Note: Descriptions are shown in the official language in which they were submitted.
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A NATURAL FIBER PRODUCT COATED WITH A
THERMOPLASTIC BINDER MATERIAL
Back~round of th~ Invention
The present invention relates to discontinuous
natural fibers coated with thermopl~stic binder materials
and also to adhering solid part:iculate materials to the
binder. The particulate material is adhered to the fibers
by the thermoplastic binder mat:erial as the binder
material dries.
A number of techniques for applying binders to
webs of fibers are known. For example, U.S. Patent No.
4,600,462 of Watt describes a process in which an adhesive
binder is sprayed onto one or both surfaces of an air laid
cellulose fiber web. Submersion of the web in the
adhesive binder is another method disclosed in this patent
of applying the binder. Individual binder coated fibers
for mixing with other fibers are not produced by this
process. A hydrophile solution is also applied to the
web. As another example, U.S. Patent Nos. 4,425,126 and
4,129,132 of Butterworth, et al. describe a fiberous
material formed by combining thermoplastic fibers and wood
pulp, heat fusing the combined fibers, and thereafter
depositing a binder on the heat fused web. Because the
fibers are heat fused prior to adding the binder,
individual binder coated fibers for mixing with other
fibers are not produced by this process.
U.S. Patent No. 4,584,357 of Harding discloses a
latex treated cationic cellulose product and method for
its manufacture. In the Harding approach, cationized
cellulose is treated in an aqueous suspension with an
anionic polymer emulsion of from 0.1 to 30 percent on a
dry weight basis. The patent mentions that the resulting
resin treated products can be prepared in sheet form, as
loose fibers or in another form. The approach of the
Harding patent is limited to cationic fibers. Also, the
fiber coating applied as described in the Harding patent
had a tendency to flake off or separate from the fibers.
Moreover, because the Harding approach uses a wet process,
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the lumen of the cellulose fibers is penetrated by the
polymer emulsion. Since the binder on the surface of the
fibers contributes principally to the desired
characteristics of the fiber, any polymer that penetrates
the lumen of the fiber adds lit:tl2 to these desirsd
characteristics.
U.S. Patent No. 4,469,746 of Weisman et al.
discloses fiberous webs comprised of fibers coated with a
continuous film of silica. The fibers are understood to
be dispersed in a charged silica aquasol to accomplish the
coating. Because silica is an inorganic material, the
silica does not contribute to subsequent bonding of
fibers. In addition, because Weisman et al. discloses a
wet process, the silica will tend to penetrate the lu~en
of cellulose fibers in the event such fibers are being
treated in accordance with this patent.
U.S. Patent Application Serial No. 067,669, filed
June 26th, 1987, and entitled "Treated Wood Fiber Having
Hydrophobic and Oleophilic Properties", by Jewell et al.,
mentions an approach of treating fiberi2ed wood with
surfactant material to penetrate the surface of the wood
fibers. In this approach, Piberized wood at the outlet of
a first fiberizing machine passes through an orifice into
a blow line. At the outlet of the fiberizing machine,
liquid surfactant is injected into the line. At the point
of addition of the surfactant, the fiber is still wet as
it has been carried by steam through the fiberizing
machine. Surfactants are not suitable for use in
subsequent bonding of the fibers. The Jewell et al.
patent application also describes a process in which
fibers are treated with a copolymer latex, such as a
combination of a paraffin wax emulsion and a styrene
butadiene copolymer latex. Tha patent describes a
suitable treating process as involving the blending of the
aqueous latex emulsion with wood fiber in a typical
mechanical wood fiber blender. This approach tends to
produce fibers which are bound together by the latex.
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U.S. Patent No. 2,757,150 of Heritage mentions a
fiber treatment approach in which fibers are carried by
steam under pressure and in which a thermoset resin, in
contrast to a thermoplastic binder material in accordance
with the present invention, is introduced into the fiber
stream. Other materials (i.e./ rosin and wax) are
mentioned as being simultaneously introduced into the
fiber stream. The patent indicates that such materials
penetrate the surface of the f:ibers. This patent mentions
the individualization of thess treated fibers. A
relatively low concentration of the thermoset resin (i.e.
two percent by weight phenol formaldehyde) is specifically
described in this patent. At such low concentrations, the
resin is in discontinuous random non-interconnected areas
(blobs or globules) on the fibers. These treated fibers
are typically used in hardboard. In current hardboard
resin products produced using the approach of the Heritage
patent and known to the inventors, a phenolic resin
concentration of from a maximum of five to six percent by
weight is used. Even at these concentrations, the resin
forms random non-interconnected globules on the fibers.
As a result, the uncoated resin free areas of the fibers
lack the capacity to bond in comparison to the areas of
the fibers covered by the resin. In addition, the
untreated surface areas of the fibers may lack desired
characteristics of the resin covered areas of the fibers.
For example, these uncoated areas may cause the fibers to
be more water absorbent than if the entire fiber were
coated.
U.S. Patent No. 4,006,887 of Engels describes a
process for treating wood fibers in which the fibers are
supported as an annular loose fluidized bed in a mixer
which delivers glue by way of shaft mounted mixing rods to
the fibers. The patent mentions that radial air vortices
are established with the mixer inlet and outlet funnels
being connected to an air transport pipe. The patent
describes the resulting product as homogenous lump free
uniformly coated wood fibers. The patent mentions that
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the coating of fibers is useful in the manufacture of wood
fiber panels. The glue used in the Engels patent and the
percentage of the glue that is used is not discussed.
The background portion of the Engels patent
describes German Auslegeschrift 1,048,013 as disclosing an
impeller or agitator mixer for the coating of wood chips
with dusty components. Glue i'3 described as being sprayed
through nozzles into a mixing container. An air stream is
described as being blown axially through the mixing
container in order to reduce the residence time of dusty
chip particles to reduce excessive coating of such dusty
particles. Also, German Offenlegunge 1,632,~50 is
mentioned by Engels as disclosing wood chips agitated in
an air stream in a mixing tube in which glue spray nozzles
are mounted.
Heretofore, synthetic bicomponent fibers have
been formed by extruding two materials in air in
side-by~side strands which are connected together along
their length. Such bicomponent fibers have also been
formed with one material being extruded as a concentric
sheath surrounding the other material. These extruded
strands are then chopped or broken into discontinuous
fibers. Although synthetic bicomponent fibers provide
good structural efficiency, they are very expensive in
comparison to natural fibers, and, therefore, their use is
limited.
U.S. Patent No. 4,261,943 of McCorsley, III
describes the extrusion of filaments and the application
of a solution o~ a nonsolvent liquid to the filaments. In
this application process, the filaments are passed through
a chamber having a nonsolvent vapor laden atmosphere, i.e.
a fog of minute particles of nonsolvent. Spraying of the
nonsolvent liquid onto the filaments is also mentioned.
The approach of the McCorsley, III patent is not
understood to apply to discon-tinuous fibers.
U~S. Patent No. 4,010,308 of Wiczer describes
foamed porous coated fibers. Fibers, described as organic
or inorganic fibers of any character, are described as
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being coated with a foamable plastic material.
Thermoplastic and thermosetting coatings are mentioned.
In several examples, the coated fibers are made by passing
continuous extruded filaments through a first bath of a
ten percent polystyrene solution in toluene, evaporating
the solvent, and passing the polystyrene coated Eiber
through a second bath containing a blowing agent, such as
liquid n-pentane. The treated filamPnts are then heated
to foam the coating. Rolls are used to rub solid
particles into the porous sur~ace of the foam coating.
Fireproofing agents, lubricants such as graphite,
pigments, and insecticides are among the examples of solid
materials mentioned as suitable for rubbing into the
coating. In another example, short lengths of cotton
linters are described as being wet with a ten percent
solution of a copolymer of polystyrene and acrylonitrile
in about equal proportions dissolved in benzene. The
solvent is evaporated in an air stream and the resulting
coated cotton fiber is dipped in mixed pentanes. The
product is then ~tirred in boiling water to cause foaming.
Following foaming, the product is centrifugally dried and
again dried in an air stream. The fiber is then mixed
with a dry powder to fill the pores in the foamed coating
with the powder. The placement of this fiber product in a
container and heating th~ product to cause the adherence
of the fiber sur~ace contact points is also mentioned.
The Wiczer patent appears to use a solution dipping
approach as a means of applying the coating to the fibers.
U.S. Patent No. 4,160,059 of Samejima describes a
process in which a natural cellulose fiber (such as wood
pulp fiber) is shredded and blended in air with a
heat-fusible fiber. The blend is fed to a disintegrator
to form supporting fibers to which an absorptive material
is added. Heated air is applied to the resulting web to
heat the web to a temperature above the melting point of
the heat fusible fiber to form bonds between the
supporting fibers and absorptive material by heat fusion.
Activated carbon black, Japanese acid clay, active
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alumina, and diatomaceous earth are mentioned as
representative absorptive materials. Other powders,
including superabsorbents, are also mentioned as beiny
bonded in place in this manner. The background portion of
this particular pakent also mentions a process in which
wood pulp is disintegrated by a dry process, blended with
active carbon black, and the blend spread on a wire
screen. A binding material such as latex, starch and the
like can also be sprayed on both surfaces of the web.
With this latter approach, the active surface of the
absorptive material is covered with a thin film of the
binding material. Thus, under the Samejima approach, heat
fusion is used to bind the particles to the fibers. As a
result, a bound fiber web, as opposed to individuali~ed
fibers, is formed with the particles heat fused to the
fibers.
In U.S. Patent No. 4,429,001 of Kolpin et al.,
melt-blown fibers are prepared by extruding liquid
fiber-forming materials into a high-velocity gaseous
stream. The stream of fibers is collected on a screen
disposed in the stream with the fibers being collected as
an entangled coherent mass. Absorbent particles are
introduced into the stream of fibers at the point where
the fibers are solidified sufficiently that the fibers
will form only a point contact with the particles. The
patent mentions that the particles can also be mixed with
the fib~rs under conditions that will produce an area of
contact with the particles. The introduction of other
fibers besides melt-blown fibers into the resulting sheet
product is also mentioned. The patent mentions that
surfactants in powder form can be mixed with the sorbent
particles used in forming the web or surfactants in liquid
form can be sprayed onto the web after it is formed.
Finally, U S. Patent No. 4,392,908 of Dehnel
describes a process for forming a thermoplastic adhesive
resin on a surface of water soluble particles. The coated
particle~ in a dry state are heated and pressed to bond
them to a dry substrate (i.e. cellulose fluff). Mixing of
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absorbent particles with an aqueous latex, spraying resin
onto the particles, and mixing the particles in a slurry
are mentioned as approaches for coating the particles.
Milling of the particles after coating with thermoplastic
is mentioned as usually being necessary to produce free
flowing particles. Thus, the Dehnel patent illustrates
another approach for heat fusing particles to fibers.
Although prior art approaches are known, a need
exists for an improved method o~ treating discontinuous
fibers with a hindar material and for adhering particles
to fibers treated in this manner.
Summary of the Invention
In accordance with the present invention,
discontinuous natural fibers have a thermoplastic binder
coating thereon in an amount which is sufficient to
produce bicomponent fibers having a substantially
continuous layer of khe binder material on their surface.
A substantial majority of the resulting bicomponent fibers
are unbonded. By using a heat bondable organic polymeric
thermoplastic material as the binder, the fibers may be
subsequently heated to fus~ them together. The fibers may
also be combined with other nontreated fibers and heat
fused to provide a bonded web.
In accordance with the present invention, the
fibers may have substantial amounts of thermoplastic
binder material yet still comprise individualized coated
fibers. It has been found that the thermoplastic binder
material must be included in an amount of at least about
seven percent of the combined dry weight of the binder
material and fibers in order to produce a substantially
continuous binder coating on the fibers. With a
substantially continuous coating, little or no surface
area of the fibers is exposed and the desired
characteristics added to the fibers by the binder material
are not nullified or significantly altered by uncoated
areas of the fiber. With a thermoplastic binder level of
at least about 10 percent of the combined dry weight of
the binder material and fibers, the coated fibers are
capable of bonding relatively strongly to one another when
heat fused. In addition, fibers with thermoplastic binder
levels of 30 percent to 50 percent and higher, such as
above 90 percent and with no maximum limit yet being
determined, are included within the invention, while stlll
resulting in a product comprised of substantially unbonded
individualized fibers. At these higher levels of binder,
the treated fibers may readily be mixed or blended with
untreated Eibers and used in heat fusing the blended
fibers. Also, higher binder levels are preferably used to
adhere solid particulate materials to the fibers as
explained below.
As another aspect of the present invention, the
fiber product may include one or more solid particulate
materials adhered to the fibers by the thermoplastic
binder material. Solid particulate material is applied to
the fibers while the liquid binder material on the fibers
is still at least partially wet. As ths liquid binder
material dries, the particulate material is adhered to the
fibers. Although not limited to specific materials, the
particulate materials may comprise at least one material
selected from the group comprising a pigment material, a
super absorbent material, an abrasive material, an
oleophilic material, an electrically conductive material
and a fire retardant material.
Although not as beneficial for many applications,
such as when the properties of individual fibers are
desired, in addition to individual fibers, the fiber
product may comprise fiber bundles. A fiber bundle is an
interconnected group of two or more fibers that are not
separated during processing. Fiber bundles, like
individual fibers are much longer than wide. For example,
when mechanically fiberized wood is produced, some
individual fibers result along with fiber bundles of
fibers that are not separated during the mechanical
fiberization process.
It is accordingly one object o~ the present
invention to provide discontinuous natural fibers coated
with a thermoplastic binder material.
It is another object of the present invention to
provide such thermoplastic bincler coated fibers which are
substantially individualized or unbonded.
A further object of the present invention is to
provide thermoplastic binder coated discontinuous natural
fibers with the binder being present in an amount which is
sufficient to substantially continuously coat the fibers,
or in much higher amounts, with the fibers being
substantially individualized or unbonded.
A still further object of the present invention
is to provide thermoplastic binder coated fibers having
one or more solid particulate materials, which impart
functional benefits to the fibers, adhered to the fibers
by the binder material.
Another object of the present invention is to
provide substantially individualized discontinuous
thermoplastic binder coated fibers, with or without
particulate materials adhered thereto, for use in the
manufacture of articles by heat fusing the ~ibers, with or
without additional untreated fibers being added.
A further object of the invention is to form an
air laid web directly with dried coated fibers and with
partially wet coated fibers.
A subsidiary object of the present invention is
to provide fiber bundles treated in the same manner as
individual fibers are treated.
These and other objects, features and advantages
of the present invention will be apparent with reference
to the ~ollowing detail~d description and drawings.
Brief Description of the Drawings
Fig. 1 is a schematic illustration of one form of
apparatus in which discontinuous fibers can be treated in
accordance with the method of the present invention.
Fig. 2 is a side elevational section view of one
form of binder application mechanism which can be used to
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apply liquid binder material to discontinuous fibers in
accordance with the method of the present invention.
Fig. 3 is a front elevational section view of the
binder application mechanism of Fig. 2.
Fig. 4 is a schematic illustration of another
form of binder application mechanism which can be used to
produce the fiber product of the present invention.
~iy. 5 is a schematic illustration of an
altarnative apparatus used in producing the fiber product
of the present invention.
Fig. 6 is a schematic illustration of another
apparatus ~or producing the fiber product of the present
invention.
Detailed Description_of the Preferred Embodiments
The present invention i5 a fiber product
comprised of treated discontinuous natural fibers. The
term natural fibers refers to fibers which are naturally
occurring, as opposed to synthetic fibers. Non~cellulosic
natural fibers are included, with chopped silk fibers
being one example. In addition, the term natural fibers
includes cellulosic fibers such as wood pulp, bagasse,
hemp, jute, rice, wheat, bamboo, corn, sisal, cotton,
flax, kenaf, and the l.ike, and mixtures thereof. The term
discontinuous fibers refers to fibers of a relatively
short length in comparison to continuous fibers treated
during an extrusion process used to produce such fibers.
The term discontinuous fibers also includes fiber bundles.
The term individual fibers refers to fibers that are
comprised substantially of individual separated fibers
with at most only a small amount of fiber bundles.
Wood pulp fibers can be obtained from well-known
chemical processes such as the kraft and sulfite
processes. Suitable starting materials for these
processes include hardwood and softwood species, such as
alder, pine, douglas fir, spruce and hemlock. Wood pulp
fibers can also be obtained from mechanical processes,
such as ground wood, refiner mechanical, thermomechanical,
chemi-mechanical, and chemi-thermomechanical pulp
processes. However, to the extent such processes produce
fiber bundles as opposed to individually separated fibers
or individual fibers, they are less preferred However,
treated fiber bundles is within the scope of the present
invention. Recycled or secondary wood pulp fibers and
bleached and unbleached wood pulp fibers can also be used.
Details of the production of wood pulp fibers are
well-known to those skilled in the art. These fibers are
commercially available from a number of companies,
including Weyerhaeuser Company~ the assignee of the
present patent application.
For purposes of convenience, and not to be
construed as a limitation, the following description
proceeds with reference to thermoplastic binder treated
chemical wood pulp fibers. Individual treated fibers of
other types, and obtained by other methods, as well as
treated fiber bundlesl can be obtained in the same manner.
When relatively dry wood pulp fibers are being
treated, that is fibers with less than about 10 to 12
percent by weight moisture content, the lumen of such
fibers is substantially collapsed. As a result, when
binder materials, in particular thermoplastic latex binder
materials, are applied to these relatively dry wood pulp
fibers, penetration of the binder into the lumen ls
minimized. In comparison, relatively wet fibers tend to
have open lumen through which binder materials can flow
into the fiber in the event the fiber is immersed in the
binder. Any binder that penetrates the lumen contributes
less to the desired characteristics of the treated fiber
than the binder which is present on the surface of the
fiber. Therefore, when relatively dry wood pulp fibers
are treated, less binder material is required to obtain
the same effect than in the case where the fibers are
relatively wet and the binder penetrates the lumen.
Thermoplastic binder materials used in producing
the fibers typically include substances which can be
applied in liquid form to entrained fibers during one
illustrated treatment process. These binder materials are
capable of subsequently binding the fihers produced by the
process to one another or to okher fibers during the
manufacture of webs and other products using the treated
fibers. Most preferably these thermoplastic binders
comprise organic polymer materials which may be heat fused
at elevated temperatures to bond the fibers when the
fibers are used in manufacturing products. Also, in
applications where solid partic:ulate material is to be
adhered to the fibers by the thermoplastic binder, the
binder must be of a type which is suitable for this
purpose.
Suitable thermoplastic binders include polymeric
materials in the form of aqueous emulsions or solutions
and nonaqueous solutions. To prevent agglomeration of
fibers during the illustrated treatment process,
preferably the total liquid content of the treated fibers
during treatment, including the moisture contributed by
the binder together with the liquid content of the fibers
(in the case of moisture containing fibers such as wood
pulp), must be no more than about 45 to 55 percent of the
total weight, with a 25 to 35 percent moisture content
being more typical. Assuming wood pulp is used as the
natural fiber, the moisture contributed by the wood pulp
can be higher, but is preferably less than about 10 to 12
percent and more typically about six to eight percent.
The remaining moisture or liquid is typically contributed
by the binder. These polymer emulsions are typically
referred to as '~latexes." In the present application, the
term "latex" refers very broadly to any aqueous emulsion
of a thermoplastic polymeric material. The term solution
means binders dissolved in water or other solvents, such
as acetone or toluene. Polymeric materials used in
binders in accordance with the present method can range
from hard rigid types to those which are soft and rubbery.
The thermoplastic polymers may ba a material which remains
permanently thermoplastic. Alternatively, such polymers
may be of a type which is partially or fully
cross-linkable, with or without an external catalyst, into
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a thermosetting type polymer~ As a few specific examples,
suitable thermoplastic binders can be made of the
following materials:
ethylene vinyl alcohol
polyvinyl acetate
acrylic
polyvinyl ac~etate acrylate
acrylates
polyvinyl dichloride
ethylene vinyl acetate
ethylene vinyl chloride
polyvinyl chloride
styrene
styrene acrylate
styrene/butadiene
styrene/acrylonitrile
butadiene/acrylonitrile
acrylonitrile/butadiene/styrene
ethylene acrylic acid
polyethylene
urethanes
polycarbonate
polyphenylene oxide
polypropylene
polyesters
polyimides
Surfactants may also be included in the liquid
thermoplastic binder as desired. Other materials may also
be mixed with the liquid binder to impart desired
charac$eristics to the treated fibers.
Certain types of binders enhance the fire
resistance of the treated fibers, and thereby of products
made from these fibers. For example, poly vinyl chloride,
poly vinyl dichloride and ethylene vinyl chloride are fire
retardant.
In addition, the fiber product of the invention
may have one or more solid particulate materials adhered
to the fibers to provide desired functional
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characteristics. ~he solid particulate materials are
typically applied to a binder wetted surface of the fibers
and then adhered to the fibers by the binder as the binder
dries. In this case, heat fusion of the binder is not
used to adhere the particles to the fibers. Although not
limited to specific materials, examples of suitable
particulate materials include ]pigments, such as titanium
dioxide; fire retardant materials, such as alumina
trihydrate and antimony oxide; electrically conductive
materials, such as metallic powders and carbon black;
abrasive materials, such as ceramics, grit and metallic
powders; acidular materials, such as clay, talc and mica,
used as paper making additives; oleophilic materials;
hydrophobic materials; and hydrophilic materials, such as
super absorbent particles; insecticides; and fertilizers.
Thus, the solid particulate materials are not limited to
narrow categories.
The super absorbent particulate materials are
granular or powdered materials which have the a~ility to
absorb liquids, including body f]uids. These super
absorbents are generally hydrophilic polymeric materials.
Super absorbents are defined herein as materials which
exhibit the ability to absorb large quantities of liquids,
i.e. in excess of 10 to 15 parts o~` liquid per part
thereof. These super absorbent materials generally fall
into three classes, namely, starch graft copolymers,
cross-linked carboxymethylcellulose derivatives and
modified hydrophilic polyacrylates. Without limiting the
generality of the term super absorbent, examples of super
absorbents include carboxylated cellulose, hydrolyzed
acrylonitrile-grafted starch, acrylic acid derivative
polymers, polyacrylonitrile derivatives, polyacrylamide
type compounds and saponified vinyl acetate/methyl
acrylate copolymers. Specific examples of super absorbent
particles are marketed under the trademarks "Sanwet"
(supplied by Sanyo Kasei Kogyo Kabushiki Kaisha) and
"Sumika Gel" (supplied by Sumitomo Kagaku Kabushiki
Kaisha).
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An abrasive is a hard substance that, in
particulate form, is capable of effecting a physical
change in a surface, ranging from the removal of a thin
film of tarnish to the cutting of heavy metal cross
sections and cutting stone. Abrasives are used in scores
of different abrasive product~. The two principal
categories of abrasives are: (l) natural abrasives, such
as quartz, emery, corundum, garnet, tripoli, diatomaceous
earth ~diatomite~, pumice, and diamond; and (2) synthetic
abrasives, such as fused alumina, silicon carbide, boron
nitride, metallic abrasives, and synthetic diamond.
Oleophilic materials are those capable of rapid
wetting by oil while hydrophil:ic materials are those
capable of rapid wetting by water.
Pigments or colorants can be broadly defined as
capable of reflecting light of certain wavelengths while
absorbing light of other wavelengths and which are used to
impart color~
Electrically conductive materials are those which
readily conduct electric current.
In addition, fire retardant materials are those
which reduce the flammability of the fibers to which they
are attached. Preferably these materials are active fire
retardants in that they chemically inhibit oxidation or
they emit water or other fire suppressing substances when
burned.
One apparatus for producing the fiber product of
the present invention is shown in Fig. 1. With reference
to this figure, a sheet of chemical wood pulp 10 is
unrolled from a roll 12 and delivered to a refiberizing
apparatus, such as a conventional hammer mill 14. The
sheet 10 is readily converted into individual fibers 16
within the hammer millO These individual fibers are
delivered, as by a conveyor 18, to a fiber loading zone 20
of a fiber treatment apparatus. In the case of a
continuous process, fibers 16 are continuously delivered
to the zone 20. In a batch or semi-batch process, fibers
are loaded at zone 20 at intervals.
Z O~ D2 ~
In the Fig. 1 fiber treatment apparatus, loadiny
zone 20 forms part of a fiber treatment conduit 24. The
illustrated conduit 24 comprises a recirculating loop. A
blower or fan 26 in loop 24 is positioned adjacent to the
fiber loading zone 20. Blower 26 i5 capable of moviny a
gaseous medium, such as air, at a velocity and volume
sufficient to entrain the fibers which have been loaded
into zone 20. The entrained ~:ibers circulate in a
direction indicated by arrow 28 through the loop and pass
through the loading zone 20 and blower 26 each time the
loop is traversed.
The velocity of air traveling in the loop is
preferably set at a level where solids are uniformly
dispersed and transported b~ the air flow. In addition,
the velocity is preferably established at a level which is
sufficient to avoid saltation, that is the dropping of
solids or liquids from a horizontal air stream. As a
specific example, when Type NB316 chemical wood pulp,
available from Weyerhaeuser Company, was used as the
fiber, a velocity of 5,000 feet per minute worked
extremely well in the production of these fibers.
However, this velocity can be varied and adjusted for
optimum results.
Also, the ratio of the volume of air per pound
of entrained fiber is variable over relatively large
ranges. One suitable example is 23.4 ft3 of air per pound
of fiber. As another example, 11.7 ft3 of air per pound
of fiber produced equivalent results~ The entrained
fibers traveling in the loop pass one or more binder
material application zones, with one such zone being
indicated in Fig. 1 at 30. This binder material
application zone 30 forms a part of the conduit 24. A
mechanism is provided at the binder application zone for
applying a liquid binder solution to the entrained fibers.
In the Fig. 1 form of this mechanism, plural nozzles, in
this case nozzles 32, 34 and 36, are used to apply the
liquid binder material. These nozzles produce an
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atomized spray or mist of binder drops which impact andcoat the fibers as the fibers pass the nozzles.
In the Fig. 1 apparatus, plural valves 40, 42 and
44 are operated to control the flow of liquid binder
material to the respective nozzles 32, 34 and 36. In the
illustrated configuration, a first liquid binder materia]
from a tank or other source 46 is delivered to the three
nozzles 32, 34 and 36 when valves 40 and 42 are open and
valve 44 is closed. As the fibers recirculate throuyh the
conduit 24, and each time they pass the nozzles, an
additional amount of the first liquid binder material is
applied. Different surfaces of the fibers are exposed to
the nozzles 32, 34 and 36 as the fibers travel through the
material application zone 30. After the desired amount of
the first llquid binder material is applied, the valve 40
is closed~ If desired for a particular application, a
second liquid binder material from a tank or other source
48 may also be applied to the fibers. With valves 42 and
44 open and valve 40 closed, this second liquid binder
material is applied to the fibers through each of the
nozzles 32, 34 and 36. In addition, the two liquid binder
materials may be simultaneously applied, at successive
locations in zone 30. For example, the valve 42 may be
closed and valve 44 opened so that the first liquid binder
material is applied through nozzles 32, 34 and the second
liquid binder material is applied through nozzle 36. More
than two types of liquid binder materials may be applied
by adding additional binder sources and suitable valving
and nozzles.
In general, the material application zone 30
typically ranges from two to one hundred feet long, with
longer application zones allowing the application of
binder over a longer period of time during passage of
fibers through the material application zone. Also,
longer material application zones facilitate the use of
more nozzles spaced along the length of the zones.
The nozzles 32, 34 and 36 are commercially
available and produce a fine mist of droplets. Typically,
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these nozzles provide a fan spray. Any suitable nozzles
may be used, but it is desirable that the nozzles not
produce a continuous stream o~ liquid binder material, but
instead produce droplets or a mist of such material. The
nozzles are typically spaced apart from three to four feet
along the length of the conduit:, although they may be
closer or further apart as desi.red.
Virtually any amount of binder material may be
applied to the entrained fibers. However, it has been
found that the application of t:hermoplastic binder must be
at a minimum of about seven percent of the dry weight of
the combined fibers and binder in order for the fibers to
have a substantially continuous sheath or coating of the
binder material~ If the fibers lack a conkinuous coating,
it becomes more difficult to adhere significant amounts of
particulate material to the binder in the manner explained
below. In fact, a much higher percentage of binder than
this minimum is preferably used to adhere particles to the
fibers. Also, exposed portions of the core fiber, that is
surface areas of the fiber not coated with the binder,
lack the desired characteristics of the binder. For
example, if a hydrophobic binder is used to cover a water
absorbing cellulose material, failure to completely
enclose the material with the coating leaves exposed
surfaces of the fiber which can absorb water. Also, any
uncoated areas on the fibers would not bond to other
untreated fibers during subsequent heat bonding of the
treated and untreated fibers.
It has also been found that, with a thermoplastic
binder concentration of about lO percent by dry weight of
the weight of the fiber and binder combination, the
fibers, when heat fused, will bond somewhat strongly to
other fibers coated in a similar manner, but less strongly
to untreated fibers. The resulting bond strength is
similar to the strength achieved when fibers coated with a
40 percent by dry weight binder amount are mixed with
untreated fibers in a ratio of one part treated fiber to
three parts untreated fiber. A thermoplastic binder
~ 19 --
concentration by dry weight of the combined binder and
fibers of from 30 percent to 50 percent has proven
extremely suitable for use in mixing with other fibers,
heat bonding, and use in forming products such as
absorbent pads.
Thermoplastic binder concentrations in excess of
50 percent, for example 90 percent or more, can be
achieved utilizing the present invention. To achieve
these extremely high binder concentrations, one preferred
approach is to apply a first amount of the binder material
to the entrained fibers, continue to recirculate the
fibers until this first layer or coating of binder
material is substantially dry, and then apply a second
coating of the binder material. Third, fourth and
subsequent coatings can be applied to the entrained fibers
as necessary to achieve the desired level of binder
material.
Following the application of the liquid
thermoplastic binder material to the fibers, the fibers
may be retained in the loop until they have dried. The
recirculation of the fibers may then be stopped and the
fibers removed at the loading zone 20 which then functions
as a fiber removal location. However, in the Fig. 1
apparatus, a cyclone separator 60 is selectively connected
by a conduit section 61 and a gate valve 62 to the conduit
24. At the same time a valve 64 is opened to allow air to
enter the loop 24 to compensate for air exiting through
the separator 60. With the separator in the loop, the
entrained fibers are collected in the separator and then
removed from the separator at a fiber removal outlet 66.
A substantial majority of the fibers processed in this
manner are unbonded to one another by the binder material.
By substantial majority, it is meant that at least about
70 percent of the fibers remain unbonded. More
specifically, in tests conducted as of this time, the
resulting treated fibers are substantially unbonded,
meaning that approximately 95 percent of the treated
- 20 - 2 ~ 2~ ~
fibers have been found to be unbonded to one another by
the binder material.
An optional means for heating the binder coated
fibers may be included in conduit 24. For example heated
air may be blended with the air flowing through the
conduit. Similarly, a heater 70 may be included in
conduit 24 for heating the fib~ers. This added heat
accelerates the drying of the liquid binder. The fibers
are pre~erably heated above th~Q film forming temperatures
of the thermoplastic heat fusible binder and below the hot
tack temperature at which the binder becomes tacky.
Thereafter, the binder coated fibsrs may subsequently be
heat fused during processing of the fibers into products.
The fibers are preferably not heated prior to the
application of the thermoplastic binder material. It has
been found that heating the fibers results in elevated
temperatures at the binder application zone 30. These
elevated temperatures cause some of the binder to at least
partially dry (coelesce) before reaching surfaces of
fibers passing through the binder application zone 30.
The solidified binder tends to either not adhere or only
adhere weakly to the fibers. In addition, droplets of
binder which impinge heated fibers tend to dry in globules
on the fibers, rather than spread across the surface of
the fibers to provide a substantially continuous uniform
coating thereon.
The dried fibers from outlet 66 of the cyclone
separator 60 may be deposited in a conventional baling
apparatus 72. To prevent bonding of the fibers in the
baler, the fibers are at a temperature which is below
their curing or tack temperature under the pressure
applied by the baler. When compressed, these fibers
remain unbonded by the binder material and therefore can
be readily separated into individualized fibers for
subsequent use.
Also, treated fibers which have only been
partially dried, and thus which are still somewhat wet
with the thermoplastic binder material, amy be deposited
- 21 -
from ou~let 66 loosely onto a conveyor 74 or in a loose
uncompressed pile at a collecting zone (not shown). These
fibers can then be allowed to dry. Alternatively, the
treated fibers may be carried by the conveyor 74 through a
heater 76, operable like heater 70, to accelerate the
drying of the fibers. The resulting product ayain
contains a major portion of unbonded fibers. However, the
wetter the fibers and more dense the resulting web when
deposited on belt 74, or in a pile, the more binder-to-
binder bonds that occur. Thus, in many cases it ispreferable to at least partially dry the fibers within the
conduit 24 prior to removing the fibers therefrom.
However, the fiber may be air laid either dry or wet, that
is, with no more than about a 55 percent total moisture
content in the fibers and binder thereon, directly into a
web which can then be processed into various products,
such as into disposable diapers with the core of the
diaper being formed by the web. Air laying refers to the
transfer of the fibers through air of another gaseous
medium.
Solid particulate materials may be adhered to the
fibers by the binder material.
To accomplish this, the solid particulate
material is added to the loop 24, such as at the fiber
loading zone 20. The particles may also be added to the
loop 24 from a supply housing 80, using a feed screw
metering device or other conventional injection mechanism.
Preferably, the particles are added after the fibers have
been wetted with the binder materialO Consequently, the
particles will not be covered with the binder material,
which could interfere with the desired attributes
contributed by the particles. These particles contact the
wet binder material on the surfaces of the fibers and
stick to the binder material. As the binder material
dries, the particles remain stuck the surface of the
treated fibers. In one specific approach, the fibers are
treated with a binder, circulation of the fibers is
stopped momentarily to allow the addition of the solid
-- 22 ~ ~52~
particulate material at the fiber loading zone 20, and
recirculation and entrainment of the fibers is
recommenced. The particles mix with and are secured to
the sur~ace of the fibers by the liquid binder material as
the binder dries. Although lower concentrations are
effective in binding particles to fibers, it has been
found that relatively high levels of binder
concentrations, for example 20 percent or more of the dry
weight of the binder, fiber and additive, produces the
best adhesion of particles to the fibers. A 50 percent
binder concentration would perform better in adhering
particles to the fibers than a 20 percent binder
concentration in many applications. These higher binder
levels, when heat fusible binders are used, facilitate
subsequent heat fusion of the fibers and strong bondiny,
with or without other fibers being added, during use of
the fibers in manufacturing products.
The Fig. 1 apparatus may be operated in a batch
mode in which fibers are introduced, fully treated and
removed. Alternatively, a semi-batch approach may be used
in which fibers are added and some, but not all, of the
fibers removed from the loop. Also, the Fig. 1 apparatus
may be operated in a continuous mode in which fibers are
introduced at zone 20 and removed by the cyclone separator
60 with or without recirculating through the loop. The
gate valves 62, 64 may be opened to a desired extent to
control the amount of fiber that is remo~ed. This
quantity of removed fiber is preferably equal to the
amount of untreated fiber that is introduced into the
loop. In this nonrecirculating case, the zone 30 is
typically expanded.
With reference to Figs. 2 and 3, another
mechanism for applying binder material to the fibers is
illustrated. Rather than using external spray nozzles
such as 32, 34 and 36, plural nozzles (i.e., one being
shown as 82 in Figs. 2 and 3) are included in the conduit
at the binder material applying zone 30. The nozzle 82
applies a fine spray of liquid binder material cnto the
5~
- 23
fibers 16 as they move past the nozzle. The Figs. 2 and 3
binder applying mechanism includes a means for impartiny
turbulence to the air as it passes th~ nozzles. As a
result, the fibers 16 tend to tumble in front of the
nozzles and expose different surfaces to the applied
binde.r material. The illustrat:ed turbulence imparting
mechanism comprises a blunted c:onical air deflection
baffle 86 supported within the conduit 24 by rods, with
two such rods 88 and 90 being shown. Rod 90 may be hollow
to provide a pathway through which hinder material is
delivered to the nozzle 82. Of course, other turbulence
imparting mechanisms may also be used.
In Fig. 4, a rotary mixer 90 with plural mixing
paddles, some being indicated at 92, is disposed within
the conduit 24 at the material applying zone 30. This
mixer is rotated by a motor (not shown) to impart
turbulence to fibers as they pass the mixer paddles. The
nozzles 32, 34 and 36 are disposed externally of the
conduit 24 for directing the binder material through ports
to the fibers passing the mixer. These nozzles may be
enclosed in a shroud or cover as shown by dashed lines 94
in this figure. However, in the Fig. 4 approach, blower
26 has been shifted to a location downstream from the
material applying zone 30. Consequently, the material
applying zone is at a relatively low pressure with a
slight vacuum being present in the material applying zone
relative to the pressure outside tha conduit at this zone.
Consequently, fibers passing the nozzles 32, 34 and 36
tend to be drawn into the conduit rather than escaping
through the binder applying poxts. As a result, the
nozzles can be positioned outside of the conduit where
they are not subject to being clogged by the passing
f ibers.
Referring to Fig. 5, another apparatus i5 shown
for producing the fiber product of the present invention.
In Fig. 5, for purposes of convenience, elements in common
with those of Fig. 1 have been given like numbers and will
not be discussed in detail.
- 2~ 5~
In general, the Fig. 5 form of the apparatus
allows the continuous processing of fibers with the fibers
passing only once through the binder material application
zone 30. However, the zone 30 is typically of an extended
length with more nozzles (i.e. six to twelve or more) than
shown in Fig. 5. Following the application of the binder
material, solid particulate mat:erial may be added from
source 80, such as by a blower (not shown) or a feed
screw, to introduce the particles into the stream of
entrained fibers. The fibers pass through a heater or
oven 70, or heated air is blencled with the air stream
which entrains the fibers, or drying purposes and then
travel through a distance D at the elevated temperatures
created by this heat. As a typical example, D may be 150
feet with the time required to travel the distance D
enabling the binder on the entrained fibers to become
substantially dry. Optionally, cooling air from a
refrigeration unit 100 or ambient air from the environment
may be delivered by a blower 102 to the conduit 24 at a
location 104 in the conduit. This cooling air lowers the
temperature of the dried and treated fibers. The cooling
air may be dehumidified prior to introduction to conduit
24 to minimize any condensation that may otherwise occur
in the conduit. Again, the temperature is preferably kept
above the film forming temperature and below the hot tack
temperature of the thermoplastic binder material. Cyclone
separator 60 may be provided with a bleed line 106 for
ventiny the air during separation. Although less
preferred, this air may bP recirculated back to the fiber
loading zone 20. Flow control gate valves 107, 109 may be
included in the system to balance the air flow through the
various conduits of the illustrated system.
The treated fibers from outlet 66 of the
separator 60 may be fed to a hopper 110 of a conventional
fiber blending unit 112. Other fibers, such as wood pulp
fibers or synthetic fibers are fed, in a desired
proportion for the resulting product, by way of a conduit
114 to another hopper 116 and then to the blending unit
- 25 -
112. The fibers from outlet 66 can also be used without
blendi.ng them with other fibers. The blended treated and
untreated fibars 118 are shown being deposited on a facing
sheet 120 which is passed through the blending unit 112
from a roll 122. The fibers may also be deposited
directly on a conveyor without a facing sheet. The facing
sheet is carried by a conveyer 124 through the blending
unit 112. The composite web is then passed through a
thermobonding unit 130 which raises the temperature of the
fibers sufficiently to cause the treated fibers to heat
fuse to the other fibers and to the facing sheet. The
fibers may be compressed to densify the web prior to or
after delivery to the thermobonder 130. A cover sheet may
also be added to the product before or after the
thermobonder 130. Following thermobonding, to reduce the
stiffness of the webs, they may be "tenderized" by the use
of a mechanism which mechanically breaks up some of the
bonds in the web. The web still remains substantially
bonded, however. As one example, the webs may be passed
through the nips of cross machine direction and machine
direction corrugators to reduce their stiffness. The
stiffne~s can be controlled by adjusting the clearance
between the nips. Although not limited to a specific
approach, examples of suitable corrugators and tenderizing
25 procedures are disclosed in U.S. Patent Nos. 4,559,050,
4,596,567 and 4,605,402. The resulting material can be
used in a conventional manner to manufacture a wide
variety of products, such as webs, absorbent pads,
disposable diapers, webs and the like.
In the Fig. 6 form of apparatus used to produce
the fiber product of the present invention, the fibers to
be treated may be delivered in loose form or in the form
of a sheet 10 from roll 12 to a first hammer mill or
refiberizing device 140. The resulting fibers travel
through air or another gaseous medium in condui.t 24 and
through a binder applying zone 309 If the fibers are not
convsyed hor.izontally, but merely pass downwardly in the
conduit, the air velocity need not be as high. In this
- 26
sense tha fibers are not air entrained, but merely travel
through the conduit. At zone 30, a first binder material
46 is applied to the fibers by way of nozzle 32. Again,
this is a schematic representation o~ the apparatus, as
plural nozzles are preferably employed and more than one
type of binder may be used. Thus, the material applyiny
20ne is substantially elongated over that which is shown.
One or more particulate materials may also be added to the
binder coated fibers from a source of such particles 80.
The treated fibers may be air laid or otherwise deposited,
wet or dry, directly on a face sheet 120 from a roll 122
or directly on a conveyor. Typically a vacuum ~not shown)
would be used to draw the fibers against the screen so
that the fibers are not simply falling under the influence
of gravity. The face sheet is carried by a conveyor 124
past an outlet 146 of the fiber treatment apparatus. A
web of untreated fibers 148 from a roll 150 is optionally
delivered to another hammer mill 152 for fiberization and
blending with the treated fibers prior to depositing the
blend on the ~ace sheet 120. The face sheet 120 and
deposited fibers may then be processed, such as previously
described, for use in manufacturing a variety of products.
The following examples will serve to more
specifically illustrate the method of the present
invention, although it is to be understood that the
invention is not limited to these examples.
EXAMPLE 1
A bleached Kraft Southern Pine cellulose fiber
pulp sheet (NB-316 from Weyerhaeuser Company~ was
fiberized in a hammer mill. One kilogram of the fiberized
flu~f was then air entrained in a recirculating conduit.
After 20 seconds of air entrainment, 1223 grams of
Primacor 4990 ethylene acrylic acid copolymer solution, 35
percent solids, was sprayed onto the air entrained fiber
over a period of eight minutes. Primacor 4990 is a
thermoplastic binder material which is available from Dow
Chemical Corporation. The coa-ed fiber was then
recirculated for two minutes prior to separation in a
2~ ~S~
~ 27 -
cyclone. The still somewhat wet coated fiber was then
deposited in A loose pile and air dried at room
temperature for 24 hours. Even though wood fibers are of
irregular cross section and thus more difficult to coat
than surfaces with a regular cross section or smooth
surface, the resultant fibars had a uniform continuous
coating of binder. Also, approximately 95 percent of the
fibers were unbonded to one another by the binder
material. The dried fiber was then easily air laid in a
laboratory pad former. Six inch diameter pads weiyhing
ten grams were prepared. These pads were then compressed
in a press to densities of from 0.04 to 0.15 g/cm3 ancl
then thermobonded at 140 degrees Centigrade in an
air-through laboratory bonding unit. The resulting pads
were tested for tensile index (tensile strength in N/m
divided by basis weight in g/m2). The tensile index was
0.6 N-m/g for pads having a density of 0.06 g/cc.
In addition, the dried coated fiber obtained in
this manner was blended with uncoated fiber in a ratio of
1/3 coated fibers to 2/3 uncoated NB-316 fibers. The
blend was air laid and thermobonded. The tensile index of
the blend was 0.3 N-m/g at a 0.06 g/cc density. Primacor
is a hydrophobic, somewhat oleophilic thermoplastic
binder. Therefore, a Primacor coated fiber is capable of
absorbing oil without water.
A wide variety of other binders have also been
tested, including Synthemul 40-800 and 40-850 emulsions,
available from Reichhold Chemical Corporation. Cellulose
wood pulp fibers having 5 percent, 7 percent, 10 percent,
20 percent, 30 percent and 50 percent by dry weight
Synthemul 40-800 coating have been manufactured using the
present method. It is only at levels of about 7 percent
that a continuous coating of the fibers is achieved. At 5
percent, the binder material was present as
non~interconnected areas or blobs on the surface of the
fibers. These percentages are the percent of dry weight
of the fiber and binder combination which is the binder.
In a recirculating system, to achieve higher percentages
~ 28 -
of the binder concentration, the fibers were recirculated
in the loop during liquid binder application for a longer
time. Pads made in the above manner with 35 percent and
45 percent Synthemul 40-800 binder, respectively, had
tensile indices of respectively 1.98 and 1.99 N-m/g at a
0.06 g/cc density. Synthemul is a more hydrophilic binder
than Primacor. Also, Elvace 40-712, available from
Reichhold Chemical Corporation, an ethylene vinyl acetate,
has also been tested as have a number of other binder
materials. These tests have all confirmed that
substantially unbonded individualized fibers coated with a
substantially continuous coating Oe binder material can be
produced in accordance with this approach.
EXAMPLE 2
This example is similar to example 1, with the
exception that a larger volume of fibers were treated at
one time. In addition, a surfactant material was added to
the Primacor for application with the binder. In this
specific example, Aerosol OT-S Dioctyl Sodium
Sulfosuccinate 70.2 percent TS, available from American
Cyanamid Corporation, was used as the surfactant material.
A four kilogram batch of treated NB-316 fluff was
processed as explained in example 1. Sufficient Primacor
was added to generate a mixture that was 80 percent NB-316
wood pulp fibers, 20 percent Primacor with 1.74 percent
surfactant based on the Primacor solids. The treated
fibers were recirculated in the loop for 15 seconds
following the application of the Primacor and then dumped
in a pile for subsequent drying. Again, substantially0 unbonded individualized fibers resulted.
EXAMPLE 3
In accordance with this example, functional
materials in particulate form are adhered to the binder
coated fibers. It has been found that a binder
concentration of 7 percent will adhere some particulate
material to the fibers, but at binder concentrations of 20
percent of the total dry weight of the binder, fiber and
additives, and higher, much better adhesion occurs.
- 29 -
Fibers were produced in a recirculating loop of
the form shown in Fig. 1. In processing the fibers, a
sufficient amount of binder material was added to the air
entrained fibers to produce the desired concentration.
The recirculation blower was then momentarily turned off
and the particulate material was added to the system at
the fiber loading ~one 20. Recirculation of the materials
through the loop was then recommenced to mix the particles
with the still wet and entrained fibers. Continued
circulation of the fibers resulted in partial drying of
the binder and adhesion of the particle to the fibers.
In a first more specific example, fibers coated
with 20 percent Synthemul ~0-800 (the percentage being the
percent of binder in the dry fiber, pigment and binder
combination) were mixed with a granular pigment material,
specifically titanium dioxide. Various amounts of
titanium dioxlde ha~e been added to the fibers, lncluding
an amount which is sufficient to be 50 percent of the dry
weight of the binder, fiber and titanium dioxide
combination. This material is useful in paper making
processes.
Similarly, fire retardant particulate materials,
such as alumina trihydrate and antimony oxide may be
adhered to binder treated fibers for use in preparing fire
retardant materials, such as pads, paper and other
products.
To produce an electrically conductive material, a
conductive particulate material (such as 60-80 percent by
weight of the binder fiber and additive combination) may
be adhered to the fibers by the binder. Powdered metallic
materials and carbon black are examples.
For use in manufacturing abrasive pads and the
like, abrasive particulate materials, such as ceramic
powders, metallic powders, or grit~ may be secured to the
fibers by the binder material.
Also, paper making additives, such as acidular
particles of clay, talc, mica and so forth, may be adhered
to the fibers. For example, approximately 50 percent by
_ 30 ~ 5~
weight of the binder, fiber and additive content may be
made up of these additives.
Oleophilic materials, such as polynorbornene in a
desired concentration may be adhered to the fibers.
Norsorex from Norsorlor, a division of CdF Chimie of
Paris, France, is one example of such a material.
Typically a fugitive surfactant is used in this case.
Like the other particulate matlerials, these materials may
be added in varying percentages.
In addition, more than one type of particle may
be bound to the fibers if the functional characteristics
of more than one particulate material are desired.
Again, preferably the binder is of a polymeric
heat bondable thermoplastic type so that the fibers may be
subsequently heat bonded, with or without other fibers, in
manufacturing a product.
EXAMPLE 4
This example is like example 3, except that super
absorbent particles are adhered to the fibers by the
binder material. These super absorbent particles are well
known in the art. Various amounts of super absorbent
particles have been successfully adhered to the fibers,
including from 15~50 percent of the dry weight of the
resultant fiber, binder and additive combination. Lower
percentages are also possible as are higher percentages.
A specific example of super absorbent particulate material
is Sanwet lM-1000, available from Celanese Corporation.
In one more specific example of the method,
rather than stopping the fibers to permit addition of the
particulate material, super absorbent particles were fed
into the air stream containing the entrained fibers
immediately following the binder application zone. The
resultant material had fiber bonded to the super absorbent
particles so as to contain the super absorbent particles
in the resultant fluff. Yet, the fibers which were not
attached to the particles were substantially unbonded to
one another. The dried fluff was then air laid into a web
and thermobonded. The web was tested for absorbency and
- 31 -
found to be equivalent to an unbonded product, but with
virtually 100 percent containment of the super absorbent
partieles. In addition, the containment o~ the super
absorbent partieles within the fibers prior to
thermobonding was also exeellent. Also, a very uniform
distribution of super absorbent particles was present in
the resulting web and enhaneed the water absorbiny
charaeteristies of the web. Consequently, the fibers can
be stored and transported for subsequent use in products
without signifieant loss or migration of super absorbent
particles.
EX~MPLE 5
In aeeordanee with this example, the
thermoplastic binder can be mixed with a blowing agent,
such as Azodiearbonamid, and applied to the entrained
fibers. When the fibers are subsequently heated,
nitrogen, earbon dioxide, and/or other gases would be
released to produce a foamed coating of the fibers. These
foam eoated fibers ean then be used in manufaeturing, such
as in the manufaeturing of insulated paper board.
EXAMPLE 6
In aceordance with this example, the
thermoplastic binder material may be a hydrophobic latex
material with a fugitive surfaetant with the particles
hydrophobic; the binder may be of a hydrophobic material
with th~ partieles hydrophilic; the binder may be a
hydrophilie material with the particles hydrophobic; or
the binder may be a hydrophilie material with the
particles hydrophilic. ~ fugitive surfactant is typically
used when water based binders are used and the fibers or
partieles are hydrophobic.
Thus, a binder such as Primacor may be used with
hexanol as a surfaetant as explained in eonnection with
example 1 as a hydrophobic binder. While Primacor does
have a tendeney to absorb oil to a limited extent, it is
not an optimum oil absorbing material. By attaching
polynorbornene particles to the fibers, fibers having an
enhaneed eapaeity for oil absorption may be produced as
~ 32 -
the polynorbornene in effect acts like a super absorbent
for oil.
An example of a hydrophobic binder with a
hydrophilic particulate material would be ~ibers coated
with Primacor with super absorbent particles adhered to
the fibers by the binder. For example, fibers containiny
a 20 percent Primacor binder, 40 percent by weight super
absorbent particles~ and 40 percent by weight fiber, have
been produced. These percentac~es are of the total dry
weight of the binder, fiber ancl additive combination.
An example of a hydrophilic binder with
hydrophobic particles would be Synthemul ~0-800 as a
binder and polynorbornene as the particles.
Finally, an example of a hydrophilic binder with
hydrophilic particles is Synthemul 40-800 as a binder and
super absorbent particles as the hydrophilic material.
EXAMPLE 7
The binder may also be comprised of a
thermoplastic polymer material together with plasticizer
particles or liquid which cause the polymer to soften when
subjected to heat. A specific example of liquid
plasticizer is dioctyl phthalate. A specific example of a
particulate plasticizer is sold under the brand name
Santowax from Monsanto, Inc.
EXAMPLE 8
In accordance with this example, the fibers may
be coated with plural binder materials. For example,
Kraton, a styrene butadiene block copolymer, available
from Shell Chemical Corporation is a hydrophobic and
oleophilic binder material. This material does not form
very strong bonds with other ~ibers. Therefore, a highly
bondable first thermoplastic coating, such as of Primacor
may be applied to continuously coat the f.ibers. Kraton in
a lesser amount may then be applied to only partially coat
the fibersO The exposed Primacor coated areas then
enhance the bondability of these fibers.
_ 33 _ 2~
EXAMPLE 9
This example demonstrates the applicability of
the process to cellulose fibers containing fiber bundle
material. Specifically, 1111 grams of a mechanically
fiberized wood (10 percent moisture) were placed in a
recirculating conduit 24 with an in-line blower. The
blower was turned on and the wood fibers became air
entrained. 952 grams of Reichhold's Synthemul 40-800 (55
percent moisture) were sprayed onto the fiber through a
port in the conduit. After addition of the latex, the
material was shunted out of the loop 24, collected in a
cyclone 60 and spread on a bench to air dry. Subsequent
examination under a scanning electron microscope showed
individual fibers and individual fiber bundles enclosed in
a latex sheath with substantially no fiber to fiher, fiber
to fiber bundle, or fiber bundle to fiber bundle
agglomeration due to latex bonding.
Having illustrated and described the principles
of our invention with reference to several preferred
embodiments and examples, it should be apparent to those
of ordinary skill in the art that such embodiments of our
invention may be modified in detail without departing from
such principles. We claim as our invention all such
modifications as come within the true spirit and scope of
the following clalms.
