TW201510168A - Adhesive sheet for electronic devices - Google Patents

Abstract

The purpose of the present invention is to provide an adhesive sheet for electronic devices, which has a high impact-resistant adhesion property, is rarely displaced even when a load is applied to the adhesive sheet in the shear direction, and also has excellent repulsion resistance. The present invention is an adhesive sheet for electronic devices, which has an adhesive agent layer comprising 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of an adhesiveness-imparting resin having a softening point of 110 DEG C or lower and an alcoholic hydroxy group value of 30 or more, wherein the acrylic copolymer is produced by copolymerizing a monomer mixture comprising (a) 24.7 to 58.98% by weight of 2-ethylhexyl acrylate, (b) 30 to 50% by weight of butyl acrylate, (c) 10 to 20% by weight of methyl acrylate, (d) 1 to 5% by weight of acrylic acid and (e); 0.02 to 0.3% by weight of a (meth)acrylate having a hydroxy group and has a weight average molecular weight (Mw) of 800,000 or more, and the adhesive agent layer is crosslinked with a crosslinking agent to such an extent that the gel fraction becomes 20 to 50%.

Description

Adhesive sheet for electronic equipment

The present invention relates to an adhesive sheet for an electronic device which is excellent in impact resistance and is not easily offset even when a load is applied in the shearing direction, and is excellent in rebound resistance.

In an electronic device (for example, a mobile phone, an action information terminal, or the like) on which an image display device or an input device is mounted, an adhesive sheet is used for assembly. Specifically, for example, an adhesive sheet is used in order to connect the cover for protecting the surface of the electronic device to the touch panel module or the display panel module, or to connect the touch panel module to the display panel module. Such an adhesive sheet is required to have various properties represented by the adhesiveness. For example, it is also required to have an impact-resistant adhesive property which is not peeled off from the adherend even if it is subjected to an impact from the outside.

As a method of improving the impact resistance of the pressure-sensitive adhesive sheet, for example, a method of using a cushioning substrate such as a foam is used. In the patent documents 1 and 2, an electronic device including a foamed sheet of a crosslinked polyolefin-based resin and a specific acrylic-based pressure-sensitive adhesive layer laminated on one surface of the foamed sheet of the crosslinked polyolefin-based resin is described. Use adhesive sheets.

However, in recent years, with the increase in the size and design of electronic devices, adhesive sheets for finer processing are required as the adhesive sheets for assembly, but foaming as described in Patent Documents 1 and 2 The adhesive sheet of the body as a substrate is applied in the shearing direction during processing. It is easy to shift when adding a load. Moreover, there is also a problem of poor rebound resistance.

The base material which is excellent in the rebound resistance is, for example, a polyethylene terephthalate (PET) film. However, when a substrate having a small cushioning property such as a PET film is used, it is difficult to visualize the case of using a foam. Generally higher resistance to impact.

[Previous Technical Literature]

[Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-215906

Patent Document 2: Japanese Laid-Open Patent Publication No. 2011-168727

An object of the present invention is to provide an adhesive sheet for an electronic device which is excellent in impact resistance and which is not easily offset even when a load is applied in the shearing direction and which is excellent in rebound resistance.

The present invention relates to an adhesive sheet for an electronic device comprising an adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of an adhesion-imparting resin having a softening point of 110 ° C or less and an alcoholic hydroxyl value of 30 or more. The acrylic copolymer contains (a) 24.7 to 58.98% by weight of 2-ethylhexyl acrylate, (b) 30 to 50% by weight of butyl acrylate, (c) 10 to 20% by weight of methyl acrylate, and (d) acrylic acid. 1 to 5% by weight, and (e) 0.02 to 0.3% by weight of a mixed monomer having a hydroxyl group (meth) acrylate, obtained by copolymerization, weight average molecular weight (Mw) is 800,000 or more, and the above adhesive layer is crosslinked by a crosslinking agent to have a gel fraction of 20 to 50%.

The invention is described in detail below.

The present inventors have found that an adhesive sheet for an electronic device having a specific acrylic copolymer and a specific adhesive-imparting resin and which is crosslinked by a crosslinking agent to a gel fraction of a specific range, even if When the substrate having a cushioning property such as a foam is not used as a substrate having a small cushioning property such as a PET film, high impact resistance can be exhibited. Further, the present inventors have found that an adhesive sheet for an electronic device having such an adhesive layer does not require the use of a foam, and the adhesive layer has suitable hardness, cohesive force, adhesion, and the like, and thus is applied even in the shear direction. In the case of the load, it is also difficult to shift, and the rebound resistance is also excellent, thereby completing the present invention.

The pressure-sensitive adhesive sheet for an electronic device of the present invention has an adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of an adhesion-imparting resin having a softening point of 110 ° C or less and an alcoholic hydroxyl value of 30 or more.

The acrylic copolymer contains (a) 24.7 to 58.98% by weight of 2-ethylhexyl acrylate, (b) 30 to 50% by weight of butyl acrylate, and (c) 10 to 20% by weight of methyl acrylate, (d) 1 to 5% by weight of acrylic acid and (e) 0.02 to 0.3% by weight of a mixed monomer having a hydroxyl group (meth) acrylate are copolymerized.

When the 2-ethylhexyl acrylate of the above (a) is less than 24.7% by weight, the adhesive force of the above adhesive layer is lowered, and the impact resistance is lowered. When the 2-ethylhexyl acrylate of the above (a) exceeds 58.98% by weight, the above-mentioned adhesive layer becomes too soft due to a decrease in the glass transition temperature (Tg), and it is easy to apply a load in the shear direction. Offset.

When the butyl acrylate of the above (b) is less than 30% by weight, the pressure-sensitive adhesive layer becomes too soft and is likely to be displaced when a load is applied in the shearing direction. If (b) above When the butyl acrylate is more than 50% by weight, the above-mentioned adhesive layer becomes too hard, and the impact resistance is lowered.

If the methyl acrylate of the above (c) is less than 10% by weight, the impact resistance of the above-mentioned adhesive layer is lowered. It is estimated that by copolymerizing 10% by weight or more of the methyl acrylate (c), the side chain of the acrylic copolymer becomes small, whereby the linearity of the molecular chain is increased, and the entanglement of the molecular chain is increased. Therefore, when the above-mentioned adhesive layer is deformed by the impact, it is estimated that the energy absorption due to the deviation of the entanglement of the molecular chain is increased, and the impact resistance is improved.

Furthermore, since the crosslinked structure of the molecular chain is deformed mainly by elastic deformation, it is not easy to convert the impact stress into the energy of the flow deformation, and it is difficult to absorb and disperse. Therefore, the impact stress is accumulated in the form of elastic energy inside the crosslinked structure, and the stress dispersibility at the interface with the adherend is lowered, so that the impact resistance is lowered. On the other hand, the entangled structure of the molecular chain is different from the crosslinked structure, and can be plastically deformed, and the impact stress can be converted into the energy of the flow deformation to absorb and disperse. Therefore, it is considered that an increase in the degree of entanglement leads to an improvement in impact resistance.

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 the impact resistance is lowered.

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

The (meth) acrylate having a hydroxyl group in the above (e) is a component which is crosslinked by the following isocyanate crosslinking agent or the like. By copolymerizing 0.02 to 0.3% by weight of the (meth) acrylate having a hydroxyl group in the above (e), it is easy to adjust the gel fraction of the above-mentioned adhesive layer to a specific range, thereby making impact-resistant adhesion. High, and even if a load is applied in the shear direction In the case of the adhesive layer which is not easily deflected.

When the (meth) acrylate having a hydroxyl group in the above (e) is less than 0.02% by weight, the pressure-sensitive adhesive layer is too soft, and is easily offset when a load is applied in the shearing direction. When the (meth) acrylate having a hydroxyl group in the above (e) exceeds 0.3% by weight, the crosslinking density of the pressure-sensitive adhesive layer is increased, the plastic deformability is lowered, and the elastic deformation is mainly caused, so that the impact resistance is lowered. .

Examples of the (meth) acrylate having a hydroxyl group in the above (e) include 2-hydroxyethyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate.

The mixed monomer may contain, in addition to the monomers (a) to (e), other vinyl monomers copolymerizable with the monomers of the above (a) to (e).

When the above mixed monomer is copolymerized to obtain the above acrylic copolymer, the mixed monomer may be subjected to a radical reaction in the presence of a polymerization initiator. As a method of radically reacting the above-mentioned mixed monomer (that is, a polymerization method), a conventionally known method can be used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, and the like.

The polymerization initiator is not particularly limited, and examples thereof include an organic peroxide and an azo compound. Examples of the organic peroxide include 1,1-bis(peroxytrihexyl)-3,3,5-trimethylcyclohexane, peroxytrimethylacetic acid trihexyl ester, and peroxygen. Tert-butyl peroxypivalate, 2,5-dimethyl-2,5-bis(peroxy 2-ethylhexyl)hexane, peroxy 2-ethylhexanoate Grade hexyl ester, peroxy 2-ethylhexanoate tert-butyl ester, t-butyl peroxyisobutyrate, 3,5,5-trimethylhexanoic acid tert-butyl acrylate , peroxy lauric acid tertiary butyl ester and the like. As the above azo compound, for example, azobisiso Nitrile, azobiscyclohexanecarbonitrile, and the like. These polymerization initiators may be used singly or in combination of two or more.

In the case of using solution polymerization as a polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl hydrazine, ethanol, acetone, diethyl ether and the like. These reaction solvents may be used singly or in combination of two or more.

The weight average molecular weight (Mw) of the above acrylic copolymer is 800,000 or more. When the weight average molecular weight (Mw) of the above-mentioned acrylic copolymer is less than 800,000, the above-mentioned adhesive layer becomes too soft, and it is easy to shift when a load is applied in the shear direction.

The upper limit of the weight average molecular weight (Mw) of the above acrylic copolymer is not particularly limited, but is preferably 1.5 million or less. When the weight average molecular weight (Mw) of the above-mentioned acrylic copolymer exceeds 1.5 million, the adhesion of the pressure-sensitive adhesive layer may be lowered, and it is difficult to achieve impact resistance and other properties at the same time.

Further, the weight average molecular weight (Mw) is measured by a GPC (Gel Permeation Chromatography) method as a molecular weight in terms of polystyrene. Specifically, the weight average molecular weight (Mw) is measured by a GPC method as a polystyrene-converted molecular weight using a filtrate obtained by diluting an acrylic copolymer by 50 times with tetrahydrofuran (THF) using a filter. The dilution is obtained by filtration. For the GPC method, for example, a 2690 Separations Model (manufactured by Waters Co., Ltd.) or the like can be used.

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

By blending the above softening point with respect to 100 parts by weight of the above acrylic copolymer When the viscosity is 110° C. or less and the alcoholic hydroxyl group value is 30 or more, 20 to 35 parts by weight of the resin is added, whereby the adhesive strength of the pressure-sensitive adhesive layer can be increased, and the impact resistance can be improved.

When the softening point of the adhesion-imparting resin exceeds 110 ° C, the pressure-sensitive adhesive layer becomes too hard and the impact resistance is lowered.

Further, the softening point means a softening point measured by the JIS K2207 ring and ball method.

When the alcoholic hydroxyl value of the above-mentioned adhesion-imparting resin is less than 30, when it is used in an environment in which a strong repulsive force is applied, the above-mentioned adhesive layer rises from the adhesive surface, that is, the rebound resistance is lowered.

In addition, the "alcoholic hydroxyl value" means a hydroxyl value based on an alcoholic hydroxyl group. Therefore, the hydroxyl value based on the phenolic hydroxyl group is not included.

Further, the hydroxyl value can be measured by JIS K1557 (phthalic anhydride method). When the adhesive-imparting resin used does not contain a phenolic hydroxyl group and contains only an alcoholic hydroxyl group, the measured hydroxyl value itself becomes an "alcoholic hydroxyl value". On the other hand, when the phenol skeleton is present in the adhesion-imparting resin to be used, the average functional group number of the phenolic hydroxyl group contained in the molecule of the adhesion-imparting resin 1 and the average functional group number of the alcoholic hydroxyl group are calculated to obtain one molecule. The ratio of the alcoholic hydroxyl group contained in the above is determined by multiplying the hydroxyl value of the adhesion-imparting resin to the ratio of the alcoholic hydroxyl group contained in one molecule, and determining the hydroxyl value based on the alcoholic hydroxyl group.

When the adhesion-imparting resin is less than 20 parts by weight, the adhesive strength of the pressure-sensitive adhesive layer is lowered, and the impact resistance is lowered. When the softening point is 110° C. or less and the viscosity-imparting resin having an alcoholic hydroxyl value of 30 or more exceeds 35 parts by weight, the adhesive layer becomes too hard due to an increase in the glass transition temperature (Tg), and impact resistance is improved. reduce.

The adhesion-imparting resin has a softening point of 110 ° C or less and an alcoholic hydroxyl value. 30 or more is not particularly limited, but a pine ester-based adhesion-imparting resin such as a hydrogenated ester resin is preferred.

The above adhesive layer is crosslinked by a crosslinking agent to have a gel fraction of 20 to 50%.

The crosslinking agent is not particularly limited, and examples thereof include an isocyanate crosslinking agent, an aziridine crosslinking agent, an epoxy crosslinking agent, and a metal chelate crosslinking agent. Among them, the isocyanate crosslinking agent is preferred because it has excellent adhesion stability to a substrate. Examples of the isocyanate-based crosslinking agent include Coronate HX (manufactured by NIPPON POLYURETHANE INDUSTRY), Coronate L (manufactured by NIPPON POLYURETHANE INDUSTRY), and MITEC NY260A (manufactured by Mitsubishi Chemical Co., Ltd.).

The amount of the crosslinking agent to be added is preferably 0.1 to 6 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of the acrylic copolymer.

When the gel fraction of the above adhesive layer is less than 20%, the above-mentioned adhesive layer becomes too soft, and it is likely to be displaced when a load is applied in the shearing direction. When the gel fraction of the pressure-sensitive adhesive layer exceeds 50%, the crosslinking density of the pressure-sensitive adhesive layer becomes high, and the plastic deformation property is lowered to cause the elastic deformation to become a main component, so that the impact resistance is lowered.

Further, the gel fraction was measured as follows. First, a test piece was prepared by cutting an adhesive sheet for an electronic device into a rectangular shape of 50 mm × 100 mm, and the test piece was immersed in ethyl acetate for 24 hours at 23 ° C, and then the test piece was taken out from ethyl acetate at 110 ° C. Dry for 1 hour under the conditions. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1). Further, a release film for protecting the adhesive layer was not laminated in the test piece.

Gel fraction (% by weight) = 100 × (W _{2 -} W ₀ ) / (W _{1 -} W ₀ ) (1)

(W ₀ : weight of the substrate, W ₁ : weight of the test piece before immersion, W ₂ : weight of the test piece after immersion and drying)

As a method of obtaining an adhesive layer which is crosslinked to a gel fraction of the above range by the above-mentioned crosslinking agent, a method of adding the above-mentioned crosslinking agent to form a main chain between the resins constituting the above adhesive layer is preferred. Crosslinked structure. By appropriately adjusting the kind or amount of the above-mentioned crosslinking agent, the gel fraction of the above-mentioned adhesive layer can be easily adjusted to the above range, and the impact resistance can be made high, and even when a load is applied in the shearing direction, It is also not easy to offset the adhesive layer.

The adhesive layer may optionally contain an additive such as a plasticizer, an emulsifier, a softener, a filler, a pigment, and a dye, and other resins such as a rosin-based resin.

Preferably, the adhesive layer has a tan δ peak on the dynamic viscoelastic main curve at a reference temperature of 25 ° C of 800 to 10000 Hz. When the frequency of the above-described tan δ peak is 800 to 10000 Hz, an appropriate hardness can be imparted to the above-mentioned adhesive layer to obtain sufficient impact resistance. A lower limit of the frequency of the above tan δ peak is 900 Hz, and a more preferred upper limit is 5000 Hz.

Furthermore, the frequency of the tan δ peak on the dynamic viscoelastic main curve is based on a master curve measurement program (measurement mode: shearing method) using a dynamic viscoelasticity measuring apparatus (for example, DVA-200 manufactured by IT Meter and Control). Calculated by measuring the main curve.

The thickness of the above adhesive layer is not particularly limited, but is preferably 50 to 150 μm. When the thickness of the above adhesive layer is less than 50 μm, the impact resistance is lowered. When the thickness of the above-mentioned adhesive layer exceeds 150 μm, there is a case where the load is easily applied when the load is applied in the shearing direction, or the rebound resistance is lowered.

The adhesive sheet for an electronic device of the present invention may be an unsupported type having no substrate, or may be a support type having a substrate. In the case of a support type, it is preferred to form the above-mentioned adhesive layer on both sides of the substrate.

The adhesive sheet for an electronic device of the present invention has an adhesive layer containing a specific acrylic copolymer and a specific adhesive-imparting resin as described above, and the crosslinking agent is crosslinked to a specific range by a crosslinking agent. In other words, when the substrate having a cushioning property such as a foam is not used and the substrate having a small cushioning property such as a PET film is used, it is possible to exhibit high impact resistance. Further, the adhesive sheet for an electronic device of the present invention does not require the use of a foam, and the adhesive layer has moderate hardness, cohesive force, adhesion, and the like, and therefore is not easily offset even when a load is applied in the shear direction. Excellent rebound resistance.

The substrate is not particularly limited, and is preferably not a foam. Examples thereof include a polyolefin resin film such as a polyethylene film or a polypropylene film, a polyester resin film such as a PET film, and ethylene-vinyl acetate. A copolymer film, a polyvinyl chloride resin film, a polyurethane resin film, or the like. In particular, a polyester resin film is preferred because the pressure-sensitive adhesive sheet is not easily offset when the load is applied in the shearing direction, and the rebound resistance is excellent.

Further, a substrate which is printed in black to prevent light transmission, a substrate which is printed in white to improve light reflectivity, a substrate which is vapor-deposited by metal, or the like may be used.

The thickness of the substrate is not particularly limited, but is preferably 20 to 100 μm, more preferably 25 to 75 μm. When the thickness of the substrate is less than 20 μm, the rebound resistance or mechanical strength of the adhesive sheet for an electronic device may be lowered. When the thickness of the above-mentioned base material exceeds 100 μm, the toughness of the adhesive sheet for electronic devices may become too strong, and it may be difficult to adhere them in close contact with the shape of the adherend.

The thickness of the shear offset of the adhesive sheet for an electronic device of the present invention is preferably 300 μm or less. When the shear offset length is 300 μm or less, an appropriate hardness can be imparted to the pressure-sensitive adhesive layer, sufficient impact resistance can be maintained, and press workability can be easily improved. on The shear offset length is more preferably 180 μm or less, and still more preferably 150 μm or less.

Further, the shear offset length was measured as follows. Fig. 2 is a schematic view showing a method of evaluating the shear offset length of an adhesive sheet for an electronic device (two-sided adhesive sheet). The electronic device adhesive sheet was cut into a rectangular shape of 5 mm × 20 mm in width to prepare a test piece, and the release film on both sides was peeled off (made of test piece B). As shown in Fig. 2, a PET film C having a thickness of 25 μm was adhered to the adhesive layer on the upper surface of the test piece B, and a metal pedestal D (SUS) having a length of 100 mm and a width of 20 mm was adhered to the adhesive layer on the lower surface to prepare a test sample. . The PET film C on the upper surface of the test sample was applied with a load of 200 g in the horizontal direction (arrow direction) by the vertical E, and stretched for 3 minutes. The measurement was carried out at 23 °C. Thereafter, one end of the adhesive layer of the PET film C attached to the upper surface (fixed jig side end) is referenced to the position of one end (fixing jig side end) of the adhesive layer of the metal pedestal D on the lower surface. The distance L which is shifted in the stretching direction of the PET film C on the upper surface was measured and set as the shear offset length.

The method for producing the pressure-sensitive adhesive sheet for an electronic device of the present invention is not particularly limited, and examples thereof include the above-mentioned acrylic copolymer and an adhesive resin having a softening point of 110 ° C or less and an alcoholic hydroxyl value of 30 or more. The above-mentioned crosslinking agent and other mixing components as needed are mixed and stirred to prepare an adhesive solution, and then the adhesive solution is applied to the release-treated PET film to be dried to form an adhesive layer. The adhesive layer is transferred to the substrate. Further, the adhesive layer may be transferred in the same manner on the opposite side of the substrate.

The use of the adhesive sheet for an electronic device of the present invention is not particularly limited, and it is preferably an electronic device (for example, a mobile phone, an action information terminal, or the like) on which an image display device or an input device is mounted. Specifically, for example, the cover for protecting the surface of the electronic device is preferably applied to the touch panel module or the display panel module, or the touch panel module and the display surface are The board module follows. Further, the adhesive sheet for an electronic device of the present invention can also be used in a touch panel module in which a film with a metal thin film is attached to a support (PET film or the like).

Moreover, the shape of the adhesive sheet for an electronic device of the present invention in the above-described applications is not particularly limited, and may be a rectangular shape or the like, but is preferably a frame shape.

Fig. 1 is a schematic view showing an electronic device in which a cover sheet is attached to a surface of a touch panel module using the adhesive sheet for an electronic device of the present invention. In the electronic device 1 shown in FIG. 1, the cover sheet 3 is attached to the surface of the touch panel module 4 by stamping the adhesive sheet 2 for electronic devices in a frame shape.

According to the present invention, it is possible to provide an adhesive sheet for an electronic device which is excellent in impact resistance and which is not easily offset even when a load is applied in the shearing direction and which is excellent in rebound resistance.

1‧‧‧Electronic machines

2‧‧‧Adhesive sheets for electronic machines

3‧‧‧ Cover

4‧‧‧Touch panel module

5‧‧‧Display panel module

B‧‧‧ test piece

C‧‧‧PET film

D‧‧‧metal pedestal

E‧‧‧ plumb

L‧‧‧ Shear offset length (distance of one end of the adhesive layer along the stretching direction of the PET film C on the upper surface)

6‧‧‧ test strips

7‧‧‧Aluminum plate

8‧‧‧Polycarbonate resin board

9‧‧‧ test sample

10‧‧‧Clamp

Float height (mm) between H‧‧‧ aluminum plate 7 and polycarbonate resin plate 8

Fig. 1 is a schematic view showing an electronic apparatus in which a cover is attached to a surface of a touch panel module using the adhesive sheet for an electronic device of the present invention.

Fig. 2 is a schematic view showing a method of evaluating the shear offset length of an adhesive sheet for an electronic device (two-sided adhesive sheet).

Fig. 3 is a schematic view showing a method of evaluating the rebound resistance of an adhesive sheet for an electronic device (two-sided adhesive sheet).

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited to the examples.

(Examples 1 to 19 and Comparative Examples 1 to 20)

(1) Preparation of acrylic copolymer

(1-1) Copolymerization by boiling point polymerization

After adding a predetermined amount of the reaction solvent shown in the table to a reactor equipped with a thermometer, a stirrer, and a cooling tube, the reactor was heated to start reflux. Then, after adding a predetermined amount of the polymerization initiator shown in the table to the reactor, the monomer shown in the input table was added dropwise over 2 hours. After completion of the dropwise addition, the same amount of the polymerization initiator as that at the beginning was added, and the mixture was further heated under reflux for 6 hours to carry out a polymerization reaction to obtain an acrylic copolymer solution. In the table, the "boiling point" described in the column of the polymerization method means that the boiling point polymerization has been carried out.

(1-2) Copolymerization by constant temperature polymerization

After adding a predetermined amount of the monomer and the reaction solvent shown in the table to a reactor equipped with a thermometer, a stirrer, and a cooling tube, the reactor was heated to 60 °C. Then, a predetermined amount of the polymerization initiator shown in the table was added to the reactor to start the polymerization. During the reaction, the reactor was appropriately heated and cooled to adjust so that the temperature of the reactor was fixed to 60 °C. The reaction was allowed to continue for 8 hours to obtain an acrylic copolymer solution. In the table, the "fixed temperature" described in the polymerization method column means that the constant temperature polymerization has been carried out.

(2) Determination of molecular weight of acrylic copolymer

A measurement sample was prepared by filtering a dilution obtained by diluting the obtained acrylic copolymer by 50 times with tetrahydrofuran (THF) using a filter (material: polytetrafluoroethylene; pore size: 0.2 μm). The measurement sample was supplied to a gel permeation chromatography apparatus (manufactured by Waters, Inc., 2690). Separations Model) GPC measurement was carried out under the conditions of a sample flow rate of 1 ml/min and a column temperature of 40 ° C, and the molecular weight in terms of polystyrene of the acrylic copolymer was measured to determine a weight average molecular weight (Mw). As the column, GPC LF-804 (manufactured by Showa Denko Co., Ltd.) was used, and as a detector, a differential refractometer was used.

(3) Manufacture of two-sided adhesive sheets

In the obtained acrylic copolymer solution, a predetermined amount of the adhesion-imparting resin shown in the following table is added to 100 parts by weight of the non-volatile matter (dried at 110 ° C for 1 hour), ethyl acetate is added and stirred, and the table is further added. A predetermined amount of an isocyanate-based crosslinking agent (manufactured by NIPPON POLYURETHANE INDUSTRY Co., Ltd., Coronate L45) was added and stirred to obtain a non-volatile 30% by weight adhesive solution. In the table, the amount of the crosslinking agent indicates the weight % of the nonvolatile content of the crosslinking agent. The adhesive-imparting resin to be used is shown below.

. Adhesive imparting resin a) Hydrogenated pine resin (alcoholic hydroxyl value: 42; softening point: 100 ° C; manufactured by Arakawa Chemical Industries Co., Ltd.; Pine Crystal KE359)

. Adhesive imparting resin b) Polymerized pine ester resin (alcoholic hydroxyl value: 45; softening point: 135 ° C; manufactured by Arakawa Chemical Industries Co., Ltd.; Pencel D135)

. Adhesive imparting resin c) Polymerized pine ester resin (alcoholic hydroxyl value: 15; softening point: 100 ° C; manufactured by Arakawa Chemical Industries Co., Ltd.; Super Ester A100)

. Adhesive imparting resin d) Indophenol resin (alcoholic hydroxyl value: 0; softening point: 100 ° C; manufactured by YASUHARA CHEMICAL; YS Polyster T100)

. Adhesive imparting resin e) Indophenol resin (alcoholic hydroxyl value: 0; softening point: 150 ° C; manufactured by YASUHARA CHEMICAL; YS Polyster G150)

. Adhesive imparting resin f) hydrogenated pine resin (alcoholic hydroxyl value: 35; softening point: 100 ° C; Made by Pinova; Foral 105)

The obtained adhesive solution was applied to a release-treated PET film having a thickness of 50 μm so that the thickness of the dried adhesive layer became 100 μm, and then dried at 70 ° C for 10 minutes. The adhesive layer was transferred to a corona-treated PET film having a thickness of 50 μm as a substrate. Further, the adhesive layer was transferred in the same manner on the opposite side of the substrate to obtain a double-sided adhesive sheet. Furthermore, the adhesive layer on both sides of the substrate is laminated to protect the release film of the adhesive layer.

(4) Determination of gel fraction

The obtained double-sided adhesive sheet was cut into a rectangular shape of 50 mm × 100 mm to prepare a test piece, and the release film was peeled off. After the test piece was immersed in ethyl acetate for 24 hours at 23 ° C, 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 the substrate, W ₁ : weight of the test piece before immersion, W ₂ : weight of the test piece after immersion and drying)

(5) Dynamic viscoelastic test

In the same manner as in the production of the above-mentioned (3) double-sided adhesive sheet, the adhesive solution was applied to a release-treated PET film having a thickness of 50 μm so that the thickness of the dried adhesive layer became 100 μm, and then dried at 70 ° C. 10 minutes. Ten sheets of such an adhesive sheet were prepared and superposed in this order, thereby producing a laminate having a thickness of 1 mm, and then cutting out a size of 6 mm × 10 mm to prepare a measurement sample.

Dynamic viscoelasticity measuring device (manufactured by IT Meter and Control, DVA- 200) The main curve measurement program, and the measurement sample is measured.

Further, the measurement mode was set to a shearing method, and the reference temperature was set to 25 °C. The peak frequency of tan δ is calculated from the obtained main curve.

<evaluation>

The following evaluations were performed on the two-sided adhesive sheets obtained in the examples and the comparative examples. The results are shown in Tables 1 to 5.

(1) Adhesion

The obtained double-sided adhesive sheet was cut into a strip shape of 25 mm width to prepare a test piece, and the release film on one side was peeled off to expose the adhesive layer. The test piece was placed on the polycarbonate resin sheet with the adhesive layer facing the polycarbonate resin sheet, and a 2 kg rubber roller was reciprocated once on the test piece at a speed of 300 mm/min. The test piece was bonded to a polycarbonate resin plate, and then allowed to stand at 23 ° C for 30 minutes to prepare a test sample. The test sample was subjected to a tensile test in a 90° direction at a peeling speed of 300 mm/min according to JIS Z0237, and the adhesive force (N/25 mm) was measured.

(2) Shear offset length

Fig. 2 is a schematic view showing a method of evaluating the shear offset length of the double-sided adhesive sheet. The obtained double-sided adhesive sheet was cut into a rectangular shape having a length of 5 mm × a width of 20 mm to prepare a test piece, and the release film on both sides was peeled off (made of test piece B). As shown in Fig. 2, a PET film C having a thickness of 25 μm was adhered to the adhesive layer on the upper surface of the test piece B, and a metal pedestal D (SUS) having a length of 100 mm and a width of 20 mm was adhered to the adhesive layer on the lower surface to prepare a test sample. . The PET film C on the upper surface of the test sample was applied with a load of 200 g in the horizontal direction (arrow direction) by the vertical E, and stretched for 3 minutes. The measurement was carried out at 23 °C. Thereafter, the adhesion of the metal pedestal D following the lower surface The position of one end of the coating layer (the side end of the fixing jig) is used as a reference, and one end of the adhesive layer (fixed jig side end) of the PET film C attached to the upper surface is displaced along the stretching direction of the PET film C of the upper surface. The distance L is measured.

Further, the PET film C on the upper surface of the test piece B is adhered to the adhesive layer of the test piece B so that the adhesive layer of the metal pedestal D on the lower surface and the PET film C on the upper surface are flush with each other. Further, a detector (not shown) capable of measuring the amount of movement of one end of the PET film C on the upper surface in units of μm is provided.

(3) Resilience resistance

Fig. 3 is a schematic view showing a method of evaluating the rebound resistance of the double-sided adhesive sheet. The obtained double-sided adhesive sheet was cut into a rectangular shape having a length of 25 mm and a width of 150 mm to prepare a test piece, and the release film on both sides was peeled off (made of the test piece 6). As shown in Fig. 3, an aluminum plate 7 having a length of 25 mm, a width of 150 mm and a thickness of 0.3 mm was superposed on the upper surface of the test piece 6, and a polycarbonate resin plate 8 having a length of 25 mm, a width of 200 mm and a thickness of 1 mm was superposed on the lower surface. In addition, the test piece 6 is adjusted so that it may be located in the center part of the longitudinal direction of the polycarbonate resin board 8.

2 kg of the rubber roller was reciprocated once on the polycarbonate resin sheet 8 at a speed of 300 mm/min, and the polycarbonate resin sheet 8 and the aluminum plate 7 were integrated through the test piece 6, and then allowed to stand at 23 ° C for 24 hours. Test sample 9 was prepared. The test sample 9 was placed in the jig 10, and a bending stress was applied in the longitudinal direction of the test sample 9, whereby the test sample 9 was deformed so that the distance between both ends of the longitudinal direction of the polycarbonate resin sheet 8 became 180 mm. The test sample 9 was placed in an oven at 85 ° C for 24 hours in a state of being bent into an arc shape. Thereafter, the test sample 9 was taken out from the oven in a state of being bent into an arc shape, and the floating height H between the aluminum plate 7 and the polycarbonate resin plate 8 was measured by a vernier caliper.

Further, the floating height H between the aluminum plate 7 and the polycarbonate resin plate 8 means a value corresponding to the pair of the aluminum plate 7 and the polycarbonate resin plate 8 in the vertical direction with respect to the upper surface of the jig 10. The position at which the interval between the faces is maximized, and the interval between the opposite faces of the aluminum plate 7 and the polycarbonate resin plate 8 in the vertical direction with respect to the upper surface of the jig 10 at this position is subtracted from the thickness of the test piece 6. .

(4) Impact resistance

The obtained two-sided adhesive sheet was punched into a frame shape of an outer size of 46 × 61 mm and a width of 1 mm by a Thomson knife to prepare a test piece. The release film on one side of the test piece (frame shape) was peeled off and bonded to a polycarbonate plate (manufactured by TAKIRON Co., Ltd., hereinafter referred to as PC plate) having an outer size of 55 × 65 mm and a thickness of 1 mm. Then, the release film of the other surface is peeled off and removed so that the center of the opening of the PC board substantially coincides with the center of the test piece, and the center portion is provided with an opening of 38×50 mm and a size of 80×115 mm. A PC plate having a thickness of 2 mm was placed on the upper portion for 5 seconds, and two PC plates were bonded together, and then allowed to stand at 23 ° C for 24 hours, followed by solidification to prepare a test sample.

The test sample was placed on the fixing jig so that the PC plate having the opening portion was the upper surface, and 300 g of the vertical plate was passed through the PC plate of the opening tribe to the lower surface from the height of the drop of 5 cm to apply an impact. When the peeling was not confirmed, the drop height was raised every 5 cm, and the impact was again applied, and the drop height at which the peeling was confirmed was measured. The measurement was carried out at 23 °C.

(5) Stamping processability

The obtained two-sided adhesive sheet was punched into a frame shape of an outer size of 46×61 mm and a width of 1 mm by a Thomson knife to prepare a test piece. The press workability was evaluated based on the workability when the test piece was taken from the Thomson knife.

×: The test piece is not easily peeled off from the knife. In order to obtain a test piece that maintains the shape of the frame, the test piece must be carefully peeled off from the knife.

○: The test piece is easily peeled off from the knife, and the test piece which maintains the shape of the frame can be easily obtained.

[Industrial availability]

According to the present invention, it is possible to provide an adhesive sheet for an electronic device which is excellent in impact resistance and which is not easily offset even when a load is applied in the shearing direction and which is excellent in rebound resistance.

1‧‧‧Electronic machines

2‧‧‧Adhesive sheets for electronic machines

3‧‧‧ Cover

4‧‧‧Touch panel module

5‧‧‧Display panel module

Claims (4)

An adhesive sheet for an electronic device comprising an adhesive layer containing 100 parts by weight of an acrylic copolymer and 20 to 35 parts by weight of an adhesion-imparting resin having a softening point of 110 ° C or less and an alcoholic hydroxyl value of 30 or more. The content of (a) 2-ethylhexyl acrylate is 24.7 to 58.98% by weight, (b) butyl acrylate is 30 to 50% by weight, (c) methyl acrylate is 10 to 20% by weight, and (d) acrylic acid is 1 to 5 And the weight average molecular weight (Mw) is 800,000 or more, and the weight average molecular weight (Mw) is 800,000 or more, and the adhesive layer is made of a crosslinking agent, and (e) 0.02 to 0.3% by weight of a mixed monomer having a hydroxyl group (meth) acrylate. Cross-linking into a gel fraction of 20 to 50%. An adhesive sheet for an electronic device according to the first aspect of the invention, wherein the adhesive-imparting resin is a resin which is a rosin-based adhesive. The adhesive sheet for an electronic device according to claim 1 or 2, wherein the adhesive layer has a tan δ peak at a dynamic viscoelastic main curve of 25 ° C of 800 to 10000 Hz. An adhesive sheet for an electronic device according to claim 1, 2 or 3, which has a substrate, and the substrate is not a foam.