Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1992-11-25
1994-08-02
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
528302, 528481, 528483, 528486, 528503, 26421111, 26421117, 26421121, C08F 2000
Patent
active
053346696
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of high molecular weight polyester resins from resins having lower molecular weight using a new polyaddition technique in the solid state.
Particularly, the invention relates to a process in which the polyester resin is blended in the molten state with an upgrading additive capable of performing the solid state polyaddition of said polyester which is then transformed into a granulate and then upgraded using the new solid state polyaddition technique.
In Applicant's previous pending European patent application EP No. 89119049.8 a solid state upgrading process for polyester resin is described in which the resin is upgraded at temperature higher than 170.degree. C. and in general comprised in the range of 170.degree.-220.degree. C., in the presence of a dianhydride of an aromatic tetracarboxylic acid.
It has now been unexpectedly found that it is possible to carry out the upgrading reaction also operating at temperatures lower than 170.degree. C.
The process of the invention comprises the steps of mixing a molten polyester resin with an upgrading additive selected from the group of the dianhydrides of aromatic tetracarboxylic acids, granulating the resin, crystallizing the granulate at temperatures above the TG and then upgrading the crystallized polyester at temperatures comprised in the range from the TG of the polyester and 170.degree. C.
This process is preferably carried out in continuous way using continuous crystallizers and reactors where the chips are fed in counter current to a stream of a heated gas, for example air, nitrogen or carbon dioxide.
Apparatuses suitable for the crystallization and polyaddition steps can be those described in U.S. Pat. Nos. 4,161,578 and 4,064,112 whose description is herewith incorporated by reference.
The recycling of the inert gas streams can be carried out according to European application 86830340 5 the description of which is also herewith incorporated by for reference.
It is known that the solid state post-polycondensation reactions of the polyester resin are usually conducted at temperatures higher than 180.degree. C. mainly higher than 195.degree. C. (see page 3295 of Journal of Applied Poly. Sc. 28,3289-3300, 1989).
It is also known that the solid state polycondensation reactions mainly consist of post transesterification and esterification reactions which form as by-products ethylene glycol and water.
The diffusion of these by-products out the granules is a factor controlling the kinetic of the upgrading thus requiring high upgrading temperatures in order to obtain upgrading kinetics of practical interest.
In the solid state polyaddition process of this invention, in which the chain extension mechanism is based essentially on ring opening addition reactions which do not lead to the formation of by-products which could lower the kinetic of the upgrading reaction, upgrading temperatures comprised in a rather low range e.g. from 100.degree. to 170.degree. C. can therefore be used.
The possibility of using upgrading temperatures relatively low is an advantage because it makes it possible to upgrade polyester resins like copolyethyleneterephthalates (COPETs) with low melting points e.g. lower than 200.degree. C., without having sticking problems in the reactor walls which problems cannot be avoided using the upgrading processes of the prior art which needs higher upgrading temperatures.
Generally the crystallization temperature is the same or lower than the temperature used in the upgrading reactor. The term upgrading reaction or process means a thermal treatment carried out on the solid polyester resin, which leads to an increase of the molecular weight of the resin.
By polyaddition or addition reaction it is meant a reaction between the terminal groups of the polyester resin and a substance having groups capable of addition reaction with the terminal groups, thus linearly extending the length of the polyester chain.
The upgrading additive used in the process of the invention is a dianhydride of an arom
REFERENCES:
patent: 2965613 (1960-12-01), Milone et al.
Chem. Abstracts: vol. 90, 1979; 24220f.
Chem. Abstracts: vol. 80, 1974; 71956d.
Chem. Abstracts: vol. 89, 1978; 130514u.
Acquah Samuel A.
Kolomayets Andrew
M. & G. Ricerche S.p.A.
Manzo Edward D.
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