JP6411127B2 - Acrylic adhesive and adhesive sheet for electronic devices - Google Patents

Description

The present invention relates to an acrylic pressure-sensitive adhesive having excellent adhesiveness and impact resistance to a hardly adherent adherend. Moreover, this invention relates to the adhesive sheet for electronic devices which has an adhesive layer which consists of this acrylic adhesive.

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 a pressure-sensitive adhesive sheet is required to have various performances including adhesiveness. For example, it is required to have an impact resistance that does not peel off the adherend even when subjected to an impact from the outside.

Patent Document 1 describes that even when a portable electronic device in which a component member is fixed by a double-sided pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer is subjected to an impact by dropping, the component member can be prevented from being broken or damaged. Yes.

In recent years, materials that are difficult to bond with existing adhesives such as oil-repellent or water-repellent coated surfaces have been used for electronic devices in order to improve antifouling properties and emphasize design.
However, in Patent Document 1, no consideration has been given to impact resistance when such an adherend that is difficult to adhere is used.

Patent Document 2 describes a pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer containing a metal chelating agent in order to develop high adhesiveness. There was a problem that power decreased.

JP 2013-121990 A Japanese Patent Laid-Open No. 10-121000

An object of this invention is to provide the acrylic adhesive which has the outstanding adhesiveness with respect to the to-be-adhered adherend, and impact resistance. Moreover, an object of this invention is to provide the adhesive sheet for electronic devices which has an adhesive layer which consists of this acrylic adhesive.

The present invention is an acrylic pressure-sensitive adhesive containing 100 parts by weight of an acrylic copolymer having a molecular weight distribution (Mw / Mn) of 8 to 23 and 15 to 25 parts by weight of a tackifying resin having a softening point of 140 ° C. or less. is there.
The present invention is described in detail below.

The present inventors include an acrylic copolymer having a molecular weight distribution (Mw / Mn) in a specific relatively large range, and an acrylic pressure-sensitive adhesive containing a specific amount of tackifying resin is a low molecular weight acrylic copolymer. Because it contains many components and is easy to flow and deform, it improves adhesion even to difficult-to-adhere adherends and disperses stress when subjected to impact, making it easier to relax and improving impact resistance. As a result, the present invention has been completed.

The acrylic pressure-sensitive adhesive of the present invention contains 100 parts by weight of an acrylic copolymer having a molecular weight distribution (Mw / Mn) of 8 to 23, and 15 to 25 parts by weight of a tackifier resin having a softening point of 140 ° C. or lower. .
By setting it as such a composition, the acrylic adhesive can exhibit the outstanding adhesiveness and impact resistance with respect to the to-be-adhered adherend.

The acrylic copolymer has a molecular weight distribution (Mw / Mn) of 8 to 23.
When the molecular weight distribution (Mw / Mn) of the acrylic copolymer is less than 8, the adhesion of the acrylic pressure-sensitive adhesive to a difficult-to-adhere adherend decreases, and the pressure-sensitive adhesive sheet for electronic equipment using the acrylic pressure-sensitive adhesive Adhesion to a difficult-to-adhere adherend and impact resistance are also reduced. When the molecular weight distribution (Mw / Mn) exceeds 23, not only the adhesive force and cohesive force of the acrylic pressure-sensitive adhesive are reduced, but also the impact resistance is reduced.
The acrylic copolymer has a molecular weight distribution (Mw / Mn) with a preferred lower limit of 10, a preferred upper limit of 20, a more preferred lower limit of 12, and a more preferred upper limit of 18.
The molecular weight distribution (Mw / Mn) is a ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn). The weight average molecular weight (Mw) and the number average molecular weight (Mn) are GPC (Gel Permeation Chromatography). : Gel permeation chromatography) Measured as polystyrene equivalent molecular weight. Specifically, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were obtained by filtering a diluted solution obtained by diluting an acrylic copolymer with tetrahydrofuran (THF) 50 times with a filter, and obtaining the filtrate. Is measured as a polystyrene-equivalent molecular weight by the GPC method. In the GPC method, for example, 2690 Separations Model (manufactured by Water) can be used.

As said acrylic copolymer, the acrylic copolymer obtained by copolymerizing monomer components, such as (meth) acrylic acid ester, (meth) acrylic acid, a vinyl compound, is preferable.
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, 4- (Meth) acrylic acid ester having a hydroxyl group such as hydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) Acrylate, 2-butoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, polypropylene glycol mono (meth) acrylate. These (meth) acrylic acid esters may be used alone or in combination of two or more.

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 order to obtain an acrylic copolymer that satisfies the above molecular weight distribution (Mw / Mn) by copolymerizing the monomer component, the monomer component may be radically reacted in the presence of a polymerization initiator. . Examples of the method of radical reaction of the monomer component, that is, the polymerization method include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like. Among these, solution polymerization is preferable because the molecular weight distribution (Mw / Mn) can be controlled by adjusting the polymerization initiator, the polymerization temperature, and the like.
The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned.
Examples of the organic peroxide include lauroyl peroxide, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, and t-butylperoxypivalate. 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t -Butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate and the like. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether and the like. These reaction solvents may be used alone or in combination of two or more.
When solution polymerization is used as the polymerization method, the polymerization temperature is preferably about 40 to 90 ° C.

The said acrylic copolymer has a preferable minimum of a weight average molecular weight (Mw) of 400,000, and a preferable upper limit is 1 million.
When the weight average molecular weight (Mw) of the acrylic copolymer is less than 400,000, the stickiness of the acrylic pressure-sensitive adhesive becomes too high, and the punching processability may be lowered. When the weight average molecular weight (Mw) of the acrylic copolymer exceeds 1,000,000, the adhesive strength of the acrylic pressure-sensitive adhesive may be reduced, and the impact resistance may be reduced.

The acrylic pressure-sensitive adhesive of the present invention contains 15 to 25 parts by weight of a tackifier resin having a softening point of 140 ° C. or lower.
When the content of the tackifying resin is less than 15 parts by weight, the acrylic pressure-sensitive adhesive easily peels off from the adherend when a strong impact is applied to the bonding surface. When the content of the tackifying resin exceeds 25 parts by weight, the adhesive strength of the acrylic pressure-sensitive adhesive becomes too strong, so that not only the adhesion to difficult-to-adhere adherends is lowered, but also a polyolefin foam or the like is used as a base material. When it is used for the PSA sheet, it becomes difficult to re-paste, and the handleability is lowered. A preferable lower limit of the content of the tackifier resin is 18 parts by weight, a more preferable lower limit is 20 parts by weight, and a preferable upper limit is 24 parts by weight.

The softening point of the tackifying resin is 140 ° C. or lower.
When the softening point of the tackifying resin exceeds 140 ° C., the acrylic pressure-sensitive adhesive becomes too hard, the adhesion to a difficult-to-adhere adherend decreases, and the impact resistance also decreases.
A preferable upper limit of the softening point of the tackifying resin is 135 ° C, and a more preferable upper limit is 130 ° C.
Although the minimum of the softening point of the said tackifying resin is not specifically limited, A preferable minimum is 75 degreeC.
Moreover, in the range which does not impair the function of this invention, the softening point may contain tackifying resin 140 degreeC or more.
The softening point is a softening point measured by the JIS K2207 ring and ball method.

Examples of the tackifying resin include a polymerized rosin resin, a rosin ester resin, a hydrogenated rosin resin, a terpene resin, a terpene phenol resin, a coumarone indene resin, an alicyclic saturated hydrocarbon resin, and a C5 resin. Petroleum resin, C9 petroleum resin, C5-C9 copolymer petroleum resin and the like can be mentioned. These tackifying resins may be used alone or in combination of two or more.
Among these, the tackifying resin is a mixture of two types of tackifying resins including a polymerized rosin resin and a rosin ester resin, a polymerized rosin resin, a terpene phenol resin, and a rosin ester resin. It is preferable that it is a mixture of 3 types of tackifying resin to contain.

An electronic device pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one surface of a base material that is a polyolefin foam, wherein the pressure-sensitive adhesive layer is made of the acrylic pressure-sensitive adhesive of the present invention. One.
The pressure-sensitive adhesive sheet for electronic equipment of the present invention may be a single-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on only one surface of the substrate, or a double-sided pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers on both sides of the substrate. May be.

In the pressure-sensitive adhesive layer, a crosslinking structure may be formed between main chains of the resin (the acrylic copolymer and / or the tackifying resin) constituting the pressure-sensitive adhesive layer by adding a crosslinking agent. preferable.
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 etc. are mentioned. Of these, isocyanate-based crosslinking agents are preferred. By adding an isocyanate-based crosslinking agent to the pressure-sensitive adhesive layer, the isocyanate group of the isocyanate-based crosslinking agent reacts with the alcoholic hydroxyl group in the resin constituting the pressure-sensitive adhesive layer, thereby cross-linking the pressure-sensitive adhesive layer. It becomes loose. Therefore, the pressure-sensitive adhesive layer can disperse the peeling stress applied intermittently, and has a resistance to peeling from the adherend against the peeling stress caused by the deformation of the adherend when a strong impact is applied. More improved.
The addition amount of the crosslinking agent is preferably 0.01 to 10 parts by weight and more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the acrylic copolymer.

Even if the degree of cross-linking (gel fraction) of the pressure-sensitive adhesive layer is too high or too low, the pressure-sensitive adhesive layer can be easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. Therefore, 5 to 50% by weight is preferable, 10 to 40% by weight is more preferable, and 15 to 35% by weight is still more preferable.
The degree of cross-linking (gel fraction) of the pressure-sensitive adhesive layer was determined by collecting W1 (g) of the pressure-sensitive adhesive layer and immersing this pressure-sensitive adhesive layer in ethyl acetate at 23 ° C. for 24 hours to give an insoluble content of 200 mesh. The residue on the wire mesh is vacuum-dried, and the weight W2 (g) of the dry residue is measured and calculated by the following formula (1).
Cross-linking degree (gel fraction) (% by weight) = 100 × W2 / W1 (1)

Although the thickness of the said adhesive layer is not specifically limited, It is preferable that the thickness (thickness of the adhesive layer of one side) of an adhesive layer is 1-150 micrometers. When the thickness is less than 1 μm, the pressure-sensitive adhesive layer may have a reduced impact resistance. When the thickness exceeds 150 μm, the pressure-sensitive adhesive layer may have impaired reworkability or removability. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 10 μm, the more preferable upper limit is 100 μm, and the still more preferable upper limit is 50 μm.

Since the polyolefin foam has buffering properties, the impact resistance of the pressure-sensitive adhesive sheet for electronic devices can be enhanced.

The polyolefin foam is not particularly limited as long as it is a foam containing a polyolefin resin, and examples thereof include a polyethylene foam, a polypropylene foam, an ethylene-propylene foam, and the impact resistance is improved. Therefore, 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 the present specification) is preferable. 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 polyolefin foam is preferably cross-linked. By cross-linking the polyolefin foam, impact resistance can be improved.
The method for crosslinking the polyolefin foam is not particularly limited. For example, a method of irradiating the polyolefin foam with ionizing radiation such as electron beam, α ray, β ray, γ ray, Examples include a method of decomposing the organic peroxide by heating.

The method for producing the polyolefin foam is not particularly limited, but a foamable resin composition containing a polyolefin resin and a foaming agent is prepared, and the foamable resin composition is extruded into a sheet using an extruder. In this case, it is preferable to foam the foaming agent and crosslink the obtained polyolefin foam as necessary.

Although the thickness of the said base material is not specifically limited, 50-300 micrometers is preferable. When the thickness of the base material is less than 50 μm, the punching workability or mechanical strength of the pressure-sensitive adhesive sheet for electronic equipment may be lowered. If the thickness of the substrate exceeds 300 μm, the pressure-sensitive adhesive sheet for electronic equipment becomes too strong, and it may be difficult to adhere and adhere together along the shape of the adherend. The more preferable lower limit of the thickness of the substrate is 100 μm, the more preferable upper limit is 250 μm, the still more preferable lower limit is 120 μm, the still more preferable upper limit is 200 μm, and the particularly preferable upper limit is 150 μm.

The method for producing the pressure-sensitive adhesive sheet for electronic equipment of the present invention is not particularly limited. For example, the acrylic copolymer and the tackifier resin are mixed together with other compounding components such as the crosslinking agent as necessary, Stir to prepare a pressure-sensitive adhesive solution, and subsequently apply this pressure-sensitive adhesive solution to a release-treated PET film, dry it to form a pressure-sensitive adhesive layer, and transfer this pressure-sensitive adhesive layer to a substrate. Methods and the like. Further, the pressure-sensitive adhesive layer may be transferred onto the opposite surface of the substrate in the same manner.

Applications of the acrylic pressure-sensitive adhesive and the pressure-sensitive adhesive sheet for electronic devices of the present invention are not particularly limited, but the acrylic pressure-sensitive adhesive and the pressure-sensitive adhesive sheet for electronic devices are used for assembling electronic devices (for example, mobile phones, portable information terminals, etc.) equipped with image display devices or input devices. Is preferred. Specifically, for example, it is preferably used for bonding a cover panel for protecting the surface of the electronic device to the touch panel module or the display panel module, or bonding the touch panel module and the display panel module. In particular, the acrylic pressure-sensitive adhesive and electronic device pressure-sensitive adhesive sheet of the present invention can be suitably used for bonding hardly adherends.
The “hardly adherent adherend” refers to an adherend whose material is a nonpolar resin or an adherend whose surface has been subjected to a nonpolar surface treatment. Or the material by which fluorine coating etc. were carried out for water repellency, or polyethylene, a polypropylene, etc. are mentioned.
Moreover, the shape of the adhesive sheet for electronic devices of the present invention in these applications is not particularly limited and may be a rectangle or the like, but a frame shape is preferable.

ADVANTAGE OF THE INVENTION According to this invention, the acrylic adhesive which has the outstanding adhesiveness with respect to the to-be-adhered to-be-adhered body, and impact resistance can be provided. Moreover, according to this invention, the adhesive sheet for electronic devices which has an adhesive layer which consists of this acrylic adhesive can be provided.

It is a schematic diagram of the test method of the holding test of the double-sided adhesive sheet obtained by the Example and the comparative example.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

( Comparative Example 9 )
(1) Preparation of pressure-sensitive adhesive solution In a reactor equipped with a thermometer, a stirrer and a condenser, the monomers shown in Table 1 and ethyl acetate as a reaction solvent were added, and the reactor was heated to start refluxing. Subsequently, 0.1 parts by weight of lauroyl peroxide as a polymerization initiator was added to the reactor, and then refluxed at 70 ° C. for 5 hours to conduct a polymerization reaction, thereby obtaining an acrylic copolymer solution. A diluted sample obtained by diluting the obtained acrylic copolymer 50 times with tetrahydrofuran (THF) was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. This measurement sample is supplied to a gel permeation chromatograph (manufactured by Water, 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 polystyrene equivalent molecular weight of the acrylic copolymer is measured. Were measured to determine the weight average molecular weight and the molecular weight distribution (Mw / Mn). GPC LF-804 (manufactured by Showa Denko) was used as the column, and a differential refractometer was used as the detector.

To the obtained acrylic copolymer solution, a predetermined amount of polymerized rosin resin, terpene phenol resin and rosin ester resin shown in the table with respect to 100 parts by weight of the nonvolatile content are added, and ethyl acetate is added and stirred. A predetermined amount of an isocyanate-based cross-linking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., Coronate L45) was added and stirred to obtain a pressure-sensitive adhesive solution having a nonvolatile content of 30% by weight. In the table, the amount of the crosslinking agent indicates the weight part of the non-volatile content of the crosslinking agent. The polymerized rosin resin, terpene phenol resin and rosin ester resin used are shown below.
Polymerized rosin resin Softening point: 160 ° C. (Arakawa Chemical Industries, Pencel D-160)
Polymerized rosin resin Softening point: 135 ° C. (Arakawa Chemical Industries, Pencel D-135)
Terpene phenol resin Softening point: 160 ° C. (Yasuhara Chemical Co., Ltd., YS Polyster T-160)
-Terpene phenol resin Softening point: 130 ° C. (Yasuhara Chemical Co., Ltd., YS Polyster T-130)
-Terpene phenol resin Softening point: 100 ° C. (YShara Chemical Co., Ltd., YS Polyster T-100)
・ Rosin ester resin Softening point: 75 ° C. (Arakawa Chemical Industries, Super Ester A-75)
・ Rosin ester resin Softening point: 100 ° C. (Arakawa Chemical Industries, Super Ester A-100)
・ Rosin ester resin Softening point: 125 ° C. (Arakawa Chemical Industries, Super Ester A-125)

(2) Production of pressure-sensitive adhesive sheet The obtained pressure-sensitive adhesive solution was applied to the surface of a crosslinked metallocene polyethylene foam having a thickness of 140 μm and dried at 100 ° C. for 5 minutes to form a pressure-sensitive adhesive layer having a thickness of 30 μm. A PET film having a thickness of 50 μm subjected to a release treatment was bonded to the surface of the formed pressure-sensitive adhesive layer.
Next, a PET film having a thickness of 50 μm, which has been subjected to another release treatment, is prepared, an adhesive solution is applied to the release treatment surface of this PET film, and dried at 100 ° C. for 5 minutes. An agent layer was formed. This pressure-sensitive adhesive layer was bonded to the surface of a crosslinked metallocene polyethylene foam. This obtained the double-sided adhesive sheet covered with the 50-micrometer-thick PET film by which the mold release process was performed.
In addition, W1 (g) was collected for the formed pressure-sensitive adhesive layer, this pressure-sensitive adhesive layer was immersed in ethyl acetate at 23 ° C. for 24 hours, and the insoluble matter was filtered through a 200-mesh wire mesh. Was dried in vacuo, the weight W2 (g) of the dry residue was measured, and the degree of crosslinking (gel fraction) of the pressure-sensitive adhesive layer was calculated from the following formula (1).
Cross-linking degree (gel fraction) (% by weight) = 100 × W2 / W1 (1)

( Examples 3 and 4, Comparative Examples 1 to 8, 10, and 11 )
A double-sided PSA sheet was obtained in the same manner as Comparative Example 9 except that the types and amounts of the monomer and tackifying resin were changed as described in Table 1. In Comparative Example 8, 0.35 parts by weight of a metal chelate curing agent (manufactured by Kawaken Fine Chemical Co., Ltd., aluminum chelate A) was used as the metal chelate in terms of solid content.

(Evaluation)
The following evaluation was performed with respect to the double-sided pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples. The evaluation results are shown in Table 1.

(1) Retention test <Test method>
The obtained double-sided pressure-sensitive adhesive sheet was cut into a strip having a width of 25 mm to prepare a test piece, and one release film was peeled and removed to expose the pressure-sensitive adhesive layer. After placing the test piece on the polycarbonate resin plate so that the pressure-sensitive adhesive layer faces the polycarbonate resin plate, a 2 kg rubber roller was placed on the test piece at a speed of 300 mm / min under the condition of 23 ° C. By reciprocating once, the test piece and the polycarbonate resin plate were bonded together to produce a test sample. At this time, as shown in FIG. 1, the area where the test piece 1 and the polycarbonate resin plate 2 overlap is set to 25 mm × 25 mm, and then, as shown in FIG. A load 3 of 1 kg was applied, and the sample was left for 3 hours under the condition of 85 ° C., and the distance that the test piece was displaced was measured.

<Test judgment>
A: The distance by which the test piece is displaced is 1 mm or less.
X: The distance which the test piece shifted | deviated exceeds 1 mm.

(2) Impact resistance test <Test method>
The obtained double-sided pressure-sensitive adhesive sheet was punched out into a frame shape with an outer dimension of 46 × 61 mm and a width of 1 mm with a Thomson blade, a test piece was prepared, one release film was peeled and removed, and an outer dimension of 55 × 65 mm and a thickness of 1 mm of polyethylene It bonded together to the board (The Tamapoly company make, PE board below) using the roller. Subsequently, the other release film was peeled and removed, and a PE plate having an outer dimension of 80 × 115 mm and a thickness of 2 mm provided with an opening of 38 × 50 mm in the central portion, the center of the opening of the PE plate and the test piece Gently place it so that it almost coincides with the center, put a 5 kg weight from the top for 10 seconds, paste the two PE plates together, and then let it stand at 23 ° C for 24 hours to perform adhesion curing and prepare a test sample did. Set this test sample on the fixing jig so that the PE plate with the opening becomes the upper surface, and drop a 300g weight through the opening to the PE plate on the lower surface from the drop height of 5cm, and apply an impact. It was. When peeling was not recognized, the drop height was raised in steps of 5 cm, impact was applied again, and the drop height at which peeling was recognized was measured. The measurement was performed at 23 ° C.

<Test judgment>
A: The drop height was 85 cm or more.
○: The fall height was 70 cm or more.
X: The fall height was less than 70 cm.

ADVANTAGE OF THE INVENTION According to this invention, the acrylic adhesive which has the outstanding adhesiveness with respect to the to-be-adhered to-be-adhered body, and impact resistance can be provided. Moreover, according to this invention, the adhesive sheet for electronic devices which has an adhesive layer which consists of this acrylic adhesive can be provided.

1 Test piece 2 Polycarbonate resin plate (PC plate)
3 Weight (1kg)

Claims (8)

100 parts by weight of an acrylic copolymer having a weight average molecular weight (Mw) of 730,000 or more and a molecular weight distribution (Mw / Mn) of 8 to 23, and a tackifying resin having a softening point of 75 ° C or higher and 140 ° C or lower An acrylic pressure-sensitive adhesive containing 24 parts by weight and containing no metal chelate,
The acrylic copolymer is an acrylic copolymer obtained by copolymerizing a monomer component containing methyl acrylate ,
The acrylic pressure-sensitive adhesive characterized in that the tackifying resin having a softening point of 75 ° C. or higher and 140 ° C. or lower contains at least a polymerized rosin resin and a rosin ester resin. The acrylic pressure-sensitive adhesive according to claim 1, wherein the acrylic copolymer has a molecular weight distribution (Mw / Mn) of 8 to 23. The acrylic adhesive according to claim 1 or 2, wherein the acrylic copolymer has a weight average molecular weight (Mw) of 1,000,000 or less. The acrylic pressure-sensitive adhesive according to claim 1, 2 or 3, wherein the tackifying resin comprises a polymerized rosin resin, a terpene phenol resin, and a rosin ester resin. A pressure-sensitive adhesive sheet for electronic equipment having a pressure-sensitive adhesive layer on at least one side of a base material that is a polyolefin foam, wherein the pressure-sensitive adhesive layer comprises the acrylic pressure-sensitive adhesive according to claim 1, 2, 3, or 4. Adhesive sheet for electronic equipment. 6. The pressure-sensitive adhesive sheet for electronic equipment according to claim 5, wherein the pressure-sensitive adhesive layer has a gel fraction of 5 to 50% by weight. The adhesive sheet for electronic devices according to claim 5 or 6, wherein the adhesive layer has a thickness of 1 to 150 µm. The pressure-sensitive adhesive sheet for electronic equipment according to claim 5, 6 or 7, wherein the thickness of the substrate is 50 to 300 µm.

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