Energy ray-crosslinkable pressure-sensitive adhesive composition, crosslinked pressure-sensitive adhesive and pressure-sensitive adhesive sheet, and production methods thereof

Abstract

The present invention relates to: an energy ray-crosslinkable adhesive agent composition which contains (A) an acrylic resin that is energy ray-crosslinkable and (B) a tackifier, wherein the tackifier (B) contains (B1) a styrene resin; an adhesive sheet which uses this energy ray-crosslinkable adhesive agent composition; a crosslinked adhesive agent which is obtained by crosslinking this energy ray-crosslinkable adhesive agent composition by means of an energy ray; a method for producing this crosslinked adhesive agent; an adhesive sheet which uses this crosslinked adhesive agent; and a method for producing this adhesive sheet.

Description

Technical Field

[0001] The present invention relates to an energy ray crosslinkable pressure-sensitive adhesive composition, a crosslinked pressure-sensitive adhesive and a pressure-sensitive adhesive sheet, and a method for producing the same.

Background Art

[0002] Pressure-sensitive adhesive sheets are used in a wide range of industrial fields, for example, for label applications for displaying various information, for fixing or temporarily fixing parts in fields such as OA equipment, household appliances, automobiles, and construction, and for masking applications. Synthetic rubber-based pressure-sensitive adhesives can be designed with a wide range of adhesive performances by molecular design and combination with additives such as tackifiers, and are relatively inexpensive, so they are widely used as pressure-sensitive adhesives for pressure-sensitive adhesive sheets. In addition, since synthetic rubber-based pressure-sensitive adhesives can be used as hot-melt pressure-sensitive adhesives that can be applied to a base material or the like by heating and melting without using a solvent, there is an advantage that the environmental load during the production of pressure-sensitive adhesive sheets can be reduced.

[0003] As the base resin of the synthetic rubber-based pressure-sensitive adhesive, for example, block copolymers such as styrene-isoprene-styrene (SIS) block copolymers are used. In the SIS, the soft segment composed of polyisoprene blocks contributes to the adhesive force, and near room temperature, the hard segment composed of polystyrene blocks forms physical pseudo-crosslinking points by intermolecular forces and can exhibit sufficient strength. On the other hand, since the pseudo-crosslinking points have the property of being released in a high-temperature environment, the cohesive force of the pressure-sensitive adhesive using SIS is significantly reduced by heating and melts when a certain temperature is exceeded. This melting property can be an advantage in enabling use as a hot-melt pressure-sensitive adhesive, but on the other hand, it also becomes a factor in reducing the heat resistance of the pressure-sensitive adhesive.

[0004] Patent Document 1 discloses a radiation-curable hot-melt adhesive composition containing an acrylic polymer to which a photoinitiator is bonded, a long-chain alkyl acrylate monomer containing an alkyl group having 6 or more carbon atoms, a compatible tackifier, and a polyfunctional unsaturated oligomer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The adhesive composition of Patent Document 1 can be melt-coated, and the acrylic polymer undergoes a crosslinking reaction by irradiating the coating film after coating with ultraviolet rays, so that the cohesive force of the pressure-sensitive adhesive can be improved. However, its effect is limited, and further improvement is required to enable the use of hot-melt adhesives in a wider range of applications and various environments.

[0007] The present invention has been made in view of the above problems, and an energy-ray crosslinkable adhesive composition capable of forming an adhesive having good adhesive strength and excellent holding power, an adhesive sheet using the energy-ray crosslinkable adhesive composition, a crosslinked adhesive obtained by energy-ray crosslinking the energy-ray crosslinkable adhesive composition and a method for producing the same, and an adhesive sheet using the crosslinked adhesive and a method for producing the same are provided.

Means for Solving the Problems

[0008] The present inventors have found that the above problems can be solved by using an acrylic resin having a specific structure and a tackifier, and have completed the present invention. That is, the present invention relates to the following [1] to

[16] . [1] An energy-ray crosslinkable adhesive composition containing (A) an acrylic resin having energy-ray crosslinkability and (B) a tackifier, wherein the (B) tackifier contains (B1) a styrene resin. [2] The energy-ray crosslinkable pressure-sensitive adhesive composition according to [1] above, wherein the content of the (B1) styrene resin is 1 to 40 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy-ray crosslinkability. [3] The energy-ray crosslinkable pressure-sensitive adhesive composition according to [1] or [2] above, wherein the (B) tackifier further contains one or more selected from the group consisting of (B2) hydrogenated terpene phenol resins and (B3) hydrogenated rosin resins. [4] The energy-ray crosslinkable pressure-sensitive adhesive composition according to [3] above, wherein the content of one or more selected from the group consisting of the (B2) hydrogenated terpene phenol resin and the (B3) hydrogenated rosin resin is 1 to 39 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy-ray crosslinkability. [5] The energy-ray crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [4] above, wherein the total content of the (B) tackifier is 5 to 40 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy-ray crosslinkability. [6] The energy-ray crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [5] above, wherein the (A) acrylic resin having energy-ray crosslinkability is an acrylic resin having a benzophenone structure in the side chain. [7] The energy-ray crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [6] above, wherein the (B1) styrene resin is a homopolymer of a styrene monomer. [8] A pressure-sensitive adhesive sheet having an energy-ray crosslinkable pressure-sensitive adhesive composition layer composed of the energy-ray crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [7] above on a substrate or a release liner. [9] A method for producing the pressure-sensitive adhesive sheet according to [8] above, The energy-ray crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) acrylic resin having energy-ray crosslinkability and the (B) tackifier, A method for producing a pressure-sensitive adhesive sheet, wherein the energy-ray crosslinkable pressure-sensitive adhesive composition layer is formed by melt-coating the energy-ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner.

[10] A crosslinked pressure-sensitive adhesive obtained by irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [7] above with energy rays.

[11] The crosslinked pressure-sensitive adhesive according to

[10] above, wherein the gel fraction is 30 to 85% by mass.

[12] The crosslinked pressure-sensitive adhesive according to

[10] or

[11] above, wherein the haze measured in accordance with JIS K 7136:2000 is 8% or less.

[13] A method for producing the crosslinked pressure-sensitive adhesive according to any one of

[10] to

[12] above, The method for producing a crosslinked pressure-sensitive adhesive, which comprises a step of irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition with energy rays.

[14] An adhesive sheet having an adhesive layer made of the crosslinked pressure-sensitive adhesive according to any one of

[10] to

[12] above on a substrate or a release liner.

[15] A method for producing the adhesive sheet according to

[14] above, A step of forming an energy-ray crosslinkable pressure-sensitive adhesive composition layer made of the energy-ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner, And a step of irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition layer with energy rays. A method for producing an adhesive sheet.

[16] The energy-ray crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) acrylic resin having energy-ray crosslinkability and the (B) tackifier, The method for producing an adhesive sheet according to

[15] above, wherein the energy-ray crosslinkable pressure-sensitive adhesive composition layer is formed by melt-coating the energy-ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner. [Effect of the Invention]

[0009] According to the present invention, it is possible to provide an energy-ray crosslinkable pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive having good adhesive strength and excellent holding power, an adhesive sheet using the energy-ray crosslinkable pressure-sensitive adhesive composition, a crosslinked pressure-sensitive adhesive obtained by subjecting the energy-ray crosslinkable pressure-sensitive adhesive composition to energy-ray crosslinking and a method for producing the same, and an adhesive sheet using the crosslinked pressure-sensitive adhesive and a method for producing the same. [Brief Description of the Drawings]

[0010]

Figure 1

Figure 2

Figure 3

[0011] In this specification, for preferred numerical ranges (for example, ranges such as content), the lower limit value and the upper limit value described stepwise can be combined independently. For example, from the description "preferably 10 to 90, more preferably 30 to 60", it is also possible to combine the "preferred lower limit value (10)" and the "more preferred upper limit value (60)" to obtain "10 to 60".

[0012] In this specification, the "energy ray" means those having energy quanta among electromagnetic waves or charged particle beams, and examples thereof include ultraviolet rays, radiation, electron beams, etc. Ultraviolet rays can be irradiated, for example, by using an electrodeless lamp, a high-pressure mercury lamp, a metal halide lamp, a UV-LED, etc. as an ultraviolet ray source. Electron beams can be irradiated with those generated by an electron beam accelerator or the like. Among the above-mentioned ones, ultraviolet rays are preferred as the energy ray in one aspect of the present invention. In this specification, "energy ray crosslinkability" means the property of forming a crosslinked structure by irradiating an energy ray.

[0013] The mechanism of action described in this specification is a speculation and does not limit the mechanism by which the effects of the present invention are achieved.

[0014] [Energy Ray Crosslinkable Adhesive Composition and Crosslinked Adhesive] The energy ray crosslinkable adhesive composition of the present embodiment is (A) An acrylic resin having energy ray crosslinkability and (B) a tackifier are contained, and the (B) tackifier contains (B1) a styrene resin, and it is an energy ray crosslinkable pressure-sensitive adhesive composition. Further, the crosslinked pressure-sensitive adhesive of the present embodiment is a crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray crosslinkable pressure-sensitive adhesive composition of the present embodiment with an energy ray.

[0015] The crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray crosslinkable pressure-sensitive adhesive composition of the present embodiment with an energy ray has good adhesive strength and excellent holding power. The reason for this is presumed as follows. The energy ray crosslinkable pressure-sensitive adhesive composition of the present embodiment contains (A) an acrylic resin having energy ray crosslinkability (hereinafter also referred to as "(A) energy ray crosslinkable acrylic resin" or "(A) component"). (A) The energy ray crosslinkable acrylic resin can be melt-coated, and a crosslinking reaction occurs by irradiating an energy ray after coating, and the cohesive force is improved. On the other hand, only (A) the energy ray crosslinkable acrylic resin has high adhesive strength to a highly polar adherend such as stainless steel, but does not have sufficient adhesive strength to a low polar adherend such as polyolefin. As a method for improving the adhesive strength to a low polar adherend, a method of adding a tackifier to an acrylic pressure-sensitive adhesive has been proposed, but when used together with (A) the energy ray crosslinkable acrylic resin, the holding power of the pressure-sensitive adhesive may decrease. As a result of studying the tackifier used together with (A) the energy ray crosslinkable acrylic resin, the present inventors have found that when using (B1) a styrene resin, good adhesive strength is obtained while the holding power of the pressure-sensitive adhesive is greatly improved. One of the reasons for this is considered that (B1) the styrene resin has a lower content of unsaturated double bonds that inhibit the radical reaction of the (A) component compared to other tackifiers such as rosin-based or terpene phenol-based tackifiers. As a result, it is considered that the energy ray crosslinking reaction of the (A) component proceeds sufficiently, and the cohesive force and holding power of the pressure-sensitive adhesive are improved.

[0016] Hereinafter, the energy ray-crosslinkable pressure-sensitive adhesive composition of the present embodiment (hereinafter, also simply referred to as "pressure-sensitive adhesive composition"), and the crosslinked pressure-sensitive adhesive will be described in more detail.

[0017] 〔Energy ray-crosslinkable pressure-sensitive adhesive composition〕 As described above, the pressure-sensitive adhesive composition of the present embodiment forms a crosslinked structure by being irradiated with energy rays, and forms a crosslinked pressure-sensitive adhesive excellent in holding power. That is, the pressure-sensitive adhesive composition of the present embodiment is a composition that is scheduled to be irradiated with energy rays before or after being attached to an adherend. The energy rays can be irradiated to the pressure-sensitive adhesive composition of the present embodiment at any time. Therefore, the pressure-sensitive adhesive composition of the present embodiment has a high degree of freedom in its manufacturing method and usage method. Specifically, since the pressure-sensitive adhesive composition of the present embodiment does not have an intentionally formed crosslinked structure, it can be heated and melted, and is suitable as a hot melt pressure-sensitive adhesive. Furthermore, since the pressure-sensitive adhesive composition of the present embodiment does not have an intentionally formed crosslinked structure, it has excellent shape followability. Therefore, by attaching the pressure-sensitive adhesive composition of the present embodiment to an adherend having a step or the like, and then forming a crosslinked pressure-sensitive adhesive by energy ray irradiation, it is possible to highly achieve both shape followability and holding power. Next, each component contained in the pressure-sensitive adhesive composition of the present embodiment will be described in detail.

[0018] <(A) Energy ray-crosslinkable acrylic resin> (A) The energy ray-crosslinkable acrylic resin is not particularly limited as long as it is an acrylic resin having energy ray-crosslinkability. (A) The energy ray-crosslinkable acrylic resin may be used alone or in combination of two or more.

[0019] (A) Examples of the energy ray-crosslinkable acrylic resin include acrylic resins having an energy ray-reactive group that reacts by energy ray irradiation and contributes to the formation of a crosslinked structure. Examples of the energy ray-reactive group include those that generate radicals which are excited by irradiation with energy rays and trigger crosslinking reactions. Specific examples of the energy ray-reactive group include functional groups having a benzophenone structure, a benzyl structure, an o-benzoylbenzoic acid ester structure, a thioxanthone structure, a 3-ketocoumarin structure, a 2-ethylanthraquinone structure, a camphorquinone structure, and the like. Among these, it is preferable that the (A) energy ray-crosslinkable acrylic resin has a benzophenone structure in the side chain. When the (A) energy ray-crosslinkable acrylic resin has a benzophenone structure, for example, upon irradiation with energy rays, the benzophenone structure extracts a hydrogen atom from the hydrocarbon group contained in the side chain of the acrylic resin, and the radicals recombine to form a crosslinked structure. Note that from the viewpoint of facilitating the formation of a crosslinked structure, the energy ray-reactive group is preferably introduced into the side chain of the acrylic resin. That is, the (A) energy ray-crosslinkable acrylic resin is preferably an acrylic resin having a benzophenone structure in the side chain.

[0020] The content of the energy ray-reactive group in the (A) energy ray-crosslinkable acrylic resin is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 3.0% by mass, based on the total amount (100% by mass) of the (A) energy ray-crosslinkable acrylic resin.

[0021] The acrylic resin is not particularly limited as long as it is a polymer containing an acrylic monomer as a monomer component, but preferably contains a structural unit derived from an alkyl (meth) acrylate. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, and the like. Among these, alkyl (meth)acrylates having 1 to 8 carbon atoms in the alkyl group are preferred, and 2-ethylhexyl (meth)acrylate, methyl (meth)acrylate, and butyl (meth)acrylate are more preferred.

[0022] The content of the (A) energy ray-crosslinkable acrylic resin in the pressure-sensitive adhesive composition of the present embodiment may be 20 to 95% by mass, 40 to 90% by mass, or 60 to 80% by mass with respect to the total amount (100% by mass) of the pressure-sensitive adhesive composition.

[0023] <(B) Tackifier> The pressure-sensitive adhesive composition of the present embodiment further contains (B) a tackifier. (B) The tackifier is a component that improves the tack characteristics of the resulting crosslinked pressure-sensitive adhesive. In the pressure-sensitive adhesive composition of the present embodiment, (B) the tackifier contains (B1) a styrene resin. (B) The tackifier may be used alone or in combination of two or more.

[0024] ((B1) Styrene resin) (B1) The styrene resin is not particularly limited as long as it is a polymer containing a styrene monomer as a monomer component. Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-t-butylstyrene, 1,3-dimethylstyrene, 2,4-dimethylstyrene, and the like. (B1) Examples of the styrene resin include a homopolymer of a styrene monomer, a copolymer of a styrene monomer and an aliphatic hydrocarbon monomer, a copolymer of a styrene monomer and an aromatic hydrocarbon monomer, and the like. Among these, a homopolymer of a styrene monomer is preferred.

[0025] The content of the (B1) styrene resin in the pressure-sensitive adhesive composition of the present embodiment is preferably 1 to 40 parts by mass, more preferably 5 to 35 parts by mass, still more preferably 10 to 30 parts by mass with respect to 100 parts by mass of the (A) energy ray-crosslinkable acrylic resin. When the content of the (B1) styrene resin is 1 part by mass or more, the adhesive strength tends to be more easily improved. Further, when the content of the (B1) styrene resin is 40 parts by mass or less, the transparency of the pressure-sensitive adhesive is excellent.

[0026] ((B2) Hydrogenated terpene phenol resin and (B3) hydrogenated rosin resin) The pressure-sensitive adhesive composition of the present embodiment preferably contains at least one selected from the group consisting of a (B2) hydrogenated terpene phenol resin and a (B3) hydrogenated rosin resin together with the (B1) styrene resin. The (B1) styrene resin tends to have high transparency, but when mixed with the (A) energy ray-crosslinkable acrylic resin, cloudiness tends to occur to some extent due to the difference in the SP values of the two. On the other hand, when the (B2) hydrogenated terpene phenol resin and the (B3) hydrogenated rosin resin are contained, these tackifiers function as compatibilizing components that improve the compatibility between the (A) energy ray-crosslinkable acrylic resin and the (B1) styrene resin, and the transparency of the pressure-sensitive adhesive composition and the crosslinked pressure-sensitive adhesive obtained from the pressure-sensitive adhesive composition tends to be improved.

[0027] The (B2) hydrogenated terpene phenol resin is a resin obtained by hydrogenating the double bond derived from terpene and the aromatic ring double bond derived from phenols in the terpene phenol resin. The terpene phenol resin to be subjected to hydrogenation is a resin containing at least a structure derived from terpenes and a structure derived from a phenolic compound, and may be a copolymer of terpenes and a phenolic compound, or may be a terpene resin obtained by polymerizing terpenes and modified with a phenolic compound. Among these, the terpene phenol resin is preferably a copolymer of terpenes and a phenolic compound. There are no particular restrictions on the terpene raw materials, and examples include α-pinene, β-pinene, limonene, and the like. (B2) The hydrogenated terpene phenol resin may be a partially hydrogenated terpene phenol resin obtained by partially hydrogenating the terpene phenol resin. However, from the viewpoint of not inhibiting the radical reaction of the energy ray crosslinkable acrylic resin and the viewpoint of being more likely to improve transparency, a fully hydrogenated terpene phenol resin obtained by substantially completely hydrogenating the terpene phenol resin is preferred.

[0028] (B3) The hydrogenated rosin resin is a resin obtained by hydrogenating the double bond of rosin or a resin derived from rosin, and examples include hydrogenated rosin, hydrogenated rosin ester resin, and the like. In this specification, "hydrogenated rosin" means rosin obtained by adding hydrogen to purified rosin containing abietic acid as a main component in the presence of a catalyst. Further, "hydrogenated rosin ester resin" means a resin obtained by esterifying hydrogenated rosin with an alcohol such as glycerin or pentaerythritol. (B3) The hydrogenated rosin resin may be a partially hydrogenated rosin resin obtained by partially hydrogenating rosin or a resin derived from rosin. However, from the viewpoint of not inhibiting the radical reaction of the energy ray crosslinkable acrylic resin and the viewpoint of being more likely to improve transparency, a fully hydrogenated rosin resin obtained by substantially completely hydrogenating rosin or a resin derived from rosin is preferred.

[0029] When the pressure-sensitive adhesive composition of the present embodiment contains one or more selected from the group consisting of (B2) hydrogenated terpene phenol resin and (B3) hydrogenated rosin resin, the content thereof is preferably 1 to 39 parts by mass, more preferably 3 to 35 parts by mass, still more preferably 5 to 30 parts by mass with respect to 100 parts by mass of the (A) energy ray-crosslinkable acrylic resin. When the content of one or more selected from the group consisting of (B2) hydrogenated terpene phenol resin and (B3) hydrogenated rosin resin is 1 part by mass or more, the transparency and adhesiveness tend to be more easily improved. Further, when the content of one or more selected from the group consisting of (B2) hydrogenated terpene phenol resin and (B3) hydrogenated rosin resin is 39 parts by mass or less, the holding power tends to be more easily improved.

[0030] ((B) Softening point of tackifier) The softening point of the (B) tackifier is preferably 70 to 140 °C, more preferably 80 to 130 °C, still more preferably 85 to 120 °C. When the softening point of the (B) tackifier is 70 °C or higher, excellent adhesiveness tends to be obtained at high temperatures. Further, when the softening point of the (B) tackifier is 140 °C or lower, it tends to be easily mixed with the (A) energy ray-crosslinkable acrylic resin. In the present specification, the softening point of the (B) tackifier means a value measured in accordance with JIS K 5601-2-2.

[0031] In the pressure-sensitive adhesive composition of the present embodiment, the total content of the (B) tackifier is preferably 5 to 40 parts by mass, more preferably 10 to 40 parts by mass, still more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the (A) energy ray-crosslinkable acrylic resin. When the total content of the (B) tackifier is 5 parts by mass or more, the adhesiveness tends to be more easily improved. Further, when the content of the (B) tackifier is 40 parts by mass or less, the holding power tends to be more easily improved.

[0032] The pressure-sensitive adhesive composition of the present embodiment may contain an other tackifier other than (B1) a styrene resin, (B2) a hydrogenated terpene phenol resin, and (B3) a hydrogenated rosin resin. However, from the viewpoint of not inhibiting the radical reaction of the (A) energy ray crosslinkable acrylic resin and the viewpoint of more easily improving transparency, it is preferable not to contain the other tackifier. From the same viewpoint as above, the total content of (B1) a styrene resin, (B2) a hydrogenated terpene phenol resin, and (B3) a hydrogenated rosin resin in the (B) tackifier contained in the pressure-sensitive adhesive composition of the present embodiment is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, still more preferably 98 to 100% by mass with respect to the total amount (100% by mass) of the (B) tackifier.

[0033] <Other Components> The pressure-sensitive adhesive composition of the present embodiment may or may not contain other components other than the above components. Examples of the other components include a softening agent; an antioxidant; an additive for pressure-sensitive adhesives used in general pressure-sensitive adhesives, and the like. These other components may be used alone, or two or more of them may be used in combination.

[0034] The antioxidant is not particularly limited, and conventionally known ones can be used. For example, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,4-bis(octylthiomethyl)-o-cresol, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl]phenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)]acrylate, hindered phenolic antioxidants such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane; sulfur-based antioxidants such as dilauryl thiodipropionate, lauryl stearyl thiodipropionate, pentaerythritol tetrakis(3-laurylthiopropionate); phosphorus-based antioxidants such as tris(nonylphenyl)phosphite, tris(2,4-di-t-butylphenyl)phosphite; and the like.

[0035] Examples of the additives for adhesives used in the above general adhesives include waxes, fillers, extenders, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants (pigments, dyes, etc.), flame retardants, antistatic agents, thread drawing inhibitors, leveling agents, crosslinking agents, crosslinking aids, anti-aging agents, inorganic particles, organic particles, weight reducers, and the like. These additives for adhesives may be used alone or in combination of two or more for each. When these additives for adhesives are contained, the content of the additives for adhesives is, independently of each other, preferably 0.0001 to 20 parts by mass, more preferably 0.001 to 10 parts by mass, based on 100 parts by mass of the energy ray-crosslinkable acrylic resin (A).

[0036] <Method for Producing Pressure-Sensitive Adhesive Composition> The pressure-sensitive adhesive composition of the present embodiment can be produced, for example, by a method of melt-kneading (A) an energy-ray crosslinkable acrylic resin, (B) a tackifier, and optional components used as needed. In the following description, the step of melt-kneading (A) an energy-ray crosslinkable acrylic resin, (B) a tackifier, etc. may be referred to as the "melt-kneading step".

[0037] The melt-kneading step is, for example, a step of charging each component into a mixing device equipped with a heating device such as a heating kneader and mixing the components in a molten state. Examples of the mixing device equipped with a heating device include a single-screw extruder, a twin-screw extruder, a roll mill, a plast mill, a Banbury mixer, an intermix, a pressure kneader, etc. When using a mixing device capable of reducing pressure, if necessary, the inside of the mixing device may be depressurized and melt-kneaded under reduced pressure.

[0038] The kneading temperature in the melt-kneading step is not particularly limited, and temperature conditions under which each component is sufficiently mixed in a molten state may be appropriately selected. Preferably, it is 80 to 180°C, more preferably 100 to 170°C, and still more preferably 120 to 150°C.

[0039] When the pressure-sensitive adhesive composition of the present embodiment is produced by melt-kneading, the pressure-sensitive adhesive composition of the present embodiment does not need to contain a solvent, and from the viewpoint of reducing the environmental load, it is preferably solvent-free. When containing a solvent, the content of the solvent is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 1% by mass or less, based on the total amount (100% by mass) of the pressure-sensitive adhesive composition of the present embodiment.

[0040] The pressure-sensitive adhesive composition obtained after finishing melt-kneading may be applied onto a base material or a release liner by an extruder or the like while in a heat-melted state and used for the production of the pressure-sensitive adhesive sheet of the present embodiment described later. If desired, it may be filled into various containers, etc. without going through a molding process, for example.

[0041] [Crosslinked Adhesive] The crosslinked adhesive of this embodiment is a crosslinked adhesive obtained by irradiating the energy ray-crosslinkable adhesive composition of this embodiment with energy rays. That is, the crosslinked adhesive of this embodiment has a crosslinked structure formed by the energy ray crosslinking reaction of the (A) energy ray crosslinkable acrylic resin contained in the energy ray crosslinkable adhesive composition of this embodiment. The crosslinked adhesive of this embodiment itself also has good adhesive strength and exhibits excellent adhesive force to the adherend. Therefore, from the viewpoint of eliminating the need for the energy ray irradiation step after sticking to the adherend, it is preferable to irradiate the energy rays before sticking the adhesive composition to the adherend to form the crosslinked adhesive of this embodiment and stick it to the adherend as the crosslinked adhesive.

[0042] The adhesive strength of the crosslinked adhesive of this embodiment to the polyethylene plate at 23°C is preferably 3 N / 25 mm or more, more preferably 5 N / 25 mm or more, and still more preferably 6 N / 25 mm or more. When the adhesive strength of the crosslinked adhesive is 3 N / 25 mm or more, there is a tendency that peeling, detachment, etc. from the adherend are less likely to occur. The upper limit value of the adhesive strength of the crosslinked adhesive to the polyethylene plate at 23°C is not particularly limited, but from the viewpoint of maintaining good balance with ease of production and other performances, it may be 50 N / 25 mm or less, or may be 30 N / 25 mm or less. The adhesive strength of the crosslinked adhesive to the polyethylene plate at 23°C can be measured by the method described in the examples.

[0043] The gel fraction of the crosslinked adhesive of this embodiment is preferably 30 to 85% by mass, more preferably 35 to 80% by mass, and still more preferably 40 to 75% by mass. When the gel fraction of the crosslinked adhesive is 30% by mass or more, there is a tendency that the holding power is more easily improved. Also, when the gel fraction of the crosslinked adhesive is 85% by mass or less, there is a tendency that the adhesive strength is more easily improved. In this embodiment, the gel fraction of the crosslinked pressure-sensitive adhesive can be measured by the method described in the examples.

[0044] The haze of the crosslinked pressure-sensitive adhesive of this embodiment is preferably 15% or less, more preferably 8% or less, and still more preferably 4% or less. When the haze of the crosslinked pressure-sensitive adhesive is 15% or less, the crosslinked pressure-sensitive adhesive of this embodiment tends to be suitable for applications that require transparency. In this embodiment, the haze of the crosslinked pressure-sensitive adhesive can be measured by the method described in the examples.

[0045] The crosslinked pressure-sensitive adhesive of this embodiment can be produced by irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition of this embodiment with energy rays. In the following description, the step of irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition of this embodiment with energy rays may be referred to as the "energy-ray irradiation step".

[0046] [Adhesive sheet] The present invention provides the following first adhesive sheet and second adhesive sheet. The first adhesive sheet is an adhesive sheet having an energy-ray crosslinkable pressure-sensitive adhesive composition layer made of the energy-ray crosslinkable pressure-sensitive adhesive composition of this embodiment on a base material or a release liner. The second adhesive sheet is an adhesive sheet having an adhesive layer made of the crosslinked pressure-sensitive adhesive of this embodiment on a base material or a release liner. In the following description, when simply referred to as an "adhesive sheet", it means both the first adhesive sheet and the second adhesive sheet.

[0047] Next, an example of the configuration of the adhesive sheet of this embodiment will be described with reference to the drawings. However, the adhesive sheet of this embodiment is not limited to the following examples as long as the effects of this embodiment are exhibited.

[0048] Fig. 1(a) shows an example of a first adhesive sheet, an adhesive sheet 10a having a release liner 2 on one surface side of an adhesive composition layer 1 and a substrate 4 on the other surface side of the adhesive composition layer 1. Further, Fig. 1(b) shows an example of a second adhesive sheet, an adhesive sheet 10b having a release liner 2 on one surface side of an adhesive layer 3 and a substrate 4 on the other surface side of the adhesive layer 3. The adhesive sheets 10a and 10b are suitable for uses such as, for example, after removing the release liner 2 and then attaching the exposed surface of the adhesive composition layer 1 or the adhesive layer 3 to an adherend. Examples of such uses include label uses and the like. When the adhesive sheet attached to the adherend is the first adhesive sheet, after attaching to the adherend, an energy ray is irradiated to the adhesive composition layer to form an adhesive layer.

[0049] Fig. 2(a) shows another example of the first adhesive sheet, a double-sided adhesive sheet 20a having adhesive composition layers 1 on both sides of a substrate 4, a release liner 2a on the surface of one adhesive composition layer 1 opposite to the substrate 4, and a release liner 2b on the surface of the other adhesive composition layer 1 opposite to the substrate 4. Further, Fig. 2(b) shows another example of the second adhesive sheet, a double-sided adhesive sheet 20b having adhesive layers 3 on both sides of a substrate 4, a release liner 2a on the surface of one adhesive layer 3 opposite to the substrate 4, and a release liner 2b on the surface of the other adhesive layer 3 opposite to the substrate 4.

[0050] Fig. 3(a) shows another example of the first adhesive sheet, a substrate-free adhesive sheet 30a having release liners 2a and 2b on both sides of an adhesive composition layer 1. Further, Fig. 3(b) shows another example of the second adhesive sheet, a substrate-free adhesive sheet 30b having release liners 2a and 2b on both sides of an adhesive layer 3.

[0051] The adhesive sheets 20a, 20b, 30a, and 30b are suitable for bonding adherends to each other. For example, after peeling off the release liner 2a on one side, the surface of the exposed pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3 is attached to the adherend. Then, after further peeling off the release liner 2b, the surface of the exposed pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3 is attached to another adherend. Such applications include, for example, fixing or temporarily fixing various parts. In the case of the adhesive sheets 30a and 30b, when the peeling force for peeling the release liner 2a from the pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3 is approximately the same as the peeling force for peeling the release liner 2b from the pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3, if both release liners are pulled outward to peel them off, the pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3 may be separated and peeled off along with the two release liners. From the perspective of suppressing such a phenomenon, it is preferable to use two types of release liners designed to have different peeling forces for the two release liners 2a and 2b.

[0052] The thickness of the pressure-sensitive adhesive composition layer in the first adhesive sheet and the thickness of the pressure-sensitive adhesive layer in the second adhesive sheet are preferably 5 to 100 μm, more preferably 10 to 60 μm, and still more preferably 15 to 30 μm. When the thickness of the pressure-sensitive adhesive composition layer and the pressure-sensitive adhesive layer is 5 μm or more, the adhesive strength tends to be more easily improved. Also, when the thickness of the pressure-sensitive adhesive composition layer and the pressure-sensitive adhesive layer is 100 μm or less, the handleability tends to be better.

[0053] <Base material> Examples of the material for forming the base material include resins, metals, paper materials, and the like. Examples of the resin include polyolefin resins such as polyethylene and polypropylene; vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polystyrene; acrylonitrile-butadiene-styrene copolymer; cellulose triacetate; polycarbonate; urethane resins such as polyurethane and acrylic-modified polyurethane; polymethylpentene; polysulfone; polyetheretherketone; polyethersulfone; polyphenylene sulfide; polyimide resins such as polyetherimide and polyimide; polyamide resins; acrylic resins; and fluorine-based resins. Examples of the metal include aluminum, tin, chromium, titanium, and the like. Examples of the paper material include tissue paper, medium-quality paper, high-quality paper, impregnated paper, coated paper, art paper, sulfuric acid paper, glassine paper, and the like.

[0054] The forming material of the above base material may be composed of one kind or a combination of two or more kinds. Examples of the base material obtained by combining two or more forming materials include those obtained by laminating a paper material with a thermoplastic resin such as polyethylene, and those obtained by forming a metal film on the surface of a resin film or sheet containing a resin. Note that, as a method for forming the metal layer, for example, a method of depositing the above metal by a PVD method such as vacuum deposition, sputtering, or ion plating, or a method of attaching a metal foil made of the above metal using a general adhesive can be mentioned.

[0055] From the viewpoint of improving the interlayer adhesion between the base material and another layer to be laminated, when the base material contains a resin, surface treatment such as oxidation method or roughening method, easy adhesion treatment, or primer treatment may be performed on the surface of the base material.

[0056] Depending on the use of the pressure-sensitive adhesive sheet, the base material may have, for example, an easy-adhesion layer for facilitating printing; a recording layer for enabling recording such as thermal transfer recording and inkjet recording; an overcoat film or an overlaminate film for protecting these surfaces; an information area such as magnetic recording, barcodes, and micro semiconductor elements; and the like. On the other hand, when the pressure-sensitive adhesive sheet of the present embodiment is a transparent pressure-sensitive adhesive sheet having transparency, the base material preferably has transparency. Since the crosslinked pressure-sensitive adhesive of the present embodiment can be designed to have high transparency, it is suitable for manufacturing a transparent pressure-sensitive adhesive sheet in combination with a base material having transparency.

[0057] The base material may contain additives for the base material as needed. Examples of the additives for the base material include ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, slip agents, antiblocking agents, colorants, and the like. These additives for the base material may be used alone or in combination of two or more.

[0058] The thickness of the base material is preferably 5 to 1,000 μm, more preferably 15 to 500 μm, and still more preferably 20 to 200 μm. When the thickness of the base material is 5 μm or more, the deformation resistance of the pressure-sensitive adhesive sheet tends to be easily improved. On the other hand, when the thickness of the base material is 1,000 μm or less, the handleability of the pressure-sensitive adhesive sheet tends to be easily improved. Note that the "thickness of the base material" means the thickness of the entire base material. When the base material is a base material composed of a plurality of layers, it means the total thickness of all the layers constituting the base material.

[0059] <Release liner> As the release liner, a release liner subjected to a double-sided release treatment; a release liner subjected to a single-sided release treatment; and the like are used, and examples include those in which a release agent is applied on a base material for the release liner. Examples of the base material for the release liner include papers such as fine paper, glassine paper, and kraft paper; plastic films such as polyester resin films like polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin, and polyolefin resin films like polypropylene resin and polyethylene resin; and the like. Examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, and butadiene-based resins; long-chain alkyl-based resins, alkyd-based resins, fluorine-based resins, and the like. The thickness of the release liner is not particularly limited as long as the effects of the present invention are not impaired, but it is preferably 10 to 200 μm, more preferably 20 to 180 μm, and still more preferably 30 to 150 μm.

[0060] [Method for manufacturing the first pressure-sensitive adhesive sheet] The method for manufacturing the first pressure-sensitive adhesive sheet is obtained by melt-kneading the pressure-sensitive adhesive composition of the present embodiment with (A) an energy-ray crosslinkable acrylic resin and (B) a tackifier, and forming an energy-ray crosslinkable pressure-sensitive adhesive composition layer by melt-coating the energy-ray crosslinkable pressure-sensitive adhesive composition on a base material or a release liner. In the following description, the step of forming an energy-ray crosslinkable pressure-sensitive adhesive composition layer by melt-coating the energy-ray crosslinkable pressure-sensitive adhesive composition on a base material or a release liner may be referred to as the "pressure-sensitive adhesive composition layer forming step". Also, in the present embodiment, "on the release liner" means the surface that has been subjected to one-sided release treatment when the release liner has been subjected to one-sided release treatment.

[0061] In the method for manufacturing the first pressure-sensitive adhesive sheet, the description of the step of melt-kneading (A) an energy-ray crosslinkable acrylic resin and (B) a tackifier is as described in the melt-kneading step in the method for manufacturing the pressure-sensitive adhesive composition of the present embodiment.

[0062] The step of forming the adhesive composition layer may be a method of applying the adhesive composition obtained after melt-kneading onto a substrate or a release liner in a heat-melted state using an extruder, a T-die, etc. to form a layer. Thereafter, if necessary, it may have a step of cooling the adhesive composition layer.

[0063] By the above-described step of forming the adhesive composition layer, an adhesive composition layer can be formed on a substrate or a release liner. The sheet having the substrate or the release liner and the adhesive composition layer may be used as it is as the first adhesive sheet of the present embodiment, or if necessary, by performing other steps, it may be made into the configuration of a desired adhesive sheet. For example, by attaching the release-treated surface of the release liner to the exposed surface of the adhesive composition layer formed on the substrate, as in the adhesive sheet 10a shown in Fig. 1(a), an adhesive sheet having a release liner on one surface side of the adhesive composition layer and a substrate on the other surface side of the adhesive composition layer can be manufactured. Further, by attaching the substrate surface of the adhesive sheet 10a to the exposed surface of the adhesive composition layer formed on the release liner, as in the adhesive sheet 20a shown in Fig. 2(a), a double-sided adhesive sheet having adhesive composition layers on both sides of the substrate and having release liners on the surfaces opposite to the substrates of the respective adhesive composition layers can be manufactured. Further, by attaching the release-treated surface of another release liner to the exposed surface of the adhesive composition layer formed on the release liner, as in the adhesive sheet 30a shown in Fig. 3(a), a substrate-free adhesive sheet having release liners on both sides of the adhesive composition layer can be manufactured.

[0064] [Method for manufacturing the second adhesive sheet] The method for manufacturing the second adhesive sheet includes a step of forming an energy-ray crosslinkable adhesive composition layer made of an energy-ray crosslinkable adhesive composition on a substrate or a release liner, and a step of irradiating the energy-ray crosslinkable adhesive composition layer with energy rays, and is a method for manufacturing an adhesive sheet.

[0065] In the method for manufacturing the second pressure-sensitive adhesive sheet, the description of the step of forming the energy-ray crosslinkable pressure-sensitive adhesive composition layer is the same as the description of the step of forming the pressure-sensitive adhesive composition layer in the method for manufacturing the first pressure-sensitive adhesive sheet.

[0066] In the method for manufacturing the second pressure-sensitive adhesive sheet, the timing of performing energy-ray irradiation is not particularly limited, and it may be appropriately determined in consideration of the method for manufacturing the pressure-sensitive adhesive sheet, desired physical properties, and the like. For example, in a state where one surface of the pressure-sensitive adhesive composition layer is exposed, energy rays may be irradiated onto the pressure-sensitive adhesive composition layer directly or through a base material or a release liner. Alternatively, in a state where one surface of the pressure-sensitive adhesive composition layer has a base material or a release liner and the other surface has a release liner, energy rays may be irradiated through the base material or the release liner.

[0067] Also, the energy-ray irradiation may be performed once or may be performed in multiple steps. When the energy-ray irradiation is performed in multiple steps, for example, in a state where one surface of the pressure-sensitive adhesive composition layer is exposed, the first energy-ray irradiation is performed, and then, after attaching a base material or a release liner to the surface, the second energy-ray irradiation may be performed through the base material or the release liner. Furthermore, the first energy-ray irradiation may be performed at any time before attachment to the adherend, and the second energy-ray irradiation may be performed after attachment to the adherend.

[0068] <Uses of the Energy-Ray Crosslinkable Pressure-Sensitive Adhesive Composition, Crosslinked Pressure-Sensitive Adhesive, and Pressure-Sensitive Adhesive Sheet> The energy-ray crosslinkable pressure-sensitive adhesive composition, crosslinked pressure-sensitive adhesive, and pressure-sensitive adhesive sheet of the present embodiment can be used for various applications. Specifically, for example, label applications; applications for fixing or temporarily fixing various parts; surface protection applications; sealing material applications; decoration and display applications; and the like can be mentioned. Among these, label applications and applications for fixing or temporarily fixing various parts are preferred.

[0069] The pressure-sensitive adhesive sheet for label use may be directly attached to various products, or may be attached to packaging films, packaging containers, etc. of various products. Examples of the constituent materials of the packaging film and the packaging container include olefin resins such as polypropylene and polyethylene; polyester resins such as polyethylene terephthalate (PET) and polylactic acid; glass, paper, metal; and the like. Among these, since the pressure-sensitive adhesive sheet of the present embodiment exhibits high adhesive force to olefin resins, it is suitable for use in applications such as attaching to packaging films and packaging containers made of olefin resins such as polypropylene and polyethylene. As the pressure-sensitive adhesive sheet for fixing or temporary fixing, for example, it is suitable for fixing or temporary fixing of electronic components, optical components, automotive parts, mechanical parts, building materials, decorative materials, etc.

Example

[0070] The present invention will be specifically described by the following examples, but the present invention is not limited to the following examples. The physical property values in each example are the values measured by the following methods.

[0071] [Thickness of each layer] Measured at 23°C using a constant pressure thickness measuring instrument (model number: "PG-02J", standard specifications: conforming to JIS K 6783, Z 1702, Z 1709) manufactured by Techlock Co., Ltd.

[0072] The details of the materials used in the following examples and comparative examples are as follows.

[0073] <Component (A)> · Energy ray-crosslinkable acrylic resin: An acrylic resin having a benzophenone structure in the side chain, manufactured by BASF, trade name "acResin A204UV"

[0074] <Component (B)> · (B1) Styrene resin: A homopolymer of a styrene monomer, manufactured by Yasuhara Chemical Co., Ltd., trade name "SX100", softening point 100°C · (B2) Hydrogenated terpene phenol resin: manufactured by Yasuhara Chemical Co., Ltd., trade name "UH115", softening point 115°C · (B3) Hydrogenated rosin resin: hydrogenated rosin ester resin, manufactured by Arakawa Chemical Industries, Ltd., trade name "KE-311", softening point 90 - 100°C (Ring and Ball method) · Non-hydrogenated terpene phenol resin: manufactured by Yasuhara Chemical Co., Ltd., trade name "T115", softening point 115°C · Non-hydrogenated rosin resin: polymerized rosin ester, manufactured by Harima Chemicals, Inc., trade name "PCJ", softening point 118 - 128°C

[0075] Examples 1 - 5, Comparative Examples 1 - 5 (Manufacture of energy ray crosslinkable pressure-sensitive adhesive composition) Each component was blended in the composition shown in Table 1 (unit: parts by mass), and using a heat-type kneader, under nitrogen purge, kneaded at 130°C for 20 minutes to obtain an energy ray crosslinkable pressure-sensitive adhesive composition.

[0076] (Manufacture of the first pressure-sensitive adhesive sheet) The energy ray crosslinkable pressure-sensitive adhesive composition obtained above was coated on a transparent polyethylene terephthalate film (thickness: 50 μm) as a substrate in a heat-melted state using a die coater. Thereby, a first pressure-sensitive adhesive sheet having an energy ray crosslinkable pressure-sensitive adhesive composition layer made of the energy ray crosslinkable pressure-sensitive adhesive composition on the substrate was obtained.

[0077] (Manufacture of the second pressure-sensitive adhesive sheet) With respect to the energy ray crosslinkable pressure-sensitive adhesive composition layer of the first pressure-sensitive adhesive sheet obtained above, from the exposed surface side, using a high-pressure mercury lamp (manufactured by Eye Graphics Co., Ltd.), ultraviolet rays were irradiated under the condition of an integrated light quantity of 30 mJ / cm 2 in the UV-C region. Thereby, an adhesive layer was formed by energy ray crosslinking the energy ray crosslinkable pressure-sensitive adhesive composition layer of the first pressure-sensitive adhesive sheet. Thereafter, the release-treated surface of a release liner (thickness: 38 μm) was bonded to the surface of the adhesive layer opposite to the substrate to obtain a second pressure-sensitive adhesive sheet having the substrate, the adhesive layer, and the release liner in this order.

[0078] (Manufacture of Adhesive Sheet without Substrate) A pressure-sensitive adhesive sheet without a substrate, which has a release liner, an adhesive layer, and a release liner in this order, was obtained in the same manner as the manufacture of the first pressure-sensitive adhesive sheet and the second pressure-sensitive adhesive sheet, except that the substrate in the manufacture of the first pressure-sensitive adhesive sheet was changed to a release liner (thickness: 38 μm).

[0079] [Evaluation Method] The second pressure-sensitive adhesive sheet and the pressure-sensitive adhesive sheet without a substrate obtained in each example were evaluated by the methods shown below. In the following description, when simply described as "pressure-sensitive adhesive sheet", it means the second pressure-sensitive adhesive sheet.

[0080] [Measurement of Gel Fraction] The gel fraction of the adhesive layer in the pressure-sensitive adhesive sheet without a substrate obtained in each example was measured by the method shown below. From the pressure-sensitive adhesive sheet without a substrate obtained in each example, the release liners on both sides were removed, and only the adhesive layer was taken out. Hereinafter, the taken-out adhesive layer is referred to as the "measurement object". Next, the taken-out measurement object was wrapped in a polyester mesh (mesh size 200) whose mass had been measured in advance to prepare a test sample. The mass of the test sample was weighed with a precision balance, and from the measured value, the mass of the polyester mesh was subtracted to calculate the mass of only the measurement object before immersion. The mass of the measured measurement object was designated as M1. Next, the test sample was immersed in ethyl acetate at room temperature (23°C) for 72 hours. After immersion, the test sample was taken out, dried in an oven at 120°C for 2 hours, and then left standing for 24 hours in an environment of temperature 23°C and relative humidity 50%. The mass of the dried test sample was weighed with a precision balance, and from the measured value, the mass of the polyester mesh was subtracted to calculate the mass of only the measurement object after immersion and drying. The mass of the measured measurement object was designated as M2. From the value of the mass M1 of the measurement object before immersion and the value of the mass M2 of the measurement object after immersion and drying, the gel fraction was calculated by the following formula. · Gel fraction (mass%) = (M2 / M1) × 100

[0081] [Measurement of Adhesion Force] After peeling off the release liner from the adhesive sheet obtained in each example, the exposed adhesive surface was pressure-bonded to a polyethylene plate as an adherend at room temperature (23°C) by reciprocating a roller weighing 2 kg once based on JIS Z 0237:2009. After pressure-bonding, the sample left standing for 30 minutes in an environment of 23°C and 50% RH (relative humidity) was used as the adhesion force measurement sample. The adhesion force measurement sample prepared above was measured for adhesion force at a pulling speed of 300 mm / min by the 180° peeling method at 23°C and 50% RH (relative humidity) using a tensile testing machine (manufactured by A&D Company, Limited, product name "Tensilon (registered trademark)") based on JIS Z 0237:2009.

[0082] [Evaluation of Holding Power] The holding power of the adhesive sheet was measured according to the following procedure in accordance with JIS Z 0237:2009. The adhesive sheet obtained in each example was cut into strips 25 mm wide, the release liner was peeled off, and the adhesive surface of the exposed adhesive sheet was pressure-bonded to a stainless steel plate as an adherend by reciprocating a roller weighing 2 kg five times based on JIS Z 0237:2009. After pressure-bonding, the sample left standing for 15 minutes in an environment of 23°C and 50% RH (relative humidity) was used as the holding power measurement sample. The holding power measurement sample prepared above was transferred into a constant temperature layer at 40°C, a weight was attached to the adhesive sheet so that a constant load of 1 kgf was applied in the vertical direction, and it was tested for a maximum of 30,000 seconds, and the holding power of the adhesive sheet was evaluated according to the following criteria. A: No displacement or dropping of the adhesive sheet occurred 30,000 seconds after the start of the test. F: Within 30,000 seconds after the start of the test, the adhesive layer underwent cohesive failure and the adhesive sheet dropped.

[0083] [Measurement of Haze] The release liner was peeled off from the pressure-sensitive adhesive sheet obtained in each example, and the exposed pressure-sensitive adhesive layer was bonded to glass to obtain a measurement sample. For the above measurement sample, haze (%) was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000") in accordance with JIS K7136:2000.

[0084]

Table 1

[0085] From Table 1, it can be seen that the pressure-sensitive adhesive sheets obtained in Examples 1 to 5 have good adhesive strength, and no displacement or dropping occurred in the holding force test, indicating that they have high holding force. On the other hand, in Comparative Example 1 where no tackifier was added, sufficient adhesive strength could not be obtained. For the pressure-sensitive adhesive sheets of Comparative Examples 2 to 5 where (B1) a styrene-based resin was not used as the tackifier, the holding force was inferior in all cases.

Explanation of Symbols

[0086] 1 Energy ray crosslinkable pressure-sensitive adhesive composition layer 2, 2a, 2b Release liner 3 Pressure-sensitive adhesive layer 4 Substrate 10a, 20a, 30a First pressure-sensitive adhesive sheet 10b, 20b, 30b Second pressure-sensitive adhesive sheet

Claims

1. (A) an acrylic resin having energy ray crosslinkability, and (B) a tackifier, and containing, the (A) acrylic resin having energy ray crosslinkability has an energy ray reactive group that generates radicals upon irradiation with energy rays, the (B) tackifier contains one or more selected from the group consisting of (B1) a styrene resin, (B2) a hydrogenated terpene phenol resin, and (B3) a hydrogenated rosin resin, the content of the (B1) styrene resin is 10 to 35 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy ray crosslinkability, the total content of the (B) tackifier is 20 to 40 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy ray crosslinkability, the content of one or more selected from the group consisting of the (B2) hydrogenated terpene phenol resin and the (B3) hydrogenated rosin resin is 5 to 30 parts by mass with respect to 100 parts by mass of the (A) acrylic resin having energy ray crosslinkability, an energy ray crosslinkable pressure-sensitive adhesive composition.

2. The energy ray crosslinkable pressure-sensitive adhesive composition according to claim 1, wherein the (A) acrylic resin having energy ray crosslinkability is an acrylic resin having a benzophenone structure in a side chain.

3. The energy ray crosslinkable pressure-sensitive adhesive composition according to claim 1 or 2, wherein the (B1) styrene resin is a homopolymer of a styrene monomer.

4. An adhesive sheet having an energy ray crosslinkable pressure-sensitive adhesive composition layer made of the energy ray crosslinkable pressure-sensitive adhesive composition according to any one of claims 1 to 3 on a substrate or a release liner.

5. A method for producing the adhesive sheet according to claim 4, obtaining the energy ray crosslinkable pressure-sensitive adhesive composition by melt-kneading the (A) acrylic resin having energy ray crosslinkability and the (B) tackifier, forming the energy ray crosslinkable pressure-sensitive adhesive composition layer by melt-coating the energy ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner, a method for producing an adhesive sheet.

6. A crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray crosslinkable pressure-sensitive adhesive composition according to any one of claims 1 to 3 with energy rays.

7. The crosslinked pressure-sensitive adhesive according to claim 6, having a gel fraction of 30 to 85% by mass.

8. The crosslinked pressure-sensitive adhesive according to claim 6 or 7, wherein the haze measured in accordance with JIS K 7136:2000 is 8% or less.

9. A method for producing a crosslinked pressure-sensitive adhesive according to any one of claims 6 to 8, The method for producing a crosslinked pressure-sensitive adhesive, comprising a step of irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition with energy rays.

10. An adhesive sheet having an adhesive layer made of the crosslinked pressure-sensitive adhesive according to any one of claims 6 to 8 on a substrate or a release liner.

11. A method for producing the adhesive sheet according to claim 10, The method for producing an adhesive sheet, comprising: forming an energy-ray crosslinkable pressure-sensitive adhesive composition layer made of the energy-ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner; and irradiating the energy-ray crosslinkable pressure-sensitive adhesive composition layer with energy rays. The method for producing an adhesive sheet.

12. The energy-ray crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) acrylic resin having energy-ray crosslinkability and the (B) tackifier, and The method for producing an adhesive sheet according to claim 11, wherein the energy-ray crosslinkable pressure-sensitive adhesive composition layer is formed by melt-coating the energy-ray crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner.

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