Process for production of impact modified thermoplastic moulding composition with improved processing and impact strength

Abstract

The present invention relates to a process for producing a thermoplastic moulding composition comprising a thermoplastic copolymer A, a graft copolymer B and optionally a further polymer component C as well as optional further additives K, wherein the preparation of the graft copolymer B is carried out via emulsion polymerization, and wherein at least one surfactant S2 is used in grafting step of emulsion polymerization in a volume concentration in the range of 0.46 to 0.75 mol/m.sup.3, based on the volume of the graft copolymer B latex particles obtained; and wherein the mean particle diameter D.sub.w of the latex particles of graft copolymer B is in the range of 60 to 800 nm.

Claims

1. A process for the preparation of a thermoplastic moulding composition comprising: A: 5 to 95% by weight, based on the total moulding composition, at least one thermoplastic copolymer A, which comprises at least one vinylaromatic monomer A1 and optionally at least one further ethylenically unsaturated monomer A2; B: 5 to 70% by weight, based on the total moulding composition, at least one graft copolymer B comprising: B1: 50 to 90% by weight, based on the graft copolymer B, at least one graft base B1 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, at least one polyfunctional, cross-linking monomer B12; and B13 0 to 29.9% by weight, based on the graft base B1, at least one further copolymerizable, monoethylenically unsaturated monomer B13 different from B11 and B12; wherein the sum of B11, B12, and optional B13 is 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 by emulsion polymerization in the presence of the at least one graft base B1 of: B21 50 to 100% by weight, based on the graft shell B2, at least one vinylaromatic monomer B21; and B22 0 to 50% by weight, based on the graft shell B2, at least one ethylenically unsaturated monomer B22; wherein the total sum of graft base B1 and graft shell B2 is 100% by weight; C: 0 to 90% by weight, based on the total moulding composition, at least one further polymer component C; and K: 0 to 40% by weight, based on the total moulding composition, at least one further additive K; wherein the process encompasses the steps: a) preparation of the at least one graft base B1 via emulsion polymerization of the monomers B11, B12, and optional B13, wherein at least one surfactant S1 is added; b) preparation of the at least one graft copolymer B via emulsion polymerization of the at least one monomer B21 and optional B22 in the presence of the at least one graft base B1, wherein at least one surfactant S2 is added before, during, and/or after emulsion polymerization, wherein the graft copolymer B is obtained in form of a latex having a mean particle diameter D.sub.w in the range of 60 to 800 nm; and wherein the volume concentration of the total amount of surfactant S2 is in the range of 0.5 to 0.75 mol/m.sup.3, based on the volume of the graft copolymer B latex particles; c) precipitation of the graft copolymer B by mixing the graft copolymer latex obtained in step b) with a precipitation solution comprising at least one salt and/or acid; d) mechanical dewatering, optional washing, and/or optional drying of the precipitated graft copolymer B obtained in step c); and e) mixing of the precipitated graft copolymer B obtained in step d) with component A and optional the components C and/or K, wherein the thermoplastic moulding composition is obtained.

2. The process according to claim 1, wherein the at least one thermoplastic copolymer A comprises A1: 50 to 99% by weight, based on the copolymer A, of the at least one vinylaromatic monomer A1, 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 A2: 1 to 50% by weight, based on the copolymer A, of at least one further ethylenically unsaturated monomer A2, 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.

3. The process according to claim 1, wherein the at least one thermoplastic copolymer A comprises: A1: 65 to 80% by weight, based on the total copolymer A, of the at least one vinylaromatic monomer A1, selected from styrene, α-methylstyrene, or mixtures of styrene and α-methylstyrene; and A2: 20 to 35% by weight, based on the total copolymer A, of the at least one further ethylenically unsaturated monomer A2, selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile.

4. The process according to 1, claim wherein the at least one graft copolymer B, comprises: B1: 55 to 75% by weight, based on the graft copolymer B, at least one graft base B1 obtained by emulsion polymerization of: B11: 90 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, at least one polyfunctional, cross-linking monomer B12; wherein the monomer B12 is selected from allyl(meth)acrylate, divinylbenzene, diallylmaleate, diallylfumarate, diallylphthalate, triallylcyanurate, triallylisocyanurate, and dihydrodicyclopentadienylacrylate; and B13 0 to 9.9% by weight, based on the graft base B1, at least one further copolymerizable, monoethylenically unsaturated monomer B13 different from B11 and B12, wherein the monomer B13 is selected from styrene, α-methylstyrene, C.sub.1-C.sub.4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, chloroprene, methyl(meth)acrylate, alkylenglycol-di(meth)acrylate, and vinylmethylether; wherein the sum of B11, B12, and optional B13 is 100% by weight, based on all monomers of graft base B1; and B2: 25 to 45% by weight, based on the graft copolymer B, at least one graft shell B2, wherein at least one graft shell B2 is obtained by emulsion polymerization in the presence of at least one graft base B1 of: B21: 70 to 80% by weight, based on the graft shell B2, at least one vinylaromatic monomer B21, wherein the monomer B21 is selected from styrene, α-methylstyrene, and mixtures of styrene and one further monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.4-alkyl(meth)acrylate; and B22: 20 to 30% by weight, based on the graft shell B2, at least one ethylenically unsaturated monomer B22, wherein the monomer B22 is selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinylmethylether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; wherein the total sum of graft base(s) B1 and graft shell(s) B2 is 100% by weight.

5. The process according to claim 1, wherein the graft copolymer B comprises: B1: 50 to 70% by weight, based on the graft copolymer B, of the at least one graft base B1; B2′: 10 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, of: B21′: 100% by weight, based on graft shell B2′, at least one 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 40% 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″: 50 to 95% by weight, based on the graft shell B2″, at least one 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.4-alkyl(meth)acrylate; and B22″: 5 to 50% by weight, based on the graft shell B2″, at least one monomer B22″, selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinylmethylether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids.

6. The process according to claim 1, wherein the graft copolymer B comprises at least two graft copolymers B-I and B-II, wherein: graft copolymer B-I has a mean particle diameter D.sub.w in the range of 60 to 200 nm; and graft copolymer B-II has a mean particle diameter D.sub.w in the range of 300 to 800 nm.

7. The process according to claim 1, wherein the at least one vinylaromatic monomer B21 is styrene and/or α-methylstyrene and the at least one ethylenically unsaturated monomer B22 is acrylonitrile or a mixture of acrylonitrile and methacrylonitrile.

8. The process according to claim 1, wherein the at least one surfactant S1 and/or S2 are one or more anionic surfactants, selected from alkyl sulfonic acids, arylalkyl sulfonic acids, fatty acids and salts thereof, having an aliphatic linear or branched hydrocarbon chain of 5 to 30 carbon atoms.

9. The process according to claim 1, wherein the volume concentration of the surfactant S2 in step b) is in the range of 0.5 to 0.7 mol/m.sup.3, based on the volume of the graft copolymer B latex particles.

10. The process according to claim 1, wherein the preparation of the graft base B1 via emulsion polymerization in step a) and/or the preparation of the graft copolymer B via emulsion polymerization in step b) is carried out under addition of at least one persulfate as initiator, wherein the initiator is added in step a) and/or b) in an amount of 0.01 to 1% by weight, based on the total amount of monomers used in the respective emulsion polymerization step.

11. The process according to claim 1, wherein the thermoplastic moulding composition comprises 5 to 60% by weight, based on the total moulding composition, at least one further polymer component C selected from polycarbonates, polyamides, and polyesters.

12. The process according to claim 1, wherein the thermoplastic moulding composition comprises 0.01 to 10% by weight, based on the total moulding composition, at least one further additive K, selected from colorants, pigments, lubricants or mould-release agents, stabilizers, antistatic agents, flame retardants, and fillers.

13. The process according to claim 1, wherein the at least one graft copolymer B latex obtained in step b) comprises less than 0.1% by weight, based on the total solid content of the graft copolymer B, of coagulated latex particles.

14. The process according to claim 1, wherein the thermoplastic moulding composition obtained exhibits a specific surface resistivity, determined according to IEC 62631-3-2:2015, in the range of 6.4*10.sup.14 to 9.14*10.sup.14 Ohm.

15. The process according to claim 1, wherein: the surfactant S2 or the surfactants S2 and S1 are selected from arylalkyl sulfonates and alkyl sulfonates having an aliphatic linear or branched hydrocarbon chain of 5 to 30 carbon atoms; the precipitation solution comprises at least one magnesium salt; and the concentration of the surfactant S2 is selected so that the weight ratio of sulfur (S) to magnesium (Mg) in the thermoplastic moulding composition obtained is below 2.6.

Description

EXPERIMENTAL EXAMPLES

1. Preparation of Graft Copolymer B

(1) The polybutylacrylate basic latex (graft base B1) as used in the following examples 1.1 to 1.3 were produced using the same recipe (see example 1.1) having a particle diameter D.sub.w of about 75 nm. A mixture of primary and secondary sodium C.sub.12-C.sub.18 alkyl sulfonates with an average chain length of C.sub.15 and a mean molecular weight of M=288.84 g/mol is used as surfactant S1 (preparing graft base B1) and as surfactant S2 (grafting step). The volume concentration (determined according to example 3.3) of the surfactant S2 added during the graft stage, i.e. emulsion polymerization of the monomers B21 and B22, was varied. The amount of coagulum in the graft copolymer B latices was determined as described in example 3.2. The amounts and results are summarized in Table 1.

1.1 Component B-1

(2) In a first step a polybutylacrylate basic latex (graft base B1) was prepared as described in the following:

(3) The reaction vessel was charged with 86.12 parts by weight of demineralized water, 0.61 parts by weight of the surfactant S1 (sodium salt of C.sub.12-C.sub.18-paraffin sulfonic acid, M=288.84 g/mol) and 0.23 parts by weight sodium bicarbonate. When the temperature in the reaction vessel had reached 59° C., 0.18 parts by weight of potassium persulfate, dissolved in 5 parts by weight of demineralized water, were added. A mixture of 59.51 parts by weight butyl acrylate (monomer B11) and 1.21 parts by weight tricyclodecenylacrylate (dihydrodicyclopentadienylacrylate, DCPA) (monomer B12) were added within a period of 210 min. Afterwards the reaction was continued for 60 min. Finally the polymer dispersion had a total solid content of 39.6% and the latex particles had a mean particle diameter D.sub.w of 75 nm. The particle size was determined by turbidity as described in example 3.1.

(4) Afterwards, graft shell B2 was obtained by emulsion polymerization of styrene and acrylonitrile in the presence of the polybutylacrylate basic rubber latex (graft base B1). An amount of 152.87 parts by weight of the basic latex described above was added to the reaction vessel together with 90.37 parts by weight of demineralized water, 0.11 parts by weight of the surfactant S2 (sodium salt of C.sub.12-C.sub.18-paraffin sulfonic acid) and 0.16 parts by weight of potassium persulfate, dissolved in 5.22 parts by weight of demineralized water.

(5) Within a period of 190 min a mixture of 77% by weight styrene and 23% by weight acrylonitrile was added, wherein in a first step 6.49 parts styrene and 1.94 parts acrylonitrile are added within 20 mins, followed by 20 min waiting time, afterwards 24.69 parts styrene and 7.37 parts acrylonitrile are added within 150 mins. The monomer addition takes place at a temperature of 61° C., followed by a post polymerization time of 60 min at 65° C. A polymer dispersion (component B-1) with a total solid content of 39.5% was obtained. The latex particles had a mean particle diameter D.sub.w of 87 nm (determined by turbidity). Coagulum was determined as described in example 3.2 to be 0.058% by weight, based on the total solid content of the graft copolymer latex B.

1.2 Component B-2 (Comparative Example)

(6) An amount of 152.87 parts by weight of the polybutylacrylate basic rubber latex (graft base B1) as described in example 1.1 was added to the reaction vessel together with 90.37 parts by weight of demineralized water, 0.08 parts by weight of the surfactant S2 and 0.16 parts by weight of potassium persulfate, dissolved in 5.22 parts by weight of demineralized water.

(7) Within a period of 190 min a mixture of 77% by weight styrene and 23% by weight acrylonitrile was added, wherein in a first step 6.49 parts styrene and 1.94 parts acrylonitrile are added within 20 mins, followed by 20 min waiting time, afterwards 24.69 parts styrene and 7.37 parts acrylonitrile are added within 150 mins. The monomer addition takes place at a temperature of 61° C., followed by a post polymerization time of 60 min at 65° C. A polymer dispersion (component B-2) with a total solid content of 39.5% by weight is obtained. The latex particles had a mean particle diameter D.sub.w of 91 nm determined by turbidity as described in example 3.1. Coagulum was determined as described in example 3.2 to be 0.128% by weight, based on the total solid content of the graft copolymer latex B.

1.3 Component B-3 (Comparative Example)

(8) An amount of 152.87 parts by weight of the polybutylacrylate basic rubber latex (graft base B1) as described in example 1.1 was added to the reaction vessel together with 90.37 parts by weight of demineralized water, 0.12 parts by weight of the sodium salt of C.sub.12-C.sub.18 paraffin sulfonic acid (M=288.84 g/mol) and 0.16 parts by weight of potassium persulfate, dissolved in 5.22 parts by weight of demineralized water.

(9) Within a period of 190 min a mixture of 77% by weight styrene and 23% by weight acrylonitrile was added, wherein in a first step 6.49 parts styrene and 1.94 parts acrylonitrile are added within 20 mins, followed by 20 min waiting time, afterwards 24.69 parts styrene and 7.37 parts acrylonitrile are added within 150 mins. The monomer addition takes place at a temperature of 61° C., followed by a post polymerization time of 60 min at 65° C. A polymer dispersion (component B-3) with a total solid content of 39.5% by weight was obtained. The latex particles had a mean particle diameter D.sub.w of 91 nm determined by turbidity as described in example 3.1. Coagulum was determined as described in example 3.2 to be 0.106% by weight, based on the total solid content of the graft copolymer latex B.

(10) TABLE-US-00001 TABLE 1 ASA graft copolymer latices Ex.-1.1 Ex.-1.2 Ex.-1.3 Unit (Inventive) (Comparative) (Comparative) Graft B-1 B-2 B-3 copolymer Volume mol/m.sup.3 0.69 0.47 0.76 conc. S2 (θ) Coagulum % by weight 0.058 0.128 0.106

(11) It was surprisingly found that for volume concentration of the sodium alkyl sulfonate (surfactant S2) of more than 0.43 mol/m.sup.3 as well as for volume concentration of less than 0.69 mol/m.sup.3 very low amounts of coagulum is observed after the preparation of graft copolymer latex. Approximately twice of the coagulum amount is found in comparative examples Ex.-II (relating to B-2) and Ex.-III (relating to B-3). The lower amount of coagulum reduces the cleaning effort in the plant significantly.

1.4 Precipitation Step

(12) Each of the graft copolymer latices B obtained in examples 1.1 to 1.3 were separately coagulated in a magnesium sulfate solution. Each of the graft copolymer latices B obtained in examples 1.1 to 1.3 was dosed in a stirred tank together with a magnesium sulfate solution (18% by weight) at a temperature of about 88° C. The concentration of magnesium sulfate, based on the total aqueous phase in the tank was about 0,8% by weight and the concentration of the graft copolymers (B-1, B-2 or B-3), calculated as solid and based on the total content of components in the tank, was about 18% by weight.

(13) Each of the precipitated graft copolymers B-1, B-2 or B-3 was filtered off, washed twice with 21 l of water, and dried in an lab oven (2 days, 60-70° C.) afterwards. The graft copolymer components (graft copolymer powder) B-1, B-2 and B-3 having a water content of <1% by weight were obtained.

2. Preparation of Thermoplastic Moulding Compositions

(14) 2.1 Each of the graft copolymer components B-1, B-2 and B-3 (graft copolymer powders) obtained in example 1 were mixed with component A-1: Luran VLP (styrene acrylonitrile copolymer with 35% by weight acrylonitrile and viscosity number VN of 80 ml/g (determined according to DIN 53726 at 25° C., 0.5% by weight in dimethylformamide),

(15) to obtain a thermoplastic moulding composition. A Coperion ZSK 25 extruder was used for melt compounding of the components A and B, wherein the mass temperature was in the range of 220 to 250° C. The amounts of components B-1/B-2/B-3 and A-1 are given in table 2 below.

(16) 2.2 Test pieces of the thermoplastic moulding compositions used for mechanical testing and other test methods were obtained by injection moulding using an Arburg machine under standard conditions, i.e. 250° C. to 270° C. melt temperature, 70° C. tool temperature.

(17) 2.3 The compositions and test results (determined according to examples 3.4 to 3.6) are summarized in the following table 2:

(18) TABLE-US-00002 TABLE 2 Thermoplastic moulding composition and test result Ex.-2.1a Ex.-2.1b Ex.-2.1c (Inventive) (Comparative) (Comparative) A-1 % by weight 50 50 50 B-1 % by weight 50 — — B-2 % by weight — 50 — B-3 % by weight — — 50 a.sub.k kJ/m.sup.2   47.5   38.4   38.7 notched Charpy impact strength Spec. Ohm 8.05*10.sup.14 9.15*10.sup.14 6.39*10.sup.14 surface resistivity weight   2.1   2.8   2.6 ratio w(S)/w (Mg)

(19) It was found that the graft rubber copolymer B-1, produced according to the invention and compounded into SAN matrix (component A-1), yields a thermoplastic moulding composition showing higher notched Charpy impact strength compared to the graft rubber copolymers B-2 and B-3 (comparative examples).

(20) Besides the specific range of volume concentration ϑ(theta) of surfactant S2 (see table 1), the specific surface resistivity of the thermoplastic moulding composition comprising components A and B and the mass ratio of sulfur to magnesium in the thermoplastic moulding compositions can be used as feature to differentiate the samples, i.e. to characterize the result of optimization of surfactant concentration. In line with this, inventive thermoplastic moulding compositions show a surface resistivity in the range of 6.4*10.sup.14 to 9.14*10.sup.14 Ohm and/or a mass ratio of sulfur to magnesium w (S)/w (Mg) below 2.6.

3. Test Methods

(21) 3.1 The mass mean particle diameter D.sub.w of the latex particles was determined by turbidity as described in Lange, Kolloid-Zeitschrift und Zeitschrift für Polymere, Vol. 223, issue 1.

(22) 3.2 The content of coagulum after graft emulsion polymerization was determined as follows: Coagulum was filtered off from the latex obtained after grafting monomers B21 (styrene) and B22 (acrylonitrile) using a metal sieve having a mesh size of 0.5 mm and/or collected from the reactor wall, thermometer and stirrer. The obtained coagulum was dried in a lab oven at 75° C. for 14 to 20 h and weighed.

(23) The content of coagulum is given in % by weight, based on the total mass of graft copolymer B.

(24) 3.3 The volume concentration ϑ in [mol/m.sup.3] (referred to as theta) of surfactant S2, was calculated as follows:

(25) $\vartheta \left(\mathrm{theta}\right)=\frac{1}{6}.Math.\frac{w\left(S2\right).Math.\rho \left(B\right).Math.{10}^6}{M\left(S2\right)}$ wherein ϑ(theta) is the volume concentration of surfactant S2 in mol/m.sup.3 w (S2) is the mass fraction of surfactant S in grafting step relative to polymer B (i.e. w(S2)=m(S2)/m(B)), M (S2) is the molar mass of the surfactant S in [g/mol], which is M=288.84 g/mol S2 used in the examples; ρ(B) is the density of graft copolymer B in [g/cm.sup.3], which is ρ=1.087 g/cm.sup.3.

(26) The density of graft copolymer B can be calculated based on the mass fraction w and the density ρ of the corresponding homopolymers, e.g. polybutylacrylate (ρ(PBAK)=1.087 g/cm.sup.3), polyacrylonitrile (ρ(PAN)=1.184 g/cm.sup.3), and polystyrene (ρ(PS)=1.05 g/cm.sup.3). For example the density ρ(B) of graft copolymer B can be calculated: ρ(B)=[w(PBAK)+w(PAN)+w(PS)]/[[w(PBAK)/ρ(PBAK)]+[w(PAN)/ρ(PAN)]+[w(PS)/ρ(PS)]]=[0.6+0.092+0.308]/[[0.6/1.087 g/cm.sup.3]+[0.092/1.184 g/cm.sup.3]+[0.308/1 0.05 g/cm.sup.3]]=1.087 g/cm.sup.3.

(27) 3.4 The Charpy notched impact strength was measured according to DIN 53 453 (ISO 179 1eA) using test pieces obtained by injection moulding according to example 2.2.

(28) 3.5 The specific surface resistivity (given in Ohm) was determined according to norm IEC 62631-3-2:2015 using test pieces obtained by injection moulding according to example 2.2.

(29) 3.6 The amounts of the elements sulfur (S) and magnesium (Mg) and following the weight ratio w(S)/w (Mg) were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Test pieces obtained according to example 2.2. were used for ICP-OES.