Effect pigments coated with reactive orientation aids

Details Effect pigments coated with reactive orientation aids Effect pigments coated with reactive orientation aids

2001-01-02

2004-07-13

Koslow, C. Melissa (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S483000

Reexamination Certificate

active

06761762

ABSTRACT:

The present invention concerns effect or fancy pigments whose service is modified with orientation aids.
BACKGROUND OF THE INVENTION
The literature (EP 0 634 459 A2) describes coating pearl shine pigments with alkyl silanes to improve orientation of the pigments in the ambient medium (paint or lacquer, casting resin etc). The modification process used in that case controls the wetting characteristics of the pearl shine pigments by the introduction of hydrophobing alkyl silanes and results in a leafing effect, as is also known in relation to metal effect pigments.
The application of stearic acid to the pigment surface means that aluminium pigments can also be strongly hydrophobed, which then results in poorer wetting of the pigments by the individual components of the paint or lacquer. The content of the pigments is then increased at the interfaces (or the surface) of the liquid film of paint or lacquer. As after hardening of the film of paint or lacquer that results in coatings with a high level of brilliance, this is referred to as good orientation characteristics in respect of the pigments (‘leafing effect’). The aluminium pigments which are oriented at the surface are however not particularly resistant to weathering as they are not enclosed in the film of paint or lacquer and thus protected from corrosion. In the case of metallic paints for automobiles, which must satisfy particularly high levels of weathering stability, therefore only aluminium pigments which are non-leafing (which can be well wetted) are used. Paints in the automobile sector involve a layer structure which in the case of metallic paints generally consists of five layers. Disposed on the metallic substrate is a phosphate layer, followed by a cathodic dip lacquering (CDL), a filler layer (to compensate for irregularities and unevenness etc), the base lacquer and finally the clear lacquer. The actual layer which affords the effect is the base lacquer which generally contains a mixture of metal pigments and pearl shine pigments and which nowadays is already used in many cases in the form of a water-based lacquer. The clear lacquer serves to protect the base lacquer and to ‘smooth out’ the surface.
An important check in terms of the resistance of metallic lacquers is the so-called condensed water test. In that case the complete coating is exposed to a condensed water testing climate (DIN 50 017) and then checked in terms of its mechanical strength and visual considerations. In the ideal case the properties of the coating should not change before and after the test. In a worse scenario, there is a loss of adhesion between the base lacquer and the clear lacquer or a loss of adhesion between the effect pigments and the base lacquer. Such changes can be seen in the cross-cutting adhesion test or the stone impact test. A negative test result involves partial detachment of the clear lacquer from the base lacquer or even involves the base lacquer layer completely breaking away. In addition, under some circumstances optical changes are also to be observed due to the action of water vapour on the coating (a greying effect, swelling, etc).
A disadvantage of coating effect pigments with hydrophobing alkyl silanes (for example EP 0 634 459 A2) are the weak bonding forces at the pigment/binding agent interface (van der Waals forces, hydrogen bridges). Because of those weak bonding forces the pigments are incompletely wetted, in particular in aqueous lacquer systems, which results in the pigments being poorly bound into the coating. As a result, both the adhesion of the pigments in the base lacquer layer and also the adhesion between the base lacquer and the clear lacquer are adversely affected. That impaired adhesion then results in worse results in the condensed water test.
The diffusion of water vapour through the clear lacquer into the base lacquer has a severely adverse effect on adhesion between the two layers in the condensed water test if condensation of water occurs between the base lacquer and the clear lacquer. That is the case in particular if the coated pigments cannot be wetted or can be only poorly wetted by the binding agents or solvents of the paint or lacquer (organic solvent and/or water) because the pigments are then at the surface of the base lacquer and are in direct contact with respect to the clear lacquer. In that case the reduced level of resistance to condensed water results under some circumstances in the lacquer layers completely breaking away under the action of shearing forces (cross-cut test, stone impact test, etc).
SUMMARY OF THE INVENTION
Therefore the object of the present invention is to provide effect pigments which on the one hand are easily wetted by the binding agent or solvent of the paint or lacquer and which can be well oriented in the liquid film of lacquer and which on the other hand involve an intimate bond with the surrounding binding agent matrix and therefore do not suffer from the above-described disadvantages involved in use thereof.
DETAILED DESCRIPTION OF THE INVENTION
That object is attained in that the initial pigment has a layer comprising at least one reactive surface-modifying agent, wherein the surface-modifying agent is a compound which has at least two functional groups which are different from each other and which are spaced by a spacer and of which at least one functional group is chemically bound to the initial pigment.
At least one functional group which is directed outwardly, that is to say towards the binding agent, of the effect pigment according to the invention can react chemically with the binding agent in that case in a kind of cross-linking reaction. By virtue of the resulting strongly covalent bonding forces at the pigment/binding agent interface, water vapour in the finished coating can only diffuse with difficulty into the pigmented binding agent matrix. The strong linkage of the pigments to the binding agent of the base lacquer, which is caused by the relatively good wettability of the metal pigments coated with the reactive orientation agent means that there cannot be condensation and thus inclusion of water between the clear lacquer and the base lacquer. Therefore even coatings which are soaked with solvent (for example water) are highly stable in respect of shearing and impact-resistant. An effect pigment which is treated in that way has accordingly become a ‘chemical constituent’ of the ambient medium.
The effect pigments according to the invention involve either metal pigments such as aluminium, copper, zinc, gold-bronze, titanium (EP 0 796 688), zirconium, tin, iron (EP 0 673 980) and steel pigments or pigments of alloys of the above-mentioned metals. The effect pigments can also comprise flake-form glass, Al
2
O
3
, SiO
2
(EP 0 803 550 A2), TiO
2
or mica. Multi-layer pigments (DE 44 05 492 A1, EP 0 708 154; DE 196 18 569) or pearl shine pigments or mixtures thereof can also be coated in accordance with the invention. The pigments may carry a coating of metal oxides such as SiO
2
(for example: U.S. Pat. No. 2,885,366, U.S. Pat. No. 3,954,496, EP 0 678 561, DE 195 01 307, EP 0 708 155), TiO
2
(for example: 0 338 428), Al
2
O
3
(for example: DE 195 20 312, EP 0 560 144) and Fe
2
O
3
(for example: EP 0 033 457, EP 0 806 457) or organic polymers such as acrylate, methacrylate etc (for example: DE 40 30 727, EP 0 416 369). The particle size is between 1 and 200 &mgr;m.
The described demands on an orientation aid are satisfied in accordance with the invention by a bonding agent which carries two or more functional groups. One group of the bonding agent reacts with the surface of the effect pigment, which surface is possibly occupied by oxides. Alkoxysilyl groups (for example methoxy and ethoxy silanes), halosilanes (for example chlorosilanes) or acid groups of phosphoric acid esters or phosphonic acids and phosphonic acid esters are considered here. The described groups are linked by way of spacers of greater or lesser length to a second, lacquer-friendly group. The spacer involves unreactive alkyl chains, siloxanes, polyethers, thioethers

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