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
2002-10-31
2004-12-28
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...
C525S070000, C525S071000, C525S193000, C525S316000
Reexamination Certificate
active
06835775
ABSTRACT:
The invention relates to particulate emulsion polymers, graft copolymers thereof and molding compositions comprising these, which have improved impact strength. The invention further relates to a process for preparing the emulsion polymers and graft copolymers, and also to the use of the graft copolymers and of the thermoplastic molding compositions.
Impact-modified thermoplastic molding compositions such as acrylonitrile-butadiene-styrene (ABS) copolymers and acrylate-styrene-acrylonitrile (ASA) copolymers have advantageous mechanical properties and are therefore used in a wide variety of applications.
These are generally prepared by first preparing a rubber latex which, for example, after grafting can be introduced into a polymer matrix.
Rubber latices produced during homo- or copolymerization of butadiene frequently have particle diameters of the order of from 50 to 150 nm. ABS polymers prepared using rubbers of this type frequently have relatively low toughness. It is therefore desirable to produce and use rubber latices with larger particles. The small-particle rubber latex used is therefore preferably used in agglomerated form in order to achieve improved mechanical properties. DE-A-24 27 960 relates to a process for preparing impact-modified thermoplastic molding compositions based on rubbery polymers. After initial emulsion polymerization of butadiene or acrylic esters, the resultant rubber latex is agglomerated at least to some extent by adding an agglomeration agent based on an acrylate polymer dispersion. This is followed by grafting with styrene, acrylonitrile and/or methyl methacrylate, and the resultant graft rubber is introduced into a polymer matrix.
The use of graft rubbers with bimodal particle size distribution has also been described in DE-A-196 30 061, for example. This specification also gives an overview of various compositions and preparation processes for the thermoplastic molding compositions.
DE-A 197 28 629 describes ABS molding compositions with two different matrix polymers.
The agglomeration of polymer latices is generally described in “Die Angewandte Makromolekulare Chemie” 2, 1968, 1-25 (Nr. 20).
It is an object of the present invention to provide particulate emulsion polymers and graft copolymers obtainable therefrom and thermoplastic molding compositions which have better notch impact strength than known molding compositions. They should also have an advantageous combination of mechanical properties, such as toughness, penetration energy, flowability and surface gloss.
We have found that this object is achieved by means of a graft copolymer made from
a1: from 10 to 90% by weight of a particulate graft base A1, made from a particulate emulsion polymer with a glass transition temperature below 0° C. made from
a11: from 70 to 100% by weight of butadiene or of at least one C
1-8
-alkyl acrylate, or of mixtures of these, as component A11,
a12: from 0 to 20% by weight of at least one polyfunctional crosslinking monomer, as component A12,
a13: from 0 to 30% by weight of other copolymerizable monomers, as component A13, the total amount of these being 100% by weight,
a2: from 10 to 90% by weight of a graft A2 made from the following monomers, the amounts being based on A2,
a21: from 60 to 100% by weight of at least one vinylaromatic monomer, or of a (meth)acrylic ester or of mixtures of these, as component A21, and
a22: from 0 to 40% by weight of at least one ethylenically unsaturated monomer, as component A22,
which has a median particle diameter of from 130 to 500 nm and has polymodal particle size distribution in which less than 40% by weight of the particles are present in any particle size range of width 50 nm.
The graft copolymers are preferably incorporated into thermoplastic molding compositions.
The object is further achieved by means of a thermoplastic molding composition comprising, based on the amount of components A and B and, where appropriate, C and/or D, which gives 100% by weight in total,
a: from 10 to 90% by weight of a graft copolymer as defined above, as component A,
b: from 10 to 90% by weight of at least one amorphous polymer, as component B,
c: from 0 to 80% by weight of polycarbonates, polyamides, polyesters, polyether ketones, polyoxyalkylenes or polyarylene sulfides, as component C, and
d: from 0 to 50% by weight of fibrous or particulate fillers or mixtures of these, as component D.
According to the invention, it has been found that thermoplastic molding compositions with improved mechanical properties, in particular with increased notch impact strength, can be obtained if the graft copolymers used for their preparation have polymodal particle size distribution in which less than 40% by weight, preferably less than 37.5% by weight, with preference less than 35% by weight, particularly preferably less than 32.5% by weight, in particular less than 30% by weight, of the particles are present in any particle size range of width 50 nm. Unless otherwise stated, the median particle diameter here is based on weight. In particular, it is the d
50
of the integral weight distribution, determined with the aid of an ultracentrifuge. The particle size distribution is likewise preferably determined with the aid of an ultracentrifuge as described in more detail below.
According to the invention, it has been found that a broad particle size distribution of this type leads to advantageous thermoplastic molding compositions.
In determining the particle size distribution, the cumulative mass or weight is generally plotted as a function of particle size. If any desired particle size range of width 50 nm is then selected, then according to the invention the increase in cumulative weight or mass is below 40% by weight, preferably below 37.5% by weight, with preference below 35% by weight, particularly preferably below 32.5% by weight, in particular below 30% by weight. The particle sizes in an agglomerated latex are usually within the region up to 1000 nm. The 50 nm range is therefore generally within this region of particle size up to 1000 nm. According to the invention, the above condition has to be fulfilled for particle size windows of width 50 nm at any position which may be chosen.
In the particulate emulsion polymer it is preferable for the ratio D
w
/D
n
of ponderal median particle size d
50
to numeric median particle size d
50
to be <5, particularly preferably <4, in particular <3. The ponderal median d of the particle size is determined here by means of an analytical ultracentrifuge, and the numeric median particle size is likewise determined by means of an analytical ultracentrifuge, see W. Scholtan, H. Lange, Kolloid-Z. und Z. Polymere, 250 (1972), pages 782 to 796.
The ultracentrifuge measurement gives the cumulative mass distribution of particle diameter in a specimen. From this it is possible to deduce what percentage by weight of the particles have a diameter equal to or smaller than a particular size.
The d
10
is the particle diameter relative to which the diameter of 10% by weight of all of the particles is smaller and that of 90% by weight of all of the particles is larger. Conversely, 90% by weight of all of the particles have a diameter smaller than the diameter corresponding to the d
90
, and 10% by weight of all of the particles have a diameter larger than the diameter corresponding to the d
90
. The ponderal median particle diameter d
50
and the volume median particle diameter d
50
are diameters relative to which the diameters of 50% by weight and, respectively, 50% by volume of all of the particles are larger, and those of 50% by weight and, respectively, 50% by volume are smaller. d
10
, d
50
and d
90
describe the width Q of the particle size distribution, where Q=(d
90
−d
10
)/d
50
. The smaller Q is, the narrower the distribution.
The plot of cumulative weight against particle size preferably rises continuously. This means that over the course of the function from 0 to 100% by weight there is no plateau, but rather the curve is constantly rising.
The graft copolymers of the invention ma
Breulmann Michael
Duijzings Wil
Güntherberg Norbert
Mc Kee Graham Edmund
Niessner Norbert
Asinovsky Olga
BASF - Aktiengesellschaft
Keil & Weinkauf
Seidleck James J.
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