Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WOODY BOARD
BACKGRO~ND OF THE INVENTION
Fiel~_e~_~h~ ention
The present invention relates to a woody board, which has sufficient
~echanical strength as a woody material and which has a smooth surface.
Description of Prior Art
Various simplex boards prepared by separately shaping a wood powder,
woody fibers or wood chips, optionally along with a binder, under pressure
have heretofore been known, but a composite board composed of a plurality
of such simplex boards is unknown.
A wood powder and woody fibers are well known in this technical field.
Briefly, the former is one obtained by ~inely pulverizing wood like
sawdust; and the latter are obtained by disintegrating wood into fibers.
Wood chips in this case are also known, which are obtalned by shaving or
cutting a wood ba.r from the top end thereof, with the bar being rotated in
the same way that a pencil is shaven, into chips each having a si~e oE
about 1.5 mm or less as the thickness, about 30 mm or less as the width and
about 100 mm or less as the length. Examples of molded boards made oE such
woody material will be mentioned. Example of simplex boards made of a wood
powder, are particle boards; examples of simplex boards made of woody
fibers are hard boards, middle density fiber boards (MDF) and insulation
boards; and examples of simplex boards made of wood chips, are strand
boards and oriented strand boards ~OSB).
These boards have both merits and demerits, and they often cause some
inconvenience in actual use thereof.
In manufacturing stairs, service counters, doors and the like, when
substrates which have a sufficient thickness and a sufficient mechanical
strength and wh;ch have a smooth surface capable of being covered with a
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decorative sheet with screws are needed, but the above-mentioned simplex
boards could not be used as such substrates. Of these boards, a hard board
may be mentioned to have a relatively high mechanical strength and a
relatively satisfactory surface smoothness. However, it is impossible to
obtain a hard board having sufficient thickness. Additionally, since a
hard board is prepared by a wet method, it has a large specific gravity and
is therefore defectively extremely heavy. Further, screws do not hold well
in hard board as the board has a low screw-drawing resistance value.
It may be considered to laminate an MDF having a sufficient surface
smoothness onto the both surfaces of a strand board or OSB, but adhesion
between them would be poor and unstable since the strand board and OSB have
a poor surface smoothness. Fven if they could be laminated, the resulting
laminated product will have the problem that the laminating cost is high
since double lamination is necessary. In addition, as an MDF has low
mechanical strength, it is diEficult to prepare a too thin MDF. As a
result, where the both surfaces of a strand board or OSB are laminated with
such a thick MDF by double lamination, the resulting laminate would thereby
have a lowered mechanical strength, disadvantageously.
In addition to the above-mentioned boards, where a plywood or L~L
(laminated veneer lumber) is made from a coniferous tree material, there
occurs a problem that the woody product could hardly have a smooth surface.
This is because when a coniferous tree material is formed into veneers, in
general, the surfaces often have knots and cracks. There are few
coniferous trees which have no drawbacks, like lauan and other trees from
the South Sea Islands. Though there would be some knot-free good tree
materials to be derived from coniferous trees, the amount is small and the
cost thereof ls high. Additionally, even defectless coniferous tree
materials often giva shaped articles having uneven surfaces because of the
pressure as applied thereto for shaping under pressure, since the hardness
of them is not constant but various depending upon the winter-grown part
being hard and the summer-grown part being soft.
Undar the situation, in order to overcome the problems, there have
been proposed a patching method of cutting out the knots in the surface
veneer followed by embedding wood patches in the cut out parts and a method
of laminating a woody material having a smooth surface, such as an MDF
PAT 1768~-1
(middle density fiber board) to the both surEaces of a substrate woody
material. However, the former pa-tching method causes a disadvantageous
drawbac~ that the outward appearance of the patched surface is bad due to
the existence of embedding traces. Even though an additional thin
decorative paper or decorative veneer is laminated as a secondary
lamination so as to cover the patched surface, such an unfavorable outward
appearance of the patched surface would still appear through the surface of
the covered decorative paper or veneer.
On the other hand, the latter method also has a troublesome problem
that the mechanical strength of the resulting laminate board is low,
because of the following reasons. In general, an MDF could not be thinner
than 3 mm, as too thin MDF sheets would curve owing to insufficient
strength. Therefore, even when the thinnest MDF sheet having a thickness
of 3 mm is laminated to the both surfaces of a substrate woody material by
the method, the resulting plywood is to have a total thickness of the both
laminated MDF's of being 6 mm, so that the mechanical strength of the
plywood is lowered relative to the thickness. In this connection, if an
MD~ sheet is laminated onto only one surface of a subs-trate, the resulting
plywood laminate is also disadvantageous as it is often warped.
S~MMARY OF THE INVENTION
The present invention provi.des a woody board, which has good phys:Lcal
properties with respect to the mechanical strength, the surfnce smoottmess
and the screw-drawing resistance value and which is prepared at a low
manufacture cost.
The present invention also provides a method of preparing a woody
board having a good surface smoothness and a sufficient mechanical
strength.
The present invention also provides a method of preparing a woody
material of a coniferous tree material, which has a woody substrate of a
coniferous tree woody material and which has a smooth surface with neither
warp nor reduction of the mechanical strength.
Specifically, there i5 provided in accordance with the present
invention a woody board, which is characterized in that said woody board
PAT 17688-1
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uses a coniferous tree material of a coniferous tree plywood or coniferous
tree LVL as a woody substrate and is formed with molded layer of woody
material such as wood powder or woody fibers on one surface or both
surfaces of the woody substrate. In preparing such a woody board oE the
present invention, it is desired, if possible, tha-t the woody substrate and
the molded layer of a woody material are pressed simultaneously under heat
and pressure.
DETAILED DESCRIPTION OF THE INVENTION
As one embodiment, the present invention provides a method of
preparing a woody board in which a woody substrate of coniferous tree LVL,
coniferous tree plywood or the like is sandwiched between molded layers of
a woody material such as a wood powder or woody fibers to form a woody
board, and the method is carried out by first forming a woody material
layer of a wood powder or woody fibers, as previously blended with an
adhesive by spraying, then putting an LVL, plywood or the like thereon, and
thereafter further :Eorming said woody material layer thereon, whereupon al].
the piled-up layers are integrated by hot-pressing under pressure and heat.
In this case, the coniferous tree plywood or LVL may be either in the form
of a previously shaped one or in the form of a combination of plural
veneers as merely piled up prior to being shaped into a plywood.
The raw material of a board to be used in the present invention, which
comprises a woody material of a wood powder or woody fibers and an
adhesive, may be one tv be speciEica:Lly prepared for repairing or may also
be any general raw material for ordinary particle boards or fiber boards.
Therefore, as a woody material for use in the present invention, a wood
powder as well as fine wood chips to be prepared by finely pulverizing a
wood material and small wood flakes to be obtained by cutting or shaving a
wood material, and also shaped bodies to be formed by shaping such a wood
powder, wood chips or wood flakes under pressure, and fibrous materials of
them may be employed. The particle size of the wood powder as well as the
size of the wood flakes may well be selected and determined in accordance
with the intended surface smoothness of the final product of a woody board.
Recently, a special attention has been paid to a middle density fiber
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board (MDF), which is said to have a property similar t~ a plywood. As the
material of such a board is composed of fine woody fibers, the final
product to be obtained by using it may thereby have a better surface
smoothness. Therefore, it is recommended to employ the raw material.
The hot-pressing method of forming the woody board of the present
invention may be either a hot plate-pressing method or a hot roll-pressing
method. As a heating means in the method, a hot plate or a hot roll may be
applied to the materials to be laminated and molded under pressure, or hot
steam may also be applied thereto under pressure. If desired, the
materials to be laminated and molded may previously be heated by blowing
hot steam thereon or by heating them in an oven, and the thus preheated
materials may be pressed and integrated to obtain the intended woody board.
As the adhesive to be applied to the respective molding materials and
laminates of the present invention, a hot-gluing adhesive is used since the
molding materials and laminates are pressed under heat to give an
integrated woody board. Any conventional adhesives well known in this
technical field, such as phenolic resins and melamine resins, can be used
for the purpose. Where thermosetting and water-proofing resins such as
melamine resins are selectively used, the water-proofness of the molded
board layers is advantageously improved.
The thickness of the molded layer of a woody mate.rial may well be
increased or decreased in accordance with the object of the woody board to
be prepared. For instance, where the ob;ect of the board is to have merely
a smooth surface, the layer of the molded layer may be thin to have a
thickness of from 1 to 2 mm after shaped. On the other hand, where the
surface of the woody material is to be further cut and machined, the
thickness may bs approximately from 5 to 10 mm.
It is preferred that the molded layer of a woody material is put on
the both surf~ces of the substrate both in the same thickness, in view of
the balance to be formed. In accordance with the present invention,
however, since the thickness of the molded layer of a woody material may
well be similar to that of the substrate, it is possible to prepare a one
side-molded woody board with no warp and it is also possible to prepare a
both sides-molded woody board where each molded layer on each surface has a
different thickness.
PAT 17688-1
The woody material for the molded layer may be elther in the form of
an already cold-pressed sheet or an adhesive applied but no-t cold-pressed
sheet. In the latter case, the woody material is in the form of a compound
of a wood powder or woody fibers as already blended with an adhesive. If
desired, the woody material for molded layer may also be in the Eorm of a
sheet to be obtained by pre-hot-pressing the woody material along with an
adhesive. In that case, a two-staee polymerizing resin may advantageously
be used as an adhesive. Precisely, the respective woody material layers
may be preshaped by the first hot pressing and thereafter they are
integrated by the ne~t hot-pressing.
Where a plywood or LVL ls used as the woody substrate in preparing the
woody board of the present invention, a coniferous tree plywood or a
coniferous tree LVL is preferred in view of the obiect of the present
invention. An adhesive may be coated to such a coniferous tree molded to
give a molded coniferous tree plywood or LVL. The resulting coniferous
tree plywood or LVL layer can be used as a molded substrate. The woody
substrate may also be in the form of a sheet as prepared by hot-pressing
the corresponding plywood or LVL piled strips, or in the form of cold-
pressed piled strips prior to hot-pressing, or itl the form of an adhesive-
applied but not cold-pressed layer of veneers or laminates. Anyhow, all
the woody substrate materials may be hot-pressed with putting other raw
board materials thereon to give the woody board of the present invention.
Where a board only is formed of an MDF, the mechanical strength of the
resulting MDF board is lowered so that the fle~ibility of the board is
large, as mentioned above. Therefore, a satisfactory board, e.g., large-
sized board, could not be formed of such an MDF. In addition, since an MDF
board is often wavy or warped, the thickness thereoE is generally up to 3
mm. Because of these reasons, a thin and strong woody material could not
be obtained by molding of MDF layers. In accordance with the present
invention, however, where a woody substrate is a coniferous tree LVL, a
woody material layer is formed on one or both surfaces of the woody
substrate so that the board layer may well have a thickness oE 3 mm or less
in order to obtain the intended woody board. As a result, the woody board
to be obtained by the present invention may have a smooth surface and a
high mechanical strength.
PAT 17688-1
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In addition, in accordance with the present invention, an extremely
thin woody material molded layer May be formed on the surface(s) of the
woody laminate substrate. Therefore, even though the coat is formed on
only one surface of the substrate to form a one surface-molded board, the
resulting one surface-molded ~oard is advantageously free from warping.
The present invention will be explained in more detail by way of the
following examples, which, however, are not intended to restrict the scope
of the present invention. Unless otherwise specifically indicated, "%" is
% by weight in these examples.
E~AMPLE 1
A melamine resin adhesive was applied to five sheets of Douglas fir
rotary veneer each having a thickness of 2.5 mm in the direction
perpendicular to the fibrous direction of each sheet by a known method of
forming a conventional plywood, and the thus adhesive coated sheets were
cold-pressed to form a woody substrate. The veneers constituting the
surfaces of the substrate had 25 knots each having a diameter of
approximately 35 mm in an area of 1850 mm x 980 mm.
On the other hand, as woody material, wood of Douglas fir rotary
veneer was finely pulverized, and ths resulting wood powder was blended
with 12~ of a melamine resin adhesive by spraying to prepare an MDF
material. This was put in an iron plate in a thickness of 15 mm, and the
previously cold-pressed plywood was layered thereover. Further, the wood
powder was layered over the plywood in a thickness of 15 mm.
The thus piled-up woody layers were inserted into a hot pressing
machine along with the iron plate, where they are hot-pressed at a
temperature oE 130C and a pressure of 12 kg/m2 for 10 minutes.
Accordingly, a flat and smooth 14.5 mm thick woody board having a board
layer of one mm thickness on both surfaces thereof was prepared.
A decorative veneer of Douglas fir having a thickness of 0.6 mm was
stuck to one surface of the woody board to give a decorative plywood having
an extremely flat and smoothly finished surface.
PAT 17688-1
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~ 35
EX~MPLE 2
In accordance wîth the same process as in Example 1, except that the
woody material layer was put on only one surface of the cold-pressed
plywood substrate, a woody board having one smooth and flat surface was
obtained by hot-pressing.
The woody board thus obtained warped with the smooth surface being
convex in such a condition that the arrow height was 1.5 mm along the
length of 1850 mm. However, warping of such a degree has heretofore been
said to cause no problem in practical use of the board, and the board
withstood the product standard test.
COMPARATIVE EXAMPLE 1
In accordance with the same process as in Example 1, except that the
thickness of the rotary veneer of Douglas fir, which was 2.5 mm in Example
1, was varied to 1.7 mm, a laminate substrate was prepared. Both surfaces
of the substrate were coated with an MDF having a thickness of 3 mm, in
place of the woody material as used in Example 1. The thus piled-up woody
layers were then hot-pressed in the same way as in Example 1 to obtained a
woody material having the same thickness as that obtained in Example 1.
The thus prepared woody material had a low and insufficient mechanical
strength relative to the thickness thereof and therefore it was not
suitable to prac-tical use. The mechanical strength values of the product
are shown in Table 1 below.
COMPARATIVE EXAMPLE 2
The same process as in Comparative Example 1 was repeated, except -that
an MDF was coated on only one surface by hot-pressing. Though the woody
material product obtained had a smooth surface, it warped with the MDF
coated surface being convex in such a condition that the arrow height was
13 mm in the direction of the length of being 1850 mm.
The warp was too large so that the product was not useful.
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COMPARATIVE EXAMPLE 3
The same process as in Example 1 was repeated, except that the
thickness of the rotary veneer of Douglas fir rotary veneer, which was 2.5
mm in Example 1, was varied to 2.9 mm and that the woody material was not
used, but a coniferous tree plywood was only used. Accordingly, a
decorative plywood havi.ng almost the same thickness as that of the product
oE Example 1 was prepared.
The decorative plywood thus prepared had many knots and cracks, and
the outward appearance thereof did not stand the test.
The physical data of the products obtained in the above-mentioned
examples and comparative examples are shown in Table 1 below.
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Table 1
Bending
Bending Young's
Strength Modulus Arrow Height Outward
(kg/m2) (x 103 kg/m2) oE Warp (mm) Appearance
Example 1 555 5.15 0 0
Example 2 542 5.25 1.5 0
15 Comparative
Example 1 342 3.11 0 0
Comparative
Example 2 524 5.29 13 0
Comparative
Example 3 683 10.04 0
Note: Arrow height of warp Indicates the hei~ht of the warp at the center
along the length of 1850 mm.
As is understood ~rom the results and data obtained in the above-
mentioned examples and comparative examples, substantially warp-free woody
boards and decorated boards ~lich have smooth and flat outward surfaces and
which have sufficient mechanica]. strength are obtained by the method of the
prasent invention, and the industrial advantage of the present invention is
noticeable.
~ hile the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the art
that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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