U.S. patent application number 17/580790 was filed with the patent office on 2022-05-05 for wood laminate material and method for manufacturing same.
The applicant listed for this patent is DAIKEN CORPORATION. Invention is credited to Kazuhiro HIRATA, Koji NAGAOKA, Katsuhito OSHIMA, Kazuki SAKAMOTO, Yasushi SUGIO.
Application Number | 20220134715 17/580790 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220134715 |
Kind Code |
A1 |
OSHIMA; Katsuhito ; et
al. |
May 5, 2022 |
WOOD LAMINATE MATERIAL AND METHOD FOR MANUFACTURING SAME
Abstract
Provided is a strand board with improved strength and water
resistance. Reduction in productivity is prevented and
characteristics of the strand board can be varied as desired while
achieving certain strength and water resistance of the strand
board. A strand board B is formed by stacking and laminating five
strand layers 1 each formed by a large number of strands 5. The
strand board B has substantially constant density distribution in
the lamination direction of the strand layers 1. Three of the five
strand layers 1 of the strand board B are high-density strand
layers 1a having a higher density than the other strand layers 1,
and the other strand layers 1 are low-density strand layers 1b.
Inventors: |
OSHIMA; Katsuhito; (Toyama,
JP) ; SAKAMOTO; Kazuki; (Toyama, JP) ; HIRATA;
Kazuhiro; (Toyama, JP) ; NAGAOKA; Koji;
(Toyama, JP) ; SUGIO; Yasushi; (Toyama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAIKEN CORPORATION |
Toyama |
|
JP |
|
|
Appl. No.: |
17/580790 |
Filed: |
January 21, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16088904 |
Sep 27, 2018 |
11260630 |
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PCT/JP2017/033872 |
Sep 20, 2017 |
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17580790 |
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International
Class: |
B32B 21/02 20060101
B32B021/02; B32B 5/16 20060101 B32B005/16; B32B 7/03 20060101
B32B007/03; B32B 37/18 20060101 B32B037/18; B32B 21/14 20060101
B32B021/14; B32B 21/04 20060101 B32B021/04; B27N 3/14 20060101
B27N003/14; B27N 3/00 20060101 B27N003/00; B32B 21/13 20060101
B32B021/13 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2016 |
JP |
2016-194762 |
Mar 28, 2017 |
JP |
2017-063447 |
Claims
1-4. (canceled)
5. A wood laminate material formed by stacking and laminating
multiple woodbased material layers each formed by laminated
woodbased materials that are laminated multiple cut pieces or a
woodbased material that is a veneer, wherein the multiple woodbased
material layers include at least one high-density woodbased
material layer, the remainder of the multiple woodbased material
layers is a low-density woodbased material layer, and the
high-density woodbased material layer has a higher density than the
low-density woodbased material layer, and the woodbased material
layers located at both ends in the lamination direction of the
woodbased material layers are the high-density woodbased material
layers.
6. (canceled)
7. A wood laminate material formed by stacking and laminating
multiple woodbased material layers each formed by laminated
woodbased materials that are laminated multiple cut pieces or a
woodbased material that is a veneer, wherein the multiple woodbased
material layers include at least one high-density woodbased
material layer, the remainder of the multiple woodbased material
layers is a low-density woodbased material layer, and the
high-density woodbased material layer has a higher density than the
low-density woodbased material layer, and the woodbased material
layer located in a part other than the ends and a middle part in
the lamination direction of the woodbased material layers is the
high-density woodbased material layer.
8-12. (canceled)
13. A method for manufacturing a wood laminate material,
comprising: a stacking step of stacking multiple woodbased
materials, which are cut pieces or veneers, to form multiple
woodbased material layers so that at least one of the multiple
woodbased material layers is formed by a high-density woodbased
material or high-density woodbased materials having a relatively
higher density than the remainder of the woodbased material layers;
and a forming step of compressing or compacting the multiple
woodbased material layers formed in the stacking step.
Description
[0001] This is a divisional under 35 USC .sctn. 120 of U.S.
application Ser. No. 16/088,904, filed Sep. 27, 2018, which is a
national stage under 35 USC .sctn. 371 of International Application
No. PCT/JP2017/033872, filed Sep. 20, 2017, which claims priority
under 35 USC .sctn. 119 to Japanese Patent Application Nos.
2016-194762, filed Sep. 30, 2016 and 2017-063447, filed Mar. 20,
2017. The disclosure of each of these applications is incorporated
herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to wood laminate materials
that are formed by stacking and laminating multiple woodbased
material layers each formed by a woodbased material or woodbased
materials, and methods for manufacturing the same.
BACKGROUND ART
[0003] Today there are less and less tropical hardwood species
including broadleaf tress such as apitong and keruing, and it is
difficult to obtain high-quality veneer at low cost. Degradation in
quality of plywood using tropical hardwood species has therefore
become a big problem. Wood fiberboards such as oriented strand
boards (OSBs) are increasingly used as a substitute material for
plywood. However, OSBs with common densities do not provide
sufficient strength.
[0004] Conventionally, Patent Document 1, for example, discloses a
large OSB plate having a density of at most 700 kg/m.sup.3, a
length of at least 7 m, and a flexural modulus of at least 7000
N/mm.sup.2 in the primary load direction.
[0005] Patent Document 2 discloses a technique of using a strand
material, which is formed by orienting and stacking woodbased
material pieces and compressing and heating the stack, for joists,
foundations, etc.
CITATION LIST
Patent Document
[0006] PATENT DOCUMENT 1: Japanese Patent No. 4307992 [0007] PATENT
DOCUMENT 2: Japanese Patent No. 4227864
SUMMARY OF THE INVENTION
Technical Problem
[0008] In the OSB plate of Patent Document 1, a press pressure
higher than common pressures is required to form a board. This OSB
plate therefore cannot be formed without using a special press
machine.
[0009] The inventors found that a board formed at a press pressure
higher than common pressures with a special press machine as
described above has uneven density distribution in the thickness
direction of the boards. A board having uneven density distribution
tends to be weak in its low-density portion. Moreover, the
low-density portion of the board is more water absorbent and thus
has lower water resistance as compared to a high-density portion of
the board. With such uneven density distribution, strength and
water resistance are governed by the low-density portion, and
sufficient strength and water resistance cannot be obtained.
[0010] High strength and high water resistance can be achieved by
using layers with a high density as all of woodbased material
layers of a wood laminate material that is a laminate of woodbased
materials such as strands.
[0011] In this case, however, it takes a lot of time and effort to
increase the density of all of the multiple woodbased material
layers of the wood laminate material, and reduction in productivity
is therefore unavoidable. Moreover, since all of the woodbased
material layers have a high density, characteristics as the wood
laminate material are always the same, and it is difficult to vary
characteristics of the wood laminate material for various
applications.
[0012] It is an object of the present invention to allow a wood
laminate material, which is a laminate of multiple woodbased
materials, to have high strength and high water resistance by
adjusting density distribution in the lamination direction, namely
the direction in which the woodbased materials are laminated. It is
another object of the present invention to prevent reduction in
productivity for manufacturing wood laminate materials and make it
possible to vary characteristics of the wood laminate materials
while achieving a certain level of strength and water resistance of
the wood laminate materials.
Solution to the Problem
[0013] In order to achieve the above objects, in the present
invention, a wood laminate material is formed so as to have
substantially constant density distribution in the lamination
direction, thereby improving strength and water resistance of the
wood laminate material.
[0014] Specifically, in the present invention, a wood laminate
material formed by stacking and laminating multiple woodbased
material layers each formed by laminated woodbased materials that
are laminated multiple cut pieces or a woodbased material that is a
veneer is characterized by having substantially constant density
distribution in a lamination direction of the woodbased material
layers.
[0015] According to this configuration, the wood laminate material
has substantially constant density distribution in the lamination
direction. As described above, if the wood laminate material has
uneven density distribution in the lamination direction, strength
and water resistance of the wood laminate material are governed by
a low-density portion. However, the wood laminate material
according to the present invention does not have such a problem. A
wood laminate material with high strength and high water resistance
is thus implemented.
[0016] In the above configuration, the woodbased material may have
a density of 300 kg/m.sup.3 or more and 1100 kg/m.sup.3 or less,
and preferably 300 kg/m.sup.3 or more and 800 kg/m.sup.3.
[0017] Since the woodbased material has a density of 300 kg/m.sup.3
or more, the thickness of a stack of woodbased material layers (the
thickness of the stack before being laminated) required to form a
wood laminate material with the same density and strength can be
reduced. Since the thickness of the stack can be reduced,
workability of processes associated with lamination (e.g., a
stacking process and a forming process) is improved. Moreover, a
pressure for lamination which is required to form a wood laminate
material with the same density and strength can be reduced.
[0018] The multiple woodbased material layers may be composed so
that a thickness of the woodbased material layer gradually
increases from the middle woodbased material layer in the
lamination direction of the wood laminate material to the top and
bottom woodbased material layers.
[0019] The outer layers that are more likely to be subjected to
load and impact and are more susceptible to humidity etc. thus have
a larger thickness than the inner layer(s). This allows the wood
laminate layer to have improved performance regarding influences
from the external environment.
[0020] In the present invention, not all of the woodbased material
layers of the wood laminate material have a high density, but only
a part of the woodbased material layers has a high density. High
strength, high water resistance, etc. of the wood laminate material
are thus implemented by the woodbased material layer with a high
density.
[0021] Specifically, a wood laminate material formed by stacking
and laminating multiple woodbased material layers each formed by
laminated woodbased materials that are laminated multiple cut
pieces or a woodbased material that is a veneer is characterized in
that the multiple woodbased material layers include at least one
high-density woodbased material layer, the remainder of the
multiple woodbased material layers is a low-density woodbased
material layer, and the high-density woodbased material layer has a
higher density than the low-density woodbased material layer. As
used herein, the "density of the woodbased material layer" refers
to the density of a mat of cut pieces in the case where the
woodbased materials are cut pieces, and refers to the density of a
veneer if the woodbased material is a veneer.
[0022] In this configuration, at least one of the multiple
woodbased material layers is a high-density woodbased material
layer, and the remainder of the woodbased material layers is a
low-density woodbased material layer. High strength and high water
resistance of the wood laminate material are thus implemented by
the high-density woodbased material layer.
[0023] In the case where the density of the woodbased material
layer is increased, the density of the woodbased material need be
increased only in the woodbased material layer required to have a
high density, and it is not necessary to increase the density of
the woodbased material in all the woodbased material layers. Press
time with a press machine is therefore reduced accordingly and the
pressure to be used is also reduced. This improves productivity and
reduces or eliminates the risk of delamination when forming the
wood laminate material.
[0024] Moreover, since at least one of the woodbased material
layers is a high-density woodbased material layer, the layer(s) to
be used as a high-density woodbased material layer can be selected
as necessary from the multiple woodbased material layers.
Characteristics of the wood laminate material can thus be varied as
desired by changing the position(s) of the high-density woodbased
material layer(s).
[0025] In the above configuration, the woodbased material layers
located at both ends in the lamination direction of the woodbased
material layers may be the high-density woodbased material
layers.
[0026] In this case, the woodbased material layers located at both
ends in the lamination direction are the high-density woodbased
material layers and have a higher density than the woodbased
material layer(s) located in the remaining part. This improves
flexural strength of the wood laminate material and also improves
water resistance of the top and bottom parts of the wood laminate
material.
[0027] The woodbased material layer located in an intermediate part
in the lamination direction of the woodbased material layers may be
the high-density woodbased material layer.
[0028] In this case, as opposed to the case described above, the
woodbased material layer located in the intermediate part in the
lamination direction of the woodbased material layers is the
high-density woodbased material layer and has a higher density than
the woodbased material layers located in the remaining part (at
both ends in the lamination direction of the woodbased material
layers). The density in the intermediate part is therefore
increased. This allows the wood laminate material to have uniform
density distribution in the lamination direction. Moreover, since
the wood laminate material has the high-density woodbased material
layer in its intermediate part in the thickness direction and the
top and bottom parts of the wood laminate material have a low
density, the risk of delamination when forming the wood laminate
material is effectively reduced or eliminated and productivity is
improved.
[0029] The woodbased material layer located in a part other than
the ends and a middle part in the lamination direction of the
woodbased material layers may be the high-density woodbased
material layer.
[0030] In this configuration, the woodbased material layer located
in the part other than the ends and the middle part in the
lamination direction of the woodbased material layers is the
high-density woodbased material layer, and the woodbased material
layers located at the ends and in the middle part in the lamination
direction have a low density. The pressure to be used to form the
wood laminate material is thus reduced by the low-density woodbased
material layers in the top and bottom parts of the wood laminate
material, and nail pull resistance (force) of the wood laminate
material is increased by the high-density woodbased material
layer.
[0031] Fibers of the woodbased materials may extend in the same
direction in each woodbased material layer, and the fibers of the
woodbased materials in adjoining ones of the woodbased material
layers may extend in directions crossing or parallel to each
other.
[0032] As used herein, the expressions "fibers extend in the same
direction" and "fibers extend in directions parallel to each other"
are not limited to the case where the fibers of all the woodbased
materials are oriented in the same direction, but define a concept
including the case where the fibers of a part of the woodbased
materials are tilted to some extent. The fibers of a part of the
woodbased materials may be tilted by, e.g., about 20.degree. with
respect to a predetermined reference direction. Similarly, the
expression "fibers extend in directions crossing each other" is not
limited to the case where the fibers are oriented in directions
perpendicular to each other. The fibers of a part of the woodbased
materials may be tilted by, e.g., about 20.degree. with respect to
a direction perpendicular to the reference direction.
[0033] According to this configuration, in the case where the
fibers of the woodbased materials in adjoining ones of the
woodbased material layers extend in directions crossing each other,
the wood laminate material has high strength against forces acting
in various directions, as compared to the case where the fibers
extend in the same direction in all of the woodbased material
layers. Especially, the larger the number of woodbased material
layers is, the more significant the difference in strength due to
the difference in fiber direction between the woodbased material
layers is. In the case where the fibers are oriented in the same
direction along the entire thickness in the lamination direction of
the wood laminate material, the strength may vary depending on the
direction in which a force is applied. However, this problem does
not occur in the case where the fibers of the woodbased materials
in adjoining ones of the woodbased material layers extend in
directions crossing each other.
[0034] On the other hand, in the case where the fibers of the
woodbased materials in adjoining ones of the woodbased material
layers extend in directions parallel to each other, namely in the
case where the fiber directions of the woodbased materials are the
same along the entire thickness in the lamination direction of the
wood laminate material, the wood laminate material has high
strength against a force acting in a specific direction.
[0035] Of the multiple woodbased material layers, the fibers of the
woodbased materials in the top and bottom woodbased material layers
may extend in the same direction.
[0036] Performance such as load resistance and impact resistance in
the top part of the wood laminate material is therefore about the
same as that in the bottom part of the wood laminate material. That
is, this configuration allows the wood laminate material to have
similar performance in its top and bottom parts. This is
advantageous in that the user can use the wood laminate material
without having to worry about which side is the top and which side
is the bottom.
[0037] The number of woodbased material layers may be odd. In this
case, the wood laminate material is a laminate of the odd number of
woodbased material layers. This configuration allows the wood
laminate material to have similar performance in its top and bottom
parts, as in the case described above.
[0038] The multiple woodbased material layers may be laminated so
that overall density distribution provided by the multiple
woodbased material layers is plane symmetric with respect to a
center in the lamination direction. Since the overall density
distribution provided by the multiple woodbased material layers is
plane symmetric with respect to the center in the lamination
direction, the wood laminate material has similar performance in
its top and bottom parts. The user can therefore use the wood
laminate material without having to know which side is the top and
which side is the bottom.
[0039] The woodbased materials may be strands that are cut pieces.
This implements a strand material having high strength and high
water resistance or a strand material having high productivity and
varied characteristics.
[0040] A method for manufacturing a wood laminate material is
characterized by including: a stacking step of stacking multiple
woodbased materials, which are cut pieces or veneers, to form
multiple woodbased material layers so that at least one of the
multiple woodbased material layers is formed by a high-density
woodbased material or high-density woodbased materials having a
relatively higher density than the remainder of the woodbased
material layers; and a forming step of compressing or compacting
the multiple woodbased material layers formed in the stacking
step.
[0041] Since the woodbased material layers include a layer formed
by the high-density woodbased material or high-density woodbased
materials having a relatively higher density than the remainder of
the woodbased material layers, density distribution in the
lamination direction after the forming step can be adjusted,
whereby a wood laminate material with desired characteristics can
be produced. For example, density distribution in the lamination
direction of the wood laminate material can be made substantially
constant by inserting the woodbased material layer formed by the
high-density woodbased material or high-density woodbased materials
at an optimal position.
Advantages of the Invention
[0042] As described above, according to the present invention,
density distribution in the lamination direction of the wood
laminate material, which is formed by stacking and laminating
multiple woodbased material layers each formed by cut pieces or
veneer, is adjusted so that the wood laminate material has
substantially constant density distribution in the lamination
direction. High strength and high water resistance can therefore be
achieved. Moreover, the density distribution in the lamination
direction is varied so that at least one of the multiple woodbased
material layers is a high-density woodbased material layer having a
higher density than the remainder of the woodbased material layers.
Accordingly, only the woodbased material layer required to have
high strength and high water resistance has a high density, and
productivity is improved. Moreover, characteristics of the wood
laminate material can be varied as desired by changing the layer
that is to be a high-density woodbased material layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a schematic perspective view of a multi-layered
structure of a strand board according to a first embodiment of the
present invention.
[0044] FIG. 2 is a schematic perspective view of a first example of
a strand board according to a second embodiment of the present
invention.
[0045] FIG. 3 is a schematic sectional view showing a laminate of
strand layers in the first example of the strand board according to
the second embodiment.
[0046] FIG. 4 is a sectional view corresponding to FIG. 3, showing
a second example of the strand board according to the second
embodiment.
[0047] FIG. 5 is a sectional view corresponding to FIG. 3, showing
a third example of the strand board according to the second
embodiment.
[0048] FIG. 6 is a sectional view corresponding to FIG. 3, showing
a fourth example of the strand board according to the second
embodiment.
[0049] FIG. 7 is a sectional view corresponding to FIG. 3, showing
a fifth example of the strand board according to the second
embodiment.
[0050] FIG. 8 is a sectional view corresponding to FIG. 3, showing
a sixth example of the strand board according to the second
embodiment.
[0051] FIG. 9 is a table illustrating specific configurations of
the first to sixth examples of the strand board according to the
second embodiment.
[0052] FIG. 10 is a sectional image of a strand board of Example 1
of the first embodiment.
[0053] FIG. 11 is a table showing the test results of Examples 1, 2
and Comparative Examples 1, 2.
[0054] FIG. 12 is a graph showing density distribution in the
strand board of Example 1 according to the first embodiment, in
which the uniform short-dashed line represents an average density
of the woodbased material layers in the thickness direction
(lamination direction) and the long-dash short-dash line represents
a constant density value for reference.
[0055] FIG. 13 is a graph showing density distribution in a strand
board of Comparative Example 1 as compared to the first embodiment,
in which the uniform short-dashed line represents an average
density of the woodbased material layers in the thickness direction
(lamination direction) and the long-dash short-dash line represents
a constant density value for reference.
[0056] FIG. 14 is a table showing the results of a bending test for
Examples 1, 2 and Comparative Example 1 of the second embodiment,
along with their other physical properties.
[0057] FIG. 15 is a graph showing density distribution in the
thickness direction (lamination direction) of Examples 1, 2 and
Comparative Example 1 according to the second embodiment.
[0058] FIG. 16 is a table showing the results of a bending test and
a boiling test for Example 3 and Comparative Example 2, along with
their other physical properties.
[0059] FIG. 17 is a graph showing density distribution in the
thickness direction (lamination direction) of Example 3 and
Comparative Example 2 according to the second embodiment.
[0060] FIG. 18 is a table showing the results of a bending test and
a boiling test for Example 4 and Comparative Example 3, along with
their other physical properties.
[0061] FIG. 19 is a table showing the result of a nail pull test
for Example 4 and Comparative Example 4, along with their other
physical properties.
[0062] FIG. 20 is a graph showing density distribution in the
thickness direction (lamination direction) of Example 4 and
Comparative Example 3 according to the second embodiment.
DESCRIPTION OF EMBODIMENTS
[0063] Embodiments of the present invention will be described in
detail below with reference to the accompanying drawings. The
following description of the preferred embodiments is merely
exemplary in nature and is not intended in any way to limit the
invention, its applications or uses. Specific numerical values in
the embodiments are shown merely by way of example in order to
facilitate understanding of the invention and are not intended to
limit the scope of the invention and materials of the
invention.
First Embodiment
[0064] FIG. 1 schematically shows a strand board B as a wood
laminate material according to a first embodiment of the present
invention.
[0065] As shown in FIG. 1, the strand board B has an odd number of
(in FIG. 1, five) strand layers 1, 1, . . . as woodbased material
layers, and all of the strand layers 1, 1, . . . have the same
thickness. That is, FIG. 1 shows an example in which, with the
upper side in FIG. 1 being the top and the lower side being the
bottom, the thickness w1 of the top and bottom strand layers 1, 1
is the same as the thicknesses w2, w3, w2 of the three intermediate
strand layers 1, 1, . . . . The strand board B need not necessarily
have an odd number of strand layers 1. The strand board B may have
an even number of strand layers 1. The number of strand layers 1 is
not limited to five. The number of strand layers 1 may be four or
less or six or more.
[0066] Each strand layer 1 is a mat made of laminated multiple
strands 5, 5, . . . (woodbased materials) that are cut pieces of
wood etc. Multiple mats of strands 5, 5, . . . are stacked together
to form multiple strand layers 1, 1, . . . .
[0067] For example, the strands 5 are strands or flakes that are
about 150 to 200 millimeters long in the fiber direction, about 15
to 25 millimeters wide, and about 0.3 to 2 millimeters thick.
[0068] Wood species that are used for the strands 5 are not
particularly limited. For example, tropical wood species or
broadleaf trees may be used, or other wood species may be used.
Specific examples include Cedar (Cryptomeria japonica), Cypress
(Chamaecyparis), sort of firs such as Douglas fir (Pseudotsuga
menziesii), Acacia (Acacia spp.), Aspen (Populus spp.), Poplar
(Populus spp.), Pine (Pinus spp.) (Hard pine (Pinus spp.), Soft
pine (Pinus spp.), Radiata pine (Pinus radiata), etc.), Birch
(Betula spp.), and Rubber tree (Rubber wood (Hevea brasiliensis)).
However, the wood species that are used for the strands 5 are not
limited to these, and various other wood species may be used.
Examples of the various other wood species include: Japanese wood
species such as Sawara cypress (Chamaecyparis pisifera), Japanese
elkhorn cypress (Thujopsis dolabrata), Japanese nutmeg-yew (Torreya
nucifera), Southern Japanese hemlock (Tsuga sieboldii), Podocarp
(Podocarpus macrophyllus), Pinus spp., Princess tree (Paulownia
tomentosa), Maple (Acer spp.), Birch (Betula spp.) (Japanese white
birch (Betula platyphylla)), Chinquapin (Castanopsis spp.),
Japanese beech (Fagus spp.), Live oak (Quercus spp.), Abies firma,
Sawtooth oak (Quercus acutissima), Oak (Quercus spp.), Camphor tree
(Cinnamomum camphora), and Japanese zelkova (Zelkova serrata);
North American wood species such as Port Orford cedar
(Chamaecyparis lawsoniana), Yellow cedar (Callitropsis
nootkatensis), Western redcedar (Thuja plicata), Grand fir (A.
grandis), Noble fir (A. procera), White fir (A. concolor), Spruce
(Picea spp.), Western hemlock (Tsuga heterophylla), and Scots pine
(Pinus sylvestris); tropical hardwood species such as Agathis
(Agathis spp.), Terminalia (Terminalia spp.), Lauan (Shorea spp.),
Meranti (Shorea sect.), Sengon laut (A. falcataria), Jongkong
(Dactylocladus stenostachys), Kamerere (Eucalyptus deglupta),
Kalampayan (Anthocephalus chinensis), Amberoi (Pterocymbium
beccarii), Yemane (Gmelina arborea), Teak (Tectona grandis), and
Apitong (Dipterocarpus spp.); and other foreign wood species such
as Balsa (Ochroma pyramidale), Cedro (Cedrela odorata), Mahogany
(Swietenia spp.), Lignum-vitae (Guaiacum spp.), Acacia mangium,
Aleppo pine (Pinus halepensis), Bamboo, Sorghum (Sorghum nervosum
Bess.), and Kamerere (Eucalyptus deglupta). Any material can be
used.
[0069] Regarding physical properties of the strands 5, the strands
5 preferably have a density of about 300 to 800 kg/m.sup.3, more
preferably 430 to 700 kg/m.sup.3. If the density is less than 300
kg/m.sup.3, a multi-layered mat with a larger thickness is required
to form a strand board B of the same density and strength, and a
higher pressure need be used for hot pressing in a press process
described later.
[0070] The strands 5 may have a density higher than 800 kg/m.sup.3,
but it is difficult to obtain such strands 5. Namely, if strands 5
having a density higher than 800 kg/m.sup.3 can be easily obtained,
the upper limit of the density is not limited to 800 kg/m.sup.3 and
may be higher than 800 kg/m.sup.3.
[0071] The moisture content of each strand 5 is preferably about 2
to 20%, more preferably 2 to 8%. If the moisture content is less
than 2%, it takes more time to soften the strands 5 in the hot
pressing of the press process. Namely, the press time is increased,
which may cause reduction in strength.
[0072] If the moisture content of the strands 5 is higher than 20%,
it takes more time to heat and compress the strands 5 in the hot
pressing, and the strands 5 tend to be blown. Moreover, curing of
an adhesive is inhibited, which may cause reduction in
strength.
[0073] In each strand layer 1, the strands 5, 5, . . . are oriented
such that the fiber direction (longitudinal direction of the
strands 5), which is the direction in which fibers (not shown) of
the strands 5, 5, . . . extend, is a predetermined direction. As
also shown in FIG. 1, the fibers of the strands 5, 5, . . . in each
strand layer 1 need not necessarily extend in exactly the same
direction. In other words, the fiber directions of the oriented
strands 5, 5, . . . do not have to be parallel to each other.
Namely, the fiber directions of a part of the strands 5, 5, . . .
may be tilted to some extent (e.g., by about 20.degree.) with
respect to a predetermined reference direction.
[0074] The multiple strand layers 1, 1, . . . are stacked and
laminated such that the fibers of the strands 5, 5, . . . in
adjoining ones of the strand layers 1 extend in directions
perpendicular to each other. That is, in FIG. 1, the fiber
direction of the strands 5, 5, . . . in the top strand layer 1
(uppermost layer in FIG. 1) is the same as that of the strands 5,
5, . . . in the bottom strand layer 1 (lowermost layer in FIG.
1).
[0075] The first embodiment is characterized in that the strand
board B has substantially constant density distribution in the
lamination direction of the strand layers 1 (the thickness
direction of the strand board B), namely the direction in which the
strand layers 1 are laminated. Specifically, the multiple strand
layers 1, 1, . . . are laminated so that overall density
distribution provided by the multiple strand layers 1, 1, . . . is
plane symmetric with respect to the center in the lamination
direction of the strand board B.
[0076] Next, a method for manufacturing a strand board B according
to the first embodiment will be described. This manufacturing
method includes a strand producing process, a strand pretreatment
process, an adhesive coating process, a stacking process (mat
forming process), and a press process.
[0077] (Strand Producing Process)
[0078] In the method for manufacturing a strand board B, the strand
producing process is first performed in which a large number of
strands 5, 5, . . . (cut pieces of wood etc.) are produced. In this
process, green wood such as logs or thinnings is cut with, e.g., a
cutting machine to produce strands 5, 5, . . . . The strands 5, 5,
. . . may be produced from wood scraps, wood wastes, etc. that are
generated at construction sites etc. or may be produced from waste
wood pallets.
[0079] (Strand Pretreatment Process)
[0080] After the strand producing process, it is preferable that a
large number of strands 5, 5, . . . produced be subjected to at
least one of various strand pretreatment processes described below.
This pretreatment is performed in order to allow low-pressure
pressing using a pressure as low as, e.g., about 4 N/mm.sup.2 to be
performed in the later press process. At least one of a physical
treatment method, a high-frequency treatment method, a
high-temperature high-pressure treatment method, a high-water
pressure treatment method, a repeated deaeration and dehydration
treatment method, and a chemical treatment method is used.
[0081] The physical treatment method is a method in which the
strands 5 are physically compressed. Examples of the physical
treatment method include roll pressing, beating, and flat press
pressing. The roll pressing is a linear compression method in
which, although not shown in the figures, a large number of strands
5, 5, . . . (woodbased materials) are placed in a heat roll press
machine such that the strands 5, 5, . . . evenly drop thereon, and
the strands 5, 5, . . . are then compressed with heat. For example,
this roll pressing is performed under the following conditions:
heating temperature: room temperature to 200.degree. C.; clearance
between heat rolls: about 0.1 to 0.4 mm; feed rate: about 50 m/min;
and compression ratio: about 20 to 60%. The strands 5 are thus
compressed without being smashed, whereby high-density strands 5
are produced.
[0082] The beating is a point compression method in which, as in
metal forging, strands 5 are compressed and deformed by hitting
with multiple continuously installed spring hammers etc. As in the
roll pressing, the strands 5 are thus compressed without being
smashed, whereby high-density strands 5 are produced.
[0083] The flat press pressing is a surface compression method in
which strands 5, 5, . . . (woodbased materials) are placed in a
flat heat press machine and compressed with heat. For example, the
flat press pressing is performed at a temperature of 120.degree. C.
and a pressure of about 4 N/mm.sup.2 for about five minutes. In the
flat press pressing as well, the strands 5 are compressed without
being smashed, whereby high-density strands 5 are produced.
[0084] The high-frequency treatment method is a method in which
strands 5 as dielectrics (nonconductors) are irradiated with
high-frequency electromagnetic waves (high-frequency waves) between
electrodes etc. and thus dielectrically heated from the inside and
softened. This method allows low-pressure pressing using a low
pressure to be performed in the later press process without
increasing the density of the strands 5 as in the above physical
treatment method.
[0085] The high-temperature high-pressure treatment method is a
method in which strands 5 are placed in a pressure vessel where the
strands 5 are subjected to high temperature and high pressure so
that cell walls of the strands 5 (woodbased materials) are damaged
and the strands 5 are softened. For example, this method is
performed at a temperature of 180.degree. C. and a pressure of
about 10 Bar for about two minutes. This method also allows
low-pressure pressing using a low pressure to be performed in the
later press process without increasing the density of the strands 5
as in the above physical treatment method.
[0086] The high-water pressure treatment method is a method in
which strands 5 are uniformly formed within a mesh material such as
metal wire mesh and the surfaces of the strands 5 are finely
scratched by high-pressure water of, e.g., about 200 MPa through
the mesh material. This produces fine fractures in the strands 5.
The softened strands 5 are thus obtained.
[0087] The repeated deaeration and dehydration treatment method is
a method in which strands 5 are first saturated with water and then
placed in a batch type of vessel, and with the vessel being
evacuated to vacuum, moisture is removed from the strands 5 to
facilitate damage to cell walls of the strands 5 (woodbased
materials) and thus soften the strands 5. This method also allows
low-pressure pressing using a low pressure to be performed in the
later press process without increasing the density of the strands 5
as in the above physical treatment method.
[0088] The chemical treatment method is a method in which, for
example, sodium hydroxide etc. is added to strands 5 for alkaline
treatment to facilitate plasticization of the strands 5 themselves
and thus soften the strands 5. This method also allows low-pressure
pressing using a low pressure to be performed in the later press
process without increasing the density of the strands 5 as in the
above physical treatment method.
[0089] In the high-frequency treatment method, the high-temperature
high-pressure treatment method, the high water pressure treatment
method, the repeated deaeration and dehydration treatment method,
and the chemical treatment method, the state of the strands 5 after
the treatment is maintained by drying the strands 5 as necessary
after the treatment.
[0090] (Adhesive Coating Process)
[0091] After a large number of strands 5, 5, . . . are thus
produced, the adhesive coating process is performed in which the
strands 5, 5, . . . are coated with an adhesive. For example, the
adhesive may be an isocyanate adhesive or may be an amine adhesive
such as a phenol resin, urea resin, or melamine resin.
[0092] (Stacking Process)
[0093] Thereafter, the stacking process (mat forming process) is
performed in which a large number of strands 5, 5, . . . are
oriented and stacked to form strand mats and the strand mats are
stacked in multiple layers to form a multi-layered mat.
[0094] Specifically, with a mat forming machine etc., a large
number of strands 5, 5, . . . coated with the adhesive are oriented
such that fibers extend in a predetermined reference direction, and
are stacked to a thickness of, e.g., about 7 to 12 mm to form a
strand mat with a certain thickness. The thickness of the strand
mat is not limited to the above values. The thickness of the strand
mat may be less than 7 mm or more than 12 mm.
[0095] After the strand mat with a certain thickness is thus
formed, strands 5, 5, . . . oriented such that the fiber direction
of the strands 5, 5, . . . is, e.g., perpendicular to that of the
strands 5, 5, . . . in the strand mat are stacked on top of the
strand mat to form another strand mat with a certain thickness.
[0096] Subsequently, an additional strand mat is repeatedly stacked
in a similar manner until the stack has a desired number of layers
(e.g., five layers). At this time, the strand mats are stacked so
that the fiber directions of the strands 5, 5, . . . in adjoining
ones of the strand mats are perpendicular to each other. A
multi-layered mat is formed in this manner. As shown in FIG. 1, in
the case of the strand board B having the five strand layers 1, 1,
. . . , the thickness of the five-layered mat is, e.g., about 35 to
60 mm.
[0097] The number of strand mats in the multi-layered mat is
determined based on the number of layers in the strand board B.
Accordingly, the number of strand mats in the multi-layered mat may
be four or less or six or more.
[0098] The density of the strands 5, 5, . . . of the strand layer 1
may be either about the same or different between or among the
multiple strand layers 1, 1, . . . .
[0099] (Press Process)
[0100] After the multi-layered mat is thus formed by stacking
multiple strand mats, hot pressing is performed at a predetermined
pressure and temperature with a hot press machine to compress or
compact the multi-layered mat. This hot pressing is performed at a
pressure of, e.g., 2 to 4 N/mm.sup.2 for, e.g., about 10 to 20
minutes. The press time varies depending on the thickness of the
strand board B (finished product). Accordingly, in some cases, it
may take less than 10 minutes to complete the hot pressing, and in
other cases, it may take 20 minutes or more to complete the hot
pressing. Pre-heat treatment with a heater may be performed before
the hot pressing with the hot press machine.
[0101] A strand board B having a density of 750 to 950 kg/m.sup.3
and flexural strength of 80 to 150 N/mm.sup.2 is thus formed as a
laminate by these processes.
[0102] In the first embodiment, the pressure for the hot pressing
in the press process is as low as 2 to 4 N/mm.sup.2. A high
density, high strength strand board B can thus be produced without
using a special high pressure press machine.
[0103] In the strand board B, the fiber direction of the strands 5,
5, . . . in the top strand layer 1 of the strand board B is the
same as that of the strands 5, 5, . . . in the bottom strand layer
1 of the strand board B. Performance such as load resistance and
impact resistance in the top part of the strand board B is
therefore about the same as that in the bottom part of the strand
board B. That is, this configuration allows the strand board B to
have similar performance in its top and bottom parts. This is
advantageous in that the user can use the strand board B without
having to worry about which side is the top and which side is the
bottom.
[0104] The multiple strand layers 1, 1, . . . have about the same
thickness. This allows the strand board B to have uniform board
performance such as strength properties and water resistance
properties in the thickness direction.
[0105] Density distribution in the thickness direction of the
strand board B formed by the strand layers 1, 1, . . . is plane
symmetric. This allows the strand board B to have similar
performance in its top and bottom parts. The user can therefore use
the strand board B without having to know (worry about) which side
is the top and which side is the bottom.
[0106] In the case where the number of strand layers 1, 1, . . . is
odd, the strand board B has similar performance in its top and
bottom parts, as described above.
[0107] As described above, it is preferable that the strands 5, 5,
. . . produced in the strand producing process have a density of
430 to 700 kg/m.sup.3 and a moisture content of 2 to 20%. However,
the strands 5, 5, . . . produced in the strand producing process
can be used even if their properties are out of these preferred
ranges.
[0108] Specifically, the strands 5, 5, . . . having desired
properties may be separated from strands cut (or sliced) from logs
by a screening machine etc., and the strands 5, 5, . . . thus
separated may be subjected to the subsequent processes, namely the
strand producing process, the strand pretreatment process, the
adhesive coating process, the stacking process (mat forming
process), and the press process.
[0109] The substantial moisture content and density of the strands
5, 5, . . . may be adjusted by changing, e.g., the composition, the
coating method, etc. of the adhesive that is used in the adhesive
coating process as desired. A predetermined pressing process may be
performed, e.g., during or before the hot pressing in the press
process. Specifically, a pressing process (including a compressed
process) may be divided into in multiple stages to adjust the
substantial moisture content of the strands 5, 5, . . . or increase
the substantial density of the strands 5, 5, . . . for the hot
pressing.
Second Embodiment
[0110] FIGS. 2 to 8 shows a second embodiment of the present
invention (the same portions as those in FIG. 1 are denoted with
the same reference characters and detailed description thereof will
omitted). FIGS. 2 to 8 show examples of a strand board B that is a
wood laminate material according to the second embodiment. FIGS. 2
and 3 show a first example of the strand board B. FIG. 4 shows a
second example, FIG. 5 shows a third example, FIG. 6 shows a fourth
example, FIG. 7 shows a fifth example, and FIG. 8 shows a sixth
example.
[0111] In each of the first to sixth examples, the strand board B
includes strand layers 1, 1, . . . as multiple (an odd number of)
woodbased material layers. Each strand layer 1 is made of a mat of
a large number of strands 5, 5, . . . (woodbased materials) that
are cut pieces. Multiple mats of strands 5, 5, . . . are stacked
together to form multiple strand layers 1, 1, . . . .
[0112] In the second embodiment, the upper side in FIGS. 3 to 8 is
the top of the strand board B and the lower side is the bottom
thereof, and the strand layers 1, 1, . . . are sequentially
numbered from top to bottom as the first strand layer 1, the second
strand layer 1, the third strand layer 1, . . . . The strand layers
1, 1, . . . are thus marked with circled numbers in the FIGS. 3 to
8.
[0113] In the second embodiment, the strands 5 preferably have a
density of about 300 to 1100 kg/m.sup.3. If the density is less
than 300 kg/m.sup.3, a multi-layered mat with a larger thickness is
required to form high-density strand layers 1a, and a higher
pressure need be used for hot pressing in a press process.
[0114] The strands 5 may have a density higher than 1100
kg/m.sup.3, but it is difficult to obtain such strands 5. Namely,
if strands 5 having a density higher than 1100 kg/m.sup.3 can be
easily obtained, the upper limit of the density is not limited to
1100 kg/m.sup.3 and may be higher than 1100 kg/m.sup.3.
[0115] In the second embodiment as well, the strands 5, 5, . . . in
each strand layer 1 are oriented such that the fibers of the
strands 5, 5, . . . extend in a predetermined direction. As also
shown in FIG. 2, the fibers of the strands 5, 5, . . . in each
strand layer 1 need not necessarily extend in the same direction.
Namely, the fiber directions of the oriented strands 5, 5, . . . in
each strand layer 1 do not have to be parallel to each other. In
other words, the fibers of a part of the strands 5, 5, . . . in
each strand layer 1 may be tilted to some extent with respect to a
predetermined reference direction. For example, a part of the
strands 5, 5, . . . in each strand layer 1 may be oriented so as to
be tilted by about 20.degree. with respect to the reference
direction.
[0116] The second embodiment is characterized in that, unlike in
the first embodiment, at least one of the odd number of strand
layers 1, 1, . . . in the strand board B is a high-density strand
layer 1a having a density higher than the remaining strand layers
1b, and the remaining strand layers 1b are low-density strand
layers. The "density of the strand layer" as used in the second
embodiment does not refer to the density of the strands 5 but
refers to the density of the strand layer 1 itself made of a mat of
the strands 5.
[0117] Each example of the strand board B will be specifically
described in detail. In FIGS. 3 to 8, the layers shaded with dense
dots represent the high-density strand layers 1a and the layers
shaded with sparse dots represent the low-density strand layers
1b.
First Example
[0118] FIGS. 2 and 3 show the first example of the strand board B
according to the second embodiment. This strand board B has five
strand layers, namely first to fifth strand layers 1, 1, . . . .
These strand layers 1, 1, . . . are stacked and laminated such that
the fibers of the strands 5, 5 in adjoining ones of the strand
layers 1 extend in directions perpendicular to each other. The
fiber direction of the strands 5, 5 in the first strand layer 1
located at the top of the strand board B, namely in the uppermost
strand layer 1 in FIG. 3, is the same as that of the strands 5, 5
in the fifth strand layer 1 located at the bottom of the strand
board B, namely in the lowermost strand layer 1 in FIG. 3.
[0119] Two of the five strand layers 1, 1, . . . are high-density
strand layers 1a having a density higher than the other three
strand layers, which are low-density strand layers 1b. The two
high-density strand layers 1a, 1a have the same density, which is,
e.g., about 1000 kg/m.sup.3 (average value). The three low-density
strand layers 1b, 1b, . . . have the same density, which is, e.g.,
about 800 kg/m.sup.3. The density of these low-density strand
layers 1b is about the same as that of common strand boards.
[0120] Specifically, the first strand layer 1 located at the top of
the strand board B, the fifth strand layer 1 located at the bottom
of the strand board B, and the third strand layer 1 located in the
middle part in the thickness direction of the strand board B are
low-density strand layers 1b. Both the second and fourth strand
layers 1, 1 located in the parts of the strand board B other than
the top and bottom and the middle part in the thickness direction
of the strand board B are high-density strand layers 1a.
[0121] The five strand layers 1, 1, . . . have three different
thicknesses. The thickness of each of the first and fifth strand
layers 1, 1 (low-density strand layers 1b) is, e.g., 25% of the
total thickness of the strand board B, the thickness of each of the
second and fourth strand layers 1, 1 (high-density strand layers
1a) is, e.g., 20% of the total thickness of the strand board B, and
the thickness of the third strand layer 1 (low-density strand layer
1b) is, e.g., 10% of the total thickness of the strand board B. The
total thickness of the high-density strand layers 1a is therefore,
e.g., 40% of the total thickness of the strand board B. The five
strand layers 1, 1, . . . are laminated so that overall density
distribution provided by the strand layers 1, 1, . . . is plane
symmetric with respect to the center in the lamination direction,
namely in the thickness direction, of the strand board B. The total
thickness of the strand board B is, e.g., 28 mm.
[0122] A method for manufacturing a strand board B according to the
second embodiment will be described. This manufacturing method is
applied not only to the strand board B of the first example but
also to the strand boards B of the second to sixth examples.
[0123] The manufacturing method of the second embodiment is
basically the same as the first embodiment. Description of the same
parts as those in the first embodiment is omitted, and only the
differences will be described in detail.
[0124] This manufacturing method has a strand producing process, a
strand pretreatment process, an adhesive coating process, a
stacking process (mat forming process), and a press process. Of
these processes, the strand pretreatment process, the adhesive
coating process, and the press process are the same as those of the
first embodiment.
[0125] In the second embodiment, when forming a multi-layered mat
in the mat forming process by stacking another strand mat on top of
a strand mat, the strand mat that is to be a high-density strand
layer 1a is formed by the strands 5 having a density higher than
the strands 5 of the strand mat that is to be a low-density strand
layer 1b is. This allows both high-density and low-density strand
layers 1a, 1b to be stacked together.
[0126] For example, the following two kinds of strands are prepared
in advance in the first process of the manufacturing method, namely
in the strand producing process: strands with densities in a common
range; and strands with densities higher than the common range. The
strands with densities in the common range are used as the strands
5 of the strand mat that is to be a low-density strand layer 1b.
The strands with densities higher than the common range as a result
of compression etc. may be used as the strands 5 of the strand mat
that is to be a high-density strand layer 1a.
[0127] The wood species etc. of the strands 5 may be different
between the strand mat that is to be a high-density strand layer 1a
and the strand mat that is to be a low-density strand layer 1b. A
wood species having a higher density may be used to produce the
strands 5 of the strand mat that is to be a high-density strand
layer 1a than a wood species that is used to produce the strands 5
of the strand mat that is to be a low-density layer strand layer
1b.
[0128] After the multi-layered mat is formed, the press process is
performed in which hot pressing is performed at a predetermined
pressure and temperature with a hot press machine to compress or
compact the multi-layered mat. In the press process, the hot
pressing is performed at a pressure of, e.g., 2 to 4 N/mm.sup.2 as
in the first embodiment, but the press time is, e.g., about 10 to
30 minutes. In the second embodiment as well, the press time varies
depending on the thickness of the strand board B (finished
product). Accordingly, in some cases, it may take less than 10
minutes to complete the hot pressing, and in other cases, it may
take 30 minutes or more to complete the hot pressing. Pre-heat
treatment with a heater may be performed before the hot pressing
with the hot press machine.
[0129] As described above, it is preferable that the strands 5
produced in the strand producing process have a density of 300 to
1100 kg/m.sup.3 and a moisture content of 2 to 8%. However, the
strands 5 produced in the strand producing process can be used even
if their properties are out of these preferred ranges.
Second Example
[0130] FIG. 4 shows the second example of the strand board B. As in
the first example, this strand board B has five strand layers,
namely first to fifth strand layers 1, 1, . . . . These strand
layers 1, 1, . . . are stacked and laminated such that the fibers
of the strands 5 in adjoining ones of the strand layers 1 extend in
directions perpendicular to each other. The fiber direction of the
strands 5, 5 in the first strand layer 1 located at the top of the
strand board B, namely in the uppermost strand layer 1 in FIG. 4,
is the same as that of the strands 5, 5 in the fifth strand layer 1
located at the bottom of the strand board B, namely in the
lowermost strand layer 1 in FIG. 4.
[0131] Two of the five strand layers 1, 1, . . . are high-density
strand layers 1a, and the other three strand layers are low-density
strand layers 1b having a density lower than the high-density
strand layers 1a. The two high-density strand layers 1a, 1a have
the same density, which is, e.g., about 1100 kg/m.sup.3 (average
value). This density is higher than that of the high-density strand
layers 1a of the first example. The three low-density strand layers
1b, 1b, . . . have the same density, and this density is lower than
that of the low-density strand layers 1b of the first example
(because the product density of the strand board B is lower than in
the first example).
[0132] Unlike in the first example, the first strand layer 1
located at the top of the strand board B and the fifth strand layer
1 located at the bottom of the strand board B are high-density
strand layers 1a. The remaining strand layers, namely the second to
fourth strand layers 1, 1, . . . located in the intermediate part
in the thickness direction of the strand board B, are low-density
strand layers 1b.
[0133] The five strand layers 1, 1, . . . have the same thickness.
The thickness of each strand layer 1 is, e.g., 20% of the total
thickness of the strand board B. The total thickness of the
high-density strand layers 1a is therefore, e.g., 40% of the total
thickness of the strand board B. The five strand layers 1, 1, . . .
are laminated so that overall density distribution provided by the
strand layers 1, 1, . . . is plane symmetric with respect to the
center in the thickness direction of the strand board B. The total
thickness of the strand board B is, e.g., 9 mm.
Third Example
[0134] FIG. 5 shows the third example of the strand board B. Unlike
in the second example, the strand board B has seven strand layers,
namely first to seven strand layers 1, 1, . . . . These strand
layers 1, 1, . . . are stacked and laminated such that the fibers
of the strands 5 in adjoining ones of the strand layers 1 extend in
directions perpendicular to each other. The fiber direction of the
strands 5, 5 in the first strand layer 1 located at the top of the
strand board B, namely in the uppermost strand layer 1 in FIG. 5,
is the same as that of the strands 5, 5 in the seventh strand layer
1 located at the bottom of the strand board B, namely in the
lowermost strand layer 1 in FIG. 5.
[0135] Two of the seven strand layers 1, 1, . . . are high-density
strand layers 1a. The other five strand layers are low-density
strand layers 1b having a density lower than the high-density
strand layers 1a. The two high-density strand layers 1a, 1a have
the same density, which is, e.g., about 1000 kg/m.sup.3 (average
value). This density is the same as that of the high-density strand
layers 1a of the first example. The five low-density strand layers
1b, 1b, . . . have the same density, and this density is lower than
that of the low-density strand layers 1b of the first example
(because the product density of the strand board B is lower than in
the first example).
[0136] Specifically, the first strand layer 1 located at the top of
the strand board B and the seventh strand layer 1 located at the
bottom of the strand board B are high-density strand layers 1a. The
remaining strand layers, namely the second to sixth strand layers
1, 1, . . . located in the intermediate part in the thickness
direction of the strand board B, are low-density strand layers
1b.
[0137] The seven strand layers 1, 1, . . . have two different
thicknesses. The thickness of each of the first and seventh strand
layers 1, 1 (high-density strand layers 1a) is, e.g., 15% of the
total thickness of the strand board B, the thickness of each of the
second, third, fifth, and sixth strand layers 1, 1, . . .
(low-density strand layers 1b) is, e.g., 15% of the total thickness
of the strand board B, and the thickness of the fourth strand layer
1 (low-density strand layer 1b) is, e.g., 10% of the total
thickness of the strand board B. The total thickness of the
high-density strand layers 1a is therefore, e.g., 30% of the total
thickness of the strand board B. The seven strand layers 1, 1, . .
. are laminated so that overall density distribution provided by
the strand layers 1, 1, . . . is plane symmetric with respect to
the center in the thickness direction of the strand board B. The
total thickness of the strand board B is, e.g., 12 mm.
Fourth Example
[0138] FIG. 6 shows the fourth example of the strand board B.
Unlike in the second and third examples, this strand board B has
three strand layers, namely first to third strand layers 1, 1, . .
. . These strand layers 1, 1, . . . are stacked and laminated such
that the fibers of the strands 5 in adjoining ones of the strand
layers 1 extend in directions perpendicular to each other. The
fiber direction of the strands 5, 5 in the first strand layer 1
located at the top of the strand board B, namely in the uppermost
strand layer 1 in FIG. 6, is the same as that of the strands 5, 5
in the third strand layer 1 located at the bottom of the strand
board B, namely in the lowermost strand layer 1 in FIG. 6.
[0139] One of the three strand layers 1, 1, . . . is a high-density
strand layer 1a. The other two strand layers are low-density strand
layers 1b having a density lower than the high-density strand layer
1a. The density of the high-density strand layer 1a is, e.g., about
800 kg/m.sup.3 (average value), which is lower than that of the
high-density strand layers 1a of the second example. The two
low-density strand layers 1b, 1b, . . . have the same density, and
this density is the same as that of the low-density strand layers
1b of the first example.
[0140] Specifically, only the second strand layer 1 located in the
middle part (intermediate part) in the thickness direction of the
strand board B is a high-density strand layer 1a, and the first and
third strand layers 1, 1 located at the top and bottom of the
strand board B are low-density strand layers 1b.
[0141] The three strand layers 1, 1, . . . have two different
thicknesses. The thickness of each of the first and third strand
layers 1, 1 (low-density strand layers 1b) is, e.g., 20% of the
total thickness of the strand board B, and the thickness of the
second strand layer 1 (high-density strand layer 1a) is, e.g., 60%
of the total thickness of the strand board B. The thickness of the
high-density strand layer 1a is therefore, e.g., 60% of the total
thickness of the strand board B. The three strand layers 1, 1, . .
. are laminated so that overall density distribution provided by
the strand layers 1, 1, . . . is plane symmetric with respect to
the center in the thickness direction of the strand board B. The
total thickness of the strand board B is, e.g., 18 mm.
Fifth Example
[0142] FIG. 7 shows the fifth example of the strand board B. As in
the fourth example, this strand board B has three strand layers,
namely first to third strand layers 1, 1, . . . . Unlike in the
first to fourth examples, these strand layers 1, 1, . . . are
stacked and laminated such that the fibers of the strands 5 in
adjoining ones of the strand layers 1 extend in directions parallel
to each other. That is, the fiber direction of the strands 5, 5 in
the first strand layer 1 located at the top of the strand board B,
namely in the uppermost strand layer 1 in FIG. 7, is the same as
that of the strands 5, 5 in the third strand layer 1 located at the
bottom of the strand board B, namely in the lowermost strand layer
1 in FIG. 7. The fiber direction of the strands 5, 5 in the second
strand layer 1 located in the middle part in the thickness
direction of the strand board B is also the same as that of the
strands 5, 5 in the first and third strand layers 1.
[0143] Unlike in the fourth example, two of the three strand layers
1, 1, . . . are high-density strand layers 1a. The remaining one
strand layer is a low-density strand layer 1b. The two high-density
strand layers 1a, 1a have a density of, e.g., about 800 kg/m.sup.3
(average value). This density is the same as that of the
high-density strand layer 1a of the fourth example. The density of
the low-density strand layer 1b is lower than that of the
low-density strand layers 1b of the first example (because the
product density of the strand board B is lower than in the first
example).
[0144] Specifically, the first and third strand layers 1, 1 located
at the top and bottom of the strand board B are high-density strand
layers 1a, and only the second strand layer 1 located in the middle
part in the thickness direction of the strand board B is a
low-density strand layer 1b.
[0145] The three strand layers 1, 1, . . . have two different
thicknesses. The thickness of each of the first and third strand
layers 1, 1 (high-density strand layers 1a) is, e.g., 40% of the
total thickness of the strand board B, and the thickness of the
second strand layer 1 (low-density strand layer 1b) is, e.g., 20%
of the total thickness of the strand board B. The total thickness
of the high-density strand layers 1a is therefore, e.g., 80% of the
total thickness of the strand board B. The three strand layers 1,
1, . . . are laminated so that overall density distribution
provided by the strand layers 1, 1, . . . is plane symmetric with
respect to the center in the thickness direction of the strand
board B. The total thickness of the strand board B is, e.g., 15
mm.
Sixth Example
[0146] FIG. 8 shows the sixth example of the strand board B. As in
the first example, this strand board B has five strand layers,
namely first to fifth strand layers 1, 1, . . . . These strand
layers 1, 1, . . . are stacked and laminated such that the fibers
of the strands 5 in adjoining ones of the strand layers 1 extend in
directions perpendicular to each other. The fiber direction of the
strands 5, 5 in the first strand layer 1 located at the top of the
strand board B, namely in the uppermost strand layer 1 in FIG. 8,
is the same as that of the strands 5, 5 in the fifth strand layer 1
located at the bottom of the strand board B, namely in the
lowermost strand layer 1 in FIG. 8.
[0147] Three of the five strand layers 1, 1, . . . are high-density
strand layers 1a. The other two strand layers are low-density
strand layers 1b having a density lower than the high-density
strand layers 1a. The three high-density strand layers 1a, 1a, . .
. have the same density, which is, e.g., about 1000 kg/m.sup.3
(average value). This density is the same as that of the
high-density strand layers 1a of the first example. The two
low-density strand layers 1b, 1b, . . . have the same density. This
density is the same as that of the low-density strand layers 1b of
the first example.
[0148] Specifically, as opposed to the second example, the second
to fourth strand layers 1, 1, . . . located in the intermediate
part in the thickness direction of the strand board B are
high-density strand layers 1a. The remaining strand layers, namely
the first strand layer 1 located at the top of the strand board B
and the fifth strand layer 1 located at the bottom of the strand
board B, are low-density strand layers 1b.
[0149] The five strand layers 1, 1, . . . have three different
thicknesses. The thickness of each of the first and fifth strand
layers 1, 1 (low-density strand layers 1b) is, e.g., 30% of the
total thickness of the strand board B, the thickness of each of the
second and fourth strand layers 1, 1 (high-density strand layers
1a) is, e.g., 15% of the total thickness of the strand board B, and
the thickness of the third strand layer 1 (high-density strand
layer 1a) is, e.g., 10% of the total thickness of the strand board
B. The total thickness of the high-density strand layers 1a is
therefore, e.g., 60% of the total thickness of the strand board B.
The five strand layers 1, 1, . . . are laminated so that overall
density distribution provided by the strand layers 1, 1, . . . is
plane symmetric with respect to the center in the thickness
direction of the strand board B. The total thickness of the strand
board B is, e.g., 28 mm.
[0150] FIG. 9 shows specific configurations of the first to sixth
examples.
[0151] In the second embodiment, the strand board B has multiple
strand layers 1, 1, . . . , and a part (one to three) of the
multiple strand layers 1, 1, . . . is a high-density strand layer
1a having a density higher than the other strand layers 1, 1, . . .
. The high-density strand layer 1a provides high strength and high
water resistance of the strand board B, whereby the strand board B
having high strength and high water resistance is obtained.
[0152] In the case where the density of the strand layer 1 is
increased to use this strand layer 1 as a high-density strange
layer 1a in the strand board B, the density of only the strands 5
of this high-density strand layer 1a need be increased, and it is
not necessary to increase the density of the strands 5 of all the
strand layers 1, 1, . . . . The press time with a press machine is
therefore reduced accordingly and the pressure to be used is also
reduced. This improves productivity and reduces or eliminates the
risk of delamination in the press process.
[0153] Moreover, one to three of the odd number of strand layers 1,
1, . . . of the strand board B are high-density strand layers 1a.
Accordingly, as shown in the first to sixth examples, a layer(s) to
be used as a high-density strand layer(s) 1a can be selected from
the multiple strand layers 1, 1, . . . as necessary.
Characteristics of the strand board B can therefore be varied as
desired by changing the position(s) of the high-density strand
layer(s) 1a, so that the strand board B has advantageous effects
specific to each example.
[0154] That is, in, e.g., the first example shown in FIGS. 2 and 3
(the sixth example shown in FIG. 8 is substantially similar to this
configuration), the second and fourth strand layers 1, 1 located in
the parts of the strand board B other than the top and bottom and
the middle part in the thickness direction of the strand board B
are high-density strand layers 1a, and the remaining layers, namely
the first, third, and fifth strand layers 1, 1, . . . located at
the top and bottom and in the middle part in the thickness
direction of the strand board B, are low-density strand layers 1b.
This structure is advantageous in that the use of the low-density
strand layers 1b in the top and bottom parts reduces the pressure
to be used in the press process and the high-density strand layers
1a provide increased nail pull resistance (force) for a nail that
is a fastener to be driven into the strand board B. Especially, the
sixth example shown in FIG. 8 further improves productivity.
[0155] In the second example shown in FIG. 4 and the third example
shown in FIG. 5, the strand layers 1, 1 located at the top and
bottom of the strand board B are high-density strand layers 1a, and
the strand layers 1, 1, . . . located in the intermediate part of
the strand board B are low-density strand layers 1b. In this
structure, the high-density strand layers 1a in the top and bottom
parts increase flexural strength of the strand board B and improve
water resistance in the top and bottom parts of the strand board
B.
[0156] In the fourth example shown in FIG. 6, the strand layer 1
located in the intermediate part in the thickness direction of the
strand board B is a high-density strand layer 1a, and the strand
layers 1, 1 located in the remaining part of the strand board B are
low-density strand layers 1b. In this structure, the strand board B
has a higher density in its intermediate part due to the
high-density strand layer 1a, and the strand board B has uniform
overall density distribution in the thickness direction. Since the
high-density strand layer 1a is formed in the intermediate part in
the thickness direction of the strand board B and the low-density
strand layers 1b are formed in the top and bottom parts of the
strand board B, this structure effectively reduces or eliminates
the risk of delamination in the press process and improves
productivity.
[0157] In the fifth example shown in FIG. 7, the strand layer 1
located in the middle part in the thickness direction of the strand
board B is a high-density strand layer 1a, and the first and third
strand layers 1, 1 located at the top and bottom of the strand
board B are low-density strand layers 1b. Moreover, the fiber
direction of the strands 5, 5, . . . is the same in all of the
first to third strand layers 1, 1 . . . . This structure improves
flexural strength in the fiber direction and also improves shear
strength.
[0158] In the first to fourth examples of the strand board B of the
second embodiment, the fibers of the strands 5, 5, . . . extend in
the same direction in each strand layer 1, and the fibers of the
strands 5 in adjoining ones of the strand layers 1 extend in
directions perpendicular to each other. This structure has high
strength against forces acting in various directions as compared to
the case where the fibers of the strands 5 extend in the same
direction in all of the strand layers 1, 1, . . . as in the fifth
example. The larger the number of strand layers 1 is, the more
significant the difference in strength of the strand board B due to
the difference in fiber direction between the strand layers 1
is.
[0159] On the other hand, in the case where the strands 5, 5 are
oriented in the same direction along the entire thickness in the
lamination direction of the strand board B as in the fifth example,
the strand board B has high strength against a force acting in a
specific direction, as described above.
[0160] In the second embodiment as well, density distribution in
the thickness direction of the strand board B formed by the strand
layers 1, 1, . . . is plane symmetric. This allows the strand board
B to have similar performance in its top and bottom parts. The user
can therefore use the strand board B without having to know which
side is the top and which side is the bottom.
[0161] Moreover, the strand board B has an odd number of strand
layers 1, 1, . . . . This allows the strand board B to have similar
performance in its top and bottom parts.
OTHER EMBODIMENTS
[0162] The present invention is not limited to the first and second
embodiments. In the first embodiment, the thicknesses w1 to w3 of
the multiple strand layer 1, 1, . . . are the same. However, the
present invention is not limited to this, and the thicknesses W1 to
W3 of each layer 1 can be set as desired.
[0163] For example, the multiple strand layers 1, 1, . . . may be
composed so that the thickness of the strand layer 1 gradually
increases from the middle strand layer 1 in the thickness direction
(lamination direction) of the strand board B to the top and bottom
strand layers 1. That is, the thicknesses of the multiple strand
layers 1, 1, . . . in FIG. 1 may have a relation of w1>w2>w3.
The strand layers 1 on the outer sides (top and bottom) of the
strand board B, which are more likely to be subjected to load and
impact and are more susceptible to humidity etc., have a larger
thickness than the remaining strand layer(s) 1. This allows the
strand board B to have improved performance regarding influences
from the external environment.
[0164] One or more of the strand layers 1, 1, . . . may have a
different thickness from the remaining strand layer(s) 1. For
example, the thickness w1 of the top and bottom strand layers 1, 1
may be different from the thicknesses w2, w3 of the three
intermediate strand layers 1, 1, . . . . Although not shown in the
figures, all of the five strand layers 1, 1, . . . may have
different thicknesses from each other.
[0165] In the first embodiment, the fiber direction of the strands
5, 5, . . . in every strand layer 1 is perpendicular to that of the
strands 5, 5, . . . in its adjoining strand layer 1. However, the
present invention is not limited to this. For example, the fiber
direction of the strands 1, 1, . . . in a part of the multiple
strand layers 1, 1, . . . may be the same as that of the strands 5,
5, . . . in its adjoining layer 1. For example, in the case where
the strand layers 1, 1 that are different in form of the strands 5,
5, . . . such as length or density of the strands 5, 5, . . . from
each other are formed so as to adjoin each other, the fiber
directions of the strands 5, 5, . . . in these adjoining strand
layers 1, 1 may be the same.
[0166] In the first embodiment, the density or thickness of the
strands 5 (woodbased materials) may be different between or among
the strand layers 1, 1, . . . of the strand board B.
[0167] For example, in the stacking process (mat forming process),
the multiple mats of strands 5, 5, . . . may be stacked so that the
relative density of the strands 5 of the mat gradually increases
from the top and bottom strand layers 1 to the middle strand layer
1 in the thickness direction of the strand board B. When the
multi-layered mat is pressed in the press process, the relative
density of the outer strand layers 1 that are directly subjected to
the pressure of a press machine typically tends to become higher
than that of the inner strand layer(s) 1. Since the relative
density of the strands 5 of the inner strand layer(s) 1 is thus
made higher than that of the strands 5 of the outer strand layers 1
prior to the pressing, the strand board B formed by the pressing
has uniform density distribution in the lamination direction. In
this case, the wood species of the strands 5 may be different or
the same between or among the strand layers 1.
[0168] That is, in a part of the strand layers 1 or all of the
strand layers 1, the wood species, thickness, density, etc. of the
strands 5 of the strand layer 1 can be selected as appropriate
according to required characteristics, cost, etc.
[0169] In the stacking process (mat forming process) of the first
embodiment, the strand mats may be stacked so that at least one of
the multiple strand layers 1, 1, . . . is formed by the strands 5,
5, . . . with a high density. This strand layer 1 is a layer formed
by the strands 5 having a relatively higher density than the other
strand layers 1. Specifically, in the case where the strand board B
has, e.g., an odd number of strand layers 1, the strand mats may be
stacked so that an odd-numbered strand layer 1 from the top or
bottom of the strand board B is formed by the high-density strands
5. The strand mats may be stacked so that a specific one (at least
one) of the multiple strand layers 1, 1, . . . are formed by the
high-density strands 5, 5, . . . according to, e.g., the use of the
strand board B, required strength properties and other performance
of the strand board B, etc. In the case where there are multiple
strand layers 1 that are formed by the high-density strands 5, 5, .
. . , these strand layers 1, 1, . . . may be different in density
and thickness from each other.
[0170] In the second embodiment, the strand board B has an odd
number of strand layers 1, 1, . . . . However, the strand board B
may have an even number of strand layers 1. It is preferable that
the strand board B have an odd number of strand layers 1, 1, . . .
because this allows the strand board B to have similar performance
in its top and bottom parts.
[0171] In the second embodiment, the fibers of the strands 5 extend
in the same direction in each strand layers 1, and the fiber
directions of the strands 5, 5 of adjoining ones of the strand
layers 1 are either perpendicular or parallel to each other.
However, the present invention is not limited to this. The fiber
direction of the strands 5 of each strand layer 1 may be determined
as desired.
[0172] The first and second embodiments are described with respect
to the strand board B formed by stacking and laminating the mats of
the strands 5 into the shape of a board. However, the present
invention is not limited to this strand board B. For example,
multiple strand layers having a rectangular section (in the shape
of squared timber) and having no significant difference between
their thickness and width may be stacked and laminated. In this
case, a strand material (wood laminate material) can be used as a
joist, pillar, etc. formed by stacking and laminating multiple
strand layers.
[0173] The first and second embodiments are examples of the strand
board B formed by stacking and laminating the multiple strand
layers 1, 1, . . . each formed by laminated multiple strands 5, 5,
. . . . However, the present invention is also applicable to, e.g.,
plywood and laminated veneer lumber (LVL). Specifically, veneers
may be used instead of the mats of strands 5. That is, in the case
of plywood and LVL, each woodbased material layer is formed by at
least one veneer.
[0174] In the case where the wood laminate material is plywood or
LVL, a common manufacturing method is used to manufacture plywood
or LVL. Specifically, green wood such as logs or thinnings is cut
with a cutting machine to produce veneers. Multiple veneers are
then stacked together with an adhesive therebetween such that the
fiber directions of adjoining ones of the veneers are the same in
the case of LVL and the fiber directions of adjoining ones of the
veneers are perpendicular to each other in the case of plywood.
Subsequently, the staked veneers are formed by cold pressing or hot
pressing to cure the adhesive.
[0175] In the case where density distribution in the lamination
direction of the woodbased material layers is to be made
substantially uniform as in the first embodiment, the density,
thickness, etc. of each veneer are adjusted before, e.g., the
stacked veneers are formed in the press process.
[0176] In the case where the woodbased material layers consist of a
combination of high-density and low-density woodbased material
layers as in the second embodiment, the density of the woodbased
material or woodbased materials forming each woodbased material
layer is made higher in a part of the woodbased material layers
than in the remainder of the woodbased material layers by wood
species etc. before, e.g., the stacked veneers are formed in the
press process.
EXAMPLES
[0177] Next, specific examples of the strand boards according to
the first and second embodiments will be described. It should be
noted that "examples" and "comparative examples" of the first
embodiment are different from "examples" and "comparative examples"
of second embodiments even though their numbers are the same. The
examples and the comparative examples are specified for each
embodiment.
First Embodiment
Example 1
[0178] Mats of a large number of cypress strands were stacked into
a multi-layered mat having five strand layers and a thickness of 37
mm. The strands were 150 to 200 mm long in the fiber direction, 15
to 25 mm wide, and 0.8 to 2 mm thick and had a density of 500 to
600 kg/m.sup.3. The multi-layered mat was then subjected to hot
pressing at 140.degree. C. and 4 N/mm.sup.2 for 10 minutes, whereby
a strand board with a density of 818 kg/m.sup.3 and a thickness of
12.4 mm was obtained. This strand board was used as Example 1.
[0179] FIG. 10 shows an image of Example 1. In FIG. 10, reference
character "B" indicates the strand board and "1" indicates the
strand layers. FIG. 11 shows the results of a bending test, a
dimensional change test, and a water absorption test for Example 1.
FIG. 12 shows the density distribution in the thickness direction
(lamination direction) of the strand board measured with a density
profile analyzer ("DENSE-LAB X" made by ELECTRONIC WOOD SYSTEMS
GMBH).
Example 2
[0180] Mats of a large number of Douglas fir strands were stacked
into a multi-layered mat having five strand layers and a thickness
of 36 mm. The strands were 150 to 200 mm long in the fiber
direction, 15 to 25 mm wide, and 0.8 to 2 mm thick and had a
density of 450 to 550 kg/m.sup.3. The multi-layered mat was then
subjected to hot pressing at 140.degree. C. and 4 N/mm.sup.2 for 10
minutes, whereby a strand board with a density of 832 kg/m.sup.3
and a thickness of 12.2 mm was obtained. This strand board was used
as Example 2. FIG. 11 shows the results of the bending test, the
dimensional change test, and the water absorption test for Example
2.
Comparative Example 1
[0181] Mats of a large number of cypress strands were stacked into
a multi-layered mat having five strand layers and a thickness of 42
mm. The strands were 150 to 200 mm long in the fiber direction, 15
to 25 mm wide, and 0.8 to 2 mm thick and had a density of 400 to
500 kg/m.sup.3. The multi-layered mat was then subjected to hot
pressing at 140.degree. C. and 8 N/mm.sup.2 for 10 minutes, whereby
a strand board with a density of 779 kg/m.sup.3 and a thickness of
12.7 mm was obtained. This strand board was used as Comparative
Example 1. FIG. 11 shows the results of the bending test, the
dimensional change test, and the water absorption test for
Comparative Example 1. FIG. 13 shows the density distribution in
the thickness direction (lamination direction) of the strand board
measured with the density profile analyzer ("DENSE-LAB X" made by
ELECTRONIC WOOD SYSTEMS GMBH).
Comparative Example 2
[0182] Mats of a large number of Douglas fir strands were stacked
into a multi-layered mat having five strand layers and a thickness
of 35 mm. The strands were 150 to 200 mm long in the fiber
direction, 15 to 25 mm wide, and 0.8 to 2 mm thick and had a
density of 350 to 450 kg/m.sup.3. The multi-layered mat was then
subjected to hot pressing at 140.degree. C. and 8 N/mm.sup.2 for 10
minutes, whereby a strand board with a density of 812 kg/m.sup.3
and a thickness of 12.4 mm was obtained. This strand board was used
as Comparative Example 2. FIG. 11 shows the results of the bending
test, the dimensional change test, and the water absorption test
for Comparative Example 2.
[0183] The results in FIG. 11 show that Example 1 is higher in
density, flexural strength, modulus of rupture (MOR), and modulus
of elasticity (MOE) than Comparative Example 1. Percentage
dimensional change and water absorption of Example 1 are about the
same as those of Comparative Example 1. Example 2 has a higher
density than Comparative Example 2, approximately the same flexural
strength and MOR as Comparative Example 2, and a higher MOE than
Comparative Example 2. Percentage dimensional change and water
absorption of Example 2 are about the same as those of Comparative
Example 2.
[0184] The results in FIGS. 12 and 13 show that Example 1 has
substantially constant density distribution in the lamination
direction of the multiple strand layers as compared to Comparative
Example 1. The substantially constant density distribution includes
such density distribution that, in the case where the measurement
result of the density distribution varies as shown in, e.g., FIGS.
12 and 13, the median shown by dashed line as shown in each figure
does not vary significantly but is substantially constant. For
example, as can be seen from comparison between the dashed line
shown in FIG. 12 (Example 1) and the dashed line shown in FIG. 13
(Comparative Example 1), the median of the density distribution
shown in FIG. 12 varies less than the median of the density
distribution shown in FIG. 13, and the median of the density
distribution shown in FIG. 12 is substantially constant.
[0185] Since the density distribution is substantially constant,
the strand board has uniform density distribution and overall water
resistance and strength (shear strength etc.) of the strand board
are improved. Specifically, a portion with a low density has lower
water resistance and strength than a portion with a high density.
Accordingly, if the density distribution is uneven, the overall
performance of the strand board is governed by the water resistance
and strength of the portion with a low density. However, in the
case where the density distribution is substantially constant, such
a portion that becomes a bottleneck for performance can be
eliminated.
[0186] The above bending test was conducted in accordance with
IICL_Floor_Performance TB001 Ver. 2. The dimensional change test
and the water absorption test were conducted in accordance with the
cyclic boiling test of Japanese Agricultural Standard for
plywood.
Second Embodiment
Example 1
[0187] Mats of a large number of aspen strands were stacked into a
multi-layered mat having five strand layers and a thickness of 53
mm. The strands had a thickness of 0.8 mm and a density of 300 to
600 kg/m.sup.3. As in the second example (see FIG. 4) of the strand
board of the second embodiment, strands with common densities
(average value: 393 kg/m.sup.3) were used for the second to fourth
strand layers located in the intermediate part in the lamination
direction out of the five strand layers. Strands with higher
densities (average value: 557 kg/m.sup.3) than the common densities
were used for the first and fifth strand layers located at both
ends in the lamination direction.
[0188] The multi-layered mat was then subjected to hot pressing at
160.degree. C. and 4 N/mm.sup.2 for 8 minutes. The strand board
thus obtained was used as Example 1. The time required to achieve a
target thickness, namely the time required to press the
multi-layered mat to a target thickness, was 24 seconds.
Example 2
[0189] A multi-layered mat having five strand layers and a
thickness of 52 mm was formed in a manner similar to that in
Example 1. Strands having a density (average value: 805 kg/m.sup.3)
higher than Example 1 were used for the first and fifth strand
layers located at both ends in the lamination direction out of the
five strand layers. The multi-layered mat was then subjected to hot
pressing under conditions similar to those in Example 1. The strand
board thus obtained was used as Example 2. The time required to
achieve a target thickness was 12 seconds. Example 2 is otherwise
the same as Example 1.
Comparative Example 1
[0190] A multi-layered mat having five strand layers and a
thickness of 62 mm was formed in a manner similar to that in
Example 1. Strands with common densities (average value: 393
kg/m.sup.3) were used for all of the five strand layers. The
multi-layered mat was then subjected to hot pressing under
conditions similar to those in Example 1. The strand board thus
obtained was used as Comparative Example 1. The time required to
achieve a target thickness was 33 seconds. Comparative Example 1 is
otherwise the same as Example 1.
[0191] (Test A)
[0192] A normal-state bending test (bending test span: 225 mm) was
conducted on each of Examples 1, 2 and Comparative Example 1. FIG.
14 shows the test results along with other physical properties.
[0193] Density distribution in thickness direction (lamination
direction) of each strand board was measured with the density
profile analyzer ("DENSE-LAB X" made by ELECTRONIC WOOD SYSTEMS
GMBH). FIG. 15 shows the measurement results.
[0194] The results in FIG. 14 show that, as can be seen from
comparison between Examples 1, 2 and Comparative Example 1, the use
of high-density strand layers as the first and fifth strand layers
located at the top and bottom out of the five strand layers allows
the multi-layered mat before hot pressing to have a smaller
thickness (bulk height) and thus facilitates compression of the
multi-layered mat by hot pressing, thereby reducing the press time
required to press the multi-layered mat to a target thickness (time
to achieve the target thickness). Regarding flexural properties in
the normal-state bending test, MORs and MOEs of Examples 1, 2 are
about the same as those of Comparative Example 1.
Example 3
[0195] Mats of a large number of aspen strands were stacked into a
multi-layered mat having five strand layers and a thickness of 70
mm. The strands had a thickness of 0.8 mm and a density of 300 to
600 kg/m.sup.3. As in the first example (see FIG. 3) of the strand
board of the second embodiment, strands with common densities
(average value: 393 kg/m.sup.3) were used for the first, third, and
fifth strand layers of the five strand layers, namely the strand
layers other than the second and fourth strand layers located in
the intermediate part in the lamination direction. Strands with
higher densities (average value: 933 kg/m.sup.3) than the common
densities were used for the second and fourth strand layers.
[0196] The multi-layered mat was then subjected to hot pressing at
140.degree. C. and 4 N/mm.sup.2 for 10 minutes, whereby a strand
board having a density of 846 kg/m.sup.3 and a thickness of 12.5 mm
was obtained. This strand board was used as Example 3. The MDI
content or dozing was 12%.
Comparative Example 2
[0197] A multi-layered mat having five strand layers and a
thickness of 78 mm was formed in a manner similar to that in
Example 3. Strands with common densities (average value: 393
kg/m.sup.3) were used for all of the five strand layers. The
multi-layered mat was then subjected to hot pressing at 140.degree.
C. and 8 N/mm.sup.2 for 10 minutes, whereby a strand board having a
density of 846 kg/m.sup.3 and a thickness of 12.6 mm was obtained.
This strand board was used as Comparative Example 2. Comparative
Example 2 is otherwise the same as Example 3.
[0198] (Test B)
[0199] A normal-state bending test and a boiling test were
conducted on Example 3 and Comparative Example 2. The boiling test
was conducted in accordance with the cyclic boiling test defined in
Japanese Agricultural Standard for Plywood. After the boiling test
was conducted twice, thickness swelling TS, water absorption WA,
and internal bond strength IB were measured. FIG. 14 shows the
measurement results along with other physical properties.
[0200] FIG. 17 shows density distribution in the thickness
direction (lamination direction) of each strand board measured with
the density profile analyzer as in Test A.
[0201] The results in FIG. 16 show that, regarding Example 3 in
which the second and fourth strand layers located in the
intermediate part in the thickness direction out of the five strand
layers are high-density strand layers and Comparative Example 2 in
which all of the five strand layers are low-density strand layers,
flexural strength and internal bond strength IB after the boiling
tests of Example 3 are either the same or higher than Comparative
Example 2. Namely, the flexural strength and internal bond strength
IB after the boiling tests of Example 3 are not lower than
Comparative Example 2.
[0202] The results thus show that the use of high-density strand
layers as the second and fourth strand layers of the five strand
layers allows a strand board with performance similar to that of
Comparative Example 2 to be formed by using a lower pressure of 4
N/mm.sup.2 instead of such a high pressure (8 N/mm.sup.2) as used
in Comparative Example 2.
Example 4
[0203] Mats of a large number of aspen strands were stacked into a
multi-layered mat having five strand layers and a thickness of 130
mm. The strands had a thickness of 0.8 mm and a density of 300 to
600 kg/m.sup.3. As in the sixth example (see FIG. 8) of the strand
board of the second embodiment, strands with common densities
(average value: 413 kg/m.sup.3) were used for the first and fifth
strand layers of the five strand layers, namely for the strand
layers other than the second to fourth strand layers located in the
intermediate part in the lamination direction. Strands with higher
densities (average value: 1100 kg/m.sup.3) than the common
densities were used for the second to fourth strand layers.
[0204] The multi-layered mat was then subjected to hot pressing at
160.degree. C. and 8 N/mm.sup.2 for 60 minutes, whereby a strand
board having a predetermined density and thickness (see FIG. 18)
was obtained. This strand board was used as Example 4.
Comparative Example 3
[0205] A multi-layered mat having five strand layers was formed in
a manner similar to that in Example 4. Strands with common
densities (average value: 413 kg/m.sup.3) were used for all of the
five strand layers. The multi-layered mat was then subjected to hot
pressing at 140.degree. C. and 8 N/mm.sup.2 for 60 minutes, whereby
a strand board having a predetermined density and thickness (see
FIG. 18) was obtained. This strand board was used as Comparative
Example 3. The processes were otherwise the same as those of
Example 4.
Comparative Example 4
[0206] A multi-layered mat having five strand layers was formed in
a manner similar to that in Example 4. Strands with common
densities (average value: 413 kg/m.sup.3) were used for all of the
five strand layers. The multi-layered mat was then subjected to hot
pressing at 160.degree. C. and 8 N/mm.sup.2 for 30 minutes, whereby
a strand board having a predetermined density and thickness was
obtained. This strand board was used as Comparative Example 4. In
Comparative Example 4, hot pressing was performed at a higher
temperature than in Comparative Example 3 in order to avoid
insufficient curing of an adhesive during winter time. Comparative
Example 4 is small in size, and the press time was shorter than in
Example 4 and Comparative Example 3. The processes were otherwise
the same as those of Example 4.
[0207] (Test C)
[0208] A normal-state bending test, a boiling test, and a bond
durability test were conducted on Example 4 and Comparative Example
3. FIG. 18 shows the test results along with other physical
properties. In FIG. 18, "Elastic Limit Pmax" refers to elastic
limit load, "Ratio of ELP" refers to the ratio of Elastic Limit
Pmax to maximum load (Pmax), and "Inside Share Strength" refers to
internal shear fracture strength. Regarding the bending direction,
"longitudinal" refers to the longitudinal direction of the board,
"lateral" refers to the lateral direction of the board, and "N=2
(N=3)" means that the number of test pieces was 2 or 3. Moreover,
"TS" indicates thickness swelling, "WA" indicates water absorption,
and "IB" indicates internal bond strength.
[0209] A nail pull test was conducted on Example 4 and Comparative
Example 4. In the nail pull test, a lead hole with an inside
diameter of 2 mm and a depth of 25 mm was formed in advance in each
sample of Example 4 and Comparative Example 4. Three samples of
Example 4 and four samples of Comparative Example 4 were tested,
and the average value of the samples was calculated for each of
Example 4 and Comparative Example 4. FIG. 19 shows the results.
[0210] FIG. 20 shows density distribution in the thickness
direction (lamination direction) of each strand board measured with
the density profile analyzer as in Test A.
[0211] The results in FIG. 18 show that, regarding Example 4 in
which the second to fourth strand layers located in the
intermediate part in the lamination direction out of the five
strand layers are high-density strand layers and Comparative
Example 3 in which all of the five strand layers are low-density
strand layers, flexural strength of Example 4 is about the same as
that of Comparative Example 3, and internal bond strength after the
boiling test of Example 4 is higher than that of Comparative
Example 3.
[0212] These results show that the use of high-density strand
layers as the second to fourth strand layers of the five strand
layers allows a strand board with performance similar to that of
Comparative Example 3 to be formed.
[0213] The results of FIG. 19 show that the use of high-density
strand layers as the second to fourth strand layers located in the
intermediate part in the thickness direction out of the five strand
layers increases nail pull resistance (force) and achieves
improvement in performance.
INDUSTRIAL APPLICABILITY
[0214] The present invention is suitable for use as flooring
materials for containers, watercraft, vehicles, etc. The present
invention is extremely useful as new building materials that are
suitable for use as flooring materials and structural bracing
boards for buildings such as houses. The present invention thus has
high industrial applicability.
DESCRIPTION OF REFERENCE CHARACTERS
[0215] B Strand Board (Wood Laminate Material) [0216] 1 Strand
Layer (Woodbased Material Layer) [0217] 1a High-Density Strand
Layer (High-Density Woodbased Material Layer) [0218] 1b Low-Density
Strand Layer (Low-Density Woodbased Material Layer) [0219] 5 Strand
(Cut Piece)
* * * * *