Method for forming a vacuum bonded non-woven batt

A method of forming a vacuum bonded non-woven batt includes the steps of blending at least first and second staple polymer fiber constituents. One of the fiber constituents has a relatively low predetermined melting temperature and the other a relatively high melting temperature. The intermixture is formed either into a relatively thick single layer web or a relatively thin web which is then formed into a relatively thick multilayer web structure. The web structure is positioned on a rotating, air permeable drum and a vacuum is used to substantially reduce the thickness and increase the density of the web structure. The web structure is heated to a temperature at or above the relatively low melting temperature of the first fiber constituent and below the melting temperature of the second fiber constituent while under vacuum to release the plastic memory of the fibers of the first fiber constituent in their compressed configuration. The two types of fibers are fused to themselves to form a batt having intimately interconnected and fused first and second fiber constituents. The apparatus on which the above method is performed includes a housing having two perforated counter-rotating drums positioned therein with vacuum means for applying a vacuum through the drum and through the web structure to reduce the thickness and increase the density of the web structure by vacuum pressure alone. Heating means heats the web structure as it is moved through the housing to release the plastic memory of the fibers of the first fiber constituent in their compressed configuration and fuse them to themselves and to the fibers of the second fiber constituent to form a relatively dense batt.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION 
This invention relates to a method and apparatus for forming, by means of 
vacuum, a non-woven batt. The batt is characterized by having a relatively 
high density which renders it suitable for uses such as mattresses, 
furniture upholstery and similar applications where substantial density 
and resistance against compression is desired, together with substantial 
resilience which will return the batt to its shape and thickness after 
compression for an indefinite number of cycles. 
There are a number of advantages to be achieved by construction of batts 
for use as mattresses and upholstery from synthetic, staple fiber 
material. Such fibers are inherently lightweight and therefore easy to 
ship, store and manipulate during fabrication. These fibers are also 
generally less moisture absorbent than natural fibers such as cotton, or 
cellulosic based synthetic fibers such as rayon. Therefore, products made 
from these fibers can be maintained in a more hygienic condition and dried 
with much less expenditure of energy. Many such fibers also tend to melt 
and drip rather than burn. While some of these fibers give off toxic 
fumes, the escape of such fumes can be avoided or minimized by 
encapsulating the batt in a fire retardant or relatively air impermeable 
casing. PG,4 In contrast, fibers such as cotton burn rapidly at high heat 
and generate dense smoke. 
However, synthetic staple fibers also present certain processing 
difficulties which have heretofore made the construction of a relatively 
dense non-woven batt from synthetic staple fibers difficult and in some 
cases impractical. For example, the resiliency inherent in synthetic 
fibers such as nylon and polyester is caused by the plastic memory which 
is set into the fiber during manufacture. By plastic memory is meant 
simply the tendency of a fiber to return to a given shape upon release of 
an externally applied force. Unless the plastic memory is altered by 
either elevated temperature or stress beyond the tolerance of the fiber, 
the plastic memory lasts essentially throughout the life of the fiber. 
This makes formation of a batt by compressing a much thicker, less dense 
batt very difficult because of the tendency of the fibers to rebound to 
their original shape. Such fiber batts can be maintained in a compressed 
state, but this has sometimes involved the encapsulation of the batt in a 
cover or container. All of these methods create other problems such as 
unevenness and eventual deterioration of the batt due to fiber shifting, 
breakage and breakdown of the mechanical structure which maintains the 
compressed batt. 
Not only are the batts themselves subject to numerous disadvantages, but 
the manufacturing processes known in the prior art are deficient in 
numerous respects. For example, insofar as is known all processes compress 
the batt into its desired density by use of engaging members such as 
rollers or plates on both sides of the batt. In effect, the batt is heated 
simultaneously from both sides to the point where its elastic memory is 
relaxed. However, the batt must then be removed from the rollers, plates 
or the like which have held the batt in its compressed state. Even with 
the use of TFE or other similarly coated rollers or plates, sticking is a 
common problem. In addition, even heating is inherently difficult to 
obtain since the fibers in contact with the heated metal surfaces are 
heated almost instantly whereas fibers in the interior of the batt are 
heated at a much slower rate. If the rollers between which the batt is 
traveling are heated to the extent necessary to completely relax the 
plastic memory of the fibers on the interior of the batt, quite often the 
fibers in intimate contact with the rollers will melt completely or 
disintegrate. If the rollers are cooled to avoid completely melting of the 
fibers on the outer surface of the batt, the interior fibers are not 
heated sufficiently to reset their plastic memory. In this event, the 
outer fibers are constantly being pushed against from the interior by 
fibers whose plastic memory is constantly attempting to cause the fibers 
to reassume their original shape. Attempts to correct this problem have 
included varying the percentage of fibers having relatively different 
melting temperatures through the cross-section of the batt or providing 
fibers on the interior of the batt having a relatively lower temperature 
at which the elastic memory is relaxed. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the invention to provide a method and 
apparatus for forming a vacuum bonded non-woven batt. 
It is another object of the present invention to provide a method and 
apparatus for forming a vacuum bonded non-woven batt wherein the batt is 
evenly heated from one side to the other by heated air. 
It is another object of the present invention to provide a method and 
apparatus for forming a vacuum bonded non-woven batt in which an even 
distribution of fibers throughout the batt can be achieved, 
It is yet another object of the invention to provide a method and apparatus 
for forming a vacuum bonded non-woven batt wherein the desired density and 
thickness of the batt can be maintained without physically compressing the 
batt between rollers, plates or the like. 
These and other objects and advantages of the present invention are 
achieved in a method which comprises the steps of blending at least first 
and second staple polymer fiber constituents to form a homogeneous mixture 
of the fibers. The first fiber constituent has a relatively low melting 
temperature and the second fiber constituent has a relatively high melting 
temperature. A relatively thin web is formed of the blended fibers. Then, 
a plurality of these webs are used to form a relatively thick multilayer 
web structure. Alternately, a relatively thick, single layer structure can 
be formed. 
The web structure is positioned on an air permeable support and a vacuum is 
applied through the multilayer web structure downstream from one side to 
the other and through the air permeable support sufficient to 
substantially reduce the thickness and increase the density of the 
multilayer web structure by vacuum pressure alone. The multilayer web 
structure is heated to a temperature at or above the relatively low 
melting temperature of the first fiber constituent and below the melting 
temperature of the second fiber constituent while under vacuum pressure. 
The plastic memory of the fibers of the first fiber constituent is reset. 
The fibers of the first fiber constituent fuse to themselves and to the 
fibers of the second fiber constituent to form a batt having intimately 
interconnected and fused web layers and intimately interconnected and 
fused first and second fiber constituents. The multilayer web structure is 
then cooled to reset the plastic memory of the fibers of the first fiber 
constituent in their compressed state to form a batt having a density and 
thickness substantially the same as induced in the multilayer web 
structure by the vacuum. 
The multilayer web structure is positioned on a perforated rotating metal 
drum. Preferably, two metal drums are used, with the multilayer web 
structure being first applied onto the first perforated rotating drum for 
a predetermined period of time and then onto the second, counter-rotating 
perforated drum whereby the thickness of the web is reduced and the 
density of the web increased uniformly throughout the thickness of the web 
structure by sequential passage of air through the web from first one side 
to the other and then on the second drum through the other side. 
According to the embodiment disclosed, the web structure is heated by 
heating the air, movement of which through the web and the perforated 
rotating drums create the vacuum. 
The thickness and density of the web structure is varied by varying the 
amount of vacuum applied to the web structure and the beginning thickness 
of the web structure itself. The distance of the first and second drums 
can be varied at the point of transfer of the web structure from the first 
to the second drum to correspond generally to the thickness of the web 
structure in order not to alter the orientation of the fibers in the web 
structure while the transfer is taking place. 
The apparatus according to the present invention includes housing means. 
Air permeable support means are mounted in the housing means for carrying 
the multi-layer web structure, and vacuum means cooperate with the housing 
means and the air permeable support means to apply a vacuum through the 
multilayer web structure downstream from one side of the web to the other 
and through the air permeable support means sufficient to substantially 
reduce the thickness and increase the density of the multilayer web 
structure by vacuum pressure alone. 
Heating means are provided for heating the multilayer web structure to a 
temperature at or above the relatively low melting temperature of the 
first fiber constituent and below the melting temperature of the second 
fiber constituent while under vacuum and in its reduced thickness state to 
release the plastic memory of the fibers of the first fiber constituent in 
their compressed configuration and fuse the fibers of the first staple 
fiber constituent to themselves and to the fibers of the second fiber 
constituent. The result is a batt having intimately interconnected and 
fused web layers and intimately interconnected and fused first and second 
fiber constituents. 
Preferably, the air permeable support comprises first and second 
perforated, rotatably-mounted drums positioned in closely spaced-apart web 
transferring relation to each other. Preferably, adjustment means are 
provided for moving the axis of rotation of the first and second drums 
relative to each other for varying the distance between the adjacent 
surfaces of the first and second drums to correspond to the thickness of 
the web structure being carried on the drum. Preferably, the first drum is 
positioned to carry the web structure in a zone comprising approximately 
one half of its circumference. The second drum is positioned to carry the 
web structure received from the first drum in a zone comprising 
approximately one half of its circumference in diametrical opposition to 
the zone of the first drum carrying the web structure. 
Cooperating stationary baffle means positioned within the first and second 
drums restrict vacuum flow through the first and second drums to the web 
structure carrying zone of the respective drums.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now specifically to the drawings, a block diagram of the method 
according to the invention is provided in FIG. 1. The method begins by 
opening and blending suitable staple fibers. The staple fibers to be used 
are chosen from the group defined as thermoplastic polymer fibers such as 
nylon and polyester. Of course, other thermoplastic fibers can be used 
depending upon the precise processing limitations imposed and the nature 
of the compressed batt which is desired at the end of the process. For 
purposes of this application and to illustrate the process and the 
apparatus, the batt is constructed of 85 percent Type 430 15 denier, 3 
inch (7.6 cm) staple polyester and 15 percent Type 410 8 denier 2 inch (5 
cm) staple polyester, both manufactured by Eastman Fibers. The Type 430 
polyester is a conventional polyester fiber which has a melting 
temperature of approximately 480.degree. F. (249.degree. C). As used in 
the specification and claims, this fiber is referred to as having a 
relatively high predetermined melting temperature as compared with the 
Type 410 low melt polyester which has a melting temperature of 
approximately 300.degree. (149.degree. C). 
Low melt polyester of the type referred to above has a melting temperature 
of approximately 300.degree. F. (149.degree. C.), but begins to soften and 
become tacky at approximately 240.degree. to 260.degree. F. 
(115.degree.-127.degree. C.). 
As used in this application, however, the term melting does not refer to 
the actual transformation of the solid polyester into liquid form. Rather, 
it refers to a gradual transformation of the fiber over range of 
temperatures within which the polyester becomes sufficiently soft and 
tacky to cling to other fibers within which it comes in contact, including 
other fibers having its same characteristics and, as described above, 
adjacent polyester fibers having a higher melting temperature. It is an 
inherent characteristic of thermoplastic fibers such as polyester and 
nylon, that they become sticky and tacky when melted, as that term is used 
in this application. Also, thermoplastic fibers lose their "plastic 
memory" when thus heated. The process and apparatus described in this 
application take advantage of these two simultaneous occurrences by 
softening and releasing the plastic memory in the fibers having the 
relatively low melting temperature and causing these fibers to fuse to 
themselves and to the other polyester fibers in the mat which have not 
melted and which have not lost their plastic memory. 
The opened and blended fiber intermixture is conveyed to a web forming 
machine such as a garnet machine or other type of web forming machine. As 
illustrated in this application, the thickness of a single web formed in 
the web formation step will be approximately 1/2 to 3/4 of one inch 
(1.3-1.9 cm) thick, with a square foot (0.09 m.sup.2) piece of the web 
weighing approximately 1/3 of an ounce (8.5 gm). However, an air laying 
machine, such as a Rando webber can be used to form a thick, single layer 
web structure. Further discussion relates to the multilayer web structure 
formed by a garnet machine. 
Once formed, the web is formed into a multilayer web structure by means of 
an apparatus which festoons multiple thicknesses of the web onto a moving 
slat conveyor in progressive overlapping relationship. The number of 
layers which make up the multilayer web structure is determined by the 
speed of the slat conveyor in relation to the speed at which successive 
layers of the web are layered on top of each other. In the examples 
disclosed below, the number of single webs which make up a multilayer web 
structure range between 6 and 28, with the speed of the apron conveyor 
ranging between 27 feet per minute (8.2 m/min) and 6 feet per minute (1.82 
m/min). See FIG. 2. 
Once the multilayer web structure is formed, it is moved successively onto 
first and second rotating drums where the web structure batt is 
simultaneously compressed by vacuum and heated so that the relatively low 
melting point polyester melts (softens) to the extent necessary to fuse to 
itself and to the other polyester fibers having a relatively higher 
melting point. The structure is cooled to reset the plastic memory of the 
relatively low melting point polyester to form a batt having a density and 
thickness substantially the same as when the batt was compressed and 
heated on the rotating drums. See FIG. 9. 
Then, as desired, the batt may be covered with a suitable cover such as 
mattress ticking or upholstery to form a very dense and resilient 
cushion-like material. See FIG. 10. 
The resulting construction offers substantial advantages over materials of 
equivalent density such as polyurethane foam. The resulting cushions or 
mattresses are usable in environments such as aircraft and prisons where a 
relatively high degree of fire retardancy and relatively low output of 
toxic fumes is desired. Polyester is particularly desirable from this 
standpoint, since it does not flash-burn and is self-extinguishing. When 
fully melted to liquid state, polyester drops off when exposed to flame or 
rolls, with a black, waxy edge forming along the effected area. By 
enclosing the entire batt within a cover, a much safer product than either 
foam or cotton is achieved. 
Referring now to FIG. 3, an apparatus 10 according to the invention by 
which the method described above may be carried out is shown. Apparatus 10 
includes a large substantially rectangular sheet metal housing 11, the 
upper extent of which comprises an air recirculation chamber. A one 
million BTU (252,000 kg-cal) gas furnace 13 is positioned in the lower 
portion of housing 11. Upward movement of the heated air from gas furnace 
13 through the housing provides the heat necessary to soften and melt the 
polyester. 
Two counter-rotating drums 15 and 16, respectively, are positioned in the 
central portion of housing 11. Drum 15 is positioned adjacent an inlet 17 
through which the multilayer web structure W is fed. The web structure is 
delivered from the upstream processes described above by means of a feed 
apron 18 through inlet 17. Drum 15 is approximately 55 inches (140 cm) in 
diameter and is perforated with a multiplicity of holes 20 (see FIG. 8) in 
the surface to permit the flow of heated air. 
In the embodiment illustrated in this application, the drum has thirty 
holes per square inch (4.7 per sq. cm) with each hole 20 having a diameter 
of three thirty-seconds of an inch (2.4 mm). 
A suction fan 21 preferably having a diameter of 42 inches (107 cm) is 
positioned in communication with the interior of drum 15. As is also shown 
by continued reference to FIG. 3, the lower one half of the circumference 
of drum 15 is shielded by an imperforate baffle 22 so positioned inside 
drum 15 that suction-creating air flow is forced to enter drum 15 through 
the holes 20 in the upper half. 
Drum 15 is also mounted for lateral sliding movement relative to drum 16 by 
means of a shaft 23 mounted in a collar 24 having an elongate opening 25. 
Once adjusted, shaft 23 can be locked in any given position within collar 
24 by any conventional means such as a locking pillow block or the like. 
(Not shown). 
Drum 16 is mounted immediately downstream from drum 15 in housing 11. Drum 
16 includes a ventilation fan 27, also having a diameter of 42 inches (107 
cm). Note that fans 21 and 27 are shown in FIG. 3 in reduced size for 
clarity. An imperforate baffle 28 positioned inside drum 16 and enclosing 
the upper half of the circumference of drum 16 forces suction creating air 
flow to flow through the holes 20 in the lower half of the drum surface. 
Preferably, the drum 16 contains the same number and size holes 20 as 
described above with reference to drum 15. The exiting batt is 
simultaneously cooled and carried away from housing 11 by a feed apron 30. 
Both drums are ventilated and driven in the manner shown in FIG. 4. As is 
shown specifically with reference to drum 15, fan 21 recirculates heated 
air back to the ventilation chamber of 12 of housing 11 by means of a 
recirculating conduit 33. Drum 15 is driven in a conventional manner by 
means of an electric motor 35 connected by suitable drive belting 36 to a 
drive pulley 37. 
Referring again to FIG. 3, multilayer web structure W in uncompressed form 
enters housing 11 through inlet 17. Suction applied through the holes 20 
in drum 15 immediately force the web structure W tightly down onto the 
rotating surface of drum 15 and by air flow through the holes 20 and 
through the porous web structure. As is apparent, the extent to which 
compression takes place at this point can be controlled by the suction 
exerted through drum 15 by fan 21. The air temperature is approximately 
325.degree. F. (163.degree. C.). 
By continued reference to FIG. 3, it is seen that one side of the mat is in 
contact with drum 15 along its upper surface. At a point between drum 15 
and drum 16, the web is transferred to drum 16 so that the other side of 
the web is in contact with the surface of drum 16 and the surface which 
was previously in contact with drum 15 is now spaced-apart from the 
surface of drum 16. In effect, a reverse flow of air is created. It has 
been found that an extraordinarily uniform degree of heating takes place 
by doing this. Therefore, the polyester fibers having a relatively low 
melting temperature can be melted throughout the thickness of the web 
without any melting of the polyester fibers having the relatively high 
melting temperature. 
In order to maintain constant vacuum pressure on the web throughout the 
housing, it is important that intimate contact between the web structure 
and either drum 15 or 16 be maintained at all times. To do this, it is 
important that a gap not be created at the point of transfer of the web 
structure between drum 15 and drum 16. For example, if the space between 
the adjacent surfaces of drum 15 and 16 was 5 inches (12.7 cm) and the 
thickness of the web being transferred at that point was only 3 inches 
(7.6 cm), a relatively thin length of drum surface on both drums 15 and 16 
would be exposed to the free flow of air therethrough. The unrestricted 
flow of air could damage the web structure. Furthermore, vacuum would not 
be exerted on the web for a portion of the distance between drum 15 and 
16, thereby allowing the polyester fibers having the relatively high 
melting temperature and which still retain their plastic memory to begin 
to resume their uncompressed state. This would cause undesirable movement 
between the softened low melt polyester fibers and the adjacent polyester 
fibers having the higher melting temperature. Therefore, shaft 23 is 
adjusted in opening 24 as is illustrated in FIGS. 5, 6 and 7. The 
adjustment is made according to the thickness of the web being processed 
so that the distance between adjacent surfaces of drum 15 and 16 very 
closely approximate the thickness of the web in its compressed state as it 
is transferred from drum 15 to drum 16. 
Assuming a web thickness of 4 inches (10 cm) in its compressed state on 
drum 15, the distance between adjacent surfaces of drums 15 and 16 in FIG. 
5 would be 4 inches (10 cm). To manufacture a web having less thickness, 
drums 15 and 16 would be moved closer together by sliding shaft 23 forward 
in opening 24 so that, for example, the distance between drums 15 and 16 
would be 2 inches (5 cm) when processing a 2 inch (5 cm) web. Conversely, 
to process a thicker web, shaft 23 would be moved rearwardly in opening 24 
thereby moving drum 15 away from drum 16 so that, again, the thickness of 
the distance between adjacent surfaces of drums 15 and 16 closely 
approximates the thickness of the web in its compressed state. It is 
important to note that the web structure is not being compressed by the 
adjacent drum surfaces at this point. Compression continues to occur only 
because of vacuum pressure. 
As noted above, a wide variety of high density batts can be created by 
altering the manufacturing of variables in many different ways. In the 
table that follows, only a few of the many possible processing 
combinations are illustrated. In the following examples, note the dramatic 
increase in air flow consistent with the decrease in the input web 
thickness even though lower fan rpms are needed. 
TABLE I 
__________________________________________________________________________ 
FINISHED 
FINISHED PRODUCT INPUT WEB TOTAL FAN 
PRODUCT DENSITY 
THICKNESS 
THICKNESS 
NO. OF 
CAITY 
FAN APRON SPEED 
AIR TEMP. 
oz./ft.sup.3 & (kg/m.sup.3) 
inches 
(cm) 
inches 
(cm) 
LAYERS 
CFM (M.sup.3 /sec) 
RPM ft/min 
(m/min) 
.degree.F. 
(.degree.C.) 
__________________________________________________________________________ 
22.2 4.4 (11) 
20 (51) 
28 5,000 
(2.36) 
800 6.0 (1.82) 
325 
(163) 
24 3.5 (8.9) 
18.5 
(47) 
26 4,800 
(2.26) 
850 6.5 (1.98) 
325 
(163) 
20 3.0 (7.6) 
13.5 
(34) 
18 7,500 
(3.54) 
700 9.0 (2.74) 
325 
(163) 
19 2.0 (5.1) 
9.0 (23) 
12 8,000 
(3.78) 
600 13.0 
(3.96) 
325 
(163) 
20 1.0 (2.5) 
5.0 (13) 
6 10,000 
(4.72) 
550 27.0 
(8.2) 
325 
(163) 
__________________________________________________________________________ 
Once the batt leaves housing 11 it cools very rapidly into a dense batt 
having the same thickness as when processed in housing 11. Cooling resets 
the plastic memory of the low melt polyester fibers, fusing the low melt 
polyester fibers to themselves and also to the fibers having the 
relatively higher melting temperature. Because of the compression created 
by the vacuum, many fibers from adjacent web layers fuse to each other. 
The result is a homogeneous structure which, from visual observation, does 
not appear to have been constructed from a plurality of thinner layers. 
(See FIG. 9). The batt processed on the apparatus and according to the 
method described above therefore has fibers with plastic memories set at 
two different temperatures. The plastic memory of the low melting point 
fibers act as springs to pull the batt into a compressed state. The 
plastic memory of the fibers having the higher melting temperature urge 
the batt to expand but are prevented from doing so by the low melt fibers. 
The result is a batt which, while being held in a relatively dense, 
compressed state nevertheless has considerable resiliency. 
A method and apparatus for forming a vacuum bonded non-woven batt is 
described above. Various details of the invention may be changed without 
departing from its scope. Furthermore, the foregoing description of the 
preferred embodiment according to the present invention is provided for 
the purpose of illustration only and not for the purpose of 
limitation--the invention being defined by the claims.