Pipes and tubular conduits – Flexible – Distinct layers
Reexamination Certificate
1999-09-29
2001-08-28
Hook, James (Department: 3752)
Pipes and tubular conduits
Flexible
Distinct layers
C138S122000, C138S141000, C138SDIG001
Reexamination Certificate
active
06279614
ABSTRACT:
The invention relates to a multi-layer plastic tube which can be used for conducting gases and/or fluids and is particularly suited as a drinking-water, sanitary-water or heating tube.
In the field of sanitary and heating installations, use is made not only of metal pipes but also of plastic tubes made e.g. from polyethylene (PE). The plastic materials used in such tubes are permeable to oxygen and therefore will usually be provided with a (oxygen) diffusion barrier layer which normally surrounds the fluid-conducting base tube on the outside.
In practice, EVOH (ethylene-vinyl-alcohol) has proven useful as a material for said barrier layer. The drier this material is, the better it is able to fulfill its function as a diffusion barrier. Unfavorably, EVOH becomes more brittle with increasing dryness. Since an increasing brittleness is accompanied by reduced electricity, this in turn leads to a risk of fossilization and cracking and of a crumbling of the material of the barrier layer. This danger exists particularly if the plastic tube is exposed to changes in its length which are caused by variations of the temperature of the fluid in the tube.
To protect the mostly brittle diffusion barrier layer from damage, DE 296 06 533 U1 discloses a multi-layer plastic tube wherein the barrier layer is surrounded by a protective layer. As a material of this barrier layer, preferred use is made of PE. The material of the protective layer is softer than the material of the barrier layer, which, while offering the advantage of mechanical protecting the barrier layer, also entails the disadvantage that the outer surface of the plastic tube is comparatively dull. This disadvantage is particularly aggravating if the plastic tube is shifted into empty tubes which are mostly formed as corrugated tubes. Such “tube-within-a-tube” conduits are often prefabricated by the manufacturer, with plastic tubes of an overall length of several tens of meters being inserted into corrugated tubes. Due to the dull outer surface of the plastic tubes, this insertion requires relatively large forces. The process involves the risk that the drive elements of the advance means for the insertion of the plastic tube into the corrugated tube will rub against the plastic tube, possibly heating the plastic tube and thus damaging the protective layer thereof. Further, during the automatic prefabrication process at the manufacturing site, a sliding of the drive elements of the advance means on the plastic tube disadvantageously prevents that the exact preset length of plastic tube is reliably inserted into the corrugated tube.
From DE-U-81 04 908, a plastic tube is known which comprises a base tube of cross-linked PE, an oxygen diffusion barrier layer from EVOH and an outer layer of a linear PE. Also such a tube causes relatively large frictional forces while inserted into a corrugated tube or a similar encasing tube.
From U.S. Pat. No. 4,299,256, it is known to admix silicone oil to the PVC outer layer of a plastic tube so as to reduce the friction on the outer surface of the tube.
To sum up, with regard to PEX tubes applied on an adhesive layer and an EVOH layer thereon, with the layer thicknesses of these outer layers being each about 100 &mgr;m, the following difficulties arise:
Due to the varying bending stresses in the curve regions of the laid tubes, fissures may be generated as a result of the brittleness. This can lead to a detachment of the EVOH layer and a propagation of the fissures and in the worst case may result in breakage of the tube.
The oxygen barrier property of the EVOH layer material is considerably dependent on the humidity in the environment of the tube. Notably, with increased humidity absorption of the EVOH material, its barrier property will decrease correspondingly.
When connecting a tube to a connecting means, improper handling can cause damage to edges of the connecting means.
Further, certain connecting techniques require the tube to be widened. This type of connection technology finds increasing acceptance on the market since it is performed easily and at low production costs. However, when widening a plastic tube provided with an EVOH barrier layer, a danger exists that the EVOH layer might tear because its expansion behavior cannot be reproduced with sufficient reliability.
It is an object of the invention to provide a multi-layer plastic tube having an oxygen diffusion barrier layer which is protected against mechanical damage, with the plastic tube being suited for insertion into an outer tube in a relatively simple manner and without excessive application of force.
According to the instant invention, the above object is solved by a multi-layer plastic tube comprising
a base tube,
a barrier layer surrounding the base tube and being impermeable to oxygen, and
a protective layer applied on the barrier layer for protecting the barrier layer from damage, wherein the material of the barrier layer includes a lubricant.
According to the invention, the material of the protective layer has a lubricant admixed thereto which, mixed with the rest of the material of the protective layer, is applied onto the barrier layer by extrusion. During the solidifying of the material of the protective layer and in the solidified condition, the lubricant migrates to the surface of the protective layer and becomes active there, i.e. it lends its sliding properties to the multi-layer plastic tube. Thus, the lubricant is particularly a material on the basis of oleic-acid amide/erucic-acid amide. Alternatively, use can be made of materials on the basis of silicone oil or tetrafluoroethylene.
Due to the addition of a lubricant to the material of the protective layer which is preferably a material on PE-basis, the multi-layer plastic tube of the invention—in addition to the mechanical protective function of the barrier layer—is given sliding properties which facilitate the insertion of the multi-layer plastic tube into an empty tube. The combination of a plastic material and a lubricant material in the manufacture of plastic items is known e.g. from slidable films in the packaging industry. Surprisingly, it has been found that the lubricants added in the packaging industry can be used, substantially in the same concentrations, also for protective layers of plastic tubes. This could not have been expected as a matter of course because the manufacturing processes of films and plastic tubes are noticeably different from each other, and especially because plastic tubes have a substantially larger surface relative to the material volume used than is the case with plastic tubes.
The term “lubricant” in the context of the invention is meant to include also a lubricant in the form of a so-called antiblock agent which, by changing the surface structure, allows two items to rub against each other in a smooth manner. Such antiblock agents are known e.g. from the production and processing of plastic films.
Preferably, the base tube is arranged in an outer tube which is spaced from the outer protective layer of the base tube. The outer tube is made of plastic and particularly is formed as a corrugated tube.
By way of alternative, further according to the invention, a variant of the above described embodiment of the multi-layer plastic tube comprises
a base tube,
a barrier layer surrounding the base tube and being impermeable to oxygen, and
a protective layer applied on the barrier layer for protecting the barrier layer from damage, and
an outer tube having the base tube arranged therein and surrounding the protective layer of the base tube with a clearance,
wherein the inner side of the outer tube is provided with a lubricant.
According to this variant of the invention, the lubricant is arranged on the inner side of an outer tube which is suitably provided as a corrugated tube. In this case, the lubricant can be included in the material of the outer tube. If the lubricant is a material on the basis of oleic-acid amide/erucic-acid amide, the material migrates to the inner side of the outer tube where it will fulfill its sliding funct
Bruenen Josef
Eichner Harald
Riesselmann Franz-Josef
Wehmeier Nils
Wolters Paul
Birch & Stewart Kolasch & Birch, LLP
Hewing GmbH
Hook James
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