JP7615595B2 - Adhesive composition, foamable adhesive sheet, and method for producing article - Google Patents

Description

This disclosure relates to an adhesive composition, a foamable adhesive sheet, and a method for manufacturing an article using the same.

Adhesives that bond components together are used in a variety of fields, and many bonding methods are known.

In recent years, it has been proposed to use an adhesive sheet containing a foaming agent (foamable adhesive sheet) instead of a liquid adhesive. For example, Patent Document 1 discloses an adhesive sheet having an expandable adhesive layer on one or both sides of a substrate, the expandable adhesive layer containing an epoxy resin including a multifunctional epoxy resin, a phenolic resin as a curing agent, an imidazole-based compound as a curing catalyst, and a temperature-sensitive foaming agent.

International Publication No. 2016/163514 JP 2004-277458 A

A method of using a foamable adhesive sheet is known in which, for example, a foamable adhesive sheet is placed between components, and then the foamable adhesive sheet is foamed and cured to bond the components together. Since the adhesive layer of such a foamable adhesive sheet contains a curable resin and a curing agent, it is desirable that the sheet has high storage stability and good adhesion after foaming and curing. Furthermore, in order to enable transportation without refrigeration even in summer, and to suppress deterioration of foaming and adhesion after foaming and curing when the working environment is high temperature and high humidity, the sheet is also required to have high storage stability under high temperature and high humidity. However, when stored under high temperature and high humidity, the foaming property may decrease. In this case, depending on the size of the gap between the components, the gap between the components may not be filled, and the adhesion after foaming and curing may decrease.

Although it is not an adhesive composition used in a foamable adhesive sheet, it has been proposed to add a stabilizer to a one-liquid epoxy resin adhesive to improve storage stability. For example, Patent Document 2 discloses a one-liquid epoxy resin composition that contains an epoxy resin, a latent curing agent, finely divided crystalline alcohol, and a boric acid ester.

Generally, the storage stability of an adhesive is measured by observing the change in adhesive strength and viscosity when the adhesive is stored under certain conditions, but the storage stability of foamable adhesives used in foamable adhesive sheets, particularly the storage stability of foamable adhesives under high temperature and high humidity conditions, and in particular the adhesion and foaming properties of foamable adhesives after high temperature and high humidity conditions, has not been fully studied.

The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide an adhesive composition and a foamable adhesive sheet that can suppress the decrease in foamability after storage at high temperature and high humidity.

One embodiment of the present disclosure provides an adhesive composition that contains a curable resin, a curing agent, a borate ester, and a foaming agent, and the curing agent contains a compound that contains a nitrogen atom.

Another embodiment of the present disclosure provides an adhesive composition that contains a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound that contains a nitrogen atom.

Another embodiment of the present disclosure provides a foamable adhesive sheet having an adhesive layer containing a curable resin, a curing agent, a borate ester, and a foaming agent, the curing agent including a compound containing a nitrogen atom.

Another embodiment of the present disclosure provides a foamable adhesive sheet having an adhesive layer containing a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, in which at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom.

Another embodiment of the present disclosure provides a method for manufacturing an article, comprising a step of placing the foamable adhesive sheet between a first member and a second member, and a step of foaming and curing the foamable adhesive sheet to bond the first member and the second member.

The adhesive composition and foamable adhesive sheet disclosed herein have the effect of suppressing the decrease in foamability after storage at high temperature and high humidity.

1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing an example of a method for producing an article according to the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating a method for testing adhesiveness.

Below, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure can be implemented in many different forms, and should not be interpreted as being limited to the description of the embodiment exemplified below. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. In this specification and each figure, elements similar to those described above with respect to the previous figures are given the same reference numerals, and detailed explanations may be omitted as appropriate.

In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component in between. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface" is used, unless otherwise specified, to include both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component in between.

In this specification, "sheet" also includes materials called "films." In addition, "films" also includes materials called "sheets."

The adhesive composition, the foamable adhesive sheet, and the method for manufacturing an article using the same in this disclosure are described in detail below.

A. Adhesive Composition The adhesive composition according to the present disclosure has two embodiments, which will be described below separately.

I. First embodiment of adhesive composition A first embodiment of the adhesive composition in the present disclosure contains a curable resin, a curing agent, a borate ester, and a foaming agent, and the curing agent contains a compound containing a nitrogen atom.

In this embodiment, the curing agent containing a compound containing a nitrogen atom and the boric acid ester are contained, which improves storage stability under high temperature and high humidity conditions and suppresses the decrease in foaming property after storage at high temperature and high humidity. The reason for this is not clear, but it is thought to be as follows.

For example, when an adhesive composition contains a curable resin, a curing agent, and a foaming agent, it has poor storage stability under high temperature and high humidity conditions. If the curing reaction of the curable resin progresses during storage at high temperature and high humidity, the foaming of the foaming agent is suppressed by the part of the adhesive layer composed of this adhesive composition where the curing reaction of the curable resin has progressed during foaming and curing. This leads to smaller bubbles in the adhesive layer after foaming and curing, and a lower expansion ratio of the adhesive layer.

In contrast, when the adhesive composition contains a curable resin, a curing agent containing a compound containing a nitrogen atom, a borate ester, and a foaming agent, it is presumed that the borate ester coordinates with the nitrogen atom of the compound containing a nitrogen atom, which is the curing agent, thereby suppressing the activity of the compound containing a nitrogen atom, and as a result, the curing reaction of the curable resin is suppressed. This makes it possible to improve storage stability under high temperature and high humidity. Therefore, in an adhesive layer composed of such an adhesive composition, the curing reaction of the curable resin during storage at high temperature and high humidity is suppressed, so that during foaming and curing, the foaming of the foaming agent is not suppressed by the part where the curing reaction of the curable resin has progressed, and it is thought that a decrease in the foaming ratio of the adhesive layer can be suppressed.

In addition, in this embodiment, the curing agent containing a compound containing a nitrogen atom and the boric acid ester are contained, which improves storage stability under high temperature and high humidity conditions and also suppresses the decrease in adhesive strength after storage at high temperature and high humidity. The reason for this is not clear, but is thought to be as follows.

For example, if the adhesive composition has a relatively fast curing rate and a relatively low curing temperature, the curing reaction of the curable resin is likely to proceed during storage at high temperature and high humidity, and the adhesive strength of the adhesive layer made of the adhesive composition after foaming and curing after storage at high temperature and high humidity may decrease.

In contrast, when the adhesive composition contains a curable resin, a curing agent containing a compound containing a nitrogen atom, a borate ester, and a foaming agent, the storage stability under high temperature and high humidity can be improved as described above. Therefore, in an adhesive layer composed of such an adhesive composition, if the combination of the curable resin and the curing agent is such that the curing speed is relatively fast and the curing temperature is relatively low, the curing reaction of the curable resin during storage at high temperature and high humidity is suppressed, and it is thought that the decrease in adhesive strength after foaming and curing after storage at high temperature and high humidity can also be suppressed.

The components of the adhesive composition of this embodiment are described below.

1. Boric acid ester In the present embodiment, the boric acid ester is not particularly limited as long as it can suppress the activity of the compound containing a nitrogen atom contained in the curing agent, and examples thereof include trimethyl borate, triethyl borate, tripropyl borate, triisopropyl borate, tributyl borate, tripentyl borate, triallyl borate, trihexyl borate, trioctyl borate, triisooctyl borate, trinonyl borate, tridecyl borate, and tridodeca borate. sil, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tricyclohexyl borate, tribenzyl borate, tritolyl borate, triethanolamine borate, tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylenephenylene pyroborate, bis-2,2-dimethyltrimethylenepyroborate, tris(2-ethylhexyloxy)borane, bis(1,4,7,10-tetramethylphenyl)pyroborate, 2-(β-dimethylaminoisopropoxy)-4,5-dimethyl-1,3,2-dioxaborolane, 2-(β-diethylaminoethoxy)-4,4,6-trimethyl-1,3,2-dioxaborinane, 2-(β-dimethylaminoethoxy)-4,4,6-trimethyl-1,3,2-dioxaborinane, 2-(β-diisopropylaminoethoxy)-4,4,6-trimethyl-1,3,2-dioxaborinane, Examples of the boric acid ester include 2-(β-dimethylaminoethoxy)-1,3,2-dioxaborinane, 2-(β-diisopropylaminoethoxy)-4-methyl-1,3,2-dioxaborinane, 2-(γ-dimethylaminopropoxy)-1,3,6,9-tetrapyroxy-2-boracycloundecane, 2-(β-dimethylaminoethoxy)-4,4-(4-hydroxybutyl)-1,3,2-dioxaborinane, 2,2-oxybis(5,5-dimethyl-1,3,2-dioxabonaline), etc. One type of boric acid ester may be used alone, or two or more types may be used in combination.

The content of the borate ester is, for example, 0.01 parts by mass or more, may be 0.1 parts by mass or more, or may be 0.2 parts by mass or more, relative to 100 parts by mass of the resin component contained in the adhesive composition. If the content of the borate ester is too small, the effect of improving storage stability under high temperature and high humidity conditions may not be sufficiently obtained. On the other hand, the content of the borate ester is, for example, 9 parts by mass or less, may be 7 parts by mass or less, or may be 5 parts by mass or less, relative to 100 parts by mass of the resin component contained in the adhesive composition. If the content of the borate ester is too high, for example, when the borate ester is liquid at room temperature, blocking resistance may decrease.

2. Curing Agent The curing agent in this embodiment includes a compound containing a nitrogen atom.

The hardener is preferably a latent hardener. In this embodiment, a "latent hardener" is a component that is activated by an external stimulus such as heat, light, or moisture, and causes a hardening reaction with the hardenable resin, or can induce and/or accelerate the hardening reaction of the hardenable resin, but is substantially stable for a certain period of time when mixed with the hardenable resin in a state in which no specific external stimulus is applied.

If the latent curing agent is used, the curing reaction of the curable resin does not substantially occur for a certain period of time during storage of the adhesive composition, so that long-term storage is possible. A part or all of the temperature range in which the latent curing agent is at least substantially stable in a state in which no specific external stimuli are applied (hereinafter referred to as the "stable temperature range of the latent curing agent") may be included between -40°C and 80°C, or between -10°C and 30°C, from the viewpoint of facilitating storage of the adhesive composition. The adhesive composition may be stored while controlling the environment, such as temperature, humidity, and light, as necessary. In the adhesive composition, the stable temperature range of the latent curing agent includes room temperature, so that heating or cooling is not required during storage, improving the convenience of the adhesive composition. Room temperature refers to 23°C ± 2°C.

Examples of latent hardeners include heat latent hardeners, photo latent hardeners, and moisture latent hardeners. A "heat latent hardener" is a component that is activated by heat and can cause a hardening reaction with a hardening resin or can induce and/or accelerate the hardening reaction of a hardening resin, but is a component that is substantially stable for a certain period of time when mixed with a hardening resin at room temperature. A "photo latent hardener" is activated by irradiation with specific light such as ultraviolet light and can induce a hardening reaction of a hardening resin, but is a component that is substantially stable for a certain period of time when mixed with a hardening resin in the absence of specific light. A "moisture latent hardener" is a component that generates an active component such as an amine by hydrolysis and can cause a hardening reaction with a hardening resin, but is a component that is substantially stable for a certain period of time when mixed with a hardening resin in the absence of water.

The method of making the curing agent latent is not particularly limited, and examples include a method of reacting the active ingredient with another compound to form an adduct, and a method of masking the functional group of the active ingredient with a blocking agent. In addition, as a latent curing agent, a curing agent that is solid at room temperature and is insoluble or poorly soluble in the curable resin can be used.

Among these, thermally latent curing agents are preferred. Since many foaming agents undergo a foaming reaction when heated, thermally latent curing agents are efficient because they can cause the foaming reaction of the foaming agent and the curing reaction of the curable resin by the curing agent when heated. In addition, the use of a thermally latent curing agent can improve the heat resistance of the adhesive composition after it has been foamed and cured.

The curing agent may be, for example, a polyaddition type curing agent capable of undergoing a curing reaction with the curable resin, or a catalyst type curing agent capable of inducing and/or accelerating the curing reaction of the curable resin.

The reaction start temperature of the curing agent is, for example, 90°C, and may be 110°C or higher, or 130°C or higher. If the reaction start temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult. On the other hand, the reaction start temperature of the curing agent is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition to the compound containing nitrogen atoms, when a curing agent that can increase the heat resistance of the cured product, such as a phenolic curing agent, is used in combination as the curing agent, the resin component is less deteriorated, so the reaction start temperature of the curing agent may be, for example, 300°C or lower. The reaction start temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

It is preferable that the curing agent is a solid at 23°C. A curing agent that is a solid at 23°C can extend the storage stability (pot life) compared to a curing agent that is a liquid at 23°C.

As such a compound containing a nitrogen atom to be used as a hardener, hardeners generally used in adhesives can be used, and are selected appropriately depending on the type of hardenable resin.

(1) When the curable resin is an epoxy resin When the curable resin is an epoxy resin, specific examples of the compound containing a nitrogen atom contained in the curing agent include imidazole-based compounds, amine-based compounds, dicyandiamide-based compounds, hydrazide-based compounds, isocyanate-based compounds, guanidine-based compounds, biguanide-based compounds, urea-based compounds, melamine-based compounds, ketimine-based compounds, and diazonium salts.

Among these, examples of the thermal latent curing agent include imidazole compounds, amine compounds, dicyandiamide compounds, hydrazide compounds, isocyanate compounds, guanidine compounds, biguanide compounds, urea compounds, melamine compounds, ketimine compounds, diazonium salts, etc. The thermal latent curing agent may be used alone or in combination of two or more. For example, an imidazole compound and a dicyandiamide compound may be used in combination. In this case, the imidazole compound can function as a catalyst type curing agent and a curing accelerator for the dicyandiamide compound.

Examples of photolatent hardeners include diazonium salts. Photolatent hardeners may be used alone or in combination of two or more.

Examples of moisture-latent hardeners include ketimine-based compounds. Moisture-latent hardeners may be used alone or in combination of two or more types.

Examples of imidazole compounds include imidazole compounds, as well as imidazole adduct compounds such as carboxylates of imidazole compounds and reaction products of imidazole compounds and epoxy compounds.

It is also preferable that the imidazole compound has a hydroxyl group. Since crystallization occurs through hydrogen bonds between the hydroxyl groups, the reaction initiation temperature tends to be high.

As the amine compound, for example, any of primary amines, secondary amines, and tertiary amines can be used. In addition, as the amine compound, for example, aliphatic amines, aromatic amines, alicyclic amines, modified amines, amidoamines, polyamides, etc. can be mentioned. As the modified amine, for example, amine adduct compounds can be mentioned, and specifically, reaction products of amine compounds and epoxy compounds, reaction products of amine compounds and carboxylic acid compounds, reaction products of amine compounds and sulfonic acid compounds, reaction products of amine compounds and isocyanate compounds, reaction products of amine compounds and urea compounds, etc. can be mentioned. In the amine adduct compounds, as the amine compound, aliphatic amines, aromatic amines, alicyclic amines, heterocyclic amines, etc. can be used.

Examples of hydrazide compounds include organic acid hydrazide compounds.

Examples of isocyanate compounds include blocked isocyanate compounds.

Examples of urea compounds include aliphatic dimethylurea and aromatic dimethylurea.

Examples of diazonium salts include aromatic diazonium salts.

Among them, the curing agent is preferably an imidazole-based compound or a dicyandiamide-based compound, and it is more preferable to use an imidazole-based compound and a dicyandiamide-based compound in combination.

The content of the compound containing a nitrogen atom used as a curing agent is, for example, 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive composition. For example, when an imidazole-based compound is used as the main component of the curing agent, the content of the compound containing a nitrogen atom is preferably, for example, 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive composition. Note that using an imidazole-based compound as the main component of the curing agent means that the mass ratio of the imidazole-based compound is the highest in the curing agent.

(2) When the curable resin is a polyester resin or a polyol When the curable resin is a polyester resin or a polyol, a specific example of the compound containing a nitrogen atom contained in the curing agent is an isocyanate-based compound. The isocyanate-based compound may be the same as the isocyanate-based compound used when the curable resin is an epoxy resin.

(3) Other Components The curing agent may contain a compound containing a nitrogen atom, and may contain a compound other than the compound containing a nitrogen atom. As the compound other than the compound containing a nitrogen atom, a curing agent generally used in adhesives may be used, and may be appropriately selected depending on the type of curable resin.

3. Curable resin As the curable resin in this embodiment, a curable resin generally used as a base agent of a curable adhesive can be used. Examples of the curable resin include thermosetting resin and photocurable resin. Among them, thermosetting resin is preferable. Thermosetting resin can be applied even when the member does not have transparency, such as a metal member.

The curable resin is not particularly limited as long as it is a curable resin that can be cured by the above-mentioned curing agent, and examples thereof include epoxy resin, polyester resin, polyol, etc.

Among them, the curable resin is preferably an epoxy resin. In general, adhesive compositions containing an epoxy resin as the main component have excellent mechanical strength, heat resistance, insulating properties, chemical resistance, etc., have little shrinkage upon curing, and can be used for a wide range of applications.

The epoxy resin in this embodiment is a compound that has one or more epoxy groups or glycidyl groups and hardens by a crosslinking polymerization reaction when used in combination with a curing agent. Epoxy resins also include monomers that have at least one epoxy group or glycidyl group.

Epoxy resins include, for example, aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine-nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. Modified silicone resins containing epoxy groups may also be used as the epoxy resin. The epoxy resin may be one type or two or more types.

Bisphenol A type epoxy resins can exist in a liquid state at room temperature or in a solid state at room temperature, depending on the number of repeating units in the bisphenol skeleton. Bisphenol A type epoxy resins in which the main chain has 2 or more and 10 or less bisphenol skeletons are solid at room temperature. Bisphenol A type epoxy resins are particularly preferred because they can improve heat resistance.

The epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

A polyol is a compound having two or more hydroxyl groups. Examples of polyols include polyolefin polyols such as polyethylene polyol and polypropylene polyol, and acrylic polyol.

4. Foaming agent In this embodiment, the foaming agent may be any foaming agent generally used in the adhesive layer of a foamable adhesive sheet. The foaming agent may be a foaming agent that undergoes a foaming reaction due to heat or a foaming agent that undergoes a foaming reaction due to light.

The foaming start temperature of the foaming agent is preferably equal to or higher than the softening temperature of the curable resin and equal to or lower than the activation temperature of the curing reaction of the curable resin. The foaming start temperature of the foaming agent is, for example, equal to or higher than 70°C, and may be equal to or higher than 100°C. If the foaming start temperature is too low, foaming starts early, and foaming occurs in a state where the flexibility and fluidity of the resin component are low, and it may be difficult to produce uniform foaming. On the other hand, the foaming start temperature of the foaming agent is, for example, equal to or lower than 210°C. If the foaming start temperature is too high, the resin component may deteriorate.

The softening temperature of the curable resin can be measured using the ring and ball softening temperature test method specified in JIS K 2207.

The foaming agent may be, for example, a microcapsule type foaming agent. The microcapsule type foaming agent preferably has a core of a thermal expansion agent such as a hydrocarbon and a shell of a resin such as an acrylonitrile copolymer.

As the foaming agent, for example, organic foaming agents or inorganic foaming agents may be used. Examples of organic foaming agents include azo foaming agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, fluorinated alkane foaming agents such as trichloromonofluoromethane, hydrazine foaming agents such as paratoluenesulfonylhydrazide, semicarbazide foaming agents such as p-toluenesulfonylsemicarbazide, triazole foaming agents such as 5-morpholyl-1,2,3,4-thiatriazole, and N-nitroso foaming agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of inorganic foaming agents include ammonium carbonate, ammonium hydrogen carbonate, ammonium nitrite, ammonium borohydride, and azides.

The foaming agent may be used alone or in combination of two or more.

Among them, it is preferable that the foaming agent is a microcapsule type foaming agent.

The content of the foaming agent is appropriately set according to the desired expansion ratio and the strength and adhesive force required for the adhesive layer after foaming and curing. The content of the foaming agent is, for example, 0.5 parts by mass or more, and may be 2 parts by mass or more, per 100 parts by mass of the resin component contained in the adhesive composition. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, and may be 20 parts by mass or less, or may be 15 parts by mass or less, per 100 parts by mass of the resin component contained in the adhesive composition.

5. Other components (1) Acrylic resin The adhesive composition of this embodiment may further contain an acrylic resin compatible with the epoxy resin as a resin component, for example, when the curable resin is an epoxy resin. Since the acrylic resin is compatible with the epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, it is considered that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell part is an acrylonitrile copolymer resin), and uniformly disperses and foams, thereby improving the adhesiveness after foaming and curing. In addition, the hardness of the adhesive layer surface can be kept high by the compatibility of the acrylic resin with the epoxy resin. On the other hand, if the acrylic resin is incompatible with the epoxy resin, when the adhesive layer is formed using the adhesive composition, a soft portion is formed on the adhesive layer surface, making the interface with the adherend less slippery, which may reduce workability.

The acrylic resin in this embodiment is compatible with the epoxy resin. Here, the compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by the absence of micron-sized islands when an adhesive layer is formed using the adhesive composition and the cross section of the adhesive layer is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). More specifically, the average particle size of the islands is preferably 1 μm or less. In particular, the average particle size of the islands may be 0.5 μm or less, or may be 0.3 μm or less. It is preferable to have a large number of samples, for example 100 or more. The area to be observed is in the range of 100 μm x 100 μm, or in the case where the average thickness of the adhesive layer is 100 μm or less, in the range of the average thickness x 100 μm.

The acrylic resin may have a polar group. Examples of the polar group include an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, and an amide group.

The acrylic resin may be a homopolymer of an acrylic acid ester monomer, a mixed component containing two or more of the above homopolymers, or a copolymer of two or more of the acrylic acid ester monomers, containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The concept of methacrylic acid is also included in the "acrylic acid" of the acrylic acid ester monomer. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Among them, it is preferable that the acrylic resin contains a copolymer of two or more acrylic acid ester monomers ((meth)acrylic acid ester copolymer).

Examples of the monomer components constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer components may have the polar groups described above. Examples of the (meth)acrylic acid ester copolymer include ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, and butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

The above-mentioned (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an acrylic block copolymer such as a methacrylate-acrylate copolymer. Examples of (meth)acrylates constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzidyl acrylate. These "acrylic acids" also include "methacrylic acid."

Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymer. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

The acrylic copolymer may not have polar groups, or may be a modified product in which the above-mentioned polar groups have been introduced into a portion of the acrylic copolymer. The modified product is easily compatible with epoxy resins, and therefore has improved adhesive properties.

Among them, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion having a glass transition temperature (Tg) of 10°C or less and a second polymer portion having a glass transition temperature (Tg) of 20°C or more. Such a (meth)acrylic acid ester copolymer has a first polymer portion that is a soft segment and a second polymer portion that is a hard segment.

The manifestation of the above effect can be presumed as follows: By using an acrylic resin that has both soft and hard segments, such as the above (meth)acrylic acid ester copolymer, the hard segments contribute to heat resistance, and the soft segments contribute to toughness and flexibility, resulting in an adhesive layer with good heat resistance, toughness, and flexibility.

At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer has compatibility with epoxy resins. When the first polymer portion has compatibility with epoxy resins, flexibility can be increased. When the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

Among these, the (meth)acrylic acid ester copolymer is preferably a block copolymer, and is particularly preferably an A-B-A block copolymer in which the compatible portion is polymer block A and the incompatible portion is polymer block B. Furthermore, it is more preferably an A-B-A block copolymer in which the first polymer portion is the incompatible portion and the second polymer portion is the compatible portion, and the first polymer portion is polymer block B and the second polymer portion is polymer block A.

The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a portion of the first polymer portion or the second polymer portion.

A specific example of a (meth)acrylic acid ester copolymer having the above-mentioned first polymer portion and second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

The content of the acrylic resin is, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, or 10 parts by mass or more, when the resin components contained in the adhesive composition are taken as 100 parts by mass. On the other hand, the content of the acrylic resin is, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, when the resin components contained in the adhesive composition are taken as 100 parts by mass.

The total ratio of epoxy resin and acrylic resin to the resin components contained in the adhesive composition is, for example, 70% by mass or more, may be 80% by mass or more, may be 90% by mass or more, or may be 100% by mass.

(2) Others In the adhesive composition of this embodiment, for example, when the curable resin is an epoxy resin, the resin component may further contain, in addition to the epoxy resin and the acrylic resin, another resin, such as a urethane resin.

The proportion of the resin component in the solid content of the adhesive composition is, for example, 60% by mass or more, or may be 70% by mass or more, 80% by mass or more, or may be 90% by mass or more.

The adhesive composition may contain, as necessary, for example, a silane coupling agent, a filler, an antioxidant, a light stabilizer, an ultraviolet absorber, a lubricant, a plasticizer, an antistatic agent, a crosslinking agent, and a colorant. Examples of the silane coupling agent include epoxy-based silane coupling agents. Examples of the filler include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of the antioxidant include phenol-based antioxidants and sulfur-based antioxidants.

The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. The solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

6. Adhesive composition The adhesive composition of this embodiment can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary.As a mixing and dispersing method, a general kneading and dispersing machine, for example, a two-roll mill, a three-roll mill, a pebble mill, a tron mill, a Szegvari attritor, a high-speed impeller dispersing machine, a high-speed stone mill, a high-speed impact mill, a disperser, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a disperser, a homogenizer, or an ultrasonic dispersing machine can be used.

The use of the adhesive composition of this embodiment is not particularly limited, but it is preferably used in the adhesive layer of a foamable adhesive sheet. The adhesive composition of this embodiment may also be used as an adhesive as it is.

II. Second embodiment of adhesive composition A second embodiment of the adhesive composition in the present disclosure contains a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom.

In this embodiment, at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom, and the adhesive composition contains a boric acid ester, which improves storage stability under high temperature and high humidity conditions and suppresses a decrease in foaming property after storage at high temperature and high humidity. The reason for this is not clear, but is thought to be as follows.

For example, when an adhesive composition contains a curable resin, a curing agent, a curing accelerator, and a foaming agent, it has poor storage stability under high temperature and high humidity conditions. If the curing reaction of the curable resin progresses during storage at high temperature and high humidity, the foaming of the foaming agent is suppressed by the part of the adhesive layer composed of this adhesive composition where the curing reaction of the curable resin has progressed during foaming and curing. This leads to smaller bubbles in the adhesive layer after foaming and curing, and a lower expansion ratio of the adhesive layer.

In contrast, when the adhesive composition contains a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom, the borate ester coordinates with the nitrogen atom of the compound containing a nitrogen atom, which is at least one of the curing agent and the curing accelerator, thereby suppressing the activity of the compound containing a nitrogen atom, and as a result, it is presumed that the curing reaction of the curable resin is suppressed. This makes it possible to improve storage stability under high temperature and high humidity. Therefore, in an adhesive layer composed of such an adhesive composition, the curing reaction of the curable resin during storage at high temperature and high humidity is suppressed, so that during foaming and curing, the foaming of the foaming agent is not suppressed by the part where the curing reaction of the curable resin has progressed, and it is thought that a decrease in the foaming ratio of the adhesive layer can be suppressed.

In addition, in this embodiment, at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom, and the adhesive composition contains a boric acid ester, which improves storage stability under high temperature and high humidity conditions and suppresses a decrease in adhesive strength after storage at high temperature and high humidity. The reason for this is not clear, but is thought to be as follows.

For example, when the adhesive composition contains a curing agent and a curing accelerator, the curing reaction can be accelerated by relatively fast curing speed and relatively low curing temperature. In such a case, however, the curing reaction of the curable resin may be more likely to proceed during storage at high temperature and high humidity, and the adhesive strength of the adhesive layer made of the adhesive composition after foaming and curing after storage at high temperature and high humidity may decrease.

In contrast, when the adhesive composition contains a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom, the storage stability under high temperature and high humidity can be improved as described above. Therefore, in an adhesive layer composed of such an adhesive composition, if the combination of the curable resin, the curing agent, and the curing accelerator results in a relatively fast curing speed and a relatively low curing temperature, the curing reaction of the curable resin during storage at high temperature and high humidity is suppressed, and it is thought that the decrease in adhesive strength after foaming and curing after storage at high temperature and high humidity can also be suppressed.

The components of the adhesive composition of this embodiment are described below.

1. Boric acid ester In this embodiment, the boric acid ester is not particularly limited as long as it can suppress the activity of the compound containing nitrogen atoms contained in at least one of the curing agent and the curing accelerator.Specific examples of the boric acid ester can be the same as the boric acid ester in the first embodiment.The boric acid ester may be used alone or in combination of two or more kinds.

The content of the borate ester may also be the same as that in the first embodiment.

2. Curing agent and curing accelerator In this embodiment, at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom. Of the curing agent and the curing accelerator, only the curing agent may contain a compound containing a nitrogen atom, only the curing accelerator may contain a compound containing a nitrogen atom, or both the curing agent and the curing accelerator may contain a compound containing a nitrogen atom. Each case will be described below.

(1) First Aspect The first aspect of the curing agent and the curing accelerator is a case where only the curing agent contains a compound containing a nitrogen atom.

In this embodiment, it is preferable that the curing agent is a latent curing agent, or that the curing agent is a latent curing agent and the curing accelerator is a latent curing accelerator, or that the reaction between the curable resin and the curing agent exhibits latency and the curing accelerator is a latent curing agent, or that the curing agent does not exhibit latency and the curing accelerator is a latent curing accelerator.

Examples of latent hardeners include heat latent hardeners, light latent hardeners, and moisture latent hardeners.

Examples of latent curing accelerators include heat latent curing accelerators, photo latent curing accelerators, and moisture latent curing accelerators. A "heat latent curing accelerator" is activated by heat and can accelerate the curing reaction of a curable resin, but is a substantially stable component for a certain period of time when mixed with a curable resin and a curing agent at room temperature. A "photo latent curing accelerator" is activated by irradiation with specific light such as ultraviolet light and can accelerate the curing reaction of a curable resin, but is a substantially stable component for a certain period of time when mixed with a curable resin and a curing agent in a state where no specific light is irradiated. A "moisture latent curing accelerator" generates an active component such as an amine by hydrolysis and can accelerate the curing reaction of a curable resin, but is a substantially stable component for a certain period of time when mixed with a curable resin and a curing agent in a state where no water is present.

In this embodiment, "the reaction between the curable resin and the curing agent shows latency" means that a curing reaction between the curable resin and the curing agent can occur in the presence of a curing accelerator, but in the absence of a curing accelerator, the mixture of the curable resin and the curing agent is substantially stable for a certain period of time.

When the curing agent is a latent curing agent, or when the curing agent is a latent curing agent and the curing accelerator is a latent curing accelerator, or when the reaction between the curable resin and the curing agent is latent and the curing accelerator is a latent curing agent, or when the curing agent does not exhibit latency and the curing accelerator is a latent curing accelerator, the curing reaction of the curable resin does not substantially occur for a certain period of time during storage of the adhesive composition, and therefore long-term storage is possible.

A part or all of the temperature range in which the latent curing agent is at least substantially stable (hereinafter referred to as the "stable temperature range of the latent curing accelerator") may be within the range of -40°C to 80°C, or within the range of -10°C to 30°C, from the viewpoint of facilitating storage of the adhesive composition. In the adhesive composition, the stable temperature range of the latent curing agent includes room temperature, which eliminates the need for heating or cooling during storage, improving the convenience of the adhesive composition.

In addition, a part or all of the temperature range in which the latent curing accelerator is at least substantially stable (hereinafter referred to as the "stable temperature range of the latent curing accelerator") may be included in the range of -40°C to 80°C, or may be included in the range of -10°C to 30°C, from the viewpoint of facilitating storage of the adhesive composition. In the adhesive composition, the stable temperature range of the latent curing accelerator includes room temperature, which eliminates the need for heating or cooling during storage, thereby improving the convenience of the adhesive composition.

Methods for making a curing agent latent are not particularly limited, and examples include a method of reacting an active ingredient with another compound to form an adduct, a method of microencapsulating an active ingredient, a method of including an active ingredient as a guest in a host, and a method of masking a functional group of an active ingredient with a blocking agent. In addition, as a latent curing agent, a curing agent that is solid at room temperature and is insoluble or poorly soluble in a curable resin can be used.

The method of making the curing accelerator latent is not particularly limited, and examples thereof include a method of reacting the active ingredient with another compound to form an adduct, a method of microencapsulating the active ingredient, a method of including the active ingredient as a guest in a host, and a method of masking the functional group of the active ingredient with a blocking agent. In addition, as a latent curing accelerator, a curing accelerator that is solid at room temperature and is insoluble or poorly soluble in the curable resin can be used.

Among them, the latent curing agent is preferably a thermal latent curing agent. Also, the latent curing accelerator is preferably a thermal latent curing accelerator.

(a) Curing Agent In this embodiment, the curing agent includes a compound containing a nitrogen atom.

In this embodiment, the curing agent is not particularly limited as long as it contains a compound containing a nitrogen atom and can be used in combination with the curing accelerator described below. Curing agents generally used in adhesives can be used, and are appropriately selected depending on the type of curable resin.

The characteristics, specific examples, content, etc. of the curing agent can be the same as those of the curing agent in the first embodiment above, so a description thereof will be omitted here.

In addition, when the curable resin is an epoxy resin and the curing agent contains an imidazole compound and a compound other than an imidazole compound as a compound containing nitrogen atoms, the imidazole compound may be an inclusion compound with an imidazole compound as a guest, or a microencapsulated imidazole compound in which an imidazole compound is microencapsulated. In addition, when the curable resin is an epoxy resin and the curing agent contains an amine compound and a compound other than an amine compound as a compound containing nitrogen atoms, the amine compound may be an inclusion compound with an amine compound as a guest, or a microencapsulated amine compound in which an amine compound is microencapsulated.

For example, when the curable resin is an epoxy resin, from the viewpoints of heat resistance and latency, the curing agent is preferably an imidazole-based compound, an amine-based compound, or a dicyandiamide-based compound, and more preferably a dicyandiamide-based compound.

(b) Curing Accelerator In this embodiment, the curing accelerator does not include a compound containing a nitrogen atom.

The reaction start temperature of the curing accelerator is, for example, 90°C or higher, may be 110°C or higher, or may be 130°C or higher. If the reaction start temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult to occur. On the other hand, the reaction start temperature of the curing accelerator is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition to the compound containing nitrogen atoms, when a curing agent that can increase the heat resistance of the cured product, such as a phenolic curing agent, is used in combination as the curing agent, the resin component is less deteriorated, so the reaction start temperature of the curing accelerator may be, for example, 300°C or lower. The reaction start temperature of the curing accelerator can be determined by differential scanning calorimetry (DSC).

It is preferable that the curing accelerator is a solid at 23°C. A curing accelerator that is a solid at 23°C can extend the storage stability (pot life) compared to a curing agent that is a liquid at 23°C.

Such a curing accelerator is not particularly limited as long as it can be used in combination with the above-mentioned curing agent, and curing accelerators generally used in adhesives can be used, and are selected appropriately depending on the type of curable resin.

When the curable resin is an epoxy resin, a polyester resin, or a polyol, the curing accelerator may be any compound other than a compound containing a nitrogen atom, such as a phosphorus-based compound, a thiol-based compound, or a metal chelate-based compound. The curing accelerator may be used alone or in combination of two or more types.

The content of the curing accelerator is, for example, 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive composition.

(2) Second Aspect The second aspect of the curing agent and the curing accelerator is a case where only the curing accelerator contains a compound containing a nitrogen atom.

In this embodiment, it is preferable that the curing agent is a latent curing agent, or that the curing agent is a latent curing agent and the curing accelerator is a latent curing accelerator, or that the reaction between the curable resin and the curing agent exhibits latency and that the curing accelerator is a latent curing agent.

(a) Curing Agent In this embodiment, the curing agent does not include a compound containing a nitrogen atom.

In this embodiment, the curing agent is not particularly limited as long as it does not contain a compound containing a nitrogen atom and can be used in combination with the curing accelerator described below. Curing agents generally used in adhesives can be used, and are appropriately selected depending on the type of curable resin.

The reaction start temperature of the curing agent is, for example, 90°C or higher, may be 110°C or higher, or may be 130°C or higher. If the reaction start temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult. On the other hand, the reaction start temperature of the curing agent is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition, when using a curing agent that can increase the heat resistance of the cured product, such as a phenol-based curing agent, the resin component is less likely to deteriorate, so the reaction start temperature of the curing agent may be, for example, 300°C or lower. The reaction start temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

It is preferable that the curing agent is a solid at 23°C. A curing agent that is a solid at 23°C can extend the storage stability (pot life) compared to a curing agent that is a liquid at 23°C.

(i) When the curable resin is an epoxy resin When the curable resin is an epoxy resin, the curing agent may be any compound other than a compound containing a nitrogen atom, such as a phenol-based curing agent, an acid anhydride-based curing agent, a thiol-based curing agent, etc. The curing agent may be used alone or in combination of two or more kinds.

Examples of phenol-based hardeners include phenol resins. Further, examples of phenol resins include resol-type phenol resins and novolac-type phenol resins.

From the viewpoint of heat resistance, the phenolic resin is preferably a biphenyl type. The phenolic resin may also be a resin in which the phenol nucleus has been modified. By modifying the phenol nucleus, for example, it is possible to further improve heat resistance.

Examples of acid anhydride curing agents include alicyclic acid anhydrides and aromatic acid anhydrides.

Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

Among them, it is preferable that the curing agent is a phenol-based curing agent, which can improve heat resistance.

The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, when the resin component contained in the adhesive composition is taken as 100 parts by mass. For example, when a phenol-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 3 parts by mass or more and 40 parts by mass or less, when the resin component contained in the adhesive composition is taken as 100 parts by mass. Note that using a phenol-based curing agent as the main component of the curing agent means that the mass ratio of the phenol-based curing agent is the highest in the curing agent.

(ii) When the curable resin is a polyester resin or a polyol When the curable resin is a polyester resin or a polyol, the curing agent may be any compound other than a compound containing a nitrogen atom, such as an organic peroxide. The curing agent may be used alone or in combination of two or more kinds.

(b) Curing Accelerator In this embodiment, the curing accelerator includes a compound containing a nitrogen atom.

The reaction start temperature of the curing accelerator is, for example, 90°C or higher, may be 110°C or higher, or may be 130°C or higher. If the reaction start temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult. On the other hand, the reaction start temperature of the curing accelerator is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition, when using a curing agent that can increase the heat resistance of the cured product, such as a phenol-based curing agent, the resin component is less deteriorated, so the reaction start temperature of the curing accelerator may be, for example, 300°C or lower. The reaction start temperature of the curing accelerator can be determined by differential scanning calorimetry (DSC).

It is preferable that the curing accelerator is a solid at 23°C. A curing accelerator that is a solid at 23°C can extend the storage stability (pot life) compared to a curing agent that is a liquid at 23°C.

The nitrogen atom-containing compound used as such a curing accelerator is not particularly limited as long as it is a curing accelerator that can be used in combination with the above-mentioned curing agent, and curing accelerators that are generally used in adhesives can be used, and are selected appropriately depending on the type of curable resin.

(i) When the curable resin is an epoxy resin When the curable resin is an epoxy resin, specific examples of the compound containing a nitrogen atom contained in the curing accelerator include imidazole-based compounds, amine-based compounds, urea-based compounds, etc. The curing accelerator may be used alone or in combination of two or more types.

Examples of imidazole compounds include imidazole compounds, carboxylates of imidazole compounds, and imidazole adduct compounds such as reaction products of imidazole compounds and epoxy compounds. In addition, when the curing accelerator contains an imidazole compound and a compound other than an imidazole compound as a compound containing a nitrogen atom, the imidazole compound may be an inclusion compound having an imidazole compound as a guest, or a microencapsulated imidazole compound in which an imidazole compound is microencapsulated.

It is also preferable that the imidazole compound has a hydroxyl group. Since crystallization occurs through hydrogen bonds between the hydroxyl groups, the reaction initiation temperature tends to be high.

As the amine compound, for example, a tertiary amine can be used. In addition, as the amine compound, for example, an aliphatic amine, an aromatic amine, an alicyclic amine, an amidoamine, etc. can be used. In addition, when the curing accelerator contains an amine compound and a compound other than an amine compound as a compound containing a nitrogen atom, as the amine compound, an inclusion compound having an amine compound as a guest or a microencapsulated amine compound in which an amine compound is microencapsulated may be used.

Examples of urea compounds include aliphatic dimethylurea and aromatic dimethylurea.

Among them, it is preferable that the curing accelerator is an imidazole-based compound.

The content of the compound containing a nitrogen atom used as a curing accelerator is, for example, 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive composition. For example, when an imidazole-based compound is used as the main component of the curing accelerator, the content of the compound containing a nitrogen atom is preferably, for example, 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive composition. Note that using an imidazole-based compound as the main component of the curing accelerator means that the mass ratio of the imidazole-based curing agent is the highest in the curing accelerator.

(ii) When the curable resin is a polyester resin or a polyol When the curable resin is a polyester resin or a polyol, a specific example of the compound containing a nitrogen atom contained in the curing accelerator is an amine compound. The amine compound can be the same as the amine compound used when the curable resin is an epoxy resin. The curing accelerator may be used alone or in combination of two or more kinds.

(iii) Other components The curing accelerator may contain a compound containing a nitrogen atom, and may contain a compound other than the compound containing a nitrogen atom. As the compound other than the compound containing a nitrogen atom, a curing accelerator generally used in adhesives can be used, and is appropriately selected according to the type of curable resin.

(3) Third Aspect The third aspect of the curing agent and the curing accelerator is a case where both the curing agent and the curing accelerator contain a compound containing a nitrogen atom.

In this embodiment, as in the first embodiment, it is preferable that the curing agent is a latent curing agent, or that the curing agent is a latent curing agent and the curing accelerator is a latent curing accelerator, or that the reaction between the curable resin and the curing agent exhibits latency and the curing accelerator is a latent curing agent, or that the curing agent does not exhibit latency and the curing accelerator is a latent curing accelerator.

(a) Curing Agent In this embodiment, the curing agent includes a compound containing a nitrogen atom.

In this embodiment, the curing agent is not particularly limited as long as it contains a compound containing a nitrogen atom and can be used in combination with the curing accelerator described below. Curing agents generally used in adhesives can be used, and are appropriately selected depending on the type of curable resin.

The characteristics, specific examples, content, etc. of the curing agent can be the same as those of the curing agent in the first embodiment described above, so a description thereof will be omitted here.

For example, when the curable resin is an epoxy resin, from the viewpoints of heat resistance and latency, it is preferable that the curing agent is a dicyandiamide-based compound.

(b) Curing Accelerator In this embodiment, the curing accelerator includes a compound containing a nitrogen atom.

In this embodiment, the curing accelerator is not particularly limited as long as it contains a compound containing a nitrogen atom and can be used in combination with the above curing agent, and curing accelerators that are generally used in adhesives can be used and are appropriately selected depending on the type of curable resin.

The properties, specific examples, content, etc. of the curing accelerator can be the same as those of the curing accelerator in the second embodiment described above, so a description thereof will be omitted here.

For example, when the curable resin is an epoxy resin, the curing accelerator is preferably an imidazole-based compound.

For example, when the curable resin is a polyester resin or a polyol, an isocyanate-based compound can be used as the curing agent, and an amine-based compound such as a tertiary amine can be used as the curing accelerator.

4. Curable Resin The curable resin in this embodiment may be the same as the curable resin in the first embodiment.

5. Foaming Agent The foaming agent in this embodiment may be the same as the foaming agent in the first embodiment.

6. Other Components Other components in this embodiment may be similar to those in the first embodiment.

7. Adhesive Composition The preparation method and use of the adhesive composition in this embodiment can be the same as those in the first embodiment.

B. Foamable Adhesive Sheet The foamable adhesive sheet according to the present disclosure has two embodiments, which will be described below separately.

I. First embodiment of the foamable adhesive sheet A first embodiment of the foamable adhesive sheet in the present disclosure includes a curable resin, a curing agent, a boric acid ester, and a foaming agent, and the curing agent has an adhesive layer containing a compound containing a nitrogen atom.

Figures 1 to 3 are schematic cross-sectional views illustrating the foamable adhesive sheet of this embodiment. The foamable adhesive sheet 10 in Figure 1 has only an adhesive layer 1. The foamable adhesive sheet 10 in Figure 2 has a substrate 2 and an adhesive layer 1 disposed on one side of the substrate 2. The foamable adhesive sheet 10 in Figure 3 has a substrate 2 and a first adhesive layer 1a disposed on one side of the substrate 2 and a second adhesive layer 1b disposed on the other side of the substrate 2. The adhesive layer 1, the first adhesive layer 1a and the second adhesive layer 1b contain a curable resin, a curing agent, a boric acid ester and a foaming agent, and the curing agent contains a compound containing a nitrogen atom.

In this embodiment, the adhesive layer contains a curing agent containing a compound containing a nitrogen atom and a boric acid ester, which improves storage stability under high temperature and high humidity conditions and suppresses a decrease in foaming property after storage at high temperature and high humidity. Furthermore, it is possible to suppress a decrease in adhesion after storage at high temperature and high humidity.

The components of the foamable adhesive sheet of this embodiment are described below.

1. Adhesive layer The adhesive layer in this embodiment contains a curable resin, a curing agent, a borate ester, and a foaming agent, and the curing agent contains a compound containing a nitrogen atom. Note that these materials are the same as those described in "A. Adhesive composition I. First embodiment of adhesive composition" above, so the description here is omitted.

The adhesive layer can be foamed at an expansion ratio of, for example, 1.5 times or more and 15 times or less. The expansion ratio may be, for example, 3 times or more and 10 times or less.

Here, the expansion ratio can be calculated by the following formula.
Expansion ratio (times) = thickness of adhesive layer after foaming and hardening / thickness of adhesive layer before foaming and hardening

The thickness of the adhesive layer is not particularly limited, but may be, for example, 10 μm or more, and may be 20 μm or more. If the adhesive layer is too thin, sufficient adhesion may not be obtained after foaming and hardening. On the other hand, the thickness of the adhesive layer is, for example, 200 μm or less.

The thickness of the adhesive layer can be the average value of the thicknesses at any 10 locations obtained by measuring a cross section of the foamable adhesive sheet in the thickness direction observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM). The same method can be used to measure the average thickness of other layers of the foamable adhesive sheet.

The adhesive layer is preferably substantially non-adhesive (tack-free). In this case, it is preferable that the adhesive layer is disposed on the outermost surface. By making the adhesive layer substantially non-adhesive (tack-free), it is possible to obtain a foamable adhesive sheet with good slip properties and blocking resistance. This can improve the handleability and workability of the foamable adhesive sheet.

Here, non-adhesive is generally used to mean low adhesive strength, and in this disclosure, "non-adhesive" refers to a state in which the foamable adhesive sheet can be wound into a roll and then easily unwound without resistance.

When the adhesive layer is substantially non-adhesive, specifically, the adhesive strength of the adhesive layer is preferably 0 N/25 mm or more and 0.1 N/25 mm or less. By having the adhesive strength of the adhesive layer within the above range, the adhesive layer can be made substantially non-adhesive, and a foamable adhesive sheet with good slip properties and blocking resistance can be obtained.

When adhesive layers are disposed on both sides of the substrate, it is sufficient that the adhesive strength of at least one of the adhesive layers is within the above range. For example, when a foamable adhesive sheet is disposed between components to bond the components together, the foamable adhesive sheet may be disposed on one of the components first, and then the other component may be inserted into the gap left after the foamable adhesive sheet has been disposed on the one component. In such a case, when inserting the other component into the gap left after the foamable adhesive sheet has been disposed on one component, it is sufficient that the surface of the foamable adhesive sheet that comes into contact with the other component has good slip properties. Therefore, it is sufficient that the adhesive strength of at least one of the adhesive layers is within the above range.

When adhesive layers are disposed on both sides of the substrate, for example, the adhesive strength of either one of the adhesive layers may be within the above range, or the adhesive strength of both adhesive layers may be within the above range, but it is particularly preferable that the adhesive strength of both adhesive layers is within the above range.

The adhesive strength of the adhesive layer can be measured in accordance with JIS Z0237:2009 (Test methods for adhesive tapes and adhesive sheets) and Method 1 of the adhesive strength test method (a test method in which the tape or sheet is peeled off at 180° from a stainless steel test plate at a temperature of 23°C and a humidity of 50%).

In the present disclosure, the adhesive strength of the adhesive layer can be set to a predetermined value or less, for example, by adjusting the composition of the adhesive layer. Specifically, the adhesiveness of the adhesive layer can be reduced by using a curable resin that is solid at room temperature or a curing agent that is solid at room temperature. The adhesiveness of the adhesive layer can also be reduced by including a curable resin with a high softening temperature or a curable resin with a small weight average molecular weight. In addition, when the curable resin is an epoxy resin, the adhesiveness of the adhesive layer can be reduced by including an acrylic resin that is compatible with the epoxy resin.

The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

The adhesive layer can be formed, for example, by applying the above-mentioned adhesive composition and removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

2. Substrate The substrate in this embodiment may be, for example, a supporting substrate that supports the adhesive layer, or a separator that protects the adhesive layer.

(1) Supporting substrate The supporting substrate in this embodiment is preferably insulating. The supporting substrate is preferably in the form of a sheet. The supporting substrate may have a single layer structure or a multi-layer structure. The supporting substrate may or may not have a porous structure inside.

Examples of supporting substrates include resin substrates and nonwoven fabrics.

Examples of resins contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80°C or higher, may be 140°C or higher, or may be 200°C or higher. Liquid crystal polymers (LCPs) may also be used as the resin.

Examples of nonwoven fabrics include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

The supporting substrate may be surface-treated on the surface on which the adhesive layer is to be placed in order to enhance adhesion to the adhesive layer.

The thickness of the support substrate is not particularly limited, but may be, for example, 2 μm or more, 5 μm or more, or 9 μm or more. The thickness of the support substrate may be, for example, 200 μm or less, 100 μm or less, or 50 μm or less.

(2) Separator The separator in this embodiment is not particularly limited as long as it can be peeled off from the adhesive layer, and can have a strength sufficient to protect the adhesive layer. Examples of such separators include release films and release papers. The separator may have a single layer structure or a multilayer structure.

Examples of single-layer separators include fluororesin films.

In addition, examples of separators with a multi-layer structure include laminates having a release layer on one or both sides of a base layer. Examples of base layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and papers such as fine paper, coated paper, and impregnated paper. Materials for the release layer are not particularly limited as long as they have releasability, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be of any type, including emulsion, solvent, or solventless.

3. Intermediate layer When the substrate is a supporting substrate, the foamable adhesive sheet of this embodiment can have an intermediate layer between the substrate and the adhesive layer. By disposing the intermediate layer, the adhesive layer can further improve the adhesion to the substrate. Furthermore, by disposing the intermediate layer, for example, the stress applied to the bent portion when the foamable adhesive sheet is folded can be alleviated, and the stress applied to the cut portion when the foamable adhesive sheet is cut can be alleviated. As a result, the adhesive layer can be effectively prevented from lifting or peeling off from the substrate not only when the foamable adhesive sheet is bent but also when it is cut.

For example, in the foamable adhesive sheet 10 shown in FIG. 4, the substrate 2, intermediate layer 3, and adhesive layer 1 are arranged in this order in the thickness direction. In the foamable adhesive sheet 10 shown in FIG. 5, the first adhesive layer 1a is arranged on one side of the substrate 2, the second adhesive layer 1b is arranged on the other side of the substrate 2, the first intermediate layer 3a is arranged between the substrate 2 and the first adhesive layer 1a, and the second intermediate layer 3b is arranged between the substrate 2 and the second adhesive layer 1b. In FIG. 5, the foamable adhesive sheet 10 has both the first intermediate layer 3a and the second intermediate layer 3b, but may have only one of them.

When adhesive layers are disposed on both sides of the substrate, it is sufficient that an intermediate layer is disposed between the substrate and at least one of the adhesive layers. For example, an intermediate layer may be disposed only between the substrate and one of the adhesive layers, or an intermediate layer may be disposed between the substrate and both adhesive layers. Of these, it is preferable that an intermediate layer is disposed between the substrate and both adhesive layers.

The material contained in the intermediate layer is not particularly limited as long as it can increase the adhesion between the substrate and the adhesive layer and can relieve stress, and is appropriately selected depending on the materials of the substrate and the adhesive layer. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two of these, crosslinked products thereof, and mixtures thereof.

The crosslinked body is a crosslinked body obtained by crosslinking the above-mentioned resin with a curing agent. Examples of the curing agent include isocyanate-based curing agents. In addition, for example, when the reactive group/NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent in a ratio of 0.5% by mass or more and 20% by mass or less to the resin.

In particular, it is preferable that the intermediate layer contains a crosslinked resin. Note that a crosslinked resin is one that does not melt even at high temperatures. This can improve the adhesive strength at high temperatures, i.e., heat resistance. In addition, if the crosslinked resin is crosslinked, for example, by an isocyanate-based curing agent, the flexibility of the intermediate layer is improved, and cracking of the adhesive layer and lifting and peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent can be suppressed.

Examples of crosslinked resins include the crosslinked bodies described above. In particular, it is preferable that the intermediate layer contains a crosslinked polyester resin. When the intermediate layer contains a crosslinked polyester resin, the adhesion between the substrate and the adhesive layer tends to be high.

The crosslinked polyester resin is a crosslinked product of polyester, a copolymer containing polyester, or a mixture containing polyester, specifically, a crosslinked product of polyester, a copolymer containing polyester, or a mixture containing polyester crosslinked with a curing agent. Examples of polyesters include polyester polyols. Examples of curing agents include isocyanate-based curing agents. The amount of curing agent added is as described above.

The thickness of the intermediate layer is not particularly limited, but may be, for example, 0.1 μm or more, 0.2 μm or more, or 0.5 μm or more. If the intermediate layer is too thin, the effect of suppressing peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent or cut may not be sufficiently obtained. On the other hand, the average thickness of the intermediate layer is, for example, 10 μm or less. Since the intermediate layer itself does not usually have high heat resistance, if the intermediate layer is too thick, the heat resistance (adhesive strength at high temperatures) may decrease.

The intermediate layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

4. Foamable Adhesive Sheet The thickness of the foamable adhesive sheet of this embodiment is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

The foamable adhesive sheet of this embodiment preferably has good shape retention. The bending moment based on JIS P 8125 is, for example, 40 gf·cm or more, and may be 50 gf·cm or more. On the other hand, the bending moment is, for example, 600 gf·cm or less, and may be 150 gf·cm or less.

The foamable adhesive sheet of this embodiment preferably has high adhesion after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 may be, for example, 2.10 MPa or more, 2.40 MPa or more, or 3.0 MPa or more at 23°C. The shear strength (adhesive strength) may be, for example, 0.30 MPa or more, or 0.40 MPa or more at 200°C.

The foamable adhesive sheet of this embodiment preferably has high electrical insulation after foaming and curing. The dielectric breakdown voltage based on JIS C 2107 is preferably, for example, 3 kV or more, and more preferably 5 kV or more. In addition, the foamable adhesive sheet after foaming and curing preferably has a thermal conductivity of, for example, 0.1 W/mK or more, and more preferably 0.15 W/mK or more.

The use of the foamable adhesive sheet of this embodiment is not particularly limited. The foamable adhesive sheet of this embodiment can be used, for example, when bonding components together by placing the foamable adhesive sheet between components and then foaming and curing the foamable adhesive sheet. Specifically, the foamable adhesive sheet of this embodiment can be used to bond the coil and stator in a motor.

The method for producing the foamable adhesive sheet of this embodiment is not particularly limited. For example, an adhesive layer can be formed by applying the above-mentioned adhesive composition to one side of a substrate and drying it. When a first adhesive layer is formed on one side of the substrate and a second adhesive layer is formed on the other side of the substrate, the first adhesive layer and the second adhesive layer may be formed sequentially or simultaneously.

II. Second embodiment of the foamable adhesive sheet A second embodiment of the foamable adhesive sheet in the present disclosure includes a curable resin, a curing agent, a curing accelerator, a boric acid ester, and a foaming agent, and has an adhesive layer in which at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom.

Figures 1 to 3 are schematic cross-sectional views illustrating the foamable adhesive sheet of this embodiment. The foamable adhesive sheet 10 in Figures 1 to 3 has been described in the first embodiment above, so a description thereof will be omitted here. The adhesive layer 1, the first adhesive layer 1a, and the second adhesive layer 1b contain a curable resin, a curing agent, a curing accelerator, a boric acid ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom.

In this embodiment, the adhesive layer contains a curing agent, a curing accelerator, and a boric acid ester, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom, thereby improving storage stability under high temperature and high humidity conditions and suppressing a decrease in foaming property after storage at high temperature and high humidity. Furthermore, a decrease in adhesion after storage at high temperature and high humidity can also be suppressed.

The components of the foamable adhesive sheet of this embodiment are described below.

1. Adhesive layer The adhesive layer in this embodiment contains a curable resin, a curing agent, a curing accelerator, a boric acid ester, and a foaming agent, and at least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom. Note that these materials are the same as those described in "A. Adhesive composition II. Second embodiment of adhesive composition" above, so the description here is omitted.

Other aspects of the adhesive layer can be the same as those of the adhesive layer in the first embodiment above.

2. Substrate The substrate in this embodiment may be the same as the substrate in the first embodiment.

3. Intermediate layer When the substrate is a supporting substrate, the foamable adhesive sheet of this embodiment may have an intermediate layer between the substrate and the adhesive layer. The intermediate layer in this embodiment may be the same as the intermediate layer in the first embodiment.

4. Foamable Adhesive Sheet The thickness, characteristics, uses, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first embodiment described above.

C. Manufacturing Method of an Article The manufacturing method of an article in the present disclosure includes a disposing step of disposing the foamable adhesive sheet between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member.

Figure 6 is a process diagram showing an example of a method for manufacturing an article according to the present disclosure. First, as shown in Figure 6(a), a foamable adhesive sheet 10 is placed between a first member 20a and a second member 20b. Next, as shown in Figure 6(b), the foamable adhesive sheet 10 is foamed and cured, for example, by heating. The first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 11 after foaming and curing. This results in an article 100 in which the adhesive sheet 11 is placed between the first member 20a and the second member 20b.

In the method of manufacturing an article according to the present disclosure, the foamable adhesive sheet described above is used, so that the storage stability is good under high temperature and high humidity conditions, and the decrease in foamability after storage at high temperature and high humidity can be suppressed. Furthermore, the decrease in adhesion after storage at high temperature and high humidity can also be suppressed. Therefore, an article having good adhesion between the first member and the second member can be obtained.

The manufacturing method of the article disclosed herein is described below.

1. Foamable Adhesive Sheet In the method for producing an article according to the present disclosure, the foamable adhesive sheet used is the foamable adhesive sheet described above.

When the substrate in the foamable adhesive sheet is a supporting substrate, the foamable adhesive sheet may have an adhesive layer and a substrate arranged in this order. Alternatively, the foamable adhesive sheet may have a first adhesive layer and a second adhesive layer as adhesive layers, and the first adhesive layer, substrate, and second adhesive layer may be arranged in this order in the thickness direction.

On the other hand, if the substrate in the foamable adhesive sheet is a separator, the substrate is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is placed between the first and second members.

Details about the foamable adhesive sheet are described above in the section "A. Foamable adhesive sheet," so a detailed explanation will be omitted here.

2. Placement Step In the placement step of the present disclosure, the method of placing the foamable adhesive sheet between the first member and the second member is not particularly limited, and examples thereof include a method of inserting a foamable adhesive sheet into the gap between the first member and the second member, and a method of placing a foamable adhesive sheet on the first member, and then inserting the second member into the gap after placing the foamable adhesive sheet on the first member.

3. Adhesion step In the adhesion step of the present disclosure, the method of foaming and curing the foamable adhesive sheet can be, for example, heating or light irradiation. Among them, it is preferable to foam and cure the foamable adhesive sheet by heating. The method of heating can be applied even when the first member and the second member do not have transparency, such as when the first member and the second member are made of metal.

The heating conditions are set appropriately depending on the type of curable adhesive and foaming agent contained in the adhesive layer, the type of substrate, etc. The heating temperature can be, for example, 130°C or higher and 200°C or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

In addition, if the curing agent is a moisture-latent curing agent, the adhesive layer can be foamed by heating, and then cured in the presence of moisture, for example.

Here, "in the presence of moisture" refers to an environment in which there is enough moisture to allow the adhesive layer to harden through moisture absorption. For example, an environment in which the humidity is 30% RH or higher at a temperature of 23°C is preferable, and an environment in which the humidity is 50% RH or higher at a temperature of 23°C is particularly preferable.

In addition, when the curing agent is a photolatent curing agent, the adhesive layer may be foamed by heating and then cured by irradiating light, for example.

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and has similar effects is included within the technical scope of this disclosure.

[Examples 1 to 9, Comparative Examples 1 to 5]
First, an adhesive composition was prepared having the composition (mass %) shown in Table 1 below. Details of each material shown in Table 1 are shown below.

Acrylic resin: PMMA-PBuA-PMMA (partially acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000
Epoxy resin A: bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g/eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa·s
Epoxy resin B: BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000g/eq, Mw: 50,000

Hardener 1: Phenol-based hardener, α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)]
Hardener 2: Imidazole compound, 2-phenyl-4,5-dihydroxymethylimidazole, average particle size 3 μm, melting point 230° C., reaction start temperature 145° C. to 155° C., active region 155° C. to 173° C. (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)
Hardener 3: Imidazole compound, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, average particle size 2 μm, melting point 260°C, reaction start temperature 120°C to 130°C, active region 130°C to 150°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2MAOK-PW)
Hardener 4: Dicyandiamide, particle size 10 μm or less, melting point 209° C. (DYHARD100SH, manufactured by Evonik Degussa)
(Note that curing agents 2 and 3 also function as curing accelerators.)

Thermal blowing agent 1: Thermally expandable microcapsule, average particle size 10-16 μm, expansion start temperature 123-133°C, maximum expansion temperature 168-178°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 3: Thermally expandable microcapsule, average particle size 14-20 μm, expansion start temperature 120-130°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer

Composition containing borate ester: epoxy-phenol-borate ester blend (composition containing 1 to 10% by mass of borate ester) (manufactured by Shikoku Chemical Industry Co., Ltd., L-07E)
・Solvent: Methyl ethyl ketone

A highly insulating polyethylene naphthalate film (PEN film, thickness 100 μm) was prepared as the substrate. In addition, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) were mixed with 100 parts by mass of polyester polymer, and further diluted with methyl ethyl ketone (MEK) to a solid content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Furthermore, a second intermediate layer was formed on the other side of the substrate in the same manner as the first intermediate layer.

Next, the adhesive composition was applied to the surface of the first intermediate layer opposite the substrate using an applicator so that the thickness after application was 45 μm. This was then dried in an oven at 100° C. for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed in the same manner as the first adhesive layer on the surface of the second intermediate layer opposite the substrate. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[evaluation]
(Expansion Ratio)
The foamable adhesive sheet was cut into a size of 50 mm x 50 mm, hung vertically in a hot air dryer, and foam-cured at 150°C for 30 minutes, and then cooled at room temperature for 2 hours to obtain a foam-cured adhesive sheet. The thickness of the foam-cured adhesive sheet was measured using a thickness gauge according to JIS Z0237. The foaming ratio was calculated using the following formula. The foaming ratio at this time was taken as the initial foaming ratio.
Expansion ratio (times) = {thickness of adhesive sheet after foaming and curing - (thickness of substrate + thickness of first intermediate layer + thickness of second intermediate layer)} / (total thickness of first adhesive layer and second adhesive layer of foamable adhesive sheet before foaming and curing)

The foamable adhesive sheet was cut into pieces measuring 50 mm x 50 mm and then stored for 10 days at 40°C and 95% RH. The foamed and cured adhesive sheet was then obtained in the same manner as above, and the thickness of the foamed and cured adhesive sheet was measured to determine the foaming ratio. The foaming ratio at this time was taken as the foaming ratio after storage at high temperature and high humidity.

(Adhesiveness)
As shown in Fig. 6(a) and (b), two metal plates 31 (cold-rolled steel plate SPCC-SD) with a thickness of 1.6 mm, width of 25 mm, and length of 100 mm were prepared. A spacer 32 (Kapton tape) was placed at a predetermined interval at one end of one of the metal plates 31. The thickness of the spacer was about 350 µm (the thickness of five layers of Kapton tape P-221 manufactured by Nitto Denko Corporation). A foamable adhesive sheet 10 cut to a size of 12.5 mm x 25 mm was placed between the spacers 32, and another metal plate 31 was placed so that one end overlapped. Next, as shown in Fig. 6(a), a support 33 with the same thickness as the total thickness of the metal plate 31 and the spacer 32 was placed at the other end of each of the two metal plates 31 to obtain a test piece. Thereafter, the test piece was placed in a heat press machine and heated at 150° C. for 7 minutes under a press load of 500 kgf, thereby curing the foamable adhesive sheet 10 .

After heating, the test pieces were subjected to measurement of shear strength (adhesive strength) in accordance with JIS K6850 using a tensile tester Tensilon RTF1350 (manufactured by A&D Co., Ltd.). The measurement conditions were a tensile speed of 10 mm/min and a temperature of 200°C. The adhesive strength at this time was taken as the initial adhesive strength.

The foamable adhesive sheet was cut into pieces measuring 12.5 mm x 25 mm and then stored for 10 days at 40°C and 95% RH. The foamable adhesive sheet was then cured in the same manner as above, and the shear strength (adhesive strength) was measured. The foaming ratio at this time was taken as the foaming ratio after storage at high temperature and high humidity.

(Blocking resistance)
The foamable adhesive sheet was cut into two pieces measuring 5 cm x 5 cm, and the two foamable adhesive sheets were overlapped so that the first adhesive layer of one foamable adhesive sheet overlapped the second adhesive layer of the other foamable adhesive sheet. The sheets were stored in a blocking tester under conditions of 3 kg/ ^cm2 , 40°C, and 95% RH for 10 days, and the blocking properties were confirmed.
A: There is no transfer or peeling of the adhesive layer, and the sheets naturally peel off from each other.
B: There is no transfer or peeling of the adhesive layer, and the sheets do not peel off naturally, but can be peeled off with very light force.
C: The adhesive layer is transferred or peeled off, or the sheets do not peel off naturally and are so tightly attached that they make a peeling noise.

(Adhesive strength)
The foamable adhesive sheet was cut to a width of 24 mm and a length of 300 mm, and the surface of the first adhesive layer of the foamable adhesive sheet was attached to a stainless steel plate (SUS304) using a manual roller. Then, using a tensile tester (A&D Co., Ltd., Tensilon RTF1150), the adhesive force (N/25 mm) against the stainless steel plate surface was measured under conditions (tensile speed: 300 mm/min, peel distance: 150 mm, peel angle: 180°) in accordance with JIS Z0237:2009 (adhesive tape/adhesive sheet test method) and method 1 of the adhesive force test method (temperature 23°C, humidity 50%, tape and sheet peeled at 180° against stainless steel test plate).

As shown in Table 1, it was confirmed that in Examples 1 to 9 containing boric acid ester, the decrease in foaming ratio after storage at high temperature and high humidity was suppressed compared to Comparative Examples 1 to 5 which did not contain boric acid ester. Furthermore, in Examples 1 to 5 containing a phenolic hardener, dicyandiamide, and an imidazole compound, the curing speed was faster and the curing temperature was lower compared to Examples 6 to 9 containing a phenolic hardener and an imidazole compound, so there was concern about a decrease in adhesive strength after storage at high temperature and high humidity. However, it was confirmed that the inclusion of a boric acid ester also suppressed the decrease in adhesive strength after storage at high temperature and high humidity.

Reference Signs List 1 adhesive layer 2 substrate 3 intermediate layer 10 foamable adhesive sheet 11 foamed and cured adhesive sheet 20a first member 20b second member 100 article

Claims (32)

An adhesive composition for use in an adhesive layer of a foamable adhesive sheet, comprising:
A hardening resin;
A hardener;
Boric acid ester,
A foaming agent;
The curing agent comprises a compound containing a nitrogen atom,
The borate ester is selected from the group consisting of trimethyl borate, triethyl borate, tripropyl borate, triisopropyl borate, tributyl borate, tripentyl borate, triallyl borate, trihexyl borate, trioctyl borate, triisooctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tricyclohexyl borate, tribenzyl borate, tritolyl borate, and triethanolamine borate. the adhesive composition being at least one selected from the group consisting of triethylamine, tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylenephenylene pyroborate, bis-2,2-dimethyltrimethylene pyroborate, tris(2-ethylhexyloxy)borane, and bis(1,4,7,10-tetraoxaundecyl)(1,4,7,10,13-pentaoxatetradecyl)(1,4,7-trioxaundecyl)borane . An adhesive composition for use in an adhesive layer of a foamable adhesive sheet, comprising:
A hardening resin;
A hardener;
Boric acid ester,
A foaming agent;
The curing agent comprises a compound containing a nitrogen atom,
The adhesive composition, wherein the curable resin is a polyester resin or a polyol. An adhesive composition for use in an adhesive layer of a foamable adhesive sheet, comprising:
A hardening resin;
A hardener;
A curing accelerator;
Boric acid ester,
A foaming agent;
At least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom,
The borate ester is selected from the group consisting of trimethyl borate, triethyl borate, tripropyl borate, triisopropyl borate, tributyl borate, tripentyl borate, triallyl borate, trihexyl borate, trioctyl borate, triisooctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tricyclohexyl borate, tribenzyl borate, tritolyl borate, and triethanolamine borate. the adhesive composition being at least one selected from the group consisting of triethylamine, tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylenephenylene pyroborate, bis-2,2-dimethyltrimethylene pyroborate, tris(2-ethylhexyloxy)borane, and bis(1,4,7,10-tetraoxaundecyl)(1,4,7,10,13-pentaoxatetradecyl)(1,4,7-trioxaundecyl)borane . An adhesive composition for use in an adhesive layer of a foamable adhesive sheet, comprising:
A hardening resin;
A hardener;
A curing accelerator;
Boric acid ester,
A foaming agent;
At least one of the curing agent and the curing accelerator contains a compound containing a nitrogen atom,
The adhesive composition, wherein the curable resin is a polyester resin or a polyol. the curable resin is an epoxy resin,
2. The adhesive composition according to claim 1, wherein the compound containing a nitrogen atom is at least one selected from the group consisting of imidazole-based compounds, amine-based compounds, dicyandiamide-based compounds, hydrazide-based compounds, isocyanate-based compounds, guanidine-based compounds, biguanide-based compounds, urea-based compounds, melamine-based compounds, ketimine-based compounds, and diazonium salts. the curable resin is a polyester resin or a polyol,
The adhesive composition according to claim 1 , wherein the compound containing a nitrogen atom is an isocyanate compound. The adhesive composition according to claim 2 , wherein the compound containing a nitrogen atom is an isocyanate compound. the curable resin is an epoxy resin,
4. The adhesive composition according to claim 3, wherein only the curing agent contains the compound containing a nitrogen atom, and the compound containing a nitrogen atom is at least one selected from the group consisting of imidazole-based compounds, amine-based compounds, dicyandiamide-based compounds, hydrazide-based compounds, isocyanate-based compounds, guanidine-based compounds, biguanide-based compounds, urea -based compounds, melamine-based compounds, ketimine-based compounds, and diazonium salts. the curable resin is an epoxy resin,
4. The adhesive composition according to claim 3, wherein only the curing accelerator comprises the compound containing a nitrogen atom, and the compound containing a nitrogen atom is at least one selected from the group consisting of an imidazole-based compound, an amine-based compound, and a urea -based compound. the curable resin is a polyester resin or a polyol,
The adhesive composition according to claim 3 , wherein the curing agent comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an isocyanate compound. the curable resin is a polyester resin or a polyol,
The adhesive composition according to claim 3 , wherein the curing accelerator comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an amine compound. The adhesive composition according to claim 4 , wherein the curing agent comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an isocyanate compound. The adhesive composition according to claim 4 , wherein the curing accelerator comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an amine compound. 14. The adhesive composition according to claim 1, wherein the content of the boric acid ester is 0.01 parts by mass or more and 9 parts by mass or less per 100 parts by mass of a resin component contained in the adhesive composition. The adhesive layer includes a curable resin, a curing agent, a borate ester, and a foaming agent, and the curing agent includes a compound containing a nitrogen atom ;
The borate ester is selected from the group consisting of trimethyl borate, triethyl borate, tripropyl borate, triisopropyl borate, tributyl borate, tripentyl borate, triallyl borate, trihexyl borate, trioctyl borate, triisooctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tricyclohexyl borate, tribenzyl borate, tritolyl borate, and triethanol borate. The foamable adhesive sheet is at least one member selected from the group consisting of amines, tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylenephenylene pyroborate, bis-2,2-dimethyltrimethylene pyroborate, tris(2-ethylhexyloxy)borane, and bis(1,4,7,10-tetraoxaundecyl)(1,4,7,10,13-pentaoxatetradecyl)(1,4,7-trioxaundecyl)borane . The adhesive layer includes a curable resin, a curing agent, a borate ester, and a foaming agent, and the curing agent includes a compound containing a nitrogen atom;
The foamable adhesive sheet, wherein the curable resin is a polyester resin or a polyol. The adhesive layer includes a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator includes a compound containing a nitrogen atom;
The borate ester is selected from the group consisting of trimethyl borate, triethyl borate, tripropyl borate, triisopropyl borate, tributyl borate, tripentyl borate, triallyl borate, trihexyl borate, trioctyl borate, triisooctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tricyclohexyl borate, tribenzyl borate, tritolyl borate, and triethanol borate. The foamable adhesive sheet is at least one member selected from the group consisting of amines, tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylenephenylene pyroborate, bis-2,2-dimethyltrimethylene pyroborate, tris(2-ethylhexyloxy)borane, and bis(1,4,7,10-tetraoxaundecyl)(1,4,7,10,13-pentaoxatetradecyl)(1,4,7-trioxaundecyl)borane . The adhesive layer includes a curable resin, a curing agent, a curing accelerator, a borate ester, and a foaming agent, and at least one of the curing agent and the curing accelerator includes a compound containing a nitrogen atom;
The foamable adhesive sheet, wherein the curable resin is a polyester resin or a polyol. The foamable adhesive sheet according to claim 15 or 17 , wherein the curable resin is an epoxy resin. the curable resin is an epoxy resin,
16. The foamable adhesive sheet according to claim 15, wherein the compound containing a nitrogen atom is at least one selected from the group consisting of imidazole-based compounds, amine-based compounds, dicyandiamide-based compounds, hydrazide-based compounds, isocyanate-based compounds, guanidine-based compounds, biguanide-based compounds, urea-based compounds, melamine-based compounds, ketimine-based compounds, and diazonium salts. the curable resin is a polyester resin or a polyol,
The foamable adhesive sheet according to claim 15 , wherein the compound containing a nitrogen atom is an isocyanate compound. The foamable adhesive sheet according to claim 16 , wherein the compound containing a nitrogen atom is an isocyanate compound. the curable resin is an epoxy resin,
18. The foamable adhesive sheet according to claim 17, wherein only the curing agent contains a compound containing a nitrogen atom, and the compound containing a nitrogen atom is at least one selected from the group consisting of imidazole-based compounds, amine-based compounds, dicyandiamide-based compounds, hydrazide-based compounds, isocyanate-based compounds, guanidine-based compounds, biguanide-based compounds, urea-based compounds, melamine-based compounds, ketimine-based compounds , and diazonium salts. the curable resin is an epoxy resin,
18. The foamable adhesive sheet according to claim 17, wherein only the curing accelerator comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is at least one selected from the group consisting of an imidazole-based compound, an amine-based compound, and a urea -based compound. the curable resin is a polyester resin or a polyol,
The foamable adhesive sheet according to claim 17 , wherein the curing agent comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an isocyanate compound. the curable resin is a polyester resin or a polyol,
The foamable adhesive sheet according to claim 17 , wherein the curing accelerator comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an amine compound. The foamable adhesive sheet according to claim 18 , wherein the curing agent comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an isocyanate compound. The foamable adhesive sheet according to claim 18 , wherein the curing accelerator comprises a compound containing a nitrogen atom, and the compound containing a nitrogen atom is an amine compound. 29. The foamable adhesive sheet according to claim 15 , wherein the content of the boric acid ester in the adhesive layer is 0.01 parts by mass or more and 9 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive layer. 30. The foamable adhesive sheet according to claim 15 , wherein a substrate is disposed on one surface of the adhesive layer. 31. The foamable adhesive sheet according to claim 30 , wherein an intermediate layer is disposed between the substrate and the adhesive layer. a step of placing the foamable adhesive sheet according to any one of claims 15 to 31 between a first member and a second member;
a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member;
A method for producing an article having the following structure:

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