Easy-to-disassemble adhesive, cured product thereof, and structure

Abstract

To provide an adhesive and a cured product which have excellent adhesive strength and thermal cycle resistance due to high flexibility and cohesive force at the time of adhesion, and exhibit excellent thermal dismantlability at the time of heating at about 80 °C to 200 °C.SOLUTION: Specifically disclosed is an easily decomposable adhesive which comprises a polyol (A), a polyisocyanate (B), a thermally expandable filler (C), an inorganic filler (D) and / or an organic thixotropic agent (E). A theoretical value of a urethane bond concentration formed during the reaction in the resin which is a reaction product of the polyol (A) and the polyisocyanate (B) is 0.3 mmol / g to 4.0 mmol / g, and the easy-to-disassemble adhesive has a storage modulus measured at 80 °C. and a frequency of 10 Hz of 1.0 * 10 5 to 5.0 * 10 8 Pa when the cured product is cured for 7 days under an atmosphere of 23 °C. and a relative humidity of 50% so that the thickness of the cured product is 2 mm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an easily dismantlable adhesive that is suitable for bonding metal substrates and resin substrates, and for bonding different types of resin substrates together, and that combines adhesive strength and thermal cycle resistance during bonding with thermal dismantling properties during heating, and to a cured product and structure that use the adhesive and have excellent easily dismantlable properties. [Background technology]

[0002] In recent years, in the fields of automobiles, building materials, ships, and aircraft, the rate of joining dissimilar substrates, such as light metals like aluminum and magnesium and fiber-reinforced plastics (hereinafter referred to as FRP), has increased in order to reduce vehicle weight. When joining dissimilar metal substrates, welding cannot be used due to the risk of galvanic corrosion and peeling, so adhesives or special mechanical fastening methods are used. Furthermore, when joining metal substrates and resin substrates, or when joining dissimilar resin substrates, welding is not possible, and mechanical fastening can cause cracks due to stress concentration, so adhesives are used. However, dissimilar substrates joined with adhesives are difficult to separate after curing, so they are often disposed of in landfills without being recycled and cannot be separated.

[0003] Furthermore, when bonding materials with different linear expansion coefficients, such as aluminum and FRP, the difference in the expansion coefficients between the materials caused by thermal changes during the manufacturing process or in the operating temperature environment places high stress on the adhesive layer, accelerating its destruction or deterioration. Therefore, methods to impart flexibility to adhesives have been widely studied as a stress relief design, and urethane adhesives, which combine high adhesive strength with flexibility, have attracted particular attention. Furthermore, two-component urethane adhesives are needed in the process of applying adhesives to manufacture structures to shorten lead times and eliminate poor curing due to temperature changes in the operating temperature environment.

[0004] That is, there is a demand for two-component urethane adhesives that are flexible and have excellent releasability after curing, but these adhesives are required to have high adhesive strength, flexibility, and thermal cycle resistance during adhesion, while low adhesive strength during removal, which are contradictory properties, making it difficult to resolve the trade-off.

[0005] In the above-mentioned environment, for example, Patent Document 1 discloses an adhesive composition containing a moisture-curable resin, a foaming agent, a radically polymerizable compound, and a photoradical polymerization initiator. For example, Patent Document 2 discloses a urethane adhesive obtained by blending a release agent and a foaming agent into a urethane adhesive. For example, Patent Document 3 discloses a thermally disintegrable adhesive characterized by blending two or more types of thermally expandable fine particles in combination, the difference in particle size based on the average particle size being at least 3 μm. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6878289 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-286465 [Patent Document 3] Japanese Patent Application Publication No. 6-184504 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the adhesive described in Patent Document 1 has problems in that it has low film strength and shear adhesive strength after curing, and peels off due to cohesive failure of the coating film during thermal disassembly. The urethane adhesive described in Patent Document 2 has problems in that it has low film strength after curing and peels off even with the heat of a hair dryer, resulting in low thermal cycle resistance. The adhesive described in Patent Document 3 is a solvent-based pressure-sensitive adhesive, resulting in low shear adhesive strength after curing. In addition, the thermally expandable microparticles are prone to coagulation and precipitation, causing uneven expansion during thermal disassembly, resulting in insufficient reduction in adhesive strength and poor thermal disassembly between the adhesive and the substrate.

[0008] Therefore, an object of the present invention is to provide an adhesive and cured product that have excellent adhesive strength and thermal cycle resistance due to high flexibility and cohesive strength when bonded, and that exhibit excellent thermal dismantling properties when heated at about 80° C. to 200° C., and that are easily dismantled. Another object of the present invention is to provide a cured product and structure that have excellent thermal cycle resistance and exhibit excellent thermal dismantling properties when heated at about 80° C. to 200° C. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following inventions [1] to [9].

[0010] [1] An easily dismantlable adhesive comprising a polyol (A), a polyisocyanate (B), a thermally expandable filler (C), and an inorganic filler (D) and / or an organic thixotropic agent (E), wherein a theoretical value of a urethane bond concentration formed during a reaction in a resin that is a reaction product of the polyol (A) and the polyisocyanate (B) is 0.3 mmol / g to 4.0 mmol / g, and the easily dismantlable adhesive is cured for 7 days in an environment of 23°C and a relative humidity of 50% so that the thickness of the cured product becomes 2 mm, and the cured product obtained has a storage modulus of 1.0 x 10 measured at a frequency of 10 Hz at 80°C. 5 ~5.0×10 8 Pa is an easily dismantled adhesive.

[0011] [2] The easily dismantlable adhesive according to [1], wherein the thermally expandable filler (C) has an expansion starting temperature of 80°C to 200°C.

[0012] [3] The easily dismantlable adhesive according to [1] or [2], wherein the inorganic filler (D) comprises at least one selected from the group consisting of calcium carbonate, silica, talc, mica, kaolin, aluminum hydroxide, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, and carbon black.

[0013] [4] The easily dismantlable adhesive according to any one of [1] to [3], wherein the polyol (A) comprises a polyol (a1) having a number average molecular weight of 2,000 or more and a polyol (a2) having a number average molecular weight of 50 or more and less than 2,000.

[0014] [5] The easily dismantlable adhesive according to [4], wherein the content of the polyol (a1) is 5 to 95 mass % based on the mass of the polyol (A).

[0015] [6] The easily dismantlable adhesive according to any one of [1] to [5], wherein the polyisocyanate (B) includes a reaction product of a polyol (b1) and a polyisocyanate (b2).

[0016] [7] The easily dismantlable adhesive according to any one of [1] to [6], wherein the polyisocyanate (B) contains an aromatic polyisocyanate.

[0017] [8] A cured product obtained by curing the easily dismantlable adhesive according to any one of [1] to [7].

[0018] [9] A structure comprising an adhesive layer between a first adherend and a second adherend, wherein the adhesive layer is the cured product according to [8]. [Effects of the Invention]

[0019] The present invention can provide an adhesive and cured product that exhibit excellent adhesive strength and thermal cycle resistance due to high flexibility and cohesive strength during adhesion, and that exhibit excellent thermal dismantling properties when heated at about 80° C. to 200° C., making them easily dismantlable. The present invention can also provide cured products and structures that exhibit excellent thermal cycle resistance and excellent thermal dismantling properties when heated at about 80° C. to 200° C. DETAILED DESCRIPTION OF THE INVENTION

[0020] <Easy-to-dismantle adhesive> The easily dismantlable adhesive of the present invention is an easily dismantlable adhesive comprising a polyol (A), a polyisocyanate (B), a thermally expandable filler (C), and an inorganic filler (D) and / or an organic thixotropic agent (E), wherein the theoretical value of the concentration of urethane bonds formed during the reaction in a resin that is a reaction product of the polyol (A) and the polyisocyanate (B) is 0.3 mmol / g to 4.0 mmol / g, and the easily dismantlable adhesive is cured for 7 days in an environment of 23°C and a relative humidity of 50% so that the thickness of the cured product becomes 2 mm, and the cured product obtained has a storage modulus of 1.0 x 10 measured at a frequency of 10 Hz at 80°C. 5 ~5.0×10 8 The adhesive of the present invention is characterized by the fact that it is a urethane adhesive having a high temperature coefficient of thermal expansion. The adhesive of the present invention has the above-described configuration, and while maintaining the high flexibility of a urethane adhesive during adhesion, the inclusion of an inorganic filler and / or an organic thixotropic agent improves cohesive strength through interaction with the urethane bonds, resulting in high film strength and long-term stability in thermal cycle tests. Furthermore, upon peeling at temperatures of approximately 80°C to 200°C, the effect of the improved cohesive strength suppresses cohesive failure of the coating film. Furthermore, by combining an inorganic filler and / or an organic thixotropic agent with a thermally expandable filler, the thermally expandable filler can be maintained in a uniformly dispersed state within the coating film without agglomeration, allowing the entire coating film to expand and exhibiting excellent thermal disintegration properties. Therefore, the easily dismantling adhesive of the present invention can be suitably used in fields where easy dismantling performance is required, such as automobiles, building materials, ships, and aircraft. The present invention will be described in detail below. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits of the range.

[0021] <Polyol (A)> The polyol (A) is not particularly limited as long as it is a compound having two or more hydroxyl groups in the molecule. Examples of such polyols (A) that can be used include polyester polyols, polyether polyols, polyurethane polyols, polyesteramide polyols, acrylic polyols, polycarbonate polyols, polycaprolactone polyols, polyvalerolactone polyols, polybutadiene polyols, polyolefin polyols, polyhydroxyalkanes, castor oil, and mixtures thereof. The polyol (A) may be, for example, a polyether polyol or a polycarbonate polyol in which urethane bonds have been introduced by reacting a polyisocyanate with some of the hydroxyl groups (hereinafter, these may be referred to as polyether urethane polyol or polycarbonate urethane polyol), and the polyisocyanate to be reacted may be a compound described in the section <Polyisocyanate (B)> described below. The polyol (A) may also be one in which carboxyl groups have been introduced by reacting some of the hydroxyl groups with an acid anhydride. Examples of the acid anhydride include pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic ester anhydride. Examples of the trimellitic ester anhydride include ester compounds obtained by esterifying alkylene glycols or alkanetriols having 2 to 30 carbon atoms with trimellitic anhydride, and examples of usable compounds include ethylene glycol bis-anhydrotrimellitate and propylene glycol bis-anhydrotrimellitate. These polyols (A) may be used alone or in combination of two or more.

[0022] From the viewpoint of long-term resistance to moisture and heat, the polyol (A) preferably contains at least one selected from the group consisting of polyether polyols, polyurethane polyols, acrylic polyols, polycarbonate polyols and polybutadiene polyols. Particularly from the viewpoint of adhesive strength and moist heat resistance, the polyol (A) preferably contains at least one selected from the group consisting of polyether polyols, acrylic polyols, polycarbonate polyols, and polybutadiene polyols, more preferably contains at least one selected from the group consisting of polyether polyols, polycarbonate polyols, and polybutadiene polyols, and even more preferably contains at least one selected from the group consisting of polyether polyols and polycarbonate polyols.

[0023] The polyol (A) preferably contains a polyol (a1) having a number-average molecular weight of 2,000 or more and a polyol (a2) having a number-average molecular weight of 50 or more but less than 2,000. By using a polyol (a1) and a polyol (a2) having different number-average molecular weights in combination, it is possible to achieve both elongation and adhesive strength of the cured adhesive. In this specification, the number-average molecular weight is a value measured by GPC (gel permeation chromatography) and converted into standard polystyrene.

[0024] [Polyol (a1) with a number average molecular weight of 2,000 or more] The polyol (a1) is not particularly limited as long as it has a number-average molecular weight of 2,000 or more. From the viewpoint of the extensibility of the cured product, the number-average molecular weight is preferably 3,000 or more. The upper limit of the number-average molecular weight may be within a producible range, and may be 100,000 or less, 50,000 or less, or 10,000 or less. When the number-average molecular weight is 100,000 or less, the adhesive strength when cured at room temperature and the dispenser dischargeability after mixing in adhesive coating are excellent. The polyol (a1) preferably has a urethane bond from the viewpoint of adhesive strength and heat resistance.

[0025] The method for producing the polyol having the urethane bond is not particularly limited, and for example, a reaction product of a polyol and a polyisocyanate can be suitably used. As the polyol, for example, the compounds exemplified in the above section on <Polyol (A)> can be used. From the viewpoint of adhesive strength and moist heat resistance, the polyol is preferably at least one selected from the group consisting of polyether polyols, polycarbonate polyols, and polybutadiene polyols, and more preferably at least one selected from the group consisting of polyether polyols and polycarbonate polyols.

[0026] Examples of the polyisocyanate include aromatic, aliphatic, or alicyclic diisocyanates (hereinafter also referred to as polyisocyanate monomers); dimers, trimers, biurets, and allophanates derived from polyisocyanate monomers; and polyisocyanates having a 2,4,6-oxadiazinetrione ring obtained from carbon dioxide gas and the above-mentioned polyisocyanate monomers. These may be used alone or in combination of two or more.

[0027] Examples of aromatic diisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, and 1,5-tetrahydronaphthalene diisocyanate.

[0028] Examples of aliphatic diisocyanates include xylylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, lysine ester triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate tetramethylene diisocyanate, pentamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

[0029] Examples of alicyclic diisocyanates include isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-bis(isocyanatomethyl)cyclohexane, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate.

[0030] The polyol having a urethane bond may further have a urea bond in the molecule. The presence of a urea bond in the molecule improves adhesive strength and heat resistance durability. As a polyol having such a urea bond and a urethane bond, for example, a compound obtained by reacting an isocyanato group of a urethane polymer having an isocyanato group at a terminal, which is a reaction product of a polyol and a polyisocyanate, with an amino group of a monoamine compound having a hydroxyl group in the molecule is preferred from the viewpoints of viscosity and sagging properties during ejection and adhesive strength.

[0031] The content of polyol (a1) is preferably 5% by mass or more, more preferably 30% by mass or more, based on the mass of polyol (A). It is also preferably 95% by mass or less, more preferably 50% by mass or less, and may be, for example, 5 to 95% by mass. The above range is preferred because it results in excellent adhesive strength when cured at room temperature and flexibility of the cured coating film.

[0032] [Polyol (a2) having a number average molecular weight of 50 or more and less than 2,000] The polyol (a2) is not particularly limited as long as it has a number average molecular weight of 50 or more and less than 2,000. From the viewpoint of compatibility, the number average molecular weight is preferably 80 or more, more preferably 100 or more, and from the viewpoint of adhesive strength, it is preferably 1,000 or less, more preferably 500 or less. Examples of such polyols that can be used include glycols such as ethylene glycol, propane-1,2-diol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, methylpentane glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and triethylene glycol; polyalkylene glycols having a number average molecular weight of 50 or more and less than 2,000; trifunctional or tetrafunctional aliphatic alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and polyols in which the above-mentioned glycols or polyols are added to the above-mentioned trifunctional or tetrafunctional aliphatic alcohols.

[0033] In particular, from the viewpoint of long-term wet heat resistance and adhesive strength, the polyol (a2) preferably contains one selected from the group consisting of 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, and pentaerythritol. These polyols (a2) may be used alone or in combination of two or more.

[0034] The content of polyol (a2) is preferably 5% by mass or more, more preferably 10% by mass or more, based on the mass of polyol (A). It is also preferably 50% by mass or less, more preferably 30% by mass or less, and may be, for example, 5 to 50% by mass. A content in the above range is preferred because excellent adhesive strength is achieved.

[0035] <Polyisocyanate (B)> Examples of the polyisocyanate (B) include aromatic, aliphatic, or alicyclic diisocyanates (hereinafter also referred to as polyisocyanate monomers); dimers, trimers, biurets, and allophanates derived from polyisocyanate monomers; polyisocyanates having a 2,4,6-oxadiazinetrione ring obtained from carbon dioxide gas and the above-mentioned polyisocyanate monomers; and modified products thereof. These may be used alone or in combination of two or more.

[0036] [Reaction product of polyol (b1) and polyisocyanate (b2)] From the viewpoints of flexibility and viscosity, the polyisocyanate (B) preferably contains, as the modified product, a reaction product of a polyol (b1) and a polyisocyanate (b2) (hereinafter, sometimes referred to as a polyurethane polyisocyanate). The reaction product can be produced by reacting the polyol (b1) with the polyisocyanate (b2) under conditions of an excess of isocyanate groups, and the ratio [NCO / OH] of the number of isocyanate groups in the polyisocyanate (b2) to the number of hydroxyl groups in the polyol (b1) is preferably 1.1 or more, more preferably 2.0 or more. It is also preferably 10.0 or less, more preferably 5.0 or less, and may be, for example, 1.1 to 10.0. A ratio within the above range is preferred because the adhesive has excellent adhesive strength and flexibility. The polyol (b1) forming the reaction product is not particularly limited and can be selected from known polyols, such as polyester polyols, polyester urethane polyols, polycarbonate polyols, polycaprolactone polyols, polyether polyols, polyether urethane polyols, polyolefin polyols, acrylic polyols, silicone polyols, castor oil-based polyols, and fluorine-based polyols. Examples of the polyisocyanate (b2) that forms the reaction product include aromatic polyisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, and tolidine diisocyanate; aliphatic polyisocyanates such as xylylene diisocyanate and hexamethylene diisocyanate; and alicyclic polyisocyanates such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and norbornene diisocyanate. From the viewpoints of adhesive strength and heat resistance, the polyisocyanate preferably contains an aromatic polyisocyanate, and more preferably contains diphenylmethane diisocyanate.

[0037] From the viewpoint of rapid curing, the polyisocyanate (B) preferably further contains an aromatic polyisocyanate, and more preferably contains at least one selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimide-modified diphenylmethane diisocyanate.

[0038] <Thermal expansion filler (C)> The thermally expandable filler (C) expands in volume upon heating, and examples thereof include thermally expandable microcapsules and thermally expandable graphite. These may be used alone or in combination of two or more. Among these, it is preferable to use thermally expandable microcapsules because the particle size of the filler is small, adhesive strength and flexibility are not easily reduced, and the expansion start temperature can be easily controlled.

[0039] [Thermal expansion microcapsules] Examples of thermally expandable microcapsules include particles in which a substance that easily gasifies and expands when heated, such as isobutane, propane, or pentane, is encapsulated within a shell made of a thermoplastic resin. The shell is formed, for example, from a heat-fusible substance or a substance that breaks down due to thermal expansion. Examples of materials that form the shell include vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone. Commercially available products include "Matsumoto Microsphere" manufactured by Matsumoto Yushi Seiyaku Co., Ltd. and "Kureha Microsphere" manufactured by Kureha Corporation.

[0040] [Thermal expandable graphite] Thermally expandable graphite is a type of crystalline compound that maintains the layered structure of carbon and is produced by treating raw material powders such as natural flaky graphite, pyrolytic graphite, and kish graphite with an inorganic acid such as concentrated sulfuric acid, nitric acid, or selenic acid, and a strong oxidizing agent such as concentrated nitric acid, perchloric acid, perchlorates, permanganates, dichromates, dichromates, or hydrogen peroxide to produce a graphite intercalation compound. Commercially available thermally expandable graphite products include "Thermal Expandable Graphite TEG" manufactured by Air Water Co., Ltd. and "Expandable Graphite" manufactured by Fuji Graphite Industries Co., Ltd.

[0041] The thermally expandable filler (C) preferably has an average particle size of 1 to 500 μm. When the average particle size is 1 μm or more, dispersibility is good, the degree of expansion is large, and sufficient thermal disintegration property is exhibited. When the average particle size is 500 μm or less, excellent adhesive properties are exhibited. The particle size of the thermally expandable filler (C) can be measured by a laser diffraction scattering method (Microtrac MT3000) or the like.

[0042] The expansion start temperature of the thermally expandable filler (C) is not particularly limited, but from the viewpoint of heat resistance and practicality, it is preferably 80°C or higher, more preferably 105°C or higher, and preferably 200°C or lower, more preferably 160°C or lower, and may be, for example, 80 to 200°C. When the expansion start temperature is 80°C or higher, the adhesive does not expand at temperatures below 80°C, resulting in excellent heat resistance. Furthermore, when the expansion start temperature is 200°C or lower, the temperature required for dismantling can be lowered, resulting in excellent energy costs. The expansion starting temperature of the thermally expandable filler (C) can be measured by raising the temperature of the thermally expandable filler at a constant temperature and measuring the temperature at which the normal force rises using an apparatus with a temperature control function and a normal force measurement function, such as a rheometer (Anton Paar MCR102).

[0043] From the viewpoint of achieving both thermal expandability and adhesive strength, the content of the thermally expandable filler (C) is preferably 1% by mass or more, more preferably 3% by mass or more, based on the solid mass of the easily dismantlable adhesive, and is preferably 20% by mass or less, more preferably 10% by mass or less, for example, 1 to 20% by mass.

[0044] The adhesive of the present invention contains an inorganic filler (D) and / or an organic thixotropic agent (E). These interact with other resin components to form a sea-island network structure, imparting suitable rheological properties to the adhesive and improving heat resistance. From the viewpoint of superior heat resistance, the adhesive of the present invention preferably contains an inorganic filler (D) in particular. Furthermore, from the viewpoint of flexibility and ease of rheology control, it is also preferable to contain both an inorganic filler (D) and an organic thixotropic agent (E).

[0045] <Inorganic filler (D)> Examples of inorganic fillers include metal oxides such as aluminum oxide, magnesium oxide, titanium oxide, silica, talc, mica, kaolin, wollastonite, and zeolite; metal carbonates such as calcium carbonate and magnesium carbonate; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide; metal nitrides such as aluminum nitride, boron nitride, and silicon nitride; metal carbides such as silicon carbide, carbon black, and boron carbide; and particles of silver, copper, aluminum, and alloys containing these. These may be surface-treated to improve compatibility with the resin. These may be used alone or in combination of two or more.

[0046] From the viewpoint of adjusting the rheological properties and improving the heat resistance of the adhesive, the inorganic filler preferably contains at least one selected from the group consisting of calcium carbonate, silica, talc, mica, kaolin, aluminum hydroxide, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, and carbon black.

[0047] <Organic thixotropic agent (E)> Examples of the organic thixotropic agent (E) include polycarboxylic acids, polyether phosphate esters, and fatty acid amides, with fatty acid amides being particularly preferred. Fatty acid amides are powdery substances whose main component is fatty acid amide wax, and are activated by heating and dispersing them in the system, forming a strong network structure, thereby functioning as a thixotropic agent. These may be used alone or in combination of two or more.

[0048] The total content of the inorganic filler (D) and the organic thixotropy-imparting agent (E) is preferably 1% by mass or more, more preferably 10% by mass or more, based on the solid mass of the adhesive, and is preferably 97% by mass or less, more preferably 93% by mass or less.

[0049] <Solvent> The adhesive of the present invention is preferably solvent-free from the viewpoint of eliminating the need for a drying step in the curing process, but may contain an appropriate solvent depending on the required performance and application, as long as the effects of the present invention are not impaired. For example, the adhesive may contain a solvent contained in the additives described below, or a dilution solvent used when blending the additives.

[0050] <Additives> The adhesive of the present invention may further contain known additives such as reaction accelerators, silane coupling agents, leveling or defoaming agents, fillers, propellants, plasticizers, superplasticizers, wetting agents, flame retardants, viscosity modifiers, preservatives, stabilizers, and colorants. Such additives may be used alone or in combination of two or more.

[0051] Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dimaleate, etc. The blending ratio of the reaction accelerator is preferably 0.005 to 1 mass % based on the mass of the polyol (A).

[0052] Examples of silane coupling agents include trialkoxysilanes having a vinyl group, such as vinyltrimethoxysilane and vinyltriethoxysilane; trialkoxysilanes having an amino group, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane; trialkoxysilanes having a glycidyl group, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane; trialkoxysilanes having an isocyanato group, such as 3-isocyanatepropyltriethoxysilane; and trialkoxysilanes having a mercapto group, such as 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane. The blending ratio of the silane coupling agent is preferably 0.05 to 10 mass% based on the solid content mass of the adhesive.

[0053] Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl group-containing polydimethylsiloxane, polyetherester-modified hydroxyl group-containing polydimethylsiloxane, acrylic copolymer, methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, and lecithin. The blending ratio of the leveling agent is preferably 0.01 to 1 mass% based on the mass of the solid content of the easily dismantlable adhesive.

[0054] Examples of antifoaming agents include silicone resins, silicone solutions, and copolymers of alkyl vinyl ethers, alkyl acrylates, and alkyl methacrylates. The amount of antifoaming agent added is preferably 0.01 to 1% by mass based on the solid mass of the easily dismantlable adhesive.

[0055] Examples of the plasticizer include phthalate ester compounds, alkylsulfonate ester compounds, adipate ester compounds, partially hydrogenated terpenes, trioctyl phosphate, and epoxy plasticizers.

[0056] <Preparation of easily dismantlable adhesive> The easily dismantlable adhesive of the present invention is preferably a reactive adhesive comprising a base agent and a curing agent, wherein the base agent contains a polyol (A), the curing agent contains a polyisocyanate (B), and the inorganic filler (D) and / or organic thixotropy-imparting agent (E) and the thermally expandable filler (C) are each independently contained in at least one of the base agent and the curing agent. When components other than the above (A) to (E) are contained, these components may be blended in at least one of the base agent and the curing agent, or may be blended when the base agent and the curing agent are mixed.

[0057] In the adhesive of the present invention, the ratio [NCO / OH] of the number of isocyanato groups in the polyisocyanate (B) to the number of hydroxyl groups in the polyol (A) is preferably 0.7 to 1.5, more preferably 0.95 to 1.3.

[0058] <Theoretical value (mmol / g) of the concentration of urethane bonds formed during the reaction in the resin, which is the reaction product of polyol (A) and polyisocyanate (B)> From the viewpoint of obtaining an adhesive of the present invention that has an excellent balance of adhesion and flexibility and has high thermal cycle resistance, it is important that the theoretical value of the concentration of urethane bonds formed during the reaction in the resin that is the reaction product of the polyol (A) and the polyisocyanate (B) is 0.3 to 4.0 mmol / g, preferably 0.4 to 3.5 mmol / g, more preferably 0.5 to 3.0 mmol / g, and even more preferably 0.7 to 2.5 mmol / g.

[0059] In the present invention, the theoretical value of the concentration of urethane bonds formed during the reaction in the resin that is the reaction product of polyol (A) and polyisocyanate (B) is a numerical value calculated by the following formula: When the molar amount of isocyanate in polyisocyanate (B) is the same as or smaller than the molar amount of hydroxyl groups in polyol (A), the calculation is performed by the following formula (1).

number

[0060] When the molar amount of isocyanate in the polyisocyanate (B) is greater than the molar amount of hydroxyl groups in the polyol (A), the amount is calculated using the following formula (2).

number

[0061] <Method for measuring hydroxyl value and calculation of hydroxyl group molar concentration> The molar amount (mmol) of hydroxyl groups in the polyol (A) can be calculated from the molar concentration (mmol / g) of hydroxyl groups and the mass (g) of the polyol (A), and the molar concentration (mmol / g) of hydroxyl groups can be calculated from the hydroxyl value of the polyol (A) as follows. The hydroxyl value of polyol (A) is measured according to JIS K 1557-1 by the following method. Weigh 1 part of polyol (A) into a 300 ml Erlenmeyer flask and add 10 parts of an acetylating reagent (a mixed solution of 16 parts of phthalic anhydride, 2.4 parts of imidazole, and 100 parts of pyridine). Then, heat to 150°C with a hot stirrer and allow to react for 40 minutes. After cooling to room temperature, add 2 parts of pure water and stir. Then, add 30 ml of methyl ethyl ketone and 4 to 5 drops of phenolphthalein indicator. Titrate with 0.5 mol / L potassium hydroxide alcohol solution and calculate using the following formula:

number

number

[0062] <Method for measuring isocyanate group content and calculation of isocyanate group molar concentration> The isocyanate molar amount (mmol) of the polyisocyanate (B) can be calculated from the isocyanate group molar concentration (mmol / g) and the mass (g) of the polyisocyanate (B), and the isocyanate group molar concentration (mmol / g) can be calculated from the isocyanate group content (%) in the polyisocyanate (B) as follows: The isocyanate group content in polyisocyanate (B) is measured according to JIS K 1603-1 using the following method. Weigh 1 part of polyisocyanate (B) into a 300 ml Erlenmeyer flask, add 10 parts of dichlorobenzene, and dissolve using a hot stirrer. After cooling, weigh 10 parts of the mixed solution (a mixed solution of 51.75 parts of dibutylamine and 348.25 parts of dichlorobenzene) and stir using a stirrer. Next, add 47.5 parts of isopropyl alcohol and 4-5 drops of bromophenol blue solution, and titrate with 0.5 mol / L hydrochloric acid titration solution. Calculate the isocyanate content using the following formula:

number

number

[0063] <Method for measuring resin solid mass> The adhesive is heated to 600°C in a nitrogen atmosphere at a heating rate of 10°C / min using a TG / DTA device (such as Rigaku TG-DTA8122), and the remainder is taken as the filler mass, and the resin content is calculated by subtracting the filler mass from the initial mass.If the adhesive is a two-component type, the mass of polyol (A) can be calculated from the base agent containing polyol (A), and the mass of polyisocyanate (B) can be calculated from the curing agent containing polyisocyanate (B).

[0064] <Storage modulus of cured product measured at 80°C and a frequency of 10 Hz> The adhesive of the present invention is an easily dismantlable adhesive that is cured by aging for 7 days in an environment of 23°C and 50% relative humidity so that the thickness of the cured product becomes 2 mm, and the cured product has a storage modulus of 1.0 × 10 measured at a frequency of 10 Hz at 80°C. 5 That's it, 5.0 x 10 8 It is important that the storage modulus at 80°C is 1.0 x 10 Pa or less. 5 When the storage modulus at 80°C is 5.0 × 10 or more, the adhesive strength and long-term heat resistance are excellent in a high-temperature environment below the expansion starting temperature, and the cured product can maintain its shape without sagging when thermally disassembled at about 80°C to 200°C. 8 If the viscosity is less than 100 Pa, the cohesive strength of the cured product will be relatively low compared to the expansion force of the thermally expandable filler during thermal disintegration at approximately 80°C to 200°C, causing the entire cured adhesive film to expand and resulting in excellent thermal disintegration properties. The storage modulus of the cured product measured at a frequency of 10 Hz at 80°C is preferably 1.0 × 10 from the viewpoint of superior adhesive strength in high-temperature environments, long-term heat resistance, and thermal disintegration properties. 6 That's it, 1.0 x 10 8 Pa or less.

[0065] The storage modulus can be determined by the following method. First, the adhesive was filled into a mold so that the cured product would be 2 mm thick, and the surface was smoothed. The adhesive was then cured for 7 days at 23°C and 50% relative humidity to obtain a cured product. The resulting 2 mm-thick cured product was then cut into 25 mm long, 5 mm wide strips to prepare test specimens. The resulting test specimens were measured using a dynamic viscoelasticity measuring device (IT Measurement & Control Co., Ltd., "DVA-225"), with the following input values: grip length 15 mm, test specimen width 5 mm, and test specimen thickness 2 mm. The measurement temperature range was -50°C to 250°C, frequency 10 Hz, heating rate 10°C / min, and tensile mode to determine the storage modulus at 80°C.

[0066] <Cured product, structure> The cured product of the present invention is obtained by curing the above-mentioned easily dismantlable adhesive, and can be obtained, for example, by curing the adhesive for 7 days in an environment of 23°C and 50% relative humidity, or for 24 hours at 80°C. The structure of the present invention is also characterized in that it comprises an adhesive layer between a first adherend and a second adherend, and the adhesive layer is the above-mentioned cured product. The method for producing the structure is not particularly limited, and for example, an adhesive may be applied to one surface of a first adherend, and then a second adherend may be placed on the uncured adhesive surface, followed by a curing reaction at about 20 to 80° C. to cure the adhesive, thereby obtaining a structure having a cured product. The thickness of the adhesive layer after curing is preferably 0.1 μm to 300 mm.

[0067] <First adherend, second adherend> The easily dismantlable adhesive of the present invention can be used to bond a wide variety of adherends. Suitable substrates that can be used as the first and second adherends include, for example, metals such as aluminum; thermoplastic polymers such as polyethylene, polypropylene, polyurethane, polyacrylate, polycarbonate, and copolymers thereof; thermosetting polymers such as vulcanized rubber; urea-formaldehyde foam, melamine resin, wood, carbon fiber reinforced plastic, glass fiber reinforced plastic, and other fiber reinforced plastics. The first and second adherends may be the same or different, and may be composed of multiple substrates.

[0068] The easily dismantlable adhesive of the present invention has high flexibility, high film strength, and thermal cycle resistance during adhesion, and also exhibits interfacial thermal dismantling properties at temperatures between 80° C. and 200° C. Therefore, the easily dismantlable adhesive and structure of the present invention are useful in applications requiring easy dismantling performance, such as structural components (panel parts, frame parts, suspension parts, etc.) for automobiles, building materials, ships, aircraft, and other transportation equipment. [Example]

[0069] The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the scope of the invention. Unless otherwise specified, "parts" and "%" in the examples represent "parts by mass" and "% by mass".

[0070] <Number average molecular weight (Mn), mass average molecular weight (Mw)> The number-average molecular weight (Mn) and mass-average molecular weight (Mw) of the resin were determined by gel permeation chromatography (GPC) using a GPC-8020 (Tosoh Corporation) GPC system, tetrahydrofuran as the eluent, and three TSKgel SuperHM-M (Tosoh Corporation) columns connected in series at a flow rate of 0.6 mL / min, an injection volume of 10 μL, and a column temperature of 40°C.

[0071] The abbreviations for compounds used in this specification are shown below. <Polyol> P-2000: Difunctional polypropylene glycol, number average molecular weight 2,000, manufactured by ADEKA Corporation T-4000: Trifunctional polypropylene glycol, number average molecular weight 4,000, manufactured by ADEKA Corporation GI-2000: Polybutadiene polyol, number average molecular weight 2,000, manufactured by Nippon Soda Co., Ltd. PP-4000: Difunctional polypropylene glycol, number average molecular weight 4,000, manufactured by Sanyo Chemical Industries, Ltd. T5650E: Bifunctional polycarbonate polyol, number average molecular weight 500, product name "Duranol T5650E", manufactured by Asahi Kasei Corporation P-400: Difunctional polypropylene glycol, number average molecular weight 400, manufactured by ADEKA Corporation 204B: Difunctional polycaprolactone glycol, number average molecular weight 400, trade name "PLACCEL204B", manufactured by Daicel Corporation TMP: Trimethylolpropane MPD: 3-methyl-1,5-pentanediol, manufactured by Kuraray Co., Ltd.

[0072] <Polyisocyanate> 4,4'-MDI: 4,4'-diphenylmethane diisocyanate TDI: Toluene diisocyanate Liquid MDI: Millionate NM, manufactured by Tosoh Corporation XDI: Xylylene diisocyanate TDI-TMP adduct: Takenate D-101E, manufactured by Mitsui Chemicals Crude MDI: PM-200, manufactured by Wanhua Chemical Co., Ltd.

[0073] <Thermal expansion filler> F-36D: Thermally expandable microcapsules, average particle size 13 μm, expansion start temperature 80°C, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. FN-100MD: Thermally expandable microcapsules, average particle size 25 μm, expansion start temperature 130°C, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. F-230D: Thermally expandable microcapsules, average particle size 20 μm, expansion start temperature 190°C, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. F-2830D: Thermally expandable microcapsules, average particle size 25 μm, expansion start temperature 220°C, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. EXP-50S120K: Thermally expandable graphite, average particle size 250 μm, expansion start temperature 120°C, manufactured by Fuji Graphite Industries Co., Ltd.

[0074] <Inorganic filler> Hakuenka CCR-S: Surface-treated synthetic calcium carbonate, manufactured by Shiraishi Kogyo Co., Ltd. Aerosil RY-200S: Surface-treated fumed silica, manufactured by Nippon Aerosil Co., Ltd. P-4 Talc: Talc, manufactured by Nippon Talc Co., Ltd. NYAD 400: Wollastonite, manufactured by IMERYS DAW-20: Aluminum oxide, manufactured by Denka

[0075] <Organic thixotropic agents> Disparlon 3500: Polyether phosphate ester, manufactured by Kusumoto Chemicals Co., Ltd.

[0076] <Silane coupling agent> KBM-403: 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.

[0077] <Leveling agent> BYK-322: Aralkyl-modified polymethylalkylsiloxane, manufactured by BYK-Chemie

[0078] <Antifoaming agent> FLOLENE AC-2300C: Olefin polymer, manufactured by Kyoeisha Chemical Co., Ltd.

[0079] <Synthesis of polyol (a1-1) with a number average molecular weight of 2,000 or more> (Polyol (a1-1)) A reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser was charged with 100 parts of P-2000 and 8.5 parts of 4,4'-MDI, and after stirring uniformly, the mixture was reacted at 110°C for 5 hours under a nitrogen atmosphere to obtain a polyol (a1-1) having a urethane bond and a number average molecular weight of 5,700.

[0080] <Synthesis of polyol (a1-2) with a number average molecular weight of 2,000 or more> (Polyol (a1-2)) A reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser was charged with 100 parts of T-4000 and 3.7 parts of TDI, and after uniform stirring, the mixture was reacted at 110°C for 5 hours under a nitrogen atmosphere to obtain a polyol (a1-2) having a urethane bond and a number average molecular weight of 6,400. [Table 1]

[0081] <Preparation of polyol base> (Polyol A1) To 100 parts of polyol (a1-1) having a urethane bond, 20 parts of P-400, 10 parts of F-36D, 100 parts of Hakuenka CCR-S, 0.5 parts of KBM-403, 0.05 parts of BYK-322, and 0.1 parts of Floren AC-2300C were added, and the mixture was stirred and degassed using a planetary centrifugal mixer (Awatori Rentaro, manufactured by Thinky Corporation) to obtain polyol A1.

[0082] (Polyols A2 to A25) Polyols A2 to A25 were obtained in the same manner as Polyol A1, except that the types and amounts of each component were changed as shown in Table 2.

[0083] [Table 2]

[0084] <Production of polyisocyanate curing agent> (Polyisocyanate B1) A reaction vessel was charged with 24 parts of P-400 and 36 parts of 4,4'-MDI, and the mixture was reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After that, the mixture was cooled to 50°C, and 40 parts of crude MDI was added and stirred for 15 minutes to obtain polyisocyanate (B1).

[0085] (Polyisocyanate B2) A reaction vessel was charged with 3.3 parts of P-400 and 62 parts of P-2000 and stirred uniformly, after which 24.7 parts of 4,4'-MDI was charged and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After that, the mixture was cooled to 50°C, and 20 parts of crude MDI was added and stirred for 15 minutes to obtain polyisocyanate (B2).

[0086] (Polyisocyanate B3) A reaction vessel was charged with 50.0 parts of crude MDI and 50.0 parts of liquid MDI, and the mixture was stirred uniformly to obtain polyisocyanate (B3).

[0087] (Polyisocyanate B4) A reaction vessel was charged with 19.5 parts of P-400 and 31.2 parts of P-2000 and stirred uniformly, after which 29.3 parts of XDI was charged and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction, thereby obtaining polyisocyanate (B4).

[0088] (Polyisocyanate B5) A reaction vessel was charged with 40.0 parts of TDI-TMP adduct, 50.0 parts of liquid MDI, and 10 parts of crude MDI, and the mixture was stirred uniformly. The solvent was then removed under a nitrogen atmosphere at 120°C for 3 hours to obtain polyisocyanate (B5).

[0089] (Polyisocyanate B6) A reaction vessel was charged with 17.4 parts of P-400 and 27.8 parts of P-2000 and stirred uniformly. Then, 34.7 parts of 4,4'-MDI was added and the mixture was reacted at 90°C under a nitrogen atmosphere for 3 hours to carry out a urethane reaction. The mixture was then cooled to 50°C, and 20 parts of crude MDI was added and stirred for 15 minutes. After removal from the vessel, 5 parts of FN-78D and 50 parts of Hakuenka CCR-S were added, followed by stirring and degassing using a planetary centrifugal mixer (Awatori Rentaro, manufactured by Thinky Corporation) to obtain polyisocyanate (B6).

[0090] (Polyisocyanate B7~10) Polyisocyanates B7 to B10 were obtained in the same manner as polyisocyanate B6, except that the types and amounts of each component were changed to those shown in Table 3.

[0091] [Table 3]

[0092] <Preparation of adhesive mixture> [Examples 1 to 28, Comparative Examples 1 to 7] At room temperature, adhesive mixtures were prepared by stirring and mixing polyols and polyisocyanates according to the formulations shown in Tables 4 and 5. The storage moduli of the cured products of the resulting adhesive mixtures at 80°C were measured using the following procedure.

[0093] [Storage modulus measurement] The adhesive was filled into a mold so that the cured product would be 2 mm thick, the surface was smoothed, and the adhesive was cured by curing for 7 days in an environment of 23°C and 50% relative humidity. The resulting 2 mm thick cured product was cut into strips 25 mm long and 5 mm wide to prepare test specimens. The test pieces obtained above were measured using a dynamic viscoelasticity measuring device ("DVA-225" manufactured by IT Measurement Control Co., Ltd.) under the following conditions: measurement temperature range -50°C to 250°C, frequency 10Hz, heating rate 10°C / min, measurement mode tensile mode, and the storage modulus at 80°C was calculated.

[0094] <Adhesive evaluation> The adhesives obtained were evaluated as follows, and the results are shown in Tables 4 and 5.

[0095] [Adhesion to SPCC substrate] The adhesive was applied to an SPCC substrate (100 mm long, 25 mm wide, 2 mm thick) to a width of 25 mm, length of 10 mm, and thickness of 0.3 mm, and then laminated to another SPCC substrate. The resulting adhesive was then pressed to maintain a thickness of 0.3 mm and cured for 7 days at 23°C and 50% relative humidity to obtain a test specimen. The shear adhesive strength of the resulting test specimen was measured using a tensile tester at 25°C and a pulling rate of 50 mm / min, and evaluated according to the following criteria. (Evaluation criteria) A: Shear adhesive strength is 10 MPa or more (very good) B: Shear adhesive strength is 5 MPa or more and less than 10 MPa (good) C: Shear adhesive strength is 2 MPa or more and less than 5 MPa (usable) D: Shear adhesive strength is less than 2 MPa (unusable)

[0096] [Cold and heat cycle resistance] Test pieces prepared in the same manner as in the evaluation of [Adhesion to SPCC substrate] above were held in a -40°C environment for 30 minutes, followed by another 30 minutes in an 80°C environment, which constituted one cycle. This cooling-heating cycle was repeated 100 times. The shear strength of the test pieces before and after the cooling-heating cycle test was measured using a tensile tester at 25°C and a tensile speed of 50 mm / min. The shear strength retention was calculated using the following formula and evaluated according to the following criteria. (formula) Shear strength retention rate (%) = (shear strength after storage / shear strength before storage) x 100 (Evaluation criteria) A: Shear strength retention is 90% or more (very good) B: Shear strength retention is 70% or more but less than 90% (good) C: Shear strength retention rate is 50% or more and less than 70% (usable) D: Shear strength retention rate is less than 50% (unusable)

[0097] [Thermal disassembly] Test pieces prepared in the same manner as in the evaluation of [Adhesion to SPCC substrate] above were stored for 1 hour at the following thermal decomposition temperature. After removal, the test pieces were cooled to 25°C and their shear strength was measured using a tensile tester at 25°C and a pulling rate of 50 mm / min. The shear strength reduction rate of the test pieces before and after the thermal decomposition test was calculated using the following formula and evaluated according to the following criteria. Thermal decomposition temperature (℃) = expansion start temperature of thermal expansion filler (℃) + 20 (℃) Shear strength reduction rate (%) = 1 - (shear strength after thermal demolition / shear strength before thermal demolition) x 100 (Evaluation criteria) A: Shear strength reduction rate is 90% or more (very good) B: Shear strength reduction rate is less than 90% and 70% or more (good) C: Shear strength reduction rate is less than 70% and 50% or more (usable) D: Shear strength reduction rate is less than 50% (unusable)

[0098] [Table 4]

[0099] [Table 5]

[0100] According to Tables 4 and 5, a resin containing a polyol (A), a polyisocyanate (B), and a thermally expandable filler (C), and containing at least one of an inorganic filler (D) and an organic thixotropic agent (E), has a theoretical concentration of urethane bonds formed during the reaction in a resin that is a reaction product of the polyol (A) and the polyisocyanate (B), of 0.3 mmol / g to 4.0 mmol / g, and has a storage modulus of 1.0 × 10 measured at a frequency of 10 Hz at the expansion starting temperature of the contained thermally expandable filler (C). 5 Pa or higher, 5.0×10 8 Adhesives with a viscosity of 0.05 Pa or less had excellent adhesive strength and thermal cycle resistance due to their high flexibility and cohesive strength during adhesion, and also had excellent thermal decomposition properties between the adhesive and the adherend when peeled at temperatures of around 80°C to 200°C. In particular, when the inorganic filler (D) is selected from the group consisting of calcium carbonate, silica, talc, mica, kaolin, aluminum hydroxide, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, and carbon black, the cohesive strength of the cured film is reinforced, and the adhesive strength and thermal dismantling property are further improved. Furthermore, when the polyol (A) contains a polyol (a1) having a number-average molecular weight of 2,000 or more and a polyol (a2) having a number-average molecular weight of 50 or more but less than 2,000, the thermal cycle resistance is further improved, and when the content of polyol (a1) is 5 to 95 mass% based on the mass of polyol (A), the balance between adhesive strength and thermal cycle resistance is even better. Furthermore, when the polyisocyanate (B) contains a reaction product of a polyol and a polyisocyanate, the resistance to thermal cycles is further improved, and when the polyisocyanate (B) contains a reaction product of a polyol and an aromatic polyisocyanate, the aromatic skeleton further improves the adhesive strength.

Claims

1. An easily dismantlable adhesive comprising a polyol (A), a polyisocyanate (B), a thermally expandable filler (C), and an inorganic filler (D) and / or an organic thixotropic agent (E), wherein a resin that is a reaction product of the polyol (A) and the polyisocyanate (B) has a theoretical urethane bond concentration of 0.3 mmol / g to 4.0 mmol / g, and the easily dismantlable adhesive is cured for 7 days in an environment of 23°C and a relative humidity of 50% so that the thickness of the cured product becomes 2 mm, and the cured product has a storage modulus measured at a frequency of 10 Hz at 80°C of 1.0 x 10 ５ ~5.0 x 10 ８ An easily dismantlable adhesive.

2. The easily dismantlable adhesive according to claim 1, wherein the thermally expandable filler (C) has an expansion start temperature of 80°C to 200°C.

3. 2. The easily dismantlable adhesive according to claim 1, wherein the inorganic filler (D) comprises at least one selected from the group consisting of calcium carbonate, silica, talc, mica, kaolin, aluminum hydroxide, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, and carbon black.

4. The easily dismantlable adhesive according to claim 1, wherein the polyol (A) comprises a polyol (a1) having a number average molecular weight of 2,000 or more and a polyol (a2) having a number average molecular weight of 50 or more and less than 2,000.

5. The easily dismantlable adhesive according to claim 4, wherein the content of the polyol (a1) is 5 to 95 mass% based on the mass of the polyol (A).

6. The easily dismantlable adhesive according to claim 1, wherein the polyisocyanate (B) comprises a reaction product of a polyol (b1) and a polyisocyanate (b2).

7. The easily dismantlable adhesive according to claim 1 , wherein the polyisocyanate (B) comprises an aromatic polyisocyanate.

8. A cured product obtained by curing the easily dismantlable adhesive according to any one of claims 1 to 7.

9. A structure comprising an adhesive layer between a first adherend and a second adherend, wherein the adhesive layer is the cured product according to claim 8.

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