U.S. patent number 3,607,500 [Application Number 04/830,533] was granted by the patent office on 1971-09-21 for a molding fibrous webs.
This patent grant is currently assigned to E. I. du Pont de Nemours and Company. Invention is credited to Nathan D. Field.
United States Patent |
3,607,500 |
Field |
September 21, 1971 |
A MOLDING FIBROUS WEBS
Abstract
Expanded, nonwoven fibrous articles are formed by heating in a
shaped mold compressed fibrous webs impregnated with a
thermoplastic resin binder. The compressed webs may be economically
shipped and the shaped articles generated at the point of
destination.
Inventors: |
Field; Nathan D. (Allentown,
PA) |
Assignee: |
E. I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
25257159 |
Appl.
No.: |
04/830,533 |
Filed: |
June 4, 1969 |
Current U.S.
Class: |
264/119; 264/120;
264/234; 264/257 |
Current CPC
Class: |
D04H
1/54 (20130101); D04H 1/558 (20130101) |
Current International
Class: |
D04H
1/54 (20060101); D04H 1/00 (20060101); D04h
001/60 () |
Field of
Search: |
;264/119,120,257,322,234 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: White; Robert F.
Assistant Examiner: Hall; J. R.
Claims
I claim:
1. A process for producing a shaped nonwoven article of
thermoplastic fibers comprising
heating a compressed plurality of crimped, thermoplastic fibers
bonded with a thermoplastic resin binder at their crossover points,
to a temperature T.sub.2,
cooling the compressed fibers to temperature T.sub.1,
removing the compressive force,
heating the fibers in a shaped mold to a temperature T.sub.3 so as
to form an expanded, fibrous article having the shape of the
interior of said mold, and
removing said article from said mold,
wherein
T.sub.3 >t.sub.2 >t.sub.g >T.sub.1, and T.sub.m
>T.sub.2 T.sub.g being the glass-transition temperature of said
thermoplastic fibers, T.sub.m being the melting temperature of said
thermoplastic resin binder.
2. The process of claim 1 wherein T.sub.3 >T.sub.m.
3. The process of claim 2 wherein said article is cooled below
temperature T.sub.m before removal from said mold.
4. The process of claim 1 wherein said thermoplastic fibers consist
essentially of a material selected from the group consisting of
poly(ethylene terephthalate) and nylon.
5. The process of claim 1 wherein said thermoplastic resin binder
consists essentially of a material selected from the group
consisting of polyacrylates, polymethacrylates, polyesters and
polyurethanes.
6. The process of claim 5 wherein said thermoplastic resin binder
consists essentially of the copolyester poly(ethylene
terephthalate/azelate).
7. The process of claim 1 wherein said plurality of crimped,
thermoplastic fibers bonded with a thermoplastic resin binder at
their crossover points comprises a web of crimped thermoplastic
fibers impregnated with said binder.
8. The process of claim 7 wherein said fibers have about 9 crimps
per inch and are about 2 inches in length.
9. The process of claim 1 including the further steps of
heating said expanded, fibrous article above temperature
T.sub.m,
cooling said article below temperature T.sub.m,
compressing said article at temperature T.sub.5,
cooling said article to temperature T.sub.4,
removing the compressive force, and
heating said article to temperature T.sub.6 so as to cause said
article to assume substantially the same shape it had before said
further steps, wherein
T.sub.6 >T.sub.5 >T.sub.g >T.sub.4, and T.sub.m
>T.sub.5.
10. The process of claim 2 including the further steps of
cooling said article below temperature T.sub.m,
compressing said article at temperature T.sub.5,
Cooling said article to temperature T.sub.4,
Removing the compressive force, and
heating said article to temperature T.sub.6 so as to cause said
article to assume substantially the same shape it had before said
further steps, wherein
T.sub.6 >t.sub.5 >t.sub.g >T.sub.4, and T.sub.m
>T.sub.5.
11. The process of claim 3 including the further steps of
compressing said article at temperature T.sub.5,
cooling said article to temperature T.sub.4,
removing the compressive force, and
heating said article to temperature T.sub.6 so as to cause said
article to assume substantially the same shape it had before said
further steps, wherein
T.sub.6 >T.sub.5 >T.sub.g >T.sub.4, and T.sub.m
>T.sub.5 .
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns bulky, nonwoven fibrous structures and,
more particularly, the production of molded three-dimensional,
lightweight, shaped articles of nonwoven fibers.
2. Description of the Prior Art
Three-dimensional nonwoven structures of fibers such as nylon and
polyester are currently used as filling materials in such articles
of commerce as furniture cushions, pillows, sleeping bags, and the
like. Among the many advantages of using synthetic fibers are that
they are lightweight and nonallergenic. Although the qualities of
bulkiness and low density, which are inherent in these articles,
are desirable in the eyes of the consumer, they cause economic
problems in shipping. The situation is somewhat analogous to the
problems of a balloon manufacturer having to ship gas-filled
balloons instead of deflated ones and finding his trucking costs
prohibitive. A solution to the problem of shipping bulky, nonwoven
fibrous webs, batts, and the like, was proposed by Coates et al. in
U.S. Pat. No. 3,291,677, issued Dec. 13, 1966. His contribution was
to physically compress the nonwoven structure, apply heat, and cool
it while under compressive restraint. The result was a wafer-thin
fibrous article capable of being rejuvenated or restored to its
original dimensions merely by the application of heat. Thus, in
accord with these teachings, the manufacturer of nonwoven structure
could make his fibrous structure, compress it to a wafer, ship the
wafer at low cost, and the customer could rejuvenate the wafer at
the desired time in his own mill. Thus, because only thin wafers
would be shipped, space would be economized and, consequently,
trucking costs would be relatively low.
Oftentimes, as in the manufacture of auto seat cushions, it is
desirable to have a fibrous filling product molded in some
desirable three-dimensional shape. Molding techniques related to
fibrous webs are well know in the art. In the normal course of
events consistent with the technology described above, the
customers would rejuvenate the wafer, then subject the rejuvenated
web to compressive molding techniques to obtain the desired
three-dimensional shape. It has now been found, however, that if
the compressed, wafer-thin, fibrous sheet produced by the above
technology is placed in a mold and rejuvenated in the mold, as by
heating, the expanding wafer assumes the inside shape of the mold
and this shape can be made permanent.
SUMMARY OF THE INVENTION
This invention provides a process for producing a lightweight,
three-dimensional, shaped nonwoven article of thermoplastic fibers
comprising the steps of:
A. COMPRESSING A LOW-DENSITY ASSEMBLY OF CRIMPED THERMOPLASTIC
FIBERS BONDED AT THEIR CROSSOVER POINTS WITH THERMOPLASTIC RESIN,
WITH THE APPLICATION OF HEAT TO RAISE THE TEMPERATURE OF THE
ASSEMBLY TO T.sub.2 ;
B. COOLING THE ASSEMBLY TO T.sub.1 AND THEN REMOVING EXTERIOR
COMPRESSIVE FORCE;
C. PLACING THE EXPANSIBLE FIBROUS ASSEMBLY IN A SHAPED MOLD;
D. HEATING THE ASSEMBLY TO T.sub.3 thus expanding it to the inside
shape of the mold so as to form an expanded, shaped, fibrous
article; and
E. REMOVING SAID ARTICLE FROM THE MOLD, PREFERABLY PRECEDED BY
COOLING BELOW T.sub.m, wherein:
T.sub.3 >T.sub.2 >T.sub.g >T.sub.l, and T.sub.m
>T.sub.2, wherein T followed by the various subscripts indicates
various temperatures, T.sub.m being the melting temperature of the
thermoplastic resin binder and T.sub.g being the glass-transition
temperature of thermoplastic fibers. The symbol ">" indicates
"is greater than."
DETAILED DESCRIPTION
T.sub.g, the classical "glass-transition" temperature, also called
the "second-order" transition temperature of the fiber, is the
temperature at which the thermoplastic material changes from the
rubbery state to the glassy state and also the temperature at which
a discontinuity occurs in a graph showing temperature as a function
of a thermodynamic variable such as heat capacity. The T.sub.g of
poly(ethylene terephthalate) is about 67.degree. C.
By T.sub.m, the melting temperature of the thermoplastic resin
binder, is meant the temperature at which the particular binder is
sufficiently softened to be readily deformable to a new shape and
retain its new shape. For many binders, this is the typical
sticking point which is defined as temperature at which binder
leaves a molten trail upon being rubbed across a heated metal
block. For some highly cross-linked resins that have no true
melting point, this is the temperature at which a marked softening
of the binder is noted.
For convenience in understanding the present invention, reference
will be made to three structures:
A. The Starting Web
B. The Compressed Web
C. The Molded Web
A. the Starting Web
The starting material for the new process is an array, such as a
web, of crimped thermoplastic fibers bonded at their crossover
points by means of a thermoplastic resin. The web may be prepared
from a wide variety of forms of fibers and filaments, such as
continuous monofilaments, continuous multifilaments, carded webs,
warp sliver, top, roping, roving, tow, bulked tow, bulked
continuous filament yarn, spun yarn, batts, and the like. The fiber
orientation in the web may be random, partly oriented (as in a
carded web) or oriented, i.e., running almost exclusively in one
direction, as in a structure such as described by Koller, U.S. Pat.
No. 3,085,922, issued Apr. 16, 1963. A suitable method for
preparing the latter involves carding staple fibers into a web of
substantially parallel fibers or a sliver of parallel fibers,
stacking the web or the sliver in a perforated mold of the desired
size, keeping all fibers parallel during the operation,
impregnating the block of parallel fibers with latex or a solution
of the desired binder, removing excess binder from the fiber block,
preferably by suction, and forcing hot air through the block from
end to end to dry and/or cure the binder matrix. The bonded fiber
block is then removed from the mold and wafers or sheets of the
parallel fibers-on-end are cut from the block by slicing across the
end of the block perpendicular to the axis of the fibers. The
desired angle of the filamentary structures may be achieved by
varying the angle of the cut or by placing the strips in the mold
at an angle and then making the cut on a plane parallel to the face
of the block, transversely to the filamentary structures. The
resulting bonded parallel fibers in the form of a self-supporting
web may be cemented to one or more suitable backing materials
depending on the particular end use desired.
Typical fibers useful in the present invention are of a
thermoplastic nature and comprise, for instance, polyethylene
terephthalate and nylon. Other polyesters that may be used are
described in "Supplement to Book of ASTM Standards" part 10 (1960),
p. 53. Deniers may range from about 1.0 to about 45 and the fibers
may have from about 3 to about 20 crimps per inch (1.2-7.9 per cm.)
which may be of the sawtooth variety (as produced by the
stuffer-box crimper of Hitt, U.S. Pat. No. 2,311,174, issued Feb.
16, 1943) or the spiral variety (such as produced by Kilian, U.S.
Pat. No. 3,050,821, issued Aug. 28, 1962) or even the type of crimp
produced when the fiber passes in frictional contact with a sharp
edge.
A typical starting material is a carded batt or garnetted web of
the above-described fibers. A thermoplastic resin is applied to the
web by spraying, dipping, or other convenient means and the resin
is cured as by heating. Useful thermoplastic resins for nonwovens
are common in the art and may comprise polyacrylates, polyesters,
and the like, including copolymers.
B. the Compressed Web
The compressed web is an expansible, flat, waferlike sheet
resulting from compressing the starting material with the
application of heat. A useful process is to place the starting web
between the platens of a press and compress it to wafer thinness.
Heat is applied to raise the temperature of the fiber structure to
a temperature less than T.sub.m of the binder resin but greater
than T.sub.g of the fiber. The structure is then cooled to a
temperature below T.sub.g of the fibers and the compressive force
removed. The result is a thin waferlike web which has the potential
to be rejuvenated to original thickness by the application of heat.
C. The Molded Web
The compressed web is placed in a shaped mold such as the shape of
an automobile seat cushion. The wafer is then heated to a
temperature greater than T.sub.g of the fibers and preferably, if a
heat-stable structure is desired, greater than T.sub.m of the
binder resin. During this heating step, the wafer expands and
assumes the inside shape of the mold. The structure is then cooled
to at least a temperature below T.sub.m of the binder resin.
The invention will be further illustrated by the following examples
of preferred embodiments which are not intended to delimit the
invention. Example I
This example shows the expansion of a wafer-thin expansible
resin-impregnated fibrous material to the shape of a container.
Commercial poly(ethylene terephthalate) fibers of about 5 denier
per filament and having about 8 crimps per inch (per 2.54 cm.) of
the sawtooth variety is cut to staple of about 2-inch length. The
staple is carded to a web which is cut transverse to the fiber
orientation to 10-inch (25.4 cm.) lengths which are stacked on top
of each other to fill a mold 10 inches by 16 inches by 24 inches
(25.4 cm. by 40.6 cm. by 61 cm.). The fibers are substantially all
oriented in the same direction.
The mold is impregnated with a 10 percent methylene chloride
solution of a polyurethane resin having a T.sub.m of about
165.degree. C. to a pickup of 22 percent solids resin based on the
weight of the resin-impregnated structure. The structure is cured
at 140.degree. C. for 1 hour to cross-link the resin. The density
of the resin-impregnated web is about 1.33 pounds/foot.sup.3
(0.0213 gm./cc.) and it is sliced to pieces each being about 2.75
in. (6.99 cm.) high. A piece is placed between wooden boards and
compressed therebetween to a height of about 0.25 in. (0.64 cm.)
while heating at 110.degree. C. for 1 hour. On cooling to about
room temperature and release of the compressive force imposed by
the boards, the cushion is only 0.75 in. (1.90 cm.) thick. A
section of the compressed wafer-thin web is cut into chips
approximately 0.25 to 0.50 in. (0.635 to 1.27 cm.) wide. The chips
are placed in the bottom of a 400 ml. beaker, and the beaker
containing them is heated to a temperature of about 130.degree. C.
Upon heating, the fibrous material expands to fill the beaker and
surprisingly, upon removal of the fibrous web from the beaker, the
inside contour of the beaker is retained in the web.
EXAMPLE II
This example illustrates the process of the present invention as
applied to a fibrous structure the fibers of which are oriented in
a single direction.
Poly(ethylene terephthalate) containing 0.3 percent by weight
TiO.sub.2 is spun to fibers in general accordance with procedures
described in Kilian (reference above) to produce asymmetric
birefringence across their cross sections. The yarn is heated and
assumes a crimp of helical configuration and its T.sub.g is about
70.degree. C. The fibers are cut to 2.5 -inch (6.35 cm.) staple. A
blend is made comprising 30 percent by weight of this fiber with 70
percent by weight of 2.5 inch (6.35 cm.) commercially available
stuffer-box crimp (sawtooth type) poly(ethylene terephthalate)
having a T.sub.g of about 70.degree. C. The staple blend is
garnetted to a batt and cut transverse to its length in slices 10
in. (25.4 cm.) thick. The slices are compressed in a mold and
impregnated as in Example I with a binder resin comprising a
copolyester of poly(ethylene terephthalate/azelate). The resin is
cured and has a T.sub.m of approximately 170.degree. C. The process
is similar to the process described in Koller, supra. The density
of the fibrous structure upon release of the mold is 0.61
lb./ft..sup.3 (0.0098 gm./cc.). The 4 1/8 inch (10.48 cm.) thick
fibrous structure is compressed to 11/2inch (3.81 cm.) between the
platens of the press. The structure is heated while compressing to
a temperature of 125.degree. C. and cooled in an ice chest. The
wafer-thin expansible structure is then placed in a cake mold of
the form of a rabbit and expanded in the mold by heating to a
temperature 185.degree. C. for 10 minutes. It is then cooled to
room temperature and removed from the mold. The fibrous structure
is of the shape of a rabbit.
This example also describes the utility of the present invention in
making such articles of commerce as stuffed toys.
Example III
Poly(ethylene terephthalate) is spun to filaments in accordance
with the procedure Kilian, referenced above, to produce an
asymmetric birefringence across their diameters. The fibers are
heated and assume a spiral crimp configuration of about 9.5 crimp
per inch (3.7/cm.). The T.sub.g of the fibers is about 70.degree.
C. The fibers are cut to 2.5 in. (6.35 cm.) staple and garnetted
and crosslapped to a 5 oz./46 in. yard weight (110 gm./m..sup.2)
web while spraying the top with a 16 percent by weight aqueous
dispersion of a self-cross-linking acrylic resin made from
acrylates, methacrylates, N-methylolmethacrylamide and a
cross-linking agent, which has a T.sub.m of 185.degree. C. to give
8 percent by weight dry pickup. The resin is cured at 135.degree.
C. for 2 minutes and then the opposite side of the web is sprayed
in the same manner to give a total (both sides) of 16 percent by
weight, solids resin based on the weight of the resin-impregnated
web. The spray is at high pressure on the thin batting and
excellent penetration of the resin into the center of the batting
is effected so that a great majority of the fiber crossover points
are coated with resin. The thin batting is pretreated at
approximately 191.degree. C. for 5 minutes in a forced-draft over,
laminated in a stack of 10 layers by spraying a small amount of the
above resin on one surface stacking and curing the entire structure
at approximately 137.degree. C. for 30 minutes. The
resin-impregnated fibrous structure is then compressed to one-tenth
of its original height by compressing between thin aluminum plates
for 30 minutes at approximately 137.degree. C. The wafer-thin
expansible structure is then cooled, the plates removed, and it is
cut to the dimensions of a housewife's eight-section aluminum
muffin mold. The sample is then placed on the mold and clamped with
a screen. The structure is heated in an oven at approximately
181.degree. C. for 5 minutes. On cooling and removal, the fibrous
batting is found to have expanded permanently to the shape of the
depression in the mold. The expanded molded web is cut into four
sections, one section is compressed flat at approximately
149.degree. C. for 5 minutes and upon removal of the compressive
force and heating to approximately 163.degree. C. for 5 minutes, it
expands, but not into the previously molded shape. Another section
is heated in the original mold at approximately 199.degree. C. for
5 minutes and then compressed flat at approximately 149.degree. C.
and then cooled, It is 0.5 in. (1.27 cm.) thick. It is heated at
approximately 163.degree. C. for 5 minutes and surprisingly it
expands into the previously molded shape. This latter phenomenon
illustrates the fact that the new molded structures themselves can
be reheated above T.sub.m in the molded shape, cooled below T.sub.m
to temperature T.sub.5, compressed to wafer thinness, cooled to
T.sub.4 followed by removal of compression, and reheated to
temperature T.sub.6 causing them to resume their molded shape,
wherein
T.sub.6 >T.sub.5 >T.sub.g >T.sub.4, and T.sub.m
>T.sub.5. This latter procedure is a preferred embodiment of the
process of this invention; it enables articles to be molded
according to the process of claim 1, compressed to wafer thinness
convenient for shipping, and restored to the molded shape by
heating in an ordinary oven without need for a shaping mold for the
final heating.
* * * * *