Method of manufacturing molded articles

Method for manufacturing a molded article, for use, for example as a fluid filter or as a preform for a structural composite, is prepared from a batt of nonwoven structural fibers and a binder material, such as binder fibers or a thermoresponsive resin. The batt is stabilized by exposing it to a temperature slightly below the melting point of the binder material, so that the binder material becomes tacky and bonds the fiber materials at the surface of the batt. By exposing the batt to the heat for only a few seconds, only the binder material at the surface of the batt bonds the structural fibers; the structural fibers within the batt remain unbonded. Accordingly, the batt is "skinned", so that it is stiff enough to be handled, but is still flexible enough that it can be molded into complex shapes. The molding is effected in a mold in which heated air is drawn through the batt to force it to assume the contours of the mold.

BACKGROUND OF THE INVENTION 
This invention relates to a method for manufacturing a molded article for 
use, for example, as a filter or as a preform for resin impregnation to 
form a structural composite. 
U.S. patent application 858,974 discloses and claims a process for the 
manufacture of a fiber reinforced composite article. This composite 
article is manufactured from a nonwoven, airlaid batt, which is formed 
into a preform shape by molding before being injected with an appropriate 
resin to form the composite article. U.S. patent application 858,785 
discloses a process in which a molded article is formed from an airlaid, 
nonwoven batt, which is then formed in a mold and can be used, for 
example, as a fluid filter. The nonwoven batts used in both processes are 
manufactured by techniques which are in general known to those skilled in 
the art, and the batts formed thereby may be pulled apart relatively 
easily. This is because, as the batt is formed, only the electrostatic 
forces between the fibers comprising the batt are relied upon to hold the 
batt together. 
According to the above-identified application, a binder material is 
included in the batt which, upon being heated in an oven in which the batt 
was placed, at least partly melts the binder material, thus fusing the 
fibers in the batt, so that the batt could be handled. Although this 
process, in general, works well, it has been discovered that molding 
relatively thick batts into complex shapes was rendered difficult, because 
the batts had a tendency to buckle when they were molded into certain 
shapes. Accordingly, the batt became too stiff when the batt was heated 
until the binder material fused all the fibers in the batt, but the 
uncured batt was not stable enough to be molded and readily broke apart. 
SUMMARY OF THE INVENTION 
It has been discovered that a batt can be produced which is stable, and yet 
can be molded into complex shapes without buckling. This is effected by 
heating only the surface of the batt, so that the binder material at the 
surface fuses or bonds the fibers at the surface. The binder material 
within the batt is not heated above the temperature at which the binder 
material becomes tacky; accordingly, the fibers away from the surfaces of 
the batt remain unbonded. Accordingly, the exterior of the batt has been 
"skinned"; that is, a relatively stable skin has been formed on the 
surface of the batt to stiffen the surface, thereby stabilizing the batt 
to permit handling. On the other hand, the fibers within the batt have not 
been bonded; accordingly, these fibers remain pliable and can be easily 
molded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the FIG. 1 of the drawing, an airlaid, nonwoven, 
batt-formation machine is generally indicated by the numeral 10 and is of 
the type generally illustrated in U.S. Pat. No. 3,918,126. The machine 10 
is comprised of a feeding mechanism generally indicated by the numeral 12 
and a web-formation mechanism generally indicated by the numeral 14. 
Feeding mechanism 12 includes a housing 16 which encloses a relatively 
large hopper 18 which receives the fiber from which the web or batt is to 
be manufactured. Of course, the fibers are first opened and blended in the 
conventional manner before being placed in the hopper 18. The fiber 
mixture includes staple structural fibers such as curled or uncurled glass 
fibers, graphite fibers and/or high strength polyester. Also, 
thermoplastic fibers are included if the batt is not to be resinated with 
a thermoplastic material. In the preferred embodiment, the fibers in the 
hopper 18 are comprised of 52.5% curled fiberglass, available commercially 
from Owens-Corning Fiberglass Corporation; 17.5% COMPET polyester fiber, 
available commercially from Allied Corporation; and 30% of a 
thermoplastic, binder fiber know such as VINYON, available commercially 
from Celanese Corporation; or polyester fibers such as DACRON, available 
commercially from DuPont Corporation; or KODEL, available commercially 
from Eastman Kodak Company. The blended fibers are indicated by the 
reference numeral 20. A conveying apron 22 is mounted on rollers 24 
located within the hopper 18 which are turned in the direction of the 
arrows by an appropriate power source (not shown), to move the fibers 20 
to the right viewing FIG. 1 toward an elevating apron generally indicated 
by the numeral 26. The elevating apron 26 is mounted on rollers 28 located 
within the hopper and is provided with elongated spikes 30 extending 
therefrom. The rollers are operated by a power source such that the fibers 
are moved upwardly, viewing FIG. 1. A stripper apron 32 is provided with 
spikes 34 and is wrapped about rollers 36 which are also operated by a 
power source. A power source 38 operates a fan 40 which draws air through 
channel 42 defined between the stripper apron 32 and the upper wall of the 
housing 16, generally in the direction of the Arrow A. The metered airflow 
through the channel 42 removes a predetermined quantity of the fibers 20 
from the elevating apron 26. The remaining fibers are returned to the 
hopper through channel 46, defined between the elevator apron 26 and the 
corresponding wall of the housing 16. The metered airflow indicated by 
Arrow A forces the fibers into a duct 44 defined between the upper edge of 
the elevating apron 26 and the corresponding wall of the housing 16. 
The fibers are then consolidated into a feed mat 47 by the air flowing 
through the channel 42 and the duct 44. This air flow enters a 
cylindrical, porous condenser screen 48 which is rotated in the direction 
of the Arrow B by an appropriate power source (not shown). The air flow is 
ducted back to the blower 40 by ductwork generally indicated by the 
numeral 50. The rotating screen 48 compresses the feed mat 47 by 
cooperating with feed rollers 52, which cooperate with mechanical rolls 54 
to advance the feed mat toward the mat formation mechanism, generally 
indicated by the numeral 14. The fibers are then brushed off nosebar 58 
which is carried on housing 60 forming a part of the web formation 
mechanism 14 by a rotating lickerin generally indicated by the numeral 62. 
The lickerin 62 is provided with a serrated surface defining spikes or 
teeth 64 across the entire width and around the circumference of lickerin 
62. The lickerin 62 is powered for rotation as indicated by the Arrow C. 
The fibers are doffed from lickerin 62 by centrifugal forces generated by 
the rotating speed of the lickerin 62 and also by air flow provided by a 
blower 66. Blower 66 blows air into a chamber 68 defined within the 
housing 60 which is guided through a duct 70 and into a channel 72 defined 
between a saber 74 and the lickerin 62. The blended fibers are removed 
from the lickerin and are conveyed by the air stream through a duct 75 to 
a porous conveyer, generally indicated by the numeral 76. The inlet of the 
blower 66 is connected to a chamber 77 defined within the housing 60 which 
in turn in communicated to the duct 75 through the porous conveyor 76. The 
porous conveyor 76 includes a porous belt 78 mounted on rollers 80 which 
move the belt in the direction indicated by the Arrow D. Since the belt 78 
is porous and permits air flow therethrough, the blower 66 is capable of 
circulating air through the channel 72, the duct 74, the chambers 77 and 
68, and the duct 70. Accordingly, the fibers are doffed from the lockerin 
62 and blown through the duct 74 and are condensed on a portion 82 of the 
porous belt 78 to form a nonwoven mat. Since the porous belt 78 is rotated 
around the rollers 80 the mat eventually exits from the portion of the 
belt covered by the duct 74. 
The rotating speed of the lickerin 62 and the quantity of air pumped by the 
blower 66 may be adjusted in a conventional manner to adjust the weight of 
the batt formed by the web formation machine 10. Although lighter weight 
batts are acceptable, the invention prefers that relatively heavy batts, 
of a weight, for example, of four ounces/square yard or greater, are 
preferred because batts of this weight provide a sufficient quantity of 
fiber reinforcement for the structural composite to be manufactured as 
hereinafter described. It is also important that the fibers comprising the 
batt, which are randomly arrayed due to being blown through the duct 74, 
be sufficiently long that they cross each other a number of times, thereby 
providing relative attraction forces between the fibers so that each fiber 
can hold other fibers in place. It is preferred that fibers of at least 
one inch in length be used, since tests have shown that fibers of this 
length engage other fibers in the batt an average of three times, thus 
providing the number of engagements with other fibers necessary to form a 
satisfactory batt. Fibers of shorter length may be used, but they would, 
of course, engage other fibers, on average, fewer times, thus providing a 
batt with less integrity. 
As discussed above, an important feature of the invention is that 
structural composites formed from the batts produced can have strength in 
all three spatial dimensions. The strength is provided by the 
reinforcement provided by the fibers used to make the composite. 
Accordingly, the nonwoven batt formed by the machine 10 will have randomly 
arrayed fibers which extend in all three spatial dimensions, since the 
random orientation of the fibers is a necessary consequence of the air 
formation process. However, it has been shown that the percentage of 
fibers arranged in the direction of the depth of the batt varies 
considerably, depending upon the direction of air flow through the duct 
74. This direction is controlled by the spacing between the saber 74 and 
the lickerin 62. The saber 74 is mounted on an eccentric, so that its 
position relative to the lickerin, 62 is adjustable, thereby making the 
width of the channel 72 also adjustable. Normally, the saber 74 is spaced 
away from the lickerin 62 so that the air flow through the channel 72 
tends to follow the shape of the channel in the direction of the Arrow D. 
While batts formed with air flow in this direction will have some fibers 
having components oriented in the direction of the depth of the batt, the 
majority of fibers will be oriented along the length and the width of the 
batt. However, it has been discovered that by moving the saber, 74 closer 
to the lickerin 62 and by adjusting the blower 66 accordingly, a venturi 
effect is created which deflects the air flow in the direction of the 
Arrow E. Batts formed in this manner have been found to have about 30% of 
their fibers having components oriented in the direction of the depth of 
the batt. Accordingly, a composite material formed from a batt having 30% 
of the fibers oriented in the depth direction will have almost the same 
strength in all three spatial dimensions. 
The machine 10 has been described in accordance with the feeding mechanism 
12. However, the purpose of the feeding mechanism 12 is to produce the 
feed mat 46 for the web formation mechanism 14. As is well know to those 
skilled in the art, the feed web may also be formed from a roller card and 
cross-lapping machine. This latter mechanism may be more efficient for a 
high volume production. Alternatively, the feed web may also be formed by 
a picker. This system may be more efficient for producing diversified, 
short-run lots. 
The batt is transferred from the conveyor 78 onto an adjacent conveyor 84 
which includes a porous belt 86 powered for rotation about rollers 88 in 
the direction indicated by the Arrow F. If the batt is to be resinated in 
lieu of using binder fibers or in addition to using binder fibers, an 
appropriate foamed resin is poured into the hopper 90 and is dispensed 
onto the batt traveling on the belt or conveyer 86 through nozzles 92. 
Since the belt 86 is porous, the foam can be pulled through the batt to 
saturate the same by applying a vacuum on the underside of the batt 
through the vacuum puller 94. The excess foam is pulled into the vacuum 
puller 94 and is recirculated into the hopper 90. The batt is then carried 
on the belt 86 through an oven 96. 
The oven 96 is heated to a temperature of just just above the softening 
point of the thermoplastic binder fibers and/or resin. The oven 96 may, 
for example, contain a source of infra-red radiant energy to heat the 
surface of the batt above 200.degree. F. It is assumed, of course, that 
the binder material is the same as those used in the examples set forth at 
the end of this specification. The batt must be passed through the oven 96 
in a relatively short time period, because, according to the invention, 
only the binder material at the surface of the batt is to be softened, 
thus bonding the structural fibers at the surface of the batt to form 
"skin" at the surface of the batt, while leaving the structural fibers 
within batt away from the surface thereof unbonded. Formation of a "skin" 
at the surface of the batt stabilizes the batt sufficiently to permit 
handling, yet the fact that the structural fibers within the batt remain 
unbonded permits the batt to remain relatively soft so that it can be 
molded without buckling. It has been found that if the batt is prepared 
pursuant to the examples given at the end of this specification are 
exposed to the aforementioned temperature for a time period of several 
seconds, that such a relatively thin skin will be formed on the batt, 
while leaving the bulk of the fibers of the batt unbonded. By leaving the 
batt within the oven for only a few seconds, the heat does not have time 
to penetrate the batt sufficiently to raise the temperature of the fibers 
away from the surface of the batt such that the binder fibers and/or 
binder material are raised to their stick points, that is, the point at 
which they become tacky. 
As discussed hereinafter, an important feature of the invention is the fact 
that the batt is molded into a preform shape of the composite article 
before being impregnated with the appropriate resin. It is found that if 
the batt is molded while it is being impregnated, it is extremely 
difficult to assure complete saturation of the batt, particularly if the 
shape of the composite article to be formed is complex. Furthermore, the 
batt is also heated as it is molded into the preform, thus curing the batt 
and causing the thermoplastic binder fibers to at least partially melt and 
thereby hold the structural fibers in place. Accordingly, when the preform 
is injected with the resin matrix, the fibers of the preform resist 
deformation under the action of the resin being injected into them. 
Accordingly, the fibers remain in their structural skeleton position, 
thereby insuring a uniform concentration of fibers in the final product, 
to produce a consistent product of fairly uniform strength. 
The preform is made in a preform contour mold, generally indicated by the 
numeral 98 in FIG. 3. The mold 98 is preferably a conventional through-air 
mold and includes a gas-permeable screen 100 which is contoured in the 
shape of the preform to be molded. A portion of the batt is placed on the 
screen 100 and the cover 102 of the mold is closed upon the body 104 
thereof and a gas-impermeable seal is effected therebetween. A fan 106 
circulates air in the direction of the Arrow X so that the batt is forced 
to assume the contours of the screen 100 by virtue of the gas being forced 
therethrough. Although air would normally be used, it is possible in 
certain applications that a gas other than air may be necessary. The gas 
being circulated through the mold is heated by a burner 108 to a 
temperature sufficient to melt the thermoplastic binder material (either 
the binder fibers or the resin applied to the batt), thereby causing the 
batt to fuse in a shape-retaining contour of the screen 100. In the 
preferred embodiment, in which VINYON is used as a binder fiber, the air 
would be heated to about 200.degree. F., or about the sticking point of 
the binder fiber, that is, the temperature at which the fiber becomes 
tacky. 
Of course, the stiffness of the batt will depend upon the percentage of 
binder fiber and/or thermoplastic resin used in the batt. A higher 
concentration of binder fiber will produce a stiffer preform, which can 
withstand a more viscous resin in the resin injection step. However, a 
higher concentration of binder fiber necessarily reduces the concentration 
of the structural fibers, so that the final product formed from a batt 
having a higher concentration of binder material will have inherently less 
strength than a batt formed with a lower concentration of binder material 
and a corresponding higher concentration of structural fibers. 
Furthermore, a higher concentration of binder material may cause excess 
undesirable shrinkage of the batt. It is also desirable that the batt not 
be excessively compressed as it is formed into the preform sheet. 
Accordingly, the open structure of the batt is retained, thereby 
facilitating saturation of the fibers by the resin matrix in the resin 
injection step. Although molds other than the through-air mold shown in 
FIG. 3, such as a conventional press type mold, may be used, care must be 
taken that the batt not excessively compressed, although some compression 
is unavoidable in forcing the batt to assume the complex contours of the 
mold. 
The preform is then removed from the contour preform mold 98 and 
transferred to a conventional variable compression resin injection mold 
generally indicated by the numeral 110. Resin transfer mold 110 includes a 
base portion 112 which has a contoured shaped portion 114 which is the 
shape of the final composite article to be formed. The shape 114 is 
adapted to cooperate with a correspondingly shaped portion 116 of a cover 
member 118 which can be forced toward the portion 114 with a predetermined 
compressive force by a hydraulic actuator, indicated diagrammatically at 
120. A parametrically extending gasket 122 is located at the periphery of 
the interface between the mold portions 112 and 118 and is provided with a 
circumferentially spaced resin injection jets 124. One of the jets 126 is 
selected as a drain port. The preform is placed on the mold portion 114 
and the cover portion 118 is closed against the gasket 122. Preferably, 
the gap between the mold surfaces 114 and 116 is sufficiently great that 
the preform can be placed in the mold and the cover member 118 closed 
against gasket 122 without appreciably compressing the preform. An 
appropriate resin is then injected through jets 124 until the interstices 
between the fibers of the preforms are completely saturated with the resin 
and some of the resin begins draining out of the drain port 126. Although 
any of a number of resins are satisfactory, for example, EPON 828 resin 
available commercially from Shell Chemical Company may be used. As 
discussed above, it is preferred that the resin has a relatively low 
viscosity so that the batt need not be overly stiffened to prevent 
deformation under the action of the injection of the resin matrix. 
Accordingly, the resin is chosen has an inherently low viscosity at room 
temperatures, or the resin such as the aforementioned EPON 828 resin 
system can be heated to a temperature in which it has a sufficiently low 
viscosity. If necessary, the mold portions 118 and 112 can be heated to 
assist in curing the resin. As the peform becomes saturated with the resin 
(or after the preform has been saturated but before the resin is cured), 
the cover 118 is forced against the preform by action of the hydraulic 
actuator 120, thereby compressing the preform as it becomes saturated or 
immediately after it becomes saturated, thereby increasing the 
concentration of the structural reinforcing fibers to thereby increase the 
strength of the final product. Accordingly, the preform is initial of a 
relatively open structure, to permit easy saturation by the resin, but 
after the preform becomes saturated, the concentration of the fibers is 
increased by operation of the variable compression mold 110, to thereby 
mold the product to its final shape and to increase the concentration of 
the reinforcing fibers to produce na article that has acceptable strength. 
The invention has been described in connection with the use of staple 
structural fibers for the manufacture of the air-laid nonwoven batt that 
forms the skeletal material for the fiber reinforced composite article, 
fibers in forms other than cut staple fibers may be used. For example, 
continuous filament tow may be used, and may be processed and blended as 
described in U.S. Pat. No. 4,514,880. 
By way of illustration but not by way of limitation, the following examples 
are given, (all percentages are weight percent): 
EXAMPLE 1 
A nonwoven, air-laid batt was prepared, using 52.5% curled glass fiber, 
17.5% COMPET fiber, and 30% of a polyester binder fiber known commercially 
as VINYON. The batt was molded into a preform as described above. The 
preform could then be impregnated with the appropriate resin as described 
above, and would have acceptable strength in all three spatial dimensions, 
while being relatively inelastic and having a relatively good impact 
strength. 
EXAMPLE 2 
A batt was prepared and treated as described above in Example 1 of the 
foregoing specification, but the batt was made from a mixture of 35% 
curled glass fibers, 35% COMPET fiber, and 30% VINYON. Composite materials 
made from this fiber would have somewhat greater impact strength than the 
composite materials prepared as in Example 1 because of the higher 
percentage of the COMPET fiber, but would have greater elasticity because 
of the lower percentage of glass fibers. 
EXAMPLE 3 
A nonwoven, air-laid batt was prepared above as in Examples 1 and 2, but 
consisted of a mixture of 70% curled glass fibers and 30% VINYON binder 
fiber. If the mat were impregnated with a resin as described above, the 
resulting composite would be relatively inelastic, and would compare to 
glass fiber structures already on the market. However, because of the 
absence of fibers having high impact strength, the impact strength of the 
resulting composite would be relatively low. 
EXAMPLE 4 
A nonwoven batt was prepared as discussed above in Examples 1-3, but 
instead consisted of a mixture of 50% curled glass fibers and 50% of the 
VINYON binder fiber. Because of the greater percentage of binder fiber, 
the resultant preform would shrink more than the preforms having the lower 
percentage of binder fibers, but the properties would otherwise be the 
same as in Example 3. 
EXAMPLE 5 
A batt was prepared as described above in Examples 1-4, but instead of 
using glass fibers and COMPET fiber, a fiber sold commercially under the 
trademark KEVLAR was used. The resulting batt and any preform or composite 
article which could be made therefrom would have the characteristics of 
the impact strength and elastic characteristics of the KEVLAR rather than 
of the glass fibers and/or COMPET fibers. 
EXAMPLE 6 
A batt was prepared pursuant to any of these Examples 1-5, but instead of 
using the VINYON binder fiber, the batt was made without using any binder 
and instead was resinated with polyvinyl acetate. Any batt made in this 
way would have similar characteristics to a batt containing corresponding 
percentages of glass fibers, COMPET, and/or KEVLAR as discussed above in 
Examples 1-5. 
Though a number of specific embodiments and examples have been discussed in 
the foregoing specification, the invention is not limited to these 
examples and embodiments, but is instead limited only by the scope of the 
following claims.