Pretreatment of galvanized metallic substrates with aluminum oxide hydroxide containing rinsing solutions

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] PRETREATMENT OF GALVANIZED METALLIC SUBSTRATES WITH ALUMINUM OXIDE HYDROXIDE CONTAINING RINSING SOLUTIONS

[0002] The present invention relates to a method of pretreating an at least partially galvanized metallic substrate, and the thus obtainable substrate. The invention further relates to a method of coating a metallic substrate, comprising the steps of the afore-mentioned method of pretreating a metallic substrate followed by one or more coating and curing steps, and the thus obtainable coated substrate. The invention further relates to the use of an aqueous composition containing aluminum oxide hydroxide particles, as a rinsing composition after a chemical pretreatment of an at least partially galvanized metallic substrate.

[0003] BACKGROUND OF THE INVENTION

[0004] In coatings industry, particularly in the automotive coatings industry, metallic substrates must undergo several treatment and coating steps to meet the many requirements of the final multilayer coating systems, such as visual requirements, but also chemical and mechanical requirements. Visual requirements are, e.g., to show a good appearance, leveling, gloss and the like. Chemical requirements are mostly resistance requirements, such as resistance to corrosion and / or weathering or to bird droppings. Finally, there are mechanical requirements, such as scratch resistance or resistance to stone chipping.

[0005] A typical architecture of a multilayer coating in automotive industry starts with a chemical- pretreatment layer applied on the thoroughly cleaned metallic substrate, followed by an electrodeposition coating layer, a primer filler layer, a basecoat layer and finally a clearcoat layer. Sometimes more than one layer of a kind is applied.

[0006] Each of these layers provides one or more different functions or properties to the multilayer coating system. Obviously the most outer layer, typically being the clearcoat layer, is most responsible for properties such as scratch resistance, but also weathering resistance, resistance to bird droppings, and to many aspects of appearance. However, it belongs to the general knowledges of one skilled in the art of automotive coating that even the first layers applied onto the metallic substrate typically have an influence on the properties and quality of the complete multilayer coating, even on the most outer layer. Particularly, if adjacent layers are not compatible with each other this may deteriorate the whole multilayer coating system. Thus, if adhesion between layers is poor this may lead to corrosion problems, or if the flexibility of a layer is poor this may lead to a lack of sufficient stone-chip resistance. Thus, properties and functions of the multiple layers are interrelated with each other. Considering the stone impact resistance, this is typically achieved by using specific filler materials and / or polymers in the primer filler layer. However, the layers directly adjacent to the primer filler layer, such as the electrodeposition layer and / or the basecoat layer are also known to be frequently optimized to take over such task as stone impact resistance. Nevertheless, this is associated with increased efforts to find coating formulations which as such are stable, but also compatible with the adjacent coating layers. Furthermore, to increase the stone-chip resistance, such layers, like filler primer layers, should have a sufficient dry film thickness to accomplish that task, thus leading to a significant consumption of coating material.

[0007] Therefore, there is a desire to find a possibility to increase the stone-chip resistance of a multilayer coating system without the necessity to re-formulate well-established coating materials and to risk incompatibilities between coating layers which might be associated therewith.

[0008] It would be particularly preferred, if this task can be accomplished before any regular coating materials, such as electrodeposition coating materials, are applied. This is also important in those cases, where it is deviated from automotive coating architecture, e.g., if only one layer, such as a powder coating is applied on the pretreated substrate and layers such as an electrodeposition layer or primer filler layer are lacking.

[0009] Consequently, it was the aim of the present invention to find a way to improve the stone-chip resistance of a coated metallic substrate, particularly a coated at least partially galvanized metallic substrate during the pretreatment of the metallic substrate, i.e., prior to the application of an electrodeposition coating material, primer filler coating material or powder coating material, even without re-formulating the chemical pretreatment compositions applied on an at least partially galvanized metallic substrate. Moreover, the present invention should preferably encompass the possibility to treat multi-metallic substrates, which provide galvanized surfaces but also other metallic surfaces such as bare steel, cold rolled steel or aluminum and its alloys, without deteriorating the overall stone-chip resistance of such non-galvanized parts of the metallic substrates.

[0010] SUMMARY

[0011] It was surprisingly found that the aims of the present invention are achieved by providing a method of pretreating an at least partially galvanized metallic substrate, the method comprising the following steps: i. one or more cleaning steps, wherein at least part of the galvanized surface of the metallic substrate is contacted with one or more aqueous cleaning compositions, to obtain a cleaned metallic substrate; followed by ii. one or more rinsing steps, wherein at least the part of the surface of the metallic substrate obtained in step(s) i. is contacted with one or more aqueous rinsing compositions A, to obtain a cleaned and rinsed metallic substrate; followed by iii. one or more layer forming chemical pretreatment steps, wherein at least part of the galvanized surface of a metallic substrate is contacted with one or more chemical pretreatment compositions to obtain a chemically pretreated substrate; followed by iv. one or more rinsing steps, wherein at least the part of the chemically pretreated substrate obtained in step(s) iii. is contacted with one or more aqueous rinsing compositions B, wherein at least one of the rinsing compositions B used in the one or more rinsing steps iv. contains aluminum oxide hydroxide particles.

[0012] In the following, the afore-mentioned method of pretreating a metallic substrate and its preferred embodiments is denoted as “method of pretreating a metallic substrate according to the invention.”

[0013] A further subject matter of the invention is a pretreated, at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions and thereon a layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles. Such pretreated, at least partially galvanized metallic substrate, can be obtained by the method of pretreating a metallic substrate according to the invention.

[0014] In the following, the afore-mentioned pretreated, at least partially galvanized metallic substrate and its preferred embodiments are denoted as the “pretreated, at least partially galvanized metallic substrate according to the invention.”

[0015] Yet another subject matter of the present invention is a method of coating a metallic substrate, the method comprising the afore-mentioned method of pretreating a metallic substrate according to the invention, wherein after the last rinsing step v. one or more coating compositions selected from the group of solid coating compositions and liquid coating compositions are applied to form one or more coating layers, each of the one or more coating layer being cured or not cured after application; and vi. curing any one or more coating layers applied in step v. which is or are not cured in step v.

[0016] In the following, the afore-mentioned method of coating a metallic substrate and its preferred embodiments is denoted as “method of coating a metallic substrate according to the invention.”

[0017] A further subject matter of the invention is a coated, pretreated at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions, thereon a layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles, and thereon one or more cured coating layers. Such coated, pretreated, at least partially galvanized metallic substrate, can be obtained by the method of coating a metallic substrate according to the invention.

[0018] In the following, the afore-mentioned coated, pretreated at least partially galvanized metallic substrate and its preferred embodiments are denoted as the “coated, pretreated, at least partially galvanized metallic substrate according to the invention.”

[0019] Further subject matter of the invention is the use of an aqueous composition containing aluminum oxide hydroxide particles, as a rinsing composition after a chemical pretreatment of an at least partially galvanized metallic substrate.

[0020] In the following, the afore- mentioned use and its preferred embodiments are denoted as “use according to the invention.”

[0021] In the following section, the invention will be described in more detail.

[0022] DETAILED DESCRIPTION

[0023] In the following terms used in the present invention are defined and / or explained.

[0024] The term “pretreatment” or “pretreating” as used herein is used in accordance with the term “surface pretreatment” as defined in Rdmpp Lexikon “Lacke und Druckfarben” (Publisher: Ulrich Zorll, Editor: Hans-Jurgen P. Adler - Stuttgart; New York: Thieme, 1998; term: “Oberflachenvorbehandlung” page 417).

[0025] On metallic substrates, according to DIN 50902: 1994-07, the first step of a surface treatment is a layer-removing step, including one or more (chemical) cleaning steps with aqueous cleaning compositions, and is also called “surface preparation step”.

[0026] The term “chemical pretreatment” is used in accordance with EN ISO 4618:2006 (E / F / D) (term: 2.41 “chemical pretreatment,” which stands for any chemical process applied to a surface prior to the application of a coating material). According to this standard, e.g., treatments like chromating and phosphating, which belong to conversion treatment, belong to the chemical pretreatment and thus are to be distinguished from coating steps, wherein coating materials, i.e., coating compositions such as powder coating compositions, electrodeposition coating compositions, aqueous or non-aqueous liquid (solvent-borne or powder) coating materials are applied.

[0027] Besides the typical conversion treatments such as chromating and phosphating, the chemical surface pretreatment may be achieved with passivation compositions and thin-film forming compositions, which will be described in more detail herein below. Most preferred in the present invention are chemical pretreatments making use of thin-film forming compositions.

[0028] In accordance with the above internationally valid definitions of a “pretreatment” of metallic substrates, the pretreatment method according to the present invention encompasses one or more surface preparing cleaning steps and one or more chemical pretreatment steps, both followed by at least one rinsing step.

[0029] The term “metallic substrate” encompasses, in accordance with the general understanding of said term, any substrate having a surface comprising one or more pure metals and / or alloys. If a substrate comprises areas of different metals, such substrate is herein denoted as “multi- metallic substrate” as a subclass of metallic substrates.

[0030] Metallic substrates are used in the present invention are preferably selected from bare steel, cold rolled steel, galvanized steel, such as electrogalvanized steel and hot-dip galvanized steel and aluminum and its alloys. The metallic substrates can comprise or consist of preassembled parts of metallic substrates, the preassembled parts of the metallic substrate consisting of the same or different metals or alloys. The metallic substrates can be used in the automobile industry, for railway vehicles, in the aerospace industry, in apparatus engineering, in mechanical engineering, in the building industry, in the furniture industry, for the manufacture of crash barriers, lamps, profiles, sheathing or hardware, for the manufacture of car bodies or body parts, individual components or preassembled / connected elements, preferably in the automobile or aeronautical industry, or for the manufacture of appliances or installations, especially household appliances, control devices, testing devices or structural elements.

[0031] The term “at least partially galvanized metallic substrate” denotes for a metallic substrate, the surface of which is at least partially coated with a zinc layer.

[0032] The term “at least part of the metallic substrate” means, in accordance with the general understanding of said term, that in some cases it might be desired or sufficient to contact not the whole surface of the substrate with a cleaning composition, rinsing composition and / or chemical pretreatment composition. If only part of the metallic surface is contacted with the respective composition, it is typically the same part for all steps of the method. However, generally, it is desired to contact the whole surface of the metallic substrate with the respective composition(s).

[0033] The term “contacting the surface of a substrate” encompasses, in accordance with the general understanding of said term, any type of direct contacting.

[0034] The term “composition” herein means a substance which is composed of one or more ingredients, typically more than one ingredient. However, e.g., a “rinsing composition” may even be composed of water, only.

[0035] The term “aqueous” in combination with the term “composition” means that the volatile content of the composition wherein other ingredients might be dissolved or dispersed, predominantly contains or even consists of water. The content of water, based on the total weight of such composition is particularly in case of aqueous rinsing compositions preferably 97 wt.-% to 100 wt.-%, more preferred 98 wt.-% to 99.99 wt.- %, even more preferred 99 wt.-% to 99.98 wt.-% and most preferred 99.50 to 99.97wt.-%.

[0036] The term “cleaning composition” defines, in accordance with the general understanding of said term, a composition which removes impurities from the surface of the to be further treated metallic substrate, i.e., cleans the metallic substrate, but which does not permanently remain on the surface of the metallic substrate. Thus, the term “cleaning composition” differs from the term “coating composition,” since a coating composition is intended to remain permanently on a substrate.

[0037] The term “rinsing composition” defines, in accordance with the general understanding of said term, a composition which removes excessive parts of a composition which was contacted with the metallic surface in the step directly preceding the rinsing step wherein the rinsing composition is used. In the simplest case a rinsing composition can be pure, e.g., de-ionized water.

[0038] The term “chemical pretreatment composition” as used herein encompasses compositions such as “conversion treatment compositions”, “passivation treatment compositions” and “thin- film forming compositions”.

[0039] The term “conversion treatment composition” defines, in accordance with the general understanding of said term, a composition, which, if applied to a substrate metal produces a superficial layer containing a compound of the substrate metal (often referred to as conversion coating) and an anion of an environment (ISO 2080:2008 (E / F), term: 2.3 “conversion treatment”).

[0040] The term “followed by” in the context of the steps being carried out in the methods according to the invention is used in the meaning of “subsequent to” or “after.” Thus, it gives an order of steps, but it is not intended to exclude intermediate steps, such as flash-off or drying steps. For example, particularly in those cases where the steps of the methods according to the invention are carried out at spatially different locations, with a significant time gap between the steps, it might be reasonable to include intermediate drying steps, particularly after the ii. and / or iv. rinsing step(s).

[0041] Method of Pretreating According to the Invention

[0042] The method of pretreating a metallic substrate according to the present invention provides a method of pretreating metallic substrates particularly to improve stone chip resistance of surfaces of galvanized metallic substrates.

[0043] The method comprises at least a combination of one or more cleaning steps with one or more subsequent rinsing steps; followed by one or more chemical pretreatment steps with one or more subsequent rinsing steps. It is crucial to the method that in one or more rinsing steps, after the last of the one or more chemical pretreatment steps, aluminum oxide hydroxide, i.e., AIO(OH) particles are employed in the rinsing composition to achieve an improvement in stone chip resistance.

[0044] The / '. Cleaning Step(s)

[0045] In step(s) i. of the method of pretreating according to the invention an at least partially galvanized metallic substrate, is subjected to i. one or more cleaning steps, such as two or more cleaning steps, wherein at least part of the surface or preferably the complete surface of the metallic substrate is contacted with one or more cleaning compositions at least one of which is an aqueous cleaning composition, to obtain a cleaned metallic substrate. Preferably, the one or last cleaning compositions used in step(s) i. is aqueous.

[0046] Metallic substrates to be used in the coatings industry often contain impurities on their surfaces which may be attached physically or chemically on the metallic surface of the metallic substrate. Such impurities are amongst others oils and greases used in the production and customizing of the metallic substrates or oxidation products such as oxides and / or hydroxides of the metals present in the metallic surface of the metallic substrate. The presence of such impurities typically leads to defects in subsequently formed chemical pretreatment layers and coating layers. Such defects may, e.g., cause a decreased adhesion of the coating layers to the metallic substrate surface. Therefore, it is indispensable to clean contaminated metallic substrates before further use.

[0047] The term metallic substrate as used herein includes substrates of any shape, such as flat metallic substrates like simple panels or coils, but also metallic substrates with complex shapes like automotive bodies or parts thereof. The term “metallic” as used herein comprises pure metals and metal alloys as explained above. Particularly preferred examples of metals and alloys are galvanized steel such as hot-dip galvanized steel or electrolytically galvanized steel, but also cold-rolled steel and aluminum and its alloys. Particularly preferred substrates are galvanized steel substrates, such as hot-dip galvanized steel. Moreover, the term “substrate” also comprises pre-assembled metal parts, the metal parts being of the same metal or alloy or the metal parts being of at least two different metals or alloys (multi-metal capability of the method). In any case at least part of the substrate is at least partially galvanized.

[0048] Particularly substrates in the present invention are automotive bodies and parts thereof. The i. one or more steps of contacting the metallic substrate with a cleaning composition can be carried out by any common cleaning procedure. Most preferred are spray cleaning and / or dip cleaning. The temperature of the cleaning composition used in the one or more i. cleaning steps is preferably in the range from 20 to 70 °C, more preferred 30 to 65 °C and most preferred 40 to 60 °C such as 45 to 60 °C. The duration of contacting the metallic substrate with the cleaning composition preferably ranges from 0.5 min to 15 min, more preferred 1 min to 10 min, most preferred 2 to 5 min.

[0049] Aqueous Cleaning Compositions

[0050] In principle all kinds of commonly used cleaning compositions can be used in the one or more cleaning steps in the method of pretreating according to the present invention, dependent on the type of impurities to be removed and the metal or alloy the substrate comprises or consists of.

[0051] At least one cleaning composition is aqueous and preferably has a pH value at 20 °C in the range from 3.5 to 12.5. Cleaning compositions having a pH value at 20 °C in the range from

[0052] 3.5 to below 6 are commonly denoted as acidic cleaning compositions, while cleaning compositions having a pH value at 20 °C in the range from 6 to 8 are denoted as being neutral and those cleaning compositions having a pH value at 20 °C in the range of more than 8 to

[0053] 12.5 are denoted as alkaline cleaning compositions. The cleaning compositions, independent of their acidic, neutral or alkaline pH values, do preferably not contain nitrates or nitric acid.

[0054] Preferred acidic cleaning compositions have a pH value in the above-mentioned range and contain one or more ingredients selected from the groups consisting of inorganic acids such as sulfuric acid, organic acids, complexing agents, surfactants and fluorides.

[0055] Preferred neutral cleaning compositions have a pH value in the above-mentioned range and contain one or more ingredients selected from the group consisting of pH adjusting agents, alkanolamines, surfactants and complexing agents.

[0056] Preferred alkaline cleaning compositions have a pH value in the range from 8 to 12.5, more preferred 9 to 11 , such as 10 to 11. Preferably alkaline cleaning compositions comprise one or more ingredients selected from the group consisting of pH adjusting agents, surfactants and complexing agents. Suitable cleaning compositions and / or their water-dilutable concentrates are for example commercially available from Chemetall GmbH (Frankfurt, Germany) under the tradename Gardoclean®.

[0057] Since the typical ingredients of cleaning compositions and often their rather extreme pH values negatively interfere with subsequent steps such as chemical pretreatment, the cleaning step(s) are preferably directly followed by one or more rinsing steps. The one or more rinsing steps which follow the one or more cleaning steps and the rinsing compositions A as used therein will be described below.

[0058] The / ' / '■ Rinsing Step(s)

[0059] The one or more rinsing steps, preferably at least two rinsing steps, are carried out to remove excessive cleaning composition left on the surface of the metallic substrate after carrying out the i. one or more cleaning steps.

[0060] The rinsing steps are preferably carried out by spray or dip application, preferably dip application of the respective rinsing compositions A.

[0061] Aqueous Rinsing Composition(s) A

[0062] The rinsing compositions A as used in the ii. rinsing step(s) are preferably water or water containing drag over from the previous cleaning or rinsing step(s). If more than one rinsing step is carried out, the first rinsing step is preferably carried out with tap water as rinsing composition A.

[0063] If spray applied and tap water is used as the first rinsing composition in the first rinsing step, such tap water preferably has a conductivity of 200 to 3500 pS / cm2, preferably 200 to 2500 pS / cm2. Of course, water having a lower conductivity such as deionized water can also be used in the first rinsing step as rinsing composition. Thus, the rinsing composition can be composed of pure water only. Conductivity is measured with commercially available conductivity measurement device (WTW pH / Cond 340i; calibrated in a solution of potassium chloride with a conductivity of 1 .413 mS / cm at 25 °C).

[0064] If the first rinsing composition is dip applied, the same rinsing compositions as used for spray application can be used. However, if the metallic substrates are rinsed in a continuous process, the rinsing composition in the dip tank will further contain diluted ingredients of the previous pretreatment step dragged into the dip tank from the previously rinsed metallic substrates (sheets), i.e., ingredients from the cleaning step(s).

[0065] If the first rinsing composition is used for dip-rinsing, it typically has a pH value in the range from 6 to 10 due to drag-over from the previous cleaning composition and thus contains all ingredients of the cleaning composition, in a highly diluted form to preferably fulfill the above- mentioned conductivity range. Of course, the first rinsing step can also be carried out with deionized water, too.

[0066] The second rinsing composition, if used, preferably also has a pH value in the range from 6 to 10, more preferred from 6.5 to 9 due to the drag-over from the first rinsing compositions and again contains all ingredients of the first rinsing composition, but further water-diluted. Of course, the second rinsing step can also be carried out with de-ionized water.

[0067] Thus, if cascade dip-rinsing is carried out, from rinsing step to rinsing step the drag-over will contain less of the ingredients contained in the cleaning composition(s).

[0068] Preferably, the last rinsing step (can be the first rinsing step if just one rinsing step is carried out, but can also be the second or any further rinsing step) of the rinsing steps carried out subsequent to the cleaning step(s) is carried out by use of water having a conductivity of less than 500 pS / cm2, such 5 to 500 pS / cm2, more preferred 0 to 200 pS / cm2. Of course, the last rinsing step can also be carried out and is preferably carried out with de-ionized water.

[0069] The Hi. Chemical Pretreatment Step(s)

[0070] The iii. one or more steps of contacting the cleaned and rinsed metallic substrate with a chemical pretreatment composition can be carried out by any common conversion treatment procedure, passivation treatment procedure and / or thin-film forming procedure. Most preferred are spray application and / or dip application, the latter one being most preferred. The duration of contacting the metallic substrate with the chemical pretreatment composition preferably ranges from 15 seconds to 8 min, more preferred 1 min to 5 min, most preferred 2 min to 4 min.

[0071] Generally, the temperature of the chemical pretreatment composition used in the iii. one or more chemical pretreatment steps is preferably in the range from 10 to 60 °C, more preferred 15 to 55 °C, even more preferred 20 to 50 °C. In case the chemical pretreatment is the preferred thin-film formation, the temperatures preferably range from 10 to 50 °C, more preferred 15 to 45 °C and most preferred 20 to 40 °C such as 25 to 35 °C.

[0072] Using other chemical pretreatment compositions such as zinc phosphate-based compositions the temperature is preferably in the range from 20 to 60 °C, and most preferred 30 to 55 °C such as 35 to 50 °C.

[0073] Chemical Pretreatment Compositions

[0074] Generally, any known chemical pretreatment composition as used in metal surface finishing can be used in the iii. one or more chemical pretreatment steps of the method of pretreating a metallic substrate according to the present invention.

[0075] The chemical pretreatment compositions used in the present invention are preferably acidic chemical pretreatment compositions.

[0076] Preferably the chemical pretreatment compositions used in the method for coating according to the present invention are selected from a. organosilane based thin-film forming compositions containing at least one organosilane and / or its hydrolysis products and / or its condensation products; b. passivating compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds c. passivating and thin-film forming compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds and containing at least one organosilane and / or its hydrolysis products and / or its condensation products; and d. phosphate conversion treatment compositions.

[0077] The a. organosilane-based thin-film forming compositions contain at least one organosilane, such as an amino silane, the term “organosilane” including its hydrolysis products and condensation products. Such organosilanes may be fluorine-free or fluorine containing. Preferably the organosilanes are amino silanes. Fluorine-free organosilanes are preferably selected from the group of acyloxysilanes, alkoxysilanes, silanes having at least one amino group, silanes having at least one succinic acid group and / or succinic anhydride group, bis- silyl-silanes, silanes having at least one epoxy group such as a glycidyloxysilanes, (meth)acrylato-silanes, multi-silyl-silanes, ureidosilanes, vinylsilanes and their hydrolysis and / or condensation products. Suitable organosilanes are, e.g., disclosed in US 8,932,679 B2.

[0078] The a. organosilane-based thin-film forming compositions optionally contain compounds selected from the group of zirconium compounds, titanium compounds and hafnium compounds, particularly preferred the fluoro complexes of zirconium, titanium and hafnium. Examples of such fluoro complexes are, e.g., disclosed in US 2008 / 0127859 A1. If such zirconium compounds, titanium compounds and hafnium compounds are contained, the compositions belong to the c. passivating and thin-film forming compositions as defined above. Such compositions are for example available from Chemetall GmbH (Frankfurt, Germany) under the trademark Oxsilan®, such as Oxsilan® 9831 , Oxsilan® 9832, Oxsilan 9810 / 1 and Oxsilan 9810 / 3 to produce thin-film layers.

[0079] The b. passivation treatment compositions contain at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds, more preferably a fluoro complex of titanium, zirconium and / or hafnium. An example of a passivation treatment composition containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds is, e.g., Gardobond® GBX 2025 / 2.

[0080] If d., a phosphate conversion treatment step, particularly a zinc phosphating step or a trication phosphating step is carried out in iii., it is preferred to carry out an additional activation step prior to iii. If carried out, the activation step is carried out by contacting the metallic substrate prior to step iii. with an activation composition. Contacting is preferably carried out by dipping or spraying. Most preferred is contacting the metallic substrate by dip application of the activation composition. The duration of the contacting step with the activation composition preferably ranges from 5 to 300 seconds, more preferred 10 to 200 seconds and most preferred 20 to 90 seconds such as 30 to 60 seconds. Activation compositions or solutions are for example available from Chemetall GmbH (Frankfurt, Germany) under the trademark Gardolene® V. If an activation step is carried out, the activation composition used therein preferably contains zinc phosphate crystals and / or titanium phosphate crystals, which facilitate the deposition of the phosphate conversion layer.

[0081] The use of the compositions a., b. and c., particularly c., which combines the advantages of a. and b. are most preferred as chemical pretreatment compositions in the present invention. The use of a d. phosphate conversion treatment composition as a chemical pretreatment composition is not preferred in the present invention.

[0082] Most preferred in the chemical pretreatment steps of the present invention is the use of a thin- film forming composition which also passivates, i.e. , a thin-film forming composition containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds and containing at least one organosilane and / or its hydrolysis products and / or its condensation products. Amongst these, the compositions containing zirconium compounds are most preferred.

[0083] Generally, any layers formed in the chemical pretreatment step(s) have a thickness of typically less than 2 pm, such as preferably 50 nm to 2000 nm, more preferred 500 to 1500 nm for phosphate conversion treatment, such as iron- and zinc phosphating and preferably 20 nm to 300 nm, more preferred 30 to 200 nm for thin film forming pretreatment.

[0084] The dry layer thicknesses of thin-film formed from a thin-film forming composition which also passivates, i.e., a thin-film forming composition containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds, zirconium compounds being most preferred, and containing at least one organosilane and / or its hydrolysis products and / or its condensation products, is preferably in the range from 20 nm to 300 nm, more preferred 30 to 200 nm.

[0085] The iv. Rinsing Step(s)

[0086] The one or more of the iv. rinsing steps, preferably at least two rinsing steps, are carried out to remove excessive chemical pretreatment composition left on the surface of the metallic substrate after carrying out the iii. one or more chemical pretreatment steps.

[0087] The rinsing steps are preferably carried out by spray or dip application, preferably dip application of the respective rinsing compositions B.

[0088] Aqueous Rinsing Compositions B

[0089] The rinsing compositions B are defined the same way as the rinsing compositions A, with the proviso that at least one of the rinsing compositions B used in the iv. one or more rinsing steps additionally contains aluminum oxide hydroxide particles. If only one rinsing step iv. is carried out, the rinsing composition B used therein, mandatorily contains aluminum oxide hydroxide particles as described in detail herein below.

[0090] However, it is preferred that more than one rinsing step iv. is carried out.

[0091] Most preferred, subsequently to the one or last chemical pretreatment step iv. rinsing is carried out in the same way as described for the ii. rinsing steps, with rinsing composition(s) B being defined in the same way as rinsing composition(s) A, with the only difference, that excessive chemical pretreatment composition left on the surface of the substrate after carrying out the iii. one or more chemical pretreatment steps is removed instead of the cleaning composition(s).

[0092] It is further preferred that such rinsing step(s) iv. wherein rinsing compositions A are used as rinsing compositions B are carried out prior those rinsing step(s) iv. which make use of a rinsing composition B comprising aluminum oxide hydroxide particles.

[0093] It is even further preferred that subsequent to one or more rinsing step(s) iv. making use of a rinsing composition B comprising aluminum oxide hydroxide particles, one or more rinsing steps iv. are carried out wherein the rinsing composition B is the same as a rinsing composition A.

[0094] Like rinsing compositions A, rinsing compositions B, preferably do only contain water and traces of the drag-over from the compositions which are applied prior to rinsing. Therefore, rinsing compositions A and B preferably consist of water, and in case of the presence of aluminum oxide hydroxide particle in rinsing compositions B, such aluminum oxide hydroxide particles. Any further ingredients added are, e.g., pH adjusting agents or result from the drag- over. The amount of such further ingredients, despite of aluminum oxide hydroxide particles is in the range from 0 to 1.5 wt.-%, more preferably 0.02 to 1.0 wt.-% and most preferable in the range from 0.03 to 0.5 wt.-% based on the aqueous rinsing composition A or B.

[0095] Aqueous Rinsing Compositions B comprising Aluminum Oxide Hydroxide Particles

[0096] As described above, at least one of the rinsing compositions B comprises aluminum oxide hydroxide particles. Preferably, the difference between such rinsing composition B comprising aluminum oxide hydroxide particles and a rinsing composition B, which does not contain such particles, is just the presence of the aluminum oxide hydroxide particles. Most preferred the rinsing compositions B which do not contain aluminum oxide hydroxide particles are the same as rinsing compositions A, preferably just water, such as tap water or deionized water. Thus, it is preferred that a rinsing composition B which comprises aluminum oxide hydroxide particles, is a suspension of aluminum oxide hydroxide particles in a rinsing composition A, preferably a suspension in water, preferably tap water or even more preferred a suspension in deionized water.

[0097] It is preferred that the time of contacting the chemically pretreated substrate with the aqueous rinsing compositions B comprising aluminum oxide hydroxide particles, is preferably in the range of 30 s to 10 min, more preferred 45 s to 8 min, even more preferred 60 s to 5 min, most preferred 75 s to 3 min.

[0098] The temperature of the aqueous rinsing compositions B comprising aluminum oxide hydroxide particles, in step iv. is preferably in the range of 10 to 60 °C, more preferred 15 to 50 °C, even more preferred 20 to 40 °C, such as 20 to 35 °C.

[0099] The pH value (at 20 °C) of the aqueous rinsing compositions B comprising aluminum oxide hydroxide particles, in step iv. is preferably in the range from 2.5 to 7.0, more preferred, 3.0 to 6.5, even more preferred 3.5 to 5.5 and most preferred 4.0 to 5.0.

[0100] Aluminum Oxide Hydroxide Particles

[0101] The term “aluminum oxide hydroxide” is known to the skilled person. It subsumes compounds having the chemical formula AIO(OH). Amongst these, y-AIO(OH) is most preferred. Consequently, the particles are not to be confused with AI2O3 (alumina) or AI(OH)a (aluminum tri hydroxi de).

[0102] Particularly preferred examples of aluminum oxide hydroxides are boehmites. The term “boehmite” as used in this specification includes “pseudoboehmites” which are typically denoted in crystallography as a form of boehmite with a higher water content. Therefore, in this specification and claims the term “boehmite” as used includes “pseudoboehmites,”, if not stated otherwise. Boehmite particles, particularly boehmite nanoparticles, are used with preference in rinsing compositions B.

[0103] The surface of the aluminum oxide hydroxide particles, preferably the boehmite particles used in rinsing compositions B may be modified or unmodified. In the present invention, the term “modification” is understood preferably as a treatment of the aluminum oxide hydroxide particles, preferably the boehmite particles with at least one treatment agent. Preferred modifications are, e.g., modifications with nitric acid, as often used when producing water dispersible boehmites. Such product is, e.g., commercially available as Disperal® P2.

[0104] Accordingly, the at least partial modification is accomplished preferably by treatment of the aluminum oxide hydroxide particles with at least one treatment agent, preferably with formation of ionic and / or covalent groups. Aluminum oxide hydroxide particles whose surface is at least partly modified with at least one organic acid are known in the prior art: for instance, US 6,224,846 B1 describes boehmite particles modified by means of organic sulfonic acids in order to allow such boehmite particles to be dispersed in water and in polar organic solvents. US 7,244,498 B2 discloses nanoparticles such as boehmite nanoparticles which are subjected to a surface modification using organic acids to generate a negative surface charge. Lastly, corresponding boehmite products modified at least partly with at least one organic acid are available commercially and are sold for example under the designations Disperal® HP 14 / 7 (citric acid modified), Disperal® OS-1 (para-toluene sulfonic acid modified), and Dispal® 25SLR (dodecylbenzene sulfonic acid modified) by Sasol.

[0105] For the sake of completeness, it may be noted that further modifications of the surface of boehmite particles are likewise known in the prior art. For instance, M. L. Nobel et al., in Progress in Organic Coatings 2007, 58, pages 96-104, describe acrylic polymer nanocomposite materials which contain boehmite, where the surface of the boehmite particles may be modified using titanium alkoxides. Surface modification of this kind, however, does not result in anionic stabilization of the aluminum comprising surface of the boehmite.

[0106] Corresponding unmodified boehmite particles, in contrast, have a cationic surface in an aqueous medium with a pH value > 7.5. Such unmodified boehmite particles are therefore customarily employed exclusively in an acidic application medium. Such a use of such unmodified boehmite particles is disclosed for example in WO 2004 / 031090 A2, in WO 2006 / 060510 A1 and in US 2008 / 0090012 A1. Unmodified boehmite particles and the use thereof as fillers in polymer composite materials is known from WO 03 / 089508 A1.

[0107] The aluminum oxide hydroxide particles preferably possess a dispersed particle size determined by means of photon correlation spectroscopy (PCS) on their diluted sols and dispersion in the range from 10 nm to 120 nm, more preferably in the range from 15 nm to 110 nm and most preferably 20 nm to 100 nm.

[0108] The “dispersed particle size” refers to the arithmetic number average of the particle diameter, as determined by means of photon correlation spectroscopy (PCS) using the Zetasizer Nano S-173 instrument from Malvern Instruments in accordance with DIN ISO 13321 (date: October 2004) in an aqueous dispersion.

[0109] Before being incorporated into the rinsing composition B, in other words when present in the form of a solid powder, the aluminum oxide hydroxide particles used in producing the rinsing composition B preferably have a “crystallite size (120 X-ray plane)” in a range from 2 nm to 15 nm, more preferably in a range from 3 nm to 11 nm, even more preferable 4 nm to 10 nm, most preferably 4 nm to 8 nm.

[0110] The amount of any of the above aluminum oxide hydroxide particles, preferably boehmite particles, in the rinsing compositions B containing aluminum oxide hydroxide particles is preferably in the range from 0.05 to 3.0 wt.-%, more preferred in the range from 0.1 to 2.5 wt.- %, even more preferred in the range of 0.2 to 2.0 wt.-%, particularly preferred in the range from 0.25 to 1.5 wt.-% and most preferred in the range from 0.3 to 1.0 wt.-%, based on the total weight of the rinsing composition B, containing the aluminum oxide hydroxide particles.

[0111] Preferred embodiment of Pretreatinq a Metallic Substrate According to the Invention

[0112] It is preferred that the method of pretreating a metallic substrate according to the invention comprises i. one or more cleaning steps, wherein at least part of the galvanized surface of the metallic substrate is contacted with one or more aqueous cleaning compositions, to obtain a cleaned metallic substrate; followed by ii. one or more rinsing steps, wherein at least the part of the surface of the metallic substrate obtained in step(s) i. is contacted with one or more aqueous rinsing compositions A, to obtain a cleaned and rinsed metallic substrate; followed by iii. one or more layer forming chemical pretreatment steps, wherein at least part of the galvanized surface of a metallic substrate is contacted with one or more chemical pretreatment compositions to obtain a chemically pretreated substrate; followed by iv. one or more rinsing steps, wherein at least the part of the chemically pretreated substrate obtained in step(s) iii. is contacted with one or more aqueous rinsing compositions B, wherein at least one of the rinsing compositions B used in the one or more rinsing steps iv. contains aluminum oxide hydroxide particles, the aluminum oxide hydroxide particles being selected from the groups of boehmites and pseudoboehmites. It is further preferred in the afore-mentioned sequence of steps, the aluminum oxide hydroxide particles have a crystallize size determined by X-ray powder diffraction in the range from 2 nm to 15 nm and that the rinsing compositions B containing aluminum oxide hydroxide particles contain the particles in an amount in the range from 0.05 to 3.0 wt.-%, more preferred in the range from 0.1 to 2.5 wt.-%, even more preferred in the range of 0.2 to 2.0 wt.-%, particularly preferred in the range from 0.25 to 1.5 wt.-% and most preferred in the range from 0.3 to 1.0 wt.-%, based on the total weight of the rinsing composition B, containing the aluminum oxide hydroxide particles.

[0113] In the present invention, it is optional to dry the metallic substrate after carrying out the ii. or iv. one or more rinsing steps. If the method of pretreating a metallic substrate is carried out directly prior to powder coating or coating with an aqueous coating composition or solvent-based coating composition it is preferred to first dry the pretreated metallic substrate after the last rinsing step. However, if electrodeposition coating follows the last rinsing step, it is typically not necessary to dry the pretreated metallic substrate prior to electrodeposition coating, because it is typically carried out as aqueous dip-coating.

[0114] Pretreated, at least partially galvanized metallic substrate

[0115] The invention further relates to a pretreated, at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions and thereon a layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles. Such pretreated at least partially galvanized metallic substrate, can be obtained by the method of pretreating a metallic substrate according to the invention.

[0116] Since in the i. one or more cleaning steps, followed by the ii. one or more rinsing steps, all described as above, no layers are formed, those pretreatment steps i. and ii. do not further define the pretreated, at least partially galvanized metallic substrate. The cleaned and rinsed substrate just provides the at least partly galvanized surface of the metallic substrate in a condition, which is perfect for the iii. one or more, preferably one, layer-forming chemical pretreatment step(s).

[0117] Thus, the first layer on the at least partly galvanized surface of the metallic substrate is a chemical pretreatment layer. Any of the afore-described chemical pretreatment compositions can be used to produce the chemical pretreatment layer. Preferably, the chemical pretreatment layer is formed from a chemical pretreatment composition selected from a. organosilane based thin-film forming compositions containing at least one organosilane and / or its hydrolysis products and / or its condensation products; b. passivating compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds, and c. passivating and thin-film forming compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds and containing at least one organosilane and / or its hydrolysis products and / or its condensation products.

[0118] More preferred the chemical pretreatment layer is formed from the c. passivating and thin-film forming composition as defined above.

[0119] Most preferred are the c. passivating and thin-film forming compositions containing at least one compound selected from the group of zirconium compounds and containing at least one organosilane and / or its hydrolysis products and / or its condensation products, the organosilane preferably being selected from the groups of aminosilanes. Other suitable organosilanes and their hydrolysis and / or condensation products are those mentioned herein above and disclosed in US 8,932,679 B2.

[0120] The second mandatory layer being present on the at least partially galvanized metallic substrate is a layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles, preferably boehmite particles. This layer is on top of the chemical pretreatment layer.

[0121] This layer is preferably characterized by its aluminum (Al) content as determined by X-ray fluorescence analysis (XRF) as described in detail in the “method section” of the invention. The aluminum content of this layer is determined by measuring the aluminum content prior to the formation of this layer and after the formation of this layer. The difference between both values is denoted herein as the aluminum content by XRF of the layer formed from a rinsing composition, which contains aluminum oxide hydroxide particles, preferably boehmite particles.

[0122] Preferably, the aluminum content of this layer ranges from 1 to 40 mg / m2, more preferably 2 to 35 mg / m2, and most preferably 3 to 30 mg / m2. Method of Coating a Metallic Substrate

[0123] In the method of coating a metallic substrate, first the method of pretreating a metallic substrate according to the present invention is carried out, followed by applying one or more coating compositions selected from the group of solid coating compositions and liquid coating compositions to form one or more coating layers, herein also referred to as paint coating layers in contrast to any layers that might be formed in the chemical pretreatment step(s). Furthermore, curing of the one or more coating compositions is carried out.

[0124] Thus, a further subject of the present invention is a method of coating a metallic substrate, the method comprising i. one or more cleaning steps, wherein at least part of the galvanized surface of the metallic substrate is contacted with one or more aqueous cleaning compositions, to obtain a cleaned metallic substrate; followed by ii. one or more rinsing steps, wherein at least the part of the surface of the metallic substrate obtained in step(s) i. is contacted with one or more aqueous rinsing compositions A, to obtain a cleaned and rinsed metallic substrate; followed by iii. one or more layer forming chemical pretreatment steps, wherein at least part of the galvanized surface of a metallic substrate is contacted with one or more chemical pretreatment compositions to obtain a chemically pretreated substrate; followed by iv. one or more rinsing steps, wherein at least the part of the chemically pretreated substrate obtained in step(s) iii. is contacted with one or more aqueous rinsing compositions B, wherein at least one of the rinsing compositions B used in the one or more rinsing steps iv. contains aluminum oxide hydroxide particles; followed by v. applying one or more coating compositions selected from the group of solid coating compositions and liquid coating compositions to form one or more coating layers, each of the one or more coating layer being cured or not cured after application; and vi. curing any one or more coating layers applied in step iii. which is or are not cured in step v.

[0125] The solid coating compositions are preferably powder coating compositions most preferably selected from the groups consisting of thermosetting resins. Preferably, the powder coatings are selected from, but not limited to the group of resins consisting of epoxy resins, mixtures of epoxy resins with polyester resins, mixtures of polyester resins with isocyanate components, poly(meth)acrylates and mixtures of polyesters with triglycidylisocyanurates.

[0126] The liquid coating compositions can be one-pack or two-pack coating compositions, aqueous or non-aqueous coating compositions. The non-aqueous coating compositions can be solvent- borne coating compositions or preferably solvent-free radiation curing coating compositions.

[0127] Particularly in automotive OEM coating the following coating steps are preferably carried out in the order of

[0128] • applying an electrodeposition coating composition,

[0129] • applying one or more primer filler compositions,

[0130] • applying one or more basecoat compositions, and

[0131] • applying one or more clear coat compositions, and curing the coatings layers formed, either directly after their application, which is particularly and preferably the case for the electrodeposition coating compositions and (often) the primer filler compositions, or simultaneously, which is particularly and preferably the case for the basecoat and clearcoat compositions.

[0132] Thus, a further subject of the present invention is a method of coating a metallic substrate, the method comprising i. one or more cleaning steps, wherein at least part of the galvanized surface of the metallic substrate is contacted with one or more aqueous cleaning compositions, to obtain a cleaned metallic substrate; followed by ii. one or more rinsing steps, wherein at least the part of the surface of the metallic substrate obtained in step(s) i. is contacted with one or more aqueous rinsing compositions A, to obtain a cleaned and rinsed metallic substrate; followed by iii. one or more layer forming chemical pretreatment steps, wherein at least part of the galvanized surface of a metallic substrate is contacted with one or more chemical pretreatment compositions to obtain a chemically pretreated substrate; followed by iv. one or more rinsing steps, wherein at least the part of the chemically pretreated substrate obtained in step(s) iii. is contacted with one or more aqueous rinsing compositions B, wherein at least one of the rinsing compositions B used in the one or more rinsing steps iv. contains aluminum oxide hydroxide particles; followed by v. one or more of the following coating steps to form one or more coating layers by applying an electrodeposition coating composition, applying one or more primer filler compositions, applying one or more basecoat compositions and applying one or more clear coat compositions and curing or not curing the thus formed coating layer(s), and vi. curing any one or more coating compositions which were not yet cured in step v.

[0133] Any of the preferred features and embodiments described above in connection with the method of treating a metallic substrate are also preferred features and embodiments of the method of coating a metallic substrate and therefore also apply for the method of coating the metallic substrate, but are not explicitly repeated herein below.

[0134] The v. Coating Step(s)

[0135] Subsequently to the method of pretreatment according to the invention and particularly subsequently to any of the preferred embodiments of the method of pretreatment according to the invention as described above, particularly in automotive OEM coating, an electrodeposition coating composition is preferably applied onto the only or last chemical pretreatment layer.

[0136] Electrodeposition coating compositions are aqueous coating compositions which are applied by dip coating, i.e., dipping the pickled, chemically pretreated metallic substrate into the electrically conductive, aqueous electrodeposition coating composition and applying a direct voltage between the substrate and a counter electrode. The electrodeposition coating composition is an anodic or cathodic electrodeposition coating composition, preferably a cathodic electrodeposition coating composition. Cathodic electrodeposition coating compositions are preferably selected from epoxy type and poly(meth)acrylate-type electrodeposition coating compositions. They are applied according to the coating manufacturers specifications.

[0137] Subsequently to forming the electrodeposition coating layer the thus formed layer is preferably rinsed and cured according to the paint manufacturers specifications. Subsequent to the electrodeposition coating step it is preferred to apply one or more further coating compositions. Such further coating compositions are preferably selected from waterbased coating compositions, solvent-borne coating compositions or UV-curing coating compositions. However, so-called powder coating compositions can also be applied. Particularly preferred at least one of a primer filler coating composition, a basecoat composition and a clear coat composition is applied, most preferably in this order. If a plurality of coating layers is formed (i.e., at least two coating compositions are applied), the application can be carried out wet-in-wet and afterwards the coating layers can be cured simultaneously. However, it is also possible to carry out drying steps and / or curing steps between the application of at least some or all of the plurality of coating compositions.

[0138] Alternatively, with or without applying an electrodeposition coating composition, a single powder coating composition or a single aqueous or a single non-aqueous coating composition can be applied. Particularly, if a powder coating composition is applied, it is advisable to first dry the rinsed and / or electrodeposition coated substrate.

[0139] The vi. Curing Step of the not yet cured Coatings

[0140] The conditions of the curing step depend on the coating compositions applied subsequent to the method of pretreating the metallic substrate according to the invention.

[0141] The term “curing” as used herein encompasses any type of curing, preferably physically drying, radiation curing, and thermally curing, wherein thermal curing preferably encompasses any curing mechanism by chemical crosslinking other than radiation curing. E.g., the term thermal cure includes the cure of 1-pack compositions and 2-pack compositions. One-pack compositions typically cure at temperatures above 100 °C, e.g., in the range from 120 to 200 °C, while two-pack compositions typically start curing at room temperature such as temperatures from 20 °C to 100 °C and are thus typically not storage-stable under ambient conditions.

[0142] The method of coating metallic substrates according to the invention provides good adherence of the coatings and corrosion-resistance to the metallic substrate. Particularly, it was found that the use of the rinsing compositions B comprising the aluminum oxide hydroxides, preferably the boehmites, most preferred the boehmites possessing the above-mentioned crystallite sizes, employ an improved stone-chip resistance to the coated substrates at least on those parts of the surface of the metallic substrates which are at least partially galvanized. Furthermore, it was observed that if the substrates comprise non-galvanized parts on the surface, the stone-chip resistance is not negatively affected by the use of the rinsing compositions B comprising the aluminum oxide hydroxides. Thus, multi-metallic substrates can be effectively treated by the pretreatment method according to the invention, since at least the galvanized parts employ an improved stone-chip resistance to the coated substrates obtained by the method of coating according to the invention.

[0143] Coated, Pretreated at least partially Galvanized Metallic Substrate

[0144] The invention further relates to a coated, pretreated at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions, thereon a layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles, and thereon one or more cured coating layers. Such coated, pretreated, at least partially galvanized metallic substrate, can be obtained by the method of coating a metallic substrate according to the invention.

[0145] The coated, pretreated at least partially galvanized metallic substrate according to the invention only differs from the pretreated at least partially galvanized metallic substrate of the invention in that it comprises on top of the layer formed from a rinsing composition, the rinsing composition containing aluminum oxide hydroxide particles, at least one further cured coating layer.

[0146] Particularly in automotive OEM coating the following coating layers are preferably present on top of the layer formed from a rinsing composition, which contains aluminum oxide hydroxide particles, in the order of

[0147] • a cured electrodeposition coating layer,

[0148] • one or more, preferably one cured primer filler layers,

[0149] • one or more cured basecoat layers, and

[0150] • one or more cured clear coat compositions.

[0151] In other application areas, e.g., a cured powder coating layer is present as a single cured coating layer. Any cured coating layer or coating layers as described for and formed in the method of coating a metallic substrate according to the invention may be part of the coated, pretreated at least partially galvanized metallic substrate. Thus, any details with respect to the coating compositions used and coating layers formed as described in the method of coating a metallic substrate according to the invention, also apply to the coated, pretreated at least partially galvanized metallic substrate, likewise.

[0152] Use according to the Invention

[0153] Further subject matter of the invention is use of an aqueous composition containing aluminum oxide hydroxide particles, preferably boehmite particles, the particles preferably being nanoparticles, as a rinsing composition after a chemical pretreatment of an at least partially galvanized metallic substrate. The aluminum oxide hydroxide particles, preferably boehmite particles, preferably possess a crystallite size as determined by X-ray powder diffraction (for diffraction peak 120) as described in detail in the methods section, in the range from 2 nm to 15 nm.

[0154] Any further preferred embodiments of the aqueous composition containing aluminum oxide hydroxide particles and the therein contained aluminum oxide hydroxide particles are already described above under the headlines “Aqueous Rinsing Compositions B comprising Aluminum Oxide Hydroxide Particles” and “Aluminum Oxide Hydroxide Particles.” The conditions of use, such as temperature, duration, forms of contacting the substrate, and the like, are also already described above.

[0155] The use according to the invention further provides for an improved stone-chip resistance on the at least partially galvanized metallic substrate, which is coated by one or more of the coating layers as described above. The use of the aqueous composition containing aluminum oxide hydroxide particles, preferably boehmite particles, the particles preferably being nanoparticles, as a rinsing composition directly after a chemical pretreatment of an at least partially galvanized metallic substrate, is particularly suitable if used prior to applying an automotive coating system.

[0156] Metallic substrates used in the present invention are preferably selected from bare steel, cold rolled steel, galvanized steel, such as electrogalvanized steel and hot-dip galvanized steel and aluminum and its alloys. The metallic substrates can comprise or consist of preassembled parts of metallic substrates, the preassembled parts of the metallic substrate consisting of the same or different metals or alloys.

[0157] The metallic substrates can be used in the automobile industry, for railway vehicles, in the aerospace industry, in apparatus engineering, in mechanical engineering, in the building industry, in the furniture industry, for the manufacture of crash barriers, lamps, profiles, sheathing or hardware, for the manufacture of car bodies or body parts, individual components or preassembled / connected elements, preferably in the automobile or aeronautical industry, or for the manufacture of appliances or installations, especially household appliances, control devices, testing devices or structural elements.

[0158] In the following the invention will be further explained by providing working examples.

[0159] EXPERIMENTAL SECTION

[0160] Methods pH values pH measurements were done using the device “WTW pH 330 i” with the following pH electrode: “SI Analytics BlueLine 28 pH”. The calibration was done with three buffer solutions (traceable to SRM from NIST and PTB) with the following pH values: 4, 7, 10.

[0161] Free fluoride content

[0162] The free fluoride content was determined with the device “Orion 4-Star” or ’’Orion Star A324”, both from Thermo Scientific with the following fluoride combination ion selective electrode: “Thermo Scientific Orion 9609BNWP”. The electrode was calibrated using two master solutions with known fluoride concentrations (20 and 200 ppm).

[0163] Stone Chip Resistance According to DIN EN ISO 20567-1:2017, Method C

[0164] A stone chip resistance test according to DIN EN ISO 20567-1 :2017, method C, was carried out on specimens which were pretreated and coated with e-coat, filler, basecoat and clearcoat as described herein below under the headline “Sample Preparation". Method C of the stone chip test according to DIN EN ISO 20567-1 provides for climatic stress between the two shots. In the present invention the climatic stress was applied in form of the VDA 621-415 test, which is first described in the following.

[0165] The VDA 621-415 procedure is to judge the corrosion protection of vehicle paint using an accelerated laboratory test. It is claimed that testing according to this procedure can generate results that correlate well with those seen by driven vehicles. This test is cyclic in nature, i.e., test specimens are exposed to changing climates over time.

[0166] For the VDA 621-415 procedure the test specimens were placed in an enclosed chamber and exposed to a changing climate that was comprised of the following 3 part repeating cycle. 24 hours exposure to salt spray according to DIN 50 021-SS. This was followed by 96 hours exposure to a condensing water climate according to DIN 50 017-KFW. This was followed by 48 hours exposure to an ambient climate of +18 to +28 °C according to DIN 50 014. Ten cycle repeats were carried out. After the VDA 621-415 test (10 cycles), a stone chip resistance test according to DIN EN ISO 20567-1 :2017, method C, was carried out.

[0167] The stone chip resistance test in accordance with DIN EN ISO 20567-1 simulates damage to painted body parts as can occur in road traffic due to grit, road gravel or similar contaminants. In Part 1 of the stone chip resistance test, also known as the multi-impact test, 500 g of chilled cast iron granules with a grain size of 3.5 - 5.0 mm are shot onto the specimen surface in two passes using an air pressure of 200 ± 10 kPa [according to DIN EN ISO 20567-1 , method C]. In this way, the test specimen is subjected to stone impact.

[0168] The device design is specified so that the impact angle between the beam axis and the specimen of 54° on the specimen surface is maintained and the test area is a maximum of 80 x 80 mm. A pressure accumulator with connected pressure reducer and pressure gauge ensures uniform air pressure during the bombardment.

[0169] Loosely adhering coating particles are removed after the bombardment before the damage pattern is evaluated according to DIN EN ISO 20567-1. Brushes, the use of adhesive tape or compressed air can be used for this purpose. The bombarded area is assessed on the basis of comparative images. The characteristic value ranges from 0.5 (corresponding to a damaged area of 0.2%) to 5.0 (corresponding to a damaged area of 81 .3%).

[0170] The average value of five tested panels is reported in the result tables.

[0171] X-Ray Fluorescence Analysis (XRF)

[0172] The layer weights of aluminum as shown in the respective results tables were determined by X-ray fluorescence analysis.

[0173] X-ray fluorescence analysis as used herein is an analytical technique that can be used to determine the elemental composition of solid substances. A beam of X-rays strikes the surface of the sample and a core electron is ejected from the atom that absorbed the X-ray photon. When an outer electron falls into the hole created by the ejected electron, it emits energy in form of light. This light is called fluorescence and a characteristic pattern exists for each element. The spectrometer permits qualitative and quantitative determination of any number of elements from Na to II, from trace levels 0.01% to 100%. Herein, it is used as a semi-quantitative technique.

[0174] XRF was carried out on the test specimens after the pretreatment with a silane and zirconium containing pretreatment composition to determine the reference value of Al in mg / m2and again after rinsing the pretreated test specimen with the rinsing composition(s) of the present invention prior to e-coating. Before determining the Al content, the specimens were dried in each case with a compressed air gun.

[0175] XRF analyses were performed on the following instruments: Panalytical Axios max or Malvern Panalytical Zetium. There is usually one calibration per substrate for the particular element required. The calibrations are usually based on the data of ICP measurements (the surface of the panels used for calibration is detached and measured by ICP; ICP uses standards traceable to NIST). The samples are usually circular blanks with a diameter of 4 cm.

[0176] The average value of 5 tested panels is reported in the result tables.

[0177] X-ray Powder Diffraction for Characterization of Aluminum Oxide Hydroxide Particles

[0178] Crystallite sizes are expressed by the length obtained for diffraction peak 120. The 120 measurement is the distance along a line perpendicular to the (120) plane, as shown below:

[0179] X-ray powder diffraction is used for determination of the crystallite size of aluminum oxide hydroxide particles, preferably using a conventional X-ray diffractometer, such as from Siemens (Siemens D5000) or Philips (Philips X’Pert). Crystallite sizes are expressed by the length obtained for diffraction peak 120. The 120 measurement is the distance along a line perpendicular to the (120) plane. Analysis of peak-width on X-ray powder diffraction peaks at 120 gives the values commonly reported for crystallite sizes. The measured 120 crystal size is normal (90°) to the 120 plane and is represented by the arrow. This peak (crystal plane) is the most accessible in aluminum oxide hydroxide’s X-ray diffraction pattern and has been used for the characterization.

[0180] Dispersed particle sizes of the aluminum oxide hydroxide particles

[0181] The dispersed particle size of the aluminum oxide hydroxide particles is determined by means of photon correlation spectroscopy (PCS) in accordance with DIN ISO 13321 (date: October 2004) on the particles in form of their sols. Measurement took place using a “Zetasizer Nano S-173” from Malvern Instruments at 25 ± 1 °C. The “dispersed particle size” of the particles, when present in a sol, determined in this manner refers to the arithmetic number average of the particle diameter (z-average mean).

[0182] Examples

[0183] Sample Preparation

[0184] Substrates

[0185] As substrates hot dip galvanized (HDG) steel panels (10.5 x 19 cm) were used.

[0186] Cleaning

[0187] The substrates were cleaned with a mild alkaline spray cleaner as follows. Gardoclean S 5411 (15 g / L; builder, contains mainly hydroxides) and Gardobond-additive H 7401 (3 g / L; surfactant) were added to deionized water in a spraying chamber. The pH value was adjusted at a working temperature of 55 °C to a pH value of 10,5 with phosphoric acid and potassium hydroxide. The cleaning process was done by spraying at 55 °C for 3 min. Rinsing

[0188] Subsequently the substrates were rinsed with tap water and deionized water.

[0189] “Conversion Coating” by Thin Film Technology

[0190] The preparation of the conversion bath (Oxsilan 9832) was done in the following way. A tank was filled up with deionized water to a level of 80 %. The addition of the components was done while stirring. After that, the bath was filled up with deionized water to a level of 100 %.

[0191] For the adjustment of the pH value, the following products were used: OSA 9951 (contains sodium carbonate) and OSA 9960 (contains nitric acid).

[0192] The concentration of each element in the bath was adjusted as follows: zirconium: 100 ppm; silicon: 30 ppm; zinc: 400 ppm; copper: 8-12 ppm; and free fluoride: 30-35 ppm (at a pH of 4.8).

[0193] Before the throughput of the substrates, the finished bath was aged for at least 12 hours to obtain a chemical equilibrium. The bath temperature was adjusted to 30 °C. The pH value and the free fluoride content were adjusted to pH = 4.8 and 30-35 mg / L free fluoride. The cleaned substrates were immersed in the bath at 30 °C for 3 min. The substrates were rinsed with deionized water before the post-rinse was carried out.

[0194] Rinsing with Rinsing Composition B According to the Invention

[0195] The preparation of the rinsing composition B was done as follows. The appropriate amount of the boehmite (in g / L) - as indicated in the tables below - was added to deionized water under stirring. The solution was stirred for a few minutes. To change the pH value the following products were used: OSA 9951 (contains sodium carbonate) and OSA 9960 (contains nitric acid). Rinsing was carried out with specific aluminum oxide hydroxides for a specific time interval, pH value, and temperature as indicated in the tables below. Subsequently, the thus treated substrates were rinsed with deionized water. Application of Coating Compositions After the Application of the Post-Rinse

[0196] The thus pretreated HDG steel panels were coated with

[0197] • an e-coat (CathoGuard 800; BASF); curing was done at an object temperature of 175 °C at 15 min holding time (dry film thickness approx. 19.4 ± 1.7 pm), flash-off time was 30 min at 23 °C;

[0198] • a filler (PPG Hemmelrath hydro-filler); the object temperature was 70 °C at 10 min predrying time; curing was done at an object temperature of 150 °C at 17 min holding time, flash-off time was 30 min at 23 °C;

[0199] • a base coat (NPAC Nippon Paint hydro-basecoat); held for 5 min at an object temperature of 80 °C, flash-off time was 30 min at 23 °C; and

[0200] • a clear coat (Axalta Coating Systems, 2K-clearcoat), the object temperature was 60 °C at 10 min pre-drying time; curing was at an object temperature of 140 °C at 22 min holding time, flash-off time was 30 min at 23 °C;

[0201] The overall dry film thickness was 110 pm ± 4.1 pm. The dry film thickness of the primer was approx. 25 to 30 pm and that of the base coat approx. 11 to 15 pm.

[0202] Table 1 aboehmite modified with nitric acid (4.0 wt.-% NO3) (particle size dso = 45 pm; measured on the powder)bboehmite surface treated with p-toluene sulfonic acid (particle size dso = 35 pm; measured on the powder)cset to “0” (the actual value for Example 1 was subtracted from values for Examples 1 to 5)

[0203] As Table 1 is showing, rinsing with a rinsing composition B containing boehmites with different surface-treatments and different crystallite sizes, after a thin film pretreatment as described above, leads to significant improved stone-chip resistance. The increased content of Al (measured by XRF; X-ray fluorescence spectroscopy) shown for Examples 2 to 5 can be explained by the deposition of boehmites on the substrates.

[0204] It was highly surprising that this effect on the stone-chip resistance can be observed, since it was neither envisaged that aluminum oxide hydroxides could cause such remarkable effect, nor it was to be expected that a rinsing composition could have such effect, since all attempts to increase stone-chip resistance made use of coating compositions relying on high filler material amounts and / or the presence of specific organic binders therein.

[0205] Table 2 -Effect of pH value aboehmite modified with nitric acid (4.0 wt.-% NO3) (particle size dso = 45 pm; measured on the powder)cset to “0” (the actual value for Example 6 was subtracted from values for Examples 7 to 12)

[0206] Trials regarding the deposition of aluminum were done with one rinsing composition B as described in Table 2 but with different pH values. The results show that the highest amount of aluminum (detected by XRF) was found in a pH value range between 3 and 6, especially preferred at a pH value of 4.5. In general, a comparison of experimental data has to be carried out within the same test series (tables) only. Table 3 - Effect of temperature aboehmite modified with nitric acid (4.0 wt.-% NO3) (particle size dso = 45 pm; measured on the powder)cset to “0” (the actual value for Example 13 was subtracted from values for Examples 14 and 15)

[0207] Trials regarding the deposition of aluminum were done with one rinsing composition B as described in Table 3, but at different temperatures. The highest amount of aluminum (detected by XRF) was found at 50 °C.

[0208] Table 4 - Influence of Crystallite Size and pH value cset to “0” (the actual value for Example 16 was subtracted from values for Examples 17 to 18)dboehmite (particle size dso = 30 pm; measured on the powder)eboehmite (particle size dso = 30 pm; measured on the powder)

[0209] In all cases of Table 4, the pH value of the rinsing composition B was only measured and not changed after adding the boehmites.

[0210] Trials regarding the deposition of aluminum that were done with different boehmites (with different crystallite sizes) in rinsing compositions B showed that a significant amount of Al (detected by XRF) could only be found when boehmites with relatively low crystallite sizes (8 nm and lower) were used. In comparative examples, making use of non-galvanized substrates such as cold rolled steel and aluminum, it was found that there is no negative influence regarding the stone-chip resistance or any other properties studied. Thus, the method according to the invention can also be applied to substrates possessing different metallic surfaces such as is often the case for pre-assembled substrates, particularly multi-metallic substrates.

Claims

CLAIMS1. A method of pretreating an at least partially galvanized metallic substrate, the method comprising the following steps: i. one or more cleaning steps, wherein at least part of the galvanized surface of the metallic substrate is contacted with one or more aqueous cleaning compositions, to obtain a cleaned metallic substrate; followed by ii. one or more rinsing steps, wherein at least the part of the surface of the metallic substrate obtained in step(s) i. is contacted with one or more aqueous rinsing compositions A, to obtain a cleaned and rinsed metallic substrate; followed by iii. one or more layer forming chemical pretreatment steps, wherein at least part of the galvanized surface of a metallic substrate is contacted with one or more chemical pretreatment compositions to obtain a chemically pretreated substrate; followed by iv. one or more rinsing steps, wherein at least the part of the chemically pretreated substrate obtained in step(s) iii. is contacted with one or more aqueous rinsing compositions B, wherein at least one of the rinsing compositions B used in the one or more rinsing steps iv. contains aluminum oxide hydroxide particles.

2. The method according to claim 1 , characterized in that the chemical pretreatment composition is selected from the group consisting of a. organosilane based thin-film forming compositions containing at least one organosilane and / or its hydrolysis products and / or its condensation products; b. passivating compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds; and c. passivating and thin-film forming compositions containing at least one compound selected from the groups of zirconium compounds, titanium compounds and hafnium compounds and containing at least one organosilane and / or its hydrolysis products and / or its condensation products.

3. The method according to claim 1 or 2, characterized in that the aluminum oxide hydroxide particles are boehmite particles including pseudoboehmite particles.

4. The method according to any one of claims 1 to 3, characterized in that the aluminum oxide hydroxide particles are present in at least one rinsing composition in an amount of 0.05 to 2.0 wt.-% based on the total weight of said rinsing composition B.

5. The method according to any one of claims 1 to 4, characterized in that the aluminum oxide hydroxide particles possess a crystallite size (120 X-ray plane) as determined by means of X-ray diffractometry in a range from 2 nm to 15 nm.

6. The method according to any one of claims 1 to 5, characterized in that the aluminum oxide hydroxide particles possess a dispersed particle size as determined by means of photon correlation spectroscopy (PCS) in the range of 10 nm to 120 nm.

7. The method according to any one of claims 1 to 6, characterized in that at least one of the rinsing compositions B, which contains the aluminum oxide hydroxide particles possesses a pH value at 20 °C is in the range of 2.5 to 7.0.

8. The method according to any one of claims 1 to 7, characterized in that at least one of the rinsing compositions B, which contains the aluminum oxide hydroxide particles, is contacted with the chemically pretreated substrate obtained in step iii. for 30 s to 10 min, and / or at a temperature of 10 °C to 60 °C.

9. The method according to any one or more of claims 1 to 8, characterized in that the at least partially galvanized metallic substrate is a multi-metallic substrate, preferably a preassembled multi-metallic substrate.

10. A method of coating a metallic substrate, the method comprising steps i. to iv. as defined in claims 1 to 9 followed by v. applying one or more coating compositions selected from the group of solid coating compositions and liquid coating compositions to form one or more coating layers, each of the one or more coating layer being cured or not cured after application; and vi. curing any one or more coating layers applied in step iii. which is or are not cured in step v.

11. The method according to claim 10, characterized in that the one or more coating compositions in step v. applying one or more coating compositions are selected from electrodeposition coating compositions, primer filler compositions, basecoat compositions and clear coat compositions, preferably all in this order.

12. A pretreated, at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions and thereon a layer formed from a rinsing composition containing aluminum oxide hydroxide particles, the rinsing composition containing aluminum oxide hydroxide particles and the aluminum oxide hydroxide particles being defined as in claims 1 to 9.

13. A coated, pretreated at least partially galvanized metallic substrate, comprising a layer formed from one or more chemical pretreatment compositions, thereon a layer formed from a rinsing composition containing aluminum oxide hydroxide particles, and thereon one or more cured coating layers; the rinsing composition containing aluminum oxide hydroxide particles and the aluminum oxide hydroxide particles being defined as in claims 1 to 9.

14. A use of an aqueous composition containing aluminum oxide hydroxide particles, as a rinsing composition after a chemical pretreatment of an at least partially galvanized metallic substrate, the rinsing composition containing aluminum oxide hydroxide particles and the aluminum oxide hydroxide particles being defined as in claims 1 to 9.

15. The use according to claim 14, wherein the use is in the automobile industry, for railway vehicles, in the aerospace industry, in apparatus engineering, in mechanical engineering, in the building industry, in the furniture industry, for the manufacture of crash barriers, lamps, profiles, sheathing or hardware, for the manufacture of car bodies or car body parts, individual components or preassembled / connected elements, or for the manufacture of appliances or installations, especially household appliances, control devices, testing devices or structural elements.