Tape

Abstract

The invention proposes an adhesive tape with a high content of bio-derived carbon and excellent shear strength at high temperatures. The invention proposes an adhesive tape comprising an adhesive layer containing an acrylic copolymer, an acrylic copolymer containing a structural unit derived from bio-derived alkyl(met)acrylates, and an adhesive layer whose total amount of the structural compound represented by the following formula (A) and the structural compound represented by the following formula (B) is 2% by mass or less, wherein each R1 and R2 represents a C4–C12 alkyl group.

Description

adhesive tape

[0001] The present invention relates to an adhesive tape.

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

[0003] JP 2015-052050 A JP 2015-021067 A JP 2015-120876 A

[0004] In recent years, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products have become a concern. Therefore, efforts have been made to conserve petroleum resources by replacing petroleum-derived materials with bio-derived materials, primarily in the fields of medicine and packaging materials. These efforts have spread to all fields, and there is now a demand for the use of bio-derived materials in the fields of adhesives and adhesive tapes.

[0005] An object of the present invention is to provide an adhesive tape that has a high content of bio-derived carbon and has excellent shear strength at high temperatures.

[0006] Disclosure 1 relates to a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing an acrylic copolymer, wherein the acrylic copolymer contains a structural unit derived from an alkyl(meth)acrylate containing carbon of biological origin, and the pressure-sensitive adhesive layer contains a compound having a structure represented by the following general formula (A) and a compound having a structure represented by the following general formula (B) in a total content of 2 wt % or less:

[0007]

[0008] In general formulas (A) and (B), R １ and R ２ represents an alkyl group having 4 to 12 carbon atoms.

[0009] Disclosure 2 is the pressure-sensitive adhesive tape of Disclosure 1, wherein the pressure-sensitive adhesive layer contains 2 wt % or less of the compound having the structure represented by general formula (A), the compound having the structure represented by general formula (B), and the compound having the structure represented by the following general formula (C):

[0010]

[0011] In general formula (C), R １ and R ２ represents an alkyl group having 4 to 12 carbon atoms.

[0012] The present disclosure 3 is the pressure-sensitive adhesive tape of the present disclosure 1 or 2, wherein the pressure-sensitive adhesive layer contains less than 1 wt % of the compound having the structure represented by general formula (A). The present disclosure 4 is the pressure-sensitive adhesive tape of the present disclosure 1, 2, or 3, wherein the compound having the structure represented by general formula (A) is a compound having a structure represented by the following formula (a1):

[0013]

[0014] Disclosure 5 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, or 4, wherein the pressure-sensitive adhesive layer contains less than 1 wt % of a compound having a structure represented by general formula (B). Disclosure 6 is the pressure-sensitive adhesive tape of Disclosure 2, 3, 4, or 5, wherein the pressure-sensitive adhesive layer contains less than 1 wt % of a compound having a structure represented by general formula (C). Disclosure 7 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, or 6, wherein the compound having a structure represented by general formula (B) is a compound having a structure represented by the following formula (b1):

[0015]

[0016] The present disclosure 8 is the pressure-sensitive adhesive tape of the present disclosure 2, 3, 4, 5, 6, or 7, wherein the compound having a structure represented by general formula (C) is a compound having a structure represented by the following formula (c1):

[0017]

[0018] Disclosure 9 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, or 8, wherein the alkyl (meth)acrylate containing bio-derived carbon contains n-heptyl (meth)acrylate. Disclosure 10 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein the acrylic copolymer has a content of structural units derived from the alkyl (meth)acrylate containing bio-derived carbon of 85% by weight or more. Disclosure 11 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the pressure-sensitive adhesive layer further contains a tackifying resin. Disclosure 12 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the pressure-sensitive adhesive layer has a content of bio-derived carbon of 10% by weight or more. The present disclosure 13 is a pressure-sensitive adhesive tape according to the present disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, which is used for fixing electronic equipment components or vehicle-mounted components.

[0019] In this specification, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic. The acrylic copolymer may be a methacrylic copolymer. The present invention will be described in detail below.

[0020] The present inventors have investigated the use of alkyl(meth)acrylate containing carbon derived from living organisms as the acrylic monomer constituting the acrylic copolymer in an adhesive tape having a pressure-sensitive adhesive layer containing an acrylic copolymer. However, when alkyl(meth)acrylate containing carbon derived from living organisms was used, sufficient adhesive strength was not obtained, and for example, the shear holding strength at high temperatures was sometimes reduced.

[0021] The present inventors investigated the reasons why sufficient adhesive strength could not be obtained and found that the reason is that alkyl (meth)acrylates containing biological carbons contain impurities due to their biological origin. In particular, when (meth)acrylates having alkyl groups with a relatively large number of carbon atoms are used as the alkyl (meth)acrylates containing biological carbons, the glass transition temperature (Tg) of the acrylic copolymer is sufficiently low, and excellent adhesive strength can be expected. However, (meth)acrylates containing biological carbons and having alkyl groups with a relatively large number of carbon atoms contain dialkyl ethers and ether esters having alkyl groups with a relatively large number of carbon atoms as impurities. The present inventors discovered that these impurities remain in the adhesive layer, and that, when exposed to high temperatures, the impurities may bleed out, reducing cohesive strength and thereby leading to a decrease in adhesive strength. In response to this, the present inventors discovered that an adhesive tape with excellent shear holding strength at high temperatures can be obtained by adjusting the total content of specific compounds corresponding to impurities in alkyl (meth)acrylates containing biological carbons in the adhesive layer to a certain value or less, and thus completed the present invention.

[0022] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer containing an acrylic copolymer. The acrylic copolymer contains structural units derived from alkyl(meth)acrylate containing bio-derived carbon. This increases the content of bio-derived carbon in the pressure-sensitive adhesive tape of the present invention, allowing it to exhibit excellent adhesive strength and excellent shear holding strength at high temperatures.

[0023] The alkyl (meth)acrylate containing carbon atoms of biological origin is not particularly limited, but (meth)acrylates having an alkyl group containing 7 to 12 carbon atoms are preferred because they sufficiently lower the glass transition temperature (Tg) of the acrylic copolymer and further increase the adhesive strength of the pressure-sensitive adhesive layer. Examples of (meth)acrylates having an alkyl group containing 7 to 12 carbon atoms include n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, and lauryl (meth)acrylate. These alkyl (meth)acrylates containing carbon atoms of biological origin may be used alone or in combination of two or more. Of these, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, and lauryl (meth)acrylate are preferred because they further increase the adhesive strength of the pressure-sensitive adhesive layer, with n-heptyl (meth)acrylate being more preferred.

[0024] The alkyl (meth)acrylate containing carbon derived from a living organism is not particularly limited as long as it contains carbon derived from a living organism. However, it is preferable that it be synthesized by esterification of a living organism alcohol with (meth)acrylic acid or by transesterification of a living organism alcohol with a (meth)acrylic acid ester. For example, n-heptyl alcohol, a living organism, can be obtained inexpensively and easily by cracking a material extracted from plants and animals (e.g., ricinoleic acid derived from castor oil). Furthermore, n-octyl alcohol, a living organism, can be obtained easily and inexpensively by reducing a material extracted from plants and animals (e.g., caprylic acid derived from coconut oil). Furthermore, lauryl alcohol, a living organism, can be obtained easily and inexpensively by reducing a material extracted from plants and animals (e.g., lauric acid derived from palm oil or palm kernel oil).

[0025] The content of the structural units derived from alkyl (meth)acrylate containing bio-derived carbon in the acrylic copolymer is not particularly limited, but is preferably greater than 50 wt%, with a more preferred lower limit of 60 wt%, an even more preferred lower limit of 70 wt%, and an especially preferred lower limit of 85 wt%. If the content of the structural units is 85 wt% or more, the content of bio-derived carbon in the entire pressure-sensitive adhesive tape increases, the adhesive strength of the pressure-sensitive adhesive layer increases, and the shear holding strength of the pressure-sensitive adhesive tape at high temperatures becomes higher. The most preferred lower limit of the content of the structural units is 90 wt%. The upper limit of the content of the structural units derived from alkyl (meth)acrylate containing bio-derived carbon is not particularly limited, but from the viewpoint of adjusting the gel fraction of the pressure-sensitive adhesive layer, a preferred upper limit is 99 wt%, and a more preferred upper limit is 97 wt%. In particular, when the content of the structural unit derived from the n-heptyl (meth)acrylate in the acrylic copolymer is more than 50% by weight, more preferably 60% by weight, even more preferably 70% by weight, and particularly preferably 85% by weight or more, the adhesive strength of the pressure-sensitive adhesive layer is further increased.

[0026] The content of the structural unit derived from the alkyl (meth)acrylate containing the carbon of biological origin in the acrylic copolymer can be determined by mass spectrometry of the acrylic copolymer and １ H-NMR measurement can be carried out, and the ratio can be calculated from the integrated intensity ratio of the hydrogen peaks derived from each monomer.

[0027] The acrylic copolymer preferably further contains a structural unit derived from a monomer having a crosslinkable functional group. When the acrylic copolymer contains the structural unit derived from a monomer having a crosslinkable functional group, the cohesive strength of the pressure-sensitive adhesive layer increases, resulting in higher adhesive strength.

[0028] The monomer having a crosslinkable functional group is not particularly limited, and examples thereof include a monomer having a hydroxyl group, a monomer having a carboxyl group, a monomer having a glycidyl group, a monomer having an amide group, and a monomer having a nitrile group. These monomers having a crosslinkable functional group may be used alone or in combination of two or more. Among them, monomers having a hydroxyl group and monomers having a carboxyl group are preferred, as they allow for easy adjustment of the gel fraction of the pressure-sensitive adhesive layer, and monomers having a hydroxyl group are more preferred.

[0029] Examples of the monomer having a hydroxyl group include acrylic monomers having a hydroxyl group, such as 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of the monomer having a carboxyl group include acrylic monomers having a carboxyl group, such as (meth)acrylic acid. Examples of the monomer having a glycidyl group include acrylic monomers having a glycidyl group, such as glycidyl (meth)acrylate. Examples of the monomer having an 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. Examples of the monomer having a nitrile group include acrylic monomers having a nitrile group, such as (meth)acrylonitrile.

[0030] The content of the structural unit derived from the monomer having the crosslinkable functional group in the acrylic copolymer is not particularly limited, but the preferred lower limit is 0.01 wt%, and the preferred upper limit is 15 wt%.If the content of the structural unit derived from the monomer having the crosslinkable functional group is within the above range, the cohesive strength of the pressure-sensitive adhesive layer will be further increased, and the adhesive strength will be further increased.The more preferred lower limit of the content of the structural unit derived from the monomer having the crosslinkable functional group is 0.1 wt%, and the more preferred upper limit is 10 wt%, and the even more preferred lower limit is 0.5 wt%, and the even more preferred upper limit is 5 wt%.

[0031] The content of the structural unit derived from the monomer having a crosslinkable functional group in the acrylic copolymer was determined by mass spectrometry of the acrylic copolymer and １ H-NMR measurement can be carried out, and the ratio can be calculated from the integrated intensity ratio of the hydrogen peaks derived from each monomer.

[0032] The acrylic copolymer may have a structural unit derived from a monomer other than the structural unit derived from the alkyl(meth)acrylate containing carbon atoms of biological origin and the structural unit derived from the monomer having a crosslinkable functional group. The other monomer is not particularly limited, and examples thereof include (meth)acrylates (petroleum-derived monomers) having an alkyl group of 7 to 12 carbon atoms that do not contain carbon atoms of biological origin, and (meth)acrylic acid alkyl esters. Examples of the (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)octanol-1 and (meth)acrylic acid, esters of (meth)acrylic acid and alcohols having a total of 18 carbon atoms and one or two methyl groups in the linear main chain, behenyl (meth)acrylate, arachidyl (meth)acrylate, etc. These (meth)acrylic acid alkyl esters may be used alone or in combination of two or more.

[0033] Examples of the other monomers include 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 resilience, isobornyl (meth)acrylate is preferred. Furthermore, various monomers used in general acrylic polymers, such as vinyl carboxylates such as vinyl acetate and styrene, can also be used as the other monomers. When the acrylic copolymer is produced by UV polymerization, polyfunctional monomers such as 1,6-hexanediol di(meth)acrylate can also be used as the other monomers. These other monomers may be used alone or in combination of two or more.

[0034] The content of the structural units derived from the other monomers in the acrylic copolymer was determined by mass spectrometry of the acrylic copolymer and １ H-NMR measurement can be carried out, and the ratio can be calculated from the integrated intensity ratio of the hydrogen peaks derived from each monomer.

[0035] The monomer having a crosslinkable functional group and the other monomer preferably contain carbon derived from living organisms, but may also be composed solely of petroleum-derived materials without containing carbon derived from living organisms. In theory, it is also possible for all of the acrylic monomers constituting the acrylic copolymer to be monomers containing carbon derived from living organisms. From the standpoint of the cost and productivity of the pressure-sensitive adhesive tape, a relatively inexpensive and easily available monomer containing carbon derived from living organisms may be adopted and combined with a monomer composed solely of petroleum-derived materials.

[0036] The glass transition temperature (Tg) of the acrylic copolymer is not particularly limited, but is preferably -20°C or lower. If the glass transition temperature (Tg) of the acrylic copolymer is -20°C or lower, the adhesiveness of the pressure-sensitive adhesive layer to an adherend is improved, and the adhesive strength is further increased. The glass transition temperature (Tg) of the 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 acrylic copolymer is not particularly limited, and is usually -90°C or higher, preferably -80°C or higher. The glass transition temperature (Tg) of the acrylic copolymer can be determined, for example, by differential scanning calorimetry.

[0037] The weight-average molecular weight (Mw) of the 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 acrylic copolymer is within the above range, the adhesive strength of the pressure-sensitive adhesive layer will be higher. A more preferred lower limit of the weight-average molecular weight of the 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 in terms of standard polystyrene measured by GPC (gel permeation chromatography). Specifically, the acrylic copolymer is diluted 50 times with tetrahydrofuran (THF), and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. Next, this measurement sample is supplied to a gel permeation chromatograph (manufactured by Waters, trade name "2690 Separations Module" or an equivalent product), and GPC measurement is performed under conditions of a sample flow rate of 1 milliliter / minute and a column temperature of 40° C. The polystyrene-equivalent molecular weight of the acrylic copolymer is measured, and this value is taken as the weight-average molecular weight of the acrylic copolymer.

[0038] The acrylic copolymer can be obtained by radical reaction of a raw material monomer mixture in the presence of a radical polymerization initiator. The radical reaction method is not particularly limited, and examples include living radical polymerization and free radical polymerization. Living radical polymerization produces a copolymer with a more uniform molecular weight and composition compared to free radical polymerization, and can suppress the generation of low-molecular-weight components, thereby increasing the cohesive strength of the pressure-sensitive adhesive layer and further enhancing its 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 enhance the adhesive strength of the pressure-sensitive adhesive layer. Furthermore, solution polymerization is more preferred because it allows the tackifier resin to be easily mixed with the resulting acrylic copolymer, further enhancing the adhesive strength of the pressure-sensitive adhesive layer.

[0039] When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, diethyl ether, etc. These reaction solvents may be used alone or in combination of two or more.

[0040] The radical polymerization initiator is not particularly limited, and examples thereof include organic peroxides and azo compounds. Examples of the 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 the azo compounds include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These radical polymerization initiators may be used alone or in combination of two or more. In the case of living radical polymerization, examples of the radical polymerization initiator include organotellurium polymerization initiators. The organotellurium polymerization initiator is not particularly limited as long as it is one that is commonly used in living radical polymerization, and examples thereof include organotellurium compounds, organotelluride compounds, etc. In addition to the organotellurium polymerization initiator, an azo compound may also be used as the radical polymerization initiator in living radical polymerization in order to accelerate the polymerization rate.

[0041] The pressure-sensitive adhesive layer preferably does not contain a surfactant. The absence of a surfactant in the pressure-sensitive adhesive layer increases the adhesive strength of the pressure-sensitive adhesive tape, particularly at high temperatures. The absence of a surfactant in the pressure-sensitive adhesive layer means that the surfactant content in the pressure-sensitive adhesive layer is 3% by weight or less, preferably 1% by weight or less. To prevent the pressure-sensitive adhesive layer from containing a surfactant, it is preferable to not use a surfactant when obtaining the acrylic copolymer. To achieve this, for example, solution polymerization, UV polymerization, or the like may be employed as the polymerization method for obtaining the acrylic copolymer. The surfactant content can be determined, for example, by measuring the pressure-sensitive adhesive layer using a liquid chromatography mass spectrometer (e.g., NEXCERA manufactured by Shimadzu Corporation, Exactive manufactured by Thermo Fisher Scientific, etc.). More specifically, an ethyl acetate solution of the pressure-sensitive adhesive layer is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). Approximately 10 μL of the obtained 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 peak corresponding to the surfactant in the adhesive layer. It is preferable to prepare samples with known surfactant contents in the adhesive layer for each surfactant type, and create a calibration curve showing the relationship between the surfactant content and the peak area ratio for analysis. Column: Hypersil GOLD (2.1 × 150 mm), manufactured by Thermo Fisher Scientific; Mobile phase: Acetonitrile; Column temperature: 40°C; Flow rate: 1.0 mL / min; Ionization method: ESI; Capillary temperature: 350°C

[0042] The pressure-sensitive adhesive layer preferably further contains a crosslinking agent from the viewpoint of being able to appropriately adjust the gel fraction. The crosslinking agent is not particularly limited, and examples thereof include 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 they provide the pressure-sensitive adhesive layer with excellent adhesion to the adherend. The molecular weight of the crosslinking agent is not particularly limited, but from the viewpoint of manufacturing, the molecular weight is preferably less than 2000 and preferably 100 or more.

[0043] The content of the crosslinking agent in the pressure-sensitive adhesive layer 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 relative to 100 parts by weight of the acrylic copolymer. If the content of the crosslinking agent is within the above range, the gel fraction of the pressure-sensitive adhesive layer can be appropriately adjusted, resulting in higher adhesive strength. A more preferred lower limit of the content of the crosslinking agent is 0.1 parts by weight and a more preferred upper limit is 5 parts by weight. The content of the crosslinking agent indicates the amount of solids of the crosslinking agent.

[0044] The pressure-sensitive adhesive layer preferably further contains a tackifier resin. This increases the adhesive strength of the pressure-sensitive adhesive layer and increases the shear holding strength of the pressure-sensitive adhesive tape at high temperatures. Specific examples of the tackifier resin include rosin ester tackifier resins, terpene tackifier resins, coumarone-indene tackifier resins, alicyclic saturated hydrocarbon tackifier resins, C5 petroleum tackifier resins, C9 petroleum tackifier resins, and C5-C9 copolymer petroleum tackifier resins. These tackifier resins may be used alone or in combination of two or more. Of these, at least one selected from the group consisting of rosin ester tackifier resins and terpene tackifier resins is preferred.

[0045] Examples of the rosin ester-based tackifying resin include polymerized rosin ester-based resins and hydrogenated rosin ester-based resins. Examples of the terpene-based tackifying resin include terpene-based resins and terpene phenol-based resins. The rosin ester-based tackifying resins and terpene-based tackifying resins are preferably derived from living organisms. Examples of the rosin ester-based tackifying resins derived from living organisms include rosin ester-based tackifying resins derived from natural resins such as pine resin. Examples of the terpene-based tackifying resins derived from living organisms include terpene-based tackifying resins derived from plant essential oils.

[0046] The content of the tackifier resin in the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 60 parts by weight per 100 parts by weight of the acrylic copolymer. If the content of the tackifier resin is within the above range, the adhesive strength of the pressure-sensitive adhesive layer will be higher and the shear holding strength of the pressure-sensitive adhesive tape at high temperatures will be higher. A more preferred lower limit of the content of the tackifier 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.

[0047] The pressure-sensitive adhesive layer may contain additives such as a silane coupling agent, a plasticizer, a softener, a filler, a pigment, or a dye, as needed.

[0048] The pressure-sensitive adhesive layer contains a compound having a structure represented by the following general formula (A) and a compound having a structure represented by the following general formula (B) in a total content of 2 wt % or less.

[0049]

[0050] In general formulas (A) and (B), R １ and R ２ represents an alkyl group having 4 to 12 carbon atoms.

[0051] It is preferable that the pressure-sensitive adhesive layer contains a compound having a structure represented by the general formula (A) above, a compound having a structure represented by the general formula (B) above, and a compound having a structure represented by the following general formula (C) in a total content of 2 wt % or less.

[0052]

[0053] In general formula (C), R １ and R ２ represents an alkyl group having 4 to 12 carbon atoms.

[0054] The compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B) are compounds corresponding to impurities of the alkyl (meth)acrylate containing carbon derived from living organisms. Therefore, the alkyl group (R １ and R ２) is preferably the same as the alkyl group of the alkyl (meth)acrylate containing carbon of biological origin. １ and R ２ ) may be different from the alkyl group of the alkyl (meth)acrylate containing carbon derived from a living organism. The compound having the structure represented by the general formula (C) is a compound corresponding to an impurity of the alkyl (meth)acrylate containing carbon derived from a living organism. Therefore, the alkyl group (R １ and R ２ ) is preferably the same as the alkyl group of the alkyl (meth)acrylate containing carbon of biological origin. １ and R ２ ) may be different from the alkyl group of the alkyl (meth)acrylate containing carbon of biological origin. １ and R ２ The alkyl group (R ) is not particularly limited as long as it is an alkyl group having 4 to 12 carbon atoms, but is preferably an alkyl group having 7 to 12 carbon atoms. １ and R ２ ) specifically includes, for example, an n-heptyl group, an n-octyl group, an n-decyl group, a lauryl group, etc. In the above general formula (A) and the above general formula (B), R １ and R ２ In the above general formulas (A) to (C), R may be the same or different, but it is preferable that they are the same. １ and R ２ may be the same or different, but are preferably the same.

[0055] The compound having the structure represented by the general formula (A) may consist of only one compound having a structure represented by the general formula (A), or may be a combination of multiple compounds having a structure represented by the general formula (A). Similarly, the compound having the structure represented by the general formula (B) may consist of only one compound having a structure represented by the general formula (B), or may be a combination of multiple compounds having a structure represented by the general formula (B). Similarly, the compound having the structure represented by the general formula (C) may consist of only one compound having a structure represented by the general formula (C), or may be a combination of multiple compounds having a structure represented by the general formula (C).

[0056] More specifically, the compound having the structure represented by the general formula (A) is preferably a compound having a structure represented by the following formula (a1):

[0057]

[0058] More specifically, the compound having the structure represented by the general formula (B) is preferably a compound having a structure represented by the following formula (b1):

[0059]

[0060] More specifically, the compound having the structure represented by the general formula (C) is preferably a compound having a structure represented by the following formula (c1):

[0061]

[0062] When the total content of the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B) is 2 wt% or less, the decrease in adhesive strength due to bleed-out of these compounds can be suppressed, and the shear holding strength of the adhesive tape at high temperatures can be increased. The total content of the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B) is preferably 1 wt% or less, more preferably 0.1 wt% or less. The lower limit of the total content of the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B) is not particularly limited, and a value closer to 0 wt% is preferable, and even 0 wt% is acceptable. That is, the adhesive layer does not need to contain the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B).

[0063] The total content of the compound having the structure represented by the general formula (A), the compound having the structure represented by the general formula (B), and the compound having the structure represented by the general formula (C) is preferably 2 wt% or less. When the content is below the upper limit, the decrease in adhesive strength due to bleed-out of these compounds can be more effectively suppressed, and the shear holding strength of the pressure-sensitive adhesive tape at high temperatures can be increased. The total content of the compound having the structure represented by the general formula (A), the compound having the structure represented by the general formula (B), and the compound having the structure represented by the general formula (C) is more preferably 1 wt% or less, and even more preferably 0.1 wt% or less. The lower limit of the total content of the compound having the structure represented by the general formula (A), the compound having the structure represented by the general formula (B), and the compound having the structure represented by the general formula (C) is not particularly limited, and a value closer to 0 wt% is preferable, and even 0 wt% is acceptable. That is, the pressure-sensitive adhesive layer does not necessarily contain the compound having the structure represented by the general formula (A), the compound having the structure represented by the general formula (B), and the compound having the structure represented by the general formula (C).

[0064] The total content of the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B), or the total content of the compound having the structure represented by the general formula (A), the compound having the structure represented by the general formula (B), and the compound having the structure represented by the general formula (C) is calculated as follows: The sol content of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive tape is extracted using toluene and dried. The obtained sol content is dissolved in deuterated chloroform, １ H-NMR measurement and １３ By carrying out C-NMR measurement, the contents of the compound having the structure represented by the general formula (A) and the compound having the structure represented by the general formula (B) are calculated, and the total content can be calculated by adding these up.

[0065] Examples of methods for adjusting the total content of the compound having a structure represented by the general formula (A) and the compound having a structure represented by the general formula (B) within the above range include the following methods. That is, when using an alkyl(meth)acrylate containing carbon derived from a specific organism as the acrylic monomer constituting the acrylic copolymer, the alkyl(meth)acrylate containing carbon derived from the specific organism is purified to reduce the content of the compound contained as an impurity. The content of the compound contained as an impurity may also be reduced by purifying the resulting acrylic copolymer, or the content of the compound may be reduced by adjusting the heating and drying conditions during production of the pressure-sensitive adhesive tape (e.g., during formation of the pressure-sensitive adhesive layer). Among these, it is preferable to purify the alkyl(meth)acrylate containing carbon derived from a specific organism. The method for purifying the alkyl(meth)acrylate and the acrylic copolymer is not particularly limited, and conventionally known methods can be used, such as distillation, reprecipitation, preparative liquid chromatography, and column chromatography. Distillation, preparative liquid chromatography, and column chromatography are preferred methods for purifying the alkyl(meth)acrylate, and reprecipitation, preparative liquid chromatography, and column chromatography are preferred methods for purifying the acrylic copolymer.

[0066] The content of the compound having the structure represented by the general formula (A) in the pressure-sensitive adhesive layer is not particularly limited as long as the total content can be adjusted to the above range, but it is preferably less than 1 wt%. If the content of the compound having the structure represented by the general formula (A) is less than 1 wt%, the shear holding strength of the pressure-sensitive adhesive tape at high temperatures will be higher. The lower limit of the content of the compound having the structure represented by the general formula (A) is not particularly limited, and the closer to 0 wt%, the more preferable, and it may even be 0 wt%.

[0067] The content of the compound having the structure represented by the general formula (B) in the pressure-sensitive adhesive layer is not particularly limited as long as the total content can be adjusted to the above range, but it is preferably less than 1 wt %, more preferably 0.01 wt % or less. If the content of the compound having the structure represented by the general formula (B) is within the above range, the shear holding strength of the pressure-sensitive adhesive tape at high temperatures will be higher. The lower limit of the content of the compound having the structure represented by the general formula (B) is not particularly limited, and the closer to 0 wt %, the more preferable, and it may even be 0 wt %.

[0068] The gel fraction of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 10 wt % and a preferred upper limit is 70 wt %. If the gel fraction of the pressure-sensitive adhesive layer is within the above range, the adhesive strength of the pressure-sensitive adhesive layer will be higher. A more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 20 wt % and a more preferred upper limit is 50 wt %. The gel fraction of the pressure-sensitive adhesive layer is measured as follows. First, a pressure-sensitive adhesive tape is cut into a 20 mm x 40 mm flat rectangular shape to prepare a test piece, and the test piece is 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 test piece after drying is measured, and the gel fraction is calculated using the following formula (1). It is assumed that no release film for protecting the pressure-sensitive adhesive layer is laminated on the test piece. Gel fraction (wt %) = 100 x (W ２ -W ０ ) / (W １ -W ０ ) (1) (W ０ : Weight of substrate, W １ : weight of test piece before immersion, W ２ : weight of test piece after immersion and drying)

[0069] The method for adjusting the gel fraction of the pressure-sensitive adhesive layer to the above range is not particularly limited, but a method of adjusting the composition and weight average molecular weight of the acrylic copolymer, and the type and amount of the crosslinking agent as described above is preferred.

[0070] The PSA layer preferably has a bio-derived carbon content of 10% by weight or more. A bio-derived carbon content of 10% by weight or more is an indicator of a "bio-based product." A bio-derived carbon content of 10% by weight or more is preferable from the perspective of conserving petroleum resources and reducing carbon dioxide emissions. A more preferred lower limit of the bio-derived carbon content is 30% by weight, and an even more preferred lower limit is 60% by weight. The upper limit of the bio-derived carbon content is not particularly limited and may be 100% by weight. Note that while bio-derived carbon contains a certain percentage of the radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the bio-derived carbon content can be calculated by measuring the concentration of C-14 contained in the PSA layer. Specifically, it can be measured in accordance with ASTM D6866-20, a standard widely used in the bioplastics industry.

[0071] The thickness of the pressure-sensitive adhesive layer 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 pressure-sensitive adhesive layer is within the above range, the adhesive strength of the pressure-sensitive adhesive layer will be higher. A more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm, and an even more preferred lower limit is 10 μm. A more preferred upper limit of the thickness of the pressure-sensitive adhesive layer is 200 μm, and an even more preferred upper limit is 100 μm.

[0072] The pressure-sensitive adhesive tape of the present invention may be a non-supported tape without a substrate, a single-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on one side of the substrate, or a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of the substrate. The substrate is not particularly limited, and conventionally known substrates can be used. However, to increase the biocarbon content of the entire pressure-sensitive adhesive tape, it is preferable to use a bio-based substrate. Examples of the bio-based substrate include films and nonwoven fabrics made of 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). Other examples include films and nonwoven fabrics made of plant-derived polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetyl cellulose (TAC), cellulose, polyamide (PA), and the like.

[0073] From the viewpoint of substrate strength, the 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 preferable. Examples of the constituent material of the PA film 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.

[0074] Furthermore, from the perspective of reducing the use of new petroleum resources and reducing carbon dioxide emissions to reduce the environmental impact, substrates made from recycled resources may be used. Examples of resource recycling methods include collecting waste materials such as packaging containers, home appliances, automobiles, construction materials, and food, as well as waste generated during manufacturing processes, and then cleaning, decontaminating, or decomposing the extracted materials by heating or fermentation to reuse them as raw materials. Examples of substrates made from recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., which are made from recycled plastics that have been re-resinized. Furthermore, the collected waste materials may be burned and used as thermal energy for the production of substrates and their raw materials, or the oils and fats contained in the collected waste materials may be mixed with petroleum, fractionated, and purified, and then used as raw materials.

[0075] The substrate may be a foam substrate from the viewpoint of improving compression characteristics. The foam substrate is preferably a foam substrate made of PE, PP and / or PU, and more preferably a foam substrate made of PE from the viewpoint of achieving a high degree of both flexibility and strength. Examples of the constituent material of the foam substrate made of PE include PE made from sugarcane.

[0076] The method for producing the foam base material is not particularly limited, but a preferred method is, for example, to prepare a foamable resin composition containing a PE resin containing PE derived from sugarcane and a foaming agent, and then foam the foaming agent when extruding the foamable resin composition into a sheet using an extruder, and optionally crosslink the resulting polyolefin foam.

[0077] The thickness of the foam substrate 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 exhibiting high flexibility that allows it to be adhered to the shape of the adherend. A more preferred upper limit of the thickness of the foam substrate is 1000 μm, and an even more preferred upper limit is 300 μm.

[0078] The pressure-sensitive adhesive tape of the present invention has a total thickness (total thickness of the substrate and the pressure-sensitive adhesive layer) of preferably 3 μm at the lower limit and 6000 μm at the upper limit. If the total thickness of the pressure-sensitive adhesive tape is within the above range, the adhesive strength will be higher. The upper limit of the total thickness of the pressure-sensitive adhesive tape is more preferably 1200 μm, and even more preferably 500 μm.

[0079] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and it can be produced by a conventionally known production method. For example, in the case of a double-sided pressure-sensitive adhesive tape, the following method can be used. First, a solution of pressure-sensitive adhesive A is prepared by adding a solvent to an acrylic copolymer, a radical scavenger, and, if necessary, a crosslinking agent or a tackifying resin. This solution of pressure-sensitive adhesive A is then applied to the surface of a substrate, and the solvent in the solution is completely dried and removed to form a pressure-sensitive adhesive layer A. Next, a release film is superimposed on the formed pressure-sensitive adhesive layer A with its release-treated surface facing the pressure-sensitive adhesive layer A. Next, a release film separate from the above-mentioned release film is prepared, and a solution of pressure-sensitive adhesive B prepared in the same manner as above is applied to the release-treated surface of this release film. The solvent in the solution is then completely dried and removed to produce a laminate film in which pressure-sensitive adhesive layer B is formed on the surface of the release film. The obtained laminate film is superimposed on the back surface of the substrate on which pressure-sensitive adhesive layer A has been formed, with the pressure-sensitive adhesive layer B facing the back surface of the substrate, to produce a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided adhesive tape can be obtained which has adhesive layers on both sides of the substrate and in which the surfaces of the adhesive layers are covered with release films.

[0080] Alternatively, two sets of laminate films may be prepared in a similar manner, and these laminate films may be superimposed on each of both surfaces of a substrate with the pressure-sensitive adhesive layers of the laminate films facing the substrate to prepare a laminate. This laminate may then be pressed with a rubber roller or the like to obtain a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both surfaces of the substrate and in which the surfaces of the pressure-sensitive adhesive layers are covered with release films.

[0081] The applications of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but because of its high content of bio-derived carbon and excellent shear holding strength at high temperatures, it is preferably used for fixing electronic device components or vehicle-mounted components. Specifically, the pressure-sensitive adhesive tape of the present invention can be suitably used for adhesive fixing of electronic device components in large portable electronic devices, adhesive fixing of vehicle-mounted components (e.g., vehicle-mounted panels), etc.

[0082] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape having a high content of bio-derived carbon and excellent shear strength at high temperatures.

[0083] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0084] <Lauryl acrylate containing bio-derived carbon> Lauryl acrylate was prepared by esterifying lauryl alcohol (manufactured by Kao Corporation) containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0085] <n-Octyl acrylate containing bio-derived carbon> n-Octyl acrylate was prepared by esterifying n-octyl alcohol (manufactured by Kao Corporation) containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0086] <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. Next, the undecylenic acid was separated by distillation to obtain n-heptyl alcohol containing bio-derived carbon. The n-heptyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare n-heptyl acrylate. The impurity content was reduced by distilling the n-heptyl acrylate.

[0087] <Other acrylic monomers> 2-Ethylhexyl acrylate (manufactured by Mitsubishi Chemical Corporation) Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) 2-Hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd.)

[0088] <Crosslinking agent> Isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45)

[0089] <Tackifying resin> Terpene phenol (Terpene phenol G-150, manufactured by Yasuhara Chemical Co., Ltd.)

[0090] Example 1 (1) Production of Acrylic Copolymer (Solution Polymerization) Ethyl acetate was added as a polymerization solvent to a reaction vessel, and nitrogen was bubbled through the mixture. The reaction vessel was then heated while nitrogen was flowing in to initiate reflux. Subsequently, a radical polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile as a radical polymerization initiator 10 times with ethyl acetate was added to the reaction vessel, and predetermined amounts of n-heptyl acrylate, acrylic acid, and 2-hydroxyethyl acrylate were added dropwise over two hours. After the dropwise addition was completed, a radical polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile as a radical polymerization initiator 10 times with ethyl acetate was again added to the reaction vessel, and a polymerization reaction was carried out for four hours to obtain an acrylic copolymer-containing solution.

[0091] Mass spectrometry and １ H-NMR measurement was carried out, and the content of the structural unit derived from each monomer was calculated from the integrated intensity ratio of the hydrogen peak derived from each monomer.

[0092] The obtained acrylic copolymer was diluted 50 times with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. This measurement sample was supplied to a gel permeation chromatograph (Waters, 2690 Separations Module) and subjected to GPC measurement under conditions of a sample flow rate of 1 mL / min and a column temperature of 40 ° C., and the polystyrene-equivalent molecular weight of the acrylic copolymer was measured to determine the weight average molecular weight.

[0093] The obtained acrylic copolymer was subjected to differential scanning calorimetry using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation) to determine the glass transition temperature (Tg). Specifically, approximately 2 mg of the acrylic copolymer was weighed into an aluminum pan, and the aluminum pan was heated at a rate of 10°C / min under a nitrogen atmosphere. The obtained chart was read to determine the glass transition temperature.

[0094] (2) Production of Pressure-Sensitive Adhesive Tape An isocyanate-based crosslinking agent (Coronate L-45, manufactured by Tosoh Corporation) was added to the obtained acrylic copolymer-containing solution so that the solid content was 0.5 parts by weight per 100 parts by weight of the acrylic copolymer, to prepare a pressure-sensitive adhesive solution. This pressure-sensitive adhesive solution was applied to the release-treated surface of a 75 μm-thick release-treated PET film so that the thickness of the pressure-sensitive adhesive layer after drying would be 50 μm, and then dried at 110°C for 5 minutes. This pressure-sensitive adhesive layer was then overlaid on the release-treated surface of a 75 μm-thick release-treated PET film and aged at 40°C for 48 hours to obtain a pressure-sensitive adhesive tape (non-support type).

[0095] (3) Total content of the compound having a structure represented by general formula (A) and the compound having a structure represented by general formula (B) The sol content of the adhesive layer in the adhesive tape was extracted using toluene and dried. The obtained sol content was dissolved in deuterated chloroform, １ H-NMR measurement and １３ By carrying out C-NMR measurement, the total content of the compound having a structure represented by general formula (A) and the compound having a structure represented by general formula (B) was calculated. In Tables 1 and 2, compound a1 is the compound having a structure represented by general formula (A) (R １ and R ２ is an n-heptyl group), and compound a2 is a compound having a structure represented by general formula (A) (R １ and R ２ is an n-octyl group), and compound a3 is a compound having a structure represented by general formula (A) (R １ and R ２ Compound b1 is a compound having a structure represented by general formula (B) (R １ and R ２is an n-heptyl group), and compound b2 is a compound having a structure represented by general formula (B) (R １ and R ２ is an n-octyl group), and compound b3 is a compound having a structure represented by general formula (B) (R １ and R ２ is a lauryl group).

[0096] (4) Total content of the compound having a structure represented by general formula (A), the compound having a structure represented by general formula (B), and the compound having a structure represented by general formula (C) The sol content of the adhesive layer in the pressure-sensitive adhesive tape was extracted using toluene and dried. The obtained sol content was dissolved in deuterated chloroform, １ H-NMR measurement and １３ By carrying out C-NMR measurement, the total content of the compound having a structure represented by general formula (A), the compound having a structure represented by general formula (B), and the compound having general formula (C) was calculated. In Tables 1 and 2, compound c1 is the compound having a structure represented by general formula (C) (R １ and R ２ is an n-heptyl group), and compound c2 is a compound having a structure represented by general formula (C) (R １ and R ２ is an n-octyl group), and compound c3 is a compound having a structure represented by general formula (C) (R １ and R ２ is a lauryl group).

[0097] (5) Measurement of gel fraction The release film on one side of the adhesive tape was peeled off, and the tape was attached to a 23 μm thick PET film (FE2002, manufactured by Futamura Chemical Co., Ltd.), and cut into a 20 mm x 40 mm flat rectangular shape. The release film on the other side of the adhesive tape was then peeled off to prepare a test piece, and its weight was measured. The test piece 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 piece was measured, and the gel fraction was calculated using the following formula (1). Gel fraction (wt%) = 100 x (W ２ -W ０ ) / (W １ -W ０ ) (1) (W ０: Weight of substrate (PET film), W １ : weight of test piece before immersion, W ２ : weight of test piece after immersion and drying)

[0098] (Examples 2 to 15, Comparative Examples 1 to 4) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the type and amount of the acrylic monomer constituting the acrylic copolymer, the weight-average molecular weight of the acrylic copolymer, the amount of the tackifier resin, and the amount of the crosslinking agent were changed as shown in Tables 1 and 2, and the method for producing the pressure-sensitive adhesive tape was changed as shown below.

[0099] In Examples 3 to 10 and 15, the alkyl (meth)acrylate containing bio-derived carbon was not purified by distillation to reduce the content of impurities, but instead, an ethyl acetate solution of the obtained acrylic copolymer was added dropwise to methanol to perform reprecipitation. Then, the reprecipitated acrylic copolymer was used to produce an adhesive tape.

[0100] In Example 11, the adhesive solution was applied to the release-treated surface of a release-treated PET film, and then dried at 110°C for 20 minutes instead of drying at 110°C for 5 minutes. In Example 12, the adhesive solution was applied to the release-treated surface of a release-treated PET film, and then dried at 110°C for 10 minutes instead of drying at 110°C for 5 minutes. In Example 13, n-heptyl acrylate was not distilled after synthesis, but instead a portion of the fraction containing compound a1 was removed using a preparative HPLC (liquid chromatography) apparatus (GL Sciences, Inertsil SIL-150A) before use. In Example 14, n-heptyl acrylate was not distilled after synthesis, but instead a portion of the fraction containing compound b1 was removed using a preparative HPLC (liquid chromatography) apparatus (GL Sciences, Inertsil SIL-150A) before use.

[0101] In Comparative Examples 1 and 2, the impurity content of the alkyl (meth)acrylate containing biological carbon was not reduced by distillation or purification using a preparative HPLC apparatus, nor was the obtained acrylic copolymer reprecipitated. In Comparative Example 3, a portion of the fraction containing compound a3 was removed before use. In Comparative Example 4, a portion of the fraction containing compound b1 was removed before use.

[0102] <Evaluation> The pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples were evaluated by the following methods. The results are shown in Tables 1 and 2.

[0103] (1) Shear Holding Strength at High Temperature (85°C) The adhesive tape was cut to a width of 25 mm and a length of 100 mm. According to JIS Z-1528, one side of the adhesive tape was bonded to a cold-rolled stainless steel plate (SUS304 plate) having a thickness of 1.5 mm, a width of 25 mm, and a length of 100 mm at 23°C. At this time, the adhesive tape was bonded by shifting it in the lengthwise direction so that the adhesive length of the adhesive tape was 25 mm and a 75 mm portion of the adhesive tape protruded from the end of the SUS304 plate. The other side of the adhesive tape was backed with a PET film, and then pressed with a 2 kg rubber roller, moving back and forth, to prepare an adhesive test specimen. The adhesive test specimen was left in an atmosphere of 23°C and 50% humidity for 20 minutes. In an 85°C environment, a 1 kg weight was attached to the protruding portion of the adhesive tape so that a load was applied in the shear direction to the obtained adhesive test specimen. If the time from application of the load until the adhesive tape peeled off and fell was 24 hours or more, it was marked with an ⊚; if it was 1 hour or more but less than 24 hours, it was marked with an ◯; if it was less than 1 hour, it was marked with an ×.

[0104] (2) Biocarbon Content The biocarbon content of the pressure-sensitive adhesive tape was measured in accordance with ASTM D6866-20.

[0105]

[0106]

[0107] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape having a high content of bio-derived carbon and excellent shear strength at high temperatures.

Claims

1. An adhesive tape having an adhesive layer containing an acrylic copolymer, wherein the acrylic copolymer contains a structural unit derived from an alkyl (meth)acrylate containing carbon derived from a living organism, and the total content of a compound having a structure represented by the following general formula (A) and a compound having a structure represented by the following general formula (B) in the adhesive layer is 2% by weight or less. The adhesive tape is characterized by this. In general formulas (A) and (B), R １ and R ２ represent an alkyl group having 4 to 12 carbon atoms.

2. The pressure-sensitive adhesive tape according to claim 1, wherein the total content of the compound having a structure represented by the general formula (A), the compound having a structure represented by the general formula (B), and the compound having a structure represented by the following general formula (C) in the pressure-sensitive adhesive layer is 2% by weight or less. In the general formula (C), R １ and R ２ each represent an alkyl group having 4 to 12 carbon atoms.

3. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the content of the compound having the structure represented by the general formula (A) in the pressure-sensitive adhesive layer is less than 1% by weight.

4. The pressure-sensitive adhesive tape according to claim 1, 2 or 3, wherein the compound having the structure represented by the general formula (A) is a compound having the structure represented by the following formula (a1).

5. The pressure-sensitive adhesive tape according to claim 1, 2, 3 or 4, wherein the content of the compound having the structure represented by the general formula (B) in the pressure-sensitive adhesive layer is less than 1% by weight.

6. The pressure-sensitive adhesive tape according to claim 2, 3, 4 or 5, wherein the content of the compound having the structure represented by the general formula (C) in the pressure-sensitive adhesive layer is less than 1% by weight.

7. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5 or 6, wherein the compound having the structure represented by the general formula (B) is a compound having the structure represented by the following formula (b1).

8. The pressure-sensitive adhesive tape according to claim 2, 3, 4, 5, 6 or 7, wherein the compound having the structure represented by the general formula (C) is a compound having the structure represented by the following formula (c1).

9. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the alkyl (meth) acrylate containing the carbon derived from a living organism contains n-heptyl (meth) acrylate.

10. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the content of the structural unit derived from the alkyl (meth) acrylate containing the carbon derived from a living organism in the acrylic copolymer is 85% by weight or more.

11. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein the pressure-sensitive adhesive layer further contains a tackifier resin.

12. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the content rate of the carbon derived from a living organism in the pressure-sensitive adhesive layer is 10% by weight or more.

13. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, which is used for fixing electronic device parts or in-vehicle parts.