adhesive tape

Abstract

To provide an adhesive tape that contains a high proportion of biological carbon, can exhibit excellent adhesion, and features planar rebound resistance at high temperatures.SOLUTION: An adhesive tape has an adhesive layer containing an acryl copolymer. The acryl copolymer contains a constitutional unit (a) derived from n-heptyl (meth)acrylate, containing biological carbon, and at least one constitutional unit (b) selected from the group consisting of a butyl (meth)acrylate-derived constitutional unit and a 2-ethylhexyl (meth)acrylate-derived constitutional unit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to 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, 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-052050 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-021067 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-120876 Summary of the Invention [Problem to be solved by the invention]

[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, can exert excellent adhesive strength, and has excellent resistance to flat surface repulsion at high temperatures. [Means for solving the problem]

[0006] The present invention is an adhesive tape having an adhesive layer containing an acrylic copolymer, wherein the acrylic copolymer contains a structural unit (a) derived from n-heptyl (meth)acrylate, which contains carbon of biological origin, and at least one structural unit (b) selected from the group consisting of a structural unit derived from butyl (meth)acrylate and a structural unit derived from 2-ethylhexyl (meth)acrylate. 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.

[0007] In pressure-sensitive adhesive tapes having a pressure-sensitive adhesive layer containing an acrylic copolymer, the acrylic monomer constituting the acrylic copolymer is, for example, a (meth)acrylic acid alkyl ester such as butyl (meth)acrylate or 2-ethylhexyl (meth)acrylate. However, for example, when butyl acrylate is used as the main component, the pressure-sensitive adhesive tape has high adhesive strength at high temperatures and is relatively excellent in terms of heat resistance, but its flexibility is insufficient. On the other hand, when 2-ethylhexyl acrylate is used as the main component, the pressure-sensitive adhesive tape has excellent flexibility but its adhesive strength at high temperatures is insufficient. The present inventors have found that using n-heptyl(meth)acrylate, which contains bio-derived carbon, as the acrylic monomer constituting the acrylic copolymer can be expected to increase the content of bio-derived carbon and also to exhibit excellent performance as an adhesive tape. Furthermore, the present inventors have investigated the use of n-heptyl(meth)acrylate, which contains bio-derived carbon, in combination with at least one selected from the group consisting of butyl(meth)acrylate and 2-ethylhexyl(meth)acrylate. The present inventors have found that the use of such an acrylic monomer can produce an adhesive tape that not only exhibits excellent adhesive strength, but also has excellent flexibility and adhesive strength at high temperatures, making it difficult to peel even when a repulsive force is applied at high temperatures (excellent flat surface repulsion resistance), and thus have completed the present invention.

[0008] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer containing an acrylic copolymer. The acrylic copolymer contains a structural unit (a) derived from n-heptyl(meth)acrylate, which contains bio-derived carbon, and at least one structural unit (b) selected from the group consisting of a structural unit derived from butyl(meth)acrylate and a structural unit derived from 2-ethylhexyl(meth)acrylate. This allows the pressure-sensitive adhesive tape of the present invention to have a high bio-derived carbon content, exhibit excellent adhesive strength, and exhibit excellent flat surface repulsion resistance at high temperatures.

[0009] The n-heptyl (meth)acrylate is not particularly limited as long as it contains carbon derived from a living organism. Preferably, the n-heptyl (meth)acrylate is synthesized by esterification of n-heptyl alcohol, a living organism material, with (meth)acrylic acid, or by transesterification of n-heptyl alcohol, a living organism material, with a (meth)acrylic acid ester. N-heptyl alcohol, a biologically derived material, can be obtained inexpensively and easily by cracking raw materials collected from plants and animals (for example, ricinoleic acid derived from castor oil).

[0010] The content of the structural unit (a) derived from n-heptyl(meth)acrylate containing bio-derived carbon in the acrylic copolymer is not particularly limited, but a preferred lower limit is 85% by weight. If the content of the structural unit (a) is 85% by weight or more, the content of bio-derived carbon in the entire pressure-sensitive adhesive tape increases, and the pressure-sensitive adhesive tape's planar repulsion resistance at high temperatures is further improved. A more preferred lower limit for the content of the structural unit (a) is 87% by weight. The upper limit for the content of the structural unit (a) derived from n-heptyl(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% by weight, and a more preferred upper limit is 97% by weight.

[0011] The at least one structural unit (b) selected from the group consisting of structural units derived from butyl (meth)acrylate and structural units derived from 2-ethylhexyl (meth)acrylate may consist solely of structural units derived from butyl (meth)acrylate, or may consist solely of structural units derived from 2-ethylhexyl (meth)acrylate. Alternatively, it may consist of both structural units derived from butyl (meth)acrylate and structural units derived from 2-ethylhexyl (meth)acrylate. From the viewpoint of achieving both adhesive strength and high-temperature flat repulsion resistance, it is more preferable that the at least one structural unit (b) consist solely of structural units derived from butyl (meth)acrylate and structural units derived from 2-ethylhexyl (meth)acrylate.

[0012] The content of at least one structural unit (b) selected from the group consisting of structural units derived from butyl (meth)acrylate and structural units derived from 2-ethylhexyl (meth)acrylate in the acrylic copolymer is not particularly limited, but a preferred lower limit is 5% by weight and a preferred upper limit is 15% by weight. If the content of the structural unit (b) is within the above range, the pressure-sensitive adhesive tape will have higher planar repulsion resistance at high temperatures. A more preferred lower limit of the content of the structural unit (b) is 6% by weight and a more preferred upper limit is 12% by weight.

[0013] The contents of the structural unit (a) and the structural unit (b) in the acrylic copolymer can be determined by mass spectrometry of the acrylic copolymer and 1 H-NMR measurement can be performed and the ratio of the integrated intensities of the hydrogen peaks derived from each monomer can be calculated.

[0014] The acrylic copolymer preferably further contains a structural unit (c) derived from a monomer having a crosslinkable functional group. When the acrylic copolymer contains the structural unit (c) derived from the monomer having the crosslinkable functional group, the cohesive strength of the pressure-sensitive adhesive layer increases, resulting in higher adhesive strength and higher flat repulsion resistance of the pressure-sensitive adhesive tape at high temperatures.

[0015] 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.

[0016] 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.

[0017] The content of the structural unit (c) derived from the monomer having a crosslinkable functional 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 20% by weight. If the content of the structural unit (c) is within the above range, the pressure-sensitive adhesive tape will have higher flat repulsion resistance at high temperatures. A more preferred lower limit of the content of the structural unit (c) derived from the monomer having a crosslinkable functional group is 0.1% by weight, a more preferred upper limit is 10% by weight, an even more preferred lower limit is 1% by weight, and an even more preferred upper limit is 7% by weight.

[0018] The content of the structural unit (c) in the acrylic copolymer was determined by mass spectrometry of the acrylic copolymer and 1 H-NMR measurement can be performed and the ratio of the integrated intensities of the hydrogen peaks derived from each monomer can be calculated.

[0019] The acrylic copolymer may have a structural unit derived from a monomer other than the structural unit (a), the structural unit (b), and the structural unit (c). The other monomer is not particularly limited, and examples thereof include alkyl (meth)acrylates. 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, 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 alcohols having a total of 18 carbon atoms and one or two methyl groups in their linear main chain with (meth)acrylic acid, behenyl (meth)acrylate, and arachidyl (meth)acrylate. These (meth)acrylic acid alkyl esters may be used alone or in combination of two or more.

[0020] 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. Furthermore, various monomers used in general acrylic polymers, such as vinyl carboxylates (e.g., vinyl acetate) and styrene, can also be used as the other monomers. When the acrylic copolymer is produced by UV polymerization, polyfunctional monomers (e.g., 1,6-hexanediol di(meth)acrylate) can also be used as the other monomers. These other monomers can be used alone or in combination of two or more.

[0021] 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 performed and the ratio of the integrated intensities of the hydrogen peaks derived from each monomer can be calculated.

[0022] The butyl (meth)acrylate, the 2-ethylhexyl (meth)acrylate, the monomer having a crosslinkable functional group, and the other monomers 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 cost and productivity of the pressure-sensitive adhesive tape, it is also possible to adopt a relatively inexpensive and easily available monomer containing carbon derived from living organisms and combine it with a monomer composed solely of petroleum-derived materials.

[0023] 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 pressure-sensitive adhesive tape has higher flat repulsion resistance at high temperatures. 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.

[0024] 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 and the pressure-sensitive adhesive tape will have higher planar repulsion resistance at high temperatures. A more preferred lower limit of the weight-average molecular weight of the acrylic copolymer is 400,000 and a more preferred upper limit is 1,800,000, and 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 measured by gel permeation chromatography (GPC) in terms of standard polystyrene. Specifically, the acrylic copolymer is diluted 50 times with tetrahydrofuran (THF) and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm) to prepare a measurement sample. Next, this measurement sample is fed to a gel permeation chromatograph (Waters, trade name "2690 Separations Module" or equivalent), 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.

[0025] The acrylic copolymer can be obtained by subjecting a mixture of raw material monomers to a radical reaction in the presence of a radical polymerization initiator. The radical reaction method is not particularly limited, and examples include living radical polymerization, free radical polymerization, etc. Living radical polymerization can provide a copolymer having a more uniform molecular weight and composition compared to free radical polymerization, and can suppress the generation of low molecular weight components, etc., thereby increasing the cohesive strength of the pressure-sensitive adhesive layer and further increasing the 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 further increase the adhesive strength of the pressure-sensitive adhesive layer. Furthermore, solution polymerization is more preferred because it makes it easier to mix a tackifier resin with the resulting acrylic copolymer, further increasing the adhesive strength of the pressure-sensitive adhesive layer.

[0026] 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.

[0027] 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. In the case of living radical polymerization, the radical polymerization initiator may be, for example, an organic tellurium polymerization initiator. The organic tellurium polymerization initiator is not particularly limited as long as it is one that is generally used in living radical polymerization, and examples thereof include organic tellurium compounds, organic telluride compounds, etc. In addition to the organic tellurium 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.

[0028] 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, metal chelate-based crosslinking agents, etc. Among these, isocyanate-based crosslinking agents are preferred because they provide the pressure-sensitive adhesive layer with excellent adhesion to the adherend.

[0029] 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 per 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 the solid content of the crosslinking agent.

[0030] The pressure-sensitive adhesive layer preferably further contains a tackifier resin, which increases the adhesive strength of the pressure-sensitive adhesive layer and increases the plane repulsion resistance 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. Among these, at least one selected from the group consisting of rosin ester tackifier resins and terpene tackifier resins is preferred.

[0031] Examples of the rosin ester tackifying resin include polymerized rosin ester resin, hydrogenated rosin ester resin, etc. Examples of the terpene tackifying resin include terpene resin, terpene phenol resin, etc. The rosin ester tackifying resin and the terpene tackifying resin are preferably derived from a living organism. Examples of the rosin ester tackifying resin derived from a living organism include rosin ester tackifying resins derived from natural resins such as pine resin. Examples of the terpene tackifying resin derived from a living organism include terpene tackifying resins derived from plant essential oils.

[0032] 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 pressure-sensitive adhesive tape will have higher planar repulsion resistance at high temperatures. 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.

[0033] 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.

[0034] The gel fraction of the pressure-sensitive adhesive layer 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 pressure-sensitive adhesive layer is within the above range, the balance between the adhesive strength and the adhesion to the adherend of the pressure-sensitive adhesive layer will be good, and the pressure-sensitive adhesive tape will have higher anti-flat rebound properties at high temperatures. A more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 20% by weight, and a more preferred upper limit is 50% by weight. The gel fraction of the pressure-sensitive adhesive layer is measured as follows. First, a test piece is prepared by cutting the adhesive tape into a flat rectangular shape of 20 mm x 40 mm, 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). Note that no release film to protect the adhesive layer is laminated on the test piece. Gel fraction (wt%) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

[0035] 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.

[0036] The pressure-sensitive adhesive 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 a measure of a "bio-based product." A content of the biologically derived carbon of 10% by weight or more is preferable from the viewpoints of saving petroleum resources and reducing carbon dioxide emissions. A more preferable lower limit of the biologically derived carbon content is 30% by weight, and an even more preferable lower limit is 60% by weight. There is no particular upper limit for the biologically derived carbon content, and it may be 100% by weight. While carbon derived from living organisms contains a certain percentage of the radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the content of carbon derived from living organisms can be calculated by measuring the concentration of C-14 contained in the adhesive layer. Specifically, this can be measured in accordance with ASTM D6866-20, a standard widely used in the bioplastics industry.

[0037] 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.

[0038] The pressure-sensitive adhesive tape of the present invention may be a non-support tape having no substrate, a single-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on one side of a substrate, or a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of a substrate. The substrate is not particularly limited, and any conventionally known substrate can be used, but in order to increase the content of bio-derived carbon in the entire adhesive tape, it is preferable to use a bio-derived substrate. Examples of the biological 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.

[0039] 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 materials for the film made of PA include nylon 11, nylon 1010, nylon 610, nylon 510, nylon 410, etc., which are made from castor oil, and nylon 56, etc., which are made from cellulose.

[0040] 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, 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.

[0041] 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 from the viewpoint of achieving a high degree of both flexibility and strength, a foam substrate made of PE is more preferred. Examples of the constituents of the foam substrate made of PE include PE made from sugarcane.

[0042] 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, foam the foaming agent when extruding the foamable resin composition into a sheet using an extruder, and crosslink the resulting polyolefin foam as needed.

[0043] 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.

[0044] The adhesive tape of the present invention has a total thickness (total thickness of the substrate and adhesive layer) of preferably 3 μm at the lower limit and 6000 μm at the upper limit. If the total thickness of the adhesive tape is within the above range, the adhesive strength will be higher. The adhesive tape's total thickness has a more preferred upper limit of 1200 μm and an even more preferred upper limit of 500 μm.

[0045] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and the tape 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 mentioned. First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer, a radical scavenger, and, if necessary, a crosslinking agent, a tackifying resin, etc., and this solution of adhesive A is applied to the surface of a substrate, and the solvent in the solution is completely dried and removed to form adhesive layer A. Next, a release film is superimposed on the formed adhesive layer A with its release-treated surface facing the adhesive layer A. Next, a release film separate from the above-mentioned release film is prepared, and a solution of 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 adhesive layer B is formed on the surface of the release film. The obtained laminate film is overlaid on the back surface of the substrate on which adhesive layer A is formed, with adhesive layer B facing the back surface of the substrate, to produce a laminate. The laminate is then pressed with a rubber roller or the like to obtain a double-sided adhesive tape in which adhesive layers are on both sides of the substrate and the surfaces of the adhesive layers are covered with release films.

[0046] 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 adhesive layer of the laminate film 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 adhesive tape having adhesive layers on both surfaces of the substrate and the surfaces of the adhesive layers covered with release films.

[0047] The uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but because it has a high content of bio-derived carbon, can exhibit excellent adhesive strength, and has excellent resistance to flat repulsion at high temperatures, it is preferably used for fixing electronic device components or vehicle 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 components (e.g., vehicle panels), etc. [Effects of the Invention]

[0048] According to the present invention, it is possible to provide an adhesive tape that has a high content of biological carbon, can exhibit excellent adhesive strength, and has excellent resistance to flat surface repulsion at high temperatures. [Brief explanation of the drawings]

[0049] [Figure 1] FIG. 2 is a schematic diagram showing a method for testing the planar repulsion resistance of an adhesive tape at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0050] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0051] <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. The undecylenic acid was then separated by distillation to obtain n-heptyl alcohol, which contains bio-derived carbon. n-heptyl acrylate was prepared by esterifying n-heptyl alcohol, which contains bio-derived carbon, with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0052] <Other acrylic monomers> Butyl acrylate (Mitsubishi Chemical) 2-Ethylhexyl acrylate (Mitsubishi Chemical Corporation) Acrylic acid (Nippon Shokubai Co., Ltd.) 2-Hydroxyethyl acrylate (Osaka Organic Chemical Industry Co., Ltd.)

[0053] <Crosslinking agent> Isocyanate crosslinking agent (Tosoh Corporation, Coronate L-45)

[0054] <Tackifying resin> Polymerized rosin ester (Pensel D135, manufactured by Arakawa Chemical Industries, Ltd.)

[0055] Example 1 (1) Production of acrylic copolymer Ethyl acetate was added to the reaction vessel as the polymerization solvent, and nitrogen was bubbled through. 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 10 times with ethyl acetate was added to the reaction vessel, and 85 parts by weight of n-heptyl acrylate, 11.9 parts by weight of butyl acrylate, 3 parts by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate were added dropwise over two hours. After the dropwise addition, a radical polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile 10 times with ethyl acetate was added again to the reaction vessel, and the polymerization reaction was carried out for four hours to obtain an acrylic copolymer-containing solution.

[0056] 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.

[0057] The resulting acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore size: 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 at a sample flow rate of 1 mL / min and a column temperature of 40°C to measure the polystyrene-equivalent molecular weight of the acrylic copolymer and determine the weight-average molecular weight.

[0058] (2) Manufacture of adhesive tapes To the resulting acrylic copolymer-containing solution, 25 parts by weight of polymerized rosin ester (Pensel D135, manufactured by Arakawa Chemical Industries, Ltd.) was added per 100 parts by weight of the acrylic copolymer, and an isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45) was further added so that the solid content was 1.1 parts by weight 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 25 μm, and then dried at 110°C for 5 minutes. A 75 μm-thick release-treated PET film was placed on top of the resulting pressure-sensitive adhesive layer and aged at 40°C for 48 hours to obtain a pressure-sensitive adhesive tape (non-support type).

[0059] (3) Measurement of gel fraction The adhesive tape was cut into a 20 mm × 40 mm flat rectangular shape 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 (1). Gel fraction (wt%) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

[0060] (Examples 2 to 5, Comparative Examples 1 and 2) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types and amounts of the acrylic monomers constituting the acrylic copolymer were changed as shown in Table 1.

[0061] <Evaluation> The pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

[0062] (1) Adhesive strength (1-1) 180° peel strength against SUS plate One side of the adhesive tape (the side not being measured) was lined with a 23 μm-thick polyethylene terephthalate film (FE2002, manufactured by Futamura Chemical Co., Ltd.) and then cut to a width of 25 mm and a length of 75 mm to prepare a test specimen. This test specimen was placed on a SUS plate with the adhesive layer (the side being measured) facing the SUS plate, and then bonded to the test specimen by rolling a 2 kg rubber roller back and forth on the test specimen at a speed of 300 mm / min. This was then aged for 20 minutes at 23°C and 50% humidity to prepare a test sample. According to JIS Z 0237:2009, this test sample was peeled in a 180° direction at a pulling rate of 300 mm / min at 23°C and 50% humidity, and the adhesive strength (N / 25 mm) was measured.

[0063] (1-2) 180° peel strength against PP board One side of the adhesive tape (the side not being measured) was lined with a 23 μm-thick polyethylene terephthalate film (FE2002, manufactured by Futamura Chemical Co., Ltd.) and then cut to a width of 25 mm and a length of 75 mm to prepare a test specimen. This test specimen was placed on a polypropylene (PP) plate with the adhesive layer (the side being measured) facing the PP plate, and then bonded to the test specimen by rolling a 2 kg rubber roller back and forth on the test specimen at a speed of 300 mm / min. This was then aged for 20 minutes at 23°C and 50% humidity to prepare a test sample. According to JIS Z 0237:2009, this test sample was peeled in a 180° direction at a pulling rate of 300 mm / min at 23°C and 50% humidity, and the adhesive strength (N / 25 mm) was measured.

[0064] (2) Resistance to flat rebound at high temperatures FIG. 1 shows a schematic diagram illustrating a method for testing the flat repulsion resistance of adhesive tape at high temperatures. As shown in Figure 1, an aluminum plate (A) (25 mm wide x 150 mm long x 0.5 mm thick) 6 and a polycarbonate plate (B) (25 mm wide x 200 mm long x 2 mm thick) 5 were laminated together using adhesive tape 1 cut to a size of 25 mm wide x 150 mm long. This laminate was then pressed together using a roller under a load of 2 kg and allowed to stand for 24 hours to produce a test sample in which the aluminum plate (A) 6 and the polycarbonate plate (B) 5 were bonded together via the adhesive tape 1. This test sample was sandwiched between a jig 7 with the aluminum plate (A) 6 facing up, and the width of the jig 7 was narrowed to 190 mm to warp the test sample into a bow shape. The test sample was then allowed to stand for 24 hours at 60°C and 90% humidity. The height (displacement) of the adhesive tape 1 lifting from the test sample after 100 hours of standing was measured.

[0065] (3) Biological carbon content The adhesive tape was measured for its content of bio-derived carbon in accordance with ASTM D6866-20.

[0066] [Table 1] [Industrial Applicability]

[0067] According to the present invention, it is possible to provide an adhesive tape that has a high content of biological carbon, can exhibit excellent adhesive strength, and has excellent resistance to flat surface repulsion at high temperatures. [Explanation of symbols]

[0068] 1 adhesive tape 5 Polycarbonate plate (B) 6 Aluminum Plate (A) 7 Jig

Claims

1. A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing an acrylic copolymer, The acrylic copolymer contains a structural unit (a) derived from n-heptyl (meth)acrylate, which contains carbon derived from a living organism, and at least one structural unit (b) selected from the group consisting of a structural unit derived from butyl (meth)acrylate and a structural unit derived from 2-ethylhexyl (meth)acrylate; The acrylic copolymer has a content of the structural unit (a) derived from n-heptyl (meth)acrylate containing the bio-derived carbon of 85% by weight or more, and a content of at least one structural unit (b) selected from the group consisting of structural units derived from butyl (meth)acrylate and structural units derived from 2-ethylhexyl (meth)acrylate of 5% by weight or more and 15% by weight or less.

2. 2. The adhesive tape according to claim 1, wherein the adhesive layer contains 30% by weight or more of carbon derived from living organisms.

3. The pressure-sensitive adhesive tape according to claim 1 or 2, characterized in that the acrylic copolymer further contains a structural unit (c) derived from a monomer having a crosslinkable functional group, and the content of the structural unit (c) derived from the monomer having a crosslinkable functional group is 1% by weight or more and 7% by weight or less.

4. 4. The adhesive tape according to claim 1, wherein the adhesive layer further contains a crosslinking agent.

5. 5. The adhesive tape according to claim 1, which has a substrate.

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