Injection moulded polypropylene articles

Abstract

Injection molded article made from a composition containing 81-88 wt % of a propylene homopolymer (A) having a melt flow rate of between 1 and 2 g/10 min, 12-19 wt % of a propylene-ethylene copolymer (B) containing 45-65 wt % of ethylene, and 50-10000 ppm by weight of a nucleating agent. The total ethylene content of the composition is 6-10 wt %, and the melt flow rate (MFR) of the composition is 0.7-2 g/10 min.

Claims

1. Injection moulded article made from a composition comprising: 81-88 wt % of a propylene homopolymer (A) having a melt flow rate of between 1 and 2 g/10 min; 12-19 wt % of a propylene-ethylene copolymer (B) containing 45-65 wt % of ethylene; and 50-10000 ppm by weight of a nucleating agent, wherein propylene homopolymer (A) and propylene-ethylene copolymer (B) together make up at least 98 wt % of the polymer content of the composition, the total ethylene content of the composition is 6-10 wt %, and the melt flow rate (MFR) of the composition is 0.7-2 g/10 min.

2. Article according to claim 1, wherein the composition has a spiral flow, measured at a rate of 20 mm/s, of greater than 300 mm.

3. Article according to claim 1, wherein the amount of propylene-ethylene copolymer (B) in the composition is 14-17 wt %.

4. Article according to claim 1, wherein copolymer (B) of the composition contains 50-60 wt % of ethylene.

5. Article according to claim 1, wherein the total ethylene content of the composition is 6.5-9.5 wt %.

6. Article according to claim 1, wherein the total ethylene content of the composition is 7-9.5 wt %.

7. Article according to claim 1, wherein the nucleating agent in the composition is sodium benzoate, disodium hexahydrophthalate, 1,3-O-2,4-bis (3,4-dimethylbenzylidene) sorbitol, sodium 2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate, aluminum bis [2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate], and talc, or a calcium, strontium, monobasic aluminum or lithium salt of 1,2 cyclohexane dicarboxylic acid.

8. Article according claim 1, wherein the nucleating agent is the calcium salt of 1,2 cyclohexane dicarboxylic acid.

9. Article according to claim 1, wherein the composition has a flexural modulus of at least 1200 MPa.

Description

EXAMPLES

(1) Examples 1 and 2 were made in a two reactor continuous polymerisation reactor system. Each of the two reactors was a horizontal, cylindrical reactor measuring 2.7 m in diameter and 16 m in length containing a horizontal stirrer. An inter-stage gas exchange system was located between the two reactors which were capable of capturing first reactor polymerisation product, being vented to remove first reactor gas, and then refilled with fresh gas. This gas exchange system was present in order to preserve different gas compositions in each reactor stage. Both reactors were equipped with an off-gas port for recycling reactor gas through a condenser and back through a recycle line to nozzles in the reactor and liquid propylene was used as a quench liquid to help control the temperature of the polymerization reaction.

(2) Polymerisation was initiated by the introduction to the first reactor of a high activity supported titanium containing catalyst component produced according to Example 1 of U.S. Pat. No. 4,988,656 through a liquid propylene-flushed catalyst addition nozzle. Organosilane modifier and a solution of trialkylaluminum co-catalyst-(TEA) were fed separately to the first reactor through different liquid propylene-flushed addition nozzles. During polymerisation, active propylene homopolymer powder was captured from the first reactor and exposed to a series of gas venting and re-pressurization steps, before being added to the second reactor. Hydrogen was fed to each reactor in order to achieve the desired powder melt flow rate (MFR). Ethylene and propylene were fed separately in order to maintain the desired ratio of the two gases. Details of the process conditions are given in Table 1 and polymer properties are shown in Table 2. Example 3 corresponds to example 1 in WO02/38670.

(3) TABLE-US-00001 TABLE 1 EXAMPLE 1 CE2 CE3 Reactor 1 Temperature ° C. 57 57 65 Pressure MPa 2.3 2.3 3.2 Silane DIPDMS* DIPDMS* DCPDMS** Al/Si mol/mol 6 6 2 Al/Ti mol/mol 80 80 75 H2/C3 mol/mol 0.006 0.0013 0.0017 Reactor 2 Temperature ° C. 78 78 72 Pressure MPa 2.2 2.2 2.0 H2/C3 mol/mol 0.006 0.0003 0.0214 Split wt % 15.0 7.3 8.3 C2/C3 mol/mol 0.36 0.36 0.79 Formulation IRGANOX1010 ppm 1800 1800 2000 IRGAFOS 168 ppm 1800 1800 1000 HOSTANOX ppm — — 1000 Calcium stearate ppm 800 — Hydrotalcite DHT-4A ppm — 400 500 HPN-20E.sup.$ ppm 300 — — Sodium benzoate ppm — 800 2000 *Diisopropyldimethoxysilane **Dicyclopentyldimethoxysilane .sup.$HPN-20E—calcium salt of 1,2 cyclohexane dicarboxylic acid

(4) TABLE-US-00002 TABLE 2 EXAMPLE 1 CE2 CE3 Component A MFR (A) g/10 min 1.5 0.3 [A] wt % 85.0 92.7 91.7 XS (A) wt % 1.5 1.5 1.6 Component B [B] wt % 15.0 7.3 8.3 C2(B) wt % 56 56 48 XS (B) wt % 85 87 85 Final composition (ex-reactor MFR g/10 min 0.80 0.25 0.51 C2(tot) wt % 8.4 4.1 4.0 η dl/g 0.274 0.350 Xs wt % 14.0 7.6 8.7 η(Xs) dl/g 0.362 0.526 Viscosity Ratio 1.4 1.6 (η(Xs)./η(Xins)) Resin properties (after pelletisation) Flex Mod 23° C. MPa 1460 1723 1741 Izod 23° C. kJ/m.sup.2 61 69 Izod −20° C. kJ/m.sup.2 6.3 4.5 Charpy 23° C. kJ/m.sup.2 70 80 Charpy −20° C. kJ/m.sup.2 8.0 4.1 Shrinkage perp. % 0.90 1.32 Shrinkage parallel % 1.68 2.20 Spiral flow mm 340 265 (inj. speed 20 mm/s)

(5) In the table above it can be seen that the composition of the invention has a higher spiral flow than the comparative example, demonstrating its superior processability for injection moulding. However it still has satisfactory rigidity (flexural modulus) and impact resistance (Izod). The composition of the invention also has reduced shrinkage, thereby showing that it has a good combination of all the properties required for a pipe fitting or other injection moulded article.