Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-07-28
2002-03-05
Yoon, Tae H.. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S048000, C525S044000, C528S307000, C528S308300
Reexamination Certificate
active
06353036
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for producing an unsaturated polyester from polyethylene terephthalate (hereinafter abbreviated as PET), particularly waste (or scrap) PET, and an unsaturated polyester resin composition and a molding compound comprising the resulting unsaturated polyester.
BACKGROUND OF THE INVENTION
It is known that waste PET, whether post-consumer or non-post-consumer, can be recycled by depolymerization in a glycol, followed by reaction with an unsaturated polybasic acid and a glycol to produce an unsaturated polyester. This technique has recently been re-studied as disclosed in JP-A-11-60707, JP-A-8-151438, and JP-A-11-181067.
However, the unsaturated polyester obtained from waste PET has poor compatibility with unsaturated monomers such as styrene, and its solution has poor solubility stability with time. This seems attributable to the crystallinity originated in the PET segments and the intermolecular hydrogen bond strength of the ester moiety between ethylene glycol originated in PET and fumaric acid. A combined use of various glycols has been a generally followed practice to improve the compatibility as taught in JP-A-8-151438. The chief aim of the combined use of a plurality of glycols is improvement on compatibility with unsaturated monomers such as styrene. Studies taking into consideration the quality or performance of molded articles obtained from the resulting resin composition have not been made to date.
Sheet molding compounds (SMC), bulk molding compounds (BMC), etc. comprising the unsaturated polyester should contain a thermoplastic resin as a low profile additive. A polystyrene resin is of frequent use as a low profile additive for its water resistance and inexpensiveness. As stated above, the conventional unsaturated polyester prepared from waste PET has poor compatibility with the low profile additive or poor uniformity retention in a mixed state with the low profile additive so that they are liable to separate from each other during a thickening step or storage of molding compounds comprising the unsaturated polyester. Molded articles obtained from such a molding material are inferior in appearance and quality to those obtained from a molding material comprising an ordinarily produced unsaturated polyester.
SUMMARY OF THE INVENTION
An object of the present invention is to eliminate the drawbacks of molded articles of a polyester resin composition obtained from PET, i.e., to improve compatibility of the polyester resin with a low profile additive and to improve appearance and quality of the molded article.
In order to increase usefulness of the unsaturated polyester prepared out of PET, the present inventors have conducted extensive investigation and reached the present invention as a result.
The present invention provides a process for producing an unsaturated polyester comprising the steps of
(1) (A) depolymerizing polyethylene terephthalate with a polyhydric alcohol, (B) adding maleic anhydride to the depolymerization product to allow them to react with each other, and (C) adding dicyclopentadiene to a carboxyl group derived from the maleic anhydride to cause addition reaction and
(2) adding a polyhydric alcohol and/or a polybasic acid to the reaction product obtained in step (1) to cause polycondensation reaction.
Further, in the above process of the present invention, if strict control of the addition rate of the dicyclopentadiene to the carboxylic group of the maleic anhydride in step (C) is carried out, an unsaturated polyester having very stable quality can be obtained.
The invention further provides an unsaturated polyester resin composition comprising the unsaturated polyester obtained by the above process and a polymerizable unsaturated monomer.
The invention furthermore provides a molding compound comprising the unsaturated polyester resin composition.
DETAILED DESCRIPTION OF THE INVENTION
The PET which can be used as a starting material in step (A) is a polymer synthesized essentially from terephthalic acid and ethylene glycol and includes the waste generated in PET production, recycled PET of various waste PET molded articles, and regrinds of waste PET generated in production of PET molded articles. Typical are regrinds, called waste PET or regenerated polyester, obtained by physically and mechanically grinding PET bottles into chips, powder, pellets or flakes, which preferably have an average particle size of 1 to 10 mm.
The term “polyethylene terephthalate (PET)” as used herein includes not only polymers consisting of terephthalic acid and ethylene glycol but those further comprising other units of cyclohexanedimethanol, isophthalic acid, naphthalenedicarboxylic acid, etc. as a modifying comonomer.
PET does not always need to be transparent. Colored (e.g., green-colored) or printed PET is also useful unless the resulting molding article is not limited in hue, etc.
The maleic anhydride which can be added in step (B) is a compound obtained by heat dehydration of maleic acid or catalytic oxidation of benzene with air. Commercially available maleic anhydride, preferably of such a grade as has a purity of 95% or more and high resistance to thermal coloration can be used.
The dicyclopentadiene (hereinafter abbreviated as DCPD) which can be used in step (C) does not need to have high purity, and commercially available products can be employed. It is preferred to use DCPD which is composed of components that do not form a large amount of gel (heat crosslinking product) during polycondensation and has a purity of 85% or higher.
The polyhydric alcohol with which PET is depolymerized in step (A) is not particularly limited and is appropriately selected according to the purpose. It is desirable to use such a polyhydric alcohol as depolymerizes PET when added in a small amount and completes the depolymerization smoothly and rapidly at a relatively low temperature of 260° C. or lower.
Polyhydric alcohols of which two hydroxyl groups have a primary structure are preferred from the standpoint of rapid depolymerization. Such polyhydric alcohols include neopentyl glycol, 2-methyl-1,3-propanediol, and 3-methyl-1,5pentanediol. The polyhydric alcohol for PET depolymerization is selected appropriately depending on the molecular design, and the performance required, of the unsaturated polyester. If desired two or more kinds of polyhydric alcohols can be used in combination. A preferred weight ratio of the polyhydric alcohol to PET ranges from 30:37 to 90:10.
The PET depolymerization with the polyhydric alcohol is preferably carried out in a relatively low temperature ranging from 200 to 260° C. Desirably, a catalyst is used to accelerate the depolymerization. Suitable catalysts include organic acid salts, alkoxides or chelates of metals. It is desirable to decide the kind and the amount of the catalyst so as not to impair the physical properties of the resin. From this viewpoint, a preferred catalyst is a tin compound, particularly a monobutyltin compound, and a preferred amount of the catalyst is from 0.01 to 1.0% by weight based on the total weight of the polyhydric alcohol and PET.
The resulting PET depolymerization product is a mixture of ethylene terephthalate oligomers having ethylene glycol or the glycol used in step (A) at the end thereof, which further comprises glycol diterephthalate, free glycols, such as the glycol used in step (A) and ethylene glycol, and the like.
After step (A), the PET depolymerization product (mixture) is preferably cooled to 150° C. or lower. In step (B), a requisite amount of maleic anhydride is added to the mixture and allowed to react with the depolymerization product. In step (C), DCPD is added to the reaction mixture to undergo addition reaction with a carboxyl group of the maleic anhydride. The order of steps (B) and (C) is not particularly limited. The stage of adding DCPD can be decided according to the production equipment. As far as exotherm is controllable, DCPD may be added either before or after, or simultaneously with the addition of maleic anhydride. In a preferred embod
Yasumura Takashi
Yoshioka Chikara
Armstrong Westerman & Hattori, LLP
Dainippon Ink and Chemicals Inc.
Yoon Tae H..
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