Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-02-09
2001-12-25
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C525S437000, C525S444000
Reexamination Certificate
active
06333363
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a method for obtaining polyester resin products having a desired strength, as well as to a mixture used in the method. More particularly, the present invention relates to a method for obtaining polyester resin products having a desired strength by adding a carbodiimide compound to a material polyester resin, as well as to a mixture used in the method.
(2) Description of the Prior Art
In recent years, environmental pollution caused by plastic waste has become a bigger problem, and the necessity for and significance of environmental protection has become more important. Under such circumstances, ways are being sought for recovery and regeneration of used plastic materials for effective reutilization thereof.
In particular, polyethylene terephthalate resin (hereinafter abbreviated to PET resin), which is used as a container for clean drinking water or the like, is currently disposed by reclamation or incineration. Therefore, methods for effective reutilization of used PET resin are being sought from the two aspects of resource saving and environmental protection.
The reutilization methods include a material recycling method which comprises changing the form of a used material into a different form by a physical treatment, for making possible the reutilization.
This material recycling method is actually being applied to the recycling of used PET resin. In the method, however, impurities are easily taken in; therefore, there are problems that the regenerated product is lower in purity, strength and heat resistance than the original product and consequently has limited applications. These problems are considered to be caused by the following reasons.
Ordinarily, when recovered PET resin is processed for reutilization, the recovered PET resin in the form of bottles or the like is first ground into flakes and then processed into products (e.g., pellets). In this operation, the PET resin is deteriorated because it undergoes, in an extruder, hydrolysis (caused by the water which adheres thereto during washing or the like), oxidative decomposition and/or thermal decomposition.
In ordinary resin recycling, recovered resin is dried at 140 to 160° C. for about 5 hours in order to prevent the above-mentioned deterioration. This drying requires a facility investment and a running cost for the facility and, in recycling of used PET resin bottles or the like, incurs a big increase in cost; therefore, the drying is eliminated in some cases, which inevitably invites the deterioration of the PET resin.
There is a further problem. That is, PET resin bottles are produced from PET resins of various intrinsic viscosities (IV) ranging from about 0.6 to 1.2, depending upon the application of the bottles; bottles for soy sauce have an IV of 0.65, bottles for mineral water or tea have an IV of 0.75, bottles for carbonated drinks or the like have an IV of 0.8 to 8.5 and bottles for medical or cosmetic use have an IV of 1.2.
Thus, various PET resin bottles different in properties are collected and ground into flakes at a regeneration plant. Therefore, the flakes have a large fluctuation in properties, and the products, e.g., pellets obtained from the flakes by the use of an extruder are very low in quality.
For the above reason, virgin PET resin must be added to recovered PET resin in order to allow the regenerated product to have a desired strength. Generally, about 30%, based on regenerated product, of virgin PET resin has heretofore been added to recovered PET resin, and the times of reutilization have been about 3. This has made the recycling cost even higher.
Thus, while recovery and reutilization of used polyester resins, particularly used PET resin is required, no satisfactory method therefor is developed yet.
SUMMARY OF THE INVENTION
The objects of the present invention are to alleviate the above-mentioned problems of the prior art and to provide a method for obtaining polyester resin products having a desired strength and a mixture used in the method.
In other words, the objects of the present invention are to alleviate the above-mentioned problems of the prior art and provide a method for maintaining a strength of polyester resin during processing of said polyester resin and a mixture used in the method.
The present inventors made an intensive study in order to develop a method for obtaining polyester resin products having a satisfactory strength (i.e., a method for maintaining a strength of polyester resin during processing such as a result, the present inventors found out that when a carbodiimide compound (including a polycarbodiimide compound) having at least one carbodiimide group in the molecule is added to a polyester resin (e.g. a Recovered PET resin) and the resulting mixture is kneaded and shaped, the PET resin is improved in mechanical strength and, when the PET resin is a recovered PET resin wherein hydrolysis has progressed to a certain degree, the tensile strength of the recovered PET resin can be restored to about the same level as a virgin PET resin (an unused PET resin).
The present inventors further found out that the addition of the above carbodiimide compound to a recovered PET resin to be regenerated can reduce the amount of the virgin PET resin added in processing of the recovered PET resin into a regenerated product, and the addition is useful in recycling of polyester resin, particularly PET resin. The above finding has led to the completion of the present invention.
According to the present invention, there are provided:
a method for obtaining polyester resin products having a desired strength, which method comprises adding a carbodiimide compound to a material polyester resin, and
a mixture used in a method for obtaining polyester resin products having a desired strength, which mixture is obtained by adding a carbodiimide compound to a material polyester resin.
According to the present invention, there are further provided:
a method for maintaining a strength of polyester resin during processing of said polyester resin, which method comprises adding a carbodiimide compound to a material polyester resin, and
a mixture used in a method for maintaining a strength of polyester resin during processing of said polyester resin, which mixture is obtained by adding a carbodiimide compound to a material polyester resin.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is hereinafter described in detail.
The polyester resin used in the present invention is an ester between (1) at least one dihydroxy compound selected from aliphatic glycols (e.g. ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol and hexamethylene glycol), alicyclic glycols (e.g. cyclohexanedimethanol) and aromatic dihydroxy compounds (e.g. bisphenol) and (2) at least one dicarboxylic acid selected from aromatic dicarboxylic acids (e.g. terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid), aliphatic dicarboxylic acids (e.g. oxalic acid, succinic acid, adipic acid, sebacic acid and undecanedicarboxylic acid) and alicyclic dicarboxylic acids (e.g. hexahydrodicarboxylic acid).
The above polyester resin may be modified with a small amount of a triol or a tricarboxylic acid.
Specific examples of the polyester resin are polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate and polyhexamethylene terephthalate.
Of the polyester resins used in the present invention, PET resin (for which effective reutilization is sought for the reasons of resource saving and environmental protection) can generally be synthesized by subjecting terephthalic acid or dimethyl terephthalate and ethylene glycol to a condensation reaction in the presence of a catalyst under appropriate conditions. In this synthesis, addition of at least one appropriate third component before the completion of the reaction can produce a copolymer PET resin.
As the appropriate third component, there can be mentioned (a) compounds having two ester-forming functional groups, for example,
Horie Naofumi
Imashiro Yasuo
Suzuki Shigekazu
Takahashi Ikuo
Kubovcik & Kubovcik
Nisshinbo Industries Inc.
Short Patricia A.
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