Thermoplastic molding material based on ABS

A thermoplastic molding material which contains, in each case based on the molding material comprising A+B, PA0 A. from 50 to 95% by weight of a rigid matrix composed of, PA1 (a.sub.1) styrene and PA1 (a.sub.2) acrylonitrile, PA0 B. from 50 to 5% by weight of a nonrigid phase which is uniformly dispersed in the rigid matrix and which comprises a graft copolymer of the monomers (a.sub.1) and (a.sub.2) and a styrene-butadiene block copolymer, wherein the styrene-butadiene block copolymer has a styrene content of from 50 to 95% by weight and a butadiene content of from 50 to 5% by weight, each based on the block polymer, and has a molecular weight (weight average) within the range from 50,000 to 300,000, is used for producing moldings.

The present invention relates to a thermoplastic molding material which is 
based on ABS and is composed of a rigid matrix comprising a 
styrene-acrylonitrile copolymer and a nonrigid phase comprising a graft 
copolymer. The graft copolymer is formed in the course of the preparation 
of the rigid matrix in the presence of a styrene- and 
butadiene-containing, anionically produced block copolymer. 
The relevant prior art includes: 
(1) U.S. Pat. No. 4,154,715 
(2) British Patent No. 1,230,507 and 
(3) U.S. Pat. No. 4,221,883. 
Thermoplastic molding materials based on ABS can be prepared by various 
methods. In every case the result is a two-phase structure comprising a 
rigid matrix (S/AN copolymer) and, finely dispersed therein, a nonrigid 
phase in the form of a graft polymer (S/AN grafted onto polybutadiene). 
The nonrigid phase is always present in the form of discrete particles 
which vary in size. For instance, if ABS is prepared by the emulsion 
method, the size of the nonrigid phase particles can be set within the 
range from about 0.1 to 0.7 .mu.m. The particle size range of the nonrigid 
phase for mass suspension or solution ABS can extend from 0.5 to 20 .mu.m. 
The nonrigid phases of standard products generally have, in the case of 
solution ABS, an average particle size within the range from 1 to 5 .mu.m. 
All ABS products, whether prepared in an emulsion or mass suspension or 
solution process, are opaque, i.e. not even translucent. 
Transparent molding materials which are only composed of styrene, AN and 
butadiene have hitherto not been disclosed. Only by equiparating the 
refractive indices of the rigid phase (S/AN) and of the nonrigid phase (in 
general PBu grafted with S/AN) by including methyl methacrylate in the 
rigid phase is it possible to obtain a transparent ABS (so-called AMBS). 
It was therefore surprising to the skilled worker that transparent ABS 
based only on styrene, AN and butadiene would be obtainable in a simple 
manner, even in the light of the preparation of impact-resistant 
polystyrene. In particular, it was not foreseeable that the use of block 
copolymers having styrene contents of above 50% by weight [cf. (2), 
Example 2, use of styrene block copolymers with 30 or 40% by weight of 
styrene for ABS] would lead to a transparent product in which the nonrigid 
component is present not in the form of discrete particles but in the form 
of a lamelloid structure. 
(3) describes, by way of example, mass polymerization processes for 
preparing ABS on the basis of styrenebutadiene block copolymers which 
contain 70% by weight of butadienes and 30% by weight of styrene. Even on 
the basis of (3) it was not foreseeable that by using styrene-butadiene 
block copolymers having styrene contents of more than 50% by weight it 
would be possible to obtain transparent ABS. 
We have found that this object is achieved with a molding material as 
claimed in claim 1. 
The present invention therefore relates to a thermoplastic molding material 
which contains, in each case based on the molding material comprising A+B, 
A. from 50 to 95% by weight of a rigid matrix composed of, based on A, 
(a.sub.1) from 98 to 50% by weight of styrene and 
(a.sub.2) from 2 to 50% by weight of acrylonitrile, 
B. from 50 to 5% by weight of a nonrigid phase which is uniformly dispersed 
in the rigid matrix and which comprises a graft copolymer of the monomers 
(a.sub.1) and (a.sub.2) and a styrene-butadiene block copolymer. 
In the molding material, the styrene-butadiene block copolymer has a 
styrene content of from 50 to 95% by weight and a butadiene content of 
from 50 to 5% by weight, each based on the block polymer, and has a 
molecular weight (weight average) within the range from 50,000 to 400,000. 
In what follows, the constitution of the molding material according to the 
invention, i.e. in particular the morphology of the molding material 
according to the invention and the preparation thereof, are described 
together with the requisite starting materials and assistants. 
The molding material contains components A and B and preferably nothing 
else. To process the molding material, customary additives (component C) 
are incorporated. 
COMPONENT A 
The molding material according to the invention is composed of a rigid 
matrix comprising one or more copolymers of (a.sub.1) styrene and 
(a.sub.2) acrylonitrile. This rigid matrix accounts for from 50 to 95% by 
weight, preferably from 60 to 90% by weight, of the molding material 
composed of components A+B. A suitable monomer (a.sub.1) for constructing 
the rigid matrix is in particular styrene. However, it is also possible to 
use alpha-methylstyrene or mixtures with styrene; preference is, however, 
given to the use of styrene only, so that the rigid matrix is preferably 
composed of poly(styrene-acrylonitrile). The rigid matrix can have 
viscosity numbers within the range from 50 to 100 ml/g (0.5% by weight in 
dimethylformamide), in particular within the range from 60 to 90 ml/g. 
This corresponds to average molecular weights (M.sub.w) within the range 
from 70,000 to 170,000, in particular from 90,000 to 150,000. The 
preparation of copolymers of this type is familiar to those skilled in the 
art. 
The composition of the rigid matrix can be varied within wide limits. The 
monomer constituent (a.sub.1) can range from 98 to 50% by weight, 
preferably from 95 to 70% by weight, and in particular from 90 to 70% by 
weight (a.sub.2), the remainder up to 100 being acrylonitrile in each 
case). 
(It is to be noted that, on using styrene only, a different morphology of 
the nonrigid phase is obtained with formation of capsule particles.) 
COMPONENT B 
The molding material according to the invention features as component B a 
nonrigid phase which is present in the rigid matrix in the form of a fine 
dispersion. The nonrigid phase is present in the rigid matrix in an amount 
of from 5 to 50% by weight, preferably from 10 to 40% by weight. This 
nonrigid phase has a special structure. It comprises a lamelloid network 
which can be seen in electron micrographs of the end product, the molding 
material (cf. FIGS. 3 and 4). Presumably, the special properties of the 
molding material of the present invention are due to this morphology of 
the nonrigid phase. The nonrigid phase is a graft polymer of the monomers 
(a.sub.1) and (a.sub.2) of the rigid matrix, i.e. in particular of styrene 
and acrylonitrile which are grafted onto a styrene-butadiene block 
copolymer. 
It is an essential feature that the styrene-butadiene block copolymer 
contains more than 50% by weight of styrene and has a styrene content of 
from 50 to 95% by weight, preferably from 55 to 90% by weight, and in 
particular from 60 to 85% by weight, in each case based on the block 
copolymer (the other constituent being in each case butadiene, 
.SIGMA.=100%). 
For the purposes of the present invention, a styrene-butadiene block 
copolymer is one orepared by anionic polymerization with the aid of 
lithium initiators. In the block copolymer, the polybutadiene block has 
the customary medium-cis structure, which can be modified by adding polar 
solvents. The preparation of styrene-butadiene block copolymers of this 
type is known to those skilled in the art. 
The styrene-butadiene block copolymer may have a well-defined or an 
ill-defined transition. It may have a linear or a radial structure, even a 
linear coupled product being usable. Preferably, of the abovementioned 
possible structures of the block copolymer preference is given to 
styrene-butadiene 2-block copolymers of the abovementioned composition. 
Particular preference is therefore given to linear coupled and uncoupled 
styrene-butadiene 4- or 2-block copolymers with a well or ill-defined 
transition and the radial styrene-butadiene block copolymers obtainable 
from such products by means of more than bifunctional couoling agents, in 
particular to those with 2-block copolymers in the branches. The molecular 
weights of the styrene-butadiene block copolymers can be within the range 
from 50,000 to 400,000, in particular within the range from 70,000 to 
200,000. 
COMPONENT C 
In addition to components A and B, the molding material according to the 
invention may contain from 1 to 40 parts by weight, preferably from 1 to 
20 parts by weight, of a component C per 100 parts by weight of A and B. 
This component C can be added to the reaction batch before or during the 
preparation of the molding material, or be mixed into the molding material 
for processing. 
For the purposes of the present invention, component C subsumes for example 
the assistants known for the preparation of the molding material of the 
present invention, such as mineral oils, conventional esters of aromatic 
or aliphatic carboxylic acids with aliphatic alcohols, polyalkylene oxides 
based on ethylene oxide and/or propylene oxide, molecular weight 
regulants, protective colloids, antioxidants, etc. Assistants further 
include lubricants, such as zinc stearate and other stearates, and other 
customary assistants for producing moldings from the molding material, 
namely dyes, antioxidants, stabilizers or possibly flameproofing agents in 
the amounts customary to those skilled in the art. 
Preparation of the molding material according to the invention 
The preparation is effected by polymerization of the monomers (a.sub.1) and 
(a.sub.2) which comprise the rigid matrix, i.e. in particular of styrene 
and acrylonitrile, in the presence of a styrene-butadiene block copolymer. 
This polymerization can be carried out using the customary initiators or 
purely thermally or in a combined thermal/free radical process. The 
polymerization can be carried out continuously or batchwise. In the case 
of the batchwise method, a two-stage process is preferred, the first stage 
being carried out in a conventional manner in the presence or absence of a 
solvent, and the second stage in suspension. Processes for continuous 
practice and batchwise practice are described in sufficient detail in 
German Published Applications DAS No. 1,770,392 and DAS No. 2,613,352 
respectively. 
In the batchwise process, where the first stage is carried out in the 
presence or absence of a solvent, shearing forces are applied (by 
stirring) to bring about the required morphology of the nonrigid phase 
(rubber morphology). The temperatures in the first stage lie within the 
range from 50.degree. C. to 200.degree. C. In the subsequent second stage, 
which is preferably carried out in suspension, the reaction batch has 
added to it water and a customary water-soluble suspending agent, in 
particular methylcellulose, hydroxypropylcellulose, polyvinyl alcohol, 
polyvinylpyrrolidone etc. 
In the graft copolymerization of the monomers which form the eventual rigid 
matrix, which is carried out in the presence of the styrene-butadiene 
block copolymer, first the monomers are polymerized in the presence or 
absence of a solvent. In the course of the polymerization, the monomers 
which form the rigid matrix are grafted onto the block rubber. 
It is known to those skilled in the art that, depending on the process, the 
polymerization can lead to different conversions and/or solids contents. 
To obtain optimal products, the conversions required in the individual 
reactors and hence also the solids content will have to be determined by 
means of a few experiments.

The parameters described in the Examples and Comparative Experiments were 
determined as follows: 
1. Vicat temperature in .degree. C. by DIN 53,460 
2. Tensile stress in N/mm.sup.2 by DIN 53,455, with 5 mm/min takeoff speed 
3. Breaking strength in N/mm.sup.2 by DIN 53,455, with 5 mm/min takeoff 
speed 
4. Elongation at break in % by DIN 53,455, with 5 mm/min takeoff speed 
5. Notched impact strength in kJ/m.sup.2 by DIN 53,453 at 23.degree. C. 
6. Transparency: visually on molded platelets of 1 mm thickness 
The invention is further illustrated hereinafter by means of two Examples 
and three Comparative Experiments, where the parts and percentages are by 
weight. 
EXAMPLES 1 AND 2: COMATIVE EXPERIMENTS C.sub.1 to C.sub.3 
In each of the Examples and Comparative Experiments a batchwise mass 
suspension polymerization was carried out in a 5 l capacity Juvo kettle. 
The heat of reaction was removed by jacket cooling. The temperature in the 
interior was regulated. The first stage was carried out with a filling 
ratio of 40% and the subsequent second and hence final stage was completed 
in suspension with a filling ratio of 80%. The polymerization was carried 
out under isothermal conditions, namely at 110.degree.-120.degree. C. in 
the absence of dibenzoyl peroxide (BPO) and at 75.degree.-80.degree. C. in 
the presence of 0.18 part of BPO. In all cases, tertiary dodecylmercaptan 
(TDM) was present as a regulant. 
In this stage of the process the speed of the horseshoe stirrer was 200 
r.p.m. The first stage was continued to a conversion of 35%. The 
composition of the starting solution (reaction batch) is given in the 
Table. In Comparative Experiment C1, a homopolybutadiene (M.sub.w 
.about.180,000) having a medium-cis structure (.about.35% of 
1,4-cis,.about.55% of 1,4-trans and about 10% of 1,2-vinyl) was used. 
Comparative Experiments C2 and C3 and Examples 1 and 2 were carried out 
using linear styrene-butadiene 2-block copolymers with a well-defined 
transition (C2 and C3: ratio styrene:butadiene 40:60, M.sub.w about 
210,000; E.sub.1 and E.sub.2 : styrene:butadiene 70:30, M.sub.w about 
180,000) and medium-cis-PBu blocks. The polybutadiene content was the same 
in all batches. To this mixture was also added 0.12 part of a sterically 
hindered phenol (.RTM.Irganox 1076). 
After the stated conversion figure of 35% had been reached, 1.10 parts of 
dicumyl peroxide were added to the reaction mixture, followed by 1800 
parts of water, based on 2000 parts of the reaction batch from the mass 
polymerization, and 18 parts of a protective colloid based on 
polyvinylpyrrolidone (.RTM.Luviskol K 90) as well as 1.8 parts of sodium 
phosphate as stabilizers. 
In the suspension stage, the mixture was polymerized at 110.degree. C. for 
3 hours, at 130.degree. C. for a further 3 hours and finally at 
140.degree. C. for 4 hours. The bead polymer obtained was filtered off and 
dried. Samples were taken of the resulting products to prepare molded 
platelets for electron micrographs and test specimens for the mechanical 
tests. The results are shown in the Table. 
TABLE 
______________________________________ 
Properties of the molding materials of Examples (E.sub.n) 
and Comparative Experiments (C.sub.n) 
Experiment/Example 
C1 C2 C3 E1 E2 
______________________________________ 
Parts of styrene 
67.3 63.4 63.4 53.5 53.5 
Parts of AN 22.5 21.1 21.1 17.8 17.8 
Parts of SB block 
0 13.2 13.2 26.4 26.4 
rubber 
Parts of polybutadiene 
7.9 0 0 0 0 
Parts of TDM 0.20 0.20 0.18 0.20 0.18 
Parts of BPO 0 0 0.15 0 0.15 
% by weight of sty- 
- 40 40 70 70 
rene bonded in SB 
block rubber 
Polymerization tem- 
115 113 76 120 79 
perature (.degree.C.) 
Vicat temperature 
97.0 98.0 97.0 88.0 86.0 
(.degree.C.) 
Tensile stress (N/mm.sup.2) 
28.3 39.9 39.5 27.2 28.2 
Breaking strength 
28.3 39.4 34.1 27.1 26.5 
(N/mm.sup.2) 
Elongation at break 
20 5 5 3 3 
(%) 
Notched impact 
8.1 12.3 16.7 6.0 10.5 
strength (kJ/m.sup.2) 
Transparency - - - + + 
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BRIEF DESCRIPTION OF THE DRAWINGS 
FIGS. 1 to 4 
Electron micrographs of thin sections of molding materials from 
Experiment 1=FIG. 1 
Experiment 2=FIG. 2 
Example 1=FIG. 3 
Example 2=FIG. 4 
(Magnification 10,000.times., so that 1 cm in the micrograph corresponds to 
1 .mu.m)