AU749342B2

AU749342B2 - Plastics pipe

Info

Publication number: AU749342B2
Application number: AU44755/99A
Authority: AU
Inventors: Mikael Andersson; David Charles Harget; Eino Matias Holso; Jyri Jaakko Jarvenkyla
Original assignee: Uponor Ltd UK
Current assignee: Radius Systems Ltd
Priority date: 1995-01-18
Filing date: 1999-08-26
Publication date: 2002-06-27
Anticipated expiration: 2016-01-17
Also published as: AU4475599A

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): UPONOR LIMITED Invention Title: Plastics Pipe *5 *0 5 *5 S

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The following statement is a full description of this invention, including the best method of performing it known to me/us: 1 PLASTICS PIPE This invention relates to plastics pipes and more particularly to a novel construction of plastics pipe, a method for its manufacture, and a method for making joints in such a pipe.

In the handling, installation and connection of plastics pipes, the pipe surface is easily damaged. In 10 modern plastic pipe installation techniques, for example, a tunnel is bored in the ground for the pipe, and the pipe is then pushed or pulled through the tunnel, for example, into an excavated hole where the next pipe joint is to be made.

oooo The pipe-laying method can subject the pipe to substantial bending, tensile and abrasive contact forces.

This is disadvantageous since bending, stretching and abrasion of a pipe can result in a deterioration of its mechanical strength. In addition, the useful life of the pipe may be reduced by diffusible materials in the ground, or by environmental conditions.

It will be apparent that the method of pipe-laying can also result in the pipe becoming scratched and dirty.

This is disadvantageous firstly as the pipe material may be notch sensitive, in which case any scratches may cause greater damage to occur in the pipe during subsequent "11 (e 2 handling or use. Secondly, dirt on the pipe prevents successful welding. At the present time, a common technique for jointing plastic pipes is electric welding, and particularly electrofusion welding, using an electrofusion coupler. The main reason for failure of joints using an electrofusion coupler is that the surface of the pipe is dirty or has become oxidised. For this reason the pipe ends always have to be cleaned and abraded or scraped, for example with sandpaper or a metal 10 scraper, before jointing. In practice, theF cleaning and abrading or scraping is often uneven (the underside of the pipe in particular may be treated less carefully) and the quality of the end result depends upon the professional skill of the installer.

A variety of suggestions have been put forward to overcome the above-mentioned disadvantages.

In European Patent Application No. 0474583 there is described a plastic pipe to be laid in the ground which comprises a gas or water conducting core pipe provided with an outer hose of a thermoplastic material having a higher flexibility than the material of the core pipe.

The pipe is stated to be able to resist the extensive mechanical stresses to which it is subjected during direct laying into the ground. It is stated to be easy to remove the outer hose adjacent the ends of the pipe when two pipe sections are to be assembled by welding.

3 It is also stated that formation of cracks caused by damage to the protective hose does not spread to the core pipe, but stops when the hose has been penetrated.

In GB 2263524 there is described a plastics pipe for making pipe joints characterised in that the pipe is covered by a plastic surface layer as a protective coating which is easily detachable at least at the ends of the pipe, in order to uncover the joint surface of the pipe 0 necessary for making the pipe joint. -The protective o coating can contain UV stabilisers and may be applied by Sco-extrusion through a cross-head extrusion nozzle.

o o Various ways of making the protective coating easily 6:00 detachable from the core pipe are disclosed, including the *so: use of fillers in the coating, the choice of chemically different plastics materials for the coating and the pipe, extruding the coating at low temperatures, and the introduction of adhesion preventing agents.

000@ 20 In EP-A-0604907 there is described a two-layer plastics pipe which comprises a core pipe whose material, size and structure essentially meet the requirements set go by the material to be conveyed and an outer hose provided around the core pipe by a suitable coating method, the properties of the outer hose essentially meeting the requirements set by the environment and for the laying procedure. The stiffness of the outer hose, based on its material properties or the design of the outer hose, is 4 higher than the stiffness of the core-pipe manufactured from the same amount of material, and the outer hose is removable at least at the ends of the pipe. The outer hose is again applied by co-extrusion using a cross-head extrusion die. The protective outer hose is made so as to be easily detachable at least at the pipe ends and to have low adhesion thereto.

Japanese Patent Publication No. 3-24392 describes an electrofusion pipe characterised in that it consists of a S: 0 pipe body consisting of a thermoplastic resin and a protective layer consisting of an incompatible resin covering the outside surface of the pipe body. The pipe egos body can consist of a tubular crosslinked thermoplastic resin layer and a non-crosslinked thermoplastic resin *000 layer integrally formed on the outside of this thermoplastic resin layer and a protective layer consisting of an incompatible resin covering the outside 0* surface of the pipe body. The protective layer can be peeled off and an electrofusion joint made.

The entire disclosures of all the above-mentioned patent specifications are incorporated herein by reference for all purposes.

Preferably, the present invention provides a plastics Pipe comprising an inner core and an outer protective layer having an improved combination of mechanical and physical properties.

5 It has now been found, in accordance with one aspect of the present invention, that the relative dimensions of the plastics pipe and the thickness of the outer protective layer have a profound effect upon the performance of the pipe. It has also been found that, firstly in order to achieve an advantageous combination of mechanical strength to resist the severe conditions involved in laying the pipe and also to provide a sufficient degree of environmental protection, together 0 with an appropriate degree of peelability, requires a particular choice of mechanical properties and dimensions.

ooo In accordance with a first aspect of the present invention, therefore, there is provided a plastics pipe 0050 which comprises an inner core and an outer protective layer bonded thereto, in which: The dimensions of the pipe and the protective layer are such that the ratio of the external diameter of the pipe

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20 to the thickness of the protective layer is at least preferably at least 100; The cohesive strength of the outer protective layer, excluding any lines of weakness, at least at the ends of the pipe, is greater than the strength of the adhesive bond between the outer protective layer and the inner core; and the strength of the adhesive bond between the outer protective layer and the inner core is within the range of from 0.2 N/mm to 2.52 N/mm.

6 It has also been found that the extent of the adhesion between the inner core and the outer protective layer also has a substantial influence upon the performance of the pipe. If the adhesion is too great or too small, the mechanical properties of the pipe, and in particular the impact strength, may be adversely affected.

The adhesive bond preferably has relatively low peel and relatively high shear characteristics. Preferably the 1 0 adhesion between the outer protective layer and the inner core is in the range of from 0.2 to 0.5 N/mm width, ooo measured by a semi-tensile peel test as hereinafter e g.

described.

oo Whilst it may be possible to obtain an adhesion between the protective layer and the inner core within the e preferred range using a cross-head extrusion method ooo wherein the protective layer is extruded over the Ssolidified inner core, we have found that consistently improved results are obtained by dual extrusion in which both components are extruded and brought together before substantial oxidation of the outer surface of the inner ee core has taken place.

Accordingly, in another aspect the invention provides a method for the production of a plastics pipe comprising an inner core and an outer protective layer bonded thereto which comprises co-extruding molten plastics materials forming the inner core and the outer protective layer from an extruder die, bringing the molten plastics materials together whilst still hot and allowing them to cool, such that, on cooling, the outer protective layer can be peeled from the inner core, at least at the 7 ends of the pipe, to reveal an inner core surface suitable for electrofusion welding, wherein the dimensions of the pipe and the protective layer are such that the ratio of the external diameter of the pipe to the thickness of the protective layer is at least preferably at least 100, and the cohesive strength of the outer protective layer, excluding any lines of weakness, at least at the ends of the pipe is greater than the peel strength of the adhesive S: 10 bond between the outer protective layer and the inner *core; and the strength of the adhesive bond between the outer protective layer and the inner core is within the range of from 0.2 N/mm to 2.52 N/mm.

ooo In a further aspect, the invention provides a plastics pipe which comprises an inner core and an outer S. protective layer, in which: the adhesion between the outer protective layer and the inner core is such that, in an H50 Impact Test in 0OSo accordance with EN 1411 at O.9C, preferably at 2 C, if the outer core is ruptured and a crack formed, that crack is arrested at the outer :layer/inner core interface.

In a still further aspect, the invention provides a plastics pipe which comprises an inner core and an outer protective layer, in which: the plastics pipe has an impact resistance greater than 150Nm in a B50 Impact Test in accordance with ENI411, at O.OC, preferably at -202C and wherein the cohesive strength of the outer protective layer, excluding -8 any lines of weakness, at least at the ends of the pipe, is greater than the strength of the adhesive, bond between the outer protective layer and the inner core.

In a still further aspect, the invention also provides a method of making a joint in a plastics pipe according to the invention, or of joining two ends of plastics pipes according to the invention, which comprises peeling the outer protective layer from the region or 10 regions of the pipe or pipes to be joined, installing an electrofusion coupler over the bared regions of the pipe or pipes and activating the electrofusion coupler to fuse 06°' the region or regions of the pipe or pipes thereto.

The plastics pipe can comprise any suitable thermoplastic polymeric material, and particularly suitable polymeric materials include, for example, olefinieally-unsaturated polymers and co-polymers, for example, polyolefins such as polyethylene, polypropylene S 20 and polybutene, ethylene and propylene co-polymers, for example, ethylene-vinyl acetate polymers, and propylenevinyl acetate polymers, halogenated -vinyl polymers such as vinyl chloride polymers and co-polymers, polyamides, for example, nylon 6 and nylon 66, and ionomer polymers such as Surlyn.

9 The inner core of the pipe is chosen to be compatible with the particular application, and in particular with the fluid material to be conveyed by the pipe. For many applications polyethylene is the preferred material for the inner core. The grade of polyethylene chosen, that is to say, high density, medium density, low density or linear low density, will depend upon the particular application. Suitable grades of polyethylene include, for 0 example, Statoil 930 (natural), Neste NCPE 2600 (natural) 0S and Neste NCPE 2467 BL and NCPE 2418. Any suitable equivalent grade of polyethylene may of course also be used.

Gooo An advantage of the plastics pipes of the present invention is that the normal UV stabiliser and colorant go package need not be included in the plastics material of the inner core, provided that sufficient quantities of these materials are included in the outer protective layer. This enables the inner core to comprise natural polymeric material, free or substantially free from additives which add to the cost of the core material and which, in certain circumstances, may impair the mechanical or physical properties of the core material.

The outer protective layer is preferably formed from a polymeric material or blend of polymeric materials having good mechanical and physical properties, together with an ability to receive quantities of stabilising materials, in particular UV stabilisers, sufficient to protect the inner core. Preferred polymeric materials for the outer protective layer comprise propylene homoand co-polymers, and especially propylene co-polymers such as, for example, Neste SA 4020G. Other polymeric materials with suitable mechanical and physical properties, for example nylons and Surlyn, can also be used in appropriate circumstances.

Suitable stabiliser materials include, for example, titanium dioxide, carbon black, and other fillers.

Whilst carbon black is an excellent UV stabiliser and reinforcing filler, buried pipes are frequently colourcoded and its use is therefore not possible for many applications. Titanium dioxide is, therefore, the preferred filler and UV stabiliser, since this is also compatible with many colorant packages. Other filler "materials such as chalk and talc, and those mentioned in PCT/F193/00038 may also be used. The preferred filler particle size will depend on the filler being used, but for titanium dioxide, for example, the average particle size range is preferably from 0.003 to 0.025ym.

A particularly preferred plastics pipe according to the present invention comprises an inner core of polyethylene and an outer protective layer of a propylene co-polymer. The pipe can of course comprise more than two layers of polymeric material, and all suitable 11 multilayer pipes are included provided that at least one inner core and one protective outer layer are present.

The pipe can, for example, comprise a multilayer inner core and a protective outer layer.

Whilst the thickness of the outer protective layer needs to be sufficient to accept the appropriate quantities of UV stabilisers and colourants necessary to protect the inner core and also to provide appropriate 10 identification, if it is too thick, rendering the outer layer too stiff, we have found that the impact strength of the pipe is unexpectedly reduced.

Without wishing to be bound by any particular theory, it is believed that the impact strength of the plastic pipes of the invention is related in part to the adhesion between the inner core and the outer protective o0• layer. If the adhesion is too small the outer protective layer behaves as a relatively thin structurally independent tube and is therefore susceptible to impact damage. If the adhesion is too great, cracks formed by, rupture of the outer layer have a tendency to propagate through to the inner core. Ideally, therefore, the adhesion between the outer protective layer and the inner core should be sufficient that, even if the outer core is ruptured and a crack formed, the crack is arrested at the outer layer/inner core interface.

Preferably the outer protective layer has a thickness greater than 0.1mm, more preferably greater than 0.2mm, and most'preferably has a thickness in the range of from 0.3 1.0 mm.

The dimensions of the pipe and the protective layer .o are such that the ratio of the external diameter of the S* pipe to the thickness of the protective layer is at least preferably at least 100. From this it can be seen 10 that it is possible to use a thicker protective layer on .0 a pipe of greater diameter, although for easy peelability the thickness is preferably kept to a minimum.

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Examples of suitable pipe external diameters and S 15 outer protective layer thicknesses are as follows: Pipe OD (mm) Outer layer thickness (mm) SDR 30 0.3 83 100 30 50 0.3 100 166 63 125 0.4 157 312 >125 0.5 250 500 (at 250mm Pipe OD) Preferably the dimensions of the pipe and the protective layer are such that the ratio of the external diameter of the pipe to the thickness of the protective layer (standard dimension ratio SDR) is in the range of 150 to 400.

13 It is important, when stripping off the outer protective layer from the ends of the pipe, that the cohesive strength of the outer protective layer is greater than the strength of the adhesive bond between the outer protective layer and the inner core. The 0 reason for this is to prevent any substantial sized particles of the outer protective layer from adhering to the outer surface of the inner core and interfering with 0 'the jointing process, when using, for example, an 10 electrofusion coupler. Preferably the arrangement is such that when stripped off, the outer protective layer leaves no residue on the outer surface of the inner core.

In general, the cohesive strength of the outer protective layer is preferably at least 5MPa, and most preferably in the range of from 5MPa to Notwithstanding the above, the outer protective layer may be provided with lines of weakness to assist peeling back, which lines may be produced by scoring, or preferably by suitably shaping the extrusion die, or by cooling the die locally, for example, as described in GB2263524.

In order further to assist the stripping off the outer protective layer, the extrusion conditions may be arranged such that the strength properties of the outer protective layer are different in the radial and axial directions.

14 As previously mentioned, the adhesion between the outer protective layer and the inner core is preferably in the range of from 0.2 to 0.5 N/mm width as measured by a semi-tensile peel test. A suitable test is described below: A test specimen of pipe is prepared by cutting two o parallel axial notches through the whole of the surface "layer for 50mm, and extending these notches for a further 1 0 50mm with a depth such that 0.3mm is left of the surface .4 layer. A further 20mm length of specimen is allowed before the vertical alignment with the load cell.

•oe• The tear test is performed in an Instron model 1197 with a speed of 100 mm per minute. The pipe is placed so that the start of the tearing at the beginning of the through notch depth is 120 mm from the centre of the load •ece cell and the distance from the start of the tearing to the fastening point of the load cell is 750 mm. The result is that the largest tear angle is achieved whilst tearing that part of the pipe with a notch through the surface o layer.

Although not presently preferred, it may be possible to provide an adhesive layer between the inner core and the outer protective layer which would have the appropriate adhesion characteristics. If an adhesive is 15 used it should preferably have a high cohesive strength so that it does not leave a residue when stripped from the pipe, or alternatively, if any residue is left on the pipe it should be such as to aid, rather than hamper, fusion.

The impact strength of the plastics pipe of the invention is preferably comparable with the impact resistance of a plastics pipe of the same dimensions 0 formed entirely from the plastics material of the inner

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10 core. Preferably the impact strength is at least 150Nm 0e when measured at OOC in a H50 Impact Test in accordance Swith ENI411, the entire disclosure of which is *SOO incorporated herein by reference. Excellent impact go o:strength is obtained using a plastics pipe comprising an inner core of polyethylene and an outer protective layer of a propylene copolymer.

go As previously mentioned, the plastics pipe of the present invention is preferably produced by co-extrusion, for example, from an extruder die connected to a twin barrel, twin screw extruder, or connected to two *e individual extruders, the die being fed with separate streams of molten plastics material. Preferably the melt 6 00 streams are brought together in the die, that is to say, the materials are brought together in the pressure area of the die and exit as a single extrudate. Alternatively, the die may be provided with concentric die outlets fed 16 with the separate streams of molten plastics material which are to form the inner core and the outer protective layer. In this case, the extrudates, on leaving the extruder die outlets, can be brought into contact with each other in a sizing die which simultaneously adjusts the outer diameter of the pipe. The extrudates are preferably brought into contact with each other at a point close to the extruder die outlet, in order to avoid any substantial oxidation of the surface of the inner 10 core. For example, with extrudates travelling at a speed of 1 metre per minute, the sizing die is preferably not *o further than 15cm from the extruder die outlet.

Whilst it may in certain circumstances be possible to pass the inner core extrudate through an individual sizing die before applying the outer protective layer this is not preferred because it has been found that the sizing die creates an outer surface layer on the inner core which is more susceptible to degradation, possibly due to induced shear orientation or shear nucleation in the outer surface which contacts the sizing die.

The temperature of the extrudates will depend upon the nature of the polymeric material, but, for example, using a polyethylene inner core and a propylene copolymer outer protective layer the temperature of the extrudate at the die outlet is preferably from 180 to 220°C. Preferably the temperature of the extrudates when they are brought together is at least 150°C, most preferably from 180 to 220 0

C.

The method of the invention can consistently produce an inner core and an outer protective layer having an adhesion within the preferred range, and by an appropriate choice of the material of the- outer protective layer it can be arranged that the outer protective layer can be peeled from the inner core 10 without leaving any significant residue on-the surface of the inner core. If necessary, the physical properties of the outer protective layer can be adjusted by the addition of more or less fillers and other additives. A preferred polymeric material for the outer protective 15 layer comprises, for example, propylene co-polymer comprising from 1 to 6% by weight, based upon the total weight of the composition, of a filler such as titanium dioxide. Preferably the outer protective layer has a tensile strength of from 15 to In general we have found that it is preferable not to use low molecular weight additives such as, for example, processing aids, in the method of the invention.

However stearates, for example, calcium stearate, have been found to be effective as processing aids without substantially adversely affecting the adhesion between the inner core and the protective layer.

18 Antioxidants can be included in the formulation of the protective layer as required. If appropriate, they can be omitted from the formulation of the inner core provided that suitable quantities are included in the outer protective layer.

The invention is illustrated by the following Example:

EXAMPLE

A number of formulations for the inner core and the outer protective layer were made up with compositions as set out in Table 1. The formulations were extruded using "01.0 15 a main extruder and a smaller additional extruder provided with concentric die feed. The melt streams were e.00 merged prior to exit from the hot dies. In one 0* 0 experiment,the extrudate, having a diameter of 80mm, was passed through a sizing die of diameter 66.8mm to give a dual layer pipe of external diameter 63.8mm, outer protective layer thickness 0.3mm and inner core thickness 6.2mm. In another experiment, a dual layer pipe of external diameter was extruded.

Samples of the 40mm OD pipes were subjected to the semi-tensile peel test previously described, and the results are given in Table 2. Table 3 shows similar results on samples which could not be peeled at room 19 temperature and therefore were heat treated in an oven before being subjected to the peel test. These examples are included for comparison purposes.

Samples of the tubes were also subjected to ageing according to the weather durability test of ISO 4892. The test method is given below. The properties of the pipes were found to be substantially unaffected after being subjected to the ageing test showing that the natural 1 0 inner core was effectively protected by the stabiliser gee C package included in the outer protective layer. The 000 ego results are given in Table 4.

00*0 906.

e e oooo 0:66 Further samples of the pipes were subjected to impact testing in accordance with ENI411. The impact tests were performed at OOC and -20 0 C. A pipe was-considered to have passed if it had a measured impact eeo strength of greater than 150Nm.

oooo 20 It was found that pipes with a polypropylene copolymer outer layer passed all the impact tests and had approximately the same behaviour as uncoated polyethylene oe C S* pipes of the same diameter.

Pipes with a polypropylene homopolymer outer layer had reduced impact strength of 33Nm at OOC compared with more than 150 Nm for an equivalent uncoated polyethylene pipe and were considered to have failed.

A 50/50 polypropylene homopolymer and co-polymer mixture was also tested. This pipe passed the impact test at 0°C with an impact strength greater than 150Nm but the results at -20°C were the same as for the polypropylene homopolymer.

10 Failure in the impact test was due-'to a type of rupture in which a crack originated in the outer layer and propagated to the pipe. It is believed that those samples which failed the impact test did so because the adhesion between the outer layer and the inner core was too great.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, 21 except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose,. unless S: expressly stated otherwise. Thus, unless expressly 'stated otherwise, each feature disclosed is one example 10 only of a generic series 'of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. This invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

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5O o. 0. oo oo• o• o• TABLE 1 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 Material 930 930 930 2600 2600 2600 2600 2600 2600 2600 2600 2467b1 2467b1 2467b1 2467b1 2410 Pipe Material 1 2 3 1 1 1 1 1 1 1 1 1 1 1 3 1 Skin Master- 4 4 4 4 5 5 4 4 4 4 4 4 4 NONE NONE NONE batch Loading 10 10 10 10 10 15 15 15 10 0 Material Two different types of pigmented master batches were used, at two concentrations.

1 Polypropylene SA 4020 G manufactured by Neste 2 Polypropylene SA 4020 G/VA4020 E 50/50 mixture 3 Polypropylene VA 4020 E 4 84571-2009 from Wilson colour tio based 84671-2100 from Wilson Colour titanate based 930 Polyethylene Statoil 930 (natural) 2600 Polyethylene Neste 2600 (natural) 2467b1 Polyethylene Neste N2410 o: *s so** Master Batches 84567 1-2009 84671-2 100 2 Irganox 1010 Chiasorb 944 Titanate PP(mfi 5.0) 0 carrier approx carrier TAB3LE 2 r P~ei Pred. Surface Layer

I

Notch through N/mm Thick'. width El0l 0,34710,03 1,25 0,35 9,08 1,16r 0,41 9,75 1,383 2. Notch 3. F'orce wih0, 3 to break irxr. left N/rn 48 5,23- 5,36 5,6IE 7,36.

Rej narkCohesiTe 'Tensile (Hpa) 1. 3. Camne off well, big tension.- 2. Came off -ell at notch through the 6.05 115.38 -1.00 14.00 in, 00 E1i02 0,31 9,80 0,40 9, 94 ~~4_4n nA 1 9 8 2,-5 2, 51 2,24 torn at the side of the notch with 0,3rtm left.

5,39~ L.Came_ fw~1 i tension.

5,39Q 2. Camne off well, big 6 1 2 e n s i o n 32. Came off well, bigc 1,30 1,08 1,71 2.42173 0.88 18.50 20-40

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El103 0,30 0,35 0, 44 0,57 0,51 0,39 9,70 10,00 9,50 2,52 1,40 2,0G5 3,91 5,88 4,73 7, 1B 4, 22 5,11 1,19 6, 4-7* tension.

1. Camne off well, big tension.

2. Break while tearing notch with 0, 3ra left.

3. Came off well, big tension.

1. Came off -ell, big tension.

2. ~aine off well, big tension.

3. Carne off well, big 4. 41 no result 19.25 2.31237 9,75 2,36 9,r7 1 0, 5i 9,45 1,00 11, 84* 12, 20* 10,10* 8.031207 .85 3- 92 25-90 C C C C. **e C C C C C C C

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tension.

the breakage- result hona the b of the esl t,1 notc tit 0 m -et 56 2 3.a Ca.e Ca~ well torn H adhesion ofth 0,60~~noc with 0,m left. 15.6.3 Cae of ihu 0,26 9,62 0,4 3,63 64,82 nthough0 th surace Or6 ,00 3,17 13,0'9 1. 3. Campe off without Noaesn ~any load at notch 0,65 ,4 3,63 13,51O through the sraeC 1.009,30 075 87 .0 layer. i en~n 3. cm of wihot telodhsio *,01 Cohsiv strngt is obaiedatchl N o t c h 3 ,t h 0 35 t h r u g l e f t (1m8)( o c h t r u g )8Nm n 0 3 x m Coesie strength is obtained as follows: Force to break (N/mrn) thnickness N~ 0 0%V *e S

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TABLE 3 Prod. No. Surface Layer 1. Notch 2. Notch with 3. Force to Remark through N/mm 0.3 mm left break N/mm thickn. mm width mm N/mm E 97 0.25 9.75 2.20 2,87 5.12* 1. Came off well, the tearing kept on to the edge of the test piece.

0.35 10.00 2.40 3.40 6,58 2. Came off well, the tearing kept on to the edge of the test piece.

lh 0.25 9.40 2.39 4.36 4.65* 3. Came off well, big tension.

E 97 0.20 9.40 2.37 2.92 5.87* 1. Came off well, the tearing kept on to the edge of the test piece.

0.25 9.55 2.25 2.93 5.03* 2. Came off well. big tension.

lh 0.30 9.65 2.11 3.00 6.79* 3. Came off well. the tearing kept on to the edge of the test piece.

E 97 0.30 9.80 1.56 3.91 6.36* 1. Came off well, the tearing kept on to the edge of the test piece.

0.25 9.65 2.33 5.88 6.53* 2. Came off well, the tearing kept on to the edge of the test piece.

lh 0.25 9.50 2.15 4,73 4.89* 3. Came off well. big tension.

E 100 0.40 9.55 1.62 4.50 8,64* 1. Came off well. big tension.

0.43 9.75 1.23 2.61 7.67* 2. Came off well, the tearing kept on to the edge of the test piece.

S03. Came off well, big tension. lh 0.30 9.75 1.74 2.71 5.74* E 100 0.30 9.60 1.82 2.97 5.52* 1. Came off well. big tension.

0.40 9,75 2.26 4.11 8,07* 2. Came off well, big tension.

lh 0.25 9.55 2.72 3,56 6.70* 3. Came off well, big tension.

100 0.35 9.90 1.96 3.24 6.97* 1. Came off well, big tension.

0.30 9.60 2.76 4.37 7.50* 2. Came off well. the:tearing kept on to the edge of the test piece.

lh 0.30 9.50 2.00 3.16 5.63. Came off well. big tension.

lh 0.30 9.50 2.00 3.16 5.63* Maximum force at the tensile test, but there was no break.

AGEING OF POLYETHYLENE/POLYPROPYLENE PIPES Weather-durability Testing According to ISO 4892 Test Object 61 pieces of polyethene pipes with a length of 465mm and a diameter of a.

a 9 pieces, yellow tubes marked 9"- 9"- 9"- 8"- 8 pieces, white"- 9 pieces, black/orange, E100 E102 E103 E104 E106 E107 E108 Test Performance The polyethene tubes were exposed in an Atlas Type Weather-o-meter® according to the rain cycle 102/18.

The temperature on a black standard thermometer was 63 3 C and the relative humidity 50 The light source was filtrated to reach a lower limit of 290nm.

The irradiance was 61±6W/m 2 in the bandpass 280 400nm.

28 The exposure was completed after 250 hours, which corresponds to a 3 months of light dose in the UV visible wavelength interval (280 800nm) for London, England.

e C C

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C S C C. *C C CCC S.C CC C C. C* C *CC C C C C C C. TABLE 4 TENSILE STRENGTH SKIN/TESTING INFLUENCE OF UV AGEING UV aged Av tensile str (rnpa) 29,53 26,98 27,82 30,74 28,32 Variation ()1,20 1,30 1,60 2,60 0,80 Elongation ()average 413 368 507 173 120 Elong min 400 480 20 0 Elong max 420 580 540 100 280 Ref Av tensile str (mpa) 27,26 __26,33 32,17 28,24 28,99 ________Variation ()3,80 0,40 5,80 ______Elongation ()average 706 540 153 507 453 min 700 540 200 500 140 max 720 540 400 5920 640 TENSILE STRENGTH SKIN/TESTING INFLUENCE OF UV AGEING UV aged AV tensile str (mpa) 24,40 [24,49124,61-125,24 26,10 _______Variation M% 10,90 10,50 0,70 7,40__ _____JElongation average 1673 1650 1673 1673 680 4* .4 4 4*4 4 .44 444 4 4 44 44 4 4* 44 4 4 4 4 4 4 4 4 4 4* _Elong min 640 1 J 640 1 660 1 640 1 1660 max j720 1 680 1 680 1700 -1720 Ref AV tensile str(mpa) 24,35 24,45 24,79 25,17 25,37 ______Variation ()1,10 1,80 0,50 0,70 0,50 ______Elongation ()average 673 690 667 685 645 min 640 640 640 660 600 max 740 1740 720 1700-- 680

Claims

2. A plastics pipe in accordance with claim 1, in which: the adhesion between the inner core and the outer protective layer is such that, in a B50 impact test in accordance with EN1411, at DOC, if the outer core is ruptured and a crack formed, that crack is arrested at the outer layer/innher core interface.
3. A plastics pipe in accordance with either claim 1 or claim 2, in which: 2S the plastics pipe has an impact resistance greater than 150Nm in a H50 impact test in accordance with EN1411 measured at 0OC, and wherein the cohesive strength of the outer protective layer, excluding any lines of weakness, at least at the ends of the pipe, is greater than the peel strength of the adhesive bond between the outer protective layer and the inner core. 01/05 '02 WED 14:28 [TX/RX NO 76361 01/05 '02 WED 14:34 FAX 61 2 9957 3582 GRIFFITH HACK I010 32
4. A plastics pipe according to any one of the preceding claims, in which the adhesion between the outer protetive layer and the inner core is in the range of from 0.2 to 5 Nm width e measured by a semi-tensile peel test as N/mm width, measured by hereinbefore described. A plastics pipe according to any of the preceding claims, in which the inner core comprises polyethylene
6. A plastics pipe according to any of the preceding S: claims, in which the outer protective layer comprises a propylene homo or co-polymer. 0%*
7. A plastics pipe according to any of the preceding claims, in which the inner core is substantially free from antioxidants and/or UV stabilisers. S8 A plastics pipe according to any of the preceding claims, in which the outer protective layer comprises titanium dioxide filler. 9 A plastics pipe according to any of the preceding claims, in which the outer protective layer has a thickness in the range of from 0.3 to
10. A plastics pipe according to any of the preceding claims, in which the ratio of the external diameter of the pipe to the thickness of the protective layer is in the range of 150 to 400. the preceding
11. A plastics pipe according to any of the preceding claims, in which the cohesive strength of the outer 01/05 '02 WED 14:28 [TX/RX NO 7636] 01/05 '02 WED 14:34 FAX 61 2 9957 3582 GRIFFITH HACK 1o011 33 protective layer as measured by a semi-tensile peel test is in the range of from 5MPa to lOMPa-
12. A plastics pipe according to any of the preceding claims, in which the outer protective layer has a tensile strength of from 15MPa to
13. A plastics pipe according to any of the preceding claims substantially as described in the Example.
14. A plastics pipe substantially as hereinbefore described.
15. A method for the production of a plastics pipe **coprising an inner core and an outer protective layer bonded thereto which comprises co-extruding molten plastics materials forming the inner core and the outer protective layer from an extruder die, bringing the molten plastics materials together whilst still hot and allowing ~them to cool, such that, on cooling, the outer protective 20 layer can be peeled from the inner core, at least at the ends of the pipe, to reveal an inner core surface suitable for electrofusion welding, wherein the dimensions of the pipe and the protective layer are such that the ratio of the external diameter of the pipe to the thickness of the protective layer is at least 70, preferably at least 100, and the cohesive strength of the outer protective layer, excluding any lines of weakness, at least at the ends of the pipe is greater than the peel strength of the adhesive bond between the outer protective layer and the inner core; and the strength of the adhesive bond between the outer protective layer and the inner core is within the range of from 0.2 N/mm to 2.52 N/mm 01/05 '02 WED 14:28 [TX/RX NO 7636] 01/05 '02 WED 14:34 FAX 61 2 9957 3582 GRIFFITH HACK [012 34 16 A process according to Claim 15, in which the inner core comprises polyethylene and the outer protective layer comprises a propylene homo or co-polymer.
17. A process according to Claim 15 or 16, in which the molten plastics materials are brought into contact with each other in the pressure area of an extruder die.
18. A process according to any of Claims 15 to 17, in which the inner core and the outer protective layer are .brought together at a temperature of from 150 0 C to 220'C.
19. A process according to any of Claims 15 to 18 substantially as described in the example. A process according to any of Claims 15 to 19 substantially as hereinbefore described. 9 20 21. A method of making a joint in a plastics pipe according to any of Claims 1 to 14, or of joining two plastics pipes according to any of Claims 1 to 14, which comprises peeling the outer protective layer from the region or regions of the pipe to be joined to reveal an inner core surface for electrofusion welding, installing an electrofusion coupler over the bared region or regions of the pipe or pipes and activating the electrofusion coupler to fuse the region or regions of the pipe or pipes thereto.
22. An electrofusion joint made in accordance with a method according to claim 21. 01/05 '02 WED 14:28 [TX/RX NO 7636] 01/05 '02 WED 14:35 FAX 61 2 9957 3582 GRIFFITH HACK 1 013 35
23. A plastics pipe which comprises an inner core and an outer protective layer in which the outer protective layer has a thickness greater than O.lmm, the dimensions of the pipe and the outer protective layer are such that the ratio of the external diameter of the pipe to the thickness of the outer layer is at least preferably at least 100, the cohesive strength of the outer protective layer, excluding any lines of weakness, at least at the ends of the pipe is greater than the strength of the adhesive bond between the outer protective layer and the inner core, and the adhesion between the outer protective layer and the inner core is in the range of from 0.2 to 2.52 N/mm width, measured by a semi-tensile peel test as hereinbefore described.
24. A plastic pipe according to claim 2, wherein the impact test is carried out at a temperature of -202C. A plastic pipe according to claim 3, wherein the impact test is carried out at 01/05 '02 WED 14:28 [TX/RX NO 7636]