WO2013072070A1

WO2013072070A1 - Use of polyethylene composition in wire and cable jacketing and /or insulation.

Info

Publication number: WO2013072070A1
Application number: PCT/EP2012/004796
Authority: WO
Inventors: De Roelof Franciscus Gerardus Maria VOS; Hao Ding; Van den Bart Albertus Hubertus ESSCHERT
Original assignee: Saudi Basic Industries Corporation (Sabic)
Priority date: 2011-11-18
Filing date: 2012-11-19
Publication date: 2013-05-23

Abstract

The invention relates to the use of an ethylene polymer composition for the production of wire and cable jacketing and /or insulation characterised in that the ethylene polymer composition comprises polyethylene and a mixture of a calcium salt of saturated straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated straight chained fatty acid having 8 to 30 carbon atoms. The weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1:5.

Description

Use of a polyethylene composition

in wire and cable jacketing and /or insulation

The present invention relates to the use of a polyethylene composition in wire and cable jacketing and /or insulation.

Wire and cable products are critical to the modern economy. Examples of wire and cable constructions are building wire, power cable and fibre optics. Their application is increasing with the growing use of computers, the Internet, cable television, and the increase in electrical power service worldwide. Each type of cable, however, has several common elements including the core (typically copper or fiber optic), insulation, and jacketing. One of the key components of a wire is its insulation. Its selection is determined by a number of factors such as stability and long life, dielectric properties, resistance to high temperature, resistance to moisture, mechanical strength, and flexibility. There is no single insulation that is ideal in every one of these areas. It is necessary to select a cable with the type of insulation, which fully meets the requirements of the application. Jackets cover and protect the enclosed wires or core against damage, chemical attack, fire and other harmful elements that may be present in the operating environment.

A wire and cable formulation may comprise for example polymers for insulation and jacketing; suitable polymers include for example polyethylene, cross linked polyethylene, chlorinated polyethylene and polyvinyl chloride; plasticizers to make the plastic flexible and easy to process; stabilizers to provide heat resistance during manufacturing as well as visible light, UV rays and heat resistance during product use; flame retardants to slow the spread of an accidental fire and reduce the amount of heat and smoke released; fillers to reduce formulation costs and improve insulation resistance; lubricants to improve the ease of processing; and colorants to give the desired colour for identification purposes.

The manufacturing of coated wire and cable is a multi-stage process. Raw materials are combined in a series of manufacturing steps including resin and additive manufacturing, resin compounding, wire drawing (or fiber optic), extrusion, cabling, and jacketing. Polymers and additives are combined together, directly to the reactor powder prior to pelletizing or via an extra compounding operation afterwards to produce materials formulated to meet the various insulation or jacketing performance

requirements. These pellets are later re-melted in a for this specific technical field suitable extrusion equipment to insulate or jacket wire and cable. In the manufacture of extruded products there are a number of surface defects referred to as sharkskin, snakeskin and orange peel which all generally related to the rheology of the polymer melt. A severe form of surface defect is "melt fracture". The melt fracture manifests itself in the extruded article as surface roughness, sharkskin and orange peel. As disclosed in "Plastics Additives Handbook (6th edition, November 2008 at page 588 melt fraction elimination has historically been the primary benefit imparted by fluor polymer processing aids. Fluor polymers contain halogens which are toxic by burning. Therefore the market requires a halogen free product.

It is the object of the present invention to provide a polyethylene composition which results in a jacketing and/ or insulation for wire and cable without melt fracture.

The present invention is characterised in that the polyethylene composition comprises a polyethylene and a mixture of a calcium salt of saturated monobasic straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated monobasic straight chained fatty acid having 8 to 30 carbon atoms wherein the weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1 :5.

The use of the polyethylene composition results wire and cable production without melt fracture.

WO94/07946A1 discloses that a process for the stabilization of recycled plastics, predominantly thermoplastics, obtained from domestic, commercial and industrial waste or from useful material collections, which comprises adding from 0.01 to 10% by weight of a mixture of a) at least one sterically hindered phenol, b) at least one organic phosphorous or phosphonous ester and c) at least one metal salt of a fatty acid to these plastics. Component c may be a mixture of various metal stearates, in which the metal is an element of main or sub-group II or tin.

US2003/0175459A1 discloses a shaped article comprising a polymer composition, wherein the polymer composition includes: an olefinic polymer, a polar polymer; and a third polymer, wherein the third polymer is a graft or block copolymer, and wherein the third polymer comprises first and second polymer portions, the first polymer portion being compatible with the olefinic polymer and the second polymer portion being compatible wjth the polar polymer, wherein the polymer composition has a limiting oxygen index of at least about 25.

Another advantage is that uniformity of the product surface is achieved.

These advantages are obtained with all possible line speeds of the wire and cable production lines.

A further advantage is that the melt fracture problem is solved without using a fluor polymer and consequently a halogen free product is obtained. According to a preferred embodiment of the invention the composition does not comprise a fluoro polymer.

According to a preferred embodiment of the invention the weight ratio of the calcium salt: zinc salt ranges between 4:1 and 1 : 2.

According to a further preferred embodiment of the invention the weight ratio of the calcium salt: zinc salt ranges from 5: 1 and 1 : 1 , for example 4: 1 and 1 :1 , for example between 3:1 and 1 : 1 , for example from 5:1 to 3:2. Most preferably, the weight ratio of the calcium salt: zinc salt is around 2:1. It is advantageous that the amount of calcium is higher than the amount of zinc because the combination of these metal salts shows a synergistic effect with increasing calcium salt:zinc salt ratio.

Most preferably the weight ratio of the calcium salt: zinc salt is about 2:1.

In case the weight ratio of the calcium salt: zinc salt is higher than 5:1 or lower than 1 :5 the salt mixture does not improve the surface quality compared with the use of a pure calcium or the use of a pure zinc salt.

Preferably, the total amount of calcium salt and zinc salt in the ethylene composition is from 1500 to 4500ppm, more preferably from 2500 to 3500ppm.

Suitable polyethylenes include linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and low density polyethylene (LDPE).

Preferably, for wire and cable jacketing, the ethylene polymer composition comprises LLDPE or HDPE, whereas for wire and cable insulation, preferably the ethylene polymer composition comprises LLDPE or LDPE.

According to a preferred embodiment of the invention the polyethylene composition comprises linear low density polyethylene.

Generally the polyethylene has a density in the range between 910 and 970 kg/m3 and an MFI in the range between 0.1 and 10 g/10 minutes (measured at 190°C, 2.16 kg according to ASTM-D-1238).

The ethylene composition may comprise other polymers than polyethylene and/or may also comprise mixtures of LLDPE, LDPE and/or HDPE. For example, if LLDPE is present, HDPE and/or LDPE may be present in amount from 2-30wt%, for example 5-25wt%, for example 10-20wt% based on the polyethylene. For example, if LDPE is present, HDPE and/or LLDPE may be present in amount from 2-30wt%, for example 5-25wt%, for example 10-20wt% based on the polyethylene. For example, if HDPE is present, LLDPE and/or LDPE may be present in amount from 2-30wt%, for example 5-25wt%, for example 10-20wt% based on the polyethylene. Preferably, however, the ethylene composition comprises one of LLDPE, LDPE or HDPE and does not comprise mixtures of polyethylenes. Preferably, the ethylene composition also does not comprise other polymers. Generally, the ethylene composition comprises more than 80% by weight of polymer, more preferably more than 80% by weight of LLDPE, LDPE and/or HDPE. Preferably, the ethylene composition comprises more than 95% by weight of polyethylene, more preferably more than 95% by weight of one of LLDPE, LDPE or HDPE. More preferably, the ethylene composition consists essentially of polyethylene and a mixture of a calcium salt of a saturated straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of a saturated straight chained fatty acid having 8 to 30 carbon atoms, wherein the weight ratio of the calcium salt:zinc salt ranges between 5:1 and 1 :5. More preferably, the amount of polyethylene in the ethylene composition is substantially at least 90%, for example substantially at least 95%, for example substantially at least 99% by weight of the total amount of polymers in the ethylene composition.

Preferably, the polyethylene in the ethylene composition is not recycled.

According to a preferred embodiment of the invention the mixture of calcium salt and zinc salt is added in the polyethylene production plant to the reactor polyethylene powder and extruded and pelletized to polyethylene granules. The amount of salt mixture may range between for example 0.1 and 0.5 % by weight relative to the polyethylene powder.

It is also possible that the mixture of calcium salt and zinc salt is compounded with the polyethylene base resin for example LLDPE via compounding extrusion to a masterbatch. The amount of salt mixture may range between for example 1 and 30 % by weight relative to the base resin.

The masterbatch can be added to the base polymer for example LLDPE during cable production to enhance the performance. The amount of the masterbatch may range between 0.5 and 30 % by weight relative to the base resin.

Suitable examples of the calcium salt of a fatty acid having 8 to 30 carbon atoms include calcium laurate, calcium palmitate, calcium stearate, calcium behenate and calcium montanate. For the avoidance of doubt with fatty acid having 8 to 30 carbon atoms is meant an unsubstituted fatty acid.

According to a preferred embodiment of the invention the calcium salt of a fatty acid having 8 to 30 carbon atoms is calcium stearate.

Suitable examples of the zinc salt of a fatty acid having 8 to 30 carbon atoms include zinc laurate, zinc palmitate, zinc stearate, zinc behenate and zinc montanate.

According to a preferred embodiment of the invention the zinc salt of a fatty acid having 8 to 30 carbon atoms is zinc stearate. The composition according to the invention may also comprise other additives for example amides, preferably fatty acid amides. These additives may be present in an amount of for example from 100 to 3000ppm, for example from 500 to 2500, for example from 1000-3000ppm, for example from 500 to 2500ppm.

Suitable fatty acid amides include for example amides of saturated or unsaturated monobasic or straight chained fatty acids having 8 to 30 carbon atoms, for example having 8 to 20 carbon atoms, ethylene bis-stearamide, erucamide, oleamide, ethylene bis-oleamide, stearamide, behenamide, preferably ethylene bis-stearamide. It is of course also possible to use a mixture of fatty acid amides.

According to a preferred embodiment of the invention the polyethylene composition comprises a polyethylene and a mixture of a calcium salt of saturated or unsaturated monobasic or straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated or unsaturated monobasic or dibasic branched or straight chained fatty acid having 8 to 30 carbon atoms wherein the weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1 :5 and a fatty acid amide is present in an amount from 100 to 3000ppm, for example from 100-1500 ppm.

These additives such as the amides can be added together with the mixture of calcium salt and zinc salt in the plant to the reactor powder and extruded and pelletized to granules. The additives such as the amides can be compounded together with the mixture of calcium salt and zinc salt and the base resin carrier such as LLDPE via compounding extrusion to produce a master batch. This masterbatch can be added to the base polymer during cable production to enhance the performance.

The production processes of polyethylenes for example LLDPE are summarised in "Handbook of Polyethylene" by Andrew Peacock (2000; Dekker; ISBN 0824795466) at pages 43-66. The catalysts can be divided in three different subclasses including Ziegler Natta catalysts, Phillips catalysts and single site catalysts.

The wire and cable formulation obtained with the polymer composition according to the invention may be applied for example in building wire, telephone and telegraph wire, power cable coaxial and antennae cable, electronic and data wire and magnet wire.

The wire and cable formulations may comprise also other additives such as for example plasticizers; stabilizers; flame retardants; fillers; lubricants colorants. These additives are generally added during the production of wire and cable together with the base polymer.

Although the invention has been described in detail for purposes of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the claims.

It is further noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims.

It is further noted that the term 'comprising' does not exclude the presence of other elements. However, it is also to be understood that a description on a product comprising certain components also discloses a product consisting (essentially) of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps.

The invention will be elucidated by means of the following non-limiting examples. Example I

LLDPE (density 918 kg/m³ ; MFI 3 g/10min (190°C, 2.16kg)) was used as masterbatch carrier. The masterbatch was obtained by mixing 10% by weight (relative to the total amount of the masterbatch) calcium stearate and 5% by weight (relative to the total amount of the masterbatch) zinc stearate with the LLDPE carrier via compounding extrusion process.

2 % by weight (relative to the total composition) of this masterbatch was dosed to a LLDPE base resin (density 918 kg/m³ ; MFI is 3 g/10min (190°C, 2.16kg) ) together with 3 % by weight black colour masterbatch during the cable jacketing process. The line speed of the single screw extruder for the jacketing process was 20 m/min.

The temperature setting for the extruder was:

Figure I shows a picture of the surface of the cable as obtained. Comparative Example A

Example I was repeated with the only difference no mixture of calcium stearate and zinc stearate was used. Figure A shows a picture of the surface of the cable as obtained without use of the mixture according to the invention. Figure I shows a picture of the surface of the cable as obtained with the use of the mixture of calcium stearate and zinc stearate using the exact same processing conditions as Figure A.

As can be seen from Figure A, this strand displays a rough surface. This rough surface is due to the fact that melt fracture occurred during processing.

As can be seen in Figure I, the surface is uniform and smooth and there is no indication of melt fracture.

The conclusion of the comparison between figure A and figure I is that the surface quality of the cable according to Example I is improved in comparison with the surface quality of the cable according to Comparative Example A.

Example II

Example I was repeated, and line speed was increased from 20m/min to 80 m/min. Figure II shows a picture of the surface of the cable as obtained at a speed of 80 m/min.

Comparison of figure I and figure II shows that the surface quality of the cables was uniform when applying a line speed of 20 m/min and 80 m/min.

Comparative Example B

Example II was repeated with the only difference no mixture of calcium stearate and zinc stearate was used. Figure B shows a picture of the surface of the cable as obtained without use of the mixture according to the invention. The conclusion of the comparison between figure B and figure II is that the surface quality of the cable according to Example II is improved in comparison with the surface quality of the cable according to Comparative Example B.

In Figure B, the strand displays a rough surface. This rough surface is due to the fact that melt fracture occurred during processing.

In Figure II, the surface is uniform and smooth and there is no indication of melt fracture.

By comparing pictures Figure I and Figure II (compositions as used in the invention, but with processing at different line speeds), it is clear that both samples display the same smooth uniform surface. This is due to the fact that no melt fracture occurred.

This shows that an ethylene polymer composition, wherein the ethylene polymer composition comprises polyethylene and a mixture of a calcium salt of saturated straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated straight chained fatty acid having 8 to 30 carbon atoms wherein the weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1 :5, preferably wherein the weight ratio is from 5:1 to 3:2, for example around 2:1 , preferably wherein the total amount of calcium salt and zinc salt ranges from 1500 to 4500, for example from 2500 to 3500 can suitably be used for the production of wire and cable jacketing and /or insulation as melt fracture is reduced or may even be completely absent.

Example III

LLDPE (density 918 kg/m³ ; MFI 3 g/10min (190°C, 2.16kg)) samples were compounded on a DSM Xplore 15 cc micro compounder. The melt temperature was set at 180°C. The materials were premixed as a powder and compounded for 2 min at 100 rpm. The powder premix of all samples also contained 2000ppm Irganox™ B225 as a processing stabilizer. Irganox™ B225 is a mixture of Irganox™ 1010 and Irgafos™ 168 in a ratio of 1 :1.

The recipes are displayed in Table 1. In Table 1 :

- Ca (ppm) indicates the amount of calcium stearate in ppm,

- Zn (ppm) indicates the amount of zinc stearate in ppm

- total stearates, indicates the sum of the amount of calcium stearate and zinc stearate in ppm

- ratio indicates the ppm ratio between calcium stearate and zinc stearate

- fatty acid amide indicates the amount of Crodamide EBS which is an ethylene bis- stearamide in ppm. During compounding the total sample loading was 8 grams. The force in dependence of time during compounding was recorded on the Xplore micro

compounder.The force during compounding is an indication for the processability of the material. The lower the force, the better the processability that is achieved.

The results from the different tried recipes are also displayed in Table 1. The force (or processability) during the compounding for the different samples relative to one another was indicated by a figure from 1 to 8. The highest force and therefore the worst processability was indicated with 1. The lowest force and therefore the best processability is indicated with 8.

From the results it can be concluded that the best processability was achieved by using 3000ppm of a Ca- and Zn- stearate combination with the addition of 500 ppm of a ethylene bis stearamide. The best Ca:Zn stearate ratio was 2:1.

A lower force during compounding is also associated with less or even a prevention of melt fracture during processing. Therefore, an ethylene polymer composition, wherein the ethylene polymer composition comprises polyethylene and a mixture of a calcium salt of saturated straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated straight chained fatty acid having 8 to 30 carbon atoms wherein the weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1 :5, preferably wherein the weight ratio is from 5:1 to 3:2, for example around 2:1 , preferably wherein the total amount of calcium salt and zinc salt ranges from 1500 to 4500, for example from 2500 to 3500 can suitably be used for the production of wire and cable jacketing and /or insulation. Not only will such composition be easily processable, but this will also have a reduced melt fracture and may even show no melt fracture at all.

Furthermore, the processing of such composition is further improved and melt fracture of such composition is also further reduced when such ethylene polymer composition further comprises a fatty acid amide, for example ethylene bis stearamide, in an amount from 100 to 3000ppm, for example in an amount of around 500ppm. Table 1

Ca Zn Total Ratio fatty Force or ppm ppm stearates acid process- amide ability lll-C 0 0 0 0 2 lll-D 1000 0 1000 0 1 lll-E 3000 0 3000 0 3 lll-F 5000 0 5000 0 3 lll-G 0 5000 5000 0 3 lll-H 0 1000 1000 0 4

111-1 1500 1500 3000 1 :1 0 5

III-2 666 333 999 2:1 0 6

III-3 3330 1665 4995 2:1 0 6

III-4 2000 1000 3000 2:1 0 7

III-5 2000 1000 3000 2:1 500 8

Claims

1. The use of an ethylene polymer composition for the production of wire and cable jacketing and /or insulation characterised in that the ethylene polymer

composition comprises polyethylene and a mixture of a calcium salt of saturated straight chained fatty acid having 8 to 30 carbon atoms and a zinc salt of saturated straight chained fatty acid having 8 to 30 carbon atoms wherein the weight ratio of the calcium salt: zinc salt ranges between 5:1 and 1 :5.

2. The use according to Claim 1 characterised in that the weight ratio of the calcium salt: zinc salt ranges between 4:1 and 1 : 2.

3. The use according to Claim 2 characterised in that the weight ratio of the calcium salt: zinc salt ranges from 5:1 to 1 :1 , preferably from 5:1 to 3:2..

4. The use according to any one of claims 1-3, characterized in that the total amount of calcium salt and zinc salt is from 1500 to 4500ppm.

5. The use according to any one of Claims 1 -4 characterised in that the polyethylene is linear low density polyethylene.

6. The use according to any one of claims 1-5, characterized in that the ethylene composition comprises one of LLDPE, LDPE or HDPE and does not comprise mixtures of polyethylenes.

7. The use according to any one of claims 1- 6, characterized in that the ethylene composition does not comprise other polymers

8. The use according to any one of Claims 1 -7 characterised in that the calcium salt is calcium stearate.

9. The use according to any one of Claims 1-8 characterised in that the zinc salt is zinc stearate.

10. The use according to any one of claims 1 -9, wherein the ethylene composition further comprises a fatty acid amide.

1 1. The use according to claim 10, wherein the fatty acid amide is present in the ethylene composition in an amount of from 100 to 3000ppm.

12. The use according to any one of Claims 1 -11 characterised in that the composition does not comprise a fluoro polymer.

13. The use according to any one of Claims 1-12 characterised in that the mixture of calcium salt and zinc salt is added in the polyethylene production plant to the reactor polyethylene powder and extruded and pelletized to polyethylene granules.

14. The use according to any one of Claims 1-13 characterised in that the mixture of calcium salt and zinc salt is compounded with the polyethylene base resin via compounding extrusion to a masterbatch.

A wire or cable comprising a jacket comprising the polyethylene composition of any one of Claims 1 -14.