Process for producing a stabilizer dispersion and process for producing a thermoplastic composition stabilized with the stabilizer dispersion

Abstract

The invention relates to a process for producing a stabilizer dispersion S, wherein the stabilizer dispersion is an aqueous composition comprising at least one phenolic stabilizer A, at least one thio co-stabilizer B, at least one surfactant C and at least one silicon oil component D. Further the present invention is directed to a process for producing a thermoplastic moulding composition, in particular an composition based on acrylonitrile butadiene styrene copolymers (ABS), using the stabilizer dispersion S.

Claims

1. A process for producing a stabilizer dispersion S comprising: a) at least one phenolic stabilizer A; b) at least one thio co-stabilizer B; c) at least one surfactant C; d) at least one silicon oil component D; e) optionally, at least one further component E; and f) an aqueous phase P comprising at least 80% by weight, based on the total aqueous phase P, water, wherein the process comprises the following steps: i) providing an aqueous composition comprising an aqueous phase P; ii) adding at least one thio co-stabilizer B to the aqueous composition obtained in step i), wherein the temperature of the aqueous composition is higher than or equal to the melting point of the at least one thio co-stabilizer B; iii) adding at least one phenolic stabilizer A to the aqueous composition obtained in step ii), wherein the temperature of the aqueous composition is higher than or equal to the melting point of the at least one thio co-stabilizer B; iv) adding at least one surfactant C; v) adding at least one silicon oil component D and optionally at least one further component E; and vi) homogenization of the aqueous composition obtained in steps i) to v) wherein the aqueous composition is passed at least once through at least one homogenization device, wherein a stabilizer dispersion S, consisting of a continuous phase and at least one disperse phase, formed by particles of the disperse phase, is obtained, wherein the weight median particle size D50 of disperse phase particles of the stabilizer dispersion S obtained in step vi) is less than or equal to 3 m.

2. The process according to claim 1, wherein the at least phenolic stabilizer A is selected from the group consisting of octadecyl 3-(3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)propionate; a butylated reaction product of p-cresol and dicyclopentadiene according to formula (IId) ##STR00012## with n=1-3; 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane; 2,2-methylenebis(6-(1,1-dimethylethyl)-4-methyl-phenol); 4,4-thiobis(3-methyl-6-tert-butylphenol); and compounds of the formula (I) ##STR00013## wherein R.sup.1 is methyl or ethyl, R.sup.2 is C.sub.2-C.sub.20-alkyl, and R.sup.3 is C.sub.1-C.sub.4-alkyl.

3. The process according to claim 1, wherein the at least one thio co-stabilizer B is a sulfide compound selected from the group consisting of dilauryl thiodipropionate, pentaerythritol tetrakis(octyl thiodipropionate), distearyl thiodipropionate, dimyristyl thiodipropionate, pentaerythritol tetrakis(-lauryl thiodipropionate), 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, trimethylolpropane tris(octyl thiodipropionate), trimethylolethane tris(octyl thiodipropionate), ethylene glycol bis(lauryl thiodipropionate), and didodecyl monosulfide.

4. The process according to claim 1, wherein the surfactant C is selected from the group consisting of sodium and potassium salts of alkylsulfonates, arylalkylsulfonates, fatty acids, and salts of fatty acids.

5. The process according to claim 1, wherein the solid content of the aqueous composition obtained in obtained in steps i) to v) is in the range of 65 to 90% by weight, based on the total aqueous composition.

6. The process according to claim 1, wherein the temperature of the aqueous composition in steps ii) and iii) is in the range of 50 to 100 C.

7. The process according to claim 1, wherein the process encompasses the steps i) and iv) providing an aqueous composition comprising the aqueous phase P and the at least one surfactant C selected from fatty acids; and v) adding the at least one silicon oil component D and as component E at least one alkaline compound.

8. The process according to claim 1, wherein the process is carried out in a stirred tank equipped with at least one by-pass, wherein the at least one by-pass includes one or more homogenization nozzle and wherein the homogenization in step vi) is carried out by piping the aqueous composition through the at least one by-pass.

9. The process according to claim 1, wherein the stabilizer dispersion S comprises: 0.1 to 65% by weight, based on the total weight of the stabilizer dispersion S, of the at least one phenolic stabilizer A; 0.1 to 65% by weight, based on the total weight of the stabilizer dispersion S, of the at least one thio co-stabilizer B; 0.1 to 20% by weight, based on the total weight of the stabilizer dispersion S, of the at least one surfactant C; 0.1 to 40% by weight, based on the total weight of the stabilizer dispersion S, of the silicon oil D; and an amount of the aqueous phase P to make the total weight of the stabilizer dispersion 100% by weight.

10. The process according to claim 1, wherein the stabilizer dispersion S comprises: 0.1 to 65% by weight, based on the total weight of the stabilizer dispersion S, of the at least one phenolic stabilizer A; 0.1 to 65% by weight, based on the total weight of the stabilizer dispersion S, of the at least one thio co-stabilizer B; 0.1 to 20% by weight, based on the total weight of the stabilizer dispersion S, of the at least one surfactant C; 0.1 to 40% by weight, based on the total weight of the stabilizer dispersion S, of the silicon oil D; 0.01 to 30% by weight, based on the total weight of the stabilizer dispersion S, of at least one further component E; and an amount of the aqueous phase P to make the total weight of the stabilizer dispersion 100% by weight.

Description

(1) FIG. 1 shows a stirred tank equipped with a by-pass and a homogenization slit nozzle that can be used for the inventive process for producing a stabilizer dispersion S. The symbols in FIG. 1 have the following meanings:

(2) (1) stirred tank (2) slit nozzle (3) stirrer (4) compressor pump (5) by-pass pipe (6) valves (7) temperature control unit (A) storage and supply tank for the at least one phenolic stabilizer A (B) storage and supply tank for at least one thio co-stabilizer B (C) storage and supply tank for the at least one surfactant C (D) storage and supply tank for the at least one silicon oil component D (E) storage and supply tank for the at least one further component E (P) storage and supply tank for the aqueous phase P

(3) The components A and B are added successively through supply pipes from (A) and (B) into the stirred tank (1) as described in claim 1. The other components are typically added via pipe into the stirred tank as indicated in FIG. 1 and described above. After preparation of the pre-dispersion in the stirred tank the mixture is passed via by-pass pipe (5) through the homogenization slit nozzle (2).

(4) For example a typical embodiment encompasses (1) stirred tank with a volume of 10 m.sup.3 (A) storage and supply tank for Wingstay L (component A) in form of Big Bags (B) storage and supply tank for Irganox@PS 800 (component B) in form of Big Bags, (C) storage and supply tank for oleic acid (surfactant C) in form of an intermediate bulk container of 1 m.sup.3 (D) storage and supply tank for silicon oil in form of an intermediate bulk container of 1 m.sup.3 (E) storage and supply tank for further component, e.g. causic soda solution (P) storage and supply tank for hot and cold demineralized water.

(5) The present invention is further illustrated by the following examples and claims.

EXPERIMENTAL EXAMPLES

Example I. Preparation of Stabilizer Dispersions S

(6) a. The Following Compounds are Used

(7) A: phenolic stabilizer, Wingstay L from Omnova Solutions Inc., US (butylated reaction product of p-cresol and dicyclopentadiene, CAS Reg. No. 68610-51-5), B: thio co-stabilizer, Irganox PS 800 from BASF SE (didodecyl-3,3-dithiopropionate), C1: surfactant, potassium stearate, C2: surfactant, oleic acid, D: silicon oil, polydimethylsiloxane with a kinematic viscosity of 30,000 mm.sup.2/s, E1: caustic soda solution (sodium hydroxide) with solid content of 30% by weight or 32% by weight.

(8) The solid contents of stabilizer dispersions S were measured by evaporation of the samples at 180 C. for 25 min in a drying cabinet.

(9) b. Stabilizer Dispersion S1

(10) A stabilizer dispersion S1 were prepared in accordance with DE 199 46 519 A1 using a rotor-stator mixer with a tip speed of 21 m/s.

(11) 55 parts of demineralized water and 5 parts of potassium stearate C1 are provided first at 60 C. in a glass baker and mixed with a stirrer. 20 parts of B are added and molten and the temperature is maintained at 60 C. After completion of the melting the mixture is mixed with a rotor-stator-mixer with a tip speed of 21 m/s for 5 minutes. After this 20 parts of A is added to the mixture at 60 C. and mixed with a stirrer followed by mixing with the rotor-stator-mixer with a tip speed of 21 m/s for 3 minutes. Total batch size: 200.0 g Solid content by theory: 45.0% by weight Solid content measured: 46.17% by weight

(12) Under a microscope particles in the range of 2 to 6 m and some large particles in the range of 20 m are visible. After one day at room temperature the dispersion segregated into a lower solid part and an upper liquid part.

(13) c. Stabilizer Dispersion S2

(14) A stabilizer dispersion S2 were prepared in accordance with DE 199 46 519 A1 using a rotor-stator mixer with a tip speed of 21 m/s.

(15) 14.95 parts of demineralized water and 2.96 parts of potassium stearate C1 were provided first at 80 C. in a glass baker and mixed with a stirrer. 26.02 parts of B were added and molten and the temperature was maintained at 80 C. After completion of the melting the mixture was mixed with a rotor-stator-mixer with a tip speed of 21 m/s for 5 minutes. After this 26.02 parts of A was added to the mixture at 80 C. while simultaneously the mixing with the rotor-stator-mixer with a tip speed of 21 m/s is continued for for 3 minutes. Finally, 30.05 parts of demineralized water was added and mixed with stirrer. Total batch size: 200.0 g Solid content by theory: 55.0% by weight Solid content measured: 54.67% by weight

(16) Under a microscope particles in the range of 2 to 6 m and some large particles in the range of up to 40 m were visible. After one day at room temperature the dispersion segregated into a lower solid part and an upper liquid part.

(17) d. Stabilizer Dispersion S3 (Inventive Example)

(18) A stabilizer dispersion S3 comprising components A, B and C was prepared using a batch type rotor-stator mixer with a tip speed of 21 m/s.

(19) 16.83 parts of demineralized water and 2.90 parts of oleic acid were provided first at 80 C. in a glass baker and mixed with a stirrer. 23.98 parts of B were added and molten whereat the temperature was maintained at 80 C. After this 28.15 parts of A was added to the mixture at 80 C. under stirring and the components A and B form a melt. 5.80 parts of component D (silicon oil) was added and mixed with a stirrer. Finally 1.29 parts of caustic soda (with solid content of 30% by weight) was added and mixed by stirring. The aqueous composition was mixed with a rotor-stator-mixer with a tip speed of 21 m/s for 5 minutes. Finally 21.05 parts of demineralized water were added and mixed with stirrer. Total batch size: 400.0 g Solid content by theory: 61.04% by weight Solid content measured: 62.39% by weight

(20) A stable dispersion was achieved; the particles sizes were measured with the procedure described under Example IV. The average particle diameter D.sub.50 was determined to 0.96 m and D.sub.W to 0.98 m.

(21) e. Stabilizer Dispersion S4 (Inventive Example)

(22) A stabilizer dispersion S4 comprising components A, B and C was prepared using a stirred tank equipped with by-pass pipe including a homogenization nozzle.

(23) 15.87 parts of demineralized water and 2.90 parts of oleic acid were provided first at 80 C. in 7 cbm (m.sup.3) vessel and mixed with a stirrer. 23.98 parts of B were added and molten whereat the temperature was maintained at 80 C. After this 28.16 parts of A were added to the mixture at 80 C. under stirring, whereat A and B form a melt. 5.80 parts of component D (silicon oil) were added and mixed with a stirrer. Finally 1.30 parts of caustic soda (with solid content of 32.0% by weight sodium hydroxide) were added and mixed by stirring. The mixture was then pumped through a by-bass pipe (loop pipe) and through a homogenization nozzle placed in the by-pass pipe for 4 hours with pressure drop over the nozzle from 11 to 15 bar. The homogenization nozzle is a perforated plate having eight slit like nozzles each with a dimension of 50 mm2 mm. The throughput through the by-pass pipe is 35,000 kg/hour. During the homogenization step the temperature was maintained at 80 C.

(24) Finally 21.99 parts of demineralized water were added and mixed with stirrer. All amounts given above in parts means parts per weight. Total batch size: 6,003 kg Solid content by theory: 61.1% by weight Solid content, measured: 61.1% by weight

(25) A stable dispersion was achieved; the particles sizes were measured with the procedure described in Example IV. The average particle diameter D.sub.50 was determined to 0.93 m and the D.sub.W to 0.93 m. The stabilizer dispersions S1 to S4 are summarized in the Table 1.

(26) TABLE-US-00001 TABLE 1 Stabilizer dispersions S1 to S4 (all amounts given in % by weight unless indicated otherwise) S1 S2 S3 S4 A 20.00 26.02 28.15 28.16 B 20.00 26.02 23.98 23.98 C1 5.00 2.96 C2 2.90 2.90 D 5.80 5.80 E1 1.29 1.30 Water 55.00 45.00 37.88 37.86 Solid content 46.17 54.67 62.39 61.10 measured [%]

Example II: Preparation of ABS Graft Copolymers CB

(27) The following mixture of two ABS rubber latexes was used as graft copolymer CB: 2352.9 g of a first graft rubber latex with a solid content of 34.0% by weight obtained by emulsion polymerization of 50% by weight of a mixture of styrene and acrylonitrile in a ratio of 73:27 by weight onto 50% by weight of a polybutadiene latex (calculated as solids of the polybutadiene latex) with a D.sub.50 size of 125 nm using potassium peroxodisulfate as initiator and tert-dodecylmercaptane as chain transfer agent and 3191.5 g of a second graft rubber latex with a solid content of 37.6% by weight obtained by emulsion polymerization of 41% by weight of a mixture of styrene and acrylonitrile in a ratio of 73:27 by weight onto 59% by weight of a polybutadiene latex (calculated as solids of the polybutadiene latex) with a D.sub.50 size of 340 nm using potassium peroxodisulfate as initiator and tert-dodecylmercaptane as chain transfer agent

(28) The mixing ratio of the first graft rubber latex to the second graft rubber latex was 40:60 by weight based on the solids content.

(29) The graft copolymer CB was mixed with each one of the stabilizer dispersions S1 to S4. The stabilizer dispersion was fed into the graft copolymer CB (which was an aqueous emulsion polymer) and stirred for 1 hour. Then the precipitation of the stabilized latex was performed by feeding this latex under stirring into a magnesium sulfate/sulfuric acid solution and heating up to 95 C. The final solid content of the precipitated dispersion was 12.5% by weight.

(30) The amount of magnesium sulfate (100% by weight) and sulfuric acid (96% by weight) was used in such way that the concentration of magnesium sulfate was 0.5% by weight, based on the total aqueous phase (in the precipitation mixture) and the concentration of sulfuric acid (96% by weight) was 0.07% by weight, based on the total aqueous phase (in the precipitation mixture).

(31) With specific values for the precipitation of the ABS graft copolymer CB1, the following amounts were used:

(32) Demineralized water (10,981 g) was provided first then adding and solving of 55.23 g of magnesium sulfate (100% by weight) and 7.74 g of sulfuric acid (96% by weight). Afterwards the mixture of the graft rubber latexes and stabilizer dispersion S1 (32.49 g) was added under stirring and heating up to 95 C.

(33) The ABS graft copolymers CB2 to CB4 were precipitated in the same manner; the amount of demineralized water which is provided first was adjusted slightly to achieve the same final solid content of the precipitated dispersion, which was in each case 12.5% by weight.

(34) The mixture of graft copolymer CB and stabilizer dispersion was centrifuged, washed with water and dried to achieve residual humidity less than 1.0% by weight. An ABS graft rubber powder was obtained and used as graft copolymer CB in example Ill. The compositions of ABS graft copolymers are summarized in Table 2. The amounts, e.g. of stabilizers A and B, are calculated based on an corrected solid content, wherein a correction factor based on the measured solid content and the calculated solid content is used.

(35) The thermal stability of said graft rubber powder was tested by a scorch test. A layer of about 1 cm of powder is stored in an oven at 180 C. The time in minutes was recorded when the colour of the powder change to dark brown.

(36) The results are summarized in the following Table 2.

(37) TABLE-US-00002 TABLE 2 Composition of the ABS graft copolymers CB1 to CB4 ABS graft copolymer CB CB1 CB2 CB3 CB4 Stabilizer dispersion S1 S2 S3 S4 Amount of stabilizer 32.49 27.44 28.76 29.35 dispersion [g] Amount of graft 2000 2000 2000 2000 copolymer CB [g solids] Amount of stabilizer 0.744 0.744 0.889 0.889 dispersion in CB [% by weight, based on solids stabilizer per solids graft co-polymer] A in graft copolymer CB 0.331 0.352 0.403 0.430 powder [% by weight] B in graft copolymer CB 0.331 0.352 0.343 0.343 powder [% by weight] D in graft copolymer CB 0 0 0.083 0.083 powder [% by weight] Scroch test at 285 270 467 497 180 C. [min]

Example III: Preparation and Characterization of Thermoplastic Moulding Compositions

(38) a. Styrene-Acrylonitrile Copolymer CA (SAN Copolymer)

(39) A statistical copolymer from styrene (monomer CA1) and acrylonitrile (monomer CA2) with a ratio of polymerized styrene to acrylonitrile of 73:27 was produced by free radical solution polymerization. The SAN copolymer (copolymer CA) exhibited a melt flow rate (MVR) of 56 mL/10 min, determined at 220 C. and 10 kg load according to ISO 1133.

(40) b. Compounding Thermoplastic Moulding Compositions

(41) The thermoplastic moulding compositions were produced by compounding and pelletized the compositions with a twin screw extruder ZSK25 at 240 C. and 660 rpm. The following components were used: Copolymer CA: SAN copolymer prepared according to Example IIIa, Graft copolymer CB: One of ABS graft rubber powders CB1 to CB4 according to Example II, Silicon oil D1: Polydimethylsiloxane with a kinematic viscosity of 30,000 mm.sup.2/s Further component E: E1 Ethylene bis(stearamide) (EBS) E2 Magnesium stearate

(42) The thermoplastic moulding compositions are described in the following Table 3.

(43) TABLE-US-00003 TABLE 3 Thermoplastic moulding compositions (all amounts given in % by weight) Thermoplastic Composition TC1 TC2 TC3 TC4 ABS rubber powder (CB) CB1 CB2 CB3 CB4 29.344 29.344 29.368 29.368 SAN polymer (CA) 68.527 68.527 68.527 68.527 E1 1.958 1.958 1.958 1.958 E2 0.147 0.147 0.147 0.147 silicon oil D 0.024 0.024 0 0

(44) The melt volume rate MVR [mL/10 min] is measured on a polymer melt at 220 C. and 10 kg load according to ISO 1133.

(45) The thermoplastic moulding compositions described above were processed to ISO test bars (80104 mm) by injection moulding at a mass temperature of 240 C. and a mould temperature of 70 C. The following tests were performed using these test bars: notched Izod impact strength [kJ/m.sup.2] according to ISO 180-1A at 23 C., Vicat softening temperatures B/120 (50N, 120 C./h) according to ISO 306.

(46) The test results are summarized in the following Table 4.

(47) TABLE-US-00004 TABLE 4 Properties of thermoplastic moulding composition Thermoplastic Composition TC1 TC2 TC3 TC4 MVR [mL/10 min] 23.8 26.1 27.8 32.1 Notched Izod impact strength [kJ/m.sup.2] 16.1 15.5 12.7 18.7 Vicat B/120 [ C.] 95.6 96.2 97.4 101.0

(48) The results of tables 2 and 4 clearly demonstrate the advantageous technical properties of the stabilizer dispersions and the thermoplastic mouldings prepared in accordance with the inventive processes in comparison to the state of the art.

(49) The ABS graft copolymers CB comprising the stabilizer dispersion S3 and S4 show improved heat stability in comparison to the comparative examples CB1/S1 and CB2/S2 (table 2).

(50) The thermoplastic moulding compositions which were prepared according to the inventive process and with a stabilizer dispersion produced in accordance with the inventive process (examples TC3 and TC4) showed good impact strength and a good ratio of melt flow. Further these compositions showed improved thermal stability, i.e. higher Vicat temperature, in comparison to the comparative examples TC1 and TC2.

(51) Additionally, it can be stated that the thermoplastic composition TC4 comprising a stabilizer dispersion S, which is produced by homogenization via a homogenization nozzle (TC4), shows further improved heat stability, impact strength and melt flowability in comparison to the examples using a homogenization device based on a rotor/stator principle. Thus, the homogenization in a stirred tank with homogenization via by-pass pipe is the most preferred homogenization method.

Example IV: Particles Size Measurement

(52) The particle size distribution and in particular the weight mean average particle diameter D.sub.W were determined by a measurement with an ultracentrifuge (see W. Scholtan, H. Lange: Kolloid Z. u. Z. Polymere 250, pp. 782 to 796 (1972)) or a disc centrifuge. The definition of the weight mean average particle size diameter D.sub.W is given by:
D.sub.W=sum(n.sub.i*D.sub.i.sup.4)/sum(n.sub.i*D.sub.i.sup.3) n.sub.i: number of particles with the diameter D.sub.i

(53) (G. Lagaly, O. Schulz, R. Ziemehl: Dispersionen und Emulsionen: Eine Einfhrung in die Kolloidik feinverteilter Stoffe einschlielich der Tonminerale, Darmstadt: Steinkopf-Verlag 1997, ISBN 3-7985-1087-3, page 282, formula 8.3b).

(54) The summation is normally performed from the smallest to largest diameter of the particles size distribution. It should be mentioned that for a particles size distribution of particles with the same density the volume mean average particle size diameter D.sub.v is equal to the weight mean average particle size diameter D.sub.W.

(55) The weight median particle size D.sub.50 is the diameter which divides the population exactly into two equal parts. 50% by wt. of the particles are larger than the weight median particle size D.sub.50 and 50% by wt. are smaller.

(56) In particular the weight average particle size D.sub.W and D.sub.50 of the stabilizer dispersion were measured with a disc centrifuge DC 24000 by CPS Instruments Inc. equipped with a low density disc at a rotational speed of the disc of 24,000 rpm. A polybutadiene latex with a narrow distribution and a mean particle size of 405 nm was used for calibration. An aqueous sugar solution of 17.1 mL with a density gradient of 8 to 20% by weight of saccharose was used, in order to achieve a stable flotation behaviour of the particles. The measurements were carried out at a rotational speed of the disc of 24,000 rpm by injecting 0.1 mL of a diluted dispersion prepared in an aqueous saccharose solution (24% by weight), containing about 0.2-2% by weight of rubber particles, into the disc containing the aqueous sugar solution with a density gradient of 8 to 20% by weight of saccharose.

(57) For stabilizer emulsions containing Wingstay L as phenolic stabilizer A and didodecyl-3,3-dithiopropionate (Irganox PS 800) as thio co-stabilizer B, the density of particles was determined to 1.016 g/ccm and the refractive index to 1.516.

(58) For stabilizer emulsions containing Wingstay L as phenolic stabilizer A, didodecyl-3,3-dithiopropionate (Irganox PS 800) as thio co-stabilizer B and silicon oil component D the density of particles was determined to 1.012 g/cm.sup.3 and the refractive index to 1.504.