US 3540488 A
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United States Patent  Inventor Robert F. Voorhees  References Cited 7 l l UNITED STATES PATENTS g Qf 133 1 2,159,948 5/1939 1161611 His/Mela] F611 1 1 2,355,584 8/1944 Douglas... 138/Metal F611  Patented Nov. 17, 1970  A ee El Du Hume Nemours and Com m 2,561,891 7/1951 Tucker.... l38/Metn1 F011 a; m t Mum P Y 2,150,314 6/1956 Bemmels..... 138/Metal F611 8 m2; omdawm 2,798,510 7/1957 Martin 6161. 138/Me1a1 F611 2,998,339 8/1961 Barneset a1. 138/Metal F611 2,999,788 9/1961 Morgan 162/146 3,190,856 6/1965 Lavin et al. 260/65 Primary Examiner-Houston S. Bell, Jr. 541 FLEXIBLE CORRUGATED TUBING 2 Claims, 2 Drawing Figs.
ABSTRACT: Flexible corrugated tubing of concentric layers  US. 138/ 121, of 1 a fibrous aromatic polyamide thermally stable at 180C. 138/145 and (2) metal foil, adhered to each other by a polyamide acid  Int. F161 9/14 and/0r polyimid'e of an aromatic diamine and a benzophenone Field of Search 138/121, tetracarboxylic acid dianhydride, useful for hot gas conduction.
Patented Nov. 17, 1970 INVENTOR ROBERT F. VOORHEES ORNEY l FLEXIBLE CORRUGATED TUBING BACKGROUND OF THE INVENTION The need exists for good quality flexible tubing or duct for a variety of uses such as hot gas conductors, electrical cable conduits and the like.
ldeally, a good quality duct must rate high in a large number of desired properties including temperature resistance, pressure resistance, flame resistance,'water resistance, resistance 4 SUMMARY OF THE INVENTION This invention comprises flexible corrugated tubing having concentric layers of (l) a fibrous aromatic polyamide thermally stable at 180C. and (2) aluminum foil. These layers are adhesively bonded to each other by a polyamide acid and/or polyimide of an aromatic diamine of 6 to 16 carbon atoms with at least one benzophenone tetracarboxylic acid.
The thermally stable fibrous aromatic polyamide layer is a known material and is a paperlike sheet structure made from polyamide fibrids as described in Morgan U.S. Pat. No. 2,999,788 issuedSept. I2, 1961. The entire disclosure of the Morgan patent is incorporated herein by reference.
The polyamide acids and polyimides are also known and are described for example in Lavin et al. U.S. Pat. No. 3,190,856 issued June 22, 1965. The entire disclosure of the Lavin et al. patent is also incorporated herein. As described therein, the polyamide acids are polymeric condensation products of an aromatic primary diamine containing from 6 to 16 carbon atoms with the dianhydride of an acid ofthe group 2,2", 3,3-, 2,3,3, 4', and 3,3',4,4-benzophenone'tetracarboxylic acids and mixtures thereof. The corresponding polyimides are obtained from the polyamide acids by heat and/or chemical treatment according to known methods. As starting materials instead of the dianhydride, a lower alkyl ester or diester can of course be used.
Suitable aromatic diamines include meta-phenylene diamine, para phenylene diamine, l,8-naphthalene diamine, 2,7'-naphthalene diamine, 2,2'-biphenylene diamine, 3,3- biphenylene diamine, 4,4'-biphenylene diamine, 4'- diaminodiphenyl methane, 4,4'-diaminodiphenyl ethane, 4,4- diaminodiphenyl propane, 4,4-diaminodiphenyl ether, ketodianiiine, 4,4'-diaminodiphenyl sulfide, 3,3- diaminodiphenyl sulfide, 4,4-diaminodiphenyl sulfone and 3,3diaminodiphenyl sulfone.
The tubing of this invention can be assembled by known techniques such as by spiral wrapping of tapes of. the layer material about a mandrel, followed by corrugation or crimping of the tubing. Conveniently the fabrication can be done using two tapes, one of aluminum and the other of the aromatic polyamide coated with a thin layer of polyamide acid,
range from inch to 20 inches, with 2, 2.5, 6 and 10 inches being typical. The tapes used in the fabrication can typically be about 2 inches wide and will usually each beabout 'l to 5 or some of which may be converted to polyimide. The spiral wrapping can provide a single layer of each material or multiple layers and can be all spirals in the same direction or crossspiral, i.e. where the two spirals are right and left hand spirals respectively. After forming the tubing and before or after mechanical crimping, the article is heated to convert all or most ofthe polyamide acid to polyimide.
The tubing will ordinarily have an inside diameter in the 10 mils thick. Instead of or in addition to the aluminum layer other metals can be used such as copper, titanium and steel including stainless steel. Multiple layers of the polyamide can be used, being bonded to any adjacent layer with polyamide acid and/or polyimide.
ln an exemplary and preferred embodiment of this invention, a 5 mil polyamide sheet structure is formed according to Example 3 of the above-identified Morgan patent and is then calendered using'heat and pressure. This structure is then coated with the polyamide acid reaction product of 8 parts by weight of 4,4"diaminodiphenyl methane and i2 partsby weight of 3,3',4,4-benzophenone tetracarboxylic acid dianhydride in a 20 percent solids solution in N-mcthyl pyrrolidone to give a coating having a weight in the range of 0.2
to 0.7 ounces per square yard. The article is heated for about 1-0 minutes at l50C. to dry the coating and partially convert.
the polyamide acid to polyimide. Tubing ismade using the spiral wrappingtechnique referred to above using 2 inch wide tapes of 2 mil aluminum foil and the coated polyamide, with the layers so positioned to make the tubing a three-layer composite having the polyamide on the inside, the aluminum on the outside and the polyamide acid/polyimide in between. The product is then moved through a forming die to effect corrugation, following which the product is heated for about 5 minutes at 180C. to cause further imidization and firm interlayer bonding. The final product has an inside diameter of 2.5 inches and canbe highly useful as a duct for conveying hot gases. It is strong, useful at high temperature and'will resist attack by a wide variety of corrosive media.
In the accompanying drawing forming a part of this specification:
FIG. I is a perspective view of the tubular body constructed in accordancewith the present invention; and
FIG. 2 is a cross section through the tubular body taken along the plane 2-2 of FlG. 1.
In the drawing, the spiral lines indicate the corrugations of the tubing. The tubing is shown here as a straight section but this is not meant to restrict it as the tubing can be contorted and still maintain its desirable properties.
in the drawings, the thickness of the layers in FIG. 2 is exaggerated in orderto show the component layers of the tubing.
The member I indicates theinnermost or outermost layer consisting of a metal foil. 2 represents adhesive layer which consists of polyamide acid; a polyimide, or a combination of a polyamide acid and a polyimide. 3 represents a fibrous aromatic polyamide thermally stable at 180C. FIG. 2 is not meant to limit the invention to the number of layers shown but merely to describe accurately the construction of a basic layer.
1. Flexible corrugated tubing of concentric layers of l a fibrous aromatic polyamide thermally stable at lC.-and (2) metal foil, said layers being adhesively secured to each other with a polymer selected from the group consisting of the polyamide acid and the polyimide of an aromatic diamine containing from 6 to 16 carbon atoms with the dianhydride of an