Note: Descriptions are shown in the official language in which they were submitted.
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WO 99/54103 PCT/SE99/00631
A THROUGH-COLOURED WOODEN ELEMENT AND A M ETHOD OF
PRODUCING THROUGH-COLOURED WOODEN ELEMENTS
The present invention relates to a method of producing through-coloured wooden
elements, particularly sawn wood products, and also to a through-coloured
wooden
element.
By through-coloured is meant here that the wooden element has been coloured or
stained
homogeneously throughout the wood. A sawn surface of the element will
therefore be
coloured or stained regardless of the direction in which the wood rS sawn or
cut. The term
through-coloured is used in this significance hereinafter.
Coloured and stained wooden products become worn with time. Such wean, gouges,
lacerations and like impairments of the wooden products are particularly
noticeable
because they expose the plain wood located beneath the coloured or stained
surface.
Surfaces that shall be re-stained or re-coloured require a significant amount
of
preparatory work, such as sanding, etc., which is very time-consuming. The
actual
colouring process is also very time-consuming. These problems are solved in
accordance
with the present invention with the aid of a method of through-colouring wood
as
hereinbefore defined. Lacerations, gouges, marks and wear' in and on the wood
are not as
noticeable in this case. Furthermore, the wood can be sanded down or worked
whilst
retaining the same colour throughout. The through-colouring process is also
less
laborious than a manually performed colouring or staining process. This
affords
significant benefits. Flooring materials and table tops are examples of the
areas in which
2~ such benefrts are afforded. Thus, the invention enables the production of
thnough-
coloured wooden floors and table tops which when showing signs of wear need
only be
sanded down and then treated perhaps with an appropriate oil or varnish.
Another area of
use is found in the wooden handles of cutlery. Coloured or stained wooden
cutlery
washed in dishwashers quickly become disfigured as a result of the stain
wearing-off in
the dishwasher. This problem is solved when using tlwough-coloured wood in
accordance
with the invention, since there is no colour surface that can be impaired, by
virtue of the
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fact that the wood is through-coloured. It is now possible to produce wooden
handles for
cutlery that withstand being washed in dishwashers.
Swedish Patent Application SE 9500689-6 describes a method of producing
impregnated
wooden products. This method involves pressing a wooden element, or wooden
blank,
isostatically in a so-called Quintus press or with the aid of some other
appropriate
pressing method in a first stage of manufacture, at a pressure grater than 800
ban,
preferably greater than 1000 bar. The degree of compression to which the wood
is
subjected will depend on the dryness, fibre direction, hardness and other
properties of the
wood. Normally, this compression will result in the reduction ol~ one of the
cross-
sectional dimensions by between 20-50%, wherewith the cells in said element
are pressed
together. The load on the wooden element is then removed.
In a second step, the element is placed in a bath that contains an
impregnating agent,
wherewith the element progressively swells as a result of liquid entering into
and being
absorbed by the cells. The liquid penetrates the cells such as to obtain
complete
impregnation of the element in its entirety. The extent to which the clement
expands will
depend, inter alia, on the material properties of the element and its
residence time in the
bath. Pronounced expansion normally takes place within the space of some hours
and, in
some instances, the material returns to its original foam within this t ine
period. Suitable
impregnating agents are liquid fire retardants, liquid fungicides and glue.
The first two method steps may be supplemented with a third step in which the
element is
again compressed isostatically with a pressure greater than 800 b.r,
preferably greater
than 1000 bar, resulting in a hard element that is fire-resistant, fungus-
resistant and also
resistant to deformation when glue is used.
The aforedescribed pressing process, which is also described in Swedish Patent
Application 9303821-4, raises the quality of low-quality wood by providing a
much
harder end product. For instance, pine can be made as hard as oak, and oak can
be made
twice as hard as its natural hardness. According to Swedish Patent
.\pplication 9500689-
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6, it has been found that this pressing process makes it possible to
impregnate wood that
could not earlier be impregnated. Such impregnation can be achieved with large
wooden
products that are several square metres in area.
It has not earlier been possible to through-colour wood. However, it Iras
surprisingly been
found that wood can be through-coloured in accordance with the invention
claimed in this
Application by placing the wood in a colour bath after the first isostatic
pressing step.
The colour penetrates into the wood, which is then allowed to dry in a
conventional
manner, and may optionally be pressed again. This colour penetration results
in wood
that is coloured throughout. In addition, all the benefits of hardwoods axe
obtained by
further pressing the wood in accordance with SE 9303821-4, after' tln-ough-
colouring the
wood.
According to the inventive method, a wooden element is pressed isostatically
in a first
1 ~ step at a pressure greater than 800 bar', preferably greater than 1000
bar, in a so-called
Quintus press or by some other suitable pressing process, wherewith
compressing the
wood cells in said element. This process is described in SE 9303821-4. In a
second step,
the element is placed in a colour bath comprising, e.g., water and a water-
dissolved
colorant. As the pressure-treated wood comes into contact with water, the wood
swells
and draws water thereinto. The cellulose in the wood and the water are both
polar,
whereby the water is readily absorbed by the wood. The colorants are also
polar and
therewith accompany the water into the wood cells, said colorants having a
molecular
size, i.e. a smallness, that enables them to penetrate into the wood cells.
The colorant
shall not be excessively polar, since this would cause it to stop at the
surface of the wood
instead of penetrating into the wood. This also applies when the molecular
size of the
colorant is excessively large and therefore unable to penett~ate into the
wood. The
molecular' size and polarity of the colorant varies slightly, depending: on
the type of wood
concerned. One of normal skill in this art will be able to decide upon a
suitable colorant
experimentally. This is achieved by through-colouring the type of wood
concerned with
different colorants in combination with solvents, e.g. water, after having
pressed a
wooden element isostatically.
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4
The solvent used will be one that is absorbed by the wood. Water is a suitable
solvent.
Another suitable solvent is linseed oil, which has good penetrability and
wetability due to
its small molecules. The colorant is dissolved in the solvent and is
sufficiently polar to
accompany the solvent as it is absorbed in the wood, and shall have a
molecular size
which ensures that it has "room" to accompany said solvent into the wood. Azo
dyes are
suitable colorants in the present context. Monomers, dimers or polyners of the
azo dyes
may be applicable, depending on the molecular size of the azo dye or colorant
and the
choice of wood. The colorant shall also have the polarity necessary for it to
be able to
enter the wood. The skilled person is able to determine which colorant
together with
which solvent will penetrate into the wood.
Woods that can be coloured in accordance with the invention include hardwoods
or
leafwood, such as aspen and birch, and softwoods or coniferous wood such as
spruce and
1 ~ pine (redwood). The first step in which the wood is pressed isostatically
enables a large
number of different types of wood to be through-coloured in accordance with
the
invention.
A number of trials have been run using aspen and spruce which was through-
coloured
with Herdins Akta Bets, which was made up by mixing sodium cl~ioride with an
azo
dyestuff according to the description of goods for genuine stain in powder
form having
product number 102051 and obtained from Herdins Fargverk AB. 'These trials
will be
described below.
The invention will now be described in more detail with reference to the
following
examples. The inventive method comprises pressing a wooden element
isostatically lIl a
first method step at a pressure greater than 800 bar, preferably greatrr than
1000 bar, in a
so-called Quintus press or by some other suitable pressing process in which
the wood
cells in the element are compressed. The element is then relieved of load. In
a second
i0 method step, the element is placed in a liquid bath containing a coUorant
dissolved in a
solvent, such as water, wherewith water and colorant are absorbed by the
element. The
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colorant shall have a molecular size which enables it to penetrate the wooden
element and
shall have a polarity which enables it to penetrate the wood together with the
water.
Water and colorant migrate into the wood as it swells. This takes place over
some hours,
and may be effected at room temperature or at an elevated temperature of up to
100°C.
The through-colouring process proceeds more quickly at temperatures above room
temperature. Water containing colorant penetrates into the wood clement as the
wood
swells, thereby resulting in a through-coloured element.
The element is then dried conventionally.
Alternatively, the wooden element can be through-coloured by means of a
conventional
pressure impregnation process.
It has also been found that it is possible to through-colour wet wood or raw
wood. In a
1 ~ first step of isostatically pressing the raw wood at a pressure greater
than 800 bar,
preferably greater than 1000 bar. the lamina are opened up or some properties
of the
wood are changed. The opened up lamina will be able to absorb lie colorant and
the
solvent, in a later step, which makes the wooden element through-coloured. In
a later step
the wooden element is placed in a chamber and the colorant and the solvent is
delivered.
2U This later step can be done with a conventional pressure impreg,oation
process, with
vacuum and/or pressure. This step is necessary since the wood keeps a quite
high content
of sap. The pressure and/ or vacuum step makes the sap already contained in
the wood
able to be exchanged against the colorant and the solvent.
25 It is even possible to through-colour wet or raw spruce, which has been
known to be
impossible to impregnate.
Subsequent to having through-coloured the wooden element, said element may be
pressed
isostatically at least one more time in a third step, at a pressure ~.a,reater
than 800 bar,
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preferably greater than 1000 bar. This results in a through-coloured wood that
has the
hardness of a hardwood.
The wood through-colouring process can also conceivably be combined with the
impregnation process described in SE 9500689-6, therewith incorporating a fire
retardant,
an anti-fungus agent or glue into the through-coloured wooden element.
The invention also relates to a through-coloured wooden element tlrn has been
through-
coloured in accordance with the aforedescribed method.
Example 1
A piece of aspen wood measuring 7x4.5x15.5 cm was pressed isost.~tically in a
Quintus
press (in accordance with the method described in SE 9303821-4). '1'I~e wood
was pressed
I S at 1300 bar for two minutes at room temperature.
A colouring bath was prepared by mixing HERDINS iAKTA BET'S, No. 59, ebony
black
in powder form with water, in accordance with the instructions on the packet
(without
ammonia). The solution was brought to a boiling point and the pressure-
tt~eated wood
piece then placed in the solution and kept there for about two hours while
boiling the
solution, after which the wood was removed and dried. The wood w as then sawn
in two,
whereby it could be seen that the piece of wood was coloured throughout.
Example 2
A piece of spruce measuring 4x4x5 cm was pressed in a second ten in the same
way as
that described in Example 1. The colouring bath was prepared in the same way
as that
described in Example 1 and the wood was through-coloured in the same way with
the
exception that HERDINS AKTA BETS, No. 51, red, was used instead. The wood was
removed from the bath and dried and then sawn in two, from which it could be
seen that
the wood had been coloured throughout.
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The present invention provides a unique method of through-coloured wood that
has a
wide area of use. Practically all types of wood can be tz~eated in accordance
with the
invention. In addition, the invention can be applied to produce through-
coloured wood of
enhanced hardness. The through-colouring process is not so laborious as
painting or
staining wood by hand. As previously mentioned, the areas of use include
flooring
materials and table tops, and also wooden panels, wooden stairs, kitchen
elements, glued
wooden beams, shafts, sport equipment, etc. When such wooden products and
articles
become damaged and worn, their surfaces can be sanded down to expose new,
blemish-
free coloured surfaces that do not require re-colouring. Damage and wear to
the surface
of the wood will not be as noticeable as would otherwise be the case, since
the wood is
through-coloured and consequently no "white" wood will show through a damaged
surface. It is also possible to produce cutlery with stained wooden handles
that can
withstand being washed in a dishwasher.
