JPWO2015037378A1 - Adhesive sheet for electronic equipment - Google Patents

Abstract

An object of the present invention is to provide a pressure-sensitive adhesive sheet for electronic equipment that has high impact resistance adhesion, is not easily displaced even when a load is applied in the shear direction, and has excellent resilience. The present invention has an adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of a tackifying resin having a softening point of 110 ° C. or less and an alcoholic hydroxyl value of 30 or more, The acrylic copolymer comprises (a) 2-ethylhexyl acrylate 24.7 to 58.98% by weight, (b) butyl acrylate 30 to 50% by weight, (c) methyl acrylate 10 to 20% by weight, and (d) acrylic. It is obtained by copolymerizing a mixed monomer containing 1 to 5% by weight of acid and (e) 0.02 to 0.3% by weight of (meth) acrylate having a hydroxyl group, and has a weight average molecular weight (Mw) of 800,000. That is the above, and the pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet for electronic equipment that is crosslinked to a gel fraction of 20 to 50% by a crosslinking agent.

Description

The present invention relates to a pressure-sensitive adhesive sheet for electronic equipment that has high impact resistance adhesion, is not easily displaced even when a load is applied in the shear direction, and has excellent resilience.

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 impact-resistant adhesive that does not peel from the adherend even when subjected to an impact from the outside.

Examples of a method for improving the impact resistance adhesion of the pressure-sensitive adhesive sheet include a method using a buffering base material such as a foam. Patent Documents 1 and 2 describe a pressure-sensitive adhesive sheet for electronic equipment, which includes a crosslinked polyolefin resin foam sheet and a specific acrylic pressure-sensitive adhesive layer laminated and integrated on one surface of the cross-linked polyolefin resin foam sheet. Yes.

However, in recent years, with the enlargement of screens of electronic devices and diversification of designs, there is a demand for pressure-sensitive adhesive sheets that can be processed more finely as pressure-sensitive adhesive sheets used for assembly. However, the pressure-sensitive adhesive sheet having a foam as a base material has a problem that it is easily displaced when a load is applied in the shearing direction during processing. Moreover, there also existed a problem that it was inferior in resilience resistance.
Examples of the base material excellent in resilience resistance include a polyethylene terephthalate (PET) film, but when a base material having a low buffering property such as a PET film is used, a foam is used. It was difficult to develop high impact resistance adhesion.

JP 2010-215906 A JP 2011-168727 A

An object of the present invention is to provide a pressure-sensitive adhesive sheet for electronic equipment that has high impact resistance adhesion, is not easily displaced even when a load is applied in the shear direction, and has excellent resilience.

The present invention has an adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of a tackifying resin having a softening point of 110 ° C. or less and an alcoholic hydroxyl value of 30 or more, The acrylic copolymer comprises (a) 2-ethylhexyl acrylate 24.7 to 58.98% by weight, (b) butyl acrylate 30 to 50% by weight, (c) methyl acrylate 10 to 20% by weight, and (d) acrylic. It is obtained by copolymerizing a mixed monomer containing 1 to 5% by weight of acid and (e) 0.02 to 0.3% by weight of (meth) acrylate having a hydroxyl group, and has a weight average molecular weight (Mw) of 800,000. That is the above, and the pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet for electronic equipment that is crosslinked to a gel fraction of 20 to 50% by a crosslinking agent.
The present invention is described in detail below.

The present inventor includes a specific acrylic copolymer and a specific tackifying resin, and the pressure-sensitive adhesive sheet for electronic equipment has a pressure-sensitive adhesive layer that is cross-linked to a gel fraction in a specific range by a cross-linking agent. It has been found that high impact-resistant adhesiveness can be exhibited even when a base material having a low buffering property such as a PET film is used instead of a base material having a buffering property such as a foam. Furthermore, the present inventor does not need to use a foam, and the pressure-sensitive adhesive layer has an appropriate hardness, cohesive force, adhesive strength, etc. It has been found that even when a load is applied in the shear direction, it is difficult to shift and has excellent resilience, and the present invention has been completed.

The pressure-sensitive adhesive sheet for electronic equipment according to the present invention is a pressure-sensitive adhesive containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of a tackifying resin having a softening point of 110 ° C. or lower and an alcoholic hydroxyl value of 30 or higher. It has an agent layer.
The acrylic copolymer comprises (a) 2-ethylhexyl acrylate 24.7 to 58.98% by weight, (b) butyl acrylate 30 to 50% by weight, (c) methyl acrylate 10 to 20% by weight, and (d) acrylic. It is obtained by copolymerizing a mixed monomer containing 1 to 5% by weight of an acid and (e) 0.02 to 0.3% by weight of a (meth) acrylate having a hydroxyl group.

When the amount of 2-ethylhexyl acrylate (a) is less than 24.7% by weight, the adhesive strength of the pressure-sensitive adhesive layer is reduced, and impact resistance is reduced. When the amount of 2-ethylhexyl acrylate in (a) exceeds 58.98% by weight, the pressure-sensitive adhesive layer becomes too soft due to a decrease in glass transition temperature (Tg), and tends to shift when a load is applied in the shear direction. .

When the amount of butyl acrylate (b) is less than 30% by weight, the pressure-sensitive adhesive layer becomes too soft and easily shifts when a load is applied in the shear direction. When the amount of butyl acrylate (b) exceeds 50% by weight, the pressure-sensitive adhesive layer becomes too hard, and impact resistance adhesion is lowered.

When the methyl acrylate of (c) is less than 10% by weight, the impact resistance adhesiveness of the pressure-sensitive adhesive layer is lowered. It is estimated that by copolymerizing 10% by weight or more of the methyl acrylate of (c) above, the side chain of the acrylic copolymer is reduced, thereby improving the linearity of the molecular chain and increasing the entanglement of the molecular chain. The For this reason, when the pressure-sensitive adhesive layer is deformed by receiving an impact, it is presumed that the energy absorption due to the entanglement of molecular chains is increased, and the impact resistance adhesion is improved.
In addition, since the cross-linked structure of the molecular chain is deformed mainly by elastic deformation, it is difficult to convert impact stress into fluid deformation energy, and it is difficult to absorb and disperse. For this reason, the impact stress is stored as elastic energy in the cross-linked structure, the stress dispersibility at the interface with the adherend is lowered, and the impact resistance adhesion is lowered. On the other hand, the entangled structure of molecular chains is different from the crosslinked structure, and can be plastically deformed, and can absorb and disperse by converting impact stress into energy of flow deformation. For this reason, it is thought that the increase in a certain amount of entanglement leads to an improvement in impact resistance adhesion.
When the methyl acrylate of the above (c) exceeds 20% by weight, the pressure-sensitive adhesive layer becomes too hard due to an increase in the glass transition temperature (Tg), and impact resistance adhesion is lowered.

When the acrylic acid (d) is less than 1% by weight, the adhesive strength of the pressure-sensitive adhesive layer is lowered. When the acrylic acid of (d) exceeds 5% by weight, the pressure-sensitive adhesive layer becomes too hard due to an increase in the glass transition temperature (Tg), and impact resistance adhesion is lowered.

The (e) hydroxyl group-containing (meth) acrylate is a component that is cross-linked by an isocyanate-based cross-linking agent described later. By copolymerizing the (meth) acrylate having a hydroxyl group (e) above in an amount of 0.02 to 0.3% by weight, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive layer to a specific range, and impact resistance is improved. The pressure-sensitive adhesive layer is high and is difficult to shift even when a load is applied in the shear direction.
When the (meth) acrylate having a hydroxyl group of (e) is less than 0.02% by weight, the pressure-sensitive adhesive layer becomes too soft and is easily displaced when a load is applied in the shear direction. When the (meth) acrylate having a hydroxyl group of (e) exceeds 0.3% by weight, the cross-linking density of the pressure-sensitive adhesive layer is increased, and the plastic deformation is reduced and elastic deformation is mainly performed. Adhesiveness decreases.
Examples of the (meth) acrylate having a hydroxyl group (e) include 2-hydroxyethyl (meth) acrylate and 2-hydroxybutyl (meth) acrylate.

In addition to the monomers (a) to (e), the mixed monomer may contain other vinyl monomers copolymerizable with the monomers (a) to (e) as necessary.

In order to copolymerize the mixed monomer to obtain the acrylic copolymer, the mixed monomer may be radically reacted in the presence of a polymerization initiator. A conventionally known method is used as a method of radically reacting the mixed monomer, that is, a polymerization method, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization 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 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5 -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. 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.

The acrylic copolymer has a weight average molecular weight (Mw) of 800,000 or more. When the weight average molecular weight (Mw) of the acrylic copolymer is less than 800,000, the pressure-sensitive adhesive layer becomes too soft and easily shifts when a load is applied in the shear direction.
The upper limit of the weight average molecular weight (Mw) of the acrylic copolymer is not particularly limited, but is preferably 1.5 million or less. If the weight average molecular weight (Mw) of the acrylic copolymer exceeds 1,500,000, the adhesive strength of the pressure-sensitive adhesive layer decreases, and it may be difficult to achieve both impact resistance and other performances.
In addition, a weight average molecular weight (Mw) is measured as a polystyrene conversion molecular weight by GPC (Gel Permeation Chromatography: gel permeation chromatography) method. Specifically, the weight average molecular weight (Mw) is obtained by filtering a diluted solution obtained by diluting an acrylic copolymer with tetrahydrofuran (THF) 50 times with a filter, and using the obtained filtrate, polystyrene by GPC method. It is measured as a converted molecular weight. In the GPC method, for example, 2690 Separations Model (manufactured by Waters) or the like can be used.

The weight average molecular weight (Mw) of the acrylic copolymer can be adjusted by appropriately adjusting the polymerization conditions (for example, the type or amount of the polymerization initiator, the polymerization temperature, the monomer concentration, etc.).

By adding 20 to 35 parts by weight of a tackifier resin having a softening point of 110 ° C. or less and an alcoholic hydroxyl value of 30 or more to 100 parts by weight of the acrylic copolymer, Adhesive strength increases, impact resistance adhesion improves.
When the softening point of the tackifying resin exceeds 110 ° C., the pressure-sensitive adhesive layer becomes too hard, and impact resistance adhesiveness decreases.
The softening point is a softening point measured by the JIS K2207 ring and ball method.

When the alcoholic hydroxyl value of the tackifying resin is less than 30, the pressure-sensitive adhesive layer is lifted from the adhesive surface when used in an environment where a strong repulsive force is applied, and so-called repulsion resistance is lowered.
The “alcoholic hydroxyl value” means a hydroxyl value based on an alcoholic hydroxyl group. Accordingly, hydroxyl values based on phenolic hydroxyl groups are excluded.
The hydroxyl value can be measured by JIS K1557 (phthalic anhydride method). When the tackifying resin used does not contain a phenolic hydroxyl group but contains only an alcoholic hydroxyl group, the measured hydroxyl value itself becomes the “alcoholic hydroxyl value”. On the other hand, when a phenol skeleton is present in the tackifying resin to be used, the average functional group number of the phenolic hydroxyl group and the average functional group number of the alcoholic hydroxyl group contained in one molecule of the tackifying resin are calculated, and one molecule The ratio of the alcoholic hydroxyl group contained in the solution is obtained, and the hydroxyl value of the tackifying resin measured separately is multiplied by the ratio of the alcoholic hydroxyl group contained in one molecule to obtain the hydroxyl value based on the alcoholic hydroxyl group. .

When the tackifying resin is less than 20 parts by weight, the pressure-sensitive adhesive strength of the pressure-sensitive adhesive layer is reduced, and impact resistance adhesiveness is reduced. When the tackifying resin having a softening point of 110 ° C. or lower and an alcoholic hydroxyl value of 30 or higher exceeds 35 parts by weight, the pressure-sensitive adhesive layer becomes too hard due to an increase in the glass transition temperature (Tg), resulting in resistance to resistance. Impact adhesion decreases.

The tackifying resin is not particularly limited as long as it has a softening point of 110 ° C. or less and an alcoholic hydroxyl value of 30 or more, but a rosin ester-based tackifying resin such as a hydrogenated rosin ester resin is preferable.

The pressure-sensitive adhesive layer is crosslinked to a gel fraction of 20 to 50% by a crosslinking agent.
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 a base material, 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).
0.1-6 weight part is preferable with respect to 100 weight part of said acrylic copolymers, and, as for the compounding quantity of the said crosslinking agent, 0.3-5 weight part is more preferable.

When the gel fraction of the pressure-sensitive adhesive layer is less than 20%, the pressure-sensitive adhesive layer becomes too soft and easily shifts when a load is applied in the shear direction. When the gel fraction of the pressure-sensitive adhesive layer exceeds 50%, the cross-linking density of the pressure-sensitive adhesive layer becomes high, the plastic deformability is lowered and the elastic deformation is the main component, so that the impact resistance adhesion is lowered.
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. After the test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate. , And dried at 110 ° C. for 1 hour. 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 × (W ₂ −W ₀ ) / (W ₁ −W ₀ ) (1)
(W ₀ : weight of substrate, W ₁ : weight of test piece before immersion, W ₂ : weight of test piece after immersion and drying)

As a method for obtaining a pressure-sensitive adhesive layer that has been crosslinked to the above-mentioned gel fraction by the above-mentioned cross-linking agent, the above-mentioned cross-linking agent is added to form a cross-linked structure between the main chains of the resin constituting the pressure-sensitive adhesive layer. The method is preferred. By appropriately adjusting the type or amount of the cross-linking agent, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive layer to the above range, high impact adhesiveness, and even when a load is applied in the shear direction, it is difficult to slip. It can be used as an agent layer.

The pressure-sensitive adhesive layer may contain plasticizers, emulsifiers, softeners, fillers, additives such as pigments and dyes, and other resins such as rosin resins, if necessary.

The pressure-sensitive adhesive layer preferably has a tan δ peak frequency in a dynamic viscoelasticity master curve at a reference temperature of 25 ° C. of 800 to 10,000 Hz. When the frequency of the tan δ peak is 800 to 10000 Hz, the pressure-sensitive adhesive layer can be provided with an appropriate hardness, and sufficient impact resistance adhesiveness can be obtained. A more preferable lower limit of the frequency of the tan δ peak is 900 Hz, and a more preferable upper limit is 5000 Hz.
The frequency of the tan δ peak in the dynamic viscoelastic master curve is determined using a master curve measurement program (measurement mode: shearing method) of a dynamic viscoelasticity measuring apparatus (for example, DVA-200, manufactured by IT Measurement Control Co., Ltd.). Calculated from the measured master curve.

Although the thickness of the said adhesive layer is not specifically limited, 50-150 micrometers is preferable. If the thickness of the pressure-sensitive adhesive layer is less than 50 μm, impact resistance adhesion may be deteriorated. When the thickness of the pressure-sensitive adhesive layer exceeds 150 μm, it may be easily displaced when a load is applied in the shear direction, or the resilience resistance may be reduced.

The pressure-sensitive adhesive sheet for electronic equipment of the present invention may be a non-support type that does not have a base material, or a support type that has a base material. In the case of a support type, it is preferable that the said adhesive layer is formed on both surfaces of a base material.
The pressure-sensitive adhesive sheet for electronic equipment of the present invention contains a specific acrylic copolymer and a specific tackifying resin as described above, and these are cross-linked to a specific range of gel fraction by a cross-linking agent. Therefore, even if it is not a buffering base material such as a foam but a base material having a low buffering property such as a PET film, high impact adhesiveness can be exhibited. Furthermore, the pressure-sensitive adhesive sheet for electronic devices according to the present invention does not require the use of a foam, and the pressure-sensitive adhesive layer has an appropriate hardness, cohesive force, adhesive force, etc., so that even when a load is applied in the shear direction, Difficult and excellent in resilience.

The substrate is not particularly limited, but is preferably not a foam. For example, a polyolefin resin film such as a polyethylene film or a polypropylene film, a polyester resin film such as a PET film, an ethylene-vinyl acetate copolymer film, a poly Examples thereof include a vinyl chloride resin film and a polyurethane resin film. Among these, a polyester resin film is preferable because the pressure-sensitive adhesive sheet is not easily displaced even when a load is applied in the shear direction, and is excellent in resilience resistance.
Further, a black-printed base material for preventing light transmission, a white-printed base material for improving light reflectivity, a metal-deposited base material, and the like can also be used.

Although the thickness of the said base material is not specifically limited, 20-100 micrometers is preferable and 25-75 micrometers is more preferable. When the thickness of the substrate is less than 20 μm, the resilience resistance or mechanical strength of the electronic device pressure-sensitive adhesive sheet may be lowered. When the thickness of the base material exceeds 100 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 shear deviation length of the electronic device pressure-sensitive adhesive sheet of the present invention is preferably 300 μm or less. When the shear deviation length is 300 μm or less, the pressure-sensitive adhesive layer can be given an appropriate hardness, and punching workability can be easily improved while maintaining sufficient impact resistance adhesion. The shear deviation length is more preferably 180 μm or less, and further preferably 150 μm or less.
The shear deviation length is measured as follows. In FIG. 2, the schematic diagram which shows the evaluation method of the shear shift | offset | difference length of the adhesive sheet for electronic devices (double-sided adhesive sheet) is shown. The electronic device pressure-sensitive adhesive sheet is cut into a flat rectangular shape having a length of 5 mm and a width of 20 mm to produce a test piece, and the release films on both sides are peeled and removed (referred to as test piece B). As shown in FIG. 2, a PET film C having a thickness of 25 μm is formed on the adhesive layer on the upper surface of the test piece B, and a metal base D (manufactured by SUS) having a length of 100 mm and a width of 20 mm is formed on the adhesive layer on the lower surface. A test sample is prepared by pasting each of them. A 200 g load is applied in the horizontal direction (arrow direction) to the PET film C on the upper surface of the test sample by a weight E and pulled for 3 minutes. The measurement is performed at 23 ° C. Thereafter, one end (fixing jig) of the pressure-sensitive adhesive layer bonded to the PET film C on the upper surface with reference to the position of one end (end on the fixing jig side) of the pressure-sensitive adhesive layer bonded to the metal base D on the lower surface. The distance L in which the side edge) is displaced in the pulling direction of the PET film C on the upper surface is measured and is defined as the shear displacement length.

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 tackifying resin having a softening point of 110 ° C. or lower and an alcoholic hydroxyl value of 30 or higher. , Mixed with the above-mentioned cross-linking agent and other ingredients as necessary, and stirred to prepare a pressure-sensitive adhesive solution. Subsequently, the pressure-sensitive adhesive solution was applied to a release-treated PET film and dried. Examples include a method of forming an adhesive layer and transferring the adhesive layer to a substrate. Further, the pressure-sensitive adhesive layer may be transferred onto the opposite surface of the substrate in the same manner.

Although the use of the adhesive sheet for electronic devices of the present invention is not particularly limited, it is preferably used for assembling an electronic device (for example, a mobile phone, a portable information terminal, etc.) equipped with an image display device or an input device. 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. Furthermore, the adhesive sheet for electronic devices of the present invention may be used for bonding a film with a metal thin film to a support (PET film or the like) or the like in a touch panel module.
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.

In FIG. 1, the schematic diagram which shows the electronic device which bonded the cover panel on the surface of the touch panel module using the adhesive sheet for electronic devices of this invention is shown. In the electronic device 1 shown in FIG. 1, a cover panel 3 is bonded to the surface of the touch panel module 4 by an electronic device pressure-sensitive adhesive sheet 2 punched into a frame shape.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive sheet for electronic devices which is high in impact-resistant adhesiveness, cannot be easily shifted even when a load is applied in the shearing direction, and is excellent in resilience can be provided.

It is a schematic diagram which shows the electronic device which bonded the cover panel on the surface of the touch panel module using the adhesive sheet for electronic devices of this invention. It is a schematic diagram which shows the evaluation method of the shear shift | offset | difference length of the adhesive sheet for electronic devices (double-sided adhesive sheet). It is a schematic diagram which shows the evaluation method of the resilience resistance of the adhesive sheet for electronic devices (double-sided adhesive sheet).

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.

(Examples 1-19 and Comparative Examples 1-20)
(1) Preparation of acrylic copolymer (1-1) A predetermined amount of a reaction solvent shown in the table was added to a reactor equipped with a thermometer, a stirrer and a cooling tube by boiling point polymerization, and then the reactor was Heating was started to reflux. Subsequently, after adding a predetermined amount of the polymerization initiator shown in the table to the reactor, the monomers shown in the table were added dropwise over 2 hours. After completion of the dropwise addition, the same amount of polymerization initiator as that at the start was added, and the mixture was further heated to reflux for 6 hours to conduct a polymerization reaction, thereby obtaining an acrylic copolymer solution. In the table, “boiling point” described in the polymerization method column means that boiling point polymerization was performed.
(1-2) A predetermined amount of monomer and reaction solvent shown in the table were added to a reactor equipped with a copolymer thermometer, a stirrer, and a cooling tube by constant temperature polymerization, and then the reactor was heated to 60 ° C. Subsequently, a predetermined amount of a polymerization initiator shown in the table was added to the reactor to initiate the polymerization reaction. During the reaction, the reactor was appropriately heated and cooled so that the temperature of the reactor became constant at 60 ° C. The reaction was continued for 8 hours to obtain an acrylic copolymer solution. In the table, “constant temperature” described in the polymerization method column means that constant temperature polymerization was performed.

(2) Molecular Weight Measurement of Acrylic Copolymer Diluted solution obtained by diluting the obtained acrylic copolymer 50 times with tetrahydrofuran (THF) is filtered (material: polytetrafluoroethylene, pore diameter: 0.2 μm) And a measurement sample was prepared. This measurement sample is supplied to a gel permeation chromatograph (manufactured by 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 polystyrene equivalent molecular weight of the acrylic copolymer is measured. Was measured to determine the weight average molecular weight (Mw). GPC LF-804 (manufactured by Showa Denko) was used as the column, and a differential refractometer was used as the detector.

(3) Manufacture of double-sided pressure-sensitive adhesive sheet To the acrylic copolymer solution obtained, a predetermined amount of tackifying resin shown in the table is added to 100 parts by weight of its nonvolatile content (dried at 110 ° C. for 1 hour), and ethyl acetate is added. In addition, the mixture was further stirred, and an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., Coronate L45) was added in a predetermined amount as shown in the table and stirred to obtain an adhesive solution having a nonvolatile content of 30% by weight. In the table, the amount of the crosslinking agent indicates the weight percent of the non-volatile content of the crosslinking agent. The tackifying resin used is shown below.
-Tackifying resin a) Hydrogenated rosin ester resin (alcoholic hydroxyl value: 42, softening point: 100 ° C, manufactured by Arakawa Chemical Industries, Pine Crystal KE359)
-Tackifying resin b) Polymerized rosin ester resin (alcoholic hydroxyl value: 45, softening point: 135 ° C, manufactured by Arakawa Chemical Industries, Pencel D135)
-Tackifying resin c) Polymerized rosin ester resin (alcoholic hydroxyl value: 15, softening point: 100 ° C, Arakawa Chemical Industries, Superester A100)
-Tackifying resin d) Terpene phenol resin (alcoholic hydroxyl value: 0, softening point: 100 ° C, YShara Chemical Co., YS Polystar T100)
-Tackifying resin e) Terpene phenol resin (alcoholic hydroxyl value: 0, softening point: 150 ° C, YShara Chemical Co., YS Polystar G150)
Tackifying resin f) Hydrogenated rosin ester resin (alcoholic hydroxyl value: 35, softening point: 100 ° C., Pinova, Foral 105)

The obtained pressure-sensitive adhesive solution was applied to a 50 μm-thick release PET film so that the thickness of the pressure-sensitive adhesive layer after drying was 100 μm, and then dried at 70 ° C. for 10 minutes. The pressure-sensitive adhesive layer was transferred onto a corona-treated PET film having a thickness of 50 μm serving as a base material. Further, the pressure-sensitive adhesive layer was transferred onto the opposite surface of the substrate in the same manner to obtain a double-sided pressure-sensitive adhesive sheet. In addition, the release film for protecting an adhesive layer was laminated | stacked on the adhesive layer of both surfaces of a base material.

(4) Measurement of gel fraction The obtained double-sided PSA sheet was cut into a flat rectangular shape of 50 mm x 100 mm to produce a test piece, and the release film was peeled off. After immersing the test piece in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from 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 × (W ₂ −W ₀ ) / (W ₁ −W ₀ ) (1)
(W ₀ : weight of substrate, W ₁ : weight of test piece before immersion, W ₂ : weight of test piece after immersion and drying)

(5) Dynamic viscoelasticity test (3) In the same manner as in the production of the double-sided pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer after drying the pressure-sensitive adhesive solution on a PET film having a thickness of 50 μm is 100 μm. After coating, it was dried at 70 ° C. for 10 minutes. Ten sheets were prepared and laminated one after another to produce a 1 mm thick laminate, and then cut into a size of 6 mm × 10 mm to obtain a measurement sample.
This measurement sample was measured using a master curve measurement program of a dynamic viscoelasticity measurement apparatus (DVA-200, manufactured by IT Measurement Control Co., Ltd.). The measurement mode was a shear method, and the reference temperature was 25 ° C. The peak frequency of tan δ was calculated from the obtained master curve.

<Evaluation>
The following evaluation was performed about the double-sided adhesive sheet obtained by the Example and the comparative example. The results are shown in Tables 1-5.

(1) Adhesive strength 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 off to expose the pressure-sensitive adhesive layer. After placing this test piece on a polycarbonate resin plate so that the pressure-sensitive adhesive layer faces the polycarbonate resin plate, a test was performed by reciprocating a 2 kg rubber roller on the test piece at a speed of 300 mm / min. The piece and the polycarbonate resin plate were bonded together, and then allowed to stand at 23 ° C. for 30 minutes to prepare a test sample. This test sample was subjected to a tensile test in the 90 ° direction at a peeling speed of 300 mm / min according to JIS Z0237, and the adhesive strength (N / 25 mm) was measured.

(2) Shear deviation length FIG. 2 is a schematic diagram showing a method for evaluating the shear deviation length of the double-sided PSA sheet. The obtained double-sided pressure-sensitive adhesive sheet was cut into a plane rectangular shape of 5 mm in length and 20 mm in width to produce a test piece, and the release films on both sides were peeled and removed (referred to as test piece B). As shown in FIG. 2, a PET film C having a thickness of 25 μm is formed on the adhesive layer on the upper surface of the test piece B, and a metal base D (manufactured by SUS) having a length of 100 mm and a width of 20 mm is formed on the adhesive layer on the lower surface. A test sample was prepared by pasting each of them. The PET film C on the upper surface of this test sample was pulled by a weight E in the horizontal direction (arrow direction) with a load of 200 g for 3 minutes. The measurement was performed at 23 ° C. Thereafter, one end (fixing jig) of the pressure-sensitive adhesive layer bonded to the PET film C on the upper surface with reference to the position of one end (end on the fixing jig side) of the pressure-sensitive adhesive layer bonded to the metal base D on the lower surface. The distance L in which the side edge) was shifted in the pulling direction of the PET film C on the upper surface was measured.
In addition, the upper surface PET film C was affixed on the adhesive layer of the test piece B so that the adhesive layer adhering to the metal pedestal D on the lower surface and the PET film C on the upper surface were flush with each other. Moreover, the detector (not shown) which can measure the moving amount | distance of the end of PET film C of an upper surface per micrometer was installed.

(3) Resilience resistance FIG. 3 is a schematic diagram showing a method for evaluating the resilience of the double-sided PSA sheet. The obtained double-sided pressure-sensitive adhesive sheet was cut into a flat rectangular shape of 25 mm wide × 150 mm long to produce a test piece, and the release films on both sides were peeled and removed (referred to as test piece 6). As shown in FIG. 3, an aluminum plate 7 having a width of 25 mm, a length of 150 mm, and a thickness of 0.3 mm was superimposed on the upper surface of the test piece 6, and a polycarbonate resin plate 8 having a width of 25 mm, a length of 200 mm, and a thickness of 1 mm was superimposed on the lower surface. In addition, it adjusted so that the test piece 6 may be located in the center part of the length direction of the polycarbonate resin board 8. FIG.
A 2 kg rubber roller is reciprocated once on the polycarbonate resin plate 8 at a speed of 300 mm / min to integrate the polycarbonate resin plate 8 and the aluminum plate 7 through the test piece 6, and then statically kept at 23 ° C. for 24 hours. A test sample 9 was prepared. The test sample 9 is set on a jig 10 and bending stress is applied in the longitudinal direction of the test sample 9 so that the test sample 9 has an arc shape so that the distance between both ends in the length direction of the polycarbonate resin plate 8 is 180 mm. In this state, the test sample 9 was placed in an oven at 85 ° C. and allowed to stand for 24 hours. Thereafter, the test sample 9 was taken out of the oven while being curved in an arc shape, and the height H of the floating between the aluminum plate 7 and the polycarbonate resin plate 8 was measured with a caliper.
The floating height H between the aluminum plate 7 and the polycarbonate resin plate 8 is the maximum value of the distance between the facing surfaces of the aluminum plate 7 and the polycarbonate resin plate 8 in the direction perpendicular to the upper surface of the jig 10. A position where the thickness of the test piece 6 is subtracted from the distance between the facing surfaces of the aluminum plate 7 and the polycarbonate resin plate 8 in the direction perpendicular to the upper surface of the jig 10 is specified. .

(4) Impact resistance adhesion The obtained double-sided pressure-sensitive adhesive sheet was punched out into a frame shape having an outer dimension of 46 × 61 mm and a width of 1 mm with a Thomson blade to prepare a test piece. One release film of this test piece (frame shape) was peeled and removed, and bonded to a polycarbonate plate (made by Takiron, hereinafter referred to as PC plate) having an outer dimension of 55 × 65 mm and a thickness of 1 mm using a roller. Subsequently, the other release film was peeled and removed, and the center of the opening of the PC plate and the test piece were placed on a PC 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 center. Gently place it so that it is almost coincident with the center, put a 5 kg weight from the top for 10 seconds and paste the two PC plates together, and then let stand at 23 ° C for 24 hours to perform adhesion curing and prepare a test sample did.
This test sample is set on a fixing jig so that the PC plate with the opening is on the upper surface, and a shock is applied by dropping a 300 g weight through the opening to the PC plate on the lower surface from a drop height of 5 cm. 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.

(5) Punching workability The obtained double-sided pressure-sensitive adhesive sheet was punched out into a frame shape having an outer dimension of 46 × 61 mm and a width of 1 mm with a Thomson blade to produce a test piece. From the workability when removing this test piece from the Thomson blade, the punching workability was evaluated.
×: The test piece was difficult to peel off from the blade, and in order to obtain a test piece maintaining the frame shape, the test piece had to be carefully peeled off from the blade. ○: The test piece was easily peeled off from the blade, and the frame shape was maintained. I was able to get the specimen easily.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive sheet for electronic devices which is high in impact-resistant adhesiveness, cannot be easily shifted even when a load is applied in the shearing direction, and is excellent in resilience can be provided.

DESCRIPTION OF SYMBOLS 1 Electronic device 2 Adhesive sheet 3 for electronic devices Cover panel 4 Touch panel module 5 Display panel module B Test piece C PET film D Metal base E Weight L Shear deviation length (Pull direction of PET film C with one end of adhesive layer on top Distance)
6 Test piece 7 Aluminum plate 8 Polycarbonate resin plate 9 Test sample 10 Jig H Height of floating between aluminum plate 7 and polycarbonate resin plate 8 (mm)

Claims (4)

Having a pressure-sensitive adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of a tackifying resin having a softening point of 110 ° C. or less and an alcoholic hydroxyl value of 30 or more,
The acrylic copolymer is
(A) 2-ethylhexyl acrylate 24.7 to 58.98% by weight,
(B) 30-50% by weight of butyl acrylate,
(C) 10-20% by weight of methyl acrylate,
(D) 1-5% by weight acrylic acid, and
(E) obtained by copolymerizing a mixed monomer containing 0.02 to 0.3% by weight of a (meth) acrylate having a hydroxyl group, the weight average molecular weight (Mw) is 800,000 or more,
The pressure-sensitive adhesive layer is crosslinked to a gel fraction of 20 to 50% with a crosslinking agent, and is a pressure-sensitive adhesive sheet for electronic equipment. The pressure-sensitive adhesive sheet for electronic equipment according to claim 1, wherein the tackifying resin is a rosin ester-based tackifying resin. The pressure-sensitive adhesive layer has a frequency of a tan δ peak in a dynamic viscoelastic master curve at 25 ° C of 800 to 10,000 Hz. The pressure-sensitive adhesive sheet for electronic equipment according to claim 1 or 2, The pressure-sensitive adhesive sheet for electronic devices according to claim 1, wherein the pressure-sensitive adhesive sheet has a base material, and the base material is not a foam.

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