Method for recycling thermoset epoxy resin materials

Abstract: A method of recycling a thermosetting resin such as acid anhydride cured epoxy resin, polyurethane resin, unsaturated polyester resin and the like is provided. The thermosetting resin is plasticized by adding an amino compound as decomposer to the thermosetting resin to produce a plasticized resin. The plasticized resin is hardened again by adding a re-hardener to the plasticized resin. For the re-hardener, a compound which works on the amino compound to cause hardening, e.g. epoxy prepolymer, is used. The amino compound breaks the network structure of thermoset resin to bond or associate with the broken network structure, and the re-hardener reacts with both of the amino compound and the plastiziced resin.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for recycling thermoset resin materials, in which the reuse of thermoset plastics that is believed to be difficult is made easy to promote the recycling thereof. Related Art Recently, space for burying wastes is not easily obtained particularly in cities and their environs, and it is therefore an urgent subject to be solved quickly, by what means the disposal of general wastes and industrial wastes should be promoted. Accordingly, development in the reuse and reclamation of wastes is an important matter. Particularly, thermoset resins such as epoxy resins, phenolic resins, unsaturated polyester resins and the like are not melted by heat after once hardened, and reuse thereof as a resin material is therefore said to be difficult. Under present conditions, they are usually buried or burned for disposal, accordingly. Due to the disposal, the burying disposal of thermoset plastic waste have not only a problem that land acquisition is necessary but also a problem that there is some fear of pollution of soil and ground water with heavy metals which are typified by antimony and the like and which are often used as the additive of flame retardants and the like. On the other hand, in burning disposal, there are other problems of generation of dioxin and of disposal of a large amount of remaining ash due to fillers which are contained in the resin. As described above, in the conventional technique, recycling of thermoset plastics has been difficult, and the wastes thereof have to be subjected to disposal while causing a lot of problems. Journal of Applied Polymer Science, 56(2), 1995, p127-134 discloses a method of recycling waste rigid polyurethane and polyisocyanurate foams by decomposing with aliphatic amine compounds and reacting the decomposed product as curing agent with epoxy resin. US-A-5,776,989 discloses a method of recycling cured unsaturated polyester resin waste by decomposing with a diamine compound and reacting the decomposed product as a hardener with epoxy resin. WO-A-96/16112 discloses a method of recycling epoxy resin by mixing with a polar solvent such as diaminohexane and reacting the decomposed product with a hardener such as phthalic acid anhydride. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in the conventional technique. With the above problems in mind, therefore, it is an object of the present invention to provide novel recycling measures which enable the reuse of thermoset plastics. In order to achieve the above-mentioned object, a method of recycling a thermoset resin, according to the present invention comprises the steps of: plasticizing the thermoset resin by adding an amino compound as decomposer to the thermoset resin, to produce a plasticized resin; and re-hardening the plasticized resin by adding a re-hardener to the plasticized resin, the re-hardener acting on both the amino compound and the plasticized resin to effect hardening, wherein the thermoset resin comprises an epoxy resin, and the re-hardener comprises a compound having at least two epoxy groups. In the above method, at least the surface of the thermoset epoxy resin is decomposed and liquefied at the plasticizing step by the addition of the amino compound. The recycling method may further comprise, before the plasticizing step, the step of breaking the thermoset epoxy resin into particles. The thermoset epoxy resin at the plasticizing step is partially plasticized by controlling the amount of the amino compound added to the thermoset resin. In the above method, the amino compound at the plasticizing step breaks a network structure of the thermoset epoxy resin to bond or associate with the broken network structure, and the re-hardener at the re-hardening step reacts with both of the amino compound and the plasticized resin to form a bond. The re-hardener at the re-hardening step may be added so that the ratio of the re-hardener to the decomposer by the epoxy equivalent amount is from approximately 0.6 to 1.1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors of the present application have intensively studied for attaining the above-mentioned object, and resultantly, found that plasticization and re-hardening of a thermoset epoxy plastic are possible by using a decomposer and a re-hardening agent which satisfy a specific requirement, thereby completing a method for recycling a thermoset epoxy plastic according to the present invention. The present invention will be illustrated in detail below. Thermoset plastics or resins, i.e. thermally hardened products of thermosetting resins, are polymer materials having a so-called network structure in which molecules are three-dimensionally bonded, and examples thereof include cured epoxy resins, phenolic resins, polyurethane resins, melamine resins, urea resins, unsaturated polyester resins, silicone resins and the like. Such thermoset resins are obtained by, for example, allowing a hardener to act on a prepolymer resin, or polycondensing two kinds of polymerizable compounds using a catalyst, or by other like methods. More specifically, in the case of an epoxy resin, a hardener which is generally used for epoxy resin, such as an acid anhydride, a phenolic resin, an imidazole compound, a polyamino compound and the like, is added to a prepolymer having two or more epoxy groups such that is typified by a prepolymer produced from bisphenol A and epichlorohydrin, and the obtained mixture is cured at a normal temperature or a raised temperature to prepare a hardened resin product. Since the hardener molecule is three-dimensionally bonded to the prepolymer molecules to form a steric network structure with crosslinkage, relative movement and deformation of the prepolymer chains are suppressed in the hardened resin. As a result, the cured resin is not melted even in heating at higher temperature, and, if reaching the decomposition temperature, it is decomposed and gasified. As described above, the thermosetting property of a resin is due to formation of a network structure with molecules, and this matter is generally common to thermosetting plastics. In order to make possible the recycling of a thermoset resin material, it is necessary to realize that, first, a three-dimensionally bonded network structure of the thermoset resin material is once cut to plasticize the hard resin material, and secondly, the cut molecular chains of the resin are then bonded again to reproduce a three-dimensional network. Accordingly, the present invention comprises, for realizing of a thermoset resin by chemical measures, a decomposing step at which a decomposer is allowed to act on the thermoset resin material to dissociate the network structure of the thermoset resin material, and a re-hardening step at which a network structure is formed again by allowing a re-hardener to act on the decomposed resin material obtained at the decomposing step and form a bond. In accordance with the above-described construction, a thermoset resin article can be reclaimed into another thermoset resin product by subjecting the decomposed resin material being plasticized at the decomposing step to a re-hardening treatment at the re-hardening step, while an appropriate molding treatment is carried out. Therefore, recycling of used or discarded products of thermoset resin becomes possible. Here, it should be noted that, in a conventional case, the re-hardening of decomposed resin which is caused by the re-hardener is not accomplished in the presence of the decomposer in the decomposed resin material, because the effect of the decomposer and that of the re-hardener counteract each other and the re-hardener does not substantially work under such a condition. In this case, it is naturally necessary, for re-hardening the decomposed and plasticized resin material, to remove the decomposer before the re-hardening step from the decomposed and plasticized resin material. However, the removal of decomposer is practically troublesome, and complete removal thereof is in fact difficult. In contrast, the recycling method of the present invention has an advantage in connection with the above that re-hardening of the resin decomposed material is possible in the presence of the decomposer, and has a feature that the decomposer and the re-hardener are adopted in specific combination for realizing this advantage. Specifically, the decomposer and the re-hardener are so selected that the re-hardener is capable of acting not only on the decomposed epoxy resin material but also on the decomposer to make a bond. By satisfying this selection requirement, re-hardening of the epoxy resin decomposed material owing to the re-hardener is possible without removing the decomposer from the epoxy resin decomposed material. Such a combination of the decomposer and the re-hardener can be selected, for example, from combined compounds in which one is a resin and the other is a hardener for that resin. For example, in a case where the thermoset epoxy resin to be recycled is an acid anhydride cured epoxy resin (an epoxy resin hardened by using an acid anhydride), an amino compound can be used as the decomposer, and a compound having two or more epoxy groups (hereinafter, referred to as a polyepoxy compound) can be used as the re-hardener. The network structure of the cured epoxy resin material can also be decomposed by using sulfuric acid, hydrogen peroxide, alkali metal hydroxide, vapor under high temperature and high pressure, or the like. However, in a case of using one of these as a decomposer, no substance has been found that is effective as a re-hardener for the decomposed epoxy resin material in co-existence with the decomposer. Since the kind of bonds which form the network structure in the cured resin material differs depending on the kind of thermosetting resin, a suitable selection of the decomposer and the re-hardener may vary depending on the resin to be recycled. However, if the same decomposer works on different kinds of thermoset resins, it must be possible for each of those resins to make re-hardening of the decomposed resin by means of the same re-hardener that can be used in combination with that decomposer. Among various thermoset resins, the resin that can be most efficiently recycled using the above-mentioned amino compound and polyepoxy compound as a decomposer and a re-hardener is an epoxy resin, particularly, an acid anhydride cured epoxy resin. An acid anhydride cured epoxy resin is obtained by hardening an epoxy resin (prepolymer) using as the hardener an acid anhydride, namely, a compound having a -CO-O-CO- group, and examples of the acid anhydride usable as the hardener include compounds such as phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride and the like. As described above, the amino compound has a function to decompose the network structure of the cured epoxy resin material, and, if the amino compound is allowed to act as a decomposer on the cured epoxy resin material, the cured epoxy resin material is decomposed and plasticized (softened or liquefied). In this time, the amino compound is bonded or associated with the cut molecular chain of the decomposed epoxy resin material. When the polyepoxy compound (a compound having two or more epoxy groups) is added as a re-hardener to this decomposed and plasticized epoxy resin material and allowed to act on it, the polyepoxy compound reacts with the above-mentioned amino compound to form a bond therebetween. At the same time, a bonding reaction of the decomposed epoxy resin material with the polyepoxy compound is caused, resulting in re-hardening of the decomposed epoxy resin material. As described above, a waste, thermoset epoxy resin material can be reclaimed into another thermoset epoxy resin product via a simple treatment process, and the re-hardened resin has strong network structure and keeps excellent property. In addition, since removal and purification operations such as removal of a decomposer from the plasticized resin material can be omitted, the recycling process is simple and treatment cost is low. The decomposer and the re-hardener in the present invention should not be restricted to a specific example, and they may be appropriately selected within a scope in which the above-mentioned requirement is satisfied, depending on the kind of the thermoset epoxy resin to be recycled and the application and intention of use of the reclaimed resin. Namely, a combination of a decomposer and a re-hardener is selected such that the re-hardener reacts with the decomposer to form a bond. For efficiently conducting the decomposition, such a decomposer is preferable as is in a liquid state at normal temperature and has a boiling point higher than the glass transition temperature of the resin to be recycled. When the boiling point of the decomposer is higher than the glass transition temperature of the resin to be recycled, the treating temperature in the decomposition step can be set at a temperature not lower than the glass transition temperature of the resin, therefore, the decomposition of the resin progresses rapidly and the decomposition efficiency can be raised. Now, details of a recycling process in a case where the thermoset epoxy resin is an acid anhydride hardened epoxy resin will be illustrated below. At the decomposition step, an amino compound is added as the decomposer to the thermoset epoxy resin material for progressing the decomposition reaction. As the amino compound used as the decomposer, any of aliphatic amino compounds and aromatic amino compounds can be used, and examples thereof include benzyldimethylamine, ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenediamine, trimethylhexamethylenediamine, bis-(hexamethylene)triamine, polyoxypropylenediamine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, N-dimethylcyclohexylamine, xylylenediamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, mononoethanol amine, diethanol amine, triethanolamine, pyridine and imidazole, and particularly, secondary amines such as diethylenetriamine, triethylenetetramine or xylylenediamine are preferable. Among the above matters, xylylenediamine is most effective. A secondary amine reacts advantageously with a polyepoxy compound used as the re-hardener to form a suitable hardened material. Xylylenediamine has a merit that the boiling point thereof is higher than the glass transition temperature of a normal epoxy resin and can be applied for treatment of various thermoset epoxy resin materials. A resin to be recycled may also be broken into appropriate dimensions of granulate before the decomposition step. If the thermoset epoxy resin material to be recycled is cut into particles of suitable size, the decomposer possibly works on the hard resin material with high efficiency and the resin material is decomposed rapidly. Moreover, in a case where a metal matter such as aluminum, copper and the like adheres to the resin to be recycled, it is also useful for accelerating peeling from the metal matter to subject the resin to ultrasonic treatment during the decomposition step with the decomposer. Moreover, if the thermoset epoxy resin material to be recycled is heated at the decomposition step, the decomposition reaction is promoted. For example, in a case where an amino compound is used in an amount of about 100 % by weight to the amount of the thermoset epoxy resin material to be recycled, decomposition into a viscous liquid matter is usually possible through a treating time of about a few hours if the epoxy resin material is heated at about 100 °C, and of about 1 hour if the epoxy resin material is heated at about 150 °C. Even at around the room temperature, the decomposition reaction progresses. However, the decomposition speed is significantly reduced. At the decomposition step, the epoxy resin material can also be continuously treated by using an apparatus such as a single screw extruder, twin screw extruder and the like. The decomposed resin material after subjecting to the decomposition treatment is hardened again by addition of a re-hardener and simultaneously molded into a product form. The molding is possibly performed by appropriately using common molding means which are used in usual molding such as a metal mold, roll and the like as occasion requires. For the re-hardener for hardening the decomposed epoxy resin material, a compound having two or more epoxy groups is utilized, and examples thereof include epoxy prepolymers such as bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol AD epoxy resins, biphenyl epoxy resins, alicyclic epoxy resin, cresol novolak epoxy resins and polyfunctional epoxy resins. Examples of available articles of such compounds include bisphenol A epoxy resin articles sold by the trade name of EP828, EP1001 or EP1004 (manufactured by Yuka Shell Epoxy Co. of Japan), bisphenol A epoxy resin articles sold by the trade name of CT200 (manufactured by Asahi-CIBA Co. of Japan), bisphenol F epoxy resin articles sold by the trade name of EP807 (manufactured by Yuka Shell Epoxy Co.), biphenyl epoxy resin articles sold by the trade name of YX4000 (manufactured by Yuka Shell Epoxy Co.) or alicyclic epoxy resin articles sold by the trade name of CY2021 (manufactured by Daicel Chemical Industry Co.). At the step of re-hardening the decomposed epoxy resin material, heat is not particularly necessary, and in general, the decomposed epoxy resin material is sufficiently hardened at room temperature by allowing the mixture of the decomposed material and the re-hardener to stand still for about 30 to 300 minutes. The hardening speed increases by heat. The amount of the used re-hardener may advantageously be changed so that the reclaimed resin material has suitable properties for the use in recycling. If the control of quality of the reclaimed resin material is particularly important, the supplying amounts of the decomposer and the re-hardener are determined by using the epoxy equivalent amount of the re-hardener that is calculated relative to the amino group of the decomposer, in order to accurately adjust the supplying ratio. In general, it is preferable to add the re-hardener at a supplying ratio such that the ratio of the re-hardener to the decomposer by the epoxy equivalent amount is from about 0.6 to 1.1. For improving property of the reclaimed resin obtained after the re-hardening step, it is also useful to mix a metal or non-metal inorganic filler, organic filler, coloring agent, flame retardant, releasing agent, stress-lowering agent and the like with the decomposed resin material before re-hardening. Moreover, it is also possible to add other kind of resin to the decomposed resin material before the re-hardening, as necessity arises, for improvement of the reclaimed product. Alternatively, the property of reclaimed resin may also be improved by subjecting the decomposed resin material to purification such that a specific component or a solid matter such as a filler and the like contained in the thermoset resin is removed from it. Recycling of thermoset epoxy resin is possible even when the thermoset epoxy resin is not so decomposed as to produce a completely liquid material at the decomposition step, and a reclaimed resin material suitable for recycling can also be obtained by re-hardening a partially decomposed resin material. For example, if a thermoset epoxy resin material to be recycled is broken into small particles, it is possible to obtain a molded article of the reclaimed resin material by: decomposing only the surface of the resin particles; and re-hardening the partially decomposed resin particles with the re-hardener and simultaneously charging them into a metal mold or the like having a desired product form, whereby the surfaces of the resin particles are mutually adhered before the hardening is completed. In this case, if necessary, the resin particles in the mold may also be compressed. The reclaimed resin obtained in this manner possibly has a structure containing a phase of the epoxy resin composition before decomposition and a phase of the resin composition obtained after re-hardening. In view of the above, it is therefore advantageous that the decomposition degree is set in accordance with the properties required for the reclaimed resin material, and that the particle size of the broken thermoset resin, the amount of the decomposer used at the decomposing step and the decomposition temperature of the thermoset epoxy resin are appropriately controlled in accordance with the extent of decomposition of the resin hardened material. In a case of preparing a partially decomposed resin particles, it is preferred to break the thermoset epoxy resin into particles having a particle size of about 0.1 mm or more and control the supply ratio of the decomposer to the resin particles within a range of 0.5 to 10 % by weight. It is unnecessary for recycling the thermoset epoxy resin material to continuously conduct the decomposing step and the re-hardening step. In other words, it is possible to conduct these steps in series or at a certain interval therebetween, as occasion arises. Therefore, it is permissible that, after the decomposition step of a thermoset resin material is conducted, the decomposed resin material is transferred to other place before conducting the re-hardening step. Moreover, it is also possible that the decomposed resin material before hardening is provided in the market as a raw material for producing a reclaimed resin article and that the purchase carries out the re-hardening treatment of the decomposed resin material. As understood from the descriptions above, the concept of the recycling method by the decomposition of a resin and re-hardening according to the present invention is specifically applied to epoxy resins. EXAMPLES Below, the present invention will be illustrated in detail, referring to the following examples. (Example 1) To 100 g of bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP828) added were 85 g of a hardener (manufactured by New Japan Chemical Co., Ltd. of Japan and sold by the trade name of MH700) for methylhexahydrophthalic anhydride and 0.5 g of BDMA (benzyldimethylamine) as a catalyst, and the mixture was heated at 120 °C for 10 hours for conducting hardening to produce a thermoset epoxy resin plate having a thickness of 2 mm. The glass transition temperature of this epoxy resin plate was measured by the DSC (Differential Scanning Calorimeter), and the result was 130 °C. The thermoset epoxy resin plate obtained in the above-described procedure was broken into particles which were passed through a sieve of 80 mesh to obtain a minus sieve fraction of epoxy resin particles. This fraction of epoxy resin particles (100 g) was charged into a flask, and 100 g of ethylenediamine (boiling point: 116 to 117 °C) was added to the epoxy resin particles to mix them. The mixture was heated at 117 °C for 5 hours while stirring. Then the decomposition of the epoxy resin progressed with time, and, as a result, a liquid presenting the appearance of being transparent was obtained. A 5 g portion of the liquid obtained above was placed into a dish. To this liquid added was 20 g of a bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP828), and these were mixed sufficiently, followed by leaving the mixture at room temperature. About 30 minutes after, the liquid in the dish had been hardened. The glass transition temperature of this hardened material was measured by the DSC, and the result of measurement was then 120 °C. The hardened material exhibited complete resinification. (Example 2) To 100 g of bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP828) added were 85 g of a hardener (manufactured by New Japan Chemical Co., Ltd. and sold by the trade name of MH700) for methylhexahydrophthalic anhydride and 0.5 g of BDMA (benzyldimethylamine) as a catalyst, and the mixture was heated at 120 °C for 10 hours for conducting hardening to produce a thermoset epoxy resin plate having a thickness of 2 mm. The glass transition temperature of this epoxy resin plate was measured by the DSC, and the result was 130 °C. The thermoset epoxy resin plate obtained in the above-described procedure was broken into particles which were passed through a sieve of 80 mesh to obtain a minus sieve fraction of epoxy resin particles. This fraction of epoxy resin particles (100 g) was charged into a flask, and 100 g of xylylenediamine (boiling point: 274 °C) was added to the epoxy resin particles to mix them. The mixture was heated at 150 °C for 45 minutes while stirring. Then the decomposition of the epoxy resin progressed with time, and, as a result, a liquid presenting the appearance of being transparent was obtained. A 5 g portion of the liquid obtained above was placed into a dish. To this liquid added was 20 g of a bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP828), and these were mixed sufficiently, followed by leaving the mixture at room temperature. About 30 minutes after, the liquid in the dish had been hardened. The glass transition temperature of this hardened material was measured by the DSC, and the result of measurement was then 115 °C. The hardened material exhibited complete resinification. (Example 3) To 100 g of bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP807) added were 90 g of a hardener (manufactured by Hitachi Chemical Co., Ltd. of Japan and sold by the trade name of HN2200) for methyltetrahydrophthalic anhydride, 300 g of silica (manufactured by Tatsumori Ltd. and sold by the trade name of A1) as a filler, and 0.5 g of BDMA as a catalyst, and the mixture was heated at 120°C for 10 hours for conducting hardening to produce a thermoset epoxy resin plate having a thickness of 2 mm. The glass transition temperature of this epoxy resin plate was measured by the DSC, and the result was 126 t. The thermoset epoxy resin plate obtained in the above-described procedure was broken into particles which were passed through a sieve of 80 mesh to obtain a minus sieve fraction of epoxy resin particles. This fraction of epoxy resin particles (80 g) was charged into a flask, and 20 g of xylylenediamine (boiling point: 274 °C) was added to the epoxy resin particles to mix them. The mixture was heated at 150 °C for one hour while stirring. Then the decomposition of the epoxy resin progressed with time, and, as a result, a highly viscous liquid was obtained. A 50 g portion of the liquid obtained above was placed into a dish. To this liquid added was 50 g of a bisphenol A epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of EP828), and these were mixed sufficiently, followed by heating the mixture at 80 °C for 20 minutes. As a result, the liquid in the dish had been solidified. The glass transition temperature of this solidified material was measured by the DSC, and the result of measurement was then 108 °C. The solidified material exhibited complete hardening and resinification. (Example 4) To 300 g of bisphenol A epoxy prepolymer (manufactured by Asahi-CIBA Co. and sold by the trade name of CT200) added were 90 g of a hardener (manufactured by Asahi-CIBA Co. and sold by the trade name of HT903) for phthalic anhydride and 900 g of alumina (manufactured by Taiheiyo Random K.K. and sold by the trade name of LA1200) as a filler, and the mixture was heated at 150 °C for 15 hours for conducting hardening to produce a thermoset epoxy resin plate having a thickness of 2 mm. The glass transition temperature of this epoxy resin plate was measured by the DSC, and the result was 104 °C. The thermoset epoxy resin plate obtained in the above-described procedure was broken into particles which were passed through a sieve of 8 mm to obtain a minus sieve fraction of epoxy resin particles. This fraction of epoxy resin particles (1000 g) was charged into a Henschel mixer, and 20 g of xylylenediamine (boiling point: 274 ° C) was added to the epoxy resin particles to mix them. The mixture was left for 1 day at room temperature and then subjected to observation by a microscope. As a result, it was found that the surface of the epoxy resin particles had got rough which meant partial progressing of the decomposition at only the surface of the epoxy resin. To the resin mixture described above (containing 1000 g of partially decomposed resin and 20 g of xylylenediamine) added were 100 g of a biphenyl epoxy prepolymer (manufactured by Yuka Shell Epoxy Co. and sold by the trade name of YX4000), 100 g of a glass chopped strand having a length of 3 mm, 3 g of a carbon coloring agent and 3 g of carnauba wax, and these components were mixed in a Henschel mixer for 2 minutes. Thus obtained mixture was charged into a metal mold and compression-molded at 100 °C for 5 minutes to produce a molded article. The glass transition temperature of the molded article obtained above was measured by the DSC and the result of measurement was 90 °C. The molded article exhibited complete hardening. (Example 5) A waste material of a semiconductor molding compound (phenol cured epoxy resin, manufactured by Toshiba Chemical Co. of Japan and sold by the trade name of KE-300) obtained from processing thereof was broken into pieces of about 5 millimeters square. To 10 g of the obtained resin pieces, 10 g of xylylenediamine was added and the mixture was placed in a vessel which was then closed. It was heated at 400 °C for 1 hour. The vessel was then cooled to room temperature, and the contents were taken out of the vessel and mixed with 30 g of a bisphenol A epoxy prepolymer (manufactured by Asahi Denka Kogyo of Japan and sold by the trade name of EP-4100), followed by leaving at room temperature. As a result, the mixture was hardened to produce a mass of black-colored durable resin. The glass transition temperature of this product was measured by the DSC, and the result of measurement was 90 °C. (Example 6) From a used personal computer, a printed circuit board made of epoxy cured by dicyandiamide was taken out and broken into pieces of about 2 millimeters square. To 20 g of the broken pieces, 20 g of xylylenediamine was added and they were placed in a vessel which was then closed. It was heated at 400 °C for 1 hours. The vessel was then cooled to room temperature, and the contents were taken out of the vessel and filtered through a wire netting to remove the matters which had not been decomposed such as copper-solid, glass fibers and solder material, to obtain a filtered liquid. Taking a 10 g portion of the filtered liquid, it was mixed with 30 g of a bisphenol A epoxy prepolymer (manufactured by Asahi Denka Kogyo and sold by the trade name of EP-4100), followed by leaving the mixture at room temperature. As a result, the mixture was hardened to produce a mass of brown-colored resin. The glass transition temperature of this hardened material was measured by the DSC, and the result of measurement was 93 °C. As described above, the recycling method of the present invention is a method in which a thermoset epoxy resin material which has been once hardened is plasticized before it is hardened again and subjected to molding processing, to enable the reuse of the thermoset epoxy resin material as a new product, and the industrial value thereof is extremely high. It must be understood that the invention is in no way limited to the above embodiments and that many changes may be brought about therein without departing from the scope of the invention as defined by the appended claims.

Claims: A method of recycling a thermoset resin, comprising the steps of: plasticizing the thermoset resin by adding an amino compound as decomposer to the thermoset resin, to produce a plasticized resin; and re-hardening the plasticized resin by adding a re-hardener to the plasticized resin, the re-hardener acting on both the amino compound and the plasticized resin to effect hardening, characterized in that the thermoset resin comprises an epoxy resin, and the re-hardener comprises a compound having at least two epoxy groups. A method according to claim 1, wherein the thermoset resin to be recycled comprises an acid anhydride cured epoxy resin. A method according to any preceding claim, wherein the decomposer is a liquid whose boiling point is not lower than the glass transition temperature of the thermoset resin to be recycled. A method according to any preceding claim, wherein at least the surface of the thermoset resin is decomposed and liquefied at the plasticizing step by the addition of the amino compound. A method according to any preceding claim, further comprising, before the plasticizing step, the step of: breaking the thermoset resin into particles. A method according to claim 5, wherein the thermoset resin at the breaking step is broken into particles having a particle size of 0.1 mm or more, and the thermoset resin at the plasticizing step is partially plasticized by controlling the amount of the amino compound added to the thermoset resin. A method according to any preceding claim, wherein the thermoset resin at the plasticizing step is heated to a temperature which is not lower than the glass transition temperature of the thermoset resin. A method according to any preceding claim, wherein the amino compound at the plasticizing step breaks a network structure of the thermoset resin to bond or associate with the broken network structure, and the re-hardener at the re-hardening step reacts to form a bond with both the amino compound and the plasticized resin. A method according to any preceding claim, wherein the amino compound comprises an aliphatic or aromatic amino compound which is selected from the group consisting of benzyldimethylamine, ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenediamine, trimethylhexamethylenediamine, bis-(hexamethylene)triamine, polyoxypropylenediamine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, N-cimethylcyclohexylamine, xylylenediamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, monoethanolamine, diethanolamine, triethanolamine, pyridine and imidazole. A method according to claim 9, wherein the amino compound comprises a secondary amine which is selected from the group consisting of diethylenetriamine, triethylenetetramine and xylylenediamine. A method according to any preceding claim, wherein the re-hardener comprises a epoxy prepolymer. A method according to claim 11, wherein the epoxy prepolymer is selected from the group consisting of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD epoxy resin, biphenyl epoxy resin, alicyclic epoxy resin, cresol novolak epoxy resin and polyfunctional epoxy resin. A method according to claim 1, wherein the re-hardener at the re-hardening step is added so that the ratio of the re-hardener to the decomposer by the epoxy equivalent amount is from 0.6 to 1.1. A method according to any preceding claim, further comprising, after the plasticizing step, the step of: removing a solid matter from the plasticized resin. A method according to any preceding claim, further comprising the step of: molding the plasticized resin during the re-hardening step to reclaim a resin article.

Inventors: GOTANDA TAKESHI, TAI CAO MINH, TSUDA KEN, GOTANDA, TAKESHI, TAI, CAO MINH, TSUDA, KEN, Gotanda, Takeshi, Intellectual Property Division, Tai, Cao Minh, Intellectual Property Division, Tsuda, Ken, Intellectual Property Division
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 2000
Main classification: C08J11
IPC codes: C08J11, C08G63, C08G59, C08G18