Method for Preparing a Pigment Composition for Wood and Use of the Pigment Composition-EP 3115427 A1

Method for making an oil based total treatment formulation with stabilized pigments for treatment of wood surfaces, where the total treatment formulation comprises a treatment oil and a tone paste package, where the method comprises the step of

1. The invention relates to a pigment composition. More particularly, the invention relates to an oil based pigment composition for wood and a method for making the composition. The composition is suitable for staining of wet wood in a process where the composition is added to the surface of the wood at sub-atmospheric conditions whereby the pigments and oil penetrate into the wood. The oil based pigment composition is also suitable for traditional painting of wood.

2. Paint is an exterior coating with limited penetration of wood. Focus is on curing of a protective polymeric film that incorporates other ingredients such as pigments, onto the surface. Coating formulation is “painted” onto the surface. Application of a pressure or a vacuum is not required.

3. Impregnation treatment means immersing the wood in an impregnation liquor. Then pressure and / or vacuum is used to effect some impregnation of the impregnation liquor into at least the wood surface layers. There is less or no reliance on fast curing / cross-linking of an exterior film.

4. A “Royal Treatment” regime or a “royal-process” is a known and documented set of procedures for treating and protecting wood / timber intended for outdoor use. Such wood / timber may be wood paneling on facades. This treatment was originally developed by Bror Olof Häger and is disclosed in the patent documents US 4305978 and GB 2088422.

5. The process is a combined process and can be summarized as follows: A water-based, copper-salt-impregnation is followed by a hot, approximately 80°C, oil-impregnation, which often utilizes modified linseed oil or mixes of linseed oil with other oils, including mineral derived oils. Significant for the “royal-process” is that it involves a sequence of two process steps. In most cases, different vessels are used for each step.

Step 1. Water-based copper treatment

6. This step is often based on a modified “Lowry process”. This typically involves a pressure phase where the wood / timber is covered by an aqueous copper solution and exposed to a pressure exceeding 9 bar for approximately 1 hour. Thereafter the wood / timber is exposed to a sub-atmospheric pressure for approximately 20 min.

Step 2. Oil-impregnation

7. Wood / timber from step 1 is covered with hot oil at sub-atmospheric pressure. The aim is to dry the wood / timber from nearly wet state to a moisture content from 12% to 18%, and to hydrophobize the surface in order to prevent leaching of preservatives. Typically the pressure is about 200 mbar and the oil is linseed oil heated to about 80°C. Step 2 lasts for several hours. In the following, the oil added at step 2 is named a treatment oil. The treatment oil may be a single pure oil or a blend of two or several oils. This step is also named the oil and pigment impregnation stage in the “royal process” sequence.

8. Pigments, in the art named a tone paste, may be added to the treatment oil in order to impart a final color to the wood / timber. Ideally the oil and the pigments penetrate a number of millimeters into the wooden substrate. This is usually done by blending a pigment mix into the treatment oil. Such pigments are commercially available and supplied as a “tone paste package” for direct addition to, and mixing with the treatment oil. Dispersion agents for the pigments are often supplied as an integral part of the tone paste package. The pigments are typically iron oxide, titanium dioxide, carbon black and blends of these pigments. A tone paste package suitable for dispersion in non-aqueous systems may contain pigments, aldehyde or other resins, xylene or white spirit, dispersants / surfactants / wetting agents, and dispersion stabilizers.

9. Such tone paste packages formulations are normally mixed into the treatment oil prior to wood treatment. Depending on the specific pigment contents of the actual tone paste package, the preferred level of addition of the tone paste package often falls in the range 2 wt% – 8 wt%, preferably 4 wt% – 6.5 wt% of the total treatment formulation for the wood. Total treatment formulation means the treatment oil, which may be a blend of oils, and any additives to the treatment oil used in step 2.

10. In spite of careful adherence to the instructions provided by tone paste package producers regarding mixing techniques and mixing conditions, the inventor has observed that considerable separation and uneven distribution of the pigments in the total treatment formulation can be encountered.

11. Particular problems may for example be encountered during application of a grey color to wood using a specific grey color tone paste package dispersed in treatment oil. A grey color tone paste package will typically comprise titanium dioxide, TiO₂, and carbon black as pigments. However, application of other colors can also be problematic with uneven distribution and even streaking of colors on a wood surface after treatment and product drying.

12. Studies have shown that this is due to separation of the pigments within the applied dispersion, i.e. the mix of treatment oil and tone paste package, or during actual wood treatment, i.e. during step 2, leading to uneven distribution of color when applied to wood and after product drying. This is connected to the overall stability of the pigment / oil mix after mixing in of the tone paste package formulation itself, or indeed mixing in of the tone paste package into the treatment oil. Such instability and uneven treatment is observed by the appearance of uneven coloring, streaking or even formation of intense color spotting on the wood surface. Furthermore, color can quickly disappear from the treated wood, reflecting uneven application during the “royal-process”.

13. The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

14. The object is achieved through features, which are specified in the description below and in the claims that follow.

15. The inventor have found that the problem of uneven coloring, streaking or spotting is solved by adding a pigment mix, or a tone paste package together with a stabilizing component. During mixing of the pigments with an oil, the blend is also thickened and stabilized. The stabilizing component comprises inorganic particulates and organically modified inorganic particulates. Bentonite type clays and the like such as tonstein have been found to be suitable stabilizers.

16. Bentonite is classified as an absorbent aluminum phyllosilicate clay, consisting of mainly montmorinollite. Bentonite may be modified organically as known in the art, e.g. by use of a quaternary alkyl-ammonium compound. The organically modified bentonite is suitable for dispersion in no-polar to medium polar solvents and liquid systems. Bentonite may be a sodium bentonite, a calcium bentonite or a potassium bentonite. For example, commercially available products such as “Bentone^® 34″, “Bentone SD^® 1″, “Viscogel^® ED”, Viscogel^®ED2, Viscogel^® S4 or Viscogel^® SD are suitable bentonite derived materials for the application. These are not limiting examples as organically modified clays suitable for addition to oil-based systems and low-medium polarity oil and solvent blends are suitable.

17. Bentonites and organically modified bentonites are used as rheological additives in paints. They act as gels and are used as thickeners to make the paint thixotropic. This adds anti-sagging properties to the paint.

18. In a process using sub-atmospheric pressure for impregnation of a wood surface, it is desirable that the total treatment formulation has a low viscosity. Thereby the total treatment formulation can better penetrate into the pores. It is therefore surprising that an additive which increases the viscosity of the total treatment formulation, can be used as a pigment stabilizer in the last stage of a wood impregnation process such as “royal process”.

19. The inventor have further found that the method of mixing and the stage in the process were the mixing takes place, are critical factors in achieving stability of the pigment mix in the oil.

20. In the following, an inorganic particulate shall mean bentonite, tonstein, clay or silica. In the following, an organically modified inorganic particulate shall mean bentonite, tonstein, clay or silica and which has been treated with a suitable chemical such as a quaternary alkyl-ammonium compound. In the following, a stabilizing particulate is used as a name for an inorganic particulate and an organically modified inorganic particulate.

21. An efficient way to achieve this stabilization was found to be the production of a “pre concentrate” as a first step. An aliquot of the treatment oil may be provided. The treatment oil may be a pure single oil, such as linseed oil, or a mixture of two or several oils as explained previously. The aliquot may as an alternative be an oil different from the treatment oil. In the following, an oil aliquot is used as the general term for the possible options.

22. The “pre concentrate” was made by blending the stabilizing particulate with the oil aliquot. The stabilizing particulate, was blended into the oil aliquot using an intensive shear mixer. The finished “pre concentrate” may contain from 5 wt% to 25 wt% stabilizing particulate. More preferably the “pre concentrate” may contain 7 wt% to 20 wt% stabilizing particulate. Even more preferably the “pre concentrate” may contain 10 wt% to 18 wt% stabilizing particulate.

23. This “pre-concentrate” was then added into a bulk oil prior to wood treatment, using conventional mixing. In an alternative embodiment the “pre-concentrate” was mixed with the bulk oil by using a shear mixer. In the following a bulk oil means the treatment oil less the oil provided by the oil aliquot.

24. In one embodiment the tone paste package was added to the treatment oil as a final component to make the total treatment formulation. In an alternative embodiment the tone paste package was added to the “pre-concentrate” prior to adding the mix of “pre-concentrate” and tone paste package to the bulk oil.

25. Making the “pre concentrate” was the most efficient method to obtain a stabilized pigment composition in the total treatment formulation. However, in an alternative embodiment it is possible to stabilize the pigment composition in the total treatment formulation by adding the stabilizing particulate to the treatment oil. The total treatment oil with the stabilizing particulate is than passed through the intensive shear mixer. Thereafter the “tone paste package” is mixed in to make up the total treatment formulation.

26. The “pre concentrate” may be produced at a shear rate from 15 m/s to 25 m/s. The shear rate may also be above 25 m/s. Suitable equipment may be a dissolver with a dissolver plate of 100 mm run at 3000 rpm which gives a shear rate of 15.7 m/s. An alternative dissolver may have a dissolver plate of 300 mm run at 1450 rpm which gives a shear rate of 22.8 m/s. Mixing the stabilizing particulate to the treatment oil may be done at a shear rate from 20 to 35 m/s. The shear rate may also be above 35 m/s. A dissolver with a dissolver plate of 100 mm run at 6000 rpm gives a shear rate of 31.4 m/s.

27. In the following four different embodiments are disclosed for making the total treatment formulation.

28. To provide an oil aliquot means to provide a pure cooked linseed oil, or to provide a pure vegetable oil, or to provide a mineral derived oil, or to provide a mixture of cooked linseed oil and other oils, or to provide a mixture of vegetable oils and other oils, or to provide a mixture of mineral derived oils. The other oils may be mineral derived oils or other vegetable oils. An oil aliquot is sampled from this pure oil or mixture of oils.

29. The first, second and third embodiments have in common to provide a stabilizing particulate and to add the stabilizing particulate to the oil aliquot to make the “pre concentrate”. The “pre concentrate” may contain from 5 wt% to 25 wt% stabilizing particulate. More preferably the “pre concentrate” may contain 7 wt% to 20 wt% stabilizing particulate. Even more preferably the “pre concentrate” may contain 10 wt% to 18 wt% stabilizing particulate. The oil aliquot may hold an ambient temperature. The ambient temperature may range from 10°C to 25°C. The oil aliquot may be heated. The heated oil aliquot may hold a temperature from 25°C to 150°C.

30. A provided tone paste package contains one or more pigments. The pigments may be one or more of iron oxide, titanium oxide and carbon black. A grey tone paste package contains titanium oxide and carbon black. A suitable tone paste package has a desired pigment composition.

31. As an optional action, xylene is provided and added to total treatment formulation. Xylene will ensure even dispersion and stabilization of more hydrophobic pigments such as carbon black in the total treatment formulation, for example a total treatment formulation of grey color.

32. A process or method for the oil treatment and coloring of impregnated wood, utilizing the new invented procedure is in a first embodiment the following sequence of actions:

33. The provided total treatment formulation is used to treat wood. The wood may be treated according to the “royal-process” as known in the art. The wood is positioned in the treatment chamber and impregnated with an aqueous copper solution at high pressure. Thereafter heated total treatment formulation is added at a sub-atmospheric pressure as known in the art. The heated total treatment formulation may have a temperature in the range of from 50°C to 100°C. The treatment chamber may be an autoclave. The total treatment formulation may also be used in any oil based impregnation process on wood elements. The total treatment formulation may also be used as a paint for dipping or spraying or brush application.

34. As an alternative, wood may be treated with the provided total treatment formulation by dipping, spraying or brush application.

35. A process or method for the oil treatment and coloring of impregnated wood, utilizing the new invented procedure is in a second alternative embodiment the following sequence of actions:

36. A process or method for the oil treatment and coloring of impregnated wood, utilizing the new invented procedure is in a third alternative embodiment the following sequence of actions:

37. A process or method for the oil treatment and coloring of impregnated wood, utilizing the new invented procedure is in a forth alternative embodiment the following sequence of actions:

38. The provided stabilized pigment composition according to the second, third or forth embodiment may be used in the same manner as described in the first embodiment. Application of the described method according to the first, second, third and forth embodiment for preparation of the total treatment formulation, resulted in an even or homogenous dispersion in which the pigment particles were stabilized in the total treatment formulation. Even coloring was achieved on the wood surface when the total treatment formulation was added to wood in the oil and impregnation stage in the “royal-process” sequence.

39. Mixing of the stabilizing particulate with oil to make a stable dispersion of the stabilizing particulate was done as intensive mixing and was achieved by using a dissolver with an attached shearing mixer. Such equipment is known from the paint industry and is used for dispersion of pigments into coating formulations.

40. As an alternative a colloid mill, for example a “Fryma” type with milling head fitted with toothed colloid milling stator and rotor may also be used for the intensive mixing.

41. As a further alternative a “Ytron-Z” type, shear pump set up in shearing and deagglomerating mode, may be used. Other known types of mixers for in-line mixing may also be used.

42. The dissolver can be used alone, or in combination with one of the other intensive shear mixing devices, either preferably as the initial mixer, or as a follow-up to an intensive shear mixer.

43. As a further alternative a 3-roll mill of the type used for pigment or other particulate grinding and dispersion into a carrier fluid can be employed to aid dispersion alongside the other intensive shear mixing devices. As an even further alternative a wet mill of the type used for pigment or other particulate grinding and dispersion into a carrier fluid can be employed.

44. The dispersion generated via the mixing of the stabilizing particulate material with oil or a mixture of oils should be of a viscosity that is not higher than needed to pass through a 4 mm cup in maximum 100 seconds, at a temperature consistent with the operational temperature of the method.

45. The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

46. The invention relates to a method, or sequence of steps, to achieve a stable dispersion of pigments into an oil blend, for example a linseed oil-based oil blend. The oil-based dispersion is suitable for use, for example, in the second “oil treatment” stage of a typical “royal-process” on wood, or in a stand-alone, separate penetrating, protective and decorative oil based treatment and coloring of timber / wood elements. The invention solves an often encountered problem when coloring wood using oil based treatment, which is streaking or spotting of color on the wood surface. This is due to lack of stability, during wood treatment, of a dispersion of mixed or even single pigments in the oil.

47. In a first aspect, the invention relates more particularly to a method for making an oil based total treatment formulation with stabilized pigments for treatment of wood surfaces, where the total treatment formulation comprises a treatment oil and a tone paste package, where the method comprises the step of a) providing a treatment oil;b) providing a tone paste package, where the method further comprises the steps of:

48. Step e) may comprise to use a shear mixing device chosen from a group consisting of a dissolver, a toothed colloid mill, a wet mill and a shear pump, in shearing and deagglomerating mode.

49. Step e) may comprise to mix the stabilizing particulate and the oil aliquot in a ratio where the mix of step e) contains stabilizing particulate from 5 wt% to 25 wt%. The mix may more preferably contain stabilizing particulate from 7 wt% to 20 wt%. The mix may even more preferably contain stabilizing particulate from 10 wt% to 18 wt%.

50. The method may further comprise that the total treatment formulation contains from 0.2 wt% to 5 wt% of the stabilizing particulate. The total treatment formulation may more preferably contain from 0.5 wt% to 3 wt% of the stabilizing particulate. The total treatment formulation may even more preferably contain from 1 wt% to 2 wt% of the stabilizing particulate.

51. The total treatment formulation described above may be used for the treatment of wood in an oil and pigment impregnating stage in a “royal-process” sequence. The total treatment formulation described above may be used for the treatment of wood in an oil based impregnation process on wood elements. The total treatment formulation described above may be used for the treatment of wood as a paint for dipping or spraying or brush application.

52. In a second aspect, the invention relates more particularly to a use of a stabilizing particulate chosen from a group consisting of sodium bentonite, calcium bentonite, potassium bentonite, silica, tonstein and organically modified inorganic bentonite to make a total treatment formulation with stabilized pigments for use in an oil based impregnation process. The oil based impregnation process may be an oil and pigment impregnation stage in a “royal process” sequence.

53. In the following is described an example of a preferred embodiment.

Example 1; comparative example, prior art

54. A grey tone paste package was provided. A first sample was made by mixing the tone paste package with linseed oil such that the blend contained 3 wt% of the tone paste package. A second sample was made by mixing the grey tone paste package with linseed oil such that the blend contained 7 wt% of the tone paste package.

55. The first sample was applied to wood in a “royal-process” sequence as known in the art. The second sample was applied to wood in a “royal-process” sequence as known in the art.

56. It was immediately apparent for both samples that the pigments inadequately adhered to the wood. The pigments were uneven in shade with abundant streaking and spotting. This was due to separation of the pigment components. It was also observed that the linseed oil with tone paste package itself was visibly unstable with regard to pigment separation.

Example 2

57. A “pre-concentrate” was made up by blending 20% by weight organically modified bentonite to linseed oil, the oil aliquot, using a Pilvad Diaf dissolver. As an alternative a Dispermat dissolver, a Torusmill dissolver or a Ytron dissolver may be used. Other known dissolvers may also be used. A combination of a dissolver and a colloid mill may also be used as is known in the art. The linseed oil was of the same batch as used in Example 1.

58. The mixing continued for 4 hours. Due to the mechanical action, the temperature of the blend increased from ambient temperature to about 90°C. At termination, the or-ganically modified bentonite was homogenous distributed in the “pre-concentrate”.

59. The “pre-concentrate” was then mixed into the remaining linseed oil, the bulk oil, in a proportion of 10 parts linseed oil to 1 part “pre-concentrate” to form a stabilized oil blend, the treatment oil. The linseed oil was of the same batch as used in Example 1.

60. Grey tone paste package was mixed with the treatment oil to form a total treatment formulation. The total treatment formulation contained 6% by mass of tone paste package.

61. The total treatment formulation was applied to the wood using a “royal-process” sequence. It was apparent that a more even grey color was imparted to the wood with no noticeable streaking or spotting of color shades. It was also observed that no visible separation of the pigments occurred within the total treatment formulation.

Example 3; Comparative example

62. A “pre-concentrate” was made with the same ingredients as described in Example 2. Mixing was however carried out with a static mixer. The static mixer did not expose the organically modified bentonite to real shear forces and real grinding action.

63. Thereafter the example was carried out in the same manner as described in Example 2. The result was comparable to the result described in Example 1 and the result was inferior to the result described in Example 2.

64. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

65. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.