GB2347428A

GB2347428A - Retroreflective inks

Info

Publication number: GB2347428A
Application number: GB9904972A
Authority: GB
Inventors: Brian Sagar
Original assignee: Reflective Tech Ind Ltd
Current assignee: Reflective Tech Ind Ltd
Priority date: 1999-03-05
Filing date: 1999-03-05
Publication date: 2000-09-06
Also published as: GB9904972D0; AU2558800A; WO2000053686A1

Abstract

There is disclosed a retroreflective ink comprising a plastisol containing microbeads treated with a substance that causes them to float in a layer of the plastisol whereby the beads on printing rise to the surface of the printed plastisol layer where they are exposed for retroreflectivity.

Description

RETROREFLECTIVE INKS This invention relates to retroreflective inks, methods for making retroreflective inks and methods for printing with retroreflective inks.

Retroreflective inks are known which comprise retroreflective materials, usually hemispherically silvered microbeads, in suspension in a liquid medium. The liquid medium usually comprises a binder in a solvent or water. On printing, the solvent or water evaporates, leaving the beads partly exposed, a necessary condition for retroreflection. Because there is minimal volatile component in a plastisol ink, there is little or no change in the thickness of the printed layer on curing, and the thickness of the polymer deposited is commensurate with the bead diameter. Retroreflective microbeads added to conventional plastisol inks tend to remain covered by the polymer after printing and curing, and no significant retroreflectivity is achieved.

The present invention provides retroreflective plastisol inks.

The invention provides a retroreflective ink comprising a plastisol containing microbeads treated with a substance that causes them to float in a layer of the plastisol whereby the beads on printing rise to the surface of the printed plastisol layer where they are exposed for retroreflectivity.

The substance may comprise a fluorosilane.

The beads may be treated with an aminosilane.

Retroreflective inks may be made using unmetallised microbeads. Where silvered beads, e. g. beads hemispherically coated with aluminium, are used, the beads may be pretreated prior to metallisation with a metal adhesion enhancer, such, for example, as stannous chloride.

A blocked isocyanate may be added in the plastisol formulation, such, for example, as Trixene BI 7770.

The plastisol may comprise polyvinyl chloride (PVC). The ink may contain a thickening agent. The ink may contain a surfactant.

The ink may comprise 30-50% w/w of microbeads and may also contain a pigment, possibly up to 5% w/w of pigment, which may comprise a metallic pigment.

The invention also comprises a method for making a retroreflective ink comprising a plastisol, comprising treating microbeads with a substance that causes them to float in a layer of the plastisol incorporating the so treated microbeads in the plastisol The substance may comprise a fluorosilane.

In a particular method, deionised water (6 parts by weight) is added to isopropyl alcohol (114 parts by weight) and the pH adjusted to 5.0 0.5 with acetic acid, fluorosilane (1.1 parts by weight) added and the solution stirred to hydrolyse the silane, and the resulting solution used to treat the microbeads.

The microbeads may be treated with an aminosilane, which may be added (1 part by weight) to the fluorosilane solution after the fluorosilane is hydrolysed and the solution stirred again before being used to treat the microbeads.

60 parts by weight of the solution may be added to 1000 parts by weight of microbeads so as to wet them thoroughly, the solvent then being evaporated off, after which the microbeads may be heated, cooled and sieved.

Metallised microbeads may be pretreated with stannous chloride before metallisation.

The treated microbeads may be mixed with a plastisol formulation comprising a base plastisol, a thickening agent, a surfactant and a blocked isocyanate.

The invention also comprises a method for printing comprising applying an ink as above disclosed to a substrate and curing the print. Where the ink contains a blocked isocyanate, the print is cured at above the unblocking temperature thereof.

Fluorosilane FC 405 manufactured by 3M Corporation and aminosilane Z-6020 manufactured by Dow Coming are suitable for use in the inks.

Blocked isocyanates other than the Trixene BI 7770 may be used, for example Trixene BI 7960 (unblocking temperature 120 C) and Trixene BI 7960 (90 C), but the Trixene BI 7770 has an unblocking temperature of 160 C above which the print must be heated in any event, e. g for two minutes, to ensure adequate fusion of the plastisol.

The beads themselves are desirably 40-60 micron beads in order to pass through conventional printing screens. For optimum reflectivity, the refractive index of the glass should be close to 1.9.

The fluorosilane reaction appears to occur mainly on the uncoated glass surface, causing a greater proportion of the beads than would be expected on random orientation to face in the required direction for retroreflective, namely uncoated side facing outwards.

Without the aminosilane treatment, the fluorosilane treated beads are only poorly held in the PVC matrix and are easily lost on washing. The aminosilane treatment, together with the presence of the blocked isocyanate in the plastisol composition, gives satisfactory washfastness, however.

Silane treatment solution preparation Deionised water (6g) is added to isopropyl alcohol (114g) and the pH adjusted to 5.0 0.5 with acetic acid. Fluorosilane FC 405 (l. lg) is added and the solution stirred for 5-15 minutes to hydrolyse the silane. The aminosilane Z-6020 (l. Og) is added and the solution stirred for a further 30 minutes.

Bead Treatment To 1 kg of metallised beads (pretreated with stannous chloride before metallising to improve adhesion of the 0.03 micron thick aluminium layer) is added 60g of the isopropyl alcohol solution ensuring that the beads are completely wetted. The solvent is evaporated off, and the beads heated for 1 hour at 120 C. The treated beads are finally cooled and sieved.

Base plastisol formulation PVC powder 600g Plasticiser 450g Cd/Zn Stabiliser 12g Plastisol ink formulation % w/w Base plastisol 53.24 Thickening agent 0.16 Surfactant 0.60 Blocked isocyanate 6.00 Fluorosilane/amino-silyated metallised beads 40.00 Coloured prints can be obtained by including plastisol compatible pigments; loss of reflectivity is minimal with pigment levels below about 5% w/w. Metallic pigments can be used to produce attractive visual effects.

Claims

1. A retroreflective ink comprising a plastisol containing microbeads treated with a substance that causes them to float in a layer of the plastisol whereby the beads on printing rise to the surface of the printed plastisol layer where they are exposed for retroreflectivity.

2. An ink according to claim 1, in which the substance comprises a fluorosilane.

3. An ink according to claim 2, in which the beads are treated with an amino silane.

4. An ink according to any one of claims 1 to 3, in which the beads are hemispherically metallised.

5. An ink according to claim 4, in which the beads are hemispherically coated with aluminium.

6. An ink according to claim 4 or claim 5, in which the beads have been pretreated prior to metallisation with a metal adhesion enhancer.

7. An ink according to claim 6, in which the metal adhesion enhancer comprises stannous chloride.

8. An ink according to any one of claims 1 to 7, in which a blocked isocyanate is included in the plastisol formulation.

9. An ink according to claim 8, in which the blocked isocyanate comprises Trixene BI 7770.

10. An ink according to any one of claims 1 to 9, in which the plastisol comprises PVC.

11. An ink according to any one of claims 1 to 10, containing a thickening agent.

12. An ink according to any one of claims 1 to 11, comprising a surfactant.

13. An ink according to any one of claims 1 to 12, containing 30-50% w/w of microbeads.

14. An ink according to any one of claims 1 to 14, containing a pigment.

15. An ink according to claim 14, containing up to 5% w/w of pigment.

16. An ink according to claim 14 or claim 15, containing metallic pigment.

17. An method for making a retroflective ink comprising a plastisol comprising treating microbeads with a substance that causes them to float in a layer of the plastisol incorporating the so treated microbeads in the plastisol

18. A method according to claim 17, in which the substance comprises a fluorosilane.

19. A method according to claim 18, in which de-ionised water (6 parts by weight) is added to isopropyl alcohol (114 parts by weight) and the pH adjusted to 5.0 0.5 with acetic acid, fluorosilane (1. 1 parts by weight) added and the solution stirred to hydrolyse the silane and the resulting solution used to treat the microbeads.

20. A method according to any one of claims 17 to 19, in which the microbeads are treated with an aminosilane.

21. A method according to claim 19, in which the aminosilane is added (1 part by weight) to the solution after the fluorosilane is hydrolysed and the solution stirred again.

22. A method according to claim 19 or claim 21, in which 60 parts by weight of the solution are added to 1000 parts by weight of microbeads so as to wet them thoroughly and the solvent evaporated off.

23. A method according to claim 22, in which the microbeads are heated after the solvent has evaporated, cooled and sieved.

24. A method according to any one of claims 17 to 23, in which the microbeads are metallised, pretreated before metallisation with stannous chloride.

25. A method according to any one of claims 17 to 24, in which the beads are mixed into a plastisol formulation comprising a base plastisol, a thickening agent, a surfactant and a blocked isocyanate.

26. A method for printing comprising applying an ink according to any one of claims 1 to 16 or made by a method according to any one of claims 17 to 25 to a substrate and curing the print.

27. A method for printing according to claim 26, in which the ink contains a blocked isocyanate having an unblocking temperature and curing the print at above the unblocking temperature thereof.

28. A print made with an ink according to any one of claims 1 to 16 or an ink made by a method according to any one of claims 17 to 25 or a print made by a method according to claim 26 or claim 27.