WATER-IN-OIL-COMPOSITION FOR WOOD STAINS

Abstract: The present invention comprises an oil-in-water emulsion used to stain wood. In addition, the present invention comprises a method of applying the oil-in-water emulsion to a substrate.

Description: WATER-IN-OIL-COMPOSITION FOR WOOD STAINS FIELD OF INVENTION The present invention relates to stains. In particular, the present invention relates to stains which comprise water-in-oil emulsions. BACKGROUND OF THE INVENTION Wood can be enhanced by the use of stains. For instance, stains can be used to change the color of the wood or they can be used to embellish the wood's grain structure. A stain is defined as a transparent, semitransparent or opaque solution or suspension of coloring matter consisting of pigments or dyes which imparts color effects to a substrate. Stains utilizing pigment are usually mixed with a solvent and a binder. Pigments are solid, inert particles of mineral which deflect light thereby causing a change in color on a wood substrate. The particles are not soluble, but rather are suspended in their application medium. In contrast, dyes differ from pigments in that they are in solution rather than in suspension. Moreover, binders are rarely used for dyes. In addition to being listed as dyes or pigments, stains can also be classified into two other broad groups: (1) aqueous types of solutions or emulsions, which use water as the primary liquid or continuous phase and (2) non-aqueous solutions which use organic solvents as the primary or continuous phase. The non-aqueous stains usually contain an oil- soluble alkyd resin either alone or in combination with certain other film-forming agents such as drying oils. Non-aqueous stains can also comprise in addition to colorant, just drying oils and/or combinations of drying oils. However, the non-aqueous stains are generally made by blending alkyds and non-drying oils with colored pigments and extender pigments such as clays and silicates in an organic solvent. If dyes are utilized, the alkyd resins are not necessary. Although these non-aqueous coatings are characterized by good wetting penetration and adhesion to the wood substrate, the organic solvents may exhibit adverse effects upon the Earth's atmosphere. Moreover, the organic solvents provide handling problems because of their volatility. Because of these adverse effects, these non-aqueous coatings are less than desirable. To overcome some of the adverse effects caused by organic solvents, there have been many attempts to utilize aqueous stains. Generally, aqueous stains are characterized by the use of oil-in-water emulsions. Most aqueous stains utilizing pigments use acrylic resins as the binder, but can also use water reducible or dispersable linseed oil or alkyd resin. These binders which can be neutralized and dissolved, are preferably emulsified so that they can be suspended in water. These emulsions may then be blended with pigments, extender pigments, and water to make the sta t in. In contrast to organic solvent-based stains, aqueous stains exhibit fewer adverse effects upon the atmosphere. However, aqueous stains are not without their drawbacks. One drawback is that the wood fibers tend to swell causing an effect known as "grain raising." Because the fibers do not return to their original shape and location after the water is removed, a rough surface remains which often requires sanding to provide a smooth surface for a top coating. Moreover, when the wood fibers swell, more of the pigments and/or dyes are left in the wood. This additional colorant causes the wood to have a more uniform color in contrast to the desired result of heightened wood highlight. In addition, aqueous stains generally dry at a quicker rate than non-aqueous stains causing finishing problems when larger surfaces are stained. To overcome some of the difficulties associated with aqueous stains, U.S. Patent No. 4,615,739 ("Clark et al.") discloses the use of an oil-in-water-in-oil emulsion. The Clark et al. composition comprises an aqueous latex emulsion added to an non-aqueous coating composition so that the non-aqueous phase is continuous and the aqueous phase is dispersed or suspended in the non-aqueous phase. To accomplish this, Clark et al. utilize a dispersing agent which consists essentially of hydrated starch or a hydrated starch component. Another patent, U.S. Patent No. 4,386,171 ("Graham et al.") discloses the use of a water-in-oil emulsion having a solids content between 50 and 75 weight percent and emphasizes the importance of minimizing the content of the solvent(s). If the solids content is lowered below 50 weight percent, Graham teaches that both the protective properties of the composition and the dry coating weight of the composition are reduced. The water-in-oil emulsion is stabilized by titanium dioxide in amounts ranging from 5 to about 40 weight percent. Thus, there currently exists a need for an oil-in- water wood stain emulsion having a solids content of less than 50 weight percent and a reduced propensity to result in the swelling of wood fibers. There also exists a need for an oil-in-water emulsion which improves the highlighting of the wood grain. SUMMARY OF THE INVENTION The present invention comprises a water-in-oil emulsion for staining wood having a solids content of less than 50 weight percent. As a wood stain, the oil- in-water emulsion reduces the grain raising and the swelling of wood fibers. In addition, the reduction of swelling allows improved highlighting of the wood grain. The wood stain of the present invention imparts color effects to a wood substrate by coloring the wood and highlighting the wood's grain structure. The emulsion comprises an oil continuous phase including an organic liquid, a binder and colorant and a discontinuous phase comprising an aqueous medium. The colorant can either be a pigment and/or a dye. In a preferred embodiment of the present invention, the composition comprises up to about 45 weight percent of said binder, up to about 50 weight percent of said organic liquid, sufficient colorant to stain wood and up to about 60 weight percent aqueous medium. The present invention also includes a method of staining wood using the composition. DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a water-in-oil emulsion which can be used to stain wood. By definition a water-in-oil emulsion comprises an oil continuous phase which is substantially free of water, and an aqueous discontinuous phase which is essentially free of organic solvent. The water-in-oil emulsion of the present invention has an oil continuous phase which includes a binder and colorant in solution with an organic liquid and a discontinuous phase comprising an aqueous medium. The organic liquid which comprises the continuous phase of the water-in-oil emulsion of the present invention must be water immiscible. Examples of suitable solvents include mineral spirits, VMP naphtha, kerosene, mineral oil, pine oil and turpentine. Other suitable organic liquids include solvents such as aromatic hydrocarbons. Examples of aromatic hydrocarbons include toluene, xylene and cycloparaffins. Especially preferred aromatic hydrocarbons include: (a) a blend of aromatic distillates containing xylene, cumene and trimethyl benzene sold under the tradename "Hi Sol 10" and commercially available from Ashland Chemical Company or under the tradename "Aromatic 100" commercially available from the Exxon Company, or (b) a blend of aromatic distillates containing naphthalene and trimethyl benzene sold under the tradename "Aromatic 150" by the Exxon Company, or (c) an aromatic solvent blend of hydrocarbons containing naphthalene and consisting predominantly of C 9 -C 15 aromatic hydrocarbons sold under the tradename "Aromatic 200" by the Exxon Company. Acetate solvents can be utilized. For example, Exxate™ 600, a hexane acetate, commercially available from the Exxon Company and Exxate™ 1300, a tridecyl acetate, sold by the Exxon Company can be used as organic solvents. In addition, dearomatized aliphatic solvents composed of paraffins and cycloparaffins commercially available as Exxsol™ D80 and Exxsol™ DUO and sold by the Exxon Company can also be utilized. The binders useful in the present invention hold the colorant to the wood. Any number of binders can be utilized as long as they remain stable in the water-in- oil emulsion of the present invention and are compatible with the continuous oil phase. Usually, the binder and/or resin is dispersed or suspended in the solution. Examples of useful binders include oil soluble resins and drying oils. Representative binders include such oil-based binders as Tung Oil and Linseed Oil and such drying oils as oiticica oil and perilla oils. Typical commercial water reducible binders include a water reducible polyolefin sold under the tradename Cargill™ 7358 sold by Cargill, Inc., a water reducible modified Linseed Oil sold under the tradename Cargill™ 7319 by Cargill, Inc. and a water reducible modified Linseed Oil sold as Aquamac™ 1610 by McWhorter Inc. Any type of pigment may be used as the colorant in the present stain formulations. The pigments can be either organic or inorganic. Representative inorganic pigments include titanium pigments, carbon black, iron oxide, chromium oxide, cobalt phosphate, CoLiP0 4 , cadmium pigments, lead chromates and lead molybdates. Examples of organic pigments include onoazo pigments, diazo pigments, diazo condensation pigments, perylene pigments, thioindigo pigments, phthalocyanine pigments and tetrachloroisoindolinones. These pigments can be blended together to achieve the desired color for staining the wood surface. If a pigment is not used, a dye can be used as the colorant instead. Indeed, both a pigment and a dye can be used simultaneously in the composition of the present invention. Representative dyes which can be used include, but are not limited to, azo dyes, aniline dyes, anthraquinone dyes, xanthene dyes, azine dyes and fluorescent dyes. As was the case with pigments, the dyes can be blended together to achieve the desired color to be imparted on the wood. Preferred wood stain compositions of the present invention comprise pigment(s) and/or dye(s) of a type and an amount which result in a substantially transparent staining of the wood such that the very fine or very small wood grain features are highlighted and not hidden as might occur with a composition more appropriately characterized as a paint. Pigments such as titanium dioxide or zinc oxide which have a relatively high hiding power are preferably used in sparing amounts only. For example, the titanium dioxide will not be present in an amount greater than one percent by weight if the maximal highlighting of the fine wood features is desired. If desired, a filler can be added. Examples of suitable fillers include hydrophilic treated silica and hydrophobic treated silica. Dryers which accelerate the crosslinking of drying oils can also be utilized. Conventional dryers such as cobalt naphthenate, zirconium octanoate and the like can be utilized. Although the composition of the present invention is stable and can be tailored to achieve the desired flow control, nonetheless, a thickener can be added if desired. Thickeners that are preferred for the composition of the present invention include gums, e.g., xanthan, guar, locust bean, alginates, polyvinyl alcohol, polyacrylates, starches and clay derivatives, e.g., amine treated ammonium silicate and cellulose derivatives, e.g., hydroxypropyl methylcellulose. In addition, oil soluble thickeners such as aluminum stearate, hydroxyethyl cellulose and the like can also be utilized. Emulsifiers can be utilized in formulating the water-in-oil emulsion. Emulsifiers that are useful in the composition of the present invention include, anionic, nonionic and cationic surfactants. The hydrophilic-lipophilic balance ("HLB") of non-ionic emulsifiers suitable for the composition of this invention is dependent upon the type and quantity of binder as well as any oils, solvents and water selected. Preferably, the emulsifiers have an HLB from about 4 to about 8. More preferably, the emulsifiers have a HLB range from about 5 to about 7. If a blend of emulsifiers is used, it is preferred that the blend, also have an overall HLB value from about 4 to about 8. Examples of suitable emulsifiers would include a blend of Span ™ 80, a sorbitan monooleate available from ICI Americas, Inc. and Tween ™ 80, a polyoxyethylene 20 sorbitan monooleate also commercially available from ICI Americas, Inc. The aqueous or non-continuous phase of the present invention comprises water. The amount of water added depends upon the desired composition. For example, the ratio of the aqueous phase to the oil phase can be adjusted to provide a desired viscosity. The present invention comprises a solids content less than 50 weight percent. The solids content of the present invention includes the binder, the colorant, the filler, the dryer, the thickener and any additional solid particulate added to the water-in-oil emulsion. Preferably, the present invention comprises a solids content from about 5 to about 45 weight percent of the composition. Most preferably, the solids content comprises from about 10 to about 30 weight percent of the composition. The amounts of the various individual components vary in the composition according to use. For example, the composition can comprise up to about 60 weight percent water, up to about 50 weight percent organic liquid, up to about 45 weight percent binder, a sufficient amount of colorant to stain wood and e ulsifier. Preferably, the colorant comprises less than 5 weight percent of the composition. The amount and type of emulsifier employed depends upon the type and amount of binder and the amount of solvent and water used in the composition of the present invention. More preferably, the composition comprises from about 40 to about 60 weight percent water, from about 10 to about 30 weight percent organic liquid, from about 5 to about 20 weight percent binder. The composition of the present invention can be prepared in a number of ways. In general, water is dispersed in the organic liquid wherein the binder and colorant have either been dissolved or suspended. In a preferred method of preparing the composition of the present invention, the binder is dispersed in the organic liquid. Next, the colorant is added to the organic liquid. Finally, water is added to the composition to provide a water-in-oil emulsion. The composition can be applied to a wood substrate in any conventional manner such as by brush, rag, nylon scrub pad, spray gun or sponge. It is coated in an amount sufficient to leave the desired stain although greater amounts can be applied and then wiped off the wood substrate. The following examples are set forth to illustrate this invention and are not intended to limit the scope of this invention thereof. TEST METHODS The ability of a composition to stain a wood substrate is tested by applying the composition onto a sample and allowing the composition to penetrate the sample from two to ten minutes. Then the excess composition is removed from the sample with a clean cloth and the remaining composition allowed to dry on the sample. Next, samples are visually examined for color, highlighting of wood grain, uniform coverage and grain raising. The highlighting of the wood grain is measured on a visual scale: ii+ n _ Different amounts of colorants absorbed by large and small cell growth areas. "-" - Similar amounts of colorants absorbed by large and small cell growth areas. The coverage of the samples is also measured on a visual scale: ιι+ιι _ Aii areas show similar colorant penetration into wood surface. 11 -" - Some areas show a lack of colorant penetration into surface. In addition, the grain raising is observed on the following scale: ii + n _ Minimal amount of wood fibers raised after stain dries. "-" - Substantial amount of wood fibers raised after stain dries. The color of the wood is measured on a visual scale: n + ii _ Good absorption of colorant into wood surface. n _ n _ Poor absorption of colorants into wood. Moreover, the composition, itself, is examined for viscosity and conductivity utilizing an ohmmeter. The viscosity was measured in centipoises by a Brookfield LTV viscosimeter manufactured by Brookfield and the conductivity was measured by an ohmmeter. Oil-in-water emulsions have conductivity similar to that of water. In distinction, water-in-oil emulsions do not conduct electrical current significantly. TEST SAMPLES The samples used in Examples 1- 14 were 2 in. (5.08 cm) X 12 in. (30.48 cm) by 0.25 in. (.635 cm) wood panels. The wood from which the panels were made included oak, maple, pine, cherry and birch. The panels were sanded by a 180 grit abrasive. EXAMPLE 1 The test sample of Example 1 was prepared in the following manner: 10.2 gms. of resin, Cargill™ 73-7358, was added to 23.5 g s. of solvent, Exxsol™ D-110. Next, pigment in the amount of 5.6 gms. of Formulator ™ 24-A Series, 10- 5C-24-A232 which is a blend of yellow iron oxide comprising 33% by weight yellow iron oxide pigment, 44% by weight resin and 77% by weight solids having a specific gravity of 1.20 sold by Hilton Davis, 5.6 gms. of Formulator™ 24-A Series, 10-5C-A103, which is a 33% by weight blend of red iron oxide pigment, 37% by weight blend of resin and a 77% blend of solids having a specific gravity of 1.18 commercially available from Hilton Davis and 1.0 gms. of Formulator ™ 24-A Series, 10-5C-24-A711 which is a blend comprising 55% by weight carbon black pigment, 20% by weight resin and 75% by weight solids having a specific gravity of 1.22 and is commercially available from Hilton Davis (hereinafter "carbon black") was blended in the solvent suspension. Then 0.2 grams of the additive Magnacat™, a manganese drier commercially available from Ultra Additives Corporation , Paterson, N.J., was added to the mixture. Upon the addition of the additive, 0.2 gms. of Tween™ 80, 0.8 gms. of Span™ 80 and 2.0 gms. of OK 412, a flattening agent containing Si0 2> commercially available from Degussa Corporation, were blended into the mixture. 50.9 gms. of water was then added to the mixture in order to prepare the oil-in-water emulsion. The test panel, the ingredients used, the weight percentage of the ingredients and test results are reported in Table 1. EXAMPLES 2-5 These examples, all of which were prepared utilizing the methods described in Example 1, illustrate various compositions found within the scope of the present invention. Examples 2-5 varied in that different amounts of the various components were utilized. The test panels used, the ingredients utilized, the weight percentage of the ingredients and the test results are reported in Table 1. TABLE 1 'OK 412 is the tradename of a flattening agent containing Si0 2 commercially available from Degussa Corporation. 2 Magnacat is the tradename of a manganese drier commercially available from Ultra Additives Corporation, Paterson, N.J. As seen by the test results, the samples treated with the water-in-oil emulsion of the present invention showed that effective stain performance was achieved. EXAMPLES 6-8 These examples, all of- which were prepared utilizing the methods described in Example 1, illustrate various compositions found within the scope of the present invention. Examples 6-8 varied in that different types of binders, colorants and organic liquids were used. The test panels used, the ingredients utilized, the weight percentage of the ingredients and the test results are reported in Table 2. TABLE 2 As shown by the test results, the samples treated with the water-in-oil emulsion of the present invention showed that effective stain performance was achieved. EXAMPLES 9-11 These examples, all of which were prepared utilizing the methods described in Example 1, illustrate various compositions found within the scope of the present invention. Examples 9-11 varied in that varying amounts of binder, organic liquid and water were used. The test panels employed, the ingredients utilized, the weight percentage of the ingredients and the test results are reported in Table 3. TABLE 3 As shown by the test results, the samples treated with the water-in-oil emulsion of the present invention showed that effective stain performance was achieved. EXAMPLES 12-13 These examples, all of which were prepared utilizing the methods described in Example l , illustrate various compositions found within the scope of the present invention. The test panels used, the ingredients utilized, the weight percentage of the ingredients and the test results are reported in Table 4. TABLE 4 As shown by the test results, the samples treated with the water-in-oil emulsion of the present invention showed that effective stain performance was achieved. COMPARATIVE EXAMPLE 1 The test sample of Comparative Example 1 was prepared as an oil-based stain having binder dissolved therein. This stain had no water. The test panel, the ingredients used, the weight percentage of the ingredients and the test results are reported in Table 5. COMPARATIVE EXAMPLE 2 The test sample of Comparative Example 2 was prepared as an example of a composition wherein oil was dispersed in a continuous phase of water. It was prepared in accordance with the Natural Pine Transparent Stain Specification P-1909B for the binder Cargill™ 7358 except that two colorants, red iron oxide and yellow iron oxide, were mixed instead of using only one, yellow iron oxide. The test sample was prepared by dispersing 2.0 gms. of Cargill™ 7358 and 12 gms. of ethylene glycol butyl ether in 57.5 gms of water. Thereafter, 5 gms. of Seatone Trans Oxide Yellow (a yellow iron oxide) , commercially available from Hilton- Davis and 5 gms. of Seatone Trans Oxide Red (a red iron oxide) , sold by Hilton-Davis were blended into the mixture. The test panel, the ingredients used, the weight percentage of the ingredients and the test results are reported in Table 5. COMPARATIVE EXAMPLE 3 The composition of Comparative Example 3 illustrating an oil-in-water-in-oil emulsion was prepared in accordance with the Clark et al. Patent. The test panel, the ingredients used, the weight percentage of the ingredients and the test results are reported in Table 5. TABLE 5 Rhoplex * AC 64 is an acrylic emulsion sold by Rohm and Haas Company. Samples treated with a composition of the present invention appeared better than samples with the stain of Comparative Examples 2 and 3. The Examples show that effective performance could be obtained with the composition of the present invention similar to oil- based stains in terms of ability to highlight wood grain while minimizing the raising of wood grain. EXAMPLE 14 The composition of Example 14 explored the hydrophilic nature of the water-in-oil emulsion of the present invention. It was prepared by adding 30 gms. of Cargill™ 7358 to 30 gms. of Exxsol™ D80. Next, 5 grams of Formulator™ Trans Oxide Yellow and 5 gms. of Formulator™ Trans Oxide Red were blended into the solvent suspension. Thereafter, 0.1 gms. of the additive Magnacat™ was added to the suspension. Upon addition of the additive, 0.25 gms. of Tween ™ 80 and 0.75 gms. of Span ™ 80 were blended into the suspension in order to achieve a HLB of about 7.0. Thirty (30) gms. of water was then added to the mixture to prepare the oil-in-water emulsion. EXAMPLE 15 Example 15 examined the phase stability of the composition of the present invention. The composition was prepared by adding 10 gms. of Cargill™ 7358 to 25.6 gms. of Exxsol™ DUO. Next, 6.3 gms. of Formulator™ Trans Oxide Yellow, 4 gms. of Formulator™ Trans Oxide Red and 0.6 gms. of Formulator™ Tinting Black were blended into the solvent suspension. Thereafter, 0.1 gms. of the additive Magnacat™ was added to the suspension. Upon addition of the Magnacat™, 0.2 gms. of Tween™ 80 and 0.8 gms. of Span™ 80 were blended into the suspension followed by 51.1 gms. of water was then added to prepare the oil-in-water emulsion. The composition of this Example was stored for 4 months at 50°C. A portion of this composition was frozen and thawed 5 times during this four (4) month period. Both portions of the water-in-oil emulsion of the present invention was visually inspected for stability at the end of this period and found that the two phases did not separate. Although specific embodiments and examples have been disclosed therein, it should be borne in mind that these have been provided by way of explanation and illustration and that the present invention is not limited thereby. Certainly modifications which are within the ordinary skill in the art are considered to lie within the scope of this invention as defined by the following claims including all equivalents.

Claims: I Claim: 1. A water-in-oil wood stain composition comprising: (a) an oil continuous phase comprising a solution of a binder, and at least one colorant in an organic liquid and (b) a discontinuous phase comprising an aqueous medium wherein said composition has a solids content less than 50 percent by weight of said composition and is effective in highlighting wood. 2. The composition of Claim 1 wherein said colorant is at least one pigment. 3. The composition of Claim 1 wherein said colorant is at least one dye. 4. The composition of Claim 1 wherein said colorant comprises at least one pigment and at least one dye. 5. The composition of Claim 1 wherein said composition further comprises an emulsifier. 6. The composition of Claim 1 further comprising a dryer. 7. The composition of Claim 1 further comprising thickener. 8. The composition of Claim 1 wherein said binder is selected from the group comprising a drying oil, an oil soluble resin, a water reducible resin and mixtures of two or more of the foregoing. 9. The composition of Claim 1 further comprising a filler. 10. The composition of Claim 1 wherein said solids content comprises from about 5 to about 45 weight percent of said composition. 11. A method of staining wood comprising the steps of: a. applying to a substrate a wood stain in an effective amount of a composition according to Claim 1 to highlight wood grain thereon; and b. allowing said composition to dry on said substrate. 12. The method of Claim 11 wherein said composition comprises as a colorant at least one pigment. 13. The method of Claim 11 wherein composition comprises as a colorant at least one dye. 14. The method of Claim 11 wherein said composition comprises as colorants at least one dye and at least one pigment. 15. The method of Claim 11 wherein said composition further comprises an emulsifier. 16. The method of Claim 11 wherein said composition further comprises a dryer. 17. The method of Claim 11 wherein said composition further comprises thickener. 18. The method of Claim 11 wherein said composition further comprises a binder selected from the group comprising a drying oil, an oil soluble resin, a water reducible resins and a mixture of two or more of the foregoing. 19. The method of Claim 11 wherein said composition further comprises a filler. 20. The method of Claim 11 wherein said the solids content of said composition comprises from about 5 to about 45 weight percent of composition.

Inventors: ERISMANN DAVID W, ERISMANN, DAVID, W.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1993
Main classification: C09D15
IPC codes: C08L101, C09D15