Active energy ray curable hot melt adhesive composition, and adhesives and adhesive tapes using the same.

Abstract

To provide an active energy ray-curable adhesive composition, in which the adhesive composition itself has excellent thermal stability and in an adhesive sheet using such an adhesive composition, the adhesive composition has an excellent sticking property to a curved surface while having high adhesive strength and holding power for various adherends and, further, has also excellent heat resistance under high temperature.SOLUTION: Provided is an active energy ray-curable adhesive composition, comprising an acrylic resin (A) and a tackifier (B), where the acrylic resin (A) has a weight average molecular weight of 200,000 or more and is obtained by polymerizing a copolymerization component comprising an alkyl (meth)acrylate (a1) and a monomer (a2) having an ultraviolet active site, and a content of the tackifier (B) is 10-40 pts.wt. relative to 100 pts.wt. of the acrylic resin (A).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an active energy ray-curable adhesive composition, and more particularly to an adhesive composition that can be used for adhesive tapes, adhesive labels, etc. for hot melt coating. The present invention relates to an active energy ray-curable adhesive composition that, in addition to the excellent thermal stability of the active energy ray-curable adhesive composition, the adhesive sheet produced using such a composition is excellent in adhesion at room temperature, holding power, and curvature adhesion to various adherends, and also excellent in long-term heat resistance after being bonded to the adherend, and an adhesive, an adhesive tape using the same.

Background Art

[0002] Conventionally, rubber-based adhesives or acrylic-based adhesives are known as adhesives for adhesive tapes or adhesive sheets. As acrylic-based adhesives, (co)polymers having a specific alkyl (meth)acrylate as an essential constituent unit have been developed.

[0003] In recent years, due to the increasing interest in the environment, adhesive compositions that do not use organic solvents have attracted attention. For example, in Patent Document 1, Patent Document 2, etc., acrylic hot melt type adhesive compositions characterized by applying a heat-melted resin in a substrate form have been proposed. However, adhesive tapes and the like using these conventional acrylic hot melt type adhesive compositions have the drawback that adhesive properties such as adhesive force and holding power are inferior.

[0004] In order to solve the above drawbacks, for example, Patent Document 3 proposes crosslinking an acrylic adhesive composition applied by hot melt coating by irradiation with active energy rays.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, while Patent Document 3 described high adhesive strength and static shear resistance to various substrates, the adhesive sheet was thick and did not consider its ability to adhere to curved surfaces. Furthermore, although Patent Documents 1 to 3 described the heat resistance of the adhesive sheet, the test results were based on relatively low temperatures (70°C for one week), leaving room for improvement regarding heat resistance at higher temperatures. Furthermore, since hot-melt adhesive compositions generally do not flow at room temperature, they usually need to be heated to a high temperature of 100-160°C for coating. However, when exposed to high-temperature conditions, some adhesive compositions exhibit poor thermal stability, such as an increase in the molecular weight of the acrylic resin in the adhesive composition, or increased viscosity leading to a decrease in coatability.

[0007] Therefore, against this background, the present invention aims to provide an active energy ray curable adhesive composition, an adhesive and adhesive sheet made using the same, which exhibits excellent thermal stability of the adhesive composition itself, and in which the adhesive using the same has high adhesive strength and holding power to various adherends, as well as excellent curved surface adhesion and heat resistance at high temperatures. [Means for solving the problem]

[0008] However, in view of these circumstances, the present inventors conducted extensive research and found that by using an acrylic resin with a weight-average molecular weight above a certain level and adjusting the content of the tackifier in an active energy ray-curable adhesive composition, the adhesive composition exhibits excellent thermal stability at high temperatures. Furthermore, adhesive sheets using such an adhesive possess high adhesive strength and holding power to various substrates, while also exhibiting excellent adhesion to curved surfaces and superior heat resistance over long periods at high temperatures.

[0009] In other words, the gist of this invention is as follows: <1> An active energy ray curable adhesive composition containing an acrylic resin (A) and a tackifier (B), The weight-average molecular weight of the acrylic resin (A) is 200,000 or more. An acrylic resin (A) obtained by polymerizing a copolymer component (a) containing an alkyl (meth)acrylate (a1) and a monomer (a2) having an ultraviolet active site, The content of the tackifier (B) is 10 to 40 parts by weight per 100 parts by weight of the acrylic resin (A). the law of nature, The softening point of the tackifier (B) is 115°C or higher. A hot-melt adhesive composition that is curable by active energy rays. <2> The softening point of the tackifier (B) is 115 The temperature is ~130℃ <1> The active energy ray curable adhesive composition described. <3> The tackifier (B) is a rosin-based tackifier (B1). <1> or <2> The active energy ray curable adhesive composition described. <4> The copolymer component (a) of the acrylic resin (A) contains a polar group-containing ethylenically unsaturated monomer (a3). <1> ~ <3> An active energy ray curable adhesive composition as described in any of the following. <5> A claim further containing a crosslinking agent (C) <1> ~ <4> An active energy ray curable adhesive composition as described in any of the following. <6> <1> ~ <5> An active energy ray-curable adhesive comprising an active energy ray-curable adhesive composition described in any of the above, which is crosslinked. <7> <6> An adhesive tape comprising a hot-melt adhesive that is curable by active energy rays, as described above, formed on a substrate. [Effects of the Invention]

[0010] The active energy ray-curable adhesive composition of the present invention is excellent in thermal stability. An adhesive sheet using such a composition has adhesiveness to various adherends, excellent holding power, excellent curvature adhesion, and excellent long-term heat resistance after being adhered to an adherend. Therefore, it provides an adhesive suitable for various labels.

Embodiments for Carrying Out the Invention

[0011] The present invention will be described in detail below. In the present invention, “(meth)acrylic” means acrylic or methacrylic, “(meth)acryloyl” means acryloyl or methacryloyl, and “(meth)acrylate” means acrylate or methacrylate, respectively. In addition, the “acrylic resin” is a resin obtained by polymerizing a polymerization component containing at least one (meth)acrylate monomer. In addition, “tape” conceptually includes tape, film, and sheet.

[0012] The adhesive composition of the present invention contains an acrylic resin (A) and an adhesion promoter (B). Hereinafter, these constituent components will be described in order.

[0013] <Acrylic resin (A)> The acrylic resin (A) used in the present invention contains an alkyl (meth)acrylate (a1) and a monomer (a2) having an ultraviolet active site as copolymerization components (a).

[0014] 〔Alkyl (meth)acrylate (a1)〕 Examples of the alkyl(meth)acrylate(a1) mentioned above include methyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, iso-butyl(meth)acrylate, tert-butyl(meth)acrylate, n-propyl(meth)acrylate, n-hexyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, stearyl(meth)acrylate, and the like. In particular, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred in terms of adhesive strength.

[0015] The alkyl (meth)acrylate (a1) preferably contains at least one monomer having a glass transition temperature of less than -60°C. Examples of monomers having a glass transition temperature of less than -60°C include 2-ethylhexyl acrylate, n-octyl acrylate, and isodecyl acrylate. The content of alkyl(meth)acrylate(a1) having a glass transition temperature of less than -60°C is 0 to 85% by weight, preferably 15 to 75% by weight, and particularly preferably 20 to 60% by weight, relative to the amount of alkyl(meth)acrylate(a1). If the content is too low, the coating properties tend to decrease, and if the content is too high, the adhesive strength after heating tends to decrease.

[0016] The alkyl (meth)acrylate (a1) is typically present in an amount of 1 to 99% by weight relative to copolymer component (a), preferably 30 to 97% by weight, and particularly preferably 50 to 95% by weight. If the content is too low, the glass transition temperature will rise, which tends to degrade the overall performance of the adhesive. Conversely, if the content is too high, the holding power and adhesion to curved surfaces tend to worsen.

[0017] [Monomers with UV-active sites (a2)] As the monomer (a2) having the above-mentioned UV-active site, for example, a (meth)acrylic acid ester can be used, which has a site that is activated by ultraviolet light and can form crosslinks with another part of the (meth)acrylic copolymer molecule or with another acrylic copolymer molecule. Examples of UV-active sites include benzophenone structures, benzyl structures, o-benzoylbenzoic acid ester structures, thioxanthone structures, 3-ketocoumarin structures, 2-ethylanthraquinone structures, and camphaquinone structures. Each of these structures can be excited by UV irradiation, and in its excited state, it can abstract a hydrogen radical from the (meth)acrylic copolymer molecule. In this way, radicals are generated on the (meth)acrylic copolymer. Various reactions are triggered in the system, such as the formation of crosslinked structures by the bonding of the generated radicals to each other, the generation of peroxide radicals by reaction with oxygen molecules, the formation of crosslinked structures via the generated peroxide radicals, and the abstraction of other hydrogen radicals by the generated radicals, and the (meth)acrylic copolymer is ultimately crosslinked.

[0018] Among the structures described above, the benzophenone structure is preferred when considering transparency, reactivity, etc. Examples of (meth)acrylates having such a benzophenone structure include, but are not limited to, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof.

[0019] The monomer (a2) having an ultraviolet-active site is typically 0.1 to 5% by weight, preferably 0.3 to 2% by weight, and more preferably 0.5 to 1.5% by weight, relative to copolymer component (a). If the content is too low, the curing properties during irradiation with active energy rays tend to be low, and if the content is too high, the gel fraction increases too much, which tends to worsen the ability to adhere to curved surfaces.

[0020] [Polar group-containing ethylenically unsaturated monomer (a3)] Examples of the polar group-containing ethylenically unsaturated monomer (a3) ​​mentioned above include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and cyano group-containing monomers. These may be used individually or in combination of two or more. Among these, carboxyl group-containing monomers are preferred because they exhibit excellent adhesive strength as a copolymerized acrylic resin.

[0021] Examples of the hydroxyl group-containing monomers mentioned above include hydroxyalkyl ester monomers of (meth)acrylate such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and other primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, N-methylol (meth)acrylamide, and hydroxyethylacrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate. Among these, hydroxyalkyl ester monomers of (meth)acrylate are preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are more preferred, with 4-hydroxybutyl acrylate being particularly preferred, due to their low levels of impurities such as di(meth)acrylate and ease of production.

[0022] Examples of the above-mentioned carboxyl group-containing monomers include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid.

[0023] Examples of the above-mentioned amino group-containing monomers include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and their quaternary derivatives.

[0024] Examples of the above-mentioned amide group-containing monomers include (meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, vinylpyrrolidone, and acryloylmorpholin.

[0025] Examples of the above-mentioned cyano group-containing monomers include acrylonitrile and methacrylonitrile.

[0026] The content of the polar group-containing ethylenically unsaturated monomer (a3) ​​is preferably less than 10% by weight relative to copolymer component (a), more preferably 0.1% to less than 9% by weight, more preferably 0.5% to 8% by weight, even more preferably 1% to 7% by weight, and particularly preferably 2% to 6% by weight, from the viewpoint of achieving both thermal stability and adhesive properties of the resin. If the content is too high, the thermal stability of the copolymerized acrylic resin tends to decrease. Conversely, if the content is too low, the adhesive strength tends to decrease.

[0027] [Other polymerizable monomers (a4)] The above-mentioned other polymerizable monomer (a4) may be any polymerizable monomer other than (a1), (a2), and (a3), such as alicyclic structure-containing monomers; aromatic monomers; alkoxy group-containing monomers; vinyl monomers, etc. These can be used individually or in combination of two or more.

[0028] Examples of monomers containing the above-mentioned alicyclic structure include (meth)acrylates having an alicyclic structure, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and 2-adamantyl (meth)acrylate.

[0029] Examples of the above aromatic monomers include (meth)acrylates having one aromatic ring, such as phenyl(meth)acrylate, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate, phenoxypropyl(meth)acrylate, phenoxydiethylene glycol(meth)acrylate, phenoxydipropylene glycol(meth)acrylate, phenoxypolyethylene glycol(meth)acrylate, phenoxypolyethylene glycol(meth)acrylate, and phenoxypolypropylene glycol-(meth)acrylate; and (meth)acrylates having two aromatic rings, such as phenoxybenzyl(meth)acrylate and ethoxylated o-phenylphenol(meth)acrylate.

[0030] Examples of the above-mentioned alkoxy group-containing monomers include alkoxyalkyl (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, and 2-butoxyethyl (meth)acrylate.

[0031] Examples of the vinyl monomers mentioned above include vinyl propionate, vinyl stearate, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyltoluene, vinylpyridine, vinylpyrrolidone, methyl vinyl ketone, and dimethylallyl vinyl ketone.

[0032] Other polymerizable monomers (a4) can be included in amounts that do not impair the effects of the present invention, but are preferably 20% by weight or less, and more preferably 15% by weight or less, relative to the total copolymer component (a).

[0033] <Method for manufacturing acrylic resin (A)> As a method for producing the acrylic resin (A), conventionally known methods such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used with the copolymer component (a) described above. For example, one method involves mixing or dropping appropriately selected polymerization components and polymerization initiators into an organic solvent and polymerizing under predetermined polymerization conditions. Among these, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred because it allows for the stable acquisition of the acrylic resin (A).

[0034] Examples of organic solvents used in the above polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol; and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These organic solvents may be used individually or in combination of two or more.

[0035] Among these organic solvents, esters such as ethyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone are preferred, with ethyl acetate being the most preferred, from the standpoint of ease of polymerization, chain transfer effect, ease of drying during application of the adhesive composition, and safety. These can be used individually or in combination of two or more. The amount of organic solvent used is typically 10 to 900 parts by weight per 100 parts by weight of copolymer component (a).

[0036] Furthermore, examples of polymerization initiators used in such solution radical polymerization include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(methylpropionic acid), which are common radical polymerization initiators; organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide; and others. These can be appropriately selected and used depending on the monomer used. These polymerization initiators may be used individually or in combination of two or more. The amount of polymerization initiator used is typically 0.01 to 10 parts by weight per 100 parts by weight of copolymer component (a).

[0037] In this way, the acrylic resin (A) used in the present invention is obtained.

[0038] <Physical properties of acrylic resin (A)> The weight-average molecular weight (Mw) of the acrylic resin (A) is preferably 200,000 or more, more preferably 210,000 to 1,500,000, more preferably 230,000 to 1,000,000, and especially preferably 250,000 to 500,000. If the weight-average molecular weight is too low, the cohesive force will be low and the adhesiveness will decrease, and if it is too high, the melt viscosity will be too high, making it unsuitable for hot-melt coating.

[0039] Furthermore, the degree of dispersion of the acrylic resin (A) [weight-average molecular weight (Mw) / number-average molecular weight (Mn)] is preferably 10 or less, and more preferably 7 or less. If the degree of dispersion is too high, the cohesive force tends to decrease. The lower limit of the degree of dispersion is usually 1.

[0040] The weight-average molecular weight of acrylic resin (A) is the weight-average molecular weight converted to the standard polystyrene molecular weight. The analysis was performed using a high-performance liquid chromatograph (Waters Japan, "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10⁶). 7 Separation range: 100~2×107 The measurement can be performed by connecting three of the following in series (theoretical plates: 10,000 stages / unit, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm), and the number-average molecular weight can be measured in the same way. Furthermore, the degree of dispersion can be determined from the measured values ​​of the weight-average molecular weight and the number-average molecular weight.

[0041] The glass transition temperature (Tg) of the acrylic resin (A) is preferably -85°C or higher, more preferably -80 to 20°C, even more preferably -75 to 0°C, particularly preferably -70 to -10°C, and especially preferably -65 to -30°C. If the glass transition temperature is too low, the adhesive strength after curing tends to decrease, and if it is too high, the tack before curing tends to decrease.

[0042] The glass transition temperature mentioned above is calculated using Fox's formula, which is shown below.

[0043]

number

[0044] Specifically, these are values ​​calculated by applying Fox's formula to the glass transition temperature and weight fraction of each monomer constituting the acrylic resin (A) as a homopolymer. The glass transition temperature of the monomers constituting the acrylic resin (A) when they are homopolymers is usually measured using a differential scanning calorimeter (DSC), and can be measured according to methods compliant with JIS K7121-1987 or JIS K 6240.

[0045] The acrylic resin (A) is the main component of the adhesive composition, preferably at 50% by weight or more, more preferably 60-98% by weight, even more preferably 70-95% by weight, and particularly preferably 75-93% by weight relative to the adhesive composition. Outside this range, the effects of the present invention tend to be difficult to obtain.

[0046] The viscosity of the diluted acrylic resin (A) described above is preferably 500 to 30,000 mPa·s / 25°C, and more preferably 1,000 to 10,000 mPa·s / 25°C. If the viscosity is too low, when a component with a high specific gravity is used, that component tends to settle, and the concentration of the component in the acrylic resin (A) tends to become uneven.

[0047] <Tackifier (B)> The content of the tackifier (B) used in the present invention is preferably 10 to 40 parts by weight, more preferably 12 to 35 parts by weight, and even more preferably 15 to 30 parts by weight, per 100 parts by weight (solids) of acrylic resin (A). Particularly preferably it is 18 to 25 parts by weight. If the content is too high or too low, the effects of the present invention tend to be difficult to obtain.

[0048] The softening point of the tackifier (B) is preferably 20 to 180°C, more preferably 50 to 160°C, and even more preferably 70 to 130°C. If the temperature is too high or too low, the tackiness tends to decrease.

[0049] Examples of tackifiers (B) include rosin resins (B1), phenolic resins, terpene resins, modified terpene resins, hydrocarbon resins, epoxy resins, polyamide resins, elastomer resins, and ketone resins, but rosin resins (B1) are preferred from the viewpoint of adhesion to low-polarity substrates such as PE. These can be used individually or in combination of two or more types.

[0050] Examples of the rosin resin (B1) mentioned above include modified rosin resins such as hydrogenated rosin, disproportionated rosin, and polymerized rosin, as well as rosin esters obtained by esterifying unmodified rosin with alcohols. Among these, modified rosin resins are preferred from the viewpoint of forming a hot melt composition because they have high thermal stability at high temperatures when mixed with solvent-free acrylic resins.

[0051] <Optional ingredients> In the present invention, in addition to the above-mentioned components, optional components such as conductive agents (e.g., carbon or metal), inorganic fillers (e.g., metal particles or glass particles), fillers, antioxidants, ultraviolet absorbers, crosslinking promoters (e.g., ionic compounds, peroxides, silane coupling agents, urethane catalysts), crosslinking retarders (e.g., acetylacetone), monofunctional monomers, polyfunctional monomers, and various other additives may also be included. These may be used individually or in combination of two or more.

[0052] In addition to the optional components mentioned above, the adhesive composition of the present invention may also contain impurities, etc., contained in the raw materials for the production of the constituent components of the adhesive composition, to the extent that they do not impair the effects of the present invention.

[0053] When using the above optional components, their content is preferably 5 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, per 100 parts by weight of acrylic resin (A). If the content is too high, it tends to impair the effects of the present invention.

[0054] <Adhesive composition> The adhesive composition of the present invention can be obtained by mixing the above-mentioned acrylic resin (A) and tackifier (B) with any optional components as needed.

[0055] The method of mixing these components is not particularly limited, and various methods can be employed, such as mixing each component all at once, or mixing any component first and then mixing the remaining components all at once or sequentially.

[0056] The content of the acrylic resin (A) and tackifier (B) in the adhesive composition is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 98% by weight or more.

[0057] The active energy ray-curable resin composition of the present invention is useful as an adhesive component, and is particularly useful as an adhesive component for hot melts. When used for hot melts, the above components are blended to obtain an adhesive composition solution, and then the solvent is removed by distillation.

[0058] The step of removing the solvent from the compounded adhesive composition solution can be carried out by known and general methods. Methods for removing the solvent include heating and reducing the pressure, but from the standpoint of efficiently removing the solvent, heating under reduced pressure is preferred.

[0059] When removing the solvent by heating, the temperature is preferably between 60 and 150°C. In particular, it is preferable to maintain the reaction solution after polymerization of the acrylic resin at 60 to 80°C to distill off the solvent, and then distill off the remaining solvent at 80 to 150°C, as this minimizes the amount of residual solvent. Furthermore, to suppress gelation of the acrylic resin, it is preferable not to perform solvent removal at temperatures above 150°C.

[0060] When removing the solvent by reducing the pressure, it is preferable to do so at a pressure of 20 to 101.3 kPa, and in particular, it is preferable to maintain the pressure in the range of 50 to 101.3 kPa to distill off the solvent in the reaction solution, and then distill off the remaining solvent at 0 to 50 kPa, as this minimizes the amount of remaining solvent. Thus, an active energy ray-curable resin composition for use in the present invention can be produced.

[0061] <Adhesive sheet> The active energy ray-curable adhesive composition of the present invention is preferably used in adhesive sheets in which an adhesive layer made therefrom is provided on a base sheet, double-sided adhesive sheets in which an adhesive layer is provided on a release sheet, and the like. The adhesive layer may be the active energy ray-curable resin composition of the present invention itself, or it may be formed by curing (crosslinking) the active energy ray-curable resin composition of the present invention. Examples of curing methods include curing with active energy rays, curing by crosslinking with a crosslinking agent, and methods combining these.

[0062] Adhesive sheets can be manufactured, for example, as follows: In this invention, the term "sheet" is not specifically distinguished from "film" or "tape," but rather encompasses all of these terms.

[0063] First, an adhesive layer of a predetermined thickness is formed on one or both sides of a base sheet by methods such as applying an active energy ray-curable adhesive composition to one or both sides of a base sheet in a molten state by heating and then cooling, or by melting the adhesive composition by heating and extruding it onto the base sheet using a T-die or the like, or by drying the solvent after coating if a solvent is included. Then, if necessary, a release sheet is attached to the surface of the adhesive layer to produce an adhesive sheet.

[0064] Furthermore, after forming an adhesive layer on a base sheet, an adhesive sheet can be produced having an adhesive layer formed by curing (crosslinking) the adhesive composition by performing an active energy ray irradiation treatment as needed and then aging.

[0065] Furthermore, by forming an adhesive layer on a release sheet and attaching the release sheet to the adhesive layer on the opposite side, a substrate-less double-sided adhesive sheet can also be produced. The resulting adhesive sheet or double-sided adhesive sheet is used after peeling off the release sheet from the adhesive layer.

[0066] Examples of base sheets include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyfluoroethylene; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; synthetic resin sheets such as polystyrene, polycarbonate, polyarylate, and polyimide; metal foils of aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven or nonwoven fabrics made of glass fibers, natural fibers, and synthetic fibers. These base sheets can be used as single layers or as multi-layered structures made by laminating two or more types. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and other factors.

[0067] Furthermore, as the release sheet, for example, various synthetic resin sheets, paper, cloth, nonwoven fabrics, etc., as exemplified in the support substrate above, can be used after being subjected to a release treatment. It is preferable to use a silicone-based release sheet.

[0068] Furthermore, the coating method for the above-mentioned adhesive composition is not particularly limited as long as it is a general coating method, and examples include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0069] By irradiating with active energy rays, the acrylic resin (A) in the active energy ray-curable adhesive composition forms crosslinked structures within and / or between molecules.

[0070] When irradiating with active energy rays, various types of light rays can be used, including far-ultraviolet, ultraviolet, near-ultraviolet, and infrared rays, as well as electromagnetic waves such as X-rays and gamma rays, and electron beams, proton beams, and neutron beams. However, due to factors such as curing speed, availability of irradiation equipment, and cost, curing by ultraviolet irradiation is advantageous.

[0071] The above aging treatment is particularly preferable when a crosslinking agent is used in the adhesive composition. The conditions for the above aging treatment are typically a temperature of room temperature (25°C) to 100°C and a duration of typically 1 to 30 days. Specifically, for example, it may be carried out at 23°C for 1 to 20 days, preferably at 23°C for 3 to 10 days, or at 40°C for 1 to 7 days.

[0072] The gel fraction of the adhesive layer of the above-mentioned adhesive sheet is preferably 10-90%, more preferably 20-70%, and especially preferably 30-50%, from the viewpoint of adhesive strength and durability. If the gel fraction is too low, the cohesive force decreases, which tends to reduce durability. Conversely, if the gel fraction is too high, the cohesive force increases, which tends to reduce adhesive strength.

[0073] In adjusting the gel fraction to the above range, for example, this can be achieved by adjusting the amount of active energy irradiation or the type and amount of monomers having (a2) UV-active sites, or, if a crosslinking agent is used, by adjusting the type and amount of the crosslinking agent.

[0074] The gel fraction mentioned above serves as an indicator of the degree of crosslinking (degree of hardening) and can be calculated, for example, by the following method: An adhesive sheet (without a separator), which consists of a polymer sheet (e.g., polyethylene terephthalate (PET) film) as the base material with an adhesive layer formed on it, is wrapped in a 200-mesh stainless steel wire mesh and immersed in toluene at 23°C for 24 hours. The weight percentage of the insoluble adhesive component remaining in the wire mesh is taken as the gel fraction. However, the weight of the base material is subtracted.

[0075] The thickness of the adhesive layer of the above adhesive sheet is usually preferably 5 to 2000 μm, more preferably 10 to 100 μm, and particularly preferably 15 to 25 μm. If the thickness of the adhesive layer is too thin, the adhesiveness tends to decrease, and if it is too thick, the adhesive tends to ooze out when used as an adhesive label.

[0076] In this invention, the film thickness is determined by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive layer-containing laminate, using a Mitutoyo ID-C112B.

[0077] In addition to excellent thermal stability, the active energy ray-curable adhesive composition of the present invention provides adhesive sheets made using this adhesive with excellent adhesion, holding power, and curved surface adhesion to various substrates at room temperature, as well as excellent heat resistance over long periods after being bonded to a substrate.

[0078] Therefore, the adhesive composition of the present invention is useful for various applications in hot melt coating, such as caution labels, frozen food labels, building materials, automotive parts, electronic components, heat dissipation sheets, FPC manufacturing, semiconductor manufacturing processes, component sealing, aerospace parts, and sporting goods, and is particularly suitable for caution labels (adhesive sheets, adhesive tapes). [Examples]

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to weight basis. Furthermore, the weight-average molecular weight and glass transition temperature of the acrylic resin and acrylic resin composition were measured according to the method described above.

[0080] <Acrylic resin (A)> The following were prepared as acrylic resin raw material monomers. (a1-1) n-butyl acrylate (hereinafter referred to as "BA"): Manufactured by Mitsubishi Chemical Corporation (a1-2)2-Ethylhexylacrylate (hereinafter referred to as "2EHA"): Manufactured by Mitsubishi Chemical Corporation (a2) 4-Methacryloyloxybenzophenone (hereinafter referred to as "MBP"): Manufactured by Shinryo Co., Ltd. (a3-1) Acrylic acid (hereinafter referred to as "Aac"): Manufactured by Osaka Organic Chemical Industry Co., Ltd. (a4) Vinyl acetate (hereinafter referred to as "Vac"): Manufactured by Mitsubishi Chemical Corporation

[0081] [Manufacturing of acrylic resin solution (A-1)] In a four-necked round-bottom flask equipped with a reflux condenser, stirrer, nitrogen gas inlet, and thermometer, 122 parts of ethyl acetate and 0.087 parts of azobisisobutyronitrile (hereinafter referred to as AIBN) as a polymerization initiator were charged. After heating under reflux in the flask, a mixed solution of 70.5 parts BA, 20.0 parts 2EHA, 0.5 parts MBP, 5 parts Vac, 4 parts Aac, and 3.6 parts ethyl acetate was added dropwise over 2 hours. One hour after the completion of monomer dropwise addition, 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours. Then, another 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours. Finally, another 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours, after which the mixture was diluted with 30.2 parts of ethyl acetate to obtain an acrylic resin (A-1) solution [solid content concentration 38.9%, weight-average molecular weight (Mw) 308,000, dispersion degree 3.45 (Mw / Mn)].

[0082] [Manufacturing of acrylic resin solution (A-2)] In a four-necked round-bottom flask equipped with a reflux condenser, stirrer, nitrogen gas inlet, and thermometer, 133 parts of ethyl acetate and 0.087 parts of AIBN as a polymerization initiator were charged. After heating under reflux in the flask, a mixed solution of 90.5 parts of BA, 0.5 parts of MBP, 5 parts of Vac, 4 parts of Aac, and 3.6 parts of ethyl acetate was added dropwise over 2 hours. One hour after the completion of monomer addition, 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours. Then, another 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours. Finally, another 0.087 parts of polymerization initiator (AIBN) were added and the mixture was reacted for 2 hours. The mixture was then diluted with 30.2 parts of ethyl acetate to obtain an acrylic resin (A-2) solution [solid content concentration 37.4%, weight-average molecular weight (Mw) 370,000, dispersion degree 3.19 (Mw / Mn)].

[0083] [Production of acrylic resin solution (A'-1)] In a four-necked round-bottom flask equipped with a reflux condenser, stirrer, nitrogen gas inlet, and thermometer, 14.3 parts of ethyl acetate, 28.6 parts of methyl ethyl ketone, and 0.014 parts of azobis(2,4-dimethylvaleronitrile) (hereinafter referred to as ADVN) as a polymerization initiator were charged. After heating under reflux in the flask, a mixed solution of 70.50 parts of BA, 20 parts of 2EHA, 0.5 parts of MBP, 5 parts of Vac, 4 parts of Aac, 2.9 parts of methyl ethyl ketone, and 0.1 parts of ADVN was added dropwise over 2 hours. One hour after the completion of monomer dropwise addition, 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for one hour. Then, another 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for another hour. Finally, another 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for two hours. The mixture was then diluted with 8.6 parts of methyl ethyl ketone to obtain an acrylic resin (A'-1) solution [solid content concentration 63.7%, weight-average molecular weight (Mw) 179,000, dispersion degree 2.61 (Mw / Mn)].

[0084] [Production of acrylic resin solution (A'-2)] In a four-necked round-bottom flask equipped with a reflux condenser, stirrer, nitrogen gas inlet, and thermometer, 42.9 parts of methyl ethyl ketone and 0.014 parts of ADVN as a polymerization initiator were charged. After heating under reflux in the flask, a mixed solution of 90.50 parts of BA, 0.5 parts of MBP, 5 parts of Vac, 4 parts of Aac, 2.9 parts of methyl ethyl ketone, and 0.1 parts of ADVN was added dropwise over 2 hours. One hour after the completion of monomer dropwise addition, 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for one hour. Then, another 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for another hour. Finally, another 0.057 parts of polymerization initiator (ADVN) were added and the mixture was reacted for two hours. The mixture was then diluted with 8.6 parts of methyl ethyl ketone to obtain an acrylic resin (A'-2) solution [solid content concentration 63.3%, weight-average molecular weight (Mw) 136,000, dispersion degree 2.51 (Mw / Mn)].

[0085] <Tackifier (B)> The following materials were prepared as tackifiers (B). (B-1) Modified rosin resin (Harima Chemicals, M-113S, softening point: 115℃) (B-2) Rosin ester (Harima Chemicals Co., Ltd., Hariestar DS-70L, softening point: 74℃) (B-3) Rosin ester (manufactured by Arakawa Chemical Co., Ltd., Super Ester A-75, softening point: 70~80℃) (B-4) Rosin ester (manufactured by Arakawa Chemical Co., Ltd., Super Ester A-125, softening point: 120~130℃)

[0086] <Example 1~ 3, Reference examples 1-2 Comparative Examples 1-4> The above acrylic resin solution (A) and tackifying resin (B) were blended according to Table 1 below (NET / NET blending amounts). The resulting mixture was placed in a flask with a T-shaped connecting tube to allow the solvent to be removed from the system, and the solvent was removed by leaving it at a jacket temperature of 80°C for 1 hour, then by reducing the pressure to 10kPa and leaving it at a jacket temperature of 90°C for 2 hours. Examples 1- 3. Reference Examples 1-2 and The active energy ray-curable adhesive compositions described in Comparative Examples 1 to 4 were obtained.

[0087] <Thermal stability of resins> After removing the solvent, 2g of the composition was placed in a glass bottle. The resin-filled glass bottle was then placed in a mini jet oven heated to 160°C and left to stand for 4 hours before the active energy ray-curable adhesive composition was removed. Subsequently, the weight-average molecular weight of the active energy ray-curable adhesive composition was measured by gel permeation chromatography. As shown in Formula 1 below, the weight-average molecular weight of the active energy ray-curable adhesive composition after heat treatment at 160°C for 4 hours was M2, and the weight-average molecular weight of the active energy ray-curable adhesive composition before such heat treatment was M1. The percentage change in weight-average molecular weight M(%) was calculated and evaluated according to the following evaluation criteria.

[0088] [Formula 1] M(%) = (|M2 - M1| / M1) × 100 M2: Weight-average molecular weight of the active energy ray-curable adhesive composition after heat treatment at 160°C for 4 hours. M1: Weight-average molecular weight of the active energy ray-curable adhesive composition before the above heat treatment.

[0089] (Evaluation Criteria) ◎··M is less than 10 〇··M is 10 or more, but less than 20 ×...M is 20 or more

[0090] [Making adhesive sheets] Example 1~ 3, Reference examples 1-2 Each of the active energy ray-curable adhesive compositions of Comparative Examples 1-4 was mixed with ethyl acetate, diluted to a solid content concentration of 40%, and then coated onto a 50 μm thick PET (Toray Industries, Ltd., "Lumirror #50-T60") using an applicator to form an adhesive layer with a dry thickness of 20 μm. A 38 μm thick separator (Mitsui Chemicals Tohcello, Ltd., "SPPET01 38BU") was bonded to the surface of the adhesive layer, and then treated with a UV irradiation device using a high-pressure mercury lamp at a predetermined dose (140 mW / cm²). 2 900 mJ / cm² 2An adhesive sheet was fabricated by irradiating it with ultraviolet light. (A laminate of PET film / adhesive layer / lightly release silicone separator).

[0091] <Adhesion at room temperature> Test specimens measuring 25 mm in width and 200 mm in size were prepared from the adhesive sheets obtained above. After removing the separator, the specimens were pressed onto the substrates [SUS304-BA plate, PE (polyethylene) plate] by rolling a 2 kg rubber roller back and forth twice at 23°C and in a 50 RH atmosphere, and left to stand at 23°C for 30 minutes. Subsequently, the 180° peel strength (N / 25 mm) was measured at a peeling speed of 300 mm / min in accordance with JIS Z 0237 and evaluated as follows.

[0092] (Evaluation criteria) vs. SUSBA plate ◎··15.0N / 25mm or more ○··12.0N / 25mm or more, less than 15.0N / 25mm △··8.0N / 25mm or more, less than 12.0N / 25mm ×··8.0N / less than 25mm

[0093] (Evaluation criteria) vs. PE plate ◎··8.0N / 25mm or more ○··6.0N / 25mm or more, less than 8.0N / 25mm △··4.0N / 25mm or more, less than 6.0N / 25mm ×··4.0N / less than 25mm

[0094] <Adhesive strength after heating> A test specimen measuring 25 mm x 200 mm was prepared from the adhesive sheet obtained above. After removing the separator, it was pressed onto the substrate [SUS304-BA plate] by rolling a 2 kg rubber roller back and forth twice at 23°C in a 50 RH atmosphere, and left to stand at 23°C for 30 minutes. Subsequently, it was heated in a mini jet oven heated to 120°C for 10 days. After that, the 180° peel strength (N / 25 mm) was measured at a peeling speed of 300 mm / min in accordance with JIS Z 0237 and evaluated as follows.

[0095] (Evaluation Criteria) ◎··15.0N / 25mm or more ○··12.0N / 25mm or more, less than 15.0N / 25mm △··8.0N / 25mm or more, less than 12.0N / 25mm ×··8.0N / less than 25mm

[0096] <Adhesion to curved surfaces> A test specimen measuring 25 mm x 40 mm was prepared from the adhesive sheet obtained above. After removing the separator, it was pressed and attached to protective paper attached to the surface of a 25 mm diameter graduated cylinder, and then left to stand at 40°C for 72 hours. After that, the width of the test specimen that peeled off the protective paper was measured and evaluated as follows.

[0097] (Evaluation Criteria) Less than 1mm △··1mm or more, less than 10mm × 10mm or more

[0098] <Gel fraction> The adhesive was collected from the adhesive sheet obtained above by picking, wrapped in a 200-mesh stainless steel wire mesh, and immersed in toluene adjusted to 23°C for 24 hours. The weight of the adhesive layer was measured before and after immersion in ethyl acetate, and the difference between the two weights was taken as the weight of the insoluble adhesive component remaining in the wire mesh. The weight percentage of the insoluble adhesive component remaining in the wire mesh relative to the weight of the adhesive layer before immersion in ethyl acetate was taken as the gel fraction (%).

[0099] <Holding force> A 25mm x 25mm test piece was prepared from the adhesive sheet obtained above. After removing the separator, it was pressed and attached to a stainless steel plate (SUS304) polished with sandpaper by moving a 2kg roller back and forth (attachment area 25mm x 25mm). The holding force was measured using a creep tester (BE-501, high-temperature constant-humidity chamber equipped holding force tester, manufactured by Tester Sangyo Co., Ltd.) with a load of 1kg applied under a 40°C atmosphere for 24 hours. The evaluation criteria for holding force are as follows.

[0100] (Evaluation Criteria) ◎··Hold for 1440 minutes or more, and without slippage. 〇··Held for over 1440 minutes, but there was a discrepancy. △··Held for 100 minutes or more, but less than 1440 minutes ×...Held for less than 100 minutes

[0101] [Table 1]

[0102] Based on the above results, Examples 1 to 2020 satisfy the configuration of the present invention. 3 Therefore, it can be seen that all of these resins exhibit excellent thermal stability, and adhesive sheets using these adhesives have adhesive strength to various substrates such as SUS and PE, while also having excellent holding power, flexibility for application to curved surfaces, and long-term heat resistance after being bonded to a substrate. In contrast, in Comparative Example 1, where the amount of tackifier (B) exceeds 40% of 100 parts by mass of acrylic resin (A), it can be seen that the adhesive exhibits poor adhesion to PE, poor adhesion after heating, and even poor holding power. Furthermore, in Comparative Example 2, where the amount of tackifier (B) is less than 10% of 100 parts by mass of acrylic resin (A), it can be seen that the adhesive has poor adhesion to PE and poor adhesion to curved surfaces. Furthermore, in Comparative Examples 3 and 4, although the amount of tackifier (B) was the same as in Example 1, the weight-average molecular weight of the acrylic resin (A) was 200,000 or less, resulting in inferior holding power and adhesion to curved surfaces. Therefore, in order to achieve the effects of the present invention, it is necessary that the present invention has the effects, and in particular that the weight-average molecular weight of the acrylic resin (A) and the content of the tackifier (B) satisfy a predetermined ratio. [Industrial applicability]

[0103] The active energy ray-curable adhesive composition of the present invention exhibits excellent thermal stability, and adhesive sheets using this adhesive composition have excellent adhesion to various substrates, as well as excellent holding power, and furthermore, excellent adhesion to curved surfaces and long-term heat resistance after being bonded to a substrate, thus providing an adhesive suitable for various labels.

Claims

1. An active energy ray curable hot melt adhesive composition containing an acrylic resin (A) and a tackifier (B), The weight-average molecular weight of the acrylic resin (A) is 200,000 or more. An acrylic resin (A) obtained by polymerizing a copolymer component (a) containing an alkyl (meth)acrylate (a1) and a monomer (a2) having an ultraviolet active site, The content of the tackifier (B) is 10 to 40 parts by weight per 100 parts by weight of the acrylic resin (A). An active energy ray-curable hot-melt adhesive composition in which the tackifier (B) has a softening point of 115°C or higher.

2. The active energy ray curable hot melt adhesive composition according to claim 1, wherein the softening point of the tackifier (B) is 115 to 130°C.

3. The active energy ray-curable hot-melt adhesive composition according to claim 1 or 2, wherein the tackifier (B) is a rosin-based tackifier (B1).

4. The active energy ray curable hot melt adhesive composition according to any one of claims 1 to 3, wherein the copolymer component (a) of the acrylic resin (A) contains a polar group-containing ethylenically unsaturated monomer (a3).

5. The active energy ray curable hot melt adhesive composition according to any one of claims 1 to 4, further comprising a crosslinking agent (C).

6. An active energy ray-curable hot melt adhesive comprising a crosslinked active energy ray-curable hot melt adhesive composition according to any one of claims 1 to 5.

7. An adhesive tape comprising an active energy ray-curable hot-melt adhesive as described in claim 6, formed on a substrate.

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