PROCESS FOR THE PRODUCTION OF STRONGLY ADHERENT (EMBOSSED) FILMS ON FLEXIBLE SUBSTRATES

Abstract

Processes can produce strongly adherent, particularly embossed, films on flexible substrates. Security elements may be obtained by such processes as may be security documents, e.g., comprising the security elements. By coating a flexible substrate first with a primer layer and then with an embossed film, the adherence of the embossed film to the substrate may be improved while keeping the optical performance of the embossed film.

Claims

1. A process for producing strongly adherent films on a flexible substrate, the process comprising: (a) optionally exposing the flexible substrate to a corona discharge or a plasma discharge treatment; (b) applying a primer composition on the substrate, the primer composition comprising (b1) a polyurethane (A) comprising as synthesis components (b1a) a polyisocyanate having a functionality of at least 2, (b1b) a compound comprising an isocyanate-reactive group and a radically polymerizable unsaturated group, (b1c) a photoinitiator comprising an isocyanate-reactive group, (b2) a polyfunctional polymerizable compound (B), and (b3) a solvent; (c) evaporating the solvent by applying IR-radiation and/or thermal drying, to obtain a primer layer on the substrate; (d) curing the primer layer by UV/VIS radiation or electron beam, to obtain a primered substrate; (e) optionally, exposing the primered substrate to a corona discharge or a plasma discharge treatment; (f) applying a curable composition onto the primer coating; (g) optionally, contacting at least a portion of the curable composition with surface relief micro-structure former, to obtain an optionally embossed film; (h) curing the optionally embossed film by UV/VIS radiation or electron beam; and (i) optionally, depositing a layer of a transparent high refractive index material and/or a metallic layer on at least a portion of the cured composition.

2. The process of claim 1, comprising: (a) exposing the flexible substrate to a corona discharge or a plasma discharge treatment; (g) contacting at least a portion of the curable composition with surface relief micro-structure former; and (h) curing the embossed film by UV/VIS radiation.

3. The process of claim 1, wherein the flexible substrate is a biaxially oriented polyethylene terephthalate film or a biaxially oriented polypropylene film.

4. The process of claim 1, wherein the applying (b) comprises slot die-coating, knife-coating, reverse roll-coating, metering rod coating, gravure-printing, flexo-printing, screen-printing, or ink jet printing the primer composition.

5. The process of claim 1, wherein a liquid crystal composition is applied by slot die-coating, knife-coating, reverse roll-coating, metering rod coating, gravure-printing, flexo-printing, screen-printing, or ink jet printing.

6. The process of claim 1, wherein the embossed film is present and has a peelforce >20 N/m.

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

8. The process of claim 1, wherein the polyurethane (A) is a compound of formula ##STR00037## wherein n is a positive number which is on average 1 up to 5, and R.sup.11 is a group of formula ##STR00038## wherein R.sup.13, R.sup.14, and R.sup.15 are independently H, an alkyl group comprising 1 to 4 carbon atoms, or an alkyloxy group comprising 1 to 4 carbon atoms, p is 0 or an integer in a range of from 1 to 10, and Y.sub.i for i=1 to p is independently CH.sub.2CH(CH.sub.3)O, CH(CH.sub.3)CH.sub.2O, CH.sub.2C(CH.sub.3).sub.2O, C(CH.sub.3).sub.2CH.sub.2O, CH.sub.2CHVin-O, CHVin-CH.sub.2O, CH.sub.2CHPh-O, or CHPh-CH.sub.2O, in which Ph is phenyl and Vin is vinyl.

9. The process of claim 8, wherein the polymerizable compound (B) comprises 1,2-propanediol diacrylate, 1,3-propanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ditrimethylol tetracrylate, dipentaerythritol hexaacrylate, triacrylate of singly to vigintuply alkoxylated trimethylolpropane, triacrylate of singly to vigintuply alkoxylated glycerol, and/or polycrylate of singly to vigintuply alkoxylated pentaerythritol.

10. The process of claim 8, wherein the solvent (b3) comprises a C.sub.2-C.sub.6-alcohol, C.sub.2-C.sub.6-ether, and/or ether-C.sub.2-C.sub.6-alcohol, optionally further comprising water.

11. A security element, comprising: a flexible substrate; a primer layer; and an optionally embossed film; obtained by the process of claim 1.

12. The security element of claim 11, comprising a black layer, white layer, metallic layer, plasmonic layer, liquid crystalline layer, magnetic layer, fluorescent layer, interference layer, colored layer, IR-absorbing layer, IR-transparent layer, and/or conductive layer.

13. A security document, comprising the security element of claim 11 as a laminate onto the document or embedded as a (windowed) thread into the document or as a window on the document.

14. A primer composition, comprising: (b1) a polyurethane (A) comprising as synthesis components (b1a) an organic polyisocyanate having a functionality of at least 2, (b1b) a compound comprising an isocyanate-reactive group and a radically polymerizable unsaturated group, (b1c) a photoinitiator comprising an isocyanate-reactive group; (b2) a polyfunctional polymerizable compound (B); (b3) a solvent; wherein a proportion of the solvent is in a range of from 90.0 to 99.5 wt. %, a proportion of the compound (B) and the polyurethane (A) is in a range of from 10.0 to 0.5 wt %, the proportions adding up to 100 wt %.

15. The composition of claim 14, wherein the polyurethane (A) is a compound of formula ##STR00039## wherein n is a positive number which is on average 1 up to 5, and is a group of formula ##STR00040## wherein R.sup.13, R.sup.14, and R.sup.15 are independently H, an alkyl group comprising 1 to 4 carbon atoms, or an alkyloxy group comprising 1 to 4 carbon atoms, p is 0 or an integer in a range of from 1 to 10, and Y.sub.i for i=1 to p is independently CH.sub.2CH.sub.2O, CH.sub.2CH(CH.sub.3)O, CH(CH.sub.3)CH.sub.2O, CH.sub.2C(CH.sub.3).sub.2O, C(CH.sub.3).sub.2CH.sub.2O, CH.sub.2CHVin-O, CHVin-CH.sub.2O, CH.sub.2CHPh-O, and CHPh-CH.sub.2O, preferably from the group of CH.sub.2CH.sub.2O, CH.sub.2CH(CH.sub.3)O, or CH(CH.sub.3)CH.sub.2O, in which Ph is phenyl and Vin is vinyl.

16. The composition of claim 14, wherein the polymerizable compound (B) comprises 1,2-propanediol diacrylate, 1,3-propanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ditrimethylol tetracrylate, dipentaerythritol hexaacrylate, triacrylate of singly to vigintuply alkoxylated trimethylolpropane, triacylate of singly to vigintuply alkoxylated glycerol, and/or polycrylate of singly to vigintuply alkoxylated pentaerythritol.

17. The composition of claim 14, wherein the solvent (b3) comprises a C.sub.1-C.sub.6-alcohol and/or ether-C.sub.1-C.sub.6-alcohol.

18. A process for improving adherence of a curable layer to a flexible substrate, comprising: priming the flexible substrate with the primer composition of claim 14 to obtain a primed substrate; then adhering the curable layer optionally in uncured form, to the primed substrate.

Description

EXAMPLES

[0197] Primer Formulation:

TABLE-US-00003 Compound Weight (g) Photoinitiator.sup.1) 6.07 Sartomer 344 (polyethylene glycol (400) diacrylate) 3.45 Isopropanol 495.24 1,2-dimethoxypropanol 495.24 .sup.1)Compound of formula (V), wherein n is 1, and R.sup.11 is a group of formula

##STR00036##

in which R.sup.13 and R.sup.14 each independently of one another are an alkyl group containing 1 to 4 carbon atoms, Y.sub.i for is a group of CH.sub.2CH.sub.2O, CH.sub.2CH(CH.sub.3)O, and CH(CH.sub.3)CH.sub.2O, preferably CH.sub.2CH.sub.2O.

[0198] The UV curable composition is shown below:

TABLE-US-00004 UV curable composition % by weight Bisphenol A epoxyacrylate with 25% TPGDA 1-35 Dipropylene glycol diacrylate (DPGDA) 30-45 Ethoxylated trimethylol propane triacrylate (TMEOPTA) 10-50 Reactive tertiary amine 1-15 Photoinitiator blend: 5-10 Bis(2,4,6-trimethylbenzoyl)phenyl-phosphine oxide/4-phenyl benzophenone/2-hydroxy-1-{1-[4-(2-hydroxy-2-methyl- propionyl)-phenyl]-1,3,3-trimethyl-indan-5-yl}-2-methyl- propan-1-one

Comparative Example 1

[0199] Hostaphan RNK (Mitsubishi), a 23 micron biaxially oriented coextruded film made of polyethylene terephthalate (PET), is corona treated (Softal CLNE015-130-1KB3) at 300 W min/m.sup.2 and printed with the UV curable composition. UV casting is done on a nickel shim containing holographic structures using a UV lamp GEW, E2C-35-3 mercury lamp (140 W/cm), 50% power intensity and 5 bar pressure on nip rollers at 30 m/min. The holographic image transfer on PET is assessed visually and the adhesion of the hologram on PET is done with a tape test (Tesa 4104 adhesive)

Example 1

[0200] The primer formulation is printed by gravure using a 3051/cm ceramic cylinder on Hostaphan RNK, which is corona treated at 300 Watt at 10 m/min speed, press temperature 70 C. and UV cured with an IST lamp 150 Watt/cm mercury lamp.

[0201] The PET foil coated with the primer formulation is overprinted with UV curable composition using a 701/cm gravure cylinder and UV casting is done on a nickel shim containing holographic structures using a UV lamp GEW, E2C-35-3 mercury lamp (140 W/cm), 50% power intensity, 5 bar pressure on nip rollers at 30 m/min. The holographic image transfer on PET is assessed visually and the adhesion of the hologram on PET is done with a tape test (Tesa 4104 adhesive)

Comparative Example 2

[0202] Comparative Example 1 is repeated, except that Hostaphan RNK is replaced by Hostaphan RD (Mitsubishi), a 19 micron biaxially oriented coextruded film made of polyethylene terephthalate having an antislip treatment on surface.

Example 2

[0203] Example 1 is repeated, except that Hostaphan RNK is replaced by Hostaphan RD.

Comparative Example 3

[0204] Comparative Example 1 is repeated, except that Hostaphan RNK is replaced by Hostaphan RLDM (Mitsubishi), a 19 micron biaxially oriented coextruded film made of polyethylene terephthalate having an extremely flat surface and modified shrinking properties.

Example 3

[0205] Example 1 is repeated, except that Hostaphan RNK is replaced by Hostaphan RLDM.

Comparative Example 4

[0206] Comparative Example 1 is repeated, except that Hostaphan RNK is replaced by Melinex 4000 W (DuPont, Teijin Films), a 50 micron low cost polyethylene terephthalate.

Example 4

[0207] Example 1 is repeated, except that Hostaphan RNK is replaced by Melinex 400CW.

TABLE-US-00005 TABLE 1 Assessment of holographic image transfer and adhesion of the hologram to substrate Transfer of UV Sample of Treatment Tape test casted holograms Comparative Example 1 corona bad poor Example 1 corona/primer good good Comparative Example 2 corona bad poor Example 2 corona/primer good good Comparative Example 3 corona bad poor Example 3 corona/primer good good Comparative Example 4 corona bad poor Example 4 corona/primer good good

[0208] A bad hologram transfer is observed in case of only corona treatment with all tested films. The UV casted hologram is sticking on the shim. No or very poor hologram transfer is visible on filmic substrates.

[0209] A good hologram transfer occurs on the surface of all tested filmic substrates when first the primer formulation is printed. The primer formulation provides strong adhesion properties of UV curable composition on filmic substrates, therefore a good transfer of UV casted holograms at the printing speed is obtained.

[0210] Similar results are obtained when the primer formulation is printed with a 701/cm instead of a 3051/cm gravure cylinder