Adhesive for high-frequency dielectric heating

Abstract

An adhesive (1A) for high-frequency dielectric heating contains a thermoplastic resin (A) and a dielectric filler (B). When a cut surface obtained by cutting, along the thickness direction, the adhesive (1A) for high-frequency dielectric heating is observed by a scanning electron microscope, the relationship of the distance Dg between nearest centroids of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) satisfies formula (F1).　(F1): 1.55 ≤ Dg / Dn ≤ 1.85

Description

High frequency dielectric heating adhesive

[0001] The present invention relates to an adhesive for high frequency dielectric heating.

[0002] Conventionally, dielectric composite materials containing a resin and a filler made of an inorganic compound have been proposed.

[0003] Patent Document 1 discloses a dielectric composite material having the following configuration: (1) The dielectric composite material includes a matrix made of a resin and filler particles dispersed within the matrix. (2) The filler particles are made of a perovskite-type compound, and have a half-width of an X-ray diffraction peak of the 111 plane of 0.20° or less, a ratio of the c-axis length to the a-axis length (c / a axial ratio) determined by powder X-ray diffraction of 1.006 or more, and a uniformity number (n) of the Rosin-Rammler distribution function of 2.3 or more. (3) The coefficient of variation of the interparticle distance of the filler particles dispersed within the matrix is ​​0.9 or less.

[0004] As a method for bonding adherends using an adhesive, a method for bonding adherends by high-frequency dielectric heating or the like has been proposed.

[0005] Patent Document 2 discloses an adhesive in which a dielectric heating medium having dielectric heating properties is filled into an adhesive base made of a material that has affinity with the base materials to be bonded. The adhesive satisfies C × {(tan δ) / ε'} 1 / 2 ≧ d, where ε' is the relative permittivity, tan δ is the dielectric loss tangent, and d (mm) is the total thickness of the base materials to be bonded, with coefficient C in the range of 78 to 85.

[0006] Patent Document 3 describes a polyolefin resin having a melting point in the range of 80 to 200°C and a volume resistivity of 10 －２ The present invention discloses a resin composition for dielectric heating and bonding, which contains a conductive material having a dielectric constant of Ω cm or less, and a dielectric loss tangent of 0.03 or more at a frequency of 40 MHz and a temperature of 23°C, and the content of the conductive material is in the range of 1 to 30 volume % relative to the total resin composition.

[0007] JP 2019-065094 A JP 2014-037489 A JP 2003-193009 A

[0008] The dielectric composite material disclosed in Patent Document 1 is a material used in capacitors, etc. Materials used in capacitors are required to have a low dielectric loss tangent and to suppress heat generation. For this reason, the dielectric composite material disclosed in Patent Document 1 is not suitable as a material to be used in high-frequency dielectric heating adhesives.

[0009] A high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler can bond to an adherend in a short time and easily achieves strong adhesion. The adhesive disclosed in Patent Document 2 contains a dielectric substance as a dielectric heating medium. The adhesive disclosed in Patent Document 2 does not take into consideration the relationship between the distance between the dielectric heating media filled in the adhesive and the heat generation during high-frequency dielectric heating treatment (hereinafter sometimes simply referred to as dielectric heating treatment), nor the distance between the dielectric heating media and the adhesion to the adherend.

[0010] The dielectric heating adhesive resin composition disclosed in Patent Document 3 uses a conductive material with a specific volume resistivity or less as a dielectric heating medium, so the volume resistivity of the dielectric heating adhesive resin composition itself becomes too low. If the volume resistivity of the dielectric heating adhesive resin composition itself becomes too low, the high-frequency dielectric heating adhesive may suffer electrical breakdown when subjected to a dielectric heating treatment using the high-frequency dielectric heating adhesive.

[0011] As described above, conventional high-frequency dielectric heating adhesives have a low heating rate and may not provide sufficient improvement in adhesive performance. Furthermore, if the volume resistivity of a high-frequency dielectric heating adhesive is too low, there is a concern that electrical breakdown may occur during dielectric heating. Therefore, conventional high-frequency dielectric heating adhesives have room for further improvement.

[0012] The object of the present invention is to provide a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler, which can firmly bond to an adherend in a shorter time than conventional high-frequency dielectric heating adhesives while suppressing electrical breakdown during dielectric heating treatment.

[0013] [1] A high-frequency dielectric heating adhesive, the high-frequency dielectric heating adhesive containing a thermoplastic resin (A) and a dielectric filler (B), wherein, when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the relationship between the particle diameter Dn of the dielectric filler (B) and the distance Dg between the nearest centers of gravity of the dielectric filler (B) satisfies the following mathematical formula (F1): 1.55≦Dg / Dn≦1.85 (F1)

[0014] [2] The adhesive for high-frequency dielectric heating according to [1], wherein the thermoplastic resin (A) is a polyolefin resin.

[0015] [3] The high-frequency dielectric heating adhesive according to [1] or [2], wherein the content of the dielectric filler (B) is 3% by volume or more and 40% by volume or less relative to the entire high-frequency dielectric heating adhesive.

[0016] [4] The high-frequency dielectric heating adhesive according to any one of [1] to [3], wherein the dielectric filler (B) is at least one selected from the group consisting of zinc oxide, silicon carbide, and titanium oxide.

[0017] [5] The high-frequency dielectric heating adhesive according to any one of [1] to [4], wherein when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the particle diameter Dn of the dielectric filler (B) is 1.0 μm or more and 4.0 μm or less.

[0018] [6] The high-frequency dielectric heating adhesive according to any one of [1] to [5], wherein when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the distance Dg between nearest centers of gravity of the dielectric filler (B) is 2.2 μm or more and 6.0 μm or less.

[0019] [7] The high-frequency dielectric heating adhesive according to any one of [1] to [6], wherein the high-frequency dielectric heating adhesive is a high-frequency dielectric heating adhesive sheet.

[0020] According to one aspect of the present invention, a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler can be provided, which can firmly bond to an adherend in a shorter time while suppressing electrical breakdown during dielectric heating treatment compared to conventional high-frequency dielectric heating adhesives.

[0021] Fig. 4 is a schematic cross-sectional view showing an example of a high-frequency dielectric heating adhesive according to the present embodiment; Fig. 5 is a schematic cross-sectional view showing another example of a high-frequency dielectric heating adhesive according to the present embodiment; Fig. 6 is a schematic view illustrating an example of a high-frequency dielectric heating process using a high-frequency dielectric heating adhesive and a dielectric heating device according to the present embodiment; Fig. 7 is an example of a binarized image of a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive according to the present embodiment; Fig. 8 is an example of a Delaunay diagram created based on the binarized image of Fig. 3;

[0022] [High-frequency dielectric heating adhesive] The high-frequency dielectric heating adhesive according to this embodiment contains a thermoplastic resin (A) and a dielectric filler (B), and when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the relationship between the particle diameter Dn of the dielectric filler (B) and the distance Dg between the nearest centers of gravity of the dielectric filler (B) satisfies the following formula (F1): 1.55≦Dg / Dn≦1.85 ... (F1)

[0023] Due to the above-described configuration, the high-frequency dielectric heating adhesive of this embodiment is able to suppress electrical breakdown during dielectric heating treatment and to firmly bond to the adherend in a shorter time than conventional high-frequency dielectric heating adhesives.

[0024] As a result of studying ways to improve the adhesive performance of high-frequency dielectric heating adhesives, the inventors discovered that the heat generation rate of the high-frequency dielectric heating adhesive improves and the volume resistivity of the high-frequency dielectric heating adhesive changes depending on the relationship between the particle diameter of the dielectric filler (B) and the distance between the particles of the dielectric filler (B). The inventors speculate as follows about why the high-frequency dielectric heating adhesive according to this embodiment can be firmly bonded to an adherend in a shorter time while suppressing electrical breakdown when subjected to dielectric heating treatment.

[0025] The relationship between the particle diameter Dn of the dielectric filler (B) and the distance Dg between the nearest centers of gravity of the dielectric filler (B) satisfies the relationship of the above formula (F1), which means that the particles of the dielectric filler (B) are spaced at an appropriate distance from each other relative to the particle diameter of the dielectric filler (B).

[0026] In a high-frequency dielectric heating adhesive, if the value of the above formula (F1) is too large, the distance between the particles of the dielectric filler (B) becomes too great relative to the particle diameter of the dielectric filler (B). If the distance between the particles of the dielectric filler (B) becomes too great relative to the particle diameter of the dielectric filler (B), the electric field generated between the particles of the dielectric filler (B) becomes weaker during dielectric heating treatment, and the reversal motion when high frequency is applied decreases, thereby reducing the heat generation ability of the high-frequency dielectric heating adhesive. As a result, it is thought that the adhesion between the high-frequency dielectric heating adhesive and the adherend decreases. Therefore, if the high-frequency dielectric heating adhesive satisfies the upper limit value of the above formula (F1), the heat generation rate of the high-frequency dielectric heating adhesive improves, allowing for strong bonding to the adherend in a shorter time.

[0027] On the other hand, if the value of the above formula (F1) in a high-frequency dielectric heating adhesive is too small, the distance between the particles of the dielectric filler (B) becomes too close relative to the particle diameter of the dielectric filler (B), which may result in a significant decrease in the volume resistivity of the high-frequency dielectric heating adhesive. If the volume resistivity of the high-frequency dielectric heating adhesive decreases too much, the high-frequency dielectric heating adhesive will tend to become conductive, which may make it easier for electricity to flow through the high-frequency dielectric heating adhesive when subjected to a dielectric heating treatment. Therefore, if the value of the above formula (F1) is equal to or greater than the lower limit, it is believed that the volume resistivity of the high-frequency dielectric heating adhesive will be prevented from decreasing too much. As a result, it is believed that the occurrence of electrical breakdown will be suppressed when the high-frequency dielectric heating adhesive is subjected to a dielectric heating treatment.

[0028] From the above, the high-frequency dielectric heating adhesive of this embodiment, due to the above-mentioned configuration, can firmly bond to the substrate in a shorter time while suppressing electrical breakdown during dielectric heating treatment compared to conventional high-frequency dielectric heating adhesives.

[0029] The materials used in the high-frequency dielectric heating adhesive according to this embodiment will be described below.

[0030] <Thermoplastic resin (A)> The type of thermoplastic resin (A) is not particularly limited. For example, from the viewpoint of being easily meltable and having a predetermined heat resistance, the thermoplastic resin (A) is preferably at least one selected from the group consisting of polyolefin resins, styrene resins, polyacetal resins, polycarbonate resins, acrylic resins, polyamide resins, polyimide resins, polyvinyl acetate resins, phenoxy resins, and polyester resins. It is preferable to select a type of thermoplastic resin (A) that has high affinity with the material of the adherend.

[0031] In the high-frequency dielectric heating adhesive according to this embodiment, the thermoplastic resin (A) is preferably a polyolefin resin or a styrene resin, and more preferably a polyolefin resin. If the thermoplastic resin (A) is a polyolefin resin or a styrene resin, the high-frequency dielectric heating adhesive is easily melted when a high-frequency electric field is applied, and the high-frequency dielectric heating adhesive according to this embodiment can be easily bonded to an adherend.

[0032] In this specification, polyolefin-based resins include polyolefin-based resins having polar moieties and polyolefin-based resins not having polar moieties, and when specifying whether or not a polar moiety is present, the resins are described as polyolefin-based resins having polar moieties or polyolefin-based resins not having polar moieties.

[0033] It is also preferable that the thermoplastic resin (A) is a polyolefin-based resin having a polar moiety. The thermoplastic resin (A) may be a polyolefin-based resin having no polar moiety.

[0034] (Polyolefin Resin) Examples of the polyolefin resin as the thermoplastic resin (A) 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, and 4-methyl-1-pentene, etc. The polyolefin resin as the thermoplastic resin (A) may be a single resin or a combination of two or more resins.

[0035] [Polyolefin Resin Having Polar Moieties] The polar moieties in the polyolefin resin having polar moieties are not particularly limited as long as they can impart polarity to the polyolefin resin. Furthermore, it is preferable that the high-frequency dielectric heating adhesive contains a polyolefin resin having polar moieties as the thermoplastic resin (A), as this tends to improve the dielectric properties and increase the adhesive strength to the adherend. The polyolefin thermoplastic resin having polar moieties may be a copolymer of an olefin monomer and a monomer having a polar moiety. Furthermore, the polyolefin thermoplastic resin having polar moieties may be a resin obtained by introducing polar moieties into an olefin polymer obtained by polymerization of an olefin monomer through modification such as an addition reaction.

[0036] The type of olefin monomer constituting the polyolefin resin having a polar moiety is not particularly limited. Examples of olefin monomers include ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene. The olefin monomer may be used alone or in combination of two or more. From the viewpoint of obtaining excellent mechanical strength and stable adhesive properties, the olefin monomer is preferably at least one of ethylene and propylene. The olefin-derived structural unit in the polyolefin resin having a polar moiety is preferably a structural unit derived from ethylene or propylene.

[0037] Examples of the polar moiety include a hydroxyl group, a carboxyl group, a vinyl acetate structure, an acid anhydride structure, etc. Examples of the polar moiety also include an acid-modified structure that is introduced into a polyolefin resin by acid modification.

[0038] The acid-modified structure as a polar moiety is a moiety introduced by acid-modifying a thermoplastic resin (e.g., a polyolefin-based resin). Compounds used to acid-modify 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. In this specification, a polyolefin-based resin having an acid-modified structure may be referred to as an acid-modified polyolefin-based resin.

[0039] Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0040] Examples of the acid anhydrides of unsaturated carboxylic acids include maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0041] Examples of esters of unsaturated carboxylic acids include 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.

[0042] [Maleic Anhydride-Modified Polyolefin] The polyolefin resin as a thermoplastic resin preferably has an acid anhydride structure as the acid-modified structure. The acid anhydride structure is preferably a structure introduced when the polyolefin resin is modified with maleic anhydride.

[0043] 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.

[0044] <Dielectric filler (B)> The dielectric filler (B), which is a preferred material as a dielectric material, will be described. The dielectric filler (B) is a filler that generates heat when a high-frequency electric field is applied. A high-frequency electric field is an electric field whose direction is reversed at high frequencies. The dielectric filler (B) is preferably a filler that generates heat when a high-frequency electric field in a frequency range of 3 MHz or more and 300 MHz or less is applied. The dielectric filler (B) is preferably a filler that generates heat when a high-frequency electric field in a frequency range of 3 MHz or more and 300 MHz or less is applied, for example, at a frequency of 13.56 MHz, 27.12 MHz, or 40.68 MHz.

[0045] The dielectric filler (B) is preferably a single inorganic material having water of crystallization such as zinc oxide, silicon carbide (SiC), anatase type titanium oxide, barium titanate, barium titanate zirconate, lead titanate, potassium niobate, rutile type titanium oxide, hydrated aluminum silicate, hydrated aluminosilicates of alkali metals, or a combination of two or more inorganic materials having water of crystallization such as hydrated aluminosilicates of alkaline earth metals. The dielectric filler (B) may be a single inorganic material having water of crystallization such as zinc oxide, silicon carbide (SiC), anatase type titanium oxide, rutile type titanium oxide, hydrated aluminum silicate, hydrated aluminosilicates of alkali metals, or a combination of two or more inorganic materials having water of crystallization such as hydrated aluminosilicates of alkaline earth metals.

[0046] From the viewpoint of obtaining higher heat generation properties, the dielectric filler (B) is preferably at least one selected from the group consisting of zinc oxide, silicon carbide, and titanium oxide, and more preferably at least one of zinc oxide and titanium oxide.

[0047] Among the dielectric fillers listed above, zinc oxide is available in a wide variety of shapes and sizes, allowing for the adhesive properties and mechanical properties of the high-frequency dielectric heating adhesive to be improved to suit the application. For this reason, zinc oxide is more preferred as the dielectric filler (B). By using zinc oxide as the dielectric filler (B), a high-frequency dielectric heating adhesive with low transmittance and no design issues can be obtained. Zinc oxide is not too hard among ceramics, making it less likely to damage the manufacturing equipment for high-frequency dielectric heating adhesives. Because zinc oxide is an inactive oxide, it causes less damage to thermoplastic resins when blended with them. Furthermore, titanium oxide as the dielectric filler (B) is preferably at least one of anatase titanium oxide and rutile titanium oxide, and anatase titanium oxide is more preferred from the viewpoint of its excellent dielectric properties.

[0048] The shape of the dielectric filler (B) is not particularly limited, and various shapes can be adopted. From the viewpoint of the manufacturing cost of the dielectric filler (B), the shape of the dielectric filler (B) is preferably, for example, amorphous or spherical, and more preferably amorphous. In this specification, the dielectric filler (B) having an amorphous shape means that it does not have a specific shape such as a perfect sphere or a cube. From the same viewpoint, it is also preferable that the dielectric filler (B) is not surface-modified. In this specification, the dielectric filler (B) is not surface-modified means that the surface of the dielectric filler (B) has not been modified by introducing an organic group.

[0049] The volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive is preferably 2% by volume or more, more preferably 3% by volume or more, even more preferably 4% by volume or more, even more preferably 6% by volume or more, and even more preferably 8% by volume or more. The volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive is preferably 40% by volume or less, more preferably 35% by volume or less, even more preferably 30% by volume or less, even more preferably 25% by volume or less, and even more preferably 22% by volume or less.

[0050] When the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive is 2% by volume or more, heat generation is improved and it is easy to firmly bond the high-frequency dielectric heating adhesive to the adherend. When the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive is 40% by volume or less, a decrease in adhesive strength can be prevented, and as a result, use of this adhesive can prevent a decrease in adhesive strength. Furthermore, when the high-frequency dielectric heating adhesive according to this embodiment is in the form of an adhesive sheet, when the volume content of the dielectric filler (B) in the adhesive sheet is 40% by volume or less, flexibility as a sheet can be easily obtained and a decrease in toughness can be easily prevented, making it easy to process the high-frequency dielectric heating adhesive sheet into the desired shape in a subsequent process.

[0051] When a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope (hereinafter referred to as SEM), the particle diameter Dn of the dielectric filler (B) is preferably 1.0 μm or more and 4.0 μm or less. In this specification, the particle diameter Dn of the dielectric filler (B) represents the number average value based on the arithmetic average of the particle diameters measured by the measurement method described below.

[0052] The particle diameter Dn of the dielectric filler (B) is preferably 1.1 μm or more, more preferably 1.2 μm or more, and even more preferably 1.3 μm or more. The particle diameter Dn of the dielectric filler (B) is preferably 3.8 μm or less, more preferably 3.6 μm or less, even more preferably 3.4 μm or less, and even more preferably 3.2 μm or less.

[0053] When the particle diameter Dn of the dielectric filler (B) is 1.0 μm or more, the high-frequency dielectric heating adhesive exhibits high heat-generating performance when a high-frequency electric field is applied, and can be firmly bonded to an adherend in a short time. When the particle diameter Dn of the dielectric filler (B) is 4.0 μm or less, the high-frequency dielectric heating adhesive exhibits high heat-generating performance when a high-frequency electric field is applied, and can be firmly bonded to an adherend in a short time. Furthermore, when the high-frequency dielectric heating adhesive according to this embodiment is an adhesive sheet, a decrease in the strength of the high-frequency dielectric heating adhesive sheet can be prevented by having the particle diameter Dn of the dielectric filler (B) be 4.0 μm or less.

[0054] When a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed using an SEM, the distance Dg between the nearest centers of gravity of the dielectric fillers (B) is preferably 2.2 μm or more and 6.0 μm or less. In this specification, the distance Dg between the nearest centers of gravity of the dielectric fillers (B) represents the average value of the distances between the nearest centers of gravity measured using the measurement method described below. The distance between the nearest centers of gravity is the distance between the center of gravity of one dielectric filler (B) and the center of gravity of the dielectric filler (B) closest to that dielectric filler (B). In other words, between adjacent dielectric fillers (B), it means the distance from the center of gravity of one dielectric filler (B) to the center of gravity of the other dielectric filler (B) located closest to it. Here, the concept of adjacent dielectric fillers (B) encompasses both cases where one dielectric filler (B) and the other dielectric filler (B) are in direct contact with each other, and where they are not in direct contact but are spaced apart by a certain distance.

[0055] The distance Dg between the nearest centers of gravity of the dielectric filler (B) is preferably 2.3 μm or more, more preferably 2.4 μm or more, and even more preferably 2.5 μm or more. The distance Dg between the nearest centers of gravity of the dielectric filler (B) is preferably 5.8 μm or less, more preferably 5.6 μm or less, even more preferably 5.4 μm or less, and even more preferably 5.2 μm or less.

[0056] When the distance Dg between the nearest centers of gravity of the dielectric filler (B) is 2.2 μm or more, the high-frequency dielectric heating adhesive exhibits high heat-generating performance when a high-frequency electric field is applied, and can be firmly bonded to an adherend in a short time. Furthermore, when the distance Dg between the nearest centers of gravity of the dielectric filler (B) is 2.2 μm or more, a decrease in the volume resistivity of the high-frequency dielectric heating adhesive is suppressed. When the distance Dg between the nearest centers of gravity of the dielectric filler (B) is 6.0 μm or less, the high-frequency dielectric heating adhesive exhibits high heat-generating performance when a high-frequency electric field is applied, and can be firmly bonded to an adherend in a short time. Furthermore, when the high-frequency dielectric heating adhesive according to this embodiment is an adhesive sheet, a decrease in the strength of the high-frequency dielectric heating adhesive sheet can be prevented by having the distance Dg between the nearest centers of gravity of the dielectric filler (B) be 6.0 μm or less.

[0057] <Additives> The high-frequency dielectric heating adhesive according to this embodiment may or may not contain additives, as long as the adhesive does not impair short-term adhesion.

[0058] When the high-frequency dielectric heating adhesive 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, and an inorganic filler. The organic filler and inorganic filler as additives are different from the dielectric filler.

[0059] Tackifiers and plasticizers can improve the melting and adhesive properties of high-frequency dielectric heating adhesives. Examples of tackifiers include rosin derivatives, polyterpene resins, aromatic-modified terpene resins, hydrogenated aromatic-modified terpene resins, terpene-phenolic 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 paraffinic 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.

[0060] When the high-frequency dielectric heating adhesive according to this embodiment contains an additive, the content of the additive in the high-frequency dielectric heating adhesive is usually 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. Also, the content of the additive in the high-frequency dielectric heating adhesive is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0061] The high-frequency dielectric heating adhesive according to this embodiment preferably does not contain a solvent. A solvent-free high-frequency dielectric heating adhesive is less likely to cause problems with volatile organic compounds that are caused by the adhesive used to bond the adhesive to the adherend.

[0062] The high-frequency dielectric heating adhesive according to this embodiment preferably does not contain conductive materials such as carbon or carbon compounds containing carbon as a main component, metals, etc. For example, the high-frequency dielectric heating adhesive according to this embodiment preferably does not contain carbon steel, α-iron, γ-iron, δ-iron, copper, iron oxide, brass, aluminum, iron-nickel alloy, iron-nickel-chromium alloy, carbon fiber, or carbon black.

[0063] When the high-frequency dielectric heating adhesive according to this embodiment contains a conductive substance, the content of the conductive substance in the adhesive is preferably, independently, 7% by mass or less, more preferably 6% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, based on the total amount of the adhesive. It is particularly preferable that the content of the conductive substance in the adhesive is 0% by mass. If the content of the conductive substance in the adhesive is 7% by mass or less, it becomes easier to prevent problems such as electrical breakdown during dielectric heating treatment, resulting in carbonization of the bonded joint and the adherend.

[0064] In the high-frequency dielectric heating adhesive according to this embodiment, the total content of the thermoplastic resin (A) and the dielectric filler (B) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0065] <Characteristics of High-Frequency Dielectric Heating Adhesive> Next, the characteristics of the high-frequency dielectric heating adhesive according to this embodiment will be described.

[0066] (Distance between nearest neighbor centers of gravity Dg / Particle diameter Dn) In the high-frequency dielectric heating adhesive according to this embodiment, when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with an SEM, the relationship (Dg / Dn) between the particle diameter Dn of the dielectric filler (B) and the distance between nearest neighbor centers of gravity Dg satisfies the relationship of the above-mentioned mathematical formula (F1). That is, the ratio of the distance between nearest neighbor centers of gravity Dg of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) is 1.55 or more and 1.85 or less. From the viewpoint of suppressing electrical breakdown during dielectric heating treatment and achieving strong adhesion to the adherend in a short period of time, the ratio of the distance between nearest neighbor centers of gravity Dg of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) is more preferably 1.56 or more, and even more preferably 1.57 or more. Furthermore, from the viewpoint of being able to firmly bond to the adherend in a short time, the ratio of the distance Dg between the nearest centers of gravity of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) is more preferably 1.83 or less, even more preferably 1.80 or less, even more preferably 1.75 or less, and even more preferably 1.70 or less.

[0067] In this embodiment, the particle diameter Dn of the dielectric filler (B), the distance Dg between the nearest centers of gravity of the dielectric filler (B), and the ratio of the distance Dg between the nearest centers of gravity of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) are measured by the procedures shown in (1) to (5) below.

[0068] Step (1): The cross section of the high-frequency dielectric heating adhesive cut along the thickness direction is polished using a cross-section processing device, and one or more fields of view are observed using an SEM at 500x magnification or greater. From the viewpoint of efficient processing, the cross-section processing device is preferably a device that processes the cross section using an ion beam. Step (2): The obtained SEM image is binarized using image analysis software, and blobs (hereinafter, binary large objects) obtained from the obtained binarized image are detected as particles of the dielectric filler (B). The blobs are areas in the binarized image where adjacent pixels determined to be white are connected. Figure 3 shows an example of a binarized image obtained by the above binarization process. The example of the binarized image shown in Figure 3 is a binarized image obtained using Otsu's binarization method. In the binarized image shown in Figure 3, the white areas represent particles of the dielectric filler (B). Step (3): By performing Blob analysis on the detected particles of the dielectric filler (B), the circle-equivalent diameters of 100 or more particles of the dielectric filler (B) to be measured are measured, and the number average value obtained by the arithmetic mean of the measured circle-equivalent diameters is calculated as the particle diameter Dn of the dielectric filler (B) using the numpy mean function. Step (4): For the dielectric filler (B) to be measured in step (3) above, the particle centroids are determined using the Open CV moments function. Next, a Delaunay diagram connecting the determined particle centroids is created using the Open CV Subdiv2D function. The three sides of the triangle in the created Delaunay diagram are compared, and the length of the shortest side of the three sides of the compared triangle is measured as the nearest-neighbor centroid distance. The average value of 100 or more measured nearest-neighbor centroid distances is taken as the nearest-neighbor centroid distance Dg. FIG. 4 shows an example of a Delaunay diagram created based on the binarized image obtained in the above step (2). The line segments shown in FIG. 4 are sides connecting the centers of gravity of the particles of the dielectric filler (B). As shown in FIG. 4, a triangle is formed by the three sides connecting these centers of gravity. The sides forming the triangle are compared, and the shortest side among the compared sides is measured as the distance between nearest neighbor centers of gravity. The average value of 100 or more measured distances between nearest neighbor centers of gravity is the distance Dg between nearest neighbor centers of gravity.Step (5): The nearest center-to-center distance Dg obtained in step (4) above is divided by the particle diameter Dn obtained in step (3) above to calculate the ratio of the nearest center-to-center distance Dg to the particle diameter Dn (nearest center-to-center distance Dg / particle diameter Dn).

[0069] The particle diameter Dn of the dielectric filler (B), the distance Dg between the nearest centers of gravity of the dielectric filler (B), and the ratio of the distance Dg between the nearest centers of gravity of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) are specifically determined by the method described in the examples below.

[0070] (Volume Resistivity) The volume resistivity of the adhesive for high-frequency dielectric heating according to this embodiment is 1.0×10 １３ The volume resistivity of the adhesive for high frequency dielectric heating according to this embodiment is preferably 1.0×10 １４ It is preferable that the resistance is Ω cm or more, and 1.0 × 10 １５ More preferably, it is 1.0×10 Ω cm or more. １６ The upper limit of the volume resistivity of the adhesive for high-frequency dielectric heating according to this embodiment is not particularly limited, and is, for example, 1.0 × 10 １８ The volume resistivity of the adhesive for high frequency dielectric heating according to this embodiment may be, for example, 1.0×10 １３ When the resistivity is Ω·cm or more, it is easy to ensure that electrical breakdown is suppressed during dielectric heating treatment. As a result, it is easy to firmly bond to the adherend in a short time while suppressing electrical breakdown during dielectric heating treatment. The volume resistivity is specifically determined by the method described in the examples below. Note that when the volume resistivity of the high-frequency dielectric heating adhesive is 1.0 × 10 １３ If the volume resistivity is less than Ω cm, electrical breakdown does not necessarily occur immediately when subjected to dielectric heating treatment, but electrical breakdown becomes more likely to occur when subjected to dielectric heating treatment. The lower the volume resistivity of the high-frequency dielectric heating adhesive, the more likely electrical breakdown occurs when subjected to dielectric heating treatment. When the volume resistivity of the high-frequency dielectric heating adhesive is, for example, 1.0 × 10 １０The higher the volume resistivity of the high-frequency dielectric heating adhesive according to this embodiment, the more likely it is that electrical breakdown will occur during dielectric heating. １３ If the electrical resistance is Ω·cm or more, it is easy to ensure that electrical breakdown is suppressed when a dielectric heat treatment is performed.

[0071] (Dielectric Properties) The dielectric properties (tan δ / ε'r) of the high frequency dielectric heating adhesive according to this embodiment will be described. The high frequency dielectric heating adhesive according to this embodiment preferably has a dielectric property (tan δ / ε'r) of 0.004 or more. (Tan δ is the dielectric loss tangent at 23°C and a frequency of 40.68 MHz, and ε'r is the relative dielectric constant at 23°C and a frequency of 40.68 MHz.)

[0072] If the dielectric properties of the high-frequency dielectric heating adhesive are 0.004 or higher, the high-frequency dielectric heating adhesive will easily generate heat when subjected to a dielectric heating process, making it easier to firmly bond the high-frequency dielectric heating adhesive to the adherend in a short period of time.

[0073] Even if the dielectric properties of a high-frequency dielectric heating adhesive are 0.004 or more, if the relationship (Dg / Dn) between the particle diameter of the dielectric filler (B) and the distance between the dielectric filler (B) particles does not satisfy the relationship of the aforementioned formula (F1), it may be difficult to achieve the effect of suppressing electrical breakdown during dielectric heating treatment while firmly adhering to the adherend in a shorter time.

[0074] The dielectric properties of the high-frequency dielectric heating adhesive according to this embodiment are preferably 0.005 or more, more preferably 0.008 or more, and even more preferably 0.010 or more. If the high-frequency dielectric heating adhesive according to this embodiment has a dielectric property of 0.008 or more, the high-frequency dielectric heating adhesive will be more likely to generate heat when subjected to a dielectric heating treatment, making it easier to firmly bond the high-frequency dielectric heating adhesive to the adherend in a short period of time.

[0075] The upper limit of the dielectric properties of the high-frequency dielectric heating adhesive according to this embodiment is not particularly limited, but from the viewpoint of preventing overheating of the high-frequency dielectric heating adhesive, it is preferably 0.04 or less, more preferably 0.02 or less, even more preferably 0.014 or less, and particularly preferably 0.011 or less. If the dielectric properties of the high-frequency dielectric heating adhesive are 0.04 or less, overheating is easily prevented, and damage to the contact area between the adherend and the high-frequency dielectric heating adhesive is less likely to occur. If the adherend has low heat resistance and there is concern about the thermal impact of overheating on the adherend, it is preferable that the upper limit of the dielectric properties of the high-frequency dielectric heating adhesive be, for example, 0.011 or less. In this case, it is preferable that the dielectric properties of the high-frequency dielectric heating adhesive be, for example, 0.004 or more and 0.011 or less.

[0076] The dielectric property (tan δ / ε'r) is the value obtained by dividing the dielectric loss tangent (tan δ) measured using an impedance material apparatus, etc., by the relative dielectric constant (ε'r) measured using an impedance material apparatus, etc. The dielectric loss tangent (tan δ) and relative dielectric constant (ε'r), which are the dielectric properties of a high-frequency dielectric heating adhesive, can be measured simply and accurately using an impedance material analyzer.

[0077] The details of the method for measuring the dielectric properties of the high-frequency dielectric heating adhesive and the adherend are as follows. First, a measurement sheet of the high-frequency dielectric heating adhesive is obtained. If a measurement sheet needs to be obtained from a structure, a measurement sheet of uniform thickness is obtained by cutting or scraping it from the structure. For non-sheet-formed high-frequency dielectric heating adhesives, such as pellet-shaped ones, the measurement sheet is obtained by sheeting them using a heat press or the like. The thickness of the measurement sheet is, for example, 10 μm or more and 2 mm or less. The relative permittivity (ε'r) and dielectric loss tangent (tanδ) of the sheet obtained in this manner 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.

[0078] <Shape of High-Frequency Dielectric Heating Adhesive> The shape of the high-frequency dielectric heating adhesive according to this embodiment is not particularly limited. The high-frequency dielectric heating adhesive according to this embodiment may be, for example, a molded adhesive formed into a desired shape by injection molding or the like, or a sheet-like adhesive obtained by extrusion molding or the like. In this embodiment, the molded body and the sheet have different shapes. A sheet typically refers to a long strip or sheet-like shape with a thickness of 1 mm or less, 2 mm or less, or 5 mm or less. A molded body refers to a shape obtained by molding a material containing each component of the high-frequency dielectric heating adhesive, and refers to various shapes other than a sheet.

[0079] The high-frequency dielectric heating adhesive according to this embodiment is preferably in sheet form. That is, the high-frequency dielectric heating adhesive according to this embodiment is preferably a high-frequency dielectric heating adhesive sheet (sometimes referred to as an adhesive sheet). When the high-frequency dielectric heating adhesive is an adhesive sheet, the time required for the manufacturing process of the structure can be further shortened.

[0080] The high-frequency dielectric heating adhesive according to this embodiment may have the shape of a frame-shaped sheet (frame-shaped adhesive sheet) including a frame portion and an opening penetrating from one opposing surface to the other. The shape of the opening is not particularly limited. When the adhesive sheet is frame-shaped, the frame-shaped adhesive sheet may have one opening or two or more openings. The frame-shaped sheet may have a cutout in a portion of the frame portion. In this case, the opening may be shaped so that a portion of the frame portion is connected to the outside of the frame portion. That is, in a plan view of the frame-shaped sheet, the frame portion may have an open shape (for example, a discontinuous shape of the frame portion, such as a C-shape or a U-shape). The frame-shaped sheet may not have a cutout in the frame portion. In this case, the opening may be shaped so that the periphery of the opening is surrounded by the frame portion (for example, a continuous shape of the frame portion, such as an O-shape). That is, in a plan view of the frame-shaped sheet, the frame portion may have a closed shape. When the frame-shaped sheet has two or more openings, the openings may be a combination of openings of the same shape or a combination of openings of different shapes when viewed in plan of the frame-shaped sheet. The high-frequency dielectric heating adhesive according to this embodiment may be a sheet without any openings. Furthermore, the high-frequency dielectric heating adhesive according to this embodiment can be molded into an adhesive sheet of the desired shape by molding methods such as extrusion molding and injection molding.

[0081] In one aspect, the high-frequency dielectric heating adhesive according to this embodiment is composed of only one adhesive layer made of the high-frequency dielectric heating adhesive sheet according to this embodiment. When the high-frequency dielectric heating adhesive is a high-frequency dielectric heating adhesive sheet composed of only one adhesive layer, the adhesive layer itself corresponds to the high-frequency dielectric heating adhesive sheet, and the shape and characteristics of the high-frequency dielectric heating adhesive sheet correspond to the shape and characteristics of the adhesive layer. It is preferable that the high-frequency dielectric heating adhesive sheet consists of only a single adhesive layer. This allows the high-frequency dielectric heating adhesive sheet to be thin and the high-frequency dielectric heating adhesive sheet to be easily formed.

[0082] Since a high-frequency dielectric heating adhesive sheet may consist of only one adhesive layer with high-frequency dielectric heating adhesive properties, in this specification the terms "high-frequency dielectric heating adhesive sheet" and "adhesive layer" may be interchangeable in some cases.

[0083] The high-frequency dielectric heating adhesive according to this embodiment is not limited to an adhesive sheet for high-frequency dielectric heating consisting of only one adhesive layer, and may be any of the adhesives shown in Figures 1A, 1B, and 1C.

[0084] The high frequency dielectric heating adhesive 1A shown in FIG. 1A is an adhesive sheet consisting of only a single adhesive layer 10.

[0085] The high-frequency dielectric heating adhesive 1B shown in FIG. 1B is an adhesive sheet having an adhesive layer 10 and a substrate 30 that supports the adhesive layer 10. The adhesive layer 10 has a first surface 11. The substrate 30 is not particularly limited as long as it is a material that can support the adhesive layer 10. Examples of the substrate 30 include a resin sheet containing at least one resin selected from the group consisting of polyolefin resin, polyester resin, acetate resin, acrylonitrile-butadiene-styrene copolymer resin, polystyrene resin, and vinyl chloride resin. Examples of polyolefin resins include polyethylene resin and polypropylene resin. Examples of polyester resins include polybutylene terephthalate resin and polyethylene terephthalate resin. The substrate 30 may contain a dielectric filler. The dielectric filler (B) in the adhesive layer 10 and the dielectric filler in the substrate 30 may be the same or different.

[0086] The high-frequency dielectric heating adhesive 1C shown in FIG. 1C is an adhesive sheet having an adhesive layer 10 and an intermediate layer 40 disposed between the adhesive layer 20. The high-frequency dielectric heating adhesive 1C has a first surface 11 and a second surface 21 opposite the first surface 11. In the high-frequency dielectric heating adhesive 1C, the adhesive layer 10 only needs to satisfy the requirements of the adhesive layer of the high-frequency dielectric heating adhesive sheet according to this embodiment. In one aspect, both the adhesive layer 10 and the adhesive layer 20 have the same composition and properties. In another aspect, the adhesive layer 20 is a high-frequency dielectric heating adhesive layer that differs from the adhesive layer 10 in at least one of its composition and properties. In another aspect, the adhesive layer 20 is a general adhesive layer that is not a high-frequency dielectric heating adhesive layer. In this case, the adhesive layer 20 that is not a high-frequency dielectric heating adhesive layer may be, for example, a layer of a drying-and-solidifying adhesive that dries and solidifies upon evaporation of water or a solvent, or a layer of an adhesive formed from a pressure-sensitive adhesive.

[0087] When the high-frequency dielectric heating adhesive according to this embodiment is an adhesive sheet consisting of only one adhesive layer, the thickness of the adhesive sheet according to this embodiment is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 30 μm or more, and particularly preferably 50 μm or more. If the adhesive sheet is 5 μm or more thick, the heat generation properties of the adhesive sheet in contact with the adherend when a high-frequency electric field is applied are improved, making it easier to firmly bond the adhesive sheet and the adherend in a short period of time. Furthermore, when bonding to the adherend, the adhesive sheet easily conforms to the unevenness of the adherend, making it easier to develop adhesive strength.

[0088] When the adhesive sheet has a multilayer structure made up of multiple layers, the thickness of the adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 30 μm or more, and even more preferably 50 μm or more. When the adhesive sheet for high-frequency dielectric heating is a multilayer sheet, if the thickness of the adhesive layer is 5 μm or more, the adhesive layer will easily follow the irregularities of the adherend when adhering to the adherend, and adhesive strength will be easily exhibited.

[0089] The upper limit of the thickness of the adhesive sheet is not particularly limited. The thicker the adhesive sheet, the greater the weight of the entire structure obtained by adhering the adhesive sheet to the adherend. For this reason, the adhesive sheet preferably has a thickness within a range that does not pose any problems in practical use, such as processability and handling. Taking into consideration the practicality and formability of the high-frequency dielectric heating adhesive sheet, the thickness of the adhesive sheet according to this embodiment is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 600 μm or less. The upper limit of the adhesive sheet thickness is preferably the above value, regardless of whether the adhesive sheet has a single adhesive layer or a multilayer structure including multiple layers including the adhesive layer.

[0090] An adhesive sheet used as a high-frequency dielectric heating adhesive is easier to handle than a liquid adhesive that must be applied, and workability during bonding to an adherend is improved.

[0091] Furthermore, the thickness of the adhesive sheet used as a high-frequency dielectric heating adhesive can be appropriately controlled. This allows the adhesive sheet to be applied to the roll-to-roll method, and the adhesive sheet can be processed into any area and shape by punching or other processes to match the adhesive area with the adherend and the shape of the adherend. Therefore, adhesive sheets used as high-frequency dielectric heating adhesives have great advantages from the viewpoint of the manufacturing process.

[0092] The high-frequency dielectric heating adhesive according to this embodiment is preferably used by applying a high-frequency electric field in a frequency range from short waves to ultra-short waves. When a high-frequency electric field in this frequency range is applied, the heatable depth is deep, improving heat generation during high-frequency application. Therefore, even if the high-frequency dielectric heating adhesive is thick, it is easy to firmly bond the adhesive sheet to the adherend in a short time.

[0093] <Method for Manufacturing High-Frequency Dielectric Heating Adhesive> The high-frequency dielectric heating adhesive according to this embodiment can be manufactured, for example, by mixing the above-described components. When the high-frequency dielectric heating adhesive according to this embodiment is an adhesive sheet, for example, the above-described components are premixed and kneaded using a known kneading device such as an extruder or a heated roll, and the adhesive can be manufactured by a known molding method such as extrusion molding, calendar molding, injection molding, or casting molding. When the high-frequency dielectric heating adhesive according to this embodiment is a molded body, for example, the material obtained by premixing the above-described components can be manufactured by a known molding method such as injection molding or compression molding. Furthermore, when the high-frequency dielectric heating adhesive according to this embodiment is a frame-shaped sheet, the frame-shaped sheet can be manufactured by forming an opening in the sheet-shaped high-frequency dielectric heating adhesive obtained by the above-described adhesive sheet molding method, for example, by subjecting it to a known punching process. Alternatively, the frame-shaped sheet can be manufactured by using a mold having a shape that allows the desired opening to be obtained in the above-described adhesive sheet molding method.

[0094] The distance Dg between the nearest neighboring centers of gravity of the dielectric filler (B) and the ratio of the distance Dg between the nearest neighboring centers of gravity of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) can be adjusted, for example, by the particle diameter Dn of the dielectric filler (B) and the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive. Furthermore, the distance Dg between the nearest neighboring centers of gravity of the dielectric filler (B) and the ratio of the distance Dg between the nearest neighboring centers of gravity of the dielectric filler (B) to the particle diameter Dn of the dielectric filler (B) can also be adjusted by, for example, considering the conditions when mixing the thermoplastic resin (A) and the dielectric filler (B) contained in the high-frequency dielectric heating adhesive according to this embodiment, in addition to the particle diameter Dn of the dielectric filler (B) and the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive.

[0095] High frequency dielectric heating adhesives have superior water resistance and moisture resistance compared to general pressure sensitive adhesives.

[0096] The high-frequency dielectric heating adhesive according to this embodiment is locally heated by the application of a high-frequency electric field, which makes it easy to prevent the problem of the entire adherend being damaged when the adhesive is bonded to the adherend.

[0097] [Adherend] The material of the adherend is not particularly limited, and may be any of organic materials, metal materials, and inorganic materials, or a composite material thereof.

[0098] The material of the adherend is preferably an organic material. Examples of organic materials that can be used as the material of the adherend include plastic materials and rubber materials. Examples of plastic materials include polypropylene resin, polyethylene resin, epoxy resin, polyurethane resin, acrylonitrile-butadiene-styrene copolymer resin, polycarbonate resin, polyamide resin (such as nylon 6 and nylon 66), polyester resin (such as polyethylene terephthalate and polybutylene terephthalate resin), polyacetal resin, polymethyl methacrylate resin, and polystyrene resin. Examples of rubber materials include styrene-butadiene rubber, ethylene propylene rubber, and silicone rubber. The adherend may also be a foamed organic material.

[0099] When the material of the adherend is a thermoplastic resin, the thermoplastic resin contained in the adherend and the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive may be different resins, in which case bonding is facilitated without damaging the shape of the adherend.

[0100] Furthermore, when the material of the adherend is a thermoplastic resin, from the viewpoint of adhesiveness, the main composition of the thermoplastic resin contained in the adherend may be the same as the main composition of the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive.

[0101] 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 the most abundant repeating unit in the polymer. When the thermoplastic resin is a polymer derived from a single monomer, the repeating unit derived from that monomer 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 the most abundant repeating unit 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 is a repeating unit contained in an amount of 30% by mass or more, in one embodiment, a repeating unit contained in an amount of more than 30% by mass, in another embodiment, a repeating unit contained in an amount of 40% by mass or more, and in yet another embodiment, a repeating unit contained in an amount of 50% by mass or more. Furthermore, when the thermoplastic resin is a copolymer, the repeating unit contained in the most abundant amount may be two or more types.

[0102] Examples of inorganic materials used as the adherend include glass, cement, ceramic, and metal materials. The adherend may also be a fiber-reinforced resin, which is a composite material of fibers and the aforementioned plastic materials. The plastic material in this fiber-reinforced resin is at least one selected from the group consisting of polypropylene resin, polyethylene resin, polyurethane resin, acrylonitrile-butadiene-styrene copolymer resin, polycarbonate resin, polyamide resin (e.g., nylon 6 and nylon 66), polyester resin (e.g., polyethylene terephthalate and polybutylene terephthalate resin), polyacetal resin, polymethyl methacrylate resin, epoxy resin, and polystyrene resin. Examples of fibers in the fiber-reinforced resin include glass fiber, Kevlar® fiber, and carbon fiber.

[0103] The adherend preferably has low electrical conductivity.

[0104] When a plurality of adherends are bonded together using the adhesive for high-frequency dielectric heating according to this embodiment, the adherends may be made of the same material or different materials.

[0105] The shape of the adherend is not particularly limited, but when the high-frequency dielectric heating adhesive according to this embodiment is an adhesive sheet, the adherend preferably has a surface to which the adhesive sheet can be attached, and is preferably in the shape of a sheet, plate, or block. When multiple adherends are to be bonded together, the shapes and dimensions of the adherends may be the same or different.

[0106] [Bonding method] Next, as an example of a bonding method for bonding an adherend using the high-frequency dielectric heating adhesive according to this embodiment, a method for manufacturing a structure by bonding the high-frequency dielectric heating adhesive according to this embodiment to an adherend will be described. The method for manufacturing a structure when manufacturing a structure by bonding the high-frequency dielectric heating adhesive according to this embodiment to an adherend includes, for example, the following steps.

[0107] When a structure is produced by bonding one or more adherends to the high-frequency dielectric heating adhesive according to this embodiment, the method for producing a structure according to this embodiment includes the steps of placing the high-frequency dielectric heating adhesive according to this embodiment on one or more adherends, and applying a high-frequency electric field to the high-frequency dielectric heating adhesive to bond the one or more adherends. The frequency of the applied high-frequency electric field is, for example, 1 MHz or more and 300 MHz or less.

[0108] When a structure is produced by bonding two or more adherends to the high-frequency dielectric heating adhesive according to this embodiment, the method for producing a structure according to this embodiment includes the steps of placing the high-frequency dielectric heating adhesive according to this embodiment between the two or more adherends, and applying a high-frequency electric field to the high-frequency dielectric heating adhesive to bond the two or more adherends. In this case, too, the frequency of the applied high-frequency electric field is, for example, 1 MHz or more and 300 MHz or less.

[0109] In the method for manufacturing a structure according to this embodiment, it is preferable to place two or more adherends and a high-frequency dielectric heating adhesive between electrodes of a dielectric heating device, and apply a high-frequency electric field while applying pressure to the two or more adherends and the high-frequency dielectric heating adhesive with the electrodes. Applying a high-frequency electric field while applying pressure with the electrodes in this manner makes it easier to manufacture a structure in a shorter time. In this specification, the term "dielectric heating device" may also be referred to as "high-frequency dielectric heating device."

[0110] According to the manufacturing method using the high-frequency dielectric heating adhesive of this embodiment, it is possible to locally heat only predetermined locations from the outside using a dielectric heating device. Therefore, the manufacturing method using the high-frequency dielectric heating adhesive of this embodiment is effective even when the adherend is a large and complex three-dimensional structure or a thick and complex three-dimensional structure, etc., and even when high dimensional accuracy is required.

[0111] Below, as an example of a method for manufacturing a structure according to this embodiment, an embodiment in which two or more adherends are bonded using the high-frequency dielectric heating adhesive according to this embodiment will be described, but the present invention is not limited to this embodiment.

[0112] The bonding method according to one aspect of this embodiment includes the following steps P1 and P2.

[0113] Step P1 is a step of placing the high-frequency dielectric heating adhesive according to this embodiment between two or more adherends. When producing a laminate as the structure according to this embodiment, in step P1, for example, the adherends and the high-frequency dielectric heating adhesive are alternately placed to stack the two or more adherends with the high-frequency dielectric heating adhesive interposed therebetween.

[0114] It is preferable to sandwich the high-frequency dielectric heating adhesive between the adherends so that they can be bonded together. The high-frequency dielectric heating adhesive may be sandwiched between a portion of the adherends, between multiple portions of the adherends, or across the entire surface of the adherends. From the viewpoint of improving the adhesive strength between the adherends, it is preferable to sandwich the high-frequency dielectric heating adhesive over the entire bonding surface between the adherends. Another example of sandwiching the high-frequency dielectric heating adhesive between a portion of the adherends is to arrange the high-frequency dielectric heating adhesive in a frame shape along the periphery of the bonding surface between the adherends and sandwich it between the adherends. By arranging the high-frequency dielectric heating adhesive in this frame shape, adhesive strength between the adherends can be obtained and the weight of the structure can be reduced compared to when the high-frequency dielectric heating adhesive is arranged over the entire bonding surface. Furthermore, according to one embodiment in which high-frequency dielectric heating adhesive is sandwiched between a portion of the adherends, the amount of high-frequency dielectric heating adhesive used can be reduced and the size can be made smaller, thereby shortening the high-frequency dielectric heating processing time compared to when high-frequency dielectric heating adhesive is placed over the entire bonding surface.

[0115] Process P2 is a process for bonding two or more adherends by applying a high-frequency electric field to the high-frequency dielectric heating adhesive placed between the adherends in process P1. In one embodiment, the frequency of the applied high-frequency electric field is 1 MHz or more and 300 MHz or less. For example, a dielectric heating device can be used to apply the high-frequency electric field to the high-frequency dielectric heating adhesive.

[0116] <Dielectric Heating Device> FIG. 2 is a schematic diagram illustrating a high-frequency dielectric heating process using the high-frequency dielectric heating adhesive and dielectric heating device according to this embodiment. The dielectric heating device 50 shown in FIG. 2 includes a first high-frequency electric field application electrode 51, a second high-frequency electric field application electrode 52, and a high-frequency power supply 53. The first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 are arranged opposite each other. The first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 each have a press mechanism. The press mechanism for the electrodes (first high-frequency electric field application electrode 51 and second high-frequency electric field application electrode 52) of the dielectric heating device 50 can pressurize the first adherend 110, the high-frequency dielectric heating adhesive 1A, and the second adherend 120 between the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52. In other words, the dielectric heating device 50 can also apply a high-frequency electric field while applying pressure to two or more adherends and the high-frequency dielectric heating adhesive arranged between the electrodes.

[0117] When the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 form a pair of parallel plate electrodes, this type of electrode arrangement is sometimes referred to as a parallel plate type. It is also preferable to use a parallel plate type high-frequency dielectric heating device to apply the high-frequency electric field. With a parallel plate type high-frequency dielectric heating device, the high-frequency electric field penetrates the high-frequency dielectric heating adhesive located between the electrodes, so the entire high-frequency dielectric heating adhesive can be heated and the adherend and the high-frequency dielectric heating adhesive can be bonded in a short time. Furthermore, when manufacturing a laminate as a structure, it is preferable to use a parallel plate type high-frequency dielectric heating device.

[0118] A high-frequency power supply 53 is connected to each of the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 to apply a high-frequency electric field having a frequency of, for example, about 13.56 MHz, about 27.12 MHz, or about 40.68 MHz. As shown in FIG. 2 , the dielectric heating device 50 performs a dielectric heating process via a high-frequency dielectric heating adhesive 1A sandwiched between a first adherend 110 and a second adherend 120. In addition to the dielectric heating process, the dielectric heating device 50 also bonds the first adherend 110 and the second adherend 120 by a pressure process using the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52. Note that two or more adherends may be bonded together without pressure, for example, by the weight of the high-frequency dielectric heating adhesive and the adherends alone.

[0119] When a high-frequency electric field is applied between the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52, the high-frequency dielectric heating adhesive 1A absorbs the high-frequency energy, causing the thermoplastic resin component in the high-frequency dielectric heating adhesive 1A to melt, and the first adherend 110 and the second adherend 120 can be firmly bonded together even in a short treatment time.

[0120] When a high-frequency electric field is applied between the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52, the dielectric filler dispersed in the adhesive component of the high-frequency dielectric heating adhesive 1A absorbs the high-frequency energy. The dielectric filler then functions as a heat source, and the heat generated by the dielectric filler melts the thermoplastic resin component, ultimately firmly bonding the first adherend 110 and the second adherend 120 together, even in a short treatment time.

[0121] The electrodes of the dielectric heating device 50 (the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52) have a press mechanism, so the dielectric heating device 50 also functions as a press device. Therefore, the first adherend 110 and the second adherend 120 can be more firmly bonded together by the compression direction pressure applied by the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 and the heating and melting of the high-frequency dielectric heating adhesive 1A. Note that, although the method for manufacturing a structure has been described using an example in which the structure 100 shown in FIG. 2 is manufactured, the present invention is not limited to this example.

[0122] <High Frequency Dielectric Heating Conditions> The high frequency dielectric heating conditions can be changed as appropriate, but the following conditions are preferred.

[0123] The output of the high-frequency electric field 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 output of the high-frequency electric field 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 output of the high-frequency electric field is 10 W or more, the problem of temperature not rising easily during dielectric heating treatment can be prevented, making it easier to obtain good adhesive strength. If the output of the high-frequency electric field is 50,000 W or less, it is easier to prevent the problem of temperature control being difficult during dielectric heating treatment. The output of the high-frequency electric field indicates the amount of energy transmitted to the object.

[0124] The application time of the high-frequency electric field is preferably 1 second or more. The application time of the high-frequency electric field is preferably 300 seconds or less, more preferably 240 seconds or less, even more preferably 180 seconds or less, even more preferably 120 seconds or less, even more preferably 90 seconds or less, even more preferably 50 seconds or less, even more preferably 20 seconds or less, particularly preferably 10 seconds or less, and extremely preferably 6 seconds or less. If the application time of the high-frequency electric field is 1 second or more, the problem of the temperature not rising easily during the dielectric heating treatment can be prevented, making it easier to obtain good adhesive strength. If the application time of the high-frequency electric field is 300 seconds or less, it is easier to prevent problems such as a decrease in the manufacturing efficiency of the structure, an increase in manufacturing costs, and even thermal deterioration of the adherend.

[0125] The frequency of the applied high-frequency electric field is preferably 1 MHz or higher, more preferably 3 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 electric field is preferably 300 MHz or lower, more preferably 100 MHz or lower, even more preferably 80 MHz or lower, and even more preferably 50 MHz or lower. Specifically, the industrial frequency bands of 13.56 MHz, 27.12 MHz, or 40.68 MHz assigned by the International Telecommunication Union are also used in the high-frequency dielectric heating manufacturing method and bonding method of this embodiment. The frequency of the applied high-frequency electric field indicates the manner (speed) of energy transmission.

[0126] When a high-frequency electric field is applied while pressure is being applied, the initial setting value of the pressure applied to the high-frequency dielectric heating adhesive is preferably 1 kPa or more, more preferably 5 kPa or more, even more preferably 10 kPa or more, even more preferably 30 kPa or more, and even more preferably 50 kPa or more. When a high-frequency electric field is applied while pressure is being applied, the initial setting value of the pressure applied to the high-frequency dielectric heating adhesive is preferably 10 MPa or less, more preferably 5 MPa or less, even more preferably 1 MPa or less, and even more preferably 750 kPa or less. Here, the area used as the basis for the initial setting value of the pressure applied to the high-frequency dielectric heating adhesive is the smallest area among the areas of the electrode and the adherend when viewed in plan.

[0127] [Modifications of the Embodiments] The present invention is not limited to the above-described embodiments, and may include modifications and improvements within the scope of achieving the object of the present invention.

[0128] The high-frequency dielectric heating process is not limited to the dielectric heating device with opposing electrodes 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 simplicity, the figures show an example using a dielectric heating device with opposing electrodes.

[0129] 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.

[0130] [Preparation of high-frequency dielectric heating adhesive] <Examples 1 to 3 and Comparative Examples 1 to 3> As materials for preparing high-frequency dielectric heating adhesives (adhesive sheets), thermoplastic resin (A) and dielectric filler (B) were each weighed out in the proportions shown in Table 1 on a volume basis.

[0131] Next, the thermoplastic resin (A) and the dielectric filler (B) were premixed under specified conditions. The premixed material of the thermoplastic resin (A) and the dielectric filler (B) was fed into the hopper of a 30 mmφ twin-screw extruder, the cylinder and die were heated to a specified temperature, and the premixed material was melt-kneaded. The melt-kneaded material was cooled and then cut to produce granular pellets. The produced granular pellets were then fed into the hopper of a single-screw extruder equipped with a T-die, the cylinder and die were heated to a specified temperature, and a film-like melt-kneaded material was extruded from the T-die and cooled on a cooling roll to produce 400 μm-thick sheet-shaped high-frequency dielectric heating adhesives (high-frequency dielectric heating adhesive sheets) according to Examples 1 to 3 and Comparative Examples 1 to 3.

[0132] The thermoplastic resin (A) and the dielectric filler (B) shown in Table 1 are explained below.

[0133] (Thermoplastic resin (A)) (A1) r-PP: Polypropylene resin (manufactured by Prime Polymer Co., Ltd., product name "Prime Polypro F-744NP", density 0.90 g / cm ３ )

[0134] (Dielectric filler (B)) (B1) ZnO: zinc oxide (manufactured by Hakusui Tech Co., Ltd., product name "DW-4") (B2) ZnO: zinc oxide (manufactured by Hakusui Tech Co., Ltd., product name "calcined zinc oxide") (B3) to (B5) ZnO: zinc oxide (shape: irregular, zinc oxide obtained by crushing ZnO after granulation and adjusting to the particle size Dn shown in Table 2) (B6) ZnO: zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., product name "LPZINC11") Note that the zinc oxides (B1) to (B6) above are all zinc oxides that have not been surface-modified.

[0135] [Evaluation of Physical Properties of High-Frequency Dielectric Heating Adhesive] <Distance between Nearest Centers of Gravity Dg / Particle Diameter Dn> The prepared high-frequency dielectric heating adhesive was cut in the thickness direction, and the cut surface of the cut adhesive sheet was polished using a cross-section ion polisher (manufactured by JEOL Ltd., product name "SM-09010") as a cross-section processing device. Next, an SEM image was obtained at 500x magnification using an SEM (Carl Zeiss Crossbeam 550). The obtained SEM image was binarized using the Otsu binarization method using the programming language Python, resulting in a binarized image divided into white and black. Furthermore, the blobs obtained during the binarization process were detected as dielectric filler particles.

[0136] The circle-equivalent diameters of 100 or more dielectric filler particles to be measured were measured, and the number average value obtained by arithmetic averaging of the measured circle-equivalent diameters was calculated as the particle diameter Dn using the numpy mean function. Furthermore, for the dielectric filler particles to be measured, the particle centers of gravity were determined using the Open CV moments function. Next, a Delaunay diagram connecting the determined particle centers of gravity was created using the Open CV Subdiv2D function, and the three sides of the triangles in the created Delaunay diagram were compared. The length of the shortest side of the three sides of the compared triangle was measured as the nearest center-of-gravity distance. The average value of the measured nearest center-of-gravity distances for 100 or more particles was taken as the nearest center-of-gravity distance Dg.

[0137] Next, the ratio of the nearest neighbor center-of-gravity distance Dg to the particle diameter Dn (nearest neighbor center-of-gravity distance Dg / particle diameter Dn) was calculated from the values ​​of the particle diameter Dn and the nearest neighbor center-of-gravity distance Dg obtained above. In Table 2, the particle diameter Dn is represented as Dn, the nearest neighbor center-of-gravity distance Dg is represented as Dg, and the ratio of the nearest neighbor center-of-gravity distance Dg to the particle diameter Dn is represented as Dg / Dn.

[0138] <Dielectric Properties> The prepared high-frequency dielectric heating adhesive was cut into a length of 30 mm and a width of 30 mm. The cut high-frequency dielectric heating adhesive sheet was measured for its relative permittivity (ε'r) and dielectric loss tangent (tanδ) using a parallel plate method at 23°C and a frequency of 40.68 MHz using an RF Impedance Material Analyzer E4991A (Agilent). Based on the measurement results, the dielectric property (tanδ / ε'r) was calculated.

[0139] <Heating Rate> Two glass fiber reinforced polypropylene resin plates (25 mm long, 100 mm wide, 1.5 mm thick) were prepared as adherends. The prepared high-frequency dielectric heating adhesive (adhesive sheet) was cut to dimensions of 25 mm long and 12.5 mm wide. The cut adhesive sheet was placed between two adherends and laminated. The adherends and adhesive sheet laminated as described above were fixed between two electrodes of a high-frequency dielectric heating device (manufactured by Yamamoto Vinita Co., Ltd., product name "YRP-400T-A"). Next, while fixed in place, an electric field was applied under the following high-frequency electric field application conditions to bond the adhesive sheet and adherend. The sheet temperature at this time was measured using a thermographic camera T860 manufactured by FLIR Systems Japan Inc., and the application time and adhesive sheet temperature were plotted to calculate the heating rate during the initial application time of 5 seconds. The pressing pressure during high-frequency electric field application was the initial setting value for the pressure applied to the adhesive sheet.

[0140] (High frequency electric field application conditions) Frequency: 40.68 MHz Output: 100 W Application time: Maximum 30 seconds Pressing pressure: 0.5 MPa

[0141] <Volume Resistivity> The prepared high-frequency dielectric heating adhesive was cut into a length of 100 mm and a width of 100 mm. The cut high-frequency dielectric heating adhesive sheet was left for 24 hours in an environment of 23°C and a relative humidity of 50% RH. Next, under the same environment, the resistivity was measured when a voltage of 200 V was applied using a resistance meter (manufactured by ADC Corporation, "Digital Ultra-High Resistance / Micro Current Meter 5451").

[0142]

[0143]

[0144] The adhesive sheets of Examples 1 to 3 all achieved a higher heating rate than the adhesive sheets of Comparative Examples 1 and 2. These results show that the high-frequency dielectric heating adhesive according to this embodiment, which satisfies the above-mentioned formula (F1), can be firmly bonded to the adherend in a shorter time than the high-frequency dielectric heating adhesive of the comparative example. Furthermore, the adhesive sheets of Examples 1 to 3 had a higher volume resistivity than the adhesive sheet of Comparative Example 3. These results show that the high-frequency dielectric heating adhesive according to this embodiment, which satisfies the above-mentioned formula (F1), can suppress electrical breakdown during dielectric heating treatment compared to the high-frequency dielectric heating adhesive of the comparative example.

[0145] From the above results, it was confirmed that the high-frequency dielectric heating adhesive of this embodiment can firmly bond to the substrate in a shorter time while suppressing electrical breakdown during dielectric heating treatment compared to conventional high-frequency dielectric heating adhesives.

[0146] DESCRIPTION OF SYMBOLS 10, 20... Adhesive layer, 11... First surface, 21... Second surface, 30... Base material, 40... Intermediate layer, 100... Structure, 1A, 1B, 1C... High frequency dielectric heating adhesive, 50... Dielectric heating device , 51... Electrode (first high frequency electric field applying electrode), 52... Electrode (second high frequency electric field applying electrode), 53... High frequency power source, 110... Adherent (first adherend), 120... Adherent (second adherend).

Claims

1. A high-frequency dielectric heating adhesive comprising a thermoplastic resin (A) and a dielectric filler (B), and when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the relationship between the particle diameter Dn of the dielectric filler (B) and the distance Dg between the nearest centers of gravity of the dielectric filler (B) satisfies the following formula (F1): 1.55≦Dg / Dn≦1.85 ... (F1) 2. The adhesive for high frequency dielectric heating according to claim 1, wherein the thermoplastic resin (A) is a polyolefin resin.

3. A high-frequency dielectric heating adhesive according to claim 1 or 2, wherein the content of the dielectric filler (B) is 3 volume % or more and 40 volume % or less of the entire high-frequency dielectric heating adhesive.

4. A high-frequency dielectric heating adhesive according to claim 1 or 2, wherein the dielectric filler (B) is at least one selected from the group consisting of zinc oxide, silicon carbide, and titanium oxide.

5. A high-frequency dielectric heating adhesive as claimed in claim 1 or 2, wherein when a cross section cut along the thickness direction of the high-frequency dielectric heating adhesive is observed with a scanning electron microscope, the particle diameter Dn of the dielectric filler (B) is 1.0 μm or more and 4.0 μm or less.

6. A high-frequency dielectric heating adhesive as claimed in claim 1 or 2, wherein when a cross section of the high-frequency dielectric heating adhesive cut along the thickness direction is observed with a scanning electron microscope, the distance Dg between nearest neighboring centers of gravity of the dielectric filler (B) is 2.2 μm or more and 6.0 μm or less.

7. The high frequency dielectric heating adhesive according to claim 1 or 2, wherein the high frequency dielectric heating adhesive is an adhesive sheet for high frequency dielectric heating.

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