Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR IMPREGNATING POROUS MATERIALS
1 BACKGROUND O_ THE INVENTION
This lnventlon relates to a method for
impregnating selected solutions, such as sealants and
antl-rot solutions, into porous materials, particularly
wood.
In the past, many methods have been employed to
mpregnate porous materials with solutions which would
lmpart deslred qualltles to the materials. Generally, a
two-step process has been employed comprising, ~irstly, a
drylng step to reduce the material's moisture content to
as little as possible, and secondly, an impregnation step
in which the material is exposed to the solution and the
solution penetrates into the materlal.
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1 In drying me~hods known in the prior art, the
materlal lS conductlvely heated by an external means, such
as ln a kiln, to evaporate tne molsture within the
material. Such a method heats the surface of the material
more rapidly than the interior of the material because of
the insulative properties of porous materials. As a
result, drying occurs more rapidly at the external
portions oE the material than at the internal portions.
Because porous materials are generally poor conductors of
heat, a large amount of heat may be required to
suf iciently heat, to the point of evaporation, the
moisture contained in the interior of the material. This
gives rise to potentially hazardous effects such as heat
damage to the exposed surfaces of the material.
On the other hand, at temperatures where there
is little risk of such hazards, another disadvantage of
the prior art methods arises. In particula{, liquid
moisture within the material may not be sufficiently
heated to the point of evaporation, thereby trapping
liquid moisture within the material. The presence of the
dense water molecules within the material may provide an
undesired barrier to the full and/or uniform penetration
of the impregnating solution. During the subsequent
impregnation step of the prior art methods, unsatisfactory
results may be achieved where residual moisture remains in
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1 the interior portions of the mater1al.
Passive lmpregnation methods/ wherein the
SOlUtlOn lS applied by lmmersion, brushing, spraying or
other such method, at standard atmospherlc pressuret may
be slow. This is because the internal pressure within the
material lS the same as the pressure of the ambient air,
so no driving pressure diEferential exists to assist in
the lmpregnation process. To overcome this disadvantage,
prior art methods have often employed the expensive
addltlonal step of providing an external pressurization
means to increase the rate of impregnation.
S~MMARY_OF THE INVENTION
Accordingly, it is in object of this invention
to overcome at least some of the disadvantages of the
prior art by providing an efficient and economical
alternatlve process for impregnating porous materlal with
solutions capable of imparting desired qualities to the
material.
It is another object of this invention to
provlde an impregnation method for porous materials
includlng a drying stage which min1mizes the risk of heat
damage to the material, while effectively removing liquld
moisture from the material.
It is another object of this invention to
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1 provlde a method of lmpregnating a porous material which
provides rapid removal of liquid moisture ~rom the porous
material by creating a pressure differential between the
pressure within the material and the external pressure of
tne amblent environment.
It is a further object of this invention to
provide a method of lmpregnating a porous material which
provides for rapid impregnation of porous materials by
creating a pressure differential between the internal
pressure within the material and the external pressure of
the ambient environment.
With these and other objects in mind, in one of
its broad aspects this lnvention resides in providing a
process for impregnating a solution into a porous material
comprising heating the porous material by microwave energy
for a prescribed time, applying the solutlon to the porous
material after the prescribed time, and cooling the porous
material for a further prescribed time.
In another of its broad aspects the invention
resides in providing a process for impregnating a solution
into a porous material wherein the porous material is
surrounded by an ambient environment having a pressure and
the porous material contains liquid moisture having a
temperature of vaporization and a pressure; the process
comprising heating the liquid moisture by microwave energy
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1 ~o a temperature at least as great as the temperature of
vaporlzation so as to conver~ the liquid moisture to
gaseous moisture having a temperature of condensation and
having a pressure greater than the pressure o~ the liquld
moisture and greater than the pressure of the ambient
environment; applying the solution to the porous material;
coollng the gaseous moisture to a temperature less than
the temperature of condensation so as to convert the
gaseous moisture to liquid moisture having a pressure less
than the pressure of the solution, thereby inducing entry
of the solution into the porous material.
In another of its broad aspects the invention
resides in providing a process for impregnating a solution
into a porous material, the porous material having an
outer surEace, an outer portion and an lnner portion, and
the porous material containing at least a prescribed
amount of liquid moisture; the process comprising a first
step of heating the porous material by microwave energy
for a prescribed time, wherein the outer surface of the
porous material is ln substantial contact with ambient air
having a temperature less than a temperature of
vaporization of the liquid moisture contained within the
porous material; whereln liquld moisture in the inner
portion of the porous material having a volume is heated
more rapidly than liquid moisture in the outer portion of
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1 the porous material to a temperature at least as great as
the temperature of vaporization of the liquid moisture;
converting the liquid moisture in the inner portion to
gaseous moisture having a volume greater than the previous
volume of the liquid moisture in the inner portion of the
porous material; driving liquid moisture in the outer
portion of the porous material to the outer surface of the
porous material; the first step continuing until an
acceptable amount of the liquid moisture contained within
the porous material has been replaced by gaseous moisture
and then followed by a second step of applying the
solution to the outer surface of the porous material;
cooling the gaseous moisture in the outer portion of the
porous material to a temperature less than the temperature
of condensation of the gaseous moisture; converting the
gaseous moisture in the outer portion oE the porous
material to liquid moisture having a volume less than the
previous volume of the gaseous moisture in the outer
portion. thereby creating a relative vacuum in the outer
portion of the porous material; inducing the solution to
impregnate the outer portion of the porous material by the
relatlve vacuum in the outer portion of the porous
material; and preferably further comprising cooling the
gaseous moisture in the inner portion of the porous
25 material to a temperature less than the temperature of
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1 condensatlon of the gaseous moisture; converting the
gaseous moisture in the inner portion of the porous
material to ll~uid moisture having a volume less than tne
volume of the gaseous molsture; creating a relative vacuum
in the lnner portlon of the porous material; and inducing
the solution to impregnate the lnner portion of the porous
material by the relative vacuum in the inner portion of
the porous material.
Further aspects of the invention will become
apparent upon reviewing the following detailed description
and drawings, which illustrate the invention and
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which illustrate embodiments of
the inventlon:
Fiy. 1 is a schematic perspective view oE one
embodlment of the heating stage of the inventlon;
Flg 2 is a cross-sectional view along the line
II-II of Figure l;
Flg 3 is a cross-sectional vlew of one
embodlment of the invention; and
Fig ~ lS a cross-sectional view of another
embodiment of the process.
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l DETAILED DESCRIPTION OF THE INVENTION
AND PREFERRED EMBODIMENTS THEREOF
_
Tne lmpregnation process of this invention is
applicable to any material of a porous or semi-porous
nature. The phrase "porous material" includes all
materials of porous or semi-porous nature, and materials
having porous characteristics. Wood is particularly well-
suited to the process. However, other materials such as
stone, masonry, ceramics, textiles and paper can be used
in the invention.
A porous material 10 is shown is Figure 1. The
dimensions, shape and configuration illustrated in Figure
1, and all other Figures, are not actual characteristics,
but are shown only for the purpose of illustration.
As shown is Figure 2, the porous material 10 has
an inner portion 16, an outer portion 18 and an outer
surface 20. Tne outer surface 20 of the porous material
10 comprises the exposed ex~erior of the porous material
10. The outer portion 18 is the interior part of the
porous material 10 which is relatively proximal to the
outer surface 20. The inner portion 16 is that part of
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1 the interior of the porous material 10 relatively less
proximal to the outer surface 20 than tne outer portion
18.
When porous material 10 contains little or no
water, or other liquids, a preliminary step of this
process may be necessary. The added step is to add
sufficient liquid moisture 22 to the porous material 10 by
soaking, steaming or suitable other method. The liquid
moisture 22 present or added to the porous material 10 is
preferably water, but any other liquid capable of
vaporization by induction heating can be employed.
In Figure 2, liquid moisture 22 is shown
schematically in only a portion of the porous material
10. It should be understood, however, that liquid
moisture 22 is preferably, and in the case of wood most
likely, distributed throughout the entire interior of the
porous material lOo The liquid moisture 22 may be in
uniform or varying concentrations throughout the porous
material 10.
Prior to the impregnation stage, the porous
material 10 is subjected to a neating stage to remove from
the porous material 10 some or all of the liquid moisture
22.
The process uses high frequency induction
heating, more commonly called microwave heating, to heat
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1 the porous materlal 10. In Figure 1, m1crowaYeS are
schematically lndicated as 14. The transmitter of the
mlcrowaves (not shown) and the manner of transmission of
the microwaves are not features of the lnvention.
Preferably however, the microwaves 14 have a frequency of
about 2450 MHz.
The heating process takes place in an ambient
environment 26, preferably an area filled with ordinary
atmospheric air at ordinary "room" temperature.
The ambient environment 26 could also be an
inert gas, such as argon, or other gas. Also, it could be
a liquid such as the impregnation solution. Such liquid,
however, must have a temperature of vaporization higher
than the temperature o vaporization of the liquid
moisture 22 within the porous material 10. The temperature
of the ambient environment 26 is lower than the
temperature of vaporization of the liquid moisture 22.
The porous material 10 is subjected to induction
heating by microwave energy 14 at such a rate and quality
that the liquid moisture 22 contained within the porous
material is rapidly converted into gaseous moisture 24.
Having more proximal contact with the cooler ambient
environment 26, the outer portion 18 of the poro~s
material loses heat energy to a greater extent than does
the inner portion 16 of the porous material 10. As a
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1 result,the liquid moisture 30 in the inner portion 16
heats up more rapidly to the temperature of vaporization
of the moisture 22 than does the liquid moisture 34 ln the
outer portion 18. ~ccordingly the liquid moisture 30 in
the inner portion 16 is converted to gaseous moisture 32
more quickly than the liquid moisture 34 in the outer
portion 18 is converted to gaseous moisture 36.
As vaporization of the liquid moisture 30 into
gaseous moisture 32 takes place, there is a corresponding
increase in the molecular activity of the moisture 30,
thereby causing a corresponding increase in pressure or
volume, or both, of the moisture 30 in the inner portion
16. An increase in the pressure of the gaseous moisture
32 in the inner portion 16 of the porous material 10
results in expansion of the gaseous moisture 32 outwards
in the direction of the outer surface 20 of the porous
material 10.
The liquid moisture 34 in the outer portion 18
of the porous material ln is displaced by the expanding
gaseous moisture 32 from the inner portion 16.
Accordinglyl at least some of the liquid moisture 34 is
driven out of the porous material 10 to the outer surface
20. Preferably, the heating stage continues until the
porous material 10 is substantially saturated by gaseous
moisture 24 and contains minimal liquid moisture 22.
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1 However, the heating need only continue for a prescribed
time such that a suitable amount of gaseous moisture 24 is
Eormed ln the porous material 10 so as to create a
sultable pressure difference as described below.
At this point in the process, the vapour-filled
porous material 10 is subjected to a quenching stage,
wnerein the porous material 10 is cooled and the selected
solution 12 is impregnated into the porous material 10.
Although it is convenient for descriptive
purposes only to consider the heating and quenching stages
as two distinct steps within the invention, it should be
understood that the two stages are intimately
interconnected and should be thought of as two aspects, a
forward aspect and a reverse aspect, of one another.
The quenching stage is initiated by the
termlnation of induction heating by the microwaves 14 and
~he introduction of the solution 12. Preferably, these
two events are substantially coincidental such that the
solution 12 is applied to the porous material 10 before
the porous materlal 10 has an opportunity to cool below
the temperature of condensation of the gaseous moisture 24
contained therein. Alternatively, the quenching stage
could take place some time after the termination of
heating, if a means to maintain the vapour condition of
porous material 10 was provided for the intervening period
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1 before the solution 12 was applied to the porous material
10 .
The solution 12 to be impregnated into porous
material 10 is preferably one which will impart
advantageous physical, electrical, chemlcal and/or other
properties to the porous material 10. Wood, for example,
may be impregnated with solutions 12 such as a
strengthener, a sealant against moisture or rot, a fire
retardant, a parasite retardant, a colouring pigment or
1~ other such solutionsO
In a preferred embodiment, the solution 12 is
applied to the porous material 10 at a temperature below
the temperature at which the gaseous moisture 24 will
condense into liquid moisture 22.
The selected solution 12 may be applied to the
porous material 10 ln a variety of ways. Preferably, the
material 10 is immersed in the solution 12 (see Fig. 3)
providing complete exposure of the outer surface 20 to the
porous material 10 to the solution 12.
In a second embodiment, a coating 28 of the
solution 12 is applied to the material 10 by spraying (see
Fig. 4), brus~ing or other suitable means, other than
immersion. Preferably, a coating method would take place
in an ambient environment 26 having a temperature less
than the temperature of condensation of the gaseous
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I moisture 24 and at standard atmospheric pressure.
Preferably, the application of the solution 12
is concurrent with the conductive cooling of the porous
material 10. Preferably, it is the cooler solution 12, in
the case of an immersion application, and the cooler
solution 12 and the cooler ambient environment 26 in the
case of a non-immersion or coating method, that cools the
porous material 10 and the gaseous moisture 24 within the
porous material 10.
When the porous material 10 is cooled, the
gaseous moisture 24 in the porous material 10 that is
closest to the outer surface in 20 of the porous material
10 is condensed and converted to liquid moisture 22. This
creates a reduced pressure at the region where the newly-
condensed moisture 22 is located in comparison to the
pressure prior to condensation. The pressure in this area
is less than the pressure of the ambient enviroment.
Accordingly, the ambient environment 26 forces the
impregnating solution 12 into the material 10.
Preferably, the cooling takes place quickly so as to
ensure that there is sufficient pressure difference
between the ambient environment 26 and/or the solution 12
and the interior of the porous material 10 so as to cause
impregnation of the solution 12.
As the porous material 10 is progressively
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1 cooled towards its inner portion 16, gaseous moisture 2~
further from the surface 20 is progressively converted to
liquid moisture 22, and the impregnating solution 12 is
progressively penetrated further into the porous material
10 such that penetration of the solution 12 to all areas
of the porous material 10 is possible, if desired,
depending on the length of time the porous material 10 is
allowed to cool quickly.
The residual heat from the heating process is
generally sufficient to dry the impregnating solution 12.
Although the disclosure describes and
illustrates certain preferred embodiments of the
invention, it is to be understood that the invention is
not restricted to these particular embodiments. The
invention includes all embodiments which are functional,
mechanical or electrical equivalents to the embodiments
disclosed and illustrated nerein.
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