CA1049388A - Combining fibers and thermoplastic films by a chemical adhesive - Google Patents

Abstract

??stract of the Disclosure This invention relates to the production of composite materials, and, more particularly to the production of strips of fibrous and thermoplastic materials which may then be combined in layers for subsequent molding under selected pressure and temperature con-ditions to form a composite product. A thin composite strip or tape or sheet of thermoplastic material is united with reinforcing fibers by a chemical addition at room temperatures. With such a procedure, the formed strip may be handled and easily "laid up"
in successive layers in a mold prior to coalescing the composite under suitable temperature and pressure conditions.

Description

Case 3959 ~049388 This invention relates to the production of composite materials, and, more particularly to the production of strips of fibrous and thermoplastic materials which may then be combined in layers for subsequent molding under selected pressure and temperature conditions to form a composite product.
The use of fiber reinforced plastic materials to form a composite for specific uses in a rapidly developing art through-out the world. In general, composite fiber reinforced plastic products are formed by manual or machine "lay up" of success-sive layers of the composite materials in desired patterns atroom temperatures with the layers bonded or coalesced together in molds by heat and pressure.
Fiber reinforced strips of thermosetting materials are available for use in the "lay up" of successive layers to form preferred shapes which may then be molded to form composite products. Generally, thermosetting plastic materials involve a chemical reaction while subjected to heat and pressure, and after molding are resistant to physical changes on further applications of heat. Generally speaking, strips of continuous fiber and thermoplastic materials are not generally available.
, As a result of the lack of availability o~ such strips, the lay up of separate layers of the thermoplastic materials and thè
fiber becomes costly and time consuming in preparing the com- -~
posite for molding. The reason for the lack of availability of fiber and thermoplastic material in combined strips or heets, is basically due to the characteristics of the thermo-plastic materials where it is very difficult to combine the f~ber and the thermoplastic by use of heat or solvents since either procedure has a tendency to either degrade the thermo-- plastic material or when a solvent is used the solvents are ordinarily extremely toxic and difficult to use.
A specific example of the problem described, relates to ., 1 Case 3959 the formation of a composite strip of graphite fibers and nylon.
When such composites are laid up, it is extremely time consuming to maintain the align~ent of the fibers on a nylon film during successive lay up of alternate layers of nylon and fiber. The graphite fibers have a tendency to become tangled and misaligned in each successive layer, and they will not wet or combine with the nylon until the entire sandwich of successive layers has been molded under the required temperature and pressure condi-tions to make a composite article.
Other fibers which may be involved in such lay ups can include both inorganic, organic and metallic fibers. The thermo-plastic material can, of course, include many materials other than nylon such as, for example, cellulose derivatives, vinyl resins, polystyrenes, polyamides and acrylic resins, for example.
According to the present invention, a thin composite strip or tape or sheet of thermoplastic material is united with rein-forcing fibers by a chemical addition at room temperatures.
With such a procedure, the formed strip may be handled and easily "laid up" in successive layers in a mold prior to coa-lescing the composite under suitable temperature and pressure conditions. The chemical addition used as an adhesive at room temperatures must in general be compatable with both the fiber and the thermoplastic material, l.e. the adhesive must not degrade the thermoplastic material nor the fiber either ~uring initial drying nor during subsequent pressure and temperature molding.
As an example in forming composite strip~ or sheet of nylon and graphite fiber, an adhesive consisting basically of low molecular weight nylon dissolvable in a solvent that will not rapidly attack the nylon film can be used. Terpolymers of nylon dissolved ~n the lower alcohols are a good example of Case 3959 such a solution. Two commercially available examples of such A chemical materials, are ~merican Cyanamid BR-~9~-8 tack primer and Belding Chemical Industries ser~es 651 nylons. These chemicals are placed in solution in alcohol with approximately 5 to 25~ solids by weight so that the solution may be brushed or sprayed on the composite of nylon film and grahhite fibers.
With the chemical adhesive described, we have found we can continuously, or on a batch basis, form a composite strip or layer of thermoplastic material and fiber which can be conveniently handled during lay up of a multilayer composite article. me article is subsequently molded under desired temperature and pressure and time conditions to complete coa-lescence of the fiber and thermoplastic materials in a finished product.
As an example of the process, a film of nylon which may be l/lO0 of an inch thick and of any desired width and length is positioned on a stationary track or former. In a specific example, the nylon film was 2 7/8 inches wide and 45 inches long and the track was made of wood with the track milled therein 3 inches wide, l/16 inches deep and 45 inches in length. A tow of graphite fiber 45 inches long and having approximately 150,000 fibers therein was laid on the nylon film, rolled to distribute the fibers generally uniformly on the film, and in longitudinal fiber alignment. The fibers were secured at both ends and when the tacking agent, the chemi~al solution hereinbefore described, was applied by a brush and dried in situ for slightly over one minute,the composite strip was removed and allowed to further dry. The~strip of nylon and graphite fiber was found to have sufficient integrity to permit handling without difficulty.
Thereafter, the strips so formed were "laid up" to form a multilayer composite and molded to form a finished product.

In a continuous Qr semi-cont~nu~us process the thermo-Case 3959 1049388e plastic film and fiber ~ passed over a track with a spring loaded roller used to distribute the fiber over the width of the track. Both the fiber and the thermoplastic materials are maintained under tension and a uniform flow of the chemical adhesive applied to the composite at a uniform rate by a brush positioned downstream of the distributing roller. It has been found of some advantage to form the track in a convex form to insure contact between fiber and thermoplastic material, and sufficient time and or distance must be provided to permit at least initial drying of the chemical adhesive.
The chemical adhesive described above is compatable with the nylon and graphite fiber composite. Physical tests of com-posite articles made up of composite strips made according to the invention indicate some increase in strength due to the use of the chemical adhesive, even though such improvement was not expectedi The ratio by weight of graphite fiber to nylon plus fiber/usually be in excess of 25~ while the chemical adhesive brushed or sprayed thereon will represent 1 to 2~
by weight of the total composite strip weight. With the chemical adhesives described above, the composite strip will completely air dry in 10 to 15 minutes producing a composite strip which has sufficient adhesion between the nylon and the graphite to maintain the unity between the two parts while at the same time maintaining the alignment of the fibers in their initially formed condition so that the composite may then be handled such as by reeling and the like. Th~ strip so formed may be only a few hundredths of an inch thick and then be laid up to form the desired thickness of the composite product desired. Once the lay up is completed, the composite may be placed in amold for temperature and pressure treatment so as to form the desired product. -The temperature and pressure treatment necessary for form-Case 3959 ing a nylon and graphite fiber composite will in general followthe requirements set forth in British Patent 1,228,573. The time of molding will be dependent upon the total thickness of layers of graphite and nylon composite, as laid up.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of nylon tapes reinforced by graphite fibers which comprises the steps of (a) providing, on an open former, a thermoplastic nylon film;
(b) laying, on the thermoplastic film, a layer of graphite fiber filaments such that the ratio, by weight, of graphite fiber to the nylon film and graphite fiber will be more than 1.25;
(c) simultaneously applying by brushing or spraying, a wet chemical adhesive to the fibers and the thermoplastic film, wherein the chemical adhesive consists of terpolymers of nylon dissolved in lower alcohols, and applied in an amount ranging from one to two weight percent of the composite tape;
and (d) air drying the combination of film, fibers and chemical adhesive at room temperature to cause adhesive adher-ence therebetween and thereby form a composite tape.