RADAR-ENABLED COATING CONTAINING METAL EFFECT PIGMENTS ON A SUBSTRATE

Abstract

The present invention relates to a radar-compatible coating comprising metal-effect pigments on a substrate, to a process for the production of such a coating, and to the use of a substrate coated in this manner, in particular in vehicle construction.

Claims

1. Radar-compatible coating comprising metal-effect pigments on a substrate, characterised in that the coating has at least one layer package consisting of: a layer (A) which comprises at least one pigment having absorbent properties and is free from metal-effect pigments, and a layer (B) which comprises flake-form effect pigments, where the flake-form effect pigments are exclusively metal-effect pigments, and where layer (B) has a layer thickness in the range from 2 to ≤10 μm.

2. Coating according to claim 1, characterised in that the first layer comprises organic absorption pigments, inorganic absorption pigments and/or flake-form effect pigments having absorbent properties.

3. Coating according to claim 1, characterised in that the layer package comprising layers (A) and (B) has a total layer thickness in the range from 10 to 40 μm.

4. Coating according to claim 1, characterised in that layer (A) comprises, as flake-form effect pigment, an interference pigment which has a silver-grey absorption color.

5. Coating according to claim 1, characterised in that layer (A) comprises, as flake-form effect pigment, an interference pigment which has a red absorption color.

6. Coating according to claim 1, characterised in that the metal-effect pigment of layer (B) is an aluminium pigment.

7. Coating according to claim 1, characterised in that layer (B) comprises the metal-effect pigments in a concentration in the range from 3 to 25% by weight, based on the weight of layer (B).

8. Coating according to claim 1, characterised in that layer (A) comprises the pigment(s) having absorbent properties in a concentration in the range from 10 to 25% by weight, based on the weight of layer (A).

9. Coating according to claim 1, characterised in that the substrate is a plastic plate or film, where the plate or film may optionally have a three-dimensional outer shape.

10. Coating according to claim 1, characterised in that further layers are optionally located between the substrate and the layer package comprising layers (A) and (B) and/or above this layer package.

11. Coating according to claim 10, characterised in that the further layer or layers is (are) a primer layer and/or an outermost clear coat.

12. Coating according to claim 1, characterised in that said coating is a vehicle finish.

13. Process for the production of a radar-compatible coating comprising metal-effect pigments on a substrate, characterised in that a layer (A) which comprises at least one pigment having absorbent properties and is free from metal-effect pigments is applied to an optionally pre-coated substrate comprising a plastic plate or plastic film, and subsequently a layer (B) which comprises flake-form effect pigments, where the flake-form effect pigments are exclusively metal-effect pigments, and where layer (B) has a dry layer thickness in the range from 2 to ≤10 μm, is applied to layer (A), or a layer (B) which comprises flake-form effect pigments, where the flake-form effect pigments are exclusively metal-effect pigments, and where layer (B) has a dry layer thickness in the range from 2 to ≤10 μm, is applied to an optionally pre-coated substrate comprising a plastic plate or plastic film, and subsequently a layer (A) which comprises at least one pigment having absorbent properties and is free from metal-effect pigments is applied to layer (B).

14. Process according to claim 13, characterised in that layers (A) and (B) are applied by means of a spray process, brushing process, roller coating process, coil coating process, curtain coating process or in-mould process.

15. Process according to claim 13, characterised in that the substrate has been pre-coated with a primer layer.

16. Process according to claim 13, characterised in that a clear coat is applied to layer (B) of layer package (A)(B) or layer (A) of layer package (B)(A) as outermost layer of the coating.

17. A method of covering a radar device with a cover having a metallic finish comprising covering the radar device with a substrate according to claim 1 wherein said cover does not adversely affect the functionality of the radar device.

18. Vehicle part containing a substrate comprising a plastic plate or plastic film which has at least one coating according to claim 1.

Description

EXAMPLES

[0087] The substrate employed is in each case a PET film with a thickness of 350 μm (Hostaphan RN 350, Mitsubishi Polyester Film GmbH, DE). For determination of the L* values and the colour separation ΔE, black/white Leneta panels are coated in an analogous manner to the PET film. The coating is carried out as pneumatic spray coating. The binder employed is the preparation WBC 000 from MIPA SE, DE.

Example 1 (Reference)

[0088] As reference for the target visual appearance of the coating, a coating composition which is pigmented exclusively with aluminium pigments is applied to the film as a single layer.

TABLE-US-00001 Pigment (PMC in DLT L* 15° over L* 75° over Flop %) Al % (μm) black black index ΔE* 75° Al 18.0 100 21.8 150.085 34.058 16.913 0.082

[0089] PMC: pigment mass concentration

[0090] Al: aluminium pigment (Stapa® IL Hydrolan 2156, Stapa® IL Hydrolan

[0091] 8154, 1:1 mixture, Eckart)

[0092] DLT: dry layer thickness

[0093] L*: lightness value L*in the L*a*b* colour space at a certain measurement angle

[0094] Flop index: measure of the lightness flop when the viewing angle is changed, determined in accordance with the formula:

[00001]$\mathrm{flop}\mathrm{index}=\frac{2.69{\left(L_{15°}^{*}-L_{110°}^{*}\right)}^{1.11}}{{\left(L_{45°}\right)}^{0.86}}$

[0095] ΔE*: colour separation of samples in the L*a*b* colour space over standardised black and white background, determined in accordance with the formula:

ΔE*=√(ΔL*.sup.2+Δa*.sup.2+Δb*.sup.2)

Examples 2 to 4 (Invention)

[0096]

TABLE-US-00002 TABLE 1 Pigment (PMC in DLT L* 15° over L* 75° over Flop %) Al % (μm) black black index ΔE 75° Al 12.0 + 23.8 18.5 141.486 33.214 17.007 3.965 9602 (3x) Al 15.0 + 20.5 21.5 144.586 29.528 18.512 1.845 9602 (3x) Al 18.0 + 20.8 18.1 150.674 29.540 19.270 0.650 9602 (3x)

[0097] In each case, 4 coating operations are carried out, with the first 3 coating operations being carried out with a coating composition pigmented exclusively with 18% by weight of Iriodin® 9602 Silver Grey SW (silver-grey interference pigment having a silver-grey absorption colour, containing iron oxide, Merck KGaA, Darmstadt). Since no interim drying takes place, the three coating operations give rise to layer (A) of the layer package according to the invention (triple application technologically necessitated here). As layer (B), a coating composition pigmented exclusively with 12% weight (Ex. 2), 15% by weight (Ex. 3) or 18% by weight (Ex. 4) of aluminium pigment mixture (see above) is applied.

[0098] The table shows the dry layer thickness of the coating as a whole comprising layers (A) and (B). With each coating operation, approximately the same amount of coating composition is applied in in each case.

[0099] The colorimetric measurement of the samples is carried out using a model BYKMac i colorimeter (Byk-Gardner) in SMC5 mode.

[0100] The L*15 values of layer (A) over black are carried out on sole use of organic or inorganic absorption pigments on a four-area, completely opaque coating on a standardised black/white-coated substrate. If flake-form effect pigments having absorbent properties are employed in layer (A), the colorimetric measurement of layer (A) and in particular the determination of the L*15 value over black is carried out by means of a coating having a pigment mass concentration of 18% by weight on the substrate.

[0101] The concentrations of the pigments employed and the layer thickness of the coating are indicated in each case for the individual layers and layer packages of the coating according to the invention.

[0102] The black/white panels used as substrate here comply with the ASTM E 1347 standard and are marketed by Leneta under the name Metopac T12G panels.

[0103] It can be seen from the table that an increasing concentration of aluminium pigment in the second layer, which is in each case only about 4 to 5 μm thick, leads to an increasing flop index and decreasing ΔE value, and the visual appearance of a conventional silver metallic finish in accordance with the reference example can be simulated well to very well with Examples 2 to 4.

[0104] Transmissivity of Radar Waves:

[0105] The following table shows the dielectric constant (permittivity) of the respective layer structure and the attenuation of the radar signal in dB for a single beam passage (76.5 GHz)

TABLE-US-00003 TABLE 2 Attenuation at Example Permittivity 76.5 GHz (dB) Reference Ex. 1 74.887 4.47 2 9.037 1.37 3 10.856 1.39 4 20.327 1.73 PET substrate 3.219 1.05

[0106] The inventive examples show a clear reduction in the attenuation of the radar radiation for a single beam passage compared with the original metallic finish in accordance with the reference example. At the same time as good hiding power and very good lightness flop, all coatings according to the invention are, depending on the technological requirements, significantly more suitable as radar-compatible coating for vehicle parts located in the beam path of radar devices than a conventional opaque metallic finish comprising aluminium pigments.

Examples 5 to 7

[0107] With PET substrates and a coating process as described in Example 1, a completely opaque coating in the RAL shades 7030 (stone grey, Example 5), 7033 (cement grey, Example 6) and 7035 (light grey, Example 7) is in each case applied to the substrate as layer (A). A layer (B) pigmented with 15% by weight of flake-form aluminium pigments (Stapa® IL Hydrolan 2156, Stapa® IL Hydrolan 8154, 1:1 mixture, Eckart) is in each case applied to layer (A).

[0108] The individual results with respect to the colorimetric properties or radar capability of the respective coatings can be seen in Tables 3 and 4.

TABLE-US-00004 TABLE 3 Pigment DLT L* 15° over L* 75° over Flop (PMC in %) Al % (μm) black black index RAL 7030 + 22 25.2 135 38.8 13.3 Al 15.0 RAL 7033 + 22 25.2 134 37.5 13.3 Al 15.0 RAL 7035 + 22 27.1 137 44.3 12.1 Al 15.0

TABLE-US-00005 TABLE 4 Attenuation at Example Permittivity 76.5 GHz (dB) 5 15.0 1.67 6 15.9 1.75 7 21.1 2.07 PET substrate 3.219 1.05

[0109] The examples show that a metallic-like visual appearance can be obtained with high hiding power and satisfactory flop index, where the coatings in Examples 5 and 6 have one-way attenuation of the radar signal in the target range and in Example 7 merely with minimal exceeding of the target range.

Example 8

[0110] A coating (B) pigmented with 18% by weight of aluminium pigments as described above is applied to a PET substrate in accordance with Example 1 and by means of the spray application mentioned in Example 1. A coating pigmented with 18% by weight of Colorstream® F10-51 Lava Red (Merck KGaA, iron oxide on SiO.sub.2 substrate) is applied in three coating operations as layer (A).

[0111] The individual results with respect to the colorimetric properties or radar capability of the respective coatings can be seen in Tables 5 and 6.

TABLE-US-00006 TABLE 5 Pigment (PMC in DLT L* 15° over L* 75° over Flop %) Al % (μm) black black ΔE 75° index Al 18.0 + 25 18.1 85 19.2 1.26 16.2 3x Lava Red

TABLE-US-00007 TABLE 6 Attenuation at Example Permittivity 76.5 GHz (dB) 8 4.1 1.80 PET substrate 3.219 1.05

[0112] Example 8 shows that a coating which has a good light/dark flop and exhibits significantly lower one-way attenuation of the radar signal than a standard commercial metallic coating exclusively with aluminium pigments is also obtained in the case of a layer structure (B)-(A) on a substrate. The coating according to the invention exhibits a visually attractive red metallic character and good hiding powers.