Acrylic adhesive composition and adhesive tape

Abstract

The objective is to provide an acrylic adhesive composition that exhibits excellent compatibility with high molecular weight tackifying resins and can be used to manufacture adhesive tapes with superior constant load holding capacity, and to provide an adhesive tape made from the acrylic adhesive composition that has superior constant load holding capacity compared to conventional adhesives. [Solution] An acrylic adhesive composition comprising at least an acrylic adhesive containing an acrylic random copolymer or an acrylic block copolymer, and a tackifying resin, wherein the weight-average molecular weight of the tackifying resin is 3000 or more, and the acid value is 20 to 150 mgKOH / g, and the content of the tackifying resin is 20 parts by mass or more per 100 parts by mass of the acrylic adhesive.

Description

Technical Field

[0001] The present invention relates to an acrylic adhesive composition, and more specifically, to an acrylic adhesive composition comprising at least an acrylic adhesive containing an acrylic random copolymer or an acrylic block copolymer, and a tackifier resin, wherein the weight average molecular weight of the tackifier resin is 3000 or more, and the acid value is 20 to 150 mgKOH / g, and the content of the tackifier resin is 20 parts by mass or more with respect to 100 parts by mass of the acrylic adhesive.

Background Art

[0002] Acrylic adhesives are excellent in weather resistance, transparency, heat resistance, solvent resistance, etc. Therefore, adhesive tapes using them are widely used as joining means in relatively large electronic devices such as thin TVs, home appliances, and OA equipment, or in fixing parts constituting relatively small electronic devices such as portable electronic terminals, cameras, and personal computers. More specifically, in each industrial field such as OA equipment, IT / home appliances, and automobiles, it is used not only for fixing parts such as fixing sheet metals to each other or fixing exterior parts to the housing in large electronic devices, and fixing rigid parts such as exterior parts or batteries to small electronic devices, but also for temporary fixing of such parts, and for label applications for displaying product information.

[0003] An adhesive tape of an acrylic adhesive may add a tackifier resin to improve the adhesive performance (for example, Patent Documents 1 and 2). There are various types of tackifier resins, and among them, high molecular weight tackifier resins are known to improve adhesive performance such as constant load holding power. However, high molecular weight tackifier resins have poor compatibility with acrylic adhesives, and when the added tackifier resin is not sufficiently compatible, the adhesive performance deteriorates, so there is a limit to the amount that can be added. As a result, there has been a problem that the adhesive performance such as constant load holding power cannot be sufficiently improved.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-157789 [Patent Document 2] International Publication No. 2016 / 035747 [Overview of the project] [Problems that the invention aims to solve]

[0005] The double-sided adhesive tape having an adhesive layer containing an acrylic polymer and a tackifying resin having hydroxyl groups, as described in Patent Document 1, exhibits excellent heat resistance, and the acrylic double-sided adhesive tape containing a tackifying resin, as described in Patent Document 2, exhibits high adhesive strength after heat pressing and excellent impact resistance, even in narrow widths. Since the adhesive tapes in Patent Documents 1 and 2 are not designed with the addition of high molecular weight tackifying resin in mind, the high molecular weight tackifying resin cannot be sufficiently compatible, and it is considered that the constant load holding force required for strong adhesive double-sided tapes used for fixing parts as described above is insufficient.

[0006] Therefore, the object of the present invention is to provide an acrylic adhesive composition that has excellent compatibility with high molecular weight tackifying resins and can be used to produce adhesive tapes with excellent constant load holding power, and to provide an adhesive tape made from the acrylic adhesive composition that has better constant load holding power than conventional adhesives. [Means for solving the problem]

[0007] The present inventors conducted diligent research to solve the problems of the prior art described above, and as a result obtained the following findings, they discovered the present invention. Specifically, they found that the compatibility between acrylic adhesives and high molecular weight tackifying resins can be improved by adjusting the molecular weight, acid value, and content of the tackifying resin to a certain range, leading to the present invention.

[0008] The present invention encompasses the following embodiments. [1] An acrylic adhesive composition comprising at least an acrylic adhesive containing an acrylic random copolymer or an acrylic block copolymer, and a tackifying resin, wherein the weight-average molecular weight of the tackifying resin is 3000 or more, and the acid value is 20 to 150 mgKOH / g, and the content of the tackifying resin is 20 parts by mass or more per 100 parts by mass of the acrylic adhesive.

[0009] [2] The acrylic adhesive composition according to [1], wherein the tackifying resin is a rosin-based tackifying resin.

[0010] [3] The acrylic adhesive composition according to [1] or [2], wherein the softening point of the tackifying resin is 150°C or higher.

[0011] [4] The acrylic adhesive composition according to any one of [1] to [3], wherein the haze of the adhesive layer having a thickness of 40 μm is 60% or less, obtained by adding 50 parts by mass of the tackifying resin to 100 parts by mass of the acrylic adhesive composition.

[0012] [5] The acrylic adhesive composition according to any one of the above [1] to [4], wherein the weight-average molecular weight of the acrylic random copolymer is 150,000 to 2,500,000.

[0013] [6] The acrylic adhesive composition according to any one of the above [1] to [5], wherein the weight-average molecular weight of the acrylic block copolymer is 10,000 to 500,000.

[0014] [7] The acrylic adhesive composition according to [1] to [6], wherein the peak temperature of tanδ (T2) of the acrylic adhesive composition obtained by adding 50 parts by mass of the tackifying resin having a weight-average molecular weight of 3000 or more to 100 parts by mass of the acrylic adhesive is 30°C or higher than the peak temperature of tanδ (T1) of the acrylic adhesive.

[0015] An adhesive tape comprising an adhesive layer made of an acrylic adhesive composition according to any one of the above [1] to [7].

[0016] The adhesive tape according to [8], further comprising a base material, wherein the adhesive layer is provided on at least one surface of the base material. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an acrylic adhesive composition that has excellent compatibility with high molecular weight tackifying resins and can be used to produce adhesive tapes with excellent constant load holding power, and an adhesive tape made from the acrylic adhesive composition that has better constant load holding power than conventional adhesives. [Modes for carrying out the invention]

[0018] The acrylic adhesive composition of the present invention comprises at least an acrylic adhesive containing an acrylic random copolymer or an acrylic block copolymer, and a tackifying resin, wherein the weight-average molecular weight of the tackifying resin is 3000 or more, and the acid value is 20 to 150 mgKOH / g, and the content of the tackifying resin is 20 parts by mass or more per 100 parts by mass of the acrylic adhesive.

[0019] The acrylic adhesive composition of the present invention, having the above-mentioned characteristics, exhibits excellent compatibility with high molecular weight tackifying resins, resulting in an adhesive tape with superior constant load holding power compared to conventional adhesives.

[0020] The acrylic adhesive composition of the present invention will be described in more detail below based on its constituent elements. In this specification, numerical ranges indicated using "~" represent a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In this specification, "(meth)acrylic" is a general term referring to acrylic, methacrylic, and both.

[0021] <Acrylic adhesive> The acrylic adhesive composition of the present invention has no particular limitation as long as it has the above characteristics and can be appropriately selected from known materials. It contains an acrylic adhesive and a tackifier resin, and may contain other components as necessary.

[0022] The acrylic adhesive in the present invention contains an acrylic random copolymer or an acrylic block copolymer as the main component of the acrylic adhesive. The "main component of the acrylic adhesive" in this specification refers to the main component of the resin component contained in the acrylic adhesive (typically, a component contained in an amount exceeding 30% by mass).

[0023] When the main component of the acrylic adhesive in the present invention is an acrylic random copolymer, it is preferable that 30 to 100% by mass of the entire acrylic adhesive composition is occupied by the acrylic random copolymer, more preferably 40 to 95 parts by mass is occupied by the acrylic random copolymer, and still more preferably 50 to 90% by mass is occupied by the acrylic random copolymer.

[0024] When the main component of the acrylic adhesive in the present invention is an acrylic block copolymer, it is preferable that 30 to 100% by mass of the entire acrylic adhesive composition is occupied by the acrylic block copolymer, more preferably 40 to 90 parts by mass is occupied by the acrylic block copolymer, and still more preferably 40 to 85% by mass is occupied by the acrylic block copolymer.

[0025] (Acrylic random copolymer) When the acrylic adhesive in the present invention contains an acrylic random copolymer, it is preferable that the acrylic adhesive composition contains a crosslinking agent in addition to the acrylic random copolymer and the tackifier resin.

[0026] The acrylic random copolymer in the present invention is obtained by polymerizing monomer components containing a (meth)acrylic monomer. Examples of (meth)acrylic monomers that can be used in the production of the acrylic random copolymer include (meth)acrylic acid esters having alkyl groups with 1 to 12 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0027] In particular, the (meth)acrylic monomer is preferably one whose Tg when homopolymerized is in the range of -70°C to 0°C, more preferably -60°C to -10°C, and even more preferably -60°C to -20°C. Examples of (meth)acrylic monomers whose homopolymer Tg is in the range of -60°C to -20°C include ethyl (meth)acrylate (-24°C), n-butyl (meth)acrylate (-55°C), isononyl (meth)acrylate (-58°C), and lauryl (meth)acrylate (-23°C). The numbers in parentheses for each monomer are the Tg of the homopolymer of each monomer as described in, for example, "Polymer Handbook (4th ed.)". Using these (meth)acrylic monomers makes it easy to balance wettability to the adherend and cohesive force of the adhesive layer, and provides excellent 180° peel adhesion, constant load holding strength, and shear holding strength.

[0028] The (meth)acrylic acid ester having an alkyl group with 1 to 12 carbon atoms is preferably used in an amount of 60% by mass or more, more preferably in the range of 80% to 98.5% by mass, and even more preferably in the range of 90% to 98.5% by mass, based on the total amount of monomers used in the production of the acrylic random copolymer. Furthermore, it is preferable that 70% by mass or more of (meth)acrylic monomers having a homopolymer Tg in the range of -60°C to -20°C are used, preferably 80% by mass or more, and more preferably in the range of 80% to 98.5% by mass.

[0029] In the present invention, when the acrylic adhesive composition contains an acrylic random copolymer and a crosslinking agent, and when a crosslinking agent described later is used, it is preferable to use an acrylic random copolymer having a functional group that reacts with the functional group of the crosslinking agent. Examples of functional groups of the acrylic random copolymer include hydroxyl groups, carboxyl groups, and amide groups. These functional groups can be introduced into the acrylic random copolymer, for example, by using a vinyl monomer having a hydroxyl group, a carboxyl group, or an amide group as the monomer. The vinyl monomer having the above functional group is preferably used in an amount of 0.01% to 10.0% by mass, and more preferably in an amount of 0.03% to 5.0% by mass, relative to the total amount of monomer used in the production of the acrylic random copolymer. In addition, multiple reactive functional groups can be used in combination.

[0030] As monomers having a hydroxyl group, for example, (meth)acrylic acid esters having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate can be used.

[0031] Examples of vinyl monomers having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth)acrylic acid dimer, crotonic acid, ethylene oxide-modified succinic acid acrylate, etc., with acrylic acid being the preferred choice.

[0032] Examples of monomers having an amide group include N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, and N,N-dimethylacrylamide.

[0033] In addition to those mentioned above, vinyl acetate, ethylene oxide-modified succinic acid acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and others can also be used as the highly polar vinyl monomers.

[0034] The above-mentioned highly polar vinyl monomer is preferably used in an amount of 1.5% to 20% by mass, more preferably in an amount of 1.5% to 10% by mass, and most preferably in an amount of 2% to 8% by mass, relative to the total amount of monomer used in the production of the acrylic random copolymer. Within this range, it is preferable because it exhibits excellent 180° peel adhesion, constant load holding strength, and shear holding strength.

[0035] In the present invention, it is preferable to use an acrylic random copolymer having a weight-average molecular weight (Mw) of 150,000 to 2,500,000 because it exhibits excellent adhesive performance, and it is more preferable to use one having a weight-average molecular weight (Mw) of 400,000 to 2,500,000 because it provides good constant load holding strength, shear holding strength, and reliability under high temperature and high humidity environments.

[0036] In this invention, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the acrylic adhesive refer to values ​​calculated by gel permeation chromatography (GPC) and converted to standard polystyrene equivalent. Specifically, these can be measured using a GPC device (HLC-8320GPC) manufactured by Tosoh Corporation under the following conditions.

[0037] • Sample concentration: 0.5% by mass (tetrahydrofuran solution) • Sample injection volume: 100 μl • Eluent: Tetrahydrofuran ·Flow rate: 0.8ml / min ·Measurement temperature: 40℃ • Main column: TSKgelGMHHR-R(S) 2 pieces • Guard column: TSKgel HHR(S) 1 piece • Detector: Differential refractometer • Weight-average molecular weight of standard polystyrene: 5 million to 5 million (manufactured by Tosoh Corporation)

[0038] The acrylic random copolymer in the present invention can be produced by polymerizing the above monomer by methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. Adopting solution polymerization is preferable for improving the production efficiency of the acrylic random copolymer. Examples of the solution polymerization method include mixing and stirring the above monomer, a known polymerization initiator, and an organic solvent at a temperature of preferably 40°C to 90°C to carry out radical polymerization. The acrylic random copolymer obtained by the above method may be dissolved or dispersed in the organic solvent, for example, if produced by solution polymerization.

[0039] (Crosslinking agent) In the present invention, it is preferable to use a crosslinking agent in the acrylic random copolymer to ensure excellent adhesive strength. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, and aziridine-based crosslinking agents. In particular, it is preferable to use either or both of isocyanate-based crosslinking agents and epoxy-based crosslinking agents, which have high reactivity with the acrylic random copolymer, and it is more preferable to use an isocyanate-based crosslinking agent.

[0040] Examples of the above-mentioned isocyanate-based crosslinking agents include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and trimethylolpropane-modified tolylene diisocyanate, with tolylene diisocyanate and trimethylolpropane-modified tolylene diisocyanate being preferred.

[0041] It is preferable to select and use an amount of the above-mentioned crosslinking agent such that the gel fraction relative to toluene in the adhesive layer is 20% to 80% by mass, more preferably an amount such that the gel fraction is 30% to 70% by mass, and even more preferably an amount such that the gel fraction is 35% to 65% by mass in order to obtain an adhesive tape exhibiting excellent adhesive strength.

[0042] The gel fraction of the adhesive layer refers to the value measured by the method shown below. First, an adhesive was applied to the release surface of a release liner so that the thickness after drying was 50 μm. This was dried at 100°C for 3 minutes, and then aged at 40°C for 2 days to form an adhesive layer. The adhesive layer was then cut into 50 mm x 50 mm squares to form test specimens. After measuring the mass (G1) of the test specimens, they were immersed in toluene at 23°C for 24 hours. The mixture of the immersed specimens and toluene was filtered using a 300-mesh wire mesh to extract the insoluble components in toluene, and the mass (G2) of the insoluble components dried at 110°C for 1 hour was measured. The gel fraction was calculated based on the masses (G1) and (G2) and the following formula. Gel fraction (mass %) = (G2 / G1) × 100

[0043] (Acrylic block copolymer) In the present invention, when the acrylic adhesive contains an acrylic block copolymer, it is preferable that the acrylic adhesive composition contains an acrylic block copolymer (X), an acrylic block copolymer (Y), and a tackifying resin.

[0044] (Acrylic block copolymer (X)) The acrylic block copolymer (X) is preferably a block copolymer having segment A and segment B. Here, "segment" as used in the present invention refers to the structural unit that constitutes each block in the block copolymer. For example, in the case of an ABA-type triblock copolymer in which structural unit (polymer or oligomer) A made of monomer a, structural unit (polymer or oligomer) B made of monomer b, and structural unit (polymer or oligomer) A made of monomer a are bonded together in order, structural units A and B become segments A and B, respectively (the same applies to the acrylic block copolymer (Y) described later).

[0045] The acrylic block copolymer (X) may be a diblock copolymer (sometimes referred to as an acrylic diblock copolymer) consisting of one segment A and one segment B, a triblock copolymer (sometimes referred to as an acrylic triblock copolymer) consisting of two segments A and one segment B, or a multiblock copolymer having a total of four or more segments A and B. In particular, the acrylic block copolymer (X) is preferably a block copolymer in which segment A is a polymer mainly composed of alkyl methacrylate monomer units and segment B is a polymer mainly composed of alkyl acrylate monomer units, and it is more preferable to use an acrylic triblock copolymer (X) in which the segment bonds are of the ABA type, as this can exhibit high cohesive force. Furthermore, it is desirable that segment A is located at the end. When segment A is located at the end, it is easy for them to aggregate and form domains, which in turn forms a pseudo-crosslinked structure and improves the cohesiveness of the adhesive. Furthermore, the acrylic block copolymer (X) may be used by one type or by two or more types.

[0046] (Segment A) The segment A of the acrylic block copolymer (X) is preferably one in which methacrylic acid esters are the main monomer component. Examples of such methacrylic acid esters include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, sec-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, 1-methylcyclohexyl methacrylate, 2-methylcyclohexyl methacrylate, 3-methylcyclohexyl methacrylate, and 4-methylcyclohexyl methacrylate. Examples include methylcyclohexyl, 2-phenoxyethyl methacrylate, 2-methoxyethyl methacrylate, 2-(N,N-dimethylamino)ethyl methacrylate, trifluoromethyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, 2-methoxypentyl methacrylate, 2-(N,N-dimethylamino)pentyl methacrylate, perfluoropentyl methacrylate, and 2-trimethoxysilylpentyl methacrylate.

[0047] Of the above monomers, in order to particularly improve the shear holding power at high temperatures, it is preferable to use monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, etc., which are esters of methacrylic acid with aliphatic alcohols having 3 or fewer carbon atoms, or cyclohexyl methacrylate, isobornyl methacrylate, etc., as the main constituent monomer of segment A, and it is even more desirable to use methyl methacrylate in order to impart high cohesive force.

[0048] In this context, for something to be considered "the main component," it is preferable that it is contained in a composition ratio (mass ratio) of 50% or more of the total monomers constituting segment A, more preferably 80% or more by mass, and even more preferably 90% or more by mass.

[0049] In addition to the methacrylic acid esters mentioned above, other monomers that can be used as constituent monomers of segment A of the acrylic block copolymer (X) include, for example, methacrylamides such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-isopropylmethacrylamide, N,N-dimethylmethacrylamide, and N,N-diethylmethacrylamide; acrylamides such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide; vinyl monomers having carboxyl groups such as methacrylic acid, acrylic acid, crotonic acid, maleic acid, maleic anhydride, and fumaric acid; aromatic vinyl monomers such as styrene, o-methylstyrene, and p-methylstyrene; conjugated diene monomers such as butadiene and isoprene; olefins such as ethylene and propylene; and lactones such as ε-caprolactone and valerolactone.

[0050] The glass transition temperature (Tg) of segment A is not particularly limited as long as the acrylic block copolymer (X) can exhibit the desired physical properties, but is preferably 50 to 150°C, more preferably 70 to 140°C, and even more preferably 90 to 130°C. When the glass transition temperature is within the above range, segment A acts as a physical pseudo-crosslinking point at the normal operating temperature of the adhesive and functions as a hard segment, allowing it to exhibit excellent shear holding power and constant load holding power when used in an acrylic adhesive composition.

[0051] (Segment B) The segment B of the acrylic block copolymer (X) is preferably one in which acrylic acid esters are the main monomers. Examples of such acrylic acid esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, 2-methylbutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylate, isononyl acrylate, decyl acrylate, lauryl acrylate, tridecyl acrylate, stearyl acrylate, cyclohexyl acrylate, isobornyl acrylate, 2-methoxyethyl acrylate, 2-(N,N-dimethylamino)ethyl acrylate, trifluoromethyl acrylate, trimethoxysilylpropyl acrylate, 4-methyl-2-pentyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate.

[0052] Among the above monomers, in order to improve the adhesive strength and tack, and to exhibit stable adhesive strength under a wide range of peeling speed conditions, it is preferable to use monomers such as n-butyl acrylate, n-heptyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate as the main constituent monomer of segment B, which are esters of acrylic acid and aliphatic alcohols having 4 to 9 carbon atoms. It is also preferable to use monomers whose Tg when formed into a homopolymer is in the range of -60°C to -20°C. Examples of monomers whose homopolymer Tg is in the range of -60°C to -20°C include ethyl acrylate (-24°C), n-butyl acrylate (-55°C), isononyl acrylate (-58°C), and lauryl acrylate (-23°C), and it is particularly preferable to use n-butyl acrylate.

[0053] In this context, for something to be considered "the main component," it is preferable that it is contained in a composition ratio (mass ratio) of 50% or more of the total monomers constituting segment B, more preferably 80% or more by mass, and even more preferably 90% or more by mass.

[0054] In addition to the acrylic acid esters mentioned above, other monomers that can be used as constituent monomers for segment B of the acrylic block copolymer (X) include, for example, alkyl methacrylates (e.g., methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, sec-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, and other methacrylate esters that are constituent monomers of segment A as mentioned above), as well as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, N-isopropyl methacrylamide, and N,N-dimethyl methacrylamide. Examples include methacrylamides such as N,N-diethylmethacrylamide, acrylamides such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide, vinyl monomers having carboxyl groups such as methacrylic acid, acrylic acid, crotonic acid, maleic acid, maleic anhydride, and fumaric acid, aromatic vinyl monomers such as styrene, o-methylstyrene, and p-methylstyrene, conjugated diene monomers such as butadiene and isoprene, olefins such as ethylene and propylene, and lactones such as ε-caprolactone and valerolactone.

[0055] The glass transition temperature (Tg) of segment B is not particularly limited as long as the acrylic block copolymer (X) can exhibit the desired physical properties, but is preferably -80 to 40°C, more preferably -70 to 10°C, and even more preferably -60 to 0°C. When the glass transition temperature is within this range, segment B functions as a soft segment with excellent flexibility, and when used in an acrylic adhesive composition, it can exhibit excellent low-temperature properties and impact resistance.

[0056] The glass transition temperatures of segments A and B constituting the acrylic block copolymer (X) are the extrapolated start temperatures of the transition regions of segments A and B, as observed in the curves obtained by analyzing the acrylic block copolymer (X) using differential scanning calorimeter (DSC). Multiple glass transition temperatures originating from segments A and B of the acrylic block copolymer (X) can be identified based on the curves obtained by DSC measurement, and the glass transition temperatures originating from segments A and B can be assigned based on the glass transition temperatures of polymers having a similar chemical structure (monomer composition, stereoregularity, etc.) to each polymer block.

[0057] The acrylic block copolymer (X) may be modified, as necessary, with functional groups such as hydroxyl groups, carboxyl groups, acid anhydride groups, amino groups, and trimethoxysilyl groups in its molecular side chains or at the ends of its molecular main chain, without impairing the effects of the present invention.

[0058] In the present invention, the weight-average molecular weight (Mw) of the acrylic block copolymer (X) is preferably 10,000 to 500,000, more preferably 110,000 to 300,000, even more preferably 130,000 to 300,000, and particularly preferably 150,000 to 300,000. When the weight-average molecular weight (Mw) of the acrylic block copolymer (X) is within the above range, the adhesive properties of the acrylic adhesive composition, such as adhesive strength, cohesive strength, and tack, are good.

[0059] The molecular weight distribution (weight-average molecular weight Mw / number-average molecular weight Mn) of the acrylic block copolymer (X) is preferably in the range of 1.0 to 2.0, more preferably in the range of 1.0 to 1.7, and even more preferably in the range of 1.0 to 1.5. Having the molecular weight distribution of the acrylic block copolymer (X) within the above range results in excellent shear holding power and constant load holding power when blended with the acrylic block copolymer (Y), described later, within a predetermined range.

[0060] In the present invention, the content of segment A in the acrylic block copolymer (X) is preferably 5 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass, based on the total mass of the acrylic block copolymer (X). When the content of segment A in the acrylic block copolymer (X) is within the above range, it exhibits excellent shear holding power and constant load holding power when blended with the acrylic block copolymer (Y) within a predetermined range.

[0061] In the present invention, the content of segment B in the acrylic triblock copolymer (X) is preferably 70 to 95% by mass, more preferably 75 to 95% by mass, and even more preferably 80 to 90% by mass, based on the total mass of the acrylic triblock copolymer (X). When the content of segment B in the acrylic triblock copolymer (X) is within the above range, it exhibits excellent shear holding power and constant load holding power when blended with the acrylic triblock copolymer (Y) within a predetermined range.

[0062] The acrylic block copolymer (X) in the present invention may be synthesized by polymerizing raw material monomers, or a commercially available product may be used. The polymerization method is not particularly limited, but for example, anionic polymerization, atom transfer radical polymerization (ATRP), etc., can be used. A detailed explanation of each polymerization method is omitted here, but as anionic polymerization, for example, known methods such as anionic polymerization in the presence of mineral salts such as alkali metal or alkaline earth metal salts using an organoalkali metal compound as a polymerization initiator, anionic polymerization in the presence of organoaluminum compounds using an organoalkali metal compound as a polymerization initiator, and anionic polymerization using an organorare earth metal complex as a polymerization initiator can be used. As for ATRP, for example, known methods such as polymerization in the presence of transition metal compounds and nitrogen-containing compounds using an organohalide or halogenated sulfonyl compound as an initiator can be used. Examples of commercially available products include the "Clarity® series" manufactured by Kuraray Co., Ltd.

[0063] In the present invention, it is preferable that the acrylic block copolymer (X) is solid at 23°C. By appropriately adjusting the types of monomers constituting segments A and B, the content ratio of segments A and B, and the weight-average molecular weight of segments A and B, the polymerization reaction can be adjusted so that the polymerized acrylic block copolymer (X) is solid at 23°C.

[0064] (Acrylic block copolymer (Y)) The acrylic block copolymer (Y), like the acrylic block copolymer (X), is a block copolymer having segment A and segment B. Furthermore, it is preferable that the acrylic block copolymer (Y) is liquid at 23°C.

[0065] The acrylic adhesive composition of the present invention, by incorporating an acrylic block copolymer (Y) that is liquid at 23°C in addition to the acrylic block copolymer (X) described above, can exhibit superior shear holding power at high temperatures without a decrease in adhesive strength or constant load holding power.

[0066] The acrylic block copolymer (Y) may be a diblock copolymer (sometimes referred to as an acrylic diblock copolymer) consisting of one segment A and one segment B, a triblock copolymer (sometimes referred to as an acrylic triblock copolymer) consisting of two segments A and one segment B, or a multiblock copolymer having a total of four or more segments A and B. In particular, the acrylic block copolymer (Y) is preferably a block copolymer in which segment A is a polymer mainly composed of alkyl methacrylate monomer units and segment B is a polymer mainly composed of alkyl acrylate monomer units, and it is more preferable to use an acrylic triblock copolymer (Y) in which the segment bonds are of the ABA type, as this can exhibit high cohesive strength and suitability for hot melt coating. Furthermore, the acrylic block copolymer (Y) may be used by one type or by two or more types.

[0067] (Segment A) Segment A of the acrylic block copolymer (Y) can use the same constituent monomers as segment A of the acrylic block copolymer (X) described above. In the acrylic adhesive composition of the present invention, the constituent monomers of segment A of acrylic block copolymer (X) and segment A of acrylic block copolymer (Y) may be the same or different, but it is preferable that they be the same because it improves the compatibility between acrylic block copolymer (X) and acrylic block copolymer (Y). Furthermore, in order to improve the shear holding power at high temperatures, it is preferable to use monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, etc., which are esters of methacrylic acid and aliphatic alcohols having 3 or fewer carbon atoms, or cyclohexyl methacrylate, isobornyl methacrylate, etc., as the main constituent monomer of segment A.

[0068] (Segment B) Segment B of the acrylic block copolymer (Y) can use the same constituent monomers as segment B of the acrylic block copolymer (X) described above. In the acrylic adhesive composition of the present invention, the constituent monomers of segment B of acrylic block copolymer (X) and segment B of acrylic block copolymer (Y) may be the same or different, but it is preferable that they be the same because it improves the compatibility between acrylic block copolymer (X) and acrylic block copolymer (Y). Furthermore, since excellent low-temperature properties and impact resistance can be obtained when used in the acrylic adhesive composition, it is preferable that the main component of segment B be selected from the group consisting of acrylic acid and aliphatic alcohols having 4 to 9 carbon atoms, such as n-butyl acrylate, n-heptyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate, isononyl acrylate, and isononyl acrylate.

[0069] In the present invention, the weight-average molecular weight (Mw) of the acrylic block copolymer (Y) is preferably 20,000 or more and 100,000 or less, and more preferably 40,000 or more and 80,000 or less. When the weight-average molecular weight (Mw) of the acrylic block copolymer (Y) is within the above range, it is possible to suppress the bleed-out of the acrylic block copolymer (Y) from the adhesive layer made of the acrylic adhesive composition.

[0070] In the present invention, the content of segment A in the acrylic block copolymer (Y) is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and even more preferably 5 to 13% by mass, based on the total mass of the acrylic block copolymer (Y). When the content of segment A in the acrylic block copolymer (Y) is within the above range, the adhesive composition containing the block copolymer exhibits superior cohesive force, resulting in improved adhesive strength and constant load holding capacity. Furthermore, it exhibits superior shear holding capacity and constant load holding capacity at high temperatures.

[0071] In the present invention, the content of segment B in the acrylic block copolymer (Y) is preferably 80 to 99% by mass, more preferably 85 to 97% by mass, and even more preferably 87 to 95% by mass, based on the total mass of the acrylic block copolymer (Y). When the content of segment B in the acrylic block copolymer (Y) is within the above range, flexibility and stress relaxation properties are imparted, adhesive properties are improved, while bleed-out is suppressed, and superior shear holding power at high temperatures is achieved.

[0072] The acrylic block copolymer (Y) in this invention may be synthesized by polymerizing raw material monomers, or a commercially available product may be used. The polymerization method is not particularly limited, but a specific example of the polymerization method is the same as that for the acrylic block copolymer (X). Examples of commercially available products include the "Clarity® series" manufactured by Kuraray Co., Ltd.

[0073] In the present invention, it is preferable that the acrylic block copolymer (Y) is liquid at 23°C. By appropriately adjusting the types of monomers constituting segments A and B, the content ratio of segments A and B, and the weight-average molecular weight (Mw) of segments A and B, the polymerization reaction can be adjusted so that the polymerized acrylic block copolymer (X) is liquid at 23°C.

[0074] In the present invention, the content of acrylic block copolymer (Y) per 100 parts by mass of acrylic block copolymer (X) is preferably 1 to 140 parts by mass, more preferably 15 to 120 parts by mass, and even more preferably 20 to 100 parts by mass. When the content of acrylic block copolymer (Y) per 100 parts by mass of acrylic block copolymer (X) is within the above range, an adhesive layer can be made that achieves both high tackiness and excellent cohesiveness, exhibiting shear holding power and constant load holding power.

[0075] (Adhesive-granting resin) The acrylic adhesive composition of the present invention further contains a tackifying resin in addition to the acrylic adhesive described above. By containing the tackifying resin, the acrylic adhesive composition of the present invention increases the adhesive strength to a practically sufficient level and satisfies the properties of adhesive strength, shear holding strength, and constant load holding strength.

[0076] The tackifying resin used in the present invention is preferably compatible with the acrylic adhesive described above to form a polymer blend. While there are no particular limitations on the compatible resin, it can be appropriately selected from various known tackifying resins, such as petroleum resins, styrene resins, coumarone-indene resins, terpene resins, modified terpene resins, rosin resins, rosin derivative resins, and ketone resins.

[0077] Examples of petroleum resins include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, and hydrogenated versions thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins).

[0078] Examples of styrene-based resins include those mainly composed of a styrene homopolymer, a α-methylstyrene homopolymer, a vinyltoluene homopolymer, and copolymers mainly composed of two or more of styrene, α-methylstyrene, and vinyltoluene in their monomer composition (for example, α-methylstyrene / styrene copolymer resins mainly composed of α-methylstyrene / styrene copolymer).

[0079] As a coumarone-indene resin, a resin containing coumarone and indene as monomer components that constitute the resin's backbone (main chain) can be used. Examples of monomer components that may be included in the resin's backbone other than coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

[0080] Examples of terpene resins include α-pinene polymers, β-pinene polymers, and dipentene polymers. Examples of modified terpene resins include those obtained by modifying the above terpene resins (phenol modification, catechol modification, styrene modification, hydrogenation modification, hydrocarbon modification, etc.). Specifically, examples include terpene phenol resins, styrene-modified terpene resins, hydrogenated terpene resins, and terpene catechol resins.

[0081] The term "terpene phenol resin" above refers to a polymer containing terpene residues and phenol residues, and is a concept that encompasses both copolymers of terpenes and phenol compounds (terpene-phenol copolymer resins) and phenol-modified homopolymers or copolymers of terpenes (terpene resins, typically unmodified terpene resins) (phenol-modified terpene resins). Preferred examples of terpenes constituting the above terpene phenol resin include monoterpenes such as α-pinene, β-pinene, and limonene (including d-isomers, l-isomers, and d / l-isomers (dipentenes)).

[0082] Specific examples of rosin-based resins include unmodified rosin (gum rosin, wood rosin, tall oil rosin, etc., also called raw rosin), modified rosin (rosin modified by hydrogenation, disproportionation, polymerization, or other chemical modifications of unmodified rosin), etc. Examples of rosin derivative resins include esterified products of unmodified rosin and modified rosin, unsaturated fatty acid-modified rosins of unmodified rosin and modified rosin, unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids, rosin alcohols obtained by reducing the carboxyl groups of unmodified rosin, modified rosin, unsaturated fatty acid-modified rosin or unsaturated fatty acid-modified rosin esters, metal salts of rosins (especially rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives, and rosinphenol resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and then thermal polymerization.

[0083] Of these, rosin-based resins are preferred, and polymerized rosin-based resins are more preferred, from the viewpoint of good compatibility with the aforementioned resins and improved constant load holding capacity.

[0084] In the present invention, it is preferable to use a tackifying resin having polar functional groups in its molecular skeleton, from the viewpoint of excellent compatibility with segment B of the acrylic block copolymer (X) and the acrylic block copolymer (Y). The polar functional groups are not particularly limited, but examples include hydroxyl groups, carbonyl groups, carboxyl groups, cyano groups, amino groups, and nitro groups. Of these, it is preferable to have a hydroxyl group or a carboxyl group, and more preferably a carboxyl group, from the viewpoint of achieving a high level of both 180° peel adhesion, constant load holding strength, and shear holding strength.

[0085] The weight-average molecular weight (Mw) of the tackifying resin in this invention is 3000 or more. Preferably it is 3200 or more, more preferably 3200 to 5000, and even more preferably 3200 to 4000. When the weight-average molecular weight (Mw) of the tackifying resin is within the above range, the compatibility between the tackifying resin and the acrylic adhesive is good, resulting in an adhesive layer with high transparency that fully exhibits the adhesive performance of the tackifying resin.

[0086] The weight-average molecular weight of the tackifying resin in this invention refers to the value calculated by gel permeation chromatography (GPC) and converted to standard polystyrene equivalent. Specifically, the above weight-average molecular weight was measured using a GPC device (HLC-8320GPC) manufactured by Tosoh Corporation under the following conditions.

[0087] • Sample concentration: 0.5% by mass (tetrahydrofuran solution) • Sample injection volume: 100 μl • Eluent: Tetrahydrofuran ·Flow rate: 1.0ml / min ·Measurement temperature: 40℃ • This column contains: 2 x TSKgelG2500HXL + 1 x TSKgelG3000HXL + 1 x TSKgelG4000HXL + 1 x TSKgelG5000HXL • Guard column: TSKgel HXL-H • Detector: Differential refractometer • Weight-average molecular weight of standard polystyrene: 5 million to 5 million (manufactured by Tosoh Corporation)

[0088] The acid value of the tackifying resin in this invention is 20 to 150 mg KOH / g. Preferably, it is 50 to 150 mg KOH / g, more preferably 50 to 100 mg KOH / g, and even more preferably 50 to 75 mg KOH / g. When the acid value of the tackifying resin is within the above range, the polarity of the tackifying resin increases, resulting in good compatibility with acrylic adhesives, and an adhesive layer can be formed that is highly transparent and fully exhibits the adhesive performance of the tackifying resin.

[0089] The acid value of the tackifying resin in this invention is the value obtained by a neutralization titration method in accordance with JIS K0070.

[0090] In the present invention, the tackifying resin preferably contains at least one type having a softening point of 100°C or higher from the viewpoint of high-temperature retention. By incorporating such a tackifying resin with a high softening point, the constant load retention force can be significantly improved in addition to the adhesive force and shear retention force. From the viewpoint of further improving this property, the softening point of the tackifying resin is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, and most preferably 150°C or higher.

[0091] Furthermore, the softening point of the tackifying resin is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 180°C or lower, and most preferably 160°C or lower. When the softening point of the tackifying resin is within the above range, it prevents the resin from becoming too hard and allows for a viscosity suitable for use as an adhesive. In addition, it is possible to improve the shear holding force and constant load holding force in high-temperature environments. Note that one type of tackifying resin or two or more types may be used, but when two or more types are used, the tackifying resin having the above-mentioned preferred softening point is preferably 50% by mass or more, and more preferably 60% by mass or more, based on the total mass of all tackifying resins.

[0092] The softening point of the tackifying resin in this invention is determined by the ring-and-ball method in accordance with JIS K5902.

[0093] The amount of tackifying resin in the present invention is 20 parts by mass or more, based on 100 parts by mass of acrylic adhesive. Preferably, it is 25 parts by mass or more and 200 parts by mass or less, more preferably 25 parts by mass or more and 150 parts by mass or less, even more preferably 30 parts by mass or more and 120 parts by mass or less, and most preferably 50 parts by mass or more and 100 parts by mass or less. By setting the amount of tackifying resin within the above range, the adhesive strength and holding strength can be improved more significantly. In particular, the shear holding strength and constant load holding strength in high-temperature environments can be improved.

[0094] (Anti-aging agent) The acrylic adhesive composition of the present invention may optionally contain an antioxidant. The use of an antioxidant prevents thermal degradation of the adhesive and improves its quality stability. The antioxidant may be used alone or in combination of two or more types. Examples of antioxidants include phosphorus-based antioxidants, phenol-based antioxidants (such as hindered phenol-based antioxidants), hindered amine-based antioxidants, aromatic amine-based antioxidants, and sulfur-based antioxidants.

[0095] (optional ingredient) The acrylic adhesive composition of the present invention may optionally contain one or more rubber-like polymers other than acrylic block copolymers and aromatic block copolymers, to the extent that the effects of the present invention are not significantly impaired. Such rubber-like polymers are various polymers known in the field of adhesives, such as rubber-based, acrylic-based, polyester-based, urethane-based, polyether-based, silicone-based, polyamide-based, and fluorine-based polymers.

[0096] The acrylic adhesive composition of the present invention contains, as necessary, various additives common in the field of adhesives, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, ultraviolet absorbers, and light stabilizers, to the extent that the effects of the present invention are not significantly impaired. Such additives can be conventionally used by conventional methods. <Acrylic adhesive composition> In the present invention, the acrylic adhesive preferably has a tanδ peak temperature T1 of -80 to 20°C, more preferably -70 to 0°C, and even more preferably -60 to -5°C.

[0097] When tackifying resin is added to an acrylic adhesive, the peak temperature of tanδ shifts to higher temperatures as the amount of resin added increases. When the amount of tackifying resin added exceeds a certain range and reaches the compatibility limit of the acrylic adhesive, the amount by which the peak temperature of tanδ shifts to higher temperatures decreases. Therefore, the amount by which the peak temperature of tanδ shifts when tackifying resin is added to an acrylic adhesive can be used as an indicator of whether the tackifying resin is sufficiently compatible with the acrylic adhesive.

[0098] When T1 is the peak temperature of tanδ of the acrylic adhesive in the present invention, and T2 is the peak temperature of tanδ of an acrylic adhesive composition obtained by adding 50 parts by mass of a tackifying resin with a weight-average molecular weight of 3000 or more to 100 parts by mass of the acrylic adhesive of the present invention, it is preferable that T2 is 30°C or more higher than T1, and more preferably 30 to 60°C or more higher. When T2 is 30°C or more higher than T1, the tackifying resin in the present invention is sufficiently and uniformly compatible with the acrylic adhesive, and can exhibit good adhesive strength, constant load holding strength, and shear holding strength.

[0099] The above tanδ is determined by measuring dynamic viscoelasticity by temperature dispersion. Using a viscoelasticity tester (manufactured by T.A. Instrument Japan, product name: ARES G2), an acrylic adhesive composition is formed to a thickness of approximately 2 mm, and the test piece is sandwiched between parallel discs with a diameter of 8 mm, which are the measurement parts of the tester. The storage modulus (G') is measured from 30°C to 200°C at a frequency of 1 Hz and a heating rate of 2°C / min. Next, the loss modulus (G”) is measured in the same manner as the storage modulus (G'), and tanδ is calculated from G' and G”). Note that the peak temperature of tanδ is the glass transition temperature (Tg), which is the temperature at which tanδ is maximum.

[0100] In the acrylic adhesive composition of the present invention, if the compatibility between the tackifying resin and the acrylic adhesive is excellent, the haze of the resulting adhesive layer can be kept low.

[0101] The acrylic adhesive composition of the present invention preferably has a haze of 60% or less, more preferably 50% or less, and most preferably 45% or less, of the acrylic adhesive composition obtained by adding 50 parts by mass of the tackifying resin to 100 parts by mass of the acrylic adhesive. When the haze of the adhesive layer is within the above range, the tackifying resin and the acrylic adhesive are sufficiently compatible, and the effect of improving physical properties by incorporating the tackifying resin can be fully obtained.

[0102] The haze in this invention is measured by the method described in the examples.

[0103] <Form of acrylic adhesive composition> The composition of the acrylic adhesive composition of the present invention has been described in detail above. This acrylic adhesive composition can be a hot-melt type acrylic adhesive composition obtained by melting and kneading the above-mentioned acrylic adhesive, a tackifying resin if necessary, and optional components (other adhesive raw materials), or it can be a solution type acrylic adhesive composition obtained by dissolving it in a predetermined organic solvent (toluene, ethyl acetate, etc.).

[0104] <Uses of acrylic adhesive compositions> The acrylic adhesive composition of the present invention is suitably used in adhesive products in the form of an adhesive layer made of the acrylic adhesive composition, or a laminate containing the adhesive layer (for example, an adhesive tape). Below, as an example of the use of the acrylic adhesive composition of the present invention, a double-sided adhesive tape made by applying the above-described acrylic adhesive composition to both sides of a substrate will be described. In the case of a single-sided adhesive tape, the same applies except that the adhesive is applied to one side of the substrate.

[0105] In a double-sided adhesive tape to which the acrylic adhesive composition of the present invention is applied, the above-mentioned acrylic adhesive composition is coated on both sides of the substrate, and furthermore, a release liner is attached to the surface of the acrylic adhesive composition as needed.

[0106] The substrate is not particularly limited as long as it is in the shape of a film or sheet to which an acrylic adhesive composition can be applied. For example, plastic films such as polypropylene film, ethylene-propylene copolymer film, polyester film, polyvinyl chloride film, cellophane, polyimide, polycarbonate (PC), and polystyrene (PS); foam sheets made from foams such as polyurethane foam, polyethylene foam, polypropylene foam, ethylene-vinyl acetate copolymer foam, butyl rubber foam, and polyacrylic acid ester foam; woven and nonwoven fabrics made from various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, and metal fibers such as stainless steel) alone or in blends; paper such as kraft paper, Japanese paper, and crepe paper; and metal foils such as aluminum foil and copper foil can be appropriately selected and used depending on the application of the adhesive tape. As for the plastic film, any unoriented film, uniaxially oriented film, or biaxially oriented film can be used. Furthermore, the surface of the substrate to which the adhesive layer is provided may be treated with an easy-adhesion treatment such as the application of a primer or corona discharge treatment.

[0107] The thickness of the substrate can be appropriately selected depending on the purpose, but it is generally preferable to have a thickness of 1 μm or more and 2 mm or less.

[0108] Conventional release paper or the like can be used as the release liner, and there are no particular limitations. For example, a release liner having a release treatment layer on the surface of a substrate such as a plastic film or paper, or a release liner made of a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can be used. The release treatment layer is formed by surface-treating the substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, or fluorine-based agent.

[0109] Furthermore, there are no particular limitations on the method for applying the acrylic adhesive composition to the substrate, but known methods such as the method of dissolving the adhesive raw material in an organic solvent and applying it (solvent application method), the method of applying it by spreading it thinly with multiple hot rolls (calendering method), and the method of applying it by thermally melting the adhesive raw material (hot melt method) can be used.

[0110] The acrylic adhesive composition of the present invention can be used for a variety of applications. Furthermore, the adhesive layer made from the acrylic adhesive composition can be used as an adhesive tape on its own, and laminates containing the adhesive layer can also be applied to a variety of applications. Examples include adhesives and adhesive tapes for fixing electronic components, fixing automotive components, protective applications such as surface protection, masking, labeling, bonding, dicing tape, sealing, corrosion and waterproofing, electrical insulation, semiconductor manufacturing, optical display films, adhesive optical films, electromagnetic shielding, or as encapsulants for electrical and electronic components. [Examples]

[0111] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0112] (Example 1) 50 parts by mass of acrylic block copolymer (X) (Clarity LA#3710, manufactured by Kuraray Co., Ltd., Mw=195,000, Mw / Mn=1.1), 50 parts by mass of acrylic block copolymer (Y) (Clarity LA#2114, manufactured by Kuraray Co., Ltd., Mw=64,000, Mw / Mn=1.1), 30 parts by mass of tackifying resin (Harima Chemicals Co., Ltd., Haritack SDR-160, polymerized rosin ester, Mw3500, softening point 150-160℃, acid value 62 mgKOH / g), and 130 parts of toluene were placed in a container and stirred until completely dissolved to obtain an acrylic adhesive composition. This acrylic adhesive composition was applied to the release surface of a 100 μm thick release liner using an applicator so that the thickness after drying would be 50 μm, and an adhesive tape with an adhesive layer thickness of 40 μm was prepared by drying at 80℃ for 3 minutes.

[0113] (Example 2, Comparative Examples 1-2) Adhesive tapes were prepared using the same procedure as in Example 1, except that the composition of the acrylic adhesive composition was changed as shown in Tables 2 and 3.

[0114] (Example 3) In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel, 94 parts by mass of n-butyl acrylate, 4 parts by mass of acrylic acid, 0.06 parts by mass of 4-hydroxybutyl acrylate, and 200 parts by mass of ethyl acetate were charged, and the mixture was heated to 65°C while stirring and blowing in nitrogen to obtain mixture (1). Next, 4 parts by mass of 2,2'-azobisisobutyronitrile solution (2.5% by mass of solids), which had been previously dissolved in ethyl acetate, was added to mixture (1), and the mixture was held at 65°C for 10 hours while stirring to obtain mixture (2). Next, mixture (2) was diluted with 50 parts by mass of ethyl acetate and filtered through a 200-mesh wire mesh to obtain a solution of acrylic random copolymer (1) with a weight-average molecular weight of 1 million (polystyrene equivalent).

[0115] Next, 30 parts by mass of a tackifying resin (Harima Chemicals, Haritack SDR-160, polymerized rosin ester, Mw3500, softening point 150-160°C, acid value 62 mgKOH / g) was mixed and stirred with 100 parts by mass of the solid content of the above acrylic random copolymer (1) solution, and then ethyl acetate was added to obtain an acrylic adhesive composition (1) with a solid content of 45% by mass. 2.3 parts by mass (based on solid content) of CH-Y-1872 (trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7% by mass, non-volatile content 40% by mass, manufactured by DIC Corporation) was added as a crosslinking agent to 100 parts by mass of the solid content of the acrylic random copolymer (1), and the mixture was stirred and mixed until homogeneous to obtain an acrylic adhesive composition (2). An acrylic adhesive composition (2) was applied to the release surface of a 100 μm thick release liner using an applicator so that the thickness after drying was 50 μm, and an adhesive tape with an adhesive layer thickness of 40 μm was prepared by drying at 80°C for 3 minutes.

[0116] (Example 4, Comparative Examples 3-5) Adhesive tapes were prepared using the same procedure as in Example 3, except that the composition of the acrylic adhesive composition was changed as shown in Tables 2 and 3.

[0117] <Explanation of ingredients> The ingredients used are as follows:

[0118] [Acrylic block copolymer]

[0119] [Table 1]

[0120] [Adhesion-enhancing resin] D-135: Pencel D-135 (polymerized rosin, Mw2250, softening point 135℃, acid value 10-16 mgKOH / g, manufactured by Arakawa Chemical Industries) D-160: Pencel D-160 (polymerized rosin, Mw2700, softening point 160℃, acid value 10-16 mgKOH / g, manufactured by Arakawa Chemical Industries) SDR-160: Haritack SDR-160 (polymerized rosin ester, Mw 3500, softening point 150-160°C, acid value 62 mg KOH / g, manufactured by Harima Chemicals)

[0121] <Evaluation Method> The adhesive tape having an adhesive layer made of the acrylic adhesive composition prepared as described above was measured according to the method described below. The results are shown in Table 1.

[0122] (180° peel adhesion) Under conditions of 23°C and 50% RH relative humidity, one side of the adhesive tapes prepared in the examples and comparative examples was backed with a 25 μm thick polyethylene terephthalate film, and then cut to a length of 120 mm and a width of 20 mm. Next, the other adhesive side was attached to a stainless steel plate (SUS304 with a hairline finish using #360 sandpaper), and a 2 kg roller was passed back and forth once over the top surface of the adhesive tape. Finally, the two were left to stand for 1 hour under conditions of 23°C and 50% RH relative humidity to prepare a test specimen in which the adhesive tape and the stainless steel plate were pressed together. Next, using a Tensilon tensile testing machine, with the stainless steel plate constituting the test specimen fixed, the strength was measured when the adhesive tape was peeled off in a 180° direction at a tensile speed of 300 mm / min.

[0123] (Shear holding strength) Under conditions of 23°C and 50% RH relative humidity, one side of the adhesive tapes prepared in the examples and comparative examples was backed with 50 μm thick aluminum foil, and then cut to a length of 100 mm and a width of 20 mm. Next, the adhesive side of the cut adhesive tape was attached to a stainless steel plate (SUS304 with a hairline finish using #360 sandpaper) so that the bonding area was 20 mm x 20 mm (4 cm²), and a 2 kg roller was passed back and forth once over the top surface of the adhesive tape to create a test specimen. By leaving it to stand for 1 hour under conditions of 23°C and 50% RH relative humidity, a test specimen was prepared in which the adhesive tape and the stainless steel plate were pressed together.

[0124] Next, the portion of the adhesive tape on the test specimen that was not attached to the stainless steel plate was folded over. The stainless steel plate side of the test specimen was then fixed to a force meter at a measurement temperature of 70°C, and a 500g weight was attached to the folded portion of the adhesive tape. The specimen was left in a 70°C environment with the weight attached, and the time until the adhesive tape peeled off (fell) was measured. If the test was held for 1440 minutes, the test was terminated, and the distance the adhesive tape had peeled off was measured.

[0125] (Constant load holding power) Under conditions of 23°C and 50% RH relative humidity, one side of the adhesive tapes prepared in the examples and comparative examples was backed with a 25 μm thick polyethylene terephthalate film, and then cut to a length of 100 mm and a width of 10 mm. Next, the adhesive side of the cut adhesive tape was attached to a stainless steel plate (SUS304 with a hairline finish using #360 sandpaper) so that the attachment length was 50 mm. After applying pressure to the upper surface of the adhesive tape eight times back and forth with a 2 kg roller, the test piece was left to stand for 1 hour under conditions of 40°C to create a test piece in which the adhesive tape and the stainless steel plate were pressed together.

[0126] Next, the stainless steel plate side of the test piece was fixed to a constant load force meter with the adhesive tape side facing downwards. Then, a 100g weight was attached to the portion of the adhesive tape that was not attached to the stainless steel plate. The test piece was left in an environment with a temperature of 23°C and a relative humidity of 50%RH, and the time until the adhesive tape peeled off (fell) was measured. If the test was held for 180 minutes, the test was terminated and the distance the adhesive tape had peeled off was measured.

[0127] (tanδ) Each adhesive layer prepared in the examples and comparative examples was aged for two days at 40°C, then stacked to a thickness of approximately 2 mm and punched out to a diameter of 8 mm to prepare test specimens. A viscoelasticity tester (ARESG2, manufactured by TA Instruments Japan) was fitted with an 8 mm diameter parallel plate, and the test specimens were placed in it. The temperature was measured from -40°C to 180°C at a frequency of 1 Hz and a heating rate of 2°C / min to determine the storage modulus G'. Next, the loss modulus (G”) was measured using the same method as for the storage modulus (G'), and tanδ was calculated from G' and G”). The peak temperature of tanδ is the glass transition temperature (Tg), which is the temperature at which tanδ is maximum.

[0128] (Weight-average molecular weight (GPC) of acrylic adhesives) The weight-average molecular weight of acrylic adhesives as defined herein refers to the value calculated by gel permeation chromatography (GPC) and converted to standard polystyrene equivalent. Specifically, the above weight-average molecular weight was measured using a GPC device (HLC-8320GPC) manufactured by Tosoh Corporation under the following conditions.

[0129] • Sample concentration: 0.5% by mass (tetrahydrofuran solution) • Sample injection volume: 100 μl • Eluent: Tetrahydrofuran ·Flow rate: 0.8ml / min ·Measurement temperature: 40℃ • Main column: TSKgelGMHHR-R(S) 2 pieces • Guard column: TSKgel HHR(S) 1 piece • Detector: Differential refractometer • Weight-average molecular weight of standard polystyrene: 5 million to 5 million (manufactured by Tosoh Corporation)

[0130] (Weight-average molecular weight (GPC) of tackifying resins) The weight-average molecular weight of the tackifying resin as defined herein refers to the value calculated by gel permeation chromatography (GPC) and converted to standard polystyrene equivalent. Specifically, the above weight-average molecular weight was measured using a GPC instrument (HLC-8320GPC) manufactured by Tosoh Corporation under the following conditions.

[0131] • Sample concentration: 0.5% by mass (tetrahydrofuran solution) • Sample injection volume: 100 μl • Eluent: Tetrahydrofuran ·Flow rate: 1.0ml / min ·Measurement temperature: 40℃ • This column contains: 2 x TSKgelG2500HXL + 1 x TSKgelG3000HXL + 1 x TSKgelG4000HXL + 1 x TSKgelG5000HXL • Guard column: TSKgel HXL-H • Detector: Differential refractometer • Weight-average molecular weight of standard polystyrene: 5 million to 5 million (manufactured by Tosoh Corporation)

[0132] (Method for measuring haze) Under conditions of 23°C and 50% RH relative humidity, a 1mm thick, 50mm long, and 50mm wide piece of glass (manufactured by Nippon Sheet Glass Co., Ltd.) was attached to one side of the adhesive sheets prepared in the examples and comparative examples, and the resulting test specimen consisted of glass, adhesive layer, and PET separator. The haze of the test specimen was measured using a reflectance / transmittance meter (HM-100, manufactured by Murakami Color Technology Laboratory Co., Ltd.). The haze of the glass alone used to prepare the test specimen was 0.7%, and the haze of the PET separator alone was 2.1%.

[0133] [Table 2]

[0134] [Table 3]

[0135] Tables 2 and 3 show that the adhesive tape made from the acrylic adhesive composition of the present invention exhibited superior 180° peel adhesion and constant load holding power compared to conventional tapes. According to this disclosure, because it exhibits excellent compatibility with high molecular weight tackifying resins, even when the amount added is increased, a highly transparent adhesive layer is formed, and the effect of improving the adhesive performance of the tackifying resin can be fully demonstrated. As a result, an adhesive tape with particularly excellent constant load holding capacity can be made.

Claims

1. An acrylic adhesive composition comprising at least an acrylic adhesive containing an acrylic random copolymer or an acrylic block copolymer, and a tackifying resin, The weight-average molecular weight of the tackifying resin is 3000 or more, and the acid value is 20 to 150 mgKOH / g. An acrylic adhesive composition in which the content of the tackifying resin is 20 parts by mass or more per 100 parts by mass of the acrylic adhesive.

2. The acrylic adhesive composition according to claim 1, wherein the tackifying resin is a rosin-based tackifying resin.

3. The acrylic adhesive composition according to claim 1, wherein the softening point of the tackifying resin is 150°C or higher.

4. The acrylic adhesive composition according to claim 1, wherein the haze of an adhesive layer with a thickness of 40 μm is 60% or less, which is made of an acrylic adhesive composition obtained by adding 50 parts by mass of the tackifying resin to 100 parts by mass of the acrylic adhesive.

5. The acrylic adhesive composition according to claim 1, wherein the weight-average molecular weight of the acrylic random copolymer is 150,000 to 2,500,000.

6. The acrylic adhesive composition according to claim 1, wherein the weight-average molecular weight of the acrylic block copolymer is 10,000 to 500,000.

7. The acrylic adhesive composition according to claim 1, wherein the peak temperature of tanδ (T2) of the acrylic adhesive composition obtained by adding 50 parts by mass of the tackifying resin having a weight-average molecular weight of 3000 or more to 100 parts by mass of the acrylic adhesive is 30°C or higher than the peak temperature of tanδ (T1) of the acrylic adhesive.

8. An adhesive tape comprising an adhesive layer made of an acrylic adhesive composition according to any one of claims 1 to 7.

9. The adhesive tape according to claim 8, further comprising a base material, wherein the adhesive layer is provided on at least one surface of the base material.

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