Adhesive composition, adhesive, and adhesive sheet

Abstract

Provided is an adhesive composition containing: a (meth)acrylate ester polymer (A) that includes butyl methacrylate and a monomer containing a reactive functional group as monomeric units that constitute the polymer; and an inorganic filler (C). Also provided are an adhesive obtained by cross-linking said adhesive composition, and an adhesive sheet 1 provided with at least an adhesive layer 12, wherein the adhesive layer 12 is formed from said adhesive composition. Said adhesive composition enables the uniform dispersion of the inorganic filler (C) in a short period of time, even without containing a dispersant. Additionally, the adhesive and the adhesive layer 12 of the adhesive sheet 1 have the inorganic filler (C) uniformly dispersed therein.

Description

Technical Field

[0001] The present invention relates to a pressure-sensitive adhesive composition and an adhesive containing an inorganic filler, and a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer containing an inorganic filler.

Background Art

[0002] By adding various fillers, the adhesive can exhibit various functions such as conductivity, thermal conductivity, insulation, mechanical strength, and light diffusibility. Adhesives containing such fillers are used in a wide range of technical fields. For example, Patent Document 1 discloses a filler-containing pressure-sensitive adhesive tape including a pressure-sensitive adhesive resin containing an acrylic polymer and a filler dispersed in the pressure-sensitive adhesive resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional filler-containing pressure-sensitive adhesive layer as disclosed in Patent Document 1, the dispersion of the filler, particularly the inorganic filler, may not be sufficient. When the degree of dispersion of the filler is low, the filler remains aggregated in the pressure-sensitive adhesive layer. In such a pressure-sensitive adhesive layer, not only can the desired functions not be fully exhibited, but also problems such as a decrease in adhesive strength and breaking strength occur.

[0005] In addition, in order to enhance the dispersibility of the filler, a dispersant may be added to the adhesive, but the addition of the dispersant may adversely affect physical properties such as adhesive strength and elongation at break.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a pressure-sensitive adhesive composition in which an inorganic filler can be uniformly dispersed in a short time without containing a dispersant, a pressure-sensitive adhesive in which the inorganic filler is uniformly dispersed, and a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer in which the inorganic filler is uniformly dispersed.

Means for Solving the Problems

[0007] First, in order to achieve the above object, the present invention provides a pressure-sensitive adhesive composition characterized by containing a (meth)acrylic acid ester polymer (A) containing butyl methacrylate and a monomer containing a reactive functional group as monomer units constituting the polymer, and an inorganic filler (C) (Invention 1).

[0008] In the above invention (Invention 1), since the (meth)acrylic acid ester polymer (A) contains butyl methacrylate and a monomer containing a reactive functional group as monomer units constituting the polymer, aggregation of the inorganic filler (C) is suppressed. Thereby, even if the pressure-sensitive adhesive composition does not contain a dispersant, the inorganic filler (C) can be uniformly dispersed in a short time.

[0009] In the above invention (Invention 1), it is preferable that the monomer containing a reactive functional group is a monomer containing a carboxy group (Invention 2).

[0010] In the above invention (Inventions 1 and 2), it is preferable that the inorganic filler (C) is composed of barium sulfate (Invention 3).

[0011] In the above invention (Inventions 1 to 3), it is preferable that the average particle diameter of the primary particles of the inorganic filler (C) is 0.01 μm or more and 10 μm or less (Invention 4).

[0012] In the above invention (Inventions 1 to 4), it is preferable that the pressure-sensitive adhesive composition contains a crosslinking agent (B) (Invention 5).

[0013] Second, the present invention provides a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition (Inventions 1 to 5) (Invention 6).

[0014] Thirdly, the present invention provides an adhesive sheet comprising at least an adhesive layer, wherein the adhesive layer is formed from the above-mentioned adhesive composition (Inventions 1 to 5) (Invention 7).

[0015] In the above invention (Invention 7), it is preferable that the adhesive sheet includes a base material and the adhesive layer provided on one surface side of the base material (Invention 8).

[0016] In the above inventions (Inventions 7 and 8), it is preferable that the thickness of the adhesive layer is 1 μm or more and 50 μm or less (Invention 9).

Advantages of the Invention

[0017] According to the adhesive composition of the present invention, the inorganic filler can be uniformly dispersed in a short time without containing a dispersant. Further, in the adhesive and the adhesive layer of the adhesive sheet according to the present invention, the inorganic filler is uniformly dispersed without containing a dispersant.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described. 〔Adhesive Composition〕 The pressure-sensitive adhesive composition according to this embodiment (hereinafter sometimes referred to as "pressure-sensitive adhesive composition P") contains a (meth)acrylate polymer (A) containing butyl methacrylate and a monomer containing a reactive functional group as monomer units constituting the polymer, and an inorganic filler (C), and preferably further contains a crosslinking agent (B). By the (meth)acrylate polymer (A) containing butyl methacrylate and a monomer containing a reactive functional group as monomer units constituting the polymer, aggregation of the inorganic filler (C) is suppressed. Although the reason is not clear, it is presumed that the bulky structure of butyl methacrylate, the polarity of the monomer containing a reactive functional group, and their behavior in solution are related. By suppressing the aggregation of the inorganic filler (C) as described above, the inorganic filler (C) can be uniformly dispersed in a short time even if the pressure-sensitive adhesive composition P does not contain a dispersant.

[0020] In this specification, (meth)acrylate means both acrylate and methacrylate. The same applies to other similar terms. Also, the concept of "copolymer" is included in "polymer".

[0021] 1. Each component (1) (meth)acrylate polymer (A) The (meth)acrylate polymer (A) contains butyl methacrylate and a monomer containing a reactive functional group as monomer units constituting the polymer.

[0022] Examples of butyl methacrylate include n-butyl methacrylate, isobutyl methacrylate, and t-butyl methacrylate. Among these, n-butyl methacrylate is preferred from the viewpoint of exhibiting excellent dispersibility. These may be used alone or in combination of two or more.

[0023] (Meth)acrylic acid ester polymer (A) preferably contains butyl methacrylate as a monomer unit constituting the polymer in an amount of 1% by mass or more, particularly preferably 5% by mass or more, and more preferably 10% by mass or more. Further, (meth)acrylic acid ester polymer (A) preferably contains butyl methacrylate as a monomer unit constituting the polymer in an amount of 45% by mass or less, more preferably 40% by mass or less, particularly preferably 30% by mass or less, and more preferably 20% by mass or less. When (meth)acrylic acid ester polymer (A) contains butyl methacrylate in the above amounts as monomer units, the dispersibility of inorganic filler (C) becomes more excellent.

[0024] Examples of the reactive functional group-containing monomer include preferably monomers having a carboxy group in the molecule (carboxy group-containing monomers), monomers having a hydroxy group in the molecule (hydroxy group-containing monomers), monomers having an amino group in the molecule (amino group-containing monomers), and the like. Among these, from the viewpoint of exhibiting excellent dispersibility, carboxy group-containing monomers and hydroxy group-containing monomers are preferred, and particularly carboxy group-containing monomers are preferred. These may be used alone or in combination of two or more.

[0025] Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of exhibiting more excellent dispersibility. These may be used alone or in combination of two or more.

[0026] Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These may be used alone or in combination of two or more.

[0027] Examples of the amino group-containing monomer include aminoethyl (meth)acrylate, n-butylaminoethyl (meth)acrylate, and the like. These may be used alone or in combination of two or more.

[0028] The (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 0.5% by mass or more, particularly preferably 1% by mass or more, and more preferably 3% by mass or more, as a monomer unit constituting the polymer. Further, the (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 30% by mass or less, particularly preferably 20% by mass or less, and more preferably 9% by mass or less, as a monomer unit constituting the polymer. When the (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer in the above amount as a monomer unit, the dispersibility of the inorganic filler (C) becomes more excellent.

[0029] The (meth)acrylic acid ester polymer (A) in the present embodiment preferably contains a (meth)acrylic acid alkyl ester other than butyl methacrylate as a monomer unit constituting the polymer, whereby good adhesiveness can be exhibited. The alkyl group may be linear or branched, or may have a cyclic structure.

[0030] As the (meth)acrylic acid alkyl ester other than butyl methacrylate, from the viewpoint of adhesiveness, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group is preferable. Examples of the (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate and the like. Among these, 2-ethylhexyl (meth)acrylate is preferable because it has high adhesiveness and does not inhibit excellent dispersibility in combination with the aforementioned butyl methacrylate and the monomer containing a reactive functional group. These may be used alone or in combination of two or more.

[0031] The (meth)acrylic acid ester polymer (A) preferably contains 50% by mass or more, more preferably 60% by mass or more, particularly preferably 70% by mass or more, and still more preferably 80% by mass or more of a (meth)acrylic acid alkyl ester other than butyl methacrylate as a monomer unit constituting the polymer. When the content of the (meth)acrylic acid alkyl ester other than butyl methacrylate is as described above, the (meth)acrylic acid ester polymer (A) can exhibit suitable adhesiveness. Further, the (meth)acrylic acid ester polymer (A) preferably contains 99% by mass or less, particularly preferably 95% by mass or less, and still more preferably 90% by mass or less of a (meth)acrylic acid alkyl ester other than butyl methacrylate as a monomer unit constituting the polymer. When the content of the (meth)acrylic acid alkyl ester other than butyl methacrylate is as described above, other monomer components can be introduced into the (meth)acrylic acid ester polymer (A) in a suitable amount.

[0032] (Meth)acrylic acid ester polymer (A) may, if desired, contain other monomers other than the above as monomer units constituting the polymer.

[0033] Examples of the other monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, (meth)acrylic acid esters having a non-crosslinkable tertiary amino group such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and (meth)acryloylmorpholine, (meth)acrylamide, dimethylacrylamide, vinyl acetate, styrene, and the like. These may be used alone or in combination of two or more.

[0034] (Meth)acrylic acid ester polymer (A) may be a solution polymerized product, a solventless polymerized product, or an emulsion polymerized product. Among them, it is preferably a solution polymer obtained by a solution polymerization method. By being a solution polymer, it becomes easier to suppress the aggregation of the inorganic filler (C) and to make the dispersibility excellent.

[0035] (Meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer in terms of the polymerization mode.

[0036] The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 50,000 or more as a lower limit value, particularly preferably 250,000 or more, and even more preferably 500,000 or more. Further, the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 2,500,000 or less as an upper limit value, particularly preferably 1,500,000 or less, and even more preferably 950,000 or less. When the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is within the above range, the dispersibility of the inorganic filler (C) becomes more excellent. The weight average molecular weight in this specification is a value in terms of standard polystyrene measured by gel permeation chromatography (GPC) method.

[0037] In the pressure-sensitive adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more.

[0038] (2) Crosslinking agent (B) The crosslinking agent (B) may be any one that reacts with the reactive functional group of the (meth)acrylic acid ester polymer (A). Examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, ammonium salt-based crosslinking agents, and the like. The crosslinking agent (B) may be used alone or in combination of two or more.

[0039] Among the above, when the reactive functional group of the (meth)acrylic acid ester polymer (A) is a carboxy group, it is preferable to use an isocyanate-based crosslinking agent from the viewpoint of reactivity with the carboxy group.

[0040] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and their biuret bodies, isocyanurate bodies, and adduct bodies which are reaction products with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferred.

[0041] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably at least 0.1 part by mass, particularly preferably at least 0.5 part by mass, and more preferably at least 1 part by mass, based on 100 parts by mass of the (meth)acrylate polymer (A). Also, the content is preferably at most 20 parts by mass, particularly preferably at most 15 parts by mass, and more preferably at most 10 parts by mass, as the upper limit. When the content of the crosslinking agent (B) is within the above range, a good crosslinked structure is formed, and the cohesive force of the resulting pressure-sensitive adhesive becomes moderately high.

[0042] (3) Inorganic filler (C) As the inorganic filler (C), those that enable the resulting adhesive layer to exhibit desired functions may be selected. For example, powders such as calcium carbonate, aluminum hydroxide, alumina, titania, silica, boehmite, talc, iron oxide, silicon carbide, barium sulfate, boron nitride, zirconium oxide, etc., beads obtained by spheroidizing these, single crystal fibers, glass fibers, etc. may be mentioned. These may be used alone or in combination of two or more. Among these, alumina, silica or barium sulfate is preferable, and barium sulfate is particularly preferable. Although these inorganic fillers (C) generally have poor dispersibility, they exhibit excellent dispersibility in the adhesive composition P according to the present embodiment.

[0043] Examples of the shape of the inorganic filler (C) include granular, acicular, plate-like, scaly, amorphous, etc. Among the granular ones, there are round, spherical, polygonal, etc. Although generally having poor dispersibility in the case of granular, they exhibit excellent dispersibility in the adhesive composition P according to the present embodiment.

[0044] The inorganic filler (C) in the present embodiment may or may not be subjected to a desired surface treatment. In the case of an inorganic filler without a surface treatment, although generally having poor dispersibility, it exhibits excellent dispersibility in the adhesive composition P according to the present embodiment.

[0045] The average particle size of the primary particles of the inorganic filler (C) is preferably 0.01 μm or more, more preferably 0.1 μm or more, particularly preferably 0.2 μm or more, and further preferably 0.3 μm or more. Also, the average particle size of the primary particles of the inorganic filler (C) is preferably 10 μm or less, particularly preferably 5 μm or less, and further preferably 1 μm or less. When the average particle size of the primary particles of the inorganic filler (C) is within the above range, the dispersibility of the inorganic filler (C) becomes more excellent. Note that the average particle size of the inorganic filler (C) is measured by the laser diffraction / scattering method.

[0046] Also, the content of the inorganic filler (C) in the pressure-sensitive adhesive composition P is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, particularly preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more with respect to 100 parts by mass of the (meth)acrylate polymer (A). Thereby, the desired functions of the inorganic filler (C) can be sufficiently exhibited. Also, the content is preferably 500 parts by mass or less, more preferably 250 parts by mass or less, particularly preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. Thereby, the adhesive strength of the obtained adhesive layer can be maintained well.

[0047] (4) Various additives The pressure-sensitive adhesive composition P can contain, if desired, various additives commonly used in acrylic pressure-sensitive adhesives, such as tackifiers, antioxidants, softeners, etc. The pressure-sensitive adhesive composition P can also contain a dispersant, but since excellent filler dispersibility can be obtained even without containing a dispersant, it is not necessary to contain a dispersant. Note that the polymerization solvent and the dilution solvent described later are not included in the additives constituting the pressure-sensitive adhesive composition P.

[0048] 2. Production of pressure-sensitive adhesive composition The pressure-sensitive adhesive composition P can be produced by producing the (meth)acrylate polymer (A), and mixing the obtained (meth)acrylate polymer (A) with the inorganic filler (C), and, if desired, the crosslinking agent (B) and the additives. Note that the crosslinking agent (B) may be added before the dispersion treatment described later or after the dispersion treatment. In this embodiment, even when the pressure-sensitive adhesive composition P does not contain the crosslinking agent (B), the inorganic filler (C) exhibits excellent dispersibility.

[0049] (Meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a conventional radical polymerization method. The polymerization of (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator if desired. However, the present invention is not limited thereto, and polymerization may be carried out without a solvent. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more kinds may be used in combination.

[0050] Examples of the polymerization initiator include azo compounds, organic peroxides, etc., and two or more kinds may be used in combination. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane 1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], etc.

[0051] Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxyisobutyrate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide, etc.

[0052] In addition, in the above polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by blending a chain transfer agent such as 2-mercaptoethanol.

[0053] Once the (meth)acrylic acid ester polymer (A) is obtained, an inorganic filler (C), and optionally a crosslinking agent (B), additives, etc. are added to a solution of the (meth)acrylic acid ester polymer (A) and thoroughly mixed to obtain a pressure-sensitive adhesive composition P.

[0054] The pressure-sensitive adhesive composition P may be diluted with a dilution solvent, etc. in addition to the aforementioned polymerization solvent as appropriate to adjust the viscosity suitable for dispersion treatment and coating, or to adjust the adhesive layer to a desired film thickness, and may be used as a coating solution. Examples of the dilution solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more of them may be used in combination.

[0055] The concentration and viscosity of the coating solution may be within the range that allows dispersion treatment and coating, and are not particularly limited, and can be appropriately selected according to the situation. For example, it is diluted so that the concentration of the pressure-sensitive adhesive composition P becomes 10 to 60% by mass. In addition, when obtaining the coating solution, the addition of a dilution solvent, etc. is not a necessary condition, and if the pressure-sensitive adhesive composition P has a viscosity, etc. that allows dispersion treatment and coating, the dilution solvent may not be added. In this case, the pressure-sensitive adhesive composition P becomes a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer (A) as the dilution solvent as it is.

[0056] 3. Dispersion treatment of the pressure-sensitive adhesive composition The pressure-sensitive adhesive composition P (coating solution) is subjected to a dispersion treatment for dispersing the inorganic filler (C), and in a short time, a coating solution in which the inorganic filler (C) is uniformly dispersed without aggregates of the inorganic filler (C) is obtained. The dispersion treatment can be performed using a conventionally known disperser. Examples of such a disperser include a rotor-stator type disperser, a jet mill, a bead mill, etc. Among them, considering the prevention of contamination caused by dispersion beads, a rotor-stator type disperser or a jet mill, which is a media-less disperser, is preferable.

[0057] The dispersion treatment time is preferably 50 minutes or less, more preferably 40 minutes or less. Even if the dispersion treatment time is short as described above, the adhesive composition P becomes a coating liquid in which the inorganic filler (C) is uniformly dispersed. That is, the adhesive composition P allows the production of an adhesive sheet having a homogeneous adhesive layer with high production efficiency.

[0058] The adhesive composition P (coating solution) was dispersed for 40 minutes (a rotor-stator type disperser was used in the test example) at a shear rate of 10 s -1 Shear viscosity at (η 10 , unit: mPa s) and shear rate 1 s -1 Shear viscosity at (η 1 , unit: mPa s), RI = η 10 / η 1 The RI (Rheology Index) calculated by the formula is preferably 0.85 or more, more preferably 0.86 or more, and even more preferably 0.87 or more. Generally, if the mixture is close to a completely dispersed state, the shear viscosity does not change from the low shear region to the high shear region, so that the above RI indicates that the inorganic filler (C) is sufficiently uniformly dispersed.

[0059] [Adhesive] The adhesive according to the present embodiment is obtained by crosslinking the above-mentioned adhesive composition P. The crosslinking of the adhesive composition P can usually be carried out by a heat treatment. This heat treatment can also serve as a drying treatment for volatilizing a diluting solvent and the like from a coating film of the adhesive composition P applied to a desired object.

[0060] The heating temperature in the heat treatment is preferably 50 to 150° C., and more preferably 70 to 120° C. The heating time is preferably 30 seconds to 10 minutes, and more preferably 50 seconds to 5 minutes.

[0061] After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23°C, 50% RH). If this curing period is necessary, after the curing period has elapsed, or if the curing period is not necessary, the adhesive layer is formed after the heat treatment is completed.

[0062] 〔Adhesive Sheet〕 The adhesive sheet according to this embodiment is an adhesive sheet including at least an adhesive layer (an adhesive layer made of the aforementioned adhesive) formed from the aforementioned adhesive composition P. The adhesive sheet according to this embodiment may be formed by laminating a base material on one surface side of the adhesive layer and a release sheet on the other surface, or may be formed by laminating release sheets on both surfaces of the adhesive layer.

[0063] A specific configuration as an example of the adhesive sheet according to this embodiment is shown in FIG. 1. As shown in FIG. 1, the adhesive sheet 1 according to this embodiment includes a base material 11, an adhesive layer 12 laminated on one surface side of the base material 11, and a release sheet 13 laminated on the surface of the adhesive layer 12 opposite to the base material 11. The release sheet 13 is laminated such that its release surface contacts the adhesive layer 12. Note that the release surface of the release sheet in this specification refers to the surface having releasability in the release sheet, and includes both the surface subjected to the release treatment and the surface showing releasability without the release treatment.

[0064] 1. Each Element (1) Base Material As the base material 11 in this embodiment, it can be appropriately set according to the use of the adhesive sheet 1, and it is preferably a resin film mainly made of a resin-based material. Specific examples thereof include polyolefin films such as polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, ethylene-norbornene copolymer film, norbornene resin film; polyester films such as polyethylene terephthalate film, polybutylene terephthalate film, polyethylene naphthalate; ethylene-vinyl acetate copolymer film; ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid methyl copolymer film, and other ethylene-(meth)acrylic acid ester copolymer films; ethylene-based copolymer films; polyvinyl chloride films, polyvinyl chloride copolymer films, etc.; (meth)acrylic acid ester copolymer films; polyurethane films; polyimide films; polystyrene films; polycarbonate films; fluororesin films and the like. Also, modified films such as these crosslinked films and ionomer films are also used. Further, the base material 11 may be a laminated film formed by laminating a plurality of the above-described films. In this laminated film, the materials constituting each layer may be the same or different.

[0065] The base material 11 may contain various additives such as flame retardants, plasticizers, antistatic agents, lubricants, antioxidants, colorants, infrared absorbers, ultraviolet absorbers, and ion scavengers. The content of these additives is not particularly limited, and it is preferably within the range where the base material 11 exhibits desired functions.

[0066] On the surface of the base material 11 where the adhesive layer 12 is laminated, surface treatments such as primer treatment, corona treatment, and plasma treatment may be performed to enhance the adhesion to the adhesive layer 12. On the other hand, the base material 11 may be a release sheet, and in that case, the surface where the adhesive layer 12 is laminated may be subjected to a release treatment.

[0067] The thickness of the base material 11 can be appropriately set according to the use of the adhesive sheet 1. Generally, it is preferably 5 μm or more, particularly preferably 10 μm or more, and even more preferably 15 μm or more. Also, the thickness is preferably 200 μm or less, particularly preferably 100 μm or less, and even more preferably 70 μm or less.

[0068] (2) Adhesive layer The adhesive layer 12 is an adhesive layer formed from the above-described adhesive composition P (an adhesive layer made of the above-described adhesive), and is an adhesive layer in which the inorganic filler (C) is uniformly dispersed. In this adhesive layer 12, aggregates of the inorganic filler (C) are not observed on the coating surface and cross-section.

[0069] The thickness of the adhesive layer 12 (a value measured according to JIS K7130) can be appropriately set according to the use of the adhesive sheet 1. Generally, the thickness of the adhesive layer 12 is preferably 1 μm or more, particularly preferably 3 μm or more, and even more preferably 5 μm or more. Thereby, the desired functions by the inorganic filler (C) and the desired adhesive force can be exhibited. Also, the thickness of the adhesive layer 12 is preferably 50 μm or less, particularly preferably 13 μm or less, and even more preferably 9 μm or less.

[0070] On the other hand, the thickness of the adhesive layer 12 is preferably 1.1 times or more, more preferably 5 times or more, particularly preferably 10 times or more, and even more preferably 15 times or more the average particle diameter of the inorganic filler (C). Thereby, the surface smoothness of the adhesive layer 12 becomes excellent, and a high adhesive force can be effectively obtained. The upper limit of the magnification of the thickness of the adhesive layer 12 based on the average particle diameter of the inorganic filler (C) is not particularly limited, but is preferably 100 times or less, more preferably 60 times or less, and particularly preferably 30 times or less.

[0071] (3) Release sheet The release sheet 13 protects the adhesive layer 12 until the pressure-sensitive adhesive sheet 1 is used, and is peeled off when the pressure-sensitive adhesive sheet 1 is used. In the pressure-sensitive adhesive sheet 1 according to the present embodiment, the release sheet 13 is not necessarily required.

[0072] Examples of the release sheet 13 include a polyethylene film, a polypropylene film, a polybutene film, a polybutadiene film, a polymethylpentene film, a polyvinyl chloride film, a vinyl chloride copolymer film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, a polyurethane film, an ethylene vinyl acetate film, an ionomer resin film, an ethylene·(meth)acrylic acid copolymer film, an ethylene·(meth)acrylate copolymer film, a polystyrene film, a polycarbonate film, a polyimide film, a fluororesin film, a liquid crystal polymer film, etc. Further, crosslinked films of these are also used. Furthermore, laminated films of these may also be used.

[0073] It is preferable that the release surface (the surface in contact with the adhesive layer 12) of the release sheet 13 is subjected to a release treatment. Examples of the release agent used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

[0074] There is no particular limitation on the thickness of the release sheet 13, but it is usually about 20 to 150 μm.

[0075] 2. Method for manufacturing a pressure-sensitive adhesive sheet As a method for manufacturing the pressure-sensitive adhesive sheet 1 according to the present embodiment, there is no particular limitation as long as the pressure-sensitive adhesive layer 12 can be formed on one side of the base material 11. For example, the above-described pressure-sensitive adhesive composition P and a coating liquid containing a solvent as desired are applied to the release surface of the release sheet 13, and heat treatment is performed to form a coating layer. Then, one side of the base material 11 is bonded to the surface of the coating layer opposite to the release sheet 13. If a curing period is required, a curing period is provided. If a curing period is not required, the coating layer directly becomes the pressure-sensitive adhesive layer 12 as it is. Thereby, the above-described pressure-sensitive adhesive sheet 1 is obtained. The conditions for heat treatment and curing are as described above.

[0076] Further, as another manufacturing method of the pressure-sensitive adhesive sheet 1 according to the present embodiment, after applying a coating liquid containing the pressure-sensitive adhesive composition P and a solvent as desired to one side of the base material 11, the pressure-sensitive adhesive layer 12 is formed, and if desired, the release sheet 13 may be laminated on the pressure-sensitive adhesive layer 12 to obtain the pressure-sensitive adhesive sheet 1. The application, heat treatment, and curing of the pressure-sensitive adhesive composition P in this case can be performed in the same manner as the above-described method.

[0077] 3. Use of the pressure-sensitive adhesive sheet The use of the pressure-sensitive adhesive sheet 1 according to the present embodiment is not particularly limited and can be appropriately selected according to the functions exhibited by the inorganic filler (C). Examples of the functions exhibited by the inorganic filler (C) include conductivity, heat conductivity, insulation, mechanical strength, light diffusibility, and the like. When the inorganic filler (C) is made of alumina, silica, or barium sulfate, excellent insulation is exhibited.

[0078] Examples of the components to which the pressure-sensitive adhesive sheet 1 according to the present embodiment is applied include electronic components, semiconductor components, optical components, mechanical components, and the like. Examples of electronic components include substrates such as flexible substrates, rigid substrates, and rigid-flexible substrates, batteries such as lithium-ion batteries and nickel-metal hydride batteries, and motors.

[0079] The embodiments described above are provided for facilitating the understanding of the present invention and are not provided for limiting the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

[0080] For example, in the adhesive sheet 1, the release sheet 13 may be omitted. Further, in the adhesive sheet 1, another layer may be provided between the base material 11 and the adhesive layer 12.

Example

[0081] Hereinafter, the present invention will be described more specifically by way of examples and the like, but the scope of the present invention is not limited to these examples and the like.

[0082] 〔Example 1〕 1. Preparation of (meth)acrylate polymer 80 parts by mass of 2-ethylhexyl acrylate, 5 parts by mass of acrylic acid, and 15 parts by mass of n-butyl methacrylate were copolymerized by solution polymerization to prepare a (meth)acrylate polymer (A). When the molecular weight of this (meth)acrylate polymer (A) was measured by the method described later, the weight average molecular weight (Mw) was 840,000.

[0083] 2. Preparation of adhesive composition 100 parts by mass of the (meth)acrylate polymer (A) obtained above (in terms of solid content; the same shall apply hereinafter), 3.75 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem Co., Ltd., product name “BHS-8515”) as a crosslinking agent (B), and 72 parts by mass of barium sulfate particles (manufactured by Sakai Chemical Industry Co., Ltd., product name “BARIACE B-55”, average particle diameter of primary particles: 0.6 μm) as an inorganic filler (C) were mixed, sufficiently stirred, and diluted with methyl ethyl ketone to obtain a pre-dispersion solution of an adhesive composition having a solid content concentration of 37.2% by mass.

[0084] Here, Table 1 shows the respective formulations (in terms of solid content conversion value) of the pressure-sensitive adhesive composition when the (meth)acrylate polymer (A) is 100 parts by mass (in terms of solid content conversion value). The details of the abbreviations and the like described in Table 1 are as follows. [(meth)acrylate polymer (A)] 2EHA: 2-ethylhexyl acrylate BMA: n-butyl methacrylate BA: n-butyl acrylate AA: acrylic acid [inorganic filler (C)] C1: Barium sulfate particles with an average primary particle size of 0.6 μm, surface unmodified (manufactured by Sakai Chemical Industry Co., Ltd., product name "BARIACE B-55") C2: Silica particles with an average primary particle size of 0.6 μm, surface unmodified (manufactured by Denka Co., Ltd., product name "SFP-30M") C3: Alumina particles with an average primary particle size of 0.7 μm, surface unmodified (manufactured by Sumitomo Chemical Co., Ltd., product name "AKP-3000")

[0085] [Examples 2 to 5, Comparative Examples 1 to 3] Except for changing the composition and weight-average molecular weight (Mw) of the (meth)acrylate polymer (A), and the type and blending amount of the inorganic filler (C) as shown in Table 1, a pre-dispersion solution of the pressure-sensitive adhesive composition P was prepared in the same manner as in Example 1.

[0086] Here, the weight-average molecular weight (Mw) described above is the weight-average molecular weight in terms of polystyrene measured under the following conditions (GPC measurement) using gel permeation chromatography (GPC). [Measurement conditions] · Measuring device: HLC-8320 manufactured by Tosoh Corporation · GPC column (passing in the following order): manufactured by Tosoh Corporation TSK gel superH-H TSK gel superHM-H TSK gel superH2000 · Measuring solvent: Tetrahydrofuran · Measuring temperature: 40°C

[0087] Example 1 (Measurement of Particle Size Distribution) The particle size distribution of the inorganic filler (C) in the pre-dispersion solution of the pressure-sensitive adhesive compositions prepared in the examples and comparative examples was measured using a particle size distribution analyzer (manufactured by Malvern, product name "Mastersizer 3000"). Table 1 shows the content rate (volume %) of the inorganic filler having a particle diameter of 10 μm or more.

[0088] For reference, a graph (dotted line) of the particle size distribution of the inorganic filler (C) in the pre-dispersion solution of the pressure-sensitive adhesive composition prepared in Example 1 is shown in FIG. 2.

[0089] Example 2 (Evaluation of Dispersibility) With respect to 400 mL of the pre-dispersion solution of the pressure-sensitive adhesive compositions prepared in the examples and comparative examples, dispersion treatment was performed using a rotor-stator type disperser (manufactured by Primix, product name "Neo Mixer") to obtain a dispersion solution of the pressure-sensitive adhesive composition. The dispersion treatment was carried out while maintaining the solution temperature at 20°C using temperature control equipment, and the rotation speed of the disperser was 10,000 rpm.

[0090] The particle size distribution in the dispersion solution of the pressure-sensitive adhesive composition obtained by sampling every 10 minutes from the start of the dispersion treatment was measured using a particle size distribution analyzer (manufactured by Malvern, product name "Mastersizer 3000"). Then, the dispersion treatment time (minutes) when coarse particles having a particle diameter (secondary particles) of 10 μm or more were no longer detected was measured, and the dispersibility was evaluated according to the following evaluation criteria. The results are shown in Table 2. Note that since coarse particles having a particle diameter of 10 μm or more were continuously detected even after 90 minutes of dispersion treatment of the pressure-sensitive adhesive composition of Comparative Example 2, it was determined that dispersion was impossible. 〇: Coarse particles were no longer observed within 40 minutes from the start of the dispersion treatment. ×: Coarse particles were observed even after 40 minutes had elapsed from the start of the dispersion treatment.

[0091] For reference, a graph (solid line) of the particle size distribution 40 minutes after the start of the dispersion treatment in the dispersion solution of the pressure-sensitive adhesive composition prepared in Example 1 is shown in FIG. 2.

[0092] Example 3 (Evaluation of Dispersibility by Rheology) The pre-dispersion solutions of the pressure-sensitive adhesive compositions prepared in the examples and comparative examples were subjected to a dispersion treatment for 40 minutes in the same manner as in Test Example 2. For the obtained dispersion solution, steady flow measurement was carried out using a rheometer (manufactured by Anton Paar, product name "MCR302"), and the shear viscosity was measured. Then, the shear viscosity (η -1 , unit: mPa·s) at a shear rate of 10 s 10 and the shear viscosity (η -1 at a shear rate of 1 s 1 , unit: mPa·s), the value of RI (Rheology Index) = η 10 / η 1 was calculated. Based on the following criteria, the dispersibility by rheology was evaluated from the calculated RI values. The results are shown in Table 2. 〇: The value of RI is 0.85 or more ×: The value of RI is less than 0.85

[0093] 〔Test Example 4〕(Evaluation of Aggregates) The pre-dispersion solutions of the pressure-sensitive adhesive compositions prepared in the examples and comparative examples were subjected to a dispersion treatment for 40 minutes in the same manner as in Test Example 2. The obtained dispersion solution was applied to one side of a polyethylene terephthalate film (manufactured by Toray Industries, Inc., product name "Lumirror T-60", thickness: 50 μm) with a knife coater. Then, the coated layer was heated and dried at 100 °C for 2 minutes to form an adhesive layer with a thickness of 8 μm to obtain an adhesive sheet. Whether there were aggregate defects on the surface (size: 5 mm × 5 mm) of the adhesive layer of the obtained adhesive sheet was visually observed, and the aggregates were evaluated based on the following criteria (surface / visual). The results are shown in Table 2. The thickness of the adhesive layer is the value obtained by subtracting the thickness of the polyethylene terephthalate film (50 μm) from the thickness of the adhesive sheet measured according to JIS K7130. 〇: No aggregate defects were observed. ×: Aggregate defects were observed.

[0094] Also, for the cross-section (length: 5 mm) of the obtained adhesive layer, the presence or absence of aggregates larger than the film thickness was observed using an optical microscope (magnification 100 times), and the aggregates were evaluated based on the following criteria (cross-section / microscope). The results are shown in Table 2. 〇: No aggregates larger than the film thickness were observed. ×: Aggregates larger than the film thickness were observed.

[0095]

Table 1

[0096]

Table 2

[0097] As is clear from Table 2, in the pressure-sensitive adhesive composition of the examples, the inorganic filler (C) was uniformly dispersed in a short time. Further, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the examples had no aggregates observed on the coated surface and cross-section, and the inorganic filler (C) was uniformly dispersed.

Industrial Applicability

[0098] The pressure-sensitive adhesive composition, pressure-sensitive adhesive, and pressure-sensitive adhesive sheet according to the present invention can be used, for example, to attach a desired member in various electronic components and the like.

Explanation of Reference Numerals

[0099] 1... Pressure-sensitive adhesive sheet 11... Substrate 12... Pressure-sensitive adhesive layer 13... Release sheet

Claims

1. As monomer units constituting the polymer, a (meth)acrylic acid ester polymer (A) containing butyl methacrylate and a monomer containing a reactive functional group, an inorganic filler (C), a solvent are contained, the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is 500,000 or more and 2,500,000 or less, the (meth)acrylic acid ester polymer (A) contains 1% by mass or more and 45% by mass or less of the butyl methacrylate as monomer units constituting the polymer, and contains 0.5% by mass or more and 20% by mass or less of the monomer containing a reactive functional group, the content of the inorganic filler (C) is 30 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic acid ester polymer (A), the solvent is one or more selected from the group consisting of ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone A pressure-sensitive adhesive composition characterized by the above.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer containing a reactive functional group is a monomer containing a carboxy group.

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the inorganic filler (C) consists of barium sulfate.

4. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the average particle diameter of the primary particles of the inorganic filler (C) is 0.01 μm or more and 10 μm or less.

5. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive composition contains a crosslinking agent (B).

6. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 5.

7. A pressure-sensitive adhesive sheet having at least a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 5 A pressure-sensitive adhesive sheet characterized by the above.

8. The pressure-sensitive adhesive sheet according to claim 7, comprising a base material and the pressure-sensitive adhesive layer provided on one surface side of the base material.

9. The pressure-sensitive adhesive sheet according to claim 7 or 8, wherein the thickness of the pressure-sensitive adhesive layer is 1 μm or more and 50 μm or less.

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