Epoxy adhesive and method for removing epoxy adhesive

Abstract

To provide an epoxy adhesive that can be easily removed from the objects to which it is bonded. [Solution] This epoxy adhesive contains an epoxy resin, melamine polyphosphate as a foaming agent that imparts heat decomposition properties, and hydrazide as a curing agent.

Description

Technical Field

[0001] This invention relates to an epoxy adhesive and a method for peeling an epoxy adhesive.

Background Art

[0002] Conventionally, epoxy adhesives are known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an epoxy adhesive containing an epoxy resin and hydrazine. This epoxy adhesive is decomposed and removed by oxidation with an oxidizing agent such as sodium hypochlorite.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, from the viewpoint of effectively utilizing resources, objects adhered using an epoxy adhesive are often disassembled after use to reuse the members. Therefore, an epoxy adhesive that has adhesive performance and can be removed from the object is used.

[0006] The epoxy adhesive described in Patent Document 1 above is decomposed and removed by oxidation with an oxidizing agent such as sodium hypochlorite. However, when epoxy adhesives are used to bond objects together, they are positioned between the objects, resulting in a small surface area being exposed to the outside. This makes it difficult to increase the contact area between the epoxy adhesive and the oxidizing agent when removing it with an oxidizing agent such as sodium hypochlorite. Therefore, it is difficult to apply the oxidizing agent to the entire epoxy adhesive, making it difficult to remove the epoxy adhesive from the bonded objects. Thus, there is a need for an epoxy adhesive that can be easily removed from bonded objects even when the epoxy adhesive is positioned between objects and a small surface area is exposed to the outside.

[0007] This invention was made to solve the above-mentioned problems, and one of its objectives is to provide an epoxy adhesive and a method for removing the epoxy adhesive that can be easily removed from the objects to which it is bonded. [Means for solving the problem]

[0008] To achieve the above objective, the inventors of this application diligently conducted trial and error studies on the composition of epoxy adhesives that can be easily removed from objects to which the epoxy adhesive is bonded. As a result, they discovered that by including melamine polyphosphate as a foaming agent that imparts thermal decomposition properties, it is possible to easily remove the epoxy adhesive from the bonded objects.

[0009] In other words, the epoxy adhesive according to the first aspect of this invention contains an epoxy resin, melamine polyphosphate as a foaming agent that imparts thermal decomposition properties, and hydrazide as a curing agent.

[0010] In the epoxy adhesive according to the first aspect of this invention, as described above, by containing melamine polyphosphate as a foaming agent that imparts thermal decomposition properties, foaming can be caused by heating, thereby weakening the adhesive strength. Furthermore, the polyphosphate generated by heating melamine polyphosphate can decompose the epoxy resin, which also weakens the adhesive strength. As a result, with the adhesive strength weakened, the bonded objects can be separated and decomposed, exposing the epoxy adhesive. This allows the epoxy adhesive to be easily removed from the bonded objects by applying an oxidizing agent such as sodium hypochlorite to the objects from which the epoxy adhesive has been exposed. This point has been confirmed by experiments (examples) described later.

[0011] In the epoxy adhesive according to the first aspect described above, preferably, the melamine polyphosphate is contained in an amount of 0.5 parts by weight or more and 80 parts by weight or less. With this configuration, by including 0.5 parts by weight or more of melamine polyphosphate, sufficient foaming can be generated when removing the epoxy adhesive, so that objects bonded with the epoxy adhesive can be easily separated. Furthermore, by limiting the melamine polyphosphate content to 80 parts by weight or less, it is possible to suppress an excessive amount of foaming component, thereby preventing a decrease in adhesive performance due to a large amount of melamine polyphosphate when the epoxy adhesive hardens. This point has also been confirmed by experiments (examples) described later.

[0012] In the epoxy adhesive according to the first aspect described above, preferably, the epoxy resin includes an epoxy silicone resin having siloxane bonds. With this configuration, the heat resistance of the epoxy adhesive can be improved by the epoxy silicone resin having siloxane bonds. This makes it possible to achieve both thermal decomposition and heat resistance in the epoxy adhesive.

[0013] In this case, preferably, the epoxy silicone resin includes an epoxy functional silicone prepolymer. With this configuration, the heat resistance can be effectively improved by the epoxy functional silicone prepolymer. This makes it possible to effectively achieve both thermal decomposition and heat resistance in epoxy adhesives.

[0014] In the epoxy adhesive having the above-mentioned epoxy silicone resin containing an epoxy functional silicone prepolymer, preferably, the epoxy functional silicone prepolymer is contained in an amount of 1 to 20 parts by weight. With this configuration, the heat resistance can be reliably improved by including 1 part by weight or more of the epoxy functional silicone prepolymer. Furthermore, by limiting the amount of epoxy functional silicone prepolymer to 20 parts by weight or less, it is possible to suppress the decrease in thermal decomposition properties due to foaming of polyphosphate melamine, which is used as a foaming agent to impart thermal decomposition properties, when the epoxy adhesive is removed.

[0015] In the epoxy adhesive according to the first aspect described above, preferably, a filler further comprising one selected from the group consisting of calcium carbonate, alumina, and aluminum hydroxide is further included. With this configuration, the mechanical strength of the epoxy adhesive can be improved by the filler comprising one selected from the group consisting of calcium carbonate, alumina, and aluminum hydroxide. Furthermore, since the thermal conductivity can be improved by the filler, the heat generated when removing the epoxy adhesive can be effectively transferred to the polyphosphate melamine, which acts as a thermal decomposition foaming agent.

[0016] Furthermore, in order to achieve the above objective, the inventors of this application diligently conducted trial and error studies to find a method that would allow for easy removal of epoxy adhesive from objects to which it is bonded. As a result, they discovered that by curing an epoxy adhesive containing melamine polyphosphate as a thermal decomposition foaming agent and hydrazide as a curing agent, and then heating the object to which the adhesive is bonded to cause the melamine polyphosphate to foam, and simultaneously immersing the object in a decomposition solution containing water, the epoxy adhesive can be easily removed from the bonded object.

[0017] In other words, the method for peeling off an epoxy adhesive according to the second aspect of this invention is a method for peeling off an epoxy adhesive from an object, comprising the steps of: heating an object to which an epoxy adhesive containing an epoxy resin, melamine polyphosphate as a heat-decomposing foaming agent, and hydrazide as a curing agent has hardened and adhered to, thereby causing the melamine polyphosphate, as a heat-decomposing foaming agent, to foam; and immersing the object in a decomposition solution containing water.

[0018] In the second aspect of this invention, the method for removing epoxy adhesives, by configuring the method as described above, the polyphosphate melamine, which acts as a thermal decomposition foaming agent, can be foamed by heating, thereby weakening the adhesive strength. Furthermore, the polyphosphate generated by heating the polyphosphate melamine can decompose the epoxy resin, which also weakens the adhesive strength. As a result, with the adhesive strength weakened, the bonded objects can be separated and decomposed, exposing the epoxy adhesive. This provides a method for removing epoxy adhesives that allows the epoxy adhesive to be easily removed from the bonded objects by applying an oxidizing agent such as sodium hypochlorite to the object from which the epoxy adhesive has been exposed. This point has been confirmed by experiments (examples) described later.

[0019] In the method for peeling an epoxy adhesive according to the second aspect, preferably, the step of heating the object includes a step of foaming melamine polyphosphate as a thermal decomposable foaming agent by heating at a temperature of 200°C or higher and 350°C or lower. With this configuration, by heating to 200°C or higher and 350°C or lower, which is higher than the temperature at the time of curing the epoxy adhesive, melamine polyphosphate as a thermal decomposable foaming agent can be foamed, so that foaming during curing can be suppressed.

[0020] In the method for peeling an epoxy adhesive according to the second aspect, preferably, the decomposition liquid contains water and sodium hypochlorite. With this configuration, after foaming the melamine polyphosphate of the epoxy adhesive to weaken the adhesive force, the epoxy adhesive can be effectively decomposed by the oxidizing action of sodium hypochlorite.

Effects of the Invention

[0021] According to the present invention, as described above, the epoxy adhesive can be easily removed from the adhered object.

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described.

[0023] (Epoxy Adhesive) The epoxy adhesive of the present embodiment is used to adhere objects. For example, the epoxy adhesive is disposed between the objects to adhere the objects to each other. In addition, from the viewpoint of effectively utilizing resources, the objects adhered using the epoxy adhesive are decomposed and reused after use. The objects to be adhered are, for example, members constituting a rotor of a rotating electric machine (motor, generator). In this case, the object is a rotor core and a permanent magnet containing rare earths. The epoxy adhesive may be a one-component type or a two-component type.

[0024] Epoxy adhesives are used to bond objects that are used in an environment where the temperature is above 100°C and below 200°C. That is, epoxy adhesives have heat resistance. Also, epoxy adhesives contain thermosetting resins. After the epoxy resin is applied to an object, it is heated and thermosets to bond the object.

[0025] Here, in this embodiment, the epoxy adhesive contains an epoxy resin, melamine polyphosphate as a heat-decomposable blowing agent, and a hydrazide as a curing agent.

[0026] The epoxy resin contained in the epoxy adhesive may contain bifunctional epoxy as a main matrix. For example, the epoxy resin of the main matrix may contain bis(4-glycidyloxyphenyl) disulfide (BGPDS), 1,2-bis((oxiran-2-ylmethoxy)methyl) disulfane, 1,2-bis(4-(oxiran-2-ylmethoxy)cyclohexyl) disulfane, 1,2-bis(4-(oxiran-2-ylmethoxy)phenyl) disulfane, bisphenol A type epoxy resin, bisphenol F type epoxy resin, diglycidyl ether of bisphenol A (DGEBA), ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

[0027] In addition, separately from the main matrix, the epoxy resin may contain an epoxy silicone resin having a siloxane bond in order to improve the heat resistance of the epoxy adhesive. The epoxy silicone resin may be a compound in which the above epoxy resin is crosslinked by a siloxane bond. For example, the epoxy silicone resin may contain an epoxy-functional silicone prepolymer. Also, separately from the main matrix, the epoxy resin may contain monofunctional epoxy.

[0028] The epoxy silicone resin (epoxy functional silicone prepolymer) may be contained in an amount of 1 to 20 parts by weight per 100 parts by weight of the epoxy resin as the main matrix. Preferably, the epoxy silicone resin (epoxy functional silicone prepolymer) is contained in an amount of 1 to 3 parts by weight per 100 parts by weight of the epoxy resin as the main matrix.

[0029] The melamine polyphosphate used as a thermal decomposition foaming agent in epoxy adhesives may be present in an amount of 0.5 parts by weight or more and 80 parts by weight or less per 100 parts by weight of epoxy resin as the main matrix.

[0030] Examples of hydrazides used as curing agents in epoxy adhesives include acethydrazide, propionic acid hydrazide, pentanoic acid hydrazide, lauryl acid hydrazide, cyclohexanecarbohydrazide, salicylic acid hydrazide, p-hydroxybenzoic acid hydrazide, and naphthoic acid hydrazide. Other monobasic acid hydrazides may also be used, specifically monobasic acid hydrazides such as benzenesulfonohydrazide. Furthermore, examples of hydrazides used as curing agents in epoxy adhesives include dihydrazide oxalate, dihydrazide malonate, dihydrazide succinate, dihydrazide adipic acid, dihydrazide pimelic acid, dihydrazide suberic acid, dihydrazide azelaic acid, dihydrazide sebacate, dihydrazide dodencanedioate, dihydrazide hexadecanedioate, dihydrazide isophthalic acid, and dihydrazide terephthalic acid. Other dibasic acid hydrazides may include, specifically, carbohydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, diglycolic acid dihydrazide, tartrate dihydrazide, malic acid dihydrazide, 2,6-naphthoic acid dihydrazide, 1,4-naphthoic acid dihydrazide, 4,4'-bisbenzene dihydrazide, hydroquinone diglycolic acid dihydrazide, resorcinol diglycolic acid dihydrazide, catechol diglycolic acid dihydrazide, 4,4'-ethylidenebisphenol-diglycolic acid dihydrazide, and 4,4'-vinylidenebisphenol-diglycolic acid dihydrazide. Furthermore, the hydrazide used as a curing agent in epoxy adhesives may also be a tribasic acid hydrazide such as 1,3,5-tris(2-hydrazinocarbonylalkyl)isocyanurate, such as 1,3,5-tris(2-hydrazinocarbonylethyl)isocyanurate.

[0031] The hydrazide used as a curing agent may be contained in an amount of 10 to 30 parts by weight per 100 parts by weight of the epoxy resin that forms the main matrix.

[0032] Furthermore, epoxy adhesives may contain fillers. The fillers contained in epoxy adhesives may include one selected from the group consisting of calcium carbonate, alumina, and aluminum hydroxide.

[0033] The filler may be contained in an amount of 10 to 50 parts by weight per 100 parts by weight of epoxy resin as the main matrix.

[0034] Furthermore, epoxy adhesives may contain substances that promote curing. These curing-promoting substances may include, for example, substances with catalytic properties. The curing-promoting substances may also include, for example, modified aliphatic polyamines.

[0035] The substance that promotes curing may be contained in an amount of 0.1 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the epoxy resin that serves as the main matrix.

[0036] Furthermore, epoxy adhesives may contain coupling agents. Coupling agents are included to improve adhesion. Coupling agents included in epoxy adhesives may include, for example, silane coupling agents. Silane coupling agents may include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane, which have epoxy as a functional group.

[0037] The coupling agent may be contained in an amount of 0.1 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the epoxy resin that serves as the main matrix.

[0038] (Method for removing epoxy adhesives) Next, we will explain how to remove epoxy adhesives. Epoxy adhesives need to be removed from objects when they are to be reused. In this case, the epoxy adhesive is removed by peeling it off the object.

[0039] The method for removing epoxy adhesive is a method for removing epoxy adhesive from an object, comprising the steps of: heating an object to which an epoxy adhesive containing an epoxy resin, melamine polyphosphate as a heat-decomposing foaming agent, and hydrazide as a curing agent has hardened and adhered to, thereby causing the melamine polyphosphate to foam; and immersing the object in a decomposition solution containing water.

[0040] Furthermore, in the method for removing epoxy adhesives, the step of heating the object includes, for example, a step of heating to a temperature of 200°C to 350°C, which is higher than the temperature at which the object is used, to foam the polyphosphate melamine, which acts as a foaming agent that imparts thermal decomposition properties. The method for removing epoxy adhesives also includes a step of separating and decomposing the bonded objects after heating to foam the polyphosphate melamine, which acts as a foaming agent that imparts thermal decomposition properties, while the adhesive strength is weakened. In the method for removing epoxy adhesives, after the objects are separated and decomposed, the objects are immersed in a decomposition solution at room temperature to decompose and remove the epoxy adhesive from the objects. When the bonded objects are used in rotating electric machinery (motors, generators), the temperature at which the rotating electric machinery is used is less than 200°C (for example, around 180°C). The temperature at which the adhesive is heated to foam and remove it is higher than the temperature at which the rotating electric machinery is used, between 200°C and 350°C.

[0041] Furthermore, the decomposition solution contains water and sodium hypochlorite.

[0042] When the object in question is a component of the rotor of a rotating electric machine (motor, generator), and the rotor is disassembled for reuse of the component (for example, a permanent magnet containing rare earth elements), a demagnetization process is required to heat and demagnetize the component (for example, a permanent magnet containing rare earth elements). The method for removing epoxy adhesive is performed simultaneously with this demagnetization process, when heating (300°C or higher). In other words, when the demagnetization process is performed, the epoxy adhesive removal process is also performed in parallel, eliminating the need for separate heating to remove the adhesive. This makes it possible to simplify the epoxy adhesive removal process.

[0043] (Examples) Next, embodiments of the present invention will be described.

[0044] In each example, epoxy adhesive was applied to the flat surface of the object (test specimen), and the two specimens were bonded together by aligning their flat surfaces. The curing conditions were 150°C for 30 minutes. The test specimens used were made of 10 mm x 25 mm aluminum.

[0045] Furthermore, the thermal decomposition properties of epoxy adhesives were evaluated according to the following criteria. The thermal decomposition properties of epoxy adhesives were evaluated by measuring the shear bond strength after heating objects bonded with the epoxy adhesive at 300°C for 20 minutes. Shear bond strength is the force per unit area required to displace the test specimens when a lateral force is applied to the bonded surface. 3 points: Shear bond strength is less than 1 MPa 2 points: Shear bond strength is 1 MPa or more and less than 2.5 MPa. 1 point: Shear bond strength of 2.5 MPa or higher The less force required to separate bonded objects, the easier they are to dismantle; therefore, lower shear bond strength indicates better thermal dismantling properties. A score of 2 or higher was considered sufficient for thermal dismantling (a level that poses no practical problems).

[0046] Furthermore, the heat resistance of epoxy adhesives was evaluated according to the following criteria. The heat resistance of epoxy adhesives was evaluated by measuring the shear bond strength after aging objects bonded with epoxy adhesive at 180°C for 500 hours. In other words, it was evaluated whether the adhesive strength (shear bond strength) was maintained even when aged at high temperatures (180°C) for a long period of time (500 hours). 3 points: Shear bond strength of 10 MPa or more 2 points: Shear bond strength is between 5 MPa and less than 10 MPa 1 point: Shear bond strength is less than 5 MPa Furthermore, two or more items were evaluated as having sufficient heat resistance (at a level that poses no practical problems).

[0047] Examples 1 to 9 yielded the results shown in Table 1. Examples 1 to 9 show different content levels of melamine polyphosphate as a foaming agent that imparts thermal decomposition properties.

[0048] [Table 1]

[0049] (Example 1) The epoxy adhesive of Example 1 was prepared to contain 100 parts by weight of bisphenol A type epoxy as the main matrix, 23 parts by weight of adipic acid dihydrazide as a curing agent, 1 part by weight of modified aliphatic polyamine as a curing accelerator, 1 part by weight of glycidoxypropyltrimethoxysilane as a coupling agent, 30 parts by weight of calcium carbonate as a filler, and 0.5 parts by weight of polyphosphate melamine as a foaming agent that imparts thermal decomposition properties. The epoxy adhesive of Example 1 showed good thermal decomposition properties, with a shear adhesive strength of 2.2 MPa and a thermal decomposition rating of 2 after heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 1 showed very good heat resistance, with a shear adhesive strength of 10 MPa or more and a heat resistance rating of 3 after aging at 180°C for 500 hours.

[0050] (Example 2) The epoxy adhesive of Example 2 was prepared in the same manner as in Example 1, except that it contained 1 part by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 2 showed good thermal decomposition properties, with a shear adhesive strength of 2.0 MPa and a thermal decomposition rating of 2 after heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 2 showed very good heat resistance, with a shear adhesive strength of 10 MPa or more and a heat resistance rating of 3 after aging at 180°C for 500 hours.

[0051] (Example 3) The epoxy adhesive of Example 3 was prepared in the same manner as in Example 1, except that it contained 5 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 3 showed good thermal decomposition properties, with a shear adhesive strength of 1.5 MPa and a thermal decomposition rating of 2 after heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 3 showed very good heat resistance, with a shear adhesive strength of 10 MPa or more and a heat resistance rating of 3 after aging at 180°C for 500 hours.

[0052] (Example 4) The epoxy adhesive of Example 4 was prepared in the same manner as in Example 1, except that it contained 10 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 4 showed good thermal decomposition properties, with a shear adhesive strength of 1.4 MPa and a thermal decomposition rating of 2 after heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 4 showed very good heat resistance, with a shear adhesive strength of 10 MPa or more and a heat resistance rating of 3 after aging at 180°C for 500 hours.

[0053] (Example 5) The epoxy adhesive of Example 5 was prepared in the same manner as in Example 1, except that it contained 20 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 5 showed a shear adhesive strength of 0.9 MPa and a thermal decomposition rating of 3 when heated to 300°C for 20 minutes, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 5 showed good heat resistance, with a shear adhesive strength of 5 MPa or more and less than 10 MPa after aging at 180°C for 500 hours, and a heat resistance rating of 2.

[0054] (Example 6) The epoxy adhesive of Example 6 was prepared in the same manner as in Example 1, except that it contained 30 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 6 showed excellent thermal decomposition properties, with a shear adhesive strength of 0.8 MPa and a thermal decomposition rating of 3 after heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 6 showed good heat resistance, with a shear adhesive strength of 5 MPa or more and less than 10 MPa after aging at 180°C for 500 hours and a heat resistance rating of 2.

[0055] (Example 7) The epoxy adhesive of Example 7 was prepared in the same manner as in Example 1, except that it contained 50 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 7 showed a shear adhesive strength of 0.7 MPa and a thermal decomposition rating of 3, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 7 showed good heat resistance, with a shear adhesive strength of 5 MPa or more and less than 10 MPa after aging at 180°C for 500 hours and a heat resistance rating of 2.

[0056] (Example 8) The epoxy adhesive of Example 8 was prepared in the same manner as in Example 1, except that it contained 70 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 8 showed excellent thermal decomposition properties, with a shear adhesive strength of 0.4 MPa and a thermal decomposition rating of 3 after thermal decomposition by heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 8 showed good heat resistance, with a shear adhesive strength of 5 MPa or more and less than 10 MPa and a heat resistance rating of 2 after aging at 180°C for 500 hours.

[0057] (Example 9) The epoxy adhesive of Example 9 was prepared in the same manner as in Example 1, except that it contained 80 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 9 showed excellent thermal decomposition properties, with a shear adhesive strength of 0.4 MPa and a thermal decomposition rating of 3 after thermal decomposition by heating at 300°C for 20 minutes. Furthermore, the epoxy adhesive of Example 9 showed good heat resistance, with a shear adhesive strength of 5 MPa or more and less than 10 MPa and a heat resistance rating of 2 after aging at 180°C for 500 hours.

[0058] The results for Comparative Examples 1-3 are shown in Table 2. Comparative Examples 1-3 show examples with different content of melamine polyphosphate as a foaming agent that imparts thermal decomposition properties.

[0059] [Table 2]

[0060] (Comparative Example 1) The epoxy adhesive of Comparative Example 1 was the same as that of Example 1, except that it was prepared to contain 0 parts by weight of melamine polyphosphate as a foaming agent that imparts thermal decomposition properties. In other words, the epoxy adhesive of Comparative Example 1 did not contain melamine polyphosphate as a foaming agent that imparts thermal decomposition properties. The epoxy adhesive of Comparative Example 1, which did not contain melamine polyphosphate, had a shear adhesive strength of 2.6 MPa when heated to 300°C for 20 minutes, and its thermal decomposition properties were rated at 1, indicating poor thermal decomposition properties. On the other hand, the epoxy adhesive of Comparative Example 1 had a shear adhesive strength of 10 MPa or more after aging at 180°C for 500 hours, and its heat resistance was rated at 3, indicating very good heat resistance.

[0061] (Comparative Example 2) The epoxy adhesive of Comparative Example 2 was prepared in the same manner as in Example 1, except that it contained 0.1 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Comparative Example 2, which contained only a small amount of 0.1 parts by weight of melamine polyphosphate, had a shear adhesive strength of 2.6 MPa when heated to 300°C for 20 minutes, and its thermal decomposition properties were rated 1, indicating poor thermal decomposition properties. On the other hand, the epoxy adhesive of Comparative Example 2 had a shear adhesive strength of 10 MPa or more and a heat resistance of 3 after aging at 180°C for 500 hours, indicating very good heat resistance.

[0062] (Comparative Example 3) The epoxy adhesive of Comparative Example 3 was prepared in the same manner as in Example 1, except that it contained 90 parts by weight of melamine polyphosphate as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Comparative Example 3 containing 90 parts by weight of melamine polyphosphate showed a shear adhesive strength of 0.4 MPa and a thermal decomposition score of 3 when heated to 300°C for 20 minutes, indicating very good thermal decomposition properties. On the other hand, the epoxy adhesive of Comparative Example 3 containing 90 parts by weight of melamine polyphosphate showed poor heat resistance, with a heat resistance score of 1.

[0063] From the evaluation results of thermal decomposition properties and heat resistance of Examples 1 to 9 and Comparative Example 1 described above, it was found that epoxy adhesives containing melamine polyphosphate as a thermal decomposition-imparting foaming agent exhibited good thermal decomposition properties and heat resistance. Furthermore, from the evaluation results of thermal decomposition properties and heat resistance of Examples 1 to 9 and Comparative Examples 1 to 3 described above, it was found that epoxy adhesives containing 0.5 parts by weight to 80 parts by weight of melamine polyphosphate as a thermal decomposition-imparting foaming agent exhibited good thermal decomposition properties and heat resistance.

[0064] Examples 10-16 yielded the results shown in Table 3. Examples 10-13 show different epoxy silicone resin content to improve heat resistance.

[0065] [Table 3]

[0066] (Example 10) The epoxy adhesive of Example 10 was prepared to contain 100 parts by weight of bisphenol A type epoxy as the main matrix, 0.1 parts by weight of epoxy functional group silicone prepolymer for improved heat resistance, 23 parts by weight of adipic acid dihydrazide as a curing agent, 1 part by weight of modified aliphatic polyamine as a curing accelerator, 1 part by weight of glycidoxypropyltrimethoxysilane as a coupling agent, 30 parts by weight of calcium carbonate as a filler, and 30 parts by weight of polyphosphate melamine as a foaming agent to impart thermal decomposition properties. The epoxy adhesive of Example 10 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 3, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 10 containing 0.1 parts by weight of epoxy functional group silicone prepolymer had a heat resistance rating of 2, indicating good heat resistance.

[0067] (Example 11) The epoxy adhesive of Example 11 was the same as in Example 10, except that it was prepared to contain 0.5 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 11 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 3, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 11 containing 0.5 parts by weight of epoxy functional silicone prepolymer had a heat resistance rating of 2, indicating good heat resistance.

[0068] (Example 12) The epoxy adhesive of Example 12 was prepared in the same manner as in Example 10, except that it contained 1 part by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 12 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 3, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 12 containing 1 part by weight of epoxy functional silicone prepolymer had a heat resistance rating of 3, indicating very good heat resistance.

[0069] (Example 13) The epoxy adhesive of Example 13 was the same as that of Example 10, except that it was prepared to contain 3 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 13 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 3, indicating very good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 13 containing 3 parts by weight of epoxy functional silicone prepolymer had a heat resistance rating of 3, indicating very good heat resistance.

[0070] (Example 14) The epoxy adhesive of Example 14 was prepared in the same manner as in Example 10, except that it contained 5 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 14 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 2, indicating good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 14 containing 5 parts by weight of epoxy functional silicone prepolymer had a heat resistance rating of 3, indicating very good heat resistance.

[0071] (Example 15) The epoxy adhesive of Example 15 was the same as that of Example 10, except that it was prepared to contain 10 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 15 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 2, indicating good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 15 containing 10 parts by weight of epoxy functional silicone prepolymer had a heat resistance rating of 3, indicating very good heat resistance.

[0072] (Example 16) The epoxy adhesive of Example 16 was the same as that of Example 10, except that it was prepared to contain 20 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Example 16 containing 30 parts by weight of polyphosphate melamine had a thermal decomposition rating of 2, indicating good thermal decomposition properties. Furthermore, the epoxy adhesive of Example 16 containing 20 parts by weight of epoxy functional silicone prepolymer had a heat resistance rating of 3, indicating very good heat resistance.

[0073] The results for Comparative Examples 4 and 5 are shown in Table 4. Comparative Examples 4 and 5 show examples with different epoxy silicone resin contents for improving heat resistance.

[0074] [Table 4]

[0075] (Comparative Example 4) The epoxy adhesive of Comparative Example 4 was the same as that of Example 10, except that it was prepared to contain 25 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Comparative Example 4, which contained 25 parts by weight of epoxy functional silicone prepolymer and 30 parts by weight of polyphosphate melamine, was found to have poor thermal decomposition properties, with a score of 1. On the other hand, the epoxy adhesive of Comparative Example 4 was found to have very good heat resistance, with a score of 3.

[0076] (Comparative Example 5) The epoxy adhesive of Comparative Example 5 was the same as that of Example 10, except that it was prepared to contain 30 parts by weight of epoxy functional silicone prepolymer to improve heat resistance. The epoxy adhesive of Comparative Example 5, which contained 30 parts by weight of epoxy functional silicone prepolymer and 30 parts by weight of polyphosphate melamine, was found to have poor thermal decomposition properties, with a score of 1. On the other hand, the epoxy adhesive of Comparative Example 5 was found to have very good heat resistance, with a score of 3.

[0077] From the evaluation results of thermal decomposition properties and heat resistance of Examples 10-16 and Comparative Examples 4 and 5 described above, it was found that epoxy adhesives containing epoxy functional silicone prepolymers for improved heat resistance exhibited good heat resistance. Specifically, it was found that epoxy adhesives containing polyphosphate melamine and epoxy functional silicone prepolymers of 20 parts by weight or less, or less than 25 parts by weight, exhibited good thermal decomposition properties. Furthermore, from the evaluation results of heat resistance of Examples 10 and 11, it was found that epoxy adhesives exhibited good heat resistance even when containing trace amounts of epoxy functional silicone prepolymer, such as 0.1 parts by weight or 0.5 parts by weight. In addition, from the evaluation results of thermal decomposition properties and heat resistance of Examples 10-16 and Comparative Examples 4 and 5 described above, it was found that epoxy adhesives containing 1 part by weight or more of epoxy functional silicone prepolymers for improved heat resistance exhibited particularly good heat resistance. Furthermore, epoxy adhesives containing 1 to 20 parts by weight of epoxy-functional silicone prepolymer for improved heat resistance were found to have good thermal decomposition properties and particularly good heat resistance. Additionally, epoxy adhesives containing 1 to 3 parts by weight of epoxy-functional silicone prepolymer for improved heat resistance were found to have particularly good thermal decomposition properties and particularly good heat resistance. However, it was found that even when polyphosphate melamine was present, the thermal decomposition properties decreased when the epoxy-functional silicone prepolymer was present in 25 parts by weight or more.

Claims

1. Epoxy resin and Melamine polyphosphate as a foaming agent that imparts thermal decomposition properties, An epoxy adhesive containing hydrazide as a hardening agent.

2. The epoxy adhesive according to claim 1, wherein the melamine polyphosphate is contained in an amount of 0.5 parts by weight or more and 80 parts by weight or less.

3. The epoxy adhesive according to claim 1, wherein the epoxy resin comprises an epoxy silicone resin having siloxane bonds.

4. The epoxy adhesive according to claim 3, wherein the epoxy silicone resin comprises an epoxy functional group silicone prepolymer.

5. The epoxy adhesive according to claim 4, wherein the epoxy functional silicone prepolymer is contained in an amount of 1 to 20 parts by weight.

6. The epoxy adhesive according to claim 1, further comprising a filler selected from the group consisting of calcium carbonate, alumina, and aluminum hydroxide.

7. A method for removing epoxy adhesive from an object, A step of heating the object to which the epoxy adhesive containing an epoxy resin, melamine polyphosphate as a heat-decomposable foaming agent, and hydrazide as a curing agent has hardened and adhered, thereby causing the melamine polyphosphate, which is the heat-decomposable foaming agent, to foam, A method for removing an epoxy adhesive, comprising the step of immersing the object in a decomposition solution containing water.

8. The method for peeling off an epoxy adhesive according to claim 7, wherein the step of heating the object includes a step of heating at a temperature of 200°C to 350°C to foam the polyphosphate melamine, which is the thermal decomposition foaming agent.

9. The method for removing epoxy adhesive according to claim 7, wherein the decomposition solution contains water and sodium hypochlorite.

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