Composition for treating materials, method for treatment of materials and materials treated with the composition

Field of the invention

The invention relates to a composition and a method for treatment of materials, such as wood, for the purpose of improving primarily the preservability and other properties of the materials.

Background of the invention

In Europe, raw wood material is expensive, and raising the degree of processing is widely seen as the only choice in the field to secure the growth or even maintenance of the industry at the present level. The inhibition of biological decay of wood and the improvement of fire resistance and water resistance of wood are known to be areas in which the degree of wood processing should be particularly increased. For example, fire safety is a significant barrier to wood construction. Changes in dimensions and cracking of wood are also significant aspects in this respect.

Wood microbes are often classified into two groups according to their enzymatic activity and decomposing capacity. Group 1 consists of fungi that utilize the contents of a dead vegetable cell but do not decompose the lignified cell wall of a wood cell. These include surface moulds and blue stain fungi. Group 2 includes microbes that utilize the lignified cell wall. The most effective decomposers are brown and white rot fungi, but also actinobacteria and soft rot fungi are capable of decomposing the lignified cell wall of wood cells (Hatakka, Annele, 2002. Chapter 6.4.1. Puun lahoaminen, pp. 480-488 in Salkinoja-Salonen et al. (eds.), Mikrobio- logian perusteita, Gummerus, Jyvaskyla, ISBN 951 -45-9502-5).

Publication WO 03/002318 discloses the uses of potassium formate and calcium formate in aqueous solutions for preserving wood, particularly against wood-rotting fungi and termites. Also, document WO 03/088745 discloses the use of solutions of various formates (salts of formic acid) for treating porous materials, such as wood, for the purpose of inhibiting the growth of mould and fungi from spores. Publication US 6 652 921 discloses a method, in which wood is pre-treated with an organic acid that is preferably citric acid, fumaric acid or lactic acid, the list also including formic acid as a less advantageous alternative. After the pretreatment,

the wood is dried and finally treated with sorbic acid or a salt of the same. The concentration of the organic acid in the pretreatment solution is preferably from 1.0 to 5.0 wt-%. The aim is to provide the wood with a constant "depot" of poorly soluble sorbic acid by impregnating the wood, pretreated with the acid, with a sorbate, for example potassium sorbate. The treatment steps may also be arranged in a reverse order, but also in that case, the treatment is characterized by drying between the steps.

Publication EP 1 361 938 B discloses an impregnating agent that is based on a particular mixture of potassium diformate, which is a double salt of formic acid and potassium formate, with organic acids. The aqueous solution of potassium diformate is acidic as such.

Potassium formate is known for its effect of inhibiting the growth of wood-rotting fungi and for its fire-retarding effect, when its aqueous solution is used for the treatment of wood. Its advantage is non-toxicity compared with, for example, conventional CCA (chromated copper arsenite) impregnation methods. Potassium formate is also biodegradable, and wood treated with it can be, for example, disposed of without problems. One advantage of potassium formate is its good solu- bility in water (one of the best water-soluble salts), but a disadvantage due to this is its easy leaching from the wood. Another disadvantage is that even though it works well against wood-rotting fungi and insects, it does not give the best result in the control of mould fungi thriving on the surface of wood.

The use of acids in the preservation of wood (for example in the way known from the publications US 6 652 921 and EP 1 361 938 B) has been found to have the disadvantage that in time, the acidic conditions have a harmful effect on the original structure of the wood material.

WO 06/072672 discloses a composition for treating wood containing formate together with sorbate and/or benzoate dissolved in an aqueous liquid carrier.

All the documents referred in this specification are incorporated herein by reference.

It is an aim of the invention to provide a composition for treating several materials that is safe (not harmful),

- is absorbed by or penetrates well all different kinds of wood materials, but remains in the wood substantially without leaching out,

- preserves the materials both against mould and fungi, such as wood-rotting fungi and blue stain fungi, - protects the wood from dimensional changes and cracking, improves the fire resistance of the materials, and

- is not harmful for the structure of the materials after the treatment, even in long-term use.

Summary of the invention

To achieve the aims of the invention, the composition is primarily characterized in what will be presented in the characterizing part of the appended claim 1. The composition according to the invention contains formate as a first salt and alkylke- tene dimer. Surprisingly, such a composition inhibits efficiently the growth of surface mould and blue stain fungi as well as the decay of wood. It also keeps off pest insects and increases the fire resistance of the treated material. Moreover, the composition inhibits dimensional changes in wood and the cracking of wood during storage and use. The aqueous solutions of the above-mentioned agents are neutral or slightly alkaline, which is beneficial for the treatment of especially wood material.

In this context, the wood, for which the composition is intended, refers to all materials and products that contain wood material, including raw timber, sawn timber, wooden building materials and elements, and various finished wood products (round logs, all sawn timber, such as boards, planks and laths, elements with a large surface area, such as plates, panels, blocks, wall elements, etc., furniture, outdoor furniture, and other wooden objects). The wood to be treated may also be present in fixed structures, particularly outdoors (wooden buildings, fences, racks, poles, bridges, piers, etc.). Wood also refers to a converted wood product that contains the original structure of wood (for example, wood material that has been ground or chipped and reworked).

Other materials to be treated with the composition of the invention include all suit- able materials, such as concrete, ground, tiles or any construction materials. The examples and descriptions given herein mainly refer to treatment of wood, but are not intended to be restricting but presented only to enlighten the invention.

When dissolved in an aqueous carrier, the treatment composition according to the invention forms a fluid composition that can be entered at least partly in the wood or other materials by a variety of methods. In its simplest form, it is an aqueous solution of various salts. It can be absorbed in the material to be treated through- out or in a certain depth from the surface, for example by impregnation, immersion, spraying, steaming (atomizing) or brushing. Thanks to the many alternatives, the treatment can be implemented in a suitable step in the processing of the material, for example during the final drying of the wood. The physical properties (such as viscosity) of the composition may be adjusted according to the method and need of treatment. It is possible to heat the preservative composition according to the invention, and/or to use an elevated temperature in the process, which improves the absorption further. The use of negative pressure or overpressure, known from conventional CCA impregnation, also improves the absorption. In general, the composition according to the invention is suitable for use in all the conventional ways of impregnating wood, including pressure impregnation. However, the environmental safety of the composition offers many other possibilities which have been impossible to implement with more toxic compositions.

In one embodiment of the present invention the treating composition contains aux- iliary agents, such as magnesium, calcium, aluminum or silicate ions, or any mixture of these, which further improve the binding of the first salt, i.e. the formate, and alkylketene dimer, to the material treated. In addition, the aluminum ion further reduces the absorption of moisture into the wood material and thereby improves the dimensional stability of the wood and reduces the cracking of the wood. For example, the combination of formate and aluminum provides a composition that preserves the wood well outdoors, the aluminum reducing the penetrability of water into the wood in this composition. Preferably, a combination of potassium formate and aluminum sulfate is used.

In the composition, the first main component, the formate, is a formate of a monovalent or divalent cation or aluminum or boron. The mono- or divalent cations are selected from the group of alkali metals, alkali earths, ammonium, copper, and zinc. The cation of the formate may be one of the following: K, NH ₄ , Na, Cs, Ca, Mg, Al, Cu or Zn or a mixture thereof. If good penetrability is desired, an alkali metal salt or an ammonium salt is preferably used, wherein it is advantageous to use an auxiliary agent to bind the well-soluble formate to the structure of the wood when the wood dries after the treatment. On the other hand, if good stability without a need for auxiliary agents is aimed at, alkaline-earth formates, zinc or copper

formate, or aluminum formate is used. In particular, magnesium formate remains well in wood as such.

Preferably, the cation of the formate is one of the following: K, Na, Ca and Mg.

The "alkylketene dimer" (AKD) as used herein refers to any alkylketene dimer(s) having variable length side chains or combinations thereof. AKDs are wax-like alkaline agents generally used for paper sizing and they are synthesized from fatty acids. They are also generally used as disinfection chemicals. In the composition of the present invention AKD gives the materials treated surprisingly good resistance against e.g. water and helps keeping the composition in the treated material, such as wood.

In one embodiment, the composition further contains polyhexamethyleneguanidine (PHMG) and/or polyhexamethylenebi-guanidine (PHMB) which act as environmentally safe biocides. Also other biocides may be used, such as Tanagard®, but they may be very harmful and poisonous. Further, the drying properties of BHMG/BHMB are very good which speeds up the treating process.

In still another embodiment the composition further contains boron. The boron may be applied in several forms, e.g. as normal boron in aqueous solution, borate, or glycol borate to gain extra penetration. Typically a 10% solution of boric acid is applied by pressure impregnation. Boron has also biocide activity, e.g. against mold, and it is also effective against termites and the like.

Furthermore, it is possible to use other salts of organic acids. In addition to the above-mentioned first salt, the same aqueous carrier may contain, as such an auxiliary salt, particularly salts of C2-C8 carboxylic acids, such as acetate, lactate, citrate, oxalate and propionate, which act primarily in the way of the sorbate and the benzoate as auxiliary agents supplementing the effect of the formate. For example, it is possible to use acetate, lactate, citrate, oxalate and propionate of the following cations: alkali metals, alkali earths, ammonium, aluminum, copper and zinc. Mixtures of these auxiliary salts are also possible. The selection and dosage of the auxiliary salts are influenced by the use, and in the selection and the content one must take into account, for example, their characteristic smell which may come out at high concentrations, particularly in the case of propionates or acetates. The solubility of the salts must also be taken into account in the dosage (for

example, oxalates), as must be done in the selection of all the anions and cations and their concentrations in the composition in general.

The composition according to the invention is prepared by dissolving the above- mentioned agents (formate and alkylketene dimer as well as one or more of the above-mentioned auxiliary salts) in water and possibly also adding other auxiliary agents and additives depending on the use of the composition, which will be discussed later on.

The first salt is a formate which is also effective against blue stain fungi. Similarly, it preserves the wood against termites, which is advantageous in countries where the termites cause damage in wooden structures.

Formate salts, as such, have an effect that augments the fire resistance of wood. Of particular advantage is calcium formate which effectively inhibits the burning of wood.

The content of potassium formate in the solution may be 1 to 70 wt-%, preferably 2 to 40 wt-%. A part of the formate can be replaced, particularly by acetate.

The preferable composition containing an alkali metal formate and alkylketene dimer is one in which the formate is potassium formate in a content of 2 to 40 wt-% and in which the alkylketene dimer is in a content of 0.1 to 20 wt-%

The fire resistance can be improved further, for example, by adding the following substances into the composition containing the formate and the alkylketene dimer:

1 ) magnesium, calcium, aluminum or silicate ions, or mixtures thereof;

2) any known fire retarding chemicals based on phosphorus and nitrogen, such as, for example, diammonium hydrogen phosphate, monoammonium dihydrogen phosphate, ammonium polyphosphate, phosphonates, urea, or urea phosphate, or mixtures of these.

The composition may also contain a mixture of the above-mentioned substances of the categories 1 and 2 (or mixtures thereof). The composition may also contain a second salt, such as sorbate and/or benzoate.

The total content of magnesium, aluminum and/or silicate ions is thus preferably 0.1 to 20 wt-%.

In one embodiment the composition contains both A) an alkali metal formate and alkylketene dimer and B) magnesium ions. The alkali metal formate may be calcium formate, whose content may be 1 to 70 wt-%, preferably 2 to 40 wt-%. The magnesium ions originate preferably from magnesium sulfate, and the content of Mg ions may be 0.1 to 20 wt-%, preferably 0.1 to 5 wt-%.

The treatment composition according to the invention, based on a formate and alkylketene dimer, may also contain rheological auxiliary agents, such as car- boxymethyl cellulose (CMC), which - thanks to its adhesive property - binds the preservative composition to the surface of the product and inside the same. If there is little CMC, the composition can be used as an agent penetrating into the wood. With a higher CMC content, it is possible to obtain a composition to be brushed onto the surface of the wood for surface treatment. Furthermore, it is known that CMC can be used for controlling the deposition of e.g. pigments onto the roughness of the wood, if the composition is used as a brushable treatment composition that also affects the visual properties of wood. Other rheological auxil- iary agents include, for example, natural polymers, such as xanthan, and polyacry- lates.

The treatment composition according to the invention can also be used against damage caused by insects, particularly termites. Against the termites, toxic agents have been conventionally used, for example the above-mentioned CCA, known from pressure impregnation, as well as zinc borate, ACZA (ammoniacal copper zinc arsenate) and CTL (tetrachloroisophthalonitrile).

Consequently, the composition according to the invention suits particularly well against surface moulds, blue stain fungi and wood-rotting fungi, and also for the inhibition of damage caused by termites.

One embodiment of the present invention provides a paste, such as silicone paste generally used in construction, containing the composition of the invention. Still another embodiment of the invention provides a paint, primer, varnish or the like containing the composition of the invention. Such pastes, paints, varnishes, primers or the composition itself may be applied to the buildings, ground or any suitable objects to protect from insects, such as termites. For example the ground

around a building or the tiles of the building may be treated with the composition to repel the insects, generally once in two months.

Another advantageous property that should be mentioned of the composition ac- cording to the invention is the fact that it does not contain heavy metals classified to be particularly hazardous on the basis of toxicity, such as chromium or arsene, which are known from compositions of prior art; nor does it contain lead, mercury or cadmium. However, it is possible that the composition contains heavy metal residues from the raw materials used in the preparation, for example from the wa- ter used as a carrier for the composition. However, the content of these is infinitesimal when compared with compositions in which heavy metals have been added as active agents. The composition according to the invention contains salts of natural organic acids which are harmless to the environment (formic acid, sorbic acid, benzoic acid), preferably together with alkali metals or alkali earths or ammo- nium. The above-mentioned salts of other organic acids used as auxiliary agents, "auxiliary salts", are also safe to use.

The composition according to the invention may also contain aluminum, copper or zinc ions, by means of which the preservability of wood materials can be made more efficient but which are much safer to use than the above-mentioned hazardous heavy metal compounds. To include copper and/or zinc ions, which increase the anti-fungal effect, in the composition, it is possible to use copper and/or zinc salts of formate, sorbate and/or benzoate or, for example, copper sulfate or zinc sulfate. The aluminum can be included in the form of aluminum sulfate or alumi- num formate (aluminum thformate).

Furthermore, the pH of the composition according to the invention is primarily neutral or slightly alkaline, because instead of acids it contains salts of formic acid and/or acetic acid, the pH being higher than 7, advantageously higher than 8, when measured directly from the solution. For example, strongly acidic wood- preserving or fire-retarding compositions easily damage the structure of wood in course of time. Similarly, they are harmful if metallic construction materials (for example, nails, screws) are used in connection with such wood, due to the susceptibility of rusting. In some cases, an acidic component may be added to adjust the pH to a value of 6 or more, which is still higher than the pH of known compositions based on acids. The pH is in the range from 6 to 12, preferably in the range from 7 to 1 1 , the ideal situation being in the range from 8 to 10, measured directly from the solution.

The treatment solution according to the invention may contain known buffer chemicals (for example borax, carbonate, phosphate, etc.) as needed. The content of the buffer chemical ranges from 0.001 to 5.0 wt-%.

The method for treating wood according to the invention comprises bringing the wood in contact with said composition. Depending on the physical properties of the composition, the result is impregnation of the wood to a certain depth, surface treatment of the wood, or a combination of these.

The action of the treatment solution according to the invention is based on the chemical modification of the wood with formate and AKD. Small-sized carboxylic ions (such as, for example, formate) penetrate into the wood and form corresponding salts in the wood. Together with particular binding agents, such as calcium, magnesium, aluminum and/or silicate, the carboxylic ions according to the inven- tion inhibit the absorption of water and moisture, which are essential for the organisms that biologically decompose wood and also for all biological action, into the wood or into the cell system of the wood.

The invention is suitable for the treatment of both processed timber and raw tim- ber, and the treatment can be given either at wood storage sites or in a separate processing mill for timber, wherein the treatment composition and the wood can be brought into contact in a variety of ways. Similarly, the invention is suitable for the preservation of stationary structures already erected, particularly outdoors, wherein primarily spraying and brushing of the surfaces can be used. It should be noted that thanks to the safety of the composition, it can be used for the treatment of erected wooden structures in their locations of use without particular safety measures.

The solution containing formate can be stored in unheated rooms also during win- ter time, because it has good resistance to freezing, in the case of strong solutions down to a minimum of -50 °C. Thanks to these properties, it is possible to prepare, for example, a solution that is more concentrated than the above-described ready- to-use solutions, i.e. a concentrate that is suitable for storage at cold temperatures below 0°C and which can be diluted before the use. In the preparation of such a concentrate, one should naturally take into account the solubility of the substances and in its storage recommendations the freezing point of the resulting solution.

The invention suits particularly well for treatment processes requiring good penetrability into wood, such as impregnation. The composition can be entered into the wood, for example, in the known pressure impregnation process, in which the wood is at first kept under negative pressure to remove water from its inside, after which the composition is brought into contact with the wood and its penetration into the wood is enhanced by overpressure.

The solution according to the invention may contain various additives, depending on the use. If the composition is to be used for surface treatment, coloring agents, such as organic coloring agents or pigments, may be added into it if the wood surface to be treated should also be given a visual change in the way of painting. In this case, for example CMC (carboxymethyl cellulose) can be used as an adhesive, which at the same time acts as a rheological auxiliary agent. The pigments and organic coloring agents are preferably free of heavy metals. For example, known iron oxide pigments can be used as the pigment. The physical properties of the compositions to be brushed onto the surfaces can also be selected on the basis of the use; in other words, it can be more viscose than the composition intended for impregnation, which should penetrate well into the wood. However, it should be noted that also when brushable compositions are used, some penetra- tion of the active agents into the wood takes place (of the order of millimeters), also with viscose compositions.

The invention is also suitable for objects which are not completely made of wood but, for example, a combination of wood and another material.

Similarly, the invention is suitable for wood from different tree species, for example pine, which is conventionally treated with CCA, for example by pressure impregnation. However, the invention is particularly well suited for tight grained wood material which is difficult to impregnate with CCA, such as spruce, if the penetration properties of the composition are adjusted to be suitable. In this way, the composition whose efficiency is at least comparable to that of CCA but which is safer for the environment can be used to improve the preservation of such types of wood which have previously not been preservable in a proper way.

The invention makes it possible to treat wood materials in a light and cost-efficient way, and the treatment can be easily included in other present-day steps of wood treatment. The process may be one step in a processing line of timber or wooden

objects comprising successive steps. The composition according to the invention is also pleasant to handle, because it does not emit strongly irritating odors.

In the following, practical examples will be given of methods how the treatment composition can be used for the treatment of wood and how the treatment can be integrated in a wood material processing line in mills for wood processing.

1 ) Pressure impregnation

A conventional method for entering great amounts of impregnation substance in wood, and thereby providing the most effective treatment by means of different steps (negative pressure and overpressure, elevated temperature). By this method, the best penetrability of compositions is obtained, and the wood can normally be impregnated to the core. The composition according to the invention has a very good penetrability, wherein it is possible to reduce the negative pressures/overpressures used in conventional CCA impregnation and thereby to improve the cost-effectiveness of the process. Also, a tighter-grained type of wood, such as spruce, can be pressure impregnated with the composition according to the invention, which has not been possible with conventionally used substances.

2) Immersion impregnation

The penetrability of the composition according to the invention is good, and in some cases, mere immersion impregnation is also possible. This method is simple but it requires separate immersion basins and is carried out in batch processes, like the pressure impregnation.

3) Spraying

The composition according to the invention can be sprayed onto the surface of wood, for example, in connection with the planing of sawn timber. In this way, preservation against microorganisms can be achieved during storage and delivery before a surface treatment (painting etc.) later on.

4) Painting or other surface treatment line

The composition according to the invention may also be added into the wood in connection with a painting or another surface treatment line. From a paint dosing

tank, a wooden board can be impregnated with the solution under overpressure or negative pressure through a separate painting unit. Depending on the pressure and the speed of the line, relatively good penetrability and thereby a reasonable resistance to weather and fire can be achieved by this method.

5) Drying of the wood and the control of final moisture content

In the processing of timber in sawmills, it is more and more important that the final moisture content of the wood is suitable to prevent cracking and dimensional changes, as well as to prevent too good a substrate from forming for biological life. In connection with the drying, the tree often dries to a moisture content that is lower than desired. At the end, the moisture content can be adjusted, for example, by a technique based on spraying with water. In this step, it is very easy to add the composition according to the invention into the wood, wherein it is possible to eliminate cracking and dimensional changes due to the drying of wood. Furthermore, this method can be used to improve the fire resistance and to provide at least a short-term preservation against microorganisms.

In connection with the treatment methods according to points 1 to 4, however, it is important to dry the wood well (for example, at a temperature from 40 to 80 ⁰ C), wherein the extra water absorbed in the wood during the process can be removed and the moisture content can be stabilized to a desired final level.

In the following, the invention will be described in more detail by means of exam- pies on the preservation of wood with the wood treatment composition according to the invention. The examples are intended to illustrate and not to limit the invention.

Examples

Example 1. Decay/fungi and mould tests

1.1 Laboratory impregnations

All the laboratory impregnations were performed with the same procedure.

Impregnation 1 was made with formate only. The depths of penetration were uniform with a few exceptions. The solution was penetrated to the wood on average 76.3 kg/m ³ .

Impregnation 2 was made with the composition of the invention (formate together with alkylketene dimer). The depths of penetration were clearly smaller than in Impregnation 1. There was also more deviation in the penetration. During the impregnation the weight set on the test objects was not properly set and some of the test objects were above the fluid level still after the pressure was settled. This may have affected to the low penetration in some objects. The solution was penetrated to the wood on average 65.7 kg/m ³ .

Impregnation 2 was made with the composition of the invention (formate together with alkylketene dimer). The depths of penetration were uniform with a few excep- tions. The solution was penetrated to the wood on average 21.1 kg/m ³ .

The objects impregnated with the composition of the invention seemed grayer when compared to the reference.

1.2 Decay test

The decay tests were started 19-20 December 2006 and ended 1 1-12 April 2007. The mass losses with different fungi were the following:

Oligoporus placenta "Porta placenta "19.8% Gloeophyllum trabeum 33.3%

Coniophera puteana 32.5%

The mass loss with test objects was adequate with Gloeophyllum trabeum and Coniophera puteana. With Oligoporus placenta the mass loss was slightly less than the target 20%, but this may still be considered valid. Moreover, said fungi degraded the test objects 30^10% which is far over the target.

Composition 1 , formate only

The test objects impregnated with composition 1 were decayed the most by Gloeophyllum trabeum. The average mass loss was 22.06% and the mass loss of reference objects (no treatment) was 45.61 %. The X-value calculated from this

was 0.48 which means decay resistance class 3 (moderately resistant). The test objects of composition 1 were highly wetted with different fungi to humidities 90.1 %, 98.4% and 105% correspondingly. The results for decay test for composition 1 are presented in Table 1.

Table 1 .

Composition 2, formate + alkylketene dimer

The test objects impregnated with composition 2 were decayed the most by Gloeophyllum trabeum. The average mass loss was 10.07% and the mass loss of reference objects (no treatment) was 46.82%. The X-value calculated from this was 0.22 which means decay resistance class 2 (resistant). The test objects of composition 2 were highly wetted with different fungi to humidities 99.8%, 102.5% and 85.5% correspondingly. Some of the test objects were rejected because of

high humidity. The humidity should be in the range of 25-80% if the mass loss of a single object is less than 3%. The results for decay test for composition 2 are presented in Table 2. The underlined values are rejected.

Table 2.

Composition 3, formate + alkylketene dimer

The test objects impregnated with composition 3 were decayed the most by Gloeophyllum trabeum. The average mass loss was 14.2% and the mass loss of reference objects (no treatment) was 42.44%. The X-value calculated from this was 0.33 which means decay resistance class 3 (moderately resistant). The test

objects of composition 3 were wetted clearly less than 1 and 2 and the humidities by different fungi were 59.0%, 74.8% and 105.9% correspondingly. With Conio- phera puteana the humidities were clearly higher than with other two fungi. Some of the test objects were rejected because of high humidity, especially with Conio- phera puteana. The result for said fungi is rejected because only three out of required four objects were accepted. The humidity should be in the range of 25-80% if the mass loss of a single object is less than 3%. The evaluation is however made according to most decaying Gloeophyllum trabeum so the rejection does not affect the final results. The results for decay test for composition 3 are presented

Table 3.

Table 4 shows the decay resistance classes and mass losses for different compositions using different fungi. The evaluation was made according to Gloeophyllum trabeum in every case.

Table 4.

By the solution of the invention, it possible to facilitate the treatment of wood under winter conditions where the processing of frozen wood (for example, melting, impregnation, planing, painting, etc.) is problematic and constitutes an extra cost item.