HOSE FOR REFRIGERATING SYSTEMS

TECHNICAL FIELD This invention relates to hoses for transporting or otherwise handling refrigerants. More specifically, this invention relates to improved inner tubes and outer covers for these hoses.

BACKGROUND ART Prior hoses of this type comprise an inner tube and an outer cover, the inner tube being made up of a polymeric inner wall and a rubbery outer peripheral wall. Certain polymeric materials are known which render the hose highly resistant to refrigeration gases. These materials include polyamides such as nylon-6, nylon-6/66, nylon-1 1 , nylon-12 and the like Many nylons, however, produce inner walls which are very stiff and not very flexible. Flexibility is highly desirable, particularly in automotive applications for ease of routing and damping of noise transmission. Attempts to modify the nylons through the use of traditional plasticizers such as oils or excess monomer to provide more flexible inner walls have resulted in hoses with higher gas permeability. In addition, normal A/C system use can cause these plasticizers to be extracted from the nylon, stiffening the hose and potentially contaminating the refrigeration system. Normal A/C systems often see temperatures in excess of 200°F.

DISCLOSURE OF THE INVENTION

Our development provides a hose suitable for use in transporting refrigerants. The hose has an inner tube with improved flexibility while maintaining low gas permeability without the use of extractable plasticizers. The inner tube includes a resinous inner peripheral wall and a rubbery outer peripheral wall, wherein the resinous inner peripheral wall consisting essentially of nylon and a non-extractable elastomeric plasticizer, and wherein the rubbery outer peripheral wall is a butyl rubber or a halogenated butyl rubber. The non-extractable elastomer plasticized inner wall has numerous positive attributes over traditional plasticized nylons, however, permeability is essentially equivalent. By combining, however, with a butyl or halobutyl outer wall, a hose with improved permeation resistance is achieved effectively obtaining all desirable properties in a single hose. The hose also has a reinforcing layer laminated over the outer peripheral wall, and an outer cover laminated over the reinforcing layer. In one preferred embodiment, the outer cover is a halogenated butyl rubber.

In another preferred embodiment, the resinous inner wall has an increased nylon content relative to the elastomeric plasticizer content. We prefer this embodiment in hoses on the low or discharge side of a compressor where the refrigeration gases are under high pressure and permeate more readily due to higher temperatures. Typically, the discharge hoses have a smaller diameter than hoses on the low pressure, suction side.

The resulting hoses in both embodiments are more flexible with lower gas impermeability. The hoses also have better refrigerant oil resistance, favorable inner wall characteristics, high temperature resistance and maintain their flexibility after prolonged use. Traditional walls have negative swell; i.e., they shrink or decrease in size. Shrinking may contribute to leakage. Our development provides a positive swell and actually creates a tighter, more leak proof seal.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a perspective view, partly cut away, illustrating a hose according to our invention.

BEST MODE OF CARRYING OUT INVENTION

Referring now to Fig. 1 , we show hose 10 according to this invention. Hose 10 is a multi-layered structure which comprises inner tube 20, outer cover 40 and reinforcing layer 30 disposed therebetween. Inner tube 20 includes resinous inner peripheral wall 21 and rubbery outer peripheral wall 22.

Inner wall 21 of inner tube 20 is made of the combination of nylon and a non-extractable elastomeric plasticizer, preferably grafted ethylene-propylene-diene rubber (EPDM). The nylon can vary widely and comes from the family of polyamide polymers characterized by the amide radical: -CONH. By far, the most common nylons are nylon 66 and nylon 6. Nylon 66 is a condensation product of adipic acid and hexamethylenediamine. Nylon 6 is a polymer of caprolactam. Nylon 4 is based on butyl-rolactam (2-pyrrolidone). Nylon 1 1 is the self-condensation product of aminoundecanoic acid and nylon 12 is made from butadiene.

Preferably, inner wall 21 is made from a mix of nylon 66 and grafted EPDM.

Another key to our invention is that rubbery outer wall 22 of inner tube 20 is made of butyl rubber or halogenated butyl rubber. The butyl rubbers can vary widely. Generally, they are a copolymer of isobutylene and small amounts of a diolefin. A typical butyl rubber is made from isobutylene and isoprene (II R). Typically, the II R copolymer contains 3% isoprene. A typical halogenated butyl rubber is chlorinated butyl rubber (Cl-ll R). In the preferred embodiment of this invention, we use butyl rubber (II R).

In one preferred embodiment the resinous inner peripheral wall consisting essentially of 24 to 80 percent by weight nylon and 10 to 60 percent by weight elastomeric plasticizer. Materials for the inner wall are described in U.S. Patent No. 5,091 ,478 which is herein incorporated by reference. The preferred halogenated butyl rubber for outer cover 40 is chlorinated butyl rubber.

To attain firm lamination of the inner tube, suitable bonding adhesives may be applied between the peripheral walls, thereby rendering the resulting hose mechanically strong and durable. The hose according to the invention may be fabricated by any suitable known methods. One such method involves passing a release-treated mandrel through an extruder equipped with heads from which resins are extruded peripherally on the mandrel and thus form an inner wall. The mandrel is allowed to successively enter a rubber extruder at which time an outer wall of rubbery material is laminated over the plastic wall.

A layer of reinforcement is laminated by braiding suitable textile yarns over the outer rubbery wall of the inner tube. An outer cover is disposed outwardly about the braided layer by extrusion of the rubbery material.

The resulting hose body is vulcanized under pressure at elevated temperatures, and subsequently cooled. The mandrel is afterwards pulled out of the vulcanized hose body, whereby a desired hose product is obtained. Braided layer 30 may be made from any number if fibers including glass fibers, polyester fibers, nylon, graphite, rayon and polyamide fibers (Kevlar). We prefer that braided layer 30 be made of polyester fibers.

Example

We prepared different hoses according to this invention. Tests were conducted on gas permeability under SAE J2064 and flex modulus under ASTM D790.

The hoses we tested had an inside diameter, typically 8 to 16 mm. The inner tube was made of 60 to 80 percent by weight nylon

66 and 20 to 40 percent by weight grafted-EPDM. The reinforcing layer was braided polyester and the outer cover was chlorinated butyl rubber.

The hoses we tested are Type E hoses under SAE J2064. The refrigerant we used was Refrigerant 134A. The gas permeations we measured under SAE J2064 ranged from 0.25 to 0.75 lbs/ft ² /yr.

Acceptable gas permeations under the SAE spec allow for a maximum of 2.0 lbs/ft ² /yr.

The material of the inner wall of the hoses of this Example have a flex modulus under ASTM D 790-86 of less than, 100,000 psi.

Typically they have a flex modulus ranging from 50,000 psi to 100,000 psi. Typically, unplasticized nylon is very stiff and has a flex modulus of 250,000 psi. Conventional oil plasticized nylon 66 have a stiffness of 100,000 to 125,000 psi. Oil, however, extracts from the conventional oil plasticized nylons at usual operating temperature in excess of 200°F.