Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-09-13
2002-10-15
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S047500, C521S048000
Reexamination Certificate
active
06465531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for recycling thermoset resin materials, through which the recycling of difficult to reuse thermoset plastics is made easy.
2. Discussion of the Background
Recently, space for burying wastes is not easily obtained particularly in cities and surrounding areas. It is therefore urgent to quickly solve the problem of how to dispose of general wastes and industrial wastes. 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 once they are hardened, and reuse thereof as a resin material is difficult. Currently, they are usually buried or burned for disposal. Disposal by burial of the thermoset plastic waste is not only a problem form the aspect of land acquisition, but is also a problem from the viewpoint of fear of pollution of soil and ground water with heavy metals such as antimony and the like, and which are often used as catalysts, 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.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method for recycling thermoset resin that avoids the above problems and is convenient and simple to perform.
A further object of the present invention is to provide a method for recycling thermoset resin that provides a resin product suitable for a wide variety of uses.
A further object of the present invention is to provide a recycled thermoset resin.
These and other objects of the present invention have been satisfied by the discovery of a method of recycling a thermoset resin, comprising:
contacting at least a portion of the thermoset resin with a decomposer having at least one functional group capable of reacting at a crosslink site on the thermoset resin, under conditions sufficient to break said crosslink site, to give a fluid thermoset preresin, wherein a plurality of chain ends of said preresin have functional groups thereon; and
re-hardening said fluid thermoset preresin by reacting said plurality of chain ends with a rehardener having two or more groups reactive with said chain end functional groups,
and the recycled thermoset resin obtained thereby.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention further relates to a method of recycling a thermoset resin, comprising:
contacting at least a portion of the thermoset resin with a decomposer having at least one functional group capable of reacting at a crosslink site on the thermoset resin, under conditions sufficient to break said crosslink site, to give a fluid thermoset preresin, wherein a plurality of chain ends of said preresin have functional groups thereon; and
re-hardening said fluid thermoset preresin by reacting said plurality of chain ends with a rehardener having two or more groups reactive with said chain end functional groups.
In the above method, at least the surface of the thermoset resin is decomposed and liquefied in the contacting step by the addition of the decomposer.
The recycling method may further comprise, before the contacting step, the step of breaking the thermoset resin into particles. The thermoset resin at the contacting step is partially plasticized by controlling the amount of the decomposer compound added to the thermoset resin. Within the context of the present invention the term “fluid thermoset preresin” defines the resulting composition obtained by action of the decomposer on the thermoset resin, which results in at least a partial plasticization, or liquification, of at least a portion of the surface of the resin particles. The liquification can be partial or complete in this step.
In the above method, the decomposer compound breaks the network structure of the thermoset resin to bond or associate with the broken network structure, and the re-hardener reacts with both of the decomposer compound and the resin to form a bond.
The re-hardener 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.
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, xylene resins, firan resins, melamine phenol resins, polybutadiene 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 recycle 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 recycle of a thermoset resin by chemical measures, a contacting step in 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 in which a network structure is formed again by allowing a re-hardener to act on the decomposed resin material obtained in the contacting 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 to a re-hardening treatment in 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 resin decomposed 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 conditions. In this case, it is naturally necessary, for re-hardening the decomposed resin material, to remove the decomposer before the re-hardening step from the decomposed resin material. However, the removal of decomposer is practically troublesome, and complete removal thereof is in fact difficult.
In contrast, the recycling method o
Gotanda Takeshi
Thai Cao Minh
Kabushiki Kaisha Toshiba
Michl Paul R.
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