MODIFIED POLYETHYLENE, PROCESS FOR PREPARING MODIFIED POLYETHYLENE, AND PRODUCTS PRODUCED FROM MODIFIED POLYETHYLENE

Abstract: A polymer comprising ethylene, one or more higher alkenes-1 with 3-18 carbon atoms in an amount of 0 to 15 mole.-% calculated on the ethylene and such a small amount of one or more poly-unsaturated compounds with at least 7 carbon atoms and at least two non-conjugated double bonds polymerizable under the influence of transition metal catalysts, that the activation energy of the viscous flow of the polymer is not significantly influenced by the presence of the poly-­ unsaturated compound(s).

Description: The invention relates to a polymer substantially formed from ethylene, one or more higher alkenes-1 with 3-18 carbon atoms in an amount of 0 to 15 mole.-% calculated on the ethylene and one or more linear α,ω-dienes with at least 7 carbon atoms and at least two non-­ conjugated double bonds both non- conjugated double bonds being poly­ merizable under the influence of transition metal catalysts. Ter­ polymers consisting of ethylene, a higher alkene and a diene are described frequently in literature. They usually concern rubber-like polymers, i.e. polymers having a crystallinity lower than 10%; in the present invention there is no question hereof. Non-rubber-like polymers of ethylene, optionally a higher alkene-1 and diene are known, for instance, from DE-A 30 21 273. The double bonds in the dienes used can, however, not both of them be polymerized under the influence of transition metal catalysts. A polymer of ethylene, propylene and ethylidenenorbornene is described in EP-A 0 120 503. The diene, whose double bonds cannot both of them be polymerized under the influence of transition metal cata­ lysts either, is present in an amount of 2.3 mole.-% calculated on the total polymer. Polymers of ethylene, optionally a higher alkene-1 and a diene whose double bonds are not conjugated and can be polymerized under the influence of transition metal catalysts are described in the German patent application DE-A 22 18 160. The diene is added here in order to influence the processability of the polymer, notably to increase the activation energy of the viscous flow (calculated from the melt flow index ratio of the melt at 150, resp. 190¤C). Therefore, the amount of diene used in the polymer is between 0.33 and 2.7 wt.-% calculated on the total polymer. Such amounts of diene increase the activation energy of the viscous flow of the polymer by crosslinking or branching. As a result, however, the mechanical properties deteriorate. Copolymers of ethylene and one or more alkenes-1 with 3-18 carbon atoms in an amount of at most 15 mole.-% calculated on the ethylene have been known for some time under the name of LLDPE (linear low-density polyethylene). Such copolymers are generally prepared according to a so-called low-pressure process in the presence of tran­ sition metal catalysts and have a density of 940 kg/ M³ at most. Like LDPE, which can be prepared according to a high-pressure process known for long, LLDPE is usually processed to form film. In many respects the mechanical properties of LLDPE film are better than those of LDPE. In addition to good mechanical properties, films must also have good optical properties, such as a high gloss and a low opacity. Blown films of both LLDPE and HDPE (polyethylene having a density higher than 940 kg/ M³ ) leave much to be desired in this respect. The object of the invention is a HDPE and/or LLDPE producing better optical properties when processed into blown film than the HDPE and LLDPE known so far without influencing the favourable mechanical properties. This object is achieved by modifying a polymer substantially formed from ethylene, one or more higher alkenes-1 with 3-18 carbon atoms in an amount of 0-15 mole.-% calculated on the ethylene with one or more poly-unsaturated compounds with at least 7 carbon atoms and at least two non-conjugated double bonds, both non-conjugated double bonds being polymerizable under the influence of transition metal catalysts that the amount of poly-unsaturated compound(s) is not higher than 0.03 mole.-% calculated on the total polymer. This small amount to some degree depends on the poly­ unsaturated compound(s) applied. If the polyunsaturated compound(s) has/have a lower molecular weight, the mole percentage required to reach the desired optical effect is generally higher than with higher molecular weights. If the molecular weights are higher, the very small amount of 0.001 mole % may suffice for a distinct optical effect without the mechanical properties of the blown film, for instance puncture resistance and tear resistance, being affected. Generally the presence of at least 0.001 mole.-% poly-unsatured compound(s) is to be recommended, more specifically an amount of between 0.005 and 0.03 mole.-%. Surprisingly the HDPE and/or LLDPE thus modified has better optical properties when processed to form blown film than the HDPE and LLDPE known so far and processed into blown film under the same conditions, while the activation energy of the viscous flow of the polymer, according to the now prevailing measuring methods, is not significantly affected. This is all the more surprising, because it concerns such small amounts of poly-unsaturated compound(s) that, besides the acti­ vation energy, other rheological polymer properties, for instance the melt flow index ratio and the viscosity ratio, are not appreciably influenced by the presence of the unsaturated compound(s) either. Herein, also, lies the advantage of the invention. The properties of polymers can be influenced by applying different catalyst systems. Depending on the catalyst, different combinations of properties (for instance flow properties, sealing properties, mechanical properties), and so different grades of material can be produced. By the addition of a small amount of poly-unsaturated compound(s) according to the invention the optical properties can be improved without the other properties being influenced. Hence the best catalyst can always be used, independent of the optical properties. Polymers according to the invention generally have an activation energy < 9 kcal/mole, mostly even ≦ 8 k cal/mole. The linear poly-unsaturated compound(s) according to the invention must at least contain two double bonds polymerizable under the influence of transition metal catalysts. They are chosen from the group consisting of 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,4,9-decatriene and 1,5,9-decatriene. It is recommendable for the unsaturated compounds to be linear α,ω-dienes. 1,9-decadiene in particular is a compound producing good results. The presence of a small amount of poly-unsaturated compound(s) having at least 7 C-atoms and at least two non-conjugated double bonds polymerizable under the influence of transition metal catalysts improves the optical properties of blown films produced from all kinds of grades of HDPE and LLDPE, such as LLDPE in which butene is the comonomer and also hexene LLDPE or octene LLDPE. The most favourable combination of properties is obtained with LLDPE modified according to the invention, in which the comonomer has at least 4 and at most 10 carbon atoms. The invention also relates to a process for preparing modified polyethylene according to the invention in wich process ethylene, one or more alkenes-1 with 3-18 carbon atoms in an amount of 0 to 50 mole.-% calculated on the ethylene and one or more of said linear poly-unsaturated compound(s) having at least 7 C-atoms and at least two non-conjugated double bonds both non-conjugated double bonds being polymerizable under the influence of transition metal catalyst are reacted with each other in an inert dispersant in the presence of a transition metal catalyst whereby the amount of poly-unsaturated compound(s) in the reaction vessel is not higher than 0.3 mole.-% calculated ont the total amount of monomers. This amount depends on the reactivity of the compound in question, notably on the degree to which it allows itself to be incor­ porated into the polymer under the influence of the catalyst in question. The person skilled in the art and acquainted with the degree of reactivity of various monomers in respect of different catalysts will be able to determine with ease what amount of poly-unsaturated compound(s) is required to reach an optimum optical effect. The amount of poly-unsaturated compound(s) present in the reaction vessel will not be larger than 0.3 mole.-% calculated ont the total number of mononomers, preferably not larger than 0.09 mole % and more specifically not larger than 0.06 mole.-%. For the preparation of a polymer producing the desired effects to a high degree it is to be recommended that the polymerization be carried out in the presence of a titanium- and/or vanadium-containing catalyst system with (a) linear, α,ω-unsaturated compound(s). The polymerization in the presence of 1,9-decadiene produces good results. The polymerization can be effected in a manner known per se in the presence of a transition metal catalyst, preferably in a so­ called suspension system or solution system in which the inert disper­ sant is present in a liquid form. Particularly suitable is a system in which the polymerization temperature is so high that it can be referred to as solution polymerization, viz higher than 135¤C. The usual additives, such as stabilizers, lubricants, and antiblocking agents can be added in the usual way. The invention also relates to articles, particularly to films, produced from modified LLDPE or HDPE. The invention will now be elucidated by means of examples without, however, being limited thereto. Polymerization To a 2-litre continuous polymerization reactor 12.3 litres petrol (boiling point fraction 66-74¤C) is fed, Ethylene (1.98 kg/hr) dissolved in petrol, octene (1.1 kg/hr) and a third compound according to the table are fed to the reactor, which is operated at a temperature of 185¤C and a pressure of 50 bar. Solutions of the catalyst ingredients are prepared in petrol: SEAC: 50 mmoles/l, EBM: 10 mmoles/l, TBT: 4 mmoles/l and IpCl: 10 mmoles/l. The catalyst flow thus mixed is then fed to the reactor. The residence time in the reactor is about 5 minutes. SEAC : sesquiethylaluminiumchloride EBM : ethylbutylmagnesium TBT : tetrabutoxytitanium IpCl : isopropylchloride. Film preparation Blown film having a thickness of 50 µm is produced by means of a Collin extruder with three-zone screw, screw diameter 20 mm, and a length : diameter ratio of 20 with a yield of 1,2 kg/hr. The slit diameter is 20 mm, the slit width 2 mm. The temperature of the melt is 190¤C, the blow-up ratio is 3, the frost line height is 8 cm. Measuring methods - The activation energy of the viscous flow of the polymer was defined as in DE-A 2 218 160: where MFI 190 means the melt flow index measured according to ASTM D 1238 at 190/2.16 and MFI 150 means the melt flow index measured according to ASTM D 1238 at 150/2.16. - The density (d) according to ASTM D 1505. - The melt flow index (MFI) according to ASTM D 1238, cond. E. - The melt flow index at high load (HLMFI) according to ASTM D 1238, cond. F. - The gloss (45¤) according to ASTM D 2457. - The opacity according to ASTM D 1003. - The intrinsic viscosity ([n] dec. 135 ) has been determined in decalin at 135¤C - The viscosity ratio (VR) is the ratio of the intrinsic viscosities of polymers with the same MFI prepared without, respectively with one or more poly-unsaturated compounds.

Claims: 1. Polymer substantially formed from ethylene, one or more higher alkenes-1 with 3-18 carbon atoms in an amount of 0 to 15 mole.-% calculated on the ethylene and one or more linear poly-unsaturated compound(s) with at least 7 carbon atoms and at least two non-conjugated double bonds both non-conjugated double bonds being polymerizable under the influence of transition metal catalysts, which polymer is non rubber-like and has a crystallinity not lower than 10%, characterized in that the linear poly-unsaturated compounds are chosen from the group consisting of 1,6-heptadiene 1,7-octadiene 1,8 nonadiene, 1,9-decadiene, 1,4,9-decatriene, and 1,5,9-decatriene and in that the amount of poly-unsaturated compound(s) is not higher than 0.03 mole.-% calculated on the total polymer. 2. Polymer according to claim 1, characterized in that the higher alkenes-1 contain 4-10 carbon atoms. 3. Polymer according to claims 1 or 2, characterized in that the amount of poly-unsaturated compounds is at least 0.001 mole.-% of the total polymer. 4. Polymer according to claim 3, characterized in that the amount of poly-unsaturated compounds is at least 0.005 mole.-% of the total polymer. 5. Process for preparing a polymer according to any one of claims 1-4, in which process ethylene, one or more alkenes-1 with 3-18 carbon atoms in an amount of 0 to 50 moles % calculated on the ethylene and one or more of said linear poly-unsaturated compound(s) having at least 7 carbon atoms and at least two non-conjugated double bonds both non-conjugated double bonds being polymerizable under the influence of transition metal catalysts are reacted with each other in an inert dispersant, which polymer is non rubber-like and has a cristallinity not lower than 10%, the process being characterized in that the amount of poly-unsaturated compound(s) in the reaction vessel is not higher than 0.3 mole.-% calculated on the total amount of monomers. 6. Process according to claim 5, characterized in that the reaction takes place in the presence of a titanium- and/or vanadium-containing catalyst system and at least one linear α,ω-unsaturated compound. 7.Object prepared form a polymer according to any one of claims 1-4. 8. Film produced form a polymer according to any one of claims 1-4. 9. Bag produced form a film according to claim 8.

Inventors: COOSEMANS, LUC MARIA CONSTANT, EVENS, GEORGES GERARD, TIJSSEN, JOHANNES
Applicants: STAMICARBON B.V.
Application year: 1986
Main classification: C08F210
IPC codes: C08F210, C08F2, C08F10