Process for the manufacturing of ABS-molding compositions

Abstract

A process for preparing a thermoplastic polymer composition or a thermoplastic polymer blend, comprising: from 20 to 80% by weight of at least one water-moist elastomer component A containing up to 40%, preferably up to 30% by weight of residual water, from 20 to 80% by weight of at least one thermoplastic polymer B, from 0 to 40% by weight of at least one further polymer C, and from 0 to 60% by weight of additive(s) D, by mixing the elastomer component A with the thermoplastic polymer B and, if present, the further polymer C and, if present, the additive(s) D in an extruder, comprising the steps of precipitating the elastomer component A, and mechanical dewatering of the elastomer component A leads to improved salt-free products.

Claims

1. A process for preparing a thermoplastic polymer composition or a thermoplastic polymer blend, comprising: A) from 20 to 80% by weight of at least one water-moist elastomer component A containing up to 40% by weight of residual water B) from 20 to 80% by weight of at least one thermoplastic polymer B, C) from 0 to 40% by weight of at least one further polymer C, and D) from 0 to 60% by weight of at least one additive D, by mixing the elastomer component A with the thermoplastic polymer B and, if present, the further polymer C and, if present, the at least one additive D in an extruder, comprising the steps of: a) precipitating the elastomer component A, separately or together with parts of one or several other components, in an aqueous precipitation step (I), wherein the aqueous composition used for precipitation contains less than 5.0% by weight, relating to the weight of the dry elastomer component A, of a salt, b) mechanical dewatering of the elastomer component A in one or more dewatering steps (V), wherein the components A, B and, if present, C and D are fed into an extruder, which has at least two screws rotating in the same direction or in opposite directions and having a screw diameter Ds, and, in the conveying direction, the extruder is essentially composed of: at least one metering section MS into which elastomer component A is fed to the extruder by a metering device, at least one squeeze section SS which serves for dewatering the elastomer component A and contains at least a first retarding element and at least one dewatering orifice which is present upstream of the first retarding element, at least one feed section FS in which the thermoplastic polymer B is introduced as a melt into the extruder, at least one plastication section PS provided with mixing or kneading elements, at least one last devolatilization section VS which is provided with at least one devolatilization orifice and in which the remaining water is removed as steam, and a discharge zone ZZ, wherein the components C and/or D, if present, are fed to the extruder together or separately from one another wherein the aqueous precipitation step (I) is directly or indirectly followed by a sintering step (II), wherein the precipitated component A is agglomerated to a larger particle size, characterized by using a temperature from 100 to 125 C. and wherein the elastomer component A is washed, directly or indirectly after the sintering step (II), with an amount of water which corresponds to 10 to 50% by weight of water, relating to the dry weight of the elastomer component A.

2. A process as claimed in claim 1, wherein the elastomer component A is precipitated, separately from the other components, in an aqueous precipitation step (I), using an aqueous precipitation composition containing less than 3.5% by weight of a salt, relating to the dry weight of the elastomer component A.

3. A process as claimed in claim 1, wherein the sintering step (II) is characterized by using a temperature from 100 to 115 C.

4. A process as claimed in claim 1, wherein the sintering step (II) is effectuated at a pressure above atmospheric pressure.

5. A process as claimed in claim 1, wherein the salt used for the precipitation step (I) is chosen from the group consisting of anhydrous magnesium sulfate, magnesium sulfate with crystal water, anhydrous aluminum sulfate, aluminum sulfate with crystal water, calcium chloride, magnesium chloride, magnesium hydroxide, and a bi-valent salt or a tri-valent salt of sulphuric acid, and combinations thereof.

6. A process as claimed in claim 1, wherein sulphuric acid is used for the precipitation step (I).

7. A process as claimed in claim 1, wherein the precipitation step (I) comprises more than one subsequent steps, which differ in at least one of the parameters chosen from the group consisting of: salt used for the precipitation, amount of salt and/or acid used for the precipitation, pH-value, temperature, concentration of salt and/or acid used for the precipitation, residence time, vessel size, pressure, stirrer speed, and stirrer type.

8. A process as claimed in claim 1, wherein at least a part of the water emerging from the dewatering orifices is present in the liquid phase.

9. A process as claimed in claim 1, wherein the screw elements of the extruder have a flight depth ratio DS.sub.,external/DS.sub.internal of from 1.2 to 1.8 and contain 3-flight and 2-flight high volume elements.

Description

EXAMPLES

a) Extruder Configuration

(1) A twin-screw extruder of the type ZSK133 from Coperion, Stuttgart, was used, said extruder consisting of 15 sections. Their arrangement in the downstream direction was as follows:

(2) Section 1 (VeS): 520 mm (Length 4D), unheated, with metering orifice at the top, which is provided with metering via a conveying screw for elastomer component A.

(3) Section 2 (MS): 520 mm (Length 4D), unheated, without orifices and with conveying screw.

(4) Section 3 (SS): 520 mm (Length 4D), unheated, with dewatering orifice on the top (bore in the extruder barrel in the form of a horizontal figure eight with its longitudinal axis in the conveying direction), which is provided with a retaining and conveying screw for squeezing out water from the elastomer. Extruder contains kneading blocks.

(5) Section 4 (MS): 260 mm (Length 2D), unheated, without orifices and with conveying screw.

(6) Section 5 (SS): 520 mm (Length 4D), unheated, with dewatering orifice on the top (bore in the extruder barrel in the form of a horizontal figure eight with its longitudinal axis in the conveying direction), which is provided with a retaining and conveying screw for squeezing out water from the elastomer. Extruder contains kneading elements.

(7) Section 6 (SS): 520 mm (Length 4D), unheated, Fuji plate filters on the size for squeezing out water from the elastomer with conveying elements.

(8) Section 7 (FS): 520 mm (Length 4D), heated, with orifice at the top through which the melt of polymer B is introduced with kneading elements.

(9) Section 8 (MS): 520 mm (Length 4D), heated, without orifices and with kneading and conveying screw.

(10) Section 9 (VS): 520 mm (Length 4D), heated, with devolatilization orifice at the top and conveying screw, devolatilization is operated under atmospheric pressure (first (atmospheric) devolatilization).

(11) Section 10 (FS): 520 mm (Length 4D), heated, with orifice at the top through which a second dosing of the melt of polymer B is introduced.

(12) Section 11 (VS): 520 mm (Length 4D), heated, with devolatilization orifice at the top and conveying screw, devolatilization is operated under 400-700 mbar (second (vacuum) devolatilization).

(13) Section 12 (FxS): 520 mm (Length 4D), Heated, with lateral orifice through which melt of rework and additives are introduced via a ZSK70 side extruder (from Coperion). Contains conveying and kneading blocks.

(14) Sections 13-15 (ZZ): 520 mm (Length 4D), heated, without orifices and with conveying screw (discharge)

(15) Termination: Die head with cylindrical holes for underwater pelletizing.

(16) The screw diameter is Ds=133 mm. The screw is deep-flighted (large flight depth) and the flight depth ratio Ds, external /Ds, internal is 1.55. The screw has a two-flight design.

(17) Polymer Components Used

(18) The following graft rubbers were used as elastomer component A:

(19) A: Graft Polymer Based on Butadiene, Grafted with SAN

(20) Butadiene was polymerized in emulsion, the latex obtained was agglomerated, a latex having an average particle size d50 of 238 nm being formed, and graft polymerization was then effected with a mixture of styrene and acrylonitrile. Further details are given in German Published Application DE-A 2,427,960, column 6, line 17 to column 7, line 27. The graft polymer is precipitated, sintered and washed as outlined in table.

(21) B: Styrene/Acrylonitrile Copolymer

(22) A SAN-copolymer with 75% by weight of styrene and 25% by weight of acrylonitrile was prepared by the continuous solution polymerization method, as described in Kunststoff-Handbuch, Editors Vieweg and Daumiller, Vol. V Polystyrol, Hanser-Verlag Munich 1969, pages 122-124. The viscosity number VN (determined according to DIN 53726 at 25 C., 0.5% strength by weight in dimethylformamide) was 64 ml/g.

(23) Processing Steps:

(24) A mixture of 46% component A and 54% component B relating to the dry weight of the mixture was compounded under aforementioned conditions at melt temperatures of 220-260 C., extruded as pellets in underwater granulation, dried 4 hours at 80 C. in a hot oven or dryer and then molded into 6060 mm^2 and 4 mm thick plaques and subsequently stored 3 days in deionized water at 23 C. Subsequently, the plaques were taken out of the water, remaining water droplets wiped off and the plaques put into a heated vacuum oven at 100 C. for 1 hour.

(25) TABLE-US-00001 TABLE Precipitate concentration in 20 wt % Sintering Precipitated elastomer Sintering time Washing Score Sample no with suspension at ( C.) (min) water points 1 (Comparison) MgSO.sub.4 0.8% 124 40 No 1 2 MgSO.sub.4 0.7% 124 40 No 1 3 MgSO.sub.4 0.6% 124 40 No 1-2 4 MgSO.sub.4 0.6% 120 40 No 1-2 5 MgSO.sub.4 0.6% 116 40 No 2 6 MgSO.sub.4 0.6% 110 40 No 2-3 7 MgSO.sub.4 0.6% 108 40 No 2-3 8 MgSO.sub.4 0.6% 108 40 300 l/h 2-3 9 MgSO.sub.4 0.6% 108 40 600 l/h 2-3 10 MgSO.sub.4 0.6% 108 40 900 l/h 3 11 MgSO.sub.4 0.6% 108 40 2000 l/h 3

(26) The visibility of specks on the surface of the plaques, being stored in a heated vacuum oven at 100 C. for 1 hour, were assessed independently by 5 different persons, using following score points: 1 point: very rough and uneven surface 2 points: rough surface 3 points: smooth surface, specks hardly visible 4 points: perfectly smooth surface.

(27) The magnesium content in the final product is reduced from ca. 0.6% to 0.3% by weight with reduced MgSO.sub.4 from 0.7 to 0.6 wt % per dry weight elastomer in the precipitation stage at lower sintering temperatures from 124 to 108 C., and at higher washing rates. The salt specs are reduced by a factor between 2 and 3.