High gloss metal effect papers

Abstract

The instant invention pertains to a method for the production of brilliant glossy metal coatings on paper substrates. Further aspects of the invention are a paper product obtainable using the method and the use of such a paper for decorative or packaging purposes.

Claims

1. A method for forming a smooth decorative surface coating exhibiting gloss on a paper or board substrate, the method comprising: A) applying a curable composition comprising one or more ethylenically unsaturated compounds and one or more photoinitiators to at least a portion of the frontside of the paper substrate by a process selected form the group consisting of gravure printing, flexographic printing, screen printing, coating with a slot coater, coating with a knife coater, coating with a wire bar and coating with a doctor blade; B) curing the composition by using a UV lamp; and C) printing an aluminium layer on the cured composition wherein the aluminium layer comprises a binder and vapour deposited aluminium particles with an mean diameter of from 8.0 m to 12 m and the thickness is from 11 to 18 nm, wherein said printing is a process selected from the group consisting of gravure printing, rotogravure printing, flexographic printing, lithographic printing, offset printing, letterpress intaglio printing, and screen printing, wherein the gloss, as measured under a 20 geometry has a value higher than 500 relative gloss units and the roughness of the coated paper (S.sub.z value) equal or below 300 nm.

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

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

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

5. The method according to claim 1, wherein the paper or board substrate has a weight of from 30 g/m2 to 300 g/m2.

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

7. The method according to claim 1, wherein the photoinitiator is selected from the group consisting of mono and bisacylphosphine oxide, alpha-hydroxy ketone, alpha-alkoxyketone, or alpha-aminoketone compounds and mixtures thereof.

8. The method according to claim 1, wherein the curable composition comprises an ethoxylated oligo ether acrylate, a polyester acrylate or an urethane acrylate.

9. The method according to claim 1, wherein the curable composition comprises an ethoxylated amine modified polyether acrylate or an epoxy acrylate.

10. 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.

11. The method according to claim 10, wherein the cationic polymer is a polyvinylamine.

12. A paper or board product obtained by the method according to claim 1.

13. A method, comprising employing the paper or board product of claim 12 for decorative or packaging purposes.

14. The method according to claim 1, wherein the curable composition comprises an ethoxylated oligo ether acrylate, an ethoxylated amine modified polyether acrylate, an epoxy acrylate, a polyester acrylate or an urethane acrylate.

15. The method according to claim 1, wherein the curable composition comprises 1 to 25 wt % tripropylene glycol diacrylate, 30 to 45 wt % dipropylene glycol diacrylate, 10 to 50 wt % ethoxylated trimethylol propane triacrylate, 1 to 15 wt % of a reactive tertiary amine, and 5 to 9 wt % of a photoinitiator.

16. The method according to claim 15, wherein the photoinitiator is a blend of Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and 2,4,6-Trimethylbenzoyl-phenyl phosphinic acid ethyl ester.

17. The method according to claim 1, wherein the coating comprises a pigment and a pigment to binder ratio ranging from 3:1 to 1:3.

18. The method according to claim 1, wherein the binder is nitrocellulose.

19. The method according to claim 1, wherein the curable composition further comprises a solvent.

20. The method according to claim 19, wherein the solvent is an ester/alcohol blend.

21. The method according to claim 19, wherein the solvent is a propyl acetate and ethanol blend.

Description

EXAMPLE 1: PRINTING UV AND METAL INK ON CARD BOARD BY GRAVURE

(1) Substrate: White board, Invercote T 220 g/m.sup.2, 275 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

(2) The composition of the UV lacquer is shown below:

(3) TABLE-US-00001 UV lacquer % by weight Tripropylene glycol diacrylate (TPGDA) 1-25 Dipropylene glycol diacrylate (DPGDA) 30-45 Ethoxylated trimethylol propane triacrylate 10-50 (TMEOPTA) Reactive tertiary amine 1-15 Photoinitiator blend 5-9 Photoinitiator blend

(4) Nitrocellulose Varnish

(5) Varnish preparation: 75.3 g of nitrocellulose (DHX 3/5 IPA, 70% solids, Nobel Enterprises, UK) are slowly added to 220.5 g of ethyl acetate (99-100% rein, Brenntag), 557.2 g n-Propylacetate, 147 g Dowanol PM in a 2000 mL glass bottle and gently stirred until complete dissolution at room temperature. Solid content measurements are then performed and quantity of ethyl acetate is adjusted to achieve a value of 5.27% solid content in the varnish preparation.

(6) Al-Pigment Slurry (Supplied by BASF SE Under the Trade Name Metasheen)

(7) 10% aluminum pigment+45% ethylacetate+45% isopropylacetate.

(8) Metallic Ink 1 (D50, 8.5-11.5 m, Thickness 17 nm)

(9) Procedure for metallic ink preparation: aluminum pigment slurry is added to the above nitrocellulose varnish in such a proportion as to adjust the pigment to binder ratio to 1:1, 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.

(10) Metallic Ink 2 (D50, 8.0-12.0 m, Thickness 13 nm):

(11) Procedure for metallic ink preparation: aluminum pigment slurry is added to above nitrocellulose varnish in such a proportion as to adjust the pigment to binder ratio to 3:1; 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.

(12) Substrate: 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.

(13) UV-laquer and metallic ink are applied with Moser press comprising a UV gravure unit machine and a solvent gravure printing unit in-line.

(14) Printing speed 30 m/min, UV curing intensity 50 Watt/cm.sup.2, solvent ink drying temperature 80 C.,

(15) UV gravure cylinder 30 l/cm screen, solvent ink gravure cylinder 120 l/cm screen. The results are given in Table 1.

(16) TABLE-US-00002 TABLE 1 Gloss of the printed samples is measured by means of a Zehnter Glossmeter ZGM 1120 at 20 angle Print Invercote T Metal Metal UV UV and UV and as delivered ink 1 ink 2 varnish metal ink 1 metal ink 2 Gloss 8 10 20 90 510 820 units (GU)

EXAMPLE 2

(17) Substrate: Raflabrite RH1 85 g/m.sup.2, 71 min (Multipurpose label paper for high quality multi-colour labels requiring good print definition and fine detail, UPM Raflatac). Roughness 0.7 m.

(18) The inks and the print process are the same as in Example 1.

(19) Gloss of the printed samples is measured by means of a Zehnter Glossmeter ZGM 1120 at 20 angle. The results are given in Table 2.

(20) TABLE-US-00003 TABLE 2 Gloss of metallic ink on paper and board is considerably increased when printing UV varnish first and overprinting a metallic ink containing fine grade aluminium pigment. Print Raflabrite Metal Metal UV UV and UV and RH1 ink 1 ink 2 varnish metal ink 1 metal ink 2 Gloss 8 70 90 70 530 640 units (GU)

EXAMPLE 3

(21) Gloss comparison of different aluminum pigment grades on UV coated and uncoated board.

(22) The UV-laquer and the metallic inks are prepared as described in Example 1. Table 3 summarizes the different metallic inks.

(23) TABLE-US-00004 TABLE 3 Product D50 Thickness Ink 1 8.5-11.5 m 17 nm Ink 2 8.0-12.0 m 13 nm Ink 3 11.0-13.0 m 25 nm Ink 4 11.5-14.5 m 32 nm

(24) Application Procedure:

(25) Paper is coated with metal ink using a wire bar 1 and dried with an air dryer.

(26) UV varnish is coated on Invercote T board using wire bar 2 (12 micron). UV coated paper is cured under UV light (Aktiprint mini 18-2, mercury tube power 80 watt/cm, position 10) and overcoated with metal ink 1 using a wire bar 1 (6 micron wet film thickness) and dried with an air dryer.

(27) Substrate: White Invercote T 220 g/m.sup.2, 275 m (High quality coated paper, Iggesund Paperboard Europe). The printing side is fully coated and finished to a matt level. Surface roughness is 1.1 m. The results are presented in Table 4.

(28) TABLE-US-00005 TABLE 4 Gloss of the samples is measured using a Zehnter Glossmeter ZGM 1120 at 20 angle Ink no./ Gloss units 1 2 3 4 Metal ink on 24 20 20 20 board UV varnish and 1030 900 690 670 metal ink on board

(29) The samples coated with the UV varnish and overcoated with the metallic inks exhibit a far higher gloss value in all cases. The best values are achieved with ink no 1 and no 2.

EXAMPLE 4: GLOSS COMPARISON OF RADIATION CURING RESINS ON PAPER

(30) Test procedure: UV varnish is manufactured by adding 5 parts by weight Irgacure 1173, BASF to 95 parts by weight resin. The UV varnish is coated on Invercote T board using wire bar 0 (4 micron), 1 (6 micron), 2 (12 micron), 3 (24 micron). Coated paper is cured under UV light (Aktiprint mini 18-2, mercury tube, position 20) and overcoated with metal ink 1 using wire bar 1 (6 micron wet film thickness). The results are presented in Table 5.

(31) TABLE-US-00006 TABLE 5 Gloss of the samples is measured using a Zehnter Glossmeter ZGM 1120 at 20 angle Gloss UV varnish Units Composition Laromer PO 525 80% TMPEOTA + 20% DGEBA diacrylate 43F(ethoxylated (CAS 28961-43-5 + 55818-57-0) oligo ether acrylate) Laromer LR8863 350 100% TMPEOTA (CAS 28961-43-5) (ethoxylated oligo ether acrylate) Laromer PO77F 615 Ethoxylated amine modified polyether (ethoxylated amine acrylate modified polyether acrylate) Laromer LR8765 550 1,4-butanediylbis[oxy(2-hydroxy- (aliphatic epoxy 3,1-propanediyl)] diacrylate acrylate) (CAS 52408-42-1) Laromer LR8986 700 40% TMPEOTA + 60% DGEBA diacrylate (modified aromatic (CAS 28961-43-5 + 55818-57-0) epoxy acrylate) Ebecryl 605 690 75% Bisphenol A Diglycidylether (epoxy acrylate) Diacrylat (BADGE-DA) + 25% TPGDA (CAS 55818-57-0 + 42978-66-5) Laromer UA9073 210 50% Urethane acrylate + 50% (aromatic urethane DPGDA (CAS 57472-68-1) acrylate) Laromer PE9024 330 Polyester acrylate (Polyester acrylate) Laromer DPGDA 33 Oxybis(methyl-2,1-ethanediyl) diacrylate CAS 57472-68-1

EXAMPLE 5: ROUGHNESS OF UV COATING AT DIFFERENT THICKNESSES

(32) UV varnish 1: 37% Laromer DPGDA, 24% Laromer LR8863, 23% Laromer 8986, 10% Ebecryl P115, 3% Irgacure 127, 3% Irgacure 819

(33) UV varnish 2: 46% Laromer LR8986, 36% Laromer PO77F, 14% Laromer TPGDA, 4% Irgacure 127

(34) Metal Ink 1:

(35) Nitrocellulose varnish as prepared in Example 1 with aluminum particles of ink 2 (D50, 8.0-12.0 m, thickness 13 nm).

(36) Susbtrate: White Invercote T 220 g/m.sup.2, 275 m (High quality coated paper, Iggesund Paperboard Europe). Surface roughness 1.1 m

(37) Surface texture or roughness of UV-coated papers is measured by digital microscope holography (DHM) using a magnification5 objective lens in the 1.sup.st-WL mode. The surface area measured is 1 mm1 mm.

(38) Sz values indicated in the table are the average distance of largest height (peak) and largest depth (whole) value found in the profile in nanometer. The results are given in Table 6.

(39) TABLE-US-00007 TABLE 6 Sz values UV coating thickness and roughness (nm) 4 micron 6 micron 12 micron 24 micron UV varnish 1 and 220 235 230 270 metal ink 1 UV varnish 2 and 290 300 290 300 metal ink 1

(40) Invercote T board surface roughness, sz value: 620 nm

(41) Invercote T coated with 6 micron wet film thickness metal ink 1, sz value: 795 nm

(42) Conclusion: The surface texture of Invercote T board is increased when directly coated with metal ink 1, the aluminum flakes are not flat oriented on the paper surface. The surface texture of the paper becomes smooth when coated with UV varnish and gloss increases considerably. The results correlate with gloss values as highest gloss and lowest roughness are measured with a UV coating thickness of 12 micron. The deposit of UV varnish on the paper surface leads to a smooth surface that enables the optimum orientation of aluminum flakes.