GB2347366A - Reflective tape - Google Patents

Abstract

In the manufacture of a retroreflective tape by hemispherically metallising a layer of microbeads 14 held in a melt adhesive coating 16 on a web 15, and then transferring the layer of beads, unmetalled side facing outwards, on to a substrate, (i) an excess of microbeads is fed on to the coating, which has a thickness about half the diameter of the beads, (ii) the web is heated to melt the adhesive and allow the beads to sink into it, (iii) the web is cooled and excess beads are removed, (iv) after metallising the layer of beads an adhesive 32 is applied for attachment to, e.g., a textile substrate, and (v) the web 15 and adhesive coating 16 are removed. The adhesive 32 is applied as a film by laminating and may be a hot melt adhesive of polyester based polyurethane containing a blocked isocyanate. One or more further melt adhesive films 33 may be included.

Description

REFLECTIVE TAPE This invention relates to retroreflective tapes and methods for making them.

Retroreflective tapes are used to impart night conspicuity to garments, and are required to be made to exacting standards.

Conventionally, such tapes are made by hemispherically metallising a layer of microbeads while held on a web half submerged in a coating on the web and transferring the layer of metallised beads, unmetallised side facing outwards, on to a substrate.

There are problems associated with manufacture of such tapes, principally in connection with the various adhesive operations some of which must be adapted to be "permanent", especially where washfastness is required, but one of which, critically, has to have controlled release for the transfer of the bead layer to the substrate.

The present invention provides methods for the manufacture of such tapes that are not subject to problems of prior art production methods.

The invention comprises a method for making a retroreflective tape by hemispherically metallising a layer of microbeads while held on a web half submerged in a coating on the web and transferring the layer of metallised beads, unmetalled side facing outwards on to a substrate, in which the coating on the web is a melt adhesive, with a thickness about half the diameter of the beads; an excess of the microbeads is fed on to the coating on the web; the web with the excess of microbeads is heated to melt the melt adhesive and allow the layer of beads immediately in contact therewith to sink in to the adhesive layer; the web is cooled; excess microbeads are removed; the exposed surface of the layer of microbeads held on the web is metal-coated ; the metal-coated microbeads on the web are coated with an adhesive; and the web and melt adhesive removed to expose the unmetallised side of the microbead layer.

The melt adhesive may comprise a linear low density polyethylene (LLDPE).

The web may comprise kraft paper.

The melt adhesive coated web may be unwound from a roll and passed through a beading station at which the excess of microbeads is applied then through an oven heated to a temperature above the melting point of the melt adhesive.

The microbeads may be dispensed on to the moving web by a vibratory feeder. Excess microbeads not adhered to the web may be removed after the web has cooled on leaving the oven, preferably by suction so as not to disturb the microbeads attached to the web.

Before application to the web, the microbeads may be treated with stannous chloride, in a dilute solution, followed by rinsing with deionised water.

The microbeads may be hemispherically metallised in a vacuum metalliser.

A roll of the beaded web may be placed in a vacuum metalliser fitted with a reel-to-reel mechanism, the metalliser sealed and evacuated, then aluminium heated to melt and volatilise in the chamber whereby to condense on the microbeads as the web is fed from reel-to-reel.

The adhesive coating for the metallised microbeads may be applied by laminating with a second melt adhesive in film form. The second melt adhesive may comprise a polyurethane film, which may be a polyester-based polyurethane, and which may contain a blocked isocyanate.

A further melt adhesive film (or films) may be laminated to the second melt adhesive, such further film, for example, comprising a thermoplastic co-polyamide, copolyester or polyurethane. The, or any of these, melt adhesive films may be precoated with an adhesion promoter, which may comprise an organo-functional silane.

The laminated film may be made sufficiently robust to permit the web to be removed and leave a microbead layer, unmetallised face out, on the film. The web may be removed, and the beaded laminated film laminated, in turn, to a substrate such as a textile.

The web may, however, be removed after lamination to a substrate such as a textile.

The substrate may be a tape for sewing or otherwise attaching to a garment or other artefact. The substrate may, however, be a garment panel.

The invention also comprise a retroreflective tape comprising a layer of hemispherically coated microbeads, uncoated face directed outwardly, with their metallised halves embedded in a melt adhesive film.

The microbeads may have added stannous chloride, in an amount about 0.01% by weight (order of magnitude) of the beads.

The melt adhesive film may comprise a blocked isocyanate which has reacted above its unblocking temperature to cross-link the polymer structure of the film and bond to the beads.

The melt adhesive film may also contain a blocked isocyanate adapted to react on lamination of the tape to a substrate to bond to the substrate.

The microbeads may be between 53 and 75 microns in diameter (200-270 US mesh size).

The microbeads may have a refractive index close to 1. 9-say 1.92 or 1.93, and are preferably of near perfect sphericity for optimum reflectivity.

The exposed metal-free faces of the microbeads may be treated with a perfluorosilane or an organo-silane.

Retroreflective tapes and methods for manufacturing them according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross section of a web loaded with microbeads at three stages A, B, C in the production of the retroreflective tape; Figure 2 is a diagrammatic illustration of an arrangement for beading a web as a step in the production of the retroreflective tape; Figure 3 is a diagrammatic illustration of a metallising process; Figure 4 is a diagrammatic cross section of a web loaded with metallised microbeads laminated to a second melt adhesive film as well as a further film ; Figure 5 is a diagrammatic cross section of a melt adhesive film composite with microbeads having been stripped off the web and laminated to a textile substrate; and Figure 6 is a diagrammatic illustration showing a laminating/delaminating operation.

The drawings illustrate the production of retroreflective tape 11 (Fig. 5) by hemispherically metallising in a vacuum metalliser 12 (Fig. 3) a layer 13 of microbeads 14 while held on a web 15 half submerged in a coating 16 on the web 15 and transferring the layer 13 of metallised beads 14, unmetalled side facing outwards, on to a substrate 17 (Fig. 5). In the drawings, the beads are shown slightly separated-in practice, they are desirably closely packed, but, of course, almost any cross-section will show gaps between the beads.

The coating 16 on the web 15 is a melt adhesive, with a thickness about half the diameter of the beads-the bead diameter, for optimum reflectivity under standard EN471, should be between about 53 and 75 microns, the beads preferably having a refractive index of around 1.92 or 1.93, and being of near perfect sphericity. Flex-o-Lite X TSTF (twice sieved, twice fired) have been found to be suitable beads.

In order to enhance cohesion of the metallic (aluminium) layer, the beads are pretreated in an agitated bath of dilute stannous chloride in deionised water. The beads are rinsed in water after the supernatant liquor has been poured off, then dried.

The melt adhesive coating 16 on the web 15 may comprise a linear low density polyethylene (LLDPE), while the web 15 itself comprises a Kraft paper-any other suitable carrier, such, for example, as a polyester film could, of course, be used.

As seen diagrammatically in Figure 1A, an excess of microbeads 14 is fed on to the melt adhesive face of the web, as by a vibratory feeder or other suitable feeder 18 (Figure 2) as the web 15 is unwound from a supply roll 19. The web 15 then passes through an oven 21 heated to above the melting temperature of the melt adhesive coating 16. A monolayer 13 of microbeads 14 sinks into the molten adhesive layer 16, as seen diagrammatically in Figure 1B. On emerging from the oven 21 and cooling, the excess microbeads 14 not adhering to the web 15 are removed by suction at 22 in order not to disturb any adhered beads, and the beaded web then appearing as in Figure 1C, wound up on a roll 23.

The LLDPE is selected to afford adequate temporary anchorage of the monolayer 13 of beads 14 to the web 15 to withstand the mechanical handling involved in winding on the roll 23, and unwinding from it in the next succeeding step of vacuum metallising, and the stresses and temperatures involved in metallising, while facilitating its eventual release from the web 15.

Metallising is carried out in vacuum metalliser 12 which comprises a sealable chamber comprising a reel-to-reel mechanism 24 which accepts reel 23 (Figure 3) as a supply reel and has a take up reel 25. When the reels are loaded into the chamber, the chamber is evacuated by pump means 26 down to approximately 5 x 10-5 torr.

Substantial pure aluminium wire 27 is then fed into boats 28 which are heated to melt and volatilise the aluminium which then condenses on to the beads as they pass from reel 23 to reel 25.

After metallisation, the reel 25 is removed from the vacuum metalliser 12 and passed to a laminating arrangement 29, Figure 6, comprising a hot-nip laminating arrangement 31 and supports for the roll 24, further rolls of melt adhesive film 32,33, a take-up roll for the product, and a take-up roll 35 for the web 15.

Here, a second melt adhesive film 32 is laminated to the bead side of the web 15, so that the metallised face of the microbead monolayer 13 is against the adhesive film 32.

The primary purpose of film 32 is to bond to the monolayer 13 with a bond which is stronger than that of the melt adhesive 16 and, indeed, one that is sufficiently strong to bind the beads against removal through mechanical forces encountered during the expected usage of the tape. While a melt adhesive could be applied by conventional coating techniques, such could disturb the monolayer 13 which is comparatively weakly held on the web 15, and lamination not only avoids this possibility but also enables accurate control of adhesive thickness and the ability to use reactive melt adhesives and the opportunity to use more than one adhesive film with optimum bonding on the one hand to the monolayer 13 and on the other hand to a substrate.

The durability of the final product to laundering, dry cleaning and abrasion in use is ultimately dependent on the performance of the melt adhesive system. Any one of a number of commercially available melt adhesive films may be used at this stage.

Polyester based polyurethanes give good results. Results however are enhanced if the polymer contains a blocked isocyanate that reacts above the unblocking temperature to cross link the polymer structure and bond to the aluminium surface.

While a single layer of melt adhesive 32 can be used to bond both to the monolayer and to a textile substrate, better results can be obtained by interposing an additional layer (or layers) 33, again by lamination, such further layer or layers being based on thermoplastic co-polyamides, co-polyesters or polyurethanes, and the choice will depend upon the particular textile or other substrate to which the monolayer is to be attached.

While the textile substrate, particularly in the case of a tape for sewing or otherwise attaching to a garment or other artefact, could be incorporated during the laminating operation illustrated in Figure 6, it need not be so. The finished product from the operation of Figure 6 can be simply a melt adhesive film with the monolayer, which is suitable e. g. for laminating on to a garment panel prior to assembling the panel into a garment. In this case, the melt adhesive layer which bonds to the garment could contain a blocked isocyanate which is unblocked at the bonding temperature to the garment, but which has survived the laminating process.

The web 15 may be stripped away to be rolled up on reel 35 during the laminating operation of Figure 6, but need not be so, it being left as a protective layer to be stripped off at point of use.

For improved and/or assured wet retroreflectivity, treatment of the exposed, unmetallised face of the monolayer 13 with a perfluorosilane such as FC 405 manufactured by 3M or an organo-silane such as isobutyltrimethoxy silane, after removal of the LLDPE carrier paper 15 is recommended over conventional pre-treatment of the beads with a hydrophobic polymer, which causes marked reduction in washfastness.

Claims (33)

1. A method for making a retroreflective tape by hemispherically metallising a layer of microbeads while held on a web half submerged in a coating on the web and transferring the layer of metallised beads, unmetalled side facing outwards on to a substrate, in which the coating on the web is a melt adhesive, with a thickness about half the diameter of the beads; 'an excess of the microbeads is fed on to the coating on the web; the web with the excess of microbeads is heated to melt the melt adhesive and allow the layer of beads immediately in contact therewith to sink in to the adhesive layer; the web is cooled; excess microbeads are removed; the exposed surface of the layer of microbeads held on the web is metal-coated; the metal-coated microbeads on the web are coated with an adhesive; and the web and melt adhesive removed to expose the unmetallised side of the microbead layer.

2. A method according to claim 1, in which the melt adhesive comprises a linear low density polyethylene (LLDPE).

3. A method according to claim 1 or claim 2, in which the web comprises Kraft paper.

4. A method according to any one of claims 1 to 3, in which the web is unwound from a roll and passes through a beading station at which the excess of microbeads is applied then through an oven heated to a temperature above the melting point of the melt adhesive.

5. A method according to claim 4, in which the microbeads are dispensed on to the moving web by a vibratory feeder.

6. A method according to claim 4 or claim 5, in which the excess microbeads not adhered to the web are removed after the web has cooled on leaving the oven.

7. A method according to claim 6, in which the excess microbeads are removed by suction.

8. A method according to any one of claims 1 to 7, in which, before application to the web the microbeads have been treated with stannous chloride.

9. A method according to claim 8, in which the microbeads are treated with a dilute solution of stannous chloride in deionised water followed by rinsing with water.

10. A method according to any one of claims 1 to 9, in which the microbeads are hemispherically metallised in a vacuum metalliser.

11. A method according to claim 10, in which a roll of beaded web is placed in a vacuum metalliser fitted with a reel-to-reel mechanism, the metalliser sealed and evacuated, then aluminium is heated to melt and volatilise in the chamber whereby to condense on the microbeads as the web is fed from reel to reel.

12. A method according to any one of claims 1 to 11, in which the adhesive coating for the metallised microbeads is applied by laminating with a second melt adhesive in film form.

13. A method according to claim 12, in which the second melt adhesive comprises a polyurethane film.

14. A method according to claim 12, in which the polyurethane comprises a polyester based polyurethane.

15. A method according to any one of claims 12 to 14, in which the second melt adhesive contains a blocked isocyanate.

16. A method according to any one of claims 12 to 15, in which a further melt adhesive film is laminated to the second melt adhesive.

17. A method according to claim 16, in which said further film comprises a thermoplastic co-polyamide, co-polyester or polyurethane.

18. A method according to any one of claims 12 to 17, in which the or any of the melt adhesive films is precoated with an adhesion promoter.

19. A method according to claim 18, in which the adhesion promoter comprises an organo-functional silane.

20. A method according to any one of claims 12 to 19, in which the laminated film is sufficiently robust to permit the web to be removed and leave a microbead layer, unmetallised face out, on the film.

21. A method according to claim 20, in which the web and its coating is so removed, and the beaded, laminated film laminated to a substrate such as a textile.

22. A method according to any one of claims 12 to 20, in which the web is removed after lamination to a substrate such as a textile.

23. A method according to claim 21 or claim 22, in which the substrate is a tape for sewing or otherwise attaching to a garment or other artefact.

24. A method according to claim 21 or claim 22, in which the substrate is a garment panel.

25. A retroreflective tape comprising a layer of hemispherically coated microbeads, uncoated face directed outwardly, with their metallised halves embedded in a melt adhesive film.

26. A tape according to claim 25, in which the microbeads have added stannous chloride.

27. A tape according to claim 26, having 0.01 % (order of magnitude) by weight of stannous chloride on the beads.

28. A tape according to any one of claims 25 to 27, in which the melt adhesive film contains a blocked isocyanate which has reacted above its unblocking temperature to cross-link the polymer structure of the film and bond to the beads.

29. A tape according to any one of claims 25 to 28, in which the melt adhesive film contains a blocked isocyanate adapted to react on lamination of the tape to a substrate to bond to the substrate.

30. A tape according to any one of claims 25 to 29, in which the microbeads are between 53 and 75 microns in diameter (200-270 US mesh size).

31. A tape according to any one of claims 25 to 30, in which the microbeads have a refractive index close to 1.9.

32. A tape according to any one of claims 25 to 31, in which the microbeads are of near perfect sphericity.

33. A tape according to any one of claims 25 to 32, of which the exposed metalfree faces of the microbeads are treated with a perfluorosilane or an organo-silane.