EP4791927A1 - Cathodic electrodeposition process - Google Patents

Abstract

The present invention relates to a cathodic electrodeposition coating process comprising a specific rinsing cascade conducted via specific rinsing media. Also, the present invention relates to a corresponding system for conducting a cathodic electrodeposition process.

Description

Cathodic electrodeposition process

The present invention relates to a cathodic electrodeposition coating process comprising a specific filtration cascade and a rinsing step including at least two specific and successively conducted rinsing sub-steps. The present invention also relates to a corresponding system for conducting a cathodic electrodeposition process.

Prior art / background

In the automobile sector, the metallic components used for manufacture must customarily be protected against corrosion. The requirements in terms of the corrosion control to be achieved are very exacting, not least because the manufacturers often offer a guarantee against rust perforation over many years. Such corrosion control is customarily achieved through the coating of the components, or of the substrates used to manufacture them, with at least one coating suitable for that purpose. In order to be able to ensure the necessary corrosion control, it is common practice to apply a cathodic electrodeposition coating film to the metallic substrate. Cathodically depositable electrocoat materials (also named cathodic electrodeposition coating materials) and processes of applying these (i.e. depositing these materials on respective substrates) are known in the prior art, for example in EP 1 041 125 A1 , DE 197 03 869 A1 and in WO 91/09917 A2.

One crucial aspect of such processes, in particular in context with industrial scale processes, is the rinsing of the coated substrate (i.e. rinsing of the substrate after the coating process has been finished and the coated substrate has been removed from the electrodeposition bath) and, even more importantly, the provision and consumption of water in the context of such rinsing processes (with water being the major part of respective rinsing media). Without an appropriate rinsing of the coated substrate, excessive coating material on the substrate is not rinsed off and thus removed properly, meaning that the final electrocoating (after curing) is lacking sufficient quality. On the other side, excessive consumption of water is of disadvantage due to economic and ecological reasons.

A standard approach in the prior art to encounter the above challenges is to establish a rinsing cascade in which rinsing media originating from the electrocoat material itself are applied. Thereby, the rinsing media are provided by ultrafiltration of the electrocoat material, i.e. the ultrafiltrate is applied as rinsing media, whereby the retentate of the ultrafiltration is recirculated into the electrodeposition bath. Thereby, after initial provision of respective rinsing media (i.e ultrafiltrate and/or media essentially I majorly consisting of ultrafiltrate) in successively positioned rinsing baths, the last rinsing bath is, during course of the overall process, continuously replenished by further fresh ultrafiltrate. Also, the rinsing medium of this last rinsing bath I rinsing sup-step is continuously recirculated into the previous rinsing bath. By this means, one the one side, the respective previous rinsing medium is replenished (as the last rinsing bath will have lower degree of contamination compared to the previous bath). On the other side, the rinsing medium of the last bath is disposed of medium having - compared to the desired condition of the last rinsing medium - a higher degree of contamination, meaning that this also is an (indirect) replenishment of the last bath. In case of more than two rinsing baths and thus media, this principle is correspondingly continued. The first rinsing medium, however, is normally recirculated into the electrodeposition bath and thus coating material. During the course of the process and thus consecutive rinsing, the rinsing media are contaminated by rinsed off electrocoat material, but likewise directly or indirectly replenished as mentioned above. Quite obviously, the first rinsing bath will be contaminated to the greatest extent, while the last bath will undergo the least contamination. Accordingly, the purity I quality of the rinsing media and baths will improve with the position, whereby the medium and bath at the last position will have the best purity and this cleaning quality. Within a serial coating process, the different ways of filling, replenishing and removal of material, filtrate and rinsing media are adjusted in a way that finally a constant electrodeposition process is established.

While the above indeed already leads to advantages in terms of water consumption, the ultrafiltrate as rinsing medium in the last rinsing sub-step still contains a solids content being too high to actually provide for a high-quality cleaning, meaning that a certain amount of excessive material and thus debris often remains on the coated surface. This, quite understandably, then leads to a rather low-quality surface of a finally cured coating.

A way of encountering this is to introduce a final rinsing step by means of externally added water as rinsing medium. This, quite obviously, serves for a high-quality cleaning of the surface. However, a likewise obvious drawback lies in excessive water consumption. Also, in such a scenario, under normal circumstances, it is unavoidable to individually add biocides to this last rinsing medium based on externally added water to prevent bacterial contamination of the rinsing bath/medium. Reason is that, as is known, electrodeposition coating materials and respective processes are vulnerable for such contamination, meaning that within such processes it is virtually unavoidable to make use of biocides. These are normally applied from the start within the electrodeposition coating material and/or are added regularly I on occasion during the course of a running electrodeposition process/setup (to replenish the concentration level of biocides). In context of the latter, the biocides may be added to the electrodeposition coating material as such or at any other position, for example to a rinsing medium, as the within a running process the biocides are successively distributed throughout the electrodeposition setup. An ultrafiltrate as mentioned above still does contain enough biocide content (as enough biocide is passed through the filtration membrane). Consequently, the ultrafiltration does not hinder the distribution of initially or during the course of the process added biocides throughout the electrodeposition setup. However, in the case of externally added water as rinsing medium, this part of the setup, quite obviously, is not supplied with biocides applied and present in the overall setup. Therefore, individual addition of biocide content is unavoidable.

Further strategies to encounter the above problem of water consumption is to realize a filtration cascade in which, after ultrafiltration, the ultrafiltrate is once more filtrated by reverse osmosis. For example, DE 102012218495 A1 discloses a process in which such a cascade is conducted, resulting finally in separating water of demineralized quality from the coating material. This water, then, can be applied within the last rinsing step. However, while by this means water consumption can be reduced to a great extent, again the individual addition of further biocide content to at least this last specific rinsing medium is unavoidable in at least industrial scale processes under standard conditions. Reason is that this filtrate, having the already mentioned quality of demineralized water, does not contain organic-based biocide compounds. More particularly, no organic-based biocide compounds are able to effectively pass the filtration system. These organic-based biocides are, however, of crucial importance for electrodeposition processes. Specifically, and in particular contrary to hydrogen peroxide (also known as biocide), organic-based biocides do not have significant negative impact on the electrodeposition material (i.e. the polymeric species to be deposited on substrates). Hydrogen peroxide, however, due to its high oxidation power, does often have significant perishing impact on the to be deposited polymer material, thus sometimes being less favorable under certain conditions and in certain situations in terms of its applicability.

Objective and technical solution

From the above, it is apparent that there is a need of a cathodic electrodeposition coating process which is advantageous both from the perspective of water consumption and also biocide addition. More specifically, a process in which a last rinsing step with externally added water is avoidable and likewise separate addition of certain biocides to this last rinsing step is avoidable or at least can be significantly decreased would be of great advantage.

It was found that the above objectives are solved by a novel cathodic electrodeposition coating process comprising the following steps: a) immersing a to be coated metallic substrate in an electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20) comprising at least on organic-based biocide component, b) connecting the to be coated substrate as the cathode of a circuit required for the electrodeposition process, then conducting the electrodeposition process by applying an electric voltage and then removing the coated substrates from the electrodeposition bath (10), c) successively rinsing the coated substrate by means of a rinsing cascade including at least two rinsing sub-steps comprising at least one rinsing sub-step c1) and then at least one rinsing sub-step c2), wherein the process further comprises a filtration cascade comprising d) a step of ultrafiltration, wherein this step comprises conducting an ultrafiltration of cathodic electrodeposition coating material (20) resulting in a retentate and an ultrafiltrate, e) a step of a further filtration, wherein this step comprises conducting a further filtration of ultrafiltrate of step d) resulting in a further retentate and a further filtrate, whereby the at least one rinsing sub-step c1) is conducted via a first type of rinsing medium (30), whereby each first-type rinsing medium (30) comprises the retentate of step e), and the at least one rinsing sub-step c2) is conducted via a second type of rinsing medium (40), whereby each second-type rinsing medium (40) comprises the further filtrate of step e) and wherein both the further filtrate of step e) and each second-type rinsing medium (40) comprise at least one organic-based biocide component, and each second-type rinsing medium (40) has a lower solids content compared to each first-type rinsing medium (30).

In the following, the novel process will also be called process of the invention or inventive process. Specific and preferred embodiments will be elucidated in the description and are also part of the dependent claims. A further subject-matter of the present invention is a system for conducting a cathodic electrodeposition process, whereby the system is configured to allow performing the inventive process. The system may be called inventive system or system of the invention. Brief description of Figures

Figure 1 shows relevant parts of an inventive system including a total of three rinsing media, i.e. two first type rinsing media (30a, 30b) and one second type rinsing medium (40). Rinsing medium (30a) is part of a rinsing sub-unit configured for spray rinsing, while rinsing media (30b) and (40) are part of rinsing sub-units configured for immersion rinsing. The system comprises an electrodeposition bath (10) which contains a cathodic electrodeposition coating material (20). Electrodeposition coating material (20) is conveyed to an ultrafiltration sub-unit (50), for example via a pipe system and use of a feed pump. While the retentate of the respective ultrafiltration is recirculated into the electrodeposition bath (10), the ultrafiltrate is further conveyed to the further filtration sub-unit (60). The retentate of the respective filtration step conducted in sub-unit (60) is directly conveyed into a container (i.e. a rinsing bath), i.e. a container which contains (or is meant to contain) a first type rinsing medium (30b). The filtrate of the filtration step conducted in sub-unit (60) also is directly conveyed into a container (i.e. a rinsing bath), here a container which contains (or is meant to contain) a second type rinsing medium (40). Figure 1 also shows schematically means (and the way of) recirculation of rinsing media (i.e. by successive transfer of rinsing medium from the rinsing bath positioned behind) and thus a continuous replenishment setup of the rinsing media. Also, a further way of replenishment is shown, i.e. intermediate spray rinsing procedure I setups (111). As known, such intermediate spraying may take place between two successive rinsing sub-steps. Thereby, the substrate is preliminarily sprayed with the rinsing medium of the subsequent rinsing sub-step, i.e. before the subsequent rinsing sub-step is actually starts and thus before the substrate is actually contacted with the overall storage of the rinsing medium of the subsequent sub-step. The low amount of the rinsing medium of the subsequent sub-step applied for the preliminary spraying is the recirculated into the rinsing medium of the previous sub-step. Thereby, quite obviously, also a certain degree of replenishment takes place.

Detailed description

In step a) of the process of the invention a to be coated metallic substrate is immersed in an electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20).

In step b) of the process of the invention the to be coated substrate is connected as the cathode of a circuit required for the electrodeposition process, the electrodeposition process is conducted by applying an electric voltage and the coated substrate is removed from the electrodeposition bath. Steps a) and b) are standard steps in electrodeposition coating processes and do not require a particular detailed description. The person skilled in the art may choose respective electrodeposition coating materials and process conditions according to individual needs.

Cathodic electrodeposition coating materials, obviously, comprise least one cathodically depositable polymer, whereby this polymer preferably is selected from epoxide-amine adducts. Also, preferably, the cathodic electrodeposition coating materials comprise at least one crosslinking agent, preferably a blocked polyisocyanate. Also, the cathodic electrodeposition coating material comprises at least one organic-based biocide component. Depending on the types and combination of organic-based biocide components, the content (also called amount or fraction) in the electrodeposition coating material may vary and be adapted according to individual needs. However, it may be specified that the overall content of organic-based biocides may be chosen from, for example, 10 to 500 mg/kg, preferably from 50 to 250 mg/kg (based on the overall weight of the cathodic electrodeposition coating material; within the present application corresponding contents I fractions I amounts always refer to the overall weight, if not explicitly mentioned differently)).

As organic-based biocide components, those being known to the person skilled in the art and regularly applied in electrodeposition coating materials may be applied. Examples are isothiazolinone compounds, ammonium-based organic biocide compounds, bromide compounds, iodide compounds or aldehyde compounds and also peroxide-based organic biocide compounds.

Explicit examples of isothiazolinone compounds are 2-Octyl-2H-isothiazol-3-one (OIT), 2- Methyl-1 ,2-thiazol-3(2H)-one (MIT), 5-Chloro-2-methyl-2H-isothiazol-3-one (CIT), 2-Methyl- 1 ,2-thiazol-3(2H)-one (BIT), examples of ammonium-based organic biocide compounds are dimethylbenzyl ammonium chloride or alkyl dimethyl ethyl ammonium ethyl sulfates, examples of bromide and iodide compounds are 2-bromo-2-nitropropane-1 ,3-diol (bronopol), 1 ,2- Dibromo-2,4-dicyanobutane, 2,2-dibromo-3-nitrilopropionamide and 3-iodo-2-propynyl- butylcarbamate, examples of aldehyde compounds are glutaral, glyoxal, (Ethylenedioxy)dimethanol and formaldehyde, examples of peroxide-based organic biocide compounds are tert-Butyl hydroperoxide and peroxyacetic acid.

Preferred organic biocide compounds are isothiazolinone compounds, ammonium-based organic biocide compounds, bromide compounds and iodide compounds.

In one preferred embodiment, the cathodic electrodeposition coating material comprises a combination of organic-based biocide components (i.e. at least two different organic-based biocide components), whereby the combination comprises CIT and MIT (and thus optionally at least one further organic-based biocide component). Such further organic-based biocide component could be, for example, bronopol. Accordingly, in one preferred embodiment, a combination including CIT, MIT and bronopol is applied. Even more preferably, the combination of organic-based biocide components consist of CIT, MIT and bronopol.

In another preferred embodiment, the cathodic electrodeposition coating material comprises a combination of organic-based biocide components, whereby the combination comprises MIT and bronopol (and thus optionally at least one further organic-based biocide component). For example, in one embodiment, as further organic-based biocide components, at least glutaral and OIT are applied. Accordingly, in one preferred embodiment, a combination including MIT, bronopol, OIT and glutaral is applied.

In one preferred embodiment, the cathodic electrodeposition coating material comprises a combination of organic-based biocide components which comprises CIT and MIT, whereby the cumulated amount of CIT and MIT is from 5 to 100 mg/kg, preferably from 6 to 50 mg/kg or even 7 to 25 mg/kg. Even more preferred, the mass ratio of CIT to MIT is from 1 :1 to 10:1 , preferably 2:1 to 6:1. As pointed out above, this combination preferably may further contain bronopol, for example in an amount of 50 to 150 mg/kg.

In another preferred embodiment, the cathodic electrodeposition coating material comprises a combination of organic-based biocide components which comprises MIT, whereby the amount of MIT is from 5 to 100 mg/kg, preferably from 6 to 50 mg/kg or even 7 to 25 mg/kg. As pointed out above, this combination preferably may further contain bronopol, for example in an amount of 50 to 150 mg/kg and glutaral, for example in an amount of 20 to 80 mg/kg.

Connecting the to be coated substrate as a cathode of a circuit quite obviously means to also provide at least one counter electrode which then functions as anode. Applying an electric voltage then leads to passage of electrical current between anode and cathode, ultimately leading to firmly adhering a coating film to the cathode and thus substrate. The voltage applied here is preferably in a range from 30 to 450 volts.

Suitable metallic substrates are automotive metallic vehicle bodies or parts thereof, i.e. metallic automotive component parts lie, for example transverse control arms, spring-loaded control arms or dampers. Preferred substrates are automotive metallic vehicle bodies.

The metal may be chosen from, in particular, the group consisting of steel, preferably steel selected from the group consisting of bare steel, cold rolled steel (CRS), hot rolled steel, galvanized steel such as hot dip galvanized steel (HDG), alloy galvanized steel (such as, for example, Galvalume, Galvannealed or Galfan) and aluminized steel, aluminum and magnesium, and also Zn/Mg alloys and Zn/Ni alloys. As known, the metallic substrate and thus metal to be applied in electrodeposition coating processes is electrically conductive.

The metallic substrate used in accordance with the invention is preferably a pretreated metallic substrate, for example pretreated with at least one metal phosphate such as zinc phosphate or with the known so-called “thin film pretreatment” systems.

Before the electrically conductive substrate is used in step a) of the inventive method, it is preferably cleaned and/or degreased.

Step c) of the present invention is a step of successively rinsing the coated substrate, after its removal from the electrodeposition bath, by means of a rinsing cascade including at least two rinsing sub-steps comprising at least one rinsing sub-step c1) and at least one rinsing sub-step c2). The rinsing sub-steps, quite obviously, require rinsing media which serve for the actual rinsing process and thus cleaning of the coated substrate. The rinsing may be conducted, for example, via immersion rinsing and/or spray rinsing. As mentioned above, at least two rinsing sub-step are conducted, for example one rinsing sub-step c1) and one rinsing sup-step c2). Of course, it is also possible to have more than two rinsing sup-steps conducted, for example one rinsing sub-step c) and two successive rinsing sub-steps c2). Also rinsing sub-steps being different from rinsing sub-steps c1) and c2) are in principle conceivable (even if not being preferred). In a preferred embodiment, a rinsing sub-step c2) is the last rinsing sub-step conducted within the rinsing cascade c) and thus also the last rinsing sub-step of the overall process.

For provision of the rinsing media, the inventive process comprises a specific filtration cascade, namely a filtration cascade comprising as step d) a step of ultrafiltration, wherein this step comprises conducting an ultrafiltration of cathodic electrodeposition coating material resulting in a retentate and an ultrafiltrate, and as step e) a step of a further filtration, wherein this step comprises conducting a further filtration of ultrafiltrate of step d) resulting in a further retentate and a further filtrate.

At first the filtration cascade shall be elucidated in more detail.

Step d) and thus the step of ultrafiltration of cathodic electrodeposition coating material is a well-known filtration step in electrodeposition coating processes for provision of rinsing media (cf. also introductory part). Respective ultrafiltration systems (50) are known to the person skilled in the art and may be conveniently implemented into process and plant setups. Thereby, normally, the electrodeposition bath and thus electrodeposition coating material is fluidly connected via a pipe system with the ultrafiltration system / equipment and the electrodeposition coating material is conveyed, for example via use of a feed pump, to the ultrafiltration system. The ultrafiltration may then be conducted, for example, continuously or semi-continuously. Continuously, quite obviously, means that during the course of the process, electrodeposition coating material is continuously transferred to the ultrafiltration unit and then likewise continuously filtrated. Adjustment parameters like flow rate and throughput rate may be adjusted and/or in-situ adapted according to individual needs. Semi-continuously, quite obviously, means in the context of the present invention that a prementioned continuous procedure may be interrupted from time to time, for example due to a change in overall process throughput and/or other influencing factors like having built up storage of ultrafiltrate or breaks I interruptions in the overall process.

Preferably, at least part of the retentate of the ultrafiltration conducted in step d) is recirculated into the electrodeposition bath comprising the cathodic electrodeposition coating material. More preferably, even all of the produced retentate is correspondingly recirculated. Again, this normally is conducted via fluidly connecting pipe systems, for example via use of feed pumps. By this means, the electrodeposition bath is replenished by concentrated electrodeposition coating material (i.e. the retentate) partly compensating for consumption of material during the deposition process.

The ultrafiltrate, quite obviously, is a medium being significantly reduced in solids content compared to the electrodeposition coating material (in fact, reduction of the solids content is the overall purpose of this filtration). While a standard electrodeposition coating material has a solid content of, for example, 5 to 25 %, an ultrafiltrate may have a solids content of not more than 1.5 % or not more than 1.25 % or even not more than 1.0 % (0.5 h, 180°C).

The ultrafiltrate, again quite obviously, thus is a medium preferably also being reduced in the content of organic-based biocide components compared to the electrodeposition coating material. However, the ultrafiltrate, likewise obviously, in any case contains such organicbased biocide components.

It is essential that at least part of the ultrafiltrate, after its preparation, is subjected to a further filtration step e) leading to a further retentate and a further filtrate. Another part of ultrafiltrate, if present, may be conveyed into at least one rinsing bath (i.e. a container which already contains or is intended to contain a rinsing medium for immersion and/or spray rinsing) and thus made part of at least one rinsing medium, preferably of a first-type rinsing medium as described below. The fraction of ultrafiltrate subjected to further filtration and the fraction of ultrafiltrate which may be made part of a first-type rinsing medium may be adapted according to individual needs and circumstances, thereby considering aspects like capacities I throughput rates of the ultrafiltration system and the successive system for further filtration or individual target properties of rinsing media (which may speak for or make necessary the addition of ultrafiltrate to stay within preset target properties)

The further filtration step e), quite obviously, leads to a further retentate and a further filtrate. Thereby, the further retentate is concentrated compared to the ultrafiltrate, while the further filtrate, quite obviously, has a solids content being smaller than that of the ultrafiltrate. This is an inherent feature and consequence, respectively, of the further filtration step (as a filtration in any case leads to a filtrate having a lower solids content compared to the medium which is subjected to filtration).

Similar to what is described above for the ultrafiltration, normally, the ultrafiltrate is conveyed via a fluidly connecting pipe system, for example via use of a feed pump, to the system for further filtration. Again, the further filtration may be conducted, for example, continuously or semi-continuously. Adjustment parameters like flow rate and throughput rate may be adjusted and/or in-situ adapted according to individual needs.

The solids content of the further filtrate, quite obviously, is a medium being reduced in solids content compared to the ultrafiltrate. Preferably, the solids content is not more than 0.25 %, even more preferably not more than 0.15 % or even not more than 0.1 % (0.5 h, 180°C).

On the other side, the further filtrate in any case comprises at least one organic-based biocide component. This at least one organic-based biocide component, quite obviously, originates from the ultrafiltrate (and thus, ultimately, from the electrodeposition coating material).

Accordingly, while the further filtrate has a comparably low solids content (i.e. a solids content being in any case lower than an ultrafiltrate), it still contains an effective amount of biocides. This, in turn, brings the great benefit of being able to provide, based on the further filtrate, rinsing media (i) having a very low solids content (meaning that a great quality in cleaning effect may be achieved), (ii) being producible with such low solids content without the need of adding external water and (iii) still comprising an effective amount of biocides originating from the cathodic electrodeposition coating material, meaning that likewise the individual addition of external biocide amounts to a corresponding rinsing medium may be omitted. More particularly, it has been found that - while filtration with the result of low residual solid content filtrate is acceptable - it is in line with providing a filtrate still having a residual biocide content. Therefore, the filtration step as outlined above brings together the advantages of low water consumption and avoidance of separate biocide addition.

The wording “biocides (or biocide component) originating from the cathodic electrodeposition coating material”, quite obviously is meant to embrace not only the scenario where initially such a material actually contains such biocides, but also the scenario where biocides are added regularly I on occasion during the course of a running electrodeposition process (and then successively distributed throughout the electrodeposition setup as elucidated in the introductory part).

The cumulative amounts of organic-based biocide components in the further filtrate preferably is at least 2 mg/kg. For example, in the preferred embodiment of a cathodic electrodeposition coating material comprising a combination of organic-based biocide components which comprises CIT and MIT, the cumulative amount of CIT and MIT preferably is from 2 to 10 mg/kg.

It has been figured out that the above characteristics of the further filtrate may be achieved by membrane filtration and respective membrane filtration systems I setups. While membrane filtration setups and systems as well as the underlying principles are generally known, the prior art did not recognize the great benefits of the respective filtrates achievable in connection with electrodeposition coating materials and respective ultrafiltrates (i.e. filtration of ultrafiltrates). Therefore, preferably a membrane filtration system is selected as further filtration sub-unit (60).

Next, the rinsing media, more particularly the first type rinsing media (30) and second type rinsing media (40) as well as the rinsing cascade c) shall be elucidated in more detail.

As mentioned above, each first type rinsing medium (30) comprises the retentate of step e) while each second type rinsing medium (40) comprises the filtrate of step e). “Comprising”, quite obviously, means that the respective medium does not necessarily consist of the respective retentate I filtrate, but may contain also further fractions and portions. For example, as outlined above, a first type rinsing medium also may contain ultrafiltrate of filtration step d). Also, it has to be taken into account that the inventive process preferably is a process in which more than one substrate is coated and then rinsed, whereby, quite obviously and thus preferably, the rinsing media are not exchanged I completely refreshed after rinsing of just one substrate. More particularly, the inventive process is a serial process in which a plurality of substrates is successively coated and then successively rinsed by means of the rinsing cascade c). Therefore, it is also evident that a rinsing bath and medium, after its initial provision, will successively be contaminated by the rinsing process itself (i.e. by washing off debris I residual coating material I rinsing media of previous rinsing sub steps). Likewise, in such serial processes, after initial provision of a rinsing medium, it is standard to replenish a rinsing medium continuously or semi-continuously. Such replenishing may mean to add fresh composition, for example respective retentate I filtrate of step e). Also, often a replenishing is conducted by recirculation processes, i.e. to recirculate, for example continuously or semi- continuously, a rinsing medium applied in a sub-step x of a rinsing cascade to the rinsing medium applied in the previous sub-step x-1 (meaning that the rinsing medium of step x is replenished by disposing of medium having - compared to its desired/optimal condition - a higher degree of contamination and rinsing medium x-1 is replenished by addition of medium having - compared to its standard condition - a lower degree of contamination). Also, intermediate spray rinsing procedure I setups (111) like described above may play a role in such replenishment.

While the above measures, in sum, intend to provide for comparably constant rinsing media to provide for a stable and predictable rinsing process, it of course also means that the exact composition of a rinsing medium will vary during execution of such a serial process. Still, in each case and also within the context of serial processes, each first type rinsing medium will contain the retentate of step e), while each second type rinsing medium will contain the filtrate of step e). The term “comprise” is to be understood in a way that a respective component like retentate or filtrate (in inherently varying amounts I portions, cf. above) is comprised for the entire duration of the process. Also, the term “comprise” encompasses that the respective component, for example retentate or filtrate, does not need to be identifiable anymore in an individualized manner (as, quite obviously, after initial provision, replenishment via conveying fresh composition or via recirculation and also successive contamination will lead to composites in which added portions cannot be identified anymore. However, the respective media will still comprise the respective components. Determination of respective quantities may be derived from comparison of properties of a certain medium with the properties and portions of components added to the medium and/or by considering flow rates I throughput rates of addition and/or discharge of components).

Preferably, each first type rinsing medium comprises as major portion the retentate of step e) while each second type rinsing medium comprises as major portion the filtrate of step e). Therefore, also in the context of serial processes and thus contamination as outlined above, initial provision of a rinsing bath and then, during the course of the process, replenishment by (i) conveying further retentate I filtrate into respective containers I rinsing media (again, for example, via fluidly connecting pipe systems, for example via use of feed pumps) and/or (ii) recirculation provide for rinsing media comprising further retentate I filtrate as major portion. This aspect also could be described by the term “the rinsing medium is based on the retentate I filtrate”.

These exact amounts may be steered by the filling and replenishment processes as outlined above (in particular filling I replenishment with retentate and/or filtrate of step e and/or via recirculation). More particularly, adjustment parameters like flow rate or throughput rate of these processes allow adjustment of respective amounts. It follows from the above that preferably at least one first-type rinsing medium is initially provided by a filling process comprising filling retentate of step e) into a container and at least one second-type rinsing medium is initially provided by a filling process comprising filling filtrate of step e) into a further container.

Even more preferably, exactly one first type rinsing medium is initially provided by a process comprising directly conveying retentate of step e) to a container (i.e. rinsing bath), while any potential further first type rinsing medium is initially provided by only a recirculation process as outlined above (i.e. by successively transferring rinsing medium into the respective rinsing bath from the rinsing bath positioned behind). The one first type rinsing medium provided by directly conveying retentate of step e), quite obviously, then is the last first type rinsing medium in the process, i.e. the first-type rinsing medium of the last rinsing sub-step conducted by means of a first-type rinsing medium. Provision of this one first-type rinsing medium preferably also comprises directly conveying ultrafiltrate of step d) to the respective container (i.e. rinsing bath). Accordingly, preferably, after rinsing with this one first-type rinsing medium a rinsing sub-step with a second-type rinsing medium follows.

Likewise, exactly one second type rinsing medium is initially provided by a process comprising directly conveying filtrate of step e) to a container (i.e. rinsing bath), while any potential further second type rinsing medium is initially provided by only a recirculation process as outlined above. Again, the one second type rinsing medium provided by directly conveying filtrate of step e), quite obviously, then is the last second type rinsing medium in the process, i.e. the second type rinsing medium of the last rinsing sub-step conducted by means of a second-type rinsing medium. Therefore, this one second-type rinsing medium preferably is the rinsing medium of the last rinsing sub-step of the inventive process.

For example, in a scenario where two first-type rinsing media and thus baths and two second- type rinsing media and thus baths are applied, it is preferred that each the second first-type and second second-type medium is provided by the above-mentioned direct conveying process, while each the first first-type and first second-type medium is provided by the above- mentioned recirculation process.

In case of, for example, application of more than two first-type and more than two second-type rinsing media, preferably, only the respective last first-type and second-type rinsing medium is applied by the above-mentioned direct conveying process.

It also follows from the above, that preferably at least one first-type rinsing medium, after its initial provision, is replenished by directly adding further retentate of step e) and at least one second-type rinsing medium, after its initial provision, is replenished by directly adding further filtrate of step e). Obviously, preferably, exactly one first-type and exactly one second-type rinsing medium is replenished as outlined in the presentence, whereby - in case of more than one of first-type and/or second-type rinsing medium, the this way replenished rinsing medium is the last first-type I second-type rinsing medium.

Likewise, it follows from the above, that preferably a further replenishment is conducted by recirculating at least one rinsing medium of at least one sub-step of rinsing step c) to the rinsing medium of the previous sub-step. More preferably, this further replenishment involves recirculation of each except the rinsing medium applied in the first rinsing sub-step to the rinsing medium of the previous sub-step, while the rinsing medium of the first sub-step is recirculated into the electrodeposition coating material.

As already pointed out above, the further filtrate of step e) comprise at least one organic-based biocide component. This likewise apply for each second type rinsing medium, i.e. any second type rinsing medium comprise at least one organic-based biocide component. Also in line with the above on the further filtrate, the cumulative amounts of organic-based biocides in any second type rinsing medium preferably is at least 2 mg/kg. For example, in the preferred embodiment of a cathodic electrodeposition coating material comprising a combination of organic-based biocide components which comprises CIT and MIT, the cumulative amount of CIT and MIT preferably is from 2 to 10 mg/kg in any second type rinsing medium. This again shows the dependency of second type rinsing media and further filtrate of step e) (i.e. a second type rinsing medium comprises I is based on this further filtrate).

As mentioned above, the further filtrate, preferably, has a solids content of not more than 0.25 %, even more preferably not more than 0.15 % or even not more than 0.1 %. The solids content of each second type rinsing medium preferably is not more than 0.3 or preferably not more than 0.15 or even 0.1 (0.5 h, 180°C). These values, in comparison to the values of the filtrate of step e), reflect the fact that a rinsing medium may be successively contaminated by its use for rinsing. Even if a replenishment may take place (cf. above), the solids content may be higher than that of the filtrate of step e).

Similar to what is outlined above with regard to the further filtrate and second type rinsing media, a certain relation between the further retentate and first type rinsing media exist. However, as also pointed out above, a first type rinsing media also may comprise a portion of ultrafiltrate from step d), meaning that the ultrafiltrate also may have a significant influence on properties of the first type rinsing media.

Accordingly, and anyway evident from the above, preferably any second-type rinsing medium has a lower biocide content compared to any first-type rinsing medium. Also, any second-type rinsing medium has a lower solids content compared to any first-type rinsing medium.

The above properties and parameters of the rinsing media are to be understood in a way that they are fulfilled for the entire duration of the process.

As within the rinsing cascade c) any rinsing sub-step conducted via a first type rinsing medium is conducted before any rinsing sup-step conducted via a second type rinsing medium, the rinsing with rinsing medium having lower solids content will therefore be conducted after rinsing with rinsing medium having higher solids content.

From the above follows that preferably both each first-type and each second-type rinsing medium applied within the process comprise organic-based biocide content originating from the cathodic electrodeposition coating material, whereby at least a part of this organic-based biocide content is introduced into each first-type rinsing medium via the retentate of step e) and into each second-type rinsing medium via the filtrate of step e). Even more preferably, the process does not include any individual external addition of organic-based biocides into any specified rinsing medium applied within the process, meaning that any such organic-based biocide content originates from the cathodic electrodeposition coating material. Again, the wording “organic-based biocides (or organic-based biocide component) originating from the cathodic electrodeposition coating material”, is meant to embrace not only the scenario where initially such a material contains such biocides, but also the scenario where these biocides are added regularly I on occasion during the course of a running electrodeposition process and then are successively distributed throughout the electrodeposition system. Accordingly, the wording “does not include any individual external addition of organic-based biocides into any specified rinsing medium” means that such biocide is not added individually into a specified and individual rinsing medium for the reason that no or at least no effective amount of such biocides is reaching the respective specified and individual medium via the successive distribution as mentioned above (either because the rinsing medium is not connected to the overall setup, e.g. in the case of externally added water, or the rinsing medium is provided in a way which does not allow for a transfer of biocides into the medium, e.g. in the case of reverse osmosis).

Also, preferably, the process does not comprise any rinsing sub-step which is conducted via a rinsing medium consisting or essentially consisting of externally added water.

As mentioned above, the inventive process preferably is a serial process. In other words: The present invention also relates to a serial process, wherein i. to be coated substrates are consecutively immersed, coated and rinsed under steps a) to c), ii. wherein the filtration steps d) and e) are conducted as continuous or semi- continuous filtration steps, iii. wherein, after initial provision of the to be applied rinsing media,

- these rinsing media are continuously or semi-continuously replenished by recirculating each except the rinsing medium applied in the first rinsing sub-step to the rinsing medium of the previous sub-step and recirculating the rinsing medium applied in the first sub-step to the electrodeposition coating material,

- at least one first-type rinsing medium is further replenished by directly adding, continuously or semi-continuously, adding further retentate of step e) and at least one second-type rinsing medium is further replenished by directly adding, continuously or semi-continuously, further filtrate of step e).

The present invention also relates to a system for conducting a cathodic electrodeposition process comprising

1) an electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20) and means for connecting to be coated substrates as the cathode of a circuit and for applying an electric voltage required for an electrodeposition process

2) a filtration unit comprising

2.1) an ultrafiltration sub-unit (50) suitable for filtration of cathodic electrodeposition coating material resulting in a retentate and an ultrafiltrate, and

2.2) a further filtration sub-unit suitable (60) for filtration of an ultrafiltrate of step 2.1) resulting in a further retentate and a further filtrate,

3) a rinsing unit for successively rinsing coated substrates comprising at least two rinsing sub-units, wherein

3.1) at least one first-type rinsing sub-unit comprises a container containing a first-type rinsing medium (30), whereby the first-type rinsing medium (30) comprises the retentate produced in filtration unit 2.2)

3.2) at least one second-type rinsing sub-unit comprises a container containing a second-type rinsing medium (40), whereby the second-type rinsing medium (40) comprises the filtrate produced in filtration unit 2.2), and wherein

- the filtrate produced in filtration unit 2.2) and each second-type rinsing medium (40) has a biocide content of at least 2 mg/kg and

- each second-type rinsing medium (40) has a lower solids content compared to each first-type rinsing medium (30). Any essential and preferred embodiments of the inventive process correspondingly apply for the inventive system.

The invention shall be elucidated in more detail via the following examples. These examples do not intend to limit the scope of the present invention.

Examples

Example 1 :

An inventive system as in principle shown in Figure 1 (i.e. including two rinsing media (30) and one rinsing medium (40)) was assembled and then used for conducting an inventive cathodic electrodeposition process in a continuous manner. As further filtration sub-unit (60) a commercially available membrane filtration setup was applied. As electrodeposition coating material (20) a standard product from BASF Coatings GmbH was used. This electrodeposition coating material comprised a combination of organic-based biocide components, whereby the combination contained CIT and MIT. The amounts of CIT and MIT, based on the overall weight of the electrodeposition coating material (20), were pre-set at the start of the process and then correspondingly controlled and supplemented occasion-wise.

The amount of CIT and MIT for different media I retentates I filtrates were measured. Table 1 gives an overview of representative values. It may be mentioned that the rinsing medium (40) never contained less than 1.0 mg/kg CIT and also never less than 0.5 mg/kg MIT. Also, Table 2 shows the solids content (0.5 h, 180°C, 1 g sample) of different media.

Table 1 : - Biocide contents

Table 2 - solids contents

As shown, the membrane filtration leads to a filtrate in any case still having a residual content of CIT and MIT despite of having a very low solids content. Therefore, likewise, the same is true for the rinsing medium (40). Overall, it was possible to stably run the process without any individual addition of organic-based biocide components to the last rinsing bath and thus rinsing medium (40). No interfering bacterial and/or fungal contamination could be detected. Still, the overall rinsing process and in particular the last rinsing step provided for a high quality cleaned surface, ultimately leading to high-quality surfaces of the eventually cured electrodeposition coatings.

Example 2:

Example 1 was repeated with the only exception that a reverse osmosis filtration system was applied as further filtration sub-unit (60). As a result, a respective filtrate and thus rinsing medium (40) with non-detectable solids content and CIT/MIT amounts was generated. Accordingly, it was not possible to omit individual addition of organic-based biocides to the last rinsing bath and thus rinsing medium (40) to prevent bacterial and fungal contamination.

Claims

Claims

1. A cathodic electrodeposition coating process comprising the following steps: a) immersing a to be coated metallic substrate in an electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20) comprising at least on organic-based biocide component, b) connecting the to be coated substrate as the cathode of a circuit required for the electrodeposition process, then conducting the electrodeposition process by applying an electric voltage and then removing the coated substrate from the electrodeposition bath (10), c) successively rinsing the coated substrate by means of a rinsing cascade including at least two rinsing sub-steps comprising at least one rinsing sub-step c1) and then at least one rinsing sub-step c2), wherein the process further comprises a filtration cascade comprising d) a step of ultrafiltration, wherein this step comprises conducting an ultrafiltration of cathodic electrodeposition coating material (20) resulting in a retentate and an ultrafiltrate, e) a step of a further filtration, wherein this step comprises conducting a further filtration of ultrafiltrate of step d) resulting in a further retentate and a further filtrate, whereby

- the at least one rinsing sub-step c1) is conducted via a first type of rinsing medium (30), whereby each first-type rinsing medium (30) comprises the retentate of step e), and the at least one rinsing sub-step c2) is conducted via a second type of rinsing medium (40), whereby each second-type rinsing medium (40) comprises the refined filtrate of step e) and wherein both the further filtrate of step e) and each second-type rinsing medium comprise at least one organic-based biocide component, and each second-type rinsing medium has a lower solids content compared to each first- type rinsing medium.

2. A process according to claim 1 , wherein a rinsing sub-step c2) is the last rinsing step of the process.

3. A process according to claim 1 or 2, wherein no rinsing sub-step takes place which is conducted via a rinsing medium consisting or essentially consisting of externally added water.

4. A process according to any of claims 1 to 3, wherein step c) is a cascade-type rinsing step in which the rinsing medium of at least one sub-step is recirculated into the rinsing medium of the previous sub-step, thereby replenishing the rinsing medium of the previous sub-step.

5. A process according to claim 4, wherein each except the rinsing medium applied in the first rinsing sub-step is recirculated to the rinsing medium of the previous sub-step and wherein the rinsing medium applied in the first sub-step is recirculated to the electrodeposition coating material.

6. A process according to any of claims 1 to 5, wherein at least one first-type rinsing medium (30) is initially provided by a filling process comprising filling retentate of step e) into a container and at least one second-type rinsing medium (40) is initially provided by a filling process comprising filling filtrate of step e) into a further container.

7. A process according to claim 6, wherein the at least one first-type rinsing medium (30), after its initial provision, is replenished by adding further retentate of step e) and the at least one second-type rinsing medium, after its initial provision, is replenished by adding further filtrate of step e).

8. A process according to any of claims 1 to 7, wherein at least part of the retentate of step d) is recirculated into the electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20).

9. A process according to any of claims 1 to 8, wherein the filtrate of step e) has a cumulative amount of organic-based biocide components of at least 2 mg/kg and wherein each second- type rinsing medium also has a cumulative amount of organic-based biocide components of at least 2 mg/kg.

10. A process according to any of claims 1 to 9, wherein any second-type rinsing medium (40) has a solids content of not more than 0.3 %.

11. A process according to any of claims 1 to 10, wherein the filtrate of step e) has a solids content of not more than 0.25 %.

12. A process according to any of claims 1 to 11 , wherein both each first-type and each second- type rinsing medium (30, 40) applied within the process comprise organic-based biocide content originating from the cathodic electrodeposition coating material (20), whereby at least a part of this organic-based biocide content is introduced into each first-type rinsing medium (30) via the retentate of step e) and into each second-type rinsing medium (40) via the filtrate of step e).

13. A process according to any of claims 1 to 12, wherein the process does not include any individual external addition of organic-based biocides into any specific rinsing medium applied within the process.

14. A process according to any of claims 1 to 13, wherein the process is a serial process, wherein i. to be coated substrates are consecutively immersed, coated and rinsed under steps a) to c), ii. wherein the filtration steps d) and e) are conducted as continuous or semi- continuous filtration steps, iii. wherein, after initial provision of the to be applied rinsing media,

- these rinsing media are continuously or semi-continuously replenished by recirculating each except the rinsing medium applied in the first rinsing sub-step to the rinsing medium of the previous sub-step, and

- at least one first-type rinsing medium (30) is further replenished by directly adding, continuously or semi-continuously, further retentate of step e) and at least one second-type rinsing medium (40) is replenished by directly adding, continuously or semi-continuously, further filtrate of step e).

15. A system for conducting a cathodic electrodeposition process comprising

1) an electrodeposition bath (10) comprising a cathodic electrodeposition coating material (20) comprising at least one organic-based biocide component and means for connecting to be coated substrates as the cathode of a circuit and for applying an electric voltage required for an electrodeposition process

2) a filtration unit comprising

2.1) an ultrafiltration sub-unit (50) suitable for filtration of cathodic electrodeposition coating material resulting in a retentate and an ultrafiltrate, and

2.2) a further filtration sub-unit (60) suitable for filtration of an ultrafiltrate of step 2.1) resulting in a further retentate and a further filtrate,

3) a rinsing unit for successively rinsing coated substrates comprising at least two rinsing sub-units, wherein

3.1) at least one first-type rinsing sub-unit comprises a container containing a first-type rinsing medium (30), whereby the first-type rinsing medium (30) comprises the retentate produced in the filtration sub-unit according to 2.2)

3.2) at least one second-type rinsing sub-unit comprises a container containing a second-type rinsing medium (40), whereby the second-type rinsing medium (40) comprises the filtrate produced in filtration sub-unit according to 2.2), and wherein - the filtrate produced in filtration sub-unit 2.2) and each second-type rinsing medium (40) comprise at least one organic-based biocide component and

- each second-type rinsing medium (40) has a lower solids content compared to each first-type rinsing medium (30).