PMMA provided with impact resistance and having improved optical properties

Abstract

The invention relates to a molding composition modified for impact resistance, in particular to impact-resistant PMMA with improved optical properties at elevated temperatures, to molded items obtainable therefrom, and also to the use of the molding composition and of the molded items.

Claims

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) ##STR00006## wherein moieties R.sup.1 to R.sup.5 are each independently hydrogen, a halogen, a C.sub.1-6-alkyl group, or a C.sub.2-6-alkenyl group, and moiety R.sup.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.sup.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.sup.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.

Description

EXAMPLES

(1) Core-Shell-Shell Particle I

Inventive Example 1

(2) Production of the Seed Latex

(3) A seed latex was produced by emulsion polymerization of a monomer composition comprising 98% by weight of ethyl acrylate and 2% by weight of allyl methacrylate. The product comprised about 10% by weight of these particles of diameter about 20 nm in water.

(4) Production of the Core-Shell-Shell Particles

(5) All of the core-shell-shell particles described below were produced by emulsion polymerization in accordance with production specification A below (Inventive Examples IE1, IE2, IE3, IE4 and also IE5) and, respectively, production specification B below (Comparative Example CE1). The emulsions (i) to (iii) stated in Table 1 were used here.

Inventive Examples IE1, IE2, IE3, IE4 and IE5

(6) Production of the Core-Shell-Shell Particles by Production Process A

(7) 1.711 kg of water were used as initial charge in a polymerization tank at 83? C. (internal tank temperature), with stirring. 1.37 g of sodium carbonate and seed latex were then added. The emulsion (i) was then metered into the system over 1 h. 10 min after feed of the emulsion (i) had ended, the emulsion (ii) was metered into the system over a period of about 2 h. About 60 min after feed of the emulsion (ii) had ended, emulsion (iii) was then metered into the system over a period of about 1 h. 30 min after feed of the emulsion (iii) had ended, the system was cooled to 30? C.

(8) In order to separate the core-shell-shell particles, the dispersion was frozen at ?20? C. over 2 days, and then thawed, and the coagulated dispersion was separated by way of a filter fabric. The solid was dried at 50? C. in a drying oven (duration: about 3 days). The particle size of the core-shell-shell particles (see Table 2) was determined with the aid of a Nano-sizer? N5 from Coulter, the particles here being measured in dispersion.

Comparative Example CE1

(9) Production of the Core-Shell-Shell Particles by a Production Process B

(10) 1.711 kg of water were used as initial charge in a polymerization tank at 52? C. (internal tank temperature), with stirring, and 0.10 g of acetic acid, 0.0034 g of iron(II) sulphate, 0.69 g of sodium disulphite, and also the seed latex, were added. The emulsion (i) was then metered into the system over 1.5 h. 10 min after feed of the emulsion (i) had ended, 7.46 g of sodium disulphite dissolved in 100 g of water were added, and the emulsion (ii) was metered into the system over a period of about 2.5 h. About 30 min after feed of the emulsion (ii) had ended, 0.62 g of sodium disulphite dissolved in 50 g of water was then added, and the emulsion (iii) was metered into the system over a period of about 1.5 h. 30 min after feed of the emulsion (iii) had ended, the system was cooled to 30? C.

(11) In order to separate the core-shell-shell particles, the dispersion was frozen at ?20? C. over 2 days, and then thawed, and the coagulated dispersion was separated by way of a filter fabric. The solid was dried at 50? C. in a drying oven (duration: about 3 days). The particle size of the core-shell-shell particles (see Table 2) was determined with the aid of a Nano-sizer? N5 from Coulter, the particles here being measured in dispersion.

(12) TABLE-US-00001 TABLE 1 Summary of the individual emulsions (all data in [g]) IE1 IE2 IE3 IE4 IE5 CE1 Seed latex 93.00 58.00 28.00 20.00 16.00 5.00 Emulsion (i) Water 878.70 878.70 878.70 878.70 878.70 732.69 Sodium 0.70 0.70 0.70 0.70 0.70 0.51 persulphate Aerosol OT75 5.60 5.60 5.60 5.60 5.60 4.67 Methyl 1071.62 1071.62 1071.62 1071.62 1071.62 703.47 methacrylate Ethyl 44.74 44.74 44.74 44.74 44.74 29.40 acrylate Allyl 2.24 2.24 2.24 2.24 2.24 2.21 methacrylate Emulsion (ii) Water 606.90 606.90 606.90 606.90 606.90 628.65 Sodium 1.58 1.58 1.58 1.58 1.58 1.44 persulphate Aerosol OT75 7.20 7.20 7.20 7.20 7.20 7.46 Butyl acrylate 1160.63 1160.63 1160.63 1160.63 1160.63 1219.72 Styrene 256.00 256.00 256.00 256.00 256.00 262.87 Allyl 21.57 21.57 21.57 21.57 21.57 19.53 methacrylate Emulsion (iii) Water 404.30 404.30 404.30 404.30 404.30 381.56 Sodium 0.70 0.70 0.70 0.70 0.70 0.44 persulphate Aerosol OT75 1.08 1.08 1.08 1.08 1.08 1.34 Methyl 614.27 614.27 614.27 614.27 614.27 920.45 methacrylate Ethyl acrylate 24.93 24.93 24.93 24.93 24.93 38.35
Blending of the Moulding Compositions

Inventive Examples 2, 3, 4, 5, 7, 8, 9 and 10 and Comparative Example 6

(13) A low-molecular-weight moulding composition (LMC) with M.sub.w about 50000 g/mol was produced, composed of 85% by weight of methyl methacrylate units and of 15% by weight of methyl acrylate units.

(14) The moulding composition Altuglas? HT 121 (Arkema, France), featuring high heat resistance, was also provided (high-TG moulding composition comprising methacrylic acid).

(15) One of the following: a) a moulding composition based on polymethyl methacrylate, PLEXIGLAS? 7N (Evonik Industries AG, Darmstadt), optionally mixed with a proportion of the above low-molecular-weight moulding composition (LMC) and/or with a proportion of Altuglas? HT 121, or b) a moulding composition based on polymethyl methacrylate, PLEXIGLAS? 8H (Evonik Industries AG, Darmstadt) was blended with the respective core-shell-shell particles IE1-IE5 and, respectively, CE1 by means of an extruder where the moulding composition and, respectively, blended moulding composition used corresponded in each case to the (meth)acrylic polymer II. Table 2 documents the compositions of the individual inventive examples and of the comparative example.

(16) 4 kg of the respective (meth)acrylic polymer II. and 2450 g of the respective core-shell-shell particles I. (38% by weight) were weighed into a 10 l mixing vessel. The mixture was mixed intensively by means of a tumbling mixer for 3 minutes and then charged to the hopper of a Stork single-screw extruder with 35 mm screw diameter. The components were mixed at a melt temperature of 235? C., and strands were drawn off from the extruder die, cooled in the water bath and pelletized to give pellets of uniform grain size.

(17) 500 test specimens in accordance with ISO 294 were injection-moulded from the resultant pellets in a Battenfeld BA injection-moulding machine. In order to determine impact resistance, test specimens measuring 80?10?4 mm were injection-moulded at 250? C. In order to determine optical properties, 65?40?3 mm plaques were injection-moulded at a melt temperature of 250? C.

(18) Testing of the Moulding Compositions

(19) Test specimens were produced from the blended moulding compositions. The moulding compositions or the corresponding test specimens were tested in accordance with the test methods below: Vicat softening point (B50, 16 h/80? C.): DIN ISO 306 (August 1994) Charpy impact resistance: ISO 179 (1993) Modulus of elasticity: ISO 527-2 Transmittance (D 65/10?): DIN 5033/5036 Haze (BYK Gardner Hazegard-plus hazemeter): ASTM D1003 (1997) MVR (230? C., 3.8 kg): ISO 1133

(20) Table 2 shows the results of the tests. The advantages of the blends of the invention are clearly seen in comparison with the conventionally impact-modified moulding compositions of Comparative Example 6. Even at relatively high temperature (80? C.), the blends of the invention have low haze values of less than 5%, determined in accordance with ASTM D1003. However, the moulding compositions of the invention are similar to the known moulding compositions (Comparative Example 6) in providing a level of toughness and in providing impact resistance, without any impairment of the other important properties of the moulding composition, in particular the Vicat softening point and the modulus of elasticity. Some of the values obtained for these properties are actually better than those for the known moulding compositions (cf. inventive example 10).

(21) TABLE-US-00002 TABLE 2 Test results for the impact-modified moulding compositions (on blending with 38% by weight of core-shell-shell particles I. in (meth)acrylic polymer II. Inventive Inventive Inventive Inventive Comparative Example 2 Example 3 Example 4 Example 5 Example 6 Core-shell-shell IE1 IE2 IE3 IE4 CE1 particles Moulding 7N 7N 7N 8H 7N composition Particle radius [nm] 72 88 101 116 165 Vicat [? C.] 97.5 97.8 97.9 99.6 99.6 Charpy IR @ 23? C. 49.4 71.3 91.5 96.7 95.9 [kJ/m.sup.2] Light transmittance 91.3 91.4 91.5 91.3 91.0 Haze @ 23? C. [%] 0.71 0.56 0.68 1.3 1.9 Haze @ 60? C. [%] 1.35 1.22 1.57 5.4 5.2 Haze @ 80? C. [%] 2.04 2.34 3.71 11.8 22.4 Modulus of elasticity [MPa] 2043 1946 1943 2220 1828 MVR [cm.sup.3/10 min] 1.00 1.16 1.59 0.5 1.83 Inventive Inventive Inventive Inventive Example 7 Example 8 Example 9 Example 10 Core-shell-shell IE3 IE3 IE3 IE5 particles Moulding 7N + 10% by wt. Altuglas? HT Altuglas? HT 7N composition of LMC 121 121 + 10% by wt. of LCM Particle radius [nm] 101 101 101 122 Vicat [? C.] 95.9 106.7 105.6 96.1 Charpy IR @ 23? C. 92.3 89.4 62.8 107.9 [kJ/m.sup.2] Light transmittance 91.0 90.8 89.9 91.5 Haze @ 23? C. [%] 1.1 1.4 1.4 0.9 Haze @ 60? C. [%] 2.1 4.5 4.8 5.6 Haze @ 80? C. [%] 4.6 8.4 8.5 9.7 Modulus of elasticity 1923 2191 2097 1875 [MPa] MVR [cm.sup.3/10 min] 2.35 0.53 0.88 1.68

(22) FIG. 1 shows the test results for Charpy impact resistance and haze values at 23? C., and also at 80? C., for the impact-modified moulding compositions (on blending with 38% by weight of core-shell-shell particles I. in the respective moulding composition) for Inventive Examples 2, 3, 4 and 10, and also Comparative Example 6.

(23) The markedly reduced haze increase of the moulding compositions of the invention at elevated temperature can be seen from FIG. 1 and also from Table 2, and they are therefore suitable for applications such as lighting and glazing. In particular, compliance has been achieved with the requirements placed upon automobile glazing: toughness combined with optical properties such as high transparency with very low haze even at elevated temperatures. Inventive Example 7 reveals the effect of the addition of the low-molecular-weight (meth)acrylic polymer or the flow improver via the significant change of MVR in comparison with Comparative Example 6 and the other Inventive Examples.