Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
The present invention relates to a process for
the treatment of wood material impregnated with an
ammoniacal solution of a water insoluble treating
chemical to produce a treated wood material with a
"clean" surface.
BACXGROUND OF THE INVENTION
A common procedure for the treatment of wood
material such as plywood, lumber or the like with an
ammoniacal solution of water-insoluble treating
chemicals (such as those derived from copper, zinc or
arsenic) is to treat the wood material with the
ammoniacal solution under pressure in a treating vessel,
for a time sufficient to impregnate the wood material
with a requisite amount of the treating solution,
release the pressure, remove the treating solution from
the vessel and withdraw the impregnated wood therefrom.
The impregnated wood is then left in open air to permit
the gradual loss of ammonia from the wood material
causing a deposition of the treating chemical therein.
This is generally followed by a drying cycle.
This procedure may result in the surface of
the wood material being marred by unsightly blotches and
stains due to deposits of the treating chemical. These
deposits are not only objectionable on aesthetic
grounds, in that they detract from the appearance of the
wood; but also because they represent a loss of chemical
since such chemicals residing on the surface can be
subject to erosion and do little to protect the wood.
It is believed that this problem is related to
the loss of ammonia from pools of the solution which
remain on the surface of the wood after impregnation.
Additional treating solution is brought to the surface
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as a result of "kickback", a phenomenon whereby the air
pressure within the wood cells equilibrates itself with
the ambient pressure, forcing out some of the solution
close to the surface. The wood surface is tilted and
the solution is permitted to drain freely from the wood
material during and immediately following the
impregnation step.
Good practice additionally calls for a brief
reduction of pressure immediately following the removal
of the excess treating solution from the impregnation
vessel in an attempt to accelerate the equilibration of
the pressure inside and outside the wood while permit-
ting this expelled liquid to drop off the wood within
the vessel. Despite these preventive measures, the
surface of the resultant product is often stained, spot-
ted or streaked with deposits of the treating chemical.
The term "clean" is intended to mean a
condition where the surface of the wood appears like
colored wood and shows substantially no evidence of
adhering solid, dust, etc. To an experienced eye, the
difference between wood material having a "dirty"
surface as described above and that having a "clean"
surface will be quite pronounced.
It is the object of the present invention to
provide a means of providing an impregnated wood
- material with a clean surface.
A method for preventing stains on the surface
of wood material impregnated with ammoniacal
preservative solutions, by maintaining the impregnated
wood, after release of pressure and withdrawal of the
impregnating liquid from the treating vessel in an
atmosphere of carbon dioxide gas, is disclosed in United
States patent 4,008,342, issued February 15, 1977 to
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Domtar Limited. This technique is not wholly effective
if significant kickback occurs aEter treatment.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, the present invention relates
to a process for providing impregnated wood material
with a clean surface, the wood material having been
pressure impregnated with an aqueous ammoniacal liquor
containing an ammoniacal compound and a water-insoluble
treating chemical and subsequently at least partially
dried, thereby substantially equilibrating pressure
within the wood material and causing deposits of the
treating chemical on surface of the wood material, the
process comprising: submerging the wood material having
the deposits on surface thereof in an aqueous ammoniacal
treating solution having substantially the same concen-
tration of the ammoniacal compound and the treating
chemical as the aqueous ammoniacal liquor, dissolving
at-least a portion of the deposits in the solution,
separating the ammoniacal solution from the wood
material thereby to leave the wood material with a
wetted surface, maintaining the wetted surface in an
atmosphere containing ammonia gas until the surface is
substantially free of the solution and reusing the
separated ammoniacal treating solution.
In another aspect, the present invention
relates to a process of treating wood material compris-
ing pressure impregnating the wood material with an
aqueous ammoniacal solution having a water-insoluble
treating chemical dissolved therein, thereby to obtain a
pressure impregnated wood material with treating chemi-
cal deposits on the surface thereof, and including the
steps of contacting the impregnated wood material with
the ammoniacal solution, and dissolving at least a
portion of the deposits on the surface, thereby to
obtain a pressure impregnated wood material with a clean
suface.
DETAILED DESCRIPTION OF THE INVENTION
As noted earlier, wood material such as
plywood, lumber or the like, is treated with an aqueous
ammoniacal solution of a water insoluble treating chemi-
cal, by placing the wood material in a pressure vessel,
optionally subjecting it to a sub-atmospheric pressure
before introducing the treating solution in a quantity
sufficient to submerge the wood, maintaining an elevated
pressure in the vessel for a time sufficient to impreg-
nate the wood with a requisite amount of the solution,
releasing the pressure and removing excess treating
solution from the vessel before withdrawing the impreg-
nated wood material. This is followed by the step of
drying the wood material either in a kiln or in open air
to a desired moisture content.
The appearance of the dried wood material is
often marred by blotches and stains due to deposits of
treating chemical. Before further treatment of the
wood to eliminate such blotches, the pressure within the
wood pores must have substantially reached equilibrium
with the ambient pressure, i.e. kickback must have
substantially terminated. The process according to the
present invention provides the further step of contact-
ing such equilibrated, stained wood material with the
ammoniacal solution. The ammoniacal and treating chemi-
cal concentrations in this solution should not differ
substantially from that of the impregnating solution, in
order to avoid or minimize treating chemical depletion
in the wood layers immediately adjacent the surface.
Normally the solution will be applied by submerging the
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impregnated, blotched wood material in the ammoniacal
solution, however other contacting techniques such as
spraying, etc. can be envisaged. Irrespective of the
contacting technique employed, the solution should
thoroughly wet the surface and be sufficient to dissolve
the deposits. The time for dissolution, will normally
be between 1/2 and 4 hours and will be inversely related
to the temperature of the contacting solution and its
ammoniacal concentration but will primarily be determin-
ed by the thickness and amount of the deposits. Thetemperature will normally lie between 10 and 50C,
preferably between 35 and 45C, and will probably be
carried out at the elevated temperatures at which
impregnation is usually carried out. The solution in
excess of that required to wet the surface is removed
from contact with the wood material and the wood
material is kept in an ammoniacal atmosphere to prevent
deposition of the treating chemical on the wood surface
until the surface is substantially free of the solu-
tion. It is desirable to subject the wood material to abrief reduction in pressure following the withdrawal of
the contacting liquid, to remove any residual liquid
which may subsequently seep out and leave behind
deposits on the wood surface. Following the optional
step of pressure reduction, the wood material is main-
tained as mentioned above, in an ammoniacal atmosphere
to prevent the loss of ammonia from the residual layer
of solution on the surface of the wood, thereby inhibit-
ing reprecipitation of the wood treating chemical from
the liquid layer prior to its disappearance from the
surface, either by absorption into the wood or by drip-
ping off the wood. When the wood surface is substan-
tially free of liquid, a state discernible by the
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substantial absence of pools or films of free liquid on
the wood surface; the wood material may be withdrawn
from the contacting vessel and dried in the usual way.
In the preferred embodiment, the present
process will be a step in an overall process for the
production of clean, treated wood material. In addition
to the attractiveness inherent in providing a process,
the end result of which is clean, treated wood material;
another feature of such an operation is the reincorpora-
tion of the deposited treating chemical dirtying thewood into the ammoniacal solution (or into the wood)
thereby minimizing treating chemical wastage by permit-
- ting its reuse in subsequent impregnations.
Typically, such a process would comprise the
steps of pressure impregnating the wood material with a
requisite amount of the ammoniacal solution, separating
the impregnated wood material from the excess solution,
partially drying the wood material; preferably to a
dryness where the wood fibre lumen (i.e. cavities
bounded by the wood cell walls) are substantially devoid
of water, i.e. about 30% moisture content, so as to
permit rapid reabsorption of the liquid which subse-
quently rewets the surface. During this partial drying
deposits of treating chemical form on the surface and
the pressure in the wood cells is simultaneously permit-
ted to equilibrate with the ambient pressure, thereby
terminating kickback before any further treatment. This
is followed by immersing the partially dried wood
material in the ammoniacal solution and dissolving any
deposits of the treating chemical on the surface of the
wood material, separating the ammoniacal solution from
contact with the wood, which leaves the surface of the
wood wetted leaving the wood material in an ammoniacal
atmosphere to maintain the treating chemical in the
solution wetting the wood surface until the surface is
substantially free of the ammoniacal treating solution.
The ammoniacal solution removed from contact with the
rewetted wood material is recycled to the impregnation
step for reuse in impregnating another batch of wood
material after adjusting the treating chemical
concentration and solution volume.
The following examples illustrate some embodi-
ments of the present invention.
EXAMPLE 1
Western hemlock and Douglas fir lumber impreg-
nated in the standard fashion (described earlier) with a
3% solution of copper arsenate in 3% aqueous ammonium
hydroxide (normally known as "Chemonite"-(TM)) was kiln
dried for about 5 days to a moisture content of about
19~. This resulted in a product having deposits of
copper-arsenic compounds on the surface.
This wood material was charged to a treating
vessel where it was submerged in a contacting liquid of
a Chemonite (TM) solution at about 38C for 1 1/2 hour.
This solution was equivalent to th`at used to impregnate
the wood earlier. The contacting liquid was then pumped
out of the contacting cylinder and the wood material
subjected to a vacuum equivalent to 23" (mercury) for 1
1/2 hour. The vacuum was broken and the wood material
was permitted to drain for 2 hours in the contacting
vessel in the ammoniacal atmosphere.
The treated lumber was then withdrawn from the
vessel and allowed to dry. The dried wood material had
a clean surface.
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EXAMPLE 2
Impregnated lumber, similar to that employed
in the previous example was air dried for three days and
found to be contaminated with surface deposits. It was
then immersed in a Chemonite (TM) solution at about 38C
for 1 hour. Following the withdrawal of the solution
from the vessel, the lumber was allowed to drain in the
vessel for 1 1/2 hour in the ammoniacal atmosphere. The
product was withdrawn from the vessel and was kiln dried
following a brief period (3-5 hours) of seasoning in
open air. The resultant was a clean, treated wood
material.
_AMPLE 3
Lumber similar to that used in the previous
examples was impregnated, dried and which had surface
deposits of treating chemical; was charged to a pressure
vessel, subject to an initial vacuum of 22" (mercury)
for 1/2 hour, the chemonite (TM) solution was permitted
to fill the cylinder, the vacuum broken, and the lumber
was left in the solution at 40C for 1 hour. Following
withdrawal of the solution from the vessel, the lumber
was left in the vessel and allowed to drain for 1 1/2
hour in an ammoniacal atmosphere, before it was
withdrawn. This procedure resulted in a clean product
which was first briefly (3-5 hours) subjected to an air
seasoning before commencing kiln drying. The resultant
kiln dried lumber had a clean surface.
EXAMPLE 4
Kiln dried western hemlock lumber was
impregnated with Chemonite (TM), in substantially the
same fashion as the full cell process described above.
This was kiln dried for 5 days, to a moisture content of
19~. The resultant wood product had deposits of the
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copper arsenic compound on its surface.
The lumber was then submerged in a Chemonite
(TM) solution at about 40C for about 1 1/2 hour. The
liquid was pumped out of the contacting vessel and the
wood material permitted to drain in the vessel for 1 1/2
hour. After this drainage period, the lumber was
removed from the cylinder, and air dried for a day. The
resultant was a clean, treated wood product.
The description and examples provided above
are for the purpose of providing a complete disclosure
of the invention, and alterations and modifications
within the scope of the appended claims, may occur to
those skilled in the art.
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