Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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-
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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-
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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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