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
2001-09-26
2003-09-16
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S071000, C525S077000, C525S084000, C525S087000, C525S263000
Reexamination Certificate
active
06620883
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the preparation of graft rubber polymers of the ABS type, more specifically to the preparation by emulsion polymerization.
SUMMARY OF THE INVENTION
The invention relates to a process for the preparation of graft rubber polymers of the ABS type by emulsion polymerization according to the so-called fed batch process, in which latexes having markedly reduced residual monomer contents are obtained, and to compositions containing the mentioned graft rubber polymers. The polymers so prepared have no negative effects at all on other properties.
BACKGROUND OF THE INVENTION
ABS molding compositions are two-phase plastics that contain:
I. a thermoplastic copolymer of styrene and acrylonitrile, in which the styrene may be replaced wholly or partially by &agr;-methylstyrene or methyl methacrylate; this copolymer, also known as SAN resin or matrix resin, forms the external phase;
II. at least one graft rubber polymer (of the ABS type) that has been prepared by the graft reaction of one or more of the monomers mentioned under I. onto butadiene homo- or co-polymer (“graft base”). This graft polymer (“elastomer phase” or “graft rubber”) forms the disperse phase in the matrix resin.
While the matrix resin I can easily be prepared by free-radical polymerization in solution or in suspension or by mass polymerization, it is necessary in order to produce glossy moldings to prepare the graft rubber polymer II by emulsion polymerization using rubber latexes having the necessary mean particle diameters, in order to obtain specific finely divided polymers having mean particle diameters d
50
of approximately from 0.08 to 0.5 &mgr;m.
A critical point in the case of emulsion polymerization, especially in the preparation of rubber-containing graft polymers using the so-called fed batch process (feeding of the monomers to a rubber latex located in the reactor in the course of a batch reaction) is the often very high content of unreacted monomers at the end of the reaction.
Although methods of lowering the residual monomer content in emulsion polymers are indicated in the literature, they are not suitable for achieving low residual monomer values in graft rubber polymers while retaining the other properties that are necessary.
For example, DE-A 19 741 188 describes the use of long-chained, surface-active initiator components for reducing the residual monomers. WO-A 00/12569 recommends the use of combinations of an oxidizing agent, a reducing agent prepared from aldehyde and inorganic dithionite, and polyvalent metal ions for the treatment of polymer dispersions, while WO-A 00/14123 describes treatment using an initiator system consisting of an oxidising agent and an &agr;-hydroxycarbonyl compound. However, all those measures require the use of new auxiliary components, as a result of which the properties of the graft rubber polymers are generally altered in an undesirable manner.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that graft rubber polymers of the ABS type may be prepared by emulsion polymerization according to the fed batch process with markedly reduced residual monomer contents using conventional free-radical initiator systems without the addition of novel substances if during the reaction the initiator components are added in a specific manner.
The invention provides a process for the preparation of graft rubber polymers of the ABS type by emulsion polymerization according to the fed batch process, which process is characterised in that the free-radical initiator used for initiating polymerization or the initiator system used is added to the reaction mixture in portions or continuously in such a manner that, in the course of the reaction, a minimum of initiator or initiator system added per time interval is passed and in at least 50%, preferably at least 70% and especially at least 90% of the total reaction time, the amount of initiator added in each time interval corresponds at least to an amount ≧0.5 wt. %, preferably ≧1 wt. % and especially ≧2.5 wt. %, of the total amount of initiator, the total reaction time comprising n time intervals where n=from 3 to 20, preferably from 3 to 15 and especially from 3 to 10, and each time interval being from 5 to 90 minutes, preferably from 10 to 80 minutes and especially from 15 to 60 minutes in length. Preferably, the amount of initiator added during every one of said time intervals is greater than zero.
In a preferred embodiment of the invention, the minimum of added initiator or initiator system per time interval is passed in the first half of the total reaction time.
Also preferably, the minimum is passed in the first or second third of the total reaction time.
The process according to the invention is usually carried out in practice by placing a rubber latex or a mixture of a plurality of rubber latexes in a stirred reactor, heating the contents of the reactor to a suitable temperature for the initiation of polymerization with free-radical initiators, adding the free-radical initiator in the manner indicated above, metering in the graft monomers and, optionally, metering in an aqueous emulsifier in parallel.
There are suitable as rubbers in the use of the process according to the invention for the preparation of graft rubber polymers in principle all rubber-like polymers in emulsion form having a glass transition temperature below 0° C.
The following may be used, for example:
diene rubbers, that is to say homopolymers of conjugated dienes having from 4 to 8 carbon atoms, such as, for example and preferably, butadiene, isoprene, chloroprene or copolymers thereof with up to 60 wt. %, preferably up to 30 wt. %, of a vinyl monomer, for example and preferably acrylonitrile, methacrylonitrile, styrene, &agr;-methylstyrene, halostyrenes, C
1
-C
4
-alkylstyrenes, C
1
-C
8
-alkyl acrylates, C
1
-C
8
-alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates, divinylbenzene;
acrylate rubbers, that is to say homo- and co-polymers of C
1
-C
10
-alkyl acrylates, for example and preferably homopolymers of ethyl acrylate, butyl acrylate or copolymers with up to 40 wt. %, preferably not more than 10 wt. %, mono-vinyl monomers, for example and preferably styrene, acrylonitrile, vinyl butyl ether, acrylic acid (ester), methacrylic acid (ester), vinylsulfonic acid. There are preferably used acrylate rubber homo- and co-polymers that contain from 0.01 to 8 wt. % divinyl or polyvinyl compounds and/or N-methylolacrylamide or N-methylolmethacrylamide or other compounds acting as crosslinking agents, for example divinylbenzene and, preferably, triallyl cyanurate.
Preference is given to polybutadiene rubbers, SBR rubbers having up to 30 wt. % styrene polymerized therein, and acrylate rubbers, especially those having a core/shell structure, for example as described in DE-A 3 006 804.
For the preparation of graft rubber polymers by the process according to the invention latexes having mean particle diameters d
50
of from 0.05 to 2.0 &mgr;m, preferably from 0.08 to 1.0 &mgr;m and especially from 0.1 to 0.5 &mgr;m may be considered. The gel contents of the rubbers that are used may be varied within wide limits; they are preferably from 30 to 95 wt. % (determined by the wire cage method in toluene).
Very special preference is given to mixtures of rubber latexes having
a) mean particle diameters d
50
≦320 nm, preferably from 260 to 310 nm, and gel contents ≦70 wt. %, preferably from 40 to 65 wt. %, and
b) mean particle diameters d
50
≧370 nm, preferably from 380 to 450 nm, and gel contents ≧70 wt. %, preferably from 75 to 90 wt. %.
The breadth of particle size distribution of the rubber latex (a) is preferably from 30 to 100 nm, especially from 40 to 80 nm, and that of the rubber latex (b) is from 50 to 500 nm, especially from 100 to 400 nm (in each case measured as the d
90
-d
10
value from the integral particle size distribution).
The mixtures contain the rubber latexes (a) and (b) preferably in a weight ratio of from 90:10 to 10:90, especially fro
Eichenauer Herbert
Gasche Hans-Erich
Jansen Ulrich
Moss Stefan
Vanhoorne Pierre
Asinovsky Olga
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Seidleck James J.
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