DESCRIPTION
Title of lnvention
FIBERBOARD
Technical Field
[OOOI]
The present invention relates to a fiberboard.
Background Art
[0002]
Conventionally, it is known that a fiberboard is produced by heat
compression molding wood fibers which have been supplied with an adhesive(s)
(see Patent Document 1 for example). Such a fiberboard is widely used as a
material for housirlg members such as a floor material, a wall material and a ceiling
material, as a material for door members, as a material for fixture members such
as baseboards and ceiling cornices, and as a material for furniture.
[0003]
Patent Literature I: JP 2001-030212 A
Summary of lnvention
Technical Problem
[0004]
In manufacture of fiberboard, generally, wood chips are added with water
by stearning or the like for defibration, in the process of obtaining wood fibers from
raw materials, as shown in Patent Literature 1. For this reason, water-repellency
inherent to the raw materials is sometimes reduced. As a result, the ,fiberboard
has an increased expansion and contraction of the dimensions due to absorbing or
discharging moisture, as compared with plywood. Accordingly, in some cases
where the fiberboard is used as a floor material, construction is limited in adhesion
process etc., or it becomes necessary to use materials to block moisture.
Therefore, improvement in dimensional stability against absorbing or discharging
moisture has been desired.
[0005]
-The present invention is made in view of the above circumstances, and
aims to provide a fiberboard with a small dimensional change due to absorbing or
discharging moisture.
Solution to Problem
[0006]
In order to solve the above described problem, the fiberboard of the
present invention is characterized in being made of a rr~ixtureo f plant fibers which
are obtained by mechanically grinding a sub-product which is produced by making
a primary product from herbaceous plants, bast fibers, and an adhesive(s).
[0007]
In the fiberboard, it is preferred that the sub-product is a bagasse.
[0008]
In the fiberboard, it is preferred that the bast fibers are those nipped and
cut by a pair of cutting blades.
[0009]
In the fiberboard, the bast fibers are preferably contained in a sutface layer
of the fiberboard.
Advantageous Effects of Invention
[OO 1 01
According to the present invention, it is possible to obtain a fiberboard
having a small dimensional change due to absorbing or discharging moisture.
Brief Description of Drawings
[OOI I ]
Fig. 1 is a sectional view showing one embodiment of the fiberboard of the
present invention.
Fig. 2 is an explanatory view of a cutting process of a fiber bundle by a
cutting machine.
Description of Embodiments
[OOI 21
Hereinafter, embodiments of the present invention will be explained in
detail.
[00 1 31
A fiberboard according to the present embodiment is formed by heat
compression molding a mixture of plant fibers and has a constant area and
thickness. It is possible to use such a fiberboard as a material for housing
members such as a floor material, a wall material and a ceiling material, as a
material for door members, as a material for fixture members such as baseboards
and ceiling cornices, and as a material for furniture.
[00 141
Fig. I is a sectional view showing one embodiment of the fiberboard of the
present invention. A fiberboard 1 of Fig. 1 has a three-layer structure including a
core layer 2 as a middle layer and surface layers 3 as layers laminated on each of
the both outer surfaces of the core layer 2. Each layer contains plant fibers. Plant
,fibers in the core layer 2 are adhered with each other with adhesive, and the plant
fibers in the surface layer 3 are adhered with each other with adhesive. Also in the
interface between the surface layer 3 and the core layer 2, plant fibers are adhered
with each other with adhesive so that the core layer 2 and the surface layer 3 are
adhered to each other.
[OOI 51
It is possible to use fibers different in fiber length or fibers different in plant
species respectively in each of the core layer 2 and the surface layers 3. For
example, as plant fibers for the surface layer 3, it is possible to use plant fibers with
an average fiber length shorter than that of plant fibers for the core layer 2. In that
case, the fiberboard 1 with a better surface smoothness can be obtained. It is also
possible that fibers different in fiber length or fibers different in plant species are
contained in combination in a same layer.
[00 161
Layer structure of the fiberboard is not limited to the three-layer structure
as shown in Fig. 1, but may include a single-layer structure.
[OOI 71
The present embodiment uses plant fibers which are obtained by
mechanically grinding a sub-product which is produced by making a primary
product from herbaceous plants (hereinafter sometimes simply referred to as plant
fibers) as components of the fiberboard. The sub-product which is produced by
making a primary product from herbaceous plants (hereinafter sometimes simply
referred to as a sub-product) is discarded without being used, in many cases. The
present embodiment utilizes such a sub-product of herbaceous plant as a raw
material for the plant fibers, to allow us to reduce waste and to save precious
resources. For its inexpensive availability, the present embodiment also has an
advantage of reducing the cost of ,the fiberboard.
[OOI 81
Concrete examples of the sub-products of herbaceous plant may include
bagasse, rice straw, wheat straw, and the like. Among them, bagasse which is a
residue left after squeezing juice from sugarcane has a good water-repellency, and
is better than the others in improving the effect of cor~trollingth e dimensional
change due to absorbing or discharging moisture, and therefore, is preferably used
as the raw material for .the plant fibers.
[00 1 91
In the present embodiment, the sub-product of herbaceous plant is
mechanically grinded. For example, it may be grinded by a grinder such as a
hammer mill, a ball mill, and a refiner. Since herbaceous plants are easily grinded
mechanically, it is possible to omit a process of distributing water for the defibration,
such as steaming as conventionally performed. Accordingly, it is possible to avoid
reduction of water-repellency inherent to herbaceous plants due to a process such
as steaming. Thus, plant fibers, having a controlled reduction of water-repellency
can be obtained.
[OOZO]
The thus obtained plant fibers is adjusted to have a predetermined length.
It may be cut by a publicly known conventional cutting machine, where necessary.
The length of the plant fibers may have an average fiber length, for example, in a
range of from 1 to 8 mm. When the average fiber length is in the range of from 1
to 8 mm, it is possible to prevent an occurrence of an aggregated state (a lumpy
state) wherein the plant fibers are tangled together, in a mixing step after a
blending of an adhesive(s) in the manufacture of the fiberboard. This allows the
plant fibers to be uniformly dispersed, and it becomes possible to produce a
fiberboard having a uniform quality. As a result, it becomes possible to obtain a
fiberboard having a good suppressive effect against the dimensional change due
to absorbing or discharging moisture. Moreover, the obtained ,fiberboard will have
a good surface smoothness.
[0021]
When the fiberboard with a three-layer structure is produced, it is possible
to use plant fibers with an average fiber length shorter than that of plant fibers for
the core layer, as plant fibers for the surface layer. For example, plant fibers with
an average fiber length of more than or equal to1 mm and less than 4 mm may be
used as the plant fibers for the sutface layer, and plant fibers with an average fiber
length of 4 mm or more and 8 mm or less may be used as the plant fibers for the
core layer.
[0022]
The fiberboard of the present embodiment is formed by mixing bast fibers
to plant fibers. Bast fibers used herein are fibers which are obtained from bast
plants such as kenaf, jute, flax, ramie, hemp, and sisal. These bast plants have
already been distributed as general industrial materials in the spinning or
nonwoven industry, and can be stably procured.
[0023]
Bast fibers are rich in cellulose component and have a high tensile
strength. Therefore, by use of bast fibers, it is possible to obtain a fiberboard
having a good strength characteristic, by in- parting a strength characteristic thereto.
Furthermore, from a viewpoint of dimensional stability, bast fibers obtained from
bast plants show the following characteristics. In common plant fibers,
swellirrglcontraction behaviors at a change of water content are different between
in the fiber direction and in the radial direction. For example, occurrence of
dimensional charrge is about 0.1 to 0.2% relative to 1 % change in moisture content
in the radial direction of the plant fiber, while the dimensional change in the fiber
direction is as extremely small as about 0.01 % relative to 1 % change in moisture
content. Therefore, a dimensional changing behavior of a fiberboard formed from
such plant fibers is determined by a balance between the large dimensional
change in the radial direction and the small dimensional change in the fiber
direction. Bast fibers obtained from bast plants have an extremely large elastic
modulus in the fiber direction, and therefore, a restraining force acts against the
,fiber direction where the dimensional change is small. As a result, a fiberboard
formed from bast fibers shows an excellent dimensional stability. Having a greater
restraining force with a longer fiber length, the fiberboard shows an extremely
excellent dimensional stability compared to common wood fiberboards. 'Thus, by
containing the bast fibers, it is possible to obtain a fiberboard with a good
dimensional stability such that a dimensional change due to absorbing or
discharging moisture is small.
[0024]
The bast fibers desirably have an average fiber length of 3 mm or more
and 10mm or less. Fiber length in the range allows the bast fibers to be dispersed
more uniforrr~ly.A s a result, it is possible to obtain a fiberboard having a better
suppressive effect against the dimensional change due to absorbing or discharging
moisture, and a better strength characteristic.
[0025]
Such bast fibers may be obtained by defibrating a fiber bundle obtained
from a bast part of a bast plant until a predetermined length is obtained by a
publicly known conventional defibration method. For example, by use of a
defibration machine, the fiber bundle is ripped off so as to obtain fibers of the
predetermined length. In that case, certain parts in the fiber bundle with a smaller
strength are ripped off, and the parts ripped off become the end parts of the
obtained bast fibers.
[0026]
It is also possible to cut the fiber bundle to a predetermined length by a
cutting machine. As the cutting machine, a device which linearly cuts a fiber
bundle along a cut line may be used. Fig. 2 is an explanatory view of the cutting
process of the fiber bundle by the cutting machine. A cutting machine 5 of Fig. 2 is
equipped with a flat blade-shaped a cutting blade 6 (guillotine blade) which moves
linearly along the cut line. The cutting blade 6 is vertically movable. The edge part
of the cutting blade 6 gets thinner toward the edge, being formed in a V-shape in a
cross sectional view. The cutting machine 5 is also equipped with a fiber bundle
mounting table 8 which supports a fiber bundle 7 including bast plants 14 and a
cutting blade 9. The cutting blade 9 is fixed to the fiber bundle mounting table 8 as
a fixed blade. Fiber bundle 7 may be cut by lowering the cutting blade 6 from the
top of the fiber bundle 7 which is supported by the fiber bundle mounting table 8
and cutting blade 9, so as to nip and cut the fiber bundle 7 by a pair of cutting
blades 6 and 9.
[0027]
When the fiber bundle 7 is cut by the pair of cutting blades 6 and 9, the
tips of the fibers slightly bow. Accordingly, a microscopic view of the cross section
by cutting of each of cut bast fibers 4 shows a state of ,the cross section wherein
,the upper part is cut by the cutting blade 6, and the lower part is ripped off. The
end parts of the thus cut the bast fibers 4 may be formed of parts which are hard to
be ripped off (parts with a greater strength in the fiber bundle), unlike the end parts
of bast fibers obtained by the publicly known conventional defibration method
described above. The parts which are hard to be ripped off are rigidly formed. In
addition, the ripped off part in the cross section of the bast fibers 4 is easy to be
permeated with the adhesive as compared with the part that is cut by the cutting
blade 6. Therefore, the use of the bast fibers 4 which are cut as described above
facilitates adhesion of the rigid parts of the bast fibers 4 to the other plant fibers.
As a result, the adhesion between the rigid parts of the bast fibers 4 and the other
plant fibers is strengthened to further enhance the strength of the fiberboard or the
suppressive effect against the dimensional change due to absorbing or discharging
moisture.
[0028]
Such bast fibers may be contained throughout an entire fiberboard
including fiberboards of multilayer structure. For example, in the fiberboard having
a three-layer structure as shown in Fig. 1, the bast fibers may also be contained in
the surface layer 3 and the core layer 2.
[0029]
It is also possible to contain the bast fibers only in the surface layer of a
fiberboard. Even in a case where the bast fibers are contained only in the surface
layer of a fiberboard, it is possible, by the presence of the bast fibers, to enhance
the strength of the fiberboard or to enhance the suppressive effect against the
dimensional change due to absorbing or discharging moisture. In that a case, the
content of the plant fibers in the entire fiberboard may be increased. Since the
plant fibers used in the present embodiment are available at a low cost, it is
possible to reduce cost of a fiberboard, while enhancing the strength of the
fiberboard and enhancing the suppressive effect against the dimensional charrge
due to absorbing or discharging moisture.
[0030]
As for the volume, the bast fibers have a low bulk density compared to that
of the plant fibers. Therefore, when the plant fibers and the bast fibers are mixed,
it is desirable that the bast fibers are smaller than the plant fibers in weight ratio, in
order to easily realize a uniform dispersion of the bast fibers to the plant fibers.
From this viewpoint, in the fiberboard having a three-layer structure as shown in
Fig. 1, it is preferred that, when the bast fibers are contained only in the surface
layer 3 of the fiberboard, the mixing ratio of the bast fibers is 40% by weight or less
to the plant fibers which constitute the surface layer 3. Also from the viewpoint of
further improving the s~nppressivee ffect against the dimensional change due to
absorbing or discharging moisture, it is preferred that the mixing ratio of the bast
fibers is 10% by weight or more to the plant fibers which constitute the surface
layer 3. More preferably, the mixing ratio of the bast fibers to the surface layer 3 is
15% by weight or more and 25% by weight or less. In the case of containing the
bast ,fibers throughout the entire fiberboard, it is preferred that the bast fibers are
contained at a proportion of 3% by weight or more and 30% by weight or less
based on the total amount of the above described plant fibers in the entire
fiberboard.
[003'1]
As the adhesives used in the present embodiment, adhesives used in
fiberboards that are conventionally publicly known may be used. For example, it is
possible to use isocyanate resin adhesives such as MDI (diphenylmethane
diisocyanate), TDI (tolylene diisocyanate), MDI prepolymer, TDI prepolymer, and
the like. It is also possible to use urea resin adhesives, melamine resin adhesives,
and urea-melamine co-condensation resin adhesives, phenolic resin adhesives,
and the like. These may be used in combination of two or more. Among them, the
isocyanate resin adhesives and the phenolic resin adhesives are well suited with
plant fibers including bast fibers, and easy to permeate the fibers. Therefore, it is
possible by using isocyanate resin adhesives or phenolic resin adhesives, to
enhance the adhesion among the plant fibers to further enhance the strength of
the fiberboard and the suppressive effect against the dimensional change due to
absorbing or discharging moisture. Also in particular, the melamine resin
adhesives are easily spreadable over the surfaces of plant fibers including bast
fibers, and are able to effectively adhere plant fibers together. Therefore, it is
desirable to use either the isocyanate resin adhesives or the phenolic resin
adhesives, in combination with the melamine resin adhesives.
[0032]
Such adhesives may be used, for example, in a range of from 5% by
weight or more and 30% by weight or less based on a total amount of the plant
fibers including bast fibers. By use of the adhesive in the ratio within the range, it
is possible to effectively adhere plant fibers together.
[0033]
In the next place, a method for manufacturing the fiberboard will be
explained.
[0034]
The fiberboard of the present embodiment may be manufactured by heat
compression molding a mixture of plant fibers and an adhesive@). More concrete
examples for such a method for manufacturing the fiberboard may include a
method which follows steps of grinding a sub-product of herbaceous plants, cutting
bast fibers, blending an adhesive(s), mat molding, and heat compression molding.
The manufacture of the fiberboard requires no special equipment which is used in
a common manufacture of fiberboard, such as a carding machine which defibrates
long fibers while forming it into a mat, or a device which air-disperses long fibers.
[0035]
Hereinafter explained is a method for manufacturing a fiberboard of a
three-layer structure of Fig. 1, the surface layers of which contain bast fibers.
[0036]
For grinding of the sub-product of the herbaceous plants which is a raw
material for the plant fibers of the core layer 2 or the surface layers 3, for example,
a grinder as described above is used. After grinding, the plant fibers are cut into a
predetermined length as necessary. As the plant fibers for the surface layer 3,
plant fibers with an average fiber length shorter than that of plant fibers for the core
layer 2 may be used.
[0037]
For the cutting of the bast fibers, for example, the cutting machine 5 of Fig.
2 is used. Thus, the adhesion between the rigid parts of the bast fibers and the
other plant fibers is strengthened to further enhance the strength of the fiberboard
1 and the suppressive effect against the dimensional change due to absorbing or
discharging moisture.
[0038]
The blending of the adhesive may be performed in a condition of stirring
the plant fibers and the bast fibers. For example, the adhesive is blended while
stirring the above described plant fibers and the bast fibers in a drum blender.
[0039]
The stirring is continued after blending the adhesive. In this manner, a
mixture for forming the surface layer, which is t-rrixed with the plant fibers and the
bast fibers is prepared. The prepared mixture for forming the surface layer forms
surface layers 3 of the fiberboard having a three-layer structure. In the mixture for
forming the surface layer, the plant fibers and the bast fibers are uniformly
dispersed.
[0040]
A mixture for forming the core layer to form the core layer 2 of the
fiberboard 1, which includes the plant fibers and an adhesive(s), is also prepared in
the same manner as the mixture for forming the surface layer is prepared.
[0041]
A water-repellent, ammonium sulfide or other additives may be added to
the mixture for forming the surface layer or to the mixture for formling the core layer,
within a range where the effects of the present invention are not in-~paired.
[0042]
In a mat molding, a fiber mat is formed by distributing ,the mixture for
forming the surface layer, the mixture for forrrling the core layer, and the mixture
for forming the surface layer in order, in a mold frame.
[0043]
Then, the fiber mat is removed from the mold frame and placed between
thermal plates. Subsequently, the fiber mat is applied with heat compression by
the thermal plates, so that ,the fiber mat is formed into a board shape and the
adhesive is cured to adhere the fibers together, and in this manner, the fiberboard
1 can be formed. The temperature and the pressure during the heat compression
molding is appropriately set depending on type of the adhesive or thickness or
density of the fiberboard. For example, the temperature may be 20 to 180°C, and
the pressure may be 3 to 5 MPa. As for the pressing method in the heat
corrlpression molding, a batch-type flat plate pressing or a continuous pressing
may be adopted. In this manner, the fiberboard 1 having a three-layer structure
can be obtained.
[0044]
Although the present invention has been explained as the above on the
basis of the embodiment, the present invention is by no means limited to the above
embodiment, and various modifications can be made unless departing from the
gist of the present invention.
[0045]
Hereinafter, although the present invention will be described further in
detail by describing examples, the present invention is by no means limited to
those examples.
Examples
[0046]
A fiberboard having a three-layer structure was prepared in the following
process.
(Example 1)
Plant fibers with an average fiber length of 3.5 mm and plant fibers with an
average fiber length of 5 mm were prepared by cutting bagasse which had been
grinded by a hammer mill. Bast fibers with an average fiber length of 5 mm were
also prepared by cutting a jute bast fiber bundle by the cutting machine shown in
Fig. 2.
[0047]
The plant fibers with the average fiber length of 3.5 mm were added with
the bast fibers with the average fiber length of 5 mm at a proportion of 20% by
weight based on the amount of the plant fibers, to obtain mixed fibers. The mixed
fibers were stirred with a blender, while an isocyanate resin adhesive was blended
thereon at a proportion of 5% by weight based on the amount of the mixed fibers,
and a melamine resin adhesive was blended thereon at a proportion of 5% by
weight based on the amount of the mixed fibers. The stirring was continued after
the blending of the adhesives, and thus, a mixture for forming the surface layer
was prepared.
[0048]
Likewise, the plant fibers with the average fiber length of 5 mm was stirred
with the blender, while the isocyanate resin adhesive was blended thereon at a
proportion of 5% by weight based on the amount of the plant fibers, and the
melamine resin adhesive was blended thereon at a proportion of 5% by weight
based on the amount of ,the plant fibers. The stirring was continued after the
blending of the adhesives, and ,thus, a mixture for forming the core layer was
prepared.
[0049]
A fiber mat was obtained by distributing the mixture for forming the surface
layer, ,the mixture for forming the core layer, and the mixture for forming the
surface layer in order into a mold frame, so as for the mat to be made into a
fiberboard with a three-layer structure having a weight ratio of the surface layer :
the core layer : the surface layer = 25 : 50 : 25. The three-layered composition
was heat compression molded under a condition of 200°C and 3 MPa, for 5
minutes to obtain a fiberboard with an aspect ratio of 300 x 300 mm and a
thickness of 12 mm.
(Comparative Example I )
Plant fibers with an average fiber length of 3.5 mm and plant fibers with an
average fiber length of 5 mm were prepared by cutting bagasse which had been
grinded by a hammer mill.
[0050]
The plant fibers with the average fiber length of 3.5 mm were stirred with
the blender, while the isocyanate resin adhesive was blended thereto at a
proportion of 5% by weight based on the weight of the plant fibers, and the
melamine resin adhesive was blended thereon at a proportion of 5% by weight
based on the weight of the plant fibers. The stirring was continued after the
adhesives were blended, and thus, a mixture for forming the surface layer was
prepared.
[005 1 ]
Likewise, the plant fibers with the average fiber length of 5 mm was stirred
with the blender, while the isocyanate resin adhesive was blended thereon at a
proportion of 5% by weight based on the weight of the plant fibers, and the
melamine resin adhesive was blended thereon at a proportion of 5% by weight
based on the weight of the plant fibers. The stirring was continued after the
adhesives were blended, and thus, a mixture for forming the core layer was
prepared.
[0052]
A fiber mat was obtained by distributing the mixture for forming the surface
layer, the mixture for forming the core layer, and the mixture for forming the
surface layer in order into a mold frame, so as for the mat to be made into a
fiberboard with a three-layer structure having a weight ratio of the surface layer :
the core layer : the surface layer = 25 : 50 : 25. The three-layered composition
was heat compression molded under a condition of 200°C and 3 MPa, for 5
minutes to obtain a fiberboard with an aspect ratio of 300 x 300 mm and a
thickness of 12 mm.
[0053]
The fiberboards obtained in Example 1 and Comparative Example 1 were
measured for the rate of dimensional change. The measurement for the rate of
dimensional change was conducted also on a medium density fiberboard (MDF)
which was produced by use of wood fibers prepared by steaming and defibrillating
wood chips. 'The measurement for the rate of dimensional change was carried out
by measuring rates of dimensional change after the weights had changed until it
became constant weights at a 40°C/90% RH environment, from the dimensions
when the weights became constant weights at a 40°C/30% RH environment.
[0054]
As a result, the fiberboard of Example 1 showed a rate of dimensional
change of 0.25%, while the fiberboard of Comparative Example 1 showed a rate of
dimensional change of 0.29%. MDF showed a rate of dimensional change of
0.40%. From the result, it was confirmed that the fiberboard of Example 1 had a
smaller rate of dimensional chaqge as compared with that of the fiberboard
produced by use of wood fibers of steamed and defibrated wood chips, or that of
the fiberboard of Comparative Example 1 which did not contain the bast fibers, and
that the dimensional change due to absorbing or discharging moisture was small in
the fiberboard of Example 1.
Reference Signs List
[0055]
1 Fiberboard
4 Bast fibers
6, 9 Cutting blades
14
CLAIMS
1. A fiberboard made of a mixture comprising plant fibers which are obtained
by mechanically grinding a sub-product which is produced by making a primary
product from herbaceous plants, bast fibers, and an adhesive(s).
2. The fiberboard according to claim 1, wherein the sub-product is a
bagasse.
3. The fiberboard according to claim 1 or 2, wherein the bast fibers are those
nipped and cut by a pair of cutting blades.
4. The fiberboard according to any one of claims 1 to 3, wherein the bast
fibers are contained in a surface layer of the fiberboard.