METAL EFFECT PIGMENTS FOR USE IN THE CATHODIC ELECTRODEPOSITION PAINTING, METHOD FOR THE PRODUCTION AND USE OF THE SAME, AND ELECTRODEPOSITION PAINT

- Eckart GMBH

The invention relates to electrocoat material pigments, said electrocoat material pigments comprising metal effect pigment platelets coated with at least one coating material, said coating material comprising one or more functional groups for adhesion or attachment to the pigment surface and at least one amino-functional group, said amino-functional group being protonatable or positively charged. The invention further relates to a process for producing these electrocoat material pigments and to the use thereof, and to a cathodic electrocoat material which comprises the inventive pigments.

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Description

The invention relates to pigments based on metal effect pigment platelets which can be deposited in the course of cathodic electrocoating. The invention further relates to a process for producing these electrocoat material pigments and to the use thereof in a cathodic electrocoat material or in cathodic electrocoating. The invention finally also relates to a cathodic electrocoat material.

Electrocoating (EC) is a process for applying particular water-soluble coating materials, so-called electrocoat materials, to electrically conductive substrates, for example a workpiece. Between a workpiece immersed into a coating bath and a counterelectrode, an electrical direct current field is applied. A distinction is drawn between anodic deposition, so-called anodic electrocoating (AEC), in which the workpiece is connected as the anode or plus pole, and cathodic deposition, so-called cathodic electrocoating (CEC), in which the workpiece is connected as the cathode or as the minus pole.

The coating material binder contains functional groups of particular polarity, which are present in salt form due to neutralization and as a result colloidally dissolved in water. In the vicinity of the electrode (within the diffusion boundary layer), owing to hydrolysis, hydroxide ions form in CEC or H+ ions in AEC. These ions react with the binder salt, causing the functionalized binders to lose their salt form (“salting out”), become insoluble and coagulate at the surface of the workpiece. Later, the coagulated binder particles lose water owing to electroosmosis procedures, which causes further compaction. Finally, the workpiece is withdrawn from the immersion bath, freed of noncoagulated coating material particles in a multistage rinsing process and fired at temperatures of 150-190° C. (Brock, Groteklaes, Mischke, “Lehrbuch der Lacktechnologie” [Textbook of coating technology] 2nd edition, Vincentz Verlag 1998, p. 288 ff.).

Electrocoating has several economic and ecological advantages over conventional coating methods such as wet coating or powder coating.

A primary factor which should be mentioned here is the comparatively exactly adjustable layer thickness. Compared to powder coatings, electrocoating also homogeneously coats difficult-to-access parts of the workpiece. This results from the following fact: first, the deposition of the binder takes place at points of high field strength, such as corners and edges. However, the film which forms has a high electrical resistance. The field lines therefore shift to other regions of the workpiece and are concentrated toward the end of the coating operation entirely on the most inaccessible points, for example regions or points in the interior of the workpiece (inner coating). The coating of particularly difficult-to-access points of a workpiece can be improved once more by the provision of auxiliary electrodes. With electrocoating (EC) it is therefore possible to coat workpieces of any shape, provided that they are electrically conductive. EC is additionally associated advantageously with properties such as minimal solvent emissions, optimal material yield and noncombustibility. Droplet- and run-free paintwork is obtained. Electrocoating is performed in an automated manner and is as a result a very inexpensive coating method, especially since it can be performed at comparatively low current densities of a few mA/cm2.

Owing to the simple and highly inexpensive application method, electrocoating at present finds use in numerous systems. The most common are basecoats, for example in automotive OEM finishing, and single-layer topcoats. Electrocoats are found, for example, on radiators, control cabinets, office furniture, in construction, in iron and household products, in storage technology or in rack construction, in climate control and lighting technology, and in apparatus construction and mechanical engineering.

Compared to the older process, anodic electrocoating (AEC), cathodic electrocoating (CEC) has become increasingly established since the mid-1970s. It has various advantages: in addition to improved corrosion protection, mention should be made of homogeneous layer thickness distribution, and also better throwing power and good edge coverage.

CEC finds use especially in chassis coating. This process firstly achieves corrosion protection, and secondly protects the coating from stonechipping. CEC can be used as a corrosion protection coating for all metallic substrates; mention should be made here, for example, of supports or racks for outside use. Owing to the substantial absence of organic solvent, environmental compatibility completes the advantages of cathodic electrocoating as a highly efficient and attractive coating method.

Electrocoat materials in use to date have especially been waterborne coating materials which usually comprise self-crosslinking or extraneously crosslinking synthetic resins as binders, which can be dispersed through protonation with acid in water. Protonation of the functional groups present in the synthetic resins forms ammonium, phosphonium or sulfonium groups. The synthetic resins are, for example, polymerization, polyaddition or polycondensation products containing primary or tertiary amino groups, such as amino epoxy resins, amino poly(meth)acrylate resins or amino polyurethane resins. The electrocoat materials may contain conventional color pigments, which are generally organic and inorganic color pigments. However, the range of color shades which is actually used commercially is very limited. The use of effect pigments in electrocoat material is commercially unknown to date.

The CEC bath contains binder, pigment paste, water-miscible organic solvent and water. The essential constituent of binder and pigment paste is frequently epoxy resin. Binder and pigment paste make up the majority of the about 20% solids content of the coating material. The electrocoat material further consists to an extent of about 80% by weight of water. There is additionally a small portion of organic solvents (1-2%), acids (0.4%) and additives. The epoxy resin is converted to a water-dispersible form by adding a neutralizing agent. An organic acid is used for this purpose (principally acetic acid). Often only a portion of the functional groups is reacted with neutralizing agent. The molar ratio of acid to functional group is referred to as the degree of neutralization. A degree of neutralization of about 30% is sufficient to achieve the desired water dispersibility. An organic acid is also used to establish the slightly acidic pH in the CEC bath.

DE 10 2005 020 763.4, which was yet to be published at the priority date of the present application, describes metal effect pigments which can find use in anodic electrocoat materials.

EP 0 477 433 A1 discloses metal effect pigments coated with synthetic resins, a very thin siloxane layer being applied as an adhesion promoter between metal effect pigment surface and the synthetic resin layer. This document does not make any reference to electrocoating.

EP 0 393 579 B1 discloses a metal pigment-containing waterborne coating material which is said to be applicable to a substrate by means of electrocoating. EP 0 393 579 B1 does not disclose any metal effect pigments suitable for cathodic electrocoating.

It is an object of the present invention to provide metal effect pigments which can be deposited in a coating material on a workpiece in cathodic electrocoating.

The metal effect pigments must be corrosion-stable to the aqueous electrocoat material medium and be depositable reproducibly even after more than 60 days of bath time. Electrocoatings thus produced should have a metallic effect whose optical quality preferably corresponds to at least that of powder coatings.

It is a further object of the present invention to find a process for producing such metal effect pigments.

The object is achieved by providing electrocoat material pigments which are metal effect pigment platelets coated with at least one coating material, said coating material comprising

  • (a) one or more functional groups for adhesion or attachment to the pigment surface and
  • (b) at least one amino-functional group, said amino-functional group being protonatable or positively charged.

Preferred developments of the electrocoat material pigments are specified in subclaims 2 to 12.

The object is additionally achieved by providing a process for producing electrocoat material pigments as claimed in one of claims 1 to 12, wherein the process comprises the following steps:

  • (a) coating a metal effect pigment with the coating material having an amino-functional group dissolved or dispersed in a solvent, said amino-functional group being protonatable or positively charged,
  • (b) optionally drying the metal effect pigments coated with the coating material in step (a),
  • (c) optionally converting the metal effect pigments dried in step (b) to a paste.

A development of the process according to the invention is specified in subclaim 14.

The object underlying the invention is also achieved by the use of electrocoat material pigments as claimed in one of claims 1 to 12 in a cathodic electrocoat material or in cathodic electrocoating.

The invention further relates to a cathodic electrocoat material comprising electrocoat material pigments as claimed in one of claims 1 to 12.

The metal effect pigments may consist of metals or alloys which are selected from the group consisting of aluminum, copper, zinc, tin, brass, iron, titanium, chromium, nickel, steel, silver and alloys and mixtures thereof. Preference is given here to aluminum pigments and brass pigments, particular preference being given to aluminum pigments.

The metal effect pigments are always platelet-shaped in nature. This is understood to mean pigments in which the longitudinal dimension is at least ten times, preferably at least twenty times and more preferably at least fifty times the mean thickness. In the context of the invention, when metal effect pigments are mentioned, what is meant is always metal effect pigment platelets.

The metal effect pigments used in the inventive electrocoat material possess mean longitudinal dimensions which are determined as sphere equivalents by means of laser granulometry (Cilas 1064, from Cilas) and are reported as the d50 value of the corresponding cumulative undersize distribution. These d50 values are 2 to 100 μm, preferably 4 to 35 μm and more preferably 5 to 25 μm.

It has been found that, surprisingly, it is virtually no longer possible to deposit very large pigment particles with a d50 above 100 μm. It appears that the migration and deposition properties are considerably reduced for relatively large particles. From such coarse pigment distributions, only the fractions below approx. 100 μm are now deposited (fines fraction). However, this considerably reduces the size and size distribution of the particles deposited compared to those used. For this reason, smaller particles with a d50 of less than <100 μm are preferred. From a d50 of approx. 2 to 35 μm, the inventive pigments are deposited over their entire size distribution without any problems. In addition, pigments from this size enable a bath time of more than 60 days.

Below a d50 of 4 μm, the particles are too fine to produce an appealing visual effect. Here too, owing to the very high specific surface area of the fine pigments, gassing problems can occasionally occur in the aqueous electrocoat medium.

The mean thickness of the inventive metal effect pigments, in contrast, is preferably 40 to 5000 nm, more preferably 65 to 800 nm and most preferably 250 to 500 nm.

Electrocoat materials are always waterborne systems. For this reason, metal effect pigments present in an electrocoat material have to be stabilized for use in aqueous systems. For example, they are provided with a protective layer in order to prevent the corrosive influence of water on the metal effect pigment. In addition, they must have suitable surface charges in order to possess sufficient electrophoretic mobility in the electrical field.

These properties are surprisingly provided when metal effect pigments are coated with a coating material, said coating material having one or more functional groups for adhesion or attachment to the pigment surface and at least one protonatable or positively charged amino-functional group.

In the context of the invention, the term “adhesion” is understood to mean noncovalent interactions, for example hydrophobic interactions, hydrogen bonds, ionic interactions, van der Waals forces, etc., which lead to immobilization of the coating material on the pigment surface.

In the context of the invention, the term “attachment” is understood to mean covalent bonds which lead to covalent immobilization of the coating material on the pigment surface.

It has been found, entirely surprisingly, that metal effect pigments in cathodic electrocoating have outstanding electrophoretic mobility when the metal effect pigments are provided with a coating material which contains an amino-functional group.

The protonatable or positively charged amino-functional group, after introduction of the coated metal effect pigments into the electrocoat medium, preferably projects into the electrocoat medium. The protonatable or positively charged amino-functional group is preferably arranged spaced apart from the metal effect pigment surface by a spacer. The spacer is a preferably organic structural element which is unreactive under electrocoating conditions and binds the adhering or attaching group on the metal effect pigment surface and the protonatable or positively charged amino-functional group to one another.

The unreactive organic structural element may, for example, be a linear or branched alkyl chain having 1 to 20 carbon atoms, preferably having 2 to 10 carbon atoms, more preferably having 3 to 5 carbon atoms. Optionally, this linear or branched alkyl chain may contain heteroatoms or heteroatom groups such as O, S or NH.

More preferably, the protonatable or positively charged amino-functional group is a terminal, substituted or unsubstituted amino group, i.e. an amino group arranged terminally on the spacer, which is spaced apart to the maximum degree from the group which provides attachment or adhesion to the metal effect pigment surface.

The amino-functional group is preferably a protonatable amino group or a positively charged amino group.

In one variant of the invention, the positively charged amino-functional group is preferably a quaternary ammonium compound. Such quaternary ammonium compounds are preferably obtained by alkylating amine compounds.

In a further preferred compound, the charge state can be controlled by lowering the pH, by adding acid to protonate the amino-functional group(s).

In one variant of the present invention, the amino-functional group is an —NH2 group arranged on the spacer.

In a further variant, the amino-functional group is an —NR1R2 group arranged on the spacer,

where R1 and R2 may be the same or different from one another and may each independently be hydrogen, alkyl having 1 to 20 carbon atoms, preferably having 2 to 10 carbon atoms, more preferably having 3 to 5 carbon atoms, or
R1 and R2 may be joined to one another and, together with the nitrogen atom, form a heterocycle which preferably contains 4 or 5 carbon atoms.

In a further variant, the amino-functional group is an —NR1R2R3 group arranged on the spacer,

where R1, R2 and R3 may be the same or different from one another and
may each independently be hydrogen, alkyl having 1 to 20 carbon atoms, preferably having 2 to 10 carbon atoms, more preferably having 3 to 5 carbon atoms.

In a preferred development of the invention, the metal effect pigments are provided with an inorganic and/or organic coating, optionally in the form of an inorganic/organic mixed layer, coated with synthetic resin or surface oxidized so as to inhibit corrosion (ALOXAL® product series from Eckart GmbH & Co.) or colored metal effect pigments (for example ALUCOLOR® product series from Eckart GmbH & Co.) and treated with at least one coating material which contains binder functionalities suitable for electrocoat materials.

The metal effect pigments coated with synthetic resins contain a coating of polymers. These polymers are polymerized onto the metal effect pigments proceeding from monomers. The synthetic resins include polyacrylates, polymethacrylates, polyesters and/or polyurethanes.

In a preferred embodiment, the coated metal effect pigment is coated with at least one polymethacrylate and/or polyacrylate.

Particular preference is given to using metal effect pigments which have been produced according to the teaching of EP 0 477 433 A1, which is hereby incorporated by reference. Such pigments preferably contain, between the metal effect pigment and the synthetic resin coating, an organofunctional silane which serves as an adhesion promoter. Particular preference is given here to coatings composed of preferably multiply crosslinked polyacrylates and/or polymethacrylates. Such coatings already constitute a certain though not completely reliable corrosion-inhibiting protection against the aqueous medium of electrocoat materials. Similar pigments are described in DE 36 30 356 C2, an ethylenically unsaturated carboxylic acid and/or phosphoric mono- or diester as an adhesion promoter being arranged here between the metal effect pigment and the synthetic resin coating.

Examples of such crosslinkers which can be used with preference in the present invention are: tetraethylene glycol diacrylate (TEGDA), triethylene glycol diacrylate (TIEGDA), polyethylene glycol-400 diacrylate (PEG400DA), 2,2′-bis(4-acryloyloxyethoxyphenyl)propane, ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DEGDMA), triethylene glycol dimethacrylate (TRGDMA), tetraethylene glycol dimethacrylate (TEGDMA), butyldiglycol methacrylate (BDGMA), trimethylolpropane trimethacrylate (TMPTMA), 1,3-butanediol dimethacrylate (1,3-BDDMA), 1,4-butanediol dimethacrylate (1,4-BDDMA), 1,6-hexanediol dimethacrylate (1,6-HDMA), 1,6-hexanediol diacrylate (1,6-HDDA), 1,12-dodecanediol dimethacrylate (1,12-DDDMA), neopentyl glycol dimethacrylate (NPGDMA). Particular preference is given to trimethylolpropane trimethacrylate (TMPTMA).

These compounds are commercially available from Elf Atochem Deutschland GmbH, D-40474 Dusseldorf, Germany, or Rohm & Haas, In der Kron 4, D-60489 Frankfurt/Main, Germany.

The thickness of the corrosion-inhibiting coating, preferably organic coating or synthetic resin coating, is preferably 2 to 50 nm, more preferably 4 to 30 nm and especially preferably 5 to 20 nm. The proportion of organic coating or synthetic resin coating, based in each case on the weight of the uncoated metal effect pigment, depends in the individual case on the size of the metal effect pigments and is preferably 1 to 25% by weight, more preferably 2 to 15% by weight and especially preferably 2.5 to 10% by weight.

The coating material is applied to the metal effect pigments after the application of the organic coating or of the synthetic resin layer and/or of another corrosion-inhibiting layer, for example of an inorganic coating such as a metal oxide-containing layer or metal oxide layer.

The corrosion-inhibiting coating may, for example, comprise essentially metal oxide, especially silicon dioxide, or consist thereof. A metal oxide layer can be applied using different processes known to those skilled in the art. For example, a silicon dioxide layer can be applied by means of sol-gel methods with hydrolysis of tetraalkoxysilanes, where the alkoxy group may be methoxy, ethoxy, propoxy or butoxy. However, it is also possible to apply an SiO2 coating to the metal effect pigment surface using waterglass.

The corrosion-inhibiting coating may also be a surface oxide layer. For example, it is possible to provide aluminum effect pigments with an impervious surface oxide layer which is corrosion-inhibiting with respect to aqueous media.

In a preferred embodiment, the oxide layer may additionally comprise color pigments. The color pigments can be introduced during the application of the metal oxide layer, especially silicon dioxide layer, or during the surface oxidation of the surface of the metal oxide layer.

The corrosion-inhibiting coating, for example synthetic resin layer, may completely surround the pigments, but it may also be present in not entirely continuous form or have cracks. Use of the coating material with protonatable or positively charged amino-functional group and with functional groups for adhesion and/or attachment to the pigment surface in the present invention covers possible corrosion sites which can be caused by such cracks or by an incomplete corrosion-inhibiting coating on the metal effect pigment.

The coating material used in the present invention is capable, especially when it attaches to the metallic pigment surface, of penetrating into such gaps or cracks in the corrosion-inhibiting coating, preferably synthetic resin coating, thus bringing about the required corrosion stability.

Even though it has been found that, surprisingly, the coating material used in the present invention also has corrosion-inhibiting properties in the case of metal effect pigments, this coating material is used primarily in order to make the metal effect pigments cathodically depositable. The coating material with protonatable or positively charged amino-functional group makes the metal effect pigments electrophoretically mobile in the electrocoating bath, i.e. they migrate in the direction of the object to be coated which is connected as the cathode.

Metal effect pigments which are coated only with synthetic resin or other corrosion-inhibiting coatings and have not been treated with the coating material with amino-functional group used in the present invention can be cathodically deposited only insufficiently, or cannot be cathodically deposited effectively, in cathodic electrocoating.

In electrocoating, conventional color pigments added to an electrocoat material are deposited on the workpiece by a comparatively random process. The electrocoat material is always stirred vigorously here during the deposition. As a result, essentially mass transfer toward the workpiece takes place (convection). Only within the Nernst diffusion layer which forms does electrophoretic migration of the charged binder particles within the electrical field proceed. The concentration of the color pigments in the deposition bath is very high (approx. 10% by weight). The binder which is deposited entrains the color pigments. There is no electrophoretic migration of the color pigments in the electrical field.

Metal effect pigments are not usable per se in electrocoat materials. Even if they are corrosion-stable to the aqueous medium of the electrocoat material as a result of a suitable protective layer, for example a metal oxide or a synthetic resin, they are either not or are no longer deposited after a few hours to days after an initial deposition, which is referred to as inadequate bath stability.

It has been found that, surprisingly, the inventive metal effect pigments can be deposited reliably and over long periods in cathodic electrocoating, and the electrocoat material has a bath stability of more than 60 days. The inventive metal effect pigments present in the cathodic electrocoat material are therefore deposited reliably on the workpiece even after 60 days, preferably after 90 days. Moreover, they have sufficient corrosion stability, such that no significant gassing (in the case of aluminum or iron pigments) or release of metal ions (in the case of brass pigments) occurs within this time in the electrocoat material.

It has been found that the coating material in this case must have one or more amino-functional groups. These are at least partly protonated in the electrocoat material. These protonated amino groups are thought to impart sufficient positive surface charges to the inventive electrocoat material pigment to be well-dispersed in the predominantly aqueous medium of the electrocoat material. Moreover, the inventive metal effect pigments are thought to be positively charged at their surface such that migration in the electrical field applied toward the cathode is enabled within the Nernst diffusion layer. It is thought that the surface of the inventive metal effect pigments is matched chemically in this way to the binders of the cathodic electrocoat material. This enables the effect that the metal effect pigments can firstly migrate electrophoretically in the electrical field and secondly take part in the deposition mechanism of the electrocoat materials at the cathode.

Furthermore, the coating materials contain functional groups which bring about or can bring about adhesion and/or attachment to the surface of the metal effect pigment or the stabilizing coating thereof. The pigment surface may directly be the metal effect pigment surface. The pigment surface may, however, also be the metal effect pigment surface coated with an inorganic or organic coating, preferably with synthetic resin. In this way, the coating materials can be anchored to the metal effect pigments reliably and to a sufficient degree.

These functional groups for adhesion or attachment to the coated or uncoated metal effect pigment surface are, for example, phosphonic ester, phosphoric ester, carboxylate, metallic ester, alkoxysilyl, silanol, sulfonate, hydroxyl, polyol groups, and mixtures thereof. Particular preference is given to the alkoxysilyl and/or silanol groups of suitable organofunctional silanes.

Such functionalized coating materials contribute to the corrosion stability of the metal effect pigments in the aqueous electrocoat material. For example, in the case of iron or aluminum pigments, gassing, i.e. evolution of hydrogen, can surprisingly be suppressed effectively.

It has been found to be essential that the coating material must necessarily have at least one protonatable or positively charged amino-functional group and at least one functional group for adhesion or attachment to the pigment surface. For example, aliphatic amines which lack the at least one functional group for adhesion or attachment to the pigment surface are unsuitable for providing metal effect pigments which are effectively cathodically depositable in a cathodic electrocoat material system.

In the inventive electrocoat material pigments, preference is given to using, as coating materials, amines which can be protonated to ammonium salts. Particularly preferred coating materials comprise amino-functional silanes of the formula


R1aR2bSi(OR′)(4-a-b)  (I)

where R1 is an organofunctional group which contains at least one amino-functional group, R2 is a further organofunctional group which does not contain an amino-functional group, R′ is independently H or an alkyl group having 1 to 6 carbon atoms, preferably having 1 to 3 carbon atoms, and where
a and b are integers, with the proviso that a may be 1 to 3 and b may be 0 to 3, where a and b in total are not more than 3.
R′ is preferably ethyl or methyl.
R2 is preferably substituted or unsubstituted alkyl having preferably 1 to 6 carbon atoms, for example methyl or ethyl. In addition, R2 may be substituted by functional groups, for example acrylate, methacrylate, vinyl, isocyanato, hydroxyl, carboxyl, thiol, cyano, epoxy or ureido groups.

In a preferred embodiment, b=0. In a particularly preferred embodiment, a=1 and b=0.

The at least one protonatable or positively charged amino-functional group which contains R1 is preferably a primary, secondary, tertiary amine or an ammonium group. The amino-functional group is preferably as defined above.

Such silanes are commercially available. For example, these are many representatives of the products which are produced by Degussa, Rheinfelden, Germany and are sold under the trade name Dynasylan®, or the Silquest® silanes produced by OSi Specialties, or the GENOSIL® silanes produced by Wacker, Burghausen, Germany.

Examples thereof are N-benzyl-N-aminoethyl-3-aminopropyltrimethoxysilane (Dynasylan 1161), N-vinylbenzyl-N-(2-aminoethyl)-3-aminopropylpolysiloxane (Dynasylan 1172), N-vinylbenzyl-N-(aminoethyl)-3-aminopropylpolysiloxane (Dynasylan 1175), aminopropyltrimethoxysilane (Dynasylan AMMO; Silquest A-1110), aminopropyltriethoxysilane (Dynasylan AMEO) or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (Dynasylan DAMO, Silquest A-1120) or N-(2-aminoethyl)-3-aminopropyltriethoxysilane, triamino-functional trimethoxysilane (Silquest A-1130), bis-(gamma-trimethoxysilylpropyl)amine (Silquest A-1170), N-ethyl-gamma-aminoisobutyltrimethoxysilane (Silquest A-link 15), N-phenyl-gamma-aminopropyltrimethoxysilane (Silquest Y-9669), 4-amino-3,3-dimethylbutyltrimethoxy-silane (Silquest Y-11637), N-cyclohexylaminomethyl-methyldiethoxysilane (GENIOSIL XL 924), (N-cyclohexylaminomethyl) triethoxysilane (GENIOSIL XL 926), (N-phenylaminomethyl)trimethoxysilane (GENIOSIL XL 973), aminopropyldimethylethoxysilane, aminopropylmethyldiethoxysilane, N-methylaminopropyl-dimethylethoxysilane, N-methylaminopropylmethyl-diethoxysilane, N-methylaminopropyltriethoxysilane, N-ethylaminopropyldimethylethoxysilane, N-ethylamino-propylmethyldiethoxysilane, N-ethylaminopropyl-triethoxysilane, N-cyclohexylaminopropyltriethoxy-silane, N-cyclohexylaminopropylmethyldiethoxysilane, N-phenylaminotriethoxysilane, N-phenylaminopropyl-triethoxysilane, N,N-dimethylaminopropyldimethylethoxy-silane, N,N-dimethylaminopropylmethyldiethoxysilane, N,N-dimethylaminopropyltriethoxysilane, N,N-diethyl-aminopropyldimethylethoxysilane, N,N-diethylamino-propylmethyldiethoxysilane, N,N-diethylaminopropyl-triethoxysilane, N,N-dipropylaminopropyldimethyl-ethoxysilane, N,N-dipropylaminopropylmethyl-triethoxysilane, N,N-dipropylaminopropyltriethoxy-silane, N,N-methylethylaminopropyldimethylethoxysilane, N,N-methylethylaminopropylmethyldiethoxysilane, N,N-methylethylaminopropyltriethoxysilane, anilinopropyldimethylethoxysilane, anilinopropylmethyldiethoxysilane, anilinopropyltriethoxysilane, morpholinopropyldimethyl-ethoxysilane, morpholinopropylmethyldiethoxysilane, morpholinopropyltriethoxysilane, N,N,N-trimethyl-ammoniumpropyldimethylethoxysilane, N,N,N-trimethylammoniumpropylmethyldiethoxysilane, N,N,N-trimethylammoniumpropyltriethoxysilane, N,N,N-triethyl-ammoniumpropyldimethylethoxysilane, N,N,N-triethylammoniumpropylmethyldiethoxysilane, N,N,N-triethylammoniumpropyltriethoxysilane, trimethoxysilylpropyl-substituted polyethyleneimine, dimethoxymethylsilylpropyl-substituted polyethyleneimine and mixtures thereof.

The coating materials with protonatable or positively charged amino-functional group are preferably used in amounts of 1 to 100% by weight based on the weight of the uncoated metal effect pigment. Below 1% by weight, the effect may be too minor, such that the metal effect pigments can no longer be deposited reliably, especially after more than 60 days of bath time. Above 100% by weight, an unnecessarily large amount of coating material with amino-functional group is used. In addition, excess coating material with an amino-functional group can adversely affect the properties of the electrocoat material. The coating material(s) with an amino-functional group are preferably used in amounts of 5 to 70% by weight and especially preferably of 7 to 50% by weight, more preferably of 10 to 30% by weight, based in each case on the weight of the metal effect pigment uncoated with coating material. These figures are based in each case on the coating material itself and not on any solvent which is possibly present and in which the coating material with an amino-functional group is supplied in its commercially available administration form.

The coating material may, but need not, completely surround the metal effect pigments.

A process for providing the inventive metal effect pigments comprises the coverage of the metal effect pigment with the coating material with an amino-functional group. It comprises the following steps:

  • (a) coating a metal effect pigment with the coating material having an amino-functional group dissolved or dispersed in a solvent, said amino-functional group being protonatable or positively charged,
  • (b) optionally drying the metal effect pigments coated with the coating material in step (a),
  • (c) optionally converting the metal effect pigments dried in step (b) to a paste.

The coverage can take place in many different ways. The metal effect pigment can be initially charged, for example, in a mixer or kneader in the form of a paste, for example in an organic solvent or in a mixture of organic solvent and water. Subsequently, the coating material with a protonatable or positively charged amino-functional group is added and allowed to act on the metal effect pigment preferably for at least 5 min. The coating material is preferably added in the form of a solution or dispersion. This may be an aqueous solution or a predominantly organic solution.

In addition, the metal effect pigment can first be dispersed in a solvent. The coating material is then added thereto with stirring. In this case, the solvent in which the coating material is dissolved should preferably be miscible with that in which the metal effect pigment is dispersed. If required, higher temperatures up to the boiling point of the solvent or of the solvent mixture can be established, but room temperature is usually sufficient to apply the coating material effectively to the metal effect pigment.

Thereafter, the pigment is freed from the solvent and either dried to give the powder and/or optionally converted to a paste in another solvent. Useful solvents include water, alcohols, for example ethanol, isopropanol, n-butanol, or glycols, for example butylglycol. The solvent should be miscible with water. The inventive pigment is traded as a paste or powder. The pastes have a nonvolatile component of 30 to 70% by weight based on the weight of the overall paste. The paste preferably has a nonvolatile component of 40 to 60% by weight and more preferably of 45 to 55% by weight.

The paste form is a preferably dust-free and homogeneous preparation form of the inventive electrocoat material pigments. The inventive electrocoat material pigments may also be present in dust-free and homogeneous form as pellets, sausages, tablets, briquettes or granules. The aforementioned preparation forms can be produced in the manner known to those skilled in the art by pelletization, extrusion, tabletting, briquetting or granulation. In these compacted preparation forms, the solvent has substantially been removed. The residual solvent content is typically within a range of less than 15% by weight, preferably less than 10% by weight, more preferably between 0.5 and 5% by weight, based in each case on the weight of the pigment preparation.

The coating material with a protonatable or positively charged amino-functional group may, before the coating of the metal effect pigment, be present in a neutralized or partly neutralized form. However, it can also be neutralized after the coating operation. The neutralization/partial neutralization can also not be effected until the pH adjustment of the electrocoat material.

Customary acids are suitable for neutralization of the basic functionalities. Examples thereof are: formic acid, acetic acid, hydrochloric acid, sulfuric acid or nitric acid, or mixtures of these acids. A sufficient amount of acid should be used that at least 25%, preferably 40%, of the basic groups of the metal effect pigment covered with the coating material are present in neutral form. In this context, basic groups also include functional groups which may originate from the metal effect pigment itself.

It is also possible to combine steps (a) and (b) of the process according to the invention to one step, by applying the coating material as a solution or dispersion to metal effect pigments moving in a gas stream.

In a particular embodiment, the inventive electrocoat material pigments can be produced by a process with the following steps:

  • a) producing a solution or dispersion of the coating material with protonatable or positively charged amino-functional group in an organic solvent,
  • b) coating the metal effect pigment with the coating material by
    • i) dispersing the metal effect pigment in the solution or dispersion of a) and then spraying or
    • ii) spraying the solution or dispersion from a) onto metal effect pigments fluidized in a gas stream,
  • c) optionally drying the metal effect pigments coated with binder in a moving gas stream,
  • d) optionally converting the pigment to paste in water and/or an organic solvent,
  • e) optionally neutralizing with an acid.

The pigments can be neutralized and converted to paste as described above.

Preference is given to combining steps b) and c) in one process step, by performing the spraying and drying in a spray drier.

Preference is given to using volatile solvents, for example acetone and/or ethyl acetate.

The inventive electrocoat material pigments are used in cathodic electrocoat materials or in cathodic electrocoating.

The invention further provides a cathodic electrocoat material comprising the inventive electrocoat material pigments, a binder and water. The binders are, for example, polymerization, polyaddition or polycondensation products containing primary or tertiary amino groups, for example amino epoxy resins, amino poly(meth)acrylate resins or amino polyurethane resins. In addition, further customary additions such as fillers, additives, organic and/or inorganic color pigments, etc. may be present in the electrocoat material.

By means of acids, the amino groups of the binders and preferably the amino groups of the coating material of the inventive electrocoat material pigments are at least partly protonated. This has the effect that the binders and the inventive electrocoat material pigments move toward the cathode in the applied electrical field and take part in the deposition mechanism of the cathodic electrocoating. The coatings obtained in this way have an attractive metal effect which has been unknown to date in cathodic electrocoat material and are exceptionally abrasion-stable.

The inventive electrocoat material pigments can optionally also be neutralized as early as after the coating with coating material.

The examples which follow illustrate the invention in detail, but without restricting it.

INVENTIVE EXAMPLE 1

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, with D50=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with a solution of 7 g of Dynasylan 1161 (N-benzyl-N-aminoethyl-3-aminopropyltrimethoxysilane from Degussa, Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

INVENTIVE EXAMPLE 2

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, with D50=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with a solution of 7 g of Dynasylan 1172 (N-vinylbenzyl-N-(2-aminoethyl)-3-aminopropylpolysiloxane from Degussa, Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

The paste is dried cautiously in a vacuum drying cabinet at approx. 60° C. to give the powder.

INVENTIVE EXAMPLE 3

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, with D50=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with a solution of 7 g of Dynasylan 1175 (N-vinylbenzyl-N-(aminoethyl)-3-aminopropylpolysiloxane from Degussa, Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

INVENTIVE EXAMPLE 4

The preparation is effected as in Example 3, but with an aluminum effect pigment of greater particle size D50=32 μm, PCA 214 (from Eckart GmbH & Co. KG).

Production of the Electrocoat Materials and Testing Thereof:

27 g of the pastes from Examples 1, 3 or 4 are admixed with 27 g of butylglycol.

15 g of the powder from Example 2 are admixed with 39 g of butylglycol.

10 g of VEK 40871-02 CEC binder (800 by weight epoxy resin from Cytech, Austria) and 1.5 g of wetting agent (from FreiLacke, Bräunlingen, Germany), 465 g of VEK 40871-0-03 CEC binder (34.5% by weight epoxy resin from Cytech, Austria) and 662 g of water are added.

The dip-coating materials produced according to this formulation for cathodic dip-coating feature a viscosity of 9±1 seconds, measured at a temperature of 20° C. in a DIN 4 flowcup. The electrocoat materials possess a solids content of 13 to 17% by weight based on the weight of the overall electrocoat material. The proportion of the aluminum pigments is approx. 1% by weight. The measured pH of the electrocoating baths at 25° C. is a pH of about 5.5 to 6.5.

COMPARATIVE EXAMPLE 1

PCA 9155 (from Eckart GmbH & Co. KG), a synthetic resin-coated aluminum effect pigment of mean particle size D50=18 μm in paste form (solids 50% by weight) is used in the electrocoat material without further coating. In contrast to inventive example 1, 7 g of Dynasylan 1161 coating material are introduced here into the electrocoating bath only on addition of the commercial cathodic dip-coating material (from Frei Lacke).

COMPARATIVE EXAMPLE 2

PCA 9155 (from Eckart GmbH & Co. KG), a synthetic resin-coated aluminum effect pigment of mean particle size D50=18 μm in paste form (solids 50% by weight) without further coating.

Here, no further additive (coating material) is added to the dip-coating material.

The electrochemical deposition operation is effected in an electrically conductive vessel, a so-called tank, which consists of an electrically conductive material and is connected as the anode in the circuit. The workpiece to be coated, in the inventive example a metal sheet of dimensions 7.5 cm×15.5 cm is connected as the cathode and immersed into the electrocoating bath for ⅔ of its length.

In order to prevent sedimentation and the formation of dead spaces, the electrocoat material is moved with a mean flow rate of approx. 0.1 m/s. Subsequently, a voltage of 100 V is applied over a period of 120 seconds. The temperature of the electrocoating bath is 30° C. The workpiece thus coated is subsequently rinsed off thoroughly with distilled water in order to remove residues of uncoagulated resin. The workpiece is then left to vent for a period of 10 minutes. Subsequently, the electrocoat material is crosslinked and fired at 170° C. for 20 minutes. The coating layer thickness thus achieved is 30±2 μm.

The cathodic electrocoat materials produced with the pigments from inventive examples 1 to 4 have an exceptionally high storage and deposition stability in relation to the aluminum effect pigments present therein. This is evident from Table 1. The coating materials were stored at room temperature and, within a time interval of 7 days, metal sheets as described above were electrocoated. These tests were stopped after 60 days.

In addition, samples of inventive examples 1 to 4 were stored at 40° C. for 30 days. Subsequently, they were incorporated into an electrocoating material as described above, and metal sheets were electrocoated. With regard to the optical properties of these applications, no difference from applications with freshly produced samples were found.

Gassing tests were carried out with the electrocoat materials produced using the pigments from inventive examples 1 to 4 and comparative examples 1 and 2. For this purpose, 250 g of the electrocoat materials were heat treated at 40° C. in a gas bottle with a double chamber tube attachment, and the amount of gas evolved (H2, which is formed by the reaction of the aluminum effect pigments with water) is measured. The test is considered to be passed when not more than 20 ml of hydrogen have evolved after 30 days.

The test results are compiled in Table 1.

TABLE 1 Performance of the cathodic dip-coating materials which have been produced using the pigments from examples 1 to 4 and comparative examples 1 and 2. Deposition Gassing after stability 30 days Sample (in d) (ml of H2) Example 1 >60 d 12 Example 2 >60 d 5 Example 3 >60 d 10 Example 4 >60 d 6 Comparative example 1  <7 d 12 Comparative example 2  <7 d After 10 days >25 ml

For the electrocoat materials comprising pigments of inventive examples 1 to 4, reproducible results with regard to the visual appearance of the coated test sheets were obtained even after more than 60 days of storage time at room temperature. Moreover, they did not exhibit any significant gassing in the aqueous electrocoat materials.

The electrocoat material comprising pigments of comparative example 1 was likewise gassing-stable, but had virtually no deposition stability. The aluminum effect pigments not provided with a coating of comparative example 2 are neither gassing-stable in the electrocoat material nor do they possess sufficient deposition stability.

COMPARATIVE EXAMPLE 3 Metal Effect Pigment-Containing Powder Coating Material

9 g of a commercial metal effect pigment for powder coating material, Spezial PCA 214, d50=32 μm (from Eckart GmbH & Co. KG), are mixed intimately in a plastic bag with 291 g of a powder clearcoat material, AL 96 Polyester PT 910 System (from DuPont) and 0.6 g of a “free-flow additive”, Acematt OK 412 (from Degussa). The contents are subsequently transferred directly into a mixing vessel which approximates to a commercial kitchen mixer in terms of construction and form (Thermomix from Vorwerk), and mixed at a moderate stirrer speed level at 25° C. for 4 minutes. This procedure corresponds to the “dry-blend method” common in powder coating materials. The powder coating material thus produced is applied by means of the customary corona discharge technique (GEMA electrostatic spray gun PG 1-B) to a customary test sheet (“Q panel”). The application conditions of the powder coating technique applied here corresponds to the following: powder hose connection: 2 bar; purge air connection: 1.3 bar; voltage: 60 kV; material flow regulator: approx. 500; gun-sheet distance: approx. 30 cm.

This is followed by the firing and the crosslinking of the powder coating material system in an oven. The firing time is 10 minutes at a temperature of 200° C. The dry layer thickness to be achieved in this process is 50-75 μm.

COMPARATIVE EXAMPLE 4 Metal Effect Pigment-Containing Powder Coating Material

As comparative example 3, except that the metal effect pigment used was Spezial PCA 9155, d50=16 μm (from Eckart GmbH & Co. KG).

The different applications in inventive examples 1 to 4 were compared with the substrates of comparative examples 3 and 4 coated by powder coating technology. For comparative assessment, as is evident from inventive examples 1 to 4 and comparative examples 3 and 4, aluminum effect pigments of similar particle size and coloristic properties were used.

Surprisingly, the applications in inventive examples 1 to 4 exhibit excellent covering capacity, which corresponds in terms of goodness and quality to the powder coating material of comparative examples 3 and 4.

The optical properties are compared via the visual impression of the observer. It is found here that, surprisingly, inventive examples 1 to 4 have no significant differences with regard to brightness and metallic effect from the conventional powder coating material application in comparative examples 3 and 4.

For the assessment of the optical properties, reference is made to DIN 53230. In the testing of paints, coating materials and similar coatings, the properties and/or changes therein often have to be assessed subjectively. For this case, DIN 53 230 lays down a homogeneous assessment system. This describes how test results which cannot be reported by means of directly obtained measurements should be assessed.

To assess the coating materials which have been obtained with pigments according to inventive examples 1 to 4 and comparative examples 1 to 4, reference is made to the “fixed rating scale” explained under 2.1 in DIN 53 230. This fixed rating scale constitutes a scale for assessing the degree of properties. In this, the best possible value is designated with the index 0, the lowest possible value with the index 5, the term “lowest possible value” being understood to mean that a change or deterioration over and above this value is no longer of interest in performance terms. Tab. 2 reproduces the coloristic and optical properties determined in relation to DIN 53 230 section 2.1. The indices are determined by the subjective impression of several test subjects. In all cases, an agreement of the subjective impression of the assessing test subjects could be found.

TABLE 2 Visual comparison of the electrocoat material applications of the pigments of inventive examples 1 to 4, of comparative examples 1 to 2 and of the powder coating material applications of comparative examples 3 and 4 Mean particle Covering size D50 capacity Brightness General visual Sample [μm] [index] [index] impression Inventive 18 0 1 Very metallic, example 1 relatively minor “sparkling” effect Inventive 18 0 1 Very metallic, example 2 relatively minor “sparkling” effect Inventive 18 0 1 Very metallic, example 3 relatively minor “sparkling” effect Inventive 32 1 0 Very good metallic, example 4 “sparkling” effect Comparative 18 3 3 Relatively minor example 1 metallic effect as a result of lack of covering capacity Comparative 18 5 5 Virtually no metal example 2 effect pigment deposited Comparative 32 0 1 Very good metallic, example 3 “sparkling” effect Comparative 16 0 0 Very metallic, example 4 relatively minor “sparkling” effect

It can be seen from the comparison displayed above that the applications with the inventive electrocoat material pigments and pigment preparations according to examples 1 to 4 are comparable with regard to optical properties with the powder coating material pigments and applications which have already been established on the market for many years. From the comparison of the indices of the electrocoatings which have been obtained using inventive examples 1 to 4 with the powder coatings in comparative examples 3 and 4 shows clearly that the optical properties are virtually identical to one another in relation to coverage, shine and metallic effect.

The coatings in comparative example 1, in which the coating material was only introduced directly into the electrocoat material production in the last step thereof, have deviations. In these variants, significant losses are found with regard to coverage, shine and, associated with these, in the metallic effect.

A metal effect pigment treated without coating material (comparative example 2) virtually cannot be deposited in the cathodic electrocoat material or in the electrocoating, even though the metal effect pigment has a synthetic resin shell.

It is suspected that it is necessary that the coating material with protonatable or positively charged amino-functional group has to be applied directly to the metal effect pigment and cannot be added later to the electrocoat material. It is further suspected that the coating material with its functional groups for adhesion or attachment forms a physisorptive and/or chemisorptive adhesion or attachment to the pigment surface, which then appears to play a crucial key role in the deposition performance of the pigment.

Claims

1. An electrocoat material pigment,

said electrocoat material pigment comprising metal effect pigment platelets coated with at least one coating material, said coating material comprising
a) one or more functional groups for adhesion or attachment to the pigment surface and
b) at least one amino-functional group, said amino-functional group being protonatable or positively charged.

2. The electrocoat material pigment as claimed in claim 1,

wherein
the metal effect pigments have a coating which inhibits corrosion by aqueous systems or media.

3. The electrocoat material pigment as claimed in claim 1,

wherein
the metal effect pigments are selected from the group comprising metal effect pigments provided with at least one of inorganic and organic coatings, metal effect pigments provided with inorganic/organic mixed layers, metal effect pigments coated with synthetic resin, surface-oxidized metal effect pigments and colored metal effect pigments.

4. The electrocoat material pigment as claimed in claim 1,

wherein
the metal effect pigment platelets consist of metals or alloys which are selected from the group consisting of aluminum, copper, zinc, tin, brass, iron, titanium, chromium, nickel, steel, silver and alloys and mixtures thereof.

5. The electrocoat material pigment as claimed in claim 3,

wherein
the synthetic resin coating of the metal effect pigment comprises at least one of a polyacrylate, a polymethacrylate and a combination thereof.

6. The electrocoat material pigment as claimed in claim 2,

wherein
the corrosion-inhibiting coating consists essentially of a metal oxide.

7. The electrocoat material pigment as claimed in claim 2,

wherein
the corrosion-inhibiting coating is a surface oxide layer.

8. The electrocoat material pigment as claimed in claim 6

wherein
the oxide layer additionally comprises color pigments.

9. The electrocoat material pigment as claimed claim 1,

wherein
the coating material has one or more functional groups for adhesion or attachment to the metal effect pigment surface or to at least one of a synthetic resin surface and an inorganic coating applied to the metal effect pigment surface.

10. The electrocoat material pigment as claimed in claim 9,

wherein
one or more functional groups of the coating material are selected from the group consisting of phosphonic ester, phosphoric ester, carboxylate, metallic ester, alkoxysilyl, silanol, sulfonate, hydroxyl, polyol groups and mixtures thereof.

11. The electrocoat material pigment as claimed in claim 1,

wherein
the coating material is applied to the pigment in an amount of 1 to 100% by weight based on the weight of the metallic component of the metal effect pigment.

12. The electrocoat material pigment as claimed in claim 1,

wherein
the coating material is a cathodic electrocoat material binder.

13. A process for producing electrocoat material pigments as claimed in claim 1,

wherein
the process comprises the following steps: (a) coating a metal effect pigment with the coating material having an amino-functional group dissolved or dispersed in a solvent, said amino-functional group being protonatable or positively charged, (b) optionally drying the metal effect pigments coated with the coating material in step (a), and (c) optionally converting the metal effect pigments dried in step (b) to a paste.

14. The process as claimed in claim 13,

wherein
steps (a) and (b) are combined into a single step, by applying the coating material as a solution or dispersion to metal effect pigments moving in a gas stream.

15. A method of making a cathodic electrocoat material for use in cathodic electrocoating, said method comprising incorporating into said cathodic electrocoat material a plurality of electrocoat material pigments as claimed in claim 1.

16. A cathodic electrocoat material comprising electrocoat material pigments as claimed in claim 1.

17. The electrocoat material pigment as claimed in claim 6, wherein the metal oxide is silicon dioxide.

Patent History
Publication number: 20100163420
Type: Application
Filed: Oct 27, 2007
Publication Date: Jul 1, 2010
Applicant: Eckart GMBH (Furth)
Inventors: Harald Weiss (Furth), Christian Schramm (Hersbruck), Carolin Heckel (Velden)
Application Number: 12/447,997
Classifications
Current U.S. Class: Electrolytic Coating (process, Composition And Method Of Preparing Composition) (205/80)
International Classification: C25D 3/00 (20060101);