U.S. patent application number 12/029012 was filed with the patent office on 2008-08-28 for infusion fabric for molding large composite structures.
Invention is credited to Matthew W. Dunn, David R. Hartman.
Application Number | 20080206551 12/029012 |
Document ID | / |
Family ID | 35789198 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080206551 |
Kind Code |
A1 |
Hartman; David R. ; et
al. |
August 28, 2008 |
INFUSION FABRIC FOR MOLDING LARGE COMPOSITE STRUCTURES
Abstract
An infusion fabric includes a mat selected from a group
consisting of continuous filament mat, direct chopped mat, direct
continuous mat and combinations thereof and a woven roving or
bonded reinforcement layer. The mat and woven roving reinforcement
layer are stitched together. The continuous filament mat includes
E-glass and/or ECR-glass fibers, a binder and a size.
Inventors: |
Hartman; David R.;
(Granville, OH) ; Dunn; Matthew W.; (Lewisville,
NC) |
Correspondence
Address: |
OWENS CORNING
2790 COLUMBUS ROAD
GRANVILLE
OH
43023
US
|
Family ID: |
35789198 |
Appl. No.: |
12/029012 |
Filed: |
February 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10971286 |
Oct 22, 2004 |
7358202 |
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12029012 |
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Current U.S.
Class: |
428/327 ;
428/332; 428/426 |
Current CPC
Class: |
B32B 5/024 20130101;
B32B 2605/12 20130101; Y10T 442/2992 20150401; Y10T 442/3528
20150401; B32B 2605/08 20130101; Y10T 428/254 20150115; B32B
2260/023 20130101; B60R 13/02 20130101; Y10T 442/2926 20150401;
B32B 5/06 20130101; B32B 5/12 20130101; B32B 2307/718 20130101;
B32B 5/02 20130101; B32B 2419/00 20130101; Y10T 428/24091 20150115;
Y10T 428/24074 20150115; Y10T 442/3715 20150401; B32B 2264/0278
20130101; Y10T 428/249924 20150401; Y10T 442/3537 20150401; B32B
2307/50 20130101; B32B 2264/0214 20130101; Y10T 442/3065 20150401;
B32B 2264/12 20130101; B32B 5/26 20130101; B32B 2262/14 20130101;
B32B 2260/046 20130101; Y10T 442/378 20150401; Y10T 428/24132
20150115; B32B 2262/101 20130101; B32B 2264/102 20130101; Y10T
442/3707 20150401; B32B 3/20 20130101; B60R 13/04 20130101; Y10T
428/26 20150115 |
Class at
Publication: |
428/327 ;
428/426; 428/332 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B32B 17/06 20060101 B32B017/06 |
Claims
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45. A continuous filament mat, comprising: glass fibers selected
from a group consisting of E-glass fibers, ECR-fibers and mixtures
thereof; a binder; and a size; said continuous filament mat being
characterized by a loop formation ratio of about 2.0 to about 8.0
and a cure of between about 50 and about 100 percent when measured
as acetone extractables.
46. The continuous filament mat of claim 45, wherein said glass
fibers are provided as glass filament bundles.
47. The continuous filament mat of claim 46, wherein said glass
filament bundles include between about 20 and about 140 glass
filaments per bundle.
48. The continuous filament mat of claim 47, wherein said glass
filaments of said glass filament bundles have a mean diameter of
between about 11 and about 20 microns.
49. The continuous filament mat of claim 48, wherein said glass
filament bundles have a mean diameter of about 0.3048 mm and a
diameter range of between about 0.127 and about 1.27 mm.
50. The continuous filament mat of claim 45, wherein said binder is
a polyester.
51. The continuous filament mat of claim 50, wherein said polyester
binder is ground to a particle size of between about 25 to about
200 mm.
52. The continuous filament mat of claim 51, wherein said binder
also includes talc.
53. The continuous filament mat of claim 51, wherein said binder
also includes benzoyl peroxide.
54. The continuous filament mat of claim 51, wherein said binder
includes: between about 95 and about 99.8 weight percent polyester;
between about 0.05 and about 3 weight percent talc; and between
about 0.2 and about 2 weight pet cent benzoyl pet oxide.
55. The continuous filament mat of claim 51 wherein said cure is
between about 60 and about 90 percent when measured as acetone
extractables.
56. The continuous filament mat of claim 45 wherein said cute is
between about 60 and about 90 percent when measured as acetone
extractables.
57. The continuous filament mat of claim 49 wherein said cure is
between about 60 and about 90 percent when measured as acetone
extractables.
58. (canceled)
59. (canceled)
60. (canceled)
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
[0001] This invention relates generally to an infusion fabric that
may be molded into large composite structures as well as to a novel
continuous filament mat and a novel binder.
BACKGROUND OF THE INVENTION
[0002] Reinforcement fabrics made from fibrous materials formed
into woven, knitted and non-woven material, are well known in the
art. Yarns of glass, carbon and aramid are typically formed into
fabrics, and a plurality of layers of fabric are stacked and cut
into dry fabric kits or performs. The preforms are then infused or
impregnated with a resin binder and cured to form a rigid
composite.
[0003] Typically a glass reinforced fibrous mat is preformed and
then placed in a mold for molding into a fiber-reinforced article.
Glass fiber-reinforcement mats are used in situations where a
desired strength is necessary, such as in truck fenders, auto
chassis or bus components and the like. For example, layers of the
continuous strand mat and layers of unidirectional or
multidirectional reinforcement material are fabricated separately.
These layers are individually placed in a set of preformed screens,
which generally consist of an upper screen and a lower screen. The
upper and lower screens are moved together in order to conform the
layers to the shape of the preformed screens. The layers are thus
shaped into what is known as a preform. The preform is then placed
in a mold and injected with a suitable resinous material to make
the fiber reinforced article.
[0004] U.S. patent application Ser. No. 10/674,987, filed on Sep.
30, 2003, (OC Case No. 25253) owned by the assignee of the present
invention, discloses a crimp-free infusible reinforcement fabric.
The unidirectional fabric has small size tows spaced between large
size tows. The "channels" that are formed from the small tows
between the larger tows permit faster resin infusion and increased
productivity.
[0005] The present invention relates to an improved infusion fabric
that better optimizes kitting, performing, conformability to
tooling, resin infusion rate, consolidation thickness, surface
aesthetics, and composite structural performance in a range of
closed molding processes including VIP, RTM and RTM Lite or VARTM
processes. This represents the full range of composite closed
molding processes used by marine, wind, construction,
transportation and industrial customers. In addition, the present
invention relates to a novel continuous filament mat and binder
useful in making that improved infusion fabric mat.
SUMMARY OF THE INVENTION
[0006] The infusion fabric comprises a mat selected from a group
consisting of continuous filament mat, direct chopped mat, direct
continuous mat and combinations thereof along with a woven or
bonded reinforcement layer. In one possible embodiment the mat and
woven roving or bonded reinforcement layer are stitched
together.
[0007] More specifically describing the invention, the mat is
constructed from a material selected from a group consisting of
glass fibers, carbon fibers, graphite fibers, vitreous carbon
fibers, non-graphite carbon fibers, boron monolithic graphite
fibers, boron monolithic non-graphite carbon fibers, silicone,
aramid fibers, ceramic fibers, thermoplastic polymer fibers and
mixtures thereof. Natural fibers such as, for example, cotton,
kenaf, sisal and jute may also be used alone or in combination with
any of the above. The woven roving reinforcement layer may also be
constructed from the same list of materials.
[0008] Typically the woven roving reinforcement layer has an areal
weight of between about 8 to about 60 oz/sq. yd. Further, the woven
roving reinforcement layer is selected from a group consisting of
plain, twill and satin style. The woven roving reinforcement layer
can include multiple parallel tows at least two tows of which have
differing yields so as to form spaced channels. Typically a first
tow of the two tows has a yield A of between about 750 to about
2500 yds/lb. and a second tow of said two tows has a yield B of
between about 52 to about 450 yds/lb.
[0009] In accordance with still another possible embodiment of the
present invention the infusion fabric may include a surfacing mat.
The mat is sandwiched between the surfacing mat and the woven
roving reinforcement layer.
[0010] In accordance with one particular embodiment of the present
invention, the mat of the infusion fabric is a continuous filament
mat including E-glass fibers and/or ECR-glass fibers, a binder and
a size. More specifically, this continuous filament mat includes
between about 80 and about 99 weight percent glass fibers, between
about 1 and about 20 weight percent binder and between about 0.01
and about 1 weight percent size on the fiber. The glass fibers are
provided as glass filament bundles. The glass filament bundles
include between about 20 to about 140 filaments per bundle. Each
filament has a mean diameter of between about 11 to about 26
microns. The bundle diameter is between about 0.127 to about 3.175
mm. The loop formation ratio ranges from about 2.0 to about
8.0.
[0011] The binder is a polyester or an epoxy compatible binder such
as epoxy resin and epoxy novolak. The polyester binder is ground to
a particle size of between about 25 to about 200 mm. The binder
also includes talc and benzoyl peroxide. More specifically, the
binder includes between about 92.5 and about 99.9 weight percent
polyester, between about 0.01 and about 5 weight percent talc and
between about 0.1 and about 2.5 weight percent benzoyl
peroxide.
[0012] Still further, the continuous filament mat has a degree of
cure expressed as acetone extractables of between about 50 and
about 100 percent. More typically, the continuous filament mat has
a degree of cure expressed as acetone extractables of between about
60 and about 90 percent.
[0013] In accordance with yet another aspect of the present
invention, a continuous filament mat is provided. The continuous
filament mat comprises E-glass fibers and/or ECR-glass fibers, a
binder and a size. The continuous filament mat includes between
about 90 and about 98 weight percent E-glass or ECR-glass fibers,
between about 2 and about 10 weight percent binder and between
about 0.1 and about 1.0 weight percent size on the fiber. The glass
fibers are provided as glass filament bundles. The glass filament
bundles include between about 20 to about 140 filaments per bundle.
Each filament has a mean diameter of between about 11 and about 26
microns. The bundle diameter is between about 0.127 and about 3.175
mm. The loop formation ratio ranges from about 2.0 to about 8.0.
The cure, measured as acetone extractables, is between about 50 and
about 100 percent and more typically between about 60 and about 90
percent.
[0014] In a particularly useful embodiment, the continuous filament
mat includes E-glass or ECR-glass fiber bundles having between
about 44 to about 50 filaments per bundle or loop strand. The
bundle diameter mean is about 0.3048 mm and the range is from about
0.127 to about 1.27 mm. The strand to mat architecture or loop
formation ratio is between about 6.0 and 6.6.
[0015] In accordance with still another aspect of the present
invention, a binder is provided for preparing a glass fiber mat.
The binder comprises between about 95 and about 99.8 weight percent
polyester, between about 0.05 and about 3 weight percent talc and
between about 0.2 and about 2 weight percent benzoyl peroxide. The
polyester binder is ground to a particle size of between about 25
to about 200 mm. The polyester is based upon ethylene glycol and
fumaric acid.
[0016] In the following description there is shown and described
several different embodiments of this invention, simply by way of
illustration of some of the modes best suited to carry out the
invention. As it will be realized, the invention is capable of
other different embodiments, and its several details are capable of
modification in various, obvious aspects all without departing from
the invention. Accordingly, the drawings and descriptions will be
regarded as illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings incorporated in and forming a part
of the specification, illustrate several aspects of the present
invention, and together with the description serve to explain
certain principles of the invention. In the drawings:
[0018] FIG. 1 is a partially sectional perspective view of one
possible embodiment of the infusion fabric of the present
invention;
[0019] FIG. 1a is a full cross sectional view of the infusion
fabric illustrated in FIG. 1;
[0020] FIG. 2 is a partially sectional perspective view of another
possible embodiment of the infusion fabric of the present
invention; and
[0021] FIG. 2a is a full cross sectional view of the infusion
fabric illustrated in FIG. 2.
[0022] Reference will now be made in detail to the present
preferred embodiment of the invention, an example of which is
illustrated in the accompanying drawings.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
[0023] A first embodiment of the infusion fabric 10 of the present
invention is illustrated in FIGS. 1 and 1a. As illustrated the
infusion fabric 10 includes a mat 12 and a woven roving or bonded
reinforcement layer 14. Both the mat 12 and the woven roving
reinforcement layer 14 may be constructed from a material selected
from a group consisting of glass fibers, carbon fibers, graphite
fibers, vitreous carbon fibers, non-graphite carbon fibers, boron
monolithic graphite fibers, boron monolithic non-graphite carbon
fibers, silicone, aramid, ceramic fibers, thermoplastic polymer
fibers, natural fibers (e.g. cotton, kenaf, sisal, jute) and
mixtures thereof. Of course, the mat 12 and woven roving
reinforcement layer 14 may be constructed from the same or
different materials from this list as desired.
[0024] The woven roving reinforcement layer 14 has an areal weight
of between about 8 to about 60 oz/sq. yd. The woven roving
reinforcement layer 14 is selected from a group consisting of
plain, twill and satin style. The woven roving or bonded
reinforcement layer 14 also includes multiple parallel tows 18, 20
at least two tows of which have differing yields so as to form
spaced channels 21. The first tow 18 of the two tows has a yield A
of between about 750 to about 2500 yds/lb. The second tow 20 of the
two tows has a yield B of between about 52 to about 450 yds/lb. By
placing one or more of the smaller first tows 18 between two or
more of the larger second tows 20, a channel 21 is provided. A
typical woven roving reinforcement layer 14 includes a group of
these channels 21 that allow rapid infusion of resin across the
infusion fabric 10 during the molding process.
[0025] The spacing of the tows 18, 20 is typically determined by
the resin utilized in the molding process. More specifically, a
more viscous resin requires a greater number of channels per
surface area in order to better enhance the flow of resin during
the molding process. Alternatively, a less viscous resin flows more
easily and requires fewer channels per surface area. In such a
situation a fewer number of small tows 18 are required between a
larger number of large tows 20.
[0026] The woven roving or bonded reinforcement layer 14 typically
includes unidirectional fiber orientation. Various methods may be
utilized to maintain the primary fibers in position in the
unidirectional layer. Those methods include weaving, stitching and
bonding as is known in the art. In one particularly useful
embodiment the layer 14 is constructed from crimp-free warped
knitted fabric otherwise known as stitch-bonded fabric. In the
illustrated embodiment, the tows 18 and 20 of the woven roving or
bonded reinforcement layer 14 are held in place by a secondary,
non-structural stitching thread 22. This may typically be a
polyester thread or any other thread conventionally used in the
art.
[0027] The mat 12 and woven roving or bonded reinforcement layer 14
are connected together by any appropriate means. In the illustrated
embodiment the connection is completed by stitch-bonding using
conventional stitch-bonding techniques and styles such as chain,
tricot, modified tricot or promat. Conventional machines known in
the art such as Liba stitch-bonding machines may be used for this
purpose.
[0028] As also illustrated in FIGS. 1 and 1a, the infusion fabric
10 may also include a second woven roving or bonded reinforcement
layer 24. The second woven roving reinforcement layer 24 has a
structure similar to the first woven roving reinforcement layer 14;
that is, the second woven roving or bonded reinforcement layer
includes multiple parallel tows 26, 28 at least two tows of which
have differing yields so as to form spaced channels for resin
infusion. The tows 26, 28 do not have to have identical yields to
the tows 18, 20 in the first woven roving reinforcement layer 14.
It should be appreciated, however, that the tows 18, 20 of the
first woven roving reinforcement layer 14 extend in a first
direction while the tows 26, 28 of the second woven roving
reinforcement layer 24 extend in a second direction at a bias to
the first direction. Typically that bias is one of approximately 90
degrees. This structural arrangement adds additional strength to
the infusion fabric 10.
[0029] An alternative embodiment for the infusion fabric 10 is
illustrated in FIGS. 2 and 2a. This embodiment includes a mat 12
and a woven roving or bonded reinforcement layer 14 substantially
identical to that described above with respect to the FIG. 1
embodiment. In addition, the infusion fabric 10 includes a
surfacing mat 30. The surfacing mat 30 is connected to the face of
the mat 12 opposite the woven roving reinforcement layer 14 so that
the mat 12 is sandwiched between the surfacing mat 30 and the woven
roving reinforcement layer 14. The surfacing mat 30 is formed from
a print blocking media such as another continuous fiber mat or a
veil incorporating glass fibers, polyester fibers, natural fibers
(e.g. cotton, kenaf, sisal, jute), polymer particles and binder.
The surfacing mat 30 may, for example, be connected to the mat 12
by spin bonding, wet bonding, dry bonding and needle punching.
[0030] As previously noted, the mat 12 may be a continuous filament
mat. For purposes of this document, "continuous filament" is
defined as a collimated assembly of individual fibers treated,
sized or finished appropriately for wetting and adhering resin or
polymer upon composite consolidation.
[0031] Also for purposes of this document, a "continuous filament
mat" is defined as a random swirl placement of continuous bundled
fibers which has orientation defined by the loop formation ratio in
the process creating a mat with planar isotropy. A useful
continuous filament mat 12 is made utilizing a loop formation ratio
of between about 2.0 to about 8.0 and typically between about 6.0
and 6.6 (loop formation ratio is strand or bundle speed/oscillation
rate).
[0032] A continuous filament mat 12 particularly useful in the
present invention also includes E-glass and/or ECR-glass fibers, a
binder and a size. The glass fibers are provided as glass filament
bundles. The glass filament bundles include between about 20 to
about 140 filaments per bundle. Each filament has a mean diameter
of between about 11 and about 26 microns. The bundle diameter is
between about 0.127 and about 3.175 mm.
[0033] In a particularly useful embodiment, the mean filament
diameter is between about 17.0 and about 20.0 microns. Further,
there are between about 44 and about 50 filaments per bundle or
loop strand. The strand or bundle diameter mean is about 0.3048 mm
and the bundle diameter falls in an overall range of between about
0.127 to about 1.27 mm. The strand to mat architecture or preferred
loop formation ratio is between about 6.0 and about 6.6.
[0034] The binder is a polyester or an epoxy compatible binder such
as a powdered epoxy resin or an epoxy novolak. Epoxy resins include
those made from epichlorohydrin and bisphenol A. Epoxy novolaks
include resins made by reaction of epichlorohydrin with a novolak
resin (phenol-formaldehyde).
[0035] In one possible embodiment that polyester binder is based
upon ethylene glycol and fumaric acid. The binder also includes
talc and benzoyl peroxide. For a typical application the binder is
ground to a particle size of between about 25 to about 200 mm. The
talc is added as a crystallization enhancer. The binder is prepared
by cryogenically grinding the crystalline polymer with a little
zinc stearate to the desired particle size. The powder is then dry
blended with the benzoyl peroxide. More specifically describing the
binder, the binder includes between about 95 to about 99.8 weight
percent polyester, between about 0.05 to about 3 weight percent
talc and between about 0.2 to about 2 weight percent benzoyl
peroxide.
[0036] The size utilized in the continuous filament mat 12 includes
one or more formulations incorporating water, acetic acid, silane,
and a biocide. Silane coupling agents useful in the present
invention include but are not limited to A-187, A-171, A-174 and
A-1100 silane available from General Electric Silanes. Lubricants
useful in the present invention include but are not limited to
Cirrosol 185AE and 185AN, each manufactured and sold by ICI America
and Omega 16407. Biocides useful in the present invention include
but are not limited to quaternary ammonium compounds containing
bis/tributyltinoxide. One such biocide is sold under the trademark
Biomet 66 and is available from Atochem.
[0037] The continuous filament mat 12 is manufactured by
transporting glass filament bundles through the binder application
process on a conveyor chain. A portion of the conveyor chain is
supported within an open-ended trough called a flood pan. The
purpose of the flood pan is to allow sufficient slurry to
accumulate and fully submerse the non-woven web for some period of
time. The slurry is fed from a reservoir located above and toward
the inlet end of the flood pan (i.e. the curtain coder). The
reservoir discharges the slurry through its slot on the lowermost
portion of the reservoir. The reservoir and slot extend across the
width of the floor pan. The major axes of the reservoir and slot
are oriented perpendicular to the machine direction (major axis) on
the process conveyor.
[0038] The slurry is discharged vertically down from the reservoir
slot, in a continuous curtain, toward the upper surface of the
non-woven web of glass strands. The velocity of the curtain of
slurry is a function of the discharge velocity of the slurry from
the reservoir slot, the vertical distance between the slot and the
surface of the web and the viscosity of the slurry.
[0039] The non-woven web of glass strands and the conveyor chain
are substantially permeable to the flow of the slurry, allowing the
slurry to flow easily around both the glass strands and the
conveyor chain wires and down to the impermeable flood pan. When
the vertical slurry flow from the reservoir impinges on the flat
surface of the flood pan (perpendicular to the surface of the flood
pan), the flow is redirected to a horizontal flow. The flow of
slurry upon interacting with the web, conveyor chain and flood pan,
is generally redirected to flow in the same direction as the
conveyor and web. The removal rate of the slurry from the flood pan
is a function of the supply rate of slurry into the flood pan, the
thickness of the conveyor chain, the drag of the chain and the
slurry, the viscosity of the slurry, depth of slurry in the flood
pan and other factors. The volumetric flow of slurry supplied by
the reservoir is, by design, sufficient to ensure the web is fully
submerged as it is carried through the majority of the length of
the flood pan. The slurry flows through the glass strands and
leaves a binder deposit which is subsequently cured in the oven
into a bound mat structure.
[0040] In order for the continuous filament mat 12 to allow the
desired resin infusion, the glass fiber bundles must not be too
large or too close together. Both these aspects affect the openness
or permeability of the mat construction for purposes of resin
infusion. Continuous filament mats 12 useful in the present
invention include but are not limited to CFM 8610, CFM 8620, CFM
8630, CFM 8635, CFM 8636 and CFM 8643, commercially available from
the assignee of the present invention.
[0041] Factors influencing resin infusion for RTM, RTM lite or VIP
processes follow Darcy's law on the need to reduce resin viscosity
and increase mat/fabric in-plane permeability. Continuous filament
mat permeability to balance resin infusion with mold conformability
has been shown to improve with reduced filamentization, proper
solids and cure of the binder. The random swirl of the mat,
continuous fiber and proper sizing/binder chemistry allow good
composite mechanical and structural performance. For purposes of
this document cure is measured as acetone extractables. The
continuous filament mat has a cure of between about 50 to about 100
percent and more typically about 60 to about 90 percent as measured
by acetone extractables.
[0042] The various embodiments of the infusion fabric 10 of the
present invention including those illustrated in FIGS. 1 and 2 are
particularly useful in molding processes where resin must move
through a fabric to create a consolidated composite. One particular
process is resin transfer molding (RTM). Resin transfer molding
(RTM) is a process by which a resin is pumped at low viscosities
and low pressures into a closed mold die set containing a preform
of dry fabric, i.e., fabric 10 to infuse resin into the preform and
to make a fiber-reinforced composite part. The RTM process can be
used to produce at low cost composite parts that are complex in
shape. These parts typically require continuous fiber reinforcement
along with inside mold line and outside mold line controlled
surfaces. The ability to include and place continuous fiber
reinforcement in large and small structures sets RTM apart from
other liquid molding processes.
[0043] The fabric 10 is also useful in a vacuum assisted resin
transfer molding (VARTM) system. In VARTM, the preform is covered
by a flexible sheet or liner, such as fabric 10. The flexible sheet
or liner is clamped onto the mold to seal the preform in an
envelope. A catalyzed matrix resin is then introduced into the
envelope to wet the preform. A vacuum is applied to the interior of
the envelope via a vacuum line to collapse the flexible sheet
against the preform. The vacuum draws the resin through the preform
and helps to avoid the formation of air bubbles or voids in the
finished article. The matrix resin cures while being subjected to
the vacuum. The application of the vacuum draws off any fumes
produced during the curing process. The fabric 10 of the present
invention is useful in standard vacuum infusion molding processes
as well as processes where the reinforced fabric is under
vacuum.
[0044] In summary, numerous benefits are provided by the fabric 10
of the present invention. The fabric 10 is characterized by
excellent handling qualities, ease of use and unsurpassed resin
permeability. The faster flow rate allows for higher production and
mold turnover, while potentially decreasing cost by eliminating
local resin distribution media. Further, VOC loss to the
environment is reduced. In addition, laminate bulk can be built
with minimal labor and cost.
[0045] The foregoing description of the preferred embodiments of
the invention have been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Obvious modifications or
variations are possible in light of the above teachings.
[0046] The embodiments were chosen and described to provide the
best illustration of the principles of the invention and its
practical application to thereby enable one of ordinary skill in
the art to utilize the invention in various embodiments and with
various modifications as are suited to the particular use
contemplated. All such modifications and variations are within the
scope of the invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are
fairly, legally and equitably entitled. The drawings and preferred
embodiment do not and are not intended to limit the ordinary
meaning of the claims and their fair and broad interpretation in
any way.
* * * * *