U.S. patent application number 11/056480 was filed with the patent office on 2006-08-17 for durable wood-plastic composite flooring for trailers.
This patent application is currently assigned to Havco Wood Products, L.L.C.. Invention is credited to Gopalkrishna Padmanabhan.
Application Number | 20060179733 11/056480 |
Document ID | / |
Family ID | 36814184 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060179733 |
Kind Code |
A1 |
Padmanabhan; Gopalkrishna |
August 17, 2006 |
Durable wood-plastic composite flooring for trailers
Abstract
A composite wood flooring system for a vehicular trailer floor
comprising: a plurality of wood boards, each wood board comprising
a top surface and a bottom surface opposite the top surface; and a
filled thermoplastic composite layer comprising a thermoplastic
polymer and a discontinuous filler, the thermoplastic layer being
substantially bonded to the top surface of each wood board.
Inventors: |
Padmanabhan; Gopalkrishna;
(Fenton, MO) |
Correspondence
Address: |
Paul D. Greeley, Esq.;Ohlandt, Greeley, Ruggiero & Perle, L.L.P.
10th Floor
One Landmark Square
Stamford
CT
06901-2682
US
|
Assignee: |
Havco Wood Products, L.L.C.
|
Family ID: |
36814184 |
Appl. No.: |
11/056480 |
Filed: |
February 11, 2005 |
Current U.S.
Class: |
52/177 |
Current CPC
Class: |
B32B 27/20 20130101;
B32B 2307/7246 20130101; B62D 25/2072 20130101; E04F 15/048
20130101; B32B 21/08 20130101; B32B 21/14 20130101; B32B 2307/554
20130101; B32B 2605/003 20130101; B32B 2250/02 20130101 |
Class at
Publication: |
052/177 |
International
Class: |
E04F 15/00 20060101
E04F015/00 |
Claims
1. A composite wood flooring system for a vehicular trailer floor
comprising: a plurality of wood boards, each said wood board
comprising a top surface and a bottom surface opposite said top
surface; and a filled thermoplastic composite layer comprising a
thermoplastic polymer and a discontinuous filler, said
thermoplastic layer being substantially bonded to said top surface
of each said wood boards.
2. The flooring system according to claim 1 wherein the said wood
is selected from the group consisting of: hardwood and
softwood.
3. The flooring system according to claim 1, wherein said wood
boards extend longitudinally along the length of said vehicular
trailer floor, each said wood board comprising a top surface, a
bottom surface opposite said top surface, and a first side surface
and second side surface extending between said top surface and said
bottom surface, and a board width that is less than the lateral
width of said vehicular trailer floor, each said wood board being
formed of a plurality of solid wood segments joined to one another
by coupling portions.
4. The flooring system according to claim 1, wherein said filler is
at least one selected from the group consisting of:
lignocellulosics, natural plant fibers, milled fibers, short
fibers, and minerals.
5. The flooring system according to claim 1, wherein said
thermoplastic polymer comprises at least one polymer selected from
the group consisting of: polypropylene, polyethylene, polystyrene,
poly-vinyl-chloride, acrylonitrile-butadiene-styrene,
styrene-acrylonitrile, low density polyethylene, high density
polyethylene and high impact polystyrene.
6. The flooring system according to claim 4, wherein said
lignocellulosic is at least one selected from the group consisting
of: flour, fiber, chips, flakes, dust, particles, shavings,
slivers, and strands.
7. The flooring system according to claim 3, wherein said
thermoplastic layer is additionally bonded to at least one surface
selected from the group consisting of: said first side surface,
said second side surface, and said bottom surface of said floor
boards.
8. The flooring system according to claim 7, wherein said
thermoplastic layer, when bonded to said first side surface or said
second side surface of said wood boards, is shaped to form shiplaps
of said wood boards.
9. The flooring system according to claim 3, wherein said plurality
of wood boards are arranged such that at least one of said first
side surface and said second side surface of each of said wood
boards approximates one of said first side surface and said second
side surface of adjacent boards or a mating portion of a metallic
component of said vehicular trailer to form a continuous trailer
floor having an upper thermoplastic surface and a bottom surface
for extending for the lateral width of said vehicular trailer
floor, a joint region being formed at locations at which said first
side surface or said second side surface of adjacent wood boards
approximate one another.
10. The flooring system according to claim 1, further comprising an
undercoating disposed about said bottom surface of each of said
wood boards for moisture protection.
11. A composite board for a load carrying floor comprising a
lignocellulosic particulate filled thermoplastic polymer composite
layer bonded to a non-veneer wood layer, wherein said
lignocellulosic particulate is discontinuous.
12. The composite board according to claim 11, wherein said
thermoplastic polymer composite layer and said wood layer are
adhesively bonded to each other.
13. The composite board according to claim 11, wherein said
thermoplastic polymer comprises at least one polymer selected from
the group consisting of: polypropylene, polyethylene, polystyrene,
poly-vinyl-chloride, acrylonitrile-butadiene-styrene,
styrene-acrylonitrile, low density polyethylene, high density
polyethylene and high impact polystyrene.
14. The composite board according to claim 11, wherein said
lignocellulosic particulate is a wood particulate, which is at
least one selected from the group consisting of; flour, fiber,
chips, flakes, dust, particles, shavings, slivers and strands.
15. The composite board according to claim 11, wherein said
thermoplastic polymer composite comprises one or more additional
fillers selected from the group consisting of: milled fibers, short
fibers and minerals.
16. The composite board according to claim 11, further comprising
an undercoating disposed about at least the surface of said
non-veneer wood layer opposite to said composite layer for moisture
protection.
17. A composite wood flooring system for a vehicular trailer floor
comprising: a plurality of wood boards, each said wood board
comprising an unexposed top surface and a bottom surface opposite
said top surface; and a thermoplastic layer comprising an exposed
first surface and an unexposed second surface, wherein said
unexposed second surface of said thermoplastic layer is
substantially bonded to said unexposed top surface of each said
wood boards and said exposed first surface of said thermoplastic
layer comprises a rough texture.
18. The flooring system according to claim 17, wherein said
thermoplastic layer comprises: a thermoplastic polymer and a
discontinuous filler.
19. The flooring system according to claim 18, wherein said
thermoplastic layer is shaped to form shiplaps of boards.
20. The flooring system according to claim 19, further comprising a
polymeric undercoating disposed about said bottom surface of each
wood board.
Description
1. FIELD OF THE INVENTION
[0001] This invention relates to improved laminated wood flooring
suited for both covered and exposed floors of vehicular trailers.
In particular, the invention provides for flooring that allows the
use of wood species of low hardness to produce moisture and scuff
resistant floor boards.
2. DISCUSSION OF THE BACKGROUND ART
[0002] Conventional wood flooring for over-the-road closed van
trailers, truck bodies and containers is normally manufactured with
hardwoods, such as oak, hard maple, birch, beech, ash, etc. Lower
grades of green lumber at the thickness of 4/4 (nominal 1 inch) or
5/4 (nominal 11/4 inch) are used as the starting material. This
lumber has a large amount of defects, which are not allowed in the
flooring product. An average of more than 50% of the lumber is
either discarded or lost in the flooring manufacturing process. The
lumber is suitably dried in special drying chambers under
controlled conditions to moisture content of about 8%. The dried
lumber is then sawed into strips of rectangular cross-section and
defective portions are eliminated by cross cutting the strips.
These strips or components are about 1 inch wide and 1 to 6 feet
long. During the cross-cutting process, "hooks" are formed at the
ends of the lumber strips. Alternatively, other shapes such as
fingers, bevel, etc., may be incorporated at the ends of strips or
components. These shapes are primarily designed to form a
mechanical connection or joint between the ends of strips. The
joint thus formed can be a hook, finger, butt, scarf or some other
joint. The dimensional design of each shape can vary from one
manufacturer to another. For example, thicker and shorter fingers
can be used to prevent breakage of tips of finger during manual
assembly.
[0003] The relatively defect-free lumber strips are coated on their
vertical sides or edges with an adhesive such as urea-melamine
formaldehyde, polyvinyl acetate, isocyanate, or another such wood
adhesive. The glue coated lumber strips are then manually assembled
on a conveyor by placing them side to side and behind other strips,
which were previously assembled. The adhesive is cured in a press
by applying heat and pressure to large sections of the assembled
lumber strips thus forming a unitary panel. Pressure is mainly
applied to the components from the lateral side in the horizontal
plane. The lateral pressure is responsible for the straightening of
any crooked wood components, squeezing out of excess adhesive, and
bonding of components. This process is known in the art as
edge-gluing. A restraining pressure is applied on the top side of
the wood components by a large plate. The vertical force helps to
prevent buckling of the assembled components from the lateral side
pressure. Longitudinal pressure can be applied on the components to
close the joints at the ends of components, but it is difficult to
obtain consistent pressure at all of the end-joints. Part of the
reason is the need to handle about 50 rows and about 400 individual
components during each curing cycle. There may be as many as 400
end-joints per press charge depending on the press size. During the
assembly of the lumber strips, mechanical joints are formed at each
end of every strip. Irrespective of the type of joint at the ends
of components, these end-joints are structurally weak mechanical
couplings without significant adhesive bonding.
[0004] An adhesive can be used to impart significant amount of
strength to the end-joints of wood strips. Adhesive bonding
requires the application of very high and consistent longitudinal
pressure. In the absence of such consistent pressure, the glue
develops porosity upon heating leading to little or no strength of
end-joint. Since adhesive joints are normally not used to join the
ends of a large number of components during edge-gluing of trailer
flooring panel, it has been critical to manually control the
placement of components during assembly. For example, the industry
specification does not allow an end-joint in one row of components
to be placed next to another end-joint of an adjacent row of
components. A solid wood component from a middle row of components
needs to separate the two side-by-side end-joints. Further, the
specification details the allowed distribution of the end-joints
and so forth. Manual assembly and control of the end joint
distribution is a labor intensive part of manufacturing laminated
trailer flooring.
[0005] The glue laminated wood panel is cut to a desired length (up
to about 60 feet) and width (about 6 to 18 inches) to form
floorboards. Most boards are 10 to 13 inches wide, and about 43 to
53 feet in length. The boards are then planed to a desired
thickness and shiplaps and crusher beads are machined at the
longitudinal edges. A shiplap is a rectangular projecting lip
running along the length at an edge of a floorboard. Typically, the
lip extends along the width of a board by about 3/8 inch to 1/2
inch and has about half the thickness of the board. A "top shiplap"
has the lip extending from the top half thickness of the board.
Similarly, a "bottom shiplap" has the lip at the bottom half of the
board. The crusher bead is a small semi-circular projection running
along the length on each edge of a board and placed over or below a
lip. When the floorboards are assembled in a trailer such that the
side edges of corresponding boards are squeezed together, the top
and bottom shiplaps of adjacent boards overlap to form a seam at a
board or shiplap joint. The shiplap joint between adjacent boards
helps to transfer some of the applied load from one board to its
adjacent board. The shiplap joint also helps to prevent the entry
of road debris and water into the trailer. The crusher beads
provide spacing between adjacent boards and help in preventing
buckling of the boards due to expansion on absorption of moisture.
Wood putty is applied at the end-joints of components on the top
and bottom surfaces of the boards to fill any resident gaps.
Finally, the underside and lateral sides of the floor boards are
coated with a polymeric coating, which is generally referred to as
"undercoating" or "board coating" to provide moisture protection.
The coating is usually applied by spraying. The finished
floorboards are packaged as kits, by stacking one board on top of
another, with about eight boards per kit for installation in
trailers. Normally, a kit consists of two boards with special edge
profiles so that they will fit along the road and curb sides of a
trailer. The other boards may be identical in design and they are
placed between the road and curb side boards. All the boards are
supported by thin-walled cross-members of I, C or hat sections,
each having an upper flange, which span the width of the trailer
and are regularly spaced along the length of the trailer. Each
floor board is secured to the cross-members by screws extending
through the thicknesses of the board and the upper flanges of the
cross-members. In some cases, laminated wood boards may be affixed
to the bottom part of the side walls of the trailer and used as
scuff boards to prevent damage to the sidewalls.
[0006] Hardwood based laminated wood flooring is popularly used in
covered van trailers, truck bodies and containers since it offers
many advantages. The surface characteristics of hardwoods such as
hardness, wear resistance and traction are most desirable. The
strength and stiffness of the flooring is important for efficient
and safe transfer of the applied loads to the cross-members of the
trailer. The impact resistance of wood is useful to withstand any
sudden dropping of heavy cargo on the floor. Nail holding
capability and ability to absorb small amounts of water, oil or
grease without significantly affecting traction are yet additional
favorable properties of hardwood flooring.
[0007] One significant draw back to laminated hardwood flooring in
general is their inability to perform in an exposed environment as
in a flat-bed trailer floor. When the laminated floor gets wet and
wood absorbs moisture, the wood components of the boards swell.
Upon drying of the wood components in a dry environment, the wood
components shrink. Multiple cycles of wetting and drying of
flooring in service causes cycles of expansion and shrinkage and
leads to delamination of the floorboard. Therefore, it is not
possible to wash a laminated wood floor for cleaning even though it
is desirable to do so after hauling certain products like nursery
plants, food products or to clean up spills of chemicals, etc.
While, laminated oak flooring can last 10 or more years in a van
trailer, it may not last even a few months in a flat-bed trailer.
Some hardwoods such as maple, beech, birch and ash are
significantly less resistant to decay compared to oak in
above-ground use. Therefore, laminated flooring made from these
hardwoods with low resistance to decay can undergo both
delamination and decay when subjected to wetting and drying.
[0008] Further, even in a closed van trailer, it is possible for
flooring to get wet and absorb a significant amount of moisture at
the top side of flooring. It is somewhat common for truckers to
leave the doors of the trailers open at the dock, parking lot or
yard for loading, unloading, maintenance or due to simple neglect.
An open door in times of rain means flooring will get wet at the
top side for a few feet from the door. It is also possible for the
body or roof of the trailer to have a leak. Any water accumulation
on the top side of the trailer flooring will cause damage to the
flooring over time.
[0009] Typically, a 1 to 2 feet long steel plate is laid on top of
the flooring near the door of the trailer. This plate, called
threshold plate covers the wood and protects it from impact of
heavy lift trucks coming off the trailer loading dock. However, if
water gets trapped below the plate, wood flooring made of
non-resistant wood species can decay in as little as 2 years of
service. It is not unusual for truckers to replace a section of the
floor board underneath the threshold plate during the life service
of trailers.
[0010] For reasons stated above, laminated wood flooring cannot be
installed on the fifth-wheel plate at the front end of the van
trailer. Sometimes water can get trapped between the bottom side of
board and the top side of plate. Typically, oak flooring will warp
under these conditions. Non-resistant wood flooring can not only
warp, but also decay much earlier under the same conditions.
[0011] A significant improvement to conventional laminated wood
flooring is provided by continuous fiber reinforced composite wood
flooring (U.S. Pat. Nos. 5,928,735; 6,183,824; and 6,179,942). This
composite wood flooring consists of conventional laminated wood
floorboards with an underlay of continuous glass fiber reinforced
polymer. The reinforcing layer is continuously bonded to the
underside of each floorboard. The top surface of the composite wood
flooring is exposed wood, which is the same as that of the
conventional wood flooring. Since the reinforcing layer is
impervious to the passage of water, it seals the bottom of the
floorboards. The fiber reinforcement improves the mechanical
properties of the flooring and therefore the thickness of laminated
wood can be reduced. However, this approach leads to a product that
is approximately about 40% to 50% more expensive than conventional
hardwood flooring. Further, the top side of flooring, which is
exposed wood, can be subject to weathering in exposed environments
and the effects of moisture just as a conventional wood floor. This
flooring is also not suitable for washing with water at the top
side of flooring.
[0012] U.S. Pat. No. 6,601,357 describes conventional laminated
wood flooring with a layer of un-reinforced polymer sheet bonded to
the bottom side of floor boards to provide moisture protection to
the flooring at the bottom side. This flooring has an exposed wood
surface at the top side of boards and therefore it is subject to
the same limitations as mentioned before.
[0013] U.S. Pat. No. 5,509,715 describes conventional laminated
wood flooring with a layer of plastic film or fabric
discontinuously bonded to the bottom side of floor boards to
provide moisture protection to the flooring at the bottom side.
This flooring has an exposed wood surface at the top side of boards
and therefore it is subject to the same limitations as mentioned
before.
[0014] U.S. Pat. No. 6,318,794 describes a composite wood floor
similar to that described in U.S. Pat. No. 5,928,735. In addition
to a reinforced composite layer of glass, carbon or polymer fibers
bonded to the bottom side of conventional laminated floor board,
the composite floorboard is further coated with a polymeric coating
of polyurethane having a granular constituent to provide anti-slip
surface. The polyurethane coating is used to prevent absorption of
water by the wood. To improve wear resistance, a second reinforced
composite layer is proposed for the top side with anti-slip
coating.
[0015] A major drawback of using continuous fiber reinforced
composite layer containing glass, carbon, Kevlar or other polymer
fibers is the high cost of these continuous fibers and fabrics made
from these materials. Furthermore, these materials are more
slippery than wood. Therefore, when they are used on the top side
of a floor board, they require an anti-slip coating, which further
increases the cost of the product. It is already know in the
industry that high strength glass fiber reinforcement at one side
of a floorboard approximately adds about 40% to 50% more to the
cost of conventional hardwood flooring.
[0016] U.S. Pat. No. 6,318,794 also describes laminated wood
flooring with a polymeric polyurethane coating with anti-slip
granular constituent covering the top surface to inhibit water
penetration. However, these coatings are normally too thin (about
0.001'' to 0.01'') and they can be worn out by dragging pallets and
by scraping the surface of floor with forks of lift trucks. Gouging
of hardwood flooring is somewhat common in trailers. Part of the
reason for gouging of wood flooring is the directional properties
of wood. For example, it is easy to split wood along the grain
compared to its transverse direction. For similar reasons,
longitudinal gouges along the length of flooring/grain of wood
caused by impacting or scraping forks can be quite long and
sometimes about half the thickness of the floor in depth. In
practice, a polyurethane or epoxy coating called floor restorer is
sometimes applied to laminated wood flooring to fix a delaminating
floor in service. This practice has been well known in the industry
over the decades. The advantage of this coating is that it
penetrates and seals any delamination and crack in the
flooring.
[0017] U.S. Pat. No. 5,143,418 describes the use of composite
plywood panels as flooring in open platform trailers. The plywood
is composed of veneers of wood with a majority of the veneers
oriented with the wood grain along the longitudinal direction while
the remaining veneers are oriented with the wood grain along the
perpendicular direction. The top and bottom surfaces of the plywood
panels are overlaid with cured resin impregnated cellulose sheets
for providing moisture and slip resistance. Since plywood based
flooring is relatively weak, the veneer panels cannot be used in
van trailers due to severe structural load conditions arising from
the use of lift trucks when moving cargo in and out of van
trailers. Plywood is generally not available in lengths up to 53
feet, which is preferred for efficient installation of trailer
flooring. Further, curing of thermosetting resin of the cellulose
sheet in a hotpress is a cumbersome process for floor boards of
long lengths.
[0018] U.S. Pat. No. 5,679,191 describes a method of fabricating
trailer length flooring for flat-bed trailers using defect-free
hardwoods such as oak, hickory and imported keruing. Essentially,
shorter planks of wood are finger-jointed at their ends across the
width of board to increase the length of the jointed board to
suitably match the length of the trailer. The planks are not
edge-glued, which makes these boards narrower compared to laminated
trailer floor. Further, having a finger joint across the full width
of the board leads to a large weaker spot with lower fatigue
strength compared to the strength of solid wood.
[0019] Flooring for North American trailers (vans and flat-beds)
has been traditionally made out of hardwoods for several decades.
The manufacturing process for laminated hardwood flooring for van
trailers is labor intensive due to the steps of manual defect
removal of lumber, manual assembly and manual control of assembly
of lumber strips for lamination. The lumber used is of lower grades
that are not suitable for higher value products like furniture and
veneer. The labor cost component of the laminated flooring product
is quite significant. Further, quality of product depends on a well
trained labor force. Laminated hardwood flooring is almost never
used for open platform or flat-bed trailers due to the inadequacy
of this flooring in exposed environments.
[0020] On the contrary, finger jointed hardwood flooring used for
flatbed trailers, which is composed of solid wood planks is not
suitable for van trailers due to narrower widths of natural
hardwood planks compared to laminated trailer floor board. A finger
joint across the full width of the plank leads to a large weaker
spot with lower fatigue strength compared to the strength of solid
wood. It should be noted that the mechanical hook joint or finger
joint of laminated flooring for van trailers is about one tenth the
width of the floor board. Even though five joints may occur per
square foot of flooring, the controlled joint spacing provides more
uniform strength to the floor board. Plywood panels with overlay of
cured resin impregnated cellulose sheets are relatively inferior in
strength and they are not available in the preferred long lengths
of 40 to 50 feet for trailer flooring. Due to all of the factors
discussed above, flooring for flatbed and van trailers have been
non-interchangeable and mutually exclusive in use.
[0021] Prior art of wood flooring for van and flat-bed trailers
includes the technologies of edge-gluing of small width hardwood
strips, finger jointing of hardwood planks, use of high strength
continuous fiber (glass, carbon, Kevlar) reinforced composites and
use of un-reinforced polymer sheets at the bottom sides of floor
boards, water based undercoating and polyurethane coating with
slip-resistant granules. The available technologies have led to two
types of flooring, one for closed van trailers and another for
exposed flat-bed trailers. There is no cost-effective flooring ever
designed that would be suitable for both interior and exterior use.
In practice, almost all of the North American van and flatbed
trailer flooring with solid wood are made from three hardwoods,
namely oak, hard maple and imported keruing. Many other
commercially available lower cost woods can meet the strength
requirements of trailer flooring, but not the wear resistance and
hardness of the above mentioned woods.
[0022] Therefore, it is an objective of this invention to provide a
way to use any strong wood for trailer flooring by overcoming any
issue of the lack of hardness.
SUMMARY OF THE INVENTION
[0023] One aspect of this invention is to provide wood flooring
with all of the attributes of conventional laminated hardwood
flooring and improvements in the areas of moisture resistance,
durability, surface characteristics, manufacturability and cost.
Such improvements allow the floor board of this invention to be for
use in all types of vehicular trailers, including vans, flatbeds,
containers, truck bodies, horse trailers, etc., and also for other
applications such as decks. Specifically, the floor board of this
invention relies on the strength of conventional laminated wood
flooring. To improve the manufacturing process, certain relatively
lower cost wood species such as southern yellow pine, Douglas fir,
spruce, western larch and yellow poplar are preferred. These woods
are typically about 50% to 60% of the cost of oak for the same or
similar grade. At the price of lower grade oak, it is possible to
purchase the above mentioned woods in a high strength grade (such
as MSR or machine stress rated) with little or no structural
defect. This allows tremendous cost savings over conventional oak
and maple hardwoods. However, these woods have much lower surface
hardness compared to oak and maple. Hardness is important to
prevent wear at the top side of flooring. To solve this issue, a
low-cost filled plastic layer is bonded to the top side at a
minimum and further to the other sides of floor board depending on
the application or end-use environment of flooring. The plastic can
be a thermosetting or a thermoplastic polymer, but thermoplastic
polymer is preferred for lower cost and ease of manufacturing.
Fillers can be flour, chips, flakes, strands, dust, shavings and
particles of wood, lignocellulosics, natural plant fibers,
minerals, dis-continuous synthetic fibers and milled fibers.
Natural plant fibers include such materials as wood fiber, coconut
coir, hemp, sisal, jute, bamboo, kenaf, wheat straw, corn stalk,
and bagasse. Synthetic short fibers can be glass, carbon, and
Kevlar, but short glass fiber is preferred for lower cost. Minerals
can be clay, wollastonite, calcium carbonate, limestone, barytes,
alumina, talc and other such materials. One or more fillers are
combined with thermoplastics polymer such as polyethylene (PE),
polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS),
acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile
copolymer (SAN), low density polyethylene (LDPE), high density
polyethylene (HDPE), high impact polystyrene (HIPS),
ethylene-vinyl-acetate (EVA), polyamide, recycled plastics, or
other suitable thermoplastics to make filled plastic composite
(FPC). While the FPCs are weaker than many solid woods and common
laminated floor boards of oak and maple, they are durable in
exposed environments, resistant to moisture and weathering, harder
than many available wood species and provide a high coefficient of
friction in dry and wet conditions. Further, FPC provides
significant improvement in the surface gouging characteristics
compared to solid wood and virgin or unfilled plastics. Even though
unfilled plastics can be used in some applications where hardness
is not an issue, FPC is preferred for most applications. The
surface coefficient of friction of wood particulate filled FPC is
higher under wet condition compared to dry condition. This provides
improved traction when wet. By incorporating a durable wear and
protective layer of FPC with laminated wood floor board, superior
and low cost flooring is provided.
[0024] A composite wood flooring system for a vehicular trailer
floor comprises: a plurality of wood boards, each wood board
comprising a top surface and a bottom surface opposite the top
surface; and a filled thermoplastic composite layer comprising a
thermoplastic polymer and a discontinuous filler, the thermoplastic
layer being substantially bonded to the top surface of each wood
board.
[0025] The wood is preferably selected from the group consisting of
a hardwood or softwood.
[0026] The wood boards preferably extend longitudinally along the
length of the vehicular trailer floor, each the wood board
comprising a top surface, a bottom surface opposite the top
surface, and a first side surface and second side surface extending
between the top surface and the bottom surface, and a board width
that is less than the lateral width of the vehicular trailer floor,
each the wood board being formed of a plurality of solid wood
segments joined to one another by coupling portions.
[0027] The filler is at least one selected from the group
consisting of: lignocellulosics, natural plant fibers, milled
fibers, short fibers, and minerals.
[0028] The thermoplastic polymer comprises at least one polymer
selected from the group consisting of: polypropylene, polyethylene,
polystyrene, poly-vinyl-chloride, acrylonitrile-butadiene-styrene,
styrene-acrylonitrile, low density polyethylene, high density
polyethylene and high impact polystyrene.
[0029] The lignocellulosic is at least one selected from the group
consisting of: flour, fiber, chips, flakes, dust, particles,
shavings, slivers, and strands.
[0030] The thermoplastic layer is additionally bonded to at least
one surface selected from the group consisting of: the first side
surface, the second side surface, and the bottom surface of the
floor boards.
[0031] The thermoplastic layer, when bonded to the first side
surface or the second side surface of the wood boards, is shaped to
form shiplaps of the wood boards.
[0032] The plurality of wood boards are arranged such that at least
one of the first side surface and the second side surface of each
of the wood boards approximates one of the first side surface and
the second side surface of adjacent boards or a mating portion of a
metallic component of the vehicular trailer to form a continuous
trailer floor having an upper thermoplastic surface and a bottom
surface for extending for the lateral width of the vehicular
trailer floor, a joint region being formed at locations at which
the first side surface or the second side surface of adjacent wood
boards approximate one another.
[0033] The flooring system further comprises an undercoating
disposed about the bottom surface of each of the wood boards for
moisture protection.
[0034] A composite board for a load carrying floor comprises a
lignocellulosic particulate filled thermoplastic polymer composite
layer bonded to a non-veneer wood layer, wherein the
lignocellulosic particulate is discontinuous.
[0035] A composite wood flooring system for a vehicular trailer
floor comprises: a plurality of wood boards, each wood board
comprising an unexposed top surface and a bottom surface opposite
the top surface; and a thermoplastic layer comprising an exposed
first surface and an unexposed second surface, wherein the
unexposed second surface of the thermoplastic layer is
substantially bonded to the unexposed top surface of each wood
board and the exposed first surface of the thermoplastic layer
comprises a rough texture. Preferably, the thermoplastic layer
comprises: a thermoplastic polymer and a discontinuous filler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The invention is illustrated by, but not limited to, the
embodiment shown in the accompanying drawings in which:
[0037] FIG. 1 is a schematic view, partially cut away, of a dry van
trailer with laminated hardwood flooring;
[0038] FIG. 2 is a perspective view of a conventional laminated
wood panel with narrow width wood components;
[0039] FIG. 3 is a perspective view of a conventional undercoated
laminated floor board for a dry van trailer;
[0040] FIG. 4 is a sectional view of two adjacent floor boards on a
cross-member of a dry van trailer;
[0041] FIG. 5 is a sectional view of a conventional laminated wood
floor board for a dry van trailer.
[0042] FIG. 6 is a perspective view of a laminated wood panel made
of broad width wood components;
[0043] FIG. 7 is a perspective view of an undercoated laminated
wood floor board with broad width wood components;
[0044] FIG. 8a is a sectional view of an extruded FPC panel;
[0045] FIG. 8b is a sectional view of an extruded FPC profile;
[0046] FIG. 9a is a sectional view of a laminated wood floor board
with FPC layer at the top side;
[0047] FIG. 9b is a sectional view of a laminated wood floor board
with FPC layer on three sides;
[0048] FIG. 9c is a sectional view of a laminated wood floor board
with FPC layer on three sides and with FPC shiplaps;
[0049] FIG. 9d is a sectional view of a laminated wood floor board
with FPC layer on four sides and with FPC shiplaps; and
[0050] FIG. 10 is a cross-sectional representation of a sandwich
FPC layer with a higher toughness thermoplastic core.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] Conventional laminated wood floor board 11 for over-the-road
van trailers 12 such as that shown in FIG. 1 is normally
manufactured with hardwoods such as oak, hard maple, birch, beech,
ash and the like. Any wood can be used for this purpose. However,
in commercial practice, laminated wood flooring for van trailers
and containers are made from oak and hard maple. These woods are
preferred for their availability, strength, and hardness. Many
other available woods are not used due to their lack of strength
and/or hardness. Examples of strong woods that are not used due to
low hardness are southern yellow pines, yellow-poplar, western
larch, Douglas-fir, etc.
[0052] Lower grade lumber (such as No. 2 Common and No. 3A Common
for hardwoods) of oak and hard maple (sugar maple) are the most
common hardwoods used for laminated wood flooring. The lumber used
is 4/4 (1 inch nominal) or 5/4 (11/4 inch nominal) in thickness
with varying widths of boards that are allowed in the selected
grades. The green lumber is suitably dried in kilns under
controlled conditions. In preparation of lumber for lamination to
produce a floor board, the dried lumber is sawed into strips or
components 13 (FIG. 2) of rectangular cross-section and defective
portions are eliminated by cross cutting the strips. The
cross-section of sawed lumber strips uniformly measures less than
about 11/2inch in sawed width and roughly approximates the
thickness of the lumber in height or thickness. The strips are
turned about their longitudinal axis by 90 degrees for side-by-side
lamination or edge-gluing to produce a panel. Due to the 90 degree
turning of the strips, sawed width of the lumber strip becomes the
thickness of the laminated panel. Typically, 11/2 inch sawed width
of strip is useful to make a floor board with a finished thickness
of 13/8inch. The sawed width of the strips is varied depending on
the finished thickness of the floor boards made. 1 5/16 inch and
13/8 inch thick boards are most commonly used for van trailer
floors. 11/8 inch thick floor boards are commonly used for
container floors. The thickness of lumber is reflected in the
finished width of strips in the laminated panel and floor boards.
Finished width of the strips in the panel is uniformly about 7/8 or
11/8inches depending on the thickness of the lumber ( 4/4 or 5/4)
used. Length of the strips varies from about 1 to 6 feet after
removal of defects by cross-cutting of strips. As many as 11 to 14
strips are needed side-by-side to make a common 12 inch wide floor
board 11. In summary, the thickness of lumber ( 4/4 or 5/4) has no
consequence on the thickness of the flooring in the conventional
flooring production process.
[0053] During the cross-cutting process, "hooks" are formed at the
ends of the lumber strips. Alternatively, laps, fingers, bevel or
other shapes can be formed at the ends of the strips. The
relatively defect-free lumber strips are coated on their vertical
sides or edges (which were originally the faces of lumber boards)
with an adhesive such as urea-melamine formaldehyde or polyvinyl
acetate. The uncured glue coated lumber strips are then manually
assembled on a conveyor by placing them side to side and behind
other strips, which were previously assembled, thus forming glue
lines 14 between adjacent strips 13. The adhesive is cured by
applying heat and pressure along 2 or 3 axes to large sections of
the assembled lumber strips thus forming a unitary panel of
laminated wood 15. The panel may have as many as 50 or more strips
of lumber side-by-side to provide a required panel width, which can
be used to make about four floor boards. The relatively small sized
strips of wood used in the conventional process are herein referred
to as "narrow width" wood strips or components.
[0054] During the assembly of the lumber strips, mechanical joints
16 such as hook, lap, finger, butt or scarf joints are formed at
each end of every strip. These end-joints of strips are simple
mechanical couplings with no significant adhesive bonding.
Therefore, they have no significant strength compared to the
strength of solid wood, irrespective of the type and quality of the
joint. Often times, due to imperfect assembly, a readily visible
gap 17 is formed at the end-joints of strips, which can be seen
from the top and bottom sides of the laminated wood floor board.
Certain rules are followed during the assembly of lumber strips to
ensure proper distribution of end-joints of strips in the floor
boards. One such rule involves the discarding of strips with a
length less than 12 inches. Another rule does not allow the
side-by-side assembly of two end-joints of adjacent strips. A solid
wood strip needs to separate such inline placement of joints or the
joints should be away from each other by at least a specified
distance. The application of these rules in manual assembly of a
very large number of narrow width strips to produce a laminated
panel results in a labor intensive and time-consuming process.
[0055] The cured laminated wood panel is sawed to a desired length
(up to about 60 feet) and width (about 6 to 18 inches) and then
machined to form several laminated wood boards. Each laminated wood
board is planed to a desired thickness and shiplaps 18 and crusher
beads 19 (FIGS. 3 to 5) are machined on its sides. When the floor
boards are assembled in a trailer such that the side edges of
corresponding boards are squeezed together, the shiplaps 18 of
adjacent boards overlap to form a seam. The bead 19 provides
spacing between adjacent boards and helps in preventing crushing
and warping of the boards when they expand upon absorbing moisture.
Wood putty is applied at the end-joints 16 on the top and bottom
surfaces of the boards to fill any resident gaps. Finally, the
underside and lateral sides including the shiplaps of the floor
boards are coated by spraying a polymeric coating termed as
"undercoating" or "board coating" 20 to provide moisture
protection. The top side of each board is normally uncoated or
exposed wood. Sometimes a thin coating of polyurethane or epoxy is
applied to the top surface of flooring. This improves aesthetics
and helps to slide household items in a moving van trailer at the
time of loading the trailer. The finished floor boards are
assembled into a kit of about eight boards for installation in
trailers. Normally, a kit consists of two boards with special edge
profiles so that they will fit along the road and curb sides, which
are usually metallic components of the trailer 12. The other boards
may be identical in design and they are placed between the road and
curb side boards. All the boards are supported by thin-walled
cross-members 21 (FIG. 1) of I, C or hat sections, each having an
upper flange, which span the width of the trailer and are spaced
along the length of the trailer. Each floor board is secured to the
cross-members by screws 22 extending through the thickness of the
board and the flanges of the cross-members.
[0056] Irrespective of the specie of wood used to make the trailer
flooring, the above described process can be used with little
change. However, the efficiency of this process does not
significantly improve when using small sized and narrow width
strips of wood and manual assembly techniques. For example, a
common floor board measuring 48 feet by 12 inches has about 240
end-joints of strips. It also has about 200 to 250 strips of wood
of varying lengths that are bonded together. Manual assembly of a
large number of strips is a tedious process. It is an objective of
this invention to significantly improve the efficiency and
productivity of the floor manufacturing process. Accordingly, in
one embodiment, the invented product is made using lumber, which is
thicker than 4/4 and 5/4 lumber or by using a suitable specified
dimension of lumber based on the required finished thickness of
floor board. As an example, lumber can be 6/4 with a nominal
thickness of 11/2 inch. The reason for using thicker lumber is
explained in the following paragraph. Further, to significantly
improve the manufacturing efficiency, higher grade lumber of
certain low cost wood species is used. This type of lumber is
significantly free of structural defects like loose knots, splits,
wanes, etc., which helps to reduce or eliminate labor necessary for
removal of these defects.
[0057] High grade dimension lumber of oak and hard maple is cost
prohibitive for trailer flooring. Lumber of softwoods such as
southern yellow pine, fir, larch, spruce and certain hardwoods such
as yellow-poplar are available at specified uniform dimensions in
large volumes necessary to produce trailer flooring. By specifying
a grade such as MSR (machine stress rated), structural grade lumber
of softwood species can be obtained at a cost comparable to or
below the cost of lower grade oak and hard maple. For example, MSR
grade southern yellow pine lumber (2.times.4) is almost fully
usable. However, an average of less than 50% of the board cuttings
of No. 2 and No. 3A common oak lumber is good for structural use.
Further, the strength and modulus of elasticity of MSR grade lumber
is high and consistent. As an illustration, typical properties of
various relevant hardwoods and softwoods are listed below at 12%
moisture content (Reference: Wood Handbook: Wood as an Engineering
Material, Published by Forest Products Society, 1999).
TABLE-US-00001 Wood Species Bending Bending Currently Used Strength
Modulus Hardness for Trailer Flooring (psi) (million psi) (lb)
Chestnut Oak 13,300 1.59 1130 White Oak 15,200 1.78 1360 Sugar
Maple 15,800 1.83 1450
[0058] TABLE-US-00002 Wood Species Bending Bending Unused or
disallowed Strength Modulus Hardness for Trailer Flooring (psi)
(million psi) (lb) Longleaf Pine 14,500 1.98 870 Slash Pine 16,300
1.98 -- Douglas- Fir 12,400 1.95 710 Western Larch 13,000 1.87 830
Yellow-Poplar 10,100 1.58 540 Sweetgum 12,500 1.64 850 Red Maple
13,400 1.64 950
[0059] The wood species in the above second table have high modulus
of elasticity or bending modulus and strength, but suffer from low
hardness, which makes them less resistant to abrasion, scuffing,
and gouging. Forklift trucks used to load and unload trailers can
easily damage the surface of wood floors made with these wood
species. Several other woods with high strength and low hardness
are listed in the Wood Handbook such as black ash, paper birch, red
spruce, tamarack, western hemlock, etc. Many of these softer woods
have high strength and are available at low cost. They also offer
significant advantages in the production of trailer flooring.
[0060] For example, the advantages of using 2.times.4 lumber of
longleaf and slash pine is described below. Other dimensions of
lumber such as 2.times.6, 2.times.8, 2.times.12 can also be used
with equal or better efficiency. The 2.times.4 lumber is nominally
11/2 inches thick and 31/2 inches wide. The boards of lumber can be
readily obtained at a uniform length of 8, 12, 16 or 20 feet. The
conventional process of production for making laminated floor
boards can be employed with this lumber. However, much higher
efficiency and productivity is obtained by using the 2.times.4
boards of lumber as individual strip or component of laminated wood
panel 23 (FIG. 6). Each component is about 31/2 inches wide with
average length exceeding 8 feet. These components of large size and
wider width are herein referred to as "broad width" components. By
using long boards of broad width components of uniform dimensions,
the number of end-joints of components needed to make the panel is
significantly reduced. The end-joints of the components can be of
any suitable kind such as conventional finger, modified spaced
apart finger, lap, hook, scarf or butt joints. The larger
cross-section of each component 24 helps to adhesively join the
ends of the components by stronger conventional finger joints 25.
This improves the strength of the board. By using the thickness of
the lumber to reflect in the thickness of the laminated panel and
width of the lumber to reflect in the width of the component 24 of
laminated panel 23, the number of components needed to produce a
panel is greatly reduced. This leads to significantly reduced
assembly time and also much lower curing time due to fewer
gluelines to make a panel of laminated wood. For example, 50 strips
of 4/4 lumber can be replaced by 14 strips of 2.times.4 broad width
components. The cure time to make the laminated panel with
2.times.4 pine is reduced by about 70% compared to 4/4 oak. The
strength and stiffness of the resulting laminated floor board 26
(FIG. 7) of broad width components of pine is sufficient to qualify
for trailer flooring. Even though many low-cost woods allow the
dramatic improvement of production efficiency, these woods such as
southern yellow pine, Douglas-fir, yellow-poplar, etc., do not have
sufficient hardness needed for trailer flooring. Therefore, it is
the first objective of this invention to provide sufficient
hardness to the surface of a trailer floor made with woods of low
hardness.
[0061] One significant draw back to laminated hardwood flooring in
general is their inability to perform in an exposed environment as
in a flat-bed trailer floor. Multiple cycles of wetting and drying
of laminated flooring in service leads to delamination of the
floorboard. Therefore, it is not possible to wash and clean a
laminated wood floor in van trailers even though it is desirable to
do so after hauling certain products like nursery plants, food
products or to clean up spills of chemicals, etc. While, laminated
oak flooring can last for 10 or more years in a van trailer, it may
not last even a few months in a flat-bed trailer. Some hardwoods
such as maple, beech, birch and ash are significantly less
resistant to decay compared to oak in above-ground use. Therefore,
laminated flooring made from these hardwoods with low decay
resistance can prematurely undergo both delamination and decay when
subjected to wetting and drying. Other aspects related to
construction of floor system in trailers combined with the use of
woods that are non-resistant to decay can also affect performance.
For example, a 1 to 2 feet long steel plate is laid on top of the
flooring near the door of the trailer. This plate, called threshold
plate covers the wood and protects it from impact of heavy lift
trucks entering the trailer at the loading dock. It has been found
that when water gets trapped below the threshold plate, wood
flooring made of non-resistant wood species can decay in as little
as 2 years of service. Laminated wood flooring is typically not
installed over the fifth-wheel plate at the front end of the van
trailer. In past experience, water has been found to be trapped
between the bottom side of floor boards and the top side of plate.
Hardwood floor boards were found to expand at the bottom side and
warp under these conditions, thus causing the floor screws to
break. Non-resistant wood flooring can not only warp, but also
decay much earlier under the same conditions. Therefore, it is the
second objective of this invention to provide for water resistant
flooring. In one embodiment, the invented flooring is suitable for
van trailers and containers, wherein resistance to weathering at
the rear section near the doors of trailer and resistance to
moisture effects on wood flooring below the threshold plate are
needed. In another embodiment of this invention the invented
flooring is suitable for periodic washing and for both interior and
exterior use.
[0062] Ideal flat-bed trailer flooring should have resistance to
decay, resistance to UV, resistance to moisture, light weight,
resistance to scuffing, consistent strength, high coefficient of
friction in dry and wet conditions and a length of floor board
equal to the length of trailer and width of floor board wider than
conventional solid wood plank or as wide as necessary. Conventional
flat-bed flooring made of wood does not provide all of these
attributes. Therefore, the third objective of this invention is to
provide more desirable flooring for flat-bed trailers.
[0063] In accordance with the aforementioned objectives, a layer of
a thermoplastic panel 27 (FIG. 8a) or a thermoplastic profile 28
(FIG. 8b) is adhesively bonded to the top side of edge-glued
laminated floor board. The thermoplastic panel and profile can be a
filled, un-filled or a reinforced polymer composite. In a preferred
embodiment, the thermoplastic panel is made of a Filled Plastic
Composite or FPC without any synthetic continuous fiber
reinforcement. In the simplest form, the filler is a discontinuous
material of low cost, which is compounded with a thermoplastic
polymer along with other additives for extruding a panel or a
profile of FPC. Panel thickness is about 0.02 inch to 0.25 inch.
Wall thickness of profile is about 0.02 inch to 0.75 inch. Examples
of fillers are wood articulates, natural plant fiber,
lignocellulosics, minerals, metal particulates, synthetic short
fibers and milled fibers. The wood particulate can be in one or
more forms of flour, dust, fiber, particles, chips, flakes, strands
and slivers. Natural plant fibers can be materials such as wood
fiber, coconut coir, hemp, sisal, jute, bamboo, kenaf, wheat straw,
corn stalk and bagasse. Minerals can be in the form of powder,
particles, or short fibers such as barytes, limestone, clay,
wollastonite and talc. Metal particulates can be powders, filings,
and short fibers. Synthetic short fibers can be chopped glass
strands and milled glass fibers. The thermoplastic polymer can be
any suitable polymer such as PP (polypropylene), PE (polyethylene),
PS (polystyrene), PVC (polyvinyl chloride), LDPE, HDPE, ABS, SAN,
HIPS, EVA, polyamide, recycled plastics, regrinds, and their
mixture. Addition of fillers to plastic makes a filled plastic
composite or FPC with superior hardness compared to virgin
plastics. (For example, commercially available Trex wood
polymer.RTM. lumber, which is made of recycled plastic and wood
particulates, has a hardness of 1124 lbs. Reference: Trex Product
Information, www.trex.com.) Wood particulate filled plastic is
harder than many of the solid woods. Addition of a second filler
such as milled glass fiber or minerals helps to further increase
hardness. Filled plastic composite is known in the art to be
compounded with suitable colorants, impact modifiers, adhesion
promoters to bond the filler to the plastic, UV inhibitors,
plasticizer, impact modifiers, and lubricants. Filled plastics can
also be foamed to lower cost of materials. In a preferred
embodiment, wood particulates are compounded with a thermoplastic
polymer, wherein the wood content of the resulting composite is
between 5% to 60%. In another preferred embodiment, the plastic is
a PVC or ABS with a lignocellulosic filler. In a yet another
preferred embodiment, the FPC has multiple types of filler,
including wood particulates to enhance a desirable property such as
hardness and fracture toughness.
[0064] FPC differs from Fiber Reinforced Plastic or FRP, which is
used to make high strength and light weight composite wood flooring
for trailers. FRP is made with continuous fibers of glass, carbon,
steel and Kevlar embedded in a polymer, wherein the fibers are
aligned for high strength along a specified axis. FRP is primarily
used for reinforcing a weaker structure and it is about 3 or 4
times more expensive than FPC. Further, any surface damage from
gouging or scuffing of aligned FRP causes a very long sliver of the
composite to peel off like banana skin or bamboo sliver. Woven
fabric or chopped strand mat of synthetic fibers can improve the
abrasion resistance of FRP, but it adds even more cost compared to
continuous rovings of fibers. Therefore, a low cost filled plastic
composite panel for this invention is made of discontinuous
particulates and short fibers that can be compounded with
thermoplastics.
[0065] FRP is several times stronger than solid wood. FPC is a low
cost extruded thermoplastic composite that has much lower strength
compared to FRP. At best, the strength of FPC compares with the
strength of solid wood such as oak, but most commercial
compositions of FPC are about 50% weaker than solid wood. (For
example, a 40% wood filled HIPS composite has a flexural strength
of 8170 psi. Source: North Wood Plastics, Inc., Sheboygan, Wis.).
For this reason, the flooring of this invention is not entirely
composed of FPC even though it is possible to do so. On the
contrary, the strength of laminated wood is combined with the
durability, resistance to moisture and wear of FPC. It is possible
to use high-strength continuous fibers of synthetic materials with
floor boards of this invention to further increase the strength of
the boards and/or provide weight savings, if necessary. Continuous
fibers can be incorporated into the FPC or used separately as an
under layer for floorboards.
[0066] In one embodiment of this invention, a panel of FPC is
adhesively bonded to the top side of a laminated wood floor board
composed of broad width components of softer woods such as pine and
Douglas-fir. The resulting composite floor board 29, such as shown
in FIG. 9a, is a representative example of this embodiment, which
fulfills the first objective stated before. This invention makes it
possible to use a strong yet softer wood for van trailer and
container flooring. It also helps to enhance the manufacturing
efficiency in the production of laminated wood panel 23 (FIG. 6)
and floor boards 26 (FIG. 7). Further, it helps overcome the
effects of weathering at the rear section of flooring near the
doors of trailers. The FPC also protects the top surface of wood
flooring from any trapped moisture under the threshold plate of
trailers. In some cases, where moisture protection at the top side
of flooring is a low priority than resistance to gouging and
abrasion such as in locations of the drier southwest regions of the
United States, not all of the floorboards need a top layer of FPC.
Typically, the outer boards along the sidewall of trailer are not
subjected to much wear and tear in service since fork lift trucks
stay closer to the center of trailer. In such cases some floor
boards of the flooring may not need the FPC top layer.
[0067] In another embodiment of this invention, a profile 28 of FPC
is adhesively bonded to a laminated wood floor board at the top
side and the lateral sides of the board. The bottom side of the
board is undercoated with a polymeric coating. The resulting
composite floor boards 30 and 31 (FIGS. 9b and 9c) are
representative examples of this embodiment, which fulfills the
second objective stated before. The laminated wood board can be
composed of broad width or narrow width components. The shiplaps of
boards are formed of FPC or they are made of wood and covered by
FPC. FPC shiplaps can be solid or hollow. In addition to providing
hardness to the top surface of a softer wood, a higher degree of
moisture protection is provided to the flooring at the top side and
at the shiplaps. Flooring composed of these floor boards are suited
for periodic washing and cleaning in van trailers without causing
delamination of the laminated wood board. Other advantages as
stated before apply here as well.
[0068] In a yet another embodiment of this invention, one or more
profiles of FPC or a combination of a panel 27 and profile 28 are
adhesively bonded to a laminated wood floor board at the top side,
bottom side and the lateral sides of the board. The resulting
composite floor board 32 (FIG. 9d) is a representative example of
this embodiment fulfilling the third objective stated before. The
laminated wood board can be composed of broad width or narrow width
wood components. The shiplaps of boards are formed of FPC or they
are made of wood and covered by FPC. FPC shiplaps can be solid or
hollow. In addition to providing hardness to the top surface of a
softer wood, a higher degree of moisture protection is provided to
the flooring at all four sides. Flooring composed of these floor
boards are suited for frequent washing and cleaning in van trailers
without causing delamination of the laminated wood board. Further,
this flooring is also suitable for any exposed floor such as in
flat-bed trailers and decks. To further improve the performance of
the flooring, the lumber used to make this flooring can be suitably
treated with fungicides and preservatives or the lumber can be
selected from a list of naturally decay resistant woods.
[0069] Due to their chemical nature in general, some thermoplastics
such as PP and PE are very difficult to bond to wood with
adhesives. Other thermoplastics like PVC and ABS are less difficult
to bond. However, it has been found that FPCs in general are easier
to bond with common adhesives. A bonding surface of FPC is sanded,
scuffed or abraded to expose some of the embedded fillers such as
wood particulates, plant fibers, lignocellulosics, etc. Common
adhesives such as epoxy, polyurethane, isocyanate, PF, PRF, UF,
MUF, PVA, hotmelt, EVA, polyamide, reactive hotmelt, pressure
sensitive hotmelt, thermoplastic tie layer, film adhesive and the
like can be used for bonding. In a preferred embodiment a reactive
hotmelt is used to provide durable bonds.
[0070] FPC provides high coefficient of friction or COF under wet
condition. (For example, commercially available Trex wood
polymer.RTM. lumber, which is made of recycled plastic and wood
particulates has a dry COF of 0.59 to 0.7 and wet COF of 0.7 to
0.75. Reference: Trex Product Information, www.trex.com.) The high
COF of FPC is beneficial in trailer flooring in wet conditions when
washing the floor in a van trailer or when loading on a rainy day.
In a preferred embodiment, the FPC layer at the top side of floor
boards is lightly sanded to expose the lignocellulosic filler. The
exposed lignocellulosic filler tends to swell up in wet condition
resulting in a high COF for the surface. The FPC layer with some of
the wood particulates exposed at the surface has a rough texture.
This provides a significant advantage over polyurethane, epoxy, or
other polymer coatings, which tend to have a smooth texture and low
friction under wet conditions.
[0071] As an alternative, thermoplastic panel or profile can be
made of an unfilled thermoplastic polymer such as PVC and ABS.
These plastics can be adhesively bonded to the top side of
laminated wood boards. However, it is necessary to roughen the
exposed surface of the panel or profile to ensure a high COF.
Roughness can be imparted to the surface of the panel or profile by
forming a textured surface at the time of extrusion of the panel or
profile. A secondary operation such as rough sanding with a 40 grit
belt can also be employed. However, many of the unfilled
thermoplastics lack hardness and resistance to abrasion. Even then
this type of flooring is suitable for a small minority of trailers
that are not loaded with forklift trucks, but rather by hand
trucks. Slip and moisture resistance are needed for these
applications as well. For example, dedicated trailers used by some
grocery retailers, postal service, and parcel service are in this
category.
[0072] A short coming of FPC is their relatively lower elongation
to failure compared to unfilled plastics, which makes them more
brittle with reduced toughness. By layering unfilled plastic 33 and
FPC to produce a sandwich FPC panel 34 (FIG. 10), the resulting
panel has improved toughness, while preserving the surface
hardness. Such a panel or profile is produced by co-extruding
filled and unfilled thermoplastics. Sanding the surfaces of the
sandwich panel provides improved adhesive bonding to wood floor
boards and high wet friction due to the exposed
lignocellulosics.
[0073] Experiments were carried out to determine the bonding
characteristics of a wood particle filled polypropylene FPC panel
(NWP-431-A-1, supplied by Northwood Plastics, Inc., Sheboygan,
Wis.). A reactive hotmelt adhesive (PUR-FECT LOK.RTM. 34-9029,
supplied by National Starch and Chemical Company, Bridgewater,
N.J.) was used as the adhesive. The wood filled PP composite panel
was bonded to a pine board of size 36 inch by 12 inch. Both
as-received panels and panels with two lightly sanded opposing
surfaces were used. The as-received wood filled PP panel did not
have exposed wood particles and this panel showed very poor bonding
to pine. It also had a slick polymer rich surface. This panel could
be peeled off from the pine board completely intact and with ease.
On the contrary, light sanding of the panel exposed some of the
wood particles in the FPC. Upon attempting to peel this FPC panel,
the panel fractured and failed indicating good bonding of the
substrates. The sanded surface with exposed wood filler was not
slick upon wetting with water. The experiments showed that even a
difficult to bond thermoplastic such as PP can provide
significantly improved bonding when used in a wood filled
thermoplastic composite. Other FPCs having thermoplastics such as
PVC and ABS provide even more durable bonds to wood.
[0074] While the invention has been described herein with reference
to the specific embodiments thereof, it will be appreciated that
changes, modification and variations can be made without departing
from the spirit and scope of the inventive concept disclosed
herein. Accordingly, it is intended to embrace all such changes,
modification and variations that fall with the spirit and scope of
the appended claims.
* * * * *
References