AU2006257893A1

AU2006257893A1 - Process for moisture-proofing wood

Info

Publication number: AU2006257893A1
Application number: AU2006257893A
Authority: AU
Inventors: Thomas Scharling Christensen; Flemming Correll Frank; Lars Norden; Lars Nyborg
Original assignee: Osmose Inc
Current assignee: Osmose Inc
Priority date: 2005-06-10
Filing date: 2006-06-12
Publication date: 2006-12-21
Also published as: SE0700293L; EA200800012A1; EP1888260A4; EP1888260A1; WO2006135858A1

Description

WO 2006/135858 PCT/US2006/022763 PROCESS FOR MOISTURE-PROOFING WOOD This application claims priority to U.S. provisional application number 60/689,657, filed on June 10, 2005, the disclosure of which is incorporated herein by reference. FIELD OF THE INVENTION This invention relates to processes for water-proofing wood, and more particularly to processes by which wood can be water-proofed and treated with additives in the same process step. BACKGROUND The absorption of moisture by wood is generally considered to interfere with the usefulness of wood and wood products. Moisture can shorten the useful lifespan of wood by increasing the susceptibility of the wood to fungal and bacterial decay. Moisture can also reduce the effectiveness of wood treatments such as painting in that condensation which is trapped inside the wood by an overcoat such as, for example, a layer of paint, can cause the overcoat to blister and separate from the wood. Furthermore, the absorption of moisture by wood can result in swelling and warping, and cyclic absorption and drying can cause permanent distortion of the wood over time, thus reducing the service life of the timber. However, current processes for moisture-proofing wood can be difficult to implement because they often involve lengthy processes conducted at high temperatures. The wood is exposed to oils at temperatures which can be as high as 75'C for times which can be longer than 12 hours. The requirement for such conditions limits the types of additives which can be used. For example, a common vacuum drying process which is widely used for moisture proofing, requires process parameters such as those mentioned above. While it would be particularly convenient to treat the wood with biocides during the process, the process conditions are such that many common additives, such as some organic biocides, such as for example, IPBC, and colorant additives, such as, for example, pigments and dyes, can be thermally degraded. Moreover, moisture-proofed wood is often further treated with additional surface coats such as paints or stains. Moisture-proofing oils must not prevent the overcoat from adhering to the wood.

WO 2006/135858 PCT/US2006/022763 A process which is less time-consuming than existing processes and which has the ability to 1) water-proof wood and treat it with temperature sensitive additives in the same process step and 2) result in a wood product which retains desirable overcoat adhesion properties would be welcome in the art of wood preservation. SUMMARY OF THE INVENTION The present invention is an improvement over currently available processes for the protection of wood or wood products, particularly timber, from moisture absorption. The present invention enables wood to be water-proofed in much less time than required by existing processes, allowing the use of additives which would otherwise be degraded by long exposure to high temperatures. In one embodiment is provided a process for water-proofing wood comprising the steps of 1) providing pre-dried wood or wood product; 2) providing a mixture comprising one or more high-boiling point oils, one or more drying oils, and preferably, a siccative; 3) contacting the wood or wood product with the mixture for a time in the range of from 0.1-5 (hours) at one or more temperatures in the range of from 350 C to 900 C, at one or more pressures in the range of from 0-15 atmospheres. The present invention enables treatment with additives and waterproofing to take place in a single step. Thus in another embodiment, the present invention provides a process as elucidated above, wherein the mixture of oils further comprises one or more additives. In an additional embodiment, one or more of the additives are temperature sensitive. In a further embodiment, the temperature-sensitive additive is IPBC. Unlike other water-proofing methods, the method of the present invention is particularly useful in the protection of wood from moisture in the period between the manufacture of the boards and its first painting. Wood treated with the process of the present invention can remain sufficiently dry for time periods of up to 10 months without the necessity of a follow up overcoat application. Also provided is water-repellent wood which is treated according to the inventive process. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A-iF show a schematic of the process of the invention. Fig. 1A - Timber is transferred into the treatment vessel. Fig. lB - A vacuum pulls air out of the vessel. - 2- WO 2006/135858 PCT/US2006/022763 Fig. 1 C - Oil mixture fills the vessel. Fig. 1D - Vessel is pressurized, forcing the preservative into the timber. Fig. 1E - Oil mixture preservative is withdrawn and final vacuum is applied. Fig. 1F - Preserved timber. Fig. 2 - Wood which has been treated with oil stabilization according to the inventive process described herein. Oils used were linseed oil and mineral oil. Treatment parameters were: -0.9 bar for 20 minutes followed by 5 minutes holding at atmospheric pressure and finally -0.9 bar for 20 minutes. Fig. 3 - Wood which has been treated according to a commonly used vacuum drying process. DETAILED DESCRIPTION OF THE INVENTION The wood to be treated with the process of the present invention is preferably dry prior to treatment. Wood which is "dry" as used herein has a moisture content of less than about 28 weight % water, and preferably a moisture content less than about 20 weight % water. In the present invention, a wood or a wood product is treated with an oil mixture comprising a drying oil and a high boiling point oil. Generally, a drying oil is an oil that oxidizes in contact with air and thereby hardens and dries. The drying oils which can be used in the present invention include linseed oil, "ricin" oil, tall oil, cottonseed oil, corn oil, soybean oil, tung oil, and other oils that oxidize and harden upon contact with air. Preferred are drying oils, such as linseed oil, which result in a dry surface which can adhere to water-based stains and coatings and which has little or no stickiness. The oil mixture also comprises a "high-boiling point" oil, i.e., an oil with a boiling point in the range of from 250<X<400 *C at atmospheric pressure. High-boiling point oils which can be used include mineral oil and other technical White Oils. The high boiling point oil content should be in the range of from 30 - 70 wt %, and preferably in the range of 40 - 60 wt %, where the wt % is based upon the total weight of the high-boiling point and drying oil components. In one embodiment, the mineral oil content is about 50 wt %, based upon the total weight of the high-boiling point and drying oil components. When the oil hardens/dries it slows water uptake and evaporation, thereby stabilizing the timber by reducing twisting, warping and cracking. -3- WO 2006/135858 PCT/US2006/022763 Additionally, the oil mixture preferably comprises a siccative in order to catalyze the drying reaction of oxygen with the drying oil, decreasing the drying time. Examples of siccatives which can be used in the present invention include cobalt-, manganese-, lead-, zirconium-, zinc- or calcium-carboxylate containing siccatives. The siccative is used in a weight percent which is in the range of from .005 and .5 wt %, and preferably .05 to .2 wt %, based on the weight of the oil mixture. The oil mixture may comprise additional components, including as non-limiting examples; biocides, pigments, dyes, uv filters, and flame retardants. UV-filters can be incorporated to protect the water-proofing oil and the wood, especially when they are unpigmented, from UV degradation. Non-limiting examples of biocide types which can be included in the oil mixture include fungicides, insecticides, bactericides, termiticides, etc. In general, it is preferred that additives such as uv filters be "oil soluble." By "oil soluble," it is meant that the biocide has a solubility in the oil mixture to be used of more than about .05 wt % , based upon the combined weight of the oil and biocide. Other additives can generally be either oil soluble, present as particles, or both. Biocides are preferred additives. In general, it is also preferred that biocide additives be oil soluble. Examples of biocides which generally have such solubility in the oil mixtures of the present invention include iodopropynyl butyl carbamate (IPBC), azoles, isothiazolones, bifenthrin, permethrin, cypermethrin, etofenprox, clothianidin and quaternary ammonium compounds, many copper compounds, and mixtures of the foregoing. Many desirable biocides, and other additives as well, may not have such a solubility in the oil mixture to be used. In such cases it is permissible to use the biocide or additive in a dispersion or other particulate form, given that the particles are small enough to penetrate the wood. These particle size parameters are given in co-pending U.S. application 11/126,839, filed on May 11, 2005, published as 2005/0265893 and incorporated herein by reference. In general, a great range of biocides and other additives can be used in the method of the present invention, including many or all BPD Notified biocides available in Europe. Exemplary Fungicides include, Dazomet (CAS # 533-74-4 ), Sorbic acid (CAS # 110 44-1 ), IPBC (CAS # 55406-53-6 ), Tebuconazole (CAS # 107534-96-3 ), Thiabendazole ( CAS # 148-79-8 ), Fenpropimorph (CAS # 67564-91-4 ), Borate polymer (CAS # 214710 34-6), Copper oxide ( CAS # 1317-38-0 ), Copper ( II ) carbonate ( CAS # 12069-69-1 ), copper dihydroxide ( CAS # 20427-59-2 ), Tolyfluanid (IPreventol A5) (CAS # 731-27-1) Propiconazole (CAS # 60207-90-1 ), DDAC (CAS # 7173-51-5 + another), BAC (CAS # -4- WO 2006/135858 PCT/US2006/022763 68424-85-1), Bardap 26 (CAS # 94667-33-1 ), TMAC (Quat) (CAS # no number), Imazalil (CAS # 35554-44-0 ), Diboron trioxide (CAS # 1303-86-2 ), Disodium tetraborate (CAS # 1330-43-4 ), Boric acid (CAS # 10043-35-3 ), DOT ( CAS # 12280-03-4 ), Lonzabac 12.100 (CAS # 2372-82-9 ), Dichlofluanid (Preventol A4 S ) (CAS # 1085-98-9), and Guazatine triacetate (CAS # 115044-19-4 ). Exemplary Insecticides include Etofenprox (CAS # 80844-07-1 ), Clothianidin (CAS # 210880-92-5 ), Thiamethoxam (CAS # 153719-23-4 ), Flufenoxuron (CAS # 101463-69-8) Bifenthrin (CAS # 82657-04-3 ), Permethrin (CAS # 52645-53-1 ), Chlorfenapyr (CAS # 122453-73-0 ) and Sulphuryl difluride (CAS # 2699-79-8 ). Pigments and dyes are preferred additives, and they do not need to be soluble in the oil solution in order to be used in the process of the present invention. As with biocides, they can be applied as a suspension, dispersion or other particulate form if necessary. Examples of pigments which can be included in the present invention are iron oxide, titanium oxide, etc. iron oxides including red iron oxides, yellow iron oxides, black iron oxides and brown iron oxides, carbon black, graphite, black micaceous iron oxide, aluminum flake pigments, pearlescent pigments, iron hydroxide, calcium carbonate, calcium phosphate, calcium oxide, calcium hydroxide, bismuth oxide, bismuth hydroxide, bismuth carbonate, copper carbonate, copper hydroxide, basic copper carbonate, silicon oxide, zinc carbonate, barium carbonate, barium hydroxide, strontium carbonate, zinc oxide, zinc phosphate, titanium dioxide, zinc sulfide, antimony oxide. Non-limiting examples of organic pigments include groups of Monoazo (arylide) such as Diacylide yellows, diniraniline orange, BON reds and lithol rubine; Disazo (diarylide), Disazo condensation, Benzimidazolone, Beta Naphthol, Naphthol, Metal complex, Isoindoline & Isoindolinone, Quinacridone, perylene, perinone, anthraquinone, diketo-pyrrolo pyrrole, dioxazine, triacrylcarbonium, the phthalocyanine pigments, such as cobalt phthalocyanine, copper phthalocyanine, copper semichloro- or monochlorophthalocyanine, copper phthalocyanine, metal-free phthalocyanine, copper polychlorophthalocyanine, etc. organic azo compounds, organic nitro compounds, polycyclic compounds (such as phthalocyanine pigments, quinacridone pigments, perylene and perinone pigments), diketopyrrolo-pyrrole(DPP) pigments, thioindigo pigments, dioxazine pigments, quinophthalone pigments, and triacrylcarbonium pigments; Diaryl pyrrolopyroles, such as PR254. -5- WO 2006/135858 PCT/US2006/022763 Organic pigments are also grouped according to the color they produce, e.g. blues, blacks, greens, yellow, reds and browns. Examples of organic pigments based on their color index include: Pigment yellows 1, 3, 12, 13, 14, 17, 81, 83, 65, 73, 74, 75, 97, 111, 120, 151, 154, 175, 181, 194, 93, 94, 95, 128, 166, 129, 153, 109, 110, 173, 139, 185, 138, 108, 24; and Pigment Oranges 5, 36, 60, 62, 65, 68, 61, 38, 69, 31, 13, 34, 43, 51, 71, 73; Pigment Reds 3, 4, 171, 175, 176, 185, 208, 2, 5, 12, 23, 112, 146, 170, 48, 57, 60, 68, 144, 166, 214, 220, 221, 242, 122, 192, 202, 207, 209, 123, 149, 178, 179, 190, 224, 177, 168, 216, 226, 254, 255, 264, 270, 272; Pigment violets 32, 19, 29, 23, 37; Pigments Browns 25, 23; Pigments Black 1, 31, 32, 20; Pigments Blues 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 60; Pigments Green 7, 36. An advantage of the process of the present invention is that it can be used with temperature-sensitive additives. By temperature sensitive, it is meant that the additive is thermally degraded by exposure to temperatures above 60'C for times greater than 1 hour such that greater than 20% of the additive molecules are destroyed. Such a biocide is IPBC. The wood and wood products which can be treated according to the process of the present invention include timber, lumber, multi-ply wood and other wood products, such as composite wood products and wooden cladding boards. The treatment of cladding with the process of the present invention is particularly economical and effective. The wood or wood product to be treated is pre-dried before treatment with the present process. The pre-dried wood is contacted with the oil mixture at a temperature in the range of from 35"C to 90"C, preferably at between 75*C to 85 "C. The oil mixture is applied at a pressure of from 0 to 15 atm, with a preferred range of pressures being 0-2 atmospheres for a time in the range of from 0.1 to 5 hours, with a time in the range of from .25 to 2.5 h being preferred. Herein, the convention wherein ambient pressure is 0 atm and complete vacuum is -1 atm, is adopted. If desired, additional pressure steps can be implemented before and/or after the above. For instance, a preceding step, conducted at pressures which are below atmospheric (i.e., below 0 atm with the convention used herein) can be used to extract some or all of the air from the wood. Such a step can be conducted for a time greater than 5 minutes, and at one or more pressure differentials in the range of from 0 to -.9 atm, not inclusive of 0 atm. The pressure differential created in this step can be used to pump the oil into the treatment vessel, if desired. -6- WO 2006/135858 PCT/US2006/022763 A step which removes excess oil from the treated wood or wood product can be implemented following treatment. The wood is exposed to one or more pressure differentials in the range of from 0 to -.9 atm, not inclusive of 0 atm, for a time greater than 3 minutes. The pressure differential created in this step can be used to pump the oil out of the treatment vessel, if desired. The treatment of the wood can be carried out in vessels which are known in the art for treating wood. In one embodiment, the treatment is carried out as a double-vacuum process. The details of such a process are known in the art. The treatment of the entire surface of the wood will generally result in the greatest degree of protection from moisture absorption. This feature - treatment of all surfaces is one of the characteristics of the process makes it superior to brushing/painting machines which normally only cover 3 sides of a board. Wood which has been treated according to the present invention generally has a surface which accepts paint or other treatments which are oil or water-based. Accordingly, the treated surfaces can be treated further ("post-treatment"), such as with paints or stains. Wood which has been treated according to the process of the present invention has the ability to remain sufficiently dry for long periods of time after water-proofing. The method of the present invention slows the absorption of water such that during wet seasons, the rate of water absorption is low enough that there is no "shock effect" to the wood due to sudden absorption of water. Furthermore, in countries having cold, wet winters, the wood water content is generally low enough such that decay is retarded. However, as with other water proofing processes, the moisture inhibiting properties of the treatment may decline with time. It is thus preferable to post-treat the wood within about 10 months of water-proofing treatment. This invention is further illustrated by the following example. EXAMPLE 1 This example provides an illustration of the process of the present invention. Pre dried Scots pine - Pinus Sylvestris, was used. The treatment was as follows. Treatment time and length: -0.9 bar for 20 minutes followed by 5 minutes holding at atmospheric pressure and finally -0.9 bar for 20 minutes., treatment temperature was 70-75 *C, type of oils used: linseed oil and mineral oil in a 50 wt% based upon the combined weight of the linseed and mineral oils. Manganese and Cobalt carboxylates were used in .15 wt % and .05 wt%, -7- WO 2006/135858 PCT/US2006/022763 respectively. Red iron oxide pigment paste was also present in 5 wt %. The results are shown in Figure 2. The following example is a counterexample of a widely used process. EXAMPLE 2 This example provides a comparative example using a vacuum drying process. The treatment was as follows. Treatment vessel was flooded with a mixture of linseed oil and mineral oil in a 50 wt% based upon the combined weight of the oils at about 75 *C. The oil was circulated for about 1 hour, and drying was initiated under vacuum, drying was carried out for 10 hours (water is extracted as steam which is condensed and collected for mass balance calculation), vessel was drained and final vacuum pulled for 45 minutes. Results are shown in Figure 3. The results of examples 1 and 2, illustrated in Figures 2 and 3, respectively, indicate that the process of the present invention has a water-proofing efficacy which is similar to existing processes which are more time consuming and conducted under conditions which can degrade thermally sensitive additives. -8-

Claims

We claim:

1) A process for water-proofing wood or wood product comprising the steps of:

a) providing pre-dried wood or wood product; b) providing a mixture comprising one or more high-boiling point oils and one or more drying oils; c) contacting the wood or wood product, in a treatment vessel, with the mixture for a time in the range of from 0-5 (hours) at one or more temperatures in the range of from 35° C to 90° C, at one or more pressures in the range of from 0-15 atmospheres.

2) A process as in claim 1 wherein the mixture further comprises one or more siccatives.

3) A process as in claim 1 wherein the process comprises the step of removing some or all of the air from the wood at one or more a pressure differentials in the range of from 0 to - .9 atm.

4) A process as in claim 3 wherein the pressure differential also causes treatment oil to enter the treatment vessel.

5) A process as in claim 1 wherein the process comprises the step of removing excess oil from the wood or wood product at one or more pressure differentials in the range of from 0 to -.9 atm after step c).

6) A process as in claim 5 wherein the pressure differential also causes treatment oil to leave the reaction vessel.

7) A process as in claim 1 wherein the mixture further comprises an additive.

8) A process as in claim 7 wherein the additive is a biocide.

9) A process as in claim 7 wherein the additive is a pigment or a dye. 10) A process as in claim 7 wherein the additive is particulate.

11) A process as in claim 2 wherein the one or more siccatives comprise cobalt carboxylate and manganese carboxylate.

12) A process as in claim 1 wherein the one or more drying oils comprise linseed oil, and the one or more high boiling oils comprise mineral oil.

13) A process as in claim 1 wherein the ratio of high boiling point oil to drying oil is in the range of 30 - 70 wt %, based upon the total weight of the high-boiling point and drying oil components

14) A process as in claim 1 wherein the one or more temperatures in Step c are between 75⁰C and 85 ⁰C, wherein the one or more pressures in Step c are in the range of 0-2 atmospheres; and wherein the time in Step c is in the range of from 0.25 to 2.5 h.

15) A process as in claim 1 wherein the pre-dried wood or wood product has a water content of less than 20 wt%.

16) Wood which has been treated with the process of claim 1.

17) A process for water-proofing wood comprising the steps of:

a) providing pre-dried wood or wood product; b) providing a treatment vessel; c) placing the wood in the treatment vessel; d) removing at least some of the air from the wood at a pressure differential in the treatment vessel in the range of from 0 to -.9 ami; e) providing a treatment oil mixture comprising one or more high-boiling point oils, one or more drying oils and one or more siccatives; f) contacting the wood in Step d with the treatment oil mixture in f) for a time in the range of from 0-5 (hours) at one or more temperatures in the range of from 35° C to 90° C, at one or more pressures in the range of from 0-15 atmospheres. g) removing excess oil from the wood or wood product at a pressure differential in the treatment vessel in the range of from O to -.9 atm.

18) A process as in claim 17 wherein the ratio of high boiling point oil to drying oil is in the range of 30 - 70 wt %, based upon the total weight of the high-boiling point and drying oil components.

19) A process as in claim 17 wherein the one or more temperatures in Step fare between 75⁰C to 85 ⁰C, wherein the one or more pressures in Step fare in the range of 0-2 atmospheres; and wherein the time in Step f is in the range of from 0.25 to 2.5 h.

20) A process as in claim 17 wherein the pre-dried wood or wood product has a water content of less than 20 wt%.