Methylene chloride phosphatized coating

BACKGROUND OF THE INVENTION
Phosphatizing operations carried on in water have typically provided drawbacks, including sludging and the need for a multistep operation, to achieve dry, coated articles. In an early attempt to overcome such problems, as described in U.S. Pat. 2,515,934, from 1% to 7% of the commercial phosphoric acid 85% syrup was used in an organic mixture, rather than in water. Representative of these mixture was a 50/50 blend of acetone and carbon tetrachloride. With the blend, only a few steps were needed for phosphatizing.
A different approach to overcoming the problems that are found in water-based phosphatizing systems, was taken in the process of U.S. Pat. No. 2,992,146. Therein, by means of special equipment, an aqueous phosphatizing solution was sprayed onto a metal article, while the article was being maintained in a vapor degreasing zone. The vapor degreasing zone contained the vapors from a chlorinated hydrocarbon such as trichlorethylene. The operation thereby permitted enhanced drying of panels after phosphatizing.
In many phosphatizing opertions that relied on using chlorinated solvents, the water solution for the phosphatizing was altogether eliminated. In typical operations, a metal article for phosphatizing might be dipped in a chlorinated hydrocarbon degreasing solution, then come in contact with a non-aqueous phosphatizing solution, and thereafter be returned to the chlorinated hydrocarbon degreasing solution for a final rinse operation. Such operation has been described for example in U.S. Pat. Nos. 3,100,728 and 3,197,345. As also discussed in the U.S. Pat. No. 3,197,345 Patent, it was becoming recognized that there was a water-based process, also called an "aqueous" method of phosphatizing metal articles, and on the other hand a solvent-based process, which was therein noted as the "dry"process. The latter process typically employed a solution of phosphoric acid in a chlorinated hydrocarbon solvent. Since the compositions of the 3,197,345 Patent relied on chlorinated hydrocarbons, the phosphatizing method used was the "dry" process and the useful compositions were substantially water-free compositions.
As early as in the U.S. Pat. No. 2,515,934, it was recognized that the commercial phoshoric acid would introduce a small amount of water into organic phosphatizing compositions. In the U.S. Pat. No. 3,197,345 teachings, it was regarded that substantially all of the water could be distilled from the phosphatizing bath as the "dry" treatment progressed. Getting away from a dependence on phosphoric acid was also explored. From this, it was found that special organic phosphate complexes could be useful in the non-aqueous solutions. They had the advantage of providing protective coatings of enhanced corrosion resistance. This approach was taken in U.S. Pat. No. 3,249,471. Another approach to the dry process, or to the "non-aqueous" process as it was also called, and that was employed in U.S. Pat. No. 3,297,495, was the use of a high strength acid. In such Patent, the acid used was preferably one of 96-100% phosphoric acid. This concentrated acid presented sludge problems, but these were overcome by employing special additives.
Other techniques, to maintain the non-aqueous phosphatizing process "dry", included the use of drying agents such as magnesium sulfate and the use of powdered metals. These concepts have been discussed in U.S. Pat. No. 3,338,754. Therein it was emphasized that small amounts of water are detrimental to the phosphate coatings obtained from the non-aqueous phosphatizing solutions. It was also early recognized in the U.S. Pat. No. 2,515,934 that the presence of water in an organic phosphatizing system could lead to the formation of two liquid phases, with attendant problems developing. Phase separation, and especially with regard to the formation of a separate aqueous phase, was discussed in U.S. Pat. No. 3,306,785. It is also noted, from the U.S. Pat. No. 3,306,785 that in developing the "dry" process with chlorinated hydrocarbons, emphasis was being placed on the commercially important trichlorethylene and perchlorethylene solvents.
One variation in the prior art efforts involves the addition of a stabilizing agent to a coating bath to prolong the formation of adherent coatings from the bath. In West German Pat. No. 1,222,351, the use of an agent such as dimethyl glyoxime, as a stabilizer, has been shown. The baths, even with stabilizer, are of dubious quality without the use of commercial ethanol. This necessarily introduces a minor amount of water into the coating composition. However, resulting coatings can display deleterious characteristics with topcoats.
SUMMARY OF THE INVENTION
It has been found that a chlorinated hydrocarbon phosphatizing composition can produce highly desirable coating when such composition is maintained in a more "wet" condition. An initial key ingredient for the composition is methylene chloride. A further critical ingredient, in addition to a phosphatizing proportion of phosphoric acid, is an amount of water exceeding such proportion of phosphoric acid. But such water is not present in sufficient amount to provide a liquid composition that does not retain liquid phase homogeneity. Moreover, it has been found possible to increase the coating weight of the resulting phosphate coating, by increasing the water content of the phosphatizing composition well beyond a content of just minute amounts.
A further and most significant discovery, is the achievement of phosphatized coatings of extremely reduced water sensitivity. Because of this, phosphate coatings are now achieved wherein the coatings can be successfully topcoated with water based compositions. Such compositions can include aqueous chrome rinses. They can additionally include such coatings as water reduced paints and electrocoat primers. Highly desirable, rust-free topcoated substrates can now be achieved.
Broadly, the invention is directed to a coated ferruginous substrate having an adherent and water-insoluble surface coating that is complex coating of the iron phosphate type obtained by contacting the ferruginous substrate with a methylene chloride and water-containing liquid phosphatizing composition containing water in minor amount, such surface coating containing, in addition to trace elements, the elements iron, phosphorus and oxygen, plus carbon and nitrogen, and having a coating surface ration of oxygen atoms to phosphorus atoms of at least about 4:1.
Another aspect of the invention is directed to a coated substrate characterized by having a composite coating with the first coating being as aforedescribed and the subsequent coating of the composite being an adherent coating from a non-phosphatizing solution for treating metal surfaces.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The methylene chloride, or the "methylene chloride constituency" as it is sometimes referred to herein, is typically commercially available methylene chloride, and may contain additional ingredients, although the use of a more purified methylene chloride is contemplated. The methylene chloride may then contain very minor amounts of stabilizers such as cyclohexane. Useful, commercially available methylene chloride may contain very minor amounts of additional substances such as other chlorinated hydrocarbons, including chloroform and vinylidene chloride. It is further contemplated to use as the methylene chloride constituency, methylene chloride blended with a minor amount of additional solvent. This would be solvent in addition to the organic solvent discussed in greater detail hereinbelow. Preferably, the additional solvent will be non-flammable and will form an azeotrope with the methylene chloride on heating, e.g., trichloro trifluoroethane. Although the methylene chloride constituency will generally provide the major amount of the liquid phosphatizing solution and will typically provide between about 60 to about 90 weight percent of such solution, this is not always the case. Most always, when the methylene chloride constituency does not form the major amount of the solution, the solubilizing solvent will be the predominant substituent in the solution.
The solubilizing solvent needs to be one or a mixture that is capable of solubilizing phosphoric acid in methylene chloride. The solvent can also affect other characteristics of the phosphatizing solution, e.g., the solvent may have an effect on the solubility of water in the phosphatizing solution. It is advantaeous that the solubilizing solvent not create a readily flammable phosphatizing liquid. It is preferable that it effect enhanced solubilization of water in the methylene chloride. It is further preferred, for efficient phosphatizing operation, that the solvent have a boiling point higher than the boiling point of methylene chloride, or that the solvent, on boiling, form an azeotrope with methylene chloride. The solvent can be, and on occasion most desirably is, a blend of organic substances. Such blends are particularly useful for augmenting the solubility of water in the phosphatizing solution.
Particularly where the phosphatizing solution will be used as a liquid phosphatizing bath, at elevated temperature, thereby forming a rinse zone immediately above the bath that contains constituents of the bath in vapor state, it is desirable that the solubilizing solvent be present in such vapor. When phosphatized metal articles are removed from the phosphatizing bath into such rinse zone, one ingredient that may be present on the article for rinsing is phosphoric acid. Since methylene chloride even as a vapor in the rinse zone will exert little solubilizing activity towards the phosphoric acid, it is desirable to have solvent vapor also present in the rinse zone.
Most advantageously for efficiency of operation the solubilizing solvent is an alcohol having less than six carbon atoms. Alcohols of six carbon atoms or more may be used, but should always be present in minor amount with at least one less than six carbon atoms alcohol being in major amount. Representative alcohols that can be or have been used include methanol, ethanol, isopropanol, n-pentanol, n-propanol, n-butanol, allyl alcohol, sec-butanol, tert-butanol and their mixtures wherein liquid phase homogeneity is maintained when in mixture with methylene chloride. However, additional substances, e.g., 2butoxyethanol, can also be serviceable, alone or in combination with alcohol. As mentioned hereinabove, useful phosphatizing solutions can be achieved when the solvent provides the predominant constituent of the phosphatizing composition. Preferably for efficiency and economy the organic solvent is methanol.
As inferred hereinabove, phosphoric acid has only an extremely limited solubility in methylene chloride. However, this situation is obviated by using the solubilizing solvent. Therefore, although the phosphoric acid is a critical ingredient that is generally present in a very minor amount, with the solubilizing solvent present in the phosphatizing solution the phoshoric acid may be contained in the phosphatizing solution in substantial amount. Such amount might be up to 2-3 weight percent or more. But, for efficient and economical coating operation, the phosphoric acid is generally used in an amount below about one weight percent, basis total weight of the phosphatizing composition. A much greater amount than about 1%, will typically leave a coating on the metal substrate that is tacky to the touch. Preferably, for most efficient coating operation, the phosphoric acid is present in an amount between about 0.2-0.8 weight percent, basis the phosphatizing solution although an amount below even 0.1 weight percent can be serviceable.
If it is contemplated that the phosphatizing solution will be used for the coating of metals that have been heretofore recognized as susceptible to phosphatizing, i.e., capable of reacting with phosphoric acid. Thus, it is contemplated that the phosphatizing solution will be useful for phosphatizing aluminum, zinc, cadmium and tin substrates as well as the more typical ferruginous metal substrates. The "phosphatizing proportion of phosphoric acid", as such term is used herein, may well be a "phosphatizing substance", as it might more appropriately be termed. That is, the use of such terms herein is not meant to exclude any substances that may be, or have been, useful in the solvent phosphatizing art for providing a phosphate coating. Such substances might thus include organic phosphate substance as well as the more typical acidic substances of phosphorous, e.g., the usual orthophosphoric acid. Further, it is contemplated that such substance include salts of such acids in phosphatizing. Since water is present in the phosphatizing solution in amounts greater than the phosphatizing substance, although concentrated acids are contemplated, e.g., phospholeum, the resulting solution contains the acid in dilution in water. Preferably, for economy, the orthosphosphoric acid is always the phosphoric substance used in the phosphatizing solution.
As mentioned hereinbefore, the amount of the phosphatizing substance in the phosphatizing solution is exceeded by the amount of water present in such solution. Water must be present in at least an amount sufficient to provide a phosphatized coating on ferrous metal of substantial water insolubility. As is discussed in greater detail hereinbelow, this means that the coating will be, at most, about 20% water soluble. On the other hand, water may typically be present in an amount as great as water saturation of the phosphatizing solution, at the temperature of phosphatizing. However, saturation is not exceeded as the solution will then lose liquid phase homogeniety. Homogeniety as used herein refers to solution uniformity free from liquid phase separation. When water separates, the separate water phase may attract phosphoric acid into such phase, to the detriment of further coating operation.
For many phosphatizing solutions of the present invention, on one hand water insoluble coatings are achieved, coupled with an acceptable coating weight, when the water content of the solution reaches about 1.5-2.5 weight percent. On the other hand, phase separation for many solutions can occur when the water content reaches about 5-7 weight percent-basis total solution weight. Such is shown in greater detail, by reference to the Examples. But, since the solubilizing solvent can affect the ability of a phosphatizing solution to solubilize water, then especially those solutions wherein the solubilizing solvent predominates, may be solutions able to contain substantial amounts of water, for example 10-25 weight percent of water might be reached without achieving saturation. But the water will always provide a minor weight amount of the phosphatizaing solution.
Water in the solution will exert a vapor pressure; the solution water content will thereby directly influence the water content of the vapor zone associated with the solution. When such zone is over a bath of phosphatizing solution, a substantial amount of water vapor may retard the drying time of coated metal substrates that are phosphatized in the bath and then removed to the vapor zone for drying. Thus attention to the water content of a bath, when such might exceed about the 5-10 weight percent range is advisable. SInce water is present in the phosphatizing solution in an amount in excess of phosphoric acid, it will most always be present in an amount within the range of about 2-5 weight percent.
Basic to the "phosphatizing solution" or "phosphatizing composition" as such terms are used herein, are the methylene chloride constituency, solubilizing solvent, phosphatizing proportion of phosphoric acid, and the water. A further substance that may be present in the phosphatizing solution is a aprotic organic substance. Although it is contemplated to use aprotic polar organic compounds for such substance, it is preferred for efficient coating operation to use dipolar aprotic organic compounds. These compounds act in the coating solution to retard the formation of an undesirable, grainy coating. The aprotic organic compound can also influence the level at which water saturation will occur in the phosphatizing compositions containing such compound, particularly when they are present in substantial amount. Although it is contemplated that such compound will always be present in minor weight amount of the phosphatizing solution, and generally present in an amount less than the amount of the solubilizing solvent, serviceable phosphatizing solutions can be prepared that contain on the order of ten to fifteen weight percent or more of such aprotic organic compound.
It is preferred, for extended retention of the aprotic organic compound in the phosphatizing solution during the phosphatizing operation, that such compound have a boiling point above the boiling point of the methylene chloride. Preferably, for most extended presence in the coating solution, such compound boils at least about 20.degree. C higher than the methylene chloride. The aprotic organic compound is often a nitroen-containing compound; these plus other useful compounds include N,N-dimethyl formamide, dimethyl sulfoxide, acetonitrile, acetone, nitromethane, nitrobenzene, tetramethylenesulfone and their inert and homogeneous liquid mixtures where such exist. By being inert, it is meant that such mixtures do not contain substituents that will chemically react with one another, in the phosphatizing solution, at the temperature attained for the solution to be at boiling condition. Dimethyl sulfoxide is useful as an aprotic organic compound; but, such may further be used as an accelerator compound, as is discussed herein below. In such case when the dimethyl sulfoxide is present as an accelerator compound, substance other than dimethyl sulfoxide is used to supply aprotic organic compound.
Another substance generally found in the phosphatizing composition is the organic accelerator compound. Such compound serves to increase the rate of formation of the coating during the phosphatizing process. Acceleration is accomplished without deleteriously affecting the nature of the coating, e.g., desirable uniform and non-grainy crystal structure for the coating. Serviceable compounds typically act in such manner even when present in the composition in very minor amount, as for example, in amount much less than one weight percent basis total composition weight. Advantageously, for efficient operation, the accelerator compound has a boiling point greater than the boiling point of methylene chloride. Many of the useful accelerator compounds are nitrogen-contaning organic compounds. More specifically, compounds that can be, or have been, used include urea, pyridine, thiourea, dimethyl sulfoxide, dimethylisobutylene amine, ethylenediaminetetraacetic acid and dinitrotoluene.
The use of stabilizers has been taught in the prior art and such are contemplated for use herein, such as the hydrogen and hydrogen chloride acceptor substituents that can retard the corrosive nature of phosphatizing compositions. Stabilizers against oxidation of a halohydrocarbon, for example, are also known. These can likewise assist in reducing the corrosive nature of the phosphatizing composition. Useful substances can include p-benzoquinone, p-tertiaryamyl phenol, thymol, hydroquinone and hydroquinone monomethyl ether.
The methylene chloride containing phosphatizing composition is suitable for use with any of the phosphatizing operations that can be, or have been, used with solvent phosphatizing. Solventphosphatizing operations can provide, quickly and efficiently, phosphatizing. Solvent dry, coated metal substrates; and thus, such operations will most always provide for quickly achieving same. Sequentially, metal articles for phosphatizing may be typically degreased in methylene chloride degreasing solution and then immersed in a bath of the phosphatizing composition with such bath being most always heated to boiling condition. The phosphatized article, upon removal from the bath, can then be maintained in the vapor zone above the bath for evaporating volatile constituents from the coated article to coating dryness. During such maintenance, the article may be subjected to a spray rinse. The composition may also be spray applied to a metal article, such as in a vapor zone that might be formed and/or replenished by vapor from the spray composition. Other contemplated aspects of successful operation include initial rinsing of a metal article with warm rinse liquid, e.g., immersion rinsing in such liquid, wherein the liquid is formed from the constituents of the vapor from the phosphatizing solution. Such rinsing is then followed by phosphatizing, and this can be further followed by an additional rinse in the warm rinse liquid. For efficiency in all operations, the temperature of the phosphatizing composition is maintained at boiling condition. At normal atmospheric pressure this will typically be at a temperature within the range of about 100.degree.-105.degree. F. although lower temperatures of operation are contemplated, e.g., to about 95.degree. F. In th ambient atmosphere adjacent to the phosphatizing solution, constituents of such solution may be present in the vapor state. For convenience, this atmospheric region is thereby termed the "vapor zone"
During phosphatizing, which will take place typically in degreaser apparatus, the vapor zone, in addition to containing trace amounts of other substances, will be found to contain methylene chloride vapor, vapor from the solubilizing solvent that solubilizes the phosphoric acid in methylene chloride as well as water vapor. Since such substances are the chief ingredients of the vapor zone, they are the chief ingredients of the phosphatizing composition that can be expected to be lost from such composition as vapor loss. It has therefore been found to be most serviceable to formulate a replenishing liquid composition containing methylene chloride, solubilizing solvent and water. Further, it has been found that such replenishing liquid can be successfully used for sustaining the phosphatizing composition, and that such can form a homogeneous and storage-stable blend. Thus, for convenience, this liquid is often referred to herein as the "sustaining solution." The sustaining solution can be prepared ahead, for later use after storage and/or shipment. It can be useful for sustaining the formation of water-resistant and uniform coatings, especially when used for in-service phosphatizing solutions. The coatings from in-service solutions might be exhibiting loss of coating uniformity, for example.
In the make-up of the sustaining solution, the methylene chloride will be the predominant ingredient, generally supplying between 70-97 weight percent of the solution. In the balance, the solubilizing solvent will supply the major amount, being usually present in an amount between about 2-25 weight percent of the total solution. The water is present in minor amount, e.g. 0.5-2 percent or less, and always together with sufficient solubilizing solvent to insure solution homegeneity. For the preferred solvent methanol, the sustaining solution will preferably contain, for best sustaining action, between about 90-96 percent methylene chloride, about 2-9 percent methanol and 0.4-4 percent water, with the three components totalling 100 weight percent. Preferably, for enhanced phosphatizing operation, the water, solubilizing solvent and methylene chloride will be combined in the sustaining solution in the equivalent proportions of such substances in the phosphatizing medium vapor zone. To efficiently prepare a homogeneous sustaining solution, it is preferred to first preblend the water with solubilizing solvent. Then the methylene chloride is admixed with the preblend to quickly obtain a homogeneous sustaining solution. After the methylene chloride addition, additional ingredients, if present, are generally added. Typically these are present in combination in an amount less than about 1-2 weight percent based on the weight of the sustaining solution. Such ingredients can include accelerator compound, stabilizer compound, aprotic organic compound and phosphoric acid. Where the composition is prepared for extended storage, the phosphoric acid is generally not included to avoid the use of special, acid-resistant containers.
For phosphatizing compositions that contain some of the solubilizing solvents, typically the C.sub.1 C.sub.4 alcohols and including the preferred solvent methanol, it is advantageous that the phosphatizing medium be maintained at a specific gravity between about 1.12 and about 1.17 at the temperature of use. That is, be maintained at such specific gravity at a temperature between about 95.degree. F and about 105.degree. F. Desirable coatings can be efficiently achieved while the phosphatizing medium specific gravity is maintained within such range, and coating formation will not require undesirably delicate control. The composition specific gravity can be readily determined by use of a hydrometer.
As a pre-packaged blend, the sustaining solution in addition to being useful for sustaining, has further utility in the make-up of a fresh phosphatizing composition. When using the sustaining solution for fresh solution make-up, it has been found that typical additional ingredients for the solution make-up may also be prepared ahead in a storage-stable and uniform blend. This additional blend will generally contain, as chief ingredients, solubilizing solvent, aprotic organic compound and water. Further, such additional blend will often contain accelerator compound and stabilizer compound. Such blend is often referred to herein simply as the "precursor composition." As a precursor composition to the make-up of a fresh bath, substances are generally simply mixed together for preparing this precursor composition and then the composition is packaged for storage and/or handling. Most usually, the solubilizing solvent will comprise the major amount of this precursor composition, and preferabily will supply between about 55-80 weight percent of the composition. Further, the water and aprotic organic compound may be present in substantially equivalent amounts. Each ingredient will generally be present in an amount between about 10-30 weight percent. Additional ingredients, e.g., accelerator compound or stabilizer compound, are each often present in an amount less than one weight percent, basis the weight of such precursor composition. In a typical fresh bath make-up, the precursor composition and the above described sustaining solution, with one or both of such generally containing accelerator plus stabilizer, are mixed together, often for use in degreasing apparatus, with phosphoric acid being added during the blending. Thus, only these two solutions plus phosphoric acid need be on hand at the inception of phosphatizing solution make-up.
After coating formation on a metal article, the article can then proceed into a vapor zone that will be supplied and replenished by vaporized substituents from the phosphatizing composition. As discussed herein before, such vapor zone can have a highly desirable make-up of methylene chloride vapor, water vapor and solubilizing solvent vapor as chief constituents. This vapor blend has been found to be highly suitable as a rinsing and drying medium for phosphatized articles. Typically, as in immersion phosphatizing, the coated article may be simply removed from the phosphatizing bath into the vapor zone, maintained in such zone until dry, and then removed for subsequent operation. The constituency of the vapor zone, in addition to supplying a desirable rinsing medium, will also form, on condensation, a stable, uniform liquid blend. This phenomenon enhances the simplicity of recirculation systems, as when coating operation is handled in degreaser apparatus. Also, such recirculation systems can be adapted to have the recirculating, condensed vapor replenished with fresh sustaining solution, which solution has been discussed hereinabove, with the replenished liquid then being recirculated to the phosphatizing solution medium.
As such medium in this operation will typically be maintained at a temperature at boiling condition, the temperature at the vapor zone will typically be within the range of about 100.degree.-105.degree. F. Further, the methylene chloride will form the predominant substance in the vapor zone. For example, in a phosphatizing composition wherein methanol is the solubilizing solvents, the vapor zone can be expected to contain above 90% by weight of methylene chloride, exclusive of the ambient air in such zone. But, because the vapor zone will also contain methanol vapor, as well as water vapor, such combination insures a highly desirable rinse vapor. More particularly, with the methanol as solvent, the vapor zone at normal pressure may be at a temperature from about 101.degree. F. to about 104.degree. F. and contain between about 0.6- 0.7 weight part water, with between about 5.5-6.5 weight parts methanol and the balance methylene chloride to provide 100 weight parts.
The phosphatizing composition will typically provide a desirable phosphate coating, i.e., one having a weight of twenty milligrams per square foot or more on ferrous metal, in fast operation. Although contact times for ferrous metal articles and the phosphatizing composition may be as short as fifteen seconds for spray application, it will typically be on the order of about 45 seconds to three minutes for dip coating, and may even be longer. The coating weights, in milligrams per square foot, can be on the order as low as ten to twenty to be acceptable, i.e., provide incipient corrosion protection with initial enhancement of topcoat adhesion, and generally on the order of as great as one hundred to one hundred and fifty although much greater weights, e.g., three hundred or so, are contemplated. Preferably, for best coating characteristics including augmented topcoat adhesion and corrosion protection, the coating will be present in an amount between about 20-100 milligrams per square foot. Such coatings are readily and consistently produced with desirable coating uniformity.
The coatings that are obtained on ferrous metal will have at least substantial water insolubility, and hence are also termed herein to be "water-resistant" coatings. For determining water solubility, the test employed is sometimes referred to as the "water soak test". In this test, as is also described in connection with the examples, a coated ferruginous article is weighed and then immersed in distilled water for ten minutes. The water is maintained at room temperature, typically 65.degree.-75.degree. F, and with no agitation. After this ten minute immersion, the article is removed from the water, rinsed in acetone and air dried. Subsequently, on re-weighing, the amount of water solubility of the coating is shown by any weight loss. This loss is generally expressed as a percentage loss of the total original coating. The method used for determining the original coating weight has been more specifically described in connection with the examples. Advantageously, for enhanced corrosion protection, the water soak solubility of the coating will be on the order of less than 20%. Such a coating, for convenience, is often termed herein as a "phosphatized coating of substantial water insolubility". Preferably, for best coating performance, the water solubility of the coating will be less than 5%.
In addition to previously noted characteristics, coatings have been subjected to further analysis. As detailed more specifically in the examples, coatings of the iron phosphate type have been subjected to analysis by the Electron Spectroscopy for Chemical Analysis (ESCA) technique. Further, such coatings have been subjected to Auger Spectroscopy. For convenience, these may be referred to simply as "spectroscopic analysis". Such analysis confirms that the water insoluble coatings obtained on a ferruginous substrate, contain in their make-up, the elements sodium and calcium in trace amounts. The balance of the elements is provided by phosphorous, iron, oxygen, carbon and nitrogen. Moreover, the coating surface ratio of oxygen atoms to phosphorus atoms is at least about 4:1 and may be as great as about 5:1. Such coating surface ratio of carbon atoms to phosphorus atoms may range from on the order of about 1:1 to as great as 10:1 or more, with coatings of about 50 milligrams, or less, per square foot showing enhanced topcoat adhesion when the carbon to phosphorus is above about 5:1. Further, the coating surface nitrogen and iron atoms are each present in minor amount, basis total coating surface atoms, and generally are within a ratio of nitrogen atoms to iron atoms of between about 0.5:1 to about 1:0.5. Under similar analysis, comparative phosphatized coatings, which are water soluble coatings prepared from prior art phosphatizing techniques based on chlorinated hydrocarbon phosphatizing methods, fail to show such combination of elements in a phosphatized coating. Although all of the coatings are complex, because of the nature of the spectroscopic analysis techniques used in analyzing the coating, the make-up of the coating under analysis is expressed in the form of the elements. That is, it is to be understood that the coating is basically and completely defined by setting forth the elements. Although the elements will or may form various bonding relationships, the coating is defined by the elements is not limited to various particular relationships.
Because of the water resistant nature of the phosphate coating, the resulting coated metal substrates are especially adapted for further treatment with water based coating and treating systems. For example, the coated substrates may be further treated with acidified aqueous solutions typically containing a multivalent metal salt or acid in solution. Such treating solutions can contain hexavalent-chromium-containing substance, including the simplistic rinse solutions of chromic acid and water as mentioned in U.S. Pat. Nos. 3,116,178 or 2,882,189, as well as their equivalent solutions, for example the molybdic and vanadic acid solutions discussed in U.S. Pat. No. 3,351,504. Further these treating solutions may be non-aqueous, it being contemplated to use chromic acid solutions such as disclosed in U.S. Pat. No. 2,927,046. The treatment can include solutions containing additional, reactive ingredients, as for example the combination of chromic acid and formaldehyde disclosed in U.S. Pat. No. 3,063,877. Additional treatments that are contemplated include the complex chromic-chromates from solutions typically containing trivalent chromium, as has been discussed in U.S. Pat. No. 3,279,958. Further treatments that can be used include such as the blended complex chromate salts disclosed in U.S. Pat. No. 3,864,175 as well as solutions containing salts of other metals, as exemplified in U.S. Pat. No. 3,720,547, wherein salts of manganese are employed in treating solutions. All of these treatments will generally provide a coating having a weight of from about 2 to about 40 milligrams per square foot of treated substrate, although such weight may be lower, and is often greater, e.g., 100 milligrams per square foot or more. For convenience, these treatments and solutions collectively are sometimes referred to herein as "non-phosphatizing solutions for treating metal substrates".
The phosphatized coating also lends itself to topcoating from electrically deposited primers, such as the electrodeposition of film-forming materials in the well known electrocoating processes. Further, the phosphatized coatings can form the base coating for a water reducible topcoating. Such topcoating compositions typically contain solubilized polymers, similar to conventional alkyd, polyester, acrylic and epoxy types, that are typically solubilized with smaller amounts of organic amine. Also the resulting phosphate coated substrate can be further topcoated with any other suitable resin-containing paint or the like, i.e., a paint, primer, enamel, varnish or lacquer including a solvent reduced paint. Additional suitable paints can include the oil paints and the paint system may be applied as a mill finish.
Before applying the phosphate coating, it is advisable to remove foreign matter from the metal surface by cleaning and degreasing. Although degreasing may be accomplished with commercial alkaline cleaning agents which combine washing and mild abrasive treatments, the cleaning will generally include degreasing. Although such degreasing can be accomplished with typical degreasing systems, such degreasing can be readily and efficiently handled with methylene chloride degreasing solvent.
The following examples show ways in which the invention has been practiced but should not be construed as limiting the invention. In the examples all parts are parts by weight unless otherwise specifically stated. In the examples the following procedures have been employed.
PREPARATION OF TEST PANELS
Bare steel test panels, typically 6 inches .times. 4 inches or 3 inches by 4 inches unless otherwise specified, and all being cold rolled, low carbon steel panels are typically prepared for phosphatizing by degreasing for 15 seconds in a commercial, methylene chloride degreasing solution maintained at about 104.degree. F. Panels are removed from the solution permitted to dry in the vapor above the solution, and are thereafter ready for phosphatizing.
PHOSPHATIZING OF TEST PANELS AND COATING WEIGHT
In the examples, cleaned and degreased steel panels are phosphatized by typically immersing the panels into hot phosphatizing solution maintained at its boiling point, for from one to three minutes each. Panels removed from the solution pass through the vapor zone above the phosphatizing solution until liquid drains from the panel; dry panels are then removed from the vapor zone.
Unless otherwise specified in the examples, the phosphatized coating weight for selected panels, expressed as weight per unit of surface area, is determined by first weighing the coated panel and then stripping the coating by immersing the coated panel in an aqueous solution of 5% chromic acid which is heated to 160.degree.-180.degree. F. during immersion. After panel immersion in the chromic acid solution for 5 minutes, the stripped panel is removed, rinsed first with water, then acetone, and air dried. Upon reweighing, coating weight determinations are readily calculated. Coating weight data is presented in milligrams per square foot (mg/ft.sup.2).
MANDREL TEST BENDING (ASTM-D 522)
The conical mandrel test is carried out by the procedure of ASTM D-522. Briefly, the testing method consists in deforming a paint-coated metal panel by fastening the panel tangentially to the surface of a conical steel mandrel and forcing the sheet to conform to the shape of the mandrel by means of a roller bearing, rotatable about the long axis of the cone and disposed at the angle of the conical surface, the angle of deformation or arc travel of the roller bearing being approximately 180.degree.. Following the deformation, a strip of glass fiber tape coated with a pressure-sensitive adhesive is pressed against the painted surface on the deoformed portion of the test panel and is then quickly removed. The coating is evaluated quantitatively according to the amount of paint removed by the adhesive on the tape, in comparison with the condition of a standard test panel.
REVERSE IMPACT STRENGTH
In the reverse impact test, a metal ram of specified weight, in pounds, with a hemispherical contact surface is allowed to drop from a predetermined height in inches onto the test panel. Paint removal is measured qualitatively or quantitatively on the convex (reverse) surface. In the qualitative measurement the impacted surface is merely observed by visual inspection and comparative panels, i.e., those subjected to the same impact in inch-pounds, are rated according to a numerical scale presented in Example 6 hereinbelow.
CROSS-HATCH
This test is conducted by scribing, through the coating to the metal panel with a sharp knife, a first set of parallel lines one-eighth inch apart. A second, similar set of lines, is then scribed on the panel at right angles to the first set. Following this, a strip of glass fiber tape coated with a pressure-sensitive adhesive is pressed against the painted surface on the scribed portion of the test panel and is then quickly removed. The coating is rated in accordance with the numerical scale presented in Example 6 hereinbelow, based on the amount of paint removed by the adhesive on the tape.
COIN ADHESION
A fresh nickel coin is firmly secured in vise-grip pliers; the pliers are manually held in a position such that a portion of the rim of the nickel coin contacts the coated substrate at about a 45.degree. angle. The nickel coin is then drawn down across the panel for about two inches. The type of coating flaking and/or chipping is evaluated qualitatively by visual observance, and panels are compared with the condition of a standard test panel.

EXAMPLE 1
To 288 parts of methylene chloride there is added, with vigorous agitation, 102.4 parts methanol, 1.3 parts ortho phosphoric acid, and 15.8 parts N,N-dimethyl formamide. These blended ingredients are thereafter boiled for one hour using a reflux condenser and the solution is permitted to cool. The water content of the resulting boiled solution, provided principally by the phosphoric acid, is found to be about 0.1 weight percent. This water content is directly determined by gas chromatograph analysis of a sample wherein the column packing is Porapak Q manufactured by Waters Associates, Inc. The resulting solution is then heated to 102.degree.-103.degree. F. and panels are phosphatized in the manner described hereinabove.
Some of the resulting coated panels, selected in sets of two with each panel in the set being coated under identical conditions, are then subjected to testing. One panel in the set is used for coating weight determination in the manner described hereinabove. The other panel in the set is subjected to the water solubility test. For this test the panel is weighed and then immersed in distilled water for ten minutes, the water being maintained at ambient temperature and with no agitation. Thereafter, the test panel is removed from the water, rinsed in acetone and air dried. Subsequently, on reweighing, the amount of water solubility of the coating is shown by the weight loss. This loss, basis total original coating weight, is reported in the Table below as the percentage or degree, of coating loss.
Coating weights and water solubility of coatings, are determined initially for test panels that have been phosphatized in the above-decribed phosphatizing composition. Such data are determined thereafter for additional coated panels that have been phosphatized in compositions of differing water contents, all as shown in the Table below. These baths of varying water content are prepared in step-wise fashion by starting with the above-described bath, and then adding about one weight percent water to the bath followed by boiling the resulting solution for one hour. This procedure is repeated with additional water increments of one weight percent, as shown in the Table below. The phosphatizing coating operation for each bath of varying water content has been described hereinabove. For each phosphatizing bath, water content determinations are made prior to phosphatizing by the above-described method.
TABLE I______________________________________Coating Degree of -Bath Water Panel Coating Solubility ofContent, Wt. % Weight: mg/ft.sup.2 Coating in Water______________________________________0.1 4 60%1.1 6 50%2.1 10 20%3.1 13 <5%4.1 24 <5%______________________________________
The tabulated results demonstrate the enhancement in the degree of water insolubility for the phosphate coating as the water content in the phosphatizing bath increases. As determined by visual inspection, it is also noted that the degree of uniformity of the phosphate coating is increasing as the water content of the phosphatizing bath increases. For the particular system of this Example, the desirable water content is deemed to be between about 2 weight percent and about 5 weight percent. Below about 2 weight percent, the degree of water solubility for the coated panels is regarded as being excessive. By continuing the step-wise water addition discussed hereinabove, this system is found to separate free water, i.e., lose liquid phase homogeneity, when the water content reaches 5.1 weight percent.
EXAMPLE 2
A photophatizing solution is prepared from 7510 parts of methylene chloride, 1731 parts methanol, 5 parts ortho phosphoric acid, 374 parts N,N-dimethyl formamide, and 7 parts dinitrotoluene. Prior to phosphatizing of steel panels the water content of the phosphatizing bath is determined, as described in Example 1, to be 373 parts.
Panels coated in the phosphatizing solution are subjected to the water solubility test. Such testing shows the panels to have a degree of solubility in water of below 5%. Coating weights for similar panels, but phosphatized for different coating times, are determined to be 35 mg/ft.sup.2 for one panel (lower coating weight) and 60 mg/ft.sup.2 for another panel (higher coating weight).
One of each panel of the lower and the higher coating weight is then selected for analysis by the Electron Spectroscopy for Chemical Snalysis (ESCA) technique. This technique is used to evaluate the surface phenomena of the coated panels by providing a determination of the elements present. The instrument used is the HP 5950A, a spectrometer system with monochromatized X-radiation and manufactured by the Hewlett Packard Company. Under such evaluation, the surface of test panels is found to contain sodium and calcium in trace amounts and a balance of phosphorus, iron, oxygen, carbon and nitrogen.
Such determination for the principal elements found in the phosphatized coating is further evaluated, using similar test panels, with Auger spectroscopy. For this analysis the instrument used is the PHI Model 540A thin film analyzer manufactured by Physical Electronics Industries, Inc. Such analysis confirms the presence at the surface of the test panels of the elements phosphorous, iron, oxygen, carbon and nitrogen.
EXAMPLE 3
To 380.2 parts of methylene chloride there is added, with vigorous agitation, 81 parts methanol, 2.3 parts ortho phosphoric acid, 14.9 parts N,N-dimethyl formamide and 0.4 part dinitrotoluene. These blended ingredients are thereafter processed in the manner of Example 1 to prepare a phosphatizing solution having a water content of about 0.1 weight percent.
Degreased steel panels are then phosphatized in the composition. Additional phosphatizing compositions but having differing water contents, as shown in the Table below, are prepared as described in Example 1. Phosphatizing operation for each bath of varying water content is also as has been described hereinbefore. As shown in the Table below, for each phosphatizing bath, water content determinations are made prior to phosphatizing and coating weights and water solubility testing for coatings, are determined for all phosphatized panels.
TABLE II______________________________________Coating Degree ofBath Water Panel Coating Solubility ofContent, Wt. % Weight; mg/ft.sup.2 Coating in Water______________________________________0.1 9 17%0.8 9 8%2.1 14 <5%4.2 31 <5%______________________________________
The tabulated results demonstrate the enhancement in the degree of water insolubility of the phosphate coating as the water content in the phosphatizing bath increases; also, visual inspection confirms that the degree of uniformity of the phosphate coating is increasing as the water content of the phosphatizing bath increases. Also the coating weight shows a dramatic increase along with the increase in water content of the coating bath at a water content level above 2 weight percent. For the particular system of this Example, the desirable water content is deemed to be between about 2 weight percent and about 5 weight percent. Below about 2 weight percent, a desirable coating is not efficiently achieved. Coating weight is very small. By further water addition to the bath, this system is found to separate free water, i.e., lose liquid phase homogeneity, when the water content reaches 5.1 weight percent.
EXAMPLE 4
In the manner described hereinabove, a phosphatizing solution is prepared to contain, by weight, the following ingredients: 60 parts water, 1188 parts methylene chloride, 253 parts methanol, 7.3 parts ortho phosphoric acid, 47.2 parts N,N-dimethyl formamide and 1.0 part dinitrotoluene. Hereinafter, for convenience, the resulting phosphatizing solution is referred to as the "new organic phosphatizing composition".
Steel panels were phosphatized in this new organic phosphatizing composition. Further, in the manner described hereinbefore, but for comparative purposes, panels were phosphatized in a well-known and extensively-used commercial phosphatizing bath based on trichloroethylene. Hereinafter for convenience, this bath is referred to as the "standard organic phosphatizing composition". This standard organic phosphatizing composition was prepared by blending together ortho phosphoric acid, with two products sold under the tradenames of "Triclene-L" and "Triclene-R", to contain a commercially acceptable amount of phosphoric acid in the blend. The use of such a commercial phosphatizing bath has been described, for example, in U.S. Pat. No. 3,356,540.
Additional comparative test panels used herein for evaluation are panels phosphatized with an aqueous phosphatizing composition and prepared in accordance with specifications that are generally accepted as standards for performance in the automotive and household appliance industries. These comparative test panels, for convenience, are generally referred to herein as prepared from the "comparative aqueous phosphatizing composition". Such composition is a solution that can contain zinc acid phosphate, with the test panels being dipped in this aqueous solution typically for one minute. Thereafter, the test panels are rinsed and then immersed in a dilute solution of chromic acid. Such test panels are then dried and are thus provided with a chromic acid rinse coating.
All test panels are painted, before testing, with a commercial enamel topcoat. The enamel is a commercial white alkyd baking enamel; the enamel ostensibly contains a modified alkyd resin based upon a system of partially polymerized phthalic acid and glycerin, and has 50 weight percent solids. After coating panels with the enamel, the coating is cured on all panels by baking in a convection oven for 20 minutes at a temperature of 320.degree.-325.degree. F.
Panels are then selected and subjected to the various tests described hereinbefore for testing paint film retention and integrity. The tests used, and the results obtained, are listed in the Table below. In the conical mandrel test, the numbers listed in the Table are centimeters of paint removal after taping; the reverse impact test is conducted at 64 inch-pounds. For the reverse impact test and the conical mandrel test, where a range is presented in the Table, such range results from the testing of a series of panels.
In the following Table the efficacy of the total coating obtained on the coated parts in the cross hatch and reverse impact tests is quantatively evaluated on a numerical scale from 0 to 10. The parts are visually inspected and compared with one another and the system is used for convenience in the reviewing of results. In the rating system the following numbers are used to cover the following results:
10. complete retention of film, exceptionally good for the test used;
8. some initial coating degradation;
6. moderate loss of film integrity;
4. significant film loss, unacceptable degradation of film integrity;
2. some coating retention only;
0. complete film loss.
TABLE III______________________________________Phosphatizing Cross Conical Reverse CoinsComposition Hatch Mandrel Impact Adhesion______________________________________New Organic 10 0-7 6-9 GoodPhosphatizingCompositionStandard Organic 10 0.4-1.9 4-8 GoodPhosphatizingCompositionComparative Aqueous 10 1.9 4-9 GoodPhosphatizingComposition______________________________________
The above-tabulated results show that the phosphate coating from the new organic phosphatizing composition can provide paint adhesion that will compare under a variety of tests as the equal of or superior to, comparative systems based either on organic commercial baths or aqueous compositions.
In further and related testing, panels from the new organic phosphatizing composition are provided with a chrome rinse from a dilute chromic acid solution. This is done to equate the nature of the coating on the panels with that from the aqueous phosphatizing composition. All test panels are topcoated with an alkyd enamel paint system and then panels are subjected to a variety of tests. Comparable results, for each specific test, are obtained among all tested panels. Such equality of test results is achieved even when testing of comparative panels in the standard salt spray (fog) test, ASTM B-117-64.
EXAMPLE 5
To 356.4 parts of methylene chloride there is added, with vigorous agitation, 106.6 parts ethanol, 2.4 parts ortho phosphoric acid and 15.3 parts N,N-dimethylformamide. These blended ingredients are thereafter processed in the manner of Example 1 to prepare a phosphatizing solution having a water content of about 0.1 weight percent.
Degreased steel panels are then phosphatized in the composition. Additional phosphatizing compositions, but having differing water contents, as shown in the Table below, are prepared as described in Example 1. Phosphatizing operation for each bath of varying water content is also as has been described hereinbefore. As shown in the Table below, for each phosphatizing bath, coating weights and water solubility testing for coatings, are determined for phosphatized panels.
TABLE IV______________________________________Coating Degree ofBath Water Panel Coating Solubility ofContent, Wt. % Weight; mg/ft.sup.2 Coating in Water______________________________________0.1 14 28%1.1 10 30%2.1 22 7%3.1 27 <5%4.1 125 <5%______________________________________
The tabulated results demonstrate the enhancement in the degree of water insolubility of the phosphate coating as the water content in the phosphatizing bath increases; also, visual inspection confirms that the degree of uniformity of the phosphate coating is increasing as the water content of the phosphatizing bath increases. Also, after an initial reversal, the coating weight increases right along with the increase in water content of the coating bath. For the particular system of this Example, the desirable water content is deemed to be greater than 2.1 weight percent and up to about 5 weight percent. By further water addition to the bath, this system is found to separate free water, i.e., lose liquid phase homogeneity, when the water content reaches 5.1 weight percent.
EXAMPLE 6
To 82.5 parts of methylene chloride there is added, with vigorous agitation, 17.0 parts methanol and 0.5 part ortho phosphoric acid. The resulting phosphatizing solution has a water content of about 0.1 weight percent, at least principally contributed by the acid. A degreased steel panel is then phosphatized in the composition. Additional phosphatizing compositions, but having differing water contents, are prepared as described in Example 1, and panels are phosphatized in such compositions. All phosphatizing operations are as have been described hereinbefore. Coating weights and water solubility testing for coatings, are determined for selected phosphatized panels. As the bath water content goes from 3% to 4%, the coating weight goes from 20 to 97 mg/ft.sup.2 respectively. However, with a bath at the 3.2 percent water level, the most desirable coating, at a weight of about 35 mg/ft.sup.2 and having less than 5% water solubility, is achieved. This result is obtained although the bath contains no aprotic polar organic compound.
EXAMPLE 7
A comparative formulation, prepared for test purposes, was made in accordance with Example 3 of West German Pat. No. 1,222,351, by blending together 700 parts ethanol, 4.7 parts phosphoric acid, 7.8 parts water, 6,050 parts trichloroethylene and 0.15 part of dimethyl glyoxime. The 4.7 parts of phosphoric acid were 4.7 parts of 100% acid in accordance with the teachings of the patent that the composition concentration of the phosphoric acid is calculated on the basis of 100% acid. The ethanol used was 200 proof ethanol whereby the 7.8 parts of water used is equivalent to the 1.56 grams of the Patent's Example 1.
The water content of the resulting composition was determined as 0.11 weight percent using the method described in Example 1, but with the column packing being with Porapak Q. The resulting composition is identified in the Table hereinbelow initially as an "Ex. 3, 200 proof" bath and then further by said 0.11% water content.
A substantial replicate to the aforedescribed formulation, also prepared for comparative purposes, was made in accordance with Example 3, with the exception that the 700 parts ethanol used was the typical commercial 190 proof ethanol thereby supplying sufficient additional water to the replicate formulation to provide a second phosphatizing solution having 0.65 weight percent water, as determined by the aforedescribed method. This second solution is referred to in the Table as an "Ex. 3, 190 proof" composition further identified by such 0.65% water content.
A phosphatixing composition, identified in the Table as the "New Composition" or "New Comp.", was prepared by blending together 4,436 parts methylene chloride, 958.4 parts methanol, 221.5 parts water, 27.3 parts of 100% phosphoric acid, and 204.4 parts N,N-dimethylformamide. On analysis, as abovedescribed, the New Comp. was found to contain 3.9 weight percent water.
The Example 3 bath with the 0.11 weight percent water content was heated to a temperature near its boiling point, being a temperature of 164.degree. F, and also prior to use the Example 3 replicate bath with the 0.65 weight percent water content was likewise heated to a temperature near its boiling point, being a temperature of 158.degree. F. Steel test panels were held in the vapor zone above the bath for 30 seconds, then dipped from the vapor zone and immersed in the bath below the zone for a dip time of 3 minutes, the panel being then removed from the bath, maintained in the vapor above the bath for 15 seconds, removed from such vapor above the bath and dipped into a beaker of trichloroethylene solvent at ambient temperature for 15 seconds to provide condensate rinse and cool the panel.
The New Composition was heated to about is boiling temperature, being a temperature of 102.degree. F. Steel panels were then held in the vapor zone in the above described manner, followed by dip coating in the bath for 3 minutes, then removing the panels from the bath and holding them in the vapor zone for 15 seconds, followed by dipping into a beaker of methylene chloride solvent at ambient temperature for 15 seconds.
As shown in the Table below, coating weights and water solubility for coatings, all accomplished as hereinbefore described, are determined for phosphatized panels.
A selected set of coated panels having been cooled for five minutes in the ambient air, were painted with a water-based semigloss latex paint containing 24.6 weight percent pigments that were 19.1% titanium dioxide and 5.5% silicates, and a 75.4 weight percent balance being vehicle that was 22% acrylic resin and 53.4% water. The paint was applied by first magnetically clamping the panel and then pouring a line of paint across the panel face. The paint is drawn down over the panel with a No. 40, wire-wound steel draw bar followed by immediately setting the panels out for air drying. Five minutes following the setting out for air drying, the panels are visually inspected. By such inspection, the percentage of the surface area showing rust spots is determined in accordance with the evaluation described in ASTM D 610-68, using the illustrative examples shown therein. The results of such determination are set forth in the Table hereinbelow, with the percentage range for the panels being determined by inspection of both sides.
TABLE V______________________________________ Water Cont. of Coating Coating % Coating % RustingBath Bath in Wt. Wt. Water of PaintedIdent. % (and g/l) .vertline.Mg/ft.sup.2 Solubility Surface______________________________________Ex. 3(200 0.11% 2 N.A. 80-100%proof) (1.5 g/l)Ex. 3(190 0.65% 53 7% 30-80%proof) (8.8 g/l)NewComp. 3.9% 47 8% 0-5%______________________________________ N.A. = Not Applicable
Similar results, although not as dramatic, can be obtained with differing steel panels. As shown in the Table, although the modified Ex. 3 bath, i.e., the 190 proof bath, will provide a desirable water insoluble coating, the coating does not have the excellent properties of the coating from the New Comp., as exhibited by topcoat performance. Interestingly, on ESCA analysis, the Ex. 3 coat has a surface ratio of oxygen atoms to phosphorus atoms of well below 4:1, and more nearly 3:1.

Number	Name	Date
3197345	Uullo et al.	Jul 1965
3249471	Higgins	May 1966
3853593	Baudo et al.	Oct 1974

Methylene chloride phosphatized coating

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