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
2001-05-15
2002-05-07
Mullis, Jeffrey (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...
C525S067000, C525S068000, C525S069000, C525S071000
Reexamination Certificate
active
06384133
ABSTRACT:
ABS moulding compositions have now been used for many years and in large amounts as thermoplastic resins for producing moulded items of all types. The range of properties of these resins can be varied within wide limits.
ABS polymers which are characterised by a combination of good values for the key properties toughness (in particular at low temperature), hardness (i.e. the E-modulus), processability and surface gloss are of particular interest.
When using the emulsion polymerisation process, these types of products are generally prepared by the joint use of different graft rubber components in a thermoplastic resin matrix.
Thus, for instance, DE-OS 24 20 357 and DE-OS 24 20 358 describe thermoplastic moulding compositions of the ABS type with high toughness, high surface gloss and ready processability resulting from a combination of a coarsely divided graft rubber and a finely divided graft rubber, wherein the ratios by weight of styrene to acrylonitrile in the graft rubbers and in the matrix resin have to assume specific values.
EP-A 470 229, EP-A 473 400 and WO 91/13118 disclose the production of an impact resistant, high-gloss, thermoplastic resin by combining a graft polymer with a low rubber content and a small particle diameter with a graft polymer with a high rubber content and a large particle diameter.
DE-OS 4113 326 discloses thermoplastic moulding compositions with two different graft products, wherein the rubber content of each of the graft rubbers is a maximum of 30 wt. %.
For all the moulding compositions described here, at least two separately prepared graft rubber polymers are required to produce the desired properties. This means that optimisation of the graft reaction conditions, graft polymerisation reactions, working-up, etc. has to be performed separately for each graft rubber. In addition, in general at least one of the graft rubber components required has to have a low rubber content, i.e. a relatively high proportion of the graft rubber polymer which is costly to produce has to be used. In many cases, however, the requisite degree of reliability when adjusting the desired combination of properties is not produced.
Attempts to synthesise graft rubbers for producing improved ABS products have also been made by using mixtures of two rubber latices as the graft substrate.
Thus, EP-A 288 298 describes the preparation of products with a finely divided and a coarsely divided rubber latex as graft substrates, wherein however only graft rubbers with low rubber contents of about 40% are described. The thermoplastic resins prepared from these do not exhibit satisfactory processability due to poor thermoplastic flow characteristics; in addition, resin components with high acrylonitrile content have to be used, which usually leads to discoloration of the ABS products.
EP-A 745 624 describes the use of a mixture of two rubber latices with defined widths of particle size distributions for preparing ABS moulding compositions which do not darken in colour for producing moulded parts with a ribbed structure. However, these products lead to unsatisfactory low temperature toughness and in particular to a poor relationship between toughness and thermoplastic processability (flow characteristics).
The object therefore arose of providing thermoplastic moulding compositions of the ABS type which can be prepared by using only a single graft rubber polymer, wherein the combination of high toughness, high hardness or E-modulus, high surface gloss and in particular very good thermoplastic processability mentioned above can be reliably adjusted. In addition, the graft rubber polymer used should have a rubber content of greater than 50 wt. %, preferably greater than. 55 wt. %.
The invention therefore provides ABS moulding compositions containing
I) a graft rubber polymer which is obtainable by emulsion polymerisation of styrene and acrylonitrile in the ratio by weight of 90:10 to 50:50, wherein styrene and/or acrylonitrile may be entirely or partly, replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleic imide, in the presence of a mixture of a butadiene polymer latex (A) with an average particle diameter d
50
≦230 nm, preferably 150 to 220 nm, particularly preferably 170 to 215 nm and very particularly preferably 175 to 200 nm, and a gel content of 40 to 95 wt. %, preferably 50 to 90 wt. % and particularly preferably 60 to 85 wt. %, a butadiene polymer latex (B) with an average particle diameter d
50
of 250 to 330 mn, preferably 260 to 320 nm and particularly preferably 270 to 310 nm and a gel content of 35 to 75 wt. %, preferably 40 to 70 wt. % and particularly preferably 45 to 60 wt. % and a butadiene polymer latex (C) with an average particle diameter d
50
≧350 nm, preferably 370 to 450 nm, particularly preferably 375 to 430 nm and very particularly preferably 380 nm to 425 nm and a gel content of 60 to 90 wt. %, preferably 65 to 85 wt. % and particularly preferably 70 to 80 wt. %, wherein the butadiene polymer latices each contain 0 to 50 wt. % of another copolymerised vinyl monomer and wherein the ratio by weight of the graft monomers used to the butadiene polymers used is 10:90 to 60:40, preferably 20:80 to 50:50 and particularly preferably 25:75 to 45:55, and
II) at least one rubber-free copolymer of styrene and acrylonitrile in the ratio by weight of 90:10 to 50:50, wherein styrene and/or acrylonitrile may be entirely or partly replaced by a-methylstyrene, methyl methacrylate or N-phenylmaleic imide.
When preparing graft rubber polymer (I), the butadiene polymer latices (A), (B) and (C) are preferably used in the proportions 10 to 40 wt. %, preferably 20 to 37.5 wt. % and particularly preferably 22.5 to 35 wt. % of (A), 10 to 70 wt. %, preferably 20 to 65 wt. % and particularly preferably 30 to 60 wt. % of (13) and 5 to 50 wt. %, preferably 7.5 to 45 wt. % and particularly preferably 10 to 40 wt. % of (C) (each with respect to the particular solids content of the latices).
Another preferred group, when preparing graft rubber polymer (I), is the use of the butadiene polymer latices (A), (B) and (C) in the proportions 10 to 40 wt. %, preferably 20 to 37.5 wt. % and particularly preferably 22.5 to 35 wt. % of (A), 30 to 70 wt. %, preferably 35 to 65 wt. % and particularly preferably 40 to 60 wt. % of (B) and 5 to 45 wt. %, preferably 7.5 to 40 wt. % and particularly preferably 10 to 35 wt. % of (C) (each with respect to the particular solids content of the latices).
In particular, butadiene polymer latices (A), (B) and (C) are used in amounts such that the equations B≦A+C, B>A and B>C are satisfied for the amounts of rubber.
In general, moulding compositions according to the invention may contain 1 to 60 parts by wt., preferably 5 to 50 parts by wt. of (I) and 40 to 99 parts by wt., preferably 50 to 95 parts by wt. of (II).
In addition, moulding compositions according to the invention may contain other rubber-free thermoplastic resins which are not built up from vinyl monomers, wherein these thermoplastic resins are used in amounts of up to 500 parts by wt., preferably up to 400 parts by wt. and particularly preferably up to 300 parts by wt. (each with respect to 100 parts by wt. of I+II).
Butadiene polymer latices (A), (B) and (C) may be prepared by the emulsion polymerisation of butadiene. This polymerisation process is known and is described, for example, in Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, part 1, p. 674 (1961), Thieme Verlag Stuttgart. Up to 50 wt. %, preferably up to 30 wt. % (with respect to the total amount of monomers used to prepare the butadiene polymer) of one or more monomers which can copolymerise with butadiene may be used as comonomers.
Examples of these monomers are isoprene, chloroprene, acrylonitrile, styrene, &agr;-methylstyrene, C
1
-C
4
-alkylstyrenes, C
1
-C
8
-alkyl acrylates, C
1
-C
8
-alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates, divinylbenzene; butadiene alone is preferably used. During the preparation of (A), (B) and (C), it is also
Bayer Aktiengesellschaft
Gil Joseph C.
Mullis Jeffrey
Preis Aron
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