WO2001083613A2

WO2001083613A2 - Weldable articles made of cross-linked polyolefins

Info

Publication number: WO2001083613A2
Application number: PCT/IL2001/000380
Authority: WO
Inventors: Yosef Bar
Original assignee: Golan Plastic Products
Priority date: 2000-04-28
Filing date: 2001-04-25
Publication date: 2001-11-08
Also published as: IL142083A0; EP1240001A2; AU2001252523A1; WO2001083613A3

Abstract

Disclosed are polymeric articles with welding-aimed portions, said portions designed to allow cross-linking across the welding surface when two such articles are welded together. The welding-aimed portions contain silane-grafted polyolefin with no cross-linking catalyst. The other portions of the article may or may not differ in composition from the welding-aimed portions.

Description

WELD ABLE ARTICLES MADE OF CROSS-LINKED POLYOLEFINS

FIELD OF THE INVENTION

This invention relates to polymeric articles with welding-aimed portion.

BACKGROUND OF THE INVENTION

Cross-linked polyolefins are polymers in which the polyolefin chains are interconnected, so that the basic molecular structure of the material is a net-like molecule rather than a chain. Some examples of polyolefins that undergo cross-linking are polyethylene, polypropylene, polyethylvinylacetate (EVA) and ethylene-propylene copolymer. Cross-linked polyethylene is usually referred to as PEX. The cross-linking is achieved by one of three common methods:

Cross-linking by peroxides - in this method the polyolefin is mixed with a peroxide compound that cross-links the polyolefin molecules when the polymeric mixture is exposed to heat. Polyethylene cross-linked by peroxide is usually referred to as PEX-a. The raw material that is conventionally used for fabricating polyolefin cross-linked by peroxide will be referred hereinafter as RM-a.

Cross-linking by silane - in this method the polyolefin is grafted with a silane, to give a so called 'silane grafted polyolefin', and blended with a suitable catalyst. The silane cross-links the polyolefin molecules when exposed to moisture. In the absence of a catalyst the process is extremely slow and may take weeks or months, depending on the degree of cross-linking required and the amount of moisture. A polymer that is cross-linked in this manner is sometimes referred to as water-curable polymer. Polyethylene cross-linked by silane is usually referred to as PEX-b. The raw material that is conventionally used for fabricating water curable polyolefin will be referred hereinafter as RM-b. Cross-linking by electron beam - in this method a polyolefin article is bombarded by electrons, and thus its molecules cross-link. Polyethylene that is cross-linked by this method is usually referred to as PEX-c. Raw material for preparing polyolefins that are crosss-linked by radiation will be referred hereinafter as RM-c. RM-c typically contains some additives that are usually referred to as radiation-cross-linking coagents.

Cross-linked polyolefins are advantageous over similar polyolefins, which are not cross-linked, in their durability under pressure and in their chemical, mechanical and thermal stability and are most useful for water pipes, gas pipes and other pipes used in the industry. In many of these applications it is particularly advantageous to be able to weld the articles made of cross-linked polyolefins either to each other or to other components in a system.

However, it is known in the art that cross-linked polyolefins do not weld satisfactorily. It is also known that it is possible to weld together two articles made of polyethylene (that is not cross-linked) and to cross-link them after welding, with satisfactory results. Satisfactory welding results have also been obtained with polyethylene with some degree of cross-linking (up to 30%) before welding.

One known method to weld cross-linked polyethylene was described in KWD 26 (1005) of September 17, 1999. This technology is based on using temperature of above 350°C, which breaks the cross-links near the welding surface, to form a thermoplastic that is reported to weld satisfactorily.

DE 3628958, US 4868022, and DE3627911 describe a variety of polymeric articles that are mainly made of cross-linked polyethylene (PEX) and can be welded in specific regions made of non-cross-linked polyethylene (hereinafter PE). These regions may contain peroxides.

JP 91019878 describes a rod made of water-curable polyolefin containing no cross-linking catalyst. The rod may be heated and its melt may be used to join together two articles made of cross-linked polyolefins. SUMMARY OF THE INVENTION

The invention provides polymeric articles having integral portions designed to allow that welding of two such articles will result in cross-linking across the welding surface. These portions are characterized by containing Silane Grafted Polyolefin with No Cross-linking catalyst, (hereinafter SGPNC) and referred to hereinafter as welding-aimed portions. The other portions of the article may or may not differ in composition from the welding-aimed portions, and are referred hereinafter as main portions. Thus, the invention provides, according to one of its aspects, a polymeric article designed for use as a component in a system or structure, the article having at least a portion comprising silane-grafted cross-linkable polyolefin that is free from cross-linking catalyst, said portion being integral with the article.

A welding-aimed portion may exhibit cross-linking to some degree, but should always contain some polyolefin that may undergo further cross-linking.

A substance is to be considered free from cross-linking catalyst if it contains 0.5% of a catalyst, or less.

Typically, a welding-aimed portion will be formulated to include SGPNC with RM-a and peroxide, if the main portion is cross-linked by peroxide; SGPNC alone, if the main portion is cross-linked by silane; or SGPNC with RM-c and cross-linking co-agent, if the main portion is cross-linked by electron bombardment. However, the RM-a and the RM-c may be omitted from the above formulations.

The degree of cross-linking in the welding-aimed portion may be restricted by the welding method, by which the article is to be welded. If the article is to be welded under conditions similar to those at which non-cross-linked articles are usually welded, the cross-linking degree at the welding-aimed portion is restricted to less than 50%, preferably less than 30%. Higher degrees of cross-linking might prevent the article from being efficiently welded under such conditions, as explained in the background section. If the article is to be welded under conditions that were specifically designed for welding of cross-linked polyolefin, the above restriction does not necessarily apply. After the article is manufactured, its welding-aimed portions will slowly cross-link to give a fully cross-linked welded article. This slow cross-linking requires moisture or presence of water, but no further deliberate action, and may be accelerated to happen within a week or two in the presence of hot water. When it happens after welding it provides for cross-linking across the welding surface, however, when it happens before welding it restricts the shelf-life of the article. Therefore, it is preferable to manufacture the article according to the invention with no cross-linking catalyst at all. In order to check if a portion is integral with an article, the article should be first fully cross-linked. This may be ensured by immersing the article in hot water for about two weeks. The fully cross-linked article should then behave as a single body in any physical test. For example, if a portion is integral with an article, the probability that the article tears under drawing force or burst under pressure at the interface between the article and the portion should not exceed the probability that the article will tear or burst elsewhere. Another test that may be applied is that if the fully cross-linked article is heated to above its melting point the article and the portion remain intact.

Non-limiting examples of polymeric articles according to the invention are pipes, sheets and couplers.

Non-limiting examples of polyolefins to be used according to the invention are polyethylene (PE), polypropylene (PP), ethylene/propylene copolymer, EVA, and mixtures thereof. Typically, the polyolefin is selected from polyethylene, polypropylene and mixtures thereof, and most typically it is polyethylene. In order to obtain articles with integral welding-aimed portions, it is advisable to use in the main portion and in the welding-aimed portion polyolefins that are compatible with each other, non-limiting example of those are PE and PEX, PE and PP, etc.

A cross-linking catalyst is of a kind known in the art for the catalysis of cross-linking of silane-grafted polymers in the presence of moisture or water. In some embodiments, the polymeric article of the invention may further comprise at least one main portion comprising a cross-linked polyolefin. In such cases the welding-aimed portion of the article typically comprises a mixture of SGPNC and said cross-linked polyolefin, to ensure that the welding-aimed portion is integral with the article. In such embodiments, the main portion is turning into the welding-aimed portion at a narrow bridging region, wherein the SGPNC concentration increases and the cross-linked polyolefin concentration decreases from the main portion towards the end of the welding-aimed portion. The polymeric article of the invention may be welded to another article, which is made from a non-cross-linked polymer compatible therewith, for instance: PEX and PE. However, welding together an article according to the invention to an article, which is cross-linked, is preferable. Welding together an article according to the invention to another article according to the invention is most preferable.

According to one embodiment of the present invention, the outer surface of at least the welding-aimed portion of a polymeric article is coated, for example, by extrusion, with a hydrophobic material. The hydrophobic material protects the welding-aimed portion from ambient humidity and thus lengthens the article shelf-life. The coating may be compatible with SGPNC, but non-compatible coatings may be preferable, since they may be peeled off easily. An article according to the invention may be welded by any welding process known in the art, for example: butt welding, socket welding, branch-off saddles welding, electro-fusion welding, etc. The exact welding parameters may differ according to the specific embodiment of the present invention.

According to another aspect of the present invention there are provided welding methods that make use of the polymeric articles of the invention.

In particular the invention provides a method for welding together polymeric articles, at least one of the articles being according to the invention, said method comprising the steps of:

(a) providing a first polymeric article according to the invention; (b) providing a second polymeric article; and (c) welding a welding aimed portion of said first article to a portion of said second article..

Preferably the polymeric article provided in step (b) is made of cross-linked polyolefin. Even more preferably the polymeric article provided in step (b) is an article according to the invention and it is welded in a welding-aimed portion thereof.

The welding in step (c) may be under conditions at which non-cross-linked polyolefins are conventionally welded, or under conditions specifically designed for welding of fully cross-linked polyolefins, such as high temperature welding that breaks the cross-linking near the welding surface.

Another aspect of the present invention is a method for producing cross-linked welded polymeric articles, having cross-linking across the welding surface, said process comprising:

(a)providing at least two polymeric articles according to the invention; (b)welding said two polymeric articles at welding-aimed portions thereof; and (c) allowing the SGPNC to cross-link.

Step (c) may be especially efficient if the SGPNC is subjected to water, preferably hot water. A similar method may be used to weld together two welding-aimed portions of a single article, two parts of a single welding-aimed portion of an article, etc.

The invention also provides for the welded article produced by any one of the above methods. Such welded articles may be characterized as having a welding surface and at least at one side of said welding surface a SGPNC-containing portion, integral with the rest of the article that lies at least at one side of the welding surface. Whether all the silane groups near the welding surface of a welded article are linked to each other or not is a matter that depends on the period that passed since the fabrication of the article according to the invention that was welded to give the welded article, and on its exposure to water during this period. Welded articles that were fabricated by welding together two articles according to the present invention are characterized by having near the welding surface silane grafted polyolefin and no cross-linking catalyst, and containing cross-linking across the welding surface, at least after being immersed in hot water for two weeks.

The degree of cross-linking across the welding surface depends on the time that passed since the article was welded. The longer this time is, the more cross-linking is expected to be found, until the SGPNC at the two sides of the welding surface is fully cross-linked. Immersing the article for two weeks in hot water may fully cross-link the SGPNC.

The invention also provides for methods for extruding polymeric articles according to the invention. One such method comprises the following steps: a) loading the extruder with conventional raw material for cross-linked polyolefin; b) extruding the main portion of the polymeric article using the raw material loaded at step a); c) loading the extruder with SGPNC; d) extruding a welding-aimed portion of the polymeric article with the material loaded at step c); and e) cross-linking the conventional raw material.

According to one embodiment, the SGPNC used in step c) is mixed with a conventional raw material for cross-linked polyolefin and a proper additive. The proper additive is peroxide if the raw material of step a) is RM-a, and radiation-cross-linking coagents in case the raw material of step a) is RM-c. In case the raw of step a) is RM-b no additive is needed.

According to the method of the invention it is possible to extrude first the welding-aimed portion and then the main portion or vice versa.

If the article produced according to the invention is to be welded under conditions similar to those, under which non-cross-linked polyolefins are usually welded, the welding-aimed portion must have low degree of cross-linking. Therefore, such an article should have in its welding-aimed portion only low concentration of peroxide (if any), and in case electron bombardment is used in step e), at least partial masking. Low degree of cross-linking in this context is a cross-linking degree lower than 50%, preferably lower than 30%. The existence of some cross-linking in the welding-aimed portion of the article is advantageous, since it allows cross-linking over the region bridging the welding-aimed portion and the main portion.

Such constraints on the amount of cross-linking in the welding-aimed portion may become unnecessary, if the article of the invention is to be welded by a welding procedure specifically designed to weld cross-linked polyolefins, such as high temperature technology that includes breaking the cross-linking near the welding surface.

Naturally, an article according to the present invention is not necessarily produced by extrusion. Other methods, such as injection, may also be applied for producing an article according to the invention.

One method that may be of particular interest for producing pipes according to the invention comprises the following steps:

(a) providing a pipe made of PEX-a and possibly containing free peroxide;

(b) providing a pipe portion made of SGPNC and containing free peroxide; (c) butt welding the pipe provided in step (a) to the pipe portion provided in step (b) to obtain a welded article; and (d) cross-linking the free peroxide in the welded article obtained in step (c) to obtain a pipe according to the present invention. Free peroxide in this context is a peroxide that is capable of undergoing a cross-linking reaction.

As may be appreciated, similar methods may be applied to obtain articles of various shapes, having main portions of various cross-linked and non-cross-linked polyolefins. BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, some specific embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates two pipes according to the present invention that are to be butt-welded.

Fig. 2 schematically illustrates a welded article according to the present invention.

Fig. 3A schematically illustrates a sheet in accordance with the invention, Figs. 3B illustrates how the sheet of Fig. 3 A may be rolled and welded into a pipe, and Fig. 3C illustrates a PEX pipe reinforced by the pipe of Fig. 3B.

Fig. 4 schematically illustrates an electro-fusion connector connecting two pipes.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In the following, only polyethylene (either cross-linked or not) is referred to, but it is clear to the artisan that any other polyolefin may replace it to obtain similar results.

Figure 1 schematically shows two pipes (1 and 1') that are to be butt- welded at their edges 3 and 3'. The pipes have main portions 5 and 5' and welding-aimed portions 7 and 7' that are integrally connected to the main portions along the bridging regions 9 and 9'.

The article obtained by welding the pipes of Fig 1 is illustrated in Figure 2, wherein portions of the welded article are numbered with a refernce numeral greater by 20 than they had in Fig. 1 (before welding). The welded article 20 has a welding surface 23 connecting the two sub-articles 21 and 21', each lying on a separate side of the welding surface, and each of them having an integral SGPNC-containing portion (27 and 27' respectively). Since both articles 1 and 1 ' are according to the invention, the welded article 20 has cross-linking across the welding surface.

Example 1

According to one embodiment the pipes 1 and 1' are made of PEX-b and their welding-aimed portions 7 and 7' comprise SGPNC. The welding-aimed portions may be also described as being made of PEX-b with less cross-linking than exists in the main portions 5 and 5' and containing no cross-linking catalyst.

The pipes 1 and 1 ' according to this embodiment are to be welded to each other via the welding-aimed portions 7 and 7' under conditions that are conventionally used to weld non-cross-linked polyethylene.

During welding, the SGPNC in the welding-aimed portions 7 and 7' melts and joins together the two pipes 1 and 1'.

After welding the SGPNC cross-links, due to exposure to moisture, to give PEX-b, characterized in higher cross-linking degree than it had before.. The resulting welded article 20 has a welding surface 23. On one side of the welding surface 23 the article 20 has a portion 27 that is integral with the rest of the article that lies at the same side of the welding surface and contains SGPNC. On the other side of the welding surface 23 the article 20 has a portion 27' that is integral with the rest of the article (25', 27' and 29') that lies at the same side of the welding surface and contains SGPNC.

After post-welding cross-linking is completed the welded surface 20 is made of PEX-b in its entirety, and in particular has cross-linking across the welding surface 23 and the bridging regions 29 and 29'. The region enclosed between the connecting surfaces 29 and 29' may have lower degree of cross-linking than the other regions, depending on the time that passed from the manufacture of the original pipes 1 and 1' and their exposure to water during this time. The fact that all the parts of the welded article 20 are cross-linked to each other may be especially advantageous when there may be a need to heat the pipe to such a degree that parts that are not cross-linked to each other will be departed. Such a need may arise, for example, if the welded article 20 is used for relining.

As defined above, articles that are weldable in all their parts are also provided according to the present invention. Such articles may have the disadvantage of having a lesser amount of cross-linking in comparison to the articles described above, however, they may also have advantages. For example, they may be cut anywhere along their length and be welded at the cut.

Example 2 According to another embodiment of the invention the main portions 5 and

5' of the pipes 1 and 1' are made of PEX-a and their welding-aimed portions 7 and 7' comprise PEX-a, at least part of which is silane grafted.

Immediately after the pipes are produced, they exhibit a cross-linking degree, which decreases towards the end of the pipe. In addition, the concentration of silane groupsincreases towards the end of the pipe.

The welding-aimed portions of the pipes according to this embodiment of the present invention may exhibit some degree of cross-linking, as long as it does not exceed the value, above which welding is practically impossible. This exact value is to be determined according to the strength of welding that is necessary, and is typically 30% or lower, although it may sometimes be as high as 50%.

Preparation of Such a Welded Article

Two PEX-a pipes of a 50mm diameter and 7mm thickness were extruded from the following blends:

Main portion - from a blend made of RM-a (Lupolene™ 5261Z by BASF) and 0.3% DTBP (ditertbutylperoxide); and

Welding-aimed portions - from a blend of 40% Lupolene™ 5261Z, 60% SGPNC, and 0.08% DTBP. Immediately after extrusion, the welding-aimed portions exhibited a cross-linking degree of 23%, while the main portion exhibited a cross-linking degree of 80%.

The two pipes were butt- welded by a conventional RTMO 160 butt welding equipment, manufactured by RITMO, Padova, Italy, applying 30 sec preliminary heating, 70 seconds heating with no pressure and 20 min cooling. These conditions are usually applied for the welding of non-cross-linked pipes.

Example 3 Another embodiment of the invention is similar to the previous one in that the main portions 5 and 5' of the pipes 1 and 1' are made of PEX-a and their welding-aimed portions 7 and 7' comprise both PEX-a and SGPNC. However, according to this embodiment the welding-aimed portion is made of SGPNC with peroxide. The peroxide is enough to have in the main portion and in the welding-aimed portion the same degree of cross-linking. This embodiment, as not as the previously described one, is fully cross-linked even before welding.

In this embodiment, the welding is to be carried out using a technology specifically designed for welding of fully cross-linked polyolefins. With time the SGPNC cross-links to yield PEX-b and creates cross-linking across the welding surface 23, just like in the embodiment described above. If the applied welding technology includes welding at a temperature that breaks the cross-linking near the welding surface 23 and in its vicinity, the only source for cross-linking at the vicinity of the welding surface is the SGPNC. An article according to this embodiment does not suffer from the disadvantage mentioned above (see Example 1), of having a low pre-welding degree of cross-linking. The welded article 20 will have main portions 25 and 25' and welding-aimed portions 27 and 27'. After post-welding cross-linking occurs, the main portions 25 and 25' will be made of PEX-a, and the welding-aimed portions 27 and 27' will be made of a mixture of PEX-a and PEX-b. If welding at a temperature that breaks the cross-linking near the welding surface was used, the regions at the vicinity of the welding surface 23 will contain a mixture of PEX-b (that was cross-linked after the welding) and broken PEX-a.

Pipes according to this embodiment and the one illustrated in Example 2 may be made of SGPNC and peroxide in all their parts. In such cases, the pipes may be cut anywhere and welded at the cut.

Example 4

According to yet another embodiment of the present invention the main portions 5 and 5' of the pipes 1 and 1' are made of PEX-c and their welding-aimed portions 7 and 7' comprise both PEX-c and SGPNC. Such welding-aimed portions may be produced by first preparing a pipe made of RM-c with a welding-aimed portion made of a mixture of RM-c and SGPNC and than bombarding it with electrons while at least that end of the welding-aimed portion that is to include the welding surface is shielded from the bombardment, in order to allow the low cross-linking degree needed when the article is to be welded under conditions that are usually used to weld non-cross-linked articles. The non-shielded parts, which include the bridging regions 9 and 9', are cross-linked by the electron bombardment. Therefore, adding to the SGPNC radiation cross-linking coagents may be advisable.

Example 5

According to another embodiment, intended for welding under conditions specifically designed for the welding of fully cross-linked polyoethylene, the shielding of the welding-portion end is not necessary.

Example 6

Fig. 3A shows a sheet 30 according to the invention, comprising a main portion 31, and welding-aimed portions 32 and 34. Fig. 3B shows the sheet 30 with the welding-aimed portions 32 and 34 brought to overlap with each other, so they can be welded along the overlap to form a pipe 30' having a welding surface 36. The main portion 31 is made of a reinforcing material that may be saturated (or combined in another manner) with SGPNC, which is possibly mixed with other cross-linkable polyolefin. If the main portion 31 is indeed combined with SGPNC-containing mixture, the portions 32 and 34 may be omitted, and the whole sheet 30 may be conceived as one large welding-aimed portion. After the SGPNC goes post-welding cross-linking, the pipe 30' has cross-linking across the welding surface 36, and thus becomes a reinforced pipe which is fully cross-linked. The reinforcing material may be a woven or knitted fabric, a scrim, a plaited fabric, a nonwoven, etc. After welding, the pipe 30' may be further coated (by coextrusion) on its outer surface, inner surface, or both. Figure 3C shows such further coatings 38 and 40 and their interfaces 42 and 44 with the pipe 30'. The coating layers 38 and/or 40 preferably comprise SGPNC.

Non-limiting examples of other materials that may be contained in the coating layers 38 and 40 (together with SGPNC or without it) are polyolefin, such as PE or PP; and cross-linked polyolefin, such as PEX.

Example 7

Figure 4 shows an electro-fusion (EF) coupler 45 fabricated in accordance with the present invention, connecting two PEX pipes 46 and 46'. The EF coupler is made of a body 47 having a surface 50 and embedding a coiled electrical wire 48, optionally covered by an insulating layer 49. In operation, the coupler 45 is attached to the pipes 46 and 46' at the surface 50, and electrical current passes through the wire 48, heats it, and melts the insulating layer 49. The melt of the insulating layer 49 creates a joining layer (not shown) that joins the pipes 46 and 46' to the coupler 45.

According to one embodiment of the invention the body 47 comprises SGPNC at least from the parts adjacent the coiled electrical wire 48 to the surface 50, inclusive. The insulating layer 49 may be absent or made of SGPNC. Preferably the whole body 47 is made of SGPNC.

The use of a coupler as described in Figure 4 may be especially advantageous when the pipes 46 and 46' are also in accordance with the present invention. In such a case, post-coupling cross-linking will result in cross-linking between each of the pipes 46 and 46' and the joining layer.

Similar embodiments may be utilized for welding by induction-heating, microwave, and the like.

Claims

CLAIMS:

1. A polymeric article designed for use as a component in a system or structure, the article having at least one welding-aimed portion integral therewith, said portion comprising silane-grafted cross-linkable polyolefin that is free from cross-linking catalyst.

2. A polymeric article according to claim 1 having a form of a sheet.

3. A polymeric article according to claim 1 having a shape of a pipe.

4. A polymeric article according to claim 1 being a coupler.

5. A polymeric article according to claim 1 wherein said polyolefin is selected from the group consisting of polyethylene, polypropylene, ethylene/propylene copolymer, EVA copolymer, and mixtures thereof.

6. A polymeric article according to claim 6 wherein said polyolefin is selected from polyethylene, polypropylene, and mixtures thereof.

7. A polymeric article according to claim 7 wherein said polyolefin is polyethylene.

8. A polymeric article according to claim 1, wherein said at least one welding-aimed portion exhibits a cross-linking degree of 50% or less.

9. A polymeric article according to claim 8, wherein said at least one welding-aimed portion exhibits a cross-linking degree of 30% or less.

10. A polymeric article according to any one of claims 1 to 9 further comprising at least one main portion made of cross-linked polyolefin.

11. A polymeric article according to any one of claims 1 to 9 further comprising at least one main portion made of cross-linked polyolefin, and wherein the at least one welding-aimed portion thereof comprises a mixture of silane grafted polyolefin free from cross-linking catalyst and said cross-linked polyolefin.

12. A polymeric article according to claim 10 or 11 wherein said main portion is cross-linked by peroxide and the welding-aimed portion comprises peroxide and silane grafted polyolefin free from cross-linking catalyst.

13. A polymeric article according to claim 12 further comprising raw material that is conventionally used for fabricating polyolefin cross-linked by peroxide.

14. A polymeric article according to claim 10 or 11 wherein said main portion is cross-linked by radiation and the welding-aimed portion comprises silane grafted polyolefin free from cross-linking catalyst and cross-linking co-agent.

15. A polymeric article according to claim 14 further comprising raw material that is conventionally used for fabricating polyolefin cross-linked by radiation.

16. An article according to any one of claims 1 to 15 wherein the outer surface of at least one welding-aimed portion is coated with a hydrophobic material.

17. An article according to claim 16 wherein the hydrophobic coating is non-compatible with the silane grafted polyolefin of the coated welding-aimed portion.

18. An article according to any one of claims 1 to 3 or 5 to 17 further comprising reinforcing material.

19. An article according to claim 18 wherein said reinforcing material is selected from the group consisting of woven fabric, knitted fabric, scrim, plaited fabric, and nonwoven fabric.

20. A welded article having a welding surface and at least at one side of said welding surface a portion that contains silane grafted polyolefin free of cross-linking catalyst, said portion being integral with the rest of the article that lies at said at least one side of the welding surface.

21. A welded article having near the welding surface silane and no cross-linking catalyst, and containing cross-linking across the welding surface.

22. A welded article according to claim 20 or 21 further comprising reinforcing material.

23. A welded article according to claim 22 wherein said reinforcing material is selected from the group consisting of woven fabric, knitted fabric, scrim, plaited fabric, and nonwoven fabric.

24. A reinforcing material combined with silane grafted polyolefin that is free from cross-linking catalyst.

25. A reinforcing material according to claim 23 wherein said silane grafted polyolefin free from cross-linking catalyst is mixed with a cross-linkable polyolefin.

26. A reinforcing material according to claim 24 or 25 wherein said reinforcing 5 material is selected from the group consisting of woven fabric, knitted fabric, scrim, plaited fabric, and nonwoven fabric.

27. A coupler according to claim 4, which is an electrofusion coupler having a body and an electrical wire, wherein at least the immediate surrounding of the electrical wire comprises silane-grafted cross-linkable polyolefin that is free from io cross-linking catalyst.

28. An electrofusion coupler according to claim 27 wherein the whole body comprises silane-grafted cross-linkable polyolefin that is free from cross-linking catalyst.

29. A method for welding together polymeric articles, at least one of which ₁₅ being an article according to the invention said method comprising the steps of:

(a) providing a first polymeric article according to any one of claims 1 to 15;

(b) providing a second polymeric article; and

(c) welding a welding-aimed portion of said first article to a portion of said second article.

₂₀

30. A method according to claim 29 wherein step (c) is carried out under conditions similar to those, which are usually applied in order to weld non-cross-linked polyolefins.

31. A method according to claim 29 wherein step (c) is carried out under conditions specifically designed to weld cross-linked articles. ₂₅

32. A method according to claim 31 wherein said conditions include high temperature that breaks the cross-linking near the welding surface.

33. A method according to any one of claims 29 to 32, wherein the article provided in step (b) is made of cross- linked polyolefin.

34. A method according to any one of claims 29 to 32, wherein the article provided in step (b) is an article according to any one of claims 1 to 15 and the welding of step (c) takes place at a welding-aimed portion thereof.

35. A method for producing a welded cross-linked polymeric article having cross-linking across the welding surface, said process comprising the steps of:

(a) providing two polymeric articles, each according to any one of claims 1 to 15;

(b) welding said two polymeric articles at welding-aimed portions thereof

(c) allowing said silane-grafted cross-linkable polyolefin that is free from cross-linking catalyst to cross-link.

36. A method according to claim 35 wherein step (b) is carried out under conditions similar to those, which are usually applied in order to weld non-cross-linked polyolefins.

37. A method according to claim 35 wherein step (b) includes applying high temperature that breaks the cross-linking near the welding surface.

38. A method according to any one of claims 33 to 37 wherein step (c) includes subjecting the silane grafted cross-linkable polyolefin that is free from cross-linking catalyst to hot water..

39. A method for extruding polymeric articles according to any one of claims 1 to 15, said method comprises the following steps:

(a) loading the extruder with conventional raw material for cross-linked polyolefin;

(b) extruding the main portion of the polymeric article using the raw material loaded at step a); (c) loading the extruder with SGPNC;

(d) extruding a welding-aimed portion of the polymeric article; and

(e) cross-linking the conventional raw material.

40. A method for fabricating a polymeric pipe according to claim 3, the method compring the following steps: (a) providing a pipe made of PEX-a and containing free peroxide; (b) providing a pipe portion made of SGPNC and containing free peroxide;

(c) butt welding the pipe provided in step (a) to the pipe portion provided in step (b) to obtain a welded article; and

(d) cross-linking the free peroxide in the welded article obtained in step (c) to obtain a pipe according to claim 3.

41. A polymeric article according to claim 1 as herein described and exemplified.

42. A welded article according to claim 20 as herein described and exemplified.

43. A welded article according to claim 21 as herein described and exemplified.