Energy ray-crosslinkable adhesive composition, crosslinked adhesive, adhesive sheet, and production methods therefor
Patent Information
- Application Number
- JP2024512639
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2024-08-29
- Publication Date
- 2024-12-17
Abstract
Description
Energy ray crosslinkable adhesive composition, crosslinked adhesive, adhesive sheet, and methods for producing the same
[0001] The present invention relates to an energy ray-crosslinkable pressure-sensitive adhesive composition, a crosslinked pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and methods for producing these.
[0002] Pressure-sensitive adhesive sheets are used in a wide range of industrial applications, including labels for displaying various information, fixing or temporarily fixing parts in fields such as office automation equipment, home appliances, automobiles, and construction, and masking. Hot-melt pressure-sensitive adhesives are widely used as pressure-sensitive adhesive sheets. They can be easily applied to substrates by heating and melting without the use of solvents, offering the excellent advantage of reducing the environmental impact of producing pressure-sensitive adhesive sheets. Synthetic rubber-based hot-melt pressure-sensitive adhesives are widely known as hot-melt pressure-sensitive adhesives. In addition, due to the growing need for reduced environmental impact, development of acrylic hot-melt pressure-sensitive adhesives has also been progressing in recent years (see, for example, Patent Document 1). Pressure-sensitive adhesives, including hot-melt pressure-sensitive adhesives, may require cohesive strength. One method for imparting cohesive strength is to crosslink the pressure-sensitive adhesive by irradiating it with energy rays. For example, Patent Documents 2 and 3 disclose pressure-sensitive adhesives that abstract hydrocarbons from an acrylic resin using a hydrogen abstraction photoinitiator to generate radicals in the acrylic resin, which then undergo a coupling reaction to promote a crosslinking reaction.
[0003] JP 2021-130760 A JP 2011-140576 A JP 2016-169304 A
[0004] However, when a low molecular weight hydrogen abstraction photoinitiator is used as in the pressure-sensitive adhesives of Patent Documents 2 and 3, low molecular weight compounds generated by a radical coupling reaction of the photoinitiator during the crosslinking reaction remain, and when the pressure-sensitive adhesive sheet is attached to an adherend and then peeled off, there is a risk of contamination of the adherend, such as traces (cloudiness, ghost) of the attachment of the pressure-sensitive adhesive sheet originating from the low molecular weight compounds remaining on the adherend.
[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an energy ray-crosslinkable pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive having good adhesive strength and causing little contamination of adherends, a pressure-sensitive adhesive sheet using the energy ray-crosslinkable pressure-sensitive adhesive composition, a crosslinked pressure-sensitive adhesive obtained by crosslinking the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays and a method for producing the crosslinked pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet using the crosslinked pressure-sensitive adhesive and a method for producing the crosslinked pressure-sensitive adhesive.
[0006] The present inventors have found that the above-mentioned problems can be solved by using a (meth)acrylic resin and an acrylic resin having a specific structure, and have thus completed the present invention. That is, the present invention provides the following [1] to
[11] . [1] An energy ray-crosslinkable pressure-sensitive adhesive composition containing (A) a (meth)acrylic resin that is not energy ray-crosslinkable and (B) an acrylic resin that is energy ray-crosslinkable. [2] The energy ray-crosslinkable pressure-sensitive adhesive composition according to [1] above, in which the content of the (B) energy ray-crosslinkable acrylic resin is 5 to 90 parts by mass per 100 parts by mass of the (A) non-energy ray-crosslinkable (meth)acrylic resin. [3] The energy ray-crosslinkable pressure-sensitive adhesive composition according to [1] or [2] above, in which the (B) energy ray-crosslinkable acrylic resin is an acrylic resin having a benzophenone structure in a side chain. [4] The energy ray-crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [3] above, wherein the glass transition temperature of the (A) non-energy ray-crosslinkable (meth)acrylic resin is 0°C or lower, and the glass transition temperature of the (B) energy ray-crosslinkable acrylic resin is 0°C or lower. [5] A pressure-sensitive adhesive sheet having an energy ray-crosslinkable pressure-sensitive adhesive composition layer formed on a substrate or a release liner, the energy ray-crosslinkable pressure-sensitive adhesive composition being the energy ray-crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [4] above. [6] A method for producing the pressure-sensitive adhesive sheet according to [5] above, comprising melt-kneading the (A) non-energy ray-crosslinkable (meth)acrylic resin and the (B) energy ray-crosslinkable acrylic resin, and melt-coating the energy ray-crosslinkable pressure-sensitive adhesive composition on the substrate or the release liner to form the energy ray-crosslinkable pressure-sensitive adhesive composition layer. [7] A crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition according to any one of [1] to [4] above with energy rays. [8] A method for producing the crosslinked pressure-sensitive adhesive according to the above-mentioned [7], comprising a step of irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays. [9] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the crosslinked pressure-sensitive adhesive according to the above-mentioned [7] on a substrate or a release liner.
[10] A method for producing the pressure-sensitive adhesive sheet described in [9] above, comprising the steps of: forming an energy ray-crosslinkable pressure-sensitive adhesive composition layer composed of the energy ray-crosslinkable pressure-sensitive adhesive composition on the substrate or release liner; and irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition layer with energy rays.
[11] A method for producing the pressure-sensitive adhesive sheet described in
[10] above, wherein the energy ray-crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) non-energy ray-crosslinkable (meth)acrylic resin and the (B) energy ray-crosslinkable acrylic resin, and melt-coating the energy ray-crosslinkable pressure-sensitive adhesive composition on the substrate or release liner to form the energy ray-crosslinkable pressure-sensitive adhesive composition layer.
[0007] 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 causing little contamination of adherends, a pressure-sensitive adhesive sheet using the energy ray-crosslinkable pressure-sensitive adhesive composition, a crosslinked pressure-sensitive adhesive obtained by crosslinking the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays and a method for producing the crosslinked pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet using the crosslinked pressure-sensitive adhesive and a method for producing the crosslinked pressure-sensitive adhesive.
[0008] It is a schematic cross-sectional view showing one example of the configuration of the pressure-sensitive adhesive sheet of the present invention.It is a schematic cross-sectional view showing another example of the configuration of the pressure-sensitive adhesive sheet of the present invention.It is a schematic cross-sectional view showing another example of the configuration of the pressure-sensitive adhesive sheet of the present invention.
[0009] In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower limit and upper limit values described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."
[0010] As used herein, "energy rays" refers to electromagnetic waves or charged particle beams that have an energy quantum, and examples thereof include ultraviolet rays, radioactive rays, and electron beams. Ultraviolet rays can be irradiated using, for example, an electrodeless lamp, a high-pressure mercury lamp, a metal halide lamp, a UV-LED, or the like as an ultraviolet light source. Electron beams can be irradiated using electron beam accelerators or the like. Among the above-mentioned energy rays, ultraviolet rays are preferred as the energy rays in one embodiment of the present invention. As used herein, "energy ray crosslinkability" refers to the property of forming a crosslinked structure by irradiation with energy rays.
[0011] In addition, in this specification, "(meth)acrylic" is used as a term meaning either or both of "acrylic" or "methacrylic". Similarly, "(meth)acrylate" is used as a term meaning either or both of "acrylate" or "methacrylate". Furthermore, in this specification, "weight average molecular weight (Mw)" is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene, specifically, a value measured based on the method described in the examples. The mechanism of action described in this specification is speculation and does not limit the mechanism by which the effects of the present invention are achieved.
[0012] [Energy ray-crosslinkable pressure-sensitive adhesive composition] The energy ray-crosslinkable pressure-sensitive adhesive composition according to one embodiment of the present invention is an energy ray-crosslinkable pressure-sensitive adhesive composition containing (A) a (meth)acrylic resin that is not energy ray-crosslinkable (hereinafter also referred to as "(A) non-energy ray-crosslinkable (meth)acrylic resin" or simply "component (A)") and (B) an energy ray-crosslinkable acrylic resin (hereinafter also referred to as "(B) energy ray-crosslinkable acrylic resin" or simply "component (B)"). The energy ray-crosslinkable pressure-sensitive adhesive composition (hereinafter also referred to simply as "pressure-sensitive adhesive composition") forms a crosslinked structure upon irradiation with energy rays, thereby forming a crosslinked pressure-sensitive adhesive. That is, the pressure-sensitive adhesive composition is a composition that is intended to be irradiated with energy rays before or after being attached to an adherend. The pressure-sensitive adhesive composition can be irradiated with energy rays at any time. Therefore, the pressure-sensitive adhesive composition has a high degree of freedom in its production method and usage method. Specifically, since the pressure-sensitive adhesive composition does not have an intentional crosslinked structure, it can be heated and melted, making it suitable as a hot-melt pressure-sensitive adhesive. Furthermore, since the pressure-sensitive adhesive composition does not have an intentional crosslinked structure, it has excellent shape conformability. Therefore, the pressure-sensitive adhesive composition can also be used in applications where it is applied to an adherend having a step or the like, and then a crosslinked pressure-sensitive adhesive is formed by energy ray irradiation. Next, each component contained in the pressure-sensitive adhesive composition will be described in detail.
[0013] <(A) Energy ray non-crosslinkable (meth)acrylic resin> The (A) energy ray non-crosslinkable (meth)acrylic resin is not particularly limited as long as it is a (meth)acrylic resin that is not energy ray crosslinkable. However, from the viewpoint of suppressing an increase in viscosity when the pressure-sensitive adhesive composition is continuously heated at high temperatures, it is preferable that the resin does not have a radical polymerizable unsaturated double bond. The (A) energy ray non-crosslinkable (meth)acrylic resin may be used alone or in combination of two or more.
[0014] The (A) non-energy ray crosslinkable (meth)acrylic resin is a polymer containing an acrylic monomer as a monomer component, and is not particularly limited as long as it is not energy ray crosslinkable, but preferably contains a structural unit derived from an alkyl(meth)acrylate. As the alkyl(meth)acrylate used in component (A), for example, an alkyl(meth)acrylate in which the alkyl group has 1 to 18 carbon atoms is suitably used. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.
[0015] The content of the (A) non-energy ray-crosslinkable (meth)acrylic resin in the pressure-sensitive adhesive composition according to one embodiment of the present invention may be 40 to 95 mass %, 50 to 90 mass %, or 60 to 85 mass %, relative to the total amount (100 mass %) of the pressure-sensitive adhesive composition.
[0016] The glass transition temperature (Tg) of the (meth)acrylic resin (A) not having energy ray crosslinkability is usually 0°C or lower, preferably -20°C or lower, and more preferably -30°C or lower. A glass transition temperature (Tg) of 0°C or lower makes it easier for adhesive performance to be exhibited, a glass transition temperature (Tg) of -20°C or lower makes it possible to obtain sufficient adhesive strength when applied in a low-temperature environment, and a glass transition temperature (Tg) of -30°C or lower makes it possible to obtain even more sufficient adhesive strength. Here, the glass transition temperature (Tg) refers to a value measured in accordance with JIS K 7121:1987 using a differential scanning calorimeter at a temperature rise rate of 20°C / min.
[0017] <(B) Energy ray-crosslinkable acrylic resin> The (B) energy ray-crosslinkable acrylic resin is not particularly limited as long as it is an acrylic resin having energy ray crosslinkability. One type of (B) energy ray-crosslinkable acrylic resin may be used alone, or two or more types may be used in combination.
[0018] Examples of the (B) energy ray-crosslinkable acrylic resin include acrylic resins having energy ray-reactive groups that react upon energy ray irradiation and contribute to the formation of a crosslinked structure. Examples of the energy ray-reactive group include groups that are excited by energy ray irradiation to generate radicals that trigger the crosslinking reaction. 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, the (B) energy ray-crosslinkable acrylic resin preferably has a benzophenone structure in its side chain. When the (B) energy ray-crosslinkable acrylic resin has a benzophenone structure, for example, upon energy ray irradiation, the benzophenone structure abstracts a hydrogen atom from a hydrocarbon group contained in the side chain of the acrylic resin, and the resulting radical recombines to form a crosslinked structure. It should be noted that the energy ray-reactive group is preferably introduced into the side chain of the acrylic resin from the viewpoint of facilitating the formation of a crosslinked structure. That is, the energy ray crosslinkable acrylic resin (B) is preferably an acrylic resin having a benzophenone structure in the side chain.
[0019] The content of the energy ray reactive group in the energy ray cross-linkable acrylic resin (B) is preferably 0.02 to 5.0 mass%, more preferably 0.05 to 3.0 mass%, based on the total amount (100 mass%) of the energy ray cross-linkable acrylic resin (B).
[0020] The acrylic resin is a polymer containing an acrylic monomer as a monomer component, and is not particularly limited as long as it is energy ray crosslinkable, but preferably contains a structural unit derived from an alkyl(meth)acrylate. Examples of the alkyl(meth)acrylate used in component (B) 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, and lauryl(meth)acrylate. Among these, alkyl(meth)acrylates in which the alkyl group has 1 to 8 carbon atoms are preferred, and 2-ethylhexyl(meth)acrylate, methyl(meth)acrylate, and n-butyl(meth)acrylate are more preferred. The energy ray reactive group may be introduced into component (B) by, for example, copolymerizing a monomer having a functional group, such as a vinyl group, reactive with the acrylic monomer and also having the energy ray reactive group, with the acrylic monomer. Alternatively, the energy ray reactive group may be introduced by reacting a compound having the energy ray reactive group with the side chain of an acrylic resin by a known method.
[0021] The content of the component (B) in the pressure-sensitive adhesive composition is preferably 5 to 90 parts by mass relative to 100 parts by mass of the component (A), and from the viewpoint of adhesiveness, is more preferably 10 to 80 parts by mass, even more preferably 15 to 50 parts by mass, and still more preferably 15 to 30 parts by mass.
[0022] Furthermore, from the viewpoint of making it easier to achieve the effects of the present invention, the total content of the component (A) and the component (B) is preferably 60% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more, and is 100% by mass or less, based on 100% by mass of the total amount of the pressure-sensitive adhesive composition.
[0023] The glass transition temperature (Tg) of the energy ray-crosslinkable acrylic resin (B) is preferably 0°C or lower, more preferably -20°C or lower, and even more preferably -30°C or lower. When the glass transition temperature (Tg) is within this range, sufficient adhesive strength can be obtained even when applied in a low-temperature environment. Here, the glass transition temperature (Tg) refers to a value measured in accordance with JIS K 7121:1987 using a differential scanning calorimeter at a temperature rise rate of 20°C / min.
[0024] <Other Components> The pressure-sensitive adhesive composition may or may not contain other components in addition to the above-mentioned components. Examples of other components include tackifiers, softeners, antioxidants, and pressure-sensitive adhesive additives used in general pressure-sensitive adhesives. These other components may be used alone or in combination of two or more. In the present invention, the pressure-sensitive adhesive composition does not contain (C) a low-molecular-weight (Mw: 1000 or less) hydrogen abstraction photoinitiator. When the pressure-sensitive adhesive composition contains the component (C), when the low-molecular-weight hydrogen abstraction photoinitiator crosslinks the components (A) with each other, the components (B) with each other, or the components (A) and (B), a low-molecular-weight compound that causes contamination of the adherend is generated as a by-product by a radical coupling reaction of the component (C). Examples of low-molecular-weight hydrogen abstraction photoinitiators include aromatic ketones such as acetophenone, benzophenone, P,P'-dimethoxybenzophenone, 4-methylbenzophenone, P,P'-dichlorobenzophenone, P,P'-dimethylbenzophenone, acetonaphthone, etc. Other examples include aromatic aldehydes such as terephthalaldehyde, and quinone-based aromatic compounds such as methylanthraquinone.
[0025] The tackifier is not particularly limited, and any conventionally known tackifier can be used, such as rosin-based resins, terpene-based resins, petroleum resins, and styrene-based resins.
[0026] The antioxidant is not particularly limited, and conventionally known antioxidants can be used, such as hindered phenol-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.
[0027] Examples of adhesive additives used in the above-mentioned general adhesives include waxes, fillers, extenders, heat stabilizers, light stabilizers, UV absorbers, colorants (pigments, dyes, etc.), flame retardants, antistatic agents, stringing inhibitors, antioxidants, inorganic particles, organic particles, and weight-reducing agents. These adhesive additives may be used alone or in combination of two or more. When these adhesive additives are contained, the content of each adhesive additive is preferably 0.0001 to 20 parts by mass, more preferably 0.0001 to 10 parts by mass, per 100 parts by mass of the total of (A) the non-energy ray-crosslinkable (meth)acrylic resin and (B) the energy ray-crosslinkable acrylic resin.
[0028] Furthermore, when the pressure-sensitive adhesive composition further contains, in addition to the component (A) and the component (B), one or more types selected from the other components, the total content of the component (A) and the component (B) and one or more types selected from the other components is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, and is 100% by mass or less, based on 100% by mass of the total amount of the pressure-sensitive adhesive composition.
[0029] <Method for producing pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition can be produced, for example, by a method of melt-kneading (A) a (meth)acrylic resin not having energy ray crosslinkability, (B) an acrylic resin having energy ray crosslinkability, and any optional components used as needed. In the following description, the step of melt-kneading (A) a (meth)acrylic resin not having energy ray crosslinkability, (B) an acrylic resin having energy ray crosslinkability, etc., may be referred to as a "melt-kneading step."
[0030] The melt-kneading step is, for example, a step in which each component is charged into a mixer equipped with a heating device such as a heated kneader, and the components are mixed in a molten state. Examples of mixers equipped with a heating device include a single-screw extruder, a twin-screw extruder, a roll mill, a Banbury mixer, an intermix, and a pressure kneader. When a mixer capable of reducing pressure is used, the inside of the mixer may be reduced in pressure as necessary, and the components may be melt-kneaded under reduced pressure.
[0031] The kneading temperature in the melt-kneading step is not particularly limited, and may be appropriately selected so that the components are sufficiently mixed in a molten state. The kneading temperature is preferably 80 to 180°C, more preferably 100 to 170°C, and even more preferably 120 to 150°C.
[0032] In addition, when the pressure-sensitive adhesive composition is produced by melt-kneading, the pressure-sensitive adhesive composition does not need to contain a solvent, and from the viewpoint of reducing the environmental load, it is preferable that the pressure-sensitive adhesive composition is substantially free of solvent, and more preferably free of solvent. Here, the pressure-sensitive adhesive composition being "substantially free of solvent" means, for example, that the content of the solvent is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, relative to 100% by mass of the total amount of the pressure-sensitive adhesive composition.
[0033] The PSA composition obtained after the melt-kneading step may be applied in a heated and molten state onto a substrate or a release liner using an extruder or the like, and used to produce a PSA sheet, which is one embodiment of the present invention, as described below, or, as desired, may be filled into various containers or the like without undergoing a molding step, for example.
[0034] [Crosslinked Pressure-Sensitive Adhesive] The crosslinked pressure-sensitive adhesive of one embodiment of the present invention is a crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition of one embodiment of the present invention with energy rays. That is, the crosslinked pressure-sensitive adhesive has a crosslinked structure formed by an energy ray crosslinking reaction of the energy ray-crosslinkable acrylic resin (B) contained in the energy ray-crosslinkable pressure-sensitive adhesive composition. The crosslinked pressure-sensitive adhesive itself also has good adhesive strength, and can also exhibit excellent adhesive strength to an adherend. For example, from the viewpoint of eliminating the need for an energy ray irradiation step after application to an adherend, an embodiment may be such that the pressure-sensitive adhesive composition is irradiated with energy rays before application to an adherend to form the crosslinked pressure-sensitive adhesive, and then the pressure-sensitive adhesive composition is applied to the adherend as a crosslinked pressure-sensitive adhesive.
[0035] The crosslinked pressure-sensitive adhesive can be produced by irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays. In the following description, the step of irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays may be referred to as the "energy ray irradiation step."
[0036] [Adhesive Sheet] As one aspect of the present invention, the following first and second adhesive sheets can be provided. The first adhesive sheet is an adhesive sheet having an energy ray-crosslinkable adhesive composition layer comprising the energy ray-crosslinkable adhesive composition on a substrate or a release liner. In the following description, the "energy ray-crosslinkable adhesive composition layer comprising the energy ray-crosslinkable adhesive composition" of the first adhesive sheet is also simply referred to as the "adhesive composition layer". Furthermore, the "adhesive layer comprising the crosslinked adhesive" of the second adhesive sheet is also simply referred to as the "adhesive layer". Furthermore, when simply referred to as the "adhesive sheet", it refers to both the first adhesive sheet and the second adhesive sheet.
[0037] Next, an example of the configuration of the pressure-sensitive adhesive sheet according to one embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following example.
[0038] FIG. 1( a ) shows, as an example of a first pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet 10a having a release liner 2 on one side of a pressure-sensitive adhesive composition layer 1 and a substrate 4 on the other side of the pressure-sensitive adhesive composition layer 1. FIG. 1( b ) shows, as an example of a second pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet 10b having a release liner 2 on one side of a pressure-sensitive adhesive layer 3 and a substrate 4 on the other side of the pressure-sensitive adhesive layer 3. The pressure-sensitive adhesive sheets 10a and 10b are suitable for applications in which, for example, the release liner 2 is peeled off and removed, and the exposed surface of the pressure-sensitive adhesive composition layer 1 or pressure-sensitive adhesive layer 3 is then attached to an adherend. Examples of such applications include label applications. When the pressure-sensitive adhesive sheet to be attached to an adherend is the first pressure-sensitive adhesive sheet, after attachment to the adherend, the pressure-sensitive adhesive composition layer is irradiated with energy rays to form a pressure-sensitive adhesive layer comprising the crosslinked pressure-sensitive adhesive.
[0039] Figure 2(a) shows, as another example of the first PSA sheet, a double-sided PSA sheet 20a having PSA composition layers 1 on both sides of a substrate 4, with a release liner 2a on the side of one PSA composition layer 1 opposite the substrate 4, and a release liner 2b on the side of the other PSA composition layer 1 opposite the substrate 4. Figure 2(b) also shows, as another example of the second PSA sheet, a double-sided PSA sheet 20b having PSA layers 3 on both sides of a substrate 4, with a release liner 2a on the side of one PSA layer 3 opposite the substrate 4, and a release liner 2b on the side of the other PSA layer 3 opposite the substrate 4.
[0040] Figure 3(a) shows, as another example of the first PSA sheet, a substrate-less PSA sheet 30a having release liners 2a and 2b on both sides of a PSA composition layer 1. Figure 3(b) shows, as another example of the second PSA sheet, a substrate-less PSA sheet 30b having release liners 2a and 2b on both sides of a PSA layer 3.
[0041] The PSA sheets 20a, 20b, 30a, and 30b are suitable for bonding adherends together, for example, by peeling and removing the release liner 2a on one side, then attaching the exposed side of the PSA composition layer 1 or PSA layer 3 to an adherend, and then peeling and removing the release liner 2b, and then attaching the exposed side of the PSA composition layer 1 or PSA layer 3 to another adherend. Examples of such uses include applications for fixing or temporarily fixing various components. In the PSA sheets 30a and 30b, if the peel force when peeling the release liner 2a from the PSA composition layer 1 or PSA layer 3 is similar to the peel force when peeling the release liner 2b from the PSA composition layer 1 or PSA layer 3, then attempting to peel both release liners outward may result in the PSA composition layer 1 or PSA layer 3 being torn apart and peeled off along with the two release liners. In order to prevent such a phenomenon, it is preferable to use two types of release liners 2a, 2b that are designed to have different release forces.
[0042] The thickness of the pressure-sensitive adhesive composition layer in the first pressure-sensitive adhesive sheet and the thickness of the pressure-sensitive adhesive layer in the second pressure-sensitive adhesive sheet are each independently preferably 5 to 100 μm, more preferably 10 to 60 μm, and even 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. Furthermore, 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 more easily improved.
[0043] <Substrate> Examples of materials for forming the substrate include resins, metals, and paper materials. Examples of resins 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; polyether ether ketone; polyether sulfone; polyphenylene sulfide; polyimide resins such as polyetherimide and polyimide; polyamide resins; acrylic resins; and fluorine-based resins. Examples of metals include aluminum, tin, chromium, and titanium. Examples of paper materials include tissue paper, medium-grade paper, wood-free paper, impregnated paper, coated paper, art paper, parchment paper, and glassine paper.
[0044] The substrate may be made of one material or two or more materials. Examples of substrates made of two or more materials include a paper laminated with a thermoplastic resin such as polyethylene, and a resin film or sheet having a metal film formed on the surface thereof. Examples of methods for forming the metal layer include a method of depositing the metal by a PVD method such as vacuum deposition, sputtering, or ion plating, or a method of attaching a metal foil made of the metal using a general adhesive.
[0045] In addition, from the viewpoint of improving the interlayer adhesion between the substrate and another layer to be laminated thereon, when the substrate contains a resin, the surface of the substrate may be subjected to a surface treatment such as an oxidation method or a roughening method, or a primer treatment.
[0046] Depending on the application of the pressure-sensitive adhesive sheet, the substrate may have, for example, an easy-adhesion layer for facilitating printing, a recording layer for enabling recording such as thermal transfer recording or ink jet recording, an overcoat film or overlaminate film for protecting the surface thereof, an information region for magnetic recording, a barcode, a microsemiconductor element, etc. On the other hand, when the pressure-sensitive adhesive sheet is to be a transparent pressure-sensitive adhesive sheet having transparency, the substrate is preferably transparent.
[0047] The substrate may contain a substrate additive as needed. Examples of the substrate additive include an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a slip agent, an antiblocking agent, and a colorant. These substrate additives may be used alone or in combination of two or more.
[0048] The thickness of the substrate is preferably 5 to 1,000 μm, more preferably 15 to 500 μm, and even more preferably 20 to 200 μm. When the thickness of the substrate 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 substrate 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 substrate" refers to the thickness of the entire substrate, and when the substrate is a substrate made up of multiple layers, it refers to the total thickness of all layers constituting the substrate.
[0049] <Release Liner> Examples of release liners include double-sided release-treated release liners and single-sided release liners, and examples thereof include release liner substrates coated with a release agent. Examples of release liner substrates include paper such as fine paper, glassine paper, and kraft paper; polyester resin films such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin; and plastic films such as polyolefin resin films such as polypropylene resin and polyethylene resin. Examples of release agents include rubber elastomers such as silicone resins, olefin resins, isoprene resins, and butadiene resins; long-chain alkyl resins, alkyd resins, and fluorine-based resins. The thickness of the release liner is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 10 to 200 μm, more preferably 20 to 180 μm, and even more preferably 30 to 150 μm.
[0050] [Method for producing first pressure-sensitive adhesive sheet] The method for producing the first pressure-sensitive adhesive sheet is, for example, a method for producing a pressure-sensitive adhesive sheet, in which the pressure-sensitive adhesive composition is obtained by melt-kneading (A) a (meth)acrylic resin and (B) an energy-ray-crosslinkable acrylic resin, and the energy-ray-crosslinkable pressure-sensitive adhesive composition is melt-coated on a substrate or a release liner to form an energy-ray-crosslinkable pressure-sensitive adhesive composition layer. In the following description, the step of melt-coating the energy-ray-crosslinkable pressure-sensitive adhesive composition on a substrate or a release liner to form an energy-ray-crosslinkable pressure-sensitive adhesive composition layer may be referred to as the "pressure-sensitive adhesive composition layer forming step." In addition, in this specification, "on a release liner" means on the release-treated surface when the release liner is one-sided release-treated.
[0051] In the first method for producing a pressure-sensitive adhesive sheet, the step of melt-kneading (A) the (meth)acrylic resin and (B) the energy ray-crosslinkable acrylic resin is as described in the melt-kneading step in the method for producing a pressure-sensitive adhesive composition that is one aspect of the present invention.
[0052] The pressure-sensitive adhesive composition layer forming step may be a method in which the energy ray-crosslinkable pressure-sensitive adhesive composition obtained after the melt-kneading step is applied in a heated and molten state onto a substrate or a release liner using an extruder, a T-die, etc. Thereafter, if necessary, a step of cooling the pressure-sensitive adhesive composition layer may be included.
[0053] The above-mentioned PSA composition layer forming step can form a PSA composition layer on a substrate or a release liner. A sheet having the substrate or release liner and the PSA composition layer can be used as is as a first PSA sheet, which is one embodiment of the present invention, or can be subjected to other steps as necessary to form a desired PSA sheet configuration. For example, by attaching the release-treated side of a release liner to the exposed surface of the PSA composition layer formed on the substrate, a PSA sheet having a release liner on one side of the PSA composition layer and a substrate on the other side of the PSA composition layer can be produced, as in PSA sheet 10a shown in FIG. 1(a). Furthermore, by attaching the substrate side of PSA sheet 10a to the exposed surface of the PSA composition layer formed on the release liner, a double-sided PSA sheet can be produced, as in PSA sheet 20a shown in FIG. 2(a), having PSA composition layers on both sides of the substrate and a release liner on the side of each PSA composition layer opposite the substrate. Furthermore, by attaching the release-treated surface of another release liner to the exposed surface of the pressure-sensitive adhesive composition layer formed on a release liner, a substrate-less pressure-sensitive adhesive sheet having release liners on both sides of the pressure-sensitive adhesive composition layer, such as the pressure-sensitive adhesive sheet 30a shown in Figure 3(a), can be produced.
[0054] [Method for producing second pressure-sensitive adhesive sheet] The method for producing the second pressure-sensitive adhesive sheet is a method for producing a pressure-sensitive adhesive sheet, which includes, for example, the steps of forming an energy ray-crosslinkable pressure-sensitive adhesive composition layer made of the energy ray-crosslinkable pressure-sensitive adhesive composition on a substrate or a release liner, and irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition layer with energy rays.
[0055] In the second method for producing a pressure-sensitive adhesive sheet, the step of forming an energy ray-crosslinkable pressure-sensitive adhesive composition layer is the same as the step of forming a pressure-sensitive adhesive composition layer in the first method for producing a pressure-sensitive adhesive sheet.
[0056] In the step of irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition layer with energy rays in the second method for producing a pressure-sensitive adhesive sheet, the timing of energy ray irradiation is not particularly limited and may be determined appropriately taking into consideration the pressure-sensitive adhesive sheet production method, the desired physical properties, etc. For example, with one surface of the pressure-sensitive adhesive composition layer exposed, the pressure-sensitive adhesive composition layer may be irradiated with energy rays directly or via a substrate or a release liner, or with a substrate or a release liner on one surface of the pressure-sensitive adhesive composition layer and a release liner on the other surface, the pressure-sensitive adhesive composition layer may be irradiated with energy rays via the substrate or release liner.
[0057] The energy ray irradiation may be carried out once or in multiple separate steps. When the energy ray irradiation is carried out in multiple separate steps, for example, a first energy ray irradiation may be carried out with one surface of the pressure-sensitive adhesive composition layer exposed, and then a substrate or a release liner may be attached to that surface, and then a second energy ray irradiation may be carried out through the substrate or release liner. Furthermore, the first energy ray irradiation may be carried out at any time before attachment to the adherend, and then the second energy ray irradiation may be carried out after attachment to the adherend.
[0058] [Uses of 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, which are one embodiment of the present invention, can be used in various applications. Specific examples include label applications; applications for fixing or temporarily fixing various parts; surface protection applications; sealant applications; decorative and display applications; etc. Among these, label applications and applications for fixing or temporarily fixing various parts are preferred.
[0059] The pressure-sensitive adhesive sheet for labeling purposes may be attached directly to various products, or may be attached to the packaging film, packaging container, etc. of various products. Examples of materials constituting packaging films and packaging containers include olefin-based resins such as polypropylene and polyethylene; polyester-based resins such as polyethylene terephthalate (PET) and polylactic acid; glass, paper, metal; and the like. Among these, the pressure-sensitive adhesive sheet of one embodiment of the present invention is suitable for use in attaching to various products and packaging containers made of glass, metal, or polyester-based resin, as it is less likely to leave stains on the adherend after peeling. The pressure-sensitive adhesive sheet for fixing or temporary fixing purposes is suitable for fixing or temporary fixing, for example, electronic components, optical components, automobile parts, mechanical components, architectural components, decorative components, etc.
[0060] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The physical properties in each example were measured by the following methods.
[0061] [Weight-average molecular weight (Mw)] The weight-average molecular weight (Mw) was measured using a gel permeation chromatograph under the following conditions and calculated in terms of standard polystyrene. (Measurement equipment) Measuring device: Product name "HLC-8320GPC", manufactured by Tosoh Corporation Detector: Differential refractometer Column: One "TSK guard column super H-H", two "TSK gel super HM-H" columns in series, and one "TSK gel super H2000" column (all manufactured by Tosoh Corporation) were connected in this order from the inlet side of the measurement sample. (Measurement conditions) Column temperature: 40°C Developing solvent: tetrahydrofuran Flow rate: 1.0 mL / min
[0062] [Glass transition temperature (Tg)] The glass transition temperature (Tg) was measured using a differential scanning calorimeter in accordance with JIS K 7121: 1987. (Measurement sample mass) 10 mg (Measurement equipment) Measurement device: Product name "DSC Q2000", manufactured by TA Instruments Japan (Measurement conditions) Measurement temperature range: -80°C to 50°C Heating rate: 20°C / min
[0063] [Thickness of Each Layer] The thickness was measured at 23° C. using a constant pressure thickness measuring instrument manufactured by Teclock Corporation (model number: PG-02J, standard specifications: compliant with JIS K 6783, Z 1702, Z 1709).
[0064] Details of the materials used in the following examples and comparative examples are as follows:
[0065] <(A) Energy ray non-crosslinkable (meth)acrylic resin> (Meth)acrylic resin: P(BA): poly-n-butyl acrylate, weight average molecular weight Mw: 700,000 <(B) Energy ray crosslinkable acrylic resin> Energy ray crosslinkable acrylic resin: acrylic resin having a benzophenone structure in the side chain, manufactured by BASF, trade name "acResin A204UV" <Other components> Photoinitiator: 4-methylbenzophenone (manufactured by Lambson, trade name "SpeedCure MBP")
[0066] Examples 1 to 3, Comparative Examples 1 and 2 (Production of energy ray-crosslinkable pressure-sensitive adhesive compositions) Component (A) and component (B) were blended in the compositions (unit: parts by mass) shown in Table 1, and kneaded using a heated kneader at 130°C for 20 minutes under nitrogen purging to obtain energy ray-crosslinkable pressure-sensitive adhesive compositions.
[0067] (Production of first pressure-sensitive adhesive sheet) The energy ray-crosslinkable pressure-sensitive adhesive composition obtained above, while still in a heat-molten state, was coated on a transparent polyethylene terephthalate film (thickness: 50 μm) as a substrate using a die coater, thereby obtaining a first pressure-sensitive adhesive sheet having an energy ray-crosslinkable pressure-sensitive adhesive composition layer (thickness: 20 μm) made of the energy ray-crosslinkable pressure-sensitive adhesive composition on the substrate.
[0068] (Production of second pressure-sensitive adhesive sheet) The energy ray-crosslinkable pressure-sensitive adhesive composition layer of the first pressure-sensitive adhesive sheet obtained above was irradiated from the exposed surface with a UV-C region integrated light dose of 30 mJ / cm using a high-pressure mercury lamp (manufactured by Eye Graphics Co., Ltd.). ２The sheet was irradiated with ultraviolet light under the conditions of
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[0069] [Evaluation Method] The second pressure-sensitive adhesive sheets obtained in each example were evaluated by the methods described below.
[0070] [Measurement of Adhesive Strength] After peeling the release liner from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, the exposed adhesive surface was pressed against a stainless steel plate (adherend) at room temperature (23°C) by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237:2009. After pressing, the sheet was left to stand for 30 minutes in an environment of 23°C and 50% RH (relative humidity), and this was used as a sample for measuring adhesive strength. The adhesive strength of the adhesive test sample prepared above was measured at 23°C and 50% RH (relative humidity) using a tensile tester (manufactured by A&D Co., Ltd., product name "Tensilon (registered trademark)") by the 180° peel method at a pulling speed of 300 mm / min in accordance with JIS Z 0237:2009.
[0071] [Evaluation of Adherend Staining] The second pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were cut into 25 mm x 50 mm pieces in an environment of 23°C and 50% RH (relative humidity) to prepare two test pieces for each. The release liners of the test pieces were removed, and the exposed pressure-sensitive adhesive layers were attached to the adherends (stainless steel plates). The test pieces attached to the adherends were then left standing in an environment of 70°C for 7 days, and then left standing in an environment of 23°C and 50% RH for 1 day. One of the test pieces was manually peeled from the adherend in a 180° direction at a speed of approximately 300 mm / min (low-speed peeling) in an environment of 23°C and 50% RH. The other test piece was manually peeled in a 180° direction at a speed of approximately 30 m / min (high-speed peeling). After peeling, the state of each layer of the pressure-sensitive adhesive layer of the test pieces was visually observed, and the contamination of the adherend was confirmed according to the following criteria. No staining: The adhesive layer peels off at the interface with the adherend, and no adhesive remains on the adherend, with no discernible difference from the unadhered area. Cloudy: The adhesive layer peels off at the interface with the adherend, but the adhered area is observed to be whiter than the unadhered area. Cohesive failure: The adhesive layer breaks down, and residue of the adhesive layer is observed on the adherend.
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[0073] As can be seen from Table 1, the pressure-sensitive adhesive sheets obtained in Examples 1 to 3 had good adhesive strength, but in the evaluation of adherend contamination, no traces of the pressure-sensitive adhesive sheet (cloudiness) or cohesive failure occurred, and no adherend contamination occurred. On the other hand, the pressure-sensitive adhesive sheet of Comparative Example 1, which did not use (B) the energy-ray-crosslinkable acrylic resin but used a photoinitiator instead, did show traces of the pressure-sensitive adhesive sheet (cloudiness). Furthermore, the pressure-sensitive adhesive sheet of Comparative Example 2, which did not use (B) the energy-ray-crosslinkable acrylic resin, showed cohesive failure.
[0074] REFERENCE SIGNS LIST 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. An energy ray-crosslinkable pressure-sensitive adhesive composition comprising (A) a (meth)acrylic resin not having energy ray crosslinkability, and (B) an acrylic resin having energy ray crosslinkability.
2. 2. The energy ray-crosslinkable pressure-sensitive adhesive composition according to claim 1, wherein a content of the (B) energy ray-crosslinkable acrylic resin is 5 to 90 parts by mass relative to 100 parts by mass of the (A) non-energy ray-crosslinkable (meth)acrylic resin.
3. 3. The energy ray-crosslinkable pressure-sensitive adhesive composition according to claim 1, wherein the (B) energy ray-crosslinkable acrylic resin is an acrylic resin having a benzophenone structure in a side chain.
4. 3. The energy ray-crosslinkable pressure-sensitive adhesive composition according to claim 1, wherein the (A) (meth)acrylic resin not having energy ray crosslinkability has a glass transition temperature of 0°C or lower, and the (B) acrylic resin having energy ray crosslinkability has a glass transition temperature of 0°C or lower.
5. A pressure-sensitive adhesive sheet comprising a substrate or a release liner and an energy ray-crosslinkable pressure-sensitive adhesive composition layer comprising the energy ray-crosslinkable pressure-sensitive adhesive composition according to claim 1 or 2.
6. A method for producing the pressure-sensitive adhesive sheet according to claim 5, comprising the steps of: The energy ray crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) (meth)acrylic resin not having energy ray crosslinkability and the (B) acrylic resin having energy ray crosslinkability, The method for producing a pressure-sensitive adhesive sheet comprises melt-coating the energy ray-crosslinkable pressure-sensitive adhesive composition onto the substrate or release liner to form the energy ray-crosslinkable pressure-sensitive adhesive composition layer.
7. A crosslinked pressure-sensitive adhesive obtained by irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition according to claim 1 or 2 with energy rays.
8. A method for producing the crosslinked adhesive of claim 7, comprising the steps of: A method for producing a crosslinked pressure-sensitive adhesive, comprising the step of irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition with energy rays.
9. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the crosslinked pressure-sensitive adhesive according to claim 7 on a substrate or a release liner.
10. A method for producing the pressure-sensitive adhesive sheet according to claim 9, comprising the steps of: forming an energy ray crosslinkable pressure-sensitive adhesive composition layer comprising the energy ray crosslinkable pressure-sensitive adhesive composition on the substrate or release liner; and a step of irradiating the energy ray-crosslinkable pressure-sensitive adhesive composition layer with energy rays.
11. The energy ray crosslinkable pressure-sensitive adhesive composition is obtained by melt-kneading the (A) (meth)acrylic resin not having energy ray crosslinkability and the (B) acrylic resin having energy ray crosslinkability, The method for producing a pressure-sensitive adhesive sheet according to claim 10 , wherein the energy ray-crosslinkable pressure-sensitive adhesive composition layer is formed by melt-coating the energy ray-crosslinkable pressure-sensitive adhesive composition onto the substrate or release liner.