PMMA provided with impact resistance and having improved optical properties

1. A moulding composition comprising respectively, based on its total weight:

I. from 10.0 to 50.0% by weight of a core-shell-shell particle having a core, a first shell, and a second shell, produced by the process comprising

a) employing water and an emulsifier as an initial charge,

b) adding to the initial charge from 20.0 to 45.0 parts by weight of a first composition comprising:

A) from 50.0 to 99.9 parts by weight of alkyl methacrylates having from 1 to 20 carbon atoms in the alkyl moiety,

B) from 0.0 to 40.0 parts by weight of alkyl acrylates having from 1 to 20 carbon atoms in the alkyl moiety,

C) from 0.1 to 10.0 parts by weight of crosslinking monomers, and

D) from 0.0 to 8.0 parts by weight of styrenic monomers of formula (I)

wherein moieties R 1 to R 5 are each independently hydrogen, a halogen, a C 1-6 -alkyl group, or a C 2-6 -alkenyl group, and moiety R 6 is hydrogen or an alkyl group having from 1 to 6 carbon atoms, to obtain a first mixture, and polymerizing the first mixture until conversion is at least 85.0% by weight, based on the total weight of components A), B), C), and D),

c) adding to the first mixture 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 (meth)acrylates,

F) from 0.05 to 5.0 parts by weight of crosslinking monomers, and

G) from 0.0 to 25.0 parts by weight of styrenic monomers of formula (I) to obtain a second mixture, and polymerizing the second mixture until conversion is at least 85.0% by weight, based on the total weight of components E), F) and G),

d) adding to the second mixture 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 alkyl methacrylates having from 1 to 20 carbon atoms in the alkyl moiety,

I) from 0.0 to 40.0 parts by weight of alkyl acrylates having from 1 to 20 carbon atoms in the alkyl moiety, and

J) from 0.0 to 10.0 parts by weight of styrenic monomers of formula (I) to obtain a third mixture, and polymerizing the third mixture until conversion is at least 85.0% by weight, based on the total weights of components H), I), and J),

and wherein the stated parts by weight of the compositions b), c), and d) represent a total of 100.0 parts by weight, wherein the relative proportions of all the substances A) to J) provide, after polymerizing the third mixture, the core-shell-shell particles with a total radius, measured by the Coulter method, in the range of 70.0 to 125.0 nm, wherein the core, the first shell, and the second shell comprise compositions b), c), and d), respectively;

II. from 1.0 to 90.0% by weight of at least one (meth)acrylic polymer,

III. from 0.0 to 45% by weight of styrene-acrylonitrile copolymers, and

IV. from 0.0 to 10.0% by weight of additives,

wherein II. or mixture of II., III., and/or IV. provide a measurement in accordance with ASTM D542 a refractive index that differs from the refractive index of I. by no more than 0.01 unit.

2. The moulding composition according to claim 1 , wherein in the process in accordance with I. each polymerization is carried out at a temperature in the range from above 60° C. to below 90° C. or each polymerization is initiated by a redox initiator system.

3. The moulding composition according to claim 1 , wherein in the process for obtaining I. the polymerization in the steps b) to d) is initiated with a peroxodisulphate.

4. The moulding composition according to claim 1 , wherein the moulding composition

has a Charpy impact resistance in accordance with ISO 179 of at least 40.0 kJ/m 2 at 23° C. and

has a haze in accordance with ASTM D1003 (1997) of at most 15.0% at 80° C.

5. The moulding composition according to claim 1 , wherein the process for obtaining I. employs, as initial charge, from 90.00 to 99.99 parts by weight of water and from 0.01 to 10.00 parts by weight of emulsifier, where the stated parts by weight give a total of 100.00 parts by weight.

6. The moulding composition according to claim 1 , wherein the process for obtaining I. employs, as the emulsifier, an anionic emulsifier or a non-ionic emulsifier.

7. The moulding composition according to claim 1 , wherein the at least one (meth)acrylic polymer according to II. comprises, in each case based on its total weight,

a) from 52.0 to 100.0% by weight of alkyl methacrylate units having from 1 to 20 carbon atoms in the repeating alkyl moiety,

b) from 0.0 to 40.0% by weight of alkyl acrylate units having from 1 to 20 carbon atoms in the repeating alkyl moiety and

c) from 0.0 to 8.0% by weight of repeating styrenic units of formula (I),

wherein the percentages by weight obtain a total of 100.0% by weight.

8. The moulding composition according to claim 1 , wherein the moulding composition comprises styrene-acrylonitrile copolymers in accordance with III., wherein the styrene-acrylonitrile copolymers were obtained by polymerization of a mixture comprising

from 70 to 92% 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 mixture.

9. The moulding composition according to claim 1 , wherein the moulding composition comprises, based on its total weight, as additive in accordance with IV., from 0.1 to 10.0% by weight of another polymer which has a weight-average molecular weight that is higher by at least 10% than that of the at least one (meth)acrylic polymer according to 11.

10. A moulded item obtained from the moulding composition according to claim 1 .

11. The moulded item according to claim 10 , wherein the moulded item

has a Charpy impact resistance in accordance with ISO 179 of at least 40.0 kJ/m 2 at 23° C. and

has a haze in accordance with ASTM D1003 (1997) of at most 15.0% at 80° C.

12. The moulding composition according to claim 1 , wherein the composition is suitable for the production of glazing.

13. The moulded item according to claim 10 , wherein the item is suitable as glazing.

14. The moulding composition according to claim 1 , wherein the composition is suitable for the production of displays for communication devices, for mobile telephones, or for cellphones; tablet PCs; TV devices; kitchen devices and other electronic devices.

15. The moulded item according to claim 10 , wherein the item is suitable as display for a communication device, a mobile telephone, a cellphone; a TV device; a tablet PC; a kitchen device or any other electronic device.

16. The moulding composition according to claim 1 , wherein the composition is suitable for the production of lamp covers.

17. The moulded item according to claim 10 , wherein the item is suitable as a lamp cover.