Adhesive composition and foamable adhesive sheet

Abstract

To provide a foamable adhesive sheet good in blocking resistance, adhesiveness and crack resistance, and a method for manufacturing an article using the foamable adhesive sheet.SOLUTION: The foamable adhesive sheet includes at least an adhesive layer. The adhesive layer contains an epoxy resin, a resin X compatibilized with the epoxy resin, a curing agent, and a foaming agent. The adhesive layer contains a first epoxy resin and a second epoxy resin as the epoxy resin. The softening temperature of the second epoxy resin is higher than the softening temperature of the first epoxy resin. The epoxy equivalent of the second epoxy resin is larger than the epoxy equivalent of the first epoxy resin. The resin X contains at least one of an acrylate, vinyl acetate, an acetal, urethane, an ethylene-vinyl acetate copolymer, acrylamide, styrene, vinyl chloride, an amide, acrylonitrile, cellulose acetate, phenol, vinylidene chloride and the like as a monomer component or a polymer component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an adhesive composition and a foamable adhesive sheet. [Background technology]

[0002] Adhesives that bond components together are used in various fields, and many bonding methods are known. For example, Patent Document 1 discloses a method for attaching a rubber grip to a golf club shaft, in which a double-sided adhesive tape or adhesive tape is wrapped around the grip part of the shaft, a highly volatile solvent such as thinner is applied to the surface of the tape and the inside of a shaft insertion hole in the rubber grip, the grip part is inserted into the shaft insertion hole, and the grip is left for a while until the solvent evaporates. Patent Document 2 discloses a method for bonding a CFRP pipe and a metal part with a one-liquid epoxy adhesive.

[0003] Patent Document 3 discloses an adhesive sheet having an expandable adhesive layer containing an epoxy resin including a multifunctional epoxy resin, a phenolic resin as a curing agent, an imidazole compound as a curing catalyst, and a temperature-sensitive foaming agent, and a release agent is applied to the surface of at least one of the expandable adhesive layers. Patent Document 4 discloses an adhesive containing an acrylic polymer, an epoxy resin, a thermoplastic resin such as a phenoxy resin or a polyvinyl butyral resin, and an epoxy resin curing agent. Patent Document 4 also discloses that the adhesive is in the form of a sheet (adhesive sheet) and that the adhesive contains a foaming agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-222445 A [Patent Document 2] JP 2016-221784 A [Patent Document 3] Patent No. 6220100 Specification [Patent Document 4] JP 2017-203114 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Documents 3 and 4 disclose adhesive sheets (foamable adhesive sheets) containing a foaming agent. A method of using a foamable adhesive sheet is known in which, for example, the foamable adhesive sheet is inserted into a gap between components, and then the foamable adhesive sheet is foamed and cured to bond the components together. It is desirable for such foamable adhesive sheets to have good blocking resistance before foaming, and good adhesion and cracking resistance after foaming and curing.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide an adhesive composition with which a foamable adhesive sheet having good blocking resistance, adhesion, and cracking resistance can be obtained. [Means for solving the problem]

[0007] The present disclosure provides an adhesive composition comprising an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, wherein the epoxy resin comprises a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or higher, and the acrylic resin has a weight average molecular weight of 50,000 or higher.

[0008] The present disclosure also provides a foamable adhesive sheet having at least an adhesive layer, the adhesive layer containing an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, the adhesive layer containing, as the epoxy resin, a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or higher, the acrylic resin having a weight average molecular weight of 50,000 or higher. Effect of the Invention

[0009] The adhesive composition according to the present disclosure has the effect of being able to obtain a foamable adhesive sheet having good blocking resistance, adhesion and cracking resistance. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Diagram 3] FIG. 2 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 4] FIG. 2 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Diagram 5] FIG. 2 is a schematic cross-sectional view showing an example of a method for producing an article according to the present disclosure. [Figure 6] FIG. 2 is a schematic cross-sectional view illustrating a method for testing adhesiveness. [Figure 7] 1 shows the results of dynamic viscoelasticity measurement for the acrylic resin in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The adhesive composition and the foamable adhesive sheet according to the present disclosure will be described in detail below.

[0012] A. Adhesive Composition The adhesive composition according to the present disclosure contains an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, and the epoxy resin contains a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or higher, and the acrylic resin has a weight average molecular weight of 50,000 or higher.

[0013] According to the present disclosure, by using a combination of a first epoxy resin, a second epoxy resin, and an acrylic resin, it is possible to obtain an adhesive composition that is capable of obtaining a foamable adhesive sheet that has good blocking resistance, adhesion, and cracking resistance.

[0014] For example, when only improving adhesiveness is required, it is more effective to use an epoxy resin with a low molecular weight (low epoxy equivalent) than an epoxy resin with a high molecular weight (high epoxy equivalent). However, when a low molecular weight (low epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins are assimilated with each other, and blocking is likely to occur.

[0015] In contrast, in the present disclosure, a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent) is used. When the first epoxy resin reaches a temperature equal to or higher than the softening temperature, it rapidly melts and changes to a low-viscosity liquid. Therefore, it is easy to improve the adhesiveness. On the other hand, since the first epoxy resin has a relatively high crystallinity, it can suppress the occurrence of blocking compared to an epoxy resin having a relatively low crystallinity or an epoxy resin having no crystallinity. However, when only the first epoxy resin is used, there is a possibility that the effect of suppressing the occurrence of blocking is insufficient, or the adhesive layer has too high a tackiness (tackiness). Therefore, in the present disclosure, a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight is further used. This can improve the effect of suppressing the occurrence of blocking, and can suppress the adhesive layer's tackiness (tackiness) to be low. On the other hand, when the above-mentioned first epoxy resin and second epoxy resin are used as the epoxy resin, a new problem occurs in that the toughness of the adhesive layer is reduced and the crack resistance is reduced. In response to such new problems, in the present disclosure, by further using an acrylic resin compatible with the epoxy resin, it is possible to improve the cracking resistance while improving the blocking resistance and adhesion. In addition, for example, when an acrylic resin and a first epoxy resin are used without using a second epoxy resin, the adhesion is good, but the product is hard and brittle, and the diffusion of the first epoxy resin is large. Therefore, not only is the cracking resistance reduced, but blocking is also likely to occur. In addition, for example, when an acrylic resin and a second epoxy resin are used without using a first epoxy resin, it is difficult to obtain good adhesion.

[0016] In addition, the adhesive composition in the present disclosure is preferably used to prepare an adhesive layer of a foamable adhesive sheet. In this case, the foamable adhesive sheet has the following advantages. For example, Patent Document 1 discloses a method for attaching a rubber grip to a golf club shaft, in which a double-sided adhesive tape or adhesive tape is wrapped around the grip part of the shaft, a highly volatile solvent such as thinner is applied to the surface of the tape and the inside of the shaft insertion hole provided in the rubber grip, the grip part is inserted into the shaft insertion hole, and the solvent is left for a while until it evaporates. However, it was necessary to wait until the solvent evaporates. In contrast, the adhesive sheet of the foamable adhesive sheet basically does not contain a solvent, and therefore has the advantage of improving work efficiency.

[0017] Also, for example, Patent Document 2 discloses a method of bonding CFRP pipes and metal parts using a one-component epoxy adhesive. However, when using a one-component epoxy adhesive, it may be necessary to wipe off any adhesive that has protruded from the joints and to protect areas that should not come into contact with the adhesive with masking tape. In contrast, the adhesive sheet of a foamable adhesive sheet expands somewhat when foamed and hardened, but has the advantage of being easier to handle than liquid adhesives.

[0018] 1. Epoxy Resin The adhesive composition of the present disclosure contains a first epoxy resin and a second epoxy resin as epoxy resins. The epoxy resin of the present disclosure is a compound that has at least one epoxy group or glycidyl group and is cured by crosslinking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0019] (1) First Epoxy Resin The first epoxy resin has a softening temperature of 50° C. or higher and an epoxy equivalent of 5000 g / eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. The first epoxy resin has relatively high crystallinity and a low molecular weight, which makes it easy to improve adhesion and blocking resistance. In addition, the first epoxy resin has a low molecular weight, which makes it possible to increase the crosslink density, and to obtain an adhesive layer with good mechanical strength, chemical resistance, and curing properties. In addition, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23° C.).

[0020] The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or may be 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature can be measured by the ring and ball method in accordance with JISK 7234.

[0021] The epoxy equivalent of the first epoxy resin is, for example, 5000 g / eq or less, may be 3000 g / eq or less, may be 1000 g / eq or less, or may be 600 g / eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g / eq or more, may be 100 g / eq or more, or may be 110 g / eq or more. The epoxy equivalent can be measured by a method in accordance with JIS K7236, and is the number of grams of a resin containing 1 gram equivalent of epoxy groups.

[0022] The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0023] The weight average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight average molecular weight (Mw) of the second epoxy resin described below. The Mw of the first epoxy resin is, for example, 6,000 or less, and may be 4,000 or less, or may be 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a value calculated in terms of polystyrene as measured by gel permeation chromatography (GPC).

[0024] The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, may be 0.015 Pa·s or more, may be 0.03 Pa·s or more, may be 0.05 Pa·s or more, or may be 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. In addition, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the adhesive layer obtained may have high tackiness. The reason for this is presumably that if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), when it is mixed with the second epoxy resin or the acrylic resin, its crystallinity is greatly reduced, and the Tg of the entire adhesive composition is reduced. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, may be 5 Pa·s or less, or may be 2 Pa·s or less. If the melt viscosity is too high, the uniformity of the obtained adhesive layer may be reduced. The melt viscosity can be determined in accordance with JIS K6862 by measurement using a Brookfield type single cylinder rotational viscometer and a thermocell for heating the solution.

[0025] Next, the constitution of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin 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, triphenol methane type epoxy resins, alkyl modified triphenol methane 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. The first epoxy resin may be one type or two or more types.

[0026] 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 of the bisphenol skeleton. Bisphenol A type epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. In particular, bisphenol A type epoxy resins are preferred in that they can improve heat resistance.

[0027] In particular, the first epoxy resin is preferably a bisphenol A novolac type epoxy resin represented by the following general formula (1).

[0028] [ka]

[0029] In the general formula (1), R1 is C m H 2m (m is 1 or more and 3 or less), R2 and R3 are each independently a group represented by C p H 2p+1(p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0030] In general formula (1), m in R1 is preferably 1, i.e., R1 is -CH2-. Similarly, p in R2 and R3 is preferably 1, i.e., R2 and R3 are preferably -CH3. In addition, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with other elements or other groups.

[0031] The content of the first epoxy resin may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 25 parts by mass or more, based on 100 parts by mass of the resin component contained in the adhesive composition. If the content of the first epoxy resin is too small, the adhesiveness and blocking resistance may be reduced. On the other hand, the content of the first epoxy resin may be, for example, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, or 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive composition. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and the acrylic resin become relatively small, and blocking resistance, adhesiveness, and cracking resistance may not be compatible.

[0032] (2) Second epoxy resin The second epoxy resin has a higher softening temperature than the first epoxy resin and a weight average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the above-mentioned first epoxy resin. The second epoxy resin has relatively low crystallinity and high molecular weight, so that it is easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and high molecular weight, so that it is possible to suppress an increase in adhesion (tackiness) caused by the first epoxy resin. Moreover, it is preferable that the second epoxy resin is an epoxy resin that is solid at room temperature (23°C).

[0033] The weight average molecular weight (Mw) of the second epoxy resin is usually larger than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, may be 30,000 or more, or may be 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

[0034] The epoxy equivalent of the second epoxy resin may be larger, smaller, or the same as that of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, 5000 g / eq or more, or 6000 g / eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g / eq or less.

[0035] The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0036] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two is, for example, 10° C. or more, and may be 20° C. or more, or may be 30° C. or more. The softening temperature of the second epoxy resin is, for example, 80° C. or more, and may be 90° C. or more. On the other hand, the softening temperature of the second epoxy resin is, for example, 180° C. or less.

[0037] The composition of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore the description thereof will be omitted here.

[0038] The content of the second epoxy resin may be, for example, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more, when the resin component contained in the adhesive composition is 100 parts by mass. If the content of the second epoxy resin is too small, the blocking resistance may be reduced. On the other hand, the content of the second epoxy resin may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less, when the resin component contained in the adhesive composition is 100 parts by mass. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and the acrylic resin become relatively small, and there is a possibility that blocking resistance, adhesion, and cracking resistance cannot be achieved simultaneously.

[0039] The ratio of the first epoxy resin to the total of the first epoxy resin and the second epoxy resin is, for example, 5 mass% or more, optionally 10 mass% or more, optionally 15 mass% or more, or optionally 20 mass% or more, whereas the ratio of the first epoxy resin is, for example, 80 mass% or less, optionally 75 mass% or less, or optionally 60 mass% or less.

[0040] Furthermore, the total proportion of the first epoxy resin and the second epoxy resin to all epoxy resins contained in the adhesive composition is, for example, 50 mass% or more, optionally 70 mass% or more, optionally 90 mass% or more, or optionally 100 mass%.

[0041] 2. Acrylic resin The acrylic resin in the present disclosure is a resin compatible with the epoxy resin, and further, a resin having a weight average molecular weight of 50,000 or more. 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 crack resistance can be improved. Furthermore, the adhesiveness can be improved by improving the toughness of the adhesive layer. 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 is uniformly dispersed and foamed, thereby improving the adhesiveness. In addition, the first epoxy resin has a relatively high crystallinity, and the melt viscosity (or dynamic viscoelasticity) during heating becomes too low, and there is a possibility that shrinkage occurs during hardening after foaming (between the end of foaming of the foaming agent and the hardening of the adhesive composition). However, by using an acrylic resin having a certain molecular weight, it is possible to suppress the melt viscosity from becoming too low, and shrinkage is less likely to occur during hardening after foaming. In addition, the acrylic resin is compatible with the epoxy resin, and the hardness of the adhesive layer surface can be kept high. Furthermore, when the sheet is made into a sheet, if the acrylic resin is incompatible with the sheet, soft portions are formed on the surface of the sheet, which may make the interface with the adherend less slippery and reduce workability.

[0042] The acrylic resin in the present disclosure 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 prepared 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 that the number of samples is large, for example, 100 or more. The area to be observed is in the range of 100 μm × 100 μm, or in the case where the thickness of the adhesive layer is 100 μm or less, in the range of the thickness × 100 μm.

[0043] The weight average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, may be 70,000 or more, or may be 100,000 or more. On the other hand, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard substance: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40° C.).

[0044] The glass transition temperature (Tg) of the acrylic resin is, for example, 90° C. or higher, and may be 100° C. or higher. On the other hand, the Tg of the acrylic resin is, for example, 180° C. or lower. Tg can be measured by thermal analysis such as a differential scanning calorimeter (DSC) in accordance with JISK 7121.

[0045] Acrylic resin has a storage modulus (E') of 1 x 10 at the foaming start temperature. 6 Pa or less. When E' at the foaming start temperature is low, the fluidity is improved and good foaming properties can be obtained. On the other hand, E' at the foaming start temperature may be, for example, 1×10 5 The foaming initiation temperature is a temperature that differs depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the initiation temperature of the main foaming reaction.

[0046] Acrylic resin has a storage modulus (E') of 1 x 10 at the curing start temperature. 5 Pa or more. As described above, shrinkage may occur during curing after foaming (from the end of foaming of the foaming agent to the curing of the adhesive composition), but by having a large E' at the curing start temperature, shrinkage can be suppressed and good shape retention can be obtained. The curing start temperature is a temperature that differs depending on the type of curing agent. In addition, when two or more types of curing agents are used as the curing agent, the start temperature of the main curing reaction is taken as the curing start temperature.

[0047] In addition, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1×10 6The average value of storage modulus (E') at temperatures between 0°C and 100°C may be, for example, 1 x 10 8 Pa or less.

[0048] The acrylic resin may have a polar group, such as an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, or an amide group.

[0049] 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, a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The "acrylic acid" of the acrylic acid ester monomer also includes the concept of methacrylic acid. 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, the acrylic resin preferably contains a copolymer of two or more of the acrylic acid ester monomers ((meth)acrylic acid ester copolymer).

[0050] 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 above-mentioned polar group. 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.

[0051] The (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."

[0052] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymers. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0053] The acrylic copolymer may not have a polar group, or may be a modified product having the above-mentioned polar group partially introduced therein. The modified product is easily compatible with the epoxy resin, and therefore the adhesiveness is further improved.

[0054] 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 lower and a second polymer portion having a glass transition temperature (Tg) of 20° C. or higher. Such a (meth)acrylic acid ester copolymer has the first polymer portion that becomes a soft segment and the second polymer portion that becomes a hard segment.

[0055] The manifestation of the above-mentioned effect can be presumed as follows: By using an acrylic resin having both a soft segment and a hard segment, such as the above-mentioned (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so that an adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0056] 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.

[0057] When either the first polymer portion or the second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible portion, which is a polymer portion that is compatible with the epoxy resin, and an incompatible portion, which is a polymer portion that is incompatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added to the adhesive composition, the compatible portion is compatible with the epoxy resin, and the incompatible portion is incompatible with the epoxy resin, so that fine phase separation occurs. As a result, a fine sea-island structure is developed. The sea-island structure varies depending on the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and the presence or absence of modification by introduction of a polar group, and examples thereof include a sea-island structure in which the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is a sea, and the incompatible portion of the (meth)acrylic acid ester copolymer is an island, a sea-island structure in which the incompatible portion of the (meth)acrylic acid ester copolymer is a sea, and the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island, and a sea-island structure in which the (meth)acrylic acid ester copolymer is a sea, and the cured epoxy resin is an island. By having such a sea-island structure, stress can be easily dispersed, so that interfacial destruction can be avoided, and excellent adhesion can be obtained after foaming and curing.

[0058] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an ABA block copolymer in which the compatible portion is polymer block A and the incompatible portion is polymer block B. Furthermore, it is preferable that the ABA block copolymer is an ABA block copolymer in which the first polymer portion is an incompatible portion, the second polymer portion is an compatible portion, the first polymer portion is polymer block B, and the second polymer portion is polymer block A. By using such an ABA block copolymer as the acrylic resin, in the case of a sea-island structure in which the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is the sea, and the incompatible portion of the (meth)acrylic acid ester copolymer is the island, the island portion can be made small. In addition, in the case of a sea-island structure in which the incompatible portion of the (meth)acrylic acid ester copolymer is the sea, and the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is the island, or in the case of a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea, and the cured epoxy resin is the island, the sea portion can be made small.

[0059] The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a part of the first polymer segment or the second polymer segment.

[0060] The Tg of the first polymer portion contained in the above (meth)acrylic acid ester copolymer is 10°C or lower, and can be within the range of -150°C or higher and 10°C or lower, particularly within the range of -130°C or higher and 0°C or lower, and particularly within the range of -110°C or higher and -10°C or lower.

[0061] The Tg of the first polymer portion can be calculated using the following formula based on the Tg(K) of each homopolymer described in "POLYMERHANDBOOK, 3rd Edition" (published by John Wiley & Sons, Inc.). 1 / Tg(K)=W1 / Tg1+W2 / Tg2+····+W n / Tg n W n ; Mass fraction of each monomer Tgn Tg(K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and EH Immergut, WILEY INTERSCIENCE) may be used. The same applies to the Tg of the second polymer portion described below.

[0062] The first polymer portion contained in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component and polymer component constituting the first polymer portion may be a monomer component and polymer component capable of obtaining a first polymer portion having a Tg in a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

[0063] The Tg of the second polymer portion contained in the above (meth)acrylic acid ester copolymer is 20°C or higher, and can be within the range of 20°C or higher and 150°C or lower, particularly within the range of 30°C or higher and 150°C or lower, and particularly within the range of 40°C or higher and 150°C or lower.

[0064] The second polymer portion contained in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component constituting the second polymer portion may be any monomer component capable of obtaining a second polymer portion having a Tg in a predetermined range, and examples thereof include acrylic acid ester monomers such as methyl methacrylate, other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, and methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups.

[0065] A specific example of the (meth)acrylic acid ester copolymer having the above-mentioned first polymer portion and second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

[0066] The content of the acrylic resin may be, 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, based on 100 parts by mass of the resin component contained in the adhesive composition. If the content of the acrylic resin is too small, the crack resistance and adhesiveness may be reduced. On the other hand, the content of the acrylic resin may be, 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, based on 100 parts by mass of the resin component contained in the adhesive composition. If the content of the acrylic resin is too high, the contents of the first epoxy resin and the second epoxy resin become relatively small, and blocking resistance, adhesiveness, and crack resistance may not be compatible.

[0067] 3. Hardener As the curing agent in the present disclosure, a curing agent generally used in an epoxy resin adhesive can be used. The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can extend the storage stability (pot life) compared with a curing agent that is liquid at 23°C. The curing agent may be a latent curing agent. The curing agent may be a curing agent that undergoes a curing reaction by heat, or may be a curing agent that undergoes a curing reaction by light. In the present disclosure, the curing agent may be used alone or in combination of two or more kinds.

[0068] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction initiation 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 initiation temperature of the curing agent is, for example, 200°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate. In addition to the epoxy resin, when a resin with high heat resistance, such as a phenolic resin, is used, the resin component is less deteriorated, so the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0069] Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

[0070] Examples of imidazole-based curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-phenylimidazole, carboxylates of imidazole compounds, and adducts with epoxy compounds. It is also preferable that the imidazole-based curing agent has a hydroxyl group. Since crystallization occurs due to hydrogen bonds between hydroxyl groups, the reaction initiation temperature tends to be high.

[0071] Examples of the phenol-based curing agent include phenol resins. Examples of the phenol resin include resol-type phenol resins and novolac-type phenol resins. From the viewpoint of crack resistance, etc., phenol-type novolac resins having a Tg of 110° C. or less are particularly preferred. Also, a phenol-based curing agent and an imidazole-based curing agent may be used in combination. In this case, it is preferable to use an imidazole-based curing agent as a curing catalyst.

[0072] Examples of the amine-based curing agent include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. In addition, examples of the amine-based curing agent that can be used include dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents.

[0073] Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0074] The isocyanate-based curing agent may, for example, be a blocked isocyanate.

[0075] Examples of the thiol-based curing agent include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0076] 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 100 parts by mass. For example, when an imidazole-based curing agent is used as the main component as the curing agent, the content of the curing agent is, for example, 1 part by mass or more and 15 parts by mass or less, when the resin component contained in the adhesive composition is 100 parts by mass. On the other hand, when a phenol-based curing agent is used as the main component as the curing agent, the content of the curing agent is, for example, 5 parts by mass or more and 40 parts by mass or less, when the resin component contained in the adhesive composition is 100 parts by mass. In addition, using an imidazole-based curing agent or a phenol-based curing agent as the main component as the curing agent means that the mass ratio of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0077] 4. Foaming agent The foaming agent in the present disclosure may be a 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.

[0078] The foaming start temperature of the foaming agent is preferably equal to or higher than the softening temperature of the epoxy resin and equal to or lower than the activation temperature of the curing reaction of the epoxy resin. The softening temperature of the epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K 2207. The foaming start temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the reaction start temperature is too low, the reaction 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 generate uniform foaming. On the other hand, the reaction start temperature of the foaming agent is, for example, 210°C or lower. If the reaction start temperature is too high, the resin component may deteriorate.

[0079] Examples of the foaming agent include organic foaming agents and inorganic foaming agents. Examples of the organic foaming agent 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. Examples of the inorganic foaming agent include ammonium carbonate, ammonium hydrogen carbonate, ammonium nitrite, ammonium borohydride, and azides.

[0080] Alternatively, a microcapsule type foaming agent may be used as the foaming agent. The microcapsule type foaming agent preferably has a core made of a thermal expansion agent such as a hydrocarbon and a shell made of a resin such as an acrylonitrile copolymer.

[0081] The expansion ratio of the foaming agent is, for example, 1.5 times or more, and may be 3 times or more. On the other hand, the content ratio of the foaming agent is, for example, 15 times or less, and may be 10 times or less.

[0082] 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, based on 100 parts by mass of the resin component contained in the adhesive composition, while the content of the foaming agent is, for example, 20 parts by mass or less and may be 15 parts by mass or less.

[0083] 5. Adhesive Composition The adhesive composition in the present disclosure contains at least the above-mentioned epoxy resin and acrylic resin as the resin component. The adhesive composition may contain only the epoxy resin and the acrylic resin as the resin component, or may further contain other resins. Examples of the other resins include urethane resins. The total ratio of the first epoxy resin, the second epoxy resin, and the 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.

[0084] The proportion of the resin component in the solid content of the adhesive composition is, for example, 60 mass % or more, optionally 70 mass % or more, optionally 80 mass % or more, or optionally 90 mass % or more.

[0085] The adhesive composition may contain 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, as necessary. Examples of the silane coupling agent include an epoxy-based silane coupling agent. Examples of the filler include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, a molybdenum compound, and titanium dioxide. Examples of the antioxidant include a phenol-based antioxidant and a sulfur-based antioxidant.

[0086] The adhesive composition may or may not contain a solvent. In this specification, the solvent is used in a broad sense including 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.

[0087] The adhesive composition of the present disclosure 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.

[0088] The use of the adhesive composition in the present disclosure is not particularly limited, but it is preferably used in the adhesive layer of a foamable adhesive sheet. The adhesive composition in the present disclosure may also be used as an adhesive as it is.

[0089] B. Foam adhesive sheet The foamable adhesive sheet according to the present disclosure is a foamable adhesive sheet having at least an adhesive layer, the adhesive layer containing an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, the adhesive layer containing, as the epoxy resin, a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or higher, the acrylic resin having a weight average molecular weight of 50,000 or higher.

[0090] In this specification, the term "sheet" also includes a member called a "film." Furthermore, the term "film" also includes a member called a "sheet."

[0091] 1 and 2 are schematic cross-sectional views illustrating a foamable adhesive sheet according to the present disclosure. The foamable adhesive sheet 10 in FIG. 1 has only an adhesive layer 1. The foamable adhesive sheet 10 in FIG. 2 has a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b in this order in the thickness direction. FIG. 3 is a schematic perspective view illustrating a foamable adhesive sheet according to the present disclosure. The foamable adhesive sheet 10 in FIG. 3 is rolled up so that one surface of the adhesive layer 1 and the other surface of the adhesive layer 1 are in contact with each other. Although not shown, the foamable adhesive sheet according to the present disclosure may be rolled up so that the first adhesive layer 1a and the second adhesive layer 1b in FIG. 2 are in contact with each other.

[0092] According to the present disclosure, since the adhesive layer contains a specific epoxy resin and a specific acrylic resin, it is possible to obtain a foamable adhesive sheet having good blocking resistance, adhesion, and cracking resistance. In addition, since the foamable adhesive sheet in the present disclosure has good blocking resistance, it is not necessary to provide a release layer or release sheet for the purpose of preventing blocking.

[0093] 1.Adhesive layer The foamable adhesive sheet of the present disclosure has at least an adhesive layer. The adhesive layer contains at least an epoxy resin, an acrylic resin, a curing agent, and a foaming agent. These materials are the same as those described in "A. Adhesive composition" above, so the description here is omitted.

[0094] 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 adhesiveness may not be obtained. On the other hand, the thickness of the adhesive layer is, for example, 200 μm or less.

[0095] The adhesive layer in the present disclosure is preferably non-tacky (tack-free). Non-tacky is generally used mainly to mean low adhesive strength, and in the present disclosure, "non-tacky" refers to a state in which the foamable adhesive sheet is wound into a roll and can be easily unwound without resistance. In addition, when the adhesive strength is, for example, 0 (N / 25mm) or more and 0.1 (N / 25mm) or less in a measurement (adherend SUS304 BA) in accordance with JIS Z0237 (10.4.1_180° peeling), it can be determined to be non-tacky.

[0096] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of the discontinuous layer include a pattern such as a stripe or a dot. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

[0097] The adhesive layer can be formed, for example, by applying an adhesive composition and removing the solvent. Examples of the application method 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.

[0098] 2. Base material The foamable adhesive sheet of the present disclosure may have a substrate. The substrate is preferably insulating. The substrate is preferably in the form of a sheet. The substrate sheet may have a single layer structure or a multilayer structure. The substrate sheet may or may not have a porous structure inside.

[0099] Examples of the substrate include resins and nonwoven fabrics. Examples of the resin 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. In addition, liquid crystal polymers (LCPs) may be used as the substrate.

[0100] On the other hand, 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.

[0101] The thickness of the substrate is not particularly limited, but is, for example, 2 μm or more, may be 5 μm or more, or may be 9 μm or more, while the thickness of the substrate is, for example, 200 μm or less, may be 100 μm or less, or may be 50 μm or less.

[0102] 3. Foam adhesive sheet The foamable adhesive sheet in the present disclosure may have a stress relaxation layer between the substrate and the adhesive layer. By providing the stress relaxation layer, the crack resistance of the adhesive layer is further improved, and the adhesion between the substrate and the adhesive layer is also improved. For example, in the foamable adhesive sheet 10 in FIG. 4, the first adhesive layer 1a, the substrate 2, and the second adhesive layer 1b are arranged in this order in the thickness direction, the first stress relaxation layer 3a is arranged between the first adhesive layer 1a and the substrate 2, and the second stress relaxation layer 3b is arranged between the substrate 2 and the second adhesive layer 1b. Note that the foamable adhesive sheet 10 in FIG. 4 has both the first stress relaxation layer 3a and the second stress relaxation layer 3b, but may have only one of them.

[0103] The stress relaxation layer preferably contains a resin and a curing agent. Examples of the resin include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, and a polymer obtained by copolymerizing at least two of them. On the other hand, examples of the curing agent include an isocyanate-based curing agent. In addition, for example, when the reactive group / NCO equivalent is 1, it is preferable to add an isocyanate-based curing agent at a ratio of 0.5% by mass or more and 10% by mass or less to the resin (e.g., polyester).

[0104] The thickness of the stress relaxation layer is not particularly limited, but may be, for example, 0.1 μm or more, may be 0.2 μm or more, or may be 0.5 μm or more. If the stress relaxation layer is too thin, there is a possibility that a sufficient crack resistance improvement effect cannot be obtained. On the other hand, the thickness of the stress relaxation layer is, for example, 10 μm or less. Since the stress relaxation layer itself usually does not have high heat resistance, if the stress relaxation layer is too thick, there is a possibility that the heat resistance (adhesive strength at high temperatures) will decrease.

[0105] When the foamable adhesive sheet of the present disclosure has a stress relaxation layer, the adhesive layer may contain a phenolic resin. The addition of a phenolic resin can improve heat resistance, but on the other hand, crack resistance may decrease. In contrast, by providing a stress relaxation layer, even if the adhesive layer contains a phenolic resin, the decrease in crack resistance can be suppressed. As a result, a foamable adhesive sheet that achieves both improved heat resistance and suppressed decrease in crack resistance can be obtained. The phenolic resin is preferably a biphenyl type from the viewpoint of heat resistance. The phenolic resin may also be a resin in which a phenolic nucleus has been modified. By modifying the phenolic nucleus, for example, heat resistance can be further improved.

[0106] The stress relaxation layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the application method 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.

[0107] The thickness of the foamable adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more, whereas the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

[0108] The foamable adhesive sheet of the present disclosure 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.

[0109] The foamable adhesive sheet of the present disclosure preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 is preferably 2.10 MPa or more at 23°C, more preferably 2.40 MPa or more, and even more preferably 3.0 MPa or more. Moreover, the shear strength (adhesive strength) is preferably 0.28 MPa or more at 200°C, and more preferably 0.30 MPa or more.

[0110] The foamable adhesive sheet of the present disclosure preferably has high electrical insulation after foaming and curing. The dielectric breakdown voltage based on JIS C 2107 is preferably 3 kV or more, more preferably 5 kV or more. In addition, the foamable adhesive sheet after foaming and curing preferably has a thermal conductivity of 0.1 W / mK or more, more preferably 0.15 W / mK or more.

[0111] The use of the foamable adhesive sheet of the present disclosure is not particularly limited. For example, the foamable adhesive sheet of the present disclosure can be used for bonding a coil and a stator in a motor.

[0112] In addition, the present disclosure can provide a method for manufacturing an article using the above-mentioned foamable adhesive sheet. That is, it can provide a method for manufacturing an article having a placement step of placing the above-mentioned 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. For example, as shown in FIG. 5, the above-mentioned foamable adhesive sheet 10 is placed between a first member 20a and a second member 20b (FIG. 5(a), placement step). Next, the foamable adhesive sheet 10 is foamed and cured, for example, by heating (FIG. 5(b), bonding step). The first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 11 after foaming and curing.

[0113] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0114] [Examples 1 to 12, Comparative Examples 1 to 4] Adhesive compositions were prepared with the compositions (mass%) shown in Tables 1 and 2 below. Although not shown in Tables 1 and 2, the adhesive compositions contained ethyl acetate as a solvent, and the solids concentration was adjusted to 35 mass% in each case. Details of the materials shown in Tables 1 and 2 are shown in Table 3.

[0115] Next, a highly insulating polyphenylene sulfide film (PPS film, thickness 100 μm) was prepared as a substrate, and the adhesive composition was applied to one side of this substrate using an applicator so that the thickness after application was 45 μm to 55 μm. The substrate was then dried in a drying oven at 100° C. for 3 minutes to form an adhesive layer. An adhesive layer was similarly formed on the other side of the substrate, and a foamable adhesive sheet was obtained in which an adhesive layer was formed on each of the front and back sides of the substrate.

[0116] [evaluation] (Blocking resistance) The obtained foamable adhesive sheet was cut into a 10 cm x 10 cm piece, and the two cut pieces were stacked together. The sheet was stored for 3 days in a blocking tester under conditions of 3 kg / cm, 40°C, and dry, and the blocking resistance was evaluated. The blocking resistance was evaluated according to the following criteria. ◯: There is no transfer or peeling of the adhesive layer, and the sheets naturally peel off from each other. △: 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. ×: Transfer or peeling of the adhesive layer occurs, or the sheets do not peel off naturally and are so tightly attached that a peeling sound is heard.

[0117] (Crack resistance) The obtained foamable adhesive sheet was cut into a length of 100 mm at a speed of 20 mm / s to 100 mm / s with a cutter (OLFA cutter knife A Plus), and the cut surface was checked for chipping. The crack resistance was evaluated according to the following criteria. 〇: No chipping or cracking on the cut surface ×: The cut surface is chipped and the broken resin scatters.

[0118] (Adhesiveness) As shown in FIG. 6, two aluminum pieces 31 (length 100 mm × width 25 mm × thickness 1.5 mm) were prepared. Spacers 32 (Kapton tape) were placed on one of the aluminum pieces 31 at a predetermined interval. The thickness of the spacer was 351 μm (thickness of five sheets of P-221 made by Nitto Denko Corporation stacked) or 418 μm (thickness of six sheets of P-221 made by Nitto Denko Corporation stacked). A foamable adhesive sheet 10 cut to 12.5 mm × 25 mm was placed between the spacers 32, and the other aluminum piece 31 was placed and fixed with a clip to obtain a test piece.

[0119] The test piece was placed in a heat oven and heated to cure the foamable adhesive sheet 10. The heating conditions were 150°C for 30 minutes or 180°C for 30 minutes. After heating, the shear strength (adhesive strength) of the test piece was measured using Tensilon RTF1350 (manufactured by A&D Co., Ltd.) in accordance with JIS K6850. The tensile speed was 10 mm / min. The measurement temperature was 23°C or 200°C. Evaluation criteria (23℃) 〇: 2.40MPa or more △: 2.10MPa or more, less than 2.40MPa ×: Less than 2.10MPa Evaluation criteria (200℃) 〇: 0.28MPa or more ×: Less than 0.28MPa

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] As shown in Tables 1 and 2, it was confirmed that in Examples 1 to 12, blocking resistance, adhesion, and crack resistance were all good. In contrast, in Comparative Example 1, an epoxy resin with a low molecular weight was used, so blocking was likely to occur. In Comparative Examples 2 to 4, since the acrylic resin, the first epoxy resin, and the second epoxy resin were not contained, it was not possible to achieve both blocking resistance, adhesion, and crack resistance.

[0124] [Reference example] The dynamic viscoelasticity of the acrylic resin alone used in Example 1 was measured. First, the acrylic resin was dissolved in ethyl acetate so that the solid content was 30% by mass. Next, the solution was applied to a PET separator (PET50×1J2 manufactured by Nippa Co., Ltd.) using an applicator so that the thickness was 50 μm, and dried in a drying oven at 100° C. for 3 minutes to form a polymer layer. The storage modulus (E′) and loss tangent (tan δ) of the polymer layer peeled off from the separator were measured using a solid viscoelasticity analyzer (RSA-III manufactured by TA Instruments Co., Ltd.) by a dynamic viscoelasticity measurement method (attachment mode: compression mode, frequency: 1 Hz, temperature: −30° C. to 200° C., heating rate: 10° C. / min) in accordance with JIS K7244-1. The results are shown in FIG. 7.

[0125] As shown in FIG. 7, the acrylic resin used in Example 1 has a storage modulus (E′) of 1×10 at the foaming start temperature (120° C.) of the thermal blowing agent 2. 6 Pa or less. Therefore, at the start of foaming, the fluidity is improved and good foaming properties can be obtained. In addition, the acrylic resin used in Example 1 has a storage modulus (E') of 1 x 10 at the curing start temperature (145°C) of the curing agent 2, for example. 5Pa or more. As mentioned above, shrinkage may occur during curing after foaming (between the end of foaming of the foaming agent and the curing of the adhesive composition), so at this time, it is preferable for the adhesive composition to have a certain degree of viscoelasticity. For example, the first epoxy resin becomes almost liquid-like at temperatures above its softening temperature. In contrast, the acrylic resin used in Example 1 has an E' of 1×10 even at the curing start temperature of the curing agent 2 (145°C). 5 Since the elastic modulus of the acrylic resin used in Example 1 is 1×10 Pa or more, shrinkage can be suppressed and good shape retention can be obtained. 6 Since the viscosity is 0.1 Pa or more, good blocking resistance can be obtained.

[0126] [Example 13] Adhesive compositions having the compositions (mass%) shown in Table 4 below were prepared. Although not shown in Table 4, the adhesive compositions contained ethyl acetate as a solvent, and the solid content concentration of each was adjusted to 35 mass%. Details of each material shown in Table 4 are shown in Table 3.

[0127] Next, a highly insulating polyphenylene sulfide film (PPS film, thickness 100 μm) was prepared as a substrate, and stress relaxation layers were formed on both sides. Specifically, a hardener (polyisocyanate) was prepared at a ratio of 2 parts by mass to 100 parts by mass of polyester / vinyl chloride vinyl acetate copolymer, and further diluted with methiethyl ketone (MEK) so that the solid content was 15%, and applied to the substrate with a bar coater and dried at 120 ° C for 3 minutes in a heat oven. In this way, stress relaxation layers (first stress relaxation layer and second stress relaxation layer) with a thickness of 2 μm were formed on both sides of the substrate. Thereafter, adhesive layers (first adhesive layer and second adhesive layer) were formed on the obtained stress relaxation layer by the same method as in Example 1. As a result, a foamable adhesive sheet was obtained in which the first adhesive layer, first stress relaxation layer, substrate, second stress relaxation layer, and second adhesive layer were arranged in this order. The obtained foamable adhesive sheet was evaluated for blocking resistance, crack resistance, and adhesion in the same manner as in Example 1. The results are shown in Table 4.

[0128] [Table 4]

[0129] As shown in Table 4, it was confirmed that Example 13 had good blocking resistance, adhesion, and crack resistance. In Example 13, the heat resistance is improved because the phenolic resin is contained, but on the other hand, there is a concern that the crack resistance may decrease. However, it was confirmed that the provision of the stress relaxation layer can achieve both improved heat resistance and suppression of the decrease in crack resistance.

[0130] [Examples 14 and 15] Adhesive compositions having the compositions (mass%) shown in Table 5 below were prepared. Although not shown in Table 5, the adhesive compositions contained ethyl acetate as a solvent, and the solid content concentration was adjusted to 35 mass% in each case. Details of each material shown in Table 5 are shown in Table 3.

[0131] Next, a highly insulating polyphenylene sulfide film (PPS film, thickness 100 μm) was prepared as a substrate, and the adhesive composition was applied to one side of this substrate using an applicator so that the thickness after application was 45 μm. Then, the substrate was dried in a drying oven at 100° C. for 3 minutes to form an adhesive layer. An adhesive layer was similarly formed on the other side of the substrate, and a foamable adhesive sheet was obtained in which an adhesive layer was formed on each of the front and back sides of the substrate.

[0132] [Table 5]

[0133] As shown in Table 5, it was confirmed that in Examples 14 and 15, the blocking resistance, adhesion, and cracking resistance were all good. On the other hand, it was confirmed that in Examples 14 and 15, the blocking resistance was somewhat low. This is presumably because the adhesion (tackiness) of the obtained adhesive layer was high due to the high crystallinity (low melt viscosity) of the first epoxy resin used in Examples 14 and 15. Therefore, it was suggested that the crystallinity of the first epoxy resin is preferably not too high. [Explanation of symbols]

[0134] 1 … Adhesive layer 2 … Base material 10... Foam adhesive sheet 11 ... Adhesive sheet after foaming and hardening 20 … Materials 100 … Goods

Claims

1. A foamable adhesive sheet having at least an adhesive layer, the adhesive layer contains an epoxy resin, a resin X compatible with the epoxy resin, a curing agent, and a foaming agent; the adhesive layer contains a first epoxy resin and a second epoxy resin as the epoxy resin, the softening temperature of the second epoxy resin is higher than the softening temperature of the first epoxy resin; the epoxy equivalent of the second epoxy resin is greater than the epoxy equivalent of the first epoxy resin; The resin X contains, as a monomer component, at least one of an acrylic acid ester and an acetal, the foamable adhesive sheet has a bending moment based on JIS P 8125 of 40 gf cm or more and 600 gf cm or less; The foamable adhesive sheet was cut into a 10 cm x 10 cm piece, and two of the cut pieces were stacked on top of each other. The pieces were then stored in a blocking tester under conditions of 3 kg / cm, 40°C, and dry for 3 days, and a blocking resistance test was performed in which the pieces were peeled off. When this test was performed, there was no transfer or peeling of the adhesive layer. A foamable adhesive sheet, wherein when a crack resistance test is conducted in which the foamable adhesive sheet is cut with a cutter to a length of 100 mm at a speed of 20 mm / s or more and 100 mm / s or less and the resulting cut surface is observed, no chipping or cracking occurs on the cut surface.

2. A foamable adhesive sheet having at least an adhesive layer, the adhesive layer contains an epoxy resin, a resin X compatible with the epoxy resin, a curing agent, and a foaming agent; the adhesive layer contains a first epoxy resin and a second epoxy resin as the epoxy resin, the softening temperature of the second epoxy resin is higher than the softening temperature of the first epoxy resin; the weight average molecular weight of the second epoxy resin is greater than the weight average molecular weight of the first epoxy resin; The resin X contains, as a monomer component, at least one of an acrylic acid ester and an acetal, the foamable adhesive sheet has a bending moment based on JIS P 8125 of 40 gf cm or more and 600 gf cm or less; The foamable adhesive sheet was cut into a 10 cm x 10 cm piece, and two of the cut pieces were stacked on top of each other. The pieces were then stored in a blocking tester under conditions of 3 kg / cm, 40°C, and dry for 3 days, and a blocking resistance test was performed in which the pieces were peeled off. When this test was performed, there was no transfer or peeling of the adhesive layer. A foamable adhesive sheet, wherein when a crack resistance test is conducted in which the foamable adhesive sheet is cut with a cutter to a length of 100 mm at a speed of 20 mm / s or more and 100 mm / s or less and the resulting cut surface is observed, no chipping or cracking occurs on the cut surface.

3. a placement step of placing the foamable adhesive sheet according to claim 1 or 2 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 together; A method for manufacturing an article having the following structure:

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