Adhesion method using high-frequency dielectric heating adhesive sheet

Abstract

A bonding method in which an adhesive sheet (10) comprising a first thermoplastic resin and an adhesive sheet (20) comprising a second thermoplastic resin are used, wherein the adhesive sheet (10) has a volume content VA1 of the first thermoplastic resin of 60-100 vol%, the adhesive sheet (20) has a volume content VA2 of the second thermoplastic resin of 60-100 vol%, and changes Vx1 and Vx2 shown by the following expressions are less than 80% each, VB1 being the volume content of the first thermoplastic resin in a layer coming into direct contact with the first adhesive layer (10) and VB2 being the volume content of the second thermoplastic resin in a layer coming into direct contact with the second adhesive layer (20). The bonding method includes a step in which a high-frequency voltage is applied to the adhesive sheets (10, 20) disposed between adherends (110, 120) to bond the adherends.　Numerical expression 1: Vx1={(VA1-VB1) / VA1}×100 Numerical expression 2: Vx2={(VA2-VB2) / VA2}×100

Description

[Technical Field]

[0001] The present invention relates to a bonding method using a high-frequency dielectric heating adhesive sheet. [Background technology]

[0002] In recent years, methods have been proposed for bonding adherends that are generally difficult to bond together, such as by interposing an adhesive made of a specific resin blended with a heat-generating material between the adherends and performing dielectric heating treatment, induction heating treatment, ultrasonic welding treatment, laser welding treatment, or the like.

[0003] For example, Patent Document 1 describes a sheet-shaped thermal adhesive containing at least one fine powder selected from the group consisting of carbon black, silicon oxide, metals, and metal oxides. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 58-174474 Summary of the Invention [Problem to be solved by the invention]

[0005] When attempting to bond adherends (first and second adherends) made of different materials using the thermal adhesive described in Patent Document 1, sufficient adhesive strength may not be obtained, particularly when the adherends are made of poorly adhesive materials.

[0006] An object of the present invention is to provide a bonding method using a high-frequency dielectric heating adhesive sheet that can firmly bond a first adherend and a second adherend made of different materials. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a bonding method for bonding a first adherend and a second adherend made of a different material from the first adherend using a plurality of high-frequency dielectric heating adhesive sheets, the method comprising: the plurality of high-frequency dielectric heating adhesive sheets include at least a first adhesive sheet and a second adhesive sheet; the first adhesive sheet contains a first thermoplastic resin, the second adhesive sheet contains a second thermoplastic resin, the first thermoplastic resin and the second thermoplastic resin are different resins, a volume content VA1 of the first thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet is 60% by volume or more and 100% by volume or less; a volume content VA2 of the second thermoplastic resin relative to all thermoplastic resins in the second adhesive sheet is 60% by volume or more and 100% by volume or less; the rate of change Vx1, expressed by the following formula (Mathematical Formula 1), between the volume content VA1 of the first thermoplastic resin and the volume content VB1 of the first thermoplastic resin relative to all thermoplastic resins in a sheet disposed so as to be in direct contact with the first adhesive sheet is less than 80%, the rate of change Vx2, expressed by the following formula (Equation 2), between the volume content VA2 of the second thermoplastic resin and the volume content VB2 of the second thermoplastic resin relative to all thermoplastic resins in the sheet arranged so as to be in direct contact with the second adhesive sheet is less than 80%, a step of placing the first adhesive sheet between the first adherend and the second adherend so as to be in contact with the first adherend, and placing the second adhesive sheet between the first adherend and the second adherend so as to be in contact with the second adherend; a step of applying a high frequency to the first adhesive sheet and the second adhesive sheet while sandwiching the first adhesive sheet and the second adhesive sheet between the first adherend and the second adherend, thereby bonding the first adhesive sheet to the first adherend and bonding the second adhesive sheet to the second adherend, A bonding method using a high frequency dielectric heating adhesive sheet is provided. Vx1 = {(VA1 - VB1) / VA1} x 100... (Equation 1) Vx2 = {(VA2 - VB2) / VA2} x 100... (Equation 2)

[0008] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, the first adherend contains a third thermoplastic resin, the second adherend contains a fourth thermoplastic resin, The main composition of the first thermoplastic resin is the same as the main composition of the third thermoplastic resin; The main composition of the second thermoplastic resin is preferably the same as the main composition of the fourth thermoplastic resin.

[0009] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, It is preferable to further place an intermediate sheet between the first adhesive sheet and the second adhesive sheet.

[0010] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, It is preferable that at least one of the first adhesive sheet and the second adhesive sheet is in direct contact with the intermediate sheet.

[0011] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, The intermediate sheet preferably contains the first thermoplastic resin and the second thermoplastic resin.

[0012] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, It is preferable that the sheet in direct contact with the first adhesive sheet is the second adhesive sheet.

[0013] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, At least one of the first adhesive sheet and the second adhesive sheet preferably contains a dielectric filler that generates heat at high frequency.

[0014] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, It is preferable that the volume content of the dielectric filler in at least one of the first adhesive sheet and the second adhesive sheet is 5% by volume or more and 50% by volume or less.

[0015] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, At least one of the dielectric fillers in the first adhesive sheet and the second adhesive sheet preferably contains at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide, and barium titanate.

[0016] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, At least one of the volume average particle diameter of the dielectric filler in the first adhesive sheet and the volume average particle diameter of the dielectric filler in the second adhesive sheet is 1 μm or more and 30 μm or less, The volume average particle diameter is preferably a volume average particle diameter calculated from the particle size distribution measurement results in accordance with JIS Z 8819-2:2001 by measuring the particle size distribution by a laser diffraction / scattering method.

[0017] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, The first thermoplastic resin is preferably a polyolefin resin.

[0018] In a bonding method using a high-frequency dielectric heating adhesive sheet according to one aspect of the present invention, It is preferable that the absolute value of the difference between the flow starting temperature Tx1 of the first thermoplastic resin and the flow starting temperature Tx2 of the second thermoplastic resin satisfy the relationship of the following mathematical formula (Mathematical Formula 4). |Tx1-Tx2|≦70…(Number 4)

[0019] According to one aspect of the present invention, it is possible to provide a bonding method using a high-frequency dielectric heating adhesive sheet that can firmly bond a first adherend and a second adherend made of different materials. [Brief explanation of the drawings]

[0020] [Figure 1] 1(A), 1(B), and 1(C) are schematic cross-sectional views illustrating examples of steps included in the bonding method according to the first embodiment. [Figure 2] 5(A), (B), and (C) are schematic cross-sectional views illustrating another example of steps included in the bonding method according to the first embodiment. [Figure 3] FIG. 1 is a schematic diagram illustrating a high-frequency dielectric heating process using a high-frequency dielectric heating adhesive sheet and a dielectric heating device according to a first embodiment. [Figure 4] 10(A), (B), (C) and (D) are schematic cross-sectional views illustrating examples of steps included in a bonding method according to a second embodiment. [Figure 5] 10(A), 10(B), and 10(C) are schematic cross-sectional views illustrating another example of steps included in the bonding method according to the second embodiment. [Figure 6] FIG. 10 is a schematic diagram illustrating a high-frequency dielectric heating process using a high-frequency dielectric heating adhesive sheet and a dielectric heating device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] [First embodiment] The bonding method using a high-frequency dielectric heating adhesive sheet according to this embodiment is a bonding method in which a first adherend and a second adherend made of a different material from the first adherend are bonded together using multiple high-frequency dielectric heating adhesive sheets. The multiple high-frequency dielectric heating adhesive sheets used in the bonding method according to this embodiment include at least a first adhesive sheet and a second adhesive sheet. At least one of the first adhesive sheet and the second adhesive sheet is preferably a single-layer sheet, and more preferably both the first adhesive sheet and the second adhesive sheet are single-layer sheets.

[0022] The bonding method according to this embodiment includes the steps of: placing a first adhesive sheet between a first adherend and a second adherend so that the first adhesive sheet is in contact with the first adherend; and placing a second adhesive sheet in contact with the second adherend; and sandwiching the first adhesive sheet and the second adhesive sheet between the first adherend and the second adherend and applying high frequency to the first adhesive sheet and the second adhesive sheet, thereby bonding the first adherend to the first adhesive sheet and bonding the second adherend to the second adhesive sheet. First, a high-frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment will be described, and then a bonding method using the high-frequency dielectric heating adhesive sheet will be described.

[0023] [High frequency dielectric heating adhesive sheet] The first adhesive sheet and the second adhesive sheet as the plurality of high-frequency dielectric heating adhesive sheets used in the bonding method according to this embodiment each contain a thermoplastic resin. The first adhesive sheet contains a first thermoplastic resin. The second adhesive sheet contains a second thermoplastic resin. The first thermoplastic resin and the second thermoplastic resin are different resins.

[0024] The volume content VA1 of the first thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet is 60% by volume or more and 100% by volume or less. The volume content VA2 of the second thermoplastic resin relative to all the thermoplastic resins in the second adhesive sheet is 60% by volume or more and 100% by volume or less.

[0025] The rate of change Vx1, expressed by the following formula (Equation 1), between the volume content VA1 of the first thermoplastic resin and the volume content VB1 of the first thermoplastic resin relative to all thermoplastic resins in the sheet placed in direct contact with the first adhesive sheet is less than 80%.

[0026] The rate of change Vx2, expressed by the following formula (Equation 2), between the volume content VA2 of the second thermoplastic resin and the volume content VB2 of the second thermoplastic resin relative to all thermoplastic resins in the sheet arranged so as to be in direct contact with the second adhesive sheet is less than 80%. Vx1 = {(VA1 - VB1) / VA1} x 100... (Equation 1) Vx2 = {(VA2 - VB2) / VA2} x 100... (Equation 2)

[0027] The rate of change Vx1 is preferably more than 0%, more preferably 10% or more, even more preferably 20% or more, and even more preferably 25% or more. The rate of change Vx1 is preferably 75% or less.

[0028] The rate of change Vx2 is preferably more than 0%, more preferably 10% or more, even more preferably 20% or more, and even more preferably 25% or more. The rate of change Vx2 is preferably 75% or less. The rates of change Vx1 and Vx2 may be the same as or different from each other.

[0029] Since both the change rates Vx1 and Vx2 are less than 80%, interfacial peeling is unlikely to occur between the adhesive sheets.

[0030] The volume contents VA1, VB1, VA2 and VB2 are expressed in volume percent.

[0031] (thermoplastic resin) The types of the first thermoplastic resin and the second thermoplastic resin are not particularly limited. The first thermoplastic resin and the second thermoplastic resin are preferably at least one selected from the group consisting of polyolefin-based resins, polyolefin-based resins having polar moieties, styrene-based resins, polyacetal-based resins, polycarbonate-based resins, polyacrylic-based resins, polyamide-based resins, polyimide-based resins, polyvinyl acetate-based resins, phenoxy-based resins, and polyester-based resins, for example, from the viewpoint of being easily melted and having a predetermined heat resistance.

[0032] The first thermoplastic resin is preferably a polyolefin resin.

[0033] The second thermoplastic resin is preferably a styrene-based resin.

[0034] It is also preferable that at least one of the first thermoplastic resin and the second thermoplastic resin is a polyolefin resin or a polyolefin resin having a polar moiety, or at least one of the first thermoplastic resin and the second thermoplastic resin may be a polyolefin resin not having a polar moiety.

[0035] (Polyolefin resin) Examples of polyolefin resins as thermoplastic resins include resins made of homopolymers such as polyethylene, polypropylene, polybutene, and polymethylpentene, and α-olefin resins made of copolymers of monomers selected from the group consisting of ethylene, propylene, butene, hexene, octene, 4-methylpentene, etc. The polyolefin resin as thermoplastic resin may be a single resin or a combination of two or more resins.

[0036] (Polyolefin resin with polar moieties) The polar moiety in the polyolefin resin having a polar moiety is not particularly limited as long as it is a moiety that can impart polarity to the polyolefin resin. Polyolefin resins having a polar moiety are preferred because they exhibit high adhesive strength to adherends. The thermoplastic resin may be a copolymer of an olefinic monomer and a monomer having a polar moiety, or may be a resin obtained by introducing a polar moiety into an olefinic polymer obtained by polymerization of an olefinic monomer through modification such as an addition reaction.

[0037] The type of olefinic monomer constituting the polyolefinic resin having a polar moiety as a thermoplastic resin is not particularly limited. Examples of the olefinic monomer include ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene. The olefinic monomer may be used alone or in combination of two or more. The olefin-based monomer is preferably ethylene or propylene, from the viewpoint of excellent mechanical strength and stable adhesive properties. The olefin-derived structural unit in the polyolefin-based resin having a polar moiety is preferably a structural unit derived from ethylene or propylene.

[0038] Examples of polar moieties include a hydroxyl group, a carboxyl group, a vinyl acetate structure, an acid anhydride structure, and an acid-modified structure introduced into a polyolefin resin by acid modification.

[0039] The acid-modified structure as a polar moiety is a moiety introduced by acid-modifying a thermoplastic resin (e.g., a polyolefin-based resin). Examples of compounds used for graft-modifying a thermoplastic resin (e.g., a polyolefin-based resin) include unsaturated carboxylic acid derivative components derived from unsaturated carboxylic acids, acid anhydrides of unsaturated carboxylic acids, and esters of unsaturated carboxylic acids.

[0040] Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0041] Examples of the acid anhydrides of unsaturated carboxylic acids include acid anhydrides of unsaturated carboxylic acids such as maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0042] Examples of the esters of unsaturated carboxylic acids include esters of unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dimethyl maleate, monomethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl itaconate, diethyl itaconate, dimethyl citraconate, diethyl citraconate, and dimethyl tetrahydrophthalic anhydride.

[0043] When the thermoplastic resin is a copolymer of an olefinic monomer and a monomer having a polar moiety, the copolymer preferably contains 2% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and even more preferably 6% by mass or more of structural units derived from the monomer having a polar moiety. The copolymer also preferably contains 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less of structural units derived from the monomer having a polar moiety. When the copolymer contains 2% by mass or more of structural units derived from monomers having polar moieties, the adhesive strength of the high-frequency dielectric heating adhesive sheet is improved. Furthermore, when the copolymer contains 30% by mass or less of structural units derived from monomers having polar moieties, the tackiness of the thermoplastic resin can be prevented from becoming too strong. As a result, it becomes easier to prevent difficulties in molding the high-frequency dielectric heating adhesive sheet.

[0044] When the polyolefin resin as the thermoplastic resin has an acid-modified structure, the modification rate with acid is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. When the polyolefin resin as the thermoplastic resin has an acid-modified structure, the modification rate with acid is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. When the thermoplastic resin has an acid-modified structure, the acid modification rate of 0.01% by mass or more improves the adhesive strength of the high-frequency dielectric heating adhesive sheet. Furthermore, the acid modification rate of 30% by mass or less prevents the thermoplastic resin from becoming too tacky. As a result, it becomes easier to prevent difficulties in molding the high-frequency dielectric heating adhesive sheet. In this specification, the modification rate is the percentage of the mass of the portion derived from the acid relative to the total mass of the acid-modified polyolefin.

[0045] (Maleic anhydride modified polyolefin) The polyolefin resin as the thermoplastic resin more preferably has an acid anhydride structure as the acid-modified structure, and the acid anhydride structure is preferably a structure introduced when the polyolefin resin is modified with maleic anhydride. In the maleic anhydride-modified polyolefin, the modification rate with maleic anhydride is preferably in the same range as the modification rate when the polyolefin resin as the thermoplastic resin has an acid-modified structure, and the effects obtained by being in this range are also the same as when the polyolefin resin as the thermoplastic resin has an acid-modified structure.

[0046] The olefin-derived structural units in the maleic anhydride-modified polyolefin are preferably structural units derived from ethylene or propylene, i.e., the maleic anhydride-modified polyolefin is preferably a maleic anhydride-modified polyethylene resin or a maleic anhydride-modified polypropylene resin.

[0047] (olefin-vinyl acetate copolymer resin) The thermoplastic resin according to this embodiment is also preferably a copolymer containing structural units derived from an olefin and structural units derived from vinyl acetate (olefin-vinyl acetate copolymer resin). The olefin-vinyl acetate copolymer resin as the thermoplastic resin preferably contains constituent units derived from vinyl acetate in the same range as the constituent units derived from the monomer having a polar moiety in the copolymer of the thermoplastic resin with an olefin-based monomer and a monomer having a polar moiety, and the effects obtained within this range are the same as when the thermoplastic resin is a copolymer of an olefin-based monomer and a monomer having a polar moiety.

[0048] The olefin-derived structural unit in the olefin-vinyl acetate copolymer resin is preferably a structural unit derived from ethylene or propylene, from the viewpoint of achieving excellent mechanical strength and stable adhesiveness. Therefore, the thermoplastic resin is preferably at least one of an ethylene-vinyl acetate copolymer resin and a propylene-vinyl acetate copolymer resin, and more preferably an ethylene-vinyl acetate copolymer resin. The vinyl acetate-derived structural units in the ethylene-vinyl acetate copolymer resin and the propylene-vinyl acetate copolymer resin are also preferably in the same range of percentage (mass %) as described for the olefin-vinyl acetate copolymer resin.

[0049] (styrene resin) The styrene-based resin may be a homopolymer of a styrene-based monomer (polystyrene: PS), such as a homopolymer of styrene, a homopolymer of α-methylstyrene, or a homopolymer of β-methylstyrene. The PS may be a general purpose polystyrene resin (GPPS resin) or a high impact polystyrene resin (HIPS resin) which includes a GPPS resin and a rubber-like elastomer. Examples of styrene-based resins include resins obtained by copolymerizing a styrene-based monomer such as α-methylstyrene or β-methylstyrene with an aliphatic monomer, and hydrogenated styrene-based resins obtained by hydrogenating such resins may also be used. The styrene-based resin is preferably a styrene-based elastomer. Examples of the styrene-based elastomer include a styrene-conjugated diene copolymer and a styrene-olefin copolymer. Specific examples of the styrene-conjugated diene copolymer include unhydrogenated styrene-conjugated diene copolymers such as styrene-butadiene copolymer, styrene-butadiene-styrene copolymer (SBS), styrene-butadiene / butylene-styrene copolymer, styrene-isoprene copolymer, styrene-isoprene-styrene copolymer (SIS), and styrene-ethylene / isoprene-styrene copolymer; and hydrogenated styrene-conjugated diene copolymers such as styrene-ethylene / propylene-styrene copolymer (SEPS) and styrene-ethylene / butylene-styrene copolymer (SEBS). Furthermore, examples of industrially usable styrene elastomers include trade names such as Tufprene (manufactured by Asahi Kasei Corporation), Kraton (manufactured by Kraton Polymer Japan Co., Ltd.), Sumitomo TPE-SB (manufactured by Sumitomo Chemical Co., Ltd.), Epofriend (manufactured by Daicel Corporation), Rabalon (manufactured by Mitsubishi Chemical Corporation), Septon (manufactured by Kuraray Co., Ltd.), and Tuftec (manufactured by Asahi Kasei Corporation). The styrene elastomer may be hydrogenated or unhydrogenated.

[0050] (acrylic resin) The acrylic resin is preferably a homopolymer of a (meth)acrylic acid ester such as polymethyl methacrylate (PMMA) or polymethyl acrylate (PMA), or a copolymer of at least one of a monomer unit derived from methyl methacrylate (MMA) and a monomer unit derived from methyl acrylate (MA) with a monomer unit derived from one or more other monomers. The acrylic resin may be one selected from the group consisting of these homopolymers and copolymers, or a mixture of two or more. In this specification, the term "(meth)acrylic acid" encompasses both "acrylic acid" and "methacrylic acid." Examples of other monomers copolymerizable with at least one of MMA and MA include alkyl (meth)acrylates in which the alkyl group has 2 to 18 carbon atoms; α,β-unsaturated acids such as acrylic acid and methacrylic acid; unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, and alkyl esters of these unsaturated group-containing dicarboxylic acids; aromatic vinyl compounds such as styrene, α-methylstyrene, and nuclear-substituted styrene; cyanide vinyl compounds such as acrylonitrile and methacrylonitrile; maleic anhydride, maleimide, and N-substituted maleimide. The other monomer copolymerizable with at least one of MMA and MA may be at least one selected from the group consisting of these monomers, or two or more may be selected from the group consisting of these monomers.

[0051] In the bonding method according to this embodiment, it is preferable that the absolute value of the difference between the flow start temperature Tx1 of the first thermoplastic resin and the flow start temperature Tx2 of the second thermoplastic resin satisfy the relationship of the following mathematical formula (Mathematical Formula 4). |Tx1-Tx2|≦70…(Number 4) The absolute value |Tx1-Tx2| of the difference between the flow initiation temperatures Tx1 and Tx2 is more preferably 60°C or less, even more preferably 50°C or less, and even more preferably 40°C or less. The absolute value |Tx1-Tx2| of the difference between the flow initiation temperatures Tx1 and Tx2 is usually 0°C or higher.

[0052] If the absolute value of the difference between Tx1 and Tx2 is 70° C. or less, adhesion between the first adhesive sheet and the second adhesive sheet in contact with the first adhesive sheet is easily obtained. The flow initiation temperature of the thermoplastic resin can be measured by the method described in the Examples section below.

[0053] It is also preferable that at least one of the first thermoplastic resin and the second thermoplastic resin is a thermoplastic resin that generates heat at high frequency. The thermoplastic resin that generates heat at high frequencies is preferably a thermoplastic resin that generates heat when a high-frequency voltage in the frequency range of 3 MHz or more and 300 MHz or less is applied, and more preferably a thermoplastic resin that generates heat when a high-frequency voltage in the frequency range of 3 MHz or more and 300 MHz or less is applied, such as a frequency of 13.56 MHz, 27.12 MHz, or 40.68 MHz.

[0054] (Dielectric filler) At least one of the first adhesive sheet and the second adhesive sheet preferably contains a dielectric filler that generates heat at high frequency. The dielectric filler contained in the first adhesive sheet may be referred to as the first dielectric filler. The dielectric filler contained in the second adhesive sheet may be referred to as the second dielectric filler.

[0055] The first dielectric filler and the second dielectric filler are fillers that generate heat at high frequencies. The first dielectric filler and the second dielectric filler are preferably fillers that generate heat when a high-frequency voltage in the frequency range of 3 MHz or more and 300 MHz or less is applied to them. The first dielectric filler and the second dielectric filler are preferably fillers that generate heat when a high-frequency voltage in the frequency range of 3 MHz or more and 300 MHz or less is applied to them, for example, at a frequency of 13.56 MHz, 27.12 MHz, or 40.68 MHz.

[0056] ·kinds The first dielectric filler and the second dielectric filler are each preferably independently one or a combination of two or more of inorganic materials having water of crystallization such as zinc oxide, silicon carbide (SiC), titanium oxide, barium titanate, barium titanate zirconate, lead titanate, potassium niobate, hydrated aluminum silicate, hydrated aluminosilicate of alkali metals, or hydrated aluminosilicate of alkaline earth metals. The types of the first dielectric filler and the second dielectric filler may be the same or different.

[0057] At least one of the first dielectric filler and the second dielectric filler is preferably at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide, and barium titanate. The first dielectric filler and the second dielectric filler are preferably each independently at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide, and barium titanate. Among the dielectric fillers listed above, zinc oxide is more preferably used as at least one of the first and second dielectric fillers, since a wide variety of types are available, allowing selection from a variety of shapes and sizes, thereby enabling the adhesive and mechanical properties of the high-frequency dielectric heating adhesive sheet to be improved according to the application. Using zinc oxide as the dielectric filler allows for the production of a colorless high-frequency dielectric heating adhesive sheet. Because zinc oxide has a low density among dielectric fillers, when adherends are bonded using a high-frequency dielectric heating adhesive sheet containing zinc oxide as the dielectric filler, the total weight of the bonded body is less likely to increase compared to when sheets containing other dielectric fillers are used. Zinc oxide is not too hard, even among ceramics, and therefore is less likely to damage the manufacturing equipment for high-frequency dielectric heating adhesive sheets. Because zinc oxide is an inactive oxide, it causes less damage to thermoplastic resins when blended with them. Furthermore, the titanium oxide used as the dielectric filler is preferably at least one of anatase type titanium oxide and rutile type titanium oxide, and from the viewpoint of excellent dielectric properties, anatase type titanium oxide is more preferable.

[0058] ·Volume content It is preferable that at least one of the volume content of the first dielectric filler in the first adhesive sheet and the volume content of the second dielectric filler in the second adhesive sheet is 5% by volume or more, and more preferably 8% by volume or more. It is preferable that at least one of the volume content of the first dielectric filler in the first adhesive sheet and the volume content of the second dielectric filler in the second adhesive sheet is 50 volume % or less, more preferably 40 volume % or less, and even more preferably 35 volume % or less. If the volume content of the first dielectric filler is 5% by volume or more, the first adhesive sheet and the first adherend are likely to be firmly bonded together. If the volume content of the second dielectric filler is 5% by volume or more, the second adhesive sheet and the second adherend are likely to be firmly bonded together. If the volume content of the first dielectric filler is 50% by volume or less, flexibility of the first adhesive sheet is easily obtained and a decrease in toughness is easily prevented, so that the adhesive sheet can be easily processed into a desired shape. If the volume content of the second dielectric filler is 50% by volume or less, flexibility of the second adhesive sheet can be easily obtained and a decrease in toughness can be easily prevented, making it easy to process the adhesive sheet into a desired shape. If the volume content of the first dielectric filler and the volume content of the second dielectric filler are both 5% by volume or more, the bonding method of this embodiment makes it easy to firmly bond the first adherend and the second adherend, which are made of different materials. If the volume content of the first dielectric filler and the volume content of the second dielectric filler are both 50 volume % or less, both the first adhesive sheet and the second adhesive sheet are more likely to be flexible and a decrease in toughness is more likely to be prevented, making it easier to process the adhesive sheets into the desired shape. The volume content of the first dielectric filler in the first adhesive sheet and the volume content of the second dielectric filler in the second adhesive sheet may be the same as or different from each other.

[0059] Volume average particle size At least one of the volume average particle diameter of the first dielectric filler and the volume average particle diameter of the second dielectric filler is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. At least one of the volume average particle diameter of the first dielectric filler and the volume average particle diameter of the second dielectric filler is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. If the volume average particle size of the first dielectric filler in the first adhesive sheet is 1 μm or more, the first adhesive sheet can exhibit high heat generation performance when high frequency is applied. If the volume average particle size of the first dielectric filler in the first adhesive sheet is 30 μm or less, it is possible to prevent a decrease in the strength of the first adhesive sheet, and also to achieve high heat generation performance when high frequency is applied. If the volume average particle size of the second dielectric filler in the second adhesive sheet is 1 μm or more, the second adhesive sheet can exhibit high heat generation performance when high frequency is applied. If the volume average particle size of the second dielectric filler in the second adhesive sheet is 30 μm or less, the strength of the second adhesive sheet can be prevented from decreasing, and high heat generation performance can be achieved when high frequency waves are applied. If the volume average particle diameter of the first dielectric filler and the volume average particle diameter of the second dielectric filler are both 1 μm or more, both the first adhesive sheet and the second adhesive sheet will exhibit high heat-generating performance when high-frequency voltage is applied, and the first adherend and the second adherend can be firmly bonded together in a shorter time. Furthermore, since the volume average particle diameter of the first dielectric filler and the volume average particle diameter of the second dielectric filler are both 30 μm or less, a decrease in the strength of the high-frequency dielectric heating adhesive sheet can be prevented, and the adhesive sheet as a whole can exhibit high heat generation performance when high frequency is applied. The volume average particle size of the first dielectric filler in the first adhesive sheet and the volume average particle size of the second dielectric filler in the second adhesive sheet may be the same as or different from each other.

[0060] The volume average particle diameter of the dielectric filler is measured by the following method: The particle size distribution of the dielectric filler is measured by the laser diffraction / scattering method, and the volume average particle diameter is calculated from the results of the particle size distribution measurement in accordance with JIS Z 8819-2:2001.

[0061] (additives) The high-frequency dielectric heating adhesive sheet according to this embodiment may or may not contain an additive. When the high-frequency dielectric heating adhesive sheet according to this embodiment contains an additive, it is preferable that at least one of the first adhesive sheet and the second adhesive sheet contains the additive.

[0062] When the high-frequency dielectric heating adhesive sheet according to this embodiment contains an additive, examples of the additive include a tackifier, a plasticizer, a wax, a colorant, an antioxidant, an ultraviolet absorber, an antibacterial agent, a coupling agent, a viscosity modifier, an organic filler, an inorganic filler, etc. The organic filler and the inorganic filler as additives are different from the dielectric filler.

[0063] The tackifier and plasticizer can improve the melting and adhesive properties of the high frequency dielectric heating adhesive sheet. Examples of tackifiers include rosin derivatives, polyterpene resins, aromatic modified terpene resins, hydrogenated aromatic modified terpene resins, terpene phenol resins, coumarone-indene resins, aliphatic petroleum resins, aromatic petroleum resins, and hydrogenated aromatic petroleum resins. Examples of plasticizers include petroleum-based process oils, natural oils, dialkyl dibasic acids, and low-molecular-weight liquid polymers. Examples of petroleum-based process oils include paraffin-based process oils, naphthenic process oils, and aromatic process oils. Examples of natural oils include castor oil and tall oil. Examples of dialkyl dibasic acids include dibutyl phthalate, dioctyl phthalate, and dibutyl adipate. Examples of low-molecular-weight liquid polymers include liquid polybutene and liquid polyisoprene.

[0064] When the high-frequency dielectric heating adhesive sheet according to this embodiment contains an additive, the content of the additive in the high-frequency dielectric heating adhesive sheet is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the total amount of the high-frequency dielectric heating adhesive sheet. The content of the additive in the high-frequency dielectric heating adhesive sheet is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0065] The high-frequency dielectric heating adhesive sheet according to this embodiment preferably does not contain conductive materials such as carbon or carbon compounds containing carbon as a main component (e.g., carbon black), metals, etc. The content of each conductive material is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0% by mass, based on the total mass of the high-frequency dielectric heating adhesive sheet. If the content of the conductive substance in the high-frequency dielectric heating adhesive sheet is 5 mass % or less, it becomes easier to prevent the problem of carbonization of the adhesive joint and the adherend due to electrical breakdown during dielectric heating treatment.

[0066] In the high-frequency dielectric heating adhesive sheet according to this embodiment, at least one of the total mass of the thermoplastic resin and the dielectric filler relative to the total mass of the first adhesive sheet and the total mass of the thermoplastic resin and the dielectric filler relative to the total mass of the second adhesive sheet is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. With respect to the total mass of the high-frequency dielectric heating adhesive sheet according to this embodiment, the total mass of the thermoplastic resin and the dielectric filler is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more.

[0067] [Form and characteristics of high frequency dielectric heating adhesive sheet] (Thickness of high frequency dielectric heating adhesive sheet) The thickness of at least one of the first adhesive sheet and the second adhesive sheet is preferably 5 μm or more, more preferably 25 μm or more, and even more preferably 50 μm or more. The thickness of at least one of the first adhesive sheet and the second adhesive sheet is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less. If the thickness of the first adhesive sheet is 5 μm or more, the heat generation property when high frequency is applied is improved. If the thickness of the second adhesive sheet is 5 μm or more, the heat generation property when high frequency is applied is improved. If the thickness of the first adhesive sheet is 1000 μm or less, the weight of the first adhesive sheet will not be too heavy. If the thickness of the second adhesive sheet is 1000 μm or less, the weight of the second adhesive sheet will not be too heavy. If the thickness of both the first adhesive sheet and the second adhesive sheet is 5 μm or more, the heat generation properties of both the first adhesive sheet and the second adhesive sheet that come into contact with the adherend when high frequency is applied are improved, making it easier to firmly bond the adherends together in a short period of time. If the thickness of both the first adhesive sheet and the second adhesive sheet is 1000 μm or less, the weight of the first adhesive sheet and the second adhesive sheet will not be too heavy, and the weight of the bonded body obtained by bonding the adherends together can be prevented from becoming heavy due to the weight of the adhesive sheets. The thicknesses of the first adhesive sheet and the second adhesive sheet as the high-frequency dielectric heating adhesive sheet according to this embodiment may be the same as or different from each other.

[0068] In the high-frequency dielectric heating adhesive sheet according to this embodiment, the average particle diameter D of the first dielectric filler F1 and the thickness T1 of the first adhesive sheet, T1 / D F1 and the average particle diameter D of the second dielectric filler F2 and the thickness T2 of the second adhesive sheet, T2 / D F2At least one of these is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and even more preferably 5 or more. Ratio T1 / D F1 and ratio T2 / D F2 At least one of these is preferably 2500 or less, preferably 2000 or less, preferably 1750 or less, more preferably 1000 or less, even more preferably 500 or less, even more preferably 100 or less, and even more preferably 50 or less. Ratio T1 / D F1 If is 1 or more, it is possible to prevent a decrease in adhesive strength caused by contact between the first dielectric filler and the adherend during bonding. Ratio T2 / D F2 When the ratio is 1 or more, it is possible to prevent a decrease in adhesive strength caused by contact between the second dielectric filler and the adherend during adhesion. Ratio T1 / D F1 If the value is 2500 or less, the load on the sheet manufacturing apparatus can be reduced when the first adhesive sheet is produced. Ratio T2 / D F2 If the value is 2500 or less, the load on the sheet manufacturing apparatus can be reduced when the second adhesive sheet is produced. Ratio T1 / D F1 and ratio T2 / D F2 When both are 1 or more, it is possible to prevent a decrease in adhesive strength caused by contact between the dielectric filler and the adherend in both the first adhesive sheet and the second adhesive sheet during adhesion. Ratio T1 / D F1 and ratio T2 / D F2 If both are 2500 or less, the load on the sheet manufacturing apparatus can be reduced when producing the high-frequency dielectric heating adhesive sheet. Ratio T1 / D F1 and the ratio T2 / D F2 are the same as or different from each other.

[0069] The total thickness of the multiple high-frequency dielectric heating adhesive sheets placed between the first adherend and the second adherend is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more. If the total thickness of the multiple high-frequency dielectric heating adhesive sheets is 10 μm or more, adhesive strength is easily achieved. There is no particular upper limit to the total thickness of multiple high-frequency dielectric heating adhesive sheets. As the total thickness of the adhesive sheets increases, the weight of the entire bonded body obtained by bonding the first adherend and the second adherend also increases. Therefore, it is preferable that the total thickness of the adhesive sheets be within a range that does not cause problems in practical use. Taking into consideration the practicality and formability of the high-frequency dielectric heating adhesive sheet, the total thickness of the adhesive sheets is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 600 μm or less.

[0070] (Dielectric properties of high frequency dielectric heating adhesive sheet (tanδ / ε'r)) The dielectric properties of the first adhesive sheet and the second adhesive sheet, that is, the dielectric loss tangent (tan δ) and the relative dielectric constant (ε'r), can be measured simply and accurately using an impedance material analyzer. At least one of the dielectric properties (tanδ / ε'r) of the first adhesive sheet and the second adhesive sheet is preferably 0.005 or greater, more preferably 0.008 or greater, and even more preferably 0.01 or greater. The dielectric property (tanδ / ε'r) of the high-frequency dielectric heating adhesive sheet is preferably 0.08 or less, more preferably 0.05 or less. The dielectric property (tanδ / ε'r) is the value obtained by dividing the dielectric loss tangent (tanδ) measured using an impedance material device or the like by the relative permittivity (ε'r) measured using an impedance material device or the like. If the dielectric properties of the first adhesive sheet are 0.005 or more, the problem of not generating the required amount of heat when subjected to dielectric heating treatment, making it difficult to firmly bond the first adhesive sheet to the adherend, can be prevented. If the dielectric properties of the second adhesive sheet are 0.005 or more, the problem of not generating the required amount of heat when subjected to dielectric heating treatment, making it difficult to firmly bond the second adhesive sheet to the adherend, can be prevented. If the dielectric property of the first adhesive sheet is 0.08 or less, the adherend in contact with the first adhesive sheet is less likely to be damaged. If the dielectric property of the second adhesive sheet is 0.08 or less, the adherend in contact with the second adhesive sheet is less likely to be damaged. If the dielectric properties of both the first adhesive sheet and the second adhesive sheet are 0.005 or higher, the above-mentioned problems can be prevented for both the first adhesive sheet and the second adhesive sheet that come into contact with the adherend, making it easier to firmly bond the adherends together. If the dielectric properties of both the first adhesive sheet and the second adhesive sheet are 0.08 or less, the adherends in contact with the first adhesive sheet and the second adhesive sheet are less likely to be damaged. The details of the method for measuring the dielectric properties of the high-frequency dielectric heating adhesive sheet are as follows: For the high-frequency dielectric heating adhesive sheet cut to a predetermined size, the relative permittivity (ε'r) and dielectric loss tangent (tanδ) are measured using an RF Impedance Material Analyzer E4991A (manufactured by Agilent) at 23°C and a frequency of 40.68 MHz, and the value of the dielectric property (tanδ / ε'r) is calculated.

[0071] [Method of manufacturing high frequency dielectric heating adhesive sheet] There are no particular limitations on the method for producing the first adhesive sheet and the second adhesive sheet as the high-frequency dielectric heating adhesive sheet according to this embodiment. When the first adhesive sheet and the second adhesive sheet are single-layer sheets, the above-mentioned components are premixed and kneaded using a known kneading device such as an extruder or a heated roll, and the sheet can be produced by a known molding method such as extrusion molding, calendar molding, injection molding, or casting molding.

[0072] [Adhesion method] The bonding method according to this embodiment uses a first adhesive sheet and a second adhesive sheet to bond a first adherend and a second adherend which are made of different materials.

[0073] The first adherend contains a third thermoplastic resin, and the first adhesive sheet preferably has the same main composition as the third thermoplastic resin. The first adhesive sheet is adhered to the first adherend. The second adherend contains a fourth thermoplastic resin, and the second adhesive sheet preferably has the same main composition as the fourth thermoplastic resin. The second adhesive sheet is adhered to the second adherend.

[0074] The third thermoplastic resin and the fourth thermoplastic resin are preferably each independently a resin appropriately selected from the thermoplastic resins described for the first adhesive sheet and the second adhesive sheet.

[0075] In this specification, the "main composition of the thermoplastic resin" refers to, for example, when the thermoplastic resin is a polymer, the repeating unit contained in the polymer that is most abundant in the polymer. When the thermoplastic resin is a polymer derived from a single monomer, the monomer unit (repeating unit) is the "main composition of the thermoplastic resin." When the thermoplastic resin is a copolymer, the repeating unit contained in the polymer that is most abundant is the "main composition of the thermoplastic resin." When the thermoplastic resin is a copolymer, the "main composition of the thermoplastic resin" in the copolymer refers to repeating units (monomer units) that are contained in an amount of 30% by mass or more, in one embodiment, repeating units that are contained in an amount of more than 30% by mass, in another embodiment, repeating units that are contained in an amount of 40% by mass or more, and in yet another embodiment, repeating units that are contained in an amount of 50% by mass or more. Furthermore, when the thermoplastic resin is a copolymer, the repeating units contained in the majority may be two or more types.

[0076] For example, if the first thermoplastic resin is an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene units as repeating units, and the third thermoplastic resin is also an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene units as repeating units, the main composition (repeating units) of the first thermoplastic resin and the main composition (repeating units) of the third thermoplastic resin are both ethylene, and the main compositions of the first thermoplastic resin and the third thermoplastic resin are the same.

[0077] For example, if the first thermoplastic resin is maleic anhydride-modified polypropylene containing 50% by mass or more of propylene units as repeating units, and the third thermoplastic resin is polypropylene, the main composition (repeating unit) of the first thermoplastic resin and the main composition (repeating unit) of the third thermoplastic resin are both propylene, and the main composition of the first thermoplastic resin and the third thermoplastic resin are the same.

[0078] Furthermore, for example, when the thermoplastic resin is a homopolymer, the repeating units constituting the polymer are the main composition of the thermoplastic resin. For example, when the first thermoplastic resin is polyethylene and the third thermoplastic resin is also polyethylene, the main composition (repeating unit) of both the first thermoplastic resin and the third thermoplastic resin is ethylene, and the main composition (repeating unit) of the first thermoplastic resin and the third thermoplastic resin is the same. The above-mentioned examples can also be applied to the "main composition of the thermoplastic resin" regarding the second thermoplastic resin and the fourth thermoplastic resin.

[0079] Examples of the combination of the first thermoplastic resin and the third thermoplastic resin, and the combination of the second thermoplastic resin and the fourth thermoplastic resin include the following combinations. (R1) Polyethylene and ethylene-vinyl acetate copolymer (R2) Polyethylene and EMAA (ethylene-methyl methacrylate copolymer) (R3) Polyethylene and EMA (ethylene methacrylate copolymer) (R4) Polyethylene and ethylene cycloolefin copolymer (R5) Polypropylene and modified polypropylene (R6) PS and SEBS (R7) PS and SBR (styrene butadiene rubber) (R8) PS and SEES (styrene-ethylene-ethylene-styrene block copolymer) (R9) PS and ABS (Acrylonitrile-Butadiene-Styrene Copolymer) (R10)PS and SIS

[0080] The surface of the first adherend that directly contacts the first adhesive sheet is preferably composed of a third thermoplastic resin. It is also preferable that the entire first adherend is composed of a third thermoplastic resin. Furthermore, when the first adherend has a multilayer structure, it is also preferable that the layer located on the outermost surface of the first adherend (outermost layer) is composed of a third thermoplastic resin. When the entire first adherend or the outermost layer of the first adherend is composed of a blend resin containing multiple resins, the volume content of the third thermoplastic resin in the entire first adherend or the outermost layer of the first adherend is preferably 50% by volume or more, more preferably 60% by volume or more, even more preferably 70% by volume or more, even more preferably 80% by volume or more, and even more preferably 90% by volume or more.

[0081] The surface of the second adherend that directly contacts the second adhesive sheet is preferably composed of a fourth thermoplastic resin. It is also preferable that the entire second adherend is composed of a fourth thermoplastic resin. Furthermore, when the second adherend has a multilayer structure, it is also preferable that the layer located on the outermost surface (outermost layer) of the second adherend is composed of a fourth thermoplastic resin. When the entire second adherend or the outermost layer of the second adherend is composed of a blend resin containing multiple resins, the volume content of the fourth thermoplastic resin in the entire second adherend or the outermost layer of the second adherend is preferably 50% by volume or more, more preferably 60% by volume or more, even more preferably 70% by volume or more, even more preferably 80% by volume or more, and even more preferably 90% by volume or more.

[0082] The shapes of the first and second adherends are not particularly limited, but are preferably sheet-like. The shapes of the first and second adherends may be the same or different in shape and size as long as they are made of the materials described above.

[0083] The bonding method according to this embodiment preferably includes the following steps P1 and P2.

[0084] ·Process P1 Step P1 is a step of placing the adhesive sheet according to this embodiment between a first adherend and a second adherend. In step P1, the first adherend is brought into contact with the first adhesive sheet. Also, in step P1, the second adherend is brought into contact with the second adhesive sheet. Step P1 is preferably one of Step P11, in which the first and second adhesive sheets, both of which are single-layer sheets, are simply placed in contact with each other without being integrated, Step P12, in which the first and second adhesive sheets are placed one on top of the other without being integrated, or Step P13, in which the first and second adhesive sheets are placed one on top of the other without being integrated. Examples of integration methods include thermal lamination and punching. For example, the first and second adhesive sheets may be punched (die-cut) together and the edges of the die-cut sheet crushed to simulate integration of the sheets.

[0085] In the bonding method according to the present embodiment, it is preferable that the sheet in direct contact with the first adhesive sheet is the second adhesive sheet, in which case the relationship between the rates of change Vx1 and Vx2 expressed by the above formulas (Equation 1) and (Equation 2) holds between the first adhesive sheet and the second adhesive sheet.

[0086] A schematic cross-sectional view for explaining an example of the bonding method according to this embodiment is shown in Fig. 1. Fig. 1 shows, as an example of step P11, the procedure for arranging a first adhesive sheet 10 and a second adhesive sheet 20 between a first adherend 110 and a second adherend 120. FIG. 1(A) is a diagram showing the step of placing a second adhesive sheet 20 in contact with a second adherend 120. As shown in FIG. FIG. 1(B) is a diagram showing the step following FIG. 1(A), in which the first adhesive sheet 10 is placed in direct contact with the second adhesive sheet 20. As shown in FIG. FIG. 1(C) shows the step following FIG. 1(B), in which a first adherend 110 is placed in contact with the first adhesive sheet 10. As shown in FIG.

[0087] In Figure 1, the sheet in direct contact with the first adhesive sheet 10 is the second adhesive sheet 20. When the first adhesive sheet 10 and the second adhesive sheet 20 are in direct contact, the meanings of the symbols in the above formulas (Equation 1) and (Equation 2) are as follows: VA1: Volume content of the first thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet 10 VB1: Volume content of the first thermoplastic resin relative to all thermoplastic resins in the second adhesive sheet 20 VA2: Volume content of the second thermoplastic resin relative to all thermoplastic resins in the second adhesive sheet 20 VB2: Volume content of the second thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet 10

[0088] Fig. 2 shows a schematic cross-sectional view illustrating an example of the bonding method according to this embodiment. Fig. 2 shows, as an example of step P13, a procedure in which the first adhesive sheet 10 and the second adhesive sheet 20 are laminated in direct contact with each other to obtain an integrated high-frequency dielectric heating adhesive sheet 1 by thermal lamination or the like, and then the high-frequency dielectric heating adhesive sheet 1 is placed between the first adherend 110 and the second adherend 120. FIG. 2(A) is a diagram showing a process for directly laminating a first adhesive sheet 10 and a second adhesive sheet 20 to obtain an integrated high-frequency dielectric heating adhesive sheet 1. FIG. 2(B) shows a step following FIG. 2(A) in which the second adhesive sheet 20 side of the high-frequency dielectric heating adhesive sheet 1 is placed in contact with a second adherend 120. As shown in FIG. FIG. 2(C) shows the step following FIG. 2(B) in which a first adherend 110 is placed in contact with the first adhesive sheet 10 side of the high-frequency dielectric heating adhesive sheet 1.

[0089] The first adhesive sheet and the second adhesive sheet may be disposed between the first and second adherends so as to bond them together. The first adhesive sheet and the second adhesive sheet may be in contact with each other at a portion, multiple locations, or the entire surface of the first and second adherends. From the viewpoint of improving the adhesive strength between the first and second adherends, it is preferable that the first adhesive sheet and the second adhesive sheet be in contact with each other over the entire adhesive surface between the first and second adherends. Another example of an embodiment in which the first adhesive sheet and the second adhesive sheet are sandwiched between the first and second adherends in a portion of the space between the first and second adherends is an embodiment in which the first adhesive sheet and the second adhesive sheet are disposed in a frame shape along the periphery of the adhesive surface between the first and second adherends and are in contact with the first and second adherends. By arranging the first adhesive sheet and the second adhesive sheet in a frame shape in this way, adhesive strength between the first adherend and the second adherend can be obtained, and the joined body can be made lighter than when the first adhesive sheet and the second adhesive sheet are arranged over the entire adhesive surface. Furthermore, according to one embodiment in which the first adhesive sheet and the second adhesive sheet are arranged partially between the first adherend and the second adherend, the size of the first adhesive sheet and the second adhesive sheet used can be reduced, and therefore the high-frequency dielectric heating treatment time can be shortened compared to when the first adhesive sheet and the second heating adhesive sheet are arranged over the entire adhesive surface.

[0090] ·Process P2 Step P2 is a step of bonding a first adherend to a first adhesive sheet and bonding a second adherend to a second adhesive sheet. In step P2, the first adhesive sheet and second adhesive sheet arranged in step P1 are sandwiched between the first adherend and the second adherend, and high-frequency voltage is applied to the first adhesive sheet and the second adhesive sheet. In step P2, a high-frequency voltage can be applied to the high-frequency dielectric heating adhesive sheet by using, for example, a dielectric heating bonding device. Unlike the case where multiple adhesive sheets are laminated in advance as shown in Figure 2, in the case of a bonding method in which individual adhesive sheets are placed between a first adherend and a second adherend as shown in Figure 1, the adhesive sheets are bonded to each other while bonding the adherends to the adhesive sheets in step P2. Furthermore, even if multiple adhesive sheets have been temporarily fixed to each other in advance, the adhesive sheets are bonded to each other more firmly by the application of high frequency.

[0091] FIG. 3 shows a schematic diagram illustrating a high-frequency dielectric heating treatment using the high-frequency dielectric heating adhesive sheet and dielectric heating device according to this embodiment.

[0092] (Dielectric heating bonding device) FIG. 3 shows a schematic diagram of a dielectric heating bonding apparatus 50. The dielectric heating bonding device 50 includes a first high-frequency applying electrode 51 , a second high-frequency applying electrode 52 , and a high-frequency power supply 53 . The first high-frequency applied electrode 51 and the second high-frequency applied electrode 52 are disposed opposite each other. The first high-frequency applied electrode 51 and the second high-frequency applied electrode 52 have a pressing mechanism. This pressing mechanism allows the first adherend 110, the high-frequency dielectric heating adhesive sheet (the first adhesive sheet 10 and the second adhesive sheet 20), and the second adherend 120 to be pressurized between the first high-frequency applied electrode 51 and the second high-frequency applied electrode 52.

[0093] When the first high-frequency applying electrode 51 and the second high-frequency applying electrode 52 form a pair of parallel plate electrodes, this type of electrode arrangement is sometimes called a parallel plate type. It is also preferable to use a parallel plate type high frequency dielectric heating device for applying high frequency waves. With a parallel plate type high frequency dielectric heating device, the high frequency waves penetrate the high frequency dielectric heating adhesive sheet (first adhesive sheet 10 and second adhesive sheet 20) located between the electrodes, so the entire high frequency dielectric heating adhesive sheet can be heated and the adherend and the high frequency dielectric heating adhesive sheet can be bonded in a short time.

[0094] A high frequency power supply 53 is connected to each of the first high frequency applying electrode 51 and the second high frequency applying electrode 52 to apply a high frequency voltage with a frequency of, for example, about 13.56 MHz, about 27.12 MHz, or about 40.68 MHz. 3, the dielectric heating bonding apparatus 50 performs a dielectric heating treatment via high-frequency dielectric heating adhesive sheets (first adhesive sheet 10 and second adhesive sheet 20) sandwiched between a first adherend 110 and a second adherend 120. In addition to the dielectric heating treatment, the dielectric heating bonding apparatus 50 also bonds the first adherend 110 and the second adherend 120 by a pressure treatment using a first high-frequency application electrode 51 and a second high-frequency application electrode 52. Note that the first adherend 110 and the second adherend 120 may also be bonded without performing the pressure treatment. Furthermore, if the first adhesive sheet 10 and the second adhesive sheet 20 are not laminated together in advance, the first adhesive sheet 10 and the second adhesive sheet 20 will also be bonded together during the dielectric heating treatment.

[0095] When a high-frequency electric field is applied between the first high-frequency applying electrode 51 and the second high-frequency applying electrode 52, if the first adhesive sheet 10 and the second adhesive sheet 20 in the high-frequency dielectric heating adhesive sheet contain a dielectric filler (not shown), the dielectric filler absorbs the high-frequency energy. The dielectric filler functions as a heat source, and the heat generated by the dielectric filler melts the thermoplastic resin components in the first adhesive sheet 10 and the second adhesive sheet 20, ultimately firmly bonding the first adherend 110 and the second adherend 120 even after a short treatment. If the adhesive sheet does not contain a dielectric filler, a thermoplastic resin that can generate heat at high frequency is used, and the thermoplastic resin is made to function as a heat source.

[0096] The first high-frequency applied electrode 51 and the second high-frequency applied electrode 52 have a pressing mechanism, and therefore also function as a pressing device. Therefore, the first adherend 110 and the second adherend 120 can be more firmly bonded together by the application of pressure in the compression direction by the first high-frequency applied electrode 51 and the second high-frequency applied electrode 52 and the heating and melting of the high-frequency dielectric heating adhesive sheets (first adhesive sheet 10 and second adhesive sheet 20).

[0097] (High frequency dielectric heating bonding conditions) The high-frequency dielectric heating bonding conditions can be changed as appropriate, but the following conditions are preferred.

[0098] The high frequency output is preferably 10 W or more, more preferably 30 W or more, even more preferably 50 W or more, and even more preferably 80 W or more. The high frequency output is preferably 50,000 W or less, more preferably 20,000 W or less, even more preferably 15,000 W or less, even more preferably 10,000 W or less, and even more preferably 1,000 W or less. If the high frequency output is 10 W or more, the problem of the temperature not rising easily during the dielectric heating process can be prevented, and good adhesive strength can be easily obtained. If the high frequency output is 50,000 W or less, it is easy to prevent problems that make it difficult to control the temperature by dielectric heating treatment.

[0099] The application time of the high frequency is preferably 1 second or more. The application time of the high frequency is preferably 60 seconds or less, more preferably 45 seconds or less, even more preferably 35 seconds or less, even more preferably 25 seconds or less, and even more preferably 10 seconds or less. If the high frequency application time is 1 second or more, the problem of the temperature not rising easily during the dielectric heating process can be prevented, and good adhesive strength can be easily obtained. If the high frequency application time is 60 seconds or less, it is easy to prevent problems such as a decrease in the production efficiency of the bonded body in which the first adherend and the second adherend are bonded, an increase in the production cost of the bonded body, and thermal deterioration of the adherends.

[0100] The frequency of the applied high frequency is preferably 1 kHz or higher, more preferably 1 MHz or higher, even more preferably 5 MHz or higher, and even more preferably 10 MHz or higher. The frequency of the applied high frequency is preferably 300 MHz or less, more preferably 100 MHz or less, even more preferably 80 MHz or less, and even more preferably 50 MHz or less. Specifically, the industrial frequency bands of 13.56 MHz, 27.12 MHz, and 40.68 MHz assigned by the International Telecommunication Union are also used in the high frequency dielectric heating bonding method (bonding method) of this embodiment.

[0101] The bonding method according to this embodiment is a bonding method for bonding a first adherend and a second adherend made of a different material to the first adherend using a plurality of high-frequency dielectric heating adhesive sheets. The change rates Vx1 and Vx2, expressed by the above formulas (1) and (2), for the first and second adhesive sheets used in the bonding method according to this embodiment are less than 80%. Therefore, the bonding method according to this embodiment can firmly bond the first and second adherends made of different materials. Furthermore, the bonding method according to this embodiment makes it difficult for the first and second adhesive sheets to peel from each other.

[0102] According to the bonding method of this embodiment, a first adhesive sheet and a second adhesive sheet are prepared separately depending on the material of the first adherend and the material of the second adherend, and are placed between the adherends, and then high-frequency dielectric heating is performed, thereby bonding the first adherend and the second adherend. Therefore, according to the bonding method of this embodiment, it is possible to provide bonding that flexibly corresponds to the material of the adherend by simply preparing a single-layer sheet, without having to previously manufacture and prepare multilayer adhesive sheets with compositions depending on the material of the first adherend and the second adherend.

[0103] The high-frequency dielectric heating adhesive sheets (first and second adhesive sheets) used in the bonding method according to this embodiment are easier to handle than adhesives that require application, and the workability when bonding the first and second adherends is improved. According to the bonding method according to this embodiment, the adherends can be bonded by applying high frequency for a short period of time.

[0104] According to the bonding method of this embodiment, it is possible to locally heat only a predetermined location from the outside using a dielectric heating bonding device, so the bonding method of this embodiment is effective even when the adherend has a large and complex three-dimensional structure or a thick and complex three-dimensional structure, etc., and even when high dimensional accuracy is required.

[0105] The high frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment has superior water resistance and moisture resistance compared to general adhesives.

[0106] The high-frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment does not contain a solvent, and therefore is less likely to cause problems with VOCs (Volatile Organic Compounds) that are caused by the adhesive used to bond to the adherend.

[0107] The high-frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment is heated by applying a high-frequency voltage, which causes the high-frequency dielectric heating adhesive sheet to be heated locally, making it easier to prevent the entire adherend from melting when being bonded to the adherend.

[0108] Furthermore, the high-frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment allows for the thickness of the high-frequency dielectric heating adhesive sheet to be appropriately controlled. Therefore, the high-frequency dielectric heating adhesive sheet according to this embodiment can be applied to the roll-to-roll method, and the high-frequency dielectric heating adhesive sheet can be processed into any area and shape by punching or other processes to match the bonding area with the adherend and the shape of the adherend. Therefore, the high-frequency dielectric heating adhesive sheet used in the bonding method according to this embodiment has great advantages from the viewpoint of the manufacturing process.

[0109] Second Embodiment In the bonding method according to this embodiment, an intermediate sheet is further disposed between the first adhesive sheet and the second adhesive sheet. The multiple high-frequency dielectric heating adhesive sheets used in the bonding method according to this embodiment include at least a first adhesive sheet, a second adhesive sheet, and an intermediate sheet. The bonding method according to this embodiment differs from the bonding method according to the first embodiment in that an intermediate sheet is used, but is otherwise similar to the bonding method and high-frequency dielectric heating adhesive sheets according to the first embodiment. Therefore, in the following explanation, differences from the first embodiment will be mainly explained, and overlapping explanations will be omitted or simplified. The same components as those in the first embodiment will be assigned the same reference numerals, and explanations will be omitted or simplified.

[0110] (middle seat) In this embodiment, the intermediate sheet preferably contains one or more types of thermoplastic resins, and more preferably contains a first thermoplastic resin and a second thermoplastic resin.

[0111] In this embodiment, it is preferable that at least one of the first adhesive sheet and the second adhesive sheet is in direct contact with the intermediate sheet, and it is also preferable that both the first adhesive sheet and the second adhesive sheet are in direct contact with the intermediate sheet.

[0112] In this embodiment, when the first adhesive sheet and the intermediate sheet are in direct contact with each other and the second adhesive sheet and the intermediate sheet are in direct contact with each other, the meanings of the symbols in the above formulas (1) and (2) are as follows: VA1: Volume content of the first thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet VB1: Volume content of the first thermoplastic resin relative to all thermoplastic resins in the intermediate sheet VA2: Volume content of the second thermoplastic resin relative to all thermoplastic resins in the second adhesive sheet VB2: Volume content of the second thermoplastic resin relative to all thermoplastic resins in the intermediate sheet

[0113] In this embodiment as well, it is preferable that the first adhesive sheet, the intermediate sheet, and the second adhesive sheet satisfy the same relationship between the change rates Vx1 and Vx2 as in the first embodiment.

[0114] In this embodiment, the intermediate sheet preferably contains a third dielectric filler that generates heat at high frequency. When the intermediate sheet contains the third dielectric filler, the intermediate sheet is also heated when a high-frequency voltage is applied, making it easier to melt the first adhesive sheet and the second adhesive sheet that are in contact with the intermediate sheet in a short period of time. As a result, according to this embodiment, the first adherend and the second adherend can be firmly bonded in a short period of time.

[0115] The third dielectric filler can be the same as the first dielectric filler and the second dielectric filler described in the first embodiment. The third dielectric filler and the first dielectric filler may be the same as or different from each other. The third dielectric filler and the second dielectric filler may be the same as or different from each other. The first dielectric filler, the second dielectric filler and the third dielectric filler are preferably each independently at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide and barium titanate. The first dielectric filler, the second dielectric filler and the third dielectric filler are preferably the same type of dielectric filler, and more preferably, all of them are zinc oxide.

[0116] The volume average particle size and volume content of the third dielectric filler and the first dielectric filler may be the same or different. The volume average particle size and volume content of the third dielectric filler and the second dielectric filler may be the same or different.

[0117] It is also preferable that the intermediate sheet does not contain a third dielectric filler that generates heat at high frequencies. If the intermediate sheet does not contain a third dielectric filler, the intermediate sheet will not generate heat when a high-frequency voltage is applied, which makes it easier to prevent the first adhesive sheet, intermediate sheet, and second adhesive sheet from melting too much and spilling out from the adhesive surfaces of the adherends.

[0118] The high-frequency dielectric heating adhesive sheet according to this embodiment may or may not contain an additive. If the high-frequency dielectric heating adhesive sheet according to this embodiment contains an additive, it is preferable that at least one of the first adhesive sheet, the intermediate sheet, and the second adhesive sheet contains the additive. For example, the same additive as that described in the first embodiment can also be used in the high-frequency dielectric heating adhesive sheet according to this embodiment.

[0119] In the high-frequency dielectric heating adhesive sheet according to this embodiment, the average particle diameter D F1 and the thickness T1 of the first adhesive sheet, T1 / D F1 It is preferable that the same relationship as in the first embodiment is satisfied. In the high-frequency dielectric heating adhesive sheet according to this embodiment, the average particle diameter D F2 and the thickness T2 of the second adhesive sheet, T2 / D F2 It is preferable that the same relationship as in the first embodiment is satisfied.

[0120] (Thickness of high frequency dielectric heating adhesive sheet) In the high-frequency dielectric heating adhesive sheet according to this embodiment, the thicknesses of the first adhesive sheet and the second adhesive sheet are preferably each independently within the thickness ranges described in the first embodiment. The thickness of the intermediate sheet is preferably 5 μm or more, more preferably 25 μm or more, and even more preferably 50 μm or more. The thickness of the intermediate sheet is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less. If the thickness of the intermediate sheet is 5 μm or more, the intermediate sheet is easy to form. If the thickness of the intermediate sheet is 1000 μm or less, the weight of the intermediate sheet will not be too heavy.

[0121] In this embodiment, for the same reasons as in the first embodiment, the total thickness of the multiple high-frequency dielectric heating adhesive sheets placed between the first adherend and the second adherend is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 30 μm or more, and even more preferably 50 μm or more. Furthermore, for the same reasons as in the first embodiment, the total thickness of the multiple high-frequency dielectric heating adhesive sheets placed between the first adherend and the second adherend is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 600 μm or less.

[0122] [Method of manufacturing high frequency dielectric heating adhesive sheet] The manufacturing method of the first adhesive sheet, intermediate sheet, and second adhesive sheet as the high-frequency dielectric heating adhesive sheet according to this embodiment is not particularly limited, and they can be manufactured, for example, by the same method as in the first embodiment.

[0123] [Adhesion method] The bonding method according to this embodiment is a method for bonding a first adherend to a second adherend using the high-frequency dielectric heating adhesive sheet according to this embodiment. As with the first embodiment, the thermoplastic resin in the adherend and the thermoplastic resin in the adhesive sheet have the same main composition. The bonding method according to this embodiment preferably includes the following steps PX1 and PX2.

[0124] ·Process PX1 Step PX1 is a step of placing a first adhesive sheet, an intermediate sheet, and a second adhesive sheet according to this embodiment between a first adherend and a second adherend. In step PX1, the first adherend is brought into contact with the first adhesive sheet, the second adherend is brought into contact with the second adhesive sheet, and the intermediate sheet is placed between the first adhesive sheet and the second adhesive sheet. Step PX1 is preferably any one of Step PX11, in which the first adhesive sheet, intermediate sheet, and second adhesive sheet, which are all single-layer sheets, are simply placed in contact with each other without being integrated, Step PX12, in which the first adhesive sheet, intermediate sheet, and second adhesive sheet are placed one on top of the other without being integrated, or Step PX13, in which the first adhesive sheet, intermediate sheet, and second adhesive sheet are placed together beforehand. The method for integrating the adhesive sheets and intermediate sheets is not particularly limited, but examples include the thermal lamination and punching process described in the first embodiment.

[0125] A schematic cross-sectional view for explaining an example of the bonding method according to this embodiment is shown in Fig. 4. Fig. 4 shows, as an example of step PX11, the procedure for arranging the first adhesive sheet 10, the intermediate sheet 30, and the second adhesive sheet 20 between the first adherend 110 and the second adherend 120. FIG. 4(A) is a diagram showing the step of placing the second adhesive sheet 20 in contact with the second adherend 120. As shown in FIG. FIG. 4(B) shows a step following FIG. 4(A) in which an intermediate sheet 30 is placed in direct contact with the second adhesive sheet 20. As shown in FIG. FIG. 4(C) is a diagram showing the step following FIG. 4(B), in which the first adhesive sheet 10 is placed in direct contact with the intermediate sheet 30. As shown in FIG. FIG. 4(D) is a diagram showing the step following FIG. 4(C), in which the first adherend 110 is placed in contact with the first adhesive sheet 10. As shown in FIG.

[0126] Fig. 5 shows a schematic cross-sectional view illustrating an example of the bonding method according to this embodiment. As an example of PX13, Fig. 5 shows a procedure in which a first adhesive sheet 10, an intermediate sheet 30, and a second adhesive sheet 20 are laminated in direct contact with each other to obtain an integrated high-frequency dielectric heating adhesive sheet 1A by thermal lamination or the like, and then the high-frequency dielectric heating adhesive sheet 1A is placed between a first adherend 110 and a second adherend 120. FIG. 5(A) is a diagram showing a process for laminating a first adhesive sheet 10, an intermediate sheet 30, and a second adhesive sheet 20 in this order to obtain an integrated high-frequency dielectric heating adhesive sheet 1A. FIG. 5(B) shows a step following FIG. 5(A), in which the second adhesive sheet 20 side of the high-frequency dielectric heating adhesive sheet 1A is placed in contact with a second adherend 120. As shown in FIG. FIG. 5(C) shows the step following FIG. 5(B) of placing a first adherend 110 in contact with the first adhesive sheet 10 side of the high-frequency dielectric heating adhesive sheet 1A.

[0127] ·Process PX2 Step PX2 is a step of bonding a first adherend to a first adhesive sheet and bonding a second adherend to a second adhesive sheet. In step PX2, the first adhesive sheet, intermediate sheet, and second adhesive sheet arranged in step PX1 are sandwiched between the first adherend and the second adherend, and high-frequency voltage is applied to the first adhesive sheet, intermediate sheet, and second adhesive sheet. In step PX2, a high-frequency voltage can be applied to the high-frequency dielectric heating adhesive sheet, for example, by using a dielectric heating bonding device similar to that in the first embodiment. Unlike the case where multiple adhesive sheets are laminated in advance as shown in Fig. 5, in the case of a bonding method in which individual adhesive sheets and intermediate sheets are placed between a first adherend and a second adherend as shown in Fig. 4, the adhesive sheets and intermediate sheets are bonded to each other while bonding the adherends to the adhesive sheets in step PX2. Furthermore, even if multiple adhesive sheets and intermediate sheets have been temporarily fixed together in advance, the adhesive sheets and intermediate sheets are more firmly bonded together by applying high frequency.

[0128] FIG. 6 shows a schematic diagram illustrating a method for bonding a first adherend 110 and a second adherend 120 using a dielectric heating bonding apparatus 50 and a high-frequency dielectric heating adhesive sheet (a first adhesive sheet 10, an intermediate sheet 30, and a second adhesive sheet 20). The high-frequency dielectric heating bonding conditions can be changed as appropriate, but are preferably the same as those described in the first embodiment.

[0129] The bonding method according to this embodiment is also a bonding method in which a first adherend and a second adherend made of a different material from the first adherend are bonded together using a plurality of high-frequency dielectric heating adhesive sheets, and has the same effects as those of the first embodiment. In the first adhesive sheet, intermediate sheet, and second adhesive sheet used in the bonding method according to this embodiment, the change rates Vx1 and Vx2 expressed by the above formulas (Mathematical Formula 1) and (Mathematical Formula 2) are all less than 80%. Therefore, the bonding method according to this embodiment can firmly bond a first adherend and a second adherend made of different materials. Furthermore, the bonding method according to this embodiment also makes it difficult for peeling to occur between the first adhesive sheet and the intermediate sheet, and between the second adhesive sheet and the intermediate sheet.

[0130] [Modifications of the embodiment] The present invention is not limited to the above-described embodiment, and may include modifications and improvements within the scope of achieving the object of the present invention.

[0131] In the above embodiments, a high-frequency dielectric heating adhesive sheet consisting of only two adhesive sheets, a first adhesive sheet and a second adhesive sheet, or a high-frequency dielectric heating adhesive sheet consisting of three sheets, a first adhesive sheet, an intermediate sheet, and a second adhesive sheet, has been described as an example, but the present invention is not limited to such examples. One aspect of the present invention also includes a high-frequency dielectric heating adhesive sheet consisting of a total of four or more sheets, for example, with the first adhesive sheet and the second adhesive sheet each arranged as the outermost layer.

[0132] The order in which the adhesive sheet and intermediate sheet are placed between the first adherend and the second adherend is not limited to the order shown in the above-described embodiment in Figures 1, 2, 4, and 5. For example, instead of placing the adhesive sheet and intermediate sheet one by one as shown in Figures 1 and 4, a method in which the sheets are overlapped with each other and then placed together between the adherends without performing an integration process such as thermal lamination may be used.

[0133] The high-frequency dielectric heating adhesive sheet may have an adhesive portion. By having an adhesive portion, it is possible to prevent misalignment when sandwiching the high-frequency dielectric heating adhesive sheet between two adherends and to position it accurately. The adhesive portion may be provided on one side of the high-frequency dielectric heating adhesive sheet or on both sides. The adhesive portion may also be provided partially on one side of the high-frequency dielectric heating adhesive sheet. Even if the high-frequency dielectric heating adhesive sheet does not have an adhesive portion, it can firmly bond a first adherend and a second adherend.

[0134] The high-frequency dielectric heating process is not limited to the dielectric heating bonding device with electrodes arranged opposite to each other as described in the above embodiment, and a grid-type high-frequency dielectric heating device may also be used. A grid-type high-frequency dielectric heating device has a grid electrode in which electrodes of a first polarity and electrodes of a second polarity opposite to the first polarity are alternately arranged at regular intervals on the same plane. For example, when producing a bonded body in which the end of a first adherend and the end of a second adherend are overlapped and bonded, a grid electrode type high frequency dielectric heating device is placed on the first adherend side or the second adherend side to apply high frequency.

[0135] When a first adherend and a second adherend are bonded using a grid electrode type high-frequency dielectric heating device, a first grid electrode may be placed on the side of the first adherend and a second grid electrode may be placed on the side of the second adherend, and the first adherend, high-frequency dielectric heating adhesive sheet, and second adherend may be sandwiched between the first grid electrode and the second grid electrode and high-frequency waves may be applied simultaneously.

[0136] When a first adherend and a second adherend are bonded using a grid electrode type high-frequency dielectric heating device, the grid electrode may be placed on one side of the first adherend and the second adherend, high frequency may be applied, and then the grid electrode may be placed on the other side of the first adherend and the second adherend, and high frequency may be applied.

[0137] It is also preferable to use a grid electrode type high-frequency dielectric heating device for applying high-frequency waves. By using a grid electrode type high-frequency dielectric heating device, the adherends can be bonded together by dielectrically heating the surface side of the first and second adherends, for example, the side of the adherend closest to the high-frequency dielectric heating adhesive sheet, without being affected by the thickness of the first and second adherends. Furthermore, using a grid electrode type high-frequency dielectric heating device can achieve energy savings in the production of bonded bodies.

[0138] For the sake of simplicity, the drawings show an example in which a dielectric heating bonding device is used in which electrodes are arranged opposite each other. [Example]

[0139] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0140] [High frequency dielectric heating adhesive sheet manufacturing method] Example 1 The materials for forming the first adhesive sheet were premixed in a first container with the composition (volume %) shown in Table 1. The materials for forming the second adhesive sheet were also premixed in a second container with the composition (volume %) shown in Table 1. PP in Table 1 is an abbreviation for polypropylene, and SEBS is an abbreviation for styrene-ethylene / butylene-styrene copolymer. PP: The main component is propylene (95% by mass or more), and the flow starting temperature is 175°C. SEBS: The main component is styrene (67% by mass), and the flow temperature is 137°C.

[0141] The premixed materials were fed into the hopper of a 30 mm diameter twin-screw extruder, and the cylinder temperature was set to 180°C or higher and 220°C or lower, and the die temperature was set to 220°C, where the premixed materials were melt-kneaded. The melt-kneaded materials were cooled and then cut to produce granular pellets. Granular pellets for a first adhesive sheet and a second adhesive sheet were produced. The produced granular pellets were then fed into the hopper of a single-screw extruder equipped with a T-die having a feed block. A film-like melt-kneaded material was extruded from the T-die under conditions of a cylinder temperature of 220°C and a die temperature of 220°C, and cooled on a cooling roll to produce the first adhesive sheet (thickness: 200 μm) and the second adhesive sheet (thickness: 200 μm) used in the bonding method of Example 1.

[0142] (Examples 2 to 6) In Examples 2 to 6, a first adhesive sheet, a second adhesive sheet, and an intermediate sheet were prepared. The materials for forming the intermediate sheet were premixed in a third container with the composition (volume %) shown in Table 1. In the same manner as in Example 1, granular pellets for the first adhesive sheet, granular pellets for the second adhesive sheet, and granular pellets for the intermediate sheet were prepared with the composition (volume %) shown in Table 1. Next, the granular pellets for the first adhesive sheet, the intermediate sheet, and the second adhesive sheet were loaded into the hopper of a single-screw extruder equipped with a T-die having a feed block, and a film-like molten mixture was extruded from the T-die at cylinder and die temperatures set appropriately according to the type of resin contained in each sheet, and cooled with a cooling roll to produce the first adhesive sheet (thickness: 135 μm), intermediate sheet (thickness: 130 μm), and second adhesive sheet (thickness: 135 μm) used in the bonding methods of Examples 2 to 5, and the first adhesive sheet (thickness: 200 μm) and second adhesive sheet (thickness: 200 μm) used in the bonding method of Example 6. In Table 1, PMMA is an abbreviation for polymethyl methacrylate, PS is an abbreviation for polystyrene, EVA is an abbreviation for ethylene-vinyl acetate copolymer, and m-PP is an abbreviation for maleic anhydride-modified polypropylene. PMMA: The main component is methyl methacrylate (95% by mass or more), and the flow starting temperature is 165°C. PS: The main component is styrene (95% by mass or more), and the flow starting temperature is 162°C. EVA: The main component is ethylene (72% by mass), and the flow starting temperature is 94°C. m-PP: The main component is propylene (90% by mass or more), and the flow temperature is 153°C.

[0143] (Comparative Examples 1 to 3) The adhesive sheets used in the bonding methods of Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that the compositions of the materials used to form the first adhesive sheet and the second adhesive sheet were changed to those shown in Table 1, and extrusion molding was performed at cylinder and die temperatures set appropriately depending on the type of resin contained in each layer of the adhesive sheet. In Comparative Examples 1 to 3, the thicknesses of the first adhesive sheet and the second adhesive sheet were also the same as in Example 1.

[0144] Comparative Example 4 The adhesive sheets used in the bonding method of Comparative Example 4 were produced in the same manner as in Example 2, except that the compositions of the materials for forming the first adhesive sheet, intermediate sheet, and second adhesive sheet were changed to the compositions shown in Table 1, and extrusion molding was carried out at cylinder and die temperatures set appropriately depending on the type of resin contained in each layer of the adhesive sheet. In Comparative Example 4, the thicknesses of the first adhesive sheet, intermediate sheet, and second adhesive sheet were also the same as in Example 2.

[0145] Table 2 shows the volume content of each thermoplastic resin in the first adhesive sheet, second adhesive sheet, and intermediate sheet that were produced, as well as the values ​​of the change rates Vx1 and Vx2 expressed by the above formulas (Equation 1) and (Equation 2).

[0146] [High frequency adhesiveness] The high-frequency dielectric heating adhesive sheet (adhesive sheet and intermediate sheet) was cut to a size of 25 mm x 12.5 mm. A first adherend and a second adherend were prepared from the materials shown in Table 1. The dimensions of both the first adherend and the second adherend were 25 mm x 100 mm x 2 mm (thickness). The adhesive sheet and intermediate sheet cut to the aforementioned size were sandwiched between the first adherend and the second adherend in the combination shown in Table 1. At this time, the first adhesive sheet was in contact with the first adherend, and the second adhesive sheet was in contact with the second adherend. In Examples 1 and 6 and Comparative Examples 1 to 3, the first adhesive sheet and the second adhesive sheet were placed in direct contact with each other. In Examples 2 to 5 and Comparative Example 4, an intermediate sheet was placed between the first adhesive sheet and the second adhesive sheet, directly contacting both. Next, the first adherend, high-frequency dielectric heating adhesive sheet, and second adherend were fixed between the electrodes of a high-frequency dielectric heating device (YRP-400T-A manufactured by Yamamoto Vinita Co., Ltd.). In this fixed state, high frequency was applied under the high-frequency application conditions described below to bond the high-frequency dielectric heating adhesive sheet and the adherend, thereby producing an initial test piece. In this example, the sheet sandwiched between the first adherend and the second adherend may be collectively referred to as the high-frequency dielectric heating adhesive sheet. In Table 1, PP, which is the material of the first adherend, is an abbreviation for polypropylene, PMMA is an abbreviation for polymethyl methacrylate, PE is an abbreviation for polyethylene, and PS, which is the material of the second adherend, is an abbreviation for polystyrene. PP: The main component is propylene (95% by mass or more). PMMA: The main component is methyl methacrylate (95% by mass or more). PS: The main component is styrene (95% by mass or more). PE: The main component is ethylene (70% by mass or more).

[0147] High frequency application conditions Frequency: 40.68MHz Output: 200W Application time: 10 seconds

[0148] [Adhesion strength (tensile shear strength)] The initial test pieces obtained in the high-frequency adhesiveness evaluation were measured for tensile shear strength as adhesive strength. A universal tensile tester (Instron 5581, manufactured by Instron) was used to measure the tensile shear strength. The tensile speed in measuring the tensile shear strength was set to 100 mm / min. The tensile shear strength was measured in accordance with JIS K 6850:1999. The fracture morphology of the test piece during the measurement of tensile shear force was observed, and the adhesive strength was evaluated according to the following evaluation criteria. The evaluation results of adhesive strength are shown in Table 1. Destruction form Cf: At least one of the adhesive sheet and the intermediate sheet underwent cohesive failure. BC: At least one of the first adherend and the second adherend was destroyed. IF S : Interfacial peeling occurred between at least one of the adhesive sheet and the intermediate sheet. IF A : Interfacial peeling occurred between the first adherend and the first adhesive sheet. IF B : Interfacial peeling occurred between the second adherend and the second adhesive sheet.

[0149] [Volume average particle size of dielectric filler] The particle size distribution of the dielectric filler was measured by laser diffraction / scattering. The volume average particle diameter was calculated from the particle size distribution measurement results in accordance with JIS Z 8819-2:2001. The calculated average particle diameter (volume average particle diameter) of the dielectric filler (zinc oxide) was 11 μm.

[0150] [Flow start temperature] The flow initiation temperature of the thermoplastic resin used to prepare the adhesive sheet and intermediate sheet was measured using a drop-type flow tester (Shimadzu Corporation, model number "CFT-100D"). Using a 5.0 kg load, a die with a 2.0 mm diameter hole and a 5.0 mm length, and a cylinder with an inner diameter of 11.329 mm, the temperature of the sample was increased at a rate of 10 °C / min, while the stroke displacement rate (mm / min) was measured as it varied with the temperature increase. A temperature dependence chart of the sample's stroke displacement rate was obtained. The temperature at which the stroke displacement rate began to increase again after passing the peak on the low-temperature side was taken as the flow initiation temperature.

[0151] [Dielectric properties] The prepared adhesive sheet was cut into a size of 30 mm x 30 mm. The dielectric constant (ε'r) and dielectric loss tangent (tanδ) of the cut high-frequency dielectric heating adhesive sheet were measured using a parallel plate method at a frequency of 40.68 MHz at 23°C using a dielectric material test fixture 16453A (Agilent) attached to an RF impedance material analyzer E4991A (Agilent). Based on the measurement results, the dielectric property (tanδ / ε'r) was calculated. For example, the dielectric properties (tanδ / ε'r) of the first adhesive sheet and second adhesive sheet according to Examples 1 to 6 are shown in Table 1.

[0152] [Table 1]

[0153] [Table 2]

[0154] In the bonding methods of Examples 1 to 6, the compositions of the first adhesive sheet, second adhesive sheet, and intermediate sheet satisfied the relationship between the change rates Vx1 and Vx2 expressed by the above-mentioned formulas (Mathematical Formula 1) and (Mathematical Formula 2). Therefore, the bonding methods of Examples 1 to 6 were able to firmly bond the first adherend and the second adherend without peeling between the sheets. In the bonding method according to Comparative Example 1, the volume content of the first thermoplastic resin (PP) in the first adhesive sheet was less than 60% by volume, and interfacial peeling occurred between the first adhesive sheet and the first adherend. In the bonding method according to Comparative Example 2, the volume content of the second thermoplastic resin (SEBS) in the second adhesive sheet was less than 60% by volume, and interfacial peeling occurred between the second adhesive sheet and the second adherend. In the bonding methods of Comparative Examples 3 and 4, the compositions of the first adhesive sheet, the second adhesive sheet, and the intermediate sheet did not simultaneously satisfy the relationship between the change rates Vx1 and Vx2 expressed by the above-mentioned formulas (Equation 1) and (Equation 2), and peeling occurred between the sheets. The bonding methods according to Comparative Examples 1 to 4 were unable to bond the first adherend and the second adherend. [Explanation of symbols]

[0155] 1...high frequency dielectric heating adhesive sheet, 1A...high frequency dielectric heating adhesive sheet, 10...first adhesive sheet, 20...second adhesive sheet, 30...intermediate sheet, 50...dielectric heating adhesive device, 51...first high frequency application electrode, 52...second high frequency application electrode, 53...high frequency power supply, 110...first adherend, 120...:second adherend.

Claims

1. A bonding method for bonding a first adherend and a second adherend made of a material different from that of the first adherend using a plurality of high-frequency dielectric heating adhesive sheets, comprising: the plurality of high-frequency dielectric heating adhesive sheets include at least a first adhesive sheet and a second adhesive sheet; the first adhesive sheet contains a first thermoplastic resin; the second adhesive sheet contains a second thermoplastic resin, the first adherend contains a third thermoplastic resin, the second adherend contains a fourth thermoplastic resin, the first thermoplastic resin and the second thermoplastic resin are different resins, the main composition of the first thermoplastic resin is the same as the main composition of the third thermoplastic resin; the main composition of the second thermoplastic resin is the same as the main composition of the fourth thermoplastic resin; a volume content VA1 of the first thermoplastic resin relative to all thermoplastic resins in the first adhesive sheet is 60% by volume or more and 100% by volume or less; a volume content VA2 of the second thermoplastic resin relative to all thermoplastic resins in the second adhesive sheet is 60% by volume or more and 100% by volume or less; a rate of change Vx1, expressed by the following formula (Mathematical Formula 1), between a volume content VA1 of the first thermoplastic resin and a volume content VB1 of the first thermoplastic resin relative to all thermoplastic resins in a sheet disposed so as to be in direct contact with the first adhesive sheet is less than 80%, the rate of change Vx2, expressed by the following formula (Mathematical Formula 2), between the volume content VA2 of the second thermoplastic resin and the volume content VB2 of the second thermoplastic resin relative to all thermoplastic resins in the sheet arranged so as to be in direct contact with the second adhesive sheet is less than 80%, a step of placing the first adhesive sheet between the first adherend and the second adherend so as to be in contact with the first adherend, and placing the second adhesive sheet between the first adherend and the second adherend so as to be in contact with the second adherend; and applying high frequency to the first adhesive sheet and the second adhesive sheet while sandwiching the first adhesive sheet and the second adhesive sheet between the first adherend and the second adherend, thereby bonding the first adhesive sheet to the first adherend and bonding the second adhesive sheet to the second adherend. A bonding method using a high-frequency dielectric heating adhesive sheet. Vx1={(VA1-VB1) / VA1}×100 (Equation 1) Vx2={(VA2-VB2) / VA2}×100 (Equation 2)

2. 2. The bonding method using the high-frequency dielectric heating adhesive sheet according to claim 1, further disposing an intermediate sheet between the first adhesive sheet and the second adhesive sheet; A bonding method using a high-frequency dielectric heating adhesive sheet.

3. 3. The bonding method using the high-frequency dielectric heating adhesive sheet according to claim 2, At least one of the first adhesive sheet and the second adhesive sheet is in direct contact with the intermediate sheet. A bonding method using a high-frequency dielectric heating adhesive sheet.

4. 4. A bonding method using the high-frequency dielectric heating adhesive sheet according to claim 2 or 3, The intermediate sheet contains the first thermoplastic resin and the second thermoplastic resin. A bonding method using a high-frequency dielectric heating adhesive sheet.

5. 2. The bonding method using the high-frequency dielectric heating adhesive sheet according to claim 1, the sheet in direct contact with the first adhesive sheet is the second adhesive sheet; A bonding method using a high-frequency dielectric heating adhesive sheet.

6. A bonding method using the high-frequency dielectric heating adhesive sheet according to any one of claims 1 to 5, At least one of the first adhesive sheet and the second adhesive sheet contains a dielectric filler that generates heat at high frequency. A bonding method using a high-frequency dielectric heating adhesive sheet.

7. 7. The bonding method using the high-frequency dielectric heating adhesive sheet according to claim 6, At least one of the volume content of the dielectric filler in the first adhesive sheet and the second adhesive sheet is 5 volume % or more and 50 volume % or less. A bonding method using a high-frequency dielectric heating adhesive sheet.

8. 8. A bonding method using the high-frequency dielectric heating adhesive sheet according to claim 6 or 7, At least one of the dielectric filler in the first adhesive sheet and the dielectric filler in the second adhesive sheet contains at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide, and barium titanate. A bonding method using a high-frequency dielectric heating adhesive sheet.

9. A bonding method using the high-frequency dielectric heating adhesive sheet according to any one of claims 6 to 8, At least one of the volume average particle diameter of the dielectric filler in the first adhesive sheet and the volume average particle diameter of the dielectric filler in the second adhesive sheet is 1 μm or more and 30 μm or less, The volume average particle diameter is a volume average particle diameter calculated from the particle size distribution measurement results in accordance with JIS Z 8819-2:2001 by measuring the particle size distribution by a laser diffraction / scattering method. A bonding method using a high-frequency dielectric heating adhesive sheet.

10. A bonding method using the high-frequency dielectric heating adhesive sheet according to any one of claims 1 to 9, The first thermoplastic resin is a polyolefin resin. A bonding method using a high-frequency dielectric heating adhesive sheet.

11. A bonding method using the high-frequency dielectric heating adhesive sheet according to any one of claims 1 to 10, The absolute value of the difference between the flow starting temperature Tx1 of the first thermoplastic resin and the flow starting temperature Tx2 of the second thermoplastic resin satisfies the relationship of the following mathematical formula (Mathematical Formula 4): A bonding method using a high-frequency dielectric heating adhesive sheet. |Tx1-Tx2|≦70... (Equation 4)

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