PROCESS OF MANUFACTURING A MULTISTAGE POLYMER, ITS COMPOSITION, ITS USE AND COMPOSITION COMPRISING IT

Abstract

The present invention relates to a multistage polymer, its composition, its process of preparation, and its use as impact modifier in thermoplastic compositions. More particularly the present invention relates to a process for manufacturing a polymer composition comprising a multistage polymer and its use as impact modifier in thermoplastic compositions.

Claims

1. A process for manufacturing a polymer composition comprising a multistage polymer comprising the steps of: a) polymerizing by emulsion polymerization of a trionomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less then 0° C., b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., c) coagulating the multistage polymer with an alkali metal salt, d) washing the multistage polymer, e) adjusting the pH value after the coagulation to a value between 5 to 10, f) addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

2. The process according to claim 1, wherein step a) and b) use in the emulsion polymerization a surfactant chosen from the group consisting of an anionic surface-active agent.

3. The process according to claim 1 wherein said alkali metal salt is a sodium or potassium salt.

4. The process according to claim 1 comprising an additional step g): drying the polymer composition.

5. The process according to claim 1 wherein said polymer composition comprises at least 350 ppm of phosphorous.

6. The process according to claim 1 wherein said polymer composition comprises at at most 2000 ppm of phosphorous that has the oxidation stage of +III or +V.

7. The process according to claim 1 wherein said polymer composition comprises between 350 ppm and 2000 ppm of phosphorous that has the oxidation stage of +III or +V.

8. The process according to claim 1 wherein no multivalent cations are voluntary added.

9. The process according to claim 1 wherein initiator does not contain any voluntary added earth alkali metals.

10. The process according to claim 1 wherein no earth alkali metals either as ions or in form of salts are voluntary added during the process.

11. The process according to claim 1 wherein earth alkali metals as traces or minor impurity present less than 30 ppm of the polymer composition.

12. The process according to claim 1 wherein earth alkali metals as traces or minor impurity present less than 9 ppm of the multistage polymer composition.

13. The process according to claim 1 wherein said multivalent cations present less than 50 ppm of the multistage polymer composition.

14. The process according to claim 1 wherein the multivalent cations present less than 20 ppm of the multistage polymer composition.

15. The process according to claim 1 having an adjusted pH after coagulation between 6 and 9.

16. The process according to claim 1 wherein the phosphorous containing compound is chosen from the group costing organophosphorous compound, a phosphate salt, phosphoric acid, phosphonate salts, phosphonic acid and their respective esters and mixtures thereof.

17. The process according to claim 1 wherein in step f) the aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added by washing the multistage polymer which contains less than 60 wt % of water with said aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

18. The process according to claim 1 wherein in step f) the aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added on the wet cake after coagulation step and filtration step.

19. The process according to claim 1 wherein in step f) the aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added during drying step of the multistage polymer, when the multistage polymer composition comprises still at least 10 wt % of water.

20. (canceled)

21. (canceled)

22. A process for manufacturing a polymer composition comprising a multistage polymer and a thermoplastic polymer comprising the steps of: a) polymerizing by emulsion polymerization of a monomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less than 0° C., b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., c) coagulating the multistage polymer with an alkali metal salt, d) washing the multistage polymer, e) adjusting the pH value after the coagulation to a value between 5 to 10, f) addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V g) drying the multistage polymer h) mixing the multistage polymer with a thermoplastic polymer

23. A thermoplastic polymer composition comprising the polymer composition obtained by the process according to claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0039] In a first aspect the present invention relates to a process for manufacturing a polymer composition comprising a multistage polymer comprising the steps of [0040] a) polymerizing by emulsion polymerization of a monomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less then 0° C., [0041] b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., [0042] c) coagulating the multistage polymer with an alkali metal salt, [0043] d) washing the multistage polymer, [0044] e) adjusting the pH value after the coagulation to a value between 5 to 10, [0045] f) addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0046] According to a second aspect, the present invention relates to a thermoplastic composition comprising a multistage polymer obtained by a process for manufacturing a polymer composition comprising said multistage polymer comprising the steps of [0047] a) polymerizing by emulsion polymerization of a monomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less then 0° C., [0048] b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., [0049] c) coagulating the multistage polymer with an alkali metal salt, [0050] d) washing the multistage polymer, [0051] e) adjusting the pH value after the coagulation to a value between 5 to 10, [0052] f) addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0053] By the term “polymer powder” as used is denoted a polymer comprising powder grain in the range of at least 1 micrometer (μm) obtained by agglomeration of primary polymer comprising particles in the nanometer range.

[0054] By the term “primary particle” as used is denoted a spherical polymer comprising particle in the nanometer range. Preferably the primary particle has a weight average particle size between 50 nm and 500 nm.

[0055] By the term “particle size” as used is denoted the volume average diameter of a particle considered as spherical.

[0056] By the term “copolymer” as used is denoted that the polymer consists of at least two different monomers.

[0057] By “multistage polymer” as used is denoted a polymer formed in sequential fashion by a multi-stage polymerization process. Preferred is a multi-stage emulsion polymerization process in which the first polymer is a first-stage polymer and the second polymer is a second-stage polymer, i.e., the second polymer is formed by emulsion polymerization in the presence of the first emulsion polymer, with at least two stages that are different in composition.

[0058] By the term “(meth)acrylic” as used is denoted all kind of acrylic and methacrylic monomers.

[0059] By the term “(meth)acrylic polymer” as used is denoted that the (meth)acrylic polymer comprises essentially polymers comprising (meth)acrylic monomers that make up 50 wt % or more of the (meth)acrylic polymer.

[0060] By the term “impact modifier” as used is denoted a compound comprising an elastomer or rubber that can be added or incorporated in a thermoplastic compound to improve its impact resistance.

[0061] By the term “rubber” as used is denoted the thermodynamic state of the polymer above its glass transition.

[0062] With regard to the multistage polymer of the invention, it is a polymer particle having a multilayer structure comprising at least one layer (A) comprising a polymer (A1) having a glass transition temperature below 0° C. and at least another layer (B) comprising a polymer (B1) having a glass transition temperature over 45° C.

[0063] The ratio of layer (A)/layer (B) in the multistage polymer is not particularly limited, but preferably it is in a range in weight between 10/90 and 95/5, more preferably 40/60 and 95/5 advantageously 60/40 to 90/10 and most advantageously between 70/30 and 90/10.

[0064] The polymer particle having a multilayer structure is spherical. The polymer particle having a multilayer structure is also called the primary particle. The polymer particle has a weight average particle size between 20 nm and 500 nm. Preferably the weight average particle size of the polymer particle is between 50 nm and 400 nm, more preferably between 75 nm and 350 nm and advantageously between 80 nm and 300 nm.

[0065] The polymer particle according to the invention is obtained by a multistage process such as two or three stages or more stages.

[0066] Preferably the polymer (A1) having a glass transition temperature below 0° C. in the layer (A) is not made during the last stage of the multistage process. The polymer (A1) is having a glass transition temperature below 0° C. in the layer (A) never forms the external layer or outer shell of the polymer particle having the multilayer structure.

[0067] Preferably the polymer (B1) having a glass transition temperature above 45° C. in the layer (B) is the external layer of the polymer particle having the multilayer structure.

[0068] There could be additional intermediate layers made by intermediate steps between the polymer (A1) having a glass transition temperature below 0° C. in the layer (A) and the layer (B) comprising a polymer (B1) having a glass transition temperature over 45° C. This would lead to a multilayered particle.

[0069] The glass transition temperature (Tg) of the polymer (A1) is less than 0° C., preferably less then −10° C., advantageously less than −20° C. and most advantageously less than −25° C. and more most advantageously less than −40° C.

[0070] More preferably the glass transition temperature Tg of the polymer (A1) is between −120° C. and 0° C., even more preferably between −90° C. and −10° C. and advantageously between −80° C. and −25° C.

[0071] Preferably the glass transition temperature Tg of the polymer (B1) is between 45° C. and 150° C. The glass transition temperature of the polymer (B1) is more preferably between 60° C. and 150° C., still more preferably between 80° C. and 150° C. and advantageously between 90° C. and 150° C.

[0072] The glass transition temperature Tg can be estimated for example by dynamic methods as thermo mechanical analysis.

[0073] The polymer composition of the invention in form of polymeric particles of a multistage polymer can also be in form of a polymer powder. The polymer powder comprises agglomerated primary polymer particles made by the multistage process.

[0074] With regard to the polymer powder of the invention, it has a volume median particle size D50 between 1 μm and 500 μm. Preferably the volume median particle size of the polymer powder is between 10 μm and 400 μm, more preferably between 15 μm and 350 μm and advantageously between 20 μm and 300 μm.

[0075] The D10 of the particle size distribution in volume is at least 7 μm and preferably 10 μm.

[0076] The D90 of the particle size distribution in volume is at most 800 μm and preferably 500 μm, more preferably at most 350 μm.

[0077] With regard to the polymer (A1), mention may be made of homopolymers and copolymers comprising monomers with double bonds and/or vinyl monomers.

[0078] In a first embodiment the polymer (A1) is chosen from isoprene homopolymers or butadiene homopolymers, isoprene-butadiene copolymers, copolymers of isoprene with at most 98 wt % of a vinyl monomer and copolymers of butadiene with at most 98 wt % of a vinyl monomer. The vinyl monomer may be styrene, an alkylstyrene, acrylonitrile, an alkyl (meth)acrylate, or butadiene or isoprene. In a specific embodiment polymer (A1) is a butadiene homopolymer.

[0079] In a second embodiment the polymer (A1) is a (meth) acrylic polymer. A (meth) acrylic polymer according to the invention is a polymer comprising at least 50 wt % preferably at least 60 wt % and more preferably at least 70 wt % of monomers coming from acrylic or methacrylic monomers. The (meth) acrylic polymer according to the invention comprise less than 50 wt % preferably less than 40 wt % and more preferably less than 30 wt % of non acrylic or methacrylic monomers, which can copolymerize with the acrylic or methacrylic monomers.

[0080] More preferably the polymer (A1) of the second embodiment comprises at least 70 wt % monomers chosen from C1 to C12 alkyl (meth)acrylates. Still more preferably the polymer (A1) comprises at least 80 wt % of monomers C1 to C4 alkyl methacrylate and/or C1 to C8 alkyl acrylate monomers.

[0081] Most preferably the acrylic or methacrylic monomers of the polymer (A1) are chosen from methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and mixtures thereof, as long as polymer (A1) is having a glass transition temperature of less than 0° C.

[0082] The polymer (A1) may be completely or partly crosslinked. All that is required is to add at least one difunctional monomer during the preparation of the polymer (A1). These difunctional monomers may be chosen from poly(meth)acrylic esters of polyols, such as butanediol di(meth)acrylate and trimethylolpropane trimethacrylate. Other multifunctional monomers are, for example, divinylbenzene, trivinylbenzene, and triallyl cyanurate. The core can also be crosslinked by introducing into it, by grafting or as a comonomer during the polymerization, unsaturated functional monomers such as anhydrides of unsaturated carboxylic acids, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, by way of example, of maleic anhydride, (meth)acrylic acid and glycidyl methacrylate. The crosslinking may also be carried out by using the intrinsic reactivity of the monomers, for example in the case of the diene monomers.

[0083] With regard to the polymer (B1), mention may be made of homopolymers and copolymers comprising monomers with double bonds and/or vinyl monomers.

[0084] The polymer (B1) is chosen from styrene homopolymers, alkylstyrene homopolymers or methyl methacrylate homopolymers, or copolymers comprising at least 70 wt % of one of the above monomers and at least one comonomer chosen from the other above monomers, another alkyl (meth)acrylate, vinyl acetate and acrylonitrile. The shell may be functionalized by introducing into it, by grafting or as a comonomer during the polymerization, unsaturated functional monomers such as anhydrides of unsaturated carboxylic acids, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, for example, of maleic anhydride, (meth)acrylic acid glycidyl methacrylate, hydroxyethyl methacrylate and alkyl(meth)acrylamides.

[0085] Preferably the polymer (B1) is also a (meth) acrylic polymer.

[0086] Preferably the polymer (B1) comprises at least 70 wt % monomers chosen from C1 to C12 alkyl (meth)acrylates. Still more preferably the polymer (B1) comprises at least 80 wt % of monomers C1 to C4 alkyl methacrylate and/or C1 to C8 alkyl acrylate monomers.

[0087] Most preferably the acrylic or methacrylic monomers of the polymer (B1) are chosen from methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and mixtures thereof, as long as polymer (B1) is having a glass transition temperature of at least 60° C.

[0088] Advantageously the polymer (B1) comprises at least 70 wt % of monomer units coming from methyl methacrylate.

[0089] The polymer (B1) may be crosslinked by adding at least one multifunctional monomer during the preparation of the polymer (B1).

[0090] The multistage polymer of the invention, having a multilayer structure comprising at least one layer (A) comprising a polymer (A1) having a glass transition temperature below 0° C. and another layer (B) comprising a polymer (B1) having a glass transition temperature over 45° C., comprises no voluntary added earth alkali metals neither as ions nor in form of salts.

[0091] By no voluntary added is meant that traces of earth alkali metals in form of ions or salts could be accidentally added as a minor impurity with other ions or salts to the composition. Example notably impurities of calcium in sodium compounds are mentioned.

[0092] The earth alkali metals as traces or minor impurity present less than 30 ppm, preferably less than 20 ppm and more preferably less than 10 ppm and advantageously less than 9 ppm of the multistage polymer composition.

[0093] Furthermore multivalent cations present less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, still more preferably less than 25 ppm and advantageously less than 20 ppm of the multistage polymer composition and preferably the final dry multistage polymer composition. Multivalent cations have the general formula M.sup.b+, wherein M present the cation, with b>1, and preferably 5>b>1.

[0094] The multivalent cations is the sum of all the eventually non-voluntary added traces of earth alkali metals in form of ions or salts and the eventually voluntary added multivalent cations. The voluntary added multivalent cations have the general formula M.sup.b−, wherein M present the cation, with b≧2, and preferably 4≧b≧2. The voluntary added multivalent cations exclude earth alkali metals.

[0095] The multivalent cations including the earth alkali metals in the composition can be analysed by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES).

[0096] The multistage polymer of the invention, having a multilayer structure has a pH value between 5 and 10 and preferable 6 and 9 more preferable between 6 and 7.5 and advantageously between 6 and 7.

[0097] The multistage polymer of the invention comprises a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0098] The multistage polymer comprises at least 350 ppm, preferably at least 360 ppm, more preferably at least 370 ppm, still more preferably at least 380 ppm, advantageously at least 390 ppm and more advantageously at least 400 ppm of phosphorous that has the oxidation stage of +III or +V. The phosphorous is part of a phosphorous containing compound. The content of the phosphorous containing compound is calculated and expressed as phosphorous in view of the multistage polymer composition and not as phosphorous containing compound.

[0099] The multistage polymer comprises at most 2000 ppm, preferably at most 1900 ppm and more preferably at most 1800 ppm of phosphorous that has the oxidation stage of +III or +V. The phosphorous is part of a phosphorous containing compound.

[0100] The multistage polymer comprises between 350 ppm and 2000ppm, preferable between 370 pmm and 1900 ppm and more preferably between 390 ppm and 1800 ppm of phosphorous that has the oxidation stage of +III or +V. The phosphorous is part of a phosphorous containing compound.

[0101] The quantity of phosphorous in the multistage polymer can be estimated by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES).

[0102] The oxidation stage is linked to the nature of the phosphorous containing compound added to the composition. Preferably there is no voluntary addition of any reducing or oxidizing agents, in order to change the oxidation stage of the phosphorous in the phosphorous containing compound.

[0103] The phosphorous containing compound is preferably chosen from organophosphorous compound, a phosphate salt, phosphoric acid, phosphonate salts, phosphonic acid and their respective esters and mixtures thereof.

[0104] By organophosphorous compound in the present invention are understood compounds with P—C and P—O—C bonds.

[0105] More preferably the phosphorous containing compound is chosen from organophosphorous compound having a P—O—C bond, a phosphate salt, phosphoric acid, phosphonate salts, phosphonic acid and ester and mixtures thereof.

[0106] Phosphate salts are salts that have as anion dihydrogenophosphate (H.sub.2PO.sub.4.sup.−), hydrogenophosphate (HPO.sub.4.sup.2−) or phosphate (PO.sub.4.sup.3−).

[0107] Phosphonate salts are salts that have as anion dihydrogenophosphonate (H.sub.2PO.sub.3.sup.−) or hydrogenophosphate (HPO.sub.3.sup.2−).

[0108] With regard to the process for manufacturing a polymer composition comprising a multistage polymer comprising the steps of [0109] a) polymerizing by emulsion polymerization of a monomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less then 0° C., [0110] b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., [0111] c) coagulating the multistage polymer with an alkali metal salt, [0112] d) washing the multistage polymer, [0113] e) adjusting the pH value after the coagulation to a value between 5 to 10, [0114] f) addition of an aqueous solution comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0115] Preferably the process for manufacturing a polymer composition comprising the multistage polymer comprises the steps in the order as indicated.

[0116] Preferably in step d) the pH value is adjusted between 6 and 9, more preferable between 6 and 7.5 and advantageously between 6 and 7.

[0117] The process might comprise the additional step g) of drying the polymer composition. A dry polymer composition according to the invention is a composition that comprises less than 1% of humidity or water. The humidity of a polymer composition can be measure with a thermo balance.

[0118] The drying of the polymer can be made in an oven or vacuum oven with heating of the composition for 48 hours at 50° C.

[0119] The process of the invention, for manufacturing the polymer composition comprising the multistage polymer having a multilayer structure comprising at least one layer (A) comprising a polymer (A1) having a glass transition temperature below 0° C. and another layer (B) comprising a polymer (B1) having a glass transition temperature over 45° C., said process comprises no voluntary added earth alkali metals neither as ions nor in form of salts.

[0120] By no voluntary added is meant that traces of earth alkali metals in form of ions or salts could be accidentally added as a minor impurity with other ions or salts during the respective process steps for manufacturing the composition. As examples notably impurities of calcium in sodium compounds are mentioned.

[0121] The earth alkali metals as traces or minor impurity present less than 30 ppm, preferably less than 20 ppm and more preferably less than 10 ppm and advantageously less than 9 ppm of the final multistage polymer composition and preferably the final dry multistage polymer composition.

[0122] Furthermore multivalent cations present less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, still more preferably less than 25 ppm and advantageously less than 20 ppm of the multistage polymer composition. Multivalent cations have the general formula M.sup.b+, wherein M present the cation, with b>1, and preferably 5>b>1.

[0123] The multivalent cations is the sum of all the eventually non-voluntary added traces of earth alkali metals in form of ions or salts and the eventually voluntary added multivalent cations. The voluntary added multivalent cations have the general formula M.sup.b−, wherein M present the cation, with b≧2, and preferably 4≧b≧2. The voluntary added multivalent cations exclude earth alkali metals.

[0124] The respective monomers or monomer mixtures (A.sub.m) and (B.sub.m) for forming the layers (A) and (B) respectively comprising the polymers (A1) and (B1) respectively and the characteristics of the respective polymers (A1) and (B1) are the same as defined before for the definition of the polymers (A1) and (B1) for the composition.

[0125] The emulsion polymerization during the stage for layer (A) can be a grow-out process, a seeded grow-out process or an microagglomeration process.

[0126] Chain transfer agents are also useful in forming the polymer (A1). Useful chain transfer agents include those known in the art, including but not limited to ter-dodecylmercaptan, n-dodecylmercaptan, n-octylmercaptan, and mixtures of chain transfer agents. The chain transfer agent is used at levels from 0 to 2 percent by weight, based on the total core monomer content in monomer mixture (A.sub.m).

[0127] Preferably the polymer (B1) is grafted on the polymer made in the previous stage.

[0128] Polymerization initiators useful in producing the polymer (A1) and (B1) include, but are not limited to a persulfate salt such as potassium persulfate, ammonium persulfate, and sodium persulfate; an organic peroxide such as tert-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, p-menthane hydroperoxide, and diisopropylbenzene hydroperoxide; an azo compound such as azobisisobutyronitrile, and azobisisovaleronitrile; or a redox initiator. However, it is preferable to use catalytic systems of redox type formed by the combination of a peroxide compound, for example as mentioned above, with a reducing agent, in particular such as alkali metal sulfite, alkali metal bisulfite, sodium formaldehyde sulfoxylate (NaHSO.sub.2HCHO), a alkali salt of an organic sulfinic acid derivative, ascorbic acid, glucose, and in particular those of the said catalytic systems which are water-soluble, for example potassium persulfate/sodium metabisulfite or alternatively diisopropylbenzene hydroperoxide/sodium formaldehyde sulfoxylate or even more complicate systems as for example ferrous sulfate/dextrose/sodium pyrophosphate.

[0129] The initiators do not contain any voluntary added earth alkali metals (group IIA from the periodic system of elements). The initiator might contain however other multivalent cations that are not earth alkali metals.

[0130] For the emulsion polymerization during the two stages for making layer (A) comprising polymer (A1) and layer (B) comprising a polymer (B1) as emulsifying agent any one of the known surface-active agents, whether anionic, nonionic or even cationic may be used. In particular, the emulsifying agent may be chosen from anionic emulsifying agents, such as sodium or potassium salts of fatty acids, in particular sodium laurate, sodium stearate, sodium palmitate, sodium oleate, mixed sulphates of sodium or of potassium and of fatty alcohols, in particular sodium lauryl sulphate, sodium or potassium salts of sulphosuccinic esters, sodium or potassium salts of alkylarylsulphonic acids, in particular sodium dodecylbenzenesulphonate, and sodium or potassium salts of fatty monoglyceride monosulphonates, or dodecyl diphenyl ether disulfonic acid, potassium dodecyl diphenyl ether disulfonate, ammonium dodecyl diphenyl ether disulfonate and sodium dodecyl diphenyl ether disulfonate, or alternatively from nonionic surfactants, such as the reaction products of ethylene oxide and of alkylphenol or of aliphatic alcohols, alkylphenols. Use may also be made of mixtures of such surface-active agents, if necessary.

[0131] More preferably the emulsifying agent is chosen from an anionic surface-active agent.

[0132] Coagulation in step c) of the process of the invention is made by aggregation of the primary polymer particles at the end of the emulsion polymerization by adding an aqueous electrolyte solution under stirring. Multivalent cations are to be avoided in the electrolyte solution. No multivalent cations are voluntary added to the electrolyte solution.

[0133] Preferably the coagulation is made with a solution comprising a salt of an alkali metal. More preferably the coagulation is made with a solution comprising a salt of an alkali metal that has solubility in water of at least 10 g/l.

[0134] More preferably the alkali metal salt is a sodium or potassium salt. For example the alkali metal salt can be chosen from NaCl, KCl, Na.sub.2SO.sub.4, Na.sub.3PO.sub.4 Na.sub.2HPO.sub.4, but is not limited on this list.

[0135] The washing in step d) of the process of the invention is made by water, diluted aqueous solutions or aqueous buffer solutions.

[0136] Adjusting the pH in step e) of the process of the invention is preferably made by adding sodium or potassium hydroxide or aqueous buffer solution after the coagulation step. After the adjusting step the pH is between 5 and 10, preferably between 6 and 9, more preferable between 6 and 7.5 and advantageously between 6 and 7.

[0137] Step f) concerns the addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0138] Preferably the step f) concerning the addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is made after the coagulation step c).

[0139] In order to add aqueous solution or dispersion comprising a phosphorous containing compound, said the solution or dispersion is prepared by simple mixing of a known defined quantity of the phosphorous containing compound with water.

[0140] In one embodiment the aqueous solution or dispersion comprising the phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added by washing the multistage polymer which contains less than 60 wt % of water with said aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V.

[0141] In a second embodiment the aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added on the wet cake after coagulation step and filtration step. After the filtration a wet cake is obtained that contains less than 60 wt % of water. Afterwards the wet cake is dried.

[0142] In a third embodiment the aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V is added during drying step of the multistage polymer, when the multistage polymer composition comprises still at least 10 wt % of water. No further separation between liquid phase that can contain solids or salts and solid phase takes place. All added phosphorous stays with the multistage polymer.

[0143] The phosphorous containing compound is preferably chosen from organophosphorous compound, a phosphate salt, phosphoric acid, phosphonate salts, phosphonic acid and their respective esters and mixtures thereof.

[0144] Phosphate ester general structure P(═O) (OR).sub.3, where at least one group R is an alkyl group. Phosphonates are esters of phosphonic acid and have the general formula RP(═O) (OR′).sub.2, where at least one group R or R′ is an alkyl group.

[0145] By organophosphorous compound in the present invention are understood compounds with P—C and P—O—C bonds.

[0146] More preferably the phosphorous containing compound is chosen from organophosphorous compound having a P—O—C bond, a phosphate salt, phosphoric acid, phosphonate salts, phosphonic acid and ester and mixtures thereof.

[0147] Phosphate salts are salts that have as anion dihydrogenophosphate (H.sub.2PO.sub.4.sup.−), hydrogenophosphate (HPO.sub.4.sup.2−) or phosphate (PO.sub.4.sup.3−).

[0148] Phosphonate salts are salts that have as anion dihydrogenophosphonate (H.sub.2PO.sub.3.sup.−) or hydrogenophosphate (HPO.sub.3.sup.2−).

[0149] The present invention relates also to the use of the multistage polymer as impact modifier in thermoplastic polymers.

[0150] The present invention relates further to a thermoplastic composition comprising the multistage polymer and a thermoplastic polymer.

[0151] In an additional aspect the present invention relates to a process for manufacturing a polymer composition comprising a multistage polymer and a thermoplastic polymer comprising the steps of [0152] a) polymerizing by emulsion polymerization of a monomer or monomer mixture (A.sub.m) to obtain during this stage one layer (A) comprising polymer (A1) having a glass transition temperature of less then 0° C., [0153] b) polymerizing by emulsion polymerization in presence of the polymer obtained in step a) of a monomer or monomer mixture (B.sub.m) to obtain during this subsequent stage a layer (B) comprising a polymer (B1) having a glass transition temperature of at least 45° C., [0154] c) coagulating the multistage polymer with an alkali metal salt, [0155] d) washing the multistage polymer, [0156] e) adjusting the pH value after the coagulation to a value between 5 to 10, [0157] f) addition of an aqueous solution or dispersion comprising a phosphorous containing compound wherein the phosphorous has the oxidation stage of +III or +V [0158] g) drying the multistage polymer [0159] h) mixing the multistage polymer with a thermoplastic polymer

[0160] With regard to the thermoplastic polymer that is part of the thermoplastic composition according to the invention it can be chosen among poly(vinyl chloride) (PVC), chlorinated poly(vinyl chloride) (C-PVC), polyesters as for example poly (ethylene terephtalate) (PET) or poly(butylen terephtalate) (PBT) polyhydroxyalkanoates (PHA) or polylactic acid (PLA), cellulose acetate, polystyrene (PS), polycarbonates (PC), polyethylene, poly (methyl methacrylate)s (PMMA), (meth)acrylic copolymers, thermoplastic poly(methyl methacrylate-co-ethylacrylates), poly(alkylene-terephtalates), poly vinylidene fluoride, poly(vinylidenchloride), polyoxymethylen (POM), semi-crystalline polyamides, amorphous polyamides, semi-crystalline copolyamides, amorphous copolyamides, polyetheramides, polyesteramides, copolymers of styrene and acrylonitrile (SAN), and their respective mixtures or alloys. According to a preferred embodiment the thermoplastic resin composition comprises polycarbonate (PC) and/or polyester (PET or PBT) or PC or polyester alloys. The alloys for example may be PC/ABS (poly(Acrylonitrile-co-butadiene-co-styrene), PC/ASA, PC/polyester or PC/PLA.

[0161] Preferably, if the thermoplastic polymer in the thermoplastic polymer composition comprises polycarbonate (PC) and/or polyester (PET or PBT) or PC or polyester alloys the polymer (A) of the multistage polymer is chosen from isoprene homopolymers or butadiene homopolymers, isoprene-butadiene copolymers, copolymers of isoprene with at most 98 wt % of a vinyl monomer and copolymers of butadiene with at most 98 wt % of a vinyl monomer.

[0162] Concerning the polycarbonate (PC), it can be aromatic, semi-aromatic and/or aliphatic (particularly based on isosorbide).

[0163] With regard to the thermoplastic composition comprising the multistage polymer and a thermoplastic polymer, the proportions between the multistage polymer of the invention and the thermoplastic polymer are between 0.5/99.5 and 50/50, preferably between 1/98 and 30/70, more preferably between 2/98 and 20/80 and advantageously between 2/98 and 15/85.

Methods of Evaluation

[0164] Glass Transition Temperature

[0165] The glass transitions (Tg) of the polymers are measured with equipment able to realize a thermo mechanical analysis. A RDAII “RHEOMETRICS DYNAMIC ANALYSER” proposed by the Rheometrics Company has been used. The thermo mechanical analysis measures precisely the visco-elastics changes of a sample in function of the temperature, the strain or the deformation applied. The apparatus records continuously, the sample deformation, keeping the stain fixed, during a controlled program of temperature variation.

[0166] The results are obtained by drawing, in function of the temperature, the elastic modulus (G′), the loss modulus and the tan delta. The Tg is higher temperature value read in the tan delta curve, when the derived of tan delta is equal to zero.

[0167] Particle Size Analysis

[0168] The particle size of the primary particles after the multistage polymerization is measured with a Zetasizer Nano S90 from MALVERN. The particle size of the polymer powder is measured with Malvern Mastersizer 3000 from MALVERN.

[0169] For the estimation of weight average powder particle size, particle size distribution and ratio of fine particles a Malvern Mastersizer 3000 apparatus with a 300 mm lenses, measuring a range from 0.5-880 μm is used.

[0170] D (v, 0.5) or more short D50 is the particle size at which 50% of the sample has size less then and 50% of the sample have a size larger then that size, or in other words the equivalent volume diameter at 50% cumulative volume. This size is also known as volume median diameter that is related to the mass median diameter by the density of the particles by the density of the particles assuming a size independent density for the particles.

[0171] D (v, 0.1) or D10 is the particle size at which 10% of the sample is smaller then that size, or in other words the equivalent volume diameter at 10% cumulative volume.

[0172] D (v, 0.9) or D90 is the particle size at which 90% of the sample are smaller then that size.

EXAMPLES

Example 1

[0173] First Stage: Polymerization of Core 1 and Core 2

[0174] To a 20 litres high-pressure reactor was charged: de-ionized water 116.5 parts, emulsifier sodium salt of dodecyl benzene sulfonic acid 0.1 parts, 1,3-butadiene 20 parts, t-dodecyl mercaptan 0.1 parts, and p-menthane hydroperoxide 0.1 parts as an initial charge. The solution was heated, with agitation, to 43° C. at which time a redox-based catalyst solution was charged (water 4.5 parts, sodium tretrapyrophosphate 0.3 parts, ferrous sulfate 0.004 parts and dextrose 0.3 parts), effectively initiating the polymerization. Then the solution was further heated to 56° C. and held at this temperature for a period of three hours.

[0175] Three hours after polymerization initiation, a second monomer charge (71 parts BD, t-dodecyl mercaptan 0.2 parts), additional emulsifier and reductant charge (de-ionized water 30.4 parts, emulsifier sodium salt of dodecyl benzene sulfonic acid 0.9 parts, dextrose 0.5 parts) and additional initiator (p-menthane hydroperoxide 0.8 parts) were continuously added over eight hours. Following the completion of the second monomer addition, the remaining emulsifier and reductant charge plus initiator was continuously added over an additional five hours.

[0176] Thirteen hours after polymerization initiation, the solution was heated to 68° C., additional initiator (p-menthane hydroperoxide 0.09 parts) and Styrene (0.9 parts) were continuously added during additional 3 hours, and allowed to react until at least twenty hours had elapsed since polymerization initiation, producing butadiene corel-BD/ST gradient core2 latex (R1).

[0177] The resultant polybutadiene rubber latex (R1) contained 40.3 wt % solids and had an average particle size of about 180 nm.

[0178] Second Stage: Polymerization of Shell 1 and Shell 2

[0179] Into a 3.9 litres reactor was charged 80.75 parts, on a solids basis, of polybutadiene rubber latex R1, 1.3 parts de-ionized water, and 0.004 parts sodium formaldehyde sulfoxylate. The solution was agitated, purged with nitrogen, and heated to 55° C. When the solution reached 62° C., continuously during 60 minutes 7.1 part of styrene, 0.09 parts of divinyl benzene and 0.03 part of t-butyl hydroperoxide are added. Afterwards the temperature is increased to 75° C. for 40 minutes. In batch, a mixture of 1.4 parts de-ionized water, 0.003 parts sodium formaldehyde sulfoxylate is added,then continuously 10.5 parts methyl methacrylate, 0.13 parts de divinyl benzene and 0.04 parts t-butyl hydroperoxide initiator were added over 30 minutes. Thirty minutes after the previous addition 0.1 parts t-butyl hydroperoxide were added to the reactor at once, followed by a hold period of 60 minutes.

[0180] Following the 60-minute hold period, a stabilization emulsion was added to the graft copolymer latex. The stabilization emulsion was prepared by mixing 5.4 parts de-ionized water (based on graft copolymer mass), 0.1 parts sodium salt of dodecyl benzene sulfonic acid and 0.38 parts octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate.

[0181] The resultant core shell latex (E1) had an average particle size of about 190 nm.

[0182] Example of Coagulation

[0183] In a jacketed vessel of 3 L, equipped with a stirrer is put successively 500 g of latex of core-shell particles for having a solid content of 14.1%. Under stirring at 300 r/min., the heat of the latex dispersion is raised at 50° C. and then injected the solution of salt (27.1 g of sodium chloride in 245 mL of deminerelized water). Coagulation occurs very rapidly. After 15 min., at 50° C. under stirring, the temperature is increased up to 85° C. and maintained for further 30 min. at this temperature. Then it is cooled down to 30° C. Subsequently, the coagulated material was filtered on centrifuge, washed with de-ionized water and filtered to produce a powder, P1.

[0184] Addition of Phosphate Buffer Solution.

[0185] In a 2 litres calibrated flask is put 750 g of graft copolymer (solid content 60 wt %) P1 and are added 99 mL of a aqueous solution of Na.sub.2HPO.sub.4 (disodium hydrogeno phosphate) and KH.sub.2PO.sub.4 (potassium dihydrogeno phosphate) comprising expressed in phosphorous concentration of 2.97 mg/ml, for being between 6 and 7.5 and preferably between 6 and 7 (neutral pH).

[0186] Drying. The powder PP1 is put in a ventilated oven during 48 h at 50° C. and recovered after complete drying.

Example 2 (Comparative)

[0187] Example 1 is repeated until the powder P1 at the end of the coagulation. No phosphate buffer solution is added. The powder is dried as in example 1.

Example 3 (Comparative)

[0188] Example 1 is repeated concerning the synthesis but the coagulation is made with magnesium sulphate (MgSO4). An aqueous solution of Na.sub.2HPO.sub.4 (disodium hydrogeno phosphate) is added. The powder is dried as in example 1.

Example 4 (Comparative)

[0189] Example 1 is repeated concerning the synthesis but the coagulation is made with calcium chloride (CaCl.sub.2). An aqueous solution of Na.sub.2HPO.sub.4 (disodium hydrogeno phosphate) is added. The powder is dried as in example 1.

TABLE-US-00001 TABLE 1 recovering conditions by coagulation pH adjustment at the Coagulating end to obtain Example agent neutral pH Example 1 NaCl Yes, with Na.sub.2HPO.sub.4 and KH2PO4 solution Example 2 NaCl no Example 3 MgSO.sub.4 Yes, with Na.sub.2HPO.sub.4 Example 4 CaCl.sub.2 Yes, with Na.sub.2HPO.sub.4

[0190] The composition of example 1 comprises less than 9 ppm of Ca2+ and less than 5 ppm of iron ions. The composition of comparative example 2 comprises less than 350 ppm of P. The compositions of comparative example 3 and 4 comprise more than 30 ppm of earth alkali metal cations.

[0191] The dry multistage polymer powders from examples 1 to 4 are compounded with polycarbonate at 5 wt % for producing compounds 1 to 4.

[0192] Preparation of the impact modified compound compositions, the respective impact modifier powders from examples 1 to 4 are mixed with the thermoplastic resin polycarbonate Lexan ML5221 from SABIC (at 5 wt % with the help of an extruder type Clextral (double diameter 25 mm, length 700 mm) using temperatures between from 100° C. up to 320° C. depending on the respective zones throughout the whole extruder.

[0193] The respective obtained compounds are heat aged at 120° C. The optical properties of the compounds are evaluated. The color change is observed by measuring the parameter b*. The b* value is used to characterize the principal yellowing off the samples. The b* value measures the blue and the yellow of the colour. Colours tending toward the yellow have a positive b* value while those tending toward the blue have a negative b* value. The b* values is measured using a colorimeter (especially according to the ASTM E 308 standard). The colour change is observed as a function of time: samples kept at 120° C. for 4 days.

[0194] If the initial color is close to zero it is considered that the thermoplastic composition comprising the impact modifiers of the invention is acceptable. The b* value should not larger than 10 after 4 days of thermal aging.

TABLE-US-00002 TABLE 2 optical properties expressed by b* of impact modified PC composition with respective multistage polymers b* after 4 days at Example b* initial 120° C. Example 1 −0.63 3.5 Example 2 −0.6 7.2 Example 3 −2.4 2.3 Example 4 0.1 4.5

TABLE-US-00003 TABLE 3 Izod Impact strength of impact modified polycarbonate composition with respective multistage polymers IZOD impact strength [kJ/m2] at Example 23° C. −30° C. Example 1 49.2 31.8 Example 2 44.0 31.7 Example 3 35.3 17.4 (−20° C.) Example 4 52.0 32.3

[0195] The composition according to the invention (example 1) possesses satisfying thermal aging stability and impact performance at ambient temperature and at −30° C. The other compositions (comparative examples) possess either no satisfying thermal aging stability or no satisfying impact performance at ambient temperature and at −30° C. or the two at the same time.