Adhesive tape

Abstract

To provide an adhesive tape having excellent tackiness and constant load peelability at high temperatures.SOLUTION: An adhesive tape has an adhesive layer containing an acryl copolymer. The acryl copolymer contains a constitutional unit derived from n-heptyl (meth)acrylate and has a weight average molecular weight (Mw) of more than 200,000 to 2000,000 or less and a molecular weight distribution (Mw / Mn) of 1.1 or more and 3.5 or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, when fixing components in electronic components, vehicles, houses, and building materials, an adhesive tape having an adhesive layer containing an adhesive has been widely used (for example, Patent Documents 1 to 3). Specifically, for example, an adhesive tape is 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 and a display panel module.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in adhesive tapes having an adhesive layer containing an acrylic copolymer, there has been growing interest in using acrylic copolymers with a narrow molecular weight distribution (Mw / Mn) (low value) synthesized by precise polymerization methods. Adhesive layers containing acrylic copolymers with a narrow molecular weight distribution (Mw / Mn) have high heat resistance and can exhibit excellent adhesive strength (e.g., constant-load peelability) even at high temperatures, due to the extremely low amount of low molecular weight components. On the other hand, such adhesive layers have the problem of reduced fluidity and poor tackiness due to the low amount of low molecular weight components. Therefore, it has been difficult to achieve both high levels of tackiness and constant-load peelability at high temperatures.

[0005] The present invention aims to provide an adhesive tape with excellent tackiness and constant load peelability at high temperatures. [Means for solving the problem]

[0006] Disclosure 1 is an adhesive tape having an adhesive layer containing an acrylic copolymer, wherein the acrylic copolymer contains constituent units derived from n-heptyl(meth)acrylate, has a weight-average molecular weight (Mw) greater than 200,000 and 2,000,000 or less, and a molecular weight distribution (Mw / Mn) of 1.1 or more and 3.5 or less. Disclosure 2 is an adhesive tape of Disclosure 1 wherein the n-heptyl (meth)acrylate contains bio-derived carbon. Disclosure 3 is an adhesive tape according to Disclosure 1 or 2, wherein the acrylic copolymer contains 30% by weight or more of constituent units derived from the n-heptyl (meth)acrylate. Disclosure 4 is an adhesive tape according to Disclosure 1, 2, or 3, wherein the acrylic copolymer further contains constituent units derived from monomers having crosslinkable functional groups. Disclosure 5 is an adhesive tape according to Disclosure 1, 2, 3, or 4, wherein the adhesive layer further contains a crosslinking agent. Disclosure 6 is an adhesive tape according to Disclosure 1, 2, 3, 4, or 5, wherein the adhesive layer further contains a tackifying resin. Disclosure 7 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, or 6, wherein the adhesive layer has a gel fraction of 10% by weight or more and 70% by weight or less. Disclosure 8 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, or 7 used for fixing electronic equipment components or automotive components. In this specification, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic. Acrylic copolymer may also be methacrylic copolymer. The present invention will be described in detail below.

[0007] The inventors investigated the use of n-heptyl(meth)acrylate (number of carbon atoms in the acrylic group = 7) as an acrylic monomer constituting the acrylic copolymer. As a result, the inventors found that the glass transition temperature obtained from the temperature at which tanδ is maximum for n-heptyl(meth)acrylate was lower than expected. In other words, contrary to the predictions based on the glass transition temperature trend obtained by differential scanning calorimetry (DSC), it was found that, for example, n-heptyl acrylate had a lower glass transition temperature obtained from the temperature at which the tanδ of the homopolymer is maximum compared to butyl acrylate and 2-ethylhexyl acrylate (number of carbon atoms in the acrylic group = 4 and 8). The reason for this is not entirely clear, but it is thought that because the n-heptyl group in n-heptyl (meth)acrylate has an odd number of carbon atoms, it is less likely to cause molecular packing compared to n-hydrocarbon groups with an even number of carbon atoms. The inventors of the present invention have found that by using n-heptyl (meth)acrylate, which lowers the glass transition temperature of the polymer and enhances flexibility, in an acrylic copolymer, and by narrowing the molecular weight distribution (Mw / Mn) of the acrylic copolymer (reducing the value), an adhesive tape with excellent tackiness and constant load peelability at high temperatures can be obtained. This led to the completion of the present invention.

[0008] The adhesive tape of the present invention has an adhesive layer containing an acrylic copolymer. The above acrylic copolymer contains constituent units derived from n-heptyl(meth)acrylate, has a weight-average molecular weight (Mw) greater than 200,000 and 2,000,000 or less, and a molecular weight distribution (Mw / Mn) of 1.1 or more and 3.5 or less. n-heptyl(meth)acrylate can lower the glass transition temperature of the polymer and increase its flexibility. Therefore, if the acrylic copolymer contains constituent units derived from n-heptyl(meth)acrylate, and furthermore, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) satisfy the above range, the adhesive tape of the present invention will be an adhesive tape that is excellent in both tackiness and constant load peelability at high temperatures.

[0009] The n-heptyl(meth)acrylate in the constituent units derived from the above-mentioned n-heptyl(meth)acrylate may consist solely of petroleum-derived materials, but it is preferable that it contains bio-derived carbon. In recent years, the depletion of petroleum resources and the emission of carbon dioxide from the combustion of petroleum-derived products have become serious concerns. Therefore, attempts are being made to conserve petroleum resources by using bio-based materials instead of petroleum-derived materials. If the above n-heptyl (meth)acrylate contains bio-derived carbon, it is preferable from the standpoint of conserving petroleum resources. Furthermore, if the above n-heptyl (meth)acrylate contains bio-derived carbon, since bio-derived materials are originally produced by taking in carbon dioxide from the atmosphere, it is thought that burning it will not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the standpoint of reducing carbon dioxide emissions.

[0010] When the above-mentioned n-heptyl (meth)acrylate contains bio-derived carbon, it is preferable that the n-heptyl (meth)acrylate be synthesized by esterification of n-heptyl alcohol, which is a bio-derived material, with (meth)acrylic acid. It is also preferable that it be synthesized by transesterification of n-heptyl alcohol, which is a bio-derived material, with (meth)acrylic acid ester. The above-mentioned bio-derived material, n-heptyl alcohol, can be obtained inexpensively and easily by cracking materials extracted from plants and animals (for example, ricinoleic acid derived from castor oil).

[0011] The content of the constituent units derived from the above-mentioned n-heptyl(meth)acrylate in the above-mentioned acrylic copolymer is not particularly limited, but a preferred lower limit is 30% by weight. If the content of the constituent units derived from n-heptyl(meth)acrylate is 30% by weight or more, the flexibility of the acrylic copolymer is improved, and the tackiness of the adhesive layer is increased. Also, if the content of the constituent units derived from n-heptyl(meth)acrylate is 30% by weight or more, and the n-heptyl(meth)acrylate contains bio-derived carbon, the bio-derived carbon content of the adhesive tape as a whole can be increased. A more preferable lower limit for the content of the constituent units derived from n-heptyl(meth)acrylate is 48% by weight, an even more preferable lower limit is over 50% by weight, an even more preferable lower limit is 60% by weight, an even more preferable lower limit is 70% by weight, and an even more preferable lower limit is 85% by weight. There is no particular upper limit for the content of the constituent units derived from n-heptyl(meth)acrylate, but from the viewpoint of adjusting the gel fraction of the adhesive layer, a preferred upper limit is 99% by weight, and a more preferable upper limit is 97% by weight.

[0012] The content of the constituent units derived from the n-heptyl(meth)acrylate in the above acrylic copolymer was determined by mass spectrometry of the above acrylic copolymer and 1 This can be calculated by performing 1H-NMR measurements and analyzing the integral intensity ratio of the hydrogen peaks originating from each monomer.

[0013] The above acrylic copolymer preferably further contains constituent units derived from monomers having crosslinkable functional groups. The inclusion of structural units derived from monomers having the above-mentioned crosslinkable functional groups in the above-mentioned acrylic copolymer increases the cohesive force of the adhesive layer, resulting in improved constant-load peelability at high temperatures.

[0014] The monomer having the 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, a monomer having a nitrile group, and the like. These monomers having crosslinkable functional groups may be used alone or in combination of two or more. Among them, since it is easy to adjust the gel fraction of the adhesive layer, a monomer having a hydroxyl group and a monomer having a carboxyl group are preferable, and a monomer having a hydroxyl group is more preferable.

[0015] 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.

[0016] The content of the structural unit derived from the monomer having the crosslinkable functional group in the above acrylic copolymer is not particularly limited, but the preferable lower limit is 0.01% by weight and the preferable upper limit is 20% by weight. If the content of the structural unit derived from the monomer having the crosslinkable functional group is within the above range, the cohesive force of the adhesive layer will be further increased and the peelability under a constant load at high temperature will be further improved. The more preferable lower limit of the content of the structural unit derived from the monomer having the crosslinkable functional group is 0.1% by weight, the more preferable upper limit is 15% by weight, the further preferable lower limit is 0.5% by weight, the further preferable upper limit is 10% by weight, and the even more preferable upper limit is 5% by weight.

[0017] The content of the structural unit derived from the monomer having the crosslinkable functional group in the above acrylic copolymer can be calculated from the integral intensity ratio of the peaks of hydrogen derived from each monomer by performing mass spectrometry and 1 1H-NMR measurement of the above acrylic copolymer.

[0018] The above acrylic copolymer may have a structural unit derived from another monomer other than the structural unit derived from the above n-heptyl (meth) acrylate and the structural unit derived from the monomer having the crosslinkable functional group. The above other monomer is not particularly limited, and examples thereof include alkyl (meth) acrylate. Examples of the alkyl (meth)acrylate esters mentioned above include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)octanol-1 with (meth)acrylic acid, esters of (meth)acrylic acid with an alcohol having 1 or 2 methyl groups in a linear main chain and a total of 18 carbon atoms, behenyl (meth)acrylate, arachidyl (meth)acrylate, and the like. These alkyl (meth)acrylates may be used individually or in combination of two or more.

[0019] Other monomers include, for example, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and polypropylene glycol mono(meth)acrylate. From the viewpoint of excellent rebound resistance, isobornyl (meth)acrylate is preferred. Furthermore, other monomers such as vinyl carboxylates like vinyl acetate and various monomers commonly used in acrylic polymers like styrene can also be used. When producing the acrylic copolymer by UV polymerization, polyfunctional monomers such as 1,6-hexanediol di(meth)acrylate can also be used as other monomers. These other monomers may be used individually or in combination of two or more.

[0020] The content of constituent units derived from the other monomers in the above acrylic copolymer is determined by mass spectrometry of the above acrylic copolymer and 1This can be calculated by performing 1H-NMR measurements and analyzing the integral intensity ratio of the hydrogen peaks originating from each monomer.

[0021] The monomers having the above-mentioned crosslinkable functional group, and the other monomers, preferably contain bio-derived carbon, but may also consist only of petroleum-derived materials without containing bio-derived carbon. Theoretically, it is also possible to make all of the acrylic monomers constituting the above-mentioned acrylic copolymer monomers containing bio-derived carbon. From the viewpoint of cost and productivity of adhesive tape, it is also possible to use monomers containing bio-derived carbon, which are relatively inexpensive and readily available, and combine them with monomers consisting only of petroleum-derived materials.

[0022] The glass transition temperature (Tg) of the above acrylic copolymer is not particularly limited, but is preferably -20°C or lower. If the glass transition temperature (Tg) of the above acrylic copolymer is -20°C or lower, the flexibility of the acrylic copolymer is improved, and the tackiness of the adhesive layer is further increased. The glass transition temperature (Tg) of the above acrylic copolymer is more preferably -30°C or lower, even more preferably -40°C or lower, and even more preferably -50°C or lower. The lower limit of the glass transition temperature (Tg) of the above acrylic copolymer is not particularly limited, but is usually -90°C or higher, and is preferably -80°C or higher. The glass transition temperature (Tg) of the above acrylic copolymer can be determined, for example, by differential scanning calorimetry.

[0023] The weight-average molecular weight (Mw) of the above acrylic copolymer has a lower limit of over 200,000 and an upper limit of 2,000,000. Having the weight-average molecular weight of the above acrylic copolymer within this range enhances the constant-load peelability of the adhesive layer at high temperatures. The preferred lower limit for the weight-average molecular weight of the above acrylic copolymer is 300,000, a more preferred lower limit is 400,000, an even more preferred lower limit is 500,000, a preferred upper limit is 1,800,000, and an even more preferred upper limit is 1,500,000. The weight-average molecular weight (Mw) is the weight-average molecular weight on a standard polystyrene basis, measured by GPC (Gel Permeation Chromatography). Specifically, the acrylic copolymer is diluted 50-fold with tetrahydrofuran (THF), and the resulting dilution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare the measurement sample. Next, this measurement sample is supplied to a gel-permeation chromatograph (Waters, product name "2690 Separations Module" or equivalent) and GPC measurement is performed under conditions of a sample flow rate of 1 ml / min and a column temperature of 40°C. The polystyrene-based molecular weight of the acrylic copolymer is measured, and this value is taken as the weight-average molecular weight of the acrylic copolymer.

[0024] The molecular weight distribution (Mw / Mn) of the above acrylic copolymer has a lower limit of 1.1 and an upper limit of 3.5. Having the molecular weight distribution of the above acrylic copolymer within this range improves the constant-load peelability of the adhesive layer at high temperatures. A preferred lower limit for the molecular weight distribution of the above acrylic copolymer is 1.2, a preferred upper limit is 3.0, a more preferred lower limit is 1.5, and a more preferred upper limit is 2.5. The molecular weight distribution (Mw / Mn) is a value obtained from the weight-average molecular weight (Mw) and the number-average molecular weight (Mn). The number-average molecular weight (Mn) can be determined in the same way as the weight-average molecular weight (Mw).

[0025] The method for adjusting the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the above acrylic copolymer to the above range is not particularly limited, but methods such as adjusting the composition of the acrylic copolymer or adjusting the polymerization conditions (e.g., polymerization method, polymerization temperature, polymerization time, monomer concentration, polymerization initiator concentration, chain transfer agent concentration, etc.) are preferred.

[0026] The above-mentioned 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 method of radical reaction is not particularly limited, and examples include living radical polymerization and free radical polymerization. Living radical polymerization yields copolymers with more uniform molecular weight and composition compared to free radical polymerization, and the generation of low molecular weight components can be suppressed. As a result, the molecular weight distribution (Mw / Mn) of the acrylic copolymer is more likely to satisfy the above range, the cohesive force of the adhesive layer is increased, and the constant load peelability at high temperatures is further improved. 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 the molecular weight distribution (Mw / Mn) of the acrylic copolymer is more likely to satisfy the above range, the cohesive force of the adhesive layer is increased, and the constant load peelability of the adhesive layer at high temperatures is further improved. Furthermore, solution polymerization is more preferred because it is easier to mix the tackifying resin with the obtained acrylic copolymer, and the constant load peelability of the adhesive layer at high temperatures can be further improved.

[0027] When solution polymerization is used as the polymerization method, examples of reaction solvents include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, and diethyl ether. These reaction solvents may be used individually or in combination of two or more.

[0028] The radical polymerization initiators mentioned above are not particularly limited and include, for example, organic peroxides and azo compounds. Examples of organic peroxides include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of azo compounds include azobisisobutyronitrile and azobiscyclohexanecarbonilonitrile. These radical polymerization initiators may be used individually or in combination of two or more. Furthermore, in the case of living radical polymerization, various polymerization methods may be employed. For example, iron, ruthenium, or copper catalysts and halogen-based initiators may be used (ATRP), alkoxyamine initiators such as TEMPO may be used (NMP), organic halogen compound initiators such as alkyl iodide compounds may be used (iodine transfer polymerization), organic tellurium polymerization initiators may be used (TERP), and organic peroxides, azo compounds, etc. may be used in the presence of a chain transfer agent (RAFT agent) such as a dithioester (RAFT). The above radical polymerization initiators are not particularly limited as long as they are commonly used in living radical polymerization. Examples of organic halogen compound initiators include alkyl iodide compounds. Examples of organic tellurium polymerization initiators include organic tellurium compounds and organic telluride compounds. Examples of RAFT agents include dithiobenzoate compounds, trithiocarbonate compounds, dithiocarbamate compounds, xanthanate compounds, etc. In addition, in living radical polymerization, organic peroxides, azo compounds, etc. may be used as radical polymerization initiators to accelerate the polymerization rate.

[0029] The adhesive layer described above preferably does not contain a surfactant. The absence of surfactants in the adhesive layer enhances the adhesive strength of the tape, particularly at high temperatures. Note that the absence of surfactants in the adhesive layer means that the surfactant content in the adhesive layer is 3% by weight or less, preferably 1% by weight or less. In order for the above adhesive layer to not contain a surfactant, it is preferable not to use a surfactant when obtaining the above acrylic copolymer. To achieve this, for example, solution polymerization, UV polymerization, etc., may be used as the polymerization method when obtaining the above acrylic copolymer. The content of the above-mentioned surfactant can be determined, for example, by measuring the adhesive layer using a liquid chromatography-mass spectrometer (e.g., NEXCERA from Shimadzu Corporation, Exactive from Thermo Fisher Scientific, etc.). More specifically, the ethyl acetate solution of the 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 peaks corresponding to the surfactant in the adhesive layer. It is preferable to prepare samples with known surfactant content in the adhesive layer for each surfactant type, create a calibration curve showing the relationship between surfactant content and peak area ratio, and analyze it. Column: Thermo Fisher Scientific, Hypersil GOLD (2.1 x 150 mm) Mobile phase: acetonitrile Column temperature: 40°C Flow rate 1.0mL / min Ionization method ESI Capillary temperature 350℃

[0030] From the viewpoint of being able to appropriately adjust the gel fraction, it is preferable that the above adhesive layer further contains a crosslinking agent. The above crosslinking agent is not particularly limited and examples 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 the adhesive layer exhibits excellent adhesion to the adherend. The molecular weight of the crosslinking agent is not particularly limited, but from a manufacturing standpoint, a molecular weight of less than 2000 is preferred, and 100 or more is preferred.

[0031] The content of the crosslinking agent in the 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 adhesive layer is appropriately adjusted, and the tackiness and constant load peelability at high temperatures are further improved. A more preferred lower limit for the content of the crosslinking agent is 0.1 parts by weight and a more preferred upper limit is 5 parts by weight. The above-mentioned crosslinking agent content indicates the amount of solids contained in the crosslinking agent.

[0032] Preferably, the adhesive layer further contains a tackifying resin. This further improves the constant-load peelability of the adhesive layer at high temperatures. Examples of the tackifying resins mentioned above include rosin ester tackifying resins, terpene tackifying resins, coumarone indene tackifying resins, alicyclic saturated hydrocarbon tackifying resins, C5 petroleum tackifying resins, C9 petroleum tackifying resins, and C5-C9 copolymer petroleum tackifying resins. These tackifying resins may be used individually or in combination of two or more. Among these, at least one selected from the group consisting of rosin ester tackifying resins and terpene tackifying resins is preferred.

[0033] Examples of the rosin ester-based tackifying resins mentioned above include polymerized rosin ester resins and hydrogenated rosin ester resins. Examples of the terpene-based tackifying resins mentioned above include terpene resins and terpene phenol resins. The rosin ester-based tackifying resin and the terpene-based tackifying resin described above are preferably of biological origin. Examples of biologically derived rosin ester-based tackifying resins include rosin ester-based tackifying resins derived from natural resins such as pine resin. Examples of biologically derived terpene-based tackifying resins include terpene-based tackifying resins derived from plant essential oils, etc.

[0034] The content of the tackifying resin in the 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 relative to 100 parts by weight of the acrylic copolymer. If the content of the tackifying resin is within the above range, the constant load peelability of the adhesive layer at high temperatures will be higher. A more preferred lower limit for the content of the tackifying resin is 15 parts by weight, a more preferred upper limit is 50 parts by weight, and an even more preferred upper limit is 35 parts by weight.

[0035] The adhesive layer may, if necessary, contain additives such as silane coupling agents, plasticizers, softeners, fillers, pigments, and dyes.

[0036] The gel fraction of the adhesive layer described above is not particularly limited, but a preferred lower limit is 10% by weight and a preferred upper limit is 70% by weight. If the gel fraction of the adhesive layer is within the above range, the tackiness and constant-load peelability at high temperatures of the adhesive layer will be higher. A more preferred lower limit for the gel fraction of the adhesive layer is 20% by weight and a more preferred upper limit is 50% by weight. The gel fraction of the adhesive layer described above is measured as follows. First, a test specimen is prepared by cutting the adhesive tape into a 20mm x 40mm rectangular shape. The test specimen is then immersed in ethyl acetate at 23°C for 24 hours, removed from the ethyl acetate, and dried at 110°C for 1 hour. The weight of the dried test specimen is measured, and the gel fraction is calculated using the following formula (1). Note that the test specimen does not have a release film laminated on it to protect the adhesive layer. Gel fraction (weight %) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: Weight of the substrate, W1: Weight of the test specimen before immersion, W2: Weight of the test specimen after immersion and drying)

[0037] The method for adjusting the gel fraction of the adhesive layer to the above range is not particularly limited, but it is preferable to adjust the composition and weight-average molecular weight of the acrylic copolymer, as well as the type and amount of the crosslinking agent, as described above.

[0038] The adhesive layer described above preferably contains 10% by weight or more of bio-derived carbon. A bio-derived carbon content of 10% by weight or more is an indicator that a product is "bio-based." A bio-derived carbon content of 10% by weight or more is preferable from the viewpoint of conserving petroleum resources and reducing carbon dioxide emissions. A more preferable lower limit for the bio-derived carbon content is 30% by weight, and an even more preferable lower limit is 60% by weight. The upper limit for the bio-derived carbon content is not particularly limited and may be 100% by weight. Furthermore, while bio-derived carbon contains a certain percentage of the radioactive isotope C-14, petroleum-derived carbon contains almost no C-14. Therefore, the content of bio-derived carbon can be calculated by measuring the concentration of C-14 contained in the adhesive layer. Specifically, this can be measured in accordance with ASTM D6866-20, a standard widely used in the bioplastics industry.

[0039] The thickness of the 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 adhesive layer is within the above range, the constant load peelability of the adhesive layer at high temperatures will be higher. A more preferred lower limit for the thickness of the adhesive layer is 5 μm, and an even more preferred lower limit is 10 μm. A more preferred upper limit for the thickness of the adhesive layer is 200 μm, and an even more preferred upper limit is 100 μm.

[0040] The adhesive tape of the present invention may be a non-support tape without a base material, a single-sided adhesive tape having an adhesive layer on one side of the base material, or a double-sided adhesive tape having adhesive layers on both sides of the base material. The above-mentioned substrate is not particularly limited, and conventionally known substrates can be used, however, in order to increase the content of bio-derived carbon in the adhesive tape as a whole, it is preferable to use a bio-derived substrate. Examples of the above-mentioned bio-derived substrates include films and nonwoven fabrics made from plant-derived polyesters (PES) such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polylactic acid (PLA), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). Also included are films and nonwoven fabrics made from plant-derived polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetylcellulose (TAC), cellulose, and polyamide (PA).

[0041] From the viewpoint of substrate strength, the above-mentioned substrate is preferably a film made of PES or a film made of PA. Furthermore, from the viewpoint of heat resistance and oil resistance, a film made of PA is preferred. Examples of materials that make up a film made of the above-mentioned PA include nylon 11, nylon 1010, nylon 610, nylon 510, nylon 410, etc., which are made from castor oil, and nylon 56, etc., which are made from cellulose.

[0042] Furthermore, from the perspective of reducing environmental impact by decreasing the use of new petroleum resources and suppressing carbon dioxide emissions, base materials made from recycled resources may be used. Methods for recycling resources include, for example, recovering waste from packaging containers, home appliances, automobiles, construction materials, food, etc., or waste generated in the manufacturing process, and using the extracted materials again as raw materials by washing, decontamination, or decomposition by heating or fermentation. Examples of base materials using recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., using recovered plastics that have been re-resinated as raw materials. Alternatively, recovered waste may be burned and used as thermal energy for the manufacture of base materials and their raw materials, or the oils and fats contained in the recovered waste may be mixed with petroleum, fractionated, and refined to be used as raw materials.

[0043] The above-mentioned substrate may be a foam substrate from the viewpoint of improving compression characteristics. As the foam substrate mentioned above, a foam substrate made of PE, PP, and / or PU is preferred, and a foam substrate made of PE is more preferred from the viewpoint of achieving a high degree of both flexibility and strength. Examples of components of the foam substrate made of PE include PE derived from sugarcane.

[0044] The method for producing the foamed substrate described above is not particularly limited, but for example, it is preferable to prepare a foamed resin composition containing a PE resin containing PE made from sugarcane and a foaming agent, and to foam the foaming agent when extruding the foamed resin composition into a sheet using an extruder, and to crosslink the obtained polyolefin foam as needed.

[0045] The thickness of the foam substrate described above is not particularly limited, but a preferred lower limit is 50 μm and a preferred upper limit is 5000 μm. When the thickness of the foam substrate is within this range, it can exhibit high impact resistance while also exhibiting high flexibility that allows it to adhere closely to the shape of the substrate. A more preferred upper limit for the thickness of the foam substrate is 1000 μm, and an even more preferred upper limit is 300 μm.

[0046] The adhesive tape of the present invention has a preferred lower limit for the total thickness of the adhesive tape (sum of the thickness of the base material and the adhesive layer) of 3 μm and a preferred upper limit of 6000 μm. If the total thickness of the adhesive tape is within the above range, the constant load peelability at high temperatures will be higher. A more preferred upper limit for the total thickness of the adhesive tape is 1200 μm, and an even more preferred upper limit is 500 μm.

[0047] The method for manufacturing the adhesive tape of the present invention is not particularly limited and can be manufactured by conventionally known manufacturing methods. For example, in the case of double-sided adhesive tape, the following method can be used. First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer, a radical scavenger, and, if necessary, a crosslinking agent or tackifying resin. This solution of adhesive A is then applied to the surface of the substrate, and the solvent in the solution is completely dried and removed to form adhesive layer A. Next, a release film is placed on top of the formed adhesive layer A with its release-treated surface facing the adhesive layer A. Next, a separate release film is prepared, and a solution of adhesive B, prepared in the same manner as above, is applied to the release surface of this release film. By completely drying and removing the solvent in the solution, a laminated film is created in which adhesive layer B is formed on the surface of the release film. The obtained laminated film is then placed on the back surface of a substrate on which adhesive layer A is formed, with adhesive layer B facing the back surface of the substrate, to create a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided adhesive tape is obtained in which adhesive layers are present on both sides of the substrate, and the surface of the adhesive layer is covered with a release film.

[0048] Alternatively, two sets of laminated films may be prepared in the same manner, and these laminated films may be superimposed on each of the two sides of a substrate with the adhesive layer of the laminated film facing the substrate to create a laminate. This laminate may then be pressed with a rubber roller or the like to obtain a double-sided adhesive tape having adhesive layers on both sides of the substrate, with the surface of the adhesive layer covered with a release film.

[0049] The applications of the adhesive tape of the present invention are not particularly limited, but because its resistance to planar rebound does not easily decrease even when exposed to high temperatures, it is preferably used for fixing electronic equipment components or automotive components. Specifically, the adhesive tape of the present invention can be suitably used for adhesive fixing of electronic equipment components in large portable electronic devices, and for adhesive fixing of automotive components (e.g., automotive panels). [Effects of the Invention]

[0050] According to the present invention, it is possible to provide an adhesive tape with excellent tackiness and constant load peelability at high temperatures. [Brief explanation of the drawing]

[0051] [Figure 1] This is a schematic diagram illustrating a method for evaluating the constant-load peelability of adhesive tape at high temperatures. [Modes for carrying out the invention]

[0052] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] <n-ヘプチルアクリレート> Ricinoleic acid derived from castor oil was cracked to obtain a mixture containing undecylenic acid and heptyl alcohol. Then, by distillation, the undecylenic acid was separated to obtain n-heptyl alcohol containing bio-derived carbon. The obtained n-heptyl alcohol was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare n-heptyl acrylate.

[0054] <Other acrylic monomers> • Butyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) • 2-Ethylhexyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) • Lauryl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) • Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) • 2-hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)

[0055] <Crosslinking agent> • Isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45)

[0056] <Adhesive-granting resin> • Terpene phenol (Terpene phenol G-150, manufactured by Yasuhara Chemical Co., Ltd.)

[0057] (Example 1) (1) Production of acrylic copolymer In a reaction vessel, 200 parts by weight of ethyl acetate, 96.9 parts by weight of n-heptyl acrylate, 3 parts by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate were placed as polymerization solvents. After purging with nitrogen, the reaction vessel was placed in a water bath set to 58°C, and the reaction vessel was heated to initiate reflux. Thirty minutes after the start of reflux, 0.06 parts by weight of azobisisobutyronitrile was added to the reaction vessel as a polymerization initiator, and the reaction was allowed to proceed for 8 hours. Subsequently, an acrylic copolymer-containing solution was obtained by cooling while diluting the reaction vessel with ethyl acetate.

[0058] Mass spectrometry of the obtained acrylic copolymer and 1 1H-NMR measurements were performed, and the content of constituent units derived from each monomer was calculated from the integral intensity ratio of the hydrogen peaks derived from each monomer.

[0059] The obtained acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting dilution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare the measurement sample. This measurement sample was supplied to a gel permission chromatograph (Waters, 2690 Separations Module), and GPC measurement was performed under conditions of sample flow rate of 1 mL / min and column temperature of 40°C. The polystyrene-equivalent molecular weight of the acrylic copolymer was measured, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined. Furthermore, the molecular weight distribution (Mw / Mn) was determined. Furthermore, the glass transition temperature (Tg) of the obtained acrylic copolymer was determined by differential scanning calorimeter (DSC7000X, Hitachi High-Tech Science Corporation) measurement. Specifically, approximately 2 mg of the acrylic copolymer was weighed into an aluminum pan, and the measurement was performed under a nitrogen atmosphere with a heating rate of 10°C / min. The resulting chart was read to determine the glass transition point.

[0060] (2) Manufacturing of adhesive tape To the obtained acrylic copolymer-containing solution, an adhesive solution was prepared by adding an isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L-45) in a solid content of 0.5 parts by weight per 100 parts by weight of the acrylic copolymer. This adhesive solution was applied to the release-treated surface of a 75 μm thick release-treated PET film so that the thickness of the adhesive layer after drying was 50 μm, and then dried at 110°C for 5 minutes. This adhesive layer was then placed on top of the release-treated surface of a 75 μm thick release-treated PET film and cured at 40°C for 48 hours to obtain an adhesive tape (non-support type).

[0061] (3) Measurement of gel fraction The release film was peeled off one side of the adhesive tape and bonded to a 23 μm thick PET film (Futamura Chemical Co., Ltd., FE2002). The tape was then cut into a 20 mm x 40 mm rectangular shape. The release film was then peeled off the other side of the adhesive tape to prepare a test specimen, and its weight was measured. The test specimen was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The weight of the dried test specimen was measured, and the gel fraction was calculated using (1) below. Gel fraction (weight %) = 100 × (W2 - W0) / (W1 - W0) (1) (W0: Weight of the substrate (PET film), W1: Weight of the test specimen before immersion, W2: Weight of the test specimen after immersion and drying)

[0062] (Examples 2-11, Comparative Examples 1-5) An adhesive tape was obtained in the same manner as in Example 1, except that the composition of the acrylic copolymer, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn), the amount of tackifying resin, and the amount of crosslinking agent were changed as shown in Table 1. The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the acrylic copolymer were adjusted by changing the polymerization conditions (e.g., polymerization method, polymerization temperature, polymerization time, monomer concentration, polymerization initiator concentration, chain transfer agent concentration, etc.) in addition to the composition of the acrylic copolymer.

[0063] <Rating> The adhesive tapes obtained in the examples and comparative examples were evaluated using the following method. The results are shown in Table 1.

[0064] (1) Tuck An adhesive tape was placed on a tack tester (TAC-1000, manufactured by Resca Co., Ltd.) with the adhesive layer facing upwards. A cylindrical stainless steel probe with a diameter of 5 mm was pressed against the adhesive layer of the tape at a pressing speed of 1.0 mm / s and a pressing load of 100 gf, and held in this position for 1.0 second. After that, the probe was pulled up at a pulling speed of 1.0 mm / s, and the stress on the adhesive tape during this time was measured. The maximum stress (peak top) of the obtained stress curve was defined as the tack force. A value of ○ was used if the tack force was greater than 1500 gf, a △ was used if it was greater than 1000 gf and less than or equal to 1500 gf, and a × was used if it was less than or equal to 1000 gf.

[0065] (2) Peelability under constant load at high temperatures Figure 1 shows a schematic diagram illustrating a method for evaluating the constant load peelability of adhesive tape at high temperatures. As shown in Figure 1, a 20mm x 50mm backed adhesive tape 2 was attached to a polycarbonate (PC) board 1 and cured overnight at 23°C and 50% humidity to create test sample 3. A 50g weight 4 was attached to test sample 3 (adhesive tape 2) at a 90° angle at 85°C, and the peeling time was measured. A peeling time longer than 24 hours was marked with ◎, a peeling time longer than 3 hours but 24 hours or less was marked with ○, a peeling time longer than 1 hour but 3 hours or less was marked with △, and a peeling time of 1 hour or less was marked with ×. In Figure 1, L represents the peeled portion of the adhesive tape 2.

[0066] [Table 1] [Industrial applicability]

[0067] According to the present invention, it is possible to provide an adhesive tape with excellent tackiness and constant load peelability at high temperatures. [Explanation of Symbols]

[0068] 1. Polycarbonate (PC) sheet 2 Adhesive tape 3 Test Samples 4. 50g weight

Claims

1. An adhesive tape having an adhesive layer containing an acrylic copolymer, The acrylic copolymer contains 30% by weight or more of constituent units derived from n-heptyl (meth)acrylate, has a weight-average molecular weight (Mw) greater than 200,000 and 2,000,000 or less, and a molecular weight distribution (Mw / Mn) of 1.1 or more and 3.5 or less. The adhesive layer has a gel fraction of 10% by weight or more and 70% by weight or less. An adhesive tape characterized by the following features.

2. The adhesive tape according to claim 1, characterized in that the n-heptyl (meth)acrylate contains bio-derived carbon.

3. The adhesive tape according to claim 1 or 2, characterized in that the acrylic copolymer further contains constituent units derived from monomers having crosslinkable functional groups.

4. The adhesive tape according to claim 1 or 2, characterized in that the adhesive layer further contains a crosslinking agent.

5. The adhesive tape according to claim 1 or 2, characterized in that the adhesive layer further contains a tackifying resin.

6. The adhesive tape according to claim 1 or 2, characterized in that it is used for fixing electronic equipment components or in-vehicle components.

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