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
2002-11-21
2004-12-07
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...
C525S069000, C525S071000, C525S263000, C525S333500
Reexamination Certificate
active
06828380
ABSTRACT:
The invention provides thermoplastic moulding compositions of the ABS type and of the ABS blend type comprising improved graft rubber components, which are obtained by emulsion polymerization while maintaining defined reaction conditions.
Moulding compositions of the ABS type are two-phase plastics of
I) a thermoplastic copolymer, in particular of styrene and acrylonitrile, in which all or some of the styrene can be replaced by &bgr;-methylstyrene or methyl methacrylate; this copolymer, also called SAN resin or matrix resin, forms the external phase;
II) at least one graft polymer which has been prepared by a grafting reaction of one or more of the monomers mentioned under I on a butadiene homo- or copolymer (“graft base”). This graft polymer (“elastomer phase” or “graft rubber”) forms the disperse phase in the matrix resin.
These mixtures of plastics can additionally also comprise other polymer components, such as e.g. aromatic polycarbonate resins, polyester-carbonate resins, polyester resins or polyamide resins, as a result of which so-called ABS blend systems are obtained.
Graft rubbers prepared using redox initiator systems have proved particularly suitable as impact modifiers both for ABS moulding compositions and for ABS blend systems (see e.g. EP-A 482 451 and the literature cited there), as a rule good impact strengths being achieved. A disadvantage is that the surface gloss, elongation at break and thermoplastic flow properties are often not adequate or are subject to wide variations.
Graft rubbers prepared by redox initiation moreover tend towards an increased content of unreacted monomers, which can indeed be decreased by addition of metal ions (e.g. Fe ions) in the reaction mixture, but this leads to sacrifices in other properties (e.g. heat stability, colour of the polymers).
DE-A 2,101,650 describes a rubber latex obtained by the agglomeration of a starting latex. Example 2 describes a process for the production of a polybutadiene latex grafted with styrene and acrylonitrile by emulsion polymerization using a redox initiator (Fe(II)/cumene hydroperoxide), the rubber latex being adjusted to a pH value of 10 before the beginning of the graft polymerization reaction. Example 2 does not contain any suggestion that if reaction conditions according to the subject matter of the invention are adhered to graft polymers having a low residual monomer content of styrene would result and display excellent mechanical properties, in particular impact strength and elongation at break.
EP-A 540 470 describes a process for the production of graft polymers by emulsion polymerization in the presence of iron(II) redox systems as the catalyst and subsequent coagulation of the graft polymer latex with alkaline earth metal compounds, the pH of the coagulated slurry being in the range of 8 to 12. It is clear from Examples III and IV that the pH value of 7.2 increases due to the addition of KOH and at the end of the reaction a pH value of 9.2 is reached.
DE-A 37 30 205 describes a process for the production of graft polymers on acrylate rubber, an initiator system of organic hydroperoxide and ascorbic acid being used and the pH value during the graft polymerization being lower than 11.
DE-A 1 98 31 735 describes thermoplastic moulding compounds of the ABS type which are produced by the specified feed of the monomer into the rubber latex using persulphate compounds.
In none of the abovementioned references is it stated that the production takes place inter alia by keeping the pH value constant (within the normal range of variation of approx. ±0.5 units) and that graft polymers with a low residual monomer content of styrene result.
There is therefore a need for graft rubbers which do not have these disadvantages and for a process by which ABS and ABS blend moulding compositions can be prepared without the disadvantages mentioned.
It has now been found that moulding compositions with a very good surface gloss, high elongation at break and good thermoplastic processability can be obtained without an adverse influence on the other properties if the preparation of the graft rubber employed is carried out while maintaining precisely defined reaction conditions.
The invention provides compositions of the ABS type and of the ABS blend type comprising
A) at least one elastic-thermoplastic graft polymer obtained by free-radical emulsion polymerization of resin-forming vinyl monomers, preferably of compounds of the formulae (I) and (II) described below, particularly preferably of styrene and/or acrylonitrile, it being possible for all or some of the styrene and/or acrylonitrile to be replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of rubber which is in latex form and has a glass transition temperature of ≦0° C., using a redox initiator system and
B) at least one copolymer of styrene and acrylonitrile, it being possible for all or some of the styrene and/or acrylonitrile to be replaced by &agr;-methylstyrene or methyl methacrylate or N-phenylmaleimide or mixtures thereof and optionally
C) a resin chosen from the group consisting of polycarbonates, polyester-carbonates, polyesters and polyamides or mixtures thereof,
characterized in that the preparation of the graft polymer A) is carried out by a procedure in which before the start of the grafting polymerization reaction the rubber latex is brought to a pH of 9 to 11, preferably 9.5 to 10.5 and particularly preferably 9.7 to 10.3, the redox initiator components are employed in amounts of 0.1 to 2.5 wt. %, preferably 0.2 to 2.0 wt. % and particularly preferably 0.5 to 1.5 wt. % (in each case based on the monomers metered in) and during the entire grafting polymerization reaction the pH should not exceed a value of 11.0, preferably 10.8, and should not fall below a value of 8.8, preferably 9.0, the pH remains constant during the entire reaction within the normal range of variation (approx. ±0.5 units) and the temperature difference between the start and end of the reaction is at least 10° C., preferably at least 15° C. and particularly preferably at least 20° C.
With the aid of the process according to the invention graft polymers are obtained with a residual monomer content of styrene of less than 2500 ppm, preferably less than 2000 ppm, and in particular less than 1600 ppm (based on the resulting graft polymer). It is clear from the examples that where deviations occur from the reaction conditions to be adhered to according to the description of the process graft polymers with high residual monomer contents of styrene are obtained
Suitable rubbers for the preparation of the elastic-thermoplastic graft polymers according to the invention are in principle all rubber-like polymers which are in emulsion form and have a glass transition temperature below 0° C.
Polymers which can preferably be used are e.g.
diene rubbers, i.e. homopolymers of conjugated dienes having 4 to 8 C atoms, such as butadiene, isoprene, chloroprene or copolymers thereof with up to 60 wt. %, preferably up to 30 wt. % of a vinyl monomer, e.g. acrylonitrile, methacrylonitrile, styrene, &agr;-methylstyrene, halogenostyrenes, C
1
-C
4
-alkyl-styrenes, C
1
-C
8
-alkyl acrylates, C
1
-C
8
-alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates or divinylbenzene;
acrylate rubbers, i.e. homo- and copolymers of C
1
-C
10
-alkyl acrylates, e.g. homopolymers of ethyl acrylate or butyl acrylate or copolymers with up to 40 wt. %, preferably not more than 10 wt. % of mono-vinyl monomers, e.g. styrene, acrylonitrile, vinyl butyl ether, acrylic acid (esters), methacrylic acid (esters) or vinylsulfonic acid. Those acrylate rubber homo- or copolymers which comprise 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/or N-methylolacrylamide or N-methylolmethacrylamide or other compounds which act as crosslinking agents, e.g. divinylbenzene or triallyl cyanurate, are preferably employed.
Preferred rubbers are polybutadiene rubbers, SBR rubbers with up to 30 wt. % of polymerized-in styrene and ac
Alberts Heinrich
Eichenauer Herbert
Gasche Hans-Erich
Hauertmann Hans-Bernhard
Jansen Ulrich
Akorli Godfried R.
Asinovsky Olga
Bayer Aktiengesellschaft
Denesvich Jill
Seidleck James J.
LandOfFree
Thermoplastic molding materials based on special graft... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermoplastic molding materials based on special graft..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermoplastic molding materials based on special graft... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3295096