Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-11-15
2002-01-22
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...
C521S079000, C521S082000, C521S098000, C521S146000, C521S056000, C521S059000, C521S907000
Reexamination Certificate
active
06340713
ABSTRACT:
The present invention relates to particulate, expandable styrene polymers containing graphite particles, their production and foams produced therefrom.
Expanded polystyrene foams have been known for a long time and have proven themselves in many fields. Such foams are produced by foaming polystyrene particles impregnated with blowing agents and subsequently welding together the foam particles produced in this way to give moldings. A significant application area is thermal insulation in building and construction.
In many applications of foams, in particular in building and construction, it is a requirement that the foams be self-extinguishing. Although it is known that this can be achieved by addition of flame retardants, e.g. bromine compounds, whether a foam passes a particular burning test depends on various factors such as composition and density of the foam, type and amount of flame retardant and also type and amount of further additives.
The foam boards made of expanded polystyrene foam which are used for thermal insulation usually have densities of at least 30 g/l, since the thermal conductivity of the expanded polystyrene foam has a minimum at these densities. To save material, 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 not a problem in technical terms. However, such foam boards having a lower density have a drastically worse thermal insulation performance, so that they do not meet the requirements for 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 and a surface area of from 10 to 1500 m
2
/g. The polystyrene foams described there are predominantly produced by the extrusion method and preferably have a density of 32-40 g/l, as is typical for these foams. The addition of flame retardants is mentioned, but the expanded polystyrene foams described in the examples containing 1.7% by weight of hexabromocyclododecane do not pass the burning test B2 in accordance with DIN 4102.
WO 94/13721 describes similar foams in which the size of the carbon black particles is >150 nm.
EP-A 620 246 describes moldings made of expanded polystyrene foam which contain a particulate athermanous material, in particular carbon black, and also graphite. The density of the moldings is less than 20 g/l. The particles are preferably incorporated into the moldings by surface coating of the prefoamed polystyrene beads or by embedding into the not yet foamed polystyrene granules. However, this distribution of the particles on the surface leads to severe impairment of the welding together of the prefoamed beads and consequently to foams of low quality; in addition, the particles can be rubbed off from the surface of the molding. In both cases, the particles are in any case not homogeneously distributed in the interior of the polystyrene particles; an addition of flame retardants is not described.
A similar process is described in GB-A 1 588 314, according to which antistatic polystyrene foams are produced by coating unfoamed or prefoamed particles with a graphite suspension.
It is an object of the present invention to provide expandable styrene polymers containing graphite particles which can be processed to give expanded polystyrene foams which have both a low density and a low thermal conductivity and have good processing properties, good physical properties and, in particular, very good flame retardant properties.
We have found that this object is achieved by particulate, expandable styrene polymers containing homogeneously distributed graphite particles and can be processed to give foams which have a density of <35 g/l and are preferably self-extinguishing and pass the burning test B2 (in accordance with DIN 4102).
The invention also provides processes for producing the expandable styrene polymers and also provides the expanded polystyrene foams produced therefrom.
For the purposes of the present invention, expandable styrene polymers are styrene polymers containing blowing agents.
The polymer matrix present in the expandable styrene polymers of the present invention is, in particular, homopolystyrene or a styrene copolymer containing up to 20%, based on the weight of the polymers, of ethylenically unsaturated comonomers, in particular alkylstyrene, divinylbenzene, acrylonitrile or &agr;-methylstyrene. Blends of polystyrene and other polymers, in particular with rubber and polyphenylene ether are also possible.
The styrene polymers can contain the customary and known auxiliaries and additives, for example flame retardants, nucleating agents, UV stabilizers, chain transferrers, blowing agents, plasticizers, pigments and antioxidants.
The expandable particles are coated with the customary and known coating materials, for example metal stearates, glyceryl esters and finely divided silicates.
The particle size is preferably in the range 0.2-2 mm.
The graphite used preferably has a mean particle size of from 1 to 50 &mgr;m, in particular from 2.5 to 12 &mgr;m, a bulk density of from 100 to 500 g/l and a specific surface area of from 5 to 20 m
2
/g. Either natural graphite or milled synthetic graphite can be used. The graphite particles are preferably present in the styrene polymer in amounts of from 0.05 to 25% by weight, in particular from 2 to 8% by weight. Surprisingly, it has been found that graphite particles are effective even in amounts of less than 0.5% by weight.
A problem associated with the use of graphite particles is the ready flammability of the expanded polystyrene foams containing graphite particles. Thus, graphite-containing polystyrene foams have hitherto not been able to pass the burning tests required for use in building and construction (B1 and B2 in accordance with DIN 4102).
To rectify this defect, flame retardants, particularly ones based on organic bromine compounds, are added to the expandable styrene polymers in a preferred embodiment of the invention. The bromine compound (without a synergist) should be added in an amount of more than 3% by weight, based on the weight of the expandable styrene polymers. B1 and B2 are not passed when the customary amount of flame retardant is used. The organic bromine compounds should have a bromine content of ≧70% by weight.
Surprisingly, this amount of flame retardants leads to no deterioration whatever in the mechanical properties of the expanded polystyrene foams containing carbon black.
Particularly suitable flame retardants are aliphatic, cycloaliphatic and aromatic bromine compounds, for example hexabromocyclododecane, pentabromomonochlorocyclohexane and pentabromophenyl allyl ether.
The effect of the bromine-containing flame retardants is considerably improved by addition of C—C- or O—O-labile organic compounds. Examples of suitable flame retardant synergists are bicumyl and dicumyl peroxide. A preferred combination comprises 0.6 to 5% by weight of an organic bromine compound and 0.1 to 1.0% by weight of the C—C- or O—O-labile organic compound.
The expandable styrene polymers of the present invention can be produced by various methods.
In a preferred embodiment, the graphite particles are mixed with a melt of the styrene polymer, preferably in an extruder. At the same time, the blowing agent is metered into the melt. The graphite particles can also be compounded into a melt of styrene polymer containing blowing agent; in this case, it is convenient to use oversize and undersize fractions of polystyrene beads containing blowing agent formed in a suspension polymerization. The polystyrene melt containing blowing agents and graphite particles is extruded and granulated to form granules containing blowing agent. Since graphite has a strong nucleating action, the compounded polystyrene should be quickly c
Braun Frank
Glück Guiscard
Hahn Klaus
Kaempfer Knut
Naegele Dieter
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