KR20160098024A - Can pretreatment for improved coating adhesion - Google Patents

Abstract

The present invention relates to the use of an acidic aqueous composition for the pretreatment of a can in which an inorganic-organic conversion layer providing a good adhesive substrate for wax and subsequent coating to improve the sliding behavior of the shaped can sheet metal is formed during the pretreatment will be. The present invention relates to a can-cylinder in which a canned cylinder is first contacted with an acidic aqueous composition containing a water soluble inorganic compound of elemental Zr, Ti, Si, Hf or Ce and a water soluble polymer having a carboxyl or hydroxyl group and then contacted with an aqueous dispersion of the wax, And a chemical pretreatment method. In this way, the slidability and moldability required for the other method steps of the can manufacturing process are imparted to the can cylinder and an excellent adhesive substrate for coating is also provided. The present invention also relates to acidic aqueous compositions which are particularly suitable for the pretreatment process which comprises a water-soluble polymer selected from condensation products of glycoluril and aldehydes. The present invention also relates to a method of manufacturing a can cylinder comprising a pretreatment according to the present invention.

Description

CAN PRETREATMENT FOR IMPROVED COATING ADHESION < RTI ID = 0.0 >

The present invention relates to the use of an acidic aqueous composition for the pretreatment of cans in the course of forming an inorganic-organic conversion layer, which provides an excellent adhesive substrate for wax and subsequent coating to improve the sliding behavior of the formed can sheet metal . The present invention relates to a process for the preparation of a canned cylinder by first contacting a can cylinder with an acidic aqueous composition containing a water soluble inorganic compound of the elemental Zr, Ti, Si, Hf or Ce and a water soluble polymer having a carboxyl or hydroxyl group and subsequently contacting the aqueous dispersion of the wax And a preprocessing method. In this way, the slidability and moldability required for the other process steps of the can making process are imparted to the can cylinder and an excellent adhesive substrate for the coating is also provided. In the method according to the present invention, both the outer surface and the inner surface of the metal can cylinder are pretreated. The present invention also relates to an acidic aqueous composition comprising a water-soluble polymer selected from the condensation products of glycoluril and aldehyde, and particularly suitable for the pretreatment process. Further, the present invention relates to a method of manufacturing a can cylinder including a pretreatment according to the present invention.

Tin-plated steel (beech steel), aluminum (or simply an aluminum alloy summarized as "aluminum") and cans made of steel are widely used for storage of foods, especially beverages. After the can sheet metal is deep drawn to form a can cylinder, the can is usually degreased, cleaned and typically is eroded and pretreated, for the purpose of this, for example, an acidic or alkaline detergent and a passivating solution, . At least the detergent solution should have sufficient solubility to the metal to effectively remove the metal residue from the can. Through the cleansing pickling, the can surface is already roughened to such an extent that proper surface roughness is maintained, even in the subsequent anticorrosive pretreatment with the passivating solution. The roughness of the outer surface of the cylindrical can results in increased friction between the mutually contacting cans and between the can and the device for receiving and further forming the can cylinder. Such friction may be produced during a subsequent manufacturing step, for example during a period of time during the transportation of the can, for example, by a stopping time at the location where the can of the can is formed due to the separation of the can, The speed of transportation and processing is reduced by the acceptance of the cylinder and the deceleration of the molding process. Efforts have been made to condition the can surface so as to minimize the friction between the can-making contacts, as the capacity of the production facility is thereby reduced.

For this purpose, the can cylinders are provided with a friction-reducing coating which is generally applied in a conditioning flushing process, which is usually followed by erosion pretreatment. In this flushing step, the can cylinders are typically wetted with aqueous solutions of organic materials which increase the slidability of certain surfactants and / or metal surfaces. Such materials are referred to as "mobility improvers" in the prior art of can manufacturing. Thus, the pretreatment of the deep drawn can sheet metal to form the can cylinder typically includes a plurality of wet chemical pretreatment steps to remove the can of the can cylinder by a flushing process containing "mobility improver" in addition to degreasing or cleaning and erosion pretreatment Surface conditioning of the outer surface is also performed.

However, the application of the friction-reducing layer adversely affects the adhesion of coatings, markings or other surface coatings applied for protection against corrosion and / or for decorative reasons. Particularly when the cylinder rim is drawn ("necked") and subsequently molded to form a flange, the coating must not be damaged due to lack of coating adhesion. However, cracking of the coating is often observed in this molding process, and the damaged can cylinder must be cleaned.

Patent document US 4,859,351 discloses the surface conditioning of metal can to reduce the frictional resistance containing fatty acids which are compatible with water-soluble organic ethoxylated phosphate esters, alcohols and / or subsequent coatings.

Patent document US 6,040,280 also discloses surface conditioning for aluminum can based on ethoxylated fatty acid esters and polyoxyalkylene ethers immediately after the chromium-based conversion treatment without adversely affecting subsequent coatings.

However, in the surface treatment and coating of the can cylinder, it is to be ensured that the different requirements relating to various corrosion resistance are satisfied according to the filling of the can. In general, only active substances which are harmless in terms of ecology, especially in the food industry, are available. This relates to the selection of the active ingredient in the surface treatment, as well as the choice of binder in the outer and inner coatings of the can cylinder, whether or not a part of the material is technically intended to be treated only on the outer surface of the can, This is because a spraying process which can not be prevented from occurring due to the manufacturing technique is performed.

The prior art includes various non-corrosive materials for the erosion treatment of metal cans, generally using inorganic acids, especially phosphoric acid, hydrofluoric acid or other sources of fluoride and / or fluoride complexes and with or without additional organic polymers. - chromium method is known.

For example, patent document US-A-4,992,116 discloses an aqueous system containing a polyphenol compound constituting the Mannich adduct of substituted amines with phos- phates, Zr, Ti, Hf or Si hydrofluoric acid, and tannin or polyalkenylphenols Thereby starting an acidic treatment solution.

The patent document EP-B-8942 discloses a composition comprising a) 0.5 to 10 g / l of polyacrylic acid or its esters and b) 0.2 to 8 g / l of at least one hexafluorozirconic acid, hexafluorotitanic acid or hexafluorosilicic acid compound ≪ / RTI > and preferably an aluminum can containing water.

It is an object of the present invention to provide a method of treating a surface of a metal can having an improved performance spectrum with respect to the above-mentioned different requirements. Especially to improve the sliding and deformation behavior of the can sheet metal which is being deep drawn to form the can cylinder, while at the same time providing an excellent corrosion-resistant adhesive substrate for the protective coating.

The above problem is solved by a method of manufacturing a can cylinder,

(i) a) at least one water-soluble inorganic compound of elemental Zr, Ti, Si, Hf and / or Ce, and

b) at least one water-soluble organic resin having at least a carboxyl group or a hydroxyl group and having an acid value and / or a hydroxyl group content of at least 50 mg KOH / g

With an acidic aqueous composition containing an acidic aqueous phase, and then - without intervening or intervening intermediate flashing steps -

(ii) contacting the wax with an aqueous dispersion of the wax

Which is deeply drawn from the metal sheet and is open at one end.

In the sense of the present invention, when 50 g of inorganic compound can be dissolved in one kilogram of water having a pH value of 3 without forming a sediment which is insoluble in water phase at a temperature of 20 캜, the inorganic compound is water-soluble.

In the sense of the present invention, 10 g of polymer can be dissolved in one kilogram of water having a pH value of 3 at a temperature of 20 DEG C and the organic polymer is water-soluble if present as a clear solution. If the turbidity (NTU) measured according to DIN ISO 7027 is less than 50 at a wavelength of 860 nm by light scattering at a solution temperature of 20 ° C, it is present as a clear solution.

According to the present invention, the acid value is the degree of the number of free acid groups in the polymer or polymer mixture as an empirically measured measurement variable. The acid is determined by dissolving the metered amount of polymer or polymer mixture in a solvent mixture of methanol and distilled water in a volume ratio of 3: 1, followed by potentiometric titration with 0.05 mol / L KOH in methanol. The potential difference measurement is carried out with a composite electrode (LL-Solvotrode® from Metrohm; reference electrolyte: tetraethylammonium bromide in ethylene glycol, 0.4 mol / L). The acid number corresponds to the amount of KOH added per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

Similarly, in accordance with the present invention, the hydroxyl value can be determined experimentally by potentiometric titration as the degree of the number of free hydroxyl groups in the polymer or polymer mixture. To this end, a metered amount of the polymer or polymer mixture is heated in a reaction solution of phthalic anhydride in 0.1 mol / L pyridine for 45 minutes at 130 ° C and then a 1.5-fold volume of pyridine reaction solution and then 1.5-fold volume of deionized water (κ < ¹ μScm ^-1 ). The free amount of phthalic acid is titrated with 1 M sodium hydroxide in this mixture. The potential difference measurement is carried out with a composite electrode (LL-Solvotrode® from Metrohm; reference electrolyte: tetraethylammonium bromide in ethylene glycol, 0.4 mol / L). Where the hydroxyl value corresponds to the amount of NaOH added per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

In the sense of the present invention, the flushing step is used exclusively to remove the wet film attached to the can surface containing the active ingredient from the previous wet chemical treatment step, unless otherwise stated. Thus, the flushing step is preferably carried out with water, and the flushing water preferably has a dry residue of less than 1 g / L, particularly preferably less than 100 ppm, particularly preferably less than 10 ppm.

The wax in the sense of the present invention can be kneaded at 20 ° C and is solid to weakly cured, has a coarse or microcrystalline structure and is transparent or opaque but is not glassy and melts at temperatures above 40 ° C without decomposition, (Low viscosity) and which has a strong temperature-dependent concentration and solubility, and which can be polished at a reduced pressure. The organic material is not a wax unless at least one of the characteristics described above is met.

The method according to the invention first realizes good adhesion of the wax applied to the surface of the can cylinder in the second essential step of the method. The adhesion of the wax is such that no significant detachment of the wax layer is observed in the downstream flushing step in the process according to the invention, which is carried out before application of the can coating. The good adhesion of the wax significantly reduces the friction of the mutually contacting shell surfaces of the can cylinders, thus increasing the mobility of the can cylinders in industrial cans manufacturing, especially at the exit of each manufacturing stage, Speed can be guaranteed.

Further, after the application of the can coating, the molding behavior of the canned cylinder treated according to the present invention is improved, and during the tapering ("necking") of the can diameter at the upper end and after the molding of the upper end to form the flange, Occurs less frequently and takes place in a much lesser extent.

Thus, the method according to the invention can be used for the manufacture of a connection in the sealing cap of the can cylinder, for example, for drawing the open end of the can cylinder for tapering ("necking") the diameter of the can cylinder in the rim region and / It is very advantageous for molding in the edge region of the open end of the can cylinder including each molding directly required for forming the can cylinder for forming the flange.

According to the present invention, the content of the water-soluble inorganic compound of the element Zr, Ti, Si, Hf and / or Ce according to the component a) in the acidic aqueous composition in the step (i) 1 g / L, and the amount of the water-soluble inorganic compound of the element Zr and / or Ti is preferably 0.01 g / L or more, particularly preferably 0.02 g / L or more, based on the total content of the elements Zr and Ti .

In this context, the water-soluble compound according to component a) of the acidic aqueous composition in step (i) of the process according to the invention is preferably selected from fluorine complexes of elemental Zr, Ti and / or Si, Is selected from fluorine complexes of elemental Zr and / or Ti.

In the sense of the present invention, the fluorine complex means a complex with the above-mentioned metal or semimetal element, which has at least one fluorine atom as a ligand and is present in an aqueous solution as an anion.

The amount of the organic resin according to component b) used in step (i) in the process according to the invention is preferably in the range of 0.1 to 50 g / L, particularly preferably in the range of 0.5 to 10 g / L in the acidic aqueous composition do.

The water-soluble organic resin according to component b) in the acidic aqueous composition in step (i) used in the process according to the invention is preferably selected from vinyl ethers, vinyl alcohols, polymers derived from (meth) acrylic acid, maleic acid or fumaric acid Or from a copolymer, from a polyester containing a hydroxyl group, and from a condensation product of glycoluril or melamine and an aldehyde; Particularly preferred is the condensation product of glycoluril or melamine with aldehyde, in particular the organic resin constituting the condensation product of glycoluril and aldehyde, which has a hydroxyl value of preferably at least 50 mg KOH / g. Wherein the alkylation degree of the condensation product of glycoluril or melamine and aldehyde is preferably less than 20%, particularly preferably less than 10%. For the condensation products mentioned above, a primary aldehyde is preferred and acetaldehyde and formaldehyde are particularly preferred.

It is also preferred that in step (i) of the process according to the invention the acidic aqueous composition additionally contains phosphate ions in an amount of preferably at least 0.1 g / L. The use of phosphate improves the erosion resistance properties of the conversion layer formed in step (i). For reasons of economical efficiency of the process and prevention of phosphate sludge, the amount of phosphate ions preferably does not exceed 10 g / L.

In the process according to the invention, the pH value of the acidic aqueous composition of step (i) is preferably at least 2, particularly preferably at least 3, preferably at most 6, particularly preferably at most 5.

The can cylinder which is once opened in the method according to the invention is in contact with the aqueous dispersion of the wax in order to ensure a sufficient slipperiness of the shell surface of the can cylinder upon contact with the receiving tool or other can in the can manufacturing process in step (ii) do. The wax to be used for this purpose is preferably selected from synthetic waxes, particularly preferably from oxidized polyalkylene waxes, particularly preferably from oxidized polyethylene waxes, and is applied to the surface of the canned cylinder pre-processed according to step (i) The content of wax in the aqueous dispersion in step (ii) is preferably 0.1 g / L or more, and particularly preferably 1 g / L or more so that a sufficient amount of wax can be developed. For reasons of efficiency of the process according to the invention, the amount of wax in the aqueous dispersion in step (ii) is preferably not more than 50 g / L, particularly preferably not more than 10 g / L.

Step (ii) of the process according to the invention is usually preceded by a further wet chemical treatment step which comprises finally coating the can cylinder with a can coating. When applying can coating, there is a difference between the inner coating and the outer coating in can manufacturing. The process according to the present invention provides suitable coating adhesion-improving and erosion pretreatment for both external and internal coating applications.

Thus, in a preferred method according to the invention, a protective coating is provided on the outer surface of the can cylinder at least one end opened after contact with the aqueous composition in step (ii) and optionally after the flushing step immediately following step (ii) .

Since the inner coating of the can is often in contact with food, there is a special requirement for the inner coating of the can. The use of, for example, bisphenol A-based epoxide resin as the inner coating of the can is prohibited in the prior art. Various national legislations are underway to establish maximum limits for the migration of bisphenol A from food packaging to food, and some were introduced by the EU Directive 2002/72 / EU.

A coating suitable for food is also preferably used for coating the outer region of the can, since it is not possible, from the point of view of processing techniques, to completely prevent the incorporation of the sprayed coating into the can during application of the coating to the outer surface of the can.

The process according to the invention has also been found to be particularly suitable for protective coatings having a binder based on acrylic resin and polyester resin.

Thus, in a preferred method according to the invention for the surface treatment of deep drawn can cylinders, a protective coating is provided on the outer surface of the can cylinder, at least one end of which is open, having a binder selected from acrylic resin and / or polyester resin , Wherein the acrylic resin is preferably selected from the group consisting of alkenes, especially ethene, propene, 1-butene, 2-butene, isobutene, 1,3-butadiene and / Unsaturated carboxylic acids, in particular cinnamic acid, crotonic acid, fumaric acid, itaconic acid, maleic acid, acrylic acid and / or methacrylic acid.

The contact of each aqueous composition in steps (i) and (ii) and the application of the protective coating are preferably carried out in a process according to the invention, for example by spraying, e.g.

In the so-called airless method, each liquid is atomized without air and applied to the material surface. In this spraying method, a predetermined amount of liquid is applied by a spray gun, and the can is rotated about its longitudinal axis to form a homogeneous wet film.

After the wet film is applied for coating with a protective coating, the can cylinders that have been pre-treated in this manner and are open at one end are preferably cured at a temperature (object temperature) in the range of 120 ° C to 200 ° C to form a coating film.

In an additional process of can manufacture, one end open can cylinder, which is pretreated in a wet-chemically manner and provided with a protective coating in the process according to the invention, is usually molded in one open end rim region, ("Necking"), and shaping to form a flange.

Therefore, when the above-mentioned forming process is followed by wet-chemical pretreatment according to process steps (i) and (ii), in addition to corrosion resistance, coating adhesion and low sliding friction coefficient, The improved molding behavior of the &lt; RTI ID = 0.0 &gt;

The surface treatment method according to the present invention preferably results in a subsequent step of applying process steps (i) and (ii) and optionally a protective coating, is not molded in the open edge area, Which is not formed to form a flange therefrom, is carried out only in one open can cylinder.

The can cylinder with one end opened for use in the surface treatment method according to the present invention is preferably deep drawn from a steel plate, a steel plate or an aluminum plate.

The present invention also includes an acidic aqueous composition particularly suitable for wet-chemical pretreatment according to process step (i) of the surface treatment method according to the invention for the surface treatment of an open-ended can cylinder.

The acidic aqueous composition for surface treatment of metal can according to the present invention has a pH value in the range of 2 to 5,

a) a fluorine complex of elemental Zr, Ti and / or Si in an amount of 0.005 to 0.5% by weight, preferably 0.01 to 0.1% by weight, based on each element; and

b) from 0.05 to 3% by weight, preferably from 0.1 to 2% by weight, of a condensation product of glycoluril and an aldehyde, said condensation product preferably having a hydroxyl value of at least 50 mg KOH / g, Preferably comprises less than 20% water soluble resin.

Primary aldehydes, especially acetaldehyde and formaldehyde, are preferred for the condensation products.

The acidic aqueous compositions according to the invention preferably contain less than 0.1% by weight of an organic polymer selected from the group of epoxides, urethanes and polyesters, preferably less than 0.1% by weight of such organics, not condensation products of glycoluril and aldehydes Lt; / RTI &gt;

The present invention also relates to

(A) deep-drawing a circular sheet of metal sheet to form a can cylinder having one end open;

(B) wet chemical pretreatment and subsequent coating of the one end open can cylinder, wherein in the wet chemical pretreatment, at least the outer surface of the can cylinder,

(i) a) at least one water-soluble inorganic compound of elemental Zr, Ti, Si, Hf and / or Ce, and

b) at least one water-soluble organic resin having at least a carboxyl group or a hydroxyl group and having an acid value and / or a hydroxyl group content of at least 50 mg KOH / g

With an acidic aqueous composition containing an acidic aqueous phase, and then - without intervening or intervening intermediate flashing steps -

(ii) contacting the wax with an aqueous dispersion of the wax; And

(C) drawing the can-cylinder with the wet-chemically pretreated and coated can at one end open to form a flange in an open edge area by tapering and / or shaping the diameter of the can cylinder To a method of manufacturing a can cylinder.

The drawing of the circular sheet metal to form the can cylinder once opened is followed by a cleaning step, preferably for the removal of the metalworking liquid.

The same preferred embodiments as described above for the surface treatment method according to the present invention apply to wet-chemical pretreatment and subsequent protective coating coatings used for can cylinders in the production process according to the present invention. The same is true for the method for the contact of the composition in the pretreatment, the coating of the can cylinder and the selection of the material of the metal sheet.

Example:

As a basic formulation for the pretreatment of the aluminum can (EN AW-3104), an acidic aqueous treatment solution having the following composition was used:

H ₂ ZrF ₆ to 50 ppm Zr

From the boric acid, 40 ppm of B

80 ppm of PO ₄ from phosphoric acid

300 ppm NO ₃ from nitric acid

25 ppm of free fluoride (measured with ion selective electrode)

pH-value 3.2

The first step entails a conversion treatment of the outer surface of the can with the aforementioned treatment solution further containing an organic polymer. The following organic polymers were used for this conversion treatment:

Org1: Tetramethylolglycoluril resin (having a hydroxyl value of 450 to 480 mg KOH / g)

Org2: Maleic acid-methyl vinyl ether copolymer (acid value 220-280 mg KOH / g)

Org3: Polyacrylic acid

After spraying the pretreatment solution described in Table 1 on the outer surface of the aluminum can, deionized water (kappa < ¹ mu S cm ^-1 ) was flushed and then 7 g / L of emulsified non-ionogenic polyethylene wax Was immediately flushed with deionized water (? < ¹ ? S cm ^-1 ), and then dried at a temperature of 60 ° C.

Properties of the outer surface of the can prepared by the two-step method described above are shown in Table 2 with respect to the sliding behavior and the coating adhesion.

The sliding behavior was measured by stacking three cans in a triangular shape, wherein the two cans at the bottom forming the base were lifted at one end perpendicular to the longitudinal direction of the cans. The angle between the can axis and the horizontal axis at which the upper can begins to slide when lifting one end of the can stack is referred to as "slip angle ". This test was repeated 5 times with different pre-treated different cans and the average value of each measured "slip angle" was determined.

The pre-treated can was tapered or compressed ("necked") to an open cans border after external coating with a commercially available can coating (coating base: acrylate-modified polyester, DSM, Uradil®SZ250; And after 90 ° flanging of the cans rim, the coating adhesion was measured. The evaluation was performed visually in the can forming area for each of five cans according to the following criteria.

One: No visible cracks or coatings

2: Cracks and weak coatings

3: Strong coating cracking

The results show that the minimum slip angle and the best coating adhesion are achieved with the composition (E-1) containing the glycoluril resin in the first step, especially in the two-step surface treatment method according to the invention (E1-E3).

Claims (15)

At least the outer surface of the can cylinder,
(i) a) at least one water soluble inorganic compound of elemental Zr, Ti, Si, Hf and / or Ce, and
b) at least one water-soluble organic resin having at least a carboxyl group or a hydroxyl group, the sum of the acid value and / or the hydroxyl value of each organic resin being 50 mg KOH / g or more
With an acidic aqueous composition containing an acidic aqueous phase, and then - without intervening or intervening intermediate flashing steps -
(ii) contacting the wax with an aqueous dispersion of the wax
And the one end of the can is deep drawn from the metal sheet. The method according to claim 1,
Characterized in that in step (i) the water-soluble compound according to component a) of the acidic aqueous composition is selected from fluorine complexes of elemental Zr, Ti and / or Si. 3. The method according to claim 1 or 2,
The content of the water-soluble inorganic compound of the element Zr, Ti, Si, Hf and / or Ce according to the component a) in the acidic aqueous composition in the step (i) is in the range of 0.01 to 1 g / L , And the amount of the water-soluble inorganic compound of the element Zr and / or Ti is preferably 0.01 g / L or more, particularly preferably 0.02 g / L or more, based on the total content of the elements Zr and Ti . 4. The method according to any one of claims 1 to 3,
Wherein the water-soluble organic resin according to component b) of said acidic aqueous composition in step (i) is selected from polymers or copolymers based on vinyl ether, vinyl alcohol, (meth) acrylic acid, maleic acid or fumaric acid, From polyesters, and from condensation products of glycolurils or melamine with aldehydes. 5. The method according to any one of claims 1 to 4,
Characterized in that the content of the water-soluble organic resin according to component b) in said acidic aqueous composition in step (i) is in the range of 0.1 to 50 g / L, preferably in the range of 0.5 to 10 g / L. 6. The method according to any one of claims 1 to 5,
Characterized in that in step (i) said acidic aqueous composition additionally contains a phosphate ion in an amount of preferably at least 0.1 g / L but preferably at most 10 g / L. 7. The method according to any one of claims 1 to 6,
Wherein the acidic aqueous composition in step (i) has a pH value of at least 2, preferably at least 3, and up to 6, preferably up to 5. 8. The method according to any one of claims 1 to 7,
In the step (ii), the wax in the aqueous dispersion is selected from a synthetic wax, preferably an oxidized polyalkylene wax, particularly preferably an oxidized polyethylene wax, and the content of the wax in the aqueous dispersion is 0.1 to 50 g / L, particularly preferably in the range of 1 to 10 g / L. 9. The method according to any one of claims 1 to 8,
Wherein contact with each of the aqueous compositions in process steps (i) and (ii) is carried out by spraying, respectively. 10. The method according to any one of claims 1 to 9,
Characterized in that a protective coating is provided at least on the outer surface of the can cylinder which has been opened after said contacting with said aqueous composition in step (ii) and optionally after the flushing step immediately following step (ii). 11. The method according to any one of claims 1 to 10,
Characterized in that said can cylinder is not formed in the edge region of which one end is open, in particular drawn for tapering the diameter of the can cylinder, or not formed for the formation of a flange. 12. The method according to any one of claims 1 to 11,
Characterized in that the can cylinder is deep drawn from both steel plates, steel plates or aluminum plates. (A) deep-drawing a circular sheet of metal sheet to form an open can cylinder,
(B) pre-treating and coating the one-end open can cylinder with the method according to claim 10, and
(C) a step of drawing the canned cylinder, which has been pretreated and coated, by pulling out the canned cylinder in one opened edge region to taper and / or form the diameter of the canned cylinder to form a flange in an open-
Wherein the can cylinder is formed of a metal. a) 0.005 to 0.5% by weight of a fluorine complex of elemental Zr, Ti and / or Si, based on each element, and
b) 0.1 to 3% by weight of a water-soluble resin selected from condensation products of glycoluril and aldehyde
And has a pH value in the range of 2 to 5. The acidic aqueous composition for surface treatment of metal can. 15. The method of claim 14,
Wherein the condensation product of glycoluril and aldehyde has a hydroxyl value of at least 50 mg KOH / g and the degree of alkylation is preferably less than 20%.