Patterned rolled zinc alloy sheet

Abstract

The present disclosure concerns specially patterned zinc sheets for coverage and protection of building roofs and facades. A recurrent problem linked with the use of zinc sheets in building applications is the development of white rust. As the complete avoidance of white rust is difficult to achieve, additional means to reduce its impact are most welcome. It is now proposed to limit the visibility of white rust by providing a camouflaging pattern on the surface of the zinc. The invention more specifically concerns an unweathered rolled zinc alloy sheet with at least one patterned face having an optical reflectivity that varies from region to region, characterized in that said regions are of a pseudo-random shape, having characteristic dimensions in the range of 0.1 mm to 10 cm; and in that the optical reflectivity, when measured across the sheet in any arbitrary direction, presents a specular reflectivity RMS deviation of more than 3 GU and/or a diffuse reflectivity RMS deviation of more than 0.2. A laser-aided imprinting process is disclosed to generate suitable camouflage patterns on the zinc.

Claims

1. An un-weathered rolled zinc alloy sheet for coverage and protection of buildings, the sheet comprising a patterned face having a pattern resulting in a varying optical reflectivity defining a reflectivity map of the face, said face having regions, wherein: the pattern is pseudo-random and said regions are of a pseudo-random shape, with no repeating patterns in the reflectivity map over distances within a range of 0.1 mm to 2 m; said regions include darker regions delimited by two successive maxima on the reflectivity map in any arbitrary direction, and brighter regions delimited by two successive minima on the reflectivity map in any arbitrary direction, said two successive maxima and said two successive minima being respectively separated by characteristic dimensions in the range of 0.1 mm to 10 cm; and the optical reflectivity, when measured across the sheet in any arbitrary direction, presents a specular reflectivity RMS deviation of more than 3 GU and/or a diffuse reflectivity RMS deviation of more than 0.2.

2. The zinc sheet according to claim 1, wherein said patterned face has microstructures imprinted thereon and wherein some of the regions comprise microstructures having a higher optical reflectivity, and some of the regions comprise microstructures having a lower optical reflectivity.

3. The zinc sheet according to claim 2, wherein the imprinted microstructures are formed by either one or both of hills and dales situated within a range of 1 to 100 m above or below the mean surface of the sheet.

4. The zinc sheet according to claim 1, wherein the mean optical reflectivity of the patterned face of the sheet has a diffuse reflectivity value of more than 75.

5. The zinc sheet according to claim 1, wherein the mean saturation level of the patterned face of the sheet has a value of less than 20% in the hue-saturation-lightness (HLS) color space.

6. The zinc sheet according to claim 1, wherein the zinc alloy is a ZnCuTi alloy according to the EN 988 norm.

Description

(1) The above is illustrated in FIG. 1, showing the resulting surface appearance on microphotographs. The pattern shown is obtained by using a pulse rate of 45 kHz, a linear scanning speed of 2 m/s, and 50 m line spacing (also known as hatch spacing).

(2) The desired pseudo-random pattern that is to be transferred to the zinc sheet is pre-calculated using pseudo-random pattern generation. After conversion into a compatible digital format, the data is uploaded to the laser marking workstation.

(3) This station comprises all software and hardware needed to scan the zinc sheet, line by line, and for pulsing the laser beam according to the desired pattern. In the present example, the equipment manufacturer's standard conditions for imprinting metals are adopted.

(4) FIG. 2 shows a pre-calculated pseudo-random pattern as printed on paper.

(5) FIG. 3 shows a photo of the pattern transferred to the zinc sheet. Although brightness and contrast are different from the paper print, the result is adequate for masking white rust.

(6) The specular reflectivity of the obtained zinc is about 9.9 GU (measured at) 60) with a RMS deviation of 4 GU.

(7) The surface of the obtained imprinted products can be further subjected to chemical treatment such as phosphate conversion. This preserves the general aspect of the product while improving its corrosion resistance.