Adhesive tape and electronic device

Abstract

The purpose of the present invention is to provide an adhesive tape capable of achieving both excellent bending resistance and excellent impact absorption. Another purpose of the present invention is to provide an electronic device including the adhesive tape. The present invention is an adhesive tape having a foam layer. The foam layer has a shear storage modulus of 0.3 MPa or more at 23°C as measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz, and the foam layer has a loss tangent of 0.50 or more at 23°C as measured by dynamic viscoelasticity measurement at a measurement frequency of 100 Hz.

Description

Adhesive tape, and electronic devices

[0001] This invention relates to an adhesive tape. Furthermore, this invention relates to an electronic device including the adhesive tape.

[0002] Adhesive tape is widely used for securing electronic components. Specifically, for example, it is used to secure the surface cover panel to the housing of display devices such as televisions and monitors.

[0003] In recent years, as a result of pursuing design and functionality, display devices such as televisions and monitors have become narrower in bezel size, and expectations for bezel-less display devices are also rising. In the manufacturing of conventional display devices, cover panels were sometimes fixed to the casing by snapping or screwing them in, but with display devices that have narrow bezels, snapping or screwing in is difficult, so the demand for fixing with adhesive tape is increasing, and adhesive tapes are also becoming thinner and narrower.

[0004] As an example of an adhesive tape that can be used in such a display device, Patent Documents 1 and 2 describe an impact-absorbing tape in which an acrylic adhesive layer is laminated and integrated on at least one side of a base layer, and the base layer is a crosslinked polyolefin resin foam sheet having a specific degree of crosslinking and a specific aspect ratio of bubbles.

[0005] Japanese Patent Publication No. 2009-242541 Japanese Patent Publication No. 2009-258274

[0006] In recent years, electronic components have tended to become thinner, and a problem has arisen with adhesive tapes used to fix panels and casings of smartphones and tablets: if the adhesive tape itself deforms, the components are more likely to be damaged.

[0007] The present invention aims to provide an adhesive tape that can achieve both excellent bending resistance and excellent shock absorption. Furthermore, the present invention aims to provide an electronic device containing the adhesive tape.

[0008] Disclosure 1 is an adhesive tape having a foam layer, wherein the foam layer has a shear storage modulus of 0.30 MPa or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 1 Hz, and the foam layer has a loss tangent of 0.50 or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 100 Hz. Disclosure 2 is the adhesive tape of Disclosure 1, wherein the foam layer has a 180° peel force of 10 N / 25 mm or more against SUS at 23°C. Disclosure 3 is the adhesive tape of Disclosure 1 or 2, wherein the foam layer is formed using an adhesive resin composition. Disclosure 4 is the adhesive tape of Disclosure 3, wherein the adhesive resin composition contains foaming particles, and the foam layer has bubbles derived from the foaming particles. Disclosure 5 is the adhesive tape of Disclosure 4, wherein the foaming particles contain thermally expandable microcapsules. Disclosure 6 is an adhesive tape according to Disclosure 4 or 5, wherein the foamed particles have an average particle size of 60 μm or less. Disclosure 7 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5 or 6, wherein the foamed layer contains a copolymer having macromonomers as constituent units having a number average molecular weight of 2,000 to 30,000. Disclosure 8 is an adhesive tape according to Disclosure 7, wherein the foamed layer contains an acrylic copolymer having constituent units derived from (meth)acrylic acid ester and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal. Disclosure 9 is an adhesive tape according to Disclosure 8, wherein the constituent units derived from (meth)acrylic acid ester include constituent units derived from (meth)acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms, and the content ratio of constituent units derived from (meth)acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms in the (meth)acrylic acid alkyl ester is 50% by mass or more and 100% by mass or less. Disclosure 10 is an adhesive tape according to Disclosure 8 or 9, which includes a constituent unit derived from the (meth)acrylic acid ester having an aliphatic cyclic structure within the constituent unit derived from the (meth)acrylic acid ester.Disclosure 11 is an adhesive tape according to Disclosure 8, 9, or 10, wherein the acrylic copolymer has structural units derived from a vinyl aromatic compound, and the content of structural units derived from the vinyl aromatic compound in the acrylic copolymer is 2.5% by mass or more and 20% by mass or less. Disclosure 12 is an adhesive tape according to Disclosure 8, 9, 10, or 11, wherein the structural units derived from the (meth)acrylic acid ester include structural units derived from an alkyl (meth)acrylic acid ester having a linear or branched alkyl group with 6 to 8 carbon atoms. Disclosure 13 is an adhesive tape according to Disclosure 12, wherein the structural units derived from the (meth)acrylic acid ester further include structural units derived from an aliphatic cyclic structure. Disclosure 14 is an adhesive tape according to Disclosure 8, 9, 10, 11, 12, or 13, wherein the content of structural units derived from an olefin polymer having a polymerizable unsaturated double bond at its end in the acrylic copolymer is 5% by mass or more and 50% by mass or less. Disclosure 15 is an adhesive tape according to Disclosures 8, 9, 10, 11, 12, 13, or 14, wherein the acrylic copolymer has constituent units derived from polar functional group-containing monomers, and the content of constituent units derived from polar functional group-containing monomers in the acrylic copolymer is 0.1% by mass or more. Disclosure 16 is an adhesive tape according to Disclosures 8, 9, 10, 11, 12, 13, 14, or 15, wherein the acrylic copolymer has a weight-average molecular weight of 300,000 or more and 1,500,000 or less. Disclosure 17 is an adhesive tape according to Disclosures 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the foam layer does not contain a tackifying resin, or the adhesive resin composition contains a tackifying resin, and the content of the tackifying resin per 100 parts by mass of the acrylic copolymer is 50 parts by mass 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 foam layer contains at least one elastomer selected from styrene-based elastomers, olefin-based elastomers, and urethane-based elastomers.Disclosure 19 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, wherein the foam layer is colored. Disclosure 20 is an adhesive tape according to Disclosures 3, 4, or 5, wherein the adhesive resin composition contains a crosslinking agent. Disclosure 21 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the foam layer has a bio-derived carbon content of 15% or more. Disclosure 22 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, wherein the foam layer has an average major diameter of bubbles of 0.80 times or less the thickness of the foam layer. Disclosure 23 is an adhesive tape of Disclosure 21, wherein the foam layer has a deemed density of 0.59 g / cm³. ３ 1.15g / cm or more ３The following are adhesive tapes according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22. Disclosure 24 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, wherein the foam layer has a structure in which no air bubbles are exposed on the surface in the thickness direction. Disclosure 25 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24, consisting only of the foam layer. Disclosure 26 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24, having a base material and having the foam layer on at least one surface of the base material. Disclosure 27 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 26, having an adhesive layer on at least one surface of the foam layer. Disclosure 28 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, or 27 used for bonding to internal components of electrical and electronic equipment. Disclosure 29 is an electronic device including the adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, or 28. The present invention will be described in detail below. Hereinafter, embodiments of the present invention or one thereof will be described as "this embodiment".

[0009] Because the housings of thin electronic devices are prone to deformation, adhesive tapes used to secure these housings must be designed with excellent bending resistance to suppress this deformation. However, adhesive tapes with excellent bending resistance tend to have high rigidity and reduced flexibility, resulting in insufficient stress distribution (stress relaxation) necessary for absorbing impacts such as drops, which can easily lead to peeling of the adhesive tape or damage to the housing. Therefore, the inventors investigated using an adhesive tape with a foam layer as an adhesive tape with excellent stress relaxation properties, and adjusted the shear storage modulus and loss tangent of the foam layer to a specific range. As a result, they found that it is possible to obtain an adhesive tape that can achieve both excellent bending resistance and excellent shock absorption, thus completing the present invention.

[0010] The adhesive tape of this embodiment has a foam layer. Because the foam layer has a foamed structure, it has excellent stress relaxation properties. Therefore, the presence of the foam layer in the adhesive tape of this embodiment improves the stress relaxation properties of the adhesive tape and makes it superior in shock absorption.

[0011] The shear storage modulus of the foam layer at 23°C, measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz (hereinafter sometimes simply referred to as "shear storage modulus at 23°C and 1 Hz"), has a lower limit of 0.30 MPa. A shear storage modulus of 0.30 MPa or higher at 23°C and 1 Hz of the foam layer further improves the bending resistance of the adhesive tape in this embodiment. Furthermore, the bulk cohesive force of the foam layer is further improved, resulting in improved adhesive strength. A preferred lower limit for the shear storage modulus of the foam layer at 23°C and 1 Hz is 0.40 MPa, a more preferred lower limit is 0.50 MPa, an even more preferred lower limit is 0.75 MPa, and a particularly preferred lower limit is 0.90 MPa. A preferred upper limit for the shear storage modulus of the foam layer at 23°C and 1 Hz is 5.00 MPa. The shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz is 5.00 MPa or less, which improves the wettability of the interface of the foam layer, resulting in superior adhesive strength for the adhesive tape of this embodiment. A more preferable upper limit for the shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz is 4.00 MPa, an even more preferable upper limit is 3.50 MPa, an even more preferable upper limit is 2.00 MPa, an even more preferable upper limit is 1.50 MPa, and a particularly preferable upper limit is 1.30 MPa. Examples of shear storage moduli for the foam layer at 23°C and a measurement frequency of 1 Hz include 0.30 MPa to 5.00 MPa, 0.40 MPa to 4.00 MPa, 0.50 MPa to 3.50 MPa, 0.75 MPa to 2.00 MPa, 0.90 MPa to 1.50 MPa, 0.90 MPa to 1.30 MPa, etc. Furthermore, the shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz can be measured using a viscoelastic spectrometer (such as the "DVA-200" manufactured by IT Measurement Control Co., Ltd.) under conditions of shear direction, measurement frequency of 1 Hz, and temperature range from -50°C to 300°C.

[0012] Methods for adjusting the shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz include, for example, adjusting the thickness of the foam layer, adjusting the composition, weight-average molecular weight, and polydispersity (weight-average molecular weight / number-average molecular weight) of the acrylic copolymer contained in the foam layer, and adjusting the type and amount of crosslinking agent and tackifying resin contained in the foam layer.

[0013] The loss tangent of the foam layer described above, measured by dynamic viscoelasticity measurement at a measurement frequency of 100 Hz, is 0.50 at 23°C (hereinafter sometimes simply referred to as "loss tangent at 23°C and 100 Hz"). Generally, the higher the loss tangent of an adhesive layer, the more effectively the energy from impact is dissipated by heat or deformation, thus increasing the shock absorption of the adhesive tape and suppressing peeling due to impact. Therefore, by having a loss tangent of 0.50 or higher at 23°C and 100 Hz for the foam layer described above, the shock absorption of the adhesive tape of this embodiment is improved. In addition, the wettability of the interface of the foam layer is further improved, and the adhesive strength of the adhesive tape of this embodiment is further improved. The preferred lower limit for the loss tangent of the foam layer described above at 23°C and 100 Hz is 0.60, and the more preferred lower limit is 0.65. The preferred upper limit for the loss tangent of the foam layer described above at 23°C and 100 Hz is 2.5. Since the loss tangent of the foam layer at 23°C and a frequency of 100 Hz is 2.5 or less, the cohesive force of the bulk foam layer is improved, and the adhesive tape of this embodiment has superior adhesive strength. A more preferable upper limit for the loss tangent ratio of the foam layer at 23°C and a frequency of 100 Hz is 2.0, an even more preferable upper limit is 1.8, an even more preferable upper limit is 1.5, and an even more preferable upper limit is 1.0. Examples of loss tangents of the foam layer at 23°C and a frequency of 100 Hz include 0.50 to 2.5, 0.60 to 2.0, 0.65 to 1.8, 0.65 to 1.5, and 0.65 to 1.0. Furthermore, the loss tangent of the foam layer at 23°C and a frequency of 100 Hz can be measured using a viscoelastic spectrometer (such as the "DVA-200" manufactured by IT Measurement Control Co., Ltd.) under the conditions of a simple heating mode with a heating rate of 10°C / min, shear direction, frequency of 100 Hz, and a temperature range from -50°C to 300°C.

[0014] Methods for adjusting the loss tangent of the foam layer at 23°C and a frequency of 100 Hz include, for example, adjusting the thickness of the foam layer, adjusting the composition, weight-average molecular weight, and polydispersity (weight-average molecular weight / number-average molecular weight) of the acrylic copolymer contained in the foam layer, and adjusting the type and amount of crosslinking agent and tackifying resin contained in the foam layer.

[0015] The preferred lower limit of the 180° peel force of the foam layer against SUS (stainless steel) at 23°C is 10 N / 25 mm. Because the 180° peel force of the foam layer against SUS at 23°C is 10 N / 25 mm or higher, the foam layer has excellent adhesive properties, and the adhesive tape can be made solely of the foam layer, thus the adhesive tape of this embodiment has superior shock absorption. A more preferred lower limit of the 180° peel force of the foam layer against SUS at 23°C is 12 N / 25 mm, an even more preferred lower limit is 15 N / 25 mm, and an even more preferred lower limit is 20 N / 25 mm. There is no particular upper limit for the 180° peel force of the foam layer against SUS at 23°C, but approximately 80 N / 25 mm is a practical upper limit. A more preferred upper limit for the peel force is 50 N / 25 mm. Furthermore, examples of the 180° peel force of the foam layer against SUS at 23°C include 10N / 25mm to 80N / 25mm, 12N / 25mm to 80N / 25mm, 15N / 25mm to 50N / 25mm, 20N / 25mm to 50N / 25mm, etc. The 180° peel force of the foam layer against SUS at 23°C is measured by the following method. Specifically, one side of the obtained foam layer (the side not to be measured) is backed with a polyethylene terephthalate film with a thickness of 23 μm, and then cut to a width of 25 mm and a length of 75 mm to prepare a test piece. Next, the obtained test specimen was bonded to a SUS304 plate (a SUS304 plate that had been washed with ethanol and then wiped dry), and pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. After that, it was cured at 23°C and 50% RH for 20 minutes to prepare a test sample. The obtained test sample could be measured by leaving it standing for 20 minutes in an environment of 23°C and 50% RH, and then peeling the foam layer from the SUS304 plate in accordance with JIS Z 0237:2009, under conditions of 23°C and 50% RH, a tensile speed of 300 mm / min, and a peel angle of 180°.

[0016] Methods for adjusting the 180° peel force of the foam layer against SUS at 23°C include, for example, changing the composition of the acrylic copolymer contained in the foam layer (for example, increasing the mass percentage of polar functional group-containing monomers), adding a tackifying resin to the foam layer, adjusting the thickness of the foam layer, and adjusting the amount of crosslinking agent.

[0017] Methods for forming the foam layer include, for example, applying foaming particles to a resin composition that forms the foam layer and heating and drying it, forcibly mixing and dispersing a gas in the resin composition that forms the foam layer, and mixing liquefied gas in the resin composition that forms the foam layer. Among these, the method of applying foaming particles to a resin composition that forms the foam layer and heating and drying it is preferred from the viewpoint of ensuring foam dispersibility during high-temperature drying.

[0018] The foam layer is preferably formed from an adhesive resin composition. By forming the foam layer of this embodiment from an adhesive resin composition, it becomes easier to form an adhesive foam layer. Furthermore, it becomes easier to adjust the shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz, the loss tangent of the foam layer at 23°C and a frequency of 100 Hz, the 180° peel force of the foam layer against SUS at 23°C, and the thickness of the foam layer, which will be described later, to a suitable range. As a method for forming the foam layer from the adhesive resin composition, for example, one can apply the adhesive resin composition to a release film or the like, and then heat-dry the adhesive resin composition.

[0019] The above adhesive resin composition preferably contains foaming particles. The inclusion of foaming particles in the adhesive resin composition improves the dispersion of air bubbles in the resulting foam layer, resulting in superior stress relaxation properties of the resulting foam layer.

[0020] The foam layer described above preferably has bubbles derived from foaming particles. The foam layer having bubbles derived from foaming particles can be formed by heating and foaming an adhesive resin composition containing foaming particles. Examples of foaming particles include those that foam when heated. Specifically, examples include pyrolysis-type foaming agents and thermally expandable microcapsules, and among these, it is preferable that the foaming particles include thermally expandable microcapsules. Thermally expandable microcapsules become hollow particles with bubbles inside their outer shell when heated. Therefore, in this embodiment, by including thermally expandable microcapsules in the foaming particles, it is possible to prevent gas generated from the foaming particles from escaping to the outside of the foam layer, making it easier to have an appropriate amount of bubbles coexisting in the foam layer, and thus making it easier to improve the foaming ratio of the foam layer. As a result, the foam layer has appropriate flexibility, and the stress relaxation properties of the adhesive tape are further improved, so the adhesive tape of this embodiment has better shock absorption properties. Furthermore, in this embodiment, the inclusion of thermally expandable microcapsules in the foaming particles makes it easier to achieve a uniform average diameter of bubbles in the resulting adhesive layer, thereby enabling uniform strength throughout the foam layer. Additionally, the foaming particles may include thermally expanded particles.

[0021] The above-mentioned heat-expandable microcapsules contain a volatile substance such as a low-boiling point solvent inside an outer resin shell. When heated, the outer resin softens, causing the contained volatile substance to volatilize or expand. This expansion of the outer shell increases the particle size due to the resulting pressure. The outer shell of the heat-expandable microcapsules is preferably formed from a thermoplastic resin. The thermoplastic resin can be one or more selected from vinyl polymers and copolymers thereof, such as ethylene, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, butadiene, and chloroprene, as well as polyamides such as nylon 6 and nylon 66, and polyesters such as polyethylene terephthalate. Among these, acrylonitrile copolymers are preferred because they do not easily allow the contained volatile substance to permeate.

[0022] Examples of the volatile substances encapsulated inside the above-mentioned thermally expandable microcapsules include hydrocarbons having 3 to 7 carbon atoms such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, hexane, and heptane, petroleum ether, methyl halides such as methyl chloride, and methylene chloride, halogenated methanes, chlorofluorocarbons such as CCl ３ F, CCl ２ F ２ and the like, and one or more low-boiling liquids selected from tetraalkylsilanes such as tetramethylsilane and trimethylethylsilane are used. Among these, it is preferable to use hydrocarbons having 3 to 7 carbon atoms.

[0023] Further, as the above-mentioned foaming particles, the adhesive resin composition may previously contain hollow particles. When the adhesive resin composition contains hollow particles as foaming particles, compared with the case of heating the adhesive resin composition containing thermally expandable microcapsules to form hollow particles in the foam layer, the average diameter of the bubbles is likely to be made uniform, so the uniformity of the thickness of the foam layer is likely to be improved, and the resulting adhesive tape has better shock absorbency.

[0024] Examples of the above-mentioned hollow particles previously included in the adhesive resin composition include particles obtained by heating and expanding thermally expandable microcapsules, particles produced by the core-shell method, particles produced by the bubble template method, and the like.

[0025] The upper limit of the average particle diameter of the above-mentioned expandable particles is preferably 60 μm. By the average particle diameter of the above-mentioned expandable particles being 60 μm or less, the balance between the strength and impact resistance of the resulting adhesive tape can be further enhanced. A more preferable upper limit of the average particle diameter of the above-mentioned expandable particles is 55 μm, and an even more preferable upper limit is 50 μm. The lower limit of the average particle diameter of the above-mentioned expandable particles is preferably 15 μm. By the average particle diameter of the above-mentioned expandable particles being 15 μm or more, the flexibility of the resulting adhesive tape can be ensured. A more preferable lower limit of the average particle diameter of the above-mentioned expandable particles is 20 μm, and an even more preferable lower limit is 25 μm. Further, examples of the average particle diameter of the above-mentioned expandable particles include 15 μm or more and 60 μm or less, 20 μm or more and 55 μm or less, 25 μm or more and 50 μm or less, etc. In this specification, the above-mentioned "average particle diameter of the expandable particles" means the average particle diameter of the expandable particles in the unexpanded state observed from the adhesive resin composition containing the expandable particles. Note that the average particle diameter may be obtained by randomly selecting particles with an optical microscope or the like and averaging 10 points.

[0026] Also, although not particularly limited, those having an expansion start temperature (also referred to as "foaming start temperature") of about 95°C to 150°C may be used for the above-mentioned expandable particles. The expansion start temperature of the above-mentioned expandable particles is the temperature at which the expansion of the thermally expandable microcapsules starts, and can be measured by a thermomechanical analyzer (TMA) or the like.

[0027] Examples of commercially available expandable particles include Expancel 920DU40 (manufactured by Nippon Shokubai Co., Ltd., average particle diameter 40 μm), Expancel 920DU80 (manufactured by Nippon Shokubai Co., Ltd., average particle diameter 80 μm), EMC-20(B)R (manufactured by Nippon Shokubai Co., Ltd., average particle diameter 20 μm), Advance EML101 (manufactured by Sekisui Chemical Co., Ltd., average particle diameter 50 μm), etc.

[0028] The above-mentioned foam layer preferably contains a copolymer having a structural unit derived from a macromonomer having a number average molecular weight of 2000 or more and 30000 or less. By the above-mentioned foam layer containing a copolymer having a structural unit derived from a macromonomer having a number average molecular weight of 2000 or more and 30000 or less, the adhesive tape of the present embodiment becomes excellent in impact absorbency.

[0029] The number average molecular weight of macromonomers having a number average molecular weight of 2,000 to 30,000 is not particularly limited as long as it is between 2,000 and 30,000, but from the viewpoint of ensuring a balance between tape strength and flexibility, a preferred lower limit is 4,000 and a preferred upper limit is 25,000. Examples of the number average molecular weight of macromonomers having a number average molecular weight of 2,000 to 30,000 include 2,000 to 30,000 and 4,000 to 25,000. Furthermore, in this specification, "weight average molecular weight" and "number average molecular weight" refer to the weight average molecular weight measured as polystyrene-equivalent molecular weight by gel permeation chromatography (GPC). For example, the weight-average molecular weight, number-average molecular weight, and polydispersity can be measured using a Waters 2690 Separations Module as the measuring instrument, a Showa Denko GPC KF-806L as the column, a sample flow rate of 1 mL / min, and a column temperature of 40°C.

[0030] Examples of macromonomers having a number-average molecular weight of 2,000 to 30,000 include styrene polymers having polymerizable unsaturated double bonds at their terminals and olefin polymers having polymerizable unsaturated double bonds at their terminals. Among these, olefin polymers having polymerizable unsaturated double bonds at their terminals are preferred from the viewpoint of ensuring a balance between flexibility and strength.

[0031] Examples of olefin polymers having a polymerizable unsaturated double bond at one or both ends include ethylene-butylene copolymers, ethylene-propylene copolymers, ethylene polymers, propylene polymers, and butene polymers, which have a group containing a polymerizable unsaturated carbon-carbon double bond at one or both ends. Examples of the group containing a polymerizable unsaturated carbon-carbon double bond include (meth)acryloyl groups, vinyl ether groups, and styryl groups. Among these, (meth)acryloyl groups are preferred because they exhibit excellent copolymerization with alkyl (meth)acrylate esters, etc. Specific examples of olefin polymers having a polymerizable unsaturated double bond at one end include ethylene macromonomers having a (meth)acryloyl group at one end, propylene macromonomers having a (meth)acryloyl group at one end, ethylene-butylene macromonomers having a (meth)acryloyl group at one end, and ethylene-propylene macromonomers having a (meth)acryloyl group at one end.

[0032] The foam layer preferably contains an acrylic copolymer (hereinafter sometimes simply referred to as "acrylic copolymer") having constituent units derived from a macromonomer with a number average molecular weight of 2,000 or more and 30,000 or less, and comprising constituent units derived from an alkyl (meth)acrylate ester and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal. In this specification, "(meth)acrylic" means acrylic or methacrylic.

[0033] When the above-mentioned acrylic copolymer has constituent units derived from alkyl (meth)acrylate ester and constituent units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals, the acrylic copolymer has a structure in which the constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its terminals are located in the side chains of the acrylic copolymer. In this case, the constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its terminals, located in the side chains of the acrylic copolymer, aggregate through interaction, forming a pseudo-crosslink structure. Because the acrylic copolymer adopts such a structure, when peel stress is applied and the strain becomes large, the pseudo-crosslink breaks and the molecules of the acrylic copolymer stretch, so the foam layer exhibits high flexibility and excellent stress relaxation properties. Therefore, the adhesive tape of this embodiment of acrylic has better shock absorption properties. On the other hand, when the strain is small, the molecules of the acrylic copolymer become hard as if they were in a crosslinked structure due to the pseudo-crosslink, so the foam layer has appropriate hardness. Therefore, the adhesive tape of this embodiment has better bending resistance. In other words, because the acrylic copolymer contains structural units derived from alkyl (meth)acrylate esters and structural units derived from olefin polymers having polymerizable unsaturated double bonds at their terminals, the adhesive tape of this embodiment has superior bending resistance, superior shock absorption, and superior holding power.

[0034] The above acrylic copolymer preferably has a constituent unit derived from an alkyl (meth)acrylate. The alkyl (meth)acrylate in the constituent unit derived from the alkyl (meth)acrylate may consist only of petroleum-derived materials, but it is preferable that it also contains a bio-derived material. In recent years, the depletion of petroleum resources and the emission of carbon dioxide from the combustion of petroleum-derived products have become serious concerns. Therefore, attempts are being made to conserve petroleum resources by using bio-derived materials instead of petroleum-derived materials. The above alkyl (meth)acrylate containing a bio-derived material is preferable from the viewpoint of conserving petroleum resources, and furthermore, since bio-derived materials are originally produced by taking in carbon dioxide from the atmosphere, it is thought that burning them will not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the viewpoint of reducing carbon dioxide emissions.

[0035] When the alkyl (meth)acrylate in the constituent unit derived from the above alkyl (meth)acrylate contains a bio-derived material, it is preferable that the alkyl (meth)acrylate is synthesized by esterification of an alcohol, which is a bio-derived material, with (meth)acrylic acid.

[0036] The constituent units derived from the alkyl (meth)acrylate ester preferably include constituent units derived from the alkyl (meth)acrylate ester having an alkyl group with 1 to 8 carbon atoms (hereinafter sometimes referred to as "constituent unit (a-1)"). By including the constituent unit (a-1) derived from the alkyl (meth)acrylate ester, the glass transition temperature of the acrylic copolymer described later is more likely to satisfy a suitable range, the adhesive strength of the foam layer is further improved, and the adhesive tape of this embodiment has better adhesive strength and better retention.

[0037] Examples of the above-mentioned structural unit (a-1) include structural units derived from alkyl esters of (meth)acrylate, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-heptyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. In particular, from the viewpoint of the adhesive tape of this embodiment having superior bending resistance, structural units derived from alkyl esters of (meth)acrylate having a linear or branched alkyl group with 6 to 8 carbon atoms are preferred. Furthermore, the above constituent unit (a-1) may consist of only one type, or two or more types may coexist.

[0038] The preferred lower limit for the content of the above-mentioned structural unit (a-1) in the structural unit derived from the above-mentioned alkyl (meth)acrylate is 50% by mass. When the content of the above-mentioned structural unit (a-1) is 50% by mass or more, the adhesive strength of the foam layer is further improved, and the adhesive tape of this embodiment has better adhesive strength and better retention. A more preferred lower limit for the content of the above-mentioned structural unit (a-1) is 60% by mass, and an even more preferred lower limit is 65% by mass. In addition, the content of the above-mentioned structural unit (a-1) may be 100% by mass, but from the viewpoint of bending resistance, a preferred upper limit is 95% by mass, a more preferred upper limit is 90% by mass, an even more preferred upper limit is 85% by mass, and an even more preferred upper limit is 80% by mass. Examples of the content ratio of the above constituent unit (a-1) include 50% by mass or more and 100% by mass or less, 60% by mass or more and 95% by mass or less, 65% by mass or more and 90% by mass or less, 65% by mass or more and 85% by mass or less, 65% by mass or more and 80% by mass or less, etc.

[0039] The above-mentioned alkyl (meth)acrylate constituent unit preferably includes a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having an aliphatic cyclic structure (hereinafter sometimes referred to as "constituent unit (a-2)"). By including the above-mentioned alkyl (meth)acrylate constituent unit (a-2), the adhesive tape of this embodiment exhibits superior bending resistance.

[0040] Examples of the above-mentioned constituent unit (a-2) include constituent units derived from alkyl esters of (meth)acrylate having an aliphatic cyclic structure, such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate. Note that the above-mentioned constituent unit (a-2) may consist of only one type, or two or more types may coexist.

[0041] The preferred lower limit for the content of the above-mentioned structural unit (a-2) in the structural unit derived from the above-mentioned alkyl (meth)acrylate is 5% by mass. By having a content of 5% by mass or more of the above-mentioned structural unit (a-2), the adhesive tape of this embodiment will have superior bending resistance. A more preferred lower limit for the content of the above-mentioned structural unit (a-2) is 8% by mass, an even more preferred lower limit is 10% by mass, and an even more preferred lower limit is 20% by mass. Furthermore, from the viewpoint of ensuring adhesive strength and flexibility, a preferred upper limit for the content of the above-mentioned structural unit (a-2) is 50% by mass, and a more preferred upper limit is 40% by mass. Examples of the content of the above-mentioned structural unit (a-2) include 8% by mass or more and 50% by mass or less, 10% by mass or more and 40% by mass or less, 20% by mass or more and 40% by mass or less, etc.

[0042] If the above-mentioned alkyl (meth)acrylate-derived structural unit includes a structural unit derived from an alkyl (meth)acrylate-derived structural unit having an alkyl group with 6 to 8 carbon atoms, it is more preferable that the above-mentioned alkyl (meth)acrylate-derived structural unit further includes the above-mentioned structural unit (a-2) from the viewpoint of further improving the shock absorption performance of the adhesive tape of this embodiment.

[0043] The constituent units derived from the above alkyl (meth)acrylate may include other constituent units derived from alkyl (meth)acrylate other than the above constituent units (a-1) and (a-2) (hereinafter sometimes referred to as "constituent unit (a-3)").

[0044] Examples of the above constituent units (a-3) include constituent units derived from alkyl esters of (meth)acrylate, such as n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. Note that only one type of above constituent unit (a-3) may be included, or two or more types may coexist.

[0045] The preferred lower limit and preferred upper limit of the content of the constituent units derived from the alkyl (meth)acrylate in the above acrylic copolymer is 50% by mass. By having the content of the constituent units derived from the alkyl (meth)acrylate within the above range, the adhesive tape of this embodiment will have better adhesive strength and better retention. A more preferred lower limit for the content of the constituent units derived from the alkyl (meth)acrylate is 60% by mass, a more preferred upper limit is 90% by mass, an even more preferred lower limit is 65% by mass, and an even more preferred upper limit is 85% by mass. Examples of the content of the constituent units derived from the alkyl (meth)acrylate include 50% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, 65% by mass or more and 85% by mass or less, etc.

[0046] The above acrylic copolymer preferably has constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal. The above olefin polymer having a polymerizable unsaturated double bond at its terminal may have a polymerizable unsaturated double bond at one terminal or at both terminals. Among these, an olefin polymer having a polymerizable unsaturated double bond at one terminal is preferred from the viewpoint of less intramolecular chemical crosslinking and further improving the retention of the adhesive tape of this embodiment.

[0047] Examples of olefin polymers having a polymerizable unsaturated double bond at one or both ends include ethylene-butylene copolymers, ethylene-propylene copolymers, ethylene polymers, propylene polymers, and butene polymers, which have a group containing a polymerizable unsaturated carbon-carbon double bond at one or both ends. Examples of the group containing a polymerizable unsaturated carbon-carbon double bond include (meth)acryloyl groups, vinyl ether groups, and styryl groups. Among these, (meth)acryloyl groups are preferred because they exhibit excellent copolymerization with alkyl (meth)acrylates. Specific examples of olefin polymers having a polymerizable unsaturated double bond at one end include ethylene macromonomers having a (meth)acryloyl group at one end, propylene macromonomers having a (meth)acryloyl group at one end, ethylene-butylene macromonomers having a (meth)acryloyl group at one end, and ethylene-propylene macromonomers having a (meth)acryloyl group at one end. In particular, ethylene-butylene macromonomers having a (meth)acryloyl group at one end and ethylene-propylene macromonomers having a (meth)acryloyl group at the other end are preferred, from the viewpoint that the glass transition temperature of the acrylic copolymer described later is more likely to be within a suitable range and the adhesive strength of the foam layer is further improved. These olefin polymers having polymerizable unsaturated double bonds at the ends may be used individually or in combination of two or more.

[0048] In the above acrylic copolymer, the preferred lower limit for the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 5% by mass, and the preferred upper limit is 50% by mass. When the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 5% by mass or more, an appropriate number of pseudo-crosslinks are formed, further improving the adhesive strength and retention of the foam layer. When the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 50% by mass or less, the bulk strength of the foam layer is further improved, and thus the retention of the adhesive tape of this embodiment is further improved. A more preferred lower limit for the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 8% by mass, a more preferred upper limit is 45% by mass, an even more preferred lower limit is 10% by mass, an even more preferred upper limit is 40% by mass, an even more preferred lower limit is 15% by mass, and an even more preferred upper limit is 30% by mass. Examples of the content of constituent units derived from olefin polymers having polymerizable unsaturated double bonds at their ends include 5% by mass or more and 50% by mass or less, 8% by mass or more and 45% by mass or less, 10% by mass or more and 40% by mass or less, and 15% by mass or more and 30% by mass or less.

[0049] The above acrylic copolymer preferably has structural units derived from a polar functional group-containing monomer. Because the acrylic copolymer has structural units derived from a polar functional group-containing monomer, it can sufficiently form a crosslinked structure through chemical crosslinking via a crosslinking agent between molecules, thereby improving the cohesive force of the foam layer. As a result, the retention of the adhesive tape of this embodiment is further improved. Furthermore, because the acrylic copolymer has structural units derived from the polar functional group-containing monomer, the polar functional groups in the acrylic copolymer interact with each other, further improving the cohesive force of the foam layer, and thus improving the adhesive strength and retention of the adhesive tape of this embodiment.

[0050] Examples of constituent units derived from the above polar functional group-containing monomers include constituent units derived from carboxyl group-containing monomers, constituent units derived from hydroxyl group-containing monomers, constituent units derived from amide group-containing monomers, and constituent units derived from amino group-containing monomers. In particular, from the viewpoint of further improving the adhesiveness and retention of the foam layer, it is preferable that the constituent units derived from the above polar functional group-containing monomers include at least one selected from the group consisting of constituent units derived from carboxyl group-containing monomers and constituent units derived from hydroxyl group-containing monomers. Specific examples of constituent units derived from the above carboxyl group-containing monomers include unsaturated monocarboxylic acids such as (meth)acrylic acid, (meth)acryloylacetic acid, (meth)acryloylpropionic acid, (meth)acryloylbutyric acid, (meth)acryloylpentanoic acid, and crotonic acid, as well as constituent units derived from maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Specific examples of constituent units derived from the above hydroxyl group-containing monomers include constituent units derived from 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Specific examples of structural units derived from the above-mentioned amide group-containing monomers include those derived from N-vinyl-2-pyrrolidone, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, etc. Specific examples of structural units derived from the above-mentioned amino group-containing monomers include those derived from (meth)acryloylmorpholine, dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, etc. Note that only one type of structural unit derived from these polar functional group-containing monomers may be included, or two or more types may coexist.

[0051] In the above acrylic copolymer, the preferred lower limit of the content of constituent units derived from the polar functional group-containing monomer is 0.1% by mass, and the preferred upper limit is 10% by mass. When the content of constituent units derived from the polar functional group-containing monomer is within the above range, the acrylic copolymer can sufficiently form a crosslinked structure, thereby improving the holding power of the adhesive tape of this embodiment. Furthermore, when the content of constituent units derived from the polar functional group-containing monomer is 0.1% by mass or more, the interaction between polar functional groups can be further enhanced, thereby improving the adhesive strength and holding power of the foam layer. When the content of constituent units derived from the polar functional group-containing monomer is 10% by mass or less, the foam layer does not become too hard, and the adhesive strength is further improved. A more preferred lower limit for the content of constituent units derived from the above polar functional group-containing monomer is 0.5% by mass, a more preferred upper limit is 9.0% by mass, an even more preferred lower limit is 1.0% by mass, an even more preferred upper limit is 8.0% by mass, an even more preferred lower limit is 3.0% by mass, an even more preferred upper limit is 7.0% by mass, and a particularly preferred lower limit is 5.0% by mass. Examples of the content of constituent units derived from the above polar functional group-containing monomer include 0.1% by mass or more and 10% by mass or less, 0.5% by mass or more and 9.0% by mass or less, 1.0% by mass or more and 8.0% by mass or less, 3.0% by mass or more and 7.0% by mass or less, 5.0% by mass or more and 7.0% by mass or less.

[0052] The above-mentioned acrylic copolymer preferably has structural units derived from vinyl aromatic compounds. Having structural units derived from vinyl aromatic compounds in the above-mentioned acrylic copolymer results in superior shock absorption of the adhesive tape of this embodiment.

[0053] Examples of structural units derived from the above-mentioned vinyl aromatic compounds include structural units derived from styrene, structural units derived from α-methylstyrene, and structural units derived from their hydrogenated products. Among these, structural units derived from styrene are preferred from the viewpoint of balancing flexibility and strength. Note that only one type of structural unit derived from these vinyl aromatic compounds may be included, or two or more types may coexist.

[0054] When the above acrylic copolymer has structural units derived from a vinyl aromatic compound, the above acrylic copolymer may be a random copolymer, or it may be a block copolymer (hereinafter sometimes simply referred to as "block copolymer (A)") of a block having structural units derived from the above vinyl aromatic compound (hereinafter sometimes simply referred to as "block (A-1)") and a block having structural units derived from the above alkyl (meth)acrylate and structural units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal (hereinafter sometimes simply referred to as "block (A-2)"). In the above block copolymer (A), block (A-1) becomes a hard segment and imparts shock absorption to the adhesive tape, and block (A-2) becomes a soft segment and imparts adhesive strength and retention to the adhesive tape. In particular, from the viewpoint of achieving superior adhesive strength and conformability of the adhesive tape of this embodiment, it is preferable that the above acrylic copolymer includes block copolymer (A) when it has structural units derived from a vinyl aromatic compound.

[0055] The block copolymer (A) may be a diblock copolymer or a triblock copolymer. Among these, a triblock copolymer is preferred from the viewpoint of phase separation suitable for ensuring strength, and among triblock copolymers, a triblock copolymer having the structure of block (A-1) - block (A-2) - block (A-1) is more preferred.

[0056] The preferred lower limit for the content of block (A-1) in the block copolymer (A) is 3% by mass, and the preferred upper limit is 15% by mass. When the content of block (A-1) is 3% by mass or more, the adhesive tape of this embodiment has superior holding properties. When the content of block (A-1) is 15% by mass or less, the adhesive tape of this embodiment has superior adhesive strength and shock absorption properties. The more preferred lower limit for the content of block (A-1) is 5% by mass, the more preferred upper limit is 12% by mass, and the still more preferred upper limit is 10% by mass. Examples of the content of block (A-1) include 3% by mass or more and 15% by mass or less, 5% by mass or more and 12% by mass or less, and 5% by mass or more and 10% by mass or less.

[0057] The method for producing the block copolymer (A) is not particularly limited, and conventionally known methods can be used. Specifically, for example, a vinyl aromatic compound may be added to the block (A-2) synthesized in the same manner as the acrylic copolymer described above, and copolymerized. Alternatively, the pre-synthesized blocks (A-1) and (A-2) may be copolymerized.

[0058] The preferred lower limit for the content of constituent units derived from the vinyl aromatic compound in the above acrylic copolymer is 2.5% by mass. A content of 2.5% by mass or more of constituent units derived from the vinyl aromatic compound results in superior holding power for the adhesive tape of this embodiment. A more preferred lower limit for the content of constituent units derived from the vinyl aromatic compound is 3.0% by mass, an even more preferred lower limit is 3.5% by mass, and an even more preferred lower limit is 4.5% by mass. Furthermore, the preferred upper limit for the content of constituent units derived from the vinyl aromatic compound is 20% by mass. A content of 20% by mass or less of constituent units derived from the vinyl aromatic compound results in superior adhesive strength and shock absorption for the adhesive tape of this embodiment. A more preferred upper limit for the content of constituent units derived from the vinyl aromatic compound is 18% by mass, and an even more preferred upper limit is 15% by mass. Examples of the content ratio of constituent units derived from the vinyl aromatic compound in the above acrylic copolymer include 3.5% by mass or more and 20% by mass or less, 4.5% by mass or more and 18% by mass or less, and 4.5% by mass or more and 15% by mass or less.

[0059] The weight-average molecular weight (Mw) of the above acrylic copolymer has a preferred lower limit of 300,000 and a preferred upper limit of 1,500,000. Having the weight-average molecular weight (Mw) of the above acrylic copolymer within this range further improves the tackiness and retention of the foam layer. A more preferred lower limit for the weight-average molecular weight (Mw) of the above acrylic copolymer is 500,000, a more preferred upper limit is 1,200,000, an even more preferred lower limit is 600,000, an even more preferred upper limit is 1,000,000, and an even more preferred lower limit is 800,000. Examples of weight-average molecular weight (Mw) of the above acrylic copolymer include 300,000 to 1,500,000, 500,000 to 1,200,000, 600,000 to 1,000,000, and 800,000 to 1,000,000.

[0060] The polydispersity (weight-average molecular weight / number-average molecular weight, Mw / Mn) of the above acrylic copolymer has a preferred lower limit of 1.0 and a preferred upper limit of 8.0. Having the polydispersity (Mw / Mn) of the above acrylic copolymer within this range further improves the tackiness and retention of the foam layer. A more preferred lower limit for the polydispersity (Mw / Mn) of the above acrylic copolymer is 1.5, a more preferred upper limit is 7.5, an even more preferred lower limit is 2.0, and an even more preferred upper limit is 7.0. Examples of polydispersity (Mw / Mn) values ​​for the above acrylic copolymer include 1.0 to 8.0, 1.5 to 7.5, and 2.0 to 7.0.

[0061] The preferred lower limit for the content of the acrylic copolymer in the foam layer is 30% by mass. A content of 30% by mass or more of the acrylic copolymer further improves the adhesive strength and retention of the foam layer. A more preferred lower limit for the content of the acrylic copolymer is 40% by mass, and an even more preferred lower limit is 45% by mass. Furthermore, a preferred upper limit for the content of the acrylic copolymer is 98% by mass. A content of 98% by mass or less of the acrylic copolymer results in a more superior shock absorption of the adhesive tape of this embodiment.

[0062] The polymerization method for synthesizing the above-mentioned acrylic copolymer can be a conventionally known method in which a mixture of monomer raw materials is subjected to a radical reaction in the presence of a polymerization initiator. Examples include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization is preferred because it is easy to synthesize.

[0063] When solution polymerization is used as the polymerization method described above, examples of reaction solvents include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, and diethyl ether. These reaction solvents may be used individually or in combination of two or more.

[0064] Examples of polymerization initiators include organic peroxides and azo compounds. Examples of 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. Examples of azo compounds include azobisisobutyronitrile and azobiscyclohexanecarbonilonitrile. These polymerization initiators may be used alone or in combination of two or more.

[0065] The foam layer preferably contains at least one elastomer selected from styrene-based elastomers, olefin-based elastomers, and urethane-based elastomers. By containing at least one elastomer selected from styrene-based elastomers, olefin-based elastomers, and urethane-based elastomers in the adhesive resin composition, the adhesive tape of this embodiment exhibits superior shock absorption.

[0066] The styrene-based elastomer is not particularly limited, but it is preferable to include at least one of an aromatic block copolymer (X) having a vinyl aromatic polymer block and a conjugated diene polymer block, and a hydrogenated version thereof. In the aromatic block copolymer (X), the vinyl aromatic polymer block acts as a hard segment portion, and the conjugated diene polymer block and the hydrogenated version of the conjugated diene polymer block act as a soft segment portion, imparting rubber elasticity to the adhesive layer. Therefore, by including the aromatic block copolymer (X) in the styrene-based elastomer, the adhesive tape of this embodiment has superior shock absorption properties.

[0067] The vinyl aromatic polymer block described above may be any block having structural units derived from a vinyl aromatic compound, and may also contain structural units derived from other compounds such as ethylene and 1,3-butadiene (which is converted to an ethylene-butylene structure by hydrogenation). Examples of the vinyl aromatic compound described above include alkylstyrene, halogenated styrene, halogen-substituted alkylstyrene, alkoxystyrene, carboxyalkylstyrene, alkyl ether styrene, alkylsilyl styrene, vinyl benzyl dimethoxy phosphide, vinyl naphthalene, vinyl anthracene, N,N-diethyl-p-aminoethylstyrene, and vinylpyridine.

[0068] Examples of alkylstyrenes include styrene, methylstyrene, dimethylstyrene, and t-butylstyrene. Examples of halogenated styrenes include chlorostyrene, bromostyrene, and fluorostyrene. Examples of halogen-substituted alkylstyrenes include chloromethylstyrene. Examples of alkoxystyrenes include methoxystyrene and ethoxystyrene. Examples of carboxyalkylstyrenes include carboxymethylstyrene. Examples of alkyl ether styrenes include vinyl benzylpropyl ether. Examples of alkylsilyl styrenes include trimethylsilylstyrene. These vinyl aromatic compounds may be used individually or in combination of two or more. Among them, styrene, methylstyrene, and dimethylstyrene are preferred, and styrene is more preferred because it is readily available industrially.

[0069] In the vinyl aromatic polymer block described above, the preferred lower limit for the constituent units derived from the vinyl aromatic compound is 7% by mass, from the viewpoint of retention. A more preferred lower limit for the constituent units derived from the vinyl aromatic compound is 10% by mass. Furthermore, from the viewpoint of flexibility and shock absorption, the preferred upper limit for the constituent units derived from the vinyl aromatic compound is 35% by mass, and a more preferred upper limit is 30% by mass. Examples of the content ratio of the constituent units derived from the vinyl aromatic compound in the vinyl aromatic polymer block include 7% by mass or more and 35% by mass or less, and 10% by mass or more and 30% by mass or less.

[0070] The above-mentioned conjugated diene polymer block has 60.0% by mass or more of constituent units derived from the conjugated diene compound. Examples of the above-mentioned conjugated diene compound include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-octadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, chloroprene, and the like. These conjugated diene compounds may be used individually or in combination of two or more. Among them, 1,3-butadiene and isoprene are preferred due to their high polymerization reactivity and ease of industrial availability. In addition to the above-mentioned conjugated diene compounds, an example of a usable compound is 2,5-dihydrofuran-2,5-dione.

[0071] The hydrogenated product of the above-mentioned conjugated diene polymer block refers to a block in which the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound are converted to saturated bonds by hydrogenation. From the viewpoint of preventing degradation due to heat, ultraviolet rays, etc., it is preferable that 80% or more of the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound of the aromatic block copolymer (X) are converted to saturated bonds by hydrogenation, more preferably 90% or more, even more preferably 95% or more, and even more preferably 96% or more. Furthermore, it is most preferable that 100% are converted to saturated bonds by hydrogenation (i.e., a fully hydrogenated product). That is, it is preferable that 80% to 100% of the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound are converted to saturated bonds by hydrogenation, more preferably 90% to 100%, even more preferably 95% to 100%, and even more preferably 96% to 100%.

[0072] Examples of the structure of the above aromatic block copolymer (X) include, when the vinyl aromatic polymer block is B and the conjugated diene polymer block and the hydrogenated product thereof are C, a triblock copolymer represented by formula B-C-B, a diblock copolymer represented by formula B-C, a pentablock copolymer represented by formula C-B-C-B-C, and so on.

[0073] Examples of aromatic block copolymers (X) having the structure represented by the above formula B-C-B include styrene-isoprene-styrene (SIS) block copolymer, styrene-butylene-styrene (SBS) block copolymer, styrene-ethylene-butylene-styrene (SEBS) block copolymer, styrene-ethylene-propylene-styrene (SEPS) block copolymer, styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymer, and styrene-isobutylene-styrene (SIBS). Among these, SIS block copolymer and SEBS block copolymer are preferred from the viewpoint of compatibility with acrylic copolymers.

[0074] The preferred lower limit for the weight-average molecular weight (Mw) of the above aromatic block copolymer (X) is 50,000. A weight-average molecular weight (Mw) of 50,000 or more results in superior shock absorption. A more preferred lower limit for the weight-average molecular weight of the above aromatic block copolymer (X) is 100,000, and an even more preferred lower limit is 150,000. While there is no particular preferred upper limit for the weight-average molecular weight of the above aromatic block copolymer (X), from the viewpoint of compatibility with acrylic copolymers, it is practically limited to around 500,000. Examples of weight-average molecular weights for the above aromatic block copolymer (X) include 50,000 to 500,000, 100,000 to 500,000, and 150,000 to 500,000.

[0075] The preferred upper limit for the content of the aromatic block copolymer (X) per 100 parts by mass of the acrylic copolymer is 60 parts by mass. A content of 60 parts by mass or less of the aromatic block copolymer (X) further improves the adhesive strength of the foam layer. A more preferred upper limit for the content of the aromatic block copolymer (X) is 55 parts by mass, an even more preferred upper limit is 50 parts by mass, and an even more preferred upper limit is 45 parts by mass. Furthermore, the preferred lower limit for the content of the aromatic block copolymer (X) is 10 parts by mass. A content of 10 parts by mass or more of the aromatic block copolymer (X) further improves the adhesive strength of the foam layer, resulting in the adhesive tape of this embodiment having superior shock absorption. A more preferred lower limit for the content of the aromatic block copolymer (X) is 15 parts by mass, an even more preferred lower limit is 20 parts by mass, and an even more preferred lower limit is 25 parts by mass. Examples of the content of the aromatic block copolymer (X) include 10 parts by mass or more and 60 parts by mass or less, 15 parts by mass or more and 55 parts by mass or less, 20 parts by mass or more and 50 parts by mass or less, 25 parts by mass or more and 45 parts by mass or less, etc.

[0076] The above-mentioned olefin-based elastomer is an elastomer composed of olefin compounds. In the above-mentioned olefin-based elastomer, the crystalline olefin polymer acts as a hard segment portion, and the amorphous olefin copolymer acts as a soft segment portion, thereby imparting rubber elasticity to the adhesive layer.

[0077] Examples of the crystalline olefin polymers (compounds constituting the hard segment) mentioned above include ethylene and propylene.

[0078] Examples of the amorphous olefin copolymer (compound constituting the soft segment) mentioned above include isobutylene.

[0079] Examples of the olefin-based elastomers mentioned above include Tuffmer (manufactured by Mitsui Chemicals, Inc.).

[0080] The above-mentioned urethane-based elastomer is an elastomer composed of a urethane compound obtained by the reaction of a polyol compound and a polyisocyanate compound. In the above-mentioned urethane-based elastomer, the portion containing a large amount of the above-mentioned urethane bonds acts as a hard segment portion, and the portion containing a large amount of the above-mentioned polyol-derived structure acts as a soft segment portion, thereby imparting rubber elasticity to the adhesive layer.

[0081] Examples of the polyol compounds mentioned above include polyester polyols (polycondensates of divalent alcohols and divalent basic acids such as adipic acid, azelaic acid, and sepatic acid), polyether polyols (obtained by addition polymerization of ethylene oxide, tetrahydrofuran, etc.), polyacrylate polyols, polycarbonate polyols, polyolefin polyols, polybutadiene polyols or their hydrogenated products, polyisoprene polyols or their hydrogenated products, phenolic polyols, epoxy polyols, caprolactone polyols, and polysulfone polyols. Copolymer polyols such as polyester-polyether polyols can also be cited as polyol compounds.

[0082] Examples of the polyisocyanate compounds mentioned above include diphenylmethane diisocyanate, tolylene diisocyanate, naphthalene-1,5-diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, norbornane diisocyanate, transcyclohexane-1,4-diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, cyclohexane diisocyanate, bis(isocyanate-methyl)cyclohexane, and dicyclohexylmethane diisocyanate. Alternatively, modified forms of the polyisocyanate compounds mentioned above may be used as the polyisocyanate compounds. Examples of modified polyisocyanate compounds include the bilate modified polyisocyanate compounds mentioned above, the isocyanurate modified polyisocyanate compounds mentioned above, adduct compounds obtained by reacting the polyisocyanate compounds mentioned above with glycerin, trimethylolpropane, or polyols obtained by addition polymerization of these with alkylene oxides such as propylene oxide and ethylene oxide, and polymethylene polyphenyl polyisocyanate, also known as polymeric MDI.

[0083] Examples of the above-mentioned urethane-based elastomers include Elastran (manufactured by BASF).

[0084] The preferred upper limit of the elastomer content per 100 parts by mass of the acrylic copolymer is 60 parts by mass. A content of 60 parts by mass or less of the elastomer further improves the adhesive strength of the foam layer. A more preferred upper limit of the elastomer content is 55 parts by mass, an even more preferred upper limit is 50 parts by mass, and an even more preferred upper limit is 45 parts by mass. Furthermore, the preferred lower limit of the elastomer content is 10 parts by mass. A content of 10 parts by mass or more of the elastomer further improves the adhesive strength of the foam layer, resulting in the adhesive tape of this embodiment having superior shock absorption. A more preferred lower limit of the elastomer content is 15 parts by mass, an even more preferred lower limit is 20 parts by mass, and an even more preferred lower limit is 25 parts by mass. Examples of elastomer content include 10 parts by mass or more and 60 parts by mass or less, 15 parts by mass or more and 55 parts by mass or less, 20 parts by mass or more and 50 parts by mass or less, and 25 parts by mass or more and 45 parts by mass or less.

[0085] The foam layer may contain a tackifying resin. The tackiness of the foam layer is further improved by the inclusion of a tackifying resin. However, the foam layer does not necessarily have to contain a tackifying resin; from the viewpoint of further improving the shock absorption of the adhesive tape, it is preferable that it does not contain a tackifying resin.

[0086] Examples of the tackifying resins mentioned above include rosin resins, rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5-C9 copolymer petroleum resins. Among these, rosin resins, terpene resins, or terpene phenol resins are preferred from the viewpoint of compatibility with the acrylic copolymers mentioned above, and among these, rosin resins having hydroxyl groups, terpene resins having hydroxyl groups, or terpene phenol resins are more preferred. These tackifying resins may be used alone or in combination of two or more types.

[0087] Examples of rosin-based resins having the hydroxyl group mentioned above include Pencel D-135 and Super Ester A-75 (both manufactured by Arakawa Chemical Industries, Ltd.). Examples of terpene-based resins having the hydroxyl group mentioned above include YS Polystar G150 and YS Polystar T160 (both manufactured by Yasuhara Chemical Co., Ltd.).

[0088] If the foam layer contains the tackifying resin, it is preferable that the tackifying resin contains bio-derived carbon. By including a tackifying resin containing bio-derived carbon, the content of bio-derived carbon in the adhesive layer described later can be increased, and the environmental impact of the resulting adhesive tape can be further reduced. Specific examples of tackifying resins containing bio-derived carbon include KE-100, KE-359, KE-604, KR-140, A-75, and 803L (all manufactured by Arakawa Chemical Industries, Ltd.).

[0089] If the foam layer contains the tackifying resin, it is preferable that the tackifying resin has a softening point of 70°C or higher and 170°C or lower. By including a tackifying resin with a softening point of 70°C or higher, the foam layer's retention is further improved. By including a tackifying resin with a softening point of 170°C or lower, the wettability of the interface of the foam layer is improved, and therefore the adhesive strength of the adhesive tape of this embodiment is further improved. It is more preferable that the tackifying resin includes a tackifying resin with a softening point of 100°C or higher and 160°C or lower, even more preferable that it includes a tackifying resin with a softening point of 120°C or higher and 150°C or lower, and even more preferable that it includes a tackifying resin with a softening point of 130°C or higher and 140°C or lower. In this specification, "softening point of tackifying resin" means the softening temperature measured by JIS K2207 (ring-sphere method).

[0090] If the foam layer contains the tackifying resin, it is preferable that the tackifying resin has a hydroxyl value of 25 mg KOH / g or more. By including the tackifying resin with a hydroxyl value of 25 mg KOH / g or more, the wettability of the interface of the foam layer is improved, and the adhesive tape of this embodiment has improved adhesive strength. It is more preferable that the tackifying resin includes a tackifying resin with a hydroxyl value of 30 mg KOH / g or more, and even more preferable that it includes a tackifying resin with a hydroxyl value of 35 mg KOH / g or more. There is no particular upper limit to the hydroxyl value of the tackifying resin, but from the viewpoint of compatibility with the elastomer, the practical upper limit is 50 mg KOH / g. Examples of the hydroxyl value of the tackifying resin include 25 mg KOH / g or more and 50 mg KOH / g or less, 30 mg KOH / g or more and 50 mg KOH / g or less, 35 mg KOH / g or more and 50 mg KOH / g or less, etc. Furthermore, within this specification, the hydroxyl value of the tackifying resin can be measured by JIS K1557 (phthalic anhydride method).

[0091] When the foam layer contains the tackifying resin, the preferred upper limit of the tackifying resin content is 50 parts by mass per 100 parts by mass of the acrylic copolymer. Having the tackifying resin content within this range results in superior adhesive strength for the adhesive tape of this embodiment. A more preferred upper limit for the tackifying resin content is 40 parts by mass, an even more preferred upper limit is 30 parts by mass, an even more preferred upper limit is 20 parts by mass, and a particularly preferred upper limit is 10 parts by mass. Furthermore, when the foam layer contains the tackifying resin, a preferred lower limit for the tackifying resin content is 0.1 parts by mass, and a more preferred lower limit is 1.0 part by mass. Note that the foam layer does not necessarily have to contain the tackifying resin. Examples of the content of the tackifying resin include 0 parts by mass or more and 50 parts by mass or less, 0.1 parts by mass or more and 50 parts by mass or less, 1.0 part by mass or more and 40 parts by mass or less, 1.0 part by mass or more and 30 parts by mass or less, 1.0 part by mass or more and 20 parts by mass or less, 1.0 part by mass or more and 10 parts by mass or less, and so on.

[0092] The above adhesive resin composition preferably contains a crosslinking agent. The inclusion of a crosslinking agent in the adhesive resin composition results in a crosslinked structure in the foam layer, thus providing the adhesive tape of this embodiment with superior holding power. From the viewpoint of storage stability, the crosslinking agent may be added to the adhesive resin composition immediately before forming the foam layer.

[0093] Examples of the crosslinking agents include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred from the viewpoint of further improving the adhesion of the foam layer to the substrate.

[0094] The preferred lower limit of the crosslinking agent content per 100 parts by mass of the acrylic copolymer is 0.05 parts by mass, and the preferred upper limit is 5.0 parts by mass. By having the crosslinking agent content within this range, the adhesive tape of this embodiment exhibits superior adhesive strength. A more preferred lower limit for the crosslinking agent content is 0.10 parts by mass, a more preferred upper limit is 3.0 parts by mass, an even more preferred lower limit is 0.15 parts by mass, an even more preferred upper limit is 2.0 parts by mass, an even more preferred upper limit is 1.0 part by mass, and a particularly preferred upper limit is 0.5 parts by mass. Examples of crosslinking agent content include 0.05 parts by mass or more and 5.0 parts by mass or less, 0.10 parts by mass or more and 3.0 parts by mass or less, 0.15 parts by mass or more and 2.0 parts by mass or less, 0.15 parts by mass or more and 1.0 part by mass or less, 0.15 parts by mass or more and 0.5 parts by mass or less.

[0095] The foam layer is preferably colored. Coloring the foam layer provides light-shielding properties, allowing the adhesive tape of this embodiment to be suitably used by being attached to internal components of electrical and electronic equipment.

[0096] If the foam layer is colored, it contains a coloring agent. Examples of coloring agents include pigments and dyes. From the viewpoint of heat resistance in particular, examples of pigments include carbon black, aniline black, and titanium dioxide. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

[0097] The preferred lower limit of the coloring agent content per 100 parts by mass of the acrylic copolymer is 0.2 parts by mass, and the preferred upper limit is 5.0 parts by mass. A coloring agent content within this range results in more sufficient adhesive strength for the resulting adhesive tape. A more preferred lower limit for the coloring agent content is 0.5 parts by mass, a more preferred upper limit is 4.0 parts by mass, an even more preferred lower limit is 0.8 parts by mass, and an even more preferred upper limit is 3.5 parts by mass. Examples of suitable coloring agent content ranges include 0.2 parts by mass to 5.0 parts by mass, 0.5 parts by mass to 4.0 parts by mass, and 0.8 parts by mass to 3.5 parts by mass.

[0098] The foam layer described above may contain conventionally known additives such as antioxidants, organic fillers, and inorganic fillers, as needed.

[0099] The preferred lower limit for the bio-derived carbon content in the foam layer is 15%. A bio-derived carbon content of 15% or more in the foam layer makes the adhesive tape of this embodiment superior in terms of conserving petroleum resources and reducing carbon dioxide emissions, thus reducing environmental impact. A more preferred lower limit for the bio-derived carbon content in the foam layer is 18%, and an even more preferred lower limit is 20%. The upper limit for the bio-derived carbon content in the foam layer is not particularly limited and may be 100%. Examples of bio-derived carbon content in the foam layer include 15% to 100%, 18% to 100%, and 20% to 100%. Furthermore, while bio-derived carbon contains a certain percentage of radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the "bio-derived carbon content" in this specification can be calculated by measuring the concentration of C-14 contained in the foam layer. Specifically, it can be measured in accordance with ASTM D6866-22, a standard widely used in the bioplastics industry.

[0100] Preferably, the foam layer has a structure derived from a crosslinking agent. Because the foam layer has a structure derived from a crosslinking agent, the adhesive tape of this embodiment has superior holding properties.

[0101] The foam layer may have an open-cell structure or an closed-cell structure, but it is preferable to have an closed-cell structure. Having a closed-cell structure in the foam layer increases its strength, and the adhesive tape of this embodiment can suppress cohesive failure, thus improving its adhesive strength. In this specification, when observing a cross-section of the tape randomly, a structure where the air layers between the cells are partially continuous is defined as an open-cell structure, and a structure where the air layers between the cells are not continuous is defined as an closed-cell structure. The cell structure can be confirmed, for example, by observing it at a magnification of 150 to 200 times using an optical microscope (e.g., Keyence's "VHX-6000").

[0102] The apparent density of the above foam layer preferably has a lower limit of 0.59 g / cm ３ and a preferred upper limit of 1.15 g / cm ３ . When the apparent density of the above foam layer is 0.59 g / cm ３ or more, the strength of the above foam layer increases, so that the cohesive failure of the foam layer can be further suppressed, and thus the adhesive tape of the present embodiment has better adhesive strength. When the apparent density of the above foam layer is 1.15 g / cm ３ or less, the above foam layer can have appropriate flexibility, the stress relaxation property of the adhesive tape is further improved, and it has better shock absorption property. A more preferred lower limit of the apparent density of the above foam layer is 0.65 g / cm ３ , a more preferred upper limit is 1.12 g / cm ３ , a further preferred lower limit is 0.70 g / cm ３ , a further preferred upper limit is 1.10 g / cm ３ , an even more preferred lower limit is 0.75 g / cm ３ , an even more preferred upper limit is 1.00 g / cm ３ , a particularly preferred lower limit is 0.80 g / cm ３ , a very preferred upper limit is 0.90 g / cm ３ . Note that, as the apparent density of the above foam layer, for example, it can be 0.59 g / cm ３ or more and 1.15 g / cm ３ or less, 0.65 g / cm ３ or more and 1.12 g / cm ３ or less, 0.70 g / cm ３ or more and 1.10 g / cm ３ or less, 0.75 g / cm ３ or more and 1.00 g / cm ３ or less, 0.80 g / cm ３ or more and 0.90 g / cm ３ or less, etc. can be mentioned. Further, as a method for measuring the apparent density of the above foam layer, for example, it can be measured using an electronic specific gravity meter (for example, manufactured by Mirage Co., Ltd., "ED120T", etc.) in accordance with JIS K 7222, etc.

[0103] The thickness of the foam layer described above has a preferred lower limit of 50 μm and a preferred upper limit of 500 μm. When the thickness of the foam layer is 50 μm or more, the adhesive strength of the foam layer is further improved, and the adhesive tape of this embodiment has improved adhesive strength. When the thickness of the foam layer is 500 μm or less, the foam layer can have appropriate flexibility, the stress relaxation properties of the adhesive tape are further improved, and it has better shock absorption properties. A more preferred lower limit for the thickness of the foam layer is 80 μm, a more preferred upper limit is 400 μm, an even more preferred lower limit is 100 μm, an even more preferred upper limit is 300 μm, an even more preferred upper limit is 250 μm, and a particularly preferred upper limit is 200 μm. Examples of the thickness of the foam layer include 50 μm to 500 μm, 80 μm to 400 μm, 100 μm to 300 μm, 100 μm to 250 μm, and 100 μm to 200 μm. In this specification, the thickness can be measured using a dial thickness gauge (for example, Mitutoyo's "ABS Digimatic Indicator").

[0104] The preferred lower limit for the gel fraction of the foam layer is 10% by mass, and the preferred upper limit is 60% by mass. A gel fraction of 10% by mass or more in the foam layer improves the cohesive force of the foam layer, thereby improving the adhesive strength and retention of the adhesive tape of this embodiment. A gel fraction of 60% by mass or less in the foam layer improves the flexibility of the foam layer, thereby improving the conformability of the adhesive tape of this embodiment to rough surfaces. A more preferred lower limit for the gel fraction of the adhesive layer is 20% by mass, and a more preferred upper limit is 50% by mass. Examples of gel fractions for the foam layer include 10% by mass or more and 60% by mass or less, and 20% by mass or more and 50% by mass or less. The gel fraction of the foam layer is measured by the following method. Specifically, first, a test specimen is prepared by cutting the adhesive tape having the foam layer described above into a rectangular shape with a width of 20 mm and a length of 40 mm. The test specimen is then immersed in ethyl acetate at 23°C for 24 hours, removed from the ethyl acetate, and dried at 110°C for 1 hour. The mass of the dried test specimen is measured, and the gel fraction is calculated using the following formula (I). Note that the test specimen does not have a release film laminated on it to protect the foam layer. Furthermore, if the adhesive tape in this embodiment is a non-support type tape without a base material, the measurement is performed using a test specimen obtained by attaching it to a base material and then cutting it, or W in the following formula (I) is calculated without using a base material. ０ Calculate by setting to 0. Gel fraction (mass%) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (I) (W ０ : Mass of the substrate layer, W １ : Mass of the test specimen before immersion, W ２ (Mass of the test specimen after immersion and drying)

[0105] The average major diameter of the bubbles in the foam layer described above has a preferred lower limit of 10 μm and a preferred upper limit of 80 μm. When the average major diameter of the bubbles in the foam layer is 10 μm or more, the foam layer can have appropriate flexibility, which further improves the stress relaxation properties of the adhesive tape and results in better shock absorption. When the average major diameter of the bubbles in the foam layer is 80 μm or less, the strength of the foam layer is increased, which further suppresses cohesive failure of the foam layer, thus improving the adhesive strength of the adhesive tape in this embodiment. A more preferred lower limit for the average major diameter of the bubbles in the foam layer is 15 μm, a more preferred upper limit is 70 μm, an even more preferred lower limit is 20 μm, an even more preferred upper limit is 65 μm, an even more preferred upper limit is 60 μm, a particularly preferred upper limit is 55 μm, and a very preferred upper limit is 50 μm. The average major diameter of the bubbles in the adhesive layer can be, for example, 10 μm to 80 μm, 15 μm to 70 μm, 20 μm to 65 μm, 20 μm to 60 μm, 20 μm to 55 μm, 20 μm to 50 μm, etc.

[0106] The average minor diameter of the bubbles in the foam layer has a preferred lower limit of 10 μm and a preferred upper limit of 75 μm. When the average minor diameter of the bubbles in the foam layer is 10 μm or more, the foam layer can have appropriate flexibility, which further improves the stress relaxation properties of the adhesive tape and results in better shock absorption. When the average minor diameter of the bubbles in the foam layer is 75 μm or less, the strength of the foam layer is increased, which further suppresses cohesive failure of the foam layer, thus improving the adhesive strength of the adhesive tape in this embodiment. A more preferred lower limit for the average minor diameter of the bubbles in the foam layer is 15 μm, a more preferred upper limit is 70 μm, an even more preferred lower limit is 20 μm, an even more preferred upper limit is 65 μm, an even more preferred upper limit is 60 μm, a particularly preferred upper limit is 55 μm, and a very preferred upper limit is 50 μm. The average short diameter of the bubbles in the adhesive layer can be, for example, 10 μm to 75 μm, 15 μm to 70 μm, 20 μm to 65 μm, 20 μm to 60 μm, 20 μm to 55 μm, 20 μm to 50 μm, etc.

[0107] The aspect ratio of the bubbles in the foam layer described above has a preferred lower limit of 1.00 and a preferred upper limit of 3.50. When the aspect ratio of the bubbles in the foam layer described above is 1.00 or higher, the structure of the bubbles in the foam layer becomes flattened, so the foam layer has appropriate flexibility. As a result, the stress relaxation properties of the adhesive tape are further improved, and it has better shock absorption properties. When the aspect ratio of the bubbles in the foam layer described above is 3.50 or lower, the strength of the foam layer is increased, which further suppresses cohesive failure of the foam layer, so the adhesive strength of the adhesive tape of this embodiment is further improved. A more preferred lower limit for the aspect ratio of the bubbles in the foam layer described above is 1.25, a more preferred upper limit is 3.00, an even more preferred lower limit is 1.50, and an even more preferred upper limit is 2.50. Examples of aspect ratios for bubbles in the foam layer include 1.00 to 3.50, 1.25 to 3.00, 1.50 to 2.50, etc. In this specification, "aspect ratio of bubbles" means the value obtained by dividing the average major diameter of the bubbles by the average minor diameter of the bubbles (average major diameter of bubbles / average minor diameter of bubbles).

[0108] The average major axis, average minor axis, and aspect ratio of the bubbles in the foam layer can be determined, for example, as follows: Using a razor (Feather Corporation), the foam layer is sliced ​​with a plane parallel to the MD (Machine Direction) direction and the thickness direction to obtain an MD cut sample. The obtained MD cut sample is photographed using a digital microscope (for example, Keyence Corporation's "VHX-6000") under conditions such as a magnification of 200x and a measurement screen size of 1.8 mm × 1.3 mm. In the obtained photographed image, the bubble with the largest major axis and the bubble with the second largest major axis are selected, and the major and minor axes of these bubbles are measured to calculate the aspect ratio. Perform this operation for three captured images. The average of the major axes of the six bubbles is taken as the average major axis of the bubbles in the adhesive layer, the average of the minor axes of the six bubbles is taken as the average minor axis of the bubbles in the adhesive layer, and the average of the aspect ratios of the six bubbles is taken as the aspect ratio of the bubbles in the foam layer. If the above MD direction is unknown, slice the foam layer with a plane parallel to the thickness direction to obtain a cut sample. Slice the foam so that the cutting direction is shifted by 30° from the direction from which the previous cut sample was cut, and measure the aspect ratio in the same manner as above. Repeat the above measurement until returning to the cutting direction of the first measurement. The average of the major axes of the twelve measured bubbles is taken as the average major axis of the bubbles in the foam layer, the average of the minor axes of the twelve bubbles is taken as the average minor axis of the bubbles in the foam layer, and the average of the aspect ratios of the twelve bubbles is taken as the aspect ratio of the bubbles in the foam layer.

[0109] Preferably, the average major diameter of the bubbles in the foam layer is 0.80 times or less the thickness of the foam layer. By having an average major diameter of bubbles 0.80 times or less the thickness of the foam layer, the strength of the foam layer is increased, which further suppresses cohesive failure of the foam layer, thus improving the adhesive strength of the adhesive tape in this embodiment. More preferably, the average major diameter of the bubbles is 0.70 times or less the thickness of the foam layer, even more preferably 0.60 times or less, and even more preferably 0.30 times or less. Furthermore, it is preferable that the average major diameter of the bubbles is 0.05 times or more the thickness of the foam layer. By having an average major diameter of bubbles 0.05 times or more the thickness of the foam layer, the foam layer has appropriate flexibility, which further improves the stress relaxation properties of the adhesive tape, resulting in superior shock absorption. More preferably, the average major diameter of the bubbles is 0.10 times or more the thickness of the foam layer. That is, it is preferable that the average major diameter of the bubbles is 0.05 times or more and 0.80 times or less the thickness of the foam layer, more preferably 0.10 times or more and 0.70 times or less, even more preferably 0.10 times or more and 0.60 times or less, and even more preferably 0.10 times or more and 0.30 times or less.

[0110] Preferably, the foam layer has a structure in which no air bubbles are exposed on the surface in the thickness direction. Because the foam layer has no air bubbles exposed on the surface in the thickness direction, the area of ​​the adhesive interface between the foam layer and the adherend is increased, and the adhesive strength of the adhesive tape of this embodiment is further improved. A method for creating a structure in which no air bubbles are exposed on the surface in the thickness direction of the foam layer is, for example, a method of increasing the weight of the foam particles to suppress floating to the liquid surface during solution coating.

[0111] The adhesive tape of this embodiment may have other layers besides the foam layer as needed, but from the viewpoint of ensuring shock absorption, it is preferable that the adhesive tape of this embodiment has only the foam layer. When the adhesive tape of this embodiment has only the foam layer, it can have appropriate flexibility and better shock absorption. In addition, since the adhesive tape of this embodiment is thinner, it can be used more suitably for fixing electrical and electronic components.

[0112] From the viewpoint of ensuring reworkability, the adhesive tape of this embodiment preferably has a base material, and the foam layer is provided on at least one side of the base material. Since the foam adhesive layer has strong adhesive properties, the adhesion between the foam layer and the base material in the adhesive tape having the foam layer and the base material is excellent, resulting in excellent adhesive strength even with the presence of a base material. When the adhesive tape of this embodiment has a base material, it may be a single-sided adhesive tape having the foam layer on one side of the base material, or it may be a double-sided adhesive tape having adhesive layers on both sides of the base material. Furthermore, when the adhesive tape of this embodiment is a double-sided adhesive tape, at least one adhesive layer may be the foam layer, and the other adhesive layer may be any adhesive layer as long as it does not impair the effects of the present invention.

[0113] Examples of substrates used for the above-mentioned substrate include films, nonwoven fabrics, and foamed substrates. In particular, from the viewpoint of obtaining an adhesive tape with high flexibility and thus having superior conformability in the adhesive tape of this embodiment, it is preferable that the above-mentioned substrate includes a foamed substrate.

[0114] From the viewpoint of increasing the overall bio-derived carbon content of the adhesive tape, a substrate made of bio-derived material is preferred for the substrate used in the above-mentioned substrate. Examples of the above-mentioned bio-derived materials include polyesters (PES) such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polylactic acid (PLA), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polybutylene succinate (PBS), as well as polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetylcellulose (TAC), cellulose, and polyamide (PA), all of which are derived from plants.

[0115] Furthermore, from the perspective of reducing environmental impact by decreasing the use of new petroleum resources and suppressing carbon dioxide emissions, base materials made from recycled resources may be used. Methods for recycling resources include, for example, recovering waste from packaging containers, home appliances, automobiles, construction materials, food, etc., or waste generated in the manufacturing process, and using the extracted materials again as raw materials by washing, decontamination, or decomposition by heating or fermentation. Examples of base materials using the above recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., using recovered plastics that have been re-resinated as raw materials. Alternatively, the recovered waste may be burned and used as thermal energy for the manufacture of base materials and their raw materials, or the oils and fats contained in the recovered waste may be mixed with petroleum, fractionally distilled, and refined to be used as raw materials.

[0116] The foamed substrate used in the above-mentioned substrate is preferably a foamed substrate containing at least one selected from the group consisting of PE, PP, and PU, and a foamed substrate containing PE is more preferable from the viewpoint of achieving a high degree of both flexibility and strength. Examples of components of the foamed substrate containing PE include PE made from sugarcane.

[0117] As a method for producing the foamed substrate described above, it is preferable to prepare a foamed resin composition containing a PE resin containing PE made from sugarcane and a foaming agent, and to foam the foaming agent when extruding the foamed resin composition into a sheet using an extruder, and to crosslink the obtained polyolefin foam as needed.

[0118] From the viewpoint of substrate strength, the substrate used for the above-mentioned substrate is preferably a film containing PES or a film containing PA. Furthermore, from the viewpoint of heat resistance and oil resistance, a film containing PA is preferred. Examples of PA include nylon 11, nylon 1010, nylon 610, nylon 510, nylon 410, etc., which are made from castor oil, and nylon 56, etc., which are made from cellulose.

[0119] The preferred lower limit for the thickness of the above-mentioned substrate is 3.5 μm, and the preferred upper limit is 1000 μm. By having the thickness of the above-mentioned substrate within this range, it is possible to exhibit high flexibility, allowing it to adhere closely to the shape of the adherend while maintaining high impact resistance. A more preferred lower limit for the thickness of the above-mentioned substrate is 5.0 μm, a more preferred upper limit is 500 μm, an even more preferred lower limit is 6.5 μm, an even more preferred upper limit is 300 μm, an even more preferred lower limit is 10 μm, an even more preferred upper limit is 200 μm, a particularly preferred lower limit is 30 μm, and a particularly preferred upper limit is 100 μm. Examples of the above-mentioned substrate thickness include 3.5 μm to 1000 μm, 5.0 μm to 500 μm, 6.5 μm to 300 μm, 10 μm to 200 μm, 30 μm to 100 μm, etc.

[0120] From the viewpoint of reinforcing adhesive strength and interlayer strength, it is preferable that the adhesive tape of this embodiment has an adhesive layer on at least one side of the foam layer. By having an adhesive layer on at least one side of the foam layer of the adhesive tape of this embodiment, the interlayer strength of the resulting adhesive tape is further improved, and therefore the adhesive tape of this embodiment has superior adhesive strength. The adhesive tape of this embodiment may have an adhesive layer on one side of the foam layer, or it may have an adhesive layer on both sides of the foam layer.

[0121] The adhesive contained in the adhesive layer described above is not particularly limited as long as it does not impair the effects of the present invention, and conventionally known adhesives can be used. Specifically, examples include acrylic adhesives, urethane adhesives, rubber adhesives, silicone adhesives, etc. Among these, acrylic adhesives are preferred from the viewpoint of the design range of the adhesive and the wide selectivity of the adherend, and acrylic adhesives containing the acrylic copolymer described above in the foam layer are more preferred from the viewpoint of excellent adhesive strength.

[0122] The thickness of the adhesive layer described above has a preferred lower limit of 5 μm and a preferred upper limit of 100 μm. A thickness of 5 μm or more in the adhesive layer makes it less likely to break when the foam is stretched. A thickness of 100 μm or less in the adhesive layer suppresses a decrease in conformability to the adherend. A more preferred lower limit for the thickness of the adhesive layer is 10 μm, a more preferred upper limit is 90 μm, an even more preferred lower limit is 15 μm, and an even more preferred upper limit is 80 μm. Examples of adhesive layer thicknesses include 5 μm to 100 μm, 10 μm to 90 μm, 15 μm to 80 μm, etc.

[0123] The method for manufacturing the adhesive tape of this embodiment is not particularly limited, and conventionally known methods can be used. For example, the method for manufacturing an adhesive tape consisting only of the foam layer is as follows. First, a solvent is added to an acrylic copolymer, a tackifying resin, etc., to prepare a solution of an adhesive resin composition. Next, the prepared solution of the adhesive resin composition is applied to the release surface of a release film, and the solvent in the solution is dried and removed to form a foam layer. Then, by placing the release surface of a release film on top of the formed foam layer, an adhesive tape can be obtained in which the surface of the foam layer is covered with a release film.

[0124] Furthermore, the method for manufacturing an adhesive tape having the above-mentioned base material and having the above-mentioned foam layer on at least one side of the base material is as follows. That is, a foam layer formed in the same manner as the method for manufacturing an adhesive tape consisting only of the above-mentioned foam layer is bonded to the base material, pressed together using a rubber roller to create a laminated and integrated structure, and then cured in a 40°C environment for 72 hours to obtain an adhesive tape having a foam layer on one side of the base material. Alternatively, an adhesive resin composition may be directly coated onto the base material, dried to form a foam layer, and then the release treatment surface of a release film may be placed on top of the formed foam layer. Alternatively, an adhesive tape having adhesive layers on both sides of the base material can be obtained by placing an arbitrary adhesive layer prepared on the other side of the base material and then laminating and integrating it.

[0125] Furthermore, the method for manufacturing an adhesive tape having the adhesive layer on at least one side of the foam layer is as follows. Specifically, after overlapping a foam layer formed in the same manner as the method for manufacturing an adhesive tape consisting only of the foam layer described above with an arbitrary adhesive layer, pressing them together using a rubber roller to create a laminated and integrated structure, and then curing it in a 40°C environment for 72 hours, an adhesive tape having the adhesive layer on one side of the foam layer can be manufactured. In addition, by performing the same operation on the other side of the foam layer in the manufactured adhesive tape having the adhesive layer on one side of the foam layer, an adhesive tape having the adhesive layer on both sides of the foam layer can be manufactured.

[0126] Furthermore, adhesive tapes having the adhesive layer on at least one side of the foam layer can also be manufactured using a multilayer extrusion extruder. Specifically, the composition forming the foam layer and the composition forming the adhesive layer are supplied to a multilayer extrusion extruder, and after melt-mixing, a sheet-like adhesive tape base roll in which the foam layer and adhesive layer are laminated is extruded.

[0127] The total thickness of the adhesive tape in this embodiment has a preferred lower limit of 50 μm and a preferred upper limit of 500 μm. A total thickness of 50 μm or more ensures sufficient adhesive strength and stress relaxation of the resulting tape. A total thickness of 500 μm or less ensures sufficient adhesion and fixation, as well as greater flexibility. A more preferred lower limit for the total thickness of the adhesive tape in this embodiment is 80 μm, a more preferred upper limit is 400 μm, an even more preferred lower limit is 100 μm, and an even more preferred upper limit is 300 μm. Examples of the overall thickness of the adhesive tape in this embodiment include 50 μm to 500 μm, 80 μm to 400 μm, 100 μm to 300 μm, etc. Furthermore, in this specification, "total thickness of the adhesive tape" does not include the thickness of the separator, such as a release film, that protects the outermost adhesive layer of the adhesive tape.

[0128] The adhesive tape of this embodiment has a preferred upper limit of 70% for light transmittance at a wavelength of 550 nm. By having a light transmittance of 70% or less at a wavelength of 550 nm, the adhesive tape of this embodiment can be more suitably used for fixing internal components of electrical and electronic equipment. A more preferred upper limit for the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm is 60%, an even more preferred upper limit is 50%, an even more preferred upper limit is 40%, a particularly preferred upper limit is 30%, and a very preferred upper limit is 10%. There is no particular lower limit for the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm, with 0% being the most preferred. Examples of the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm include 0% to 70%, 0% to 60%, 0% to 50%, 0% to 40%, 0% to 30%, and 0% to 10%. Furthermore, the transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm can be measured using a spectrophotometer (such as the "V-670" manufactured by JASCO Corporation).

[0129] Methods for adjusting the transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm include, for example, adding a pigment to the adhesive resin composition or adding a filler.

[0130] The adhesive tape of this embodiment has a preferred lower limit of 180° peel force against SUS at 23°C of 10 N / 25 mm. Having a 180° peel force against SUS of the adhesive tape of this embodiment of 10 N / 25 mm or higher at 23°C results in superior adhesive strength, allowing for problem-free use even in high-temperature environments. A more preferred lower limit for the 180° peel force against SUS at 23°C of the adhesive tape of this embodiment is 12 N / 25 mm, an even more preferred lower limit is 15 N / 25 mm, and an even more preferred lower limit is 20 N / 25 mm. There is no particular upper limit for the 180° peel force against SUS of the foam layer at 23°C, but approximately 80 N / 25 mm is a practical upper limit. A more preferred upper limit for the peel force is 50 N / 25 mm. Furthermore, examples of the 180° peel force of the foam layer against SUS at 23°C include 10N / 25mm to 80N / 25mm, 12N / 25mm to 80N / 25mm, 15N / 25mm to 50N / 25mm, 20N / 25mm to 50N / 25mm, etc. While there is no specific upper limit to the 180° peel force against SUS at 23°C, approximately 50N / 25mm is a practical upper limit. Examples of the 180° peel force of the adhesive tape of this embodiment against SUS at 23°C include 10N / 25mm to 50N / 25mm, 12N / 25mm to 50N / 25mm, 15N / 25mm to 50N / 25mm, etc. The 180° peel force of the adhesive tape of this embodiment against SUS at 23°C is measured by the following method. Specifically, first, one side of the obtained adhesive tape (the side not to be measured) was backed with a 23 μm thick polyethylene terephthalate film, and then cut to a width of 25 mm x length of 75 mm to prepare a test piece. Next, the obtained test piece was attached to a SUS304 plate (a SUS304 plate that had been washed with ethanol and then wiped dry), and pressed down by passing a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Finally, it was cured at 23°C and 50% RH for 20 minutes to prepare a test sample.The obtained test samples can be measured by leaving them standing for 20 minutes in an environment of 23°C and 50% RH, and then peeling the adhesive tape from the SUS304 plate in accordance with JIS Z 0237:2009, under conditions of 23°C and 50% RH, a tensile speed of 300 mm / min, and a peeling angle of 180°.

[0131] Methods for adjusting the 180° peel force of the adhesive tape of this embodiment against SUS at 23°C include, for example, changing the composition of the acrylic copolymer (for example, increasing the content (mass%) of constituent units derived from the polar functional group-containing monomer in the acrylic copolymer), adding a tackifying resin to the adhesive resin composition, adjusting the thickness of the adhesive layer, and adjusting the amount of crosslinking agent.

[0132] The adhesive tape of this embodiment is not particularly limited in its use, but because it has excellent shock absorption properties, it can be suitably used for fixing parts, and is particularly suitable for fixing internal components of electrical and electronic equipment. Examples of electrical and electronic equipment include televisions, monitors, portable electronic devices, and in-vehicle electronic devices. When using the adhesive tape of this embodiment to fix parts, a primer treatment may be performed by applying a primer (undercoat) to the surface of the parts to be bonded, and then the parts may be bonded and fixed with the adhesive tape of this embodiment. The primer is not particularly limited, and conventionally known primers can be used, such as epoxy primers, urethane primers, and acrylic primers. Furthermore, because the adhesive tape of this embodiment has excellent bending resistance, it can be suitably used for fixing display devices such as televisions and monitors, specifically for fixing the surface cover panel of the display device to a housing with uneven surfaces.

[0133] An electronic device including the adhesive tape of this embodiment is also one of these embodiments. The electronic device of this embodiment is not particularly limited as long as it includes the adhesive tape, but examples include electronic devices in which electronic components are bonded and fixed together with the adhesive tape, and specifically, for example, a display device in which a cover panel and a housing having irregularities are bonded and fixed together with the adhesive tape.

[0134] According to the present invention, it is possible to provide an adhesive tape that can achieve both excellent bending resistance and excellent shock absorption. Furthermore, according to the present invention, it is possible to provide an electronic device that includes the adhesive tape.

[0135] This is a schematic diagram illustrating the method for evaluating bending resistance. This is a schematic diagram of a sample used for evaluating impact absorption. This is a schematic diagram illustrating the method for evaluating impact absorption.

[0136] 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. The materials used in the examples and comparative examples are as follows.

[0137] <N-hexyl acrylic acid containing bio-derived carbon> Linoleic acid derived from castor oil was converted to linoleic acid hydroperoxide using lipoxygenase, and then a mixture containing n-hexylaldehyde was obtained using isomerase. By distillation of the obtained mixture, n-hexylaldehyde containing bio-derived carbon was obtained. Furthermore, by hydrogenation of the obtained n-hexylaldehyde containing bio-derived carbon, n-hexyl alcohol containing bio-derived carbon was obtained. By esterifying the obtained n-hexyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), n-hexyl acrylic acid containing bio-derived carbon was prepared.

[0138] <n-heptyl acrylic acid containing bio-derived carbon> Ricinoleic acid derived from castor oil was cracked to obtain a mixture containing undecylenic acid and n-heptyl alcohol. Then, undecylenic acid was separated from the obtained mixture by distillation to obtain n-heptyl alcohol containing bio-derived carbon. By esterifying the obtained n-heptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), n-heptyl acrylic acid containing bio-derived carbon was prepared.

[0139] <1-Methylheptyl Acrylate Containing Bio-Derived Carbon> Ricinoleic acid derived from castor oil was dissolved in alkali to obtain a mixture containing sebacic acid and 1-methylheptyl alcohol. Next, sebacic acid was separated from the obtained mixture by distillation to obtain 1-methylheptyl alcohol containing bio-derived carbon. By esterifying the obtained 1-methylheptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 1-methylheptyl acrylic acid containing bio-derived carbon was prepared.

[0140] <Isobornyl Acrylate Containing Biologically Derived Carbon> Pinene extracted from pine resin was isomerized to obtain camphene containing biologically derived carbon. By reacting camphene containing biologically derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), isobornyl acrylate containing biologically derived carbon was prepared.

[0141] <Isobornyl methacrylate containing bio-derived carbon> Pinene extracted from pine resin was isomerized to obtain camphene containing bio-derived carbon. By reacting camphene containing bio-derived carbon with methacrylic acid (manufactured by Mitsubishi Chemical Corporation), isobornyl methacrylate containing bio-derived carbon was prepared.

[0142] <Monomers that do not contain bio-derived carbon> ・Methyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Methyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・n-butyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Cyclohexyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・2-ethylhexyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) ・Lauryl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) ・Ethylene-butylene macromonomer (manufactured by Kraton Polymer Japan, "HPVM-L1253", number average molecular weight: 7000) ・AA-6: Polymethacrylic acid (MMA macromer) with a methacryloyl group at one end (manufactured by Toagosei Co., Ltd., number average molecular weight: 6000) ・Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) ・2-hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) ・Styrene (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0143] <Elastomers> ・Styrene-based elastomer A: SIS block copolymer (manufactured by Zeon Corporation, "Quintac 3620", styrene ratio 14%, diblock ratio 12%) ・Styrene-based elastomer B: SIS block copolymer (manufactured by Zeon Corporation, "Quintac 3520", styrene ratio 14%, diblock ratio 26%) ・Styrene-based elastomer C: SIS block copolymer (manufactured by Zeon Corporation, "Quintac 3280", styrene ratio 25%, diblock ratio 17%) ・Styrene-based elastomer D: SIS block copolymer (manufactured by Zeon Corporation, "Quintac 3270", styrene ratio 24%, diblock ratio 67%) ・Styrene-based elastomer E: SEPS block copolymer (manufactured by Kuraray Co., Ltd., "SEPTON2063") - Styrene-based elastomer F: SEBS block copolymer (manufactured by ENEOS Materials, "DYNARON 8300P")

[0144] <Expandable Particles> - Expandable particle A: Expancel 920DU40 (thermal expandable microcapsule, manufactured by Nippon Philite Co., Ltd., average particle size 40 μm) - Expandable particle B: Expancel 920DU80 (thermal expandable microcapsule, manufactured by Nippon Philite Co., Ltd., average particle size 80 μm) - Expandable particle C: EMC-20(B)R (thermal expandable microcapsule, manufactured by Nippon Philite Co., Ltd., average particle size 20 μm)

[0145] <Tackifying Resins> ・Tackifying Resin A: Terpene resin (Yasuhara Chemical Co., Ltd., "YS Resin PX1000", softening point: 120°C to 130°C) ・Tackifying Resin B: Terpene phenol resin (Yasuhara Chemical Co., Ltd., "YS Polystar G150", softening point: 120°C to 130°C, hydroxyl value: less than 10 mg KOH / g) ・Tackifying Resin C: Rosin resin (Arakawa Chemical Industries, Ltd., "Pencel D-135", softening point: 130°C to 140°C, hydroxyl value: 45 mg KOH / g)

[0146] <Pigments> ・Carbon black (Toyo Color Co., Ltd., "Multi-Rack A903 Black")

[0147] <Crosslinking agents> - Isocyanate-based crosslinking agent (Covestro, "Desmodule L-75") - Epoxy-based crosslinking agent (Soken Chemical Co., Ltd., "E-5C")

[0148] (Synthesis of Acrylic Copolymers) (Acrylic Copolymers A-N, P-W, Y) A reactor equipped with a thermometer, stirrer, and condenser was prepared. A mixture of the constituent unit monomers shown in Tables 1-2 and 80 parts by mass of ethyl acetate were added to the reactor, and the reactor was heated to start reflux. Subsequently, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane was added to the reactor as a polymerization initiator, and polymerization was started under reflux. Next, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane was added 1 hour and 2 hours after the start of polymerization, and further, 0.05 parts by mass of t-hexylperoxypivalate was added 4 hours after the start of polymerization to continue the polymerization reaction. Eight hours after the start of polymerization, an ethyl acetate solution of the acrylic copolymer was obtained. The weight-average molecular weight and polydispersity of the obtained acrylic copolymers were measured using a 2690 Separations Module (Waters Co., Ltd.) as the measuring instrument, a GPC KF-806L column (Showa Denko Co., Ltd.) as the column, and ethyl acetate as the solvent, under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The results are shown in Tables 1 and 2.

[0149] (Acrylic Copolymer O) Except for the monomer mixture composition shown in Table 2, acrylic copolymer O, which is a random copolymer having styrene as a constituent unit, was synthesized by the same method as the synthesis methods of acrylic copolymers A to N and P to Y described above, and the weight-average molecular weight was measured. The results are shown in Table 2.

[0150]

[0151]

[0152] (Example 1) (1) Formation of Foam Layer To the solution of acrylic copolymer A obtained in "(Synthesis of Acrylic Copolymer)" described above, 0.4 parts by mass of foaming particles A and 30 parts by mass of ethyl acetate as a solvent were added to 100 parts by mass of the solid content of acrylic copolymer A, and the mixture was thoroughly stirred to prepare an adhesive resin composition. The prepared adhesive resin composition was applied to the release treatment surface of a 50 μm thick release PET film, and then dried at 155°C for 1 hour to form a foam layer having a foamed structure and a thickness of 200 μm. By observing the surface of the foam layer in the thickness direction using an optical microscope, it was found that the obtained foam layer had a structure in which no air bubbles were exposed on the surface in the thickness direction.

[0153] (2) Measurement of loss tangent of foam layer at 23°C and frequency of 100 Hz Test specimens were prepared by stacking the obtained foam layer to a thickness of approximately 500 μm. Dynamic viscoelastic spectra were measured for the prepared test specimens using a viscoelastic spectrometer (IT Measurement Control Co., Ltd., "DVA-200") under the conditions of simple heating mode, heating rate of 10°C / min, shear direction, frequency of 100 Hz, and temperature range from -50°C to 300°C. From the obtained dynamic viscoelastic spectra, the loss tangent at 23°C and measurement frequency of 100 Hz was measured. The results are shown in Table 3.

[0154] (3) Measurement of the shear storage modulus of the foam layer at 23°C and a frequency of 1 Hz Test specimens were prepared by stacking the obtained foam layers to a thickness of approximately 500 μm. Dynamic viscoelastic spectra were measured on the prepared test specimens using a viscoelastic spectrometer (IT Measurement Control Co., Ltd., "DVA-200") under the conditions of simple heating mode, heating rate of 10°C / min, shear direction, measurement frequency of 1 Hz, and temperature range from -50°C to 300°C. The shear storage modulus (MPa) of the foam layer at 23°C and a frequency of 1 Hz was measured using this method. The results are shown in Table 3.

[0155] (4) Measurement of 180° peel force of foam layer against SUS at 23°C One side of the obtained foam layer (the side not measured) was laminated to a 23 μm thick polyethylene terephthalate film (Futamura Chemical Co., Ltd., "FE2002") and backed by passing a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Then it was cut to a width of 25 mm x length of 75 mm to prepare a test piece. Next, the obtained test piece was laminated to a SUS304 plate (SUS304 plate washed with ethanol and then wiped dry), pressed by passing a 2 kg rubber roller back and forth once at a speed of 300 mm / min, and then cured at 23°C, 50% RH for 20 minutes to prepare a test sample. The obtained test samples were left to stand for 20 minutes at 23°C and 50% RH. Then, in accordance with JIS Z 0237:2009, the foam layer was peeled from the SUS304 plate using a tensile testing machine (A&D Corporation, "RTI") at 23°C and 50% RH, with a tensile speed of 300 mm / min and a peel angle of 180°. The 180° peel force of the foam layer against SUS at 23°C was measured. The results are shown in Table 3.

[0156] (5) Measurement of the deemed density of the foam layer In accordance with JIS K 7222, the deemed density of the foam layer (g / cm³) ３ The following was measured. The results are shown in Table 3.

[0157] (6) Calculation of the ratio of the average major axis of bubbles to the thickness of the foam layer Using a razor (Feather Corporation), the foam layer was sliced ​​in a plane parallel to the thickness direction to obtain cut samples. The obtained cut samples were photographed using a digital microscope (Keyence Corporation, "VHX-6000") at a magnification of 200x and a measurement screen size of 1.8 mm × 1.3 mm. From the obtained images, the bubble with the largest major axis and the bubble with the second largest major axis were selected, and the major axes of these bubbles were measured. Furthermore, the sample was sliced ​​so that the cutting direction was shifted by 30° from the direction in which the previous cut sample was prepared, and the aspect ratio was measured using the same method. The above measurements were repeated until returning to the cutting direction from the initial measurement. The average of the major axes of the 12 measured bubbles was defined as the average major axis of the bubbles in the foam layer, the average of the minor axes of the 12 bubbles was defined as the average minor axis of the bubbles in the adhesive layer, and the average of the aspect ratios of the 12 bubbles was defined as the aspect ratio of the bubbles in the adhesive layer. The results are shown in Table 3.

[0158] (7) Measurement of the gel fraction of the foam layer The release PET film was peeled off one side of the obtained adhesive tape and bonded to a 23 μm thick base PET film (Futamura Chemical Co., Ltd., "FE2002"), and cut into a flat rectangular shape with a width of 20 mm and a length of 40 mm. The release PET film was then peeled off the other side of the adhesive tape to prepare a test specimen, and its mass was measured. The test specimen was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The mass of the dried test specimen was measured, and the gel fraction (mass %) was calculated using the following formula (I). The results are shown in Table 3. Gel fraction (mass %) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (I) (W ０ : Mass of the base material, W １ : Mass of the test specimen before immersion, W ２ (Mass of the test specimen after immersion and drying)

[0159] (8) Measurement of the bio-derived carbon content of the foam layer The bio-derived carbon content of the obtained foam layer was measured in accordance with ASTM D6866-24. The results are shown in Table 3.

[0160] (9) Preparation of adhesive tape An adhesive tape was obtained by laminating a 50 μm thick release PET film to the release surface of the obtained foam layer and curing it in a 40°C environment for 72 hours.

[0161] (Examples 2-39, 42-46, Comparative Examples 1-4) Except for the composition and thickness of the foam layer as shown in Tables 3-6 in "(1) Formation of the foam layer" described above, adhesive tapes were prepared and various measurements were performed in the same manner as in Example 1. The results are shown in Tables 3-6. In Examples 2-39, 42-46, and Comparative Examples 1, 3-4, observation of the surface in the thickness direction of the foam layer with an optical microscope confirmed that the obtained foam layer had a structure in which no air bubbles were exposed on the surface in the thickness direction. In Comparative Example 2, since the formed layer was an adhesive layer without a foam structure, "(5) Measurement of the deemed density of the foam layer" and "(6) Calculation of the ratio of the average major diameter of the air bubbles to the thickness of the foam layer" described above were not performed.

[0162] (Examples 40-41) Foam layers were formed in the same manner as in Example 1, except that the composition was as shown in Table 5. The obtained foam layer was attached to one side of the substrate shown in Table 5, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Furthermore, a foam layer with the same composition and thickness was prepared and attached to the other side of the substrate, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min to create a laminated and integrated layer. Then, by curing at 23°C for 1 hour, an adhesive tape having foam layers with a foamed structure on both sides of the substrate was obtained. When the surface of the foam layer in the thickness direction was observed with an optical microscope, it was found that the obtained foam layer had a structure in which no air bubbles were exposed on the surface in the thickness direction. Various measurements were performed in the same manner as in Example 1, except that for the measurement of the gel fraction of the foam layer, the adhesive tape was cut into a planar rectangular shape with a width of 20 mm and a length of 40 mm, and then the release PET film on both sides was peeled off to obtain a test piece. The results are shown in Table 5.

[0163] (Examples 47-55, 58-60, Comparative Example 5) 0.902 g of 1,6-hexanedithiol, 1.83 g of carbon disulfide, and 11 mL of dimethylformamide were placed in a two-necked flask and stirred at 25°C. 2.49 g of triethylamine was added dropwise over 15 minutes and stirred at 25°C for 3 hours. Next, 2.75 g of methyl-α-bromophenylacetic acid was added dropwise over 15 minutes and stirred at 25°C for 4 hours. Then, 100 mL of extraction solvent (n-hexane:ethyl acetate = 50:50) and 50 mL of water were added to the reaction mixture and liquid-liquid extraction was performed. The organic layers obtained from the first and second liquid-liquid extractions were mixed and washed sequentially with 50 mL of 1 M hydrochloric acid, 50 mL of water, and 50 mL of saturated brine. Sodium sulfate was added to the organic layer after washing and dried. The sodium sulfate was filtered off, and the filtrate was concentrated using an evaporator to remove the organic solvent. The obtained concentrate was purified by silica gel column chromatography to obtain the RAFT agent. 87.0 g of styrene (St), 12.0 g of acrylic acid (AA), 1.0 g of 2-hydroxyethyl acrylate (2-HEA), 1.9 g of the RAFT agent, and 0.2 g of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) were placed in a two-necked flask, and the flask was heated to 85°C while purging it with nitrogen gas. The polymerization reaction was then carried out by stirring at 85°C for 6 hours (first-stage reaction). After the first-stage reaction was complete, 4000 g of n-hexane was added to the flask, and the reaction products were precipitated by stirring. Unreacted monomers (St, AA, 2-HEA) and the RAFT agent were filtered, and the reaction products were dried under reduced pressure at 70°C to synthesize a block polymer (hard segment) having constituent units derived from styrene. Block copolymers were synthesized by copolymerizing the acrylic copolymers shown in Tables 7-8 with a mixture containing monomers constituting the block polymer (soft segment), ABN-E, and ethyl acetate, and the block copolymer (hard segment) synthesized above. The weight-average molecular weight of the block copolymer was synthesized using the same method as in Example 1. The results are shown in Tables 7-8.

[0164] Except for using the block copolymer synthesized as described above and changing the composition as shown in Tables 7-8, adhesive tapes were prepared in the same manner as in Example 1, and various measurements were performed. The results are shown in Tables 7-8. Furthermore, by observing the surface of the foam layer in the thickness direction with an optical microscope, it was found that the obtained foam layer had a structure in which no air bubbles were exposed on the surface in the thickness direction.

[0165] (Examples 56-57) Adhesive tapes were prepared in the same manner as in Examples 40-41, except that the block copolymer was synthesized and used in the same manner as in Examples 47-55, 58-60, and Comparative Example 5, and the composition was changed to that shown in Table 7. Various measurements were then performed. The results are shown in Table 7.

[0166] The types of substrates in Tables 5 and 7 are as follows: • PET film A (Toray Industries, Ltd., "Lumirror", 38 μm thickness) • PET film B (Toray Industries, Ltd., "Lumirror", 50 μm thickness)

[0167] <Evaluation> The adhesive tapes obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 3 to 8.

[0168] (Impact Absorption) The obtained adhesive tape 2 was cut to a size of 30 mm x 30 mm, and two SUS plates 8 measuring 125 mm x 50 mm and 2 mm thick were stacked as shown in Figure 2 to prepare a test specimen. The obtained test specimen was set up as shown in Figure 3 so that when the pendulum 10 passed its lowest point, it would collide with only one of the SUS plates 8 on the test specimen 9. Then, a pendulum with a mass of 1.0 kg was free-falled from a height of 0.20 m (H in Figure 3) and collided with the test specimen, and the highest height h reached was measured. Using the obtained height h, the impact absorption energy was calculated from the following formula. Note that the lowest point reached by the pendulum is defined as 0. Impact absorption energy (J) = mg(0.2 - h) (m: mass of the pendulum (kg), g: acceleration due to gravity (9.80 m / s) ２(h: measured height) Based on the calculated shock absorption energy, the shock absorption performance of the adhesive tape was evaluated according to the following criteria: A: Shock absorption energy was 1.00 J or more. B: Shock absorption energy was 0.50 J or more and less than 1.00 J. C: Shock absorption energy was 0.15 J or more and less than 0.50 J. D: Shock absorption energy was less than 0.15 J.

[0169] (Bending resistance) Aluminum alloy plates (SHAANXI SHWEW-E STEEL PIPE, "Aluminum 6061-T6", 1.6 mm thick, 25.4 mm wide, 203.2 mm long) were attached to both sides of the obtained adhesive tape by applying a load of 1 MPa for 20 seconds at 65°C to laminate them together, and then cured by leaving them undisturbed at 23°C for 24 hours to produce a laminate. The fabricated laminate was set up in a Tensilon (A&D Company, Limited) measuring instrument in accordance with JIS K 7171 as shown in Figure 1 (distance between compression jigs: 57.15 mm, distance between fixing jigs: 177.8 mm). Subsequently, the test piece was compressed at a constant speed of 0.05 mm / s in an environment of 23 ± 1°C and 50 ± 5% humidity until the load reached 50 N. From the obtained stress-deformation curve, the slope of the line (stress / deformation) in the stress range of 20 N to 50 N was calculated, and based on the obtained slope of the line, the bending stiffness of the adhesive tape was evaluated according to the following criteria: A: The slope of the line was 17.0 N / mm or more. B: The slope of the line was 15.5 N / mm or more and less than 17.0 N / mm. C: The slope of the line was less than 15.5 N / mm.

[0170]

[0171]

[0172]

[0173]

[0174]

[0175]

[0176] According to the present invention, it is possible to provide an adhesive tape that can achieve both excellent bending resistance and excellent shock absorption. Furthermore, according to the present invention, it is possible to provide an electronic device that includes the adhesive tape.

[0177] 2. Adhesive tape 5. Laminate 6. Compression jig 7. Fixing jig 8. SUS plate 9. Test piece 10. Pendulum

Claims

1. An adhesive tape having a foam layer, wherein the foam layer has a shear storage modulus of 0.30 MPa or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 1 Hz, and the foam layer has a loss tangent of 0.50 or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 100 Hz.

2. The adhesive tape according to claim 1, wherein the foam layer has a 180° peel strength against SUS at 23°C of 10 N / 25 mm or more.

3. The adhesive tape according to claim 1 or 2, wherein the foam layer is formed using an adhesive resin composition.

4. The adhesive tape according to claim 3, wherein the adhesive resin composition contains foaming particles, and the foam layer has bubbles derived from the foaming particles.

5. The adhesive tape according to claim 4, wherein the foaming particles include thermally expandable microcapsules.

6. The adhesive tape according to claim 4 or 5, wherein the foaming particles have an average particle size of 60 μm or less.

7. The adhesive tape according to claim 1, 2, 3, 4, 5, or 6, wherein the foam layer contains a copolymer having macromonomers with a number average molecular weight of 2,000 or more and 30,000 or less as constituent units.

8. The adhesive tape according to claim 7, wherein the foam layer contains an acrylic copolymer having constituent units derived from a (meth)acrylic acid ester and constituent units derived from an olefin polymer having polymerizable unsaturated double bonds at its ends.

9. The adhesive tape according to claim 8, wherein the constituent units derived from the (meth)acrylic acid ester include constituent units derived from an alkyl (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms, and the content ratio of the constituent units derived from the alkyl (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms in the alkyl (meth)acrylic acid ester is 50% by mass or more and 100% by mass or less.

10. The adhesive tape according to claim 8 or 9, wherein the constituent unit derived from the (meth)acrylic acid ester comprises a constituent unit having an alkyl group having an aliphatic cyclic structure.

11. The adhesive tape according to claim 8, 9, or 10, wherein the acrylic copolymer has constituent units derived from a vinyl aromatic compound, and the content ratio of the constituent units derived from the vinyl aromatic compound in the acrylic copolymer is 2.5% by mass or more and 20% by mass or less.

12. The adhesive tape according to claim 8, 9, 10, or 11, wherein the constituent units derived from the (meth)acrylic acid ester include constituent units derived from an alkyl (meth)acrylic acid ester having a linear or branched alkyl group with 6 to 8 carbon atoms.

13. The adhesive tape according to claim 12, wherein the constituent unit derived from the (meth)acrylic acid ester further comprises a constituent unit derived from the (meth)acrylic acid ester having an alkyl group having an aliphatic cyclic structure.

14. The adhesive tape according to claim 8, 9, 10, 11, 12, or 13, wherein the content of constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminals in the acrylic copolymer is 5% by mass or more and 50% by mass or less.

15. The adhesive tape according to claim 8, 9, 10, 11, 12, 13, or 14, wherein the acrylic copolymer has constituent units derived from a polar functional group-containing monomer, and the content ratio of the constituent units derived from the polar functional group-containing monomer in the acrylic copolymer is 0.1% by mass or more.

16. The adhesive tape according to claim 8, 9, 10, 11, 12, 13, 14, or 15, wherein the acrylic copolymer has a weight-average molecular weight of 300,000 or more and 1,500,000 or less.

17. The adhesive tape according to claim 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the foam layer does not contain a tackifying resin, or the adhesive resin composition contains a tackifying resin, and the content of the tackifying resin is 50 parts by mass or less per 100 parts by mass of the acrylic copolymer.

18. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, wherein the foam layer contains at least one elastomer selected from styrene-based elastomers, olefin-based elastomers, and urethane-based elastomers.

19. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, wherein the foam layer is colored.

20. The adhesive tape according to claim 3, 4, or 5, wherein the adhesive resin composition contains a crosslinking agent.

21. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the foam layer has a bio-derived carbon content of 15% or more.

22. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, wherein the foam layer has an average major diameter of bubbles that is 0.80 times or less the thickness of the foam layer.

23. The foam layer has a deemed density of 0.59 g / cm³. ３ 1.15g / cm or more ３ The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22.

24. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, wherein the foam layer has a structure in which no air bubbles are exposed on the surface in the thickness direction.

25. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24, comprising only the foam layer.

26. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24, having a base material and the foam layer on at least one surface of the base material.

27. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 26, having an adhesive layer on at least one surface of the foam layer.

28. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, or 27, which is used by being attached to the internal components of electrical and electronic equipment.

29. Electronic device comprising the adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, or 28.

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