U.S. patent application number 12/259780 was filed with the patent office on 2009-03-19 for panel containing highly-cutinized bamboo flakes.
Invention is credited to Nian-hua OU.
Application Number | 20090075021 12/259780 |
Document ID | / |
Family ID | 37804570 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090075021 |
Kind Code |
A1 |
OU; Nian-hua |
March 19, 2009 |
PANEL CONTAINING HIGHLY-CUTINIZED BAMBOO FLAKES
Abstract
A wood composite panel includes bamboo strands cut from the
outer cutinized portion of a bamboo culm and bound together with an
isocyanate binder resin.
Inventors: |
OU; Nian-hua; (Dacula,
GA) |
Correspondence
Address: |
Gardner Groff Greenwald & Villanueva, PC
2018 Powers Ferry Road, Suite 800
Atlanta
GA
30339
US
|
Family ID: |
37804570 |
Appl. No.: |
12/259780 |
Filed: |
October 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11216655 |
Aug 31, 2005 |
7459206 |
|
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12259780 |
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Current U.S.
Class: |
428/114 |
Current CPC
Class: |
B32B 2260/02 20130101;
B32B 2307/554 20130101; B32B 3/16 20130101; Y10T 428/24058
20150115; Y10T 428/31989 20150401; B32B 9/02 20130101; Y10T
428/24994 20150401; B32B 21/13 20130101; B32B 7/03 20190101; B32B
2260/046 20130101; B32B 2307/546 20130101; B27N 3/002 20130101;
B32B 2419/04 20130101; B32B 9/042 20130101; B32B 2260/026 20130101;
B32B 2307/54 20130101; B27N 3/04 20130101; Y10T 428/249925
20150401; B32B 21/02 20130101; B32B 2307/734 20130101; Y10T
428/24132 20150115 |
Class at
Publication: |
428/114 |
International
Class: |
B32B 5/12 20060101
B32B005/12 |
Claims
1. A panel, comprising: bamboo strands cut from only an outer
cutinized layer of a bamboo culm along its longitudinal axis; and
an isocyanate binder resin, wherein the isocyanate binder resin
binds the bamboo strands together.
2. The panel according to claim 1, wherein the bamboo strands are
cut from the outer half of the bamboo culm.
3. The panel according to claim 1, wherein the bamboo strands are
cut from the outer third of the bamboo culm.
4. The panel according to claim 1, wherein the bamboo strands each
have a thickness of no more than about 0.2 inches.
5. The panel according to claim 4, wherein the bamboo strands each
have a thickness of about 0.01 inches to about 0.15 inches.
6. The panel according to claim 1, wherein the bamboo strands each
have a width greater than about 0.1 inches.
7. The panel according to claim 1, wherein the bamboo strands each
have a length of at least about 2 inches.
8. The panel according to claim 1, wherein the isocyanate binder
resin is MDI.
9. The panel according to claim 1, wherein the isocyanate binder
resin is about 2 wt % to about 12 wt % of the dry weight of the
bamboo strands.
10. A panel having parallel first and second longitudinal edges,
the panel comprising: a composite wood component defining a mating
surface; a bamboo layer defining a mating surface adjacent the
composite wood component mating surface, the bamboo layer
comprising bamboo strands substantially oriented in a direction
parallel to the longitudinal edges, wherein the bamboo strands are
cut from an outer cutinized portion of the bamboo culm and are
bonded to each other by an isocyanate binder resin.
11. The panel according to claim 10, wherein the isocyanate binder
resin is MDI.
12. The panel according to claim 11, wherein the composite wood
component comprises strands selected from aspen wood and pine
wood.
13. A panel, comprising: a layer of oriented bamboo strands cut
from an outer portion of a bamboo culm, wherein the outer portion
is the portion of the bamboo culm that is within about two
millimeters of its outer diameter; an isocyanate binder resin
coating the oriented bamboo strands, wherein the isocyanate binder
comprises about 2 wt % to about 12 wt % of the dry weight of the
oriented bamboo strands, wherein the oriented bamboo strands have
lengths of at least about three inches long, widths of at least
about 0.1 inches, and thicknesses of no more than about 0.2
inch.
14. The panel according to claim 13, wherein the panel has first
and second longitudinal edges and wherein the bamboo strands are
oriented substantially parallel to the longitudinal edges.
15. The panel according to claim 14, further comprising a second
layer of oriented bamboo strands cut from the outer portion of the
bamboo culm, and an isocyanate binder resin coating the oriented
bamboo strands, wherein the isocyanate binder comprises about 2 wt
% to about 12 wt % of the dry weight of the oriented bamboo
strands, wherein the oriented bamboo strands generally all have
lengths of at least about three inches long, widths of at least
about 0.1 inches, and thicknesses no more than about 0.2 inch, and
wherein the bamboo strands of the second layer are substantially
oriented perpendicularly to the longitudinal edges.
16. The panel according to claim 14, further comprising a layer of
oriented strands, wherein the oriented strands comprises strands of
wood other than bamboo.
17. The panel according to claim 13, wherein the layer of oriented
bamboo strands further includes strands of wood other than bamboo.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of pending U.S. patent
application Ser. No. 11/216,655, which was filed on Aug. 31, 2005
and is entitled "PANEL CONTAINING HIGHLY-CUTINIZED BAMBOO FLAKES."
The disclosure of application Ser. No. 11/216,655 is hereby
incorporated by reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] Bamboo is a wood material widely used throughout Asia as a
building material because of its high strength, durability and
excellent dimensional stability, as well as its ready supply and
rapid replenishment--bamboo grows very rapidly, reaching full
maturity within 2 to 6 years, while even the fastest growing wood
tree species take as long as 15 to 30 years to grow to full
maturity.
[0003] However, in addition to these advantages, bamboo also has a
number of disadvantages. Since bamboo is hollow, it cannot be
processed into solid lumber board or planks.
[0004] And, not only is it impossible to make solid lumber from,
but bamboo can also not be processed by the conventional techniques
used to make wood composite materials. For example, it is difficult
to make plywood from bamboo because the bamboo culms are too thin
to cut plywood veneers from. Nor has bamboo been successfully
processed by techniques used to make strand composite wood
materials (which are composite materials made from resin-coated
strands given a preferred orientation and deposited in that
orientation on an underpassing conveyor belt).
[0005] Despite these disadvantages, because of bamboo's ready
supply and excellent performance characteristics, manufacturers
have developed techniques to make wood composite materials out of
bamboo. For example, composite bamboo structural panels may be made
by hand-cutting bamboo strands from the outer part or surface of a
bamboo culm, and then weaving (again, typically by hand) the
strands into mats. These hand-cut, hand-woven bamboo mats are then
stacked together along with several other similar mats, and the
mats then pressed together under high temperature.
[0006] The problem with this method of manufacture of the bamboo
boards is that it is time consuming; the steps of cutting the
bamboo strips and then weaving the bamboo strips into the form of a
mat take a significant amount of time. And, not only are these
processes time consuming, but they can lead to significant defects
in the final board product. For example, internal gaps created by
the layering of several of the mats on top of another can result in
the production of holes or other defects in the board that can lead
to failure. Additionally, bonding two woven bamboo mats together
involves bonding together two mating surfaces, which is an
additional source for defects. Yet another disadvantage of the
aforementioned processes is that because they are composed of large
numbers of bamboo layers, they are require very high doses of resin
per layer, which adds greatly to the price of the product during
periods of high petroleum prices.
[0007] Given the foregoing, there is a need in the art for
structural bamboo panels that are either partly or completely
composed of bamboo, have fewer defects, do not require a lengthy
manufacturing process, and consume a smaller amount of
petroleum-based products.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention relates to a wood panel comprising
bamboo strands cut from the outer portion of the bamboo culm.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a schematic representation of a panel according to
an example embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0010] All parts, percentages and ratios used herein are expressed
by weight unless otherwise specified. All documents cited herein
are incorporated by reference.
[0011] As used herein, "lignocellulosic material" is intended to
mean a cellular structure having cell walls composed of cellulose
and hemicellulose fibers bonded together by lignin polymer. Wood is
a species of lignocellulosic material.
[0012] By "wood composite material" or "wood composite component"
it is meant a composite material that comprises lignocellulosic
material and one or more other additives, such as adhesives or
waxes. Non-limiting examples of wood composite materials include
structural composite lumber ("SCL"), waferboard, particle board,
chipboard, medium-density fiberboard, plywood, and boards that are
a composite of strands and ply veneers. As used herein, "flakes",
"strands", and "wafers" are considered equivalent to one another
and are used interchangeably. A non-exclusive description of wood
composite materials may be found in the Supplement Volume to the
Kirk-Othmer Encyclopedia of Chemical Technology, pp 765-810,
6.sup.th Edition, which is hereby incorporated by reference.
[0013] The following describes preferred embodiments of the present
invention, which provide a SCL wood panel comprising bamboo strands
cut from the outer portion of the bamboo culm. SCL products include
laminated veneer lumber ("LVL"), parallel strand lumber ("PSL"),
laminated strand lumber ("LSL"), oriented strand lumbers ("OSL"),
and oriented strand board ("OSB"), which will be described in
greater detail below.
[0014] Forming a SCL product from strands cut from the outer
portion of the bamboo culm results in a SCL wood panel having
excellent strength durability characteristics because the outer
portion of the bamboo culm is the strongest and most durable part
of the bamboo culm.
[0015] Previously, attempts to use flakes from the outer portion of
the bamboo culm have been frustrated because conventional wood
composite resins (like phenol formaldehyde) could not penetrate
into the flakes taken from the outer layer (because of the waxy and
highly-cutinized surface coating of the flakes) and consequently
failed to form strong bonds between adjacent flakes.
[0016] This problem has been solved in the present invention by the
use of one or more isocyanate binder resins, preferably the
isocyanates are selected from the diphenylmethane-p,p'-diisocyanate
group of polymers, which have NCO-- functional groups that can
react with other organic groups to form polymer groups such as
polyurea, --NCON--, and polyurethane, --NCOON--; a binder with
about 50 wt % 4,4-diphenyl-methane diisocyanate ("MDI") or in a
mixture with other isocyanate oligomers; ("pMDI") is preferred. A
suitable commercial pMDI product is Rubinate.RTM. 1840 available
from Huntsman, Salt Lake City, Utah, and Mondur.RTM. 541 available
from Bayer Corporation, North America, of Pittsburgh, Pa. Also
suitable for use are phenol formaldehyde ("PF"), melamine
formaldehyde, melamine urea formaldehyde ("MUF") and the
co-polymers thereof. Suitable commercial MUF binders are the LS
2358 and LS 2250 products from the Dynea Corporation.
[0017] Without wishing to be limited by theory, it is believed that
MDI functions better than previously existing resin systems because
the MDI is a smaller molecule than most polymer binder resins,
and--of equal importance--because the MDI has a similar solubility
with the wax coating found on the surface of the outer culm bamboo
flakes.
[0018] The bamboo material will now be described in greater detail,
and, subsequently, methods of incorporating bamboo strands into a
composite material will be discussed in detail.
[0019] Like other wood materials, bamboo's basic components are
cellulose fibers bonded together by lignin polymer, but bamboo
differs from other wood materials in the organization and
morphology of its constituent cells. Generally, most strength
characteristics of bamboo (tensile strength, flexural strength and
rigidity) are greatest in the longitudinal direction of the bamboo
and the bamboo fibers. This is due to the relatively small
micro-fibrillar angle of the cellulose fibers in the longitudinal
direction. The hardness of the bamboo culm itself is dependent on
the density of bamboo fibers bundles and their manner of
separation. The percentage of fibers does not consist either in the
longitudinal direction of the bamboo culm or in a cross section of
the culm. In the longitudinal direction, the density of fibers
increases from the bottom of the culm to its top, while the density
of fibers in the bamboo culm cross-section is highest closer to the
outer surface and decreases going deeper into the core of the
material. Moreover, the strength and hardness of the outer portion
of the bamboo culm is further increased by the presence of the
silica-deposited, cutinized layer coated with wax, which covers the
surface of the outer part of the culm. Thus, the bamboo on or near
the outer surface of the culm has superior strength
characteristics, but in most processes for making use of bamboo
fibers, these improved strength properties are not exploited
because the outer portion of the culm is stripped off. Unlike
previous techniques for using bamboo wood in which the cutinized
layer is stripped off and, thus, the strongest part of the culm
discarded, in the present invention the cutinized layer is used
and, thus, the high strength properties of the bamboo are
maintained.
[0020] Thus, when properly utilized the cellulose fibers in bamboo
are stiffer and stronger than the fibers of most wood species, so
that boards incorporating bamboo could have a much higher strength
to weight ratio than boards made from other types of wood
fibers.
[0021] In the present invention the bamboo culm strands are sorted
depending on their location in the outer portion of the bamboo culm
into strands that come from: (a) the outer third of the bamboo
culm, (b) preferably the portion of the bamboo culm that is within
2 mm of the outer diameter of the bamboo culm. For improved
compatibility and adhesion with the conventional wood strands, the
bamboo strands are preferably cut into thicknesses of less than
about 0.2 inch, such as less than 0.15 inches, such as in the range
of about 0.01 inches to about 0.15 inches, and cut into widths of
preferably greater than about 0.1 inches, such as more than about
0.15 inches, such as more than about 0.5 inches. This cutting may
be done either manually or with mechanized clipping equipment. For
purposes of improved strength the bamboo strands should be cut
along the longitudinal axis into strands preferably longer than
about 2 inches, such as about 3 inches, such as about 5 inches.
While not intending to be limited by theory, it is believed that
the longer strip length will result in more closely aligned strands
when the strands are oriented using a disk strand orienter, and,
without being limited by theory, it is believed that more closely
aligned strands will result in a final wood composite board product
that has an improved modulus of elasticity along the longitudinal
axis.
[0022] After being cut, the bamboo strands are dried (as described
below) and coated with isocyanate polymeric resin (as described
above). The binder concentration of the isocyante resin is in the
range of about 2 wt % to about 12 wt %, based on the dry weight of
the bamboo. A wax additive is commonly employed to enhance the
resistance of the bamboo strands to moisture penetration. Preferred
waxes are slack wax or an emulsion wax. The wax solids loading
level is preferably in the range of about 0.1 wt % to about 3.0 wt
% (based on the weight of the bamboo).
[0023] As used in the present invention the bamboo is formed into
strand composite lumber panels, preferably OSB panels. The panels
may be made entirely from bamboo strands, or, instead, the bamboo
strands may be mixed with naturally occurring hard or soft woods,
singularly or mixed, whether such wood is dry (having a moisture
content of between 2 wt % and 12 wt %) or green (having a moisture
content of between 30 wt % and 200 wt %). Typically, the raw wood
starting materials, either virgin or reclaimed, are cut into
strands, wafers or flakes of desired size and shape, which are well
known to one of ordinary skill in the art. When the panels are made
from a combination of both the bamboo strands and naturally
occurring hard or soft woods, the two separate sets of woods are
separately dried and coated with polymer resin binder, and then
after the separate coating stages, the coated hard/soft wood
strands and coated bamboo strands are admixed together.
[0024] After the strands are cut they are dried in an oven and then
coated with a special formulation of one or more polymeric
thermosetting binder resins, waxes and other additives. The binder
resin and the other various additives that are applied to the wood
materials are referred to herein as a coating, even though the
binder and additives may be in the form of small particles, such as
atomized particles or solid particles, which do not form a
continuous coating upon the wood material. Conventionally, the
binder, wax and any other additives are applied to the wood
materials by one or more spraying, blending or mixing techniques; a
preferred technique is to spray the wax, resin and other additives
upon the wood strands as the strands are tumbled in a drum
blender.
[0025] After being coated and treated with the desired coating and
treatment chemicals, these coated strands are used to form a
multi-layered mat 10, preferably a three layered mat which is then
pressed to form a composite wood component as generally shown in
FIG. 1. This layering may be done in the following fashion. The
coated flakes 12 are spread on a conveyor belt to provide a first
ply or layer 14 having flakes oriented substantially in line, or
parallel, to the conveyor belt, then a second ply 16 is deposited
on the first ply, with the flakes of the second ply oriented
substantially perpendicular to the conveyor belt. Finally, a third
ply 18 having flakes oriented substantially in line with the
conveyor belt, similar to the first ply 14, is deposited on the
second ply 16 such that plies built-up in this manner have flakes
oriented generally perpendicular to a neighboring ply.
Alternatively, but less preferably, all plies can have strands
oriented in random directions. The multiple plies or layers can be
deposited using generally known multi-pass techniques and strand
orienter equipment. In the case of a three ply or three layered
mat, the first and third plies are surface layers, while the second
ply is a core layer. The surface layers each have an exterior
face.
[0026] The above example may also be done in different relative
directions, so that the first ply has flakes oriented substantially
perpendicular to conveyor belt, then a second ply is deposited on
the first ply with the flakes of the second ply oriented
substantially parallel to the conveyor belt. In the present
invention, the longitudinal edge of the board is formed parallel to
the conveyor belt, so that flakes oriented substantially parallel
to the conveyor belt will be oriented substantially arranged
substantially parallel to the conveyor belt will end up being
substantially parallel to the longitudinal edge of the final wood
panel product. Finally, a third ply having flakes oriented
substantially perpendicular with the conveyor belt, similar to the
first ply, is deposited on the second ply.
[0027] In the present invention there is another possible panel
configuration. In this configuration one or more layers are built
up according to the aforementioned process to form the layers
sufficient to form a composite wood component, and then a layer of
bamboo strands is formed on top of these layers, with the bamboo
strands substantially oriented in a direction parallel to the
longitudinal edges to form a bamboo veneer layer. The binder resins
used with the bamboo strands in this bamboo layer are as described
above, and this bamboo layer and its accompanying wood layers are
processed as described in the following paragraphs.
[0028] As discussed above, an important part of the present
invention is the use of isocyanate binder resins with the bamboo
strands. However, with conventional pine, aspen or the like wood
strands, conventional polymeric binder resins commonly used with
wood composites may be used. These resins include
urea-formaldehyde, polyvinyl acetate ("PVA"), phenol formaldehyde,
melamine formaldehyde, melamine urea formaldehyde ("MUF"), the
isocyantes mentioned and the co-polymers thereof.
[0029] Isocyanates are the preferred binders, and preferably the
isocyanates are selected from the diphenylmethane-p,p'-diisocyanate
group of polymers, which have NCO-- functional groups that can
react with other organic groups to form polymer groups such as
polyurea, --NCON--, and polyurethane, --NCOON--; a binder with
about 50 wt % 4,4-diphenyl-methane diisocyanate ("MDI") or in a
mixture with other isocyanate oligomers ("pMDI") is preferred.
[0030] As mentioned above, MDI is used in the present invention as
the polymeric resin; in addition to the 4,4-diphenyl-methane
diisocyanate ("MDI") mentioned above other isocyanate oligomers
("pMDI") may be used. A suitable commercial pMDI product is
Rubinate.RTM. 1840 available from Huntsman, Salt Lake City, Utah,
and Mondur.RTM. 541 available from Bayer Corporation, North
America, of Pittsburgh, Pa. Other polymeric resins may be used as
well in a resin blend. For example, the MDI loading levels may be
slightly reduced by inclusion of a small amount of phenol
formaldehyde.
[0031] The binder concentration in the non-bamboo layers is
preferably in the range of about 0.2 wt % to about 2 wt %. A wax
additive is commonly employed to enhance the resistance of the OSB
panels to moisture penetration. Preferred waxes are slack wax or an
emulsion wax. The wax solids loading level is preferably in the
range of about 0.1 wt % to about 3.0 wt % (based on the weight of
the wood).
[0032] After the multi-layered mats are formed according to the
process discussed above, they are compressed under a hot press
machine that fuses and binds together the wood materials, binder,
and other additives to form consolidated OSB panels of various
thickness and sizes. The high temperature also acts to cure the
binder material. Preferably, the panels of the invention are
pressed for 2-15 minutes at a temperature of about 175.degree. C.
to about 240.degree. C. The resulting composite panels will have a
density in the range of about 35 lbs/ft.sup.3 to about 48
lbs/ft.sup.3 (as measured by ASTM standard D1037-98). The density
ranges from 40 lbs/ft.sup.3 to 48 lbs/ft.sup.3 for southern pine
and 35 lbs lbs/ft.sup.3 to 42 lbs/ft.sup.3 for Aspen. The thickness
of the OSB panels will be from about 0.6 cm (about 1/4'') to about
5 cm (about 2''), such as about 1.25 cm to about 6 cm, such as
about 2.8 cm to about 3.8 cm.
[0033] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *