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
2000-12-12
Teskin, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521146, 524157, 524158, 524317, 524819, 524836, C08J 920, C08J 912
Patent
active
06160027&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the preparation of polymer particles containing a polymer of a vinylarene monomer and a physical foaming agent, and to such polymer particles.
Particles that contain such a polymer and foaming agent are generally known as expandable polymer particles. A well-known type of expandable polymer particles is expandable polystyrene. Expandable polystyrene is produced on a commercial scale by suspension polymerization. The foaming agent is usually a low-boiling hydrocarbon, such as a C.sub.3 -C.sub.8 hydrocarbon, in particular pentane isomers. The expandable polystyrene is used for making foamed articles that are produced by expanding the polystyrene particles. In the expansion process the hydrocarbon foaming agent is released and may be emitted into the environment. Such emissions are regarded undesirable and ways are sought to avoid such emissions. One way is to recover or burn the emitted hydrocarbon. Another way is to reduce the amount of hydrocarbon foaming agent in the expandable polymer particles.
In U.S. Pat. No. 5,096,931 expandable polystyrene is described which contains polystyrene, a small amount of a polar polymer, some water and a reduced amount of hydrocarbon foaming agent. Although the content of hydrocarbon foaming agent has been reduced such agent must still be present to achieve satisfactory expansion.
GB-A-1,106,143 discloses a process for preparing water-expandable polystyrene particles by mixing by vigorous mechanical agitation styrene monomer, water and an emulsifier with a free-radical initiator to obtain an emulsion containing small droplets of water. Subsequently, the emulsion is suspended in an aqueous phase and the suspension obtained is subjected to polymerisation. In order to achieve a satisfactory expansion certain amounts of organic foaming agents are included.
In experiments to verify the merits of the teaching of the above GB patent it was found that the finely dispersed water droplets obtained in the first emulsion tend to coalesce and form bigger droplets during polymerisation. In an experiment in GB-A-1,106,143 it is confirmed that droplets bigger than 40 .mu.m cause unsatisfactory foamed articles after expansion. Vigorous agitation is apparently necessary in this known-process to create and maintain the finely dispersed water droplets. However, it is awkward to stir in commercial operation at such high energy input.
Hence, it would be desirable if the tendency of the water droplets to coalesce could be reduced.
Surprisingly, it was found that the tendency for the water droplets to grow could be reduced by creating a viscous water-containing emulsion before completely polymerising the vinylarene monomer in suspension polymerisation. This makes it furthermore possible to stir less vigorously when emulsifying the water in the (partly polymerised) vinylarene monomer. Stirring can be carried out at an energy input equivalent to or less than 500 rotations per minute for a 70 l reactor, even at an energy input equivalent to or less than 350 rotations per minute for a 70 l reactor.
Accordingly, the present invention provides a process for the preparation of polymer particles containing a vinylarene polymer by suspension polymerisation, which process comprises: 70%, based on the vinylarene monomer, to yield a pre-polymerised mass, which pre-polymerised mass further contains water emulsified therein and an emulsifier, which pre-polymerisation is carried out with water already present or before water is added; suspended droplets; and complete monomer conversion to yield suspended polymer particles.
A pre-polymerised mass differs from a mixture of polymerised vinylarene and vinylarene monomer, in that the first has a monomodal molecular weight distribution while the latter will in general have a bimodal distribution. For many applications, the latter will be disadvantageous in that the physical properties of the material will vary over a wider range. In order to obtain a monomodal distribution for a mixture of polymerised vinylarene and viny
REFERENCES:
patent: 5096931 (1992-03-01), Wittenberg et al.
Crevecoeur Jeroen Joost
Neijman Eric Wilhelmus Johannes Frederik
Nelissen Laurentius Nicolaas Ida Hubertus
Zijderveld Johannes Maria
Johnson Kenneth H
NOVA Chemicals (International ) S.A.
Teskin Fred
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