EP3129525A2

EP3129525A2 - Method for activating galvanized steel plate that is to be phosphated

Info

Publication number: EP3129525A2
Application number: EP15741927.6A
Authority: EP
Inventors: Fabian JUNGE; Gregor Müller; Nicole Weiher; Heinrich Meyring; Frank Panter
Original assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Current assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Priority date: 2014-04-11
Filing date: 2015-04-07
Publication date: 2017-02-15
Anticipated expiration: 2035-04-07
Also published as: CN106471157A; KR20160145080A; EP3129525B1; JP2017510709A; US20170029954A1; US10480080B2; WO2015155163A2; DE102014105226A1; WO2015155163A3; JP6626000B2; CN106471157B

Abstract

The invention relates to a method for activating metal surfaces, in particular coated steel plate, preferably galvanized steel plate before a phosphating process, wherein the in particular coated, preferably electrolytically galvanized metal plate (2') is brought into contact with an activation bath (6) which contains activation particles dispersed in water, preferably based on phosphate and/or titanium. In order to reduce or even to resolve the problem of poor paint adhesion to preferably electrolytically galvanized, phosphated strip metal, according to the invention, at least one additive (A), which suppresses or at least slows an agglomeration of the activation particles, is supplied to the activation bath (6). Polyethylene glycol (PEG) and/or sodium stearate is preferably added as additive (A). In a particularly preferred embodiment of the method according to the invention, the particle size distribution of the activation particles in the activation bath (6) is identified and the activation bath (6) is renewed or removed from operation in dependence on the particle size distribution of the activation particles.

Description

Method for activating metal surfaces to be phosphated, preferably galvanized sheet steel

The invention relates to a method for activating metal surfaces,

in particular of coated steel sheet, preferably galvanized sheet steel before a phosphating process, in which the metal surface with a

Activating bath is brought into contact, which contains water-dispersed inorganic metal activation particles, preferably based on phosphate and / or titanium. Zinc phosphate coatings are used in the prior art for the surface treatment of galvanized sheet steel in order to improve surface-relevant properties of the galvanized steel sheet. These include in particular the increase in corrosion resistance and the improvement of formability and paint adhesion. On the part of the Applicant, it was found that in recent years, non-periodic, recurrent paint adhesion problems on, for example, electrolytically galvanized and phosphated metal strip, in particular steel strip (thin sheet) occurred. On this basis, the present invention has the object to provide a method with which the problem of poor paint adhesion to metal strip can be significantly reduced or even avoided.

This object is achieved in a method of the type mentioned in that at least one additive is supplied to the activation bath, which suppresses or at least slows down an agglomeration of the activation particles.

The inventors have studied the mechanisms of activation, nucleation and growth of zinc phosphate crystals on the zinc coating. They have noticed increasing lifetime of the activation bath agglomerates of

Form activation particles. In addition, they were able to detect a negative influence of the increasing particle sizes in the activation bath on the phosphating and the paint adhesion.

The inventive addition of an additive which suppresses agglomeration of the activation particles or at least slows down significantly, the problem of poor paint adhesion to phosphated metal strip, in particular galvanized, phosphated steel strip can be significantly reduced or even avoided.

The additive used to stabilize the activation bath may in particular be one or more of the following substances:

Nonionic, anionic, cationic and / or zwitterionic surfactants

Polyethylene glycol (PEG), in particular between 1 and 200 g / l PEG

Salts, especially alkali, alkaline earth salts of the fatty acids, e.g. Sodium stearate, but also salts of branched and unbranched, saturated and

unsaturated carboxylic acids with other cations which have no negative influence in the activation bath and in the subsequent process stages at common fatty acid salt concentrations (for example Zn)

Carboxylic acids, in particular formic acid, acetic acid, citric acid,

Tartaric acid, ascorbic acid, nitrilotriacetic acid (NTA), iminodisuccinic acid and salts thereof, in particular sodium and potassium salts

Poly (oxy-l, 2-ethanediyl) -carboxylic acid esters, in particular poly (oxy-l, 2-ethanediyl) -monododecanoic sorbityl esters, polyoxyethylene (20) sorbitan monooleate and other polysorbates

Alkylpolyethylenglycolether, in particular Isotridecylpolyethylenglycolether

Sulfates and sulfonates in general, especially alkylbenzenesulfonates

Phosphoric and phosphonic acids and their esters and salts, in particular

Phosphonates, such as, for example, 1-hydroxyethane- (1,1-diphosphonic acid), phosphonobutanetricarboxylic acids, aminophosphonates, for example aminotrimethylenephosphonic acid, itriaminpenta (methylenephosphonic acid) and

Ethylenediaminetetra (methylenephosphonic acid), N- (phosphonomethyl) glycine and its salts

Mono- and polymeric esters and ethers, in particular 2-phenoxy-l-ethanol, alkyl alcohol ethoxylates, in particular with alkyl = linear C9- to Cll hydrocarbons

Polycarboxylates, in particular polymers and copolymers of acrylic acid, the

Maleic acid and fumaric acid and their alkali, alkaline earth and

Nebengruppenmetallsalze, in particular zinc salts

Alkylphenol ethoxylates, in particular nonylphenol ethoxylates

Amino acids and in particular polyamino acids and their salts, in particular

Polyaspartic acid and its salts, in particular sodium and potassium salts

Azoles, especially Benzo- and Tolyltriazoles, Benzimidazoles Preferred and advantageous embodiments of the method according to the invention are specified in the subclaims.

An advantageous embodiment of the method according to the invention is characterized in that the activation bath of polyethylene glycol (PEG) and / or sodium stearate is added as an additive for suppressing or slowing down an agglomeration of the activation particles. These two substances have each in

Tried to be very effective.

To slow down the activation particle agglomeration in the activation bath, it is also advantageous if according to a further preferred embodiment of the method according to the invention, the activation bath is moved continuously or discontinuously by stirring and / or pumping and / or ultrasonic input. As a result, the service life of the activation bath can be further extended. The intensity of the bath movement (by stirring and / or pumping over and / or

However, ultrasound entry should not be too high, otherwise agglomeration of the activation particles in the activation bath may occur Preferably, the activation bath is stirred by means of at least one mechanical stirrer.

A further preferred embodiment of the method according to the invention is characterized in that the particle size distribution of the activation particles present in the activation bath is determined, and that the activation bath is renewed or taken out of operation as a function of the particle size distribution of the activation particles. In this way, a critical or excessive attachment (adhesion) of agglomerated activation particles to the preferably

electrolytically galvanized sheet metal largely avoided and thus a perfect paint adhesion can be achieved.

In this context, it is advantageous if, according to a preferred

Embodiment of the method according to the invention, the particle size distribution of the activation particles during operation of the activation bath at regular intervals or continuously by means of dynamic light scattering

(Photon correlation spectrometry) is determined. Alternatively or additionally, the particle size distribution of the activation particles can also during operation of the activation bath at regular intervals or continuously means

Nanoparticle Tracking Analysis (NTA) can be determined. These two measuring methods are particularly suitable and reliable for the relevant particle sizes and distribution widths. The measurement can be carried out in each case on separate, limited samples of the activation bath or alternatively also by means of at least one

Flow cell to be performed.

However, it is also possible to use other measuring methods for determining the particle sizes or particle size distribution of the activation particles in the method according to the invention. For measurement in liquid, for example on separate, limited samples and also as a flow measuring cell, the following measuring methods are conceivable, for example:

• Static laser diffraction g of light microscopy with an automatic image analysis

• Resonance Mass Measurement ("Resonant Mass Measurement")

• Acoustophoretic measurement technique

• ultrasound spectrometry

· Field Flow Fractionation

• Hydrodynamic chromatography

• Capillary hydrodynamic fractionation

• spatial filter anemometry (Spatial Filter Velocimetry)

Atomic Force Microscopy on particles on planar substrate surfaces in air, vacuum, or liquid.

Alternatively or additionally, measurements with electron microscopic methods on suitable carriers or substrates can also be carried out in this connection, for example:

Scanning Electron Microscopy (SEM), in particular on automated substrates, such as metallographically polished surfaces, preferably singulated particles, preferably also counted by image-analytical methods and classifiable by geometrical sizes in order to obtain a statistically qualified size distribution are SEM images in topography contrast and / or

Mass contrast.

(Scattering) Transmission Electron Microscopy (TEM, STEM): In particular, on transmittable supports such as e.g. a polymer film (paint film)

coated particles or particles which are embedded in radiopaque matrix (e.g., polymers), or particles adhered to supports (e.g., ridges of a commercial TEM mesh) which are laterally exposed to irradiation.

• EDX or WDX distribution images taken with SEM or REMEM concerning the chemical elements or any of them which essentially describe the composition of the particles. effective activation, nucleation, and good growth of the zinc phosphate crystals on the zinc coating, it is further advantageous if the activation bath according to a further preferred embodiment is adjusted to have an activation particle concentration in the range of 0.1 g / 1 to 10 g / l, in particular 0.5 g / 1 to 3 g / 1.

The invention will be described with reference to a drawing and several

Embodiments explained in more detail. The single figure shows schematically a

Procedure of a continuous electrolytic galvanizing and

Phosphating of (rolled) steel strip.

A cold-rolled and optionally dressed steel strip (steel sheet) is provided as coil 1. The steel strip (steel sheet) 2 is unwound from the coil 1 and welded to the end of the previous strip. Since it is at the following

electrolytic surface finishing is a continuous process, the newly entering the electrolytic processing plant belt is first passed into a tape loop storage 3, where it is stored in one or more loops, so that the coating process when welding the

Steel strip beginning at the end of the previous steel strip does not have to be stopped.

In a first stage of the refining process (coating process), the strip surface is usually first mechanically and chemically cleaned.

Subsequently, the strip surface is roughened in an acidic stain before the strip 2 is passed through the electrolytic coating cells 4 and galvanized there. There, the steel strip 2 is immersed in a sulfuric acid zinc electrolyte and switched simultaneously as a cathode. In the case of soluble zinc electrodes, these are also immersed in the electrolyte solution and connected as an anode. The zinc cations migrate from the anode through the electrolyte to the steel strip surface and are deposited there cathodically. In the case of insoluble anodes, however, the zinc is already dissolved in the electrolyte, the anodes from corresponding nobler

Materials exist. The amount of zinc deposited on the surface of the strip depends Current density and the duration of coating. In order to achieve a zinc layer thickness of a few micrometers at a belt speed of, for example, 100 m / min

Belt speed relatively short coating time and thus correspondingly low deposition rate in an electrolytic cell 4 through a plurality of consecutively connected coating cells 4. Then, the electrolyte of the

To remove strip surface and thus avoid electrolyte entrainment in the next process step, the electrolytically galvanized steel strip 2 'is passed through a multi-stage flushing device 5.

The pretreatment step for the phosphation is followed by a generally slightly alkaline activation bath 6. In the case of phosphating, activation baths serve to increase the number of nucleation sites and thus the phosphate crystals per unit area and thus to increase the crystallization rate

Increase the degree of coverage.

The activation bath 6 contains water-dispersed activation particles, generally based on phosphate and / or titanium or metal oxides. The available for example in powder form activation particles are dispersed in water and form with this a colloidal solution. For example, the activation bath 6 is adjusted to have an activation particle concentration in the range of 0.1 g / 1 to 10 g / l, in particular 5 g / 1 to 3 g / l, preferably 0.7 g / 1 to 1.5 g / 1.

Suitable activating agents (activating particles) for the phosphating of electrolytically galvanized steel sheet 2 'are, for example, under the trade names SurTec® 145, SurTec® 610 V, SurTec® 615 V, SurTec® 616 V,

Fixodine®X, Fixodine®50, Fixodine®50CF (now Bonderite® M-AC 50CF),

Fixodine®950 (now Bonderite® M-AC 950), Fixodine® G 3039, Fixodine® C 5020 A, Fixodine® G 5020 B, Fixodine® C 9114, Fixodine® 9112, Gardolene® Z26, Gardolene® V 6599, Gardolene® V 6560 A, Gardolene® V 6559, Gardolene® V 6526, Gardolene®

V 6522, Gardolene® V 6520, Gardolene® V 6518, Gardolene® V 6513, Prepalene® X ® 163 available. When used for pretreatment of phosphated metal surfaces, such as the steel sheet 2 '

Activation particles (activating agents) are usually so-called Jernstedt salts or titanyl phosphates.

In order to maintain the dispersed state of the activation particles, the activation bath 6 is stirred continuously and discontinuously and / or circulated and / or ultrasonicated. For example, that will

Activating bath 6 is stirred by means of at least one mechanical stirrer 7.

After passing through the activation bath 6, the liquid film is squeezed or stripped off the steel strip 2 'in order to avoid carryover of the possibly alkaline medium (liquid film) into the acid phosphating solution. Drying of the steel strip surface may also be expedient at this point. In the figure, accordingly, a hot air blower 8 is outlined. In the phosphating step 9, the phosphating solution is sprayed onto the activated strip surface. On the one hand, this leads to heating of the zinc surface and, on the other hand, to growth of the zinc phosphate crystals on the activated regions. The remaining supernatant phosphating solution is then squeezed off the belt and the

phosphated strip 2 "is then dried by means of a belt drier 10. In the final steps of this strip finishing process, the phosphated steel strip 2" is optionally oiled and reeled into a coil 11 so that it can be transported to the customer in a manageable form. At the customer, for example, an automobile manufacturer, are from the

phosphated steel strip blanks punched and to components, for example

Body parts, pressed. Since the forming of the boards by drawing and / or stretching of the material as well as by abrasion can lead to damage of the phosphate layer, the metal surface is reactivated and nachphosphatiert. Therefore, the forming step is usually followed by a degreasing step in a slightly alkaline solution and the rinsing of the cleaner in a multi-stage solution ; at. The rinse is followed by the re-activation step and the post-phosphation. The phosphating solution is removed by another multi-stage flushing device before the component is painted. Usually, a base coat is applied to the phosphated by cathodic dip painting

Part surface applied. The components are run with the still wet basecoat surface into an oven, typically a continuous oven, where the paint is cured at relatively high temperatures (e.g., about 180 ° C). Subsequently, if necessary, a filling and finally a topcoat is applied. In order to avoid poor paint adhesion caused by activation particle agglomerates or to achieve good paint adhesion, at least one additive A is added to the activation bath 6 preceding the phosphating, which suppresses or at least slows down agglomeration of the activation particles. The additive forms a shell around the activation particles, whereby agglomeration of the activation particles can be suppressed at least for a certain time compared to conventional activation baths. As additive A, the activation bath 6 is for this purpose, for example, polyethylene glycol (PEG),

preferably with molar masses below 6000 g / mol, in particular around 400 g / mol (so-called PEG 400). For example, between 1 and 200 g / l PEG are added to the activation bath, the activation bath 6 a

Activating particle concentration in the range of 0.1 g / 1 to 10 g / 1, in particular 0.5 g / 1 to 3 g / 1, preferably from 0.7 g / 1 to 1.5 g / 1.

Instead of polyethylene glycol (preferably PEG 400), sodium stearate as additive A is added to the activating bath 6 preceding the phosphating according to a further embodiment of the process according to the invention. Sodium stearate is the sodium salt of stearic acid and a basic ingredient of many soaps.

Sodium stearate is a water-soluble solid. For example, between about 0.01 g / l and 100 g / l of sodium stearate is added to the activating bath, wherein the activating bath 6 has an activating particle concentration in the range of 0.5 g / l to 3 g / l, preferably 0.7 g / l to 1.5 g / 1. According to a further exemplary embodiment of the process according to the invention, poly (oxy-1,2-ethanediyl) -carboxylic acid ester, in particular poly (oxy-1,2-ethanediyl) -monododecanoic sorbityl ester, is added as additive A to the activating bath preceding the phosphating. This additive, which is also commonly referred to as polysorbate 20 (trade name "Tween® 20"), is a nonionic surfactant which acts as a wetting agent, for example, for 1 l activating bath having an activation particle concentration in the range of 0 , 1 g / 1 to 10 g / l,

in particular from 0.5 g / 1 to 3.0 g / l, preferably from 0.7 g / 1 to 1.5 g / l, between 0.01 g / 1 to 100 g / l polysorbate 20 ("Tween® Instead of this additive, it is also possible to add to the activating bath 6 polysorbate 40, polysorbate 60, polysorbate 65 or polysorbate 80 (trade name "Tween® 80") as additive A.

According to a further embodiment of the process according to the invention, alkylpolyethylene glycol ether, in particular isotridecylpolyethylene glycol ether, is added to the activating bath 6. This additive is a nonionic surfactant whose physical state is liquid. It acts in particular as a wetting agent and is available in various variants under the tradename MARLIPAL®013, the different variants differing in the number of ethylene oxide moles included. For example, on 1 1 activation bath 6, the one

Activating particle concentration in the range of 0.1 g / 1 to 10 g / 1, in particular 0.5 g / 1 to 3.0 g / 1, preferably from 0.7 g / 1 to 1.5 g / 1, about 0 , 1 to 10 ml

Alkylpolyethylenglycolether added as additive A. An advantageous optional embodiment of the above

Embodiments of the method according to the invention is that in the

Activating 6 to determine existing particle size distribution of the activation particles and renew the activation bath 6 depending on the determined particle size distribution or decommissioning. The measurement of the particle size distribution takes place by means of dynamic light scattering. Alternatively or additionally, the measurement of the particle size distribution can also be carried out by means of nanoparticle tracking be carried out. The measurement of the particle size distribution of the activation particles of the activation bath 6 is preferably carried out on the basis of separate samples (partial volumes) of the activation bath 6 or by means of at least one flow measuring cell (not shown), wherein the sampling and the measurement preferably during the operation of the activation bath in regular

Time intervals or continuously performed.

The renewal or decommissioning of the activation bath 6 as a function of the determined particle size distribution of the activation particles of the activation bath 6 then preferably also takes place automatically. The phosphating process can thus be conducted more safely.

Claims

P a n t a n s p r e c h e

Method for activating metal surfaces, in particular of

coated steel sheet, preferably galvanized sheet steel prior to a phosphating process in which the in particular coated, preferably electrolytically galvanized sheet metal (2 ') is brought into contact with an activating bath (6) which comprises water-dispersed activating particles, preferably based on phosphate and / or titanium contains, characterized in that the activation bath (6) at least one additive (A) is supplied, which suppresses agglomeration of the activation particles or at least slows down.

A method according to claim 1, characterized in that the activation bath (6) one or more surfactants, preferably polyethylene glycol and / or sodium stearate is added as an additive for suppressing or slowing down an agglomeration of the activation particles.

Method according to claim 1 or 2, characterized in that the

Activating bath (6) is moved continuously or discontinuously by stirring and / or pumping over and / or by Ultraschallalleintrag.

Method according to 3, characterized in that the activation bath is stirred by means of at least one mechanical stirrer (7).

Method according to one of claims 1 to 4, characterized in that in the activation bath (6) present particle size distribution of the activation particles is determined, and that the activation bath (6) is renewed or taken out of service depending on the particle size distribution of the activation particles. n according to claim 5, characterized in that the particle size distribution of the activation particles during operation of the activation bath (6) is determined at regular intervals or continuously by means of dynamic light scattering.

A method according to claim 5 or 6, characterized in that the

Particle size distribution of the activation particles during operation of the activation bath (6) at regular intervals or continuously determined by nanoparticle tracking analysis.

Method according to one of claims 1 to 7, characterized in that the activation bath (6) is adjusted so that it has an activation particle concentration in the range of 0.1 g / 1 to 10 g / 1, in particular 0.5 g / 1 to 3 g / 1, preferably from 0.7 g / 1 to 1.5 g / 1.