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
2003-01-22
2004-11-02
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S080000, C525S087000, C525S064000, C525S071000, C525S084000
Reexamination Certificate
active
06812283
ABSTRACT:
The invention relates to a process for the agglomeration of at least one rubber (A), dispersed in an aqueous phase, by the addition of an aqueous dispersion of at least one agglomerating polymer (B).
Methods of enlarging rubber particles are known to the person skilled in the art. One variant comprises agglomeration effected during polymerization of the rubber-forming monomers. Another method comprises the agglomeration of the substantially fully polymerized dispersed rubber. In the latter process there is also the problem that the dispersion, in addition to the desired agglomeration, forms coagulum (unstable, being over-large agglomerate). The coagulum impairs the mechanical properties of the end product. Furthermore, coagulation reduces the yield of product. High yields are particularly important, especially in the case of plants operated on a large scale. In addition, when coagulum forms, the plant must be cleaned more often. Thus it is always desirable to minimize coagulation.
In EP-A 77038 describes the agglomeration of a dispersed rubber in the presence of a dispersion of an acid-group-containing agglomerating latex and in the presence of a neutral electrolyte. Since the agglomerating latex contains free acid groups, the agglomeration must be carried out at a pH of higher than 7, in order to dissociate the acid. This process suffers from the drawback that, owing to the free acid groups in the latex, the efficiency of the agglomeration is strongly influenced by pH fluctuations. The pH must thus be tuned very finely in order to obtain reproducible results. This is feasible in large-scale production plants only at high expense. The chlorides proposed as neutral electrolytes suffer from the further drawback that they corrode the reaction vessels and pollute the wastewater, and even residues of these salts lead to corrosion problems during processing. It was also known from EP-A 517 539 that rubbers can be agglomerated with emulsion polymers containing at least 30% of units containing carboxylic acid groups. U.S. Pat. No. 3,049,501 discloses an agglomeration method in which polyvinyl methyl ether containing acid groups is used at a pH from 8 to 11. GB-A 859 361 proposes an agglomerating latex free from acid groups, together with an ammonium salt electrolyte.
The processes proposed in these publications do not adequately prevent the formation of coagulum. Moreover, the use of volatile electrolytes may lead to problems such as foaming of the reaction mixture.
Agglomerating latices exhibiting no free acid groups and capable of causing agglomeration intrinsically, i.e., independently of whether the pH is above 7 during agglomeration or not, have been disclosed in H.-G. Keppler, H. Wesslau, J. Stabenow, Angew. Makromol. Chem. 2 (1968) pages 1 to 25.
It is an object of the invention to find a process by means of which dispersed rubber particles can be efficiently agglomerated, especially in large-scale production, with the formation of coagulum minimized.
Accordingly we have found a process for the agglomeration of at least one rubber (A), dispersed in an aqueous phase, by the addition of a dispersion of at least one agglomerating polymer (B) in aqueous phase, in which an agglomerating polymer containing substantially no free acid groups is used and in which the agglomeration is carried out in the presence of at least one basic electrolyte. We have also found graft polymers (C) obtainable from said agglomerated rubbers. We have also found thermoplastic molding compositions (D) which comprise said graft polymers C and can be used for the preparation of shaped articles, films or fibers.
The rubbers A underlying the process of the invention can be multifarious. For example silicone rubbers, olefin rubbers, such as ethylene, propylene, ethylene/propylene, EPDM, diene, acrylate, ethylene-vinyl acetate rubbers or ethylene-butyl acrylate rubbers or mixtures of two or more of these rubbers can be used. Preferably, however, diene rubbers are used. Special preference is given as A to diene rubbers composed of
a1) from 50 to 100% by weight of at least one diene having conjugated double bonds and
a2) from 0 to 50% by weight of one or more other monoethylenically unsaturated monomers,
the sum of the percentages by weight being 100.
Suitable dienes having conjugated double bonds, a1), are, in particular, butadiene, isoprene and the halogen-substituted derivatives thereof, e.g., chloroprene. Preference is given to butadiene or isoprene, particularly butadiene.
The other monoethylenically unsaturated monomers a2) which may be present in diene rubber A at the expense of monomers a1) may be, for example:
vinylaromatic monomers such as styrene and styrene derivatives of the general formula
in which R
1
and R
2
independently stand for hydrogen or C
1
-C
8
alkyl;
acrylonitrile, methacrylonitrile;
C
1
-C
4
-alkyl esters of methacrylic acid or acrylic acid such as methyl methacrylate, and also the glycidyl esters glycidyl acrylate and methacrylate;
N-substituted maleimides such as N-methyl-, N-phenyl- and N-cyclohexylmaleimides;
acrylic acid, methacrylic acid, and dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid and also their acid anhydrides such as maleic anhydride;
nitrogen-functional monomers such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, vinylimidazole, vinylpyrrolidone, vinylcaprolactam, vinylcarbazole, vinylaniline, acrylamide and methacrylamide;
aromatic and araliphatic esters of acrylic acid and methacrylic acid such as phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, 2-phenylethyl acrylate, 2-phenylethyl methacrylate, 2-phenoxyethyl acrylate and 2-phenoxyethyl methacrylate;
unsaturated ethers such as vinyl methyl ether,
and mixtures of these monomers.
Preferred monomers a2) are styrene, acrylonitrile, methyl methacrylate, glycidyl acrylate and methacrylate or butyl acrylate.
Generally, diene rubbers A exhibit a glass transition temperature Tg of less than 0° C. (determined as specified in DIN 53765).
The synthesis of rubbers A is known to the person skilled in the art or may be carried out by methods known to the person skilled in the art. Thus diene rubbers A can be prepared in a first step in which they are not formed in a particulate state, for example via solution polymerization or gas-phase polymerization, and are then dispersed in the aqueous phase in a second step (secondary emulsification).
Heterogenous, particle-forming polymerization processes are preferred for the synthesis of rubbers A. Dispersion polymerization can be carried out in known manner by, say, the emulsion, inverse emulsion, miniemulsion, microemulsion, or microsuspension polymerization method.
Dispersion polymerization can be carried out in an organic solvent or an aqueous phase.
The rubbers A are preferably prepared in aqueous phase. By aqueous phase is meant a solution, emulsion or suspension of the corresponding monomers or polymers in water or in a solvent mixture containing a large proportion, i.e., at least 20% by weight, of water.
In one preferred embodiment, polymerization is carried out by the emulsion method, in which the monomers are polymerized in aqueous emulsion at from 20 to 100° C., preferably at from 50 to 80° C., in which case all components of the batch can be combined (batch process), or the monomer alone or an emulsion of monomer, water and emulsifiers can be gradually added to the other components (feed process). Furthermore, it is possible to carry out the reaction by a continuous method. Preference is given to the feed process.
Suitable emulsifiers are for example alkali metal salts of alkyl- or alkylaryl-sulfonic acids, alkyl sulfates, fatty alcohol sulfonates, salts of higher fatty acids containing from 10 to 30 carbons, sulfosuccinates, ether sulfonates or resin soaps. Preferably, use is made of the alkali metal salts of alkylsulfonates or fatty acids containing from 10 to 18 carbons. Their concentration is usually from 0.5 to 5% by weight, based on monomers a) (sum of monomers a1 and a2).
Preferably, the preparation
Breulmann Michael
Duijzings Wil
Korb Hardy
Niessner Norbert
Oepen Sabine
BASF - Aktiengesellschaft
Choi Ling-Siu
Keil & Weinkauf
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