High-frequency dielectric heating adhesive

Abstract

The high-frequency dielectric heating adhesive (1A) of the present invention contains a thermoplastic resin (A) and a dielectric filler (B). When the cross-section of the high-frequency dielectric heating adhesive (1A) cut along the thickness direction is observed by scanning electron microscopy, the relationship between the nearest centroid distance Dg of the dielectric filler (B) and the particle size Dn of the dielectric filler (B) satisfies the following mathematical formula (F1): 1.55≤Dg / Dn≤1.85 ···(F1).

Description

Technical Field

[0001] This invention relates to adhesives for high-frequency dielectric heating. Background Technology

[0002] Previously, dielectric composite materials containing resin and fillers formed from inorganic compounds have been proposed.

[0003] Patent document 1 discloses a dielectric composite material having the following structure.

[0004] (1) The above dielectric composite material has a matrix formed of resin and filler particles dispersed in the matrix.

[0005] (2) The filler particles are formed from perovskite-type compounds, the half-width of the X-ray diffraction peak on the 111 plane is less than 0.20°, the ratio of the c-axis length to the a-axis length (c / a-axis ratio) obtained from powder X-ray diffraction is more than 1.006, and the uniformity (n) of the Rosin-Rammler distribution function is more than 2.3.

[0006] (3) The coefficient of variation of the interparticle distance of the filler particles dispersed in the matrix is ​​less than 0.9.

[0007] In addition, as a method for bonding objects using adhesives, methods such as high-frequency dielectric heating treatment have been proposed.

[0008] Patent Document 2 discloses an adhesive that is formed by filling a dielectric heating medium with dielectric heating properties into an adhesive base material that has affinity with the base material to be bonded. When the relative permittivity is set as ε', the dielectric loss tangent is set as tanδ, and the total thickness of the base material to be bonded is set as d (mm), and the coefficient C is set to the range of 78 to 85, the adhesive satisfies C×{(tanδ) / ε'}1 / 2≥d.

[0009] Patent document 3 discloses a dielectric heating adhesive resin composition containing a polyolefin resin with a melting point in the range of 80 to 200°C and a volume resistivity of 10. -2 The conductive material with a conductivity of less than Ω·cm has a content in the range of 1 to 30% of capacity relative to the total resin composition. The dielectric loss tangent of this dielectric heat-bonding resin composition is 0.03 or higher at a frequency of 40 MHz and a temperature of 23°C.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2019-065094

[0013] Patent Document 2: Japanese Patent Application Publication No. 2014-037489

[0014] Patent Document 3: Japanese Patent Application Publication No. 2003-193009 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] The dielectric composite material disclosed in Patent Document 1 is a material used in capacitors, etc. For materials used in capacitors, it is required to suppress the dielectric loss tangent to a low level in order to suppress heat generation. Therefore, the dielectric composite material disclosed in Patent Document 1 is not suitable as a material for use in adhesives for high-frequency dielectric heating.

[0017] High-frequency dielectric heating adhesives containing thermoplastic resins and dielectric fillers can bond to the substrate in a short time and easily achieve strong adhesion. The adhesive disclosed in Patent Document 2 contains a dielectric material as the dielectric heating medium. However, the adhesive disclosed in Patent Document 2 does not consider the relationship between the distance between the dielectric heating media filled in the adhesive and the heat generated during high-frequency dielectric heating treatment (hereinafter sometimes simply referred to as dielectric heating treatment), nor the relationship between the distance between the dielectric heating media and the adhesion to the substrate.

[0018] The dielectric heating adhesive resin composition disclosed in Patent Document 3 uses a conductive material with a specific volume resistivity below a certain value as the dielectric heating medium, resulting in an excessively low volume resistivity of the composition itself. If the volume resistivity of the dielectric heating adhesive resin composition itself becomes too low, electrical insulation breakdown may occur when using a high-frequency dielectric heating adhesive for dielectric heating treatment.

[0019] Thus, conventional adhesives for high-frequency dielectric heating suffer from low heating rates and insufficient improvement in bonding performance. Furthermore, if the volume resistivity of the adhesive is too low, there is a risk of electrical insulation breakdown during dielectric heating. Therefore, there is still room for further improvement in conventional adhesives for high-frequency dielectric heating.

[0020] The object of the present invention is to provide a high-frequency dielectric heating adhesive that, compared with conventional high-frequency dielectric heating adhesives, can suppress electrical insulation breakdown during dielectric heating treatment and can firmly bond to the substrate in a shorter time.

[0021] Problem Solving Methods [1]

[0023] A high-frequency dielectric heating adhesive comprising a thermoplastic resin (A) and a dielectric filler (B),

[0024] When the cut surface of the adhesive for high-frequency dielectric heating is observed along the thickness direction using a scanning electron microscope, the relationship between the nearest centroid distance Dg of the dielectric filler (B) and the particle size Dn of the dielectric filler (B) satisfies the following mathematical formula (F1).

[0025] 1.55≤Dg / Dn≤1.85···(F1) [2]

[0027] According to the adhesive for high-frequency dielectric heating described in [1], wherein,

[0028] The thermoplastic resin (A) mentioned above is a polyolefin resin. [3]

[0030] According to the high-frequency dielectric heating adhesive described in [1] or [2], wherein,

[0031] Compared to the above-mentioned high-frequency dielectric heating adhesive as a whole, the content of the above-mentioned dielectric filler (B) is 3% by volume or more and 40% by volume or less. [4]

[0033] The high-frequency dielectric heating adhesive according to any one of [1] to [3], wherein,

[0034] The dielectric filler (B) mentioned above is selected from at least one of zinc oxide, silicon carbide and titanium oxide. [5]

[0036] The high-frequency dielectric heating adhesive according to any one of [1] to [4], wherein,

[0037] When the cut surface of the above-mentioned high-frequency dielectric heating adhesive was observed along the thickness direction using a scanning electron microscope, the particle size Dn of the dielectric filler (B) was 1.0 μm or more and 4.0 μm or less. [6]

[0039] The high-frequency dielectric heating adhesive according to any one of [1] to [5], wherein,

[0040] When the cut surface of the above-mentioned high-frequency dielectric heating adhesive was observed along the thickness direction using a scanning electron microscope, the distance Dg between the nearest centroids of the dielectric filler (B) was 2.2 μm or more and 6.0 μm or less. [7]

[0042] The high-frequency dielectric heating adhesive according to any one of [1] to [6], wherein,

[0043] The aforementioned adhesive for high-frequency dielectric heating is an adhesive sheet for high-frequency dielectric heating.

[0044] According to one aspect of the present invention, a high-frequency dielectric heating adhesive containing a thermoplastic resin and a dielectric filler can be provided, which, compared with conventional high-frequency dielectric heating adhesives, can firmly bond to the substrate in a shorter time while suppressing electrical insulation breakdown during dielectric heating treatment. Attached Figure Description

[0045] Figure 1A This is a cross-sectional schematic diagram showing an example of the high-frequency dielectric heating adhesive of this embodiment.

[0046] Figure 1B This is a cross-sectional schematic diagram showing another example of the high-frequency dielectric heating adhesive of this embodiment.

[0047] Figure 1C This is a cross-sectional schematic diagram showing another example of the high-frequency dielectric heating adhesive of this embodiment.

[0048] Figure 2 This is a schematic diagram illustrating an example of high-frequency dielectric heating treatment using the high-frequency dielectric heating adhesive and dielectric heating device of this embodiment.

[0049] Figure 3 This is an example of a binarized image of the cut surface of the high-frequency dielectric heating adhesive cut along the thickness direction in this embodiment.

[0050] Figure 4 Based on Figure 3 An example of a Delaunay diagram created by binarizing an image.

[0051] Symbol Explanation

[0052] 10, 20... Adhesive layer, 11... First surface, 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... Adhesive (first adhesive), 120... Adhesive (second adhesive). Detailed Implementation

[0053] [Adhesive for High-Frequency Dielectric Heating]

[0054] The high-frequency dielectric heating adhesive of this embodiment contains a thermoplastic resin (A) and a dielectric filler (B). When the cross-section of the high-frequency dielectric heating adhesive cut along the thickness direction is observed by scanning electron microscopy, the relationship between the nearest centroid distance Dg of the dielectric filler (B) and the particle size Dn of the dielectric filler (B) satisfies the following mathematical formula (F1).

[0055] 1.55≤Dg / Dn≤1.85···(F1)

[0056] Compared to conventional adhesives for high-frequency dielectric heating, the adhesive for high-frequency dielectric heating of this embodiment, through the above-described configuration, can firmly bond to the substrate in a shorter time while suppressing electrical insulation breakdown during dielectric heating treatment.

[0057] The inventors have studied the improvement of the adhesive properties of the high-frequency dielectric heating adhesive. The results showed that, based on the relationship between the particle size of the dielectric filler (B) and the distance between the dielectric filler (B) particles, the heating rate of the high-frequency dielectric heating adhesive increased, and the volume resistivity of the high-frequency dielectric heating adhesive changed. The inventors hypothesize that when the high-frequency dielectric heating adhesive of this embodiment is subjected to dielectric heating treatment, it can suppress electrical insulation breakdown and achieve a firm bond with the adherend in a shorter time.

[0058] The relationship between the nearest centroid distance Dg of dielectric filler (B) and the particle size Dn of dielectric filler (B) satisfies the above mathematical formula (F1), which means that the particles of dielectric filler (B) are at a suitable distance from each other relative to the particle size of dielectric filler (B).

[0059] For adhesives used in high-frequency dielectric heating, if the value of the aforementioned mathematical formula (F1) is too large, the distance between the particles of dielectric filler (B) becomes too great relative to the particle size of dielectric filler (B). If the distance between the particles of dielectric filler (B) becomes too great relative to the particle size of dielectric filler (B), the electric field generated between the particles of dielectric filler (B) weakens during dielectric heating treatment, the reverse motion at high frequencies decreases, and thus the heating performance of the adhesive for high-frequency dielectric heating decreases. As a result, the adhesion between the adhesive for high-frequency dielectric heating and the adherend can be considered to decrease. Therefore, for adhesives used in high-frequency dielectric heating, by satisfying the upper limit of the aforementioned mathematical formula (F1), the heating rate of the adhesive for high-frequency dielectric heating can be increased, and it can be firmly bonded to the adherend in a shorter time.

[0060] On the other hand, for adhesives used in high-frequency dielectric heating, if the value of the aforementioned mathematical formula (F1) is too small, the distance between the particles of the dielectric filler (B) becomes too close relative to the particle size of the dielectric filler (B), resulting in a significant decrease in the volume resistivity of the adhesive. If the volume resistivity of the adhesive decreases excessively, it tends to become conductive, and during dielectric heating treatment, it may be easy for current to flow within the adhesive. Therefore, if the lower limit of the aforementioned mathematical formula (F1) is satisfied, the excessive decrease in the volume resistivity of the adhesive can be considered suppressed. As a result, it can be considered that electrical insulation breakdown is suppressed during dielectric heating treatment of the adhesive.

[0061] In summary, compared with conventional high-frequency dielectric heating adhesives, the high-frequency dielectric heating adhesive of this embodiment, through the above-described configuration, can suppress electrical insulation breakdown during dielectric heating treatment and firmly bond to the substrate in a shorter time.

[0062] The materials used in the high-frequency dielectric heating adhesive of this embodiment will be described below.

[0063] <Thermoplastic Resin (A)>

[0064] There are no special restrictions on the types of thermoplastic resins (A).

[0065] For example, from the viewpoint of easy melting and having given heat resistance, the thermoplastic resin (A) is preferably selected from at least one of polyolefin resins, styrene resins, polyacetal resins, polycarbonate resins, acrylic resins, polyamide resins, polyimide resins, polyvinyl acetate resins, phenoxy resins, and polyester resins. The thermoplastic resin (A) is preferably selected from a type of resin with high affinity for the material to which it is adhered.

[0066] In the high-frequency dielectric heating adhesive of this embodiment, the thermoplastic resin (A) is preferably a polyolefin resin or a styrene resin, more preferably a polyolefin resin. If the thermoplastic resin (A) is a polyolefin resin or a styrene resin, the high-frequency dielectric heating adhesive easily melts when a high-frequency electric field is applied, and can easily bond the high-frequency dielectric heating adhesive of this embodiment to the substrate.

[0067] In this specification, polyolefin resins include polyolefin resins having polar sites and polyolefin resins not having polar sites. Where it is necessary to specify whether a polar site is present or absent, the term "polyolefin resin with polar sites" or "polyolefin resin without polar sites" is used.

[0068] The thermoplastic resin (A) is preferably a polyolefin resin with polar sites. The thermoplastic resin (A) may also be a polyolefin resin without polar sites.

[0069] (Polyolefin resins)

[0070] Examples of polyolefin resins that can be used as thermoplastic resins (A) include resins formed from homopolymers such as polyethylene, polypropylene, polybutene, and polymethylpentene, and α-olefin resins formed from copolymers of monomers selected from ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene. Polyolefin resins that can be used as thermoplastic resins (A) can be a single resin or a combination of two or more resins.

[0071] Polyolefin resins with polar sites

[0072] The polar sites in polyolefin resins are any sites that can impart polarity to the polyolefin resin; there are no particular limitations.

[0073] Furthermore, by including a polyolefin resin with polar sites as a thermoplastic resin (A) in the high-frequency dielectric heating adhesive, the dielectric properties are easily improved and the adhesion to the adhered object is increased, which is therefore preferred.

[0074] Polar-site polyolefin thermoplastic resins can be copolymers of olefin monomers and monomers with polar sites. Alternatively, polar-site polyolefin thermoplastic resins can be resins obtained by modifying olefin monomers through addition reactions or other methods to introduce polar sites into olefin polymers.

[0075] There are no particular restrictions on the types of olefin monomers that constitute polyolefin resins with polar sites. Examples of olefin monomers include ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene. One of these olefin monomers can be used alone, or in combination of two or more.

[0076] From the perspective of excellent mechanical strength and stable bonding properties, olefin monomers are preferably at least one of ethylene and propylene.

[0077] The olefin-derived structural units in polyolefin resins with polar sites are preferably derived from ethylene or propylene.

[0078] Examples of polar sites include hydroxyl, carboxyl, vinyl acetate, and anhydride structures. Examples of polar sites also include acid-modified structures introduced into polyolefin resins through acid modification.

[0079] The acid-modified structure, as a polar site, is introduced by acid modification of the thermoplastic resin (e.g., a polyolefin resin). Examples of compounds used in acid modification of the thermoplastic resin (e.g., a polyolefin resin) include unsaturated carboxylic acid derivatives derived from any compound selected from unsaturated carboxylic acids, anhydrides of unsaturated carboxylic acids, and esters of unsaturated carboxylic acids. In this specification, the polyolefin resin having the acid-modified structure is sometimes referred to as an acid-modified polyolefin resin.

[0080] Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0081] Examples of acid anhydrides that are unsaturated carboxylic acids include maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0082] Examples of esters that are unsaturated carboxylic acids include: methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dimethyl maleate, monomethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl itaconic acid, diethyl itaconic acid, dimethyl citrate, diethyl citrate, and dimethyl tetrahydrophthalate.

[0083] [Maleic anhydride modified polyolefin]

[0084] Polyolefin resins, as thermoplastic resins, are more preferably characterized by an anhydride structure as an acid-modified structure. The anhydride structure is preferably the structure introduced when the polyolefin resin is modified using maleic anhydride.

[0085] The olefin-derived structural units in maleic anhydride-modified polyolefins are preferably derived from ethylene or propylene. That is, maleic anhydride-modified polyolefins are preferably maleic anhydride-modified polyethylene resins or maleic anhydride-modified polypropylene resins.

[0086] <Dielectric Filler (B)>

[0087] The preferred dielectric material, namely dielectric filler (B), will be described.

[0088] Dielectric filler (B) is a filler that generates heat when a high-frequency electric field is applied. A high-frequency electric field is an electric field whose direction reverses at high frequencies.

[0089] The dielectric filler (B) is preferably a filler that heats up when a high-frequency electric field with a frequency range of 3 MHz or higher and 300 MHz or lower is applied. The dielectric filler (B) is preferably a filler that heats up when a high-frequency electric field with a frequency range of 3 MHz or higher and 300 MHz or lower is applied, for example, frequencies such as 13.56 MHz, 27.12 MHz, or 40.68 MHz.

[0090] Dielectric filler (B) may be one or a combination of two or more of the following materials: zinc oxide, silicon carbide (SiC), anatase titanium oxide, barium titanate, barium zirconate titanate, lead titanate, potassium niobate, rutile titanium oxide, hydrated aluminum silicate, hydrated aluminosilicates of alkali metals, or hydrated aluminosilicates of alkaline earth metals. Dielectric filler (B) may be one or a combination of two or more of the following materials: zinc oxide, silicon carbide (SiC), anatase titanium oxide, rutile titanium oxide, hydrated aluminum silicate, hydrated aluminosilicates of alkali metals, or hydrated aluminosilicates of alkaline earth metals.

[0091] From the viewpoint of obtaining higher thermal performance, the dielectric filler (B) is preferably selected from at least one of zinc oxide, silicon carbide and titanium oxide, more preferably at least one of zinc oxide and titanium oxide.

[0092] Among the dielectric fillers described, zinc oxide is abundant, available in various shapes and sizes, and can improve the adhesive and mechanical properties of high-frequency dielectric heating adhesives to suit different applications. Therefore, zinc oxide is further preferred as the dielectric filler (B). By using zinc oxide as the dielectric filler (B), a high-frequency dielectric heating adhesive with good design flexibility and low transmittance can be obtained. Zinc oxide is not very hard in ceramics, therefore, it is less likely to damage the manufacturing apparatus for the high-frequency dielectric heating adhesive. Since zinc oxide is a non-reactive oxide, even when combined with thermoplastic resins, it causes minimal damage to the thermoplastic resins.

[0093] Furthermore, the titanium oxide used as dielectric filler (B) is preferably at least one of anatase titanium oxide and rutile titanium oxide, and from the viewpoint of excellent dielectric properties, anatase titanium oxide is more preferred.

[0094] The shape of the dielectric filler (B) is not particularly limited and various shapes can be adopted. From the viewpoint of manufacturing cost of the dielectric filler (B), the shape of the dielectric filler (B) is preferably, for example, irregular or spherical, and more preferably irregular. In this specification, "irregular shape" means that the dielectric filler (B) does not have a specific shape such as a perfect sphere or a cube. Furthermore, from the same viewpoint, the dielectric filler (B) is also preferably not surface-modified. In this specification, "not surface-modified" means that the dielectric filler (B) has not undergone any modification treatment by introducing organic groups onto its surface.

[0095] The volume content of dielectric filler (B) in the adhesive for high-frequency dielectric heating is preferably 2% or more, more preferably 3% or more, further preferably 4% or more, even more preferably 6% or more, and particularly preferably 8% or more.

[0096] The volume content of dielectric filler (B) in the adhesive for high-frequency dielectric heating is preferably 40% or less, more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and especially more preferably 22% or less.

[0097] By increasing the volume content of dielectric filler (B) in the high-frequency dielectric heating adhesive to 2% or more, the heating properties are improved, making it easier to firmly bond the high-frequency dielectric heating adhesive to the adhered object.

[0098] By ensuring that the volume content of dielectric filler (B) in the high-frequency dielectric heating adhesive is 40% or less, it is possible to prevent a decrease in the strength of the adhesive. As a result, it is possible to prevent a decrease in bond strength due to the use of the adhesive. Furthermore, in the case where the high-frequency dielectric heating adhesive of this embodiment is in the form of an adhesive sheet, by ensuring that the volume content of dielectric filler (B) in the adhesive sheet is 40% or less, it is easy to obtain flexibility when the sheet is manufactured, and it is also easy to prevent a decrease in toughness. Therefore, it is easy to process the high-frequency dielectric heating adhesive sheet into the desired shape in subsequent processes.

[0099] When observing the cross-section of the adhesive for high-frequency dielectric heating cut along its thickness direction using a scanning electron microscope (SEM), the particle size Dn of the dielectric filler (B) is preferably 1.0 μm or more and 4.0 μm or less. In this specification, the particle size Dn of the dielectric filler (B) represents the arithmetic mean obtained by arithmetically averaging the particle sizes measured by the method described later.

[0100] The particle size Dn of the dielectric filler (B) is preferably 1.1 μm or more, more preferably 1.2 μm or more, and even more preferably 1.3 μm or more.

[0101] The particle size Dn of the dielectric filler (B) is preferably 3.8 μm or less, more preferably 3.6 μm or less, even more preferably 3.4 μm or less, and even more preferably 3.2 μm or less.

[0102] By making the particle size Dn of the dielectric filler (B) greater than 1.0 μm, the high-frequency dielectric heating adhesive exhibits high heating performance when a high-frequency electric field is applied, and can firmly bond to the substrate in a short time.

[0103] By making the particle size Dn of the dielectric filler (B) 4.0 μm or less, the high-frequency dielectric heating adhesive exhibits high heating performance when a high-frequency electric field is applied, enabling it to firmly bond to the substrate in a short time. Furthermore, in the case where the high-frequency dielectric heating adhesive of this embodiment is an adhesive sheet, by making the particle size Dn of the dielectric filler (B) 4.0 μm or less, the strength of the high-frequency dielectric heating adhesive sheet can be prevented from decreasing.

[0104] When observing the cross-section of the adhesive for high-frequency dielectric heating along its thickness direction using SEM, the distance Dg between the nearest centroids of the dielectric filler (B) is preferably 2.2 μm or more and 6.0 μm or less. In this specification, the distance Dg between the nearest centroids of the dielectric filler (B) represents the average value of the nearest centroid distances measured by the measurement method described later. The nearest centroid distance refers to the distance between the centroid of a dielectric filler (B) and the centroid of the dielectric filler (B) that is closest to it. That is, it refers to the distance between the centroids of one dielectric filler (B) and the centroid of the nearest adjacent dielectric filler (B) among adjacent dielectric fillers (B). Here, the concept of adjacent dielectric fillers (B) includes the following two cases: (i) one dielectric filler (B) is directly connected to another dielectric filler (B), and (ii) one dielectric filler (B) is not directly connected to another dielectric filler (B) but has a certain distance between them.

[0105] The distance Dg between the nearest centroids of the dielectric filler (B) is preferably 2.3 μm or more, more preferably 2.4 μm or more, and even more preferably 2.5 μm or more.

[0106] The distance Dg between the nearest centroids of the dielectric filler (B) is preferably 5.8 μm or less, more preferably 5.6 μm or less, further preferably 5.4 μm or less, and even more preferably 5.2 μm or less.

[0107] By ensuring that the distance between the nearest centroids of the dielectric filler (B) is 2.2 μm or more, the adhesive for high-frequency dielectric heating exhibits high thermal performance when a high-frequency electric field is applied, enabling it to firmly bond to the substrate in a short time. Furthermore, by ensuring that the distance between the nearest centroids of the dielectric filler (B) is 2.2 μm or more, the decrease in the volume resistivity of the adhesive for high-frequency dielectric heating is suppressed.

[0108] By making the distance Dg between the nearest centroids of the dielectric filler (B) 6.0 μm or less, the high-frequency dielectric heating adhesive exhibits high heating performance when a high-frequency electric field is applied, enabling it to firmly bond to the substrate in a short time. Furthermore, in the case where the high-frequency dielectric heating adhesive of this embodiment is an adhesive sheet, by making the distance Dg between the nearest centroids of the dielectric filler (B) 6.0 μm or less, a decrease in the strength of the high-frequency dielectric heating adhesive sheet can be prevented.

[0109] <Additives>

[0110] Within the limits of not compromising short-term adhesion, the high-frequency dielectric heating adhesive of this embodiment may or may not contain additives.

[0111] When the high-frequency dielectric heating adhesive of this embodiment contains additives, examples of additives include: tackifiers, plasticizers, waxes, colorants, antioxidants, ultraviolet absorbers, antibacterial agents, coupling agents, viscosity modifiers, organic fillers, and inorganic fillers. The organic and inorganic fillers used as additives differ from dielectric fillers.

[0112] Tackifiers and plasticizers can improve the melting and bonding properties of adhesives used in high-frequency dielectric heating.

[0113] Examples of tackifiers include: rosin derivatives, polyterpene resins, aromatic modified terpene resins, hydrides of aromatic modified terpene resins, terpene phenol resins, coumarone-indene resins, aliphatic petroleum resins, aromatic petroleum resins, and hydrides of aromatic petroleum resins.

[0114] Examples of plasticizers include: petroleum-based processed oils, natural oils, dialkyl diacid esters, and low molecular weight liquid polymers. Examples of petroleum-based processed oils include: paraffin-based processed oils, cycloalkane-based processed oils, and aromatic-based processed oils. Examples of natural oils include: castor oil and tall oil. Examples of dialkyl diacid esters include: dibutyl phthalate, dioctyl phthalate, and dibutyl adipate. Examples of low molecular weight liquid polymers include: liquid polybutene and liquid polyisoprene.

[0115] In the case where the high-frequency dielectric heating adhesive of this embodiment contains additives, the content of additives in the high-frequency dielectric heating adhesive is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the total amount of the high-frequency dielectric heating adhesive. Furthermore, the content of additives in the high-frequency dielectric heating adhesive is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0116] The high-frequency dielectric heating adhesive of this embodiment preferably does not contain solvents. When using a solvent-free high-frequency dielectric heating adhesive, problems caused by volatile organic compounds from the adhesive used to bond to the adhered object are less likely to occur.

[0117] The adhesive for high-frequency dielectric heating in this embodiment preferably does not contain carbon or carbon compounds with carbon as the main component and conductive substances such as metals. The adhesive for high-frequency dielectric heating in this embodiment preferably does not contain, for example, carbon steel, α-iron, γ-iron, δ-iron, copper, iron oxide, brass, aluminum, iron-nickel alloys, iron-nickel-chromium alloys, carbon fibers, and carbon black.

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

[0119] The content of conductive substances in the adhesive is preferably 0 by mass.

[0120] When the content of conductive substances in the adhesive is less than 7% by mass, it is easy to prevent electrical insulation breakdown during dielectric heating treatment, which could lead to carbonization of the bonded part and the adhered material.

[0121] In the high-frequency dielectric heating adhesive of this embodiment, the total content of thermoplastic resin (A) and dielectric filler (B) is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 93% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0122] Properties of adhesives for high-frequency dielectric heating

[0123] Next, the characteristics of the high-frequency dielectric heating adhesive of this embodiment will be explained.

[0124] (Distance between nearest centroids Dg / Particle size Dn)

[0125] For the high-frequency dielectric heating adhesive of this embodiment, when observing the cross-section of the high-frequency dielectric heating adhesive along the thickness direction using SEM, the relationship (Dg / Dn) between the nearest centroid distance Dg of the dielectric filler (B) and the particle size Dn of the dielectric filler (B) satisfies the above-described mathematical formula (F1). That is, the ratio of the nearest centroid distance Dg of the dielectric filler (B) to the particle size Dn of the dielectric filler (B) is 1.55 or more and 1.85 or less. From the viewpoint of being able to suppress electrical insulation breakdown during dielectric heating treatment and to firmly bond with the adherend in a shorter time, the ratio of the nearest centroid distance Dg of the dielectric filler (B) to the particle size Dn of the dielectric filler (B) is more preferably 1.56 or more, and even more preferably 1.57 or more. From the viewpoint of being able to firmly bond with the adherend in a further shorter time, the ratio of the distance Dg between the nearest centroids of the dielectric filler (B) to the particle size Dn of the dielectric filler (B) is more preferably 1.83 or less, more preferably 1.80 or less, even more preferably 1.75 or less, and particularly more preferably 1.70 or less.

[0126] In this embodiment, the particle size Dn of the dielectric filler (B), the distance between the nearest centroids of the dielectric filler (B) Dg, and the ratio of the distance between the nearest centroids of the dielectric filler (B) Dg to the particle size Dn of the dielectric filler (B) are determined by the steps shown in (1) to (5) below.

[0127] Step (1): The cut surface formed by cutting the adhesive for high-frequency dielectric heating along the thickness direction using a profile processing device is ground, and one field of view is observed using SEM at a magnification of 500x or higher. From the viewpoint of efficient processing, the profile processing device is preferably a device that uses an ion beam to process the cut surface.

[0128] Step (2): The obtained SEM image is binarized using image analysis software to detect the blocks (hereinafter referred to as Blob: Binary Large Object) obtained from the binarized image as particles of dielectric filler (B). The Blob is the region in the binarized image where adjacent pixels are identified as white. Figure 3 An example of a binarized image obtained through the binarization process described above is shown. Figure 3 An example of a binarized image shown is a binarized image obtained using Otsu's binarization method. Figure 3 In the binarized image shown, the white parts are particles of dielectric filler (B).

[0129] Step (3): By performing Blob analysis on the detected dielectric filler (B) particles, the equivalent circle diameter of more than 100 dielectric filler (B) particles as the test objects is measured. The average number of particles obtained by the arithmetic mean of the measured equivalent circle diameter is calculated using the numpy, mean function as the particle size Dn of dielectric filler (B).

[0130] Step (4): For the dielectric filler (B) used in step (3) above, the centroids of the particles are determined using the Open CV, moments function. Next, a Delaunay diagram connecting the determined centroids of the particles is created using the Open CV, Subdiv2D function. The three sides of the triangles in the created Delaunay diagram are compared, and the length of the shortest side of the compared triangle is taken as the distance between the nearest centroids. Then, the average of more than 100 measured nearest centroid distances is taken as the nearest centroid distance Dg. Figure 4 The image shown is an example of a Delaunay map made based on the binarized image obtained through step (2) above. Figure 4 The line segment shown is the edge connecting the centroids of the particles of the dielectric filler (B). For example... Figure 4 As shown, a triangle is formed by connecting the three sides between the centroids. The sides forming the triangle are compared, and the shortest side among the compared sides is taken as the distance between the nearest centroids. The average of more than 100 measured nearest centroid distances is the nearest centroid distance Dg.

[0131] Step (5): Divide the distance between the nearest centroids Dg obtained in step (4) above by the particle size Dn obtained in step (3) above, and calculate the ratio of the distance between the nearest centroids Dg to the particle size Dn (distance between the nearest centroids Dg / particle size Dn).

[0132] The particle size Dn of the dielectric filler (B), the distance between the nearest centroids of the dielectric filler (B) Dg, and the ratio of the distance between the nearest centroids of the dielectric filler (B) Dg to the particle size Dn of the dielectric filler (B) can be specifically determined by the method described in the examples below.

[0133] (Volume resistivity)

[0134] The volume resistivity of the adhesive for high-frequency dielectric heating in this embodiment can be 1.0 × 10⁻⁶. 13 The volume resistivity of the high-frequency dielectric heating adhesive in this embodiment is preferably 1.0 × 10⁻⁶ Ω·cm or higher. 14 Ω·cm or more, more preferably 1.0×10 15 Ω·cm or higher, more preferably 1.0×10 16The volume resistivity of the adhesive for high-frequency dielectric heating in this embodiment is not particularly limited; for example, it can be 1.0 × 10⁻⁶ Ω·cm or higher. 18 Below Ω·cm. The volume resistivity of the high-frequency dielectric heating adhesive in this embodiment is, for example, 1.0 × 10⁻⁶. 13 When the volume resistivity is above Ω·cm, it is easy to ensure that electrical insulation breakdown during dielectric heating treatment is suppressed. As a result, electrical insulation breakdown during dielectric heating treatment is easily suppressed, and it adheres firmly to the substrate for a short time. Specifically, the volume resistivity can be determined by the method described in the examples below. It should be noted that the volume resistivity of the adhesive for high-frequency dielectric heating is less than 1.0 × 10⁻⁶. 13 In the case of Ω·cm, while it doesn't mean that electrical insulation breakdown will immediately occur upon dielectric heating treatment, it tends to be more likely to occur upon dielectric heating treatment. The lower the volume resistivity of the adhesive for high-frequency dielectric heating, the easier it is for electrical insulation breakdown to occur upon dielectric heating treatment. As the volume resistivity of the adhesive for high-frequency dielectric heating becomes, for example, 1.0 × 10⁻⁶, further increasing... 10 With a resistivity below Ω·cm, electrical insulation breakdown is more likely to occur during dielectric heating treatment. Therefore, the volume resistivity of the high-frequency dielectric heating adhesive in this embodiment is, for example, 1.0 × 10⁻⁶. 13 When the value is above Ω·cm, it is easy to ensure the suppression of electrical insulation breakdown during dielectric heating treatment.

[0135] (Dielectric properties)

[0136] The dielectric properties (tanδ / ε'r) of the high-frequency dielectric heating adhesive of this embodiment will be explained. For the high-frequency dielectric heating adhesive of this embodiment, the dielectric properties (tanδ / ε'r) are preferably 0.004 or higher.

[0137] (tanδ is the dielectric loss tangent at 23℃ and 40.68MHz, and ε'r is the relative permittivity at 23℃ and 40.68MHz.)

[0138] If the dielectric properties of the high-frequency dielectric heating adhesive are 0.004 or higher, the high-frequency dielectric heating adhesive will easily heat up during dielectric heating treatment, and will easily and firmly bond the high-frequency dielectric heating adhesive to the adhered object in a short time.

[0139] Even if the dielectric property of the adhesive for high-frequency dielectric heating is 0.004 or higher, it is sometimes difficult to achieve the effect of suppressing electrical insulation breakdown during dielectric heating treatment and firmly bonding with the substrate in a shorter time if the relationship between the particle size of the dielectric filler (B) and the distance between the dielectric filler (B) particles (Dg / Dn) does not satisfy the above mathematical formula (F1).

[0140] The dielectric properties of the high-frequency dielectric heating adhesive in this embodiment are more preferably 0.005 or higher, more preferably 0.008 or higher, and even more preferably 0.010 or higher.

[0141] If the dielectric property of the high-frequency dielectric heating adhesive in this embodiment is 0.008 or higher, the high-frequency dielectric heating adhesive will generate heat more easily during dielectric heating treatment, and will be able to firmly bond the high-frequency dielectric heating adhesive to the adhered object in a short time.

[0142] The upper limit of the dielectric properties of the high-frequency dielectric heating adhesive in this embodiment is not particularly limited. From the viewpoint of suppressing overheating of the high-frequency dielectric heating adhesive, it is preferably 0.04 or less, more preferably 0.02 or less, even more preferably 0.014 or less, and particularly preferably 0.011 or less.

[0143] When the dielectric property of the adhesive for high-frequency dielectric heating is 0.04 or less, overheating is easily suppressed, and damage to the portion of the adhered material in contact with the adhesive is less likely to occur. In cases where the adhered material has low heat resistance and may experience thermal effects due to overheating, the upper limit of the dielectric property of the adhesive for high-frequency dielectric heating is preferably, for example, 0.011 or less. In this case, the dielectric property of the adhesive for high-frequency dielectric heating is preferably, for example, 0.004 or more and 0.011 or less.

[0144] The dielectric property (tanδ / ε'r) is a value obtained by dividing the dielectric loss tangent (tanδ) measured using an impedance material device by the relative permittivity (ε'r) measured using an impedance material device.

[0145] The dielectric loss tangent (tanδ) and relative permittivity (ε'r) of the adhesive used for high-frequency dielectric heating can be easily and accurately measured using an impedance / material analyzer.

[0146] It should be noted that the detailed method for measuring the dielectric properties of the adhesive for high-frequency dielectric heating and the adhered material is as follows. First, a test sheet for the adhesive for high-frequency dielectric heating is obtained. When a test sheet needs to be obtained from a structure, a test sheet of uniform thickness is obtained by cutting or shaving it from the structure. For granular adhesives for high-frequency dielectric heating that are not formed into sheets, test sheets are obtained by forming them into sheets using a hot press or the like. The thickness of the test sheet is, for example, 10 μm or more and 2 mm or less. For the sheet obtained in this way, the relative permittivity (ε'r) and dielectric loss tangent (tanδ) are measured using an RF impedance / material analyzer E4991A (manufactured by Agilent Technologies) at a frequency of 40.68 MHz at 23°C, and the dielectric property (tanδ / ε'r) is calculated.

[0147] <Shape of adhesive for high-frequency dielectric heating>

[0148] The shape of the high-frequency dielectric heating adhesive in this embodiment is not particularly limited. The high-frequency dielectric heating adhesive in this embodiment can be, for example, a molded body adhesive obtained by injection molding or the like, or a sheet-like adhesive obtained by extrusion molding or the like. In this embodiment, the molded body and the sheet are different shapes. A sheet generally refers to a strip or thin layer with a thickness of 1 mm or less, 2 mm or less, or 5 mm or less. A molded body refers to a shape obtained by molding a material containing the components of the high-frequency dielectric heating adhesive, and it can be any shape other than a sheet.

[0149] The adhesive for high-frequency dielectric heating in this embodiment is preferably in sheet form. That is, the adhesive for high-frequency dielectric heating in this embodiment is preferably an adhesive sheet for high-frequency dielectric heating (sometimes called an adhesive sheet). By using an adhesive sheet as the adhesive for high-frequency dielectric heating, the manufacturing process time of the structure can be further shortened.

[0150] The high-frequency dielectric heating adhesive of this embodiment can be shaped like a frame-shaped sheet (frame-shaped adhesive sheet) having a frame-shaped portion and an opening, wherein the opening extends from one of the opposing faces toward and through the other face. The shape of the opening is not particularly limited. When the adhesive sheet is frame-shaped, it may have one or more openings. The frame-shaped sheet may have a notch in a portion of the frame-shaped portion. In this case, the opening may be a shape in which a portion of the frame-shaped portion communicates with the outside of the frame-shaped portion. That is, when viewed from above, the frame-shaped portion may appear open (e.g., a discontinuous shape such as a C-shape or U-shape). The frame-shaped portion of the frame-shaped sheet may have a notch. In this case, the opening may be a shape in which the opening is surrounded by the frame-shaped portion (e.g., a continuous shape such as an O-shape). That is, when viewed from above, the frame-shaped portion may appear closed. When the frame-shaped sheet has two or more openings, the shapes of these openings can be combined when the frame-shaped sheet is viewed from above; openings of the same shape can be combined, or openings of different shapes can be combined. The adhesive for high-frequency dielectric heating in this embodiment can be a sheet without these openings. Furthermore, the adhesive for high-frequency dielectric heating in this embodiment can also be molded into an adhesive sheet of the target shape using molding methods such as extrusion molding and injection molding.

[0151] In one embodiment, the high-frequency dielectric heating adhesive of this embodiment consists of only one adhesive layer, which is formed from the high-frequency dielectric heating adhesive sheet of this embodiment. When the high-frequency dielectric heating adhesive is a high-frequency dielectric heating adhesive sheet consisting of only one adhesive layer, the adhesive layer itself is equivalent to the high-frequency dielectric heating adhesive sheet; therefore, the shape and characteristics of the high-frequency dielectric heating adhesive sheet are equivalent to the shape and characteristics of the adhesive layer. Preferably, the high-frequency dielectric heating adhesive sheet consists of only a single adhesive layer. This allows for a reduction in the thickness of the high-frequency dielectric heating adhesive sheet and simplifies its molding process.

[0152] Since adhesive sheets for high-frequency dielectric heating sometimes consist of only one adhesive layer for high-frequency dielectric heating adhesion, the terms "adhesive sheet for high-frequency dielectric heating" and "adhesive layer" may be used interchangeably in this specification as appropriate.

[0153] The adhesive for high-frequency dielectric heating in this embodiment is not limited to a high-frequency dielectric heating adhesive sheet consisting of only one adhesive layer. The adhesive for high-frequency dielectric heating in this embodiment can be... Figure 1A , Figure 1B and Figure 1C Any of the methods shown.

[0154] Figure 1AThe high-frequency dielectric heating adhesive 1A shown is an adhesive sheet consisting of only a single adhesive layer 10.

[0155] Figure 1B The high-frequency dielectric heating adhesive 1B shown is an adhesive sheet having an adhesive layer 10 and a substrate 30 supporting the adhesive layer 10. The adhesive layer 10 has a first surface 11. The substrate 30 is not particularly limited to any component capable of supporting the adhesive layer 10. Examples of substrate 30 include resin sheets containing at least one resin selected from polyolefin resins, polyester resins, acetate resins, acrylonitrile-butadiene-styrene copolymer resins, polystyrene resins, and vinyl chloride resins. Examples of polyolefin resins include, for example, polyethylene resins and polypropylene resins. Examples of polyester resins include, for example, polybutylene terephthalate resins and polyethylene terephthalate resins. The substrate 30 may contain a dielectric filler. The dielectric filler (B) in the adhesive layer 10 may be the same as or different from the dielectric filler in the substrate 30.

[0156] Figure 1C The high-frequency dielectric heating adhesive 1C shown is an adhesive sheet having an intermediate layer 40 disposed between the adhesive layer 10 and the adhesive layer 20. The high-frequency dielectric heating adhesive 1C has a first surface 11 and a second surface 21 opposite to the first surface 11. In the high-frequency dielectric heating adhesive 1C, the adhesive layer 10 only needs to meet the conditions of the adhesive layer of the high-frequency dielectric heating adhesive sheet of this embodiment. In one embodiment, the adhesive layer 10 and the adhesive layer 20 are layers with the same composition and characteristics. In another embodiment, the adhesive layer 20 is a high-frequency dielectric heating adhesive layer that differs from the adhesive layer 10 in at least one aspect of composition and characteristics. In yet another embodiment, the adhesive layer 20 is a layer of a general adhesive that is not a high-frequency dielectric heating adhesive layer. In this case, the non-high-frequency dielectric heating adhesive layer 20 may be, for example, a layer of a dry-curing type adhesive that dries and solidifies upon evaporation of water or solvent, or a layer of an adhesive formed by an adhesive.

[0157] In the case where the adhesive for high-frequency dielectric heating in this embodiment is an adhesive sheet consisting of only one adhesive layer, the thickness of the adhesive sheet in this embodiment is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 30 μm or more, and particularly preferably 50 μm or more.

[0158] When the thickness of the adhesive sheet is 5 μm or more, the heating effect is increased when a high-frequency electric field is applied to the adhesive sheet in contact with the substrate, thus making it easier to firmly bond the adhesive sheet to the substrate in a short time. In addition, when bonding with the substrate, the adhesive sheet easily follows the unevenness of the substrate, and easily exhibits bonding strength.

[0159] When the adhesive sheet is a multilayer structure comprising multiple layers, the thickness of the adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 30 μm or more, and even more preferably 50 μm or more.

[0160] When the adhesive sheet for high-frequency dielectric heating is a multilayer sheet, if the thickness of the adhesive layer is 5μm or more, the adhesive layer can easily follow the unevenness of the adhered object when it is bonded to the adhered object, and can easily show the bonding strength.

[0161] There is no particular upper limit to the thickness of the adhesive sheet. The greater the thickness of the adhesive sheet, the greater the overall weight of the structure obtained by bonding the adhesive sheet to the adhered object. Therefore, the thickness of the adhesive sheet is preferably within a range that ensures good processability and operability in practical use. Considering the practicality and moldability of the adhesive sheet for high-frequency dielectric heating, the thickness of the adhesive sheet in this embodiment is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 600 μm or less. Whether the structure consists of only one adhesive layer or a multilayer structure consisting of multiple layers including an adhesive layer, the upper limit of the thickness of the adhesive sheet is preferably the value described above.

[0162] Compared to using liquid adhesives that require coating, adhesive sheets used as adhesives for high-frequency dielectric heating are easier to handle and offer improved operability when bonding with the substrate.

[0163] Furthermore, the adhesive sheet used as an adhesive for high-frequency dielectric heating allows for suitable control of sheet thickness and other parameters. Therefore, the adhesive sheet can be applied in roll-to-roll processes, and its area and shape can be arbitrarily customized according to the bonding area and shape of the adhered object through processes such as punching. Thus, from a manufacturing process perspective, the advantages of the adhesive sheet as an adhesive for high-frequency dielectric heating are significant.

[0164] For the high-frequency dielectric heating adhesive of this embodiment, it is preferable to apply a high-frequency electric field in a frequency band known as shortwave to ultrashortwave. When a high-frequency electric field in this frequency band is applied, the depth of heating is deep, thus improving the heating performance when the high frequency is applied. Therefore, even when the high-frequency dielectric heating adhesive is thick, it is easy to firmly bond the adhesive sheet to the substrate in a short time.

[0165] <Manufacturing Method of Adhesive for High-Frequency Dielectric Heating>

[0166] The high-frequency dielectric heating adhesive of this embodiment can be manufactured, for example, by mixing the above-described components. When the high-frequency dielectric heating adhesive of this embodiment is an adhesive sheet, it can be manufactured, for example, by premixing the above-described components and mixing them using a known mixing apparatus such as an extruder and hot rollers, and then using known molding methods such as extrusion molding, calendering, injection molding, and casting. When the high-frequency dielectric heating adhesive of this embodiment is a molded body, it can be manufactured, for example, using a material obtained by premixing the above-described components, and using known molding methods such as injection molding and compression molding. Furthermore, when the high-frequency dielectric heating adhesive of this embodiment is a frame-shaped sheet, the frame-shaped sheet can be manufactured, for example, by providing an opening in the sheet-shaped high-frequency dielectric heating adhesive obtained by the above-described adhesive sheet molding method using a known punching process. Alternatively, the frame-shaped sheet can be manufactured using a mold in the above-described adhesive sheet molding method that produces the desired shape of the opening.

[0167] The distance between the nearest centroids of the dielectric filler (B) Dg and the ratio of the distance between the nearest centroids of the dielectric filler (B) Dg to the particle size Dn of the dielectric filler (B) can be adjusted, for example, by the particle size Dn of the dielectric filler (B) and the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive. In addition to the particle size Dn of the dielectric filler (B) and the volume content of the dielectric filler (B) in the high-frequency dielectric heating adhesive, the distance between the nearest centroids of the dielectric filler (B) Dg and the ratio of the distance between the nearest centroids of the dielectric filler (B) Dg to the particle size Dn of the dielectric filler (B) can also be adjusted by, for example, by studying the conditions under which the thermoplastic resin (A) and the dielectric filler (B) contained in the high-frequency dielectric heating adhesive of this embodiment are mixed.

[0168] Compared with general adhesives, adhesives for high-frequency dielectric heating have superior water resistance and moisture resistance.

[0169] The high-frequency dielectric heating adhesive of this embodiment can be locally heated by applying a high-frequency electric field. Therefore, the high-frequency dielectric heating adhesive of this embodiment easily prevents adverse situations such as damage to the entire adhered object during adhesion.

[0170] [Substance to be adhered to]

[0171] There are no particular limitations on the material of the adherend. The material of the adherend can be any material among organic, metallic, and inorganic materials, or a composite material of them.

[0172] The material to be adhered to is preferably an organic material. Examples of organic materials that can be used as the adhered material include plastic materials and rubber materials. Examples of plastic materials include: polypropylene resin, polyethylene resin, epoxy resin, polyurethane resin, acrylonitrile-butadiene-styrene copolymer resin, polycarbonate resin, polyamide resin; nylon 6 and nylon 66, polyester resin; polyethylene terephthalate and polybutylene terephthalate resins, polyacetal resin, polymethyl methacrylate resin, and polystyrene resin. Examples of rubber materials include: styrene-butadiene rubber, ethylene propylene rubber, and silicone rubber. Additionally, the adhered material can be a foamed organic material.

[0173] When the material of the adherend is a thermoplastic resin, the thermoplastic resin contained in the adherend and the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive can be different resins. In this case, bonding can be easily performed without damaging the shape of the adherend.

[0174] Furthermore, when the material of the adhered object is a thermoplastic resin, from the point of view of adhesion, the main composition of the thermoplastic resin contained in the adhered object can be the same as the main composition of the thermoplastic resin (A) contained in the high-frequency dielectric heating adhesive.

[0175] In this specification, "major component of thermoplastic resin" refers, for example, when the thermoplastic resin is a polymer, the polymer containing the most repeating units among the repeating units it comprises. If the thermoplastic resin is a polymer derived from a single monomer, then the repeating units based on that monomer unit are the "major component of the thermoplastic resin." When the thermoplastic resin is a copolymer, the polymer containing the most repeating units is the "major component of the thermoplastic resin." When the thermoplastic resin is a copolymer, the "major component of the thermoplastic resin" in the copolymer contains 30% by mass or more repeating units; in one embodiment, it contains more than 30% by mass; in another embodiment, it contains 40% by mass or more repeating units; and in yet another embodiment, it contains 50% by mass or more repeating units. Furthermore, when the thermoplastic resin is a copolymer, the most repeating units can be two or more types.

[0176] Inorganic materials that can be used as the adherend can include glass, cement, ceramics, and metals. Alternatively, the adherend can be a fiber-reinforced resin, a composite material of fibers and the aforementioned plastic materials. The plastic material in this fiber-reinforced resin can be, for example, at least one selected from polypropylene resin, polyethylene resin, polyurethane resin, acrylonitrile-butadiene-styrene copolymer resin, polycarbonate resin, polyamide resin; nylon 6 and nylon 66, polyester resin, polyethylene terephthalate and polybutylene terephthalate resins, polyacetal resin, polymethyl methacrylate resin, epoxy resin, and polystyrene resin. The fibers in the fiber-reinforced resin can include, for example, glass fiber, Kevlar fiber (registered trademark), and carbon fiber.

[0177] The preferred material to be adhered to has low conductivity.

[0178] When multiple objects are bonded together using the high-frequency dielectric heating adhesive of this embodiment, the multiple objects may be made of the same material or different materials.

[0179] The shape of the adhered object is not particularly limited. In the case of the adhesive for high-frequency dielectric heating in this embodiment being an adhesive sheet, the adhered object preferably has a surface that allows the adhesive sheet to adhere, and is preferably sheet-like, plate-like, or block-like. When multiple adhered objects are bonded together, the shapes and sizes of these adhered objects may be the same or different.

[0180] [Adhesion Method]

[0181] Next, as an example of a bonding method for bonding an adhesive for high-frequency dielectric heating according to this embodiment to an adherend, a method for manufacturing a structure by bonding an adhesive for high-frequency dielectric heating according to this embodiment to an adherend will be described. The method for manufacturing a structure by bonding an adhesive for high-frequency dielectric heating according to this embodiment to an adherend includes, for example, the following steps.

[0182] When a structure is manufactured by bonding one or more substrates to the high-frequency dielectric heating adhesive of this embodiment, the manufacturing method of the structure of this embodiment includes: a step of applying the high-frequency dielectric heating adhesive of this embodiment to one or more substrates, and a step of bonding one or more substrates by applying a high-frequency electric field to the high-frequency dielectric heating adhesive. The frequency of the applied high-frequency electric field is, for example, 1 MHz or more and 300 MHz or less.

[0183] When a structure is manufactured by bonding two or more adherends to the high-frequency dielectric heating adhesive of this embodiment, the manufacturing method of the structure of this embodiment includes: a step of placing the high-frequency dielectric heating adhesive of this embodiment between two or more adherends, and a step of bonding the two or more adherends by applying a high-frequency electric field to the high-frequency dielectric heating adhesive. In this case, the frequency of the applied high-frequency electric field is, for example, 1 MHz or more and 300 MHz or less.

[0184] In the manufacturing method of the structure in this embodiment, it is preferable to place two or more adherends and a high-frequency dielectric heating adhesive between the electrodes of the dielectric heating device, and to apply a high-frequency electric field to the two or more adherends and the high-frequency dielectric heating adhesive while applying pressure using the electrodes. By applying pressure using the electrodes while applying a high-frequency electric field in this way, it is easier to manufacture the structure in a shorter time.

[0185] It should be noted that in this specification, the "dielectric heating device" is sometimes referred to as the "high-frequency dielectric heating device".

[0186] According to the manufacturing method of the high-frequency dielectric heating adhesive using this embodiment, it is possible to locally heat only a predetermined area from the outside using a dielectric heating device. Therefore, the manufacturing method of the high-frequency dielectric heating adhesive using this embodiment is effective even when the adhered object is a large and complex three-dimensional structure or a thick and complex three-dimensional structure requiring higher dimensional accuracy.

[0187] Hereinafter, as an example of the manufacturing method of the structure of this embodiment, a method of bonding two or more adherends using the high-frequency dielectric heating adhesive of this embodiment will be described, but the present invention is not limited to this method.

[0188] One aspect of the bonding method in this embodiment includes the following steps P1 and P2.

[0189] Process P1

[0190] Step P1 is the process of placing the high-frequency dielectric heating adhesive of this embodiment between two or more adherends. When manufacturing a laminate as the structure of this embodiment, in step P1, for example, adherends and high-frequency dielectric heating adhesive are alternately placed, with two or more adherends laminated with the high-frequency dielectric heating adhesive sandwiched between them.

[0191] The high-frequency dielectric heating adhesive is preferably sandwiched between the adhered objects in a manner that allows them to adhere to each other. The high-frequency dielectric heating adhesive can be sandwiched between a portion of the adhered objects, multiple portions of the adhered objects, or the entire surface between the adhered objects. From the viewpoint of improving the adhesive strength between the adhered objects, it is preferable to sandwich the high-frequency dielectric heating adhesive across the entire adhesive surface between the adhered objects.

[0192] Another method for clamping the high-frequency dielectric heating adhesive between the adhered materials is to arrange the high-frequency dielectric heating adhesive in a frame shape along the outer periphery of the adhesive surfaces between the adhered materials and clamp it between them. By arranging the high-frequency dielectric heating adhesive in a frame shape in this way, it is possible to achieve a strong bond between the adhered materials while reducing the weight of the structure compared to the case where the high-frequency dielectric heating adhesive is distributed across the entire adhesive surface.

[0193] Furthermore, by clamping a portion of the high-frequency dielectric heating adhesive between the adhered materials, the amount of high-frequency dielectric heating adhesive used or its size can be reduced. Therefore, compared to the case where the high-frequency dielectric heating adhesive is distributed throughout the entire bonding surface, the high-frequency dielectric heating processing time can be shortened.

[0194] Process P2

[0195] Step P2 is a step in which a high-frequency electric field is applied to the high-frequency dielectric heating adhesive disposed between the adherends in step P1 to bond 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, a high-frequency electric field can be applied to the high-frequency dielectric heating adhesive using a dielectric heating device.

[0196] <Dielectric heating device>

[0197] Figure 2 A schematic diagram illustrating the high-frequency dielectric heating process using the high-frequency dielectric heating adhesive and dielectric heating device of this embodiment is shown.

[0198] Figure 2 The dielectric heating device 50 shown includes: a first high-frequency electric field applying electrode 51, a second high-frequency electric field applying electrode 52, and a high-frequency power supply 53.

[0199] The first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52 are arranged opposite to each other. Both the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52 have a pressurizing mechanism. By using the pressurizing mechanism of the electrodes (first high-frequency electric field applying electrode 51 and second high-frequency electric field applying electrode 52) of the dielectric heating device 50, pressure can be applied between the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52 to the first adherend 110, the high-frequency dielectric heating adhesive 1A, and the second adherend 120. That is, by using the dielectric heating device 50, a high-frequency electric field can be applied simultaneously while pressurizing two or more adherends and the high-frequency dielectric heating adhesive disposed between the electrodes.

[0200] In the case where a pair of flat plates are configured such that the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52 are parallel to each other, such an electrode configuration is sometimes referred to as a parallel flat plate type.

[0201] The application of the high-frequency electric field is preferably achieved using a parallel-plate type high-frequency dielectric heating device. In the case of a parallel-plate type high-frequency dielectric heating device, the high-frequency electric field penetrates the high-frequency dielectric heating adhesive located between the electrodes, thus heating the entire high-frequency dielectric heating adhesive and bonding the adhered material and the high-frequency dielectric heating adhesive in a short time. Furthermore, when manufacturing a laminated body as a structural structure, a parallel-plate type high-frequency dielectric heating device is preferred.

[0202] The high-frequency power supply 53, used to apply a high-frequency electric field, for example, at a frequency of about 13.56 MHz, about 27.12 MHz, or about 40.68 MHz, is connected to the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52, respectively.

[0203] like Figure 2 As shown, the dielectric heating device 50 performs dielectric heating treatment using a high-frequency dielectric heating adhesive 1A sandwiched between the first adherend 110 and the second adherend 120. In addition to dielectric heating treatment, the dielectric heating device 50 also bonds the first adherend 110 and the second adherend 120 by applying pressure using a first high-frequency electric field application electrode 51 and a second high-frequency electric field application electrode 52. It should be noted that it is also possible to bond two or more adherends together without applying pressure, for example, by compression based solely on the high-frequency dielectric heating adhesive and the weight of the adherends themselves.

[0204] When a high-frequency electric field is applied between the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52, the high-frequency dielectric heating adhesive 1A absorbs high-frequency energy. As a result, the thermoplastic resin component in the high-frequency dielectric heating adhesive 1A melts, and even with a short processing time, the first adherend 110 and the second adherend 120 can be firmly bonded together.

[0205] When a high-frequency electric field is applied between the first high-frequency electric field applying electrode 51 and the second high-frequency electric field applying electrode 52, the dielectric filler dispersed in the adhesive component of the high-frequency dielectric heating adhesive 1A absorbs high-frequency energy.

[0206] Then, the dielectric filler functions as a heat source, melting the thermoplastic resin components through the heating of the dielectric filler, and even with a short treatment time, the first adherend 110 and the second adherend 120 can be firmly bonded together.

[0207] The electrodes (first high-frequency electric field application electrode 51 and second high-frequency electric field application electrode 52) of the dielectric heating device 50 have a pressurizing mechanism, thus the dielectric heating device 50 also functions as a pressurizing device. Therefore, by applying pressure in the compression direction using the first high-frequency electric field application electrode 51 and the second high-frequency electric field application electrode 52, and by heating and melting the high-frequency dielectric heating adhesive 1A, the first adherend 110 and the second adherend 120 can be bonded more firmly. It should be noted that the manufacturing method of the structure is described in the following section. Figure 2 The present invention has been described using the example of structure 100, but is not limited to this example.

[0208] <High-frequency dielectric heating conditions>

[0209] The high-frequency dielectric heating conditions can be appropriately changed, and the following conditions are preferred.

[0210] The output power of the high-frequency electric field is preferably 10W or more, more preferably 30W or more, even more preferably 50W or more, and even more preferably 80W or more.

[0211] The output power of the high-frequency electric field is preferably 50,000W or less, more preferably 20,000W or less, even more preferably 15,000W or less, even more preferably 10,000W or less, and even more preferably 1,000W or less.

[0212] When the output power of the high-frequency electric field is above 10W, it can prevent the undesirable situation that the temperature is difficult to rise during dielectric heating treatment, thus making it easy to obtain good bonding strength.

[0213] When the output power of a high-frequency electric field is below 50,000 W, it is easier to prevent adverse conditions such as difficulty in temperature control caused by dielectric heating treatment. The output power of a high-frequency electric field represents the amount of energy transferred to the object.

[0214] The application time of the high-frequency electric field is preferably more than 1 second.

[0215] The application time of the high-frequency electric field is preferably 300 seconds or less, more preferably 240 seconds or less, even more preferably 180 seconds or less, even more preferably 120 seconds or less, even more preferably 90 seconds or less, even more preferably 50 seconds or less, even more preferably 20 seconds or less, particularly preferably 10 seconds or less, and very preferably 6 seconds or less.

[0216] When the high-frequency electric field is applied for more than 1 second, it can prevent the undesirable situation that the temperature is difficult to rise during dielectric heating treatment, thus making it easy to obtain good adhesion.

[0217] When the application time of the high-frequency electric field is less than 300 seconds, it is easy to prevent adverse conditions such as reduced manufacturing efficiency, increased manufacturing costs, and thermal degradation of the adhered material.

[0218] The frequency of the applied high-frequency electric field is preferably 1 MHz or more, more preferably 3 MHz or more, even more preferably 5 MHz or more, and even more preferably 10 MHz or more.

[0219] 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 even more preferably 50 MHz or less. Specifically, the industrial frequency bands of 13.56 MHz, 27.12 MHz, or 40.68 MHz allocated by the International Telecommunication Union can also be used in the manufacturing and bonding methods based on high-frequency dielectric heating in this embodiment. The frequency of the applied high-frequency electric field indicates the mode (speed) of energy transfer.

[0220] When applying a high-frequency electric field while performing pressurization, the initial setting value for the pressure loaded on the adhesive for high-frequency dielectric heating is preferably 1 kPa or more, more preferably 5 kPa or more, even more preferably 10 kPa or more, even more preferably 30 kPa or more, and particularly more preferably 50 kPa or more.

[0221] When applying a high-frequency electric field while performing pressurization, the initial setting value for the pressure loaded on the adhesive for high-frequency dielectric heating is preferably 10 MPa or less, more preferably 5 MPa or less, further preferably 1 MPa or less, and even more preferably 750 kPa or less.

[0222] Here, the area that serves as the reference for the initial setting value of the pressure loaded by the adhesive for high-frequency dielectric heating is the smallest area among the areas when viewed from above the electrode and the adhered object.

[0223] [Variations on the implementation method]

[0224] This invention is not limited to the above-described embodiments. This invention may include variations and improvements within the scope of achieving the purpose of this invention.

[0225] High-frequency dielectric heating is not limited to the dielectric heating device with oppositely arranged electrodes described in the above embodiments; a lattice electrode type high-frequency dielectric heating device can also be used. The lattice electrode type high-frequency dielectric heating device has lattice electrodes in which electrodes of a first polarity and electrodes of the opposite polarity to the first polarity are alternately arranged at regular intervals on the same plane. It should be noted that the accompanying drawings illustrate, for simplicity, a method of using a dielectric heating device with oppositely arranged electrodes.

[0226] Example

[0227] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments in any way.

[0228] [Preparation of adhesives for high-frequency dielectric heating]

[0229] <Examples 1-3 and Comparative Examples 1-3>

[0230] As materials for making adhesives (adhesive sheets) for high-frequency dielectric heating, thermoplastic resin (A) and dielectric filler (B) were weighed and made to reach the proportions shown in Table 1 on a volume basis.

[0231] Next, thermoplastic resin (A) and dielectric filler (B) were premixed under given conditions. The premixed material of thermoplastic resin (A) and dielectric filler (B) was fed into the hopper of a 30mm Φ twin-screw extruder, and the barrel and die were heated to a given temperature to melt-mix the premixed material. The melt-mixed material was cooled and then cut to produce granular granules. Next, the granules were fed into the hopper of a single-screw extruder equipped with a T-die, and the barrel and die were heated to a given temperature to extrude a film-like melt-mixed compound from the T-die. The compound was cooled using cooling rollers to produce sheet-like high-frequency dielectric heating adhesives (high-frequency dielectric heating adhesive sheets) with a thickness of 400μm for Examples 1-3 and Comparative Examples 1-3, respectively.

[0232] The thermoplastic resin (A) and dielectric filler (B) shown in Table 1 are described below.

[0233] (Thermoplastic resin (A))

[0234] (A1) r-PP: Polypropylene resin (manufactured by PRIME POLYMER, product name "PRIME POLYPRO F-744NP", density 0.90 g / cm³). 3 )

[0235] (Dielectric filler (B))

[0236] (B1) ZnO: Zinc oxide (manufactured by HAKUSUI TECH, product name "DW-4")

[0237] (B2) ZnO: Zinc oxide (manufactured by HAKUSUI TECH, product name "Sintered Zinc Oxide")

[0238] (B3)~(B5) ZnO: Zinc oxide (shape: irregular shape, ZnO granulated and then crushed, and adjusted to the particle size Dn shown in Table 2)

[0239] (B6) ZnO: Zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., product name "LPZINC11")

[0240] It should be noted that the zinc oxides (B1) to (B6) mentioned above are all zinc oxides without surface modification.

[0241] [Physical Property Evaluation of Adhesives for High-Frequency Dielectric Heating]

[0242] <Distance between nearest centroids Dg / Particle size Dn>

[0243] The high-frequency dielectric heating adhesive was cut along its thickness, and the cut surface of the adhesive sheet was ground using a cross-sectional ion polisher (manufactured by Nippon Electron Ltd., product name "SM-09010") as a cross-sectional processing device. Next, SEM images were obtained at 500x magnification using a SEM (Carl Zeiss Crossbeam 550). The obtained SEM images were then binarized using the Otsu binarization method in Python, resulting in binary images consisting of white and black values. Furthermore, the blobs obtained during binarization were detected as dielectric filler particles.

[0244] The equivalent circle diameters of over 100 dielectric filler particles were measured. The average number of these particles, calculated using the `numpy.mean` function, was taken as the particle size `Dn`. Additionally, the centroids of the dielectric filler particles were determined using the `OpenCV.moments` function. Next, a Delaunay plot connecting the determined centroids was created using the `OpenCV.Subdiv2D` function, and the three sides of the triangles in the plot were compared. The shortest side of each triangle was determined as the distance between the nearest adjacent centroids. Finally, the average of the distances between the more than 100 nearest adjacent centroids was taken as the distance between the nearest adjacent centroids `Dg`.

[0245] Next, based on the particle size Dn and the distance between the nearest centroids Dg obtained above, the ratio of the distance between the nearest centroids Dg to the particle size Dn is calculated (distance between the nearest centroids Dg / particle size Dn).

[0246] In Table 2, the particle size Dn is denoted as Dn, the distance between the nearest centroids Dg is denoted as Dg, and the ratio of the distance between the nearest centroids Dg to the particle size Dn is denoted as Dg / Dn.

[0247] <Dielectric Properties>

[0248] The fabricated high-frequency dielectric heating adhesive was cut into pieces 30 mm in length and 30 mm in width. For the cut adhesive pieces, a dielectric material testing fixture 16453A (Agilent Technologies) was mounted on an RF impedance / material analyzer E4991A (Agilent Technologies), and the relative permittivity (ε'r) and dielectric loss tangent (tanδ) were measured using the parallel plate method at 23°C and 40.68 MHz. Based on the measurement results, the dielectric property (tanδ / ε'r) was calculated.

[0249] <Heating rate>

[0250] Two glass fiber reinforced polypropylene resin boards (25 mm in length, 100 mm in width, and 1.5 mm in thickness) were prepared as the substrates. The fabricated high-frequency dielectric heating adhesive (adhesive sheet) was cut to a length of 25 mm and a width of 12.5 mm. The cut adhesive sheet was then placed between the two substrates and stacked.

[0251] The substrate and adhesive sheet, stacked as described above, are fixed between two electrodes of a high-frequency dielectric heating device (manufactured by Yamamoto Vinita, product name "YRP-400T-A"). Next, with the substrate fixed, an electric field is applied according to the high-frequency electric field application conditions described below to bond the adhesive sheet to the substrate. The sheet temperature is measured using a FLIR Systems Japan thermal imaging camera T860 at this time, and the application time and the temperature of the adhesive sheet are plotted to calculate the initial application time of 5 seconds and the heating rate. The pressing pressure during the application of the high-frequency electric field is the initial set value of the pressure applied to the adhesive sheet.

[0252] (Conditions for applying a high-frequency electric field)

[0253] Frequency: 40.68MHz

[0254] Output power: 100W

[0255] Application time: Maximum 30 seconds

[0256] Pressing pressure: 0.5MPa

[0257] <Volume Resistivity>

[0258] The fabricated high-frequency dielectric heating adhesive was cut into pieces 100 mm in length and 100 mm in width. The cut adhesive pieces were then placed at 23°C and 50% RH for 24 hours. Next, under the same conditions, the resistivity was measured using a ohmmeter (ADC Corporation, "Digital Ultra-High Resistance / Micro-Ammeter 5451") when a voltage of 200 V was applied.

[0259]

[0260]

[0261] Compared with the adhesive sheets of Comparative Examples 1 to 2, the adhesive sheets of Examples 1 to 3 all achieved a higher heating rate. Based on this result, it can be seen that, compared with the high-frequency dielectric heating adhesive of the comparative examples, the high-frequency dielectric heating adhesive of this embodiment, which satisfies the above mathematical formula (F1), can firmly bond to the substrate in a shorter time.

[0262] Furthermore, compared to the adhesive sheet of Comparative Example 3, the adhesive sheets of Examples 1 to 3 have higher volume resistivity. Based on this result, it can be concluded that, compared to the adhesive for high-frequency dielectric heating of the comparative examples, the adhesive for high-frequency dielectric heating of this embodiment, which satisfies the above mathematical formula (F1), can suppress electrical insulation breakdown during dielectric heating treatment.

[0263] Based on the above results, it can be confirmed that, compared with conventional high-frequency dielectric heating adhesives, the high-frequency dielectric heating adhesive of this embodiment can suppress electrical insulation breakdown during dielectric heating treatment and can firmly bond to the substrate in a shorter time.

Claims

1. A high-frequency dielectric heating adhesive, comprising a thermoplastic resin (A) and a dielectric filler (B), When the cross-section of the high-frequency dielectric heating adhesive cut along its thickness direction is observed using a scanning electron microscope, the relationship between the nearest centroid distance Dg of the dielectric filler (B) and the particle size Dn of the dielectric filler (B) satisfies the following mathematical formula (F1). 1.55≤Dg / Dn≤1.85···(F1).

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

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

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

5. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein, When the cross-section of the high-frequency dielectric heating adhesive was observed by scanning electron microscopy, the particle size Dn of the dielectric filler (B) was 1.0 μm or more and 4.0 μm or less.

6. The adhesive for high-frequency dielectric heating according to claim 1 or 2, wherein, When the cut surface of the high-frequency dielectric heating adhesive is observed along the thickness direction using a scanning electron microscope, the distance Dg between the nearest centroids of the dielectric filler (B) is more than 2.2 μm and less than 6.0 μm.

7. 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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