Process for the production of graft copolymer powder compositions and thermoplastic resin compositions

Abstract

The present invention is directed to a process for the production of graft copolymer compositions which are based on acrylonitrile-styrene-acrylate (ASA) or acrylonitrile-butadiene-styrene (ABS) graft copolymers. The graft copolymers compositions are obtained by emulsion polymerization and afterwards precipitation, dewatering, drying and optionally cooling of the dried graft copolymer powder, wherein the graft copolymer B powder obtained is mixed with an aeration gas, preferably air and/or nitrogen, wherein the bulk density of the graft copolymer B powder is equal or less than 98.5% of the bulk density of the non-aerated graft copolymer B, during the whole aeration step. The graft copolymer powders show higher powder flowability and less tendency of caking during storage, for example in a silo.

Claims

1. A process for the production of a graft copolymer composition comprising: B: from 90 to 100% by weight of at least one graft copolymer B comprising: B1: 50 to 90% by weight, based on the graft copolymer B, of at least one graft base B1, obtained by emulsion polymerization of: B11: 50 to 100% by weight, based on the graft base B1, at least one monomer B11 selected from C.sub.1-C.sub.8 alkyl(meth)acrylate and butadiene; B12: 0 to 10% by weight, based on the graft base B1, of at least on polyfunctional cross-linking monomer B12; and B13 0 to 50% by weight, based on the graft base B1, of at least one further monomer B13, selected from styrene, α-methylstyrene, C1-C4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, chloroprene, methylmethacrylate, alkylenglycol-di(meth)acrylate, and vinylmethylether; where the sum of B11, B12, and B13 equals 100% by weight; and B2: 10 to 50% by weight, based on the graft copolymer B, at least one graft shell B2, which is obtained via emulsion polymerization in the presence of the at least one graft base B1 of: B21 50 to 100% by weight, based on graft shell B2, of at least one vinylaromatic monomer B21, selected from styrene, α-methylstyrene or mixtures of styrene and at least one further monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8 alkyl(meth)acrylate; and B22 0 to 50% by weight, based on graft shell B2, of at least one monomer B22 selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinylmethyl ether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; where the total sum of graft base B1 and graft shell B2 equals 100% by weight; K1: from 0 to 10% by weight, of at least one other component K1; comprising the following steps: a) preparation of the at least one graft copolymer B encompassing emulsion polymerization of the monomers B21 and B22 in the presence of the at least one graft base B1 to form the at least one graft shell B2, wherein the graft copolymer B is obtained in form of a latex; b) precipitation of the at least one graft copolymer B latex after its emulsion polymerization in step a), wherein the graft copolymer B latex is mixed with at least one precipitation solution PS resulting in a precipitation mixture; c) mechanical dewatering of the precipitated graft copolymer B, where the graft copolymer B having a water content equal or less than 50% by weight is obtained; d) optionally washing of the dewatered graft copolymer B; e) drying of the dewatered graft copolymer B obtained in step c) or d) using a drying gas having a temperature in the range from 50 to 160° C. wherein a graft copolymer B powder is obtained; f) optionally cooling of the dried graft copolymer B powder obtained in step e) using a cooling gas, where the temperature of the cooling gas is equal or less than 50° C. and wherein the cooling gas is passed through the graft copolymer B powder; g) aeration of the graft copolymer B, wherein the graft copolymer B powder obtained in step e) or f) is mixed with an aeration gas, wherein the bulk density of the graft copolymer B powder is equal or less than 98.5% of the bulk density of the non-aerated graft copolymer B, during the whole aeration step g); and h) optionally addition of one or more optional components K1.

2. The process of claim 1, wherein the at least one graft base B1 is obtained by emulsion polymerization of: B11: 70 to 99.9% by weight, based on the graft base B1, at least one C.sub.1-C.sub.8 alkyl(meth)acrylate as monomer B11; B12: 0.1 to 10% by weight, based on the graft base B1, of at least on poly-functional cross-linking monomer B12; and B13: 0 to 29.5% by weight, based on the graft base B1, of at least one further monomer, selected from styrene, α-methylstyrene, C.sub.1-C.sub.4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, chloroprene, methylmethacrylate, alkylenglycol-di(meth)acrylate, and vinylmethylether; where the sum of B11, B12, and B13 equals 100% by weight.

3. The process of claim 1, wherein the at least one graft copolymer B comprises: B1: 50 to 70% by weight, based on the graft copolymer B, exactly one graft base B1; and B2: 30 to 50% by weight, based on the graft copolymer B, exactly one graft shell B2, obtained by emulsion polymerization, in presence of the graft base B1, of: B21: 50 to 95% by weight, based on the graft shell B2, at least one vinylaromatic monomer B21, selected from styrene, α-methylstyrene, or mixtures of styrene with α-methylstyrene or methyl(meth)acrylate; and B22: 5 to 50% by weight, based on the graft shell B2, at least one ethylenically unsaturated monomer B22, selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; wherein the total sum of graft base B1 and graft shell B2 is 100% by weight, and wherein the graft copolymer B latex obtained in step a) has a particle size in the range of 60 to 140 nm.

4. The process of claim 1, wherein the graft copolymer B comprises: B1: 50 to 70% by weight, based on the graft copolymer B, at least one graft base B1; B2′: 10 to 20% by weight, based on the graft copolymer B, at least one graft shell B2′, which is obtained by emulsion polymerization, in presence of graft base B1, of: B21′: 100% by weight, based on graft shell B2′, at least one vinylaromatic monomer B21′, selected from styrene, α-methylstyrene, or a mixture of styrene and at least one further monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.4-alkyl(meth)acrylate; and B2″: 20 to 30% by weight, based on the graft copolymer B, at least one graft shell B2″, which is obtained by emulsion polymerization, in presence of graft base B1 grafted with B2′, of: B21″: 70 to 80% by weight, based on the graft shell B2″, at least one vinylaromatic monomer B21″, selected from styrene, α-methylstyrene, or mixtures of styrene and α-methylstyrene or methyl(meth)acrylate; and B22″: 20 to 30% by weight, based on the graft shell B2″, at least one ethylenically unsaturated monomer B22″, selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; wherein the total sum of graft base B1, graft shell B2′, and graft shell B2″ is 100% by weight, and wherein the graft copolymer B latex obtained in step a) has a particle size in the range of 300 to 700 nm.

5. The process of claim 1, wherein the graft copolymer composition obtained by the process is a graft copolymer B powder having a water content below 5% by weight.

6. The process of claim 1, wherein the cooling step f) is carried out subsequently to the drying step e), wherein both steps are carried out using a fluidized-bed drier.

7. The process of claim 1, wherein the bulk density of the graft copolymer B powder is in the range of 98.5 to 80% of the bulk density of the non-aerated graft copolymer B powder during the whole aeration step g).

8. The process of claim 1, wherein the temperature of the aeration gas is equal to or less than 40° C.

9. The process of claim 1, wherein the graft copolymer B powder obtained in step e) or f) is mixed with the aeration gas in step g) by stirring and/or by passing the aeration gas through the graft copolymer B powder.

10. The process of claim 1, wherein the graft copolymer B powder obtained in step e) or f) is mixed with the aeration gas in step g) by continuous or discontinuous external circular conveying with air, wherein a part of the graft copolymer B powder is transported from the outlet of a storage container back to the inlet of the storage container.

11. A process for the production of a thermoplastic molding composition comprising: A: 5 to 95% by weight, of at least one thermoplastic copolymer A produced from: A1: 50 to 95% by weight, based on the copolymer A, of a monomer A1 selected from styrene, α-methylstyrene, and mixtures of styrene and at least one other monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate; and A2: 5 to 50% by weight, based on the copolymer A, of at least one monomer A2 selected from acrylonitrile and mixtures of acrylonitrile and at least one other monomer selected from methacrylonitrile, acrylamide, vinylmethyl ether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; B: 5 to 95% by weight, of at least one graft copolymer B as defined in claim 1; C: 0 to 90% by weight, of at least one further polymeric component C; and K2: 0 to 10% by weight, of at least one further component K2; comprising the following steps: a), b), c), e), g), and optionally d), f), and/or h) as described in claim 1; and mixing the thermoplastic copolymer A, the at least one graft copolymer B, and optionally one or more further polymeric component C and/or optionally one or more further components K2.

12. The process of claim 11, wherein the thermoplastic copolymer A is produced from: A1: 64 to 95% by weight, based on the copolymer A, of monomer A1 selected from styrene and mixtures of styrene and at least one other monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate; and A2: 5 to 36% by weight, based on the copolymer A, of monomer A2 selected from acrylonitrile.

13. The process of claim 11, wherein the thermoplastic molding composition comprises: C: 20 to 60% by weight, based on the total molding composition, at least one further polymer component C selected from polycarbonates, polyamides, and polyesters.

14. The process of claim 11, wherein the mixing in step i) is carried out at temperatures in the range of 180 to 300° C.

15. A graft copolymer composition obtained by a process of claim 1.

16. A graft copolymer composition of claim 15, wherein the graft copolymer composition has a bulk density of equal to or less than 98.5% of the bulk density of the non-aerated graft copolymer B.

Description

EXAMPLES

(1) 1. Preparation of Styrene-Co-Acrylonitrile Grafted Polybutylacrylate Latices (Graft Copolymer B)

(2) The following graft copolymer B latex was prepared:

(3) a. Preparation of Graft Base B1-1

(4) The reaction vessel was charged with 90.2 parts of demineralized water, 0.61 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid and 0.23 parts sodium bicarbonate. When the temperature in the reaction vessel reached 59° C. 0.16 parts of sodium persulfate, dissolved in 5 parts of demineralized water, were added. A mixture of 59.51 parts butyl acrylate and 1.21 parts was added within a period of 210 min. Afterwards the reaction was continued for 60 min. Finally the polymer dispersion (graft base B1-1) had a total solid content of 39.6% and the latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 75 nm.

(5) b. Preparation of Graft Base B1-2

(6) The reaction vessel was charged with 70.66 parts of demineralized water, 0.3 parts of the graft base B1-1 (obtained as described above having a particle diameter of 75 nm) and 0.23 parts of sodium bicarbonate. After heating the reaction vessel to 60° C., 0.16 parts of sodium persulfate, dissolved in 5 parts demineralized water, were added to the reaction mixture. A mixture of 59.51 parts butyl acrylate and 1.21 parts tricyclodecenylacrylate was added within a period of 210 min. In parallel to the first feed a solution of 0.36 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid in 16.6 parts demineralized water was also added over a period of 210 min. After 200 min, from starting the feed, the temperature was ramped to 65° C. Afterwards the reaction was continued for 60 min at 65° C. Finally the polymer dispersion (graft base B1-2) had a total solid content of 39.4% and the latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 440 nm.

(7) c. Preparation of Graft Shell B2

(8) An amount of 154 parts of the graft base B1-2 as described above was added to the reaction vessel together with 88.29 parts of demineralized water, 0.11 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid and 0.14 parts of sodium persulfate, dissolved in 5.61 parts of demineralized water. The reaction mixture was heated to 61° C. Within a period of 60 min 13.16 parts were added at a temperature of 61° C., followed by a post polymerization time of 90 min, where the temperature was increased from 61° C. to 65° C. Then a mixture of 20.5 parts of styrene and 6.83 parts of acrylonitrile were added to the reaction over a period of 150 min. The reaction was continued at 65° C. for another 60 min. A polymer dispersion with a total solid content of 35.2% was obtained. The latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 500 nm.

(9) d. Precipitation of the Graft Copolymer B Latex, Dewatering and Drying

(10) 112.5 g of a MgSO.sub.4 solution (19.9% by weight) is mixed with 2143.1 g demineralized water. 451.1 g of this solution is used as pre-charge and heated to 60° C. 900 g of a polymer latex of step b) and 1804.5 g of the remaining diluted MgSO4 solution are added separately within 10 min, while the temperature is kept at 60° C. Then the resulting mixture is heated to 92° C. for 5 min.

(11) The resulting slurry is filtered off and washed with once with 500 ml demineralized water. Graft copolymer B powder is obtained after drying the dewatered graft copolymer B in a lab oven at 70° C. for 2 days. The dried graft copolymer B had a water content of about 0.25% by weight.

(12) 2. Powder Flow Analysis

(13) Flowability has been determined according to ASTM 6773-2008 using a ring shear tester at consolidation stress σ1 of about 12 kPa. The consolidation stress σ1 was constant for all samples and has been calculated for a 100 m.sup.3 silo with a diameter of 3.5 m and average graft copolymer B powder density.

(14) The practical determination of flow properties can be carried out in a ring shear tester. Generally, the uniaxial compression test can be used as a model to define powder flowability. The powder is put into a container having walls which are assumed to be frictionless and consolidated with a normal stress σ.sub.1 (consolidation stress) for a short period of time. After removing the walls a constantly increasing normal stress σ is applied. At failure the normal stress σ.sub.c (unconfined yield strength) is measured. The ratio FFC=σ.sub.1/σ.sub.c gives the flowability of the powder. As a rule, the greater FFC (Jenike flow factor FFC value) the better is the flowability of the powder. When different powders are to be compared the consolidation stress has to be constant.

(15) When a bulk solid is stored for certain period of time the unconfined yield strength is typically increased with respect to the original value for some powders. This behavior is called time consolidation. Time consolidation can also be measured in a ring shear tester when the powder is stored at a consolidation stress σ.sub.1 for a certain period of time after pre-shear and before shear to failure.

(16) The initial flowability FFC (0 h) of graft copolymer B powder as obtained in example 1 above (after drying) was measured according to ASTM 6773-2008 as described above at different temperatures T of 60° C., 40° C., 21° C. and 15° C. Further, the flowability FFC (6 h) was determined after 6 h under 12 kPa normal load (according to ASTM 6773-2008) at the temperatures T (60° C., 40° C., 21° C. or 15° C.). The results are given is given for the following table 1.

(17) TABLE-US-00001 TABLE 1 Flowability FFC (0 h) and FFC (6 h) of graft copolymer B powder at different temperatures T (storage) Example [° C.] FFC (0 h) FFC (6 h) 1 60 3.9 1.2 2 40 4.0 1.4 3 21 4.5 2.1 4 15 5.2 2.1

(18) The higher the FFC value, the better is the flowability of a particular powder. Usually a powder having an FFC value above 4 is considered as easy flowing. It can be clearly seen that cooling (below 40° C., preferably cooling at 15 to 21° C.) significantly improves flowability of graft copolymer B powder. Furthermore, time consolidation is also reduced at temperature below 40° C. The flowability FFC (6 h) at temperatures below 40° C. is 33 to 43% higher compared to flowability FFC (6 h) at temperatures of 40° C. and higher.

(19) 3. Aeration Trials

(20) a. Aeration in a Bubble Column

(21) The graft copolymer B powder obtained in example 1 (after drying) was filled in a acrylic glass cylinder. The filing level was determined via the volume scaling of the cylinder. The initial filing height was measured after consolidation time of 10 minutes (non-aerated state). Afterwards the powder in the cylinder was aerated with an air flow of 3-4 m.sup.3/h, at a temperature in the range of 11-12.5° C. and at atmospheric pressure (977-987 mbar) until bubble formation on the surface of the powder was visible. The filing height was measured again (aerated state).

(22) The aeration was stopped and the filing height was measured after different waiting times (1 to 30 minutes). The trial was repeated with a different amount of the sample of graft copolymer B. The results are summarized in Table 2. The bulk density given in kg/m.sup.3 was determined using the filing level and the mass of the graft copolymer sample.

(23) TABLE-US-00002 TABLE 2 Aeration in a bubble column Series 2 Series 1 bulk time t bulk density density after relative to relative to stop of bulk non-aerated bulk non-aerated aeration density state density state [min] [kg/m.sup.3] [%] [kg/m.sup.3] [%] non-aerated 0 433 100%  431 100%  state aerated state 0 387 89% 364 84% after aeration 1 407 94% 400 93% 5 408 94% 402 93% 10 410 95% 404 94% 20 411 95% 404 94% 30 412 95% 404 94%

(24) The bulk density after aeration remains about 5% lower compared to the bulk density in the non-aerated state before aeration.

(25) b. Flowability Test

(26) A glass cylinder (1 L) was filed with about 600 ml of graft copolymer B powder obtained in example 1 (after drying) and stored for a period of 24 h at a certain temperature (20 or 40° C.). After storage the powder can be considered as fully vented (non-aerated state). The cylinder was brought to a tilt angle of 45° and the time is measured for the powder to completely flow out of the cylinder. This powder was again filled in the cylinder and aerated by agitating the cylinder for 5 min. After agitation the powder can be considered as completely aerated. After agitation the “flowing out time” was measured again.

(27) This procedure was repeated for different storage times after aeration (agitation). The temperature of the powder and the cylinder is controlled by a lab oven. The results are summarized in the following Table 3. It can be clearly seen that the completely fluidized powder has the best flow properties (short “flowing out time”). With increased storage time (increasing bulk density, see Table 2) the flowability is reduced (longer “flowing out time”). Both temperatures (20 and 40° C.) give the same overall picture. However, at lower temperature the initial flowability is higher.

(28) TABLE-US-00003 TABLE 3 Results from flow properties trials measured at 20 and 40° C. Flow-out time at 45° time t after stop from a 1 l cylinder of aeration 20° C. 40° C. [min] [sec] [sec] non-aerated 0 7.39 No flow aerated state 0 2.76 4.64 after aeration (by 10 2.88 9.55 agitation) 30 3.67 10.7