component.

  The crosslinkable group may be a radically polymerizable group such as a (meth) acryloyl group. In this case, since a crosslinking reaction occurs at the same time when the copolymer is formed (at the time of polymerization), it is not necessary to add a crosslinking agent separately. Examples of the monomer having such a group include polyfunctional groups such as 1,2-ethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, and 1,6-hexanediol di (meth) acrylate ( And (meth) acrylate monomers.

  The monomer component used in the copolymer contained in the transparent pressure-sensitive adhesive sheet may contain a monomer other than the monomer component as long as the properties of the transparent pressure-sensitive adhesive sheet are not impaired. Examples thereof include acrylic monomers such as benzyl acrylate, trifluoroethyl methacrylate, and methacrylic acid-modified silicone oil, and vinyl monomers such as vinyl acetate, vinyl propionate, vinyl versatate, and styrene.

  The copolymer can be formed by polymerizing the above monomer components in the presence of a polymerization initiator. There is no restriction | limiting in particular as a polymerization method, What is necessary is just to superpose | polymerize the said monomer according to a normal radical polymerization method, for example, solution polymerization, emulsion polymerization, suspension polymerization, block polymerization, etc. In a certain aspect, you may employ | adopt the radical polymerization system by a thermal-polymerization initiator. Examples of the thermal polymerization initiator include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate and di (2-ethoxyethyl). ) Organic peroxidation such as peroxydicarbonate, t-butylperoxyneodecanoate, t-butylperoxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane 1-carbonitrile) and 2,2′-azobis ( 2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronite) ), Dimethyl 2,2′-azobis (2-methylpropionate), 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis (2-hydroxymethylpropionitrile), And azo compounds such as 2,2′-azobis [2- (2-imidazolin-2-yl) propane].

  In another embodiment, the copolymer can be prepared by photopolymerization using a suitable polymerization initiator. Specifically, there is a polymerization method in which the monomer component is polymerized by irradiating the monomer with ultraviolet rays (UV) or the like in the presence of a photopolymerization initiator. Suitable polymerization initiators include, for example, acetophenone, diethoxyacetophenone, 2- [4- (methylthio) -methyl-1-phenyl] -2-morpholinopropanone, benzoin, benzoin ethyl ether, benzylmethyl ketal, benzophenone, 2- Ethylanthraquinone, thioxanthone, diethylthioxanthone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (Lucirin ™ TPO, manufactured by BASF), 2,4,6-trimethylbenzoyl diethoxyphosphine oxide (Lucirin ™ TPO- L, manufactured by BASF), bis (2,4,6-trimethylbenzoyl) phenylphosphine (IRGACURE ™ 819, manufactured by Ciba Japan) 2-hydroxy-2-methyl-1-phenylpropan-1-one (DAROCURE (Trademark) 1173, manufactured by Ciba Japan), 4- (2-hydroxyethoxy) phenyl (2- Hydroxy-2-propyl) ketone (IRGACURE ™ 2959, manufactured by Ciba Japan), 4- (2-acryloyloxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl phenylketone (IRGACURE (Trademark) 184, manufactured by Ciba Japan), 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-2-methylpropane -1-one, 2-methyl-2-morpholino (4-thiomethylphenyl) propan-1-one (IRGACURE ™ 907, manufactured by Ciba Japan), 2-benzyl-2-dimethylamino-1- (4 -Morpholinophenyl) -butanone (IRGACURE ™ 369, manufactured by Ciba Japan), N, N`-octamethylenebisacridine (ADEKA Optomer ™ N1717), acryloylbenzophenone (Daicel UCB Ebercryl ™ P36), etc. To list It can be.

  The transparent adhesive sheet may contain other components such as dyes, pigments, UV absorbers, other fillers, and antioxidants in addition to the copolymer. However, since the copolymer itself has the necessary properties as a transparent adhesive sheet, the surface protective layer or the touch panel in the image display device can be used without including additives such as a plasticizer and a tackifier. It can be used as it is for attaching to the display surface of the image display unit or attaching the surface protective layer and the touch panel. For this reason, when the copolymer is used as it is as a transparent adhesive sheet, contamination due to bleeding of components other than the copolymer and changes in the properties of the transparent adhesive sheet do not occur.

  The thickness of the transparent adhesive sheet does not pose a problem in attachment to the image display device (attachment between the surface protective layer in the image display device or the touch panel and the display surface of the image display unit, or attachment between the surface protective layer and the touch panel). If it is thickness, there will be no restriction | limiting in particular. For example, the thickness can be 0.025 to 1 mm. When the thickness of the transparent adhesive sheet is increased, the adhesive force to an adherend (a polymer sheet such as polycarbonate or PMMA or a glass plate) is increased.

  Then, the image display apparatus containing the transparent adhesive sheet mentioned above is demonstrated, referring FIGS. Here, the image display device includes an image display unit, a transparent adhesive sheet, and a surface protective layer. In the transparent adhesive sheet included in the image display device, the internal residual stress in the transparent adhesive sheet is relaxed.

  The image display unit is not particularly limited, and includes a reflection type or backlight type liquid crystal display unit, a plasma display unit, an electroluminescence (EL) display, an image display unit such as electronic paper, and the like. An additional layer (which may be a single layer or multiple layers), for example, a polarizing plate (which may have an uneven surface) may be provided on the display surface of the image display unit. Further, a touch panel as described later may be present on the display surface of the image display unit.

  The surface protective layer is a layer disposed on the outermost surface when disposed on the image display device. The surface protective layer may be composed only of a polymer sheet, a glass plate, or the like, or may be composed of a plurality of layers together with other layers. The surface protective layer is not particularly limited as long as it is conventionally used as a protective film for an image display device. For example, an acrylic resin sheet such as polymethyl methacrylate (PMMA), a sheet containing a polycarbonate layer, or glass Can be a board. Although the thickness of this sheet | seat or a glass plate is not limited, Usually, it is 0.1-5 mm. In the present invention, not only an acrylic resin sheet or glass plate containing polymethyl methacrylate (PMMA) but also a sheet containing a polycarbonate layer is used as a surface protective layer. It becomes possible to prevent.

  When the surface protective layer is a laminate composed of multiple layers, the observer side of the image display device has functions such as wear resistance, scratch resistance, antifouling properties, antireflection properties, and antistatic properties. A layer for imparting characteristics can be provided. The layer for imparting abrasion resistance and scratch resistance can be formed by applying and curing a curable resin composition capable of forming a hard coat. For example, a paint composed of colloidal silica and a partial condensation reaction product of a silane mixture containing alkyltrialkoxysilane as a main component is applied and then cured by heating to form a cured film, or a polyfunctional acrylate as a main component. A cured coating film can be formed by applying the coating material described above and irradiating the coating film with ultraviolet rays. In order to ensure antifouling properties, a resin layer containing an organosilicon compound or a fluorine-based compound can be formed. In a surface protective layer including a polycarbonate layer, a hard coat layer is generally provided on both sides of the polycarbonate layer. Furthermore, in order to obtain antistatic properties, a resin layer containing a surfactant and conductive fine particles can be formed. The layer for imparting such functions / characteristics is desirably a layer that does not hinder the transparency of the surface protective layer, and is preferably as thin as possible within a range where the function can be exhibited. Although the layer which provides a functional characteristic is not limited, Usually, it is 0.05-10 micrometers.

  When the surface protective layer is a laminate composed of a plurality of layers, an additional layer such as a printing layer, a hard coat layer, or a vapor deposition layer is formed on the entire surface of the surface protective layer or a partial region on the transparent adhesive sheet side. May be included. When such an additional layer is formed in a partial region of the surface protective layer, the surface protective layer becomes a surface having an uneven shape. The thickness of the surface protective layer is usually 0.1 to 6 mm as a whole, including such additional layers. In addition, when an additional layer is a printing layer or vapor deposition layer used as a light shielding layer as described later, the thickness of the layer is usually 10 μm or less. In other embodiments, the layer thickness is generally 100 μm or less, or 50 μm or less.

  FIG. 1 shows a cross-sectional view of one embodiment of an image display device including the transparent adhesive sheet described above. The image display device 10 has a structure in which the transparent adhesive sheet 3 and the surface protective layer 4 are laminated in this order on the display surface of the image display unit 1. The surface protective layer 4 is composed of a continuous layer 5 and a light shielding layer 6 provided in a partial region on the lower surface of the continuous layer 5 (on the transparent adhesive sheet 3 side), and the surface has an uneven shape. In addition, the light shielding layer 6 is applied to a predetermined region of the continuous layer 5 by applying a liquid in which a coloring agent is mixed into the coating solution of the curable resin composition, by an appropriate method such as screen printing, and the like. It is formed by curing with a proper curing method. The transparent adhesive sheet 3 is affixed to the concavo-convex shape side of the surface protective layer 4. Since the transparent adhesive sheet 3 has flexibility, even if the surface protective layer 4 has an uneven shape, a layer (for example, a polarizing plate) having an uneven surface shape is further provided on the display surface of the image display unit. Even in such a case, the internal residual stress of the sheet itself is alleviated, and display unevenness in the image display device can be prevented. Moreover, since the transparent adhesive sheet 3 has sufficient adhesive force and hydrophilicity, even in a high temperature and high humidity environment, the interface between the display surface of the image display unit 1 and the transparent adhesive sheet 3, and the transparent adhesive sheet 3 No bubbles or peeling occurs at the interface with the surface protective layer 4. Here, the image display device 10 is obtained, for example, by bonding the laminate 2 composed of the surface protective layer 4 and the transparent adhesive sheet 3 to the display surface of the image display unit 1.

  FIG. 2 is a cross-sectional view of another aspect of the image display device including the transparent adhesive sheet. In FIG. 2, the image display device 20 has a structure in which the transparent adhesive sheet 3 and the surface protective layer 4 are laminated in this order on the touch panel 7 existing on the display surface of the image display unit 1. The structure of the laminate 2 in which the transparent adhesive sheet 3 and the surface protective layer 4 are laminated in this order is the same as that shown in FIG. The touch panel 7 is disposed on the display surface of the image display unit 1, and the image display on the image display device 20 can be seen through the touch panel. The touch panel 7 is transparent. For example, a transparent conductive layer is disposed on the back surface of two transparent plates made of glass or polyethylene terephthalate (PET), and the transparent conductive layers of the transparent plates are arranged with a small gap therebetween. And have a configuration in which they face each other in a non-contact state. When the touch panel operator presses the corresponding position on the surface of one transparent plate with a finger or a pen, the transparent conductive layer on the back of one transparent plate comes into contact with the transparent conductive layer on the other transparent plate and is conductive only at the corresponding position. It becomes possible. The position on the touch panel pressed by the operator can be specified by the sensor that electrically senses the position at which this conduction is possible. Such touch panel displays are used in portable terminals such as PCs (personal computers), mobile phones, and PDAs. Since the transparent adhesive sheet 3 has flexibility, even if the surface protective layer 4 has an uneven shape, the internal residual stress of the sheet itself is relaxed, and display unevenness in the image display device can be prevented. Moreover, since the transparent adhesive sheet 3 has sufficient adhesive force and hydrophilicity, even in a high temperature and high humidity environment, the interface between the touch panel 7 and the transparent adhesive sheet 3, and the transparent adhesive sheet 3 and the surface protective layer 4 Bubbles and peeling do not occur at the interface. Here, the image display device 20 is obtained, for example, by bonding the laminate 2 composed of the surface protective layer 4 and the transparent adhesive sheet 3 to the touch panel 7 existing on the display surface of the image display unit 1. As described above, by using the transparent adhesive sheet 3 of the present invention, the transparent conductive layer and the transparent adhesive sheet can be directly bonded together without providing a protective layer on the transparent conductive layer disposed on the surface of the touch panel 7. This is also possible (the same applies to the embodiments of FIGS. 3 and 4 below).

  FIG. 3 is a cross-sectional view of still another aspect of the image display device including the transparent adhesive sheet. In FIG. 3, the image display device 30 has a structure in which a transparent adhesive sheet 3, a touch panel 7, a transparent adhesive sheet 3 ′, and a surface protective layer 4 are laminated in this order on the display surface of the image display unit 1. Yes. The structure of the laminate in which the transparent adhesive sheet 3 ′ and the surface protective layer 4 are laminated in this order is the same as that described in FIG. 1. The transparent pressure-sensitive adhesive sheet 3 and the transparent pressure-sensitive adhesive sheet 3 ′ may contain the same copolymer or different copolymers. Since the transparent adhesive sheets 3 and 3 ′ have flexibility, even if the surface protective layer 4 has an uneven shape, a layer having an uneven surface shape on the display surface of the image display unit (for example, a polarizing plate). Even if this is provided, the internal residual stress of the sheet itself is relaxed, and display unevenness in the image display apparatus can be prevented. Moreover, since the transparent adhesive sheets 3 and 3 ′ have sufficient adhesive force and hydrophilicity, the display surface of the image display unit 1, the transparent adhesive sheet 3, and the transparent adhesive sheet 3 ′ even under a high temperature and high humidity environment. In addition, bubbles and peeling do not occur at each interface such as the surface protective layer 4. Here, the image display apparatus 30 bonds the laminate 2 composed of the surface protective layer 4, the transparent adhesive sheet 3 ′, the touch panel 7, and the transparent adhesive sheet 3 on the display surface of the image display unit 1, for example. Can be obtained.

  FIG. 4 is a cross-sectional view of still another aspect of the image display device including the transparent adhesive sheet. In FIG. 4, the image display device 40 has a structure in which a transparent adhesive sheet 3, a touch panel 7, and a surface protective layer 4 are laminated in this order on the image display unit 1. As in FIG. 1, the surface protective layer 4 has a light shielding layer 6 in a partial region, and the surface has an uneven shape. The transparent adhesive sheet 3 is present on the concave and convex surface side of the surface protective layer 4 via the touch panel 7. Since the transparent adhesive sheet 3 has flexibility, even if a layer having an uneven surface shape (for example, a polarizing plate) is provided on the display surface of the image display unit, the internal residual stress of the sheet itself is relaxed, Display unevenness in the image display device can be prevented. Moreover, since the transparent adhesive sheet 3 has sufficient adhesive force and hydrophilicity, even in a high temperature and high humidity environment, the interface between the display surface of the image display unit 1 and the transparent adhesive sheet 3, and the transparent adhesive sheet 3 Bubbles and peeling do not occur at the interface with the touch panel 7. Here, the image display device 40 is obtained, for example, by bonding the laminate 2 composed of the surface protective layer 4, the touch panel 7 and the transparent adhesive sheet 3 to the display surface of the image display unit 1.

  According to still another aspect of the present invention, an electronic device including the image display device is provided. The electronic device is not particularly limited, and includes a mobile phone, a personal digital assistant (PDA), a portable game machine, an electronic reading terminal, a car navigation system, a portable music player, a clock, a television (TV), a video camera, a video player, Examples include digital cameras, global positioning system (GPS) devices, and personal computers (PCs).

  Hereinafter, although it demonstrates still in detail using an Example, it is not limited to these Examples.

1. Preparation method examples 1 to 29 of acrylic copolymer
In accordance with the description in Table 1 below, 0.04 parts by mass of each monomer component and Irgacure (trademark) 651 (2,2-dimethoxy-2-phenylacetophenone) (manufactured by Ciba Japan) as a photopolymerization initiator in a glass container After thoroughly mixing and substituting the dissolved oxygen with nitrogen gas, ultraviolet rays were irradiated for several minutes with a low-pressure mercury lamp and partially polymerized to obtain a viscous liquid having a viscosity of about 1500 cP. In accordance with Table 1 below, the obtained composition was replaced with the component (D-1) or (D-2) (the component (D-1) or the component (D-2) instead of M2050 in Example 28, Example 29). Then, KBM403), HDDA (1,6-hexanediol diacrylate) as a cross-linking agent, and 0.15 part by mass of an additional polymerization initiator (Irgacure 651) were added and sufficiently stirred. This mixture was vacuum degassed and then coated on a 50 μm-thick polyester film (release film) that had been subjected to a release treatment so as to have a thickness of 175 μm. Irradiation from both sides with a low-pressure mercury lamp for about 4 minutes gave a transparent adhesive sheet. According to the following method, tan δ, storage elastic modulus, and acid value of the obtained sheet were measured. The measurement results are shown in Table 1.

Measurement method of storage elastic modulus and tan δ (loss tangent) (dynamic viscoelastic property) (Preparation of sample) The release film was removed from the transparent adhesive sheet prepared by the above method, and a sheet of about 3 mm thickness obtained by laminating 16 sheets was 7 A cylindrical sample was obtained by punching with a 9 mmφ punching blade.
(Measurement) Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific was used for dynamic viscoelastic properties. The sample fixing jig was a 7.9 mmφ parallel plate, and the sample prepared by the above method was placed between the plates to adjust the tension. The dynamic viscoelastic properties are measured in air, measured in a shear mode at a frequency of 1.0 Hz, at a temperature increase rate of 5 ° C./min at −50 to 200 ° C., and a storage elastic modulus G ′ (Pa ) And tan δ (loss tangent) at 140 ° C.

Acid value measurement method Calculated from the amount of monomer used.

2. Evaluation method of transparent adhesive sheet (1) Liquid crystal display unevenness test Using the transparent adhesive sheet (175 μm thickness) obtained above, an acrylic board (Mitsubishi Rayon MR-200, size) bordered by about 8 μm thick black printing Was 45 × 65 mm, 1 mm thick) was pressure-bonded to a liquid crystal module from which a protective cover for the entire surface of a commercially available mobile phone (Sharp 904SH) was removed. The obtained acrylic plate / adhesive sheet / liquid crystal module laminate was placed in an autoclave and treated at 40 ° C. and 0.5 MPa for 15 minutes. After that, when the cellular phone was turned on and a white screen was displayed and the unevenness was visually confirmed, the transparent adhesive sheet of Example 1 (storage elastic modulus: 1.9 × 10 ⁴ [Pa] (25 ° C.), tan δ: 0.33 (140 ° C.) )), The transparent adhesive sheet of Example 21 (storage elastic modulus: 4.8 × 10 ⁴ [Pa] (25 ° C.), tan δ: 0.25 (140 ° C.)), no unevenness was observed, and the transparent adhesive sheet of Example 28 (storage) When using elastic modulus: 2.9 × 10 ⁴ [Pa] (25 ° C.) and tan δ: 0.08 (140 ° C.), unevenness was clearly observed.

(2-1) Reliability test 1
The release film of the sheet to be evaluated was peeled off on one side and attached to a polycarbonate plate (CW06, 1.2 mm thickness, 55 × 85 mm) manufactured by Sumitomo Chemical Co., Ltd. so that air did not enter with a roller, and the protruding part was removed with a cutter. On the other hand, a polarizing plate with an adhesive (manufactured by Sanritz) was similarly attached to a 0.55 mm thick float glass (50 × 80 mm) with a rubber roller. The release film of the pressure-sensitive adhesive sheet affixed to the polycarbonate plate was peeled off and pressure-bonded using a rubber roller so that the pressure-sensitive adhesive surface was adhered to the polarizing plate. The obtained polycarbonate plate / adhesive sheet / polarizing plate / glass laminate was placed in an autoclave and treated at 40 ° C. and 0.5 MPa for 30 minutes. After removing from the autoclave and allowing to stand at room temperature for 12 hours, it was placed in a constant temperature and humidity chamber at 65 ° C./90% RH and 85 ° C. (dry). One day later, the product was taken out and visually checked for peeling and foaming in the laminate. The results are shown in Table 2.

(2-2) Reliability test 2
About the transparent adhesive sheet of Examples 21, 22, 23, and 24, the following evaluation was also performed. First, the release film of the sheet was peeled off on one side and attached to a polycarbonate plate (CW06 manufactured by Sumitomo Chemical Co., Ltd., 1.2 mm thickness, 55 × 85 mm) so as not to enter air with a roller, and the protruding portion was removed with a cutter. On the other hand, a polyethylene terephthalate (PET) film with ITO (manufactured by Oike Kogyo Co., Ltd., Tetraite TCF KB500NS3-175) is used on a 0.55 mm thick float glass (50x80 mm) with a rubber roller in a similar manner so that the ITO is on the surface side through an adhesive. Pasted. The release film of the adhesive sheet affixed to the polycarbonate plate was peeled off and pressure-bonded using a rubber roller so that the adhesive surface adhered to ITO. The obtained polycarbonate plate / adhesive sheet / PET / glass laminate with ITO was placed in an autoclave and treated at 40 ° C. and 0.5 MPa for 30 minutes. After removing from the autoclave and allowing to stand at room temperature for 12 hours, it was placed in a constant temperature and humidity chamber at 65 ° C./90% RH and 85 ° C. (dry). One day later, the product was taken out and visually checked for peeling and foaming in the laminate. The results are shown in Table 2.

  In Table 2, “slight foaming” is observed when 1 to 2 bubbles larger than 30 μm are observed in the laminate, and “with foaming” when 3 or more bubbles larger than 30 μm are observed in the laminate. The case where peeling of 1 mm or less from the end of the body was observed was defined as “slight peeling”, and the case where peeling greater than 1 mm was observed from the end of the laminate or bubbles was regarded as “peeling”.

DESCRIPTION OF SYMBOLS 10, 20, 30, 40 Image display apparatus 1 Image display unit 2 Laminated body 3 Transparent adhesive sheet 4 Surface protective layer 5 Continuous layer 6 Light shielding layer 7 Touch panel

Claims (8)

A transparent adhesive sheet for affixing the surface protective layer or touch panel and the display surface of the image display unit in the image display device, or affixing the surface protective layer and the touch panel,
The transparent adhesive sheet contains a copolymer of monomer components containing the following (A), (B) and (C),
(A) (meth) acrylic acid alkyl ester whose alkyl group has 4 to 18 carbon atoms;
(B) an amide group-containing monomer;
(C) (meth) acrylic acid ester represented by the following formula (1);
_{CH 2 = C (R) COO-} (AO) p- (BO) q-R '··· (1)
(Here, in formula (1),
A is at least one group selected from the group consisting of (CH ₂ ) rCO, CH ₂ CH ₂ , CH ₂ CH (CH ₃ ), CH ₂ CH ₂ CH ₂ CH ₂ ,
B is _{(CH 2) rCO, CO (} CH 2) r, CH 2 CH 2, CH 2 CH (CH 3), at least one group selected from the group consisting of _{CH 2 CH 2 CH 2 CH 2} ,
R is hydrogen or CH ₃ ;
R ′ is hydrogen, or an optionally substituted alkyl group or aryl group,
p, q and r are each an integer of 1 or more)
The copolymer is further
(D-1) 0.1 to 5 parts by mass of an amino group-containing monomer (wherein the amino group-containing monomer is a monomer component with respect to 100 parts by mass of the total amount of monomer components (A), (B) and (C)) (A), (B) and (C) can be copolymerized to form a copolymer with the monomer components (A), (B) and (C)), or (D-2) the monomer component Including 0.01 to 1 part by mass of an amino group-containing alkoxysilane compound with respect to 100 parts by mass of the total amount of (A), (B) and (C),
The said transparent adhesive sheet whose acid value of a copolymer is 5 mgKOH / g or less.   The copolymer further comprises (E) (meth) acrylic acid hydroxyalkyl ester, and the (meth) acrylic acid hydroxyalkyl ester is copolymerizable with the monomer components (A), (B) and (C). The transparent adhesive sheet of Claim 1 which comprises a copolymer with the monomer components (A), (B), and (C). The copolymer has a tan δ at 140 ° C. and 1.0 Hz of 0.13 or more, and a storage elastic modulus at 25 ° C. and 1.0 Hz of 8.9 × 10 ⁴ Pa or less. Transparent adhesive sheet.   The component (C) is a polyalkylene glycol alkyl ether acrylate in which R is hydrogen in the formula (1), R ′ is an alkyl group having 1 to 12 carbon atoms, and 2 ≦ p + q ≦ 10. The transparent adhesive sheet of any one of 1-3.   (D-1) The transparent adhesive sheet of any one of Claims 1-4 whose component is a tertiary amino group containing monomer. (D-2) Component is the following general formula (2)
(R ¹ O) _n R ² _3-n Si—X—NR ³ R ⁴ (2)
(Where R ¹ represents an alkyl group, R ² represents hydrogen, or an optionally substituted alkyl group or aryl group, and R ³ and R ⁴ each independently represent hydrogen or an optionally substituted alkyl. A group, an aralkyl group or an aryl group, or (R ⁵ O) _m R ⁶ _3-m Si—Y—, wherein R ³ and R ⁴ may form a ring, and n is 2 or 3. X represents a divalent linking group, R ⁵ represents an alkyl group, R ⁶ represents hydrogen, an optionally substituted alkyl group or an aryl group, m represents 2 or 3, and Y represents 2 A valent linking group.)
The transparent adhesive sheet according to any one of claims 1 to 4, wherein   The image display apparatus containing an image display unit, the transparent adhesive sheet of any one of Claims 1-6, and a surface protective layer.   The image display device according to claim 7, wherein the surface protective layer is a sheet including a polycarbonate layer.

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