HIGH GLOSS METAL EFFECT PAPERS AND BOARDS

Abstract

The instant invention pertains to a method for the production of brilliant glossy metal coatings on paper or board substrates. Further aspects of the invention are a paper or board product obtainable by using the method and the use of such a paper or board for decorative or packaging purposes. In particular the instant invention is directed to a method, wherein a UV curable composition is applied/printed on a paper or board substrate and cured through the paper or board from the reverse side by UV/Visible light. Simultaneously with the curing step the coated/printed paper or board is pressed from the coated/printed side against a mirror like shim. The shim has no structure and should be of mirror quality. In a second step this glazed and cured surface is overcoated/overprinted with an aluminium layer. The result is a metallized surface exhibiting excellent gloss and brilliance.

Claims

1. A method for forming a smooth surface coating exhibiting gloss on a paper or board substrate, comprising: A) applying a curable composition to at least a portion of the frontside of the paper or board substrate; B) contacting the curable composition with a shim and simultaneously curing the composition by using at least one UV lamp which is arranged on the backside of the paper substrate; and C) depositing an aluminum layer on the cured composition, wherein the lamp has emission peak(s) in the UV-A range and near VIS range and the curable composition comprises at least a photoinitiator which absorbs in the UV-A region and in addition in the near VIS range.

2. The method according to claim 1, wherein the curable composition comprises a photoinitiator which is at least one selected from the group consisting of mono and bisacylphosphine oxide compounds, alpha-amino ketone type compounds, and oxim ester compounds.

3. The method according to claim 1, wherein the lamp is a gallium or iron doped medium pressure mercury lamp.

4. The method according to claim 1, wherein the lamp is a Focussed Reflected Diode Array (FRDA) system, having an emission in the UVA range and in addition an emission peak above 400 nm.

5. The method according to claim 1, wherein the photoinitiator is at least one selected from the group consisting of mono and bisacylphosphine oxide compounds.

6. The method according to claim 1, wherein the curable composition comprises a mixture of a mono, or a bisacylphosphine oxide compound with a benzophenone compound, an alpha-hydroxy ketone, alpha-alkoxyketone, or alpha-aminoketone compound.

7. The method according to claim 1, wherein the curable composition comprises (a) 1.0 to 20.0 by weight of a photoinitiator, and (b) 99.0 to 80.0 by weight of a resin, wherein the sum of components a) and b) adds up to 100%.

8. The method according to claim 1, wherein the surface of the shim is without a microstructure and the shim material is selected from the group consisting of a nickel sleeve, a nickel plate, and another metal material, mounted on a metal cylinder.

9. The method according to claim 8, wherein the shim is a nickel plate mounted on a metal cylinder.

10. The method according to claim 1, wherein the paper substrate is selected from the group consisting of regular paper, banknote paper, synthetic paper, and a polymer banknote substrate.

11. The method according to claim 1, wherein the gloss value of the final metallized coating is higher than 500 relative gloss units as measured under a 20 geometry.

12. The method according to claim 1, wherein the mean diameter of the vapor deposited aluminum particles is from 8.0 m to 12 m and the thickness is from 11-18 nm.

13. The method according to claim 1, wherein the mean diameter of the vapor deposited aluminum particles is from 8.0 m to 12 m and the thickness is from 12-14 nm.

14. The method according to claim 1, wherein the paper or board substrate has a roughness of less than 1.5 m.

15. The method according to claim 1, wherein the paper or board substrate has a weight of from 30 g/m.sup.2 to 300 g/m.sup.2.

16. The method according to claim 1, wherein the paper or board has been treated with a cationic polymer on the frontside before applying a curable composition to at least a portion of the frontside of the paper substrate.

17. The method according to claim 16, wherein the cationic polymer is a polyvinylamine.

18. A paper or board product obtained by the method of claim 1.

19. The paper or board product of claim 18, which is a banknote, an identification document, an identification card, a drivers license, a packaging material, apparel, software, cosmetic, tobacco or any other product to be decorated.

Description

EXAMPLE

[0231] Metallic Ink

[0232] (D50, 8.0-12.0 m, thickness 13 nm):

[0233] Procedure for metallic ink preparation: aluminium pigment slurry is added to above nitrocellulose varnish in such a proportion as to adjust 2.7:1 the pigment to binder ratio, ethylacetate is added to adjust ink to print viscosity (20 sec Zahn cup 2). The obtained dispersion is stirred with a Dispermat at 800 rpm for 10 minutes.

[0234] Substrate:

[0235] White board, Invercote T 220 g/m.sup.2, 275 m m (high quality coated paper, Iggesund Paperboard Europe). The printing side is fully coated and finished to a matt level. Surface roughness 1.1 m.

[0236] UV laquer is as described in the examples of WO 2012/176126 using photoinitiator 3.

[0237] UV-laquer and metallic ink are applied with Moser press comprising a UV gravure unit machine and a solvent gravure printing unit in-line.

[0238] Printing speed 30 m/min, UV curing intensity 50 Watt/cm.sup.2, solvent ink drying temperature 80 C.,

[0239] UV gravure cylinder 701/cm screen, solvent ink gravure cylinder 701/cm screen. The results are given in Table 1.

TABLE-US-00001 TABLE 1 Gloss of the printed samples is measured by means of a Zehntner Glossmeter ZGM 1110 Gloss units/substrate 20 angle 60 angle 85 angle Invercote T 2 11 60 Metal ink 18 108 90 3 micron UV lacquer 88 97 101 UV and metal ink 730 580 143

[0240] Gloss of metallic ink on paper and board is considerably increased when curing UV varnish on top of a mirror Nickel shim first through the substrate and overprinting a metallic ink containing fine grade aluminium pigment.