U.S. patent application number 13/757603 was filed with the patent office on 2013-08-08 for binderless panel made from wood particles and cellulosic fibers.
The applicant listed for this patent is John F. Hunt, Christine M. Lee. Invention is credited to John F. Hunt, Christine M. Lee.
Application Number | 20130199743 13/757603 |
Document ID | / |
Family ID | 48901872 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130199743 |
Kind Code |
A1 |
Lee; Christine M. ; et
al. |
August 8, 2013 |
BINDERLESS PANEL MADE FROM WOOD PARTICLES AND CELLULOSIC FIBERS
Abstract
The present invention relates to pressed fiberboard articles
made using a binderless wet process from a combination of fibers
and particles. A mixture of particles (e.g., wood particles) and
cellulosic fibers is formed into a panel using only water, heat and
pressure. The present invention is further directed to fiberboard
articles having uniform density cores or higher density cores.
Inventors: |
Lee; Christine M.;
(Escondido, CA) ; Hunt; John F.; (Mt. Horeb,
WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Christine M.
Hunt; John F. |
Escondido
Mt. Horeb |
CA
WI |
US
US |
|
|
Family ID: |
48901872 |
Appl. No.: |
13/757603 |
Filed: |
February 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61594921 |
Feb 3, 2012 |
|
|
|
Current U.S.
Class: |
162/149 ;
162/141; 162/150; 162/158; 162/181.9 |
Current CPC
Class: |
D21J 1/04 20130101 |
Class at
Publication: |
162/149 ;
162/181.9; 162/158; 162/150; 162/141 |
International
Class: |
D21J 1/04 20060101
D21J001/04 |
Claims
1. A method of forming a pressed article, comprising: i) combining
particles with cellulosic fibers in an aqueous medium to form a
particle-fiber/water mixture; ii) distributing said mixture in a
form, wherein said form is configured for removal of water from
said mixture; iii) removing water from said mixture to produce an
article having a surface and a core; iv) pressing said article at
an initial pressure, under conditions wherein a fiber matrix is
dewatered on a surface of said article; and v) pressing said
article at a final pressure under conditions wherein a fiber matrix
in said core of said article is cured.
2. The method of claim 1, wherein step iii comprises applying a
vacuum to said form to remove water from said mixture.
3. The method of claim 1, wherein the ratio of particles to
cellulosic fibers is between about 25:75 to 75:25 (weight to
weight).
4. The method of claim 1, wherein said particles comprise wood
particles and/or charcoal particles.
5. The method of claim 1, wherein said cellulosic fibers comprise
paper fibers and/or agricultural fibers.
6. The method of claim 1, wherein said cellulosic fibers comprise
long fibers and/or short fibers.
7. The method of claim 1, wherein said first pressure is higher
than said final pressure.
8. The method of claim 1, wherein said first pressure is about 75
and 500 psi board pressure.
9. The method of claim 1, wherein said final pressure is between 10
and 50 psi board pressure.
10. The method of claim 1, wherein said pressing at said first
pressure is done at a temperature not to exceed 212.degree. F.
11. The method of claim 1, wherein said pressing at said final
pressure is done at a temperature between 350 and 400.degree.
F.
12. The method of claim 1, further comprising pressing at a second
pressure after pressing at said first pressure, wherein said second
pressure is lower than said first pressure or said final
pressure.
13. The method of claim 12, wherein said first pressure is between
about 75 and 500 psi board pressure; said second pressure is
between about 10 and 50 psi board pressure; and/or said final
pressure is between about 75 and 500 psi board pressure.
14. The method of claim 12, wherein said pressing at said first
pressure is done at a temperature not to exceed 212.degree. F.
15. The method of claim 12, wherein said pressing at said second
pressure is done at 350 and 400.degree. F.
16. The method of claim 12, wherein said pressing at said final
pressure is done at a temperature between 350 and 400.degree.
F.
17. The method of claim 1, wherein said article is a panel.
18. The method of claim 17, wherein said panel is a flat panel or a
curved panel.
19. A composition comprising a binderless panel comprising wood
particles and cellulosic fibers, wherein said panel is at least
0.125 inches to 1.0 inch thick or greater, and wherein said panel
has uniform density through the thickness of the panel.
20. A composition comprising a binderless panel comprising wood
particles and cellulosic fibers, wherein said panel is at least
0.125 inches thick, and wherein said panel has core portion
disposed between a first outer portion and a second outer portion,
wherein said core portion has higher density than said first outer
portion and said second outer portion.
Description
[0001] The present application claims priority to U.S. Provisional
Application Ser. No. 61/594,921, filed Feb. 3, 2012, which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to pressed fiberboard articles
made using a binderless wet process from a combination of fibers
and particles. A mixture of particles (e.g., wood particles) and
cellulosic fibers is formed into a panel using only water, heat and
pressure. The present invention is further directed to fiberboard
articles having uniform density cores or higher density cores.
BACKGROUND OF THE INVENTION
[0003] Wood-based composites and pressed wood products are
engineered sheet goods made from wood elements held together by an
adhesive bond. Examples of commercial wood-based composites include
such products as S2S (smooth 2 sides) hardboard, medium density
fiberboard (MDF), particleboard (PB), and oriented strand board
(OSB). The type of wood elements, adhesive(s), and the
panel-forming method used to make a panel determines the final
composite product and its performance. The essential steps of
manufacturing can be reduced to: a) the generation of wood elements
and b) the consolidation of those wood elements into sheet
form.
[0004] Wood or cellulosic elements used in composite formation
range in size and shape from smaller elements, like fibers,
particles, flakes, and chips, to larger elements, such as veneers
and laminates. Element morphology influences the properties of the
finished panel and the element size and/or geometry may be altered
by various conversion and reduction methods, such as pulping,
refining and/or steaming. The processed elements are then
consolidated into a panel through either a wet or a dry forming
process.
[0005] Wood composites made using a "wet-forming" method are
products made by dispersing the processed wood fibers in water. The
use of water as the distributing medium for cellulosic materials
promotes development of lignin and hydrogen bonds during heating
and drying processes. If sufficient natural lignin is retained from
refinement or processing of the raw material, it will behave like a
thermosetting adhesive and enhance the hydrogen bonds, thereby
reducing or eliminating the need to use additional binders or
adhesives (Stark et al. 2010). Panels produced by wet forming
processes are generally of low density and of limited strength,
such as low-density cardboards, composite panel products, and
agricultural fiberboards. Certain high density hardboards may be
manufactured by wet processes, but these are generally of limited
thickness. Medium density fiberboards suitable for, e.g.,
construction and furniture manufacturing, are generally not
produced using a wet forming process.
[0006] Other composite wood products, such as some hardboards,
medium density fiberboard (MDF), particle board (PB), and oriented
strand board (OSB), are made using a "dry-forming" method in which
dry wood elements are combined with resins prior to formation into
panels or other forms. Manufacturing typically begins with wood
reduction to produce the desired wood elements, screening to remove
unwanted components, and drying the wood elements to reduce the
aqueous moisture content. Typically, formaldehyde-based resins
(e.g., urea-formaldehyde, "UF") are then applied to the particles,
the mixture is distributed into a mat, and the mat is then a
pre-pressed and hot-pressed to consolidate the loose-formed mat
into a panel. Binding of the wood elements using resins is
generally faster than wet process panel production.
[0007] The relative ease-of-use, speed of processing, and lower
cost of UF resins makes them very desirable for interior panel
manufacturers. However, in particle board and other products
manufactured using UF resins, emissions of formaldehyde gasses can
present significant health concerns. There is a significant release
of formaldehyde that occurs for a short time after a panel has been
manufactured, followed by a secondary, continuous release that may
persist for the entire life of the board (Pizzi and Mittal 2003).
Phenol-formaldehyde and melamine-based resins, which are used
mostly for OSB, soft plywood or flake board, also emit
formaldehyde, but at lower rates than UF-based composite
panels.
[0008] Alternative resins exist for use in dry-forming methods. For
example, methyl diphenyl diisocyanate (MDI) is a formaldehyde-free
fast-curing resin binder being used in composite wood
manufacturing. However, MDI is costly and is not without health
risks. For example, MDI can create a severe health risk during
panel manufacturing, as it is associated with allergic reactions
and sensitivities.
[0009] There remains a need for wet-process methods of producing
panels that are free of toxic binders and that have sufficient
density, strength, and thickness for use in manufacturing, building
construction, packaging, and the like, and for panels produced by
these processes.
SUMMARY OF THE INVENTION
[0010] The present invention provides methods of making binderless
articles such as panels and boards, using wet forming processes. In
some embodiments, the invention provides methods of forming pressed
articles, including e.g., boards and panels, comprising: combining
particles with cellulosic fibers in an aqueous medium to form a
particle-fiber/water mixture, distributing the mixture in a form
configured for removal of water from the mixture, e.g., by gravity,
vacuum, cold pressing, or the like. The method comprises removing
water from the mixture to produce an article having a surface and a
core, pressing the article at an initial pressure and under
conditions in which a fiber matrix is dewatered on a surface of the
article; then pressing the article at a final pressure and under
conditions in which a fiber matrix in the core of the article is
cured.
[0011] The invention is not limited to a particular ratio of
particles to fibers. In some embodiments, the ratio of particles to
cellulosic fibers is between about 25:75 to about 75:25 (weight to
weight). In some preferred embodiments, the ratio is approximately
50:50.
[0012] It is contemplated that many different kinds of particles
may find use in the mixture of the present invention. In some
preferred embodiments, the particles comprise wood particles, while
in some embodiments, the particles comprise charcoal particles. In
some embodiments, the mixture comprises wood particles and charcoal
particles.
[0013] Cellulosic fibers from many sources find application in
embodiments of the invention. In some preferred embodiments, the
cellulosic fibers comprise paper fibers. In some embodiments, the
fibers are long fibers. It is contemplated that preparations of
fibers may comprise a mixture of fibers of different lengths. In
some embodiments, the fibers are essentially purely long fibers,
which in some embodiments, the fibers are mostly long fibers (e.g.,
>50%, >60%, >70%, >80%, >90%, etc). Alternatively,
in some embodiments, the fibers are substantially purely short
fibers, or are mostly short fibers (e.g., >50%, >60%,
>70%, >80%, >90%, etc).
[0014] In certain embodiments of the methods of the invention, the
article is pressed at a first pressure and a final pressure, and
said first pressure is higher than said final pressure. In some
particularly preferred embodiments, the first pressure is about 75
and 500 psi board pressure, and in some preferred embodiments, the
final pressure is between about 10 and 50 psi board pressure.
[0015] In certain embodiments, the first pressure is done at a
temperature not to exceed about 212.degree. F., and in certain
embodiments, the pressing at the final pressure is done at a
temperature between about 350 and 400.degree. F. In some
embodiments, the article is subjected to a cold pressing prior to
said first pressing, e.g., to remove free water from between fibers
and particles.
[0016] In some embodiments, the article is pressed in three or more
pressings. In certain preferred embodiments, the method comprises
pressing at a second pressure after pressing at the first pressure,
wherein the second pressure is lower than both the first pressure
and the final pressure. In certain preferred embodiments, the first
pressure is about 75 and 500 psi board pressure, and/or the second
pressure is between about 10 and 50 psi board pressure, and/or the
final pressure is between about 75 and 500 psi board pressure. In
particularly preferred embodiments, the first pressure is done at a
temperature not to exceed 212.degree. F., and both the second and
final pressures are both done at about 350 and 400.degree. F.
[0017] In certain preferred embodiments, the article is a board or
panel. In particularly preferred embodiments, the board or panel is
a flat board or panel.
[0018] The present invention provides an article produced according
to the methods disclosed herein. In some embodiments, the invention
provides a composition comprising a binderless panel comprising
wood particles and cellulosic fibers, wherein the panel is at least
0.125 inches to at least 1.0 inch thick, and wherein the panel has
uniform density through the thickness of the panel. In some
embodiments, the invention provides a composition comprising a
binderless panel comprising wood particles and cellulosic fibers,
wherein the panel is at least 0.25 inches thick, and wherein the
panel has core portion disposed between a first outer portion and a
second outer portion, wherein the core portion has higher density
than the first outer portion and the second outer portion.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 shows a graph comparing the bending modulus of
elasticity (BMOE) of a uniform density binderless panel as
described herein with those of particle board (PB) and medium
density fiberboard (MDF) samples. Diamond shapes represent test
results from uniform core density panels according to the present
invention, tested according to ASTM D1037. Triangle data-line
represent ANSI 208.1 particleboard and square data-line represents
ANSI 208.1 medium density fiberboard modulus of elasticity
standards.
[0020] FIG. 2 shows a density profile for a typical fiberboard or
particleboard showing lower density at the core of the panel.
[0021] FIG. 3 shoes a density profile for a binderless fiberboard
having uniform density throughout the thickness of the panel.
[0022] FIG. 4 shows a density profile for a binderless fiberboard
having higher density at the core of the panel.
[0023] FIGS. 5A and 5B show results from testing 12 samples for
emissions. Twelve emission samples were extracted from the test
specimens following California Specification 01350 (Cal. Dept. of
Health 2004) and ASTM Standard Guide D-6007-02 (ASTM 2002) at 113,
156 and 257 hours of conditioning time (Table 1 in FIG. 5A).
Formaldehyde emission factors listed in .mu.g/m.sup.2/h were
converted to parts per million (ppm) following ASTM Standard Guide
E-1333-96 (ASTM 2002) based on loading factors referenced for PB
and MDF (Table 2 in FIG. 5B).
DEFINITIONS
[0024] As used herein, "a" or "an" or "the" can mean one or more
than one. For example, "a" surface can mean one surface or a
plurality of surfaces.
[0025] "Dry-process" refers to the production of products, e.g.,
wood-product panels such as medium density fiberboard (MDF),
particleboard (PB), and oriented strand board (OSB), by combining
dried wood fibers and/or particles with resins and consolidating
the material at a low moisture content (around 10%) to form rigid
panels.
[0026] "Wet-process" formation of panels refers to the production
of products, e.g., wood-product panels by a process in which wood
products and water are processed to form a water slurry, which is
then poured into a form, with water subsequently removed by vacuum,
pressing and the like.
[0027] As used herein, the term "cellulosic fiber," refers to
natural and/or synthetic fibers containing cellulose. Cellulosic
fiber is found, for example, in the stems, leaves, hulls, husks,
and cobs of plants or leaves, branches, and wood of trees.
Cellulosic material from which cellulosic fiber can be derived
include virgin plant biomass and/or non-virgin plant biomass such
as agricultural biomass, commercial organics, construction and
demolition debris, municipal solid waste, waste paper, and yard
waste, and includes trees, shrubs, grasses, wheat, wheat straw,
sugar cane bagasse, corn, corn husks, corn kernel including fiber
from kernels, products and by-products from milling of grains such
as corn, rice, wheat, and barley (including wet milling and dry
milling), as well as municipal solid waste, waste paper, and yard
waste. The cellulosic material can also be, but is not limited to,
herbaceous material, agricultural residues, forestry residues, and
paper mill residues. Additional examples include but are not
limited to branches, bushes, canes, corn and corn husks, energy
crops, forests, fruits, flowers, grains, grasses, herbaceous crops,
leaves, bark, needles, logs, roots, saplings, short rotation woody
crops, shrubs, switch grasses, trees, vegetables, fruit peels,
vines, sugar beet pulp, wheat midlings, oat hulls, hard and soft
woods, organic waste materials generated from agricultural
processes including farming and forestry activities, specifically
including forestry wood waste, or a mixture thereof. Methods for
preparing cellulosic material to produce, e.g., pulp, for use in
the methods and systems of the present invention are common in the
art. Numerous technologies have been developed, implemented, and
improved over the last century in modern pulp and paper production.
Currently, there are several main pulp production processes: (1)
kraft pulping process uses sodium hydroxide and sodium sulfide to
produce both unbleached and bleached pulps (after subsequent
bleaching); (2) soda pulping uses sodium hydroxide to produce
bleached and unbleached pulps from non-woody biomass; (3)
mechanical pulping uses mechanical disk refining to produce
newsprint-grade pulps, (4) chemical-mechanical pulping uses
chemicals, such as sulfite and hydrogen peroxide, to pre-treat wood
chips prior to disk refining to produce pulps for certain grade
applications, such as boxes; and (5) sulfite pulping, including
acidic to alkaline sulfite pulping, produces dissolved pulp.
Neutral sulfite pulping (a special chemical-mechanical pulp, NSSC)
uses sulfite with a base. Detailed description of different pulping
processes can be found, e.g., in two series books: (I) "Pulp and
Paper Manufacture", Vol. 1-10, 3rd ed., 1985, Ed: the Joint text
book committee of the paper industry, TAPPI, ISBN: 0-919893-04-X,
and (II) "Papermaking Science and Technology", Eds: Gullichsen and
Paulapuro, Vol 1-19, Fapet Oy, 2000, ISBN: 952-5216-00-4.
[0028] As used herein, the term "long fibers" as used in reference
to cellulosic fibers refers to fibers of about 0.04 to 0.24 inches,
e.g., as obtained from pulping processes that produce paper from
virgin or recycled materials obtained from wood or agricultural
sources.
[0029] As used herein, the term "short fibers" as used in reference
to cellulosic fibers refers to fibers of about 0.004 to 0.04
inches, e.g., as obtained from pulping processes that produce paper
from primarily recycled paper or agricultural materials.
[0030] As used herein, the term "binderless" as used in reference
to boards, panels, and other articles produced from wood elements,
e.g., fibers, particles etc., refers to articles produced using a
process that comprises bonding of the natural components of the
wood elements, e.g., natural lignins, without addition of exogenous
resins or adhesives.
[0031] As used herein the terms "cured" and "dried" are used
interchangeably to refer to a condition wherein moisture is
depleted, e.g., from a board or fiber matrix and the constituent
elements are bonded.
[0032] As used herein, the term "aqueous medium" refers to water or
a solution in which water is the primary solvent of any dissolved
chemicals present.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The present invention relates to wet-forming processes and
compositions for producing wood-based articles without the use of
binders or resins. More particularly, the present invention relates
to the production of wet-formed articles having improved strength,
density, and thickness. In some embodiments, articles of the
present invention comprise additional particles, such as charcoal,
that are not suitable for use in hardboards and MDFs produced by
dry-forming methods, i.e., formed using binders or resins.
Embodiments of the invention are described in this Description, and
in the Summary of the Invention, above, which is incorporated here
by reference. Although the invention has been described in
connection with certain specific embodiments, it should be
understood that the invention as claimed should not be unduly
limited to such specific embodiments.
[0034] The wet-forming systems of the present invention take
advantage of the fact that fiber-to-particle and fiber-to-fiber
bonds can be achieved without resin through natural hydrogen and
lignin bonding, combined with the improved water drainage and
moisture release provided by the presence of particles in a fiber
matrix.
[0035] All wet-forming methods require that steps to eliminate
water during pressing and curing. Difficulties in draining and
expelling excess water through vacuum and/or pressing have either
limited the thickness of panels that could be produced from pure
fiber pulps, or have limited the pressure procedures that could be
used during pressing and curing, thereby limiting the products to
lower density and lower strength panels, or to thin, dense
hardboard.
[0036] For example, hardboard produced from cellulosic fibers
through the use of high pressure/high temperature lignin bonding
has been limited to about 3/8'' in thickness. Thicker wet process
boards have been produced from cellulosic fibers, e.g., recycled
paper, but the thicker panels are manufactured at lower pressure,
producing a very low density panel 26 to 28 lbs/ft.sup.3.
[0037] Cellulosic fibers, such as recycled paper fibers, naturally
bond when wet-formed and pressed. Without pressure, these fibers
produce a mat having a density of about around 6.2 to 12.5
lbs/ft.sup.3. A 100% fiber panel, pressed at low pressures, will
generally form a low-strength panel because the fiber-to-fiber
contact is insufficient to permit supportive bonding. A low-density
mat simply does not have sufficient material to produce the high
number of fiber-to-fiber contacts necessary to produce strong bonds
and a strong panel. A density above 37 lbs/ft.sup.3 is needed to
produce something similar to commercial particleboard or MDF
products currently on the market.
[0038] The binderless panel provided herein is made from a
combination of particles, e.g., wood particles, and cellulosic
fibers (e.g., pulped wood and/or paper fibers), that are formed
into a panel using only water, heat and pressure. The wood
particles are of such size as to be the same or larger in diameter
than the surrounding cellulosic fibers. The wood particles and
fibers are mixed in water for even distribution and homogenization
of the mixture. Once mixed and distributed into a forming box with
a screen on the bottom, a vacuum is pulled below the screen to
cause the mixture to start forming onto the screen. Particles and
fibers intertwine as the layer continues to form. The
particle-fiber interaction provides several benefits in products
made from the co-mingled material: [0039] 1. Mixing wood particles
with the cellulosic fibers reduces the particle packing density and
increases the drainage rate compared to what would occur with the
use of pulp fibers only, without particles. As the two materials
form an increasingly thick layer of material, wood particles are
dispersed throughout the paper fibers. The dispersal of the wood
particles opens up passages through the formed mat for the water to
flow through the mat structure. Better water flow increases the
drainage rates and/or decreases forming time. During pressing, the
passages assist in de-watering as well. Improved de-watering allows
formation of a thicker mat within a reasonable period of time.
[0040] 2. The fibers entrap wood particles and inter-fiber bonding
and fiber-to-particle secures the particles in the mat and panel.
Because the fibers are much longer than the particles, the fibers
form bonds crossing over several particles, resulting in an
intertwined structure that holds the particles in place. Under heat
and pressure, the fibers bond to the particles and to each other,
resulting in a thick board of medium density. [0041] 3. The panels
made from this process exhibit a density profile that is
significantly more uniform than that of typical particleboard or
medium density fiberboard because of the intertwined structure of
the materials and the drying/heating/pressing process. [0042] 4. In
some embodiments, a fiberboard having a higher density in its core
is produced by the use of a modified pressing sequence. This
contrasts with the typical structure for wet-formed fiberboards,
which are denser near the surfaces and less dense in the core. A
low density core is a configuration that is typically seen in
fiberboards used, e.g., in ready-to-assemble furniture fabrication,
in applications where screws are used for assembly, and for
fastening into the core of the board (either through a face, or
edge-on). Low-density core fiberboard does not have significant
screw-holding power, so screws can be dislodged, weakening
assembled products. Uniform density and high density cores in
fiberboard increase screw holding strength. [0043] 5. When no resin
binder is used, beneficial properties of natural wood extractives
(low molecular weight organic compounds, e.g., fatty acids, resin
acids, waxes and terpenes) found naturally in the wood particles
are not masked. Reclaimed or recycled cedar wood particles, for
example, may be combined with paper fibers to make a board panel
that has the aromatic properties of cedar, for use in place of
cedar, e.g., in moth protection for stored clothing (e.g., in
closets or drawers), or in interior closed spaces that benefit from
an ambient cedar aroma, such as in spa or other therapeutic
settings. Such beneficial properties can be inhibited or masked if
binding resins having harmful off-gassing characteristics are used
to bond the wood particles and fibers. [0044] 6. Particles other
than wood particles may also be used, alone or in combination with
wood particles. For example, charcoal particles may be used to
replace or supplement wood particles in combination with cellulosic
fiber in the manufacture of articles. Charcoal particles find use,
e.g., in the absorbance of harmful gases or compounds in closed
interior environments, such as in hospital rooms, offices, or
homes, where panels may be used to "soak up" harmful compounds over
time. In some embodiments, panel installations may be configured
such that used panels may be replaced from time to time with fresh
panels, to provide fresh charcoal particles.
Selection of Particles and Fibers
[0045] Wood residues and pulp fibers may be selected from any
number of raw and post-consumer waste sources. For example,
particles and fibers may be derived from waste wood, residue from
lumber processing or construction (e.g., waste wood and sawdust)
and/or from farming and agriculture (e.g., crop residue,
landscaping waste). The wet-processing method allows for the use of
these particles in combination with cellulosic fibers, and creates
minimal damage to the fibers.
[0046] In some embodiments, secondary raw wood particle processing,
such as refinement and screening, may be used for improved
performance or appearance. Additional processing increases
utilization of otherwise non-useable material. Large pieces of wood
(chunk wood), for example, may generally be considered
less-than-ideal panel material. Large pieces, however, may be
mechanically reduced to smaller and more homogeneous particles.
These particles, in turn, allow for improved mixing with recycled
paper fiber, resulting in a better-bonded board with a more uniform
appearance. In certain preferred embodiments, particles greater in
size than the length of the average fiber length are re-sized to
smaller sizes so the fibers can best entrap the particles.
[0047] Different fiber types may be used in different process
embodiments. Fibers may be pulped from virgin wood or waste wood,
for example. In certain preferred embodiments, fibers are generated
through processing recycled or waste paper, such as office paper or
newsprint or corrugated cardboard. Fibers may be selected for
properties they contribute to the process or finished article. For
example, longer fibers from selected grades of paper find
application in processes having faster water drainage faster and
resulting in increased wet mat strength (Maloney, Thomas M. 1977.
Modern Particleboard & Dryprocess Fiberboard Manufacturing San
Francisco, Calif.:182; Suchsland and Woodson, supra).
Panel Formation
[0048] A mixture of particles, fibers and water is made. In certain
preferred embodiments, the particles are selected as being those
that pass through no. 7 mesh (2,830 micrometer; 0.111 inches) or
smaller. In other embodiments, larger particles may be used. In
some preferred embodiments, the ratio of particles to fibers (p:f)
is approximately 50:50 (weight to weight), while in other
embodiments, the ratio can vary between about 25:75 to about 75:25
by weight, depending on the properties desired in the final
article. In certain preferred embodiments, the wet-forming
consistency (consistency=dry fiber weight/water weight) is
approximately 1.5%, but in other embodiments, the consistency may
vary by up to about .+-.1% (e.g., from about 0.5% to about 2.5%).
In certain preferred embodiments the panel is flat, but in other
embodiments, non-flat (e.g., curved) sections are formed using this
panel formation process.
Pressing and Curing
[0049] After vacuum formation of the wet mat or article, the mat is
hot pressed. In some embodiments, the wet mat is cold pressed using
standard methods to remove residual water prior to hot pressing and
drying.
Uniform Core Density Panels
[0050] In some preferred embodiments, the article is first pressed
between two flat, hot platens at about 75 to 500 psi board pressure
(e.g., at 200 psi board pressure), at temperature not to exceed
212.degree. F., and held for 5 to 30 seconds to squeeze out as much
water as possible. The pressure is released, then the board is
pressed at a temperature of about 350 to 400.degree. F.
(177-204.degree. C.), according to a single or multi-linear
thickness schedule to achieve the final thickness when the board is
dry. The second press cycle includes either a constant pressure
process of 10 to 50 psi board pressure, or as a thickness profile
that follows board moisture content as it leaves the board. The
board thickness decreases while the moisture leaves the board. The
closure rate follows the thickness. This produces a constant board
density through the thickness of the board.
High Core Density Panels
[0051] In some embodiments, an alternative pressing process is used
to reverse the density profile from low density in the core to a
high-density core product. As with the procedure above, the article
is first pressed between two flat, hot platens at about 75 to 500
psi board pressure (e.g., at 200 psi board pressure) at temperature
not to exceed 212.degree. F., and held for 5 to 30 seconds to
squeeze out as much water as possible. The board is then pressed at
low pressure (10 to 50 psi board pressure, at 350 to 400.degree. F.
(177-204.degree. C.)) for sufficient length of time to cure or dry
the fiber matrix on the outside surface of the board, followed by
higher pressure (75 to 500 psi board pressure) before the board is
completely dry or cured, and held for a length of time to cause the
center of the board to cure or dry under high pressure. For a 5/8''
board, the high pressure is applied for about 5 to 30 minutes, but
the time may be adjusted, depending on the density and final
thickness of the board, and on the particular mixture of particles
and fibers.
[0052] Standard methods of producing PB, MDF, and hardboard also
follow a process where high pressure is applied for 30 to 120
seconds followed by significant reduction in pressure to de-gas the
board of steam pressure, followed by higher pressure at the end of
the pressing cycle (High-low-high). However, both the rationale for
the high-low-high pressing process and the outcome in board density
are very different. A primary goal of prior art processes is to
produce boards as quickly as possible. To facilitate this, the
process comprises an intermediate step of reducing the pressure in
order to de-gas and to release moisture. The high pressure applied
at the end of the pressing sequence does not increase the density
in the core of the board because the board's residual moisture
content is no longer sufficient to cause bonding. In contrast, in
the modified press sequence of the present invention, the increase
in pressure at the end of the pressing sequence is done when the
center of the board is moist, and has the effect of bringing the
moist fibers together to initiate improved fiber-to-fiber bonding,
thereby increasing the density in the core of the panel. Little
increase in density occurs in the outer face portions that were
dried during the first phase of the pressing, so the process yields
a board with higher density in the core than at the faces.
[0053] In certain embodiments, screens are used on both sides of
the board during pressing to allow the panels to release moisture
through the both faces, providing a more uniform process on top and
bottom. Further processing may include post heat treatment for
further natural enhancements of performance properties.
EXPERIMENTAL EXAMPLE
Panel Fabrication
[0054] Test panels were wet-formed from 50% poplar sawdust and 50%
paper pulp. The particles used in the mixture were passable through
no. 7 mesh. The ratio of particles to fibers (p:f) was
approximately 50:50, and the wet-forming consistency was
approximately 1.5%. The mixture was spread in a form comprising a
bottom screen, and most of the free water was removed by
vacuum.
[0055] Wet mats were placed between two flat cold platens and
pressed at a temperature <212.degree. F., with pressure
increasing up to 200 psi board pressure within 120 seconds, and
held at pressure for an additional 5 to 30 seconds to squeeze out
more water. Pressure was released, and the panel was then further
hot-pressed at 350 to 400.degree. F. (177-204.degree. C.) using a
single or multi-linear thickness schedule.
[0056] The board shown to have a uniform density was obtained using
position control during hot-pressing to go from 1.5 inches to 1.25
inches in 120 seconds; 1.25 inches to 0.75 inches in 600 seconds;
from 0.75 inches to 0.625 inches in another 600 seconds; followed
by additional drying time of 600 seconds held at 0.625 inches.
Modifications to the time and rates may be adjusted so that the
pressure during the drying is done with less than 50 psi board
pressure.
[0057] For high core density panels, the particle/fiber slurry was
prepared and formed as described above. The board was hot-pressed
using position control to go from 1.5 inches to 1.25 inches in 120
seconds; 1.25 inches to 0.75 inches in 600 seconds; from 0.75
inches to 0.625 inches in another 600 seconds; followed by
high-pressure of 200 psi board pressure at an additional drying
time of 600 seconds. Modifications to the time and rates may be
adjusted so that the pressure during the initial drying is done
with less than 50 psi board pressure. The high pressure at the end
creates the high density core.
Testing
[0058] Test specimens were cut from the flat panels to evaluate
bending properties as outlined in ASTM Standard D 1037 (ASTM 1996).
Twenty-five specimens were conditioned in a 50% relative humidity
(RH), 72F conditioning room. Static bending tests were performed
and the modulus of elasticity (MOE) was calculated (see ASTM
Designation: D 1037-06a (ASTM 2006)). Comparison properties are
ANSI 208.1 Standard property values for PB and MDF.
[0059] FIG. 1 compares the bending modulus of elasticity (BMOE) of
the uniform density test board with the particle board (PB) and
medium density fiberboard (MDF) ANSI 208.1
Emissions Testing
[0060] Four test specimens were cut from panels to extract and
analyze their emissions at the Indoor Environment Department,
Environmental Energy Technologies Division of the Lawrence Berkeley
National Labs. Twelve emission samples were extracted from the test
specimens following California Specification 01350 (Cal. Dept. of
Health 2004) and ASTM Standard Guide D-6007-02 (ASTM 2002) at 113,
156 and 257 hours of conditioning time (refer to Table 1 in FIG.
5A). Formaldehyde emission factors listed in .mu.g/m.sup.2/h were
then converted to parts per million (ppm) following ASTM Standard
Guide E-1333-96 (ASTM 2002) based on loading factors referenced for
PB and MDF (refer to Table 2 in FIG. 5B).
[0061] The maximum allowable emissions, as stated in the
Formaldehyde Standards for Composite Wood Products Act, for
Particleboard (PB) range from 0.09-0.18 ppm and for Medium Density
Fiberboard (MDF) range from 0.11-0.21 ppm. Formaldehyde emissions
analysis of the results from these specimens shows that these
emissions factors for the tested samples are significantly lower
than those for either PB or MDF. This can be calculated by starting
with Equation (5) in the ASTM-E1333-96 (2002) document (see below)
and solving for the steady state concentration (Cs), then using the
experimental parameters specified in the standard to convert the
emission factor (EF) to concentration (Cs).
[0062] Different materials use different specified loading factors
that reference the conversion. For PB flooring or industrial PB,
the loading factor=0.43 m2/m3 and for MDF the loading factor=0.26
m2/m3. Using the appropriate reference loading factor (L), one can
use the equation derived from Equation 5 in the ASTM-E1333-96
(2002) to estimate the steady state concentrations in ppm. The
panels of these embodiments of the present invention show
significantly lower ppm concentration values than the standard
limits as shown in Table 2, (FIG. 5B).
Physical Panel Properties
[0063] For boards produced using standard and modified press
sequences, density profiles were determined and compared to the
density profile for standard MDF. FIG. 2 shows a typical density
profile through the thickness for PB or MDF representing a common
high-low-high density core panel. FIG. 3 shows the uniform density
profile achieved using the particle-fiber mixture of the present
invention. FIG. 4 shows a higher core density profile at the
mid-point of thickness that is obtained using the particle-fiber
mixture and the modified press sequence of the present
invention.
[0064] When using 100% recycled newsprint fibers (as are used to
make paper), drainage to form a 5/8'' thick mat takes 10 minutes or
longer. Use of the mixture of wood particles and fibers decreased
drainage time by about 50%. Drainage times will vary depending on
the particle geometry and fiber-to-particle weight
distribution.
These data showed that: [0065] Medium density binderless
fiberboards can be made from a combination of pulp fiber and
particles. The particles improve water drainage compared to
fiber-only slurries, allowing production of thicker panels than can
be formed by wet-forming from fiber alone, without loss of the
strength that comes from fiber-to-fiber bonding at high
temperatures and pressures. [0066] A modified pressing sequence
yields binderless fiberboard with high density core.
BIBLIOGRAPHY
[0066] [0067] ASTM International (2002) "Standard Test Method for
Determining Formaldehyde Concentrations in Air and Emission Rates
from Wood Products Using a Large Chamber". Designation: E 1333-96
(Reapproved 2002) [0068] ASTM International (2002) "Standard Test
Method for Determining Formaldehyde Concentration in Air from Wood
Products Using a Small Scale Chamber". Designation:D 6007-02 [0069]
ASTM International (2006) "Standard Test Methods for Evaluating
Properties of Wood Base Fiber and Particle Panel Materials".
Designation: D1037-06a [0070] California Department of Health
Services (2004) "Standard Practice for the Testing of Volatile
Organic Emissions from Various Sources Using Small-Scale
Environmental Chambers". Environmental Health Laboratory Branch.
Jul. 15, 2004 [0071] Maloney, Thomas M. 1977. Modern Particleboard
& Dryprocess Fiberboard Manufacturing San Francisco, Calif.:182
[0072] Pizzi, Antonio and K. L. Mittal. 2003. Handbook of adhesive
technology:646 [0073] Siegel, David M.; Frankos, Vasilios H. and
Marvin A. Schneiderman. 1983. Formaldehyde Risk Assessment for
Occupationally Exposed Workers. Abstract:355 [0074] Stark, Nicole
M.; Cai, Zhiyong; Carll, Charlie G. 2010. Wood-Based Composite
Materials-Panel Products-Glued-Laminated Timber, Structural
Composite Lumber, and Wood-Nonwood Composite Materials. Wood
Handbook, Wood as an Engineering Material. General Technical Report
FPL-GTR-190. Madison, Wis.: U.S. Department of Agriculture, Forest
Service, Forest Products Laboratory: Chapter 11: 11-1-11-28. [0075]
Suchsland, O. and, G. E Woodson. 1986. Fiberboard manufacturing
practices in the United States. U.S. Dept. of Agriculture, Forest
Service. [0076] Zhang, Luoping; Freeman, Laura E. Beane; Nakamura,
Jun; Hecht, Stephen S.; Vandenberg, John J.; Smith, Martyn T.; and
Babasaheb R. Sonawane. 2010. Formaldehyde and Leukemia:
Epidemiology, Potential Mechanism, and Implications for Risk
Assessment. Environmental and Molecular Mutagenesis. Review
Article. 51:181-191
[0077] All publications, patents and patent applications referenced
above are incorporated herein by reference in their entireties, for
all purposes. The description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
invention. Various modifications to these embodiments will be
readily apparent to those skilled in the art, and the generic
principles described herein can be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
it is to be understood that the description and drawings presented
herein represent a presently preferred embodiment of the invention
and are therefore representative of the subject matter which is
broadly contemplated by the present invention. It is further
understood that the scope of the present invention fully
encompasses other embodiments that may become obvious to those
skilled in the art and that the scope of the present invention is
accordingly limited by nothing other than the appended claims.
* * * * *