Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1999-11-15
2000-10-10
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 57, 521 82, 521146, C08J 918
Patent
active
061302651
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for preparing particulate, expandable styrene polymers containing graphite particles.
Expanded polystyrene foams have been known for a long time and have proven themselves in many areas. Such foams are produced by foaming polystyrene particles impregnated with blowing agents and subsequently welding the resulting foam particles together to form moldings. An important field of application is thermal insulation in building and construction.
The expanded polystyrene foam boards used for thermal insulation usually have densities of about 30 g/l since the thermal conductivity of the expanded polystyrene foam has a minimum at these densities. To save material and space, it would be desirable to use foam boards having lower densities, in particular <15 g/l, for thermal insulation. The production of such foams is technically not a problem. However, foam boards having such a low density have a drastically reduced thermal insulation capability so that they do not meet the requirements of the thermal conductivity class 035 (DIN 18 164, Part 1).
It is known that the thermal conductivity of foams can be reduced by incorporation of athermanous materials such as carbon black, metal oxides, metal powder or pigments.
Thus, EP-A 372 343 describes polystyrene foams containing from 1 to 25% by weight of carbon black. The carbon black has a particle size of from 10 to 100 nm. The polystyrene foams described there are produced predominantly by the extrusion method and preferably have a density of 32-40 g/l. In addition, the production of particulate polystyrene containing blowing agent by mixing a carbon black concentrate in polystyrene together with blowing agents into a polystyrene melt and extruding and granulating the mixture is described. This is a rather complicated procedure.
WO 94/13721 describes similar foams in which the size of the carbon black particles is>150 nm.
EP-A 620 246 describes expanded polystyrene foam moldings containing a particulate athermanous material, in particular carbon black but also graphite. The density of the moldings is below 20 g/l. The incorporation of the particles into the moldings is preferably carried out by coating the surface of the prefoamed polystyrene beads or by embedding into the not yet foamed polystyrene granules. However, this distribution of the particles on the surface of the polystyrene particles greatly impairs the welding of the prefoamed beads and consequently leads to low-quality foams; in addition, the particles can be rubbed off the surface of the moldings. In both cases, the particles are not homogeneously distributed in the interior of the polystyrene particles.
It is an object of the present invention to provide a simple process for preparing expandable styrene polymers containing graphite which can be processed to form expanded polystyrene foams having a low density and a particularly low thermal conductivity and have good processing properties and good physical properties.
We have found that this object is achieved by suspension polymerization of styrene in the presence of graphite.
The present invention provides a process for preparing expandable styrene polymers containing graphite particles, which comprises polymerizing styrene, if desired together with 20% of its weight of comonomers, in aqueous suspension in the presence of graphite particles and adding a blowing agent before, during or after the polymerization.
The invention further provides expandable styrene polymers which contain from 0.05 to 25% by weight of homogeneously distributed graphite particles and are in the form of round beads having a mean diameter in the range from 0.2 to 2 mm.
In WO 95/10558, it is recommended that the compatibility of carbon black with polystyrene be improved by coating the carbon black with plasticizers. A number of methods of producing such foams are indicated, including the polymerization of styrene in the presence of coated thermal black, addition of blowing agents and cooling the resulting expandable particles. However, such a b
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Chemical Abstract, vol. 106, No. 8, Feb. 23, 1987, Mishima, Seizo et al, "Carbon black-containing polystyrene beads".
Chemical Abstracts, vol. 105, No. 26, Dec. 29, 1986, Bryk, M. T. et al: "Structure and properties of polystyrene prepared by polymerization in the presence of carbon fillers" & Polym., Compos., Proc., Microsymp. Macromol., 28.sup.th (1986).
Chemical Abstracts, vol. 110, No. 22, May 29, 1989, Bryk, M. T. et al: "Polystyrene synthesis in the presence of dispersed carbon fillers".
Batscheider Karl-Heinz
Glueck Guiscard
Hahn Klaus
Hohwiller Frieder
Husemann Wolfram
BASF - Aktiengesellschaft
Foelak Morton
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