DE19549872B4 - Paint containing a pigment with viewing angle dependent color, as well as its use - Google Patents

Abstract

Varnish, characterized in that it contains a pigment having a viewing angle dependent color, wherein the pigment was obtained by three-dimensional crosslinking of oriented substances liquid crystal structure with chiral phase, wherein the crosslinking in the presence of at least one further, at least two crosslinkable double bonds containing color neutral Compound has been carried out in a proportion of 5 wt .-% to 20 wt .-%, based on the total weight of the total mixture to be crosslinked.

Description

The invention relates to a varnish comprising a pigment having a viewing angle-dependent color, obtained by three-dimensional crosslinking of oriented substances of liquid-crystalline structure with chiral phase.

The invention further relates to the use of the paint containing such a pigment for painting motor vehicle bodies and their parts.

Such a pigment and its preparation and use as a paint, especially as a paint for motor vehicles, is from the DE 42 40 743 A1 known.

Liquid crystalline substances for the preparation of such pigments have a twisted structure with a pitch corresponding to a wavelength of the light in the range of UV to IR. This structure is found, for example, in cholesteric liquid crystals. Cholesteric liquid crystals, or generally chiral phase liquid crystalline substances, having a twisted structure with a desired pitch can be obtained from nematic, smectic or discotic structures by adding a chiral substance thereto. The type and proportion of the chiral substance determine the pitch of the twisted structure and thus the wavelength of the reflected light. The twist of the structure can be left-handed as well as right-handed. The starting materials also have polymerizable, polycondensable or a polyaddition accessible groups.

These substances are oriented, for example during application with a squeegee to a film. Subsequently, the substances are crosslinked, for example by irradiation with UV light. This produces the pigment that can be brought to the desired particle size after detachment from the film.

A large field of application of such pigments is the incorporation into paints or coating systems, in particular paints for painting motor vehicles. A motor vehicle painted in this way, depending on the viewing angle, displays a different coloration at one and the same place, for example a blue, a green or a reddish color.

In the practical use of such pigments in the painting of motor vehicles has now been found that the color varies greatly depending on the stoving temperature of the paint.

While it is desirable to have different color effects with such color pigments at different viewing angles, it is not desirable that different shades result at a particular viewing angle, depending on the stoving temperature or temperature treatments of the pigments.

This is undesirable not only in the field of use of the pigments for paints, in particular for motor vehicle paints, but in all applications of the pigments in which these heat treatments are subjected. Thus, another application of such pigments is the cosmetics industry, in which, for example, for reasons of sterilization, creams, pastes o. The like. Are heated. Even in these applications, no color shift should occur depending on the temperature.

In the aforementioned use of the pigments in paint systems for painting motor vehicles, the paints are baked at the initial coating of the body at about 130 ° C. In later refinish such high temperatures can no longer be used / otherwise other components of the vehicle are affected. Therefore, refinishes are performed at about 80 ° C. It has been found in practical use that cause these different stoving temperatures in one and the same initial pigment strong color shifts, especially blue shifts.

It is therefore an object of the present invention to remedy this situation and further develop pigments of the type mentioned in the beginning / that their color remains weitgehenst at a certain viewing angle by the action of elevated temperatures unchanged.

This object is achieved by a paint having the features of claim 1 and its use according to claim 7.

By adding crosslinkable compounds which contain at least two double bonds, the crosslinking density of the pigments can be increased. At the same time, a certain dilution of the reactive components forming the color pigments is achieved, these "reactive diluents" being integrated into the resulting three-dimensional matrix on crosslinking.

It has surprisingly been found that the color of the resulting pigments as such is not changed by the dilution on the one hand and the increase in the crosslinking density and at the same time a very high color fastness is achieved at elevated temperatures, thus the color shift can be reduced.

For the purposes of the present invention, "color-neutral" compounds are to be understood as meaning, on the one hand, not exerting themselves undesirable effects on the color result of the reactive substances of liquid-crystalline structure with chiral phase and, on the other hand, creating the possibility of additional crosslinking points through their functionality.

Thus, the task is completely solved.

In a further embodiment of the invention, the color-neutral compounds have more than three crosslinkable double bonds. This increased functionality opens up the possibility of greatly increased crosslinking densities in the pigments according to the invention and in particular contributes to the color fastness to elevated temperatures.

In a further embodiment of the invention, the color-neutral compounds have double bonds of the acrylate, methacrylate, vinyl, allyl type.

These measures now have the considerable practical advantage that these double bond types are similar to those functional groups that provide for the three-dimensional crosslinking in the substances of liquid-crystalline structure with chiral phase, so that the now additionally admixed compounds can be crosslinked by means of the same initiator or initiators, such as the actual substances forming the pigments. If, for example, those substances of liquid-crystalline structure which can be crosslinked with UV light are selected, appropriate color-neutral compounds which can be crosslinked by UV light can be added in order to achieve the desired color retention effect. This is thus procedurally and manufacture technically very easy to do, it must be admixed only the corresponding compounds before crosslinking, so that no different or additional starters or initiators must be used or applied.

Advantageously, colorless compounds selected from the group consisting of the acrylates, polyurethanes, epoxies, siloxanes, polyesters and alkyd resins are used.

Particularly advantageous is the at least one color-neutral compound selected from 1,6-hexanediol diacrylate, divinylbenzene, trivinylalkoxysilanes, trifunctional polyurethane acrylate oligomers, mixtures of pentaerythritol tri- and tetraacrylates, tetrafunctional acrylate oligomers, tetraallylsilane, tetra-, vinylsilane, tetrakis (2-methacryloxyalkoxy) silanes , 1,3,5,7-tetravinyltetraalkylcydotetrasiloxanes, hexafunctional polyurethane acrylate oligomers, dipentaerythritol hexaacrylate.

The color-neutral compound is present at 5 to 20 wt .-%, preferably 5 to 15 wt .-%, based on the total weight of the total mixture to be crosslinked.

The pigments can be incorporated into conventional coating systems, for which purpose the pigments are ground to a suitable particle size and optionally classified.

If a motor vehicle is lacquered with such a lacquer or a lacquer system, a color shift which is greatly reduced compared to the corresponding pigments without additional color-neutral compounds is observed even with high stoving temperature differences. For example, the ΔE value of lacquers provided with color pigments of the type mentioned above can be reduced by well over 70% when comparing the colors of lacquered samples at baking and drying temperatures of room temperature and 130 ° C, respectively. Correspondingly pronounced results are obtained by comparing the colors of coated sheets at baking temperatures of 80 ° C and 130 ° C. The same applies to the Δλ values.

It is understood that the features mentioned above and to be explained below can be used not only in the specified combinations, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention will be described in more detail below with reference to some selected embodiments and explained.

A Representation of liquid-crystal mixtures

A polyorganosiloxane is prepared as in Example 1, A: "polyorganosiloxanes with acrylic acid side chains" of DE 42 40 743 A1 described. The core of the siloxane oligomer consists of a Si-O-half ring, of which two Si atoms carry a methacrylic acid-containing side chain each having a terminal double bond, the two other Si atoms of the Achtringes are each linked to a Benzoesäurecholesterinesterrest.

To prepare a red liquid-crystal mixture, 80% by weight of the polyorganosiloxane described above is mixed with 20% by weight of 4-ethylphenyl methacryloxybenzoate (such a mixture being obtainable under the name CC3767 from Wacker Chemie).

To prepare a blue liquid-crystal mixture, 70% by weight of the polyorganosiloxane described above is mixed with 30% by weight of methacrylic acid cholesterol ester (such a mixture is obtainable under the name CC3939 from Wacker Chemie).

B Production of pigments, paints and varnished samples

Comparative Example 1

A mixture of red liquid crystal (CC3767) and blue liquid crystal (CC3939) in a weight ratio of 60:40 is prepared. 4% by weight of Irgacure 907 photoinitiator (obtainable from Ciba Marienburg GmbH, 2-methyl-1- (4- (methylthio) phenyl) -2-morpholino-propanone-1) are added to this mixture and mixed thoroughly. Subsequently, the liquid-crystal mixture is knife-coated at 90 ° C. onto a plastic film and crosslinked at 80 ° C. by means of UV light. The crosslinked liquid crystal is separated from the film and ground.

After grinding, the liquid crystal is present as a pigment and is incorporated into a binder system from Herberts (available under the designation 58L 90057). The pigment is added at 4% by weight, well dispersed and then diluted 2 to 1 with Herbert's MSB dilution.

The lacquer containing the liquid-crystalline pigments obtained in this way is applied to black metal sheets by means of immersion, which are then subsequently covered with a BASF 2K clearcoat.

The samples (painted sheets) are then dried for one hour, in each case at different drying temperatures, namely at room temperature, 80 ° C, 100 ° C and 130 ° C.

Subsequently, the reflection maxima in the range between 380 and 760 nm are determined on each sample by means of a colorimeter "Colorview" from Byk-Gardner (measurement geometry 45 ° or 0 °).

The difference (Δλ) of the maximums of the samples, which were dried at room temperature and at 130 ° C., and the difference between those samples which were dried at 80 ° C. and 130 ° C. were formed.

Furthermore, the corresponding ΔE values (color difference according to CIE) of these samples were determined on this colorimeter.

Embodiment 1

A mixture of red liquid crystal CC3767 and blue liquid crystal CC3939 was prepared as described above under Comparative Example 1 in a ratio of 60:40 and 4% by weight Irgacure 907 photoinitiator was added.

In addition, this mixture is 5 wt .-% of a mixture of pentaerythritol tri and tetraacrylate (sold by the company UCB under the name PETIA) and 5 wt .-% of a tetrafunctional Acrylate oligomers (sold by UCB under the name EBECRYL 40) added and mixed well. Subsequently, the mixture is doctored on a film as described above, processed to a lacquer and applied to black plates, which were dried at room temperature, 80 ° C, 100 ° C and 130 ° C respectively. Also of these samples corresponding Δλ and ΔE values were determined.

Comparative Example 2

There is a mixture of red liquid crystal CC3767 and blue liquid crystal CC3939, as described in Comparative Example 1, but prepared in the ratio 80:20. 4% by weight of Irgacure 907 photoinitiator are added to this mixture.

The procedure is then the same as in Comparative Example 2, ie the Δλ and ΔE values of the samples to be compared (RT-130 ° C, 80 ° C-130 ° C) are determined.

Embodiment 2

The 80:20 mixture of CC3767 and CC3939 described in Comparative Example 2 is prepared using the Irgacure 907 photoinitiator.

Further, to this mixture, 5 wt .-% of a mixture of pentaerythritol tri and tetraacrylate (sold by the company UCB under the name PETIA) and 5 wt .-% of a hexafunctional Polyurethanacrylatoligomeren (sold by the company UCB under the name EBECRYL 5129, molecular weight 2000) and mixed. This mixture is processed as described in Example 1 and in the samples to be compared the ΔE or Δλ values are determined.

The results are summarized in the table below. TABLE RT-130 ° C 80 ° C-130 ° C Comparative Example 1 AE 15 10 Δλ (nm) 35 25 Embodiment 1 AE 8th 5 Δλ (nm) 24 14 Comparative Example 2 AE 11 5 Δλ (nm) 40 20 Embodiment 2: AE 3.5 2 Δλ (nm) 17 10 RT-130 ° C = difference of the measured value of a sample, which was dried at room temperature to the measured value of a sample, which was dried at 130 ° C.
80 ° C-130 ° C = difference of the measured value of a sample dried at 80 ° C to the measured value of a sample dried at 130 ° C.

From the TABLE it can be seen that in the embodiments in which compared to the comparative examples in crosslinking additional, at least two crosslinkable double bonds containing color-neutral compounds are present, significantly lower ΔE or Δλ values are obtained, d. H. These additions make the pigments much more color-rich with respect to elevated temperatures.

In addition, when comparing the results of Embodiment 1 with those of Embodiment 2, it can be found that, with higher functionality of the added color-neutral compounds, lower ΔE or Δλ values are obtained. It can be concluded that a higher functionality causes a greater reduction of the color shift at elevated temperatures.

Claims (7)

Varnish, characterized in that it contains a pigment having a viewing angle dependent color, wherein the pigment was obtained by three-dimensional crosslinking of oriented substances liquid-crystalline structure with chiral phase, wherein the crosslinking in the presence of at least one further, at least two crosslinkable double bonds containing color neutral Compound has been carried out in a proportion of 5 wt .-% to 20 wt .-%, based on the total weight of the total mixture to be crosslinked. Paint according to claim 1, characterized in that the color-neutral compound has more than three crosslinkable double bonds. Lacquer according to claim 1 or 2, characterized in that the color-neutral compound has double bonds of the acrylate, methacrylate, vinyl, allyl type. Lacquer according to one of claims 1 to 3, characterized in that color-neutral compounds selected from the group consisting of acrylates, polyurethanes, epoxies, siloxanes, polyesters and alkyd resins are included. Lacquer according to one of claims 1 to 4, characterized in that colorless compounds selected from the group consisting of 1,6-hexanediol diacrylate, divinylbenzene, trivinylalkoxysilanes, trifunctional Polyurethanacrylatoligomeren, mixtures of pentaerythritol tri and tetraacrylates, tetrafunctional acrylate oligomers, tetraallylsilane, tetravinylsilane, tetrakis (2-methacryl-oxyalkoxy) silanes, 1,3,5,7-tetravinyltetraalkylcyclotetrasiloxanes, hexafunctional polyurethane acrylate oligomers, dipentaerythritol hexaacrylate are included. Paint according to one of claims 1 to 5, characterized in that the color-neutral compound with up to 15 wt .-% based on the total weight of the total mixture to be crosslinked. Use of the paint according to one of claims 1 to 6 for painting motor vehicle bodies and their parts.