Flame resistant polyvinylarene polymer compositions

Details Flame resistant polyvinylarene polymer compositions Flame resistant polyvinylarene polymer compositions

2002-03-01

2003-04-08

Wu, David W. (Department: 1731)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S430000, C524S500000, C524S524000

Reexamination Certificate

active

06545078

ABSTRACT:

The present invention relates to polyvinylarene polymer compositions having good flame resistant properties and adequate friability behaviour, to a process for their preparation and to a kit of parts.
Polyvinylarene polymers, such as polystyrene, are used in many applications. Some of these applications require good flame resistance. Examples are insulating and building materials.
From e.g. BE 8 901 199 it is known that coating of partly expanded polystyrene polymer particles with a silicate containing liquid can result in sandwich panels having improved flame resistance. However, Applicant has found that the articles formed from such coated polystyrene particles are friable, i.e. disintegrate easily at low levels of strain.
It is an object of the present invention to provide polyvinylarene polymer compositions having a good flame resistance, combined with an adequate degree of non-friability.
It has surprisingly been found that the object of the invention can be attained by preparing a composition containing polyvinylarene polymer particles, which are bound to each other by a mixture of a silicate and an organic polymer having a relatively high molecular weight. Such compositions have a good flame resistance, as well as an improved friability behaviour compared to polyvinylarene polymer particles merely coated with a silicate-containing liquid.
Accordingly, the present invention relates to a composition containing polyvinylarene polymer particles, which particles are bound to each other by a binder composition based on a silicate and an organic polymer having a weight average molecular weight of at least 500,000 g/mol, as measured in accordance with gel permeation chromatography.
Furthermore, the present invention also relates to the binder composition per se.
The polyvinylarene polymer particles for use in the present invention are typically based on vinylarene monomers like styrene, &agr;-methylstyrene, p-methylstyrene, dimethylstyrene, divinylbenzene and styrenic derivates such as ring-halogenated styrenes. Preferably, they are based on styrene, optionally mixed with at most 50% wt of any other monomer, based on the polyvinylarene polymer particles. Most preferably, the polyvinylarene polymer particle is polystyrene.
Polyvinylarene polymer particles are conveniently prepared by solution, suspension, emulsion or bulk polymerisation processes. Such processes have been extensively described in the art. The polymerisation reaction itself may be initiated thermally, via free radical polymerisation or via anionic polymerisation. Advantageously, the polyvinylarene polymer particles are prepared in a suspension polymerisation process in which vinylarene is polymerised in aqueous suspension in the presence of from 0.1 to 1% by weight of a free radical initiator. For the suspension polymerisation many methods and initiators are known. In this respect reference is made to, e.g., U.S. Pat. Nos. 2,656,334 and 3,817,965, and European patent application No. 488,040. The initiators mentioned therein are also applicable in the preparation of the particles of the present invention. In particular suitable are organic peroxy compounds, such as peroxides, peroxy carbonates and peresters. Typical examples of these peroxy compounds are C
6-20
acyl peroxides, such as decanoyl peroxide, benzoyl peroxide, octanoyl peroxide, stearyl peroxide, peresters, such as t-butyl perbenzoate, t-butyl peracetate, t-butyl perisobutyrate, tertiair-butyl (2 ethylhexyl) monoperoxycarbonate, hydroperoxides and dihydrocarbyl peroxides, such as those containing C
3-10
hydrocarbyl moieties, including di-isopropyl benzene hydroperoxide, di-t-butyl peroxide, dicumyl peroxide or combinations thereof. Other initiators different from peroxy compounds are also possible, e.g., &agr;,&agr;′-azobisisobutyronitrile.
The suspension polymerisation is suitably carried out in the presence of suspension stabilisers. Suitable suspension stabilisers are well known in the art and comprise poly(vinyl-alcohol), gelatine, agar, polyvinyl pyrrolidine, polyacrylamide, inorganic stabilisers such as alumina, bentonite, magnesium silicate or phosphates, like tricalciumphosphate and/or disodiumhydrogen phosphate, optionally in combination with any of the stabilising compounds mentioned earlier. The amount of stabiliser may suitably vary from 0.1 to 0.9% wt, based on the weight of the aqueous phase.
The suspension polymerisation is suitably carried out at two temperature stages, in which the temperature in the first stage is from 85 to 110° C. and in the second stage is from 115 to 140° C.
In order to render polyvinylarene polymer particles expandable, a blowing agent may be added before, during or after the polymerisation. Examples of suitable blowing agents are C
2
-C
6
hydrocarbons or halogenated hydrocarbons, water, inorganic blowing agents, such as carbon dioxide or, nitrogen or air. Further examples are so-called chemical blowing agents, i.e. compounds that release gaseous components upon heating. The latter compounds are usually solid and are particularly used in bulk polymerisation techniques. Examples are e.g. carbon dioxide or nitrogen-liberating solid compounds. The amount of blowing agent to be used depends very much on the kind of blowing agent applied. For hydrocarbon blowing agents, typical amounts are 1-8% by weight, based on the weight of the polymer particle.
It will be appreciated that the polyvinylarene polymer particles may contain additional additives, such as flame-retarding compounds, dyes, fillers, lubricants, stabilisers, regulators for foam porosity, nucleating agents such as waxes, like polyethylene wax or paraffin wax, which are well-known in the art.
The silicate for use in the present invention is suitably selected from alkali metal silicates, such as sodium silicate, potassium silicate, lithium silicate, or may be selected from quartenary ammonium silicates. The use of sodium silicate is preferred. The weight of the silicate with respect to the weight of the polyvinylarene polymer particles in the compositions of the present invention preferably varies from 2:1 up to 1:2. Most preferably, this ratio is around 1:1.
It is preferred to apply the silicate to the polyvinylarene polymer particles in the form of a silicate-containing liquid. The use of “water glass” is preferred. Water glass is a substance well known in the art and represents an aqueous solution of a water soluble alkali metal silicate, preferably sodium silicate. Taking e.g. sodium silicate, the silicate in water glass is commonly assigned the chemical formula Na
2
O.(x)SiO
2
wherein x can vary widely, but is usually in the range of from 0.5 to 5.0 and more commonly in the range of from 1.0 to 4.0. The amount of alkali metal silicate in the water glass solution to be used may vary. Preferably, water glass solutions having a viscosity below 500 Centipoise (at 23° C.) are used, more preferably below 300 Centipoise, most preferably below 200 Centipoise.
The organic polymer to be applied in the binder of the compositions of the present invention must have a weight average molecular weight of at least 500,000 g/mol. This molecular weight is determined by analysing the polymer samples at 25° C. by gel permeation chromatography, using tetrahydrofuran as mobile phase and polystyrene calibration. Subsequently, the molecular weight of the organic polymer is calculated from the polystyrene mass using the Mark Houwink equation. The values K=0.000141 dL/g and a=0.7 should be used for polystyrene and K=0.000350 dL/g and a=0.63 for the organic polymer. The Mark-Houwink equation (also called Mark-Houwink-Sakurada equation) is well known in the art and can be found in e.g. “J. Brandrup en E. H. Immergut, Polymer handbook, third edition”, page VII/1 and further. Preferably, the weight average molecular weight is at least 650,000 g/mol, most preferably at least 700,000 g/mol. In this patent document, an “organic polymer having a weight average molecular weight of at least 500,000 g/mol” and a “high molecular weight organic polymer” ar

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