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
2001-11-30
2003-11-11
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...
C525S064000, C525S066000, C525S067000, C525S068000, C525S073000, C525S080000, C525S260000, C525S261000, C525S219000, C525S201000, C525S219000, C525S223000, C525S225000
Reexamination Certificate
active
06646045
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to thermoplastic molding compositions and more particularly to compositions containing grafted rubbers.
SUMMARY OF THE INVENTION
Thermoplastic molding compositions containing graft polymers produced with different initiator systems are disclosed. The compositions are distinguished by a combination of good toughness and reduced opacity. As a result, appreciably smaller quantities of pigment are needed to colour the molding composition.
BACKGROUND OF THE INVENTION
ABS molding compositions have, for many years, been used in large quantities as thermoplastic resins for the production of all kinds of moldings. The range of properties of these resins can be varied within broad limits.
In view of the constantly growing demands made on plastics materials, and of new areas of application, ABS polymers with special combinations of properties are increasingly required.
One of these special combinations of properties relates to ABS polymers for the production of coloured mouldings with notched impact strength, particularly in the area of application of housings and covers. The smallest possible quantities of colorants should be required to obtain the desired colour in these applications, and this can be achieved e.g. by means of a lower opacity of the polymer material and a lighter colour in the non-coloured state (low yellowness index).
When the technology of emulsion polymerisation is used, the attempt is usually made to achieve the desired properties by combining different graft rubber components with a thermoplastic resin matrix.
Thus, for example, DE-A 24 20 357 and DE-A 24 20 358 describe the use of special graft polymers obtained by persulfate initiation with defined values for, inter alia, rubber contents, particle size, degree of grafting, styrene:acrylonitrile ratio in the graft polymers and in the styrene/acrylonitrile copolymer used to achieve improved values for toughness, processability and surface gloss. Despite the relatively complicated production of these moulding compositions, no optimum toughness/flowability and toughness/gloss relationships, and only unsatisfactory inherent colours, are achieved.
Similar problems are displayed in the products produced in accordance with EP-A 470 229, EP-A 473 400 and WO 91/13118 wherein, by combining a graft polymer having a low rubber content and small particle diameter obtained by redox initiation with a graft polymer having a high rubber content and larger particle diameter obtained by redox initiation, impact-resistant, high-gloss thermoplastic resins are obtained. However, the flow characteristics and the opacities of these moulding compositions do not meet the constantly increasing demands made on materials of this kind.
In DE-A 41 13 326, thermoplastic moulding compositions with two different graft products are described, wherein the rubber contents of the graft rubbers are a maximum of 30 wt. % in each case. No more detailed information on the properties can be derived from the document; however, the variability of the products or of the product properties is probably severely limited owing to the low rubber contents of the graft polymers.
DE-A 196 49 255 teaches the production of ABS moulding compositions with very high gloss values while preserving good values for toughness and processability, wherein a combination of a coarse-particle graft polymer produced by persulfate initiation and a fine-particle graft polymer produced by persulfate initiation is employed, adhering to special values for particle size distribution and gel content of the rubbers used.
Disadvantages of these products are, in addition to the necessity of adhering to numerous parameters during production, the sometimes inadequate toughness values together with unsatisfactory inherent colour and too high an opacity.
The object therefore existed of providing compositions that are not characterized by the above-mentioned disadvantages and that feature a combination of good toughness, low yellowness index and reduced opacity and wherein other properties are not be negatively affected.
Even small reductions in the opacity, which can be determined very accurately, lead to a noticeable reduction in the quantity of pigment needed to colour the moulding compositions.
The invention provides compositions containing
A) at least one grafted rubber produced by free-radical emulsion polymerisation of at least one vinyl monomer, preferably a copolymer of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, styrene and/or acrylonitrile optionally being completely or partly replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleimide, particularly preferably of styrene and acrylonitrile in the presence of at least one rubber a) present in the form of a latex, with a glass transition temperature of less than 0° C., preferably a butadiene rubber, particularly preferably polybutadiene, using at least one persulfate compound as the initiator,
B) at least one grafted rubber produced by free-radical emulsion polymerisation of at least one vinyl monomer, preferably a copolymer of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, styrene and/or acrylonitrile optionally being completely or partly replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleimide, particularly preferably of styrene and acrylonitrile in the presence of at least one rubber b) present in the form of a latex, with a glass transition temperature of less than 0° C., preferably a butadiene rubber, particularly preferably polybutadiene, using at least one azo compound as the initiator, and optionally
C) at least one thermoplastic, rubber-free polymer obtained by polymerisation of at least one resin-forming vinyl monomer, preferably a copolymer of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, styrene and/or acrylonitrile optionally being completely or partly replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleimide.
In general, the compositions according to the invention can contain the grafted rubbers A) and B) in any quantitative proportions, usually in the range of 5 to 95 parts by weight A) and 95 to 5 parts by weight B); 20 to 90 parts by weight A) and 10 to 80 parts by weight B) are preferred, 30 to 80 parts by weight A) and 20 to 70 parts by weight B) are particularly preferred, and 40 to 75 parts by weight A) and 25 to 60 parts by weight B) are especially preferred (based in each case on 100 parts by weight A+B).
The optional thermoplastic rubber-free vinyl polymer C) may be used in quantities of 50 to 2000 parts by weight, preferably 100 to 1500 parts by weight and particularly preferably 150 to 1000 parts by weight (based in each case on 100 parts by weight A+B).
The grafted rubber polymers A) and B) used preferably have rubber contents of more than 50 wt. %, particularly preferably more than 55 wt. % and especially preferably more than 58 wt. %.
The compositions may further contain additional rubber-free thermoplastic resins that are not built up from vinyl monomers, these thermoplastic resins may be used in quantities of up to 1000 parts by weight, preferably up to 700 parts by weight and particularly preferably up to 500 parts by weight (based in each case on 100 parts by weight A+B+C).
The rubber a) present in the form of a latex used to produce the grafted rubber A) and also the rubber b) present in the form of a latex used to produce the grafted rubber B) may be present in the form of latices with monomodal, bimodal, trimodal or multimodal particle size distributions.
Those combinations of grafted rubbers A) and B) in the production of which at least one of the rubber latices a) and b) used has a bimodal or trimodal particle size distribution are preferred.
Those combinations of grafted rubbers A) and B) in the production of which the rubber latex a) used has a monomodal particle size distribution and the rubber latex b) used has a bimodal particle size distribution, or in the production of which the rubber latex a) used has a monomodal particle size dist
Mullis Jeffrey
Preis Aron
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