Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MANUFACTURING METHOD FOR WOOD BOARDS
Background of the Invention
Field of the Invention
The present invention relates to a manufacturing method for
wood boards, and in particular, relates to a manufacturing
method for strand boards which are capable of maintaining
superior surface smoothness over a long period of time.
Background Art
In recent years, the insufficiency of lumber resources and
the protection of the forests have become problems, and it is
clear that it will be increasingly difficult to obtain timber
from forests. Accordingly, the supply of board materials such
as plywood, which are produced using large amounts of raw
material lumber, will be uncertain, or will be insufficient, and
the cost thereof is also expected to rise greatly. Accordingly,
wood boards which can be obtained from the efficient use of
wooden strands or ligneous fibers of wooden strands, or the
like, which were conventionally regarded as waste materials,
have attracted attention, and the application of such wood
boards to such various uses has been strongly desired.
Among such wood boards, fiber boards formed from ligneous
fibers and strand boards formed from wooden strands are known.
Commonly, in cases in which materials having small dimensions
such as ligneous fibers are employed, the wood board which is
obtained is uniform, and the surface thereof is smooth; however,
the density thereof is high, and the strength and rigidity are
insufficient. On the other hand, in the case of strand boards
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which employ wooden strands, since strands are employed which
are large in comparison with the ligneous fibers, it is possible
to provide strength and density which approach those of natural
lumber.
Such strand boards are produced by applying binder to
wooden strands and subjecting these to forming and thermal
compression molding. After molding, the surface of such strand
boards has a large degree of irregularity, so that normally,
such boards are employed after sanding the surface thereof and
bonding a decorative single sheet or the like thereto. This
sanding is commonly carried out after storing the strand boards
for a period within a range of from a few hours to a few days at
room temperature after the thermal compression molding thereof.
However, during the thermal compression molding of the
strand boards described above, a high temperature and high
pressure are applied under conditions of high humidity caused by
the moisture contained in the adhesive, so that irregularities
resulting from the cutting of the wooden strands or
irregularities present in the wooden strands are subject to
plastic deformation, and desiccation is conducted in this state.
After the molding, the wood board is stored at room temperature
for a period of a few days, and thus the strand boards were
subjected to the sanding process. Accordingly, even though the
surface of such strand boards was sanded so as to provide smooth
surfaces, nevertheless, the wood board is gradually swelled over
a period of time after the sanding by moisture in atmosphere, so
that, for example, there were problems in that after finished
products were shipped, irregularities appeared on a surface
sanded once so as to provide a smooth surface.
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Furthermore, recently, wood boards have been obtained which
have improved surface smoothness as a result of the provision of
a layer comprising ligneous fibers at the surface of a strand
board produced by thermal compression molding. However, in such
a case, while the surface smoothness is improved, this leads to
an increase in manufacturing costs of the wood board as a whole,
and furthermore, a ligneous fiber layer having poor strength is
provided at the surface, and there are thus problems in that the
physical characteristics as a flooring material worsen.
Summary of the Invention
Accordingly, it is an object of the present invention to
provide a method for producing a strand board which is capable
of maintaining superior surface smoothness over a long period of
time without the provision of a surface-smoothed layer, such as
a ligneous fiber layer or the like, at the surface thereof.
This object can be attained by means of a manufacturing
method for wood boards which is characterized in comprising: a
molding process including the steps of: shaving lumber to
produce wooden strands; applying a binder to the wooden strands;
and subjecting the wooden strands, to which a binder has been
applied, to forming and to thermal compression molding so as to
obtain a molded material; and
a smoothing process including the steps of: moisturizing
the molding material obtained by means of the molding process;
and then abrading a surface thereof.
In accordance with the manufacturing method of wood boards
of the present invention, a process is conducted in which the
plastic deformation resulting from the thermal compression
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molding of the wooden strands, which was a cause of the
degradation of the surface smoothness of the wood boards, is
forcibly manifested in advance by means of forcible
moisturizing, and after this, abrading of the surface is
conducted and irregularities in the surface are removed.
Accordingly, wood boards produced in accordance with the
manufacturing method of the present invention contain no plastic
deformation therein, and are capable of maintaining surface
smoothness over a long period of time.
Furthermore, in the manufacturing method in accordance with
the present invention, it is possible to conduct the molding
process and the smoothing process in a continuous manner, or to
conduct these processes in a separated manner, so that
commercially available strand boards can be used effectively,
and it is possible to obtain a wood board having superior
durability.
Brief Description of the Drawings
Fig. 1 shows an example of a highly suitable apparatus for
conducting moisturizing in the smoothing process of the method
in accordance with the present invention.
Fig. 2 shows the structure of a steam injection plate which
is used in the apparatus shown in Fig. 1.
Fig. 3 is a graph showing the relationship between the
water content and the flexural strength of the wood board.
Fig. 4 is a graph showing the relationship between the
water content and the flexural Young's modulus of the wood
board.
Fig. 5 is a graph showing the relationship between the
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water content and the wet swelling coefficient of the wood
board.
Fig. 6 shows the surface contours, in a wet state, of a
wood board produced according to the manufacturing method of the
present invention.
Fig. 7 shows the surface contours, in a wet state, of a
conventional wood board.
Fig. 8 is a graph showing the relationship between the
moisturizing period and the water content of the wood board when
the moisturizing conditions are altered.
Fig. 9 is a graph showing the relationship between the
moisturizing period and the degree of swelling of the wood board
when the moisturizing conditions are changed.
Fig. 10 is a graph showing the change in the degree of
swelling of the wood board in cases in which the water content
is increased and decreased.
Fig. 11 is a flow chart showing an example of processes in
the manufacturing method in accordance with the present
invention.
Description of the Preferred Embodiments
Hereinbelow, the preferred embodiment of the present
invention will be explained in detail with accompanied drawings.
In a preferred embodiment of the manufacturing method for
oriented strand boards in accordance with the present invention,
first, wooden strands are shaved from lumber as in S1 of Fig.
11. Here, the lumber is not particularly restricted; for
example, pulp wood or small diameter trees, or odd ends
discarded by sawmills or lumber mills as waste material, of a
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coniferous or broadleaf type such as Japanese red pine, larch,
silver fir, fir, aspen, lodgepole pine, or the like, may be
suitably employed. This raw lumber may be dressed, where
necessary, and is supplied to a cutting machine such as a
shaving machine or the like and is cut, and thus wooden strands
are produced. The length, width, thickness and the like of the
wooden strands which are produced are not particularly
restricted; these dimensions may be appropriately set in
accordance with the use of the wood board which is to be
produced or the characteristics which are required.
Next, a binder is applied to these wooden strands (S2 in
Fig. 11): The method of application is not particularly
restricted; however, application by means of a spray method is
preferable. For example, a method in which the wooden strands
described above.are placed in a rotating drum rotating at low
speed, and the binder is applied by means of a spray as the
strands tumble within the drum, or a similar method, may be
advantageously employed.
The binder which is applied here may comprise a foaming
binder, a non-foaming binder, or a mixture thereof; however, in
the case in which a decrease in density of the wood board is
primarily desired, it is preferable that a foaming binder be
used as the main component, while in the case in which an
increase in releasability from the thermal compression plate
used for molding is primarily desired, it is preferable that a
non-foaming binder be the primary component.
Here, what is meant by a "foaming binder" is a binder which
bonds the wooden strands in the wood board to one another and
which itself creates foam; it is preferable that the resin
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component be present solely at the intersection points between
wooden strands, which reduces the amount of resin component used
by expanding the small spaces between wooden strands with foam
cells, and which thus reduces the density of the wood board.
Such a foaming binder may comprise a self-foaming resin, or may
comprise a non-foaming resin and a foaming agent. Examples of
self-foaming resin include foaming polyurethane resin. Examples
of non-foaming resins which are made to foam using a foaming
agent include, for example, a polyurethane resin, a polystyrene
resin, an epoxy resin, a polyvinyl chloride resin, a phenol
resin, a urea resin, or mixtures thereof. Furthermore, examples
of the foaming agent include volatile foaming agents, for
example, CClgF, CC12F2, CC12F-CC1F2, and the like, or pyrolytic
foaming agents, for example, azodicarbon amide,
azohexahydrobenzonitrile, 2,2'-azoisobutyronitrile,
benzenesulfonohydrazide, N,N'-dimethylterephthalamide, or the
like.
Examples of non-foaming binder include, for example, a urea
resin, a melamine resin, a phenol resin, or the like.
When foaming binders and non-foaming binders are used in a
mixed -fashion, it is preferable that the mixing ratio thereof be
within a range of 4:1 - 1:4; however, this is not necessarily so
restricted, and this ratio may be appropriately set in
consideration of the density or releasability of the wood board
which are desired.
Furthermore, it is preferable that the amount of binder
which is applied to the wood strands be within a range of 10 -
30 parts per weight with respect to 100 parts per weight of the
wooden strands.
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Next, the wooden strands to which binder has been applied
in this manner are subjected to forming (shown in S3 in Fig.
11). In the manufacturing method for wood boards in accordance
with the present invention, the use of dry forming, in which,
after the wooden strands to which binder has been applied are
heated and desiccated, these are dispersed on a thermal
compression plate, is preferable. Methods and apparatuses which
were conventionally employed may be used in an unchanged manner
in this forming. Furthermore, the direction of orientation of
the wooden strands is not particularly restricted; however, in
order to increase the strength of the wood board, it is
preferable that the grain directions of the wooden strands be
oriented so as to be essentially in a single direction.
Furthermore, thermal compression is applied to the wooden
strands which were subjected to forming, these are molded, and a
wood board is formed. It is preferable that the thermal
compression conditions be such that the temperature is within a
range of 150 - 200°C, and the period is within a range of 5 - 30
minutes; however, these ranges may be appropriately set in
accordance with the thickness or density of the wood board.
The above processes will be termed the "molding process" in
the present specification as in Fig. 11.
In the manufacturing method for wood boards in accordance
with the present invention, a smoothing process which will be
discussed hereinbelow is conducted subsequently to the molding
process which was described above. In this smoothing process as
in Fig. 11, first, the wood board which was obtained by thermal
compression molding in the molding process described above is
subjected to a moisture ambient so as to be forcibly moisturized
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(shown in S4 in Fig. 11). Concretely, the wood board which was
subjected to thermal compression molding is placed in a process
apparatus and is subjected to the moisture ambient; in
particular, a steam injection method, which a steam is injected
into wood boards, is preferable.
In the moisturizing process, moisture is forcibly injected
into the molded wood board, as a result, the wood board also
forcibly swells prior to the smoothing operation such as
sanding. Without the moisturizing process prior to the
smoothing operation, the wood board after the smoothing
operation gradually swells to arise irregularities on the
surface due to moisture of the atmosphere.
Fig. 1 shows an example of a suitable apparatus for
processing a wood board by means of such a steam injection
method; in the Figure, reference numeral 1 indicates the wood
board which is to be moisturized. This wood board 1 is disposed
so as to be sandwiched between two steam injection plates 2
having hollows therein. As shown in Fig. 2, in these steam
injection plates 2, steam injection apertures 7 are formed in
one surface to be opposed to wood boards, and the surface in
which these steam injection apertures 7 are formed is disposed
so as to be in contact with the wood board 1 which is to be
moisturized. Furthermore, the layered unit of these steam
injection plates 2 and wood board 1 is compressed by means of
two heating plates 3 and thus affixed. Furthermore, piping 11
from a steam generating apparatus 5 is connected to the steam
injection plates 2 via a valve 4, and steam is thus supplied to
the hollow portions within the steam injection plates 2. In
addition, piping 12 is connected to the steam injection plates
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2, and by opening the valve 6 provided in this piping 12, steam
can be discharged from the hollow portions of the steam
injection plates through the steam injection apertures 7.
In this type of moisturizing apparatus, the moisturizing of
the wood board 1 is conducted in the following manner. First,
in the state in which the valve 6 which is provided in piping 12
is closed, the valve 4 is adjusted, and high pressure steam is
supplied to steam injection plates 2 from a steam generating
apparatus 5 such as a boiler or the like through piping 11.
When this is done, the steam which is introduced into the hollow
portions within the steam injection plates 2 is injected from
the injection apertures 7 which are formed in steam injection
plates 2 as a result of the pressure thereof. Accordingly, both
surfaces of the wood board 1 are moisturized by steam which is
injected from injection apertures 7 of the steam injection
plates 2 which are disposed at both surfaces thereof.
Here, the steam pressure during moisturizing is within a
range of 3 - 10 kg/cm2, and preferably within a range of 5 - 7
kg/cm2, and the steam injection period is set, for example with
respect to a wood board having a thickness of 13 mm, to a period
within--a range of 5 - 45 seconds, and preferably within a range
of 15 - 25 seconds. Furthermore, it is preferable that the
temperature of the heating plates be within a range of from room
temperature ~ 170°C. However, the steam pressure, the steam
injection period, and the temperature of the heating plates can
be appropriately set in accordance with conditions such as the
thickness or moisture.absorption of the wood board 1 which is to
be moisturized, or the number or size of the injection apertures
formed in the steam injection plates.
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It is preferable that the injection apertures 7 formed in
one steam injection plate 2 and the injection apertures 7 formed
in the other steam injection plate 2 be formed in such a manner
as not to be in mutual opposition when these steam injection
plates 2 and 2 are disposed in a mutually opposing manner, that
is to say, these apertures are formed so as to be non-
symmetrical, and by means of forming the injection apertures 7
in a non-symmetrical manner, the occurrence of irregularities in
moisturizing becomes less likely, and it is possible to improve
the effectiveness of the moisturizing.
Furthermore, although not shown in the Figure, a mechanism
for adjusting temperature, such as, for example, a water cooling
mechanism, may be provided on the surfaces of the steam
injection plates 2 which are in contact with the heating plates
3, and thus the temperature of the steam injection plates 2 may
be adjusted.
Furthermore, a seal material of a shape such as to enclose
the wood board 1 and having a thickness which is slightly
greater than that of wood board 1 may be disposed between steam
injection plates 2 and 2, and the steam may be enclosed during
moisturizing in the enclosure of this seal material, and thus
the amount of steam employed may be reduced.
High pressure steam is used in the moisturizing by means of
the steam injection method described above, so that the steam
penetrates forcibly into the interior of the wood board, the
moisturizing is conducted efficiently, and it is possible to
greatly shorten the moisturizing time.
However, the method for the moisturizing of the wood board
in the smoothing process of the method in accordance with the
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12
present invention is not limited to a steam injection method
such as that described above; for example, a method in which the
wood board is stored in a moisturizing apparatus having a high
humidity may be employed. The moisturizing conditions in such a
case are such that the temperature is within a range of 60°C -
80°C, the humidity is within a range of 800 - 900, and
moisturizing is conducted for a period of 4 hours or more, and
preferably overnight. In conducting this moisturizing, other
methods may be employed, such as methods in which a water spray
is applied to the surfaces of the wood board, or the wood board
is immersed for a short period of time in a water tank, and is
then placed in a heating furnace at a temperature within a range
of 30 - 50°C for a period of approximately 10 hours, or the
like.
It is preferable that the moisturizing in the present
invention be conducted until the water content of the wood board
is within a range of 5 - 7%. Furthermore, it is preferable that
after the water content of the wood board reaches a level of 130
or more, and preferably a level within a range of 15 - 200, at
least once, desiccation be conducted so as to reduce the water
content to less than or equal to 120, and preferably to within a
range of 5 - 7 0 .
A wood board which is moisturized in this manner swells
prior to the smoothing operation such as sanding, i.e.,
irregularities to be caused by moisture in atmosphere appears on
the surface prior to the smoothing operation.
Next, the surface of the wood board which has been forcibly
moisturized as described above is smoothed, and the
irregularities therein are removed (shown in SS in Fig. 11).
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Therefore, thickness swelling of the wood board to be generated
by moisture in atmosphere is reduced. This removal of the
surface irregularities may be conducted by means of a
conventionally employed method such as sanding or the like, and
a sanding apparatus such as, for example, a drum sander, a wide
belt sander, or the like, may be employed.
The smoothing process which was explained in detail above
may be conducted in a continuous manner after the molding
process, or may be conducted separately from the molding
process.
Here, what is meant by "conducting these processes in a
continuous manner" is that the molding process and the smoothing
process are conducted continuously as a single operation, so
that the time gap between these two processes is at the longest
1 week or less, and is normally 3 days or less.
In addition, what is meant by "conducting these processes
separately" is that the molding process and the smoothing
process are conducted at different places or are conducted so as
to be independent of one another in time; the time gap between
these two processes is not strictly limited, but is preferably 1
week or more, and more preferably 1 month or more. Accordingly,
cases in which boards manufactured by a different process or
method at a different site are obtained, such as the purchase of
commercially-available wooden boards, and these are subjected to
the smoothing process, are also included in the meaning of
"processes separately carried out".
In the manufacturing method for wooden boards in accordance
with the present invention, it is preferable that a decorative
veneer or the like be bonded to the surface of the wood board,
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the irregularities of the surface of which have been removed and
the surface of which has been smoothed, or that various coatings
be executed thereon. An oak veneer having a conventionally
employed thickness within a range of 0.2 - 0.8 mm or the like
may be suitably employed as the decorative veneer.
The above explanation discussed only one example of the
manufacturing method for wood boards in accordance with the
present invention; a variety of applications are possible. For
example, a wood board in which layers comprising wooden strands
of different dimensions are laminated together may be employed
as the wood board which is produced by means of the
manufacturing method of the present invention, in addition to
strand boards comprising only one layer. In such a case, after
shaving the wooden strands, an operation in which the wooden
strands are separated in accordance with the dimensions thereof
such as the thickness, length, width, or the like, or an
operation in which a binder is applied to the separated wooden
strands, may be provided.
Furthermore, it is preferable that an operation in which
the wooden strands are acetylated after being shaved be
provided. In the case in which the wooden strands are
acetylated, it is preferable that after desiccating the wooden
strands so as to reduce the water content to 30 or less, and
preferably to 10 or less, the wooden strands be brought into
contact with a vapor of acetic acid, acetic anhydride,
chloroacetic acid, or the like, in the gas phase, and
acetylation be carried out until an acetylation degree within a
range of 12 - 20% is achieved.
Furthermore, a variety of operations may be included, where
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necessary, in the manufacturing method in accordance with the
present invention, such as, for example, an operation in which
the shaved wooden strands are stored, an operation in which, in
the case in which the water content has become excessive as a
result of the forced moisturizing, heating is conducted and
adjustment to an appropriate water content is carried out, or
the like.
As explained above, in the wood board produced in
accordance with the manufacturing method of the present
invention, the thickness swelling is reduced by forcible
moisturizing, and thereinafter, the irregularities in the
surface of the wood board are removed prior to a smoothing
operation, so that surface smoothness can be maintained over a
long period of time.
Furthermore, in the manufacturing method in accordance with
the present invention, the moisturizing temperature is set to a
high level, and thereby it is possible to shorten the
moisturizing period; after raising the water content at least
once, the water content is reduced to a predetermined value, and
thereby, it is possible to effectively remove the plastic
deformation present in the interior of the wood board.
Hereinbelow, the present invention will be explained on the
basis of examples for the purposes of clarity.
(Example 1)
Wood strands having a thickness within a range of 0.1 - 0.8
mm, a length within a range of 75 - 80 mm, and a width within a
range of 5 - 50 mm were produced using a shaving machine
(produced by Iwakura Corporation). These wooden strands were
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16
desiccated so as to have a water content of 50.
parts per weight of a mixture of foaming urethane resin
(crude MDI, produced by Sumitomo Bayer Urethane Co., Ltd.) and
aqueous phenol resin in a weight ratio of 2:1 were prepared, 100
parts per weight of the wooden strands described above were
placed in a rotating drum rotating at low speed, and the binder
was applied to the wooden strands by means of dispersion using a
spray as the wooden strands tumbled within the drum.
After the wooden strands to which the binder had been
applied were desiccated, these were dispersed on a thermal
compression plate so that the grain directions of the wooden
strands were arranged so as to be essentially identical, and
thus a forming member having a thickness of 250 mm was obtained.
This forming member was subjected to thermal compression molding
for a period of 4 hours at a temperature of 210°C and at a
pressure of 2 MPa. The thickness of the wood board which was
obtained was 12 mm, and the density thereof was 0.58 g/cm3.
Next; this thermal compression molded wood board was placed
in a moisturizing apparatus in a continuous manner, and was
moisturized for a period of 12 hours at a temperature of 70°C
and at--a humidity of 90 0 .
This forcibly moisturized wood board was placed in a drum
sander, and the surface irregularities therein were removed by
sanding.
A decorative veneer comprising an oak veneer having a
thickness of 0.3 mm was bonded to one surface of this wood board
using an aqueous polymeric isocyanate-type adhesive (produced by
Koyo Sangyo, KR7800) for a period of 3 minutes at a temperature
of 110°C and at a pressure of 1.0 MPa. The surface of the wood
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17
board was smooth, so that the decorative veneer bonded
satisfactorily. Furthermore, after the surface thereof was
sanded, a urethane coating having a thickness of approximately
50 elm was executed thereon. The appearance of the wood board
thus obtained was smooth and favorable. Furthermore, even when
this wood board was subjected to an accelerating test
corresponding to the passage of 3 years at normal temperatures,
irregularities did not develop in the surface thereof, and the
smoothness was maintained.
(Example 2)
As in Example 1, wooden strands having a thickness of 0.5
mm, a length within a range of 20 - 100 mm, and a width within a
range of 3 - 50 mm were shaved, and after these wooden strands
were acetylated, an aqueous phenol resin (a resin component of
30) was applied thereto. After these wooden strands to which a
binder had been applied were desiccated, they were divided into
three parts, and were dispersed on a thermal compression plate
so as to form a three-layered forming member in which the grain
directions of the wooden strands in each layer were essentially
identical, and the directions of orientation of adjoining layers
were mutually perpendicular. This three-layered forming member
was subjected to thermal compression molding for a period of 200
seconds at a temperature of 200°C. The wood board which was
obtained had a thickness of 13 mm.
Next, this thermal compression molded wood board was placed
in a continuous manner in a moisturizing apparatus, and the
interior of this moisturizing apparatus was adjusted so as to
attain a temperature of 35°C and a humidity of 950 (an
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equilibrium moisture content of 220). Here, what is meant by
the "equilibrium moisture content" is a value indicating the
moisture content of the wood board when the wood board is placed
in such an environment and reaches a state of equilibrium.
After the passage of an appropriate amount of time, this
wood board was removed from the moisturizing apparatus, and the
water content, the flexural strength, the flexural Young's
modulus, and the thickness swelling thereof were measured. The
relationship between the water content and each of these values
is shown in Figs. 3 to 5.
It can be seen from Figs. 3 to 5 that as the water content
of the wood board increases, the flexural strength, flexural
Young's modulus, and thickness swelling thereof decline.
Judging from these results, if the water content is 70 or less,
a wood board can be obtained which has a flexural strength of
approximately 40 MPa or more, and a flexural Young's modulus of
approximately 45 x 102 MPa, and if the water content is 50 or
more, it is possible to limit the thickness swelling to
approximately 5.50 or less.
Next, a wood board which was moisturized so as to have a
water content within a range of 5 - 7o was placed in a drum
sander, and the surface thereof was smoothed by means of
sanding. Furthermore, after this smoothed wood board was
immersed in water for a period of 12 hours, a sample having a
length of 150 mm and a width of 150 mm was cut therefrom, and
the surface contour thereof was measured using a universal
surface contour measuring apparatus (SE-3AK, produced by Kosaka
Laboratory, KK). The results of the measurements are shown in
Fig. 6. In Fig. 6, the horizontal axis indicates the
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19
longitudinal direction of the measurement sample, and the
vertical axis indicates the irregularity present in the surface;
measurement was conducted over a length of 10 cm at 20 locations
at 5 mm intervals, and the results thereof are shown.
(Comparative Example 1)
A wood board which was molded in a manner identical to that
of Example 2 was subjected to sanding identical to that of
Example 2 without being moisturized. After immersing this wood
board in water for a period of 12 hours, the surface contour
thereof was measured in a manner identical to that of Example.2.
However, measurement was conducted at 15 locations. The results
thereof are shown in Fig. 7.
When these results are compared, it can be seen that in the
wood board in accordance with Example 2 in which sanding was
conducted after moisturizing, the largest irregularity present
in the surface was approximately on the level of 0.3 mm, and
little irregularity was present overall; however, in the wood
board in accordance with Comparative Example 1, which was not
subjected to moisturizing, the irregularity present in the
surface was maximally on the level of approximately 0.6 mm, and
a large amount of irregularity was present overall.
(Example 3)
Commercially available strand boards were placed in a
moisturizing apparatus, and were moisturized in accordance with
the three sets of conditions (A, B, C) shown below. The
relationship between the moisturizing period and the water
content and swelling of these strand boards are shown in Figs. 8
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' 20
and 9.
Conditions A: temperature 80°C, humidity 90% (equilibrium
water content 150)
Conditions B: temperature 60°C, humidity 900 (equilibrium
water content 170)
Conditions C: temperature 35°C, humidity 950 (equilibrium
water content 230)
From the results shown in Fig. 8, it can be seen that using
conditions C, even though the humidity was the highest, the rate
of increase in water content was the slowest, and comparing
conditions A and B, the amount of time required until a water
content of 7o was achieved was essentially identical at
approximately 4 hours; however, thereinafter, the water content
stabilized at 12 - 13o when conditions A were employed, while
the water content increased slowly when conditions B were
employed. Furthermore, while it took a period of 20 hours to
reach a water content of, for example, 12o using conditions A, a
period of approximately 50 hours was required when conditions B
were employed. A similar trend can also be observed in Fig. 9;
when conditions A were employed, the swelling reached a level of
approximately 2o at a point in time 20 hours after the
initiation of moisturizing, and stabilized thereafter, while
when conditions B were employed, a period of approximately 70
hours was required; and when conditions C were employed, a
swelling of 2o was not achieved even after a period of 120
hours. That is to say, it can be seen that when conditions A
were employed, recovery from the plastic deformation which was
present in the strand board was achieved as a result of the
moisturizing and swelling occurred.
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(Example 4y
A commercially-available strand board was placed in a
moisturizing apparatus, and this was moisturized under
conditions such that the temperature thereof was 60°C and the
humidity was 900, so as to achieve a water content of
approximately 150, and thereinafter, the interior of the
moisturizing apparatus was set so that the temperature thereof
was 35°C and the humidity thereof was 200, and the water content
was reduced. The relationship between water content and
thickness at this time is shown in Fig. 10.
In accordance with Fig. 10, when, for example, a water
content of 7o was attained, the case in which the water content
was first raised to a level of approximately 15o and then was
reduced to 7o exhibits. greater swelling than the case in which
moisturizing to a water content of 7o was conducted from a
desiccated state. Accordingly, it can be seen that by first
raising the water content at least once and then lowering the
water content to a predetermined value, the effect of recovery
from the internal plastic deformation is greater.
(Example 5)
A wood board having a thickness of 13 mm was produced by
thermal compression molding in a manner identical to that of
Example 2.
Next, this thermal compression molded wood board was placed
in a continuous manner in a moisturizing apparatus such as that
shown in Fig. 1. A valve provided on piping coupled to a steam
generation apparatus and the steam injection plates was
' 22
adjusted, and high pressure steam having a pressure of 6 kg/cm2
was injected for a period of 20 seconds from the steam injection
apertures, and moisturizing was conducted. The heating plate
temperature was the temperature of the chamber (30°C).
As a result, it was determined that whereas the water
content of the wood board prior to moisturizing was within a
range of 1 - 30, the water content of the wood board after
moisturizing was within a range of 17 - 20%, and thus,
sufficient moisturizing was conducted by processing for 20
seconds.
Next, the wood board was removed from the moisturizing
apparatus, and was stored under conditions such that the
temperature was within a range of 25 - 30°C and t he humidity was
within a range of 60 - 70%, and was thus desiccated, and the
water content thereof declined to a level within a range of 10 -
120. When the flexural strength, flexural Young's modulus, and
wet swelling coefficient of the desiccated wood board were
measured, it was determined that these physical values were
essentially identical to the values of the wood board of Example
2, and-a decline therein was not observed.
Next, the wood board, the water content of which had been
reduced to a level within a range of 10 - 120, was placed in a
drum sander, and the surface thereof was smoothed by sanding.
Furthermore, after this smoothed wood board was immersed in
water for a period of 12 hours, a sample having a length of 150
mm and a width of 150 mm was cut therefrom, and the surface
contour thereof was measured using a universal surface contour
measurement apparatus (SE-3AK, produced by Kosaka Laboratory,
KK). As a result, it was determined that the irregularity in
.. ~ ~~~~~5
23
the surface had a maximum level of 0.3 mm, and thus surface
smoothness equivalent to that of the wood board in accordance
with Example 2 was maintained.
Although the invention has been described in detail herein
with reference to its preferred embodiments and certain
described alternatives, it is to be-understood that this
description is by way of example only, and is not to be
construed in a limiting sense. For example, preferred
embodiment is explained along with an oriented strand board, it
shall not be so limited. It is further understood that numerous
modifications in the details of the embodiments of the invention
and additional embodiments of the invention will be apparent,
and will be made by, persons of ordinary skill in the art having
reference to this description. It is contemplated that all such
changes and additional embodiments are within the spirit and
true scope of the invention as claimed below.
