PROCESS FOR PREPARING AN IMPACT-RESISTANT ETHYLENE-PROPYLENE BLOCK COPOLYMER

Abstract: Present invention pertains to a process for preparing an impact-resistant ethylene-propylene block copolymer, characterized in that in a first polymerization step a propyl­ ene prepolymer is prepared consisting for at least 98% (wt) of propylene groups having a melt index measured accord­ ing to ASTM-D-1238 at 503K and 21.6 N of 0.1-100 dg/min, in that in the presence of the propylene prepolymer produced in the first polymerization step ethylene and propylene are polymerized in a second polymerization step in such a manner that a starting ethylene-propylene block copolymer is formed at least consisting of an at least almost completely homopolymeric propylene part and a copoly­ meric ethylene-propylene part, the weight ratio between the at least almost completely homopolymeric propylene part and the copolymeric ethylene-propylene part being be­ tween 3:2 and 9:1, containing a total amount of 10-25% (wt) ethylene groups and having a melt index measured accord­ ing to ASTM-D-1238 at 503K and 21.6 N which is ¹/100 to ¹/2 part of the melt index measured according to ASTM-D-1238 at 503K and 21.6 N of the propylene prepolymer and in that this starting ethylene-propylene block copolymer is subse­ quently subjected to a kneading treatment consisting of one or more kneading operations, which kneading treatment takes place in the presence of free radicals at a temperature of a least 450K.

Description: The invention relates to a process for preparing an impact-resistant ethylene-propylene block copolymer (C), characterized in that in a first polymerization step a propylene prepolymer (A) is prepared consisting of at least 98 % (wt) of propylene groups and having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N of 0.1-100 dg/min, preferably 0.5-50 dg/min, in that in the presence of the propylene prepolymer (A) produced in the first polymerization step ethylene and propylene are polymerized in a second polymerization step in such a manner that a ethylene-propylene block copolymer (B) is formed comprising a homopolymeric propylene part, consisting for at least 98% (wt) of propylene groups, and a copolymeric ethylene-propylene part, the weight ratio between the homopolymeric propylene part and the copolymeric ethylene-propylene part being from 3 : 2 to 9 : 1, containing a total amount of 10-25 % (wt) ethylene groups and having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N which is 1/100 to 1/2, preferably 1/50 to 1/4 part of the melt index measured according to ASTM-D-1238 at 503K and 21.6N of the propylene prepolymer (A), and in that ethylene-propylene block copolymer (B) is subsequently subjected to a kneading treatment consisting of one or more kneading operations, which kneading takes place in the presence of free radicals as a temperature of at least 450 K, preferably at 470-570 K. Similar copolymers as obtained by this process are known from EP-A-94818 and EP-A-77532. These prior art copolymers do not meet the impact properties in combination with the stiffness and good processability of the block copolymers, obtained by the process of the present invention. A treatment, similar to the kneading treatment mentioned above is known from (CA Vol 79 (1973) p. 55 no. 54505 t). However, this known treatment results in a deterioration of impact properties whereas in the special combination of polymerisation steps and treatment according to the invention impact and stiffness properties are improved. The ethylene content is measured by means of IR analysis of the polymer in melted condition. The Izod value is measured on an injection-moulded test sheet and the E-modulus on a compression-moulded test sheet with a thickness of 1.6 mm. The kneading treatment can be effected in various ways. It implies the exertion of mechanical forces on the starting ethylene-propylene block copolymer e.g. by means of a kneading and/or transport screw of e.g. extruding or injection-moulding equipment or by means of a rolling devide. Preference is given to single-screw or multi-screw kneading, which kneading operation can be repeated more than once, and in which one or more of the kneading operations can be followed by extrusion. The duration of the kneading treatment is at least 1/4 minute, particularly at least 1 minute. If the kneading treatment consists of more than one kneading operation, there may be a longer period of time between two kneading operations. Thus in a first kneading operation a pre-product (for instance a granulate) can be prepared, subsequently be transported to another place and finally be processed in a second kneading operation according to the invention to form an end product according to the invention. The presence of free radicals in the process according to the invention can be realized in any suitable manner. A suitable manner consists in the addition, before and/or during the said kneading treatment of a total amount of 10-20000 parts by weight of one or more peroxides per 10 6 parts by weight starting ethylene-propylene block copolymer to the substance or substances subjected or to be subjected to the kneading treatment. Preference is given to using peroxides having at the average temperature of a kneading operation, a half-time value less than 1/5 of the duration of the relative kneading treatment. Suitable peroxides are di-(t-butylperoxyisopropyl)-benzene, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, t-butylperoxyisopropylcarbonate, t-butylperoxybenzoate, di-cumylperoxide, di-t-butylperoxide, 2,2-di-t-butylperoxybutane, di-benzoylperoxide, 2,5-di-methylhexane-2,5-di-t-butylperoxide and 2,5-di-methylhexyn-2,5-di-t-butylperoxide. Another suitable manner for realizing the presence of free radicals is the high-energy irradiation, for instance electron radiation or gamma radiation, of the starting ethylene-propylene block copolymer subjected or to be subjected to the kneading treatment, preferably in the almost complete absence of stabilizers, at a dose of 0.1-4 Mrad. All kinds of combinations of the use of peroxides and of the said irradiation are suitable as well. The kneading treatment according to the invention is preferably effected in whole or in part in the presence of at least 50 parts by weight of one or more zinc and/or cadmium compounds, calculated as zinc and/or cadmium atoms, per 10 6 parts by weight starting ethylene-propylene block copolymer. Other additives, too, may be present or be added during this kneading treatment, for instance heat stabilizers, UV-stabilizers and nucleation agents. Very suitable fillers for ethylene-propylene block copolymers produced by a process according to the invention are chalk, with by preference an average particle size of below 2 µm, and talcum, with by preference an average particle size of below 5 µm. Suitable are quantities of filler of below 25 % (wt). A higher weight percentage of filler quickly leads to very bad mechanical properties of the copolymer-filler mixture compared with the pure copolymer. The impact-resistant ethylene-propylene block copolymers produced by a process according to the invention are very suitable for use in car bumpers, front ends, spoilers, liners, motor car underside coats and wheel archlining for motor cars.

Claims: Process for preparing an impact-resistant ethylene-propylene block copolymer (C), characterized in that in a first polymerization step a propylene prepolymer (A) is prepared consisting of at least 98 % (wt) of propylene groups having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N of 0.1-100 dg/min, in that in the presence of the propylene prepolymer (A) produced in the first polymerization step ethylene and propylene are polymerized in a second polymerization step in such a manner that an ethylene-propylene block copolymer (B) is formed comprising a homopolymeric propylene part, consisting of at least 98% (wt) of propylene groups, and a copolymeric ethylene-propylene part, the weight ratio between the homopolymeric propylene part and the copolymeric ethylene-propylene part being from 3 : 2 to 9 : 1, containing a total amount of 10-25 % (wt) ethylene groups and having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N which is 1/100 to 1/2 part of the melt index measured according to ASTM-D-1238 at 503K and 21.6 N of the propylene pre-polymer (A), and in that ethylene-propylene block copolymer (B) is subsequently subjected to a kneading treatment consisting of one or more kneading operations, which kneading treatment takes place in the presence of free radicals at a temperature of at least 450K. Process according to claim 1, characterized in that in the first polymerization step a propylene prepolymer (A) is produced having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N of 0.5-50 dg/min. Process according to claim 1 or 2, characterized in that in the second polymerization step an ethylene-propylene block copolymer (B) is produced having a melt index measured according to ASTM-D-1238 at 503K and 21.6 N which is 1/50 to 1/4 part of the melt index measured according to ASTM-D-1238 at 503K and 21.6N of the propylene prepolymer (A). Process according to any one of claims 1-3, characterized in that the kneading treatment is effected at 470-570K. Process according to any one of claims 1-4, characterized in that the kneading treatment is effected wholly or partly in the presence of at least 50 parts by weight of one or more zinc and/or cadmium compounds, calculated as zinc and/or cadmium atoms, per 10 6 parts by weight ethylene-propylene block copolymer (B). Process according to any one of claims 1-5, characterized in that before and/or during the said kneading treatment 10-20000 parts by weight of one or more peroxides per 10 6 parts by weight starting ethylene-propylene block copolymer (B) is added to the substance or substances subjected or to be subjected to the kneading treatment. Process according to any one of claims 1-6, characterized in that the ethylene-propylene block copolymer (B) subjected or to be subjected to the kneading treatment is subjected to high-energy irradiation. Process according to claim 7, characterized in that in the irradiation an irradiation dose of 0.1-4 Mrad is applied. Impact-resistant ethylene-propylene block copolymer (C) obtainable by a process according to any one of claims 1-8. Article wholly or partly made from an impact-resistant ethylene-propylene block copolymer (C) according to claim 9.

Inventors: KISTERS, MATHIJS JOSEPH M.G., REPIN, JOHANNES FREDERICUS
Applicants: STAMICARBON B.V.
Application year: 1984
Main classification: C08F297
IPC codes: C08L53