TECHNICAL FIELD The present invention relates to a multilayer pipe made of polymer material, and in particular for conducting cooling fluid. BACKGROUND ART

As is known, civil and automotive air conditioning systems employ pipes made of thermoplastic or elastomeric material and preferably comprising a number of layers of different chemical compositions. For safety reasons, a multilayer air conditioning system pipe must be outwardly impermeable to cooling fluid, flame-resistant, and capable of withstanding both high and low pressure.

Currently used pipes made of elastomeric material normally comprise a nitrile elastomer layer, a plastic- fibre reinforcing layer, and an elastomeric cover layer, and are widely used by the inner layer of elastomeric material simplifying connection by eliminating the need for seals.

Elastomeric pipes of the above type, however, are permeable to the cooling fluid circulating in the air

conditioning system.

Pipes made of thermoplastic material are also used, but are permeable to atmospheric damp and so fail to protect the cooling fluid, in particular the lubricating oils contained in it, from hydrolysis.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a multilayer pipe designed to replace currently used pipes of elastomeric or thermoplastic material, and which is impermeable to both cooling fluid and atmospheric damp, is high-pressure resistant, and of guaranteed high- and low-temperature and flame resistance.

According to the present invention, there is provided a multilayer pipe for conducting cooling fluid, and comprising at least one barrier layer, at least one reinforcing layer, and at least one cover layer, characterized in that said cover layer comprises a thermoplastic elastomer obtained from monomers containing a butyl or halobutyl group. In a preferred embodiment of the present invention, in particular, the thermoplastic elastomer comprises an olefin.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the attached Figure 1, which shows a partial section of a multilayer pipe 1.

BEST MODE FOR CARRYING OUT THE INVENTION More specifically, a multilayer pipe 1 in accordance with the invention comprises a barrier layer 3; a reinforcing layer 5 for increasing the mechanical strength of the pipe; and a cover layer 7.

A covinyl ester is preferably used as the main component of the mix of barrier layer 3, and is even more preferable EVOH. The thickness of barrier layer 3 ranges on average between 0.05 and 0.25 mm, and is preferably 0.10 mm.

Barrier layer 3 advantageously provides for greatly reducing permeation by oxygen into the pipe, thus reducing oxidation of the metal parts of the system coming into contact with the cooling fluid. A reinforcing layer 5, preferably comprising braided yarn, is provided on the outside of barrier layer 3.

The yarn is preferably made of material comprising polyester.

The thickness of reinforcing layer 5 ranges on average between 0.4 and 0.6 mm, and is preferably 0.5 mm. Reinforcing layer 5 advantageously provides for good resistance to high system operating pressure, by being burst-resistant, e.g. is capable of withstanding pressure of over 250 bars. According to the present invention, the multilayer pipe comprises a cover layer 7 comprising an olefin-based thermoplastic elastomer, and a butyl or halobutyl elastomer, i.e. obtained from monomers containing a butyl

or halobutyl group, preferably chlorobutyl. The thermoplastic elastomer is preferably at least partly cured.

The olefin used preferably comprises a styrene- butadiene-styrene copolymer.

Even more preferably, the thermoplastic elastomer is, for example, TREFSIN.

The thickness of cover layer 7 preferably ranges between 0.5 and 0.7 mm, and is more preferably 0.6 mm. A cover layer 7 advantageously solves the problem of absorption of atmospheric damp, thus protecting the lubricating oils in the cooling fluid circulating in the system from hydrolysis.

Multilayer pipe 1 according to the present invention may also comprise at least one layer 2 comprising polyamide, which reduces outward permeation of the cooling fluid, thus minimizing efficiency loss of the system.

The thickness of layer 2 ranges between 0.4 and 0.6 mm, and is preferably 0.5 mm.

The multilayer pipe may also comprise an adhesive layer 6 comprising modified EPDM, preferably a

SANTOPRENE. Adhesive layer 6 ensures adhesion of cover layer 7 and reinforcing layer 5 with no need for adhesives in between.

The thickness of adhesive layer 6 preferably ranges between 0.30 and 0.70 mm, and is preferably 0.50 mm.

In a preferred embodiment of the present invention,

multilayer pipe 1 comprises, in sequence, an inner first layer comprising polyamide (2) ; a barrier layer (3) ; a second layer comprising polyamide (4); a reinforcing layer (5); an adhesive layer (6); and a cover layer (7). The structure of multilayer pipe 1 according to the present invention combines high pressure resistance and temperature resistance within a range of -3O ⁰ C and 130°C. Moreover, it is extremely impermeable to cooling fluid vapours, such as R.134-HCF, R.22-HCFC, R404-HFC, R.407C-HFC, R.410. G-HFC, R.507-HFC, to natural gas, such as ammonia, carbon dioxide, butane and propane, and to atmospheric damp, by virtue of the particular cover layer comprising butyl material.

Given the impermeability of the materials from which they are made, multilayer pipes according to the invention are especially suitable for use over long tracts of civil air conditioning systems.

In particular, multilayer pipes according to the invention prevent cooling fluid leakage of air conditioning systems, while at the same time preventing entry into the pipes themselves of natural gases in the atmosphere.

The multilayer pipe according to the present invention is advantageously compatible, i.e. does not interact, with compressor lubricating oils, such as esters, glycols, and mineral oils such as Artie 155.

Even more advantageously, the multilayer pipe according to the present invention is flexible, and can

therefore be fitted into tight spaces, as, for example, in the case of automotive air conditioning systems.

Clearly, changes may be made to the multilayer pipe as described and illustrated herein - in particular, to the percentage ratio of the chemical components of the various layers, and to the thickness and number of layers without, however, departing from the scope of the present invention.

The pipe according to the present invention is produced using the known process for producing thermoplastic cooling fluid pipes, but using innovative materials and material combinations.

The invention will now be described by way of a number of non-limiting examples. . Example 1

Table 1 shows the composition of the layers of a pipe in accordance with the present invention.

Table 1

Example 2

Permeation is measured as per DIN 13192 and EN 1736 standards .

The test method employs a helium tracer gas; and the exact loss of the pipe, expressed in Kg/year, is determined using a sensor for detecting each single gas molecule.

Given the small size of helium gas molecules, testing is highly selective, and comprises the steps of: connecting a metre of test pipe at both ends, and sealing one end; inserting the pipe inside an airtight chamber, bringing the pipe to the desired temperature, controlled using an optical pyrometer, and forming a vacuum in both the airtight chamber and the test pipe; filling the pipe with helium tracer gas to the desired pressure; and analysing the outside environment of the pipe, i.e. the airtight chamber, for at least an hour using a mass spectrometer. The resulting value is the permeation of the pipe, including the fitting. The cycle is fully automated, with no labour required.

Table 2 shows the permeation values of the pipe

according to the present invention with the composition shown in Example 1.

Table 2