Process for preparing aqueous dispersions

Abstract

The present invention relates to a process for preparing aqueous dispersions. The invention also relates to the formation of core-shell particles in aqueous dispersions. The core-shell particles are useful as impact-modifiers for poly(meth)acrylate moulding compositions.

1 . Core-shell particles obtained by a process comprising:
 (1) preparing an aqueous polymer dispersion, and   (2) separating core-shell particles therefrom,   wherein (1) comprises:
 a) preparing an initial charge of an aqueous emulsion of a long chain alkyl alcohol or a seed latex by polymerization of an alkyl (meth)acrylate in an aqueous medium comprising an emulsifier to a seed particle radius ranging from 3.0 to 20.0 nm 
 b) adding from 25.0 to 45.0 parts by weight of a first composition 
 comprising:
 A) from 50.0 to 99.9 parts by weight of an alkyl (meth)acrylate having from 1 to 20 carbon atoms in the alkyl radical, 
 B) from 0.0 to 40.0 parts by weight of an alkyl acrylate having from 1 to 20 carbon atoms in the alkyl radical, 
 C) from 0.1 to 10.0 parts by weight of a crosslinking monomer, and 
 D) from 0.0 to 8.0 parts by weight of a styrenic monomer of the formula (I) 
 
   
       
         
           
           
               
               
           
         
         
           where each of the radicals R 1  to R 5 , independently of the others, is hydrogen, a halogen, a C 1-6 -alkyl group or a C 2-6 -alkenyl group, and the radical R 6  is hydrogen or an alkyl group having from 1 to 6 carbon atoms, emulsified in water with an emulsifier, to said aqueous emulsion or seed latex, and 
           polymerizing the added monomers to a conversion of at least 85.0% by weight, based on the total weight of components A), B), C) and D), 
           c) adding from 35.0 to 55.0 parts by weight of a second composition 
           comprising
 E) from 80.0 to 100.0 parts by weight of a (meth)acrylate, 
 F) from 0.05 to 10.0 parts by weight of a crosslinking monomer, and 
 G) from 0.0 to 20.0 parts by weight of a styrenic monomer of the formula (I), emulsified in water with an emulsifier, to the aqueous polymer emulsion of step (b), and 
 polymerizing the added monomers to a conversion of at least 85.0% by weight, based on the total weight of components E), F) and G), 
 
           d) adding from 10.0 to 30.0 parts by weight of a third composition comprising:
 H) from 50.0 to 100.0 parts by weight of an alkyl (meth)acrylate having from 1 to 20 carbon atoms in the alkyl radical, 
 I) from 0.0 to 40.0 parts by weight of an alkyl acrylate having from 1 to 20 carbon atoms in the alkyl radical, and 
 J) from 0.0 to 10.0 parts by weight of a styrenic monomer of the formula (I), emulsified in water with an emulsifier, to the aqueous polymer emulsion of step (c), 
 and polymerizing to a conversion of at least 85.0% by weight, based on the total weight of components H), I) and J), 
 
         
         where the parts by weight given for the compositions b), c) and d) give a total of 100.0 parts by weight,
 wherein 
 e) each polymerization is carried out at a temperature in the range from above 60 to below 90° C. and 
 f) the relative proportions of all of the substances are selected in such a way that the total weight of components A) to J), based on the total weight of the aqueous dispersion, is greater than 50.0% by weight, the product particles have a particle size ranging from 150 to less than 250 nm, and the amount of coagulate in the dispersion is 0.1% or less by wt, based on the total weight of the dispersion. 
 
       
     
     
         2 . A moulding composition comprising, based in each case on its total weight, of
 A) from 1.0 to 50.0% by weight of at least one core-shell particle according to  claim 1 ,   B) from 1.0 to 99.0% by weight of at least one (meth)acrylic polymer,   C) from 0.0 to 45% by weight of at least one styrene-acrylonitrile polymer, and   D) from 0.0 to 10.0% by weight of other additives,   where the percentages by weight give 100.0% by weight in total.   
     
     
         3 . The moulding composition according to  claim 2 , wherein the (meth)acrylic polymer encompasses, based in each case on its total weight, of
 a) from 50.0 to 100.0% by weight of alkyl methacrylate repeat units having from 1 to 20 carbon atoms in the alkyl radical,   b) from 0.0 to 40.0% by weight of alkyl acrylate repeat units having from 1 to 20 carbon atoms in the alkyl radical and   c) from 0.0 to 8.0% by weight of styrenic repeat units of the formula (I),   
       where the percentages by weight give 100.0 W by weight in total. 
     
     
         4 . The moulding composition according to  claim 2 , wherein the moulding composition comprises styrene/acrylonitrile copolymers, where the styrene/acrylonitrile copolymers are obtained by polymerizing any mixture which comprises
 from 70 to 92 W by weight of styrene,   from 8 to 30% by weight of acrylonitrile, and   from 0 to 22% by weight of other comonomers, based in each case on the total weight of the monomers to be polymerized.   
     
     
         5 . The moulding composition according to  claim 2 , wherein the moulding composition comprises, based on its total weight, from 0.1 to 10.0% by weight of another polymer whose weight-average molecular weight is higher by at least 10% than that of the (meth)acrylic polymer. 
     
     
         6 . A moulding obtained from a moulding composition according to  claim 2 . 
     
     
         7 . The moulding according to  claim 6 , wherein the moulding has a Vicat softening point ISO 306 (B50) of at least 85° C., a notched impact strength NIS (Charpy179/1eA) to ISO 179 of at least 6.0 kJ/m 2  at 23° C. and of at least 2.5 kJ/m 2  at −10° C., a modulus of elasticity to ISO 527-2 of at least 1500 Pa s, a haze to ASTM D 1003 (1997) of at most 2.5%, a transmittance (D) 65/10° to DIN 5033/5036 of at least 88.5%. 
     
     
         8 . The moulding according to  claim 7 , wherein the moulding has a Vicat softening point ISO 306 (B50) of at least 90° C. 
     
     
         9 . The moulding according to  claim 8 , wherein the moulding has a Vicat softening point ISO 306 (B50) of at least 93° C. 
     
     
         10 . The core-shell-particles according to  claim 1 , wherein a seed latex whose particle radius, measured by the Coulter method, is in the range from 5.0 to 20.0 nm is used to form the initial charge. 
     
     
         11 . The core-shell-particles according to  claim 1 , wherein said initial charge is an aqueous emulsion of said long chain alkyl alcohol having from 12 to 20 carbon atoms in the alkyl radical. 
     
     
         12 . The moulding composition according to  claim 2 , wherein the (meth)acrylic polymer has a number-average molar mass of from 1000 to 100,000,000 g/mol. 
     
     
         13 . The moulding composition according to  claim 12 , wherein the number-average molar mass is from 10,000 to 1,000,000 g/mol. 
     
     
         14 . The moulding composition according to  claim 12 , wherein the number-average molar mass is from 50,000 to 500,000 g/mol. 
     
     
         15 . The moulding composition according to  claim 3 , wherein the (meth)acrylic polymer comprises from 85.0 to 100.0% by weight of alkyl methacrylate repeat units. 
     
     
         16 . The moulding composition according to  claim 5 , wherein said weight-average molecular weight is higher by at least 50% than that of the (meth)acrylic polymer. 
     
     
         17 . The moulding composition according to  claim 5 , wherein said weight-average molecular weight is higher by at least 100% than that of the (meth)acrylic polymer. 
     
     
         18 . The moulding composition according to  claim 2 , wherein the (meth)acrylic polymer encompasses, based in each case on its total weight, of
 a) from 85.0 to 99.5% by weight of alkyl methacrylate repeat units having from 1 to 4 carbon atoms in the alkyl radical,   b) from 0.1 to 15.0% by weight of alkyl acrylate repeat units having from 1 to 4 carbon atoms in the alkyl radical and   c) from 0.0 to 8.0% by weight of styrenic repeat units of the formula (I),   
       where the percentages by weight give 100.0% by weight in total.