IE912398A1

IE912398A1 - Polypropylene molding composition

Info

Publication number: IE912398A1
Application number: IE239891A
Authority: IE
Original assignee: Hoechst Ag
Priority date: 1990-07-10
Filing date: 1991-07-09
Publication date: 1992-01-15
Also published as: DE4021899A1; EP0470380A2; PT98267A; EP0470380A3; ES2151475T3; EP0470380B1; JPH04226552A; PT98267B; DE59109198D1; JP3163116B2

Abstract

A polypropylene moulding composition which essentially comprises a syndiotactic propylene polymer and an ethylene/propylene copolymer rubber having a glass transition temperature of below -30 DEG C is distinguished by low hardness, rubber-elastic behaviour and high impact strength.

Description

HOECHST AKTIENGESELLSCHAFT, a Joint Stock Company organized and existing under the laws of the Federal Republic of Germany, of D-6230 Frankfurt am Main 80, Federal Republic of Germany HOECHST AKTIENGESELLSCHAFT HOE 90/F 209 Dr.DA/sch - laDescription Polypropylene molding composition The invention relates to a high-impact polypropylene 5 molding composition made from a syndiotactic propylene polymer or a syndiotactic propylene copolymer and an ethylene-propylene copolymer rubber.

Soft polypropylene molding compositions are known in principle. They are prepared by mixing melts of isotactic polypropylene (IPP) with a rubber, for example ethylenepropylene rubber (EPM) or ethylene-propylene-diene rubber (EPDM). However, low hardnesses are only achieved using uneconomically large amounts of rubber.

It is also known to mix isotactic polypropylene, atactic polypropylene (APP) and a rubber. However, the admixing of APP results in tacky products. The low melting point of the APP causes processing problems and poor thermal stability, and the normally low melt viscosity of the APP results in products which are inhomogeneous during melt mixing. Although the use of kneaders during mixing improves the homogeneity, the economic efficiency of the preparation of the molding composition drops at the same time. In addition, APP no longer functions as a plasticizer in the molding composition if the temperature drops below its glass transition temperature, but instead, on the contrary, results in embrittlement.

The object was to find a soft polypropylene molding composition which, on the one hand, has high impact strength and flexibility, even at very low temperatures, and, on the other hand, is economic to prepare.

The object has been achieved by using a syndiotactic propylene polymer in place of isotactic polypropylene and - 2 mixing the melt with a rubber.

The invention thus relates to a polypropylene molding composition essentially comprising from 20 to 99% by weight, based on the molding composition, of a syndiotac5 tic propylene polymer and from 1 to 80% by weight, based on the molding composition, of a rubber having a glass transition temperature of below -30°C.

The syndiotactic propylene polymer to be used for the preparation of the polypropylene molding composition according to the invention is a polymer in which each second tertiary carbon atom in some of the molecule chains has the same configuration.

The propylene polymer is either a propylene homopolymer having a syndiotacticity index of at least 75% or one or two propylene copolymers having a syndiotacticity index of at least 75%.

If the propylene polymer is only a single propylene copolymer, it comprises from 99.5 to 50% by weight, preferably from 99 to 70% by weight, of propylene units having a syndiotacticity index of at least 75%, and from 0.5 to 50% by weight, preferably from 1 to 30% by weight, of units of ethylene or an olefin having at least 4 carbon atoms, of the formula Ra-CH=CH-Rb in which Ra and Rb are identical or different and are hydrogen or alkyl having 1 to 10, preferably 1 to 6, carbon atoms, or R“ and Rb, together with the carbon atoms connecting them, form a ring having from 4 to 22 carbon atoms. Preferred comonomers are ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, norbornene and pentene.

If the propylene polymer comprises two propylene copolymers, the first is a copolymer (a) comprising from to 100% by weight, preferably from 98 to 100% by weight, of propylene units having a syndiotacticity index of at least 75%, and from 0 to 5% by weight, preferably - 3 from 0 to 2% by weight, of units of ethylene or an olefin as defined above, and the other is a copolymer (b) comprising from 20 to 90% by weight, preferably from 40 to 90% by weight, of propylene units having a syndiotac5 ticity index of at least 75%, and from 10 to 80% by weight, preferably from 10 to 60% by weight, of units of ethylene or an olefin as defined above. The proportion of the two copolymers (a) and (b) in the propylene polymer is from 20 to 99% by weight, preferably from 40 to 95% by weight, of copolymer (a) and from 1 to 80% by weight, preferably from 5 to 60% by weight, of copolymer (b), in each case based on the amount of propylene polymer.

The molding composition according to the invention contains from 20 to 99% by weight, preferably from 40 to 95% by weight, of the syndiotactic propylene polymer.

From 1 to 80% by weight, preferably from 5 to 60% by weight, of the molding composition according to the invention is a rubber having a glass transition temperature of below -30°C. Examples of suitable rubbers are styrene-butadiene rubbers, silicone rubbers, ethylene-propylene rubbers (EPM) or ethylene-propylene-diene rubbers (EPDM). EPM and EPDM rubbers may additionally contain up to 40% by weight of polyethylene. The diene component may be 1,4-hexadiene, norbornadiene or cyclo25 pentadiene in an amount of up to 10% by weight, based on the total amount of rubber. The amounts of ethylene and propylene are not limited so long as a glass transition temperature of the amorphous component of less than -30 eC is achieved. A typical commercially available EPM rubber comprises, for example, 10-60% by weight of propylene units and 90-40% by weight of ethylene units. 0-40% by weight of the ethylene units are in a pure polyethylene component, and the remainder form the copolymer component together with the propylene.

EPDM rubbers have the same composition, but the copolymer component contains, in addition to propylene and - 4 ethylene, 1-10% by weight of a diene of the abovementioned type. The melt viscosity of typical EPM and EPDM rubbers is between 3 and 300 g/10 min (MFI 230/5).

The Mooney viscosity (measured at 121 °C, ML) is typically 5 between 20 and 80. The yield stress at 60% elongation is typically 10-300 psi (pounds per square inch, 1 psi = 6894.8 kg/m. sec2 = 1 Pa).

Examples of typically usable rubbers are commercially available under the current trade names Vistalon, Exxelor (Exxon Chemicals), Dutral (Dutral S.A.), Nordel (DuPont) or Buna (Veba).

In addition to the syndiotactic propylene polymer and the rubber, the molding composition according to the invention may also contain the conventional additives, for example stabilizers, antioxidants, UV absorbers, light screens, metal deactivators, free-radical scavengers, fillers and reinforcing agents, plasticizers, lubricants, emulsifiers, pigments, optical whiteners, flameproofing agents, antistatics and blowing agents.

The molding composition according to the invention can be prepared by methods which are conventional in plastics processing for mixing polymers and additives.

If all the constituents of the molding composition are in powder form, one possibility is sintering in a high-speed mixer.

A further possibility is to use an extruder having mixing and kneading elements on the screw.

Finally, kneaders, as employed in the rubber industry, are also suitable mixing machines.

The mixing temperature depends on the make-up of the particular molding composition. - 5 The molding composition according to the invention has low hardness in combination with high impact strength, even at temperatures below 0°C. In general, this molding composition can be used for all applications where rubber-elastic behavior in combination with high impact strength is desired.

It is suitable, for example, as a substitute for soft PVC. In automobile manufacture, it can be employed, for example, for side strips, spoilers, seals, fender linings, tractor fenders, paneling parts or sound-insulation layers. In the construction sector, it is suitable for seals, damp-proof courses or flat-roof sheeting and for insulating cladding for pipes.

Foam extrusion gives elastic, high-insulation cladding and coatings.

The molding composition according to the invention is furthermore suitable for the production of heavy-duty sacks and heat-sealing films, and antileak sheeting for landfill sites.

The examples below are intended to illustrate the invention in greater detail.

SI = syndiotacticity index (determined by 13C-NMR spectroscopy). nsyn = mean syndiotactic chain length (determined by 13C-NMR) . nPE = mean polyethylene block length. npp = mean polypropylene block length.

VN = viscosity number, measured at 135 °C as a 0.1% strength solution in decahydronaphthalene in a capillary viscometer.

MFI 230/5 = melt flow index at 230°C, 5 kg load, in accordance with DIN 53 735. 1^/Mn = polydispersity.

BIH = ball indentation hardness (in accordance with - 6 DIN 53 456, 4 mm-thick plates, injection temperature of 240°C) an = notched impact strength in accordance with DIN 753-V-0,l, small standard specimen (50 x 6 x 4 mm).

MEB = modulus of elasticity in bending in accordance with DIN 53 457 (injection-molded test specimens, 80 x 10 x 4 mm).

The molding compositions were produced using a ZSK 28 10 twin-screw extruder (Werner & Pfleiderer).

Example 1 A molding composition was produced by extrusion, comprising 80% by weight of syndiotactic polypropylene, based on the total molding composition, and 20% by weight of a rubber comprising 37% by weight of propylene units and 63% by weight of ethylene units; 20% by weight of the rubber composition was polyethylene and 80% by weight was an ethylene-propylene copolymer (EMP) comprising 46% by weight of propylene units and 54% by weight of ethylene units. The MFI 230/5 was 11 g/10 min, and the viscosity number was 284 cm3/g.

The syndiotactic polypropylene used had an SI of 94.5%, an nsyn of 32 and an MFI 230/5 of 266 g/10 min, corresponding to a viscosity number of 97 cm3/g. The mechanical data determined were as follows: BIH = 45 N/mm2; MEB = 792 N/mm2; an = 5.8 mJ/mm2 (23°C), 1.9 mJ/mm2 (-20°C) . kg of the syndiotactic polypropylene powder were mixed with 2 kg of the rubber, and the mixture was stabilized against chemical degradation under extrusion conditions using 10 g of pentaerythrityl tetrakis[3-(3,5-di-t-butyl4-hydroxyphenyl)propionate]. The five heating zones of the extruder were set to 100°C (feed zone), 170°C, 200°C, 200°C and 190°C (die plate). - 7 The extruder screw was operated at 100 rpm; the material temperature of the mixer in the extruder was 210eC. The following data were measured on the molding composition prepared in this way: MFI 230/5 = 148 g/10 min; viscosity number = 123 cm3/g; BIH = 32 N/mm2; MEB = 694 N/mm2; an = 13.8 mJ/mm2 (23’C), 5.9 mJ/mm2 (-20°C).

Comparative Example A Example 1 was repeated using the same conditions, but the syndiotactic polypropylene was replaced by isotactic polypropylene having an MFI 230/5 of 169 g/10 min, corresponding to a viscosity number of 128 cm3/g. The molding composition obtained in this way had the following data: MFI 230/5 = 100 g/10 min; viscosity number = 150 cm3/g; BIH = 68 N/mm2; MEB = 1380 N/mm2; an = 6.8 mJ/mm2 (23°C), 3.5 mJ/mm2 (-20°C).

The result of the comparative example shows that replacement of syndiotactic polypropylene by isotactic polypropylene gives neither the desired low hardness nor the high impact strength.

Example 2 Example 1 was repeated, but the syndiotactic component used was a syndiotactic polypropylene having an SI of 93.8%, an nsyn of 25 and an MFI 230/5 of 153 cm3/g. The mechanical data determined on this polymer were as follows: BIH = 40 N/mm2; MEB = 604 N/mm2 and a„ = 17.5 mJ/mm2 (23°C), 2.8 mJ/mm2 (-20'C).

The five heating zones of the extruder were set to 110eC (feed zone), 190°C, 230°C, 230°C and 200°C (die plate).

The extruder screw was operated at 40 rpm. The material temperature of the mixture in the extruder was 250°C.

The following data were determined on the molding composition produced in this way: MFI 230/5 = 19 g/10 min; - 8 viscosity number = 147 cm3/g; BIH = 27 N/mm2; MEB = 555 N/mm2; a„ = 35.9 mJ/mm2 (23°C), 9.4 mJ/mm2 (0°C), 6.9 mJ/mm2 (-20°C).

Comparative Example B Example 2 was repeated under comparable conditions, but with the syndiotactic polypropylene replaced by isotactic polypropylene having the following data: MFI 230/5 = 13 g/10 min, corresponding to a viscosity number of 258 cm3/g. The molding composition obtained in this way had the following data: MFI 230/5 = 15 g/10 min; viscosity number = 250 cm3/g; BIH = 52 N/mm2; MEB = 1052 N/mm2; an = 16.3 mJ/mm2 (23°C), 7.7 mJ/mm2 (0°C), 5.3 mJ/mm2 (-20°C).

The result shows that the use of isotactic polypropylene in place of syndiotactic polypropylene gives neither the desired low hardness (BIH, MEB) nor the high impact strength (a,J .

Example 3 Example 2 was repeated, but the syndiotactic component used was a syndiotactic polypropylene having an SI of 94.8%, an nsyn of 29 and an MFI 230/5 of 0.7 cm3/g, corresponding to a viscosity number of 317 cm3/g. The mechanical data determined for this polymer were as follows: BIH = 36 N/mm2; MEB = 527 N/mm2 and an = 46.6 mJ/mm2 (23°C), 7.8 mJ/mm2 (-20°C).

The five heating zones of the extruder were set to 180°C (feed zone), 230°C, 280°C, 280°C and 275C (die plate). The extruder screw was operated at 35 rpm.

The material temperature of the mixture in the extruder was 300°C. The following data were measured on the molding composition produced in this way: MFI 230/5 = 1.3 g/10 min; viscosity number = 308 cm3/g; BIH N/mm2; MEB = 400 N/mm2; = 53.4 mJ/mm2, in some cases without fracture (23°C), 23.2 mJ/mm2 (0°C), 10.0 mJ/mm2 (-20°C). Examples 4, 5 and 6 Example 2 was repeated, but the amounts of rubber employed were 5% (Example 4), 10% (Example 5) and 40% 5 (Example 6), composition. in each case based on the entire molding The results: Example 4 Example 5 Example 6 MFI 230/5 10 [g/10 min] 21 20 17 Viscosity number [cm3/g] 150 151 145 BIH [N/mm2] 37 34 10 15 MEB [N/mm2] 590 578 465 (mJ/mm2) 23°C 20.0 31.1 no 20 fracture 0°C 5.9 7.0 35.9 - 20°C 3.0 3.5 12.1 Example 7 Example 2 was repeated, but the syndiotactic component 25 used was a syndiotactic ethylene-propylene copolymer having the following properties: Mean polypropylene block length (nPP) = 26, mean polyethylene block length (nPE) = about 1, M^Mn = 2.2, SI = 97.2%, viscosity number = 149 cm3/g, copolymerized ethyl30 ene content = 2.5% by weight.

In addition, only 10% of rubber was used in place of 20%, based on the entire polymer composition. The blend - 10 described here had the following data: MFI 230/5 = 26 g/10 min; viscosity number = 150 cm3/g; BIH = 17 N/mm2; an = 40.4 mJ/mm2 (23’C), 12.6 mJ/mm2 (O’C), 7.3 mJ/mm2 (-20°C).

Example 8 Example 7 was repeated, but the syndiotactic component used was a syndiotactic block copolymer polymerized in two steps (1st step: syndiotactic polypropylene, 2nd step: ethylene-propylene copolymer).

The syndiotacticity index of the polypropylene component (77.5% by weight, based on the total amount of the block copolymer) was 96.4%; the viscosity number was 275 cm3/g. The ethylene-propylene copolymer, making up 22.5% by weight of the entire block copolymer, comprised 22.1% by weight of ethylene units and the remaining 77.9% by weight of syndiotactically linked propylene units. The viscosity number was 304 cm3/g, and 40.5% of the ethylene was in isolated form (nPE = 1), 10.5% had an nPE of 2 and 49.0% was incorporated in blocks (nPE > 3).

The following data were measured on the molding composition prepared in this way: MFI 230/5 = 8 g/10 min; viscosity number = 260 cm3/g; BIH = 13 N/mm2; an = no fracture at 23’C, 24.7 mJ/mm2 (O’C), 10.0 mJ/mm2 (-20°C).

Comparative Example C Example 3 was repeated under comparable conditions, but the syndiotactic polypropylene used was replaced by isotactic polypropylene having a melt flow index of 1.1 g/10 min, corresponding to a viscosity number of 451 cm3/g. The molding composition obtained in this way had the following data: MFI 230/5 = 2.3 g/10 min; viscosity number = 360 cm3/g; BIH = 47 N/mm2; MEB = 1151 N/mm2; = 32.7 mJ/mm2 (23’C), 9.8 mJ/mm2 (O’C), 4.3 mJ/mm2 (-20°C). - 11 The result of the comparative example shows that the use of isotactic polypropylene instead of syndiotactic polypropylene gives neither the desired low hardness (BIH, MEB) nor the high impact strength (a„) .

Claims

1. Patent Claims

1. A polypropylene molding composition, essentially comprising from 20 to 99% by weight, based on the molding composition, of a syndiotactic propylene 5 polymer, and from 1 to 80% by weight, based on the molding composition, of a rubber having a glass transition temperature of below -30°C.

2. A molding composition as claimed in claim 1, wherein the syndiotactic propylene polymer is a poly10 propylene having a syndiotacticity index of at least 75%.

3. A molding composition as claimed in claim 1, wherein the syndiotactic propylene polymer is a copolymer comprising from 99.5 to 50% by weight of propylene 15 units having a syndiotacticity index of at least 75%, and from 0.5 to 50% by weight of units of ethylene or an olefin having at least 4 carbon atoms, of the formula R a -CH=CH-R b in which R a and R b are identical or different and are hydrogen or alkyl 20 having 1 to 10 carbon atoms, or R a and R b , together with the carbon atoms connecting them, form a ring having from 4 to 22 carbon atoms.

4. A molding composition as claimed in claim 1, wherein the syndiotactic propylene polymer is a mixture of 25 from 20 to 99% by weight of a copolymer (a) and from 1 to 80% by weight of a copolymer (b), where copolymer (a) comprises from 95 to 100% by weight of propylene units having a syndiotacticity index of at least 75%, and from 0 to 5% by weight of units of 30 ethylene or an olefin having at least 4 carbon atoms, of the formula R a -CH=CH-R b in which R a and R b are as defined above, and copolymer (b) comprises from 20 to 90% by weight of propylene units having a syndiotacticity index of at least 75%, and from 35 10 to 80% by weight of units of ethylene or an - 13 olefin having at least 4 carbon atoms, of the formula R a -CH=CH-R b in which R“ and R b are as defined above.

5. A molding composition as claimed in claim 1, which additionally contains stabilizers, antioxidants, UV absorbers, light screens, metal deactivators, freeradical scavengers, fillers and reinforcing agents, plasticizers, lubricants, emulsifiers, pigments, optical whiteners, flameproofing agents, antistatics or blowing agents. The use of a polypropylene molding composition as claimed in claim 1 for the production of moldings of low hardness, rubber-elastic behavior and high impact strength.

6. - 14

7. A polypropylene molding composition as claimed in claim 1 substantially as hereinbefore described and exemplified.