Aqueous acid pickling composition without phosphonate and its uses

Abstract

The present invention relates to a phosphonate-free aqueous pickling composition having a pH value of 5-9 at 55 °C, which comprises at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone; the water content is 95.0-99.9% by weight, based on the total weight of the composition. The present invention further relates to a concentrate for preparing the composition, a pickling method for pickling a metal substrate using the composition, a method for coating a metal substrate including the pickling method, and the use of the composition for pickling a metal substrate.

Description

[0001] The present invention relates to a phosphonate-free aqueous neutral pickling composition for removing rust and scale in a method for pickling metal substrates, and to a concentrate for preparing such a composition. The present invention further relates to the method and to the use of said composition for pickling metal surfaces. In addition, the present invention relates to a method of coating metal substrates, in particular for improving corrosion protection.

[0002] Background

[0003] Oxide layers and other residues that are not removed after heat treatment of metal substrates usually cause problems in subsequent conversion coating steps, resulting in reduced adhesion of subsequent coatings (especially coatings obtained by cathodic electrodeposition coating), thereby reducing corrosion protection.

[0004] Therefore, it is common, and especially in the automotive industry, to use aqueous cleaning and pickling solutions with rather extreme pH values before conversion coating. A typical problem associated with highly acidic pickling solutions is the tendency to form rust films after rinsing the surface. In addition, when using highly acidic or highly alkaline compositions, more stringent occupational and industrial safety as well as transport safety requirements must be complied with. In addition, the pickling composition is more aggressive towards the metal substrates and equipment to be pickled.

[0005] To overcome such problems, an increasing number of fluid, neutral rust and scale removal compositions suitable for ferrous and non-ferrous metals and alloys have been developed in recent years and can be used in dipping methods, immersion methods and spraying methods. They are suitable for removing oxide layers that appear after hot trimming, laser cutting and welding operations from metal surfaces. Compared with pickling compositions based on inorganic acids or strong base compositions, the neutral pickling composition has many advantages. Contrary to strong acids and strong bases, they are much easier to handle and can usually clean and pickle the surface in one process step. Therefore, additional cleaning steps can usually be omitted.

[0006] In particular, neutral compositions based on phosphonic acids such as 1-hydroxyethane-1,1-diphosphonic acid or aminophosphonic acids are used for the above purposes because they are known to be complexing agents even in a substantially neutral environment. The term "neutral" as used herein refers to an aqueous composition having a pH value of about 5 - 9 at 55 °C and thus encompasses slightly acidic and slightly alkaline aqueous compositions.

[0007] On the other hand, phosphonates are generally not the first choice when cleaning and pickling metal surfaces composed of different metals. This is particularly important in the case of pickling pre-assembled metal parts with different compositions (such as especially steel and galvanized steel) when using the same cleaning and pickling compositions successively or simultaneously. This is because phosphonate-based cleaning and pickling solutions generally lack balanced pickling weight loss for different substrates and have significantly different effects on the surfaces to be cleaned and pickled depending on the type of metal or alloy.

[0008] In addition, phosphonates and other complexing agents have come under criticism due to ecological concerns and problems in wastewater treatment. In addition, in some cases, for example due to insufficient rinsing after pickling treatment, these substances may be introduced into subsequent conversion coating baths, thus interfering with these baths, resulting in insufficient conversion coating and thus insufficient corrosion protection and adhesion of the subsequent coating.

[0009] Therefore, there is a continuing need for improved aqueous, neutral and especially phosphonate-free pickling compositions that provide improved, especially balanced, pickling behavior when used on different substrates and do not have an adverse effect on subsequent conversion coating processes. In particular, the adhesion of subsequent coatings (such as electrodeposition coatings, fillers, primer surfacers and / or clear coats) should not deteriorate.

[0010] Overview

[0011] This need is met by providing a phosphonate-free pickling composition having a pH value of 5 - 9 at 55 °C, which comprises at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone; wherein the water content is 95.0 - 99.9 wt%, based on the total weight of the composition.

[0012] Hereinafter, this composition is referred to as "the composition of the present invention" or "the pickling composition of the present invention".

[0013] The present invention further provides a concentrate that contains higher concentrations of the components of the composition of the present invention and allows the preparation of the composition of the present invention at the place where needed by diluting with a diluent containing water and optionally an organic solvent and, if necessary, subsequently adjusting the pH value.

[0014] The present invention further provides a method for pickling a metal substrate, which comprises at least one step of bringing the metal substrate into contact with the composition of the present invention.

[0015] Hereinafter, this method is referred to as "the pickling method of the present invention".

[0016] Another object of the present invention is a method for coating a metal substrate, which at least comprises:

[0017] (a) The acid pickling method of the present invention, subsequently

[0018] (b) The step of coating the acid pickled metal substrate with a conversion coating composition, optionally subsequently

[0019] (c) The step of applying an electrodeposition coating composition; optionally subsequently

[0020] (d) One or more steps of applying one or more other coating compositions.

[0021] Hereinafter, this method is referred to as "the coating method of the present invention".

[0022] Another object of the present invention is the use of the composition of the present invention for acid pickling a metal substrate.

[0023] Hereinafter, this use is referred to as "the use of the present invention".

[0024] Detailed description

[0025] The composition of the present invention

[0026] Since the composition of the present invention is an aqueous composition, the main component is water. Based on the total weight of the composition, the water content is 95 - 99.9% by weight, more preferably 97 - 99.8% by weight, even more preferably 98 - 99.8% by weight, and most preferably 99 - 99.7% by weight.

[0027] The composition of the present invention may also contain a small amount of one or more organic solvents, which are preferably miscible with water or soluble in water. Based on the total weight of the composition of the present invention, their amount is preferably 4% by weight or less, more preferably less than 3% by weight, even more preferably less than 2% by weight or less than 1% by weight. Most preferably, the only solvent used in the composition of the present invention is water.

[0028] The composition of the present invention is preferably an aqueous solution or an aqueous dispersion, and most preferably an aqueous solution.

[0029] When used for acid pickling different metal substrates, the composition of the present invention generally provides a more balanced acid pickling. By measuring the acid pickling weight loss, the degree of acid pickling of different substrates can be compared. The acid pickling weight loss is the loss of material in the acid pickling process, in g / m 2 calculated. This amount should not be too low, which indicates insufficient acid pickling; nor should it be too high, which indicates too rough surface treatment, thus increasing the risk of damaging the substrate surface, resulting in an uneven surface, and thus poor adhesion of the subsequent coating.

[0030] A sufficient acid pickling weight loss preferably starts from about 0.5 g / m 2 and preferably does not exceed about 2.5 g / m 2, so depending on the desired application, exceptions to this range may be acceptable. When comparing the difference in acid pickling weight loss (Δpwl) of different metal substrates pickled with the same acid pickling composition, it is preferably not more than about 0.6 g / m 2 , even more preferably not more than 0.4 g / m 2 , most preferably not more than 0.3 or 0.2 g / m 2 , a balanced acid pickling is usually obtained. The acid pickling weight loss, especially the above values and (Δpwl), is determined as described in the experimental section of this application. The above acid pickling weight loss values and Δpwl values are preferably applicable to CRS (cold rolled steel) and HDG (hot dip galvanized steel) and the comparison between the two. However, the acid pickling composition of the present invention is also applicable to other substrates.

[0031] Water-soluble or water-dispersible copolymer

[0032] As used herein, the term "copolymer" refers to a polymer composed of at least two different monomers, preferably two different monomers or three different monomers (terpolymer).

[0033] Polyvinylpyrrolidone

[0034] A preferred polyvinylpyrrolidone copolymer is a vinyl acetate-vinylpyrrolidone copolymer. In particular, polyvinylpyrrolidone is preferably polymerized from a mixture of vinylpyrrolidone and vinyl acetate and optionally other monoethylenically unsaturated monomers.

[0035] The vinyl acetate-pyrrolidone copolymer is preferably a random copolymer, preferably having a molar ratio of vinyl acetate to vinylpyrrolidone of 30:70 to 70:30, more preferably 30:70 to 60:40, even more preferably 30:70 to 50:50, such as 40:60.

[0036] Generally, these copolymers are prepared by free radical polymerization. Since the monomers used in their synthesis carry only one polymerizable group, the copolymers are linear copolymers.

[0037] Preferably, the weight average molecular weight Mw of the copolymer determined by gel permeation chromatography (GPC) is 15,000 - 100,000 g / mol, more preferably 20,000 - 90,000 g / mol, even more preferably 30,000 - 80,000 g / mol, such as 50,000 - 70,000 g / mol. GPC can be carried out according to DIN 55672-3:2016-03. The polydispersity M w / M n of the copolymer is preferably 3 - 7, more preferably 4 - 6.

[0038] The following copolymers can also be used, the only difference from the above vinyl acetate-vinyl pyrrolidone copolymer being that the combined amount of vinyl acetate and vinyl pyrrolidone, preferably 0-10 mol%, more preferably 1-8 mol%, most preferably 1-5 mol%, is replaced by a third monoethylenically unsaturated monomer selected from vinyl monomers, acrylate monomers and methacrylate monomers. The above weight average molecular weight ranges are also applicable to these copolymers.

[0039] pH value

[0040] The aqueous composition of the present invention has a pH value (measured at 55 °C) of 5-9, preferably 5.5-8.5, more preferably 6.0-8.0, most preferably 6.5-7.5.

[0041] Amount of polyvinylpyrrolidone

[0042] The composition of the present invention must contain at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone.

[0043] The amount of all polyvinylpyrrolidones defined for use in the composition of the present invention is preferably 0.05-2.0% by weight, more preferably 0.10-1.5% by weight, even more preferably 0.15-1.0% by weight, most preferably 0.2-0.8% by weight, for example 0.3-0.7% by weight, based on the total weight of the composition of the present invention.

[0044] All weight % ranges used throughout the context of the specification apply not only to the broadest definition of each component, but also to any other preferred embodiment of that component.

[0045] Other components

[0046] The composition of the present invention may also contain other components such as additives, which are necessarily different from the polyvinylpyrrolidone defined for use in the composition of the present invention. The other components are also different from water and organic solvents.

[0047] If present, such additives generally do not interfere with the pickling effect provided by the composition of the present invention, but rather enhance other properties, such as an increased shelf life obtained by adding a preservative; or a combined cleaning or degreasing effect obtained, for example, by adding a surfactant, preferably a non-ionic surfactant.

[0048] Unlike household cleaning compositions (such as detergents, especially laundry detergents), the composition of the present invention does not contain proteases and preferably contains no enzymes at all, because the pickling action is significantly different from an enzymatic cleavage reaction, such as the cleavage of protein-based dirt and / or contaminants.

[0049] Preferably, the total amount of other ingredients different from the polyvinylpyrrolidone defined for the composition of the present invention is less than 50% by weight, more preferably less than 40% by weight, even more preferably less than 30% by weight or less than 20% by weight, for example less than 10% by weight, based on the combined amount of the other ingredients and the polyvinylpyrrolidone defined for the composition of the present invention.

[0050] Preferably, the composition of the present invention does not contain a polymer or a metal ion chelator other than the polyvinylpyrrolidone defined for the composition of the present invention.

[0051] The concentrate of the present invention

[0052] The present invention further relates to a concentrate comprising a liquid medium consisting of water and / or an organic solvent; and at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone. The sum of the amount of the at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone and optionally included other ingredients is preferably 4-90% by weight, more preferably 10-90% by weight, even more preferably 20-90% by weight or 30-90% by weight, most preferably 40-90% by weight, for example 50-90% by weight, based on the total weight of the concentrate.

[0053] The concentrate of the present invention most preferably does not contain protease and preferably does not contain enzymes.

[0054] The concentrate allows the preparation of the composition of the present invention when needed by diluting with a diluent containing water and optionally an organic solvent and, if necessary, subsequently adjusting the pH value to 5-9, preferably 5.5-8.5, more preferably 6.0-8.0, most preferably 6.5-7.5 at 55°C. The concentrate is preferably an aqueous concentrate.

[0055] Preferably, the dilution ratio (concentrate volume: diluent volume) is 1:1 to 1:50, more preferably 1:5 to 1:50, most preferably 1:10 to 1:50.

[0056] Using this concentrate reduces the need for large storage capacity and facilitates transportation to the point of use.

[0057] The acid leaching method of the present invention

[0058] The acid leaching method of the present invention includes at least one step of bringing a metal substrate into contact with the composition of the present invention.

[0059] Metal substrate

[0060] The term "metal substrate" as used herein includes substrates of any shape, such as flat metal substrates like simple plates or coils, and also includes metal substrates with complex shapes, such as automobile bodies or their parts. The term "metal" as used herein includes pure metals and metal alloys. Particularly preferred examples of metals and alloys are cold-rolled steel, galvanized steel (such as hot-dip galvanized steel or electrolytically galvanized steel), and aluminum and its alloys. Particularly preferred substrates are cold-rolled steel and galvanized steel, such as hot-dip galvanized steel. In addition, the term "substrate" also includes pre-assembled metal parts, which are made of the same metal or alloy, or which are made of at least two different metals or alloys (the multi-metal capability of the process). Contact of the metal substrate with the composition of the present invention

[0061] The step of contacting the metal substrate with the composition of the present invention is preferably a step selected from the following steps:

[0062] (a) Immersing the metal substrate in the composition of the present invention,

[0063] (b) Submerging the metal substrate with the composition of the present invention; and

[0064] (c) Spraying the metal substrate with the composition of the present invention.

[0065] When contacting the metal substrate, the substrate can move or rotate in the composition, and / or the composition can be agitated, for example, by stirring or the like.

[0066] The metal substrate is preferably contacted with the composition of the present invention for a time of 1 - 15 minutes, more preferably 3 - 12 minutes, and most preferably 5 - 10 minutes.

[0067] The temperature of the composition of the present invention during the step of contacting the metal substrate is preferably 20 - 70 °C, more preferably 30 - 65 °C, and most preferably 40 - 60 °C, such as 50 - 60 °C.

[0068] Taking into account maintaining the temperature of the composition of the present invention within the above range and optimizing the contact area of the substrate during contact, it is most preferred to contact the metal substrate by immersing the metal substrate in the composition of the present invention.

[0069] Optional additional steps of the pickling method of the present invention

[0070] The pickling method of the present invention may include one or more steps carried out before the at least one step of contacting the metal substrate with the composition of the present invention.

[0071] It should be emphasized that the optional additional steps described below are not necessarily the only optional steps possible in the pickling method of the present invention. If necessary, any other cleaning, rinsing, and / or drying steps may be carried out in addition to the preferred optional steps.

[0072] In particular, the acid pickling method may include, before said at least one step (iv) of bringing the metal substrate into contact with the composition of the present invention, at least one cleaning step (i), preferably followed by at least one rinsing step (ii), and even more preferably followed by two rinsing steps (ii) and (iii).

[0073] Thus, the preferred acid pickling method of the present invention comprises

[0074] (i) a step of bringing the metal substrate into contact with a cleaning composition, optionally followed

[0075] (ii) a step of rinsing the metal substrate with a first rinsing composition, optionally followed

[0076] (iii) a step of rinsing the metal substrate with a second rinsing composition, followed by (iv) a step of bringing the metal substrate into contact with the composition of the present invention.

[0077] The step (i) of bringing the metal substrate into contact with the cleaning composition can be carried out in the same manner as the step of bringing the metal substrate into contact with the composition of the present invention, except that a cleaning composition is used instead of the composition of the present invention. Most preferably, it is spray cleaning and / or dip cleaning. The temperature of the cleaning composition used in step (i) is preferably 20 - 70 °C, more preferably 30 - 65 °C, most preferably 40 - 60 °C, for example 45 - 60 °C. The time for which the metal substrate is in contact with the cleaning composition is preferably 0.5 - 15 minutes, more preferably 1 - 10 minutes, most preferably 3 - 5 minutes.

[0078] The cleaning composition preferably has an alkaline pH value of 8 - 12, more preferably 9 - 11, for example 10 - 11 and preferably contains at least one of an alkali, a phosphonate, a surfactant and a complexing agent.

[0079] Suitable cleaning agents can be commercially obtained, for example, from Chemetall GmbH (Frankfurt, Germany) under the trade name commercially available.

[0080] The rinsing steps (ii) and (iii) are preferably carried out by spraying or dip coating, preferably dip coating with the respective rinsing compositions. The rinsing composition is usually water, or if dip coating is selected, water containing diluted components of the previous treatment step due to inevitable drag from the previous bath.

[0081] Due to drag from the previous cleaning composition, the first rinsing composition preferably has a pH value of 9 - 12 and preferably contains all the components of the cleaning composition but diluted with water.

[0082] Due to drag from the first rinsing composition, the second rinsing composition preferably has a pH value of 8 - 11 and preferably contains all the components of the first rinsing composition but diluted with water.

[0083] The rinsing step can also be carried out only with water, especially in laboratory-scale experiments.

[0084] The above sequence of steps (i) to (iv) is also a preferred embodiment of step (a) of the coating method of the present invention.

[0085] The pickling method of the present invention may further include one or more steps after the at least one step of contacting the metal substrate with the composition of the present invention (iv), that is, one or more rinsing steps (v) to (vii).

[0086] Therefore, the preferred pickling method of the present invention may further include:

[0087] (iv) the step of contacting the metal substrate with the composition of the present invention, followed by

[0088] (v) the step of rinsing the metal substrate with a third rinsing composition, optionally followed by (vi) the step of rinsing the metal substrate with a fourth rinsing composition, and optionally followed by (vii) the step of rinsing the metal substrate with a fifth rinsing composition.

[0089] The rinsing steps (v), (vi) and (vii) are preferably carried out by spraying or dipping the corresponding rinsing compositions. The rinsing composition may consist only of water, but is usually a water-diluted composition from the previous steps due to drag. If the pickling method of the present invention is carried out continuously, it is particularly preferred to carry out the rinsing steps (v) to (vii). In this case, if a metal substrate containing iron is pickled, an accumulation of iron compounds will occur in the pickling composition. The iron compounds can be rinsed off in each rinsing step.

[0090] The above sequence of steps (iv) to (vii) is also a preferred embodiment of step (a) of the coating method of the present invention.

[0091] In order to keep the iron compounds in solution, the third cleaning composition preferably has an acidic pH value of 1-3 and preferably further contains the components of the previous pickling composition, but is diluted with water.

[0092] In order to avoid the formation of a rust film after acidic rinsing, the fourth rinsing composition preferably has an alkaline pH value of 10-11 and preferably contains caustic alkali and a complexing agent. If the pickling method is run in a continuous process and the process is interrupted and / or the time between steps is too long, a rust film can be formed in particular.

[0093] If the pickling method of the present invention is followed by, in particular, a phosphate conversion coating step, the fifth rinsing composition preferably has a pH value of 9.5-10 and contains the components of the fourth rinsing composition due to drag, but is diluted with water.

[0094] Typically, an activation step is carried out before the phosphate conversion coating step, and before this conversion coating step, preferably, the pH value of the rinsing composition is neither too high nor too low. Therefore, it is particularly preferred that the pH value of the fifth rinsing solution is within the above-mentioned slightly alkaline or neutral range. Particularly preferably, rinsing is carried out with water in step (vii).

[0095] Of course, all steps before the step of contacting the metal substrate with the composition of the present invention and steps after the step of contacting the metal substrate with the composition of the present invention can be carried out in combination in the pickling method of the present invention.

[0096] In this case, the pickling method of the present invention preferably comprises:

[0097] (i) a step of contacting the metal substrate with a cleaning composition, optionally followed by

[0098] (ii) a step of rinsing the metal substrate with a first rinsing composition, optionally followed by

[0099] (iii) a step of rinsing the metal substrate with a second rinsing composition, followed by

[0100] (iv) a step of contacting the metal substrate with the composition of the present invention, followed by

[0101] (v) a step of rinsing the metal substrate with a third rinsing composition, optionally followed by (vi) a step of rinsing the metal substrate with a fourth rinsing composition, optionally followed by (vii) a step of rinsing the metal substrate with a fifth rinsing composition.

[0102] The cleaning composition, rinsing composition and composition of the present invention are defined as above. The above sequence of steps (i) to (vii) is also a preferred embodiment of step (a) of the coating method of the present invention.

[0103] The coating method of the present invention

[0104] Further provides a method for coating a metal substrate, which at least comprises:

[0105] (a) the pickling method of the present invention, followed by

[0106] (b) a step of coating the metal substrate thus treated with a conversion coating composition to obtain a conversion coating,

[0107] optionally followed by

[0108] (c) a step of applying an electro-deposition coating composition to obtain an electro-deposition coating; optionally followed by

[0109] (d) a step of applying one or more other coating compositions to obtain one or more other coatings

[0110] Multiple steps.

[0111] It should be emphasized that the steps of the coating method of the present invention as described above are not necessarily the only possible steps in the coating method of the present invention. If necessary, any other rinsing, drying, and / or curing steps may be implemented in addition to the above steps.

[0112] Therefore, it is preferred to have at least one rinsing step (b”) after step (b) and before step (c). It is also preferred to have at least one rinsing step (c’) followed by a curing step (c”) after step (c).

[0113] Preferably, the coating obtained by the coating method of the present invention is a multi-layer coating. Even more preferably, the coating obtained by the coating method of the present invention is a coating comprising a conversion coating, an electrodeposition coating, and preferably at least one other coating.

[0114] Step (a)

[0115] Therefore, as a pretreatment step, the coating method of the present invention includes at least step (a), that is, the pickling method of the present invention, especially at least step (iv) of the pickling method of the present invention.

[0116] More preferably, step (a) included in the coating method of the present invention includes steps (iv), (v), (vi), and (vii) of the pickling method of the present invention.

[0117] Even more preferably, step (a) included in the coating method of the present invention includes steps (i) to (vii) of the pickling method of the present invention.

[0118] Step (b)

[0119] Generally, any known conversion coating composition can be used in step (b) of the coating method of the present invention.

[0120] The conversion coating composition used in the present invention is preferably an acidic conversion coating composition.

[0121] Preferably, the conversion coating composition used in the coating method of the present invention is selected from: i. Phosphate conversion coating compositions, such as Ni-containing and Ni-free zinc phosphating compositions and trication phosphating compositions, the phosphate conversion coating compositions containing zinc ions and at least one manganese ion and nickel ion,

[0122] ii. Organosilane-based conversion coating compositions comprising at least one organosilane and / or its hydrolysis products and / or condensation products; and

[0123] iii. Passivation conversion coating compositions comprising at least one compound selected from zirconium compounds, titanium compounds, and hafnium compounds.

[0124] If the phosphate conversion step, in particular the zinc phosphating step or the tri-cationic phosphating step, is carried out as step (b), it is preferred to carry out an additional activation step (a') after step (a) and before step (b). If carried out, the activation step (a') is carried out by bringing the metal substrate into contact with an activation composition after step (a) and before step (b). The contact is preferably carried out by dipping, immersion or spraying, as described for the contact of the metal substrate with the composition of the present invention. Most preferably, the metal substrate is contacted by dip-coating with the activation composition. The contact time with the activation composition is preferably 5 - 300 seconds, more preferably 10 - 200 seconds, most preferably 20 - 90 seconds, for example 30 - 60 seconds. For example, the activation composition or solution can be commercially obtained, for example, from Chemetall GmbH (Frankfurt, Germany) under the trade name V and ZL.

[0125] If the activation step is carried out, the activation composition used therein preferably contains zinc phosphate crystals and / or titanium phosphate crystals, which contribute to the deposition of the phosphate conversion layer.

[0126] If the phosphate conversion step, in particular the zinc phosphating step or the tri-cationic phosphating step, is carried out as step (b), it is preferred to carry out an additional passivation step (b') after step (b) and before step (c). The passivation composition can be commercially obtained, for example, from Chemetall GmbH (Frankfurt, Germany) under the trade name D.

[0127] In the zinc phosphating composition, Ni-containing compositions can be used. However, for environmental reasons, Ni-free zinc phosphating conversion coating compositions, which contain Zn ions and Mn ions, are preferred. Another variant of the zinc phosphating conversion coating composition is the so-called tri-cationic phosphate conversion coating composition containing Zn, Mn and Ni ions. The phosphate conversion coating composition can be commercially obtained, for example, from Chemetall GmbH (Frankfurt, Germany) under the trade name obtained commercially.

[0128] The organosilane-based conversion coating composition preferably contains at least one organosilane, the term "organosilane" including its hydrolysis products and condensation products, and optionally compounds selected from zirconium compounds, titanium compounds and hafnium compounds. Such compositions can be commercially obtained, for example, from Chemetall GmbH (Frankfurt, Germany) under the trade name obtained commercially, which is used for preparing a thin film system.

[0129] The passivating conversion coating composition preferably comprises at least one compound selected from zirconium compounds, titanium compounds, and hafnium compounds, more preferably fluoro complexes of titanium, zirconium, and / or hafnium. The conversion coating composition optionally comprises one or more organosilanes, and the term "organosilane" includes its hydrolysis products and condensation products.

[0130] Step (c)

[0131] In step (c), an electrodeposition coating composition is applied to the conversion coating formed in step (b). The electrodeposition coating composition is an aqueous coating composition applied by dip coating, i.e., immersing the acid-etched, conversion-coated metal substrate in a conductive aqueous electrodeposition coating composition and applying a DC voltage between the substrate and the counter electrode.

[0132] The electrodeposition coating composition is an anodic or cathodic electrodeposition coating composition, preferably a cathodic electrodeposition coating composition.

[0133] The cathodic electrodeposition coating composition is preferably selected from epoxy-type and poly(meth)acrylate-type electrodeposition coating compositions. They are applied according to the instructions of the coating manufacturer.

[0134] After step (c), the formed electrodeposition coating is preferably rinsed (step (c')) and cured (step (c'')) according to the instructions of the coating manufacturer.

[0135] One or more steps (d)

[0136] After the electrodeposition coating step (c), one or more other coating compositions are preferably applied. The other coating compositions are preferably selected from water-based coating compositions, solvent-based coating compositions, or UV-curable coating compositions. However, so-called powder coating compositions can also be used.

[0137] Particularly preferably, at least one of a filler coating composition, a primer composition, and a clear coating composition is applied. If multiple coatings (i.e., at least two coating compositions) are applied, the application can be carried out in a wet-on-wet manner, and then the coatings can be cured simultaneously. However, drying steps and / or curing steps can also be carried out during the application of at least some or all of the multiple coating compositions available in step (d).

[0138] The method for coating a metal substrate of the present invention provides a coating with good adhesion and corrosion resistance, preferably a multi-layer coating.

[0139] Use of the present invention

[0140] The present invention further provides the use of the composition of the present invention for acid-etched metal substrates, wherein the metal substrate is the metal substrate as described above.

[0141] When applied to different metal substrates, the composition and its use provide a balanced and mild, yet sufficiently high, acid pickling, allowing for successive acid pickling of different metal substrates with the same acid pickling composition, or, if desired, in the form of pre-assembled parts comprising different metal substrates.

[0142] Hereinafter, the present invention will be further explained by providing working examples. Examples

[0143] Test procedures

[0144] Determination of acid pickling weight loss

[0145] Before treatment with an acid pickling solution, two plates made of CRS (cold rolled steel) and HDG (hot dip galvanized steel) were weighed.

[0146] After acid pickling, all plates were rinsed with deionized water, dried and weighed. In each case, the weight loss caused by treatment with the acid pickling solution (i.e., acid pickling weight loss) represents the removal of material. In each case, the average value of three plates was calculated.

[0147] The acid pickling weight loss should preferably not exceed 2.5 g / m 2 , as surface defects may occur, leading to insufficient adhesion of any subsequent coating. Furthermore, the acid pickling weight loss should preferably not be less than 0.5 g / m 2 , as otherwise the acid pickling may be insufficient.

[0148] If the difference in acid pickling weight loss between CRS and HDG is 0.6 g / m 2 or less, and the acid pickling weight loss of both materials is 0.5 - 2.5 g / m 2 , then a balanced acid pickling weight loss of a specific acid pickling composition can be achieved.

[0149] Determination of conversion coating weight

[0150] The conversion coating weight of acid pickled and zinc phosphated metal substrates was determined by XRF analysis and expressed in g / m 2 , calculated as P2O5.

[0151] For acid pickled and zinc phosphated metal substrates, if the conversion coating weight of CRS does not exceed 4.0 g / m 2 , and the conversion coating weight of HDG does not exceed 3.5 g / m 2 , then the conversion coating weight is considered good.

[0152] Acid pickling The conversion coating weight of the treated metal substrate was determined by Zr and expressed in mg / m 2 , calculated as Zr.

[0153] In acid pickling In the case of a metal substrate treated with 9832, if the conversion layer weight of CRS does not exceed 150 g / m 2 , and the conversion layer weight of HDG does not exceed 150 g / m 2 , then the conversion layer weight is considered good. In acid pickling In the case of a metal substrate treated with 9810 / 2, if the conversion layer weight of CRS does not exceed 200 g / m 2 , and the conversion layer weight of HDG does not exceed 150 g / m 2 , then the conversion layer weight is considered good.

[0154] Cross - cut adhesion test

[0155] According to DIN EN ISO 2409, cross - cut adhesion tests are carried out on acid - pickled conversion - coated and electrodeposited - coated metal substrates.

[0156] If no delamination is observed, the result is rated "0", and complete delamination is rated "5". All other delamination grades are between "0" and "5". An acceptable delamination rating is "0" or "1". The result is the average result of two plates.

[0157] Electrochemical delamination test

[0158] According to the current AA - 0175 standard of BMW, electrochemical delamination tests are carried out on acid - pickled conversion - coated and electrodeposited - coated metal substrates.

[0159] Delamination is measured in millimeters [mm]. An acceptable delamination is less than 2 mm. The result is the average result of two plates.

[0160] Preparation of examples

[0161] Acid pickling of metal substrates

[0162] Acid pickling to determine acid - pickling weight loss

[0163] Using An aqueous solution of S5411 (20 g / L; pH 10.5) is used to spray - clean and dip - clean plates made of CRS (cold - rolled steel) and HDG (hot - dip galvanized steel) at a temperature of 55 °C for 3 minutes and 5 minutes respectively. Then, the plate is rinsed with water containing the drag component of the previous composition (cleaning bath).

[0164] In each case, two plates were immersed in a bath containing one of the pickling compositions I1 and I2 of the present invention for 10 minutes; or in a bath containing one of the comparative pickling compositions C1 to C5 (see Table 1) for 10 minutes. The compositions were aqueous solutions of compounds A, B, C, D, and E (comparative); or an aqueous solution of compound F of the present invention (I1), as shown in Table 1. The temperature of the bath was 55 °C. The plates were rotated at a rate of 250 rpm.

[0165] Table 1

[0166] Acid leaching composition Compound Amount [wt%] <![CDATA[pH value 1 > C1 A 1.3 7.5 C2 B 1.3 7.5 C3 C 1.3 7.5 C4 D 0.5 7.5 C5 E 0.4 7.5 I1 F 0.5 7.5

[0167] 1 Adjustment was carried out by adding 50 wt% aqueous KOH solution;

[0168] A: 1-Hydroxyethane-1,1-diphosphonic acid;

[0169] B: Aminotris(methylenephosphonic acid);

[0170] C: Ethylenediaminetetra(methylenephosphonic acid);

[0171] D: Acrylic acid-maleic acid (50:50) copolymer, Mw = 70000 g / mol;

[0172] E: Copolymer of acrylic acid, maleic acid, and a carboxyl-free hydrophilic ethylenically unsaturated monomer;

[0173] F: Vinyl acetate-vinylpyrrolidone (40:60) copolymer (molar ratio)

[0174] After pickling the plates, the plates were removed from the bath and rinsed with water containing some drag from the previous step. The plates pickled in this way were dried and used for the determination of pickling weight loss according to the above procedure.

[0175] Pickling as a pretreatment before the coating step

[0176] Other plates made of CRS and HDG were cleaned and rinsed as described above, and then immersed in a bath containing one of the pickling compositions shown in Table 2 for 5 minutes and 10 minutes, respectively. The pickling composition was an aqueous solution (I2) of the corresponding amount of compound F of the present invention and a comparative solution (C5) of compound D. The temperature of the bath was 55 °C, and stirring was carried out at a rate of 250 rpm.

[0177] Table 2

[0178]

[0179]

[0180] 1Adjusted by adding 50 wt% aqueous KOH solution;

[0181] D: Acrylic acid-maleic acid (50:50) copolymer, Mw = 70000 g / mol;

[0182] F: Vinyl acetate-vinyl pyrrolidone (40:60) copolymer (molar ratio).

[0183] Before conversion coating, the acid-leached plate is first rinsed with tap water, then with deionized water, and then the acid-leached metal substrate is used in a wet state before performing the conversion coating.

[0184] Conversion coating of acid-leached metal substrate

[0185] In each case, the acid-leached plates made of CRS and HDG (acid-leached with the acid-leaching composition in Table 2) are contacted with a zinc phosphate-based conversion coating composition (available from Chemetall GmbH, Frankfurt, Germany) or a silane-based conversion coating composition ( 9832, available from Chemetall GmbH, Frankfurt, Germany).

[0186] Zinc phosphating conversion coating

[0187] By immersing the plate in 1 g / L of V 6559 solution at room temperature (about 23 °C) for 30 - 60 seconds to activate the plate to be coated with the zinc phosphate conversion coating composition using V 6559 (commercially available from Chemetall GmbH, Frankfurt, Germany).

[0188] Zinc phosphating is carried out by dip-coating the activated plate in 24T (commercially available from Chemetall GmbH, Frankfurt, Germany) for 3 minutes at 55 °C.

[0189] Subsequently, the plate coated with the zinc phosphate conversion coating composition is passivated by immersing the plate in 2.1 g / L of D68000 / 8 (pH 4.3) solution at room temperature (about 23 °C) for 30 seconds using D 6800 / 8 (commercially available from Chemetall GmbH, Frankfurt, Germany).

[0190] Silane-based conversion coating

[0191] The plate to be coated with the silane-based conversion coating composition is neither activated before the conversion coating nor passivated after the conversion coating.

[0192] To prepare the conversion coating, the acid-leached plate is at a temperature of 35 °C in a solution containing Immerse in a bath of the conversion coating composition (9832 or 9810 / 2 respectively) for 3 minutes. After conversion coating and before electrodeposition coating, rinse the conversion-coated pickled metal substrate in deionized water.

[0193] Determine the weight of the conversion layer on the thus conversion-coated plate as described above.

[0194] Electrodeposition coating of the conversion-coated pickled metal substrate

[0195] Electrodeposit coat the conversion-coated pickled CRS plate with the 800 electrodeposition coating composition commercially obtained from BASF Coatings GmbH (Hiltrup, Münster, Germany).

[0196] Rinse the plate thus electrodeposition-coated and dry it in an oven at a temperature of 175 °C for 15 minutes, with a final thickness of 18 - 22 μm, and then conduct the cross-hatch test and electrochemical delamination test as described above.

[0197] Test results

[0198] Table 3 below shows the results of the pickling weight loss determination and confirms that Composition I1 of the present invention shows mild but sufficient pickling, with the pickling weight loss of both CRS and HDG within the range of 0.8 - 1.4 g / m 2 and an excellent pickling weight loss balance of only 0.6 g / m 2 On the contrary, the use of comparative pickling solutions containing different phosphonates (C1 to C3) shows erosive pickling on HDG and is accompanied by unbalanced pickling (C1, C2), or shows insufficient pickling on HDG (C3). The use of only anionic polymers (C3 and C4) shows insufficient pickling on HDG. 2

[0199]

[0200] Table 3

[0201]

[0202]

[0203] The results shown in Table 4 below reflect the weights of the zinc phosphate conversion layers obtained on CRS and HDG plates pickled for 5 minutes and 10 minutes respectively, calculated as P2O5 in g / m 2 . The target value for CRS is preferably 4 g / m 2 or lower, and the target value for HDG is preferably less than 3.5 g / m 2 2 ​Although the HDG target was observed for both compositions over two time spans of acid leaching, at 5 and 10 minutes of acid leaching, the comparative composition failed on the CRS, while the composition of the present invention met the requirements.

[0204] Table 4

[0205]

[0206]

[0207] The results shown in Table 5 below reflect those obtained on the CRS and HDG plates with acid leaching for 5 and 10 minutes respectively of the weight of the 9832 conversion layer, in g / m 2 calculated as Zr. The target values for CRS and HDG are preferably below 150 g / m 2 , which was observed in all cases, except for Comparative Example C6 on the CRS for 5 and 10 minutes.

[0208] Table 5

[0209]

[0210] The results shown in Table 6 below reflect those of the 9810 / 2 conversion layer obtained on the CRS and HDG plates with acid leaching for 5 and 10 minutes respectively, in g / m 2 calculated as Zr. The target value for CRS is preferably below 200 g / m 2 , and the target value for HDG is below 150 g / m 2 , which was observed in all cases, except for Comparative Example C6 on the CRS for 5 and 10 minutes.

[0211] Table 6

[0212]

[0213] Table 7 shows the cross - hatch adhesion test results obtained on CRS plates after acid leaching for 5 and 10 minutes respectively and coating with 9832 conversion before applying, rinsing, drying and curing the 800 cathodic electrodeposition coating. As shown in the examples, no adhesion failure was observed for any of the samples of the examples of the present invention, while the comparative examples failed completely.

[0214] Table 7

[0215]

[0216] Table 8 shows the CRS / Results of the electrochemical delamination test of 9832.

[0217] Table 8

[0218]

[0219] Therefore, Tables 7 and 8 show that only the coatings applied to the acid-leached metal substrates of the present invention have perfect adhesion in the cross-hatch adhesion test and the electrochemical delamination test. A good delamination value is a value < 2.0 mm. Only the samples of the present invention show very good values below 1 mm, while the comparative samples delaminate severely.

Claims

1. A phosphonate-free aqueous acid pickling composition having a pH value of 5 - 9 at 55°C, which comprises at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone; the water content is 95.0 - 99.9 wt%, based on the total weight of the composition, wherein the polyvinylpyrrolidone is a random polymer polymerized from a mixture of vinylpyrrolidone and vinyl acetate and optionally other monoethylenically unsaturated monomers, wherein the molar ratio of vinyl acetate to vinylpyrrolidone is 30:70 to 70:30, and wherein the polyvinylpyrrolidone has a weight-average molecular weight of 15,000 - 100,000 g / mol as determined by gel permeation chromatography.

2. The aqueous acid pickling composition according to claim 1, wherein the polyvinylpyrrolidone comprises other monoethylenically unsaturated monomers.

3. The aqueous acid pickling composition according to claim 1, wherein 0 - 10 mol% of the combined amount of vinyl acetate and vinylpyrrolidone is replaced by other monoethylenically unsaturated monomers selected from vinyl monomers, acrylate monomers, and methacrylate monomers.

4. The aqueous acid pickling composition according to claim 2, wherein the other monoethylenically unsaturated monomers are selected from vinyl monomers, acrylate monomers, and methacrylate monomers.

5. The aqueous acid pickling composition according to claim 1, which has a pH value of 6.0 - 8.

0.

6. The aqueous acid pickling composition according to claim 2, which has a pH value of 6.0 - 8.

0.

7. The aqueous acid pickling composition according to claim 3, which has a pH value of 6.0 - 8.

0.

8. The aqueous acid pickling composition according to claim 4, which has a pH value of 6.0 - 8.

0.

9. The aqueous acid pickling composition according to any one of claims 1 - 8, wherein the amount of all the water-soluble or water-dispersible copolymers is 0.05 - 2.0 wt%, based on the total weight of the aqueous acid pickling composition.

10. The aqueous acid pickling composition according to any one of claims 1 - 8, wherein the total amount of other components different from the water-soluble or water-dispersible copolymer is less than 50 wt%, based on the combined amount of the components consisting of the other components and the water-soluble or water-dispersible copolymer.

11. The aqueous acid pickling composition according to claim 9, wherein the total amount of other components different from the water-soluble or water-dispersible copolymer is less than 50 wt%, based on the combined amount of the components consisting of the other components and the water-soluble or water-dispersible copolymer.

12. The aqueous acid pickling composition according to any one of claims 1 - 8, which does not contain protease and / or does not contain polymers other than the water-soluble or water-dispersible copolymer.

13. The aqueous acid pickling composition according to claim 11, which does not contain protease and / or does not contain polymers other than the water-soluble or water-dispersible copolymer.

14. A concentrate for preparing the aqueous acid pickling composition according to any one of claims 1 - 13, which comprises: a liquid medium consisting of water and / or an organic solvent, the water-soluble or water-dispersible copolymer, and Any other components of the aqueous pickling composition, wherein the sum of the amounts of the water-soluble or water-dispersible copolymer and any other optionally contained components is 10-90% by weight, based on the total weight of the concentrate.

15. A method for pickling a metal substrate, comprising at least one step of contacting the metal substrate with a phosphonate-free aqueous pickling composition having a pH value of 5-9 at 55 °C, the aqueous pickling composition comprising at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone; the water content is 95.0-99.9% by weight, based on the total weight of the composition, wherein the polyvinylpyrrolidone is a random polymer polymerized from a mixture of vinylpyrrolidone and vinyl acetate and optionally other monoethylenically unsaturated monomers, and wherein the molar ratio of vinyl acetate to vinylpyrrolidone is from 30:70 to 70:

30.

16. The method for pickling a metal substrate according to claim 15, which comprises: (i) a step of contacting the metal substrate with a cleaning composition, optionally followed by (ii) a step of rinsing the metal substrate with a first rinsing composition, optionally followed by (iii) a step of rinsing the metal substrate with a second rinsing composition, followed by (iv) a step of contacting the metal substrate with a phosphonate-free aqueous pickling composition having a pH value of 5-9 at 55 °C, the aqueous pickling composition comprising at least one water-soluble or water-dispersible copolymer selected from polyvinylpyrrolidone; the water content is 95.0-99.9% by weight, based on the total weight of the composition, wherein the polyvinylpyrrolidone is a random polymer polymerized from a mixture of vinylpyrrolidone and vinyl acetate and optionally other monoethylenically unsaturated monomers, and wherein the molar ratio of vinyl acetate to vinylpyrrolidone is from 30:70 to 70:30, subsequently (v) a step of rinsing the metal substrate with a third rinsing composition, optionally followed by (vi) a step of rinsing the metal substrate with a fourth rinsing composition, optionally followed by (vii) a step of rinsing the metal substrate with a fifth rinsing composition.

17. The method for pickling a metal substrate according to claim 15 or 16, wherein the metal substrate is selected from steel, aluminum or aluminum alloy.

18. The method for pickling a metal substrate according to claim 15 or 16, wherein the metal substrate is selected from galvanized steel.

19. A method for coating a metal substrate, which at least comprises: (a) the method for pickling a metal substrate according to any one of claims 15-18, subsequently (b) a step of coating the thus pickled metal substrate with a conversion coating composition, optionally followed by (c) a step of applying an electro-deposition coating composition, optionally followed by (d) one or more steps of applying one or more other coating compositions.

20. The method for coating a metal substrate according to claim 19, wherein the conversion coating composition used in step (b) is selected from the following group: i. A phosphate conversion coating composition comprising zinc ions and at least one of manganese ions and nickel ions; ii. an organosilane-based conversion coating composition comprising at least one organosilane and / or its hydrolysis product and / or its condensation product; and iii. a passivating conversion coating composition comprising at least one compound selected from zirconium compounds, titanium compounds, and hafnium compounds; and in the case of using a phosphate conversion coating composition, before performing step (b), contacting the acid-etched metal substrate obtained in step (a) with an activation composition comprising zinc phosphate crystals and / or titanium phosphate crystals; and in the case of using a phosphate conversion coating composition, contacting the conversion-coated metal substrate obtained in step (b) with a passivation composition comprising at least one compound selected from zirconium compounds, titanium compounds, and hafnium compounds.

21. The method for coating a metal substrate according to claim 19, wherein the electrodeposition coating composition used in step (c) is selected from anodic and cathodic electrodeposition coating compositions; and in the case of using a cathodic electrodeposition coating composition, the cathodic electrodeposition coating composition is selected from epoxy-type electrodeposition coating compositions and poly(meth)acrylate-type electrodeposits; and after step (c), the electrodeposited coating is dried and cured.

22. The method for coating a metal substrate according to claim 20, wherein the electrodeposition coating composition used in step (c) is selected from anodic and cathodic electrodeposition coating compositions; and in the case of using a cathodic electrodeposition coating composition, the cathodic electrodeposition coating composition is selected from epoxy-type electrodeposition coating compositions and poly(meth)acrylate-type electrodeposits; and after step (c), the electrodeposited coating is dried and cured.

23. The method for coating a metal substrate according to any one of claims 19-22, wherein the other coating composition used in step (d) is selected from filler compositions, primer surfacer compositions, and clear coating compositions.

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