An all purpose cleaner for hard surfaces comprises an aqueous solution of a secondary alcohol ethoxylate surfactant, an alkylpolyglycoside surfactant, and water, optionally comprising a chelating agent and sufficient pH modification agent to provide an alkaline solution. The ethoxylate surfactants preferably have HLB values of from 12.2 to 14.6, and each surfactant may comprise up to about 5 weight percent of the solution. The solution may be essentially free of organic solvents, such as alkylene glycol or alkylene glycol ethers, or other volatile organic compounds. As a result, the solution may be fragrance free, and, if so desired, colorless. Optionally, however, the cleaning solution may contain fragrances, coloring agents, anti-bacterials, stabilizers, preservatives, and other constituents, including a minor amount of a co-surfactant.

Not applicable.
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1. Technical Field
The present invention relates to hard surface cleaning compositions having low concentrations of organic solvent chemicals, or volatile organic compounds, frequently referred to as VOCs. The cleaning compositions of this invention deliver a high level of cleaning performance without reliance upon significant amounts of glycol ether solvents generally included in all purpose cleaner formulations. The use of a specific surfactant as the primary cleaning ingredient permits the exclusion or limitation of solvent, resulting in a significantly lower level of solvent odor, permitting the use of significantly less fragrancing.
2. Background Art
It is known that all purpose liquid cleaning compositions are widely accepted for cleaning hard surfaces, such as tile, wash bowls, toilets, bathtubs, walls, floors, painted and washable wall papered surfaces, etc. These all purpose cleaners generally comprise aqueous mixtures of water soluble organic detergents and water soluble detergent builder salts. Many previous such compositions relied upon the use of water soluble inorganic phosphate salts, which have now been replaced, for environmental reasons. For example, early phosphate containing compositions are set forth in U.S. Pat. Nos. 2,560,839; 3,234,138; and 3,350,319.
In light of harmful effects upon ground water caused by phosphates in cleaning compositions, improved liquid cleaners, as well as laundry detergents, containing reduced concentrations of phosphate builder salts have been developed, such as disclosed in U.S. Pat. No. 4,244,840. However, such all purpose cleaners containing detergent builder salts or other equivalents tend to leave films, spots, or streaks upon poorly rinsed cleaned surfaces, particularly noticeable on shiny surfaces for which these cleaners are most often used. Accordingly, such cleaners require thorough rinsing of the surfaces to which they are applied, a time consuming and annoying requirement, often neglected in use.
Alkyl glycoside materials such as, for example, higher alkyl monoglycosides and higher alkyl polyglycosides are known to function as nonionic surfactants, and have been suggested as being suitable for use in some detergent compositions, such as in U.S. Pat. No. 4,627,931. This reference teaches the use of nonionic glycoside surfactants in a hard surface liquid cleaning composition which comprises a nonionic surfactant component containing at least about 75 weight percent nonionic glycoside surfactant, a water miscible organic solvent, a water soluble detergent builder, and water. Examples of nonionic surfactants suitable for use with the glycosides include polyethylene oxide condensates of alkyl phenols, and condensation products of aliphatic alcohols. This reference, moreover, requires the presence of organic solvents, such as alkylene glycols and/or ethers thereof, and detergent builders such as alkali metal, ammonium or substituted ammonium polyphosphates, polyphosphonates, carbonates, polycarboxylates, carboxylated carbohydrates, etc.
In addition, all purpose cleaners have been developed employing anionic and nonionic detergents in combination with glycol ether solvent and organic amines, such as taught in U.S. Pat. No. 3,935,130. Such glycol ether solvents and organic amines are effective as grease removal solvents, and are especially helpful against oily and greasy soils. However, in addition to the need for thorough rinsing necessitated by the presence of high levels of organic detergents, such cleaners frequently also require high amounts of fragrancing to overcome the odors of the solvent materials present. Further, such solvents, frequently referred to as volatile organic compounds or VOCs, are in themselves objectionable, particularly in an age of increasing environmental awareness and concern.
Accordingly, there is a need for all purpose cleaners comprising a clear, aqueous solution having good interfacial tension for cleaning hard surfaces and good grease removal capability as a result thereof, without the presence of such objectionable components as phosphates or VOCs.
The present invention provides an improved all purpose cleaner, comprising a clear aqueous solution having acceptable interfacial tension properties, permitting good removal of greasy soil from hard surfaces such as plastic, ceramic, vitreous and metal surfaces, particularly those having a shiny finish, such as tiles, wash bowls, toilets, bathtubs, walls, floors, painted and washable wall papered surfaces, etc. The improved cleaner composition exhibits good soil removal properties with minimal rubbing, may be used diluted or undiluted, dries relatively quickly after wiping, and leaves the cleaned surface free of streaks or visible residue without rinsing. The cleaning solution is suitable for a wide range of possible uses, including (in diluted form) as a glass cleaner.
Moreover, the present cleaning composition achieves these results without the use of objectionable polyphosphate or other inorganic or organic detergent builder salts, and essentially or completely in the absence of grease removal solvents or VOCs.
Accordingly, the present composition is capable of being formulated without the addition of fragrancing agents to overcome the objectionable odors of organic solvents, and may thus be odor-free, or nearly so. As such, the present composition provides a capable all purpose liquid cleaner which may be applied by spraying upon a surface and wiping away, which is both effective as a cleansing means and environmentally acceptable.
The objects of the present invention therefore include providing an all purpose liquid cleaning composition which is environmentally acceptable, has little or no perceptible odor, and is effective in removal of grease and oil from hard surfaces. It is yet another object of the invention to provide a hard surface cleaning composition which may be sprayed upon the surface and removed by wiping, which will dry without streaking or visible residue, and requires no rinsing.
These and other objects are accomplished by provision of a cleaning composition comprising a secondary alcohol ethoxylate nonionic surfactant, an alkylpolysglycoside nonionic surfactant, and having an alkaline pH. More specifically, the all purpose cleaner of the present invention comprises from about 0.05 to about 5.0 weight percent of alkyloxypolyethylene oxyethanol, from about 0.075 to about 5.0 weight percent C8-C16 alkylpolyglycoside, and sufficient pH adjustment composition, if needed, to achieve a pH between 7.0 and 12.5, and preferably between 11.8 and 12.4. Additional components may include a chelating agent to prevent precipitation of hard water salts from materials present in the composition when hard water is employed, and optionally, coloring agents, fragrancing agents, anti-bacterial additives, drying agents, thickeners, and co-surfactants to boost the effectiveness of the primary surfactant. The entire composition is in the form of a water solution, preferably using soft water as the carrier, and may be provided in concentrated form for dilution prior to use by the consumer.
The all purpose cleaning composition of the present invention comprises an essentially clear aqueous composition comprising a secondary alcohol ethoxylate nonionic surfactant, an alkylpolyglycoside nonionic surfactant, and, optionally a pH modifying agent and a chelating agent. The primary cleaning agent, the ethoxylate surfactant, is preferably present in a range of from about 0.25 to about 2.50 weight percent, while the alkylpolyglycoside, which assists in surface wetting and film forming, is preferably present in a range of from 0.10 to about 1.50 weight percent. There does not appear to be a critical relationship between the two surfactant components, either in terms of ratio or sum, as long as both are present. In preferred embodiments, accordingly, the sum of the two surfactant components may range from about 0.125 to about 10 weight percent of the total solution. Unless otherwise indicated, all percentages expressed herein are weight percentages based upon the weight of active ingredients.
The primary nonionic surfactants suitable for the present invention comprise water soluble alcohol ethylene oxide condensates of a secondary aliphatic alcohol containing from 9 to 18 carbon atoms in a straight or branched configuration, condensed with from 5 to 30 moles, preferably from about 7 to 12 moles, of ethylene oxide. Examples of preferred commercially available surfactants of this composition are C11-C15 secondary alkanols condensed with 7,9, or 12 moles of ethylene oxide, available from Union Carbide under the tradenames Tergitol(copyright) 15-S-7, 15-S-9, and 15-S-12, for example, believed to comprise alkyloxypolyethylene oxyethanol. Additional suitable surfactants, of the same type, are marketed by Union Carbide under the tradenames Tergitol(copyright) TMN-6 and TMN-10, believed to comprise reaction products of trimethyl-nonanol with ethylene oxide.
A key property held in common by these compositions is an HLB value greater than 11.5 but less than 15.0. The term HLB value refers to hydrophobic lipophilic balance value, a measure of water solubility and ability to give good emulsification, critical properties for a detergent composition. In general, compositions with an HLB value of less than about 10 tend to be poorly soluble in water.
A single member of this group of surfactant compositions may be employed, or mixtures of such suitable surfactant materials may be employed, provided that the average HLB values of the surfactant or the mixture of surfactants is from about 11.5 about 15.0, preferably from about 12.2 to about 14.6, and most preferably from about 12.4 to about 14.4.
The quantity of secondary alcohol ethoxylate employed may range from as low as about 0.05 weight percent of the composition, an amount suitable for use in a ready-to-use glass cleaning composition, up to concentrations at which streaking and solubility issues arise. Generally, up to about 5 percent by weight of the composition may comprise a secondary alcohol ethoxylate surfactant, above which amount streaking becomes a factor. A preferred range for the ethoxylate surfactants is from about 0.25 to about 2.5 weight percent, with a range of from about 0.5 to about 1.5 weight percent being more preferred.
In addition to the secondary alcohol ethoxylate surfactants, the present cleaning compositions comprise an alkylpolyglycoside surfactant. Glycoside surfactants suitable for use in the present invention may be selected from those of the general formula RO(Rxe2x80x2O)y(Z)x, wherein R is a monovalent organic radical, (such as an monovalent saturated aliphatic, unsaturated aliphatic, or aromatic radical such as alkyl, hydroxyalkyl, alkenyl, aryl, arylalkyl, etc.) containing from about 8 to about 18 carbon atoms; Rxe2x80x2 is a divalent hydrocarbon radical containing from 2 to 4 carbon atoms such as ethylene, propylene, or butylene; Z represents a moiety derived from a reducing saccharide containing 5 or 6 carbon atoms (preferably a glucose unit); y is a number having an average value of from 0 to about 12; and x is a number having an average value of from 1 to about 10, preferably from 1 to 3.
Most suitable among these glycoside surfactants are the alkylpolyglycosides, particularly those available from Cognis, Inc., under the tradenames APG(copyright) 325, based upon a synthetic alcohol having from 9 to 11 carbon atoms, and GLUCOPON(copyright) 425, based upon a natural alcohol having from 8 to 16 carbon atoms. The alkylpolyglycoside surfactant may be present in an amount of from about 0.075 weight percent, an amount suitable for use in a ready-to-use window composition, for example, up to about 5.0 weight percent, the upper limit being a function of solubility, streaking, and cost. Preferably, the alkylpolyglycoside is present in a range of from about 0.1 to about 1.5 weight percent, and most preferably in a concentration of about 0.5 to about 1.0 weight percent.
As previously indicated, both the alcohol ethoxy surfactant and the alkylpolyglycoside surfactants are necessarily present in the present invention. The ratio of the two does not appear to be critical to the success of the cleaning composition, and the total quantity of the two may be merely the sums of the two components used.
In addition, it has been found that the presence of a small amount of a chelating agent may be necessary to prevent precipitation of components present in the components of the cleaner if the solution utilizes hard water. Conventional chelating agents such as the tetrasodium salt of EDTA, sodium nitrilotriacetate, and sodium citrate may be employed, in a suitable concentration of from about 0.004 to about 0.4 weight percent, preferably about 0.1 percent active. Such chelating agents are appropriate to prevent the precipitation of hard water salts of materials frequently present in commercially available alkylpolyglycosides, but are unnecessary if deionized water is employed.
The pH of the solution should be above 7.0, and preferably from about 8.0 to about 12.5. The most preferred pH may range from about 11.8 to about 12.4. If necessary for pH adjustment, sodium hydroxide, or caustic, is employed in sufficient quantity to adjust the pH to the desired alkalinity. Alternatively, sulfuric acid and citric acid, or similar acidic compositions, may be employed to lower pH if appropriate. It has been found that raising the pH above about 8.0 has a beneficial effect upon the grease cleaning capability of the surfactants used in the present invention, and while lower pH may be acceptable for light duty cleaning where little or no greasy soil is present, such as with a glass cleaner, elevation of the pH to a value of from about 11.8 to about 12.4 is preferred. Above a pH of about 12.5, however, the cleaning solution becomes excessively caustic, presenting possible injuries to the skin, and damage to surfaces upon which the solution is used. Moreover, such highly caustic solutions create an unstable system, and can be damaging to processing, handling, and storage equipment.
Since the cleaning composition is an aqueous solution, the active ingredients should be mixed with water to the desired concentrations. It is desirable that soft water be used, but one may use distilled, deionized, or filtered tap water, containing no compounds reactive with the cleaning solution ingredients, and containing no materials which would leave a residue or streaking on surfaces to which the cleaning composition is applied. Since the compositions as prepared are aqueous liquid formulations, and since water comprises the major ingredient, no particular mixing is required to obtain a uniform solution, and the cleaning composition may be prepared simply by combining all of the ingredients in a suitable vessel or container. The order of mixing the ingredients is not particularly important, and generally the various ingredients may be added sequentially or all at once, or in the form of aqueous solutions of each, or all of the ingredients may be separately prepared and combined with each other. The pH adjustment should be made last, however, after all other ingredients have been mixed and a stable solution formed.
While the above combination of a secondary alcohol ethoxylate surfactant, an alkylpolyglycoside surfactant, and water, comprises a preferred embodiment of the all purpose cleaner of the present invention, other optional modifications and additions may be made. Another preferred embodiment of the invention comprises the above combination plus a chelating agent and a pH modifier to bring the solution to a pH of from about 11.8 to about 12.4. Further, fragrances may be present in the cleaning solution, although the avoidance of glycol ethers and other VOCs commonly employed in all purpose cleaning solutions greatly lowers the necessity or desirability for the addition of a perfume. Fragrances suitable for use in the present invention include all suitable perfumes or essential oils, selected, for example and without limitation, from the group consisting of Aniseed oil, Balsam, Basil, Camphor, cinnamon, Citronella, Clove, Coriander, Coumarin, Eucalyptus, Fennel, Ginger, Grapefruit, Juniper berry, Lemon, Lemongrass oil, Musk ketone, Nutmeg, Orange, Patchouli, Peppermint, Sage, Sassafras, Spearmint, Lavender, Wintergreen, Geraniol, and the like.
Optionally, other ingredients which are compatible with the water soluble surfactants may be included, such as up to about 5 weight percent of a thickening if agent such as hydroxyethyl cellulose, xanthan gum, or other conventional thickening and agents. Particulate additives such as silica and other high surface area particles are to be avoided in accordance with the purpose of the present invention, which is to provide a non streaking cleaning solution. Similarly, other conventional additives such as dyes, preservatives, disinfectants, and buffering agents, may be included in the aqueous solutions of the present invention provided that they are compatible with the other ingredients present.
In addition, small quantities of alkylene glycols and/or ethers thereof may also be added as co-surfactants, to boost the cleaning power of the other surfactants present. These conventional cleaning agents may be present in an amount preferably less than about 4 weight percent, but possibly in ranges from zero to about 10 weight percent, up to limits of solubility, odor, and VOC contribution to the cleaning composition of the invention. Preferred examples of such co-surfactants include, without limitation, such organic solvents as ethylene glycol monohexyl ether, butyl proposol, and butyl cellosolve, and the like.
Still further, small quantities, such as from zero to about 3 weight percent, of drying agents may be included. Suitable drying agents include such alcohols as isopropanol, ethanol, tert-butanol, and the like.

All purpose cleaner with low organic solvent content


A method of coating metallic substrates with weldable primer and at least one powder coating is provided by the present invention. The base powder coating contains flake pigments that align parallel to the surface when the powder coating is heated. Optionally, a clear top coating is applied over the base powder coating. Substrates coated by the method of coating are also provided. The method of coating allows substrates coated with weldable primer to be assembled into assemblies or finished parts by welding, and then to be coated with the powder basecoat and clear coat. The parts prepared have striking visual effects and performance comparable to conventional automotive parts but are prepared more efficiently and economically.

This invention relates to an improved method of producing visually attractive weldable parts, in particular automotive parts, with attractive metallic-like appearance, without the need of expensive electrodeposition baths, using weldable prepainted metal substrate to which are applied essentially zero VOC powder coatings. The powder coatings comprise flake pigments, which give the metallic-like appearance. The invention also relates to parts prepared by this method.
Light gauge continuous sheet metal is produced by rolling mill lines in various thickness and widths. In the case of steel sheet metal, it may be coated at the mill with a thin layer of zinc or zinc alloy in order to provide steel sheet with improved corrosion resistance. After production of the sheet, mill oil is applied in the case of steel sheet and the sheet metal is wound into a coil for shipment to a customer for further processing. Such sheets are used by customers for a number of industrial and automotive applications. At the customer, the metal sheet is unwound and cleaned to remove any mill oil and dirt and to reduce the amount of metal oxide on the surface of the metal, after which the metal is coated with one or more layers of coating. The coatings usually include at least one primer to provide improved corrosion protection as well as adhesion of subsequent coating layers to the substrate. One common and very effective method of applying primer to metal substrates is the electrodeposition method in which a primer with an ionic, often cationic, species on the polymer backbone, is attracted to and deposits itself on a metal part which has the opposite charge, after which the coated parts are baked to cure the primer. Following the application of the primer, other layers of coating such as primer-surfacer can be applied for improved adhesion and smoothness. The final layers of coating to be applied are what is generally seen by the end user of the part, and these coatings, in addition to providing protection, such as hardness, weathering protection, and the like to the part, provide a visually attractive finish.
In the production of parts for automobile and other vehicle bodies, sheet metal from the mill, usually galvanized steel, is generally formed into the desired shape. The forming oil is then cleaned from the sheet. Following the cleaning step, the metal is pretreated with a phosphate pretreatment. The phosphated metal parts are then assembled into an automobile body with various forms of attachment such as clenching, gluing, and particularly spot welding.
The vehicle body is then primed with a cationic electrodeposition primer. The application of the electrodeposition primer (ED primer) at the automotive manufacturer requires large immersion baths. Such baths require large capital investment and continuous monitoring during production and occupy large areas of plant space. Moreover, the ED primer often does not form a film of sufficient thickness to be effective in confined or partially enclosed areas. Such areas may be seen where one piece of metal is bent over and clenched to another piece of metal to connect the two pieces of metal. In such a configuration, the ED primer often fails to deposit adequately in the region of the bend, leaving an area of metal relatively unprotected against corrosion. Another area in which an adequate layer of ED primer may not form is the interior of enclosed parts such as doors.
The process of applying a weldable anticorrosive primer to the metal sheet after cleaning and prior to forming of the metal sheet into an automotive part ensures the presence of an adequate thickness of anticorrosive primer in enclosed or confined areas of vehicle assemblies. Furthermore, application of the primer to the continuous sheet of metal can be done by roll coating in which the primer is applied by a roll moving in the same direction, or more commonly the opposite direction, as the moving sheet of metal. After the weldable primer is applied and dried and/or cured, the continuous sheet of primed metal can be wound into a coil. Roll coat application of primer to a continuous strip of metal has the advantage that it is nearly 100% efficient, that is, virtually all of the liquid primer is applied to the metal strip and cured, and the volatiles emitted during the baking process are commonly collected and burned as fuel for the oven, leading to low atmospheric emissions. The roll coat application and cure of the weldable primer can be done at a location separate from the vehicle manufacturing plant. Typically it is done at a company specializing in coil coating application, but it may even be done at the steel mill itself. Removal of the priming step from the vehicle manufacturing plant can eliminate the need for the large expensive ED immersion tanks and can lead to more efficient use of space and resources in the vehicle plant.
Although use of such coating processes are well known to those practicing the coil-coating art, conventional coil coating primers generally can not be used because the steel sheet, after being cut and formed into parts in a stamping press, is usually assembled into assemblies and vehicle bodies by spot welding. Conventional coil coating primers do not allow sufficient electric current to pass during the spot welding process to cause a weld to form in the metal. If conventional coil coatings are applied at very low dry film thickness enough current may pass to form a weld, but at such low thickness corrosion protection is inadequate. The weldable primer of the current invention avoids such limitations by inclusion of electrically conductive pigments as well as anticorrosive pigments to give a weldable formable primer with good corrosion protection. Because the primer is electrically conductive, additional corrosion protection can be realized, if needed, by coating the parts formed from the prepainted metal with ED primer after they are assembled.
In the current invention, after assembly of the parts formed from the metal sheet coated with weldable primer, the parts may optionally be given an additional phosphate pretreatment. The parts are then coated with a colored powder basecoat and optionally a powder clearcoat. Powder basecoats and clearcoats are desirable because they provide: superior appearance and chip resistance vs. liquid primers; essentially zero VOC vs. liquid primers; and 98 to 99% utilization in most facilities vs. 70 to 80% maximum for liquids.
The colored powder basecoat comprises metallic or non-metallic flake pigments. The pigments themselves may be colored, or uncolored. The parts are baked for a period of time sufficient to melt and coalesce the powder coating and to allow the flakes to align with the surface. The use of the flake pigments, especially colored flake pigments, in colored basecoats allows a wide range of striking visual effects.
The powder basecoat may be used without further coatings, but improved hardness, weathering and UV resistance, and visual appeal will be realized with application of a powder clearcoat. These powder clearcoats provide similar VOC and utilization advantages as those gained with powder basecoats with appearance and durability comparable to liquid clear coats. U.S. Pat. No. 5,407,707 describes the preparation of powder clear coats with excellent physical and chemical properties prepared from epoxy functional copolymers and polycarboxylic acid curing agents.
The advantages of the invention are the ability to produce panels and parts, particularly for automotive applications, with striking visual effects, good hardness, and weather and UV resistance by a method that does not require the use of large expensive electrodeposition baths. Although the conductive coating is positioned beneath the powder basecoat, primer surfacers are not needed, and preferably are not used. A further advantage of the invention is the ability to produce these panels and parts using a virtually zero VOC topcoat system with the same high utilization rates as those all ready demonstrated by the automotive powder primer and powder clear products currently in commercial use.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term xe2x80x9cabout.xe2x80x9d Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of xe2x80x9c1 to 10xe2x80x9d is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
As used herein, the term xe2x80x9ccurexe2x80x9d as used in connection with a composition, e.g., xe2x80x9ccomposition when cured,xe2x80x9d and xe2x80x9cthermosetxe2x80x9d as used in connection with a composition, e.g. xe2x80x9cthermoset compositionxe2x80x9d shall mean that any crosslinkable components of the composition are at least partially crosslinked. In certain embodiments of the present invention, the crosslink density of the crosslinkable components, i.e., the degree of crosslinking, ranges from 5% to 100% of complete crosslinking. In other embodiments, the crosslink density ranges from 35% to 85% of full crosslinking. In other embodiments, the crosslink density ranges from 50% to 85% of full crosslinking. One skilled in the art will understand that the presence and degree of crosslinking, i.e., the crosslink density, can be determined by a variety of methods, such as dynamic mechanical thermal analysis (DMTA) using a TA Instruments DMA 2980 DMTA analyzer conducted under nitrogen. This method determines the glass transition temperature and crosslink density of free films of coatings or polymers. These physical properties of a cured material are related to the structure of the crosslinked network.
As used herein, the terms xe2x80x9ctypicallyxe2x80x9d, e.g., xe2x80x9cThe temperature of the treating solution at application is typically about 10xc2x0 C. to about 85xc2x0 C.xe2x80x9d; xe2x80x9cgenerallyxe2x80x9d, e.g., xe2x80x9cThe width of the continuous metal sheet generally ranges from about 30.5 to about 183 centimetersxe2x80x9d; and xe2x80x9ccommonlyxe2x80x9d, e.g., xe2x80x9cmore commonly, the substrates coated by this method will be metallicxe2x80x9d as used in the detailed description of the invention is intended to describe methods frequently used, but is not intended to limit the application of the invention.
The present invention relates to a method of coating a substrate with a conductive, weldable primer, optionally pretreating and applying other primers, such as electrodeposition primers to the weldable primer, and applying a visually attractive powder color coat and optionally a clear coat. The present invention also relates to the substrate prepared by this method.
The substrates of this invention may be non-metallic or metallic. More commonly, the substrates coated by this method will be metallic. The metal substrates used in the practice of this invention include ferrous metals, non-ferrous metals, and combinations thereof. Suitable ferrous metals include iron, steel, and alloys thereof. Non-limiting examples of useful steel materials include cold rolled steel, zinc coated steels such as hot dip galvanized and electrogalvanized steel, stainless steel, pickled steel, zinc-iron alloy such as GALVANEAL, zinc-aluminum alloys coated over steel such as GALVALUME, AND GALFAN, and combinations thereof. It is possible for different portions of the same substrate to be different forms of ferrous metal, for example, for the zinc coating to be applied to only certain portions or one side of the steel substrate. Useful non-ferrous metals include aluminum, zinc, magnesium, and alloys thereof. Combinations or composites of ferrous and non-ferrous metals can also be used. Preferred metallic substrates are anti-corrosive steels such as the zinc coated steels and the zinc-iron alloy and the zinc-aluminum alloys mentioned above. Although substrates of any desired shape can be used, the substrate is preferably in the form of a sheet, and more preferably in the form of a continuous sheet wound about a spool in the form of a coil. The thickness of the continuous sheet preferably ranges from about 0.254 to about 3.18 millimeters (mm) (about 10 to about 125 mils), and more preferably about 0.3 mm although the thickness can be greater or less, as desired. The width of the continuous metal sheet generally ranges from about 30.5 to about 183 centimeters (about 12 to 72 inches), although the width can vary depending on metal manufacturer and intended use.
Before depositing the coatings of the present invention upon the surface of the metal substrate, it is preferred to remove dirt, oil, or foreign matter from the metal surface by thoroughly cleaning and degreasing the surface. The surface of the metal substrate can be cleaned by physical or chemical means, such as mechanically abrading the surface or cleaning/degreasing with commercially available alkaline or acidic cleaning agents which are well known to those skilled in the art, such as sodium metasilicate and sodium hydroxide. Non-limiting examples of suitable alkaline cleaning agents include CHEMKLEEN 163 and CHEMKLEEN 177 phosphate cleaners that are commercially available from PPG Industries, Inc. of Pittsburgh, Pa.
Following the cleaning step, the metal substrate is usually rinsed with water, preferably deionized water, in order to remove any residue. The metal substrate can optionally be dried using an air knife, by flashing the water off by brief exposure to a high temperature, or by passing the metal between squeegee rolls.
Following the cleaning and optional drying steps, the metal substrate may be optionally pretreated with a thin layer of pretreatment. The advantages of pretreatment include protection of the metallic substrate from corrosion and improvement of adhesion of subsequent coating layers to the substrate. Pretreatments may be chrome containing or preferably chrome-free. The choice of pretreatment is generally determined by the substrate and environmental considerations. Appropriate pretreatments are well known to those skilled in the art. An example of a suitable chrome pretreatment is Granodine 1415A available from Henkel Surface Technologies, NA. An example of a chrome-free pretreatment is Nupal 456BZ available from PPG Industries, Inc. Some weldable compositions, in particular those with phosphatized epoxy resinous binder systems, perform well in the absence of pretreatment.
The pretreatment solution is applied to the surface of the metal substrate by any conventional application technique, such as spraying, immersion or roll coating in a batch or continuous process. The temperature of the treating solution at application is typically about 10xc2x0 C. to about 85xc2x0 C., and preferably about 15xc2x0 C. to about 40xc2x0 C. The pH of the preferred treating solution at application generally ranges from about 2.0 to about 9.0, and is preferably about 3 to about 5.
The film coverage of the residue of the pretreatment coating generally ranges from about 0.1 to about 1000 milligrams per square meter (mg/m2), and is preferably about 1 to about 400 mg/m2.
Hereafter, the term xe2x80x9csubstratexe2x80x9d shall refer to the cleaned, optionally pretreated, substrate.
Following the optional pretreatment step, the conductive, weldable coating is applied to the cleaned substrate.
The conductive, weldable coating is formed from a weldable composition comprising one or more electroconductive pigments which provide electroconductivity to the weldable coating and one or more binders which adhere the electroconductive pigment to the substrate. Non-limiting examples of suitable electroconductive pigments include zinc, iron phosphide, aluminum, iron, graphite, nickel, tungsten and mixtures thereof. The zinc, iron phosphide, and mixtures thereof are preferred. Preferred zinc particles are commercially available from Stolberger ZINCOLI as ZINCOLI S 620 or from US Zinc as Superfine 7 zinc dust. The iron phosphide is available as Ferrophos Microfine grade 2132 from Glenn Springs Holdings of Lexington, Ky. The average particle size (equivalent spherical diameter) of the electroconductive pigment particles generally is less than about 10 micrometers, preferably ranges from about 1 to about 5 micrometers, and more preferably about 3 micrometers.
Since the metal substrates are to be subsequently welded, the weldable coating must comprise a substantial amount of electroconductive pigment, generally greater than about 10 volume percent and preferably about 30 to about 60 volume percent on a basis of total volume of electroconductive pigment and binder.
The binder is present to secure the electroconductive pigment and other pigments in the composition to the substrate. Preferably, the binder forms a generally continuous film when applied to the surface of the substrate. Generally, the amount of binder can range from about 5 to about 50 weight percent of the coating composition on a total solids basis, preferably about 10 to about 30 weight percent and more preferably about 10 to about 20 weight percent.
The binder can comprise oligomeric binders, polymeric binders and mixtures thereof. The binder is preferably a resinous polymeric binder material selected from thermosetting binders, thermoplastic binders or mixtures thereof. Non-limiting examples of suitable thermosetting materials include polyesters, epoxy-containing materials, phenolics, polyurethanes, and mixtures thereof, in combination with crosslinkers such as aminoplasts or isocyanates which are discussed below. Non-limiting examples of suitable thermoplastic binders include high molecular weight epoxy resins, defunctionalized epoxy resins, vinyl polymers, polyesters, polyolefins, polyamides, polyurethanes, acrylic polymers and mixtures thereof.
Preferred binder materials are polyglycidyl ethers of polyhydric phenols, such as those discussed above, having a weight average molecular weight of at least about 2000 and preferably ranging from about 5000 to about 100,000. These materials can be epoxy functional or defunctionalized by reacting the epoxy groups with phenolic materials. Such binders can have epoxy equivalent weights of about 2000 to about one million. Non-limiting examples of useful epoxy resins are commercially available from Shell Chemical Company as EPON(copyright) epoxy resins. Preferred EPON(copyright) epoxy resins include EPON(copyright) 1009, which has an epoxy equivalent weight of about 2300-3800. Useful epoxy defunctionalized resins include EPONOL resin 55-BK-30 which is commercially available from Shell. Other preferred binders are the reaction product of epoxy resins as described above with a compound containing phosphorous acid groups.
Suitable crosslinkers or curing agents are described in U.S. Pat. No. 4,346,143 at column 5, lines 45-62 and include blocked or unblocked di- or polyisocyanates such as DESMODUR(copyright) BL 1265 toluene diisocyanate blocked with caprolactam, which is commercially available from Bayer, and aminoplasts such as etherified derivatives of urea-melamine- and benzoguanamine-formaldehyde condensates which are commercially available from Cytec Industries under the trademark CYMEL(copyright) and from Solutia under the trademark RESIMENE(copyright).
Preferably, the coating composition comprises one or more diluents for adjusting the viscosity of the composition so that it can be applied to the metal substrate by conventional coating techniques. The diluent should be selected so as not to detrimentally affect the adhesion of the weldable coating to the pretreatment coating upon the metal substrate. Suitable diluents include ketones such as cyclohexanone (preferred), acetone, methyl ethyl ketone, methyl isobutyl ketone and isophorone; esters and ethers such as 2-ethoxyethyl acetate, propylene glycol monomethyl ethers such as DOWANOL PM, dipropylene glycol monomethyl ethers such as DOWANOL DPM or propylene glycol methyl ether acetates such as PM ACETATE which is commercially available from Dow Chemical; and aromatic solvents such as toluene, xylene, aromatic solvent blends derived from petroleum such as SOLVESSO(copyright) 100. The amount of diluent can vary depending upon the method of coating, the binder components and the pigment-to-binder ratio, but generally ranges from about 10 to about 50 weight percent on a basis of total weight of the weldable coating.
The coating can further comprise optional ingredients such as phosphorus-containing materials, including metal phosphates or the organophosphates; inorganic lubricants such as GLEITMO 1000S molybdenum disulfide particles which are commercially available from Fuchs of Germany; coloring pigments such as iron oxides; flow control agents; thixotropic agents such as silica, montmorillonite clay and hydrogenated castor oil; anti-settling agents such as aluminum stearate and polyethylene powder; dehydrating agents which inhibit gas formation such as silica, lime or sodium aluminum silicate; and wetting agents including salts of sulfated castor oil derivatives such as RILANIT R4.
Other pigments such as carbon black, magnesium silicate (talc), zinc oxide and corrosion inhibiting pigments including calcium modified silica, zinc phosphate and molybdates such as calcium molybdate, zinc molybdate, barium molybdate and strontium molybdate and mixtures thereof can be included in the coating composition. Generally, these optional ingredients comprise less than 20 weight percent of the coating composition on a total solids basis, and usually about 5 to about 15 weight percent. Preferably, the weldable coating is essentially free of chromium-containing materials, i.e., comprises less than about 2 weight percent of chromium-containing materials and more preferably is free of chromium-containing materials.
The preferred coating compositions contain EPON(copyright) 1009 epoxy-functional resin or the reaction product of Epon(copyright) 1004 with phosphoric or superphosphoric acid, zinc dust, salt of a sulfated castor oil derivative, silica, molybdenum disulfide, red iron oxide, the blocked isocyanate formed by the reaction of polymeric MDI with the reaction product of bisphenol A and polyethylene oxide, melamine resin, dipropylene glycol methyl ether, propylene glycol methyl ether acetate and cyclohexanone.
The coating compositions can be applied to the surface of the substrate by any conventional method well known to those skilled in the art, such as dip coating, direct roll coating, reverse roll coating, curtain coating, air and airless spraying, electrostatic spraying, pressure spraying, brushing such as rotary brush coating or a combination of any of the techniques discussed above.
After application, the conductive, weldable coating compositions are preferably dried and/or cured to set the coating composition and form a substantially continuous coating upon the substrate. The coating can be formed at ambient temperature or preferably at an elevated temperature ranging up to about 300xc2x0 C. peak metal temperature. Many of the binders such as those prepared from epoxy-containing materials require curing at an elevated temperature for a period of time sufficient to vaporize any diluents in the coating and to set the binder. In general, baking temperatures will be dependent upon film thickness and the components of the binder. For preferred binders prepared from epoxy-containing materials, peak metal temperatures of about 150xc2x0 C. to about 300xc2x0 C. are preferred. For preferred binders prepared from phosphated epoxy-containing materials, peak metal temperatures of about 140xc2x0 C. to about 190xc2x0 C. are preferred. The period of baking in conventional conveyor ovens is typically from 20 seconds to 60 seconds, preferably from 24 seconds to 30 seconds. The period of baking is usually determined by the time required to reach desired peak metal temperature in a given oven. It will be recognized by those skilled in the art that alternate means of heating the substrate such as infrared or induction heating will require much shorter times to reach peak metal temperature, often less than 10 seconds. After the baking the coated substrate is typically cooled with water, followed by drying with an air knife.
The thickness of the dried, conductive, weldable coating can vary depending upon the use to which the coated substrate will be subjected. Generally, to achieve sufficient corrosion resistance for coil metal for automotive use, the applied coating should have a dry film thickness of at least about 1 micrometer (about 0.04 mils), preferably about 1 to about 20 micrometers and more preferably about 3 to about 8 micrometers. For other substrates and other applications thinner or thicker coatings can be used. Lower dry film thickness is associated with better welding whereas higher dry film thickness is associated with better corrosion protection. Preferred dry film thickness for zinc pigmented coatings in this invention is between 3 micrometers and 5 micrometers, preferred dry film thickness for the iron phosphide-pigmented weldable coatings in this invention is between 5 micrometers and 8 micrometers.
After the conductive weldable coating has been dried and/or cured, the metal substrate may be optionally lubricated, and the metal may be wound into a coil for storage or for transport to another location for further operations.
The steps described above may be conducted at a mill, or more commonly, the metal is wound into a coil at the mill and shipped to a separate location, such as a coil coater, for the coating operation where the above-described steps are carried out. After coating the sheet is rewound into a coil and shipped to another location, such as an automotive assembly plant where the metal is unwound, cleaned, optionally lubricated, cut into appropriate sized sheets, formed into discrete shapes, spot welded into a unit assembly, such as an automobile body, the unit assembly is then optionally cleaned and pretreated, typically with a phosphate type pretreatment and optionally primed with electrodeposited primer.
The unit assembly is then coated with a decorative color coating composition and optionally further coated with a clear coat. The color coating composition is in the form of a solid particulate material commonly called a powder coating. The composition of the powder coating comprises a polymeric film-forming binder and a flake coloring pigment such as aluminum flake and/or metal oxide coated micas.
Preferably, the polymeric, film-forming binder of the base powder coating is of the thermoset type wherein the binder comprises: (a) one or more polymers having reactive functional groups and; (b) one or more curing agents selected to react with the functional groups of (a).
Polymers Containing Functional Groups
The powder base coat compositions of the present invention comprise polymers containing functional groups such as hydroxyl, carboxylic acid, epoxy, carbamate, amide and carboxylate functional groups.
The use in powder coatings of acrylic, polyester, polyether and polyurethane oligomers and polymers having hydroxyl functionality is well known in the art. Monomers for the synthesis of such oligomers and polymers are chosen such that the resulting oligomers and polymers have a Tg greater than 40xc2x0 C. Examples of such oligomers and polymers having hydroxyl functional groups suitable for use in the powder coating compositions of the present invention are those described in U.S. Pat. No. 5,646,228 at column 5, line 1 to column 8, line 7, incorporated by reference herein.
The use in powder coatings of acrylic polymers having carboxylic acid functionality is well known in the art. Monomers for the synthesis of the acrylic polymers having carboxylic acid functionality suitable for use in the powder coating compositions of the present invention are chosen such that the resulting acrylic polymer has a Tg greater than 40xc2x0 C. Examples of carboxylic acid group containing acrylic polymers are those described in U.S. Pat. No. 5,214,101 at col. 2, line 59 to col. 3, line 23, hereby incorporated by reference.
The use in powder coatings of polyester polymers having carboxylic acid functionality is well known in the art. Monomers for the synthesis of the polyester polymers having carboxylic acid functionality suitable for use in the powder coating compositions of the present invention are chosen such that the resulting polyester polymer has a Tg greater than 40xc2x0 C. Examples of carboxylic acid group containing polyester polymers are those described in U.S. Pat. No. 4,801,680 at col. 5, lines 38 to 65, hereby incorporated by reference.
Besides carboxylic acid group-containing acrylic polymers, the powder coating compositions of the present invention can, and typically do, contain a second carboxylic acid group-containing material selected from the class of C4 to C20 aliphatic dicarboxylic acids, polymeric polyanhydrides, low molecular weight polyesters having an acid equivalent weight from about 150 to about 750 and mixtures thereof. This material is crystalline and is preferably a low molecular weight crystalline carboxylic acid group-containing polyester.
Also useful in powder coating compositions are acrylic, polyester and polyurethane polymers containing carbamate functional groups and epoxy functional groups, such as those well known in the art. Examples of such polymers having carbamate functionality suitable for use in the powder coating compositions of the invention are described in international application WO 94/10213. Examples of polymers having epoxy functionality suitable for use in powder coating compositions are described in U.S. Pat. No. 5,407,707. Monomers for the synthesis of such polymers for use in the powder coating compositions are chosen such that the resulting polymer has a high Tg, that is, a Tg greater than 40xc2x0 C.
For the powder color coat, the preferred polymer containing functional groups is a carboxylic acid group-containing polymer, preferably a polyester polymer. For the powder clear coat, the preferred polymer is an epoxy functional polymer, preferably an epoxy group-containing acrylic polymer.
Curing Agents
Blocked isocyanates as curing agents for (OH) and primary and/or secondary amino group containing materials are well known in the art. Examples of blocked isocyanates suitable for use as curing agents in the powder coating compositions of the present invention are those described in U.S. Pat. No. 4,988,793, col. 3, lines 1 to 36, hereby incorporated by reference.
Polyepoxides as curing agents for (COOH) functional group containing materials are well known in the art. Examples of polyepoxides suitable for use as curing agents in the powder coating compositions of the present invention are those described in U.S. Pat. No. 4,681,811 at col. 5, lines 33 to 58, hereby incorporated by reference.
Polyacids as curing agents for epoxy functional group containing materials are well known in the art. Examples of polyacids suitable for use as curing agents in the powder coating compositions of the present invention are those described in U.S. Pat. No. 4,681,811 at col. 6, line 45 to col. 9, line 54, hereby incorporated by reference.
Polyols, that is, material having an average of two or more hydroxyl groups per molecule, can be used as curing agents for (NCO) functional group containing materials and anhydrides, and are well known in the art. Polyols for use in the powder coating compositions of the present invention are selected such that the resultant material has a high glass transition temperature, i.e., greater than 50xc2x0 C.
Beta-hydroxyalkylamide materials as crosslinkers for carboxylic acid-functional polymers (a) are disclosed in U.S. Pat. No. 4,801,680. The hydroxyl functionality of the beta-hydroxyalkylamide should be on an average basis at least two, preferably greater than two, and more preferably from greater than two up to about four in order to obtain optimum curing response.
The beta-hydroxyalkylamide materials can be depicted structurally as follows:
wherein R1 is H or C1-C5 alkyl; R2 is H, C1-C5 alkyl or:
wherein R1 is as described above; A is a bond, monovalent or polyvalent organic radical derived from a saturated, unsaturated or aromatic hydrocarbon including substituted hydrocarbon radicals containing from 2 to 20 carbon atoms, m is equal to 1 to 2, n is equal to 0 or 2, and m+n is at least 2, preferably greater than 2, usually within the range of from 2 up to and including 4. Preferably, A is an alkylene radical xe2x80x94(CH2)xxe2x80x94 where x is from 2 to 12, preferably from 4 to 10.
The beta-hydroxyalkylamide can be prepared by reacting a lower alkyl ester or mixture of esters of carboxylic acids with a beta-hydroxyalkylamine at a temperature ranging from ambient temperature up to about 200xc2x0 C. depending on the choice of reactants and the presence or absence of a catalyst. Suitable catalysts, include base catalysts such as sodium methoxide, potassium methoxide, sodium butoxide, potassium butoxide, sodium hydroxide, potassium hydroxide and the like, present in amounts of about 0.1 to about 1 percent by weight based on the weight of the alkyl ester.
To bring about the most effective cure of the powder coating composition, the equivalent ratio of beta-hydroxyalkylamide (hydroxy equivalents) to carboxy-containing polyester (carboxylic acid equivalents) is preferably from about 0.6 to 1.6:1, more preferably from 0.8 to 1.3:1. Ratios outside the range of 0.6 to 1.6:1 are undesirable because of poor cure.
Anhydrides as curing agents for epoxy functional group containing materials are well known in the art. Examples of such curing agents include trimellitic anhydride, benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, tetrahydrophthalic anhydride, and the like as described in U.S. Pat. No. 5,472,649 at col. 4, lines 49 to 52.
Aminoplasts as curing agents for OH, COOH and carbamate functional group containing materials are well known in the art. Examples of such curing agents suitable for use in the present invention are aldehyde condensates of glycoluril, which give high melting crystalline products useful in powder coatings. While the aldehyde used is typically formaldehyde, other aldehydes such as acetaldehyde, crotonaldehyde, and benzaldehyde can be used.
The preferred curing agents for the powder color coat are hydroxyalkylamides that are used with the preferred carboxylic acid functional polymers. Such a binder system is described in U.S. Pat. No. 4,801,680.
The preferred curing agent for the powder clear coat is a polycarboxylic acid that is used with the preferred epoxy-functional polymer. Such a binder system is described in U.S. Pat. No. 5,407,707.
Examples of flake pigments include aluminum flake pigments such as PCA9155 manufactured by Eckart. Other metal flake compositions may be used such as bronze flake, stainless steel flake, and the like; silver flake, and other precious metal flakes. Preferred flake pigments range from 1.0 to 50.0 micron in size. In addition to the flake pigments described, other metallized polymeric particles may be used. Examples include aluminized Mylar and aluminized polyester fibers.
Preferred flake pigments useful in this invention comprise metal oxide coated mica particles. The metal oxides used as coatings on the mica particles can comprise titanium dioxide, ferric oxide, chromium hydroxide, and the like and combinations thereof. Suitable mica flake pigments are available commercially as Afflair pigments from EM Chemicals and the Mearl Corporation""s pearlescent pigments.
The flake pigment is incorporated into the powder coating at a level of 0.1% to 20.0% based on the total weight of the powder coating. More preferred amounts of the flake pigment is between 1.0% and 10.0% based on total weight of the coating composition.
In order for the attractive visual effects caused by the orientation of the flake pigment in the resultant coating to be realized, the flake pigment particles are incorporated into the powder coating by either dry blending rather than extrusion. The dry blending operation can be conducted with cooling or with heating. Dry blending with heat is referred to as xe2x80x9cbondingxe2x80x9d. The bonding method is believed to attach the flake pigment to the binder particles, but not to actually disperse the flake pigment in the binder powder particles. The xe2x80x9cbondingxe2x80x9d method of dispersion is particularly useful in the dispersion of metal flake particles since it eliminates the undesirable electrostatic effects that occur in the electrostatic spraying of metallic particles.
In addition to the colored flake pigments, one or more additional non-flake pigments can be included in the coating composition typically in amounts from about 1 to about 50 percent by weight, based on the total weight of the powder coating composition. Pigments which are suitable for powder coating compositions may be organic or inorganic and include basic lead silica chromate, titanium dioxide, ultramarine blue, phthalocyanine blue, phthalocyanine green, carbon black, black iron oxide, chromium green oxide, ferrite yellow and quinto red.
Other additives, such as flow control agents, anti-popping agents, and anti-caking agents, may be added to the powder coating. Suitable as flow control agents are acrylic polymers, such as polylauryl acrylate, polybutyl acrylate, poly(2-ethylhexyl) acrylate, poly(ethyl-2-ethylhexyl) acrylate, polylauryl methacrylate, polyisodecyl methacrylate and the like, and fluorinated polymers such as esters of polyethylene glycol or polypropylene glycol with fluorinated fatty acids, e.g., an ester of polyethylene glycol having a molecular weight over about 2,500 and perfluorooctanoic acid. Polymeric siloxanes with molecular weights over 1,000 may also be used as a flow control agent, for example, polydimethylsiloxane or poly(methylphenyl)siloxane. The flow control agents can aid in reduction of surface tension during heating of the powder and in eliminating crater formation. Generally, the flow control agent, when used, is present in amounts from about 0.05 to about 5 percent by weight based on the total weight of the powder coating composition.
Anti-popping agents can be added to the compositions to allow any volatile material present to escape from the film during baking. Benzoin is a highly preferred degassing agent and when used is present amounts ranging from about 0.5 to about 3 percent by weight based on total weight of the powder coating composition. The powder coating compositions may also preferably contain UV absorbing agents, such as TINUVIN, which when used are typically present in the compositions in amounts of about 0.5 to about 6 percent by weight based on the total weight of the powder coating composition.
In addition, the powder coating composition may contain fumed silica or the like as a powder flow additive to reduce caking of the powder during storage. An example of fumed silica is sold by Cabot Corporation under the trademark CAB-O-SIL RTM. The powder flow additive, when used, is generally present in amounts ranging from about 0.1 to about 0.5 percent by weight based on the total weight of the powder coating composition. The powder flow additive is generally added to the particulate powder coating composition after preparation of the particulate mixture.
The colored powder coating can be applied by electrostatic spraying or by the use of a fluidized bed. Electrostatic spraying is preferred. The powder coating composition can be applied in one pass or in several passes to provide a film thickness after cure of about 12.7 to about 102 micrometers (0.5 to about 4 mils). Preferred coating thickness is such that good chip resistance, U.V. opacity, and visual hiding is realized. Preferred film thickness is 51 to 102 micrometers (2 to 4 mils). The substrate to be coated can optionally be preheated prior to application of the powder to promote a more uniform powder deposition.
After application of the color powder coating to the substrate, the substrate is heated to a temperature sufficient to melt and coalesce the coating. This is an important step in the present invention because when done correctly the flake pigment migrates to the air interface and aligns itself in a substantially parallel direction to the substrate, resulting in a distinctive, visually pleasing appearance. The heating step should be conducted such that the color powder coating coalesces to a substantially continuous fluid layer, but not so high as to cause viscosity increase and crosslinking of the coating before the flake pigment rises to the coating-air interface and aligns with the coating surface. The layer is maintained in the fluid state for a period of time sufficient for the flake pigment to rise to the coating-air interface and to align so that the two largest dimensions of the pigment flake are almost parallel with the coating surface. After the pigment has aligned itself with the coating surface, the coating may continue to be heated until, in the case of thermoset powder basecoats, partial or complete cure is accomplished. Alternatively, the coating may be cooled prior to cure. In the case where thermoplastic or radiation cured clear topcoat is applied to a thermoset powder color coat, the coated substrate must be heated for a period sufficient to cure the color coat. Typically, the color coat is heated to a temperature between 120xc2x0 C. and 185xc2x0 C. for a period of 4 minutes to 40 minutes. Alternatively when a heat curable thermosetting clear coat is used, the color coat does not have to be completely cured and complete cure can occur during the cure cycle of the thermosetting clear coat.
Preferably the color coat is topcoated with a clear coat to enhance the appearance of the color coat and/or to improve the physical properties of the color coats. The clear topcoat may be any known in the art, but preferred topcoats are thermoset types. Particularly preferred topcoats are thermoset powder clear topcoats.
The clear powder topcoat may optionally contain additives for flow and wetting such as waxes, degassing additives such as benzoin, adjuvant resin to modify and optimize coating properties, ultraviolet (UV) light absorbers and curing catalyst. These optional additives, when present, are used in amounts up to 11.0% by weight based on weight of resin solids of the coating composition.
The clear powder topcoat may be applied by electrostatic spray or fluidized bed, but electrostatic spray is preferred. The preferred film thickness is between 38 and 90 micrometers (1.5 and 3.5 mils). The clear powder topcoat is heated to a temperature and for a period of time sufficient to melt and coalesce the powder particles, and in the case of a heat-cured thermoset clear topcoat, to cure the topcoat and any uncured portions of the basecoat and weldable primer. Liquid clearcoats may also be used. The crosslink mechanism of thermoset coatings may be thermal cure or ultraviolet radiation or ionizing radiation cure, although thermal cure is preferred. Also thermoplastic clear coats may be used.
The powder coatings compositions are typically prepared by blending the polymers containing the functional groups, crosslinking agents (for thermosetting compositions) and optional ingredients for 15 minutes in a Henschel blade blender. The powder is then usually extruded such as through a Baker-Perkins twin-screw extruder. The extrudate is particulized typically by first chipping into flake and then milling in a hammer mill. The finished powder can be then classified to a particle size of usually between 20 and 30 micrometers in a cyclone grinder/sifter.

Method of powder coating weldable substrates


Provided is a method for preparing an explosive emulsion. The method comprises first preparing an oil phase containing a hydrocarbyl-substituted anhydride, and preparing an aqueous phase containing an hydroxy amine, and preferably an oxidizer salt. The two phases are then mixed sufficiently to create a water-in-oil emulsion, with the anhydride and amine reacting at the interface of the two phases.

1. Field of the Invention
The present invention relates to a water-in-oil emulsion explosive and a method of preparing same. More particularly, the present invention relates to a PIBSA-based explosive emulsion and a more efficient and economical method of preparing same.
2. Description of the Related Art
Water-in-oil emulsion explosives are well-known in the art, See, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives are found to have certain advantages over conventional aqueous slurry explosives, which have a continuous aqueous phase, as described in U.S. Pat. No. 4,141,767.
An inherent problem with emulsion explosives, however, is their relative instability, due to the act that they comprise a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable these supercooled droplets are prevented from crystallizing or solidifying into a lower energy state. If the emulsion weakens or becomes unstable, however, then crystallization or solidification of the droplets results, and the explosive generally loses at least some of its sensitivity to detonation and becomes too viscous to handle for certain blasting applications. Moreover, it is common to add solid components to emulsion explosives, such as glass microspheres for density reduction and prills or particles of oxidizer salt such as porous prilled ammonium nitrate (AN) for increased energy. These solid components, however, tend to destabilize emulsions.
Emulsion explosives commonly are used as a repumpable explosive, i.e., an explosive that is formulated at a remote facility, loaded or pumped into a bulk container and then transported in the container to a blasting site where it then is xe2x80x9crepumpedxe2x80x9d from the container into a borehole. Alternatively, the explosive may be delivered (repumped) into a centrally located storage tank fro which it will be further repumped into a vehicle for transportation to a blasting site and then again repumped into the borehole. Thus the emulsion explosive must remain stable event after being subjected to repeated handling or searing action, which normally also tends to destabilize an emulsion. Additionally, the emulsion""s viscosity must remain low enough to allow for repumping at reasonable pressures and at the low ambient temperatures that may be experienced during colder months. Repeated handling or hearing action also tends to increase the emulsion""s viscosity.
Since a density control agent is required in many instances to reduce the density of an explosive and thereby increase its sensitivity to a required level for detonation, and since hollow microspheres are a preferred form of density control, it is important that the emulsion remain stable and have a low viscosity even when containing solid density control agents.
Proposals have been made to improve the stability of water-in-oil emulsion explosives by employing particular surfactants which function to a high level of efficiency in the harsh environment of an oxidizer salt solution. A particularly effective and useful surfactant has been the reaction product of a hydrocarbyl-substituted succinic acid or anhydride and an amine, e.g., a PIBSA (polyisobutenyl succinic anhydride) based emulsifier.
For example, U.S. Pat. No. 4,708,753 discloses water-in-oil emulsions containing as the emulsifier a salt derived from a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or amide derivative thereof, and an amine.
U.S. Pat. No. 4,615,751 discloses the use of an unspecified polybutenyl succinic anhydride derivative (with a tradename of EXPERSE 60) as a water-resisting agent in emulsions containing prills but not as an emulsifier. European Patent Application No. 0 155 800 discloses alkanolamine derivatives of polyisobutenyl succinic anhydride as emulsifiers. See also U.S. Pat. Nos. 4,822,433; 4,919,179 also describes a PIBSA-based surfactant for use in explosive emulsions.
U.S. Pat. No. 4,710,248 discloses water-in-oil emulsion explosives containing as an emulsifier underivatized polyisobutenyl succinic anhydride or polyisobutenyl succinic acid.
U.S. Pat. No. 4,357,184 discloses water-in-oil emulsions containing graft block or branched polymer emulsifiers. One type of block copolymer which is taught contains polyisobutenyl succinic anhydride as the hydrophobic block and polyethylene glycol or polyethylenimine as the hydrophillic block.
Conventional polyisobutenyl succinic anhydride emulsifier chemistry requires that the emulsifier be formed in a 2-step chemical reaction comprising the hydrolysis of polyisobutenyl succinic anhydride, followed by the amination of the hydrolyzed product. The reactions can be burdensome, and add to the cost of using polyisobutenyl succinic anhydride based emulsifiers.
It is therefore an object of the present invention to provide a method of preparing an explosive emulsion which uses a PIBSA-based emulsifier which is more economical, yet still provides the advantages.
These and other objects of the present invention will become apparent to the skilled artisan upon a review of the following description and the claims appended hereto.
The xe2x80x9cin-situxe2x80x9d process of the present invention does away with the conventional amination reaction needed to form a PIBSA-based emulsifier, and forms the emulsifier species during the emulsification process. Reaction times for preparing a water-in-oil emulsion, such as an explosive emulsion, are thereby greatly reduced and the only required materials are the hydrocarbyl-substituted anhydride, preferably polyisobutenyl succinic anhydride; a hydroxy amine, preferably diethylethanol amine; an oxidizer salt solution such as an ammonium nitrate solution; and a continuous phase oil (e.g., pale oil).
The process of the present invention comprises preparing a water-in-oil emulsion, which is comprised of a continuous oil phase and a discontinuous aqueous phase. The process comprises first preparing an oil phase containing a hydrocarbyl-substituted anhydride. An aqueous phase containing an hydroxy amine is then prepared. The two phases are then sufficiently mixed to create a water-in-oil emulsion, with the anhydride and amine reacting at the interface of the two phases. The reaction of the anhydride and amine at the interface creates an emulsifier product which stabilizes the water-in-oil emulsion. In a preferred embodiment, the hydrocarbyl-substituted anhydride is a polyisobutenyl succinic anhydride, and the hydroxy amine is diethylethanol amine. The method is particularly useful for preparing an explosive emulsion, wherein the aqueous phase comprises an oxidizer salt, preferably ammonium nitrate.
The resulting water-in-oil emulsion prepared comprises a continuous oil phase containing a hydrocarbyl-substituted anhydride, a discontinuous aqueous phase containing a hydroxy amine, preferably an N-(hydroxyl substituted hydrocarbyl)amine, whereby the anhydride and amine form a reaction product at the interface of the continuous and discontinuous phases. This reaction product is an emulsifier product which stabilizes the water-in-oil emulsion. The anhydride is preferably polyisobutenyl succinic anhydride, and the amine is preferably diethylethanol amine. It is also preferred to prepare explosive emulsions, whereby an oxidizer salt such as ammonium nitrate is contained in the discontinuous aqueous phase.
The water-in-oil emulsion of the present invention comprises a continuous oil phase containing a hydrocarbyl-substituted anhydride, as well as a discontinuous aqueous phase containing an hydroxy amine, e.g., an N-(hydroxyl substituted hydrocarbyl)amine. Mixing of the two phases creates a stable water-in-oil emulsion as the anhydride and amine form a reaction product at the interface of the continuous and discontinuous phases.
The hydrocarbyl-substituted anhydrides, e.g., PIBSA, can be prepared by any of several known procedures which are described in the following U.S., British and Canadian patents: U.S. Pat. Nos. 3,024,237; 3,087,936; 3,172,982; 3,215,707; 3,219,666; 3,231,587; 3,245,910; 3,254,025; 3,271,310; 3,272,743; 3,272,746; 3,278,550; 3,288,714; 3,307,928; 3,312,619; 3,341,542; 3,367,943; 3,373,111; 3,374,174; 3,381,022; 3,394,179; 3,454,607; 3,346,354; 3,470,098; 3,630,902; 3,652,616; 3,755,169; 3,868,330; 3,912,764; and 4,368,113. British Patent Nos. 944,136; 1,085,903; 1,162,436; and 1,440,219, and Canadian Patent No. 956,397. These patents are incorporated herein by reference.
The olefinic monomers used in the preparation of the hydrocarbyl-substituted anhydride are generally of a length of from C4 through C18, and may be used singly or in combination. However, the average chain length of the olefinic or vinyl addition polymer (excluding branching or side chains) should be within the range of 10 to 32 carbon atoms. The olefinic or vinyl addition polymers, e.g., polyisobutene, are conveniently bis-carboxylated or converted to an acid anhydride derivative by reaction with such materials as succinic or maleic anhydride, succinic maleic acid, tetrahydrophthalic anhydride, mesaconic acid, glutaconic acid, sorbic acid, itaconic acid, itaconic anhydride and the like. For purposes of the present invention, it is preferred that polyisobutene be reacted with succinic anhydride to form polyisobutenyl succinic anhydride (PIBSA), as is known in the art.
The amines used in the present invention for reaction with the PIBSA or other hydrocarbyl-substituted anhydride are hydroxyamines. These hydroxyamines can be primary, secondary, or tertiary amines. Typically, the hydroxyamines are primary, secondary or tertiary alkanol amines or mixtures thereof. Such amines can be represented, respectfully, by the formulae:
wherein each R is independently a hydrocarbyl group of one to about eight carbon atoms or hydroxyl-substituted hydrocarbyl group of two to about eight carbon atoms and Rxe2x80x2 is a divalent hydrocarbyl group of about two to about 18 carbon atoms. The group -Rxe2x80x2-OH in such formulae represents the hydroxyl-substituted hydrocarbyl group. Rxe2x80x2 can be an acyclic, alicyclic or aromatic group. Typically, Rxe2x80x2 is an acyclic straight or branched alkylene group such as an ethylene, 1,2-propylene, 1,2-butylene, 1,2-octadecylene, etc. group. Where two R groups are present in the same molecule they can be joined by a direct carbon-to-carbon bond or through a heteroatom (e.g., oxygen, nitrogen or sulfur) to form a 5-, 6-, 7- or 8-membered ring structure. Examples of such heterocyclic amines include N-(hydroxyl lower alkyl)-morpholines, -thiomorpholines, -piperidines, -oxazolidines, -thiazolidines and the like. Typically, however, each R is a lower alkyl group of up to seven carbon atoms.
Examples of the N-(hydroxyl-substituted hydrocarbyl)amines include mono-, di-, and triethanol amine, diethylethanol amine, di-(3-hydroxyl propyl)amine, N-(3-hydroxyl butyl)amine, N-(4-hydroxyl butyl)amine, N,N-di-(2-hydroxyl propyl)amine, N-(2-hydroxyl ethyl)morpholine and its thio analog, N-(2-hydroxyl ethyl)cyclohexyl amine, N-3-hydroxyl cyclopentyl amine, o-, m- and n-aminophenol, N-(hydroxyl ethyl)piperazine, N,Nxe2x80x2-di(hydroxyl ethyl)piperazine, and the like. Diethylethanol amine is most preferred for purposes of the present invention.
In another embodiment, the hydroxyamines can also be an ether N-(hydroxy-substituted hydrocarbyl)amine. These are hydroxyl-substituted poly(hydrocarbyloxy)analogs of the above-described hydroxy amines (these analogs also include hydroxyl-substituted oxyalkylene analogs). Such N-(hydroxyl-substituted hydrocarbyl)amines can be conveniently prepared by reaction of epoxides with afore-described amines and can be represented by the formulae:
wherein x is a number from about 2 to about 15 and R and Rxe2x80x2 are as described above.
Polyamine analogs of these hydroxy amines, particularly alkoxylated alkylene polyamines (e.g., N,N-(diethanol)-ethylene diamine) can also be used. Such polyamines can be made by reacting alkylene amines (e.g., ethylenediamine) with one or more alkylene oxides (e.g., ethylene oxide, octadecene oxide) of two to about 20 carbons. Similar alkylene oxide-alkanol amine reaction products can also be used such as the products made by reacting the afore-described primary, secondary or tertiary alkanol amines with ethylene, propylene or higher epoxides in a 1:1 to 1:2 molar ratio. Reactant ratios and temperatures for carrying out such reactions are known to those skilled in the art.
Specific examples of alkoxylated alkylene polyamines include N-(2-hydroxyethyl)ethylene diamine, N,N-bis(2-hydroxyethyl)-ethylene-diamine, 1-(2-hydroxyethyl)piperazine, mono(hydroxypropyl)-substituted diethylene triamine, di(hydroxypropyl)-substituted tetraethylene pentamine, N-(3hydroxybutyl)tetramethylene diamine, etc. Higher homologs obtained by condensation of the above-illustrated hydroxy alkylene polyamines through amino groups or through hydroxy groups are likewise useful. Condensation through amino groups results in a higher amine accompanied by removal of ammonia while condensation through the hydroxy groups results in products containing ether linkages accompanied by removal of water. Mixtures of two or more of any of the aforesaid mono- or polyamines are also useful.
The oxygen-supplying component of the discontinuous phase when an explosive emulsion is to be prepared suitably comprises any oxidizer salt capable of releasing oxygen in an explosive environment in an amount and at a rate sufficient to confer acceptable explosive characteristics on the emulsion composition. Inorganic oxidizer salts conventionally employed in the production of emulsion explosive compositions, and suitable for inclusion in the compositions of the present invention, are disclosed, for example, in U.S. Pat. No. 3,447,978 and include ammonium salts and salts of the alkali- and alkaline-earth metalsxe2x80x94such as the nitrate, chlorate and perchlorate salts, and mixtures thereof. Other suitable salts include hydrazine nitrate and urea perchlorate. The oxygen-supplying component may also comprise an acid, such as nitric acid.
Ammonium nitrate is preferably employed as the oxidizer salt for purposes of the present invention. From about 10% to about 65% of the total oxidizer salt may be added in particle or prill form. For example, AN prills or ANFO can be combined with and mixed into the emulsion. The present invention exhibits good emulsion stability in the presence of such prills.
The organic medium capable of forming the continuous phase of an emulsion explosive composition in accordance with the present invention serves as a fuel for the explosive composition and should be substantially insoluble in the component(s) of the discontinuous phase, with which it should be capable of forming an emulsion in the presence of an effective amount of the emulsifying agent of the present invention. Ease of emulsification depends, inter alia, on the viscosity of the organic medium and although the resultant emulsion may have a substantially solid continuous phase, the organic medium should be capable of existing initially in a sufficiently fluid state, if necessary, in response to appropriate temperature adjustment, to permit emulsification to proceed.
Suitable organic media which are capable of existing in the liquid state at convenient emulsion formulation temperatures include saturated and unsaturated aliphatic and aromatic hydrocarbons, and mixtures thereof. Preferred media include refined (white) mineral oil, diesel oil, paraffin oil, petroleum distillates, benzene, toluene, dinitrotoluene, styrene, xylenes, and mixtures thereof. Pale oil is preferred for the present invention.
In addition to the organic fuel medium, the continuous phase may optionally comprise a wax to control the rheology of the system, although the presence of a wax is not necessary to achieve the desired conductivity levels. Suitable waxes include petroleum, mineral, animal, and insect waxes. The preferred waxes have melting temperatures of at least 30xc2x0 C. and are readily compatible with the formed emulsion. A preferred wax has a melting temperature in a range of from about 40xc2x0 C. to 75xc2x0 C.
Generally, the continuous phase (including wax(es), if present) comprises from 1 to 10, and preferably from 2 to 8% by weight of the total explosive composition, but higher proportions, for example in a range of from 1 up to 15 or even 20% may be tolerated.
When the inventive emulsions are employed as explosive emulsions, such emulsions typically contain other additional additives such as sensitizing components. The sensitizing components are distributed substantially homogeneously throughout the emulsions. These sensitizing components are preferably occluded gas bubbles which may be introduced in the form of glass or resin microspheres or other gas-containing particulate materials. Alternatively, gas bubbles may be generated in-situ by adding to the composition and distributing therein a gas-generating material such as, for example, an aqueous solution of sodium nitrite. Other suitable sensitizing components which may be employed alone or in addition to the occluded or in-situ generated gas bubbles include insoluble particulate solid self-explosives such as, for example, grained or flaked TNT, DNT, RDX and the like and water-soluble and/or hydrocarbon-soluble organic sensitizers such as, for example, amine nitrates, alkanolamine nitrates, hydroxyalkyl nitrates, and the like. The explosive emulsions of the present invention may be formulated for a wide range of applications. Any combination of sensitizing components may be selected in order to provide an explosive composition of virtually any desired density, weight-strength or critical diameter.
The quantity of solid self-explosive ingredients and of water-soluble and/or hydrocarbon-soluble organic sensitizers may comprise up to about 40% by weight of the total emulsion. The volume of the occluded gas component may comprise up to about 50% of the volume of the total explosive emulsion.
Optional additional materials may be incorporated in the explosive emulsions of the invention in order to further improve sensitivity, density, strength, rheology and cost of the final explosive. Typical of materials found useful as optional additives include, for example, emulsion promotion agents such as highly chlorinated paraffinic hydrocarbons, particulate oxygen-supplying salts such as prilled ammonium nitrate, calcium nitrate, perchlorates, and the like, particulate metal fuels such as aluminum, silicon and the like, particulate non-metal fuels such as sulfur, gilsonite and the like, particulate inert materials such as sodium chloride, barium sulphate and the like, water phase or hydrocarbon phase thickeners such as guar gum, polyacrylamide, carboxymethyl or ethyl cellulose, biopolymers, starches, elastomeric materials, and the like, crosslinkers for the thickeners such as potassium pyroantimonate and the like, buffers or pH controllers such as sodium borate, zinc nitrate and the like, crystals habit modifiers such as alkyl naphthalene sodium sulphonate and the like, liquid phase extenders such as formamide, ethylene glycol and the like and bulking agents and additives of common use in the explosives art.
The quantities of optional additional materials used may comprise up to about 50% by weight of the total explosive composition, the actual quantities employed depending upon their nature and function.
In the method of the present invention, the PIBSA-based emulsifier is created in essence xe2x80x9cin-situxe2x80x9d, during the emulsification process, thereby eliminating the amination step of the reaction. In order to perform this in-situ emulsification, only a slight modification to the conventional process to make an emulsion is needed. The fuel blend is comprised of only the hydrocarbyl-substituted anhydride, e.g., polyisobutenyl succinic anhydride, and the oil phase, comprised of, for example, pale oil, and the weight percentages are adjusted for the absence of the reacted amine. The raw amine (e.g., diethylethanol amine) is then added directly to the aqueous solution, e.g., containing ammonium nitrate. After this point, the emulsification process is conventional, with the two phases being mixed sufficiently to create a water-in-oil emulsion.
In theory, it is believed that after the ingredients are emulsified and micelles form, the polyisobutenyl succinic anhydride molecules are correctly oriented at the interface so that the carboxyl groups are in contact with the aqueous phase. The carboxyl groups are then able to react with the free amine present in the aqueous ammonium nitrate solution. The formation of the emulsifier occurs in-situ at the interface. The formation is schematically illustrated below:
The resulting emulsions made by the in-situ process of the present invention exhibit slightly lower viscosities as compared to those made using a premade emulsifier such as a PIBSA/amine emulsifier. The main advantages of the present invention, however, are in the process. The present method is more economical as it avoids the PIBSA/amine reaction step. Furthermore, it has been found that the presence of the amine in the aqueous phase is advantageous as well. The amine actually decreases the interfacial tension of the ammonium nitrate phase, thereby making it easier to form a water-in-oil emulsion.