US3420715A - Additive for phosphate coating solution - Google Patents

Description

ABSTRACT OF THE DISCLOSURE An additive for rejuvenating phosphate conversion coating materials to thereby restore same to substantially their original chemical balance Which consists essentially of phosphoric acid, a synthetic non-ionic detergent, an accelerating agent, and water.

This invention relates in general to conversion coating and, more particularly, to an additive for phosphate coating solutions.

It is an object of the present invention to provide an additive for phosphate conversion coating solutions which is adapted to restore such solutions, after usage, to substantially their initial properties, thereby obviating the conventionally practiced expedient of addingadditional quantities of the original phosphate coating material. It has been "consistently recognized that the addition of further amounts of such material will, at best, bring about extremely temporary rejuvenation of the used solutions as there is not effected a replenishment of the depleted ingredients of the solution in the requisite proportionality for efficacious phosphatizing whereby the growing chemical imbalance becomes progressively greater. 1

It is another object of the present invention to provide an additive for phosphate conversion coating solutions which is adapted to return a used solution to substantially its starting chemical balance, such additive being peculiarly constituted so as to properly compensate for the depletion or exhaustion, at varying rates, of constituents of the solution.

It is another object of the present invention to provide an additive of the character stated, the use of which will substantially eliminate: undesired concentration increase; the development of sludge with possible blocking of fluid passageways, such as risers, headers, and nozzles; as well as the building-up of solid resulting in the coating and scaling-of heating equipment with interference of the heat transfer" capabilities thereof.

It is, a still further object of the present invention to provide an additive of the character stated, the use of which-is relatively inexpensive; substantially increases the life of the solution thereby effecting considerable economies in practice; and which may be used with solutions for coating ferrous, as well as non-ferrous surfaces.

It is another object of the present invention to provide an additive of the character stated which adapts the phosphate coating solution for maximum effectiveness under varying conditions as encountered in plant equipment. Furthermore, such additives are adapted for use with solutions designed for various means of application, that is, for example, by spraying or immersion, as well as under varying temperature ranges.

With the above noted objects in view, my invention resides in the novel compositions, methods and processes presently described in the following specification and pointed out in the claims.

In essence, the present invention contemplates the provision of an additive solution adapted to be added to a phosphate conversion coating solution after the latter has been used for a reasonable period of time so as to effect United States Patent the return to the coating solution of those ingredients which have been consumed or depleted during such usage. Thus, the additive solution of this invention is of an extremely selective character, incorporating specific constituents, within a predetermined relationship so as to effect a restoration of the coating solution to its initial chemical balance and cleaning properties. The present additive solution is entirely distinct from the coating solution and its usage eliminates the time-worn practice of merely continuously adding fresh quantities of the coating material to the used coating solution, which procedure, in addition to being expensive, contributes to the progressive chemical imbalance of the solution with deleterious buildup of solids, sludging, and the like; which disadvantages are only offset by a momentary restrengthening of the coating solution.

Heretofore there has been a total failure to recognize the basic fact that the ingredients of the coating solution are not depleted at a uniform rate so that, actually, after a period of usage the coating solution may be entirely devoid of certain of its original ingredients, with others being in a greatly diminished state, while still others, such as, for instance, the primary acid phosphate salt may still be retained, to all intents and purposes, in its basic starting strength. It is imperative that in order torestore the solution for continued efiicient usage, the depleted and near depleted ingredients be returned in proper inter-relationship.

The so-called iron phosphate coating solutions are designed to provide two primary functions; one being to clean the metallic surface treated for removal therefrom of all soils such as oil, grease, lubricants, and the like; and the other being to chemically convert the metallic surface wherein the metal ions from the surface are combined with anions, in the present instance, phosphates, from the coating solution, so as to create. a surface which is substantially inert and devoid of the; properties associated with the metal such as steel, zinc, aluminum, or the like. Consequently, such solutions must contain agents which will effect the surface cleaning action, and also bring about the chemical conversion of the metallic surface. It is recognized that phosphate solutions may be of specifically varying character dependent upon the factors of the peculiar usage such as, for example, the type of equipment, the manner of application," the metal to be treated, the temperature obtaining, etc. However, recognizing these variations, the following may be considered as a fundamental or basic formulation for a phosphate conversion coating to be used upon ferrous metal. Ingredients: Percentage by weight Primary acid phosphate salts 97.5-87 Synthetic, non-ionic detergents 2.0-8.0 Accelerators .55.0

The foregoing constitutes the minimum formulation for coating agents of the type under study. It is recognized that in practice various other additional ingredients may be added such as phosphoric acid for pH control; complexing compounds, dispersing agents, and sequestering or chelating materials for assisting in and promoting the chemical conversion of the surface being treated; and of foam suppressants to be used in accordance with wellknown techniques for foam reduction as in utilizing pressure spray equipment.

The primary acid phosphate salts, which provide the source of phosphate ions for conversion purposes, may include the primary ammonium, potassium or sodium salts of orthophosphoric or pyrophosphoric acid.

The synthetic non-ionic detergents which provide the surface cleaning properties for the coating solution, being selected for acid stability, cloud point and foaming characteristics, are taken from such classes as the octyl or nonyl phenyl polyethoxyethanols, aliphatic polyethers, alkylphenol ethoxylates, and alkylaryl polyethers.

Accelerators, or more commonly known as activators, which are specific for the particular metal being treated and which promote the conversion reaction, may be selected from compounds of such metals as cobalt, nickel, Wolfram, chromium, moylbdenum, zirconium, vanadium and titanium, and of such non-metallic salts as fluorides, including bifluorides, and borates. The compounds of the stated metals may be of any character, such as acids, salts, etc. and may be either organic or inorganic. As exemplary only of salts are cobaltous nitrate, and nickel formate; while an exemplary acid form is molybdic acid. Thus, the possible number of useful compounds of these stated metals is myriad.

Complexing agents being generally organic materials having a relatively large number of metal-reactive groups, such as hydroxyl groups, aldehyde structures, unsaturated bonds, and the like, comprehend compounds such as sugars, starches, tannins, gluconates, levulinates, glycols, polyhydroxy phenols, and other polyhydroxy organic compounds.

Dispersants which prevent sludge-formation by maintaining solid foreign matter in suspension, include such compounds as the lignosulfonates, polymeric carboxylic acids, condensed napthalene sulfonic acid salts, and sulfonated naphaleneformaldehyde condensates. Sequestering and chelating agents, to remove excess free metal ions from the metal being treated as Well as from hard water to prevent undesired build-up, may comprise one or more of such compounds as salts of ethylene diamine tetraacetic acid, nitrilo-acetic acid, diethylenetriamine pentaacetic acid, diethanol glycine, and the polyphosphates.

Foam suppressants suitable for use with the present invention may be from the low foaming species of the synthetic, non-ionic detergents set forth hereinabove, or may be compounds such as high molecular Weight glycols, terpenes, petroleum hydrocarbons, or the fatty alcohols.

Utilizing the foregoing general formula for illustrative purposes, it has been found in actual practice, that the relatively extensive reservoir of phosphate ions, as provided by the primary acid phosphate salt, will seldom be depleted so that there is but infrequent need for the restoration of the coating solution to initial phosphate ion concentration. However, substantially all other ingredients with the possible exception of the complexing agent are preferentially consumed or exhausted. There is also an elevation of pH of the coating solution; it being observed that due to the nature of the intricate complex chemical reactions involved the pH of the solution is critical for maintaining the appropriate environment for the chemical conversion. The acid phosphates which serve to establish the initial pH within the range of about 4.0-4.5 will become partially neutralized through reaction with the metal being treated, causing a relatively gradual but steady increase in pH toward a lesser acidity with impeding effect upon the basic conversion reaction. Additionally, the cleaning agents, that is, the synthetic nonionic detergents, eventually are entirely consumed by the reaction with the soils, thereby requiring replenishment. Also the accelerators, dispersants, complexing agents, chelating agents and foam suppressants are used up through the various involved reactions.

Accordingly, the additive of the present invention is comprised of a solution of agents for addition to the used coating solution so as to return same to its starting characteristics. The following constitutes a basic, general formulation for such an additive or re-balancing preparation:

Ingredients: Percentage by weight Synthetic, non-ionic detergents 540 Phosphoric acid 15 Accelerators 0.25-5 Water 93.7550

The foregoing constitutes minimum effective formulation for additives of the present invention. The phosphoric acid is included for pH control, that is, to reduce the pH of the now-used solution to its original pH range. It has been found that pure acid will more effectively lower the pH than the addition of acid phosphates, which being buffered, have but limited acidifying capacity. If desired, additional ingredients may be provided, such as complexing agents, dispersants, sequestering and chelating materials, and foam suppressants in adequate proportions to efiectuate restoration of the corresponding elements or components of the initial coating solution.

Since the particular accelerators utilized in phosphate coating solutions are specific to the metal being treated, the accelerators Within the additive solution are generally the same as in the basic coating solution. However, the other ingredients such as the complexing agents, dispersants, and non-ionic detergents, need not necessarily be identical with those in the solution being restored as compounds from the categories above specified are compatible and equally useful in all formulations herein contemplated.

EXAMPLE I In order to demonstrate the effectiveness of the present invention with a typical formulation of phosphate conversion coating for a ferrous metal surface, such as steel parts, the following may constitute the initial solution having a concentration of 2 ounces per gallon.

Ingredients: Percentage by weight Primary acid sodium orthophosphate 1.40 Cobaltous nitrate 0.03 Alkylaryl polyether 0.08

Water, balance.

The foregoing formulation must be recognized as being merely an example of a suitable phosphate coating solution. The selected accelerator, cob-altous nitrate, may be replaced by any of the compounds in the above described category with the possible exception of the fluorides which have been found to be more effective with zinc and aluminum surfaces. Similarly, the synthetic, nonionic detergent, in this instance alkylaryl polyether, may be any one of these set forth in the pertinent category hereinabove set forth.

Correspondingly, the sodium orthophosphate may be replaced by potassium or ammonium orthophosphate as well as by salts of pyrophosphoric acid.

The composition of the above solution might be further refined by incorporation of the other types of ingredients stated, such as complexing agents, dispersants, sequestering or chelating materials, and foam suppressants.

The foregoing coating solution has a pH of approximately 4.0 and is designed for use at a temperature of about F. During the course of processing 100,000 square feet of soiled steel by the foregoing solution through spraying, a particular juncture was noted wherein the cleaning ability of the solution was observed to decrease continuously, with the phosphate coating results becoming increasingly less effective. An analysis of the composition of the solution disclosed the following.

Ingredients: Percentage by weight Primary sodium orthophosphate 1.20 Cobaltous nitrate Nil Alkylaryl polyether Nil Water, balance.

The pH had been found to have risen to 5.0 through neutralization reaction with the metal. The cobaltous nitrate, the accelerator, had become exhausted, as had the non-ionic detergent, alkylaryl polyether, through overloading soil contamination. Only the primary sodium orthophosphate had remained at substantial strength, so that manifestly the solution had reached a state of com- Ingredients: Percentage by weight Phosphoric acid 1-5 Cobaltous nitrate /2-4 Alkylaryl polyether 5-40 Water, balance.

The above formulation is added in suflicient quantity to reactivate the coatingsolution, being generally in the range of 1 to 3% of the volume of the original solution. The foregoing additive will thus be seen to restore to the solution the ingredients which had become consumed. The phosphoric facid will act to reduce the pH from the undesired relatively high value that had been reached and bring the solution back down in the neighborhood of 4.0 while the other constituents of the foregoing additive return the solution to substantially its initial cleaning capability as well as to an effective accelerator level for conversion purposes. In actual practice the consistent use of an. additive of the above general composition set forth will extend the life of a processing solution by a factor of 4- -or 5 times that obtained by the practice of current techniques among which is primarily the mere addition of further quantities of the coating solution.

In contrast, the coating solution at the aforesaid specific juncture was enhanced by an addition of .5 ounce per gallon of the original coating material which temporarily, and but partially, restored the cleaning and coating capabilities. But; the efiiciency of the thus enhanced solution was noted to quickly fall off. A further like addition was made to the already enhanced solution and the restoration thereof to cleaning and coating abilities was attained but for a considerably shorter time than with the first addition. With each further additional increment of theoriginal coating material there was a decreasing effectiveness with an eventual total failure to restore the solution, even though by titration it was observed that the concentration was returned each time to the original 2 ounces per gallon. The continual additions of the originalcoating material served to progressively place the solution in chemical imbalance with ultimate failure. Furtheri'hore, it will be observed that the utilization of additions ofthe type described is a relatively costly process as it incorporates ingredients which do no require replenishing.

EXAMPLE II The present invention also contemplates the provision of an additive which will adapt phosphate coating solutions for cleaning and phosphatizing of aluminum and zinc surfaces as Well as steel. Utilizing the coating solution set forth in Example I above, there may be added thereto a liquid additive containing an accelerator for use with non-ferrous metals. As an example of such an additive the following may be noted.

Ingredients: Percentage by weight Phosphoric acid 1-5 Ammonium bifiuoride 1-5 Alkylaryl polyether 5-40 Water, balance.

The ammonium 'bifluoride thus serves as an accelerator for adapting the solution for treating zinc and aluminum. The coating solution is rendered suitable for utilization with non-ferrous metals by the mere addition of an additive of the type stated which is also added in like volume as the additive of Example I.

EXAMPLE III If it is desired to spray the solution set forth in Example I at a relatively reduced temperature such as within the range of 100 to 120 F. (as contradistinguished from the approximate F. temperature of Example I) an additive may be provided which will suitably adapt the solution since in its stated constituency it would be productive of copious foam at such reduced temperatures. Accordingly, the indicated additive in addition to providing maintenance of the cleaning and chemical converting characteristics of the solution may be also designed to control foam production. The following formulation would be illustrative of an additive for such purposes.

Ingredients: Percentage by weight Phosphori acid 1-5 Cobaltous nitrate /2-4 Polypropylene glycol 1-5 Alkylaryl polyether 5-40 Water, balance.

Thus, the polypropylene glycol is incorporated for foam suppression and by the inclusion of this type of compound effectively renders the novel additive of this invention capable of making the coating solution suitable for etficacious utilization in the relatively lower temperature range.

EXAMPLE IV The phosphate coating solution set forth in Example I may be adapted for use as a tank immersion solution by addition to the additive of the present invention of a cleaning agent, of the aforesaid synthetic, non-ionic detergent type, which has relatively increased hydrophilic properties and high foaming action. A formulation for such an additive is as follows.

Ingredients: Percentage by weight Phosphoric acid 1-5 Cobaltous nitrate /2-4 Nonyl phenyl polyethoxyethanol 5-40 Water, balance.

Thus, the particular selection of detergent from the class stated will render the additive suitable for making the coating solution effective for immersion usage. The relatively elevated foaming action will: produce cleaning action immediately comparable to that brought about through spraying.

Accordingly, the foregoing demonstrates an entirely new departure in the field of restoring or re-balancing phosphate conversion coating solutions. In the various examples hereinabove presented the constituency of the additives have been maintained relatively constant in that in most instances phosphoric acid, cobaltous nitrate and alkylaryl polyether have been presented as the components of such additive to demonstrate that a constant formulation for the additive has wide applicability. However, it is to be observed that the particular accelerator might be varied dependent upon the metal to be treated and the detergent might be selected with respect to the foaming characteristics thereof without departing from the scope and character of this invention. Substantially extensive testing has proved that accelerators and detergents from the types hereinabove specified may be freely used without adversely affecting the efficacy of the present additives. The criterion, however, is that the additive have a basic formulation incorporating phosphoric acid, an accelerator from the class stated, and a synthetic non-ionic detergent from the category presented so as to bring about the unusual results herein described.

It should be understood that changes in the methods, compositions, percentages and combinations set forth may be made without departing from the nature and principle of my invention.

Having described my invention, what I desire to obtain by Letters Patent is:

1. An additive for rejuvenating a phosphate conversion coating solution consisting essentially of:

fluorides, bifluorides, and borates 1-5 A synthetic non-ionic detergent from the class consisting of octyl and nonyl phenyl polyethoxyethanols, aliphatic polyethers, alkylphenol ethoxyl- 1 ates, and alkylaryl polyethers 5-40 Water, balance.

2. An additive for rejuvenating a phosphate conversion coating solution for treating ferrous metal surfaces consisting essentially of:

Percent by weight Phosphoric acid l-5 An accelerating agent from the class consisting of compounds of cobalt, nickel, Wolfram, chromium, molybdenum, zirconium, vanadium, titanium and non-metallic borates A synthetic, non-ionic detergent from the class consisting of octyl and nonyl phenyl polyethoxyethanols, aliphatic polyethers, alkylphenol ethoxylates, and alkylaryl polyethers 5-40 Water, balance.

3. An additive for rejuvenating phosphate conversion coating solutions for treatment of non-ferrous metal surfaces consisting essentially of:

Percent by weight Phosphoric acid 1-5 An accelerating agent from the class consisting of non-metallic fluorides and bifluorides A synthetic, non-ionic detergent from the class consisting of octyl and nonyl phenyl polyethoxyethanols, aliphatic polyethers, alkylphenol ethoxylates, and alkylaryl polyethers 5-40 Water, balance.

References Cited UNITED STATES PATENTS 2,200,615 5/1940 Boyle 1486.16 2,516,685 7/1950 Doulty et a1 1486.16 X 2,665,231 1/1954 Amundsen et al 1486.15 2,886,477 5/1959 Smith 1486.15 3,140,245 7/1964 Gallaccio et al. 148-6.16 X 3,185,596 5/1965 Schiifman 1486.l6 3,331,710 7/1967 Lodeesen et al. 1486.16 X

ALFRED L. LEAVITT, Primary Examiner.

J. R. BATIEN, 111., Assistant Examiner.

US. Cl. X.R. 148-6.15