EP0630427B1

EP0630427B1 - Composition and process for cleaning tinplate stock

Info

Publication number: EP0630427B1
Application number: EP93907235A
Authority: EP
Inventors: Masayuki Yoshida; Tomoyuki Aoki
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1992-03-13
Filing date: 1993-03-11
Publication date: 1996-10-09
Anticipated expiration: 2013-03-11
Also published as: JPH05255875A; JP3199824B2; EP0630427A1; WO1993018205A1; ZA931801B; KR930019866A; DE69305329D1; DE69305329T2; CN1082120A; CN1038952C; KR100254533B1

Abstract

Tinplate stock is cleaned with a cleaning bath that has a pH of 8 to 11 and that consists of water; 0.5 to 10.0 g/L of alkali builder comprising one or more selections from the alkali metal hydroxides, alkali metal and ammonium salts of inorganic phosphoric acid, alkali metal borates, alkali metal silicates, and alkali metal and ammonium carbonates; 0.05 to 1.0 g/L of chelating agent comprising one or more selections from the hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acids, and the alkali metal and ammonium salts of the preceding; and 0.05 to 2.0 g/L of surfactant. The use of this bath composition allows continuous cleaning in which the production of Sn sludge is inhibited and the amount of sludge produced by wastewater treatment is reduced substantially.

Description

Technical Field

The present invention relates to a liquid composition, generally denoted for brevity hereinafter as a "bath" or more specifically as a "tinplate-cleaning bath", that is used to clean the surface of tinplate (i.e., tin plated steel), especially in the form of sheet, strip, and products made by shaping them, e.g., cans and other containers and the like. These various forms of tinplate are collectively known as tinplate stock. The present invention also relates to a process for cleaning tinplate stock. In particular, the present invention is excellently suited for cleaning "DI" tinplate cans that are fabricated by the drawing and ironing of tinplate sheet and strip.
More particularly, the present invention relates to a novel tinplate-cleaning bath and process that, when applied to the surface of tinplate, results in the removal of organic materials (e.g., oil, lubricants, etc.) and inorganic materials (e.g., abrasives, etc.) and the generation of a surface condition that is well adapted for conversion treatment. Moreover, this novel tinplate-cleaning bath and process are strongly resistant to the deposition of the sludge that is caused by the insolubilization of tin eluted by cleaning into the bath from the surface of the tinplate stock.

Background Art

The prior art for tinplate-cleaning baths is exemplified by Japanese Patent Publication [Kokoku] Number Sho 59-2752 [2,752/1984] and Japanese Patent Application Laid Open [Kokai or Unexamined] Numbers Hei 3-59993 [59,993/1991] and Hei 3-59994 [59,994/1991].
The alkaline cleaning bath of Japanese Patent Publication Number Sho 59-2752 contains alkali metal silicate, alkali metal salt and alkali metal bicarbonate at ≤ 1.5-fold (weight basis) of the amount of alkali metal silicate, and surfactant at ≤ 0.4-fold (weight basis) of the amount of alkali metal silicate. This particular alkali component (known as builder) is specified in order to inhibit excessive dissolution of the tinplate surface due to line stoppage caused by problems in the degreasing line.
As for the bath discussed above, the alkaline cleaning bath of Japanese Patent Application Laid Open Number Hei 3-59993 is intended to inhibit excess dissolution of the tinplate surface. This bath is an aqueous solution that contains 1.5 to 10 grams per liter (hereinafter often abbreviated "g/L") of alkali metal or ammonium salt of orthophosphoric acid and 0.5 to 2 g/L of alkali metal nitrite. These two components are used in a molar ratio (former : latter) of 1 : 1 to 3.86 : 1. Bath pH is regulated to 9 to 11 with alkali metal carbonate.
Again as for the baths discussed above, the alkaline cleaning bath of Japanese Patent Application Laid Open Number Hei 3-59994 is intended to inhibit excess dissolution of the tinplate surface. This bath is an alkaline aqueous solution with pH 9 to 13 that contains surfactant, alkali metal or ammonium salt of orthophosphoric acid, and at least 0.005 g/L of at least 1 selection from the group comprising the alkaline earth metal oxides, hydroxides, chlorides, bromides, iodides, carbonates, nitrates, sulfates, and phosphates. This bath does not contain organic acid nor the salts of organic acids.
Tinplate stock is typically cleaned by spraying. For example, the equipment for treating the surface of tinplate DI can is generally known as a washer. The formed DI can is continuously treated - while inverted - with the cleaning bath and conversion bath. Existing washers are organized into 6 stations (preliminary cleaning, cleaning, water wash, conversion treatment, water wash, and de-ionized water wash), and all the steps are executed by spraying. The alkaline cleaning bath is sprayed onto a plural number of DI cans in the preliminary cleaning and cleaning steps, and is then recycled to a tank and returned to the spray.
The alkaline cleaning bath of Japanese Patent Publication Number Sho 59-2752 initially has a good cleaning performance when actually used in a washer, but silicate salts gradually precipitate and sediment from this cleaning bath. A satisfactory cleaning operation is ultimately precluded because this precipitate - a solid generally known as sludge - clogs the pipe system and nozzles in the spray equipment.
Japanese Patent Application Laid Open Number Hei 3-59993 teaches that the presence of condensed phosphate salts in alkaline cleaning baths causes an increase in metal solubilization and a deterioration in corrosion resistance both for unpainted and painted tinplate stock. While the omission of condensed phosphate salts from this bath does result in the inhibition of tin dissolution, moderate amounts of dissolved tin still precipitate as, for example, tin phosphate. This results in the production of sludge and thus the appearance of the same problem as outlined above.
An excellent cleaning performance is initially obtained for the use of the alkaline earth metal oxides, hydroxides, and chlorides in the case of the alkaline cleaning bath of Japanese Patent Application Laid Open Number Hei 3-59994. However, the tin gradually eluting from the tinplate stock reacts with phosphoric acid or carbonic acid present in the cleaning bath. This results in the precipitation and sedimentation of phosphate or carbonate salts with the appearance of sludge.
EP-A-0 206 222 discloses a cleaning agent for tin-plated iron materials in a concentration of 1-30 g/l and a pH of 10.5-13, comprising 0.5 to 25 parts by weight alkali silicate, 0.1-3 parts by weight alkali phosphate, 0.1-3 parts by weight complexing agent, such as EDTA, and surfactants such as 0.05-1.5 parts by weight ethoxylated alcohols (nonionic) and such as 0.05-1.5 parts by weight chloride derivatives of polyethoxylated aliphatic alcohols (anionic). Spraying of the solution with a contact time of 30 to 60 s is disclosed.
The application of phosphonic acid derivatives as complexing or chelating agents and the selection of a pH above 8, preferably 9 to 12 can be derived from EP-A-0 111 284 and EP-A-0 124 815.
With regard to the sludge that is produced by continuous cleaning as described above, a portion will sediment in the liquid tank while another portion will clog the pipe system and nozzles of the spray equipment as the result of its circulation through the pipe system. Clogging of the pipe system and/or nozzles results in a poor cleaning performance due to a diminished quantity of spray on each DI can and nonuniform contact with the DI cans.
Moreover, in the case of the industrial use of alkaline cleaning baths, small quantities of the bath are continuously or intermittently drawn off in a method known as autodraining, and the bath is supplemented with fresh cleaning bath. The released cleaning bath is discharged through a wastewater treatment process. While the alkaline cleaning baths as described above do not require a particularly high level of wastewater treatment, their wastewater treatment nevertheless produces a solid product. Although this solid product is generally known as "sludge", for the purposes of this application it will be referred to as "wastewater treatment sludge" in order to differentiate it from the sludge already discussed above.
As a result of the high alkali concentration during the cleaning process in the prior alkaline cleaning baths, the corresponding wastewater treatment generates large overall quantities of wastewater treatment sludge that must be processed. This wastewater treatment sludge is currently disposed of as an industrial waste, but reductions in the quantity of wastewater treatment sludge would be desirable from the standpoints of reducing costs and environmental protection.

Disclosure of the Invention

Problems to Be Solved by the Invention

Thus, use of the prior alkaline cleaning baths is burdened by the requirement that the pipe system and nozzles of the spray equipment be cleaned on a frequent and regular basis. Since improvements in productivity in the cleaning of tinplate stock have recently become a critical issue, there is strong demand for the provision of a cleaning bath that lessens the burden of preventive cleaning, i.e., that does not lead to the development of sludge in the bath even when subjected to continuous use. In addition, permissible values for effluents have become increasingly stringent due to environmental considerations. As a result, reducing the load on wastewater treatment has become an important topic.

Summary of the Invention

In order to solve the problems described hereinbefore, a tinplate-cleaning bath was discovered that characteristically has a pH of 8 to 11 and comprises, preferably consists essentially of, or more preferably consists of: water; 0.5 to 10.0 g/L of alkali builder comprising one or more selections from the alkali metal hydroxides, alkali metal and ammonium salts of inorganic phosphoric acid, alkali metal borates, and alkali metal and ammonium carbonates; 0.05 to 1.0 g/L of chelating agent comprising one or more selections from the hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acids, and the alkali metal and ammonium salts of the preceding; and 0.05 to 2.0 g/L of surfactant. The present invention was achieved based on this discovery.
The tinplate-cleaning bath of the present invention removes organic materials (e.g., oil, lubricants, etc.) and inorganic materials (e.g., abrasives, etc.) from the surface of tinplate stock (sheet, strip, and moldings thereof such as can, etc.) and generates a surface condition that is well suited for conversion treatment. Moreover, the tinplate-cleaning bath of the present invention produces only vanishingly small quantities of the sludge that forms from the tin eluting into the cleaning bath and the hard water components present in the water used to make up the bath.
The cleaning bath of the present invention is excellently suited for cleaning DI cans. In this process, large numbers of DI cans may be continuously cleaned with the cleaning bath of the present invention - without the production of a hard water component/tin sludge - by conveying the tinplate-cleaning bath of the invention from a storage tank through a pipe system, then spraying the same from a nozzle onto the tinplate stock to be cleaned, returning the bath to said storage tank, and subsequently re-spraying the bath.
In other words, with regard to the cleaning of DI can using washers, the tinplate-cleaning process under consideration makes possible continuous and long-term cleaning without the production of the sludge that forms from tin eluting into the cleaning bath and hard water components present in the water used to make up the bath. Moreover, during this run, the tinplate-cleaning process of the present invention removes organic materials (e.g., oil, lubricants, etc.) and inorganic materials (e.g., abrasives, etc.) from the surface of tinplate stock (sheet, strip, and products therefrom such as can, etc.) and generates a surface condition that is strongly adapted for conversion treatment. Sludge production is evaluated by the following procedure: Liquid is withdrawn into a transparent container from the storage tank for the alkaline cleaning bath, and the transparency of the sample is then evaluated with the unaided eye. The process of the present invention makes possible a continuous sludge-free cleaning run under the usual continuous treatment conditions, i.e., cleaning temperature = ambient to 80° C, spray time = 2 to 60 seconds/can, bath renewal/discharge = 0.04 to 0.08%/1,000 cans.

Description of Preferred Embodiments

The composition of the alkaline cleaning bath of the present invention and the cleaning process of the present invention will be explained in greater detail below.
Among its various components, the alkaline cleaning bath of the present invention contains 0.05 to 10.0 g/L of an alkali builder comprising one or more selections from the alkali metal hydroxides, alkali metal and ammonium salts of inorganic phosphoric acid, alkali metal borates, alkali metal silicates, and alkali metal and ammonium carbonates. This component is designated as component A in the examples.
The alkaline cleaning bath of the present invention also contains 0.05 to 1.0 g/L of compound(s) comprising one or more selections from the hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acids, and the alkali metal and ammonium salts of these compounds. This component is designated as component B in the examples.
The alkaline cleaning bath of the present invention also contains 0.05 to 2.0 g/L of surfactant (designated as component C in the examples). Water is the balancing component, and this water can be industrial-grade water or tapwater as well as deionized, distilled, or other purified water. The tinplate-cleaning bath of the present invention should have a pH of 8 to 11.
The alkali metal salts comprising the alkali builder consist of the potassium and sodium hydroxides, carbonates, borates, and inorganic phosphates. Examples are potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, borax, trisodium phosphate, and so forth. These may be used singly or in combinations of two or more selections. The particular alkali builder concentration should be selected so as to provide a cleaning power (etching capacity) adapted to the surface condition of the tinplate stock. The alkali builder will generally be used at a concentration of from 0.5 to 10.0 g/L and is preferably used at a concentration of from 1.0 to 5.0 g/L. At a concentration below 0.5 g/L, cleaning will normally be unsatisfactory due to inadequate etching. While an excellent cleaning performance can be obtained at above 10.0 g/L, the use of such concentrations normally leads to an increase in the wastewater treatment sludge.
The chelating agent (hydroxyalkyldiphosphonic acid, aminotrialkylphosphonic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acid, and the alkali metal and ammonium salts of the preceding) is added in order to promote stable dispersion and/or solubility of the tin ions released from the tinplate stock in the cleaning bath. Thus, tin ion accumulates in the bath during the continuous cleaning of tinplate stock, and this tin ion reacts with phosphoric acid, silicic acid, or carbonic acid to produce sludge. The listed compounds are believed to chelate the tin ions and thereby inhibit the production of sludge (tin phosphate, etc.) in the cleaning bath. This inhibition of sludge production results in a substantial reduction in the work inputs for cleaning the pipe system and nozzles of the spray equipment.
In contrast to the preceding, the calcium and magnesium ions present as hard water components in tapwater do not accumulate in the cleaning bath and thus will not hamper the continuous process from this standpoint. Moreover, they will not be present in the sludge as, e.g., calcium carbonate, etc., because they are also chelated by the hydroxyalkyldiphosphonic acid, etc.
The hydroxyalkyldiphosphonic acid is exemplified by 1-hydroxyethylidene-1,1-diphosphonic acid, with the formula given below:
Aminotrialkylphosphonic acid is exemplified by aminotrimethylenephosphonic acid. Condensed phosphoric acid is exemplified by pyrophosphoric acid, tripolyphosphoric acid, and tetrapolyphosphoric acid. Hydroxyalkyldiphosphonic acid, aminotrialkylphosphonic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and condensed phosphoric acid can be used in the cleaning bath in acid form or as the alkali metal salt or ammonium salt. These compounds can be used singly or in combinations of two or more selections, and this component should be present at 0.05 to 1.0 g/L and preferably at 0.1 to 0.5 g/L. At less than 0.05 g/L, there will normally be a strong tendency for sludge to be produced in the cleaning bath because of an inadequate chelating capacity. Quantities in excess of 1.0 g/L do not cause any particular problems, but are less economical due to the associated increase in costs.
Ethylenediaminetetraacetic acid, nitrilotriacetic acid, and condensed phosphoric acids are refractory to wastewater treatment because they are only poorly sedimentable by slaked lime (calcium hydroxide). When the amenability to wastewater treatment becomes particularly critical as discussed above, the use of the hydroxyalkyldiphosphonic acids and their metal (ammonium) salts is recommended, since these species are very sedimentable by slaked lime. Moreover, inasmuch as the eutrophication of rivers, lakes, and marshes has recently become a serious problem, the use of condensed phosphoric acid-free cleaning agents has become correspondingly desirable. Finally, the effects of the present invention are not impaired by the supplemental addition of another type of chelating agent, for example, an organic acid such as gluconic acid as well as the alkali metal and ammonium salts of such organic acids.
A cleaning agent that leads readily to a wastewater that is free from phosphorus and nitrogen will be particularly useful in regions where wastewater regulations are particularly stringent. In such a case, the alkali builder for the present invention may be selected from the hydroxides, carbonates, and borates and the chelating agent may be selected from the hydroxyalkyldiphosphonic acids and aminotrialkylphosphonic acids. This can be managed to produce a wastewater that is free from phosphorus and nitrogen since the hydroxyalkyldiphosphonic acids and aminotrialkylphosphonic acids - while containing phosphorus and in the latter case also containing nitrogen - are easily sedimented with slaked lime as noted above.
Furthermore, because hydroxyalkyldiphosphonic acid, etc., has a cleaning activity, the cleaning bath of the present invention can employ alkali salt concentrations as low as ≤ 4 g/L, which is lower than that reported in experimental examples of the prior art. This reduction in the use quantity of alkali builder also makes possible a reduction in the quantity of wastewater treatment sludge produced during wastewater treatment.
The surfactant is selected from the anionic and nonionic surfactants. Nonionic surfactants are exemplified by hydrocarbon derivatives, abietic acid derivatives, ethoxylated primary alcohols, and modified polyethoxylated alcohols. In either case, the surfactant can be used in the form of a single species or as a combination of two or more species. It should be present at a concentration of from 0.05 to 2.0 g/L and preferably at a concentration of from 0.2 to 1.0 g/L. The organic material on the surface of the tinplate stock will sometimes not be completely removed when the surfactant is used at a concentration of less than 0.05 g/L. On the other hand, the use of more than 2.0 g/L surfactant is not associated with any particular problems in terms of cleaning effects, but rather is economically undesirable due to the higher cost.
The cleaning bath should have a pH in the range of 8 to 11 and preferably in the range of 9 to 10. At a pH below 8, the etching capacity is diminished and it becomes difficult if not impossible to obtain a good cleaning effect. Moreover, there is a strong tendency for sludge production to occur at a pH below 8. In contrast, etching is undesirably strong at pH values above 11, resulting in a deterioration in appearance. The pH can be adjusted using the usual alkalis and acids, i.e., sodium hydroxide, potassium hydroxide, sulfuric acid, phosphoric acid, and the like, and no specific restriction exist in this regard.
The cleaning bath of the present invention may be used at treatment temperatures ranging from ambient temperature to 80° C, but it is preferably heated generally to 40 to 60 ° C for use. The treatment time should be 2 to 60 seconds. A satisfactory cleaning effect is not usually obtained at below 2 seconds, while treatments in excess of 60 seconds do not usually result in any further improvement in cleaning effect. The treatment method may be either immersion or spray, but as discussed above the present invention produces particularly good effects when used with spray equipment.
For wastewater treatment of the tinplate-cleaning bath, the metal ion is first dissociated from the chelate compound in the acidic pH range. Solid-liquid separation is then carried out by the addition of calcium hydroxide and polymer flocculent to give the wastewater treatment sludge. Since the cleaning bath of the present invention has a low alkali concentration, it generates only small quantities of sludge for disposal. Moreover, the wastewater treatment efficiency is also good because the hydroxyalkyldiphosphonic acids and aminotrialkylphosphonic acids are highly sedimentable by calcium hydroxide and polymer flocculants.
As discussed hereinbefore, tin ions accumulate during the cleaning of tinplate stock, and it is estimated that the tin ion concentration in the cleaning bath is 0.01 to 0.1 g/L when sludge is produced. The sludge produced by its precipitation is very sticky and adheres to the interior of the nozzles and pipe system and thus impedes the cleaning operation. This adhesion problem can be avoided by inhibiting dissolution of the tinplate surface in order to prevent an increase in tin ion concentration. However, there are limitations on the application of this approach to large-scale cleaning runs. The present invention has therefore devised the use of a particular component, as described above, in addition to alkali builder and surfactant
As a result use of the cleaning bath of the present invention to clean the surface of tinplate stock (sheet, strip, and moldings) leads to a removal of both organic and inorganic materials from the surface of the tinplate stock and thereby provides a surface state that is very well adapted for conversion treatment. Moreover, this cleaning is accomplished with the precipitation of vanishingly small quantities of the sludge that is produced by tin eluting into the cleaning bath.

Examples

The cleaning bath of the present invention will be explained in greater detail below using illustrative examples. Its utility will be demonstrated with reference to comparison examples.

(1) Test material

The test material consisted of 1,000 uncleaned cans (66 mm diameter x 124 mm height) that had been fabricated by the drawing and ironing of tin-plated steel sheet. Cleaning was conducted in a conventional washer.

(2) Treatment process

Treatment was conducted in accordance with the following process [1] or process [2].

Process [1]

1. Cleaning
2. Water wash (10 seconds, spray)
3. Wash with deionized water (10 seconds, spray)
4. Drying (180° C, hot air)

Process [2]

1. Cleaning
2. Water wash (10 seconds, spray)
3. Conversion treatment (30 seconds, spray)
Treatment agent: PALFOS® K3482, registered brand name of Nihon Parkerizing Company, Limited concentration: 3 %, temperature: 60° C
4. Water wash (10 seconds, spray)
5. Wash with de-ionized water (10 seconds, spray)
6. Drying (180° C, hot air)

(3) Test methods for property evaluation

Water wettability

After completion of the wash with de-ionized water in step 3 of process [1], the can was allowed to stand for 30 seconds. The water-wetted surface area at this point was evaluated in %. Values of at least 90 % are generally considered to be excellent.

Degreasing performance

The degreasing performance was evaluated based on the quantity of residual oil on the surface. After treatment by process [1], the can was ultrasonically cleaned using carbon tetrachloride, and the oil fraction eluted into the carbon tetrachloride from the can surface was determined using an instrument for measuring the oil concentration (POC-100 from Kabushiki Kaisha Shimadzu Seisakusho). This value is reported as the residual quantity of oil per unit surface of the can. Values ≤ 2 mg/m² are generally considered excellent.

Corrosion resistance

After treatment by process [2], the corrosion resistance was evaluated using the iron exposure value (IEV). The IEV was measured based on United States Patent Number 4,332,646. Lower IEV values indicate a better corrosion resistance. Values ≤ 150 are generally considered excellent.

Paint adherence

In order to measure the paint adherence, the can was first treated by process [2], and the surface of the can was then coated with an epoxy/urea can paint to a paint film thickness of 5 to 7 micrometers. After baking for 4 minutes at 215° C, the can was cut into 5 x 150 mm strips, and the test specimen was prepared by hot-press bonding with polyamide film. This was peeled using the 180° peel test method in order to evaluate the peel strength. Larger peel strength values indicate a better paint adherence. Values ≥ 1.5 kgf/5 mm width are generally considered excellent.

Sludge production in the cleaning bath

The cleaning bath used in the particular example or comparison example was prepared without using the surfactant. 0.1 g/L of tin was added (using stannic chloride) to the cleaning bath thus prepared, and after this addition the pH was adjusted with potassium hydroxide. After standing for 1 day, the condition of the bath was inspected. In the preferred state, the bath was transparent and free of precipitate.

Wastewater treatability

The wastewater treatability was evaluated as follows. The treatment bath was first diluted 1/10, which is equivalent to the degree of dilution in the wastewater treatment of process baths in actual operations, and the pH of the resulting bath was brought to 2.5 with sulfuric acid. Aqueous aluminum sulfate solution was then added to give 20 ppm as aluminum, and the pH was subsequently brought to 10 with calcium hydroxide. 10 ppm of polymer flocculant was added and a solid-liquid separation was then carried out. The residual sludge (solids) was dried for 24 hours at 100° C, then cooled and weighed. The wastewater treatability was evaluated based on this weight, i.e., low quantities of sludge production are desirable.

Example 1

Cleaning was conducted at 50° C for 30 seconds using cleaning bath 1. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 1.

cleaning bath 1

sodium carbonate (A) 2.0 g/L

sodium bicarbonate (A) 2.0 g/L

sodium tripolyphosphate (B) 0.4 g/L

nonylphenol/11 EO adduct (C) 0.2 g/L

pH 9.6 (adjusted with sodium hydroxide)

Example 2

Cleaning was conducted at 50° C for 30 seconds using cleaning bath 2. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 2.

cleaning bath 2

potassium carbonate (A) 1.0 g/L

potassium bicarbonate (A) 2.0 g/L

1-hydroxyethylidene-1,1-diphosphonic acid (B) 0.2 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.3 g/L

pH 9.6 (adjusted with sodium hydroxide)

Example 3

Cleaning was conducted at 50° C for 30 seconds using cleaning bath 3. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 3.

cleaning bath 3

sodium carbonate (A) 2.0 g/L

sodium bicarbonate (A) 2.0 g/L

sodium ethylenediaminetetraacetate (B) 0.5 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.2 g/L

pH 10.0 (adjusted with sodium hydroxide)

Example 4

Cleaning was conducted at 50° C for 60 seconds using cleaning bath 4. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 4.

cleaning bath 4

sodium carbonate (A) 1.0 g/L

sodium bicarbonate (A) 2.0 g/L

1-hydroxyethylidene-1,1-diphosphonic acid (B) 0.3 g/L

nonylphenol/11 EO adduct (C) 0.2 g/L

pH 8.7 (adjusted with sulfuric acid)

Example 5

Cleaning was conducted at 40° C for 15 seconds using cleaning bath 5. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 5.

cleaning bath 5

sodium hydroxide (A) 0.3 g/L

disodium hydrogen phosphate (A) 1.0 g/L

1-hydroxyethylidene-1,1-diphosphonic acid (B) 0.3 g/L

nonylphenol/11 EO adduct (C) 0.4 g/L

pH 10.5 (adjusted with sodium hydroxide)

Example 6

Cleaning was conducted at 60° C for 60 seconds using cleaning bath 6. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 6.

cleaning bath 6

sodium carbonate	(A)	1.0 g/L
sodium bicarbonate	(A)	2.0 g/L
sodium tripolyphosphate	(B)	0.1 g/L
1-hydroxyethylidene-1,1-diphosphonic acid	(B)	0.3 g/L
higher alcohol/5 EO/10 PO adduct	(C)	0.4 g/L

pH 8.7 (adjusted with sulfuric acid)

Example 7

Cleaning was conducted at 30° C for 60 seconds using cleaning bath 7. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 7.

cleaning bath 7

sodium carbonate (A) 1.0 g/L

sodium bicarbonate (A) 2.0 g/L

borax (A) 1.0 g/L

1-hydroxyethylidene-1,1-diphosphonic acid (B) 0.3 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.4 g/L

pH 10.2 (adjusted with sodium hydroxide)

Comparison Example 1

Cleaning was conducted at 50° C for 30 seconds using cleaning bath 8. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 8.

cleaning bath 8

sodium carbonate (A) 1.0 g/L

sodium bicarbonate (A) 2.0 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.4 g/L

pH 9.6 (adjusted with sodium hydroxide)

Comparison Example 2

Cleaning was conducted at 50° C for 30 seconds using cleaning bath 9. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 9.

cleaning bath 9

potassium carbonate (A) 1.0 g/L

potassium bicarbonate (A) 2.0 g/L

1-hydroxyethylidene-1,1-diphosphonic acid (B) 0.2 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.4 g/L

pH 7.5 (adjusted with sulfuric acid)

Comparison Example 3

Cleaning was conducted at 60° C for 60 seconds using cleaning bath 10. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 10.

cleaning bath 10

sodium metasilicate (A) 2.5 g/L

sodium carbonate (A) 2.5 g/L

higher alcohol/5 EO/10 PO adduct (C) 0.3 g/L

pH 11.0 (adjusted with sodium hydroxide)

Comparison Example 4

Cleaning was carried out for 30 seconds at 50° C using the 1% cleaning bath of a commercial cleaning agent for tinplate DI can that contained alkali builder and surfactant as effective components (FINE CLEANER™ 4361A, registered brand name of Nihon Parkerizing Company, Limited). The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for this cleaning bath.
In all the descriptions of the specific cleaning baths above, "EO" means ethylene oxide, "PO" means propylene oxide, and the number preceding these symbols in the description of the adducts indicates the average number of moles of the indicated oxyalkylene groups in the adduct per mole of the alcohol or phenol first specified in the description.

The results are shown in Table 1.

TABLE 1

	Water Wettability, %	Degreasing Performance, mg/m ²	Corrosion Resistance, IEV	Adherence, kgf/5 mm	Sludge Production	Wastewater Treatability, grams
Ex. 1	100	1.5	100	3.0	transparent	0.8
Ex. 2	100	1.2	70	3.0	transparent	0.6
Ex. 3	100	1.6	100	3.0	transparent	0.8
Ex. 4	100	1.3	70	3.0	transparent	0.6
Ex. 5	100	1.4	70	3.0	transparent	0.6
Ex. 6	100	1.5	70	3.0	transparent	0.6
Ex. 7	100	1.5	70	3.0	transparent	0.6
Comp. Ex. 1	100	1.8	120	2.5	white turbidity, precipitation	0.9
Comp. Ex. 2	80	2.1	200	1.5	moderate turbidity	0.9
Comp. Ex. 3	100	1.7	120	2.5	white turbidity, precipitation	2.5
Comp. Ex. 4	100	1.5	100	3.0	moderate turbidity	2.0

Benefits of the Invention

As demonstrated by Table 1 (summary of examples and comparison examples), the present invention exhibits an excellent cleaning performance in the cleaning of tin-plated DI can as evaluated on the basis of the generally critical properties of water wettability, degreasing performance, corrosion resistance, and adherence. This cleaning performance is equivalent to that afforded by the prior art. However, the present invention is superior to the prior art with regard to sludge inhibition and wastewater treatability.
While the examples concern the cleaning of DI can, it is clear that the same performance will be obtained for other types of products formed from sheet and strip as well as for the starting tinplate sheet and strip. Thus, the present invention provides extremely good results in terms of increasing the efficiency in the cleaning of tinplate stock and reducing the load on wastewater treatment.

Claims

A liquid aqueous composition of matter suitable for cleaning tinplate stock, said composition having a pH value in the range from 8 to 11 and consisting essentially of water and:
(A) from 0.5 to 10.0 g/L of alkali builder component selected from the group consisting of alkali metal hydroxides, alkali metal and ammonium salts of inorganic phosphoric acid, alkali metal borates, alkali metal and ammonium carbonates, and mixtures of any two or more thereof;

(B) from 0.05 to 1.0 g/L of a chelating agent component selected from the group consisting of hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acids, the alkali metal and ammonium salts of these acids, and mixtures of any two or more thereof; and

(C) from 0.05 to 2.0 g/L of a surfactant component selected from the group consisting of nonionic and anionic surfactants.
A composition according to claim 1, wherein component (B) is selected from the group consisting of hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, their alkali metal and ammonium salts, and mixtures of any two or more thereof.
A composition according to claims 1 or 2, wherein the concentration of component (A) is in the range from 1.0 to 5.0 g/L.
A composition according to claims 1 to 3, wherein the concentration of component (B) is in the range from 0.1 to 0.5 g/L.
A composition according to any one of claim 1 to 4, wherein the concentration of component (C) is in the range from 0.2 to 1.0 g/L.
A composition according to claim 5, wherein the pH is in the range from 9 to 10.
A process for cleaning tinplate stock by contacting the tinplate stock for a time in the range from 2 to 60 seconds with a composition according to any one of claims 1 to 6.
A process according to claim 7 comprising steps of:
(1) conveying the cleaning composition from a storage tank through a pipe system;

(2) spraying the cleaning composition from the pipe system through a nozzle onto the tinplate stock to be cleaned;

(3) returning the cleaning composition that has contacted the tinplate stock to be cleaned during step (2) to said storage tank; and

(4) subsequently again conveying the cleaning composition from the storage tank through a pipe system and spraying the cleaning composition onto additional tinplate stock to be cleaned.
A process according to claim 8, wherein the cleaning composition is maintained within the temperature range of 40 to 60 ° C during step (2).