Adhesive for high-frequency dielectric heating

Abstract

Provided is an adhesive (1A) for high-frequency dielectric heating, which contains a thermoplastic resin (A) (13) and a dielectric filler (B) (15), and which satisfies at least one condition selected from the following conditions (1) and (2): (1) the circularity of the two-dimensional shape of the dielectric filler (B) (15) observed on a cut surface obtained by cutting the adhesive (1A) for high-frequency dielectric heating in the thickness direction is 0.40 or less; (2) The transmittance ratio (T1 / T2) of the transmittance (T1) at a wavelength of 500 nm to the transmittance (T2) at a wavelength of 1000 nm of the adhesive (1A) for high-frequency dielectric heating is 0.65 or less.

Description

Technical Field

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

[0002] As a method of bonding adherends using an adhesive, a method of bonding the adherends by high-frequency dielectric heating treatment or the like has been proposed.

[0003] For example, Patent Document 1 describes a dielectric heating adhesive film for bonding multiple adherends made of the same or different materials by dielectric heating. The dielectric heating adhesive film described in Patent Document 1 contains (A) a polyolefin resin and (B) a dielectric filler having an average particle size within a range of 1 μm to 30 μm as measured in accordance with JIS Z 8819-2:2001, and has a thickness of 10 μm to 2000 μm.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2018 / 079354 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] For example, adhesives for high-frequency dielectric heating containing thermoplastic resins and dielectric fillers can bond to adherends in a short time and easily achieve strong adhesion. Adhesives for high-frequency dielectric heating containing thermoplastic resins and dielectric fillers are sometimes required to bond to adherends in a shorter time.

[0009] Furthermore, adhesives for high-frequency dielectric heating, which contain thermoplastic resins and dielectric fillers, are sometimes required to have not only strong adhesion but also the ability to suppress visible light transmittance while maintaining infrared light transmittance. This characteristic is particularly useful in devices that require both visible light shielding and position detection adaptability using infrared sensors.

[0010] One object of the present invention is to provide a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler, which can be firmly bonded to an adherend in a shorter time than conventional high-frequency dielectric heating adhesives.

[0011] One of the other objects of the present invention is to provide a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler. Compared with conventional high-frequency dielectric heating adhesives, the high-frequency dielectric heating adhesive can ensure light transmittance in the infrared region and has excellent visible light concealment.

[0012] Problem-solving method

[0013] [1] An adhesive for high-frequency dielectric heating, comprising a thermoplastic resin (A) and a dielectric filler (B),

[0014] The adhesive for high-frequency dielectric heating satisfies at least one condition selected from the following (1) and (2):

[0015] (1) The circularity of the two-dimensional shape of the dielectric filler (B) observed on a cut surface obtained by cutting the adhesive for high-frequency dielectric heating in a thickness direction is 0.40 or less;

[0016] (2) The transmittance ratio (T1 / T2) of the transmittance T1 at a wavelength of 500 nm to the transmittance T2 at a wavelength of 1000 nm of the adhesive for high-frequency dielectric heating is 0.65 or less.

[0017] [2] The adhesive for high-frequency dielectric heating according to [1], wherein,

[0018] The perimeter envelope of the two-dimensional shape of the dielectric filler (B) observed on the cut surface obtained by cutting the adhesive for high-frequency dielectric heating in the thickness direction is 0.80 or less.

[0019] [3] The adhesive for high-frequency dielectric heating according to [1] or [2], wherein,

[0020] The thermoplastic resin (A) is a polyolefin-based resin.

[0021] [4] The adhesive for high-frequency dielectric heating according to any one of [1] to [3], wherein,

[0022] The content of the dielectric filler (B) is 2% by volume or more and 40% by volume or less with respect to the entire adhesive for high-frequency dielectric heating.

[0023] [5] The adhesive for high-frequency dielectric heating according to any one of [1] to [4], wherein,

[0024] The dielectric filler (B) has a concave-convex structure on a surface.

[0025] [6] The adhesive for high-frequency dielectric heating according to any one of [1] to [5],

[0026] The dielectric filler (B) is at least one selected from the group consisting of zinc oxide, silicon carbide, titanium oxide, and barium titanate.

[0027] [7] The adhesive for high-frequency dielectric heating according to any one of [1] to [6], wherein,

[0028] The dielectric filler (B) is plate-like stacked spherical zinc oxide.

[0029] [8] The adhesive for high-frequency dielectric heating according to any one of [1] to [7], wherein:

[0030] The volume average particle size of the dielectric filler (B) is 0.01 μm or more and 25 μm or less.

[0031] The volume average particle size is a volume average particle size calculated based on JIS Z 8819-2:2019 from the particle size distribution measurement results of the dielectric filler (B) measured by a laser diffraction / scattering method.

[0032] [9] The adhesive for high-frequency dielectric heating according to any one of [1] to [8], wherein:

[0033] The transmittance T1 of the adhesive for high-frequency dielectric heating at a wavelength of 500 nm is 0.1% or more and 20% or less.

[0034]

[10] The adhesive for high-frequency dielectric heating according to any one of [1] to [9], wherein:

[0035] The dielectric property (tanδ / ε'r) of the high-frequency dielectric heating adhesive is 0.005 or more.

[0036] Tanδ is the dielectric loss tangent at 23°C and a frequency of 40.68 MHz.

[0037] ε'r is the relative dielectric constant at 23°C and a frequency of 40.68 MHz.

[0038]

[11] The adhesive for high-frequency dielectric heating according to any one of [1] to

[10] , wherein:

[0039] The adhesive for high-frequency dielectric heating is an adhesive sheet for high-frequency dielectric heating.

[0040] According to one embodiment of the present invention, there is provided a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler, which can be firmly bonded to an adherend in a shorter time than conventional high-frequency dielectric heating adhesives.

[0041] According to one embodiment of the present invention, a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler can be provided. Compared with conventional high-frequency dielectric heating adhesives, the high-frequency dielectric heating adhesive can ensure light transmittance in the infrared region and has excellent visible light shielding properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] [ Figure 1 ]is a cross-sectional enlarged view schematically showing a cross section of the adhesive for high-frequency dielectric heating of the present embodiment.

[0043] [ Figure 2 ]is an explanatory view of circularity and perimeter envelope.

[0044] [ Figure 3A ]is a cross-sectional view showing an example of the adhesive for high-frequency dielectric heating of the present embodiment.

[0045] [ Figure 3B ]is a cross-sectional view showing another example of the adhesive for high-frequency dielectric heating of the present embodiment.

[0046] [ Figure 3C ]is a cross-sectional view showing another example of the adhesive for high-frequency dielectric heating of the present embodiment.

[0047] [ Figure 4 ]is a view for explaining an example of high-frequency dielectric heating treatment using the adhesive for high-frequency dielectric heating and the dielectric heating device of the present embodiment.

[0048] [ Figure 5 ]is an SEM image of a cross section in the adhesive for high-frequency dielectric heating of Example 1.

[0049] Explanation of symbols

[0050] 10, 20...adhesive layer, 11...first surface, 13...thermoplastic resin, 15, 15A...dielectric filler, 21...second surface, 30...substrate, 40...intermediate layer, 100...structure, 1A, 1B, 1C...adhesive for high-frequency dielectric heating, 50...dielectric heating device, 51...electrode (first high-frequency electric field application electrode), 52...electrode (second high-frequency electric field application electrode), 53...high-frequency power supply, 110...adherend (first adherend), 120...adherend (second adherend). DETAILED DESCRIPTION

[0051] Hereinafter, the adhesive for high-frequency dielectric heating of the preferred embodiment of the present application will be explained.

[0052] [Adhesive for high-frequency dielectric heating]

[0053] The adhesive for high-frequency dielectric heating of the present embodiment contains a thermoplastic resin (A) and a dielectric filler (B), and satisfies at least one condition selected from the following (1) and (2):

[0054] (1) a circularity of a two-dimensional shape of the dielectric filler (B) observed on a cut surface obtained by cutting the above-described adhesive for high-frequency dielectric heating in a thickness direction is 0.40 or less;

[0055] (2) The adhesive for high-frequency dielectric heating has a transmittance ratio (T1 / T2) of 0.65 or less, where T1 is the transmittance at a wavelength of 500 nm and T2 is the transmittance at a wavelength of 1000 nm.

[0056] The adhesive for high-frequency dielectric heating of the present embodiment, by being configured to satisfy the condition of the above (1), can be strongly adhered to an adherend in a shorter time compared to conventional adhesives for high-frequency dielectric heating. When the cross section of the adhesive for high-frequency dielectric heating is observed, the circularity of the dielectric filler (B) is low, indicating that the dielectric filler (B) has a complex profile shape. Since the dielectric filler (B) has a complex profile shape, when high-frequency is applied to the adhesive for high-frequency dielectric heating of the present embodiment, the high-frequency electric field energy is easily concentrated in the convex portions of the profile shape of the dielectric filler (B). It is considered that since the high-frequency electric field energy is easily concentrated in the dielectric filler (B), the dielectric filler (B) easily heats more efficiently. Therefore, the adhesive for high-frequency dielectric heating of the present embodiment can be adhered to an adherend in a shorter time and can obtain a stronger adhesive strength compared to conventional adhesives for high-frequency dielectric heating.

[0057] The adhesive for high-frequency dielectric heating of the present embodiment, by being configured to satisfy the condition of the above (2), has excellent hiding property of visible light while ensuring the light transmittance in the infrared region compared to conventional adhesives for high-frequency dielectric heating. It is considered that when light in the visible region is incident to the adhesive for high-frequency dielectric heating of the present embodiment, the light in the visible region is scattered in various directions in the adhesive for high-frequency dielectric heating, and thus the light in the visible region is not easily transmitted. On the other hand, it is considered that for the adhesive for high-frequency dielectric heating of the present embodiment, when light in the infrared region is incident, the scattering of the light in the infrared region is less in the adhesive for high-frequency dielectric heating, and the light in the infrared region is easily transmitted. It is thus considered that the adhesive for high-frequency dielectric heating of the present embodiment can suppress the light transmittance in the visible region while ensuring the light transmittance in the infrared region.

[0058] Hereinafter, the materials used in the adhesive for high-frequency dielectric heating of the present embodiment will be described.

[0059] <Thermoplastic Resin (A)>

[0060] The type of the thermoplastic resin (A) is not particularly limited.

[0061] For example, from the viewpoint of easy occurrence of melting and given heat resistance, the thermoplastic resin (A) is preferably at least one selected from the group consisting of polyolefin-based resins, styrene-based resins, polyacetal-based resins, polycarbonate-based resins, acrylic-based resins, polyamide-based resins, polyimide-based resins, polyvinyl acetate-based resins, phenoxy-based resins, and polyester-based resins. The thermoplastic resin (A) is preferably selected from a resin type having high affinity with the material of the adherend.

[0062] In the adhesive for high-frequency dielectric heating of the present embodiment, the thermoplastic resin (A) is preferably a polyolefin-based resin or a styrene-based resin, and more preferably a polyolefin-based resin. If the thermoplastic resin (A) is a polyolefin-based resin or a styrene-based resin, the adhesive for high-frequency dielectric heating easily melts upon application of a high-frequency electric field, and the adhesive for high-frequency dielectric heating of the present embodiment can be easily adhered to the adherend.

[0063] In the present specification, the polyolefin-based resin includes a polyolefin-based resin having a polar site and a polyolefin-based resin not having a polar site, and is described as a polyolefin-based resin having a polar site or a polyolefin-based resin not having a polar site when it is intended to define the presence or absence of a polar site.

[0064] The thermoplastic resin (A) is preferably a polyolefin-based resin having a polar site. The thermoplastic resin (A) can also be a polyolefin-based resin not having a polar site.

[0065] (Polyolefin-based resin)

[0066] As the polyolefin-based resin of the thermoplastic resin (A), for example, a resin formed of a homopolymer such as polyethylene, polypropylene, polybutene, and polymethylpentene, and an α-olefin resin formed of a copolymer of monomers selected from the group consisting of ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene, and the like can be exemplified. The polyolefin-based resin of the thermoplastic resin (A) can be a single type of resin, or a combination of two or more types of resins.

[0067] [Polyolefin-based resin having a polar site]

[0068] The polar site in the polyolefin-based resin having a polar site is not particularly limited as long as it is a site capable of imparting polarity to the polyolefin-based resin.

[0069] In addition, by containing a polyolefin-based resin having a polar site as the thermoplastic resin (A) in the adhesive for high-frequency dielectric heating, the dielectric properties are easily improved, and the adhesion to the adherend is increased, and thus it is preferable.

[0070] The polyolefin-based thermoplastic resin having a polar site can be a copolymer of an olefin-based monomer and a monomer having a polar site. In addition, the polyolefin-based thermoplastic resin having a polar site can be a resin in which a polar site is introduced into an olefin-based polymer obtained by polymerization of an olefin-based monomer by modification such as an addition reaction.

[0071] There is no particular limitation on the kind of the olefin-based monomer constituting the polyolefin-based resin having a polar site. As the olefin-based monomer, for example, ethylene, propylene, butene, hexene, octene, and 4-methyl-l-pentene, etc. can be listed. The olefin-based monomer can be used alone as one of them, or two or more kinds in combination.

[0072] The olefin-based monomer is preferably at least any one of ethylene and propylene from the viewpoint of excellent mechanical strength and obtainment of stable adhesion properties.

[0073] The structural unit derived from an olefin in the polyolefin-based resin having a polar site is preferably a structural unit derived from ethylene or propylene.

[0074] As the polar site, for example, a hydroxyl group, a carboxyl group, a vinyl acetate structure, an anhydride structure, etc. can be listed. As the polar site, an acid-modified structure introduced into the polyolefin-based resin by acid modification, etc. can also be listed.

[0075] The acid-modified structure as the polar site is a site introduced by acid modification of a thermoplastic resin (for example, a polyolefin-based resin). As the compound used when the thermoplastic resin (for example, a polyolefin-based resin) is subjected to acid modification, an unsaturated carboxylic acid derivative component derived from any of an unsaturated carboxylic acid, an anhydride of an unsaturated carboxylic acid, and an ester of an unsaturated carboxylic acid can be listed. In the present specification, the polyolefin-based resin having an acid-modified structure is sometimes referred to as an acid-modified polyolefin-based resin.

[0076] As the unsaturated carboxylic acid, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid, etc. can be listed.

[0077] As the anhydride of an unsaturated carboxylic acid, for example, maleic anhydride, itaconic anhydride, and citraconic anhydride, etc. can be listed.

[0078] As the ester of an unsaturated carboxylic acid, for example, 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 tetrahydrophthalate, etc. can be listed.

[0079] [Maleic anhydride-modified polyolefin]

[0080] The polyolefin resin as the thermoplastic resin more 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.

[0081] The structural unit derived from olefin in the maleic anhydride-modified polyolefin is preferably a structural unit derived from ethylene or propylene. That is, the maleic anhydride-modified polyolefin is preferably a maleic anhydride-modified polyethylene resin or a maleic anhydride-modified polypropylene resin.

[0082] <Dielectric filler (B)>

[0083] The dielectric filler (B), which is a preferred material as the dielectric material, will be described.

[0084] The dielectric filler (B) 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.

[0085] The dielectric filler (B) is preferably a filler that generates heat when a high-frequency electric field in the frequency range of 3 MHz to 300 MHz is applied. The dielectric filler (B) is preferably a filler that generates heat when a high-frequency electric field in the frequency range of 3 MHz to 300 MHz is applied, for example, a filler having a frequency of 13.56 MHz, 27.12 MHz, or 40.68 MHz.

[0086] The dielectric filler (B) is suitably one of the following materials alone or in combination of two or more: zinc oxide, silicon carbide (SiC), anatase titanium oxide, barium titanate, barium zirconate titanate, lead titanate, potassium niobate, rutile titanium oxide, hydrated aluminum silicate, inorganic materials having crystalline water such as hydrated aluminum silicate of alkali metals, or inorganic materials having crystalline water such as hydrated aluminum silicate of alkaline earth metals.

[0087] From the viewpoint of achieving higher heat generation properties, the dielectric filler (B) is preferably at least one selected from zinc oxide, silicon carbide, titanium oxide, and barium titanate, more preferably at least one selected from zinc oxide, barium titanate, and titanium oxide, even more preferably at least one selected from zinc oxide, silicon carbide, and titanium oxide, and further preferably at least one selected from zinc oxide and titanium oxide.

[0088] Among the dielectric fillers (B) exemplified, zinc oxide is abundant in variety, can be selected in various shapes and sizes, and can improve the bonding properties and mechanical properties of the high-frequency dielectric heating adhesive in accordance with the intended use. Therefore, the dielectric filler (B) is further preferably zinc oxide. By using zinc oxide as the dielectric filler (B), a high-frequency dielectric heating adhesive with no design problems and low transmittance can be obtained. Zinc oxide has a low hardness among ceramics and is therefore not easily damaged in the manufacturing device of the high-frequency dielectric heating adhesive. Since zinc oxide is an inactive oxide, even when combined with a thermoplastic resin, the damage caused to the thermoplastic resin is small.

[0089] The titanium oxide as the dielectric filler (B) is preferably at least one of anatase-type titanium oxide and rutile-type titanium oxide, and is more preferably anatase-type titanium oxide from the viewpoint of excellent dielectric properties.

[0090] The shape of the dielectric filler (B) is not particularly limited, and various shapes can be adopted.

[0091] The dielectric filler (B) is preferably a dielectric filler having a concavo-convex structure on its surface, for example.

[0092] It is believed that when the dielectric filler (B) has a surface with a concavo-convex structure, the high-frequency electric field energy is more likely to be concentrated on the convex portions of the dielectric filler (B), and thus the high-frequency electric field energy is more likely to be concentrated on the dielectric filler (B), so that the dielectric filler (B) tends to generate heat more efficiently. As a result, when the dielectric filler (B) has a surface with a concavo-convex structure, it is easier to obtain a high-frequency dielectric heating adhesive that can firmly bond to the adherend in a shorter time.

[0093] It is believed that if the dielectric filler (B) has a concavo-convex structure on its surface, when light in the visible light region (sometimes referred to as the visible light region) is incident, it is more likely to be scattered in multiple directions, thereby making it difficult for light in the visible light region to pass through. On the other hand, it is believed that when light in the infrared region is incident, the scattering of light in the infrared region is less, so light in the infrared region is easily transmitted. As a result, if the dielectric filler (B) has a concavo-convex structure on its surface, it is easy to obtain a high-frequency dielectric heating adhesive that can ensure light transmittance in the infrared region while having excellent concealment in the visible light region.

[0094] When the shape of the dielectric filler (B) contained in the high-frequency dielectric heating adhesive of this embodiment has a concave-convex structure on the surface, it can be confirmed by observing the cross-section obtained by cutting the high-frequency dielectric heating adhesive along the thickness direction using a scanning electron microscope (hereinafter referred to as SEM: Scanning Electron Microscope).

[0095] In the case where the dielectric filler (B) has a concavo-convex structure on the surface, the shape of the dielectric filler (B) is not particularly limited, and examples thereof include a star shape, a tetrapod shape, a chestnut shape, and a petal shape. The shape of the dielectric filler (B) can be at least one selected from among these shapes. In the case where the dielectric filler (B) has a concavo-convex structure on the surface, the dielectric filler (B) is preferably at least one selected from among zinc oxide, silicon carbide, titanium oxide, and barium titanate, more preferably at least one selected from among zinc oxide, titanium oxide, and barium titanate, more preferably at least one selected from among zinc oxide, silicon carbide, and titanium oxide, further preferably at least one selected from among zinc oxide and titanium oxide, and more further preferably zinc oxide.

[0096] In the case where the dielectric filler (B) has a concavo-convex structure on the surface, for example, it can be a particle aggregate formed by aggregation or accumulation of a plurality of particles, or it can be a particle aggregate formed by further aggregation or accumulation of a particle aggregate. In the case where the dielectric filler (B) having a concavo-convex structure is at least one of a particle aggregate and a particle aggregate, for example, the shape of the convex portion forming the concavo-convex structure can have at least any one of a spherical shape, a needle shape, and a plate shape. The convex portion can further have a protrusion, which can be at least any one of a spherical shape, a needle shape, and a plate shape, for example. As such a shape of the dielectric filler (B), for example, at least one selected from among a spherical accumulation type which is a shape formed by accumulation of spherical particles, a needle accumulation type which is a shape formed by accumulation of needle-shaped particles, and a plate accumulation type which is a shape formed by accumulation of plate-shaped particles is particularly preferable. The overall shape of the dielectric filler (B) of these accumulation types is not particularly limited, and can be various shapes. The dielectric filler (B) is preferably at least one selected from among a spherical accumulation type spherical zinc oxide, a needle accumulation type spherical zinc oxide, and a plate accumulation type spherical zinc oxide, and more preferably a plate accumulation type spherical zinc oxide. The spherical accumulation type spherical zinc oxide, the needle accumulation type spherical zinc oxide, and the plate accumulation type spherical zinc oxide each represent a particle of zinc oxide having an overall shape similar to a spherical shape and having a concavo-convex structure on the surface, which is formed by accumulation of particles having any one of a spherical shape, a needle shape, or a plate shape. The overall shape similar to a spherical shape represents a shape that appears to be a spherical shape or a shape that appears to be substantially a spherical shape in an external appearance.

[0097] The method for obtaining the plate-stacked spherical zinc oxide is not particularly limited. The plate-stacked spherical zinc oxide can be obtained, for example, by a production method having a process of neutralizing an aqueous zinc salt solution in the presence of a hydrophilic dispersant. As the aqueous zinc salt solution, at least one zinc salt selected from the group consisting of zinc salts of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, oxalic acid, and fatty acid, and zinc salts of other organic acids can be mentioned. As the hydrophilic dispersant, for example, a surfactant of anionic type, cationic type, or nonionic type, or the like can be mentioned. As the aqueous alkali solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous lithium hydroxide solution, or the like can be mentioned.

[0098] If the dielectric filler (B) is the plate-stacked spherical zinc oxide, the circularity of the two-dimensional shape of the dielectric filler (B) observed at the cut surface of the high-frequency dielectric heating adhesive cut in the thickness direction more easily satisfies the range of 0.4 or less, and a high-frequency dielectric heating adhesive capable of being strongly bonded to an adherend in a shorter time is more easily obtained. In addition, the perimeter envelope of the two-dimensional shape of the dielectric filler (B) observed at the cut surface of the high-frequency dielectric heating adhesive cut in the thickness direction more easily satisfies the range of 0.8 or less. Specific descriptions of the circularity and the perimeter envelope are described below.

[0099] In addition, if the dielectric filler (B) is the plate-stacked spherical zinc oxide, the transmittance ratio (T1 / T2) of the transmittance T1 at a wavelength of 500 nm to the transmittance T2 at a wavelength of 1000 nm of the high-frequency dielectric heating adhesive more easily satisfies the range of 0.65 or less, and a high-frequency dielectric heating adhesive having excellent hiding properties in the visible light region while ensuring light transmittance in the infrared region is more easily obtained. Specific descriptions of the transmittance ratio are described below.

[0100] The volume content ratio of the dielectric filler (B) in the high-frequency dielectric heating adhesive is preferably 2% by volume or more, more preferably 4% by volume or more, further preferably 6% by volume or more, and still further preferably 8% by volume or more.

[0101] The volume content ratio 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, further preferably 30% by volume or less, still further preferably 25% by volume or less, and yet further preferably 22% by volume or less.

[0102] By making the volume content ratio of the dielectric filler (B) in the high-frequency dielectric heating adhesive 2% by volume or more, the heat generation property is improved, and the high-frequency dielectric heating adhesive is easily strongly bonded to an adherend.

[0103] By limiting the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive to 40% by volume or less, it is possible to prevent a decrease in the strength of the adhesive, thereby preventing a decrease in bonding strength due to the use of the adhesive. Furthermore, when the high-frequency dielectric heating adhesive of this embodiment is an adhesive sheet, limiting the volume content of the dielectric filler (B) in the adhesive sheet to 40% by volume or less facilitates achieving flexibility when formed into a sheet and also prevents a decrease in toughness. This facilitates processing the high-frequency dielectric heating adhesive sheet into a desired shape in subsequent steps.

[0104] The volume average particle size of the dielectric filler (B) is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more.

[0105] The volume average particle size of the dielectric filler (B) is preferably 25 μm or less, more preferably 15 μm or less, further preferably 5 μm or less, and particularly preferably 1.5 μm or less.

[0106] When the volume average particle size of the dielectric filler (B) is 0.01 μm or more, the adhesive for high-frequency dielectric heating exhibits high heat generation performance when a high-frequency electric field is applied, and can be strongly bonded to an adherend in a short time.

[0107] By setting the volume average particle size of the dielectric filler (B) to 25 μm or less, the high-frequency dielectric heating adhesive exhibits high heat generation performance when a high-frequency electric field is applied, enabling strong adhesion to the adherend in a short period of time. Furthermore, when the high-frequency dielectric heating adhesive of this embodiment is a sheet, setting the volume average particle size of the dielectric filler (B) to 25 μm or less prevents a reduction in the strength of the sheet.

[0108] The volume average particle size of the dielectric filler (B) can be measured by the following method: the particle size distribution of the dielectric filler (B) is measured by laser diffraction / scattering method, and the volume average particle size is calculated based on the results of the particle size distribution measurement in accordance with JIS Z 8819-2:2019.

[0109] <Additives>

[0110] The high-frequency dielectric heating adhesive of the present embodiment may or may not contain additives as long as the adhesiveness in a short period of time is not impaired.

[0111] In the case where the adhesive for high-frequency dielectric heating of the present embodiment contains an additive, as the additive, for example, tackifiers, plasticizers, waxes, colorants, antioxidants, ultraviolet absorbers, antibacterial agents, coupling agents, viscosity modifiers, organic fillers, and inorganic fillers, and the like can be exemplified. The organic fillers and the inorganic fillers as the additive are different from the dielectric fillers.

[0112] The tackifiers and the plasticizers can improve the melting properties and the adhesive properties of the adhesive for high-frequency dielectric heating.

[0113] As the tackifiers, for example, rosin derivatives, polyterpene resins, aromatic modified terpene resins, hydrogenates of the aromatic modified terpene resins, terpene phenol resins, coumarone-indene resins, aliphatic petroleum resins, aromatic petroleum resins, and hydrogenates of the aromatic petroleum resins can be exemplified.

[0114] As the plasticizers, for example, petroleum-based processing oils, natural oils, dibasic acid dialkyl esters, and low-molecular-weight liquid polymers can be exemplified. As the petroleum-based processing oils, for example, paraffin-based processing oils, naphthene-based processing oils, and aromatic-based processing oils, and the like can be exemplified. As the natural oils, for example, castor oil and tall oil, and the like can be exemplified. As the dibasic acid dialkyl esters, for example, dibutyl phthalate, dioctyl phthalate, and dibutyl adipate, and the like can be exemplified. As the low-molecular-weight liquid polymers, for example, liquid polybutene and liquid polyisoprene, and the like can be exemplified.

[0115] In the case where the adhesive for high-frequency dielectric heating of the present embodiment contains an additive, the content of the additive in the adhesive for high-frequency dielectric heating is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more, based on the total amount of the adhesive for high-frequency dielectric heating. In addition, the content of the additive in the adhesive for high-frequency dielectric heating is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less.

[0116] The adhesive for high-frequency dielectric heating of the present embodiment preferably does not contain a solvent. When the adhesive for high-frequency dielectric heating that does not contain a solvent is used, the problem of volatile organic compounds caused by the adhesive used for adhesion to an adherend is less likely to occur.

[0117] The adhesive for high-frequency dielectric heating of the present embodiment preferably does not contain an electrically conductive substance such as carbon or a carbon compound in which carbon is a main component, and a metal. The adhesive for high-frequency dielectric heating of the present embodiment preferably does not contain, for example, carbon steel, alpha iron, gamma iron, delta iron, copper, iron oxide, brass, aluminum, iron-nickel alloy, iron-nickel-chromium alloy, carbon fiber, and carbon black.

[0118] In the case where the adhesive for high-frequency dielectric heating of the present embodiment contains an electrically conductive substance, the content of the electrically conductive substance in the adhesive is each independently preferably 7% by mass or less, more preferably 6% by mass or less, further preferably 5% by mass or less, more further preferably 1% by mass or less, further more preferably 0.1% by mass or less, based on the total amount of the adhesive.

[0119] The content of the electrically conductive substance in the adhesive is particularly preferably 0% by mass.

[0120] When the content of the electrically conductive substance in the adhesive is 7% by mass or less, it is easy to prevent an adverse event in which carbonization of the adhesive portion and the adherend occurs due to electrically insulating breakdown when dielectric heating treatment is performed.

[0121] In the adhesive for high-frequency dielectric heating of the present 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, further preferably 93% by mass or more, more further preferably 95% by mass or more, and further more preferably 99% by mass or more.

[0122] <Properties of the adhesive for high-frequency dielectric heating>

[0123] Next, the properties of the adhesive for high-frequency dielectric heating of the present embodiment will be described.

[0124] The adhesive for high-frequency dielectric heating of the present embodiment can satisfy the condition of any one of the above (1) or (2), or can satisfy both of the above (1) and (2).

[0125] (Circularity)

[0126] In the case where the adhesive for high-frequency dielectric heating of the present embodiment satisfies the condition of the above (1), the circularity of the two-dimensional shape of the dielectric filler (B) observed in the cross section obtained by cutting in the thickness direction is 0.40 or less. The circularity is preferably 0.38 or less, more preferably 0.36 or less, and further preferably 0.34 or less. The lower limit of the circularity is not particularly limited, and is preferably 0.10 or more, more preferably 0.15 or more, and further preferably 0.20 or more. If the above circularity is 0.40 or less, it is possible to strongly adhere to the adherend in a shorter time.

[0127] In the present embodiment, the circularity is the circularity determined by the steps shown in the following (Ci1) to (Ci4).

[0128] (Ci1): The cross section of the adhesive for high-frequency dielectric heating obtained by cutting in the thickness direction is observed for one field of view or more at 500 times or more using a scanning electron microscope (SEM).

[0129] (Ci2) : The obtained SEM image was subjected to binary processing by an image analysis software, and a blob (Binary Large Object) obtained from the binary-processed image was detected as a particle of the dielectric filler (B). The blob is a region in which pixels determined as white are adjacently connected in the binary-processed image.

[0130] (Ci3) : The circumference LI and the area S of the dielectric filler (B) were calculated by subjecting the detected particles of the dielectric filler (B) to blob analysis. The measurement targets of the circumference LI and the area S were the particles of the dielectric filler (B) having an equivalent circle diameter of 0.088 μm or more among the detected particles of the dielectric filler (B).

[0131] (Ci4) : The circularity was calculated by the following mathematical expression (Mathematical Expression 1) using the circumference LI and the area S of each particle of the dielectric filler (B) that became the measurement target, and the arithmetic average of the number of the measured dielectric fillers (B) was obtained.

[0132] Circularity = 4πS / (LI) 2 (Mathematical Expression 1)

[0133] (In the above mathematical expression (Mathematical Expression 1), the area S is the area of the dielectric filler (B) obtained from the binary-processed image, and the circumference LI is the circumference of the dielectric filler (B) obtained from the binary-processed image.)

[0134] The circumference LI of the dielectric filler (B) represents the length of the outer periphery of the outline itself of the dielectric filler (B) obtained from the two-dimensional planar image. The circularity of the dielectric filler (B) represents the circularity obtained from the two-dimensional planar image. The smaller the circularity, the more the outline shape of the two-dimensional planar image represents a shape far from a perfect circle. Specifically, the circularity can be obtained by the method described in the Examples described later.

[0135] (Circumference Envelope Degree)

[0136] The circumference envelope degree of the two-dimensional shape of the dielectric filler (B) observed on a cut surface obtained by cutting in the thickness direction is preferably 0.80 or less for the adhesive for high-frequency dielectric heating of the present embodiment. The circumference envelope degree is more preferably 0.79 or less, and further preferably 0.78 or less. The lower limit of the circumference envelope degree is not particularly limited, and is preferably 0.30 or more, more preferably 0.50 or more, and further preferably 0.70 or more.

[0137] In the case where the perimeter envelope degree is 0.80 or less, the condition where the perimeter envelope degree is 0.80 or less is sometimes referred to as a condition satisfying (3). That is, the adhesive for high-frequency dielectric heating of the present embodiment is further preferably satisfies the following condition (3).

[0138] (3) The perimeter envelope degree of the two-dimensional shape of the dielectric filler (B) observed in the cross section of the adhesive for high-frequency dielectric heating cut in the thickness direction is 0.80 or less.

[0139] The adhesive for high-frequency dielectric heating of the present embodiment is preferably satisfies any one of the above conditions (1) or (2), and further satisfies the condition (3), and is also preferably satisfies both of the conditions (1) and (2), and further satisfies the condition (3).

[0140] In the present embodiment, the perimeter envelope degree is the perimeter envelope degree determined by the steps shown in the following (Co1) to (Co4).

[0141] (Co1): The cut surface of the adhesive for high-frequency dielectric heating cut in the thickness direction is observed for one field of view or more using an SEM at 500 times or more.

[0142] (Co2): The obtained SEM image is subjected to binary processing by image analysis software, and the Blob obtained from the resulting binary processed image is detected as a particle of the dielectric filler (B).

[0143] (Co3): The perimeter L1 and the envelope perimeter L2 of the dielectric filler (B) are calculated by subjecting the detected particles of the dielectric filler (B) to Blob analysis. The measurement targets of the perimeter L1 and the envelope perimeter L2 are set to the particles of the dielectric filler (B) having an equivalent circle diameter of 0.088 μm or more among the detected particles of the dielectric filler (B).

[0144] (Co4): The perimeter envelope degree is calculated using the obtained perimeter L1 and the envelope perimeter L2 by the following mathematical formula (Mathematical Formula 2), and is calculated as the arithmetic mean of the number of the dielectric filler (B) determined.

[0145] Perimeter envelope degree = L2 / L1 ··· (Mathematical Formula 2)

[0146] (In the above mathematical formula (Mathematical Formula 2), the perimeter L1 is the perimeter of the dielectric filler (B) calculated from the binary processed image, and the envelope perimeter L2 is the envelope perimeter of the dielectric filler (B) calculated from the binary processed image.)

[0147] The perimeter envelope degree is observed in the same manner as the circularity, with respect to the particles of the dielectric filler (B) detected in the binary processed image. If the conditions of the particles of the dielectric filler (B) to be measured are the same, in both the measurement of the circularity and the perimeter envelope degree, the field of view of the SEM image to be observed can be either the same or different, but it is preferable that the measurement of both is performed with the same field of view.

[0148] The envelope perimeter L2 of the dielectric filler (B) represents the perimeter obtained by adding the lengths of the outer perimeters of the polygons formed by connecting the vertices of the convex portions of the dielectric filler (B) in the two-dimensional planar image with straight lines. Hereinafter, the "polygon formed by connecting the vertices of the convex portions with straight lines" is sometimes referred to as a convex hull. The perimeter envelope degree of the dielectric filler (B) represents the perimeter envelope degree obtained from the two-dimensional planar image. The smaller the perimeter envelope degree, the more the outline shape of the two-dimensional planar image is a shape with more concavities and convexities. Specifically, the perimeter envelope degree can be obtained by the method described in the Examples described later.

[0149] Here, the circularity and the perimeter envelope degree are described with reference to Figure 1 and Figure 2 . Figure 1 An enlarged view of a cross section obtained by cutting the high-frequency dielectric heating adhesive 1A in the thickness direction is schematically shown in FIG. 1. As shown in FIG. 1, the high-frequency dielectric heating adhesive 1A contains a thermoplastic resin 13 and a plurality of dielectric fillers 15 each having a concavo-convex structure on the surface. Figure 1

[0150] In FIG. 1, as an example of one of the dielectric fillers 15 observed in the cross section of the cross section obtained by cutting the high-frequency dielectric heating adhesive 1A in the thickness direction, a dielectric filler 15A is shown. The dielectric filler 15A has an area S, a perimeter L1 which is the entire circumference of the outline of the dielectric filler 15A, and an envelope perimeter L2 which is the entire circumference of the convex portions of the dielectric filler 15A. Figure 2

[0151] For example, in the observation of the dielectric filler 15A using SEM, the dielectric filler 15A is observed in the field of view of the SEM image shown in FIG. 2. Figure 1 ​​The cross section shown is binarized using image analysis software, and the resulting SEM image is processed so that pixels (pixcels) having a pixel value above a given binarization threshold are white, and pixels having a pixel value below the given binarization threshold are black. For example, if the pixel value 128 is set as the binarization threshold, pixels having a pixel value of 128 or more are all converted to white by being assigned the pixel value 255, and pixels having a pixel value of less than 128 are all converted to black by being assigned 0. When the SEM image is binarized, the region in which the pixels having the pixel value 255 are adjacently connected is recognized as one Blob, and thus the dielectric filler 15 having a profile of a concave-convex structure is detected.

[0152] Further, as shown in Figure 2 In the detected dielectric filler 15, the dielectric filler 15A is selected as one of the dielectric fillers for the determination of the circularity and the perimeter envelope degree. For the area S, the perimeter LI, and the envelope perimeter L2 of the dielectric filler 15A, the total number of pixels of the entire portion corresponding to the dielectric filler 15A is determined as the area S of the dielectric filler 15A, the number of pixels calculated from the total of the numbers of pixels of the portions corresponding to the profile of the dielectric filler 15A is determined as the perimeter LI of the dielectric filler 15A, and the number of pixels calculated from the total of the numbers of pixels of the portions corresponding to the profile of the region of the convex hull of the dielectric filler 15A is determined as the envelope perimeter L2 of the dielectric filler 15A. The envelope perimeter L2 of the dielectric filler 15A is calculated based on the perimeter LI. Here, the number of pixels calculated from the total of the numbers of pixels of the portions corresponding to the profile of the dielectric filler 15A is the number of pixels of the portions surrounding the dielectric filler 15A. The numbers of pixels calculated in the perimeter LI and the envelope perimeter L2 can be calculated by using an appropriate calculation method. The calculation method is not particularly limited, and for example, it can be a method in which, in the above-described blob, the pixels of the portions connected in the horizontal and vertical directions are each regarded as one pixel, and the pixels of the portions connected in the diagonal direction are each regarded as one pixel. The circularity is calculated by the above-described mathematical expression (Mathematical Expression 1) and the perimeter envelope degree is calculated by the above-described mathematical expression (Mathematical Expression 2) from the values of the area S, the perimeter LI, and the envelope perimeter L2 of the dielectric filler 15A. The circularity and the perimeter envelope degree are each calculated as an average value of the number of the dielectric fillers for the determination in the dielectric filler 15.

[0153] (transmittance ratio)

[0154] In the adhesive for high-frequency dielectric heating of the present embodiment, in the case where the condition of the above (2) is satisfied, the transmittance ratio (T1 / T2) of the transmittance T1 at a wavelength of 500 nm with respect to the transmittance T2 at a wavelength of 1000 nm of the adhesive for high-frequency dielectric heating is 0.65 or less. The transmittance ratio (T1 / T2) is preferably 0.60 or less, more preferably 0.50 or less, and further preferably 0.40 or less. The lower limit value of the transmittance ratio (T1 / T2) is not particularly limited, and can be, for example, 0.01 or more.

[0155] The transmittance ratio is a transmittance ratio measured by the following measurement method. For the adhesive for high-frequency dielectric heating of the present embodiment, the transmittance spectrum (total of direct transmittance and diffuse transmittance) in the wavelength range of 300 nm to 2000 nm is measured, the transmittance T1 at a wavelength of 500 nm and the transmittance T2 at a wavelength of 1000 nm are extracted from the obtained transmittance spectrum, and the transmittance ratio is calculated by the following mathematical expression (Mathematical Expression 3). Specifically, the transmittance ratio can be calculated by the method described in the Examples described later.

[0156] Transmittance ratio = T1 / T2 (Mathematical Expression 3)

[0157] (In the above Mathematical Expression (Mathematical Expression 3), the transmittance T1 is the transmittance at a wavelength of 500 nm, and the transmittance T2 is the transmittance at a wavelength of 1000 nm.)

[0158] If the transmittance ratio of the adhesive for high-frequency dielectric heating is 0.65 or less, the light transmittance in the visible light region can be suppressed while ensuring the light transmittance in the infrared region. The adhesive for high-frequency dielectric heating of the present embodiment is useful in applications where design properties and the like are required, and in applications of infrared sensors and the like, for example, in the case where the transmittance ratio satisfies 0.65 or less.

[0159] In the adhesive for high-frequency dielectric heating of the present embodiment, the transmittance T1 at a wavelength of 500 nm is preferably 20% or less, more preferably 15% or less, further preferably 10% or less, and particularly preferably 7% or less. If the transmittance T1 at a wavelength of 500 nm is 20% or less, the light transmittance in the visible light region can be easily suppressed.

[0160] In the adhesive for high-frequency dielectric heating of the present embodiment, the lower limit value of the transmittance T1 at a wavelength of 500 nm is not particularly limited, and can be, for example, 0.1% or more.

[0161] In the adhesive for high-frequency dielectric heating of the present embodiment, the transmittance T2 at a wavelength of 1000 nm is preferably 5% or greater, more preferably 7% or greater, further preferably 9% or greater, and particularly preferably 11% or greater. If the transmittance T2 at a wavelength of 1000 nm is 5% or greater, the light transmittance in the infrared region is excellent.

[0162] In the adhesive for high-frequency dielectric heating of the present embodiment, the upper limit value of the transmittance T2 at a wavelength of 1000 nm is not particularly limited, and for example, can be 100% or less, can be 99% or less, or can be 95% or less.

[0163] (Dielectric properties)

[0164] The dielectric properties (tan δ / ε' r) of the adhesive for high-frequency dielectric heating of the present embodiment are described. In the case of the adhesive for high-frequency dielectric heating of the present embodiment, the dielectric properties (tan δ / ε' r) of the adhesive for high-frequency dielectric heating are preferably 0.005 or greater.

[0165] (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.)

[0166] If the dielectric properties of the adhesive for high-frequency dielectric heating are 0.005 or greater, the adhesive for high-frequency dielectric heating easily generates heat when dielectric heating treatment is performed, and the adhesive for high-frequency dielectric heating and the adherend are easily strongly bonded in a short time.

[0167] The dielectric properties of the adhesive for high-frequency dielectric heating of the present embodiment are more preferably 0.008 or greater, and further preferably 0.010 or greater.

[0168] If the dielectric properties of the adhesive for high-frequency dielectric heating of the present embodiment are 0.008 or greater, the adhesive for high-frequency dielectric heating more easily generates heat when dielectric heating treatment is performed, and the adhesive for high-frequency dielectric heating and the adherend are easily strongly bonded in a short time.

[0169] The upper limit of the dielectric properties of the adhesive for high-frequency dielectric heating of the present embodiment is not particularly limited. The dielectric properties of the adhesive for high-frequency dielectric heating of the present embodiment can be, for example, 0.1 or less, can be 0.08 or less, or can be 0.05 or less. The dielectric properties of the adhesive for high-frequency dielectric heating can satisfy, for example, 0.005 or greater and 0.1 or less.

[0170] If the dielectric properties of the adhesive for high-frequency dielectric heating are 0.1 or less, overheating is easily suppressed, and damage to the portion at which the adherend and the adhesive for high-frequency dielectric heating are in contact is not easily caused.

[0171] The dielectric characteristic (tan δ / ε'r) is a value obtained by dividing the dielectric loss tangent (tan δ) measured using an impedance material device or the like by the relative dielectric constant (ε'r) measured using an impedance material device or the like.

[0172] The dielectric loss tangent (tan δ) and relative permittivity (ε'r), which are dielectric properties of the adhesive for high-frequency dielectric heating, can be measured simply and accurately using an impedance / material analyzer.

[0173] It should be noted that 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 measuring sheet of the high-frequency dielectric heating adhesive is obtained. When it is necessary to obtain a measuring sheet from a structure, a measuring sheet of uniform thickness is obtained by cutting or shaving it from the structure. For a high-frequency dielectric heating adhesive that is not formed into a sheet, such as a granular material, a measuring sheet is obtained by forming a sheet using a hot press or the like. The thickness of the measuring sheet is, for example, greater than 10 μm and less than 2 mm. For the sheet thus obtained, the relative dielectric constant (ε'r) and the dielectric loss tangent (tanδ) are respectively measured at a frequency of 40.68 MHz at 23°C using an RF impedance / material analyzer E4991A (manufactured by Agilent), and the value of the dielectric property (tanδ / ε'r) is calculated.

[0174] <Shape of Adhesive for High-Frequency Dielectric Heating>

[0175] The shape of the high-frequency dielectric heating adhesive of the present embodiment is not particularly limited. The high-frequency dielectric heating adhesive of the present embodiment can be, for example, a molded body-shaped adhesive formed into a target shape by injection molding, or a sheet-shaped adhesive obtained by extrusion molding. In the present embodiment, the molded body and the sheet are different shapes. The sheet generally refers to a long strip or thin layer with a thickness of less than 1 mm, less than 2 mm, or less than 5 mm. The molded body refers to a shape obtained by molding the materials containing the various components of the high-frequency dielectric heating adhesive, which is a variety of shapes other than a sheet.

[0176] The high-frequency dielectric heating adhesive of this embodiment is preferably in sheet form. That is, the high-frequency dielectric heating adhesive of this embodiment is preferably a high-frequency dielectric heating adhesive sheet (sometimes referred to as an adhesive sheet). By making the high-frequency dielectric heating adhesive an adhesive sheet, the manufacturing process time of the structure can be further shortened.

[0177] The shape of the adhesive for high-frequency dielectric heating of the present embodiment can be such that a frame-shaped sheet (a frame-shaped adhesive sheet) having a frame-shaped portion and an opening portion that penetrates from one of the opposing surfaces to the other surface is formed. The shape of the opening portion is not particularly limited. In the case where the adhesive sheet is frame-shaped, the frame-shaped adhesive sheet can have one opening portion, or two or more opening portions. The frame-shaped sheet can have a notch in a portion of the frame-shaped portion. In this case, the opening portion can be a shape in which a portion of the frame-shaped portion communicates with the outside of the frame-shaped portion. That is, when the frame-shaped sheet is viewed from above, the frame-shaped portion can exhibit an open shape (for example, a shape in which the frame-shaped portion is discontinuous, such as a C shape or a U shape). The frame-shaped portion of the frame-shaped sheet can have a notch. In this case, the opening portion can be a shape in which the periphery of the opening portion is surrounded by the frame-shaped portion (for example, a shape in which the frame-shaped portion is continuous, such as an O shape). That is, when the frame-shaped sheet is viewed from above, the frame-shaped portion can exhibit a closed shape. In the case where the frame-shaped sheet has two or more opening portions, the same shape of opening portion can be combined, or different shapes of opening portion can be combined, with respect to the shape of the opening portion, when the frame-shaped sheet is viewed from above. The shape of the adhesive for high-frequency dielectric heating of the present embodiment can be a sheet that does not have the opening portion. Furthermore, the adhesive for high-frequency dielectric heating of the present embodiment can be formed into an adhesive sheet of a target shape by a molding method such as extrusion molding or injection molding.

[0178] In one mode, the adhesive for high-frequency dielectric heating of the present embodiment is composed of only one adhesive layer, and the adhesive layer is formed of the adhesive sheet for high-frequency dielectric heating of the present embodiment. In the case where the adhesive for high-frequency dielectric heating is an adhesive sheet for high-frequency dielectric heating composed of only one adhesive layer, the adhesive layer itself corresponds to the adhesive sheet for high-frequency dielectric heating, and thus the form and properties of the adhesive sheet for high-frequency dielectric heating correspond to the form and properties of the adhesive layer. The adhesive sheet for high-frequency dielectric heating is preferably composed of only one adhesive layer. By doing so, the thickness of the adhesive sheet for high-frequency dielectric heating can be reduced, and the adhesive sheet for high-frequency dielectric heating can be easily molded.

[0179] Since the adhesive sheet for high-frequency dielectric heating is sometimes composed of only one adhesive layer having high-frequency dielectric heating adhesiveness, the term "adhesive sheet for high-frequency dielectric heating" and the term "adhesive layer" can be replaced with each other in the present specification, depending on the situation.

[0180] The adhesive for high-frequency dielectric heating of the present embodiment is not limited to the mode in which the adhesive sheet for high-frequency dielectric heating is composed of only one adhesive layer. The adhesive for high-frequency dielectric heating of the present embodiment can be in any of the modes shown in Figure 3A , Figure 3B and Figure 3C .

[0181] Figure 3AThe high-frequency dielectric heating adhesive 1A shown is an adhesive sheet composed of only a single adhesive layer 10.

[0182] Figure 3B The high-frequency dielectric heating adhesive 1B shown 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. As the substrate 30, there is no particular limitation as long as it is a member that can support the adhesive layer 10. The substrate 30 can be exemplified by, for example, a resin sheet containing at least one or more resins selected from among polyolefin resins, polyester resins, acetate resins, acrylonitrile-butadiene-styrene copolymer resins, polystyrene resins, and vinyl chloride resins. As the polyolefin resins, there can be exemplified, for example, polyethylene resins and polypropylene resins. As the polyester resins, there can be exemplified, for example, polybutylene terephthalate resins and polyethylene terephthalate resins. The substrate 30 can contain a dielectric filler. The dielectric filler (B) in the adhesive layer 10 and the dielectric filler in the substrate 30 can be the same as or different from each other.

[0183] Figure 3C The high-frequency dielectric heating adhesive 1C shown is an adhesive sheet having an intermediate layer 40 disposed between the adhesive layer 10 and an adhesive layer 20. The high-frequency dielectric heating adhesive 1C has a first surface 11 and a second surface 21 on the side opposite the first surface 11. In the high-frequency dielectric heating adhesive 1C, the adhesive layer 10 satisfies the conditions for the adhesive layer of the high-frequency dielectric heating adhesive sheet of the present embodiment. In one mode, both the adhesive layer 10 and the adhesive layer 20 are layers of the same composition and properties. In one mode, the adhesive layer 20 is a layer of high-frequency dielectric heating adhesion that is different from the adhesive layer 10 in at least either the composition or the properties. In one mode, the adhesive layer 20 is a layer of a general-purpose adhesive that is not a layer of high-frequency dielectric heating adhesion. In this case, as the adhesive layer 20 that is not a layer of high-frequency dielectric heating adhesion, there can be exemplified, 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 an adhesive.

[0184] In the case where the high-frequency dielectric heating adhesive of the present embodiment is an adhesive sheet composed of only one adhesive layer, the thickness of the adhesive sheet of the present embodiment is preferably 5 μm or more, more preferably 10 μm or more, further preferably 30 μm or more, and particularly preferably 50 μm or more.

[0185] If the thickness of the adhesive sheet is 5 μm or more, the heat generation property when a high-frequency electric field is applied to the adhesive sheet in contact with an adherend is improved, and thus the adhesive sheet is easily strongly adhered to the adherend in a short time. In addition, when adhered to the adherend, the adhesive sheet easily follows the unevenness of the adherend, and easily exhibits adhesion strength.

[0186] In the case where the adhesive sheet is a multi-layered structure composed of a plurality of layers, the thickness of the adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, further preferably 30 μm or more, and still further preferably 50 μm or more.

[0187] In the case where the adhesive sheet for high-frequency dielectric heating is a multi-layered structure, if the thickness of the adhesive layer is 5 μm or more, the adhesive layer easily follows the unevenness of the adherend at the time of adhesion to the adherend, and the adhesive strength is easily exhibited.

[0188] The upper limit of the thickness of the adhesive sheet is not particularly limited. The more the thickness of the adhesive sheet increases, the more the weight of the structure obtained by adhesion of the adhesive sheet to the adherend as a whole increases. Therefore, the adhesive sheet is preferably, for example, a thickness in a range in which processability, handleability, and the like are not problematic in actual use. In view of the practicality and moldability of the adhesive sheet for high-frequency dielectric heating, the thickness of the adhesive sheet of the present embodiment is preferably 2000 μm or less, more preferably 1000 μm or less, and further preferably 600 μm or less. The upper limit of the thickness of the adhesive sheet is preferably the above-described value in both the case where the structure is composed of only one adhesive layer and the case where the structure is a multi-layered structure composed of a plurality of layers including the adhesive layer.

[0189] The adhesive sheet as the adhesive for high-frequency dielectric heating is easy to handle compared to the case where a liquid adhesive that needs to be applied is used, and the workability at the time of adhesion to the adherend is also improved.

[0190] In addition, with the adhesive sheet as the adhesive for high-frequency dielectric heating, the sheet thickness and the like can be appropriately controlled. Therefore, the adhesive sheet can also be applied to a roll-to-roll system, and the adhesive sheet can be processed into an arbitrary area and shape by punching processing or the like in correspondence with the adhesion area to the adherend and the shape of the adherend. Therefore, the advantages of the adhesive sheet as the adhesive for high-frequency dielectric heating are also significant from the viewpoint of the manufacturing process.

[0191] For the adhesive for high-frequency dielectric heating of the present embodiment, it is preferable to apply a high-frequency electric field in a frequency band called so-called short wave to ultrashort wave. When a high-frequency electric field in this frequency band is applied, the depth of heating is deep, and therefore the heat generation property at the time of high-frequency application is improved. Therefore, even in the case where the thickness of the adhesive for high-frequency dielectric heating is thick, the adhesive sheet and the adherend are easily strongly adhered in a short time.

[0192] <Manufacturing method of adhesive for high-frequency dielectric heating>

[0193] The high-frequency dielectric heating adhesive of the present embodiment can be produced, for example, by mixing the above-described components. In the case where the high-frequency dielectric heating adhesive of the present embodiment is an adhesive sheet, it can be produced, for example, by premixing the above-described components, kneading using a known kneading device such as an extruder and a hot roll, and using a known molding method such as extrusion molding, calender molding, injection molding, and flow casting. In the case where the high-frequency dielectric heating adhesive of the present embodiment is a molded body, it can be produced, for example, by using a material obtained by premixing the above-described components, and using a known molding method such as injection molding and compression molding. In the case where the high-frequency dielectric heating adhesive of the present embodiment is a frame-shaped sheet, the frame-shaped sheet can be produced, for example, by providing an opening to a sheet-shaped high-frequency dielectric heating adhesive obtained by the above-described molding method of the adhesive sheet, by implementing a known method of punching processing. Alternatively, the frame-shaped sheet can be produced by using a mold that can obtain a shape of the opening of interest in the above-described molding method of the adhesive sheet.

[0194] The high-frequency dielectric heating adhesive has excellent water resistance and humidity resistance compared to general adhesives.

[0195] The high-frequency dielectric heating adhesive of the present embodiment is locally heated by application of a high-frequency electric field. Therefore, according to the high-frequency dielectric heating adhesive of the present embodiment, it is easy to prevent the occurrence of damage to the entire adherend during adhesion to the adherend.

[0196] [Adherend]

[0197] The material of the adherend is not particularly limited. The material of the adherend can be any of an organic material, a metallic material, and an inorganic material, or a composite material thereof.

[0198] The material of the adherend is preferably an organic material. As the organic material of the adherend, for example, a plastic material and a rubber material can be given. As the plastic material, for example, 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, polyethylene terephthalate and polybutylene terephthalate resin, polyacetal resin, polymethyl methacrylate resin, and polystyrene resin can be given. As the rubber material, for example, styrene-butadiene rubber, ethylene-propylene rubber, and silicone rubber can be given. In addition, the adherend can be a foamed material of an organic material.

[0199] In the case where the adherend is made of a thermoplastic resin, the thermoplastic resin contained in the adherend and the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive can be different resins. In this case, the adherend can be easily bonded without damaging the shape of the adherend at the time of bonding.

[0200] In addition, in the case where the adherend is made of a thermoplastic resin, the main component of the thermoplastic resin contained in the adherend and the main component of the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive can be the same from the viewpoint of adhesion.

[0201] In the present specification, the "main component of the thermoplastic resin" means, for example, in the case where the thermoplastic resin is a polymer, the repeating unit contained in the polymer in the largest amount. If the thermoplastic resin is a polymer from a single monomer, the repeating unit based on the monomer unit is the "main component of the thermoplastic resin". In the case where the thermoplastic resin is a copolymer, the repeating unit contained in the polymer in the largest amount is the "main component of the thermoplastic resin". In the case where the thermoplastic resin is a copolymer, the "main component of the thermoplastic resin" in the copolymer is a repeating unit contained in an amount of 30% by mass or more, in one mode, a repeating unit contained in an amount of more than 30% by mass, in another mode, a repeating unit contained in an amount of 40% by mass or more, and in still another mode, a repeating unit contained in an amount of 50% by mass or more. In addition, in the case where the thermoplastic resin is a copolymer, the repeating unit contained in the largest amount can be two or more.

[0202] As the material of the adherend, inorganic materials such as glass materials, cement materials, ceramic materials, and metal materials can be exemplified. In addition, the adherend can be a fiber-reinforced resin which is a composite material of a fiber and the above-described plastic material. The plastic material in the fiber-reinforced resin is, for example, at least one selected from the group consisting of polypropylene resins, polyethylene resins, polyurethane resins, acrylonitrile-butadiene-styrene copolymer resins, polycarbonate resins, polyamide resins; nylon 6 and nylon 66, and the like, polyester resins, polyethylene terephthalate and polybutylene terephthalate resins, and the like, polyacetal resins, polymethyl methacrylate resins, epoxy resins, and polystyrene resins, and the like. The fiber in the fiber-reinforced resin can be exemplified by, for example, glass fibers, Kevlar (registered trademark) fibers, and carbon fibers, and the like.

[0203] It is preferable that the adherend have low electrical conductivity.

[0204] In the case where a plurality of adherends are bonded to each other using the high-frequency dielectric heating adhesive of the present embodiment, the plurality of adherends can be of the same material or of different materials.

[0205] The shape of the adherend is not particularly limited. In the case where the adhesive for high-frequency dielectric heating of the present embodiment is an adhesive sheet, the adherend preferably has a surface to which the adhesive sheet can be attached, and is preferably in the form of a sheet, a plate, or a block. In the case where a plurality of adherends are adhered to each other, the shapes and sizes of the adherends can be the same or different.

[0206] [Adhesion method]

[0207] Next, as an example of an adhesion method using the adhesive for high-frequency dielectric heating of the present embodiment and an adherend, a method of manufacturing a structure by adhering the adhesive for high-frequency dielectric heating of the present embodiment and an adherend will be described. The method of manufacturing a structure when a structure is manufactured by adhering the adhesive for high-frequency dielectric heating of the present embodiment and an adherend, for example, has the following steps.

[0208] In the case where one or more adherends are adhered to the adhesive for high-frequency dielectric heating of the present embodiment to manufacture a structure, the method of manufacturing a structure of the present embodiment includes a step of arranging the adhesive for high-frequency dielectric heating of the present embodiment on one or more adherends, and a step of adhering the one or more adherends by applying a high-frequency electric field to the adhesive for high-frequency dielectric heating. The frequency of the applied high-frequency electric field is, for example, 1 MHz or more and 300 MHz or less.

[0209] In the case where two or more adherends are adhered to the adhesive for high-frequency dielectric heating of the present embodiment to manufacture a structure, the method of manufacturing a structure of the present embodiment includes a step of arranging the adhesive for high-frequency dielectric heating of the present embodiment between two or more adherends, and a step of adhering the two or more adherends by applying a high-frequency electric field to the adhesive for high-frequency dielectric heating. In this case, the frequency of the applied high-frequency electric field is also, for example, 1 MHz or more and 300 MHz or less.

[0210] In the method of manufacturing a structure of the present embodiment, it is preferable to arrange two or more adherends and the adhesive for high-frequency dielectric heating between electrodes of a dielectric heating device, and to apply a high-frequency electric field to the two or more adherends and the adhesive for high-frequency dielectric heating while pressing them with the electrodes. By applying a high-frequency electric field while pressing with the electrodes as described above, it is easy to manufacture a structure in a shorter time.

[0211] Note that, in the present specification, the "dielectric heating device" is sometimes referred to as a "high-frequency dielectric heating device".

[0212] According to the manufacturing method using the adhesive for high-frequency dielectric heating of the present embodiment, it is possible to locally heat only predetermined portions from the outside using a dielectric heating device. Therefore, even in the case where the adherends are large and complex three-dimensional structures or thick and complex three-dimensional structures, etc. that require higher dimensional accuracy, the manufacturing method using the adhesive for high-frequency dielectric heating of the present embodiment is effective.

[0213] Hereinafter, as an example of the manufacturing method of the structure of the present embodiment, a method of adhering two or more adherends using the adhesive for high-frequency dielectric heating of the present embodiment will be described, but the present application is not limited to this method.

[0214] The adhesive method of one embodiment of the present embodiment includes the following process P1 and process P2.

[0215] • Process P1

[0216] Process P1 is a process of disposing the adhesive for high-frequency dielectric heating of the present embodiment between two or more adherends. In the case of manufacturing a laminate as a structure of the present embodiment, in process P1, for example, the adherends and the adhesive for high-frequency dielectric heating are alternately disposed, and two or more adherends are laminated with the adhesive for high-frequency dielectric heating interposed therebetween.

[0217] In order to be able to adhere the adherends to each other, it is preferable to interpose the adhesive for high-frequency dielectric heating between the adherends. The adhesive for high-frequency dielectric heating can be interposed between a part of the adherends, a plurality of parts of the adherends, or the entire surface of the adherends. From the viewpoint of improving the adhesion strength between the adherends, it is preferable to interpose the adhesive for high-frequency dielectric heating over the entire adhesion surface between the adherends.

[0218] In addition, as one method of interposing the adhesive for high-frequency dielectric heating between a part of the adherends, a method of interposing the adhesive for high-frequency dielectric heating between the adherends in a frame shape along the outer periphery of the adhesion surface between the adherends can be given. By disposing the adhesive for high-frequency dielectric heating in a frame shape as such, it is possible to achieve lightweight of the structure compared to the case where the adhesive for high-frequency dielectric heating is disposed over the entire adhesion surface while obtaining the adhesion strength between the adherends.

[0219] In addition, according to one method of interposing the adhesive for high-frequency dielectric heating between a part of the adherends, it is possible to reduce the amount of the adhesive for high-frequency dielectric heating used or to reduce the size, and thus, it is possible to shorten the high-frequency dielectric heating processing time compared to the case where the adhesive for high-frequency dielectric heating is disposed over the entire adhesion surface.

[0220] • Process P2

[0221] Process P2 is a process of applying a high-frequency electric field to the high-frequency dielectric heating adhesive disposed between the adherends in process P1 to adhere two or more adherends. In one embodiment, the frequency of the applied high-frequency electric field is 1 MHz or more and 300 MHz or less. For example, by using a dielectric heating device, a high-frequency electric field can be applied to the high-frequency dielectric heating adhesive.

[0222] <Dielectric heating device>

[0223] Figure 4 A diagram illustrating a high-frequency dielectric heating process using the high-frequency dielectric heating adhesive and the dielectric heating device of the present embodiment is shown.

[0224] Figure 4 The dielectric heating device 50 shown has a first high-frequency electric field application electrode 51, a second high-frequency electric field application electrode 52, and a high-frequency power source 53.

[0225] The first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 are disposed opposite each other. The first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 have a pressurizing mechanism. By the pressurizing mechanism of the electrodes (the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52) of the dielectric heating device 50, a pressurizing process can be performed on 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. That is, by the dielectric heating device 50, a high-frequency electric field can be applied while pressurizing two or more adherends and the high-frequency dielectric heating adhesive disposed between the electrodes.

[0226] In a case where the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 are constituted as one pair of parallel plate electrodes, the form in which such electrodes are disposed is sometimes referred to as a parallel plate type.

[0227] The application of a high-frequency electric field is also preferably performed using a high-frequency dielectric heating device of the parallel plate type. In the case of a high-frequency dielectric heating device of the parallel plate type, a high-frequency electric field penetrates the high-frequency dielectric heating adhesive located between the electrodes, and thus the entire high-frequency dielectric heating adhesive can be warmed, and the adherends and the high-frequency dielectric heating adhesive can be adhered in a short time. In addition, in a case where a laminate is manufactured as a structure, a high-frequency dielectric heating device of the parallel plate type is preferably used.

[0228] A high-frequency power source 53 for applying a high-frequency electric field having a frequency of, for example, about 13.56 MHz, about 27.12 MHz, or about 40.68 MHz is connected to the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52, respectively.

[0229] As shown in Figure 4 , the dielectric heating device 50 performs dielectric heating treatment by means of the high-frequency dielectric heating adhesive 1A clamped between the first adherend 110 and the second adherend 120. Further, the dielectric heating device 50 bonds the first adherend 110 and the second adherend 120 by means of pressure treatment performed by the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 in addition to the dielectric heating treatment. Note that the two or more adherends can be bonded together by, for example, only extrusion based on the self-weight of the high-frequency dielectric heating adhesive and the adherends without performing the pressure treatment.

[0230] 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 high-frequency energy. Thereby, the thermoplastic resin component in the high-frequency dielectric heating adhesive 1A melts, and the first adherend 110 and the second adherend 120 can be strongly bonded even with short-time treatment.

[0231] 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 15 dispersed in the adhesive component in the high-frequency dielectric heating adhesive 1A absorbs high-frequency energy. Figure 1 The dielectric filler 15 shown in

[0232] Further, the dielectric filler functions as a heat source, and the thermoplastic resin component melts by the heat generation of the dielectric filler, and the first adherend 110 and the second adherend 120 can be strongly bonded even with short-time treatment.

[0233] The electrodes (the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52) of the dielectric heating device 50 have a pressure mechanism, and thus the dielectric heating device 50 also functions as a pressure device. Therefore, the first adherend 110 and the second adherend 120 can be more strongly bonded by the pressure in the compression direction performed by the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52 and the heating melting of the high-frequency dielectric heating adhesive 1A. Note that the case of the structure 100 shown in Figure 4

[0234] <High-frequency Dielectric Heating Conditions>

[0235] The high-frequency dielectric heating conditions can be appropriately changed, and the following conditions are preferable.

[0236] ​The output power of the high-frequency electric field is preferably 10 W or more, more preferably 30 W or more, further preferably 50 W or more, still further preferably 80 W or more.

[0237] The output power of the high-frequency electric field is preferably 50,000 W or less, more preferably 20,000 W or less, further preferably 15,000 W or less, still further preferably 10,000 W or less, yet further preferably 1,000 W or less.

[0238] When the output power of the high-frequency electric field is 10 W or more, it is possible to prevent a poor situation in which the temperature does not increase during the dielectric heating treatment, and thus it is easy to obtain a good adhesive strength.

[0239] When the output power of the high-frequency electric field is 50,000 W or less, it is easy to prevent a poor situation in which the temperature control becomes difficult due to the dielectric heating treatment. The high-frequency output power indicates the magnitude of the energy transferred to the object.

[0240] The application time of the high-frequency electric field is preferably 1 second or more.

[0241] The application time of the high-frequency electric field is preferably 300 seconds or less, more preferably 240 seconds or less, further preferably 180 seconds or less, still further preferably 120 seconds or less, yet further preferably 90 seconds or less, still further preferably 50 seconds or less, yet further preferably 20 seconds or less, particularly preferably 10 seconds or less, and very preferably 6 seconds or less.

[0242] When the application time of the high-frequency electric field is 1 second or more, it is possible to prevent a poor situation in which the temperature does not increase during the dielectric heating treatment, and thus it is easy to obtain a good adhesive strength.

[0243] When the application time of the high-frequency electric field is 300 seconds or less, it is easy to prevent a poor situation in which the manufacturing efficiency of the structure is reduced, the manufacturing cost is increased, and the adherend is thermally deteriorated.

[0244] The frequency of the applied high-frequency electric field is preferably 1 MHz or more, more preferably 3 MHz or more, further preferably 5 MHz or more, and still further preferably 10 MHz or more.

[0245] The frequency of the applied high-frequency electric field is preferably 300 MHz or less, more preferably 100 MHz or less, further preferably 80 MHz or less, and still further preferably 50 MHz or less. Specifically, the industrial frequency bands of 13.56 MHz, 27.12 MHz, and 40.68 MHz, which are assigned by the International Telecommunication Union, can also be used in the manufacturing method and the adhesive method using high-frequency dielectric heating according to the present embodiment. The frequency of the applied high-frequency electric field indicates the energy transfer mode (speed).

[0246] In the case where the high-frequency electric field is applied while the pressure treatment is performed, the pressing pressure at the time of application of the high frequency is preferably 1 kPa or more, more preferably 5 kPa or more, further preferably 10 kPa or more, still further preferably 30 kPa or more, and particularly further preferably 50 kPa or more, as the initial set value of the pressure to be applied to the high-frequency dielectric heating adhesive.

[0247] In the case where the high-frequency electric field is applied while the pressure treatment is performed, the pressing pressure at the time of application of the high frequency is preferably 10 MPa or less, more preferably 5 MPa or less, further preferably 1 MPa or less, still further preferably 750 kPa or less, as the initial set value of the pressure to be applied to the high-frequency dielectric heating adhesive.

[0248] Here, the area that becomes the reference of the initial set value of the pressure to be applied to the high-frequency dielectric heating adhesive is the smallest area among the areas when the electrode and the adherend are viewed from above.

[0249] [Modification of the Embodiment]

[0250] The present application is not limited to the above-described embodiments, and the present application can include modifications and improvements, etc. within a range capable of achieving the object of the present application.

[0251] The high-frequency dielectric heating treatment is not limited to the dielectric heating device in which the electrodes are arranged opposite to each other as described in the above-described embodiments, and a high-frequency dielectric heating device of a grid electrode type can also be used. The high-frequency dielectric heating device of the grid electrode type has a grid electrode in which electrodes of a first polarity and electrodes of a second polarity that are opposite to the electrodes of the first polarity are alternately arranged at regular intervals on the same plane. Note that, in the drawings, a mode using the dielectric heating device in which the electrodes are arranged opposite to each other is exemplified for simplicity.

[0252] Example

[0253] Hereinafter, the present application will be described in more detail by citing examples, but the present application is not limited at all by these examples.

[0254] [Production of the High-Frequency Dielectric Heating Adhesive]

[0255] <Examples 1 to 3, and Comparative Examples 1 to 7>

[0256] As the materials for producing the high-frequency dielectric heating adhesive (adhesive sheet), the thermoplastic resin (A) and the dielectric filler (B) were weighed, respectively, and made to reach the proportions shown in Table 1 on a volume basis.

[0257] Next, the thermoplastic resin (A) and the dielectric filler (B) were premixed. The premixed material of the thermoplastic resin (A) and the dielectric filler (B) was supplied to a hopper of a 30 mmφ twin-screw extruder, and the barrel and the die were heated to a given temperature, and the premixed material was melt-kneaded. The melt-kneaded material was cooled, and then the material was cut, whereby pelletized pellets were produced. Next, the produced pelletized pellets were put into a hopper of a single-screw extruder provided with a T-die, and the barrel and the die were heated to a given temperature, and a film-like melt-kneaded material was extruded from the T-die, and was cooled by a cooling roll, whereby the adhesive for high-frequency dielectric heating (adhesive sheet for high-frequency dielectric heating) of Examples 1 to 3 and Comparative Examples 1 to 7 each having a thickness of 400 μm were produced.

[0258] The thermoplastic resin (A) and the dielectric filler (B) shown in Table 1 are described below.

[0259] (A1) r-PP: polypropylene resin (manufactured by PRIME POLYMER Co., Ltd., product name "PRIME POLYPRO F-744NP", density 0.90 g / cm 3 )

[0260] (A2) MAH-PP: maleic anhydride-modified polypropylene resin (manufactured by Mitsui Chemicals, Inc., product name "ADMER QE060", density 0.90 g / cm 3 )

[0261] (Dielectric filler (B))

[0262] (B1) ZnO: plate-piled spherical zinc oxide (manufactured by SAKAI CHEMICAL INDUSTRY Co., Ltd., product name "CANDY ZINC 1000", volume average particle diameter 1 μm, density 5.61 g / cm 3 )

[0263] (B2) ZnO: irregularly shaped zinc oxide (manufactured by SAKAI CHEMICAL INDUSTRY Co., Ltd., product name "LP-ZINC 11", volume average particle diameter 11 μm, density 5.61 g / cm 3 )

[0264] (B3) ZnO: hexagonal plate-like zinc oxide (manufactured by SAKAI CHEMICAL INDUSTRY Co., Ltd., product name "XZ-3000FLP", volume average particle diameter 3 μm, density 5.61 g / cm 3 )

[0265] (Volume average particle diameter of dielectric filler)

[0266] The particle size distribution of the dielectric filler was measured using a laser diffraction particle size analyzer (Mastersizer 3000, manufactured by Malvern Panalytical) based on JIS Z 8825:2022. The volume average particle diameter was calculated based on JIS Z 8819-2:2019 from the results of the particle size distribution measurement. The calculated volume average particle diameters of the ZnO are described above, respectively.

[0267] [Property evaluation of adhesive for high-frequency dielectric heating]

[0268] <Circularity>

[0269] The prepared adhesive for high-frequency dielectric heating was cut in the thickness direction, and the cut surface of the cut adhesive sheet was imaged using an SEM (Crossbeam 550, manufactured by Carl Zeiss) at a magnification of 10,000 times. Figure 5 An SEM image of the cut surface of the adhesive sheet prepared in Example 1 is shown in FIG. 6. The region that appears relatively white corresponds to the dielectric filler.

[0270] Next, for the obtained SEM image, a given pixel value was used as a binarization threshold to perform binarization processing using the programming language Python, and a binarized image in which the white and black were divided was obtained. Further, the Blob obtained at the time of binarization was detected as a particle of the dielectric filler.

[0271] The dielectric filler particles having an equivalent circle diameter of 0.088 μm or more were taken as the measurement object. For these dielectric filler particles, the number of pixels corresponding to the area of each particle of the dielectric filler was counted, and the total of the counted number of pixels was taken as the area "S". The number of pixels corresponding to the outline of each particle of the dielectric filler, that is, the number of pixels of the portion surrounding each particle of the dielectric filler was counted, and the number of pixels calculated from the total of the counted number of pixels was taken as the circumference "L1". The circularity was calculated from the area S of each particle of the dielectric filler and the circumference L1 of each particle of the dielectric filler by the following mathematical expression (Mathematical Expression 1). The circularity was calculated as the average value of the measured particles.

[0272] Circularity = 4πS / (L1) 2 (Mathematical Expression 1)

[0273] <Circumferential Envelopment>

[0274] The SEM image was taken and binarized in the same manner as the roundness measurement, and the blobs obtained by the binarization were detected as the particles of the dielectric filler. The particles of the dielectric filler having an equivalent circle diameter of 0.088 μm or more among the detected particles of the dielectric filler were taken as the measurement target. For these particles of the dielectric filler, the number of pixels of the portion corresponding to the outline of each particle of the dielectric filler detected was counted, and the total of the number of pixels calculated from the counted number of pixels was taken as the circumference "L1". The circumference of the convex hull "L2" was calculated by the cv2.convexHull() function in the library "OpenCV" of Python. The circumference envelope degree was calculated from the circumference L1 of each particle of the dielectric filler and the circumference L2 of the convex hull of each particle of the dielectric filler by the following mathematical expression (Mathematical Expression 2). The circumference envelope degree was calculated as the average of the measured particles.

[0275] Circumference envelope degree = L2 / L1... (Mathematical Expression 2)

[0276] <Transmittance ratio>

[0277] The transmittance spectrum of the adhesive sheet in the wavelength range of 300 nm to 2000 nm was measured using an ultraviolet-visible near-infrared spectrophotometer (Shimadzu Corporation, Model "UV-3600"). The transmittance T1 (unit: %) at 500 nm and the transmittance T2 (unit: %) at 1000 nm were extracted from the obtained transmittance spectrum. The transmittance ratio was calculated from these transmittances T1 and T2 by the following mathematical expression (Mathematical Expression 3).

[0278] Transmittance ratio = T1 / T2... (Mathematical Expression 3)

[0279] <Evaluation of concealability in the visible light region>

[0280] As the adherend, a glass plate was used, and the high-frequency dielectric heating adhesive produced in each of the examples and comparative examples was adhered to the glass plate under the same high-frequency electric field application conditions as in the adhesiveness evaluation described later, and evaluation samples for concealability in the visible region were produced. Next, a television remote controller equipped with a near-infrared light source was disposed so that the surface of the near-infrared light source side of the television remote controller faced the surface of the high-frequency dielectric heating adhesive side of the evaluation sample. In addition, the distance between the near-infrared light source and the evaluation sample, and the distance between the evaluation sample and the eyes of the tester were each set to 1 cm. The concealability in the visible region was evaluated based on the following evaluation criteria. Note that in the adhesiveness evaluation described later, in each of the comparative examples in which the tensile shear stress was 0 MPa, the high-frequency dielectric heating adhesive of the comparative example was attached to the extent that it would not fall from the glass plate due to its own weight. In this state, the evaluation of the concealability in the visible region, and the evaluation of the detection performance of near-infrared light were performed.

[0281] (Evaluation Criteria)

[0282] A: The outline of the television remote controller could not be visually recognized.

[0283] F: The outline of the television remote controller could be visually recognized.

[0284] (Evaluation of the Detection Performance of Near-Infrared Light)

[0285] In the evaluation of the concealability in the visible region, the lens of the camera of a digital camera-equipped mobile phone was disposed instead of the eyes of the tester without changing the disposition of the evaluation sample. In a state in which the camera function of the digital camera-equipped mobile phone was activated, any button of the television remote controller was pressed to cause the near-infrared light source to emit light. Furthermore, it was confirmed that the near-infrared light emitted from the near-infrared light source was received by the camera in the digital camera-equipped mobile phone, and was displayed on the display screen of the digital camera-equipped mobile phone. The detection performance of the near-infrared light was evaluated in accordance with the following evaluation criteria.

[0286] (Evaluation Criteria)

[0287] A: A clear image of the near-infrared light could be confirmed.

[0288] F: A clear image of the near-infrared light could not be confirmed.

[0289] (Dielectric Properties)

[0290] The prepared high-frequency dielectric heating adhesive was cut into pieces 30 mm long and 30 mm wide. The cut high-frequency dielectric heating adhesive sheets were mounted on an RF impedance / material analyzer E4991A (Agilent) using a dielectric material test fixture 16453A (Agilent). The relative dielectric constant (ε'r) and dielectric loss tangent (tanδ) were measured using the parallel plate method at 23°C and a frequency of 40.68 MHz. The dielectric properties (tanδ / ε'r) were calculated based on the measurement results.

[0291] [Evaluation of Adhesive Properties of Adhesives for High-Frequency Dielectric Heating]

[0292] <Adhesion Evaluation>

[0293] The high-frequency dielectric heating adhesive (adhesive sheet) was cut into pieces 25 mm long and 12.5 mm wide. Two glass fiber reinforced polypropylene resin sheets (25 mm long, 100 mm wide, and 1.5 mm thick) were prepared as adherends. The cut adhesive sheet was placed between the two adherends and laminated.

[0294] The adherend and adhesive sheet, stacked as described above, were fixed between two electrodes of a high-frequency dielectric heating device (Yamamoto Vinita, product name "YRP-400T-A"). Next, an electric field was applied under the following high-frequency electric field application conditions while the device was fixed, causing the adhesive sheet and adherend to adhere to each other, thereby producing a test piece for evaluating adhesion. The pressing pressure during electric field application was the initial setting for the pressure applied to the adhesive sheet.

[0295] (High-frequency electric field application conditions)

[0296] Frequency: 40.68MHz

[0297] Output power: 200W

[0298] Application time: 5 seconds

[0299] Pressing pressure: 0.5MPa

[0300] The obtained test pieces were measured for tensile shear force (unit: MPa) as the adhesive strength using a universal tensile testing machine (manufactured by INSTRON, INSTRON 5581). The tensile shear force was measured in accordance with JIS K 6850:1999 at a tensile speed of 100 mm / min.

[0301]

[0302]

[0303] The adhesive sheets of Examples 1 to 3 satisfy the condition of (1) described above. The adhesive sheets of Examples 1 to 3 all obtained strong adhesive strength in a short time, as compared with the adhesive sheets of Comparative Examples 1 to 7. From the above results, it was found that the adhesive for high-frequency dielectric heating of the present embodiment can be strongly adhered to an adherend in a shorter time, as compared with the conventional adhesive for high-frequency dielectric heating.

[0304] In addition, the adhesive sheets of Examples 1 to 3 satisfy the condition of (2) described above. The transmittance ratio (T1 / T2) of the adhesive sheets of Examples 1 to 3 is excellent, as compared with the adhesive sheets of Comparative Examples 1 to 7. From the above results, it was found that the adhesive for high-frequency dielectric heating of the present embodiment is excellent in concealability while ensuring the light transmittance in the infrared region, as compared with the conventional adhesive for high-frequency dielectric heating.

Claims

1. An adhesive for high-frequency dielectric heating, comprising a thermoplastic resin (A) and a dielectric filler (B). The high-frequency dielectric heating adhesive satisfies at least one of the following conditions (1) and (2): (1) The circularity of the two-dimensional shape of the dielectric filler (B) observed in a cross section obtained by cutting the high-frequency dielectric heating adhesive in the thickness direction is 0.40 or less; (2) The transmittance ratio (T1 / T2) of the high-frequency dielectric heating adhesive of transmittance T1 at a wavelength of 500 nm to transmittance T2 at a wavelength of 1000 nm is 0.65 or less.

2. The adhesive for high-frequency dielectric heating according to claim 1, wherein The perimeter envelope of the two-dimensional shape of the dielectric filler (B) observed in the cut surface obtained by cutting the adhesive for high-frequency dielectric heating in the thickness direction is 0.80 or less.

3. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The thermoplastic resin (A) is a polyolefin resin.

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

5. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The dielectric filler (B) has a concavo-convex structure on its surface.

6. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The dielectric filler (B) is at least one selected from zinc oxide, silicon carbide, titanium oxide and barium titanate.

7. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The dielectric filler (B) is plate-like stacked spherical zinc oxide.

8. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The volume average particle size of the dielectric filler (B) is 0.01 μm or more and 25 μm or less, The volume average particle size is a volume average particle size calculated based on JIS Z 8819-2:2019 from the particle size distribution measurement results of the dielectric filler (B) measured by a laser diffraction / scattering method.

9. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The adhesive for high-frequency dielectric heating has a transmittance T1 of 0.1% to 20% at a wavelength of 500 nm.

10. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The dielectric property (tanδ / ε'r) of the high-frequency dielectric heating adhesive is 0.005 or more, in, Tanδ is the dielectric loss tangent at 23°C and a frequency of 40.68 MHz. ε'r is the relative dielectric constant at 23°C and a frequency of 40.68 MHz.

11. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein: The adhesive for high-frequency dielectric heating is an adhesive sheet for high-frequency dielectric heating.

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