JP6424034B2 - Adhesive sheet for electronic equipment - Google Patents

Description

The present invention relates to an adhesive sheet for electronic equipment that can maintain high water tightness even if it is narrow.

In an electronic device (for example, a mobile phone, a portable information terminal, etc.) equipped with an image display device or an input device, an adhesive sheet is used for assembly. Specifically, for example, an adhesive sheet is used to bond a cover panel for protecting the surface of an electronic device to a touch panel module or a display panel module, or to bond a touch panel module and a display panel module. Yes.
Such an adhesive sheet is used, for example, by being punched into a frame shape or the like and arranged around the display screen.

Various properties including adhesiveness are required for pressure-sensitive adhesive sheets used in electronic devices. For example, water tightness is required to prevent liquids such as water from entering the electronic devices. .
Patent Document 1 describes a pressure-sensitive adhesive sheet for electronic equipment comprising a cross-linked polyolefin resin foam sheet and a predetermined acrylic pressure-sensitive adhesive layer laminated and integrated on one surface of the cross-linked polyolefin resin foam sheet. It is described that this pressure-sensitive adhesive sheet for electronic equipment has sufficient shock absorption and water tightness although it is thin.

In recent years, the area of the opening has been increased with the increase in the size of the display screen, and as a result, the joint fixing portion around the display screen has been narrowed. For this reason, the pressure-sensitive adhesive sheet has become narrower year by year, and when used with a narrow width, there has been a problem that high water tightness cannot be maintained when a strong water pressure is applied or the water is immersed for a long time.

On the other hand, a polymer obtained by polymerizing a radical polymerizable monomer such as a vinyl monomer or an acrylic monomer is frequently used for the adhesive of the adhesive sheet. As a type of radical polymerization, free radical polymerization is common. However, free radical polymerization cannot sufficiently control the molecular weight, molecular weight distribution, copolymer composition, etc., and low molecular weight components are produced, and even in the case of copolymerization, homopolymers are produced. This component has a disadvantage that it causes a decrease in heat resistance of the pressure-sensitive adhesive, a decrease in cohesive force, and the like.

On the other hand, living radical polymerization has been studied as a more controlled radical polymerization. Living radical polymerization is a polymerization in which a molecular chain grows without being hindered by a side reaction such as a termination reaction or a chain transfer reaction, so that it is easy to control the molecular weight and molecular weight distribution, copolymer composition, etc. Generation of a low molecular weight component and formation of a homopolymer that occurs without copolymerization can be suppressed.
Patent Document 2 describes a pressure-sensitive adhesive containing a copolymer obtained by copolymerizing a monomer by a living radical polymerization method using an organic tellurium compound as a polymerization initiator. However, it has been difficult to obtain a sufficiently high watertightness when the pressure-sensitive adhesive sheet is used in a narrow width only by using such a pressure-sensitive adhesive.

JP 2010-215906 A Japanese Patent No. 5256515

An object of this invention is to provide the adhesive sheet for electronic devices which can maintain high watertightness even if it is narrow.

The present invention is a pressure-sensitive adhesive sheet for electronic equipment having a cross-linked polyolefin resin foam sheet and a pressure-sensitive adhesive layer laminated and integrated on at least one surface of the cross-linked polyolefin resin foam sheet, the pressure-sensitive adhesive layer is a living radical polymerization Containing an acrylic polymer having a molecular weight distribution (Mw / Mn) of 1.05 to 2.5 and a rosin-based tackifying resin, the acrylic polymer having an alcoholic hydroxyl group, and the rosin-based polymer The tackifier resin is a pressure-sensitive adhesive sheet for electronic equipment having a hydroxyl value of 25 to 55 and a content of 5 to 40 parts by weight with respect to 100 parts by weight of the acrylic polymer.
The present invention is described in detail below.

In the pressure-sensitive adhesive sheet for electronic equipment having a crosslinked polyolefin resin foamed sheet and a pressure-sensitive adhesive layer, the present invention adheres an acrylic polymer having a narrow molecular weight distribution obtained by living radical polymerization and a rosin-based tackifying resin. The adhesive layer for electronic devices is used in a narrow width by blending in the agent layer, having an acrylic polymer having an alcoholic hydroxyl group, and further adjusting the hydroxyl value and content of the rosin-based tackifying resin to a specific range. Even in such a case, it was found that a sufficiently high adhesive force was obtained and high water tightness could be maintained, and the present invention was completed.

The pressure-sensitive adhesive sheet for electronic equipment of the present invention has a crosslinked polyolefin resin foam sheet and a pressure-sensitive adhesive layer laminated and integrated on at least one surface of the crosslinked polyolefin resin foam sheet.
The electronic device pressure-sensitive adhesive sheet of the present invention may have an adhesive layer on at least one surface of the crosslinked polyolefin resin foamed sheet, and may have an adhesive layer on both surfaces of the crosslinked polyolefin resin foamed sheet.

Since the crosslinked polyolefin resin foamed sheet has buffering properties, the pressure-sensitive adhesive sheet for electronic equipment of the present invention has sufficiently high impact resistance even if the adhesive layer is not necessarily provided on both sides of the crosslinked polyolefin resin foamed sheet. Can have. Moreover, by having the said crosslinked polyolefin resin foam sheet, the adhesive sheet for electronic devices of this invention can improve the adhesive follow-up property with respect to a level | step difference, and can maintain high water-tightness.
The said crosslinked polyolefin resin foam sheet is not specifically limited, For example, it can obtain by bridge | crosslinking a polyolefin resin foam sheet.
The method for crosslinking the polyolefin resin foam sheet is not particularly limited. For example, the polyolefin resin foam sheet is irradiated with ionizing radiation such as electron beam, α-ray, β-ray, γ-ray, etc. Examples thereof include a method of decomposing an organic peroxide that has been blended in advance by heating.

The polyolefin resin foam sheet is not particularly limited as long as it is in the form of a sheet and contains a polyolefin resin, and examples thereof include polyethylene foam, polypropylene foam, and ethylene-propylene foam. However, since the impact resistance is improved, a foam containing a polyolefin resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (also referred to as “metallocene polyolefin foam” in this specification). Is preferred). Among these, a foam containing a polyethylene resin obtained by using a metallocene compound (also referred to as “metallocene polyethylene foam” in the present specification) is more preferable.
Examples of the metallocene compounds include Kaminsky catalysts.

As a polyethylene resin obtained using the metallocene compound contained in the metallocene polyethylene foam, for example, using the metallocene compound, ethylene and another α-olefin blended as necessary may be used. Examples thereof include polyethylene-based resins obtained by polymerization. Examples of the other α-olefin include propene, 1-butene, 1-pentene, 1-hexene and the like.

The metallocene polyethylene foam may further contain another olefin resin in addition to the polyethylene resin obtained using the metallocene compound. Examples of the other olefin-based resin include polyethylene, polypropylene, ethylene-propylene copolymer, and the like.
In this case, the content of the polyethylene resin obtained by using the metallocene compound in the metallocene polyethylene foam is preferably 40% by weight or more. When the content of the polyethylene resin obtained by using the metallocene compound is 40% by weight or more, high compressive strength can be obtained even if the metallocene polyethylene foam is thin.

The thickness of the crosslinked polyolefin resin foamed sheet is not particularly limited because it is set depending on the application, but is preferably 10 to 500 μm, and more preferably 60 to 400 μm. When the thickness is less than 10 μm, the mechanical strength of the pressure-sensitive adhesive sheet for electronic devices is reduced, and the pressure-sensitive adhesive sheet is cut when punched with a narrow width, or the pressure-sensitive adhesive sheet is destroyed when a strong impact is applied. Sometimes. If the thickness exceeds 500 μm, improvement in adhesion followability and water tightness of the pressure-sensitive adhesive sheet for electronic equipment cannot be expected, and the economic efficiency is reduced, or the dimensional accuracy of the width when punched with a narrow width is reduced. There are things to do.

The method for producing the crosslinked polyolefin resin foamed sheet is not particularly limited, but a foamable polyolefin resin composition containing a polyolefin resin and a foaming agent (for example, azodicarbonamide) is prepared, and the foamable polyolefin resin composition is prepared. A method of foaming a foaming agent when extruding into a sheet using an extruder and cross-linking the obtained polyolefin resin foam sheet as necessary is preferable.
Moreover, the foamable polyolefin resin composition is extruded into a sheet without foaming the foaming agent using an extruder, and the foamable polyolefin resin sheet is crosslinked as necessary, and then foamed. You may use the method to make.
Furthermore, you may extend | stretch the obtained foam sheet as needed.

The pressure-sensitive adhesive layer contains an acrylic polymer having a molecular weight distribution (Mw / Mn) of 1.05 to 2.5 obtained by living radical polymerization and a rosin-based tackifying resin.
The acrylic polymer is obtained by living radical polymerization, more preferably by living radical polymerization using an organic tellurium polymerization initiator.
Living radical polymerization is polymerization in which molecular chains grow without the polymerization reaction being hindered by side reactions such as termination reactions or chain transfer reactions. According to living radical polymerization, for example, a polymer having a more uniform molecular weight and composition than that of free radical polymerization can be obtained, and generation of low molecular weight components and the like can be suppressed. For this reason, it becomes easy to adjust the molecular weight distribution of the acrylic polymer to the above range, and a sufficiently high adhesive force can be obtained even when the adhesive sheet for electronic equipment is used in a narrow width, and high water tightness is maintained. be able to.

The organic tellurium polymerization initiator is not particularly limited as long as it is generally used for living radical polymerization, and examples thereof include organic tellurium compounds and organic telluride compounds.
Examples of the organic tellurium compound include (methylterranyl-methyl) benzene, (1-methylterranyl-ethyl) benzene, (2-methylterranyl-propyl) benzene, 1-chloro-4- (methylterranyl-methyl) benzene, 1-hydroxy- 4- (methylterranyl-methyl) benzene, 1-methoxy-4- (methylterranyl-methyl) benzene, 1-amino-4- (methylterranyl-methyl) benzene, 1-nitro-4- (methylterranyl-methyl) benzene, 1- Cyano-4- (methylterranyl-methyl) benzene, 1-methylcarbonyl-4- (methylterranyl-methyl) benzene, 1-phenylcarbonyl-4- (methylterranyl-methyl) benzene, 1-methoxycarbonyl-4- (methylterranyl-methyl) ) Benzene, 1- Enoxycarbonyl-4- (methylterranyl-methyl) benzene, 1-sulfonyl-4- (methylterranyl-methyl) benzene, 1-trifluoromethyl-4- (methylterranyl-methyl) benzene, 1-chloro-4- (1 -Methyl terranyl-ethyl) benzene, 1-hydroxy-4- (1-methyl terranyl-ethyl) benzene, 1-methoxy-4- (1-methyl teranyl-ethyl) benzene, 1-amino-4- (1-methyl terranyl-ethyl) Benzene, 1-nitro-4- (1-methylterranyl-ethyl) benzene, 1-cyano-4- (1-methylterranyl-ethyl) benzene, 1-methylcarbonyl-4- (1-methylterranyl-ethyl) benzene, 1- Phenylcarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-meth Sicarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-phenoxycarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-sulfonyl-4- (1-methylterranyl-ethyl) benzene, 1-trifluoromethyl -4- (1-methylteranyl-ethyl) benzene, 1-chloro-4- (2-methylterranyl-propyl) benzene, 1-hydroxy-4- (2-methylterranyl-propyl) benzene, 1-methoxy-4- (2 -Methyl teranyl-propyl) benzene, 1-amino-4- (2-methyl teranyl-propyl) benzene, 1-nitro-4- (2-methyl teranyl-propyl) benzene, 1-cyano-4- (2-methyl teranyl-propyl) Benzene, 1-methylcarbonyl-4- (2-methylterranyl-propyl ) Benzene, 1-phenylcarbonyl-4- (2-methylterranyl-propyl) benzene, 1-methoxycarbonyl-4- (2-methylterranyl-propyl) benzene, 1-phenoxycarbonyl-4- (2-methylterranyl-propyl) benzene 1-sulfonyl-4- (2-methylterranyl-propyl) benzene, 1-trifluoromethyl-4- (2-methylterranyl-propyl) benzene, 2- (methylterranyl-methyl) pyridine, 2- (1-methylterranyl-ethyl) ) Pyridine, 2- (2-methylterranyl-propyl) pyridine, 2-methylterranyl-methyl ethanoate, methyl 2-methylterranyl-propionate, methyl 2-methylterranyl-2-methylpropionate, 2-methylterranyl-ethyl ethanoate, 2 -Methylterranil Ethyl propionate, 2-Mechiruteraniru -2-methylpropionic acid ethyl, 2-methyl-Terra alkylsulfonyl acetonitrile, 2-methyl-Terra sulfonyl propionitrile, 2-methyl-2-methyl-Terra sulfonyl propionitrile, and the like. The methyl terranyl group in the above compound may be an ethyl terranyl group, n-propyl terranyl group, isopropyl terranyl group, n-butyl terranyl group, isobutyl terranyl group, t-butyl terranyl group, phenyl terranyl group, etc. These organic tellurium compounds may be used alone or in combination of two or more.

Examples of the organic telluride compound include dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, diisopropyl ditelluride, dicyclopropyl ditelluride, di-n-butyl ditelluride, di-sec-butyl ditelluride. , Di-tert-butyl ditelluride, dicyclobutyl ditelluride, diphenyl ditelluride, bis- (p-methoxyphenyl) ditelluride, bis- (p-aminophenyl) ditelluride, bis- (p-nitrophenyl) ditelluride, bis -(P-cyanophenyl) ditelluride, bis- (p-sulfonylphenyl) ditelluride, dinaphthyl ditelluride, dipyridyl ditelluride and the like can be mentioned. These organic telluride compounds may be used alone or in combination of two or more. Of these, dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, di-n-butyl ditelluride and diphenyl ditelluride are preferable.

In addition, within the range which does not impair the effect of this invention, in addition to the said organic tellurium polymerization initiator, you may use an azo compound as a polymerization initiator for the purpose of acceleration | stimulation of a polymerization rate. The azo compound is not particularly limited as long as it is generally used for radical polymerization. For example, 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2-methylbutyronitrile) ), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis (cyclohexane-1-carbonitrile) ), 1-[(1-cyano-1-methylethyl) azo] formamide, 4,4′-azobis (4-cyanovaleric acid), dimethyl-2,2′-azobis (2-methylpropionate), Dimethyl-1,1′-azobis (1-cyclohexanecarboxylate), 2,2′-azobis {2-methyl-N- [1,1′-bis (hydroxymethyl) -2-hydride Xylethyl] propionamide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2′-azobis [N- (2-propenyl) -2-methylpropionamide] 2,2′-azobis (N-butyl-2-methylpropionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide), 2,2′-azobis [2- (2-imidazoline) -2-yl) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl)- -Methylpropionamidine] tetrahydrate, 2,2'-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2'-azobis (2,4,4-trimethylpentane) Etc. These azo compounds may be used alone or in combination of two or more.

The acrylic polymer has an alcoholic hydroxyl group.
When the acrylic polymer has an alcoholic hydroxyl group, the peel resistance of the pressure-sensitive adhesive sheet for electronic devices is improved. In particular, when a cross-linking structure such as an isocyanate cross-linking agent is reacted with an alcoholic hydroxyl group to form a cross-linked structure between the main chains of the acrylic polymer, the peel resistance is significantly improved, and the pressure-sensitive adhesive for electronic equipment is used. Even when the sheet is used in a narrow width, high water tightness can be maintained.

The method for introducing an alcoholic hydroxyl group into the acrylic polymer is not particularly limited, and examples thereof include a method of copolymerizing a (meth) acrylic acid ester having an alcoholic hydroxyl group in the living radical polymerization.
The (meth) acrylic acid ester having an alcoholic hydroxyl group is not particularly limited. For example, 4-hydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (Meth) acrylate, polypropylene glycol mono (meth) acrylate and the like can be mentioned. These (meth) acrylic acid esters having an alcoholic hydroxyl group may be used alone or in combination of two or more. Of these, 2-hydroxyethyl acrylate or 4-hydroxybutyl (meth) acrylate is preferable.
Unlike other living radical polymerizations, living radical polymerization using an organic tellurium polymerization initiator protects all monomers having a polar functional group such as a carboxyl group, a hydroxyl group, an amino group, an amide group, and a nitrile group. The molecular weight and molecular weight distribution can be controlled with the same initiator. For this reason, a monomer having a polar functional group can be easily copolymerized.

When the (meth) acrylic acid ester having an alcoholic hydroxyl group is used, the content thereof is not particularly limited, but the preferred lower limit in the radical polymerizable monomer polymerized by the living radical polymerization is 0.01% by weight, and the preferred upper limit. Is 10% by weight. When the content is less than 0.01% by weight, the water-tightness of the pressure-sensitive adhesive sheet for electronic equipment may be lowered, or the pressure-sensitive adhesive layer may be too soft and the heat-resistant adhesive strength may be lowered. When the content exceeds 10% by weight, the gel fraction of the pressure-sensitive adhesive layer becomes too high, and it may be easily peeled off or water tightness may be lowered. The more preferable lower limit of the content is 0.05% by weight, and the more preferable upper limit is 3% by weight.

Examples of the radical polymerizable monomer that is polymerized by the living radical polymerization include (meth) acrylic acid ester, (meth) acrylic acid, vinyl compound, and the like in addition to the (meth) acrylic acid ester having the alcoholic hydroxyl group. .
The (meth) acrylic acid ester is not particularly limited, and methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (Meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate and other (meth) acrylic acid alkyl esters, cyclohexyl ( (Meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, Tiger tetrahydrofurfuryl (meth) acrylate, polypropylene glycol mono (meth) acrylate. These (meth) acrylic acid esters may be used alone or in combination of two or more. Of these, ethyl acrylate is preferred.

In the acrylic polymer, if the content of the (meth) acrylic acid ester in the radical polymerizable monomer is small, the adhesive strength of the pressure-sensitive adhesive layer is reduced, and the pressure-sensitive adhesive layer is easily peeled off or watertight. In some cases, for example, 50% by weight or more is preferable and 80% by weight or more is more preferable.
Especially, it is preferable that the said acrylic polymer contains 5-30 weight% of ethyl acrylate components. When the content is less than 5% by weight, the pressure-sensitive adhesive layer may be easily peeled off or water tightness may be deteriorated. When the content exceeds 30% by weight, the viscosity at the time of coating is too high, resulting in uneven thickness of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer becomes too hard to be easily peeled off, or water tightness is reduced. There are things to do. The more preferable lower limit of the content of the ethyl acrylate component is 10% by weight, and the more preferable upper limit is 25% by weight.

Moreover, it is also preferable to use (meth) acrylic acid, and the content thereof is not particularly limited, but a preferable lower limit in the radical polymerizable monomer is 0.1% by weight, and a preferable upper limit is 10% by weight. If the content is less than 0.1% by weight, the pressure-sensitive adhesive layer may become too soft, heat resistance may be reduced, and peeling may easily occur. Even if the content exceeds 10% by weight, the pressure-sensitive adhesive layer may become too hard to be easily peeled off or the water tightness may be lowered.

The vinyl compound is not particularly limited, and examples thereof include (meth) acrylamide compounds such as N, N-dimethylacrylamide, N, N-diethylacrylamide, N-isopropylacrylamide, N-hydroxyethylacrylamide, and acrylamide, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylacetamide, N-acryloylmorpholine, acrylonitrile, styrene, vinyl acetate and the like can be mentioned. These vinyl compounds may be used alone or in combination of two or more.

In the living radical polymerization, a dispersion stabilizer may be used. Examples of the dispersion stabilizer include polyvinyl pyrrolidone, polyvinyl alcohol, methyl cellulose, ethyl cellulose, poly (meth) acrylic acid, poly (meth) acrylic acid ester, and polyethylene glycol.
As the living radical polymerization method, conventionally known methods are used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.
When a polymerization solvent is used in the living radical polymerization, the polymerization solvent is not particularly limited. For example, a nonpolar solvent such as hexane, cyclohexane, octane, toluene, xylene, water, methanol, ethanol, propanol, butanol, acetone, Highly polar solvents such as methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, N, N-dimethylformamide can be used. These polymerization solvents may be used alone or in combination of two or more.

The acrylic polymer has a molecular weight distribution (Mw / Mn) of 1.05 to 2.5. When the molecular weight distribution exceeds 2.5, the low molecular weight components and the like generated in the polymerization increase, so that the electronic device pressure-sensitive adhesive sheet is easily peeled off or the water tightness is lowered. A preferable upper limit of the molecular weight distribution is 2.0, and a more preferable upper limit is 1.8.

The acrylic polymer has a preferred lower limit of the weight average molecular weight (Mw) of 450,000 and a preferred upper limit of 1.1 million. When the weight average molecular weight is less than 450,000, the pressure-sensitive adhesive layer may become too soft and easily peel off or water tightness may be reduced. When the weight average molecular weight exceeds 1,100,000, the viscosity at the time of coating may be too high, resulting in uneven thickness of the pressure-sensitive adhesive layer. A more preferable lower limit of the weight average molecular weight (Mw) is 500,000, a more preferable upper limit is 1.05 million, a still more preferable lower limit is 600,000, and a further preferable upper limit is 800,000.

The molecular weight distribution (Mw / Mn) is a ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn).
A weight average molecular weight (Mw) and a number average molecular weight (Mn) are measured as a polystyrene conversion molecular weight by the gel permeation chromatography (GPC) method. Specifically, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are obtained by filtering a diluted solution obtained by diluting an acrylic polymer with tetrahydrofuran (THF) 50 times with a filter, and obtaining the obtained filtrate. And measured as a polystyrene-equivalent molecular weight by the GPC method. In the GPC method, for example, 2690 Separations Model (manufactured by Waters) or the like can be used.

The rosin-based tackifying resin has a hydroxyl value of 25 to 55 and a content of 5 to 40 parts by weight with respect to 100 parts by weight of the acrylic polymer.
When the pressure-sensitive adhesive sheet for electronic equipment is used in a narrow width by blending the rosin-based tackifier resin in the pressure-sensitive adhesive layer and further adjusting the hydroxyl value and content of the rosin-based tackifier resin to the above ranges Even so, a sufficiently high adhesive strength can be obtained and high water tightness can be maintained.

When the hydroxyl value is out of the above range, the pressure-sensitive adhesive layer is easily peeled off or water tightness is lowered. The preferable lower limit of the hydroxyl value is 30 and the preferable upper limit is 50.
The hydroxyl value can be measured by JIS K1557 (phthalic anhydride method).

The rosin-based tackifier resin has a preferable lower limit of the softening temperature of 70 ° C. and a preferable upper limit of 170 ° C. When the softening temperature is less than 70 ° C., the pressure-sensitive adhesive layer may become too soft and may be easily peeled off or water tightness may be reduced. When the softening temperature exceeds 170 ° C., the pressure-sensitive adhesive layer may become too hard to be easily peeled off or the water tightness may be lowered. A more preferable lower limit of the softening temperature is 120 ° C.
The softening temperature is a softening temperature measured by the JIS K2207 ring and ball method.

The rosin-based tackifying resin is not particularly limited, but a rosin ester-based resin is preferable. The rosin ester-based resin includes a rosin resin mainly composed of abietic acid, a disproportionated rosin resin and a hydrogenated rosin resin, and a dimer (polymerized rosin resin) of a resin acid such as abietic acid. It is a resin obtained by esterification with a kind. A part of hydroxyl groups of alcohols used for esterification are contained in the resin without being used for esterification, whereby the hydroxyl value is adjusted to the above range.
Esterified rosin resin is rosin ester resin, disproportionated rosin resin is esterified disproportionated rosin ester resin, hydrogenated rosin resin is esterified hydrogenated rosin ester resin, polymerized rosin resin The esterified product is a polymerized rosin ester resin. Examples of the alcohols used for the esterification include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.

Examples of the hydrogenated rosin ester resin include Pine Crystal KE-359 (hydroxyl value 42, softening temperature 100 ° C.) manufactured by Arakawa Chemical Industries, and ester gum H (hydroxyl value 29, softening temperature 70 ° C.) manufactured by the same company. .
Examples of the polymerized rosin ester resin include Pencel D135 (hydroxyl value 45, softening temperature 135 ° C.) manufactured by Arakawa Chemical Industries, Pencel D130 (hydroxyl value 45, softening temperature 130 ° C.) manufactured by Arakawa Chemical Co., Ltd. , Softening temperature 125 ° C.), Pencel D160 (hydroxyl value 42, softening temperature 160 ° C.) manufactured by the same company.
These rosin-based tackifier resins may be used alone or in combination of two or more.

The content of the rosin-based tackifying resin is 5 parts by weight with respect to 100 parts by weight of the acrylic polymer, and 40 parts by weight with the upper limit. When the content is less than 5 parts by weight, the pressure-sensitive adhesive layer is easily peeled off or water tightness is lowered. Even if the content exceeds 40 parts by weight, the pressure-sensitive adhesive layer becomes too hard due to an increase in the glass transition temperature (Tg), and it becomes easy to peel off or the water tightness is lowered. The minimum with said preferable content is 7 weight part, and a preferable upper limit is 30 weight part.

The pressure-sensitive adhesive layer may further contain a terpene tackifying resin. The terpene-based tackifier resin is not particularly limited, but a terpene phenol-based resin is preferable. The terpene phenol-based resin is a resin obtained by polymerizing terpene in the presence of phenol.
As the terpene-based tackifier resin, for example, YS Polystar G150 (softening point 150 ° C.) manufactured by Yashara Chemical Co., Ltd. YS Polystar T100 (softening point 100 ° C.) manufactured by Yasuhara Chemical, YS Polystar G125 (softening point 125 ° C.) manufactured by Yasuhara Chemical Co., Ltd. (Softening point 115 ° C.), YS Polystar T130 (softening point 130 ° C.) manufactured by the same company.

The pressure-sensitive adhesive layer may contain other resins such as additives such as a plasticizer, an emulsifier, a softener, a filler, a pigment, a dye, a silane coupling agent, and an antioxidant, if necessary. Good.

The pressure-sensitive adhesive layer has a preferred lower limit of the gel fraction of 3% by weight and a preferred upper limit of 60% by weight. When the gel fraction is less than 3% by weight, the pressure-sensitive adhesive layer may become too soft and may be easily peeled off or water tightness may be reduced. If the gel fraction exceeds 60% by weight, the cross-linking density of the pressure-sensitive adhesive layer may become too high and may be easily peeled off or water tightness may be reduced. A more preferable lower limit of the gel fraction is 5% by weight, and a more preferable upper limit is 55% by weight.
The gel fraction is measured as follows. First, a pressure-sensitive adhesive sheet for electronic equipment was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece. The test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, then taken out from ethyl acetate, and 110 ° C. For 1 hour under the following conditions. The weight of the test piece after drying is measured, and the gel fraction is calculated using the following formula (1). In addition, the release film for protecting an adhesive layer shall not be laminated | stacked on the test piece.
Gel fraction (% by weight) = 100 × (W2-W0) / (W1-W0) (1)
(W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

Examples of a method for obtaining a pressure-sensitive adhesive layer having a gel fraction in the above range include a method in which a crosslinking agent is added to form a crosslinked structure between the main chains of the acrylic polymer. At this time, the gel fraction of the said adhesive layer can be adjusted to the target range by adjusting the kind or quantity of the said crosslinking agent suitably.

The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy-type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Especially, since it is excellent in the adhesive stability with respect to the said crosslinked polyolefin resin foam sheet, an isocyanate type crosslinking agent is preferable. Examples of the isocyanate-based crosslinking agent include Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.), Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Mytec NY260A (manufactured by Mitsubishi Chemical Corporation).

As for the compounding quantity of the said crosslinking agent, the preferable minimum with respect to 100 weight part of said acrylic polymers is 0.01 weight part, and a preferable upper limit is 5 weight part. If the blending amount is less than 0.01 parts by weight, the gel fraction of the pressure-sensitive adhesive layer may be too low and may be easily peeled off or water tightness may be reduced. If the blending amount exceeds 5 parts by weight, the gel fraction of the pressure-sensitive adhesive layer may become too high and may be easily peeled off or water tightness may be reduced. A more preferable lower limit of the amount is 0.05 parts by weight, and a more preferable upper limit is 3 parts by weight.

The thickness of the pressure-sensitive adhesive layer is not particularly limited because it is set depending on the application, but a preferred lower limit is 1 μm and a preferred upper limit is 200 μm. When the thickness is less than 1 μm, the adhesive strength of the pressure-sensitive adhesive layer is reduced, and it may be easily peeled off or water tightness may be reduced. When the said thickness exceeds 200 micrometers, the shear holding performance of the adhesive sheet for electronic devices may fall, or punching workability may fall. The more preferable lower limit of the thickness is 2.5 μm, and the more preferable upper limit is 100 μm.

The method for producing the electronic device pressure-sensitive adhesive sheet of the present invention is not particularly limited. For example, the acrylic polymer and the rosin-based tackifying resin are mixed together with other compounding ingredients as necessary, and stirred to be adhesive. A pressure-sensitive adhesive solution is prepared. Subsequently, this pressure-sensitive adhesive solution is coated and dried on a release-treated PET film (manufacturing release film) to form a pressure-sensitive adhesive layer, and the resulting pressure-sensitive adhesive layer is foamed with a crosslinked polyolefin resin. Examples thereof include a method of transferring to a sheet, a method of directly coating and drying the above-mentioned pressure-sensitive adhesive solution on a crosslinked polyolefin resin foam sheet, and the like.

The application of the pressure-sensitive adhesive sheet for electronic equipment of the present invention is not particularly limited as long as it is used for electronic equipment. For example, it is suitable for being used by being punched into a frame shape and disposed around the display screen. ing.
The width of the frame at this time is not particularly limited, but is usually 2.5 mm or less. The pressure-sensitive adhesive sheet for electronic equipment of the present invention can maintain high water tightness even when the frame width is 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.5 mm or less. .
Further, when the size of the display screen is large, the joint fixing portion around the display screen is narrowed. For this reason, the adhesive sheet for electronic devices of the present invention is suitable for a display device having a large display screen size, for example, a display device having a display screen size of 8 inches or more, more preferably a display device of 9 inches or more, More preferably, it is suitable for a display device of 10 inches or more.

ADVANTAGE OF THE INVENTION According to this invention, even if it is narrow, the adhesive sheet for electronic devices which can maintain high watertightness can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Synthesis 1-7)
(Synthesis of living radical polymerization acrylic polymer)
Tellurium (40 mesh, metal tellurium, manufactured by Aldrich) 6.38 g (50 mmol) was suspended in tetrahydrofuran (THF) 50 mL, and 1.6 mol / L n-butyllithium / hexane solution (Aldrich) 34 was added thereto. 4 mL (55 mmol) was slowly added dropwise at room temperature. The reaction solution was stirred until the metal tellurium disappeared completely. To this reaction solution, 10.7 g (55 mmol) of ethyl-2-bromo-isobutyrate was added at room temperature and stirred for 2 hours. After completion of the reaction, the solvent was concentrated under reduced pressure, followed by distillation under reduced pressure to obtain a yellow oily ethyl 2-methyl-2-n-butylteranyl-propionate.

In a glove box substituted with argon, in a reaction vessel, ethyl 2-methyl-2-n-butylterranyl-propionate and V-60 (2,2′-azobisisobutyronitrile, Wako Pure) The amount (prepared amount) shown in Table 1 was weighed and 1 mL of ethyl acetate was added, and then the reaction vessel was sealed and the reaction vessel was taken out of the glove box. Subsequently, while flowing argon gas into the reaction vessel, the monomers shown in Table 1 (2EHA: 2-ethylhexyl acrylate, BA: butyl acrylate, EA: ethyl acrylate, Aac: acrylic acid, HEA: 2- A total of 100 g of hydroxyethyl acrylate) and 66.5 g of ethyl acetate as a polymerization solvent were added, and a polymerization reaction was performed at 60 ° C. for 20 hours to obtain a living radical polymerization acrylic polymer-containing solution.
The obtained living radical polymerization acrylic polymer was diluted 50-fold with tetrahydrofuran (THF) and the resulting diluted solution was filtered with a filter (material: polytetrafluoroethylene, pore size: 0.2 μm), and the resulting filtrate was obtained. Is supplied to a gel permeation chromatograph (Waters, 2690 Separations Model), GPC measurement is performed under the conditions of a sample flow rate of 1 ml / min and a column temperature of 40 ° C., and the molecular weight of the polymer in terms of polystyrene is measured. Average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined. GPC KF-806L (Showa Denko) was used as the column, and a differential refractometer was used as the detector.

(Synthesis 8, 9)
(Synthesis of free radical polymerization acrylic polymer)
50 g of ethyl acetate was added as a polymerization solvent in the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing nitrogen and refluxing was started. Subsequently, a polymerization initiator solution in which 0.15 g of V-60 (2,2′-azobisisobutyronitrile, manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was diluted 10-fold with ethyl acetate was placed in the reaction vessel. A total of 100 g of the monomers shown in Table 1 was added dropwise over 2 hours. After completion of dropping, a polymerization initiator solution in which 0.15 g of V-60 (2,2′-azobisisobutyronitrile, manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was diluted 10 times with ethyl acetate was added to the reaction vessel. Was added again, and a polymerization reaction was conducted for 4 hours to obtain a free radical polymerization acrylic polymer-containing solution. In the same manner as in Synthesis 1, the weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) were determined.

(Examples 1-9, Comparative Examples 1-7)
(1) Preparation of pressure-sensitive adhesive solution Ethyl acetate was added to the radical-polymerized acrylic polymer-containing solution obtained above. “Coronate L”, manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanate derivative, or “TETRAD-X”, manufactured by Mitsubishi Gas Chemical Co., Inc., tetraglycidyl-m-xylenediamine) and stirred, and adhesive having a nonvolatile content of 30% by weight An agent solution was obtained. The tackifying resin used is shown below.
Pencel D130 (polymerized rosin ester resin, hydroxyl value 45, softening temperature 130 ° C., manufactured by Arakawa Chemical Industries)
KE-359 (hydrogenated rosin ester resin, hydroxyl value 42, softening temperature 100 ° C., manufactured by Arakawa Chemical Industries)
・ Mighty Ace G150 (terpene phenol resin, softening temperature 150 ° C, manufactured by Yasuhara Chemical)
・ YS Polystar T130 (terpene phenol resin, softening temperature 130 ° C, manufactured by Yasuhara Chemical)

(2) Production of Crosslinked Polyolefin Resin Foam Sheet Linear low-density polyethylene obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (exxon chemical company, trade name “EXACT3027”, density 0. 900 g / cm ³ , melting point 98 ° C., softening point 85 ° C.) 100 parts by weight, azodicarbonamide 5 parts by weight as a blowing agent, 2,6-di-t-butyl-p-cresol 0.3 part by weight, and zinc oxide 1 The foamable polyolefin resin composition containing parts by weight was supplied to an extruder, melt-kneaded at 130 ° C., and extruded into a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 0.8 mm.
Next, both sides of the obtained expandable polyolefin resin sheet were irradiated with 5 Mrad of an electron beam having an acceleration voltage of 800 kV to crosslink the expandable polyolefin resin sheet. This foamable polyolefin resin sheet was continuously fed into a foaming furnace maintained at 250 ° C. by hot air and an infrared heater and heated to foam.
After the obtained foamed sheet was continuously fed out from the foaming furnace, the foamed sheet was stretched on the CD at a stretch ratio of 3 while maintaining the temperature of both surfaces at 200 to 250 ° C. At the same time, the foamed sheet was stretched to MD at a stretch ratio of 3 by winding the foamed sheet at a winding speed faster than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the foaming furnace. As a result, the foamed cells were stretched and deformed into CD and MD to obtain a crosslinked polyolefin resin foamed sheet having a width of 1050 mm, a thickness of 0.1 mm, a crosslinking degree of 25% by weight, and an expansion ratio of 4.7 times.

(3) Production of pressure-sensitive adhesive sheet The cross-linked polyolefin resin foamed sheet was coated on both sides of the obtained crosslinked polyolefin resin foamed sheet so that the thickness after drying was 50 μm and dried at 105 ° C. for 5 minutes. A pressure-sensitive adhesive layer having a thickness of 50 μm was laminated and integrated on both surfaces of the sheet to obtain a pressure-sensitive adhesive sheet for electronic devices.
The obtained adhesive sheet was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece. The test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, then taken out from the ethyl acetate and dried at 110 ° C. for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1).
Gel fraction (% by weight) = 100 × (W2-W0) / (W1-W0) (1)
(W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

<Evaluation>
The following evaluation was performed about the adhesive sheet obtained by the Example and the comparative example. The results are shown in Table 2.

(1) Watertightness A1 and watertightness A2
The pressure-sensitive adhesive sheet was punched into a ring shape having an outer diameter of 60 mm and an inner diameter of 50 mm to obtain a ring-shaped test piece A1 having a width of 5 mm. Further, the pressure-sensitive adhesive sheet was punched into a ring shape having an outer diameter of 60 mm and an inner diameter of 55 mm to obtain a ring-shaped test piece A2 having a width of 2.5 mm.
The test piece A1 or the test piece A2 is sandwiched between two parallel acrylic resin plates so that the compression rate of the test piece becomes 10% (that is, the thickness of the test piece after compression is 10% of the thickness before compression). %), The test piece was compressed with two acrylic resin plates in the thickness direction.
One acrylic resin plate of the two acrylic resin plates has a through hole in a portion corresponding to the center portion of the test piece. Through this through hole, the opposing surface of the two acrylic resin plates and the test surface are opened. The space surrounded by the pieces was filled with water. The time until water leakage started in accordance with JIS C0920 IPX7 with a pressure of 10 kPa applied. The evaluation results when using the test piece A1 and the evaluation results when using the test piece A2 are shown in Table 2.

ADVANTAGE OF THE INVENTION According to this invention, even if it is narrow, the adhesive sheet for electronic devices which can maintain high watertightness can be provided.

Claims (2)

A pressure-sensitive adhesive sheet for electronic equipment having a crosslinked polyolefin resin foam sheet and a pressure-sensitive adhesive layer laminated and integrated on at least one surface of the crosslinked polyolefin resin foam sheet,
The pressure-sensitive adhesive layer contains an acrylic polymer having a molecular weight distribution (Mw / Mn) of 1.05 to 2.5 obtained by living radical polymerization, and a rosin-based tackifying resin.
The acrylic polymer has an alcoholic hydroxyl group,
The rosin-based tackifier resin has a hydroxyl value of 25 to 55 and a content of 5 to 40 parts by weight with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive sheet for electronic equipment according to claim 1, wherein the acrylic polymer contains 5 to 30% by weight of an ethyl acrylate component.