CN116034185A

CN116034185A - Resource-saving method for zinc phosphating metal surface

Info

Publication number: CN116034185A
Application number: CN202180056390.2A
Authority: CN
Inventors: R·波斯纳; C·安格嫩特; M·巴尔策; F-A·齐卡; S·辛韦尔; J-W·布劳沃; K·瓦普内尔
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2020-08-11
Filing date: 2021-06-28
Publication date: 2023-04-28
Also published as: JP2023538000A; WO2022033759A1; KR20230050387A; EP4196625A1; MX2023001656A; EP3954805A1; US20230175138A1

Abstract

The invention relates to a method for phosphating metallic surfaces in a layered manner using an aqueous colloidal solution as an activation stage, in which method step after activation a layer weight of less than 2.0g/m is deposited on the zinc surface ² Is a zinc phosphate layer. The activation stage is based on a colloidal aqueous solution containing dispersed particulate components which, in addition to the dispersed inorganic compound comprising phosphate of polyvalent metal cations, comprise as dispersant a polymeric organic compound which is at least partially composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms, which polymeric organic compound additionally comprises units of maleic acid, its anhydride and/or its imide, and which polymeric organic compound additionally comprises polyoxyalkylene units. Is thatThe formation of a closed zinc phosphate coating which is sufficiently corrosion-resistant and which can be supplied to a subsequent electrocoat must be such that the particulate component of the aqueous colloidal solution is present in an amount of at least 4g/kg based on the aqueous colloidal solution.

Description

Resource-saving method for zinc phosphating metal surface

The invention relates to a method for zinc phosphating (zinc phosphating) metal surfaces in a layered manner using an aqueous colloidal solution as an activation stage, in which method step after activation a layer weight of less than 2.0g/m is deposited on the zinc surface ² Is a zinc phosphate layer. The activation stage is based on a colloidal aqueous solution containing dispersed particulate components which, in addition to the dispersed inorganic compound of phosphate of polyvalent metal cations, contain as dispersant a polymeric organic compound which is at least partially composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms, which polymeric organic compound additionally comprises units of maleic acid, its anhydride and/or its imide, and which polymeric organic compound additionally comprises polyoxyalkylene units. In order to form a closed zinc phosphate coating that is sufficiently corrosion-resistant and can be supplied to a subsequent electrocoat, it is necessary to have a particle content of the colloidal aqueous solution of at least 4g/kg based on the colloidal aqueous solution.

Stratified phosphating is a process for applying crystalline corrosion-resistant coatings to metal surfaces, particularly metallic iron, zinc and aluminum materials, which has been used for decades and has been under intense investigation. Zinc-phosphorusThe conversion, which is particularly well established for corrosion protection, is carried out with a layer thickness of a few micrometers and is based on the corrosive pickling of metallic materials in an acidic aqueous composition containing zinc ions and phosphate. During the pickling process, an alkaline diffusion layer is formed on the metal surface, which layer extends into the solution, in which slightly soluble crystallites are formed, which precipitate directly at the interface with the metal material and continue to grow there. In order to support the pickling reaction on the metallic aluminium material and to mask the bath poison aluminium interfering in dissolved form with the formation of layers on the metallic material, water-soluble compounds are generally added as fluoride ion sources. By default, zinc phosphating is set to at least 2g/m ² The layer weights of (2) achieve a closed crystalline coating, especially on the zinc surface of the component, for good corrosion protection and coating priming. Depending on the metal surface to be phosphated, the concentration of the active components in the above-mentioned pickling and zinc phosphating stages must be adjusted accordingly to ensure a correspondingly high layer weight on the metal iron or steel, zinc and aluminum surfaces. Zinc phosphating is always initiated by activating the metal surface of the component to be phosphated. Wet chemical activation is typically carried out by contact with aqueous colloidal solutions of phosphates ("activation stage"), as long as they are immobilized on the metal surface, which serve as growth nuclei in subsequent phosphating to form a crystalline coating within the alkali diffusion layer. In this case, suitable dispersions are colloidal, mainly based on neutral to alkaline aqueous compositions of phosphate crystallites, whose crystal structure has only a small crystallographic deviation from the type of zinc phosphate layer to be deposited. In this context, WO 98/39498A1 teaches in particular divalent and trivalent phosphates of the metal Zn, fe, mn, ni, co, ca and Al, it being technically preferable to use phosphates of metallic zinc for the subsequent activation of zinc phosphating.

The activation stage of the divalent and trivalent phosphate based dispersions requires a high level of process control in order to constantly maintain the activation performance at an optimal level, especially when treating a range of metal components. To ensure that the process is sufficiently robust, foreign ions carried over from previous treatment baths or aging processes in the colloidal aqueous solution must not lead to deterioration of the activation performance. In the subsequent phosphating, the significant deterioration initially occurs in an increase in the layer weight and eventually leads to the formation of defective or inhomogeneous phosphate layers. In summary, layering zinc phosphating is thus a technically complex multistage process and has so far been carried out in a resource-intensive manner both in terms of process chemicals and in terms of energy to be consumed. This is especially true for the zinc phosphating process steps, which firstly require high material requirements due to layer formation, especially on components with zinc surfaces, and also remove large amounts of material into the phosphating bath in a manner which is related to the required pickling rate. The high pickling rate has the effect that measures must be taken to prevent or prepare and treat the phosphated sludge, which in turn requires the use of additional process chemicals.

Thus, there is a need to optimize the pretreatment line for zinc phosphating, including the activation stage and the phosphating stage, so that the whole process can be carried out in a less resource intensive manner, in particular in the pretreatment of components having zinc surfaces. However, the whole method of saving resources must not come at the cost of zinc phosphating performance, which must be provided as a uniform, closed coating with high charge transfer resistance, so that good corrosion protection and correspondingly good coating coverage can be obtained in the subsequent electrocoating.

This complex task profile can surprisingly be achieved by depositing a relatively thin phosphate coating, requiring activation based on the use of a specific polymeric dispersant to stabilize the colloidal component of the activation stage, provided that the minimum amount of particulate component in the activation stage is ensured not to be exceeded. Due to the extremely efficient stabilization of the particle components leading to activation, the specific dispersants ensure that a high proportion of the colloid can also set in a quasi-continuous process of zinc phosphating, which surprisingly leads to improved activation of the metal surface and formation of a particularly thin but uniform blocked phosphate coating with high electrical penetration resistance.

The invention therefore relates to a method for the corrosion protection pretreatment of metallic materials having at least partially zinc surfaces or components made up of such metallic materials, in which method the metallic materials or the components are first activated (i) and subsequently zinc phosphating (ii) in successive method steps, wherein the activation in method step (i) is carried out by contacting the metallic materials or the components with an aqueous colloidal solution containing, in the dispersed particulate component (a) of the solution:

(a1) At least one particulate inorganic compound consisting of a phosphate of a polyvalent metal cation, said phosphate being at least partially selected from hopeite, phosphophyllite, phosphomide and/or rhodochrosite, and

(a2) At least one polymeric organic compound at least partially composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms, said polymeric organic compound additionally comprising units of maleic acid, anhydride thereof and/or imide thereof, and said polymeric organic compound additionally comprising polyoxyalkylene units,

the content of particulate components of the colloidal aqueous solution is at least 4g/kg based on the colloidal aqueous solution; and is also provided with

In method step (ii), a layer weight of less than 2.0g/m is deposited on the zinc surface ² Is a zinc phosphate layer.

In the context of the method according to the invention, a metallic material has at least one surface made of zinc if more than 50 at.% of the metallic structure on such a surface is constituted by zinc up to a material penetration depth of at least 1 μm. This generally applies to metallic materials, as homogeneous materials, in which more than 50 at% consists of zinc, but also to materials with zinc metal coatings, such as electrolytic galvanised or hot dip galvanised strip steel, which can also be alloyed with iron (ZF), aluminium (ZA) and/or magnesium (ZM).

The component treated according to the invention may be a three-dimensional structure of any shape and design resulting from the manufacturing process, in particular also including semi-finished products such as strips, sheets, rods, tubes, etc., and composite structures assembled from said semi-finished products, preferably by gluing, welding and/or hemming (flashing) to form a composite structure.

In the activation (i) of the process of the invention, the dispersed particulate component (a) of the colloidal aqueous solution is in an aqueous state that will define a partial volumeThe solid content remaining after drying of the ultrafiltration retentate of the dispersion, said ultrafiltration having a nominal cut-off of 10kD (NMWC: nominal molecular weight cut-off (nominal molecular weight cutoff)). By adding deionized water (kappa) <1μScm ^-1 ) Ultrafiltration was performed until a conductivity of less than 10. Mu.Scm was measured in the filtrate ^-1 。

The dispersed particulate component (a) of the aqueous colloidal solution in the activation (i) of the process according to the invention is the solids content which remains after drying of a defined partial volume of the ultrafiltration retentate of an aqueous dispersion having a nominal cut-off limit of 10kD (NMWC: nominal molecular weight cut-off). By adding deionized water (kappa)<1μScm ^-1 ) Ultrafiltration was performed until a conductivity of less than 10. Mu.Scm was measured in the filtrate ^-1 。

In the context of the present invention, an organic compound is polymeric if its weight average molar mass is greater than 500 g/mol. The molar mass was determined using a molar mass distribution curve of a sample of the relevant reference value, which curve was established experimentally by size exclusion chromatography at 30 ℃ using a concentration-dependent refractive index detector and calibrated against polyethylene glycol standards. The average molar mass is estimated by means of a computer from a bar method using a third-order calibration curve. Hydroxylated polymethacrylates are suitable as column materials, and aqueous solutions of 0.2mol/L sodium chloride, 0.02mol/L sodium hydroxide and 6.5mmol/L ammonium hydroxide are suitable as eluents.

The method according to the invention is characterized in that the uniform, closed zinc phosphate coating has grown on the surface of the metallic material, which represents a comparable coating primer to the prior art zinc phosphate coating for subsequent electrocoating, at an unusually low layer weight, in excess of the amount of the particulate component of 4g/kg in the colloidal aqueous solution, while providing excellent coverage. Nevertheless, the present invention is directed to depositing a uniform, closed zinc phosphate coating onto a zinc surface such that, according to the present invention, it is assumed that in method step (ii), a layer weight of greater than 0.5g/m is provided on the zinc surface ² Preferably greater than 1.0g/m ² Is a zinc phosphate coating.

The reduction in layer weight also allows for shorter wet chemical exposure times or contact times with the zinc phosphating acidic aqueous composition, which in turn is associated with lower acid wash removal and overall shorter pretreatment duration. A further reduction of the layer weight or contact time in zinc phosphating can be achieved if the content of the particulate component in the colloidal aqueous solution is further increased, so that the method according to the invention is preferred, wherein the content of the particulate component of the colloidal aqueous solution is at least 6g/kg, particularly preferably at least 8g/kg, more particularly preferably at least 10g/kg. However, the layer weight reduction achievable in zinc phosphating with further increases in the colloid content in the activation stage is only marginal and increasingly competes with the disadvantages in process control and lower colloid stability in the activation stage. Therefore, the content of the particulate component of the colloidal aqueous dispersion is preferably limited to 20g/kg, particularly preferably to 15g/kg, based in each case on the colloidal aqueous solution.

In the process according to the invention, the zinc phosphate layer coating on the zinc surface should be limited to 2.0g/m for the resource-saving operation of the pretreatment line ² . According to the invention, a sufficiently uniform and closed zinc phosphate coating with excellent covering behaviour in the subsequent electrocoating is provided due to the minimal amount of particulate components in the colloidal aqueous dispersion of the activation stage. The activation of the zinc surface is effective in method step (i) of the method according to the invention in such a way that the layer coating and thus the material consumption can be further reduced in the zinc phosphating stage in method step (ii). Thus, it is preferred to limit the layer weight of zinc phosphate on the zinc surface to less than 1.8g/m in method step (ii) ² Particularly preferably less than 1.6g/m ² More particularly preferably less than 1.5g/m ² . The limitation of the layer weight in process control may be carried out by reducing the contact time with the acidic aqueous composition for zinc phosphating in process step (ii) and/or by increasing the content of particulate components of the colloidal aqueous dispersion in process step (i). The layer weight of zinc phosphate was determined within the scope of the invention by: using 5 wt% CrO ₃ Removing the zinc phosphate layer by using aqueous solution as acid washing solution, wherein The pickling solution is contacted with a defined area of the phosphated material or component at 25 ℃ for 5 minutes immediately after zinc phosphating and with deionized water (κ)<1μScm ^-1 ) Washed and then the phosphorus content in the same pickling solution was determined by means of ICP-OES. The layer weight of zinc phosphate can be obtained by multiplying the amount of phosphorus relative to the surface area by a factor of 6.23.

A further particular advantage of the method according to the invention is that in addition to the zinc surface, the iron and aluminum surfaces are also activated very effectively in method step (i) and that in method step (ii) a very uniform, closed zinc phosphate coating with a relatively low layer weight is obtained on said surfaces as well. Thus, according to the invention, it is preferred to treat components having iron and/or aluminium surfaces in addition to zinc surfaces, it being preferred in method step (ii) to deposit a layer weight of less than 2.0g/m on the iron and aluminium surfaces ² Particularly preferably less than 1.8g/m ² And more particularly preferably less than 1.6g/m ² Very particularly preferably less than 1.5g/m ² But preferably at least 0.5g/m ² Particularly preferably at least 1.0g/m ² Is a zinc phosphate layer. Similarly, if more than 50 atomic percent of the metallic structure on such a surface is comprised of iron or aluminum up to a material penetration depth of at least 1 micron, the metallic material has at least one surface made of iron or aluminum.

In addition, it has been found in the context of the present invention that condensed phosphate which is dissolved in water and which is generally added for colloidal stabilization in the activation phase in the prior art processes is only secondary to maintaining a consistently good phosphate coating in the context of the present invention. It is obvious and surprising to the person skilled in the art that in the process according to the invention based on an activation stage based on the particulate component (a) which is present in an amount of at least 4g/kg based on the aqueous colloidal solution, the addition of condensed phosphate can be largely or completely omitted. In a preferred embodiment of the process according to the invention, the content of condensed phosphate dissolved in water in the activation phase is less than 0.25, particularly preferably less than 0.20, more particularly preferably less than 0.15, and very particularly preferably less than 0.10, based on the phosphate content of the at least one particulate compound in the colloidal aqueous solution (in each case based on element P).

Furthermore, it is preferred in this context that the content of condensed phosphate dissolved in water (calculated as P) in the aqueous colloidal solution of the process according to the invention is less than 100mg/kg, particularly preferably less than 20mg/kg, more particularly preferably less than 15mg/kg, and very particularly preferably less than 10mg/kg, based on the aqueous colloidal solution. In summary, in the context of the present invention, the addition of condensed phosphates can thus be omitted entirely, and thus the activation involves only small amounts of condensed phosphates which bring them from the previous cleaning stage involving the components to be pretreated into the activation stage, in particular when a large number of components are to be treated in series.

In the context of the present invention, condensed phosphates are metaphosphates and polyphosphates, preferably polyphosphates, particularly preferably pyrophosphates. The condensed phosphates are preferably in the form of monovalent cationic compounds, preferably selected from Li, na and/or K, particularly preferably Na and/or K.

The content of condensed phosphate can be determined by analyzing the difference in total phosphate content in the non-particulate component of the aqueous colloidal solution from oxidative digestion and non-oxidative digestion, for example by peroxodisulfates, and the dissolved orthophosphate content is quantified photometrically. Alternatively, if polyphosphates are used as condensed phosphates, enzyme digestion with pyrophosphatase may be used instead of oxidative digestion. The non-particulate component of the aqueous colloidal solution is the solids content of the aqueous colloidal solution in the permeate of the ultrafiltration described above after drying to a constant mass at 105 ℃, i.e. after separation of the particulate component (a) by ultrafiltration.

The high tolerance of the process according to the invention to carried foreign ions also allows the cleaning and rinsing phases, which are carried out before the activation phase, and the activation phase itself to be carried out with industrial water (service water) instead of deionized water. In this way, the method according to the invention is performed in a particularly resource-efficient manner. It is therefore preferred according to the invention that the aqueous colloidal solution in activation contains at least 0.5mmol/L, particularly preferably at least 1.0mmol/L, very particularly preferably at least 1.5mmol/L, but preferably not more than 10mmol/L of alkaline earth metal ions dissolved in water.

If the tolerance of the method according to the invention reaches a system-specific limit in each case with an exceptionally high ionic strength (e.g. high permanent water hardness) and at the same time a high content of carried foreign ions from the previous cleaning stage, organic complexing agents can be added to mask the foreign ions in order to maintain a long bath life. In this case, it must be assessed whether the economic advantages of carrying out the activation phase and, if appropriate, the cleaning phase and flushing with technical water are not hampered by the addition of organic complexing agents and their technical monitoring in the system tank of the activation phase. Suitable organic complexing agents which are preferred in this context are selected from the group consisting of: alpha-hydroxy carboxylic acids, which in turn are preferably selected from the group consisting of gluconic acid, hydroxy malonic acid, hydroxy acetic acid, citric acid, tartaric acid, lactic acid, very particularly preferably gluconic acid; and/or organic phosphonic acids, which in turn are preferably selected from hydroxyethylphosphonic acid, aminotri (methylenephosphonic acid), butane-1, 2, 4-tricarboxylic acid, diethylenetriamine penta (methylenephosphonic acid), hexamethylenediamine tetra (methylenephosphonic acid) and/or hydroxyphosphonoacetic acid, particularly preferably from hydroxyethylphosphonic acid.

In order to maintain stable activation properties, the organic complexing agent should be added only to such an extent that its amount in the aqueous colloidal solution preferably does not exceed twice the amount of alkaline earth metal ions, particularly preferably does not exceed 1.5 times, and very particularly preferably does not exceed an equimolar amount with respect to alkaline earth metal ions.

The aqueous colloidal solution in the activation (i) of the process according to the invention preferably has a basic pH, particularly preferably a pH above 8.0, more particularly preferably a pH above 9.0, but preferably a pH below 11.0, compounds influencing this pH, such as phosphoric acid, sodium hydroxide solution, ammonium hydroxide or ammonia, being used for adjusting the pH. The "pH" used in the context of the present invention corresponds to the negative base 10 logarithm of hydronium ion activity at 20 ℃ (negative decadic logarithm) and can be determined by pH sensitive glass electrodes.

In order to obtain good activation properties, it is necessary to use phosphatesThe phosphate should be contained in a correspondingly high proportion in the dispersed particulate component (a) for activation. The phosphate content contained in the at least one particulate inorganic compound (a 1) is therefore preferably at least 25% by weight, particularly preferably at least 35% by weight, more particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight, based on the dispersed particulate component (a) of the colloidal aqueous solution. The inorganic particulate component of the colloidal aqueous solution is accordingly the remaining material when: by supplying CO-free in a reaction furnace at 900 ℃ without mixing catalysts or other additives ₂ Pyrolysis of the particulate component (a) obtained from drying the ultrafiltration retentate until the infrared sensor provides a gas free of CO in the outlet of the reaction furnace ₂ The same signal as the carrier gas (blank value). At 25℃with 10% by weight of HNO ₃ After the inorganic particulate component was acid-digested in the aqueous solution for 15 minutes, the phosphate contained in the inorganic particulate component was directly measured as the phosphorus content from the acid digestion by atomic emission spectrometry (ICP-OES).

As previously mentioned, the active ingredient of the colloidal aqueous dispersion, which is effective to promote the formation of a closed phosphate coating on the metal surface and to this end activates the metal surface, consists essentially of phosphate which in turn forms a finely crystalline coating and is therefore at least partly selected from hopeite, phosphophyllite, volcanite and/or rhodochrosite (hureaulite), preferably at least partly selected from hopeite, phosphophyllite and/or phosphozincite, particularly preferably at least partly selected from hopeite and/or phosphophyllite, and very particularly preferably at least partly selected from hopeite. Activation within the meaning of the present invention is therefore essentially based on the phosphate contained in the form of particles in the activation phase. The hopeite stoichiometrically contains Zn without regard to the water of crystallization ₃ (PO ₄ ) ₂ And variant Zn containing nickel and manganese ₂ Mn(PO ₄ ) ₃ 、Zn ₂ Ni(PO ₄ ) ₃ Whereas phosphophyllite is composed of Zn ₂ Fe(PO ₄ ) ₃ The hopeite is composed of Zn ₂ Ca(PO ₄ ) ₃ Is composed of red phosphorus manganese ore and Mn ₃ (PO ₄ ) ₂ The composition is formed. After separation of the particulate component (a) by ultrafiltration with a nominal cut-off of 10kD (NMWC: nominal molecular weight cut-off) as described above and drying of the retentate to a constant mass at 105 ℃, the presence of the crystalline phases of hopeite, phosphophyllite, phosphocalcierite and/or rhodochrosite in the aqueous dispersion according to the invention can be confirmed by X-ray diffraction (XRD).

Since it is preferred that a phosphate containing zinc ions and having a certain crystallinity is present, in the process according to the invention, in order to form a firmly adhering crystalline zinc phosphate coating after successful activation, it is preferred for the colloidal aqueous dispersion to use PO based on the phosphate content of the inorganic particulate component ₄ The inorganic particulate component of the colloidal aqueous solution contains at least 20% by weight, particularly preferably at least 30% by weight, and more particularly preferably at least 40% by weight of zinc.

However, activation within the meaning of the invention is preferably not achieved by means of a colloidal solution of titanium phosphate, since layering zinc phosphating on iron, in particular steel, cannot be reliably achieved. Thus, in a preferred embodiment of the process according to the invention, the content of titanium in the inorganic particulate component of the aqueous colloidal solution is less than 0.01% by weight, particularly preferably less than 0.001% by weight, based on the aqueous colloidal solution. In a particularly preferred embodiment, the aqueous colloidal solution of the activation stage (i) contains less than 10mg/kg, particularly preferably less than 1mg/kg, of titanium in total.

The activation stage in the process according to the invention can additionally be characterized by its D50 value above which the activation performance is significantly reduced. The D50 value of the aqueous colloidal solution is preferably less than 1. Mu.m, particularly preferably less than 0.4. Mu.m. In the context of the present invention, the D50 value represents a particle size of not more than 50% by volume of the particulate component contained in the colloidal aqueous solution. Refractive indices n of spherical particles and scattering particles may be used according to ISO 13320:2009 _D =1.52-i.0.1 determination of D50 value from volume weighted cumulative particle size distribution by scattered light analysis at 20 ℃ according to Mie theory immediately after sample removal from the activation stage。

Within the meaning of the present invention, the polymeric organic compound (a 2) used as dispersant is partly composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms and maleic acid, its anhydride and/or its imide, and additionally comprises polyoxyalkylene units. These polymeric organic compounds (a 2) lead to colloidal aqueous solutions having very high stability in the activation stage of the process according to the invention.

In this case, the α -olefin is preferably selected from ethylene, 1-propylene, 1-butene, isobutene, 1-pentene, 2-methyl-but-1-ene and/or 3-methyl-but-1-ene, and particularly preferably from isobutene. It is clear to the person skilled in the art that the polymeric organic compounds (a 2) contain these monomers as building blocks in unsaturated form covalently linked to each other or to other building blocks. Suitable commercially available representatives are, for example

CX 4320 (BASES), maleic acid-isobutylene copolymer modified with polypropylene glycol, +.>

Dispers 752W (Evonik Industries AG), maleic acid-styrene copolymer modified with polyethylene glycol, or +.>

490 Mu nzing Chemie GmbH), maleic acid-styrene copolymers modified with EO/PO and imidazole units. In the context of the present invention, polymeric organic compounds (a 2) which are composed in part of styrene are preferred.

The polymeric organic compound (a 2) used as the dispersant has a polyoxyalkylene unit composed of preferably 1, 2-ethylene glycol and/or 1, 2-propylene glycol, particularly preferably composed of both 1, 2-ethylene glycol and 1, 2-propylene glycol, and the content of 1, 2-propylene glycol in the entire polyoxyalkylene unit is preferably at least 15% by weight, but particularly preferably not more than 40% by weight based on the entire polyoxyalkylene unit. Further, the polyoxyalkylene unit is preferably contained in a side chain of the polymeric organic compound (a 2). The content of the polyoxyalkylene unit in the whole of the polymeric organic compound (a 2) is preferably at least 40% by weight, particularly preferably at least 50% by weight, but preferably not more than 70% by weight, which is advantageous in terms of dispersibility.

In order to anchor the dispersant to the inorganic particulate component of the colloidal aqueous solution, which is formed at least in part from polyvalent metal cations selected from the phosphate forms of hopeite, phosphophyllite, phosphohalcone and/or rhodochrosite, the organic polymeric compound (a 2) also has imidazole units, preferably such that the polyoxyalkylene units of the polymeric organic compound (a 2) are at least partially capped with imidazole groups, so in a preferred embodiment terminal imidazole groups are present in the polyoxyalkylene side chains, the covalent attachment of the polyoxyalkylene units to the imidazole groups preferably being through nitrogen atoms of the heterocycle.

In a preferred embodiment, the amine number of the organic polymeric compound (a 2) is at least 25mg KOH/g, particularly preferably at least 40mg KOH/g, but preferably less than 125mg KOH/g, particularly preferably less than 80mg KOH/g, so that in a preferred embodiment the polymeric organic compound in the particulate component (a) as a whole also has these preferred amine numbers. The amine number is determined in each case by weighing about 1g of the relevant reference value-the organic polymeric compound (a 2) or the polymeric organic compound as a whole in the particulate component-in 100mL of ethanol and titrating the indicator bromophenol blue with a 0.1N HCl titrant solution at an ethanol solution temperature of 20℃until the color turns yellow. The amount of HCl titrant solution used in milliliters multiplied by the factor 5.61 divided by the exact mass of the weight in grams corresponds to the amine value of the relevant reference value in milligrams KOH/gram.

The presence of maleic acid may impart increased water solubility to the dispersant, particularly in the alkaline range, as long as maleic acid is used as the free acid and is not a component of the organic polymeric compound (a 2) in the form of an anhydride or imide. Therefore, it is preferable to make the polymeric organic compound (a 2) as a whole, and also preferably make the polymeric organic compound in the particulate component (a) have an acid value of at least 25mg KOH/g, but preferably less than 100mg KOH/g, particularly preferably less than 70mg KOH/g, according to DGF CV 2 (up to 2018, month 4), so as to ensure a sufficient number of polyoxyalkylene units. It is also preferred to let the polymeric organic compound (a 2), and also preferred to let the polymeric organic compound in the particulate component (a) as a whole have a hydroxyl number of less than 15mg KOH/g, particularly preferred less than 12mg KOH/g, more particularly preferred less than 10mg KOH/g, in each case determined according to method a from european pharmacopoeia 9.0, 01/2008:20503.

For sufficient dispersion of the inorganic particulate component in the colloidal aqueous dispersion, it is sufficient to make the content of the polymerizable organic compound (a 2), preferably the content of the polymerizable organic compound in the particulate component (a) as a whole, at least 3% by weight, particularly preferably at least 6% by weight, but preferably not more than 15% by weight, based on the particulate component (a).

In a preferred embodiment, the present invention relates to a method for corrosion protection pretreatment involving aqueous dispersions. In this preferred process according to the invention, the aqueous colloidal solution in process step (i) is obtainable as an aqueous dispersion diluted 20 to 100,000 times, comprising:

-at least 5% by weight, based on the aqueous dispersion, of a dispersed particulate component (a), which in turn comprises:

(A1) At least one particulate inorganic compound consisting of a phosphate of a polyvalent metal cation, said phosphate being at least partially selected from hopeite, phosphophyllite, phosphocalcieite and/or rhodochrosite,

(A2) At least one polymeric organic compound at least partially composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms, said polymeric organic compound additionally comprising units of maleic acid, anhydride thereof and/or imide thereof, and said polymeric organic compound additionally comprising polyoxyalkylene units, and

At least one thickener (B) optionally present, preferably selected from urea urethane resins, particularly preferably from urea urethane resins having an amine number of less than 8mg KOH/g, preferably less than 5mg KOH/g, particularly preferably less than 2mg KOH/g.

The same definitions and preferred specifications as given above for the colloidal aqueous solution apply equally to the dispersed particulate component (a) and to the at least one particulate inorganic compound (A1) and the polymeric organic compound (A2).

Due to the excellent colloidal stability of the particle component (A) by means of the polymeric organic compound (A2) as dispersant, deionized water (κ) is preferred<1μScm ^-1 ) Dilution with industrial water is particularly preferred in order to make the process according to the invention as resource-saving as possible. According to the potential technical application, the industrial water contains at least 0.5mmol/L of alkaline earth metal ions.

The presence of the thickener according to component (B) imparts thixotropic flow behaviour to the aqueous dispersion in combination with its particulate ingredients and thereby helps to prevent irreversible formation of agglomerates in the particulate ingredients of the dispersion from which primary particles cannot be separated. The addition of the thickener is preferably controlled such that the aqueous dispersion is at a temperature of 25℃for 0.001 to 0.25s ^-1 Has a maximum dynamic viscosity in the shear rate range of at least 1000 Pa-s, but preferably below 5000 Pa-s, and preferably exhibits shear thinning behavior (i.e., the viscosity decreases with increasing shear rate) at 25 ℃ at shear rates that are higher than the maximum dynamic viscosity, such that the aqueous dispersion as a whole has thixotropic flow behavior. In this case, the viscosity in the specific shear rate range can be measured by a cone-plate viscometer having a cone diameter of 35mm and a gap width of 0.047 mm.

The thickener according to component (B) is a polymeric compound or a defined mixture of compounds which is present as deionized water (kappa) at a temperature of 25 DEG C<1μScm ^-1 ) Has a brookfield viscosity of at least 100 mPa-s at a shear rate of 60rpm (=revolutions per minute) using spindle No. 2. When determining the thickener properties, the mixture should be mixed with water in the following manner: the corresponding amount of polymeric compound was added to the aqueous phase at 25 ℃ while stirring, and then the homogenized mixture was bubble removed in an ultrasonic bath and allowed to stand for 24 hours. The viscosity measurements were then read in 5 seconds immediately after a shear rate of 60rpm was applied through spindle No. 2.

The aqueous dispersion according to the invention preferably contains a total of at least 0.5% by weight, but preferably not more than 4% by weight, particularly preferably not more than 3% by weight, of one or more thickeners according to component (B), the total content of polymeric organic compounds in the non-particulate constituents of the aqueous dispersion preferably also not being more than 4% by weight, based on the dispersion. The non-particulate component is the solids content of the aqueous dispersion in the permeate of the ultrafiltration described above after drying to a constant mass at 105 ℃, i.e. after separation of the particulate component by ultrafiltration.

Certain types of polymeric compounds are particularly suitable thickeners according to component (B) and are also readily commercially available. In this connection, the thickener according to component (B) is most preferably selected from polymeric organic compounds, which in turn are preferably selected from polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohols, polyvinylpyrrolidone, polyurethanes and/or urea urethane resins, and particularly preferably from urea urethane resins.

The urea urethane resin as thickener of component (B) of the preferred process according to the invention for providing an aqueous colloidal solution starting from an aqueous dispersion is a mixture of polymeric compounds obtained from the reaction of a polyvalent isocyanate with a polyol and a monoamine and/or diamine. In a preferred embodiment, the urea urethane resin is produced from a polyvalent isocyanate, preferably selected from the group consisting of 1, 4-tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate, 2 (4), 4-trimethyl-1, 6-hexamethylene diisocyanate, 1, 10-decamethylene diisocyanate, 1, 4-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2, 6-toluene diisocyanate, 2, 4-toluene diisocyanate and mixtures thereof, p-xylylene diisocyanate and m-xylylene diisocyanate, and 4-4' -diisocyanato dicyclohexylmethane, particularly preferably selected from the group consisting of 2, 4-toluene diisocyanate and/or m-xylylene diisocyanate. In a particularly preferred embodiment, the urea urethane resin is produced from a polyol selected from polyoxyalkylene glycols, particularly preferably selected from polyoxyethylene glycols, which in turn preferably consist of at least 6, particularly preferably at least 8, more particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23, alkylene oxide units.

Particularly suitable and therefore preferred urea urethane resins according to the invention can be obtained in the following way: the method includes first reacting a diisocyanate (e.g., toluene-2, 4-diisocyanate) with a polyol (e.g., polyethylene glycol) to form an NCO-terminated urethane prepolymer, and then further reacting with a primary monoamine and/or with a primary diamine (e.g., m-xylylenediamine). Particularly preferred are urea urethane resins having neither free nor blocked isocyanate groups. Such urea urethane resins as an ingredient of an aqueous dispersion from which the colloidal aqueous solution according to the method of the invention can be obtained by dilution can promote the formation of loose agglomerates of primary particles, which, however, are stable in the aqueous phase and protected from further agglomeration, thus largely preventing sedimentation of the particulate ingredients in the aqueous dispersion. To further promote this performance characteristic, it is preferable to use as component (B) a urea urethane resin having neither free or blocked isocyanate groups nor terminal amine groups. In a preferred embodiment, the thickener according to component (B), which is a urea urethane resin, therefore has an amine number of less than 8mg KOH/g, particularly preferably less than 5mg KOH/g, more particularly preferably less than 2mg KOH/g, which is in each case determined according to the method as described previously for the organic polymeric compound (A2). Since the thickener is substantially dissolved in the aqueous phase and can therefore be classified as a non-particulate component of the aqueous dispersion, while component (A2) is substantially incorporated in the particulate component (a), an aqueous dispersion for providing an activated colloidal aqueous solution, wherein the polymeric organic compound in the non-particulate component as a whole preferably has an amine number of less than 16mg KOH/g, particularly preferably less than 10mg KOH/g, more particularly preferably less than 4mg KOH/g, is preferred. It is further preferred to have the hydroxyl number of the urea urethane resin in the range of 10 to 100mg KOH/g, particularly preferably in the range of 20 to 60mg KOH/g, determined according to method A of 01/2008:20503 from European Pharmacopeia 9.0. With respect to the molecular weight, the weight average molar mass of the urea urethane resin in the range of 1000 to 10000g/mol, preferably in the range of 2000 to 6000g/mol, is advantageous according to the invention and is therefore preferred, which is in each case determined experimentally, as described previously in connection with the definition of the polymerizable compounds according to the invention.

The pH of the dispersion of the aqueous solution of the activated colloid used to provide the process according to the invention is generally in the range of 6.0-9.0 without the addition of auxiliaries, so that such a pH range is preferred according to the invention. However, in order to be compatible with the actual and customary alkaline aqueous colloidal solutions in the activation stage, it is advantageous if, as a result of the addition of the compounds which react in an alkaline manner, the pH of the aqueous dispersion is above 7.2, particularly preferably above 8.0. Since some polyvalent metal cations have amphoteric character and can therefore be separated from the particulate component at higher pH values, the basicity of the aqueous dispersion according to the invention is desirably limited such that the pH of the aqueous dispersion is preferably below 10, particularly preferably below 9.0.

The aqueous dispersion for providing an aqueous colloidal solution described above is preferably obtainable by the following steps in itself:

i) Pigment paste is provided by grinding and milling 10 parts by mass of an inorganic particulate compound (A1) with 0.5 to 2 parts by mass of a polymeric organic compound (A2) in the presence of 4 to 7 parts by mass of water until reaching a D50 value of less than 1 μm, which D50 value is obtained by dynamic light scattering after 1000-fold dilution with water, for example by a method from Malvern Panalytical GmbH

Nano ZS;

ii) with an amount of water, preferably deionized water (kappa)<1μScm ^-1 ) Or diluting the pigment paste with technical water and a thickener (B) to set at least 5% by weight of the dispersed particulate component (A) and at a temperature of 25 ℃ for 0.001 to 0.25s ^-1 A maximum dynamic viscosity of at least 1000 Pa-s in the shear rate range; and is combined with

iii) The pH is set in the range of 7.2 to 10.0 using a compound that reacts in an alkaline manner,

preferred embodiments of the dispersions are likewise obtained by selecting the corresponding components (A1), (A2) and (A) in the amounts provided or desired in each case as required, as described in connection with the aqueous colloidal solutions.

The aqueous dispersion may also contain adjuvants, for example selected from preservatives, wetting agents and defoamers, in amounts which meet the requirements of the function concerned. The content of auxiliaries, particularly preferably other compounds of the non-particulate constituents which are not thickeners and are not compounds which react in an alkaline manner, is preferably less than 1% by weight. In the context of the present invention, the compounds which react in an alkaline manner are water-soluble (water-solubility: at least 10g/kg of kappa<1μScm ^-1 Water) and has a pK higher than 8.0 for the first protonation step _B Values.

The resource-efficient method control according to the invention is particularly effective in the case of zinc phosphating of a series of components, i.e. during operation of a pretreatment line for zinc phosphating. Thus, in a preferred embodiment of the method according to the invention, a number of specific components, which at least partly consist of a metallic material having at least one zinc surface, are subjected to a series of treatments. The series pretreatment is to bring the individual components into contact one after the other and thus at different times when the series components are each first activated and then zinc phosphatized according to the invention and for this purpose are brought into contact with the baths provided in the system tank for activation and zinc phosphatization. In this case, the system tank is a container in which a colloidal aqueous solution is placed for activation purposes or in which an acidic aqueous composition is placed for phosphating purposes.

There may be a rinse step between the activation (i) and zinc phosphating (ii) to reduce the carry-over of alkaline components into the acidic aqueous composition for zinc phosphating, but preferably the rinse step is omitted to fully maintain activation of the metal surface. The rinsing step is dedicated to the complete or partial removal of soluble residues, particles and active ingredients from the component to be treated, which residues, particles and active ingredients are carried from the component to be treated by adhering to the component from the previous wet-chemical treatment step and which are free of active ingredients based on metallic elements or on semi-metallic elements, which are consumed only by bringing the metallic surface of the component into contact with the rinsing liquid (contained in the rinsing liquid itself). For example, the rinse may simply be municipal or deionized water, or may be a rinse containing a surface active compound, if necessary, to improve wetting by the rinse.

For layered zinc phosphating and semi-crystalline coating formation, which is the purpose of activating the metallic material, it is preferred that the phosphating is carried out in process step (ii) by contacting the surface with an acidic aqueous composition containing 5-50g/L phosphate ions, 0.3-3g/L zinc ions and an amount of free fluoride. According to the invention, said amount of phosphate ions comprises orthophosphoric acid and anions of salts of orthophosphoric acid dissolved in water (in PO ₄ Meter).

The amount of free fluoride or free fluoride source is necessary for the layered zinc phosphating process because components comprising not only zinc surfaces but also iron or aluminum surfaces are zinc phosphated as desired in a layered manner, for example for automotive bodies which are also at least partially made of aluminum. In this context, it is advantageous if the amount of free fluoride in the acidic aqueous composition is at least 0.5mmol/kg, particularly preferably at least 2 mmol/kg. The concentration of free fluoride should not exceed the value at which phosphate coatings have predominantly readily erasable adhesion, since these adhesion cannot be avoided even by disproportionately increasing the amount of particulate component in the activated colloidal aqueous solution. Thus, in the process according to the invention, it is also economically advantageous and therefore preferred that the concentration of free fluoride in the zinc phosphating acidic aqueous composition is below 15mmol/kg, particularly preferably below 10mmol/kg, more particularly preferably below 8mmol/kg, based on the activation (i) and the subsequent zinc phosphating (ii).

After calibration with a fluoride-containing buffer solution without pH buffering, potentiometrically measured at 20℃in the relevant acidic aqueous composition by means of fluoride-sensitive measuring electrodes To determine the amount of free fluoride. Suitable sources of free fluoride ions are hydrofluoric acid and its water soluble salts (such as ammonium bifluoride and sodium fluoride), and complex fluorides of the elements Zr, ti and/or Si, in particular complex fluorides of the element Si. Thus, in the phosphating process according to the invention, the free fluoride source is preferably selected from hydrofluoric acid and its water-soluble salts and/or complex fluorides of the elements Zr, ti and/or Si. If the salt of hydrofluoric acid has a solubility (κ) in deionized water at 60 DEG C<1μScm ^-1 ) At least 1g/L (in F), the salts of hydrofluoric acid are water soluble within the meaning of the present invention.

In order to suppress so-called "pinholes" on the surface of the metallic material made of zinc, it is preferred that in such a process according to the invention, in which zinc phosphating is carried out in step (ii), the free fluoride source is at least partially selected from complex fluorides of the element Si, in particular from hexafluorosilicic acid and salts thereof. Those skilled in the art of phosphating will understand that the term pinhole refers to the phenomenon of localized deposition of amorphous white zinc phosphate on a treated zinc surface or in a crystalline phosphate layer on a treated galvanized or alloyed galvanized steel surface.

In process step (ii) of the process according to the invention, the acidic aqueous composition preferably has a pH of above 2.5, particularly preferably above 2.7, but preferably below 3.5, particularly preferably below 3.3. The free acid content in points (in points) in the acidic aqueous composition of zinc phosphating in process step (ii) is preferably at least 0.4, but preferably not more than 3.0, particularly preferably not more than 2.0. The proportion of free acid in dots was determined by diluting a 10mL sample volume of the acidic aqueous composition to 50mL and titrating to pH 3.6 with 0.1N sodium hydroxide solution. The mL consumption of sodium hydroxide solution represents the number of free acid points.

In the context of the present invention, the conventional addition of additives for zinc phosphating can also be carried out analogously, so that the acidic aqueous composition in process step (ii) can contain conventional accelerators, such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and/or N-methylmorpholine-N-oxide and further cations of metallic manganese, calcium and/or iron in the form of water-soluble salts, which have a positive effect on the layer formation. From an ecological point of view, embodiments in which the acidic aqueous composition for zinc phosphating in process step (ii) contains less than 10ppm total of nickel and/or cobalt ions are particularly preferred.

In the method according to the invention, a good coating primer is prepared for subsequent dip coating, during which a substantially organic cover layer is applied. Thus, in a preferred embodiment of the method according to the invention, dip coating is performed after zinc phosphating with or without an intermediate rinsing and/or drying step, but preferably with a rinsing step and without a drying step, particularly preferably electrocoating, more particularly preferably cathodic electrocoating, which preferably comprises water-soluble or water-dispersible salts of yttrium and/or bismuth in addition to the dispersed resin, which preferably comprises an amine-modified polyepoxide.

Claims

1. Method for the corrosion-protection pretreatment of a metallic material having at least partially a zinc surface or of a component consisting at least partially of such a metallic material, in which method the metallic material or the component is first activated (i) and subsequently zinc phosphating (ii) in successive method steps, wherein the activation in method step (i) is carried out by contacting the metallic material or the component with an aqueous colloidal solution containing, in the dispersed particulate component (a) of the solution:

2. A method according to claim 1, characterized in that in the colloidal aqueous solution the content of condensed phosphate dissolved in water, based on the phosphate content of at least one particulate compound, in each case on element P, is less than 0.25, preferably less than 0.20, particularly preferably less than 0.15, more particularly preferably less than 0.10.

3. The method according to one or both of the preceding claims, characterized in that the aqueous colloidal solution in the activation (i) has a basic pH, preferably a pH above 8.0, particularly preferably above 9.0, but preferably below 11.0.

4. The process according to one or more of the preceding claims, characterized in that the content of phosphate contained in at least one particulate inorganic compound (a 1) is defined as PO, based on the dispersed inorganic particulate component of the colloidal aqueous solution ₄ Preferably at least 25% by weight, particularly preferably at least 35% by weight, very particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight.

5. The process according to one or more of the preceding claims, characterized in that the polymeric organic compound (a 2) of the colloidal aqueous solution contains, in its side chains, polyalkylene oxide units, the content of which in the polymeric organic compound (a 2) as a whole is preferably at least 40% by weight, particularly preferably at least 50% by weight, but particularly preferably not more than 70% by weight.

6. The process according to one or more of the preceding claims, characterized in that said organic polymeric compound (a 2) of the colloidal aqueous solution also has imidazole units, preferably in such a way that said polyoxyalkylene units of said polymeric organic compound (a 2) are at least partially blocked by imidazole groups.

7. The process according to one or more of the preceding claims, characterized in that the colloidal aqueous solution contains as further component (b) at least one thickener, preferably selected from urea-urethane resins, preferably urea-urethane resins having an amine number of less than 8mg KOH/g, particularly preferably less than 5mg KOH/g, very particularly preferably less than 2mg KOH/g.

8. The method according to one or more of the preceding claims, characterized in that the polymeric organic compound in the particulate component of the colloidal aqueous solution as a whole is at least 3 wt%, preferably at least 6 wt%, but preferably not more than 15 wt%, based on the particulate component of the colloidal aqueous solution.

9. The method according to one or more of the preceding claims, characterized in that said colloidal aqueous solution has a D50 value lower than 1 μm, preferably lower than 0.4 μm.

10. The method according to one or more of the preceding claims, characterized in that the content of particulate components of the colloidal aqueous solution is in each case at least 6g/kg, preferably at least 8g/kg, particularly preferably at least 10g/kg, but preferably not more than 20g/kg, particularly preferably not more than 15g/kg, based on the colloidal aqueous solution.

11. The method according to one or more of the preceding claims, characterized in that said aqueous colloidal solution is obtainable as an aqueous dispersion diluted 20 to 100,000 times, comprising:

-at least 5% by weight, based on the aqueous dispersion, of a dispersed particulate component (a), which in turn contains:

(A2) At least one polymeric organic compound at least partially composed of styrene and/or an alpha-olefin having not more than 5 carbon atoms, wherein the polymeric organic compound additionally has units of maleic acid, anhydride thereof and/or imide thereof, and the polymeric organic compound additionally comprises polyoxyalkylene units, and

At least one thickener, optionally present, preferably selected from urea urethane resins, particularly preferably selected from urea urethane resins having an amine number of less than 8mg KOH/g, preferably less than 5mg KOH/g, particularly preferably less than 2mg KOH/g.

12. The method according to one or more of the preceding claims, characterized in that in method step (ii) a layer weight of less than 1.8g/m is deposited on the zinc surface ² Preferably less than 1.6g/m ² Particularly preferably less than 1.5g/m ² Is a zinc phosphate layer.

13. The process according to one or more of the preceding claims, characterized in that the zinc phosphating in process step (ii) is carried out by contact with an acidic aqueous composition containing PO dissolved in water ₄ 5-50g/kg of phosphate, 0.3-3g/kg of zinc ions and an amount of free fluoride which may contain ions of elemental nickel and cobalt in total less than 0.1 g/kg.

14. The method according to one or more of the preceding claims, characterized in that the component having an iron and/or aluminum surface in addition to a zinc surface is treated and that in method step (ii) a layer weight of less than 2.0g/m is deposited, preferably on all zinc, iron and aluminum surfaces ² Particularly preferably less than 1.8g/m ² And more particularly preferably less than 1.6g/m ² And very particularly preferably less than 1.5g/m ² Is a zinc phosphate layer.