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
1999-12-30
2001-11-27
Boykin, Terressa M. (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...
Reexamination Certificate
active
06323279
ABSTRACT:
The present invention relates to thermoplastic molding compositions comprising, as components A) to F), based on the total weight of the molding composition,
A) from 5 to 80% by weight of a graft polymer A) having bimodal particle size distribution made from, based on A),
a1) from 40 to 90% by weight of an elastomeric particulate graft base a1), obtainable by polymerization of, based on a1),
a11) from 70 to 100% by weight of at least one conjugated diene,
a12)from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer and
a2) from 10 to 60% by weight of a graft a2) made from, based on a2),
a21)from 65 to 95% by weight of at least one vinylaromatic monomer,
a22)from 5 to 35% by weight of acrylonitrile, and
a23) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer,
B) from 20 to 95% by weight of a thermoplastic polymer B) having a viscosity number VN (determined according to DIN 53726 at 25° C., 0.5% strength by weight in dimethylformamide) of from 50 to 120 ml/g, made from, based on B),
b1) from 69 to 81% by weight of at least one vinylaromatic monomer,
b2) from 19 to 31% by weight of acrylonitrile, and
b3) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer and
C) from 0 to 50% by weight of a thermoplastic polymer C) having a viscosity number VN of from 50 to 120 ml/g made from, based on C),
c1) from 69 to 81% by weight of at least one vinylaromatic monomer,
c2) from 19 to 31% by weight of acrylonitrile and
c3) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer,
where components B) and C) differ in their viscosity numbers VN by at least 5 units [ml/g], or in their acrylonitrile content by at least 5 units [% by weight], or in both characteristics, viscosity number VN and acrylonitrile content, by at least 5 units and
D) from 0 to 95% by weight of a thermoplastic polymer D) made from, based on D),
d1) from 63 to less than 69% by weight of at least one vinylaromatic monomer,
d2) from greater than 31 to 37% by weight of acrylonitrile,
d3) from 0 to 40% by weight of at least one other monoethylenically unsaturated monomer and
E) from 0 to 50% by weight of a thermoplastic polymer E) made from, based on E),
e1) from 4 to 96% by weight of at least one vinylaromatic monomer,
e2) from 4 to 96% by weight of at least one monomer selected from the class consisting of methyl methacrylate, maleic anhydride and maleimides and
e3) from 0 to 50% by weight of acrylonitrile,
where the polymer E) is different from the polymers B) and from C) and D) if they are present and
F) from 0 to 50% by weight of additives F), obtainable by
1) preparing the graft polymers A) by emulsion polymerization,
2) mixing the graft polymer A) with the polymer B) and the other components C), D), E) and/or F) if they are present, in a mixing apparatus, giving an essentially molten polymer mixture, and
3) rapid cooling of the essentially molten polymer mixture.
The invention further relates to a process for preparing the thermoplastic molding compositions, the use of the thermoplastic molding compositions for producing moldings, and finally the moldings produced from the thermoplastic molding compositions.
Moldings made from ABS (polybutadiene rubber particles grafted with polystrene-acrylonitrile in a matrix of polystyrene-acrylonitrile) have good mechanical properties, for example high strength and toughness and especially, due to the low glass transition temperature Tg of the polybutadiene, good impact strength, even at low temperatures.
ABS polymers, however, especially those prepared by emulsion polymerization, often have an intrinsic color, for example yellowish to brownish. This intrinsic color can, for example, be expressed using the Yellowness Index (YI), which for ABS polymers of this type having marked intrinsic color is from above 30 to well above 50. The Yellowness Index YI here depends on a number of factors, including the rubber content of the ABS. In addition, yellowish/brownish discolorations, for example, can frequently occur during preparation of the molding compositions and their further processing to give moldings, and during use of the moldings. The yellowing or brown coloration is favored by high temperatures, as encountered, for example, during injection molding or during blending with additives in an extruder; the stronger the intrinsic color of the unprocessed ABS pellets for injection molding or extrusion, the more marked the yellowing or brown coloration. In particular, there are problems in the coloration of polymers which are subject to yellowing, since the yellow tinge distorts the desired shade (unsatisfactory color fidelity) or requires the use of large amounts of expensive colorants (increased pigmentation costs). A meagre depth of color is, furthermore, often observed in pigmented ABS molding compositions, and results from their high level of light scattering. Since the initial level of intrinsic color and the depth of color of pigmented molding are responsible for the perceived color of the molding, the intrinsic color and the yellowing greatly reduce the usefulness of the molding compositions.
EP-A 6341 proposes processing an acrylonitrile rubber in an extruder flushed with inert gases, such as N
2
or CO
2
, the yellow tinge of the polymer being thereby reduced. The operation of an extruder under inert conditions is disadvantageous, since it makes the process complicated and costly.
DE-B-2503966 proposes ABS molding compositions whose stability of color is improved by the additional use of a C
1
-C
8
-alcohol during the emulsion polymerization of the butadiene. The extent of reduction of the yellow tinge, however, is not always satisfactory. In addition, the alcohol can have a disadvantageous effect on certain properties of the molding compositions.
DE-B-2427960 discloses ABS molding compositions some of whose rubber particles have been agglomerated by adding an agglomerating dispersion to the finely divided polybutadiene latex, and which therefore have a broad or bimodal particle size distribution.
DE-A-3505749 proposes that a polybutadiene rubber grafted with styrene and acrylonitrile is precipitated from its latex by adding a sulfur-containing graft product based on polybutadiene, improving the thermal stability of the polybutadiene rubber when it has been precipitated and converted into molding compositions. The high contents of sulfur compounds, however, often give the molding compositions an unpleasant odor.
EP-A-678531 describes ABS molding compositions with a polybutadiene graft rubber having bimodal particle size distribution, where styrene and acrylonitrile, the monomers grafted onto the polybutadiene particles, are metered in predominantly during the first half of the monomer feed time. Although ABS compositions of this type have high toughness and are easy to process, they have a marked yellow tinge.
WO 95/22570 discloses a process for preparing an ABS polymer in which a finely divided rubber latex is prepared in emulsion, partially agglomerated, and the now bimodal latex is grafted in emulsion with SAN. The graft polymer is then separated from the aqueous phase and mixed, in melted form, with an SAN matrix polymer, the AN content of the SAN graft shell and of the SAN matrix differing by not more than 6% by weight. During the removal of water and/or the mixing in melt form of graft polymers and SAN matrix, a further, partial agglomeration of the graft particles takes place. Molding compositions of this type also have a disadvantageous yellowish intrinsic color.
It is an object of the present invention to remedy the disadvantages described, and in particular to provide molding compositions which have little intrinsic color, ie. a low initial level of the yellow tinge, and added to this a low yellowing tendency. In particular, the molding compositions should show hardly any yellowing even after prolonged heat aging or as a result of hot processing (eg. during injection molding or blending in an extruder).
An additional object is to pro
Czauderna Bernhard
Grabowski Sven
Guntherberg Norbert
Heinen Hartmut
Ittemann Peter
BASF - Aktiengesellschaft
Boykin Terressa M.
Keil & Weinkauf
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