Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1993-01-19
1993-12-14
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521128, C08J 910
Patent
active
052703479
DESCRIPTION:
BRIEF SUMMARY
FIELD OF USE
The present invention can be employed in the sector of foamed plastics manufacture and relates to a process for the manufacture of polyurethane foamed plastics, in which the foaming process is carried out with pure nitrogen being used as blowing agent.
PRIOR ART
Foamed plastics that possess a closed cellular structure or a porous cellular structure are obtained either by means of a pressure-less foam production or by a sudden expansion of gases, by blowing agents or solvents which, at more elevated pressures, cause an expansion pressure within the plastic or liquid plastic mass. In this case the foam structure is produced due to chemical reactions as, e.g. in the case of polyurethane, by the addition of expanding agents which decompose at a certain temperature during the processing white forming such gases as N.sub.2 or CO.sub.2 ; the addition of volatile solvents during the polymerization being also known. The foaming process itself takes place either when exiting from the extrusion die, i.e. following the extrusion or injection molding, or in the open mold. In this case, foam stabilizers prevent the foam from collapsing prior to the final curing. Poreforming blowing agents (expanding agents), such as azo compounds and diazo compounds spat off, inter alia, N.sub.2 when being acted upon by heat or catalysts.
Among the foamed plastics, the polyurethane foamed plastics (PUR) possess the greatest technical importance, these are obtained by a gradual polyaddition of diisocyanates to dioles when water and/or carbonylic acids are present, for these react with the isocyanates white forming carbon dioxide which possesses an expanding and foam-forming effect. As isocyanates, mainly low-molecular diisocyanates, and as dioles, polyester and polyether-polyoles are suitable. Additionally required processing aids in this polyaddition are catalysts, emulsifiers, foam stabilizers and suchlike.
It is known that, in the manufacture of PUR foamed plastics, fluorohydrocarbons are employed as principal blowing agents. Apart from these, the CO.sub.2 also possesses an expanding effect, this being formed by the reaction of the added water with the existing cyanate. A fluorohydrocarbon-free foamed plastic in which CO.sub.2 were to be employed as the sole expanding agent, would be subject to the following disadvantages: takes less time than the reversed diffusion of the air into the cells. Due to this, a low pressure with respect to the atmosphere is produced in the cells which, during the final curing time of the cellular plastic, causes a collapsing of the foam body. This instability would have to be compensated by a substantially increased volumetric weight of the foamed plastic. additionally developed heat, cracks and core discolorations are produced, e.g. in foam stabs.
The employment of ammonium nitrite as expanding agent in the manufacture of hollow bodies, such as spheres and the like is known according to DE-Literature H. Rompp "Chemie-Lexikon", 5th edition, keyword: "Ammoniumnitrit", Page 232. The FR-A-1.009.505 describes a process for the manufacture of cellular substances which consists in that, as means for the foaming of the mass to be treated, a mixture of components is employed which, in each case, comprises an inert carrier material wherein an active substance has been finely distributed which is suitable for the manufacture of the cellular substances for reacting with the active substance or substances. As inert carrier materials, all natural, higher organic polymers, all synthetic higher polymers, all solvents, expanding agents, softening agents and plasticizers of the higher polymers quoted, as well as mixtures of the same can be employed. As an active substance with the reaction of a gas release, any substance may be used which reacts with at least one other substance in such a way that at least one of the reaction products is a gas, in which case the substance itself may release gas. The active substance for the release of gas is comprised of any ammonium compound whatever, in particular of an
REFERENCES:
patent: 2250192 (1941-07-01), Cuthbertson
Prignitz Herbert
Redha Najdat
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