Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-07-24
2002-10-15
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S092000
Reexamination Certificate
active
06465533
ABSTRACT:
The invention relates to particulate, expandable styrene polymers (EPS) capable of being processed into hard foamed plastic materials having a fine cellular structure and a small density, containing, therefore, at least one foaming agent, and comprising at least aluminum in particle shape for improving their thermal insulation properties. Furthermore, the invention relates to a method for producing such expandable styrene polymer particles.
Styrene polymer particles (EPS) of the above mentioned type are known (EP 620,246 A). It deals with polystyrene particles which contain a foaming agent and can be expanded by heating with steam (pre-foaming procedure), thus multiplying their volume, and which can be processed afterwards into shaped parts of any shape, particularly into blocks, by heat-sealing. Preferred applications of such foams of polystyrene particles are heat insulation plastics, e.g. for the facade walls of buildings, cold storages or packaging materials, the thermal insulation effect of the foamed plastic being of decisive importance for its quality. Therefore, it has already been suggested to reduce the ability of heat conduction of hard foamed polystyrene plastic materials by adding some additives to the styrene polymer which reduce the permeability for infrared radiation through the foamed plastic. From the above-mentioned document it is known to this end to use athermanous materials, i.e. infrared radiation absorbing materials, for which purpose metal oxides, e.g. Al
2
O
3
, non-metallic oxides, aluminum powder or carbon black or graphite are suggested. In particular, these additives should be used for coating the surface of the polystyrene particles. However, this method has the disadvantage that an undefined proportion of this coating will be lost during processing which leads to a likewisely undefined reduction of heat insulation and, moreover, to contamination of waste water. Furthermore, such a surface coating of the polystyrene particles will result in a substantial impairment of the heat-sealing properties of the polystyrene particles due to a separating effect which in turn, leads to higher heat conductivity and to a reduced mechanical strength of the respective part of hard foamed plastic.
Certainly, it is also known from the above-mentioned document to embed athermanous materials into not yet foamed granules for forming the hard polystyrene foam, particularly together with a foaming agent. However, the results obtained were not sufficient up to now, because difficulties occurred with embedding the athermanous materials. Normally, EPS is produced by suspension polymerization. This is done by suspending styrene in water while stirring so that droplets are formed which are polymerized by means of reaction ini-produced by suspension polymerization. This is done by suspending styrene in water while stirring so that droplets are formed which are polymerized by means of reaction initiators and are impregnated with the foaming agent in the course of the procedure. The athermanous materials, however, cannot simply be added, because these materials are insoluble in styrene and are, therefore, not absorbed by the droplets. Likewise, introducing the athermanous materials into EPS by mixing these materials with a melt of polystyrene in an extrusion process was not satisfying. In this process, polystyrene is heated together with the additives and the foaming agent up to a temperature above the glass point of polystyrene, is mixed by friction, cooled and pressed through a perforated die. Immediately after leaving the die, the extruded strand has to be cooled by a bath of cold water in order to prevent foaming. The cooled strand is then granulated into short individual particles. However, the problem occurs that the suggested athermanous materials have a strong nuclei forming effect so that foaming of the material cannot be prevented after leaving the die. This nuclei forming effect depends on concentration, size, shape and composition of the nuclei forming material as well as on the melt temperature, the content of foaming agent and the formulation of the polystyrene used.
These properties of the athermanous materials require subaqueous granulating under pressure in order to prevent foaming of the granular particles. This involves a substantially higher expenditure than the usual granulation of a strand, and it is not possible to attain particle sizes of the granules below 1 mm by this type of granulation. Furthermore, the admixture of carbon black or graphite increases inflammability of the foamed particles which makes it necessary to increase the addition in flame protection systems to be able to achieve fire characteristics admissible in the field of civil engineering. Moreover, it is to be observed that produced insulating plates may heat up strongly and, thus, will deform when stored in open air and sun shine due to the property of athermanous materials, particularly carbon black or graphite, of absorbing infrared radiation.
The procedure described (EPS) differs basically from the production of plates of foamed plastic material (XPS) wherein foaming occurs directly at the nozzle of an extruder (DE 195 45 097 A1). In this type of process, inorganic materials are added in an aimed manner to the mass of plastic material to be extruded in order to provoke foaming of the plastic mass after leaving the nozzle. Thus, adding athermanous materials, which provoke precisely this foaming, is no problem in this process.
It is an object of the invention to improve particulate, expandable styrene polymers (EPS) of the type described at the outset in such a manner that the difficulties discussed are avoided, in particular so that no difficulties arise with embedding heat insulating aluminum particles, and that heat insulating properties as well as the sensitivity to sun rays of the styrene polymers produced are improved. The invention solves this problem in that the styrene polymer particles contain the aluminum particles incorporated in a homogetiators distribution as an infrared radiation reflecting material, the main proportion of the aluminum particles being in the form of platelets having a size between 1 and 15 &mgr;m. In a distribution as an infrared radiation reflecting material, the main proportion of the aluminum particles being present as platelets having a maximum size of between 1 and 15 &mgr;m each. In a surprising manner it has been shown that the admixture of aluminum platelets of the above-mentioned size, when distributed homogeneously in the styrene polymer, does not only not impair the fine cellular structure of the expanded styrene polymer particles in any way, which is attained by appropriate organic nuclei forming agents, e.g. paraffins, chlorparaffins, Fischer-Tropsch waxes as well as ester and amides of fatty acids, but that also substantially improved heat insulation characteristics of the styrene polymer particles and of the hard foamed plastic materials produced from them will result. Thus, the aluminum particles do not disturb the nuclei formation. Above all, the shape of platelets of the aluminum particles results in a larger surface area of the aluminum particles as compared to a spherical shape and, thus, they act strongly reflecting to incident infrared radiation. Optimum result will be obtained if the maximum diameter of the aluminum platelets amounts to at least the 10-fold of the medium thickness of the platelets. It may be put down to the strong reflection effect of the embedded aluminum platelets that the above-mentioned disadvantage of known insulating plates produced from EPS styrene polymer particles, i.e. to heat up considerably by sun radiation and then to deform, is avoided, because, due to the reflection of the infrared radiation, no remarkable absorption of it takes place.
For producing a dielectric material for a radar reflector it is known (JP-A-56010432 and Derwent Abstract AN 1981-22167D) to impregnate polystrene with a foaming agent and to add aluminum platelets having a surface area of 0.4 to 1 mm
2
. The mixture thus produced i
Arduini-Schuster Mariacarla
Eberstaller Roman
Kuhn Joachim
Foelak Morton
SUNPOR Kunstoff Ges. m.b.H.
Townsend and Townsend / and Crew LLP
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