Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02575185 2007-01-24
IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
METHOD FOR TREATING WOOD
FIELD OF INVENTION
[0001 ] The present invention relates to a process for treating wood and other
cellulosic
materials to render the resistance to wood attacking organisms, such as
termite, fungi and insects.
More particularly, the present invention relates to a process for impregnating
wood and other
cellulosic materials with a borate preservative, in such a manner that the
borate wood
preservative is leach-resistant when the wood is in contact with water,
thereby allowing its use
for exterior applications.
BACKGROUND OF THE INVENTION
[0002] Copper chrome arsenate (CCA), a leach-resistant wood preservative known
for
exterior application, was recently banned because of the toxic nature of
arsenic and chromium.
Since then, there has been a continuing effort to develop suitable alternative
systems. A number
of alternative, non-arsenical pesticidal treatments containing heavy metals
(primarily copper)
have been proposed. For example, U.S. Patent No. 4,929,454 teaches the
treatment of wood with
a mixture of a copper compound and a quaternary ammonium compound. This
technology has
been commercialized under the name ammoniated copper quaternary amine (ACQ).
It has
excellent insect resistance, but it is considerable more costly than CCA, and
it has a tendency to
promote the growth of white mold on the wood surface. Furthermore, ACQ-treated
wood may
exhibit corrosion problems with most metal fasteners when the treated wood is
placed into
service. Special fasteners having high corrosive resistance are required for
the ACQ treated-
wood, causing an additional cost of using ACQ-treated wood for construction.
Furthermore,
there has been increasing concerns on the toxicity and environmental impact of
wood
preservatives containing heavy metals.
[0003] Borate has been used as wood preservative for more than 50 years, since
it is
CA 02575185 2007-01-24
effective against most wood destroying organisms such as fungi, termite and
wood-boring
beetles. Furthermore, borate has a low acute mammalian toxicity and low
environmental impact.
Borate has been considered as an excellent candidate for the CCA replacement
for wood
preservative application. However, the well-known disadvantage of borate wood
preservative is
that borate is readily soluble in water, and easily leaches out of the treated
wood upon contact
with water. As a result, the use of borate preservative is limited to the
treated wood for interior
applications.
[0004] Several methods have been used to prevent the leaching of impregnated
borate
preservatives from the treated wood. U.S. Patent No. 2,194,827 uses
solubilized metals such as
zinc and copper to fix borate in wood. This method requires high
concentrations of ammonia to
solubilize such metals and borates, resulting in excessive ammonia volatility
and noxious fumes
that are undesirable for large scale preparation. U.S. Patent No. 6,896,908
addresses the
ammonia off-gas issue by dissolving a high concentration of copper and/or zinc
metal fixative
agent in an aqueous solution of ammonia, volatile organic acid and ammonium
salts. The
combination of a volatile organic acid and ammonia provides a high rate of
metal dissolution
without requiring excessive levels of ammonia in solution, and the ammonium
salt reduces the
level of free ammonia needed for dissolution of metals. U.S. Patent No.
5,207,823 discloses
copper borate and/or zinc borate in combination of amine as a leach-resistant
borate wood
preservative. PCT Patent No. 95/27,600 teaches the use of nitrite to improve
fixation of
preservatives in wood, when the preservatives contains one or more copper
and/or zinc salts of
weak acid, and optionally boric acid and quaternary ammonium salt. U.S. Patent
No. 6,146,766
discloses the use of water soluble sodium silicate/borax mixture wherein the
impregnated silicate
component can be polymerized to reduce its water-solubility, thereby
decreasing the leaching rate
of water-soluble preservative from the treated wood. U.S. Patent No. 6,508,869
uses amine
oxide to improve leaching resistance of boron preservatives from the treated
wood. In U.S.
Patent No. 5,087,457, polyammonium salts formed through the reaction of
diamine and dihalide,
are used in combination with borate to reduce leaching rate. However, the
problem with these
methods is that even the most water-insoluble borates, boric esters, and
borate complexes will,
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on prolonged contact with water, hydrolyze to form boric acid which will leach
out of the wood.
[0005] U.S. Patent No. 4,276,329 discloses a method of enhancing the
dimensional
stability of wood by swelling and impregnating the cell walls of the wood with
a solution of low
molecular weight polymer in water and water-miscible solvent. It also teaches
that additives
such as borates can be carried into the cell walls along with the polymer. In
this method, the
water-miscible organic cosolvent is a disadvantage for environmental reasons.
It would be
desirable to have a resinous material that would fix the borate in the wood
without the necessity
of using such a solvent.
[0006] The present invention offers an alternative mechanism for fixing borate
compounds in wood, that of making the wood so hydrophobic that water can not
enter the wood
in sufficient amount to leach out the borate. It is well known in the art that
the surface of wood
can be rendered hydrophobic by coating it with paints, varnishes, waxes, and
similar materials.
However, doing so can be labor-intensive and relatively costly. Applying a
traditional
hydrophobic coating at the wood mill, as is often done with railroad ties or
telephone poles, is
much less labor-intensive than painting or varnishing. However, lumber used in
construction is
usually cut, drilled, routed, and otherwise machined in the course of its use,
which would tend to
breach such traditional factory coatings, allowing water penetration.
[0007] It is an object of the present invention to provide a method for making
wood
resistant to damage caused by soil microbes and/or insects by treating the
wood with a
formulation containing at least one boron-containing compound and at least one
hydrophobic
compound chosen from rosin-based compound, tall oil-based compound, and
mixtures thereof.
[0008] It is another object of the present invention to provide borate wood
preservatives
that not only enhance boron retention in the treated wood or other cellulosic
materials, but also
minimize toxicity and environmental impact. More particularly, it is an object
of the present
invention to provide a borate wood preservative containing no heavy metal,
thereby eliminating
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the concerns on the toxicity and environmental impact of heavy metals such as
chromium, zinc
and copper.
[0009] It is yet another objective of the present invention to provide borate
wood
preservatives that use naturally-occurring materials to retain the impregnated
boron inside the
treated wood.
[0010] It is a further objective of the present invention to provide a process
for treating
wood or other cellulosic materials with borate preservatives having improved
boron retention
that can be readily done using the equipment and process commonly available
and known for
impregnation of typical wood preservatives such as CCA.
[0011] It is yet a further object of the present invention to provide treated
wood with
enhanced boron retention that can be used for exterior applications.
[0012] Other objects, features and advantages of the present invention will
become
apparent from the following detailed description.
SUMMARY OF THE INVENTION
[0013] The objects of this invention are met by a process of treating wood
with borate
preservative formulation which contains at least one boron-containing
component and at least
one resinous component capable of retaining impregnated borate inside the
treated wood even
upon contact with water. The resinous component may be rosin, rosin
derivative, tall oil-based
compound, or mixtures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
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[0014] FIG.1 is a graph showing the percentage of boron retention at different
time
intervals under the accelerated weathering conditions for the treated boards
obtained from a two-
step process, wherein the boards are treated first with boric acid and then
resinous component.
[0015] FIG.2 is a graph showing the percentage of boron retention at different
time
intervals under the accelerated weathering conditions for the treated boards
obtained from a two-
step process, wherein the boards are treated first with resinous component and
then boric acid.
[0016] FIG.3 is a graph showing the percentage of boron retention at different
time
intervals under the accelerated weathering conditions for the treated boards
obtained from a two-
step process, wherein the boards are treated first with a liquid containing
resinous and chelating
components and then boric acid.
[0017] FIG.4 is a graph showing the percentage of boron retention at different
time
intervals under the accelerated weathering conditions for the treated boards
obtained from a one-
step process.
DESCRIPTION OF THE INVENTION
[0018] The following detailed description illustrates embodiments of the
present
invention; however, it is not intended to limit the scope of the appended
claims in any manner. It
is to be understood that changes and modifications may be made therein as will
be apparent to
those skilled in the art. Such variations are to be considered within the
scope of the invention as
defined in the claims.
[0019] The advantages and purposes of the invention will be set forth in part
in the
description which follows, and in part will be obvious from the description,
or may be learned by
practice of the invention.
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[0020] The borate preservatives of the present invention offer several
benefits. They
contain no heavy metals such as zinc, copper or chromium; therefore, they are
more
environmental friendly than the currently available CCA alternatives. They
readily penetrate into
wood and retain in the treated wood for a prolong period of time even after
exposure to rigorous
leaching conditions such as those for exterior applications. They contain low
level of ammonia,
thus avoiding the corrosion of metals in contact with the treated woods such
as metal fasteners.
Furthermore, the invention borate preservatives do not leave unsightly residue
on the surface of
the treated wood, typically observed with other CCA alternative.
[0021 ] The term "wood" in the present invention refers to any wooden article
including,
but are not limited to, structural lumbers, decking, facia boards, exterior
grade plywood,
construction elements for outdoor furniture or playground equipment, fencing,
and the like.
[0022] A method of preparing treated wood for the present invention comprises
a step of
treating wood with a borate preservative formulation, wherein the non-volatile
content of the
preservative formulation comprises:
(a) at least one boron-containing compound; and
(b) at least one resinous component comprising at least one member selected
from the
group consisting of rosin, rosin derivatives, tall oil-based compounds, and
mixtures thereo~
[0023] In one embodiment, a method of preparing treated wood for the present
invention
comprises a step of treating wood with a borate preservative formulation,
wherein the non-
volatile content of the preservative formulation comprises:
(a) from about 10% to about 90% by weight of at least one boron-containing
compound; and
(b) from about 10% to about 90% by weight of a resinous component comprising
at
least one member selected from the group consisting of rosin, rosin
derivatives,
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and mixtures thereof.
[0024] In one embodiment of the present invention, a method of treating wood
comprises
a step of treating wood with a borate preservative formulation, wherein the
non-volatile content
of the preservative formulation comprises:
(a) from about 30% to about 70% by weight of at least one boron-containing
compound; and
(b) from about 30% to about 70% by weight of a resinous component comprising
at
least one member selected from the group consisting of rosin, rosin
derivatives,
and mixtures thereof.
[0025] The boron-containing compounds suitable for use in the present
invention include,
but are not limited to, boric acid, borate salts, borate esters, and mixtures
thereof.
[0026] The resinous component of the present invention comprises at least one
member
selected from the group consisting of rosin, rosin derivatives, tall oil-based
compounds, and
mixtures thereof.
[0027] Suitable rosins for use in the present invention include, but are not
limited to, tall
oil rosin, gum rosin, wood rosin, and mixtures thereof. Rosin derivatives
suitable for use in the
present invention include, but are not limited to, the following: hydrogenated
rosins,
disproportionated rosins, formaldehyde-treated rosins, dimerized rosins,
polymerized rosin,
fumarated rosins, maleated rosins, styrenated rosins, phenolic-modified
rosins, acrylic-modified
rosins, hydrocarbon-modified rosins, rosin-vinylic copolymers, rosin salts,
hydrogenated rosin
salts, disproportionated rosin salts, formaldehyde-treated rosin salts,
dimerized rosin salts,
polymerized rosin salts, fumarated rosin salts, maleated rosin salts,
styrenated rosin salts,
phenolic-modified rosin salts, acrylic-modified rosin salts, hydrocarbon-
modified rosin salts,
rosin-vinylic copolymer salts, rosin esters, hydrogenated rosin esters,
disproportionated rosin
esters, formaldehyde-treated rosin esters, dimerized rosin esters, polymerized
rosin esters,
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fumarated rosin esters, maleated rosin esters, styrenated rosin esters,
phenolic-modified rosin
esters, acrylic-modified rosin esters, hydrocarbon-modified rosin esters,
rosin-vinylic copolymer
esters, rosin amides, hydrogenated rosin amides, disproportionated rosin
amides, formaldehyde-
treated rosin amides, dimerized rosin amides, polymerized rosin amides,
fumarated rosin amides,
maleated rosin amides, styrenated rosin amides, phenolic-modified rosin
amides, acrylic-
modified rosin amides, hydrocarbon-modified rosin amides, rosin-vinylic
copolymer amides, and
mixtures thereof.
[0028] Tall oil-based compounds suitable for use in the present invention
include, but are
not limited to, tall oil pitch; crude tall oil (CTO); tall oil fatty acids
(TOFA); and TOFA
derivatives such as esters, salts, dimer acids, trimer acids, triglycerides,
amides, adducts of
acrylic acids, adducts of unsaturated fatty acids, and mixtures thereof
Adducts of acrylic acids
and unsaturated fatty acids such as WESTVACO DIACID available from
MeadWestvaco are
also suitable for use in the present invention. Other similar non-TOFA-derived
fatty acids and
derivatives may also be used.
[0029] Where desired, one or more non-rosin containing resinous materials can
be
admixed with the rosins and/or rosin derivatives. Additive non-rosin
containing resinous
materials suitable for admixture with the rosins and/or rosin derivatives may
be those that are
hydrophobic and that have solubility parameters similar to those of rosin
acids. Suitable
examples include, but are not limited to, the following: fatty acids, dimer
acids, trimer acids,
triglycerides, terpenes, phenolic resins, hydrocarbon resins, phenolic-
modified terpene resins,
phenolic-modified hydrocarbon resins, tall oil pitch, adducts of acrylic
acids, adducts of
unsaturated fatty acids, adducts of acrylic acids and unsaturated fatty acids
such as WESTVACO
DIACID available from MeadWestvaco, and mixtures thereof.
[0030] In one embodiment of the present invention, the aforementioned resinous
component comprises:
(a) from about 20% to about 100% by weight of the resinous component of at
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least one member selected from the group consisting of rosins, rosin
derivatives, and mixtures thereof; and
(b) up to about 80% by weight of the resinous component of at least one non-
rosin
containing resinous material.
[0031 ] The borate preservative formulations of the present invention may be
emulsion,
dispersion, or solution. Aqueous or other common solvents known in arts such
as mineral oil or
toluene may be used as liquid medium for the preservative formulation. The
liquid containing
the boron component can be either a solution obtained from dissolving boron
components
directly into an aqueous phase, or an emulsion obtained from homogenizing an
aqueous phase
and an oil phase with an emulsifier.
[0032] Where desired, the method of the present invention may be practiced at
a neutral
pH in the range of about 6.0 to about 10.0 to minimize potential corrosion
problems with
fasteners (such as nails, screws, and the like).
[0033] The impregnation of board with the invention borate may be done by any
method
known to one of ordinary skill in the art including, but are not limited to,
pressure treating,
vacuum impregnating, soaking, spraying, painting, brushing, washing, dipping,
rubbing, mixing,
blending, infusion and the like.
[0034] In some embodiments of the present invention, wood was immersed in the
borate
preservative formulation at an ambient temperature or elevated temperature.
[0035] In some embodiments, the impregnation was carried out at elevated
pressures.
"Loading" refers to the absorption of the impregnating borate preservative by
the wood.
Methods of treating wood with chromated copper arsenate solutions and similar
pesticidal
mixtures at elevated pressures are well known in the art. The same equipment
(e.g., pressure
vessels) employed in such currently-used pesticide treatment methods can be
readily adapted to
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the treatment of wood with the borate preservative of the present invention.
The upper limit of
the applicable pressure depends on the respective crushing strength of the
wood, as collapsing of
the wood should be avoided. In one embodiment, the applied pressure is in the
range of about 50
psi to about 200 psi. Where desired, a vacuum may be applied during the
impregnation step to
enhance the efficiency of the loading.
[0036] Wooden boards may be treated with the invention borate preservative
using one-
step process and two-step processes. In the two-step process, wood was treated
with the first
liquid formulation and allowed to dry prior to the application of the second
liquid formulation.
[0037] After treating with the invention borate preservative formulation, the
treated
boards may be dried under ambient condition. Kiln drying or other heat
treatment may also be
used to help fix the preservative components in the wood.
[0038] The treated boards were then placed under an accelerated weathering
conditions
simulating rainfall volumes of 90 inches per day, using a 24 hour-cycle water
spray consisting of
3 hours of water spray, 3 hours of drying, 3 hours of water spray and 15 hours
of drying. The
treated boards were subjected to these accelerated weathering conditions for
14 weeks which
equaled to a total of 8,820 inches of rain for an entire period. The sample of
treated board was
taken each week for the measurement of boron content. The boards treated with
either only boric
acid or disodium octaborate tetrahydrate (DOT) were included in the
accelerated weathering as a
control condition along with the boards treated with the invention borate
preservatives. An
inductively coupled plasma (ICP) device was used to measure the content of
boron in each board
before the treatment, and after every week of accelerated weathering. The
retention of boron as a
percentage of the initial impregnated boron level was calculated, and compared
to those of the
control boards.
[0039] In one embodiment of the two-step process, wooden boards were first
treated with
an aqueous 4% boric acid solution. After one-week drying, the treated boards
were secondarily
CA 02575185 2007-01-24
treated with a liquid containing resinous component having about 10% to about
20% solid in
toluene solvent. (Table 1, Figure 1)
Table 1
1" Treating 2 d Treating Amount of Boron in the Board
Formulation Formulation Initial 14-week % Retention
(ppm) weathering after 14-week
(ppm) weathering
4% Boric Acid 10% Depitched CTO 3199 1088 34%
4% Boric Acid 20% Stafor L-50 2812 872 31%
4% Boric Acid None 3963 277 7%
[0040] The control boards treated with only boric acid retained about 7% of
the initial
impregnated boron after 14 weeks of accelerated weathering test. Boards
treated with boric acid
and followed with depitched crude tall oil resin (CTO) retained about 34% of
the initial boron
content after 14 weeks of accelerated weathering test. Boards treated with
boric acid and
followed with Stafor L-50, a potassium salt of fumarized rosin commercially
available product
from MeadWestvaco, retained about 31% of the initial boron content after 14
weeks of
accelerated weathering test. Secondary treating of the boards, after the
treatment with boric acid,
showed a significant improvement in boron retention after severe weathering
test.
[0041 ] In one embodiment of the two-step process, wooden boards were first
treated with
a liquid containing resinous component. After one-week drying, the treated
boards were
secondarily treated with a 4% boric acid solution. (Table 2, Figure 2)
Table 2
lst Treating 2 Treating Amount of Boron in the Board
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Formulation Formulation Initial 14-week % Retention
(ppm) weathering after 14-week
(ppm) weathering
10% Depitched CTO 4% Boric Acid 4465 938 21%
20% Stafor L-50 4% Boric Acid 2963 563 19%
4% Boric Acid None 3963 277 7%
[0042] The control boards treated with only boric acid retained about 7% of
the initial
impregnated boron after 14 weeks of accelerated weathering test. Boards
treated with depitched
crude tall oil resin (CTO) followed with boric acid retained about 21 % of the
initial boron
content after 14 weeks of accelerated weathering testing. Boards treated with
the potassium salt
of fumarized rosin, Stafor L-50, followed with boric acid, retained about 19%
of the initial
boron content after 14 weeks of accelerated weathering test.
[0043] In some embodiments of the present invention, the preservative
formulation
further comprises at least one component capable of chelating with boron to
additionally enhance
the retention of borate preservative in the treated wood. Boards were first
treated with a liquid
formulation containing a resinous component and a chelating component. After
one-week of
drying, the treated boards were secondarily treated with a 4% boric acid
solution. (Table 3,
Figure 3)
Table 3
Ist Treating Formulation 2 d Treating Amount of Boron in the Board
Formulation Initial 14-week % Retention
(ppm) weathering after 14-week
(ppm) weathering
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20% Stafor L-50 4% Boric Acid 2963 56 19%
20% Stafor , 10% Wood extract 4% Boric Acid 1663 998 60%
20% Stafor , 10% Fructose 4% Boric Acid 1945 856 44%
20% Stafor , 6% PVOH 4% Boric Acid 1700 578 34%
4% Boric Acid None 3963 277 7%
[0044] The control board treated with only boric acid retained about 7% of the
initial
impregnated boron after 14 weeks of accelerated weathering test. Boards
treated with only the
potassium salt of fumarized rosin, Stafor L-50, retained about 19% of the
initial boron. When
the 1St treating formulation contained a chelating component, in addition to
the potassium salt of
fumarized rosin, Stafor L-50, the treated wood showed a significant increase
in boron retention.
Wood extract from spent kraft pulping liquor generally contains organic acids,
lignin,
hemicellulose, terpenes, natural wax, sodium salts, and several other minor
organic ingredients.
When wood extract was used as a chelating component, the boron retention
increased to about
60%. When fructose and polyvinylalcohol (PVOH) were used as chelating
component, the boron
retention after 14 weeks of accelerated weathering test increased to about 44%
and 34%,
respectively.
[0045] In some embodiments, boards were treated in a one-step process with a
preservation formulation containing a boron-containing component such as DOT
and a resinous
component, optionally with a chelating component. (Table 4, Figure 4)
Table 4
Treating Formulation Amount of Boron in the Board
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Initial 14-week % Retention after
(ppm) weathering 14-week
(ppm) weathering
20% Stafor , 10% Wood extract, 4% DOT 3861 1660 43%
20% Stafor , 10% Glycerin, 4% DOT 3696 924 25%
4% DOT
4100 656 16%
L-- ~ J
[0046] The control board treated with only boric acid retained about 16% of
the initial
impregnated boron after 14 weeks of accelerated weathering testing. When the
preservative
formulation containing a potassium salt of fumarized rosin, wood extract
chelating agent and
DOT was used, the treated wood retained about 43% of the initial boron. When
glycerin was
used as a chelating component, the boron retention of the treated wood was
about 25%.
[0047] One embodiment of the present invention comprises the steps of:
(i) immersing wood in a borate preservative formulation, wherein the non-
volatile content
of the formulation comprises:
(a) at least one boron-containing compound; and
(b) at least one resinous component comprising at least one member selected
from
the group consisting of rosin, rosin derivatives, tall oil-based compounds,
and
mixtures thereof;
(ii) loading the immersed wood with the formulation under excess pressure for
a period of
time sufficient to impregnate the wood with a biocidally effective level of
borate,
thereafter relieving the excess pressure; and
(iii) removing the wood from the liquid.
[0048] One embodiment of the present invention comprises the steps of:
(i) immersing wood in a liquid containing at least one borate-containing
component;
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(ii) loading the immersed wood with the liquid under excess pressure for a
period of time
sufficient to impregnate the wood with a biocidally effective level of borate,
thereafter
relieving the excess pressure;
(iii) removing the wood from the liquid;
(iv) drying the wood;
(v) loading the resulting wood with a liquid containing a resinous component,
wherein the
resinous component comprises at least one member selected from the group
consisting
of rosin, rosin derivatives, tall oil-based compounds, and mixtures thereof;
and
(iv) removing the wood from the liquid.
[0049] One embodiment of the present invention comprises the steps of:
(i) immersing wood in a liquid containing a resinous component, wherein the
resinous
component comprises at least one member selected from the group consisting of
rosin,
rosin derivatives, tall oil-based compounds, and mixtures thereof;
(ii) loading the immersed wood with the liquid containing a resinous
component;
(iii) removing the wood from the liquid;
(iv) drying the wood;
(v) loading the resulting wood with a liquid containing at least one borate-
containing
component under excess pressure for a period of time sufficient to impregnate
the wood
with a biocidally effective level of borate, thereafter relieving the excess
pressure; and
(vi) removing the wood from the liquid.
[0050] The upper limit of the applicable pressure in steps (ii) and (v) mainly
depends on
the respective crushing strength of the wood, as collapsing of the wood should
be avoided. In
one embodiment, the applied pressure was in the range of about 50 psi to about
200 psi. Where
desired, a vacuum may be applied during steps (ii) and (v) to support the
efficiency of the
loading.
CA 02575185 2007-01-24
[0051 ] Pesticidal wood treatments currently in use, such as CCA and ACQ,
impart a
color to the wood due to the nature of the metal ions present. This color also
serves as a
convenient indication for the consumer that the wood has been so treated.
Where desired, at least
one dye and/or pigment may be added to the borate preservative formulation of
the present
invention in order to impart a color to the resulting wood to serve as a
similar indicator. A
combination of lignin and a green pigment such as chlorinated copper
phthalocyanine is
particularly effective in mimicking the color of CCA-treated wood. The use of
light-fugitive
dyes may be particularly advantageous in this application; as the use of such
dyes permits the
wood to be colored for identification but, once the wood is in place in or on
an outdoor structure,
the exposure to sunlight will bleach the dye and the wood will revert to its
natural color.
[0052] The following examples are provided to further illustrate the present
invention
and are not to be construed as limiting the invention in any manner.
EXPERIMENTAL
[0053] One-Step Treatment Process:
[0054] Fourteen-inch mature southern pine sapwood boards were placed inside a
treating
container and immersed completely in a liquid containing 3200 g of a treating
formulation. The
treating container was placed inside an eight-inch diameter treater vessel.
After the vessel was
sealed, a vacuum of 22 inches of Hg was applied inside the vessel for 10
minutes. Then, the
vessel was filled with air and pressurized to 150 psig. The pressure was held
for 20 minutes
before being released. The boards were removed from the treating container,
and the container
was emptied of solution. After drying with a paper towel, the treated boards
were placed back in
the treating container, which was then transferred back inside the vessel.
Once the vessel was
sealed, a vacuum of 25 inches of Hg was drawn for 10 minutes. After releasing
the vacuum, the
treated boards were removed from the pan and air dried for a minimum of one
week.
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[0055] Two-Step Treatment Process:
[0056] (a) Pressure Treatment with Primary Treatment Solutions
[0057] Fourteen-inch mature southern pine sapwood boards were placed inside a
treating
container and immersed completely in a liquid containing 3200 g of the first
treating formulation.
The treating container was placed inside an eight-inch diameter treater
vessel. After the vessel
was sealed, a vacuum of 22 inches of Hg was applied inside the vessel for 10
minutes. Then, the
vessel was filled with air and pressurized to 150 psig. The pressure was held
for 20 minutes
before being released. The boards were removed from the treating container,
and the container
was emptied of solution. After drying with a paper towel, the treated boards
were placed back in
the treating container, which was then transferred back inside the vessel.
Once the vessel was
sealed, a vacuum of 25 inches of Hg was drawn for 10 minutes. After releasing
the vacuum, the
treated boards were removed from the pan and air dried for a minimum of one
week.
[0058] (b) Pressure Treatment with Secondary Treatment Solutions
[0059] The boards previously treated with the primary solution were in placed
inside a
treating container and immersed completely in a liquid containing 3200 g of
the 2 d treating
solution. The treating container was placed inside an eight-inch diameter
treater vessel, and the
same treating cycle as for the primary treatment process was applied to the
treater vessel. After
the treatment, the treated boards were removed from the vessel and air dried
for a minimum of
one week.
[0060] Accelerated Weathering of the Treated Board:
[0061 ] After one-week of drying, the treated boards were attached by screws
to a deck
frame, and the initial level of boron impregnated in the treated boards was
determined using an
ICP device. The deck was then placed under a simulated condition of 90 inches
of rain using a
24 hour-cycle water spray consisting of 3 hours of water spray, 3 hours of
drying, 3 hours of
water spray, and 15 hours of drying. The treated boards were sampled weekly
during the first six
weeks and then every the other week from week 8 to week 14.
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