Polymer particles

Details Polymer particles Polymer particles

2000-07-19

2003-03-04

Cain, Edward J. (Department: 1714)

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...

C523S218000, C524S445000, C524S492000, C524S493000

Reexamination Certificate

active

06528570

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polymer particles containing a polymer of a vinylarene monomer and a foaming agent and to a process for their preparation.
Particles that contain a polymer of a vinylarene monomer and a foaming agent are generally known as expandable polymers. A well-known expandable polymer 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
3-6
hydrocarbon, in particular pentane. The expandable polystyrene is used for making foamed articles that are produced by expanding the polystyrene particles. In the expansion process the foaming agent is (partially) released and may be emitted into the environment. Such emissions are regarded undesirable and ways are sought to reduce the amount of hydrocarbon foaming agent.
BACKGROUND OF THE INVENTION
In DE 196 10 330 the use of zeolites in polymer foams, such as polystyrene foams, is disclosed. Herein, zeolite is added to the molten polymer. The resulting mixture is heated to cause the crystal water of the zeolite to evaporate, thereby creating little gas nuclei. These nuclei serve to collect hydrocarbon foaming agent that is added to the composition. The actual expansion thus still requires the presence of a hydrocarbon foaming agent.
It was an object of the present invention to obtain expandable polymer particles containing a polymer of a vinylarene monomer, in which the amount of water that can be used as foaming agent is such that one may refrain from incorporating any amount of hydrocarbon foaming agent.
Surprisingly, it was found that this object can be achieved by a polymer particle, containing a porous silicate compound, which polymer particle contains at least 1.5% by weight of water.
SUMMARY OF THE INVENTION
Accordingly, the present invention relates to polymer particles containing a polymer of a vinylarene monomer, a porous silicate compound and at least 1.5% by weight of water, based on the weight of vinylarene, water and porous silicate compound, wherein the porous silicate compound is selected from alumino silicates and amorphous silica particles.
Polymer particles according to the present invention have satisfactory expandability properties without the need to contain an organic foaming agent. They can be expanded to yield pre-expanded particles, which are optionally treated further to obtain foamed articles.
Suitable vinylarene monomers to be used in the present process are well known in the art and can suitably be selected from styrene, &agr;-methylstyrene, chlorostyrene, dimethylstyrene, vinyltoluene and similar styrenic derivatives. Preferably, the vinylarene is styrene, optionally mixed with at most 50 weight % of any other vinylarene, based on the total amount of vinylarene incorporated in the final polymer. Most preferably, styrene is used as the sole monomer.
The porous silicate compound is selected from alumino silicates and amorphous silica particles.
Examples of alumino silicates are clays and zeolites. Clays are hydrated alumino silicates of the generalized formula Al
2
O
3
.SiO
2
.H
2
O. Examples are kaolinite, montmorillonite and bentonite.
Zeolites are substances well known in the art. Reference is made to e.g. D. W. Breck “zeolite molecular sieves”, which contains extensive background on zeolites. The term “alumino silicate zeolite” is used to indicate a collection of crystalline, hydrated alumino silicates with small, uniform pores and a big inner surface. The empirical formula of these zeolites is M
2

O.Al
2
O
3
.xSiO
2
.yH
2
O, wherein M is a cation, n is the cation valency, and x and y are the amount of respectively SiO
2
and crystal water molecules. Suitably, M is selected from group I or II elements in particular sodium, potassium, magnesium, calcium, strontium and barium. M may also be selected from ammonium, alkylammonium or hydrogen cations.
BEST MODE
In the present invention, it is preferred to use alumino silicate zeolites having a Si/Al molar ratio of 1 to 30, preferably from 1 to 4. Particularly good results have been obtained with zeolite A wherein part of the sodium cations have been exchanged for calcium cations. Further good results have been obtained with zeolite Y in which part of the sodium cations have been exchanged by ammonium cations.
The porous silicate compound may also be an amorphous silica particle. Such compounds are suitably built from more than 95% by weight of SiO
2
, more suitably from more than 98% by weight. Examples are compounds sold under the trade name “SIPERNAT” or “AEROSIL” by Degussa. Good results have been obtained with silica compounds having the trade name “SIPERNAT 50” and “SIPERNAT 50 S”. They both contain 98.5% by weight SiO
2
, based on the substance which has been dried for 2 hours at 2000° C. Also good results are obtained with “AEROSIL 200”, which contains more than 99.8% by weight SiO
2
, based on the substance which has been dried for 2 hours at 2000° C. (AEROSIL is a trademark).
The average particle size of the porous silicate compound is thought to have an effect on the cell size and cell size distribution of the pre-expanded polymer particles and resulting foam. In this patent document, the average particle size is understood to be the value at which 50 volume % of the particles have a smaller particle size and 50 volume % of the particles have a bigger particle size, as measured by laser light diffraction using a Malvern Mastersizer Microplus apparatus. It is preferred to use a porous silicate compound having an average particle size of 50 &mgr;m or less, preferably from 0.1 &mgr;m to 40 &mgr;m, more preferably from 0.5 &mgr;m to 20 &mgr;m. The use of porous silicate compounds having an average particle size between the cited ranges results in foams having an improved strength, improved fusion and less shrinkage.
The porous silicate compound should be present in the polymer particles of the current invention in an amount capable of adsorbing at least 1.5% by weight of water. Typically, the amount used is from 0.1 to 10% by weight, based on the weight of vinylarene, water and porous silicate compound. Preferably, the amount is from 0.5 to 5% by weight. If the amount of porous silicate compound is too low, the water-adsorbing capacity of the resultant particle may remain unsatisfactorily low. If the amount is too high, the mechanical properties of the foamed article, made from the resultant particles, may be adversely affected.
The amount of water present in the polymer particles of the current invention is at least 1.5% by weight, based on the weight of the vinylarene, water and porous silicate compound, as measured in accordance with the Karl Fischer method. Preferably, the amount is from 2 to 20% by weight, more preferably from 3 to 11% by weight. Such particles are expandable without the presence of a C
3-6
hydrocarbon foaming agent. This makes that the particles can contain less than 0.5% weight of a C
3-6
hydrocarbon, more preferably less than 0.25% weight, based on weight of the particle. Most preferably, the particles do not contain any C
3-6
hydrocarbon.
It will be appreciated that polymer particles according to the invention may further contain several additives or coatings in effective amounts. Such additives include dyes, fillers, stabilizers, flame retarding compounds, nucleating agents, anti-static compounds and lubricants. Of particular interest are coating compositions containing glycerol or metal carboxylates. Such compounds reduce the tendency of the particles to agglomerate. Suitable carboxylates are glycerol mono-, di- and/or tristearate and zinc stearate Examples for such additive compositions are disclosed in GB-A-1,409,285. The coating compositions are deposited onto the particles via known methods, e.g., via dry-coating in a ribbon blender or via a slurry or solution in a readily vaporizing liquid.
The particles advantageously have an average diameter of 0.1 to 6 mm, preferably from 0.4 to 3 mm.
In addition to the polymer particle per se, the present i

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