WO2015029834A1

WO2015029834A1 - Adhesive sheet, article, and electronic device

Info

Publication number: WO2015029834A1
Application number: PCT/JP2014/071623
Authority: WO
Inventors: 央深澤; 岩崎　剛; 秀晃武井; 優紀小川
Original assignee: Dic株式会社
Priority date: 2013-08-30
Filing date: 2014-08-19
Publication date: 2015-03-05
Also published as: JPWO2015029834A1; JP5812223B2

Abstract

The problem to be solved by the present invention is to provide an adhesive sheet which can exert a peel property at such a level that the adhesive sheet and an object to which the adhesive sheet is adhered can be separated from each other easily upon the application of a certain amount of force. The present invention relates to an adhesive sheet characterized by comprising a foam base material (A) that has a density of 550 to 800 kg/m³ and an adhesive agent layer (B) that is provided on one surface or both surfaces of the foam base material (A). The adhesive sheet has an excellent peel property. An adhesive sheet which is included within the scope of the aforementioned adhesive sheet and has a more proper density has an excellent peel property as mentioned above and also has excellent impact resistance.

Description

Adhesive sheet, article and electronic device

The present invention relates to a pressure-sensitive adhesive sheet that can be used for fixing various parts constituting electronic equipment and the like.

¡Adhesive sheets are used to fix parts that make up various electronic devices. For example, in the manufacturing scenes of small electronic devices such as mobile phones, cameras, and personal computers, adhesive sheets are used to secure the protective panel and housing of the image display unit, exterior parts, batteries, and various member modules. Yes.

As a pressure-sensitive adhesive sheet that can be used for fixing components constituting a small electronic device or the like, a thin pressure-sensitive adhesive sheet having good followability is suitably used. For example, a pressure-sensitive adhesive sheet using a flexible foam as a base material. A sheet is known (see, for example, Patent Document 1).

On the other hand, as the functions of the small electronic devices increase, expensive parts such as a thin plate-shaped rigid body such as a protective panel for an image display unit, an image display module, and a thin battery are often used. Yes. Therefore, in the event of a malfunction of the electronic device, in order to promote the reuse of normal parts, etc., it has a level of releasability that allows the adhesive sheet to be separated from the parts relatively easily and efficiently. There is a demand for adhesive sheets.

However, since the foam constituting the conventional pressure-sensitive adhesive sheet is relatively flexible and has a low density, when the pressure-sensitive adhesive sheet is peeled from the surface of the component, the foam is cracked, and the surface of the component In some cases, a part of the pressure-sensitive adhesive sheet remains.

JP 2010-155969 A

The problem to be solved by the present invention is that when a certain force is applied, the adherend and the pressure-sensitive adhesive sheet can be easily separated without causing a crack in the foam base material. It is to provide an adhesive sheet.

The present inventors have found that the above problem can be solved by using the specific foam substrate (A).

That is, the present invention relates to a pressure-sensitive adhesive sheet characterized by having a pressure-sensitive adhesive layer (B) on one or both sides of a foam substrate (A) having a density of 550 kg / m ³ to 800 kg / m ^3. .

The pressure-sensitive adhesive sheet of the present invention has a level of releasability that allows the adherend and the pressure-sensitive adhesive sheet to be easily separated without causing cracking of the foam base material when a certain force is applied. Moreover, the adhesive sheet of this invention is excellent in the said peelability, and excellent in impact resistance. For this reason, even when an impact such as dropping is applied to an electronic device manufactured using the pressure-sensitive adhesive sheet of the present invention, it is difficult for parts to be detached and the like. Specific parts can be efficiently separated from recycled products. The pressure-sensitive adhesive sheet of the present invention can be suitably applied to, for example, fixing parts for small electronic devices, particularly fixing thin plate-like rigid parts such as protective panels, image display modules, and thin batteries for information display units of small electronic devices. .

It is the conceptual diagram which looked at the test piece used for the test for impact tests from the upper surface. It is the conceptual diagram which looked at the test piece used for the test for impact tests from the upper surface. It is a conceptual diagram of the test method of an impact resistance test.

The pressure-sensitive adhesive sheet of the present invention is characterized by having a pressure-sensitive adhesive layer (B) on one side or both sides of a foam substrate (A) having a density of 550 kg / m ³ to 800 kg / m ³ .

As the foam base material (A) constituting the pressure-sensitive adhesive sheet of the present invention, one having a density of 550 kg / m ³ to 800 kg / m ³ is used. By using a foam substrate having a density in the above range, a pressure-sensitive adhesive sheet excellent in peelability can be obtained. The density is preferably in the range of 570 kg / m ³ to 800 kg / m ³ , more preferably in the range of 600 kg / m ³ to 800 kg / m ³ , and in the range of 650 kg / m ³ to 770 kg / m ³ . It is preferable for obtaining a pressure-sensitive adhesive sheet excellent in impact resistance and peelability. In addition, the said density refers to the value measured by the method according to JISK6767.

Moreover, it is preferable to use a foam base material (A) having an interlayer strength of 4 N / cm or more in order to obtain a pressure-sensitive adhesive sheet having more suitable impact resistance. It is more preferable to use what is cm or more.

The interlayer strength can be measured by the following method.

On both sides of the foam substrate (A), a pressure-sensitive adhesive layer having a thickness of 50 μm is formed with strong adhesiveness (a polyethylene terephthalate film (2) described later and a material that does not peel off from the foam substrate in the following high-speed peel test). The provided sheet is aged in an environment of 40 ° C. for 48 hours to produce an adhesive sheet for measuring interlayer strength.

Next, a 25 μm-thick polyethylene terephthalate film (1) attached to the pressure-sensitive adhesive layer on one side of the pressure-sensitive adhesive sheet for measuring interlaminar strength and backed is cut into a size of 1 cm in width and 15 cm in length. A test piece was obtained.

Next, after placing a polyethylene terephthalate film (2) having a thickness of 50 μm, a width of 3 cm and a length of 20 cm on the other pressure-sensitive adhesive layer constituting the test piece at 23 ° C. and 50% RH, a 2 kg roller The polyethylene terephthalate film (2) is reciprocated once by reciprocating the film, and left in a 60 ° C. environment for 48 hours, and then left in a 23 ° C. environment for 24 hours. I got a thing.

Next, the polyethylene terephthalate film (2) constituting the pressure-bonded product is fixed to a mounting jig of a high-speed peel tester at 23 ° C. and 50% RH, and the polyethylene terephthalate film (1) is pulled at a speed of 15 m / min. The maximum strength when the foam substrate (A) is torn is measured by pulling in the 90 degree direction. The maximum strength was defined as the interlayer strength.

The foam substrate (A) preferably has a tensile strength in the flow direction of 15 N / cm to 30 N / cm, more preferably 15 N / cm to 20 N / cm, and the foam substrate (A It is preferable to use a sheet having a tensile strength in the width direction of 5 N / cm to 15 N / cm in order to obtain a pressure-sensitive adhesive sheet with even more suitable peelability.

The foam substrate (A) has a tensile strength in the range of 5 N / cm to 10 N / cm when the tensile elongation in the flow direction is 10%, and the foam substrate (A) In order to obtain a pressure-sensitive adhesive sheet having even more preferable peelability, it is preferable to use a material having a tensile strength in the range of 4 N / cm to 10 N / cm when the tensile elongation in the width direction is 10%. preferable.

In addition, the tensile strength of the width direction and flow direction of the said foam base material (A) can be measured according to JISK6767. Specifically, a test piece obtained by cutting the foam base material (A) into a mark with a length of 2 cm and a width of 1 cm in an environment of 23 ° C. and 50% RH was used as a Tensilon tensile tester (tensile The maximum strength measured using a speed of 300 mm / min was defined as the tensile strength. The said tensile strength is a value with respect to the magnitude | size of width 1cm of a foam base material (A), and is a value which does not consider the thickness of the said foam base material (A).

The average cell diameter in the width direction and the flow direction of the foam substrate (A) is not particularly limited, but is preferably in the range of 10 μm to 300 μm, more preferably in the range of 10 μm to 150 μm. The range of 100 μm is more preferable for obtaining a pressure-sensitive adhesive sheet having more suitable impact resistance and peelability.

The average cell diameter in the thickness direction of the foam substrate (A) is preferably 3 μm to 100 μm, more preferably 5 μm to 80 μm, and even more preferably 5 μm to 50 μm. The average cell diameter in the thickness direction is preferably 1/2 or less, and preferably 1/3 or less of the thickness of the foam substrate (A). By using a foam base material in which the ratio of the average cell diameter and thickness in the thickness direction is in the above-described range, a pressure-sensitive adhesive sheet excellent in peelability and impact resistance can be obtained.

The average cell diameter in the width direction, the flow direction, and the thickness direction of the foam base material (A) is a value measured in the following manner.

First, the foam base material (A) is cut into a square of 1 cm in the width direction and 1 cm in the flow direction to obtain a test piece.

Next, an image obtained by enlarging the test piece with a digital microscope (trade name “KH-7700”, manufactured by HiROX) at a magnification of 200 times is taken. To do.

From the image, the bubble diameter in the flow direction and the thickness direction of all the bubbles present in the range of the cut surface of “length 1.52 mm × thickness” among the cut surfaces in the flow direction of the test piece. Each bubble diameter is measured, and the average bubble diameter is calculated from each average value.

In addition, the bubbles in the flow direction and the bubbles in the thickness direction of all the bubbles present in the range of the cut surface consisting of “length 1.52 mm × thickness” among the cut surfaces in the width direction of the test piece. Each diameter is measured, and the average bubble diameter is calculated from each average value.

The foam substrate (A) preferably has a thickness of 250 μm or less, more preferably 50 μm to 250 μm, and more preferably 80 μm to 200 μm. It is more preferable to use one having a thickness of 100 μm to 150 μm because a pressure-sensitive adhesive sheet having both suitable impact resistance and peelability can be obtained even if it is thin.

The density, interlayer strength, and tensile strength of the foam base material (A) can be appropriately adjusted by selecting the material and foam structure of the foam base material to be used.

The foam substrate (A) is not particularly limited as long as it can realize the above interlayer strength, etc., but is obtained using polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, or the like. Polyolefin foam, polyurethane foam, rubber foam obtained using acrylic rubber or other elastomers can be used, and a pressure sensitive adhesive sheet with even better impact resistance can be obtained. It is preferable to use a polypropylene-based foam.

As the polyolefin foam, a foam obtained by foaming the polyolefin resin can be used. The polyolefin-based foam may be partially formed with a crosslinked structure, but in the case of a polypropylene-based foam, a crosslinked structure is formed as much as possible in order to provide suitable peelability and impact resistance. It is preferable to use those not present.

The foam base material (A) can be produced, for example, by mixing the polypropylene or the like with a foaming agent such as sodium hydrogencarbonate, a crosslinking agent, or the like, if necessary, and heating as necessary. it can. The heating can be performed, for example, at a temperature of 50 ° C. to 120 ° C. for about 3 hours to 24 hours.

The foam substrate (A) is prepared by, for example, extruding a mixture of a polyolefin such as polypropylene or polyethylene and, if necessary, a foaming agent such as sodium hydrogen carbonate, a metallocene catalyst, a crosslinking agent, or the like. It can be produced by foaming and molding by a molding method or the like.

The foam base material (A) is a gas at room temperature such as carbon dioxide or nitrogen to a polymer composition containing a polyolefin such as polypropylene or polyethylene and, if necessary, a thermoplastic elastomer such as ethylene-propylene rubber. A substance impregnated under a high temperature and high pressure condition such as a supercritical state can be produced by releasing the pressure by an extrusion molding method or the like and foaming and molding.

As the foam substrate (A), a colored one can be used for obtaining an adhesive sheet having excellent design properties, light shielding properties, concealing properties, light reflection properties, and light resistance.

As the colorant, conventionally known pigments and dyes such as carbon black can be used alone or in combination of two or more.

As the colored foam base material, for example, when obtaining a pressure-sensitive adhesive sheet having light-shielding property, concealing property, and light resistance, it is preferable to use a black-colored foam base material.

Examples of the foam base material (A) include plasticizers, antioxidants, foaming aids such as zinc oxide, cell core modifiers, thermal stabilizers, flame retardants such as aluminum hydroxide and magnesium hydroxide, and antistatic properties. An agent, a hollow balloon made of glass or plastic, beads, a filler such as a metal or a metal compound, a conductive filler, a thermally conductive filler, or the like can be used.

As the foam substrate (A), for the purpose of further improving the adhesion with the pressure-sensitive adhesive layer (B) and other layers, corona treatment, flame treatment, plasma treatment, hot air treatment, ozone treatment, Those subjected to surface treatment such as UV treatment and application of an easy-adhesion treatment agent can be used.

As the foam base material (A), it is preferable to use a material having a surface wetting index of 36 mN / m or more, measured using a wetting reagent, and 40 mN / m. More preferably, it is more preferably 48 mN / m or more because the adhesiveness of the pressure-sensitive adhesive layer (B) and the like can be further improved.

As the pressure-sensitive adhesive layer (B) constituting the pressure-sensitive adhesive sheet of the present invention, those formed using a conventionally known pressure-sensitive adhesive can be used.

Examples of the pressure-sensitive adhesive that can be used for forming the pressure-sensitive adhesive layer (B) include an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a synthetic rubber-based pressure-sensitive adhesive, a natural rubber-based pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive. It contains an acrylic polymer (b1) obtained by polymerizing a monomer component containing a (meth) acrylic monomer, and contains a tackifier resin, a crosslinking agent (b2) and the like as necessary. It is preferable to use an acrylic pressure sensitive adhesive.

Examples of the (meth) acrylic monomer that can be used for the production of the acrylic polymer (b1) include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl (meth) acrylate. , T-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate (Meth) acrylates having an alkyl group having 1 to 12 carbon atoms, such as, can be used.

Among these, as the (meth) acrylic monomer, it is preferable to use a (meth) acrylate having an alkyl group having 4 to 12 carbon atoms, and having an alkyl group having 4 to 8 carbon atoms. It is more preferable to use (meth) acrylate, and it is particularly preferable to use one or both of n-butyl acrylate and 2-ethylhexyl acrylate in order to achieve both excellent adhesive strength and excellent peelability. .

The (meth) acrylate having an alkyl group having 1 to 12 carbon atoms is preferably used in an amount of 60% by mass or more based on the total amount of monomers used for the production of the acrylic polymer (b1). It is more preferable to use in the range of mass% to 98.5% by mass, and to use in the range of 90% to 98.5% by mass in order to achieve both excellent adhesive strength and excellent peelability. Further preferred.

Further, when the acrylic polymer (b1) is produced, a highly polar vinyl monomer can be used as a monomer. As the highly polar vinyl monomer, a vinyl monomer having a hydroxyl group, a vinyl monomer having a carboxyl group, a vinyl monomer having an amide group, or the like can be used alone or in combination.

Examples of the monomer having a hydroxyl group include a hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate. (Meth) acrylates can be used.

As the vinyl monomer having a carboxyl group, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth) acrylic acid dimer, crotonic acid, ethylene oxide-modified oxalic acid acrylate, etc. can be used. Of these, acrylic acid is preferably used.

As the monomer having an amide group, for example, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N, N-dimethylacrylamide and the like can be used.

As the highly polar vinyl monomer, vinyl acetate, 2-acrylamido-2-methylpropane sulfonic acid and the like can be used in addition to those described above.

The highly polar vinyl monomer is preferably used in the range of 1.5% by mass to 20% by mass with respect to the total amount of monomers used for the production of the acrylic polymer (b1). More preferably, it is used in the range of 5% by mass to 10% by mass, and more preferably in the range of 2% by mass to 8% by mass in order to achieve both excellent adhesive strength and excellent peelability.

When using what contains the crosslinking agent (b2) mentioned later as said adhesive, as said acrylic polymer (b1), the acrylic type which has the functional group which reacts with the functional group which the said crosslinking agent (b2) has It is preferred to use a polymer. Examples of the functional group that the acrylic polymer may have include a hydroxyl group.

The hydroxyl group can be introduced into the acrylic polymer (b1) by using, for example, a vinyl monomer having a hydroxyl group as the monomer.

The vinyl monomer having a hydroxyl group is preferably used in the range of 0.01% by mass to 1.0% by mass with respect to the total amount of monomers used for the production of the acrylic polymer (b1). More preferably, it is used in the range of 0.03% by mass to 0.3% by mass.

The acrylic polymer (b1) can be produced by polymerizing the monomer by a method such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, or an emulsion polymerization method. Adopting it is preferable for improving the production efficiency of the acrylic polymer (b1).

Examples of the solution polymerization method include a method in which the monomer, a polymerization initiator, and an organic solvent are mixed and stirred at a temperature of preferably 40 ° C. to 90 ° C. for radical polymerization.

Examples of the polymerization initiator include peroxides such as benzoyl peroxide and lauryl peroxide, azo thermal polymerization initiators such as azobisisobutylnitrile, acetophenone photopolymerization initiators, benzoin ether photopolymerization initiators, benzyl A ketal photopolymerization initiator, an acyl phosphine oxide photopolymerization initiator, a benzoin photopolymerization initiator, a benzophenone photopolymerization initiator, or the like can be used.

The acrylic polymer (b1) obtained by the above method may be in a state of being dissolved or dispersed in an organic solvent, for example, when produced by a solution polymerization method.

As the acrylic polymer (b1), those having a weight average molecular weight of 400,000 to 3 million are preferably used, and those having a weight average molecular weight of 800,000 to 2.5 million are more preferably used.

The weight average molecular weight is a value measured by gel permeation chromatography (GPC method) and calculated in terms of standard polystyrene. Specifically, the weight average molecular weight can be measured using a GPC apparatus (HLC-83209 GPC) manufactured by Tosoh Corporation under the following conditions.

Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μl
Eluent: Tetrahydrofuran Flow rate: 1.0 ml / min Measuring temperature: 40 ° C
This column: TSKgel GMHHR-H (20) 2 Guard column: TSKgel HXL-H
Detector: Differential refractometer Weight average molecular weight of standard polystyrene: 10,000 to 20 million (manufactured by Tosoh Corporation)

The pressure-sensitive adhesive that can be used to form the pressure-sensitive adhesive layer (B) includes excellent adhesion to the adherend and foam substrate (A), and excellent peeling to the adherend when a certain force is applied. From the standpoint of compatibility, it is preferable to use one containing a tackifier resin.

Examples of the tackifying resin include a rosin tackifying resin, a polymerized rosin tackifying resin, a polymerized rosin ester tackifying resin, a rosin phenol tackifying resin, a stabilized rosin ester tackifying resin, and a disproportionated rosin ester. -Based tackifier resins, hydrogenated rosin ester-based tackifier resins, terpene-based tackifier resins, terpene phenol-based tackifier resins, petroleum resin-based tackifier resins, (meth) acrylate resin-based tackifier resins, and the like. . When using an emulsion-type pressure-sensitive adhesive as the pressure-sensitive adhesive, it is preferable to use an emulsion-type tackifying resin as the tackifying resin.

Examples of the tackifying resin include disproportionated rosin ester tackifying resin, polymerized rosin ester tackifying resin, rosin phenol tackifying resin, hydrogenated rosin ester tackifying resin, (meth) acrylate, among others. It is preferable to use one or a combination of two or more of resins, terpene phenol resins, and petroleum resins.

As the tackifying resin, those having a softening point in the range of 30 ° C. to 180 ° C. are preferably used, and those having a softening point in the range of 70 ° C. to 140 ° C. are preferably used. It is more preferable to achieve both excellent adhesive strength with respect to) and excellent peelability with respect to the adherend when a certain force is applied. When the (meth) acrylate tackifying resin is used, the (meth) acrylate tackifying resin preferably has a glass transition temperature of 30 ° C. to 200 ° C., and preferably has a glass transition temperature of 50 ° C. to 160 ° C. It is more preferable.

The tackifying resin is preferably used in the range of 5 to 65 parts by mass, and preferably in the range of 8 to 55 parts by mass with respect to 100 parts by mass of the acrylic polymer (b1). It is more preferable to achieve both excellent adhesion to the adherend and foam substrate (A) and excellent peelability to the adherend when a certain force is applied.

As the pressure-sensitive adhesive used for forming the pressure-sensitive adhesive layer (B), excellent adhesion to the adherend and the foam substrate (A) and excellent peeling to the adherend when a certain force is applied. It is preferable to use a crosslinking agent (b2) when forming the pressure-sensitive adhesive layer (B) having both properties.

As the crosslinking agent (b2), for example, an isocyanate crosslinking agent, an epoxy crosslinking agent, a metal chelate crosslinking agent, an aziridine crosslinking agent and the like can be used. Among these, as the crosslinking agent (b2), it is preferable to use either or both of an isocyanate crosslinking agent and an epoxy crosslinking agent that are highly reactive with the acrylic polymer (b1). More preferably, an agent is used.

Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, trimethylolpropane modified tolylene diisocyanate, and the like. It is preferable to use trimethylolpropane-modified tolylene diisocyanate.

The crosslinking agent (b2) is preferably used in an amount such that the gel fraction of the pressure-sensitive adhesive layer (B) with respect to toluene is 70% by mass or less, and the gel fraction is 20% by mass to 60% by mass. It is more preferable to select and use an amount, and to select and use an amount with a gel fraction of 25% by mass to 55% by mass has excellent adhesion to the adherend and the foam substrate (A). Further, it is more preferable to obtain a pressure-sensitive adhesive sheet that achieves both excellent releasability from an adherend when a certain force is applied.

In addition, the said gel fraction points out the value measured by the method shown below.

The pressure-sensitive adhesive coated on the release treatment surface of the release liner so that the thickness after drying is 50 μm is dried for 3 minutes in an environment of 100 ° C., and then 2 in an environment of 40 ° C. The pressure-sensitive adhesive layer was formed by aging for a day.

The test piece was prepared by cutting the pressure-sensitive adhesive layer into a square having a length of 50 mm and a width of 50 mm.

After measuring the mass (G1) of the test piece, the test piece was immersed in toluene in a 23 ° C. environment for 24 hours.

After the immersion, the insoluble component in toluene was extracted by filtering the mixture of the test piece and toluene using a 300 mesh wire net. The mass (G2) of the insoluble component dried at 110 ° C. for 1 hour was measured.

The gel fraction was calculated based on the mass (G1), mass (G2) and the following formula.

Gel fraction (% by mass) = (G2 / G1) × 100

Examples of the pressure-sensitive adhesive include plasticizers, softeners, antioxidants, flame retardants, glass and plastic fibers and balloons, beads, metals, metal oxides, metal nitride fillers, pigments, dyes, and the like. What contains additives, such as a coloring agent, a leveling agent, a thickener, a water repellent, an antifoamer, can be used.

The pressure-sensitive adhesive layer (B) that can be formed using the above-mentioned pressure-sensitive adhesive preferably has a temperature that exhibits a peak value of loss tangent (tan δ) at a frequency of 1 Hz, preferably -40 ° C. to 15 ° C. By making the peak value of the loss tangent of the pressure-sensitive adhesive layer within the above range, it becomes easy to impart good adhesion to the adherend at room temperature. In particular, in improving the drop impact resistance in a low temperature environment, it is more preferably −35 ° C. to 10 ° C., and further preferably −30 ° C. to 6 ° C.

The loss tangent (tan δ) at a frequency of 1 Hz is obtained from the equation of tan δ = G ″ / G ′ from the storage elastic modulus (G ′) and loss elastic modulus (G ″) obtained by dynamic viscoelasticity measurement by temperature dispersion. It is done. In the measurement of dynamic viscoelasticity, a pressure-sensitive adhesive layer formed to a thickness of about 2 mm was used using a viscoelasticity testing machine (trade name: ARES G2 manufactured by T.A. Instruments Japan). A test piece is sandwiched between parallel disks having a diameter of 8 mm, which is a measuring part, and a storage elastic modulus (G ′) and a loss elastic modulus (G ″) from −50 ° C. to 150 ° C. are measured at a frequency of 1 Hz.

The thickness of the pressure-sensitive adhesive layer (B) used in the present invention is excellent adhesion to the adherend and foam substrate (A), and excellent peelability to the adherend when a certain force is applied. In other words, the thickness is preferably 5 μm to 100 μm, more preferably 10 μm to 80 μm, and particularly preferably 15 μm to 80 μm.

The pressure-sensitive adhesive sheet of the present invention is, for example, a direct method in which the pressure-sensitive adhesive is directly applied to the foam substrate (A) and dried, or a pressure-sensitive adhesive layer ( After forming B), it can be produced by a transfer method in which it is bonded to the foam substrate (A). When an adhesive containing an acrylic polymer (b1) and a crosslinking agent (b2) is used as an adhesive for forming the adhesive layer (B), the foam substrate (A ) And the adhesive layer (B) laminated on one side or both sides is preferably aged in an environment of 20 ° C. to 50 ° C., more preferably 23 ° C. to 45 ° C. for about 2 to 7 days. It is preferable in order to achieve both excellent adhesion to the adherend and foam substrate (A) and excellent peelability to the adherend when a certain force is applied.

As the pressure-sensitive adhesive sheet of the present invention, it is preferable to use a sheet having a thickness of 300 μm or less because it is easy to contribute to thinning of a small electronic device, and it is more preferable to use a sheet having a thickness of 80 μm to 300 μm. It is more preferable to use a film having a thickness of 300 μm because it is possible to achieve both suitable impact resistance, peelability and thinness.

As the pressure-sensitive adhesive sheet of the present invention, a release sheet may be laminated on the surface of the pressure-sensitive adhesive layer (B).

As the release sheet, for example, a film obtained by using a synthetic resin such as polyethylene, polypropylene, polyester, paper, non-woven fabric, cloth, foamed sheet, metal substrate, and at least one side of a laminate thereof is treated with silicone. In addition, those subjected to a peeling treatment such as a long-chain alkyl treatment or a fluorine treatment can be used.

The pressure-sensitive adhesive sheet of the present invention is a component of a small electronic device, for example, a protection panel or an image display module for an information display unit of a small electronic device, a thin battery, a speaker, a receiver, a piezoelectric element, a printed circuit board, a flexible printed circuit board (FPC), It can be suitably applied to digital camera modules, sensors, other modules, cushioning rubber members such as polyurethane and polyolefin, decorative parts and various members. In particular, the present invention can be suitably applied to fixing thin plate-like rigid parts such as a protection panel, an image display module, and a thin battery for an information display unit of a small electronic device.

(Preparation of adhesive composition (I))
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 44.94 parts by mass of n-butyl acrylate, 50 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of vinyl acetate, acrylic acid 2 Mass part, 0.06 part by mass of 4-hydroxybutyl acrylate, 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator was dissolved in a solvent consisting of 100 parts by mass of ethyl acetate, and 70 ° C. For 12 hours to obtain a solvent solution of an acrylic copolymer having a weight average molecular weight of 1,200,000 (in terms of polystyrene).

Next, 10 parts by weight of “Pencel D135” (pentaerythritol ester of polymerized rosin) manufactured by Arakawa Chemical Industries, Ltd. is added to 100 parts by weight of the acrylic copolymer, and ethyl acetate is further added to the mixture. A pressure-sensitive adhesive composition (I) having a nonvolatile content of 45% by mass was obtained.

(Preparation of adhesive composition (II))
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 97.97 parts by mass of n-butyl acrylate, 2.0 parts by mass of acrylic acid, 0.03 parts by mass of 4-hydroxybutyl acrylate Part by weight, 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator was dissolved in a solvent consisting of 100 parts by mass of ethyl acetate, and polymerized at 70 ° C. for 12 hours to obtain a weight average molecular weight. A solvent solution of 2 million (polystyrene equivalent) acrylic copolymer was obtained.

Next, 25 parts by mass of “Super Ester A100” (glycerin ester of disproportionated rosin) manufactured by Arakawa Chemical Industries, Ltd. and “Pencel D135” manufactured by Arakawa Chemical Industries, Ltd. By adding 5 parts by mass of polymerized rosin pentaerythritol ester) and 20 parts by mass of “FTR6100” (styrene-based petroleum resin) manufactured by Mitsui Chemicals, Inc. and further mixing with ethyl acetate, an adhesive having a nonvolatile content of 40% by mass Agent composition (II) was obtained.

(Preparation of pressure-sensitive adhesive composition (III))
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 92.9 parts by mass of n-butyl acrylate, 3 parts by mass of vinyl acetate, 4 parts by mass of acrylic acid, 2-hydroxyethyl acrylate 0.1 parts by mass, 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator was dissolved in a solvent consisting of 100 parts by mass of ethyl acetate and polymerized at 70 ° C. for 12 hours. A solvent solution of an acrylic copolymer having a weight average molecular weight of 1,700,000 (polystyrene conversion) was obtained.

Next, with respect to 100 parts by mass of the acrylic copolymer, 9.4 parts by mass of “Superester A100” (glycerin ester of disproportionated rosin) manufactured by Arakawa Chemical Industries, Ltd. and “Pencel D135 manufactured by Arakawa Chemical Industries, Ltd.” ”(Polymeric rosin pentaerythritol ester) 9.4 parts by mass was added, and ethyl acetate was further added and mixed to obtain an adhesive composition (III) having a nonvolatile content of 40% by mass.

Example 1
1.1 parts by mass of “Coronate L-45” (isocyanate-based crosslinking agent, solid content 45% by mass) manufactured by Nippon Polyurethane Industry Co., Ltd. is added to 100 parts by mass of the pressure-sensitive adhesive composition (I), and the mixture is stirred for 15 minutes. After that, the pressure-sensitive adhesive layer was coated on the release-treated surface of the peeled polyethylene terephthalate film having a thickness of 75 μm so that the thickness of the pressure-sensitive adhesive layer after drying was 50 μm and dried at 80 ° C. for 3 minutes. Formed. The pressure-sensitive adhesive layer had a gel fraction of 50% by mass.

Next, black polyolefin foam (1) (thickness 100 μm, density 657 kg / m ³ , interlayer strength 5.4 N / cm, flow direction tensile strength: 17.1 N / cm, width direction tensile strength: 11. The pressure-sensitive adhesive layer was transferred and bonded to both surfaces of a substrate made of 2N / cm), and then laminated with a roll at 23 ° C. and a linear pressure of 5 kgf / cm. Then, the double-sided adhesive sheet with a total thickness of 200 μm was obtained by aging at 40 ° C. for 48 hours.

(Example 2)
Instead of the black polyolefin foam (1), the black polyolefin foam (2) (thickness 100 μm, density 735 kg / m ³ , interlayer strength 7.4 N / cm, flow direction tensile strength: 19.6 N / cm A double-sided PSA sheet having a total thickness of 200 μm was obtained in the same manner as in Example 1 except that the tensile strength in the width direction was 11.6 N / cm.

Example 3
Instead of the black polyolefin foam (1), the black polyolefin foam (3) (thickness 100 μm, density 762 kg / m ³ , interlayer strength 7.6 N / cm, flow direction tensile strength: 19.8 N / cm A double-sided PSA sheet having a total thickness of 200 μm was obtained in the same manner as in Example 1 except that the tensile strength in the width direction was 12.0 N / cm.

Example 4
To 100 parts by mass of the pressure-sensitive adhesive composition (II), 1.3 parts by mass of “Coronate L-45” (isocyanate-based crosslinking agent, solid content 45% by mass) manufactured by Nippon Polyurethane Industry Co., Ltd. was added and stirred for 15 minutes. After that, the pressure-sensitive adhesive layer was coated on the release-treated surface of the peeled polyethylene terephthalate film having a thickness of 75 μm so that the thickness of the pressure-sensitive adhesive layer after drying was 50 μm and dried at 80 ° C. for 3 minutes. Formed. The gel fraction of the pressure-sensitive adhesive layer was 43% by mass.

Next, the pressure-sensitive adhesive layer was transferred and bonded to both surfaces of the base made of black polyolefin foam (1), and then laminated with a roll at 23 ° C. and a linear pressure of 5 kgf / cm. Then, the double-sided adhesive sheet with a total thickness of 200 μm was obtained by aging at 40 ° C. for 48 hours.

(Example 5)
Instead of black polyolefin foam (1), black polyolefin foam (4) (thickness 100 μm, density 550 kg / m ³ , interlayer strength 2.9 N / cm, flow direction tensile strength: 15.1 N / cm A double-sided PSA sheet having a total thickness of 200 μm was obtained in the same manner as in Example 1 except that the tensile strength in the width direction was 8.8 N / cm.

(Example 6)
A double-sided PSA sheet was obtained in the same manner as in Example 1 except that 100 parts by mass of the PSA composition (III) was used instead of 100 parts by mass of the PSA composition (I).

(Comparative Example 1)
Instead of the black polyolefin foam (1), the black polyolefin foam (5) (thickness 100 μm, density 330 kg / m ³ , interlayer strength 8.9 N / cm, flow direction tensile strength: 12.9 N / cm A double-sided PSA sheet having a total thickness of 200 μm was obtained in the same manner as in Example 1 except that the tensile strength in the width direction was 7.6 N / cm.

(Comparative Example 2)
In place of the black polyolefin foam (1), a polyethylene terephthalate film (6) (thickness 25 μm, density 1394 kg / m ³ , tensile strength in the flow direction: 47.6 N / cm, tensile strength in the width direction: 54.7 N / Cm), a double-sided PSA sheet having a total thickness of 200 μm was obtained in the same manner as in Example 1.

[Adhesive strength of adhesive layer by 180 ° peeling]
Under a temperature of 23 ° C. and a relative humidity of 50% RH, a 25 μm thick polyethylene terephthalate film is attached to one adhesive layer of the double-sided adhesive sheets obtained in the examples and comparative examples, thereby backing the adhesive layer. After that, it was cut into a rectangle having a length of 120 mm and a width of 20 mm.

Next, after placing an aluminum plate on the surface of the other pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet, they were pressure-bonded by reciprocating the upper surface of the aluminum plate once using a 2 kg roller.

Next, the pressure-bonded product was allowed to stand in an environment of a temperature of 23 ° C. and a relative humidity of 50% RH for 1 hour to obtain a test piece 1 in which the double-sided pressure-sensitive adhesive sheet and the aluminum plate were bonded.

Next, using the Tensilon tensile tester [manufactured by A & D Co., Ltd., model: RTM-100], the double-sided pressure-sensitive adhesive sheet is attached to the surface to which the double-sided pressure-sensitive adhesive sheet is attached in a state where the stainless steel plate constituting the test piece 1 is fixed. The strength at the time of peeling at a tensile speed of 300 mm / min in the direction of ° was measured.

[Thickness of foam substrate and adhesive sheet]
The thickness of the pressure-sensitive adhesive sheet from which the foam base material and the release liner were removed was measured using a dial series gauge G type manufactured by Ozaki Seisakusho.

[Density of foam substrate]
The density was measured by a method according to JISK6767.

[Interlayer strength of foam substrate]
Strong adhesive (both polyethylene terephthalate film (2), which will be described later and not peeled from the foam base material at the time of the following high-speed peel test), and a 50 μm thick adhesive layer on both surfaces of the foam base material Was aged for 48 hours in an environment of 40 ° C. to prepare an adhesive sheet for measuring interlayer strength.

Next, the polyethylene terephthalate film (2) constituting the pressure-bonded product is fixed to a mounting jig of a high-speed peel tester at 23 ° C. and 50% RH, and the polyethylene terephthalate film (1) is pulled at a speed of 15 m / min. The maximum strength was measured when the foam substrate was torn by pulling in the 90 degree direction. The maximum strength was defined as the interlayer strength of the foam base material.

[Tensile strength and tensile elongation of foam substrate]
The tensile strength between the width direction and the flow direction of the foam substrate was measured according to JISK6767. Specifically, a test piece obtained by cutting a foam base material into a size having a marked line length of 2 cm and a width of 1 cm in an environment of 23 ° C. and 50% RH was measured using a Tensilon tensile tester. The maximum strength obtained by measurement under the condition of 300 mm / min was taken as the tensile strength of the foam substrate.

Further, the tensile strength when the tensile elongation was 10% was measured by the same method as described above when the foam substrate was pulled 2 mm.

In addition, any of the above-mentioned tensile strengths is a value with respect to the size of the width 1 cm of the foam base material, and is a value not considering the thickness of the foam base material.

[Peelability evaluation method]
Prepare two double-sided PSA sheets that are 4cm long (flow direction of the foam base material) and 5mm wide (width direction of the foam base material) and mass (G0, release-treated polyethylene terephthalate film) Was not measured). Also, two polycarbonate plates having a length of 5 cm, a width of 5 cm, and a thickness of 2 mm were prepared, and the mass (G0 ′) was measured.

The two double-sided pressure-sensitive adhesive sheets are placed on the surface of one polycarbonate plate having a length of 5 cm, a width of 5 cm, and a thickness of 2 mm. On the surface, a length of 5 cm, a width of 5 cm, and a thickness of 2 mm different from the above are placed. A test piece was obtained by placing one polycarbonate plate and press-bonding it for 10 seconds with a load of 2 kg from the upper part, and allowing it to stand in an environment of 23 ° C. and 50% RH for 24 hours.

The peelability was evaluated based on the broken state of the double-sided pressure-sensitive adhesive sheet when the two polycarbonate plates constituting the test piece were peeled off and disassembled.

To the extent possible, pinch the edge of the double-sided PSA sheet and the residue left on the surface of the two polycarbonate plates and slowly pull the double-sided PSA sheet in the 135 ° direction with respect to the polycarbonate plate surface. They were peeled off.

Next, the mass (G1 ′) of the two polycarbonate plates after peeling was measured, and the mass of the residue derived from the double-sided PSA sheet on the surface of the polycarbonate plate was calculated based on the following formula.

Residual mass (g) = [mass of two polycarbonate plates after peeling (G1 ′)] − [mass of two polycarbonate plates before peeling (G0 ′)]

A: The double-sided pressure-sensitive adhesive tape was not cut and the foam base material layer was not broken by the peel test, and the residue derived from the double-sided pressure-sensitive adhesive sheet was less than 10% by mass relative to the mass (G0) of the double-sided pressure-sensitive adhesive sheet before application. It was.

○: The double-sided pressure-sensitive adhesive tape was cut or the foam base material layer was broken by the peel test, and the residue derived from the double-sided pressure-sensitive adhesive sheet was less than 10% by mass with respect to the mass (G0) of the double-sided pressure-sensitive adhesive sheet before application. It was.

X: The double-sided pressure-sensitive adhesive tape was cut or the foam base material layer was broken by the peel test, and the residue derived from the double-sided pressure-sensitive adhesive sheet was 10% by mass or more based on the mass (G0) of the double-sided pressure-sensitive adhesive sheet before application. It was.

[Impact resistance test]
Two double-sided pressure-sensitive adhesive sheets cut to a size of 40 mm in length and 5 mm in width on an acrylic plate (Mitsubishi Rayon Co., Ltd., Acrylite L, hue: transparent) having a thickness of 2 mm and an outer shape of 50 mm × 50 mm are spaced by 40 mm. And opened in parallel (FIG. 1).

After placing an acrylonitrile-butadiene-styrene plate (ABS plate) having a thickness of 2 mm and an outer shape of 150 mm × 100 mm (Taface R, hue: natural, no wrinkles) on the upper surface of the double-sided pressure-sensitive adhesive sheet, By reciprocating the upper surface of the ABS plate once using a 2 kg roller, they were pressure-bonded and allowed to stand in an environment of 23 ° C. for 1 hour to obtain a test piece.

2) A U-shaped measuring table (made of aluminum with a thickness of 5 mm) having a length of 150 mm, a width of 100 mm and a height of 45 mm is installed on the base of the DuPont impact tester (manufactured by Tester Sangyo Co., Ltd.). On the top, the test piece was placed so that the surface on the acrylic plate side faced downward (FIG. 3).

In an environment of 23 ° C., five stainless steel hitting cores having a diameter of 25 mm and a mass of 300 g were dropped from the position of 10 cm in height at intervals of 10 seconds on the surface of the test piece on the ABS plate side. After the dropping, when the destruction of the test piece and the peeling of the members constituting the test piece were not observed, the hitting core was dropped from the position of 20 cm in height at intervals of 10 seconds five times. Thereafter, after the dropping, when the test piece was not broken or the members constituting the test piece were not peeled off, the above test was repeated while increasing the fall height of the strike core by 10 cm. The height when the breakage of the material and the peeling of the members constituting the test piece occurred was measured.

Also, under a 0 ° C. environment, five stainless steel hitting cores having a diameter of 25 mm and a mass of 300 g were dropped from the position of 10 cm in height at intervals of 10 seconds on the surface of the test piece on the ABS plate side. After the dropping, when the destruction of the test piece and the peeling of the members constituting the test piece were not observed, the hitting core was dropped from the position of 20 cm in height at intervals of 10 seconds five times. Thereafter, after the dropping, when the test piece was not broken or the members constituting the test piece were not peeled off, the above test was repeated while increasing the fall height of the strike core by 10 cm. The height when the breakage of the material and the peeling of the members constituting the test piece occurred was measured.

As in Examples 1 to 5, the pressure-sensitive adhesive sheet of the present invention was provided with excellent peelability and impact resistance. In addition, the double-sided PSA sheets described in Examples 1 to 3 had excellent impact resistance even at low temperatures. On the other hand, the pressure-sensitive adhesive sheet described in Comparative Example 1 was not sufficient in terms of peelability. Moreover, although the adhesive sheet described in Comparative Example 2 did not have the cut of the double-sided PSA sheet or the destruction of the base material layer by the peel test, there were many residues derived from the double-sided PSA sheet, and it was easily removed from the surface of the polycarbonate plate. Could not be removed.

DESCRIPTION OF SYMBOLS 1 Adhesive sheet 2 Acrylic board 3 ABS board 4 U-shaped measuring stand 5 Strike core

Claims

A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer (B) on one side or both sides of a foam substrate (A) having a density of 550 kg / m 3 to 800 kg / m 3 .
The pressure sensitive adhesive sheet according to claim 1 whose total thickness is 300 micrometers or less.
The tensile strength in the flow direction of the foam substrate (A) is 15 N / cm to 30 N / cm, and the tensile strength in the width direction of the foam substrate (A) is 5 N / cm to 15 N / cm. Item 3. The pressure-sensitive adhesive sheet according to item 1 or 2.
The tensile strength when the tensile elongation in the flow direction of the foam substrate (A) is 10% is in the range of 5 N / cm to 10 N / cm, and the width direction of the foam substrate (A) The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the tensile strength when the tensile elongation of the resin is 10% is in the range of 4 N / cm to 10 N / cm.
The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the foam substrate (A) is a polypropylene-based foam.
The pressure-sensitive adhesive according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive layer (B) is a layer formed using a pressure-sensitive adhesive containing an acrylic polymer (b1) and a crosslinking agent (b2). Sheet.
An article having a configuration in which two or more adherends are bonded by the pressure-sensitive adhesive sheet according to any one of claims 1 to 6.
An electronic apparatus having a configuration in which two or more cases are bonded by the pressure-sensitive adhesive sheet according to any one of claims 1 to 6.