Adhesive composition and adhesive tape

Abstract

The present invention provides a pressure-sensitive adhesive composition which is less apt to corrode metals and can exhibit excellent adhesive force. Also provided is a pressure-sensitive adhesive tape including a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition. This pressure-sensitive adhesive composition includes an acrylic copolymer comprising 50 wt% or more constituent unit derived from n-heptyl (meth)acrylate, and has an acid value of 22 mgKOH / g or less and a 23°C shear storage modulus of 6×104 to 5×105 Pa.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition and an adhesive tape. [Background technology]

[0002] Conventionally, adhesive tapes having an adhesive layer containing an adhesive have been widely used to fix components in electronic components, vehicles, housing, and building materials (for example, Patent Documents 1 to 3). Specifically, for example, adhesive tapes are used to adhere a cover panel for protecting the surface of a portable electronic device to a touch panel module or display panel module, or to adhere a touch panel module to a display panel module. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-052050 [Patent Document 2] Japanese Patent Publication No. 2015-021067 [Patent Document 3] Japanese Patent Publication No. 2015-120876 [Overview of the project] [Problems that the invention aims to solve]

[0004] Traditionally, metals have been commonly used in electronic equipment components, automotive parts, and other applications, particularly in areas such as sensors and copper wiring. When adhesive compositions were used around such metals, the metals would corrode, leading to malfunctions over time.

[0005] The present invention aims to provide an adhesive composition that is less likely to corrode metals and exhibits excellent adhesive strength. Furthermore, the present invention aims to provide an adhesive tape having an adhesive layer containing the adhesive composition. [Means for solving the problem]

[0006] Disclosure 1 is an adhesive composition containing an acrylic copolymer, wherein the acrylic copolymer contains 50% by weight or more of structural units derived from n-heptyl (meth)acrylate, and the adhesive composition has an acid value of 22 mgKOH / g or less and a shear storage modulus of 6 × 10 at 23°C. 4 Pa or more 5×10 5 This is an adhesive composition with a Pa value of 0.75 or less. Disclosure 2 is the adhesive composition of Disclosure 1, wherein the acrylic copolymer has an acid value of 22 mg KOH / g or less. Disclosure 3 is an adhesive composition of Disclosure 1 or 2, wherein the acrylic copolymer further contains a constituent unit derived from a monomer having a polar functional group, and the monomer having a polar functional group contains a monomer having an amide group. Disclosure 4 is the adhesive composition of Disclosure 3, wherein the acrylic copolymer contains 2% by weight or more and 30% by weight or less of constituent units derived from the monomer having the amide group. Disclosure 5 is an adhesive composition of Disclosure 3 or 4, wherein the monomer having the polar functional group further contains a monomer having a hydroxyl group. Disclosure 6 is an adhesive composition of Disclosure 5, wherein the acrylic copolymer contains 0.01% by weight or more and 5% by weight or less of constituent units derived from the monomer having a hydroxyl group. Disclosure 7 further contains a tackifying resin, wherein the tackifying resin has an acid value of 10 mg KOH / g or less, and is an adhesive composition of Disclosure 1, 2, 3, 4, 5 or 6. Disclosure 8 is the adhesive composition of Disclosure 7, wherein the tackifying resin has a hydroxyl value of 50 mgKOH / g or less. Disclosure 9 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, or 8, wherein the content of bio-derived carbon is 30% by weight or more. Disclosure 10 is an adhesive tape having an adhesive layer containing the adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, or 9. Disclosure 11 is an adhesive tape according to Disclosure 10, wherein the adhesive layer has a gel fraction of 20% by weight or more and 50% by weight or less. Disclosure 12 is an adhesive tape according to Disclosure 10, wherein the adhesive layer has a gel fraction of 60% by weight or more and 95% by weight or less. In this specification, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic. Acrylic copolymer may also be methacrylic copolymer. The present invention will be described in detail below.

[0007] The inventors investigated the use of bio-derived carbon-containing acrylic monomers as acrylic monomers constituting the acrylic copolymer in an adhesive composition containing an acrylic copolymer. In particular, they found that using a certain amount or more of n-heptyl(meth)acrylate (number of carbon atoms in the acrylic group = 7) can be expected to exhibit excellent adhesive strength. However, the inventors further discovered that the glass transition temperature of n-heptyl(meth)acrylate, obtained from the temperature at which the tanδ of the homopolymer is maximum, is lower than expected, resulting in a lower cohesive force of the adhesive composition than expected. In other words, contrary to predictions based on the glass transition temperature trend obtained by differential scanning calorimetry (DSC), it was found that, for example, n-heptyl acrylate has a lower glass transition temperature obtained from the temperature at which the tanδ of the homopolymer is maximum compared to butyl acrylate and 2-ethylhexyl acrylate (acrylic group carbon numbers = 4 and 8).

[0008] In order to increase the cohesive strength of the adhesive composition and exhibit excellent adhesiveness while using n-heptyl (meth)acrylate, one possible approach is to copolymerize a relatively large amount of acrylic acid. However, when an adhesive composition containing an acrylic copolymer with a relatively large amount of acrylic acid is used around metal, there is a problem that the metal corrodes and malfunctions occur over time. In response to this, the present inventors have found that by adjusting the acid value of the adhesive composition to below a certain value and adjusting the shear storage modulus at 23°C to a specific range, an adhesive composition can be obtained that exhibits excellent adhesive strength while reducing metal corrosion, thus completing the present invention.

[0009] The adhesive composition of the present invention contains an acrylic copolymer. The above acrylic copolymer contains structural units derived from n-heptyl(meth)acrylate. As a result, the adhesive composition of the present invention can exhibit excellent adhesive strength.

[0010] The above acrylic copolymer preferably contains structural units derived from n-heptyl(meth)acrylate containing bio-derived carbon. By including structural units derived from n-heptyl(meth)acrylate containing bio-derived carbon in the above acrylic copolymer, the content of bio-derived carbon in the entire adhesive composition can be increased. By using bio-derived materials instead of petroleum-derived materials, petroleum resources can be conserved, thus helping to address the depletion of petroleum resources and the emission of carbon dioxide from the combustion of petroleum-derived products. The above-mentioned n-heptyl (meth)acrylate containing bio-derived carbon is not particularly limited as long as it contains bio-derived carbon, but it is preferably synthesized by esterification of n-heptyl alcohol, which is a bio-derived material, with (meth)acrylic acid. It is also preferable that it be synthesized by transesterification of n-heptyl alcohol, which is a bio-derived material, with (meth)acrylic acid ester. The above-mentioned bio-derived material, n-heptyl alcohol, can be obtained inexpensively and easily by cracking materials extracted from plants and animals (for example, ricinoleic acid derived from castor oil).

[0011] In the above acrylic copolymer, the content of the structural unit derived from the above n-heptyl (meth)acrylate has a lower limit of 50% by weight. If the content of the above structural unit is 50% by weight or more, the adhesive strength of the adhesive composition will increase. Also, if the content of the structural unit derived from the n-heptyl (meth)acrylate containing the above bio-derived carbon is 50% by weight or more, the content rate of the bio-derived carbon in the entire adhesive composition can be increased. The content of the structural unit derived from the above n-heptyl (meth)acrylate is not particularly limited, but it is preferably more than 50% by weight, more preferably the lower limit is 60% by weight, and even more preferably the lower limit is 70% by weight. The upper limit of the content of the structural unit derived from the above n-heptyl (meth)acrylate is not particularly limited, but from the viewpoint of adjusting the shear storage modulus of the adhesive composition at 23°C to the range described later, the preferable upper limit is 99% by weight, and more preferably the upper limit is 97% by weight.

[0012] The content of the structural unit derived from the above n-heptyl (meth)acrylate in the above acrylic copolymer can be calculated from the integral intensity ratio of the peaks of hydrogen derived from n-heptyl (meth)acrylate by performing mass spectrometry and 1 1H-NMR measurement of the above acrylic copolymer.

[0013] The above acrylic copolymer preferably further contains a structural unit derived from a monomer having a polar functional group. Since the above acrylic copolymer contains a structural unit derived from the above monomer having a polar functional group, the cohesive force of the adhesive composition increases, and it becomes easier to satisfy the range described later for the shear storage modulus at 23°C, and the adhesive strength becomes higher.

[0014] The monomers having the polar functional groups described above are not particularly limited, and examples include monomers having hydroxyl groups, monomers having carboxyl groups, monomers having ether groups, monomers having glycidyl groups, monomers having amide groups, monomers having nitrile groups, and so on. These monomers having polar functional groups may be used alone or in combination of two or more. Among these, monomers having hydroxyl groups, monomers having carboxyl groups, and monomers having amide groups are preferred because they make it easier for the shear storage modulus of the adhesive composition at 23°C to satisfy the range described later. In addition to the shear storage modulus of the adhesive composition at 23°C, monomers having hydroxyl groups and monomers having amide groups are more preferred because they make it easier for the acid value to satisfy the range described later, and the adhesive strength can be increased while further reducing metal corrosion. From the viewpoint of sufficiently suppressing the acid value of the adhesive composition and further reducing metal corrosion, it is even more preferable not to use monomers having carboxyl groups.

[0015] Examples of monomers having a hydroxyl group include acrylic monomers having a hydroxyl group, such as 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of monomers having a carboxyl group include acrylic monomers having a carboxyl group, such as (meth)acrylic acid. Examples of monomers having a glycidyl group include acrylic monomers having a glycidyl group, such as glycidyl (meth)acrylate. Examples of monomers having the above-mentioned amide group include acrylic monomers having an amide group such as (meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, isopropyl(meth)acrylamide, t-butyl(meth)acrylamide, methoxymethyl(meth)acrylamide, and butoxymethyl(meth)acrylamide. Among these, (meth)acrylamide, dimethyl(meth)acrylamide, and diethyl(meth)acrylamide are preferred because they are readily available and easy to handle. Examples of monomers having a nitrile group include acrylic monomers having a nitrile group, such as (meth)acrylonitrile.

[0016] The content of constituent units derived from the monomer having the polar functional group in the above acrylic copolymer is not particularly limited and can be determined depending on the type of monomer having the polar functional group. When the monomer having the polar functional group contains the monomer having the hydroxyl group, the content of the constituent units derived from the monomer having the hydroxyl group in the acrylic copolymer is not particularly limited, but a preferred lower limit is 0.01% by weight and a preferred upper limit is 5% by weight. If the content of the constituent units is within the above range, the shear storage modulus of the adhesive composition at 23°C is more likely to satisfy the range described later, and the adhesive strength is further increased. A more preferred lower limit for the constituent units is 0.05% by weight and a more preferred upper limit is 1% by weight. When the monomer having the polar functional group contains the monomer having the amide group, the content of the constituent units derived from the monomer having the amide group in the acrylic copolymer is not particularly limited, but a preferred lower limit is 2% by weight and a preferred upper limit is 30% by weight. If the content of the constituent units is within the above range, the shear storage modulus of the adhesive composition at 23°C will more easily satisfy the range described later, and the adhesive strength will be further increased. A more preferred lower limit for the constituent units is 5% by weight, a more preferred upper limit is 25% by weight, an even more preferred lower limit is 10% by weight, and an even more preferred upper limit is 20% by weight.

[0017] The content of the constituent units derived from the monomer having the polar functional group in the above acrylic copolymer is determined by mass spectrometry of the above acrylic copolymer and 1 This can be calculated by performing 1H-NMR measurements and analyzing the integral intensity ratio of the hydrogen peaks originating from each monomer.

[0018] The above-mentioned acrylic copolymer may have constituent units derived from monomers having a glass transition temperature (Tg) of -35°C or higher. The presence of constituent units derived from monomers having a glass transition temperature (Tg) of -35°C or higher in the acrylic copolymer results in higher adhesive strength in the resulting adhesive layer. A monomer having a glass transition temperature (Tg) of -35°C or higher is defined as a monomer whose homopolymer has a glass transition temperature (Tg) of -35°C or higher. The glass transition temperature (Tg) of the homopolymer can be determined, for example, by differential scanning calorimetry. For monomers with a glass transition temperature (Tg) of -35°C or higher, the glass transition temperature (Tg) is more preferably -15°C or higher. The upper limit of the glass transition temperature (Tg) is not particularly limited, but a preferred upper limit is 180°C, and a more preferred upper limit is 150°C. The monomers with a glass transition temperature (Tg) of -35°C or higher are not particularly limited, but monomers without crosslinking functional groups are preferred. Specifically, examples include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, tert-butyl (meth)acrylate, n-butyl methacrylate, isobutyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropaneformal (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, acrylamide, dimethylacrylamide, diethylacrylamide, etc. Among these, isobornyl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate are preferred.

[0019] The content of constituent units derived from monomers with a glass transition temperature (Tg) of -35°C or higher in the above acrylic copolymer is not particularly limited, but is preferably 5% by weight or more and 70% by weight or less. If the content of constituent units derived from monomers with a glass transition temperature (Tg) of -35°C or higher is 70% by weight or less, the conformability to irregularities of the resulting adhesive layer will be higher. A more preferred upper limit for the content of constituent units derived from monomers with a glass transition temperature (Tg) of -35°C or higher is 65% by weight, an even more preferred upper limit is 60% by weight, an even more preferred upper limit is 55% by weight, and a particularly preferred upper limit is 50% by weight. A more preferred lower limit for the content of constituent units derived from monomers with a glass transition temperature (Tg) of -35°C or higher is 10% by weight. The content of constituent units derived from monomers with a glass transition temperature (Tg) of -35°C or higher in the above acrylic copolymer is also determined by mass spectrometry of the above acrylic copolymer. 1 This can be calculated by performing 1H-NMR measurements and analyzing the integral intensity ratio of the hydrogen peaks originating from each monomer.

[0020] The above acrylic copolymer preferably has structural units derived from monomers having a ring structure. The presence of structural units derived from monomers having a ring structure in the acrylic copolymer allows for the suitability of the adhesive tape as an optical adhesive tape. The above-mentioned ring structure is not particularly limited and examples include alicyclic structures, aromatic ring structures, heterocyclic structures, etc. Among those mentioned above, examples of monomers having the above-mentioned ring structure include isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropaneformal (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. Among these, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and trimethylolpropaneformal (meth)acrylate are preferred. In particular, monomers of biological origin are preferred, and isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and trimethylolpropaneformal (meth)acrylate of biological origin are more preferred.

[0021] The above acrylic copolymer may have constituent units derived from monomers other than the above n-heptyl (meth)acrylate, the above monomer having a polar functional group, the monomer having a glass transition temperature (Tg) of -35°C or higher, and the monomer having a ring structure. The other monomers mentioned above are not particularly limited and include, for example, alkyl (meth)acrylates. Examples of the alkyl (meth)acrylate esters mentioned above include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)octanol-1 with (meth)acrylic acid, esters of (meth)acrylic acid with an alcohol having 1 or 2 methyl groups in a linear main chain and a total of 18 carbon atoms, behenyl (meth)acrylate, arachidyl (meth)acrylate, and the like. These alkyl (meth)acrylates may be used individually or in combination of two or more.

[0022] Other monomers include, for example, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and polypropylene glycol mono(meth)acrylate. From the viewpoint of excellent rebound resistance, isobornyl (meth)acrylate is preferred. Furthermore, other monomers such as vinyl carboxylates like vinyl acetate and various monomers commonly used in acrylic polymers like styrene can also be used. These other monomers may be used individually or in combination of two or more.

[0023] The content of constituent units derived from the other monomers in the above acrylic copolymer is determined by mass spectrometry of the above acrylic copolymer and 1 This can be calculated by performing 1H-NMR measurements and analyzing the integral intensity ratio of the hydrogen peaks originating from each monomer.

[0024] The monomers having the polar functional groups described above, and the other monomers described above, preferably contain bio-derived carbon, but may also consist only of petroleum-derived materials without containing bio-derived carbon. Theoretically, it is also possible to make all of the acrylic monomers constituting the acrylic copolymer monomers containing bio-derived carbon. From the viewpoint of cost and productivity of the adhesive composition, it is also possible to use monomers containing bio-derived carbon, which are relatively inexpensive and readily available, and combine them with monomers consisting only of petroleum-derived materials.

[0025] The acid value of the above acrylic copolymer is not particularly limited, but a preferred upper limit is 22 mgKOH / g. If the acid value of the above acrylic copolymer is 22 mgKOH / g or less, the acid value of the adhesive composition is more likely to meet the range described later, and metal corrosion can be further reduced. A more preferred upper limit for the acid value of the above acrylic copolymer is 10 mgKOH / g. The lower limit for the acid value of the above acrylic copolymer is not particularly limited and may be 0 mgKOH / g. The acid value of the above acrylic copolymer can be determined, for example, by the same method as the acid value of an adhesive composition. Specifically, the acid value of the acrylic copolymer of the present invention is the number of mg of potassium hydroxide required to neutralize the acid contained in 1 g of the sample, and can be determined, for example, by potentiometric titration in accordance with JIS K 0070.

[0026] The glass transition temperature (Tg) of the above acrylic copolymer is not particularly limited, but is preferably -20°C or lower. If the glass transition temperature (Tg) of the above acrylic copolymer is -20°C or lower, the conformability of the adhesive composition to the adherend is improved, and the adhesive strength is increased. The glass transition temperature (Tg) of the above acrylic copolymer is more preferably -30°C or lower, even more preferably -40°C or lower, and even more preferably -50°C or lower. The lower limit of the glass transition temperature (Tg) of the above acrylic copolymer is not particularly limited, but is usually -90°C or higher, and is preferably -80°C or higher. The glass transition temperature (Tg) of the above acrylic copolymer can be determined, for example, by differential scanning calorimetry.

[0027] The weight-average molecular weight (Mw) of the above acrylic copolymer is not particularly limited, but a preferred lower limit is 200,000 and a preferred upper limit is 2,000,000. If the weight-average molecular weight of the above acrylic copolymer is within the above range, the adhesive strength of the adhesive composition will be higher. A more preferred lower limit for the weight-average molecular weight of the above acrylic copolymer is 400,000, a more preferred upper limit is 1,800,000, an even more preferred lower limit is 500,000, and an even more preferred upper limit is 1,500,000. The weight-average molecular weight (Mw) is the weight-average molecular weight on a standard polystyrene basis, measured by GPC (Gel Permeation Chromatography). Specifically, the acrylic copolymer is diluted 50-fold with tetrahydrofuran (THF), and the resulting dilution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare the measurement sample. Next, this measurement sample is supplied to a gel-permeation chromatograph (Waters, product name "2690 Separations Module" or equivalent) and GPC measurement is performed under conditions of a sample flow rate of 1 ml / min and a column temperature of 40°C. The polystyrene-based molecular weight of the acrylic copolymer is measured, and this value is taken as the weight-average molecular weight of the acrylic copolymer.

[0028] The above-mentioned acrylic copolymer can be obtained by subjecting a monomer mixture to a radical reaction in the presence of a polymerization initiator. The method of radical reaction is not particularly limited, and examples include living radical polymerization and free radical polymerization. Living radical polymerization yields copolymers with more uniform molecular weight and composition compared to free radical polymerization, and the generation of low molecular weight components can be suppressed, thus increasing the cohesive force of the adhesive composition and resulting in higher adhesive strength. The polymerization method is not particularly limited, and conventionally known methods can be used. Examples of polymerization methods include solution polymerization (boiling point polymerization or constant temperature polymerization), UV polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization and UV polymerization are preferred because they result in higher adhesive strength of the adhesive composition. Furthermore, solution polymerization is more preferred because it facilitates mixing of the tackifying resin with the obtained acrylic copolymer and can further increase the adhesive strength of the adhesive composition.

[0029] When solution polymerization is used as the polymerization method, examples of reaction solvents include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, and diethyl ether. These reaction solvents may be used individually or in combination of two or more.

[0030] The polymerization initiators mentioned above are not particularly limited and include, for example, 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 individually or in combination of two or more. Furthermore, in the case of living radical polymerization, examples of polymerization initiators include organic tellurium polymerization initiators. The organic tellurium polymerization initiator is not particularly limited as long as it is commonly used in living radical polymerization, and examples include organic tellurium compounds and organic telluride compounds. In addition to the organic tellurium polymerization initiator, an azo compound may also be used as a polymerization initiator in living radical polymerization to accelerate the polymerization rate.

[0031] The above adhesive composition preferably does not contain a surfactant. The absence of surfactants in the above adhesive composition results in increased adhesive strength of the adhesive tape, particularly at high temperatures. Note that the absence of surfactants in the above adhesive composition means that the surfactant content in the adhesive composition is 3% by weight or less, preferably 1% by weight or less. In order for the above adhesive composition to be free of surfactants, it is preferable not to use surfactants when obtaining the acrylic copolymer. To achieve this, for example, solution polymerization, UV polymerization, etc., may be used as the polymerization method when obtaining the acrylic copolymer. The content of the above-mentioned surfactant can be determined, for example, by measuring the adhesive composition using a liquid chromatography-mass spectrometer (e.g., NEXCERA from Shimadzu Corporation, Exactive from Thermo Fisher Scientific, etc.). More specifically, an ethyl acetate solution of the adhesive composition is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). Approximately 10 μL of the resulting filtrate is injected into a liquid chromatography-mass spectrometer and analyzed under the following conditions. The content of the surfactant can be determined from the area ratio of the peaks corresponding to the surfactant in the adhesive composition. It is preferable to prepare samples with known surfactant content in the adhesive composition for each surfactant type, create a calibration curve showing the relationship between surfactant content and peak area ratio, and analyze the results. Column: Thermo Fisher Scientific, Hypersil GOLD (2.1 x 150 mm) Mobile phase: acetonitrile Column temperature: 40°C Flow rate 1.0mL / min Ionization method ESI Capillary temperature 350℃

[0032] From the viewpoint of adjusting the shear storage modulus at 23°C, the adhesive composition of the present invention preferably further contains a crosslinking agent. The above crosslinking agents are not particularly limited and include, for example, isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred because the adhesive composition exhibits excellent adhesion to the adherend. The molecular weight of the crosslinking agent is not particularly limited, but from a manufacturing standpoint, a molecular weight of less than 2000 is preferred, and 100 or more is preferred.

[0033] The content of the crosslinking agent in the adhesive composition of the present invention is not particularly limited, but a preferred lower limit is 0.05 parts by weight and a preferred upper limit is 7 parts by weight per 100 parts by weight of the acrylic copolymer. If the content of the crosslinking agent is within the above range, the shear storage modulus of the adhesive composition at 23°C will more easily satisfy the range described later, and the adhesive strength will be further increased. A more preferred lower limit for the content of the crosslinking agent is 0.1 parts by weight and a more preferred upper limit is 5 parts by weight. The above-mentioned crosslinking agent content indicates the amount of solids contained in the crosslinking agent.

[0034] The adhesive composition of the present invention may further contain a crosslinking catalyst for promoting crosslinking by the above-mentioned crosslinking agent. The above crosslinking catalyst is not particularly limited, and examples of crosslinking catalysts for the isocyanate-based crosslinking agent include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate. The content of the crosslinking catalyst in the adhesive composition of the present invention is not particularly limited, but a preferred lower limit is 0.001 parts by weight, a preferred upper limit is 3 parts by weight, a more preferred lower limit is 0.01 parts by weight, and a more preferred upper limit is 1 part by weight, relative to 100 parts by weight of the acrylic copolymer.

[0035] The adhesive composition of the present invention preferably further contains a tackifying resin. This increases the adhesive strength of the adhesive composition. The acid value of the tackifying resin is not particularly limited, but a preferred upper limit is 10 mg KOH / g. If the acid value of the tackifying resin is 10 mg KOH / g or less, the acid value of the adhesive composition is more likely to meet the range described later, and metal corrosion can be further reduced. A more preferred upper limit for the acid value of the tackifying resin is 5 mg KOH / g. The lower limit for the acid value of the tackifying resin is not particularly limited and may be 0 mg KOH / g. The acid value of the tackifying resin described above can be determined, for example, by the same method as the acid value of the adhesive composition. Specifically, the acid value of the tackifying resin of the present invention is the number of mg of potassium hydroxide required to neutralize the acid contained in 1 g of the sample, and can be determined, for example, by potentiometric titration in accordance with JIS K 0070.

[0036] The hydroxyl value of the tackifying resin is not particularly limited, but a preferred upper limit is 50 mgKOH / g. If the hydroxyl value of the tackifying resin is 50 mgKOH / g or less, the adhesive composition can suppress excessive absorption of moisture from the air, thereby further reducing metal corrosion. A more preferred upper limit for the hydroxyl value of the tackifying resin is 40 mgKOH / g. The lower limit for the hydroxyl value of the tackifying resin is not particularly limited, but a preferred lower limit is 10 mgKOH / g. The hydroxyl value of the tackifying resin mentioned above is the number of milligrams of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl group when 1 g of the sample is acetylated. This can be determined, for example, by a neutralization titration method in accordance with JIS K 0070.

[0037] Examples of the tackifying resins mentioned above include rosin ester tackifying resins, terpene tackifying resins, coumarone indene tackifying resins, alicyclic saturated hydrocarbon tackifying resins, C5 petroleum tackifying resins, C9 petroleum tackifying resins, and C5-C9 copolymer petroleum tackifying resins. These tackifying resins may be used individually or in combination of two or more. In particular, at least one selected from the group consisting of rosin ester tackifying resins and terpene tackifying resins is preferred because its acid value and hydroxyl value tend to satisfy the above ranges.

[0038] Examples of the rosin ester-based tackifying resins include polymerized rosin ester resins and hydrogenated rosin ester resins. Examples of the terpene-based tackifying resins include terpene resins and terpene phenol resins. The rosin ester-based tackifying resin and the terpene-based tackifying resin described above are preferably of biological origin. Examples of biologically derived rosin ester-based tackifying resins include rosin ester-based tackifying resins derived from natural resins such as pine resin. Examples of biologically derived terpene-based tackifying resins include terpene-based tackifying resins derived from plant essential oils, etc.

[0039] The content of the tackifying resin in the adhesive composition of the present invention is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 60 parts by weight relative to 100 parts by weight of the acrylic copolymer. If the content of the tackifying resin is within the above range, the adhesive strength of the adhesive composition will be higher. A more preferred lower limit for the content of the tackifying resin is 15 parts by weight, a more preferred upper limit is 50 parts by weight, and an even more preferred upper limit is 35 parts by weight. Furthermore, when the adhesive composition of the present invention is used in an optical adhesive tape, the content of the tackifying resin in the adhesive composition of the present invention is not particularly limited, but a preferred lower limit is 0 parts by weight and a preferred upper limit is 40 parts by weight relative to 100 parts by weight of the acrylic copolymer. If the content of the tackifying resin is within the above range, the adhesive tape can be suitably used as an optical adhesive tape. A more preferred upper limit for the content of the tackifying resin is 30 parts by weight.

[0040] The adhesive composition of the present invention may optionally contain additives such as silane coupling agents, plasticizers, softeners, fillers, pigments, and dyes.

[0041] The acid value of the adhesive composition of the present invention has an upper limit of 22 mgKOH / g. Thereby, the adhesive composition of the present invention is less likely to corrode metals. A more preferable upper limit of the acid value of the adhesive composition of the present invention is 10 mgKOH / g. The lower limit of the acid value of the adhesive composition of the present invention is not particularly limited and may be 0 mgKOH / g. The acid value of the adhesive composition of the present invention is the number of mg of potassium hydroxide required to neutralize the acid contained in 1 g of the sample, and can be determined by, for example, the potentiometric titration method in accordance with JIS K 0070.

[0042] The method for adjusting the acid value of the adhesive composition of the present invention to the above range is not particularly limited, but a method of adjusting the composition and acid value of the above acrylic copolymer, and the type and acid value of the above tackifier resin as described above is preferable.

[0043] The adhesive composition of the present invention has a lower limit of the shear storage modulus at 23°C of 6×10 4 Pa and an upper limit of 5×10 5 Pa. If the shear storage modulus at 23°C is within the above range, the adhesive composition can exhibit excellent adhesive strength and the adhesion to the adherend is also improved. The preferable lower limit of the shear storage modulus at 23°C is 7×10 4 Pa, the preferable upper limit is 4×10 5 Pa, the more preferable lower limit is 8×10 4 Pa, and the more preferable upper limit is 3×10 5 Pa. The shear storage modulus at 23°C of the adhesive composition of the present invention can be determined, for example, by the following method. The adhesive composition of the present invention is applied and dried on the release-treated surface of a release-treated PET film so that the thickness of the dried adhesive layer is 100 μm. Alternatively, the adhesive layer is formed to have a thickness of 100 μm by laminating the adhesive layers. For the obtained adhesive layer, a dynamic viscoelastic spectrum from -50°C to 200°C is measured using a viscoelastic spectrometer (for example, DVA-200 manufactured by IT Measurement & Control Co., Ltd.) under the conditions of a shear mode of 5°C / min and 10 Hz.

[0044] The method for adjusting the shear storage modulus of the adhesive composition of the present invention at 23°C to the above range is not particularly limited, but it is preferable to adjust the composition and weight-average molecular weight of the acrylic copolymer, as well as the type and amount of the crosslinking agent, as described above.

[0045] The adhesive composition of the present invention preferably contains 10% by weight or more of bio-derived carbon. A bio-derived carbon content of 10% by weight or more is an indicator that a product is "bio-based." A bio-derived carbon content of 10% by weight or more is preferable from the viewpoint of conserving petroleum resources and reducing carbon dioxide emissions. A more preferable lower limit for the bio-derived carbon content is 30% by weight or more, and an even more preferable lower limit is 60% by weight. The upper limit for the bio-derived carbon content is not particularly limited and may be 100% by weight. Furthermore, while bio-derived carbon contains a certain percentage of the radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the content of bio-derived carbon can be calculated by measuring the concentration of C-14 contained in the adhesive composition. Specifically, it can be measured in accordance with ASTM D6866-20, a standard widely used in the bioplastics industry.

[0046] An adhesive tape having an adhesive layer containing the adhesive composition of the present invention is also one of the present inventions. The gel fraction of the adhesive layer described above is not particularly limited, but a preferred lower limit is 10% by weight and a preferred upper limit is 70% by weight. If the gel fraction of the adhesive layer is within the above range, the adhesive strength of the adhesive layer will be higher and the adhesion to the substrate will also be improved. A more preferred lower limit for the gel fraction of the adhesive layer is 20% by weight and a more preferred upper limit is 50% by weight. Furthermore, when the adhesive tape of the present invention is used as an optical adhesive tape, the gel fraction of the adhesive layer is not particularly limited, but a preferred lower limit is 60% by weight and a preferred upper limit is 98% by weight. If the gel fraction of the adhesive layer is within the above range, the adhesive tape can be suitably used as an optical adhesive tape. A more preferred lower limit for the gel fraction of the adhesive layer is 70% by weight and a more preferred upper limit is 95% by weight. The gel fraction of the adhesive layer described above is measured as follows. First, a test specimen is prepared by cutting the adhesive tape into a 20mm x 40mm rectangular shape. 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 weight of the dried test specimen is measured, and the gel fraction is calculated using the following formula (1). Note that the test specimen does not have a release film laminated on it to protect the adhesive layer. Gel fraction (weight %) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: Weight of the substrate, W1: Weight of the test specimen before immersion, W2: Weight of the test specimen after immersion and drying)

[0047] The above adhesive layer has a lower limit of 6 × 10⁻¹⁰ shear storage modulus at 23°C. 4 Pa, upper limit 5 x 10 5 Pa is preferable. If the shear storage modulus at 23°C is within the above range, the adhesive layer can exhibit excellent adhesion and its adhesion to the adherend will also improve. The preferred lower limit of the shear storage modulus at 23°C is 7 × 10⁻⁶. 4 Pa, the preferred upper limit is 4 × 10 5 Pa, and a more preferable lower limit is 8 × 10 4 Pa, a more preferable upper limit is 3 × 10 5 It is Pa. The shear storage modulus of the above-mentioned adhesive layer at 23°C can be determined, for example, by the following method: Using a viscoelastic spectrometer (e.g., DVA-200, manufactured by IT Measurement Control Co., Ltd.), the dynamic viscoelastic spectrum of the adhesive layer from -50°C to 200°C is measured under shear mode conditions of 5°C / min and 10Hz. If the adhesive layer is less than 100μm thick, the adhesive layer for measurement is formed by stacking adhesive layers to a thickness of 100μm or more. Using a viscoelastic spectrometer (e.g., DVA-200, manufactured by IT Measurement Control Co., Ltd.), the dynamic viscoelastic spectrum of the obtained adhesive layer for measurement is measured from -50°C to 200°C under shear mode conditions of 5°C / min and 10Hz.

[0048] The adhesive tape of the present invention has a preferred lower limit of 5 N / 25 mm and a more preferred lower limit of 7 N / 25 mm for the 180° peel force on a SUS plate, as measured in accordance with JIS Z 0237:2009. The upper limit of the above 180° peel force is not particularly limited, and a higher value is preferable, but it is practically around 25 N / 25 mm. The 180° peel force on a SUS plate, measured in accordance with JIS Z 0237:2009, is measured as follows: First, an adhesive tape is cut to a width of 25 mm and a length of 75 mm to prepare a test piece. This test piece is placed on the SUS plate so that its adhesive layer faces the SUS plate, and then a 2 kg rubber roller is passed back and forth once at a speed of 300 mm / min to bond it to the test piece. After that, it is cured at 23°C and 50% humidity for 20 minutes to prepare a test sample. In accordance with JIS Z 0237:2009, this test sample is peeled in the 180° direction at a tensile speed of 300 mm / min under conditions of 23°C and 50% humidity, and the adhesive force (N / 25 mm) is measured. Furthermore, if the adhesive tape is a non-support tape without a base material or a double-sided adhesive tape with adhesive layers on both sides of the base material, a 23 μm thick polyethylene terephthalate film (for example, FE2002 or equivalent manufactured by Futamura Chemical Co., Ltd.) is backed onto the surface of the adhesive layer on the other side (the side not measured) before bonding it to the SUS plate.

[0049] The thickness of the adhesive layer in the adhesive tape of the present invention is not particularly limited, but a preferred lower limit is 3 μm and a preferred upper limit is 300 μm. If the thickness of the adhesive layer is within the above range, the adhesive strength of the adhesive composition will be higher. A more preferred lower limit for the thickness of the adhesive layer is 5 μm, and an even more preferred lower limit is 10 μm. A more preferred upper limit for the thickness of the adhesive layer is 200 μm, and an even more preferred upper limit is 100 μm.

[0050] The adhesive tape of the present invention may be a non-support tape without a base material, a single-sided adhesive tape having an adhesive layer on one side of the base material, or a double-sided adhesive tape having adhesive layers on both sides of the base material. When the adhesive tape of the present invention is used as an optical adhesive tape, a non-support tape without a base material is preferred. The above-mentioned substrate is not particularly limited, and conventionally known substrates can be used, however, in order to increase the content of bio-derived carbon in the adhesive tape as a whole, it is preferable to use a bio-derived substrate. Examples of the above-mentioned bio-derived substrates include films and nonwoven fabrics made from plant-derived polyesters (PES) such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polylactic acid (PLA), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). Also included are films and nonwoven fabrics made from plant-derived polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetylcellulose (TAC), cellulose, and polyamide (PA).

[0051] From the viewpoint of substrate strength, the above-mentioned substrate is preferably a film made of PES or a film made of PA. Furthermore, from the viewpoint of heat resistance and oil resistance, a film made of PA is preferred. Examples of materials that make up a film made of the above-mentioned 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.

[0052] 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 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, 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, fractionated, and refined to be used as raw materials.

[0053] The above-mentioned substrate may be a foam substrate from the viewpoint of improving compression characteristics. The foam substrate described above is preferably made of PE, PP, and / or PU, and is more preferably made of PE from the viewpoint of achieving a high degree of both flexibility and strength. Examples of components of the foam substrate made of PE include PE derived from sugarcane.

[0054] The method for producing the foamed substrate described above is not particularly limited, but for example, 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.

[0055] The thickness of the foam substrate described above is not particularly limited, but a preferred lower limit is 50 μm and a preferred upper limit is 5000 μm. When the thickness of the foam substrate is within this range, it can exhibit high impact resistance while also exhibiting high flexibility that allows it to adhere closely to the shape of the substrate. A more preferred upper limit for the thickness of the foam substrate is 1000 μm, and an even more preferred upper limit is 300 μm.

[0056] The adhesive tape of the present invention has a preferred lower limit for the total thickness of the adhesive tape (sum of the thickness of the base material and the adhesive layer) of 3 μm and a preferred upper limit of 6000 μm. If the total thickness of the adhesive tape is within the above range, the adhesive strength will be higher. A more preferred upper limit for the total thickness of the adhesive tape is 1200 μm, and an even more preferred upper limit is 500 μm.

[0057] The haze of the adhesive tape of the present invention is not particularly limited, but when the adhesive tape of the present invention is used as an optical adhesive tape, the preferred upper limit is 1, and the more preferred upper limit is 0.6 or less. The haze of the above adhesive tape is measured in accordance with JIS K7136:2000.

[0058] The method for manufacturing the adhesive tape of the present invention is not particularly limited and can be manufactured by conventionally known manufacturing methods. For example, in the case of double-sided adhesive tape, the following method can be used. First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer and, if necessary, a crosslinking agent or tackifying resin. This solution of adhesive A is then applied to the surface of the substrate, and the solvent in the solution is completely dried and removed to form adhesive layer A. Next, a release film is placed on top of the formed adhesive layer A with its release-treated surface facing the adhesive layer A. Next, a separate release film is prepared, and a solution of adhesive B, prepared in the same manner as above, is applied to the release surface of this release film. By completely drying and removing the solvent in the solution, a laminated film is created in which adhesive layer B is formed on the surface of the release film. The obtained laminated film is then placed on the back surface of a substrate on which adhesive layer A is formed, with adhesive layer B facing the back surface of the substrate, to create a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided adhesive tape is obtained in which adhesive layers are present on both sides of the substrate, and the surface of the adhesive layer is covered with a release film.

[0059] Alternatively, two sets of laminated films may be prepared in the same manner, and these laminated films may be superimposed on each of the two sides of a substrate with the adhesive layer of the laminated film facing the substrate to create a laminate. This laminate may then be pressed with a rubber roller or the like to obtain a double-sided adhesive tape having adhesive layers on both sides of the substrate, with the surface of the adhesive layer covered with a release film.

[0060] The applications of the adhesive tape of the present invention are not particularly limited, but because it can exhibit excellent adhesive strength while reducing metal corrosion, it is preferably used for fixing electronic equipment components or automotive components. Specifically, the adhesive tape of the present invention can be suitably used for adhesive fixing of electronic equipment components in large portable electronic devices, and for adhesive fixing of automotive components (e.g., automotive panels). [Effects of the Invention]

[0061] According to the present invention, it is possible to provide an adhesive composition that is less likely to corrode metals and exhibits excellent adhesive strength. Furthermore, according to the present invention, it is possible to provide an adhesive tape having an adhesive layer containing the adhesive composition. [Modes for carrying out the invention]

[0062] 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.

[0063] <n-heptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was cracked to obtain a mixture containing undecylenic acid and heptyl alcohol. Then, by distillation, the undecylenic acid was separated to obtain n-heptyl alcohol containing bio-derived carbon. n-heptyl acrylate was prepared by esterifying the n-heptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0064] <Other acrylic monomers> • Acrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) • Dimethylacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) • Diethylacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) • Isobornyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) • Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) • 2-hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)

[0065] <Crosslinking agent> • Isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45)

[0066] <Adhesive-granting resin> • Rosin ester (Rosin ester D-135, acid value 13 mg KOH / g, hydroxyl value 45 mg KOH / g, manufactured by Arakawa Chemical Industries, Ltd.) • Terpene phenol A (Terpene phenol G-150, acid value 0 mg KOH / g, hydroxyl value 135 mg KOH / g, manufactured by Yasuhara Chemical Co., Ltd.) • Terpene phenol B (Terpene phenol UH-115, acid value 0 mg KOH / g, hydroxyl value 25 mg KOH / g, manufactured by Yasuhara Chemical Co., Ltd.)

[0067] (Example 1) (1) Production of acrylic copolymer Ethyl acetate was added to the reaction vessel as the polymerization solvent, and after bubbling with nitrogen, the reaction vessel was heated while introducing nitrogen to initiate reflux. Subsequently, a polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile 10-fold with ethyl acetate was added to the reaction vessel as a polymerization initiator, and 98.9 parts by weight of n-heptyl acrylate, 1 part by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate were added dropwise over 2 hours. After the dropwise addition was complete, the polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile 10-fold with ethyl acetate was added again to the reaction vessel as a polymerization initiator, and the polymerization reaction was carried out for 4 hours to obtain an acrylic copolymer-containing solution.

[0068] Mass spectrometry of the obtained acrylic copolymer and 11H-NMR measurements were performed, and the content of constituent units derived from each monomer was calculated from the integral intensity ratio of the hydrogen peaks derived from each monomer.

[0069] The obtained acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting dilution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare the measurement sample. This measurement sample was supplied to a gel permission chromatograph (Waters, 2690 Separations Module), and GPC measurement was performed under conditions of sample flow rate of 1 mL / min and column temperature of 40°C. The polystyrene-equivalent molecular weight of the acrylic copolymer was measured, and the weight-average molecular weight was determined.

[0070] Furthermore, the acid value of the obtained acrylic copolymer was determined by potentiometric titration in accordance with JIS K 0070. Furthermore, the glass transition temperature (Tg) of the obtained acrylic copolymer was determined by differential scanning calorimeter (DSC7000X, Hitachi High-Tech Science). Specifically, approximately 2 mg of the acrylic copolymer was weighed into an aluminum pan, and the pan was measured under a nitrogen atmosphere at a heating rate of 10°C / min. The resulting chart was read to determine the glass transition point.

[0071] (2) Manufacturing of adhesive tape To the obtained acrylic copolymer-containing solution, 30 parts by weight of terpene phenol B were added per 100 parts by weight of acrylic copolymer, and then an isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45) was added so that the solid content was 0.5 parts by weight to prepare an adhesive composition-containing solution. This adhesive composition-containing solution was applied to the release-treated surface of a 75 μm thick release-treated PET film so that the thickness of the adhesive layer after drying was 50 μm, and then dried at 110°C for 5 minutes. This adhesive layer was placed on top of the release-treated surface of a 75 μm thick release-treated PET film and cured at 40°C for 48 hours to obtain an adhesive tape (non-support type).

[0072] (3) Measurement of acid value The acid value of the adhesive composition was determined by potentiometric titration in accordance with JIS K 0070.

[0073] (4) Measurement of shear storage modulus at 23°C (4-1) Adhesive composition The adhesive composition was diluted 2:1 with ethyl acetate and coated onto the release-treated surface of a 75 μm thick release-treated PET film to a dry thickness of 50 μm. The film was then dried at 110°C for 5 minutes. Measurement samples were prepared by stacking the films to a thickness of 100 μm. The dynamic viscoelastic spectra of the measurement samples were measured from -50°C to 200°C using a viscoelastic spectrometer (e.g., DVA-200, manufactured by IT Measurement Control Co., Ltd.) under shear mode conditions of 5°C / min and 10 Hz. The shear storage modulus at 23°C was determined from these measurements.

[0074] (4-2) Adhesive layer For the adhesive layer of adhesive tape, measurement samples were prepared by stacking them to a thickness of 100 μm. The dynamic viscoelastic spectra of the measurement samples were measured from -50°C to 200°C using a viscoelastic spectrometer (e.g., DVA-200, manufactured by IT Measurement Control Co., Ltd.) under shear mode conditions of 5°C / min and 10 Hz. From this, the shear storage modulus at 23°C was determined.

[0075] (5) Measurement of gel fraction The release film was peeled off one side of the adhesive tape and bonded to a 23 μm thick PET film (Futamura Chemical Co., Ltd., FE2002). The tape was then cut into a 20 mm x 40 mm rectangular shape. The release film was then peeled off the other side of the adhesive tape to prepare a test specimen, and its weight 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 weight of the dried test specimen was measured, and the gel fraction was calculated using (1) below. Gel fraction (weight %) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: Weight of the substrate (PET film), W1: Weight of the test specimen before immersion, W2: Weight of the test specimen after immersion and drying)

[0076] (Examples 2-16, Comparative Examples 1-4) An adhesive tape was obtained in the same manner as in Example 1, except that the type and amount of acrylic monomers constituting the acrylic copolymer, the weight-average molecular weight of the acrylic copolymer, and the type and amount of tackifying resin and crosslinking agent were changed as shown in Table 1.

[0077] <Rating> The adhesive tapes obtained in the examples and comparative examples were evaluated using the following method. The results are shown in Table 1.

[0078] (1) 180° peel force on SUS plate One side of the adhesive tape (the side not measured) was backed with a 23 μm thick polyethylene terephthalate film (Futamura Chemical Co., Ltd., FE2002), and then cut to a width of 25 mm x length of 75 mm to prepare a test specimen. This test specimen was placed on a stainless steel plate so that its adhesive layer (the side to be measured) faced the stainless steel plate, and then bonded to the specimen by passing 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% humidity for 20 minutes to prepare a test sample. In accordance with JIS Z 0237:2009, this test sample was peeled in a 180° direction at a tensile speed of 300 mm / min under conditions of 23°C and 50% humidity, and the adhesive strength (N / 25 mm) was measured. In Table 1, "cohesive failure" means that the adhesive layer failed to cohesively because the cohesive force of the adhesive layer was low, preventing delamination at the interface with the SUS plate.

[0079] (2) Corrosion of copper foil One side of the adhesive tape was backed with a 50 μm thick polyethylene terephthalate film (Toyobo Co., Ltd., E5200), and then cut to a width of 25 mm x length of 25 mm to create an evaluation adhesive tape. Two of these evaluation adhesive tapes were prepared. The adhesive side of evaluation adhesive tape 1 was placed facing one side of a copper foil (C1020R-H, 20 μm thick, 25 mm wide x 25 mm long, manufactured by Takeuchi Metal Foil & Powder Industry Co., Ltd.), and then bonded to evaluation adhesive tape 1 by passing a 2 kg rubber roller back and forth at a speed of 300 mm / min. Subsequently, the adhesive side of evaluation adhesive tape 2 was placed facing the other side of the copper foil, and then bonded to evaluation adhesive tape 2 by passing a 2 kg rubber roller back and forth at a speed of 300 mm / min, creating a laminate with a width of 25 mm and a length of 25 mm. After bonding, the laminate was cured for 20 minutes at 23°C and 50% humidity to prepare a test sample. The test samples were left in an environment with a temperature of 85°C and a humidity of 85%. After 3 days, 14 days, and 28 days, evaluation adhesive tape 1 and evaluation adhesive tape 2 were peeled off the copper foil, and the presence or absence of corrosion of the copper foil was visually checked. If corrosion of the copper foil was observed, it was marked with ×, and if no corrosion was observed on either side, it was marked with ○.

[0080] (3) Content of bio-derived carbon The bio-derived carbon content of the adhesive tape was measured in accordance with ASTM D6866-20.

[0081] (4) Hayes Adhesive tape was attached to a glass slide (Matsunami Glass Industry Co., Ltd., large white-rimmed polished slide No. 2), and the haze was measured using a haze meter (Murakami Color Technology Laboratory, HM-150) in accordance with JIS K7136:2000.

[0082] [Table 1] [Industrial applicability]

[0083] According to the present invention, it is possible to provide an adhesive composition that is less likely to corrode metals and exhibits excellent adhesive strength. Furthermore, according to the present invention, it is possible to provide an adhesive tape having an adhesive layer containing the adhesive composition.

Claims

1. An adhesive composition containing an acrylic copolymer, The acrylic copolymer contains 50% by weight or more of constituent units derived from n-heptyl (meth)acrylate, The acrylic copolymer further contains a constituent unit derived from a monomer having a polar functional group, and the monomer having a polar functional group contains a monomer having an amide group. The aforementioned adhesive composition has an acid value of 22 mg KOH / g or less and a shear storage modulus of 6 × 10 at 23°C. ４ Pa or more 5×10 ５ It is less than or equal to Pa. An adhesive composition characterized by the following features.

2. The adhesive composition according to claim 1, characterized in that the acrylic copolymer has an acid value of 22 mg KOH / g or less.

3. The adhesive composition according to claim 1 or 2, characterized in that the acrylic copolymer contains 2% by weight or more and 30% by weight or less of structural units derived from the monomer having the amide group.

4. The adhesive composition according to claim 1 or 2, characterized in that the monomer having the polar functional group further contains a monomer having a hydroxyl group.

5. The adhesive composition according to claim 4, characterized in that the acrylic copolymer contains 0.01% by weight or more and 5% by weight or less of constituent units derived from the monomer having a hydroxyl group.

6. Furthermore, the adhesive composition according to claim 1 or 2 is characterized in that it contains a tackifying resin, wherein the tackifying resin has an acid value of 10 mg KOH / g or less.

7. The adhesive composition according to claim 6, characterized in that the tackifying resin has a hydroxyl value of 50 mgKOH / g or less.

8. The adhesive composition according to claim 1 or 2, characterized in that it contains 30% by weight or more of bio-derived carbon.

9. An adhesive tape characterized by having an adhesive layer containing the adhesive composition described in claim 1 or 2.

10. The adhesive tape according to claim 9, characterized in that the adhesive layer has a gel fraction of 20% by weight or more and 50% by weight or less.

11. The adhesive tape according to claim 9, characterized in that the adhesive layer has a gel fraction of 60% by weight or more and 95% by weight or less.

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