WO1998044167A1

WO1998044167A1 - Oxide removal from metallic surface

Info

Publication number: WO1998044167A1
Application number: PCT/US1998/006192
Authority: WO
Inventors: Adrian W. Pullen
Original assignee: Petroferm Inc.
Priority date: 1997-03-31
Filing date: 1998-03-31
Publication date: 1998-10-08

Abstract

A cleaning composition having a pH of about 4 to about 9 and consisting essentially of the following ingredients present in proportions effective to clean from a metallic surface contacted therewith metal oxide and other soil adhered to the metallic surface: (A) acid; (B) imidazole; and (C) a surfactant; and also a cleaning composition having a pH of about 4 to about 6 and consisting essentially of the following ingredients present in proportions effective to clean from a metallic surface contacted therewith metal oxide and other soil adhered to the metallic surface: (A) acid; (B) triazole; and (C) a surfactant.

Description

OXIDE REMOVAL FROM METALLIC SURFACE

Field of the Invention

This invention relates to an aqueous cleaning composition. More particularly, this invention relates to an aqueous cleaning composition which is effective in removing a metal oxide from a metallic surface. The present invention can be used also to remove from metallic surfaces soils such as oils and greases.

The formation of a metal oxide on a metallic surface is a well-known phenomenon. There are numerous applications where it is desirable or even mandatory that the metal oxide be removed from the metallic surface for aesthetic or functional reasons.

In the manufacture of metallic parts utilizing processing steps such as, for example, stamping, drilling, machining or tooling, the parts are contaminated with machining oils and surface oxides that need to be removed prior to further treatment or prior to display or sale of the part. The formation of an oxide layer on the metallic surface of a part during manufacture is particularly prevalent when the metal being used is soft, that is, non- ferrous, for example, copper and copper alloys.

A popular method for cleaning such substrates is a multi-step process. The first step usually involves the removal of processing fluids from the surface. This typically involves the use of an alkaline cleaner (pH>9) which can be either sprayed onto the parts or used as a dip into which the parts are immersed. After this step, the parts are rinsed with clean water. A further step in the process is brightening. In this step, metal oxide which formed on the surface during the previous manufacturing and cleaning steps is removed. This is often accomplished by use of an acidic composition, the specific nature of which depends upon the type of metal being treated. Contact between the metallic part and the acid composition may be accompanied by some physical means of removal, for example, scrubbing. After the "brightening" step, the parts are rinsed with clean water. A final step may follow brightening. This involves the use of a fixing agent (often benzotriazole) which forms a seal on the surface of the part and deters further oxidation. Accordingly, the fixing agent functions as a corrosion-inhibitor. Typically, the fixing agent is dissolved in an aqueous/alcohol composition into which the parts are dipped.

The present invention relates to improved means for brightening the metallic surface of parts in various stages of manufacture or post manufacture by the removal therefrom of metal oxides and other contaminants that may be present on the metallic surface.

Reported Developments As mentioned above, it is known in the cleaning industry to clean and brighten metal substrates by utilizing a combination of alkaline and acidic cleaning compositions.

This process of cleaning a metal substrate by contact with an alkaline cleaning composition followed by an acid rinse is disclosed, for example, in U.S. Patent No. 4,599,116 to King et al. The use of such combination of alkaline and acidic cleaners is necessary because each cleaner by itself is not effective in a cleaning and brightening the substrate. Alkaline cleaners are known to clean certain types of soils, such as fatty oils, but they are not effective for removing metal oxides which are formed on metallic surfaces. Acidic cleaners are known to remove such oxides, but their use is limited to certain substrates.

Several disadvantages are associated with the use of this combination of acidic and alkaline cleaning compositions. Because more than one composition is required in order to achieve the desired result of a cleaned and brightened part, efficiency is decreased relative to the use of a single cleaner for achieving the same result. The versatility of alkaline and acidic cleaners is also limited, as various metal surfaces are vulnerable to attack by alkaline and acidic cleaners. Additionally, the handling of alkaline and acidic cleaners requires a significant degree of care since these cleaners can be caustic to human skin and corrode rubber hosing, pumps, concrete, or pipes. In industrial processes, the use of alkaline or acidic aqueous cleaners carries the additional disadvantage of requiring the costly step of neutralization before disposal.

A pickling solution for removing oxides and cleaning surfaces of copper and its alloys is disclosed in U.S. Patent No. 4,051,057 to Ericson et al. The pickling solution comprises: (a) sulf ric or phosphoric acid; (b) a hydroxy acid such as citric or gluconic acid; (c) hydrogen peroxide; (d) a substituted triazole, preferably benzotriazole; and (e) a tertiary fatty a ine surfactant. The pH of the pickling solution is not identified in the patent, but it appears to be highly acid in that the exemplary solutions identified in the patent contain 20 to 80 g/1 of sulfuric acid and a total acid concentration of 50 to 110 g/1. Problems associated with such highly acidic compositions have been discussed above .

U.S. Patent No. 5,411,595 to Bokisa, Sr. et al. discloses an acidic cleaning solution for removing contaminants from plated surfaces of an etched printed circuit board and from copper and pewter surfaces and the surfaces of silver utensils. The acidic cleaning solution contains an imidazole-2-thione compound and an inorganic or organic acid and, optionally, a water miscible solvent. Although this patent discloses that the pH of the solution can be higher when the water miscible solvent is used, the solution is described as having typically a pH 4 or less, for example, 1 or less when using HC1.

An acidic aqueous cleaning solution comprising an inorganic or organic acid and an alkylimidazole is disclosed in U.S. Patent No. 3,933,531 to Sawa et al. The acid component is said to promote cleaning of the copper or copper alloy surface and the alkylimidazole is characterized as functioning to prevent a clean copper or copper alloy surface from tarnishing or rusting. The patent discloses precleaning the copper surface before it is treated with the aforementioned cleaning solution by subjecting the surface to conventional cleaning methods such as polishing, acid pickling, or cleaning with an aqueous, solution of metal cyanide. The cleaning process described in this patent is typical of multi-step prior art processes and has the disadvantages associated therewith.

The present invention relates to an improved environmentally attractive and efficient cleaning process foiremoving from a metallic surface a metal oxide and other soils that may be adhered to the surface.

Summary of the Invention

In accordance with the present invention, there is provided an aqueous-based cleaning composition in which an imidazole or a triazole (or a mixture thereof) functions effectively to remove a metal oxide from a metallic surface contacted therewith.

In accordance with one aspect of- the present invention, there is provided a method for cleaning a metallic surface comprising: (A) contacting a metallic surface having thereon a metal oxide, an acid, and other soil with an aqueous solution of an imidazole and a cleaning material which is effective in removing said other soil from the surface; and (B) maintaining said metallic surface and said solution in contact for a sufficient period of time to remove metal oxide and other soil from said surface. In preferred form, the aqueous solution of the present invention has a pH of about 4 to about 9 and consists essentially of an acid, an imidazole, and a surfactant which is effective in removing said other soil from the surface. Preferably the acid is a hydroxy tricarboxylic acid, most preferably citric acid. Most preferably, the pH of the aqueous solution is about 6 to about 8. In accordance with another aspect of the present invention, there is provided a method for cleaning a metallic surface comprising contacting a metallic surface having thereon a metal oxide with an aqueous solution which has a pH of about 4 to about 6 and which consists essentially of a triazole and an acid and maintaining said metallic surface and said solution in contact for a sufficient period of time to remove metal oxide from said surface. In preferred form, the aqueous solution includes a surfactant which is effective in removing other soil, for example, a lubricant that is adhered to the metallic surface. Preferably, the aqueous solution contains a hydroxy tricarboxylic acid, most preferably citric acid. Preferably the pH of the aqueous solution is about 4.5 to about 5.5. The cleaning compositions of the present invention can be used to remove the metal oxides that form on metallic surfaces in general. It is believed that the present invention will be used most widely to remove a metal oxide from a surface comprising a relatively soft metal, for example, copper, tin, or nickel or an alloy which includes one or more of the aforementioned metals.

The compositions of the present invention which include an imidazole or a triazole as the effective "brightening agent" are to be distinguished from prior art cleaning compositions in which the brightening of the metallic surface is effected principally by use of an acid constituent, for example, highly acidic aqueous compositions such as pickling baths. (The pHs of such baths are typically about 1 or 2 or even less.) The nature of such prior art acidic cleaning compositions is such that layers of unoxidized metal underlying the metal oxide layer which is present on the metallic surface are also removed as a result of vigorous acid attack of the metal. In contrast, the cleaning compositions of the present invention are capable of functioning as oxide removers at pHs at which there is little or no dissolution or removal of metal which underlies the metal oxide that is removed from the metallic surface. In use of the aqueous cleaning solution, the imidazole or triazole is protonated as the double bond of the -C-N=C- moiety is broken. This results in the molecule having a positive charge delocalized among the -N-C-N- bonds. It is believed that this material reacts with the metal oxide to form a product which is soluble in the cleaning solution. There are a number of attributes associated with the use of the compositions of the present invention. For example, metallic parts which are dull in appearance due to the presence of a metal oxide on the surface thereof can be brought to a condition of brightness such that they can be displayed attractively or used in additional manufacturing steps without the interference that would tend to be caused by the presence of a metal oxide on the surface. The compositions of the present invention are characterized by being non-toxic or low in toxicity. They can be used over a wide range of pH including, for example, neutral pH. The present invention provides marked safety improvements over prior art methods which involve the removal of metal oxides by use of cleaning compositions that contain strong acids in relatively large amounts. Such acid-containing compositions can cause severe burns to personnel and the disposal and handling costs which are associated with their use are expensive. An additional advantage of the present invention is that the cleaning composition can be used effectively without the need to use chlorinated hydrocarbon solvents or other hydrocarbon materials which function as ozone depleters. Other advantages of the present invention are described below.

Detailed Description of the Invention Cleaning compositions within the scope of the present invention can be used to clean from a metallic surface metal oxide and other soil that may be present on the surface. The term "soil" is used herein to include a metal oxide that is formed on the metallic surface and any other unwanted material that may be present on the surface, for example, water-soluble and water-insoluble contaminants such as, for example, metal working fluids, including, for example, greases and oils. An essential ingredient of the cleaning compositions of the present invention is water. This constituent functions to disperse or otherwise remove any number of different types of soils that tend to be present on substrates that need to be cleaned. In addition, water functions as the principal carrier for other of the ingredients comprising the cleaning compositions. Deionized water is used preferably. The cleaning compositions of the present .invention comprise an aqueous solution in which all of the ingredients are dissolved or are miscible. It is believed that the most widely used compositions will comprise water in a major amount, that is, in excess of about 50 wt.% of the composition. However, there are applications in which water will comprise a minor proportion of the composition, for example, about 25 to about 50 wt.% Nevertheless, for most applications, water will be present in an amount greater than any other ingredient.

The various embodiments of the present invention include aqueous-based cleaning compositions containing an imidazole or a triazole or a mixture of these materials. Each of the materials constitutes a class of heterocyclic compounds characterized by a five-member ring. The ring of the imidazole contains two nitrogen and three carbon atoms. The ring of the triazole contains three nitrogen atoms and two carbon atoms. These classes of compounds include species which are non-toxic or which are substantially non-toxic and which are environmentally acceptable. Such species are expected to be the most widely used imidazoles and triazoles that are used in the practice of the present invention.

The Imidazole Embodiment

This embodiment of the invention encompasses a cleaning composition comprising an aqueous solution of an imidazole which is effective in removing a metal oxide from a metallic surface and another cleaning material which is effective in removing from the metallic surface other soil that is present thereon, each of the ingredients being present in proportions effective to remove the soils from the metallic surface. The aqueous cleaning solution can be alkaline, acidic, or neutral. Thus, the pH of the solution can vary over a wide range. A preferred pH is about 4 to about 9, with a pH of about 6 to about 8 being particularly preferred.

Any imidazole (including a substituted imidazole) which is soluble or miscible in the water-based composition and which is effective in removing oxide from a metallic surface can be used in the practice of the present invention. The basic ring structure of the imidazole is represented by the structural formula below.

N₃ IN Formula I

\ \ C

Examples of imidazoles which can be used in the practice of the present invention include imidazole and substituted imidazoles in which the substituted group is in one or more of the 1, 2, 4 or 5 positions. Examples of such substituted groups include straight or branched chain alkyl groups (long chain with 5 to about 20 carbon atoms or short chain with 1 to 4 carbon atoms) , alcohols and carboxylic acids. Examples of imidazoles that can be used are histidine, histamine, imidazole, 1-methyl-imidazole, 4-methyl-imidazole, 2- isopropyl-imidazole, 2-methyl-imidazole, 2-ethyl-imidazole, and 1-undecyl-imidazole.

The imidazole should be incorporated in the composition in an amount sufficient to remove met.al oxide from the metallic surface being cleaned. The amount used for any particular application will depend on the particular imidazole used, the type of metal oxide being removed, the conditions of cleaning, and other factors. It is believed that most applications will necessitate the use of at least about 0.05 wt.% of the imidazole. It is believed also that the use of amounts in excess of about 5 wt.% of the imidazole will not be necessary for most applications. A preferred amount of imidazole is about 0.1 to about 1 wt.%.

The cleaning composition prepared from the imidazole includes also another material which is effective in removing from the metallic surface other soil that may be present on the metallic surface. The nature of such cleaning material will depend on the nature of the "other" soils present. In general, the cleaning material should function to remove the soil by dispersing the same in the liquid phase of the composition, for example, in emulsified form. It should preferably be a material which is non-toxic or substantially non-toxic.

In cleaning soils comprising fatty type materials such as oils and greases, it is preferred to use surfactants which function to displace the soil from the surface and most preferably emulsify the soil. Such surfactants can be anionic, cationic, nonionic, or amphoteric. Examples of species of preferred surfactants include tertiary thioether ethoxylate, alkyl aminopropionate, and sodium xylene sulfonate. Examples of other surfactants that can be used are: an ethoxylated nonionic surfactant, for example, a nonionic alcohol ethoxylate, including, for example, linear alkyl phenols of about 8 to about 10 carbon atoms condensed with from about 3 to about 20 ethylene oxide groups such as, for example, a nonylphenol condensed with 10 ethylene oxide groups; an ester of oleic acid and sorbitan, preferably esters which contain about 5 to about 20 moles of ethylene oxide, most preferably about 5 moles of ethylene oxide.

The cleaning material should be present in an amount sufficient to clean the other soil(s) from the metallic surface. The amount used for any particular application will depend on the particular surfactant or mixture of surfactants used, the type of soils present on the metallic surface, the cleaning conditions and other factors. It is believed that most applications will necessitate the use of at least about 0.2 wt.% of the surfactant. The surfactant constituent may comprise more than one surfactant. It is believed also that the use of amounts in excess of about 3 wt.% of the surfactant will not be necessary for most applications. A preferred amount of surfactant is about 0.5 to about 2 wt.%. An acid can be used to adjust the pH of the aqueous cleaning composition to the desired value, for example, about 4 to about 9 or to the preferred pH of about 6 to about 8. Any suitable acid can be used, including inorganic acids such as mineral acids and organic acids, preferably weak organic acids. Examples of acids that can be used are hydrochloric acid, propionic acid, gluconic acid, glutaric acid, acetic acid, and hydroxy acetic acid. Hydroxy-containing tricarboxylic acids are preferred. Citric acid is particularly preferred. A mixture of two or more acids can comprise the acid constituent.

The acid or mixture of acids should be used in an amount that imparts to the composition the desired pH. Speaking generally, it is believed that for most applications the amount of acid will not exceed about 0.5 wt.% of the composition and will typically fall within the range of about 0.005 to about 0.05 wt.%.

The cleaning composition of this embodiment of the present invention can be formulated conveniently from an aqueous concentrate of the ingredients. Such concentrate car comprise water, an imidazole, a cleaning material, and acid, one hundred parts of which upon being diluted with about 900 to about 2000 parts of water provides an aqueous cleaning solution of the present invention, for example, a solution having a pH of about 4 to about 9 and consisting essentially of about 0.05 to about 5 wt.% of the imidazole, about 0.2 to about 3 wt.% of the cleaning material and about 0.005 to about 0.05 wt.% of the acid.

The Triazole Embodiment

This embodiment of the present invention encompasses a cleaning composition comprising an aqueous solution having a pH of about 4 to about 6 and consisting essentially of a triazole which is effective in removing a metal oxide from a metallic surface and an acid. In preferred form, the solution contains another cleaning material which is effective in removing from the metallic surface other soil that may be present thereon. Each of the "cleaning" ingredients is incorporated in the solution in proportions effective to remove the soils from the metallic surface. The aqueous cleaning solution has preferably a pH of about 4.5 tc about 5.5. Any triazole (including a substituted triazole) which is soluble or miscible in the water-based composition and which is effective in removing oxide from a metallic surface can be used in the practice of the present invention. The basic ring structure of the triazole is represented by the structural formula below.

=N

N3 IN Formula II

\\₂/ \ C

Examples of triazoles which can be used in the practice of the present invention include triazole and substituted triazoles in which the substituted group is in one or more of the 1, 2, or 4 positions. Examples of such substituted groups include straight or branched chain alkyl groups, preferably short chain alkyl groups with 1 to 4 carbon atoms, alcohols, carboxylic acids, and aminoalkyl groups.

Preferably, the substituted groups are aliphatic groups which contain no aromatic constituents. It is preferred to use triazole.

The triazole should be incorporated in the composition in an amount sufficient to remove metal oxide from the metallic surface being cleaned. The .amount used for any particular application will depend on the particular triazole used, the type of metal oxide being removed, the conditions of cleaning, and other factors. It is believed that most applications will necessitate the use of at least about 0.05 wt.% of the triazole. It is believed also that the use of amounts in excess of about 5 wt.% of the triazole will not be necessary for most applications. A preferred amount of triazole is about 0.1 to about 1 wt.%. The aqueous solution having incorporated therein the triazole includes also an acid. Any suitable acid can be used, including inorganic acids such as mineral acids and organic acids, preferably weak organic acids. Examples of acids that can be used are hydrochloric acid, propionic acid, gluconic acid, glutaric acid, acetic acid, and hydroxy acetic acid. Hydroxy-containing tricarboxylic acids are preferred. Citric acid is particularly preferred. A mixture of two or more acids can comprise the acid constituent. The acid or mixture of acids should be used in an amount that imparts to the composition a pH of about 4 to about 6. Speaking generally, it is believed that for most applications the amount of acid will not exceed about 0.5 wt.% of the composition and will typically fall within the range of about 0.005 to about 0.05 wt.%.

The aforementioned triazole/acid composition is effective in removing from a metallic surface a metal oxide thereon. To clean metallic surfaces contaminated with other soils, the composition should include also another material which is effective in removing from the metallic surface such other soil. The nature of such cleaning material will depend on the nature of the "other" soils present. In general, the cleaning material should function to remove the soil by dispersing the same in the liquid phase of the composition, for example, in emulsified form. It should be preferably a material which is non-toxic or substantially non-toxic.

In cleaning soils comprising fatty type materials such as oils and greases, it is preferred to use surfactants which function to displace the soil from the surface and most preferably emulsify the soil. Such surfactants can be anionic, cationic, nonionic or amphoteric. Examples of species of preferred surfactants include tertiary thioether ethoxylate, alkyl aminopropionate, and sodium xylene sulfonate. Examples of other surfactants that can be used are: an ethoxylated nonionic surfactant, for example, a nonionic alcohol ethoxylate, including, for example, linear alkyl phenols of about 8 to about 10 carbon atoms condensed with from about 3 to about 20 ethylene oxide groups such as, for example, a nonylphenol condensed with 10 ethylene oxide groups; an ester of oleic acid and sorbitan, preferably esters which contain about 5 to about 20 moles of ethylene oxide, most preferably about 5 moles of ethylene oxide.

The cleaning material should be present in an amount sufficient to clean the other soil(s) from the metallic surface. The amount used for any particular application will depend on the particular surfactant or mixture of surfactants used, the type of soils present on the metallic surface, the cleaning conditions and other factors. It is believed that most applications will necessitate the use of at least about 0.2 wt.% of the surfactant. The surfactant constituent may comprise more than one surfactant. It is believed also that the use of amounts in excess of about 3 wt.% of the surfactant will not be necessary for most applications. A preferred amount of surfactant is about 0.5 to about 2 wt.%. The cleaning composition of this embodiment of the present invention can be formulated conveniently from an aqueous concentrate of the ingredients. Such concentrate can comprise water, a triazole, acid, and optionally a cleaning material, one hundred parts of which upon being diluted with about 900 to about 2000 parts of water provides an aqueous cleaning solution of the present invention, for example, a solution having a pH of about 4 to about 6 and consisting essentially of about 0.05 to bout 5 wt.% of the triazole and about 0.005 to about 0.05 wt.% of acid, and optionally about 0.2 to about 3 wt.% of the cleaning material.

Other Information Relating to the Invention

As an optional ingredient, the cleaning compositions of the present invention can include also an organic solvent, but an organic solvent that is not an ozone-depleter .

(Indeed, the cleaning compositions of the present invention are substantially free of any materials that are considered to be ozone depleters.) The organic solvent can be a material which is effective in dissolving soils that might otherwise not be removed from the metallic surface by the imidazole, or triazole, or other cleaning material, or the organic solvent can be a material which is effective in solubilizing _. or rendering miscible one or more of the constituents which comprise the cleaning composition. When used, it is preferred that the organic solvent be water-soluble. Examples of such solvents include glycol ethers, more preferably propylene glycol ethers. Suitable propylene glycol ethers include, for example, propylene glycol n-propyl ether, propylene glycol monomethyl ether, dipropylene monomethyl ether, and tripropylene glycol monomethyl ether. The amount of organic solvent can comprise about 0.5 to about 5 wt.% of the composition. It should be understood that the organic solvent is an optional ingredient and that there are any number of applications in which excellent cleaning results can be obtained by the use of compositions of the present invention which are free or substantially free of a material which constitutes an organic solvent.

The compositions of the invention can contain other ingredients or additives of the type that are used typically in cleaning compositions. Examples of such additives are defoamers and corrosion inhibitors of the type used to deter corrosion of iron-containing surfaces. The additives can be used in amounts normally used in cleaning compositions, for example, about 0.01 to about 0.15 wt.%.

In addition to being effective in causing removal of the metal oxide from the metallic surface, the aqueous solutions having incorporated therein the imidazole and/or triazole are effective also in providing corrosion-resistant properties to the treated metallic surface. This has the desirable effect of prolonging the shiny bright appearance of the cleaned metallic surface as oxidation and accompanying tarnishing thereof are inhibited.

Any suitable means can be used to bring into contact the cleaning composition of the present invention and the substrate to be cleaned. For example, the substrate can be wiped or sprayed with the cleaning composition or the substrate can be immersed in the cleaning composition. The following techniques of application can be used: spray-in- air; ultrasonic; and spray-under-immersion. Available aqueous cleaning equipment can be used in the cleaning process. Examples of equipment commonly used in industrial processes for use in the practice of the present invention include batch or in-line machines with one cleaning tank and from 1 to 3 water rinses, with spray-under-immersion and ultrasonics in all sumps. In cleaning parts that include a metal oxide and other soil, it is preferred that the soiled parts be sprayed with the cleaning composition, for example, by use of industrial spray equipment. This can be accomplished by use of industrial dip tanks which may involve physical agitation vie recirculation of the fluid, ultrasonic agitation within the fluid, or lift stages where the parts are lifted repeatedly from and lowered into the bath, for example, by automatic means . Although the cleaning composition can be applied at ambient temperature, it is preferred to use it in heated form, for example, up to a temperature of 212 "F. In general, the rate of brightening is increased by use of a heated cleaning composition. The particular temperature used will vary depending on the particular composition used. It is believed that the most widely used temperatures will be within the range of about 140 °F to about 180 "F, and particularly, about 140 °F to about 160 °F. Cleaning time is dependent on different factors, for example, the type and quantity of soil and the temperature of operation. It is believed that a contact time of about 1 to about 10 minutes will be satisfactory for most applications. After contact between the metallic surface and the cleaning composition is terminated, the metallic surface can be rinsed, for example, with water to remove residuals that are present on the surface. It is preferred to use deionized water for rinsing. Drying of the surface can be effected by any suitable means. The cleaning compositions of the present invention can be used effectively to clean any metal. They are particularly suitable for cleaning relatively soft metallic surfaces. Examples of relatively soft metallic surfaces which can be cleaned in accordance with the present invention are surfaces of copper, nickel, and tin, and alloys of such metals, for example, brass. It is believed that the present invention will be used widely in the cleaning of copper and copper alloys, for example, various bronzes and brasses.

The present invention may be used in a number of applications, including, for example, brightening parts at the end of a manufacturing process, brightening oxidized, post-manufactured metallic goods, and brightening parts concurrently in an oils-cleaning operation. In addition to being used in large-scale industrial cleaning processes, the cleaning compositions can be used also in smaller-scale laboratory cleaning processes or in general purpose home use cleaning processes. Cleaning can be effected in a manner such that the surface is left bright and shiny.

Cleaning compositions within the scope of the present invention can function effectively even in applications in which relatively large quantities of soil are dispersed in the composition. The cleaning effectiveness of the composition does not deteriorate significantly when loaded down with soil. This characteristic permits the composition to be used for relatively long periods of time without needing to be replaced, thus increasing its efficiency in industrial settings relative to other popularly used cleaners.

The following examples are illustrative of cleaning compositions of the present invention.

Examples

The cleaning compositions of Example Nos. 1 to 7 in the table below were prepared by mixing water and the ingredients in the proportions stated in the table. The amounts of the ingredients are stated in percent by weight based on the total weight of the composition. Water comprises the balance of each of the compositions.

Concentration, Wt.% for Compositions of Examples:

Ex. Ex. Ex. Ex. Ex. Ex. Ex.

1 2 3 4 5 6 7

imidazole o.i

1-methyl-imidazole - 0.1 _ _ _ _ _

4-methyl-imidazole - 0.1 - _ _ _

2-isopropyl-imidazole - - - 0.1 -

2-methyl-imidazole - - - - 0.1 2-ethyl-imidazole - - - - - 0.1

1,2,4 triazole - - - - - - 0.1 tertiary thioether ethoxylate (nonionic detergent surfactant) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 5 citric acid 0.04 0.04 0.04 0.04 0.03 0.03 0.01 defoamer^(I) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 water softening sequestrant^® 0.5 0.5 0.5 0.5 0.5 0.5 0.5 water softening/ 0 sequestrant/pH balance 0) 0.27 0.27 0.27 0.27 0.27 0.27 0.27 coupling agent/ detergent⁽⁾ 0.6 0.6 0.6 0.6 0.6 0.6 0.6 coupling agent/wetting agent⁽⁵⁾ 1.0 1.0 1.0 1.0 1.0 1.0 1.0 5 pH 7 7 7.5 7.5 8 8 4

(l .nonioni block copolyvi comprising clhyl.ne oxick /propylene oxide linear copolymer (2) nonionic acrylic copolymei cυinpi ising aciylic/mclhacryhc copolymer 0) 0 wl % aqu ous solution of μ!υ_onιc acid ( ) amphotenc aininopropionate (5) 5(1 wt % aqueous solution of sodium xylenesulfonale

Cleaning compositions of Example Nos. 1 to 7 above are used to clean the following parts which had thereon a light oxide layer as well as other soil, as indicated below. Parts Soil copper tubes drawing lube copper screws tooling oils copper plates shop dirts brass valves tooling oils brass fittings water soluble tooling oils brass hardware tooling oils

The parts are cleaned by subjecting them to the cleaning compositions of the examples in a spray-in-air cleaning machine. The temperature and time of cleaning are respectively 145 °F and 4 minutes. The parts are withdrawn from the cleaning machine, rinsed for one minute in water, and dried. The parts appear bright and shiny and free of any soils.

In summary, it can be said that the present invention provides an effective, efficient, economical, safe and environmentally attractive way for removing from a metallic surface a metal oxide and other soil that may be present on the surface. It should be appreciated from the above description of the invention that the multi-step processes of prior art cleaning methods can be reduced to one step by the use of the present invention. As an alternative to prior art processes which involve: (a) cleaning in one step; (b) brightening in a second step; and (c) applying to the metallic surface a corrosion-inhibitor in a third step, all of the functions performed by such multi-step process can be achieved in a single step by subjecting the metallic surface to a cleaning composition within the scope of the present invention. Furthermore, in the practice of the present invention, the environmental, health, and safety issues and costs associated with the use and disposal of highly caustic and corrosive acidic compositions are eliminated.

Claims

Claims 1. A method for cleaning a metallic surface comprising:

(A) contacting a metallic surface having thereon a metal oxide and other soil with an aqueous solution of an imidazole, an acid, and a cleaning material which is effective in removing said other soil from the surface; and

(B) maintaining said metallic surface and said solution in contact for a sufficient period of time to remove metal oxide and other soil from said surface.

2. A method for cleaning a metallic surface comprising (A) contacting a metallic surface having thereon a metal oxide and other soil with an aqueous solution having a pH of about 4 to about 9 and consisting essentially of an acid, an imidazole, and a surfactant which is effective in removing said other soil from the surface; and (B) maintaining said metallic surface and said solution in contact for a sufficient period of time to remove metal oxide and other soil from said surface.

3. A method according to Claim 2 wherein the aqueous solution contains a hydroxy tricarboxylic acid.

4. A method according to Claim 3 wherein the aqueous solution contains citric acid.

5. A method according to Claim 2 wherein the pH of the aqueous solution is about 6 to about 8.

6. A method according to Claim 2 wherein the aqueous solution contains surfactant selected from the group consisting of an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant, and a mixture thereof.

7. A method according to Claim 2 wherein the aqueous solution contains imidazole.

8. A method according to Claim 2 wherein the aqueous solution consists essentially of: (A) about 0.05 to about 5 wt.% of said imidazole; and (B) about 0.2 to about 3 wt.% of said surfactant.

9. A method according to Claim 2 including cleaning a metallic surface comprising copper, tin, or nickel or an alloy of copper, tin, or nickel.

10. A cleaning composition having a pH of about 4 to about 9 and consisting essentially of the following ingredients present in proportions effective to clean from a metallic surface contacted therewith metal oxide and other soil adhered to the metallic surface: (A) acid; (B) imidazole; and (C) a surfactant.

11. A composition according to Claim 10 including at least about 0.05 wt.% of imidazole and at least about 0.2 wt.% of surfactant.

12. A method for cleaning a metallic surface comprising contacting a metallic surface having thereon a metal oxide with an aqueous solution having a pH of about 4 to about 6 and consisting essentially of a triazole and an acid and maintaining said metallic surface and said solution in contact for a sufficient period of time to remove metal oxide from said surface.

13. A method according to Claim 12 wherein said metallic surface has thereon other soil also and wherein said solution includes surfactant which is effective in removing said other soil from said surface.

14. A method according to Claim 12 wherein the aqueous solution contains a hydroxy tricarboxylic acid.

15. A method according to Claim 14 wherein the aqueous solution contains citric acid.

16. A method according to Claim 12 wherein the pH of the aqueous solution is about 4.5 to about 5.5.

17. A method according to Claim 12 including cleaning a metallic surface comprising copper, tin, or nickel or an alloy of copper, tin or nickel.

18. A method according to Claim 13 wherein said aqueous solution consists essentially of: about 0.05 to about 5 wt.% of triazole; and (B) about 0.2 to about 3 wt.% of surfactant.

19. A cleaning composition having a pH of about 4 to about 6 and consisting essentially of the following ingredients present in proportions effective to clean from a metallic surface contacted therewith metal oxide and other soil adhered to the metallic surface: (A) acid; (B) triazole; and (C) a surfactant.

20. A composition according to Claim 19 including at least about 0.05 wt.% of imidazole and at least about 0.2 wt.% of surfactant.