JP6894282B2 - Adhesive tape and adhesive tape for fixing electronic device parts - Google Patents

Description

The present invention relates to an adhesive tape having excellent resistance to sebum and capable of maintaining adhesive strength even in a portion frequently touched by human hands, and an adhesive tape for fixing electronic device parts made of the adhesive tape.

Conventionally, adhesive tapes have been widely used for fixing parts in electrical equipment. In addition to the adhesiveness, such an adhesive tape is provided with functions such as heat resistance, thermal conductivity, and impact resistance depending on the environment of the part to be used (for example, Patent Documents 1 to 3).

In recent years, due to the miniaturization, weight reduction, and cost reduction of electronic devices, electronic devices such as mobile phones, smart phones, and wearable terminals that are always worn or kept at hand have become widespread. Since such devices are frequently used and operated with bare hands using a touch panel or the like, if adhesive tape is used in areas that are frequently touched by hands, the adhesive tape swells due to sebum and becomes adhesive. There was a problem that the tape would come off.

Japanese Unexamined Patent Publication No. 2015-052050 Japanese Unexamined Patent Publication No. 2015-021067 Japanese Unexamined Patent Publication No. 2015-120876

The present invention provides an adhesive tape having excellent resistance to sebum and capable of maintaining adhesive strength even in a portion frequently touched by human hands, and an adhesive tape for fixing electronic device parts made of the adhesive tape. With the goal.

The present invention is an adhesive tape having an adhesive layer containing an acrylic copolymer on at least one surface, wherein the acrylic copolymer contains 10 to 20% by weight of a structural unit derived from acrylonitrile. It is an adhesive tape.
Hereinafter, the present invention will be described in detail.

The present inventors have investigated a pressure-sensitive adhesive that is resistant to oleic acid, which is the main component of sebum. As a result, they have found that the resistance to oleic acid is increased by using an acrylic copolymer containing a structural unit derived from acrylonitrile in a specific range as a pressure-sensitive adhesive, and have completed the present invention.

The adhesive tape of the present invention has an adhesive layer made of an acrylic copolymer on at least one surface, and the acrylic copolymer contains a structural unit derived from acrylonitrile in a specific range. By including the structural unit derived from acrylonitrile in the acrylic copolymer, the adhesive tape of the present invention can exhibit high resistance to oleic acid. It is unclear why the inclusion of structural units derived from acrylonitrile enhances resistance to oleic acid, but the inclusion of a specific range of nitrile groups causes nitrile groups with low affinity for oleic acid as adhesives. It is thought that this is because it suppresses the interaction between oleic acid and oleic acid.

In the above-mentioned acrylic copolymer, the lower limit of the structural unit derived from acrylonitrile is 10% by weight, and the upper limit is 20% by weight. When the content of the structural unit derived from the acrylonitrile is 10% by weight or more, the resistance to oleic acid can be sufficiently exhibited. When the content of the structural unit derived from the acrylonitrile is 20% by weight or less, sufficient adhesive strength can be exhibited. The lower limit of the more preferable content of the structural unit derived from acrylonitrile is 13% by weight, and the upper limit is 17% by weight.

In the above-mentioned acrylic copolymer, the structural unit other than the structural unit derived from acrylonitrile is not particularly limited, but it is preferable to include the structural unit derived from butyl acrylate. By containing a structural unit derived from butyl acrylate, the acrylic copolymer can form a pressure-sensitive adhesive layer having excellent cohesive force, adhesiveness, adhesion and the like.

The preferable lower limit of the content of the constituent unit derived from butyl acrylate in the acrylic copolymer is 25% by weight, and the preferable upper limit is 90% by weight. When the content of the structural unit derived from the butyl acrylate is 25% by weight or more, the adhesion to the adherend is improved, and a more reliable pressure-sensitive adhesive layer can be formed. When the content of the structural unit derived from the butyl acrylate is 90% by weight or less, the cohesive force is improved and the processability can be improved. A more preferable lower limit of the content of the constituent unit derived from the butyl acrylate is 50% by weight, and a more preferable upper limit is 80% by weight.

The acrylic copolymer may further contain a structural unit derived from 2-ethylhexyl acrylate. By including a structural unit derived from 2-ethylhexyl acrylate, tack is imparted and the adhesion to the adherend can be improved.

The preferable lower limit of the content of the structural unit derived from 2-ethylhexyl acrylate in the acrylic copolymer is 0% by weight, and the upper limit is 60% by weight. When the content of the structural unit derived from the 2-ethylhexyl acrylate is 60% by weight or less, the cohesive force is improved and the processability can be improved. The more preferable lower limit of the content of the structural unit derived from the 2-ethylhexyl acrylate is 10% by weight, and the more preferable upper limit is 35% by weight.

The acrylic copolymer further includes methyl acrylate, hydroxyethyl acrylate, ethyl acrylate, methyl methacrylate, propyl acrylate, cyclohexyl acrylate, octyl acrylate, nonyl acrylate, isobornyl acrylate, hydroxybutyl acrylate, acrylic acid, benzyl acrylate, and phenoxy. It may contain a structural unit derived from ethyl acrylate, vinyl acetate, acrylamide, N, N-dimethylacrylamide and the like.

The preferable lower limit of the weight average molecular weight of the acrylic copolymer is 900,000. When the weight average molecular weight of the acrylic copolymer is 900,000 or more, the adhesive strength can be further improved. The weight average molecular weight of the acrylic copolymer can be adjusted by the polymerization conditions (for example, the type or amount of the polymerization initiator, the polymerization temperature, the monomer concentration, etc.).

In order to synthesize the acrylic copolymer, the acrylic monomer may be radically reacted in the presence of a polymerization initiator. The polymerization method is not particularly limited, and conventionally known methods can be used. Examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like. Of these, solution polymerization is preferable because it is easy to synthesize. In addition, emulsion polymerization is particularly suitable when the content of the structural unit derived from acrylonitrile is increased.

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

The above-mentioned polymerization initiator is not particularly limited, and examples thereof include organic peroxides and azo compounds. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5. -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples thereof include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

The pressure-sensitive adhesive layer preferably contains a silane coupling agent. Since the adhesive tape of the present invention contains a silane coupling agent, the adhesion of the adhesive layer to the adherend can be improved, so that the resistance of the adhesive tape of the present invention to oleic acid can be further enhanced. it can.
The silane coupling agent is not particularly limited, and for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane. , Γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-amino Propyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethylmethoxysilane, N- (2-aminoethyl) 3-aminopropyltriethoxysilane, N- (2-aminoethyl) 3-aminopropylmethyl Examples thereof include dimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptobutyltrimethoxysilane, and γ-mercaptopropylmethyldimethoxysilane. Of these, γ-glycidoxypropyltriethoxysilane is preferable.

The content of the silane coupling agent is not particularly limited, but the preferable lower limit is 0.1 parts by weight and the preferable upper limit is 5 parts by weight with respect to 100 parts by weight of the acrylic copolymer. When the content of the silane coupling agent is 0.1 parts by weight or more, the resistance to oleic acid can be further enhanced. When the content is 5 parts by weight or less, it is possible to suppress the adhesive residue at the time of re-peeling. The more preferable lower limit of the content of the silane coupling agent is 0.5 parts by weight, and the more preferable upper limit is 3 parts by weight.

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

The pressure-sensitive adhesive layer is preferably the lower limit is 2.2 × ¹⁰ 5 Pa of a storage modulus at 23 ° C., a preferred upper limit is 10.0 × ¹⁰ 5 Pa. When the storage modulus is less than 2.2 × 10 5 ^Pa, the pressure-sensitive adhesive layer is soft, because oleic acid easily enters inside the adhesive layer, the adhesive force after resistance to sebum (immersion oleate ) May be low. When the storage elastic modulus is more than 10.0 × 10 5 ^Pa, the pressure-sensitive adhesive layer is hard, because the tack is lower, it may not be possible to exhibit sufficient adhesive strength. More preferable lower limit of the storage elastic modulus is 3.0 × ¹⁰ 5 Pa, and more preferable upper limit is 6.0 × ¹⁰ 5 Pa.
The storage elastic modulus at 23 ° C. is -40 ° C. to 140 ° C. at a frequency of 10 Hz and a heating rate of 3 ° C./min using a dynamic viscoelasticity measuring device (for example, DVA-200 manufactured by IT Measurement Control Co., Ltd.). It can be obtained by measuring up to ° C.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the upper limit of the preferable thickness of the pressure-sensitive adhesive layer is 50 μm, and the preferable lower limit is 5 μm. When the thickness of the pressure-sensitive adhesive layer is 5 μm or more, the adhesiveness can be made more excellent. When the thickness of the pressure-sensitive adhesive layer is 50 μm or less, the workability can be further improved.

The adhesive tape of the present invention may be a support type having a base material or a non-support type having no base material. In the case of the support type, the pressure-sensitive adhesive layer may be formed on one side of the base material, or the pressure-sensitive adhesive layer may be formed on both sides.

The base material is not particularly limited, and for example, a polyolefin resin film such as a polyethylene film or a polypropylene film, a polyester resin film such as a PET film, an ethylene-vinyl acetate copolymer film, a polyvinyl chloride resin film, or a polyurethane film is used. Examples include resin films. Of these, PET film is preferable.
Further, a black-printed base material for preventing light transmission, a white-printed base material for improving light reflectivity, a metal-deposited base material, and the like can also be used.

The shape of the adhesive tape of the present invention is not particularly limited and may be rectangular or the like, but a frame shape is preferable. Further, since the adhesive tape of the present invention can maintain high adhesive strength even in a portion frequently touched by human hands, it can be preferably used even if the width of the adhesive tape is narrow, and in particular, the width of the adhesive tape is 5 mm. It can be suitably used in the following cases.

The use of the adhesive tape of the present invention is not particularly limited, but it can be particularly preferably used for fixing parts of electronic devices such as mobile phones and personal digital assistants that are frequently touched by human hands.
An adhesive tape for fixing electronic device parts using such an adhesive tape of the present invention is also one of the present inventions.

According to the present invention, an adhesive tape having excellent resistance to sebum and capable of maintaining adhesive strength even in a portion frequently touched by human hands, and an adhesive tape for fixing electronic device parts using the adhesive tape are provided. Can be provided.

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

( Reference Examples 1 to 5, Comparative Examples 1, 3, 5 to 7)
(Manufacturing of acrylic copolymer)
Ethyl acetate was added as a polymerization solvent to the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing nitrogen to start reflux. Subsequently, a polymerization initiator solution obtained by diluting 0.1 part by weight of azobisisobutyronitrile with ethyl acetate 10 times as a polymerization initiator was put into the reaction vessel, and the monomers shown in Table 1 or 2 were added over 2 hours. It was added dropwise. After completion of the dropwise addition, a polymerization initiator solution obtained by diluting 0.1 part by weight of azobisisobutyronitrile with ethyl acetate 10 times as a polymerization initiator was put into the reaction vessel again, and the polymerization reaction was carried out for 4 hours to carry out an acrylic copolymer weight. A coalescence-containing solution was obtained.

(Measurement of weight average molecular weight of acrylic copolymer)
The obtained acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the obtained diluent was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. This measurement sample was supplied to a gel permeation chromatograph (2690 Separations Model manufactured by Waters), and GPC measurement was performed under the conditions of a sample flow rate of 1 ml / min and a column temperature of 40 ° C. to determine the polystyrene-equivalent molecular weight of the acrylic pressure-sensitive adhesive. The weight average molecular weight (Mw) was determined by measurement. A GPC LF-804 (manufactured by Showa Denko KK) was used as the column, and a differential refractometer was used as the detector.

(Manufacturing of adhesive tape)
To the obtained acrylic copolymer-containing solution, Tetrad C (manufactured by Mitsubishi Gas Chemicals, Inc.) as a cross-linking agent was added to 100 parts by weight of the acrylic copolymer-containing solution in the amounts shown in Tables 1 and 2, and the thickness was 75 μm. The mold-treated PET film was coated so that the thickness of the pressure-sensitive adhesive layer after drying was 40 μm, and then dried at 110 ° C. for 5 minutes. This pressure-sensitive adhesive layer was transferred to a corona-treated PET film having a thickness of 50 μm as a base material to obtain a pressure-sensitive adhesive tape.

(Measurement of gel fraction)
The obtained adhesive tape was cut into a flat rectangular shape of 20 mm × 40 mm to prepare a test piece. After immersing the test piece in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate and dried under the condition of 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 x (W _2- W ₀ ) / (W _1- W ₀ ) (1)
(W ₀ : Weight of base material, W ₁ : Weight of test piece before immersion, W ₂ : Weight of test piece after immersion and drying)

(Measurement of storage elastic modulus at 23 ° C)
Regarding the adhesive layer of the obtained adhesive tape, using a dynamic viscoelasticity measuring device (DVA-200 manufactured by IT Measurement Control Co., Ltd.), the frequency was 10 Hz and the heating rate was 3 ° C./min at -40 ° C to 140 ° C. The storage elastic modulus at 23 ° C. was calculated.

(Examples 6 to 8, Comparative Examples 2 and 4)
Reference Examples 1 to 5, Comparative Examples 1, 3, 5 to 7 except that 1 part by weight of the silane coupling agent was added to the acrylic copolymer-containing solution obtained in the production of the acrylic copolymer before coating. An adhesive tape was produced in the same manner, and the weight average molecular weight, gel fraction and storage elastic modulus were measured.

<Evaluation>
The adhesive tapes obtained in Reference Examples, Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

(180 ° peeling adhesive strength)
The obtained adhesive tape was cut into strips having a width of 10 mm to prepare test pieces, and one of the release films was peeled off to expose the adhesive layer. This test piece is placed on a stainless steel plate so that its adhesive layer faces the stainless steel plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min to form a test piece. A test sample was prepared by adhering it to a stainless steel plate and then allowing it to stand at 23 ° C. for 24 hours. This test sample is heated in an oven at 60 ° C. and 90% humidity for 100 hours, allowed to stand at 23 ° C. for 24 hours, and then subjected to a tensile test in the 180 ° direction at a peeling speed of 300 mm / min according to JIS Z0237. The 180 ° peeling adhesive strength (N / 5 mm) before acid immersion (blank) was measured.
Next, the test sample was immersed in a bath of oleic acid at 60 ° C. and a humidity of 90% for 100 hours, taken out, washed with water, and allowed to stand for 24 hours to be subjected to the above tensile test. The 180 ° peeling adhesive strength after the acid immersion was measured.
The ratio (%) of the residual adhesive force was determined using the following formula (2) for the 180 ° peeling adhesive force of the blank and the 180 ° peeling adhesive force after immersion in oleic acid. A residual adhesive strength ratio of 40% or more was evaluated as ⊚, a residual adhesive strength ratio of 3% or more and less than 40% was evaluated as ◯, and a residual adhesive strength ratio of less than 3% was evaluated as x.
Ratio of residual adhesive strength (%) = (180 ° peeling adhesive strength after oleic acid immersion / 180 ° peeling adhesive strength before oleic acid immersion) x 100 (2)

According to the present invention, an adhesive tape having excellent resistance to sebum and capable of maintaining adhesive strength even in a portion frequently touched by human hands, and an adhesive tape for fixing electronic device parts using the adhesive tape are provided. Can be provided.

Claims (6)

An adhesive tape having an adhesive layer containing an acrylic copolymer on at least one surface.
The acrylic copolymer, the structural unit 10-17 wt% observed including that derived from acrylonitrile,
The pressure-sensitive adhesive layer is a pressure-sensitive adhesive tape containing 0.1 to 5 parts by weight of a silane coupling agent with respect to 100 parts by weight of the acrylic copolymer. The adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer has a storage elastic modulus at 23 ° C. of 2.2 × 10 ⁵ Pa or more and 10.0 × 10 ^{5 Pa or less.} The adhesive tape according to claim 1 or 2, wherein the acrylic copolymer contains 25 to 90% by weight of a structural unit derived from butyl acrylate. The adhesive tape according to claim 1, 2 or 3, wherein the acrylic copolymer has a weight average molecular weight of 900,000 or more. The adhesive tape according to claim 1, 2, 3 or 4 , wherein the width of the adhesive tape is 5 mm or less. An adhesive tape for fixing electronic device parts, which comprises the adhesive tape according to claim 1, 2, 3, 4 or 5.