Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-12-03
2000-10-03
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521133, 521155, 521170, C08G 1814
Patent
active
061274429
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process and an apparatus for the production of foams by means of carbon dioxide dissolved under pressure as a foaming agent, wherein the composition to be foamed is mixed under pressure with what is preferably liquid carbon dioxide and is subsequently depressurised with the formation of foam. Liquid starting materials for plastics, which harden to form the foamed plastic due to an addition polymerisation or condensation polymerisation reaction which sets in after foaming, are used in particular as the foamable compositions. This invention relates in particular to polyurethane foamed materials.
BACKGROUND OF THE INVENTION
The use of physically dissolved carbon dioxide as a foaming agent in the production of polyurethane foams is known from GB-A 803 771, U.S. Pat. No. 3,181,199 and U.S. Pat. No. 3,184,419. However, these known, prior proposals have not resulted in an industrial use, since the foam structure produced was very non-uniform; in particular, the foam comprised large voids. The reason for this is considered to be that the dissolved carbon dioxide has a pronounced tendency to remain in solution, even when the mixture which reacts to form polyurethane is supersaturated with carbon dioxide. In order to release the carbon dioxide during or after depressurisation it is necessary to provide seed bubbles which promote the controlled release of the carbon dioxide during depressurisation.
This problem is also known to occur when other foaming agents are used, such as low molecular weight hydrocarbons, chlorofluorocarbons, methylene chloride or water (chemical evolution of carbon dioxide by the reaction of the isocyanate with water). In these situations, bubble seeds have been provided by dispersing finely distributed air and/or nitrogen in at least one of the components of the mixture which reacts to form polyurethane.
When carbon dioxide which is physically dissolved under pressure is used as the foaming agent, it has similarly been proposed according to EP-A 645 226 that a nitrogen be introduced as a nucleating gas into the mixing chamber for the polyol and isocyanate components. In the course of this procedure, the amount of nitrogen has to be increased compared with conventional mixing processes which operate substantially at normal pressure, so that it corresponds to the prevailing pressure. However, polyurethane foams produced in this manner still have an unsatisfactory foam structure, apparently because the seed bubble structure is not sufficiently fine and uniform.
It has also been proposed according to DE-A 44 22 568.7 that high shearing forces be produced at the depressurisation element for nucleating the release of CO.sub.2. Even though very good grades of foam are obtained according to this proposal using high carbon dioxide contents between 4 and 6% by weight and with depressurisation from a correspondingly high pressure, at lower carbon dioxide contents in the reactive mixture the supersaturation of the reactive mixture which is produced on depressurisation is not sufficient to provide uniformly good grades of foam by means of high shearing forces. Another disadvantage is that the mixing chamber pressure has to be maintained very closely above the solution pressure of the carbon dioxide, which constitutes an obstacle to a volume flow control procedure.
SUMMARY OF THE INVENTION
The object of the present invention is to improve the foam qualities of multi-component foamed materials using carbon dioxide dissolved under pressure, by producing a very uniform bubble seed structure.
It has been found that the mixing chamber pressure can be varied within wide limits, in the interest of effecting mass flow control of the components, if air or nitrogen is firstly dissolved as a nucleating agent in one of the (main) components and carbon dioxide is secondly dissolved in the other (main) component, and if the component containing the nucleating agent is injected under high pressure into the component containing carbon dioxide.
BRIEF DESCRI
REFERENCES:
patent: 3181199 (1965-05-01), Voelker
patent: 3184419 (1965-05-01), Merriman
patent: 5055272 (1991-10-01), Wheeler et al.
patent: 5118720 (1992-06-01), Wheeler et al.
patent: 5620710 (1997-04-01), Fiorentine et al.
patent: 5639483 (1997-06-01), Fiorentini et al.
patent: 5665287 (1997-09-01), Fiorentini et al.
J.B. Blackwell et al, Comparison of the VPF and Liquid CO.sub.2 Foaming Processes, Cellular Polymers, Vo. 15, No. 2, Jan. 1, 1996, pp. 105-116.
Ebeling Wilfried
Eiben Robert
Raffel Reiner
Steilen Herbert
Sulzbach Hans-Michael
Bayer Aktiengesellschaft
Cheung Noland J.
Cooney Jr. John M.
Gil Joseph C.
Hennecke GmbH
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