JP7844576B2 - Adhesive tape - Google Patents

Description

This invention relates to adhesive tape.

Adhesive tape is used for assembly in portable electronic devices such as mobile phones and personal digital assistants (PDAs) (for example, Patent Documents 1 and 2). Adhesive tape is also used for bonding optical components (for example, Patent Document 3).

Japanese Patent Publication No. 2009-242541 Japanese Patent Publication No. 2009-258274 Japanese Patent Publication No. 2012-214544

One environmental problem that needs to be considered on a global scale is global warming caused by greenhouse gases. Recently, the concept of carbon neutrality—where greenhouse gas emissions minus absorption and removal amounts equal zero—is gaining traction worldwide. In the field of electronic devices that utilize adhesive tape as a component, efforts to create environmentally friendly products are accelerating.
The adhesive used to form the adhesive layer of adhesive tape typically contains a solvent, and therefore, _CO2 is emitted during the manufacturing process of adhesive tape due to this solvent. While reducing the amount of solvent in the adhesive can reduce the amount of _CO2 emitted during the manufacturing process, simply reducing the amount of solvent increases the viscosity of the adhesive, leading to a problem of reduced processability. In order to reduce the amount of solvent, that is, to increase the solid content of the adhesive without increasing viscosity, it is necessary to lower the molecular weight of components such as (meth)acrylic copolymers contained in the adhesive. On the other hand, the functions required of the adhesive layer include retention performance consisting of bulk cohesive force and heat resistance, and adhesion consisting of interface wettability and bulk fluidity. In order to satisfy these performance requirements, components such as (meth)acrylic copolymers used in conventional adhesives needed to have a molecular weight of around 500,000 or more.

The present invention aims to provide an adhesive tape having an adhesive layer with excellent retention and adhesion properties, even while using a (meth)acrylic copolymer with a low molecular weight.

Disclosure 1 is an adhesive tape having an adhesive layer, wherein the adhesive layer contains a crosslinked product of an adhesive comprising a (meth)acrylic copolymer, a crosslinking agent, and a tackifying resin, and when a GPC measurement is performed on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinked product using differential refractometer RI detection, the weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight of 5000 or more is 80,000 or more and less than 500,000, and in a holding test in which a 1 kg load is applied in the shear direction at 80°C for 24 hours to the adhesive tape bonded to a SUS plate, the adhesive tape does not fall off, and the 180° peel adhesive strength of the adhesive tape to the SUS plate is 15 N/25 mm or more.
Disclosure 2 is an adhesive tape having an adhesive layer, wherein the adhesive layer contains a crosslinked product of an adhesive comprising a (meth)acrylic copolymer, a crosslinking agent, and a tackifying resin, and the weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight of 5,000 or more, when GPC measurement is performed by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinked product, is 80,000 or more and less than 500,000, and the adhesive tape satisfies the following first configuration, second configuration, or third configuration.
First composition: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more. Second composition: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, the gel fraction of the adhesive layer is less than 5% by mass, and the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more, obtained by GPC measurement of the sol component of the adhesive layer using differential refractometer RI detection, is determined from the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more. A third configuration is an adhesive tape of the present disclosure 2 that satisfies the first configuration, wherein the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the bridge products is subjected to GPC measurement by differential refractometer RI detection, and the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight of 5000 or more is 80,000 or more: the adhesive contains 0.1 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass.
Disclosure 4 is an adhesive tape of Disclosure 2 that satisfies the second configuration described above.
Disclosure 5 is the adhesive tape of Disclosure 2, satisfying the third configuration described above.
Disclosure 6 is an adhesive tape according to Disclosure 1, wherein the adhesive layer satisfies the following first configuration, second configuration, or third configuration.
First configuration: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more. Second configuration: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, the gel fraction of the adhesive layer is less than 5% by mass, and the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more when the sol component of the adhesive layer is measured by GPC by differential refractometer RI detection. The weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight 5000 or more when the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product is measured by GPC by differential refractometer RI detection. A third configuration in which the value after subtracting is 80,000 or more: The adhesive contains 0.1 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass. Disclosure 7 is an adhesive tape of Disclosure 2 or 6 in which, as the first configuration, the adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more and less than 30% by mass, or as the third configuration, the adhesive contains 1.5 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass.
Disclosure 8 is an adhesive tape according to Disclosure 7, wherein the adhesive layer, as the first configuration, contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more and less than 30% by mass.
Disclosure 9 is an adhesive tape according to Disclosure 7, wherein the adhesive layer, as the third component, contains 1.5 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass.
Disclosure 10 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein, when the sol component of the adhesive layer is subjected to GPC measurement by differential refractometer RI detection, the weight-average molecular weight of the sol component in the region of molecular weight of 5,000 or more is 50,000 or more and 500,000 or less.
Disclosure 11 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the peak top molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product is 70,000 or more and 300,000 or less when GPC measurement is performed by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the above crosslinking product.
Disclosure 12 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the adhesive contains 0.03% by mass or more of a compound having a hydroxyl group in the solid content, and 2% by mass or more of a compound having a carboxyl group in the solid content.
Disclosure 13 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the (meth)acrylic copolymer has 50% by mass or more of constituent units derived from monomers having alkyl groups with 6 or more carbon atoms.
Disclosure 14 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the adhesive layer has a glass transition temperature of -10°C or higher and 30°C or lower.
Disclosure 15 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the adhesive layer has a storage modulus G' (80°C) of 1.0 × ^10⁴ Pa or more.
Disclosure 16 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, wherein the adhesive layer has a thickness of 10 μm or more and 100 μm or less.
Disclosure 17 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the adhesive tape has a base material, the base material is a polyester resin film or a polypropylene resin film, and the thickness of the base material is 5 μm or more and 200 μm or less.
Disclosure 18 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 17, wherein the adhesive tape has a base material and adhesive layers on both sides of the base material.
The present invention will be described in detail below.
Furthermore, the adhesive tape of Disclosure 1 will also be referred to as "the adhesive tape of Invention 1," and the adhesive tape of Disclosure 2 will also be referred to as "the adhesive tape of Invention 2." In addition, matters common to the adhesive tape of Invention 1 and the adhesive tape of Invention 2 will not be specifically specified, or will be described as "the adhesive tape of the present invention."

The inventors of the present invention have discovered that even when using an adhesive containing a (meth)acrylic copolymer with a specific low molecular weight to form the adhesive layer, it is possible to obtain an adhesive tape having an adhesive layer with excellent retention performance and adhesion by providing the adhesive layer with a specific configuration, thereby completing the present invention.

The adhesive tape of the present invention is an adhesive tape having an adhesive layer.
The above adhesive layer contains a crosslinking product of an adhesive comprising a (meth)acrylic copolymer, a crosslinking agent, and a tackifying resin.
In this specification, "(meth)acrylic" means acrylic or methacrylic.

In the adhesive tape of the present invention, the adhesive layer has a weight-average molecular weight of 80,000 or more (hereinafter also simply referred to as "weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product") when GPC measurement is performed by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product (hereinafter also referred to simply as "weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition") in the region of molecular weight of 5,000 or more, which is less than 500,000.
If the weight-average molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is 80,000 or more, the bulk cohesive force in the resulting adhesive layer will be increased, and the adhesive layer will have excellent heat resistance. If the weight-average molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is less than 500,000, the viscosity of the adhesive used to form the adhesive layer can be reduced, improving processability and reducing the amount of solvent that is the source of _CO2 emitted in the manufacturing process. The preferred lower limit for the weight-average molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is 100,000, the more preferred lower limit is 150,000, the preferred upper limit is 490,000, the more preferred upper limit is 450,000, and the even more preferred upper limit is 400,000.
In this specification, the "(meth)acrylic copolymer obtained by alkaline decomposition" may be the (meth)acrylic copolymer contained in the adhesive, or it may be another compound. Examples of other compounds include (meth)acrylic copolymers in which a part of the structure of the (meth)acrylic copolymer contained in the adhesive is modified and/or deficient.
Furthermore, the alkaline decomposition of the crosslinking points of the above crosslinking product is carried out by the following method.
Specifically, 300 mg of the adhesive layer, 6 mL of ethanol, and 7 mL of a 60% KOH aqueous solution are added to a pressure vessel, and hydrolysis is carried out under pressure in an oven at 160°C for 60 hours, thereby alkaline decomposing the crosslinking points of the crosslinked product and obtaining a (meth)acrylic copolymer.
Furthermore, when performing GPC measurements by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the above crosslinking product, the following method can be used, for example.
Specifically, the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the above crosslinking product is analyzed by gel permeation chromatography (GPC) (Waters, Inc., "2690 Separations Model"), and the molecular weight distribution in polystyrene terms is measured. The above GPC can be performed under the following conditions.
Eluent: Tetrahydrofuran (THF)
Flow rate: 0.4mL/min
Detector: Differential Refractometer RI
Column: LF-804 (manufactured by SHOKO Corporation)
Column temperature (measurement temperature): 40°C
Injection volume: 20μL

In the adhesive tape of the present invention, the adhesive layer has a preferred lower limit of 70,000 and a preferred upper limit of 300,000 for the peak top molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product, when GPC measurement is performed by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking product, in the region of molecular weight of 5,000 or more.
If the peak top molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is 70,000 or more, the bulk cohesive force in the resulting adhesive layer will be greater, and the adhesive layer will have better heat resistance. If the peak top molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is 300,000 or less, the viscosity of the adhesive used to form the adhesive layer can be lowered, improving processability and reducing the amount of solvent that is the source of _CO2 emitted in the manufacturing process. A more preferable lower limit for the peak top molecular weight of the (meth)acrylic copolymer obtained by the above alkaline decomposition is 80,000, an even more preferable lower limit is 100,000, a more preferable upper limit is 250,000, and an even more preferable upper limit is 230,000.
In this specification, "peak-top molecular weight" refers to the molecular weight at the highest peak in the molecular weight distribution curve. Even if there are shoulders or more than one peak in the molecular weight distribution curve, the peak-top molecular weight refers to the molecular weight at the highest peak in the molecular weight distribution curve.

In the adhesive tape of the present invention, from the viewpoint of adjusting the molecular weight distribution, when GPC measurement is performed by differential refractometer RI detection on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product, the preferred lower limit of the polydispersity of the (meth)acrylic copolymer in the region of molecular weight of 5000 or more (hereinafter also simply referred to as "polydispersity of the (meth)acrylic copolymer obtained by alkaline decomposition") is 15,000, the preferred upper limit is 100,000, and the more preferred upper limit is 60,000.
The polydispersity mentioned above refers to the ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn).

In the adhesive tape of the present invention, the weight-average molecular weight of the sol component of the adhesive layer, when measured by GPC using differential refractometer RI detection, in the region of molecular weight of 5,000 or more, is preferably 50,000 at a lower limit and preferably 500,000 at an upper limit. A weight-average molecular weight of 50,000 or more for the sol component of the adhesive layer results in greater bulk cohesive force in the resulting adhesive layer, making it superior in heat resistance and high-temperature rebound resistance. A weight-average molecular weight of 500,000 or less for the sol component allows for a lower viscosity of the adhesive used to form the adhesive layer, improving processability and reducing the amount of solvent that contributes to _CO2 emissions during the manufacturing process. A more preferable lower limit for the weight-average molecular weight of the sol component is 70,000, an even more preferable lower limit is 100,000, an even more preferable upper limit is 400,000, and an even more preferable upper limit is 300,000.
Here, the term "sol component" refers to the component remaining after removing the "gel component" from the adhesive layer. The "gel component" is the low-flow component remaining in the mesh after the gel fraction measurement process, in which the (meth)acrylic copolymer, the tackifying resin described later, etc., form a cross-linked structure via the cross-linking agent described later. The "sol component" is the high-flow component remaining after removing the gel component in the above process.
The sol component of the adhesive layer described above can be obtained, for example, by immersing the adhesive layer in tetrahydrofuran (THF) at 23°C for 24 hours, filtering out the insoluble material through a 200-mesh wire mesh, and removing the gel component.
When performing GPC measurements on the sol component of the above-mentioned adhesive layer using differential refractometer RI detection, for example, the following method can be employed.
Specifically, the sol component of the adhesive layer is analyzed by gel permeation chromatography (GPC) (Waters, Inc., "2690 Separations Model") to measure the molecular weight distribution in terms of polystyrene. The above GPC can be performed under the following conditions.
Eluent: Tetrahydrofuran (THF)
Flow rate: 0.4mL/min
Detector: Differential Refractometer RI
Column: LF-804 (manufactured by SHOKO Corporation)
Column temperature (measurement temperature): 40°C
Injection volume: 20μL

In the adhesive tape of the present invention, the adhesive layer has a preferred lower limit of 30,000 and a preferred upper limit of 300,000 for the peak top molecular weight of the sol component of the adhesive layer (hereinafter also simply referred to as "peak top molecular weight of the sol component") in the region of molecular weight of 5,000 or more, when GPC measurement is performed on the sol component of the adhesive layer by differential refractometer RI detection. A peak top molecular weight of 30,000 or more for the sol component results in a greater bulk cohesive force in the resulting adhesive layer, which has superior heat resistance. A peak top molecular weight of 300,000 or less for the sol component allows for a lower viscosity of the adhesive used to form the adhesive layer, improving processability and reducing the amount of solvent that is the source of _CO2 emitted during the manufacturing process. A more preferred lower limit for the peak top molecular weight of the sol component is 70,000, an even more preferred lower limit is 80,000, an even more preferred upper limit is 250,000, and an even more preferred upper limit is 230,000.

The adhesive tape of the present invention 1 does not fall off when subjected to a holding test in which a 1 kg load is applied in the shear direction at 80°C for 24 hours after being bonded to a SUS plate. The adhesive tape that shows the results of the above holding test has excellent heat resistance and, for example, provides good fixation to components used in electronic devices. In the above holding test, it is preferable that there is no displacement of 1 mm or more, and more preferably that there is no displacement of 0.5 mm or more.
Furthermore, it is preferable that the adhesive tape of the present invention 2 does not fall off when subjected to a holding test in which a 1 kg load is applied in the shear direction at 80°C for 24 hours after being bonded to a SUS plate. The adhesive tape that shows the results of the holding test described above has superior heat resistance and, for example, provides better fixation to components used in electronic devices. It is more preferable that there is no displacement of 1 mm or more in the above holding test results, and even more preferable that there is no displacement of 0.5 mm or more.
The above retention test can be performed by the following method. A schematic diagram illustrating the method of the above retention test is shown in Figure 1.
Specifically, first, the adhesive tape 1 is cut into strips 25 mm wide, and then adhered to the SUS plate 2 by moving a 2 kg rubber roller back and forth at a speed of 300 mm/min once. Next, cuts are made in the adhesive tape 1 so that the bonding area is 25 mm x 25 mm. After that, it is left to stand at 23°C for 20 minutes, then placed in an 80°C oven and heated for another 15 minutes. Then, while maintaining the temperature at 80°C, a 1 kg load is applied in the shear direction using a 1 kg weight 3 as shown in Figure 1. The presence or absence of the adhesive tape being dropped is checked, and if it does not fall after 24 hours, the amount of displacement (shift) from the cut position is measured with a scale magnifier.

The adhesive tape of the present invention 1 has a 180° peel adhesive strength of 15 N/25 mm or more when applied to a SUS plate. Specifically, after bonding to a SUS plate, a 180° peel adhesive strength of 15 N/25 mm or more is obtained when a tensile test is performed in the 180° direction under the conditions of 23°C and a peeling speed of 300 mm/min in accordance with JIS Z0237. The above 180° peel adhesive strength of 15 N/25 mm or more allows the adhesive tape to have sufficient adhesion, and for example, it provides good fixation to components used in electronic devices. The above 180° peel adhesive strength is preferably 18 N/25 mm or more, and more preferably 20 N/25 mm or more.
Furthermore, the adhesive tape of the present invention 2 preferably has a 180° peel adhesive strength of 15 N/25 mm or more when applied to a SUS plate. Specifically, it is preferable that the 180° peel adhesive strength is 15 N/25 mm or more when a tensile test is performed in the 180° direction at 23°C and a peeling speed of 300 mm/min in accordance with JIS Z0237 after bonding to the SUS plate. Having a 180° peel adhesive strength of 15 N/25 mm or more allows the adhesive tape to have more sufficient adhesion, resulting in better fixation to components used in electronic devices, for example. The 180° peel adhesive strength is more preferably 18 N/25 mm or more, and even more preferably 20 N/25 mm or more.
The above 180° peel-off adhesive strength can be measured by the following method.
Specifically, first, the adhesive tape is cut into strips 25 mm wide, and then adhered to a SUS plate by passing a 2 kg rubber roller back and forth at a speed of 300 mm/min. Next, a test specimen is obtained by leaving it undisturbed for 20 minutes at a temperature of 23°C and a relative humidity of 50%. The obtained test specimen can be subjected to a tensile test using a tensile testing machine in accordance with JIS Z0237, under conditions of 23°C, a peeling speed of 300 mm/min, and a peeling angle of 180°, thereby measuring the 180° peel adhesion strength.

In the adhesive tape of the present invention 2, the adhesive layer satisfies the following first configuration, second configuration, or third configuration. Furthermore, in the adhesive tape of the present invention 1, it is preferable that the adhesive layer satisfies the following first configuration, second configuration, or third configuration.
First composition: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more. Second composition: The adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, the gel fraction of the adhesive layer is less than 5% by mass, and the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more, obtained from the alkaline decomposition of the crosslinking point of the crosslinking product, when GPC measurement is performed on the sol component of the adhesive layer by differential refractometer RI detection. A third configuration in which, when GPC measurement is performed on the acrylic copolymer using differential refractometer RI detection, the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight of 5000 or more is 80,000 or more: The adhesive tape of the present invention 2 contains 0.1 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass, wherein the adhesive layer satisfies the first configuration, the second configuration, or the third configuration, resulting in an adhesive layer with excellent holding performance and adhesion. Furthermore, in the adhesive tape of the present invention 1, the adhesive layer satisfies the first configuration, the second configuration, or the third configuration, resulting in an adhesive layer with even better holding performance and adhesion.

In the first configuration described above, if the adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more, the bulk cohesive force in the resulting adhesive layer will be greater, and the adhesive layer will have excellent heat resistance. This is because even if the molecular weight of the (meth)acrylic copolymer is small and the gel fraction is low, if the amount of crosslinking agent is large, it can be considered that crosslinking and high molecular weight formation are progressing within the sol component. In the first configuration described above, the gel fraction of the adhesive layer is preferably 10% by mass or more, and more preferably 15% by mass or more.
Furthermore, the following methods can be used, for example, to measure the gel fraction of the adhesive layer in the first configuration, the second configuration, and the third configuration described above.
Specifically, first, _W1 (g) of the adhesive layer is taken, and the taken adhesive layer is immersed in ethyl acetate at 23°C for 24 hours, and the insoluble matter is filtered through a 200-mesh wire mesh. The residue on this wire mesh is heated and dried at 110°C, and the mass _W2 (g) of the obtained dried residue is measured. From the obtained _W1 and _W2 , the gel fraction (degree of crosslinking) is calculated using the following formula (I).
Gel fraction (mass %) = 100 × _W² / _W¹ (I)

In the first configuration described above, the gel fraction of the adhesive layer is preferably less than 30% by mass. In the first configuration, having a gel fraction of less than 30% by mass in the adhesive layer suppresses the decrease in bulk fluidity due to an increase in the elastic modulus of the adhesive layer, resulting in superior adhesion without significantly reducing the wettability of the interface. In the first configuration, it is more preferable that the gel fraction of the adhesive layer is 28% by mass or less.

In the first configuration described above, the content of the crosslinking agent in the adhesive is preferably 12 parts by mass or less per 100 parts by mass of the (meth)acrylic copolymer. In the first configuration, having a crosslinking agent content of 12 parts by mass or less in the adhesive suppresses the decrease in bulk fluidity due to an increase in the elastic modulus of the adhesive layer, resulting in superior adhesion without significantly reducing the wettability of the interface. In the first configuration, it is more preferable that the crosslinking agent content in the adhesive is 10 parts by mass or less.

In the second configuration described above, when GPC measurement is performed on the sol component of the adhesive layer using differential refractometer RI detection, the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition from the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more is 80,000 or more. This results in a state where, even with a small gel fraction in the adhesive layer, polymer crosslinking within the sol component progresses, increasing the molecular weight and resulting in high bulk cohesive force in the adhesive layer. In the second configuration described above, the preferred lower limit for the gel fraction of the adhesive layer is 0.1% by mass, and the more preferred lower limit is 1% by mass. Furthermore, in the second configuration described above, the preferred lower limit for the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition from the weight-average molecular weight of the sol component is 100,000, and the more preferred lower limit is 120,000.

In the third configuration described above, when the gel fraction of the adhesive layer exceeds 30% by mass, the bulk cohesive force in the adhesive layer increases, and the adhesive layer becomes excellent in heat resistance. In the third configuration described above, the gel fraction of the adhesive layer is preferably 31% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more.
Furthermore, in the third configuration described above, the gel fraction of the adhesive layer is preferably 70% by mass or less. In the third configuration described above, having a gel fraction of 70% by mass or less of the adhesive layer suppresses a decrease in bulk fluidity in the adhesive layer, resulting in superior adhesion without significantly reducing the wettability of the interface. In the third configuration described above, the gel fraction of the adhesive layer is more preferably 65% by mass or less, and even more preferably 60% by mass or less.
Furthermore, in the third configuration described above, it is preferable that the content of the crosslinking agent in the adhesive is 0.1 parts by mass or more per 100 parts by mass of the (meth)acrylic copolymer. In the third configuration described above, when the content of the crosslinking agent in the adhesive is 0.1 parts by mass or more, the gel fraction of the resulting adhesive layer tends to increase, and the bulk cohesive force becomes greater. In the third configuration described above, it is more preferable that the content of the crosslinking agent in the adhesive is 1.5 parts by mass or more, and even more preferable that it is 2 parts by mass or more.

The adhesive layer preferably has the following configurations: Firstly, the adhesive contains 6 parts by mass or more of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is 5% by mass or more and less than 30% by mass; or thirdly, the adhesive contains 1.5 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer is greater than 30% by mass.

The method for adjusting the weight-average molecular weight, peak-top molecular weight, and polydispersity of the (meth)acrylic copolymer obtained by alkaline decomposition, as well as the weight-average molecular weight and peak-top molecular weight of the sol component, and the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition from the weight-average molecular weight of the sol component, to the above-mentioned range is not particularly limited. Specifically, for example, a method can be used in which the (meth)acrylic copolymer contained in the adhesive is obtained by polymerization methods such as living radical polymerization or free radical polymerization. Among these, from the viewpoint of shortening the reaction time and reducing costs, a method using a (meth)acrylic copolymer obtained by free radical polymerization is preferred. Furthermore, from the viewpoint of uniformly introducing crosslinking points, living radical polymerization is preferred. When crosslinking points are introduced uniformly, the resulting adhesive layer has a uniform crosslinked structure, the bulk cohesive force increases, and creep resistance improves. On the other hand, if the bulk cohesive force becomes too high, the flexibility of the adhesive layer is impaired, and the adhesion force to the interface decreases.
Furthermore, by controlling the weight-average molecular weight of the (meth)acrylic copolymer obtained by the polymerization method described above, the weight-average molecular weight and peak-top molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition can be adjusted.

Among the (meth)acrylic copolymers obtained by the above polymerization method, it is preferable to use (meth)acrylic copolymers obtained under relatively mild polymerization conditions that maintain a constant polymerization temperature and monomer mixture concentration. This makes it possible to make the composition of the (meth)acrylic copolymer more uniform and to reduce the polydispersity of the (meth)acrylic copolymer obtained by alkaline decomposition, thereby facilitating the adjustment of the molecular weight distribution of the sol component in the adhesive layer. Examples of polymerization methods that provide such relatively mild polymerization conditions include free radical isothermal polymerization and, in the case of free radical boiling point polymerization, methods in which half of the monomer mixture and a polymerization initiator are added to the reactor to initiate polymerization, and then the remaining half of the monomer mixture is added dropwise or all at once.

In the polymerization method described above, it is preferable to carry out the reaction for 2 to 10 hours. If the polymerization time is not appropriately adjusted, in free radical polymerization, the reaction rate of the crosslinkable functional group-containing monomer is fast, which can lead to uneven introduction of crosslinking sites in the polymer chain, or a large amount of residual monomer remaining, resulting in a decrease in creep resistance.
The preferred lower limit for the polymerization reaction time in the above polymerization method is 2 hours, and the preferred upper limit is 10 hours. This range of polymerization reaction time makes it easier to adjust the weight-average molecular weight of the (meth)acrylic copolymer obtained by the alkaline decomposition to the aforementioned range. A more preferred lower limit for the polymerization reaction time is 3 hours, and a more preferred upper limit is 8 hours.

Examples of polymerization initiators used in the above polymerization method include azo compounds and organic peroxides.
Examples of the above azo compounds include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis(cyclohexane-1-carbonitride), 1-((1-cyano-1-methylethyl)azo)formamide, 4,4'-azobis(4-cyanovaleric acid), dimethyl-2,2'-azobis(2-methylpropionate), dimethyl-1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis(2-methyl-N-(1,1'-bis(hydroxymethyl)-2-hydroxyethyl)propionamide), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2 '-Azobis(N-(2-propenyl)-2-methylpropionamide), 2,2'-Azobis(N-butyl-2-methylpropionamide), 2,2'-Azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-Azobis(2-(2-imidazoline-2-yl)propane) dihydrochloride, 2,2'-Azobis(2-(1-(2-hydroxyethyl)-2-imidazoline-2-yl)propane) Examples include azobis(2-(2-imidazolin-2-yl)propane), azobis(2-amidinopropane) dihydrochloride, azobis(N-(2-carboxyethyl)-2-methylpropionamidine) tetrahydrate, azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, and azobis(2,4,4-trimethylpentane). These azo compounds may be used individually or in combination of two or more.
Examples of the above-mentioned organic peroxides 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-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. These organic peroxides may be used individually or in combination of two or more.

Among the polymerization initiators mentioned above, polymerization initiators having functional groups are preferred.
By using a polymerization initiator having the above-mentioned functional group, a functional group can be introduced to the ends of the (meth)acrylic copolymer. In particular, a functional group can be introduced to the ends of molecular chains with relatively small molecular weights that have few constituent units derived from the crosslinkable functional group-containing monomers in the (meth)acrylic copolymer. Since such low molecular weight chains have a functional group at their ends, they are incorporated into the crosslinked structure via the crosslinking agent described later, resulting in a greater bulk cohesive force in the resulting adhesive layer and improved heat resistance. Furthermore, even if they do not participate in the crosslinked structure, the low molecular weight chains can form conjugates (e.g., dimers) with each other via the crosslinking agent described later, or via a combination of the crosslinking agent described later and a tackifying resin described later, due to the presence of a functional group at their ends. In such cases, the (meth)acrylic copolymer contained in the sol component of the adhesive layer can be said to have a higher molecular weight overall. Therefore, it becomes easier to adjust the weight-average molecular weight of the sol component to the range described above, resulting in a greater bulk cohesive force in the resulting adhesive layer and improved heat resistance.
Examples of the above-mentioned functional groups include hydroxyl groups, carboxyl groups, silyl groups, glycidyl groups, amino groups, amide groups, nitrile groups, alkoxy groups, and acetoacetyl groups. Among these, hydroxyl groups and carboxyl groups are preferred. Examples of polymerization initiators having the above-mentioned functional groups include 2,2'-azobis(2-methyl-N-(1,1'-bis(hydroxymethyl)-2-hydroxyethyl)propionamide) and 4,4'-azobis(4-cyanovaleric acid (valeric acid)). These polymerization initiators having functional groups may be used alone or in combination of two or more types.

The amount of polymerization initiator added is preferably 0.01 parts by mass and preferably 0.5 parts by mass per 100 parts by mass of the monomer mixture. This range of polymerization initiator makes it easier to adjust the weight-average molecular weight of the sol component to the aforementioned range. A more preferable lower limit for the amount of polymerization initiator added is 0.02 parts by mass, and a more preferable upper limit is 0.3 parts by mass.

In the above free radical polymerization, a chain transfer agent may be used.
Examples of the above-mentioned chain transfer agents include lauryl mercaptan, mercaptopropionic acid, mercaptosuccinic acid, 3-mercapto-1,2-propanediol, 1-butanethiol, cyclohexyl 3-mercaptopropionate, 2-ethylhexyl mercaptoacetate, 1-hexadecanethiol, 2-mercaptoethanol, mercaptoacetic acid, ethyl mercaptoethyl acetate, 1-octanethiol, tridecyl 3-mercaptopropionate, thiophenol, and other thiol compounds. Also, 2,4-diphenyl-4-methyl-1-pentene is another example. These chain transfer agents may be used individually or in combination of two or more.

Among the above-mentioned chain transfer agents, it is preferable to use a chain transfer agent having a functional group.
By using a chain transfer agent having the above-mentioned functional group, it becomes easier to adjust the weight-average molecular weight of the sol component to the range described above.
In other words, by using a chain transfer agent having the above-mentioned functional group, a functional group can be introduced to the end of the low molecular weight chain, similar to the case where a polymerization initiator having the above-mentioned functional group is used. As a result, the bulk cohesive force in the resulting adhesive layer becomes greater, and the adhesive layer exhibits superior creep resistance.
Examples of the above-mentioned functional groups include hydroxyl groups, carboxyl groups, silyl groups, glycidyl groups, amino groups, amide groups, nitrile groups, alkoxy groups, and acetoacetyl groups. Among these, hydroxyl groups and carboxyl groups are preferred, with hydroxyl groups being more preferred. In particular, in systems where carboxyl groups are biased towards high molecular weight polymer chains, the crosslinking reaction of low molecular weight chains can be advantageously advanced by using a chain transfer agent having a hydroxyl group as a functional group to introduce a hydroxyl group to the end of the low molecular weight chain.
The number of functional groups in the chain transfer agent having the above functional groups is preferably multiple, as this facilitates the formation of a higher-dimensional crosslinking structure and network, and increases the bulk cohesive force in the adhesive layer. Examples of the above-mentioned chain transfer agents having the above functional groups include mercaptopropionic acid, mercaptosuccinic acid, and 3-mercapto-1,2-propanediol. These chain transfer agents having functional groups may be used individually or in combination of two or more types.

The amount of the chain transfer agent added is preferably 0.01 parts by mass and preferably 0.5 parts by mass per 100 parts by mass of the monomer mixture. By keeping the amount of the chain transfer agent within this range, it becomes easier to adjust the weight-average molecular weight of the sol component to the aforementioned range. A more preferable lower limit for the amount of the chain transfer agent is 0.02 parts by mass and a more preferable upper limit is 0.3 parts by mass.

In the above free radical polymerization, a dispersion stabilizer may be used.
Examples of the above-mentioned dispersion stabilizers include polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, ethylcellulose, poly(meth)acrylic acid, poly(meth)acrylic acid esters, and polyethylene glycol. These dispersion stabilizers may be used individually or in combination of two or more.

When a polymerization solvent is used in the above-described free radical polymerization, the polymerization solvent can be, for example, a nonpolar solvent such as hexane, cyclohexane, octane, toluene, or xylene, or a highly polar solvent such as water, methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, or N,N-dimethylformamide. These polymerization solvents may be used individually or in combination of two or more.

Furthermore, the polymerization temperature in the above-mentioned free radical polymerization is preferably between 0°C and 110°C from the viewpoint of polymerization rate.

The (meth)acrylic copolymer preferably has structural units derived from monomers having an alkyl group with 6 or more carbon atoms. Having structural units derived from monomers having an alkyl group with 6 or more carbon atoms in the (meth)acrylic copolymer makes the bulk of the adhesive layer more flexible and the viscosity of the adhesive solution lower, thus improving processability.
In the monomer having an alkyl group with 6 or more carbon atoms, it is preferable that the alkyl group has 6 to 16 carbon atoms. The (meth)acrylic copolymer having structural units derived from a monomer having an alkyl group with 6 to 16 carbon atoms increases the bulk fluidity of the resulting adhesive layer, resulting in superior adhesion to rough surfaces. In the monomer having an alkyl group with 6 or more carbon atoms, it is more preferable that the alkyl group has 6 to 12 carbon atoms. Furthermore, the monomer having an alkyl group with 6 or more carbon atoms may or may not have branching, but it is preferable that it does not have branching. Because the alkyl group of the monomer having an alkyl group with 6 or more carbon atoms is not branched, the adhesive layer has a low storage modulus at low to room temperature, while its storage modulus is high at high temperatures, resulting in superior heat resistance and superior adhesion to rough surfaces.

Examples of monomers having an alkyl group with 6 or more carbon atoms include alkyl (meth)acrylates having an alkyl group with 6 or more carbon atoms.
Examples of alkyl (meth)acrylates having an alkyl group with 6 or more carbon atoms include n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, isostearyl acrylate, and arachidyl (meth)acrylate. These alkyl (meth)acrylates having an alkyl group with 6 or more carbon atoms may be used alone or in combination of two or more. Among these, n-heptyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred.
In this specification, "(meth)acrylate" means acrylate or methacrylate.

The preferred lower limit for the content of constituent units derived from monomers having 6 or more C14 alkyl groups in the above (meth)acrylic copolymer is 50% by mass. When the content of constituent units derived from monomers having 6 or more C14 alkyl groups is 50% by mass or more, the glass transition temperature of the (meth)acrylic copolymer is lowered, the bulk fluidity of the resulting adhesive layer is increased, and the adhesive layer has better adhesion to rough surfaces. In addition, the bulk of the adhesive layer becomes more flexible and the viscosity of the adhesive solution is lowered, so processability is further improved. Furthermore, compatibility with tackifying resins, which will be described later, is also improved. A more preferred lower limit for the content of constituent units derived from monomers having 6 or more C14 alkyl groups is 60% by mass, and an even more preferred lower limit is 70% by mass.
Furthermore, the preferred upper limit for the content of constituent units derived from monomers having 6 or more C14 alkyl groups in the (meth)acrylic copolymer is 98% by mass. By having a content of constituent units derived from monomers having 6 or more C14 alkyl groups of 98% by mass or less, the glass transition temperature of the (meth)acrylic copolymer does not become too low, the bulk cohesive force in the resulting adhesive layer becomes greater, and the adhesive layer has superior heat resistance. A more preferred upper limit for the content of constituent units derived from monomers having 6 or more C14 alkyl groups is 97% by mass, and an even more preferred upper limit is 95% by mass.

The above (meth)acrylic copolymer may have constituent units derived from alkyl (meth)acrylate having an alkyl group with 5 or fewer carbon atoms.
Examples of alkyl (meth)acrylates having an alkyl group with 5 or fewer carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, and butyl (meth)acrylate. These alkyl (meth)acrylates having an alkyl group with 5 or fewer carbon atoms may be used individually or in combination of two or more. Among these, butyl (meth)acrylate is preferred.

The content of the constituent units derived from alkyl (meth)acrylate having an alkyl group with 5 or fewer carbon atoms is preferably 25% by mass or more and less than 50% by mass. A content of 25% by mass or more of the constituent units derived from alkyl (meth)acrylate having an alkyl group with 5 or fewer carbon atoms results in a sufficiently high glass transition temperature of the (meth)acrylic copolymer, leading to greater bulk cohesive force in the resulting adhesive layer and superior heat resistance. If the content is less than 50% by mass, the glass transition temperature of the (meth)acrylic copolymer does not become too high, increasing the bulk fluidity in the resulting adhesive layer and resulting in superior adhesion to rough surfaces. A more preferable lower limit for the content is 30% by mass, and a more preferable upper limit is 45% by mass.

The (meth)acrylic copolymer preferably has structural units derived from a monomer containing a crosslinkable functional group. Because the (meth)acrylic copolymer has structural units derived from the above-described monomer, the (meth)acrylic copolymer and the tackifying resin described later form a crosslinked structure via the crosslinking agent described later. This results in a greater bulk cohesive force in the resulting adhesive layer, and the adhesive layer exhibits superior heat resistance. Examples of the above-described crosslinkable functional groups include hydroxyl groups, carboxyl groups, silyl groups, glycidyl groups, amino groups, amide groups, nitrile groups, alkoxy groups, and acetoacetyl groups. Among these, hydroxyl groups and carboxyl groups are preferred because they allow for easy adjustment of the bulk cohesive force in the adhesive layer.

Examples of monomers containing a crosslinkable functional group having a hydroxyl group as the above-mentioned crosslinkable functional group include 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate.
Examples of monomers containing a crosslinkable functional group having a carboxyl group as the above-mentioned crosslinkable functional group include (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, and fumaric acid. Among these, acrylic acid is preferred.
Examples of crosslinkable functional group-containing monomers having a glycidyl group as the above-mentioned crosslinkable functional group include glycidyl (meth)acrylate.
Examples of monomers containing a crosslinkable functional group having an amide group as the above-mentioned crosslinkable functional group include hydroxyethylacrylamide, isopropylacrylamide, and dimethylaminopropylacrylamide.
Examples of crosslinkable functional group-containing monomers having a nitrile group as the above-mentioned crosslinkable functional group include acrylonitrile.

The preferred lower limit for the content of structural units derived from the above-mentioned crosslinkable functional group-containing monomer in the above-mentioned (meth)acrylic copolymer is 0.05% by mass, and the preferred upper limit is 20% by mass. A content of 0.05% by mass or more of structural units derived from the above-mentioned crosslinkable functional group-containing monomer results in greater bulk cohesive force in the resulting adhesive layer, leading to superior heat resistance. A content of 20% by mass or less of structural units derived from the above-mentioned crosslinkable functional group-containing monomer increases bulk fluidity in the resulting adhesive layer, leading to superior adhesion to rough surfaces. A more preferred lower limit for the content of structural units derived from the above-mentioned crosslinkable functional group-containing monomer is 0.1% by mass, and a more preferred upper limit is 15% by mass.

When the (meth)acrylic copolymer has structural units derived from a crosslinkable functional group-containing monomer having a hydroxyl group as the crosslinkable functional group, the preferred lower limit of the content of structural units derived from the crosslinkable functional group-containing monomer is 0.03% by mass, and the preferred upper limit is 1% by mass. When the content of structural units derived from the crosslinkable functional group-containing monomer having a hydroxyl group as the crosslinkable functional group is 0.03% by mass or more, the bulk cohesive force in the resulting adhesive layer becomes greater, and the adhesive layer has better heat resistance. When the content of structural units derived from the crosslinkable functional group-containing monomer having a hydroxyl group as the crosslinkable functional group is 1% by mass or less, the gel fraction of the resulting adhesive layer does not become too high, and the adhesive layer has better adhesion to rough surfaces. The more preferable lower limit for the content of constituent units derived from a crosslinkable functional group-containing monomer having a hydroxyl group as the above crosslinkable functional group is 0.05% by mass, the even more preferable lower limit is 0.06% by mass, the more preferable upper limit is 0.5% by mass, the even more preferable upper limit is 0.3% by mass, and the particularly preferable upper limit is 0.1% by mass.
Furthermore, when the (meth)acrylic copolymer contains structural units derived from a crosslinkable functional group-containing monomer having a carboxyl group as the crosslinkable functional group, the preferred lower limit of the content of structural units derived from the crosslinkable functional group-containing monomer is 2% by mass, and the preferred upper limit is 15% by mass. When the content of structural units derived from the crosslinkable functional group-containing monomer having a carboxyl group as the crosslinkable functional group is 2% by mass or more, the gel fraction of the resulting adhesive layer tends to be high, and the glass transition temperature of the (meth)acrylic copolymer becomes sufficiently high, resulting in greater bulk cohesive force in the resulting adhesive layer. As a result, the adhesive layer has superior heat resistance. When the content of structural units derived from the crosslinkable functional group-containing monomer having a carboxyl group as the crosslinkable functional group is 15% by mass or less, the glass transition temperature of the (meth)acrylic copolymer does not become too high, and the adhesive layer has superior adhesion to rough surfaces. The more preferable lower limit for the content of constituent units derived from a crosslinkable functional group-containing monomer having a carboxyl group as the above crosslinkable functional group is 3% by mass, the even more preferable lower limit is 5% by mass, the more preferable upper limit is 10% by mass, and the even more preferable upper limit is 8% by mass.

The above (meth)acrylic copolymer may optionally contain structural units derived from monomers having 6 or more C6 alkyl groups, structural units derived from alkyl (meth)acrylates having 5 or fewer C6 alkyl groups, and structural units derived from other copolymerizable polymerizable monomers other than those derived from the above crosslinkable functional group-containing monomers.

The above adhesive contains a crosslinking agent.
As the crosslinking agent, depending on the type of crosslinkable functional group of the (meth)acrylic copolymer, for example, isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-type crosslinking agents, etc., can be selected and used. Among these, isocyanate-based crosslinking agents are preferred because they can selectively crosslink hydroxyl groups and carboxyl groups and the crosslinking structure is easy to control. In particular, it is preferable to include 80 parts by mass or more of an isocyanate-based crosslinking agent having two or more isocyanate molecules in one molecule in 100 parts by mass of the crosslinking agent.
Examples of commercially available isocyanate-based crosslinking agents include Coronate HX and Coronate L (both manufactured by Tosoh Corporation), and Mytec NY260A (manufactured by Mitsubishi Chemical Corporation).

The number of functional groups in the above-mentioned crosslinking agent is preferably multiple, as this facilitates the formation of a higher-dimensional crosslinking structure and network formation, resulting in greater bulk cohesive force in the resulting adhesive layer.

The above adhesive includes a tackifying resin.
By including the above-mentioned tackifying resin in the adhesive, the resulting adhesive layer exhibits excellent adhesion to the adherend.

The preferred lower limit of the softening temperature of the tackifying resin is 90°C, and the preferred upper limit is 180°C. When the softening temperature of the tackifying resin is 90°C or higher, the adhesive layer becomes more heat resistant, and creep resistance at high temperatures is further improved. When the softening temperature of the tackifying resin is 180°C or lower, the adhesive layer becomes more flexible, and adhesion to rough surfaces becomes more superior. The more preferred lower limit of the softening temperature of the tackifying resin is 100°C, an even more preferred lower limit is 110°C, a particularly preferred lower limit is 120°C, an even more preferred upper limit is 170°C, and an even more preferred upper limit is 165°C.
The "softening temperature" mentioned above refers to the softening temperature measured by the JIS K2207 ring-and-ball method.

The preferred lower limit of the hydroxyl value of the tackifying resin is 10 mg KOH/g, and the preferred upper limit is 200 mg KOH/g. When the hydroxyl value of the tackifying resin is 10 mg KOH/g or higher, the softening temperature of the tackifying resin tends to be higher. When the hydroxyl value of the tackifying resin is 200 mg KOH/g or lower, the reactivity with the crosslinking agent does not become too high, which can suppress the inhibition of crosslinking of the (meth)acrylic copolymer or graft reactions with the (meth)acrylic copolymer. The more preferred lower limit of the hydroxyl value of the tackifying resin is 20 mg KOH/g, an even more preferred lower limit is 25 mg KOH/g, a particularly preferred lower limit is 30 mg KOH/g, a more preferred upper limit is 150 mg KOH/g, an even more preferred upper limit is 120 mg KOH/g, and a particularly preferred upper limit is 100 mg KOH/g.
The above-mentioned "hydroxyl value" can be measured according to JIS K1557 (phthalic anhydride method).

Examples of the tackifying resins mentioned above include rosin-based resins such as rosin ester resins, terpene-based resins such as terpene phenol resins, and petroleum-based resins. These tackifying resins may be used individually or in combination of two or more types.
Among these, rosin ester resins, terpene phenol resins, and combinations thereof are preferred, with terpene phenol resins being more preferred.

The above-mentioned terpene phenol resin is a resin obtained by polymerizing terpenes in the presence of phenol. This terpene phenol resin exhibits good compatibility with the (meth)acrylic copolymer, facilitates grafting with the (meth)acrylic copolymer, and is easily incorporated into the adhesive layer. Therefore, the surface of the adhesive layer becomes polymer-rich and flexible, resulting in higher adhesion to rough surfaces. Furthermore, the grafting of the terpene phenol resin with the (meth)acrylic copolymer increases the bulk cohesive force of the adhesive layer, resulting in superior creep resistance.

Examples of commercially available terpene resins include YS Polystar G150 (hydroxyl value 140 mg KOH/g, softening temperature 150°C), YS Polystar T100 (hydroxyl value 60 mg KOH/g, softening temperature 100°C), YS Polystar G125 (hydroxyl value 140 mg KOH/g, softening temperature 125°C), YS Polystar T115 (hydroxyl value 60 mg KOH/g, softening temperature 115°C), YS Polystar T130 (hydroxyl value 60 mg KOH/g, softening temperature 130°C), and YS Polystar T160 (hydroxyl value 60 mg KOH/g, softening temperature 160°C) (all manufactured by Yasuhara Chemical Co., Ltd.).

The rosin ester resins mentioned above are resins obtained by esterifying rosin resins mainly composed of abietic acid, disproportionated rosin resins, hydrogenated rosin resins, or dimers of resin acids such as abietic acid (polymerized rosin resins) with alcohol. Some of the hydroxyl groups of the alcohol used in esterification are not used and remain in the resin, thereby adjusting the hydroxyl value to the range described above. Examples of alcohols include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.
Furthermore, rosin ester resin is obtained by esterifying rosin resin, disproportionate rosin ester resin is obtained by esterifying disproportionate rosin resin, hydrogenated rosin ester resin is obtained by esterifying hydrogenated rosin resin, and polymerized rosin ester resin is obtained by esterifying polymerized rosin resin.

Examples of commercially available disproportionated rosin ester resins include Super Ester A75 (hydroxyl value 23 mg KOH/g, softening temperature 75°C), Super Ester A100 (hydroxyl value 16 mg KOH/g, softening temperature 100°C), Super Ester A115 (hydroxyl value 19 mg KOH/g, softening temperature 115°C), and Super Ester A125 (hydroxyl value 15 mg KOH/g, softening temperature 125°C) (all manufactured by Arakawa Chemical Industries, Ltd.).
Examples of the above-mentioned hydrogenated rosin ester resins include Pine Crystal KE-359 (hydroxyl value 42 mg KOH/g, softening temperature 100°C) and Ester Gum H (hydroxyl value 29 mg KOH/g, softening temperature 70°C) (both manufactured by Arakawa Chemical Industries, Ltd.).
Examples of the polymerized rosin ester resins mentioned above include Pencel D135 (hydroxyl value 45 mg KOH/g, softening temperature 135°C), Pencel D125 (hydroxyl value 34 mg KOH/g, softening temperature 125°C), and Pencel D160 (hydroxyl value 42 mg KOH/g, softening temperature 160°C) (all manufactured by Arakawa Chemical Industries, Ltd.).

The content of the tackifying resin is preferably 10 parts by mass and preferably 60 parts by mass per 100 parts by mass of the (meth)acrylic copolymer. When the content of the tackifying resin is within this range, the adhesive layer exhibits superior interfacial adhesion and superior retention performance. A more preferable lower limit for the content is 15 parts by mass, an even more preferable lower limit is 20 parts by mass, a more preferable upper limit is 50 parts by mass, and an even more preferable upper limit is 45 parts by mass.

The above adhesive may optionally contain additives such as solvents, plasticizers, emulsifiers, softeners, fillers, pigments, dyes, silane coupling agents, and antioxidants. The adhesive tape of the present invention can reduce the amount of the above solvent that is the source of _CO2 emitted during the manufacturing process.

The above adhesive preferably contains 0.03% by mass or more of a compound having a hydroxyl group and 2% by mass or more of a compound having a carboxyl group in its solid content. When the above adhesive contains 0.03% by mass or more of a compound having a hydroxyl group and 2% by mass or more of a compound having a carboxyl group in its solid content, the bulk cohesive force in the resulting adhesive layer becomes greater, and the adhesive layer becomes more heat resistant. The above adhesive more preferably contains 0.05% by mass or more of the compound having a hydroxyl group. Furthermore, the above adhesive more preferably contains 3% by mass or more of the compound having a carboxyl group.
The hydroxyl group compound and the carboxyl group compound may be any of the components contained in the solid portion of the adhesive.
Note that the "solid content" mentioned above refers to the components excluding the solvent.

The preferred upper limit of viscosity when applying the above adhesive is 10,000 mPa·s. A viscosity of 10,000 mPa·s or less makes it easy to apply the adhesive smoothly without defects such as air bubbles or adhesive streaks. A more preferred upper limit of viscosity when applying the above adhesive is 9,000 mPa·s, and an even more preferred upper limit is 8,000 mPa·s.
Furthermore, the preferred lower limit of viscosity when applying the above-mentioned adhesive is 1500 mPa·s. A viscosity of 1500 mPa·s or higher ensures sufficient pressure for extruding the adhesive, making it easy to apply the adhesive to the desired thickness and width. A more preferred lower limit of viscosity when applying the above-mentioned adhesive is 2000 mPa·s.
The viscosity of the above adhesive when applied can be measured using a B-type viscometer under the conditions of 23°C and 12 rpm.

The preferred lower limit for the glass transition temperature of the adhesive layer is -10°C, and the preferred upper limit is 30°C. A glass transition temperature of -10°C or higher for the adhesive layer results in high heat resistance and increased bulk cohesive force, thus providing superior holding performance and high-temperature rebound resistance. A glass transition temperature of 30°C or lower for the adhesive layer provides superior adhesion to the interface. A more preferred lower limit for the glass transition temperature of the adhesive layer is -5°C, an even more preferred lower limit is 0°C, an even more preferred lower limit is 5°C, a more preferred upper limit is 25°C, an even more preferred upper limit is 20°C, and an even more preferred upper limit is 15°C.
In this specification, the "glass transition temperature" refers to the temperature at which a maximum of loss tangent (tanδ) obtained by dynamic viscoelasticity measurement occurs, which is attributed to micro-Brownian motion.
For the dynamic viscoelasticity measurement performed in the measurement of the glass transition temperature and the storage modulus of the adhesive layer described above, the following method can be used, for example.
Specifically, first, samples of the adhesive layer described above are stacked to create a laminate with a thickness of approximately 1 mm, which is then cut into 6 mm x 10 mm pieces to obtain test specimens. Dynamic viscoelasticity measurements are performed on the obtained test specimens using a dynamic viscoelasticity measuring device (IT Measurement Control Co., Ltd., "DVA-200") in shear mode under a nitrogen atmosphere, with a measurement temperature of -40°C to 140°C, a heating rate of 5°C/min, a frequency of 10 Hz, and a strain of 0.08%.

A preferred lower limit for the storage modulus G'(80°C) of the adhesive layer is 1.0 × ^10⁴ Pa. A storage modulus G'(80°C) of the adhesive layer of 1.0 × ^10⁴ Pa or higher results in greater bulk cohesive force at high temperatures, leading to superior creep resistance and high-temperature rebound resistance. A more preferred lower limit for the storage modulus G'(80°C) of the adhesive layer is 1.5 × ^10⁴ Pa, an even more preferred lower limit is 2.0 × ^10⁴ Pa, an even more preferred lower limit is 5.0 × ^10⁴ Pa, and a particularly preferred lower limit is 8.0 × ^10⁴ Pa.
If the storage modulus G' (80°C) of the adhesive layer is too high, the storage modulus at room temperature will also be high, and the adhesive strength to rough surfaces will decrease. Therefore, a preferred upper limit for the storage modulus G' (80°C) of the adhesive layer is 2.0 × ^10⁵ Pa.

The preferred lower limit for the thickness of the adhesive layer is 10 μm, and the preferred upper limit is 100 μm. A thickness of 10 μm or more increases the adhesion of the adhesive layer to the substrate and increases peel resistance, resulting in superior adhesion to rough surfaces. A thickness of 100 μm or less reduces the amount of slippage when shear force is applied to the adhesive layer, resulting in superior retention performance. A more preferred lower limit for the thickness of the adhesive layer is 12 μm, an even more preferred lower limit is 15 μm, an even more preferred upper limit is 60 μm, and an even more preferred upper limit is 50 μm.

The adhesive tape preferably has a base material.
A resin film is preferred as the substrate.
The above-mentioned resin film is preferably a polyester resin film or a polypropylene resin film. Among these, polyester resin film is preferred because it is flat, has little variation in thickness, and has high strength, and among polyester resin films, polyethylene terephthalate film is more preferred.

The above-mentioned substrate may contain additives such as fillers, UV absorbers, light stabilizers, and antistatic agents, as long as these do not impair its physical properties.

The thickness of the above substrate can be appropriately selected according to the application, but the preferred lower limit is 5 μm and the preferred upper limit is 200 μm. A substrate thickness of 200 μm or less makes it suitable for use in fixing electronic components and reduces _CO2 emissions during manufacturing. A more preferred lower limit for the thickness of the above substrate is 10 μm, an even more preferred lower limit is 15 μm, a more preferred upper limit is 100 μm, and an even more preferred upper limit is 50 μm.

The adhesive tape of the present invention may have the adhesive layer on only one side of the substrate, or it may have the adhesive layer on both sides of the substrate. In particular, it is preferable that the adhesive layer be on both sides of the substrate.

The method for manufacturing the adhesive tape of the present invention is not particularly limited. For example, when the substrate has adhesive layers of the same composition and thickness on both sides, the following method can be used.
First, an adhesive is prepared containing a (meth)acrylic copolymer, a crosslinking agent, a tackifying resin, and a solvent and other components as needed. Next, the adhesive obtained above is applied to the release-treated surface of a release film, which has one side treated for release, and dried to produce a laminated sheet having an adhesive layer on the release-treated surface of the release film. A total of two laminated sheets are produced in the same manner. Next, the adhesive layers of the two laminated sheets are transferred to a substrate and laminated together to obtain an adhesive sheet having adhesive layers on both sides of the substrate.

From the viewpoint of improving both the holding performance and adhesiveness of the adhesive tape of the present invention, it is preferable that the adhesive tape of the present invention has excellent resistance to rebound at high temperatures.
High-temperature rebound resistance can be evaluated by methods such as those described below. Figure 2 shows a schematic diagram illustrating the method of the high-temperature rebound resistance test.
Specifically, the adhesive tape 1 of the present invention is cut into strips measuring 25 mm wide x 300 mm long, and the adhesive layer on the side not to be measured is bonded to a PET film 4 (100 μm thick, 25 mm wide, 300 mm long). Next, the adhesive layer on the side to be measured is bonded to a SUS plate 2 (a SUS304 plate that has been cleaned with ethanol and then wiped dry) so that the short side of the adhesive tape 1 overlaps with one side of the SUS plate. Then, a 2 kg rubber roller is pressed onto the tape by making five back-and-forth passes at a speed of 300 mm/min, and the test specimen is left to stand at 23°C for 72 hours to prepare the test specimen. The prepared test specimen is then heated in an 80°C oven for 15 minutes, and then, under 80°C conditions, a high-temperature rebound resistance test is performed in which a 100 g load is applied to the tip of the test specimen using a 100 g weight 5 so as to be perpendicular to the test specimen, and this condition is maintained for 144 hours. If the entire adhesive tape falls, the fall time is measured with the time under a 100g load set to 0 hours. If the entire adhesive tape does not fall, the peel length (the length between the double-headed arrows in Figure 2) is measured visually. If the result of this high-temperature rebound resistance test is that the entire adhesive tape does not fall and the peel length is 60 mm or less, the adhesive tape of the present invention is considered to have excellent high-temperature rebound resistance.

According to the present invention, it is possible to provide an adhesive tape having an adhesive layer with excellent retention performance and adhesion, even while using a (meth)acrylic copolymer with a low molecular weight.

This is a schematic diagram illustrating the method of the retention test. This is a schematic diagram illustrating the method for high-temperature rebound resistance testing.

The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Preparation of acrylic copolymers A to S)
In a reactor equipped with a thermometer, stirrer, and condenser, the solvents shown in Table 1 were added, followed by nitrogen purging. The reactor was then heated and reflux was initiated. After the solvent boiled, polymerization initiator 1 shown in Table 1 was added, and then a mixed solution of monomer and chain transfer agent shown in Table 1 was added dropwise into the reactor from a dropping funnel over a period of 2 hours. Subsequently, polymerization initiator 2 shown in Table 1 was added, and the time at which the dropwise addition began was defined as the polymerization start time. The polymerization reaction was carried out for a total of 6 hours from the start of polymerization to obtain a solution containing acrylic copolymers A to S.
The materials listed in Table 1 are as follows:
BA: Butyl acrylate 2EHA: 2-Ethylhexyl acrylate C7: n-Heptyl acrylate HEA: Hydroxyethyl acrylate Aac: Acrylic acid AIBN: 2,2'-Azobis(isobutyronitrile)

(Examples 8, 9, 19; Reference Examples 1-7, 10-18 , 20-23; Comparative Examples 1-8)
(1) Preparation of the adhesive Each material was added to the solution containing the obtained acrylic copolymers A to S in the compositions shown in Tables 2 and 3, and stirred to obtain the adhesive. The percentage of compounds having hydroxyl groups in the solid content and the percentage of compounds having carboxyl groups in the solid content of the obtained adhesive are shown in Tables 2 and 3.
The materials listed in Tables 2 and 3 are as follows:
Coronate L45: Isocyanate-based crosslinking agent (manufactured by Tosoh Corporation)
KE388: Hydrogenated rosin ester resin (manufactured by Arakawa Chemical Industries, Ltd., hydroxyl value 45 mg KOH/g, softening temperature 150°C)
KE359: Hydrogenated rosin ester resin (manufactured by Arakawa Chemical Industries, Ltd., hydroxyl value 40 mg KOH/g, softening temperature 100°C)
D135: Polymerized rosin ester resin (manufactured by Arakawa Chemical Industries, Ltd., hydroxyl value 40 mg KOH/g, softening temperature 135°C)
G150: Terpene resin (manufactured by Yasuhara Chemical Co., Ltd., hydroxyl value 100 mg KOH/g, softening temperature 150°C)

(2) Preparation of adhesive tape A polyethylene terephthalate film was prepared with one side treated for release. The adhesive obtained in "(1) Preparation of adhesive" above was applied to the release-treated side of this polyethylene terephthalate film and dried at 110°C for 5 minutes to promote crosslinking of the (meth)acrylic copolymer in the adhesive, thereby creating a laminated sheet having an adhesive layer on the release-treated side of the polyethylene terephthalate film. Another laminated sheet was made in the same manner, resulting in a total of two of the above laminated sheets.
Next, a polyethylene terephthalate film (25 μm thick) was prepared as the base material. One laminated sheet was laminated onto one side of the base material, with the adhesive layer facing outwards, to transfer and integrate the adhesive layer with the base material. The other laminated sheet was laminated onto the other side of the base material, with the adhesive layer facing outwards, to transfer and integrate the adhesive layer with the base material. As a result, a double-sided adhesive tape was obtained in which adhesive layers with the thicknesses shown in Tables 2 and 3 were provided on both sides of the base material.

(Weight-average molecular weight (Mw copolymer), peak-top molecular weight (Mp copolymer), and polydispersity (Mw copolymer/Mn copolymer) of (meth)acrylic copolymers obtained by alkaline decomposition)
300 mg of the adhesive layer was taken from the obtained double-sided adhesive tape. The taken adhesive layer, 6 mL of ethanol, and 7 mL of 60% KOH aqueous solution were added to a pressure vessel and hydrolyzed under pressure in an oven at 160°C for 60 hours. This caused alkaline decomposition of the crosslinking points of the crosslinking product in the adhesive layer, yielding a (meth)acrylic copolymer.
The obtained (meth)acrylic copolymer was analyzed by gel permeation chromatography (GPC) (Waters, "2690 Separations Model"), and the molecular weight distribution in polystyrene equivalent was measured. The weight-average molecular weight (Mw copolymer), peak-top molecular weight (Mp copolymer), and polydispersity (Mw copolymer/Mn copolymer) of the (meth)acrylic copolymer obtained by alkaline decomposition, derived from the obtained molecular weight distribution, are shown in Tables 2 and 3. The above GPC was performed under the following conditions.
Eluent: Tetrahydrofuran (THF)
Flow rate: 0.4mL/min
Detector: Differential Refractometer RI
Column: LF-804 (manufactured by SHOKO Corporation)
Column temperature (measurement temperature): 40°C
Injection volume: 20μL

(Weight-average molecular weight of the sol component (Mw sol), and Mw sol-Mw copolymer)
The adhesive layer of the obtained double-sided adhesive tape was immersed in tetrahydrofuran (THF) at 23°C for 24 hours, and the insoluble components were removed by filtering through a 200-mesh wire mesh to obtain the sol component of the adhesive layer.
The sol component of the obtained adhesive layer was analyzed by gel permeation chromatography (GPC) (Waters, Inc., "2690 Separations Model"), and the molecular weight distribution in polystyrene equivalent was measured. The weight-average molecular weight of the sol component (Mw sol) derived from the obtained molecular weight distribution, and the value obtained by subtracting the weight-average molecular weight of the (meth)acrylic copolymer obtained by alkaline decomposition from the weight-average molecular weight of the sol component (Mw sol - Mw copolymer) are shown in Tables 2 and 3. The above GPC was performed under the following conditions.
Eluent: Tetrahydrofuran (THF)
Flow rate: 0.4mL/min
Detector: Differential Refractometer RI
Column: LF-804 (manufactured by SHOKO Corporation)
Column temperature (measurement temperature): 40°C
Injection volume: 20μL

(Gel fraction of the adhesive layer)
A sample of _W1 (g) of the adhesive layer from the obtained double-sided adhesive tape was taken, and the sampled adhesive layer was immersed in ethyl acetate at 23°C for 24 hours. The insoluble matter was filtered through a 200-mesh wire mesh. The residue on the wire mesh was heated and dried at 110°C, and the mass _W2 (g) of the obtained dried residue was measured. From the obtained _W1 and _W2 , the gel fraction (degree of crosslinking) was calculated using the following formula (I). The obtained gel fractions are shown in Tables 2 and 3.
Gel fraction (mass %) = 100 × _W² / _W¹ (I)

(Storage modulus G' (80°C) and glass transition temperature of the adhesive layer)
The adhesive layers of the obtained double-sided adhesive tapes were stacked to create a laminate with a thickness of approximately 1 mm, which was then cut into 6 mm x 10 mm pieces to obtain test specimens. Dynamic viscoelasticity measurements were performed on the obtained test specimens using a dynamic viscoelasticity measuring device (IT Measurement Control Co., Ltd., "DVA-200") in shear mode under a nitrogen atmosphere, with a measurement temperature of -40°C to 140°C, a heating rate of 5°C/min, a frequency of 10 Hz, and a strain of 0.08%, to obtain the storage modulus G'(80°C). Furthermore, the temperature at which the maximum loss tangent (tanδ) obtained by the dynamic viscoelasticity measurement, which was attributable to micro-Brownian motion, appeared was defined as the glass transition temperature. The obtained storage modulus G'(80°C) and glass transition temperature are shown in Tables 2 and 3.

<Evaluation>
The adhesives and double-sided adhesive tapes obtained in the examples, reference examples, and comparative examples were evaluated as follows. The results are shown in Tables 4 and 5.

(Workability)
The obtained adhesive was adjusted to a solid content concentration of 60% by mass, and its viscosity was measured at 23°C and 12 rpm using a B-type viscometer (RVDV-2+PRO, manufactured by Eiko Seiki Co., Ltd.) and spindle S04. The viscosity of the adhesive adjusted to a solid content concentration of 70% by mass was also measured in the same manner, and processability was evaluated by marking "○" if the obtained viscosity was 10,000 mPa·s or less, and "×" if it exceeded 10,000 mPa·s.

(retention performance)
The obtained double-sided adhesive tape was cut into 25 mm wide strips and then adhered to a SUS plate (SUS304 plate cleaned with ethanol and then wiped dry) by running a 2 kg rubber roller back and forth at a speed of 300 mm/min once. Next, cuts were made in the adhesive tape so that the bonding area was 25 mm x 25 mm. After that, it was left to stand at 23°C for 20 minutes, then placed in an 80°C oven and heated for another 15 minutes. While maintaining the temperature at 80°C, a 1 kg load was applied in the shear direction using a 1 kg weight 3 as shown in Figure 1. The presence or absence of the adhesive tape falling was checked, and if it did not fall after 24 hours, the amount of displacement (slippage) from the cut position was measured with a scale magnifier.
The holding performance was evaluated as follows: "○" if the adhesive tape did not fall and the displacement was 1 mm or less, "△" if the adhesive tape did not fall but the displacement exceeded 1 mm, and "×" if the adhesive tape fell.

(Adhesiveness)
The adhesive tape was cut into 25 mm wide strips and then adhered to a SUS plate (SUS304 plate cleaned with ethanol and then wiped dry) by rolling a 2 kg rubber roller back and forth at a speed of 300 mm/min once. Next, test specimens were obtained by leaving them to stand for 20 minutes at a temperature of 23°C and a relative humidity of 50%. The obtained test specimens were subjected to a tensile test using a tensile testing machine (A&D Corporation, "RTI-1310") in accordance with JIS Z0237, under the conditions of 23°C, a peeling speed of 300 mm/min, and a peeling angle of 180°, and the adhesive strength at 180° peel was measured.
Adhesion was evaluated by assigning a "○" if the obtained 180° peel adhesion strength was 18 N/25 mm or higher, a "△" if it was 15 N/25 mm or higher but less than 18 N/25 mm, and a "×" if it was less than 15 N/25 mm.
Furthermore, instead of a SUS plate (SUS304 plate cleaned with ethanol and then wiped dry), a rough-surfaced SUS plate was used, and the adhesion strength was measured by peeling it off at 180° in the same manner. The rough-surfaced SUS plate was prepared by polishing a SUS304 plate, which had been cleaned with ethanol and then wiped dry, with abrasive paper of grit 80. In addition, observation of the surface of the rough-surfaced SUS plate using a laser microscope revealed that the Ra value was 1.7 μm and the Rz value was 10 μm.

According to the present invention, it is possible to provide an adhesive tape having an adhesive layer with excellent retention performance and adhesion, even while using a (meth)acrylic copolymer with a low molecular weight.

1. Adhesive tape 2. Stainless steel plate 3. 1 kg load (weight)
4. PET film 5. 100g load (weight)

Claims (11)

An adhesive tape having an adhesive layer,
The adhesive layer contains a crosslinked product of an adhesive comprising a (meth)acrylic copolymer, a crosslinking agent, a tackifying resin, and a chain transfer agent having at least one selected from the group consisting of hydroxyl groups and carboxyl groups .
When GPC measurements were performed on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the aforementioned crosslinking product using differential refractometer RI detection, the weight-average molecular weight of the (meth)acrylic copolymer in the region of molecular weight 5000 or more was 80,000 or more and less than 400,000,
An adhesive tape characterized by satisfying the following third configuration.
Third configuration: The adhesive contains 0.1 parts by mass or more and less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass. The adhesive tape according to claim 1, wherein the adhesive layer, as the third component, contains 1.5 to less than 6 parts by mass of the crosslinking agent per 100 parts by mass of the (meth)acrylic copolymer, and the gel fraction of the adhesive layer exceeds 30% by mass. The adhesive tape according to claim 1 or 2, wherein, when the sol component of the adhesive layer is subjected to GPC measurement by differential refractometer RI detection, the weight-average molecular weight of the sol component in the region of molecular weight 5000 or more is 50,000 or more and 500,000 or less. The adhesive tape according to claim 1 or 2, wherein, when a GPC measurement is performed on the (meth)acrylic copolymer obtained by alkaline decomposition of the crosslinking points of the crosslinking product using differential refractometer RI detection, the peak top molecular weight of the (meth)acrylic copolymer in the region of molecular weight 5000 or more is 70,000 to 300,000. The adhesive tape according to claim 1 or 2, wherein the adhesive contains 0.03% by mass or more of a compound having a hydroxyl group in its solid content, and 2% by mass or more of a compound having a carboxyl group in its solid content. The adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer contains 50% by mass or more of constituent units derived from monomers having an alkyl group with 6 or more carbon atoms. The adhesive tape according to claim 1 or 2, wherein the adhesive layer has a glass transition temperature of -10°C or higher and 30°C or lower. The adhesive tape according to claim 1 or 2, wherein the adhesive layer has a storage modulus G' (80°C) of 1.0 × ^10⁴ Pa or more. The adhesive tape according to claim 1 or 2, wherein the adhesive layer has a thickness of 10 μm or more and 100 μm or less. The adhesive tape according to claim 1 or 2, wherein the adhesive tape has a base material, the base material is a polyester resin film or a polypropylene resin film, and the thickness of the base material is 5 μm or more and 200 μm or less. The adhesive tape according to claim 1 or 2, wherein the adhesive tape has a base material and the adhesive layer is provided on both sides of the base material.