DE1965586C3 - Steel sheets which, following shaping, are provided with a coating, in particular an enamel layer, method for their production and use of the steel sheets - Google Patents

Description

Direct white enamelling of sheet steel has become a reliable production method in recent years Procedure. By rationalizing the production process and introducing continuous, programmed production methods ensure a constant quality of the enamelled products, combined with a reduction in enamel costs. achieved. Another simplification of the workflow in the enamelling factory is given by the fact that one used to manufacture the rtohtcile Strip already pretreated in the steelworks for single-layer enamelling, d. H. so z. B. a corresponding Pickling process followed by nickel plating. The adhesive base thus achieved for the single-layer white enamelling must then of course be protected from deformation in such a way that the applied layer is not damaged. A Such protection is achieved in already known strip pretreatment processes by means of an electrolytic applied zinc layer.

ίο The disadvantage of such a metallic protective layer The complicated after-treatment that the enamelling plant forces has to be one of several Steps to build an existing system (degreasing, rinsing, pickling of the protective layer with acid, e.g.

Hydrochloric acid, rinsing, neutralizing).

In the same way it is more rational to produce metallic materials by drawing, pressing, teizan or other non-cutting processing brought into the desired shape and then with

be provided with a firmly adhering metallic or non-metallic layer, degreasing and pickling immediately after their production and then provided with a cover that protects the surfaces but is easy to remove. Coatings made of metal, which are electrodeposited or chemically deposited, or stoving varnishes, dipping varnishes and other plastic coatings, also require a substrate that is as pure as possible in order to ensure permanent protection of the surfaces. The task of supplying metal processors with a starting material that can be used as directly as possible for subsequent coating is therefore not limited to the enamelling industry.
The advantages are many; In addition to saving material by eliminating additional rust removal or removing other corrosion layers, the pickling and the associated processing of the wastewater can be carried out more economically in large plants.

From the German Auslegeschrift I 192 487 a method has become known, according to which to achieve or improving the corrosion resistance of metals or alloys these with a tannic one Phosphating solution are treated.

However, the coatings formed in this way remain on the metal and can be in the coating, especially when ^Direktwe: 3 enamel. lead to significant difficulties.

The present invention now relates to

5 <> steel sheets provided with a removable cover, which optionally have an additional metallic intermediate layer and which are not subjected to a cutting deformation and then provided with a firmly adhering protective layer, in particular an enamel layer, and which are characterized in that they are a removable cover made of water-soluble Possess polyphosphates.
The present invention also relates to a process for the production of the steel sheets described above, which is characterized in that, following a surface treatment to be carried out in a known manner, the removable cover is applied to the steel sheets with the aid of a solution containing water-soluble polyphosphates and then a firmly adhering protective layer , in particular an enamel layer, is applied in a known manner.

i 965

The steel sheets according to the invention are advantageously used in the emulsifying technique and here particularly efficient when enamelling with enamel, for which specially pretreated metal surfaces are necessary are.

The steel sheets to be deformed are advantageously degreased and pickled directly after production and provided with a nickel layer. The surface treatment is carried out according to known methods Process, either purely chemical or fully electrolytic or by a combination of chemical or electrolytic steps. For example, an electrolytic degreased, electrolytically pickled and electrolytically nickel-plated sheet metal by connecting a alkaline coarse degreasing.

In this case, the sequence of the pre-treatment stages would look like this:

Alkaline rough degreasing,

Electrolytic fine degreasing,

Flushing,

Elektrolytis- '. Ie stain.

Flushing

Electrolytic ^ nickel plating.

Flushing,

Drying.

The advantage of electrolytic pretreatment over the purely chemical method is one Shortening of the total residence time by about 65 "". The water-soluble PoK then becomes phosphate ζ. B. applied by immersion or spraying. The whole treatment can be done including sheet metal fabrication perform fully continuously. The sheet metal provided with the cover layer can then be passed through Rolling, pressing, drawing or ar..lere non-cutting Deforming methods. Following the deformation, the cover can be enamelled peeled off or washed off with water without affecting the enamelling prepared surfaces.

Surprisingly, it was found that the cover from the inventively to be used Polyphosphates act as a lubricant in sheet metal forming, especially when organic additives be added, and that even if insufficient or completely missing removal before enamelling no impairment of the enamel adhesion and enamel surface can be determined.

This results in the interesting possibility of making the presses work fat-free and such a thing Completely bypass post-treatment. In practice, this is not always the case be possible, as contamination by the enameling disturbing substances can hardly be avoided is. After all, it is very advantageous that even if the protective layer is not completely removed flawless enamelling is guaranteed.

The method according to the invention is not limited to enamelling, but can also be used in similar technical fields in which deformed metallic objects are then provided with a protective layer, especially if a carefully cleaned substrate, possibly also a a specially pretreated substrate is necessary. As already stated, the method offers advantages, e.g. B. also in the production of metallic objects that are galvanically uder chemically metallized after deformation or provided with plastic coatings .

Polyphosphates which Ahren for the inventive steel sheets Ver the invention and ^f are suitable are salts of phosphoric acids having the general formula HO [HOPO _2] "H, where η is an integer of at least 10, preferably above 100 means. The hydrogen is through monovalent cations, like Na% K \ Li ', NH ₁ *. or substituted ammonium ions, polyphosphates are used with one type of ion, but also with different ions. For reasons of solubility in polar, preferably aqueous media, mixed salts such as l. B. Na / K salts are used.

The polyphosphate solutions used for the production of the steel sheets according to the invention are produced by methods known per se. One usually starts with polyphosphates such as Kurotl salts. Madretl salts with graham salts and exchanged if there is insufficient water solubility. part of the cations by different types of cations. You can z. B. suspend the water-insoluble K-Kurollat [KPO ₃ ] ,, m water and by adding 0.5 to 6 parts of a sodium phosphate such. B. a sodium polyphosphate [NaPO ₃ J _n or the phosphates Na ₁ P ₂ O ₇ . Na ₆ P ₃ O ₁₀ . (NaPO ₃ )., (Na trimetaphosphate). Bring (NaPO ₁ J) ₆ (Na-hexametaphosphaU or Na ₃ PO ₁ among others into solution.

It is also possible to disperse the potassium polyphosphate in water and with the help of sodium ions containing ion exchangers to exchange part of the potassium ions for sodium ions, so that a soluble Na / K polyphosphate is obtained.

Of course it is possible, numerous other salts of monovalent cations with polyphosphates of the composition [KPO.,] ,, and [NaPO _3] implement n, wherein the polymer molecules of the cations by foreign cations can be more insoluble, even after the replacement of a part, which in in most cases is based on the presence of foreign ions in the supernatant solution. By decanting and adding salt-free water, solution cm. For the process according to the invention, the low-foreign-salt or foreign-salt-free solutions, which generally have higher viscosities, and also the polyphosphate solutions containing foreign salts can be used.

Em is possible by adding organic substances with high or low molecular weights the properties of the polyphosphate protective layers / u influence. Additions of water-soluble polymers with medium to low molecular weights can exert a painful effect, the coatings Make it supple, elastic and smooth and also bring about a lubricating effect when the block is deformed. By adding low molecular weight substances it is bcbeispielswci-si; possible the Auflöseggschwindigkcit to increase the protective coatings when removing them before enamelling.

As substances that primarily affect the physical properties of the protective layers such as strength. Affect elasticity, lubricity, etc. are, for example: Polyethylene oxide b / w. Polyglycol ether. Polypropylene glycol. Polyvinyl alcohol. Polyvinyl ether, polyvinyl pyrrolidone, polyacrylamides. Polyacrylates, modified maleic anhydride copoly-

rnerisate with /. U. styrene, isobutylene, etc., water-soluble Polyester, etc. and mixtures of such water-soluble polymers and corresponding copolymers. Depending on the molecular weight of the organic polymers added, they are more favorable and softer (low molecular weights of the polymer additives) or the properties of the Protective layers directed towards the properties of the organic polymer (high molecular weights of polymer additives).

Substances that also have the physical properties of the protective layers, but primarily that Resolving the protective layers affect, are mainly those that have a surface-active effect have, such as nonionic, anionic or cationic emulsifiers. From this group of substances Examples include: polyglycol ethers, reaction products of phenols or alcohols with Ethylene oxide, peracid salts, sorbitan esters. Sulfonates such as U. alkylbenzenesulfonates. Sulfuric acid half esters of long-chain alcohols, etc. The rate of dissolution is of course also made by adding oligomers or polymers with low molecular weights increased. The additives based on organic substances on the Polyphosphai, everyone can in principle Accept relationships. With the addition of organic polymers or plasticizers, the desired results are achieved Effects in general at amounts between 1 and 75 ", while the emulsifiers partially are effective in very small amounts. d. H. in 3 "concentration ranges between 0.01 and 10" ,,. based on the polyphospluit. It is of course possible to use organic poles and compounds of emulsifier types to be used together. The polyphosphates and the organic additives can be applied separately, with a thorough mixing by diffusion in the applied Solution layers can occur. However, it is advantageous to measure the solutions to be applied beforehand Polyphosphates and organic additives. When using mixtures of pol} phosphates and organic substances can also contain small amounts of anti-aging agents or stabilizers the organic substances are added.

The coatings with those to be used according to the invention Substances can be applied by methods known per se, e.g. U. sprayed on, dipped, painted on, etc. To apply particularly thin films, it is preferable to spray a aqueous or optionally organic solution on the substrate and evaporates the solvent.

The method according to the invention is explained in more detail below with the aid of examples.

13 eis ρ ic II
A cold-rolled smell of the Kichlanulysc

C - 0.004%
Mn = 0.320%

S = 0.035%

P = 0.040%

Si - 0.020%

Cu = 0.027%

Was alkaline degreased, rinsed warm and cold, _{pickled in 9% ipsr H 2} SO ₄ at 75 C for 6 minutes, rinsed, 6 minutes in 1.2% NiSO ₁ , 7 H ₂ O solution at 70 "C and pH -Wcr ¹ 3 nickel, rinsed and finally neutralized. Subsequently, the finished pretreated Ulech with a Q, 35% aqueous solution of K / Na-polyphosphate solution was coated by spraying. Now, there was a deformation of the coated panel using a non-fat Werkrsuges and finally a direct line with a B-Ti white enamel of the following composition:

55

60

38 "" SiO., 0.5 % AI., O, 21 ■; "B., O _a 15th "" Alkali Oxide 2 "" Fluorine 19th % TiO., 0.5 ·; !! Mgö

without prior removal of the polyphosphate layer.

The enamelling showed very good enamel adhesion according to the usual unity at 820 ° C. Enamel surface.

The Polvphiisphatliisting was made by repositioning from (KPf).,) ,, with NaCl in a viol ratio of I: 3, putting a suspension win (KPC).,) ,, in water with NaL! (1: 3) was added, after 1 sturdy. Depending on the stirring time The swollen precipitate is separated off and dissolved in pure water.

The molecular weight of the polyphosphate is given by (. \ Cn

Viscose value

expressed.

Concentration in g 100 ml solvent.

30 Determination in water at 25 C at pH 7. Kon /. 0.05 "" in the presence of 0.1 "" NaCl at τ 0.9S dvn cnr. The solvent phosphate contains 7.5 "" potassium and I 3.1 "" sodium.

Example 2

A steel sheet of the above-mentioned Anaivse was pre-stripped in an alkaline way. electrolytically fine lines. rinsed, electrolytically pickled in a solution of 150 g Na ₂ SO ₁ · 10 ll.pl and 5 ml H ₂ SO ₁ conc./l at a current density of 10 A.dm- 1 minute, rinsed and finally in a solution of

SO g NiSO, 7 Η., Ο / Ι
1OgNH ₁ CI.!
20 g MgSO ₁ 7 11th, oil
5gH., B ()., L

Nickel-plated for 1 minute at iJtroriKtichten of 0.5 A / dm ^2.

After previous rinsing, the sheet metal was coated with a 0.35 "strength aqueous K / Na polyphosphate solution by dipping and, after drying, subjected to the usual deformation in enamel materials on a hydraulic press ₂ C) removed, the part dried and then directly white enameled with a II-Ti white enamel of the above composition. Both adhesion and enamel surface were excellent. The same polyphosphate solution as in Example I was used.

Example 3

A steel sheet of the above analysis was pretreated as in Example 1. That vorbchandelte Sheet was coated with a 2% aqueous K / Na poly

7 ^ 8

phosphate solution. The 6 "" K / Na-Hexametaphosphat It followed an Oircktwcißenaillicrung with a

contained as foreign salt, coated by brushing. H-Ti white enamel with no composition. As well as After the applied layer had dried, adhesion and the enamel surface were no longer there Sheet metal with the usual deformation in the enamelling factory.

subject to change. The poly-phosphate layer was then removed by spraying it off with water. Subsequently, the deformed sheet was three thin sheets with the designation A. B and C of the analysis given above with a B-Ti white enamel of the above composition were in example 2 white enamel. Both adhesion and pre-treated in the manner described in the enamel. Panel A was awarded with no surface. The polyphosphate in polymer protective layer in the enamelling plant was formed into a solution by stirring [KPO ₃ ] _n with the cover plate of an electric cooker. Obtain the ver (NaPOj) ₈ (1: 3) in water. Sheet A formed viscosity was enamelled in direct white with a B-Ti white enamel ^ln 'i ^r _ q ι of the above composition. So- c ~~ '' adhesion and the enamel surface were very good

Example 4 ' ^{5 bad}

Sheet B was deformed in the same way as sheet A.

A steel sheet of the above analysis, however, then hosed down with water,

was pretreated as in Example I. The pre-The direct white enamelling with the B-Ti white

punched sheet was coated with a 2 ° _o by weight aqueous composition of email provided above with respect to

K / Na polyphosphate solution, the S ",; Polyethylene glycol ao adhesion and enamel surface poor results.

(M. G. 1000) contained as a plasticizer, by spraying sheet C was nrt one before deforming

coated. After the applied 2% K / Na polyphosphate solution has dried (see Example 3),

The sheet was put through a layer in the enamelling plant containing 1.5 "■ '" nonylphenol polyglycol ether

subject to severe deformation. Syringes were then coated. After the poly-

the polymer coating by brushing under the layer of fluid became sheet C - like the sheets

removed from the water. This was followed by a direct white A and B - deformed. Then the poly-

enamelling with a B-Ti white enamel of the above phosphate layer by spraying off with water.

composition. Both liability and enamel over- all. Subsequently, the deformed sheet C

area were excellent. It was the same with the B-Ti enamel of the above composition directly

K / Na polyphosphate solution as used in Example 3. 30 white enameled. Both liability and email

_n . -ic surface were - in contrast to the sheets A

Example 5 and B - excellent.

A steel sheet of the above analysis was made. · Ι ο

pretreated as in Example 2. The pretreated example 8

Sheet was treated with a 2 / igen, aqueous K / Na-Poly-35 A steel sheet of the analysis given above

phosphate solution, the 6% K / Na hexametaphosphate alkaline degreased, rinsed warm and cold, 3 minutes

as a foreign salt and 8% polyvinyl ethyl ether (MW 1500) in 9 ° _o iger H ₂ SO ₁ at 20 ⁰ C pickled, rinsed, in a

as a plasticizer, coated by spraying. Solution of 200 g CuSO ₄ · 7 H ₂ O / 1 and 70 g H ₂ SO., /]

After the applied layer had dried, electrolytic treatment ^{was carried out at 30 °} C. with 4 A / dm ^{2 for 10 minutes}

the sheet metal in the enamelling factory a strong deformation 40 copper-plated and rinsed. Then there was «

subject. Subsequently, the poly sheet was in a 2% aqueous solution of K / Na

phosphate layer removed by spraying with water. Polyphosphate coated and dried. After your

The subsequent direct white enamelling with a deformation was the polymer layer only mi

B-Ti white enamel of the above composition delivered rinsed in water,

Excellent in terms of adhesion and enamel surface. .

nice results. The polyphosphate solution corresponded to the example

the solution used in Example 3. A steel sheet of the above analysis was used

electrolytically degreased, rinsed, 3 minutes. n 9%

Example ⁶ H ₂ SO ₄ at 20 ⁰ C pickled, rinsed in a Lösunj

A steel sheet of the above analysis was 50%

pretreated as in Example 1. The pretreated 320 g zinc sulfate / l,

Sheet was with a 2% aqueous K / Na-Poly- 30 g ammonium chloride / l,

phosphate solution containing 0.8 % oleic acid oxethane sulfonate 20 g magnesium sulfate / l and

contained, covered with the help of two rubber rollers. 15 g sodium acetate / l

After the applied layer had dried, 55

the sheet in the enamelling factory to a cover plate at pH 4.0 and 30 ° C with 10 A / dm ² 9 minutes

of a commercially available electric cooker. long electrolytically galvanized and rinsed. Connect!

The polymer layer was then passed through the sheet in a 2% strength aqueous solution

Splash away with water. It was found that K / Na polyphosphate was coated at 60 ° C and ge

that this coating dries through 60 particularly quickly. After the deformation, the Polymei

Washing is to be removed. layer just rinsed off with water.

409 635/36

Claims (8)

Patent claims: 1. Steel sheets provided with a removable cover, possibly an additional have metallic intermediate layer and are not subjected to a cutting deformation and then provided with a firmly adhering protective layer, in particular an enamel layer are characterized by a removable cover made of water-soluble polyphosphates. 2. A method for producing the steel sheets according to claim I, characterized in that on the steel sheets following a surface treatment to be carried out in a known manner the removable Cover applied with the help of a water-soluble polyphosphate-containing solution and then a firmly adhering solution Protective layer, in particular an enamel layer, is applied in a known manner. 3. The method according to claim 2, characterized in that the removable cover is made with an aqueous solution which, as water-soluble polyphosphates, the sodium, potassium, lithium, ammonium and / or substituted ammonium salts of polyphosphoric acids of the general formula HO [HOP (X] _n H, where // is an integer of at least IO. 4. The method according to any one of claims 2 and 3, characterized in that the removable cover is prepared with an aqueous solution, which as water-soluble polyphosphates contains mixed sodium and potassium salts. 5. The method according to any one of claims 2 to 4, characterized in that the removable cover is prepared with an aqueous solution, in addition to the water-soluble polyphosphates additionally contains water-soluble polymers with a plasticizer effect. 6. The method according to any one of claims 2 to 5, characterized in that the removable Cover with an aqueous solution is made, in addition to the water-soluble polyphosphates additionally contains water-soluble polymers with film-forming properties. 7. The method according to any one of claims 2 to 6. characterized in that the removable cover is made with an aqueous solution which contains emulsifiers in addition to the water-soluble polyphosphates. 8. Use of water-soluble polyphosphates for coating steel sheets, clic enameled after deformation.