NZ235875A - Manufacture of extruded plastics product - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £35875 235 875 3^ AMENDED under Section of the Patents Act 1953 from- ^ t- assistant commissioner of patents Priority Dsie(sf: Complete Specification ,.2^.r..lC\ Clsss: (5)...C.G5.T3.j.2L.i+.f..CLQ.^XTl . /• csttf.,. .T7.C .rTl t n i*., . .£ .Q a. F. 2.^1../. OO- ■ •'• P«??!fC8tlar< Date: P.O. Journal, No: |Oi+.,.

NO DRAWINGS c29 OCTWOl ■' £ \ Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION MANUFACTURE OF EXTRUDED PRODUCTS WE, BICC PUBLIC LIMITED COMPANY, a British company of Devonshire House, Mayfair Place, London W1X 5FH, ENGLAND oil hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) 235875 -Id- MJP/8913743 Manufacture of Extruded Products This invention relates to the manufacture by 5 extrusion of products made wholly or in part from polymeric materials, and more especially to electric cables, pipes and the like.

The art of formulating polymeric materials to secure desired properties is well developed, but the 10 design of particular formulations often entails compromise between the properties needed in different parts of the extruded product; for example, abrasion resistance (needed only at exposed surfaces) can often be gained at the expense of reduced flexibility. 15 Compromise of this kind can, of course, be avoided by using two (or more) different polymeric compositions, but this entails the use of a separate extruder for each composition, or at least two operations using the same extruder, either of which is expensive. Additionally, 20 if two extruders are used to feed to a common extrusion head (which is the most satisfactory way of getting good adhesion between the materials) the machines need to be set up with their screw axes at considerable angles to one another (for example at right angles) and this makes 25 efficient floor layout difficult if the line is to be incorporated in a standard rectangular building amongst a number of simple extrusion lines.

It has been known for some years that extruded products with a separate surface layer of pigmented (followed by page 2) ROW AMENDED 235^7 / / / material can be obtained at relatively low cost by/ bleeding off a minor part of the output of an ex'truder, / mixing it with a suitable pigment and reinjecting it to the head of the extruder so as to form the/outer layer, and plant from this purpose is commercially available (for example from Francis Shaw Ltd of^anchester) .

However, it has not hitherto been recognised that this / / technique could be adapted to provide surface layers, or other portions, that differed in more than the presence ./ or quantity of some admixed ^ingredient.

/ In accordance with the present invention, a process / / for the manufacture of an extruded product comprising / / the steps of plastifying a polymeric material in an / extruder, separating it into a major part and a minor j part, modifying .one of the said p-^rts and passing both the said parts7to an extrusion/head so that the modified / / and unmodified polymeric materials form distinct parts of a product formed by extrusion therefrom is / characterised by the fact that the plastified polymeric / material is modified/by a chemical reaction.

Appropriate chiemical reactions include the grafting /of side-chains to the polymeric material to modify its chemical, physical, rheological and other properties, / and the introduction of reactive sites for subsequent / / crosslinking.

/ The polymeric material may already be blended with / appropriate compounding ingredients before the minor / part is separated from it, or by suitable design of the •' extruder some compounding ingredients might be added to AS AMENDED material can be obtained at relatively low cost by bleeding off a minor part of the output of an extruder, mixing it with a suitable pigment and reinjecting it to the head of the extruder so as to form the outer layer, 5 and plant from this purpose is commercially available (for example from Francis Shaw Ltd of Manchester). However, it has not hitherto been recognised that this technique could be adapted to provide surface layers, or other portions, that differed in more than the presence 10 or quantity of some admixed ingredient.

According to the invention there is provided a process for the manufacture of an extruded product comprising the steps of plastifying a polymeric material in an extruder, separating it into a major part and a minor 15 part, modifying one of the said parts and passing both the said parts to an extrusion head so that the modified and unmodified polymeric materials form distinct parts of a product formed by extrusion therefrom wherein the plastified polymeric material is modified by the 20 grafting of sidechains to the polymeric material.

Side-chains are grafted to the polymeric material to modify its chemical, physical, rheological and/or other properties, and/or to introduce reactive sites for subsequent crosslinking.

The polymeric material may already be blended wich appropriate compounding ingredients before the minor part is separated from it, or by suitable design of the extruder some compounding ingredients might be added to 235 8 75 the major part after the minor part has been separated from it.

Separation of the minor part from the major can be controlled by a gear pump. In most cases, the 5 incorporation of chemical reagents into the appropriate part of the polymeric material will be a precondition for useful chemical reactions, and this can be effected, in the case of the minor part, by injecting them, preferably in a liquid form, into a cavity transfer 10 mixer. Chemical reaction may then take place in the mixer, in the extrusion head and/or in an interconnecting duct, and the material can be appropriately heated when the nature of the reaction requires it. In the case of the major part, mixing and 15 chemical reaction can take place in a part of the extruder downstream of the separation point.

The following examples are given for the purpose of illustrating the invention only.

Example 1 Freshly-drawn glass fibres have a high tensile strength, but this diminishes markedly over a period of time if the glass surface is exposed to the air, and a particular polymeric coating or matrix is conventionally used to protect the surfaces of glass fibre strength 25 members. Polyethylene is inexpensive and readily available, and meets most of the property requirements, but is seriously deficient in the strength of its adhesion to the glass surface. Ethylene/acrylic acid copolymers adhere strongly to glass but are very 235875 expensive and have a lower softening point than polyethylenes.

In accordance with the invention, low density polyethylene of melt flow rate 2 (as received, without 5 additives) is plasticised in a 90mm 26D extruder fitted with a polyethylene type screw. Ten percent of the plastified material is withdrawn, using the gear pump supplied with the machine, and modified by injecting into it 2% (by volume) of acrylic acid with 0.2% (by 10 weight) of dicumyl peroxide dissolved in it, mixing with a Francis Shaw cavity transfer mixer (driven independently of the extruder) and heating to a temperature of about 190°C for about a minute to graft acrylic side-chains to the polyethylene. The grafted 15 sidestream is then recombined with the unmodified mainstream in an extrusion cross-head so designed that a glass fibre strength member is coated with a thin inner layer of the modified polymer and a thicker outer layer of plain polyethylene.

This example can be modified by using high-density polyethylene, to achieve a result not readily available even with two extruders, since high density grades of ethylene/acrylic acid copolymer are not available on the market.

Example 2 Plasticised polyvinyl chloride (PVC) is a widely used insulating/sheathing material for low voltage power cables, with many attractive properties; it suffers however from a low melting-point and mediocre abrasion 2 3 5 8 7 5 resistance. These weaknesses can be significantly diminished by crosslinking, but this requires the use of considerable amounts (5-10%) of expensive additives that are liable to degrade the flame retardance of the 5 material as well as needing, in nearly all cases, the use of irradiation techniques that are also expensive and limit the dimensions of the product.

In accordance with the invention, a conventional PVC formulation is plastified using the same apparatus 10 as used in Example 1. Ten percent of the output is separated by the gear pump, and to this is added 5% by weight of (3,4 diamino-n-butyl) trimethoxy silane and trace amounts (around 0.02%) of dibutyl tin dilaurate. The mix is heated to about 200°C for 1 minute to effect 15 grafting of the silane to the polymer, and then recombined with the mainstream in a dual wire-covering crosshead so that the polymer so modified forms the outer skin of the wire covering. After exposure to water at 85°C for 24 hours, the outer layer is usefully 20 crosslinked and the wire is resistant to the abrasion encountered when drawn into conduit, and is also suitable for equipment wiring where there may be risk of short-term contact with a soldering iron as well as for service in high-temperature environments, such as 25 under-bonnet vehicle wiring.

This example can be modified by using the other amino or imino silanes described in GB patent no 1485263. 2358 Example 3 This is similar to Example 1, except that the two-layer extrusion is of much larger dimensions and is applied as the sheath of a cable over a thin metal foil moisture barrier (aluminium, lead, or copper). The 5 acrylic-acid grafted polyethylene promotes adhesion and avoids the need to use a preformed metal plastics laminate.

Example 4 This is similar to Example 3, except that the 10 acrylic-acid grafted polyethylene forms the outer part of the two-layer extrusion, which is applied as dielectric on a television downlead cable; a copper tape is longitudinally applied to the still-soft extrudate with a longitudinal butt joint, relying on the strong 15 adhesive bond between the graft polymer and the copper tape to ensure an adequately loss-free joint.

Example 5 The heat resistance of polyethylene packaging film can be dramatically improved by crosslinking, but this 20 entails difficulty, if not total impossibility, in making heat seals.

In accordance with the invention, low density polyethylene of melt flow rate 2 containing about 0.05% dibutyl tin dilaurate is plastified in the first section 25 of a specially designed 30D extruder with a barrier type homogenising screw. The machine is vented at a point 10D from the inlet, and at this point ten percent of the plastified material is bled off, as in the previous 235 8 75 examples; however, in this case this minor part of the material is directly fed by the gear pump to the extrusion head, and it is the main stream of polymer remaining in the extruder which is modified.

At a point about 2D beyond the separation point, there is injected into the polymer a solution comprising 0.265% dicumyl peroxide in 2.5% vinyl trimethoxysilane (percentages being by weight of the polymer) and after the mixture has been uniformly blended by the 10 homogenising zone of the extruder screw the temperature is raised to about 230°C to graft the silane to the polymer. The mainstream and sidestream are now recombined in a film-blowing crosshead in such a way that at least one surface of the film is constituted by 15 the unmodified sidestream material. After standing in moist ambient atmosphere for a week or so, the modified polymer becomes crosslinked by a silanol condensation reaction, but the surface formed by unmodified polymer remains fully heat-sealable.

Example 6 Polypropylene, coloured orange with a commercial colourant masterbatch is plastified in a single-screw extruder at 180°C. About 28% is extracted, using a gear pump as in the previous examples, near the end of the 25 extruder barrel and fed to an independently-driven cavity transfer mixer. A liquid mixture of 10 parts by weight trimethylolpropane trimethacrylate, 1 part by weight 4'-benzoyl-3'-hydroxy-2-phenoxyethy1 acrylate

Claims (5)

235875 -8- (BHPEA) and 0.02 parts by weight dicumyl peroxide was injected into the cavity transfer mixer using a metering pump and a positive displacement injector at a rate of 1.2 parts of mixture per hundred parts of polymer (by 5 weight); the residence time in the cavity transfer mixer was 2 minutes. The output of the cavity transfer mixer and the remaining output of the extruder were fed through separate passages to a common crosshead and applied as concentric layers to a copper wire 1mm in 10 diameter to from a brightly-coloured farm-wiring cable with the unmodified polypropylene forming the inner layer (notionally insulation) and the modified polypropylene from the cavity transfer mixer forming an outer, integral sheathing layer. The total radial 15 thickness of polypropylene was about 1mm, of which about 0.02mm was modified to render it resistant to ultraviolet light and thus enable the cable to be used outdoors. Analysis by UV spectroscopy on samples shaved from the outer layer and extracted with dichloromethane 20 showed that about 0.7 3% of BHPEA was not extractable, i.e. was grafted to the poymer; this represents nearly three-quarters of the BHPEA consumed. 235/8 ] ROW AMENDED / / -9- claims what*we claim is:-;1. A process for the manufacture of an extruded product comprising the steps of plastifying; a polymeric;/ /;material in an extruder, separating it into a major part/;/;and a minor part, modifying one of the said parts and/;/ /' /' /;passing both the said parts to an extrusion head so/that the modified and unmodified polymeric materials form distinct parts of a product formed by extrusior/;/;therefrom, characterised by the7''fact that;✓;the plastified polymeric material is modified by a chemical reaction.;/;/;/' /;2. A process as claimed in claim 1 in which the said;/;chemical reaction is the grafting oi sidechains to the;/;polymeric material.;/;3. A process as claimed in claim 2 in which the sidechains;introduce into the polymeric material active;/;sites for subsequent crosslinking.;/ /;4. A" process for making an extruded product;Ji* / / substantially as described with reference to one of / / Examples 1 - 5. f 5. A process/for making an extruded product substantially' as described with reference to Example 6. 6. An extruded product made by the process claimed in any one/of the preceding claims. BICC PUBLIC LIMITED COMPANY / j-4. ./IMITWO , s / // Ifj / fj By Their Attorneys ^ / / BALDWIN SON & CAREY '{ 2 9 OCT 1990' V-: rp-sv' { St -9- • WHAT WE CLAIM IS:

1. A process for the manufacture of an extruded product comprising the steps of plastifying a polymeric material in an extruder, separating it into a major part and a minor part, modifying one of the said parts and passing both the said parts to an extrusion head so that the modified and unmodified polymeric materials form distinct parts of a product formed by extrusion therefrom, wherein the plastified polymeric material is modified by the grafting of sidechains to the polymeric material.

2. A process as claimed in claim 1 in which the sidechains introduce into the polymeric material active sites for subsequent crosslinking.

3. A process for making an extruded product substantially as described with reference to one of Examples 1 - 5.

4. A process for making an extruded product substantially as described with reference to Example 6.

5. An extruded product made by the process claimed in any one of the preceding claims. BICC PUBLIC LIMITED COMPANY By Aheirj Attorneys BMIOTNJ SON & CAREY