Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-12
2003-02-04
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S458000, C524S460000, C525S083000, C525S085000, C525S086000, C525S087000, C525S243000, C525S261000, C525S310000, C525S313000, C525S316000
Reexamination Certificate
active
06515079
ABSTRACT:
The invention relates to a process for preparing thermoplastic molding compositions modified using a rubber.
Rubber-modified thermoplastics are used in producing a very wide variety of moldings and articles for daily use. Examples which may be mentioned are ABS (acrylonitrile-butadiene-styrene) copolymers and ASA (acrylonitrile-styrene-acrylate) copolymers. In these molding compositions use is often made of rubber particles which have been at least to some extent agglomerated.
By way of example, DE-A 24 27 960 describes processes for preparing impact-modified thermoplastic molding compositions by polymerizing butadiene or acrylates to give rubber particles and then agglomerating these by adding, to the rubber latex, an agglomerating agent based on an acrylate polymer dispersion. The agglomerated rubber latex is then grafted with styrene, acrylonitrile, methyl methacrylate or mixtures of these and, where appropriate, incorporated into a polymer matrix. An example of an agglomerating agent used is an aqueous dispersion of an ethyl acrylate copolymer built up from 96% by weight of ethyl acrylate and 4% by weight of methacrylamide.
WO 99/01489 relates to thermoplastic molding compositions with a low level of intrinsic color. The molding compositions have from 5 to 80% by weight of a graft polymer with bimodal particle size distribution. The bimodal particle size distribution is obtained by some degree of agglomeration of a rubber latex. Again, the agglomerating agents used are dispersions of copolymers, preferably copolymers of ethyl acrylate with methacrylamide. In preparing the graft polymer it is possible to use molecular weight regulators, but these cannot be used in preparing the agglomerating agent.
The known thermoplastic molding compositions have advantageous properties for use in a variety of application sectors. However, some application sectors demand that toughness values be further increased.
It is an object of the present invention to provide a process for preparing thermoplastic molding compositions leading to thermoplastic molding compositions with improved toughness values.
We have found that this object is achieved by means of a process for preparing thermoplastic molding compositions by
a) polymerizing, in aqueous emulsion, dienes, C
1
-C
12
-alkyl acrylates or mixtures of these, where from 0 to 30% by weight of these monomers may have been replaced by other copolymerizable monomers, and where from 0 to 10% by weight of these monomers may have been replaced by crosslinking monomers, to give a rubber latex with a glass transition temperature below −10° C.,
b) agglomerating, at least to some extent, the rubber latex obtained in a), by adding, as agglomerating agent, a dispersion of a polymer made from 80 to 100% by weight of C
1
-C
12
-alkyl acrylates and from 0 to 20% by weight of comonomers forming water-soluble polymers, where from 0 to 50% by weight of these monomers may have been replaced by other copolymerizable monomers,
c) polymerizing, in aqueous emulsion, from 10 to 90 parts by weight of styrene, &agr;-methylstyrene, (meth)acrylonitrile, C
1
-C
12
-alkyl acrylate, C
1
-C
6
-alkyl methacrylate or mixtures of these, where up to 30% by weight of these monomers may have been replaced by other copolymerizable monomers, in the presence of from 10 to 90% by weight of the agglomerated latex obtained in b), based on the solid, to give a graft polymer,
where the agglomerating agent is prepared by polymerizing the monomers mentioned in b) in the presence of from 0.001 to 10% by weight of a molecular weight regulator, based on the amount of the monomers mentioned in b).
According to the invention it has been found that the use of a molecular weight regulator during the preparation of the agglomerating agent gives the thermoplastic molding compositions prepared using this agglomerating agent better mechanical properties, in particular higher toughness values. When the agglomerating agent used according to the invention has been incorporated into the agglomerated rubber particles, these rubber particles are better able to absorb energy during deformation, for example during impact. This means that thermoplastic molding compositions comprising these rubber particles are tougher.
The average particle size in the agglomerating agent is preferably from 0.05 to 1 &mgr;m (weight average), and the particle size distribution here is monodisperse to broad. Mixtures of these agents may also be used.
The average particle size (weight average) in the latex to be agglomerated is preferably from 0.05 to 1 &mgr;m, particularly preferably below 0.3 &mgr;m, in particular below 0.2 &mgr;m. The particle size distribution may be from narrow to broad. After the agglomeration, some or all of the particles may have been agglomerated.
In a further stage d), from 5 to 70 parts by weight of the graft polymers obtained as a result of steps a), b) and c) may be blended with from 30 to 95 parts by weight of a polymer made from styrene, &agr;-methylstyrene, methyl methacrylate, (meth)acrylonitrile or vinyl chloride, or from mixtures of these, where up to 30% by weight of these monomers may have been replaced by other copolymerizable monomers.
The individual stages are described in more detail below.
Stage a)
In the first stage a), a rubber latex is prepared in a known manner, for example as described in DE-A-24 27 960 or WO 99/01489. The specification for the base rubber uses its glass transition temperature, which should be below −10° C., preferably below −20° C. The preferred diene, butadiene, is preferably the sole monomer used. Since butadiene-acrylate rubbers are advantageous for some purposes, it is also possible to use monomer mixtures made from butadiene and acrylate and preferably comprising up to 70% by weight of acrylate, based on the mixture. Preference is given to acrylates derived from alcohols having from 1 to 8 carbon atoms, for example ethyl acrylate, butyl acrylate or ethylhexyl acrylate. In the same way it is also possible to use the acrylates alone, where appropriate together with up to 10% by weight of bifunctional, crosslinking monomers. The resultant polymers are then ASA polymers, which are weathering-resistant. Where appropriate, up to 30% by weight of other comonomers may in each case also be present during the polymerization, examples being isoprene, styrene, acrylonitrile or vinyl ethers.
The polymerization is carried out in the usual way in aqueous emulsion at from 30 to 90° C., in the presence of emulsifiers, such as the alkali metal salts of alkyl- or alkylarylsulfonates, alkyl sulfates, fatty alcohol sulfonates or fatty acids having from 10 to 30 carbon atoms. It is preferable to use salts of alkylsulfonates or fatty acids having from 12 to 18 carbon atoms. The amounts preferably used of the emulsifiers are from 0.1 to 10% by weight, in particular from 0.5 to 4.0% by weight, based on the monomers. It is preferable also to use the usual buffer salts, such as sodium carbonate and sodium pyrophosphate. In addition, use may also be made of a protective colloid in combination with the emulsifier. Examples of protective colloids are polyvinyl alcohol and polyvinylpyrrolidone.
Use is likewise made of the usual initiators, such as persulfates or organic peroxides with reducing agents, and also, where appropriate, of molecular weight regulators, such as mercaptans, terpinols or dimeric &agr;-methylstyrene, which are added at the start of the polymerization or during its course. The ratio by weight of water to monomers is preferably from 4:1 to 3:7.
Further details may be found in the publications cited above.
Stage b)
In the second stage, the rubber latex obtained in stage a) is agglomerated. This is done by adding a dispersion of an acrylate polymer as agglomerating agent. It is preferable to use dispersion of copolymers of from 80 to 99.9% by weight acrylates of alcohols having from 1 to 4 carbon atoms, preferably of methyl acrylate or ethyl acrylate, with from 0.1 to 20% by weight of monomers forming water-soluble polymers, for example acrylic acid, met
Barghoorn Peter
Breulmann Michael
McKee Graham Edmund
Niessner Norbert
Ramsteiner Falko
BASF - Aktiengesellschaft
Keil & Weinkauf
Niland Patrick D.
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