Thermal Expansion Sheet

Abstract

To provide a heating expansion sheet which can suppress occurrence of a resin flow while sufficiently bonding two adherend surfaces facing each other with a gap therebetween by heating expansion.SOLUTION: A heating expansion sheet which is arranged inside a gap formed of two surfaces and is heated and expanded to bond the two surfaces includes a base material, and a first resin layer and a second resin layer as adhesion layers that are formed on the base material and contain a thermosetting resin, wherein a temperature rising rate of the first resin layer is larger than a temperature rising rate of the second resin layer depending on conditions in heating, and the thickness of the first resin layer before heating is smaller than the thickness of the second resin layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat-expandable sheet.

Background Art

[0002] As a method of adhering an adherend surface without applying external pressure such as by pressing, as described in Patent Document 1, an expanding agent that expands by heating is contained in the adhesive layer of the adhesive sheet, and by heating this adhesive sheet, it is conceivable to utilize the expansion pressure generated in the adhesive layer.

[0003] When using such a heat-expandable sheet to adhere two adherend surfaces facing each other with a narrow space (gap) in between, a method is conceivable in which the heat-expandable sheet is inserted between them and then heated and expanded to fill or reduce the gap between the two adherends.

[0004] However, in this method, a phenomenon called resin flow may occur in which the adhesive layer expanded inside the gap overflows outside the gap.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above-described problems, and an object thereof is to provide a heat-expandable sheet that can suppress the occurrence of resin flow while sufficiently adhering two adherend surfaces facing each other with a gap therebetween by heating and expanding. As a result of intensive studies by the present inventors to solve this problem, it has been found that the occurrence of resin flow is caused by a decrease in the viscosity of the resin during thermal expansion. When a resin layer containing a thermosetting resin is used for the adhesive layer, the decrease in viscosity becomes remarkable as the heating rate increases, while the decrease in the viscosity of the resin is suppressed as the heating rate decreases. The present invention has been made based on the new findings of the present inventors as described above, and has the following features.

[0007] That is, the heat-expandable sheet according to the present invention is a heat-expandable sheet that is disposed inside a gap formed by two adherend surfaces and expands by being heated to adhere the two surfaces, and includes a base material, and a first resin layer and a second resin layer that are adhesive layers containing a thermosetting resin formed on the base material, wherein the heating rate of the first resin layer is greater than the heating rate of the second resin layer depending on the conditions during heating, and the thickness of the first resin layer before heating is smaller than the thickness of the second resin layer.

[0008] According to the heat-expandable sheet configured as described above, since the thickness of the first resin layer, in which the heating rate is higher and the viscosity decrease is likely to occur, is made smaller than that of the second resin layer, the occurrence of resin flow can be suppressed more effectively than before.

[0009] In order to make the heating rate of the second resin layer smaller than the heating rate of the first resin layer, it is preferable that the first resin layer and the second resin layer are disposed with a heating rate control layer interposed therebetween for controlling their heating rates between the first resin layer and the second resin layer. For example, the base material can also be used as the heating rate control layer.

[0010] During heating, the first resin layer may be disposed at a position more susceptible to heat than the second resin layer, so that the heating rates of the first resin layer and the second resin layer are different.

[0011] When the total thickness of the first resin layer and the second resin layer is 90 μm or less and the following formula (1) is satisfied, the effects of the present invention are more significantly exhibited. (Minimum dimension of the gap - Thickness of the base material) / (Total thickness of the first resin layer and the second resin layer) ≤ 2 ··· (1)

[0012] As a specific embodiment of the present invention, examples of the first resin layer and / or the second resin layer include those containing an epoxy resin, a thermoplastic resin, and a thermal expansion agent. Further, examples of the expansion agent include microcapsule-type foaming agents.

[0013] Preferably, the resin flow amount protruding outward from the gap is 1200 μm or less.

[0014] A heat-expandable sheet disposed inside a gap formed by two adherend surfaces and expanded by heating to adhere the two surfaces, comprising a base material, and a first resin layer and a second resin layer which are adhesive layers containing a thermosetting resin formed on the base material, wherein the temperature increase rate of the first resin layer is greater than that of the second resin layer depending on the conditions during heating, and the first resin layer does not contain an expansion agent, or the content of the thermal expansion agent in the first resin layer is half or less of the content of the thermal expansion agent in the second resin layer, can similarly suppress the occurrence of resin flow.

Effects of the Invention

[0015] According to the present invention, it is possible to suppress the occurrence of resin flow while sufficiently adhering two adherend surfaces facing each other with a gap therebetween.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0017] Hereinafter, the heat-expandable sheet according to an embodiment of the present invention will be described with reference to the drawings.

[0018] <Heat-expandable sheet> FIG. 1 is a schematic cross-sectional view showing the configuration of the heat-expandable sheet 1 of the present invention. The heat-expandable sheet 1 of the present invention can be used in various fields, for example, as a conductive sheet for electronic devices or electronic devices, an insulating sheet for electronic devices or electronic devices, and the like. Specifically, this heat-expandable sheet 1 is configured to adhere two adherend surfaces facing each other with a gap therebetween by being disposed inside the gap and heated, and includes a sheet-like base material 10 and an adhesive layer 20 provided on the base material 10.

[0019] <<Base material>> The base material 10 functions as a support material for supporting the adhesive layer 20.

[0020] Specifically, this base material 10 is sheet-like and may have a single-layer structure or a laminated structure. The thickness of the entire base material 10 is, for example, 1 to 300 μm, preferably 5 to 200 μm, and more preferably 25 to 120 μm.

[0021] The material of the base material 10 is not particularly limited and may be an inorganic material or an organic material. For example, when electrical conductivity is required for the heat-expandable sheet, a metal film can be used, and when electrical insulation is required for the heat-expandable sheet, a resin film can be used.

[0022] The metal film is not particularly limited, and for example, copper foil and aluminum foil can be used. The thickness of the metal film is, for example, 1 to 100 μm, preferably 10 to 70 μm, and more preferably 15 to 50 μm.

[0023] The resin film is not particularly limited, and examples include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyesters; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyether amide; polyimide (PI), polyether imide, polyamide imide and other polyimide resins; polysulfone, polyether sulfone and other polysulfone resins; polyether ketone, polyether ether ketone and other polyether ketone resins; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The resin film may be composed of these single resins or a mixture of two or more resins. From the viewpoints of heat resistance and electrical insulation, the resin film is preferably a PEN film, a PET film, a PPS film or a PI film, and more preferably a PEN film, a PPS film or a PI film. The thickness of the resin film is, for example, 1 to 100 μm, preferably 10 to 70 μm, and more preferably 15 to 50 μm.

[0024] <<Adhesive layer>> The adhesive layer 20 includes a first resin layer 21 and a second resin layer 22 that become the outermost layer of the heat-expandable sheet 1 during heat expansion. In the present embodiment, as shown in FIG. 1, the first resin layer 21 and the second resin layer 22 are laminated on both surfaces of the base material 10, respectively. The first resin layer 21 and the second resin layer 22 may have the same composition or different compositions. In the present embodiment, the first resin layer 21 and the second resin layer 22 are resin layers having the same composition, and an adhesive layer having heat-expandability will be described.

[0025] The first resin layer 21 can be formed, for example, by applying a first resin composition constituting the first resin layer 21 onto the substrate 10 and drying it. The second resin layer 22 can be formed, for example, by applying a second resin composition constituting the second resin layer 22 onto the substrate 10 and drying it. Here, the first resin composition means a composition containing all the materials included in the first resin layer 21 and an appropriate solvent (volatile component) that suspends or dissolves these materials. Similarly, the second resin composition means a composition containing all the materials included in the second resin layer 22 and an appropriate solvent (volatile component) that suspends or dissolves these materials. In this embodiment, the first resin layer 21 and the second resin layer 22, and the first resin composition and the second resin composition have the same composition. Therefore, hereinafter, the first resin layer 21 and the first resin composition will be described. The first resin layer 21 contains a thermosetting resin, a curing agent, a thermoplastic resin, and an expanding agent.

[0026] A thermosetting resin has a crosslinkable functional group that reacts with a curing agent by heat. Examples of the crosslinkable functional group include a hydroxyl group, a phenolic hydroxyl group, a carboxyl group, an epoxy group, an oxazoline group, an oxazine group, a silanol group, an alkoxysilane group, a hydroxyl group, an amino group, an imino group, an isocyanate group, a blocked isocyanate group, a blocked carboxyl group, etc. Among these, considering the heat curing temperature and film-forming properties, the epoxy group is most preferred. Among those other than the epoxy group, the carboxyl group and the acid anhydride group are preferred. Specifically, the acid value of the thermosetting resin is preferably 5 to 90 mgKOH / g, more preferably 10 to 70 mgKOH / g. When the acid value is 5 mgKOH / g or more, heat resistance is easily obtained. When the acid value is less than 5 mgKOH / g, crosslinking is insufficient, the strength of the coating film becomes weak, and heat resistance cannot be obtained. Also, when the acid value exceeds 90 mgKOH / g, there arises a problem that the number of crosslinking points increases and the flexibility of the coating film is lost. Note that the thermosetting resin can have two or more kinds of crosslinkable functional groups. Examples of the thermosetting resin include a polyester resin, an epoxy ester resin, a polyamide resin, a polyurethane resin, a side-chain modified phenoxy resin, and the like. Among these, a urethane or epoxy resin is preferred in terms of adhesion, durability, and melt viscosity. These resins can be used alone or in combination of two or more. Hereinafter, the case where an epoxy resin is used as the thermosetting resin will be described, but the same configuration can be adopted even when other types of thermosetting resins such as urethane resins are used. Examples of the epoxy resin preferably include a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a hindered indol type epoxy resin, a biphenyl type epoxy resin, an alicyclic epoxy resin, a triphenylmethane type epoxy resin, a phenol novolac type epoxy resin, a cresol novolac type epoxy resin, a naphthol novolac type epoxy resin, a dicyclopentadiene / phenol epoxy resin, an alicyclic amine epoxy resin, an aliphatic amine epoxy resin, and epoxy resins obtained by various modifications of these. The epoxy resin may be composed of these single compounds or may be composed of a mixture of two or more. From the viewpoints of heat resistance and electrical insulation, etc., the epoxy resin is preferably a novolac type epoxy resin.

[0027] The softening point of the epoxy resin can be measured using the ring and ball softening point test method defined in JIS K 2207. The foam start temperature of the first resin layer 21 is preferably in the range of, for example, 70 to 200°C, more preferably 100°C to 180°C.

[0028] The content of the thermosetting resin is preferably 30 to 70% by mass based on the total mass of the first resin layer 21. When the content is 30% by mass or more, it is superior in heat resistance and insulation. Also, when the content is 70% by mass or less, it is superior in flexibility and film-forming property. The content is more preferably 40 to 65% by mass, and even more preferably 50 to 60% by mass. As described above, the first resin layer 21 contains both a thermosetting resin and a thermoplastic resin. As can be seen from the content, the thermosetting resin serves as a base agent, and the first resin layer 21 as a whole has the properties of a thermosetting resin.

[0029] The thermosetting resin is preferably cured using a curing agent. The curing agent may be any compound having one or more functional groups capable of reacting with the crosslinkable functional groups of the thermosetting resin and is not limited. When an epoxy resin is used as the thermosetting resin, the curing agent preferably includes at least one of, for example, amide-based curing agents such as dicyandiamide and aliphatic polyamide; amine-based curing agents such as diaminodiphenylmethane, metaphenylenediamine, ammonia, triethylamine, and diethylamine; phenolic curing agents such as bisphenol A, bisphenol F, phenol novolak resin, cresol novolak resin, and p-xylene novolak resin; acid anhydride-based curing agents. The curing agent may consist of these single compounds or may consist of a mixture of two or more. Also, since the storage stability (pot life) can be extended, it is preferable to use a latent curing agent. A latent curing agent is generally a curing agent whose curing is promoted by external stimuli such as heat and light. In the present invention, by using a latent curing agent, the foamed epoxy resin can be quickly cured at a desired timing. Among latent curing agents, from the viewpoint of the curing reaction rate, the curing agent more preferably contains at least one of an amide-based curing agent and an amine-based curing agent, and even more preferably contains dicyandiamide.

[0030] For example, when using an epoxy resin as a thermosetting resin, in order to cause an appropriate curing reaction and ensure sufficient adhesive strength, the equivalent ratio of the equivalent of the curing agent to the epoxy equivalent of the epoxy resin (equivalent of the curing agent / equivalent of the epoxy resin) is preferably 0.8 to 1.2, more preferably 0.85 to 1.15, and even more preferably 0.9 to 1.1. In particular, when the curing agent contains an amide-based curing agent, it is preferable that the above equivalent ratio is 0.8 to 1.2.

[0031] In this specification, the epoxy equivalent is the value obtained by dividing the molecular weight of the epoxy compound by the number of epoxy groups in one molecule. The epoxy equivalent can be determined by measuring the potential difference with a 0.1 mol / L perchloric acid acetic acid standard solution in accordance with JIS K7236. The curing agent equivalent is the value obtained by dividing the molecular weight of the curing agent by the number of active hydrogens (sites that react with epoxy groups) in one molecule. The curing agent equivalent can be determined by the acetyl chloride-potassium hydroxide titration method. Furthermore, component analysis can be performed using a nuclear magnetic resonance apparatus (NMR), gas chromatography (GC), or gel permeation chromatography (GPC), and it can be calculated from the analysis results. In addition, when the crosslinkable functional group of the thermosetting resin is a carboxyl group, the curing agent is preferably an epoxy compound, an alidylin compound, an isocyanate compound, a polyol compound, an amine compound, a melamine compound, a silane-based compound, a carbodiimide-based compound, a metal chelate compound, or the like. Also, when the crosslinkable functional group is a hydroxyl group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or a metal chelate compound. When the crosslinkable functional group is an amino group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or a metal chelate compound. These curing agents can be used alone or in combination of two or more. The equivalent ratio of the thermosetting resin and the curing agent in these cases can be appropriately changed according to the combination of the thermosetting resin and the curing agent used. For example, when a urethane resin is used as the thermosetting resin and an epoxy compound is used as the curing agent, the contents of these can be determined according to the equivalent ratio of the epoxy equivalent and the amine equivalent described above.

[0032] The thermoplastic resin preferably contains at least one of a polyester resin, an acetal resin (such as a butyral resin), a urethane resin, an acrylic resin, a carboxyl-terminated butadiene nitrile rubber (CTBN), and an epoxy-modified butadiene. Among them, it is more preferable to contain at least one of an acrylic resin, a urethane resin, and an acetal resin. The thermoplastic resin may be composed of these single compounds or may be composed of a mixture of two or more. Further, the thermoplastic resin preferably contains a thermoplastic elastomer, and more preferably is a thermoplastic elastomer. The glass transition temperature (Tg) of this thermoplastic elastomer is preferably 100 to 120°C. An elastomer having a Tg in such a range is also called a high softening point elastomer.

[0033] The content of the thermoplastic resin is preferably 3 to 30% by mass based on the total mass of the first resin layer 21. When the content is 3% by mass or more, the first resin layer 21 acquires flexibility and the foamability is improved. Further, when the content is 30% by mass or less, the flexibility of the first resin layer 21 is maintained within an appropriate range and sufficient adhesive strength can be ensured. The content is more preferably 4 to 25% by mass, and even more preferably 5 to 20% by mass. In particular, when the thermoplastic resin is an elastomer, it is preferable that the content is 3 to 30% by mass.

[0034] The blowing agent is not particularly limited, and either inorganic or organic blowing agents may be used. Specifically, the blowing agent may be an inorganic blowing agent such as ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, azides; an alkane fluoride such as trichloromonofluoromethane; an azo compound such as azobisisobutyronitrile; a hydrazine compound such as paratoluenesulfonyl hydrazide; a semicarbazide compound such as p-toluenesulfonyl semicarbazide; a triazole compound such as 5-morpholyl-1,2,3,4-thiatriazole; an N-nitroso compound such as N,N'-dinitrosoterephthalamide, and at least one kind of microencapsulated blowing agent obtained by microencapsulating a hydrocarbon solvent. The blowing agent may consist of these single compounds or may consist of a mixture of two or more kinds. Among these, from the viewpoint of not inhibiting the curing of the adhesive layer 20 and reducing the adverse effects on the physical properties of the epoxy resin, the blowing agent is preferably a microcapsule blowing agent as described above.

[0035] The thermally expandable microcapsule is a microcapsule having a thermoplastic resin with gas barrier properties as a shell and containing a thermal expansion agent inside the shell. When the thermally expandable microcapsule is heated, the thermoplastic resin of the shell softens, and the volume of the thermal expansion agent increases, causing the capsule to expand. For example, the vaporization of a low-boiling hydrocarbon compound can be utilized for the expansion of the capsule.

[0036] The content of the blowing agent is preferably 3 to 19% by mass based on the total mass of the first resin layer 21. When the content is 3% by mass or more, sufficient foaming properties can be ensured and the adhesive strength is improved. Also, when the content is 19% by mass or less, a decrease in the adhesive strength due to excessive foaming can be suppressed. The content is more preferably 4 to 17% by mass, still more preferably 5 to 15% by mass, and particularly preferably 7 to 12% by mass. In particular, it is preferable that the blowing agent contains thermally expandable microcapsules and the content is 3 to 19% by mass.

[0037] In addition to those described above, the first resin layer 21 may also contain other additives such as a curing accelerator and a filler, if necessary.

[0038] As the curing accelerator, it is preferable to contain at least one of imidazoles such as 2-methylimidazole, 2-methyl-4-ethylimidazole, and 2-phenylimidazole; tertiary amines such as 1,8-diazabicyclo[5.4.0]undecene-7, triethylenediamine, and benzyldimethylamine; and organic phosphines such as tributylphosphine and triphenylphosphine. The curing accelerator may consist of these single compounds or may consist of a mixture of two or more. The content of the curing accelerator is preferably 0.1 to 5% by mass, more preferably 0.5 to 4% by mass, and particularly preferably 1 to 3% by mass based on the total mass of the first resin layer 21.

[0039] The filler preferably contains at least one of inorganic fillers such as aluminum oxide, magnesium oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, boron nitride, silicon nitride, silicon oxide, and talc (magnesium silicate). The filler may consist of these single compounds or may consist of a mixture of two or more. The content of the filler is preferably 3 to 20% by mass, more preferably 5 to 17% by mass, and particularly preferably 7 to 15% by mass based on the total mass of the first resin layer 21.

[0040] In the heat-expandable sheet 1 provided with the adhesive layer 20 as described above, the thicknesses of the first resin layer 21 and the second resin layer 22 before heat expansion (during the production of the heat-expandable sheet 1) are each preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 70 μm or less, and particularly preferably 20 μm or more and 40 μm or less when alone.

[0041] In the heat-expandable sheet 1 according to this embodiment, the thickness of the first resin layer 21 before heat expansion (during the production of the heat-expandable sheet) is made smaller than that of the second resin layer 22. The thickness of the first resin layer 21 may be smaller than that of the second resin layer 22. For example, it is preferable that the ratio of the thickness (thickness of the first resin layer / thickness of the second resin layer) is in the range of 0.2 or more and 0.8 or less.

[0042] Furthermore, in the curing process of the first resin layer 21 and the second resin layer 22, it is preferable that there is a minimum viscosity temperature at which the viscosity of the epoxy resin is the lowest in the temperature range from the foam start temperature to the curing active temperature in the curing behavior of each of these resin layers 21, 22. The minimum viscosity temperature at which the viscosity of the epoxy resin is the lowest can be obtained, for example, as the temperature indicating the off-peak of the complex viscosity curve from the relationship between the temperature measured by a viscoelasticity measuring device and the melt viscosity (complex viscosity) of the resin sample. For example, FIG. 2 is a graph showing the relationship between the foam start temperature, the minimum viscosity temperature, and the curing active temperature for a resin layer (hereinafter referred to as a sample) formed using the first resin composition described in a predetermined embodiment. In FIG. 2, temperature a is the foam start temperature (135 ° C.) obtained from the TMA curve of the sample, temperature b is the minimum viscosity temperature (192 ° C.) obtained from the complex viscosity curve of the sample, and temperature c is the curing active temperature (210 ° C.) obtained from the DSC curve of a sample prepared in the same manner. Since the minimum viscosity temperature is in the temperature range from the above-mentioned foam start temperature to the above-mentioned curing active temperature, the viscosity of the epoxy resin is sufficiently reduced at the stage before the curing of the sample is activated after the foam start of the sample. Therefore, the epoxy resin does not inhibit the foaming of the sample, and a good foaming ratio can be obtained. Thus, the method for realizing the property that the minimum viscosity temperature is higher than the above-mentioned foam start temperature and lower than the above-mentioned curing active temperature is not particularly limited. For example, the ratio of the content of the thermosetting resin and the thermoplastic resin contained in the sample (content of the thermosetting resin / content of the thermoplastic resin) is 1.0 or more and 23.3 or less, preferably 1.6 or more and 16.5 or less, more preferably 2.5 or more and 12.0 or less, etc. Also, it is preferable that the thermoplastic resin contains a thermoplastic elastomer as described above, and it is more preferable to include at least one or a combination of a plurality of acrylic thermoplastic elastomers, urethane thermoplastic elastomers, and acetal thermoplastic elastomers. Further, the glass transition temperature (Tg) of the thermoplastic elastomer is preferably 100 to 120°C. The content with respect to the total mass of the sample of the thermoplastic resin (corresponding to the first resin layer or the second resin layer) is preferably 3 to 30% by mass with respect to the total mass of the sample. Further, it is more preferable that the thermoplastic resin contains a thermoplastic elastomer, or the thermoplastic resin is entirely a thermoplastic elastomer, and the content of the thermoplastic elastomer is 3 to 30% by mass with respect to the total mass of the sample. Also, as another method for realizing the property that the minimum viscosity temperature is higher than the foaming start temperature and lower than the curing active temperature, the ratio of the content of the curing accelerator to the thermosetting resin (curing accelerator / thermosetting resin) contained in the sample is 0.001 or less and 0.16 or more, preferably 0.001 or more and 0.04 or less, more preferably 0.005 or more and 0.03 or less, particularly preferably 0.01 or more and 0.02 or less, etc.

[0043] In the heat-expandable sheet according to the present embodiment, the surface roughness Ra of the outer surfaces of the first resin layer 21 and the second resin layer 22, which are the outermost surfaces of the heat-expandable sheet 1, is preferably 0.4 μm or more. When the surface roughness Ra is 0.4 μm or more, the contact between the outermost surface of the heat-expandable sheet 1 and the adherend becomes point contact, and even when contact occurs, the external force (frictional resistance) received by the heat-expandable sheet 1 is reduced. Therefore, it is possible to suppress the occurrence of wrinkles and variations in the heat-expandable sheet 1, or to reduce the coefficient of friction and improve workability. The surface roughness Ra on the outermost surface of the heat-expandable sheet 1 is more preferably 1.0 μm or more, further preferably 1.5 μm or more, and particularly preferably 1.8 μm or more. Also, the surface roughness Ra on the outermost surface of the heat-expandable sheet 1 is preferably 50 μm or less. Thereby, the first resin layer 21 and the second resin layer 22 can be foamed without variation, and sufficient adhesion to the adherend facing each of these resin layers 21, 22 can be ensured. Further, the surface roughness Ra on the outermost surface of the heat-expandable sheet 1 is more preferably 30 μm or less, further preferably 20 μm or less, and particularly preferably 10 μm or less.

[0044] In addition, when the liquid first resin composition and the second resin composition are applied to the base material 10 to form the first resin layer 21 or the second resin layer 22, the surface roughness Ra on the outermost surface of the heat-expandable sheet 1 can be a value similar to the surface roughness of the base material 10. The means for forming the surface roughness Ra on the outermost surface of the heat-expandable sheet 1 is not particularly limited. For example, by applying a liquid resin composition to the surface of the base material 10 having a desired surface roughness and drying it, the surface roughness of the base material 10 can be reflected on the outermost surface of the heat-expandable sheet 1.

[0045] <Adhesion method of adherend surface using heat-expandable sheet> When adhering an adherend using the heat-expandable sheet 1 configured as described above, as described above, the heat-expandable sheet 1 is disposed inside the gap formed between the two adherend surfaces and then heated to expand.

[0046] The expansion ratios of the first resin layer 21 and the second resin layer 22 during heat expansion only need to be expansion ratios sufficient to fill the gap and adhere the two adherend surfaces to each other, and are not particularly limited. For example, it is preferably in the range of 1.5 times or more and 4.0 times or less. The expansion ratios of the first resin layer 21 and the second resin layer 22 can be adjusted by, for example, the content of the blowing agent contained in each of these resin layers 21, 22.

[0047] The method of heating the heat-expandable sheet 1 is not particularly limited, but in order to warm the entire heat-expandable sheet 1, for example, as shown in FIG. 3, it is common to dispose the heat source at a position for warming from the thickness direction of the heat-expandable sheet 1.

[0048] The heating conditions for foaming the heat-expandable sheet 1 are appropriately adjusted. For example, the maximum temperature is in the range of 150 to 200 ° C and 35 to 70 ° C / min.

[0049] When only one heat source is used as shown in Fig. 3(a), the heat from the heat source is supplied from one side of the heat-expandable sheet 1, transmitted through the inside of the heat-expandable sheet, and spread over the entire heat-expandable sheet 1. Therefore, a surface with a higher temperature rise rate than the other will occur on one side. Also, when a plurality of heat sources are provided in Fig. 3(b) to heat the heat-expandable sheet 1 from both sides, it is difficult to make the temperatures of the plurality of heat sources exactly the same, or to make the distance from the heat sources and the conditions of the medium for transmitting heat exactly the same on both sides of the heat-expandable sheet 1. Therefore, a surface where heat from the heat source is easily transmitted and a surface where it is difficult to transmit heat will occur, and again, a surface with a higher temperature rise rate than the other will occur on one side.

[0050] Therefore, by arranging the aforementioned first resin layer 21 on the side where heat is relatively easily transmitted and the second resin layer 22 on the side where heat is relatively difficult to transmit, the temperature rise rates of the first resin layer 21 and the second resin layer 22 during heating can be made different. For example, if marks or the like are provided to make it easy to understand how the first resin layer 21 and the second resin layer 22 should be arranged when using the heat-expandable sheet 1, the first resin layer 21 and the second resin layer 22 can be surely arranged according to the environment during heating. The temperature rise rate when the heat-expandable sheet 1 according to the present embodiment is heated and expanded can be appropriately changed depending on the resin composition and the like. For example, it is preferably 15°C or higher and 150°C or lower. Also, as the temperature rise rate of the first resin layer 21, for example, it is preferably 30°C / min or higher and 150°C / min or lower, more preferably 45°C / min or higher and 120°C / min or lower, and particularly preferably 60°C / min or higher and 100°C / min or lower. As the temperature rise rate of the second resin layer 22, for example, it is preferably 15°C / min or higher and 140°C / min or lower, more preferably 35°C / min or higher and 110°C / min or lower, and particularly preferably 55°C / min or higher and 90°C / min or lower. Moreover, the difference in the heating rate between the first resin layer and the second resin layer is preferably 5 °C / min or more, more preferably 10 °C / min or more, and particularly preferably 15 °C / min or more. From the viewpoint of sufficiently foaming and curing the second resin layer, the difference in the heating rate between the first resin layer and the second resin layer is preferably 50 °C / min or less.

[0051] By heating the heat-expandable sheet 1 in this state, heat is transferred to the first resin layer 21 faster than to the second resin layer 22, and a state can be created in which the heating rate of the first resin layer 21 is higher than the heating rate of the second resin layer 22.

[0052] In the present embodiment, since the base material 10 is disposed between the first resin layer 21 and the second resin layer 22, the heating rates of the first resin layer 21 and the second resin layer 22 can be surely made different. In this case, it can also be said that the base material 10 functions as a heating rate control layer that causes a difference in the heating rates between the first resin layer 21 and the second resin layer 22.

[0053] <Effects of the present embodiment> According to the heat-expandable sheet 1 configured as described above, generation of resin flow can be suppressed while sufficiently adhering the two adherend surfaces.

[0054] As a mechanism by which such an effect can be achieved, it is considered that the properties of the thermosetting resin contained in the first resin layer 21 and the second resin layer 22 are greatly involved. When a thermosetting resin is heated, as shown in FIG. 2 described above, a decrease in viscosity due to melting and an increase in viscosity due to a curing reaction occur in parallel. The result of the inventors' more detailed investigation of the properties of this thermosetting resin is the graph of FIG. 4. From these graphs, the inventors have found that there is a correlation between the viscosity of the thermosetting resin and the heating rate. The vertical axis represents an index of viscosity. In FIG. 4, it can be seen that as the heating rate increases, the peak of the viscosity decrease shifts to the lower right of the graph. Specifically, it has been found that as the heating rate increases, the viscosity reduction of the resin becomes more prominent.

[0055] Resin flow occurs when the viscosity of the resin during thermal expansion is low, and the heat-expandable adhesive layer expands not only in the thickness direction but also on the surface of the adherend. Therefore, by making the thickness of the first resin layer 21 with a high heating rate and low viscosity smaller than that of the second resin layer 22 with a low heating rate and low viscosity reduction, it is considered that the amount of resin flowing out to the outside of the gap can be reduced.

[0056] As a method of suppressing resin flow by changing the heating rate, a method of controlling the heat source can be considered. However, since it is difficult to control the heat source in reality, as described in this embodiment, by devising the resin composition, it can be said that the very simple suppression of resin flow is a very epoch-making achievement.

[0057] The heat-expandable sheet 1 according to this embodiment is used in a very narrow gap. By setting the total thickness of the first resin layer 21 and the second resin layer 22 to, for example, 120 μm or less, more preferably 100 μm or less, and particularly preferably 90 μm or less, even when applied to a gap such that the relationship between the first resin layer 21 and the second resin layer 22 and the minimum dimension of the gap falls within the range of the following formula (1), resin flow can be sufficiently suppressed.

[0058] (Minimum dimension of the gap - Thickness of the base material) / (Total thickness of the first resin layer and the second resin layer) ≤ 2 ··· (1)

[0059] More specifically, it can be used in a gap where the shortest distance (minimum dimension of the gap) between the two adherend surfaces is 250 μm or less, or 200 μm or less, or even 100 μm or less.

[0060] If the protruding length of the resin flow from the gap can be suppressed to 1200 μm or less, it is sufficiently acceptable, and it is more preferable if it can be made 1100 μm or less, or even 1000 μm or less.

[0061] Since the heat-expandable sheet 1 according to this embodiment contains an epoxy resin, it also has excellent heat resistance, and once it is heat-expanded, the adhesive strength hardly decreases even at high temperatures. In addition, since the adhesive layer 20 of the heat-expandable sheet 1 of the present invention contains not only a thermosetting resin but also a thermoplastic resin, the adhesive layer 20 is rich in flexibility, and combined with the expansibility, it is possible to ensure high filling properties even for surfaces in places where pressure cannot be applied by pressing or the like, or surfaces having a complex shape.

[0062] Since the heat-expandable sheet 1 according to this embodiment adopts the resin compositions as described above for each of the first resin layer 21 and the second resin layer 22, the adhesiveness of the surfaces of the first resin layer 21 and the second resin layer 22 can be lowered before heat expansion to a state called tack-free. As a result, even when the heat-expandable sheet 1 is inserted into a narrow gap as described above, the friction between each of the first resin layer 21 and the second resin layer 22 and the adherend surface forming the gap can be reduced, and the workability can be improved. In addition, since the resin compositions as described above are adopted for each of the first resin layer 21 and the second resin layer 22, by well-balanced adjustment of the filling properties, rapid curing properties, flexibility, and heat resistance, the conflicting problems of expansibility and adhesive strength can be overcome, and sufficient adhesive strength and filling properties can be achieved at the same time. Thereby, it is possible to achieve high adhesion with high adhesive reliability and fixing support stability between adherends, and it is possible to provide an adhesive sheet that is also excellent in various phenomena such as heat conductivity and vibration stress.

[0063] <Other Embodiments> The heat-expandable sheet according to the present invention is not limited to the above-described one. For example, if the amount of the expanding agent contained in the first resin layer with a large temperature increase rate is set to be half or less of the amount of the expanding agent contained in the second resin layer, the expansion rate of the first resin layer whose viscosity is likely to decrease will decrease, so that the resin flow can be more effectively suppressed. Also, the same effect can be obtained when the first resin layer is an adhesive layer that does not contain an expanding agent.

[0064] In the above-described embodiments, the substrate has been described as functioning as a heating rate control layer for making the heating rates between the first resin layer and the second resin layer different. However, it is not limited to such a case, and a heating rate control layer may be provided as a layer separate from the substrate. Furthermore, even if the first resin layer and the second resin layer have entirely different compositions and are arranged in a state where they are in contact with each other, if the heating rates of these first resin layer and second resin layer are made different, the substrate and the heating rate control layer may not be necessary.

[0065] When the expansion rate of the first resin layer is sufficiently reduced in this way or the first resin layer is not expanded at all and only the adhesive layer is used, the generation of resin flow can be suppressed without making the thickness of the first resin layer smaller than that of the second resin layer. This is because resin flow is considered to be likely to occur when a heat-expandable resin layer expands. In addition, various modifications and combinations of embodiments may be made as long as they do not depart from the gist of the present invention. The surface roughness Ra of the outer surfaces of the first resin layer 21 and the second resin layer 22, which are the outermost surfaces of the heat-expandable sheet 1, is not limited to those described above, and may be a flat surface with almost no unevenness. The properties of the first resin layer and the second resin layer are not limited to those described above, and any resin layer containing a thermosetting resin may be used.

Example

[0066] Hereinafter, the present invention will be described more specifically with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the examples can be appropriately changed as long as they do not depart from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0067] <Creation of Samples> <<Fabrication of Resin Layers>> The first resin layer and the second resin layer having the compositions described in Table 1 below were each formed on a release film. As the release film, HY-US20 manufactured by Higashiyama Film Co., Ltd. was used. Specifically, resin compositions A, B, and C for forming the first resin layer or the second resin layer having the compositions described in Table 1 were each prepared, and these were applied onto the release-treated surface of the above-described release film using a baker-type applicator so that the thickness after drying would be the desired thickness. These were dried at 110 °C for 120 seconds to remove the solvent, thereby forming resin layers that would become the first resin layer or the second resin layer, respectively.

[0068]

Table 1

[0069] <<Preparation of Heat Expansion Sheet for Evaluation>> A PI (polyimide) film (manufactured by Toray DuPont, 25 μm) was used as the base material. Next, the resin layers prepared by the above-described procedure were laminated so that one resin layer would be in contact with one side of the base material, and transferred onto the base material using a roll laminator adjusted to 110 °C. Subsequently, resin layers were similarly transferred to the opposite side of the base material, and these resin layers were used as the first resin layer and the second resin layer. The combinations of the first resin layer and the second resin layer transferred onto the surface of the base material were made as shown in Table 2.

[0070]

Table 2

[0071] <Evaluation of the Occurrence Status of Resin Flow> For the heat-expandable sheet produced as described above, the resin flow was measured by the following procedure.

[0072] A 10×25 mm sheet was cut out from the heat-expandable sheet and used as a test piece. Two SPCC flat plates were prepared as adherends, and with a spacer sandwiched between them, these two SPCC flat plates were clamped from the thickness direction with a clamp or the like and fixed in a state where a certain gap was formed. The thickness of the spacer that forms the gap at this time is the one calculated by the following formula (2). This is to make the pressure in the thickness direction pressed against the adherend as uniform as possible when the resin layer expands, and to obtain sufficient adhesiveness by heating the test piece to expand. (Thickness of spacer) = (Thickness of base material) + (Thickness of first resin layer + Thickness of second resin layer) × 2 ··· (2) The test piece was placed in the gap formed in this way and heated with a heat source arranged on the first resin layer side to raise the temperature of the first resin layer from room temperature (25°C) to 160°C at a heating rate of 100°C / min, and the test piece was heated at 160°C for 5 minutes (until the curing of the resin layer was completed) to expand and cure. Regarding the heating rate of the first resin layer, a thermocouple was installed on the surface of the first resin layer, and it was calculated from the time taken for the temperature to rise from 40°C to 150°C. The heating rate of the second resin layer calculated by the same method was approximately 90°C / min.

[0073] After the test piece was completely cured, it was confirmed that the two SPCC flat plates were sufficiently adhered. Then, the clamp was removed and one of the two SPCC flat plates was peeled off, and the distance from the edge of the base material of the test piece to the tip of the first resin layer and the second resin layer of the portion overflowing laterally was measured using a microscope (VH-X7000, manufactured by Keyence Corporation). The results are shown in Table 3. The resin flow distance (resin flow amount) in Table 3 was defined as the length of the portion that protruded the most laterally from the base material when the base material was viewed from its surface direction.

[0074]

Table 3

[0075] <Discussion of Results> Comparing the results of Comparative Example 1 and Examples 1 to 4 in which the first resin layer and the second resin layer were both of the composition A in Table 1, by making the thickness of the first resin layer, whose heating rate is higher than that of the second resin layer, smaller than that of the second resin layer, even under the conditions where the adhesiveness is sufficiently exhibited, the resin flow amount is 1200 μm or less, which is within a sufficiently practical range. It can be clearly seen that the resin flow amount is suppressed to be small.

[0076] Also, comparing the results of Comparative Example 1 and Examples 5 and 6, even when the thickness of the first resin layer, whose heating rate is higher than that of the second resin layer, is made the same as that of the second resin layer, by making the amount of the blowing agent contained in the first resin layer half or less of the amount of the blowing agent contained in the second resin layer, it can be seen that the resin flow amount is very small, being 1000 μm or less. The reason for such results is considered to be due to the property that, as described above, the first resin layer and the second resin layer are resin layers containing a thermosetting resin as the base resin, and in such resin layers, the higher the heating rate, the lower the viscosity. Therefore, the effects of the present invention confirmed in this example are not limited to the specific compositions described as examples here, and it is considered that they can be widely generalized even when the first resin layer and the second resin layer contain a thermosetting resin as a base resin.

Explanation of Signs

[0077] 1 Heated foaming sheet 10 Sheet-like base material 20 Foamable adhesive layer 21 First resin layer 22 Second resin layer

Claims

1. A heat-expandable sheet disposed inside a gap formed by two surfaces and expanding upon heating to bond the two surfaces, comprising: a base material; a first resin layer and a second resin layer, which are adhesive layers containing a thermosetting resin formed on the base material; the first resin layer is disposed on the side where heat is more easily transmitted than the second resin layer such that the temperature increase rate of the first resin layer is greater than that of the second resin layer depending on the conditions during heating; the thickness of the first resin layer before heating is smaller than the thickness of the second resin layer; the first resin layer and the second resin layer contain an epoxy resin, a curing agent, a thermoplastic resin, and a thermal expansion agent; the ratio of the content of the epoxy resin to the content of the thermoplastic resin (content of epoxy resin / content of thermoplastic resin) in each of the first resin layer and the second resin layer is 1.0 or more and 23.3 or less; the content of the thermoplastic resin in each of the first resin layer and the second resin layer is 3% by mass or more and 30% by mass or less based on the total mass of the corresponding first resin layer or second resin layer; the heat-expandable sheet, wherein the thermal expansion agent is a microcapsule foaming agent.

2. The heat-expandable sheet according to claim 1, wherein the first resin layer and the second resin layer are disposed with a temperature increase rate control layer therebetween that controls the temperature increase rates between the first resin layer and the second resin layer.

3. The heat-expandable sheet according to claim 2, wherein the base material functions as the temperature increase rate control layer.

4. The heat-expandable sheet according to any one of claims 1 to 3, wherein the total thickness of the first resin layer and the second resin layer is 90 μm or less and satisfies the following formula (1): (Minimum dimension of the gap - Thickness of the base material) / (Total thickness of the first resin layer and the second resin layer) ≤ 2... (1)

5. The heat-expandable sheet according to any one of claims 1 to 4, wherein the minimum viscosity temperature of the first resin layer and / or the second resin layer is higher than the foaming start temperature and lower than the curing active temperature.

6. The thermoplastic resin includes a thermoplastic elastomer, and the content of the thermoplastic elastomer in each of the first resin layer and the second resin layer is 3% by mass or more and 30% by mass or less based on the total mass of the corresponding first resin layer or second resin layer. The heat-expandable sheet according to any one of claims 1 to 5.

7. The heat-expandable sheet according to claim 1, wherein the thermoplastic resin contains a thermoplastic elastomer having a Tg in the range of 100 to 120°C.

8. The heat-expandable sheet according to any one of claims 1 to 7, wherein the resin flow rate is 1200 µm or less.

9. A heat-expandable sheet disposed inside a gap formed by two surfaces, which expands upon heating to bond the two surfaces, comprising: a base material; a first resin layer and a second resin layer, which are adhesive layers containing a thermosetting resin formed on the base material; the first resin layer is disposed on the side where heat is more easily transmitted than the second resin layer so that the temperature rising rate of the first resin layer is greater than that of the second resin layer depending on the conditions during heating; the first resin layer does not contain a thermal expansion agent, and the second resin layer contains a thermal expansion agent, or both the first resin layer and the second resin layer contain a thermal expansion agent, and the content of the thermal expansion agent in the first resin layer is half or less of the content of the thermal expansion agent in the second resin layer; the first resin layer and the second resin layer further contain an epoxy resin, a curing agent, and a thermoplastic resin; in each of the first resin layer and the second resin layer, the ratio of the content of the epoxy resin to the content of the thermoplastic resin (content of the epoxy resin / content of the thermoplastic resin) is 1.0 or more and 23.3 or less; in each of the first resin layer and the second resin layer, the content of the thermoplastic resin is 3% by mass or more and 30% by mass or less based on the total mass of the corresponding first resin layer or second resin layer; The heat-expandable sheet, wherein the thermal expansion agent is a microcapsule blowing agent.

10. The heat-expandable sheet according to claim 9, wherein the minimum viscosity temperature of the first resin layer and / or the second resin layer is higher than the foaming start temperature and lower than the curing active temperature.

11. The thermoplastic resin contains a thermoplastic elastomer, and in each of the first resin layer and the second resin layer, the content of the thermoplastic elastomer is 3% by mass or more and 30% by mass or less based on the total mass of the corresponding first resin layer or second resin layer. The heat-expandable sheet according to claim 9 or 10.

12. The heat-expandable sheet according to any one of claims 9 to 11, wherein the thermoplastic resin contains a thermoplastic elastomer having a Tg in the range of 100 to 120°C.

13. The heat-expandable sheet according to any one of claims 1 to 12, provided with a mark that makes it easy to understand in which direction the first resin layer and the second resin layer should be arranged during use.

14. An adhesion method using a heat-expandable sheet disposed inside a gap formed by two surfaces, which expands upon heating to adhere the two surfaces, wherein the heat-expandable sheet comprises a base material, and a first resin layer and a second resin layer which are adhesive layers containing a thermosetting resin formed on the base material, the thickness of the first resin layer before heating is smaller than the thickness of the second resin layer, the first resin layer and the second resin layer contain an epoxy resin, a curing agent, a thermoplastic resin, and a thermal expansion agent, the ratio of the content of the epoxy resin to the content of the thermoplastic resin (content of the epoxy resin / content of the thermoplastic resin) in each of the first resin layer and the second resin layer is 1.0 or more and 23.3 or less, the content of the thermoplastic resin in each of the first resin layer and the second resin layer is 3% by mass or more and 30% by mass or less with respect to the total mass of the corresponding first resin layer or second resin layer, the thermal expansion agent is a microcapsule foaming agent, the heat-expandable sheet is heated and expanded in a state where the first resin layer is disposed on the side where heat is more easily transmitted than the second resin layer so that the temperature rising rate of the first resin layer is higher than the temperature rising rate of the second resin layer depending on the conditions during heating.

15. An adhesion method using a heat-expandable sheet disposed inside a gap formed by two surfaces, which expands upon heating to adhere the two surfaces, wherein the heat-expandable sheet comprises a base material, and a first resin layer and a second resin layer which are adhesive layers containing a thermosetting resin formed on the base material, the first resin layer does not contain a thermal expansion agent, and the second resin layer contains a thermal expansion agent, or the first resin layer and the second resin layer contain a thermal expansion agent, and the content of the thermal expansion agent in the first resin layer is half or less of the content of the thermal expansion agent in the second resin layer, the first resin layer and the second resin layer further contain an epoxy resin, a curing agent, and a thermoplastic resin, The ratio of the content of the epoxy resin to the content of the thermoplastic resin (content of the epoxy resin / content of the thermoplastic resin) in each of the first resin layer and the second resin layer is 1.0 or more and 23.3 or less, The content of the thermoplastic resin in each of the first resin layer and the second resin layer is 3% by mass or more and 30% by mass or less with respect to the total mass of the corresponding first resin layer or second resin layer, The thermal expansion agent is a microcapsule foaming agent, The first resin layer is arranged on the side where heat is more easily transmitted than the second resin layer so that the temperature rising rate of the first resin layer of the heat-expandable sheet is greater than the temperature rising rate of the second resin layer depending on the conditions during heating, An adhesion method for thermally expanding the heat-expandable sheet.

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