WO2000014301A1

WO2000014301A1 - Alkaline liquid composition and method for degreasing metals

Info

Publication number: WO2000014301A1
Application number: PCT/US1999/020527
Authority: WO
Inventors: Yasuhiko Nagashima; Kensuke Shimoda; Hirokastu Bannai
Original assignee: Henkel Corporation
Priority date: 1998-09-08
Filing date: 1999-09-08
Publication date: 2000-03-16
Also published as: CN1248642A; CN1213170C; KR20000022952A; TW508375B; ID23123A

Abstract

An aqueous bath for degreasing metals contains 0.5 to 8 g/l of polyoxyethylene alkyl ether with an HLB of 12 to 17 and at least one dissolved alkali metal salt or ammonium salt, contains 1 to 15 points of total alkalinity, and has a pH from 8 to 13. If the bath also contains dispersed conventional Jernstedt salt or insoluble di- or tri- valent metal phosphates with a particle size less than 5 νm, the surface treated is conditioned for subsequent deposition of high quality zinc phosphate coatings at the same time its is degreased and can be effectively conversion coated by bringing it into contact with a suitable phosphating bath, without any rinsing with water between discontinuing contact with the degreasing bath and effecting contact with the phosphating bath. By this method, conventional degreasing, rinsing, conditioning, and zinc phosphating processes are shortened, cost less, and have less adverse environmental impact.

Description

Description ALKALINE LIQUID COMPOSITION AND METHOD FOR DEGREASING METALS

BACKGROUND OF THE INVENTION

The invention relates to an aqueous alkaline liquid composition that is useful as a degreasing agent for metals such as steel sheet, zinc-plated steel sheet, and aluminum and to a method for using this aqueous alkaline liquid degreasing agent, more particularly to a method for the degreasing and conversion treatment of metals that can omit the water rinse step and surface conditioning steps, as described below, that are ordinarily carried out between alkaline degreasing and conversion treatment operations in phosphate conversion lines.

A variety of application-adapted phosphate conversion treatments are currently carried out in order to improve the post-painting corrosion resistance of various metals, the adhesion of paint thereto, and/or to improve the lubricity of metals. The phosphate conversion treatment sequence generally consists of at least the following separate operations: (1 ) alkaline degreasing, (2) water rinse, (3) phosphate conversion, (4) water rinse, and (5) drying. The water rinses (2) and (4) are in some cases run as multistage processes or as hot water rinses. When the phosphate conversion coating will be used as an underpaint coating, a surface activation treatment (surface conditioning treatment) is usually carried out as a pretreatment before (3) in order to induce the formation of uniform, fine, and dense conversion coating crystals. The surfaces of the metal workpieces intended to be submitted to phosphate treatment are almost inevitably contaminated with oil, under which circumstances the execution of the degreasing process (1 ) becomes essential.

The main components in the treatment bath used in the degreasing step in the phosphate conversion sequence are surfactant and alkali builder added for the purpose of securing the degreasing activity of the surfactant. The surfactants used in alkaline de- greasing baths have both an excellent ability to emulsify oil and an excellent ability to prevent the redeposition of oil. The surfactant present in the degreasing bath functions to emulsify, disperse, and remove the oil contaminating the metal workpiece and to prevent the emulsified and dispersed oil from redepositing on the metal. With regard to the mechanism by which redeposition of the emulsified and dispersed oil is inhibited, it is thought that a monomolecular layer of surfactant adsorbs to the already degreased metal surface and blocks redeposition of the oil on the metal surface. As a result, when a metal surface still carrying surfactant is brought into contact with a phosphate conversion bath, the surfactant retards the conversion reactions by inhibiting the etching reac- tion of the basis metal that is the initial reaction in the conversion reactions. It is for this reason that a water rinse has heretofore been required after degreasing.

Prior-art alkaline degreasing baths have also contained large amounts of inorganic builder (e.g., silicate or condensed phosphate) or organic chelating agent for the pur- pose of chelating polyvalent cations such as Ca²⁺ and Mg²⁺ (present in hard water or introduced into the bath from other sources) and thereby preventing insolubilization of the surfactant. When inorganic builder or organic chelating agent is introduced into a phosphate conversion bath, it adsorbs to the metal surface and in this manner inhibits the etching reaction. It also chelates the Zn²⁺ (a primary component for formation of the phosphate conversion coating) present in phosphate conversion baths as well as cationic components such as Ni²⁺ or Mn²⁺ added to phosphate conversion baths for the purpose of enhancing corrosion resistance. The overall result of this chelation is an inhibition of the deposition of the phosphate conversion coating crystals.

In order to avoid these problems, it has been necessary in prior-art conversion lines to place a water rinse step after the alkaline degreasing step in order to also dilute the alkaline degreasing bath carried over into the phosphate conversion step to an un- problematic concentration. This has required the continuous supply of fresh process water to the post-alkaline degreasing water rinse in order to maintain a constant water quality. Since the overflowing rinse water is forwarded to the waste water treatment facil- ities, this continuous supply of water is highly uneconomical because it raises both the cost of the water supply and the cost of waste water treatment.

In addition, the prior-art alkaline degreasing baths have frequently contained nonionic surfactant of the polyoxyalkylene alkylphenyl ether type, for example, polyoxyethyl- ene nonylphenyl ether. However, the polyoxyalkylene alkylphenyl ether-type nonionic surfactants have been the subject of great public interest from the perspective of the endocrine problem, which has created desire for the development of surfactant that can replace the polyoxyalkylene alkylphenyl ether-type nonionic surfactants and for the corresponding development of a degreasing bath that can respond to the cited environmental problem. This desire notwithstanding, surfactant that (i) would permit omission of the water rinse after alkaline degreasing, (ii) would not inhibit the conversion activity even when carried over into the ensuing phosphate conversion bath, and (iii) is not a polyoxyalkylene alkylphenyl ether, is at present either unknown or at the very least unrecognized. As a consequence, a method for the degreasing and phosphate treatment of metals using such a surfactant is also unknown. A major object of the present invention is to provide a bath for the alkaline degreasing of metals that (i) makes possible omission of the water rinse step heretofore re- quired between the alkaline degreasing step and the phosphate conversion step (omission of this water rinse step has largely been beyond the capability of the prior art), (ii) does not inhibit or impair conversion to any harmful extent, even when the alkaline degreasing bath is carried over into the ensuing phosphate conversion bath, and (iii) re- sponds to the environmental problem. Another object of the present invention is to provide a method for using the subject alkaline degreasing bath. In more specific terms, an object of the present invention is to provide a method for the degreasing and conversion treatment of metals that employs the alkaline degreasing bath encompassed by the present invention. BRIEF SUMMARY OF THE INVENTION

It has been found that a process extending from degreasing to conversion treatment can be substantially shortened when the metal surface is cleaned using a liquid alkaline degreasing composition that contains surfactant with a special structure, and the metal workpiece is thereafter brought into contact, without any intervening pro- cess step, with a liquid phosphate conversion composition. (Hereinafter, any liquid composition is usually briefly denoted as a "bath". This term is not to be understood as necessarily implying that the bath must be brought into contact with the metal surface that is being degreased with it by immersion of the metal surface in the bath.) A bath for alkaline degreasing of metals according to this invention: - comprises, preferably consists essentially of, or more preferably consists of, water and:

0.5 to 8 grams of polyoxyethylene alkyl ether with an HLB of 12 to 17 per liter of bath (the concentration unit of "grams per liter" being hereinafter usually abbreviated as "g/l"); and -- at least one alkali metal salt or ammonium salt; contains 1 to 15 points of total alkalinity; and has a pH value in a range from 8 to 13.

The invention also relates to a method for the degreasing and conversion treatment of metals that is characterized by effecting contact between a metal and the afore- said alkaline degreasing bath and then, without the execution of a water rinse, effecting contact between the metal and a phosphate conversion bath in order to form a phosphate coating on the metal.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

An alkaline degreasing bath according to the present invention preferably contains dispersed solid particles, having a size no greater than 5 micrometres

(hereinafter usually abbreviated as "μm") and comprising at least one selection from the salts formed between phosphoric acid and divalent or trivalent metals. In an even more preferred embodiment, the subject alkaline degreasing bath contains from 0.01 to 30 g/l of the aforesaid phosphate salts that contain divalent or trivalent metal ions selected from Zn²\ Ni²⁺, Mn²⁺, Co²⁺, Fe²⁺, Ca²⁺, Al³⁺, and Fe³⁺. In another preferred embodiment, the alkaline degreasing bath contains from 0.001 to 5 g/l (as titanium) of titanium colloid.

The surfactant used by the present invention should have an excellent emulsifying capacity and should also not inhibit the conversion performance when carried over into the phosphate conversion bath in the ensuing step. In order to solve the endocrine problem focused on as an environmental problem, the surfactant should be completely free of the polyoxyalkylene alkylphenyl ether-type nonionic surfactants (e.g., polyoxyethylene nonylphenyl ether) heretofore widely used in alkaline degreasing baths.

The surfactant used in the present invention must be a polyoxyethylene alkyl ether with an HLB from 12 to 17. The HLB is determined by the number of moles of addition for the polyoxyethylene and by the number of carbons in the alkyl group. It has been discovered that this type of surfactant, while having a strong emulsifying and dispersing activity for oil, exhibits less adsorption strength for the surface of the metal workpiece than other types of nonionic surfactants.

The HLB value is governed by the balance between the hydrophiiic moiety and the lipophilic moiety, that is, between the number of moles of addition for the polyoxyethylene and the number of carbons in the alkyl group. Since the invention requires an HLB value within a specific range, the number of carbons in the alkyl group is preferably from 6 to 20 and more preferably is from 8 to 12. The subject polyoxyethylene alkyl ether can be specifically exemplified by polyoxyethylene hexyi ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene undecyl ether, and polyoxyethylene dodecyl ether. These may be used individually or as combinations of two or more selections. Along with the above-specified polyoxyethylene alkyl ether, polyoxyethylene alkyl ether having less than six carbons in the alkyl group, e.g., polyoxyethylene propyl ether or polyoxyethylene butyl ether, may be present as long as the overall HLB is within the specified range.

As specified above, the HLB of the polyoxyethylene alkyl ether must be from 12 to 17. An HLB below 12 results in a poor emulsifying and dispersing capacity and hence in a reduced degreasing performance. An HLB above 17 results in a high adsorption strength for the metal surface, which negatively affects the etching reaction during phos- phate conversion treatment and results in uneven coating deposition.

The polyoxyethylene alkyl ether concentration must be adjusted into the range from 0.5 to 8 g/l in order to maintain a good degreasing performance by the alkaline degreasing bath. The preferred range for the polyoxyethylene alkyl ether concentration is from 1 to 7 g/l. A good degreasing performance cannot be secured at a concentration below 0.5 g/l. Concentrations in excess of 8 g/l are uneconomical first of all because the degreasing performance of the treatment bath no longer improves at such concentrations. Moreover, such high concentrations impose a large treatment load on waste water treatment.

The polyoxyethylene alkyl ethers employed by the present invention are biodegradable and thus are excellent surfactants from an environmental standpoint. The alkali metal salt or ammonium salt constituting the second component in the alkaline degreasing bath according to the present invention may be any such salt ordinarily used for alkaline degreasing agents. This salt has at least one of the following functions:

1 ) it reduces the surface tension of the oil adhering on the workpiece (metal) and thereby increases the surface activity of the surfactant;

2) it functions to induce a microscopic emulsification and dispersion of the oil and thereby facilitates uptake of the oil in micelles;

3) it inhibits redeposition on the workpiece by dispersing the oil particles;

4) it chelates polyvalent cation components such as calcium and magnesium and thereby prevents insolubilization of the surfactant; and

5) it maintains alkalinity, resulting in solubilization (saponification) of the oil when the oil is a fatty species.

Any alkali metal salt or ammonium salt that exhibits at least one of the functions listed above, such as the corresponding orthophosphates (including the hydrogen ortho- phosphates), carbonates, bicarbonates, sulfates (including the bisulfates), borates, and nitrites, can be used. The alkali metal salts can be exemplified by the sodium, potassium, and lithium salts. Highly suitable specific examples of the subject alkali metal and ammonium salts are sodium (or potassium or ammonium) phosphate, disodium (or dipo- tassium ordiammonium) hydrogen phosphate, sodium (or potassium or ammonium) car- bonate, sodium (or potassium or ammonium) bicarbonate, sodium (or potassium or ammonium) sulfate, sodium (or potassium or ammonium) borate, and sodium (or potassium or ammonium) nitrite.

The alkali metal or ammonium salt can be used in combination with another salt that exhibits the same functionality as the alkali metal and ammonium salts. These other salts can be exemplified by the alkali metal condensed phosphates (e.g., alkali metal metaphosphates and alkali metal pyrophosphates such as sodium diphosphate and sodium triphosphate) and alkali metal silicates (e.g., sodium silicates). This other salt should be used in an amount that will not impair conversion when the salt is carried over into the phosphate conversion bath. In specific terms, the total concentration of the alkali metal condensed phosphate and alkali metal silicate in the alkaline degreasing bath according to the present invention is preferably from 0 to 5 g/l and more preferably is from 0 to 3 g/l.

With respect to the concentration of the alkali metal or ammonium salt, the pH of the alkaline degreasing bath according to the present invention must be adjusted into the range from 8 to 13 and the total alkalinity must be adjusted to 1 to 15 points. When the water rinse is to be entirely omitted after alkaline degreasing, the total alkalinity is preferably from 1 to 13 points and more preferably is from 2 to 10 points. A satisfactory degreasing performance cannot be obtained at a pH below 8 or a total alkalinity below 1 point. At a pH in excess of 13 or a total alkalinity in excess of 15 points, the stability of the acidic phosphate conversion bath will be impaired when the alkaline degreasing bath is carried over into the ensuing phosphate conversion bath. This can prevent the formation of good-quality phosphate coatings, thereby making a pH above 13 or a total alkalinity above 15 points undesirable.

As used herein, the total alkalinity of the alkaline degreasing bath refers to the number of milliliters (hereinafter usually abbreviated as "ml") of titrant required to change the color from blue to yellow when a 10 ml sample of the alkaline degreasing bath is titrated to neutrality with 0.1 N aqueous sulfuric acid using bromphenol blue as the indicator. For example, a total alkalinity of 1 point indicates that 1 ml of titrant was consumed in the titration.

The water making up the third component in the alkaline degreasing bath accord- ing to the present invention can be, for example, pure water, deionized water, or tap water.

When the phosphate conversion coating formed after alkaline degreasing is to be used as an underpaint coating, the deposition is desired of a uniform, fine, and dense thin phosphate coating with a mass per unit area, commonly called in the art and hereinafter "coating weight", of about 2 to 5 grams per square meter, hereinafter usually abbreviated as "g/m²". In the past this has generally required that formation of phosphate conversion underpaint coatings be preceded by a surface conditioning treatment using a surface conditioning agent. However, it has been discovered that both a degreasing and a surface conditioning activity can be satisfactorily manifested when a surface conditioning agent is added to the alkaline degreasing bath according to the present invention. This surface conditioning agent can be a powder with a particle size no greater than 5 μm comprising at least one selection from the divalent and trivalent metal phosphates. The divalent or trivalent metal ions are preferably at least one selection from zinc ions (Zn²⁺), nickel (II) ions (Ni²⁺), manganese (II) ions (Mn²⁺), cobalt (II) ions (Co²⁺), iron (II) ions (Fe²⁺), calcium ions (Ca²⁺), aluminum ions (Al³⁺), and iron (III) ions (Fe³⁺). The subject divalent and trivalent metal phosphates can be specifically exemplified by Zn₃(PO₄)₂, Zn₂Fe(PO₄)₂, Zn₂Ni(PO₄)₂, Ni₃(PO₄)₂, Zn₂Mn(PO₄)₂, Mn₃(PO₄)₂, Mn₂Fe(PO₄)₂, Ca₃(PO₄)₂, Zn₂Ca(PO₄)₂, Co₃(PO₄)₂, AIPO₄, FePO₄, and their hydrates.

The lower limit for the particle size is not critical and smaller particle sizes can generally be thought of as more desirable. However, the lower limit in terms of actually acquirable particle sizes, based on such factors as production technology and ease of acquisition, is thought to be around 0.1 μm.

A titanium colloid can also be used as the surface conditioning agent.

When a surface conditioning agent is in fact used in the alkaline degreasing bath according to the present invention, its concentration when it is at least one divalent or trivalent metal phosphate preferably is in the range from 0.01 to 30 g/l, is more preferably from 0.03 to 20 g/l, and still more preferably is from 0.05 to 10 g/l. When the surface conditioning agent is titanium colloid, its concentration, expressed as titanium, preferably is in the range from 0.001 to 5 g/l, more preferably is from 0.005 to 3 g/l and still more preferably is from 0.05 to 3 g/l. For both types of surface conditioning agent, surface conditioning activity will not usually appear and a uniform, fine, and dense phosphate conversion coating will not usually be formed at a concentration below the specified lower limits. Again for both types of surface conditioning agent, exceeding the specified upper concentration limits is uneconomical because it provides no additional surface conditioning activity from contact between the metal and the surface conditioning agent- containing alkaline degreasing bath.

An excellent surface conditioning activity can be obtained in the presence of the polyoxyethylene alkyl ether used in the alkaline degreasing bath according to the present invention. It is believed, without limiting the invention to any theory, that this occurs be- cause the specified polyoxyethylene alkyl ether adsorbs only weakly to the metal surface and the component active for surface conditioning is therefore able to adsorb out from regions where degreasing has been completed even when the surface conditioning agent is used in the presence of the polyoxyethylene alkyl ether.

In addition to the already described components, the alkaline degreasing bath ac- cording to the present invention can contain auxiliary additives that enhance the cleaning activity. For example, the alkaline degreasing bath can contain an aminocarboxylic acid- type chelating agent, a hydroxycarboxylic acid-type chelating agent, or a phosphonic acid-type chelating agent added for the purpose of chelating the cationic components (Ca²⁺, Mg²⁺, etc.) in the process water and the components of the metal workpiece (Zn²⁺, Al³⁺, etc.) that elute into the alkaline degreasing bath. These chelating agents can be ex-

5 emplified by ethylenediaminetetraacetate (sodium salt, etc.), citrate (sodium salt, etc.), gluconate (sodium salt, etc.), and 2-phosphonobutane-1 ,2,4-tricarboxylic acid. A cellulose derivative such as carboxymethylcellulose, hydroxypropylmethylcellulose, or hydroxybutylmethylcellulose can be added in order to inhibit redeposition on the metal workpiece of oil that has already been desorbed by, for example, the action of the 0 surfactant. While the auxiliary additive — when used — must be used at a concentration that will not produce problems even when it is carried over into the ensuing phosphate conversion bath, the amount of additive addition is not otherwise critical insofar as a normal phosphate coating is formed. The concentration of the chelating agent in the alkaline degreasing bath according to the present invention in general will preferably be s no greater than 1 g/l and more preferably will be from 0.01 to 1 g/l. When carry over into the ensuing phosphate conversion bath is taken into consideration, an even more preferred chelating agent concentration is from 0.01 to 0.5 g/l. The concentration of the cellulose derivative is preferably no greater than 3 g/i and more preferably is from 0.01 to 3 g/l. When carry over into the ensuing phosphate conversion bath is taken into consid- o eration, the concentration of the cellulose derivative is even more preferably from 0.01 to 1 g/l.

Alkaline degreasing baths typically contain a defoamer in order to inhibit the negative effects that can arise due to foaming during the cleaning operation, and the alkaline degreasing bath according to the present invention can also contain a defoamer. 5 This defoamer can as a general rule be selected as appropriate from the defoamers in common use.

The alkaline degreasing bath according to the present invention can be built up by the dissolution or dispersion in water of the polyoxyethylene alkyl ether with HLB of 12 - 17, the at least one selection from alkali metal salts and ammonium salts, the o optional surface conditioning agent (titanium colloid or particles with a size no greater than 5 μm comprising at least one selection from the divalent and trivalent metal phosphates, and the other optional components, e.g., alkali metal condensed phosphates, alkali metal silicates, auxiliary additives, and defoamers. Mixing can be effected using, for example, a propeller-type stirrer. The total alkalinity and pH can be 5 adjusted as necessary using sodium hydroxide, aqueous ammonia, phosphoric acid, or suifuric acid. The alkaline degreasing bath according to the present invention can be used to degrease oil-contaminated metals. The metals which are submitted to phosphating typically bear an oil component left over from application in an upstream process, such as pressing or cutting. This oil contaminant can be specifically exemplified by machine oils, kerosene, light oils, cutting oils, turbine oils, rust-inhibiting oils, press oils, and spindle oils. There is no particular restriction on the amount of adhering oil contaminant, and iron powder and other contaminants can even be present in admixture with the oil.

Nor are there any particular restrictions on the type of metal with which the alkaline degreasing bath according to the present invention can be used. Applicable metals can be exemplified by various types of steels, such as steel sheet (e.g., cold-rolled and hot-rolled steel sheet) and zinc-plated steel sheet (e.g., hot-dip galvanized steel sheet, electrogalvanized steel sheet, and Al/Zn alloy-plated steel sheet), and by various types of aluminums, for example, aluminum sheet stock and aluminum alloys (e.g., JIS 2000 (Al-Cu-Mg), 5000 (Al-Mg), and 6000 (Al-Mg-Si) alloys). The shape of the metal is not critical.

The alkaline degreasing bath according to the present invention is preferably applied to the oil-contaminated metal surface by spraying or dipping for 30 to 600 seconds at a temperature from 30 to 70 °C.

The degreasing treatment — or the combination of the degreasing treatment and the surface conditioning treatment as described above — can be followed by phosphate conversion treatment without an intervening water rinse. This sequence demonstrates the advantages of the alkaline degreasing bath according to the present invention most clearly. In addition, alkaline degreasing can be carried out using the alkaline degreasing bath according to the present invention, a surface conditioning treatment can then be carried out without an intervening water rinse, and the workpiece can thereafter be submitted to phosphate conversion treatment again without an intervening water rinse. This sequence also demonstrates the advantages of the alkaline degreasing bath according to the present invention.

At the same time, however, the alkaline degreasing bath according to the present invention may be used without hindrance of any kind as a replacement for the alkaline degreasing bath in a prior-art alkaline degreasing treatment. Thus, the workpiece may be degreased with alkaline degreasing bath according to the present invention, then rinsed with water, and thereafter submitted to phosphate conversion treatment. Or the workpiece may be alkaline degreased, then rinsed with water, submitted to surface conditioning, and thereafter submitted to phosphate conversion treatment without an intervening water rinse. The invention also relates to a method for using the alkaline degreasing bath according to the present invention. More specifically, the present invention relates to a method for the degreasing and conversion treatment of metals that is characterized by effecting contact between a metal and an alkaline degreasing bath according to the present invention as described hereinabove and then, without the execution of a water rinse, effecting contact between the metal and a phosphate conversion bath in order to form a phosphate coating on the metal.

The method and conditions for effecting contact between the metal and the alkaline degreasing bath are the same as described above. The invention makes possi- ble the execution of phosphate conversion treatment after alkaline degreasing without an intervening water rinse.

This phosphate conversion treatment can in general be run using the known or usual phosphate conversion baths and treatment conditions (conversion conditions). This notwithstanding, zinc phosphate conversion baths are a preferred example of the phosphate conversion bath used in the method according to the invention. An even more preferred example is a zinc phosphate conversion bath that essentially contains 0.5 to 20 g/l zinc ion, 10 to 50 g/l phosphate ion, and water and that has a free acidity of 0.5 to 15 points. In the particular case of use as an underpaint coating, and based on the required coating weight, a preferred phosphate conversion bath will contain 0.5 to 5 g/l zinc ion, 10 to 20 g/l phosphate ion, and water and will have a free acidity of 0.5 to 4.0 points. In the particular case of use as a lubrication undercoating or as an antirust coating, and again based on the required coating weight, a preferred phosphate conversion bath will contain 5 to 20 g/l zinc ion, 10 to 50 g/l phosphate ion, and water and will have a free acidity of 4.0 to 15 points and particularly 5.0 to 13 points. The zinc ion source for these baths should be a zinc compound capable of dissolving in aqueous phosphoric acid solutions, for example, zinc oxide, zinc phosphate, zinc nitrate, and so forth. The phosphate ion source can be exemplified by phosphoric acid (orthophosphoric acid).

The free acidity is a substitute value generally employed in place of the pH to indicate the acidity of phosphate conversion baths. The free acidity is used because the accurate and highly reproducible measurement of pH with a pH meter (glass electrode) is quite difficult at low pH values on the order of 2 to 3. The free acidity is measured by taking a 10 milliliter sample of the phosphate conversion bath and titrating the sample to neutrality with 0.1 N aqueous sodium hydroxide using bromphenol blue as the indicator. The free acidity is the number of milliliters of titrant required to change the color from yellow to blue. For example, a free acidity of 1 point indicates that 1 ml of titrant was consumed in the titration.

Regardless of the particular application, the phosphate conversion bath used in the method according to the present invention can contain a conversion accelerant in order to raise the etching capacity of the acid and accelerate the conversion reactions, an etching auxiliary that destroys the oxide film on the metal surface and thereby assists the etching reaction, and other metal ions added for the purpose of improving the coating's adherence and chemical stability with respect to acid and alkali.

The conversion accelerant can be exemplified by nitrite ions (supplied by, for example, sodium nitrite), hydroxylammonium ions (supplied by, for example, hydroxyl- ammonium sulfate), chlorate ions (supplied by, for example, sodium chlorate), nitroben- zenesuifonate ions (supplied by, for example, sodium nitrobenzenesulfonate), hydrogen peroxide, and organoperoxide (such as ethyl hydroperoxide and isopropyl hydroperoxide according to Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 8-302477 (302,477/1996)). When present, the preferred concentration for the con- version accelerant will generally be from 0.05 to 2.0 g/l.

The etching auxiliary can be exemplified by the fluoride and fluorosiiicate ions. These can be furnished to the phosphate conversion bath as, for example, the sodium salt, ammonium salt, or free acid (hydrofluoric acid, fluorosilicic acid). When present, the preferred concentration for the etching auxiliary is from 0.1 to 2.0 g/l. The other metal ions can be, for example, nickel ions (Ni²⁺), copper ions (Cu²⁺), or cobalt ions (Co²⁺), which function mainly to improve the adherence of the coating, and/or manganese ions (Mn²⁺), magnesium ions (Mg²⁺), or calcium ions (Ca²⁺), which function mainly to improve the chemical stability of the coating (acid resistance, alkali resistance). These ions can be furnished to the phosphate conversion bath as, for examp- le, the nitrate or phosphate. When present, the copper ions concentration is preferably from 5 to 50 mg/l, while the concentrations for the other metal ions are preferably from 0.1 to 3.0 g/l.

No specific restrictions apply to the procedure for preparing the phosphate conversion bath used in the method according to the present invention. The bath can ordi- narily be prepared by simply dissolving the phosphate ions source, zinc ions source, and optional conversion accelerant, etching auxiliary, and/or other metal ions in water in amounts that will provide the prescribed concentrations.

After its preparation the phosphate conversion bath is applied to metal that has already been treated with the alkaline degreasing bath according to the present invention but which has not been subjected to a water rinse.

Spraying or dipping is preferably used to treat the metal with the phosphate con- version bath.

The treatment temperature, treatment time, and coating weight will vary as a function of the particular application for the coating. When the phosphate conversion bath is used to form an underpaint coating, the deposition is preferred of a uniform, fine, and dense thin zinc phosphate coating with a coating weight of about 2 to 5 g/m². The temperature of the treatment bath during treatment in this case is preferably from 35 to 60 °C and the treatment time is preferably from 30 seconds to 10 minutes.

When the phosphate conversion bath is used to form a lubrication undercoating, the deposition is preferred of a thick zinc phosphate coating with a coating weight of about 5 to 20 g/m². The temperature of the treatment bath during treatment in this case is preferably from 60 to 90 °C and the treatment time is preferably from 30 seconds to 10 minutes.

Use of the degreasing and conversion treatment method according to the present invention can produce phosphate conversion coatings that have the same appearance and properties as the phosphate conversion coatings produced from the degreasing — water rinse — (surface conditioning) — conversion treatment process sequence heretofore used in the prior art.

After phosphate conversion treatment the metal is rinsed with water or hot water in order to remove entrained phosphate conversion bath. The metal may then be dried as necessary and thereafter painted when such is the objective, or the metal may then be treated with a reactive soap or coated with a solid lubricant when the objective is lubrication. When the objective is rust prevention, the metal is dried and generally used either without further treatment or after coating with an antirust oil.

Working and comparative examples of actual treatments are provided below in order to specifically elucidate the advantageous effects of the present invention. The working examples are simply applied examples of the invention, and the applications of the invention and materials used in the present invention are in no way limited by these working examples. 1. Test materials The treatments in the working and comparative examples were run on cold-rolled steel sheet (sheet thickness = 0.8 millimeter, hereinafter usually abbreviated as "mm", SPCC-SD), steel sheet hot-dip galvanized on both sides (Silver Alloy® from Shin-Nippon Seitetsu Kabushiki Kaisha, sheet thickness = 0.8 mm, plating weight 45 g/m², one side), and aluminum/magnesium alloy sheet (sheet thickness = 1.0 mm, according to Japanese Industrial Standard- A5052). Each of the test materials was coated with 2 g/m² of a commercial detergent antirust oil (NOX-RUST® 530-40 from Parker Kosan Kabushiki Kaisha). One hundred of the oil-coated sheets were assembled into a stack, tightened down at a torque force of 70 kilograms-force per centimeter with a torque wrench, and used after standing for 4 days in a humidity cabinet maintained at a temperature of 60 °C and a relative humidity of ≥ 95 %.

The compositions of the alkaline degreasing baths used in the working and comparative examples are reported in Table 1. 2. Test and evaluation methods 2.1 Coating weight

The weight of the treated sheet was first measured after conversion treatment to

10 give the value W1 (in grams). The coating was then stripped from the conversion- treated sheet (stripping bath and conditions given below) and the weight was again measured to give W2 (in grams). The coating weight was calculated from the following equation: coating weight (in g/m²) = (W1 - W2)/(surface area of the workpiece)

15 Stripping baths and stripping conditions:

(1 ) For the cold-rolled steel sheet:

Table 1

Table I is continued on the next page.

Notes for Table 1

1. The particle sizes shown were measured using a laser diffraction/scattering instrument for measuring particle size distributions, a Model LA-920 from Kabushiki Kaisha Horiba Seisakusho.

2. PREPALENE® ZN is a concentrate for preparing a conventional Jernstedt salt, titanium- containing surface conditioning component; it is a commercial product of Nihon Parkerizing Co., Ltd.

3. For this bath, the surfactant was a polyoxyethylene nonylphenyl ether instead of a polyoxyethylene alkyl ether.

4. Tap water constituted the balance not explicitly specified in the table for all of the alkaline degreasing baths.

stripping bath: 5 wt% aqueous chromic acid solution stripping conditions: 75 °C, 15 minutes, dipping

(2) For the steel sheet hot-dip galvanized on both sides: stripping bath: 2 wt% ammonium dichromate + 49 wt% of 28 wt% aqueous ammonia + 49 wt% pure water stripping conditions: ambient temperature, 15 minutes, dipping

(3) For the aluminum-magnesium alloy sheet: stripping bath: 5 wt% aqueous chromic acid solution stripping conditions: ambient temperature, 15 minutes, dipping

2.2 Substrate coverage performance

The deposited coating crystals were inspected at a magnification of 1 ,500X with a scanning electron microscope (SEM). Using the magnified image, coverage (presence/absence of exposed substrate) of the basis metal was evaluated on the following scale:

Evaluation scale: substrate exposure entirely absent = + (good) some substrate exposure = Δ (relatively poor) exposure of entire substrate = X (poor) 2_ Appearance

The appearance after conversion treatment was evaluated using the following scale:

Evaluation scale: uniform finish, absence of nonuniform conversion and conversion defects = + (good) nonuniform conversion and conversion defects present to some degree = Δ (relatively poor) nonuniform conversion and conversion defects present throughout = X (poor) 2Λ Size of the conversion coating crystals

This was determined at a magnification of 1 ,500X using a scanning electron microscope.

2.5 Degreasing performance by the alkaline degreasing bath

The test sample was brought into contact with the alkaline degreasing bath for the same time and at the same temperature as in the corresponding working or comparative example and was then immediately rinsed with water (spray, 30 seconds) and held vertically for 1 minute. Subsequent to this the degreasing performance was evaluated by visual inspection of the proportion of water-wetted surface area. Example 1

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: dipping for 120 seconds in alkaline degreasing bath 1 heated to 45 °C; then, without a water rinse, dipping for 5 minutes at 80 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 90 g/l in tap water of PARBOND® 181 X phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of a lubrication undercoating for plastic working. Example 2

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: spraying for 120 seconds with alkaline degreasing bath 2 heated to 35 °C; then, without a water rinse, dipping for 3 minutes at 80 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® 421 WD phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of a lubrication undercoating for plastic working. Example 3

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: dipping for 120 seconds in alkaline degreasing bath 3 heated to 50 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Example 4

The test sheet was prepared by execution of the following sequence using the steel sheet hot-dip galvanized on both sides: dipping for 120 seconds in alkaline degreasing bath 4 heated to 30 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Example 5

The test sheet was prepared by execution of the following sequence using the aluminum-magnesium alloy sheet: dipping for 60 seconds in alkaline degreasing bath 5 heated to 60 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by dissolution of the following in tap water: HF to give 100 mg/l and PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for underpaint coating formation to give 50 g/l. Example 6 The test sheet was prepared by execution of the following sequence using the cold-rolled steel sheet: dipping for 180 seconds in alkaline degreasing bath 6 heated to 35 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Example 7

The test sheet was prepared by execution of the following sequence using the cold-rolled steel sheet: dipping for 120 seconds in alkaline degreasing bath 5 heated to 40 °C; water rinse; dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Example 8

The test sheet was prepared by execution of the following sequence using the cold-rolled steel sheet: spraying for 90 seconds with alkaline degreasing bath 12 heated to 50 °C; then, without a water rinse, spraying for 2 minutes at 40 °C with the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate con- version bath used in this example was prepared by the dissolution to 45 g/l in tap water of PALBOND® L3150 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Example 9

The test sheet was prepared by execution of the following sequence using the cold-rolled steel sheet: spraying for 90 seconds with alkaline degreasing bath 13 heated to 40 °C; then, without a water rinse, spraying for 2 minutes at 40 °C with the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Comparative Example 1

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: dipping for 120 seconds in alkaline degreasing bath 7 heated to 45 °C; then, without a water rinse, dipping for 5 minutes at 80 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by the dissolution to 90 g/l in tap water of PARBOND® 181X phosphate conversion bath (from Nihon Parkerizing Co., Ltd.) intended for the formation of a lubrication undercoating for plastic working. Comparative Example 2

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: spraying for 120 seconds with alkaline degreasing bath 8 heated to 35 °C; then, without a water rinse, dipping for 5 minutes at 80 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by the dissolution to 50 g/l in tap water of PALBOND® 421 WD phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of a lubrication undercoating for plastic working. Comparative Example 3

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: dipping for 120 seconds in alkaline degreasing bath 9 heated to 40 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Comparative Example 4

The test sheet was prepared by execution of the following sequence using the steel sheet hot-dip galvanized on both sides: dipping for 120 seconds in alkaline degreasing bath 10 heated to 30 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Comparative Example 5

The test sheet was prepared by execution of the following sequence using the aluminum-magnesium alloy sheet: dipping for 120 seconds in alkaline degreasing bath 10 heated to 60 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by dissolution of the following in tap water: HF to give 100 mg/l and PALBOND® L3020 phosphate con- version bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for underpaint coating formation to give 50 g/l. Comparative Example 6

The test sheet was prepared using the cold-rolled steel sheet by execution of the following sequence: dipping for 120 seconds in alkaline degreasing bath 11 heated to 40 °C; then, without a water rinse, dipping for 2 minutes at 43 °C in the phosphate conversion bath (described below); water rinse; pure water rinse. The phosphate conversion bath used in this comparative example was prepared by the dissolution to 50 g/l in tap water of PALBOND® L3020 phosphate conversion bath concentrate (from Nihon Parkerizing Co., Ltd.) intended for the formation of an underpaint coating. Table 2 reports the properties of the conversion coatings produced in the Examples, while Table 3 reports the properties of the conversion coatings produced in the Comparative Examples.

Table 3

Examples 1 to 7 used alkaline degreasing baths according to the present invention and the degreasing and conversion treatment method according to the present invention. The results confirmed that an excellent degreasing performance and an excellent phosphate conversion performance were obtained in Examples 1 to 7 for each type of metal. A surface conditioning agent was present in Examples 3 to 7, and in these examples it was confirmed that both a degreasing activity and a surface conditioning activity could be produced without impairment of the surface conditioning activity.

Comparative Example 1 lacked both an alkali metal salt and an ammonium salt, while Comparative Example 2 employed a too low concentration of the polyoxyethylene alkyl ether. The degreasing performance was inadequate in both cases and uniform phosphate conversion coatings were not obtained as a consequence. The coating had a nonuniform appearance in Comparative Example 3 (HLB of the polyoxyethylene alkyl ether outside the prescribed range), Comparative Examples 4 and 5 (upper limit for poly- oxyethylene alkyl ether addition exceeded and concentration of the surface conditioning component too low), and Comparative Example 6 (use of polyoxyethylene nonylphenyl ether).

The alkaline degreasing bath according to the present invention and the method according to the present invention for the alkaline degreasing and conversion treatment of metals using said bath represent a groundbreaking technology that can omit the heretofore indispensable water rinse between the alkaline degreasing step and the phosphate conversion step. When the phosphate conversion treatment is employed to form an underpaint coating, the present invention offers the additional advantage of permitting the usual surface conditioning process to be run at the same time as alkaline degreasing.

The surfactant used by the present invention also has the highly desirable property from an environmental standpoint of being biodegradable.

Use of the technology according to the present invention can be expected to shorten the overall treatment sequence, save on space, improve the productivity, and reduce the load on waste water treatment.

Claims

1. An aqueous liquid composition for degreasing metals, wherein said aqueous liquid composition: comprises water and: -- 0.5 to 8 g/l of polyoxyethylene alkyl ether with an HLB of 12 to 17; and at least one alkali metal salt or ammonium salt; contains 1 to 15 points of total alkalinity; and has a pH value in a range from 8 to 13.

2. A composition according to claim 1 , additionally comprising dispersed solid particles of at least one salt formed between phosphoric acid and divalent or trivalent metal ions, said salt particles having a size no greater than 5 ╬╝m.

3. A composition according to claim 2, comprising a total from 0.01 to 30 g/l of dispersed solid particles of at least one salt selected from the phosphates of Zn²⁺, Ni²⁺, Mn²⁺, Co²⁺, Fe²⁺, Ca²⁺, Al³⁺, and Fe³⁺.

4. A composition according to claim 1 , additionally comprising from 0.001 to 5 g/l of titanium that is contained in at least one solid titanium salt dispersed in the composition as a colloid.

5. A composition according to claim 4, wherein: the polyoxyethylene alkyl ether comprises from 1 to 7 g/l of molecules that contain from 8 to 12 carbon atoms each; the content of alkali metal and ammonium salts includes at least one type of anions selected from the group consisting of orthophosphate, acid orthophos- phate, carbonates, acid carbonates, sulfates, acid sulfates, borates, and nitrites and includes not more than 3 g/l of salts selected from the group consisting of condensed phosphates and silicates; the total alkalinity is from 2 to 10 points; and there is a concentration of from 0.05 to 3 g/l of titanium that is contained in at least one solid titanium salt dispersed in the composition as a colloid.

6. A composition according to claim 3, wherein: - the polyoxyethylene alkyl ether comprises from 1 to 7 g/l of molecules that contain from 8 to 12 carbon atoms each; the content of alkali metal and ammonium salts includes at least one type of anions selected from the group consisting of orthophosphate, acid orthophosphate, carbonates, acid carbonates, sulfates, acid sulfates, borates, and nitrites and includes not more than 3 g/l of salts selected from the group consisting of condensed phosphates and silicates; the total alkalinity is from 2 to 10 points; and there is a concentration of from 0.05 to 10 g/l of dispersed solid particles of at least one phosphate salt of a divalent or trivalent metal.

7. A composition according to claim 2, wherein: the polyoxyethylene alkyl ether comprises from 1 to 7 g/l of molecules that contain from 8 to 12 carbon atoms each; the content of alkali metal and ammonium salts includes at least one type of anions selected from the group consisting of orthophosphate, acid orthophosphate, carbonates, acid carbonates, sulfates, acid sulfates, borates, and nitrites and includes not more than 3 g/l of salts selected from the group consisting of condensed phosphates and silicates; the total alkalinity is from 2 to 10 points; and - there is a concentration of from 0.05 to 10 g/l of dispersed solid particles of at least one phosphate salt of a divalent or trivalent metal.

8. A composition according to claim 1 , wherein: the polyoxyethylene alkyl ether comprises from 1 to 7 g/l of molecules that contain from 6 to 20 carbon atoms each; - the content of alkali metal and ammonium salts includes at least one type of anions selected from the group consisting of orthophosphate, acid orthophosphate, carbonates, acid carbonates, sulfates, acid sulfates, borates, and nitrites and includes not more than 3 g/l of salts selected from the group consisting of condensed phosphates and silicates; and - the total alkalinity is from 2 to 10 points.

9. A process for degreasing and conversion treatment of a metal surface, said process comprising operations of:

(I) effecting contact between the metal surface and an aqueous liquid degreasing composition according to any one of claims 1 through 8 during a first interval of time; and

(II) after completing operation (I), effecting contact for a second interval of time between the metal surface as treated in operation (I) and a phosphate conversion coating composition in order to form a phosphate coating on the metal surface.

10. A process according to claim 9, wherein, in operation (I): contact is effected by spraying or dipping; the first interval of time is from 30 to 60 seconds; and the aqueous liquid degreasing composition is maintained at a temperature within a range from 30 to 70 ┬░C during the contact.

11. A process according to claim 10, wherein the phosphate conversion coating composition used in operation (II) deposits a zinc phosphate conversion coating.

12. A process according to claim 9, wherein the phosphate conversion coating composition used in operation (II) deposits a zinc phosphate conversion coating.

13. A process according to any one of claims 10 through 12, wherein there is no intermediate rinsing with water between operations (I) and (II).

14. A process according to claim 9, wherein there is no intermediate rinsing with water between operations (I) and (II).