Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1993-06-11
1994-12-27
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...
528272, 528296, 528302, 528308, 528353, 528481, 528486, 528503, 2643281, 264239, C08F 2000
Patent
active
053767349
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to an improved process for the production of high molecular weight polyester resins.
More particularly the process of the invention allows to obtain high molecular weight polyesters subjecting to solid state upgrading reaction (SSR) polyesters with values-of intrinsic viscosity lower than 0.57 dl/g.
The formed articles from polyalkylenterepthalate show several valuable characteristics such as high mechanical properties, solvent resistance and transparency.
Several technologies are used for the preparation of the formed articles. Some of them, particularly the blow molding technique require that the viscosity of polyester resin in the molten state be sufficiently high (10.000 poises or more) to avoid that the preforms collapse or break during the preforming stage.
Polyester resins having so high viscosity values in the molten state are difficult to prepare with the conventional melt polycondensation processes.
Polyethyleneterephthalate (PET) bottle grade is prepared with a two steps process wherein in the first step terepthalic acid and ethyleneglycol are polycondensed in the melt (MPC) to obtain a polymer with intrinsic viscosity not less than 0.57-0.6 dl/g and then the polymer (previous crystallization treatment) is subjected to polycondensation in the solid state (SSPC) to obtain the desired intrinsic viscosity value (0.75-0.9 dl/g).
The SSPC upgrading generally shows very low kinetics.
Recently there has been described a solid state upgrading process by polyaddition reaction (SSPA) characterized by high upgrading kinetics (European application 0422282). The European application does not disclose however, that the upgrading treatment can be usefully applied to resins with relatively low intrinsic viscosity, lower than the value of 0.57 dl/g of some of the resins used in the examples.
The possibility of obtaining high molecular weight polyester resins starting from resins with relatively low intrinsic viscosity values, lower than those up to now used presents remarkable advantages, the main of which is represented by a significant increase of the production capacity of the plant. It is indeed known that the polycondensation kinetics in the melt depends on the rate of removal of the volatile by-products (ethylenglycol); the rate of removal in turn depends on the melt viscosity; higher is the latter more difficult is the removal.
The possibility of using a polyester resin with relatively low values of intrinsic viscosity allows to operate in the melt with remarkably reduced intrinsic viscosity and significantly lowers therefore the duration of the polycondensation reaction. There are limits however to the decrease of the polymer intrinsic viscosity during the MPC step. By decreasing I.V., increases the content of oligomers; during the upgrading step cyclic compounds are released which reduce the flowability of granules and lead to line stoppages. These phenomena negatively influence the possibility of the regular plant operation. In the very severe situations it is also possible to arrive to the stop of the plant. This is due to the formation of blocks of sintered material which prevents the regular plant operation. It is for this reason that, in the MPC step, the prepared polyester resin has I.V. not less than 0.57-0.6 dl/g.
It has been now unexpectedly found that it is possible to overcome the drawbacks mentioned above and prepare polyester resins with I.V. higher than 0.7 dl/g starting from resins with I.V. less than 0.57 dl/g. The process of the invention comprises the following stages: dl/g by melt polycondensation of an alkandiol with an aromatic bicarboxylic acid, preferably with terepthalic acid or with a dialkylterepthalate; additive of molecular weight extension (upgrading) containing at least two groups capable of addition reactions with the terminal OH and COOH groups of polyester resin (polyaddition additive); crystallization treatment of the particles; up to obtain the desired increase of polymer intrinsic viscosity.
The polyester resins to which the process of the
Acquah Samuel A.
Kolomayets Andrew G.
M. & G. Ricerche S.p.A.
Manzo Edward D.
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