Adhesive composition and foamable adhesive sheet

Abstract

To provide an adhesive composition capable of giving a foamable adhesive sheet having good blocking resistance, adhesiveness and crack resistance.SOLUTION: The adhesive composition contains epoxy resins, an acrylic resin compatibilized with the epoxy resins, a curing agent, and a foaming agent. The adhesive composition contains, as the epoxy resins, a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or less 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 more. The acrylic resin has a weight average molecular weight of 50,000 or more.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 for bonding components together are used in a variety of 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 double-sided adhesive tape or pressure-sensitive adhesive tape is wrapped around the grip portion 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 portion is inserted into the shaft insertion hole, and the grip is left for a while until the solvent evaporates. Patent Document 2 also discloses a method for bonding a CFRP pipe and a metal part using a one-component epoxy adhesive.

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

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-222445 [Patent Document 2] Japanese Patent Application Publication No. 2016-221784 [Patent Document 3] Patent No. 6220100 specification [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-203114 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Documents 3 and 4 disclose adhesive sheets containing a foaming agent (foamable adhesive sheets). One known method of using a foamable adhesive sheet is to insert the foamable adhesive sheet into a gap between components and then allow the foamable adhesive sheet to foam and harden, thereby adhering 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 hardening.

[0006] The present disclosure has been made in view of the above-described circumstances, and a primary object of the present disclosure is to provide an adhesive composition that can provide a foamable adhesive sheet that has good blocking resistance, adhesion, and cracking resistance. [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 having 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, wherein the adhesive layer contains an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, and the adhesive layer contains, as the epoxy resins, 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 having a weight-average molecular weight of 50,000 or higher. [Effects of the Invention]

[0009] The adhesive composition of the present disclosure has the effect of being able to obtain a foamable adhesive sheet that has good blocking resistance, adhesion, and cracking resistance. [Brief explanation 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. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 3] FIG. 1 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 4] FIG. 1 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view showing an example of a method for manufacturing an article according to the present disclosure. [Figure 6] FIG. 1 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 INVENTION

[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 comprises 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.

[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 can provide a foamable adhesive sheet with good blocking resistance, adhesion, and cracking resistance.

[0014] For example, when only improving adhesiveness is desired, it is more effective to use a low molecular weight (low epoxy equivalent) epoxy resin than a high molecular weight (high epoxy equivalent) epoxy resin. 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 tend to assimilate with each other, making blocking more likely to occur.

[0015] In contrast, the present disclosure uses a first epoxy resin with a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight). The first epoxy resin rapidly melts and changes to a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness. Meanwhile, the first epoxy resin has relatively high crystallinity, which can suppress blocking compared to epoxy resins with relatively low crystallinity or no crystallinity. However, using only the first epoxy resin may result in insufficient blocking suppression or excessively high tackiness (stickiness) of the adhesive layer. Therefore, the present disclosure further uses a second epoxy resin with a relatively high softening temperature (relatively low crystallinity) and a high molecular weight. This improves the blocking suppression effect and reduces the tackiness (stickiness) of the adhesive layer. Meanwhile, using the above-described first epoxy resin and second epoxy resin as epoxy resins presents a new problem: the adhesive layer has low toughness and crack resistance. In response to these new challenges, the present disclosure further utilizes an acrylic resin compatible with the epoxy resin, thereby improving both blocking resistance and adhesion, while also improving crack resistance. Furthermore, for example, when an acrylic resin and a first epoxy resin are used without a second epoxy resin, the adhesiveness is good, but the resulting composition is hard and brittle, and the first epoxy resin diffuses significantly. This not only reduces crack resistance, but also makes it more susceptible to blocking. Furthermore, for example, when an acrylic resin and a second epoxy resin are used without a first epoxy resin, it is difficult to obtain good adhesion.

[0016] The adhesive composition of 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 double-sided adhesive tape or pressure-sensitive adhesive tape is wrapped around the grip portion 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 portion is inserted into the shaft insertion hole, and the grip is left for a while until the solvent evaporates. However, this requires waiting for the solvent to evaporate. In contrast, foamable adhesive sheets essentially do not contain solvents, which has the advantage of improving work efficiency.

[0017] Furthermore, for example, Patent Document 2 discloses a method for 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 spilled out from the joint and to protect areas that should not come into contact with the adhesive with masking tape. In contrast, foamable adhesive sheets expand somewhat when foamed and hardened, but have 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. Note that the epoxy resin of the present disclosure is a compound that has at least one epoxy group or glycidyl group and cures by a 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) Daiichi 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. Furthermore, the first epoxy resin has a low molecular weight, which allows for a high crosslink density, resulting in an adhesive layer with good mechanical strength, chemical resistance, and curing properties. Furthermore, 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 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, and may be 3000 g / eq or less, 1000 g / eq or less, or 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, and may be 100 g / eq or more, or 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 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 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a polystyrene-equivalent value 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, or may be 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. Furthermore, 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. This is presumably because if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), its crystallinity is significantly reduced when it is mixed with the second epoxy resin or the acrylic resin, resulting in a decrease in the Tg of the entire adhesive composition. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the uniformity of the adhesive layer obtained 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 composition 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, 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. The first epoxy resin may be one type or two or more types.

[0026] Bisphenol A epoxy resins can exist in a liquid state or a solid state at room temperature depending on the number of repeating units in the bisphenol skeleton. Bisphenol A epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A epoxy resins are particularly preferred because they can improve heat resistance.

[0027] In particular, the first epoxy resin is preferably a bisphenol A novolac 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), and 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), it is preferable that m in R1 is 1, i.e., R1 is -CH2-. Similarly, it is preferable that p in R2 and R3 is 1, i.e., R2 and R3 are -CH3. Furthermore, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with another element or another group.

[0031] The content of the first epoxy resin, relative to 100 parts by mass of the resin components contained in the adhesive composition, 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. If the content of the first epoxy resin is too low, adhesion and blocking resistance may be reduced. On the other hand, the content of the first epoxy resin, relative to 100 parts by mass of the resin components contained in the adhesive composition, 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. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and acrylic resin may be relatively low, and blocking resistance, adhesion, and cracking resistance may not be achieved simultaneously.

[0032] (2) Second epoxy resin The second epoxy resin has a softening temperature higher than that of 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 first epoxy resin. The second epoxy resin has relatively low crystallinity and a high molecular weight, which makes it easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and a high molecular weight, which can suppress an increase in adhesion (tackiness) caused by the first epoxy resin. Furthermore, the second epoxy resin is preferably 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, and may be 30,000 or more, or even 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 greater than, less than, or the same as the epoxy equivalent 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 even 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 temperatures is, for example, 10°C or higher, and may be 20°C or higher, or even 30°C or higher. The softening temperature of the second epoxy resin is, for example, 80°C or higher, and may be 90°C or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or lower.

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

[0038] The content of the second epoxy resin, relative to 100 parts by mass of the resin components contained in the adhesive composition, 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. If the content of the second epoxy resin is too low, blocking resistance may be reduced. On the other hand, the content of the second epoxy resin, relative to 100 parts by mass of the resin components contained in the adhesive composition, 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. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and acrylic resin become relatively low, and blocking resistance, adhesion, and cracking resistance may not be achieved simultaneously.

[0039] The proportion of the first epoxy resin relative to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, or alternatively 10% by mass or more, or 15% by mass or more, or even 20% by mass or more, while the proportion of the first epoxy resin is, for example, 80% by mass or less, or alternatively 75% by mass or less, or alternatively 60% by mass or less.

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

[0041] 2. Acrylic resin The acrylic resin in the present disclosure is a resin compatible with epoxy resins and has a weight-average molecular weight of 50,000 or more. Because the acrylic resin is compatible with epoxy resins, it is easy to improve the toughness of the adhesive layer. As a result, crack resistance can be improved. Furthermore, improved toughness of the adhesive layer can improve adhesion. Furthermore, it is believed that the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming the foam, thereby improving adhesion. Furthermore, the first epoxy resin has relatively high crystallinity, which can result in excessively low melt viscosity (or dynamic viscoelasticity) during heating, potentially causing shrinkage during curing after foaming (between the end of foaming of the foaming agent and the curing of the adhesive composition). However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, making it less likely to shrink during curing after foaming. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness on the surface of the adhesive layer. Furthermore, when the acrylic resin is incompatible with the sheet, flexible portions are formed on the surface of the sheet, which can 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. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of an adhesive layer prepared using the adhesive composition with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to see if micron-sized islands are not present. 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 even 0.3 μm or less. A large number of samples is preferably used, for example, 100 or more. The area to be observed is a range of 100 μm × 100 μm, or, if the thickness of the adhesive layer is 100 μm or less, a range of the thickness × 100 μm.

[0043] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, or 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 JIS K 7121.

[0045] Acrylic resin has a storage modulus (E') of 1 x 10 at the foaming initiation temperature. 6 A low E' at the foaming initiation temperature can improve fluidity and provide good foaming properties. On the other hand, E' at the foaming initiation temperature can be, for example, 1 x 10 5 The foaming initiation temperature is equal to or higher than 100 Pa. The foaming initiation temperature varies depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the temperature at which the main foaming reaction begins.

[0046] Acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. 5 The viscosity may be 100 Pa or more. As mentioned above, shrinkage may occur during curing after foaming (between the time when the foaming of the foaming agent is completed and the time when the adhesive composition is cured). However, if E' at the curing initiation temperature is large, shrinkage can be suppressed and good shape retention can be obtained. The curing initiation temperature varies depending on the type of curing agent. When two or more curing agents are used as the curing agent, the initiation temperature of the main curing reaction is taken as the curing initiation temperature.

[0047] In addition, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1 x 10 6The average value of E' before foaming may be high, thereby obtaining good blocking resistance. On the other hand, the average value of the 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 is a homopolymer of an acrylic acid ester monomer, and may be a mixed component containing two or more of the above homopolymers, or may be a copolymer of two or more acrylic acid ester monomers and may be 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 ester monomer "acrylic acid" also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or may be an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. In particular, the acrylic resin preferably contains a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0050] Examples of the monomer component constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer component may have the polar group described above. Examples of the (meth)acrylic acid ester copolymer include an ethyl acrylate-butyl acrylate-acrylonitrile copolymer, an ethyl acrylate-acrylonitrile copolymer, and a 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. In these examples, "acrylic acid" also includes "methacrylic acid."

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

[0053] The acrylic copolymer may have no polar groups, or may be a modified product in which the above-mentioned polar groups have been partially introduced. The modified product is highly compatible with epoxy resins, thereby further improving adhesion.

[0054] Among these, 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. Furthermore, 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 an adhesive composition, the compatible portion is compatible with the epoxy resin, and the incompatible portion is incompatible with the epoxy resin, causing fine phase separation. As a result, a fine sea-island structure is formed. 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 whether or not modification by introduction of polar groups has been performed, and examples include a sea-island structure in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands, a sea-island structure in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. Such a sea-island structure makes it easier to disperse stress, thereby preventing interfacial failure and achieving excellent adhesion after foaming and curing.

[0058] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an ABA block copolymer having a polymer block A as the compatible portion and a polymer block B as the incompatible portion. Furthermore, an ABA block copolymer having a first polymer portion as the incompatible portion and a second polymer portion as the compatible portion, polymer block B as the first polymer portion, and polymer block A as the second polymer portion, is preferred. By using such an ABA block copolymer as the acrylic resin, the island portions can be reduced in a case where a sea-island structure is formed in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands. Furthermore, the sea portions can be reduced in a case where a sea-island structure is formed in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in a case where the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands.

[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 (meth)acrylic acid ester copolymer is 10°C or less, and can be in the range of -150°C or more and 10°C or less, particularly in the range of -130°C or more and 0°C or less, and particularly in the range of -110°C or more and -10°C or less.

[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 "POLYMER HANDBOOK, 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 This is the Tg (K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and E.H. 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 either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer and polymer components constituting the first polymer portion may be any monomer and polymer components capable of obtaining a first polymer portion having a Tg within 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 (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 either 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 within 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 first polymer portion and the second polymer portion is the MMA-BA-MMA copolymer.

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

[0067] 3. Hardener The curing agent in the present disclosure may be a curing agent generally used in epoxy resin adhesives. The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can have a longer storage stability (pot life) than a curing agent that is liquid at 23°C. The curing agent may also be a latent curing agent. The curing agent may also be a curing agent that undergoes a curing reaction when heated, or a curing agent that undergoes a curing reaction when exposed to light. In the present disclosure, a single curing agent may be used, or two or more types of curing agents may be used.

[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 will start early, and curing will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform curing. 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. Note that when a highly heat-resistant resin such as a phenolic resin is used in addition to an epoxy resin, the resin component will deteriorate less, and 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, and 2-phenylimidazole, as well as carboxylic acid salts of imidazole compounds and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxyl groups, which tends to increase the reaction initiation temperature.

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

[0072] Examples of amine-based curing agents 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. Furthermore, examples of amine-based curing agents 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 curing agent may, for example, be a blocked isocyanate.

[0075] Examples of thiol-based curing agents 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, based on 100 parts by mass of the resin component contained in the adhesive composition. For example, when an imidazole-based curing agent is used as the main curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive composition. On the other hand, when a phenol-based curing agent is used as the main curing agent, the content of the curing agent is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive composition. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main curing agent means that the mass proportion 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 when exposed to heat or light.

[0078] The foaming initiation 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 initiation temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the reaction initiation temperature is too low, the reaction will start prematurely, and foaming will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform foaming. On the other hand, the reaction initiation temperature of the foaming agent is, for example, 210°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate.

[0079] Examples of the blowing agent include organic blowing agents and inorganic blowing agents. Examples of the organic blowing agent include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, fluorinated alkane blowing agents such as trichloromonofluoromethane, hydrazine blowing agents such as paratoluenesulfonylhydrazide, semicarbazide blowing agents such as p-toluenesulfonylsemicarbazide, triazole blowing agents such as 5-morpholyl-1,2,3,4-thiatriazole, and N-nitroso blowing agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of the inorganic blowing agent include ammonium carbonate, ammonium bicarbonate, 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 hydrocarbon and a shell made of a resin such as 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, while 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 according to the present disclosure contains at least the above-described epoxy resin and acrylic resin as resin components. The adhesive composition may contain only the epoxy resin and acrylic resin as resin components, or may further contain other resins. Examples of other resins include urethane resins. The total proportion of the first epoxy resin, second epoxy resin, and acrylic resin relative to the resin components contained in the adhesive composition is, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, or even 100% by mass.

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

[0085] The adhesive composition may contain, as necessary, 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, a molybdenum compound, and titanium dioxide. Examples of the antioxidant include phenol-based antioxidants and sulfur-based antioxidants.

[0086] 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.

[0087] The adhesive composition of the present disclosure can be obtained by mixing the above-mentioned components and, if necessary, kneading and dispersing them. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desper, a homogenizer, or an ultrasonic disperser, can be used.

[0088] The use of the adhesive composition of the present disclosure is not particularly limited, but it is preferably used in the adhesive layer of a foamable adhesive sheet. Alternatively, the adhesive composition of the present disclosure may be used as an adhesive as 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, wherein the adhesive layer contains an epoxy resin, an acrylic resin compatible with the epoxy resin, a curing agent, and a foaming agent, and the adhesive layer contains, 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, and 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 an example of 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 that order in the thickness direction. FIG. 3 is a schematic perspective view illustrating an example of 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 contacts the other surface. Although not shown, the foamable adhesive sheet according to the present disclosure may also be rolled up so that the first adhesive layer 1a and the second adhesive layer 1b in FIG. 2 contact each other.

[0092] According to the present disclosure, the adhesive layer contains a specific epoxy resin and a specific acrylic resin, so that the foamable adhesive sheet has good blocking resistance, adhesion, and cracking resistance. Furthermore, because the foamable adhesive sheet according to the present disclosure has good blocking resistance, there is no need 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 above in "A. Adhesive Composition," so further description here is omitted.

[0094] The thickness of the adhesive layer is not particularly limited, but may be, for example, 10 μm or more, or 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). The term non-tacky is generally used primarily to mean low adhesive strength, and in the present disclosure, "non-tacky" refers to a state in which a foamable adhesive sheet can be wound into a roll and then easily unwound without resistance. Furthermore, when measured in accordance with JIS Z0237 (10.4.1_180° peel) (adherend SUS304 BA), for example, if the adhesive strength is 0 (N / 25 mm) or more and 0.1 (N / 25 mm) or less, it can be determined to be non-tacky.

[0096] 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.

[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 according to the present disclosure may have a substrate. The substrate is preferably insulating. The substrate is preferably in sheet form. The substrate sheet may have a single-layer structure or a multi-layer 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, or may be 140°C or higher, or even 200°C or higher. Furthermore, a liquid crystal polymer (LCP) 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, or 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, or may be 100 μm or less, or may be 50 μm or less.

[0102] 3.Foam adhesive sheet The foamable adhesive sheet of the present disclosure may have a stress relief layer between the substrate and the adhesive layer. The provision of the stress relief layer further improves the crack resistance of the adhesive layer and also improves the adhesion between the substrate and the adhesive layer. For example, in the foamable adhesive sheet 10 shown in FIG. 4, a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b are arranged in this order in the thickness direction, with a first stress relief layer 3a arranged between the first adhesive layer 1a and the substrate 2 and a second stress relief layer 3b arranged between the substrate 2 and the second adhesive layer 1b. While the foamable adhesive sheet 10 shown in FIG. 4 has both the first stress relief layer 3a and the second stress relief layer 3b, it 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 copolymers of at least two of these. On the other hand, examples of the curing agent include isocyanate-based curing agents. Furthermore, 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 to 10% by mass or less relative 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, or 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 effect of improving crack resistance 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 relief layer, the adhesive layer may contain a phenolic resin. Adding a phenolic resin can improve heat resistance, but on the other hand, it may result in a decrease in crack resistance. By providing a stress relief layer, a decrease in crack resistance can be suppressed even when the adhesive layer contains a phenolic resin. As a result, a foamable adhesive sheet can be obtained that achieves both improved heat resistance and suppressed decreases in crack resistance. From the viewpoint of heat resistance, the phenolic resin is preferably a biphenyl type. Furthermore, the phenolic resin may 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, while 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) according to JIS K6850 at 23°C is preferably 2.10 MPa or more, more preferably 2.40 MPa or more, and even more preferably 3.0 MPa or more. Furthermore, the shear strength (adhesive strength) at 200°C is preferably 0.28 MPa or more, more preferably 0.30 MPa or more.

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

[0111] The uses of the foamable adhesive sheet of the present disclosure are not particularly limited. For example, the foamable adhesive sheet of the present disclosure can be used to bond the coil and stator of a motor.

[0112] The present disclosure also provides a method for manufacturing an article using the foamable adhesive sheet described above. Specifically, the method includes a placement step of placing the foamable adhesive sheet described above 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 foamable adhesive sheet 10 described above 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 any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[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. Table 3 shows details of each material listed in Tables 1 and 2.

[0115] Next, a highly insulating polyphenylene sulfide film (PPS film, 100 μm thick) 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. This 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, yielding a foamable adhesive sheet with adhesive layers formed on both the front and back of the substrate.

[0116] [evaluation] (blocking resistance) The resulting foamable adhesive sheet was cut into a 10cm x 10cm piece, and two of the cut pieces were stacked together. The sheet was stored in a blocking tester under conditions of 3 kg / cm, 40°C, and dry for 3 days, and the blocking resistance was evaluated. The blocking resistance was evaluated according to the following criteria. Good: There is no transfer or peeling of the adhesive layer, and the sheets peel off naturally. △: There is no transfer or peeling of the adhesive layer, and the sheets do not peel off naturally, but they can be peeled off with very little 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 resulting foamable adhesive sheet was cut into 100 mm lengths using an Olfa cutter knife (A Plus) at a speed of 20 mm / s to 100 mm / s, and the cut surface was checked for chipping. Crack resistance was evaluated according to the following criteria. 〇: No chipping or cracking occurs on the cut surface ×: Chips occur on the cut surface and 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 spacer thickness was 351 μm (thickness of five stacked Nitto Denko P-221 sheets) or 418 μm (thickness of six stacked Nitto Denko P-221 sheets). 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 clips to obtain a test specimen.

[0119] The test piece was placed in a heating 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 a Tensilon RTF1350 (manufactured by A&D Co., Ltd.) in accordance with JIS K6850. The pulling speed was 10 mm / min. The measurement temperature was 23°C or 200°C. Evaluation criteria (23℃) 〇: 2.40 MPa or more △: 2.10 MPa or more, less than 2.40 MPa ×: Less than 2.10 MPa Evaluation criteria (200℃) 〇: 0.28MPa or more ×: Less than 0.28 MPa

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] As shown in Tables 1 and 2, it was confirmed that Examples 1 to 12 all had good blocking resistance, adhesion, and cracking resistance. In contrast, Comparative Example 1 used an epoxy resin with a low molecular weight, which made blocking more likely to occur. Furthermore, Comparative Examples 2 to 4 did not contain any of the acrylic resin, the first epoxy resin, and the second epoxy resin, so it was not possible to achieve both blocking resistance, adhesion, and cracking resistance.

[0124] [Reference example] Dynamic viscoelasticity measurements were performed on the acrylic resin used in Example 1. First, the acrylic resin was dissolved in ethyl acetate to a solid content of 30% by mass. Next, the solution was applied to a PET separator (PET50x1J2, manufactured by Nippa Corporation) using an applicator to a thickness of 50 μm, and then dried in a drying oven at 100°C for 3 minutes to form a polymer layer. The storage modulus (E') and loss tangent (tanδ) of the polymer layer peeled from the separator were measured using a solid viscoelasticity analyzer (RSA-III, manufactured by TA Instruments Corporation) according to the dynamic viscoelasticity measurement method in accordance with JIS K7244-1 (attachment mode: compression mode, frequency: 1 Hz, temperature: -30°C to 200°C, heating rate: 10°C / min). The results are shown in Figure 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 initiation temperature (120°C) of the thermal blowing agent 2. 6 Pa or less. Therefore, at the start of foaming, 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 Curing Agent 2, for example. 5Pa or more. As mentioned above, shrinkage may occur during curing after foaming (between the time when foaming of the foaming agent is completed and the time when the adhesive composition is cured), so at this time, it is preferable that the adhesive composition has 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 x 10 even at the curing initiation temperature (145°C) of the curing agent 2, for example. 5 Since the storage modulus (E') 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 100 Pa or more, good blocking resistance can be obtained.

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

[0127] Next, a highly insulating polyphenylene sulfide film (PPS film, 100 μm thick) was prepared as a substrate, and stress relief layers were formed on both sides. Specifically, 100 parts by weight of polyester / vinyl chloride / vinyl acetate copolymer and 2 parts by weight of curing agent (polyisocyanate) were prepared, and further diluted with methylethyl ketone (MEK) to a solids content of 15%. The mixture was applied to the substrate using a bar coater and dried in a thermal oven at 120°C for 3 minutes. In this way, 2 μm-thick stress relief layers (first stress relief layer and second stress relief layer) were formed on both sides of the substrate. Subsequently, adhesive layers (first adhesive layer and second adhesive layer) were formed on the obtained stress relief layers using the same method as in Example 1. This resulted in a foamable adhesive sheet in which the first adhesive layer, first stress relief layer, substrate, second stress relief layer, and second adhesive layer were arranged in this order. The resulting foamable adhesive sheet was evaluated for blocking resistance, cracking 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, Example 13 was confirmed to have good blocking resistance, adhesion, and crack resistance. Although Example 13 contains a phenolic resin, which improves heat resistance, there are concerns about a decrease in crack resistance. However, it was confirmed that the provision of a stress relaxation layer can simultaneously improve heat resistance and prevent a decrease in crack resistance.

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

[0131] Next, a highly insulating polyphenylene sulfide film (PPS film, 100 μm thick) 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. The composition 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, yielding a foamable adhesive sheet with adhesive layers formed on both the front and back of the substrate.

[0132] [Table 5]

[0133] As shown in Table 5, it was confirmed that Examples 14 and 15 all had good blocking resistance, adhesion, and cracking resistance. On the other hand, it was confirmed that Examples 14 and 15 had somewhat low blocking resistance. This is presumably because the high crystallinity (low melt viscosity) of the first epoxy resin used in Examples 14 and 15 resulted in high adhesiveness (tackiness) of the resulting adhesive layer. Therefore, it was suggested that it is preferable that the crystallinity of the first epoxy resin is 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... components 100 … Goods

Claims

1. A foamable adhesive sheet having at least an adhesive layer, the adhesive layer contains an epoxy resin, an acrylic resin 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 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, an acrylic resin 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 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:

Images