EP0817871B1 - Corrosion protective cleaning agent for tin-plated steel - Google Patents

Description

The invention is in the field of cleaning and corrosion protection of tinned steel, especially food or beverage cans made of this material, so-called tinplate cans, in the can manufacturing process between can molding and Painting.

Tin cans are usually made by pre-forming, deep drawing and smoothing. They have a desirable metallic shiny surface so that after a coating treatment with a clear or opaque organic varnish or printing the outer surface are suitable as attractive packaging. The Process sequence in the manufacture of tin cans exists usually in the unwinding provided with a protective oil layer Tinplate tape from the coil, in the application of drawing lubricants, in a first preliminary deformation into a cup and in deep drawing and smoothing to form the final shape. When pulling and Smoothing process are usually additional cooling lubricants such as Water or aqueous emulsions that facilitate the deep-drawing process, used. After forming, the Remains of the protective oiling and the drawing aids as well as any metal abrasion away. After the cleaning process, the containers passed through one or more water rinsing stages and then in dried in a drying oven. Then there is an on or multi-stage painting and a decorative print on the outer Surface. The metallic surface must be such be that the paint has sufficient adhesion and a reliable corrosion protection.

In the manufacture of such cans, however, it is found that rust spots can occur during or before drying, in particular when the cans are cleaned with an acidic medium (pH 3-5) too much water is retained in certain areas or if the individual is at a standstill of the production line Process stages are not run through quickly enough. Here you can Corrosion spots occur that are visible through the paint can and cause a low paint adhesion, so that in such a can of bottled product quickly becomes inedible.

According to the teaching of EP-B-161 667, this problem can be solved tin-free steel cans, so-called black tin cans solve that the cans with after the actual cleaning step treated with an aqueous anti-corrosion solution 10 to 5,000 ppm aluminum ions, 10 to 200 ppm fluoride ions and up to 1,000 ppm ions of at least one of the metals titanium, zircon and / or hafnium and which has a pH of 2 to 5.5.

US-A-4370177 describes acidic, aqueous coating solutions for aluminum surfaces, whose pH is preferably in the range from 3.5 to 4.5. These solutions contain zirconium, titanium and / or hafnium ions in a concentration of at least 0.5 mmol / l, sufficient amounts of fluoride to deal with the above metals to form soluble complexes, and at least two surfactants, preferably nonionic Surfactants. Furthermore, such solutions can be polyhydroxy compounds, preferably Contain gluconic acid or its salts, as well as boron compounds or tannin. Such Solutions form adherent, corrosion-resistant on the aluminum surfaces Coatings which also have the adhesive strength of subsequently applied further coatings, for example, based on paint, improve.

US-A-4313769 discloses similar acidic, aqueous coating solutions for aluminum surfaces, such as the U.S. patent discussed above. These solutions also contain zirconium titanium and / or hafnium ions and fluoride, but only one surfactant, preferably a nonionic Surfactant. Possible additional components and the intended use of these Solutions correspond to the disclosure of the U.S. patent discussed above.

The object of the invention was to provide a treatment solution, a concentrate Manufacture and provide a treatment process with which Tin cans cleaned in a single treatment step and with one Corrosion-protected surfaces are provided, so that corrosion of the surfaces prevented before painting and good paint adhesion can be achieved.

In a first aspect, the invention relates to the use of an aqueous solution which has a pH in the range from 3 to 6, comprising:
100 to 400 ppm complex fluorides of the elements boron, titanium, zirconium and / or hafnium, based on the complex fluorides of the elements mentioned,
100 to 2000 ppm non-ionic surfactants,
100 to 1000 ppm corrosion inhibitor
and the remainder water or an aqueous solution of further active ingredients or auxiliaries, selected from aluminum ions, hydroxycarboxylic acids and solubilizers, for cleaning, for protection against corrosion and / or for improving the paint adhesion of tinned steel.

It has proven positive to add aluminum ions to the solution Concentration of 50 to 300 ppm, preferably about 80 to about 200 ppm to add.

The following concentration ranges are therefore particularly preferred for the individual active compounds. 150 to 300 ppm complex fluorides of the elements boron, titanium, zirconium and / or hafnium,
50 to 300 ppm aluminum ions,
300 to 1000 ppm nonionic surfactants and
150 to 500 ppm corrosion inhibitor.

The source of the aluminum ions is preferably one given in Concentration range of soluble aluminum salt used. Therefor for example the nitrate and in particular the sulfate are suitable, while the chloride is less preferred for corrosion reasons is.

Depending on the surface condition of the cans before cleaning, it may be have a favorable effect if the solution is additionally considered further active ingredient or auxiliary 200 to 800 ppm one or more one, two or three-base Hydroxycarboxylic acids with 4 to 7 carbon atoms in the molecule, the Sum of hydroxyl and carboxyl groups is at least 3. The hydroxycarboxylic acid is or are Hydroxycarboxylic acids are preferably selected from mono- or dibasic Hydroxycarboxylic acids with 6 carbon atoms and at least 4 hydroxyl groups. Gluconic acid is particularly preferred. It is it is immaterial whether the acids as such or in the form of their im specified concentration range soluble salts, especially in Form of their sodium salts, are used. At the pH of the Solution in the range of 3 to 6 will depend on the acids their acid constants partly in their acid form and partly are present as carboxylate anions.

For the complex fluorides of the elements boron, titanium, zirconium and / or Hafnium is also considered to be in the form of its acids, for example the tetrafluoroboric acid or the hexafluoro acids of titanium, Zircon and hafnium, or in the form of in the specified concentration range soluble salts, for example the alkali metal salts, can be used. Because these complex fluoride anions strong acids, they are in the pH range from 3 to 6 are largely in ionic form.

It is particularly preferred that the solution be complex Fluorides of boron in addition to complex fluorides of at least one of the Contains metals titanium, zircon and hafnium, especially of zircon. A solution that is complex is particularly preferred Fluoride of boron and zircon in a weight ratio between 4: 1 and 1: 1, especially in the weight ratio between 3: 1 and 1.5: 1.

Such surfactants or surfactant mixtures are nonionic surfactants preferred, which has a cloud point below about 40 to about Have 45 ° C. This makes it possible to add the cleaning solution a working temperature between about 50 and about 70 ° C in spraying to be used without excessive and disruptive foaming occurs. In particular, ethoxylates and Ethoxylate propoxylates of alkanols with about 10 to about 18 carbon atoms into consideration. The ethoxylates and / or the Ethoxylate propoxylates may also be end group capped and, for example exist as butyl ether. The ethoxylates preferably wear 4 to 12 ethylene oxide groups, especially about 6 to 10 Ethylene oxide groups which preferably carry ethoxylate propoxalates 3 to 7 ethylene oxide groups and 2 to 6 propylene oxide groups, preferably 4 to 6 ethylene oxide groups and 3 to 5 propylene oxide groups. A pure compound with a certain C chain length can be selected. However, it is economical more attractive, oleochemical or oleochemical on alkanols (Oxoalcohols) of origin, in which different Alkanols with different carbon chain lengths are present. For example come as an alkanol component fatty alcohol mixtures with 12 to 14 Carbon atoms or oxo alcohols with 12 to 15 carbon atoms into consideration. A surfactant mixture which both Contains alkanol ethoxylates as well as alkanol ethoxylate propoxylates, for example in a weight ratio between 1: 3 and 1: 1.

The corrosion inhibitor or the corrosion inhibitors can for example can be selected from mono-, di- or triethanolamine, aromatic carboxylic acids, pyridine or pyrimidine derivatives and Diethylthiourea. The ethanolamines are toxicological Reasons (avoidance of nitrosamine formation) especially triethanolamine prefers. Aromatic carboxylic acids in particular come Benzoic acid and its substitution products into consideration. Examples for this are methylbenzoic acids, nitrobenzoic acids, Aminobenzoic acids such as anthranilic acid or p-aminobenzoic acid and hydroxybenzoic acids such as salicylic acid. For use of the treated cans in the food sector are pyridine or pyrimidine derivatives as well Diethylthiourea less preferred. An example of a usable Inhibitor combination is a mixture of triethanolamine and benzoic acid, for example in a weight ratio between 3: 1 and 1: 3. Triethanolamine can also act as the only corrosion inhibitor be used.

If you use the complex when preparing the solution Fluorides, in the form of their acids, may be required by Base addition the pH to the desired range between about 3 and about 6, preferably between about 4 and about 5. For this are basic alkali metal compounds such as Hydroxides or carbonates are suitable. Preferably used for Adjustment of the pH value, however, ammonia.

In a further aspect, the invention relates to the use of the Solution for cleaning, characterized above Corrosion protection and / or to improve paint adhesion on objects made of tinned steel, especially for food or beverage cans. Compared to the previous approach This procedure has the advantage of being in a single treatment step cleaning and temporary corrosion protection at the same time to achieve. The corrosion protection prevents corrosion of the Metal surfaces before painting, such as in Plant downtimes could occur. At the same time, the Paint adhesion and corrosion protection in the painted state improved, without another for this after the cleaning stage Treatment level is required. After treatment with the Solution, the cans are usually rinsed with water, dried at elevated temperature and then painted.

Furthermore, the invention relates to a method for cleaning, for Corrosion protection and / or to improve the paint adhesion of objects made of tinned steel, especially of food or beverage cans, the cans having the one described above Solution for a period between about 30 and about 150 seconds at a temperature between about 50 and treated at about 70 ° C. The treatment can be by spraying the cans with the solution or by immersing the cans into the solution. Treatment by splashing is preferred.

In a further aspect, the invention relates to an aqueous cleaning solution for tinned steel, the
150 to 300 ppm complex fluorides of the elements, boron, titanium, zirconium and / or hafnium, based on the complex fluorides of the elements mentioned,
50 to 300 ppm aluminum,
300 to 1000 ppm non-ionic surfactants,
150 to 500 ppm corrosion inhibitor
and the remainder contains water or an aqueous solution of further active ingredients or auxiliaries selected from hydroxycarboxylic acids and solubilizers and has a pH in the range from 3 to 6.

The cleaning solution according to the invention can in principle be prepared by mixing the individual components together on site in the specified concentration ranges. In industry, however, it is customary to sell such solutions in the form of aqueous concentrates, which the user can adjust to the desired concentration range by diluting with water on site. Therefore, in a further aspect, the invention comprises an aqueous concentrate which, when prepared in water at a concentration between about 0.5 and about 2.5% by weight, gives the cleaning solution according to the invention. In addition to water or an aqueous solution of further active ingredients or auxiliaries, selected from hydroxycarboxylic acids and solubilizers, this concentrate preferably contains 1.5 to 3% by weight of complex fluorides of the elements boron, titanium, zirconium and / or hafnium, based on the complex fluorides of the elements mentioned,
0.5 to 3% by weight of aluminum ions,
3 to 10% by weight of nonionic surfactants and
1.5 to 5 wt .-% corrosion inhibitor.

For an aluminum-containing concentrate, it is preferable that it be used as further active substances or auxiliaries 2 to 8% by weight one or more mono-, di- or tri-basic hydroxycarboxylic acids with 4 to 7 carbon atoms in the molecule, the sum of hydroxyl and Carboxyl groups is at least 3 contains.

The statements made above apply to the preferred selection of the individual components. To improve the manufacturability of the concentrate and to increase its shelf life, it is preferable that it contains one or more solubilizers in addition to the actual active ingredients, preferably in a concentration range between about 1 and about 10% by weight and in particular from about 3 to about 7% by weight. Suitable solubilizers are substances known in the art, such as xylene sulfonates, alkyl phosphates (for example Triton ^R H66, Union Carbide) and in particular cumene sulfonate. These anionic solubilizers can preferably be used as alkali metal salts, for example as sodium and / or potassium salts.

Embodiments example 1

A cleaner concentrate according to the invention with the following composition was produced by mixing the individual components together in the order given: water 70.8% by weight Fluoroboric acid 1.1% by weight Potassium hexafluorozirconate 0.7% by weight Aluminum sulfate · 17 H ₂ O 12.4% by weight Sodium gluconate 3.3% by weight C _12/14 fatty alcohol x 5 ethylene oxide x 4 propylene oxide 3.7% by weight C _12-15 oxo alcohol x 8 ethylene oxide 1.2% by weight Na cumene sulfonate (40% solution) 4.3% by weight Triethanolamine 2.5% by weight

From this concentrate, aqueous cleaner solutions with a pH value between 4 and 4.5 were produced with various batch concentrations, with which tinplate cans soiled by residues of corrosion protection oils and deep-drawing aids were cleaned by spraying for various times at a temperature of 63 ° C. The cleaning effect was assessed by visual assessment of the water-free area (0: no cleaning, 100%: good cleaning). The results are summarized in Table 1. Cleaning effect of the concentrate from Example 1 with different batch concentrations Batch concentration (% by weight) Spraying time (seconds) % water-free area outside inside 0.7 45 60-65 / 100 90 85-90 / 100 60 75/100 0.9 45 75 / 85-90 60 85-90 / 100 90 100/100 1.2 45 90/100 60 100/100

Example 2

To check the corrosion protection effect, concentrates were prepared in accordance with Example 1, the corrosion inhibitor triethanolamine being omitted or being completely or partially substituted. Resulting differences in composition were compensated for by water. The concentrates were made up in water at 1.2% by weight and the ready-to-use cleaning solution was sprayed onto tin cans at a temperature of 63 ° C. for 60 seconds. The cans were then left in the spray chamber for 10 minutes without intermediate rinsing. The formation of rust film was assessed visually on a grading scale: 6 = very bad, 1 = very good. The results are shown in Table 2. Corrosion protection effect Corrosion inhibitor in the concentrate (% by weight) Assessment grade without 6 2.5 triethanolamine 3rd 0.83 triethanolamine + 0.83 benzoic acid 3.5 1.67 triethanolamine + 1.67 benzoic acid 2nd 1.67 triethanolamine + 1.67 benzoic acid + 0.8 diethylthiourea 1.5 2.5 benzoic acid 3.5 1.5 triethanolamine + 1.5 salicylic acid 2nd

Example 3

To check the long-term corrosion protection effect in the painted state, tin cans were cleaned with different solutions, rinsed for 15 seconds with tap water and with deionized water, dried in a drying cabinet at 170 ° C and painted once. (In practice, however, double painting is usual.) 288 cans treated in this way were filled with Coca Cola ^R (Coke ^R ) and stored for 4 months. The number of rusted cans was then determined. The results are shown in Table 3. Corrosion test (288 cans filled with Coca Cola ^R ) cleaning perforated cans Cf. 1 40 Cf. 2nd 20th Ex. 1 14

Example 4

A cleaner concentrate according to the invention with the following composition was produced by mixing the individual components together in the order given: water 68.1% by weight Fluoroboric acid (49% solution) 1.1% by weight Potassium hexafluorozirconate 0.7% by weight Aluminum sulfate · 18 H ₂ O 12.4% by weight Sodium gluconate 3.3% by weight C _12/14 fatty alcohol x 5 ethylene oxide x 4 propylene oxide 3.7% by weight C _12/14 fatty alcohol x 6 ethylene oxide 1.2% by weight Na cumene sulfonate (40% solution) 5.3% by weight Triethanolamine 4.2% by weight

A 1.1% by weight aqueous solution was also made from this concentrate a pH of 4.6. With this solution, tin cans were made by spraying at 60 ° C for one minute cleaned, then with tap water for 15 seconds each and rinsed with deionized water in a drying cabinet Dried 170 ° C and varnished twice. Subsequently, both carried out a paint adhesion text on the side and on the neck of the cans. For this purpose, the cans were placed in a boiling 1 for 30 minutes % detergent solution, rinsed with water and dried. Then a cross cut was made, a Scotch tape (no. 610) stuck on and peeled off. For some samples, an almost full, but usually complete paint adhesion found.

Claims (13)

1. The use of an aqueous solution with a pH value of 3 to 6 containing

   100 to 400 ppm

   of complex fluorides of the elements boron, titanium, zirconium and/or hafnium, based on the complex fluorides of said elements,

   100 to 2,000 ppm

   of nonionic surfactants,

   100 to 1,000 ppm

   of corrosion inhibitor

   and, for the rest, water or an aqueous solution of other active ingredients or auxiliaries selected from aluminium ions, hydroxycarboxylic acids and solubilizers
   for cleaning, corrosion-proofing and/or improving lacquer adhesion to tin-plated steel.
2. The use claimed in claim 1, characterized in that the solution contains:

   150 to 300 ppm

   of complex fluorides of the elements boron, titanium, zirconium and/or hafnium,

   50 to 300 ppm

   of aluminium ions

   300 to 1,000 ppm

   of nonionic surfactants,

   150 to 500 ppm

   of corrosion inhibitor.

3. The use claimed in one or both of claims 1 and 2, characterized in that the solution contains

   200 to 800 ppm

   of one or more monobasic, dibasic or tribasic hydroxycarboxylic acids containing 4 to 7 carbon atoms in the molecule, the sum of hydroxyl and carboxyl groups being at least 3,

   as further active ingredients or auxiliaries.
4. The use claimed in claim 3, characterized in that the hydroxycarboxylic acid(s) is/are selected from monobasic or dibasic hydroxycarboxylic acids containing 6 carbon atoms and at least 4 hydroxyl groups.
5. The use claimed in one or more of claims 1 to 4, characterized in that the solution contains complex fluorides of boron and zirconium in a ratio by weight of 4:1 to 1:1.
6. The use claimed in one or more of claims 1 to 5, characterized in that the nonionic surfactants are selected from alkanol ethoxylates and alkanol ethoxylate/propoxylates containing 10 to 18 carbon atoms and 4 to 12 ethylene oxide groups in the case of alkanol ethoxylates and 3 to 7 ethylene oxide groups and 2 to 6 propylene oxide groups in the case of ethoxylate/propoxylates.
7. The use claimed in one or more of claims 1 to 6, characterized in that the corrosion inhibitors are selected from mono-, di- or triethanolamine, aromatic carboxylic acids, pyridine or pyrimidine derivatives and diethyl thiourea.
8. The use claimed in one or more of claims 1 to 7 for cleaning, corrosion-proofing and/or improving lacquer adhesion to food or beverage cans of tin-plated steel.
9. A process for cleaning, corrosion-proofing and/or improving lacquer adhesion to food or beverage cans of tin-plated steel, characterized in that the cans are treated with a cleaning solution to be used in accordance with one or more of claims 1 to 7 for 30 to 150 seconds at a temperature of 50 to 70°C by spraying the cans with the cleaning solution or by dipping the cans in the cleaning solution.
10. An aqueous cleaning solution for tin-plated steel which contains

    150 to 300 ppm

    of complex fluorides of the elements boron, titanium, zirconium and/or hafnium, based on the complex fluorides of said elements,

    50 to 300 ppm

    of aluminium ions and

    300 to 1,000 ppm

    of nonionic surfactants,

    150 to 500 ppm

    of corrosion inhibitor

    and, for the rest, water or an aqueous solution of other active ingredients or auxiliaries selected from hydroxylcarboxylic acids and solubilizers and which has a pH value in the range from 3 to 6.
11. A water-based concentrate for preparing the cleaning solution claimed in claim 10 by dilution with water, characterized in that it contains

    1.5 to 3% by weight

    of complex fluorides of the elements boron, titanium, zirconium and/or hafnium, based on the complex fluorides of said elements,

    0.5 to 3% by weight

    of aluminium ions,

    3 to 10% by weight

    of nonionic surfactants,

    1.5 to 5% by weight

    of corrosion inhibitor

    and, for the rest, water or an aqueous solution of other active ingredients or auxiliaries selected from hydroxycarboxylic acids and solubilizers.
12. A water-based concentrate as claimed in claim 11, characterized in that it contains

    2 to 8% by weight

    of one or more monobasic, dibasic or tribasic hydroxycarboxylic acids containing 4 to 7 carbon atoms in the molecule, the sum of hydroxyl and carboxyl groups being at least 3,

    as further active ingredients or auxiliaries.
13. An aqueous concentrate as claimed in one or both of claims 11 and 12, characterized in that it additionally contains

    1 to 10% by weight

    of a solubilizer.