Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1993-09-28
1994-11-08
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 50, 264 53, 264 54, 521182, C08J 908, C08J 914
Patent
active
053627636
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to foamed cellular polyester resins and processes for their preparation.
The commercial foamed cellular polymers, such as foamed polystyrene and polyurethane, find wide application in the building, parking and padding sectors.
The foamed cellular polyester resins have up to now found little application due to the not satisfactory properties of the foamed polyester materials till now produced.
European application 0 372 846 describes foamed cellular polyester resins obtained by extrusion foaming of polyester resins added with anhydrides of tetracarboxylic acids. Pyromellitic anhydride is the preferred additive and the possibility of using amounts thereof up to 5% by weight is disclosed.
The obtained foamed cellular materials are not homogeneous and need thermal post-treatments either to obtain more homogeneous foamed structures with finer cells and to develop heat stability characteristics of the formed articles.
It is also necessary that the foamed articles be quickly cooled after the extrusion foaming step to temperatures lower than the Tg of the polyester resin. This to the effect of maintaining the crystallinity of the resin to relatively low values (lower than about 15%). U.S. Pat. No. 4,132,702 describes branched polyester resins obtained by solid state reaction of polyester resins added with branching agents containing at least three reactive groups capable of forming ester groups.
Examples of said branching agents are pentaerythritol,tri-and tetracarboxylic acids and their esters, such as trimesic and piromellitic acids.
The obtained branched polyesters show high melt strength values combined however with relatively low values of the melt viscosity.
There are described also modified polyester resins having melt viscosity sufficiently high combined, however with low values of the melt strength. The intrinsic viscosity of the branched resins is higher than 1.2 dl/g.
The above cited modified polyester resins are indicated as suitable to prepare foamed materials. No examples and data on the characteristics of the foamed materials are given.
It has now unexpectedly found that it is possible to prepare foamed cellular polyester resins having valuable morphological and mechanical properties by subjecting to extrusion foaming polyester resins having the following characteristics:
melt strength higher than about 8 centinewton;
complex melt viscosity higher than about 25,000 poises;
intrinsic viscosity higher than 0.8 dl/g.
Foamed cellular polyester resins endowed of particularly valuable properties are obtained by extrusion foaming of resins having melt strength comprised between 15 and 30 centinewton or higher, melt viscosity between 30,000 and 50,000 poises or higher and intrinsic viscosity between 0.85 and 1.95 dl/g.
The complex viscosity and the melt strength are measured at 270.degree. C. according to the analytical procedure reported in the examples. As therein indicated, in case of incomplete melting of the resin at 270.degree. C., the determination is carried out at 290.degree. C. The values corresponding to the minimum values of melt strength acid complex viscosity measured at 270.degree. C. are set forth in the analytical procedure.
The properties above indicated are shown by the resins before extrusion foaming; similar properties are also possessed by the resin after foaming.
The foamed cellular polyester resins of the invention show mechanical properties superior to the commercial foamed resins such as foamed polystyrene (STIRODUR from Bayer) and foamed polyurethane resins.
For example the compression set is higher; while the foamed polyester resins do not collapse up to compression of 15-20% the commercial foamed resins do not resist to compressions higher than about 8%.
The foamed cellular polyester resins of the invention moreover are more rigid with respect to the commercial resins: the flexural rigidity is higher than 3 MPa and the flexural modulus is generally comprised between 20-120 MPa; whereas in the case of STIRODUR and the foamed polyurethane resins the va
REFERENCES:
patent: 5000991 (1991-03-01), Hayashi et al.
Al Ghatta Hussain A. K.
Astarita Luca
Severini Tonino
Foelak Morton
M. & G. Ricerche S.p.A.
Manzo Edward D.
Ringsred Ted K.
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