Method for producing polycarbonate molding compositions with improved thermal processing stability

Abstract

The invention relates to a compounding method for producing impact-modified polycarbonate compositions using components acting as an alkali or using alkaline constituent-containing components. By using the method according to the invention, the harmful influence of the components acting as an alkali on the properties of polycarbonate molding compositions or the surface of molded bodies produced therefrom is counteracted. The method has the steps (i), (ii), and optionally (iii), wherein (i) in a first step A) 10 to 98 wt. % of at least one polymer selected from the group of aromatic polycarbonates and aromatic polyester carbonates, B) 0.001 to 0.3 wt. % of at least one organic Brnsted acid, i.e. a carbon and hydrogen-containing Brnsted acid, C) 0.0001 to 0.008 wt. % of at least one inorganic Brnsted acidic phosphorus compound, i.e. a Brnsted acidic phosphorus compound which does not contain carbon, D) 1 to 90 wt. % of at least one rubber-containing vinyl(co)polymerisate, E) 0 to 90 wt. % of at least one polyester, and F) 0 to 30 wt. % of at least one additive, the ratio of the weight percentages of the components B to C used in method step (i) ranging from 2 to 100, are heated by supplying thermal and/or mechanical energy, whereby at least the components A) and D) are melted and all of the components used are mixed together, dissolved into one another, or dispersed into one another, and in an additional step (ii), the melt (ii) resulting from method step (i) is resolidified by cooling and (iii) optionally granulated. The method steps (ii) and (iii) can be carried out in any order. The invention also relates to compositions produced according to the method, to the use thereof for producing molded bodies, to the molded bodies themselves, and to the use of the mixtures of B and C for stabilizing impact-modified polycarbonate compositions.

Claims

1. A process for producing impact-modified polycarbonate compositions containing the steps (i), (ii) and optionally (iii), wherein (i) in a first step A) 10 to 98 parts by weight of at least one polymer selected from the group of aromatic polycarbonates and aromatic polyester carbonates, B) 0.001 to 0.3 parts by weight of ethylenediaminetetraacetic acid (EDTA), C) 0.0001 to 0.008 parts by weight of at least one inorganic Brnsted-acidic phosphorus compound, D) 1 to 90 parts by weight of at least one rubber-containing vinyl (co)polymer, E) optionally up to 90 parts by weight of at least one polyester, F) optionally up to 30 parts by weight of at least one additive, wherein the ratio of the parts by weight of the components B to C employed in process step (i) is in the range from 8 to 30, are heated by supplying thermal and/or mechanical energy, at least the components A) and D) are thus melted and all employed components are thus mixed with one another, dissolved in one another or dispersed in one another and in a further step (ii) the melt resulting from process step (i) is (ii) resolidified by cooling and (iii) optionally pelletized, wherein the process steps (ii) and (iii) may be performed in any desired sequence relative to one another.

2. The process as claimed in claim 1, wherein the component B is employed in step (i) in a proportion of 0.01 to 0.1 parts by weight based on the sum of the parts by weight of the components A to F.

3. The process as claimed in claim 1, wherein the component C is employed in step (i) in a proportion of 0.001 to 0.005 parts by weight based on the sum of the parts by weight of the components A to F.

4. The process as claimed in claim 1, wherein it employs component A in a proportion of 50 to 80 parts by weight, component B in a proportion of 0.02 to 0.07 parts by weight, component C in a proportion of 0.002 to 0.004 parts by weight, component D in a proportion of 7 to 50 parts by weight, component E in a proportion of 0 to 50 parts by weight and component F in a proportion of 0.2 to 10 parts by weight.

5. The process as claimed in claim 1, wherein component D contains magnesium sulfate or calcium chloride.

6. The process as claimed in claim 1, wherein in step (i) at least one component having a polycarbonate-decomposing effect is employed.

7. A method comprising stabilizing impact-modified polycarbonate compositions utilizing acid mixtures consisting of an organic Brnsted acid and an inorganic Brnsted-acidic phosphorus compound, wherein the weight ratio of the organic Brnsted acid to the inorganic Brnsted acid is in the range from 2 to 100.

8. A composition obtainable by any of the processes as claimed in claim 1.

9. A method comprising providing compositions as claimed in claim 8 and producing molded articles.

10. A molded article containing a composition as claimed in claim 8.

11. The process as claimed in claim 1, wherein component C is phosphorous acid (H.sub.3PO.sub.3) having a water content of 0.05% to 2% by weight.

Description

EXAMPLES

(1) Components Used:

(2) Component A

(3) Linear polycarbonate based on bisphenol A having a weight-average molecular weight Mw of 25 500 g/mol (determined by gel permeation chromatography (GPC) in a methyl chloride solvent and with a polycarbonate standard).

(4) Component B

(5) Phosphorous acid ester of bis(2-hydroxy-3-cyclohexyl-5-methylphenyl)methane

(6) ##STR00007##
Component C

(7) Phosphorous acid (99%), Sigma-Aldrich Chemie GmbH.

(8) Component D

(9) ABS blend having a ratio of acrylonitrile:butadiene:styrene, based on the blend, of 19:24:57% by weight, containing an ABS polymer according to component D1 produced by emulsion polymerization, precipitated using magnesium sulfate, worked up in a basic medium and containing basic impurities and magnesium sulfate, an ABS polymer produced by bulk polymerization according to component D2 and a SAN polymer according to component D3.

(10) Component F1

(11) Pentaerythritol tetrastearate as lubricant/demolding agent

(12) Component F2

(13) Heat stabilizer, Irganox B900 (mixture of 80% Irgafos 168 (tris(2,4-di-tert-butylphenyl)phosphite) and 20% Irganox 1076 (2,6-di-tert-butyl-4-(octadecanoxycarbonylethyl)phenol); BASF (Ludwigshafen, Germany)

(14) Component F3

(15) Heat stabilizer, Irganox 1076 (2,6-di-tert-butyl-4-(octadecanoxycarbonylethyl)phenol); BASF (Ludwigshafen, Germany).

(16) Component F4

(17) Carbon black, Black Pearls 800, Cabot Corporation (USA)

(18) Process for Producing Compositions (Molding Materials) from the Employed Components

(19) In the first process step (i) the components A, B, C, D and F were passed into the feed zone of a twin-screw extruder (ZSK133SC) from Coperion, Werner & Pfleiderer (Stuttgart, Germany), brought to a temperature of about 300 C. with a specific energy input at the extruder drive of 145 Wh/kg in the melting and kneading zone of the extruder and thus melted, and kneaded at this temperature to disperse the plasticized components in one another. A speed of 355 min.sup.1 and a throughput of 5000 kg/h were employed here. The thus compounded mixture was degassed in the subsequent degassing zone of the extruder by applying a negative pressure of 200 mbar (absolute) to the melt. In the second and third process steps (ii) and (iii) the degassed melt was discharged from the extruder through a die at a temperature of about 300 C. and pelletized by underwater pelletization, cooled and thus solidified.

(20) Production of the Test Specimens and Testing

(21) The propensity for forming surficial defects having blistering topology was evaluated on sheets having dimensions of 150 mm105 mm3.2 mm which were produced on an injection molding machine (from Arburg) at a melt temperature of 260 C. and a mold temperature of 80 C. An injection mold polished to a high gloss on both sides was used here. The thus produced sheets did not exhibit any surficial defects having blistering topology before hot and humid storage. Blistering was assessed visually without using magnifying technical aids (microscopes, magnifying glasses etc.) after three-day storage of these sheets under hot and humid conditions at 40 C. and a relative humidity of >95%. All visually apparent blister defects on both sides of altogether two sheets having the above-defined dimensions (i.e. on an effective surface area of 4.Math.15 cm.Math.10.5 cm=630 cm.sup.2) were counted. From experience this purely visual assessment without magnifying technical aids accounts for all defects having a diameter above approximately 100-200 m.

(22) The MVR serves as a measure for any polycarbonate molecular weight degradation during the thermal stress during compounding and was determined on the pellets produced by compounding after drying at 100 C. for 4 h in a circulating air dryer according to ISO1133 at a melt temperature of 300 C. with a piston loading of 2.16 kg after a hold time of 5 min.

(23) The iMVR was determined under the same conditions as the MVR but with a prolonged hold time of 15 min. The difference between the iMVR and the MVR serves as an indication of a thermally induced polycarbonate molecular weight degradation to be expected at high melt temperatures in the injection mold and thus as a measure of processing stability in the injection mold.

(24) TABLE-US-00001 TABLE 1 V1 2 V3 A 69.00 68.997 68.988 B 0.075 0.05 C 0.003 0.012 D 29.56 29.56 29.56 F1 0.64 0.64 0.64 F2 0.025 0.05 0.1 F3 0.20 0.20 0.20 F4 0.50 0.50 0.50 Formulation characteristics B/C 16.7 0 Properties MVR [ml/10 min] 39 26 25 iMVR [ml/10 min] 41 28 27 Number of blisters 14 12 30

(25) The examples in table 1 show that only the inventive process (example 2), in which a combination of organic acidic compound and an amount of an inorganic acidic compound that is relatively small compared to the employed concentration of the organic acidic compound was used, results in the desired properties. Especially surprising here is that despite lower employed concentration of both organic acid compared to comparative example V1 and inorganic acid compared to comparative example V3 and also a lower total acid concentration compared to both comparative examples V1 and V3 a good thermal stability results.

(26) The process using exclusively organic acid (V1) results in elevated thermally induced polycarbonate molecular weight degradation even during compounding despite already using a higher concentration of acid than in the inventive example 2. The amount of organic acid employed in inventive example 2 is thus not on its own sufficient to inhibit the thermally induced polycarbonate molecular weight degradation during compounding.

(27) The use of exclusively inorganic acid (V3) results in inadequate blistering behavior even at a very low employed amount. Said amount was chosen such that it is still just sufficient in the chosen composition to safely inhibit thermally induced polycarbonate molecular weight degradation during compounding and during further thermal processing.