JP6548399B2 - Adhesive sheet - Google Patents

Description

  The present invention relates to an adhesive sheet, more specifically, having an adhesive layer containing a thermosetting adhesive composition in which a curing reaction proceeds to increase adhesion when heated to a predetermined temperature or higher. The present invention relates to an adhesive sheet excellent in blocking resistance and folding resistance.

  There is known a thermosetting adhesive sheet sheeted by mixing a solid epoxy resin or the like at normal temperature with an epoxy resin that is liquid at normal temperature. (Patent Document 1)

JP, 2013-107957, A

  The thermosetting adhesive sheet of Patent Document 1 contains a large amount of epoxy resin which is liquid at normal temperature, and further contains an acrylic resin component, and therefore, is characterized by having adhesiveness at normal temperature. However, in a mass production process of a glass epoxy substrate and the like, tackiness at normal temperature is rather a factor to cause undesired sticking at the time of operation, so a tack-free sheet is desired at normal temperature. Furthermore, in order to have adhesiveness at normal temperature, the release film for protecting the surface became essential, and the process of removing the release film became necessary. In addition, since a large amount of the acrylic resin component is contained, there is a concern that the heat resistance, which is a feature of the cured epoxy resin, is lowered.

  In view of the above problems, an object of the present invention is to provide an adhesive sheet excellent in workability.

  In order to prevent the resin component of the adhesive layer from tacking at normal temperature, the present inventor is in operation by laminating a coat layer which is made of resin and does not show tack at normal temperature but softens and disappears due to heat. It has been found that it is possible to prevent the occurrence of undesired sticking and blocking phenomena, and to obtain an adhesive sheet excellent in bending resistance, and to complete the present invention.

That is, the adhesive sheet of the present invention is an adhesive sheet comprising an adhesive layer comprising an adhesive composition containing a thermosetting resin, and a coating layer formed on the adhesive layer and containing a resin, wherein the coating layer is At least a part of the coating layer extends from the interface between the adhesive layer and the coating layer to the surface of the coating layer by heating the adhesive sheet at a temperature higher than the curing start temperature of the adhesive layer. It is characterized by disappearing in the range.

  The adhesive composition preferably contains a thermosetting resin having a softening temperature of 105 ° C. or less.

When the thickness of the adhesive layer before heating is t1 and the thickness of the coating layer before heating is t2, it is preferable to satisfy the relationship of t2 ≦ 2.8 · t1.
Furthermore, it is preferable that the glass transition temperature (T3) of the said coating layer is 60 degreeC or more and 140 degrees C or less.

It is preferable that said t2 (thickness of a coating layer) is 0.5 micrometer or more and 600 micrometers or less.
Moreover, it is preferable that the hardening start temperature (T2) of the said contact bonding layer is 110 degreeC or more and 250 degrees C or less. It is desirable that the relationship between T3 and T2 be T3 <T2.
Further, the thermosetting resin contained in the adhesive composition preferably has a weight average molecular weight of 450 or more and less than 1650.
The thermosetting resin is preferably an epoxy resin.
Moreover, it is preferable that said t1 is 20 micrometers or more and 1000 micrometers or less.

Although the adhesive sheet of the present invention does not exclude the aspect formed only by the adhesive layer and the coat layer, it may be configured to include the substrate on which the adhesive layer is formed. In this case, a synthetic resin film such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, acrylic, polycarbonate, polyimide, etc. is used as a substrate as a substrate, adhesive layers are formed on both sides of the substrate, and then the respective adhesions are made. It is preferable to form an adhesive sheet by forming a coating layer on a layer.
The adhesive sheet of the present invention can be used to fill voids.

  Further, the electronic circuit board, the building structural material, the image display device, the portable electronic device or the automobile part of the present invention is characterized by using any one of the above adhesive sheets.

In the adhesive sheet of the present invention, it is possible to prevent the occurrence of unwanted sticking and blocking phenomenon during the operation before heat curing the adhesive layer. That is, it can be made excellent in workability.
The adhesive sheet of the present invention is, for example, reinforcement of riveting of construction materials, lamination of decorative boards of furniture and construction materials, interior materials of automobiles, interlayer bonding of carbon fiber reinforced plastic (CFRP), structural bonding applications, flexible electronic Although it is suitable for the application to the coverlay film adhesion for circuit boards, it is not particularly limited to this application. In addition, by using an insulating base material in the adhesive layer, it is suitable for use in bonding various parts of electronic devices that require insulation, such as interlayer insulating films of electronic circuit boards, etc. It is not limited. Moreover, although the heat conductive filler is introduced into the adhesive layer, it is suitable for the bonding application of the electronic device and the heat sink, but it is not particularly limited to this application. Moreover, by introduce | transducing the thermally foamable filler to an adhesive layer, it is used suitably also for the use which carries out void filling by thermal foaming.
The size of the void is not particularly limited in the case of use for void filling applications, and may be used for applications in which small voids of, for example, 1 mm or less (for example, about several tens of μm to several hundreds of μm) are filled.

  Examples of the “small air gap” in the present invention include an image display member fixed to an image display device (liquid crystal display, electroluminescence display, plasma display, etc.), and a portable electronic device (mobile phone, portable information terminal, etc.) Gaps between fixed optical members (cameras, lenses, etc.) and the housing (window), gaps between adjacent coils of different phases in the coil end of the stator used for motors and generators, in particular A gap between an insulating sheet and a coil interposed in the gap, a gap in a slot groove of a stator core, and the like can be mentioned.

An adhesive sheet according to an embodiment of the present invention is configured by disposing a coating layer on an adhesive layer. Here, the coating layer does not show tack at normal temperature, and at least a part of the coating layer is coated from the interface between the adhesive layer and the coating layer by heating the adhesive sheet to a temperature higher than the curing start temperature of the adhesive layer. It is characterized by disappearing in the range to the surface. With such a configuration, in the adhesive sheet of the present invention, it is possible to prevent the deterioration of the workability due to the tack or the like while maintaining the adhesiveness.
The adhesive layer is formed of a thermosetting adhesive composition in which a curing reaction proceeds to increase adhesion by heating to a predetermined temperature or higher. The adhesive composition preferably contains a thermosetting resin having a softening temperature of 105 ° C. or less. By containing a thermosetting resin having a softening temperature of 105 ° C. or less, the adhesive layer shows tack at normal temperature, or cracks easily occur in the adhesive layer.
In the conventional configuration, in order to prevent the resin component of the adhesive layer from causing tack at normal temperature, the weight average molecular weight of the thermosetting resin contained in the adhesive layer is increased. When the weight-average molecular weight (800) is exceeded, (1) the tack at room temperature of the adhesive layer decreases and the decrease in workability is suppressed, but when the adhesive sheet is bent, the adhesive layer is cracked and falls off And I confirmed that I could not use what was bent once. Further, (2) it was found that the curing temperature needs to be raised because the reactivity with the curing agent to be blended if necessary becomes low, and it becomes uneconomical.
Furthermore, when the weight average molecular weight is increased to a level exceeding 1650, the crack resistance is improved. However, it has been found that (3) the reactivity with the curing agent is further reduced, and a higher curing temperature is required, which results in a further lack of economy. In addition, it was confirmed that there is a possibility that the adhesiveness may be lowered because the fluidity at the time of curing is lowered and the surface of the adherend can not be uniformly wetted.
In the present invention, by adopting the above-mentioned coat layer, it is possible to suppress a decrease in workability due to tack at normal temperature. Furthermore, in the present invention, it is possible to suppress the cost increase due to the cracking and the increase of the curing temperature which are caused by increasing the weight average molecular weight of the thermosetting resin in the conventional configuration.

In the present invention, "showing tack at normal temperature" means that adhesion is confirmed by the following method.
A sheet in which an adhesive layer and a coat layer are laminated on a substrate is cut into a size of 5 cm × 5 cm to prepare six adhesive sheets. Six sheets of coating layers of the adhesive sheet are stacked so as to face each other, and then sandwiched between glass plates. A load of 100 g is applied on the above laminate, and after standing for 24 hours at normal temperature (25 ° C.), when the load is released and the glass plate is spread up and down, the coat layers of the adhesive sheets are in close contact with each other. It is in close contact with the base of the adhesive sheet and that the peeling occurs between the adhesive layers, that is, the coated layer is tacky at normal temperature. On the other hand, when a glass plate is spread up and down, when it exfoliates between coat layers which have been in contact, the coat layer is said to exhibit no tack at normal temperature.
The phrase "cracking" means that when the adhesive sheet is bent at 180 degrees, the adhesive layer is cracked, and at least a part of the adhesive layer is in a state of falling off or falling off.

By heating the adhesive sheet of the present invention to a temperature above the curing start temperature of the adhesive layer, at least a part of the coating layer disappears in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer. The phrase "the coating layer disappears" basically means that the coating layer is softened by the application of heat exceeding the glass transition temperature of the resin forming the coating layer to the adhesive sheet of the present invention, whereby the resin of the coating layer is By mixing with a thermosetting resin (before curing) to form an adhesive layer, it is integrated with the adhesive layer, and the coat layer which has been present on the adhesive layer apparently disappears. Specifically, the adhesive sheet is cut by the method described later, and the cross section is observed with a microscope, and at least a part of the coating layer disappears in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer It is determined that the coat layer has disappeared. That is, in the present invention, even when at least a part of the adhesive layer after heat curing is exposed in a portion in contact with the adherend of the adhesive sheet after the adhesive layer is cured by heating, It is judged that the layer has disappeared. That is, in the present invention, in interpreting “the coat layer disappears”, the degree of mixing of the resin forming the coat layer with the thermosetting resin (before curing) forming the adhesive layer may not be perfect. After heat curing, the sheet surface may exhibit a function as an adhesive layer. At least a part of the adhesive layer after heat curing may be exposed on the sheet surface in a portion of the adhesive sheet after the adhesive layer is cured by heating and in contact with the adherend. If all of the adhesive layer after heat curing is exposed on the sheet surface, it means that the coating layer present on the adhesive layer is completely absent.
Here, the curing start temperature of the adhesive layer is calculated by the method to be described later, and the adhesive layer is observed by heating the adhesive sheet at a temperature higher by 100 ° C. to 250 ° C. for 5 to 60 minutes. The presence or absence of the loss of Generally, it can be judged in the state of the adhesive sheet after heating at 160 to 220 ° C. for 20 to 30 minutes.

  In the present invention, when the thickness of the adhesive layer before heating is t1 and the thickness of the coating layer is t2, t2 ≦ 2.8 · t1 (the thickness of the coating layer is 280% or less of the thickness of the adhesive layer before heating) It is preferable to satisfy the relationship of Moreover, it is preferable that the glass transition temperature (T3) of a coating layer is 60 degreeC or more and 140 degrees C or less.

[Adhesive layer]
The thermosetting resin to be contained as an essential component in the adhesive composition for forming the adhesive layer is, for example, epoxy resin, phenoxy resin, silicone resin, oxetane resin, phenol resin, (meth) acrylate resin, polyester resin Saturated polyester resin), diallyl phthalate resin, maleimide resin, polyimide resin, polyamic acid resin, polyether imide resin, polyester imide resin, polyamide imide resin, bismaleimide-triazine resin, and the like. In particular, epoxy resin, (meth) acrylate resin, phenoxy resin, polyester resin, polyimide resin, polyamide acid resin, polyetherimide resin, polyesterimide resin, polyamideimide resin, silicone resin, maleimide resin, bismaleimide-triazine resin, etc. Preferably, these resins can be used singly or in combination of two or more. Among them, epoxy resins are preferable from the viewpoint of excellent curability and storage stability, heat resistance of cured products, moisture resistance, and chemical resistance.

  As an epoxy resin, for example, bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, Hindatoin epoxy resin, biphenyl epoxy resin, alicyclic epoxy resin, triphenylmethane epoxy resin, phenol novolac Type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, dicyclopentadiene / phenol epoxy resin, alicyclic amine epoxy resin, aliphatic amine epoxy resin, and these variously modified such as CTBN modification and halogenation Epoxy resins are mentioned, and among them, bisphenol A epoxy resins and novolac epoxy resins are preferable. These can be used alone or in combination of two or more.

  The epoxy resin preferably has a viscosity at 190 ° C. of usually 0.05 Pa · s or more, and more preferably 0.1 Pa · s or more. In addition, usually 3.0 Pa · s or less is preferable, and 1.8 Pa · s or less is more preferable. If the viscosity is too low, the foaming state of the thermal foaming agent can not be maintained, and there is a possibility that continuous foam formation or foam breakage may occur. If the viscosity is too high, the foaming external pressure becomes higher than the foaming internal pressure, so the thermal foaming agent may not foam. The viscosity in this case is a value measured using a dynamic viscoelasticity measuring apparatus (Ballin C-VOR manufactured by Malvern Instruments).

  The epoxy resin has an epoxy equivalent (WPE) of usually 150 or more, preferably 180 or more, and usually 1000 or less, preferably 700 or less. When the WPE is too low, a cured product having many crosslink points and high heat resistance can be obtained, but the toughness is low and there is a possibility of becoming brittle. If the WPE is too high, the heat resistance may be reduced because the crosslinking point is small. "Epoxy equivalent weight" is defined by the molecular weight of epoxy resin per epoxy group. Here, the "epoxy group" includes oxacyclopropane (oxirane ring) which is a three-membered ring ether, and in addition to the narrowly defined epoxy group, a glycidyl group (including a glycidyl ether group and a glycidyl ester group). Is included. WPE is determined by the method (perchloric acid-tetraethyl ammonium bromide method) or the like described in JIS K 7236 and the method for determining the epoxy equivalent of epoxy resin (2001).

The epoxy resin is semisolid or solid at normal temperature, and in the case of solid, the softening temperature is preferably 105 ° C. or less, more preferably 95 ° C. or less. Moreover, 40 degreeC or more is preferable normally, 45 degreeC or more is more preferable. If it is liquid at normal temperature, the viscosity drop at the time of curing and foaming becomes remarkable, and it becomes impossible to maintain the foaming state of the epoxy resin, so there is a possibility that breakage and continuous foam formation may progress. In addition, the shape of the adhesive layer may not be maintained.

Containing a thermosetting resin (preferably epoxy resin) having a softening temperature of 105 ° C. or less to form an adhesive layer, the resin is softened by heating and mixed with the resin of the coat layer to maintain adhesion performance. it can. If the softening temperature exceeds 60 ° C. even if the softening temperature is 105 ° C. or less, the adhesive layer may be cracked. However, in the present embodiment, since the adhesive layer is coated with the coat layer, there is no risk of falling off even if the adhesive layer is cracked, and there is no problem in use.

By including a thermosetting resin (preferably an epoxy resin) having a softening temperature of 60 ° C. or less to constitute the adhesive layer, in addition to the above-mentioned function (maintaining the adhesive performance), the occurrence of cracking of the adhesive layer is suppressed This can contribute to preventing the adhesive layer from falling off.
The softening temperature here is a value measured by the method defined in JIS K 7234 (ring and ball method).

In the present embodiment, it is desirable to use a thermosetting resin having a weight average molecular weight of preferably 1650 or less, more preferably 800 or less.
By containing a thermosetting resin having a weight average molecular weight of 1650 or less to constitute the adhesive layer, the resin can be adjusted more softly by heating and the coating layer can be eliminated, so that the adhesive performance is maintained better. be able to. More preferably, the adhesive layer is made to contain a thermosetting resin having a weight average molecular weight of 800 or less. This is because, in addition to the above-mentioned action (maintaining the adhesion performance), the occurrence of cracking of the adhesion layer can be suppressed.

  In the present embodiment, in order to facilitate the sheet-like formation, the thermosetting resin to be contained in the adhesive composition preferably has a weight average molecular weight of 450 or more. If the molecular weight is less than 450, the resin will be close to a liquid at normal temperature, so the shape of the adhesive layer may not be maintained.

The adhesive composition for forming the adhesive layer may contain a thermal foaming agent in addition to the above-mentioned thermosetting resin as an essential component. Thus, when the adhesive layer is heated to a predetermined temperature or higher, the volume increases and the curing reaction proceeds to increase the adhesive strength, and therefore, the adhesive layer can be suitably used for filling a void. When the heat-blowing agent is contained, the adhesive composition preferably contains a thermosetting resin having a softening temperature of 105 ° C. or less in order to obtain good foaming characteristics.
In the conventional configuration, in order to obtain excellent foaming characteristics, it has been a problem that the adhesive layer shows tack at normal temperature. When the weight-average molecular weight of the thermosetting resin contained in the adhesive layer is increased in order to prevent the resin component of the adhesive layer from tacking at normal temperature, a certain weight-average molecular weight (800) is exceeded (1 The tackiness of the adhesive layer at room temperature decreases, and the decrease in workability is suppressed, but when the adhesive sheet is bent, the adhesive layer is cracked and falls off, and it can not be used once it is bent. In addition, (2) because the reactivity with the curing agent is lowered, it is necessary to raise the curing temperature, which is uneconomical. Furthermore, if it exceeds a certain weight average molecular weight (1650), (3) the softening temperature becomes high and the resin becomes difficult to soften, so the thermal foaming agent does not foam well when heated. If the weight average molecular weight (3000) exceeds a certain level, (4) film formation will be high and cracking will be suppressed, but the softening temperature will be high and the resin will not be soft easily, so heat is generated when heated. The blowing agent does not foam well.
On the other hand, by employing the coating layer of the present invention, excellent workability can be realized while maintaining sufficient foaming performance.
In the present invention, when the thermal foaming temperature of the thermal foaming agent is T1, the curing start temperature of the adhesive layer is T2, and the glass transition temperature of the coating layer is T3, the relationship of T3 <T1 ≦ T2 is satisfied. Is preferred.

The heat-blowing agent is not particularly limited and, for example, known heat-blowing agents (thermally-degradable, expanded graphite, microencapsulated, etc.) can be appropriately selected and used, among which microencapsulation is preferred. What was used (hereinafter referred to as "thermally expandable microspheres") can be suitably used.
As a preferred example of the heat expandable microspheres, microspheres having a structure in which a foaming agent is enclosed in an elastic outer shell and showing a heat expandable property as a whole (a property of the whole being expanded by heating) are mentioned as a preferred example. Can.
As an outer shell having elasticity, a heat melting substance, a substance which is broken by thermal expansion, etc., for example, vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone etc. Can be mentioned as a preferred example.
As the foaming agent, substances which can be easily gasified and expanded by heating, for example, hydrocarbons such as isobutane, propane, pentane and the like can mainly be mentioned. As commercially available products of thermally expandable microspheres, for example, trade name "Matsumoto Microsphere" series (made by Matsumoto Yushi-Seiyaku Co., Ltd.), Advancel EM series (made by Sekisui Chemical Co., Ltd.), Xpancel (made by Nippon Ferrite Co., Ltd. Etc. can be mentioned.

  The size of the thermally expandable microspheres may be appropriately selected according to the application of the adhesive sheet, and specifically, it may be about 10 to 20 μm in mass average particle diameter. The thermally expandable microspheres may be used after adjusting their particle size distribution. The adjustment of the particle size distribution may be performed by classifying and removing relatively large particle size contained in the thermally expandable microspheres to be used by a centrifugal force type air classifier, a dry classifier, a sieving machine or the like. Specifically, the standard deviation of the particle size distribution of the thermally expandable microspheres may be 5.0 μm or less.

  The expansion ratio of the thermally expandable microspheres is preferably 5 times or more, and more preferably 7 times or more. On the other hand, it is preferably 15 times or less, more preferably 12 times or less. When the expansion ratio of the thermally expandable microspheres is preferably in the range of 5 times to 15 times, the control of the expansion ratio becomes easy. The outer shell of the thermally expandable microspheres preferably has an appropriate strength that does not rupture even when the thermally expandable microspheres expand to the predetermined expansion ratio.

The amount of the heat-expandable microspheres is preferably 1 part by mass or more, more preferably 3 parts by mass or more, preferably 30 parts by mass or less, more preferably 20 parts by mass, with respect to 100 parts by mass of the thermosetting resin. It is preferably at most 15 parts by weight, and more preferably at most 15 parts by weight. If the amount of the heat-expandable microspheres is too small, the expansion ratio of the adhesive layer as a whole may be reduced, and the adhesive layer may not expand sufficiently. On the other hand, if the compounding amount is too large, it may not be possible to maintain sufficient strength as an adhesive to cause excessive foaming.

  The thermal foaming agent preferably has a thermal foaming temperature (T1) of preferably 100 ° C. or more, more preferably 150 ° C. or more, and preferably 200 ° C. or less, more preferably 190 ° C. or less. T1 corresponds to a thermal expansion temperature when thermally expandable microspheres are used as a thermal foaming agent, and corresponds to a thermal decomposition temperature when a thermal decomposition type foaming agent is used. "Thermal expansion temperature" is synonymous with the foaming start temperature, and in this embodiment, it means the thermal expansion start temperature determined by the thermal expansion measuring device (TMA), and the maximum thermal expansion temperature at which the volume expands maximally. It does not mean.

Further, as other thermal foaming agents, thermal decomposition type foaming agents, expanded graphite and the like can be mentioned. Thermal decomposition type foaming agents are classified into inorganic type and organic type.
As an inorganic type foaming agent, ammonium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, azides etc. are mentioned, for example. Examples of the organic foaming agent include water, salt-fluorinated alkanes (eg, trichloromonofluoromethane, dichloromonofluoromethane, etc.), azo compounds (eg, azobisisobutyronitrile, azodicarbonamide (ADCA), Barium azodicarboxylate etc.), Hydrazine compounds (eg para-toluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis (benzenesulfonylhydrazide), allylbis (sulfonylhydrazide) etc.) Semicarbazide compounds (eg ρ-toluylenesulfonyl semicarbazide, 4,4′-oxybis (benzenesulfonyl semicarbazide) etc.), triazole compounds (eg 5-morpholine-1,2,3,4-thiatriazole etc.) , - nitroso compounds (e.g., N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl -N, N'-dinitrosoterephthalamide, etc.), and the like.
These thermal blowing agents can be used alone or in combination of two or more.

  The compounding amount of such a thermal decomposition-type foaming agent is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, preferably 30 parts by mass or less, more preferably 100 parts by mass of the thermosetting resin. Is 25 parts by mass or less. If the blending amount of the thermal decomposition-type foaming agent is too small, the expansion ratio of the entire adhesive layer may be reduced, and the adhesive layer may not be sufficiently expanded. On the other hand, if the compounding amount is too large, it may not be possible to maintain sufficient strength as an adhesive to cause excessive foaming.

The adhesive composition forming the adhesive layer may further contain optional components such as a curing agent. Examples of curing agents include dicyandiamide (DICY), amide based curing agents such as aliphatic polyamide; amine based curing agents such as diaminodiphenylmethane, metaphenylene diamine, ammonia, triethylamine, diethylamine etc .; bisphenol A, bisphenol F, phenol novolac Resins, phenolic curing agents such as cresol novolac resin, p-xylene novolac resin, etc .; acid anhydride curing agents such as methyl nadic acid anhydride, etc. may be mentioned.
These curing agents can be used alone or in combination of two or more.

  The compounding quantity of a hardening agent is computed from equivalent ratio with the thermosetting resin to be used, and the suitable range of equivalent ratio is 0.8-3.0. For example, when the curing agent is dicyandiamide, the lower limit is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and the upper limit is preferably 30 parts by mass or less, with respect to 100 parts by mass of the thermosetting resin. Part or less is more preferable. For example, in the case of anhydrous methyl nadic, the lower limit is preferably 60 parts by mass or more, more preferably 80 parts by mass or more, and the upper limit is preferably 240 parts by mass or less, relative to 100 parts by mass of the thermosetting resin. Part or less is more preferable. If the compounding amount of the curing agent is less than the above lower limit, it is difficult to cure sufficiently, and there is a possibility that the characteristics as a thermosetting resin such as heat resistance and chemical resistance can not be sufficiently exhibited. On the other hand, if the compounding amount exceeds the above upper limit, the resin composition viscosity during curing is lowered more than necessary due to an excessive exothermic reaction during curing, and it becomes difficult to finally maintain a sufficient foaming state there is a possibility.

A curing accelerator can also be used in combination with the curing agent. Examples of curing accelerators include imidazoles such as 2-methylimidazole, 2-methyl-4-ethylimidazole, 2-phenylimidazole, etc .; 1,8-diazabicyclo [5.4.0] undecene-7, triethylenediamine, Tertiary amines such as benzyldimethylamine; organic phosphines such as tributylphosphine and triphenylphosphine; and the like. These may be used alone or in combination of two or more. It is preferable that the compounding quantity of a hardening accelerator shall be 5 mass parts or less with respect to 100 mass parts of thermosetting resin. If it exceeds 5 parts by mass, storage stability may be reduced.

Examples of other additives that can be added as an optional component to the adhesive composition include, as an elastomer component, natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butadiene rubber, nitrile rubber, butyl rubber, fluororubber, acrylic rubber And solid or liquid rubbers, polyurethane, urethane prepolymer and the like. As a compounding quantity, 20 mass parts or less are preferred to 100 mass parts of thermosetting resin, 10 mass parts or less are more preferred, and 5 mass parts or less are still more preferred. In addition, a foaming aid, various fillers, a foam stabilizer, an antioxidant, a UV absorber, and a colorant may be blended.

The adhesive composition of the present embodiment can be obtained by mixing the heat-foaming agent, the curing agent, the curing accelerator, the foaming aid, the various additives, etc. in any order with the above-mentioned thermosetting resin as required. You can get it. The mixing of the above-mentioned raw materials can be carried out using a mixer or a kneader such as a mixing roll, a planetary mixer, a butterfly mixer, a kneader, a single-screw or twin-screw extruder or the like. Although mixing temperature changes with compositions, it is preferable to carry out below the thermal foaming temperature (T1) of a thermal foaming agent.
In the adhesive composition of the present embodiment, it is desirable to blend each component so that the curing start temperature (T2) in the state of the adhesive layer formed into a sheet is preferably 110 ° C. or more and 250 ° C. or less.

An adhesive layer is obtained by apply | coating the adhesive composition mentioned above to the single side | surface or both surfaces of the base material mentioned later, and making it dry as needed. In addition, an adhesive layer can also be obtained by apply | coating on the coat layer mentioned later which formed the adhesive composition mentioned above in the release film prepared separately, and it is made to dry as needed.
The thickness (t1) of the adhesive layer before foaming may be appropriately selected according to the application of the adhesive sheet, but the lower limit is preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is preferably 1000 μm or less, The thickness is preferably 400 μm or less, and more preferably 200 μm or less. By setting the thickness of the adhesive layer to 20 μm or more, for example, since it is possible to follow the adherend having unevenness, stable adhesive performance can be maintained. By setting the thickness (t1) of the adhesive layer to 1000 μm or less, the adhesive layer can be suitably used for applications where thin film formation is required.

  The substrate is not particularly limited and may be appropriately selected. Polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polycarbonate, triacetyl cellulose, aramid, polyimide, polyamide, polyphenylene sulfide, polyetherimide, poly Films made of synthetic resins such as ether sulfone, aromatic polyamide, polysulfone, non-woven fabric, paper and the like can be mentioned. The substrate is selected according to the application of the adhesive sheet. In particular, in applications where insulation and heat resistance are required, it is preferable to use a polyimide film, an aramid non-woven sheet or the like.

  The thickness of the substrate can be appropriately selected according to the application to be applied. In the case where the application application is, for example, an insulating sheet described later, the thickness of the substrate is preferably 25 to 250 μm.

[Coat layer]
As a resin which forms a coating layer, a phenoxy resin, a polyester resin, a polyurethane resin, a polyimide resin, a siloxane modified polyimide resin, a polybutadiene, a polypropylene, a styrene-butadiene-styrene copolymer, a styrene- ethylene- butylene- styrene copolymer weight, for example Combination, polyacetal resin, polyvinyl butyral resin, polyvinyl acetal resin, butyl rubber, chloroprene rubber, polyamide resin, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-styrene copolymer, polyvinyl acetate And thermoplastic resins such as nylon can be used. These can be used alone or in combination of two or more. Among them, phenoxy resin, polyester resin and the like are preferably used.
As polyester resin, for example, trade name Byron 200 (made by Toyobo Co., Ltd.), trade name Polyester TP220 (made by Nippon Gohsei Kagaku Co., Ltd.), trade name Erie Ter KA series (Unitika Co., Ltd.), etc. may be mentioned.

  The phenoxy resin refers to a high molecular weight thermoplastic polyether resin (※ bisphenol type epoxy resin) based on a diphenol such as bisphenol A or bisphenol F and an epihalohydrin such as epichlorohydrin. The phenoxy resin preferably has a weight average molecular weight of 20,000 to 100,000. When the molecular weight is too low, cracking is likely to occur, while when the molecular weight is too high, the viscosity at the time of forming a coating film is too high, making it difficult to obtain a smooth, uniform coating film.

  The phenoxy resin is not particularly limited, and is not limited to bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenol acetophenone skeleton, novolak skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene What has one or more types of frame | skeleton selected from frame | skeleton, adamantane frame | skeleton, terpene frame | skeleton, and trimethyl cyclohexane frame | skeleton is mentioned.

Commercially available phenoxy resins include, for example, trade names PKHB, PKHC, PKHH, PKHJ (all manufactured by InChem), jER 1256, jER 4250, jER 4275 (all manufactured by Mitsubishi Chemical Corporation), YP-50, YP -50S, YP-70, ZX-1356-2, FX-316 (all are manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) and the like.
Moreover, what melt | dissolved phenoxy resin using a solvent is marketed, and this is used similarly. For example, jER 1256B40, jER 1255HX30, jER YX6954BH30, YX8100BH30, jER YL7174BH40 (all from Mitsubishi Chemical Corporation), YP-40 ASM40, YP-50 EK35, YPB-40 PXM40, ERF-001 M30, YPS-007 A30, FX-293 AT40 (all of them) Nippon Steel & Sumikin Chemical Co., Ltd.) and the like.

  These phenoxy resins can be used alone or in combination of two or more.

  In the present embodiment, if necessary, a curing agent such as isocyanate or organic peroxide may be further blended to the thermoplastic resin. By appropriately selecting and blending the type, molecular weight and the like of the curing agent, it becomes easy to finely adjust the affinity to the adhesive layer. The amount of the curing agent (isocyanate or the like) to be blended can be about 3 to 30 parts by mass with respect to 100 parts by mass of the polyester resin, the phenoxy resin, or the like.

  The coating layer is prepared by dissolving or dispersing the above-described resin (including the curing agent, if any) in a solvent, coating the coating layer on the adhesive layer, and drying it. can get. In addition, a coating layer can also be obtained by apply | coating the coating layer formation coating liquid mentioned above to the release film prepared separately, and making it dry.

The thickness (t2) of the coating layer is 28 of the thickness (t1) of the adhesive layer before heating (or before heating and foaming).
It is preferably 0% or less. By setting t2 to 280% or less of t1, the coating layer can be softened by heat (for example, heating of about 60 ° C. or more and about 140 ° C. or less) and can be favorably dissipated.
The mechanism by which the coat layer disappears is as follows. The coating layer is softened by the application of heat above the glass transition temperature of the resin forming the coating layer. As a result, the resin of the coating layer mixes with the thermosetting resin (before curing) which forms the adhesive layer, and is integrated with the adhesive layer (incorporated into the adhesive layer). As a result, the coat layer present on the adhesive layer apparently disappears.

If the coating layer is too thick, it may not be sufficiently incorporated into the adhesive layer, and as a result, the loss of the coating layer may not proceed well. In addition, when the heat blowing agent is contained, the heat blowing agent in the adhesive layer may not be able to sufficiently foam, and the foamability may be impaired.
In the present invention, as described above, at least a part of the adhesive layer after heat curing is exposed (contacted) to a portion of the adhesive sheet after the adhesive layer is cured by heating and in contact with the adherend. For example, it is determined that "the coat layer has disappeared".
In the present embodiment, t2 is preferably, for example, 0.5 μm or more and 600 μm or less.

It is desirable to determine the resin for forming the coating layer so that the glass transition temperature (T3) of the coating layer is preferably 60 ° C. or more and 140 ° C. or less. If the glass transition temperature (T3) of the coating layer is too low, the surface of the coating layer may become tacky (tack), making it difficult to obtain the effects of the present invention. On the other hand, if T3 is too high, the coating layer is not sufficiently softened in the heat curing temperature range of the adhesive layer, and there is a possibility that the adhesive force by the adhesive layer can not be sufficiently exhibited.

In the present embodiment, if example embodiment, to be contained in the adhesive composition forming an adhesive layer, a weight average molecular weight is less than 800 epoxy resin, trade name NC2000L (novolac type epoxy resin, Nippon Kayaku, epoxy equivalent 229-244 When a softening temperature of 47 to 57 ° C. is used (contact angle 86.4 degrees), it is desirable to use a trade name PKHH (contact angle 83.3 degrees) of bisphenol A type as a resin for forming a coating layer.

  The adhesive sheet according to an embodiment of the present invention may be produced by sequentially forming an adhesive layer and a coat layer on a substrate as described above. Further, as described above, the coating layer and the adhesive layer may be sequentially formed on a separately prepared release film, and then the substrate may be attached (laminated) to this. Furthermore, it can also be produced by bonding (laminating) one in which a coating layer is formed on a release film and one in which an adhesive layer is formed on a substrate.

The adhesive sheet of the present invention as described above includes, for example, reinforcement of riveting of construction materials, lamination of decorative panels of furniture and building materials, interior materials of automobiles, interlayer adhesion of carbon fiber reinforced plastic (CFRP) and structural adhesion It can be suitably used for applications, coverlay film bonding for flexible electronic circuit boards, and the like. In addition, by using an insulating base material in the adhesive layer, it can be used for bonding various parts of electronic devices that require insulation, such as interlayer insulating films of electronic circuit boards.
Moreover, it can be used for adhesion | attachment of an electronic device and a heat sink by introduce | transducing a heat conductive filler into an adhesive layer.
An image display member fixed to an image display device (a liquid crystal display, an electroluminescence display, a plasma display, etc.) and a portable electronic device (a liquid crystal display, an electroluminescence display, a plasma display, etc.) by introducing a thermally expandable filler into the adhesive layer. Stators used in motors and generators, as well as applications as gap fillers that occur between an optical member (camera, lens, etc.) fixed to a mobile phone, portable information terminal, etc., and a housing (window) It can be widely used in the electrical and electronic industry as an application of interposing a gap between adjacent coils of different phases in a coil end portion, a gap in a slot groove of a stator core, or the like.
In particular, where different coils cross winding bundles at coil end portions where the coils are projected from both ends of the stator core of a motor or generator, in order to ensure insulation between the phases, adjacent coils having different phases are different (Japanese Patent Application Laid-Open No. 2010-103162, Japanese Patent Application Laid-Open No. 2012-170248).

  A stator used for a motor or a generator is composed of a stator core and a coil formed by winding and bundling a thin copper wire and a coil coated with a resin composition. The stator core is generally formed in a cylindrical shape, and provided with a plurality of slot grooves extending along the longitudinal direction on the inner peripheral side, and the coils are respectively accommodated in different slot grooves. It is mounted on the stator core. Since it is necessary to ensure sufficient insulation of such a coil, an insulating sheet is inserted into the gap in the slot groove of the stator core, and a liquid (paste) resin composition seal is provided to prevent the insulating sheet from falling off. It solidifies with materials (for example, it is indicated by JP, 2003-33785, A), and a coil, an insulation sheet, and a resin composition are unified and used.

  However, in order to integrate the coil and the insulating sheet by using such a sealing material and fill the gap in the slot groove of the stator core, it is necessary to turn the sealing material from the outer layer of the stator core It has to be used more than the amount, and the loss of the sealing material increases. Moreover, since it is easy to produce adhesion to places other than a required location when using a sealing material, in order to prevent this, there exists a possibility that a complicated operation may be accompanied. Furthermore, in recent years, while downsizing and thinning of electric and electronic devices are required, an improvement in space factor of a conductor coil to a slot is required. For this reason, the gap between the inner wall of the slot and the conductor coil tends to be narrowed to 1 mm or less, and it is difficult to fill the narrow gap with a seal material whose viscosity is difficult to control.

  The adhesive sheet of the present invention is particularly useful for filling work in a narrow gap of 1 mm or less, more specifically, for the above-described solidification application in which the insulating sheet and the sealing material are separately used.

  Hereinafter, the present invention will be specifically described based on experimental examples (including examples and comparative examples), but the present invention is not limited to these examples. In the examples, unless otherwise stated, "%" and "parts" indicate% by mass and parts by mass.

[Experimental Examples 1 to 25]
1. Preparation of adhesive layer forming coating liquid The following component was uniformly mixed by solid content ratio (mass conversion) of Table 1, and adhesive layer forming coating liquid (a to k) was prepared. The total solid content in each coating liquid was 30% by mass to 50% by mass. The details of the thermosetting resin (A1 to A11) contained in each coating liquid are shown in Table 2.

<< Constituent Components of Adhesive Layer Forming Coating Liquids a to k >>
Thermosetting resin (epoxy resin): Type shown in Table 2 and part by mass listed in Table 1 Curing agent (solid content 100%): Part listed in Table 1 (Dicyandiamide (DICY), manufactured by Japan Epoxy Resins Co., Ltd.)
-Hardening accelerator (solid content 100%): The mass parts described in Table 1 (Cuazole 2MZ-A, 2,4-diamino-6- [2'-methylimidazolyl- (1 ')]-ethyl-s-triazine, Shikoku Chemical Co., Ltd.)

2. Preparation of Coating Layer-Forming Coating Liquid The following constituent components were uniformly mixed at a solid content ratio (in terms of mass) described in Table 3 to prepare coating layer-forming coating liquids (A to G). The total solid content in each coating liquid was 30% by mass to 50% by mass. The details of the thermoplastic resins (B1 to B7) contained in the respective coating liquids are shown in Table 4.

<< Constituent Components of Coating Layer Forming Coating Liquids A to G >>
Thermoplastic resin: Type shown in Table 4 and parts by mass shown in Table 3 Curing agent (solid content 75%): Table 3 parts by mass (Takenate 600, manufactured by Mitsui Takeda Chemical Co., NCO content: 43.3 %)

3. Preparation of adhesive sheet Using the coating layer forming coating solution shown in Tables 5 to 8 and the adhesive layer forming coating solution, on the release treated surface of a release film (thickness 38 μm, BINA No. 23: made by Fujimori Kogyo Co., Ltd.) Then, a predetermined coating layer forming coating solution was applied by a baker type applicator. Then, the coating layer of predetermined thickness (refer the "coat layer film thickness" column of Tables 5-8) was formed by drying at 140 degreeC for 1 minute. Next, a predetermined adhesive layer forming coating solution was applied to the surface of the coat layer in the same manner as described above. Then, the adhesive layer of predetermined thickness (refer the "film thickness t1" column of Tables 5-8) was formed by drying for 1 to 2 minutes at 120 degreeC. Thereafter, the surface of the adhesive layer and the base material (thickness 25 μm, polyimide film: Kapton 100H, made by Toray DuPont Co., Ltd.) are laminated while applying heat at 80 ° C., and then the release film is peeled off. And the adhesive sheet of Comparative Examples 1-3 was obtained.

4. Evaluation The following items were measured or evaluated for the adhesive sheets of the respective Examples and Comparative Examples obtained by the following method. The results are shown together in Tables 5-8.

[Curing start temperature of adhesive layer (T2)]
A differential scanning calorimeter (DSC 3200, manufactured by Mac Science) was used as a measurement device. The temperature at which the DSC baseline in a steady-state range crosses the DSC rising line during the curing reaction when the temperature of the produced sheet-like adhesive layer resin is raised from normal temperature to 300 ° C. at 10 ° C./min is the curing initiation temperature (T2) And

[Glass transition temperature of coat layer (T3)]
A differential scanning calorimeter (DSC 3200, manufactured by Mac Science) was used as a measurement device. The DSC baseline change point when the prepared sheet-like coat layer resin was heated from normal temperature to 300 ° C. at 10 ° C./minute was defined as a glass transition point (T3).

[Coat layer thickness (t2)]
About the adhesive sheet obtained by each Example and Comparative example, a release film and a coat layer are formed using a micrometer for the laminate 2 (laminate of the release film and the coat layer) before forming the adhesive layer. The total thickness was measured and calculated from the obtained measured values by subtracting the thickness (38 μm) of the release film.

[Thickness of adhesion layer (before heating) (t1)]
About the adhesive sheet obtained by each Example and the comparative example, about the laminated product 1 (laminated film of a mold release film, a coat layer, and an adhesive layer) before laminating a base material, using a micrometer, a mold release film The total thickness of the coat layer and the adhesive layer was measured, and the thickness was calculated from the obtained measurement values by reducing the thickness of the laminate 2 (laminate of the release film and the coat layer) before forming the adhesive layer.

[Cracks in adhesive layer (cracks 1 and 2)]
About each example and comparative example, in the state without a coat layer and the state with a coat layer, after heating the arbitrary places by the side of an adhesion layer before heating, the state of the adhesion layer was checked visually . As a result, it is possible to be good when there is no crack in the adhesive layer itself (including the detachment of the adhesive layer from the base material. The same applies to the following.) As "o", the crack was recognized or it can be bent at 180 degrees. The thing which was not was made into "x" as defect. When there is no coat layer, "crack 1" is used, and when there is a coat layer, "crack 2" is used.

[Tack of adhesive layer (tack 1, 2)]
The adhesive sheet before heating or heating and foaming of each Example and Comparative Example was cut into a size of 5 cm × 5 cm, and six sheets were stacked so that the coat layers face each other and sandwiched between glass plates of 1 mm in thickness. A load of 100 g was applied thereon, and after standing for 24 hours each under normal temperature (25 ° C.) and 30 ° C. environments, the load was released and then left at normal temperature for 30 minutes or longer. Thereafter, by checking the peeling state when the glass plate was spread up and down, it was evaluated whether the coat layers were in close contact with each other. Here, when there was no coat layer, adhesion layers were made to face each other and laminated, and it was evaluated by the same method whether adhesion layers adhered.
Here, it was judged that adhesion was caused between the base material of the adhesive sheet and the adhesive layer in a state where the coat layers of the adhesive sheets were in close contact, that is, the coat layer exhibited tack at normal temperature. On the other hand, when the glass plate was spread up and down, in the case of peeling between the coat layers which were in contact, it was judged that there was no adhesion, that is, the coat layer did not exhibit tack. Those with no adhesion in both environments are marked with “o”, those with adhesion only in a 30 ° C. environment with “Δ”, and those with adhesion in both environments with “x”. In addition, when there was no coat layer, it was set as "tack 1", and when there was a coat layer, it was set as "tack 2."

[Shear bond strength and loss of coat layer]
The adhesive layer of the laminate 1 (laminate of release film, coat layer and adhesive layer) before laminating the substrate among the adhesive sheets of each example and comparative example on the SPCC steel plate (steel plate A) with a thickness of 1 mm It was placed in contact and the release film was peeled off. Furthermore, an SPCC steel plate (steel plate B) with a thickness of 1 mm was stacked and fixed to the coat layer side (laminated product of steel plate A, adhesive layer, coat layer and steel plate B). The laminate was then left in an oven heated to 190 ° C. for 30 minutes and then taken out. After heating, the steel sheet A and steel sheet B of the laminated product are pulled parallel to the bonding surface and in mutually opposite directions (shearing direction) using the Umbilical Material Testing Machine UTM-5T (manufactured by A & D Co., Ltd.) Shear bond strength (Pm) was measured (unit: MPa).

About the adhesive sheet obtained in each Example and Comparative Example, the adhesive layer is formed on the SPCC steel plate having a thickness of 1 mm on laminate 1 (laminate of release film, coat layer and adhesive layer) before laminating the substrate. It was placed in contact and the release film was peeled off. Furthermore, an SPCC steel plate having a thickness of 1 mm was overlapped and fixed so as to form a gap twice as much as the total of the thickness of the adhesive layer and the thickness of the coat layer. Next, it was left in an oven heated to 190 ° C. for 30 minutes and then taken out. This was vertically cut so that the cross section of the SPCC steel plate and the adhesive layer (and the coat layer) could be confirmed, and the cross section was observed with a microscope to confirm the presence or absence of the coat layer. As a result, the coat layer disappears and the one stuck to the SPCC steel plate is "◎", the coat layer remains partially but the one stuck to the SPCC steel plate "○", the coat layer remains and the SPCC steel plate remains The thing which did not stick was made into "x".
As described above, the fugitive nature of the coat layer is judged by observing the cross section of the adhesive sheet with a microscope, but depending on the sample, both the adhesive layer and the coat layer may be transparent, making judgment by the above method difficult. is there. In such a case, the loss of the coat layer can be determined by the following method. When the coating layer disappears and the adhesive layer adheres to the steel plate A and the steel plate B, the shear adhesive strength becomes greater than when only the coating layer adheres to the steel plate. Therefore, in the same manner as described above, a laminate having a coating layer without providing an adhesive layer on a release film is provided between steel plate A and steel plate B, and the shear adhesive strength (Pc) of the coating layer alone is measured. . Then, the loss of the coat layer is evaluated by the ratio (Pm / Pc) of the shear bond strength (Pc) of the coat layer alone and the measured value (Pm) of the shear bond strength of the steel sheet A and the steel sheet B of the laminate after heating. can do. The shear bond strengths (Pc) of the coat layers alone produced from the coat layer-forming coating liquids A, B, C, D, E, F and G shown in Table 3 are 11 MPa, 16 MPa, 16 MPa, 15 MPa, respectively. , 13 MPa, 7 MPa and 8 MPa.
In the evaluation, those with a value of (Pm / Pc) exceeding 110% are marked with “◎”, those with more than 100% and 110% or less with “○” and those with 100% or less with “x” did. In addition, what can not be measured because the shape of an adhesive layer can not be maintained was made into "-".

As shown in Table 5, in Comparative Examples 1 and 2 and Examples 1 and 2 in which novolak having a softening temperature of 47 ° C. to 57 ° C. was used for the adhesive layer, the adhesive layer alone exhibited tack. Here, in Comparative Examples 1 and 2 in which an ethylene-vinyl acetate copolymer having a glass transition temperature of -23 ° C and a phenoxy resin having a glass transition temperature of 15 ° C were used as the coating layer, the coating layer had tack at room temperature. However, the tack of the adhesive sheet in which the coating layer is laminated on the contact layer can not be suppressed. On the other hand, in Examples 1 and 2 in which a phenoxy resin having a glass transition temperature of 92 ° C. and a polyester resin having a glass transition temperature of 67 ° C. are used as the coating layer, the coating layer does not show tack at normal temperature and coats the contact layer. It was found that the adhesive sheet in which the layers are laminated suppresses the tack and improves the workability.
Further, in Comparative Example 3 in which a solid bisphenol A type epoxy resin having a softening temperature of 112 ° C. was used as the adhesive layer, the adhesive layer alone did not exhibit tack at normal temperature, but cracking occurred. In an adhesive sheet in which a phenoxy resin having a glass transition temperature of 92 ° C. is laminated as a coat layer on this adhesive layer, no tack is observed and generation of cracks is suppressed, but disappearance of the coat layer after heating is not observed, and adhesive strength Was found to be low.
From the above results, the coated layer does not show tack at normal temperature, and at least a part of the coated layer is coated from the interface between the adhesive layer and the coated layer by heating the adhesive sheet to the curing start temperature or higher of the adhesive layer. The effect of the configuration of the present invention which disappears to the surface was confirmed.

In Examples 3 to 7, as the adhesive layer, novolac type epoxy resins having a softening temperature of 47 to 57 ° C. were used, and different types of coat layers were laminated to produce an adhesive sheet. The adhesive layer alone showed tack, but the adhesive sheet can suppress tack in any of the examples 3 to 7 using a coating layer which does not show tack at a glass transition temperature of 60 ° C. to 150 ° C. at normal temperature. all right.
In particular, in Examples 3 to 6 in which the glass transition temperature of the coating layer was 60 ° C. to 130 ° C., it was found that a more excellent coat layer depleting property was obtained.
From the above results, it can be said that the glass transition temperature of the coating layer is preferably 60 ° C. or more and 140 ° C. or less.

As shown in Table 7, in the case of “adhesive layer alone”, there were no good ones for both the crack 1 and the tack 1 (there is at least one x in all cases). Nevertheless, with "including the coat layer" to which the coat layer was added, the tackiness (tack 2) could be improved. As a result, both cracks 2 and tack 2 were found to be good (Examples 4, 5, 9 to 15).
In addition, although not described in the table, when using an adhesive layer forming coating solution a using A1 as a thermosetting resin of the adhesive composition, it is difficult to obtain good foamability etc. all right. From this, as a thermosetting resin added to an adhesive composition, semi-solid or solid resin is considered to be preferable.

  From Examples 4, 5 and 8, even if the "adhesive layer alone" is sticky, the presence of the coat layer can contribute to the suppression of the deterioration of the workability even without using the separator, since it covers the sticky film. I could confirm that (Tack 2 is ○). Further, from Examples 9 to 15, even if the "adhesive layer alone" is cracked, the cracked film is held by the presence of the coating layer, so the coating layer disappears when it is heated (taken in the adhesive layer) It can be confirmed that it does not interfere with use) (crack 2 is 〇, coat layer extinguishability is ◎).

As shown in Table 8, when the film thickness t2 of the coat layer is 2.8 times or less of the film thickness t1 of the adhesive layer (Examples 4, 5 and 16 to 24), the film thickness t2 of the coat layer is the adhesive layer In comparison with the film thickness t1 of 3.0 times (Example 25), the disappearance of the coating layer was improved. However, even the twenty-fifth embodiment can sufficiently withstand practical use.

Claims (9)

An adhesive layer comprising an adhesive composition comprising an epoxy resin having a softening temperature of 105 ° C. or less;
An adhesive sheet having a coating layer formed on the adhesive layer and containing a thermoplastic resin,
The coat layer does not show tack at normal temperature,
By heating the adhesive sheet above the curing start temperature of the adhesive layer, at least a portion of the coating layer disappears in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer, and the adhesive layer T3 is 60 ° C. or more and 140 ° C. or less, where T2 is a curing start temperature of the glass, and T3 is a glass transition temperature of the coating layer.
T3 <T2
An adhesive sheet characterized by satisfying the requirements.   The adhesive sheet according to claim 1, wherein when the thickness of the adhesive layer before heating is t1 and the thickness of the coating layer is t2, the relationship of t2 ≦ 2.8 · t1 is satisfied.   The adhesive sheet according to claim 2, wherein t2 is 0.5 μm or more and 600 μm or less.   The adhesive sheet according to claim 2 or 3, wherein t1 is 20 μm or more and 1000 μm or less.   The adhesive sheet according to any one of claims 1 to 4, wherein a curing start temperature of the adhesive layer is 110 ° C or more and 250 ° C or less.   The adhesive sheet according to any one of claims 1 to 5, wherein the epoxy resin contained in the adhesive composition has a weight average molecular weight of 450 or more and less than 1650.   The adhesive sheet according to any one of claims 1 to 6, wherein the epoxy resin is one or two selected from the group consisting of a bisphenol A epoxy resin and a novolac epoxy resin.   The adhesive sheet according to any one of claims 1 to 7, comprising a substrate on which the adhesive layer is formed. An electronic circuit board, a building structural material, an image display apparatus, a portable electronic device or an automobile part characterized by using the adhesive sheet according to any one of claims 1 to 8 .