Process for the demulsifying cleaning of metallic surfaces

Abstract

The demulsifying cleaning of metallic surfaces which may be contaminated with oil(s) with at least one further nonpolar organic compound, with fat(s), with soap(s), with particulate dirt or with at least one anionic organic compound using an aqueous, alkaline, surfactant-containing bath solutions.

Claims

1. A process for demulsifying cleaning of metallic surfaces which are contaminated with a contaminant that is an oil, at least one further non-polar organic compound, a fat, a soap, particulate dirt or at least one anionic organic compound, the process comprising: providing an aqueous, alkaline, surfactant-containing bath; contacting the metallic surfaces with the aqueous, alkaline, surfactant-containing bath in at least one cleaning zone wherein the bath becomes contaminated with the contaminant; wherein the aqueous, alkaline, surfactant-containing bath comprises: at least one demulsifying surfactant comprising at least one nonionic surfactant based on ethoxylated alkyl alcohols having an end group cap and ethoxylated-propoxylated alkyl alcohols having an end group cap, and at least one cationic organic compound; wherein oil droplets having a radius of curvature are formed in the aqueous, alkaline, surfactant-containing bath and the aqueous, alkaline, surfactant-containing bath is kept in a demulsifying state even during increasing contamination with at least one anionic organic compound; wherein the content of the at least one demulsifying surfactant in the aqueous, alkaline, surfactant-containing bath ranges from 0.1 to 10 g/l; and wherein the at least one demulsifying surfactant is selected to adjust the radius of curvature of the oil droplets so that the oil in an agitated bath is partially emulsified and does not accumulate as an oil-containing phase on a surface of the agitated bath, and the oil spontaneously deposits and accumulates as an oil-containing phase on a surface of a quiescent bath.

2. The process according to claim 1, wherein the aqueous, alkaline, surfactant-containing bath has a content of the contaminant which is kept at not more than 3 g/l during continuous operation.

3. The process of claim 2, wherein the content of the contaminant in the aqueous, alkaline, surfactant-containing bath is no more than 1 g/l.

4. The process of claim 1, wherein in continuous operation there is not a membrane filtration process or unit.

5. The process of claim 1, wherein the at least one cationic organic compound has an end cap group selected from the group consisting of a methyl, ethyl, propyl, isopropyl, butyl, isobutyl and benzyl group.

6. The process of claim 5, wherein the end group of the at least one cationic organic compound is a benzyl group.

7. The process of claim 2, wherein the aqueous, alkaline, surfactant-containing bath has a content of the at least one demulsifying surfactant kept at or below 0.7 g/l.

8. The process of claim 1, wherein the aqueous, alkaline, surfactant-containing bath has a content of the contaminant which is kept in a range from 0.03 to 2 g/l, and the aqueous, alkaline, surfactant-containing bath has a content of the at least one demulsifying surfacing at or below 0.7 g/l.

9. The process of claim 1, wherein the ethoxylated alkyl alcohols having an end group cap and ethoxylated-propoxylated alkyl alcohols each comprise an alkyl group which is saturate or unsaturated, branched or unbranched, and optionally has an average number of carbon atoms in a range from 6 to 22 carbon atoms an average number of carbon atoms in the range of from 6 to 22 carbon atoms with in each case either a linear or a branched chain construction, wherein the alkyl group optionally contains one or more aromatic and/or phenolic groups, wherein the ethylene oxide chain optionally contains in each case on average 2 to 30 ethylene oxide units, wherein the propylene oxide chain optionally contains in each case on average 1 to 25 propylene oxide units.

10. The process of claim 1, wherein the at least one cationic organic compound is at least one of : a) an amphiphilic compound which contains at least one of one quaternary ammonium group and of at least one ring group having at least one nitrogen atom as a head group, wherein either the at least one nitrogen atom of the ring group or the ring group has at least one positive charge, and the at least one alkyl group independently of one another, saturated or unsaturated, in each case contains an average number of carbon atoms in the range of from 4 to 22 carbon atoms having in each case either a linear or a branched chain construction, wherein the alkyl group optionally independently of one another is saturated or unsaturated, branched or unbranched and in each case optionally contains one or more aromatic groups or is replaced by those, and wherein optionally at least one alkyl group optionally contains a different number of carbon atoms to at least one other alkyl group, and b) a cationic polymer which contains at least one quaternary ammonium group and at least four units of a monomer base unit.

11. The process of claim 1, wherein the bath further comprises at least one demulsifying surfactant selected from the group consisting of nonionic surfactants based on block copolymers which contain at least one polyethylene oxide block and at least one polypropylene oxide block, the polyethylene oxide block of which comprising an average number of 2 to 100 ethylene oxide units and the polypropylene oxide block of which comprising an average number of 2 to 100 propylene oxide units, wherein optionally independently of one another in each case one or more polyethylene oxide blocks or polypropylene oxide blocks are contained in the block copolymer.

12. The process of claim 1, wherein the bath further comprises at least one demulsifying surfactant selected from the group consisting of nonionic surfactants based on surfactants of ethoxylated or ethoxylated-propoxylated alkanoic acids, the alkyl group of which being saturated, unsaturated or cyclic, branched or unbranched and contains an average number of carbon atoms in the range of from 6 to 22 having in each case a linear or branched chain construction and the polyethylene oxide chain of which contains an average number of ethylene oxide units in the range of from 2 to 30 and/or the average number of propylene oxide units of which is in the range of from 1 to 25.

13. The process of claim 1, wherein the bath further contains at least one demulsifying surfactant chosen from the group consisting of nonionic surfactants based on ethoxylated alkylamines, the alkyl group of which, saturated or unsaturated, contains an average number of carbon atoms in the range of from 6 to 22, having in each case a linear or branched chain construction, and the polyethylene oxide chain of which contains an average number of ethylene oxide units in the range of from 3 to 30 and/or the average number of propylene oxide units of which is in the range of from 1 to 25.

Description

EXAMPLES ACCORDING TO THE INVENTION AND COMPARATIVE EXAMPLES

(1) The invention is described in more detail hereinafter with the aid of selected examples of implementation, without however being restricted to the latter.

(2) In a phosphating plant with a downstream lacquering/paint shop for large format components, the cleaning zones upstream of the phosphating consist of two zones, namely: 1. alkaline dip-degreasing and 2. alkaline spray degreasing. Substantially the same aqueous composition is used in both degreasing baths.

(3) Before changing over to a process according to the invention, in these baths under continuous operation over three to seven weeks contents of oil(s) including further contaminants of more than 3 g/l were established per bath, in particular in the bath used for dip degreasing, in which connection these contents could often be as high as up to 10 g/l. Although cleaner framework and surfactants had been added to the bathe over this period, the baths were not completely replenished. This subsequent addition was necessary on account of the discharge of cleaning components from the baths. With oil contents of the order of magnitude of about 5 g/l of oil(s) including further contaminants, the cleaning performance gradually fell and led to an insufficient degreasing and uneven formation of the subsequently applied phosphate layer. The required high paint quality could therefore no longer be achieved with the necessary degree of certainty. The cleaning baths did not contain any additions of demulsifying surfactants that had been intentionally added and had not possibly originated from the contamination of the baths.

(4) By virtue of the changeover of the operating mode of the cleaning zones to bath compositions to which, after the establishment of a content of oil(s) including further contaminants such as for example fats, greases, further non-polar organic contaminants and/or anionic organic compounds in the bath in the range from 2.5 to 4 g/l of oil(s) including the further contaminants, at least one cationic demulsifying surfactant was added, the respective bath service life could, depending on the operating conditions, be doubled and in some cases even at least quadrupled, before the whole bath was replaced and thus renewed. Because of the addition of the at least one demulsifying surfactant the oil, including the further contaminants, had for the most part accumulated on the surface of the bath as an oil-rich phase including fats, greases and further non-polar organic contaminants. The oil-rich phase contained only 2 to 30 wt. % of aqueous phase including builders and surfactants and also 70 to 98 wt. % in the essential oil(s) and further constituents of the oil-containing phase. The oil-rich phase could then be skimmed off for example after one day. After the oil-rich phase had been skimmed off the bath still contained about 0.5 to 1 g/l of oil(s) including the further contaminants. In this connection, after the separation of the oil-rich phase the at least one anionic and/or non-ionic surfactant principally contained in the bath composition had to be replenished, since these surfactants had to some extent been removed with the oil-rich phase. In this connection the at least one cationic demulsifying surfactant was not replenished immediately, but only when the contents of oil(s) including further contaminants in the bath had readjusted to levels of 2.5 to 4 g/l after several weeks. This surfactant had been specially selected corresponding to the conditions for the demulsifying procedure.

(5) In this unit neither the process parameters of the cleaning zones nor the concentrations of the cleaning compositions that had basically also been used up to this point had to be significantly altered.

(6) In this connection it was also possible to renew the second degreasing bath only after a longer utilisation time (for example after 6 months) than the first degreasing bath (for example after 4 months), which captures the contaminants significantly more strongly than the second degreasing bath.

(7) Thanks to the procedure according to the invention the surfactant concentration of the cleaning baths no longer had to be increased in the case of very high contents of oil(s) and/or further contaminants, and the consumption of chemicals thus fell slightly, but above all because of the renewal of the baths at significantly longer intervals. Since the changeover of the operating procedure of the cleaning baths the phosphating and lacquering/painting no longer exhibited defects that could be attributed to the cleaning. The waste disposal costs of the cleaning baths were dramatically reduced since the waste disposal cycles were significantly extended and highly contaminated cleaning bathe no longer had to be disposed of. Also, the amount of reworking and finishing-off necessary after at least one painting operation, for example involving sanding by hand and in many cases also followed by renewed phosphating and painting, was thereby significantly reduced, which likewise helps to lower high process costs.