Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2002-12-03
2004-10-12
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C264S176100, C264S219000, C525S403000, C528S271000
Reexamination Certificate
active
06803442
ABSTRACT:
TECHNICAL FIELD
The present invention relates to masterbatch methods for producing high-quality polyester resins having improved processability and articles thereof by uniformly subjecting a straight-chain polyester resin having relatively low molecular weight to a coupling reaction to increase the melt viscosity and the degree of swelling, using a small amount of binder masterbatch and a trace amount of catalyst masterbatch. More specifically, the present invention relates to a masterbatch method for producing a high-quality polyester resin having improved processability and articles of the polyester resin by subjecting a recycled polyethylene terephthalate-based polyester whose molecular weight and mechanical properties have been reduced to a coupling reaction to increase the molecular weight, the melt viscosity, and the degree of swelling while preventing the byproduction of gel and fisheyes.
BACKGROUND ART
In polyesters, saturated straight-chain polyesters (hereinafter, referred to as PET-based polyesters), such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalenedicarboxylate (PEN), and PETG, have excellent characteristics and are, therefore, widely used for fibers, films, bottles, and the like. Also, the PET-based polyesters are used extensively as high-performance resin materials in many industrial fields, such as the automotive, machine, electrical and electronic material, construction material, and container industries.
From the viewpoint of resource saving and environmental conservation, it has recently been understood that waste plastics collected from manufacturing processes and public consumer markets must be recycled. As for the PET-based polyesters, waste bottles, films, sheets, fibers, and the like have also been actively recycled accordingly. However, in these PET-based polyesters, heat treatment in molding processes is liable to significantly reduce the molecular weight thereof and to increase the number of carboxyl radicals at ends of the molecules thereof. This is a bottleneck in the development of recycling techniques of collected polyesters. The molecular weight of collected waste PET-based polyesters is lower than that of a new chip. For example, the molecular weight of flakes (fragments) of recycled PET bottles, which are generated in large quantity, is reduced to substantially half the original molecular weight. Therefore, if such PET bottles are reused as a base resin, processability is degraded. The resin results in, at the best, fibers, which can be produced even from a low-molecular-weight base resin, or low-quality sheets, and thus the resulting products do not have the quality satisfying requirements of the original PET bottles or other films and sheets. Thus, the use of recycled PET-based polyesters has narrow limits.
On the other hand, plastic articles featuring light weight, elasticity, processability, and the like have recently been used for packing containers and cushioning in large quantity. If the molecular weight and melt viscosity of the flakes of low-molecular-weight recycled PET bottles or new PET are increased, inexpensive articles can be achieved.
Some methods are known as solutions for these challenges, including methods in which solid phase polymerization is performed to restore the molecular weight; a terminal group of the polyester is allowed to react with a chain-extending agent (binder) to increase the molecular weight; or another resin, such as an elastomer, is added to compensate for the mechanical properties.
It is proposed that, as the chain-extending agent (binder), a compound having a functional group, such as isocyanate, oxazoline, epoxy, aziridine, or carbodiimide be used. However, the chain-extending agent is subjected to strong constraints from the viewpoint of reactivity, thermal stability, and stability. Applicable chain-extending agents are, therefore, limited to specific compounds. Epoxy compounds are relatively useful as the chain-extending agent, and a monoepoxy compound (Japanese Unexamined Patent Application Publication No. 57-161124) and diepoxy compounds (Japanese Patent Application laid open No. 7-166419 and Japanese Patent Application laid open Nos. 48-25074 and 60-35944) are known. However, these epoxy compounds have problems with reaction velocity, formation of gel, melt viscosity, compatibility, thermal stability, physical properties of the resulting articles, and the like, and have not yet been put into practical use.
On the other hand, a method for increasing the molecular weight of polyester is proposed (PCT Japanese laid open No. 8-508776) in which collected waste PET-based polyester is melted and mixed with a difunctional epoxy resin and hydroxyphenylalkylphosphonate having steric hindrance effects. Unfortunately, the sterically hindering hydroxyphenylalkylphosphonate is expensive though this method makes reaction velocity faster. This is a problem in practical use for industries which need low-cost recycling. Although another method has also been proposed in which rubber and an elastomer are added to the polyester, this method has problems with characteristics after drying, compatibility, thermal stability, elasticity, and the like.
In general, plastics used for various types of articles are polystyrene, polyethylene, and polypropylene having high molecular weights and high melting viscosities. The melting point of PET-based polyesters is as low as about 2,000 poise at 280° C., even if the molecular weight thereof is increased (to, for example, an intrinsic viscosity of 1.0 dl/g, a number-average molecular weight of about 17,000, and a weight-average molecular weight of about 44,000) to use for bottles and, therefore, it is difficult to form the PET-based polyester into various types of articles for many applications as in polyolefins The inventors of the present invention have proposed a method for producing a PET-based polyester resin having a long chain, blanched structure and characteristic features of having a high molecular weight, a high melt tension, a high degree of swelling and the like and an article of the PET-based resin (PCT WO 98/44019) by adding both difunctional and trifunctional epoxy compounds, acting as a small amount of binder, and a trace amount of coupling reaction catalyst to the PET-based polyester in advance, and conducting a rapid reaction for about two minutes in an extruder. In this method, however, a local reaction at the ditch of the screw and vicinity of vent the extruder where the raw and high-concentration binder and catalyst have been placed is liable to intensely produce gel as a by product, and thus continuous operation for more than several hours causes gel and fisheyes. It has been found that the quality of, for example, tubular films, thin films produced by a T-die method, and foamed sheets and pipes is liable to be degraded due to large amounts of gel and fisheyes and, therefore, the prior invention has not been perfected.
In order to solve the problem of causing gel and fisheyes resulting from the local reaction during the rapid reaction of the binder and the catalyst in an extruder, an object of the present invention is to provide a masterbatch method for producing a polyester resin having an improved processability and an article of the polyester resin in which the molecular weight of a brittle PET-based polyester of, particularly, recycled PET bottles having a relatively low molecular weight is increased, and the melt viscosity of the polyester is also increased so that various types of molding can be performed.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have conducted intensive research to accomplish this object, and consequently found that the known method for producing the PET-based polyesters having a specific molecular weight and the characteristic features of high melt viscosity and large swelling and which are made suitable for tubular films, tough sheets, foamed sheets, and directly blown bottles and pipes by adding a specific epoxy resin, acting as a binder, and a coupling
Fujimaki Takashi
Kobayashi Yukio
Tanaka Toshio
Urata Yoshitomo
Boykin Terressa
FTEX, Incorporated
Sughrue & Mion, PLLC
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