JP7395709B2 - Adhesive tape - Google Patents

Description

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

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

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

Typical industrial organic solvents have low boiling points and evaporate in a short time, so they are less likely to damage adhesives and adhesives. On the other hand, oil and fat components such as oleic acid have a high boiling point and do not evaporate in living environments and remain inside electronic devices, damaging adhesives and adhesive tapes and causing parts inside electronic devices to lift or peel. Shorten the lifespan of electronic equipment.

Small portable electronic devices such as smartphones are held in the hand for a long time, and people often touch their faces when making calls. As a result, small portable electronic devices are prone to oils and fats such as sebum, sweat, food, and cosmetics, and if these oils and fats reach adhesives or adhesive tapes, their adhesive strength may decrease. Furthermore, if the adhesive layer of the adhesive tape softens due to oil or fat, the adhesive may protrude from the sides of the adhesive tape, impairing the design and functionality of the interior of the device. Furthermore, the swelling of the adhesive layer may apply pressure toward the outside, which may cause the screen display of electronic devices to malfunction.

In addition, as the screens of small portable electronic devices such as smartphones expand, internal components become narrower and thinner, and as small wearable devices become more practical, the adhesive tapes used inside such electronic devices also become narrower.・It is thought that the above-mentioned problems are more likely to occur due to miniaturization.

Patent Document 1 discloses a double-sided adhesive tape used for fixing parts of portable electronic devices, which is a double-sided adhesive tape that does not easily soften or swell even when oily components such as sebum penetrate, and does not extrude. An adhesive tape is disclosed. However, the invention of Patent Document 1 does not consider the reduction in adhesive strength that is directly linked to the lifting and peeling of adhesives and adhesive tapes that occur inside electronic devices. Furthermore, when the durability of the oil and fat component is improved, the adhesive force when applying the adhesive tape to an adherend decreases, and there is a problem that improving the durability and maintaining the adhesive force are not compatible.

Japanese Patent Application Publication No. 2009-215355

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

The adhesive tape according to the present invention has a monomer composition of 20 parts by mass or more and less than 40 parts by mass of (meth)acrylic acid alkoxyalkyl ester, and 10 parts by mass or more and less than 25 parts by mass of a (meth)acrylic monomer containing a carboxylic acid group. , 5 parts by mass or more and less than 20 parts by mass of a (meth)acrylic acid alkyl ester represented by the following formula 1, and 30 parts by mass or more and less than 50 parts by mass of a (meth)acrylic acid alkyl ester represented by the following formula 2 (The total of each of the above monomers is 100 parts by mass) An acrylic copolymer containing one or both of a difunctional or more functional isocyanate group-containing compound and a difunctional or more functional glycidyl group-containing compound as a crosslinking agent. The present invention is an adhesive tape in which an adhesive composition containing the acrylic copolymer having a crosslinked structure and a weight average molecular weight of 200,000 or more and less than 450,000 is used as an adhesive.

（式１中、Ｒ^１はＣＨ_２＝ＣＨ－又はＣＨ_２＝Ｃ(ＣＨ_３)－をあらわし、Ｒ^２は炭素原子数が１～３のアルキル基、シクロヘキシル基又はイソボルニル基をあらわす。）

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

（式２中、Ｒ^３はＣＨ_２＝ＣＨ－又はＣＨ_２＝Ｃ(ＣＨ_３)－をあらわし、Ｒ^４は炭素原子数が４～１２のアルキル基をあらわす。）

(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 pressure-sensitive adhesive tape according to the present invention, the pressure-sensitive adhesive composition may further contain a tackifying resin.

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

In the adhesive tape according to the present invention, the adhesive composition may further contain an antioxidant.

The adhesive tape according to the present invention further includes a base material, and an adhesive layer can be formed on one 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 can maintain a certain level of adhesive strength even when oil and fat components adhere to it. Possesses oil resistance. Furthermore, the adhesive tape according to the present invention has appropriate adhesive strength when applied to an adherend, and has excellent adhesive strength maintenance performance when oil and fat components are attached. Therefore, the adhesive tape according to the present invention can be suitably used, for example, for joining a display panel and a casing of a small portable electronic device such as a smartphone, or for fixing components inside a casing.

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

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

(meth)acrylic acid alkoxyalkyl ester, carboxylic acid group-containing (meth)acrylic monomer, (meth)acrylic acid alkyl ester represented by the above formula 1, and (meth)acrylic acid alkyl ester represented by the above formula 2 (hereinafter, The content of the (meth)acrylic acid alkoxyalkyl ester is 20 parts by mass or more and less than 40 parts by mass with respect to a total of 100 parts by mass of the "four types of monomers"). If this content is less than 20 parts by mass, the acrylic copolymer of the present invention will have fewer monomer units with a high SP value, resulting in a decrease in durability against oil and fat components, resulting in a reduction in sebum, sweat, food, cosmetics, etc. When oil and fat components adhere to the adhesive, the adhesive strength is significantly reduced, making it impossible to maintain the adhesive strength required for applications such as fixing parts inside electronic devices. In addition, if the content is 40 parts by mass or more, the initial adhesive strength of the adhesive will decrease, resulting in decreased workability during work such as fixing components inside electronic devices. This content is more preferably 25 parts by mass or more and less than 40 parts by mass.

Examples of the (meth)acrylic monomer containing a carboxylic acid group include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, citraconic acid, glataconic acid, 2- Acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, etc. can be used. Among these, (meth)acrylic acid is preferably used in consideration of the crosslinking density and availability of the resulting adhesive.

The content of the carboxylic acid group-containing (meth)acrylic monomer based on a total of 100 parts by mass of the four types of monomers is 10 parts by mass or more and less than 25 parts by mass. When this content is less than 10 parts by mass, the crosslinking density of the adhesive decreases, and the adhesive swells with oil and fat components such as sebum, sweat, foods, and cosmetics. Moreover, if the content is 25 parts by mass or more, the initial adhesive strength of the adhesive will decrease, resulting in decreased workability during work such as fixing components inside electronic devices. This content is more preferably 10 parts by mass or more and 23 parts by mass or less.

Examples of the (meth)acrylic acid alkyl ester represented by Formula 1 include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. can. Considering ease of availability, it is preferable to use methyl acrylate.

The content of the (meth)acrylic acid alkyl ester represented by the formula 1 based on 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 repulsion resistance of the adhesive decreases, making it impossible to satisfy the adhesive force required for applications such as fixing components inside electronic devices. Moreover, if the content is 20 parts by mass or more, the initial adhesive strength of the adhesive will decrease, resulting in decreased workability during work such as fixing components inside electronic devices. This content is more preferably 5 parts by mass or more and 15 parts by mass 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 (meth)acrylate. ) isohexyl acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, Isodecyl (meth)acrylate, 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 2-ethylhexyl (meth)acrylate, which has a low Tg (glass transition point).

The content of the (meth)acrylic acid alkyl ester represented by the formula 2 based on 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 the content is less than 30 parts by mass, the initial adhesive strength of the adhesive will decrease, resulting in decreased workability during work such as fixing components inside electronic devices. If this content is 50 parts by mass or more, durability against oil and fat components will decrease, and when oil and fat components such as sebum, sweat, food, and cosmetics adhere, the adhesive strength will decrease significantly, resulting in problems such as fixing parts inside electronic devices. cannot maintain the adhesion required for this application. This content is more preferably 30 parts by mass or more and 45 parts by mass or less.

Examples of compounds containing bifunctional or more isocyanate groups (hereinafter also referred to as "isocyanate crosslinking agents") include tolylene diisocyanate, xylene diisocyanate, chlorphenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, Hydrogenated diphenylmethane diisocyanate and the like can be used.

Examples of compounds containing bifunctional or higher glycidyl groups (hereinafter also referred to as "epoxy crosslinking agents") include 1,3 bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N' -Tetraglycidyl-m-xylene diamine, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N,N-diglycidylaminophenylglycidyl ether, N,N-diglycidyl toluidine , N,N-diglycidylaniline, pentaerythritol polyglycidyl ether, 1,6-hexanediol diglycidyl ether, etc. can be used.

The amount of the compound containing a difunctional or more functional isocyanate group or the compound containing a glycidyl group having a difunctional or higher functionality used as a crosslinking agent is not particularly limited. The amount of crosslinking agent added can be adjusted so that the degree of swelling 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 using 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 a constant temperature for a certain period of time.

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

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 adhesive will not have the necessary cohesive force, which may cause the adhesive to ooze out when the adhesive tape is applied to an adherend. If the weight average molecular weight is 450,000 or more, the followability of the adhesive tape to the adherend will be reduced, and the adhesive force required for fixing components inside electronic devices will not be obtained. The weight average molecular weight is more preferably 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, if necessary.

Examples of tackifying resins include rosin ester resins (rosin esters, disproportionated rosin esters, hydrogenated rosin esters, etc.), terpene resins (terpene resins, aromatic modified terpene resins, hydrogenated terpene resins, terpene phenols, etc.) ), petroleum resins (aliphatic petroleum resins, aromatic petroleum resins, copolymer petroleum resins, aliphatic petroleum resins, etc.), pure monomer resins (coumarone/indene resins, styrene resins, etc.), condensation resins Resins (phenol resin, xylene resin, etc.) can be used. By adding a tackifying resin, the hardness of the adhesive is reduced and the initial adhesion to the adherend is improved.

Examples of the silane coupling agent include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxy Propyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, and the like can be used. Two or more types of silane coupling agents may be used in combination. By using a silane coupling agent, it is possible to improve the repulsion resistance of the adhesive and improve the resistance to moist heat load, which decreases as the adhesive tape becomes narrower and finer processed.

As the antioxidant, for example, a hindered phenol antioxidant can be used. By adding an antioxidant, it is possible to improve the repulsion resistance of the adhesive and improve the resistance to moist heat load, which decreases as the adhesive tape becomes narrower and finer processed.

<Adhesive tape>
The adhesive tape according to the present invention is an adhesive tape in which a pressure-sensitive adhesive composition containing the acrylic copolymer described above (and optional components as necessary) is used as a pressure-sensitive 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 the adhesive composition This is an adhesive tape in which an adhesive layer is formed on one or both sides of a base material using a material.

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 adhesive tapes having a base material, an adhesive layer may be formed by coating an acrylic copolymer on the base material and then drying it, or an acrylic copolymer may be coated on a support such as release paper. After forming an adhesive layer by applying a polymer, this adhesive layer may be attached to one or both sides of the base material. The adhesive layer of the baseless type adhesive tape and the adhesive tape having a base material may be a single layer or may be a laminate of a plurality of layers.

The thickness of the adhesive layer in the adhesive tape having 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 for applying the acrylic copolymer onto a base material or a support such as release paper is not particularly limited, and any known method may be used. Specific examples thereof include methods using a roll coater, die coater, lip coater, dip roll coater, bar coater, knife coater, spray roll coater, and the like.

When the adhesive tape has a base material, the base material is not particularly limited, and any known base material may be used. Specific examples of base materials include fibrous base materials such as paper, cloth, nonwoven fabrics, and nets, olefin resins, polyester resins, polyvinyl chloride resins, vinyl acetate resins, polyamide resins, polyimide resins, and polyamide resins. Examples include resin base materials (resin films or resin sheets) such as ether ether ketone (PEEK) and polyphenylene sulfide (PPS), rubber sheets, foam sheets (foam base materials), metal foils, and metal plates. Furthermore, a laminate of these materials, for example, a laminate of a resin base material and a base material other than resin, or a laminate of resin base materials may be used. The base material may be either single layer or multilayer. The surface of the base material on which the adhesive layer is provided may be subjected to various treatments such as back surface treatment, antistatic treatment, and undercoat treatment, as required. The thickness of the base material is preferably 5 to 500 μm, more preferably 10 to 200 μm.

The adhesive tape may be protected by release paper or other film. The release paper or other film is not particularly limited, and known ones can be used as necessary.

Hereinafter, the present invention will be explained in more detail with reference to 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 using the following measuring device and conditions.
・Device: LC-2000 series (manufactured by JASCO Corporation)
・Column: Shodex KF-806M x 2, Shodex KF-802 x 1 ・Eluent: Tetrahydrofuran (THF)
・Flow rate: 1.0mL/min ・Column temperature: 40℃
・Injection volume: 100μL
・Detector: Refractometer (RI)

(Initial adhesive strength)
When using base material A: A 10 mm wide double-sided adhesive tape sample backed with a 25 μm thick polyester film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one round trip of a 2.0 kg roller, and the pressure was applied. The 180° peeling adhesive strength (N/10 mm width) 20 minutes after application was measured by the method described in JIS Z 0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed with a 50 μm thick polyester film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one round trip of a 2.0 kg roller, and pressure was applied. The 180° peeling adhesive strength (N/10 mm width) 20 minutes after application was measured by the method described in JIS Z 0237:2000.

(adhesive strength over time)
When using base material A: A 10 mm wide double-sided adhesive tape sample backed with a 25 μm thick polyester film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one round trip of a 2.0 kg roller, and the pressure was applied. The 180° peeling adhesive strength (N/10 mm width) 72 hours after application was measured by the method described in JIS Z 0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed with a 50 μm thick polyester film was applied to an SUS304 plate polished with No. 280 water-resistant abrasive paper using pressure with 2.5 reciprocations of a 2.0 kg roller. The 180° peeling adhesive strength (N/10 mm width) 72 hours after pressure application was measured by the method described in JIS Z 0237:2000.

(Adhesive strength after promotion: Na)
When using base material A: A 10 mm wide double-sided adhesive tape sample backed with a 25 μm thick polyester film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper with one round trip of a 2.0 kg roller, and the temperature was 65°C. It was left in an atmosphere of ±5°C and humidity of 90±10% for 72 hours. Thereafter, it was left in an atmosphere with a temperature of 23±5° C. and a humidity of 50±5% for 2 hours. The 180° peeling adhesive strength (N/10 mm width) of this sample was measured by the method described in JIS Z 0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed with a 50 μm thick SUS film was applied to an SUS304 plate polished with No. 280 water-resistant abrasive paper using pressure with 2.5 reciprocations of a 2.0 kg roller. The sample was left in an atmosphere with a temperature of 60±5° C. and a humidity of 90±10% for 72 hours. Thereafter, it was left in an atmosphere with a temperature of 23±5° C. and a humidity of 50±5% for 2 hours. The 180° peeling adhesive strength (N/10 mm width) of this sample was measured by the method described in JIS Z 0237:2000.

(Adhesive strength after oleic acid immersion: Nb)
When using base material A: A 10 mm wide double-sided adhesive tape sample backed with a 25 μm thick polyester film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper using pressure with one reciprocation of a 2.0 kg roller. This sample was immersed in oleic acid and left in an atmosphere with a temperature of 65±5° C. and a humidity of 90±10% for 72 hours. Thereafter, the sample was taken out from the container, and after wiping off the oleic acid and water droplets using pure water, it was left in an atmosphere with a temperature of 23±5° C. and a humidity of 50±5% for 2 hours. The 180° peeling adhesive strength (N/10 mm width) of this sample was measured by the method described in JIS Z 0237:2000.

When using base material B: A 10 mm wide double-sided adhesive tape sample backed with a 50 μm thick SUS film was applied to a SUS304 plate polished with No. 280 water-resistant abrasive paper using pressure with a 2.0 kg roller 2.5 times. This sample was immersed in oleic acid and left in an atmosphere with a temperature of 60±5° C. and a humidity of 90±10% for 72 hours. Thereafter, the sample was taken out from the container, and after wiping off the oleic acid and water droplets using pure water, it was left in an atmosphere with a temperature of 23±5° C. and a humidity of 50±5% for 2 hours. The 180° peeling adhesive strength (N/10 mm width) of this sample was measured by the method described in JIS Z 0237:2000.

(Adhesion retention rate after oleic acid immersion: X)
It was calculated using the following formula.
X=100×Nb/Na

(destruction mode)
For the sample after the measurement of the adhesive force after acceleration (Na) and the sample after the measurement of the adhesive force after immersion in oleic acid (Nb), the parts where destruction occurred were observed. Cohesive failure (cohesive failure in Tables 2 to 4) is when the adhesive is damaged, and interfacial failure is when the adhesive is broken between the adhesive and the adherend. The case was defined as base material failure ("base material" in Tables 2 to 4).

[Example 1]
(Preparation of acrylic copolymer)
In a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, the parts by mass of monomers constituting the copolymer shown in Table 1, ethyl acetate, and 0.03 mass of n-dodecanethiol, which is a chain transfer agent, were added. 1 part and 0.05 part by mass of lauryl peroxide as a radical polymerization initiator were charged, nitrogen gas was charged, and the mixture was reacted at 67° C. for 3 hours under a nitrogen gas stream while stirring. Thereafter, the mixture was reacted at 82°C for 3 hours. After the reaction was completed, the mixture was cooled to room temperature and ethyl acetate was added. As a result, a copolymer having 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)
To 100 parts by mass of the solid content of this copolymer, 1.8 parts by mass of an isocyanate crosslinking agent (crosslinking agent A) (manufactured by Tosoh Corporation, trade name L-45E) was added as a crosslinking agent, and an adhesive was prepared. did.

(Manufacture of double-sided adhesive tape)
An undercoat layer was formed on base material A by applying a separately prepared undercoat to both sides of a 12 μm thick polyethylene terephthalate film (base material A) that had been subjected to corona discharge treatment on both sides and drying at 120°C. The prepared adhesive was applied smoothly over the entire surface of the undercoat layer on the first side of the base material A, and dried by heating at 100° C. to form an adhesive layer with a thickness of 19 μm. Furthermore, a silicone-treated release paper was laminated on top of this adhesive layer. After that, an adhesive prepared in the same manner was applied and dried on the undercoat layer on the second side, a release paper was attached, and after curing for 3 days at 40°C, a double-sided adhesive tape with a total thickness of 50 μm was obtained. Ta.

[Example 2]
A double-sided adhesive tape was prepared in the same manner as in Example 1, except that the crosslinking agent was changed to an epoxy crosslinking agent (crosslinking agent B) (manufactured by Soken Kagaku Co., Ltd., trade name E-5CM) in the preparation of the adhesive. .

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

[Example 4]
In preparing the adhesive, 8 parts by mass of D-6011 (trade name) manufactured by Arakawa Chemical Co., Ltd. diluted 50% with ethyl acetate as the tackifying resin, and 5% diluted with ethyl acetate as the silane coupling agent. Implemented except that 2 parts by mass of KBM-403 (trade name) manufactured by Shin-Etsu Chemical Co., Ltd. as a liquid and 0.2 parts by mass of Irganox (registered trademark) 1010 manufactured by BASF Japan Co., Ltd. as an antioxidant were added. A double-sided adhesive tape was produced in the same manner as in Example 3.

[Comparative example 1]
(Preparation of acrylic copolymer)
Methyl acrylate was not used, 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, and the amount of crosslinking agent added was changed to 1.2 parts by mass. A copolymer having a solid content concentration of 30% was obtained in the same manner as in Example 1 except for this. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 1 was 750,000.

(Preparation of adhesive)
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, trade name L-45E) as a crosslinking agent, acetic acid as a tackifying resin, 8 parts by mass of D-6011 (trade name) manufactured by Arakawa Chemical Co., Ltd. diluted 50% with ethyl, KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd. diluted 5% with ethyl acetate as a silane coupling agent. (trade name) and 0.2 parts by mass of Irganox (registered trademark) 1010 manufactured by BASF Japan Co., Ltd. as an antioxidant were 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 preparing 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 without using methyl acrylate, and the amount of crosslinking agent added was 1 part by mass. A double-sided adhesive tape was produced in the same manner as in Example 1 except that the amount was changed to .2 parts by mass. The weight average molecular weight of the acrylic copolymer prepared in Comparative Example 2 was 1,050,000.

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

[Comparative example 4]
In preparing the acrylic copolymer, double-sided adhesive was prepared in the same manner as in Comparative Example 2, except that 86 parts by mass of 2-(ethoxyethoxy)ethyl acrylate (EOEOEA) was used instead of methoxyethyl acrylate. A tape was 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, an adhesive prepared in the same manner as in Comparative Example 1 was coated smoothly on the entire surface of a silicone-treated release paper and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, adhesive on release paper was pasted on both sides of a 100 μm thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and after curing at 40 ° C. for 3 days, A double-sided adhesive tape with a total thickness of 200 μm was obtained.

[Comparative example 6]
In the production of a double-sided adhesive tape, an adhesive prepared in the same manner as in Comparative Example 2 was coated smoothly on the entire surface of a silicone-treated release paper, and dried by heating at 90°C to form an adhesive layer with a thickness of 50 μm. Then, adhesive on release paper was pasted on both sides of a 100 μm thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and after curing at 40 ° C. for 3 days, A double-sided adhesive tape with a total thickness of 200 μm was obtained.

[Comparative Example 7]
In the production of a double-sided adhesive tape, an adhesive prepared in the same manner as in Comparative Example 3 was coated smoothly on the entire surface of a silicone-treated release paper, and dried by heating at 90° C. to form an adhesive layer with a thickness of 50 μm. Then, adhesive on release paper was pasted on both sides of a 100 μm thick base material (base material B) made of polyethylene (PE) foam that had been subjected to corona discharge treatment on both sides, and after curing at 40 ° C. for 3 days, A double-sided adhesive tape with a total thickness of 200 μm was obtained.

[Comparative example 8]
A double-sided adhesive tape was produced in the same manner as Comparative Example 2, except that 10 parts by mass of 4-hydroxybutyl acrylate was used instead of 10 parts by mass of acrylic acid in the preparation of the acrylic copolymer. 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 base material used to form the double-sided adhesive tape. In addition, the initial adhesive strength, adhesive strength over time, adhesive strength after promotion Na, adhesive strength Nb after immersion in oleic acid, adhesive strength retention rate X after immersion in oleic acid, and failure mode measured for each double-sided adhesive tape are shown in Tables 2 to 4. Shown below.

The abbreviations used in Table 1 are as follows.
AME = methoxyethyl acrylate EOEOEA = 2-(2-ethoxyethoxy)ethyl acrylate AA = acrylic acid 4-HBA = 4-hydroxybutyl acrylate MA = methyl acrylate 2-EHA = 2-ethylhexyl acrylate

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 maintained appropriate adhesive strength even after immersion in oleic acid. Therefore, these double-sided adhesive tapes must have high durability against oil and fat components such as sebum, sweat, food, and cosmetics, and have appropriate adhesive strength when applied to adherends. I understand. In addition, when comparing Example 3 and Example 4, Example 4 in which the tackifying resin was added has a smaller initial adhesive force value, but while Example 3 has interfacial failure, Since the base material was broken in No. 4, it is considered that no decrease in adhesive strength occurred.

On the other hand, the monomer composition of the acrylic copolymer used in Comparative Examples 1 to 4 and 8 (each adhesive layer thickness 19 μm, base material A) was the same as that of Examples 1 and 2 (each adhesive layer thickness 19 μm , is different from the monomer composition of the acrylic copolymer used in base material A). Furthermore, the weight average molecular weights of the acrylic copolymers used in Comparative Examples 1, 2, 4, and 8 are larger than the weight average molecular weights of the acrylic copolymers 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 after promotion Na, adhesive strength Nb after immersion in oleic acid, and The adhesive strength retention rate X after immersion in oleic acid was poor.

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

Comparative Example 3 is an example in which the weight average molecular weight of the acrylic polymer is lower than that of Comparative Example 2. As a result, Comparative Example 3 was improved in several items compared to Comparative Example 2. However, the initial adhesive strength, the aged adhesive strength, and the promoted adhesive strength Na were inferior to those of Examples 1 and 2.

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

The double-sided adhesive tapes of Comparative Examples 5 to 7 (thickness of each adhesive layer: 50 μm, base material B) had a monomer composition of the acrylic copolymer used in Examples 3 and 4 (thickness of each adhesive layer: 50 μm). , is different from the monomer composition of the acrylic copolymer used in base material B). Furthermore, the weight average molecular weights of the acrylic copolymers used in Comparative Examples 5 and 6 are larger than those of the acrylic copolymers used in Examples 3 and 4.

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

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

Comparative Example 7 is an example in which the adhesive of Comparative Example 3 was applied to base material B. As a result, Comparative Example 7 was improved in several items compared to 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 example, for joining a display panel and a casing of a small portable electronic device such as a smartphone, or for fixing components inside a casing.

Claims (5)

As the monomer composition,
20 parts by mass or more and less than 40 parts by mass of (meth)acrylic acid alkoxyalkyl ester,
10 parts by mass or more and less than 25 parts by mass of a (meth)acrylic monomer containing a carboxylic acid group,
5 parts by mass or more and less than 20 parts by mass of a (meth)acrylic acid alkyl ester 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 of the above monomers is 100 parts by mass) of a (meth)acrylic acid alkyl ester represented by the following formula 2,
A crosslinked structure is formed by using one or both of a difunctional or more functional isocyanate group-containing compound and a difunctional or more glycidyl group-containing compound as a crosslinking agent, and
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 having 1 to 3 carbon atoms, a cyclohexyl group, or an isobornyl group.)

(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.) The adhesive tape according to claim 1, wherein the adhesive composition further includes a tackifying resin. The adhesive tape according to claim 1, wherein the adhesive composition further contains a silane coupling agent. The adhesive tape according to claim 1, wherein the adhesive composition further contains an antioxidant. The adhesive tape according to claim 1, wherein 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.