WO2007028961A2

WO2007028961A2 - Retro-reflective coatings and articles

Info

Publication number: WO2007028961A2
Application number: PCT/GB2006/003236
Authority: WO
Inventors: Nicholas James Rowbottom
Original assignee: Viz Reflectives Limited
Priority date: 2005-09-05
Filing date: 2006-09-04
Publication date: 2007-03-15
Also published as: WO2007028961A3; GB0517951D0

Abstract

A retro-reflective coating comprises glass micro-beads each half coated with an aluminium film, wherein the particles have a size distribution with a peak below 50μ, and preferably between 35-45μ, substantially no particles below 20μ or above 50μ. The beads are made into an ink or paint by addition of a liquid medium and may be applied to clothing etc to improve the visibility of a wearer in poor light conditions. The greater uniformity of bead size, and reduced mean particle size compared with prior art coatings improves the reflective properties of the coating.

Description

RETRO-REFLECTIVE COATINGS AND ARTICLES

This invention relates to improved retro-reflective coatings and to articles provided with such coatings.

The purpose of retro-reflective coatings is to render articles, such as items of clothing, or accessories, visible in darkness or low light conditions and warn of the presence of any person wearing the article, by reflecting incident light from an illuminating source, such as vehicle headlamps, or a hand torch, substantially back towards the direction of incidence.

Retro-reflective coatings are characterised by the fact that they contain glass micro-beads which are each partially coated with a reflective film of a metal such as aluminium over about 50% of its surface. The micro-beads are applied to a substrate in a matrix material, and retained on the substrate by the matrix material.

WO96/17264 (Reflective Technologies Inc) teaches that beads of a mean diameter of 50μ (microns) give the best results, and that from 2000 to 20,000 beads per cm² should be used. It is stated that with a mean bead diameter over lOOμ, adverse effects in the handling properties of coated textile materials, such as increased stiffness, are encountered which detract from the utility of thus coated textiles for use in making of retro-reflective garments.

It is now a standard practice in the art to use beads having a mean diameter of 50μ, as taught by the above application. However, the spread of sizes about the mean is substantial, and it has been found in practice that the adverse handling effects claimed to occur with mean particle sizes above lOOμ are also encountered with smaller mean particle sizes, down to a mean size of 50μ, due in part to the presence of particles of sizes much larger than the mean (along with much smaller particles) due to the wide distribution range.

An object of the invention is to provide an improved retro-reflective coating, and also articles provided with such coatings, wherein these disadvantages can be substantially overcome.

According to the invention, a retro-reflective coating is characterised in that it contains micro-beads of transparent material, each partially coated with a reflective film, wherein the beads have a size distribution within the range of 30-40 μ, there being substantially no beads present with larger or smaller diameters. The invention also provides articles such as items of clothing or accessories which are at least partially coated with a retro-reflective coating according to the first aspect of the invention.

The distribution of bead sizes preferably peaks at about 38μ, and it is preferred that the beads are applied in an ink paint or aerosol. In the prior art, it is generally considered that not only is a mean bead size of

50μ the ideal, but also that the use of smaller beads entails loss of brightness in the reflected light. However we have found that when applied as an ink, or paint for example using known liquid media as a carrier, on the contrary smaller sizes of beads give brighter reflected light as a significantly higher quantity of beads is deposited per unit area than of the larger beads. A single layer of contiguous spherical beads would give the same ratio of covered to uncovered substrate whatever the size of the beads. Inking for example however gives rise to a very thin coating layer, and with larger bead sizes it is not possible to obtain evenness of bead distribution, nor full overlapping layers of beads required to approach complete coverage of the substrate needed for maximum reflectivity. With the smaller bead sizes proposed however, this is possible, within the thickness of the ink or paint film.

The ink or paint application method may be by screen or rotary printing or by aerosol, and the substrate may be a woven or non- woven fabric. In a preferred embodiment, the particle size of the beads has a very restricted range of size, with a mean diameter of 32-34μ.

Preferably glass micro-beads are used which are evenly metalized to produce a perfectly half-coated glass bead with excellent retro-reflective properties. The beads are preferably half-coated with alurninium and the uncoated area is clear of any contamination which might reduce the clarity of the glass and thus the retro-reflectivity of the beads.

The glass beads may be pre-treated with chemicals to improve the adhesion of aluminium to the glass, thus improving the wash fastness of the beads in the final product. The refractive index of the glass from which the beads are made may be in the range 1.91-1.96, and the beads themselves are preferably better than 90% spherical.

A preferred embodiment and method of using a retro-reflective coating and article will now be described by way of example, with reference to the accompanying drawings, wherein:- Figure 1 is a flow diagram of a mixing and application method according to the invention;

Figure 2 is an enlarged diagrammatic cross-section of a coating on a textile support; Figure 3 is a diagrammatic illustration of a garment furnished with retro- reflective strips in accordance -with the invention; Figure 4 is a graph showing the particle size distribution of two samples of micro-beads used in the invention; and Figure 5 is a photograph showing the result of a reflectivity test on a sample made in accordance with the invention and four comparative samples. In Figure 1 , a supply of micro-beads 10 is added to an ink medium 11 by mixing in a mixer 12 such as a static or linear mixer. The mixed retro-reflective ink 13 is then fed, possibly after transport and storage to an inking roller 14 of a printing roller 15 which prints the ink 13 onto a textile substrate 16, which after drying and/or curing of the ink layer may be cut into strips of retro-reflective material for application as required to garments or other articles such as the jacket shown in Figure 3.

The micro-beads 10 comprise substantially spherical micro-beads of glass, of better than 90% sphericity and having a mean diameter of 32-34μ, a particle size distribution of more than 90% within 30-40μ, and substantially no particles larger than 50μ. The beads are made from a glass having a refractive index of 1.91-1.96, and are half-coated with a reflective aluminium film after having been treated with chemicals to improve the adhesion of aluminium to the glass, and the uncoated hemispheres are rendered clear of any contamination which might reduce the clarity of the glass and thus the retro-reflectivity of the beads.

The ink medium 11 comprises a liquid polymer, having a viscosity suitable for application by inking roller or screen printing methods after addition of the micro-beads 10. The micro-beads are added to the ink medium in the static mixer 12 in a quantity of from 20-40% by weight of the final mixture. That is in a 40% mixture, 40Og of beads would be added to 60Og of mixture polymer or in a 20% mixture 20Og of beads would be added to 800g of polymer. The resulting retro-reflective ink 13 or polymer may then be supplied direct to a printing apparatus, or put into containers for transport and storage.

In this case, the mixture would need to be agitated or remixed before use due to possible settling of the micro-beads.

The ink 13 is then applied to a textile substrate 16, of woven or non- woven fabric to provide a retro-reflective coating 13 on the cloth, which can be cut as required after drying and/or curing of the polymer, for example cut into strips or patches of other shapes which can be stitched onto high- visibility garments.

Figure 2 is a cross-section showing the ink layer 13 on the fabric 16. The microspheres form a two or more layered structure, so that the microspheres 10 cover substantially the entire surface of the fabric 16 with spheres in the upper layer(s) covering the gaps between the spheres in the lower layer. This ensures that the maximum possible area is covered, so that with a normal random distribution of the orientation of the micro-beads, the highest possible reflectivity is obtained.

With the smaller sized beads used, this is possible within the film thickness of the ink, however with larger size beads, and with bead sizes averaging 50μ but ranging widely from the mean, quantities of oversized particles are obtained resulting in a mono-layer coverage, or patchy coverage, with incomplete coverage of the fabric and possible visible streaks or patches of the retro-reflective layer. This is substantially reduced by the use of the coating according to the present invention.

Figure 3 shows a garment 20, in the form of a jacket having retro -reflective strips 21, on the sleeves and on the body of the jacket. These are shown as vertical strips but could of course be horizontal hoops.

Two samples of reflective beads in accordance with the invention have been analysed with regard to particle size distribution, with reference to the percentage in weight terms of the sample retained by seives of progressively reducing particle size retention. The analysis is performed by passing the sample through seives with larger pore sizes first, moving down through the series to the smallest. A series of 42 sieves from 200μ to 0.20μ retained particle size were used, and the retained particles weighed to determine the percentage of particles retained by each successively finer seive. Table 1 lists the results obtained for a sample identified as "Sample A", which is a preferred sample of the reflective beads used in the invention, whilst Table 2 lists results obtained for a sample identified as "Sample B" which is a sample of beads within the broadest aspects of the invention. Figure 4 plots the distributions of particle sizes obtained, with the results for "Sample A" being plotted as a broken line, and for "Sample B" being plotted as a continuous line. As can be seen, the curve for "Sample A" shows a peak distribution at a lower particle size (37. lμ) and a narrower distribution of particle sizes, with no particles retained by a 52μ seive, and no particles passed by an 18.91μ sieve. "Sample B" shows a distribution peak at a larger retained particle size (43.9μ) and a wider range of particle sizes, over 5% being retained at 52μ, and small quantities being passed at 26.5μ, the last smallest particles being retained at 11.41 μ.

"Sample B" thus represents a less homogenous size composition than "Sample A", and it cannot be excluded that the smallest sizes represent shards of broken mircospheres, although it still represents an improvement over the prior art. TABLE l: SAMPLE A

Seive Size (μ) (Weight % retained) Cumulative weight %

11.41 0.00 0.00

13.50 0.00 0.00

15.98 0.00 0.00

18.91 0.02 0.02

22.40 0.22 0.22

26.50 2.42 2.64

31.30 25.60 28.24

37.10 70.14 98.38

43.90 1.62 100.00

52.00 0.00 100.00

61.50 0.00 100.00

TABLE 2: SAMPLE B

Seive Size ( μ) (Weight % retained) Cumulative weight %

11.41 0.01 0.01

13.50 0.03 0.04

15.98 0.09 0.13

18.91 0.34 0.47

22.40 1.22 1.69

26.50 4.30 5.99

31.30 14.04 20.03

37.10 35.38 55.41

43.90 39.19 94.60

52.00 5.40 100.00

61.50 0.00 100.00

Figure 5 shows a result of a reflectivity test using five samples, each comprising a logo printed in various preparations of reflective beads, on a non- reflective cloth background. The samples V,W,X,Y and Z are identified as follows:

V Comparative sample, prior art W Comparative sample, prior art X Comparative sample, prior art

Y Comparative sample, prior art Z Sample of invention, (composition A)

Only samples Z, at the centre of the array comprises a material made in accordance with the teachings of the invention, being much brighter than the others due to its improved retro-reflectivity. The image is a reproduction of a digital photograph showing reflection of a light source associated with the camera, namely the camera flash.

The retro-reflective coating of the invention enables a layer of about 850 beads per mm² for a mean size of 34μ, as compared to 490 beads per mm² for a mean size of 45μ.

The smaller bead size enables selective printing of finer detail and the ability to use a smaller screen mesh size which both enable finer and more defined patterns to be printed on the support. Printing using a smaller screen in turn allows a coating to be achieved using less ink than heretofore, which is correspondingly more economical. The medium used may be a paint or aerosol in place of an ink.

The feel of the fabric with the coating is improved due to the use of smaller beads, and improves the daytime look of the finished printed product, and a more consistent coating can be achieved, which produces a consistent and even reflectivity of the coating and improves the visual appearance of the fabric in retro-reflection mode.

The higher quantity of beads applied to the fabric improves the appearance after washing as even allowing for bead loss through laundering, a higher percentage of coverage overall can be maintained compared with the known coating, so that the retro-reflective capabilities are maintained after washing.

Claims

CIaims

1. A retro-reflective coating which contains micro-beads of transparent material, each bead being partially coated with a reflective film, characterised in that the beads have a size distribution having a maximum below 50 microns.

2. A coating according to claim 1, wherein the maximum has a peak between 35-45μ.

3. A coating according to claim 1 or 2, wherein there are no more than trace quantities of particles having sizes below 20μ or above 50μ.

4. A coating according to any one of claims 1 to 3, wherein more than 85% of the beads have sizes within the range 3O-5Oμ

5. A coating according to claim 1 or 2, wherein no particles of size above 55μ are present.

6. A coating according to any preceding claim which is in the form of an ink or paint and further includes a liquid medium as a carrier.

7. A coating according to any preceding claim wherein the beads comprise micro-beads of glass coated over about 50% of their surface area with a reflective film of aluminium, the remainder of the surface being clear.

8. A coating according to any preceding claim wherein the beads have a particle size distribution substantially in accordance with "Sample A" described hereinbefore.

9. A coating according to any one of claims 1 to 7, wherein the beads have a particle size distribution substantially in accordance with "Sample B" described above.