KR102686082B1 - adhesive tape - Google Patents

Abstract

20 parts by mass but less than 40 parts by mass of alkoxyalkyl (meth)acrylate, 10 parts by mass but less than 25 parts by mass of (meth)acrylic monomer containing a carboxylic acid group, alkyl group having 1 to 3 carbon atoms, cyclohexyl group, or isobor. 5 or more parts by mass but less than 20 parts by mass of alkyl (meth)acrylate having a nyl group, and 30 or more parts by mass but less than 50 parts by mass of alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms (sum of each monomer above) 100 parts by mass), a cross-linked structure is formed using one or both of an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent, and an acrylic copolymer having a weight average molecular weight of 200,000 to 450,000 is used as an adhesive. An adhesive tape is disclosed. This adhesive tape has high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and also has appropriate adhesive strength when attached to an adherend.

Description

adhesive tape

The present invention relates to an adhesive tape that has high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and also has appropriate adhesive strength when attached to an adherend.

Recently, small portable electronic devices such as smartphones and tablet PCs have become rapidly popular. In many of these, the display panel and the housing are joined using an acrylic adhesive or double-sided adhesive tape. In addition, most mobile electronic devices are equipped with a touch panel and are operated by touching them with a person's finger or touching the person's face when making a call.

When a touch panel touches a person's hand or face, oil such as sebum or grease adheres to the touch panel. This oil contains components such as oleic acid, and its SP value (solubility parameter) is close to that of industrial organic solvents, so it dissolves common acrylic resins.

General industrial organic solvents have a low boiling point and evaporate in a short period of time, so it is difficult to damage adhesives or adhesives. On the other hand, oil and fat components such as oleic acid have a high boiling point and do not vaporize under living conditions and remain in electronic devices, causing damage to adhesives and adhesive tapes and causing floating or peeling of parts within electronic devices, shortening the lifespan of electronic devices. do.

Small portable electronic devices, such as smartphones, are held and used for a long time, and may touch the face when talking on the phone. Therefore, oils and fats such as sebum, sweat, food, and cosmetics tend to adhere to small portable electronic devices, and when these fats and oils reach adhesives and adhesive tapes, there is a risk that the adhesive strength may decrease. Additionally, if the adhesive layer of the adhesive tape softens due to retention, the adhesive may peel off from the side of the adhesive tape, damaging the design or function inside the device. In addition, pressure in the outward direction is applied due to swelling of the adhesive layer, and there are cases where the screen of the electronic device is not displayed properly.

In addition, as the screens of small portable electronic devices such as smartphones become larger, internal components become thinner and narrower, and small wearable devices become more practical, the adhesive tapes used inside such electronic devices have also become thinner and finer. Therefore, it seems that problems like the above are becoming more likely to occur.

Patent Document 1 discloses a double-sided adhesive tape used for fixing components of portable electronic devices, in which the adhesive is difficult to soften or swell even when oily components such as sebum penetrate, and the adhesive does not protrude. . However, the invention in Patent Document 1 does not examine the decrease in adhesive force that is directly related to the floating or peeling of adhesives or adhesive tapes that occur inside electronic devices. In addition, when the durability of the fat component is improved, the adhesive strength when attaching the adhesive tape to the adherend decreases, and there is a problem that improvement in durability and maintenance of adhesive strength are not compatible.

Patent Document 1: Japanese Patent Application Publication No. 2009-215355

Therefore, the purpose of the present invention is to provide an adhesive tape that has high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and also has appropriate adhesive strength when attached to an adherend.

The adhesive tape of the present invention has a monomer composition of 20 parts by mass or more but less than 40 parts by mass of alkoxyalkyl (meth)acrylate and 10 parts by mass or more but less than 25 parts by mass of a (meth)acrylic monomer containing a carboxylic acid group, as follows. 5 parts by mass or more and less than 20 parts by mass of the (meth)acrylic acid alkyl ester represented by the formula 1, and 30 parts by mass or more and less than 50 parts by mass of the (meth)acrylic acid alkyl ester represented by the following formula 2 (each of the above monomers) (the total of is 100 parts by mass), wherein a cross-linked structure is formed by using one or both of a bifunctional or higher isocyanate group-containing compound and a bifunctional or higher glycidyl group-containing compound as a cross-linking agent, and the weight average molecular weight is An adhesive composition containing the above acrylic copolymer in an amount of 200,000 or more and less than 450,000 is an adhesive tape used as an adhesive.

(In Formula 1, R ¹ represents CH ₂ =CH- or CH ₂ =C(CH ₃ )-, and R ² represents an alkyl group, cyclohexyl group, or isobornyl group having 1 to 3 carbon atoms.)

(In Formula 2, R ³ represents CH ₂ =CH- or CH ₂ =C(CH ₃ )-, and R ⁴ represents an alkyl group having 4 to 12 carbon atoms.)

In the adhesive tape according to the present invention, the adhesive composition may further include a tackifying resin.

The adhesive composition of the adhesive tape according to the present invention may further include a silane coupling agent.

The adhesive tape according to the present invention may further include an antioxidant in the adhesive composition.

The adhesive tape according to the present invention further has a base material, and an adhesive layer can be formed on one side or both sides of the base material using an adhesive composition.

The adhesive tape according to the present invention has high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and specifically has oil resistance that allows it to maintain a certain adhesive force even when oil and fat ingredients adhere. In addition, the adhesive tape according to the present invention has appropriate adhesive strength when attached to an adherend and is excellent in adhesive strength maintenance performance when a holding component adheres. Therefore, the adhesive tape according to the present invention can be suitably used for applications such as joining the display panel and housing of small portable electronic devices such as smartphones and fixing components inside the housing.

<Acrylic copolymer>

The acrylic copolymer according to the present invention has, as a monomer composition, a (meth)acrylic acid alkoxyalkyl ester, a carboxylic acid group-containing (meth)acrylic monomer, a (meth)acrylic acid alkyl ester represented by the above formula (1), and the above formula (2) A crosslinked structure is formed by using a bifunctional or more isocyanate group-containing compound or a bifunctional or more glycidyl group-containing compound containing an alkyl ester of (meth)acrylate as a crosslinking agent, and having a weight average molecular weight of 200,000 or more and less than 450,000. am.

Examples of (meth)acrylic acid alkoxyalkyl esters include methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxyethyl (meth)acrylate, and (meth)acrylic acid. Toxypropyl, ethoxybutyl (meth)acrylate, etc. can be used. Considering the stability of the polymerization reaction and ease of availability, it is preferable to use methoxyethyl (meth)acrylate.

(meth)acrylic acid alkoxyalkyl esters, carboxylic acid group-containing (meth)acrylic monomers, (meth)acrylic acid alkyl esters represented by the formula 1, and (meth)acrylic acid alkyl esters represented by the formula 2 (hereinafter referred to as “4 above”) The content of (meth)acrylic acid alkoxyalkyl ester relative to a total of 100 parts by mass (referred to as “species monomer”) is 20 parts by mass or more and less than 40 parts by mass. If this content is less than 20 parts by mass, the number of monomer units with a high SP value in the acrylic copolymer of the present invention decreases, so durability against oil and fat components decreases, and oil and fat components such as sebum, sweat, food, and cosmetics adhere. The adhesive strength decreases significantly, making it impossible to maintain the adhesive strength required for applications such as fixing parts inside electronic devices. In addition, if this content is 40 parts by mass or more, the initial adhesive strength of the adhesive decreases, so workability decreases during work such as fixing parts inside electronic devices. It is more preferable that this content is 25 parts by mass or more and less than 40 parts by mass.

Examples of (meth)acrylic monomers containing a carboxylic acid group include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, citraconic acid, grataconic acid, 2- Acryloyloxyethylsuccinic acid, 2-acryloyloxyethylphthalic acid, etc. can be used. Among these, considering the crosslinking density and availability of the obtained adhesive, it is preferable to use (meth)acrylic acid.

The content of the carboxylic acid group-containing (meth)acrylic monomer relative to a total of 100 parts by mass of the above four types of monomers is 10 parts by mass or more and less than 25 parts by mass. If this content is less than 10 parts by mass, the crosslinking density of the adhesive decreases, and the adhesive swells due to oil and fat components such as sebum, sweat, food, and cosmetics. In addition, if this content is 25 parts by mass or more, the initial adhesive strength of the adhesive decreases, so workability decreases during work such as fixing parts inside electronic devices. It is more preferable that this content is 10 parts by mass or more and 23 parts by mass or less.

As the (meth)acrylic acid alkyl ester represented by the above formula (1), for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. can be used. . Considering ease of availability, it is preferable to use methyl acrylate.

The content of the alkyl (meth)acrylate represented by the formula (1) relative to a total of 100 parts by mass of the four types of monomers is 5 parts by mass or more and less than 20 parts by mass. If this content is less than 5 parts by mass, the repellency resistance of the adhesive decreases, and the adhesive strength required for applications such as fixing parts inside electronic devices cannot be satisfied. In addition, if this content is 20 parts by mass or more, the initial adhesive strength of the adhesive decreases and workability decreases in cases such as fixing parts inside electronic devices. It is more preferable that this content is 5 mass parts or more and 15 mass parts or less.

Examples of the (meth)acrylic acid alkyl ester represented by the above formula (2) include butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, and iso(meth)acrylate. Hexyl, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, iso (meth)acrylate Decyl, dodecyl (meth)acrylate, isododecyl (meth)acrylate, etc. can be used. In order to maintain the tack of the acrylic copolymer as an adhesive, it is preferable to use (meth)acrylic acid-2-ethylhexyl, etc., which has a low Tg (glass transition point).

The content of the (meth)acrylic acid alkyl ester represented by the above formula (2) relative to a total of 100 parts by mass of the four types of monomers is 30 parts by mass or more and less than 50 parts by mass. If this content is less than 30 parts by mass, the initial adhesive strength of the adhesive decreases, and therefore workability decreases in cases such as fixing parts inside electronic devices. If this content is 50 parts by mass or more, the durability of the oil and fat components decreases, and when oil and fat components such as sebum, sweat, food, and cosmetics adhere, the adhesive strength decreases significantly, making it necessary for applications such as fixing parts inside electronic devices. Adhesion cannot be maintained. It is more preferable that this content is 30 parts by mass or more and 45 parts by mass or less.

Compounds containing bifunctional or higher isocyanate groups (hereinafter also referred to as “isocyanate-based crosslinking agents”) include, for example, tolylene diisocyanate, xylene diisocyanate, chlorphenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, and isophorone diisocyanate. Isocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, etc. can be used.

Compounds containing a bifunctional or higher glycidyl group (hereinafter also referred to as “epoxy-based crosslinking agent”) include, for example, 1,3bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N' ,N'-tetraglycidyl-m-xylenediamine, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N,N-diglycidylaminophenyl Glycidyl ether, N,N-diglycidyltoluidine, N,N-diglycidylaniline, pentaerythritol polyglycidyl ether, 1,6-hexanediol diglycidyl ether, etc. can be used.

There is no particular limitation on the amount of the compound containing a bifunctional or higher isocyanate group or the compound containing a bifunctional or higher glycidyl group used as a crosslinking agent. The amount of crosslinking agent added can be adjusted so that the swelling degree of the adhesive composition is suitable for the usage environment of the adhesive tape according to the present invention.

The acrylic copolymer according to the present invention can be produced by polymerizing these monomers through various polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. For example, an acrylic copolymer can be obtained by dissolving these monomers and a polymerization initiator in a solvent such as ethyl acetate in a reaction vessel and stirring the mixture at constant temperature for a certain period of time.

Additionally, an acrylic copolymer having a crosslinked structure can be produced by adding a crosslinking agent alone or together with a polymerization initiator to the above acrylic copolymer and stirring it.

The weight average molecular weight of the acrylic copolymer according to the present invention is 200,000 or more and less than 450,000. If the weight average molecular weight is less than 200,000, the cohesive force required for the adhesive cannot be obtained, which causes honeycombs to form in the adhesive when the adhesive tape is attached to the adherend. Additionally, if the weight average molecular weight is 450,000 or more, the adhesive tape's ability to follow the adherend deteriorates, making it impossible to obtain the adhesive strength required for fixing components inside electronic devices, etc. It is more preferable that this weight average molecular weight is 250,000 or more and less than 450,000.

Optional components such as a tackifying resin, a silane coupling agent, and an antioxidant can be added to the acrylic copolymer according to the present invention as needed.

Examples of tackifying resins include rosin ester resins (rosin ester, disproportionated rosin ester, hydrogenated rosin ester, etc.), terpene resins (terpene resins, aromatic modified terpene resins, hydrogenated terpene resins, terpene phenols, etc.). , petroleum resins (aliphatic petroleum resins, aromatic petroleum resins, copolymerized petroleum resins, aliphatic petroleum resins, etc.), pure/monomer resins (coumarone/indene resins, styrene resins, etc.), condensation resins (phenolic resins, etc.) resin, xylene resin, etc.) can be used. By adding a tackifier resin, the hardness of the adhesive decreases and the initial adhesion to the adherend improves.

As a silane coupling agent, for example, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3- Glycidoxypropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, etc. can be used. Two or more types of silane coupling agents may be used in combination. By using a silane coupling agent, the repellency resistance of the adhesive can be improved, and the moisture-heat load resistance that decreases with narrowing and fine processing of the adhesive tape can be improved.

As an antioxidant, for example, hindered phenol-based antioxidants can be used. By adding an antioxidant, the repulsion resistance of the adhesive can be improved and the moist and heat load resistance, which decreases with narrowing and fine processing of the adhesive tape, can be improved.

＜Adhesive tape＞

The adhesive tape according to the present invention is an adhesive tape in which an adhesive composition containing the above-described acrylic copolymer (and optional components as necessary) is used as an adhesive. “Adhesive tape in which an adhesive composition is used as an adhesive” means, for example, an adhesive tape in which the adhesive composition is formed into a sheet (so-called baseless type adhesive tape), or an adhesive tape in which the adhesive composition is used to form a sheet on one side of a substrate. Alternatively, it is an adhesive tape with an adhesive layer formed on both sides.

A baseless type adhesive tape can be formed, for example, by applying an acrylic copolymer onto a support such as release paper and then drying it. On the other hand, for the adhesive tape with a base material, the adhesive layer may be formed by applying an acrylic copolymer on the base material and drying it thereafter, or the adhesive layer may be formed by applying the acrylic copolymer on a support such as release paper, and then forming the adhesive layer. The adhesive layer can be bonded to one or both sides of the substrate. The adhesive layer of the baseless type adhesive tape and the adhesive tape with a base material may be a single layer or may be composed of a laminated body of a plurality of layers.

The thickness of the adhesive layer in the adhesive tape with a base material is preferably 1 to 200 μm, more preferably 5 to 100 μm. The thickness of the baseless type adhesive tape is preferably 1 to 200 μm, more preferably 5 to 100 μm.

The method of applying the acrylic copolymer onto a support such as a substrate or release paper is not particularly limited, and a known method may be used. Specific examples include a method using a roll coater, die coater, lip coater, dip roll coater, bar coater, knife coater, spray roll coater, etc.

When the adhesive tape has a base material, the base material is not particularly limited, and a known base material may be used. Specific examples of the substrate include fiber-based substrates such as paper, cloth, non-woven fabric, and net, olefin-based resin, polyester-based resin, polyvinyl chloride-based resin, vinyl acetate-based resin, polyamide-based resin, polyimide-based resin, and polyether. Examples include resin substrates (resin films or resin sheets) such as ether ketone (PEEK) and polyphenylene sulfide (PPS), rubber sheets, foam sheets (foam substrates), metal foil, and metal plates. In addition, these laminates may be, for example, a laminate of a resin substrate and a substrate other than resin, or a laminate of resin substrates. The base material may be either a single layer or a double layer. The surface of the substrate on which the adhesive layer is installed may be subjected to various treatments, such as backside treatment, antistatic treatment, and undercoating treatment, as needed. The thickness of the substrate is preferably 5 to 500 μm, more preferably 10 to 200 μm.

Adhesive tapes can be protected with release paper or other films. The release paper or other film is not particularly limited, and known ones can be used as needed.

Example

Hereinafter, the present invention will be described in more detail through examples and comparative examples.

(Weight average molecular weight)

The weight average molecular weight (Mw) of the acrylic copolymer is a value obtained by measuring the molecular weight of the acrylic copolymer in terms of standard polystyrene using the GPC method under the following measuring devices and conditions.

·Device: LC-2000 series (manufactured by Nippon Spectrograph Co., Ltd.)

· Column: Shodex KF-806M × 2, Shodex KF-802M × 1

· Eluent: Tetrahydrofuran (THF)

·Flow rate: 1.0mL/min

·Column temperature: 40℃

·Injection amount: 100μL

・Detector: Refractometer (RI)

(initial adhesion)

When using base material A: A sample of a 10 mm wide double-sided adhesive tape backed by a polyester film with a thickness of 25 ㎛ was pressed and attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one reciprocation of a 2.0 kg roller, and 20 minutes had passed after the press application. After peeling off at 180°, the adhesive strength (N/10 mm width) was measured by the method described in JIS Z0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed by a polyester film with a thickness of 50 ㎛ was pressed and attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one reciprocation of a 2.0 kg roller, and 20 minutes had passed after the press application. After peeling off at 180°, the adhesive strength (N/10 mm width) was measured by the method described in JIS Z0237:2000.

(Adhesion over time)

When using base material A: A sample of a 10 mm wide double-sided adhesive tape backed with a polyester film with a thickness of 25 ㎛ is pressed and attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one reciprocation of a 2.0 kg roller. The 180° drawn peel adhesive strength (N/10 mm width) was measured by the method described in JIS Z0237:2000.

When using base material B: A sample of a 10 mm wide double-sided adhesive tape backed with a 50 ㎛ thick polyester film was pressed and attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper using 2.5 reciprocations of a 2.0 kg roller. The 180° drawn peel adhesive strength (N/10 mm width) was measured by the method described in JIS Z0237:2000.

(Adhesion after acceleration: Na)

When using base material A: A 10 mm wide double-sided adhesive tape sample backed by a 25 ㎛ thick polyester film was attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper under pressure with one reciprocation of a 2.0 kg roller, temperature 65 ± 5°C and humidity. It was left for 72 hours in an atmosphere of 90 ± 10%. After that, it was left to stand for 2 hours in an atmosphere of a temperature of 23 ± 5°C and a humidity of 50 ± 5%. The 180° pull-out peel adhesion (N/10 mm width) of this sample was measured by the method described in JIS Z0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed by a 50㎛ thick SUS film was attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper by pressure using a 2.0 kg roller with 2.5 reciprocations, temperature 60 ± 5°C, humidity 90%. It was left for 72 hours in an atmosphere of ±10%. After that, it was left to stand for 2 hours in an atmosphere of a temperature of 23 ± 5°C and a humidity of 50 ± 5%. The 180° pull-out peel adhesion (N/10 mm width) of this sample was measured by the method described in JIS Z0237:2000.

(Adhesion after oleic acid immersion: Nb)

When using base material A: A sample of a 10 mm wide double-sided adhesive tape backed with a 25 ㎛ thick polyester film was pressure-applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper using one reciprocation of a 2.0 kg roller. This sample was immersed in oleic acid and left in an atmosphere of 65 ± 5°C and 90 ± 10% humidity for 72 hours. Thereafter, the sample was taken out from the container, the oleic acid was wiped off using pure water, the water droplets were wiped off, and the sample was left in an atmosphere of a temperature of 23 ± 5°C and a humidity of 50 ± 5% for 2 hours. The 180° pull-out peel adhesion (N/10 mm width) of this sample was measured by the method described in JIS Z0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed by a 50 ㎛ thick SUS film was pressed and attached to a SUS304 plate polished with No. 280 water-resistant abrasive paper using 2.5 reciprocations of a 2.0 kg roller. This sample was immersed in oleic acid and left in an atmosphere of 60 ± 5°C and 90 ± 10% humidity for 72 hours. Thereafter, the sample was taken out from the container, the oleic acid was wiped off using pure water, the water droplets were wiped off, and the sample was left in an atmosphere of a temperature of 23 ± 5°C and a humidity of 50 ± 5% for 2 hours. The 180° pull-out peel adhesion (N/10 mm width) of this sample was measured by the method described in JIS Z0237:2000.

(Adhesion retention rate after oleic acid immersion:

It was obtained by the following formula.

X=100×Nb/Na

(Destruction Mode)

For the sample after measurement of adhesion after acceleration (Na) and the sample after measurement of adhesion after immersion in oleic acid (Nb), the area where destruction occurred was observed, respectively. When destruction occurs in the adhesive, it is called cohesive failure (“cohesion” in Tables 2 to 4), when destruction occurs between the adhesive and the adherend, it is called interfacial failure, and when destruction occurs in the substrate, it is called substrate failure (“Cohesive”). It was set to “Description” in Tables 2 to 4).

[Example 1]

(Preparation of acrylic copolymer)

　In a reaction apparatus equipped with a stirrer, thermometer, reflux condenser, and nitrogen introduction tube, parts by mass of the monomers constituting the copolymer shown in Table 1, ethyl acetate, 0.03 parts by mass of n-dodecanethiol as a chain transfer agent, and Ra as a radical polymerization initiator are added. 0.05 parts by mass of Uril peroxide was added, nitrogen gas was enclosed, and reaction was performed at 67°C for 3 hours under a nitrogen gas stream while stirring. After that, reaction was performed at 82°C for 3 hours. After completion of the reaction, the mixture was cooled to room temperature, and ethyl acetate was added. As a result, a copolymer with a solid content concentration of 30% was obtained. The weight average molecular weight of the acrylic copolymer prepared in Example 1 was 420,000.

(Preparation of adhesive)

With respect to 100 parts by mass of solid content of this copolymer, 1.8 parts by mass of an isocyanate-based crosslinking agent (crosslinking agent A) (manufactured by Tosoh Corporation, brand name L-45E) was added as a crosslinking agent to prepare an adhesive.

(Manufacture of double-sided adhesive tape)

A separately prepared primer was applied to both sides of a polyethylene terephthalate film (base material A) with a thickness of 12 μm that had been corona discharge treated on both sides and dried at 120°C to form an undercoat layer on the base material A. On the undercoat layer on the first surface side of the base material A, the prepared adhesive was applied smoothly over the entire surface and dried by heating at 100°C to form an adhesive layer with a thickness of 19 μm. Additionally, silicone-treated release paper was bonded onto this adhesive layer. After that, the adhesive prepared in the same manner was applied and dried on the primer layer on the second side, the release paper was bonded, and cured at 40°C for 3 days. This obtained a double-sided adhesive tape with a total thickness of 50 μm.

[Example 2]

In preparing the adhesive, a double-sided adhesive tape was produced in the same manner as in Example 1 except that the crosslinking agent was changed to an epoxy-based crosslinking agent (crosslinking agent B) (綜硏化學學學夾製, brand name E-5CM).

[Example 3]

In the production of a double-sided adhesive tape, the adhesive prepared in the same manner as in Example 1 was applied smoothly over the entire surface on silicone-treated release paper and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, the adhesive on the release paper was bonded to both sides of a 100㎛ thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and cured at 40°C for 3 days, after which both sides had a total thickness of 200㎛. Adhesive tape was obtained.

[Example 4]

In the preparation of the adhesive, 8 parts by mass of D-6011 (trade name) manufactured by Arakawa Chemical Industry Co., Ltd. diluted to 50% with ethyl acetate as the tackifying resin, and diluted to 5% with ethyl acetate as the silane coupling agent. Both sides were prepared in the same manner as in Example 3, except that 2 parts by mass of KBM-403 (trade name) manufactured by Shin-Etsu Chemical Co., Ltd. was added as an antioxidant, and 0.2 parts by mass of Irganox (registered trademark) 1010 manufactured by BASF Japan Co., Ltd. was added. An adhesive tape was produced.

[Comparative Example 1]

(Preparation of acrylic copolymer)

The same procedure as in Example 1 was carried out except that 50 parts by mass of methoxyethyl acrylate, 10 parts by mass of acrylic acid, and 40 parts by mass of 2-ethylhexyl acrylate were used instead of methyl acrylate, and the amount of crosslinking agent added was changed to 1.2 parts by mass. , a copolymer with a solid content concentration of 30% was obtained. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 1 was 750,000.

(Preparation of adhesive)

With respect to 100 parts by mass of the solid content of this copolymer, 1.2 parts by mass of an isocyanate-based crosslinking agent (crosslinking agent A) (manufactured by Tosoh Corporation, brand name L-45E) as a crosslinking agent and ethyl acetate as a tackifying resin were diluted 50% by Arakawa Chemical Industries. 8 parts by mass of D-6011 (brand name) manufactured by Shin-Etsu Chemical Co., Ltd. (brand name) as a silane coupling agent, 2 parts by mass of KBM-403 (brand name) manufactured by Shin-Etsu Chemical Co., Ltd. diluted by 5% with ethyl acetate, as an antioxidant, BASF Japan 0.2 parts by mass of Irganox (registered trademark) 1010 manufactured by Co., Ltd. was added to prepare an adhesive.

(Manufacture of double-sided adhesive tape)

A double-sided adhesive tape was obtained in the same manner as in Example 1, except that this adhesive was used.

[Comparative Example 2]

In the production of the acrylic copolymer, 86 parts by mass of methoxyethyl acrylate, 10 parts by mass of acrylic acid, and 4 parts by mass of 2-ethylhexyl acrylate were used instead of using methyl acrylate, except that the amount of crosslinking agent added was changed to 1.2 parts by mass. In the same manner as Example 1, a double-sided adhesive tape was produced. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 2 was 1,050,000.

[Comparative Example 3]

In the production of the acrylic copolymer, a double-sided adhesive tape was produced in the same manner as Comparative Example 2, except that the addition amount of n-dodecanethiol as a chain transfer agent was changed to 0.06 parts by mass and the addition amount of crosslinking agent A was changed to 2.4 parts by mass. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 3 was 340,000.

[Comparative Example 4]

In the production of the acrylic copolymer, a double-sided adhesive tape was made in the same manner as in Comparative Example 2 except that methoxyethyl acrylate was not used and 86 parts by mass of 2-(ethoxyethoxy)ethyl acrylate (EOEOEA) was used. made. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 4 could not be measured.

[Comparative Example 5]

In the production of a double-sided adhesive tape, the adhesive prepared in the same manner as in Comparative Example 1 was applied smoothly over the entire surface on silicone-treated release paper and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, the adhesive on the release paper was bonded to both sides of a 100㎛ thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and cured at 40°C for 3 days, after which both sides had a total thickness of 200㎛. Adhesive tape was obtained.

[Comparative Example 6]

In the production of a double-sided adhesive tape, the adhesive prepared in the same manner as in Comparative Example 2 was applied smoothly over the entire surface on silicone-treated release paper and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, the adhesive on the release paper was bonded to both sides of a 100㎛ thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and cured at 40°C for 3 days, after which both sides had a total thickness of 200㎛. Adhesive tape was obtained.

[Comparative Example 7]

In the production of a double-sided adhesive tape, the adhesive prepared in the same manner as in Comparative Example 3 was applied smoothly over the entire surface on silicone-treated release paper and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, the adhesive on the release paper was bonded to both sides of a 100㎛ thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and cured at 40°C for 3 days, after which both sides had a total thickness of 200㎛. Adhesive tape was obtained.

[Comparative Example 8]

In the preparation of the acrylic copolymer, a double-sided adhesive tape was produced in the same manner as in Comparative Example 2, except that 10 parts by mass of 4-hydroxybutyl acrylate was used instead of 10 parts by mass of acrylic acid. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 8 was 730,000.

Table 1 shows the formulations of Examples 1 to 4 and Comparative Examples 1 to 8, the weight average molecular weight of the acrylic copolymer, and the substrate used to form the double-sided adhesive tape. In addition, the initial adhesive force, adhesive force over time, adhesive force Na after acceleration, adhesive force Nb after oleic acid immersion, adhesive retention rate X after oleic acid immersion, and failure mode measured for each double-sided adhesive tape are shown in Tables 2 to 4.

The abbreviations used in Table 1 are as follows.

AME=methoxyethyl acrylate

EOEOEA=2-(2-ethoxyethoxy)ethyl acrylic acid

AA=acrylic acid

4-HBA=4-hydroxybutyl acrylic acid

MA=methyl acrylate

2-EHA=2-ethylhexyl acrylic acid

As shown in Tables 2 to 4, the double-sided adhesive tapes of Examples 1 to 4 had high initial adhesive strength and adhesive strength over time, and also maintained appropriate adhesive strength even after immersion in oleic acid. Therefore, it can be seen that these double-sided adhesive tapes have high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and also have appropriate adhesive strength when attached to an adherend. Additionally, when comparing Example 3 and Example 4, the value of initial adhesion in Example 4 to which the tackifying resin was added was smaller, but Example 3 was due to interface destruction, whereas Example 4 was due to substrate destruction. Therefore, it is thought that no decrease in adhesive strength occurs.

On the other hand, the monomer composition of the acrylic copolymer used in Comparative Examples 1 to 4 and 8 (thickness of each adhesive layer is 19 μm, base material A) is the same as that used in Examples 1 and 2 (thickness of each adhesive layer is 19 μm, base material A). It is different from the monomer composition of acrylic copolymer. In addition, the weight average molecular weight of the acrylic copolymer used in Comparative Examples 1, 2, 4, and 8 is greater than that of the acrylic copolymer used in Examples 1 and 2.

As a result, compared to the double-sided adhesive tapes of Examples 1 and 2, the double-sided adhesive tapes of Comparative Examples 1 and 8 had initial adhesive strength, adhesive strength over time, adhesive strength Na after acceleration, adhesive strength Nb after immersion in oleic acid, and adhesive retention rate X after immersion in oleic acid. was inferior.

The double-sided adhesive tape of Comparative Example 2 was inferior to the double-sided adhesive tape of Examples 1 and 2 in initial adhesive force, adhesive force over time, and adhesive force after acceleration Na.

Comparative Example 3 is an example in which the weight average molecular weight of the acrylic polymer was lowered compared to Comparative Example 2. As a result, Comparative Example 3 improved several items compared to Comparative Example 2. However, the initial adhesion, adhesion over time, and adhesion after acceleration Na were inferior to those of Examples 1 and 2.

The double-sided adhesive tape of Comparative Example 4 was inferior to the double-sided adhesive tape of Examples 1 and 2 in terms of adhesive strength over time, adhesive strength Na after acceleration, adhesive strength Nb after immersion in oleic acid, and adhesive retention rate X after immersion in oleic acid.

The double-sided adhesive tapes of Comparative Examples 5 to 7 (thickness of each adhesive layer 50 μm, base material B) had the monomer composition of the acrylic copolymer in Examples 3 and 4 (thickness of each adhesive layer 50 μm, base material B). It is different from the monomer composition of the acrylic copolymer. In addition, the weight average molecular weight of the acrylic copolymer used in Comparative Examples 5 and 6 is greater than that of the acrylic copolymer used in Examples 3 and 4.

As a result, the double-sided adhesive tape of Comparative Example 5 had lower initial adhesive force, adhesive force Nb after immersion in oleic acid, and adhesive retention rate X after immersion in oleic acid compared to the double-sided adhesive tape of Examples 3 and 4. Additionally, both failure modes (Na) and (Nb) were cohesive failure, and the cohesion of the adhesive layer was inferior.

The double-sided adhesive tape of Comparative Example 6 had lower initial adhesive strength compared to the double-sided adhesive tape of Examples 3 and 4. Additionally, both failure modes (Na) and (Nb) were cohesive failure, and the cohesion of the adhesive layer was inferior.

Comparative Example 7 is an example in which the adhesive of Comparative Example 3 was applied to substrate B. As a result, Comparative Example 7 improved several items over Comparative Example 6. However, the initial adhesive strength was inferior to Examples 3 and 4.

The adhesive tape according to the present invention can be suitably used for applications such as joining a display panel and a casing of a small portable electronic device such as a smart phone or fixing components inside the casing.

Claims (5)

As the monomer composition,
(meth)acrylic acid alkoxyalkyl ester at least 20 parts by mass and less than 40 parts by mass,
10 or more parts by mass but less than 25 parts by mass of (meth)acrylic monomer containing a carboxylic acid group,
5 parts by mass or more and less than 20 parts by mass of an alkyl (meth)acrylate represented by the following formula 1, and
An acrylic copolymer containing 30 parts by mass or more and less than 50 parts by mass (the total of each monomer above is 100 parts by mass) of an alkyl (meth)acrylate represented by the following formula 2,
A crosslinked structure is formed by using one or both of a bifunctional or higher isocyanate group-containing compound and a bifunctional or higher glycidyl group-containing compound as a crosslinking agent,
An adhesive tape in which an adhesive composition containing the acrylic copolymer having a weight average molecular weight of 200,000 or more and less than 450,000 is used as an adhesive.

(In Formula 1, R ¹ represents CH ₂ =CH- or CH ₂ =C(CH ₃ )-, and R ² represents an alkyl group, cyclohexyl group, or isobornyl group having 1 to 3 carbon atoms.)

(In Formula 2, R ³ represents CH ₂ =CH- or CH ₂ =C(CH ₃ )-, and R ⁴ represents an alkyl group having 4 to 12 carbon atoms.) According to paragraph 1,
An adhesive tape wherein the adhesive composition further includes a tackifying resin. According to paragraph 1,
An adhesive tape wherein the adhesive composition further includes a silane coupling agent. According to paragraph 1,
An adhesive tape whose adhesive composition further includes an antioxidant. According to paragraph 1,
The adhesive tape further has a base material, and an adhesive layer is formed on one or both sides of the base material using the adhesive composition.