U.S. patent application number 09/552031 was filed with the patent office on 2003-01-02 for process of manufacturing a wet-laid veil.
Invention is credited to Geel, Paul Adriaan.
Application Number | 20030000663 09/552031 |
Document ID | / |
Family ID | 24203667 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030000663 |
Kind Code |
A1 |
Geel, Paul Adriaan |
January 2, 2003 |
PROCESS OF MANUFACTURING A WET-LAID VEIL
Abstract
A method of making a microsphere-filled wet-laid veil involves
forming a non-woven fibrous veil, contacting the veil with an
impregnation binder composition having a binder and microspheres,
and impregnating the microspheres of the impregnation binder
composition into the veil to form a microsphere-filled wet-laid
veil. The microsphere-filled wet-laid veils produced according to
the method of the present invention are useful to make molded
composite articles.
Inventors: |
Geel, Paul Adriaan;
(Dooewerth, NL) |
Correspondence
Address: |
OWENS CORNING
2790 COLUMBUS ROAD
GRANVILLE
OH
43023
US
|
Family ID: |
24203667 |
Appl. No.: |
09/552031 |
Filed: |
April 18, 2000 |
Current U.S.
Class: |
162/100 ;
162/158 |
Current CPC
Class: |
D21H 13/40 20130101;
D21H 21/54 20130101 |
Class at
Publication: |
162/100 ;
162/158 |
International
Class: |
D21F 001/00; D21F
011/00 |
Claims
We claim:
1. A method of making a microsphere-filled wet-laid veil comprising
forming a non-woven fibrous veil and impregnating microspheres into
said veil to form a microsphere-filled wet-laid non-woven veil.
2. The method of claim 1, wherein said method further comprises
heating the microsphere-filled wet-laid veil to expand the
microspheres.
3. The method of claim 1, wherein said microsphere-filled wet-laid
veil is comprised of fibers selected from the group consisting of
metal fibers, ceramic fibers, mineral fibers, glass fibers, carbon
fibers, graphite fibers, polymer fibers, natural fibers, and
combinations thereof.
4. The method of claim 3, wherein said fibers are glass fibers.
5. The method of claim 1, wherein prior to said impregnation step,
said microspheres are in an impregnation binder composition further
comprising a binder selected from the group consisting of polyvinyl
acetate, ethylene vinyl acetate/vinyl chloride copolymer, lower
alkyl acrylate polymer, styrene-butadiene rubber, acrylonitrile
polymer, polyurethane, epoxy resins, polymeric powders, polyvinyl
chloride, polyvinylidene chloride, copolymers of vinylidene
chloride with other monomers, partially hydrolyzed polyvinyl
acetate, polyvinyl alcohol, polyvinyl pyrrolidone, polyester
resins, and styrene acrylate copolymers.
6. The method of claim 5, wherein the impregnation binder
composition optionally contains water, surfactants, foam
stabilizers, thickeners, fillers, colorants, carbon black, hydrated
alumina, blown silica, calcium carbonate, polymeric powders, or
combinations thereof.
7. The method of claim 1, wherein said microspheres comprise a
thermoplastic resin material selected from the group consisting of
polystyrene, styrene copolymers, polyvinyl chloride, vinyl chloride
copolymers, and vinylidene chloride copolymers.
8. The method of claim 7, wherein said thermoplastic resin material
is vinylidene chloride copolymer.
9. The method of claim 1, wherein said microspheres comprise a
blowing agent.
10. The method of claim 9, wherein said blowing agent is selected
from the group consisting of azodicarbonamide, isobutane, pentane,
isopentane, and freon.
11. The method of claim 10, wherein said blowing agent is
isopentane.
12. The method of claim 1, wherein prior to said impregnating step,
the veil is pre-bonded with a pre-binder.
13. The method of claim 12, wherein said pre-binder is polyvinyl
alcohol.
14. The method of claim 13, wherein the microspheres are
impregnated into the veil with a Foulard applicator.
15. The method of claim 14, wherein the microspheres are
impregnated into both sides of the veil with the Foulard
applicator.
16. The method of claim 3, wherein said fibers are glass fibers;
wherein said microspheres comprise a thermoplastic resin material
selected from the group consisting of polystyrene, styrene
copolymers, polyvinyl chloride, vinyl chloride copolymers, and
vinylidene chloride copolymers, and a blowing agent selected from
the group consisting of azodicarbonamide, isobutane, pentane,
isopentane, and freon; and wherein prior to said impregnating step,
the veil is pre-bonded with polyvinyl alcohol.
17. The method of claim 16, further comprising the step of
expanding the impregnated microspheres after the microspheres are
impregnated into the veil.
18. A microsphere-filled wet-laid veil produced according to the
method of claim 1.
19. A microsphere-filled wet-laid veil produced according to the
method of claim 16.
20. A microsphere-filled wet veil according to claim 19, further
comprising a binder composition optionally containing water,
surfactants, foam stabilizers, thickeners, fillers, colorants,
carbon black, hydrated alumina, blown silica, calcium carbonate,
polymeric powders, or combinations thereof.
21. A method of making an article of manufacture comprising
impregnating the veil of claim 18 with a liquid resin and hardener,
and curing.
22. A method of making an article of manufacture comprising
impregnating the veil of claim 19 with a liquid resin and hardener,
and curing.
23. The method of claim 1, wherein the non-woven fibrous veil is
formed on a forming machine selected from the group consisting of
inclined wire forming machine, wire cylinders, Foudrinier machines,
Stevens Former, Roto Former, Inver Former, and Venti Former
machines.
24. The method of claim 23, wherein the forming machine is an
inclined wire forming machine.
25. The method of claim 23, wherein the formed nonwoven fibrous
veil is impregnated with an impregnation binder composition
comprising a binder selected from the group consisting of polyvinyl
acetate, ethylene vinyl acetate/vinyl chloride copolymer, lower
alkyl acrylate polymer, styrene-butadiene rubber, acrylonitrile
polymer, polyurethane, epoxy resins, polymeric powders, polyvinyl
chloride, polyvinylidene chloride, copolymers of vinylidene
chloride with other monomers, partially hydrolyzed polyvinyl
acetate, polyvinyl alcohol, polyvinyl pyrrolidone, polyester
resins, and styrene acrylate copolymers, and microspheres, using an
applicator selected from the group consisting of a size press, a
binder wire, rotary screen, dipping roll, spraying, and coating
equipment.
26. The method of claim 25, wherein the applicator is a binder
wire.
27. The method of claim 12, wherein the prebinder is added to an
aqueous fiber slurry in the wet-end to form the non-woven fibrous
veil.
28. The method of claim 12, wherein the prebinder is contacted with
the veil using an applicator selected from the group consisting of
a size press, a binder wire, rotary screen, dipping roll, spraying,
and coating equipment.
29. The method of claim 28, wherein the applicator is a binder
wire.
30. The method of claim 27, wherein the prebinder is dried and
cured using equipment selected from the group consisting of a
rotary/thru air dryer or oven, a heated drum dryer, an infrared
heating source, hot air blowers, and microwave emitting source.
31. The method of claim 28, wherein the prebinder is dried and
cured using equipment selected from the group consisting of a
rotary/thru air dryer or oven, a heated drum dryer, an infrared
heating source, hot air blowers, and microwave emitting source.
32. The method of claim 31, wherein the dryer is a thru air belt
dryer.
33. The method of claim 15, wherein the binder composition is dried
and cured using equipment selected from the group consisting of a
rotary/thru air dryer or oven, a heated drum dryer, an infrared
heating source, hot air blowers, microwave emitting source, and an
air float dryer.
34. The method of claim 33, wherein the dryer is an air float
dryer.
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
[0001] The present invention relates to a process of manufacturing
a wet laid fibrous veil suitable for the preparation of reinforced
articles. The wet laid fibrous veils comprise microspheres, which
improve the rigidity or impact resistance of the reinforced
articles and particularly, lightweight articles.
BACKGROUND OF THE INVENTION
[0002] Microspheres have been incorporated into fibrous nonwoven
reinforcements, which are useful in the production of molded
composite articles to provide for the formation of lightweight
composites. It has been found that the use of expanded microspheres
results in a considerable savings of resin and glass fiber in
dry-laid fibrous webs. Additionally, the mechanical properties of
the product reinforced with the web, such as rigidity or impact
resistance, are at least maintained, or even improved, and the
thermal insulation capacity is enhanced.
[0003] For example, UK Patent No. 1,427,647 and U.S. Pat. No.
3,676,288 describe the application to, or incorporation of
non-expanded microspheres into a fibrous web using a binder, such
as a polyacrylonitrile latex. As the binder resin is dried and
cross-linked, the microspheres are attached to the fibrous web and
expanded. In U.S. Pat. No. 4,818,583, a method of manufacturing a
bonded fibrous web comprising microspheres were described. However,
these methods of adding the microspheres to the fibrous web were
directed to a dry-laid process.
[0004] Fibrous webs or veils, which are one form of fibrous
nonwoven reinforcements, are extremely suitable as reinforcements
for many kinds of cured synthetic plastic materials, such as
polyester or epoxy resin. Fibrous veils are typically made by a dry
or wet-laid process. Typically, glass and mineral fibers have been
integrated into the fibrous veils to provide added strength and
durability to the composite article made by molding the veil.
However, the use of glass fibers in a dry-laid process wears out
the machines typically involved in the dry-laid process.
Accordingly, integrating glass fibers in a dry-laid process may be
costly.
[0005] There is a thus a need for a wet-laid process of making
fibrous veils that can be used as a reinforcement in composite
molding, which allows for the cost-effective incorporation of glass
or other reinforcement and allows for the incorporation of
microspheres for added rigidity and impact resistance. Furthermore,
there is a need to obtain a continuous and efficient method of
producing such fibrous reinforcements.
SUMMARY OF THE INVENTION
[0006] A method of making a microsphere-filled wet-laid veil is
disclosed. In one embodiment, the method comprises forming a
non-woven fibrous veil, and impregnating microspheres into the veil
to form a microsphere-filled wet-laid veil. Preferably, the step of
impregnating microspheres into the veil is achieved by contacting
the veil with an impregnation binder composition comprising a
binder and the microspheres. In a preferred embodiment, the method
comprises forming a pre-bonded veil of glass fibers without
microspheres. Subsequently, the pre-bonded veil is impregnated
inline with a binder composition comprising a binder and
microspheres, then the microspheres are expanded.
[0007] The invention further comprises microsphere-filled wet-laid
veils produced according to the above-mentioned method. Moreover,
the invention comprises molded composite articles made using the
wet-laid veils manufactured according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1A, 1B, and 1C are flow diagrams of three embodiments
of the process of the present invention.
[0009] FIG. 2 is a cross-section of a microsphere-filled wet-laid
veil.
[0010] FIG. 3 is a cross-section of a microsphere-filled wet-laid
veil saturated with resin.
[0011] FIG. 4 is a cross-section of a laminate made with layers of
microsphere-filled wet-laid veils in the core of the laminate.
[0012] FIG. 5 is a cross-section of a laminate made with a
microsphere-filled wet-laid veil as a surfacing veil.
[0013] FIG. 6 is a schematic representation of the preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0014] The present invention relates to a process of manufacturing
a wet-laid nonwoven fibrous veil comprising microspheres. As shown
in FIG. 1A, the process involves making a non-woven wet-laid
fibrous veil 10 and impregnating microspheres into the veil 20.
[0015] The term, "wet-laid veil," as used herein, refers to a web
of intermingled, randomly oriented reinforcing fibers made
according to a wet laid process. The "veil" of the present
invention may also include "sheets" or "mats" made in accordance
with the wet-laid process. The fibers are preferably segmented and
optionally, the formed veil may be reinforced with continuous
filaments.
[0016] "Impregnating," as used herein, refers to a means of
integrating microspheres into the fibrous veil. The method of
impregnating may be conducted by any method suitable for
integrating or incorporating these materials into the fibrous veil.
In accordance with the present invention, the microspheres are
impregnated into the veil at any time after formation of the veil.
In particular, the microspheres are preferably impregnated after
formation in a formation chamber, such as on a wire, or after being
passed through a first dryer. As shown in FIGS. 1B and 1C, most
preferably, the microspheres are impregnated 40', 40" after being
passed through a first dryer 30', 30".
[0017] The "microspheres" of the present invention are particles of
thermoplastic resin material, which may have incorporated therein a
chemical or physical blowing agent, and which may be expanded upon
heating. The microspheres of the present invention can have any
desired diameter. For example, they may have a diameter of about 6
to about 45 microns, preferably, about 10 to about 16 microns, in
an unexpanded state, and a diameter of about 15 to about 90
microns, preferably about 40 to about 60 microns in an expanded
state. The microspheres may be used in either its expanded or
unexpanded state. Any suitable thermoplastic resin material may be
used to make up the microspheres. Suitable thermoplastic resin
materials include, for example, polystyrene, styrene copolymers,
acrylonitrile, polyvinyl chloride, vinyl chloride copolymers,
vinylidene chloride copolymers, and the like. The thermoplastic
synthetic resin material is preferably solid at room temperature.
Preferably, the microsphere is comprised of the thermoplastic resin
material, vinylidene chloride copolymer.
[0018] Preferably, the microspheres include a chemical or physical
blowing agent within the sphere that permits them to be expanded
upon heating. Any suitable blowing agent may be used provided that
it that causes the microspheres to expand upon heating. For
example, suitable blowing agents include azodicarbonamide,
isobutane, pentane, isopentane and freon. Preferably, the blowing
agent is isopentane.
[0019] As shown in FIG. 6, a wet lay process comprises mixing
reinforcing fiber components with water in an aqueous fiber slurry
600, known as "white water," under agitation in a mixing tank. The
reinforcing fiber component may be any reinforcing fiber suitable
for use in a wet laid process. For example, this may include metal
fibers, ceramic fibers, mineral fibers, glass fibers, carbon
fibers, graphite fibers, polymer fibers, such as aramid (e.g.,
Kevlar.RTM.), polyesters, polyacrylics, polyamides,
polyacrylonitrile, natural fibers, and combinations thereof, as
well as any other fibrous reinforcing materials that may
conventionally be used in the manufacture of reinforced composites.
Preferably, glass fibers are used. The fibers may be used as
filaments or as strands of gathered filaments in chopped form.
Optionally, continuous filaments can be used as length-oriented
reinforcement for the veil. Most preferably, the fibers are chopped
glass fibers.
[0020] Additional elements to make up the white water aqueous
slurry may be added as is known in the art. For example, antistatic
agents, coupling agents, pigments, surfactants, anti foams,
colorings, fillers, and pre-binders, such as polyvinyl alcohol.
Preferably, a pre-binder is used, which may be used in any form,
such as a powder or fiber form.
[0021] As shown in FIG. 6, the aqueous fiber slurry 600 is
transferred onto a suitable formation apparatus 610, such as a
moving screen or forming wire on an inclined wire forming machine,
wire cylinders, Foudrinier machines, Stevens Former, Roto Former,
Inver Former, or Venti Former machines. Preferably, the formation
of the veil is on an inclined wire forming machine. On the
formation apparatus 610, the fibers and the additional slurry
elements in the aqueous fiber slurry emnesh themselves into a
freshly prepared wet laid fibrous veil 615, while excess water is
separated therefrom. The dewatering step may be conducted by any
known method such as by draining, vacuum, etc. The water content of
the veil after dewatering and vacuum is preferably in the range of
about 60 to about 85%.
[0022] After the wet laid fibrous veil 615 is formed, the wet laid
fibrous veil is transferred to a transport belt 617, which carries
the veil into a means 620 for substantially removing the water. The
removal of the water may be conducted by known web drying methods,
including the use of a rotary/thru air dryer or oven, a heated drum
dryer, an infrared heating source, hot air blowers, microwave
emitting source, and the like. At least one method of drying is
necessary for removing the water, but a plurality of these methods
may be used in combination to remove the water and dry the wet laid
fibrous veil 617. The temperature of the dryer may range from about
120.degree. C. at the start until about 210.degree. C. at the end
of the 1st drying process. The airspeed may be in the range of
about 0.5 to 1 m/sec.
[0023] Optionally, as shown in FIG. 1A, a wet end pre-binder may be
applied 20 to the veil prior to being transferred to the water
removing means. If a pre-binder is used, it is bound to the fibers
in the first dryer 30 to form a pre-bonded veil.
[0024] As shown in FIG. 6, after passing through the first dryer
620, the veil 615' is made up of a fiber composition. Preferably,
the fiber composition of the veil 615' comprises glass fibers and a
wet end pre-binder. Optionally, additional agents as described
above are present. The fibers and optional pre-binder and other
agents may be present in any desired ratio. Preferably, the fiber
composition of the veil after the first dryer is comprised of about
70 to about 95% glass fibers and about 5 to about 30% wet end
pre-binder. More preferably, the fiber composition of the veil is
between about 90 to about 95% glass fibers and between about 5 to
about 10% wet end pre-binder (powder or fiber) and the total dry
substance level that is transported to the dryer is in the range of
about 28 to about 32%.
[0025] Impregnating the microspheres into formed veil involves
contacting an impregnation binder composition comprising the
microspheres with the formed veil. The microspheres are combined
with a binder resin to form an impregnation binder composition that
may be contacted with the veil. One or more binder resins suitable
for applications in reinforcing fibers may be used. Suitable
binders include polyvinyl acetate (PVA), ethylene vinyl
acetate/vinyl chloride (EVA/VC), lower alkyl acrylate polymer,
styrene-butadiene rubber, acrylonitrile polymer, polyurethane,
epoxy resins, polyvinyl chloride, polyvinylidene chloride, and
copolymers of vinylidene chloride with other monomers, partially
hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl
pyrrolidone, polyester resins, styrene acrylate, and the like.
Optionally these binders can be functionalized with acidic groups,
for example, by carboxylating with an acid. A suitable
carboxylating agent is, for example, maleic anhydride. The binder
may be used in any form, such as a powder, a fiber, or a liquid.
Preferably, the binder is styrene-compatible or a soluble binder,
such as styrene acrylate. It is further noted that the
above-mentioned binders may also be suitable as a pre-binder.
[0026] The microspheres and binders in the impregnation binder may
be present in any ratio. Preferably, the proportion of microspheres
exceeds the proportion of the binder resin. More preferably, the
ratio of microsphere to binder is in the range of 60:40 to
80:20.
[0027] The impregnation binder composition may further comprise
other components suitable for reinforcing fiber materials. For
example, the binder composition may optionally contain water,
surfactants, foam stabilizers, thickeners, fillers, colorants,
carbon black, hydrated alumina, blown silica, calcium carbonate,
polymeric powders, and the like.
[0028] The impregnation binder is contacted with the fibrous veil
after formation of the veil 615 itself. The formed veil may be
contacted with the impregnation binder 630 either prior to being
pre-bonded in a first dryer 620, or after being pre-bonded in the
first dryer. Any method suitable for impregnating the binder
composition comprising a binder and microspheres into the fibrous
veil may be used. For example, suitable methods include using a
size press 640, such as a Foulard applicator, a binder wire, rotary
screen, dipping roll, spraying, coating equipment, and the like.
While other additional agents or coatings may be applied,
preferably, only the impregnation binder 630 is contacted with the
wet-laid non-woven fibrous veil 615.
[0029] The microspheres are impregnated after formation of the
veil, preferably prior to insertion into the first dryer or before
being pre-bonded with a pre-binder, or after the wet-laid
pre-bonded nonwoven fibrous veil is formed. Most preferably, the
microspheres are added after the wet-laid pre-bonded nonwoven
fibrous veil is formed. This is done during an inline additional
impregnation process.
[0030] At the "wet-end" formation of the veil 615, such as on the
forming wire 610, and prior to the first dryer 620, the formed veil
comprises a fiber composition and water. The fiber composition is
present in an amount of about 15% to about 45% by weight,
preferably about 30% by weight. The fiber composition comprises
preferably about 70% to about 95% fibers and about 5 to about 30%
wet end pre-binder. The water is present in an amount of about 55%
to about 85% by weight, preferably about 70% water.
[0031] When the microspheres are impregnated directly after
formation at the wet-end and prior to the first dryer 10 (see FIG.
1A), the impregnation binder composition comprising a binder and
the microspheres are contacted with the veil formed from the
formation apparatus. In such case, the impregnation binder
comprising the binder and microspheres are impregnated into the
veil as set forth above. Preferably, a binder wire is used to
impregnate the impregnation binder microspheres into the veil.
Thereafter, the microsphere-impregnated veil passes through the
first dryer to form a microsphere-filled nonwoven fibrous veil.
Optionally, the veil may pass through a second dryer 650.
[0032] Alternatively, the microspheres may be impregnated after the
first dryer (see FIGS. 1B and 1C), wherein a pre-binder is
optionally bonded to the nonwoven fibrous veil to form the
prebonded nonwoven fibrous veil. In this manner, after the first
dryer, the wet-laid prebonded nonwoven fibrous veil is formed and
consolidated. The impregnation binder may be applied preferably
inline to the prebonded nonwoven fibrous veil as set forth above.
In the preferred embodiment of the present invention, the
impregnation binder composition comprising the binder and the
microspheres are impregnated using a size press or Foulard type of
applicator. It is particularly preferred that the veil be brought
into the Foulard applicator to assure that the pre-bonded nonwoven
veil is wetted on both sides. This may be accomplished by bringing
the veil into the Foulard applicator from above in a double roll
system, wherein the impregnation binder liquid is capable of
coating both sides of the veil. Subsequently, the fibrous veil may
optionally be dried and/or cured. Preferably, the impregnated
fibrous veil is dried and cured in an oven, preferably an airfloat
oven. One skilled in the art appreciates the curing oven may
alternately comprise any suitable drying device, such as a
rotary/thru air dryer or oven, a heated drum dryer, an infrared
heating source, hot air blowers, microwave emitting source, and the
like.
[0033] The most preferred embodiment is now described in greater
detail with respect to FIG. 6. Therein, glass fibers, water, and a
pre-binder are mixed to form the aqueous fiber slurry 600. The
slurry 600 is then transferred to a forming apparatus 610,
preferably a forming wire to form a veil 615 with concurrent
dewatering (not shown). The formed veil is then passed on a belt
through a first belt drier 620, wherein the pre-binder is bonded to
the nonwoven fibrous veil to form the prebonded nonwoven fibrous
veil 615'. The impregnation binder liquid 630 is then applied to
the prebonded nonwoven fibrous veil in an impregnation unit 640.
Preferably, the impregnation unit 640 is a Foulard applicator. It
is particularly preferred that the prebonded nonwoven fibrous veil
be wetted on both sides with the impregnation binder liquid 630 in
the impregnation unit 640. This may be accomplished by feeding the
veil into the impregnation unit 640 from above the unit and
allowing the impregnation binder liquid 630 to coat both sides of
the veil. Subsequently, the impregnated veil is dried in a second
drier 650, which is preferably an airfloat oven. The resulting
microsphere-filled wet-laid veil is collected on a winder 660.
[0034] It has been found that where the microspheres are added to
the impregnation binder comprising the binder and microspheres, the
drying process allows the various components, including the binder,
synthetic resin, and blowing agent, to interact effectively with
each other. For example, during the drying of the impregnated
fibrous veil according to this embodiment, the binder is hardened
and cross-linked, while, at the same temperature, the microspheres
are expanded. The expanded impregnated microspheres give a greater
volume of microspheres to the wet-laid fibrous veil.
[0035] The process of manufacturing the microsphere-filled wet-laid
veil of the present invention may be conducted either in-line,
i.e., in a continuous manner, or in individual steps. Preferably,
the process is conducted in-line. Moreover, any additional process
steps of treating the fibers, forming the wet-laid veil, and
bonding the wet-laid veil is considered within the scope of the
present invention.
[0036] The microsphere-filled wet-laid veil produced in accordance
with the present invention may comprise any desired amount of
microspheres, for example, about 5 to about 50% by weight,
preferably about 15 to about 25% by weight microspheres.
[0037] The filling degree and the product thickness can be
influenced by selecting a certain weight and pre-binder content of
the pre-bonded nonwoven as well as the subsequently used amount of
microspheres and binder. The "filling degree" determines how much
resin will be necessary to be incorporated into a reinforcing
material to fill or accommodate for interstitial openings in the
reinforcement. The greater the filling degree, the less amount of
resin is necessary for a reinforcement having the same thickness.
It has been found that a greater filling degree is attained when
the impregnation binder composition is contacted subsequent to
formation of the wet-laid nonwoven pre-bonded fibrous veil.
[0038] Referring to FIG. 2, the microsphere-filled wet-laid veil
200 of the present invention comprise microspheres 210 and the
fibers 220. The microspheres in the veil may be arranged in a
regular or random pattern. The regular pattern refers to a pattern
of "islands" of microspheres 210 having a substantially similar
shape, separated by channels or open spaces 230 between the
microspheres and the fibers 220. Alternatively, the veil may
comprise a random arrangement of microspheres, which refers to an
intermittently dispersed array of microspheres without any
uniformity in pattern. The use of a size press or Foulard type
impregnator in combination with the selected binder formulations
results in a very regular dispersion of the microspheres in the
veil. The uniformity of the dispersion patterns contribute to the
uniform wetting of the fibers in the veils.
[0039] The veil of the present invention may subsequently be used
as a reinforcement in a molding process to produce a composite
article (see FIGS. 3 and 4). For example, the veil may be molded by
impregnating with a liquid resin and a hardener therefor. The
liquid resin may be any suitable resin for forming a reinforced
fibrous material, such as polyester and epoxy resins. The hardener
may be any suitable catalyst for catalyzing the cross-linking of
the binder when the microsphere-filled wet-laid veil, liquid resin,
and hardener are cured.
[0040] Referring to FIG. 3, the composite article 300 reinforced
with the microsphere-filled veil of the present invention comprises
microspheres 310 and fiber 320 as described above. The veil is
impregnated with resin 330, which is hardened and cured in the
desired mold.
[0041] Another possible embodiment of the invention is set forth in
FIG. 4, wherein a laminate 400 is made using the microsphere-filled
veil 410 of the present invention. In this respect, a plurality of
microsphere-filled veils 410 of the present invention may be
stacked between a suitable mat 420 comprising reinforcing fibers,
as is known in the art. A surfacing veil 430 may further be applied
to the surface of the laminate 400. The laminate is hardened and
cured as known in the art. The microsphere-filled fibrous veil
produced in accordance with this invention is also very suitable
for use as core material for objects made of all kinds of synthetic
resin such as polyester resin or epoxy resin.
[0042] FIG. 5 represents another application of the fibrous veil
510 produced in accordance with this invention as a surfacing veil
in a laminate 500 using woven glass fabric 530 on the outside and
core material 520 on the inside. In this particular application,
the veils of the present invention are applied as a surfacing veil
and prevents the print through from the woven fabric.
[0043] It has been found that the in-line method of manufacturing
microsphere-filled wet-laid veils combines a high throughput or
high production rate with a very good consistency and significantly
improved fiber distribution, as compared to dry laid technology.
Moreover, the method of the present invention is advantageous over
other methods due to its ease of using glass and mineral fibers. In
particular, the use of glass fibers as the reinforcing fiber
material is a more simple procedure than when using the dry laid
process, for example. For example, whereas in a dry-laid process,
the glass fibers wear out the machines required for such processes,
in the wet-laid process of the present invention, no such wear is
found. Accordingly, the process of the present invention is less
costly and more efficient. In addition, the current use of
microsphere-filled nonwovens, which are mainly made with polyester
fiber, are predominantly used in GRP applications making laminates
using woven glass or glass mat (e.g., chopped strand mat) on the
outside and the microsphere-filled nonwoven in the core. This
creates lightweight and stiff laminates. Moreover, the use of glass
fibers results in a higher stiffness and strength. Furthermore, the
microsphere-filled wet-laid veils also exhibit lower elongation and
lower sensitivity to shrinkage, which opens the potential use in
pultrusion-type processes.
[0044] The following examples are representative, but are in no way
limiting as to the scope of this invention.
EXAMPLES
Example 1
[0045] A 40 grams per square meter (gsm) veil consisting of 89% 13
micron 6 mm glass and 11% PVA prebinder is formed using a wet laid
process using an inclined wire former. This veil is fed to a belt
dryer and dried and cured to form a prebonded sheet. The sheet is
subsequently in-line-impregnated using a size press Foulard
applicator with a binder/microsphere mixture consisting of 30%
styrene acrylic commercially available from Necarbo as "Neboplast
SBN2039" and 70% microsphere, commercially available from AKZO
NOBEL as "Expancel 054WU". The binder/microsphere mixture is
controlled with a vacuum system and the target set at 15 gsm. The
impregnated sheet is fed to an airfloat oven to dry the sheet and
expand the microsphere. Depending upon the speed, the temperature
used was between about 120.degree. C. and 180.degree. C. With these
settings, an end product thickness from about 1.2 mm and a volume
filling degree from about 30% can be reached.
Example 2
[0046] A 100 gsm veil consisting of 92% 13 micron 6 mm glass and 8%
PVA prebinder is formed using a wetlaid process using a foudrinier
formed with inclined wire. This veil is fed to a belt dryer and
dried and cured to form a prebonded sheet. The sheet is
subsequently inline impregnated using a size press Foulard
applicator with a binder/microsphere mixture consisting of 30%
styrene acrylic (Necarbo SBN2039) and 70% microsphere (Expancel
054WU). The binder/microsphere mixture is controlled with a vacuum
system and the target set at 35 gsm. The impregnated sheet is fed
to an airfloat oven to dry the sheet and expand the microspheres.
Depending upon the speed, which was usually about 55 meters/minute,
the temperatures used were between about 120.degree. C. and
180.degree. C. With these settings, an end product thickness from
about 2.7 mm and a volume filling degree from about 30% can be
reached.
Example 3
[0047] A 100 gsm veil consisting of 93% 13 micron 6 mm glass and 7%
PVA prebinder is formed using a wetlaid process using a foudrinier
formed with inclined wire. This veil is fed to a belt dryer and
dried and cured to form a prebonded sheet. The sheet is
subsequently inline impregnated using a size press Foulard
applicator with a binder/microsphere mixture consisting of 30%
styrene acrylic (Necarbo SBN2039) and 70% microsphere (Expancel
054WU). The binder/microsphere mixture is controlled with a vacuum
system and the target set at 35 gsm. The impregnated sheet is fed
to an airfloat oven to dry the sheet and expand the microspheres.
Depending upon the speed, which was usually about 55 meters/minute,
the temperatures used were between about 120.degree. C. and
180.degree. C. With these settings, an end product thickness from
about 4.1 mm and a volume filling degree from about 35% can be
reached.
[0048] It is believed that Applicants' invention includes many
other embodiments, which are not herein specifically described,
accordingly this disclosure should not be read as being limited to
the foregoing examples or preferred embodiments.
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