Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-12-30
2000-10-03
Nutter, Nathan M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 69, 521 71, 521 82, 521 841, 524700, 524732, 524733, 524734, C08J 928, C08J 930
Patent
active
061274399
DESCRIPTION:
BRIEF SUMMARY
The present patent application claims priority based upon European Patent Application 96 0 201 906.3 filed Jul. 4, 1996 (04.07.96).
The present invention relates to a process for the preparation of polymer particles containing polymer of a vinylarene monomer and a foaming agent and to polymer particles and to foamed articles.
Particles that contain such vinylarene polymer and foaming agent are generally known as expandable polymers. A well-known expandable polymer is expandable polystyrene. Expandable polystyrene is produced on a commercial scale by suspension polymerisation. The foaming agent is usually a low-boiling hydrocarbon, such as a C.sub.3 -C.sub.6 hydrocarbon, in particular pentane. The expandable polystyrene is used for making foamed articles that are produced by expanding the polystyrene particles. In the expansion process the foaming agent is (partially) released and may be emitted into the environment. Such emissions are regarded undesirable and ways are sought to reduce the amount of hydrocarbon foaming agent.
In U.S. Pat. No. 5,096,931 expandable polystyrene is described which contains a small amount of a polar polymer and some water and some hydrocarbon foaming agent. This product is manufactured by suspension polymerisation of a mixture of styrene and the polar polymer in the presence of the hydrocarbon foaming agent. The disadvantage of the product obtained is that it still requires the presence of a hydrocarbon foaming agent apart from minor amounts of water.
It would thus be desirable if the amount of water could be increased at the expense of the amount of hydrocarbon foaming agent. One possible way to increase the amount of water would be to enhance the amount of polar polymer in the polymer particles. However, it would be difficult to incorporate the polar polymer into the polystyrene by suspension polymerisation because the polar polymer would wash out into the aqueous phase of the suspension. The unsatisfactory result is that too little polar polymer is incorporated into the resulting particles and, hence, that too little water has been taken up into these particles.
Surprisingly it has been found that more water could be incorporated into the polymer particles if the polymerisation is conducting in two steps. The amount of water that can be sued as foaming agent is such that one may refrain from incorporating any amount of hydrocarbon foaming agent.
Accordingly, the present invention provides a process for the preparation of polymer particles containing the polymer of a vinylarene monomer and having an average particle diameter of 0.1 to 6 mm, which process comprises: gram dry polar polymer with a vinylarene monomer; a polymerisation degree of 15 to 5% to obtain a pre-polymerised mass; suspended particles; and
The present process is capable of yielding polymer particles with satisfactory expandability properties that do not contain an organic foaming agent. These polymer particles can be separated from the aqueous mixture and expanded to yield pre-expanded particles, which are optionally treated further to obtain foamed articles.
Suitable vinylarene monomers to be used in the present process are well known in the art and can suitably be selected from styrene, .alpha.-methylstyrene, chlorostyrene, dimethylstyrene, vinyltoluene and similar styrenic derivatives. Preferably, the vinylarene is styrene.
The polar polymers are defined as being capable of absorbing at least 0.5 g of water per gram of dry polymer. The absorption capacity is determined according to ASTM method F 716-82. Suitable absorption capacities range from 0.5 g water/g polar polymer to more than 200 g water/g polar polymer. Although any polar polymer can be used, it is suitable selected from polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, polyethylene glycols and cellulose derivatives. Polyvinylpyrrolidone (PVP) is a preferred polar polymer. This polar polymer is completely miscible with water within the temperature range of 0 to 120.degree. C. The absorption capacity is therefore taken to be higher than 200
REFERENCES:
patent: 5358998 (1994-10-01), Wendel et al.
patent: 5369163 (1994-11-01), Chiou et al.
Berghmans Hugo Angela Albert
Chorvath Igor
Kelemen Peter
Neijman Eric Wilhelmus Johannes Frederik
Zijderveld Johannes Maria
Johnson Kenneth H.
NOVA Chemicals (International ) S.A.
Nutter Nathan M.
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