Note: Descriptions are shown in the official language in which they were submitted.
~-- 1333S59
REINFORCED THERMOPLASTIC HONEYCOMB STRUCTURE
Technical Field
The present invention is directed to a simple
and economic process for the manufacture of
thermoplastic resin structures particularly,
honeycomb structures and pre-pregs utilized in the
formation of such structures.
Background Art
Paper honeycomb was first made by the Chinese
approximately two thousand years ago, but at that
time it was used primarily as ornamentation and not
as a structural material. The modern utilization of
honeycomb structures began just after 1940, and
today there are about ten companies manufacturing
the various core types.
While the primary utilization of honeycomb
structure is in the construction of sandwich panels,
it has many other applications, such as energy
absorption, air directionalization, light diffusion
and radio frequency shielding.
U.S. Patent 4,500,583, to Naul, discloses a
honeycomb structure made of resin impregnated molded
glass wool. In particular, glass wool blankets
containing about 20 to 25 percent by weight of an
uncured binder such as urea-phenol-formaldehyde
resin are molded into corrugated sheets under heat
and pressure in a two-part mold. A plurality of the
corrugated shéets can then be adhesively bonded to
one another to form a honeycomb structure.
,~ '"~ .
_ 2 1333559
U.S. Patent 2,734,843, to Steele, discloses a
method of producing honeycomb wherein longitudinaliy
extending, spaced, parallel lines of adhesive are
applied to the face surface of continuously moving
web material, the web material is cut into separate
flat sheets of uniform size, and said sheets are
adhered to one another with the obverse side of each
sheet adhered to an adjacent sheet by a plurality of
spaced parallel lines of adhesive and the reverse
side of each sheet adhered to an adjacent sheet by a
plurality of spaced parallel lines of adhesive,
which are in staggered parallel relationship to the
lines of adhesive on the obverse side.
U.S. Patent 3,032,458, to Daponte et al.,
discloses a method of making an expandable
structural honeycomb material which comprises
securing together a number of layers of flexible
sheet material in a stack by means of an adhesive
distributed between the layers in patches arranged
in arrays of intersecting rows and columns and
positioned such that the columns at the obverse face
of each intermediate layer are staggered with
respect to the columns at the reverse face of said
layer while the rows at said faces are coincident,
and slicing the stack by cutting it in the direction
of the rows at position such that the contacting
pairs of faces of the sheet material within the
slices thus produced are secured together over a
part only of their width by at least a part of a
single row of patches.
U.S. Patent 4,128,678, to Metcalfe et al.,
discloses a method and apparatus for the manufacture
3 133~559
~ of a heat insulating material from an unsecured,
strip-shaped felt of fibers containing a heat
hardenable bonding substance. The felt is first
formed into a serpentine array of corrugations
extending across the entire width of the uncured
felt and then cured. The felt is then cured and the
cured felt is cut longitudinally into two partial
felts, the corrugations being severed so as to form
a succession of U-shaped arrays along each of the
partiat felts.
U.S. Statutory Invention Registration H47, to
Monib, discloses a lightweight structural panel of
an aramid honeycomb core faced with a resin-
impregnated fiber layer, wherein peel strength
between the core surface and the facing layer is
improved by interpositioning of a spunlaced fabric,
containing at least 50% aramid fibers pervaded with
a curable resin, between the core surface and the
facing layer.
U.S. Patent 4,012,738, to Wright, discloses a
microwave radiation absorber comprising a layer of
dielectric material of relatively high dielectric
constant and a layer of magnetic material having a
relatively high coefficient of magnetic
permeability.
U.S. Patent 3,600,249, to Jackson et al.,
discloses a method and apparatus for the production
of a reinforced plastic honeycomb comprising the
steps of: ~1) impregnating a fabric which distorts
under its own weight, such as a fiber glass fabric,
with a heat-curable resin in an amount sufficient to
cause the fiber glass fabric to have sufficient body
1333S59
~_ 4
to prevent its distorting under its own weight while
permitting expansion after curing; (2) applyi~g
adhesive lines on the impregnated fiber glass
fabric, the adhesive being applied so as to avoid
penetration to the opposite side of the fiber glass
fabric, and allowing said adhesive lines to advance
to a relatively non-tacky state; (3) stacking
sheets of the so-produced fiber glass fabric with
the lines of adhesive on one sheet in staggered
relation to the lines of adhesive on adjacent
sheets; (4) applying heat and pressure to the so-
formed stack to cause the adhesive to flow and bond
to the surface of the next adjacent sheet in the
stack; (5) expanding the stack to form a honeycomb
configuration; (6) applying heat and pressure to
the expanded stack created in step (5) to fully cure
the impreqnated resin and the adhesive; (7)
dipping the rigid honeycomb structure formed in step
(6) into a mass of uncured resin; and (8) following
the dipping, curing the resin so-coated onto the
rigid honeycomb structure.
U.S. Patent 3,321,355, to Holland, discloses a
method of making a honeycomb structure from fabric
reinforced plastic wherein the warp and woof of the
fabric in the final honeycomb product are obliquely
disposed to the longitudinal axis of the honeycomb
cells. In particular, the method comprises:
providing a plurality of non-rectangular
parallelogram shaped cut sections of fabric
reinforced plastic material of substantially the
same pattern and size in which the warp of the
fabric extends parallel and the woof of the fabric
1333559
_ 5
extends perpendicular to a first pair of parallel
sides of each section and at acute ansles in
reference to a second pair of parallel sides of each
section; superimposing such sections one upon the
other in a stack; adhering such sections to one
another along spaced apart parallel bonding lines
extending perpendicular to said second pair of
parallel sides, the bonding lines of successive
superimposed sections staggered relative to one
another to form a honeycomb structure.
U.S. Patent 3,598,676, to Noble, is an
improvement over the aforementioned Holland patent,
to reduce waste material, i.e. to eliminate the step
of trimming portions of the parallelogram shaped
core to produce a rectangular shaped core. In
particular, the improved method comprises: forming
a plurality of non-rectangular parallelogram shaped
sections of fabric reinforced plastic material in
which a first and second side of the section are
substantially parallel to each other and to the
warp or woof of the fabric and in which a third and
fourth side of the section are substantially
parallel to each other and dis- posed at an oblique
angle to the warp and woof of said fabric, the
distance between the third and fourth sides of each
section being substantially equal; joining the first
and second sides of said sections together in serial
relationship to form a web having a width equal to
the distance between the third and fourth sides of
one of said sections and a length approximately
equal to the sum of the first sides of all sections
which are joined together in serial relationship,
6 13335~9
_ the third and fourth sides of said joined sections
forming the lateral edges of the web cutting a
plurality of equal rectangular shaped sections from
said web, two sides of each rectangular section
being cut perpendicular to the lateral edges of the
web; superimposing a plurality of said rectangular
sections one upon another in a stack; and adhering
said plurality of rectangular sections to one
another along spaced apart bonding lines which are
substantially parallel to each other and
perpendicular to two sides of said superimposed
rectangular sections, the bonding lines of adjacent
superimposed sections being staggered relative to
one anothèr to form a plurality of adjacent cells
having longitudinal axes which are substantially
parallel to each other and perpendicular to two
sides of said superimposed rectangular sections,
whereby a bias weave honeycomb core structure is
formed in which the warp and the woof of said fabric
are disposed at an oblique angle to the
longitudinal axes of said cells.
U.S. Patent 3,759,775, to Shepherd, discloses a
method for producing an absorbent, high bulk, very
low fiber density stabilized web. In particular, an
air laid web of fibers is thoroughly impregnated
with a volatile liquid. The volatile liquid may
contain a small amount of heat-activatable binder,
or the web of fibers may include the binder in the
form of a small amount of thermoplastic fibers or
powder dispersed throughout the web. The so-
impregnated web is then heated, preferably, by
dielectric heating or the like, so as to vaporize
13335~9
the liquid whereby the web is explosively puffed up
and the small amount of binder secures
interconnections of the fibers to maintain the web
superstructure.
U.S. Patent 3,366,525, to Jackson, discloses
a method of making honeycomb or similar laminated
structures from sheets of heat sealable plastic
which are cohered together under heat and pressure
at selected areas. In an example a polyethylene
web 10 inches wide and 4 mils thick is cut into
sheets of material 18 inches long. A release film
is printed on the sheets in lines .441 inch wide
which are spaced apart by exposed or release-film-
free regions .135 inch wide. The sheets are
stacked in a mold and then subjected to heat and
pressure to seal adjacent sheets together in those
regions free of release film. The mold is cooled,
the pressure reduced, and the stack of heat sealed
sheets removed from the mold. The stack is then
heated and pulled to expanded condition and the
so-formed honeycomb is then cooled.
As may be readily ascertained from the above-
noted documents, the preparation of honeycomb
structure from fiber-reinforced plastics reguires
numerous web handling steps including multiple
impregnation and/or dipping steps. In the case of
obtaining higher shear modulus and improved
handleability, the cutting of woven webs on the
bias and their re-orientation requires even more
handling steps.
In one aspect, the present invention includes
a method of making a thermoplastic honeycomb
structure comprising providing a longitudinally
extending fiber-reinforced web comprising a
thermoplastic resin and a reinforcing fiber, the
fiber-reinforced web comprising from about 20% by
~_ - 8 - 1333~59
weight to about 80% by weight, based on the total
weight of the fiber-reinforced web, of the
reinforcing fiber, the reinforcing fiber being in
the form of a woven web. The method further
includes consolidating the fiber-reinforced web by
application of sufficient temperature and pressure
to allow the thermoplastic resin to melt and flow
to form a matrix for the reinforcing fiber.
Another step includes forming the consolidated
fiber-reinforced web into sheets having a
substantially sinusoidal cross-section of
alternating nodes and antinodes, the sinusoidal
cross-section having a predetermined wavelength.
Further steps include stacking a first so-formed
sheet upon a second so-formed sheet to form the
cells of the honeycomb structure with the second
so-formed sheet displaced one-half wavelength from
the first so-formed sheet so as to have the
antinodes of the second so-formed sheet in contact
with the nodes of the first so-formed sheet and
disposing a heating means for selective heating of
the node/antinode contact and selectively heating
the node/antinode contact for bonding the first and
second sheets together.
In another broad aspect, the present
invention is of a method of making a thermoplastic
honeycomb structure comprising providing a
longitudinally egtending fiber-reinforced web
comprising a thermoplastic resin and a reinforcing
fiber, the fiber-reinforced web comprising from
about 20% by weight to about 80% by weight, based
on the total weight of the fiber-reinforced web, of
the reinforcing fiber, the fiber-reinforced web
comprising at least one first fibrous non-woven web
material having its fibers substantially aligned in
a first direction and at least one second fibrous
- . .
1333559
- 8a -
non-woven web material having its fibers
substantially aligned in a second direction. Other
steps include consolidating the fiber-reinforced
web by application of sufficient temperature and
pressure to allow the thermoplastic resin to melt
and flow to form a matrix for the reinforcing fiber
and forming the consolidated fiber-reinforced web
into sheets having a substantially sinusoidal
cross-section of alternating nodes and antinodes,
the sinusoidal cross-section having a predetermined
wavelength. Further steps include stacking a first
so-formed sheet upon a second so-formed sheet to
form the cells of the honeycomb structure with the
second so-formed sheet displaced one-half
wavelength from the first so-formed sheet so as to
have the antinodes of the second so-formed sheet in
contact with the nodes of the first so-formed sheet
and disposing a heating means for selective heating
of the node/antinode contact and selectively
heating the node/antinode contact for bonding the
first and second sheets together.
In yet another broad aspect, the present
invention includes a method of making a
thermoplastic honeycomb structure comprising the
steps of providing a longitudinally extending
fiber-reinforced web comprising a thermoplastic
resin and a reinforcing fiber, the fiber-reinforced
web comprising from about 20% by weight to about
80% by weight, based on the total weight of the
fiber-reinforced web, of the reinforcing fiber, the
reinforcing fiber being in the form of a
unidirectionally oriented web and consolidating the
fiber-reinforced web by application of sufficient
temperature and pressure to allow the thermoplastic
resin to melt and flow to form a matrix for the
reinforcing fiber. Another step includes forming
- 8b - 13335S9
the consolidated fiber-reinforced web into sheets
having a substantially sinusoidal cross-section of
alternating nodes and antinodes, the sinusoidal
cross-section having a predetermined wavelength.
Further steps include stacking a first so-formed
sheet upon a second so-formed sheet to form the
cells of the honeycomb structure with the second
so-formed sheet displaced one-half wavelength from
the first so-formed sheet so as to have the
antinodes of the second so-formed sheet in contact
with the nodes of the first so-formed sheet and
disposing a heating means for selective heating of
the node/antinode contact and selectively heating
the node/antinode contact for bonding the first and
second sheets together.
In another broad aspect, the present
invention is of a method of making a thermoplastic
honeycomb structure comprising forming consolidated
fiber-reinforced webs, each comprised of
thermoplastic resin and from about 20% to about 80%
by weight, based on the total weight of each web,
of reinforcing fiber, into sheets, each having a
substantially sinusoidal cross-section of
alternating nodes and antinodes, the sinusoidal
cross-section having a predetermined wavelength,
the reinforcing fiber being in the form of a woven
web, at least two non-woven webs with the fibers of
adjacent webs oriented in substantially aligned but
different directions, a unidirectionally oriented
web, or combination thereof. Another step includes
superimposing a first so-formed sheet upon a second
so-formed sheet to form the cells of the honeycomb
structure with the second so-formed sheet displaced
one-half wavelength from the first so-formed sheet
so as to have the antinodes of the second so-formed
sheet in contact with the nodes of the first
1333559
- 8c -
so-formed sheet, and an air gap filling the
resulting cells of the honeycomb structure.
Further steps include sequentially selectively
directly heating and contacting each resulting
facing node and antinode to thereby melt bond
selectively each node/antinode contact and secure
the first and second sheets together and
optionally, repeating the superimposing and heating
and contacting steps at least once.
`_ 13335~`~
g
In the drawings,
Fig. lA illustrates a method of forming a dry-
laid non-woven web of fibrous material according to
the present invention.
Figs. lB-lD illustrate methods of forming two-
layer dry-laid non-woven webs of fibrous material
according to the present invention.
Fig. 2A illustrates a method of consolidating a
web of fibrous material according to the present
invention.
Fig. 2B illustrates a method of consolidating a
web of fibrous material with a melt extruded or hot
melt coated thermoplastic resin according to the
present invention.
Fig. 2C illustrates a method of consolidating a
web of fibrous material with at least one preformed
sheet of a thermoplastic resin according to the
present invention.
Fig. 3 illustrates a flat die method for
20 corrugating a web of fibrous material according to
the present invention.
Fig. 4 illustrates a vacuum forming method for
corrugating a web of fibrous material according to
the present invention.
Fig. 5 illustrates a roller die method for
corrugating a web of fibrous material according to
the present invention.
Fiq. 6 illustrates an apparatus for printing
, ~ 13335~9
release layers on said web of fibrous material, transverse
to the direction of travel of said web, according to the
present invention.
Figs. 7A and 7B illustrate an apparatus for printing
release layers on said web of fibrous material, parallel to
the direction of travel of said web, according to the
present invention.
Fig. 8 illustrates a square corrugation pattern,
according to the present invention.
Fig. 9 illustrates a curved corrugation pattern,
according to the present invention.
Fig. 10 illustrates a hexagonal corrugation pattern,
according to the present invention.
Fig. 11 illustrates a stack of sheets to be bonded
lS together to form a honeycomb structure, after expansion,
according to the present invention.
Fig. 12A is a top view of a structural element
prepared using the present invention.
Fig. 12B is a cross-section along line B-B of the
structural element of Fig. 12A.
Modes For Carrying Out The Invention
The present invention utilizes a longitudinally
extending fiber-reinforced web as a base material. The
base material is typically formed as a dry-laid, non-woven
web. That is, staple fibers-short lengths of crimped
thermoplastic or thermosetting, organic or inorganic
materials - are distributed onto a moving conveyor via a
modified cotton carding mechanism, as is known in the art.
When a series of such cards are placed in line, a highly
oriented assemblage of fibers (know as "laps" in the non-
woven industry) is formed. If additional laps are
_ 11 13335~9
added to the machine direction (direction of conveyor
movement) laps in a cross-layered fashion, then significant
cross-directional fiber orientation is also possible. Of
course, additional layers may be built up in this manner,
and any angular orientation between adjacent laps may be
utilized. For example, in the case of honeycomb
structures, orientations relative to the intended cell axis
may vary from 0 to 90 or from -45 to +45.
Alternatively, the laps may be laid down on a
preformed woven æubstrate, e.g., fiberglass cloth, so that
in addition to the warp and weft of the woven fabric
running at relative angles of 0 and 90, the non-woven
substrate may be oriented at any desired angle, e.g., at
-45O and +45, with respect to the woven substrate.
The assemblage of laps (and/or the assemblage of laps
and preformed woven substrate) may be held together by a
number of techniques, e.g., by mechanically interlocking
the fibers as by needlepunching or water entanglement, by
chemical bonding as by an acrylic adhesive latex emulsion,
or by thermal bonding as by the use of blended
thermoplastic fibers in the web and subsequent heating of
the web to cause those fibers to soften and act as an
adhesive.
Subsequent densification of the web may be effected,
e.g., by a calendering operation, e.g., the assemblage of
laps is passed through at least one set of pressure nip
rollers, whereby the thickness of the web is reduced to
between about 0.001 and about 0.015 inch.
`~ 12 133~5~9
Preferably, the resin or matrix material, l.e.
the thermoplastic resin, is incorporated into the
web as thermoplastic resin fibers during the
production of the laps. In contrast, current
technology, as previously described, utilizes
several impregnation steps, as well as several
dipping steps (of the assembled honeycomb core) to
incorporate thermosetting resin or matrix material
into the product. Such repetitive steps are
obviously time-consuming and costly.
Alternatively, the resin or matrix material, i.e.
the thermoplastic resin, may be incorporated into
the web as a thermoplastic film during the
calendering operation. In this technique, the
lS assemblage of laps and a film of thermoplastic
resin are simultaneously fed through the calender
rollers whereby, if the thermoplastic is heated so
as to soften it, the thermoplastic film becomes
bonded to and/or may interpenetrate the fibrous
assemblage.
As a further alternative, the resin or matrix
material, i.e. the thermoplastic resin, may be
incorporated into the web as both thermoplastic
resin fibers during the production of the laps and
as a thermoplastic film during the calendering
operation. The same or different thermoplastic
resins can be utilized in each case.
Suitable thermoplastic resins for incorporation
by either technique include any of the engineering
grade thermoplastic resins such as polyethersulfone,
polyphenylenesulphide, polyetherimide, nylon-4,6,
polyamideimide, polyarylate, polyarylsulfone,
_ 13 1333559
polycarbonate, polyetherketone, polyimidesulfone,
polysulfone, and polyether-ethersulfone, as well as such
liquid crystal polymers as Vectra~ and Xydar~, and mixtures
thereof.
The advantage of the present approach is that whether
the resin or matrix material is added as a fibrous entity
or added in the calendering process as a film material, all
of the subsequent web handling, impregnation and core
dipping steps have been eliminated from the manufacturing
process.
Additionally, if the resin or matrix material is
incorporated into the web as a film material, it can be
precisely pre-coated with an "active" electrical and/or
magnetic material so that the assembled web, and the
honeycomb structure produced therefrom, will incorporate
radar absorbing (i.e., microwave absorbing) capabilities
into its properties.
Furthermore, if the resin or matrix material is
incorporated into the web as a film material, then woven
materials such as glass cloth, Kevlar~ (DuPont, polyaramid
fabric) or graphite cloth, as well as other non-woven
materials such as Nomex~ (DuPont, meta-
phenylenediamine/isophthaloyl chloride copolymer fiber) or
paper may be utilized.
Moreover, the present approach allows the shear
modulus and handleability of the web to be varied by
controlling the amount of "cross-lapping" that occurs
during formation of the non-woven web. Currently, as
previously noted, when woven glass is used, the web must be
cut on a bias in order to achieve the correct fiber
orientation in the core. This causes a tremendous waste of
raw material.
13335~9
_ 14
With the present non-woven approach, material properties
relative to the machine direction of the web are easily
varied due to the ability to crosslap as required. The net
result is little or no material waste and more
designability for the final honeycomb product.
Also, if a radar absorbing core has been desired, its
performance has been very sensitive to the direction of the
woven glass in the final honeycomb structure. This is
because the "active" materials have typically been
introduced into the honeycomb or the web in solution form
and the fibers tend to "wick up" the material in a very
oriented fashion. The result of this "wicking" is a
honeycomb which is very polarization dependent (dependent
on the direction of the electric field for performance).
The present approach eliminates the directionality aspect
of the "active" material since the "active" material will
remain uniform in distribution when applied with the resin
or matrix film during calendering, i.e. it will not align
itself with the fibers.
The fibrous web may comprise thermoplastic resin
fibers, in toto, however, it is preferred to incorporate a
reinforcing fiber in an amount of about 20% by weight to
about 80% by weight, preferably, about 30% to 70% by
weight, most preferably, about 60% to 70% by weight, based
on the total weight of the fibrous web. These reinforcing
fibers may be organic or inorganic. Preferred organic
fibers include cellulosic fibers, polyaramid fibers and
polyamide fibers. Preferred
lS 13335S9
_,
inorganic fibers include carbon fibers and glass
fibers, most preferably cardable glass fibers
(Owens-Corning Fiberglass).
Regardless, of the nature of the reinforcing
fiber, it has been found desirable to use
reinforcing fibers of a length of from about 1/2
inch up to several inches, e.g., 6 inches,
preferably 3 inches. Similar fiber lengths for the
thermoplastic resin fibers allow easy orientation
when admixed with the reinforcing fibers.
There are two basic techniques for the
manufacture of honeycomb, the expansion method and
the corrugation method. The expansion method
- consists of printing adhesive lines or release
areas on the web; cutting and stacking sheets of the
web with the adhesive lines or release areas in
staggered relation; bonding the stack along the
adhesive lines or the non-release areas; cutting
slices from the stack; and finally expanding the
slice to form the honeycomb structure.
The corrugation method consists of cutting sheets
of the web; corrugating the cut sheets to form a
substantially sinusoidal pattern of alternating
nodes and antinodes; stacking the corrugated layer
with the antinodes of a lower layer in contact with
the nodes of the sheet immediately thereabove; and
bonding the nodes and antinodes which are in contact
to one another.
The basic cell shapes of honeycomb structures are
"hexagonal", "over-expanded" and "flex-core".
"Hexagonal" is the basic shape wherein the cross-
section of the cell is substantially a regular
1333559`
16
-
hexagon. "Over-expanded" is just thQ stand~rd
hexagon over-expanded to a substantially rectangular
shape. (This allows the core to be easily formed
into a cylinder in the direction of the continuous
sheets, i.e. the "ribbon" direction.) "Flex-core"
is used when the honeycomb must be formed with
compound curves, e.g., as described in U.S. Patent
3,032,458, to Daponte et al. Other configurations
are also possible, for instance, "reinforced core"
has an extra flat sheet interposed between each node
and antinode to be bonded together so as to increase
the density and corresponding mechanical properties
and "tube core" is manufactured by spirally wrapping
a corrugated sheet and a flat sheet around a
mandrel, with the nodes and antinodes of the
corrugated sheet to be bonded to the flat sheet.
Turning now to the drawing figures, Fig. lA
illustrates a method of forming a dry-laid non-woven
web of fibrous material wherein a foraminous belt 1
is supported by a pair of rollers 3, 3' for rotation
in the direction indicated by the arrow. In the
apparatus 5, a fibrous web material 7 is laid down
on the belt 1 by carding or by passing an airborne
stream of fiber through the foraminous belt 1.
In an alternative embodiment (as shown in dotted
lines), the fibrous web material 7 may be laid down
on a preormed substrate 8, e.g., a woven substrate
such as fiberglass cloth, graphite cloth, ~evlar
cloth or a non-woven substrate such as paper or
Nomex .
Fig. lB illustrates a method of forming a two-
layer dry-laid non-woven web of fibrous material
. . .. .
~,
.
1333559
_ 17
wherein a foraminous belt lb is supported bv a pair
of rollers 3b, 3b' for rotation in the direction
indicated by the arrow. In the apparatus 5b, a
fibrous web material 7b is laid down on the belt lb
by carding, so that the fibers of the web material
7b are aligned substantially in the direction of the
belt lb. As the belt lb rotates about rollers 3b,
3b', the web material 7b, supported on belt lb,
passes through apparatus 9 wherein a second fibrous
web material 11 is laid down on top of the first
fibrous web material 7b by carding, so that the
fibers of the second web material 11 are aligned
substantially transverse to the fibers of the first
web material 7b. The fibers utilized in the
formation of the first web material 7b and the
second web material 11 may be all thermoplastic
fibers, although up to 80% of reinforcing fibers
may be included. The fibrous web 13 formed by the
first web material 7b overlaid with the second web
material 11 is passed through an oven 15 wherein the
fibrous web 13 is heated to a temperature sufficient
to soften the thermoplastic resin fibers therein to
cause adherence of the first and second web
materials to each other.
Fig. lC illustrates a method of forming a two-
layer dry-laid non-woven web of fibrous material
wherein a foraminous belt lc is supported by a pair
of rollers 3c, 3c' for rotation in the direction
indicated by the arrow. In the apparatus 5c, a
fibrous web material 7c is laid down on the belt lc
by carding, so that the fibers of the web material
7c are aligned substantially in the direction of the
18 1333559
-
belt lc. As the belt lc rotates about rollers 3e,
3c', the web material 7c, supported on belt lc,
passes through apparatus 9c wherein a second fibrous
web material llc is laid down on the top of the
first fibrous web material 7c, by carding, so that
the fibers of the second web material llc are
aligned substantially transverse to the fibers of
the first web material 7c. The fibrous web 13c
formed by the first web material 7c overlaid with
the second web material llc is passed under
needlepunch 17 whereby fibrous web 13c is pierced
by a plurality of needles which reciprocate into and
out of the fibrous web 13c to cause mechanical
interlocking of web material 7c and web material
llc. The needles may be singly or doubly barbed.
Singly barbed needles have barbs that catch fibers
when they are moving in one direction and carry them
along with the needle and then release the fibers
when they are moving in the opposite direction.
Doubly barbed needles have barbs that catch fibers
as for the singly barbed needles and barbs that are
reverse oriented so that when the first barbs are
release fibers the second barbs are catching fibers,
and vice versa.
Fig. lD illustrates a method of forming a two-
layer dry-laid non-woven web of fibrous material
wherein a foraminous belt ld is supported by a pair
of rollers 3d, 3d' for rotation in the direction
indicated by the arrow. In the apparatus Sd, a
fibrous web material 7d is laid down on the belt ld
by carding, so that the fibers of the web material
7d are aligned substantially in the direction of the
l9 13335~9
-
belt ld. As the belt ld rotates about rollers-~d,
3d', the web material 7d, supported on belt ld,
passes through apparatus 9d wherein a second fibrous
web material lld is laid down on the top of the
first fibrous web material 7d, by carding, so that
the fibers of the second web material lld are
aligned substantially transverse to the fibers of
the first web material 7d. The fibrous web 13d
formed by the first web material 7d overlaid with
the second web material lld is passed under hopper
19, which contains an acrylate binder in an aqueous
emulsion, which applies the acrylate bonder emulsion
to the top surface of fibrous web 13d. The so-
coated web is then passed over suction box 21 by
which the aqueous binder is drawn through the
fibrous web 13d and uniformly distributed
therethrough. As the water evaporates, either
naturally or through application of heat (not shown)
the acrylate binder adhesively bonds the fibers of
the fibrous web 13d together.
The non-woven fibrous web (7, 13, 13c, 13d) may
then be consolidated by ca~endaring or any other
method of applying heat and pressure. Fig. 2A
illustrates a method of consolidating the fibrous
web wherein a fibrous web 23 supported on a conveyor
belt 25 is fed between two pressure rollers 27, 27'
to form a consolidated web 29. Preferably, rollers
27, 27' are heated so as to cause softening of
thermoplastic fibers contained in the fibrous web 23
whereby the consolidated web 29 is bonded together
by the softened fibers.
Figure 2B illustrates a method of consolidating
1333559
-
the fibrous web whereir a fibrous web 23b suppoLted
on a conveyor belt 25b is hot melt coated with a
layer of thermoplastic resin 31 delivered from
extruder/coater 33 and then the so-coated web is fed
between two pressure rollers 27b, 27b' to form a
consolidated web 29b. Preferably, rollers 27b, 27b'
are heated so as to cause softening of the coated
thermoplastic resin layer and bonding thereof to the
web 23b.
10Figure 2C illustrates a method of consolidating
the fibrous web wherein a fibrous web 23c supported
on a conveyor belt 25c is fed to two pressure
rollers 27c, 27c', simultaneously with a preformed
thermoplastic resin film 35, to form a consolidated
15web 29c. Preferably, rollers 27c, 27c' are heated
so as to cause softening of the preformed
thermoplastic resin film and bonding thereof to the
web 23c. The preformed film 35 may contain or may
be coated with ~active~ electrical and/or magnetic
material to impart a radar absorbing capability into
the ultimate honeycomb structure. Suitable
electrical materials include those having a high
dielectric constant such as barium titanate (BaTiO4)
and also include particulate carbon such as carbon
2S black, graphite, etc. Suitable magnetic materials
include ferromagnetic materials such as iron,
nickel, permalloy, ferrite, etc. The techniques
illustrated in Figs. 2B or 2C are particularly
applicable to non-woven webs containing no
thermoplastic fibers or woven webs such as glass
cloth.
Alternatively, as shown in dotted lines in Fig.
21 1333~9
2C, a second preformed thermoplastic resin fi~m 35
may also be fed simultaneously to the two pressure
rollers 27C, 27C' so as to "sandwich" the fibrous
web 23C between films 35 and 35'. The films 35 and
35' may be the same or different thermoplastic
resins, preferably, the same. Additionally, the
films may be of the same or different thickness.
After the fibrous web has been consolidated it
may be cut into sheets of predetermined size and
corrugated. Fig. 3 illustrates a flat die method of
corrugation wherein a sheet 37 of the consolidated
web is placed between a pair of mating dies 39, 39'
wherein the respective die faces 41, 41' are formed
in the desired corrugation pattern. The dies may be
heated so as to soften the thermoplastic resin to
allow the sheet to be molded and, after removal from
the dies, the sheet 37 will cool and set up in the
corrugated shape. The dies 39, 39' may be mounted
on shafts 41, 41' of a hydraulic press so as to
allow the dies to be forced together.
Fig. 4 illustrates a vacuum forming method of
corrugation wherein a sheet 37 of the consolidated
web is heated to a temperature above the softening
temperature of the thermoplastic resin and placed
- 25 upon a foraminous die 43 shaped in the desired
corrugated pattern. While maintaining the sheet at
a temperature above the softening temperature of the
thermoplastic resin, a vacuum is drawn in air box 45
by applying suction to pipe 47 (by means not shown).
Ambient air pressure then forces the softened sheet
into conformance with the corrugation pattern of the
foraminous die 43. When suction is released from
22 1333~59
pipe 47, the now-corrugated sheet 37 may be removed
from the die.
Fig. 5 illustrates a roller die method of
corrugation wherein a sheet 37 of the consolidated
web is passed between a pair of corrugating rollers
49, 49' which corrugate the sheet in the desired
pattern. The rollers may be heated so as to soften
the thermoplastic resin. In a particularly
preferred embodiment, the corrugating rollers 49,
49' may be utilized in lieu of the pressure rollers
27, 27'; 27b, 27b'; 27c, 27c' of the embodiments of
Figs. 2A, 2B and 2C, respectively, and sheets may
then be cut from the corrugated strip exiting the
rollers.
In any case, the consolidation (and/or
corrugation) is effected at sufficient temperature
and pressure as to allow the thermoplastic resin to
melt and flow together in a proper manner to act as
the matrix material. It has been found that a
suitable temperature is 50F above the heat
deflection temperature (HDT) of the thermoplastic
resin, preferably, 50-300F above the E~DT, and, most
preferably, 100-200F above the HDT. For the
preferred "engineering grade" thermoplastic resins,
this typically means temperatures of 5S0-650F. The
HDT value for a number of these "engineering grade"
thermoplastic resins is set forth in the following
Table.
. .
.. . .
23 1333559
TABLE
Resin Type Trade name/Supplier HDT(F)
Liquid Crystal
P~lymer Vectra*/Celanese 350-460
Xydar/Dartco 554-655
Nylon-4,6 TS7Allied 300-545
Polyamideimide Tbrlon~ 524-540
Polyarylate Arde~/Amoco 345
Arylon/DuPont 311-340
Durel~Celanese 316-355
Polyarylsulfone Radel7Amoco 400-415
Polycarbonate AEC7Dow 320
Lexan*PPC/G.E. 305-325
Polyetherimide Ultem~G.E. 387-433
15 Polyetherketone
(PEK)Victrex PES/ICI Americas 330-645
PDlyethersulfone
(PES)Victrex PES/ICI Americas 397-421
Polyether-
etherketoneVictrex~PEEK/ICI Americas 300-600
(PEEK)
Polyketone Kadel~Amoco Similar to
PEEK
Polyphenylene
25 sulfide Ryton~Phillips 500
(PPS)
Polysulfone (PS) Udel/Amoco 335-358
.de - ~o.rk
24 1333559
~ Suitable pressures are from about atmospheric to
1,000 psi or higher, preferably, about 200 psi to
600 psi, most preferably 300 psi to 500 psi.
As shown in Fig. 10, the so-formed "half-cell"
corrugated sheets 37', 37", 37n' may then be stacked
with nodes 51', 51" of an upper sheet 37', 37" in
contact with the antinodes 53", 53n' of a lower
sheet. The contacting nodes and antinodes are then
bonded to one another either adhesively or by melt
bonding of the thermoplastic resin by resistive,
inductive, radiant or ultrasonic heating. As shown
in Fig. 10, the electrodes 55a, 55b of an inductive
(dielectric) heating device may be disposed on
opposite sides of a node/antinode contact, and melt
bonding may then be induced by application of a high
frequency oscillating current to the electrodes.
Alternatively, the consolidated web (29, 29b,
29c) may be coated with stripes of a the release
film, the so-coated web cut into sheets, which when
stacked in staggered array and melt bonded, can be
expanded to form the honeycomb structure.
Fig. 6 illustrates an apparatus for printing
release layers on the surface of the consolidated
web wherein the consolidated web 29' passes below
13335~9
printing roller 57 which has raised portions 59 and
depressed portions 61 extending across
(perpendicular to the plane of the drawing) its
entire surface. The raised portions 59 contact an
S intermediate roller 63 while the depressed portions
61 do not contact the intermediate roller 63.
Intermediate roller 63, in turn, contacts a pick-up
roller 65 which is partially immersed in a
dispersion 67 of a release film forming resin, e.g.,
cellulose acetate in ethylene glycol monomethyl
ether acetate or an aqueous polyvinylalcohol
suspension. As the rollers 65, 63, 57 rotate, the
release layer dispersion is transferred from roller
65 to roller 63 to the raised portions 59 of roller
57. Since only the raised portions 59 of the roller
57 contact moving web 29', a striped pattern of
release film dispersion, which upon drying forms a
release film, is printed onto web 29'. The w~b 29'
may then be cut into sheets of predetermined size
(by means not shown).
Figs. 7A and 7B illustrate an apparatus for
printing release layers on the surface of the web,
parallel to the direction of travel of the web,
wherein the consolidated web 29' passes below
~_ 26 1~33559
printing roller 57' which has raised portions 59'
and depressed portions 61' extending perpendicular
to the axis of rotation 69 of the roller. The
raised portions 59' contact an intermediate roller
63' while the depressed portions 61' do not contact
the intermediate roller 63'. Intermediate roller
63', in turn, contacts a pick-up roller 65' which is
partially immersed in a dispersion or solution 67'
of a release film forming resin, as previously
described. ~s the rollers 65', 63', 57' rotate,
the release layer dispersion is transferred from
roller 65' to roller 63' to the raised portions 59'
of roller 57'. Since only the raised portions 59'
of roller 57' contact moving web 29', stripes 59" of
release film dispersion, which upon drying form a
release film, are printed onto web 29'. The web 29'
can then be cut into sheets of predetermined size
(by means not shown).
As shown in Fig. 11, the so-striped sheets of
consolidated web 29' may then be stacked with the
stripes 59" of release film in staggered array.
Upon the application of pressure and heat
(sufficient to soften the thermoplastic resin) to
the stack, the adjacent sheets of web 29' are bonded
13335S9
27
to one another in the areas 71 where no release f ilm
is found.
Although the present invention has been discussed
in terms of hexagonal cell structure, any
substantially sinusoidal repeating pattern of nodes
and antinodes may be utilized to form a honeycomb
structure. Fig. 8 illustrates a square pattern;
whereas Fig. 9 shows a generalized sinusoidal
pattern with wavelength (node-to-node or
antinode-to-antinode distance) and node-to-antinode
distance of ~ /2. Any such pattern can be
utilized in the present invention.
The thermoplastic resin utilized in the present
invention may incorporate colorants, fillers, etc.,
as are conventional in the art, provided that they
are stable under the processing conditions of the
invention, in addition to the "active~ electrical
and/or magnetic materials previously noted. These
additives may be incorporated whether the
thermoplastic resin is in fiber or film form.
Additionally, microwave absorbent properties may
also be achieved by incorporation of a minor
proportion of electrically conductive fibers (e.g.,
graphite or metal fibers) of a length equal to one-
28 1333~9
half of the wavelength of the microwave radiation t^
be absorbed. Broadband microwave radiation
obviously requiring a mix of fiber lengths across
the wavelength spectrum.
The following examples are presented to
illustrate the present invention, but, are not
intended to be limitive thereof.
Comparative Example
A style 104 woven glass web was impregnated with
a curable resin to allow sufficient drapeability forsubsequent forming operations. This produced a 50
by weight resin content, which if formed into a
hexagonal honeycomb core (face length = 1/8") would
produce a honeycomb of 0.9 lb/cu. ft. density.
Additional dipping in curable resin to produce a 4
lb/cu. ft. density would reduce the fiber content to
about 10% by weight.
Preparative Example 1
A mixture of 30% by weight Ryton fiber
(polyphenylene sulfide, Phillips), average length
1.5", 1.5 denier and 70% by weight fiberglass (Owens
Corning), average length 3n, 1.5 denier, was carded
to produce a uniformly mixed web having
approximately 80~ of the fibers oriented in the
_ 29 1333~S9
machine direction. The web weight was approximately
0.25 oz/Yd2
Example 1
A style 112 woven glass web was sandwiched
between a 0.002" thick film of polyethersulfone (S-
100, ICI Americas) and a 0.010" thick film of
polyethersulfone (S-100, ICI Americas), in the
manner illustrated in Fig. 2C, and then immediately
corrugated to form hexagonal honeycomb half-cell
(face length = 1/8n) by passage through a pair of
rotary dies, as illustrated in Fig. 5, operating at
about 550F and 300 psi nip pressure. The so-formed
honeycomb half-cell corresponds to a honeycomb
density of 4.5 lb/cu. ft.
Example 2
A style 112 woven glass web was consolidated with
a single ply of 0.002" thick film of
polyethersulfone (S-100, ICI Americas), in the
manner illustrated in solid lines in Fig. 2C, and
then immediately corrugated to form hexagonal
honeycomb half cell (face length = 1/8") as in
Example 1. The so-formed honeycomb half cell
corresponds to a honeycomb density of 4 lb/cu. ft.
with a 70% glass content.
1333559
Examples 3-7
In the following examples, mixtures of Ryton0
fiber (polyphenylene sulfide, Phillips), average
length 1.5", 1.5 denier and fiberglass (Owens
Corning), average length 3n, 1.5 denier, were carded
to produce uniformly mixed webs. Consolidation
and/or corrugation was carried out at approximately
650F and 500 psi nip pressure. Unless otherwise
indicated webs were laid up by alternate layers at
0 and 90 to cell axis.
Example 3
The web produced in Preparative Example 1 was
laid up to equate to a material yielding a hexagonal
honeycomb half cell (face length = l/8n)
corresponding to a honeycomb density of 1.5 lb/cu.
ft. and then consolidated without corrugation.
Example 4
The web produced in Preparative Example 1 was
laid up to equate to a material yielding a hexagonal
honeycomb half cell (face length = 1/8n)
corresponding to a honeycomb density of 2 lb/cu. ft.
and then simultaneously consolidated and corrugated.
31 13335sg
Example ~
A web having a 60% glass content was produced in
the manner of Preparative Example 1. This web was
laid up to equate to a material yielding a hexagonal
honeycomb half cell (face length = 1/8~)
corresponding to a honeycomb density of 4 lb/cu.
ft. and then simultaneously consolidated and
corrugated.
Example 6
The web produced in Preparative Example 1 was
laid up to equate to a material yielding a hexagonal
honeycomb half cell (face length = 3/8n)
corresponding to a honeycomb density of 1.1 lb/cu.
ft. and then simultaneously consolidated and
corrugated.
Example 7
The web produced in Preparative Example 1 was
laid up by alternate layers at -45 and +4~ to the
cell axis to equate to a material yielding a
hexagonal honeycomb half cell (face length = 1/8n)
corresponding to a honeycomb density ~f 7 lb/cu.
ft. and then simultaneously consolidated ~nd
corrugated.
1333~59
Example 8
The web produced in Preparative Example 1 was
used to fill a mold and a structural element 81, as
illustrated in Figs. 12A and 12B was prepared under
5 pressure and temperature conditions, as above.
-While the present invention has been generally
described with respect to the preparation of
honeycomb structures, Example 8 clearly indicates
the far-reaching applicability of the fiber-
reinforced non-woven web of the present invention in
molding, in general.
In this regard, the present process in
conjunction with the preferred thermoplastic-resin-
fiber-containing, reinforced non-woven web, allows
the fabrication of molded articles wherein long
fiber reinforcement, i,.e. fibers greater 1 inch in
length, has traditionally been found to be
difficult, i.e. in products having corners or folded
edges, e.g., boxes, suitcases, etc., in products
having complex contours.
