Title of Invention

"POLYPROPYLENE COMPOSITIONS"

Abstract

The present invention relates to polypropylene compositions with improved processability and to a method for the manufacture of said compositions. Said compositions are particularly suitable for extrusion coating processes. The polypropylene composition comprises from 50 to 90 wt% of polypropylene selected from propylene homopolymer, random copolymer and block copolymer, from 5 to 25 wt% of high-pressure low-density polyethylene and from 5 to 40 wt% of unimodal and/or bimodal and/or multimodal high-density polyethylene.

Full Text

Field of invention The present invention relates to polypropylene compositions with improved processability. Said compositions are especially suitable for extrusion coating processes, particularly when high line speeds are used. More particularly, the invention relates to blends of polypropylene (PP) comprising low-density polyethylene (LDPE) and high-density polyethylene (HDPE). State of the Art Extrusion coating is a process wherein an extruder forces melted thermoplastic polymer through a horizontal slot die onto a moving web of a substrate material, which may comprise paper, board, film or aluminium foil. From the extruder the polymer melt, generally at a temperature from 270 to 330°C, is lead via an adapter and a pipe to a die where a thin molten film is formed. Typically the size of die lip opening is from 0.5 to 1.0 mm for extrusion coating dies and the desired coating thickness may be less than 10 ^m. Line speeds in extrusion coating processes may generally vary in the range from 300 to 700 m/min. Typically the laminator runs at a speed of at least 30 times faster than the speed that the plastic is travelling in the die lip or air gap. The plastic is then drawn down to a desired thickness. As the draw down takes place, a curtain of plastic exciting the die often necks-in i.e. it is pulled narrower in width. The draw down speed is the maximum speed, which can be reached before the molten polymer film breaks. Due to internal stress in polymers, the effective coating width is always narrower than the actual die slot width. This difference is called neck-in (= width of the die slot minus width of the coating) I | and it is measured in mm. The neck-in phenomenon may cause bunch-up at the edges resulting in edge heads, which prohibits the machine from winding a good roll of the coating product and the roll will wind along the thick edge and be lose and uncontrolled in the centre, and also draw resonance may appear. Draw resonance describes the thickness variation of the polymer web in the machine direction, as well as in the transverse direction caused by inhomogeneous instable drawing of the melt. Low-density polyethylene (LDPE) is mainly used in extrusion coating because of the ease in processing, although stiffness, barrier properties and temperature resistance of LDPE are often not satisfactory. Some high-density polyethylene (HOPE) is also used. Polypropylene, also known as propylene polymer, is a well-known commercial polymer, which is used for a variety of products, such as packaging films and moulded shapes. It is produced for example by polymerisation of propylene over transitional metal coordination catalysts. Commercial propylene polymers exhibit several desirable properties, such as good heat tolerance and transparency, which make polypropylene polymers interesting in many application fields. Polypropylene is very difficult or almost impossible to run in an extrusion coating process because of the neck-in phenomenon and draw resonance. Further, the adhesion of polypropylene on substrates is not satisfactory, typically pinholes appear in the product and line speeds are very low. Attempts have been made to manufacture blends of polypropylene with low-density polyethylene for extrusion coating applications. A blend of LDPE with a melting point of 110°C and polypropylene with a melting point of 160°C has been proposed but the processing of the blend was unsatisfactory. When a blend of polypropylene and LDPE is used in an extrusion process, the plastic leaving the die lip as a curtain of a height of approximately from 20 to 30 cm typically becomes too stiff, and it cannot be stretched/pulled sufficiently. As a result, only low line speeds can be used, additionally the neck-in problem appears and an uneven coating is obtained. Further, the product is uneconomic to produce. Also blends of HMS (high melt strength) Daploy modified polypropylene have been proposed but the manufacturing process of HMS is complicated and very expensive. US 4,508,872 discloses compositions with unproved low temperature impact resistance for injection moulded or extruded articles, such as automobile trim parts, battery containers, tote boxes, crates, bottles etc. Said compositions comprise impact-improved, sequentially polymerized propylene-ethylene copolymers, LLDPE and HDPE. Said polymers are all manufactured using Ziegler-Natta type coordination catalysts, which yield narrow molecular weight distribution in the obtained polymers. The impact-modified propylene copolymer is preferably peroxide-contacted (visbroken) and the visbroken propylene copolymer is melt blended with HDPE and LLDPE. Articles manufactured from said blends possess good impact resistance even at lower temperatures. US 5,773,123 discloses an air infiltration barrier laminate, which comprises a perforated laminate made from a woven polyolefin fabric, a resin and a polyolefm film. The resin is extrusion coated onto the woven polyolefin fabric and the resin may be low-density polyethylene, polypropylene and the like. The resin is discarded from the die to form a falling sheet of molten resin. The resin is extruded at such rate so as to form a layer of molten resin, said layer having a thickness from about 0.1 to 400 mil. US 5, 457,016 relates to photographic support,material comprising a carrier material coated with a synthetic resin on the front and backsides. Curling of the photographic support material is avoided and flatness and rigidity is assured by coating the front side of the carrier by a polyolefm adapted to receive the light sensitive layer and the back side by a blend of LDPE or LLDPE, 2 -75 wt % of i i polypropylene homopolyrrier or copolymer, preferably with narrow molecular weight distribution and 0 - 20 wt % of at least one other polyolefin. Preferably the carrier is subjected to a surface activation treatment in order to improve the adhesion of the layers. The coating was performed using low line speeds of 150 m/min in the extruder. Based on the above it can be seen that there exists a need for a polypropylene composition, which can be used in extrusion coating at high line speeds and which yields a homogenous and even coating of high quality and without any excess neck-in or draw resonance problems. Object of invention An object of the invention is to provide polypropylene compositions, which are particularly suitable for extrusion coating processes. A further object of the invention is a method for the manufacture of a polypropylene composition for extrusion coating processes. A still further object of the invention is the use of the polypropylene composition in extrusion coating processes. Characteristic features of the polypropylene composition, of the method for the manufacture of a polypropylene composition for extrusion coating processes and of the use of the polypropylene composition are provided in the claims. We Claim: 1. A polypropylene composition, the said composition comprising from 50 to 90 wt% of polypropylene, from 5 to 25 wt% of high-pressure low-density polyethylene having a density of less than 940 kg/m3 and from 5 to 40 wt% of high-density polyethylene having a density of more than 940 kg/m3, wherein the high-density polyethylene is bimodal and/or multimodal. 2. The polypropylene composition as claimed in claim 1, wherein the polypropylene is selected from propylene homopolymer, random copolymer and blockcopolymer. 3. The polypropylene composition as claimed in claim 1 or claim 2, wherein the polypropylene has a melt flow rate from 10 to 60 g/10 min (230°C, 2.16 kg), the low-density polyethylene has a melt flow rate from 3 to 18 g/10 min (190°C, 2.16 kg) and a density from 915 to 925 kg/m3, and the high- density polyethylene has a melt flow rate from 5tol5g/10n (190°C, 2.16 kg) and a density of 941 to 968 kg/m3. 4. The polypropylene composition as claimed in any one of claims 1-3, wherein it comprises from 60 to 80 wt% of polypropylene, from 10 to 20 wt% of low-density polyethylene and from 5 to 25 wt% of high-density polyethylene. 5. The polypropylene composition as claimed in any one of claims 1-4, wherein the polypropylene has a melt flow rate from 20 to 40 g/10 min (230°C, 2.16 kg), the low-density polyethylene has a melt flow rate from 4.5 to 8.5 g/10 min (190°C, 2.16 kg) and a density from 918 to 923 kg/m3 and the high-density polyethylene has a melt flow rate from 7 to 12 g / 10 min (190°C, 2.16 kg) and a density from 955 to 962 kg/m3. 6. A method for the manufacture of a polypropylene composition, the said method comprising blending from 50 to 90 wt% of polypropylene, from 5 to 25 wt% of high-pressure low-density polyethylene having a density of less than 940 kg/m3 and from 5 to 40 wt% of high-density polyethylene having a density of more than 940 kg/m , wherein the high-density polyethylene is bimodal and/or multimodal; the said ingredients being blended by: dry blending the polymer pellets, and charging the obtained blend to an extruder feeder, or by melt blending the polymer pellets in an extruder, whereby the pellets containing all the polymer components are fed to the extruder, or two of the first components are compounded together to form a master-batch and then the third component is added to the final blend as a separate operation. 7. The method as claimed in claim 6 for the manufacture of a polypropylene composition, wherein the polypropylene is selected from propylene homopolymer, random copolymer and blockcopolymer. 8. The method as claimed in claim 6 or 7 for the manufacture of a polypropylene composition, wherein the polypropylene has a melt flow rate from 10 to 60 g/10 min (230°C, 2.16kg), the low-density polyethylene has a melt flow rate from 3 to 18 g/10 min (190°C, 2.16kg) and a density from 915 to 925 kg/m3, and the high-density polyethylene has a melt flow rate from 5 to 15 g /10 min (190°C, 2.16kg) and a density from 941 to 968 kg/m3. 9. The method as claimed in claims 6-8 for the manufacture of a polypropylene composition, wherein from 60 to 80 wt% of polypropylene, from 10 to 20 wt% of low-density polyethylene and from 5 to 25 wt% of high-density polyethylene are used. 10. The method as claimed in any one of claims 6-9 for the manufacture of a polypropylene composition, wherein the polypropylene has a melt flow rate from 20 to 40 g/10 min (230 degree C, 2.16kg), the low-density polyethylene has a melt flow rate from 4.5 to 8.5 g/10 min (190°C, 2.16kg) and a density from 918 to 923 kg/m3, and the high-density polyethylene has a melt flow rate from 7 to 12 g/10 min (190°C, 2.16kg) and a density from 955 to 962 kg/m3. 11. Polypropylene composition and a method for the manufacture thereof, substantially as hereinbefore described with reference to the foregoing examples.

Documents:

3653-DELNP-2005-Abstract-(22-02-2008).pdf

3653-delnp-2005-abstract-22-02-2008.pdf

3653-delnp-2005-abstract.pdf

3653-DELNP-2005-Claims-(22-02-2008).pdf

3653-delnp-2005-claims-22-02-2008.pdf

3653-delnp-2005-claims.pdf

3653-DELNP-2005-Correspondence-Others-(22-02-2008).pdf

3653-delnp-2005-correspondence-others-22-02-2008.pdf

3653-delnp-2005-description (complete)-17-03-2008.pdf

3653-delnp-2005-description (complete)-22-02-2008.pdf

3653-delnp-2005-description (complete).pdf

3653-DELNP-2005-Form-1-(22-02-2008).pdf

3653-delnp-2005-form-1.pdf

3653-DELNP-2005-Form-2-(22-02-2008).pdf

3653-delnp-2005-form-2-22-02-2008.pdf

3653-delnp-2005-form-2.pdf

3653-delnp-2005-form-26.pdf

3653-DELNP-2005-Form-3-(22-02-2008).pdf

3653-delnp-2005-form-3.pdf

3653-delnp-2005-form-5.pdf

3653-delnp-2005-others document-22-02-2008.pdf

3653-DELNP-2005-Others-Document-(22-02-2008).pdf

3653-delnp-2005-pct-311.pdf

3653-delnp-2005-pct-search report.pdf

3653-DELNP-2005-Petition-137-(22-02-2008).pdf