Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~042791
This invention concerns a wood treating compo-
sition and a method for impregnating wood.
The utilization of halogenated hydrocarbon
solvents as carriers for the impregnation of wood with
preservatives, dyes, antiblooming agents, fire-retardants
and the like has provided the art with a process superior
to creosote oil, petroleum oil or liquefied petroleum gas
techniques. The halogenated hydrocarbon solvent process
is less expensive and more versatile, providing treated
wood which is lighter, and therefore generally less
expensive to ship. Also, wood treated in this manner has
good retention of the additives and may be painted which
was more difficult or impossible with older techniques.
Such halogenated solvent processes generally
comprise soaking wood in a solution of a wood preservative
in a relatively low boiling solvent such as methylene
chloride or trichloroethylene. Pentachlorophenol is a
commonly used preservative. The solution may also contain
an antiblooming additive such as a glycol or glycol
derivative. The soaking step may be carried out at ambient
or somewhat elevated temperature and pressure. When the
wood has been sufficiently impregnated by the treating
solution~ the excess solution is drawn off and the wood
is heated to vaporize the solvent in the wood. Solvent
removal is completed by air drying. A final treatment of
the wood by application of reduced pressure may also be
used for this purpose.
The wood treating technique using a halogenated
hydrocarbon solvent results in a loss of from 0.5 to 1.5
pounds (8-24 kg.) of solvent per cubic foot (meter) of
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wood treated in addition to the additives retained by the
wood. Thus, it has been necessary for the operator to
"test and add" to his treating tank in order to maintain
the desired concentration of treating agents and to make
up solvent lost. In the "test and add" technique, since
many of the preservatives are not readily soluble in the
halohydrocarbon solvent and preservatives such as penta-
chlorophenol are soluble only to about 10 percent by weight
in the solvent, the operator must recirculate large quan-
tities of solvent through a solid bed of the preservativeto his storage tank. The present invention provides a
composition and method for replenishing the depleted
treating solution by the continuous or intermittent
addition of the liquid concentrate, thereby maintaining the
concentration of the treating agents and replacing lost
solvent at the same time.
The present invention provides a wood treating
composition comprising A) from 5 to 40 weight percent of a
wood preservative; B) from 2 to 60 weight percent of at
least one of ethylene glycol, propylene glycol, a corres-
ponding liquid polyglycol having a molecular weight up to
4000, or a mono aLkyl ether of ethylene or propylene glycol
or polyglycol dissolved or dispersed in a halogenated
aliphatic hydrocarbon solvent of 1-2 carbon atoms, said
solvent boiling between ambient temperature and 140C.
Other wood treating additives such as dyes may also be
present in the concentrate in minor amounts, but those
listed are the essential components.
This invention further provides a process for
impregnating wood which comprisss the steps: (l) contacting
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1()4Z791
wood with a solution in a halogenated hydrocarbon solvent
of 1-2 carbon atoms containing 2-6 weight percent of a
wood preservative and 0.5-4 weight percent of a glycol
component which is at least one of ethylene glycol, pro-
pylene glycol, a corresponding liquid polyglycol ofmolecular weight up to 4000, or a lower aIkyl monoether
thereof at from ambient temperature to 140C. and at a
pressure to maintain the solvent in a liquid state, (2)
removing excess solution from contact with the wood and
returning it to storage, (3) heating the wood at least to
the boiling point of the solvent, condensing the thereby
vaporized solvent, and combining the condensed solvent with
the excess solution, characterized by adding a composition
as defined above to the depleted combined excess solution
ànd condensed solvent to restore it to about the compo-
sition of the starting solution.
The use of the polyglycol or the glycol ether
allows a larger amount of preservative to be held in the
concentrate as well as providing beneficial characteristics
to the treated wood. Thus, it acts as a co-solvent in the
three-component system and it also aids the retention of
the preservative in the wood. Only about 9/O by weight of
pentachlorophenol is soluble in methylene chloride alone,
whereas if the concentrate solution contains 20-25% by
weight of glycol, polyglycol or glycol ether, as much as
40/O by weight of the preservative can be present in
solution, the remainder being the methylene chloride.
Similarly, chloroform, ethylene dichloride, methyl chloro-
form, trichloroethylena, dichloroethylene, and perchloro-
ethylene have relatively low solvency for most wood
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104;~791
preservative agents, especially the chlorinated phenols.
With these solvents; the use of a glycol, polyglycol or
glycol ether as a co-solvent also makes it possible to
dissolve a substantially larger amount of preservative in
the concentrate solution.
A typical solvent wood treating process is here-
after described.
Wood impregnation with a preservative is achieved
by soaking wood under pressure in a solution of the desired
preservative in a halogenated hydrocarbon solvent with
glycol additive and subsequently steaming or otherwise
heating the treated wood to recover the solvent employed
to carry the preservative into the wood. A finishing
application of reduced pressure to the heated wood may be
-`~ 15 employed to remove more residual solvent and water. Wood
treated in this manner contains little or no residual
solvent, and is therefore essentially free of surface
bleeding. The process likewise provides the additional
advantage of producing a treated wood product which retains
the light color and natural appearance of untreated wood
and which does not darken with age.
The present invention is preferably used as an
added step in a wood treating process comprising the
following operations:
(1) Wood in the desired form such as poles,
lumber, or timbers is contacted in a suitable treating
chamber with a solution or dispersion in a halogenated
hydrocarbon solvent, preferably methylene chloride, con- - -
taining 2-6 percent by weight of a wood preservative such
as pentachlorophenol and 0.5-4 percent of a glycol or glycol
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1042791
ether antiblooming agent at ambient temperature to 140C.
and at a pressure sufficient to maintain the ~olvent in
the liquid state at the operating temperature. The time of
contact may be from 1 to 12 hourcl, depending upon the type
5~ and specie of wood employed.
(2) The excess solution is removed from contact
with the wood and returned to storage.
(3) The treated wood is heated at least to the
boiling point of the solvent, preferably with steam, and
the solvent vapors thereby formed are condensed and conlbined
in storage with the excess solution removed in step (2),
thereby forming a wood treating solution containing lower
concentrations of both preservative and antiblooming agent
than the original solution.
(4) (Optional) The heated wood is subjected to
- reduced pressure to vaporize most of the residual solvent
in the wood and the solvent vapors are condensed and com-
bined with the recovered solution and solvent from steps
(2) and (3).
The concentrate of the present invention is then
added as the sole source of makeup to the depleted wood
treating solution in a quantity sufficient to restore it to
its original concentrations of preservative and antiblooming
agent and the restored solution is returned to the process
for another wood treating cycle. In the above-described
- process, some modifications of procedure or materials may
be made without altering the essential nature of the
process. For example, in step (3), the wood can be heated
with superheated solvent vapors rather than steam, thereby
reducing the volume of water which has to be separated from
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11~)4Z791
the condensed vapors before returning the recovered solvent
to storage.
A preferred concentrate composition consists
essentially of 10-35 percent by weight of pentachlorophenol
and 5-55 percent of glycol antiblooming additive in methylene
chloride. Although any of the glycols and glycol ethers
described below can be used to advantage in the process,
particularly preferred antiblooming additives are diethylene
glycol and polypropylene glycol of about 750 molecular
weight.
The treated wood produced by this process as
described above has a clean, natural appearance when
removed from the treating chamber and is essentially ready
for use at that time.
The amounts of preservative and the depth of
penetration necessary to provide the desired protection
are well known to those skilled in the art of wood preser-
vation. In the case of pentachlorophenol and closely
related compounds, a desirable concentration is from about
0.35 to 0.7 lbs. (5.6-11.2 kg.) of preservative per cubic
foot (meter) of wood on a dry weight basis, depending upon
the species of wood.
Halogenated aliphatic hydrocarbon solvents suit-
able for use in the present invention are those which have
boiling points of from about room temperature up to 140C.,
` preferably up to 100C. Examples of such solvents are
the polyhalomethanes, polyhaloethanes and polyhaloethylenes
such as methylene chloride, chloroform, carbon tetrachloride,
methylene chlorobromide, l,l,l-trichloroethane, dibromo- -
difluoroethane (BrFCHCHFBr), ~richlorotrifluoroethane
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1l)~279:1
(C12FC-CF2Cl)~ tetrafluorodibromoethane (BrF2C-CF2Br),
tetrachlorodifluoroethane (C12Fc-CFC12), cis- and trans-
dichloroethylene (ClCH:CHCl), trichloroethylene, perchloro-
ethyleneJ l,l-dichloroethaneJ ethylene dichloride, or
1J 1J 2-trichloroethane. Particularly preferred solvents are
lower boiling chlorinated compounds such as methylene
chloride or ~richloroethylene.
Wood preserving agents which can be employed in
this invention include those which are solvent-soluble or
solvent-dispersibleJ unreactive with the solvent and are
essentially nonvolatile at or below the boiling point of
the solvent from which they are being impregnated into the
wood. If more than one such agent is utilizedJ it is
desirable that they do not react with one another in such
a way as to interfere with the property or properties
which they are intended to impart to the wood.
It is preferred that the agents be soluble in the
solvent selectedJ but the solubility need not be great. For
example, as little solubility as about one weight percent
of preservative is operableJ but generallyJ preservatives
are used which are soluble at least to the extent of 2 to
6 weight percent. Polyglycol and glycol ether antiblooming
agents are employed in from 0.5 to 4 weight percent based
upon the weight of solvent and these of course increase
the amount of polychlorinated phenols and other preser-
vatives that can be dissolved in the composition.
Wood preservatives for use in the process des-
cribed above and which are employed in preparing the
concentrates of this invention include pentachlorophenol,
2,3,4,6-tetrachlorophenol, 2,4,5-trichlorophenol, 2,4,6-
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1~)4;~791
-trichlorophenol, 4-chloro-2-chLoropentylphenol, beta-
-napththol, copper naphthenate, and phenyl mercury oleate.
Other known wood preservative compounds which are soluble
or can be dispersed in halogenated hydrocarbon solvents
with the aid of co-solvents or dispersants may also be
used. Pentachlorophenol and its mixtures with tetrachloro-
phenol are preferred.
Glycols suitable for preparing the concentrate
of the present invention and which are also useful in
providing antiblooming properties are ethylene glycol,
propylene glycol and corresponding liquid polyalkylene
- glycols having molecular weights of up to 4000. Glycol
ethers which are useful in accordance with the present
invention are those liquid Cl 4 alkyl monoethers of these
glycols and polyglycols such as the methyl, ethyl or butyl
monoethers of the mono-, di- and tri-ethylene and propylene
glycols. Representatives of the above class of solvents
are propylene glycol, diethylene glycol, dipropylene glycol,
tripropylene glycol, ethylene glycol methyl ether,
diethylene glycol butyl ether, propylene glycol methyl
ether, dipropylene glycol methyl ether, and tripropylene
glycol methyl ether. Mixtures of two or more of such
compounds can be used.
The following examples illustrate the invention.
EXAMPLE 1
A treating solution of pentachlorophenol and di-
ethylene glycol in methylene chloride which had been used
in the wood treating process, and which had originally
; contained about 5.0~ pentachlorophenol and 2.5% glycol
- 30 based on the total weight of ~olution, was found by analysis
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104Z791
after treatment to contaln 2.5% pentachlorophenol and
1.25% glycol. To 1000 pounds (450 kg.) of this depleted
solution was added 110 pounds (50 kg.) of concentrate con-
taining 28.6% pentachlorophenol and 14.3% diethylene glycol,
the remainder being methylene chloride. The resulting
1110 (500 kg.) pounds of solution contained 5.09% penta-
chlorophenol and 2.54% diethylene glycol, which was then
at the proper concentration for processing more wood.
EXAMPLE 2
In another instance a somewhat stronger concen-
trate was used to replenish the depleted wood treating
solution. Thus to 1000 pounds (450 kg.) of treating
solution was added 70 pounds (31.5kg.) of a concentrate
containing 33.3% pentachlorophenol and 22.2% diethylene
glycol in methylene chloride based on the total weight
of the concentrate. The treating olution was thus
brought from a concentration of 3.0% pentachlorophenol and
1.5% glycol to a useable concentration of 4.98% pentachloro-
phenol and 2.85% glycol.
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