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United States Patent |
5,030,305
|
Fell
|
July 9, 1991
|
Method of manufacturing reinforced thermoplastic honeycomb structure
Abstract
A method of manufacturing thermoplastic structures wherein the structure
comprises a fiber-reinforced thermoplastic resin. The fiber reinforcement
may be in the form of a woven or non-woven web. The thermoplastic resin
may be introduced therein in the form of staple fibers blended into the
non-woven web or by melt-coating the web or by laminating a pre-formed
thermoplastic resin film to the web. The latter technique allows uniform
distribution of a radar-absorbing material, coated on or blended into the
pre-formed thermoplastic film, throughout the honeycomb.
Inventors:
|
Fell; Barry M. (7124 Red Top Rd., Hummelstown, PA 17036)
|
Appl. No.:
|
565192 |
Filed:
|
August 9, 1990 |
Intern'l Class: |
B32B 003/12 |
Field of Search: |
156/207,208,197,292,62.2,62.4,167,242,180,181
428/116
342/1
|
References Cited
U.S. Patent Documents
2808098 | Oct., 1957 | Chavannes et al. | 156/62.
|
2953187 | Sep., 1960 | Francis, Jr. | 156/498.
|
2988469 | Jun., 1961 | Watson | 264/122.
|
3134705 | May., 1964 | Moeller | 156/197.
|
3227592 | Jan., 1966 | Coates et al. | 156/93.
|
3271215 | Sep., 1966 | Hoffman | 156/276.
|
3379594 | Apr., 1968 | Bruder | 156/73.
|
3684645 | Aug., 1972 | Temple et al. | 156/166.
|
3865661 | Feb., 1975 | Hata et al. | 156/180.
|
4725490 | Feb., 1988 | Goldberg | 342/1.
|
4734321 | Mar., 1988 | Radvan et al. | 156/62.
|
Foreign Patent Documents |
2113140 | Aug., 1983 | GB.
| |
2188866 | Oct., 1987 | GB.
| |
Primary Examiner: Ball; Michael
Assistant Examiner: Aftergut; Jeff H.
Attorney, Agent or Firm: Sherman and Shalloway
Parent Case Text
This application is a continuation of application Ser. No. 07/188,377 filed
Apr. 29, 1988, now abandoned.
Claims
What we claim is:
1. A method of making a thermoplastic honeycomb structure comprising:
(A) providing a longitudinally extending fiber-reinforced web comprising a
thermoplastic resin and a reinforcing fiber, said fiber-reinforced web
comprising from about 20% by weight to about 80% by weight, based on the
total weight of said fiber-reinforced web, of said reinforcing fiber, said
reinforcing fiber being in the form of a woven web;
(B) consolidating said fiber-reinforced web by application of sufficient
temperature and pressure to allow said thermoplastic resin to melt and
flow to form a matrix for said reinforcing fiber;
(C) forming said consolidated fiber-reinforced web into sheets having a
substantially sinusoidal cross-section of alternating nodes and antinodes,
said sinusoidal cross-section having a predetermined wavelength;
(D) stacking a first so-formed sheet upon a second so-formed sheet with
said second so-formed sheet displaced one-half wavelength from said first
so-formed sheet so as to have the antinodes of said second so-formed sheet
in contact with the nodes of said first so-formed sheet; and
(E) disposing a heating means for selective heating of said node/antinode
contact and selectively heating said node/antinode contact for bonding
said first and second sheets together.
2. The method according to claim 1, wherein said thermoplastic resin
comprises thermoplastic resin fibers.
3. The method according to claim 2, wherein said thermoplastic resin fibers
are staple fibers of said thermoplastic resin.
4. The method according to claim 1, wherein said fiber-reinforced web
comprises fibers of a microwave radiation absorbent material.
5. The method according to claim 1, wherein said reinforcing fiber is
inorganic.
6. The method according to claim 5, wherein said inorganic fiber is glass
or carbon fiber.
7. The method according to claim 1, wherein said reinforcing fiber is
organic.
8. The method according to claim 7, wherein said organic fiber is
cellulosic, polyaramid or polyamide fiber.
9. The method according to claim 1, wherein said fiber-reinforced web
comprises a lamination of a lamina of said woven web of said reinforcing
fibers and at least one lamina of said thermoplastic resin.
10. The method according to claim 9, wherein said laminate is produced by
melt-bonding a preformed film of said thermoplastic resin to said woven
web of said reinforcing fibers.
11. The method according to claim 9, wherein said lamina of said woven web
of said reinforcing fibers is sandwiched between a first lamina of said
thermoplastic resin and a second lamina of said thermoplastic resin.
12. The method according to claim 11, wherein said first lamina has a first
predetermined thickness and said second lamina has a second predetermined
thickness, said first predetermined thickness being different from said
second predetermined thickness.
13. The method according to claim 9, wherein said lamina of said
thermoplastic resin comprises a preformed film of said thermoplastic resin
and a microwave radiation absorbent material.
14. The method according to claim 13, wherein said microwave radiation
absorbent material is coated on said preformed film.
15. The method according to claim 1, wherein said fiber-reinforced web
further comprises staple fibers of a microwave radiation absorbent
material.
16. The method according to claim 1, wherein said step (C) is effected by
pressing between mating dies.
17. The method according to claim 1, wherein said step (C) is effected by
vacuum forming.
18. The method according to claim 1, wherein a honeycomb structure is
formed by melt-bonding said nodes and antinodes, which are in contact, to
each other.
19. The method according to claim 1, wherein a honeycomb structure is
formed by adhesively bonding said nodes and antinodes, which are in
contact, to each other.
20. The method according to claim 1, wherein said consolidation step (B)
and said forming step (C) are effected simultaneously by a roller die
which consolidates and corrugates said fibrous web into a substantially
sinusoidal cross-section of alternating nodes and antinodes, said
sinusoidal cross-section having a predetermined wavelength.
21. The method according to claim 1, wherein said longitudinally extending
fibrous web is coated with a microwave radiation absorbent material.
22. The method according to claim 2, wherein said fiber-reinforced web
further comprises staple fibers of a microwave radiation absorbent
material.
23. A method of making a thermoplastic honeycomb structure comprising:
(A) providing a longitudinally extending fiber-reinforced web comprising a
thermoplastic resin and a reinforcing fiber, said fiber-reinforced web
comprising from about 20% by weight to about 80% by weight, based on the
total weight of said fiber-reinforced web, of said reinforcing fiber, said
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 non-woven web material having its fibers
substantially aligned in a second direction;
(B) consolidating said fiber-reinforced web by application of sufficient
temperature and pressure to allow said thermoplastic resin to melt and
flow to form a matrix for said reinforcing fiber;
(C) forming said consolidated fiber-reinforced web into sheets having a
substantially sinusoidal cross-section of alternating nodes and antinodes,
said sinusoidal cross-section having a predetermined wavelength;
(D) stacking a first so-formed sheet upon a second so-formed sheet with
said second so-formed sheet displaced one-half wavelength from said first
so-formed sheet so as to have the antinodes of said second so-formed sheet
in contact with the nodes of said first so-formed sheet; and
(E) disposing a heating means for selective heating of said node/antinode
contact and selectively heating said node/antinode contact for bonding
said first and second sheets together.
24. The method according to claim 23, wherein said thermoplastic resin
comprises thermoplastic resin fibers.
25. The method according to claim 24, wherein said thermoplastic resin
fibers are staple fibers of said thermoplastic resin.
26. The method according to claim 23, wherein said fiber-reinforced web
comprises fibers of a microwave radiation absorbent material.
27. The method according to claim 23, wherein said reinforcing fiber is an
organic fiber.
28. The method according to claim 27, wherein said organic fiber is
cellulosic, polyaramid or polyamide fiber.
29. The method according to claim 27, wherein said fiber-reinforced web
comprises an admixture of staple fibers of said thermoplastic resin and
said reinforcing fiber.
30. The method according to claim 29, wherein said fiber-reinforced web is
a non-woven web.
31. The method according to claim 27, wherein said fiber-reinforced web
comprises a lamination of a lamina of said reinforcing fibers and at least
one lamina of said thermoplastic resin.
32. The method according to claim 31, wherein said laminate is produced by
hot melt or extrusion coating a non-woven web of said reinforcing fibers
with said thermoplastic resin.
33. The method according to claim 31, wherein said laminate is produced by
melt-bonding a preformed film of said thermoplastic resin to a non-woven
web of said reinforcing fibers.
34. The method according to claim 31, wherein said lamina of said
reinforcing fibers is sandwiched between a first lamina of said
thermoplastic resin and a second lamina of said thermoplastic resin.
35. The method according to claim 34, wherein said first lamina has a first
predetermined thickness and said second lamina has a second predetermined
thickness, said first predetermined thickness being different from said
second predetermined thickness.
36. The method according to claim 31, wherein said lamina of said
thermoplastic resin comprises a preformed film of said thermoplastic resin
and a microwave radiation absorbent material.
37. The method according to claim 36, wherein said microwave radiation
absorbent material is coated on said preformed film.
38. The method according to claim 23, wherein said reinforcing fiber is an
inorganic fiber.
39. The method according to claim 23, wherein said first direction is
substantially transverse to said second direction.
40. The method according to claim 23, wherein said at least one first
fibrous non-woven web material is mechanically affixed to said at least
one second fibrous non-woven web material.
41. The method according to claim 40, wherein said mechanical affixation is
effected by needlepunching.
42. The method according to claim 23, wherein said at least one first
fibrous non-woven web material is chemically affixed to said at least one
second fibrous non-woven web material.
43. The method according to claim 42, wherein said chemical affixation is
effected by an acrylic adhesive.
44. The method according to claim 23, wherein said at least one first
fibrous non-woven web material is thermally affixed to said at least one
second fibrous non-woven web material.
45. The method according to claim 44, wherein said thermal affixation is
effected by melt-bonding of said fibers with said thermoplastic resin.
46. The method according to claim F 38, wherein said first fibrous
non-woven web material and said second fibrous non-woven web material each
comprises an admixture of staple fibers of said thermoplastic resin and
said reinforcing fiber.
47. The method according to claim 27, wherein said fiber-reinforced web
further comprises staple fibers of a microwave radiation absorbent
material.
48. The method according to claim 23, wherein said step (C) is effected by
pressing between mating dies.
49. The method according to claim 23, wherein said step (C) is effected by
vacuum forming.
50. The method according to claim 23, wherein a honeycomb structure is
formed by melt-bonding said nodes and antinodes, which are in contact, to
each other.
51. The method according to claim 23, wherein a honeycomb structure is
formed by adhesively bonding said nodes and antinodes, which are in
contact, to each other.
52. The method according to claim 23, wherein said consolidation step (B)
and said forming step (C) are effected simultaneously by a roller die
which consolidates and corrugates said fibrous web into a substantially
sinusoidal cross-section of alternating nodes and antinodes, said
sinusoidal cross-section having a predetermined wavelength.
53. The method according to claim 23, wherein said longitudinally extending
fibrous web is coated with a microwave radiation absorbent material.
54. The method according to claim 24, wherein said fibrous web further
comprises staple fibers of a microwave radiation absorbent material.
55. A method of making a thermoplastic honeycomb structure comprising:
(A) providing a longitudinally extending fiber-reinforced web comprising a
thermoplastic resin and a reinforcing fiber, said fiber-reinforced web
comprising from about 20% by weight to about 80% by weight, based on the
total weight of said fiber-reinforced web, of said reinforcing fiber, said
reinforcing fiber being in the form of a unidirectionally oriented web;
(B) consolidating said fiber-reinforced web by application of sufficient
temperature and pressure to allow said thermoplastic resin to melt and
flow to form a matrix for said reinforcing fiber;
(C) forming said consolidated fiber-reinforced web into sheets having a
substantially sinusoidal cross-section of alternating nodes and antinodes,
said sinusoidal cross-section having a predetermined wavelength;
(D) stacking a first so-formed sheet upon a second so-formed sheet with
said second so-formed sheet displaced one-half wavelength from said first
so-formed sheet so as to have the antinodes of said second so-formed sheet
in contact with the nodes of said first so-formed sheet; and
(E) disposing a heating means for selective heating of said node/antinode
contact and selectively heating said node/antinode contact for holding
said first and second sheets together.
56. The method according to claim 55, wherein said thermoplastic resin
comprises thermoplastic resin fibers.
57. The method according to claim 56, wherein said thermoplastic resin
fibers are staple fibers of said thermoplastic resin.
58. The method according to claim 55, wherein said fiber-reinforced web
comprises fibers of a microwave radiation absorbent material.
59. The method according to claim 55, wherein said reinforcing fiber is
inorganic.
60. The method according to claim 59, wherein said inorganic fiber is glass
or carbon fiber.
61. The method according to claim 55, wherein said reinforcing fiber is
organic.
62. The method according to claim 61, wherein said organic fiber is
cellulosic, polyaramid or polyamide fiber.
63. The method according to claim 55, wherein said fiber-reinforced web
comprises a lamination of a lamina of said unidirectionally oriented web
of said reinforcing fibers and at least one lamina of said thermoplastic
resin.
64. The method according to claim 63, wherein said laminate is produced by
melt-bonding a preformed film of said thermoplastic resin to said
unidirectionally oriented web of said reinforcing fibers.
65. The method according to claim 63, wherein said lamina of said
unidirectionally oriented web of said reinforcing fibers is sandwiched
between a first lamina of said thermoplastic resin and a second lamina of
said thermoplastic resin.
66. The method according to claim 65, wherein said first lamina has a first
predetermined thickness and said second lamina has a second predetermined
thickness, said first predetermined thickness being different from said
second predetermined thickness.
67. The method according to claim 63, wherein said lamina of said
thermoplastic resin comprises a preformed film of said thermoplastic resin
and a microwave radiation absorbent material.
68. The method according to claim 67, wherein said microwave radiation
absorbent material is coated on said preformed film.
69. The method according to claim 55, wherein said fiber-reinforced web
further comprises staple fibers of a microwave radiation absorbent
material.
70. The method according to claim 55, wherein said step (C) is effected by
pressing between mating dies.
71. The method according to claim 55, wherein said step (C) is effected by
vacuum forming.
72. The method according to claim 55, wherein a honeycomb structure is
formed by melt-bonding said nodes and antinodes, which are in contact, to
each other.
73. The method according to claim 55, wherein a honeycomb structure is
formed by adhesively bonding said nodes and antinodes, which are in
contact, to each other.
74. The method according to claim 55, wherein said consolidation step (B)
and said forming step (C) are effected simultaneously by a roller die
which consolidates and corrugates said fibrous web into a substantially
sinusoidal cross-section of alternating nodes and antinodes, said
sinusoidal cross-section having a predetermined wavelength.
75. The method according to claim 55, wherein said longitudinally extending
fibrous web is coated with a microwave radiation absorbent material.
76. The method according to claim 56, wherein said fiber-reinforced web
further comprises staple fibers of a microwave radiation absorbent
material.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Prior 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. Pat. No. 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 sheets
can then be adhesively bonded to one another to form a honeycomb
structure.
U.S. Pat. No. 2,734,843, to Steele, discloses a method of producing
honeycomb wherein longitudinally 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. Pat. No. 3,032,458, to Duponte 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. Pat. No. 4,128,678, to Metcalfe et al., discloses a method and
apparatus for the manufacture 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 partial
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. Pat. No. 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. Pat. 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 to prevent its
distorting under its own weight while permitting expansion after curing;
(2) applying 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 impregnated 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. Pat. No. 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 extends perpendicular to a first pair of parallel
sides of each section and at acute angles 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. Pat. No. 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 disposed 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, 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 another 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. Pat. No. 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 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. Pat. No. 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 0.441 inch wide which are spaced apart by exposed or
release-film-free regions 0.135 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 requires
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.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome the aforementioned problems
with the prior art techniques for honeycomb structure formation.
It is a further object of the invention to provide a process which can be
operated in a continuous, high-speed manner to produce thermoplastic resin
structures, especially honeycomb structures.
These and other objects of the invention, as will become apparent
hereinafter, are achieved by the provision of a method of making a
thermoplastic structure comprising: (A) providing a longitudinally
extending fiber-reinforced web, said fiber-reinforced web comprising a
thermoplastic resin; (B) forming said fiber-reinforced web into sheets
having a predetermined configuration; (C) stacking a plurality of said
sheets to form a preform; (D) forming a structure from said preform, said
forming step including bonding of at least portions of said sheets
together by fusion of at least a portion of said thermoplastic resin.
In one embodiment of the invention, the fiber-reinforced web includes
thermoplastic resin as staple fibers.
In a further embodiment of the invention, the fiber-reinforced web may
comprise up to about 80% by weight, based on the total weight of said
fiber-reinforced web, of a reinforcing fiber; and, in a preferred form of
this embodiment, comprises an admixture of staple fibers of said
thermoplastic resin and said reinforcing fiber.
In a still further embodiment, the fibrous web comprises at least one first
fibrous non-woven web material having it fibers substantially aligned in a
first direction and at least one second fibrous non-woven web material
having its fibers substantially aligned in a second direction.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1A illustrates a method of forming a dry-laid non-woven web of fibrous
material according to the present invention.
FIGS. 1B-1D 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 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.
FIG. 6 illustrates an apparatus for printing 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 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.
DETAILED DESCRIPTION OF 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 (known as "laps" in the
non-woven industry) is formed. If additional laps are 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.degree. to 90.degree. or from
-45.degree. to +45.degree..
Alternatively, the laps may be laid down on a preformed woven substrate,
e.g., fiberglass cloth, so that in addition to the warp and weft of the
woven fabric running at relative angles of 0.degree. and 90.degree., the
non-woven substrate may be oriented at any desired angle, e.g., at
-45.degree. and +45.degree., 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 can 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.
Preferably, the resin or matrix material, i.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 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, polycarbonate,
polyetherketone, polyimidesulfone, polysulfone, and
polyether-ethersulfone, as well as such liquid crystal polymers as
Vectra.RTM. and Xydar.RTM., 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.RTM.
(DuPont, polyaramid fabric) or graphite cloth, as well as other non-woven
materials such as Nomex.RTM. (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. With the present non-woven approach,
material properties relative to the machine direction of the web are
easily varied due to the ability to cross-lap 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 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 hexagon.
"Over-expanded" is just the standard 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. Pat. No. 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. 1A 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 preformed substrate 8, e.g., a woven
substrate such as fiberglass cloth, graphite cloth, Kevlar.RTM. cloth or a
non-woven substrate such as paper or Nomex.RTM..
FIG. 1B illustrates a method of forming a two-layer dry-laid non-woven web
of fibrous material wherein a foraminous belt 1b is supported by 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 1b by
carding, so that the fibers of the web material 7b are aligned
substantially in the direction of the belt 1b. As the belt 1b rotates
about rollers 3b, 3b', the web material 7b, supported on belt 1b, 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. 1C illustrates a method of forming a two-layer dry-laid non-woven web
of fibrous material wherein a foraminous belt 1c 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 1c by
carding, so that the fibers of the web material 7c are aligned
substantially in the direction of the belt 1c. As the belt 1c rotates
about rollers 3c, 3c', the web material 7c, supported on belt 1c, passes
through apparatus 9c wherein a second fibrous web material 11c is laid
down on the top of the first fibrous web material 7c, by carding, so that
the fibers of the second web material 11c 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
11c 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 11c.
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. 1D illustrates a method of forming a two-layer dry-laid non-woven web
of fibrous material wherein a foraminous belt 1d is supported by a pair of
rollers 3d, 3d' for rotation in the direction indicated by the arrow. In
the apparatus 5d, a fibrous web material 7d is laid down on the belt 1d by
carding, so that the fibers of the web material 7d are aligned
substantially in the direction of the belt 1d. As the belt 1d rotates
about rollers 3d, 3d', the web material 7d, supported on belt 1d, passes
through apparatus 9d wherein a second fibrous web material 1d is laid down
on the top of the first fibrous web material 7d, by carding, so that the
fibers of the second web material lid 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 11d 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
calendaring 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.
FIG. 2B illustrates a method of consolidating the fibrous web wherein a
fibrous web 23b supported 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.
FIG. 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 web 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 (BaTiO.sub.4) and also include
particulate carbon such as carbon 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. 2C, a second preformed
thermoplastic resin film 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 42, 42' 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 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 to
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 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, and 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 50.degree. F., above the
heat deflection temperature (HDT) of the thermoplastic resin, preferably,
50.degree.-300.degree. F. above the HDT, and, most preferably,
100.degree.-200.degree. F. above the HDT. For the preferred "engineering
grade" thermoplastic resins, this typically means temperatures of
550.degree.-650.degree. F. The HDT value for a number of these
"engineering grade" thermoplastic resins is set forth in the following
Table.
TABLE
______________________________________
Resin Type Trade name/Supplier
HDT (.degree.F.)
______________________________________
Liquid Crystal
Vectra/Celanese 350-460
Polymer Xydar/Dartco 554-655
Nylon-4,6 TS/Allied 300-545
Polyamideimide
Torlon 524-540
Polyarylate Ardel/Amoco 345
Arylon/DuPont 311-340
Durel/Celanese 316-355
Polyarylsulfone
Radel/Amoco 400-415
Polycarbonate
AEC/Dow 320
Lexan PPC/G.E. 305-325
Polyetherimide
Ultem/G.E. 387-433
Polyetherketone
Victrex PES/ICI Americas
330-645
(PEK)
Polyethersulfone
Victrex PES/ICI Americas
397-421
(PES)
Polyether-ether-
Victrex PEEK/ICI Americas
300-600
ketone (PEEK)
Polyketone Kadel/Amoco Similar to
PEEK
Polyphenylene
Ryton/Phillips 500
sulfide (PPS)
Polysulfone (PS)
Udel/Amoco 335-358
______________________________________
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",
37"' may then be stacked with nodes 51', 51" of an upper sheet 37', 37" in
contact with the antinodes 53", 53"' 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
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 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 web 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 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. 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 roller 57' contact moving web 29',
stripes 59.increment. 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 to one another in the areas 71 where no release film 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 .gamma. (node-to-node or
antinode-to-antinode distance) and node-to-antinode distance of .gamma./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-half of the
wavelength of the microwave radiation to 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 for subsequent 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.RTM. fiber (polyphenylene sulfide,
Phillips), average length 1.5", 1.5 denier and 70% by weight fiberglass
(Owens Corning), average length 3", 1.5 denier, was carded to produce a
uniformly mixed web having approximately 80% of the fibers oriented in the
machine direction. The web weight was approximately 0.25 oz/yd.sub.2.
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=1/8") by passage through a pair of rotary dies, as
illustrated in FIG. 5, operating at about 550.degree. F. 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.
EXAMPLES 3-7
In the following examples, mixtures of Ryton.RTM. fiber (polyphenylene
sulfide, Phillips), average length 1.5", 1.5 denier and fiberglass (Owens
Corning), average length 3", 1.5 denier, were carded to produce uniformly
mixed webs. Consolidation and/or corrugation was carried out at
approximately 600.degree. F. and 500 psi nip pressure. Unless otherwise
indicated webs were laid up by alternate layers at 0.degree. and
90.degree. 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=1/8")
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=1/8")
corresponding to a honeycomb density of 2 lb/cu. ft. and then
simultaneously consolidated and corrugated.
EXAMPLE 5
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=3/8")
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.degree. and +45.degree. to the cell axis to equate to a material
yielding a hexagonal honeycomb half cell (face length=1/8") corresponding
to a honeycomb density of 7 lb/cu. ft. and then simultaneously
consolidated and corrugated.
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 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.
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